A response of volcanic rocks to the India-Asia continental collision: A case study on Linzizong volcanic rocks in Linzhou, Tibet

Intensive volcanism is usually associated with India-Asia continental collision. The Linzizong volcanic succession (shortly LVS), a result of the India-Asia continental collision, spreads as an over 1200km long volcanic rock zone in whole Gangdise belt north to the Yarlung-Zangbo collision belt. The LVS, nominated in Linzhou area, consists of andesite, rhyolite and the related pyroclastic rocks with interlayers of sedimentary rocks. With vast rhyolitic ignimbriteat at the top of the succession, the LVS can be divided into three volcanic cycles formed between 63.89Ma and 48.73 Ma. The petrological and geochemical data show that the SiO₂, K₂O and Al₂O₃ contents in the LVS increase and the magma was graded from intermediate, moderate potassium and metaluminous to acid, high potassium and peraluminous upwards. Vast hot tuff flow developed in the late stage of the succession. All the data indicate that the thickness of the crust was thickened from 30-40 km in the early stage to 50-60 km in the late stage. The volcanic rocks in LVS are relatively enriched in Cs, Rb, K, U and depleted in Ta, Nb, Ti, Sr, Ba, P. The lower part of LVS is geochemically similar to the andesite of late Mesozoic Sanri Fm., and the upper part is likely same as Miocene high potassium volcanic rocks in Wuyu and Zhaga volcanic basins. It is indicated that the early derived magma is imprinted with subducted slab of the new Tethys oceanic crust and the midlle-late magma has post-collisional characteristics. Therefore, the LVS as a response to the collision process between India and Asia continents has recorded the evolutionary process from collision to post-collision between the India and Asia continents from 64 Ma to 48 Ma in the Paleocene and Eocene.