- Current Issue
- Online First Online-CNKI Archive
-
WAN Yusheng, XIE Hangqiang, XIE Shiwen, LIU Shoujie, MA Mingzhu, DONG Chunyan, LI Pengchuan, LI Yuan
2025,99(1):1-22, DOI: 10.19762/j.cnki.dizhixuebao.2024516
Abstract:
Earth is unique in our solar system for having developed a large- scale continental crust. The genesis and evolution of this crust is a protracted geological process spanning billions of years. Rocks older than 3. 8 Ga and zircons older than 3. 9 Ga have only been discovered in nine and twenty locations worldwide, respectively. Over geological time, the volume of the continental crust has steadily increased through a complex interaction of tectonic processes. Supracrustal rocks have evolved from mainly meta- basalt and meta- ultrabasic rocks to include meta- basalt, meta- ultrabasic rocks, meta- intermediate- acidic volcanic rocks, and meta- clastic sedimentary rocks. Although banded iron formations (BIFs) predate 3. 8 Ga, their global distribution reached a peak during the late Neoarchean to early Paleoproterozoic. TTG rocks, the dominant constituents of Archean cratons, exhibit a remarkable diversity in rock types and compositions as early as 3. 8 Ga. Over time, the proportion of granodioritic rocks within these cratons gradually increased. Simultaneously, the differentiation degree of light to heavy rare earth elements in TTG rocks increased, reflecting the progressive thickening of the continental crust. A period of significant continental growth occurred during the late Mesoarchean to early Neoarchean, resulting in the widespread development of plate tectonic regimes akin to those observed in the modern era by the late Neoarchean. This period witnessed the voluminous emplacement of K- rich granites, serving as a key indicator of Archean basement cratonization. The essence of cratonization is the physical, chemical, and mechanical stability, along with the intricate interconnectivity of different layers within the craton. The formation and evolution of the Hadean- Archean continental crust can be divided into four stages: 4. 4~3. 8 Ga, 3. 8~3. 0 Ga, 3. 0~2. 6 Ga, and 2. 6~2. 5 Ga. These stages roughly correspond to the formation of the continental nucleus, the development and formation of continental blocks, and cratonization, respectively. The vital transition phase from the Archean to the Proterozoic is of milestone significance in the evolutionary history of the Earth.
-
LIU Jianhui, LI Yuanshuo, XU Weinan, DING Zhengjiang
2025,99(1):23-43, DOI: 10.19762/j.cnki.dizhixuebao.2024535
Abstract:
The origin and geodynamic evolution of the Jiao- Liao- Ji tectonic belt have long been controversial. This article summarizes comprehensive research results on the tectono- magmatic- metamorphic processes and metasedimentary- volcanic successions in this belt. It is found that the 2.2~2.0 Ga pre- orogenic granitoids are mainly A- type, formed in a high- temperature, low- pressure extensional setting. Some are I- type granitoids derived from partial melting of mafic rocks in the lower crust. These pre- orogenic granitoids, along with metamafic intrusive rocks, metarhyolite- dacite, and metabasalt, constitute a bimodal magmatism in a continental extension setting. Their geochemical “arc magma” affinity is mainly inherited from Archean TTG rocks or attributed to crustal and/or continental lithospheric assimilation- contamination during mafic magma upwelling. Litho- tectonic assemblage (residual oceanic crust, subduction accretionary complexes, retroarc structures, large strike- slip faults, paired metamorphic belts, and spatiotemporal variations in magmatic activity) similar to that produced by modern- plate subduction has not been found in the Paleoproterozoic Jiao- Liao- Ji tectonic belt. The Longgang and Nangrim blocks share a coherent Archean basement and evolutionary history. The different metasedimentary strata in the “southern belt” and “northern belt” were deposited on a stable passive continental margin between 2.20 and 1.95 Ga. These strata share a similar provenance and underwent partial medium- pressure (MP)- high- pressure (HP) and high- temperature (HT)- ultrahigh- temperature (UHT) granulite- facies metamorphism with clockwise P- T paths involving isothermal decompression at ca. 1. 95~1. 80 Ga. Based on comprehensive geological and geophysical evidence, we propose the following tectonic model for the origin and geodynamic evolution of the Paleoproterozoic Jiao- Liao- Ji tectonic belt. ① Voluminous high- density granulite- eclogite facies residuals formed in the lower crust alongside the generation of extensive Archean TTGs in the Eastern block. The stable cratonic lithospheric mantle formed at the end of the Archean allowed these high- density granulite- eclogite facies residuals to be stably preserved in the lithosphere. ② During 2. 2~2. 0 Ga, intracontinental extension driven by upwelling of an asthenospheric hotspot along the Jiao- Liao- Ji belt fractured the Eastern block into the northern Longgang block and southern Nangrim block. ③ At ca. 1. 95~1. 85 Ga, the negative buoyancy of the high- density eclogitized lower crust and lithospheric mantle triggered their subduction (sinking), forcing convergent orogeny between the Longgang and Nangrim blocks along the Jiao- Liao- Ji belt. ④ At ca. 1. 85~1. 80 Ga, orogenic belt collapse caused by delamination of the orogenic root, followed by subsequent hot asthenospheric upwelling, resulted in the rapid exhumation and post- orogenic extension of the orogenic belt.
-
ZHAO Lei, ZHANG Wei, XU Qinqin
2025,99(1):44-57, DOI: 10.19762/j.cnki.dizhixuebao.2024488
Abstract:
Many ophiolites are developedin the western part of the Paleo- Asian Ocean tectonic domain, situated between the Eastern European craton, the Siberian craton and the Tarim craton. According to the spatial and temporal distribution characteristics, these ophiolites can be divided into the following ten zones: ① Yenisei ophiolitie bel, ② Kuznets- West Sayan- Lake ophiolite belt, ③ Salayer- Altai ophiolite belt, ④ Zaysan- South Mongolia ophiolite belt, ⑤ East Kazakh- West Junggar ophiolite belt, ⑥ East Junggar ophiolite belt, ⑦ Northern Tianshan ophiolite belt, ⑧ Naman- Jalayal ophiolite belt, ⑨ Terskyi ophiolite belt, ⑩ Ural- Southern Tianshan ophiolite belt, etc. The ophiolite assemblages in these zones are mostly incomplete, accompanied by pyroclastic rocks, and the mantle rocks are dominated by harzburgite+dunite+lherzolite. The chronology of the ophiolite indicates that the evolution of the ancient ocean basin occurred within a limited time frame of approximately 80~60 Ma, reflecting the restricted scale of the ocean basin. The ancient ocean basin marked by the Kuznets- West Sayan- Lake ophiolite belt is the first generation of the Paleo- Asian Ocean, which began in the Ediacaran period. The second generation of Paleo- Asian Ocean is marked by the most widely distributed Cambrian- Ordovician ophiolites, showing a tectonic pattern of micro- blocks alternate with small ocean basins. The third generation Paleo- Asian Ocean mainly refers to the Devonian- Early Carboniferous Zaysan Ocean and the Ural- Southern Tianshan Ocean. There is no paleo- ocean that evolved continuously from the Early Paleozoic to the Late Paleozoic. The subduction orogeny of the Paleo- Asian Ocean was mainly achieved through the closure of several small ocean basins. The collision did not involve a direct interaction between the Siberia and Gondwana continents; rather, it occurred through the interaction of micro- blocks. Therefore, the orogeny was not strong, leading to a scarcity of large- scale nappe structures beyond the tectonic belt.
-
MENG Yong, ZHANG Xin, CHEN Fenning, LI Zuochen, FENG Yimin, QI Yaogang, ZHENG Ruolei
2025,99(1):58-77, DOI: 10.19762/j.cnki.dizhixuebao.2024474
Abstract:
The Paleo- Asian Ocean tectonic domain represents a composite orogenic belt encompassing accretionary arc- basin systems south of the East European Craton, the primary oceanic basin, and the continental margin system north of the Karakum- Tarim- North China Craton. This dynamic system hosts significant orogenic systems, including the Sayans- Erguna, Ural- Tianshan- Xingmeng, and Kunlun- Qilian- Qinling orogenic systems. The region preserves valuable geological records of orogenic processes from the late Neoproterozoic to the Devonian, providing critical insights into the evolution of the Paleo- Asian Ocean. This paper focuses on the central- western segment of the Paleo- Asian Ocean' s dynamic system. It synthesizes previous research findings and categorizes tectonic movements from the late Neoproterozoic to thelate Devonian into five key orogenic events: ① The Baikal orogeny, which facilitated the assembly of the Tuva and Abakan blocks onto the southern margin of the Siberian Craton, characterized by accretionary processes. ② The Sayan- Erguna orogeny, marked by the successive attachment of the Altai and South Mongolia blocks to the southern margin of the Siberian Craton, resulting in the formation of the Sayans- Erguna accretionary orogenic system. ③ The Kazakhstan orogeny, occurring during the Middle to Late Ordovician, which led to the closure of the oceanic basin between the Kokchetav, Zaisan, Kyzylkum, Balkhash- Ili, Issyk, central Tianshan, and Dzungarian blocks, ultimately forming the Kazakhstan united landmass. ④ The Caledonian orogeny, which took place at the end of the Silurian (continuing in the eastern and western Kunlun until the end of the Middle Devonian), resulted in the assembly of the Azhong, central Qilian, South Qilian, Qaidam, West Qinling united, Qinling, and Upper Yangtze blocks onto the southern margin of the central continental block area, contributing to continental accretion. ⑤ The Tianshan orogeny, occurring from the end of the Middle Devonian to the Late Devonian, which connected the central- western segment of the central continental block area with the expanded Siberian landmass. This study enhances our understanding of the complex tectonic history of the Paleo- Asian Ocean and its implications for regional geology.
-
ZHANG Jin, ZHANG Beihang, ZHAO Heng, LIU Yugang, JIANG Hai, QU Junfeng, WANG Zhenyi, ZHANG Yiping, ZHAO Shuo
2025,99(1):78-103, DOI: 10.19762/j.cnki.dizhixuebao.2024429
Abstract:
The Mesozoic period is an important phase for central- eastern China, characterized by multistage, distinct, and abundant intracontinental deformation. According to statistical analysis of paleo- stress data retrieved from fault slip vectors, the Mesozoic tectonic evolution in central- eastern China can be divided into four stages: Middle- Late Triassic, Middle Jurassic- Early Cretaceous, Early Cretaceous, and latest Early Cretaceous- early Late Cretaceous, which further refined the previous division. Regional paleo- stress patterns are crucial for outlining the tectonic settings of major tectonic stages. Statistical analysis reveals that during the Middle- Late Triassic, northern China experienced north- south compression, while southern China exhibited various paleo- stress directions due to the rotation and tectonics of multiple plates. Additionally, ductile deformation with varying kinematics also developed during the Early Triassic. These distinct deformation and paleo- stress patterns across different regions were driven by intracontinental deformation processes, initiated by the closure of the Paleo- Asian Ocean, the collision between the North China Craton and the Yangtze Craton, the collision between the Yangtze Craton and Indochina Block, and tectonic interactions between the eastern and western Cathaysia blocks. During the Middle Jurassic to Early Cretaceous, the regional paleo- stress field was characterized by west- northwest to east- southeast compression, which dominantly resulted from the low- angle subduction of the Paleo- Pacific Plate, superimposed by the Mongol- Okhotsk Orogeny. The Early Cretaceous regional northwest- southeast extension indicates a consistent tectonic setting, which may be mainly controlled by the retreating subduction of the Paleo- Pacific Plate. In the latest Early Cretaceous to early Late Cretaceous, central- eastern China experienced a short- term northwest- southeast compression, with deformation times gradually shifting from south to north. This indicates a tectonism migration from south to north along the eastern margin of Eurasia, possibly triggered by a collision with an unknown block against East Asia. The Mesozoic intracontinental deformation, or tectonic evolution, in central- eastern China was dominantly controlled by far- field effects of plate margins with different orientations across periods. However, other potential factors may contribute to the observed tectonic evolution, which remain to be fully explored.
-
SHI Yuruo, KANG Yuelan, PENG Wenxiao
2025,99(1):104-119, DOI: 10.19762/j.cnki.dizhixuebao.2024415
Abstract:
The Tanlu Fault, the largest lithospheric fault zone in eastern China, is characterized by frequent tectonic activity and is a significant zone of magmatism and mineralization from the Mesozoic to the Cenozoic. A comprehensive understanding of the Tanlu Fault is important for comprehending the tectonic evolution of eastern China during the Mesozoic and the current configuration of the Eurasian continent. Based on our recent research on Mesozoic magmatic rocks along the Tanlu Fault, and guided by the International Geological Map of Asia edited by Prof. Ren Jishun, we propose that the initiation of the Tanlu Fault' s large- scale strike- slip movement is linked to the collision between the oceanic plateau and the Eurasian continent in the early Cretaceous (~143 Ma). This profoundly deep fault, which dissects the lithosphere, is a critical factor in the destruction of the North China Craton, offering a pathway for the ascent of deep mantle- derived materials. The Tanlu Fault Zone hosts a systematic distribution of polymetallic mineral deposits, including gold fields, which formed in an extensional setting following a major compressional strike- slip event (~123 Ma) in eastern China.
-
HONG Wentao, XING Guangfu, YU Minggang, CHU Pingli, CAO Xianzhi
2025,99(1):120-138, DOI: 10.19762/j.cnki.dizhixuebao.2024510
Abstract:
Southwestern Japan, located on the eastern margin of the Eurasian continent, preserves a complex geological record shaped by oceanic subduction processes, including accretionary complexes, high- pressure metamorphism, and arc magmatism, offering crucial insights into the Late Mesozoic tectonic evolution of the East Asian continental margin. This study analyzes the tectonic evolution of Late Mesozoic Southwestern Japan, focusing on the processes of subduction- accretion complexes and volcanic- sedimentary records, and explores the links between Japan' s tectonic evolution and tectono- magmatic processes in South China. The results show that Southwestern Japan experienced sequential subduction regimes during the Late Mesozoic. The Izanagi Plate began expanding in the late Carboniferous, subducted beneath the Eurasian continent from the Early Jurassic to the Early Cretaceous, followed by the subduction of the Kula Plate during the Late Cretaceous, which terminated at the end of the Cretaceous. Based on the characteristics of Mesozoic accretionary complexes, stratigraphy, and magmatic activity, the Late Mesozoic orogeny in Southwestern Japan, induced by Paleo- Pacific Plate subduction, can be subdivided into three phases: the Early Yanshanian (~190 Ma, ~165~160 Ma), the Middle Yanshanian (~135 Ma), and the Late Yanshanian (~110~100 Ma). These phases correspond to the Yanshanian tectonic evolution observed in South China and the entire eastern part of China. These tectonic events are closely linked to the accretion of microcontinents and the process of ridge subduction. In the initial stages of Paleo- Pacific Plate (i. e. Izanagi Plate) subduction, the magmatic front rapidly advanced westward from the oceanic side to inland areas. However, from the Late Jurassic onwards, the magmatic front retreated due to the collision of microcontinents, eventually shifting to the Japan region during the Cretaceous. Cretaceous magmatism in South China was mainly controlled by asthenospheric upwelling caused by slab break- off.
-
WANG Yu, SUN Lixin, SUN Junyi, ZHOU Liyun, WANG Shuzhi
2025,99(1):139-149, DOI: 10.19762/j.cnki.dizhixuebao.2024519
Abstract:
Research and development in tectonics stand at the forefront of geosciences, establishing critical frameworks for understanding Earth' s dynamic processes. The evolution of international tectonic concepts progressed from the geosyncline- platform theory in the early 20th century, through models of continental drift and oceanic floor spreading, culminating in the establishment of the plate tectonics theory in the 1960s. Chinese tectonic studies followed a similar trajectory, initially rooted in the Geosyncline- Platform hypothesis. Subsequently, various additional theories emerged, such as geomechanics, Diwa, Bolang- Xiangqian, multiple- cycle, and fault block hypotheses. With the introduction of plate tectonics, Chinese geologists largely adopted it as the primary model, leading to significant advancements in understanding the tectonic framework and evolution of the Chinese continent. Although the accuracy of specific models may vary, Chinese tectonic studies have made substantial progress, contributing systematic insights within the plate tectonics paradigm. However, these advancements, while aligned with general or specific global tectonic trends, have yet to provide definitive or distinct contributions to broader global tectonic theory, particularly in resolving key issues regarding the formation and evolution of global tectonics. These challenges include fundamental questions about the relationship between plate tectonics and continental tectonics, the processes driving continental evolution, and the mechanisms behind supercontinental formation and breakup- issues of ongoing concern to geologists worldwide. Even within the context of Chinese continental tectonics, debates persist regarding its unique versus universal characteristics within the global tectonic framework. These unresolved issues are pivotal for future research. In this paper, we argue that the development of Chinese tectonics cannot be fully resolved through plate tectonics alone. Future studies should integrate global tectonic principles, considering the fundamental and natural features of Earth' s structure. Moreover, it is essential to consider the role of both plate tectonics and intracontinental tectonics, asserting that global tectonics encompasses more than just plate boundaries; it must also include intracontinental and transcontinental dynamics.
-
2025,99(1):150-165, DOI: 10.19762/j.cnki.dizhixuebao.2024520
Abstract:
The Proto- Tethys Ocean is an important aspect for understanding Tethyan geodynamics. However, the origin of this ocean and the affinity of multiple continental/micro- continental blocks within it are still controversial, hindering the research into its formation and evolutionary history. During the Ediacaran, a suite of glacial sedimentary strata developed on many continental/micro- continental blocks in the Proto- Tethys domain. This study presents a comprehensive analysis of Ediacaran tillites from the southern margin of the North China Craton, the Olongbuluke Terrane, and the Qilian Mountains. Integrating these findings with previous glacial literatures of the Yangtze and Tarim Cratons, as well as regional ophiolite studies, we propose that the North China, Yangtze, and Tarim Cratons, along with the intervening continental/micro- continental blocks, may have been connected and deposited the initial cover of the ancient Chinese Platform during the Ediacaran. Our findings suggest that the Proto- Tethys Ocean was not a direct successor of the Proterozoic Ocean but rather a small ocean basin- microcontinent system that developed after the breakup of the ancient Chinese Platform in the early Paleozoic.
-
ZHANG Jian, LI Huaikun, ZHANG Chuanlin, TIAN Hui, ZHOU Hongying, ZHONG Yan, YU Jianzhong
2025,99(1):166-191, DOI: 10.19762/j.cnki.dizhixuebao.2024523
Abstract:
The assemblage, growth, and breakup of global- scale supercontinents profoundly influence Earth' s systems. These events not only lead to significant changes in lithospheric composition and structure but also impact the surface environments such as the atmosphere, hydrosphere, and biosphere over geological timescales. The late Mesoproterozoic to early Neoproterozoic interval was crucial for the amalgamation of the Rodinia supercontinent, marking the onset of global- scale plate cold subduction and ultrahigh pressure metamorphism. However, scarcity geological records of magma- tectonic events in the North China Craton (NCC) during this period hinder its correlation with Rodinia and paleogeographic reconstruction. Extensive mafic sill and dyke emplacement in the Xuhuai, Dalian, and Korea Pyongnam areas provides a valuable opportunity to address these knowledge gaps. This study focuses on the petrology, geochronology, and geochemistry of mafic sills in the Xuhuai area to decipher their petrogenesis, tectonic setting, and the role of the NCC in Rodinia assembly. Our results indicate that the diabase sills emplaced during the early Neoproterozoic (940~890 Ma), spanning about 50 Ma. These sills can be subdivided into two stages: the 940~920 Ma high- Ti group, emplaced into the middle part of the Huaibei Group (Niyuan Formation), and the 920~890 Ma low- Ti group, emplaced into the upper part of the Huaibei Group (Wangshan Formation). Most diabase samples exhibit tholeiitic affinities, and some high- Ti samples display alkali characteristics. Trace element analysis reveals LREE enrichment with (La/Yb) N ratios ranging from 2.5 to 8.6. High large ion lithophile elements (e. g. , Rb, Ba) and high field strength elements (e. g. , Zr, Hf, Ti) contents are observed on PM- normalized spider diagrams, with a slight Nb- Ta trough (Nb/La=0.63~1.12, mostly below 1). High- Ti samples share OIB- like chemical compositions, while low- Ti samples display CFB- like elemental signatures. Despite these differences, both groups are associated with an intraplate extensional tectonic setting. Isotopically, the diabase shows heterogeneous Sr- Nd- Hf- O isotopic compositions. The high- Ti group exhibits more radiogenic Nd- Hf isotopes compared to the low- Ti group. Moreover, a subtle decoupling exists between whole- rock Nd and zircon Hf isotopes. Heavy oxygen isotope signatures in zircons suggest that the lithospheric mantle source regions of the diabase underwent melt/fluid metasomatism derived from dehydration melting of the subducted slab. Integrating the exotic provenance revealed by detrital zircon ages in clastic strata and the rapid latitudinal wander calculated from paleomagnetism, the large igneous province (LIP) model may not be the most plausible interpretation. Instead, a model involving plate subduction retreat or the big mantle wedge model could potentially reconcile the diverse observations obtained through geochemistry, paleomagnetism, and sedimentology.
-
CHEN Fenning, JI Wenhua, GU Pingyang, LI Rongshe, CHEN Shoujian, ZHANG Haijun, MENG Yong, ZHANG Chenbo, ZHA Xianfeng
2025,99(1):192-208, DOI: 10.19762/j.cnki.dizhixuebao.2024530
Abstract:
During the Triassic, the sedimentary characteristics of the Gonghe and Bayan Har basins, located on both sides of the Buqian- Anemaqen mountain range, are closely related to the evolution of the Buqian- Anemaqen Ocean, a branch of the Paleo- Tethys Ocean. Although previous studies have extensively focused on the eastern parts of these basins, research on their central and western parts is relatively weak. This paper selects the Longwuhe Group in the Gonghe basin and the Bayankalashan Group in the Bayan Har basin as research subjects. Through comprehensive analysis of their sedimentary sequences, paleocurrent directions, sedimentary provenances, and prototype basin types, combined with existing regional geological data, this study aims to discuss the closure timing of the Buqian- Anemaqen Ocean. Our findings suggest the following: ① Triassic sedimentation in the Gonghe basin reflects its function as a back- arc basin, receiving sediments from different source areas. North of Maqin, sediments were derived from the Eastern Kunlun and Qaidam regions, supplying the Gonghe, Guide, Zeku, and Henan County areas. North of Maqu and east of Gonghe, Guide, Zeku, and Henan County, the northeastern Qilian Mountains constituted the dominant sediment source. South of Maqin and Maqu County, the Buqian- Anemaqen region itself acted as the primary sediment source. ② During the Triassic, the Bayan Har basin existed as a remnant ocean basin, with its main sediment provenance derived from the northern Buqian- Anemaqen. ③ The Buqian- Anemaqen region had already uplifted and transitioned into an erosional area prior to Triassic sedimentation. This uplifted region subsequently served as the main provenance for the basins.
-
ZHANG Sumei, WANG Yang, REN Jishun, ZHU Junbin, ZHANG Minjie, SU Tianrui, WANG Xiaohan, YU Yanqiu, WANG Shiqi
2025,99(1):209-223, DOI: 10.19762/j.cnki.dizhixuebao.2024424
Abstract:
The absence of direct evidence for early Paleozoic magmatic activity within the South China orogenic belt has sparked considerable debates. These debates center around, the timing of the collisional amalgamation between the South China orogenic belt and the Yangtze block, the early Paleozoic tectonic setting, and the belt' s potential affiliation with Gondwana. Consequently, the discovery of Pan- African magmatic rocks has become crucial in resolving these questions. This paper focuses on the petrographic characteristics, zircon U- Pb geochronology, whole- rock geochemistry, and Lu- Hf and Sr- Nd isotopic signatures of the Wutong pluton, located north of the Zhuguangshan batholith. The results reveal that the pluton primarily consists of biotite monzogranite with a crystallization age of about 494. 4 Ma. Geochemically, it exhibits high silica and alumina content (SiO2=59. 93%~71. 31%, Al2O3=13. 43%~19. 20%), high alkali content (K2O=3. 35%~5. 93%, Na2O=2. 33%~6. 21%), and high iron content (TFe2O3=2. 09%~6. 20%), while displaying low magnesium content (MgO=0. 44%~2. 18%). The rock mass is enriched in Rb, Th, U, Nb, and LREE, and depleted in Ba, Sr, P, and Ti. These geochemical features suggest that the magmatic source material was mainly derived from the remelting of lower crustal rocks, potentially involving the multiple remelting events. A minor contribution from mantle- derived material during magma intrusion is also evident. This discovery suggests that the collisional amalgamation between the South China orogenic belt and the Yangtze block occurred during the early Paleozoic (520~480 Ma), likely along the margin of the central part of Gondwana. This study provides valuable insights into the timing, characteristics, magma genesis, and tectonic setting of the Pan- African orogenic event in the South China orogenic belt and may contribute to a better understanding of the region' s geological history.
-
ZHOU Liyun, CHEN Xin, WANG Yu, GAO Honglei
2025,99(1):224-251, DOI: 10.19762/j.cnki.dizhixuebao.2024525
Abstract:
During the Mesozoic, eastern China experienced a significant tectonic regime transition from the Paleo- Asian to the Paleo- Pacific domains, marked by a shift in tectonic trends from an approximately E- W to NE and NNE orientation. This transition was accompanied by large- scale magmatism, tectonic deformation, sedimentation, and basin formation, providing an ideal natural laboratory to investigate crust- mantle interactions and the dynamic mechanisms underlying tectonic regime transformations. This paper presents a brief analysis of multidisciplinary studies related to Mesozoic tectonic deformation, magmatism, and deep structures in the North China region of eastern China. By analyzing tectonic features in North China and the broader eastern region, the study explores the crust- mantle decoupling mechanisms involved in the transition from the Paleo- Asian to the Paleo- Pacific tectonic framework. Our findings suggest that the tectonic regime transition in eastern China initiated in the Middle to Late Jurassic. During this period, numerous syntectonic granitoid plutons formed, extending from the continental margin of the Liaodong Peninsula to inland regions of North China. Concurrently, the middle to upper crust experienced SE- NW compression, resulting in the development of faults, folds, and ductile shear zones in various zones. However, the orientation of metamorphic schists and other structures in the deep cratonic basement remained unchanged, indicating the presence of detachment zones between the basement and overlying strata. This detachment, combined with syn- tectonic magmatic flow in the lower crust, manifested as crustal interlayer detachment and decoupling of the crust. Simultaneously, the upwelling of mantle material induced partial melting of the lower crust and potentially facilitated horizontal flow of mantle material from east to west. These processes disrupted the original crust- mantle equilibrium, leading to crust- mantle material decoupling.
-
HOU Fanghui, HUANG Wei, ZHU Xiaoqing, LU Kai, QIN Ke, LI Panfeng, SUN Jun, HAN Tonggang
2025,99(1):252-264, DOI: 10.19762/j.cnki.dizhixuebao.2024486
Abstract:
The West Philippine Sea, the largest tectonic unit on the Philippine Sea Plate, remains a subject of debate regarding its origin. This article investigates its origin using isotopic dating of submarine drilling core samples. The research reveals that the age range of 93 detrital zircons from the drilling core spans from 2759 to 31 Ma. Except for 3 young zircons related to Cenozoic seafloor spreading of the West Philippine Basin, over 95% of the ages predate the Cenozoic. This suggests that most of the debris originated from older, pre- existing rock units located on the continental margin rather than within an intra- oceanic arc. A significant proportion of Proterozoic- Archean ages and Lu- Hf model ages indicate the existence of recycled ancient continental crust material. The rare earth element distribution pattern and formation environment diagrams of zircons further support a continental crust source. The zircon age spectrum shows several peaks at 2532, 2022, 1500, 792, 426, and 210 Ma. These peaks closely resemble the age spectrum of the Gondwana continent, indicating that the West Philippine Sea (proto- Philippine Sea Block) may have originated from the northeastern edge of Australia on the East Gondwana continent. With the opening of the Neo- Tethys Ocean, the proto- Philippine Sea Block (including the Daito Ridge region, the Gagua Ridge, the East Philippine terranes, and the Hamahira- Waigeo terranes) rapidly drifted northward after splitting from the northern edge of Australia. Subsequently, the opening of the West Philippine Sea Basin led to the fragmentation of this block, with its components now located in the Daito Ridge region to the north, the Gagua Ridge to the west, the Hamahira- Waigeo Islands to the south, and the Luzon- Samar- Mindanao region in the East Philippines. This study provides critical evidence for better understanding the plate tectonic patterns and evolution of the Southeast Asia- Western Pacific region.
-
XU Ziying, YAO Yongjian, WANG Jun, TANG Jianglang, GAO Hongfang, LI Xuejie, ZENG Chenghui
2025,99(1):265-276, DOI: 10.19762/j.cnki.dizhixuebao.2024527
Abstract:
Numerous high- amplitude dipping reflections in the lower oceanic crust are developed in the East sub- basin (ESB) of the South China Sea (SCS), recording the process of oceanic crust accretion. Understanding the structure and genesis of these dipping reflections is crucial for comprehending the spreading process of the SCS. Based on multi- channel seismic profiles, this paper describes the structural features and internal deformation of these lower crustal dipping reflections (LCRs) in the ESB and discusses their genesis. Our results reveal high- amplitude LCRs in both the southern and northern parts of the ESB. Most reflectors terminate at the Moho reflection, but significant differences exist in their distribution range, structural features, and genesis between the two regions. The northern LCRs are longer (approximately 15~22 km) and wider (approximately 150 km north- south extent) than their southern counterparts (approximately 5~8 km long, approximately 70 km north- south extent). The depth of the Moho surface in the lower crust inclined reflection area shows obvious differences between north and south. The northern part displays a shallower Moho (approximately 0. 5 s), compared to the southern part (approximately 1.2 s). Further, the basement topography is flat in the north and rougher in the south. This suggests that the oceanic crust is thicker in the northern LCR area and thinner in the south, indicating an asymmetrical and heterogeneous process of oceanic crust accretion in the ESB. The genesis of the ESB' s LCR may be closely related to syn- magmatic faults, hydrothermal cycles, magmatic interstitial intrusion in the crust- mantle transition zone, and deep basement faults.
-
LIU Songnan, CHEN Xin, WANG Yu
2025,99(1):277-292, DOI: 10.19762/j.cnki.dizhixuebao.2024477
Abstract:
The geological evolution of tectonic plates can be divided into several stages according to the theory of plate tectonics: continental rifting, incipient ocean formation, oceanic crust subduction (ocean death), and collisional orogeny. Global orogenic events mainly consist of accretionary and collisional types. However, in many cases, these processes are often not continuous or complete. Intracontinental orogens can arise when tectonic inversion occurs during continental rifting. A case study of the Songpan- Ganzi tectonic belt, spanning the Middle Permian to the Late Triassic, exemplifies this phenomenon. Initial rifting occurred in the Late Permian, characterized by coarse clastic deposits in the Sandaoqiao Formation, including brecciated limestone and conglomerate. These deposits are overlain by Dashibao basalt, indicating a similar tectonic setting to the Permian Panxi Rift. The Songpan- Ganzi tectonic belt evolved to a post- rift stage during the Middle to late Triassic and received debris from multiple sources to form thick sandstone and siltstone. The stress field began to reverse in the Norian- Rhaetian stage, leading to intense folding and deformation of the Triassic sedimentary layers, accompanied by large- scale felsic magma intrusion. No oceanic crust or subduction zone formed during the evolution from continental rifting to orogeny. The cessation of rifting dynamics and the reversal of the stress field may be controlled by two factors: remote compression from the Indosinian orogeny and the suspension of deep magmatic convection. This proposed evolutionary model is helpful to a deeper understanding of plate tectonics and the mechanisms driving continental dynamics.
-
LIU Jiadong, WU Qingju, ZHU Min
2025,99(1):293-305, DOI: 10.19762/j.cnki.dizhixuebao.2024476
Abstract:
The Linhe rift and Langshan uplift, located in the western section of the Hetao rift system, are important parts of both the Ordos rift system and the Yinshan orogenic belt. The crustal structure in this region is of great importance for unraveling the geodynamic processes responsible for the formation of both the Hetao rift system and the Yinshan orogenic belt. However, aspects of this crustal structure, such as the crustal thickness of the Linhe rift, remain a subject of debate. This study analyzes teleseismic waveforms from 118 broadband seismic stations deployed across the western Hetao rift and adjacent areas. P- wave receiver functions are calculated to obtain information about the crustal structure. Time delays of the sediment- converted Ps phase are employed to determine the thickness of Cenozoic and overlying sedimentary layers. Our results indicate an average sedimentary thickness of approximately 5. 3 km in the Linhe rift, compared to about 2. 7 km in the Chagandelesu rift. H- κ stacking reveals a relatively low crustal VP/VS ratio of 1. 75, suggesting a predominantly felsic composition in the crust northwest of the Langshan piedmont fault. Besides, crustal thickness obtained from H- κ stacking is consistent with Moho depths derived from CCP stacking, showing a deeper Moho beneath the Langshan uplift and a shallower one on the northwest side. Combined with the relatively low VP/VS ratio beneath the Langshan uplift, it is inferred that the uplift is primarily caused by upper crustal thickening under north- south compression. In contrast to previous findings, this study identifies a slight Moho uplift beneath the Linhe rift, suggesting crustal thinning occurred under extensional conditions and may be influenced by mantle upwelling. These new insights constrain the formation mechanisms of the Hetao rift system and the Yinshan orogenic belt.
-
Detrital zircon REE constraining orogenic evolution: A case study of the Gangdese Mountains in Tibet
HU Peiyuan, ZHAI Qingguo, TANG Yue, LIU Yiming, YANG Ning, LI Jinyong, WU Lingfang, CHANG Sheng
2025,99(1):306-319, DOI: 10.19762/j.cnki.dizhixuebao.2024372
Abstract:
Detrital zircon is a key mineral for studying the evolution of early Earth orogenic belts. However, distinguishing between oceanic subduction and continental collision settings using detrital zircon rare earth element (REE) data remains an unresolved issue. This paper reviews previous experimental petrology studies and uses the Gangdese Mountains in Tibet as a case study to investigate the potential of the correlation coefficient (rDz) between detrital zircon europium anomaly (Eu/Eu*) and light/heavy REE ratios (LREEN/HREEN) as a discriminant for these tectonic settings. Experimental petrological studies indicate that the zircon Eu/Eu* and LREEN/HREEN are influenced by the crystallization processes of plagioclase and garnet, which are in turn controlled by crystallization pressure, protolith composition, oxygen fugacity, and magmatic water content of parental melts. These controlling factors exhibit variability across different tectonic settings, leading to the hypothesis that detrital zircon REE characteristics can be used to differentiate between them. To test this hypothesis, we analyzed detrital zircon REE data from the Tibetan Gangdese Mountains. During the oceanic subduction stage, Eu/Eu* and LREEN/HREEN show coupled evolutionary trends, resulting in a stable high rDz value of 0. 62~0. 81. This stability possibly reflects consistent oxygen fugacity and magmatic water content, a low abundance of S- type granitoids, and a dominant control of crystallization pressure on Eu/Eu* and LREEN/HREEN. After slab break- off and the transition to continental collision, rDz exhibits a significant decrease. The rDz values for 40~30 Ma, 30~20 Ma, and 20~10 Ma are 0. 73, 0. 57, and 0. 18, respectively. This decline is potentially due to a higher yield of S- type granitoids and more variable oxygen fugacity and magmatic water content, leading to decoupled evolution trends of Eu/Eu* and LREEN/HREEN. Our findings suggest that rDz has the potential to be a new proxy to distinguish between oceanic subduction and continental collision settings.
-
XU Qinqin, ZHAO Lei, WANG Yannan
2025,99(1):320-336, DOI: 10.19762/j.cnki.dizhixuebao.2024517
Abstract:
The East Junggar orogenic belt, a significant segment of the Central Asian orogenic belt, represents an excellent natural laboratory for investigating the spatiotemporal evolution and the orogenic patterns of crustal deformation. This region has undergone complex, multistage evolution since the late Paleozoic, with extensive research focusing on reconstructing its Paleozoic tectonic framework and establishing tectonic evolution models. However, studies on the tectono- thermal evolution of the region remain insufficient, particularly regarding constraints on late Paleozoic exhumation. The Kalamaili Mountain, a prominent tectonic and geomorphological unit in the East Junggar orogenic belt, holds crucial information about the region' s uplift and exhumation history. Investigating its tectono- thermal evolution can provide valuable insights into the broader tectonic processes of the East Junggar. This study presents new zircon (U- Th)/He, apatite (U- Th- Sm)/He, and apatite fission track data from four sedimentary rocks collected from the eastern part of the Kalamaili Mountain. These thermochronological data are used to constrain the late Paleozoic- Mesozoic uplift and exhumation history of the region. Thermal history modeling reveals four distinct episodes of rapid exhumation in the East Junggar, including the Late Carboniferous- Early Permian (330~290 Ma), late Early Permian- Middle Permian (285~260 Ma), Triassic (250~230 Ma) and the Early Cretaceous (135~115 Ma). The first episode may be linked to the closure of the Irtysh- Zaisan in the Late Carboniferous. The second episodeis likely associated with dextral strike- slip deformation of the Kalamaili tectonic belt in the late Paleozoic. The third episode may be interpreted as a response to the distal effects of the collision between the Qiangtang and Kunlun- Qaidam blocks. The last episode is regarded to be the result of the closure of the Mongol- Okhotsk Ocean in the north and the collision between the Qiangtang and Lhasa blocks in the south.
-
2025,99(1):202501090-202501090, DOI:
Abstract:
-
2025,99(1):202501091-202501091, DOI:
Abstract:
-
2025,99(1):202501092-202501092, DOI:
Abstract:
-
2025,99(1):202501093-202501093, DOI:
Abstract:
-
2025,99(1):202501094-202501094, DOI:
Abstract:
-
2025,99(1):202501095-202501095, DOI:
Abstract:
Volume 99,2025 Issue 1
Reviews
Research Articles
Appendix
-
LOU Bode, ZHANG Qizuan, JIANG Sha, LIU Huan, LI Wanyue, DONG Jianhui, ZHOU Shangguo, CHEN Xu
Submitted date:2023-08-26,Pre-publication date:March 04, 2024
DOI: 10.19762/j.cnki.dizhixuebao.2023374
Abstract:
Karst bauxite is the most important source of bauxite in China, accounting for more than 90% of the total resources, mainly distributed in the North China Craton and the southwest margin of the South China Block. In recent years, as a kind of strategic scarce mineral resource, the prospecting prediction of bauxite has become extremely urgent. This paper systematically summarizes the results of karst bauxite prospecting prediction and explores the optimal combination of prospecting prediction methods, so as to summarize the prospecting experience. By combing the examples and methods of geology, geophysics, geochemistry, remote sensing and artificial intelligence of geological big data to review the research results of karst bauxite prospecting and prediction in China, it is considered that geology and geophysics are still the most major methods for Chinese karstic bauxite prospecting prediction at present. In addition, the limitation of geochemical and remote sensing methods in searching for paleo-karst bauxite and their causes are analyzed, and the far-reaching significance of intelligent prospecting with geological big data is pointed out in the future.
