Select All
    Display Method:: |
    Volume 98,2024 Issue 2
      Research Articles
    • JIA Baoyan, PENG Bo, WANG Jilong, YU Junjie, ZHOU Baochun, ZHAO Quanhong, LI Baohua, WANG Yaqiong

      2024,98(2):333-345, DOI: 10. 19762/j.cnki.dizhixuebao.2023325

      Abstract:

      The Fujian coastal area, with its extensive distribution of Quaternary deposits, offers an ideal location for studying relative sea level changes since the late Pleistocene. In this study, we utilized AMS 14C and optical stimulated luminescence (OSL) dating techniques to analyze the high- resolution ostracod records from core NDQK5, which was obtained from Ningde in Fujian Province. Our objective was to reconstruct the relative sea level changes during the Mid- Holocene in this area. The ostracods found incore NDQK5 were located at a depth interval of 4~17. 1 m, corresponding to approximately 8. 2~6. 9 ka BP We identified twenty- six marine ostracod species belonging to twenty- three genera from the core samples. By analyzing the relative abundance of the main ostracod elements, we identified three distinct ostracod assemblages. Ostracod assemblage A, characterized by the dominance of Bicornucytherebisanensis and Sinocytheridea impressa, indicatesa subtidal zone environment. Assemblage B, with Sinocytheridea impressa and Neomonoceratina delicata asthe dominant species, represents the nearshore inner shelf. Assemblage C, marked by the dominance of Sinocytheridea impressa and Loxoconcha ocellifera, indicates an intertidal zone environment. Our ostracod data reveals a continuous rise in sea level in the Fujian coastal area since approximately 8. 2 ka BP, with the sea level reaching its highstand between 7. 9 and 7. 4 ka BP. Subsequently, a decline in sea level existed during the period of 7. 4 to 7. 0 ka BP, followed by a minor rise. These findings indicate the presence of several minor fluctuations in sea level during the Holocene sea- level highstand period in the Fujian coastal area. Combining our result with the previous studies, we conclude that the sea level change in the Fujian coastal area was probably influenced by meltwater from the ice sheet during the period of 8. 2 to 7 ka BP. However, it is probable that the glacio- hydro isostatic adjustment (GIA) effect played a role in controlling sea level after 7 ka BP.

    • SONG Yingfan, WANG Xiangdong, LI Ying, SHI Yukun, HU Keyi, HUANG Xing, SHENG Qingyi, YAO Le

      2024,98(2):346-362, DOI: 10.19762/j.cnki.dizhixuebao.2023313

      Abstract:

      Carboniferous is an important period in the geological history when the Hercynian Orogeny occurred and the Late Paleozoic ice age (LPIA) reached its peak, which resulted in frequent fluctuations of eustatic sea level and dramatic changes in palaeoclimate and palaeoenvironment. At the Mid- Carboniferous boundary interval, a vast shallow platform dolomitization occurs widely in South China. This paper summarizes the thickness and age of dolostones in three major carbonate platforms in South China, and further clarifies their temporal and spatial distribution. In terms of characteristics of global climate and environment in this interval, we propose that the maximum glaciation could be the cause of eustatic sea- level fall which resulted in the widespread dolomitization in South China. The different temporal distributions of dolostones among sedimentary basins in South China might be related to their independent developing history of basins and different diagenetic patterns. The dolomitization in the Middle- Lower Yangtze Carbonate Platform could be the Sabkha pattern and the seepage- reflux pattern in the early burial stage, therefore, forming relatively thin- bedded dolostone deposits. The thick- bedded dolostones in the Central- southern Carbonate Platform and the southwestern Carbonate Platform could have been formed in the seepage- reflux pattern.

    • ZHANG Yingli, JIA Xiaotong

      2024,98(2):363-380, DOI: 10.19762/j.cnki.dizhixuebao.2023279

      Abstract:

      During the Cambrian period, a set of clastic and carbonate rock associations was mainly deposited in the western margin of the Yangtze block. These sedimentary deposits have commonly been interpreted as representing a vast and stable craton sourced from older rocks in the Oldland. However, the widely contemporaneous magmatism recorded within the sediments is obviously inconsistent with the craton basin identified earlier. Therefore, the tectonic background needs to be determined based on the material sources of the western margin of the Yangtze block. Field outcrops and other data are used to determine the source areas of the Cambrian sediments in the western margin of the Yangtze block through heavy mineral analysis, tourmaline electron probe microanalysis, and detrital zircon U- Pb dating of three sandstone samples from Huize and Huidong counties. We then discuss the tectonic background of the Cambrian period in combination with a comprehensive analysis of sedimentary successions. These successions show that the Canglangpu, Xiwangmiao, and Erdaoshui formations are mainly composed of sandstone and dolostone, which were deposited in shore and tidal flat environments. The sandstones are fine- to coarse- grained, with subangular to subrounded and poorly sorted fabric. Quartz is the dominant constituent, while lithic fragments consist mainly of cherts, and feldspar grains are very rare. The detrital heavy minerals are mainly zircon, hematite- limonite, tourmaline, ilmenite, rutile, and apatite, suggesting a magmatic rock source. The results of tourmaline electron probe microanalysis further confirmed that the Cambrian sediments are mainly derived from granitoids, their associated pegmatites and aplites, metapelites, and metapsammites. Detrital zircon dating provided valuable insights into the age of the parent rocks in the provenance area, indicating a distribution ranging from 983 Ma to 540 Ma. Comparisons of the geochronological data with detrital zircon ages from different blocks reveal that the sediments were derived from 663~540 Ma rocks of the East African orogeny, as well as the underlying old sediments (dated 983~708 Ma) in the Kangdian Oldland. Contrary to previous studies suggesting a simple craton setting for the Cambrian period, our analysis of detrital zircon spectra indicates an active continental margin setting during this time. The sedimentary successions, detrital zircon spectra, and detrital grain framework collectively suggest that the Cambrian sediments were formed in a collisional setting, especially a foreland basin.

    • BAO Jing, HU Yu, LI Bingshuai, YAN Maodu, LIU Yongqing, XU Kemin, CUI Mingming

      2024,98(2):381-396, DOI: 10.19762/j.cnki.dizhixuebao.2023172

      Abstract:

      Understanding the Mesozoic vertical- axis rotation of the Jiaodong Peninsula is crucial for constraining the sinistral shearing of the Tan- Lu fault. However, debates still exist regarding whether rotation occurred and, if so, the magnitude of rotation in the Jiaolai basin during the Mesozoic. In this study, we conducted a detailed paleomagnetic investigation of the Early Cretaceous red beds from the Longwangzhuang Formation at the Wulian locality in the southern Jiaolai basin. Detailed rock magnetic results indicate that hematite is the main magnetic carrier, while pyrrhotite and magnetite act as subordinate magnetic carriers in some samples. The Fisherian mean direction of the 8 sampling sites was determined as Ds=169. 5°, Is=33. 2°, ks=40. 9, and α95=8. 8, which is proposed to be the primary remanence acquired during deposition. Our results indicate that the Wulian region underwent an obvious counterclockwise rotation of 22. 8°±8. 8° relative to stable East Asia. Together with previous paleomagnetic results from the Jiaolai basin, they probably indicate a holistic counterclockwise rotation (10°~20°) of the Jiaolai basin after the Late Cretaceous. Moreover, an increasing magnitude of counterclockwise rotation towards the southwest along the Wulian fault was observed and most likely attributed to the increasing influence of sinistral strike- slip faulting along the Tan- Lu fault to the west. Different rotation senses and magnitudes were observed in different periods along the Tan- Lu fault, which were not only influenced by the sinistral shearing of the Tan- Lu fault but also related to the different nature and tectonic backgrounds of nearby blocks.

    • ZHANG Jingqi, YU Fusheng, PANG Fuji, WANG Qianjun, WANG Qianjun

      2024,98(2):397-420, DOI: 10.19762/j.cnki.dizhixuebao.2023151

      Abstract:

      Yongjin area is located in the middle of Junggar basin, northwestern China, where several hydrocarbon- bearing structures associated with strike- slip faults have recently been discovered. However, the development characteristics and genetic mechanism of strike- slip faults are not thoroughly studied. Based on detailed interpretation of three dimensional seismic data, three groups of strike- slip fault systems are identified in the Triassic- Jurassic strata in the study area, which are nearly east- west, north- west- west and north- east- east trends. The distribution characteristics of the strike- slip fault system are longitudinal stratified and planar “grid” pattern structure. Based on the similarity principle, four groups of structural physical sandbox simulation and comparison experiments were designed to reproduce the tectonic evolution process in the study area. The simulation results indicated that the formation of such kind of strike- slip faults is related to the location of pre- existing faults of the basement. This kind of distributed strike- slip fault system in Yongjin area was controlled by both pre- existing structures and stratum properties, thus a genetic model of the study area has been established. The research results have guiding significance for the genesis of strike- slip fault systems in areas with similar geological settings.

    • SHI Junhua, HAN Shuai, DU Jianjun, HAN Jian'en, SUN Dongxia, HU Daogong

      2024,98(2):421-432, DOI: 10.19762/j.cnki.dizhixuebao.2023149

      Abstract:

      Hainan Island is an important part of the South China Sea block, and its tectonic evolution can largely reflect the tectonic activity characteristics of the entire South China Sea. During the Cenozoic period, under the neotectonic movement of Hainan Island, the differential rise and fall of fault blocks was relatively obvious, forming a tectonic pattern roughly bounded by the Wangwu Wenjiao fault, with the subsidence area to the north and the fault uplift area to the south. Research on the uplift process of the faulted uplift area can reveal the history of neotectonic activity in the Hainan Island, but so far, the cause and timing of the uplift of the southern Qiongzhong Mountains are still controversial. In order to clarify the exfoliation and uplift events in the central part of Hainan Island, this paper selected the Wuzhi Mountain with the highest elevation and the largest elevation difference in the southern Qiongzhong area as the study area, and collected 8 sets of rock elevation samples in this area, with an elevation range of 203. 55~1153. 52 m. A large number of apatite fission track tests and thermal history simulation analysis were carried out on the collected samples. The results show that the Cenozoic in the Wuzhi Mountain area of the Hainan Island mainly experienced two periods of rapid uplift and exfoliation. The first period is from Oligocene to Miocene (32~17 Ma) when the uplift rate was relatively fast. During this period, the Pacific plate subducted and retreated to the Eurasian plate, and the South China Sea experienced the second expansion, making Hainan Island stretched. The activity was intense, causing the Qiongzhongshan area to uplift rapidly until it turned into a slow uplift during the Middle Miocene. The second stage is the stage of rapid denudation and uplift at the end of the Miocene (5 Ma) when the expansion of South China Sea had ended. With the subduction of the Asian plate under the Philippine plate, the entire northern continental margin of South China Sea was in the stage of accelerated thermal subsidence, and the global climate change was accelerated, resulting in extensive uplift and accelerated denudation in Hainan Island.

    • ZHANG Yaoling, QI Bangshen, HU Daogong, NI Jinyu, WANG Chaoqun

      2024,98(2):433-446, DOI: 10.19762/j.cnki.dizhixuebao.2023255

      Abstract:

      The East Kunlun orogenic belt experienced a complete process of oceanic crust formation, subduction erosion, collision orogeny and post- orogenic collapse evolution in the early Paleozoic era. But the initial continent- continent collision time and the duration of continent- continent collision are still controversial. One of the most direct and effective methods to constrain the initial continental collision time is the age of formation of the depositional environment mutation or unconformity caused by the start- up of peripheral foreland basin. In this paper, we take the Halabayigou Formation of the Silurian peripheral foreland basin, which is angular unconformity covered by the Shihuichang Formation in Shuinichang area of East Kunlun, as the object of study. The zircon U- Pb chronology of the intercalated volcanic rocks is carried out to provide the sedimentary record evidence to constrain the initial continent- continent collision time and the collision orogeny time of the early Paleozoic. The results show that the U- Pb ages of the rhyolite tuff in the lower Halabayigou Formation in the east of Shuinichang and Xueshui River are 443.0±3.9 Ma and 441.8±1.3 Ma, respectively. Combined with the reported U- Pb age of the volcanic rock of Shihuichang Formation (450.4±4.3 Ma), it can be determined that the initial continent- continent collision of East Kunlun occurred during 450~443 Ma. Based on the evidence of Paleozoic magmatism, metamorphism, tectonic deformation and related sedimentary records, it is concluded that the East Kunlun area entered the stage of continental crust subduction and continent- continent collision at least from about 450 Ma, and entered the stage of post- collision extension at about 425 Ma. The collision orogeny lasted about 25 Ma.

    • WANG Di, ZHANG Zeming, LI Wentan

      2024,98(2):447-466, DOI: 10.19762/j.cnki.dizhixuebao.2023123

      Abstract:

      Cenozoic granites are widely exposed in the Gangdese magmatic arc of the southern Tibetan Plateau. However, the origin of these granites remains controversial. We report geochronology and geochemistry study about the late Oligocene two- mica granites from the Milin area in the eastern Gangdese arc. Whole- rock chemical analyses show that these granites belong to medium- high potassium calc- alkaline series, weakly peraluminous. The samples are enriched in light rare earth elements and large ion lithophile elements such as Rb, Th and U, and depleted in heavy rare earth elements and high field strength elements such as Nb, Ta and Ti. All samples exhibit high Sr and low Y, with high Sr/Y ratio (37~85), and chemical affinity to adakites. The two- mica granites have the crystallization age of ~26. 6 Ma. Zircon Hf isotopes show that these granites have low and positive εHf(t) values (+0. 4 to +7. 3). Taking previous data into account, we conclude that the late Oligocene granites from the Milin area were derived from partial melting of the Eocene arc- type magmatic rocks in the thickened lower crust, but with contribution of ancient crustal materials. The continental collision- induced crustal shortening and thickening resulted in the partial melting of the thickened lower crust, and formation of the widespread late Oligocene adakitic granites.

    • ZHU Kunhe, WANG Kaixing, LIU Xiaodong, DUAN Jianhua, LI Yanqiang, WU Jia, YU Chida, LEI Yongliang

      2024,98(2):467-480, DOI: 10.19762/j.cnki.dizhixuebao.2023020

      Abstract:

      The Haidewula uranium deposit in the East Kunlun orogenic belt is a newly discovered independent uranium deposit related to volcanic rocks in Northwest China. The discovery of the deposit provides an indication for the exploration of hydrothermal uranium deposits in the East Kunlun orogenic belt. in this paper, the transparent minerals (pink calcite, purple black fluorite and quartz) related to the ore- forming period of the deposit are selected as the research objects. A systematic study of the C- H- O isotopes and fluid inclusions are carried out to find out the source and nature of the ore- forming fluid, and to explore the genesis of the deposit. The results show that the quartz of the ore forming period of the Haidewula uranium deposit is mainly composed of H2O gas- liquid two- phase inclusions, with few CO2- H2O two- phase inclusions; fluid inclusions in calcite vein and fluorite vein contain H2O gas- liquid two- phase inclusions. Pure liquid phase inclusions are occasionally seen, but pure gas phase and solid phase inclusions are not seen in calcite veins. The homogenization temperature range of inclusions in calcite, fluorite and quartz during mineralization is from 133℃ to 187℃ (mean 163℃), from 127℃ to 204℃ (mean 169℃), and from 183℃ to 287℃ (mean 219℃) respectively, and the salinity range is from 1. 40% NaCleq to 7. 02% NaCleq (mean 3. 65% NaCleq), from 0. 53% NaCleq to 3. 06% NaCleq (mean 1. 26% NaCleq), from 7. 17% NaCleq to 17. 26% NaCleq (mean 11. 46% NaCleq). The gas phase composition of fluid inclusions is mainly H2O, and a small amount of CO2. The experimental data of C- H- O isotope show that the variation ranges of δ13CFluid- V- PDB, δDFluid- V- SMOW, δ18OFluid- v- smow values are from 1. 59‰ to 1. 00‰, from 71‰ to 63‰, from 0. 03‰ to 3. 72‰ respectively, indicating that the ore- forming fluid is not a single source, and may be a mixed source of atmospheric precipitation and magmatic water. In addition, the precipitation of pitchblende is mainly due to the changes in physical and chemical conditions caused by the interaction between fluid and hosted- rock, as well as fluid boiling/CO2 degassing, leading to large- scale unloading and precipitation of the pitchblende and other uranium minerals.

