东海盆地西湖凹陷平北区断陷层断裂特征及其对圈闭的控制

以基底古隆精细刻画为基础，分析东海陆架盆地西湖凹陷平北区断陷层系断裂发育特征，并探讨断裂对圈闭发育的控制作用，以指导区内构造圈闭搜索与评价。根据古隆起和骨干断裂展布特征，将平北区划分为北部同向多阶断阶区、中部反向多阶断阶区和南部同向单断断阶区等3个次级区带。综合区域应力背景和火山活动期次，厘定出平北区断陷期早、晚两期断裂系统。早期断裂以NE走向为主，控制古隆起发育。晚期断裂数量多、分布广，以NNE走向为主。在南强北弱的区域伸展背景下，断陷晚期断裂发育受早期断裂及古隆起影响，局部应力场发生扭动调整，在平湖组沉积时期表现为南部强伸展、中部张扭和北部弱伸展夹扭动3种不同应力场。在此基础上，明确了张扭性断裂组合及古隆起边缘受断层影响的牵引背斜是决定有利圈闭发育的主要因素，最终提出通过平北区古隆起周边断裂精细梳理是圈闭搜索与评价的重要方向。

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