-
Apatite Fission Track Spatial Distribution Characteristics: Implications for the Evolution of Tectono-geomorphological Landscapes — A Case Study of Wugongshan
Gao Shangyan, Li Guangwei, Zhang Yuwei, Ye Zhanghuang
Abstract:
The evolution of landforms is controlled by the interaction between tectonic activities and surface processes, and exploring the contribution of both to the evolution of structural geomorphology has always been a hot and difficult point in the study of the evolution of orogenic geomorphology. In recent years, the rapidly developing low-temperature thermochronology has become a powerful method for studying the quantitative evolution of tectonic geomorphology. Therefore, this study uses low-temperature thermochronology method to investigate the exhumation processes and mechanisms of the typical granite gneiss dome in China - Jiangxi Wugong Mountain. We targeted the core of the Wugong Mountain range - the north and south sections of Mingyue Mountain for sampling and conducted apatite fission track analysis. The apatite fission track ages are mainly concentrated at ~65-42 Ma, and the ages on both sides of the mountain show a clear negative correlation with elevation. This may be due to the fact that the exhumation of the Wugong Mountain dome in the Late Cretaceous were mainly controlled by the detachment faults on both sides, while the denudation process in the Cenozoic was mainly affected by surface erosion. This indicates that for relatively old orogenic belts, the spatial distribution characteristics of low-temperature thermochronology ages can be used as an indicator to discern the main control mechanisms of tectonic geomorphological evolution. In addition, according to our thermal history simulation results, the Wugong Mountain area has experienced a rapid exhumation stage in the Late Cretaceous, a slow stage from the Paleocene to the early Miocene, and a relatively rapid exhumation stage since the early Miocene, mainly controlled by regional tectonic activities and climate change, respectively.
- 1
-
Evolution characteristics of marine nitrogen cycle and redox structure during early Cambrian in the western Hubei aulacogen of middle Yangtze Block
Meng Kang, Hu Yunpeng, Zhang Yu, Shao Deyong, Tang Lei, Song Hui, Zhang Tongwei
Abstract:
The evolution characteristic of marine redox structure during early Cambrian in the western Hubei aulacogen of middle Yangtze Block is still unclear. In this study, the Lower Cambrian shales of well LX03 in the western Hubei aulacogen were taken as the research object. Firstly, origins of differences in nitrogen isotope compositions of whole rock and kerogen were analyzed to determine which nitrogen isotope was suitable for characterizing the marine redox environment at that time. On this basis, the dynamic evolution process of marine nitrogen cycle and redox structure during the deposition of Lower Cambrian Shuijingtuo organic-rich strata in this area was reconstructed by further integrating redox-sensitive elements and benthic foraminifera. The results showed that biological assimilation occurring in anoxic pore water during sedimentation and early diagenesis stages leaded to nitrogen isotope fractionation between kerogen and silicate minerals. However, this process took place within a relatively closed system and had minimal impact on the whole rock nitrogen isotope (δ15Nbulk). Moreover, the δ15Nbulk was not affected by secondary processes such as terrestrial input, microbial degradation, thermal maturation, and metamorphism, making it a reliable geochemical indicator for reconstructing the marine redox structure during the deposition of organic-rich sediments. During the deposition of the lower part of first member of Lower Cambrian Shuijingtuo Formation, the redox interface was located at the marine’s surface, with marine primarily characterized by euxinic condition (limited NO3- pool), and organisms acquired nitrogen mainly through nitrogen fixation. When the upper part of first member and lower part of second member of Lower Cambrian Shuijingtuo Formation deposited, the redox interface descended, with the upper oxic water expanded (enlarged NO3- pool), and organisms acquired nitrogen increasingly through the less energy-consuming NO3- assimilation process. During the deposition of the upper part of second member of Lower Cambrian Shuijingtuo Formation, the upper oxic water further expanded, and the bottom water transitioned to a low-oxygen environment. The low-oxygen bottom water promoted the proliferation of benthic foraminifera and other ancient organisms adapted to extreme low-oxygen conditions, with NO3- assimilation becoming the primary pathway for organisms to acquire nitrogen.
- 1
-
The indicative significance of mica minerals to the genesis of Dangba pegmatite-type lithium deposit, western Sichuan, China
Zhao Yuan, Ran Fengqin, Tang Juxing, Peng Bo, Yang Yang, Han Jingrui, Feng Dabo, Bai Yun, Dai Yongkun, Tian Songlin
Abstract:
Located in the Songpan-Ganzi orogenic belt, the Keeryin ore field is one of the important pegmatitetype lithium ore concentration areas in China. The Dangba deposit is a super-large pegmatite lithium deposit in the ore field. For a long time, it has been considered that the two-mica monzonitic granite in the Keeryin area is the main ore-forming parent rock of lithium mineralized pegmatite in this area. In order to further reveal the evolutionprocess of Dangba pegmatite and the enrichment mechanism of rare metals, mica, a penetrating mineral in granite and pegmatite, was selected as the research object in this paper. Based on previous studies, detailed rock and mineral identification, electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis were carried out. The results show that: ①The mica series in the Keeryin two-mica monzonitic granite and Dangba pegmatite show the evolution trend of muscovite → iron-lithium mica → lithium mica, and 4AlTot?3SiIV+□VI and 3LiVI?AlVI+2□VI are the dominant substitution mechanism of this process; ② The muscovite series in the Keeryin two-mica monzonitic granite and Dangba pegmatite show theevolution trend of muscovite → iron-lithium mica→ lithium mica.The high degree of crystallization differentiation process of Dangba pegmatite, the initial melt rich in Li and the late fluid relatively poor in F, and the relatively weak scale of fluid action are of great significance for lithium mineralization.
- 1
-
Analysis of Ore-Controlling Structure of Lujing Uranium Ore Field in Hunan-Jiangxi Border
Abstract:
Analysis of Ore-Controlling Structure of Lujing Uranium Ore Field in Hunan-Jiangxi Border Chen Bailin Institute of Geomechanics，Chinese Academy of Geological Sciences，Beijing 100081，China Lujing uranium ore field is one of the most important hard-rock uranium ore fields in South China. There are many small uranium deposits and occurrences such as Lujing large uranium deposit (322), Shabazi (327), Gaoxi (326), Huangfengling (325) and Niuweiling (324). The surrounding rocks of uranium ore bodies in the ore field are Mesozoic granite and Cambrian shallow metamorphic clastic rocks. Uranium ore bodies in granite are controlled by NNE(NE)-oriented faults (a little NEE-oriented), while uranium ore bodies in shallow metamorphic clastic rocks are controlled by NWW (near east-west)-oriented faults. The ore-guiding structure of the ore field is the regional extensional tectonic environment and its related magmatic activity and rock intrusion structure; Ore-matching (transporting) structure is a high-angle normal fault and rock mass emplacement structure which is connected with deep gas-liquid thermal fluid, and its upper part is connected with ore-bearing structures in different directions. Ore-bearing structures can be structural traces formed during mineralization, structural traces formed before mineralization and active structures during mineralization, while ore-controlling structures must be those during mineralization. The ore field structure has gone through nine stages: basement fold formation, Indosinian intrusion, early Yanshan intrusion, NNE-trending ore-bearing structure formation in the late early Cretaceous, EW-trending basic dike intrusion in the late early Cretaceous, uranium mineralization in the late early Cretaceous-early late Cretaceous, uplift and denudation in the early late Cretaceous, red bed basin covering and burial in the late Cretaceous-early Paleogene, and uplift and denudation since the middle Paleogene. There is no necessary genetic relationship between Fengzhou red bed basin and uranium mineralization, and it plays a role in protecting uranium deposits formed earlier than it. The favorable areas for further prospecting are Fengshuxia-Niuweiling-Jiaoyelong-Shabazi area and Dachangping-Dongfangzi-Lujing-Miaobeilong area covered by Fengzhou red bed basin. Key words: ore-controlling structure; ore-bearing structure; further prospecting for uranium deposits; Lujing uranium ore field; Hunan-Jiangxi Border.
- 1
-
Petrogenesis and geological significance of Late Carboniferous strongly peraluminous granite in West Junggar
DUAN Fenghao, ZHI Qian, LI Wei, PENG Nanhe, WANG Qian, WANG Panlong, FU Hao, Zhang Jianye
Abstract:
The intermediate-acid intrusive rocks exposed in the West Junggar, southwestern segment of the Central Asian Orogenic Belt, are mainly metaluminous to weakly peraluminous I-type and A-type granites. This study presents petrological, zircon U-Pb geochronological and in-situ Hf isotopic, whole-rock geochemical data of the newly discovered primary-muscovite-bearing strongly peraluminous granites in the Azhaken area. Petrographic observation results show that the strong peraluminous granites are mainly composed of muscovite monzonitic granite porphyry, two-mica monzonitic granite, muscovite granite and granite porphyry. LA-ICP-MS zircon U-Pb dating reveals middle Late Carboniferous magmatism with age of 309.1±3.8 Ma, later than metaluminous I-type granites (322~310 Ma) but slightly earlier than weakly peraluminous A-type granites (307~294 Ma) in the region. It is geochemically characterized by enriched silicon, aluminum, but depleted calcium, ferrum and magnesium, and possesses high total alkali content and aluminum saturation index (A/CNK=1.06~1.24, 1.14 in average), and also enrichment in Ba, Rb, K, Th, U with pronouneed negative Nb, Ta and Ti anomalies. In addition, it is characterized by corundum content of 0.85%~2.83% (1.79% in average) and absence of diopside showed through CIPW standard mineral calculation, indicating that they are strongly peraluminous high-K calc-alkaline S-type granite. In-situ zircon Hf isotope analyses show that these granites have high positive εHf(t) values (+10.8~+15.6) and very young two-stage Hf model ages of 326~633 Ma, suggesting that the magma was sourced from juvenile crust originated from depleted mantle. In association with previous analysis, it is proposed that the newly discovered middle Late Carboniferous strongly peraluminous S-type granites were probably originated from muscovite dehydration melting of metapelites under the water-absent condition during the initial transformation from extrusion to extension regime in the rapid collage process of subduction accretion bodies under the background of northwestward subduction of the Junggar oceanic crust.
- 1
-
Indications of garnet to the age and environment of mineralization from the Pandian skarn－type Fe deposit in the Qihe－Yucheng area of Luxi, Shandong province
ZHU Xueqiang, WANG Laiming, HAO Xingzhong, QIN jie, YANG Zhenyi, YANG Shipeng, LI Fenghua, WANG Jinguang
Abstract:
The Fe deposit in the Qihe－Yucheng area is a newly discovered skarn－type iron－rich deposit in the ultra－deep cover area in Luxi area of Shandong Province, which is closely related to the Early Cretaceous dioritic magmatism, but the age of mineralization has not been well qualified. In this paper, LA-ICP-MS U-Pb isotope dating, major and trace elements analysis, hydrogen－oxygen stable isotope analysis and mineral inclusions analysis were carried out on garnet from the Pandian skarn－type Fe deposit. Garnet is mainly composed of andradite ( And = 55.55 % ~ 74.24 % ) and grossular ( Gro = 22.16 % ~ 40.05 % ), belonging to grossular－andradite series. The garnet Tera－Wasserburg diagram of the two skarn samples shows that the lower intersection ages are 122.8 ± 3.4 Ma and 123.7 ± 9 Ma, belonging to the Early Cretaceous. The rare earth compositions generally show a left－dipping type with light rare earth elements loss and heavy rare earth elements relative enrichment, with obvious Eu positive anomaliy. The inclusions are mainly molten inclusions, containing iron components such as hematite and iron complexes. The value of δDV－SMOW of inclusions is －69.50‰~－88.30‰, and the value of δ18OH2O is 8.43‰~12.21‰, which belongs to magmatic water. Comprehensive analysis suggests that the Pandian Fe deposit in the Qihe－Yucheng area is the product of the peak period of thinning and destruction of the North China Craton in the early Early Cretaceous. The ore－forming fluid is derived from the iron－rich high－temperature magmatic hydrothermal, in which the slightly acidic neutral and oxidizing environment provided conditions for the unloading and mineralization of Fe.
- 1
-
Sedimentary geochemistry of Mesozoic cherts in Tongjiang area of Northeast China: Implication on the subduction of Paleo-Pacific subduction
ZHANGWenHao, ZHOU Jianbo, ZHOU Xingui, WANG Dandan, LIU Weibin, Meng Yuanlin, LIU Xufeng
Abstract:
The Sanjiang area in Northeast China hosts the sole exposed Mesozoic siliceous rock series in northern China, which holds significant geochemical characteristics for unraveling its genesis and tectonic setting, particularly to trace the temporal and spatial initiation of paleo-Pacific subduction. In the Tongjiang area north of Sanjiang, the "Heitongdi 1 Well" reveals a silicic rock system from the late Triassic to Early Jurassic Dajiashan Formation, spanning approximately 400 meters. Through field geological investigation, microscopic observation, and petrogeochemical analysis of core samples from this well, we have conducted a comprehensive study on the origin and tectonic environment of these siliceous rocks. Radiolarian fossils are observed in the siliceous rocks of the Tongjiang area. The mean Al/(Al+Fe+Mn) value in the siliceous rock samples was 0.74, with no discernible Ce anomaly and Ce/Ce* values ranging from 1.02 to 1.54, (La/Ce)SN≈1, no significant difference in Y/Ho values, a mean Y/Ho value of 30.02, and a mean Eu/Eu* value of 1.17, indicating that these siliceous rocks were formed in a continental margin island arc environment. The present study also provides compelling evidence for the initiation of subduction of the Paleo-Pacific plate beneath the Eurasian plate during the late Triassic period, leading to the establishment of an island arc environment along the eastern margin of Jiamusi Block. The inferred location of the subduction suture between these two plates is situated westward from Tongjiang drilling hole.
- 1
-
Implications of paleoproterozoic regenerated granites on Precambrian tectonic evolution in the southwest margin of the Yangtze block
zhanghonghui, yuanyongsheng, zhenghongfu, liujunping
Abstract:
The southwest margin of the Yangtze Block played an important role in the amalgamation and fragmentation processes of the Columbia supercontinent, but the tectomagmatic evolution of the late Paleoproterozoic is insufficient and controversial. In this study, Paleoproterozoic regenerated granite was found in Lufeng area of central Yunnan Province, southwest margin of Yangtze Block. It was formed by the rapid sedimentation of weathered K-feldspar granites within the Paleoproterozoic Lüzhijiang Formation. The main components are quartz, potassium feldspar, a small amount of biotite and plagioclase. LA-ICP MS zircon U-Pb dating, Lu-Hf isotope, rock geochemistry and zircon trace element analysis showed that: the weighted average 206Pb/207Pb age of zircons is 1849±6Ma (MSWD=0.11, n=21). The εHf(t) values of 7 zircons range from -7.23 ± 0.7 to -3.58 ± 0.75, with an average of -5.2 ± 1.2, and the TDM2 is 2819±73Ma. The trace element characteristics of zircons and petrogeochemical features indicate that the protolith was S-type granite, possibly derived from the melting of metasedimentary rocks in the Middle Archean. The discovery of Paleoproterozoic regenerated granites indicates the existence of S-type granites of ~1.85Ga in the southwest margin of the Yangtze block, providing a new evidence for the tectonic chronology and petrology of the Columbia supercontinent. It also shows that the formation of Lüzhijiang Formation in central Yunnan Province is Paleoproterozoic, providing new data for the Precambrian geological research in central Yunnan Province.
- 1
-
Ordered distribution and reservoir characteristics of Lower Permian sedimentary rocks in Junggar Basin
Zheng Menglin, Wangran, Chang Qiusheng, Qin Zhijun, Wang Tao, He Wenjun, Guo huajun, Zou Yang, Sun Jing, Wu Haisheng, Shan Xiang
Abstract:
Mahu Sag is an important example of the application of the theory of the whole oil and gas system, Junggar Basin. The oil-gas reservoir pattern with normal and irregular distribution corresponds to the reservoir type with orderly distribution. In order to clarify its reservoir characteristics and control factors, the drilling, logging, analysis and laboratory analysis data of more than 50 Permian reservoirs in Mahu Sag are analyzed. The Permian sedimentary rock reservoirs in Mahu Sag are characterized by orderly lithology, facies and reservoir property from the edge of the sag to the depositional center. The lithology develops coarse clastic rocks, medium clastic rocks and fine-grained sedimentary rocks successively, and the grain size changes from coarse to fine in an orderly, continuous and sequential manner, which corresponds to the sedimentary facies changes. Coarse clastic rocks can be divided into rich shale conglomerate facies, shale conglomerate facies and lean shale conglomerate facies according to the level of shale content. Fine-grained sedimentary rocks can be divided into argillaceous lithofacies and dolomitic lithofacies according to the content of felsic and livid. The lean and argillaceous conglomerate facies and argillaceous rock facies have good reservoir property, and large-scale conventional conglomerate and unconventional shale oil reservoirs have been found respectively. Sedimentary facies control the orderly distribution of lithology, and gravity flow, torrent, traction flow, heavy flow and light flow dynamic fluid are closely related to the orderly distribution of lithofacies. The content of argillaceous complex and the composition of felsic mineral have decisive influence on the reservoir property of coarse clastic rock and fine grained sedimentary rock, respectively, and compaction diagenesis has important influence on the reservoir property of medium clastic rock. The orderly distribution of sedimentary rocks and the regularity of their reservoir properties control the gradual transition of oil and gas from continuous unconventional reservoirs to discontinuous conventional reservoirs.
- 1
-
Sequence-Stratigraphy-Filling and Reservoir-Cap rock Assemblage Distribution Under the Control of Lake Basin Types: A Case Study of the Fengcheng and Baikouquan Formations in the Mahu Sag, Junggar Basin
zhangbao, Yan Detian, Tongyong, Zheng Menglin, Chang Qiusheng, Wei Xiaosong, Zhang Lei, Bai Yu, Yu xing
Abstract:
The Junggar Basin, as one of China's important oil and gas production areas, contains abundant petroleum reserves. However, research on the basin's lake basin evolution is relatively limited, particularly regarding the relationship between lake basin types and the distribution of reservoir-cap rock assemblage during the Permian to Triassic deposition.This study, based on sequence stratigraphy frameworks, integrates structural evolution and paleoclimatic characteristics to systematically analyze the control of lake basin types on sequence-stratigraphy-filling and the distribution of reservoir-cap rock assemblage in the Junggar Basin. The results show that the Permian-Triassic sequence in the northwestern margin of the Junggar Basin has been divided into three supersequence (SSQ1-SSQ3) and eight third-order sequences (SQ1-SQ8). SQ2 is subdivided into the rift initiation system tract, rift climax system tract, and post-rift system tract. SQ6 is subdivided into the falling-stage systems tract, the lowstand system tract, expansion system tract, and the highstand system tract. The deposition period of SQ2 characterizes a typical underfilled discharge (UF-D) lake basin, where high-quality reservoirs mainly develop in the rift climax system tract, characterized by conglomerates and sandstones with residual intergranular pores and dissolution pores, resulting in relatively high porosity. The source rocks exhibit high productivity, conditions of high anoxic preservation, and weak dilution. The distribution of the Fengcheng Formation's reservoirs and source rocks is controlled by fault activities accompanied by the input of hydrothermal fluids and arid conditions induced by the Late Paleozoic glaciation.During the SQ6 deposition period, a typical overfilled lake basin is represented, with high-quality reservoirs mainly developing in the forced regressive and lake expansion system tracts, primarily consisting of sandstones. Continuous lake wave reworking and intermittent exposure increased porosity. The primary source of hydrocarbons is the SQ5 source rock, characterized by high productivity, poor preservation conditions, and strong dilution. The distribution of the Baikouquan Formation's reservoirs is controlled by tectonic uplift during the late Hercynian orogeny, the arid paleoclimate conditions of the Permian-Triassic transition, and the subsequent continuous lake transgression. This study reveals the sedimentary evolution patterns of the Permian to Triassic strata in the northwestern Junggar Basin, particularly the sequence-stratigraphy-filling characteristics and reservoir-cap rock assemblage distribution controlled by lake basin types. The findings provide important references for the study of lake basins with similar structural and climatic settings and have significant implications for oil and gas exploration.
- 1
-
Establishment of the southern margin fault zone of Bogda and its geological significance
Zhang Jianye, Li Yongjun, Zheng Menglin, Wang Tao, Li Wei, Wang Qian
Abstract:
The boundary between the Bogda stratigraphic minor-region and its neighbor, the Yilianhabierga stratigraphic minor-region, has been in dispute for a long time, and the corresponding boundary of the two tectonic units have also been disputed. Determining the contact relationships between the lithostratigraphic units in the Bogda region is the key to answering the aforementioned scientific questions. The southern margin fault of Bogda has discovered and established in Bogda area in this study, it’s a large-scale and stable extension, belonging to the levitra strike-slip fault, which was hidden in the Tuha Basin and Junggar Basin on the south and north sides, respectively. Detailed field geological investigations and refined comparisons of previous research results show that the geologic entities of the northern and southern plate of the fault have different deformation histories, sedimentary histories, and histories of magmatic activity and tectonic evolution. Detrital zircons indicates different source compositions and geological background of contemporaneous terrigenous clastic rocks in Late Carboniferous on both sides of the fault, implying that the two sets of upper Carboniferous units belong to two sedimentary basins. It is shown that the southern margin fault of Bogda has the basic property of dividing the stratigraphic minor-region. The establishment of the southern margin fault of Bogda effectively defines the boundary between Bogda stratigraphic minor-region and the Yilianhabierga stratigraphic minor-region, new information is provided for the research of zonal stratigraphic grids.
- 1
-
Research progress and exploration application of Tectono-geochemistry in the recent decade
Abstract:
On the background of the demand for deep mineral exploration, tectono-geochemistry has distinct advantages over soil and rock geochemistry in predicting hidden minerals, which has aroused the research interest of domestic and foreign scholars. This article summarizes the research progress on concepts and theories as well as exploration application results of tectono-geochemistry, leading to the following understandings: 1) Tectono-geochemistry is an emerging interdisciplinary subject that explores the intrinsic relationship between tectonic dynamics and geochemical substances and studies the behavior and results of material components in tectonic processes. 2) Tectonic action controls the physical and chemical properties of material activation in geological space, drives the migration of materials in tectonic fluids, and ultimately leads to the differentiation and enrichment of elements. 3) Tectono-geochemistry has made significant research progress in terms of "Tectonically driven geochemistry," "geochemically induced structural deformation," and "geochemical dynamic process simulation," but the "dynamic mechanism" still needs further exploration. 4) The workflow of tectono-geochemistry exploration applications includes structural analysis, structural sampling, statistical analysis of element combinations, anomaly interpretation, mineralization model construction, and target area delineation. 5) The application of tectono-geochemistry in ore deposit exploration has achieved remarkable results, including polymetallic deposits of Cu, Au, Pb, Zn, Ag, Mo, Sb, Sn, etc. Foreign scholars tend to study the mineralization mechanisms and mineralization models, while Chinese scholars focus on deep predictions and target area delineation of ore bodies. In addition, the rich deep-seated, three-dimensional, and multi-media sampling, the application of big data and machine learning methods in data analysis, and the verification of ore body spatial distribution by short-wave infrared are all future development trends of tectono-geochemistry exploration, with great research potential and broad application prospects.
- 1
-
Permian paleogeographic differentiation evolution and platform margin model comparison in Sichuan Basin
Li Wen, Chen Anqing, Zhang Xihua, Sun Shi, Huang Huiwen, Gao Zhaolong, Xu Shenglin, Huang Ganghui, Xie Hao, Yang Shuai, Chen Hongde
Abstract:
The carbonate platform margin is an important gathering place of large-scale oil and gas resources, and the study of paleogeographic differentiation is the basis to reveal the characteristics and development laws of the carbonate platform margin. Following the discovery of a trillion square meter natural gas gold accumulation zone in the platform margin reef-beach facies of the Upper Permian Changxing Formation in Sichuan Basin, the platform margin beach reservoir of the Middle Permian Maokou Formation has recently been discovered, and several open flow wells of more than one million square meters have shown great exploration potential. However, there are significant differences in sedimentary filling and reservoir characteristics between these two periods, and detailed comparative analysis will help deepen the understanding of carbonate platform model and its reservoir control effect. Based on a large number of drilling, field outcrop and seismic data from the Sichuan Basin and its surrounding Permian system, the typical sedimentary facies and lithofacies paleogeographic pattern are analyzed, and the differences between the two types of platform margins are compared. The results show the differentiation from shallow-water platform to deep water shelf by multiple synsedimentary faults occurred in Permian paleogeography of Sichuan Basin from Maokou period, with Kaijiang-Liangping trough being the most typical. The shallow-water carbonate platform of Changxing Formation is characterized by the development of thick platform margin reef-beach facies, and the shallow-water carbonate platform of Maokou Formation is characterized by the development of thin platform margin beach facies, both of which rapidly change into siliceous rock and carbonaceous shale. The Maokou period belongs to the initial geomorphic inherited platform margin, which is represented by several thin beach bodies with intermittent accretion under the background of wide margin. In the Changxing period, the platform margin was shaped by sedimentary border, showing a thick reef flat body with continuous accretion or prograding under the background of narrow margin. In general, both platform margins have the potential to develop large-scale reservoirs and are important targets for exploration of large oil and gas accumulation zones.
- 1
-
Provenance characteristics of the Yangjiazhuang Formation on Tianheng Island: constraints from detrital zircon U-Pb dating and whole-rock geochemistry
MENG Yuanku, Yang Shubo, Yang Peng, Meng Fanxue, Lu Jie, Gao Cunshan, Li Zhaoying, Wang Zhenzhen
Abstract:
The Jiaolai basin was formed in the rapid exhumation processes of the Sulu orogenic belt and Jiaobei terrane. Its evolutionary processes played a key role in constraining exhumation and denudation of the Sulu orogenic belt and Jiaobei terrane and destruction of the north China Craton (NCC). In this work, we took the Yangjiazhuang Formation of the Laiyang Group, which is located in the eastern margin of the Jiaolai Basin, as the research target to carry out systematic field geological survey, petrographic analyses, detrital zircon U-Pb dating and whole rock element measurements. Based on the systematic studies on the Yangjiazhuang Formation, we can draw the following conclusions: (1) the sedimentary age of the Yangjiazhuang Formation is well-defined between 125 and 115 Ma, belonging to the Apian stage of the Early Cretaceous; (2) the geochemical features of the mudstone revealed that provenance of the Yangjiazhuang Formation experienced relatively weak chemical weathering, and primary sedimentation played a key role, and the upper continental crustal (UCC) materials were the dominant provenance; (3) change of the sedimentary provenance of the Yangjiazhuang Formation and diversities indicated that the Jiaobei terrane was the other important provenance during the middle-late stages of sedimentaion besides the Sulu orogenic belt. Combined with the regional tectonic background, we propose that the rapid uplift and exhumation of the Sulu orogenic belt and Jiaobei terrane might have a close relationship with the crustal large-scale extension and thinning due to the destruction of the NCC.
- 1
-
Fine Study on the Characteristics and Evolution Process of Typical Evaporite StrataExposed in the Kuqa Basin, Xinjiang
YANG Sibo, XU Yang, LIU Chenglin, MO Tao, YAO Kun, FAN Kunyu, ZENG Xize, E Yuqi, LIU Lei
Abstract:
Due to the salt tectonic diapirism, a large number of evaporite geological bodies are exposed on the surface of the Kuqa Basin, providing excellent materials for the study of evaporite strata. However, there has been a lack of detailed research on them before. This paper selects the typical Dawanqi salt dome and gypsum dome as the research objects, and reveals the salt-forming evolution law through various research methods such as X-ray diffraction (XRD) analysis, thin section identification, scanning electron microscopy and energy dispersive spectroscopy, geochemical analysis, and fluid inclusion homogenization temperature analysis. It is concluded that the gypsum rocks in the Late Eocene evaporites of the Kuqa Basin can be subdivided into 7 types, and the salt rocks widely develop regular mudstone-pebble structures. It is determined that the sedimentary environment of the Late Eocene evaporites in the Kuqa Basin belongs to the inland sabkha, and the temperature range of the brine during the salt-forming period is between 11.2 - 32.5 °C, with an average of 22.3 °C. In the early stage of the saline lake period, it experienced two episodes of concentrated brine seepage or disturbance, and after stabilization, it received two freshwater replenishments; the salt lake period experienced a total of five freshwater replenishments. In addition, it is found that the rhythmic alternation of gypsum and anhydrite deposits, as well as the rhythmic variations in the quantity and size of mudstone pebbles in salt rocks, can be used as indicators to judge the concentration and desalination of brine in the salt lake. This study provides a typical case for the sedimentary evolution of evaporites exposed in the Kuqa Basin and even in domestic salt basins.
- 1
-
Current status and development trends of coverage area types and exploration techniques in China
Wang Qingsong, Yan Tingjie, Wang Yafei
Abstract:
The covered area is an important exploration region for the new round of mineral discovery breakthroughs. The cover layer acts as a barrier to geophysical anomalies, presenting challenges in delineating exploration selection areas, defining mineral target zones, and locating deep mineral bodies. Based on mineral exploration theory, this paper analyzes the physical characteristics of the cover layer and the difficulties in mineral exploration by reviewing literature and combining it with practical experiences in covered areas. It systematically summarizes the current status and development trends of geophysical and geochemical exploration techniques in mineral discovery applications within covered areas, aiming to provide references for strategic actions in the new round of mineral discovery breakthroughs. The research indicates that the difficulty of mineral exploration in covered areas is not only related to the thickness of the cover layer but also closely linked to the physical characteristics of the cover layer and hydrogeological conditions. Accordingly, the covered area is classified into eight types: low-resistivity thin cover area, low-resistivity thick cover area, water-rich low-resistivity thick cover area, low-resistivity ultra-thick cover area, desert cover area, volcanic rock cover area, thrust fault cover area, and composite cover area. Among these, the low-resistivity thick cover area, water-rich low-resistivity thick cover area, and low-resistivity ultra-thick cover area present greater challenges for mineral exploration. The study shows that China has widely tested and applied geophysical and geochemical exploration techniques in thin cover areas, achieving significant results, and has also accumulated some experience in mineral exploration in thick cover areas, initially establishing various exploration technical systems for different mineral types in different covered areas. However, the challenges of delineating mineral target zones and detecting deep mineral bodies remain unresolved. Looking ahead, research on precise detection technologies that penetrate thick cover layers will be a key development direction, with geophysical electromagnetic methods and stimulated electric/magnetic field detection technologies expected to advance rapidly. The diversification of geological information collection methods across air, ground, and well platforms, along with the integration of comprehensive information processing and artificial intelligence in mineral prediction, will become an inevitable trend. The integration of geological and geophysical research on controlling mineral structures and mineralization models in covered areas will play an increasingly important role.
- 1
-
Genesis and Tectonic Significance of Middle Triassic and Late Jurassic Gabbros in the Kaiyuan Area, Northern Margin of the North China Craton
LIU YUNXIU, LIU JIN, ZHANG DAWEI, LIU ZHENGHONG, CHENG CHANGQUAN, ZHANG HONGXIANG, DONG YACHAO, ZHANG YUANZHUHUI, ZHANG JIRUI
Abstract:
This paper presents U-Pb geochronology, whole-rock geochemistry, and zircon Lu-Hf isotopic analyses of Middle Triassic pyroxene diorite and Late Jurassic gabbro in the Kaiyuan region, along the northern margin of the North China Block. The study investigates the petrogenesis of these igneous rocks and modification of the lithospheric mantle of the North China Craton by subduction of the Paleo-Asian Ocean plate and the Paleo-Pacific plate. Zircon U-Pb dating indicates that the Middle Triassic pyroxene diorite formed at 243 ± 1 Ma, classifying it as a calc-alkaline, sub-aluminous rock. This gabbro shows geochemical characteristics typical of arc magmatic rocks, with enrichment in large ion lithophile elements (Rb and Ba) and depletion in high field strength elements (Nb and Ta), without significant Eu anomalies. The enriched zircon Hf isotopic composition (εHf(t) = -14.7 to - 8.9) suggests that the pyroxene diorite originated from partial melting of an enriched lithospheric mantle. For the Late Jurassic gabbro, zircon U-Pb dating yields an age of 160 ± 1 Ma, also categorizing it as a calc-alkaline, sub-aluminous rock. Similar to the Middle Triassic gabbro, the Late Jurassic gabbro is enriched in large ion lithophile elements (Rb and Ba) and depleted in high field strength elements (Nb, Ta, Zr, and Hf), with negative εHf(t) values (-10.6 to -7.7). These geochemical and isotopic characteristics indicate that the gabbro primarily originated from partial melting of an enriched mantle modified by subduction-related fluids. Integrating previous studies, this paper proposes that the Middle Triassic pyroxene diorite formed during the post-collision extensional phase following the final closure of the Paleo-Asian Ocean, while the Late Jurassic gabbro formed in a tectonic environment related to the subduction of the Paleo-Pacific. The prolonged subduction of the Paleo-Asian and Paleo-Pacific Oceans has imparted enriched mantle characteristics to the lithospheric mantle beneath the northern margin of the North China Craton.
- 1
-
A Preliminary Exploration of Active Fault Identification Methods in the Deep-cut River Valley Region: A Case Study of the Batang Fault
yuhao, zhong ning, zhang xianbing, yang zhen, yu xiao, wu ruian, wang yang, yang zhihua, guo changbao, li haibing
Abstract:
The Batang fault is a significant seismogenic fault in the oblique-slip Jinsha River tectonic belt, which triggered the Batang earthquake with a magnitude of 7.25 in 1870. It is mainly distributed in the deep-cut river valley regions of the Jinsha River and Lancang River. Due to the large relief in the deep-cut river valley regions, frequent landslide and debris flow disasters, and well-developed vegetation, the fault traces are not clearly visible. As a result, there are differing interpretations regarding the geometric distribution and activity nature of the Batang fault. This article, based on high-precision remote sensing, unmanned aerial vehicle (UAV) photogrammetric measurement, geophysical exploration, paleoseismic records of ancient landslides and deposits, and precise earthquake location methods, further refines the geometric distribution and activity nature of the Batang fault. The research results suggest that the Batang fault is a Holocene active fault, predominantly characterized by right-lateral strike-slip motion with a component of thrusting. The southwestern extension of the Batang fault (referred to as the Naozhong Fault), forming a V-shaped fault with the Deqin-Zhongdian-Daju fault, may serve as the southwestern boundary fault of the Zhongdian secondary block. The tectonic stress field reveals that the Batang fault experiences primarily southwest-northeast compressional stress, accompanied by a certain northwest-southeast extensional component. This may be attributed to the eastward movement of the Qiangtang Block, clockwise rotation of the Zhongdian Block, and the southeastward escape of the eastern margin of the Tibetan Plateau. Finally, a preliminary summary of research methods for active faults in deep-cut river valley regions is provided, aiming to serve as a reference for the identification and investigation of active faults in such areas.
- 1
-
The indicators of Muscovite and Feldspar to the Prospecting direction of Rare metal pegmatite——Constraint on the discovery of spodumene pegmatite in Yanlingguan, xintai city, central Shandong
LIU Qinlong, LI Jiankang, LI Peng, LI Yingjie, LI Shenghu
Abstract:
The efficient prospecting and exploration indicators of rare metal pegmatite in the eastern high coverage area is still difficult. In order to study how to delineate the mineralized pegmatite in the rare metal pegmatite in the eastern high coverage area, this studies carried out the major and trace elements of muscovite and feldspar in Yanlingguan pegmatite group in Xintai city, Shandong Province, analyzed and delineated the favorable areas of rare metal pegmatite, determined the prospecting direction by using the elemental composition and mineralization index of muscovite and feldspar, successfully found lepidolite and spodumene, and calculated the crystallization temperature of Yanlingguan pegmatite group by using feldspar thermometer. The regional zonation of Yanlingguan pegmatite group is poor, with no obvious change in lithology and mineral composition. It can be divided into Taohuayu area in the south, Tianjingyu area in the middle and Yanlingguan area in the north. The K/Rb ratio and Li of mica and feldspar show that the pegmatite dikes in Yanlingguan area have undergone highly crystalline differentiation and evolution. The conclusion that Li-rich muscovite and Cs-rich feldspar can be used as indicator minerals for lithium mineralization in the eastern high coverage area is confirmed. According to the calculation of feldspar temperature, the temperature changes are very regular when the trondhjemite in Shanggang unit and Yanlingguan pegmatite field crystallize, so the trondhjemite is the ore-forming parent rock of Yanlingguan pegmatite field.
- 1
-
Late Cenozoic Activity Characteristics of the Chenghai Fault Zone in the Qina-Binchuan Section and Its Implications for the Extrusion of the Sichuan-Yunnan Block
LI zhichao, Wu Zhonghai, Lu Haifeng, Huang Xiaolong, Song Xiyan, Yao Haitao, Huang Feipeng, Ceng Jing, Jiang Jiaqi
Abstract:
The Chenghai Fault Zone, as the eastern boundary fault of the Dali Rift System, has experienced multiple phases of tectonic evolution since the Cenozoic. During the Early Cenozoic, the Chenghai Fault Zone accommodated part of the eastward extrusion of the Tibetan Plateau through thrust nappe structures. Since the Pliocene, the fault zone has transitioned to transtensional deformation. However, there is ongoing debate regarding the initiation of this transtensional activity and the characteristics of faulting in the southern segment. This study, utilizing remote sensing interpretation, field geological investigations, paleo-tectonic stress field inversion, and focal mechanism solutions, delineates the spatial geometry, activity, and tectonic stress field of the Chenghai Fault Zone's Qina-Binchuan segment since the Pliocene. By integrating previously published geochronological data and seismic records, a tectonic evolution model of the Chenghai Fault Zone since the Pliocene is proposed. The results reveal a migration of fault activity within the southern segment of the Chenghai Fault Zone. The Qingshui-Zhoucheng Fault in the southwestern area exhibited significant activity before the Middle Pleistocene, but its activity has markedly decreased since the Late Pleistocene. Currently, the Bincuan Fault in the southeastern sector shows the highest level of activity, indicating an eastward migration of faulting in the southern segment. Analysis of the fault zone's geometry and stress field inversion suggests that the Chenghai Fault Zone has undergone rotational deformation since the Pliocene. Considering the regional tectonic context, this rotation is interpreted as a tectonic response to the clockwise rotation of the Dali Rift System. This study provides crucial insights into the migration of fault activity during the evolution of strike-slip fault systems and enhances the understanding of the mechanisms by which microblock rotation accommodates deformation during the extrusion of plateau material.
- 1
-
Meso-Cenozoic tectonic evolution and geomorphologic restoration of the west section of Bonan low uplift, Bohai Bay Basin
Wu Zihan, Hu Zhiwei, Shi Panpan, Dai Liming, Li Sanzhong, Li Fakun, Wang Zhuo, Hu Zihao
Abstract:
The west section of Bonan low uplift in the Bohai Bay Basin has been found to have great characteristics of medium-deep buried-hill type oil and gas trap in recent exploration work, and internally discovered the Bozhong 26-6 large-scale oil and gas reservoir. Discussions on the formation and evolution of buried-hills, the development sedimentary systems, and the mechanisms of oil and gas generation, storage and migration often require tectonic analysis and tectonic geomorphological restoration work. Therefore, to reveal the complete tectonic deformation and geomorphic evolution of the west section of Bonan low uplift, and to provide theoretical support for oil and gas exploration, this paper, based on the reflection seismic and drilling data in the study area, detailed the strata distribution and tectonic deformation characteristics during Mesozoic-Cenozoic, and used Move software to conduct two and three dimensional tectonic restoration, accurately restoring the geomorphological features during the major periods of tectonic activity. Results reveal that: (1) During the early Mesozoic (from the Indosinian to the early Yanshanian), under the strong compressional orogeny transitioning from a near S-N to NE direction, the study area developed a numerous near E-W and NE directed thrusts, as well as several near S-N strike slip faults. The region experienced intensive uplift, with the overall lack of the Jurassic sedimentation and extensive erosion of the Paleozoic strata. The Precambrian basement was exposed and flattened, presenting a large-scale flattened mountain landform. (2) During the late Mesozoic (from middle to late Yanshanian), under a strong NW-SE directed extensional environment, the reverse faults in the Huanghekou Depression on the south side of the uplift experienced intense negative inversion activity. This allowed the depression to receive a large amount of Cretaceous volcaniclastic and muddy-sandy sediments. The west section of Bonan low uplift and part of the Bozhong Depression on the north side still exhibit uplifted landforms and serve as sediment source areas. (3) During the early Cenozoic (from early to middle Himalayan), under the strong NW-SE directed extensional and rift environment, the study area experienced near S-N directed bidirectional detachment activity. The Huanghekou Depression continued to experience southward faulting, forming a basket-shaped and half-graben shaped structure. The strata in the Bozhong Depression underwent northward faulting and detachment. The west section of Bonan low uplift was affected by transtensional detachment, presenting a geomorphic feature of “high and narrow in the west, low and wide in the east”, ultimately forming the current tectonic pattern of “two depressions with one uplift”, providing space for the deposition of Cenozoic Shahejie Formation source rocks and Dongying Formation cap rocks.
