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Burial and exhumation history of the Xigaze forearc basin, yarlung suture zone. Tibet

Geoscience Frontiers 2019年第3期10卷 895-908页

作者： Devon A.Orme Department of Earth Sciences Montana State University

The Cretaceous-Eocene Xigaze forearc basin is a crucial data archive for understanding the tectonic history of the Asian continental margin prior to and following collision with India during the early Cenozoic Era. This study reports apatite and zircon(U-Th)/He thermochronologic data from fourteen samples from Albian-Ypresian Xigaze forearc strata to determine the degree and timing of heating(burial) and subsequent cooling(exhumation) of two localities along the yarlung suture zone(YSZ) near the towns of Saga and Lazi. Thirty-seven individual zircon He ages range from 31.5 ± 0.8 Ma to6.06 ± 0.18 Ma,with the majority of grains yielding ages between 30 Ma and 10 Ma. Twenty apatite He ages range from 12.7 ± 0.5 Ma to 3.9 ± 0.3 Ma,with the majority of grains yielding ages between 9 Ma and 4 Ma. These ages suggest that the Xigaze forearc basin was heated to 140-200 ℃ prior to cooling in Oligocene-Miocene time. Thermal modeling supports this interpretation and shows that the samples were buried to maximum temperatures of ～140-200 0 C by 35-21 Ma, immediately followed by the onset of exhumation. The zircon He and apatite He dataset and thermal modeling results indicate rapid exhumation from ～21 Ma to 15 Ma, and at ～4 Ma. The 21-15 Ma thermochronometric signal appears to be regionally extensive, affecting all the lithotectonic units of the YSZ, and coincides with movement along the north-vergent Great Counter Thrust system. Thrusting, coupled with enhanced erosion possibly related to the paleo-yarlung River, likely drove Early Miocene cooling of the Xigaze forearc basin.In contrast, the younger phase of rapid exhumation at ～4 Ma was likely driven by enhanced rock uplift in the footwall of north-striking rifts that cross-cut the YSZ.

关键词： Xigaze Tibet Forearc basin Thermochronology yarlung

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Mineralogy and Geochemistry of the High-Cr Podiform Chromitite from the Cuobuzha Ophiolite, yarlung Zangbo Suture Zone, Western Tibet, China: Implication for its Origin

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Acta Geologica Sinica(English Edition) 2020年第1期94卷 75-89页

作者： ZHAO Hui YANG Jingsui LIU Fei XIONG Fahui LIAN Dongyang YAO Hu Harbin Institute of Technology Harbin 150001China Department of Earth and Space Sciences Southern University of Science and TechnologyShenzhen 518055China Institute of Geology Chinese Academy of Geological SciencesBeijing 100037China School of Earth Sciences and Engineering Nanjing UniversityNanjing 201123China Institute of Geochemistry Chinese Academy of Sciences Guiyang 550081China

The Cuobuzha high-Cr chromitites in the western segment of yarlung Zangbo Suture Zone of Tibet are mainly hosted in the harzburgites as massive type, which are characterized by high concentrations of platinum group elements(PGE) ranging from 380 to 577 ppb, and low Pd/Ir ratios(<0.1). In mid-ocean ridge basalts(MORB)-normalized spidergrams, chromites of the Cuobuzha chromitites are depleted in Al, Ga, V, Mg and Zn, and enriched in Mn and Cr, sharing similar patterns with those of ophiolitic boninites in the Bonin and Thetford Mines. Approximately 20 platinum group mineral(PGM) grains were discovered from the samples, including laurite, erlichmanite, Os-Fe alloy, cuproiridsite, and irarsite. The PGM assemblages indicate that sulfur fugacity was initially low enough to allow the precipitation of Os-Fe alloy and increased thereafter, with the fall in temperature. Primary Fe-Ni and Fe-Cr alloys, which are stable in a highly reduced environment, occur as inclusions within chromites or clinopyroxenes. Calculated results show that the parental magma has an intimate affinity with boninites. Based on our observations, a model is proposed wherein the Cuobuzha chromitites contain high-pressure and low-pressure chromites. Low-pressure chromites were formed via reaction between boninitic melts and peridotites, during which the high-pressure chromites hosting highly reduced minerals were mobilized by melts and were reallocated to podiform chromitites.

