新生代区域伸展方向转变对珠三坳陷断裂体系发育演化的控制作用

Control of the Cenozoic transformation in regional extension direction on the development and evolution of fault system in Zhusan Depression

沉积盆地内断裂体系的复杂性与多样性及其形成演化机制长期以来备受关注。以南海北部陆缘珠三坳陷为研究目标,在大量三维地震资料构造解析的基础上,分析了新生代区域伸展方向的转变规律,探讨了其对断裂体系发育演化的控制作用。研究结果表明:珠三坳陷断裂具有多走向、多级别、多性质的特点,依据断裂走向可以划分为NNE-NE、NWW-NW和近EW向3组,不同走向断裂发育特征、断裂性质及分布规律存在差异。新生代珠三坳陷区域伸展方向经历了顺时针旋转的演化,由古新-中始新世神狐-文昌组沉积期的NW-SE向,转变为晚始新-早中新世恩平-珠江组沉积期的近SN向,到中中新世韩江组沉积期至今的NNE-SSW向。新生代区域伸展方向的转变与先存断裂共同控制了珠三断裂体系的发育演化,整体上导致各演化阶段活动断裂特征存在差异。从具体断裂上看主要表现在:古新-始新世强烈活动的南断裂带南支西段在中晚期消亡;南断裂带北支不同分段的断裂性质存在一定差异;走向弯曲的琼海1号、南断裂带北支文昌B凹北段晚期发生局部构造反转。以上几方面现象共同反映了新生代区域伸展方向转变对珠三坳陷断裂体系发育演化的控制作用。

The complexity and diversity of fault systems in sedimentary basins,as well as their formation and evolution mechanisms,have long been of great concern.Taking the Zhusan Depression on the northern margin of the South China Sea as the research objective,based on the structural analysis of a large amount of three-dimensional seismic data,the transformation in the direction of the Cenozoic regional extension was analyzed,and its role of control on the development and evolution of fault systems was explored.Results indicate that the faults in the Zhusan Depression have the characteristics of multiple strikes,levels,and properties.In fault strike,they could be divided into three groups:NNE-NE,NWW-NW,and near EW.There are differences in the development characteristics,properties,and distribution patterns of faults in different strike directions.The regional extension direction of Zhusan Depression experienced clockwise rotation evolution in the Cenozoic,from the NW-SE direction of the Paleocene-Eocene Shenhu Wenchang Formation sedimentary period,to the nearly SN direction of the Oligocene-Early Miocene Enping-Zhujiang Formation sedimentary period,and to the Middle Miocene Hanjiang Formation sedimentary period in NNE-SSW direction.The transformation of the direction of regional extension in the Cenozoic and the preexisting faults jointly controlled the development and evolution of the Pearl River Delta fault system,resulting in differences in the characteristics of active faults in different stages of evolution.This is mainly manifested in the disappearance of the southern branch of the western segment of the southern fault zone,which was strongly active during the Paleocene-Eocene in the middle and late stages.The fault properties of different segments of the northern branch of the southern fault zone are different.For example,the bending of Qionghai No.1 Fault and structural inversion in the northern section of Wenchang B Sag,reflect the control effect of direction change of the Cenozoic regional extension on development and evolution of fault system in the Zhusan Depression.