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

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.