班公湖—怒江构造带西段三叠纪—侏罗纪构造—沉积演化

班公湖－怒江构造带西段在大地构造位置上处于特提斯构造域东端，横跨班公湖－怒江断裂带。三叠纪－株罗纪期间，其构造－沉积演化经历了大陆初始裂谷（T）、原洋裂谷（J1）、残余弧后盆地（J2－J3）阶段。初始裂谷阶段的拉张是呈南断北超的半地堑式由东向西进行的，逐渐形成地堑式原洋裂谷盆地。中晚侏罗世，南部新特提斯洋壳开始北各俯冲,产生的区域挤压应力使原洋裂谷逐渐封闭，裂谷盆地的小洋壳表现出以南向俯冲为主的双向式腑冲，同时伴生区域热沉降，盆地具残余弧后盆地的性质。该阶段,羌南地区发育碳酸盐岩为主的稳定陆缘沉积，冈度斯－念青唐古拉板片北部则形成广泛南超的近源碎屑沉积。

Tectonic-sedimentary Evolution of the West Segment of the Bangong Co-Nujiang Structural Belt in the Triassic and Jurassic

The west segment of the Bangong Co-Nujiang structural belt belongs to the east Tethys tectonic domain, including the Bangong Co-Nujiang suture zone, the Gangdise-Nyainqentanglha slab and the South Qiangtang slab. On the basis of stratigraphic correlation for the Mesozoic in the belt and comprehensive study of other geologic features, this paper suggests that the tectonic-sedimentary evolution of the west segment of the Bangong Co-Nujiang structural belt in the Triassic and Jurassic includes the following stages; primary rift (Triassic), proto-oceanic rift (Early Jurassic) and remnant retroarc basin (Middle-Late Jurassic). In the Triassic, a scissors-like half-graben appeared along the Bangong Co-Nujiang suture zone. The primary rift gradually transformed to a proto-oceanic rift in the Early Jurassic, and oceanic crust occurred. In the Middle-Late Jurassic, Neo-Tethys oceanic crust began to underthrust toward the north, extrusion stress stemming from the underthrust gradually made proto-oceanic rift close. Underthrust from the south and north made the Gangdise-Nyainqentanglha slab transform into a magmatic island arc, but elevation differences of the orogenic belt were small. The Oceanic crust of proto-oceanic rift mainly underthrust toward the Gangdise-Nyainqentanglha slab with bi-directional underthrust. In the meantime, regional thermal subsidence occurred, and the proto-oceanic rift transformed into a remnant retroarc basin. The settling center of the basin was near the southern Bangong Co-Nujiang structural belt. Stable continental margin sedimentation which was mainly carbonate developed on the southern Qiangtang slab, and the Jienu Formation which was mainly made up of proximal sediments widely overlapped toward the south in the northern Gangdise-Nyainqentanglha slab. The remnant retroarc basin closed at the end of the Late Jurassic because of further subduction of the Neo-Tethys oceanic crust along the Yarlung Zangbo suture.