    • ZHANG Chi, CHU Chenglin, XU Qinqi, SUN Yaxiong, JIA Cunsha, WEI Huadong

      2024,98(2):481-493, DOI: 10.19762/j.cnki.dizhixuebao.2023134

      Abstract:

      A large number of strike- slip faults are distributed in the southeastern slope of the Akkule uplift in Tarim basin. The geometric and kinematic characteristics of strike- slip faults play an important role in controlling hydrocarbon migration and enrichment. S118- AT22- YUKE2, S113- AT13- YUKE3, AT20, AT18- YUKE5 faults are taken as the research object. Based on the theory of fine analysis technique of small and medium- sized strike- slip faults, detailed analysis is carried out on the layered deformation, plane segmentation, fault system activity intensity, late activity, source conditions, evolution mode and genetic mechanism of strike- slip faults. Then the petroleum geological significance is discussed based on production dynamic data. The strike- slip fault in the southeastern slope of Akkule uplift has a vertical deformation structure of deep linear fault combined with en echelon fault, and the middle- lower Ordovician strike- slip fault has obvious plane segment characteristics. The relative fault activity intensity of the southeastern slope is strong in the west and weak in the east, showing strong- weak- sub strong characteristics from north to south. The late activity of near SN- NE trending fault system is stronger than the NNE- NNW fault system in the Late Hercynian- Yanshanian period. The source condition of faults was controlled by the early rift. The source condition of main fault is better than the secondary fault. The source condition of main fault of NNE- NNW trending fault system is better than the SN- NE trending fault system, but the secondary fault is worse. The NNE- NNW trending fault system and SN- NE trending fault system were formed in the middle Caledonian, and the NEE fault was formed in the late Caledonian- early Hercynian. The strike- slip fault of the southeastern slope experienced the vertical superposition of the middle Caledonian, Late Caledonian- early Hercynian, middle- late Hercynian, and Indosinian- Yanshanian multi- stage tectonic activities. The opposite slip directions of NNE and SN main faults are due to the different fracture modes. The hydrocarbon expulsion period of source rock in the southeastern slope of Akkule uplift is in late hercynian- Himalayan age. The coupling of fault- active period and hydrocarbon expulsion period is favorable for oil- gas charging. The intensity of fault activity controls the faults source condition and reservoir size, and then controls the degree of oil and gas enrichment. The strike- slip faults with obvious late activity, intensity of fault activity and good source condition are favorable targets for further exploration.

    • YI Dinghong, SHI Yajun, LIU Junfeng, LIU Yingru, LI Jiyong, WANG Aiping, MA Yuankun, LI Hongzhe, JIA Zhengliang

      2024,98(2):494-510, DOI: 10.19762/j.cnki.dizhixuebao.2023281

      Abstract:

      This paper focuses on studying the upper member of the Xiaganchaigou Formation (E23) in the Late Oligocene of the Paleogene. The research objective is to deeply examine the provenance direction, sand body distribution law, and sedimentary microfacies development and evolution of the weak regressive shallow water delta in the expansion period of the E23 in the Nanbaxian area. To achieve this, a comprehensive analysis was conducted using fine core observation, drilling (logging) data, heavy mineral assemblage, ZTR index, sandstone clastic composition, grain size accumulation probability map, and sand- land ratio. The results show that: ① The provenance of the E23 sedimentary period in the Nanbaxian area mainly comes from the southern Qilian Mountains, which consist of intermediate- acid magmatic rocks and intermediate- high- grade metamorphic rocks. The provenance direction is almost northeast- southwest. The stable heavy minerals (magnetite, garnet, ilmenite, and zircon) have a high content (ranging from 81. 0% to 99. 9%), while the unstable heavy minerals (epidote and amphibole) show low content. ② The E23 sedimentary period in the Nanbaxian area is characterized by the development of a shallow delta- shallow lake sedimentary environment, primarily featuring underwater distributary channel sand bodies. The predominant lithology is lithic feldspathic sandstone, followed by feldspathic lithic sandstone. The composition maturity and sorting roundness are categorized as medium- poor. The particle size probability curve is mainly one jump and one suspension type, reflecting the influence of river action. Various sedimentary structures are present, including block bedding, normal sequence bedding, parallel bedding, and trough cross- bedding. ③ During the E23 sedimentary period, three NE- SW trending sand body enrichment zones were inherited in the Nanbaxian area (sand to ground ratio ranging from 35% to 65%). The degree of sand body development increased from the early to the middle stage, showing a progradation trend. However, the development of sand bodies weakened from the middle to the late stage, showing signs of weak retrogradation. ④ The shallow water delta front sedimentary subfacies were inherited in the Nanbaxian areaduring the E23 sedimentary period, with the continuous development of three sedimentary lobes. The underwater distributary channel microfacies are mainly developed, followed by the underwater interdistributary bay microfacies. The development scale of the shallow water delta front increases from the early to middle stage and decreases from the middle to late stage.

    • LIU Lihong, GAO Yongjin, ZHU Guangyou, YANG Youxing, YIN Chengming, SUN Xiangcan, LI Qingyao

      2024,98(2):511-529, DOI: 10.19762/j.cnki.dizhixuebao.2023282

      Abstract:

      The Ediacaran- Cambrian transition is a crucial interval in the geological timeline, marked by the widespread occurrence of various black rock series worldwide, such as siliceous rock, mudstone, and dolomite. In the northwest region of the Tarim basin, specifically within the middle and lower sections of the black series, there is a notable presence of siliceous rocks. These rocks exhibit alternating black and white chert bands, displaying diverse distribution patterns. Determining the origin of these siliceous rocks is essential for understanding the environment conducive to high- quality source rocks within the Yuertusi Formation. In this study, we focus on investigating the siliceous rock within the black rock series of well Xinkedi 1. By employing field observations, petrological analysis, and geochemical techniques, we aim to unravel the origin of these siliceous rocks and their relationship with the organic matter present within the sequence. Additionally, we systematically examine the processes responsible for the formation of the black and white chert bands. The white layers are predominantly composed of pure microquartz, while the black layers contain a mixture of detrital carbonaceous matter, quartz grains, and carbonaceous microlaminae, which are interpreted as remnants of microbial mats. These variations in coloration are believed to be influenced by glacial and interglacial periods. We also establish that the occurrence of organic matter is conducive to the formation of silica. The higher Al2O3/(Al2O3+Fe2O3) ratio and lower Lan/Cen valuesuggest a deposition environment dominantly influenced by terrigenous sources in a continental margin. Furthermore, considering paleoclimate and sea level fluctuations, it can be inferred that the deposition of siliceous rock and siliceous shale primarily took place in confined bay or lagoon environments. This study provides valuable insights into understanding the formation environment of siliceous shale and contributes to the evaluation and prediction of source rocks, offering practical implications for resource exploration and development.

    • CHEN Cheng, WU Zhenhan, ZHAO Weiyong, WANG Li, JI Changjun, ZHAO Zhen, ZHANG Hao, GONG Zan

      2024,98(2):530-543, DOI: 10.19762/j.cnki.dizhixuebao.2023262

      Abstract:

      The Qiangtang basin is the Mesozoic marine sedimentary basin with the lowest degree of oil and gas exploration in the new land area, and its main source rocks have not been clearly understood. In this paper, the organic geochemistry and element geochemistry of the source rocks of the Middle Jurassic Buqu Formation in Shenglhe area have been systematically studied, and the formation environment and organic matter enrichment mechanism of the source rocks of the Buqu Formation have been discussed. This provides a theoretical basis for predicting the distribution of high- quality source rocks in the Middle Jurassic Buqu Formation in the North Qiangtang depression. The source rocks of the Buqu Formation in Shenglihe area have high abundance of type Ⅱ of organic matter in mature stage. During the Buqu period, the climate was arid and hot, and the primary productivity level of the study area was relatively high, which was a weakly confined basin with shallow water, high salinity and oxygen- poor depositional environment. During the Buqu period, large- scale transgression occurred in the Qiangtang basin, and the study area was adjacent to the central uplift. A large number of nutrients such as phosphorus and iron from terrigenous input and hydrothermal activities were carried into the ocean, resulting in higher primary productivity, which was the main controlling factor for the enrichment of organic matter in high- quality source rocks of the Buqu Formation in the North Qiangtang depression. The study area is located in the minimum oxygen- containing zone of the North Qiangtang depression, which is conducive to the anoxic death and burial of a large number of planktons. Through the analysis of organic matter enrichment mechanism, the coastal shelf slope zone of the North Qiangtang depression may be a favorable area for the distribution of high- quality source rocks in the Middle Jurassic Buqu Formation.

    • LIN Wenjing, WANG Guiling, GAN Haonan

      2024,98(2):544-557, DOI: 10.19762/j.cnki.dizhixuebao.2023027

      Abstract:

      High heat- producing granite is one of the important intracrustal heat sources is widely distributed in the southeastern China, which provides the possibility of superficial heat generation and accumulation in the region. Based on the distribution of granite resources in the region, this paper systematically analyzes the radiogenic heat production characteristics of the main granite bodies in the region, and makes a comparative analysis of the deep temperature distribution, geothermal heat flux and crustal heat structure in the key geothermal exploration areas with the deep drilling of geothermal exploration in the region in recent years, and proposes a heat gathering model of shallow surface geothermal resources in the study area. The analysis concluded that the southeastern China has a quadratic heat gathering pattern of “mantle source heat supply- intracrustal heat generation- fracture heat transfer- cover heat preservation”, among which, the radiogenic heat production rate of granite is one of the main factors affecting the shallow geothermal field in the area. The heat production rate of the North Guangdong- South Jiangxi rock body is obviously higher than that of the granite body in Zhangzhou area, which in turn is similar to the thermal structure of lithosphere of “hot crust- cold mantle” or “warm crust- warm mantle” type but has some differences with that of “hot mantle- cold crust” type in Zhangzhou. The fracture structure and cover conditions have obvious control on subsurface heat accumulation and dissipation. The results of the study are of theoretical and guiding significance for the in- depth understanding of the genesis and heat control factors of geothermal resources in southeastern China, as well as the future exploration and development practice of geothermal resources in the region.

    • WANG Chenguang, ZHENG Mianping, ZHANG Xuefei, XING Enyuan, YE Chuanyong, REN Jianhong, LI Mingming, HE Jiangtao, WANG Fengxiang

      2024,98(2):558-578, DOI: 10.19762/j.cnki.dizhixuebao.2023025

      Abstract:

      As the important breakthrough in geothermal exploration in Southern Tibet in recent years, the Gudui (Gobdu) high- temperature geothermal system has attracted widespread attention for its typical characteristics of shallow burial, high temperature, high lithium content and intense activity. The boiling springs and hot springs in the Gudui geothermal system are mainly Na- Cl type, the warm springs and cold springs are mainly Na- Cl- HCO3, Na- HCO3- Cl and Na- HCO3 types, and the surface water mainly belong to Ca- Mg- SO4- HCO3 and Na- Ca- Mg- SO4- Cl- HCO3 types; these differences may reflect their different origins and material sources. The comprehensive analysis of Na- K, quartz, K- Mg geothermometer indicate that the reservoir temperature was up to 240. 56℃. Except for four samples, the results of Na- K geothermometer is always higher than the quartz and K- Mg geothermometers. Most geothermal water samples collected from Gudui are far from the full equilibrium line in Na- K- Mg ternary diagram, suggesting that the complete chemical re- equilibrium has not been achieved as these geothermal waters flow upward from reservoirs towards spring vents and possibly mix with cooler waters. Geochemical characteristics analysis indicates that Cl, Na, K, SiO2, B, As, Li, Rb, Cs and F are the characteristic components of Gudui geothermal waters. The good linear relations between Cl and other characteristic constituents reflect the existence of a parent geothermal liquid (PGL) below Gudui. Comprehensive comparative analysis of the chloride- enthalpy diagram suggests that there may be two kinds parent geothermal liquid below Gudui that have Cl - concentration, enthalpy value and their corresponding temperature are 567 mg/L, 1562. 5 J/g, 335. 5℃ and 697 mg/L, 1250 J/g, 282. 5℃. The PGL ascends to the surface through different channels and may cool by conduction of heat to reservoir host rocks, by boiling, or by mixing with cooler groundwater. This study is of great significance to deeply understand the hydrochemical characteristics and formation process of high- temperature lithium- rich geothermal system in southern Tibet, and has important practical significance for the rational utilization of clean geothermal energy and geothermal- type lithium resources in southern Tibet in the future.

    • SUN Bin, LI Changsuo, WEI Shanming, DING Guantao, GUO Xiujun, GAO Shuai, LIU Chunwei, YANG Zhenhua

      2024,98(2):579-590, DOI: 10.19762/j.cnki.dizhixuebao.2023044

      Abstract:

      In order to gain a comprehensive understanding of the circulation process of karst spring and geothermal water in Jinan on a larger spatial scale, this research paper analyzes the burial conditions and continuity characteristics of carbonate water- bearing media based on their spatial distribution in the north flank of Mount Tai. Furthermore, the study reveals the pattern of regional groundwater circulation through the utilization of mathematical statistics, spatial interpolation, a Piper three- line diagram, a conceptual model, and the “four fields” analysis of hydrodynamic field, hydrochemical field, water temperature field, and water age field. The results show that the spatial distribution of karst water- bearing media in the north flank of Mount Tai is controlled by surface watersheds and deep faults such as Qiguang fault, Yuwangshan fault, and Liaokao fault. There is a gradual increase in burial depth from south to north. Additionally, the hanging wall and footwall have different dislocations due to the influence of secondary faults such as Mashan fault, Dongwu fault, and Wenzu fault. However, there is still a general continuity in their East- West distribution. The regional groundwater circulation process is extremely complex. The Taishan rock group, Cambrian, and Ordovician water- bearing rock groups interact with each other through various means such as surface flow discharge, leakage, structural connectivity, and underground runoff. In certain areas of piedmont, karst water exchanges with Quaternary loose- pore water and ultimately discharges through springs or artificial mining. The regional groundwater flow exhibits a unified “four fields” and demonstrates distinct horizontal and vertical zoning characteristics. The boundary between cold springs and geothermal springs is formed along the Donge fault and its extension line, encompassing Wujiabao, Huashan, Zhangqiu and Cicun. The circulation depth boundaries of shallow, medium, and deep flow are roughly divided at 600 m and 1000 m. Cold springs are predominantly characterized by shallow circulation, supplemented by medium and deep circulation, with low groundwater mineralization, temperature, and age. On the other hand, geothermal water is dominated by medium and deep circulation, supplemented by shallow circulation, with large groundwater mineralization, temperature, and age. The flow of different aquifer media exhibits certain internal correlations, forming a complete karst water system.

    • LEI Kunchao

      2024,98(2):591-610, DOI: 10.19762/j.cnki.dizhixuebao.2023013

      Abstract:

      Land subsidence caused by over- exploitation of groundwater has become one of the important factors restricting the sustainable development of the society and economy of Beijing. In December 2014, the middle route of the South- to- North Water Diversion Project was officially opened, and more than 1 billion m3 of water was delivered to Beijing every year. As a result, the pattern of water supply in Beijing has changed, and conditions have been created to reduce the exploitation of groundwater, conserve groundwater, and control land subsidence in Beijing. This paper uses a variety of monitoring data to analyze the changes in groundwater and land subsidence in the Beijing Plain before and after the South- to- North Water Diversion Project. The deformation characteristics of soil layers with different lithologies and depths under different groundwater level variation patterns are studied. The elastic and inelastic skeletal- specific storage rates of the soil layers at different deformation stages are calculated. The reasons for the large residual deformation and hysteresis deformation of the cohesive soil layer are discussed. The results show that: ① From 2015 to 2020, the groundwater level of the first to fourth aquifer groups in most areas of the plain gradually increased, and the land subsidence gradually slowed down. ② The second and third compression layer groups in the plain are the main contributing layers to the subsidence. Except for Pinggezhuang and Yufa station, the subsidence proportion of the third compression layer group in the other stations gradually increased. The main subsidence layer is gradually transferred to the deep formation. ③ In the north and east of the plain, the groundwater levels corresponding to the second and third compression layer groups changed from falling to rising. During the drop stage of the groundwater level, the soil layer exhibits plastic and creep deformation. During the rise stage of groundwater level, the soil layer exhibits plastic deformation and elastic deformation for part of the time. which is viscoelastic plastic. The soil layer exhibits the characteristics of viscoelastic plastic. In the southern part of the plain, the groundwater levels continued to decline, and the deformation of the soil layer was always plastic and creep deformation. The sand layer mainly exhibits elastic deformation. ④ For different stages of soil deformation, the change in elastic and inelastic skeletal- specific storage rates is not constant. As the groundwater level decreases, the soil skeletal specific storage rate shows a decreasing trend. ⑤ The reasons for the large residual deformation and deformation hysteresis of the cohesive soil layer mainly include two aspects. Firstly, the inelastic skeletal specific storage rate is greater than the elastic skeletal specific storage rate. Secondly, the weak permeability of the cohesive soil layer.

