Miocene post-collisional shoshonites and their crustal xenoliths,Yarlung Zangbo Suture Zone southern Tibet: Geodynamic implications |
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| Institution: | 1. Département de géologie et de génie géologique, Université Laval, Québec, QC G1K 7P4, Canada;2. Department of Geology, Saint Mary''s University, Halifax, NS B3H 3C3, Canada;3. Research Center for Tibetan Plateau Geology, China University of Geosciences, 29 Xueyuan Road, Haidian District, 100083 Beijing, China;1. Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, P.O. Box 9825, Beijing 100029, China;2. School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK;1. Chengdu Institute of Geology and Mineral Resources, Chengdu 610081, China;2. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;1. ARC Centre of Excellence for Core to Crust Fluid Systems/GEMOC, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia;2. Faculty of Mining and Geology, Belgrade University, Đušina 7, 11000 Belgrade, Serbia;3. Institute of Geosciences, University of Mainz, Becherweg 21, Mainz 55099, Germany;1. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;2. China University of Geosciences, Beijing 100083, China;3. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi''an 710069, China;4. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;1. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China;2. Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;3. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing, 100037, China |
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| Abstract: | The convergence between the Indian plate and the southern margin of the Eurasian continent created an active continental margin from Late Jurassic until about 40 Ma ago, which then evolved to form the Himalaya and the Tibetan Plateau during the continental collision stage. Post-collisional magmatism in southern Tibet, north of the Yarlung Zangbo Suture Zone (YZSZ) has been active since 45 Ma and is related to normal faulting and extensional tectonism. To date no such magmatism was reported within the YZSZ itself. This paper reports on the discovery of Miocene shoshonites within the YZSZ. They are significant because the magma traveled, at least in part, through oceanic crust, thus limiting interaction with the continental crust to the mid-crustal level and which affected the post-collisional magmatic rocks occurring in the northern part of the subduction system. In addition, xenoliths and xenocrysts of crustal origin in these rocks constrain the nature of metamorphic rocks underlying the YZSZ at mid-crustal level. The geochemical signatures of the shoshonitic rocks, including Nd and Sr isotope systematics, indicate derivation from a garnet-bearing middle continental crustal source. Crustal imprint complicates modeling of the petrogenetic processes which occurred prior to mid-crustal ponding of the magma which took place between 11 and 17 Ma at depths of 40 to 50 km. The significant role of crustal contamination raises serious concerns about models proposed for similar magmatic activity elsewhere in the Himalaya and the Tibetan Plateau. |
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