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Granitic Magmatism in eastern tethys Domain(Western China) and their Geodynamic Implications

Acta Geologica Sinica(English Edition) 2022年第2期96卷 401-415页

作者： LAI Shaocong ZHU Renzhi QIN Jiangfeng ZHAO Shaowei ZHU Yu State Key Laboratory of Continental Dynamics Department of GeologyNorthwest UniversityXi’an 710069China

Western China locates in the eastern section of the tethys domain, granitic rocks in this region with variable formation ages and geochemistry record key information about the crust-mantle structure and thermal evolution during the convergent process of tethys. In this study, we focus on some crucial granitic magmatism in the western Yangtze, Qinling orogen, and western Sanjiang tectonic belt, where magma sequence in the convergent orogenic belt can provide important information about the crust-mantle structure, thermal condition and melting regime that related to the evolution processes from Pre-to Neo-tethys. At first, we show some features of Pre-Tethyan magmatism, such as Neoproterozoic magmatism(ca. 870–740 Ma) in the western margin of the Yangtze Block were induced by the assembly and breakup of the Rodinia supercontinent. The complication of voluminous Neoproterozoic igneous rocks indicated that the western Yangtze Block underwent the thermodynamic evolution from hot mantle-cold crust stage(ca. 870–850 Ma) to hot mantle and crust stage(ca. 850–740 Ma). The Neoproterozoic mantle sources beneath the western Yangtze Block were progressively metasomatized by subduction-related compositions from slab fluids(initial at ca. 870 Ma), sediment melts(initial at ca. 850 Ma), to oceanic slab melts(initial at ca. 825–820 Ma) during the persistent subduction process. Secondly, the early Paleozoic magmatism can be well related to three distinctive stages(variable interaction of mantle-crust to crustal melting to variable sources) from an Andeans-type continental margin to collision to extension in response to the evolution of Prototethys and final assembly of Gondwana continent. Thirdly, the Paleo-tethys magmatism, Triassic granites in the Qinling orogenic display identical formation ages and Lu-Hf isotopic compositions with the related mafic enclaves, indicate a coeval melting event of lower continental crust and mantle lithosphere in the Triassic convergent process and a continued hot mantle and crust thermal condition

关键词： granitic magmatism geodynamic western China eastern tethys

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A Toarcian Ocean Anoxic Event record from an open-ocean setting in the eastern tethys: Implications for global climatic change and regional environmental perturbation

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Science China Earth Sciences 2021年第11期64卷 1860-1872页

作者： Xiugen FU Jian WANG Huaguo WEN Chunyan SONG Zhongwei WANG Shengqiang ZENG Xinglei FENG Hengye WEI State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation Southwest Petroleum UniversityChengdu 610050China School of Geoscience and Technology Southwest Petroleum UniversityChengdu 610500China Institute of Sedimentary Geology Chengdu University of TechnologyChengdu 610059China Chengdu Center China Geological SurveyChengdu 610081China Qiangtang Institute of Sedimentary Basin Southwest Petroleum UniversityChengdu 610500China

The Early Toarcian“Oceanic Anoxic Event”(T-OAE)is recorded by marked disruption to both the climate system and marine ecosystems.Here,we present intergraded high-resolution carbon-isotope data(δ^(13)C),bulk geochemistry,mineral characterization from an open-ocean setting in the eastern tethys.With these data,we(1)construct the high-resolution record of the T-OAE from an open-ocean setting in the eastern tethys;(2)show that the T-OAE in the Sewa succession was marked by coarser-grained deposits associated with high-energy conditions within the otherwise low-energy claystone deposits that likely linked to a globally increased supply of clastic sediments into marginal and deeper marine basin;(3)propose that the low C_(org):P_(total) ratios,in combination with bioturbated structure and depletion or slight enrichment in redox-sensitive trace elements of V,Mo,and U suggest a long-term oxygenation event throughout the T-OAE interval at the Sewa succession,and hence,anoxia may not play a fundamental role during the Toarcian negative CIE in this setting;(4)exhibit that a warming and more humid climate began at the start of the T-OAE,and many episodic changes in sediment provenance throughout the T-OAE interval occurred at this location;and(5)suggest that accumulation of organic-matter sediments during the T-OAE is generally controlled by global climatic changes,but a regional environmental perturbation also might influence the preservation of organic matter.

