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    20 February 2022, Volume 28 Issue 1
    Research Progress and Prospect of the Gangdese Magmatic Belt in Southern Tibet
    MENG Yuanku, YUAN Haoqi, WEI Youqing, ZHANG Shukai, LIU Jinqing
    2022, 28(1):  1-31.  DOI: 10.16108/j.issn1006-7493.2020057
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    The Gangdese magmatic belt is the product of the northward subduction of the Neo-Tethys oceanic lithosphere beneath the Lhasa terrane and subsequent India-Asia collision. The Gangdese magmatic arc belongs to the typical continental magmatic belt and is the target area for studying plate accretion, crustal growth and reworking and collisional orogeny. Numerous lines of evidence indicate that the Neo-Tethys oceanic lithosphere experienced four distinct stages of evolution: the early-stage subduction (>152 Ma), late-stage subduction (100 to 65 Ma), main-collisional (55 to 40 Ma), and post-collision extentional stages (23 Ma to present). Multiple studies were carried out in the Gangdese belt and much progress has been made during past decades. However, the formation and evolution of the Neo-Tethys Ocean and magma source of igneous rocks are still debated, especially the detailed petrogenetic dynamic processes. This paper reviews the evolution history and tectonic background, and then summarizes related

    scientific problems from thirteen aspects. It is shown that the Gangdese magmatic belt is a typical magmatism-tectonismmineralization-deformational metamorphism belt and experienced multi-stage evolution processes rather than a simple
    continental magmatic arc aggregated in the Lhasa terrane. The review shows that (1) the Gangdese magmatic belt is a natural
    laboratory for studying the evolution history of the Neo-Tethys, and provides better constraints on the styles of the subducting
    slab. (2) The different-stage granitoid stocks and batholiths might be formed by multiple additions and incremental assembly of
    magmas over a span of millions of years or even longer. Therefore, we should use a mush model to reconstruct petrogenesis and
    petrogenetic secnarios of granitoid rocks in detail. (3) The mantle nature of the Gangdese region shows complicated features that
    are characterized by geochemical heterogeneity along the arc strike direction. (4) The reversed isotopes exist in the Gangdese belt, probably indicating an ancient nucleus. (5) The Gangdese belt is tilting and has different crustal compositions that are characterized by lower crustal compositions in the eastern segment and middle-upper crustal compositions in the middle-western segment. Crustal tilting of the Gangdese region suggests a differential and imbalanced exhumation process. (6) At present, numerous studies are focused on igneous rocks with methods mainly including radioactive Sr-Nd-Hf isotopes, whereas non-traditional stable isotopes (Mg-O-Li-B-Mo) are rarely reported. In addition, research topics are mainly associated with petrogenesis and geochronology, but few studies focus on the magma emplacement and post-magmatic deformation and uplifting-denudation processes. (7) Research in structural geology of the area is few and usually tectonic evolution is inferred from magmatic evolution in the Gangdese belt, southern Tibet. Finally, we also provide future prospects based on the current research status of the Gangdese magmatic belt in southern Tibet.

    Geochemical Characteristics of Rhododendron nivale Hook. f. and Its Indication for Concealed Lithium Deposits in Jiajika Rare Metal Mining Area
    LIU Ting, LIANG Bin, DUAN Jiaxin, XU Zhiqiang, JIANG Hui, WANG Qiubo
    2022, 28(1):  32-39.  DOI: 10.16108/j.issn1006-7493.2020034
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    Rhododendron nivale Hook. f. subsp. boreale Philipson et M. N. Philipson is the dominant plant species in the Jiajika rare metal mining area located in the eastern Tibetan Plateau. In this study, the Rhododendron nivale Hook. f. over two buried but known lithium orebodies, NO.804 and ST, was sampled, and the anomalies of rare metals in these samples were used to delineate the orebodies. The results show that notable botano-geochemical anomalies of Li, Be, Rb, Nb, and Ta have been found in Rhododendron nivale Hook. f Jiajika area, botano-geochemical anomalies have been developed above the two concealed lithium ore bodies, the positions of the anomaly and the concealed deposit agree well, which can reflect the existence of deposits at different buried depths up to 100 m. Therefore, this provides a new method for the Jiajika rare metal area to search for concealed ore deposits.