    • Research Progress
    • ZHAO Jiannan, ZHANG Shiqi, GENG Zhiqing, XIAO Long, WANG Jiang, SHI Yutong, LU Xi

      2024,98(2):611-622, DOI: 10.19762/j.cnki.dizhixuebao.2023053

      Abstract:

      The exploration and utilization of space resources is one of the important purposes of deep space exploration. Mars, being the most accessible planet with pressing resource utilization demands, necessitates the exploration and in- situ utilization of its resources. These activities are vital for the future of manned exploration and base construction on Mars. In this paper, we conduct an analysis of the various types of Martian resources, including atmospheric resources, water resources, soil and rock mineral resources, as well as wind and solar energy resources. We also create a global distribution map of Martian resources and propose the potential areas for future Mars base construction based on resource distribution. In addition, this paper provides a comprehensive summary of the research progress and issues surrounding in- situ resource utilization technology on Mars. It also highlights the need for further research in the following aspects: enhancing targeted surveys and evaluations of Martian resources, developing new resource utilization models and technologies, establishing comprehensive evaluation models for resource utilization costs, and improving laws and regulations pertaining to resource development and utilization.

    • Technical Method
    • LI Bingyuan, GUO Na, ZHI Lijia, YANG Wenwen, XIE Zhou, WANG Xiao, WEI Dexian

      2024,98(2):623-635, DOI: 10.19762/j.cnki.dizhixuebao.2023372

      Abstract:

      Dasi deposit is located in the middle of the Mesozoic Daxinganling- Yanshan volcanic belt, and it has great prospecting potential for porphyry and epithermal deposits. This area is recognized as an important metallogenic belt, characterized by extensive magmatic, volcanic, and subvolcanic activity. In our study of the Dasi deposit in Inner Mongolia, we utilized SWIR and TIR technology to measure rocks from the surface and cores. With the assistance of mineral geochemical analysis and microscope observation, we successfully completed the alteration mapping and prospecting potential prediction. The results show that: ① The main altered minerals at Dasi deposit include albite, microcline, quartz, sericite, kaolinite, montmorillonite, and chlorite, along with smaller amounts of alunite, tourmaline, gypsum, and biotite. ② The relationship between the identified alteration minerals through SWIR analysis and the Pb orebody shows a close association between mineralization and tourmaline, alunite, kaolinite, and sericite. Dasi deposit exhibits mineral assemblages typical of medium- sulfide epithermal deposits. ③ Pb mineralization dominates the deposits, mainly occurring at shallow depths of around 300 m underground. The exposed surface shows significant denudation, and the bottom plate of the Pb orebody is composed of argillization minerals, predominantly montmorillonite and chlorite. The alteration zoning, progressing from the mineralization center outward, follows the sequence of sericitization→sericite+kaolinite (+alunite+tourmaline)→sericite+montmorillonite→montmorillonite+chlorite. The orebody is located within a sericite (kaolinite) alteration zone. ④ Long- wavelength sericite indicates the presence of deep- seated thermal energy, while short- wavelength white mica reflects a combination of magmatic hydrothermal solutions and external atmospheric precipitation. Wavelength shifts at 2200 nm provide insights into the metallogenic environment, such as pH, temperature, and fluid flow. ⑤ The absorption depth of sericite at 2200 nm demonstrates a positive correlation with Pb grade, as expressed by the equation y(Pbgrade)=0. 1217 x(absorption depth)(R2=0. 9178). A threshold of 10% absorption depth can differentiate between sericite and kaolinite mineral types. ⑥ Combined with GIS spatial overlay analysis, we determined that the peripheral areas still hold promising prospecting potential.

    • Appendix
    Select All
    Display Method:: |
    • LI Zhuang, LANG Xinghai, LIU Hui, ZHAN Hongyu, TAN Hao, ZHANG Peng

      Submitted date:2022-12-14,Pre-publication date:February 02, 2024

      DOI: 10.19762/j.cnki.dizhixuebao.2023373

      Abstract:

      The Gangdese metallogenic belt (GMB) in Tibet, located within the East Tethys metallogenic domain, is one of the most famous Pb, Zn, and other nonferrous metal areas in China. A notable discovery in recent years is the Pusangguo deposit, which is rich in cobalt and contains Cu–Pb–Zn ores. The ore bodies mainly occur within the contact zone between the magma and the Early Cretaceous Takena Formation strata, displaying a complex mineralization pattern. Within the Pushangguo deposit, sphalerite is one of the main sulfides in the quartz-sulfides mineralization stage. Notably, there are two distinct types of sphalerite: dark-brown type I sphalerite (SpI) and light-brown type II sphalerite (SpII). This paper employs electron microprobe analysis (EMPA) and laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) to analyze the trace elements present in sphalerites. The results show that sphalerite is generally rich in Co, with SpI exhibiting a higher Co content than SpII. Co mainly replaces Zn (Co2+→Zn2+) through isomorphism. Both SpI and SpII showcase enrichment of Fe, Mn, and Cd, as well as depletion of Ga, Ge, and In. The occurrence of Fe, Mn, Cd, and other elements is mainly in the form of isomorphism, while Cu, Ag, Pb, and As appear as mineral inclusions within sphalerite. Based on the observed correlation between different trace elements, it is proposed that there exist potential simple complex element substitution mechanisms. These mechanisms include Fe2++Mn2+→2Zn2+, (In3+, Sn3+)+(Cu+, Ag+)→2Zn2+, As3++Ag+→2Zn2+, and Pb2++2As3++□→4Zn2+ (where □ represents a lattice vacancy). Furthermore, the ratios of Fe, Mn, Ge, In/Ga, In/Ge, and Zn/Cd in sphalerite, along with the calculations based on the sphalerite GGIMPis geothermometer, indicate that sphalerite was formed in an environment of medium-high temperature (237~345℃), low oxygen fugacity, and low sulfur fugacity (logf(S2)=-13.4~-8.3).

    • WANG Ping, SONG Jinyue, FENG Shaoying, GAO Shoujie, MENG Xiangshuai, LIU Dongliang, DENG Xiaojuan, LI Qian, JIA Jia, HUA Xinsheng, SONG Wei, WANG Shengyang

      Submitted date:2022-07-06,Pre-publication date:June 25, 2023

      DOI: 10.19762/j.cnki.dizhixuebao.2023139

      Abstract:

      Topography is formed by the complex interactions between tectonics and erosional surface processes, which is primarily mediated by tectonic activity and bedrock erodibility. The rock uplift by tectonics can be negligible in the ancient orogens for its tiny tectonic activity, then it is possible to study the contribution of rock erodibility to the landscape evolution. However, most recent results show that topography is mainly controlled by tectonics in the active orogens, and the reports of lithological control on landscape evolution are not involved. As the controlling fault for the Hetao Basin, the Seerteng mountain-front fault had been active since the Holocene, which resulted the M 6.4 and M 5.9 history earthquake in the 1979 and 1934. Previous studies show that the center section (such as the Wujiahe site) has stronger activity than its west and east sections. However, the researches of geomorphic parameters are less than other faults in the northern margin of Hetao Basin (such as the Langshan fault, Wulashan fault and Daqingshan fault), which will hinder to understand its deformation dynamics. Using the 30 m DEM, we extracted the Hypsometric integral of 33 subbasins in the Seerteng Mountain and normalized channel steepness, longitudinal profile and the Knickpoint of the corresponding streams. The HI values are clustered between 0.44 and 0.66 with the highest value at the Wujiahe town, indicating that the evolution stage of the Seerteng Mountain is the “Middle” stage. The transient and steady rivers are all distributed along the fault, which reveal that the rivers in the Seerteng mountain-front are developed during the transient state and then evolved to the steady state. By comparing the knickpoint and lithology, we find that the knickpoints are under-controlled by tectonic uplift and/or lithology. The channel steepness (Ksn) has a character of spatial difference. The Ksn near the Wujiahe town is the highest, and it gradually decreases to the east and west part, then it increases to the west part at the River S8. By analyzing the rock lithology, precipitation and tectonic, the channel steepness (Ksn) is controlled by the lithology, and its spatial distribution is in accord with the fault activity (vertical slip rates and offsets). The landscape of the Seerteng Mountain is the results of the tectonic uplift and rock lithology.

    Select All
    Display Method: |
    • 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
    • Study on heat flow in Northeast China based on the depth of Curie surface

      QIU Nansheng, XU Qing, ZHU Chuanqing, SONG Jialin

      Abstract:

      The heat flow is an important parameter that characterizes the Earth"s thermal state and is also the most basic data for deep geothermal prediction and evaluation of geothermal resources in a region. However, due to the influence of borehole temperature measurement, there is no measured heat flow value in areas without borehole temperature measurement outside the basin. At present, the relevant heat flow values are obtained by extrapolating based on the measured values of adjacent basins. Due to the close correlation between the depth of the Curie surface and temperature, the surface heat flow value can be studied through the depth of the Curie surface.Based on the existing depth distribution map of residential areas in Northeast China, and combining measured rock thermal conductivity, rock heat generation rate data, and corresponding crustal stratification conditions, this paper calculated the heat flow value and redraw a detailed map of the heat flow distribution in Northeast China. The overall heat flow of the Northeast region is between 42.5 and 95mw/m2, The high value of heat flow is located in the Wudalianchi and Dunhua-Mishan fault zones, and there are also local high heat flow values within the Songliao Basin, the Xiaoxing"anling and Changchun Yanji suture zones. The high heat flow value can correspond one-to-one with the uplifted area of Curie surface, that is, high heat flow at the raised area of the Curie surface but the heat flow in the depression area of Curie surface is relatively low. This study fills the gap in measured heat flow values in Northeast China and provides more accurate parameters for deep geothermal temperature prediction and geothermal resource evaluation in the area.

      • 1
    • Palynoflora from the Lower Jurassic Fuxian Formation in Ordos Basin and its response to the Jenkyns event

      WEI Yi, NAN Qingmin, YANG Bing, ZHANG Xinzhi, SUN Siyuan, SU Guifen

      Abstract:

      For researching the influence of Jenkyns event on the paleoclimate of inland basins, we analysis the palynological characteristics of Fuxian Formation in the southern Ordos basin. Three palynological assemblage were divided from bottom to top as: Cyathidites-Deltoidospora-Chasmatosporites assemblage, whose age is the Pliensbachian of early Jurassic; Classopollis-Quadraeculina-Chasmatosporites assemblage, whose age is the early-mid Toarcian of the early Jurassic, which coincides with the Jenkyns event; Cyathidites-Cycadopites-Psophosphaera assemblage whose age is the late Toarcian of early Jurassic. The paleoclimate reflected by sporopollen community shows that the Ordos basin experienced the transformation as subtropical humid climate→subtropical semi-humid and semi-arid climate→subtropical humid climate during the early Jurassic Fuxian period. Different from the previous conclusions of the Tethys Oceanic and Pan-Oceanic studies, the Jenkyns event appears as a drying and heating event in the Ordos Basin (the hinterland of Eurasia).

      • 1
    • Research on ophiolite belts in China based on aeromagnetic data

      XIONG Shengqing, YANG Hai, FAN Zhenyu, LIU Fuxiang

      Abstract:

      Through the accumulation of more than 60 years, China has basically completed the aeromagnetic survey of mainland, which provides detailed geophysical data for the study of regional geological structure. Aeromagnetic anomalies mainly reflect the distribution of magnetic materials in the crust, especially the obvious magnetic anomalies produced by tectono-magmatic activities, which lays a foundation for the prediction of buried magmatic rocks. Basic-ultrabasic rocks usually have strong magnetic properties and can be identified by aeromagnetic data. Based on 1:1000,000 aeromagnetic anomaly data and its lithology and structure inference results in China, this paper systematically describes the identification and delineation methods of basic-ultrabasic rocks through aeromagnetic anomalies, and analyzes the relationship between inferred basic-ultrabasic rocks and ophiolite belt. The results show that the ophiolite belt usually has the characteristics of narrow width, high anomaly, linear or bead-like magnetic anomaly, which is mainly related to the preservation of the ophiolite. The large-scale ophiolite belts are usually splices of different plates, showing the characteristics of regional magnetic anomaly boundaries, representing the differences in basement properties of different land masses. Small-scale ophiolitic belts, such as those formed by back-arc basin stretching, usually do not divide the regional magnetic field, and the basement properties of the two sides are similar. Based on the inferred distribution of basic-ultrabasic rocks, 22 ophiolitic basic-ultrabasic rock belts are divided in China, and the characteristics of these belts are described in detail. For example, the Yarlung Zangbo ophiolite belt shows double magnetic anomaly zone, the northern zone is large in scale and long in extension, and there are inferred basic-ultrabasic rocks in the deep. The southern zone are small in scale and only distributed continuously in Shigatse, while the rest are beaded magnetic anomalies and do not divide regional magnetic field. Through 3D inversion of magnetic anomalies, the deep structural characteristics of Yarlung Zangbo ophiolite belt are constructed. Through qualitative and quantitative analysis of magnetic anomalies, this paper aims to provide more information for the study of ophiolite belt, especially the hidden ophiolite, in order to guide the chromite prospecting. At present, aeromagnetic survey is mainly carried out on small and medium scale , which is insufficient for ophiolite belt research and chromite exploration, and 1:50,000 or larger scale aeromagnetic data are needed for detailed analysis and deep structure modeling.

      • 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
    • Marine carbonate hardgrounds from the Cambrian Miaolingian Series in southern of North China Plateform: Early seafloor cementation in the absence of bioturbation

      DAI Mingyue, YIN Zhonglei, QI Yongan, HAN Lanlan, CHEN Songhua, QING Shiyun

      Abstract:

      The carbonate hardgrounds developed on oncolitic wackestone and oolitic grainstone in the Cambrian Miaolingian Series in the southern of North China Platform, which sharply truncate the underlying carbonate deposits. In this study, the radial ?brous calcite cements and microcrystalline cements with a thin isopachous rim between the carbonate grains below the hardground surfaces indicate that the cements formed by early marine cementation. In the Cambrian, the early cementation zone was sufficiently close to the sediment-water interface to be susceptible to erosional reworking caused by tidal currents and wave scour,producing carbonate hardgrounds. Simple, planar hardgrounds represent early cemented surfaces which are exhumed during a period of submarine erosion that underwent little modi?cation and bioturbation after exposure. In the study area, the hardground interval from the second member of the Mantou Formation(Cambrian Miaolingian Series) was formed in the intertidal-subtidal channel with the alternation of low to high water energy, inferring that microcrystalline calcite precipitation was the main cementing agent; another hardground interval from the Zhangxia Formation(Cambrian Miaolingian Series) was formed during the high construction oolitic shoals of the platform margins, when the physicochemical precipitation and early seafloor cementation were more active. The occurrence of hardgrounds in the study area suggests that seawater chemistry conditions and benthic ecology were suitable for early cementation of carbonate sediments during this period. As outstanding evidence of early seafloor cementation, hardgrounds are of great significance to the study of early diagenesis and lithi?cation characteristics of carbonate sediments, and their formation process and genesis also provide a major basis for changes in palaeoceanographic conditions and benthic ecosystems.

      • 1
    • Numerical simulation of co-seismic deformation and seismicity following the Pingyuan M5.5 earthquake in Shandong Province on August 6, 2023

      Meng Qiu, WANG Zitao, ZHANG Huai

      Abstract:

      On August 6, 2023, M5.5 earthquake occurred in Pingyuan County, Dezhou City, Shandong Province, causing significant economic losses and ending the nearly 40-year period of M≥5.0 seismic quiet in Shandong Province. The epicenter of the Pingyuan earthquake is located in a densely populated area, with rapid economic development. The changes in regional seismicity resulting from this earthquake and the potential for future strong earthquakes are significant social concerns. We use the finite element numerical simulation with a three-dimensional model to study the co-seismic deformation and stress changes in the seismogenic environment at the epicenter and its surroundings. Additionally, we utilize the assumed rupture model to simulate the co-seismic dislocation. Based on the Coulomb stress change theory, we investigate the seismicity changes in the surroundings. The results indicate that the primary deformation caused by the earthquake is concentrated within 10 km of the seismogenic fault, and the Coulomb failure stress at the epicenter decreases by more than 500 kPa. The probability of a strong earthquake occurring is low in the near future. The Pingyuan earthquake has a significant impact on the seismicity in the surroundings. It may increase the occurrence of slip-type small and medium earthquakes in the north, while reducing the occurrence of normal fault-type earthquakes in the west. Longer seismic data and more comprehensive research are still needed to understand the seismicity changes in the North China Plain and its adjacent faults.

