The Late Jurassic Zedong ophiolite: A remnant of subduction initiation within the Yarlung Zangbo Suture Zone (southern Tibet) and its tectonic implications |
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| Affiliation: | 1. Guangdong Provincial Key Laboratory of Mineral Resources & Geological Processes, School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China;2. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, and Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Sciences, Beijing 100101, China;3. Département de Géologie et Génie Géologique, Université Laval, Québec G1V 0A6, Canada;1. School of Earth Science and Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, Guilin University of Technology, Guilin, 541004, China;2. State Key Laboratory of Ore Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550002, China;3. The Institute for Geoscience Research (TIGeR), Curtin University, Perth, WA 6845, Australia;4. Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640, China;5. Chengdu Institute of Geology and Mineral Resources, Chengdu, 610081, China;1. College of Earth Science and MLR Key Laboratory of Tectonic Controls on Mineralization and Hydrocarbon Accumulation, Chengdu University of Technology, Chengdu 610059, China;2. State Key Laboratory of Continental Dynamics, Northwest University, Xi''an 710069, China;3. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;4. Chengdu Center of China Geological Survey, Chengdu 610081, China;5. Tibet Tianyuan Mineral Exploration Co. Ltd., Shigatse 857000, China;1. School of Marine Sciences, Sun Yat-sen University, Guangzhou 510006, China;2. Key Laboratory of Western China’s Mineral Resource and Geological Engineering, Ministry of Education, School of Geological Engineering and Geomatics, Chang’an University, Xi’an 710054, China;3. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;4. Guangdong University Key Laboratory of Offshore Oil Exploration and Development/Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, School of Marine Sciences, Sun Yat-sen University, Guangzhou 510006, China;5. Southern Laboratory of Ocean Science and Engineering (Guangdong, Zhuhai), Zhuhai 519000, China;6. Tibet Autonomous Region Geological and Mineral Exploration and Development Bureau, Lhasa 850000, China |
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| Abstract: | The Zedong ophiolite is the largest ophiolite massif east of Dazhuqu in the Yarlung Zangbo Suture Zone in the southern Tibetan Plateau. However, its age, geodynamic setting and relationship to the Xigaze ophiolite remain controversial. New zircon U–Pb ages, whole-rock geochemical and Nd–Pb isotopic data from ophiolitic units provide constraints on the geodynamic and tectonic evolution of the Zedong ophiolite. U–Pb zircon geochronology of dolerite lavas and late gabbro–diabase dikes yield weighted mean ages of 153.9 ± 2.5 Ma and 149.2 ± 5.1 Ma, respectively. Strong positive εNd(t) and positive Δ7/4Pb and Δ8/4Pb values indicate derivation from a highly depleted mantle source with an isotopic composition similar to that of the Indian MORB-type mantle. The geochemistry of ophiolitic lavas and early dikes are analogous to typical island arc tholeiites whereas late dikes are similar to boninites. The geochemistry of these rock types suggests multi-stage partial melting of the mantle and gradually enhanced subduction influences to the mantle source through time. Combined with the MORB-like 162.9 ± 2.8 Ma Luobusha ophiolitic lavas, we suggest that the Luobusha lavas, Zedong lavas and early dikes originated in an infant proto-arc setting whereas late dikes in the Zedong ophiolite originated in a forearc setting. Together, they represent a Neo-Tethyan subduction initiation sequence. The Late Jurassic intra-oceanic proto-arc to forearc setting of the Zedong ophiolite contrasts with the continental margin forearc setting for the Xigaze ophiolite, which suggests a laterally complex geodynamic setting for ophiolites along the Yarlung Zangbo Suture Zone. |
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| Keywords: | Yarlung Zangbo Suture Zone Zedong ophiolite Intra-oceanic island arc subduction initiation Jurassic |
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