Abstract: Tertiary Tectonic Events, Southwestern South China Sea

Richard W. Murphy

At the beginning of the Tertiary, westward subduction under the Natuna-Mekong section of the Sunda yielded to passive margin rifting. The Luconia/Miri Block broke away from the Natuna Arch, the Subi Shelf, Vanguard Bank, Prince of Wales Bank, and Rifleman Bank, creating the very deep Bunguran Trough.

Late Eocene collision between the Luconia/Miri Block and Borneo at the Mersing subduction zone forced subduction to jump northward to the Northwest Borneo Trench and produced uplift between the Luconia Shoals and the Natuna Arch.

Oligocene extrusion of south and west Sunda produced the Sunda rift basins through an extensional left-lateral wrench couple with the Indochina Block. Rift trends follow pre-Tertiary tectonic grain, but basins fronting the South China Sea were overprinted by an east-west rifting trend.

Late Oligocene-middle Miocene north-south opening of the South China Sea had little local impact. The Miocene second extrusion formed a comprehensive right-lateral wrench couple between an extruding Indochina and a stationary Malaya. This resulted in profound inversion of the West Natuna basin and the formation of en echelon detached inversion folds in the south Malay Basin.

Northwest-southeast spreading in the southwest quadrant of the South China Sea succeeded the ending of north-south spreading consequent upon collision at the Palawan Trench. A fan-shaped array of rifts, with newly created oceanic crust in the northeast, converged with steadily decreasing width of rifting southwestward to a point about 250 km north-northeast of Natuna Island. Active rifting ceased with the late Miocene end of subduction under Borneo.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994