南海西部中建南盆地构造格架及形成机制分析

An analysis of structural framework and formation mechanism of Zhongjiannan basin in the west of South China Sea

中建南盆地地处南海西部,断层、火山岩体发育,地质条件复杂。新生代构造运动对盆地形成演化影响很大,剖面上表现为由4个不同结构特征的构造层叠置而成,平面上呈现北北东-北西走向,形态呈菱形,既具有走滑盆地的几何特征,又具有拉张盆地的地质特征。盆地整体以一个主要坳陷和两个次级坳陷为中心,穿插缓坡低隆起,形成隆坳相间排列的构造格局。盆地内发育伸展构造和走滑构造,走滑方向不同,对盆地演化的影响截然不同,左旋引起挤压,而右旋则造成盆地拉张沉降。在拉张和剪切两种应力改造作用下,经过了多次抬升、沉降的旋回,形成走滑-拉张复合型盆地。

Zhongjiannan basin, located in the west of South China Sea, has well developed faults and volcanic rocks, thus the geological conditions are very complex. The influence of the Cenozoic tectonic movement upon the formation and evolution of the basin was huge and is well reflected by its four superposed structural layers with different characteristics in profile, its NNE-NW trending, and its lozenge shape on plane. Both geometrical characteristics of strike-slip basin and geological characteristics of tensional basin can be found in the basin. Centered with a major depression and two secondary depressions, the basin has a structural framework with alternative depressions and upheavals. Extensional structures and strike-slipping structures had been developed in the basin. Different slipping directions brought about completely different effects on the evolution of the basin： sinistral strike caused extrusion while dextral strike slip resulted in extension and subsidence in the basin. The combination of tensile stress and shear stress shaped the area into a strike sllp-extensional composite basin after several uplifting and subsidence cycles.