Infant intra-oceanic arc magmatism due to initial subduction induced by oceanic plateau accretion: A case study of the Bangong Meso-Tethys,central Tibet,western China |
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| Institution: | 1. Key Laboratory of Computational Geodynamics, Chinese Academy of Sciences, Beijing 100049, China;2. Asian Tectonics Research Group, College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, China;3. School of Marine Sciences, Sun Yat-Sen University, Guangzhou 510275, China;4. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;1. State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China;2. School of Earth Sciences, Jilin University, Changchun 130061, China;1. Chengdu Institute of Geology and Mineral Resources, Chengdu 610081, China;2. Research Center for Tibetan Plateau Geology, China Geological Survey, Chengdu 610081, China;3. Department of Geosciences, National Taiwan University, Taipei 10617, China;4. Institute of Earth Sciences, Academia Sinica, Taipei 11529, China;5. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;6. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;7. Faculty of Resource and Environmental Engineering, Jiangxi University of Science and Technology, Ganzhou 341000, China |
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| Abstract: | The Meso-Tethyan oceanic plateaus are becoming conspicuous as giant units on the oceanic floor and have played important roles in both continental marginal orogenesis and Tethys oceanic evolution. In this study, we present mineralogical, geochronological, geochemical and Sm–Nd isotopic data for basaltic lavas from the Namco ophiolite and a high-Mg pillow lava–dyke–gabbro association from the Pengco ophiolite in central Tibet. Zircon U–Pb and Ar–Ar dating reveals that the Namco lavas erupted at ～181 Ma while the Pengco boninitic association formed at ～164 Ma. The Namco lavas display nearly flat rare-earth element (REE) patterns with no Nb–Ta depletions as well as high εNd values, characteristic of oceanic plateau lava. In contrast, the Pengco high-Mg rocks exhibit low REE concentrations below the normal mid-ocean ridge basalt (N-MORB), ubiquitous Nb–Ta depletions and low εNd values, and the dykes and gabbros are characterized by U-shape REE patterns, indicating that they could have derived from a depleted mantle source that was contaminated by sedimentary flux and marking a mid-Jurassic initial intra-oceanic arc magmatism erupted on the Early Jurassic Meso-Tethyan oceanic plateau represented by the Namco ophiolite. Our Pengco boninitic rocks, along with the literature data, indicate a 167–160 Ma boninitic-like initial intra-oceanic arc within the Bangong Meso-Tethys, running from the Shiquanhe area to the Naqu area with a length of ～1000 km, which was uniformly built on the Early Jurassic Meso-Tethyan oceanic plateau. Our literature investigation also indicates a ～175 Ma accretionary orogeny with distinct signature of the oceanic plateau involvements along the southern Qiangtang continental margin, which is manifested by regional metamorphic, magmatic and depositional records. We thus suggest that the accretion of the Early Jurassic Meso-Tethyan oceanic plateau onto the southern Qiangtang continental margin resulted in the extensive orogeny along the continental margin, jammed the subduction zone at ～175 Ma and induced intra-oceanic subduction initiation as well as the intra-oceanic infant arc magmatism in the Meso-Tethys at ～164 Ma. |
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| Keywords: | Tibet Meso-Tethys Bangong suture zone Oceanic plateau Accretion Intra-oceanic subduction High-Mg magmatic rock Jurassic |
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