关键词： Cuobuzha chromitites highly reduced minerals yarlung Zangbo Suture Zone Tibet

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An alternative tectonic model for the yarlung Zangbo suture zone

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Science China Earth Sciences 2010年第1期53卷 27-41页

作者： LIU XiaoHan JU YiTai WEI LiJie LI GuangWei Institute of Tibetan Plateau Research Chinese Academy of SciencesBeijing 100085China Mineral Resource Institute of China Metallurgical Geology Bureau Beijing 100025China

The new field investigations along the yarlung Zangbo ophiolites zone show that these series underwent low green-schist metamorphism and were then fractured and occurred as slabs in tectonic melanges,without regional tectonic polarity.No large shear zone in north-south direction has been identified between ophiolite bodies and flysch layers on both side and a conformable contact relationship can be observed locally between them.A great mass of tectonic mélange has been substantiated as submarine olistolith bodies.The Mesozoic sedimentary facies and its evolution in both north and south of the ophiolite zone are corresponding in time.The ophiolite zone has often been divided into parallel branches,separated by narrow flysch slats.There is also a similarity of the Paleozoic and the basement of the High Himalaya,Lhasa and Qiangtang Terranes,and they are distinctly different from those of the Indian continent.The geologic information does not warrant a postulate that the Himalaya and Tibet were once separated by a great ocean;it is therefore consistent with an alternative tectonic model by back-arc basin collapse with its juvenile narrow oceanic crust.The real plate tectonic suture,the Neotethys might be covered under the Miocene Siwalik molasse in the southern slope of the High Himalaya range.Based on the new model,the Neotethyan ocean floor was subducted beneath the Asia since the Late Triassic.The outer continental margin of Eurasia was split from the Lhasa Terrane so that a back-arc basin came into existence.Hemi-pelagic and deep sea sediments were deposited before the Late Cretaceous flysch sedimentation,with the linear juvenile oceanic crust when back-arc volcanism occurred in the Gandese region.The yarlung Zangbo back-arc basin was eventually eliminated when the High Himalayas were sutured onto Eurasia.The ocean floor lightly underthrusted to north and south sides,sediments of the basin were deformed as fold-thrusting.The Neotethys was eliminated during the Tertiary when India collided with Himalaya arc from t

关键词： yarlung Zangbo Ophiolite Zone plate boundary continental marginal arc relic back-arc basin alternative tectonic model

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Population dynamics and habitat use of the Black-necked Crane (Grus nigricollis) in the yarlung Tsangpo River basin, Tibet, China

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Avian Research 2019年第3期10卷 366-373页

作者： Ru Jia Tian Ma Fengjiang Zhang Guogang Zhang Dongping Liu Jun Lu Research Institute of Forest Ecology Environment and ProtectionChinese Academy of ForestryBeijing 100091China Key Laboratory of Forest Protection of State Forestry and Grassland Administration Beijing 100091China National Bird Banding Center of China Beijing 100091China Wildlife Conservation and Disease Surveillance Center of Liaoning Province Dalian 116000China

Background:The Black-necked Crane (Grus nigricollis)is an internationally threatened crane living on the plateau, mainly in winter, in the yarlung Tsangpo River basin in Tibet,western China. In the past five years,some economic development projects have been conducted in this area,posing potential threats to the wintering populations of the cranes and their habitats. Therefore, the current population dynamics of wintering Black-necked Cranes and habitat suitability in the yarlung Tsangpo River basin were investigated. Methods: Twenty counties were surveyed using the line transect method in December 2017 and January 2018, and we recorded the location,flock size,number of individuals,habitat types and presence of human disturbance in which they occurred.We compared the results from the middle wintering period in this survey with those from 2014. Results: The highest number of cranes recorded was 8291,and the results showed that the cranes were mainly distributed in Lhaze, Namling, Samzhubze, and Lhunzub.A total of 577 and 495 flocks were recorded in the early and middle wintering periods, respectively. In the early wintering period,there were signi ficant differences in the number of individuals across the di fferent habitats,with crop stubble land and plowed land representing more than 30% of the total habitat utilization.In the middle wintering period, there were also signi ficant differences in the number of individuals, and the utilization of crop stubble land represented over 60% of the total. Conclusions: Wintering Black-necked Cranes mainly fed on spilled grains in stubble habitat after harvest. In the middle wintering period, some of the farmlands were plowed and irrigated,which resulted in food shortages in these areas,and the cranes tended to gather in mixed flocks of large size instead of as a single family.There were still considerable regional wintering populations decreases in Quxu,Nedong,and Sakya in 2018 compared with 2014,and these decreases were mainly due to some recently emerging threats,includi

关键词： Black-necked Crane Habitat use Population dynamics Tibet yarlung Tsangpo River basin

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Mesozoic radiolarian chert from the middle sector of the yarlung Zangbo suture zone,Tibet and its tectonic implications

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Science China Earth Sciences 2006年第4期49卷 348-357页

