Early Mesozoic metamorphism and tectonic significance of the eastern segment of the Lhasa terrane,south Tibet |
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| Affiliation: | 1. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China;2. Geology Department, Lakehead University, 955 Oliver Rd, Thunder Bay, P7B 5E1, Ontario, Canada;3. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China;4. John de Laeter Center, TIGeR, Dept. Applied Geology, Curtin University, Perth, WA 6945, Australia;5. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100085, China;1. CSIRO Mineral Resources, Perth, WA 6151, Australia;2. Department of Mineral Exploration and Mining, British Columbia Institute of Technology, 3700 Willingdon Avenue, Burnaby, British Columbia V5G 3H2, Canada;3. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR China;4. Shijiazhuang University of Economics, Shijiazhuang, Hebei 050031, PR China;5. Key Laboratory of Tectonic Controls on Mineralization and Hydrocarbon Accumulation, Chengdu University of Technology, Chengdu 610059, PR China;6. Applied Geology, John de Laeter Centre, TIGeR, Curtin University, Perth, WA 6102, Australia;7. Centre for Microscopy, Characterisation and Analysis, University of Western Australia, Perth, WA 6009, Australia;8. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, PR China;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: | The metamorphic belt in the Basongco area, the eastern segment of Lhasa terrane, south Tibet, occurs as the tectonic blocks in Paleozoic sedimentary rocks. The Basongco metamorphic rocks are mainly composed of paragneiss and schist, with minor marble and orthogneiss, and considered previously to be the Precambrian basement of the Lhasa terrane. This study shows that the Basongco metamorphic belt experienced medium-pressure amphibolite-facies metamorphism under the conditions of T = 640–705 °C and P = 6.0–8.0 kbar. The inherited detrital zircon of the metasedimentary rocks yielded widely variable 206Pb/238U ages ranging from 3105 Ma to 500 Ma, with two main age populations at 1150 Ma and 580 Ma. The magmatic cores of zircons from the orthogneiss constrain the protolith age as ca. 203 Ma. The metamorphic zircons from all rocks yielded the consistent metamorphic ages of 192–204 Ma. The magmatic cores of zircons in the orthogneiss yielded old Hf model ages (TDM2 = 1.5–2.1 Ga). The magmatic zircons from the mylonitized granite yielded a crystallization age of ca. 198 Ma. These results indicate that the high-grade metamorphic rocks from the Basongco area were formed at early Jurassic and associated with coeval magmatism derived from the thickening crust. The Basongco metamorphic belt, together with the western and coeval Sumdo and Nyainqentanglha metamorphic belts, formed a 400-km-long tectonic unit, indicating that the central segment of the Lhasa terrane experienced the late Paleozoic to early Mesozoic collisional orogeny. |
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| Keywords: | Petrology Zircon U–Pb dating Metamorphism Magmatism Orogeny Lhasa terrane South Tibet |
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