- 1
-
Zirconium resources and mineralization in China
CHEN Binghan, YU Jinjie, YAO Fojun
Abstract:
This article divides China's zirconium deposits into alkaline granite type, alkaline complex type, pegmatite type, weathering crust residual slope deposit type, coastal sedimentary type, and river alluvial type. The predicted types of zirconium deposits are divided into the granite type, pegmatite type, coastal sedimentary type, river alluvial type, weathered crust and residual slope deposit type. China's zirconium ore resources are distributed in 15 provinces (autonomous regions) including Inner Mongolia, Hainan, Sichuan, and Guangdong, with zirconium ore reserves in these four provinces (autonomous regions) accounting for 93.7% of the national total. Based on the statistics, the metallogenic period of zirconium deposits in China is divided into Neoproterozoic, Late Paleozoic, Mesozoic, and Cenozoic. 14 zirconium metallogenic belts are divided. 34 Zirconium-related metallogenic series are determined and the metallogenic pedigree of zirconium deposits in China is established. The coastal sedimentary and river alluvial zirconium deposits along the southeast coast can be used as prospects for zirconium exploration.
- 1
-
Thermal History Reconstruction of Ultra-Deep Ancient Strata in Sedimentary Basins: A Case Study of the Northern Sichuan Basin
Qianqian Feng, Nansheng Qiu, Xiaodong Fu, Xin Liu, Yuhan Shan
Abstract:
Deep ancient strata are important areas for oil and gas exploration. Accurately reconstructing the thermal history is crucial for determining the depth and phase of deep oil and gas reservoirs. This study uses the Sinian-Paleozoic marine strata in the northern Sichuan Basin as a case study to introduce a method that combines multiple paleothermometers, including zircon fission tracks, (U-Th)/He, clumped isotope, U-Pb dating, and vitrinite reflectance, to reconstruct thermal history. This approach provides valuable insights regarding the thermal history reconstruction of ultra-deep ancient strata in sedimentary basins. The method involves reconstructing the paleo-geothermal gradient based on a series of deep vitrinite reflectance, simulating thermal history using fission tracks and (U-Th)/He of shallow Meso-Cenozoic clastic rocks to estimate exhumation and reconstruct the burial history, and modeling temperature evolution at different depths using fission tracks and (U-Th)/He of deep ancient clastic rocks, as well as clumped isotopes and U-Pb dating of carbonates, to reconstruct the evolution of the paleo-geothermal gradient and paleo-heat flow in the study area. The thermal history of the Northern Sichuan Basin since the Sinian is characterized by the superimposition of long-term cooling of the craton and thermal disturbances caused by Mesozoic crustal thinning.
- 1
-
Magma origin and the evolution of transcrustal magmatic system of the Changyu caldera in eastern Zhejiang Province: Evidence from zircon Hf isotope
HE Zhenyu, Guo Lei, YAN Lili, LU Tianyu
Abstract:
As an essential component of the continental crust, the products and magmatic systems of silicic volcanic activity recorded the vital information on the continental crust differentiation. Intensive Cretaceous volcanism was widespread along the coastal area of SE China, dominated by rhyodacites and rhyolites, offering a unique opportunity to unravel the growth and evolution of transcrustal magmatic systems. Here we present systematic zircon Hf isotopic data integrated with previous researches for the Changyu caldera in eastern Zhejiang Province, in order to constrain the magma sources and evolution of the magmatic system. The different eruption stages of the caldera, including caldera-forming eruptions, post-caldera eruptions and the rhyolite domes show consistent zircon Hf isotopic compositions with εHf(t) values of -7.4 to -0.2 and TDMC Hf model ages of 1.45 Ga to 1.04 Ga, suggesting the genetic link of the volcanic rocks of different eruption stages and that the magmas were mainly formed by the mixing of depleted mantle-derived magma and magma derived from ancient crust of the Cathaysia block. The compiled zircon Hf isotope data of the Late Jurassic to Cretaceous volcanic rocks from the coastal SE China reveal that the εHf(t) values are typically located far below the depleted-mantle evolution trend with a particularly wide range, and their TDMC Hf model ages cluster mainly between 1.8 and 1.0 Ga almost without Archean ages. This implies that the ancient crustal basements of the Cathaysia block should also be prevalent beneath the volcanic field east of the Zhenghe-Dapu fault, besides the sporadic outcrops of the Precambrian basement rock, and that the ancient crust materials were involved to varying degrees in the origin of volcanic magmas along the coastal SE China. Furthermore, the generation of high-silica rhyolitic magmas from the Changyu caldera and other Cretaceous calderas in the coastal SE China reflects the long-term evolution of the transcrustal magmatic system as well as crystal-melt segregation processes. Juvenile mantle-derived magmas not only contribute to the genesis of silicic magmas and the growth of continental crust, but also supply the necessary magma and heat flux for the transcrustal magmatic system of the large-scale silicic volcanism. The internal and external structures of calderas, the comprehensive mapping on genetic types, spatiotemporal distributions, as well as the volcanic eruption history are the crucial foundations and important contents of future studies on the transcrustal magmatic systems of the intensive Cretaceous volcanism in the coastal area of SE China.
- 1
-
The 3D Geological model of Daqiao super-large gold deposit in West Qinling and its ore-forming factors
HE Jinzhong, ZHANG Zhongping, HE Gandi, NIU Pengfei, ZHU Yongxin
Abstract:
The orebodies of Daqiao gold deposit in West Qinling are characterized by their large-sized scale. In this paper, the 3D model of the ore deposit is used to objectively draw out the spatial structure of gold orebodies and their relation with geological structure of the deposit, and to extract ore-forming factors. The 3D modeling of geological structure of the ore deposit was carried out by using of the geological factors such as gold orebody, special lithology layer, structure and discontinuities, and the 3D models were analyzed. The results are as follows: The matching coefficient between granodiorite dyke and gold mineralization is higher in time than that in space. The marble and part of carbonaceous rocks were related to deep heat flows in the main hydrothermal ore period. The strike-slip faults cut in bevel the fold of bedding fault, of which the axial trace had deflected northward, and they made up a thrust-strike slip tectonic system togather. The main ore-controlling structures are bending of anticline, gently dipping bedding fault, and strike-slip fault. The early hydrothermal ore period of mineralization was controlled by bending of anticline and gently dipping bedding fault, and the main hydrothermal ore period of mineralization constrained by strike-slip fault. The key ore-prospecting indicators are characterized by the silicified rocks covering gold orebodies, and around which there distribute granodiorite dykes, quartz dykes, calcite dykes, calcitized breccia, marble, and carbonaceous rocks. By comprehensive analysis, the key ore factors of the super-large gold deposit, based on ore-forming conditions and ore-forming process in the hydrothermal ore period, can be stated as follows: Products of magmatic hydrothermal mineralization in thrust tectonic system in the early hydrothermal ore period, strike-slip tectonic system, deep magmatic fluid, and large scale of wallrock alternations around the silicified rocks.
- 1
-
Mineralogical and geochemical characteristics and enrichment mecha-nisms of critical elements in the No. 3 coal seam of the Shanxi Formation in the Hengcheng mining area, Ningdong coalfield
GUO Yajie, SHI Yutao, JI Xiaoyan, MA Shaodong, HUANG Pengcheng, YANG Dequan, CAO Yongbin, SUN Jia, ZHANG Qi, LI Baoqing
Abstract:
The study of coal-related critical elements deposits has become a frontier hotspot in coal geology research and an important source for increasing reserves of critical elements mineral resources. This study focuses on the No. 3 coal seam of the Early Permian Shanxi Formation at the Maliantai Coal Mine in the Hengcheng mining area of the Ningdong coalfield. It investigates the mineral composition and geochemistry to determine the distribution, occurrence, and en-richment characteristics of elements minerals in the coal, as well as to evaluate their compre-hensive utilization. The study results show that:（1）The No. 3 coal seam at Maliantai is characterized by medium ash yield, high volatile yield, ultra-low total moisture content, and low to medium total sulfur content, with minerals in the coal mainly composed of kaolinite；（2）The major elements in the coal are primarily composed of SiO2 and Al2O3, with minor amounts of Fe2O3, CaO, and MgO. Compared to the average coal worldwide, Li and Zr reach enrichment levels, while Ga, Nb, Hf, Ta, Pb, Th, and rare earth elements (REE+Y) are slightly enriched；（3）Li and Ga are mainly found in kaolinite, Zr (Hf) and Nb (Ta) are primarily found in zircon, and REY is primarily hosted in kaolinite and aluminum phosphate (goyazite) associated with kao-linite. The Yinshan ancient land in the northeast of Ningdong coal field provides important felsic clastic material for the Malitai No. 3 coal, in addition, the Alashan block also provides some volcanic clastic material. The enrichment of critical metals such as Li, Zr (Hf), and Nb (Ta) in the coal is mainly controlled by the input of alkaline-peralkaline felsic clastic materials, with chemical weathering and water-rock interactions being secondary controlling factors. The en-richment of Ga is primarily controlled by the intensity of chemical weathering. The enrichment of REY is mainly influenced by the input of clastic materials and water-rock interaction processes. In addition, the kaolinite content also plays a role in the enrichment of Li, Ga, and REY. Malian Tai No. 3 coal has potential as a source of Li-Ga-Zr-REY metals.
- 1
-
Time limit of Mesozoic and Cenozoic uplift in the eastern margin of Yinchuan graben：evidence from fission track
Wang ShiZhe, Zhao HongGe, Liu ChiYang, Zhang YiCheng, Wang JianQiang, Wang Jian, Ma Biao, Li Xingcheng
Abstract:
The eastern margin of Yinchuan Graben is located in the northern part of the structural belt on the western margin of Ordos Basin, at the junction of Alashan Block, Ordos Block and Qinqi Fold Belt with strong activity. The Mesozoic and Cenozoic have experienced multi-stage structural activities, and its structural uplift is of great significance to the study of structural evolution and oil and gas exploration in the surrounding areas. Based on the age, length characteristics and thermal history simulation analysis of apatite and zircon fission tracks in different areas and horizons in the eastern margin of Yinchuan Graben, combined with structural characteristics and stratigraphic contact relationship, this paper points out that the study area has experienced at least Late Jurassic (160~145Ma), Late Cretaceous (100~70Ma), Early Miocene (22~20Ma) and Late Miocene (10~8Ma). There are some differences in uplift characteristics in different periods and regions. The uplift in the northern and southern parts of Mesozoic started earlier (early/middle Jurassic), and it gradually uplifted from the north and south parts to the middle part. The uplift rate in the middle part of late Jurassic was higher than that in the north and south parts, and the whole uplift was slow in the late Cretaceous. Since Miocene, the uplift has been characterized by early south and late north, and the uplift rate increased northward. This uplift period and differential uplift characteristics have corresponding geological response and regional dynamic mechanism.
- 1
-
Genesis of albitite in the Jiling Na-metasomatism Uraniumdeposit of the Longshoushan Uranium metallogenetic Belt:
Ma Xunjiao, Wang Kaixing, OuYang Hegen, Wang Wei, Yu Chida, Wang gang, Liu Xiaodong
Abstract:
The Jiling uranium deposit epitomizes a Na-metasomatic uranium deposit in China. However, the formation mechanism of its host albitite has been controversial, limiting our understanding of the ore-forming mechanisms of Nametasomatic-type uranium deposits. Apatite is a common mineral in magmatic-hydrothermal deposits and serves as an essential carrier for tracing fluid sources. In this study, electron probe microanalysis, and LA-ICP-MS isotope and trace element analyses were conducted on apatite from the albitite of the Jiling uranium deposit. Comparative analyses were also made with apatite from the granitic rocks (quartz monzonite, granodiorite, and granite) within the region. The results indicate: (1) The syenite of the Jiling deposit formed during the Late Silurian (429 ± 19 Ma and 429 ± 16 Ma), which is close to the formation ages of the granitic rocks (441~435 Ma) and syenite (428 Ma) in the region; (2) Compared to the magmatic apatite in the regional granites, the apatite in the Jiling albitite shows significantly elevated contents of Cl, Sr, Y, Th, and U, along with decreased contents of F and Fe, as well as a lower F/Cl ratio; (3) The apatite in the Jiling albitite displays similar light rare earth element contents and Sr/Y ratios as those in the apatite of the syenite. These findings suggest that the albitite of the Jiling uranium deposit originates from a hydrothermal system. The sodium metasomatic fluids (including high-temperature uranium mineralization material) originated from the crystallization differentiation of contemporaneous syenites in the region, falling within the magmatic-hydrothermal fluid category. Therefore, in the tectonic zone intersecting the main granite and the northern syenite, favorable conditions exist for the high-temperature uranium mineralization process of the Jiling uranium deposit.
- 1
-
Application and effectivity of " Satellite-UAV- Spectroscopy" remote sensing three-dimensional survey technology in Li-Be pegmatite ore survey in Altun Mountain,Xinjiang
Abstract:
The Altun metallogenic belt is an important lithium metallogenic belt, and in recent years, 9 Li-Be deposits above medium size and 11 Li-Be mine sites have been discovered in Washixia South, Tugman, Tamuqie. Two rare metal metallogenic sub-belts in the south and north have been defined, which has good prospect for finding minerals; however, the working conditions of this belt are harsh, and the degree of geological work is low. it has the importance of the area of great breakthroughs in the search for Li-Be mines. This paper adopts the "Satellite-UAV- Spectroscopy" remote sensing three-dimensional survey methodology and technology, co-operating with ground infrared spectrometer, unmanned aerial vehicle (UAV) hyperspectral and satellite remote sensing technology, sampling multi-spectral remote sensing to identify the rock body and stratum on a small scale of 1:200000-1:50000, and superimposed geochemistry to carry out the selection of Li-Be prospecting area; In the prospecing area, high-resolution remote sensing images are sampled to identify pegmatite veins on the scale of 1:10,000 to define the target area for mineral exploration; and UAV hyperspectral data is used to differentiate the Li-Be-bearing pegmatites on the scale of 1:5000 to achieve rapid and efficient positioning of Li-Be pegmatite veins. This paper shows that the " Satellite-UAV- Spectroscopy" remote sensing three-dimensional survey method is very suitable for the ore-bearing pegmatite veins in Altun Mountain by comparing with the measured ore-bearing pegmatite veins in the field. The problem of integrating "map" with "spectrum" in large-scale mineral mapping is solved and the precise positioning of Li-Be-bearing pegmatites is achieved.
- 1
-
Genetic relationship of the deposit in Qibaoshan ore-concentration area of Wulian County, Southern Margin of Jiaolai Basin: Constraints of in-situ sulfur isotope and trace element of sulfides
Tang Mingying, Ding Zhengjiang, Zhan Honglei, Zhu Wei, Wang Xin, Wei T, Li Fuhua, Chen Jian, Zou Zhanchun
Abstract:
The Au-Cu polymetallic deposits represented by the Qibaoshan ore-concentration area of Wulian county is developed in the Southern Margin of Jiaolai Basin, three typical deposits are developed, namely, Jinxiantou Au-Cu deposit, Diaoyutai pyrite deposit and Qibaoshan Pb-Zn polymetallic deposit. In order to further elucidate the genetic relationship between ore deposits, improve the study of ore-forming system in ore concentration area, and establish the ore-forming model of ore deposits, the main sulfides in the ore deposit were tested and analyzed in situ for sulfur isotopes and trace elements of pyrite.. The sulfides in the Qibaoshan ore concentration area has a relatively concentrated sulfur isotope peak distribution range (0‰ ~ 6‰), which comes from the same or similar deep magmatic system.. The Cu, Zn, As, Se, Ag, Sb, Pb and Bi in pyrite show relatively regular changes from Jinxiantou Au-Cu deposit to Diaoyutai pyrite and then to Qibaoshan Ag-Pb-Zn polymetallic deposit, The distribution characteristics of elements show that the ore-forming fluid as a whole presents an evolution process from magmatic hydrothermal to mixed hydrothermal. Comprehensive analysis shows that the deposits in Qibaoshan ore collection area are closely related in time and space. The deposits are the products of the same geological and tectonic environment and different parts of rock construction, which together constitute the porphyry-epithermal Au-Cu-Pb-Zn-Ag polymetallic metallogenic system in Qibaoshan area.
- 1
-
Sedimentary characteristics and filling model of the PermianFengcheng Formation in Mahu Area, Junggar Basin, NW China
p FontSize=''.''>SUN Jing, ZHENG Menglin, YOU Xincai, ZOU Zhiwen, HE Wenjun, CHANG Qiusheng
Abstract:
In order to clarify the sedimentary characteristics, distribution laws and filling patterns of all types of reservoirs in the Permian Fengcheng Formation in Mahu area of the Junggar Basin under the theory of the whole oil and gas system, the sedimentary facies types, basic characteristics, distribution laws, evolution characteristics and filling patterns of all types of reservoirs were systematically studied by using data such as logging, coring and 3D seismic of nearly 50 key wells. The results show that the Fengcheng Formation is a fan delta-lake sedimentary system, with fan delta facies mainly developing subfacies such as plain, inner front, and outer front, and lake facies mainly consisting of shoreline shallow and semi deep lake subfacies. The complete sequence and all types of reservoirs, including various types of coarse-grained conglomerates, medium grained sandstones, fine-grained siltstones, mudstones, and alkaline minerals, are developed. Different subfacies and microfacies develop different types of reservoirs. Different periods of fan delta overlap with each other, forming four fan delta groups in the north, west, south, and east of Mahu Area, mainly composed of distributary channel conglomerate and sandstone sediments, with a gradually expanding distribution range. The western block is mainly composed of contiguous wide and long axis fan deltas, while the eastern is mainly composed of isolated narrow and short axis fan deltas. Under the control of four main factors, It has formed three types of fan deltas under water ingress: retrogressive, composite, and progradational.Three types of mixed sedimentary filling patterns, including under , balanced, and over compensation, have developed together. The systematic study of the sedimentary characteristics and filling patterns provides a basis for deepening the analysis of all types of reservoirs and exploration and development in the field of all oil and gas systems.
- 1
-
Zircon U-Pb ages of the Xiuning Formation and Shangshu Formation in the eastern Jiangnan Orogen and their geological implications
Sun Yue, Wang Dongsheng, Sun Junjun, Zeng Renyu, Zhang Xianan, Zhai Siyang, Niu Yafei
Abstract:
The Neoproterozoic Xiuning Formation and the underlying Shangshu Formation, located on the northern side of the Jiangshan-Shaoxing fault, are significant stratigraphic unites in the eastern Jiangnan Orogen, South China. They record Neoproterozoic tectonic evolution information and provide crucial evidence for regional stratigraphic correlation and tectonic evolution. In this study, microscopic characteristics, zircon CL images, and LA-ICP-MS U-Pb geochronological data are presented for sandstone and tuff from the Xiuning Formation and Shangshu Formation, respectively. The microscopic characteristics of the sandstone and the CL images of the zircons show that the detrital particles and zircons of the sandstone predominantly exhibit angular and subangular, revealing a short-range transportation of the source, while the tuff of the Shangshu Formation exhibit plagioclase phenocrysts and zircons with zonal and rhythmic structures, representing magmatic origin. The detrital zircon U-Pb ages from the Xiuning Formation are primarily concentrated between 843 Ma and 718 Ma, with six ages from the Mesoproterozoic to Paleoproterozoic. The weighted mean U-Pb age of zircons derived from the tuff of the Shangshu Formation is 847±6.7 Ma (n=18，MSWD=1.8). Combined with the published data from eastern part of Jiangnan Orogen, it is inferred that the beginning and end deposition ages of Xiuning Formation are ~785 and ~725 Ma, respectively, while the underlying Shangshu Formation was formed during 845~785 Ma. The Shangshu Formation records magmatic activities at approximately 845, 825, and 800-785 Ma, reflecting multiple volcanic-depositional cycles in the study area. During the period of 850~785 Ma, the Yangtze and Cathaysian blocks underwent a sequence of subduction, collision and post-collision extension, with the rift basin gradually opening after ~785 Ma.
- 1
-
Evolution and genetic mechanism of high pressure in the Qianfoya Formation shale gas in the Puguang East syncline in northeastern Sichuan
zhaoniubin, lilingxi, wantao, wanggonghuai, jinda, houxianbo, zhanghao
Abstract:
In the shale gas reservoir of the Qianfoya Formation in the east-west syncline of Puguang in northeastern Sichuan, overpressure is prevalent.The distribution range, genetic mechanism, and pressure evolution process of the overpressure storage box have not been fully clarified. Based on geological data and logging data, the paper comprehensively analyzes the distribution range, genetic mechanism, and pressure evolution process of the pressure storage box in the first section of Qianfoya Formation shale gas reservoir using the Eaton method, Bowers method, fluid inclusion technology, and basin simulation technology. The results show that: ① The upper floor of the first section of Qianfoya Formation shale gas reservoir is composed of the Daanzhai Member and the bottom of the first section of Qianfoya Formation, consisting of sandy tuffaceous sedimentary tuff, tuffaceous anisotropic quartz sandstone, tuffaceous siltstone, and mudstone. The roof was mainly composed of mudstone interbedded with tight sandstone in the ④ and ⑤ sub-layers of the first section of Qianfoya Formation. Good roof, floor and lateral partition layers avoid the loss of natural gas; ② The overpressure source was mainly caused by fluid expansion due to hydrocarbon generation, followed by structural compression, with a weak relationship with uneven compaction; ③ The abnormal pressure storage box has undergone a stage of organic matter immature-low mature normal pressure, organic matter mature liquid hydrocarbon overpressure stage, organic matter high mature-overmature shale gas abnormal pressure stage, late-stage extrusion and pressure increase and uplift pressure relief collaborative transformation and finalization stage.
- 1
-
LA-ICP-MS zircon and tantalum-niobium U-Pb geochronology of the Jiabusi Ta-Nb deposit, Daxing'an Mountain
丁, Zhang Yong, Ye Huishou, Yu Jinjie, Fu Xuerui, Wu Shenghua, zhang Tong
Abstract:
Abstract：The Jibusi Ta-Nb rare metal deposit, accompanied by Li-Rb-Cs mineralization, is a medium-sized Ta-deposit located in the southwest of the Daxinganling rare metal metalization belt. In this paper, through systematic petrographic analysis, rock geochemical analysis and LA-ICP-MS U-Pb chronology analysis of tantalum-niobium, the diagenesis and metallogenic mechanism of the deposit and ore-forming rock were studied. The lithology of ore-forming granite in Jiabusi deposit is mainly jadeite-lithium muscovite-alkalic feldspar granite and lithium muscovite-albite granite. The geochemical data of ore-forming rock shows that their major elements are rich in silicom,aluminum and alkali, but poor in iron, magnesium and calcium, very poor in titanium and phosphorus, which belongs to the peraluminous high potassium calcium alkaline series. Their trace elements are rich in Rb, Th, Nd and Zr, poor in Ba, Nb, Sr and P, strong depleted in Ti. Their rare earth elements (REEs) show very lower ∑REE with average value is 47.97×10-6, have strong negative Eu anomaly and significant M-type “tetradeffect ”. The Zr/Hf of ore-forming granites are between 2.58~3.47，Nb/Ta are between 0.3~0.39, which indicate its belong to Ultra (or extremely) fractionated granite. The ore minerals in Jiabusi deposit are microlite, manganotantalite and Li-muscovite, with Rb and Cs are mainly present in minerals such as lithium mica and tantalum niobium in a similar texture. This paper reports the U-Pb dating results of different granites in the deposit by using LA-ICP-MS method. Zircon U-Pb age of ore-free biotite (hornblende) granite was 144.0±1.0 Ma (2σ, n=16, MSWD=1.3), which represents the diagenetic age of the surrounding rock Narenwula intrusive body. The weighted average age of 206Pb/238U of magmatic tantalum-niobium minerals in mineralized alkalic feldspar granite was obtained at 120.7 ± 0.2 Ma (2σ, n=17/18, MSWD=6). It shows the mineralization age and the diagenetic age of the Jiabusi ore-forming granite intrusion are late phase of Early Cretaceous, which are related to the lithospheric extension after the closure of the Mongolian-Okhotsk Ocean in the Middle Jurassic. The author indicated that the formation of Jabusi deposit can be divided into two stages. The first stage is the primary crystallization stage of magma, which is dominated by Ta and Nb mineralization. The second stage is the self metasomatism stage of hydrothermal fluids, which is dominated by li, Rb and Cs mineralization. Around the Narenwula intrusive rock foundation, there still has the potential of finding rare metal deposits as the same type.
- 1
-
Tectonic activity history and its dynamic mechanism of the Binhai fault, Hainan Island: New evidences from apatite and zircon fission track analyses
LIN Di, ZHENG Yong, HU Zailong, WEI Changxin, YUAN Qinmin, JIANG Yuhao
Abstract:
Hainan Island is the largest continental marginal island in the northwestern South China Sea, which is surrounded by Cenozoic rift basins such as Qiongdongnan Basin, Yinggehai Basin, and Beibu Gulf Basin. Thus, it constitutes the major footwall of the boundary fault of these basins. Therefore, the uplift and exhumation history of the Hainan Island contains important information on basin-range coupling process and oil, ores preservation conditions. This study first reports the analyses results of apatite and zircon fission track along the Binhai fault which is the only basin-controlling fault extends into the Hainan Island. The apatite fission track ages range from 23 Ma to 40 Ma, and the average confinement track length ranges in 12.2?13.2 μm, which is relatively small. The zircon fission track ages range from 63 Ma to 82 Ma, and the single grain ages are mainly concentrated in the age groups of 82?78 Ma and 72?69 Ma, respectively. The cooling history of Hainan Island since the Late Cretaceous is generally divided into three episodes. From the Late Cretaceous to the Early Paleocene (82~63 Ma), the whole Hainan Island uplifted rapidly with a total exhumation amount of 3.33 km. During this period, the Hainan Island was jointly affected by the NW compression caused by the subduction of the Pacific plate and the expansion of the middle ridge of the ancient South China Sea, and the Baolun gold mine along the western margin of the Baisha basin was also influenced by the large-scale compressional deformation. From Early Paleocene to Middle Miocene (63?13 Ma), the samples experienced a protracted period of slow cooling, except the western side of the Binhai fault, where also records a rapid cooling from the Middle Eocene to Late Oligocene (40?24 Ma). We attributed this rapid cooling period to the drag effect caused by the accelerated subduction of the Paleo-South China Sea, and the differential uplift on both sides could be attributed to the reactivation of the Binhai fault. During this period, the coarse clasts exhumed from the Hainan Island constitute the key reservoir of the Cenozoic basin. Since the Middle Miocene (13~0 Ma), the exhumation amount is 1.93 km. The compression stress caused by the NNW wedge of the Philippine Sea plate and the long-distance effect of the India-Eurasia plate collision has caused Hainan Island to undergo strong rapid compression and exhumation during this period.
- 1
-
Petrogenesis，age and multi–stage crustal melting / reworking of granitioid from the Yuka ultra–high pressure metamorphic terrane in the Northern Qaidam basin
Fu Xuemei, Li Meng, Yang Wei, Zhu Xiaohui, Wang Chao
Abstract:
This article conducts petrological，geochemical，zircon U–Pb geochronology，and Hf isotope studies on the widely exposed granitic rocks in the Yuka ultra–high pressure metamorphic terrane in the Northern Qaidam basin．The zircon U–Pb dating results indicate that the granitic rocks in the Yuka ultra–high pressure metamorphic terrane have obtained metamorphic ages of 929 ± 6 Ma，magmatic crystallization ages of 915 ± 6 Ma to 904 ± 5 Ma，and early Paleozoic magma crystallization ages of 420 ± 3 Ma to 402 ± 4 Ma．The geochemical characteristics of the rocks show that the K2O / Na2O ratio of the Yukahe and Kaipinggou gneiss like diorite granite is 1.53 to 2.60，which is a high potassium calcium alkaline potassium basalt series and has a low zircon εHf(t) value（- 12.86～- 0.76）indicates that the source rock is metasedimentary rock or metamorphic greywacke．Caishigou and Xigou Asbestos mine granite gneiss have K2O / Na2O < 1，belonging to the medium potassium calcium alkaline series．Compared with the Yukahe and Kaipinggou gneiss like diorite granite，the Eu anomaly is not obvious and has a Sr positive anomaly．The source rock has characteristics of amphibolite or quartz diorite source area．The granite gneiss of the Xigou asbestos mine εHf(t) value ranges from - 5.21 to + 15.52，indicating the heterogeneity of the material composition in the source area of the granite gneiss in the Xigou asbestos mine．The source area may be mainly composed of basic new crustal material，with some contamination of ancient crustal material．The samples obtained in this article have a relatively high zirconium saturation temperature（732 ℃～809 ℃）．Combined with geochemical characteristics，it is shown that the source rocks of the granite rocks in the Yuka terrane are metamorphic sedimentary rocks and metamorphic basic rocks，mainly composed of muscovite and hornblende dehydrated and melted．Combined with regional geological data，the granitic rocks in the Yuka terrane about 915～904 Ma were formed in the post–collision tectonic setting．The Xigou asbestos mine granite gneiss records metamorphic fluid transformation events of the Neoproterozoic crust at 420～400 Ma，which may be related to the melting event during the reentry process of the deep subduction continental crust．The granite rocks in the Yuka ultra–high pressure metamorphic terrane in the Northern Qaidam basin have recorded multiple melting / metamorphic fluid transformation events during the orogenic processes of the Neoproterozoic and Early Paleozoic．
- 1
-
Seismic characteristics and hydrocarbon accumulation potentiality of maar-diatreme volcanoes -take Tazhong area of Tarim Basin as an example
Zheng Xiaoli, 王志勇, Li xingyun, Tian bing, LI jianfeng
Abstract:
The Maar-diatreme volcanoes are negative geomorphic volcanic structures, result from short-term, near-surface magma/water interactions. There are currently no literature reports on its seismic characteristics and hydrocarbon potential in China. The scale, shape, structure and lithology of the Permian volcanoes in Tazhong area, Tarim Basin, are analyzed by using high-precision continuous 3D data. More than 80 volcanic craters have been identified in the study area, with a total area of approximately 105 km2, and most of them are Maar-diatreme volcanoes with negative landforms. The shapes of the Maar volcanic craters in the research area are circular or elliptical, with approx. 200-2500 m wide and 300-700 m deep. On the profile, the characteristics of the volcanoes can be divided into two parts. The chaotic weak reflection in the lower part is the diatreme structure, mainly composed of diatreme breccia and collapse breccia; The upper parallel and medium strong amplitude reflections are crater sediments, possibly lacustrine sediments of Maar Lake. The craters are surrounded by low angle tuff rings composed of ejecta from these explosions, and the normal faults formed by collapse,compaction and syn-deposition. The explosive volcanic breccia of Maar is a high-quality reservoir for oil and gas, and volcanic vents can serve as oil and gas migration channels. The mud shale and coal rocks deposited in the later stage of Maar Lake are not only source rocks, but also serve as high-quality cap rocks. The Maar-diatreme volcanoes are generally small in scale, but they are numerous and easy to identify. Areas with shallow burial have great potential for oil and gas exploration.
- 1
-
Growth and Evolution of the North China Craton: Evidence from zircon U-Pb geochronology, trace elements and Hf-O isotopes
Wang Xin, Chen Jian, Chen Jian, Meng Yuanku
Abstract:
Exploring the growth and evolution of continental crust has always been one of the most fundamental problems in earth sciences. As one of the oldest Craton blocks, the North China Craton, which is widely developed with the Precambrian tectono-thermal events, is a key area for discuss this issue. Although there is a basic consensus that Archean is the main period of crustal growth, the growth mechanism is still controversial. This paper summarized zircon U-Pb chronology, Th-U contents, Hf-O isotope data from Precambrian studies in the North China Craton in recent years, aiming to explore the growth and evolution of the continental crust of the North China Craton. The following results were obtained: (1) Archean-Paleoproterozoic rocks, especially the Neoarchean rocks, are widely developed in the North China Craton. Among them, the pre-Mesoarchean rocks are mainly distributed in the Eastern Block, and the Mesoarchean-Neoarchean rocks are mainly concentrated in the Eastern Block and the Trans-North China Orogen. While the Western Block is dominated by the Neoarchean-Paleoproterozoic rocks (2) The Hf depleted mantle model agesare similar to the U-Pb ages of the Mesoarchean-Neoarchean zircons, indicating that crustal growth was dominant at this period; however, after the Neoarchean, especially in the late Paleoproterozoic, the Hf depleted mantle model ages of the zircons are significantly older than the U-Pb age of zircon, indicating that crustal recycling was dominant. (3) The growth curve of the Precambrian continental crust in the North China Craton shows that the rapid growth of the crust occurred during the Mesoarchean and Neoarchean, while the crust grew slowly in the pre-Mesoarchean and late Paleoproterozoic. (4) The significant changes in zircon Th and U contents, Th/U ratios, and oxygen isotopes in the late Neoarchean and Paleoproterozoic marked a shift in the geodynamic mechanism. The crustal growth in the late Neoarchean was dominated by horizontal growth associated with subduction, indicating that the modern-style plate tectonics likely has initiated in the Neoarchean.
- 1
-
A comparison of the characteristics of Indosinian and Yanshanian granites and their control on the different W-Sn mineralization potential in Xitian Region, Eastern Hunan Province
Guo Feng, Lu Youyue, Fu Jianming, Guo Jungang, Zhang Fei, Cheng Shunbo, Zhang Zunzun, Zhang Shunxin, Anbang, Zhang Zhongyu
Abstract:
There are multiperiodic magmation and W-Sn mineralization in Xitian region, Eastern Hunan province, The Indosinian granite mineralization was relatively weak, while the Yanshanian granite mineralization was pronounced. The critical factors controlling the difference in the potential of W-Sn mineralization between the two periods of granite are still unclear. In this paper, we report Zircon U-Pb chronology, Zircon Lu-Hf isotope data, whole rock geochemistry and mineral composition for Indosinian and Yanshanian granites in Xitian region. The zircon LA-ICP-MS U-Pb dating yielded magmatic crystallization ages of 240.0±1.3Ma and 152.9±1.0Ma, corresponding to the Indosinian and Yanshanian periods, respectively. Both periods of granite are characterized by high Al2O3 contents, low MgO contents, enriched in Rb, K, U, Th and depleted in Ti, P, Sr, Ba, Nb. The Zircon εHf(t) values (concentrated between -7.0 and -5.0) and melting temperature(>750℃) of the two periods of granite are similar, The Zircon TDM2 values of Indosinian granite and Yanshanian granite are concentrated at 1.65-1.70Ga, 1.55-1.60Ga, suggesting a magmatic source which was partial melting of ancient crust of the Paleoproterozoic era at high temperature, but the source rocks of the Yanshanian granites are younger than Indosinian granites. The whole-rock Zr/Hf ratios of Indosinian and Yanshanian granite are 26.1-36.3 and 7.0-22.7, and the Nb/Ta ratios are 3.9-7.6 and 1.2-3.9, suggesting that both of them have experienced high differentiation evolution. The magma oxygen fugacity of the Indosinian granite (ΔFMQ=-0.42~2.61) is higher than that of the Yanshanian granite (ΔFMQ=-2.33~-0.08). The Ⅳ(F) of biotite indicates that Indosinian granites have lower concentration of F (Ⅳ(F)=1.15~1.26) than Yanshanian granites (Ⅳ(F)=0.71~0.87). Consequently, more enriched magmatic source region, lower oxygen fugacity and higher F abundance may be the main reasons why Yanshanian granites have more pronounced mineralization than Indosinian granites.
- 1
-
Spatial and temporal distribution characteristics of Indosinian unconformity in Mianzhu area in the piedmont zone of Middle Longmen Mountains
Abstract:
Due to the complexity of its geological structure and geological evolution, Longmen Mountain has always been the focus of research. The middle part of Longmen Mountains, which has large topographic gradient changes and the most complex magmatic metamorphism, has become one of the ideal areas to reveal the geological structure of Longmen Mountains. At present, there is no unified understanding of several stages of structural activities in the middle part of Longmen Mountains during the Indosinian period. In this paper, we make full use of drilling and seismic data and joint well and seismic demarcation to identify and classify the Indosinian unconformity in Mianzhu area in the piedmont zone of middle section of Longmen Mountains. According to the plane projection of the cut overlap points of the unconformity, we outline the distribution range of various types of unconformity in different periods, construct the chronostratigraphic framework in Mianzhu area, and establish the unconformity evolution model map. The results show that there are four consecutive stratigraphic faults in the early Indosinian stage, 5Myr in the middle Indosinian stage I, 5Myr in the Middle Indosinian stage II, and 28Myr in the late Indosinian stage. Four sets of unconformity were identified from the bottom up during the Indosinian period in the study area: unconformity between Leikoupo Formation and Majantang Formation, unconformity between Xiaotangzi Formation and Member 2 of Xujiahe Formation, unconformity between Member 3 and Member 4 of Xujiahe Formation, unconformity between Member 5 of Xujiahe Formation and Baitianba Formation. In general, the unconformity spread from NE to SW along the Indosinian ancient nappe, which was wide in NE and narrow in SW. From NW to SE, the unconformity changed from angle unconformity to parallel unconformity. The middle part of Longmen Mountains is characterized by multi-stage evolution and progressive deformation from north to south, among which the early and late Indosinian phases are the key structural changes affecting Longmen Mountains to Sichuan Basin. The determination of the spatial and temporal distribution of the Indosinian unconformity in the piedmont zone of middle part of Longmen Mountain and the establishment of the chronostratigraphic framework provide reference for the quantitative study of the Indosinian tectonic belt of Longmen Mountain, and provide a basis for the order of the Indosinian tectonic activity.
