西非被动大陆边缘重力滑脱构造体系下的塑性构造

DUCTILE STRUCTURES IN GRAVITATIONAL DECOLLEMENT STRUCTURE SYSTEM AT PASSIVE CONTINENTAL MARGIN OF WEST AFRICAN

论述了西非被动大陆边缘深水环境下的重力滑脱构造体系中的塑性构造。研究发现塑性地层在整个西非被动大陆边缘都有分布,且盐岩塑性层主要分布在西非被动大陆边缘的西南部和西北部,发育层位为过渡期(J-K)构造层之内;中部尼日尔三角洲等塑性层主要为泥岩塑性层,发育层位为古近系和新近系。根据重力滑脱构造体系发育特征可划分为:以正断裂和塑性焊接构造为主的上部重力滑脱伸展构造、以底辟构造为主的中部重力滑脱底辟构造、以冲断裂、塑性褶皱和塑性冲断构造为主的下部重力滑脱冲断构造。根据塑性构造上覆地层的变形过程,塑性构造演化主要经历了后生变形期和同生变形期。塑性构造变形机制主要受基底掀斜作用和上覆地层的沉积速率控制。塑性构造中的底辟、褶皱、冲断及塑性焊接构造对油气成藏的控制作用依次减弱。

This article deals with the ductile structures in the deep-water gravitational decollement structure system at the Passive Continental Margin of West African. It is found that ductile structures are widely distributed along the whole passive continental margin, and the ductile salt rocks are particularly developed in the southwest and northwest within the transitional structural layer （J-K）. In the Niger delta at the middle part of the passive margin of West Africa, ductile bed is mainly consisting of mudstone of Tertiary. According to the structural characteristics of the gravitational detachment structure system, the ductile structures could be divided into three types： the gravitational decollement extensional structures at the upper part characterized by normal fault and ductile; the gravitational decollement diapir structures at the middle part; and the gravitational decollement thrust structures at the lower part. According to the time of deformation of the ductile structure, the ductile structures could be grouped into two types of epigenetic and syngenetic structures. Deformation of ductile beds is mainly affected by the basement tilting and deposition rate of the overlying strata. The control of structures over oil and gas accumulation decreases in an order of diapir, fold, thrust and ductile welding structure.