    Marine Redox Fluctuation during the Early Cambrian Age 10: Evidence from U Isotopes
    QIU Chen, WEI Guangyi, MIN Siyu, CHEN Xi, LING Hongfei
    2022, 28(1):  40-50.  DOI: 10.16108/j.issn1006-7493.2020038
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    The marine animal diversity was generally low during late Cambrian and early Ordovician. Biogeochemical studies suggest that it may have been related with fluctuations in oceanic redox conditions, despite still lack of evidence. Well-preserved marine carbonates could record the geochemical characters of ancient seawater, and their uranium isotope compositions (δ238U) can be used to reconstruct the global oceanic redox conditions. In this study we analyzed the uranium isotope compositions of marine carbonates of the basal Cambrian Stage 10 from Wa’ergang section, South China. Our data show that the δ238U profile has three negative excursions with minima of -0.8‰ , -0.55‰ and -0.60‰ , respectively, which indicates three intervals of oceanic anoxia expansion. Modeling results based on the uranium isotope mass balance model suggest that about 22%, 3.5% and 5% of the global sea-floor were covered by anoxic water during these three intervals, respectively. We speculate that the first anoxic interval may have been related with increase in primary productivity due to enhanced weathering input of nutrients, and the latter two may have been induced by upwelling of deep anoxic water during the transgressions.
    Overview of the Application and Prospect of Common Chemical Weathering Indices
    LI Xulong, ZHANG Xia, LIN Chunming, HUANG Shuya, LI Xin
    2022, 28(1):  51-63.  DOI: 10.16108/j.issn1006-7493.2020118
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    Common chemical weathering indices such as the Weathering Index of Parker (WIP), the Chemical Index of Alteration (CIA), the Index of Compositional Variability (ICV), CIX index and αAlE are often used to evaluate the chemical weathering intensity of source areas. But the factors which controlling the above chemical weathering indices should be considered, otherwise the results of the weathering evaluation will be distorted. This paper argues that the geological survey of source area should be known when chemical weathering indices are used to study the chemical weathering process. The selection of fine sediments or suspended matter can weaken the influence of grain size on chemical weathering indices. The impurities in the sediments are removed by acid treatment. Then, the Sc/Th-CIA diagram was used to reflect the material source information, Th/SC-Zr/Sc diagram was used to further distinguish the control effect of sedimentary differentiation and sedimentary recirculation, and then the samples with ICV value less than 1 were selected to eliminate the interference of recirculation. The A-CN-K diagram or the formula proposed by Panahi (2000) were used to correct the potassium metasomatism, and the strength of chemical weathering of source rocks was evaluated by CIA eventually. To ensure that the calculation of chemical weathering indices can accurately reflect the weathering situation of the source area, SPSS software can be used to analyze the proportion of some factors which affecting the CIA to construct characteristic weathering index of the study area.
    Fluid Inclusions and Hydrocarbon Accumulation Stages of Mesoproterozoic Reservoirs in the Jibei Depression
    CHEN Ruiqian, LIU Guangdi, SUN Mingliang, CAO Yushun, LIU Xiangbai, LI Qiang
    2022, 28(1):  64-72.  DOI: 10.16108/j.issn1006-7493.2020040
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    Solid bitumen and oil seepage are widely distributed in the Mesoproterozoic strata in the Jibei Depression, North China, suggesting large scales of hydrocarbon accumulation. In this study, microscopic petrographic observations and fluid inclusion analyses were used to reconstruct the hydrocarbon accumulation history in the Lujiazhuang and Shuangdong paleo-oil-reservoirs within the Jibei Depression. Results show that there was a large scale of hydrocarbon accumulation during the Mesoproterozoic. One more stage of hydrocarbon accumulation occurred during the Yanshanian in the Lujiazhaung paleo-oil reservoirs, while two more stages in the Shuangdong paleo-oil reservoirs. The homogenization temperatures of fluid inclusion indicate that the time of hydrocarbon accumulation of the two paleo-oil reservoirs during the Yanshanian was concentrated during 185-150 Ma. Our study shows that the critical time of hydrocarbon accumulation in the Jibei Depression was related to the high paleo-geotemperature caused by regional active volcanic activity during the Yanshanian.
