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WANG Guiling，GAN Haonan，LIN Wenjing，YUE Gaofan，YAN Xiaoxue，LI Tingxin，ZHANG Wei，MA Feng
2023,97(4):1003-1013, DOI: 10.1111/1755-6724.15078
Abstract:
Southeastern China (SE China) is located in the Pacific tectonic domain and has experienced a series of tectono-magmatic events induced by the subduction of the Paleo-Pacific Plate since the late Mesozoic. The subduction formed a series of NE-NNE oriented faults under a NW–SE regional stress field, along which a number of thermal springs occur. Previous studies have focused on the genesis mechanism of specific geothermal fields in SE China, but the general characteristics of hydrothermal systems in SE China remains unclear. In this study, we investigate the correlation between geothermal activity, hydrochemical type and regional faults by studying the distribution of hydrothermal activity and geochemical properties of typical hydrothermal systems in SE China. The hydrothermal systems in SE China have a crustal thermally-dominated structural origin unique to the specific geological and tectonic conditions of the Eurasian Plate margin. The upwelling of the asthenosphere and the widespread granitoids with high radiogenic heat production in SE China provide major heat sources for regional geothermal anomalies. The NE-oriented crustal thermally-dominated faults are critical for the formation of geothermal anomalies and NW-oriented extensional faults have created favorable conditions for meteoric water infiltration, transportation and the formation of thermal springs.
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2023,97(4):1014-1025, DOI: 10.1111/1755-6724.15088
Abstract:
Two new species of Eretmophyllum Thomas are described from the lower (Toarcian) and upper (Aalenian) Prisayan Formation of the Irkutsk Basin, Eastern Siberia, Russia based on distinct morphological and cuticular features of the leaves that distinguish them from other species of the genus. Eretmophyllum polypapillosum sp. nov. is characterized by the presence of 2–3 papillae on the lower and upper epidermis of ordinary cells. Taphonomically, the leaf burials of E. polypapillosum sp. nov. indicate that it preferred mesophilic forests developed on river terraces and/or low watersheds. Eretmophyllum yershowskiensis sp. nov. is represented exclusively by leaf cuticles extracted by coal maceration, and it probably inhabited the low banks of peat bogs. The presence of the genus Eretmophyllum in the Early Jurassic of France and Eastern Siberia shows that it was already widespread in the territory of Eurasia, distributed from Western Europe to Eastern Siberia. This indicates the possible existence of Eretmophyllum species elsewhere in the Early Jurassic such as Central Asia and Northwest China.
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QIN Jiachen，LIU Yunhuan，SHAO Tiequan，WANG Qi，ZHANG Yanan，ZHOU Xingyu，LIU Mingjin
2023,97(4):1026-1037, DOI: 10.1111/1755-6724.15052
Abstract:
A wide variety of scalidophoran worms have been found in the Cambrian Fortunian in recent years, suggesting that scalidophorans diversified during this age. Here, we report new scalidophoran material obtained from the 2nd member of the Kuanchuanpu Formation (Fortunian Stage) in Zhangjiagou Lagerst?tte, Xixiang County, Shaanxi Province, South China. Three indeterminate forms of scalidophoran worms are described in detail. The morphology of these worms differs from that of any coeval worms and may represent new taxa. However, because these fossils are fragmented and lack detailed information on the arrangement pattern of introvert scalids, they are named here in open nomenclature. This study enriches the diversity of the earliest scalidophorans to 7 genera and species and 10 indeterminate forms. Based on the new fossils, Fortunian scalidophoran worms can be divided into three categories: (1) worms with microannuli; (2) worms with macroannuli; and (3) worms without annuli.
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Elaheh SATTARI，Ali BAHRAMI，Hossein VAZIRI-MOGHADDAM，Azizollah TAHERI，Iliana BONCHEVA
2023,97(4):1038-1057, DOI: 10.1111/1755-6724.15071
Abstract:
The Late Devonian–early Carboniferous deposits of the Anarak section in northeastern Isfahan, Central Iran, evaluated based on conodont biostratigraphy, sedimentary environment and sequence stratigraphy. According to the field observations, five lithological units were identified. Investigating the conodont fauna of the Late Devonian–Carboniferous (Mississippian–Pennsylvanian) deposits of Bahram, Shishtu, and Qaleh (Sardar 1) formations in Anarak section led to the identification of 67 species of 18 conodont genera, and accordingly 22 conodont biozones were differentiated. The correlation of sea-level change curves, regarding to the conodont biofacies with the global sea-level curve, demonstrates the relative correlation in the mentioned times due to the shallow condition of the central Iran basin compared to the European and American basins. The microfacies analysis led to the identification of 12 microfacies related to the open sea, bioclastic barrier, lagoon and tidal flat sub-sedimentary environments in a homoclinal carbonate ramp environment. Based on sequence stratigraphy studies, three 3rd order sequences were identified. The first sequence, which is of the Late Devonian (upper part of the Bahram Formation, 32.5 m), the second sequence (12.5 m) is the Late Devonian (uppermost part of the Bahram Formation), and the third sequence (68 m) is the early Carboniferous (the Shishtu I Formation).
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2023,97(4):1058-1077, DOI: 10.1111/1755-6724.15060
Abstract:
The North Qilian Shan fold and thrust belt, located at the northern Tibetan Plateau and southern margin of the Hexi Corridor, is a key tectonic unit to decode the formation and expansion of the plateau. Previous studies emphasize the Cenozoic deformation due to the far-field response to the Indo–Asian collision, but the Mesozoic deformations are poorly constrained in this area. We conducted detailed field mapping, structural analysis, geochronology, and structural interpretation of deep seismic reflectional profiling and magnetotelluric (MT) sounding, to address the superposed results of the Mesozoic and Cenozoic deformation. The results recognized the North Qilian thrust and nappe system (NQTS), the root and the frontal belt are the North Qilian thrust (NQT), and the Yumu Shan klippe (YK),
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WANG Wei，XIE Huiwen，YIN Hongwei，JIA Dong，XU Zhenping，LUO Haoyu，HE Wanhui，YUAN Rui，DUAN Yunjiang
2023,97(4):1078-1093, DOI: 10.1111/1755-6724.15074
Abstract:
The Kuqa fold-and-thrust belt exhibits apparent structural variation in the western and eastern zone. Two salt layer act as effective decollements and influence the varied deformation. In this study, detailed seismic interpretations and analog modeling are presented to construct the suprasalt and subsalt structures in the transfer zone of the middle Kuqa and investigate the influence of the two salt layers. The results reveal that the relationship of the two salt layers changes from separated to connected, and then overlapped toward the foreland in the transfer zone. Different structural models are formed in the suprasalt and subsalt units due to the interaction of the two salt layers. The imbricate thrust faults form two broom-like fault systems in the subsalt units. The suprasalt units develop detached folds terminating toward the east in the region near the orogenic belt. Whereas, two offset anticlines with different trends develop at the frontal edge of the lower salt layer and the trailing edge of the upper salt layer, respectively. According to exploration results in this region, the relationship between suprasalt and subsalt structures has an influence on hydrocarbon accumulation. We believe that the connected deformation contains high-risk plays while the decoupled deformation contains well-preserved plays.
