FAULT CHARACTERISTIC AND ITS CONTROL ON TRAPS OF FAULT STRUCTURAL LAYER IN THE NORTHERN PINGHU SLOPE BELT, XIHU SAG, EAST CHINA SEA SHELF BASIN

Based on the fine depiction of basement paleouplift, this paper analyses the characteristics of faults system and its control on traps of the structural layer in the northern Pinghu slope belt of Xihu Sag, East China Sea Shelf Basin. The purpose is to guide the search and evaluation of traps in this area. According to the distribution of paleouplift and main faults, the northern Pinghu slope belt can be divided into three subzones, including the co-directional multiple steps fault zone in the northern area, re-directional multiple steps zone in the central area and co-directional single step fault zone in the southern area. Comprehensive regional stress background and volcanic episodes show that there are two faulting episodes, including the early episode and the late episode. The early episode fault has a NE direction strike, and controls the development of paleouplifts, while the late episode fault has a NNE direction strike, which is more widely distributed, and is affected by pre-existing paleouplift. The results show that, under the influence of the early episode fault and paleouplift, the local stress field of the late episode fault in the northern Pinghu slope belt has a shear adjustment. Under the background of regional stretching strong in the south and weak in the north, we identified three different stress fields including strong-extension in the south, twist-extension in the central and weak- twist- extension in the north. Based on that, this paper is clear that the twist-extensional fault combination and paleouplift-wing anticlinal traction are the two important determinants of the favorable traps. Finally we point out that the fault analysis about the paleouplift is an important direction for traps search and evaluation in this area