Transition from oceanic subduction to continental collision recorded in the Bangong-Nujiang suture zone: Insights from Early Cretaceous magmatic rocks in the north-central Tibet |
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| Institution: | 1. The College of Earth Sciences, Jilin University, Changchun 130061, PR China;2. No. 5 Geological Party, Tibet Bureau of Geology and Exploration, Golmud 816000, PR China;3. School of Earth Science and Resources, China University of Geosciences, Beijing 10083, PR China;1. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;2. University of Chinese Academy of Sciences, Beijing 10069, China;3. CAS Center for Excellence in Tibetan Plateau Earth Sciences, China;4. School of Geosciences, The University of Sydney, NSW 2006, Australia;5. School of Earth Science, Guilin University of Technology, Guilin 541004, China;6. Institute of Geology and Geophysics, Chinese Academy of Science, Beijing 100029, China;1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China;2. School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China;3. Department of Earth Sciences, University of St Andrews, North Street, St Andrews KY16 9AL, UK;4. Centre for Exploration Targeting, School of Earth and Environment, University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia;5. Chengdu Institute of Geology and Mineral Resources, Chengdu 610082, China;1. Guangdong Provincial Key Laboratory of Mineral Resources & Geological Processes, School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China;2. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, and Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Sciences, Beijing 100101, China;3. Département de Géologie et Génie Géologique, Université Laval, Québec G1V 0A6, Canada |
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| Abstract: | The transition from oceanic subduction to continental collision is a key stage in the evolution of ancient orogens. We present new data for Early Cretaceous diorite and granite porphyry from north–central Tibet to constrain the evolution of the Bangong–Nujiang Tethyan Ocean (BNTO). The diorites have moderate SiO2 and high MgO contents, similar to high-Mg andesites. Zircon grains yield U–Pb ages of 128–124 Ma and positive εHf(t) values between +13.2 and + 16.3, corresponding to Hf depleted-mantle model ages (TDM) of 281–131 Ma. The high-Mg diorite was probably formed by partial melting of hydrous mantle wedge fluxed by slab-derived fluids in an oceanic subduction setting. The granite porphyries yield zircon U–Pb ages of 117–115 Ma and zircon εHf(t) values ranging from +0.1 to +4.5. Most samples have high SiO2 and Fe2O3T contents, variable FeOT/MgO and Ga/Al ratios, and are depleted in Ba, Sr, P, and Ti, similar to I- and A-type granites. The granite porphyries were most likely derived from partial melting of juvenile dioritic or granodioritic crust due to break-off of the BNTO lithosphere following collision between the Lhasa and Qiangtang blocks. The Early Cretaceous high-Mg diorite and A-type granite porphyry thus record the Early Cretaceous transition from oceanic subduction to continental collision along the Bangong–Nujiang suture zone (BNSZ). |
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| Keywords: | Tibet High-Mg diorite A-type granite Bangong-Nujiang suture zone Tethys |
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