Comparison of structures between the Qiangtang basin,northern Tibet, China, and the Tethyan basin, Western Asia, and their petroleum prospect evaluation.

The Qiangtang basin is one large Paleozoic-Cenozoic basin besides the Tarim, Qaidam and Junggar basins in western China. The basin swarm of the West Tethys belt, which is the richest petroleum-bearing region in the world presently, has a similar tectonic setting to the Qiangtang basin. On the basis of an analysis of the formation and tectonic evolution of petroleum-bearing basins in the Tethys belt, the geological conditions for petroleum accumulation in basins are discussed. By a comparative analysis, the authors think that the formation and evolution of the Qiangtang basin are similar to those of the Afghanistan massif in the West Tethys segment and its Jurassic sedimentation and evolution and tectonic framework are similar to those of the Lacum basin in Central Asia. The Qiangtang basin has the basic conditions for petroleum formation. However, the Qiangtang basin is close to the Himalayan fold belt, and since the Neogene the basin has been reworked strongly and nappe-thrusting, on the one hand, generated structural traps but, on the other hand, caused source rocks to be more mature, which is unfavorable for petroleum preservation. Because of these factors, the Qiangtang basin is markedly different from the petroleum-bearing basins in Middle East where petroleum is accumulated in considerable amount. So, we should look for areas with both favorable oil-generating conditions and preservation conditions in petroleum exploration of the Qiangtang basin.