Western Tibet relief evolution since the Oligo-Miocene |
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| Institution: | 1. Laboratoire de géologie de Lyon, Terre, Planètes et Environnement, CNRS UMR 5276, Université de Lyon, Université Lyon1, Ecole normale supérieure de Lyon, 2 rue Dubois, 69622 Villeurbanne, France;2. Laboratoire Magmas et volcans, 5 rue Kessler, 63038 Clermont-Ferrand, France;3. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100085, China;1. Novosibirsk State University, 2, Pirogova st., Novosibirsk 630090, Russia;2. A.A. Trofimuk Institute of Petroleum Geology and Geophysics SB RAS, 3, prosp. ak. Koptyuga, Novosibirsk 630090, Russia;3. A.P. Karpinsky Russian Geological Research Institute (VSEGEI), Sredny pr. 74, St. Petersburg 199106, Russia;4. Australian Research Council Centre of Excellence for Core to Crust Fluid Systems (CCFS), Australia;5. The Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtin University, GPO Box U1987, Perth, WA 6845, Australia;6. School of Earth and Environment, University of Western Australia, Crawley, WA 6009, Australia;1. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;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 for Isotope Research, TIGeR, Applied Geology, Curtin University, Perth, WA 6945, Australia;5. University of Chinese Academy of Sciences, Beijing 100049, China;1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry,Chinese Academy of Sciences, Guangzhou 510640, China;2. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;3. Australian Research Council (ARC) Centre of Excellence for Core to Crust Fluid Systems (CCFS) and the Institute for Geoscience Research (TIGeR), Department of Applied Geology, Curtin University, Perth, WA 6845, Australia;4. School of Geosciences, The University of Sydney, NSW 2006, Australia;5. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;6. State Key Laboratory of Geological Processes and Mineral Resources, Faculty of Earth Sciences, China University of Geosciences, Wuhan, 430074, China |
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| Abstract: | Western Tibet, between the Karakorum fault and the Gozha–Longmu Co fault system, is mostly internally drained and has a 1.5–2 km amplitude relief with km-large valleys. We investigate the origin of this peculiar morphology by combining a topography analysis and a study of the Cenozoic sedimentation in this area. Cenozoic continental strata correspond to a proximal, detrital fan deposition, and uncomformably rest on a palaeorelief similar to the modern one. Zircon U–Pb dating from trachytic flows interbedded within the Cenozoic continental sediments indicates that detrital sedimentation occurred at least between ca 24 and 20 Ma in the Shiquanhe basin, while K/Ar ages suggest it may have started since ~ 37 Ma in the Zapug basin. The distribution of continental deposits shows that present-day morphology features, including km-large, 1500 m-deep valleys, were already formed by Early Miocene times. We suggest that today's internally drained western Tibet was externally drained, at least during late Miocene, contemporaneously with early motion along the Karakorum Fault. Detailed study of the present day river network is compatible with a dextral offset on the Karakorum Fault of 250 km at a rate of ~ 10 ± 1 mm/yr. Displacement along the Karakorum fault possibly induced the shift from external to an internal drainage system, by damming of the Bangong Co ~ 4 Ma ago, leading to the isolation and preservation of the western Tibet relief. |
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