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Geochronology and Genetic Model for Early Cretaceous Volcanic Rocks from the Southern Qiangtang Terrane,northern tibet,China: Constraints from U-Pb Zircon Dating, Whole-Rock Geochemical and Sr-Nd Isotopic Data

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Acta Geologica Sinica(English Edition) 2018年第6期92卷 2157-2178页

作者： LIU Shen FENG Caixia M.Santosh FENG Guangying XU Mengjing Ian M.COULSON GUO Xiaolei GUO Zhuang FAN Yan State Key Laboratory of Continental Dynamics and Department of Geology Northwest UniversityXi'an 710069China China University of Geosciences Beijing 100083 BeijingChina Department of Earth Sciences University of AdelaideAdelaide SA 5005Australia Institute of Geology Chinese Academy of Geological Sciences100037 BeijingChina Solid Earth Studies Laboratory Department of GeologyUniversity of ReginaReginaSaskatchewan S4S OA2Canada

Post-collisional volcanic rocks of Mesozoic age occur in the regions adjacent to Gerze, part of the southern Qiangtang Terrane of northern tibet, China. Geochronological, geochemical, and wholerock Sr-Nd isotopic analyses were performed on the volcanic rocks to better characterize their emplacement age and models for their origin. Laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS) U-Pb zircon analyses yielded consistent ages ranging from 123.1±0.94 Ma to 124.5±0.89 Ma for six volcanic rocks from the study area. The intermediate volcanic rocks belong to the alkaline and sub-alkaline magma series in terms of K2 O+Na2 O contents(5.9%–9.0%), and to the shoshonitic and calc-alkaline series on the basis of their high K2 O contents(1.4%–3.3%). The Gerze volcanic rocks are characterized by the enrichment of light rare earth elements [(La/Yb)N=34.9–49.5] and large–ion lithophile elements(e.g., Rb, Ba, Th, U, K, Pb, and Sr), slightly negative Eu anomalies(Eu/Eu*=0.19–0.24), and negative anomalies in high field strength elements(e.g., Nb, Ta, Hf and Ti), relative to primitive mantle. The samples show slightly elevated(87 Sr/86 Sr)i values that range from 0.7049 to 0.7057, and low εNd(t) values from-0.89 to-2.89. These results suggest that the volcanic rocks studied derived from a compositionally heterogeneous mantle source and that their parent magmas were basaltic. The more mafic, parental magmas to the Gerze volcanic rocks likely underwent fractional crystallization of clinopyroxene, hornblende, biotite, and potassium feldspar, during ascent, with little to no crustal contamination, prior to their eruption/emplacement. While these volcanic rocks exhibit geochemical signatures typical of magmas formed in a destructive plate-margin setting, it is plausible that their mantle source might also have acquired such characteristics in an earlier episode of subduction.

关键词： volcanic rock U–Pb age–dating origin Qiangtang Terrane northern tibet

Jurassic Black Shales Facies from Qiangtang Basin (northern tibet): Rare Earth and Trace Elements for Paleoceanographic Implications

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Acta Geologica Sinica(English Edition) 2013年第2期87卷 540-554页

作者： CHEN Lan YI Haisheng TSAI Louis Loung-Yie XU Guiwen DA Xuejuan LIN Andrew Tien-Shun College of Petroleum Engineering Chongqing University of Science and Technology Institute of Applied Geology National Central University Institute of Geophysics National Central University Institute of Sedimentary Geology Chengdu University of Technology State Key Laboratory of Oil/Gas Reservoir Geology and Exploitation Chengdu University of Technology

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.

关键词： Jurassic black shale facies rare earth and trace elements paleoceanography northern tibet

Dynamics of Above-and Below-ground Biomass and C,N,P Accumulation in the Alpine Steppe of northern tibet

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Journal of Mountain Science 2011年第6期8卷 838-844页

作者： LU Xuyang YAN Yan FAN Jihui CAO Yingzi WANG Xiaodan Key Laboratory of Mountain Environment Evolvement and Regulation Institute of Mountain Hazards and Environment CAS Chengdu 610o41 China Shenzha Alpine Steppe and Wetland Ecosystem Observation and Experiment Station Institute of Mountain Hazards and Environment CAS Shenzha 85310o China

The temporal dynamics of the biomass, as well as the carbon （C）, nitrogen （N）, phosphorus （P） concentrations and accumulation contents, in above- and below-ground vegetation components were determined in the alpine steppe vegetation of northern tibet during the growing season of 2OLO. The highest levels of total biomass （311.68 g m-2）, total C （115.95 g m-2）, total N （2.60 g m-2）, and total P （0.90 g m-2） accumulation contents were obtained in August in 2010. Further, biomass and nutrient stocks in the below-ground components were higher than those of the above-ground components. The dominant species viz., Stipa purpurea and Carex moorcrofli had lower biomass and C, N, P accumulations than the companion species which including Oxytropis. spp., Artemisia capillaris Thunb., Aster tataricus L., and SO on.

