CENOZOIC FAULT CHARACTERISTICS AND BASIN GENESIS OF THE ENPING SAG, PEARL RIVER MOUTH BASIN

Detailed description of fault systems and basin structures is devoted by this paper to the Enping Sag of the Pearl River Mouth Basin, South China Sea. The main basin controlling fault systems formed in different periods are determined and classified by means of fault activity rate calculation and equilibrium profile analysis, upon which the evolution process of the basin is reconstructed, and the dynamic mechanism of basin development and transformation discussed. The results suggest that the evolution of the basin is controlled by both the pre-existing basement structure and the regional dynamic field. During the early rifting stage, the subduction of the Pacific plate retreated as the subduction rate decreased under the joint action of Indian plate, that led to the change in stress into an extension field in NW—SE direction and the negative inversion of the early formed NE trending low angle reverse faults. As the results, a detached half graben was formed under the control of NE trending fault. During the late rifting stage, under the joint action of the rotation and extrusion of Indosinian block and the southward subduction of the paleo-South China Sea, the regional stress field changed from clockwise transformation into nearly NS stretching, and the basin controlling faults changed from NE to nearly EW trending. And the lithospheric extension was changed from a wide rift mode to a narrow rift mode as the basin framework changed from isolated half grabens to connected extensional grabens. During the depression period, the lithospheric thinning center migrated towards the South China Sea spreading center, leading to weak tectonic activity and thermal subsidence. In the tectonic reactivation stage, the NW trending Luzon island arc collided with the Eurasian plate, which caused the NNE stretching, the revival of pre-existing near EW faults and the formation of the secondary strike slip fault zone, in addition to complex uplifting and falling of fault blocks.