关键词： Toarcian Oceanic Anoxic Event Carbonate carbon isotopes Shallow marine Oxygen-rich conditions eastern tethys

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Decoupled δ^(13)Ccarb and δ^(13)Corg records at Triassic–Jurassic boundary interval in eastern tethys: Environmental implications for spatially different global response

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Geoscience Frontiers 2021年第4期12卷 175-184页

作者： Yuzhu Ge Department of Earth Sciences Khalifa University of Science and TechnologyPO Box 127788Abu DhabiUnited Arab Emirates Institute of Geology Mineralogy and GeophysicsRuhr-University Bochum44780 BochumGermany

Althoughδ^(13)C data(eitherδ^(13)Ccarb orδ^(13)Corg)ofmany Triassic–Jurassic(T-J)sections have been acquired,pairedδ^(13)Ccarb andδ^(13)Corg from continuous T-J carbonate sections,especially in eastern tethys,have been scarcely reported.This study presents paired and decoupledδ^(13)Ccarb andδ^(13)Corg data from a continuous T-J carbonate section in Wadi Naqab.The T-J Wadi Naqab carbonate section,located in United Arab Emirates,Middle East,represents tropical and shallow marine sedimentation in eastern tethys.At the T-J boundary interval,an initial carbon isotope excursion(CIE)is observed with different magnitude of isotope excursion and timing inδ^(13)Ccarb andδ^(13)Corg,while subsequently a positive CIE is only distinct inδ^(13)Ccarb.Based on petrological,carbon isotope,Rock-Eval and elemental analyses,theδ^(13)Ccarb is thought to record marine inorganic carbon,and theδ^(13)Corg to record terrigenous organic carbon.Therefore,the pairedδ^(13)Ccarb andδ^(13)Corg herein potentially document simultaneous changes in T-J atmospheric and marine settings of eastern tethys.Their decoupled behavior may likely be caused by different changes or evolution of carbon pool between marine and atmospheric settings.The initial CIE present in bothδ^(13)Ccarb andδ^(13)Corg may indicate influence of isotopically light carbon release related to CAMP activity in both atmospheric and marine settings.The following positive CIE only inδ^(13)Ccarb suggests relatively steady carbon isotope composition in atmosphere,but enhanced burial of isotopically light carbon in marine settings.Furthermore,the T-J carbonates in the studied section were possibly deposited in normal and oxic shallow marine conditions.Global correlation based on the Wadi Naqab section and other T-J sections suggests spatially different T-J environmental parameters:in eastern tethys and western Panthalassa,oxic condition,lacking organic-rich sediment,weaker ocean acidification and less influence of isotopically light carbon are more prevalent;in western tethys and eastern P

关键词： Triassic–Jurassic δ^(13)C records eastern tethys Global difference

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Organic geochemistry and source rock potential assessment of Late Paleocene Patala Formation in Margalla Hill Range,North Pakistan

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Global Geology 2021年第4期24卷 213-225页

作者： Shams M.Kamran WANG Pujun Nasar Khan Muhammad Hassan College of Earth Sciences Jilin UniversityChangchun 130061China Department of Geology University of MalakandChakdara 18800Khyber PakhtunkhwaPakistan

Black shales of the Paleocene Patala Formation are proven source rocks for conventional hydrocarbons in southern Potwar Basin of Pakistan and are assumed to be effective source rocks towards north in the Margalla Hill Range of Pakistan.In this regard,the current study focuses on source rock geochemistry of the Paleocene Patala Formation to assess its source rock potential,organic matter types and thermal maturity levels in the Margalla Hill Range of North Pakistan.Source rock generative potential,kerogen types and thermal maturation of the analysed rock samples were unraveled by using Rock-Eval pyrolysis T_(max),TOC(total organic carbon)and vitrinite reflectance(R_(0))analyses.TOC analysis coupled with S_(2) yield revealed poor to fair source rock quality encountered within the formation.The pyrolysis T_(max) vs Hydrogen Index(HI),showed mostly Type Ⅲ kerogen dominated by thermally immature to mature organic matter.The HI and genetic potential is low and revealed poor hydrocarbon generation potential of the formation.The S_(1) vs TOC plots confirm the indigenous nature of the hydrocarbons hosted by Patala Formation.The vitrinite reflectance outcomes indicated immature to mature source rock beds lying in dry gas zone.The HI and OI signatures and abundance of Type Ⅲ kerogen are indicating dominance of terrestrial organic matter within the formation.Overall,the investigated Patala Formation exposed at the studied section of Margalla Hill Range,Pakistan acts as a poor source rock unit for liquid hydrocarbon generation but holds prospects for dry gas generation in the study area.

关键词： Patala Formation organic geochemistry thermal maturity Margalla Hill Range North Pakistan eastern tethys

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