Late Neoarchean synchronous TTG gneisses and potassic granitoids in southwestern Liaoning Province,North China Craton: Zircon U-Pb-Hf isotopes,geochemistry and tectonic implications |
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| Institution: | 1. Beijing SHRIMP Centre, Chinese Academy of Geological Sciences, 26 Baiwanzhuang Road, 100037 Beijing, China;2. Department of Geosciences, University of Mainz, D-55099 Mainz, Germany;1. Wuhan Center of Geological Survey, China Geological Survey, Wuhan 430205, China;2. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;3. Department of Earth and Environmental Sciences, University of Windsor, Ontario, Canada;4. State Key Lab of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan 430074, China;5. Key Laboratory of Marine Hydrocarbon Resources Environmental Geology, Ministry of Natural Resources, Qingdao Institute of Marine Geology, Qingdao 266071, China;6. Key Laboratory of Depositional Mineralization & Sedimentary Minerals, Shandong University of Science and Technology, Qingdao 266590, China;7. School of Earth Sciences, China University of Geosciences Wuhan, Wuhan 430074, China;1. Key Laboratory of Mineral Resources, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. School of Earth Sciences and Resources, China University of Geosciences Beijing, 29 Xueyuan Road, Beijing 100083, China |
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| Abstract: | Abundant late Neoarchean granitoids occur in southwestern Liaoning Province, part of the Eastern Ancient Terrane of the North China Craton. These rocks include intermediate gneiss, TTG gneisses and potassic granitoids, and we report on the geochemistry and zircon SHRIMP ages as well as Hf-in-zircon isotopes of these granitoids in order to determine their petrogenesis. Field relationships suggest that most of these granitoids experienced widespread metamorphism and deformation, associated with anatexis at some localities. The intermediate gneisses, TTG gneisses and potassic granitoids were all emplaced at the end of the Neoarchean (2.50–2.53 Ga), and CL images document widespread recrystallization in the zircons. The intermediate and TTG gneisses yielded similar Hf isotopic systematics (εHf(t) = ?3.73 to +6.42) as the associated potassic granitoids (εHf(t) = ?2.44 to +7.80), and both rock types yielded mean Hf crustal model ages of 2.8–2.9 Ga. Combined with the geochemistry, we propose that the formation of the intermediate and TTG gneisses was related to partial melting of mafic rocks at different depth, whereas the potassic granitoids have variable petrogenesis. The nearly coeval TTG gneisses and potassic granitoids and their widespread metamorphism, deformation and zircon recrystallization suggest that a large-scale heat source must have been present at or near the base of the crust in southwestern Liaoning Province at the end of the Neoarchean. We propose that collision and post-collisional extension is the most likely tectonic environment for generation of the above granitoids, and the formation of widespread potassic granitoids played an important role in the maturation of continental crust in the North China Craton. |
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