EVOLUTION OF THE LUNPOLA-DUBA BASIN COMPLEX, CENTRAL TIBET, FROM REPROCESSED SEISMIC DATA OF THE CHINA NATIONAL STAR PETROLEUM COMPANY

The Lunpola Basin and neighboring Duba Basin, which lie just south of the Jurassic Bangong-Nujiang Suture Zone, provide an almost continuous record of the upper crustal response to middle Eocene Indo-Asian collision in central Tibet. Re-processing and re-interpretation of 2D oil industry seismic data provided by the China National Star Petroleum Corporation indicates the following stages in the evolution of this key area: (1) Basement uplift in the Late Cretaceous to early Tertiary, followed by (2) initiation of regional subsidence and sedimentation that we interpret as a flexural response to thrust loading to the north (reactivated suture?). (3) About 45-35 Ma, the southern portion of the basin (proto-Duba) was deformed by low-angle, south vergent basement thrusting, as evidenced by growth strata. (4) Subsequent uplift of the entire basin formed the regional unconformity that marks the boundary between the Dingqing and Niubao formations. (5) Continued deformation led to partitioning of the Duba from the Lunpola basin, culminating about 32-28 Ma in the development of a major transpressional ridge (flower structure) that now separates the two basins, and formation of the Lunpola North Boundary Thrust (LNBT). This deformation is marked by a change in the direction of stratal thickening, from northward (lower sequence) to center of the basins (upper sequence). (6) After ca 34 Ma, EW extension results in pervasive development of normal faulting in the basin. The seismic data are consistent with a model of a foreland basin subsequently deformed and partitioned by a transpressional regime. The timing of these stages suggest linkage to Himalayan collision over 1000 km to the south, as well as subsequent plateau uplift and extensional collapse.