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2023,97(4):1094-1111, DOI: 10.1111/1755-6724.15062
Abstract:
The southern Great Xing’an Range is the most critical Sn-polymetallic metallogenic belt in northeast China. However, the tectonic setting of the Early Cretaceous magmatic-metallogenic “flare-up” event remains uncertain. This paper presents an integrated study on the occurrence, petrology, zircon U-Pb ages, whole-rock geochemistry, and in situ zircon Hf isotopes for Wenduerchagan granites of Xi Ujimqin Banner, central-eastern Inner Mongolia. These granites consist primarily of granite porphyry (with ages of 137 ± 1 Ma and 138 ± 1 Ma) and (porphyritic) alkali feldspar granite (with an age of 141 ± 2 Ma), corresponding to the early Early Cretaceous. They are A-type granites characterized by high silicon, alkali, and TFeO/MgO contents while being depleted of Ba, Nb, Ta, Sr, P, and Ti. They show right-dipping trend rare-earth element distribution characteristics with negative Eu anomalies (Eu/Eu* = 0.01–0.20) and weak heavy rare-earth element fractionation ((Gd/Yb)N = 0.77–2.30). They demonstrate homogeneous zircon Hf isotopic compositions (positive εHf(t) values from +5.3 to +7.1 and young two-stage Hf model ages of 851–742 Ma) and high zircon saturation temperatures (av. 810°C). These geochemical characteristics indicate that Wenduerchagan granites originated from the partial melting of juvenile crust under high-temperature and low-pressure conditions. Wenduerchagan granites most likely formed in a post-collisional compression-extension transition regime caused by the closure of the Mongol–Okhotsk Ocean, when combined with regional geology. Such a transition regime can probably be attributed to the upwelling of the asthenospheric mantle caused by the break-off of a subducted Mongol–Okhotsk oceanic slab. Upwelling asthenospheric mantle provided sufficient energy and favorable tectonic conditions for magmatism and mineralization of the Early Cretaceous.
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BAI Yuling，WANG Tao，WANG Zongqi，YAN Jie，ZHANG Ai
2023,97(4):1112-1131, DOI: 10.1111/1755-6724.14999
Abstract:
To the south of Manzhouli, Hulunbuir, Inner Mongolia, experienced a tectonic regime transformation from compression to extension in the mid-Mesozoic. Based on systematic research of the volcanics, petrology, volcanic facies, chronology and geochemistry of rocks in the Buridun area, two stages of volcanics are identified. The first stage named the trachyte series was formed in the late Middle Jurassic (167–163 Ma), its eruption rhythm is pyroxene trachyandesite–trachyandesite–trachyte, and its origin rock is basic volcanics from thickened lower crust, with a tectonic setting in the collision orogeny after the closure of the Mongolia Okhotsk Ocean (MOO). The second stage is a bimodal volcanic rock, formed in the early Late Jurassic (163–160 Ma). The eruption rhythm of basic volcanics in this stage is basaltic andesite–basalt–olivine basalt, which comes from the metasomatized lithospheric mantle, the acidic volcanics of which being characterized by the eruption rhythm of sedimentary-explosive-overflow facies, which came from the partial melting of newly formed lower crust, and this shows the characteristics of A-type granite; the tectonic setting is extension of the lithosphere after collision and closure of the MOO. The changes in the formation age and tectonic setting of the two stages of volcanics demonstrate that the transition time from the compressive system to the extensional system south of Manzhouli is about 163 Ma.
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HUANG Yanna，LI Dunpeng，XIAO Aifang，XU Songming
2023,97(4):1132-1149, DOI: 10.1111/1755-6724.15072
Abstract:
The North Qinling Orogenic Belt (NQOB) is a composite orogenic belt in central China. It started evolving during the Meso–Neoproterozoic period and underwent multiple stages of plate subduction and collision before entering intra-continental orogeny in the Late Triassic. The Meso–Cenozoic intra-continental orogeny and tectonic evolution had different responses in various terranes of the belt, with the tectonic evolution of the middle part of the belt being particularly controversial. The granites distributed in the Dayu and Kuyu areas in the middle part of the NQOB can provide an important window for revealing the geodynamic mechanisms of the NQOB. The main lithology of Dayu and Kuyu granites is biotite monzogranite, and the zircon U-Pb dating yielded intrusive ages of 151.3 ± 3.4 Ma and 147.7 ± 1.5 Ma, respectively. The dates suggest that the biotite monzogranite were formed at the end of the Late Jurassic. The whole-rock geochemistry analysis shows that the granites in the study areas are characterized by slightly high SiO2 (64.50–68.88 wt%) and high Al2O3 (15.12–16.24 wt%) and Na2O (3.55–3.80 wt%) contents. They are also enriched in light rare earth elements, large ion lithophile elements (e.g., Ba, K, La, Pb and Sr), and depleted in high field strength elements (HFSEs) (e.g., Ta, Nb, P and Ti). Additionally, the granites have weakly negative–slightly positive Eu anomalies (δEu = 0.91–1.19). Zircon Lu-Hf isotopic analysis showed εHf(t) = ?6.1–?3.8, and the two-stage model age is T2DM(crust) = 1.5–1.6 Ga. The granites in the study areas are analyzed as weak peraluminous high-K calc-alkaline I-type granites. They formed by partial melting of the thickened ancient lower crust, accompanied by the addition of minor mantle-derived materials. During magma ascent, they experienced fractional crystallization, with residual garnet and amphibole for a certain proportion in the magma source region. Comprehensive the geotectonic data suggest that the end of the Late Jurassic granite magmatism in the Dayu and Kuyu areas represents a compression–extension transition regime. It may have been a response to multiple tectonic mechanisms, such as the late Mesozoic intra-continental southward subduction of the North China Craton and the remote effect of the Paleo-Pacific Plate subduction.
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ZHU Jiang，CHEN Yuqiong，CHEN Chao，LI Zhanke，SHI Xianbin，CHEN Song，ZOU Yuanbing
2023,97(4):1150-1162, DOI: 10.1111/1755-6724.15017
Abstract:
To better understand the Paleo- to Mesoproterozoic tectonic evolution of the Dabie Orogen in the northern margin of Yangtze Block, we present geochronological data for metasedimentary and metavolcanic rocks in the Huwan complex. A total of 385 detrital zircon LA-ICP-MS analyses for metasedimentary rocks yielded three 207Pb/206Pb age populations: 1.50–1.80 Ga, 1.81–1.87 Ga and 1.93–2.0 Ga, providing a maximum depositional timing of ca. 1.50 Ga; while metafelsic volcanic gneisses yielded protolith U-Pb ages of 1893 ± 54 Ma. The peak ages are remarkably consistent with the tectonothermal events that occurred in the northern Yangtze Block, indicating the presence of Paleo- to Meso-proterozoic magmatism in the Dabie Orogen. The age range of 1.93–2.0 Ga correlates with the Paleoproterozoic collision; the age range of 1.81–1.87 Ga coincides with the period of the post-orogenic extension; and the age range of 1.50–1.80 Ga is interpreted to associate with an extensional regime. Zircon cores with age of 1732–1965 Ma have εHf(t) values ranging from ?11.70 to ?2.47, indicating that juvenile crust involved in their magma sources. Owing to the similar age spectra, we proposed that the nucleus of the Dabie Orogen was close to the Yangtze Block since the Paleoproterozoic. The Huwan complex has an intimate affiliation to the Yangtze Block, and implies multiple orogenic cycles. It was not only experienced the Paleo-Tethys ocean subduction and collision, but also recorded Paleo- to Mesoproterozoic tectono-magmatic events in the Dabie Orogen.