关键词： Biomass Nutrient concentration Nutrient accumulation Alpine steppe northern tibet

Chemo-and Biostratigraphy of the Jurassic Oil Shales from the Qiangtang Basin,northern tibet,China:A Case Study of the Toarcian Oceanic Anoxic Event

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Acta Geologica Sinica(English Edition) 2017年第2期91卷 630-643页

作者： CHEN Lan XU Guiwen DA Xuejuan YI Haisheng ZHU Zhangxiong HUANG Zhaohui LI Xiaogang Chongqing University of Science and Technology Chongqing 401331China State Key Laboratory of Ore Deposit Geochemistry Institute of GeochemistryChinese Academy of Sciences99 West Lincheng RoadGuiyang 550081China University of Chinese Academy of Sciences Beijing 100049China Institute of Sedimentary Geology Chengdu University of TechnologyChengdu 610059SichuanChina

The marine oil shales of the Qiangtang Basin, northern tibet, exposed in the Biluo Co, Tuonamu, Shenglihe and Changsheshan areas are believed to be important petroleum source rocks. This work comprehensively analyzed the carbon isotopes, trace elements, and calcareous nannofosills, ammonites and bivalves of the Biluo Co section in the Qiangtang Basin. The organic carbon isotopes show a positive excursion close to 2.17‰（relative to PDB）, which, albeit significantly smaller, may also be associated with other Early Toarcian Oceanic Anoxic Events（T-OAE） in the European epicontinental seas and the Tethyan continental margins. Coinciding with the Early Toarcian transgression, the oxygen deficiency in bottom water had led to dysoxic-anoxic conditions and deposition of black shales lacking benthic fauna. Under such condition, the redox-sensitive trace metals such as Mo, V, Ni, Cr, and U were enriched, in conjunction with high planktonic productivity of Watznaueriaceae calcareous nannofossils. Comparison of the results with the records of chemo-and biostratigraphy, as well as the palaeogeography during the Early Jurassic suggests that the anoxia linked to the Early Toarcian oceanic anoxic event was mainly caused by the high surface water temperature, sea-level rise and an increase of surface water productivity.

关键词： oil shales geochemistry palaeontology T-OAE northern tibet Proto-Tethys

Origin of Qushenla Formation Volcanic Rocks in the Nawucuo Area,northern tibet,and Constraints on the Subduction Polarity of the Bangong-Nujiang Tethys Ocean

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Journal of Earth Science 2023年第2期34卷 467-486页

作者： Chuanyang Lei Liqiang Wang Juxing Tang Wei Li Teng Gao Huayun Yuan College of Earth Science Chengdu University of TechnologyChengdu 610059China MNR Key Laboratory of Metallogeny and Mineral Assessment Institute of Mineral ResourcesChinese Academy of Geological SciencesBeijing 100037China Evaluation and Utilization of Strategic Rare Metals and Rare Earth Resource Key Laboratory of Sichuan Province Sichuan Geological SurveyChengdu 610081China Chuanyang

The Qushenla Formation volcanic rocks are widely exposed in the northern margin of the Bangong-Nujiang suture zone(BNSZ).Research on these rocks is of great significance for understanding the tectonic evolution of the Bangong-Nujiang Tethys Ocean(BNTO).In this study,a systematic geological survey was conducted on the Qushenla Formation volcanic rocks that are widely exposed in the Nawucuo area,in the northern margin of the western segment along the *** whole-rock geochemistry,zircon U-Pb dating,and in situ zircon Lu-Hf isotopes were carried out in this study,aiming to constrain the formation age,rock genesis,magma source and tectonic setting of the volcanic *** zircon U-Pb dating shows that the Qushenla Formation volcanic rocks in the western BNSZ erupted during the period of 120–108 Ma,i.e.,Early *** Qushenla Formation volcanic rocks are a suite of intermediate-basic volcanic and pyroclastic rocks belonging to the medium-K calc-alkaline *** are relatively enriched in light rare earth elements(LREEs)and incompatible elements such as Rb,K,La,Th,Sm,and Hf,whereas depleted in heavy REEs(HREEs)and high field strength elements(HFSEs)such as Nb,P,Zr,and *** in situ zirconεHf(t)values of the volcanic rocks range from 8.95 to 12.57,with an average of *** Mg#,Th/La and Th/Ce values are between those of the mantle-derived magma and the continental *** formation of the Qushenla Formation volcanic rocks can be explained through the following process:(1)As the nospheric materials that upwelled during the rollback of the subducting Tethys Ocean slab induced the large-scale partial melting of the mantle wedge and the formation of the initial basaltic magma.(2)These mantle-derived magmas ascended and induced the partial melting of the lower crust to generate peraluminous melts.(3)The mixing of the peraluminous melts and mantle-derived melts generated the initial magma with homogeneous Sr-Nd isotope compositions.(4)Last,the eruption of th