- 1
-
Structural characteristics and growth evolution of the No.8 strike-slip fault zone in Gaoshiti-Moxi area in the central Sichuan Basin
LU Guo, HE Dengfa, TIAN Fanglei, ZHANG Weikang, MA Jia, ZHAO Xiaohui, LIU Huan, LUO Wei
Abstract:
The intra-craton strike-slip fault system in the central Sichuan Basin, developed above the Neoproterozoic rift system, plays a key role in controlling hydrocarbon migration, accumulation and differential enrichment. In order to deepen the understanding of the structural geometry and kinematic characteristics of the strike-slip fault in the central Sichuan Basin, this paper describes the structural geometry characteristics of the No.8 strike-slip fault zone in the Gaoshitai-Moxi area in detail based on high-precision three-dimensional seismic data, and establishes a three-dimensional structural model of the fault zone. Combined with aeromagnetic data, the relationship between strike-slip fault system and deep rift system in central Sichuan Basin is analyzed. The growth pattern and evolution process of strike-slip fault zone are recovered by fault throw statistics and structural stripping inversion. The study indicates that: 1.The strike length of No.8 strike-slip fault zone is about 70km, and it experiences the variation of NWW-NE-NWW-NE from west to east, causing the right-lateral faulting on the platform of the second and fourth members of the Dengying Formation. The fault zone has typical strike-slip structure styles such as high steep linear structure, "Y" shape structure and negative flower-like structure in the section, and has obvious segmented characteristics in the plane, consisting of 5 main faults, mainly developed horsetail structure and linear structure. 2.The deep Neoproterozoic rift system in the central Sichuan Basin has a good positioning effect on the Sinian-Lower Triassic strike-slip fault system, and the former is the foundation of the latter. The No.8 strike-slip fault zone is controlled by the deep Gaoshitai-Moxi Neoproterozoic rift fault, and the two are "hard connected". 3.No.8 strike-slip fault zone experienced three stages of inherited tectonic superposition on the basis of fault control of deep rift system: initial development stage from Late Sinian to Early Cambrian, growth setting stage before denudation from Late Ordovician to Caledonian erosion, and partial resurrection stage of Early Triassic. 4.There are two growth modes: 1)the fault grows upward from the weak zone of the basement, and the fault throw between the upper and lower strata is the same or gradually decreases. 2)The fault ruptures first from the top, gradually expands downward during the active period, and penetrates with the existing deep weak zone. The fault throw is large on the top and small on the bottom. In summary, The fault zone has experienced the complex deformation of "extension and right strike-slip", which belongs to the multi-stage development and multi-stage link tension-torsion (strike-slip) fault caused by the activation of the pre-existing fault.
- 1
-
Sedimentary response to glaciation evolution in the Ranwu Lake area, southeastern Tibet since ca. 33 ka
LI Jing, LU Haijian, LIANG Xiao, LI Haibin, PAN Jiawei, LIU Dongliang, ZHAO Zhongbao, CHEN Huan
Abstract:
Southeastern Tibet is characterized by widespread glacial geomorphology, thus reflecting the dominating role of glaciation in the formation of geological process. However, it remains still unclear with regard to how the sediments respond continuously to the late Quaternary glaciation in this area. A continuous late Pleistocene sedimentary sequence, well exposed at the Ranwu lake area, includes stratified slope deposits, channel deposits, moraine deposits, and loess deposits from bottom to top. Here we firstly analyzed the sedimentary characteristics of this section using sedimentology, paleocurrent data, and conglomerate clast count. Secondly, we obtained the ages of this section through optically stimulated luminescence (OSL) dating. Lastly, we discussed the forming mechanisms of these four types of sediments. Preliminary results are as below: 1) Stratified slope deposits are composed of sands and gravels that exhibit a typical rhythmic layering and were formed at about 33 ka. They reflect the alternating cold and warm climate change and likely belong to a periglacial sediment which are mainly dominated by the combined gelifraction and freeze-thaw processes. 2) Channel deposits consist primarily of variably sized gravels with distinct imbrication and were formed at 32.8~25.1 ka. They were likely produced by the large-scale floods from the northeast due to glacial lake outburst floods. 3) Moraine deposits are composed primarily of poorly sorted gravels, sands, and silts and were occurred at 25.1~11.1 ka, indicating that the Ranwu Lake area was dominated by the glacier flow during the Last Glacial Maximum (LGM). 4) Loess deposits are comprised mainly of fine-grained sands and silts and were deposited during the interglacial period (11.1 ka). They are derived from glacial meltwater debris distributed in the valley which were subsequently transported by glacial wind. In brief, the stratified slope deposits and channel deposits from the lower part of this section were both developed during the interglacial of the Last Glacial Period (the weak warm period of late Marine Oxygen Isotope Stage 3, MIS 3a), while the moraine and loess deposits were formed during the LGM and the Younger Dryas (YD), respectively. This late Pleistocene sedimentary sequence in the Ranwu Lake area well reflects the influence of glaciers variations on sedimentation.
- 1
-
Geochemical characteristics of apatite and hornblende in diorite of the Zhongguan iron deposit in Hebei Province and their records of petrogenesis and mineralization
caochong, caoqing, zhangyanbo, wangling, dongboxiao, Zhang Rongfang
Abstract:
The skarn-type iron deposit is an important guarantee of iron ore resources in China. It is necessary to study the source, genesis and evolution of physical-chemical conditions of ore-forming magma for understanding formation mechanism of skarn-type iron deposits. In this paper, the BSE images and corresponding major and trace element compositions of the hornblende and apatite in diorite from the Zhongguan iron deposit are conducted. The source of magma, magma mixing and crustal contamination process, as well as the changes of magmatic physical and chemical conditions caused by these processes are identified. Finally, the necessary magmatic conditions for the formation of the Zhongguan skarn iron deposits are proposed. The results show that the ore-forming magma experienced a double magma chamber system. In the deep magma chamber, the hornblende phenocrysts crystallized in the environment of temperature (average 943 °C), pressure (average 315MPa), oxygen fugacity (average ΔNNO + 0.34) and water content (average 5.97 %). In contrast, the hornblende matrix crystallized in the environment of temperature (average 773 °C), pressure (average 89MPa), higher oxygen fugacity (average ΔNNO + 1.5) and Cl content (average 0.15 %), and lower water content (average 4.87 %) in the shallow magma chamber. The changes of Al2O3 content of hornblende, as well as the 87Sr/86Sr（i）values (from 0.7053‰ to 0.7076‰) of apatite indicate that the ore-forming magma is mainly mantle-derived and mixed with a small amount of crust-derived materials. The obvious core-rim structures are shown in the BSE images of apatite, and the core is generally brighter than that of the rim. The cores are mainly enriched in SiO2, MnO, Ga, REEs et al. In contrast, the rims are more enriched in SO3, Na2O and Cl. Besides, the δEu values of the rims are higher than those of the cores. The chemical composition differences between phenocrysts and matrix of hornblende, as well as the core-to-rim compositional variations of apatite indicate that the ore-forming magma has undergone contamination of gypsum rock strata, crustal material mixing and fluid exsolution during the upward emplacement process, resulting in a significant increase in oxygen fugacity of magma, and promoting the enrichment of volatiles and Fe in magma. In summary, gypsum rock contamination or crust-derived magma mixing and hypabyssal emplacement are necessary conditions for the formation of the Zhongguan skarn high-grade iron deposits.
- 1
-
Application of apatite fission track thermochronology to mineral deposits: a review
Ji xuan, Liu Yingchao, Yue Longlong, Ma Wang
Abstract:
Apatite fission track chronology is a low temperature thermochronology based on the radiation damage effect of 238U spontaneous fission of apatite. The apatite seal temperature is low and sensitive to temperature change, and it can record important information such as the time, duration, distribution characteristics and activity rate of thermal events. The traditional external detector method (EDM) uses thermal neutron irradiation to generate induced fission track of apatite 235U, and then obtains the age of the fission track through correction calculation. The laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) method can directly analyze the content of 238U, which is convenient and fast. Electron probe microanalysis (EPMA) and Atomic force microscope (AFM) as auxiliary means can achieve more accurate fission track statistics. At present, the accuracy and comprehensiveness of the experimental methods, annealing dynamic models, and data interpretation are still insufficient. The integration of these processing elements with the geological evidence needs to be continuously upgraded. Nevertheless, the results of apatite fission track chronology and thermal evolution simulation have played a great role in determining the metallogenic age of hydrothermal deposits, dividing metallogenic stages, restricting the duration of hydrothermal mineralization, and quantifying the uplift and exhumation amounts of deposits. It has a broader development prospect and application space in determining the preservation and change law of deposit, predicting concealed deposit and ore body and so on.
- 1
-
The out-of-sequence deformation in the Xuefeng intracontinental fold and thrust belt and evolution of continental lacustrine basin
dengbin, Xu Hongyuan, Li Yingqiang, Tu Guoyu, Jiang Lei, Li Zhi, Liu Chongjiang, He Zeliang, Yong Ziquan, Liu Shugen
Abstract:
The fold-thrust belt foreland basin system is generally controlled by the process of shallow tectonic denudation-sedimentation and its related coupling mechanism, so it has complex three-dimensional tectonic deformation characteristics and evolution process. Under the remote effect of plate collision, out-of-sequence structures were formed in Xuefeng intracontinental fold and thrust belt in Upside Yangtze region. Based on the structural analysis of deep and large fault zones in the study area, fault calcite U-Pb chronology and deep structural interpretation of seismic profiles, the deformation process of Xuefeng intracontinental fold and thrust belt is reviewed: (1) In the Late Triassic to Early Jurassic (200Ma), the intracontinental fold thrust deformation occurred initially, and the Cili-Baojing fault began to move; (2) In the Late Jurassic and Early Cretaceous (120-160Ma), the multi-layer system slip caused the thrust deformation to extend to the Hubei, Chongqing, Hunan and Guizhou regions, and Jianshi-Pengshui fault began to move. (3) In the Late Cretaceous-Early Palaeo-Modern period (71-52Ma), the Enshi-Youyang and Hefeng-Laifeng faults began to move, and further extrusion folding and thrust-deformation occurred. The fault chronology and the deformation stress field in the study area jointly reveal the process of the Xuefeng intracontinental thrust system showing overthrust deformation before the Indochinese period and the back-camel structure deformation during the Yanshan period, which together form the structural characteristics of the foreland thrust belt with low wedge top Angle and wide deformation area in the Yangtze landmass, and control the formation and evolution of the ancient Yangtze continental lake basin in the Upper Yangtze region.
- 1
-
Study on hydrochemical characteristics and formation of salt resources in lithium basin of Jiezechaka super large salt Lake, Xizang
madianzhe, zhaoyuanyi, zhengmianping, chenwenxi
Abstract:
Located in Dongru Township, Ritu County, Ngari Prefecture, Tibet, Jieze Chaka Salt Lake has 2.3 million tons of LiCl resources, 1.6 million tons of B2O3 resources, and 9.79 million tons of KCl resources. It is one of the few lithium mines under development in Tibet. It is of great significance and scientific value to study the material source of the salt lake water and its recharge water. This paper systematically analyzes the Gezechaka salt Lake and its recharge water by means of hydrogeochemical methods. A total of 65 samples of lake water, river water and spring water were collected to test their TDS, pH value and main ion composition. The main ion characteristics, control mechanism and source of lake water and recharge water were studied by Chadha hydrochemical diagram, Piper Cationonic triangle diagram and Gibbs diagram. The results show that the chemical type of salt lake water is Na-CO3, the chemical type of river water is Ca-Mg-HCO3, Na-HCO3, and the chemical type of spring water is Na-HCO3. The composition of hydrochemical ions is mainly affected by rock weathering and evaporation-crystallization. Na+ and K+ of river water and spring water are mainly derived from evaporative karst decomposition such as rock salt, and Ca2+ and Mg2+ are mainly derived from the dissolution of silicate rock. Metallogenic materials such as Li, Rb and Cs come from rock weathering and deep water-rock reaction. The annual replenishment of Hebian Spring, Dongru Spring and Qingshui River is 1,601,600 m3, 6,440,900 m3 and 93,616,500 m3, respectively. River water replenishment accounts for 92.09%, and the annual replenishment of Li, Rb and Cs in river water is about 3501.26kg, 176kg and 156.34kg. The annual replenishment of Li, Rb and Cs in spring water is about 6824.18kg, 288.87kg and 691.59kg, which are mainly spring water replenishment, accounting for 66%, 62% and 82% respectively. Chaka mud fields and membrane fields with an area of about 10.40km2. After extraction of lithium and potassium, the concentration of rubidium cesium in the brine gradually enriched, reaching the requirement of separate mining grade of rubidium cesium in Zabye Salt Lake. The water level of Geze Chaka Salt Lake has risen and its area has expanded. In April 2023, the area of Geze Chaka Salt Lake has reached 118.07km2, an increase of 12.69km2 over 1977, which has had a certain impact on the production of the salt lake. It is recommended to continuously monitor the dynamic change of the lake water.
- 1
-
Exhumation Processes of the Metamorphic Basement of the Taohua Group in the Southern Margin of the North China Craton: Evidence from U-Th/He Thermochronology
Lei Wanshan, Zhang Rui, Li Sanzhong, Zhou Mingli, Wang Ran, Zhang Haidong
Abstract:
Uplift and exhumation are important mechanisms of crustal thinning. Understanding the exhumation process of metamorphic basements is crucial for comprehending the lithospheric extension and destruction in the southern margin of the North China Craton since the Late Mesozoic. This study investigates the exhumation history of the Taihua Group metamorphic basement in the southern margin of the North China Craton since the Late Cretaceous using zircon and apatite (U-Th)/He thermochronology. Thermochronological analyses of five sample groups from the Taihua Group gneisses reveal that apatite (U-Th)/He ages range from 32.9 to 41.9 Ma and zircon (U-Th)/He ages range from 56.9 to 94.1 Ma. HeFTy modeling indicates that the Taihua Group metamorphic complex has experienced four stages of cooling and exhumation since the Late Cretaceous: (1) Rapid cooling from the Late Cretaceous to Paleocene (94.1-57 Ma), with a cooling rate of approximately 5.58 °C/Ma, an exhumation rate of about 159 m/Ma, and a total exhumation of 3142 m. This phase of rapid cooling was likely a continuation of the lithospheric thinning of the North China Craton caused by the subduction rollback of the Paleo-Pacific Plate; (2) Slow cooling from 57 to 40 Ma, with a cooling rate of around 1.18 °C/Ma, an exhumation rate of about 34 m/Ma, and a total exhumation of 571 m. This period of stable uplift may be due to the reorientation of the subducting Pacific Plate, reducing tectonic stress in eastern China; (3) Accelerated uplift and exhumation from 40 to 30 Ma, with a cooling rate of about 4.5 °C/Ma, an exhumation rate of 129 m/Ma, and a total exhumation of 1286 m. This phase of rapid uplift might result from the aging of the subducting Pacific Plate (as mid-ocean ridges disappeared and the age of oceanic crust entering the subduction zone increased) and the increase in subduction angle; (4) Slow cooling and exhumation from 30 Ma to the present, with a cooling rate of 0.167 °C/Ma, an exhumation rate of about 5 m/Ma, and a total exhumation of 143 m. This stage of tectonic quiescence likely indicates that the southern margin of the North China Craton has moved away from the active subduction zone of the Pacific Plate. The exhumation process of the Taihua Group metamorphic basement indicates that the large-scale lithospheric thinning in the southern margin of the North China Craton during the Late Mesozoic continued into the early Cenozoic. This phase of uplift and exhumation may have been crucial for the exposure of polymetallic mineral deposits in the southern margin of the North China Craton.
- 1
-
Structural patterns, ages and geodynamics of late Mesozoic multistage deformation of the Ganzhuermiao dome in the central-southern Daxinganling
YANG Qian, SHI Wei, LI Xiaogang, SHI Jinpeng, LIN Mao
Abstract:
Under the superimposed influence of the Paleo-Pacific tectonic domain to the east and the Mongol-Okhotsk tectonic domain to the north during the Mesozoic, the Daxinganling and its surrounding areas have experienced the Yanshanian intracontinental orogeny and the succeeding large-scale lithospheric extension and thinning event in Eastern China. Conducting in-depth research on the Mesozoic deformation characteristics, ages and genetic mechanisms of the aforementioned region is crucial for elucidating the Mesozoic tectonic regime transformation in East Asia. In this work, a multi-technique approach, including detailed field structural measurement, inversion of paleotectonic stress fields and zircon U-Pb dating, has been performed in the Ganzhuermiao dome in the central-southern Daxinganling. The new results indicate that this dome experienced at least three-phase deformation during the Middle Jurassic-Early Cretaceous: (1) the top-to-the-WSW ductile shearing during the Middle and Late Jurassic (ca. 160 Ma); (2) NNW-SSE contraction during the Late Jurassic to earliest Cretaceous (144-135 Ma) and subsequent (3) NW-SE extension during the middle-late Early Cretaceous (ca. 135-110 Ma). An age-crustal thickness curve, constructed by published the whole-rock (La/Yb)N and Sr/Y ratio data from the late Mesozoic igneous rocks in the central-southern Daxinganling, shows a good correspondence with the above three-phase deformation. It reveals that the regional crust underwent a remarkable thickening from ~41 km to ~66 km during the Late Jurassic to earliest Cretaceous, followed by a rapid thinning to ~45 km at ca. 125 Ma. Combined with the regional tectonic evolution, we propose that the first two stages of deformation represent the effects of the episode A and B of the Yanshanian Movement, respectively. They shared a regional unified contractional setting. The WSW-orientated ductile shearing may reflect an eastward extrusion tectonic model of NE China controlled by the low-angle subduction of the Paleo-Pacific plate beneath East Asia and the closure of the Mongol-Okhosk Ocean. The late NW-SE extension indicates a change of the regional tectonic regime and suggests the peak destruction of the North China Craton, which may result from the roll-back of the Paleo-Pacific plate and post-orogenic collapse of the Mongol-Okhotsk belt.
- 1
-
Petrogenesis of volcanic rocks of the Dianzhong Formation in the Shiquanhe area, Tibet, and indications of subduction processes of the Neo-Tethyan Ocean
Yu Jiajia, Tang Juxing, Chen Wei, Ma Xudong, Li Yang, Wang Chengyang, Liu Qingping, Liu Chang, Di Mengxiang
Abstract:
In order to explore the genesis and dynamic background of the volcanic rocks of the Dianzhong Formation in Shiquanhe area, we present detailed chronological, whole-rock geochemical, and Lu-Hf isotopic geochemistry of volcanic rocks of the Dinzhong Formation, Linzizong Group. The results show that the zircon U-Pb ages of the samples are 57.1±0.8 Ma and 55.8±0.7 Ma, and that the volcanic rocks originally belonging to the Tuocheng Formation, Zenong Group should be reclassified as the Paleocene Dianzhong Formation. The geochemical characteristics show that the samples are peraluminous, high-K calc-alkaline series, with high SiO2, low TiO2, low MgO, low Cr, Ni and Mg# (mean value 22), enriched in large ion lithophile elements such as K, Rb and Pb, and depleted in high field strength elements such as Nb, Ta, Ti, and P, showing the characteristics of arc magmatism. The fractionation of light and heavy rare earth elements is obvious, relatively enriched in LREE, and the negative anomalies of Eu, Ba, and Sr are significant, indicating the existence of stronger fractional crystallization. The zircon Hf isotope εHf(t) ranges from +2.61 to +9.51, and the TDMC ages range from 965 to 514 Ma, indicating remelting of newborn crust materials. Comprehensive analysis suggests that the initial collision of the India-Asia continent collision occurred at 70Ma, after which the New-Tethys slab continued to rollback and was accompanied by the formation of the volcanic rocks of the Dianzhong Formation. At about 56Ma, the slab breakoff induced large-scale volcanism in the Nianbo and Pana Formation, which lasted until about 40Ma.
- 1
-
Metallogenesis of early Cambrian massive barite deposits in southern China: An overview and prospects
Yuan Peng, Xu Lingang, Yan Hao, Fu Xuerui, Sun Kai, Zhou Tianji
Abstract:
The early Cambrian stratiform massive barite in southern China is one of the largest barite metallogenic provinces in the world. It includes two major metallogenic belts – the Qinling-Daba and the Jiangnan metallogenic belt – spatially distributed along the northern and eastern margins of the Yangtze platform, respectively. Based on the biogeochemical cycle of barium in the modern ocean, this paper described the geological characteristics of typical barite deposits in the Qingling-Daba and the Jiangnan belts. In particular, the similarities and differences in the mineralogical and geochemical composition of barite deposits from the two metallogenic belts are discussed. Similar geochemical and stable isotope composition suggest that barite deposits of the two metallogenic belts may have the same barium sources and deposited in a similar paleoceanographic environment. During the early Cambrian, the high primary productivity in the ocean around the Yangtze platform enhanced the barium accumulation in the seawater, providing the prerequisite for massive barite deposition. The sulfate concentration and spatial distribution in the ocean are the significant factors controlling the precipitation of the barite. The diagenetic process not only caused the dissolution, migration and recrystallization of deposited barite, but also responsible for the mineralization zonation of barite and witherite in the Qinling-Daba metallogenic belt. Compared to the barite deposits, the deposition of witherite may involve methanogenesis contributed by the organic matter degradation and production of carbonates from the anaerobic oxidation of methane. Although intensively studies, as yet, the barium sources, paleoceanographic environment, and diagenetic processes of the early Cambrian massive barite deposits in south China need to be further discussed, such as the contribution of hydrothermal overprinting and cold seep activities to the formation of barite and witherite deposits, the primary productivity and sulfate concentration of the seawater during the early Cambrian. Prospectively, the barium sources, paleoceanographic environment, and diagenetic processes could be better constrained and characterized by the detailed comparison of the Qinling-Daba and the Jiangnan metallogenic belt through in-situ Sr-S-C-O isotopic and microscopic analysis. Particularly, combined with the Ba isotope, the relationship between voluminous Ba precpitation and the paleoceanographic environment of the early Cambrian would be better constrained.
- 1
-
Body feather fossil from the Lower Cretaceous in Yumen, Gansu Province
XING Weiwei, ZHANG Jing, DU Baoxia, zhang mingchen, YAO Yu, PAN Zhilong
Abstract:
Feathers, as the most intricate integumentary appendages, exhibit remarkable morphological diversity and serve various functions in both birds and non-avian dinosaurs. The presence of feather fossils plays a pivotal role in elucidating the evolutionary history of feather in early birds or non-avian dinosaurs. This study presents an account of a feather fossil discovered in the Lower Cretaceous of the Yumen region in Gansu Province, which is identified as a body feather due to its semi-open closed pennaceous structure and elongated rachis, with the presence of the afterfeather. This intricate feather likely originated from Early Cretaceous enantiornithine inhabiting the Yumen area. By comparing the vane length of this body feather with that of modern birds alongside assessing the afterfeather length, it can be inferred that the owner has a small body size. Furthermore, the discovery of this fossil indicates that in the Early Cretaceous, some birds had developed the afterfeather structure as an adaptation to diverse environmental conditions.
- 1
-
Cambrian Andesitic volcanic activity in the Wulihe area of Duobaoshan and implications for tectonic affinity of "Xing 'an Block"
Fu Junyu, Li Yangchun, Cui Dandan, Pang Xuejiao, Yang Xiaoping, Yang Hao, Na Fuchao, Sun Wei
Abstract:
The dispute on the geological setting of early Paleozoic mineralization and the tectonic attribute of Xing 'an Block in the Duobaoshan Cu-Mo gold deposit area restricts the determination of regional prospecting direction.In this paper, a set of metamorphic Andesitic crystalline tuff exposed to the Wulihe in the Duobaoshan area has been studied by means of petrogeochemistry, zircon U-Pb chronology (LA-MC ICP-MS),in order to discuss the tectonic setting of the early Early Paleozoic and the tectonic attribute of Xing 'an Block. Sixty zircons from metamorphic andesitic crystalline tuff were randomly tested by zircon U-Pb (LA-MC-ICP-MS) method, and the weighted average age of 206Pb/238U was 502.6±2.7 Ma （n=57, MSWD=1.4）, indicating that they were formed in the late Miaolingtian of Cambrian. The average SiO2 content of metamorphic Andesitic crystalline tuff is 59.02%, with high Al2O3 (average 16.67%), high MgO (average 4.06%), and medium TiO2 (average 0.75%). Its Rittman index (σ) is 1.81 on average, belonging to the calc-alkaline series volcanic rocks. The rocks also contain high Cr (average 104×10-6), Ni (average 64×10-6) and Sr (average 414×10-6), rich in large ion lithophilic elements Rb, Ba, Th, U, and deficit high field strength elements Nb, P, Ti, formed in the continental margin arc tectonic background.The magma is mainly derived from the melt of the subduction plate and the depleted mantle material of the late Neoproterozoic and early Paleozoic. Based on the results of recent geological survey and the characteristics of regional geological construction, it is considered that a set of volcano-sedimentary structures of late Cambrian Miaoling Epoch with certain scale showing the characteristics of continental marginal arc developed along the Duobaoshan-Arong Banner-Hellerstai in southeastern margin of Xing 'an Block. It is necessary for Tongshan Formation in Duobaoshan area to disintegrate further. After the Erguna Block and Xing 'an Block collided and formed the Erguna-Xing 'an Joint Block in the late Neoproterozoic era, it was a passive continental margin background at least from 570 to 514 Ma and the block was relatively stable. At ~ 516 Ma, the mountain roots were disintegrated and the asthenosphere upwelled to form an intraconcontinental rift. With the accumulation of stress, ~ 503 Ma induced the NW subduction of the Paleo-Asian Ocean branch on the southeast side of the Erkuna-Xing 'an Combined Block, thus forming a marginal magmatic arc. Since then, the "Xingan block" has been gradually destroyed and changed into the Paleozoic arc-Basin system, which controls the regional Cu-Mo Au metallogenic geological background.
- 1
-
Insights from TTG Rock Records on the Great Oxidation Event and its Impact on Tectonic Magma-Limited period in the Xiong'ershan Region
LIU Heng, LIU Lei, ZHANG Chuangye
Abstract:
The majority of records regarding the Great Oxidation Events (GOE) are derived from the geochemical characteristics of sedimentary rocks, with minimal involvement of evidence from igneous rocks. However, the Th/U ratio of global arc magmatic rocks has successfully indicated two instances of the GOE, pioneering a new area of study using igneous rock geochemical indicators to explore GOE research. Arc magmatic rocks generally form through the melting of the overlying mantle wedge during subduction-induced dehydration of oceanic crust, exhibiting enrichment in heavy rare earth elements. Combining the results of studies on arc magmatic rocks, this paper explores whether TTG (Tonalite-Trondhjemite-Granodiorite) magmatic rocks from different periods can record GOE and what impact the formation of GOE has on TTG, especially considering that previous studies often overlooked this influence when considering the formation of TTG during and after the Great Oxidation Events. Through zircon geochronology, within the range of 2.45-2.20 Ga (Tectono-Magmatic Lull), this study demonstrates research on TTG rocks influenced by the addition of crustal material during different periods (2.43-2.18 Ga), including evidence from zircon Th/U ratios and zircon oxygen fugacity anomalies. This provides new evidence for exploring the impact of GOE on magmatic rocks at different depths.Research has demonstrated that the main and trace elements in TTG rocks from three distinct periods exhibit similar geochemical characteristics to high silica adakites. Additionally, the Great Oxidation Event (GOE) showcases a pattern of increasing and then decreasing oxygen isotope and oxygen fugacity changes throughout various periods of magmatic activity.Structural diagram of whole rock granite and trace elements of zircon suggests that TTG rocks were formed within an island arc environment situated along an oceanic subduction zone. This formation process is hypothesized to be the result of dehydration and melting of the subducted oceanic crust. Consequently, such processes lead to variances in the oxygen fugacity of TTG rocks.
- 1
-
Zircon U-Pb geochronology, geochemistry and Sr-Nd-Hf isotopes of the monzonitic granite in the Yuanpanbei tin polymetallic deposit, Guangdong Province, SE China and its geological significance
Lu Yongyan, Bao congfa, Yan Qinghe, He Xiaohu, Wang He
Abstract:
Yuanpanbei Pb-Zn-Sn polymetallic deposit, located in Lianhuashan Fault, Eastern Guangdong Province, discovered in recent years, is genetically related to the monzonitic granite. In this paper, zircon U-Pb geochronology, geochemistry, and Lu-Hf isotopes of the monzonitic granite are conducted for the first time. Zircon LA-ICP-MS dating of monzonitic granite yields concordant ages of 151.8±1.5 Ma, which demonstrated that the monzonitic granite is formed in Late Jurassic. Petrographic and geochemical data indicate that monzonitic granite is characterized by weak peraluminous and belongs to the high-K calc-alkaline series, enriched in Rb, Th, U, K, Pb, and depleted in Ba, Sr, Ti, P, Nb, Ta with strong negative anomaly of Eu. Meanwhile，the monzonitic granite shows highly fractionated I-type affinity. The highly fractionated nature, abundant ore-forming metals, low fO2, and close spatial relationship with ore bodies indicate that the monzonitic granite is genetically related to mineralization in this area. The monzonitic granite has relatively high initial Sr isotopes (0.708865 to 0.708918) and relatively low εNd(t) (-6.72 to -7.25) and εHf(t) values (-15.52 to -5.05), with high tDM2 ages of εNd(t) (1568Ma) and εHf(t) (1343~1615 Ma), indicating that the source region of the Yuanpanbei monzonitic granite is most likely from the partial melting of the Mesoproterozoic ancient crustal rocks, which is possibly added by a few mantle material. Based on the results of geochemistry and geochronology, combined with the regional tectonic evolution, the monzonitic granite and tin polymetallic mineralization of the Yuanpanbei deposit were generated in an extensional tectonic setting triggered by the“slab foundering”of Paleo-Pacific plate.
- 1
-
Formation and Shanxi Formation in Longdong area of Ordos Basin: response to disappearance of central paleo-uplift
zhusen, caogaoshe, shixiaohu, yaojingli, sunfengyu, zhouxinhang, niuyongbin
Abstract:
The characteristics of provenance area and its transformation can reflect the paleogeographic evolution and dynamic change of the basin. Based on petrology, mineralogy, and U–Pb–Hf isotope analysis of detrital zircon, revealing the provenance area, its vertical and plane difference of Lower Permian Taiyuan Formation and Shanxi Formation in the southeastern part of the central paleo-uplift of Ordos Basin, new evidence for the recovery of Late Paleogeographic evolution and dynamics of the central paleo-uplift is provided. It is resulted that the provenance aera of the aluminiferous rock series in Taiyuan Formation are mainly from North Qinling-North Qilian Orogenic Belt in the south and the vanished provenance in the east of North China Craton. However, the contribution of these two provenance area is significantly different both vertically and horizontally. From the lower part to the upper part, and from the south to the north, the contribution from North Qinling-North Qilian Orogenic Belt decreases, while the contribution from the vanished provenance area in the eastern part of the North China Craton increases rapidly. The provenance area of quartz sandstone at the bottom of Shanxi Formation has shifted to the northern Yinshan Block and its southern Khondalite Belt. Provenance transformation during the Early Permian indicates that the sedimentary period of Taiyuan Formation in Longdong area inherited the previous framework which opening to the east, low in the north and high in the south. But, the uplift in the south has gradually decreased, which is related to the weakening activity of the North Qinling-North Qilian Orogenic Belt on the southern margin of the Ordos Basin. In the early sedimentary period of Shanxi Formation, the Paleogeographic features have undergone fundamental changes. Central paleo-uplift gradually have disappeared, and transformed into an ancient slope that dips southward, which is related to the final closure of the Paleo-Asian Ocean and the intense uplift of the Inner Mongolia Paleo-uplift.
- 1
-
Nickel and Cobalt metallogenic series andprospecting direction in Qinghai Province
Abstract:
Nickel ore is the main part of nickel and cobalt ore in Qinghai, and cobalt is usually produced as associated ores of magmatic nickel ores or contact metasomatic polymetallic ores, and independent cobalt ores are rare. Nickel deposits are relatively concentrated in the Qinling-Qilian-Kunlun metallogenic domain, South Qilian metallogenic belt and East Kunlun metallogenic belt nonferrous metal ore concentration area, the deposit type is magmatic, which is closely related to mafic-ultramafic rocks intruded by mantle-derived magma through deep liquation, and the abnormal enrichment and mineralization mostly occurred in the Early Paleozoic Ordovician (South Qilian metallogenic belt) and Devonian (East Kunlun metallogenic belt). The mineralization was formed in a post-collisional extensional environment during the late evolution of the Proto-Tethys. Cobalt deposits are mainly distributed in Qinling-Qilian-Kunlun metallogenic domain and Tethyan metallogenic domain, but independent cobalt deposits and associated cobalt deposits with economic value are exposed in East Kunlun metallogenic belt, South Qilian metallogenic belt and a"nyemaqen metallogenic belt. The main types of cobalt deposits are magmatic, marine volcanic and contact metasomatic; The metallogenic epoch of cobalt deposits is complex, which can be divided into four metallogenic stages, namely, Ordovician and Silurian of Early Paleozoic, Devonian and Carboniferous of Late Paleozoic and Triassic of Mesozoic. The metallogenic geological environments of different metallogenic stages are significantly different. The metallogenesis varies with the types of deposits, but it is basically consistent with the enrichment and formation process of the main ore species. The mineralization of Ordovician-Devonian is in the extensional environment after orogenesis. Forming magmatic deposits related to mafic-ultramafic rocks of non-ophiolite type; forming marine volcanic rock deposits in the Carboniferous period in the oceanic spreading environment; forming contact metasomatic deposits in the Triassic period related to the magmatic intrusion of continental margin arc. According to the spatial and temporal distribution characteristics, mineralization and metallogenic geological background of the deposits, the nickel and cobalt deposits in Qinghai are divided into 10 metallogenic series, 15 metallogenic subseries and 9 deposit types. Base on that regional metallogenic geological setting, regional metallogenic condition, the known mineralization information and the latest prospecting results, the regional element geochemical field, the metallogenic Serie of ore deposits and the research degree analysis, the prospecting potential of different types of nickel and cobalt deposits in the metallogenic belt is proposed. The South Qilian metallogenic belt, the northern Qaidam metallogenic belt and the East Kunlun metallogenic belt in the time-space domain of the former Tethys Ocean tectonic activity are still the first possible prospecting areas, and the field investigation should focus on the Ni-rich iron series basic-ultrabasic rocks unrelated to ophiolite, and then the magmatic nickel deposits related to ophiolite mafic-ultramafic rocks should be explored in the ophiolitic melange belt. For the less studied cobalt deposits, the first is to focus on the metallogenic geological environment and favorable metallogenic conditions of independent cobalt deposits of marine volcanic rock type, and the second is to focus on the occurrence state and abnormal enrichment mechanism of Co element in known deposits; The northern Kunlun magmatic arc in the Galinge-Yemaquan area in the western part of the East Kunlun metallogenic belt and the Qimantag-Xiariha magmatic arc in the Dulan area in the eastern part of the East Kunlun metallogenic belt are favorable for finding contact metasomatic polymetallic associated cobalt deposits. The East Kunlun metallogenic belt and a"nyemaqen metallogenic belt may become important prospecting areas for marine volcanic cobalt deposits related to the oceanic ridge magmatism during the spreading period of the Paleo-Tethys Ocean. In general, magmatic nickel deposits, marine volcanic type independent cobalt deposits and paragenetic cobalt deposits, magmatic type associated cobalt deposits and contact metasomatic type associated cobalt deposits can be regarded as the main direction of future exploration of nickel-cobalt deposits.
- 1
-
The Neoarchean structure characteristics and geological significance of the Taishan Group,Western Shandong Province
Li Xiaodong, Wang Wei, Tian Zhonghua, Jia Du, LuoBowen, Zhou Jinwei
Abstract:
Due to the influence of Paleoproterozoic metamorphism and deformation, the structure characteristics of the Archean basement of the North China Craton were blurred. The central region of the Western Shandong Province, located in the eastern part of the North China Craton, developing 2.7~2.5 Ga supracrustal rocks, are almost not affected by the Paleoproterozoic events. In this study, detailed field structure analysis and geochronological work were carried out. We suggested that the Taishan Group was subjected to three stages of deformations: early foliation(S1) and tight folds(F1) formed in the stage DA-1. Large upright folds, foliation(S2) and thrust faults formed in the stage DA-2. In the stage DA-3, lots of ductile shear zones formed. Combined with some published chronological data, we proposed that the stage DA-1 occurred in >2.56~2.53 Ga, the stage DA-2 occurred in 2.53~2.52 Ga, the stage DA-3 occurred in 2.52~2.50 Ga. Large number of structural geometric features in peak deformation stage indicate that the deformations of the Taishan group is different from those of the dome and keel structure under the vertical mechanism. It is similar to the structure formed by the lateral extrusion orogeny of the Phanerozoic. Accordingly, we suggest that the Archean horizontal structure in Western Shandong is the result of horizontal movement under the plate tectonic system.
- 1
-
Indication of low-temperature metallogenic element enrichment in Lower Cambrian black rocks in Guizhou Province for large-area low-temperature mineralization
Tan Zedong, Du Lijuan, Chen Jun, Peng Rou, Yang Ruidong, Gao Junbo, Liu Xuyang, Liu Linlin, Yang Zaifeng
Abstract:
The Youjiang Basin, located in the southwest margin of the Yangtze blocks, is an important part of the large-area low-temperature metallogenic domain in China, and the metal sources and enrichment processes of the low-temperature Au、Sb and Hg deposits in the basin still need to be clarified.Prebious studies have shown that the Lower Cambrian black shale series are enriched with low-temperature metallogenic elements (such as As,Sb,Au), which may provide a material basis for low-temperature metallogenic in the Youjiang Basin.In order to further reveal the relationship between the Cambrian polymetallic black shale series and the low-temperature mineralizationin in Youjiang basin,in this paper,elemental geochemistry, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in-situ trace elements and fluid inclusions were carried out on the Lower Cambrian (Niutitang Formation and Gezhongwu Formation) black shale (phosphorus-bearing rock formations) and their later hydrothermal veins.The results showed that: 1)The content of Sb and As in this Lower Cambrian strata was higher than that in the upper crust(enrichment coefficient was 2~69).The lg(U)-lg(Th) relationship diagram shows that the enrichment of Sb-As in the hydrothermal vein-bearing phosphoblock rocks of the Lower Cambrian Gezhongwu Formation is mainly affected by hot water (liquid).2)The temperature of the later hydrothermal quartz vein fluid inclusions was concentrated in the range of 137.4~260℃, and the salinity was 0.18~5.11wt% NaCl equiv, which was basically the same as that of the low-temperature ore-forming fluid in Youjiang basin (140~270℃, 1.5~7.0 wt% NaCl equiv).3) Two types of apatite are developed in the hydrothermal vein-bearing phosphobolite rocks, which are sedimentary apatite (Fap1) and hydrothermal apatite (Fap2). Among them, Fap1 has a typical bioclastic structure, and Fap2 has a flat surface and is mainly developed near the late hydrothermal quartz veins. Electron probe (EPMA) and LA-ICP-MS analysis showed that compared with Fap1, Fap2 was more enriched in low-temperature elements such as Sb, As and Cu, and depleted rare earth elements.Based on the above analysis, this paper considers Fap1 to be a typical biosedimentary apatite, which is the main carrier of rare earth elements in phosphorites. Fap2 is a hydrothermal apatite formed in the later period, which is obviously enriched in low-temperature mineralizing elements (Sb, Cu, As).The lower content of low-temperature mineralizing elements (Sb, Cu, As) in Fap1 reveals that the Lower Cambrian strata are not sufficient to provide a material basis for low-temperature mineralization, and on the contrary,the late hydrothermal fluids (such as Carlin-type mineralizing fluids) originating from deep (such as metamorphic basement or magma) may be one of the reasons for the abnormal enrichment of low-temperature mineralizing elements in the Lower Cambrian black shales.