      • 1
    • Huang Jiqing (T. K. Huang) and Chinese Geotectonics Research

      Ren Jishun, Niu Baogui, Zhao Lei, Xu Qinqin, Liu Jianhui, Zhu Junbin, Liu Renyan

      Abstract:

      This paper summarizes the basic content and writing basis of T. K. Huang "s classic work on Major Tectonic Forms of China. We elaborate on the academic style and working methods of Huang T. K and his scientific group, emphasize the importance of field geological investigation, and highlight the use of new scientific concepts and facts to develop geotectonics in keeping with the times. We propose that the geotectonics has been advanced from the study of the crustal structure and lithospheric structure on the Earth’s surface to the new stage of the study of the multisphere tectonics of the Earth system as an integrated whole.

      • 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
    • Late Mesozoic continental deformation, deep processes and geodynamic evolution of South China

      lijianhua, Dong Shuwen, Zhao Guochun, Zhang Yueqiao, Xin Yujia, Wang Jinming, Lu Yunke

      Abstract:

      In the Late Mesozoic, South China’s eastern margin evolved into an active Andean-type convergent margin associated with the subduction of the Paleo-Pacific Plate. The continental crust underwent significant reworking, accompanied by extensive magmatism, providing an ideal natural laboratory to assess the tectono-magmatism, crust-mantle processes, and plate subduction geodynamics along the active continental margin. Here we review the essential constraints of structural deformation, magmatism, and lithospheric architecture. We recognized the Mid-Late Jurassic retro-arc shortening system and the Cretaceous back-arc extensional system, and clarified their spatial-temporal associations and overprinting relationships. The retro-arc shortening involved a northwestward thrust propagation by generating arrays of thin- and thick-skinned thrust systems, multiple decollements, and duplexes in the central Yangtze, possibly associated with the northwestward advancing subduction of the Paleo-Pacific plate. The eastern part of the retro-arc system was tectonically overprinted by several extensional and contractional events during the Cretaceous, accompanied by the flare-up, lull, and resumption of magmatism. The tectonic switching between contraction and extension was governed by changes in the slab dynamics, i.e., slab steepening and shallowing in retreating and advancing subduction settings. Despite these deformation episodes, lithospheric extension dominated the Cretaceous evolution, generating a wide (>800 km) back-arc extensional system comparable to the American Basin and Range. We analyzed the long-distance lithospheric extension and surface response by compiling all available geophysical and geological observations. The compiled data suggest a depth-dependent deformation mechanism, with vertical and lateral variations in extension modes as a function of lithospheric strength. The extensional strain fields are uniformly orientated ~NW-SE throughout the lithosphere, indicating vertically coherent deformation. Stress transmission across this coherent system likely occurred via basal traction and localized mantle shearing. Basal traction at the lithospheric base, imposed by rollback-induced mantle flow, might have integrated over long distances and caused passive stretching of the lithospheric mantle. Localized mantle shearing generated high-strain mantle shear zones that acted as strain-transfer structures, enhancing the simple shearing at the crust-mantle interface and promoting ductile stretching in the lower crust. We emphasize the tectonic coupling between slab rollback, mantle flow, and lithospheric extension. The driving forces of lithospheric extension are attributed to a combination of (1) far-field effects of slab rollback and trench retreat and (2) basal shear tractions imposed by mantle flow.

      • 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
    • Organic-matter-rich tentaculitid shales of the Devonian in the region from the southern Guizhou to central Guangxi province of South China: An importantly potential target rock for shale-gas exploration

      MEI Mingxiang, Cen Wenpan, Muhammad Riaz

      Abstract:

      The Devonian is a special geological time that was marked by an episode of Earth history noteworthy for the global deposition of organic-matter-rich shales. Within an inter-platform basin facies that is dominated by deep-water deposits in the region from the southern Guizhou to the central Guxngxi, a set of organic-matter-rich tentaculitid shales with the thickness of more than 600 meters was relatively concentrated and developed from the Emsian Age to the Frasnian Age of the Devonian. Following features not only characterize this set of organic-matter-rich tentaculitid shales but also demonstrate it is an importantly potential target rock for shale-gas exploration: 1) a relatively higher total organic carbon (TOC) value of more than 2% that can be up to 5% to 6%; 2) From the Amsian Age of the early Devonian to the middle Devonian, organic carbon content is typically enriched in massive organic-matter-rich tentaculitid shales with the monolayer thickness of more than 100 meters that is formed in the period of third-order relative sea-level rising, and depleted in the calcareous shales and muddy limestones of the shelf facies forming in the period of third-order relative sea-level falling; and 3) Within the Liujiang Formation that is dominated by silicalites of the Frasnian Age of the late Devonian, organic carbon content is typically enriched in massive organic-matter-rich tentaculitid shales with the monolayer thickness from 30 to 40 meters that is formed in the period of third-order relative sea-level falling, and depleted in silicalietes of the pelagic basin facies forming in the period of third-order relative sea-level rising. It can be certain that the accumulation of organic matter within organic-matter-rich tentaculitid shales in study area is controlled by complicated, nonlinear interactions among the three factors: productivity, preservation, and sedimentation rate. More particularly and importantly, the high-density preservation of tentaculitid fossils demonstrates that the accumulation of organic matter within organic-matter-rich tentaculitid shales in study area is genetically related to the biological carbon pump of zooplankton.

      • 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
    • Multidimensional characterization and consideration of mantle heterogeneity and mantle cycle

      郑建平

      Abstract:

      The mantle underwent core-mantle-crust differentiation in the early stage, and then was subjected to the circulation of convection at different scales, resulting in mantle heterogeneity. In the past 30 years, mantle chemistry has gradually established a complete geochemical system of the mantle through the study of oceanic basalt, which has found a variety of mantle end members and non-radioactive isotope evidence and proved the heterogeneity of the mantle. However, it is still unclear how the mantle heterogeneity corresponds to the mantle cycling at the time and space scale, and what the evolution history and law of mantle heterogeneity are. In addition, geophysical studies show that the thickness difference of the upper mantle lithosphere between the ocean and the continent, the velocity anomalies in the middle and lower mantle and the morphology of subduction plates provide evidence for the spatial heterogeneity of the transversal convective system. The combination of geochemical and geophysical methods is very important for the study of mantle heterogeneity, and it has become a consensus to use the "binocular" to see the composition and structure of the mantle well. This paper considers the internal logic of the superficial supercontinent cycle and mantle heterogeneity from the perspective of the combination of the different manifestations of geochemical field and geophysics, and the contrast of oceanic and continental patterns in the present and historical periods. The importance of mantle heterogeneity from the perspective of evolution is emphasized, and the prospect of establishing the mantle cycle driving model by multi-means is proposed.

      • 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
    • Chronostratigraphic Units and its Stratotype Sections of the Ediacaran (Sinian) of South China

      chenqicong, tangfeng, zhangheng, gaolinzhi, renliudong, zhaomingsheng, liyulan, zhanglijun, zhaomengsheng, chenjianshu, wangyue, jiaodeguang, liujunping

      Abstract:

      Based primarily on the geochemical and multiple stratigraphic correlation data from the standard section in the eastern Yangtze Gorges, SW China, the National Stratigraphic Commission (NSC) published a provisional division scheme of the Ediacaran (Sinian) System in 2014. In recent years, this scheme has been challenged by new achievements and understandings from studies in past and current biostratigraphy and isotope geochronology. It is thus imperative to propose a new, more precise division scheme and establish new stage-ranking stratotype sections in order to serve as the standard for future nationwide comparisons of the Ediacaran System, particularly in South China. In light of this, this paper suggests the establishment of top-stage stratotype sections of upper and lower strata for the Ediacaran Series in South China, namely the Jiangchuan Stage and the Wenghui Stage. Firstly, it recommends adopting a biogeological criterion as the primary basis for the biostratigraphic division of the Ediacaran Period. It also suggests the characteristic top and bottom boundary stratotype sections, key fossils, inferred ages, and internal subdivisions for these two stages. Secondly, a preliminary Ediacaran system-stage chronostratigraphic framework (stratigraphic column) is proposed, which includes the tentative names of subdivisions for the upper and lower series as well as other stages, thereby indicating the focus of future work and detailed investigations regarding stratotype sections and comparison regions.

      • 1
    • Geochemistry and zircon Hf-O isotopic characteristics of Late Carboniferous I-type granite in Northern West Junggar: insights into petrogenesis and tectonic process

      Zhang Rui, YIN Jiyuan, QIU Liang, TAO Zaili, YANG Fan, CHEN Wen

      Abstract:

      Many late Paleozoic granitic intrusions occur in the West Junggar region, however the petrogenesis of these granites and their tectonic setting remain subjects of debate. In this study, we present new petrology, geochemistry and zircon Hf-O isotopic compositions of the biotote syenogranites found in the Aerjiati Mountain, located in the northern Western Junggar. Our objective is to elucidate the origin and tectonic setting of these granites and explore the relationship between these granites and juvenile crustal growth. Zircon U-Pb dating of two samples indicates that these biotite syenogranites formed during the late Carboniferous, with ages of 301.8 ± 1.4 Ma and 303.7 ± 3.1 Ma. These samples contain hornblende and are characterized by high Si (SiO2=67.8~68.9%), Al (K2O+Na2O=9.36~9.89%) contents, but low A/CNK ratios (0.96~1.00), Ga/Al (2.27~2.34) and Rb/Sr (0.35~0.50) contents, consistent with the geochemical features of I-type granites. They are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), depleted in high field strength elements (HFSEs)(e.g., Nb, Ta, Ti), with negative Eu (δEu=0.72~0.85), akin to typical subduction-related island arc magmas. These I-type granites exhibit high and positive εHf(t) values and young TDM2 (392~604 Ma). Their δ18O (5.73~6.51‰) values are slightly higher than that of the mantle. They also display high Zr contents and zircon saturation temperatures (Tzr=854~895℃), implying that they originated from partial melting of juvenile lower crust in a high temperature geological setting. Previous studies have indicated the presence of high temperature I-A type granites, high-Mg andesite and adakitic dikes in the northern West Junggar. Combined with previous findings, we propose that these high-temperature rock associations were likely generated by ridge subduction and the formation of a slab window. The ridge subduction led to the upwelling of hot asthenospheric mantle, triggering partial melting of the juvenile lower crust formation of I- and A-type granites. Most of the lower crust was formed in the early Paleozoic, suggesting a significant contribution of juvenile crustal growth during the Phanerozoic in the West Junggar.

      • 1
    • Two-stage evolution of the Late Paleozoic Liuyuan Ocean in the southern Beishan region, Central Asian Orogenic Belt

      NIU Yazhuo, Zhang Dongdong, Yang Bo, Shi Jizhong, Zhang Yuxuan, Zhou Junlin

      Abstract:

      The Central Asian Orogenic Belt is the largest accretionary orogenic belt in Earth’s history and the long-lived evolution of the Paleo-Asian Ocean (PAO) stands as a prominent geological focal point worldwide. The Liuyuan Ocean is one of the critical branches of the PAO in the Beishan region, NW China. Its evolution perhaps spans from the Ordovician to the Permian, but the incomplete sedimentary and magmatic records result in divergent interpretations for the Liuyuan ocean/rift basin such as persisting subduction and two-stage evolution. This study reports the sandstone composition and detrital zircon U-Pb-Hf isotopic results from the Upper Paleozoic volcanic-sedimentary sequence in the Dushan area, Shibanshan Block. A two-stage evolution model is proposed for the Paleozoic evolution of the Liuyuan ocean according to the statistical comparison through published provenance data in the southern Beishan region. During the Middle Ordovician to Middle Devonian, bidirectional subduction of the Liuyuan Ocean led to two magmatic arcs (~415 Ma and ~450 Ma) on the margins of the Dunhuang–Shibanshan and the Shuangyingshan Block, respectively. The Liuyuan Ocean closed in the Late Devonian and an integrated continental margin environment occupied the Dunhuang–Dushan–Shuangyingshan blocks until the Late Carboniferous. Detrital rock samples from the southern Beishan area exhibit multiple Precambrian peaks in the age spectrum (~983 Ma, 1302 Ma, 1449 Ma, 2492 Ma). From the Early to Middle Permian, the Liuyuan rift basin gradually developed into an oceanic basin, essentially separating two source-to-sink system systems delineated by the Liuyuan ophiolite belt. The southern system was dominated by detritus from Carboniferous-Permian volcanic rocks (~289 Ma), whereas the northern one was characterized by fragments from Ordovician-Silurian intrusive rocks.

      • 1
    • Geochemical characteristics and tectonic significance of podiform chromite in the Dongqiao in the middle part of the Bangong -Nujiang suture zone, Tibet

      Zhangboyang, Xiongfahui, Xuxiangzhen, Qiutian, Zhangchengjie, Helanfang, Wangtianze, Yangjingsui

      Abstract:

      The Dongqiao ophiolite, located in the northern part of the middle part of Bangong -Nujiang suture zone, is composed of mantle peridotite and chromitite, and the mantle peridotite is manily harzburgite and dunite. Chromite is mostly lenticular and banded, and often with dunite cladding, both of which occur in the harzburgite dyke. The olivine Fo values (91.2~92.9) and Cr# values (70.16~76.60) of the para-mineral chromium spinel in the mantle peridote of Dongqiao are high, which are similar to Dingqing, Qielihu and Yilashan rocks in the Banong-Nujiang suture zone, indicating that the Dongqiao ophiolite has experienced a high degree of partial melting. The chemical composition of chromium-spinel of Dongqiao chromitite indicates that there are both high chromium-type chromitite (Cr# value is 60.67~82.67, Mg# value is 54.45~68.08) and high aluminum-type chromitite (Cr# value is 56.36~59.62, Mg# value is 67.20~72.68) in the ophiolite. The REE characteristics of the mantle peridote in Dongqiao show that it has the characteristics of pre-arc mantle peridote, and the trace element partitioning pattern is very similar to that of Izu-Bonin-Mariana, indicating that the Dongqiao ophiolite may have formed in the ocean floor spreading environment of plate subduction zone. The PGE element partitioning pattern of chromite is similar to that of Lobusa chromitite, which is characterized by enrichment of IPGE and loss of PPGE. The analysis of Dongqiao mantle peridotite and its chromite equilibrium melt shows that high-chromium type chromitite was formed in SSZ type forearc basin, high-aluminum type chromitite was formed in MORB type environment, and the adjacent ophiolite of Bangong -Nujiang suture zone indicates that Dongqiao mantle peridotite and its chromitite have undergone MOR→SSZ multi-stage evolution process. In the transition zone from dunite cladding to banded disseminated chromitite, Cr# value increases (67.22~68.48) and Mg# value decreases (57.35~74.56), which reflects the existence of different degrees of partial melting in the mantle source region. It is further indicated that the mantle peridotite and its chromitite may have undergone melt-rock reaction to a certain extent.

