南沙群岛海域断裂体系构造特征及其形成机制

Structural features and formation mechanism of fault systems in Nansha sea area

南沙地块从中生代晚期开始裂离华南陆缘,在其向南运动的过程中受到欧亚板块、太平洋-菲律宾海板块和印度-澳大利亚板块等几大板块的联合作用,导致该区断裂构造较为复杂。通过对南沙群岛海域地震资料的综合解释并结合前人的研究成果,认为南沙群岛海域断裂构造可分为伸展断裂系、走滑断裂系和逆冲断裂系3类。伸展断裂遍布全区,主要受SE—近S-N向拉张作用,经历两大期次的构造活动;走滑断裂主要分布于南沙地块的周缘,受周缘地块与南沙地块相对运动控制,经历三期构造活动;逆冲断裂主要分布于南沙地块的南缘,受古南海俯冲和逆时针旋转控制,经历三期构造活动。从不同断裂体系的活动期次可见,南沙群岛海域应力系统主要经历了3个演化阶段:早期主要受拉张作用控制,中期主要受拉张和走滑应力控制,而晚期主要受压剪应力控制。

From Late Mesozoic, the Nansha Block （NSB） began to deviate from the South China. Controlled by the movement of the Eurasian plate, the Pacific-Philippine plate and the India-Australia plate, the fault structures on the NSB are very complicated. In this paper, through multidisciplinary analysis on the seismic profile and regional geology, it is found that there are three fault systems in the Nansha sea area, including extensional fault system, strike-slip fault system and thrust fault system. The extensional fault, widely spread in this area, underwent two large stages of tectonic movements. The strike-slip fault, locating along the margin of the Nansha sea area, was controlled by the relative movement between the conterminous blocks and underwent ＂three stages of tectonic movements. The thrust fault, locating on the southern margin, was controlled by the subduction of the Proto South China Sea and the anticlockwise rotation of the Borneo, underwent three stages of tectonic movements. According to the fault activity, the tectonic stress field of the Nansha sea area is supposed to include three periods. The earliest stage is char- acterized by extensional stress, the middle period is featured by both extension and strike-slip stress, and the latest period is controlled by transpressive stress field.