New understanding of stratum of Xigaze forearc basin in the north of Qiongguo area, Zhongba, Tibet

Located in the west of Xigaze forearc basin, the Cretaceous to Eocene stratigrphic sequence reserved grows in the Zhongba region along the north bank of the Yarlung Zangbo Suture Zone. The marine Cretaceous Xigaze Gr. could be subdivided in ascending order into the Angren Fm., Padana Fm. and Qubeiya Fm. Pale-ocene Eocene Cuojiangding Gr. inclouds Quxia Fm. and Jialazi Fm.. "Rujiaozangbu psepholite"—the confining coarse clastic rock of Xigaze forearc basin, is concordant on the Cuojiangding Gr.. Four differences in sedimentology,stratig raphic palaeontology and structural geology show that there exists a nonconformity between Xigaze Gr.and Cuojiangding Gr..Speaking concretely, this nonconformity existed between Qubeiya Fm.and Quxia Fm..The nonconformity was formed between Campanian-maast richtianand danian.The whole stratigrphic sequence of Xigaze for earc basin in this region reappear the course of strong underthrust between India plate and Eurasian plate fully.The main collision between India plate and Eurasian plate took place after "Rujiaozangbu psepho lite" had been deposited,the time of collision between the two plates is later than primary under standing's.