Geochronology and geochemistry of volcanic rocks of the Bima Formation,southern Lhasa subterrane,Tibet: Implications for early Neo-Tethyan subduction |
| |
| Institution: | 1. School of Earth Sciences and Engineering, Sun Yat-sen University, Guangzhou 510275, China;2. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China;3. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;4. College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China;1. State Key Laboratory of Continental Tectonics and Dynamics, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;2. Department of Earth Sciences, University of Adelaide, SA 5005, Australia;3. School of Earth Sciences and Resources, China University of Geosciences (Beijing), 29 Xueyuan Road, Beijing 100083, China;4. Faculty of Science, Kochi University, Akebono-cho 2-51, Kochi 780-8520, Japan;5. State Key Laboratory Breeding Base of Nuclear Resources and Environment, East China Institute of Technology, Nanchang 330013, China;1. Key Laboratory of Continental Collision and Plateau Uplift, Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing 100101, China;2. University of Chinese Academy of Sciences, Beijing 100049, China;3. Chinese Academy of Sciences Center for Excellence in Tibetan Plateau Earth Sciences, Beijing 100101, China;4. School of Earth Science and Geological Engineering, Sun Yat-Sen University, Guangzhou 510275, China |
| |
| Abstract: | Bima Formation volcanic rocks, which record the history of Neo-Tethyan subduction, are found within the central and eastern segments of the southern Lhasa subterrane, Tibetan Plateau. Zircon U Pb dating, whole-rock major and trace element analysis, and Sr–Nd–Pb–Hf isotopic compositions of Bima Formation volcanic rocks from the central segment of the southern Lhasa subterrane were used to constrain the magmatic and tectonic evolution of the Lhasa terrane during the early Mesozoic. Zircon UPb dating of five samples yielded consistent ages of 184.3 ± 2.4 to 176.8 ± 3.5 Ma. The dominant volcanic rock types within the Bima Formation are basalts, basaltic andesites, andesites, and dacites, which are enriched in the large-ion lithophile elements (e.g., Rb, Sr, and Ba) and depleted in high-field-strength elements (e.g., Nb, Ta, and Ti). (87Sr/86Sr)t ratios are low (0.702900–0.704146), εNd(t) and εHf(t) values are high and positive (+4.4 to +6.9 and + 9.6 to +15.7, respectively), and Pb isotope ratios are homogeneous (initial 206Pb/204Pb = 18.28–18.40; 207Pb/204Pb = 15.53–15.56; 208Pb/204Pb = 38.21–38.38). Combining the new data with those from a previous study of Bima Formation volcanic rocks from the eastern segment of the southern Lhasa subterrane indicates that the Bima Formation formed between the Middle Triassic and Early Jurassic. It suggests that more widespread early Mesozoic volcanic rocks in the southern margin of the Lhasa terrane. The basaltic rocks of the Bima Formation were generated by partial melting of a depleted mantle wedge metasomatized by slab-derived fluids, and subsequently experienced fractional crystallization without significant crustal contamination. The andesitic and dacitic rocks were formed by fractional crystallization of the basaltic magma. Our study indicates that the Bima Formation volcanic rocks were generated within a continental island arc setting related to northward subduction of the Neo-Tethyan oceanic slab during the early Mesozoic. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