作者： ZHU Jie1,2, DU Yuansheng1, LIU Zaoxue2, FENG Qinglai1, TIAN Wangxue2, LI Jinping2 & WANG Changping2 1. Faculty of Earth Sciences,China University of Geology, Wuhan 430074, China 2. Hubei Institute of Regional Geology Survey, Wuhan 430034, China Faculty of Earth Sciences China University of Geology Wuhan China Hubei Institute of Regional Geology Survey Wuhan China

Three radiolarian fauna, aged as the Middle-Late Triassic, Late Jurassic-Early Creta- ceous and Cretaceous radiolarian fauna, have been recognised in the radiolarian cherts from the middle sector of the yarlung Zangbo suture zone, southern Tibet, China. The average contents of SiO2 in the radiolarian cherts of the Middle-Late Triassic and Late Jurassic-Early Cretaceous are 90.24% and 92.58% respectively, with average ratios of Al/(Al+Fe+Mn) as 0.75 and 0.74 respectively, the average ratios of MnO/TiO2 as 0.36 and 1.24, the average ratios of Ce/Ce* as 1.15 and 1.03, and the average ratios of LaN/CeN as 0.85 and 0.93. These geochemical features indicate that both of them are biogenic, deposited in a continental margin basin. The SiO2 content of the Early Cretaceous radiolarian chert is 94.12%, with the ratio of Al/(Al+Fe+Mn) as 0.59, ratio of MnO/TiO2 as 4.30, ratio of Ce/Ce* as 0.60, ratio of LaN/CeN as 1.59, which imply that the chert is biogenic and was deposited in a pelagic basin. The Middle-Late Triassic association of the radiolarian chert and turbidites as well as their geochemical characteristics indicates the existence of a strong rifting marginal basin in the belt of the yarlung Zangbo River then. The association of radiolarian chert and bedded basalt indicate an initial Tethyan ocean basin in southern Tibet during the Late Jurassic-Early Cretaceous. The early Cretaceous radiolarian chert coexisting with pillow basalt in top of the ophiolite suite represents sediments from the oceanic Tethyan basin.

关键词： radiolarian chert, sedimentary geochemistry, Mesozoic, yarlung Zangbo suture zone, Tibet.

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Middle Jurassic-early Cretaceous radiolarian assemblages of the western yarlung Zangbo Suture Zone: Implications for the evolution of the Neo-Tethys

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Geoscience Frontiers 2017年第5期8卷 989-997页

作者： Hanting Zhong Jingen Dai Chengshan Wang Yalin Li Yushuai Wei State Key Laboratory of Biogeology and Environmental Geology School of Earth Sciences and Resources Research Center for Tibetan Plateau Geology China University of Geosciences (Beijing) Beijing 100083 China Institute of Sedimentary Geology Chengdu University of Technology Chengdu 610059 China

Cherts in the Zhongba melange of the western yarlung Zangbo Suture Zone(YZSZ) contain well preserved radiolarian assemblages. These radiolarian assemblages indicate that the Zhongba melange has middle Jurassic-early Cretaceous remnant, are coeval with those from the central and eastern parts of the YZSZ. Cherts from the Najiu area yield Aalenian to Aptian radiolarians, while cherts interbedded with siliceous mudstones from the Bielongjiala area yield Aptian radiolarians, indicating that terrigenousderived sediments were deposited during early Aptian. The above observations indicate that the entire YZSZ have a similar geochronological framework and thus they underwent similar geological evolution:(1) during the Jurassic, the Neo-Tethys was a wide ocean with pelagic sediments distal from continents;(2) during the Cretaceous(around 130-120 Ma), the Neo-Tethys started to subduct along the southern margin of the Lhasa block, and terrigenous-derived siliceous mudstone began deposition.

关键词： Radiolarian chert Jurassic Cretaceous yarlung Zangbo Suture Zone

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Helium and neon isotopic compositions in the ophiolites from the yarlung Zangbo River,Southwestern China:The information from deep mantle

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Science China Earth Sciences 2007年第6期50卷 801-812页

作者： YE XianRen TAO MingXin YU ChuanAo ZHANG MingJie Institute of Geology and Geophysics Chinese Academy of SciencesLanzhou 730000China Department of Geology Lanzhou UniversityLanzhou 730000China