- 1
-
Genesis analysis of the Nanpu Sag, Bohai Bay Basin: Insights from Seismic Data Interpretation and 3D Sandbox analogue Modelling
wangyuheng, yufusheng, songlu, wangdandan, zhaobaoyin, qiyili, menglingjian
Abstract:
The formation process of rift basins is influenced by multiple factors, including pre-existing structures, sedimentary material properties, rift phases, and directions. Ultimately, this process results in multiple sets of fault systems with different orientations and scales, leading to the formation of various structural styles. This undoubtedly makes the structural analysis of basins highly challenging. In this study, we replicated the evolution process of the Nanpu Sag since the Dongying Formation, which underwent N-S extension under the influence of multiple factors, through the interpretation of 3D seismic data and comparison with analogue modellings of group structures. The study reveals the following findings: The Nanpu Sag is a result of multiple-phase rifting developed under pre-existing structures. Eventually, it formed a structural pattern of N-S partition deformation, connected in segments from east to west, and vertically deformed within the Minghuazhen formation. The pre-existing paleo-uplift in the southern part of the sag affects the uniformly distributed extensional deformation, while in the northern part, a segmented interconnected mesh-like fault system is formed. Reactivation of pre-existing structures in the southern part leads to the formation of E-W curved en echelon inherited fault systems on both sides. The NE pre-existing fault planes formed during multiple-phase orthogonal rifting processes are important factors restricting the late-stage oriented arrangement of faults. Ductile detachment layers are key material factors that enhance the interaction between faults, transmitting strain initiated from the preset boundary to various parts of basin deformation. They facilitate the connection of isolated faults, forming E-W segmented connected normal fault combinations. The faults accommodate oblique extension caused by pre-existing structures through their own bending.
- 1
-
Nature of the Ore-hosting Sedimentary Rocks of the Orogenic Gold Deposits in the South Tianshan: An example from Awanda Gold Deposit
Yilidanna TALATI, Nijiati ABUDUXUN, LIU Xueliang, Abidan ALIMUJIANG, YANG Gang
Abstract:
Orogenic gold deposits in the South Tianshan are commonly hosted in meta-sedimentary rocks. The age of formation and nature of these sedimentary rocks remain controversial. By integrating previous investigations on the Awanda gold deposit with our new results of recent studies, we discuss the tectonic nature of the ore-hosting meta-sedimentary rocks. The area contains fragments of Ocean Plate Stratigraphy (OPS) that are mainly composed of pillow basalts, ribbon cherts, and turbidites. Radiolarian micro-fossils are found in 30 samples of the ribbon chert. They are mostly entactinids, which are identified to be Late Devonian to Early Carboniferous in age. The ore-hosting sedimentary rocks in the Awanda gold deposit and the turbidites from the OPS have similar maximum depositional ages, which are consistent with the ages of radiolarians from the ribbon cherts. According to the conceptional model of OPS, integrated with regional geological records, we consider that the meta-sedimentary rocks are main parts of the South Tianshan accretionary complex, and they belong to orogenic non-Smith strata that formed on the leading edge of the southern Yili-Central Tianshan active margin, rather than on the passive margin of the northern Tarim Craton. Faults with various scales and structural levels are well developed in the accretionary complex, which are closely related to gold mineralization in the South Tianshan. “Convergent margin-related meta-turbidites + deformation + magmatic hydrothermal fluids” is proposed to be a key prospecting criterion for orogenic gold mineralization in the South Tianshan.
- 1
-
Study of the fine-scale sedimentary characteristics in the western margin of the Weihe basin using passive seismic imaging with a dense linear array
Xu Yong, Deng Bao, Tian Xiaofeng, Ni Hongyu, Duan Yonghong, Xiao Benfu, Li Junlun
Abstract:
In order to investigate the subsurface fine structure and sedimentary characteristics of the key areas with high earthquake risk in the western margin of the Weihe basin, we deployed a dense linear array consisting of 254 short-period three-component seismometers with an average station-spacing of 200 meters in this study, which collected data for 30 days. We calculate the vertical component cross-correlation of the ambient noise, apply the recently developed extended range phase shift method to extract the fundamental mode Rayleigh wave dispersion curves ranging from 3 Hz to 3.3 s, and then invert for high-resolution shear wave velocity structure down to the depth of 2.5 km beneath the dense linear array. Additionally, using the collected three-component seismic noise, we apply the horizontal to vertical spectral ratio (HVSR) method to calculate peak frequencies, and then use an empirical relationship to estimate the thickness of sedimentary layers in the Weihe basin. The tomographic results show horizontal pattern with a high-low-high velocity variation, corresponding to the uplift-depression-uplift geological structure in this sedimentary basin. The result also clearly delineates three major faults and two geological structural units in the region, consistent with the profile obtained by active seismic imaging. The result from HVSR reveals that the sedimentary layers are relatively thick and exhibit a distinct and complete stratigraphic sequence deposited in the Holocene, Neogene, and Quaternary periods in the Cenozoic era. A comprehensive analysis integrating results from ambient noise tomography, HVSR and active-source imaging suggests none of the three major faults beneath the 2D array penetrates through the Quaternary formation in this region. This study shows that the extended range phase shift and the HVSR methods based on seismic ambient noise are effective in characterizing structures in sedimentary basins.
- 1
-
Determination and geological significance of late Carboniferan-middle Permian basalts of the Tongjiang-Yuejinshan accretionary complex
Abstract:
The Tongjiang-Yuejinshan accretionary complex on the western margin of the Nadanhada terranein northeast of China has great significance for reconstructing the subduction-accretion process of the paleo-oceanic plate, however, the formation time of the ancient ocean and its tectonic properties constrained from Tongjiang-Yuejinshan accretionary complex are still unclear. Based on our geological survey, we present the chronological data and geochemical characteristics of magmatic blocks in the Tongjiang-Yuejinshan accretionary complex. The results show that In-situ U–Pb zircon dating of basalt from the Yuejinshan complex has yielded a mean age of 313.8 ± 2.3 Ma, and show ocean island basalt (OIB) like geochemical features. A plagioclase amphibolite from the Tongjiang complex display U-Pb zircon age of 271.7 ± 2.3 Ma, and show mid-ocean ridge basalt (MORB) like major and rare earth element patterns. A basalt from the Tongjiang complex exhibits fore arc basalt (FAB) like geochemical features. Combined with previous research, our evidence above show that the Tongjiang-Yuejinshan accretionary complex was formed in the Permian-Late Triassic subduction-accretion process of the Paleo-Pacific ocean plate.
- 1
-
Discovery and Paleoenvironmental Significance of the Coprolite Layer of the Early Jurassic Ziliujing Formation in Chongqing Area
Zhou Zhengda, Chen Yang, Luan Jinhua, Zhang Ruigang, Wang Qian, Zhang La, Li Wei, Li Dahua, Nie lei
Abstract:
Coprolites are important vestigial fossils, which can provide information on dietary structure and population diversity of organisms, as well as reconstruct nutrient structure and energy flow models of ancient ecosystems. However, coprolites are often found in separate locations, and rarely regional continuous coprolites layer has been reported. This paper reports for the first time on the fossil horizons of coprolites, associated with leptodonts, phyllopods, alamites and reptiles found in the Dongyuemiao Member of the Ziliujing Formation in Yubei, Beibei, Wanzhou of Chongqing and Linshui of Sichuan in the early Jurassic, and samples the coprolites in the fossil beds. According to the morphological observation and thin section characteristics of coprolites, it is concluded that: (1) the collected coprolites are divided into four types, and their animal sources are mainly reptiles, bony fishes and cartilaginous fishes with different feeding habits. (2) during the Dongyuemiao period, the ancient Bashu Lake formed a complex ecosystem composed of lush plants as producers, bivalves and ostracoda as primary consumers, and fish and reptiles as medium-high consumers. (3) a small anoxic event occurred in the ancient Bashu Lake during the Dongyuemiao period, which led to the death of a large number of fishes in a cluster, and reptiles may were spared the trouble because they could breathe out of the lake. This anoxic event may be the prelude to the oceanic anoxic event of the Toar Period.
- 1
-
Characteristics of the fault system in Nanpu sag and its Cenozoic evolution
SHANG Lin, GAO Guangliang, YAO Dandan, SUN Yanchun, WANG Miao, LI Chunlin
Abstract:
The Nanpu sag is located in the eastern part of the North China Craton and is a hydrocarbon-rich sag in the northern part of the Bohai Bay Basin. There has been a long-standing debate regarding the tectonic evolution model of the Nanpu sag, specifically whether it is formed by extensional faulting superimposed by strike-slip faulting to create a sag or if it is the result of multi-stage extensional faulting forming the sag. This study conducted structural interpretation on eight seismic profiles traversing the Nanpu sag and identified NE–SW-striking fault zones characterized by listric normal faults, domino-style normal faults, X-type normal faults, graben-horst structures, and extensional duplex structures, representing typical extensional deformation systems. The NW–SE-striking fault zones exhibited left-lateral strike-slip and oblique extension features, mainly serving to accommodate southward movement of the hanging wall of NE–SW-striking normal faults. Analysis of structural maps of stratigraphic boundaries during different geological periods in the Nanpu sag revealed a migratory pattern of the sedimentary center in the Cenozoic from NW to SE. Based on the above analysis and incorporating regional tectonic evolution data, this study proposed a four-stage tectonic evolution model for the Cenozoic in the Nanpu sag, suggesting it underwent a multi-stage extensional faulting. This work not only serves the purpose of aiding future oil and gas exploration in the Nanpu sag but also contributes valuable material for theoretical studies on fault systems.
- 1
-
Continuous Expansion Process of the Northeastern Margin of the Tibetan Plateau in the Middle Miocene: Evidence from Apatite Fission Track Analysis from the Upper Yellow River Region
Zhang Xiaoyue, Li Guangwei, Cai Dongxu, Lu Huayu, Wang Xianyan
Abstract:
Unraveling the tectonic geomorphological processes along the northeastern margin of the Tibetan Plateau (NETP) is essential for understanding the mechanisms of the plateau's uplift and growth. Previous studies, utilizing low-temperature thermochronology, have illuminated the erosional dynamics along the fault zones, thereby revealing the Cenozoic northeastward expansion of the Tibetan Plateau. However, sparse low-temperature thermochronological data from inter-fault block areas which exhibit pre-Cenozoic ages, appear to lack a record of the northeastward expansion of the Plateau. To further elucidate the uplift and erosional history of the relatively stable inter-fault block regions within the NETP, this study focuses on granite massifs in Longyang gorge and rock bodies promximal to the headwaters of the Hudan River, situated to the east of Qinghai Lake. Analyzed through apatite fission track, six samples were utilized to reconstruct the thermal history of the study areas. In addition, the steady-state vertical exhumation rates and eroded thickness since the middle Miocene was calculated using Age2exhume. Our findings reveal: (1) A pronounced phase of rapid cooling since <10 Ma, indicating the ongoing northeastward expansion of the plateau; (2) Elevated erosion rates and significant eroded thickness within the Laji Mountain-Jishi mountains region, influenced by robust fault activity since the middle Miocene. The integration of low-temperature thermochronological ages with sophisticated thermal history simulation techniques has shed new light on the uplift and erosional history of the stable inter-fault blocks in the NETP, thereby providing new evidence for the plateau's sustained expansion since the middle Miocene.
- 1
-
Pliocene tectonic transformation from strike-slip to thrust along the eastern margin of Pamir
Abstract:
The structural characteristics and evolution history of the eastern margin of Pamir are of great significance to reveal the deformation and evolution of the western syntaxis of the Tibetan Plateau, the basin-mountain coupling relationship between the Pamir–West Kunlun and the Tarim Basin, and to guide the exploration of oil and gas resources and earthquake disaster prevention in this region. Based on the detailed surface mapping and structural analysis of seismic profiles across key locations, the tectonic framework of the basin-range junction zone in the eastern margin of the Pamir is constrained. The mapping data, field photos, seismic profiles and other data presented in this paper reveal that a dextral strike-slip fault system outcrops in the eastern margin of the Pamir, and a buried compressional thrust belt develops in the adjacent basin, including the Qipan structural wedge and the Qimugen structural wedge. The growth strata of the Qipan structural wedge is located in the lower section of the Pliocene Artux Formation, while the growth strata of the Qimugen structural wedge is located at the top of the Pliocene Artux Formation, indicating that the thrust belt has been developed since the Pliocene. The eastern margin of the Pamir experienced a tectonic transformation from a strike-slip tectonic system to a compressional tectonic system during the Pliocene. Before the Pliocene, deformation was accommodated by dextral strike-slip of the Wuyitake-Momoke transfer system (WMTS); Since the Pliocene, deformation in this area was dominated by eastward thrusting, and the strike-slip activity decreased. These basic data and the basic viewpoints put forward in this paper have a good guiding significance for establishment of the tectonic framework and evolution sequence of this region.
- 1
-
Clay minerals and lithium content quantitative analysis based on SWIR spectra for carbonate-hosted clay-type lithium deposits, Central Yunnan
Liulei, Mei Jiacheng, Wen Hanjie, Zhang Guishan, Zhang Qunjia, Yin Chuntao
Abstract:
Lithium is an important emerging strategic resource in China. In recent years, the discovery of carbonate clay lithium deposits in the central Yunnan region has become an important direction for lithium resource exploration due to its large reserves, high grade, and easy mining characteristics. In such deposits, lithium mainly exists in the form of adsorption in the interlayer of clay minerals, with montmorillonite exhibiting the strongest adsorption capacity followed by illite. In order to investigate the coupling relationship between montmorillonite-illite and lithium content in claystone, this study adopted quantitative X-ray diffraction (QXRD) and short-wave infrared spectroscopy (SWIR) techniques, confirmed that SWIR can achieve the distinction and quantitative analysis of illite and montmorillonite through the characterisation of samples with illite-montmorillonite gradient, and preferred 18 sensitive bands; applied partial least squares algorithm and used the SWIR data as variables for quantitative analysis of illite and montmorillonite in 32 Li-rich claystone samples in central Yunnan, the R2 of montmorillonite and illite in the validation set are 0.89 and 0.87, respectively, and the accuracy of the quantitative analysis is higher; and the results of quantitative analysis of lithium content using the results of quantitative analysis of illite and montmorillonite as variables, the results are more accurate, and the R2 of the validation set is 0.86. The SWIR spectral testing method has the advantages of portable instruments, ease of operation, and non-destructive sampling, making it highly suitable for rapid field determination of clay mineral composition in carbonate clay lithium ore samples and estimation of lithium content, which is of great significance for the exploration of this type of mineral deposit.
- 1
-
VELSD1.0: a volcanic eruption landform dataset based on remote sensing image for Changbaishan area with deep learning
LI CHENGFAN, HAN JINGXIN, WU CHENGZHI, LIU LAN, YAN LILI, LIU XUEFENG, ZHAO JUNJUAN
Abstract:
As one of the most well preserved polygenetic composite active volcanoes, the surface cover types in the Changbaishan Mountain volcanic eruption landform scene are widely developed and the interpretation labels in remote sensing image are clear. The remote sensing dataset is currently an important data foundation for large range volcanic eruption landform classification based on deep learning methods from remote sensing image. In this paper, a volcanic eruption landform scene dataset (VELSD 1.0) from Sentinel-2 remote sensing image for deep learning classification in Changbaishan Mountain, China is presented in combination with geological data and field investigations. In the dataset, it includes ten kinds of surfacec over types (i.e., high vegetation coverage, middle vegetation coverage, low vegetation coverage, exposed soil, basaltic rocks, trachytic rocks, mixed rocks of trachyte and pumice, water, shadow, and artificial landscape) as well as three constituent elements (i.e., remote sensing image, labeled data, interpreted label and explanatory file). Covering an area of 2500 km2, the dataset has approximately 40000 sample images of volcanic eruption landform which the image size of each sample is 25 pixels×25 pixels and the spatial resolution is 10 m. The classical convolutional neural networks (e.g., GoogLeNet, ResNet) and Transformer-based (e.g., Vision Transformer, Swin Transformer) deep learning models are used to validate and analyze the proposed VELSD 1.0 dataset. The experiments show that the proposed dataset has good applicability and transferability for deep learning models, and the overall classification accuracy (OA), Kappa coefficient (KC), and mean average precision (mAP) reached 82.93%, 75.64%, and 84.22%, respectively. It can effectively support the deep learning classification of other volcanic eruption landform scene from remote sensing image, and improve the informatization and intellectualization of remote sensing surveys for volcanic landform.
- 1
-
A study of the cyclostratigraphy and orbital forcing of the palaeoclimate changes in the Lower Ordovician Xialingnangou section, western margin of the Ordos Basin
Abstract:
The Ordovician was a crucial period for the evolution of life and the environment on Earth. During this period, there was a remarkable radiation of life known as the Great Ordovician Biodiversification Event, and the Earth""s climate shifted from a greenhouse in the Early Ordovician to an icehouse in the Late Ordovician. The Lower Ordovician Xialingnangou section in the Helan Mountains, western margin of the Ordos Basin, has excellent exposures of the Furongian to Middle Ordovician. The conodont biostratigraphy of Xialingnangou section provides valuable time constraints on the cyclostratigraphy. In this study, Ca, Fe, and Fe/Ca series were selected as palaeoclimate proxies to carry out cyclostratigraphical analyses on the Xialingnangou section. A continuous and high-resolution astronomical time scale of ~8.9 Myr was established based on the stable 405-kyr long eccentricity cycle, and the duration of the Tremadocian Stage was calculated to be 6.9 ± 0.28 Myr. The evolution spectra of the ratio of obliquity power and short eccentricity power to total power reveal a super-long obliquity cycle of ~1.2 Myr (s4–s3) and a super-long eccentricity cycle of ~2.4 Myr (g4–g3) in the Early Ordovician. Meanwhile, the sedimentary noise models of the tuned Ca, Fe, and Fe/Ca time series show high-resolution sedimentary noise fluctuations corresponding to sea-level changes. This reveals that sea-level changes were mainly driven by the super-long eccentricity cycle (s4–s3) in the early Tremadocian Stage, whereas in the middle Tremadocian to early Floian, they were mainly controlled by the super-long eccentricity cycle (g4–g3). The adjustment of the astronomical periods in the Early Ordovician may have played an important role in promoting the Great Ordovician Biodiversification Event.
- 1
-
Petrogenesis and geological significance of the late Silurian quartz monzodiorite in the Dunhuang Block
Gan Baoping, Tang Juxing, Diwu Chunrong, Zhu Lihui, Sun Qingfei, Liu Yuanyuan
Abstract:
As a key microcontinental block/terrane in the southernmost Central Asian Orogenic Belt (CAOB), the genesis of early Paleozoic magmatism and tectonic evolution for the Dunhuang Block still remain poorly constrained, thus limiting the whole understanding of ocean-continental subduction-accretionary evolution of the southern Paleo-Asian Ocean (PAO) and the recycle of deep magmas materials. Here we have newly identified the Silurian quartz diorite from the Changshaliang area in the eastern Danghe reservoir in the central part of Dunhuang block, NW China. The petrology, zircon U-Pb dating, whole-rock geochemistry, and zircon Hf isotopes data have been carried out on the Changshaliang quartz monzodiorite. Zircon U-Pb dating results reveal that the quartz diorite was formed at ca. 428~426 Ma. Whole-rock analyses show that the quartz monzodiorite is relatively rich sodium (K2O/Na2O = 0.84~0.99), high Al2O3 (16.5~17.0%), Mg# (51.5~53.0) and low A/CNK (0.96~1.00) values, and point to the high potassium calc-alkaline metaluminous series. These samples studied exhibit negative Eu anomaly (Eu/Eu* = 0.70~0.77), enriched in larger ion lithophile elements (e.g., Rb, Ba, and Th), depleted in high field strength elements such as Nb, Ta and Ti, together with the low Y (16.3~19.0 × 10-6) contents and Sr/Y ratios (20.3~24.5), showing typical geochemistry characteristics of arc magma. Zircon Hf isotopes results indicate the Changshaliang quartz monzodiorites have a wide variable and negative εHf(t) value of -12.0 to -2.2, and older two-stage model age ranging from 2136 Ma to 1525 Ma. All the above features suggest that the Changshaliang quartz monzodiorites originated from melting of overlying mantle wedge metasomatized by subduction-related sediment melts, subsequently which triggered remelting of Paleoproterozoic lower crust materials. This study, combined with the existing research results, suggest that the Dunhuang Block was strongly involved in the orogenic events related to the southern part of the CAOB during the early Paleozoic period, which caused the modification and activation of crust, finally resulting in multi-stage magmatism events with different compositions resulted in significant activation crust. The block was at an active continental margin arc environment where the PAO continued to subducted to the Dunhuang Block.
- 1
-
Multi-stage tectonic events constrained by apatite fission-track thermochronology in the Outang-Chuxian-Shangyaopu, Anhui Province
TIAN Pengfei, He Zifei, Lv Jinliang, He Yajie, YUAN Wanming, YANG Xiaoyong, DUAN Liuan
Abstract:
The Outang-Chuxian-Shangyaopu area in Anhui is located in the southeastern margin of the North China Craton, the northern margin of the Middle-Lower Yangtze River Ore Belt, the northern frontal belt of the Qinling-Dabie orogenic belt, and the east side of the Tanlu fault zone (TLFZ). The study area is located at the intersection and transition of various large-scale regional dynamical systems, and a large number of copper deposits are developed around it, which has important economic value. However, the degree of low-temperature thermal history research in the region is low, and the analysis of the thermal history of apatite fission track in this region is of great significance for understanding the regional tectonic evolution. We used apatite fission track to study the tectonic activities in the area of Outang-Chuxian-Shangyaopu. In this paper, we obtained nine apatite fission track results with central age between 113.2±7.8 Ma and 78.6±5.3 Ma. The study reveals the TLFZ has experienced multi-phase thermal events. The Outang-Chuxian-Shangyaopu area showed rapid exhumation at 130~100 Ma, possibly related to the high-speed oblique subduction of the Izanagi plate. The exhumation of the study area was relatively slow from ~100 Ma, until ~60 Ma when the far-field effect of the Indian plate and the Eurasian plate was reflected in the Outang-Shangyaopu area. After the hard collision between the Indian plate and the Eurasian plate started, the Outang-Shangyaopu area was exhumated rapidly. Especially, the thermal history clearly reflects the impact of the hard collision between the Indian and Eurasian plates (55~52 Ma) on the thermal history of the study area, and then the study area was controlled by two tectonic systems, which are the subduction of the Pacific plate and the long-range effect of the collision between the Indian plate and the Eurasian plate.
- 1
-
The genesis and tectonic significance of the Xinchang granites in Beishan, Gansu Province and its implications for the geological disposal of High-Level Radioactive Wastes (HLWs): Constraints from geochemistry, zircon U-Pb chronology and Lu-Hf isotopes
GUI Rengao, WANG Ju, SUN Jia, SHI Kaituo, XIAO Wenzhou, ZHOU Miao, ZHANG Xiaoping, LI Nan, WU Peng, DUAN Xianzhe
Abstract:
Xinchang, located in the eastern section of the southern part of Beishan, Gansu province, is a key area for studying the tectonic evolution of the southern part of Beishan and evaluating the site selection in the geological disposal of HLWs. The Xinchang granitoids are composed of three lithofacies units: medium-fine biotite monzonitic granite, granodiorite and gneissic tonalite. Biotite monzonitic granite and granodiorite are generally rich in silicon, potassium (K2O>Na2O), and alkali, and have medium aluminum. These two granites belong to weak peraluminous and high potassium calc alkaline A2 type granite. The tonalite is rich in sodium (K2O
- 1
-
Banded iron formation: Advances and challenges in Cyclostratigraphy
BAI Yang, MA Kunyuan, ZHANG Lianchang, WANG Changle
Abstract:
Banded iron formation (BIF) is chemical marine sedimentary rock that was exclusive to the Precambrian. They constitute a significant component of early crust and provide valuable insights into the tectonic evolution, ancient environmental changes, and primitive life activities on early Earth. BIF exhibits distinctive rhythmic band at various scales. Despite considerable progress in understanding the sources of ore-forming materials and depositional conditions of BIF, ongoing debate persists regarding the formation of bands at different scales. In recent years, geologists have identified numerous reliable Milankovitch cycles records within BIF stratigraphy, leading to innovative theories proposing astronomical forcing as a driving factor for the formation of diverse rhythmic bands in BIF. This paper presents a comprehensive review on cyclostratigraphy in BIF, with specific focus on exploring the impact of climate change driven by Earth's orbital parameters on BIF. Furthermore, this study presents key unresolved issues and explores future prospects for cyclostratigraphic studies on BIF in the North China Craton.
- 1
-
The basement dipping’s control on the structural deformation of the Longmenshan thrust belt
Yu Jingqiang, zhao li, Zhang Yunyin, Dong Dawei, Yu Zhengjun, Wang Yongshi, Zhang Pengfei, Wei Wen
Abstract:
The basement dipping is an important factor controlling the structural deformation of thrust belts. However, rare attentions have been paid on the basement dipping characteristics of the Longmenshan thrust belt. Based on interpretations of seismic profiles, this paper found that the Longmenshan thrust belt in the northern, central and southern segments underwent different basement dipping. The basement dipped 2.6° toward foreland in the northern because of the uplift of thrust sheets. The basement dipped 3.2° toward hinterland in the central due to several phases of loading. The basement dipped 2.6° toward hinterland in the southern which was the result of earlier rifting and later loading. The numerical experiment shows that the basement dipping toward hinterland or horizontal subsiding will suppress the forward propagation of thrusting deformation, and superimposed the thrusting sheets. While the control effect of the pre-existing basement dip is opposite. When the basement remains horizontal or dip toward the foreland, the thrust sheets in hinterland uplifted stronger than that of the foreland, which will cause the basement dipping toward the foreland as a whole. When the basement dipped backward with syn-sedimentation will result in the back-thrusting in slope zone. Numerical simulation proved the basement evolution in southern segment of the Longmenshan thrust belt. Before the Late Cretaceous, it was in an extensional regime with thick strata in the west and thin strata in the east, and its basement dipped to the west. During the Late Cretaceous—Eocene, a foreland basin developed, and the basement dipped toward hinterland because of the loading. During the Oligocene—Miocene, the thrusting deformation strongly propagated into the basin, and the basement almost had no dipping. Since the Pliocene, the basement in hinterland has been uplifted because of the Qinghai-Tibet Plateau, which resulted in the sharp topography.
- 1
-
Numerical Simulations Reveal the Control of Lithospheric Strength Structure on Passive Continental Margins’ Evolution
Fan Qingkai, Guo Jinrui, Gao Min, Wu Gaokui, Wang Yanyang
Abstract:
The formation and evolution of passive continental margins are controlled by the pre-rifting lithospheric strength and its vertical structure. In order to investigate the effect of two factors on lithospheric breakup time, faulting styles, sizes and morphology of passive continental margins, we define two comprehensive indexes as integrated lithospheric strength (σe) and crust-mantle rigid layers coupling degree (Coc), and reveal the influences through geodynamic numerical modelling. According to simulations, the strength structure of lithosphere plays a key role in controlling its rifting duration, a stronger pre-rifting lithosphere inevitably causes a longer lasting rifting, and on this basis, the decrease of the Coc will prolong this process further. For the fully coupling lithosphere (Coc=1), upper crust usually breaks first, and will form symmetric margins through a ‘pure-shear’ mode. When Coc decreases, rigid layers of upper crust and upper mantle deforms separately, and an asymmetric continental margin will form by lateral migration of the rift center. Under such circumstances, the upper mantle with a relatively limited thickness will break first, while when a thick upper mantle develops, the upper crust will break first and lead to the exhumation of mantle rocks. In addition, a low Coc is necessary to generate large-scale passive continental margin basins with a broad and gentle geometry, and the lower Coc is, the greater the migration distance of the rift center and the conjugated margins are. Thickening of the crust will lead to the decreasing of Coc, which will also enlarge the scale of continental margins. Those understandings can be verified on the central segment of South Atlantic continental margins.
- 1
-
Metallogenic regularity and model of Paleogene-Neogene anticlinal fissure pore brine in central and western Qaidam Basin
Abstract:
In recent years, deep fissure pore brines have been found in Paleogene-Neogene anticlinal tectonic strata in the central and western Qaidam Basin, Qinghai Province. These brines have large reservoir thickness, high content of potassium, lithium and boron resource elements, and some metallogenic conditions have reached the boundary or industrial mining grade, which have great potential for further prospecting. In this study, the sedimentary and salt-forming evolution of Paleogene-Neogene strata, reservoir characteristics and element geochemistry of brine deposits in Qaidam Basin are reviewed in detail, and the spatio-temporal metallogenic characteristics and genetic mechanism of brine resource elements are summarized. The results show that the reservoirs of brines in the west of the basin are gray mudstone and mudstone, while in the central of the basin are mudstone and siltstone. The content of potassium, lithium and boron resources gradually decreases from the west (Shizigou -Nanyishan) to the central (Hongsanhan - Yanhu) and to the north (Eboliang - Lenghu - Nanbaxian), which is closely related to the migration and evolution of the sedimentary center of the ancient lake basin. The metallogenic model of the Paleogene-Neogene anticlinal fissure pore brine deposit is established, which has a good guiding significance for future exploration evaluation and metallogenic prediction.
- 1
-
Petrogenesis of granites and its relationship with uranium mineralization in the Xiazhuang pluton, northern Guangdong Province: Constraints from zircon trace element and mineral chemistry
TAO Jihua, Zhang Zefeng, Renzhi, XU Zhitian, SUN Junjie, CAO Jun, SU Xianyuan, LENG Chengbiao, XU Deru
Abstract:
The granite-hosted uranium deposits in South China are spatially associated with the U-rich granites (U﹥10×10-6). Understanting the petrogenesis of these uranium-bearing granites with high U contents is not only significant for formulating exploration strategies for granite-hosted uranium deposits in South China, but also for ta better insights into the mechanism of U enrichment and mineralization for the granite-hosted uranium deposits. Here we investigate the Xiazhuang garnites which represent typical U-bearing granites with high U contents, using zircon U-Pb dating and zircon trace elements, biotite and chlorite geochemistry data, to constrain the petrogenesis and its relationship with uranium mineralization. LA-ICP-MS zircon U-Pb dating shows that the Xiazhuang granites were emplaced 234~236 Ma. The parental magmas of Xiazhuang granites were derived from the partial melting of Paleoproterozoic metasedimentary rocks with high F contents, and then underwent relative highly degree of magma differentiation. The oxygen fugacity decreased and U contents increased with the magmatic evolution, which led to the formation of U-rich granites (U﹥10 ×10-6) containing a large amount of U-rich accessory mineral such as uraninite, monazite, xenotime and thorite. Our study suggests that the U-rich accessory minerals in Xiazhuang granites were altered by the hydrothermal fluids in relatively acidic and oxidizing conditions in response to the Yanshanian mafic magmatism, followed by uranium leaching during alteration and provided uranium sources for the uranium mineralization.
- 1
-
Geology, geochemistry and of the Chakeng copper-potash feldspar deposit in Dehua district, Fujian province，and a preliminary discussion for its genesis
Zhang Chengjie, Qiu Tian, Xiong Fahui, Wen Wu, Mu Xiaoping, Chen Qin
Abstract:
The Chakeng copper-potash feldspar deposit (236 t Cu and 41.52 wt potash feldspar), located in the central part of polymetallic mineralization concentrated area of Mesozoic magmatic belt along southeast coast, is hosted in Qiongxi biotite granite in Dehua district, Fujian province. Copper ore bodies and potash feldspar ore bodies are the mainly two kinds of orebody in this deposit, both of which are controlled by a group of NNE trending faults F1, F2 and F3, and their secondary faults. The ore-forming process consists of three stages: potassic metasomatism (I); silicification and muscovite alteration (II) and carbonatization (III). Stage I and II are the major period for potash feldspar and Cu mineralization, respectively. Cu mineralization is strictly superimposed on potash feldspar mineralization, forming Cu- and potash feldspar-rich ores. Based on the geology, mineral chemistry, whole-rock geochemistry and internal structure of zircon, we propose that the Chakeng deposit is a hydrothermal-metasomatic deposit. Magmatic zircons separated from the copper-potash feldspar ore were probably captured/inherited from Qiongxi granite by hydrothermal fluids. Zircon U-Pb dating yielded a concordant age of 159.4±1.0 Ma (MSWD=0.21), which is interpreted as the petrogenic age of Qiongxi granite, and also defined as the upper limit of ore-forming age. Granite porphyry, intruded in biotite granite in Chakeng area, is characterized by enrichment of Ba, Sr, P, Ti, Pb and Cu, which is similar with the copper-potash feldspar ore but much higher than biotite granite. It is inferred that the copper-potash feldspar mineralization possibly resulted from the evolution of granite porphyry in this area.
- 1
-
Lithology identification of Karamaili ophiolite belt in Xinjiang based on ASTER and SDGSAT-1 thermal infrared data
Liulei, Zhang Zhao, Zhang Qunjia, Mei Jiacheng
Abstract:
Thermal infrared spectrum (TIR, 7-14 μm) has unparalleled advantages for the identification of rock-forming minerals, but currently there are few available satellite borne thermal infrared data sources, and the spatial and spectral resolution of the images is generally low. The thermal infrared spectrometer (TIS) carried by China's Sustainable Development Scientific Satellite-1 (SDGSAT-1), which will be launched in 2021, is characterized by large bandwidth (300 km), high spatial resolution (30 m), and high detection sensitivity, and has a better application prospect in lithologic mapping. In this study, two kinds of thermal infrared images, ASTER and SDGSAT-1, were selected from the East Junggar Kalamari region of Xinjiang to establish rock indices of mafic–ultramafic rocks, quartz-rich rocks, feldspar-rich rocks, and granitoid rocks, and combined with the results of the principal component analysis to analyze the distribution characteristics of the different rock types in the 2D and 3D feature spaces, and constructed the lithology identification models of the two kinds of data in the multi-dimensional spectral feature space, respectively. The results show that: 1) The rock indices constructed from ASTER TIR and SDGSAT-1 TIS data can effectively identify mafic–ultramafic rocks, quartz-rich rocks, feldspar-rich rocks and granites, with an overall accuracy of 95.16% and 98.02% for lithology identification, respectively; 2) The multi-dimensional spectral feature space model constructed with two types of data also has good lithology recognition performance, with overall accuracy improved to 96.78% and 98.54%, respectively; 3) SDGSAT-1 TIS has improved the accuracy of extracting mafic-ultramafic rocks by 13.26% compared to ASTER TIR, and has stronger recognition ability for rocks with smaller outcrops. It has great potential for application in lithology mapping.
- 1
-
Computational Grid Selection in numerical modeling of Subduction Dynamics
yangshaohua, PAN Jiawei, LI Haibing
Abstract:
Various numerical models based on mathematical physics equations in geosciences, including numerical modeling of subduction dynamics, necessarily involve computational grids consisting of discrete nodes, which control the accuracy of numerical calculations and thus the credibility of numerical models in solving practical geoscientific problems. The numerical modeling of subduction dynamics has made great progress in recent years; however, the numerical accuracy due to the arbitrary use of computational grids is still unclear. In this paper, we construct numerical models based on three sets of computational grids with different accuracies for a classical scientific problem, and evaluate the possible impact of low-precision grids in practical research. It is argued that the computational grid with an accuracy of 2km×2km for the encrypted zone, which has been more commonly used in the last decade, is likely to obtain computational results containing significant numerical errors, which in turn affects the application of numerical modeling in subduction dynamics. Therefore, it may be necessary to revisit models with low precision grids and their corresponding geologic conclusions in recent years. As numerical models of subduction dynamics become more and more highly nonlinear, the choice of computational grids with the highest possible accuracy may be inevitable. For the case of using low-precision grids for highly nonlinear problems, definitive evidence of grid reliability is needed. We propose a new set of grid pattern suitable for subduction dynamics: locally encrypted structured quadrilateral grids containing hanging nodes. This grid may accomplish high-precision numerical calculations with a small total number of grids and is relatively simple to implement.
- 1
-
Identification of the Central Fault— the extension of the Red River Fault Zone in the Yinggehai Basin
Fu Yongtao, Chen Guanfei, Wu Tao, Wang Wanying, XuTao, Zhou Zhangguo, Yang An
Abstract:
The early left-lateral and late right-lateral strike-slip shearing of the Red River Fault Zone performes a crucial function in controlling the tectonic evolution and sedimentation processes of the Yinggehai Basin. While the Red River Fault has been identified in the northern and southern parts of the Central Depression of the Yinggehai Basin, it remains unclear how the Red River Fault Zone extends within the Central Depression, impacting the study of the basin's tectonic evolution and sedimentation processes. Current studies on the tectonic evolution of the Yinggehai Basin are based on the No. 1 Fault on the eastern side and the Yingxi Fault on the western side as boundaries. In this paper, utilizing satellite altimetry gravity anomaly data in the Yinggehai Basin and employing the normalized vertical derivative total horizontal derivative edge recognition (NVDR-THDR) method, we determined the distribution of the Central Fault. This recognition is verified by 2D seismic sections in the northern and central parts of the Central Depression. The Central Fault is the extension of the Red River Fault Zone in the Yinggehai Basin, developing as a left-stepping fault system north of the Dongfang Diapir area, forming an eastward dislocation in plan view. In the Changnan Diapir area, it consists of several parallel faults. In the Ledong Diapir area, a left-stepping sinistral strike-slip fault system is developed, leading to the development of the Ledongnan Subsag (pull-apart basin). Seismic profiles reveal that the buried depth of the Central Fault is larger in the Central Depression, with a two-way travel time exceeding 6 s. According to the stratigraphic sequences, the main active period of the Central Fault predates 30 Ma to 15.98 Ma. The Cenozoic sediment thickness of the Yinggehai Basin, calculated using the fast inversion method of the double-interface model of the gravity field, reveals the development of five depocenters with thicknesses exceeding 15 km in the Central Depression. Generally, to the west of the Central Fault are the depocenters, while to the east, there is a gradient zone with smaller sediment thickness. Simultaneously, the five diapir belts in the Central Depression are all distributed to the west of the Central Fault, with the left-stepping sinistral strike-slip fault system in the Ledong diapir area exerting significant control on three parallel diapir belts. The Central Fault holds great significance for the tectonic evolution and oil and gas exploration in the Yinggehai Basin.
- 1
-
New insight into the mechanism of No. 1 fault in the Yinggehai Basin: analogue modelling and discussion
Xiao Kunze, Tong Hengmao, Yang Donghui, Li Xuesong, Li Xushen, Cui Hao
Abstract:
The Yinggehai Basin has long been of great interest to academics and the petroleum industry due to its special tectonic location (the area of the Red River Fracture Zone into the sea) and its abundant natural gas resources. Since the Indo-Eurasian collision-extrusion model was proposed to explain the deformation in Southeast Asia, the Yinggehai Basin has been regarded as a typical pull-apart basin. However, based on the generalised fault theory, and through the structural analysis of the 3D seismic data system, they revealed that the tectonic features and the distribution of fault distances of the boundary fault (No.1 fault) in the Yinggehai Basin are not similar to those of the traditional strike-slip faults, but they are also strongly similar to the features of the structural deformation under oblique extension. Furthermore, our article proposes a new insight into the mechanisms of the No. 1 fault based on the analysis of the structural features of the No. 1 fault and also combined with the analogue modelling. The results show that the No.1 fault has obvious characteristics of an oblique-slip normal fault, and there are significant differences in the amount of strike-slip and dip-slip displacements in different areas along the fault strike, as well as the control of sedimentation in the basin. The boundary fault was an oblique-slip normal fault due to the reactivation of pre-existing structures under a north-south extensional stress regime during the Oligocene-Miocene period, and these r insights were also verified by analogue modelling. A new insight into the mechanism of the No. 1 fault, which theoretically reveals the mechanism of the Yinggehai Basin and can provide guidance for the structural analysis of the Yinggehai Basin and its later oil and gas exploration and development.