      • 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
    • Structural Generation and Its Application in Ore-prospecting

      Chen Bailin

      Abstract:

      Tectonic generation is an important concept of geomechanics and tectonic geology. Tectonic generation refers to the sequence in which structural planes with different mechanical properties and different orientations are formed in the same crustal movement under the continuous action of the same period and the same dynamic action mode, or because of the local change of boundary conditions, the structural features are controlled in turn. Structural generation emphasizes the genetic relationship between structural features and is the basis for determining structural types and establishing structural systems. The structural generation relationship is very common, which is different from the structural level. Different generation structures have the characteristics of time difference, derivation, absoluteness and invisibility. Low-order structures are often distributed within the influence range of higher-order structures and controlled by local stress fields. The study of ore-controlling structures should be from low order to high order. Starting with ore-bearing structure investigation, analyzing the mechanical properties and combination laws, then, the ore-controlling structure types are determined, and the ore-controlling laws of structures are summarized. The ore-prospecting prediction should be from high order to low order. According to the ore-controlling type of structure and the control law of structure generation, the possible position and direction of low-order ore-bearing structures are analyzed and the ore-prospecting prediction is carried out. Through the structure generation analysis of ore-controlling structures, it is considered that the Zoujiashan uranium deposit is not controlled by the NE-trending Zoujiashan-Shidong fault, but by the NEE-trending hidden structural belt with medium-low dip angle dipping to NNW, and the prospecting direction is along the SWW direction of the existing ore belt and the deep part with medium dip. In the Changjiang uranium ore field, uranium mineralization is not controlled by Mianhuakeng fault and Youdong fault, but by NNW (near SN)-trending structural belt with steep dip angle. The shallow secondary fault is ore-bearing (or ore-storing) structure, and the main structural belt merged from them and extended to the deep plays the role of guiding mineralization and transporting ore-forming hydrothermal solution (distributing of deposits). The ore-prospecting direction is the extension and deepening part along the NNW (near SN) –trending ore-bearing structure and the deep part of the surface mineral-free zone. When analyzing the structural generation, we should pay special attention to the genetic relationship of structural features, and also pay attention to structural periods. We should distinguish the structures before mineralization, during mineralization and after mineralization. Within a specific ore field, deposit or mineralization zone, we should objectively analyze the relationship between ore-guiding structures, ore-transporting (ore-matching) structures and ore-storing (ore-bearing) structures (that is, the relationship between ore-controlling structures and ore-bearing structures), then determining an ore-controlling structural type, constructing a structural ore-controlling model, and finally guiding the practice of ore-prospecting and prediction.

      • 1
    • Progress of prospecting prediction research for karstic bauxite in China

      lou debo, Zhang Qizuan, Jiang Sha, Liu Huan, Li Wanyue, Dong Jianhui, Zhou Shangguo, Chen Xu

      Abstract:

      The majority of bauxite in China (>90%) is karstic and widely spreads with the North China Craton and southwestern South China Block . In recent years, as a kind of strategic scarce mineral resource, prospecting prediction for bauxite is extremely urgent. It is very important to get knowledge for bauxite prospecting from historical experience by systematically summarizing progress of prospecting prediction research and effectively constructing optimal combination of prospecting prediction methods. By combing the prospecting advances of geology, geophysics, geochemistry, remote sensing and artificial intelligence for geological big data, it is stated clearly that geology and geophysics are still the most major methods for karstic bauxite prospecting prediction at present. At the same time, the reason why geochemistry and remote sensing are not good at exploring ancient karstic bauxite is analyzed and the importance of developing artificial intelligence prediction based on geological big data in the future is pointed out.

      • 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
    • Fig. 1 Schematic map of geological structure in Karamay-Baikouquan area, Western Junggar (a-schematic map of geological structure and stratigraphic area of Junggar; b- Stratigraphic subdivision map of Junggar(modified from Li et al., 2021)

      Li yongjun, HUANG Jiaxuan, Zhu zhao, Wang xulong, Peng Nanhe, YANG GaoXue, ZHENG MengLin, ZHANG YueQian

      Abstract:

      A new set of red marine sedimentary assemblages (siliceous, silty siliceous and tuffaceous siliceous rocks) with ages of late Devonian has been found in the Hongshanliang section of the northern Baijiangtan in the Baogutu stratigraphic minor-region, West Junggar. It is conformable contact with the dark-gray to gray-black carbonaceous siltstones of the overlying Baogutu Formation. Regional correlation confirmed that this set of strata is significantly different from all the Upper Devonian strata in the study area and even in the whole West Junggar stratigraphic area. This sedimentary sequence is suitable for the "four principles" of "field recognition, interface distinction, regional correlation and map expression". Therefore, a new Hongshanliang Formation was established. LA-ICP-MS zircon U-Pb ages of 365.9±5.0Ma, 370.6±7.4Ma and 374.6±3.6Ma were obtained from Hongshanliang basalt, pillow basalt and andesite, respectively, indicating a Late Devonian age. The confirmation of the continuous deposition of Hongshanliang and Baogugu formations not only eliminates the doubt of the Baogutu Formation older than the Xibeikulasi Formation , but also supplements the complete stratigraphic sequence of lower Carboniferous, and adds the Devonian sedimentary records in the Baogutu stratigraphic minor-region. This provides new data for the study on regional sedimentary and tectonic evolution of West Junggar.

      • 1
    • Biotite in highly evolved granite from the Zengjialong Sn ore deposit, China: Insights into magma source and evolution

      Sun Keke, Chen Wei

      Abstract:

      Tin is an important strategic key metal and the study of its mineralization laws has valuable theoretical significance and economic value. Primary Sn mineralization is generally associated with highly evolved and relatively reduced granitic magmas. Compared with common granites, Sn-rich highly evolved granites often undergo complex evolution processes. We can’t obtain the early-stage magmatic compositions based on whole rock geochemistry analyses, which only represent the information of the last evolved samples, hindering our understanding of magmatic source and their evolution details. In addition, the explains for the whole rock analyses are not unique. Minerals crystallized in magma such as quartz, biotite, apatite can record the dynamic composition changes and fine evolution processes of magma that are difficult to reflect in whole rock analyses, showing unique advantages in the study of petrogenesis of granite. In this paper, we present a comprehensive major and trace element (including halogen) dataset for biotites from highly evolved granites in the Zengjialong Sn ore deposit. Biotites in the Zengjialong granite have a magmatic origin. They are characterized by low Mg# (5.70―9.93, mean = 7.63), high A/CNK values (1.77―1.98, mean = 1.88), similar to biotite compositions in S-type granites worldwide, suggesting the parental magmas were of meta-sedimentary origin. Biotite trace elements show that as the K/Rb ratios decrease, the Rb, Cs, and Sn increase and Pb decrease, indicating that the magma has experienced crystal fractionation dominated by K-feldspar. Tin contents in biotite increase by 4 times due to progressive fractional crystallization, indicating the Sn riched in the residual magmas. Biotites have low IV(F), IV(F/Cl), log(fHF/fHCl) and high IV(Cl) values, along with the negative relationships between IV(Cl) and IV(F/Cl), log(fH2O/fHF) and log(fHF/fHCl), suggesting the Zengjialong magma is F-rich and Cl-depleted magma system and the biotite crystallization process is accompanied by continuous fluid exsolution. The biotites in Zengjialong granite contains almost no Fe3+. In the Fe3+—Fe2+—Mg triangle diagram, the biotites are located below the FMQ line, indicating a low oxygen fugacity. The biotites in the Zengjialong granite record that the magma has an enriched source, high degree of differentiation, low oxygen, and continuous fluid exsolution. These processes are conducive to the tin enrichment and mineralization. Our study shows that biotite geochemistry data can be used to distinguish different magmatic-hydrothermal mineralization (Cu, Mo, W, and Sn) systems.

      • 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
    • Spatiotemporal distribution, geological-geochemical characteristics, metallogenic mechanism and tectonic setting of orogenic gold deposits in the Cathayisa Block: A review

      JIANG Shao-Yong, MA Ying

      Abstract:

      Orogenic gold deposits have important economic value, and the study of their metallogenic theory is of great significance to the development of gold exploration and economic geology. The Cathaysia Block is an important W-Sn-Ag-Pb-Zn polymetallic metallogenic belt in China. In recent years, dozens of orogenic gold deposits have been discovered in the metamorphic terranes of the Cathaysia Block, which provides a new topic for the study of metallogenic theory in this area. Compared with the research on the W-Sn polymetallic deposits in the Cathaysia Block, the research on the orogenic gold deposits in the region is obviously weak, and the metallogenic mechanism has not yet been summarized. The orogenic gold deposits in the Cathaysia Block mainly include the Shuangqishan and Hebaoshan deposits in the Wuyishan area of eastern Cathaysia, the Hetai deposits in the Yunkai area of western Cathaysia, and the Baolun deposit on Hainan Island. This paper focuses on the geological-geochemical characteristics of these four typical deposits, the age of mineralization, the sources of ore-forming fluids and materials, and systematically summarizes the existing data and literature to elucidate the spatio-temporal distribution pattern, mineralization mechanism and geodynamic background of the orogenic gold deposits of the Cathaysia Block. It is found that the orogenic gold deposits in the Cathaysia Block mainly developed disseminated- and quartz-sulfide vein-type mineralization, and the gold orebodies are mianly hosted by Precambrian metamorphic rocks and controlled by brittle-ductile shear zones. The ore-forming fluids are dominated by the H2O-CO2-NaCl±CH4±N2 system, and the main mineralization stage is mainly at the temperature of 220~280°C. The mineralizing fluids may be of metamorphic, mantle or magmatic hydrothermal origin, and the fluid immiscibility, increasing oxygen fugacity and bismuth melt trapping of the hydrothermal system are the important mechanisms for the precipitation of gold ores. There are three periods of orogenic gold mineralization in the Cathaysia Block, namely the Caledonian, Indosinian and Yanshanian periods, which correspond to the geodynamic backgrounds of intracontinental orogeny, subduction and retreat of the palaeo-Pacific plate, respectively.

      • 1
    • Summary of the exploration achievements and gold mineralization of Jiaodong Xiling super large gold deposit

      jia

      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
    • The volcanic-intrusive rock sequences and metal mineralizations in rifted basin in the eastern Yunnan Province, China

      FANG Weixuan, LI Tiancheng, GUO Yuqian

      Abstract:

      Alkali magmatism have special controlling on mineralizations in the metal ore-concentrated areas. However, obstacles have all the time placed on the deep exploration and mineral predication in the study area, for cognitive difficults exist on the volcanic-intrusive rock sequsences, metal mineralizations, and the magmatic superimposing intrusive tectonic system. Focused on the Dongchuan Fe-Cu-Au ore concentrated area (the Proterozoic marginal rifted basin) and the Gejiu Sn-Cu-W-Cs-Rb- polymetal ore-concentrated area (the Triassic arc-back rifted basin), the innovated mapping techniques of the tectonic lithofacies had been applied to dissect study on the volcanic-intrusive rock sequences related to the alkali magmatic activity, rifted basin evolution, rock associations, and magmatic superimposing intrusive system, in order to disclose the superimposing mineralizations of IOCG, Cu-Co-rutile deposits and Sn-Cu-W-Cs-Rb polymetallic deposits in the eastern Yunnan Province in China. This study suggests as the followings. First, the Neoarchean alkali rocks are composed of calcite albitite(2520±14 Ma)and Fe-rich alkalipicrite(2529±77Ma)in the Dongchuan Fe-Cu-Au ore-concentrated area. The Neoarchean-Paleoproterozoic Xiaoliukou Formation Complex(>2.50Ga)and its top part, a special mapping unit with homotopy in different lithofacies(2.5 to 1.80 Ga), are the new hosting strata of Cu-Co-rutile-REE mineralizations and had been reworked by the superimposed by the Mesoproterozoic volcanic-intrsuive rocks in the Dongchuan Fe-Cu-Au ore-concentrated area. Second, in the Mesoproterozoic the first member of the Yinmin Group, alkaline rocks, including rock assications of Fe-Na-rich alkali basic rocks, Fe-K-rich trachyte, and Fe-rich alkali diabase-gabbros, were formed at the Mesoproterozoic stage of volcanic rifting basin. Xikuangshan-type Fe-Cu deposits or IOCG deposits were hosted at the second to three members of the Mesoproterozoic Yinmin Group, Moreover, Fe-K-rich trachyte at the footwall of the Fe-Cu orebody hosted the monazite-type REE mineralization layer. IOCG system and rutile superimposing mineralization were formed in alkaline Ti-Fe-rich gabbros (1097 to1047Ma), alkaline Ti-Fe-rich diorites, and alkaline monzoporphyry, all of these rock associations were formed during the Greenville Orogeny in eastern Yunnan. Third, the Triassic alkalipicrite and tephrite with primary enrichment of Sn-Cu-Zn-Li-Rb-Cs were produced at the of the Triassic arc-back rifted basin in the Gejiu area at the Eastern Yunnan Province in China. While they were superimposed by leucogranite, and they were responsibly for Sn-Cu-W-Cs-Rb-bearing phlogopite-type skarn. Final, alkali rocks with initial enrichment of metals or mineralization in the early stage of the rifted basin, were superimposed by alkaline intrusive rocks with metal mineralizations at the late stage, which may be main hypernormal mechanism for metal mineralizations the rifted basin at the Eastern Yunnan Province in China. Breccia-pipe of magmatic hydrothermal fluids in the alkaline magmatic superimposing intrusive tectonic system has evident controls on hypernormal enrichment of Cu-Co-rutile-REE superimposing mineralization, whereas leucogranite intruded the alkalipicrite and tephrite with Sn-Cu-W-Cs-Rb primary enrichment are responsibly for hypernormal enrichment of Sn-Cu-W-Cs-Rb-bearing phlogopite-type skarn.

      • 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
    • From the Yanliao sill swarms in the North China Craton to the large–scale continental rift system in the Columbia supercontinent

      Zhang Shuanhong, ZHAO Yue, PEI Junling, YANG Zhenyu, HU Guohui, ZHANG Qiqi

      Abstract:

      Twenty years of research on the Yanliao sill swarms intruded into the Mesoproterozoic strata in the northern North China Craton (NCC) shows that the Yanliao sill swarms constitute a ca. 1.32 Ga mafic large igneous province (LIP) termed as the Yanliao LIP, which is coeval with the REE–Nb rich carbonatites in the Bayan Obo giant REE deposit on the northwestern margin of the NCC. A comparison of intraplate mafic events interpreted as LIPs or portions of LIPs (LIP fragments/remnants due to continental breakup or erosion) from the NCC and North Australian Craton (NAC), in combined with paleomagnetic data indicate that the northern–northeastern margin of the NCC had been connected to the northern margin of the NAC for almost 500 Ma from ca. 1.8 Ga to 1.3 Ga. Spatial and temporal distributions of the 1.4?1.3 Ga LIPs and smaller intraplate mafic magmatic events (interpreted as LIP fragments/remnants) in the refined paleogeographic reconstruction map of Columbia supercontinent, together with previous petrological, geochemical and isotopic results reveal a 1.4–1.3 Ga large-scale continental rift system extending about 15000 km across the Columbia supercontinent. This huge continental rift zone extends along the western Laurentia (North America and Greenland), western–northern Siberia, southeastern Baltica, western–northern West Africa, southwestern Amazonia, southern–eastern Congo/S?o Francisco, eastern Kalahari, northern NCC and northern NAC and consists of a main rift zone and three branch rift zones. The main rift zone along western Laurentia, western–northern Siberia, southeastern Baltica, western–northern West Africa, southwestern Amazonia, southern–eastern Congo/S?o Francisco, eastern Kalahari, northern NCC and northern NAC and the rift zone branch between the NAC and NCC had developed to the drifting stage (new oceans) and resulted in fragmentation and final breakup of Columbia supercontinent. However, the other two rift zone branches including one extending to eastern Siberia, northern Greenland and eastern Baltica (1.38 Ga), and another extending to northern North America and southwestern Siberia (1.35–1.32 Ga) are most likely failed rifts and haven’t resulted in separation of Siberia from Laurentia and Baltica, respectively. The 1.4–1.3 Ga large-scale continental rift system is considered as the main indicator and a proximal reason for final breakup of the Columbia supercontinent. This newly identified huge continental rift zone system had also controlled the distributions of the world's first and second largest REE-Nb deposits (the Bayan Obo deposit on northwestern margin of the NCC and Mountain Pass deposit in western Laurentia) and is most likely a favorable metallogenic belt for other carbonatite-related REE(-Nb) deposits and other metallogenic types such as giant clastic-dominated Zn-Pb-Ag deposits. Future research directions are suggested to focus on the emplacement mechanism and magma plumbing system of the Yanliao LIP, quantitative estimation of greenhouse gases released during emplacement of the Yanliao sill swarms and their environmental effects, the mechanism and deep processes for formation of the 1.4–1.3 Ga huge rift system, and global environmental effects and resource potentials of the 1.4–1.3 Ga large–scale rift system.

