多期走滑拉分盆地的沉积响应:以南海北部珠江口盆地为例

南海北部陆缘位于太平洋和新特提斯两大构造域之间,其形成与演化受到多期多向构造叠加作用,珠江口盆地是南海北部陆缘的重要构造单元。自新生代早期珠琼运动以来,由于太平洋板块向华南大陆俯冲在珠江口盆地形成两期强烈的走滑拉分作用,从而导致早期弥散状地堑与后两期拉分盆地的三层盆地叠合现象。本文在综合珠江口盆地的地质、构造物理和数值模拟、南海北部新生代构造演化研究的基础上,探讨了珠江口盆地区域沉积作用对构造的响应过程;并基于其内部次级构造单元阳江东凹的地震剖面资料解剖,进一步检验珠江口盆地地堑式伸展、两期走滑拉分作用对沉积盆地的沉积相空间展布、沉积沉降中心迁移规律的控制作用。研究表明,珠琼运动一幕(~47.8 Ma)伴生的NE向走滑运动控制盆地发育规模较小的辫状三角洲沉积,珠琼运动二幕(~38Ma)伴生的NWW向走滑运动控制三角洲轴向并导致三角洲沉积范围扩大,白云运动(~23 Ma)时期的沉积展布不受NE向走滑断层控制、但三角洲轴向仍与NW-NWW向断裂体系相关;在上述多期构造运动过程中,盆地沉积沉降中心往南迁移,逐渐奠定了三角洲沉积格局。

Sedimentary Response of Multi-stage Pull-apart Basin: Insights from the Pearl River Mouth Basin in the Northern South China Sea Margin

The northern South China Sea margin is located between the Pacific and the Neo-Tethys tectonic domains,and its formation and evolution are caused by the superposition of multi-stage and multi-sense tectonics.The Pearl River Mouth Basin is an important tectonic unit of the northern South China Sea margin.Since the Cenozoic Zhuqiong Movement,the subduction of the Pacific Plate under South China formed the three-layer superposed architecture in the Pearl River Mouth Basin,which was constituted by the early dispersive graben and two late periods of strong strike-slip pull-apart sub-basins.Based on the geological,physical and numerical analogue modelling of the strike-slip pull-apart basins and the Cenozoic tectonic evolution in the northern South China Sea margin,this paper discusses the sedimentary response of the Pearl River Mouth Basin.Based on the seismic data of the sub-structural units of the eastern Yangjiang Sag and some other secondary structural units in the Pearl River Mouth Basin,this paper further stress the spatial distribution of sedimentary facies and the migration of subsidence centers or depocenters controlled by the extensional and strike-slip faulting in the Pearl River Mouth Basin.It is concluded that the NE-trending strike-slip fault of the first-stage of the Zhuqiong Movement(ca.47.8 Ma)controlled the development of smaller braided delta deposition,and the NWW-striking strike-slip fault of the second-stage of the Zhuqiong Movement(38 Ma)dominated the axis of the deltaic deposit.Moreover,the spatial distribution of sedimentation was not affected by NE-striking strike-slip fault during the Baiyun Movement(ca.23 Ma),but the deltaic axis were still controlled by the NW-NWW-trending fault system.The depocenters in the basin gradually moved southward during the Paleogene,and caused the stable deltatic sedimentary pattern in the basin.