- 1
-
Zircon U-Pb ages and Rubidium occurrence of the giant Gariatong granite-type rubidium deposit, Tibet
XIE Jinling, TANG Juxing, LIN Bin), TANG Pan, QI Jing, DENG Shilin, HE Liang, ZHANG Xiaoxu
Abstract:
Lots of highly differentiated granites are widely distributed on the Qinghai-Tibet Plateau, but their mineralization and exploration potential for rare metals were unclear. The Gariatong deposit is a newly discovered giant granite-type rubidium deposit in the central Lhasa terrane, recently. The detailed geological survey and borehole logging of the Gariatong deposit revealed that the rubidium mineralization is mainly hosted in monzogranite and surrounding rocks. Zircon U-Pb dating results show that the weighted average ages of the ore-bearing monzonite is 20.0±0.5 Ma (n=14, MSWD=1.8), which suggested that the intrusion occurred in the Miocene. Detailed petrography and electron microprobe analyses revealed that rubidium is mainly host in muscovite and biotite in an isomorphism form, and no independent rubidium minerals are seen. The geochemical characteristics of muscovite and biotite revealed that the magma associated to mineralization is the product of remelting of crustal-derived material in a low-oxygen fugacity environment, and the formation of fluoride-rich magmatic hydrothermal fluids after strong differentiation is the key to the formation of large-scale rubidium mineralization. The discovery of the giant granite-type rubidium deposit in the Gariatong not only enriched distribution of rubidium mineral resources in China, but also support the prospecting of rare metals in highly differentiated granites on the Qinghai-Tibet Plateau.
- 1
-
Enrichment process of rare earth elements in Permian sedimentary manganese carbonate deposits from the Zunyi area, northern Guizhou
Xu Hai, Gao Junbo, Yang Ruidong, Xu Jinhong, Liu Zhichen, Qiao Wenlang, Ye Fei, Zhang Xu
Abstract:
As strategic and critical minerals, rare earth elements and yttrium (REY) have long been of great concern. In recent years, previous studies have reported that numerous sedimentary manganese (Mn) ores are significantly enriched in REY (> 500x10-6). However, the provenance, carrier, and enrichment process of REY in sedimentary Mn ores still lack precise constraints. It is noteworthy that the significant enrichment of REY in the Zunyi Mn deposits has been discovered through careful compositional analysis. Specifically, the average ∑REY content in the ores and the underlying tuffaceous clay is 693.97×10-6 and 1464.54×10-6, respectively, which is mainly characterized by the enrichment of La, Ce, Nd, and Y, and is the first reported REY-bearing carbonate Mn deposits in China. The macro and micro mineralogical composition, symbiotic and intergrowth relationships, and REY differentiation highlight that the enrichment of Mn and REY primarily originates from the magmatic-hydrothermal system of the Emeishan Large Igneous Province (ELIP). The REY in ores and tuffaceous claystones mainly occurs as monazite, xenotime, and goyazite, which indicates that phosphate is the main carrier of REY in Zunyi Mn deposits. Of note, monazite and xenotime are mainly fine-grained (<10μm) anhedral particles form, coexisting with authigenic minerals (e.g., rhodochrosite and capillitite), and closely symbiosis with residual Fe-Mn oxides and altered tuffs in rhodochrosite. Meanwhile, goyazite appears in microcrystalline or colloidal form, closely symbiosis with fine-grained minerals (e.g., illite and quartz), and locally coexisting with residual altered volcanic debris. In conclusion, we suggest that REY enrichment is controlled by ELIP paleostructure-magma-hydrothermal activity, multiple carriers, and multiple sedimentary stages, therein REY initially occurs in Fe-Mn oxide and tuff, subsequently transfer to phosphate minerals during early diagenesis-alteration process.
- 1
-
Late Triassic extension in the northwest Ordos Basin: Constraints from Langshan basalts, NW China
huijie, fanliyong, zhaoweibo, kangrui, wangyufei, zhangjin, zhangbeihang, zhaoheng
Abstract:
This study reported newly discovered Triassic basalts in the Langshan region, analyzed its tectonic setting and contemporaneous deformation, and discussed the characteristics of the Late Triassic basin in the northwest margin of Ordos Basin. 40Ar/39Ar geochronology show that the basalts formed in the Late Triassic (217 Ma). Whole-rock geochemistry reveals that the basalts have OIB affinity, derived from the 5–10% partial melting of garnet and spinel lherzolite, formed by the decompression melting of the asthenosphere in the intraplate extensional setting. The Langshan region also developed a Late Triassic NE-SW trending ductile sinistral shear zone, which connected southward with a simultaneous sinistral shear zone in the Bayanwulashan and Helanshan regions and extended northward into Mongolia. Temporal simultaneity indicates the close relationship between sinistral shearing and basalts eruption. By comparing the contemporaneous basalts, Yanchang Formation, and sinistral strike-slip faults in the Langshan and Helanshan regions, we proposed that the northwest margin of the Ordos Basin was under the far-field effects of the collision of North China Plate and South China Plate in the Late Triassic, and the sinistral ductile strike-slip lead to the formation of regional pull-apart basin, accompanying the extension of lithosphere and the basaltic magmas eruption resulted from the decompression of asthenosphere.
- 1
-
Carboniferous–Middle Permian sedimentary- paleogeographic environment and source of the lithium-rich claystones in the Dianzhong Basin, SW China
ZhangJiahui, Yanzhen, XueChuandong, YuLiangjun, WeiAiying, FuChanglei, WangWei, WangYu, ZhouHonglin
Abstract:
The Carboniferous?Middle Permian sedimentary sequences are rich in bauxite, coal, calcite, limestone and other type ore deposits associated with numerous lithium-rich claystones in the Dianzhong Basin, SW China, and their metallogenic setting is constrained by spatial?temporal evolution of the sedimentary environments and relevant paleogeography. Systematical field investigation demonstrates that the Carboniferous sedimentation in the Dianzhong Basin is mainly dominated by terrigenous clastic and carbonate rocks of a littoral tidal flat-lagoon environment, and the Lower?Middle Permian sedimentary rocks mainly deposited in a lagoon-tidal flat-open platform environment. The Lower Carboniferous Datang Formation of which is mainly composed of carbonates with muddy shale interlayers of the tidal flat environment, and the lagoon deposition only occurs adjacent to the Niushoushan Paleo-high. The Middle Carboniferous Weining Formation and Maping Formation are littoral-tidal flat deposits, which are sporadically exposed around this uplift. The Lower Permian Daoshitou Formation is a suite of fine?grained terrigenous clastic rocks, with minor limestone lenses locally. The bauxite, coal ore deposits and lithium-rich claystones hosted in the Daoshitou Formation precipitated in a tidal flat?lagoon environment. The Middle Permian Qixia and Maokou formations consist of algal clastic limestone, dolomitic leucoblastic bioclastic limestone and medium- to coarse-grained dolomite, which deposited in an open-platform environment. Spatially, the thickness of the Datang and Daoshitou formations vary greatly in transversal, showing a thinning-southward trendency. The number of coal and bauxite layers also decreases to the southward. These characteristics demonstrate that the depth of seawater is shallowing to the south and the relevant deposits are close to their source area gradually. The Qixia and Maokou formations are widely exposed to the north and the corresponding thickness increases northward. This is consistent with the SE-high and NW-low paleogeography of the Dianzhong Basin indicated by paleocurrent data during the Early?Middle Permian, which also demonstrates that the Niushoushan Paleo-high is the major source region of the Daoshitou Formation. Geochemical data demonstrate that the Daoshitou Formation is rich in the aluminum- and lithium-rich claystones, and the contents of lithium and bauxite ores (Al2O3) are controlled by weathering of their source areas, and sedimentary conditions. When the contents of Al2O3 are less than 55%, and the ratios of Al2O3/SiO2 are less than 3, the contents of lithium are positively correlated with the contents of Al2O3, and of negatively correlations for other variation intervals. Regional geological data analysis demonstrates that the Niushoushan Paleo-high mainly comprises of the Precambrian intermediate-mafic volcanic and sedimentary rocks, which also occurred in a warm and humid environment during the Early?Middle Permian. This Paleo-high experienced regional uplifting and erosion because of continuous opening of the Paleo-Tethys during the Early Carboniferous to Middle Permian times, which also results in that the Precambrian volcanic rocks and relevant sedimentary rocks were eroded, and the volcanism was widespread. These eroded detritus and volcanic eruptions adjacent to the Niushoushan Paleo-high are the important source for the formation of the bauxite ore deposits and lithium-rich claystones in the Dianzhong Basin.
- 1
-
Characteristics of trace element geochemistry and the geological significance of fluorites from the Haidewula uranium deposit in Qinghai
Wu Jia, Liu Xiaodong, Wang Kaixing, Dai Jiawen, Yu Chida, Sun Liqiang, Zhu Kunhe, Yang Jianjun
Abstract:
The Haidewula uranium deposit is the first typical volcanic-related hydrothermal uranium deposit to be discovered in northwest China currently. Revealing the nature of the ore-forming fluids and the mineralized mechanism is favorable to understand the genesis of the deposit and to guide the prospecting in this area. Detailed studies on mineralogy, petrography and trace elements of fluorites from the deposit have been conducted in this paper. The results show that two stages of hydrothermal fluorite including metallogenic stage dark purple fluorite and post metallogenic stage purple fluorite have been identified, with the metallogenic stage dark purple fluorite closely associated with the uranium mineralization. The characteristics of trace elements and the REEs pattern are significantly different in two stage fluorites. The dark purple fluorite in the metallogenic stage is relatively enriched in Sr and Ba, while the purple fluorite in the post metallogenic stage is relatively enriched in REE and trace elements such as Co, Ni, Cu, Zn, Ga, Rb, Y, Zr, Nb, Mo, Cs, Pb, Th and U. The ΣREE of dark purple fluorite in the metallogenic stage ranges from 59.98×10-6 to 118.31×10-6, with a median value of 75.02×10-6, and the REE pattern is characterized by enriched LREE (LREE/HREE ratios median 5.06) and a strong fractionation between LREE and HREE ((La/Yb) N value median 12.24)), with moderate negative Eu anomaly (with median of 0.56), week Ce anomaly (with median of 0.99) and positive Y anomaly (with median of 2.21). The ΣREE of purple fluorite in the post metallogenic stage ranges from 194.12×10-6 to 207.67×10-6, with a median value of 195.55×10-6. The REE patterns of purple ?uorite is characterized by enriched LREE (LREE/HREE ratios median 4.76) and a relatively strong fractionation between LREE and HREE ((La/Yb) N value median 6.37)), with a well-pronounced negative Eu anomaly (with median of 0.09), positive Ce anomaly (with median of 1.33) and positive Y anomaly (with median of 1.90). Based on the comparison with the geochemical characteristics of the surrounding rocks and the pitchblende, two stages of fluorite (metallogenic stage dark purple fluorite and post metallogenic stage purple fluorite) in Haidewula uranium deposit were formed in the fluids with different sources. The metallogenic stage dark purple fluorite was formed in the acidic ore-forming ?uid rich in F- and Cl-, and maybe precipitated by the mixing mechanism of meteoric water with magmatic water in a reducing environment. The trace element geochemical characteristics of post metallogenic stage purple fluorite, such as with Ce positive anomaly and inheriting the Eu negative anomaly of the ore-bearing volcanic host rocks, indicated that the fluorite was formed in the oxidizing environment with higher proportion of meteoric water and higher oxygen fugacity and pH value in the fluid.
- 1
-
The multi-level structure and formation mechanism of the Kenya Rift Valley, East Africa
Jia Zhijie, Lu Quanzhong, Huang Weiliang, Zhuang JIanqi, Zhu Xinghua, Ma Penghui, Wang Feiyong, Wang Zuopeng, LIU YANG, He Ming, Zhao Junyan, He Zhiyuan, Huo Bingyao, Peng Jianbing
Abstract:
The East African Rift System, as the most famous continental rift and fault zone on earth, conducting research on the formation of ground fissures within the rift valley is of great significance for understanding the active rift process and guiding the engineering construction of the rift valley area. On the basis of field investigation, trenching, geophysical exploration, and helium isotope detection of ground fissures in the Kenya Rift Valley, East Africa, this article establishes a multi-level structure of ground fissures in the crust and analyzes their formation mechanisms. The results indicate that there are a total of 22 large ground fissures developed in the study area, mainly distributed in the rift basin between the eastern boundary fault and two volcanoes in the study area. Ground fissures appear on the surface as ruptures and collapses of loose sediments, and as simple tensile fractures with degassing on the surface of pyroclastic rocks. Resistivity detection shows that ground fissures are extensions of rock fissures in the crust. Based on the characteristics of helium isotopes, a multi-level structure consisting of ground fissures, rock fractures, faults, magma chambers, faults, and upper mantle has been revealed. On the basis of the above research, combined with the characteristics of crustal deformation and numerical simulation, the formation mechanism of ground fissures in Kenya Rift Valley, was revealed and summarized as follows: mantle upwelling-mantle intrusion-magma chamber expansion-surface fracturing.
- 1
-
Iron isotopic characteristics constraints and indicative significance of the Xiaohongshilazi Pb-Zn (Ag) deposit in Jilin Province
Wang Gaotian, Wang Da, Bai Feng, Xu Debing, Wang Guilong
Abstract:
The Xiaohongshilazi Pb-Zn (Ag) deposit is a representative medium-sized deposit within the Jizhong-Yanbian copper-nickel polymetallic metallogenic belt, the main views for deposit types mainly include VMS type, medium-low temperature hydrothermal vein type, and exhalative deposits overprinted by hydrothermal fluid. In order to constrain the ore genesis, the Fe isotope characteristics of pyrite and pyrrhotite are systematically investigated. The overall δ56Fe values range from –0.82‰ to 1.00‰; Compared with other various type deposits, we have found that the Xiaohongshilazi Pb-Zn (Ag) deposit shows the characteristics of both hydrothermal and sedimentary deposits, hence the metallogenic hydrothermal fluid should be hot spring, and MVT type is most suitable. The δ56Fe values of pyrite gradually decrease from stage 1 (1.00‰) through stage 2 (0.21‰ ~ 0.83‰) to stage 3 (0.08‰ ~ 0.12‰); in comparison, the δ56Fe values of pyrrhotite gradually increase from stage 1 (–0.82‰) through stage 2 (–0.55‰ ~ 0.13‰) to stage 3 (–0.23‰ ~ –0.21‰), which is the typical Rayleigh fractionation characteristics. Within coexisting mineral pairs, the pyrrhotite is preferentially enriched in light Fe isotopes relative to pyrite, which is the same with previous studies. In addition, a Fe isotope fractionation model has also been established, which imply that the collected samples were correspond to the intermediate period (33.96% ~ 63.70%) of the whole mineralization process, while 63.59% of the metal resources related to the early period (0.00% ~ 33.96%) and late period (63.70%~ 100.00%) have not been discovered. In summary, the Fe isotopic compositions is mainly controlled by Rayleigh process, although the Fe isotopic evidence supported the MVT genesis, the geological characteristics are slightly different hence it should be classified as an MVT-like deposit; and there is still further prospecting potential within orefield.
- 1
-
Growth model and geological significance of bedding-parallel fracture veins in Southeast Sichuan Basin1 Engineering Technology Research Institute, PetroChina Southwest Oil Gasfield Company, Chengdu, Sichuan 610017, China
Tianhe, Liyuegang, Zeng lianbo, Chenliqing, Wuqiuzi, YInyingzi, Lihong, Xuliang, Liyanyou, Yangxue, Lidu, Chenyao
Abstract:
Bedding-parallel fractures are widely developed in organic-rich shale, which are important reservoir space and lateral migration channel of shale gas, affecting the migration, enrichment, preservation of shale gas and the fracturing effect of reservoir. However, the formation of bedding-parallel fractures usually has multiple stages and causes, making the formation mechanism of bedding-parallel fracutures very complex and difficult to distinguish. This study takes the shale from the Wufeng-Longmaxi Formation in the Southeastern Sichuan Basin as an example. Based on field, core, thin section, and scanning electron microscopy data, the macroscopic characteristics of bedding-parallel fractures and the microstructure characteristics of filling veins were studied, and the formation mechanism of bedding-parallel fractures was analyzed. The results show that the surface of the unfilled bedding fractures is smooth and has obvious mirror features. The scratches and steps on the fracture surface can indicate the relative displacement direction of the surrounding rock on both sides of the fracture, and the fracture can extend several meters to tens of meters forward along the bedding plane. The bedding-parallel fractures are mostly filled with striped calcite and quartz minerals, with a width of 0.5cm~5cm. Bedding-parallel fractures contain three important microstructures, namely crack-seal bands, inclusion trails, and elongate crystals. The shape of the crack-seal band is controlled by the initial fracture, and the number of bands can indicate the times of fracture opening. The inclusion trails are parallel to the opening direction of the fracture and can track the opening trajectory of fracture. According to the different driving forces of fracture opening during the formation of veins, bedding-parallel fractures veins can be divided into three types: fluid overpressure type, tectonic compression type, and tectonic-fluid overpressure type. During the growth of bedding fractures and veins, they can serve as lateral migration channels for shale gas, affecting the enrichment and preservation of shale gas. And as mechanical weak surfaces, they have a significant impact on the hydraulic fracturing effect.
- 1
-
Study on the process of iron-aluminum differentiation in bauxite formation: a case study of the iron-aluminum rock series in the Jiujialu Formation of the Carboniferous System in Central Guizhou
Yang Ruidong, MO Hongcheng, LUO Chaokun, GAO Junbo, NI Xinran, Peng Rou, GAO Chuanqian, CHEN Jun, CHEN Jiyan
Abstract:
Based on the study of the iron-aluminum rock series of the Jiujialu Formation in the Carboniferous System of Central Guizhou, as well as the sedimentary sequence, sedimentary structures, and geochemical analysis, it is concluded that iron-aluminum differentiation primarily occurred during the depositional period. The banded, clastic, and oolitic structures observed in the ferruginous rock indicate its depositional origin rather than post-depositional iron migration. Geochemical characteristics show distinct elemental compositions between the ferruginous rock and bauxite, suggesting differences in sediment sources and depositional environments during the depositional period. The proximity of high-iron bauxite deposits to source areas and the distance of low-iron bauxite deposits from source areas further support the conclusion that iron-aluminum differentiation primarily occurred during deposition. The iron-aluminum differentiation in the Jiujialu Formation is closely related to global paleoclimatic changes, particularly the transition from a hot and arid climate to a cold climate during the early Viséan period. The abrupt intensification of rainfall led to the leaching of iron-rich material from the weathered crust, which was transported in colloidal form and deposited in lakes and swamps, forming ferruginous rock. Subsequent heavy rainfall events resulted in flood events, during which aluminum-rich weathered crust was transported as debris flows into lakes or swamps, leading to the deposition of clastic bauxite as a product of these flood events.
- 1
-
Fission track evidence of Cenozoic uplift and exhumation of Huayangchuan uranium polymetallic deposit in Xiaoqinling
Chen ZhiBai, Yan Jie, Sun Yue, Kang Qingqing, Pan Chunrong, Xia Fei, Pan Jiayong
Abstract:
The Huayangchuan uranium polymetallic deposit is a comprehensive super-large deposit dominated by U-Nb-Pb and associated with rare earth elements. In order to clarify the exhumation history of the deposit and the preservation of the ore body, this paper systematically collected 10 gneiss samples in Huayangchuan mining area according to the distribution characteristics of the ore body, and carried out apatite fission track test. The results show that the age of the samples is between 52.0 ± 2.9 ~ 35.2 ± 0.77 Ma, and the average track length is between 11.53~13.73μm. The thermal history simulation shows that the Huayangchuan area has experienced two stages of rapid uplift and denudation since the Cenozoic : ① Eocene ( 54 ~ 34 Ma ) and ③ Middle Miocene to present ( 13 ~ 0 Ma ), and ②Oligocene to Middle Miocene ( 34 ~ 13 Ma ). Combined with the regional tectonic evolution, the Cenozoic tectonic evolution model of Huayangchuan area is constructed. It is considered that the rapid uplift and denudation in the Eocene period is affected by the thrusting of Xiaohe fault from south to north and the extension of Huashan piedmont fault. During the period of 34 ~ 13 Ma, the study area was in the tectonic quiet period as a whole. The rapid uplift and exhumation since 13 Ma was mainly affected by the Huashan piedmont fault, resulting in the tilt of the study area from north to south. Fission track data and thermal history simulation show that the ore bodies on the southeast side of the study area are well preserved and have great prospecting potential.
- 1
-
Deformation and element redistribution characteristic of in-situ apatite in metamorphic rocks: a case study of metamorphic rocks in the Eastern Himalayan Syntaxis
ZHANG YanYan, ZHAO ZhongBao, DU JinXue, LIANG FengHua, MAO XiaoHong, TIAN ZuoLin, Ma XuXuan
Abstract:
The metamorphism and deformation of rocks can be well recorded by the structures and element distribution of accessory minerals. Especially, the metamorphic/deformation history can be revealed and analysized by in-situ chronologic dating. Apatite is a common accessory mineral in metamorphic rocks. With the rapid development of in-situ dating technology of apatite, it has become an important dating mineral in magmatic rocks and mineral deposit studies. In different metamorphic-deformation processes, a series of important problems about the deformation mechanism and behavior of apatite and its restriction effect on the element diffusion process have not been solved. In this study, rocks in the Eastern Himalayan syntaxis, which has the strongest tectonic deformation and metamorphism, are selected for research. SEM and CL observations show that the apatite in granulite does not show obvious compositional structure, while the apatite in mylonite shows obvious changes in light and dark, that is, composition changes. By statistical analysis of apatite distribution characteristics in thin sections, we found that the long axis direction of apatite in the two metamorphic rocks is approximately parallel to the main foliation. EBSD fabric analysis shows that the apatite in granulite shows obvious intra-granular deformation, while the apatite in mylonite shows almost no intra-granular deformation. The results of EPMA scanning of apatite composition show that the distribution of major elements of apatite in granulite is relatively uniform, while the distribution of Si elements of apatite in mylonite is obviously zonal or uneven, which is consistent with the results of CL scanning. Based on the above apatite deformation and element distribution characteristics, it can be preliminarily concluded that: (1) Although apatite in granulite is directionally distributed parallel to main foliation and occurred intra-granular deformation, it may be due to relative higher metamorphic temperature, which promotes the rapid diffusion of elements and makes the redistribution of elements tend to be uniform. Moreover, the late fluid action occurs element metasomatism along the low-angle grain boundary or near the fracture which are always perpendicular to the maximum tensile stress. (2) The apatite in mylonite is arranged parallel to the mylonite foliation, but almost no intra-granular deformation occurs, possibly due to the low deformation temperature (< 450o), or because the strain of mylonite is mainly concentrated in the quartz and mica domains, while the relatively tough apatite does not participate in deformation. The composition changes shown in the CL image and some major elements distribution maps may be indicating that the low metamorphic/deformation temperature have not led to the rapid diffusion of elements in apatite. (3) The preliminary age results show that the apatite in the granulite records multiple ages, indicating that the inherited apatite occurs in the element redistribution during metamorphism and late stage metasomatize of the apatite which has influence mineral isotope system, while the apatite in the felsic mylonite is the result of continuous fluid activity during the mylonitization process resulting in continuous crystallization of apatite. New results provide important information for the interpretation of apatite age in metamorphic and deformation rocks.
- 1
-
Sedimentary characteristics and geochemical constraints of borate deposits in salt lakes on Qinghai-Tibetan Plateau
Xiang Honglu, Fan QIshun, Li Qingkuan, Chen Tianyuan, Yang Haotian
Abstract:
Boron is a strategic key non-metallic mineral in China, widely used in new energy, new materials, electronic information and other high-tech fields. The salt lake type borate deposits are mainly distributed on the Qinghai-Tibetan Plateau and the most important and promising boron resource type in China. Boron-rich salt lakes in the Qinghai-Tibetan Plateau show hydrochemical zones and differences of borate deposit types in different hydrochemical of salt lakes from south to north, but there is lack of comparative study of boron-rich salt lakes in different zones.This paper summarizes and compares the sedimentary characteristics of solid boron deposits and the differences of geochemical parameters of boron-rich brines in carbonate type (I region), sodium sulfate-magnesium sulfate subtype (II region) and magnesium sulfate-chloride type (III region) salt lakes on the Qinghai-Tibetan Plateau. The main conclusions are obtained as follows:① Borate minerals are mostly deposited directly on top of the clastic sediments, and present interactive multilayer deposition characteristics, indicating that the deposition of borate deposits requires brackish water recharge and hydrological environment changes, which accords with the theory of "Brine diluted into salt"；② The deposition of borax and ulexite is associated with a large number of mirabilite, and the deposition of pinnoite and Kurnakovite is accompanied by a large number of magnesium-bearing carbonate mineral (Hydromagnesite and dolomite), which indicates that the deposition of borax and ulexite requires the recharge of waters high in Na+, and that the deposition of pinnoite and Kurnakovite requires the recharge of waters high in Mg2+；③ The boron precipitation conditions of salt lakes inⅠ,Ⅱ, and Ⅲ zones are similar, as shown by the brine pH value of more than 8 and the B content of more than 400 mg/L; however, there are differences between different salt lakes in terms of TDS, Mg, and Na content；④ Combined with the chemical composition of borate deposits types mainly containing Na+ and Mg2+.The B×10-Na-Mg terminary equivalent diagram in zones Ⅰ, Ⅱ and Ⅲ shows that the equivalent of Na and B are in the range of 0.2-0.6 and 0.4-0.7, respectively, whereas there are some differences in the Mg equivalence values, with zones Ⅰ < 0.1, and zones Ⅱ and Ⅲ in the ranges of 0.1-0.4.
- 1
-
Summary of the exploration achievements and gold mineralization of Jiaodong Xiling super large gold deposit
Abstract:
Jiaodong is the most important concentrated exploration area for gold deposits in China. During the 14th Five Year Plan period, Shandong gold geology and mineral exploration Co., Ltd. explored another super large gold deposit -- Xiling gold deposit between Sanshandao-Cangshang fault zone. Its accumulated detected gold resources reach 580t, with an average grade of 4.24 g/t, making it the largest single gold deposit discovered in China at present. It is located between the Sanshandao gold deposit and the northern sea area gold deposit. It is the deep extension and lateral part of the Sanshandao gold deposit in the northeast direction, and is connected to the northern sea area ore body in the deep. In fact, the three are actually the same ore body. Xiling gold ore body controls a maximum strike length of nearly 2000m and a maximum extension depth of 2057m; it is found that the ore body is in the form of "short handled axe" inclined to the Northeast in the horizontal direction, and has obvious echelon in the vertical distribution. The gold resources are mainly concentrated at the elevation of -1000 ~ -2200m; At the northeast end of the mining area, the ore body has extended to - 2600m, and continues to go deep. The thickness of the ore body becomes thinner, the grade is low, and the deep gold mineralization becomes weaker; The ore body extends from shallow to deep in multistage steps, which generally shows the characteristics of steep and gentle alternating echelon mineralization. Through the study of fluid inclusions in the deposit, it is found that the gold ore-forming fluid belongs to H2O-CO2-nacl fluid with medium temperature (199 ~ 347 ℃) and medium and low salinity (0.35 ~ 8.28 wt.%) rich in CO2, which is consistent with the large-scale gold ore-forming fluid in Jiaoxi North University, but slightly different in the process of gold deposit precipitation and migration. The precipitation mechanism of Xiling gold is mainly fluid immiscibility, and the temperature and salinity of the fluid in the main metallogenic period change most obviously, from the shallower part to the later stage of mineralization, The properties of ore-forming fluids tend to be more uniform. There is a certain coupling relationship between the emplacement of fluids and the spatial echelon mineralization. Gold mineralization is mainly concentrated in the second and third echelon spaces, corresponding to the middle and late stages of the mineralization stage. The study of S isotope shows that pyrite δ34S value has the trend of first increasing and then decreasing. The initial sulfur source of Xiling gold deposit may be closer to magmatic sulfur. In the process of mineralization, ore-forming materials and ore-forming fluids were mixed with other sources. The gold ore in the area has experienced strong assimilation, mixing and alteration metasomatism. The main element SiO2 is moderately acidic, with high Al2O3 and K2O and low Na2O、 TiO2、 MgO and CaO. It is peraluminous potassic basalt and high potassic calc-alkaline series granite. The ree distribution form is right-leaning type enriched in LREE, enriched in large ion lithophile elements (LILE) and depleted high field strength elements (HFSE), which has similar geochemical characteristics with island arc magmatites in extensional tectonic setting. Comprehensive studies have shown that,Xiling gold deposit belongs to altered rock type gold deposit formed by mesothermal magmatic hydrothermal filling metasomatism according to its genetic type. It was formed in the extensional tectonic background under the failure mechanism of North China Craton in the early Cretaceous. In the early Cretaceous, lithosphere thinning and asthenosphere upwelling caused large-scale magmatic activity. The coupling of structure, magma and fluid created large-scale gold mineralization in this area.
- 1
-
The deposit types, spatial distribution and development and utilization of gallium and germanium resources in China
Yu Jinjie, Chen Qishen, Bi Minfeng, Chen Shaocong, Chen Xiaodan, Znang Rui
Abstract:
Gallium and germanium as by product of other ore deposits are the dominant mineral resources in China. The types of gallium deposits are divided into gallium-bearing hydrothermal deposits, gallium-bearing bauxite deposits dominated by monohydrate bauxite ores and gallium-bearing coal deposits in China. The resources of the first two types of deposits are dominated and available. The types of germanium deposits in China are divided into germanium-bearing medium-low temperature lead-zinc deposit, germanium-bearing magmatic hydrothermal deposit, germanium-bearing sedimentary deposit, germanium-bearing organic rock deposit and germanium-bearing volcanic rock deposit. Among them, the resources of germanium-bearing medium-low temperature lead-zinc deposit and germanium-bearing organic rock deposit are dominant and available. The spatial distribution, development and utilization of gallium- and germanium-bearing ore deposits in China are mapped. There are 423 gallium-bearing orefields, in which 117 are fully utilized orefields, 112 are partly utilized orefields, 7 are closed and 187 are fully unutilized. There are 69 germanium-bearing orefields, in which 18 are fully utilized orefields, 12 are partly utilized orefields, 4 are closed and 35 are fully unutilized. In general, although gallium- and germanium-bearing de posits are widely distributed in China, they are mainly concentrated in a few metallogenic belts. Gallium-bearing ore deposits are divided into 22 metallogenic belts (regions), and germanium-bearing ore deposits are divided into 13 metallogenic belts (regions). China is the most significant producer and exporter of gallium and germanium in the world. The gallium and germanium industry is small. A large number of primary gallium and germanium products exported to western developed countries every year. But high-end gallium and germanium products are basically dependent on imports in China.
- 1
-
Zircon U-Pb geochronology, petrogenesis and tectonic setting of granitic pegmatite in Guanpo area, the eastern part of the North Qinling Orogenic Belt
CHEN Guochao, ZHANG Xiaofei, PEI Xianzhi, LI Ruibao, LI Zuochen, WANG Shuo, CHEN Xiaozhen, WANG Yongqiang, Zhang Rongzhen
Abstract:
The granitic pegmatites of the North Qinling tectonic belt are important pegmatite areas in China. There are controversial about the formation age and petrogenesis of the granite pegmatite. This paper presents LA-ICP-MS zircon U-Pb age, Hf isotopic and geochemical data of the Xiahecun granitic pegmatites and the Shanghecun granitic pegmatites in the Guanpo area to determine the formation age, the magma source, the petrogenesis and tectonic setting. LA-ICP-MS zircon U-Pb dating suggests that the Xiahecun granitic pegmatites and the Shanghecun granitic pegmatites crystallized 360~361 Ma and 334.8 Ma, respectively. The Xiahecun granitic pegmatites and the Shanghecun granitic pegmatites contain garnet, muscovite and tourmaline, with high contents of SiO2, Na2O and K2O, and low contents of CaO, FeOt and MgO, and are mainly peraluminous. The Xiahecun granitic pegmatites and the Shanghecun granitic pegmatites show little fractionation between LREE and HREE, and have obvious positive Eu anomalies. The magma is enriched in large ion lithophile elements (LILE) such as Rb, Th, Ba and Cs, and depleted in high field strength elements (HFSE) such as Nb, Ta and Ti, with low Nb/Ta and Zr/Hf ratios, indicating a high degree of crystallization differentiation. The Xiahecun granitic pegmatite has low εHf values ranging from －11.7 to－6.2. Shanghecun granitic pegmatite εHf values rangs from －4.9 to 1.1, higher than that of Xiahecun granitic pegmatite. Based on this, the Xiahecun granitic pegmatite is the result of partial melting of the ancient crust, while the Shanghecun granitic pegmatite is the result of partial melting of the juvenile lower crust, and then magma assimilates and contaminate the wall rocks. The granitic pegmatite in the eastern part of North Qinling can be divided into northern rare metal granitic pegmatite and southern uranium granitic pegmatite.
- 1
-
Confirming and its structural significances of Middle Silurian Xinjie plagioclase amphibolite schist in the Longshan junction of the Qinling-Qilian orogenic belts
CHANG Yinglei, LUO Jinhai, CHEN Zhuo
Abstract:
The Qinling-Qilian Junction intersects at the Long Shan Tectonic Belt in the southwestern part of the North China Block, and the Longshan tectonic belt is the key area to reveal the spatio-temporal relationship between North China block, North Qinling orogenic belt and North Qilian orogenic belt. A set of Mesoproterozoic quartz diorite in Xinjie determined by predecessors has doubts in terms of rock type, formation age and formation environment. In this paper, petrology, geochemistry and U-Pb chronology of monazite and zircon have been studied for this set of rocks and biotite monzonite gneisses inclusions. This set of rocks has been renamed as Xinjie plagioclase amphibolite schist. According to geochemistry, the protolith is a set of basic magmatic rocks. Zircon U-Pb dating gives the formation age of protolith is 433.15 ±3.42Ma (Middle Silurian).Metamorphic zircon and monazite U-Pb dating gives metamorphic age of 427.9 ±1.46Ma. The protolith was metamorphic shortly after its formation. This is an important feature of Xinjie plagioclase amphibolite schist in the history of formation and evolution. Combined with the analysis of regional geological data, it is shown that in the late Ordovician-middle Silurian, Longshan area was in a strong back-arc extensional tectonic environment under the background of northward subduction in the eastern part of North Qilian. Large-scale basic-acid magmatic activity developed in Longshan area under this extensional background. The protolith of Xinjjie plagioclase amphibolite schist is the basic magmatic rock formed under this extensional background. The protolith experienced hydrothermal metasomatism associated with magmatism in the same period and became plagioclase amphibolite schist. The detrital zircon age of biotite monzonitic gneiss enclosed in plagioclase hornblende schist is in good agreement with the detrital zircon age of Huluhe Group(S1H) in southern Longshan area, and its provenance area is closely related to Ordos block and North Qinling orogenic belt. The results of this paper show that the magmatism caused by back-arc extension in Longshan area during the late Ordovician to middle Silurian is large in scale and lasts for a long time, and there is a good time-space relationship between magmatism, metamorphism and sedimentation in this background.
- 1
-
Influence of multiple detachment layers on structural deformation of Dabashan foreland fold thrust belt--Based on discrete element numerical simulation
Zhang Xiaoyu, Li Jianghai, Dou Fangpeng, Xu Haixuan, Liu Chen
Abstract:
The Dabashan tectonic belt is a typical intracontinental orogenic belt in China, located at the transitional zone between the Qinling orogenic belt and the Sichuan Basin. It is the main distribution area for proven reserves of large and medium-sized oil and gas reservoirs in the Sichuan Basin. The study area has developed multiple sets of detachment layers, and the distribution of detachment layers controls the structural deformation. Previous studies have determined the main structural styles of the study area based on the geological outcrop data, 3D seismic data and other technical methods, but there is still a lack of quantitative analysis of the structural deformation process and Kinematics characteristics. This article uses the discrete element numerical simulation method to calculate the differences in structural styles displayed within the same time step using PFC2D software, and conducts discrete element single factor comparative simulation experiments to explore the differences in structural styles in multi detachment layer systems. The experimental results show that (1) The detachment layer plays a controlling role in the development of structures in the cross section. On the one hand, the number of faults in both the double detachment system and the multi detachment system is higher than that in the single detachment system. The introduction of detachment layers makes the structural development in the system more complex; On the other hand, from the analysis of the developed fault properties, it can be seen that as the number of detachment layers increases, the number of forward thrust faults in the system shows a gradual increase. The number of reverse thrust faults in the multi detachment layer system is less than the first two models, and is significantly less than the number of reverse thrust faults in the double detachment layer system. The middle detachment layer has an inhibitory effect on the formation of reverse thrust faults. (2) The introduction of detachment layers accelerates the vertical thrust velocity of faults, and the middle detachment layer plays a role in connecting the basement detachment layer and the upper detachment layer. The phenomenon of structural decoupling is common in the double detachment layer system, and the development of secondary faults and folds is the main feature in multi detachment layer systems. (3) The multi detachment system shows obvious characteristics of secondary folds and faults, which is more consistent with the profile of eastern Daba Mountains. The dual detachment system shows more structural decoupling characteristics, which is more consistent with the profile of western section.
- 1
-
Experimental progress and geological application of nitrogen and hydrogen impurities in diamond
Lu Zhiyun, Yang Jingsui, Lian Dongyang, Wu Weiwei, Yang Yu
Abstract:
The occurrence, content and distribution characteristics of nitrogen and hydrogen impurities, which are widely present in natural diamonds, are of great significance for understanding the material cycle and for estimating the residence time of diamond in the deep mantle. Since the first diamond crystal was produced by the high temperature and high pressure (HPHT) method, researchers have obtained a large amount of data on diamonds synthesized at different pressures, temperatures (P-T), and media components. This paper systematically summarizes the occurrences and contents of nitrogen and hydrogen impurities in diamond crystals synthesized in the metal-carbon, carbonate-carbon, carbonate-silicate-carbon, sulfide-carbon, nitride-carbon, and nitride-sulfide systems. In addition, the influence of [111] and [100] orientations on the nitrogen and hydrogen content in diamonds is analyzed from the perspective of diamond crystal structure. We also discuss the effects of P-T conditions, components on the existence forms of nitrogen and hydrogen impurities in synthetic diamonds. It is also reviewed that the aggregation of Ib→IaA, IaA→IaB nitrogen defect in diamond lattice follows a secondary kinetic process of conversion. Combining the typical forms and contents of nitrogen and hydrogen impurities in different types of natural diamonds, this article can provide further research directions for the formation environment of natural diamonds from the perspective of nitrogen and hydrogen impurities.
- 1
-
The characteristics and origin of the pre-Sinian rift in the Sichuan Basin
Tang Hao, Wu Guanghui, Zou Yu, Su Chen, Dai lan, zhang chen, Ma Bingshan
Abstract:
The Neoproterozoic supercontinent breakup is of significant role in the origin of the rift basin and its hydrocarbon on Earth. However, there is still debate on whether the superplume or subduction process has triggered the rift basin. The largest Sinian gasfiled in China has been found along the Deyang-Anyue rift in the Sichuan Basin. Owing to absence of geological data and low-resolution seismic data, it is an enigma on the origin and distribution of the pre-Sinian rifts in the ultra-deep subsurface. Together with seismic interpretation and compiled geochemical data, we discuss the characteristics and mechanism of the pre-Sinian rift in the Sichuan Basin. The results show that: (1) NE-trending Pre-Sinian rifts developed well with more than 5000 m thick deposits in the Sichuan Basin, which are different in rift architecture and distribution from the Sinian depression to show a Pre-Sinian tectonic discontinuity; (2) the ?Hf isotope values of the Neoproterozoic zircons show a distinct pattern from a decreased trend to an increased trend, and present a tectonic transition period at ca. 830~780 Ma; (3) the Pre-Sinian rifting initiated during the transition period was consistent subduction process rather than mantle plume process. In conclusion, the mid-Neoproterozoic transitional subduction has resulted in the distributed deep Pre-Sinian rifts in the Sichuan Basin, which is a new favorable hydrocarbon exploration frontier.