      • 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
    • Relationship between deep density structure and seismic in Bomi area of Tibet

      FAN Pengxiao, YU Changqing, WANG Ruixue, ZENG Xiangzhi, LI Weiqiang, ZHANG Yue

      Abstract:

      The Bomi region of Tibet is located in the northeast of the Namche Barwa tectonic junction.It is a key area for studying the evolution of tectonic junctions in the eastern Himalayas.At the same time,it holds great significance for the Sichuan-Tibet Railway project, which is a key transportation initiative during the Fourteenth Five-Year Plan period. Therefore, it is crucial to study the stability and safety of the region"s deep geological structure. However, the scarcity of geophysical data in the area, due to limitations in geological and geomorphological conditions, has resulted in limited research on the relationship between deep density structure and seismic in the Bomi region.This thesis obtains 1:200,000 bouguer gravity data in Bomi region for the first time.First,we used the wavelet transform multi-scale decomposition method, scratch analysis method and gravity 3D inversion method to divide the tectonic activity unit, we obtained the gravity anomalies of different , faults distribution and density structures. The analysis results show that the overall crust density in the Bomi region changes significantly, which is closely related to the fault distribution. At the same time, combined with the regional geological data,our inferred 20 faults in the Bomi area、found 4 large transverse density uneven zones and deduced the occurrence of Jiali fault zone which runs through the study area. In addition, using the seismic and aftershock activity records in the area, analyzing the relationship between deep density structure and earthquake. Finally, according to the transverse variation of fault structure density, seismic activty and gravity anomaly in the study area, it can be seen that the seismic, fault zone and rock density disturbance are closely related to the transverse unevenness, and the earthquakes are mainly located in the high-density area of the density difference zone. Based on the above analysis, We discussed the potential influence of deep density structure on major railway projects----Sichuan-Tibet Railway in Bomi area is discussed, and corresponding suggestions are put forward.

      • 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
    • Application of Compressed Sensing frequency lifting method in seismic data processing of well W1 in the Yingqiong Basin

      LI Lei, WANG Xiangchun, LIU Mengling, LIAO Yi, ZHANG Guodong

      Abstract:

      In order to solve the problems of low resolution seismic data and complex sand body distribution and overlapping relationship in Yingqiong Basin, a complete data processing process including preprocessing, denoising, migration and bias post-processing is designed based on the original data of three years. In post processing, compressed sensing frequency lifting method was applied to pre-stack depth migration profile, and compared with blue filtering frequency lifting method and zero phase deconvolution frequency lifting method. The advantages of compressed sensing frequency lifting method were demonstrated, and the application of compressed sensing frequency lifting method to solve current geological problems proved its rationality in the subsequent development and implementation of the Yingqiong Basin. The results show that compared with the other two frequency lifting methods, compressed sensing frequency lifting method can protect the reliable low frequency information below the main frequency, expand the high frequency, and improve the data resolution. By comparing the waveform inversion results before and after compressed sensing frequency lifting, the superimposed characteristics of sand bodies can be revealed, and it is also helpful for the subsequent inversion work. As a new seismic data processing method, compressed sensing frequency lifting method can better solve the problems of low seismic data resolution, sand body distribution and complex overlapping relationship, and it is worth popularizing and applying in practical seismic data processing.

      • 1
    • LIAO Libing* 1), ZHANG Peijun1), LIU Hao2)1 School of Materials Science and Engineering, China University of Geosciences (Beijing), Beijing 100083, China

      Liao Libing, zhang peijun, Liu Hao

      Abstract:

      Palygorskite is a 2:1 type chain-layered structure hydrated magnesium aluminosilicate mineral with important resource and material attributes. The isomorphic substitution in the octahedron of palygorskite varies greatly with different genesis and occurrence, but the influence of isomorphic substitution in the octahedron on properties of palygorskite has not been reported. In this work, three representative palygorskites from Anhui Mingguang, Jiangsu Xuyi and Gansu Linze in China were taken as the research objects. The contents and octahedral occupation of Al, Mg and Fe of the three palygorskites were studied, and the effects of the octahedral occupation of Al, Mg and Fe on the types and contents of water, surface potential and acid sites, and the adsorption capacity for Pb2+ and Cd2+ of palygorskite were discussed. The results showed that Mingguang palygorskite was relatively rich in magnesium, while Xuyi and Linze palygorskites were relatively rich in aluminum and iron. The octahedra of Mingguang palygorskite was mainly occupied by Mg2+, showing three-octahedron characteristics; the octahedra of Xuyi palygorskite had relatively more Al3+, showing more two-octahedron characteristics; Linze palygorskite also showed two-octahedron characteristics, and the cation occupation was similar to that of Xuyi palygorskite. Due to the large number of vacancies at M1, Xuyi palygorskite had lower structural water content; isomorphic substitution of palygorskite had little effect on Zeta potential; Xuyi and Linze palygorskites with two-octahedron characteristics had higher Al content in octahedra, more acid sites, and better catalytic performance. In the heavy metal adsorption experiment, Mingguang palygorskite had the largest adsorption capacity for Cd2+, Xuyi palygorskite had the largest adsorption capacity for Pb2+, and Linze palygorskite had poor adsorption performance. This work can provide guidance and reference for the modification and application of palygorskite.

      • 1
    • The occurrence state and geological significance of nanoscale colorants in red bed sandstones: a case study of red sandstone of Lower Cretaceous Zhidan Group, Ordos Basin

      MA Yong, YANG Chengyu, CAI Chao, QIN Changcai, ZAHGN Zhaohui, LI Lei, ZHONG Ningning

      Abstract:

      Red beds are widely distributed sediments on Earth with specific environmental significance. It is generally believed that hematite cement formed under water oxidation conditions is the main color-producing mineral. At present, the research on red-bed coloring minerals mostly remains at the level of mineral identification, lacking in-depth study on their microscopic occurrence states and genetic mechanisms. Taking the continental red beds of the Lower Cretaceous Zhidan Group in the Ordos Basin as an example, this paper adopts multi-scale characterization techniques of core, thin section, cathodoluminescence, and argon ion polished scanning electron microscopy to reveal the microscopic occurrence of nano-scale colorant-hematite cement in red bed sandstone for the first time, and re-explore its genetic mechanism on this basis. The study found that the colorant of red bed sandstone, hematite cement, is mainly needle-like or sheet-like, with two microscopic occurrence states: one is encapsulated and developed around the edges of clean sandstone particles, with individual mineral particles ranging in length from 500-1000nm and width below 50nm; The other type of filling development occurs in the cleavage fractures of clay minerals and mica particles, often arranged in a directional manner along the cleavage. Due to the spatial constraints of the cleavage fractures, individual mineral particles are smaller, with lengths generally less than 500 nm and widths below 30 nm. The occurrence and occurrence state of hematite in red bed sandstone indicate that it was formed by the early dehydration of limonite, followed by the development of two phases of calcite cementation. Therefore, hematite cementation should mainly occur during the sedimentation and shallow burial periods, rather than during the uplift period after sedimentation. The formation process of hematite cement in sandstone indicates an environment characterized by high atmospheric water oxygen content under a dry inland sedimentary background, which is also a glacial state during the geological history. This suggests that the red sandstone of the Lower Cretaceous Zhidan Group in the Ordos Basin also has important implications for studying the global glacial state during this period.

      • 1
    • Late Quaternary segmentation activity of the southern part of the Karakorum fault and a study of the Chaxikang surface rupture

      Hanshuai

      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
    • Identification of the middle Neoproterozoic (750 ~ 740 Ma) bimodal volcanic rocks in the Western Dabie orogenic belt, central China: Constrains for the tectonic evolution of the Yangtze Block

      XU Yang, JIN Xinbiao, DENG Xin, LIU Hao, ZhANG Weifeng, WANG Zhanling, YANG Zhenning, LI Ningning

      Abstract:

      It still remains controversial whether the Neoproterozoic tectonic setting of the northern margin of the Yangtze Block shifted from a compressional setting to an extensional setting at 820 ~ 800 Ma, or remained a subduction setting until ~ 700 Ma. Our new identification of the Taohua bimodal volcanic rocks in the Western Dabie orogenic belt provide new constraints on the Neoproterozoic tectonic evolution and dynamic mechanism of the Yangtze Block. The SIMS and LA-ICP-MS analysis on zircons from these bimodal volcanic rocks yield consistent U-Pb ages of 750 ~ 740 Ma. The basic volcanic rocks are tholeiitic, and exhibit N-MORB-like to arc-like trace element patterns, with variable whole-rock εNd(t) values (-0.05 ~ +5.96). These basic rocks were probably generated by decompression melting of a depleted asthenospheric mantle, and magma subsequently underwent fractional crystallization and wall-rock contamination. Among the acid volcanic rocks, rocks from the Xumengzhai area are enriched in silicon (SiO2≥75%), alkalis (K2O+Na2O≥7%), REE and HFSE (i.e., Zr、Hf、Nb、Y), with high Zr+Ce+Y+Nb (≥ 600×10-6) and 10000*Ga/Al ratios (≥ 2.6), showing a close affinity to fractionated A-type granites. Their evolved zircon εHf(t) (mostly of -12.32 to -1.88) and whole-rock εNd(t) (-13.29 ~ -9.60) values indicate an evolved crustal source region, which may be generated by partial melting of Early Neoproterozoic magmatic rock rocks in the region and the magma underwent fractional crystallization. Integrating the new data with previous results for Neoproterozoic rocks from the South Qinling-Tongbai-Dabie-Sulu orogenic belt, we propose that the 780~635 Ma bimodal magmas in this belt were probably formed in a continental rift environment with episodic extension-related asthenosphere upwelling and lithosphere thinning during the middle of Neoproterozoic. Melting of asthenosphere, lithospheric mantle and crust under high-temperature and low-pressure conditions, coupled with interactions between the asthenosphere and the lithosphere, played a prominent role in the formation of the 780 ~ 635 Ma bimodal-type volcanic rocks and diverse geochemical features in the magmatic counterparts.

      • 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
    • Mid-Holocene sea-level fluctuation in the Fujian coastal area: evidence from ostracod records of Core NDQK5

      JIA Baoyan, Peng Bo, WANG Jilong, YU Junjie, ZHOU Baochun, ZHAO Quanhong, LI Baohua, WANG Yaqiong

      Abstract:

      The Quaternary deposits are widely distributed in the Fujian coastal area where is the ideal place to study the relative sea level changes since the late Pleistocene. Based on AMS 14C and optical stimulated luminescence (OSL) dating techniques, the high-resolution ostracod records from the Core NDQK5 obtained from Ningde of Fujian Province were used to reconstruct the relative sea level changes in this area during the mid-Holocene. Ostracods occurred at the depth interval of 4~17.1 m in Core NDQK 5 corresponds to about 8.2~6.9 cal. ka BP. Twenty-six marine ostracod species belonging to twenty-three genera are recovered from the core samples. On the basis of the relative abundance of main ostracod elements, three ostracod assemblages were identified. The ostracod assemblage A dominated by Bicornucythere bisanensis and Sinocytheridea impressa indicates a subtidal zone environment; the assemblage B with dominant species Sinocytheridea impressa and Neomonoceratina delicata represents the nearshore inner shelf; the assemblage C with the dominant species Sinocytheridea impressa and Loxoconcha ocellifera indicates the intertidal zone environment. Our ostracod data pointed out that a continuous sea level rise occurred in the Fujian coastal area since ~ 8.2 cal. ka BP, and the sea level reached the highstand during the period of 7.9 to 7.4 cal. ka BP; a fall in seal level existed in the period of 7.4~7.0 cal. ka BP, and then a minor sea level rise has been recognized. Hence, our results indicate that several minor fluctuations in sea level existed in the Fujian coastal area during the Holocene sea-level highstand period. Combined with the previous studies, we conclude that the sea level change in the Fujian coastal area was probably controlled by the meltwater from the ice sheet during 8.2~7 cal. ka BP; however, it was probably controlled by Glacio-hydro Isostatic Adjustment (GIA) effect after 7 cal. ka BP.

      • 1
    • Spatial-temporal distribution, resource potential and exploration progress of carbonatite-type rare earth deposits in central and southern AfricaTANG Wenlong1),2)

      Tang Wenlong

      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
    • Geochemistry and Petrogenesis of Early Paleozoic alkaline rocks in the South Qinling Belts: research progress and prospects

      LAI Shaocong, Yang Hang, Zhang Fangyi

      Abstract:

      The South Qinling belt experienced large-scale and continuous alkaline magmatism during the Early Paleozoic, and the record of alkaline rocks provides a valuable geological vehicle for exploring the deep material composition, magmatic evolution, physicochemical environment and geodynamic evolution of the region. This article aims to provide a comprehensive understanding of the source area and evolution of early Paleozoic alkaline magmatism in the South Qinling Mountains, based on the team's recent work on the genesis of typical alkaline rocks in the region. The Early Palaeozoic alkaline rock types in the South Qinling belt mainly consist of a bimodal suite with a change in composition from basaltic to trachytic, and a small number of carbonatite coeval with alkaline silicate rocks (amphibole pyroxenites and syenite). Petrographic, chronological and geochemical evidence suggests that these alkaline rocks share the same mantle source area, with the mafic rocks recording partial melting of the mantle in the South Qinling Mountains, where the metasomatic agent was mainly silicate melt. The trachyte/syenite and carbonatites are all derived from magmatic differentiation of the initial mafic component, with the trachyte/syenite being controlled by segregation and crystallization of mainly feldspar and clinopyroxene. Hydrothermal processes are mainly concentrated in the Zhuxi-Zhushan area in the eastern part of the Northern Daba Mountains and the south-western margin of the Wudang region, where hydrothermal metasomatism has led to the enrichment of rare earth elements in carbonatite. Geochronology and monazite Nd isotopic signatures suggest that the hydrothermal fluids may have originated from a reactivation event in the rock itself, and that the Late Triassic orogeny of the Qinling region may have contributed to this process.

      • 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
    • Discrete Element Numerical Simulation of fault development characteristics of Strike—slip Pull—apart Basin

      LI Xin, HUANG Lei

      Abstract:

      The development and evolution of strike—slip fault zone is closely related to the formation and evolution of pull—apart basin. The secondary faults and pull—apart basins developed under different overlapping ranges of the main faults have different scales and shapes. Previous studies have mostly used physical simulation to study the evolution process and fault development characteristics of strike slip pull—apart basins. There is a lack of analysis of fault deformation characteristics during the evolution of basins and the discussion on the law of fault evolution under different degrees of overlap of main faults. Based on the discrete element simulation software PFC2D, this paper simulates the development and plane evolution law of faults in the pull—apart basin under three conditions: underlapping, neutral and overlaping. The results show that the fault development of the pull—apart basin experienced a process that faults development from the ends of the strike—slip main faults to the internal releasing bend and then expend to the exterior ,and regardless of the degree of superposition of strike—slip main faults, the law is well reflected. In addition, the high degree of overlap between the fault development position and the stretching area indicates that the development law of the fault is of great significance to the migration of the depocenter of the pull—apart basin.

      • 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
    • The Effect of Enhanced Basalt Weathering on Soil Heavy Metals

      Tang Xiaowei), Liao Libing), Wang Lijuan), Liu Hao), Xie Xiuxin), Jiao Chennan)

      Abstract:

      Enhanced basalt weathering can release heavy metals and accumulate in soil, while the weathering products of basalt have a certain passivating effect on soil heavy metals. Therefore, investigating the bioavailability of heavy metals in soil during enhanced basalt weathering process is of great significance for the practical application of enhanced-basalt weathering carbon sequestration technology. This study used Tessier method, SEM, EDS, and other characterization methods to study the effect of enhanced basalt weathering on soil heavy metals. The results showed that basalt weathering increased soil pH, making heavy metals in soil more easily passivated. Most of the Cr and the Ni leached from basalt were fixed in residual form by basalt weathering products and soil clay minerals, and only a small amount of Cr and Ni flowed out with the effluent, causing no soil pollution. The new minerals formed by Ca, Mg, and Fe ions released by basalt dissolution during weathering, as well as other basalt weathering products, can transform heavy metals in soil into stable forms, reducing their bioavailability and achieving the goal of remediating soil heavy metal pollution.

      • 1
    • Deep explanation model of the VMS-type deposit in the Ashele ore district

      Meng guixiang, Deng zhen

      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

      liubaoshan

      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
    • TECTONIC PROPOGATION AND BASIN EVOLUTION DURING THE EXTENSION AND BREAKUP OF THE SOUTH CHINA SEA

      LUO PAN, REN JIANYE, LEI CHAO

      Abstract:

      In order to clarify the time-space evolution of tectonic activities with the ocean continental transition, we interpret and analysis 2 long seismic lines which are across the conjugate margin of South China Sea. Four first order interfaces have been recognized in the ocean continental transition of SCS: Tb, SD, PD and Bi. These 4 first order horizons separated the basins on continental margin into different proto-basins: the early rifted basin (Tb-SD), the later detachment basin (SD-PD) and the transfer basin (PD-Bi). According to the comparison of syn-tectonic sequences in different domains in one seismic line, the tectonic activities youngling from continent to ocean. According to the comparison the syn-tectonic sequences in same domain between different lines, the tectonic activities youngling along the seafloor spreading direction. Thus, during the seafloor spreading stage, the lithosphere extension deformation propagated not only from continent to ocean, but also along the seafloor spreading direction.

