Abstract: Cenozoic Rifting and Sea Floor Spreading of South China Sea Region Independent of Indochina Extrusion

Da Zhou

Two competing models explain the origin of the South China Sea: (1) N-S directed rifting and spreading, and (2) as a pull-apart related to extrusion of Indochina during the India-Eurasia collision. Detailed reconstruction of the extension of the SE Eurasia margin and sea-floor spreading of South China Sea and the kinematic history of Ailo Shan-Red River fault system suggests that N-S extension, perhaps induced by subduction of the South China Sea region beneath the Borneo and Palawan, but independent of extrusion, as the fundamental cause for opening of the South China Sea.

The amount of displacement induced by Indochina extrusion is insufficient to open the South China Sea, which totals approximately 1000 km of extension across the region of attenuated continental and new oceanic crust. In contrast, extrusion-driven sinistral offset of a late Mesozoic magmatic front along the Ailo Shan-Red River fault system totals only about 600 km. Furthermore, rifting in South China Sea commenced in Paleocene, some 20 million years before extrusion tectonics generally is believed to have begun. Structural fabrics of the continental margin and adjacent South China Sea also are incompatible with the extrusion model. ENE and E-W oriented normal faults dominated the rifting margin from Early Eocene to Early Miocene. The direction of sea floor spreading was N-S from 32-20 Ma, and NW-SE from 2O-16 Ma, when the Ailo Shan-Red River fault system ceased its sinistral slip.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994