The ophiolites from the yarlung Zangbo River (Tibet),Southwestern China,were analysed for the con-tents of helium and neon and their isotopic compositions by stepwise heating. The serpentinites from Bainang showed a high 3He/4He value of 32.66Ra (Ra is referred to the 3He/4He ratio in the present air) in 700 ℃ fraction. At lower temperature,all of the dolerites displayed as very high 3He/4He ratios as ones investigated for hotspots. It was clear that the high 3He/4He ratio was one of immanent characterics in the magma source formed the dolerites,suggesting that there was a large amount of deep mantle fluids in these rocks. In the three-isotope diagram of neon,the data points from the ophiolites of the yarlung Zangbo River were arranged along the Loihi Line. This is in agreement with the characteristics of he-lium isotopes,revealing that the high-3He plume from deep mantle had played an important role in the formation of the Neo-Tethyan Ocean. The helium isotopic compositions in the basalts were far higher than atomospheric value but lower than the average value of MORB,although there were various de-grees of alteration. The possible reasons were that basaltic

关键词： yarlung Zangbo River (Tibet) ophiolite helium neon isotope plume

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Apatite fission track dating evidence for tectonic movement of yarlung Zangbo Thrust Zone

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Chinese Science Bulletin 2002年第9期47卷 765-768页

作者： YUAN Wanming HOU Zengqian WANG Shicheng LI Shengrong Institute of High Energy Physics.Chinese Academy of Sciences Beijing 100080China Institute of Mineral Resources Chinese Academy of Geological SciencesBeijing 100037China China University of Geosciences Beijing 100083China

Fission track geological chronology is an effective method of study on tectonic movement of fault zone. Apatite fission track (AFT) dating analyses of 9-apatite and 4-zircon samples collected from Lhasa to Langkazi, -70-km-long in SN provide an understanding of the age and the uplifting of both sides of the yarlung Zangbo Thrust Zone (YZTZ) in this work. The AFT ages range from-37 to 14 Ma, indicating the time of major tectono-thermal events, i.e. the continent-continent collision along the YZTZ. Based on the relationship between the AFT ages and the sample elevations, there were two tectonic active periods: -37-20 Ma and 20-14 Ma. In the first period the tectonic event did not bring on differential uplifting. Rapid differential uplifting with rapid cooling, resulting from thrusting, took place in the second period. The vertical displacement was -1020 m and total -2.9 km of overburden has been removed from the present-day surface since cooling below -110°C began. The maximum cooling and denudation

关键词： fission track dating thrusting thermal event uplifting yarlung Zangbo Zone Tibet.

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STUDY ON THE MOISTURE PASSAGE ON THE LOWER REACHES OF THE yarlung ZANGBO RIVER

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Science China Chemistry 1989年第5期32卷 580-593页

作者：杨逸畴高登义李渤生 Institute of Geography Academia Sinica Beijing Institute of Atmospheric Physics Academia Sinica Beijing Institute of Botany Academia Sinica Beijng

A series of gorges on the lower reaches of the yarlung Zangbo River is like an enormous crevice splitting the southeastern Qinghai-Xizang (Tibet)Plateau to create a passage through which warm, wet air flow from the Indian Ocean reaches the inner part of the plateau. This moisture passage was mainly strengthened after the Pleistocene epoch in the Quaternary period and has played a major role in affecting the beginning date of the rainy season and the amount of the plateau’s rainfall. It has also served as a corridor for the living things on the southern and the northern sides of the Himalayas to mingle with each other. The region along this passage is abundant in evidences of species of differentiation, variation and biological division. Also the passage has provided a favorable environment for human beings and affected natural phenomena there.

关键词： moisture passage the Great Bend Gorge of the yarlung Zangbo River the tectenic movement of the Qinghai-Xizang crust.

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THE　CAUSES　AND　DEVELOPMENTAL　TREND　OF　DESERTIFICATION　IN　THE　MIDDLE　REACHES　OF　THE　yarlung　ZANGBO　RIVER　AND　ITS　TWO　TRIBUTARIES　IN　XIZANG

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Chinese Geographical Science 1995年第4期5卷 355-364页

作者：董光荣董玉祥李森金炯靳鹤龄刘玉璋 Institute of Desert Research the Chinese Academy of Sciences Lanzhou PRC

The middle reaches of the yarlung Zangbo River and its two tributaries are an important development and construction region in Xizang(Tibet) in recent years, but the fast development of desertification has caused immense damages to its social and economic development, so the study on desertification in this region is significant. The paper studies the causes and development trend of desertification in this region through analysis of natural and human factors as well as their relationship. It can be concluded that desertification in the study area is one process which is accelerated and intensified by human activities on the basis of the slow natural desertification process. It is resulted from the dislocation of irrational and intensive human activities, fragile eec-environment and meagre natural resources, and tends to become more wide and severe.

关键词： desertification eco-environment the yarlung Zangbo River Xizang

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