      • 1
    • Spiral chirality study of three-lobes helical tube Anabarites cf. tripartitus from the Cambrian Age 2 in Three Gorges

      pengjiaxin, zhaoxiaofang, guojunfeng, qiangyaqin, songzuchen, sunjie, hanjian

      Abstract:

      Helical chirality is common in living organisms today and the fossil record, however this phenomenon has remained almost unstudied, especially in small shelly fossils from the early Cambrian. Anabaritids are a kind of tubular fossils with distinct triradial symmetry, which are known from the early Cambrian strata worldwide. Previous studies on some helical species of anabaritids were mostly limited to morphological descriptions, and the reasons for their helical chirality were poorly discussed. Based on 111 specimens of Anabarites cf. tripartitus from Member 5 of the Yanjiahe Formation (Cambrian Stage 2) in Three Gorges area of Hubei Province, China, the mechanism of their fixed right-handed (dextral) spiral chirality was investigated. The cause of right-handed helical chirality should be inferred from the biological factors (e.g. functional morphology, molecular developmental biology) perspective of molecular genetics, instead of external environmental factors (e.g. water change, taphonomy, Coriolis force).

      • 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
    • Quantitative textural analysis of cumulates from the lower zone of the Bijigou intrusion in the northern margin of the Yangtze block: Constraints on the expulsion mechanism of interstitial liquid at the early stage of solidification of layered intrusions

      WANG Jie, LI Zhongzhou, WANG Mengxi

      Abstract:

      The expulsion of interstitial liquid from the crystal mush is closely related to the abundant crystallization of Fe-Ti oxides during the mid-late stage of the solidification of layered intrusions, yet the expulsion mechanism of interstitial liquid before the abundant crystallization of Fe-Ti oxides at the early stage is still enigmatic. The highly differentiated Bijigou intrusion in the northern margin of the Yangtze block is the largest layered intrusion with Fe-Ti-(V) mineralization in China at present. The lower zone (LZ), middle zone (MZ) and upper zone (UZ) of the Bijigou intrusion are mainly composed of plagioclase peridotite, gabbro and diorite, respectively. In this study, we analyzed the crystal size distributions (CSDs) and spatial distribution patterns (SDPs) for plagioclase and clinopyroxene of samples from the plagioclase peridotite unit in the LZ, in order to examine the expulsion mechanism of interstitial liquid from the crystal mush at the early stage of solidification of layered intrusions. Modeling results show that the fraction of trapped liquid (FTL) is 9% ~ 13% for samples from the plagioclase peridotite unit of the Bijigou intrusion, suggesting the interstitial liquid was effectively expelled from the crystal mush. The consistent slopes of the CSD curves for clinopyroxene and plagioclase of samples from the plagioclase peridotite unit mainly vary from ?3.36 to ?2.45 and from ?2.99 to ?1.87, respectively, and the variable intercepts are from 0.45 to 3.35 and from 1.06 to 2.83, respectively, similar to those for the mechanical compaction. In addition, the SDP R value (ratio of observed and predicted nearest neighbor distance of the same mineral) and the mineral mode except plagioclase/clinopyroxene of the samples are negatively correlated, consistent with the trend of mechanical compaction. Therefore, the expulsion of interstitial liquid at the early stage of solidification of the Bijigou intrusion is controlled by mechanical compaction. On the other hand, we compared the Bijigou intrusion with the Skaergaar, Sept Iles and Kiglapait layered intrusions in terms of the scale, fraction of trapped liquid, density contrast of the interstitial liquid and cumulus crystal, the relationship of accumulation rate and compaction rate, and the thickness of mush layer. We propose that the compaction plays a critical role in expelling the interstitial liquid at the early stage of solidification of layered intrusions if there’s no magma replenishment and convection, but the factors controlling the degree of compaction are distinct in different conditions. When the intrusion sizes are comparable, the onset of compaction is mainly controlled by the density contrast of interstitial liquid and cumulus crystals, with a higher degree of compaction for a greater density contrast. In addition, compaction is more likely to operate in large intrusions, rather than small ones at the early stage of solidification.

      • 1
    • Large-scale autogenic stratigraphic mechanisms and Autostratigraphy

      WANG Junhui, MUTO Tetsuji, XIAN Benzhong

      Abstract:

      In response to external forcings such like eustatic changes, tectonic activities, and sediment supply, the stacking of strata is controlled by both autogenic and allogenic mechanisms. One of the main progresses in recent years is a realization that autogenic ones may take place in a wide variety of spatio-temporal scales during the deposition. Unlike small-scale autogenic mechanisms that happens on local positions of the depositional system, large-scale ones control the formation of strata regionally, which might modify and even change the allogenic processes. To check the relationship between strata stacking patterns and external forcings, large-scale autogenic processes must be determined from allogenic ones. Based on the understanding of large-scale autogenesis, autostratigraphy has developed in recent years. Autostratigraphy provides new perspectives in analyzing the relationships between strata stacking patterns and external forcings, based on two pairs of coupled notions, i.e. autogenesis and allogenesis, equilibrium and non-equilibrium responses. Autostratigraphy defines external forcings of constant rates as steady, and those of changing rates as unsteady. Strata stacking patterns or processes controlled by steady external forcings are considered as autogenesis, while by unsteady external forcings are considered as allogenesis. Autostratigraphy also defines steady strata stacking patterns or processes where the ratio of aggradation rate and progradation rate (i.e. Ragg/Rpro) remains constant during the interested period. Otherwise, the strata stacking patterns or processes are considered as unsteady. Equilibrium response is then defined as a response where steady external forcings form steady strata stacking patterns and thus is autogenic. If steady external forcings form unsteady strata stacking patterns, this response is called non-equilibrium response and is also autogenic. Moreover, unsteady external forcings may also form steady strata stacking patterns, which is also a kind of non-equilibrium response but is allogenic. Under the framework of autostratigraphy, the stacking up of strata generally takes the large-scale autogenic non-equilibrium responses and thus usually exhibits an unsteady pattern. In contrast, steady stacking patterns of strata only takes places under very rare conditions. The acquiescence of equilibrium response between strata stacking patterns and external forcings and its corollary in conventional genetic stratigraphy should be revisited.

      • 1
    • Characteristics of mylonite magnetic fabrics and constraint on the relationship between the shear zone deformation and mineralization

      likang, jiaoqianqian

      Abstract:

      Abstract:The Hetai goldfield with gold deposits strictly hosted by mylonite zones are considered to be a typical gold mineralization example related to ductile-shear deformation and have the largest gold reserves in Guangdong Province. However, the shear deformation conditions versus the gold mineralization remain unclear. The Gaocun and the Yunxi gold deposit confined to ML11 and ML9 mylonite zone respectively are the significant gold producers in the goldfield. The magnetic petrology and anisotropy of magnetism susceptibility (AMS) of the barren and auriferous mylonite in the shear zones were studied after the macroscopic deformation and petrography characteristic observation. The x-T curves of mylonite show the Curie temperature of pyrrhotite, in combination of the hysteresis loops, isothermal remanent magnetism (IRM) and petrography characteristics, indicating biotite and pyrrhotite are the dominated magnetic bearing minerals of the mylonite with no magnetite, the contribution of pyrrhotite much larger than the biotite in Hetai goldfield. Therefore, the AMS characteristics are effective to show the deformation of the shear zones. The barren mylonite in ML11 mylonite belt (Gaocun deposit) have the similar mean magnetism susceptibility value Km (<500 μSI), corrected anisotropy degree Pj, ellipsoid shape factor T, magnetism foliation F and lineation L with the ML9 mylonite belt (Yunxi deposit). Moreover, both the shear zones show consistent orientation of principle stress, nearly horizontal NNW-SSE striking maximum principle stress σ1 (K3) and steep dip NEE-SWW striking minimum principle stress σ3 (K1). Kinematic vorticity of two shear zones are also undistinguishable, varying from 0.12 to 0.63, less than 0.71. These characteristics suggest that both the shear zones in the Hetai goldfield subjected to Indosinian NNW-SSE trending severe compression which resulted in the mylonite as the S and SL tectonites with intense oblate stain ellipsoid, and the pure shear is dominated in the shear deformation. However, the AMS characteristics of auriferous mylonite is distinct from the barren mylonite, with the Km and Pj value of the former larger than that of the later, suggesting that the mylonite deformation strength tend to have positive correlation with the gold mineralization. Consequently, In the shear zone, the stronger the ductile deformation and the steeper the dip angle of the maximum strain principal axes (magnetic lineation) of mylonite, the more favorable it is for brittle fracture and gold enrichment in the later stage.

      • 1
    • Late Quaternary activity and paleoearthquake recurrence characteristics of Litang Fault in Western Sichuan

      zhangxianbing, Yangzhen, Zhongning, Yuhao, Guochangbao, Yangguifang, Lihaibing

      Abstract:

      Active faults within the block have the ability to trigger large earthquakes of magnitude 7 or above, and their spatial distribution characteristics, activity, and seismic risk cannot be ignored. The Litang fault zone is an important seismogenic structure in the Litang area of the western Sichuan plateau, which is distributed within the Sichuan-Yunnan block. There are still different understandings about the formation age of surface fractures in the Litang Basin, the recurrence characteristics of paleoearthquakes, and the kinematic characteristics of the Litang Fault. Based on remote sensing interpretation, field geological survey, unmanned aerial vehicle photogrammetry, paleoseismic trench exploration, and 14C dating, this paper has determined the spatial geometric distribution, activity, and paleoseismic history of the Litang fault. The research results indicate that the surface fracture of the Litang Basin may be formed by the superposition of the 1948 Litang M71/4 earthquake and the 1729 Litang earthquake. The recurrence behavior of paleoearthquakes along the Litang fault conforms to the characteristics of cluster earthquakes, which is relatively similar to the recurrence characteristics of strong earthquakes along the Maoyaba fault, indicating that both fractures may occur simultaneously. The movement of the Litang fault is characterized by sinistral strike-slip with normal fault components, which is controlled not only by lateral extrusion movements on the southeastern margin of the Tibet Plateau, but also by differential movements of the Yajiang and Shangri-La secondary blocks. This study provides detailed information for understanding the seismic risk and tectonic deformation mechanism of active faults within the Sichuan-Yunnan block, as well as for planning, construction, and safe operation of major regional projects.

      • 1
    • A study on the crustal structure of the east-central Great Kinghan Range margin based on geophysical data fusion

      Zhao WeiJun, Qin tao, Li JianPing, Xiao Feng, Han JiangTao, Rong Xing, Guo BaoDong, Ge Huan, Niu XingGuo

      Abstract:

      Sitting in the east segment of Central Asian orogenic belt, Xing’an block and Songliao-Xilinhaote block were separated by the Hegenshan-Heihe suture. Likewise, Xingan block and Songliao block were separated by the Nenjiang Fault subsequently. In the central segment of the great Kinghan Range, these two structures overlap and is hardly to be distinguished. To investigate the important structures, divide the structure units, and determine the depth variation of the basement in the east margin of the great Kinghan Range, we have acquired a 60-km-length gravity, magnetic and magnetotelluric coincident profile in Zhalantun-Arongqi area, Inner Mongolia. The 1:20K Buguer gravity data in Zhanlan-Arongqi area were reprocessed. Through multiple geophysical fusion, seven important faults were inferred. Among them, the Pangjiajie Fault, the Hongxing Fault, and Alunhe Fault are deep faults, at least penetrating up to middle crust. In addition, two low-resistivity belts in the middle curst were revealed, among which, C2 anomaly is interpreted as Hegenshan-Heihe suture. geographically. By correlating with 1:25K geological mapping data, the geophysical interpretation results were proofed. The research outcomes are helpful to geological studies of crustal structures at the central-east great Kinghan Range margin. It has the significant implications for regional revolution history of the two blocks.

      • 1
    • Provenance and Tectonic Setting of the Lower Carboniferous in West Section of North Qaidam Basin: Constraints from Detrital Zircon U-Pb Geochronology and Geochemistry

      HUJUNJIE, SHIHUI, MALICHENG, MAYINSHENG, lizongxing, WANGJIAQI, ZHONGCHANG

      Abstract:

      Aiming at finding out the material source and tectonic background of Early Carboniferous strata in west section of northern Qaidam Basin. In this study, the Huaitoutala Formation clastic rocks from Xiaosaishiteng Mountain area were collected for geochemical and detrital zircon U-Pb geochronology analysis. The results show that UCC-normalized trace element spider diagram of clastic sedimentary rocks is flat shaped, with the enrichment of Th, U, Hf and the loss of Co, Sc, Ni, V. The rare earth elements of the sandstones display obvious fractionation in light and heavy REE, strong enrichment in light REEs with medium negative Eu anomaly. The Cr/Zr, Sm/Nd, Th/Sc and Th/U ratios and discrimination diagrams indicating that most sediments were derived from upper crust source area with felsic- intermediate rocks as dominant contributors. Multiple geochemical parameters revealed the geochemical characteristics of test samples are close to the continental island arc sandstone. Interrelated tectonic environment discrimination also verified that Huaitoutala Formation was developed in continental island arc and active continental margin tectonic settings. The U-Pb ages of detrital zircons in Huaitoutala Formation can be divided into three populations: 401~480 Ma, 900~1493 Ma and 1803~1908 Ma, which yield a single Early Paleozoic peak (414 Ma) in histogram, indicating key tectonomagmatism episodes of the north Qaidam Caledonian Orogenic Belt during late Early Paleozoic. Based on previous research conclusions of paleogeography and paleocurrent evidence, it is inferred that the provenance of the Early Carboniferous Huaitoutala Formation have come from the north Qaidam Caledonian Orogenic Belt.

      • 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.

    • Strata missing of the Ediacaran upper Dengying Formation at the northwestern Mianyang-Changning intracratonic sag, and tectonic implications

      Dingyi, Liu Shugen, Wen Long, Ma Kui, Chen Daizhao, Song Jinming, Wang Han, Wang Linkang, Chen Mingsi, Yang Bo, Tang Pan, Li Zhiwu

      Abstract:

      Although it is well accepted that the Mianyang-Changning intracratonic sag plays an important role in petroleum accumulation, its spatio-temporal distribution and formation mechanism are still controversy. In this case, this study carries out systematic stratigraphy and lithofacies investigations on the Sinian-Cambrian successions of the Guangyuan-Ningqiang area, at the northeastern margin of the Mianyang-Changning intracratonic sag. The lithofacies indicators and biostratigraphy suggest that the lower Beiwan Member or upper Algal dolomite Member are commonly overlain by Kuanchuanpu Formation, and thus the Gaojiashan and Beiwan members are pervasively missing at Kuanchuanpu, Shujiaba and Caojiaba-Dongshanzi areas. This indicates that the strata missing of the upper Dengying Formation at eastern margin of the Mianyang-Changning intracratonic sag can extend from the Central Sichuan Basin and north slope of Central Sichuan Paleouplift to the Guangyuan-Ningqiang area. The sharp shift from tidal flat-lagoonal microbial dolomite and dolomudstone in the study area to slope-basinal chert at Datan-Yangmu area indicates the control of extensional fault. Similar sharp shift in facies is also present at the southern margin of middle Yangtze platform and eastern margin of the upper Yangtze platform, reflecting an extensional tectonic regime with the formation of fault-bounded carbonate platforms. The width of several kilometres, erosion thickness of hundreds of metres and the depositional break up to 20 Myr suggest that Mianyang-Changning intracratonic sag can be attributed to differential subsidence/uplift rather than karstic morphology. The linear distribution of strata missing area at eastern margin of the Mianyang-Changning intracratonic sag should be resulted from relative uplift at the tilted block. The climax of extensional faulting occurred at the Sinian-Cambrian transition, causing the strata missing of the upper Dengying Formation to the lowermost Kuanchuanpu Formation.

