Early Mesozoic retrograded eclogite and mafic granulite from the Badu Complex of the Cathaysia Block,South China: Petrology and tectonic implications |
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| Institution: | 1. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Science, Beijing 100029, China;2. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;3. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;4. School of Earth Sciences and Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China;5. Centre for Tectonics, Resources and Exploration, Department of Earth Sciences, University of Adelaide, SA 5005, Australia;1. Institute of Geology, Chinese Academy of Geological Science, No. 26 Baiwanzhuang Road, Beijing 100037, China;2. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Beijing 100101, China;3. Center for Excellence in Tibetan Plateau Earth Sciences, Chinese Academy of Sciences, Beijing 100101, China;4. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China;5. School of Earth Science and Mineral Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China;1. Institut de Physique du Globe de Strasbourg, UMR 7516, University of Strasbourg/EOST, CNRS, 1 rue Blessig, F-67084 Strasbourg, France;2. Department of Lithospheric Research, Czech Geological Survey, Klárov 3, 118 21 Praha 1, Czech Republic;3. Key Laboratory of Isotope Geochronology and Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;4. University of Chinese Academy of Sciences, Beijing 10069, China;5. Géosciences Montpellier, UMR 5243, University of Montpellier, CNRS, Place E. Bataillon, F-34095 Montpellier, France;6. Institute of Geophysics, Academy of Sciences of the Czech Republic, Bǒcní II/1401, 14131 Praha 4, Czech Republic;7. Institute of Geological Sciences, Polish Academy of Sciences, Senacka 1, 31-002 Kraków, Poland;1. State Key Laboratory of Geological Processes and Mineral Resources, Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China;2. ARC Centre of Excellence for Core to Crust Fluid Systems and GEMOC National Key Centre, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia |
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| Abstract: | The high-grade metamorphic terrane in the Badu region along the northeastern Cathaysia Block in South China preserves retrograded eclogites and mafic granulites. Here we present the petrology, mineral phase equilibria and P-T conditions based on pseudosection computations, as well as zircon U-Pb ages of these rocks. Mineral textures and reaction relationships suggest four metamorphic stages for the retrograded eclogite as follows: (1) eclogite facies stage (M1), (2) clinopyroxene retrograde stage (M2), (3) amphibole retrograde stage (M3), and (4) chlorite retrograde stage (M4). For the mafic granulite, three stages are identified as: (1) plagioclase-absent stage (M1), (2) granulite facies stage (M2) and (3) amphibolite facies stage (M3). Metamorphic evolution of both of the rock types follows clockwise P-T path. Conventional geothermometers and geobarometers in combination with phase equilibria modelling yield metamorphic P-T conditions for each metamorphic stage for the eclogite as 500–560 °C, 23–24 kbar (M1), 640–660 °C, 14–16 kbar (M2), 730–750 °C, and 11–13 kbar (M3). The chlorite retrograde stage (M4) is inferred to have occurred at lower amphibolite to greenschist facies conditions. Phase equilibria modelling of the mafic granulite shows P-T conditions for each metamorphic stage as 600–720 °C, > 13 kbar (M1) and 860–890 °C, 5–6 kbar (M2) and M3 at amphibolite facies conditions. LA-ICPMS zircon U-Pb dating and trace element analysis show that the high pressure metamorphism occurred at 245–251 Ma. Protolith age of the mafic granulite is 997 Ma, similar to that of the mafic to ultramafic rocks widely distributed in the Cathaysia Block and also along the Jiangnan belt. Subduction of ancient oceanic lithospheric materials (or crustal thickening) during Mesozoic and formation of eclogites suggest that the Cathaysia Block was perhaps in the Tethyan oceanic domain at this time. The granulite formation might have been aided by Mesozoic mafic magma underplating associated with lithospheric delamination, heating and retrogression of the eclogite accompanied by rapid uplift. |
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