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YAN Songtao，WU Qingsong，LI Hu，DAI Xuejian，ZHU Lidong，WANG Jie，XIN Chongyang
2023,97(4):1163-1180, DOI: 10.1111/1755-6724.15038
Abstract:
The widely distributed Early Cretaceous magmatism in the Tethys Himalaya (TH) of southern Tibet is related to the Kerguelen mantle plume. Associated magmatic activity products are distributed in the eastern TH, where the active age is earlier than the peak ages of the Kerguelen mantle plume. This study investigated magmatic activity of the Dingri area in the central TH which was coeval with the Kerguelen mantle plume. The intrusion in the Dingri area contains diabases and monzonites. The zircon age of diabase is 123 ± 1 Ma, and that of monzonite is 117 ± 1 Ma. Geochemistry and Sr-Nd isotopic analyses show that the mafic–intermediate dikes were formed in an intraplate extensional environment. The diabase is derived from the enriched lithospheric mantle and monzonite is derived from partial melting of the lower crust, with both magmatic evolutions being contaminated by crustal materials. These characteristics are similar to those of the Rajmahal–Sylhet basalt, a typical Kerguelen mantle plume product. The discovery of the Dingri mafic–intermediate dikes of the central TH suggests that the TH and Rajmahal–Sylhet Traps formed a continuous mantle plume overflow magmatic belt which was a product of the continuous eruption of the Kerguelen mantle plume.
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LI Guanlin，GUO Yinghai，WANG Huaichang，LI Mi，HAN Jiang，YANG Xiaokai
2023,97(4):1181-1195, DOI: 10.1111/1755-6724.15013
Abstract:
The continuously collected cores from the Permo–Carboniferous coal-bearing strata of the eastern Ordos Basin are essential for studying the hydrocarbon potential in this region. This study adopted sedimentological and geochemical methods to analyze the sedimentary environment, material composition, and geochemical characteristics of the coal-bearing strata. The differences in depositional and paleoclimatic conditions were compared; and the factors influencing the organic matter content of fine-grained sediments were explored. The depositional environment of the Benxi and Jinci formations was lagoon to tidal flat with weakly reduced waters with low salinity and dry-hot paleoclimatic conditions; while that of the Taiyuan Formation was a carbonate platform and shallow water delta front, where the water was highly reductive. The xerothermic climate alternated with the warm and humid climate. The period of maximum transgression in the Permo–Carboniferous has the highest water salinity. The Shanxi Formation was deposited in a shallow water delta front with a brackish and fresh water environment and alternative weak reductiveness. And the paleoclimate condition is dry-hot. The TOC content in fine-grained samples was averaging 1.52%. The main controlling mechanism of organic matter in this area was the input conditions according to the analysis on input and preservation of organic matter.
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XIAO Wei，ZHANG Bing，YANG Kai，WANG Yan，WEN Siyu，MA Kai，CAO Gaoquan
2023,97(4):1196-1213, DOI: 10.1111/1755-6724.15030
Abstract:
A set of organic-rich shales of the upper Permian Longtan Formation, which is widely developed in the northeastern part of the Sichuan Basin, is a key formation for the next step of exploration and development. At present, most studies on this set of formations have focused on the reservoir characteristics and reservoir formation mechanism of the shales, and basic studies on the palaeoenvironment and organic matter (OM) enrichment mechanism have not been fully carried out. In this paper, we recovered the sedimentary palaeoenvironment by mineralogical, elemental geochemical and organic geochemical analyses, and explored the enrichment mechanism of OM under the constraints of palaeoenvironmental evolution. The shales can be divided into two stages of sedimentary evolution: compared with the shales of the Lower Longtan Formation, the shales of the Upper Longtan Formation are relatively rich in quartz, poor in clay and carbonate minerals, and the OM type changes from type III to type II2. The depositional environment has undergone a change from sea level rise, from warm and wet climate to dry and cold climate, and from oxygen-poor condition restricted to open reduction environment; the land source input has decreased, the siliceous mineral content has increased, the biological productivity has improved, and the deposition rate has changed from high to low. A depositional model was established for the shales of the Longtan Formation, reflecting the differential reservoir formation pattern of organic matter. For the Lower Longtan Formation shales, the most important factors controlling OM content are terrestrial source input and deposition rate, followed by paleoclimate and paleo-oxygen conditions. For the Upper Longtan Formation shales, the most important controlling factor is paleoproductivity, followed by sedimentation rate. The depositional model constructed for the Upper and Lower Longtan Formation shales can reproduce the enrichment of organic matter and provide a basis for later exploration and development.
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LAI Jin，BAI Tianyu，LI Hongbin，PANG Xiaojiao，BAO Meng，WANG Guiwen，LIU Bingchang，LIU Shichen
2023,97(4):1214-1228, DOI: 10.1111/1755-6724.15065
Abstract:
Unconventional oil and gas resources require petrophysical logs to answer the question of how best to optimize geological and engineering ‘sweet spots’. Therefore, the establishment of a key well with comprehensive descriptions of lithology, reservoir properties, hydrocarbon-bearing properties, electronic well log responses, source rock properties, brittleness, and in situ stress magnitude and direction is important for the effective exploration and production of unconventional hydrocarbon resources. Cores, thin sections, scanning electron microscopy (SEM) and comprehensive well log suites are used to build a key well for the Permian Lucaogou Formation, Jimusar Sag of the Junggar Basin. The results show that there are three main types of lithologies, including siltstone, mudstone and dolostone. Lithologies can be predicted using the combination of conventional well and image logs. The pore spaces consist of interparticle pores, intragranular dissolution pores and micropores. Nuclear Magnetic Resonance (NMR) T2 components longer than 1.7 ms are superposed as effective porosity. Permeability is calculated using the Coates model from NMR T2 spectra. The ratio of T2 components >7.0 ms to T2 components >0.3 ms is used to calculate oil saturation. TOC is calculated using the ΔlogR method. Brittleness index is calculated using Poisson-Young’s method, ranging from 13.42%–70.53%. In situ stress direction is determined, and in situ stress magnitudes (maximum horizontal stress SHmax, minimum horizontal stress Shmin, vertical stress Sv) are calculated using density and sonic logs. The strike-slip stress type (SHmax > Sv > Shmin) is encountered. The key well which comprehensively includes the above seven properties is established. Geological and engineering (geomechanical) ‘sweet spots’ are then optimized from the key well by fully analyzing lithology, reservoir property, oil-bearing potential, in situ stress magnitude and brittleness. It is hoped that the results support engineers’ and geologists’ decisions for the future exploitation of unconventional hydrocarbon resources.
