珠江口盆地珠一坳陷新生代盆地结构与成因演化

Basin Structure and Genetic Evolution of the Zhu 1 Depression,During the Cenozoic, Pearl River Mouth Basin, South China

运用丰富的三维地震资料,在断裂体系的静态描述基础上,通过断层活动速率计算和平衡剖面分析,并结合残留地层展布特征,恢复了新生代盆地垂向演化与叠合过程,探讨盆地发育与转型的动力学机制。珠一坳陷新生代经历了裂陷早期、裂陷晚期、裂后拗陷和构造活动期四大演化阶段。裂陷期(E_2w-E_2e),印支地块旋转挤出和古南海俯冲,区域拉张应力场由NW向顺时针转变为近SN向,导致了裂陷早期NE、NEE向断裂控盆向裂陷晚期近EW向、NWW向断裂控盆转变,岩石圈伸展作用由宽裂谷方式向窄裂谷方式转变,导致盆地格局由彼此孤立的半地堑或窄地堑系趋于相互扩展连通;裂后拗陷期(E_3z-N_1z-N_1h),岩石圈伸展中心迁移至南海扩张中心,南海北部地区整体处于裂后热沉降阶段,构造活动微弱;构造活化期(N_1y-N_2w-Q),菲律宾海板块NWW向仰冲—碰撞联合作用下产生NNE向拉张,同时派生近EW向和NW向的共轭剪切作用,导致了先存NWW向和近EW断裂的活化,以及隆起区NWW向张性断裂和近EW向、NW向走滑断裂带的形成。该研究所揭示的盆地发育演化过程不仅对该区油气勘探提供指导,也对被动大陆边缘演化的研究有着一定的借鉴意义。

Based on investigating the general characteristics of fault systems by using abundant 3D seismic data, this paper clarified the tectonic evolution vertically and superimposition process of a Cenozoic basin by calculating the fault activity rate, analyzing the equilibrium section, and combining the distribution characteristics of residual strata. The dynamic mechanism of the development and transformation of the basin was also discussed. Results show that the Zhu 1 depression of the Pearl River Mouth Basin of this study underwent four evolution stages: early stage of rifting, late stage of rifting, depression stage and tectonic reactivation stage. In detail, during the rifting stage (E2w-E2e), due to the rotating extrusion of the Indochina block and the southward subduction of the proto-South China Sea, the regional stress field changed clockwisely from NW-trending to SN-trending. This resulted in the transformation of basincontrolling faults from early rifting WE- and NEE-trending into late rifting EW- and NWW-trending. The system of lithosphere extensional deformation transformed from the wide rift mode to the narrow rift mode. As a result, the isolated half-graben or narrow graben of the basin structure tended to be connected and extended. While during the post-rifting depression period (E3z-N1z-N1h), the activity of those faults decreased and stopped. It might because the extensional center of lithosphere had migrated southward to the spreading center of the South China Sea, and the northern margin of the South China Sea was in a post-rifting thermal subsidence stage with weak tectonic activities overall. Then during the tectonic activation stage (N1y-N2w-Q), the NWW-trending and pre-existing subparallel EW-trending faults reactivated, and the conjugate strike-slip fault system is composed of a subparallel EW-trending dextral strike-slip fault zone and a NW-trending sinistral strike-slip fault zone, and a series of NWW-trending secondary tensile fractures were formed. It might be due to the NNE-trending extensional stetting caused by the obduction and arc-continent collision of the NWW movement of the Philippine Sea Plate. Cenozoic tectonic evolution of the Zhu 1 depression revealed by this study not only provides guidance for regional oil and gas exploration, but also has certain reference implications for the study of evolution of passive continental margins.