珠江口盆地珠一坳陷始新世中-晚期构造变革特征及成因

通过不整合面、断裂体系和盆地构造格局的综合分析，研究珠一坳陷早-中始新世与晚始新世—早渐新世之间的构造变革特征，探讨构造转型机制。印支半岛的旋转挤出及古南海向南俯冲，造成了区域应力场由NW向顺时针转变为近SN向拉张，导致了NE和NEE向断裂控盆向近EW和NWW向断裂控盆转变，且发育大量近EW向新生断裂。岩石圈伸展变形由均一式的宽裂谷模式向集中式的窄裂谷模式转变，且向南海北部大陆边缘迁移，造成了盆地格局由彼此孤立、分割性强的半地堑或窄地堑系趋于相互连通，盆地范围增大。在近SN向拉张作用下，珠一坳陷北缘控盆断裂作为北部的拉伸边界，为先存薄弱带，应力较集中，断裂活动强烈且明显向北扩展，沉降中心整体向北迁移。裂陷期盆地构造变革造成了文昌组与恩平组烃源岩特征的差异，导致了油气资源分布的贫富不均。

Characterization and genesis of the Middle and Late Eocene tectonic changes in Zhu 1 Depression of Pearl River Mouth Basin

Comprehensive analyses of unconformities,faulting systems and basin tectonic framework were carried out to characterize tectonic transformation mechanisms during the periods of Early-Middle Eocene and Late Eocene-Early Oligocene in the Zhu 1 Depression of Pearl River Mouth Basin.The results show that the Indochina block's rotation and extrusion and southward subduction of the proto-South China Sea resulted in a regional stress field clockwise change from NW-into SN-extension,and a shift in fault-controlled basin from NE- and NEE-trending to near EW and NWW-trending,with numerous new faults of EW-trending developed.The lithosphere extensional deformation transformed from homogeneous wide rift mode to centralized narrow rift mode,and migrated to north margin of the South China Sea.As a result,the Basin expanded as the isolated half-grabens or narrow grabens tended to get connected.Under a SN-trending stretching,the stretch boundary at the north of the depression was defined by basin-controlling faults.As a pre-existing weak zone with concentrated stress,the northern margin experienced strong and northward faulting and significantly spread northwards,causing the sedimentary center migrating northward as well.The tectonic changes during the faulting activities of the Basin may explain the characteristic differences of the two source rocks:the Wenchang and the Enping Formations,as well as the disparity of oil and gas distribution in the area.