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WANG Zhichen，LI Jianghai，FENG Zhiqiang，WANG Lijie，LIU Chen
2023,97(4):1229-1242, DOI: 10.1111/1755-6724.15067
Abstract:
Rifted margins in the central South Atlantic portray spatial variability in terms of preserved width and thickness, which relates to complex rift-related fault activities. However, there is still a lack of systematic and quantitative explanations for the causes of the variations that are observed along the paired rifts. To elucidate this issue, 2D viscous-plastic thermomechanical numerical models are applied to capture the behavior of deformation, in which we investigate the effects of extensional rate, crustal strength and thickness on crust-mantle coupling, and timing of transition from rifting to breakup. Our numerical experiments demonstrate that crust-mantle decoupling accounts for crustal hyperextension, and that incorporating moderate-intensity rheology into lower crust may yield insights into the hyper-extended crust and asymmetric architecture observed in the central South Atlantic. The results also suggest that undulations in lithospheric basement cause asymmetric mantle upwelling. The lower crust of fold belts takes priority to be thermally weakened over craton and induces rift migration simultaneously. A new mechanism for the formation of failed rift is described, where the mechanical decoupling derived from thermally weakened lower crust gives access to dual rift migration. These results reinforce the interpretation on how crustal rheology shapes margins architectures and highlight the first-order effects of crust-mantle coupling.
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2023,97(4):1243-1251, DOI: 10.1111/1755-6724.15056
Abstract:
A great amount of new S-wave data has been combined to image the mantle structure down to lower mantle depth near the southeastern margin of Eurasia and understand the tectonics in South China since the Mesozoic. Our results reveal a large-scale structure beneath the South China Sea, with a prominent, broad low-velocity feature of at least 1500-km wide in and below the mantle transition zone (MTZ) and a pronounced low-velocity feature of nearly 500-km wide in the lowermost mantle. Together these features may represent the head-and-tail of an upwelling mantle plume that has interacted with and deformed by the subducting plates in the region. The Andaman–Sumatra plate is seen subducting steeply without stagnation in the MTZ over the large-scale low-velocity structure, suggesting that the upwelling mantle may have exerted significant influence on the overlying plate tectonics. Our results suggest a long-term extensional regime near the southeastern margin of Eurasia, which may help to understand the formation of the large-scale intra-plate magmatism and mineralization with accumulation of huge amount of rare metal elements in South China during the Mesozoic, and the continental breakup, the southeastward extrusion of Indochina, and the opening of the South China Sea during the Cenozoic.
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DUAN Jilin，LIU Yanpeng，ZHU Lixin，MA Shengming，GONG Qiuli，Alla DOLGOPOLOVA，Simone A. LUDWIG
2023,97(4):1252-1267, DOI: 10.1111/1755-6724.15053
Abstract:
Geochemical maps are of great value in mineral exploration. Integrated geochemical anomaly maps provide comprehensive information about mapping assemblages of element concentrations to possible types of mineralization/ore, but vary depending on expert's knowledge and experience. This paper aims to test the capability of deep neural networks to delineate integrated anomaly based on a case study of the Zhaojikou Pb-Zn deposit, Southeast China. Three hundred fifty two samples were collected, and each sample consisted of 26 variables covering elemental composition, geological, and tectonic information. At first, generative adversarial networks were adopted for data augmentation. Then, DNN was trained on sets of synthetic and real data to identify an integrated anomaly. Finally, the results of DNN analyses were visualized in probability maps and compared with traditional anomaly maps to check its performance. Results showed that the average accuracy of the validation set was 94.76%. The probability maps showed that newly-identified integrated anomalous areas had a probability of above 75% in the northeast zones. It also showed that DNN models that used big data not only successfully recognized the anomalous areas identified on traditional geochemical element maps, but also discovered new anomalous areas, not picked up by the elemental anomaly maps previously.
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DAI Jing，CHEN Weizhao，HUANG Liang，ZHANG Yi’nan
2023,97(4):1268-1281, DOI: 10.1111/1755-6724.15054
Abstract:
Yunnan Province, located in the southeastern margin of the Tibetan Plateau, can provide important information on how climate change was influenced by global cooling. However, its variation patterns in temperature and precipitation during the latest Neogene are not well-understood. Based on the 357 specimens assigned to 31 morphotypes of plant fossils from the upper Pliocene Ciying Formation in Yiliang County, Yunnan Province, Southwest China, paleoclimate was estimated by Leaf Margin Analysis and Climate Leaf Analysis Multivariate Program. Compared to the present climate, the mean annual temperature and coldest month temperature have not changed significantly since the late Pliocene, whereas the warmest month temperature has decreased significantly. All precipitation-related parameters have decreased, particularly winter precipitation. Combined with the climatic data of the same period in other areas of Yunnan, the western and eastern Yunnan has shown a similar pattern in temperature variation since the late Pliocene except for central Yunnan; whereas the variation in precipitation does not follow a common law except for a consistent decrease in winter precipitation. Our study reinforced the fact that under the background of global cooling and intensified monsoon systems, different areas of Yunnan exhibit different climatic responses to these changes because of their topographic heterogeneities.
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2023,97(4):1282-1282, DOI:
Abstract:
2023年第97卷第4期
2023年第97卷第4期
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青藏高原东北缘祁连–海原断裂带中段金强河断裂晚第四纪滑动行为
梁淑敏, 郑文俊, 陈干, 张培震, 张冬丽, 毕海芸, 杨雪, 张逸鹏, 段磊, 卢本添
