Reassessment of continental growth during the accretionary history of the Central Asian Orogenic Belt |
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| Institution: | 1. Beijing SHRIMP Centre, Chinese Academy of Geological Sciences, Beijing, China;2. Department of Geosciences, University of Mainz, Germany;3. Institute of Precambrian Geology and Geochronology, Russian Academy of Sciences, St. Petersburg, Russia;4. Australian Research Council Centre of Excellence for Core to Crust Fluid Systems/GEMOC, Department of Earth and Planetary Sciences, Macquarie University, Sydney, NSW 2109, Australia;5. Department of Geo- and Environmental Sciences, University of Munich, Germany;6. CERCAMS, Department of Earth Sciences, Natural History Museum, London, UK;7. Geological Institute, Russian Academy of Sciences, Moscow, Russia;8. Department of Geology and Mineralogy, University of Cologne, Germany;9. Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China;10. Institute of Geology, Chinese Academy of Geological Sciences, Beijing, China;11. Institute for Geoscience Research, Department of Applied Geology, Curtin University of Technology, Perth, WA 6845, Australia;1. Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China;2. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;3. School of Earth Sciences and Resources, China University of Geosciences Beijing, No. 29 Xueyuan Road, Haidian District, Beijing 100083, China;4. Division of Interdisciplinary Science, Faculty of Science, Kochi University, Akebono-cho, Kochi 780-8520, Japan;1. Natural History Museum, Department of Earth Sciences, CERCAMS, London SW7 5BD, UK;2. St. Petersburg State University, Geological Faculty, St. Petersburg 199034, Russia;3. All Russian Geological Research Institute (VSEGEI), St. Petersburg 199106, Russia;4. Macquarie University, CCFS/GEMOC, NSW 2109, Sydney, Australia;5. British Geological Survey, Keyworth, Nottingham NG12 5GG, UK;6. National University of Uzbekistan, Department of Geology, Tashkent, Uzbekistan;7. Institute of Mineral Resources, Gozkomgeologiya, Tashkent, Uzbekistan |
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| Abstract: | We argue that the production of mantle-derived or juvenile continental crust during the accretionary history of the Central Asian Orogenic Belt (CAOB) has been grossly overestimated. This is because previous assessments only considered the Palaeozoic evolution of the belt, whereas its accretionary history already began in the latest Mesoproterozoic. Furthermore, much of the juvenile growth in Central Asia occurred in late Permian and Mesozoic times, after completion of CAOB evolution, and perhaps related to major plume activity. We demonstrate from zircon ages and Nd–Hf isotopic systematics from selected terranes within the CAOB that many Neoproterozoic to Palaeozoic granitoids in the accreted terranes of the belt are derived from melting of heterogeneous Precambrian crust or through mixing of old continental crust with juvenile or short-lived material, most likely in continental arc settings. At the same time, juvenile growth in the CAOB occurred during the latest Neoproterozoic to Palaeozoic in oceanic island arc settings and during accretion of oceanic, island arc, and Precambrian terranes. However, taking together, our data do not support unusually high crust-production rates during evolution of the CAOB. Significant variations in zircon εHf values at a given magmatic age suggest that granitoid magmas were assembled from small batches of melt that seem to mirror the isotopic characteristics of compositionally and chronologically heterogeneous crustal sources. We reiterate that the chemical characteristics of crustally-derived granitoids are inherited from their source(s) and cannot be used to reconstruct tectonic settings, and thus many tectonic models solely based on chemical data may need re-evaluation. Crustal evolution in the CAOB involved both juvenile material and abundant reworking of older crust with varying proportions throughout its accretionary history, and we see many similarities with the evolution of the SW Pacific and the Tasmanides of eastern Australia. |
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