转换大陆边缘盆地构造特征——以西非贝宁盆地为例

THE STRUCTURAL CHARACTERISTICS OF A TRANSFORM MARGINAL BASIN:TAKING THE BENIN BASIN OF WEST AFRICA AS AN EXAMPLE

立足于大西洋的形成与演化,划分了贝宁盆地构造演化阶段,厘定了裂陷期盆地的边界,分析了盆地结构和构造特征,明确了盆地构造样式。贝宁盆地经历裂陷期、漂移期两个构造演化阶段,不发育盐岩。受早白垩世裂陷期盆地东、西部应力差异控制,盆地形成了东部拉张构造区和西部走滑构造区,盆地裂谷分布具有"东宽西窄"的特征。东部拉张构造区发育近东西向断裂体系,主要为拉张作用形成的铲式正断层,西部走滑作用区发育NE—SW向走滑断裂体系,发育陡直的走滑断裂,主要为走滑作用形成的走滑断层。受早白垩世东、西部应力差异和晚白垩世构造反转、新生代重力滑脱作用的控制,盆地发育拉张、扭张、挤压、重力滑脱4类构造样式,丰富的构造样式为盆地构造圈闭发育提供了有利的条件。

The Benin Basin is a well-developed rift basin under drifting stage without salt rock deposition.With reference to the formation and evolution of the Atlantic,this study divided the tectonic evolutionary stages,defined the boundry of the rift basin and structural styles,and analyzed the structural characteristics of the Benin Basin.Under the constraints of stress pattern in the rifting stage of early Cretaceous,the basin was composed of the eastern extensional tectonic region and the west strike-slip tectonic region,that made the rift basin wide in east and narrow in west.The eastern extensional tectonic region has a well developed E-W fault system,consisting of listric normal faults,whereas the west strike-slip tectonic region a NE-SW strike-slip fault system,consisting of steep strike slip faults.By the joint control of the stress field in early Cretaceous,the tectonic inversion in late Cretaceous and the gravitational detachment in Cenozoic,the Benin Basin has well developed in the structural types caused by stretching,transtensional,compressional,and gravitational detachment.All the four types of structural types provide favorable conditions for the formation of various structural traps in the basin.