Discovery of an eclogite belt in the Lhasa block,Tibet: A new border for Paleo-Tethys? |
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| Authors: | Jingsui Yang Zhiqin Xu Zhaoli Li Xiangzhen Xu Tianfu Li Yufeng Ren Huaqi Li Songyong Chen Paul T Robinson |
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| Institution: | 1. State Key Laboratory of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;2. Department of Earth Sciences, University of Adelaide, SA 5005, Australia;3. School of Earth Sciences and Resources, China University of Geosciences (Beijing), 29 Xueyuan Road, Beijing 100083, China;4. Faculty of Science, Kochi University, Akebono-cho 2-51, Kochi 780-8520, Japan;5. State Key Laboratory Breeding Base of Nuclear Resources and Environment, East China Institute of Technology, Nanchang 330013, China;1. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Chinese Academy of Sciences Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;4. Department of Geosciences, University of Arizona, Tucson, AZ 85721, USA;1. State Key Laboratory of Geological Processes and Mineral Resources, and School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China;2. Institute of Geology, Chinese Academy of Geological Sciences, Beijing, 100037, China;3. Department of Geosciences, National Taiwan University, Taipei 106, Taiwan;4. Institute of Earth Sciences, Academia Sinica, Taipei 11529, Taiwan;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 |
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| Abstract: | A newly discovered eclogite belt in the eastern part of the Lhasa Block, Tibet, is about 500–1000 m wide and at least 60 km long in an E–W direction. The eclogites occur as tectonic slices in garnet-bearing, mica–quartz schist. They are generally fresh and form thick, massive layers that consist chiefly of garnet (Grt) + omphacite (Omp) + phengite (Phe) + rutile (Rut) + quartz (Qtz). P–T calculations based on the Grt–Omp–Phe mineral assemblage yielded peak metamorphic conditions of 2.7 GPa and 730 °C, close to the phase boundary between coesite and quartz and thus the eclogites can be regarded as part of a very high-pressure metamorphic belt. Petrochemical data suggest that the eclogite protoliths were typical MORB basalts, derived from depleted mantle. SHRIMP U–Pb dating of zircons from the eclogite yielded metamorphic ages ranging from 242 ± 15 to 292 ± 13 Ma, with an average value of 262 ± 5 Ma. The MORB eclogites are interpreted to be remnants of Paleo-Tethyan oceanic lithosphere. The eclogites, along with Permian island arc volcanic rocks to the north, are believed to mark a Carboniferous–Permian suture zone dividing the Lhasa Block into a northern and southern segment. This newly identified suture zone suggests that the border of the Paleo-Tethyan Ocean jumped southward from north of the Bangong-Nujiang suture to within what is now the Lhasa Block. |
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