Evidence of Early Cretaceous lower arc crust delamination and its role in the opening of the South China Sea |
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| Institution: | 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 10049, China;3. Guangzhou Marine Geological Survey, Guangzhou 510760, China;4. Lamont-Doherty Earth Observatory of Columbia University, 61 Rt. 9W, Palisades, NY 10964, USA;5. Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences), Ministry of Education, Wuhan 430074, China;6. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 10037, China;1. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, China;2. College of Geoscience, China University of Petroleum, Beijing, China;3. Key Laboratory of Tectonics and Petroleum Resources of the Ministry of Education, School of Earth Resources, China University of Geosciences, Wuhan, China;4. Energy & Geoscience Institute, University of Utah, Salt Lake City, UT, USA;5. Unconventional Petroleum Research Institute, China University of Petroleum, Beijing, China;6. Centre for Earth Sciences, Indian Institute of Science, Bangalore, India;7. School of Earth Sciences and Resources, China University of Geosciences Beijing, Beijing 100083, China;8. Department of Earth Sciences, University of Adelaide, SA 50005, Australia;9. Earth Dynamics Research Group, TIGeR (The Institute of Geoscience Research), Department of Applied Geology, Curtin University, Perth, Australia;10. Department of Geology and Geophysics, University of Utah, Salt Lake City, UT, USA;11. Department of Computer Science, University of Idaho, Moscow, ID, 83843, USA;1. Beijing SHRIMP Center, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;2. School of Earth, Atmospheric and Life Sciences, University of Wollongong, Wollongong, NSW 2522, Australia;1. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi’an 710069, China;2. Xi’an Centre of Geological Survey, China Geological Survey, Xi’an 710054, China;3. Shandong Provincial Key Laboratory of Depositional Mineralization & Sedimentary Mineral, Shandong University of Science and Technology, China;4. Department of Geological Sciences, 355 Williamson Hall, University of Florida, Gainesville, FL 32611, USA;5. Shaanxi Nuclear Industry Geology Surveying Institute, Xi’an 710100, China;6. Key Laboratory of Computational Geodynamics, Chinese Academy of Sciences, College of Earth Science, University of Chinese Academy of Sciences, Beijing 100049, China;1. Key Laboratory of Marine Sedimentology and Environmental Geology, First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China;2. Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China;3. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;1. CAS Key Laboratory of Marginal Sea Geology, South China Sea Institute of Oceanology, CAS, No. 164 West Xin''gang Rd., 510301 Guangzhou, China;2. Guangzhou Marine Geological Survey, P.O. Box 1180, Nan''gang, 510760 Guangzhou, China;1. Key Laboratory of Ocean and Marginal Sea Geology, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;2. University of Chinese Academy of Sciences, Beijing 101408, China |
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| Abstract: | Understanding the formation mechanism of the South China Sea has important implications for research on plate rupture and continent-ocean transition globally. Granitoids dredged from the Xiaozhenzhu Rise provide new perspectives on lithosphere evolution processes of this region. Zircon U Pb (127–122 Ma) and amphibole/K-feldspar 40Ar/39Ar (123–115 Ma) ages indicate high cooling rates of 55–64 °C/myr and thus rapid magma emplacement and uplift in the Early Cretaceous. These calc-alkaline granitoids with intermediate Mg# (44–53) and slightly negative Eu anomalies (Eu/Eu* = 0.63–1.00) have highly variable and well-correlated Cr (4.89–531 ppm) and Ni (2.27–258 ppm) contents, which indicate melt mixing. The low CrNi sample (19.4 ppm Ni) displays much higher Sr (847 ppm), Sr/Y (93.4), and overall stronger crustal signatures than the high CrNi samples (107–258 ppm Ni) which have more mantle-like characteristics. Despite these differences, all studied samples show relatively similar and moderately enriched SrNd isotopic compositions ((87Sr/86Sr)i = 0.7055–0.7064, εNd(t) = −0.6 to −1.7) and enriched Pb isotopic compositions that are comparable with those of marine sediments. They also show mantle-like depleted zircon O (δ18O = 4.5–6.3‰) and mostly positive zircon Hf (εHf(t) = −0.4–4.1) isotopic compositions that indicate limited upper crustal contribution in the melt source. Their compositional features are best explained by magma mixing between partial melts of a delaminated lower arc crust and partial melts of a metasomatized arc mantle wedge. Combining our new results with literature studies of magmatism, metamorphism, sedimentary records and crustal structures from the region, we propose a new model of the Late Mesozoic–Early Cenozoic lithosphere deformation of the South China continental margin where lower arc crust delamination generated a tectonic weak zone that is essential for the rifting of the South China Sea. |
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