Abstract:
祁连–海原断裂带控制着青藏高原东北缘地区的强震活动。在其中段的金强河断裂是天祝地震空区一条关键的活动断裂，但目前对该断裂的滑动行为认识不足。本文针对沿金强河断裂的水平位移分布，利用WorldView-2立体像对和无人机摄影测量数据，提取断裂沿线高精度的DEM数据，并进行精细的构造地貌解译和水平位错测量。通过断错地貌标志的测量，得到135个位错量和8个位错丛集。同时，利用放射性碳测年方法构建4个典型点断错河流阶地的地貌单元年龄序列，从而通过位错与年龄的关系将位错丛集和地貌单元年龄序列关联起来，并获得金强河断裂全新世的滑动速率在 ~4–12 ka期间为4.8–5.6 mm/a ，在 ~4 ka以来为2.9–4.7 mm/a。最近的三次地震事件的复发间隔约为1000年，形成了一个地震活跃期，揭示着近1500年来缺乏破裂记录的金强河断裂可能具有较高的地震危险性。
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南阿尔金早古生代构造演化：来自茫崖花岗质岩石地球化学、锆石U-Pb和Lu-Hf同位素的证据
徐楠, 吴才来, 刘和武, 宋帅兵, 张贵生, 郑坤, 高栋
Abstract:
南阿尔金造山带是中国西南典型的俯冲造山带，由南阿尔金蛇绿混杂岩带和南阿尔金陆块组成，位于柴达木板块北侧。造山带出露大量早古生代花岗质岩石，但是这些岩石的成因及构造环境尚未查明。本文对茫崖花岗质岩石进行岩石学和地球化学研究，确定岩浆活动的期次，并深入了解南阿尔金造山带的构造演化过程。茫崖花岗质岩浆活动可以划分为三期：494-458Ma，450-436Ma和416-404Ma。根据这些岩石的成岩构造环境，我们认为第一期岩浆活动与南阿尔金洋的北向俯冲有关，形成了大量高价钙碱性、I型花岗质岩石。南阿尔金洋闭合后，柴达木板块开始向南阿尔金陆块碰撞，行了了一系列高价钙碱性、I型花岗岩。第三期岩浆活动形成了大量的造山后A-型花岗岩。
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超微量（80nanomole）硫化物硫酸盐硫同位素的EA-IRMS测试
Abstract:
常规EA-IRMS进行硫同位素测试时需硫量大于2 μmol，这限制了该技术在测试含硫量低的样品时的使用。如此大的需硫量是因为He载气携带样品气体在经过元素分析仪（EA）时的流速为~100 mL/min，而气体同位素质谱仪仅允许气体以低流速进入，所以99.7%的混合气体会通过连续流接口排出，以保证混合气体以~0.3 mL/min的流速通过连续流接口。因此，大部分的样品气体会被浪费，样品的利用率仅有0.3%。在本研究中，我们将自主研发的冷冻富集、分离与纯化系统与EA-IRMS联用测试了六种标准物质的硫同位素，并检测该系统的表现。实验结果表明，使用本研究中改进的方法进行硫化物和硫酸盐标准物质的硫同位素测试，得到的硫同位素结果与常规方法一致，即需硫量仅80 nmol即可得到硫同位素测试结果精度 ±0.24‰–±0.76‰ (1σ)，与使用吸附柱进行硫同位素测试的方法获得的精度相似。所以，改进后的EA-IRMS可以实现超微量硫化物、硫酸盐的硫同位素测试。此外，本方法也可应用至需样量低至100 nmol的碳、氮和氧同位素分析测试工作中。
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粤北早古生代强过铝质花岗岩及其共生岩石的岩石成因及对广西运动的指示意义：来自元素和Sr-Nd-Hf同位素的制约
Abstract:
本文系统报道了粤北地区早古生代强过铝质花岗岩及其共生岩石的锆石U-Pb年代学、主、微量元素及Sr-Nd-Hf同位素组成，探讨其源区特征、岩石成因及构造意义。青州花岗闪长岩为弱-强过铝质，A/CNK= 1.05–1.96。它们具有相对高的初始Sr同位素组成ISr= 0.7087– 0.7148和低的εNd(t)值(-11.2 – -10.1)，以及变化的εHf(t)值-13.4– +4.81。与之不同，大帽山花岗闪长岩为准铝质（A/CNK= 0.79– 0.94），ISr= 0.7083– 0.7110, εNd(t)= -7.92– -5.28和εHf(t)= -8.69– -2.06。高寿石英闪长岩为准铝-强过铝质（0.87– 1.24），ISr值和εNd(t)值分别为0.7104– 0.7111和-9.64– -8.63。元素和Sr-Nd-Hf同位素组成结果显示，青州、大帽山和高寿花岗质侵入岩主要分别源自变杂砂岩、英安质岩和角闪石岩的部分熔融。结合前人的研究成果，这些强过铝质花岗岩形成于同造山环境。本文尝试提出一种关于华南早古生代花岗岩的岩石成因及区域地壳重组的新思路。而广西运动动力机制的揭示需要更加广阔的视野和更加丰富的地质证据。
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Birendra P. Singh, Kapesa Lokho, Naval Kishore, Nancy Virmani
2014,88(2):380-393, DOI:
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A new locality bearing ichnofossils of the Cruziana Assemblage Zone-III from the Mussoorie syncline, Lesser Himalaya, is located in rocks of Member-B of the Dhaulagiri Formation, Tal Group, exposed along the Maldewta-Chhimoli fresh road cut section. The site yielded ichnofossils Bergaueria perata, Cochlichnus anguineus, ?Diplocraterion isp., Dimorphichnus obliquus, diplichnitiform Cruziana bonariensis, Diplichnites gouldi, Glockeria isp., Helminthopsis isp., Monomorphichnus lineatus, Phycodes palmatum, Palaeophycus striatus, Planolites beverleyensis, Planolites montanus, Treptichnus cf. T. pedum, scratch marks and an undetermined worm impression. An Early Cambrian age (Cambrian Series 2) is assigned to the ichnofossil-bearing strata based on the stratigraphic position between the Drepanuroides and Palaeoolenus trilobite zones. A revised Cambrian ichnofossil zonation is presented for the Tal Group of the Mussoorie syncline. Together with their occurrence on rippled surfaces, and the lateral displacement of some trackways (due to current action), a sub-aqueous shallow-marine depositional setting is proposed for the rocks of Member-B.
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ZHU Song, WU Zhenhan, ZHAO Xitao, LI Jianping, WANG Hua
2012,86(1):266-283, DOI:
Abstract:
Many moraines formed between Daduka and Chibai in the Tsangpo River valley since Middle Pleistocene. A prominent set of lacustrine and alluvial terraces on the valley margin along both the Tsangpo and Nyang Rivers formed during Quaternary glacial epoch demonstrate lakes were created by damming of the river. Research was conducted on the geological environment, contained sediments, spatial distribution, timing, and formation and destruction of these paleolakes. The lacustrine sediments 14C (10537±268 aBP at Linzhi Brick and Tile Factory, 22510±580 aBP and 13925±204 aBP at Bengga, 21096±1466 aBP at Yusong) and a series of ESR (electron spin resonance) ages at Linzhi town and previous data by other experts, paleolakes persisted for 691~505 kaBP middle Pleistocene ice age, 75–40 kaBP the early stage of last glacier, 27–8 kaBP Last Glacier Maximum (LGM), existence time of lakes gradually shorten represents glacial scale and dam moraine supply potential gradually cut down, paleolakes and dam scale also gradually diminished. This article calculated the average lacustrine sedimentary rate of Gega paleolake in LGM was 12.5 mm/a, demonstrates Mount Namjagbarwa uplifted strongly at the same time, the sedimentary rate of Gega paleolake is more larger than that of enclosed lakes of plateau inland shows the climatic variation of Mount Namjagbarwa is more larger and plateau margin uplifted more quicker than plateau inland. This article analyzed formation and decay cause about the Zelunglung glacier on the west flank of Mount Namjagbarwa got into the Tsangpo River valley and blocked it for tectonic and climatic factors. There is a site of blocking the valley from Gega to Chibai. This article according to moraines and lacustrine sediments yielded paleolakes scale: the lowest lake base altitude 2850 m, the highest lake surface altitude 3585 m, 3240 m and 3180 m, area 2885 km2, 820 km2 and 810 km2, lake maximum depth of 735 m, 390 m and 330 m. We disclose the reason that previous experts discovered there were different age moraines dividing line of altitude 3180 m at the entrance of the Tsangpo Grand Canyon is dammed lake erosive decay under altitude 3180 m moraines in the last glacier era covering moraines in the early ice age of late Pleistocene, top 3180 m in the last glacier moraine remained because ancient dammed lakes didn’t erode it under 3180 m moraines in the early ice age of late Pleistocene exposed. The reason of the top elevation 3585 m moraines in the middle Pleistocene ice age likes that of altitude 3180 m. There were three times dammed lakes by glacier blocking the Tsangpo River during Quaternary glacial period. During other glacial and interglacial period the Zelunglung glacier often extended the valley but moraine supplemental speed of the dam was smaller than that of fluvial erosion and moraine movement, dam quickly disappeared and didn’t form stable lake.