- 1
-
Electrical Structure of the Crust in the Jingerquan Region, Eastern Tianshan and Its Geological Implications
Hao Zejiang, Zhang Qiang, Gong Shengping, Zhao Keqiang, Li Yong, Lu Guifu, Su Wenli, Fu Yangang, Duan Zhuang, Gao Jianwong, Lin Lujun, Wang Zhenliang
Abstract:
To understand the electrical structure and geological structural characteristics of the Jingerquan region, eastern Tianshan, and to provide electrical evidence for its metallogenic mechanism, a magnetotelluric sounding profile was completed in the Jingerquan region, eastern Tianshan. A reliable electrical structure model was obtained by three-dimensional inversion. The results revealed that:(1)The shallow part of Kangur-Huangshan ductile shear zone has a high conductivity thin layer, under the strong ductile shear deformation, the shallow surface rock layer may be relatively broken and loose, thus endowed with fluids.(2)The Yamansu Fault provides a channel for fluid transport to depth, causing the fracture to exhibit high conductivity anomalies below it.(3)The mineralization model of the Hulu copper-nickel sulfide deposit is consistent with the magma channel mineralization model, where the Kangur Fault provides a channel for upward intrusion of the mantle-derived magma, and the magma carrying copper-nickel sulfides undergoes gravitational subsidence and aggregation mineralization at the channel turn, magma house or dilatation site; It is speculated that there may be basic rocks rich in sulfide at the depth of 2 km, suggesting that there may be Cu-Ni metallogenic potential in the depth.
- 1
-
Late Quaternary segmentation activity of the southern part of the Karakorum fault and a study of the Chaxikang surface rupture
Abstract:
Numerous large earthquakes have occurred in the Tibetan Plateau since the recent decades years, which has attracted widespread attention from scholars both domestically and internationally. However, there are some large-scale fault zones on the plateau, which not only have strong late Quaternary activity, but also have the tectonic conditions for generating strong earthquakes. The Karakorum fault is a large dextral strike-slip fault in the western part of the Tibetan Plateau, with the southern part of the Longmucuo Fault being the more active segment. The Perlan Ms 7.0 earthquake occurred in 1883 along this fault. It is helpful to understand the latest deformation behavior of the fault and analyze its seismogenic behavior by identifying the segmented activity characteristics of the fault and surface rupture. Based on high-resolution remote sensing image interpretation and field geological survey, the late Quaternary segmented activity of the southern section of the Karakorum fault and the Chaxikang surface rupture zone are studied in detail. The results show that the southern section of the fault can be divided into three primary segments: Ladakh-Chaxikang, Kunsha-Bar and Menshi-Gongzhu Co segment, which are respectively characterized by dextral strike-slip, dextral strike-slip tension and dextral strike-slip with with a horsetail normal fault. The minimum horizontal displacement measured at the surface rupture zone is 8-9m. Combined with the rupture length of ~200km, the magnitude of the earthquake is estimated to be ~7.5. The Karakorum fault zone, which regulates the material extrusion in the western plateau, gradually transforms from a rigid block migration mode in the northwest section to a more dispersed arc-shaped normal fault and strike slip deformation in the southeast section.
- 1
-
Jurassic anatexis and granite genesis in Amdo area,Northern Tibet
jianzhenzhu, pengyinbiao, jiangxingzhou, gaoxiangyu, jiwentao, lichuanzhi, yushengyao
Abstract:
The Ando microland massif in Tibet, as a microland massif within the Bangong Lake-Nujiang River suture zone, has recorded multiple phases of tectonothermal events since the Neoproterozoic-Mesozoic era, and is an ideal object for the study of the genesis of the deep-melt-granitoids. In order to reveal the characteristics of the fluid/melt activities during the subduction-folding process of the oceanic plate, a comprehensive study was carried out herein, combining the whole-rock geochemistry, systematic petrology, zircon internal structure, zircon U-Pb ages, and Lu-Hf isotopes. A comprehensive study was carried out. Petrographic observations show that the mixed gneiss retains key field macro- and microscopic evidence of deep melting: (1) light and dark bodies are interbedded in a laminated distribution, accompanied by weak fold deformation; (2) there are assemblages of fine grains at the boundaries of quartz and potash feldspar, and irregular crystallization of potash feldspars from edge to middle; (3) plagioclase feldspar and potash feldspar boundaries show highly acicular, elongate, or wedge-shaped quartz and feldspar grains, with "bead" structures along the quartz and feldspar grain boundaries. The cathodoluminescence images and zircon U-Pb dating results show that the zircons in the mixed-rock gneisses have a distinct core-rim structure, with a distinctive oscillatory ring in the zircon cores, which gives a magma crystallization age of ~510 Ma, and narrow metamorphic or deep-melting rims in the rims. The zircon in the light-colored body has obvious core-rim structure, and the CL image shows that the zircon core is highly luminous with oscillatory ring band, which may be inherited magmatic zircon, and the zircon rims show deep melting features such as weakly fractional bands of grayish to dark color or no fractional bands, and the age of the core is ~510-470 Ma representing the age of protolithic crystallization, and the rims have an age of ~184 Ma indicating the age of melt crystallization. The zircons of the granodiorite have typical magmatic zircon characteristics, with a magmatic crystallization age of ~180 Ma, which agrees with the age of the light-colored body within the error range. The εHf(184) values of deep-melting diagenetic zircons in the light-colored body range from -5.0 to -3.3, while those of granodiorite magmatic zircons range from -10.97 to -5.21. Whole-rock geochemical analyses indicate that Fe2O3T, MgO, TiO2, CaO, and REEs are almost completely retained in the dark-colored body, while a large number of LILEs (Rb, Sr, K, Ba ) are to the light-colored body. The light-colored body is divided into Type I light-colored body and Type II light-colored body according to the whole-rock REE characteristics and whether it carries residual hornblende, in which Type I light-colored body has higher total rare earth content and negative Eu anomaly, while Type II light-colored body has lower total rare earth content and positive Eu anomaly; the trend of the distribution of rare earths (REEs) of granodiorite eclogites is consistent with that of Type I light-colored with an enrichment of the large ionic proximate elements (Rb, Ba, and Th) and a Negative Eu anomalies; the synthesis of the existing regional data and the field relationship, microstructure, chronology and geochemical results obtained in this paper indicate that the black cloud plagioclase gneisses of the Ando microterrane occurred in the subduction and folding stage of the hydrous partial melting involving black mica, and that the type I light-colored bodies in the mixed rocks formed the contemporaneous granodiorite bodies through large-scale convergence, migratory evolution and encroachment.
- 1
-
Re-discussion on genetic type of the Daliang Uranium deposit at Motianling: evidence from elemental and isotopic compositions of pitchblende
Wangkaixing, Ye fancheng, Zhu kunhe, zhangjian, Liux iaodong, Tan shuang, Sun Liqiang, Yang Jianjun
Abstract:
The Daliang uranium deposit is located in the Motianling pluton, northern Guangxi Province. It represents the oldest uranium deposit that related to granitoid in South China. Recent studies indicate that the Daliang uranium deposit exhibits distinct characteristics from typical hydrothermal uranium deposits related to the Mesozoic granites in South China, suggesting the possibility of a different deposit genetic type. The elemental chemistry and isotopic compositions of pitchblende are favorable tools for determining the mineralization age and exploring the deposit genesis type. Therefore, based on previous research, this study conducts the chemical composition and isotopic dating of pitchblende to determine the mineralization age and genesis type of the Daliang uranium deposit. The research results demonstrate that the pitchblende in the Daliang deposit exhibits features such as insignificant fractionation between LREE and HREE with weak negative Eu anomaly, which are similar to typical pitchblende in synmetamorphic uranium deposits. Using EMPA U-Th-Pb chemical dating and LA-ICP-MS U-Pb isotopic dating, the mineralization ages of the Daliang uranium deposit are determined to be 378 Ma and 376±4 Ma (MSWD=0.62), respectively, coupled with regional ductile deformation events, indicating that the deposit formed during the Late Devonian and suggesting a connection to regional ductile deformation. Combining previous studies on the high salinity of the mineralizing fluids in the Daliang uranium deposit (average 19% NaCl equivalent) and the stable isotopic constraints on the fluid source, it can be inferred that the Daliang deposit is likely not a traditional hydrothermal vein-type uranium deposit associated with granite but should be classified as a synmetamorphic uranium deposit. During the process of forward shearing detachment at Motianling during the Devonian period, when the uplifted brittle-ductile shear zone formed in the middle to lower strata reaches shallow depths, the granitic mylonite enters the brittle-ductile deformation zone. The mineralizing fluids extract uranium from the granite and precipitate in the brittle-ductile deformation zone, forming the Daliang metasomatic uranium deposit. This study establishes, for the first time, the presence of synmetamorphic uranium deposits in granites of South China. This implies the potential involvement of different genetic models and processes in the hydrothermal uranium deposits of South China. This finding holds significant importance for future uranium exploration and research in South China and deserves attention.
- 1
-
Mineralization timing and characteristics of fluid of Na’e beryllium deposit in the Tengchong terrane
mingtianxue, He xiaohu, Tang Zhong, Chen Lei, Yang Qingbiao, Xue Ge, Wang Yunxiao, Su Xiaoyu
Abstract:
Beryllium (Be) is widely used in advanced science and technology and strategic emerging fields, and is an urgent strategic resource for our country. The Tengchong terrane, which has experienced a complex geological structural process, is an important part of the East Tethys Orogenic belt. In this terrane, frequently magmatic activities occurred during the Cretaceous-Cenozoic stage and a large number of tin (tungsten) -rare metal deposits (mineralizatioin) related to magmatism have been discovered. Geological survey and evaluation indicate that potential beryllium, rubidium, niobium, tantalum rare metal deposits may be formed in this area. The Na"e beryllium deposit is a typical granitic pegmatite type deposit discovered in the Tengchong terrane. The granitic pegmatite intruded into the wall rock of the early Cretaceous monzogranite. In this paper, we study zircon U-Pb chronology of granite pegmatite and monzogranite (the wall rocks) and fluid inclusion of beryl and quartz from the granite pegmatite to discuss the ore-forming age and physical and chemical conditions of the Na’e beryllium deposit. LA-ICP-MS zircon U-Pb dating yield ages of granitic pegmatite are 44.3 Ma~46.9 Ma, that of monzogranite is 122.9 Ma, indicating that the Na’e beryllium deposit was formed in Eocene and the wall rock of monzogranite was formed in Early Cretaceous. Thus, we suggest that they have no evolutionary relationship. Combined with the magmatic activities and tectonic evolutionary history of the Tengchong terrane, we suggest that the Na’e beryllium deposit may be the product of crustal material melting in a post collision tectonic setting caused by the convergence between India and Eurasia plates, and is a typical LCT pegmatite type beryllium deposit at a post orogenic stage. Beryl and quartz from the Na’e beryllium deposit have vapor-liquid two-phase NaCl-H2O inclusions and a small amount of pure liquid phase water inclusions and CO2 inclusions. The ore-forming fluid is characterized by medium-low temperature (172.0 oC~299.4 oC), low salinity (0.70%~3.87% NaCl eqv.), and low density (0.723 g/cm-3~0.913 g/cm-3). According to the estimation of pressure and depth for ore-forming fluid, the Na’e beryllium deposit was formed in a low-pressure shallow environment. The concentration center of lithium and beryllium in geochemical anomaly map is consistent with the tin mineralization and pegmatite belts, suggesting that the rare metal mineralization is closely related to tin mineralization and pegmatite belt in the Tengchong terrane. In combination with the discovery of niobium, tantalum, rubidium, lithium mineralization in this district, we suppose that there is a potential for rare metal mineralization in the Tengchong terrane.
- 1
-
Chemical characteristics of pyrochlore in carbonate of the Huayangchuan uranium-niobium deposit and its significance for mineralization
Huang Hui, Pan Jiayong, Wang Kaixing, Zhong Fujun, Wan Jianjun, Wu Bin, Yin Shuo, Yan Jie
Abstract:
Abstract: The Huayangchuan deposit in Shaanxi Province is located in the Xiaoqinling metallogenic belt in contact between the North China Craton and the Qinling orogenic belt. It is a world-class uranium and niobium polymetallic deposit related to carbonatite, in which pyrochlore is the major U and Nb-bearing mineral. Although the Huayangchuan metallogenic mechanism has been well studied, the magmatic-hydrothermal evolution process of the deposit and its relationship with mineralization were poorly understood. Hereby, this paper study mineralogy, chemical composition and evolution characteristics of two types of primary pyrochlore (pcl Ⅰ and pcl Ⅱ) and three types of altered pyrochlore (pcl Ⅰ alt1, pcl Ⅰ alt2 and pcl Ⅱ alt) in the Huayangchuan deposit. The results show uranium and niobium mineralization in Huayangchuan carbonatite is closely related to the Late Triassic magmatism. It was related to a mantle-derived, initially U-rich carbonatitic magma, which has been further enriched in U by crystallization differentiation and formed the primary (magmatic) pyrochlore (pcl I), primary pyrochlore (pcl Ⅱ) and primary uraninite (Ur1) through partial melting from the mantle. In the early Cretaceous, the carbonatite in Huayangchuan were subjected to high-temperature hydrothermal alteration, and part of Nb and U released from the early pyrochlore (pcl Ⅰ) were dissolved and reactivated by the high temperature high-F fluid, which formed the primary uranite (Ur2), the altered pyrochlore (pcl Ⅰ alt1) and the secondary titanite (Ttn2). The primary pyrochlore (pcl Ⅰ) and primary pyrochlore (pcl Ⅱ) can be replaced by the altered pyrochlore pcl Ⅰ alt2 and altered pyrochlore pcl Ⅱ alt in the post ore low-temperature alteration. These results indicate that two magmatic-hydrothermal uranium-niobium mineralization and one post-mineralization low-temperature hydrothermal alteration occurred in Huayangchuan deposit during late Triassic and early Cretaceous.
- 1
-
Spatial-temporal distribution, resource potential and exploration progress of carbonatite-type rare earth deposits in central and southern AfricaTANG Wenlong1),2)
Abstract:
As the most important metallogenic type of endogenetic rare earth deposits, the carbonate type rare earth deposits in central and southern Africa have superior geological metallogenic conditions and great resource potential. Combined with the spatio-temporal distribution characteristics of igneous carbonatite, this paper discussed and summarized the regional metallogenic regularity, resource potential and exploration progress of carbonatite-type rare earth deposits in central and southern Africa. Carbonate type rare earth deposits were divided into four metallogenic belts: Pilanesberg-Phalaborwa belt, which the metallogenic epoch were mainly concentrated in the Paleoproterozoic – Mesoproterozoic; Namaqualand-Bushmanland-Warmbad belt, which the metallogenic epoch were 40-80Ma; west margin of Namibia - Angola belt which could be further divided into two categories,one was the carbonate rare earth deposit influenced by the Parana- Etendeka hot spot, and the metallogenic age was 140~125Ma; the other was controlled by the Damara orogenesis, and the metallogenic age was 750~550Ma. The REE metallogenic belt of the East African Rift system could be further subdivided into three metallogenic subbelts: the southern part of the East African Rift system, the western branch of the East African Rift system and the eastern branch of the East African Rift system. The southern part of the East African Rift system subbelt ranged from Buhera, Zimbabwe to Malombe, Malawi, and the metallogenic age was mainly concentrated in 135-110Ma. The west branch of the East African Rift system subbelt extended from Chipala of Malawi through Ngualla of Tanzania, northward to Lake Albert, Uganda, whihch the metallogenic ages could be divided into three stages: 1100~1000Ma, 700~500Ma and 120~100Ma. The East branch of the East African Rift system subbelt extended fromWigu Hill in Tanzania northward to Afar triangle in Ethiopia, which the metallogenic age could be divided into two stages, 120~110Ma and 5~25Ma, respectively. The spatio-temporal distribution of each metallogenic belts, the metallogenic geological background of typical deposits, the characteristics of the deposits, and the metallogenic conditions were systematically summarized, and the resource potential of the metallogenic belt and the exploration progress in recent years were sorted and dissected. China's rare earth work in central and southern Africa started late. Although some progress has been made, it’s still necessary to accelerate the resource exploration and development activities.
- 1
-
Characteristics of melt inclusions of Miocene adakitic porphyries in the southern margin of Lhasa terrane
Zhao Xiaoyan, Yang Zhusen, Dong Yanrui, Liu Chang
Abstract:
Miocene adakite porphyries are widely distributed in the southern margin of Lhasa terrane, but there are obvious differences in the composition of ore-forming elements and the scale of mineralization. In order to better understand the constraints of different mineralization of Miocene porphyries in the southern margin of Lhasa terrane, this paper selects the ore-bearing porphyries of Jiama Cu deposit and Bangpu Mo deposit, to carry out TIMA scanning and electron probe studies of single melt inclusions in quartz phenocrysts of the different porphyries. The results show that the melt inclusions of Jiama and Bangpu are mainly crystalline whose crystalline minerals mainly include quartz, albite, orthoclase, plagioclase and mica. There is a significant negative correlation between SiO2 and K2O in the melt inclusions of Jiama and Bangpu, which all belong to the?high-K calc-alkaline to shoshonite series. The Jiama ore bearing porphyry has lower Cl (0-0.03 wt%) and higher H2O (1.12-4.35 wt%) contents compared to Bangpu porphyry. Research has shown that the injection of ultrapotassium magma and strong crystallization differentiation of potassium feldspar play an important role in the formation of porphyry deposits of collisional environment. In addition, the content of volatile matter (including H2O, Cl, etc.) plays a significant role in the differnent metallogenensis.
- 1
-
Study on lithologic classification method based on lithologic index and 3D feature space
Zhang Qunjia, Wang Le, Liu Lei, Wang Yalei
Abstract:
Remote sensing lithologic classification, especially the automatic identification of mafic-ultramafic rocks and granite, is of great significance for mineral exploration. Currently, the lithologic classification methods, which integrate visible light near-infrared (VNIR), short wave infrared (SWIR), and thermal infrared (TIR) images, are relatively lacking. In this study, the Advanced Spaceborne Emission and Reflection Radiometer (ASTER) data were employed for lithologic mapping in the Huitongshan, Beishan, Gansu Province, and Huangshan, East Tianshan, Xinjiang Province. The mafic-ultramafic rock index (MI), quartz-bearing rock index (QI), and the comprehensive ratio were established according to the reflection spectrum characteristics of rocks in the VNIR-SWIR region and the radiation characteristics in the TIR region. The lithology index and comprehensive ratio results were then used to build a three-dimensional feature space model. The specific lithology was classified and extracted according to the clustering characteristics of rocks in the feature space. The model was applied to the lithologic classification of Huitongshan in the Beishan of Gansu Province and Huangshan in the east Tianshan in Xinjiang, field observation confirms that the classification results are of high accuracy. The results showed that the proposed lithologic index and three-dimensional feature space model using VNIR-SWIR and TIR data could successfully extract target lithology with high precision and applicability, which has a good application prospect in western China.
- 1
-
Characteristics of strike-slip faults and their oil-gas-controling effect in the Ordos Basin
He Faqi, Huang Lei, Zhang Ru, Zhang Wei, Wang Zhao
Abstract:
The Ordos Basin is thought as a stable block and has few faults in its interior. In recent years,a large amount of small scale faults have been revealed in the interior of the Ordos basin using 3D seismic. The discoverychanges the thought for the structural characteristics of the basin and the exploration direction for the oil and gas. However, the geometry, kinematics characteristics and genetic mechanism of these faults are still unresolved, and the controlling factors for accumulation of oil and gas are still unclear. In this study, the characteristics of such strike-slip faults developed in different tectonic units of theOrdos basin were compared, and its effect on hydrocarbon were analyzed . Faults develops in the Ordos Basin, trending NEE, NW, N-S and E-W respectively. These faults have the common characteristics (such as subvertical dip angle, small slip distance and concealmen. All the faults show the nature of strike-slip characteristics. However, the dominant strike of faults in various regions of the basin is different: the northern is nearly E-W-trending, the southern is mainly NE-trending, the southwest is NW-trending and the fault strike in the interior of the basin is multi-direction. The formation and evolution of intra-basin faults are controlled by the tectonic stress field around the basin. The faults near the periphery of the basin formed in the similar stress field; and the stress strength is weak in the interior of the basin. Due to the layered structure style of faults in the Ordos basin, the upper and lower petroleum systems are independent. It is mainly fault-fracture clastic reservoirs in the Mesozoic and fault-karst carbonate reservoirs in the Lower Paleozoic. The faults and derived fractures assembly in the interior of the Ordos Basin compose special reservoir sweet spots.
- 1
-
Deep explanation model of the VMS-type deposit in the Ashele ore district
Abstract:
The Ashele copper deposit is the typical VMS-type Cu polymetallic deposit in northe-west of China. With the continuous deepening of exploration development of deposits, metallogenic (genetic) and exploration models of deposit have been continuously improved. Moreover, it has played a positive role in guiding prospecting and exploration of deep edges of deposits. We comb that effective geological exploration models on different scale deposit (body) structure models via studying exploration and prospecting models on metallogenic (genetic) models of the Ashele ore district from commonness to individuality, from the shallower to the deeper, simplicity to comprehensiveness. We propose "multi-channel volcanic chain" geological exploration model based on ore district scale, and discuss the construction of deep comprehensive exploration models of the VMS-type Cu metalogenic deposit in the Ashele ore district.
- 1
-
Thermodynamic and Trace element modelling of partial melting of eclogite: A case study of Xitieshan terrane, North Qaidam, China
JIANG Xiaocong, LI Chuanzhi, YU Shengyao, PENG Yinbiao, JIANG Xingzhou, GAO Xiangyu, WANG Lintao
Abstract:
Anatexis is a common phenomenon in high-grade metamorphic rocks and one of the important geological processes for tectonic evolution of orogenic belt. Eclogite is the main rock type for studying continental subduction, ultra-high pressure(UHP) metamorphism and crust-mantle interaction. Its partial melting is closely related to crustal growth, slab exhumation, and element transport and distribution in a continental subduction channel. In-situ and in source leucosomes representing the anatexis is generally retained in the Xitieshan eclogite in the North Qaidam UHP metamorphic belt, which provides favorable conditions for understanding the effect of the anatexis of the UHP eclogite. In this paper, zircon U-Pb chronology analysis was used for the leucosome in Xitieshan eclogite. LA-ICP-MS U-Pb dating yielded a weighted mean 206Pb/238U age of 425.3±5.9Ma (MSWD=0.74), representing the formation age of leucosome.The anatexis of eclogite in the Xiteshan terrane was simulated by thermodynamic and trace element modelling, and combined with the retrograde P-T paths of eclogite in the area, the temperature and pressure conditions of equilibrium crystallization of Na-rich leucosome in eclogite were limited at 12.27~10.71kbar/794~797℃. The initial partial melting of the eclogite occurred at the eclogite phase (~19.54kbar/~780℃), and the partial melt formed in the UHP eclogite through breakdown of omphacite with minor involvement of phengite and zoisite in the process of temperature rise and pressure fall. During the whole partial melting process, the eclogite produced ~8~9vol% melt, meeting the minimum requirements of the melt migration, indicating that the eclogite may have little contributionto the source area of the syn-exhumation granite in the Xiteshan terrane.
- 1
-
Discussion on S-Pb-H-O-He-Ar isotope composition and genesis of the Sanhetun gold deposit in Heilongjiang Province
Abstract:
Sanhetun gold deposit is located in Nenjiang County, Heilongjiang Province. The ore body occurs in the late Triassic granitic mylonite, near the contact zone between the volcanic rocks of the lower Cretaceous Guanghua Formation and the late Triassic granitic mylonite. In order to discuss the source of ore-forming fluid, this work systematically studied the S, Pb, H, O isotopes and inert gas He, Ar isotopic compositions in different minerals collected. Stable isotope results show that: δ34S is between -4.4‰~4.9 ‰，which is similar to meteorite sulfur δ34S value,reflects the contribution of sulfur from deep magma; 206Pb/204Pb of Pyrite =17.284-18~180290，207Pb/204Pb=15.505~15.561,208Pb/204Pb=37.656~38.116; 206Pb/204Pb of Quartz=18.206~ 18.449,207Pb/204Pb=15.526~15.652,208Pb/204Pb=38.050~38.648, which indicates that the ore-forming material mainly comes from mantle; H, O isotopes of Quartz δ DV-SMOW value is - 77.5 ‰~- 96.3 ‰, δ 18OV-SMOW is 7.4 ‰~11.6 ‰, δ18OH2O is - 0.2 ‰~4.8 ‰, which reflects that the ore-forming fluid mainly comes from atmospheric precipitation, and some magmatic water also participates; The 3He/4He ratio of Pyrite fluid inclusions is 1.19～1.54R/Ra, tens to more than hundreds times higher than the 3He/4He ratio of the crust, but obviously lower than the 3He/4He ratio of mantle fluid; 40Ar/36Ar=608.5～922.6, higher than the 40Ar/36Ar composition of crustal fluid (40Ar/36Ar＞295.5);The 40Ar*/4He ratio is 0.14～1.56, with an average value of 0.95. The 40Ar*/4He (0.14) of SHT19 sample data is close to the 40Ar*/4He (0.2) fluid of the crust, and the 40Ar */4He (0.88～1.56) of other samples is much higher than the mantle (0.33～0.56) fluid, indicating that the ore-forming fluid may be mainly meteoric water, but also the crust and deep mantle fluid. According to the regional metallogenic epoch, the Sanhetun gold deposit was formed in the late Early Cretaceous, and the source of ore-forming materials was closely related to the magmatic activity in the Guanghua period of the Early Cretaceous.
- 1
-
Geochronology, geochemistry and geological significance of Paleoproterozoic porphyritic granites in Quibala area, Angola Shield
Jin Lijie, Zhang Hongrui, Luo Dike, Jia Pengfei, Liu Wei, Wang zisheng, Li Jinzhen, Zhou Yonggang, Jiang Zhenguo
Abstract:
Angola has experienced several tectonic cycles in the Precambrian period, among which the paleoproterozoic Eburnean cycle is the most important one, which has important geological significance for understanding its tectonic evolution process. Due to the lack of accurate chronological and geochemical data, the formation age of magmatic rocks in the central Eburnean area is still not supported by effective data, which is also one of the main reasons for the unclear genesis and tectonic evolution of rocks. In this paper, the Quibala porphyritic granites in Eburnean area in the central Angolan Shield are studied in petrology, chronology and geochemistry. LA-ICP-MS zircon U-Pb chronology shows that the Quibala porphyritic granite was formed from 1987 to 1956Ma, which represents the main activity time of Eburnean movement in the Angora Shield. The geochemical study shows that porphyritic granite has high silicon, alkali, iron content, Ba, Sr, P, Ti elements deficit and Rb, Th, K, Hf elements enrichment, the total content of rare earth elements is high, indicating that it is A-type granite. In addition, the xenoliths of ancient basement such as gneiss, diorite inclusions containing potassium feldspar phenocrysts, and the ratios of Rb/Nb, Th/U, Nb/Ta and other characteristic elements indicate that the xenoliths may be the result of the mixing of crust-mantle materials. The NB-Y-3Ga and Rb- (Y+Nb) diagrams show that the granite porphyry was formed in the paleoproterozoic post-collision extensional environment.
- 1
-
Occurrence and ore-forming mechanism of beryllium in the Baishawo Be-Li-Nb-Ta pegmatite deposit in northeastern Hunan, South China
Fanzhiwei, Xiong Yi-Qu, Shao Yong-Jun, Wen Chun-Hua
Abstract:
Beryllium (Be), as a critical element, is an essential industrial raw material in advanced fields and the new energy industry. China is a major beryllium consumer with high external dependence, and beryllium resources are in short supply. The recently discovered Baishawo Be-Li-Nb-Ta deposit, located in the northeast of Hunan, is a large pegmatite type rare metal deposit. Previous studies show that the beryl is the dominant beryllium-bearing mineral occurring in pegmatite, whereas the occurrence state and ore-forming mechanism of beryllium are still unclear. Here, we combined field geological survey, optical microscope observation, SEM, X-ray maps, TIMA, EPMA and LA-ICP-MS analysis, to investigate the petrographic and mineralogical features of beryl, tourmaline, quartz, albite, and mica of 3# pegmatite dike in the Baishawo deposit. The results show that Be occurs not only in beryl as an independent mineral but also in tourmaline, quartz, albite, and mica as an isomorphic form. Beryl mainly distributes in the wall and intermediate zones of 3# pegmatite. The wall zone beryl is light green in color with 2 × 3 × 5 cm in size and coexists with albite, muscovite, and garnet. The beryl crystal from the intermediate zone has large grain size (~50 cm), and presents a short columnar, with longitudinal lines parallel to the c-axis on the crystal surface. The beryl from the wall zone has BeO, Li2O, and Cs2O content of 12.87%-14.01%, 0.14%-0.33%, and 0.05%-0.12%, respectively. The BeO content in beryl from the intermediate zone is 13.38%-13.96%, and the contents of Li2O and Cs2O are slightly higher than those in the wall zone, which are 0.25%-0.39% and 0.13%-0.39%, respectively. Additionally, the concentration of Be in quartz (0.20-7.13 ppm, with an average of 2.50 ppm) is lower than that of other Be-bearing minerals. Tourmaline (4.13-8.73 ppm, with an average of 5.94 ppm, The average content of Be in albite (4.74 ppm) was close to that in albite (1.22-6.98 pm, average 4.54 ppm). The content of Be in muscovite (16.9-53.8 ppm, average 21.77 ppm) was the highest, with up to 53.8 ppm. It is considered that the 3# pegmatite dike belongs to LCT (Li-Cs-Ta) pegmatite and is of granitic melt crystallization differentiation origin for wall zone pegmatite, while the pegmatite in the intermediate zone is in the magmatic-hydrothermal transition stage, which is subject to the metasomatism of late hydrothermal fluid. In the Baishawo deposit, beryl coexists with alkaline feldspars such as albite, and the BeO contents is up to 13.44%, which has a significant industrial value and can be used for green selection and smelting by acid flotation. This study provides a reference for the occurrence and genesis of beryllium in rare metal pegmatite deposits, and also a scientific basis for the exploration, development, evaluation, and prediction of beryllium resources in rare metal pegmatite deposits.
- 1
-
Petrogenesis of Mesozoic intermediate-acid intrusive rocks in the Tongling ore concentration area of Anhui Province: Evidence from geochemistry of zircon and apatite
XU xiaochun, Yu wen, JIN linsen, XIA cailian, XIE Qiaoqin, Yan Jun
Abstract:
Mesozoic intermediate-acid intrusive rocks are widely developed in the Tongling ore concentration area of Anhui Province, and they are closely related to the polymetallic-copper mineralization. A large number of previous studies have been issued on the genesis of these intrusive rocks, but there are still some controversies. In this paper, Tongguanshan and Dongguashan quartz diorite and Fenghuangshan and Hucun granodiorite are selected as research objects to further explore their genetic mechanism. Based on the research results of major and trace elements and Sr-Nd isotope of the whole rocks, a special effort is made to investigate the geochemical characteristics of zircon and apatite from these rocks. Integrating the previous research results and the analysis data of our job, it can be concluded that the Mesozoic intermediate-acid intrusive rocks have similar major and trace element compositions, are all of high-K calc-alkaline rock series with characteristics of arc magmatic rocks and adakitic like rocks, are also enriched in Sr-Nd isotope compositions. These geochemical characteristics combining with the petrological characteristics of mafic microgranular enclaves（MMEs）and antiband structures of amphibole and plagioclase indicate that their parental magma was generated by the mixing of mafic magma and felsic magma. Our new analytical results are as follows: the U-Pb ages of the inherited zircons are mainly in two ranges of 1.0Ga～0.8Ga and 2.4Ga～2.0Ga, the εHf(t) values of zircon grains are -20.5～-5.1 corresponding with calculated Hf two-stage model ages between 1.5Ga～2.9Ga, and the δ18O values of zircon are 5.93‰～8.85‰, the apatites have high Cl contents (average 0.3wt%) with relatively high Cl/F values (0.052～0.244), high REE contents (1714×10-6～5903×10-6) and negative δEu values (0.26～0.68). Based on the above-mentioned geochemical characteristics of major and trace elements and Sr-Nd isotopes of whole rocks, and the geochemical characteristics of singer minerals zircon and apatite obtained from this job, combined with the regional geological tectonic evolution, the different previous views on the genesis of the Mesozoic intermediate-acid intrusive rocks in the area are debated and questioned, and proposed our own point of view. It is held that the Mesozoic intermediate-acid intrusive rocks in the Tongling ore concentration area were derived from a mixture of crust-derived and mantle-derived magma, that is, the mixing of enriched lithospheric mantle derived magma and Neoproterozoic juvenile arc crustal derived magma, a small amount of ancient crustal materials from Paleo-Proterozoic to Meso-Proterozoic had also been mixed in the magma ascending process. The enriched lithospheric mantle sources magma was derived from the subducted oceanic crust or the fluid metasomatic overlying lithospheric mantle when Cathaysia oceanic slab beneath the Yangtze craton in the Neoproterozoic era, but not the Paleo-Pacific slab subducted into South China plate in the Mesozoic era. The roll-back after subduction of the Mesozoic Paleo-Pacific slab was the geodynamic mechanism that led to the ancient orogenic belt extending after thickening, the lithospheric mantle thinning and melting.
- 1
-
Restudy on the Cranium of the Early Triassic Hupehsuchus nanchangensis ( Diapsida: Hupehsuchia)
Zhao Bi, Zou Yarui, Li Jiangli
Abstract:
Hupehsuchus nanchangensis is the most representative species in the Nanzhang-Yuanan Fauna and one of the oldest marine reptiles. The information about the key features of its cranium is very scarce. Therefore, in order to supplement this part of the content, a fossil specimen collected recently has been carefully repaired and studied in comparative anatomy. This study revised the following cranial diagnoses of this species: a narrow bone space along the middle line of the skull develops along the two branches of upper jaws; the premaxilla contacts with each other at the anterior end, while the nasal only contacts at the posterior ends; groove develops on the premaxilla in the same direction as that of the maxilla; top of the skull is flat without sagittal crest; the parietal is larger than the frontal, and the pineal foramen is located in the anteromiddle part of the parietal; upper temporal fenestra is formed by parietal, postfrontal, postorbital and squamosal, excluding supratemporal; its jugal is a triradiate bone with a thin and long anterior process, and a short ventral process; supraoccipital is large and nearly round; exoccipital has clearly visible nerve opening. The comparision shows that Hupehsuchus nanchangensis, Nanchangosaurus and Eretmorhipis all bear bone spaces formed by both sides of upper jaws, which might be the homologous character of Hupehsuchia. The supratemporal of Hupehsuchus nanchangensis does not participate the upper temporal fenestra. In addition, this species has morphological vestiges of the ventral process of jugal and its inferior temporal fenestra is not completely degraded, which is similar to the oldest diapsid reptiles, but different from the advanced ichthyosauromorphs. It is speculated that with the development and evolution, ichthyosauromorph supratemporal gradually moved forward and participated the upper temporal fenestra, while the inferior temporary fenestra gradually closed. The new material also shows that the external naris of Hupehsuchus nanchangensis is upward and its bite force is not strong, so it can be inferred that this species has a unique feeding function different from other species of ichthyosauromorphs.
- 1
-
Ductile deformation of Wenchuan-Maoxian fault constrain the early uplift of Longmen Shan
GE Chenglong, LI Haibing, Philippe Hervé Leloup, ZHENG Yong, Liu Dongliang, ZHANG Lei, YE Xiaozhou, Thomas Courrier, ZHANG Jinjiang
Abstract:
Wenchuan-Maoxian fault in the eastern margin of the Tibetan Plateau (Longmen Shan) is the major fault that has developed deep ductile deformation and played an important role in controlling the early uplift of the Longmen Shan. By using the field survey, macro/micro structure analysis, and crystal fabric analysis, we have constrained the kinematic and rheological characteristics and deformation conditions of ductile deformation of the Wenchuan-Maoxian fault. The results show that (1) ductile shear zone approximately 3 km wide and steeply dipping to the north west exists within the fault; (2) two phases of deformation are identified within the shear zone: early Top-to-NW normal shearing and late Top-to-E reverse shearing; (3) The quartz CPO results show that the reverse ductile deformation is dominated by basal slip, accompanied by bulging recrystallization, with an indicated deformation temperature of 300 - 400℃. The normal ductile deformation is dominated by prism slip, accompanied by subgrain rotation recrystallization, with a corresponding temperature of 350 - 650℃. Combining with published geochronological and thermochronological data, we suggest that the Wenchuan-Maoxian fault underwent Top-to-NW normal ductile faulting in the Oligocene and Top-to-E reverse ductile deformation in the Miocene, which resulted in the uplift and exhumation of large amounts of deep material in the hinterland region of Longmen Shan.
- 1
-
The deposit types, spatial and temporal distribution and prospecting direction of rare earth deposits in China
Yu Jinjie, Chen Shaocong, Chen Xiaodan
Abstract:
Rare earth element (REE) deposits in China can be categorized into the hard rock-type, ion adsorption-type, and placer REE deposits. The hard rock-type, ion adsorption-type, and placer REE deposits account for 96.4%, 3.2% and 0.5% of the total REE resource of China, respectively. The REE deposits in China are composed of 12 metallogenic zones, and the peak periods of mineralization are mesoproterozoic and Cenozoic. The former is represented by Bayan Obo ore deposit, while the latter is represented by the REE deposits of the Mianing-Dechang metallogenic zone and ion adsorption-type REE deposits in six provinces of southern China. The available rare earth deposits in China are carbonatite and alkaline rock-related and ion adsorption type REE deposits. The former is the source of LREE and the latter is the source of HREE. The controlling factors of carbonatite and alkaline rock-related REE deposits include rifts or collision-post-collision tectonic settings along craton margins, regional deep faults, and the magmas and post-magma hydrothermal evolution. The controlling factors of ion adsorption-type REE deposits include parent rocks, favorable exogenetic factors including quasi-equilibrium between denudation and exhumation at regional scales, local geomorphology dominated by low-lying gentle slopes, adequate rainfall, and favorable groundwater conditions. In this paper, the general metallogenic models of carbonatite and alkaline rock-type and ion adsorption-type REE deposits are recommended. The prospecting of carbonate rock and alkaline rock-type REE deposits Sis concentrated in the depth and edges of known deposits, but the search for hard rock-type heavy rare earth deposit in Xingmeng and Boziguer-Yilanlik metallogenic belts should not be ignored. Southern Jiangxi and northern Guangdong provinces are the key areas to search for ion adsorption-type HREE deposits.
- 1
-
Zircon U-Pb geochronology and geochemistry of Tatuo mafic dykes in East Kunlun orogen, and its geological significance
Zhang Min, Li Ruibao, Pei Xianzhi, Li Zuochen, Pei Lei, Chen Guochao, Chen Youxin, Liu Chengjun, Wu Shukuang
Abstract:
Early Ordovician mafic dykes exposed in the North Kunlun are of great significance to the subduction processes and dynamic background of the paleo-active continental margin. In this paper, we presented detailed petrology, zircon U-Pb chronology, whole-rock geochemistry and Sr-Nd isotopes of the mafic dykes. Zircon U-Pb dating results show that the zircon U-Pb ages of these dykes range from 486 to 483 Ma, suggesting Early Ordovician. Whole-rock geochemical results show that the mafic dykes have low SiO2 (50.06%-51.68%), medium MgO (5.08%-6.77%) and TiO2 (0.99%-1.20%) content, and belong to the tholeiitic basalt series. For the trace and rare earth elements, the rocks are enriched in large-ion lithophile elements (e.g., Rb, Sr, Ba, Th, K) and depleted high-field-strength elements (e.g., Nb, Ta, Ti); The chondrite-normalized REE diagrams are featured by wild enrichment of LREE and depletion of HREE, with weak Eu anomaly. In addition, the dykes show the high (87Sr/86Sr)i (0.7126-0.7133) and relatively low εNd(t) isotopic composition (-9.80~-4.31) of the enriched lithospheric mantle. The petrogenesis research indicates that the basic magma was originated from the enriched lithospheric mantle ever metamorphosed by fluids in the subduction zone, and then experienced fractional crystallization mainly of olivine and clinopyroxene during the diagenetic processes. Based on the regional geological data, we argued that the Kunzhong Ocean subducted northward in early stage of Early Paleozoic and formed a magmatic arc system. It may have experienced the retreat of the subducting oceanic slab at 486Ma, leading to an extensional tectonic setting in the upper plate of the subduction zone and then generation of mafic dykes.
