关键词: 推覆体, 冲断层, 构造窗, 西藏

Abstract: There are two fault systems: Zangpo main nappe system(TMNS) and Zangpo backthrust system(ZBTS)along the Yarlung Zangpo River(east section).The TMNS consists of a series of the north-dipping thrust faults, such as the Renbung-Nedong subduction zone(RNSZ) and the Gangdese thrust-type ductile shear zone(GT).The former juxtaposes the Zangpo Ophiolite over the "Tethysan-Himalayan Zone" that is called as the N- Himalayan accretional complex in the paper, and it was formed from 100Ma to 40Ma.The Tethysan-Himalayan oceanic crust subducted under the Zangpo remnant oceanic crust which is composed of the basement and front ridge of the Xigaze-Sangri forearc basin; The latter juxtaposes the Gangdese batholith over the sedimentary sequence in the forearc basin or the Zangpo Ophiolite, and it was formed during the collision between the Indian plate and Asian plate from 40Ma to 26Ma. The ZBTS is consisted of a series of the south-dipping brittle thrust faults. Its main fault lies between the N-Himalayan accretional complex and the sedimentary sequence of the Xigaze-Sangri forearc basin or the Zangpo Ophiolite.The ZBTS is clearly younger than the TMNS, because its hanging wall strata overlie the TMNS. We have two guesses for the formation of the ZBTS. The first, during the late of the collision, the north part of the accretional complex locally thrust over the Zangpo ophiolite and the forearc sequence from S to N with the accretional complex shortening in NS direction;The second,the ZBTS composes the front zone of the N-Himalayan detachment fault system caused by gravity with rising of the Himalayan Mountains.

Key words: Nappe, Thrust fualt, Tectonic window, Xizang