关键词： volcanic rocks Qushenla Formation subduction polarity Bangong-Nujiang suture zone northern tibet geochemistry

Late Jurassic oceanic plateau subduction in the Bangong-Nujiang Tethyan Ocean of northern tibet

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Geoscience Frontiers 2024年第4期15卷 274-289页

作者： Hao Wu Haiyong Liu Yu Wang Xijun Liu Qinggao Zeng Panxi Wang Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration&Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources on Guangxi Guilin University of TechnologyGuilin 541006China tibet Geological Survey Lhasa 850000China tibet Bureau of Geological and Mineral Exploration and Development Lhasa 850000China

Oceanic plateau accretion and subsequent flat-slab subduction in modern convergent settings have profoundly influenced the nature of subduction and mantle ***,evaluating similar impacts in ancient convergent settings,where oceanic plateaus have been subducted but geological records are limited,remains *** this study,we present geochronological and geochemical data for a suite of ore-associated plutonic rocks from the Gaobaoyue area of northern *** rocks have zircon U-Pb ages of 152-146 Ma,with high Sr contents and Sr/Y and La/Yb ratios,low MgO,Yb,and Y contents,and depleted Sr-Nd-Hf isotopic compositions,consistent with an adakitic affinity that was generated by the partial melting of subducting oceanic *** compare the Late Jurassic adakitic magmatism with the spatiotemporal evolution of magmatism in northern tibet to infer oceanic plateau subduction and subsequent flat-slab subduction in the Bangong-Nujiang Tethyan *** tectonic model explains(ⅰ)slab-derived adakitic magmatism,(ⅱ)the observed lull in magmatic activity,(ⅲ)intraplate compression and uplift,and(ⅳ)subduction jump and *** also propose that the subduction of heterogeneous oceanic crust(i.e.,buoyant oceanic plateau subduction)provided favorable conditions for tectonic exhumation,vertical slab tearing,and the formation of Cu-Au *** findings not only have implications for establishing the fundamental process of oceanic plateau accretion in ancient subduction zones but also provide an alternative explanation for Late Jurassic complex tectonomagmatic activity in north-ern tibet.

关键词： northern tibet Adakitic magma Oceanic plateau Flat-slab subduction Vertical slab tearing

Organic Geochemistry of the Early Jurassic Oil Shale from the Shuanghu Area in northern tibet and the Early Toarcian Oceanic Anoxic Event

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Acta Geologica Sinica(English Edition) 2005年第3期79卷 392-397页

作者： CHENLan YIHaisheng HURuizhong ZHONGHong ZOUYanrong OpenLaboratoryofOreDepositGeochemistry InstituteofGeochemistryChineseAcademyofSciencesGuiyangGuizhou550002 OpenLaboratoryofOreDepositGeochemistry InstituteofGeochemistryChineseAcademyofSciencesGuiyangGuizhou550002／／GraduateSchoolofChineseAcademyofSciencesBeijing100039 InstituteofSedimentaryGeology ChengduUniversityofTechnology Chengdu Sichuan610059 StateKeyLaboratoryofOrganicGeochemistry GuangzhouInstituteofGeochemistryChineseAcademyofSciencesGuangzhouGuangdong510640