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WANG Runfu, XU Shichao, WU Xiaochun, LI Chun, WANG Suozhu
2013,87(5):1185-1197, DOI:
Abstract:
Shansisuchus shansisuchus Young, 1964 was restudied on the basis of a new specimen. Some anatomical features that were either briefly or not described at all in the original study were detailed. The new specimen not only provides further information on the skull anatomy and the vertebral column but also expands the range of the geographical distribution of the taxon. With new information, the diagnosis of S. shansisuchus was emended and its phylogenetic relationships were further analyzed. S. shansisuchus differs from other archosauriforms primarily in the presence of a large subnarial fenestra anterior to the antorbital fenestra, tongue-in-groove articulations between the ascending process of the premaxilla and nasal and between the premaxilla and maxilla, a tall and posterodorsally directed ascending process of the maxilla, a knee-shaped process of the postorbital projecting into the orbit, a broad descending process of squamosal distally well forked and a large, deeply bow-shaped intercentrum tightly anchoring/capping the sharp ventral edges of two neighboring centra together in cervical and at least first eight dorsal vertebrae. With additional information derived from the new specimen, the phylogenetic relationships of S. shansisuchus were reanalyzed; it is closely related to Erythrosuchus-Vjushkovia clade.
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CHEN Lan1, 2, 3, * , YI Haisheng4, 5, TSAI Louis Loung-Yie2, XU Guiwen1, DA Xuejuan1, LIN Andrew Tien-Shun3
2013,87(2):540-554, DOI:
Abstract:
The Biluo Co and Amdo 114 station, northern Tibet, cropping out the Early Toarcian and Middle-Late Tithonian (Jurassic) organic-rich black shales, have been a focus to petroleum geologists in discussing their oil-producing potential. This paper first reports the trace elements and rare earth elements to discuss the paleoenvironments, redox conditions and sedimentary mechanisms of those black shales. Both sections exhibit variation in trace element abundances with concentrations <0.1 ppm to 760 ppm, mostly enriched in V, Cr, Ni, Cu, Zn, Mo, Ba and U. Element ratios of Ni/Co, V/Cr, U/Th and V/(V+Ni) plus U were used to identify redox conditions. The shale-normalized rare earth element (REE) patterns are characterized by the flat-shale type with instable Ce anomalies and very weekly positive Eu anomalies. Positive Ceanom values are significant with values varying between –0.064 and 0.029 in Biluo Co, which may be interpreted as release of REE and input of riverine terrestrial matter with rich Ce (resulting in pH change) during the anoxic conditions. In the middle parts of Amdo 114 station, distinct negative Ceanom values are observed (?0.238 to ?0.111) and associated surface water warming were interpreted as being related to a major sea level rise. In contrast, the formation of the black shales in the lower and upper part of the studied succession took place during a cooler (Ceanom values >–0.10), lower surface water productivity, and lower sea-level stage. Thus, we emphasize the role of different factors that control the formation of local and regional black shales. The most important factors are sea-level fluctuations and increasing productivity.
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2014,88(1):260-275, DOI:
Abstract:
This paper reviews the current progress and problems in the study of microbialites and microbial carbonates. Microbialites and microbial carbonates, formed during growth of microbes by their calcification and binding of detrital sediment, have recently become one of the most popular geological topics. They occur throughout the entire geological history, and bear important theoretical and economic significances due to their complex structures and formative processes. Microbialites are in place benthic microbial buildups, whereas microbial carbonates can be classified into two categories: stabilized microbial carbonates (i.e., carbonate microbialites, such as stromatolites and thrombolites) and mobilized microbial carbonates (i.e., microbial carbonate grains, such as oncoids and microbial lumps). Various texture, structures, and morphologies of microbialites and microbial carbonates hamper the systematic description and classification. Moreover, complex calcification pathways and diagenetic modifications further obscure the origin of some microbialites and microbial carbonates. Recent findings of abundant sponge spicules in previously identified “microbialites” challenge the traditional views about the origins of these “microbialites” and their implications to reef evolution. Microbialites and microbial carbonates did not always flourish in the aftermath of extinction events, which, together with other evidences, suggests that they are affected not only by metazoans but also by other geological factors. Their growth, development, and demise are also closely related to sea-level changes, due to their dependence on water depth, clarity, nutrient, and sunlight. Detailed studies on microbialites and microbial carbonates throughout geological history would certainly help understand causes and effects of major geological events as well as the co-evolution of life and environment.
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SHEN Caizhi, Lü Junchang, LIU Sizhao, Martin KUNDRáT, Stephen L. BRUSATTE, GAO Hailong
2017,91(3):763-780, DOI:
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A new troodontid dinosaur, Daliansaurus liaoningensis gen. et sp. nov., is erected based on a nearly complete specimen from the Lower Cretaceous Yixian Formation of Beipiao City, Liaoning Province, China. This well preserved skeleton provides important new details of the anatomy for Liaoning troodontids, and gives new insight into their phylogenetic relationships and evolution. Daliansaurus is distinguished from other troodontids by an enlarged ungual on pedal digit IV, which is approximately the same size as the sickle-shaped second ungual, and is differentiated from other Liaoning troodontids by a number of characters of the skull, manus, pelvis, and hindlimb. A phylogenetic analysis recovers Daliansaurus within a subclade of Liaoning troodontids that also includes Sinovenator, Sinusonasus, and Mei. We erect a name for this group—Sinovenatorinae—and argue that it reflects a localized radiation of small-bodied troodontids in the Early Cretaceous of eastern Asia, similar to previously recognized radiations of Liaoning dromaeosaurids and avialans. As more Liaoning theropods are discovered, it is becoming apparent that small, feathered paravians were particularly diverse during the Early Cretaceous, and future work is needed to clarify how this diversity arose, which species coexisted, and how these numerous species partitioned niches.
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2014,88(z2):597-598, DOI:
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Please refer to the attachment(s) for more details
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DU Chunguo, WANG Jianjun, ZHANG Jun, WANG Ping, XUE Mei, ZHOU Huayao
2014,88(3):865-877, DOI:
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On the basis of field observations, microscopic thin-sections and laboratory data analysis of ten faults in Xuanhan County area, northeastern Sichuan Basin, central China, the internal and megascopic structures and tectonite development characteristics are mainly controlled by the geomechanical quality in brittle formation of the Changxing-Feixianguan Formation. The fluid transportation performance difference between the faults formed by different geomechanics or different structural parts of the same fault are controlled by the megascopic structure and tectonite development characteristics. For instance, the extension fault structure consists of a tectonite breccia zone and an extension fracture zone. Good fluid transportation performance zones are the extension fracture zone adjacent to the tectonite breccia zone and the breccia zone formed at the early evolutionary stage. The typical compression fault structure consists of a boulder-clay zone or zones of grinding gravel rock, compression foliation, tectonite lens, and dense fracture development. The dense fracture development zone is the best fluid transporting area at a certain scale of the compression fault, and then the lens, grinding gravel rock zone and compression foliation zones are the worst areas for hydrocarbon migration. The typical tensor-shear fault with a certain scale can be divided into boulder-clay or grinding gravel rock zones of the fault, as well as a pinnate fractures zone and a derivative fractures zone. The grinding gravel rock zone is the worst one for fluid transportation. Because of the fracture mesh connectivity and better penetration ability, the pinnate fractures zone provides the dominant pathway for hydrocarbon vertical migration along the tensor-shear fault.
