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RESPONSE OF VOLCANISM TO THE INDIA-ASIA COLLISION

MO Xuan-xue,ZHAO Zhi-dan,DENG Jin-fu,DONG Guo-chen,ZHOU Su,GUO Tie-ying,ZHANG Shuang-quan,WANG Liang-liang(School of Earth Sciences and Mineral Resources, China University of Geosciences,Beijing 100083, China)  
Linzizong volcanic rocks occurred in Gangdese magmatic belt in southern Tibet and regional unconformity between the volcanic strata and strata underlain provide new tectonomagmatic evidences for India-Asia continental collision. Based upon the studies of petrology, major, trace and rare earth element geochemistry, and Nd-Sr-Pb isotope systematics, it is revealed that Linzizong volcanic rocks recorded the information in the transitional process from the end of subduction of Neo-Tethyan oceanic plate to India-Asia continent collision. While volcanic rocks formed in early stage of Linzizong volcanism had fingerprints of continental margin-arc settings, those in middle and late stages reflected environments of intra-continental convergence and crust thickening. 40.84~64.47 Ma of formation ages of Linzizong volcanic rocks have been determined by ~(40)Ar/~(39)Ar dating. The formation time of the unconformity mentioned above was constrained by the ~(40)Ar/~(39)Ar age of the base of Linzizong volcanic strata (~65 Ma). The strata across the unconformity were tremendously different in sedimentary facies and structural deformation, implying a major tectonic event. In combination with evidence from the temporal evolution and spatial distribution of igneous rocks in Tibetan Plateau, and the stratigraphical and paleontological evidence in southern Tibet that documented dramatic change in sedimentary facies and microfauna content across the Cretaceous-Tertiary (K/T) boundary, it is concluded that the collision between India and Asia continents (in southern Tibet) was most likely initiated at ~K/T boundary time (~65 Ma).
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