Early Carboniferous High Ba‐Sr Granitoid in Southern Langshan of Northeastern Alxa: Implications for Accretionary Tectonics along the Southern Central Asian Orogenic Belt |
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| Authors: | ZHENG Rongguo LI Jinyi ZHANG Jin XIAO Wenjiao and LI Yi |
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| Institution: | 1 Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
2 Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, ChineseAcademy of Sciences, Urumqi 830011, China,1 Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China,1 Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China,2 Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, ChineseAcademy of Sciences, Urumqi 830011, China
3 State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
4 CAS Center for Excellence in Tibetan Plateau Earth Science, Chinese Academy of Sciences, Beijing100101, China
5 University of Chinese Academy of Sciences, Beijing 100049, China and 6 China Minmetals Corporation, Beijing 100010, China |
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| Abstract: | Voluminous granitoids are widely distributed in the Langshan region, northeast of the Alxa block, and record the evolutionary processes of the southern Central Asian Orogenic Belt. The Dabashan pluton was emplaced into the Paleoproterozoic Diebusige complex. Early Carboniferous zircon LA‐ICP MS U‐Pb ages were from 327 Ma to 346 Ma. The Dabashan pluton can be classified as monzogranite and syenogranite, and exhibits high K2O contents and K2O/Na2O ratios, which reveal a high‐K calc‐alkaline nature. The samples display strongly fractionated REE patterns, and are enriched in large ion lithophile elements (LILE) relative to high field strength elements (HFSE). The Dabashan plutons display unusually high Ba (823–2817 ppm) and Sr (166–520 ppm) contents and K/Rb ratios (315–627), but low Rb/Ba ratios (0.02–0.14), and exhibit fertile zircon Hf isotopic compositions εHf(t)=–14 to –20], which are comparable to those of typical high Ba–Sr granitoids. Based on the geochemical compositions of the samples, we suggest that subducted sediments and ancient crustal materials both played important roles in their generation. Basaltic melts were derived from partial melting of subcontinental lithophile mantle metasomatized by subducted sediment‐related melts with residual garnet in the source, which caused partial melting of ancient lower crust. Magmas derived from underplating ascended and emplaced in the middle–upper crust at different depths. The resultant magmas experienced some degree of fractional crystallization during their ascent. Given these geochemical characteristics, together with regional tectonic, magmatic, and structure analysis data, an active continental margin environment is proposed for the generation of these rocks. |
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| Keywords: | LA–ICP MS U–Pb Zircon Hf isotope high Ba–Sr granites CAOB Alxa |
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