Geochemical Characteristics and Tectonic Significance of Carboniferous Bimodal Volcanic Rocks in Aoyituolangge Area, Eastern Junggar
Journal of Jilin University(Earth Science Edition). 2021, 51 (2):
In this paper, the geological,petrological, and geochemical characteristics of volcanic rocks of the Batamayineishan formation are studied in the Aoyituolangge area at the northwestern margin of Santanghu basin of the eastern Junggar orogenic belt, and the genesis, formation environment, and tectonic evolution of the eastern Junggar orogenic belt are discussed in combination with the relevant chronological results. It is concluded that the Carboniferous volcanic rocks in this area have obvious characteristics of continental volcanic rocks and bimodal volcanic rocks. The basic end member of the rock combination is mainly basalt, and the acid end members are perlite and dacite. The characteristics of the major elements show that the basic endmembers have calc-alkaline-alkaline properties; While the acidic endmembers of perlite and dacite have alkaline and freckling properties respectively. The characteristics of trace elements show that the fundamental end elements are relatively rich in LILE, such as Ba, K, Sr, etc., while Th, Nb, Nd, and other high-field strength elements (HFSE) are poor. Among the acidic end elements, Ba, Nb, Sr, Sm, Ti and other elements are strongly depleted, while K is more enriched. The analysis of rare earth elements show that LREE at both ends are relatively enriched, while HREE are relatively depleted. The main and trace elements characteristics of perlite are obviously different from the whole. The geochemical characteristics indicate that the basic end members of the bimodal volcanic rocks came from the partial melting of mantle rocks, the acidic end member of dacite came from the separation and crystallization of the basic end members, and the perlite came from the partial melting of the lower crust. The geodynamic background was the subduction of oceanic crust, which caused the upwelling of asthenosphere heat source, the partial melting of mantle rocks, the extensional thinning of lithosphere, and the decompression and melting of the mafic rocks in the lower crust. The tectonic environment was late in the post-collision extension stage, showing the characteristics of plate chain suture.
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