    Hydrocarbon Generation Potential of Pre-Paleogene Source Rocks in the Jiyang Depression#br#
    NIU Zicheng, WANG Yongshi, WANG Xuejun, ZHANG Xuejun, WANG Xiuhong, HAN Dongmei, LIU Xuan, WANG Ru, WANG Juan
    2022, 28(1):  73-85.  DOI: 10.16108/j.issn1006-7493.2020068
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    Multiple sets of pre-Paleogene strata with relatively low exploration levels have developed in the Jiyang Depression. The Lower Paleozoic Cambrian-Ordovician, Upper Paleozoic Carboniferous-Permian and Mesozoic all host source rocks and thus can theoretically generate oil and gas for accumulation in the study area. Different tectonic and sedimentary backgrounds lead to different geochemical characteristics among different sets of source rocks. This study comprehensively analyzes  data of geology, source rock pyrolysis and TOC, vitrinite reflectance, whole rock microscopic composition, and gas chromatography-mass spectrometry of saturated and aromatic hydrocarbons. The distribution, geochemistry and resource potential of the pre-Paleogene source rocks in the Jiyang Depression were determined. The Lower Paleozoic marine carbonate source rocks have limited distribution and low abundance of organic matter, but have organic matter types favourable for certain hydrocarbon generation capacity. The widely distributed Upper Paleozoic coaly source rocks, with high abundance of organic matter and relatively poor organic matter types, are dominated by gas generation. As a result of complex tectonic evolution, this set of source rock is characterized by secondary hydrocarbon generation. The Mesozoic has developed two sets of source rocks (i.e., coaly source rocks and lacustrine mudstones) with medium organic matter types. Medium- to good-quality source rocks are developed locally with varying maturity spatially. Overall, among the thr ee sets of pre -Paleogene source rocks in the Jiyang Depression, the Upper Paleozoic coal-measure source rocks have the best quality, followed by the Mesozoic, and the Lower Paleozoic is relatively poor.

    Regional Background and Tectonic Evolution of Dingyuan Sag
    ZHAN Run, DING Hai, ZHANG Wenyong, SUN Gui, SUI Fengtang, XIN Yongchao
    2022, 28(1):  86-95.  DOI: 10.16108/j.issn1006-7493.2020062
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    Tectonic evolution and its origin of the upper Paleozoic in the Dingyuan Sag are essential for the evaluation of coal resources and exploration targets of unconventional natural gas. Based on the latest geophysical and drilling data, combined with results from previous studies, we discussed the tectonic evolution and its origin in detail via structural analysis and regional comparison. Results show that the upper Paleozoic coal-bearing strata are comparable to the middle segment of the Huainan coalfield, which show an anticline pattern. The Dingyuan Sag has been affected by the strike-slip activities of the Tan-Lu Fault Zone and uplift of the Dabie Orogenic Belt from the Mesozoic to Cenozoic. The tectonic evolution in the Dingyuan Sag can be divided into six main stages, including foreland deformation in the Indosinian (T3), relative uplift in the early-middle Jurassic (J1+2), reformation by strike-slip activities of the Tan-Lu fault zone from the late Jurassic (J3) to early Cretaceous, reformation by extension activity from the early Cretaceous (K1) to Paleogene (E), inversion by compression activity in the late Paleogene, and depression with uniform deposition from the Neogene to Quaternary (N-Q).
