Tectono-magmatic evolution of the Gaoligong belt,southeastern margin of the Tibetan plateau: Constraints from granitic gneisses and granitoid intrusions |
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| Institution: | 1. State Key Laboratory of Continental Dynamics, Northwest University, Xi''an, China;2. Department of Earth Sciences, Sun Yat-Sen University, Guangzhou, China;3. College of Earth Sciences, Guilin University of Technology, Guilin 541004, China;4. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing, 100101, China;5. State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;6. CSIRO Earth Sciences and Resource Engineering, Bentley, WA 6102, Australia;1. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550005, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;1. State Key Laboratory of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;2. State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing 210046, China;3. Geological Survey of Yunnan Province, Kunming 650051, China;4. Geologisches Institut, ETH Zurich, 8092 Zurich, Switzerland;1. State Key Laboratory of Geological Processes and Mineral Resources, and School of Earth Science and Resources, China University of Geosciences, Beijing 100083, China;2. CAS Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;1. State Key Laboratory of Continental Dynamics, Department of Geology, Northwest University, Xi''an 710069, China;2. School of Earth Science and Resources, China University of Geosciences, Beijing, China;3. Department of Earth Sciences, University of Adelaide, Adelaide, SA 5005, Australia |
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| Abstract: | The Gaoligong belt is located in the southeastern margin of the Tibetan plateau, and is bound by the Tengchong and Baoshan blocks. This paper presents new data from zircon geochronology, geochemistry, and whole-rock Sr–Nd–Pb–Hf isotopes to evaluate the tectonic evolution of the Gaoligong belt. The major rock types analysed in the present study are granitic gneiss, granodiorite, and granite. They are metaluminous to peraluminous and belong to high-K, calc-alkaline series. Laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) analyses of zircons from nine granitic rocks yielded crystallization ages of 495–487 Ma, 121 Ma, 89 Ma, and 70–63 Ma. The granitoids can be subdivided into the following four groups. (1) Early Paleozoic granitic gneisses with high εNd(t) and εHf(t) values of ? 1.06 to ? 3.45 and ? 1.16 to 2.09, and model ages of 1.16 Ga to 1.33 Ga and 1.47 Ga to 1.63 Ga, respectively. Their variable 87Sr/86Sr and Pb values resemble the characteristics of the Early Paleozoic Pinghe granite in the Baoshan block. Our data suggest that the rocks were derived from the break-off of the Proto-Tethyan oceanic slab between the outboard continent and the Baoshan block, which induced the partial melting of Mesoproterozoic pelitic sources mixed with depleted mantle materials. (2) Early Cretaceous granodiorites with low εNd(t) and εHf(t) values of ? 8.92 and ? 4.91 with Nd and Hf model ages of 1.41 Ga and 1.49 Ga, respectively. These rocks have high initial 87Sr/86Sr (0.711992) and lower crustal Pb values, suggesting that they were derived from Mesoproterozoic amphibolites with tholeiitic signature, leaving behind granulite residue at the lower crust. (3) Early Late Cretaceous granites with low εNd(t) and εHf(t) values of ? 9.58 and ? 4.61 with Nd and Hf model ages of 1.43 Ga and 1.57 Ga, respectively. These rocks have high initial 87Sr/86Sr (0.713045) and lower crustal Pb isotopic values. These rocks were generated from the partial melting of Mesoproterozoic metapelitic sources resulting from the delamination of thickened lithosphere, following the closure of the Bangong–Nujiang Ocean and collision of the Lhasa–Qiangtang blocks. (4) Late Cretaceous to Paleogene granitic gneisses with low εNd(t) and εHf(t) values of ? 4.41 to ? 10 and ? 5.95 to ? 8.71, Nd model ages ranging from 1.08 Ga to 1.43 Ga, and Hf model ages from 1.53 Ga to 1.67 Ga, respectively. These rocks show high initial 87Sr/86Sr (0.713201 and 714662) and lower crustal Pb values. The data suggest that these rocks are likely related to the eastward subduction of the Neo-Tethyan Oceanic slab, which induced partial melting of Mesoproterozoic lower crustal metagreywacke. The results presented in this study from the Gaoligong belt offer important insights on the evolution of the Proto-Tethyan, Bangong–Nujiang, and Neo-Tethyan oceans in the southeastern margin of the Tibetan Plateau. |
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