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MA Shengming, ZHU Lixin, LIU Chongmin, XI Mingjie, TANG Shixin
2013,87(3):843-857, DOI:
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This paper discusses the enrichment and depletion regularities for porphyry copper-molybdenum ore deposits in different regions and varied deposit genetic types in the same area, taking three porphyry copper-molybdenum ore deposits (i.e., the Chengmenshan in Jiangxi, Wunugetushan in Inner Mongolia, Baishantang in Gansu) and two copper deposits in Gansu Province (the Huitongshan skarn deposit and Gongpoquan composite deposit) as case studies. The results show that porphyry Cu-Mo deposits or skarn copper deposits include both enrichment of the ore-forming elements and associated elements, and depletion of some lithophile dispersed elements, rare earth elements (REE) and some major elements. And the depleted elements vary with deposits, having generality and their own features. On a deposit scale, the positive anomalies of enriched elements and negative anomalies of depleted elements follow in a sequence to comprise regular anomaly models of spatial structures. The exploration in the Tongchang deposit in Jiangxi and Huitongshan deposit in Gansu suggests that anomaly models play a key role in the identification of mineral occurrences and deposits compared to one single enriched element anomaly. And the anomaly models exert a critical effect on the optimization of prospecting targets and their potential evaluation.
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2010,84(2):241-246, DOI:
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A new boreopterid pterosaur: Zhenyuanopterus longirostris gen. et sp. nov. from the Yixian Formation of western Liaoning is erected, based on the complete skeleton with a skull and lower jaws preserved. It is characterized by: a large boreopterid pterosaur with a high number of teeth, where the anterior teeth are much larger than posterior ones; the length of the dorsal + sacral vertebrae is nearly half the length of the skull; ratio of the length of the humerus to metacarpal IV is approximately 91% and the, humerus, femur and third wing phalanx are all equal in length and the feet are specially small. It represents the largest boroepterid pterosaur discovered from western Liaoning and its surrounding areas so far
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WANG Sufen, ZHANG Tingshan, ZHOU Jixian, HU Yu
2017,91(1):320-340, DOI:
Abstract:
The distribution characteristics of the oil-water contact are the basis for the reservoir exploration and development and reserves evaluation. The reservoir with a tilted oil-water contact has a unique formation mechanism, and the understanding of its distribution and formation mechanism will directly affect the evaluations for the reservoir type, well deployment, selection of well pattern and type, determination of test section, and reserves evaluation. Based on the analysis of reservoir characteristics, petrophysical properties and geological structure in 40 reservoirs worldwide with tilted oil-water contacts, the progress of the research on the formation mechanisms of titled oil-water contacts is summarized in terms of the hydrodynamic conditions, reservoir heterogeneity, neotectonic movement and oil-gas exploitation. According to the formation mechanism of tilted oil-water contacts and the needs of exploration research, different aspects of research methods are summarized and classified, such as the calculation of equipotential surfaces for oil and water in the formation, analysis of formation pressure and analysis of reservoir physical properties and so on. Based upon statistical analysis, it is suggested that the degree of the inclination of the oil-water contact be divided based on the dip of oil-water contact (DipTOWC). The tilted oil-water contact is divided into three categories: large dip (DipTOWC≥55 m/km), medium dip (4 m/km≤DipTOWC<55 m/km), and small dip (DipTOWC<4 m/km). The classification and evaluation method can be combined with structure amplitude and reservoir property. The formation mechanism of domestic and international reservoirs with tilted oil-water contacts are summarized in this paper, which have important significance in guiding the exploration and development of the oilfield with tilted oil-water contacts, reserves evaluation, and well deployment.
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Mahboobeh JAMSHIDI BADR, Fariborz MASOUDI, Alan S. COLLINS, Ali SORBI
2012,86(1):48-64, DOI:
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The Soursat metamorphic complex (SMC) in northwestern Iran is part of the Sanandaj–Sirjan metamorphic belt. The complex is composed of different metamorphic and plutonic rocks, but is dominated by metapelites composed of garnet, staurolite, kyanite, fibrolite, cordierite, and andalusite. Porphyroblasts in schists have the same fabric, and three stages of schistosity are present. The internal schistosity (Sn) inclusion trails are also offset by conjugate sets of extensional schistosity (Sn+1) and a second (Sn+2) that crenulates (Sn+1). Polyphase metamorphisms are present in the complex. Garnet, staurolite, kyanite, and fibrolite assemblage preserves conditions during the M1 metamorphic event. This assemblage yields a P–t estimate of 645±11°C and 6.5±0.5 kbar. Other samples of the central part of SMC contain cordierite and andalusite (M2) overgrowth that yields a P–t estimate of 532±33°C and 2.1±1.1 kbar.
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ZHENG Yadong, ZHANG Qing, HOU Quanlin
2015,89(4):1133-1152, DOI:
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The essential difference in the formation of conjugate shear zones in brittle and ductile deformation is that the intersection angle between brittle conjugate faults in the contractional quadrants is acute (usually ~60°) whereas the angle between conjugate ductile shear zones is obtuse (usually 110°). The Mohr-Coulomb failure criterion, an experimentally validated empirical relationship, is commonly applied for interpreting the stress directions based on the orientation of the brittle shear fractures. However, the Mohr-Coulomb failure criterion fails to explain the formation of the low-angle normal fault, high-angle reverse fault, and the conjugate strike-slip fault with an obtuse angle in the σ1 direction. Although it is ten years since the Maximum-Effective-Moment (MEM) criterion was first proposed, and increasingly solid evidence in support of it has been obtained from both observed examples in nature and laboratory experiments, it is not yet a commonly accepted model to use to interpret these anti-Mohr-Coulomb features that are widely observed in the natural world. The deformational behavior of rock depends on its intrinsic mechanical properties and external factors such as applied stresses, strain rates, and temperature conditions related to crustal depths. The occurrence of conjugate shear features with obtuse angles of ~110° in the contractional direction on different scales and at different crustal levels are consistent with the prediction of the MEM criterion, therefore ~110° is a reliable indicator for deformation localization that occurred at medium-low strain rates at any crustal levels. Since the strain–rate is variable through time in nature, brittle, ductile, and plastic features may appear within the same rock.
