南堡凹陷Ⅱ号、Ⅲ号构造带断裂构造发育特征及成因

Fault development characteristics and genesis of theⅡandⅢstructural belts in Nanpu Sag,Bohai Sea,China

基于渤海湾盆地北部南堡凹陷三维地震解释数据,以盆地构造解析理论为指导,系统梳理南堡凹陷Ⅱ号和Ⅲ号构造带内断裂几何特征及组合样式,结合平衡剖面技术恢复不同构造活动时期盆地发育特征,探讨断裂变形的成因机制。结果表明:南堡Ⅱ号、Ⅲ号构造带是典型的伸展构造样式,平面上以NEE走向平行对倾式为主要组合样式,剖面上呈“似花状”构造。根据断距-埋深曲线厘定,南堡凹陷Ⅱ号、Ⅲ号构造带内断裂系统分为基底先存断裂系统、晚期新生断裂系统和长期活动断裂系统。沙河街组沉积时期,南堡凹陷Ⅱ号、Ⅲ号构造带内形成NE向主干边界断层;东营组沉积时期,形成反向边界断裂,与主干断裂构成“y”字形结构样式;馆陶组-明化镇组沉积时期新生大量NEE向断层与长期活动主干边界断裂共同构成密集断裂带。先存基底F_(2)、F_(3)断层影响着局部应力场的分布,与上覆构造带构成间接关联耦合关系,先存基底与控带断层构成铲式扇组合共同控制浅部断裂密集带的发育。成因上,南堡凹陷Ⅱ号、Ⅲ号构造带的形成与发育直接受控于古近纪以来太平洋板块俯冲方向的转变。

Based on the analytical theory of basin structure and 3D seismic interpretation data of Nanpu Sag in the north of Bohai Bay Basin,the geometric characteristics and combination styles of faults in theⅡandⅢstructural belts of Nanpu Sag are systematically analyzed,the genetic mechanism of fault deformation is discussed,and the basin development characteristics in different tectonic periods are recovered by using balanced profile technology.The results show that the NanpuⅡandⅢstructural belts display typical extensional structural styles,with NEE trending parallel anticline as the main combination style in plane and“flower-like”structure in section.According to the curve of fault distance and buried depth,the fault systems inⅡandⅢstructural belts in Nanpu Sag can be divided into basement pre-existing fault system,late new fault system and long-term active fault system respectively.During the sedimentary period of Shahejie Formation,NE-trending main boundary faults were formed inⅡandⅢstructural belts in Nanpu Sag.In the sedimentary period of Dongying Formation,reverse boundary faults were developed,which is connected with the main faults,forming a“y”shape structural style.During the sedimentary period of Guantao and Minghuazhen Formations,a large number of NEE trending faults and long-term active main boundary faults constitute dense fault zones.The pre-existing basement F_(2) and F_(3) faults affect the distribution of local stress field,and form an indirect correlation and coupling relationship with the overlying structural belt.The pre-existing basement and the zone control faults form a listric fan combination and jointly control the development of shallow fault dense zone.In terms of genesis,the formation and development ofⅡandⅢstructural belts in Nanpu Sag are directly controlled by the change of the subduction direction of the Pacific plate since Paleogene.