珠江口盆地阳江东凹早新生代洼陷结构差异及其控制机制分析

Structural Difference and Control Mechanism of Early Cenozoic Depression in Yangjiang East Sag,Pearl River Mouth Basin

为探究珠三坳陷阳江东凹洼陷结构差异及其控制机制,利用三维地震数据精细解释了该凹陷主要断裂的发育特征并分析了其活动性,识别并总结了岩浆底辟的分布特征,系统地研究了阳江东凹早新生代不同洼陷的构造差异性.研究表明,阳江东凹特殊的构造位置影响了凹陷的形成,构造转换带控制了研究区各洼陷差异发育.西部阳江24洼呈北断南超的简单半地堑结构,中部和东部恩平19、20、21洼呈南北双断的复式半地堑结构.区域应力场下洼陷伸展方式的不同导致裂陷初始期的岩石圈地壳变形存在差异,同裂陷期岩浆运移至压力较小的转换带下方并聚集形成岩浆房,基底深大断裂沟通地壳深部,控制了岩浆上涌和侵位.岩浆的热作用使得地壳脆性变形转变为韧性变形,地壳的快速减薄及NE、NEE向先存断裂在深大断裂转折处发育的构造转换带控制了盆地构造样式.因此靠近阳江-一统暗沙断裂带的洼陷发育斜滑断裂并呈复式半地堑结构.上述分析为研究区烃源岩预测及勘探提供了理论依据.

In order to explore the structural difference and control mechanism of Yangjiang east sag in Zhusan depression,the development characteristics of main faults in the sag are finely explained and their activity is analyzed by using three-dimensional seismic data,the distribution characteristics of magmatic diapir are identified and summarized,and the structural differences of different depressions in Yangjiang east sag in Early Cenozoic are systematically studied.The study shows that the special structural position of Yangjiang east sag influences the formation of the sag,and the structural transformation zone controls the differential development of each sag in the study area.Yangjiang No.24 depression in the west is a simple half graben structure with north fault and south overlap,while Enping No.19,No.20 and No.21 depressions in the middle and east is a compound half graben structure with north-south double faults.The deformation of lithospheric crust in the initial stage of rifting is different due to the different extension modes of subsag under the regional stress field.During the same rifting stage,the magma migrated to the lower pressure transition zone and accumulated to form magma chamber.The deep faults in the basement communicated with the deep crust and controlled the magma upwelling and emplacement.The thermal action of magma makes the crustal brittle deformation change into ductile deformation,so the sag near the Yangjiang-Yitong’ansha blind fault zone develops oblique slip fault and presents a compound half graben structure.The above analysis provides a theoretical basis for the prediction and exploration of source rocks in the study area.