BASIN-CONTROLLING FAULTS AND FORMATION MECHANISM OF THE CENOZOIC BASIN GROUPS IN THE WESTERN SOUTH CHINA SEA

A series of medium and small-scale Cenozoic sedimentary basins are developed in the western South China Sea.They are, from north to south, the Yinggehai, the Zhongjiannan, the Wan'an and the Zengmu basins, respectively.These basins are developed along the Red River Fault Belt, the Western-edge Fault Belt of South China Sea and the Eastern-edge Fault of the Wanan Basin, which occurred as sinistral, left-step faults at the earlier stage, and dextral, right-step faults at the later stage.The fault belt shows a tulip-flower structure.From north to south, the main fault planes shows a ribbon pattern with the Red River Fault dipping southwestward, and the Western-edge Fault Belt and the Eastern-edge Fault The Wanan Basin dipping eastward.The South China Sea is characterized by the east-dipping fault and the Eastern-edge Fault of the Wanan Basin acts as the east-dipping fault, too.These basins developed along the fault belt are a set of pull-apart basin groups and closely related with each other in origin.The NE-trending faults within the basins are secondary faults controlling over depressions. The displacements of these fauts are limited, and thus the basin group should not be the results of the combined effects of the 700 km extrusion tectonics of the Indochina Block or some deep mantle plumes, but Cenozoic pull-apart basins.In addition, the basin group is also related to the sustainable indentation and collision of the Indian-Australian Plate to the Eurasian Plate based on the comparison of tectonic events.Therefore, the main dynamics of the basin group is derived from the dynamic system in the west of the South China Sea.The dextral, right-step fault belt is offset by the late NWW-trending left-step, sinistral faults which are continuous and consistent in strike with the NWW-trending faults in the Luzon Arc.Therefore, the dynamic system of the indentation of the Philippine Sea Plate to the Eurasian Plate along the island arcs may extend to the study area at the later stage.