Geology of Southeast Asia with particular reference to the South China Sea

Abstract

The concentric arrangement of the Phanerozoic arc-trench systems of the western part of Southeast Asia has been previously interpreted in the light of plate tectonics as a migration of subduction zones related to the oceanic spreading centers located in the Indian Ocean and the South China Sea respectively.The Sumatra, Java, and Meratus arcs, with ages ranging from Paleozoic to the present time, were generated by spreading centers situated in the Indian Ocean, whereas the Natuna and Palawan arcs had their origin in the spreading center located in the South China Sea. The Tertiary Banda arc was generated by a spreading center in the Indian Ocean whereas the more or less Tertiary Sulawesi arc had its origin in the spreading center located in the Pacific Ocean.In the South China Sea region, the results of recent exploration drilling on the Reed Bank supports the previous concept that the intermediate shelfal region at a depth of about 2000 m represents the fragmented remains of continental crust. Oceanic crust emplaced between 32 and 17 million years (my) occupies the abyssal depths. Magnetic patterns of the basin show an east-west alignment of the spreading axis. Reconstruction by closure of this basin would place the northeastern Palawan-Mindano microcontinent against the China Shelf adjacent to the eastern Macclesfield Banks. Prior to this event, southerly directed Cretaceous and Paleogene subduction was active beneath the northern Sundaland, which already existed as an accreted crystalline core dating into the Paleozoic era.The geotectonic evolution of Southeast Asia is reconstructed with particular reference to the South China Sea Region. Several dominant basin types have been recognized on the margins of the South China Sea. These basins as a whole contain an estimated 56% or 20 billion barrels of the remaining undiscovered oil reserves in Southeast Asia.