Elemental and boron isotopic variations in tourmaline in two-mica granite from the Cuona area,Tibet: Insights into the evolution of leucogranitic melt |
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| Institution: | 1. Center of Deep-Sea Research, Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao 266071, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Laboratory for Marine Geology, Laoshan Laboratory, Qingdao 266237, China;4. CAS Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;5. Chengdu Center, China Geological Survey, Chengdu 610081, Sichuan Province, China;6. Department of Geochemistry, Chengdu University of Technology, Chengdu 610059, China;7. State Key Laboratory for Mineral Deposits Research, Institute of Continental Geodynamics, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China;8. Frontiers Science Center for Critical Earth Material Cycling, Nanjing University, Nanjing 210023, China |
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| Abstract: | Two-mica granite is the most common magmatic rock type in the Himalayan leucogranite belt, which has close relationship with rare metal mineralization. Its genesis is generally attributed to magmatic differentiation. In recent years, the mineral geochemical compositions are increasingly used to study magmatic differentiation, which are significant for deciphering the melt evolution and element migration processes. In this study, in-situ major and trace element and boron isotope compositions for tourmalines from two-mica granites in the Cuona and Cuonadong leucogranites in the Cuona area are conducted to determine microscopic changes in mineral assemblages and geochemical compositions. Analytical results show that the tourmalines in the Cuonadong leucogranite were crystallized earlier relative to the tourmalines in the Cuona leucogranite during magmatic differentiation. The volatile contents have a genetic relationship with incompatible elements in tourmaline, which is possibly responsible for the formation of tourmaline zonation and the enrichment of Sr, Zn, and Pb during magmatic differentiation. The B isotopic composition of tourmaline in the Cuona area suggests that the granitic magma was dominantly derived from the partial melting of the metasedimentary source rocks. Their B isotope variations likely resulted from fluid exsolution during B-rich melt evolution. High rare metal contents in tourmalines indicate that the two-mica granites in the Cuona area may have great mineralization potential. |
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