Proterozoic rapakivi granites from the North Qaidam orogen,NW China: Implications for basement attribution |
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| Institution: | 1. MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;2. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;3. Department of Geology, University of Huelva, Huelva 21071, Spain;4. Chang''an University, Xi''an 710054, China;1. Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Albertov 6, Prague 12843, Czech Republic;2. Institute of Petrology and Structural Geology, Faculty of Science, Charles University, Albertov 6, Prague 12843, Czech Republic;3. Institute of Geology and Paleontology, Faculty of Science, Charles University, Albertov 6, Prague 12843, Czech Republic;4. Department of Mechanics, Faculty of Civil Engineering, Czech Technical University in Prague, Thákurova 7, Prague 16629, Czech Republic;5. Institute of Physics of the Earth, Faculty of Science, Masaryk University, Tvrdého 12, Brno 60200, Czech Republic;6. Institut für Geowissenschaften, Goethe Universität, Altenhöferallee 1, D-60438 Frankfurt am Main, Germany;1. State Key Laboratory for Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;2. College of Earth Sciences, Jilin University, Changchun 130061, China;3. Department of Geological and Environmental Sciences, Stanford University, Stanford, CA 94305-2115, USA;4. Nanjing Center, China Geological Survey, Nanjing 210016, China;5. Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China;1. Department of Earth Sciences, Durham University, Durham DH1 3LE, UK;2. State Key Laboratory of Geological Processes and Mineral Resources, and School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China;3. Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;1. National Museum of Natural Sciences, Taichung 40453, Taiwan;2. Department of Earth Sciences, National Cheng Kung University, Tainan 70101, Taiwan;3. Department of Earth Sciences, Durham University, Durham DH1 3LE, UK;4. Beijing SHRIMP Centre, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;5. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;6. Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung 80424, Taiwan;7. Exploration and Development Research Institute, Chinese Petroleum Corporation, Miaoli 36010, Taiwan;1. CAS Key Laboratory of Crust–Mantle Materials and Environments, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China;2. State Key Laboratory of Geological Processes and Mineral Resources, Faculty of Earth Sciences, China University of Geosciences, Wuhan 430074, China;3. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Beijing 100029, China;4. Department of Earth and Space Sciences, University of California, Los Angeles, CA 90095, USA |
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| Abstract: | Voluminous Proterozoic (~ 1700 Ma) rapakivi granites occur in several cratons, especially in the northern hemisphere. Similar Proterozoic rapakivi granites have recently been recognized in the Paleozoic North Qaidam orogen, western segment of the China Central Orogenic System (CCOS). SHRIMP zircon U–Pb dating of these granites yielded ages of 1778 ± 17 and 1778 ± 12 Ma. These granites exhibit typical rapakivi textures. They are ferroan, alkalic to alkalic-calc, metaluminous to peraluminous and characterized by high Ga/Al ratios, Na2O + K2O and rare earth elements (apart from Eu) contents, but low MgO, CaO and Sr contents. These are typical A-type granite features. Whole-rock εNd(t) values of the granites range from ? 6.09 to ? 5.74 with Nd model ages of 2762 to 2733 Ma, and their zircon εHf(t) values are from ? 8.3 to ? 5.2 with two-stage Hf model ages of 2944 to 2800 Ma, suggesting that these rocks were derived from old continental crust. The ages, rapakivi texture and geochemical features suggest that these granites are very close to typical Proterozoic (~ 1700 Ma) rapakivi granites within the North China Craton (NCC) and belong to the group of Proterozoic rapakivi granites of the northern hemisphere. These indicate that part of the basement of the North Qaidam orogen in the western CCOS is similar to that of the NCC or was probably derived from it, and then became involved in the CCOS. This provides new data to solve the dispute on the basement origin in this orogen. |
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