西非被动大陆边缘盐构造样式与成因机制

基于三维地震资料，对西非陆缘盐构造样式及分布特征进行了刻画，剖析了其形成演化机制与控制因素。西非陆缘盐上地层滑脱形成典型的薄皮构造，前缘发育挤压变形，后缘发育拉张变形，两者之间为过渡变形。拉张区发育白垩系盐筏、前盐筏、新近系盐筏等盐构造；过渡变形区以发育各种底辟构造为特征；挤压变形区主要发育侵位盐席构造。重力滑脱作用是被动陆缘盐构造发育过程中始终存在的驱动机制，重力扩展作用在大陆边缘成熟阶段作用明显，在陆缘演化早期并不突出。陆缘构造活动控制盐构造的形成，差异沉积负载作用影响着盐上地层滑移特征，而盐下底形对盐岩流动、盐上地层滑移速率及相关断裂体系的产生与沉积响应具有重要影响。

SALT STRUCTURES ON THE WEST-AFRICA PASSIVE CONTINENTAL MARGIN AND THEIR GENETIC MECHANISM

The styles of salt structures developed on the west-Africa margin and their evolutionary mechanism and controlling factors are studied upon 3-D seismic data. The thin-skin structures were formed due to the gliding of the overlying strata,characterized by a compressional deformation zone in the frontier area and an extensional deformation zone on the backside, with a transitional zone in be- tween. Salt rafts, pre-rafts and monocline structures develop in the extensional area, whereas the transitional deformation zone is characterized by various extensional diapirs. Squeezed diapir and at- lochthonous sheets are well developed in the compressional deformation zone. Gravity gliding is the driving force of the salt tectonics on the passive margin throughout the forming time. Gravity sprea ding derived from the differentiation of sediment load significantly controls the salt tectonics in the stage while the margin is mature, but weak in the early time. Tectonic activity at the continental mar- gin is the main factor which triggers salt tectonics which starts after the cessation of tectonic activi- ties. Differentiation of sediment load influences the decollement of strata overlying the salt, and the topography below the salt layer has significant impacts on the salt flowing, the slipping velocity of the strata, the generation of related faults and the responses of sedimentation.