      • 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
    • Ocean-continent transition process in the West Junggar tectonic belt: constraints from the basalts of the Baiyanghe Formation

      LI Yongjun, ZHANG Jianye), YANG Gaoxue, DUAN fenghao), LI Wei)

      Abstract:

      West Junggar structural zone distributed in the south western of the Central Asian Orogenic Belt, It’s a key area for studying the evolution of the Paleo Asian Ocean. However, there are currently controversies over the tectonic evolution of the West Junggar tectonic zone in late Carboniferous. The newly discovered volcanic rocks from the Baiyanghe Formation in Early Permian probably can alleviate those controversies. Baiyanghe Formation volcanic rocks are mainly consist of basalts and the symbiotic subvolcanic rocks. It has angular unconformity relationship on the Early Permian Jiamuhe Formation with continental molasse sequence. In terms of geochemical compositions, the basalts are relatively high concentrations of Al2O3 and low concentrations of TiO2, they belong to the middle-low K calc-alkaline series. The ratio of ∑LREE/∑HREE ranges from 2.31 to 5.00. All the basalts of the Baiyanghe Formation are enriched in LREE without obviously Eu anomaly (δEu=0.99~1.29). Furthermore, they are enriched in light LILE, such as Ba, K, Sr. In addition, depleted in HFSE such as Nb, Ta, Zr, Hf and show the “TNT” negative anomaly. (206Pb/204Pb)i =17.924~18.000, (207Pb/204Pb)i =15.469~15.509, (208Pb/204Pb)i =37.737~37.879. εNd(t) = +5.93~+6.76, 87Sr/86Sr =0.703974~0.704299, It indicates that the source probably is the dehydration of subducted plate to produce the fluid result in metasomatic depleted mantle. These characteristics are consonant with the geochemical characteristics of late carboniferous marine island arc basalts, they have correlation in timeliness and extensity, and have the characteristics of homology, syngenesis and syntectonic background, it seems like excellent inheritance. The time of Baiyanghe Formation later than Jiamuhe Formation molasse, which confirms that Baiyanghe Formation basalts were erupted after the closure of the ocean basin, so it belongs to “Lagged arc” formation. Combining with previous researches and the regional geological background, the ocean basin was closed in Late Carboniferous, nevertheless, the deeply subduction continued until produced the Baiyanghe Formation in Early Permian. In the process of ocean-continent transition, it experienced a unique tectonic evolution process of “Lagged arc”. The “Lagged arc” formation volcanic rocks provide essential constraints for the suture location of the Paleo-Asian Ocean and the tectonic evolution process in West Junggar.

      • 1
    • Deep structure and genesis of Sanmenxia fault basin and its adjacent area ——Evidence from deep seismic reflection and magnetotelluric sounding

      He Faqi, Yu Wenhui

      Abstract:

      In recent years, a lot of work has been done on the oil, gas and geothermal resources in the Sanmenxia faulted basin, but the genetic mechanism is less studied, which seriously restricts the exploration and exploitation of mineral resources. On the basis of previous research, combined with field geological survey and the use of high -precision deep reflections seismic profile, magnetotelluric (MT), gravity and magnetic geophysical exploration technology, Sanmenxia Basin comprehensive study. It is found that the Sanmenxia Basin is mainly composed of two negative flower-like structures in the east and west, and the west flower-like structure is larger than the east flower-like structure. The eastern edge of the basin is adjacent to the Luoyang Depression and the Guanyintang uplift. The Guanyintang uplift has a lens-like low-velocity body in shell, and large scale hidden reverse faults are developed on the east and west sides of the uplift. The Moho surface in the study area is a detachment layer with a thickness of about 5 km, which shows earthworm reflection characteristics on the deep reflection seismic profile, indicating that the detachment layer moves westward. Several new arc-shaped faults were found in the upper and lower parts of the Moho detachment layer. The comprehensive study of geological and geophysical data shows that the decoupling of the Moho detachment layer is the main reason for the formation of the flower structure in the Sanmenxia fault depression basin. Under the action of different temporal and spatial tectonic forces, the Cenozoic whole crust rotating floral tectonic basin was formed in the study area.

      • 1
    • Mechanism of mineral precipitatiaon and genesis of the Shagou Ag-Pb-Zn deposit in the eastern Qinling metallogenic belt, China

      Jinhong Xu, Chengquan Wu, Zhengwei Zhang, Yanwen Tang, Yuping Jiang, Shuli Hu, Chaofei Zheng, Xiyao Li, Ziru Jin

      Abstract:

      Several vein-like silver polymetallic deposits are developed in the eastern Qinling metallogenic belt, among which the Shagou large Ag-Pb-Zn deposit commonly contain authomorphic quartz grains coeval with sulfides, which record important information on the physical-chemical conditions of different mineralization stages and metal mineral precipitation from ore-forming fluids, and provide a good opportunity to reveal mineral precipitation mechanisms and deposit genesis. In this paper, a fine mineralogical study of quartz in the Shagou deposit was carried out by cathodoluminescence, fluid inclusion microcalorimetry and individual fluid inclusion composition analysis based on detailed field geological investigations. Three stages of mineralization can be identified based on mineral assemblages: (1) quartz(Q1)-siderite-pyrite stage, Q1 is located in the core of quartz grains, and is characterized by uniform bright cathodeluminescence (CL) intensity with undeveloped growth zonings, representing pre-ore; (2) quartz(Q2)-dolomite-polymetallic sulfide stage, Q2 is located in the mantle of quartz grains, and coeval with sulfides, and is characterized by dark CL intensity with chaotic growth zonings, representing the metallogenic stage; (3) quartz(Q3)-calcite stage, Q3 is located in the edge of quartz grains, and is characterized by bright CL intensity with good growth rings, representing the post-ore stage. The compositional analysis of quartz from various stages showed that a significant positive correlation between Al and Li in quartz at all stages (R2=0.97) and a close correlation with the cathodoluminescence brightness, indicating that Al3+ and Li+ replace Si4+ into quartz. The Ti content of Q1 and Q2 ranges from 0.722 to 3.62 ppm and 0.387 to 1.12 ppm, respectively, and the Al content ranges from 81.9 to 2436 ppm and 3.67-132 ppm, indicating that the mineralization system is a medium-low temperature, medium-alkaline hydrothermal environment, with decreasing temperature and increasing pH being the main factors triggering mineral precipitation. The compositional analysis of single fluid inclusion by LA-ICP-MS shows that the mineralizing fluid is enriched in alkali metals with high Rb/Na and Cs/Na ratios, indicating that the Shagou deposit is related to magmatism. Comprehensive studies suggest that the Shagou deposit is characterized by multi-stage hydrothermal mineralization and is identified as a distal product of a magmatic-hydrothermal mineralization system, which is indicative of the exploration for hidden porphyry-type Mo(W) deposits.

      • 1
    • Response of Carnian Pluvial Episode in southern Ordos Basin

      Li Jianguo, Wei Yi, Yang Bing, Lei Xiaoting

      Abstract:

      In order to study the response of the Carnian Pluvial Episode in the southern Ordos Basin, pollen fossils, organic carbon isotopes, framboid pyrites and major elements were analyzed in Yanchang Formation in the core ZH2. Two pollen assemblages are divided as (I) Punctatisporites- Verrucosisporites-Osmundacidites assemblage and (II)Asseretospora- Apiculatisporis assemblage from bottom to top. The geological dates are the Middle Triassic Latina and the late Triassic Carnian. In the Zhangjiatan shale in lower part of the pollen assemblage (II), the total organic carbon is enriched and the organic carbon isotope has a negative drift of 4.88‰. Meanwhile, the framboid pyrites index indicates that this layer was formed in anoxia environment, and the Al2O3/MgO and CIA value are high values in this layers, indicating a high temperature, humid and enhanced weathering environment. These characteristics indicate that the Carnian Pluvial Episode had a significant impact on the Ordos Basin. Further analysis shows that these indicators can be divided into four independent high temperature, humid, anoxic and organic carbon enriched fragments in the Zhangjiatan shale, indicating four climatic fluctuations of the Carnian Pluvial Episode in the Ordos Basin, named as CPEⅠ、CPEⅡ、CPEⅢ、CPEⅣ.

      • 1
    • The Present-day strain characteristics and dynamic mechanism around the Eastern Himalayan Syntaxis revealed by the latest GPS data

      Wei Shaogang, Xu XiWei, Wu Yanqiang, Liang Shiming, Luo Jiahong

      Abstract:

      The Eastern Himalayan Syntaxis (EHS) and its vicinities, located in the tectonic front of the collision between India plate and Eurasia plate, is characterized by strong crustal shortening and tectonic rotation deformation. Based on the latest and large-scale GPS velocity data, we analyze horizontal differential crustal movement associated with the EHS and its vicinities. Furthermore, we use a ‘‘spline in tension’’ technique to get a continuous strain rate map of the EHS region. Combined with the previous research results, we focus on the present-day tectonic deformation and mechanism of the EHS and its vicinities, and try to discuss the continental internal dynamic mechanism reflected by the current tectonic deformation in this area. The following results are obtained: Under the background of continuous subduction of Indian plate beneath Eurasian plate at an angle of NE20°, the most remarkable crustal motion is the clockwise rotation of southeastern and eastern Tibetan Plateau around the Eastern Himalayan Syntaxis. The maximum rotation rates of (109.7~123.6) × 10-9 rad/a occurred to the east of the Syntaxis, around this area of Lancangjiang fault, Jinshajiang fault and Nujiang fault. High value region of tectonic strain rates in this area concentrate around the vicinity of Himalayan Main boundary thrust, Sagaing fault, Xianshuihe-Xiaojiang fault and other large strike-slip faults, as well as the ring areas of the Eastern Himalayan Syntaxis, whereas there are no significant strain anomalies in the area across Jiali fault and Red-River fault. Moreover, the maximum superficial compressive strain rates of 152.1×10-9/a is in the northeast areas of Assam sub-block, which indicates that the core position moves from the Namjagbarwa area towards its southeast to the northeast of Assam, where the Himalayan Main boundary thrust successively meets the inferred Northern Sagaing thrust. It is considered according to the research that, owing to the hyper-oblique subduction of the Indian plate, the Eastern Himalayan Syntaxis region is mainly characterized by crustal thickening, and the flow of the lower crust and upper mantle with viscoplastic characteristics in the deep drives the overall movement of the overlying brittle upper crust block.

      • 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
    • Age and rock assembly of Baogutu Formation in West Junggar

      LI Yongjun, WANG Xulong, Li wei, DUAN Fenghao, zhuzhao, ZHENG Menglin, YANG Gaoxue, ZHANG Yueqian

      Abstract:

      The Baogutu Formation is an important early Carboniferous sedimentary record in the southern margin of the West Junggar accretionary orogenic belt. To confirm the complete sedimentary sequence, rock assemblages and their contact relations with overlying and underlying strata is of great significance for the analysis of Late Paleozoic tectonic evolution of Junggar basin. The newly measuredHongshanliang section in the northern Baijiantan reveals two sets of strata with distinct rock assemblages and strong tonal distinction. The upper gray-black "carbonaceous fine clastic rock" and the underlying bright red "chert, silty chert and tuffaceous chert sandwiched with basic to intermediate volcanic rocks namely conformable contact), belonging to the Baogutu Formation and Hongshanliang Formation, respectively. LA-ICP-MS zircon U-Pb ages of 345 Ma and 365.9 Ma were obtained from the bottom of the Baogutu Formation and the top of the Hongshanliang Formation, and their ages are defined as Early Carboniferous and Late Devonian, respectively. This new discovery not only confirms that the Baogutu Formation is the oldest Carboniferous stratigraphic unit in the region, but also proves that the Baogutu Formation is older than the Xibeikulasi Formation. Moreover, this makes a complete stratigraphic sequence of the Lower Carboniferous in this region and reveals the sedimentary construction and rock assemblage at the bottom of the Carboniferous system, which provides new data for a complete understanding of the sedimentary characteristics and tectonic evolution of the basin during the Devonian to Carboniferous period.

      • 1
    • Discovery and geological significance of andesite intercalation in the “Dibuco Formation” in Nixiong area, Central Tibet

      liuhaiyong, tangjuxing, wangyu, tangzuoqi, yeqiang, zengqinggao, kongmingming

      Abstract:

      Due to the lack of high-precision chronological constraints, the age and stratigraphic attribution of the "Dibucuo Formation" in Nixiong area are controversial. In this paper, the weighted average age of ~120 Ma was obtained through zircon U-Pb dating from the andesite intercalayion in the "Dibucuo Formation". These data, in combination with the existing research data on detrital zircons of the "Dibucuo Formation" in the studied area, led us to conclude that the so-called "Dibucuo Formation" was formed in Early Cretaceous (130~120 Ma), which is consistent with the formation age of the colcanic-sedimentary strata of the Zenong Group in this region. It is thus suggested to tentatively classify the "Dibucuo Formation" into the Zenong Group. According to the whole-rock geochemistry of andesite samples and the in-situ zircon Hf isotopic composition, it is believed that the andesite was derived from of the mixture of crust-derived felsic magma and mantle-derived basaltic magma, and formed in the subduction tectonic environment. By further summarizing and analyzing the spatio-temporal transformation of Meso-Cenozoic magmatism in the Lhasa Terrane, it is revealed that the dynamic mechanism of the formation of this set of andesites is mainly related to the northward subduction of the Neo-Tethys Oceanic slab.

      • 1
    Select All
    Display Method:: |
    Volume 98,2024 Issue 2
      Research Articles
    • Zhang Yueqiao

      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.

    • linzhanju, Niu fujun

      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.

    • quxiaoming

      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 km2 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 SiO2 content varying from 68.62%~75.36%. Moreover they have relatively high K2O+Na2O(8.03%~9.37%)and Fe2O3T(0.86%~5.39%) and low Al2O3(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 87Sr/86Sr and ISr ratio values vary from 0.719842~0.786395 and 0.706900~0.710378, respectively. 143Nd/144Nd ratio values are from 0.512123~0.512392, with large negativeεNd values(-3.37~-10.34), reflecting important involvement of crustal components. Pb isotope composition 206Pb/204Pb, 207Pb/204Pb, 208Pb/204Pb 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.

    • Research Articles
    • Kuang Hongwei

      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.

    • Research Articles
    • 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。

    • 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.

    • Lichuanxin

      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.

    • QIAO Xiufu, WANG Yanbin

      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.

    • Research Articles
    • 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.

    • 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.

    • liwei, Hu jianmin, Qu hongjie

      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.

    • gaoyuan, zhengchangqing, yaowengui, wanghao, lijuan, shilu, cuifanghua, gaofeng, zhangxingxing

      2013,87(9):1293-1310, DOI:

      Abstract:

      The Luotuobozi pluton, located in the southeast of Haduohe area Great Xing’an Range, with its geotectonical position in the east of Xing’an-Mongolian Orogenic belt, is composed of syenogranite, granodiorite(with dioritic enclaves), monzonite. Such characteristics of zircons from sample imply their magmatic origin, as euhedral shape, typical oscillatory zoning and high Th/U ratios. LA-ICP-MS zircon U-Pb dating indicates that the ages of zircons from Luotuobozi pluton are syenogranite: 127±1Ma, granodiorite: 126±1Ma, dioritic enclaves: 131±1Ma, monzonite: 130±1Ma, concentrated in Early Cretaceous. The rock is weak peraluminous belonging to high potassium calc-alkaline series, characterized by high Si (SiO2=71.11%~76.89%), high Alkali (Na2O+K2O=8.04%~9.17%), high aluminum (Al2O3=12.9%~14.99%) and low titanium (TiO2=0.08%~0.22%), with A/CNK value 0.97~1.10. The rock experiences a highly fractionated and evolving stage reflected from DI (86.1~97.46) and SI (0.1~5.59), with negative and positive Eu anomalies (δEu=0.26~2.51) reveals LREE enrichment (LREE/HREE=6.35~32.16) and HREE depletion (LaN/YbN =6.35~32.16). The rock are also rich in Th, U, Hf, Zr, La, Rb and depleted in Ti, Ta, Nb. TFeO/MgO ratios are relatively low (=2.37~6.41), Zr+Nb+Ce+Y=106.48×10-6~162.74×10-6, they are less than that of the low-limit values of the A-type granites. Zircon saturation temperatures of them range from 723.43 to 760.48℃ which are also less than that of the low-limit values of the A-type granites. Combining petrography, rock geochemical characteristics, chronology, and regional geological feature, the Luotuobozi pluton belongs to highly fractionated high-potassium calc-alkaline I-type granites, the formation of this pluton is probably by the extensional continental lithosphere thinning in northeast China after the subduction of the Pacific plate in Mesozoic.

    • 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.

    • Most Read
    • Most Cited
    • Most Downloaded