Abstract:

Fault that show compresso-shear pattern in plane and intersecting inprofile is called compresso-shear vertical-intersecting fault. Within the studyarea, since the sides of major mountains and uplifts were controlled bycompresso-shear vertical-intersecting faults, a structural framework whicharranged alternately in fault-uplifts and fault-depressions was formed under theeffect of unified stress field of the plateau. In the east part of the region, thefault uplift-fault depressed zone resulted by NWW (Xiyu System) compresso-shear vertical - intersecting faults and four uplift - depression alternatedzones resulted by NNW (Hexi System) dextral shear-compression verticalintersecting faults conjoined to form four dextro-diagonal basin zones asWuwei-Lintao, Minle-Hualong, Jiudong-Xinghai,Jiuxi-Gjarring and Ngoringlakebasin zones. In the west, NWW stretched compressive fault uplift-faultdepressed zone and NEE striking conjugated compressive sinistral diagonalzone (Altun Mountains), conjoined to form Kumkuli-Jiuxi sinistral diagonalbasin zone. The Jiuxi Basin is a ladder-shaped basin placed at the joint partof two conjugated shear-compressive zone whereas the Qaidam Basin is a hugecomplex fault-depressed basin which is between two shear-compressive zonesduring the Meso-Cenozoic. The formation regime of the basins is not thatof rift, but that of compresso-rift which is between faults dipping backeach other. In the Qaidam Basin, a structural framework which is arrangedalternately in uplifts and depressions is also formed by the above men-tioned vertical-intersecting faults and it controlled the evolution of the basinand also the generation.accumulation of hydrocarbon. The Qaidam landmasswas disintegrated in the Indo-China Epoch,and a piedmont fault-depressionwith faults in marginal areas and overlaps in its inner part was formed. Inthe early stage, its subsidence center and depocenter was in the north (T,J, K) and west (J, K) margin. As the compression of the Indian Plateenhanced, these centers transfered gradually to the central (N₂) and eastparts of the basin.