- 1
-
2010,84(9):1300-1315, DOI:
Abstract:
Based on field observations and structural measurements, this paper describes basic features of the Dabashan foreland arc-shaped structural belt, its distribution pattern, zonation, segmentation, vertical stratification, deformation pattern, superimposed folding and paleostress field, then discusses main factors controlling the formation of this structural arc. It pointed out that the formation and development of the Dabashan foreland arc are different from classical model of collisional mountain built-up; it was shaped through three different stages: original boundary conditions formed during Paleozoic extension and rifting along the marginal zone of the Yangze; initiation during Middle-Late Triassic collisional orogen; and final formation during Middle-Late Jurassic intra-continental orogen. The arc-shaped Chengkou-Fangxian fault zone not only controls the Early Paleozoic deposition and magmatism, but also played key role in the foreland arc formation, and the basement uplifts at the two syntax acted as important boundary conditions. Sandbox modeling was carried out in the laboratory to model the formation and boundary condition of the Dabashan foreland arc. The model was set-up according to the real geologic data.
-
maojingwen, CHEN Maohong, YUAN Shunda, GUO Chunli
2011,85(5):636-658, DOI:
Abstract:
The Qinhang belt is located along the Qinhang (Qinzhou Bay to Hangzhou Bay) or Shihang Shiwandashan Mt. to Hangzhou Bay) Neoproterozoic suture in South China, which separates the Yangtze craton and Cathaysian Block. The most ore deposits in the belt are Mesozoic age although they occurred along the Precambrian suture. Based on the previous researches we recognize these deposits in two episodes, i.e. Neoproterozoic marine exhalative Cu-Zn deposits, and Yanshanian granitoids – related W-Sn-Cu-Pb-Zn deposits. The latter can be subdivided in Mid-Late Juarassic porphyry-skarn-vein polymetallic copper deposits, Late Jurassic granite – related W-Sn deposits, and Cretaceous epithermal Au-Ag-Pb-Zn-Sn deposits. After descriptions of the basic characteristics, ore-forming mechanics, spatial-temporal distribution of these deposits it is proposed that the Neoproterozoic marine exhalative Cu-Zn deposits occurred in the foreland basins of the oceanic islands whereas the Mid-Late Juarassic porphyry-skarn-vein polymetallic copper deposits are related the high-K calc-alkaline granites derived locally from the remelt of the subducted Izanagi plate at 180-160 Ma along the ancient Precambrian suture. The large-scale Late Jurassic granite – related W-Sn deposits associated with the crust-source granites with input of the mantle substances at 160-150 Ma, which are inferred to be the result from subducted plate window in the central part in South China and bounded in west by the Qinhang suture, where a lot of large and supper large tin and tungsten deposits developed. After 135Ma the subducted oceanic plate changed its motion direction to be along northeast, paralleling the Eurasian continental margin, which induced the large-scale lithospheric extension. Therefore, the all Cretaceous epithermal Au-Ag-Pb-Zn-Sn deposits developed within the volcanic basins and faulting basins at 120-90 Ma along the Eurasian continental margin.
-
2013,87(5):737-746, DOI:
Abstract:
Thaw lake is a common landscape in permafrost regions. The presence of a water body thus constitutes a heat source and releases the heat energy to the permafrost beneath and around lake, giving rise to the ground temperature increase. A talik, even penetrated talik maybe occur under the lake-bottom. The decline of permafrost table, elevation of permafrost base on the lakeshore accelerates the rapid permafrost degradation. This study predicted the temperature changes beneath and around lake and the process of permafrost degradation. The results showed that when the water depth is 2 m and 4℃ of mean annual lake-bottom temperature, the increase of ground temperature is about 4.7-3.2℃ beneath the lake-bottom, 2.2-1.1℃ beneath the lake-edge, and 0.3-0.1℃ beneath the lakeshore after 1000a. When the mean annual lake bottom temperature equals to or is less 0℃, a talik is impossible formation under the thaw lake; if the temperature increases to 1℃, a 25 m deep talik forms after 500a and the permafrost will be thawed completely after 900a. Therefore, the time of permafrost disappearance shortens with the increase of mean annual lake-bottom temperature.
-
2013,87(6):759-772, DOI:
Abstract:
During the geological investigation of last several years, a group of A type granitic plutons has been found in the middle segment of the Bangonghu Nujiang suture. These granitic plutons occur as stocks with an exposed area of less than1 km2 and lithologically include two types of biotite granite and granodiorite porphyry, which intrude into Cretaceous sedimentary rocks. A systematic analysis of whole rock element geochemistry and Nd, Sr, Pb isotope for these A type granites indicates that they contain high SiO2 content varying from 68.62%～75.36%. Moreover they have relatively high K2O+Na2O(8.03%～9.37%）and Fe2O3T(0.86%～5.39%) and low Al2O3(12.76%～15.54%) content, appearing weak peraluminous and metaluminous features. Trace elements N MORB normalized spider diagram displays apparent enrichment in large ion lithophile element(LILE) Rb, Th, U, K, Pb with Ba and Sr of marked depletion. High field strenth element(HFSE) Nb, Ta and Ti are sharply depleted with Zr and Hf of relative enrichment. All of these are characteristic of A type granite and different from arc granite. These granites have high REE contents(∑REE=122.37×10-6～291.19×10-6，with an average of 201.31×10-6). Light REE are rich relative to heavy REE(LREE/HREE=4.89～9.58, with an average of 5.93)and negative Eu anormalies are sharp(〖QX(Y12#〗δ〖QX)〗Eu=0.14～0.54，with mean value of 0.34), making their chondrite normalized rare earth element patterns appear slightly right dipping V type. Nd, Sr and Pb isotope results indicate that the A type granites from the middle segment of the Bangonghu Nujiang suture are rich in radioactive isotope. Their 87Sr/86Sr and ISr ratio values vary from 0.719842～0.786395 and 0.706900～0.710378, respectively. 143Nd/144Nd ratio values are from 0.512123～0.512392, with large negativeεNd values(-3.37～-10.34), reflecting important involvement of crustal components. Pb isotope composition 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb display ranges of 18.703～19.070, 15.680～15.732 and 39.121～39.576, respectively, which plot on the upper crustal line and above the orogenic evolution line in the plumtotectonic framework diagram of Zartman and Doe (1981) and show anormaly high enrichment components. The study points out that the A type granites were derived from partial melting of enriched lithospheric mantle (approximating EMⅡ), which were metasomalized by sediment melt from slab during the oceanic crust subduction and later heat by upwelling asthenospheric materials through slab windows formed as a result of slab break off during the postcollisional extension of the orogenic zone.
-
2014,88(8):1353-1371, DOI:
Abstract:
Resources of dinosaur fossils in China are the most abundant in the world. So far, Zhucheng City of China has become a significant Late Cretaceous locality of dinosaur fossils, represented by the large hadrosaurs. Based on investigation and research of taphonomy characteristics of dinosaur fossils from Late Cretaceous, this article systematically demonstrates the taphonomy characteristics of dinosaurs fossil bones from Late Cretaceous and analyzes the taphonomy geological background, the taphonomic sedimentary facies and paleocurrent, the distribution, modification and gathering characteristics of fossil bones and taxonomy, the micro fabric and taphonomic model for the bone fossils, etc. Dinosaur fossil clusters of Late Cretaceous (the dating of feldsparArAr age is 76 2~73 5 Ma) in Zhucheng City, are mostly buried in the alluvial fan debris flow(DF) and flood plain(FP) and the braided river channel(BRC). Fossils are densely distributed in stratification, which are of assorted sizes, non equidensity, singular species, and different in sizes, shapes and standards of residue bones. The majority of fossil bones are damaged without leaving intact fossil bones, being of the columnar and tabular shapes. Larger bones are arranged in certain direction, reflecting the features of dinosaur fossil clusters’ taphonomy and sedimentation undergoing the shortrange transport allochthonously and fast burial. The sedimentary petrology and the thin section analysis reveal that the geologic climate of Zhucheng under which the dinosaurs lived and the fossil bones buried is featured with semiaridarid condition. The taphonomypreservation pattern of dinosaurs can be summarized as: poor living environmentdinosaurs’ massive deathbodies’ decaybones’ washed out and transported by flood or debris flowfast burialshallow burial diagenesisexposure by the Crust uplift. The research on Late Cretaceous Dinosaur taphonomy of Zhucheng provide a series of evidences to better understand and reconstructure the Cretaceous paleogeography, Paleoclimate and paleoenvironment
-
Zhiqin Xu, Jingsui Yang, Haibing Li, Shaocheng Ji, Zeming Zhang, Yan Liu
2011,85(1):1-33, DOI:
Abstract:
The collision between India and Asia is the most spectacular tectonic event on Earth during the Cenozoic, resulting in the uplift of the Tibetan plateau and surrounding orogenic belts as well as a lot of material escaping toward the east and southeast. In this paper, the Tibetan plateau was divided into the following tectonic units: (1) the central Tibetan plateau including east Kunlun, Bayanhar-Songpanganzi, Qiangtang, and north Lhasa areas; (2) the Gangdese-Himalayan main subduction-collision belts consisting of Gangdese Andes-type subduction belt and the Himalayan-type collision belt; (3) surrounding transpressional orogenic belts characterized by thrusting and strike-slip faulting which include Western Kunlun-Altyn-Qilian transpressional belts in the north, Longmenshan-Jinpinshan belt in the east, Sino-Burma belt in the southeast, India-Pakistan-Afghanistan belt in the southwest; (4) lateral extrusion terrains including South Songpan, Lanping, Baoshan and Tenchong terrains bounded by large-scale strike-slip faults: Xianshuihe-Xiaojiang fault, Ailaoshan-Red river fault, Lancangjiang fault, Jiali-Gaoligong fault, Nabang fault and Sagaing fault around the eastern Himalayan Syntaxis, as well as Tianshuihai, Xindukushi, Kabuer and Afghanistan extrusion terrains around the western Himalayan Syntaxis. Various constraints for the India / Asia collision tectonics have been discussed, such as: collision between a small wedge of Indian plate and the larger Asian Plate, the roles of the Eastern and Western corners of the Indian plate, the impact of normal and oblique collisions, large strike-slip faulting related to lateral extrusion, transpressional mechanism with both strike-slip faulting and thrusting kinematic features related to uplift of surrounding orogenic belts, and mantle structures beneath the Tibetan Plateau.
-
Yin-Zhang Zhou, Bao-Fu Han, Zhao Xu, Rong Ren, Li Su
2014,88(1):25-35, DOI:
Abstract:
In this paper, we focused on the structural and geochronological analyses for the Yingba area in western Inner Mongolia, China. At least three stages of Late Proterozoic to Mesozoic tectonomagmatism have been identified. New and previous zircon U-Pb ages have revealed Carboniferous (325~313 Ma) granodiorite and porphyritic granite, Early Permian (291~277 Ma) alkaline granite and purple red medium-fine grained granite and Early Cretaceous (~134~130 Ma) pegmatite and quartz monzonite. The first tectonic event is characterized by NW-SE compression after the Early Permian (290.9±1.8 Ma), which generated the low-angle NW-dipping gneissic foliations in the granodiorite and alkaline granite. The second event is indicative of NW-SE extension, during which a SE dipping low-angle ductile shear zone, which is characterized by the medium-high temperature (450~650 ºC) mylonite, crosscut the gneissic granodiorite and gneissic alkaline granite, and so it apparently postdated the first tectonic event (<290.9±1.8 Ma). The ductile shear zone is crosscut by the ~134 Ma pegmatite veins, indicating that the extension occurred before the Early Cretaceous pegmatite veins. The third tectonic event is represented by NW-dipping moderate-angle brittle normal faults, which resulted from NW-SE extension after the Early Cretaceous and crushed the ~134 Ma pegmatite into cataclasite. The Yingba area has recorded a typical process from the formation of an orogen to intracontinental extension during Late Proterozoic to Mesozoic.
-
gaofeng, zheng changqing, yao wengui, lijuan, shilu, cuifanghua, gaoyuan, zhangxingxing
2013,87(9):1277-1292, DOI:
Abstract:
The granitic mylonitic gneiss is a set of metamorphic granitic rocks, located in Haduohe area, is mainly composed of fine grained biotite monzonitic granitic mylonitic gneiss, fine grained biotite granitic mylonitic gneiss and fine garnet mica granitic mylonitic gneiss. The results of geochemical study indicate that SiO2 values are in the range of 66.4%~74.52%, K2O+Na2O is between 7.36%~8.84%, Al2O3 values are in the range of 13.43%~15.74%, A/CNK=0.974~1.092, belonging to high-K calc-alkaline and quasi-aluminous to weakly peraluminous rocks; It’s higher in total rare-earth content (ΣREE= 94.15×10-6~164.30×10-6), the chondrite -normalized REE patterns demonstrate right-oblique linear REE patterns with weak negative Eu anomalies, and reveals LREE enrichment and HREE depletion; The trace element is characterized by a strong enrichment in large ion lithophile elements, such as Rb, Ba, U, K et al, depletion in Ta, Nb, P, Ti et al.. The zircon U-Pb dating results indicate that the magma formation can be divided into two periods, the first period is around 320Ma, the representative rock is fine grained biotite granitic mylonitic gneiss and fine garnet mica granitic mylonitic gneiss, the second period is around 304Ma, the representative rock is fine grained biotite monzonitic granitic mylonitic gneiss. Combining petrography, chronology and rock geochemical characteristics, the protolith of the granitic mylonitic gneiss is high-K calc-alkaline I type granite, formed in the post-collision environment of Xing'an block and Songnen block, during Late Carboniferous. And then suffered relatively strong ductile brittle metamorphism and deformation during Late Early Permian by the post-collision of Xing’an block and Songnen block.
-
DONG Shuwen, LI Tingdong, GAO Rui, Lǖ Qingtian, WU Zhenhan, CHEN Xuanhua, ZHOU Qi, LIU Gang, LIU Zhiqiang, MEI Lin
2010,84(6):743-770, DOI:
Abstract:
To explore the interior structure and composition of the Earth, the habitat of our humankind, constitutes the ambition and pursuit of geologists and geophysicists for long. This article presents the research outlines and some results of major international deep probe programs worldwide since the 1970s, including the Consortium for Continental Reflection Profiling (COCORP) and EarthScope (USA), EUROPROBE (Europe), DEKORP (Germany), the British Institutions Reflection Profiling Syndicate (BIRPS), CROP (Italy), NRP20 (Switzerland), LITHOPROBE (Canada), AGCRC, Glass-Earth and AuScope (Australia), and so on. Based on the briefly retrospection of the historic deep exploration in China, the recently launched National Scientific Program of China titled as "Deep Exploration Technology and Experimentation" (ab. as SinoProbe) is introduced briefly, including its objectives and work plan of standard magnetotellurics observational and geochemical grid networks, integrated deep exploration experiments in North and South China regions, four corridor geophysical and geochemical explorations, and multiple integrated exploration sites. It is prospected that the deep exploration into the deep interior beneath the Chinese continent has its bright future.
-
zhaowenguang, WU Ming'an, ZHANG Yiyong, WANG Keyou, FAN Yu, WANG Longyun, WEI Guohui, CHE Yingdan
2011,85(5):789-801, DOI:
Abstract:
The Nihe iron deposit, adjacect to the Tanlu fault, is located in the northwest margin of the Luzong Mesozoic volcanic basin, and is only three kilometers away from the Luohe iron deposit in the southwest. The Nihe iron deposit is a concealed deposit with multi-mineral resources, consisting of one large-scale magnetite ore deposit, one large-scale magnetite-pyrite ore deposit and one medium-scale anhydrite ore deposit. The magnetite ore bodies are situated in the south-west of the deposit, and are layer like or lenticular, occurring in the top of the intrusive dome that caused by the emplacement of pyroxene diorite-porphyrite in the Zhuanqiao formation during late Jurassic. The magnetite-pyrite ore bodies are situated in the north-east of the deposit, with two different occurrences, either in the pyroxene diorite-porphyrite body formed coevally with iron ore body, or in the volcanic rocks of the lower segment of the Zhuanqiao formation relating to strata. The anhydrite ore bodies are situated in the middle of the deposit, occurring as lens in the volcanic rocks of the lower segment of the Zhuanqiao formation. Ore types are so complex that the magnetite ore can be divided into eight natural types, while the magnetite-pyrite ore with five natural types. There are more than 40 minerals in the deposit, and the iron is rich in sulfur and phosphorus, but for the useful ore compositions of Fe, S and anhydrite, there are also other beneficial or harmful compositions in the ore, such as P, V, Ti, Cu, Zn, and so on. Within the Nihe iron deposit, there are intense alterations of the host rocks, and the alterations are widespread and variable, with obvious regularity such as transverse stratification and vertical zonality. In which, the anhydrite pyroxenitization is the most important alteration near the ore. The deposit type is similar to the Taocun-type in Nanjing-Wuhu district, and thus the genesis belongs to porphyrite-type.
-
XU Zhiqin, YANG Jingsui, JI Shaocheng, ZHANG Zeming, LI Haibing, LIU Fulai, ZHANG Jianxin, WU Cailai, LI Zhonghai, LIANG Fenghua
2010,84(1):1-29, DOI:
Abstract:
The Chinese continent, which is strongly constrained by the Tethyan, Paleo Asian and Pacific tectonic systems, is characterized by a complex tectonic framework and a particular lithospheric structure. Based on the theory of continental tectonics and dynamics, here we provide a comprehensive overview of recent research results with a particular attention to four important scientific problems on the Chinese (East Asian) continent. ①Tectonics of the mantle beneath the Chinese continental lithospheric plate. Seismic tomographic profiling reveals that the western Pacific slab is subducted westward to depths of 400~600km beneath the East Asian continent, and the subducted slab becomes subhorizontal and listric shaped in the mantle transitional zone. The Indian slab is subducted northward to a depth of ~800km far north under the Banggonghu Nujiang sutute zong between the the Lhasa and Qiangtang terrains. Double subductions are asymmetrical beneath the western syntaxis of the Himalayan belt. In the eastern syntaxis, however, the Indian slab is subducted eastward to depths of 300~500km beneath the Burma Sanjiang terrain. ②Reactivation of the Chinese continent's metamorphic basements. Most blocks of the Chinese continent have not been reactived by significant tectonic, metamorphic or igneous events since the Phanerozoic. The north Indian and Arabian blocks (northern edge of Gondwana) were shaped by pan African orogenic belts at 530 470 Ma. This tectonic field occurred mainly in the higher Himalaya, Lhasa terrain and Sanjiang terrain. The Cenozoic metamorphic reactivation appeared ubiquitously and uniquely in the Himalaya, Namche Barwa, Lhasa terrain and Burma Sanjiang terrain with the youngest metamorphic ages of 2~1 Ma. ③The tectonic backgrounds and processes for the formation and exhumation of HP UHP metamorphic belts in China. The eclogite bearing HP UHP metamorphic belts in China formed in either oceanic or continental deep subduction zones. Most of the oceanic HP UHP belts in the Tibetan plateau are related to the collisions of multiple small oceanic basins among multiple micro continental blocks. Two mechanisms of the continental deep subduction are plausible: subduction drived by interblock shear collision and subduction of wedge shaped, teared lithospheric slabs. ④Three categories of mechanisms for the extrusion of deep materials within the Chinese continental orogenic belts: constrictional extrusion; lateral extrusion; and transcompressional extrusion.
-
DONG Shuwen, ZHANG Yueqiao, LONG Changxiang, YANG Zhenyu, JI Qiang, WANG Tao, HU Jianmin, CHEN Xuanhua 1) Institute of Geomechanics , CAGS, Beijing , 100081 ; 2) Department of Earth Science, Nanjing University, Nanjing9 210093~ 3) Institute of Geology,
2007,81(11):1449-1461, DOI:
Abstract:
随着一系列新构造观察资料和高精度同位素测年数据的累积,加深了对发生在中国东部晚侏罗世—早白垩世时期构造变革事件的认识,对燕山运动的性质、时限和动力学内涵有了新的诠释。中—晚侏罗世初期(165±5Ma)东亚多板块拼贴运动学发生重大调整,构造体制发生重大转换,启动了以中朝地块为中心、来自北、东、南西不同板块向东亚大陆"多向汇聚"的构造新体制,形成以陆内俯冲和陆内造山为特征的东亚汇聚构造体系。同时大陆地壳岩石圈发生显著增厚,并紧随早白垩世以剧烈的大陆岩石圈伸展和火山—岩浆活动为特征的岩石圈巨量减薄和克拉通破坏,导致燕辽生物群灭绝和热河生物群兴盛的重大生物群更替,成为中国大陆和东亚重大构造变革事件,这是燕山运动的基本内涵。本文依据燕山运动构造变形型式、动力学背景以及产生的深部过程,将"燕山运动"定义为起始于165±5Ma的"东亚多向汇聚"构造体制及其形成的广泛陆内造山和构造变革,并将中国东部岩石圈巨量减薄视作燕山期陆内造山和陆内变形的后效。
-
chenwen, WAN Yusheng, LI Huaqin， ZHANG Zongqin，DAI Tongmo， SHI Zeen， SUN Jingbo
2011,85(11):1917-1947, DOI:
Abstract:
Isotope geochronology is a newly developed science which combines geoscience, Physics, Chemistry and technical sciences, and it is a young and energetic branch of the earth system science. Based on the decay of radioactive isotopes, this science can determine the formation age of geological body and the age of geological events, aiming to study the formation history and evolution of earth and planetary materials. This paper presents brief introduction and summary of relative high-precise isotope dating methods in aspects of theory、experiment techniques、application scope、precautions for use, expecting to provide a useful reference to geologist. Involved isotope dating methods are U-Pb method、Ar-Ar method、 Rb-Sr method、Sm-Nd method、Re-Os method and（U-Th）/He method. （1）U-Pb method: It is one of the earliest radioactive methods for geological age determination as well as the most important isotope dating method in China so far. In the past 10 years, the introduction of insitu zircon U-Pb dating technique has played a significant role in promoting geological research in China, and its application is expanding. （2）Ar-Ar method: Ar-Ar dating has become one of the most important methods of isotope geochronology. The characteristics of this method are as follows: ① wide time-domain measurements, the oldest age is 3.8Ga (the age of lunar rocks), millennium age can be measured for the youngest age (eruption age of Mount Vesuvius, Italy); ② wide range of measurement object, in principle, all the k-bearing minerals and rocks can be used as Ar-Ar isotopic dating, even there are reports on successful determination of Ar-Ar ages from non-potassium minerals such as quartz、sphalerite which contain trace amounts of kainitite inclusion; ③Unique step heating technique and the management of Ar isotope correlation diagram of internal components can not only obtain high-precision age but unfold multi-stage geological evolution of the object; ④Joining with laser technique, it can be used to determine microzonation Ar-Ar age by search the minerals to be tested in polished section, so that we can obtain the priciest time information of the metamorphic rock P-T-t research; ⑤ wide application area, it is used in almost all the branches of geology; ⑥ the most important technique of deposit chronology; ⑦ the backbone technique of isotope thermochronology. Ar-Ar dating has its limitations: Firstly, the complex analysis leads to high cost and long cycle. Secondly, the accuracy of the determination of the neutron parameters directly affects the accuracy of dating samples. Nuclear recoil effect can result in high Ar-Ar age of very fine particles of clay minerals. As samples of Early Proterozoic and Archean metamorphic rocks, there may be natural K and Ar diffusion or later metamorphism, deformation and other disturbance, which will make it difficult for us to determine the age of early metamorphic events. （3）Rb-Sr method: It is a broadly applicated method. We can determine the isotope geological ages of intrusive rocks、volcanic rocks、metamorphic rocks and certain sedimentary rocks by using isochron technique. When determining the age of intermediate and acid intrusive rocks and volcanic rocks by using Rb-Sr isotopic system, if the rocks cooled rapidly, both the whole rock isochron and mineral isochron age may be the formation ages of the rocks. For metamorphic rocks, Rb-Sr isochron age generally represent the Sr isotope homogenization time when the latest strong thermal event happened. For sedimentary rocks, we can determine the authigenic mineral diagenesis age using Rb-Sr dating. The metal deposits, we can determine the formation ages of deposits using inclusion Rb-Sr isochron. Through Rb-Sr mineral dating to determine the formation of faults and ductile shear zone, we can limit the tectonic formation time. The biggest drawback of Rb-Sr dating is that, we may get wrong age due to the mobility of Rb which will result in an open system. In addition, we often face false isochrons problems. （4）Sm-Nd method: For Sm-Nd system is good at preservation and alteration and metamorphism resistance, ages from Sm-Nd dating can represent the original time when primary rocks formed and reflect the characteristics of diagenesis source material. For basic rocks、 ultrabasic rocks and for ancient rocks of Archean, Sm-Nd isochron dating method is a good method. Sm-Nd model age represent the time when the crustal rocks differentiated from CHUR mantle, using model ages of clastic sedimentary rocks, we can identify the source, the background of tectonic, the mean crustal residence age, and the formation and evolution history of crust. The disadvantage is the similarity of Sm, Nd geochemical properties, it will be difficult to separate from each other in the geologic process, and will result in narrow range of Sm, Nd ratio, which will make the Sm-Nd isochron dating problematic and even can not give reliable age. （5） Re-Os method: Re-Os isotope dating is the only mature method to determine mineralization ages of metal deposits directly. However, there are many problems in experiment techniques and applications: ① In recent years, some scientists find that the Re-Os ages of molybdenite in some metal deposits were higher than the ages of ore-bearing rocks, the reasons are unclear; ② the amount of Re in most sulfide mineral including pyrite is significantly low, and contains certain amount of common Os, this requires very low background in the process of chemical preparation of samples, which makes it difficult for general laboratory to achieve, and the common Os is difficult to deduct; ③ sometimes, post hydrothermal activities may reset Os isotope, therefore, the closure temperature and influencting factors of the metal sulfide Re-Os isotope system is a pressing problem to be solved. （6） (U-Th) / He method: The advantage of (U-Th) / He isotope system is that its closure temperature is the lowest among the existing isotopic systems, and it can record temperature information and the time when geologic body went through a lower temperature process. The method also has considerable application in the deposits chronology. The disadvantage is that as the closure temperature is very low, we should pay special attention to the cooling rate and effects of re-heating in geological dating.
-
Ying Lijuan, Wang Denghong, Tang Juxing, Chang Zhesheng, Qu Wenjun
2010,84(8):1165-1174, DOI:
Abstract:
Molybdenite widely spreads in the different types of ores from the Jiama copper polymetallic deposit. Skarn is the major host rock, then hornfel is the secondary, and porphyry, marble and limestone contain few molybdenite. Molybdenite samples with different occurrences from skarn, hornfel and porphyry were collected and tested by Re-Os isotopic dating. Mode age of 27 samples changed between 14.2 and 17.5 Ma and the isochron age was 15.22±0.59 Ma. The isochron ages of porphyry and hornfel were 14.78±0.33 Ma and 14.67±0.19 Ma, which were consistent to metallogenic period of other porphyry copper deposits in the Gangdese metallogenic belt. The 187Re content in molybdenite was correspondingly higher in the range of 38.75~387.4 g/g. Molybdenite in the Jiama ore deposit was supposed to form in one period occurring in the different rocks. It was in the Langhian Stage of Miocene with the feature of postcollision. The metallogenic period of the Jiama ore deposit was close to that of molybdenite, therefore the previous overview of effusive sedimentary metallogeny was not scientific.
-
2010,84(12):1727-1734, DOI:
Abstract:
Based upon the fine interpretations of 3D seismic in Tazhong low uplift, four series of fault systems are classified: (1)Cambrian-early Ordovician tensional fault systems whose distribution, configuration and development scales establish the foundation of the consequent structural activities; (2)late Ordovician thrust fault systems and northwestward slip fault systems whose structural characteristics vary in different zones and fragments: thrust fault system develops in the east, and northwestward slip fault system develops in the middle-west; (3)Silurian-Devonian northeastward slip fault systems formed in extrusion stress background and spread northeastward, which are made up of three parts: the main faults, the tailed en-echelon structures and the fault troughs; (4) the fault system related to Permian magmatic pierces, which distributes spottily or in bands, and are mostly developed along earlier faults and always superimpose or reform earlier faults. In plane, the Tazhong Paleozoic fault systems are a tensional-shear broom-like structure with sinistral internal rotation layers pointing to the divergent termination.
-
2014,88(9):1623-1637, DOI:
Abstract:
The lower boundary age of Mesoproterozoic is positioned at 1600 Ma by International Commission on Stratigraphy (ICS), and the global platform covers are formed at Calymmian with time span of 1600 Ma to 1400 Ma. The North China Platform entered an epoch of extension-broken after its consolidated at 1800 Ma. Then the Luliang Mountains area in Shanxi Province, the Zhongtiao Mountains in South Shanxi Province and the Xiong’ershan area in Western Henan Province are split into a trigeminal Aulacogen. The SHRIMP and LA-ICP-MS zircon ages of the volcanic rocks from Luliang Xiaoliangling Formation are 1763±42 Ma and 1779±20 Ma respectively; and the SHRIMP zircon ages have been obtained from Xiong’er Group in Western Hennan Province are 1776±20 Ma (dated for the volcanic rocks) and 1779±29 Ma. It seems reasonable to take the 1800 Ma as the lower boundary age of the Xiaoliangling Formation and Xiong’er Group. The rocks of Hangaoshan Group of Luliang Mountains area are siliciclastic with volcanic rocks, deposited at the same time with Xiaoliangling Formation, which suggest the quick filling of the north part of Luliang-Shanxi-Henan trigeminal Aulacogen. The Hangaoshan Group and the Dagushi Formation (sedimentary rocks deposited at the bottom of Xiong’er Group) are the sediment covers after the rifting at 1800 Ma, the mafic dykes related to the volcanic rocks from Xiaoliangling Formation and the volcanic rocks from the Xiong’er Group are the products of magmatism in the stage of broken-up. The Miyun rapakivi granites from Beijing are emplaced at 1700 Ma, which indicate the start time of the broken up of the Yanshan-Taihangshan Aulacogen and the lower boundary age of Changzhougou Formation, Changcheng System. The weathering crust, overlap the Miyun rapakivi granites, is dated at 1650 Ma, represents the time began to accept the deposits after the rifting of Aulacogen. It is not the age of the lowest layer in Changzhougou Formation. The age 1700 Ma and 1650 Ma are the lower boundary ages of different areas in Changzhougou Formation. but it’s not equal to the lower boundary age of Changcheng System or Mesoproterozoic. The lower boundary age of the Gaoyuzhuang Formation is 1600 Ma, as the boundary age of Changcheng System and Jixian System. It is not only the close time of Yanshan-Taihangshan Aulacogen, but also the end of the extension-broken time of North China Platform from 1800 Ma. The new epicontinental basin began to develop at this time, and the North China Platform experienced tectonic transformation. Therefore, the significant tectonic events affected North China Platform at 1800 Ma and 1600 Ma, which reflect great regional tectonic implications. According to the determination principle of Pre-cambiran boundary age, both the two ages are used to be the lower boundary of Mesoproterozoic. But in this paper, we approve of 1800 Ma as the lower boundary age of Mesoproterozoic, because of it’s more in line with the Chinese tectonic: 1800 Ma is the lower boundary age of the platform covers from the North China Platform to intra-craton Aulacogen. There are different tectonic settings of the basins in the North China Craton at Mesoproterozoic at different times: it is Aulacogen at 1800~1600 Ma, then develop to epicontinental sea at 1600~1400 Ma, at last transfer to arc-back basin at 1400~1300 Ma; 1800 Ma、1600 Ma and 1400 Ma are three time points of regional tectonic transformation at Mesoproterozoic.
-
SUN Jiming, MA Zhongping, TANG Zhuo, LI Xiangmin
2012,86(2):247-257, DOI:
Abstract:
Yumuquan granitoid complex, located in the south margin of Altyn Tagh, northwestern China, contain many of melanocratic magmatic enclaves (MME), and its petrology and geochemical characteristics indicating the mixing between acid magma and more mafic magma in liquid phase, which belong to the corresponding period. The LA-ICP-MS zircon U-Pb isotopic dating show that the age of Yumuquan granite is 496.9±1.9Ma (MSWD=0.68), corresponding with the ages of ultrahigh-pressure metamorphic rocks (509~487 Ma )exposed at south Altyn Tagh.and the geochemical characteristics of the granitoid show high Al2O3(ave.15.88%), K2O/Na2O ratios (avg. 1.26),Sr(ave.446×10-6),（La/Yb）N ratios（24.04）and Sr/Y ratios（avg. 40）,and very lower Y(avg. 14.0 ×10-6)and Yb（avg. 1.5×10-6）, similar to high Sr and lowerY(Yb) type potash granite derived from thickened lower crust , So, The southern Altyn orogen belong to continental collision orogeny during ~500Ma, this collision rifting made the crust thickened and overlay each other. We consider that, the crustal thickening at Later Cambrain (~500Ma) in the area of south Altyn Tagh caused the lower crust part melt and product acid magma, at the same time, there are under plating of mantle-derived mafic magmas, The reason may be related to the rise of the deep hot mantle, which caused by the same period of continental deep subduction.
-
ZOU Caineng, YANG Zhi, ZHU Rukai, ZHANG Guosheng, HOU Lianhua, WU Songtao, TAO Shizhen, YUAN Xuanjun, DONG Dazhong, WANG Yuman, WANG Lan, HUANG Jinliang, WANG Shufang
2015,89(6):979-1007, DOI:
Abstract:
The new century has witnessed a strategic breakthrough in unconventional oil & gas. Hydrocarbon accumulated in micro /nano scale pore throat shale systems has become an important domain that could replace current oil & gas resources. Unconventional oil & gas plays an increasingly important role in our energy mix. Tight gas, CBM, heavy oil and asphaltic sand have served as a key domain of exploration & development, with tight oil becoming a 'bright spot' domain and shale gas becoming a 'hotspot' domain. China has made great breakthroughs in unconventional oil & gas resources, such as tight gas, shale gas, tight oil and CBM, and great progress in oil shale, gas hydrate, heavy oil and oil sand. China has an estimated (223~263)×108 t of unconventional oil resources and (890~1260)×1012 m3 of gas resources. China has made a breakthrough for progress in unconventional oil & gas study. New progress achieved in fine grained sedimentary studies related to continental open lacustrine basin large scale shallow water delta sand bodies, lacustrine basin central sandy clastic flow sediments and marine continental fine grained sediments provide a theoretical basis for the formation and distribution of basin central reservoir bodies. Great breakthroughs have been made in unconventional reservoir geology in respect of research methodology & technology, multi scale data merging and physical simulation of formation conditions. Overall characterization of unconventional reservoirs via multi method and multi scale becomes increasingly popular and facilitates the rapid development of unconventional oil & gas geological theory, method and technology. The formation of innovative, continuous hydrocarbon accumulation theory, the establishment of the framework of the unconventional oil & gas geological theory system, and the determination of the implications, geological feature, formation mechanism, distribution rule and core technology of unconventional oil & gas geological study lays a theoretical foundation for extensive unconventional oil & gas exploration and development. Theories and technologies of unconventional oil & gas exploration and development developed rapidly, including some key evaluation techniques such as 'sweet spot zone' integrated evaluation and a six property evaluation technique that uses hydrocarbon source, lithology, physical property, brittleness, hydrocarbon potential and stress anisotropy, and some key development & engineering technologies including micro seismic monitoring, horizontal drilling & completion and "factory like" operation pattern, "man made reservoir" development, which have facilitated the innovative development of unconventional oil & gas. These breakthroughs define a new understanding in four aspects: ①theoretical innovation; ② key technologies; ③ complete market mechanism and national policy support; and ④ well developed ground infrastructure, which are significant for prolonging the life cycle of petroleum industry, accelerating the upgrade and development of theories and technologies and altering the global traditional energy structure.
-
2010,84(2):171-182, DOI:
Abstract:
Through the east and west orogenic geological cross-section observation sides of Junggar Basin, the system fission track dating and thermal analysis of the evolution of simulation results, combined with previous research findings, the Junggar Basin in the peripheral orogenic belt, mainly through the late Mesozoic tectono-thermal event. Through fission-track analysis and comparison，Orogenic belts on both sides of the Junggar Basin has a different Uplift history.The northwestern margin of the Junggar basin as early as in the eastern part of the uplift, the uplift rate is greater than the eastern part of. Northwestern margin of Junggar Basin has experienced since the Cretaceous period from the edge of the Junggar Basin to the Zaire mountain uplift events followed one after another, indicating that the northwestern margin of the Junggar thrust fault system thrust to the internal basin by overstep propagation. Junggar Basin, east-west belt of rocks on both sides of fission track data are a reflection of the cooling since the Cretaceous uplift events, and fully confirmed by the late Yanshan tectonic movement prevalent in the Junggar region, which provide vital evidence for a detailed study Yanshanian intracontinental tectonic activities in northern Xinjiang.
-
Tong Hengmao, Zhao Baoyin, Cao Zhe, Liu Guoxi, Dun Xiaomei, Zhao Dan
2013,87(11):1647-1661, DOI:
Abstract:
On the basis of structural analysis of 3D seismic data in Nanpu sag, applying faulting model with pre-existing weaknesses, combining with sand modeling results, the fault system and structural styles in Nanpu sag were systematically analyzed. The results show that, the structural style is typical oblique extension. The complicated “Y” shaped style , which is jointly controlled by listric (or ramp-flat) boundary normal faults and pre-existing faults, is the basic structural style in Nanpu sag, followed by complicated “X” shaped, “domino”, “Ladder” and “imbricate faulted blocks” structural styles. 4 fault systems are divided in the plane, that are Beipu-Laoyemiao fault system, Gaoliu fault system, Baigezhuang fault system and Nanpu fault system. Among them, Gaoliu fault system and Nanpu fault system can be further divided into 2 and 3 sub-fault systems respectively. While, it can be divided into two fault systems vertically: lower fault system (E2s3 tectonic layer) and upper fault system (E2s1-Q layers). There are four kinds of fault assemblages: “parallel-like”, “parallel intertwined” “comb-like” and “broom-like”. Cenozoic structural deformation of Nanpu sag can be reasonably explained with two-phases extension model: structural deformation of E2s3 era is caused by NW-SE direction extension with Mesozoic pre-existing weaknesses, while structural deformation since E2s1 is caused by north-south direction extension with pre-existing faults formed in E2s3 era, and E2s2 era is stress transition phase. There are significant segmentations in the sag boundary faults (Xinanzhuang Fault, Baigezhuang Fault and Gaoliu Fault), the strike, properties, activation of different segments showed a significant difference, and significant changes occurred in the different stages of the tectonic evolution. The tectonic framework by the sag boundary faults, Nanpu Fault and Gatou Fault in sag played an important controlling role on the fault formation and evolution of Nanpu sag. The complicated pre-existing faults were the root causes of lateral variation of fault system.
