Paleogene rift structure and its dynamics of Qiongdongnan Basin

Qiongdongnan Basin is a Tertiary basin developed on the northwest margin of the South China Sea;it experienced two stages of extension from Eocene to early Oligocene and during late Oligocene.Two styles of structures,half-graben and graben,developed with zonation from north to south and segmentation from east to west.From the point of mechanics and lithospheric extension,both the sinistral rotational stress associated with the Indosinian plate extrusion and the SSE stretching stress caused by the sub-duction of the ancient South China Sea controlled the rifting of Qiongdongnan Basin from Eocene to early Oligocene,while the extension during late Oligocene was caused by the spreading of the subsea basin.The thermal situation of the lithosphere determined the stretching style of the upper crust.The northern depression developed half-grabens controlled by synclined faults due to relative cold lithosphere extension,while the central depression is characterized by composite rift belts,which are composed of half-graben and graben.