Tectonics of the Western and Northwestern Rim of the South China Sea---Implications to Petroleum System Parameters

Granath, James W.¹; Christ, Janice M.²; Dickson, William²
¹Granath & Assoc. Consulting Geology, Highlands Ranch, CO.
²DIGS, Houston, TX.

Despite political deadlock over sovereignty in the South China Sea (SCS), interest remains high because of its great perceived petroleum potential. Very little drilling has taken place on continental crust in the central SCS, but perhaps the single most important risk factor will be the thermal history. Because the middle Cenozoic ocean spreading ridge in the center of the basin has migrated, no single heat flow history characterizes the whole of the SCS, but the general pattern will be from low during the Mesozoic forearc history to high in stretched crust to very high in areas directly affected by successful sea floor spreading. Based on the SEATIGER database, the history of that spreading, its link to the tectonic elements on the north, south, and west edges of the SCS can be qualitatively analyzed in the context of a relatively simple plate evolution model involving the replacement of an unstable 3-plate (triple junction) model with a simpler 2-plate spreading history. We focus particularly on the western basins, where the tectonics are more complicated and exploration less mature.

The unifying concept of escape tectonics has become the overriding theme of Tertiary deformation in Indochina, in that sea floor spreading in the SCS during the Oligo-Miocene is often linked to the Himalayan collision by way of the Red River strike-slip fault system between Indochina and China. Within that context, plate kinematic principles would suggest the Red River-Ailao Shan fault system forms one arm (a transform) of an unstable transform-transform-ridge triple junction centered near Hainan Island. Extension on the south China coast led to rifting in the Pearl River Mouth Basin and eventually opening of the SCS spreading center (the ridge). A strike-slip borderland along the Vietnam coast (the other transform) permitted the southward migration of the SCS spreading center away from China. Hence the histories of the Beibuwan, Song Hong, and Phu Khanh Basins are intimately linked to (1) their foundation on thermally young Indochina crust of late Paleozoic and Mesozoic age, (2) the initiation of rifting along the Pearl River Mouth Basin, (3) hyperextension on the rim of the SCS basin, (4) the birth of spreading, and (5) its southward migration in the central SCS. All have different heat flow histories depending on their role in the evolution of the western margin of the SCS.

AAPG Search and Discovery Article #90155©2012 AAPG International Conference & Exhibition, Singapore, 16-19 September 2012