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CHI Guoxiang1, *, CHU Haixia1, Ryan SCOTT1, CHOU I-Ming2
2014,88(4):1169-1182, DOI:
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Raman peaks of various hydrates in the H2O-NaCl-CaCl2 system have been previously identified, but a quantitative relationship between the Raman peaks and XNaCl (i.e., NaCl/(NaCl+CaCl2)) has not been established, mainly due to the difficulty to freeze the solutions. This problem was solved by adding alumina powder to the solutions to facilitate nucleation of crystals. Cryogenic (-185oC) Raman spectroscopic studies of alumina-spiced solutions indicate that XNaCl is linearly correlated with the total peak area fraction of hydrohalite. Capsules of solutions made from silica capillary were prepared to simulate fluid inclusions. Most of these artificial fluid inclusions could not be totally frozen even at temperatures as low as -185oC, and the total peak area fraction of hydrohalite is not correlated linearly with XNaCl. However, the degree of deviation (DXNaCl) from the linear correlation established earlier is related to the amount of residual solution, which is reflected by the ratio (r) of the baseline “bump” area, resulting from the interstitial unfrozen brine near 3435 cm-1, and the total hydrate peak area between 3350 and 3600 cm-1. A linear correlation between DXNaCl and r is established to estimate XNaCl from cryogenic Raman spectroscopic analysis for fluid inclusions.
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DU Jianjun, LI Dunpeng, WANG Yufang, MA Yinsheng
2017,91(1):76-92, DOI:
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The Weihe Graben is not only an important Cenozoic fault basin in China but also a significant active seismic zone. The Huashan piedmont fault is an important active fault on the southeast side of the Weihe Graben and has been highly active since the Cenozoic. The well–known Great Huaxian County Earthquake of 1556 occurred on the Huashan piedmont fault. This earthquake, which claimed the lives of approximately 830000 people, is one of the few large earthquakes known to have occurred on a high–angle normal fault. The Huashan piedmont fault is a typical active normal fault that can be used to study tectonic activity and the associated hazards. In this study, the types and characteristics of late Quaternary deformation along this fault are discussed from geological investigations, historical research and comprehensive analysis. On the basis of its characteristics and activity, the fault can be divided into three sections, namely eastern, central and western. The eastern and western sections display normal slip. Intense deformation has occurred along the two sections during the Quaternary; however, no deformation has occurred during the Holocene. The central section has experienced significant high–angle normal fault activity during the Quaternary, including the Holocene. Holocene alluvial fans and loess cut by the fault have been identified at the mouths of many stream valleys of the Huashan Mountains along the central section of the Huashan piedmont fault zone. Of the three sections of the Huashan piedmont fault, the central section is the most active and was very active during the late Quaternary. The rate of normal dip–slip was 1.67–2.71±0.11 mm/a in the Holocene and 0.61±0.15 mm/a during the Mid–Late Pleistocene. As is typical of normal faults, the late Quaternary activity of the Huashan piedmont fault has produced a set of disasters, which include frequent earthquakes, collapses, landslides, mudslides and ground fissures. Ground fissures mainly occur on the hanging–wall of the Huashan piedmont fault, with landslides, collapses and mudslides occurring on the footwall.
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LI Jianjun, Martin G. LOCKLEY, ZHANG Yuguang, HU Songmei, MATSUKAWA Masaki, BAI Zhiqiang
2012,86(1):1-10, DOI:
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A large track site with multiple, well-preserved trackways of an Early Jurassic quadrupedal ornithischian dinosaur is the first report of Moyenisauripus-like trackways from Asia, herein named Shenmuichnus youngteilhardorum. The tracks occur in a clastic fluvial sequence in the Fuxian Formation in Shenmu County, Shaanxi Province, which is in the same general region as the discovery site of Sinoichnites，the first dinosaur track reported from China. Based on size and morphology, it is likely that Sinoichnites, which is now lost, also represents an ornithischian. The Shenmuichnus youngteilhardorum trackways show two modes of preservation: the first representing deeper tracks, with sediment rims, results in Deltapodus-like tracks, with indistinct pes digit traces and sub-circular manus traces, the second produces Moyenosauripus-like tracks, with clear tridactyl and pentadactyl digit traces in the pes and manus respectively. Thus the Shenmu trackways play a key role in resolving globally significant ichnotaxonomic problems surrounding the nomenclature of Sinoichnites, Moyenosauripus, Deltapodus and other named (Ravatichnus) and unnamed trackways from Asia, Africa and Europe. In addition they shed important light on the paleogeographical and paleoecological distribution of quadrupedal ornithischians in the Early Mesozoic. The track site has been the focus of a major excavation to transfer the trackways from their original remote location to the new Shenmu Museum, in Shenmu City. Other tracksites in the area which reveal Anomoepus, Grallator and the Deltapodus morphotype, together with Shenmuichnus and plant fossil evidence, suggest an Early Jurassic age for the tracksite.
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2015,89(3):715-725, DOI:
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Re-equilibration of fluid inclusions in crystals takes place by loss or gain of solvents and solutes from fluid inclusions and by changes in their volumes. Volume change of fluid inclusions are primarily dictated by elastic properties and available slip planes of host crystals. In the present study, the phase-behavior of fluids entrapped in co-precipitated calcite and barite is studied. While calcite contains only biphase fluid inclusions, barite has predominantly monophase fluid inclusions. Fluid inclusion petrography, microthermometry and leachate analysis are used to establish the nature of entrapped fluids and entrapment temperature is substantiated through independent sulfur isotope geothermometry using coexisting barite and pyrite. Phase transitions in the monophase fluid inclusions in barite are explained in terms of over-pressuring of fluids in these fluid inclusions relative to fluids entrapped in calcite owing to the low bulk modulus of barite.
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2021,95(3):1056-1056, DOI: 10.1111/1755-6724.14310
Abstract:
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ZHANG Gang, WANG Xuben, FANG Hui, GUO Ziming, ZHANG Zhaobin, LUO Wei, CAI Xuelin, LI Jun, LI Zhong, WU Xing
2015,89(2):531-541, DOI:
Abstract:
The Panxi region is located in the frontal zone of positive squeezing subduction and side squeezing shearing between the Indian plate and the Eurasian plate. The long-period magnetotelluric (LMT) and broadband magnetotelluric (MT) techniques are both used to study the deep electrical conductivity structure in this region; magnetic and gravity surveys are also performed along the profile. According to the 2-D resistivity model along the Yanyuan-Yongshan profile, a high-conductivity layer (HCL) exists widely in the crust, and a high-resistivity block (HRB) exists widely in the upper mantle in general, as seen by the fact that a large HCL exists from the western Jinpingshan tectonic zone to the eastern Mabian tectonic zone in the crust, while the HRB found in the Panxi tectonic zone is of abnormally high resistivity in that background compared to both sides of Panxi tectonic zone. In addition, the gravity and magnetic field anomalies are of high value. Combined with geological data, the results indicate that there probably exists basic or ultrabasic rock with a large thickness in the lithosphere in the Panxi axial region, which indicates that fracture activity once occurred in the lithosphere. As a result, we can infer that the high-resistivity zone in the Panxi lithosphere is the eruption channel for Permian Emeishan basalt and the accumulation channel for basic and ultrabasic rock. The seismic sources along the profile are counted according to seismic record data. The results indicate that the most violent earthquake sources are located at the binding site of the HRB and the HCL, where the tectonic activity zone is generally acknowledged to be; however, the earthquakes occurring in the HCL are not so violent, which reflects the fact that the HCL is a plastic layer, and the fracture threshold of a plastic layer is low generally, making high stress difficult to accumulate but easy to release in the layer. As a result, a higher number of smaller earthquakes occurred in the HCL at Daliangshan tectonic zone, and violent earthquakes occurred at the binding site of high- and low-resistivity blocks at the Panxi tectonic zone.