    A Review of the Establishment Methods of Training Image in Multiple-point Statistics Modeling
    WANG Mingchuan, SHANG Xiaofei, DUAN Taizhong
    2022, 28(1):  96-103.  DOI: 10.16108/j.issn1006-7493.2020049
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    Multiple-point statistics (MPS) modeling has been the research hotspot of reservoir modeling technology in recent years, and its practicability is restricted by training image. The quality of training image determines the accuracy and reliability of MPS modeling, and is a key factor for the successful application of MPS modeling. This study addresses the characteristics and significance of training image, and systematically introduces the establishment methods of training image creation from the definition, usage and instance, etc., including hand drawn, object-based simulation, 3D seismic information extraction or transformation, prototype- ased model, process-based simulation and 2D image method. Then, our study comprehensively compares the data sources, advantages and disadvantages of various training image creation methods, and discusses the problems caused by MPS modeling relying on training images. Combined with reviewing prior works and MPS modeling practice, the research direction of training image and its establishment methods in the future is pointed out, which provides reference for MPS modeling researchers and users, and provides some thoughts for improving MPS modeling methods.
    Research on Time-Space Error of Continuous Monitoring and High-precision Simulation of Shallow Ground Temperature Field
    ZHANG Liwei, LIU Chun, LI Jichen, KOU Yudong
    2022, 28(1):  104-111.  DOI: 10.16108/j.issn1006-7493.2020077
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    To investigate the temporal and spatial evolution of ground temperature, using a variety of temperature sensors comprehensively, continuous high-precision temperature data of 0 to 100 m in three boreholes in Nanjing City were obtained, and the change in ground temperature for 3 months was simulated based on the one-dimensional heat conduction equation. By analyzing the temporal and spatial variation laws of measured and simulated ground temperature, the simulation error of shallow ground temperature field under different spatial and temporal accuracy modeling conditions is explored. Compared with the average thermal diffusion coefficient, when the layered thermal diffusion coefficient is used, the shallow simulated temperature of 0-4 m reduces the error by 2%-4%. Compared with the results of high-precision boundary simulation, the results don’t show much difference when the boundary is the daily average temperature, while the accuracy of monthly average temperature is reduced by 2%-3% between 0-5 m, and the influenced depth on the homogeneous layer is smaller. For the simulation of the ground temperature at the shallow temperature layer, the use of segmented thermal diffusion efficient at the depth of 0-5 m and the daily average temperature as the boundary condition can reduce the monitoring cost while ensuring the accuracy of the results. It also provides a reference for the long-term prediction and evaluation of shallow ground temperature in Nanjing.
    Research on the Mechanics Properties and Failure Modes of Crackcontaining Shales Coupled with Seepage Flow Stress
    WU Zhonghu, LIU Guichuan, GONG Jinyuqiong, YU Xiaoyue, LI Hao
    2022, 28(1):  112-118.  DOI: 10.16108/j.issn1006-7493.2020044
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    In order to study the mechanical properties and failure modes of fractured shale under the seepage stress, the rock failure process analysis system RFPA2D-flow was used to establish 7 groups of shale models with prefabricated fractures at different angles and the fracture process was numerically simulated. The results show that the fracture process of the shale can be divided into three stages: progressive linear deformation, yield deformation and complete failure. Due to the existence of fractures, the elastic modulus and compressive strength of the shale show distinct anisotropic characteristics and the final fracture mode of the sample can be divided into four types: slash-type, X-type, λ-type and collapse-type. For the crack distributions under different bedding inclinations, the fracture of the shale sample under the coupled percolation-stress is mainly tensile failure accompanied by shear failure, and the test shows that the shear failure of the sample is most serious when α =90°. These results have important implications for shale exploitation.
