THE DECOLLEMENT IN THE QIANGTANG BASIN, TIBET

Qiangtang Basin in northern part of Tibet is significant on geological research, and it is also a prospect area for petroleum and gas exploration. Qiangtang Basin mainly consists of Triassic\|Jurassic carbonate strata, extending E—W. The basement of the Qiangtang Basin composed of Lower\|Middle Proterozoic exposed in the central part, and is called Central Upright Zone.The decollement and thrust structure occurred both in Qiangtang Basin and the Central Upright Zone, which have resulted in important influence for petroleum and gas exploration.(1) Tectonic style:① The suprastructure of Qiangtang Basin is dominated by parallel folds (Ramsay's classification Ib\|Ic) and brittle faults.② Most of the folds are open folds with interlimb angles 80～120°and lack of axial cleavage.③ The 3\|D shape of fold is cylindrical, without or little change on area and volume.④ The folds association is ejective folds (i.e. with the characteristics of the Jura\|type fold).⑤ The plastic bed flowing with the higher zone of the folds formed diapir structure, which is the important evidence indicating decol lement.