This paper presents new geological and geochemical data from the Shuanghu area in northern tibet, which recorded the Early Toarcian Oceanic Anoxic Event. The stratigraphic succession in the Shuanghu area consists mostly of grey to dark-colored alternating oil shales, marls and mudstones. Ammonite beds are found at the top of the Shuanghu oil shale section, which are principally of early Toarcian age, roughly within the Harplocearas falciferrum Zone. Therefore, the oil shale strata at Shuanghu can be correlated with early Toarcian black shales distributing extensively in the European epicontinental seas that contain the records of an Oceanic Anoxic Event. Sedimentary organic matter of laminated shale anomalously rich in organic carbon across the Shuanghu area is characterized by high organic carbon contents, ranging from 1.8% to 26.1%. The carbon isotope curve displays the δ 13C values of the kerogen (δ 13Ckerogen) fluctuating from –26.22 to –23.53‰ PDB with a positive excursion close to 2.17‰, which, albeit significantly smaller, may also have been associated with other Early Toarcian Oceanic Anoxic Events (OAEs) in Europe. The organic atomic C/N ratios range between 6 and 43, and the curve of C/N ratios is consistent with that of the δ 13Ckerogen values. The biological assemblage, characterized by scarcity of benthic organisms and bloom of calcareous nannofossils (coccoliths), reveals high biological productivity in the surface water and an unfavorable environment for the benthic fauna in the bottom water during the Oceanic Anoxic Event. On the basis of organic geochemistry and characteristics of the biological assemblage, this study suggests that the carbon-isotope excursion is caused by the changes of sea level and productivity, and that the black shale deposition, especially oil shales, is related to the bloom and high productivity of coccoliths.

关键词： oil shales Early Toarcian organic carbon isotope organic atomic C/N ratios Oceanic Anoxic Events northern tibet

Sedimentary Record of the Planation Surface in the Hoh Xil Region of the northern tibet Plateau

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Acta Geologica Sinica(English Edition) 2000年第4期74卷 827-835页

作者： YI Haisheng WANG Chengshan LIU Shun LIU Zhifei WANG Shifeng

Miocene marl is the most widespread Tertiary stratigraphic record in the northern tibet Plateau, termed the Wudaoliang Group in the Hoh Xil region and the correlative Suonahu Formation in the Qiangtang region. The uniform marl overlies red beds of the Eocene-Oligocene Fenghuoshan Group. The Wudaoliang Group is generally 100-400 m thick, but the thickest strata are 700-1300 m, located in the Haidinghu (Maiding Lake) and Tuotuohe (Tuotuo River) regions respectively. Based on observations from eight measured sections and outcrops, the thin-bedded marl, which varies in colour from grey-white to light brown-grey, is explained as a large-scale or serial lacustrine deposit stretching throughout northern *** Wudaoliang Group commonly crops out on geographic lowland at an average elevation of 4600 m above sea level within the mountain chains, showing concordant summit levels, e.g. the Fenghuoshan and Bairizhajia Mountains. These mountains with a flat ridge are considered to be remains of the palaeo-planation surface. However, the spatial distribution of the Wudaoliang Group is not confined by the current mountain-basin landform configuration. We have observed the Miocene Wudaoliang Group marl exposed on a 5233 m-high mountain peak. The largest difference in height between the current lake level and the mesa crest is 600 m; the maximum dip angle is 25°, but usually below 10°, which is obviously different from the Fenghuoshan Group red beds with moderate to strong structural deformation. The horizon of the Wudaoliang Group thin-bedded marl and its widespread occurrence throughout the northern tibetan Plateau can only be reasonably inferred to a sedimentary record relevant to the palaeo-planation. Its deposition occurred on primary land floor by erosion at 20 Ma and its bed surface is a typical sign of geomorphic rise and collapse after the erosion.

关键词： Miocene sedimentary record planation surface uplift collapse Hoh Xil northern tibet

Fluid Inclusion and Stable Isotope Geochemistry of the Shangxu Gold Deposit, northern tibet

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Acta Geologica Sinica(English Edition) 2016年第4期90卷 1545-1546页

作者： PEI Yingru YANG Zhusen ZHAO Xiaoyan ZHANG Xiong MA Wang MAO Jingtao School of Earth Sciences and Resources China University of Geosciences Institute of Mineral Resources Chinese Academy of Geological Sciences

Objective The Shangxu gold deposit is located in the south of the middle Bangong-Nujiang suture zone in northern tibet. The origin of this deposit as an orogenic gold deposit is debatable. The study of the Shangxu deposit has a profound implication on gold exploration in the Bangong- Nujiang metallogenic belt and can also improve our understanding of gold mineralization in northern tibet.

关键词： In northern tibet Fluid Inclusion and Stable Isotope Geochemistry of the Shangxu Gold Deposit