    Paleomagnetism of Permian-Lower Triassic Strata in the Southern Longmenshan Fold-Thrust Belt
    LI Wei, JIA Dong, ZHANG Yong, LI Yongxiang, ZHONG Cheng, GE Jiacheng
    2022, 28(1):  119-128.  DOI: 10.16108/j.issn1006-7493.2020066
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    In order to study and constrain the tectonic movement characteristics of the southern Longmenshan fold-thrust belt, the paleomagnetic study was carried out on the light purple gray mudstone and siltstone of the lower Triassic Feixianguan formation near Dachuan town and the Permian limestone in Baoxing in the southern Longmenshan fold-thrust belt. Paleomagnetic samples were collected from 10 sampling sites, of which 3 are Permian limestone and 7 are light purple gray mudstone and siltstone of Feixianguan Formation. We have conducted the experiments of stepwise thermal demagnetization, rock magnetism (isothermal remanent magnetization acquisition curves and triaxial isothermal remanent thermal demagnetization) and scanning electron microscope. Based on the stepwise thermal demagnetization experiments of 80 samples, we revealed a stable characteristic remanence from the Feixianguan Formation samples but not from the Permian limestone samples. The high temperature components pass simple generalized fold test, the tilt-corrected mean direction of the characteristic remanence is:Ds=36.9°, Is=16.5°,α95=5.9°, K=33.8, N=18 and the corresponding paleomagnetic pole position plots close to the Early Triassic mean pole of the apparent polar wander path for the south China Block. The results of rock magnetic show that the major magnetic mineral of Feixianguan formation is magnetite, and the scanning electron microscope observation shows that it is clastic iron oxide, and there is no obvious post diagenetic authigenic characteristics. Combined with the characteristics of demagnetization curve, scanning electron microscope, paleomagnetic pole position of characteristic remanence and rock magnetic results, the characteristic remanence of Feixianguan formation is likely to be primary remanence. The results show that there is no obvious relative tectonic rotation between the Longmenshan fold-thrust belt and Sichuan Basin. Since the Late Triassic, the northern and southern Longmenshan fold-thrust belt and Sichuan Basin are unified tectonic units in dynamics.

    A Sedimentary Record of Environmental and Paleoclimatic Changes in the North Shore of Hangzhou Bay since the Pleistocene
    LIN Zhongyang, LIU Jian, JIN Xianglong, WU Ming, ZHAO Xudong, PAN Shaojun
    2022, 28(1):  129-139.  DOI: 10.16108/j.issn1006-7493.2020035
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    The BZK04 borehole (237.80 m deep) is located in the south wing of the Yangtze River Delta and the north bank of Hangzhou Bay. The core contains a relatively complete and continuous sedimentary sequence since the Pleistocene. In this study, the sediment lithology, micropaleontology, sporopollen assemblage, particle size content, paleomagnetism and OSL dating of the core were analyzed comprehensively, the characteristics of depositional environment evolution and paleoclimatology changes since the Pleistocene in the research area were discussed, and the framework of quaternary multiple stratigraphic divisions and correlatiosn was established. The results show that from bottom to top, the BZK04 core can be divided into carbonaceous mudstone (Ech) of the Changhe Formation, and the Jiaxing Formation(N-Qp1j), Qiangang Formation( Qp2q), Dongpu Formation( Qp3d), Ningbo Formation (Qp3n) and Zhenhai Formation (Qhzh) since the early Pleistocene epoch; Foraminifera of 17 species in 11 genera were identified , including 16 benthonic foraminifera and 1 planktonic foraminifera; The ostracod of 8 species in 8 genera was identified ; Pollen analysis reveals that there were 37 types of pollen, including 18 woody plant pollen, 11 herbaceous pollen, and 8 fern spore; The content of woody plants was the highest in the palynological assemblage (85.1%), followed by fern spores (8.7%) and herb pollen (6.3%). According to the comprehensive analysis of the sedimentary environment of borehole by lithologic stratification features, sedimentary facies, sporopollen, foraminifera and ostracodes, and grain size distribution frequency curve, the depositional environmental record is characterized by 18 pollen assemblages and 7 paleoclimatic cyclic changes, among which the early Pleistocene is dominated by fluvial and lacustrine facies deposits, indicating two paleoclimatic cycles from the third warm period to the fourth cold period; The middle Pleistocene was dominated by fluvial facies, lacustrine facies, and fluvial and lacustrine facies, revealing two paleoclimatic cycles from the fifth warm period to the sixth cold period; The late Pleistocene is dominated by the tidal-flat facies, estuarine facies and neritic facies, corresponding to two paleoclimatic cycles from the seventh warm period to the eighth cold period; In the Holocene, there were tidal-flat facies, fluvial and lacustrine facies, corresponding to the Atlantic and boreal periods. This study provides an important basis for further understanding the changes in quaternary sedimentary environment, the stratigraphic divisions and the paleoclimate evolution since the Pleistocene in the southern side of the Yangtze River Delta.