The North Palawan Block, Philippines: its relation to the Asian Mainland and its role in the evolution of the South China Sea

The island of Mindoro, the northern part of Palawan island and the Reed Bank area (southwestern Philippines) together constitute a continental fragment, the North Palawan block, lying within an island arc-oceanic setting. The Permian to Palaeogene rocks of the block indicate a geological origin and history contrasting with that of the remainder of the Philippine Archipelago, and suggest that the North Palawan block, once .occupied a pre-drift position contiguous with the South China mainland. Four prominent pre-Neogene regional unconformities are recognised both on and offshore the China mainland, in Taiwan and in the Palawan block. The synchrony of these unconformities and the facies relationships of the unconformity-bounded sedimentary units strongly suggest a common pre-Neogene history for all these areas. By contrast, throughout the Palawan area, an important regional unconformity occurs at the top of the Middle Miocene which is absent from the Asian mainland. Extension in the South China Sea Basin since the Mesozoic, which has separated the North Palawan block from the Asian mainland, has been approximately uniform from west to east. However, there is strong evidence to suggest that this extension has been achieved by temporally separated phases of continental crustal attenuation and more recent sea-floor spreading. From the above observations and using the most recent magnetic spreading anomaly data for the South China Sea, a suite of palinspastic reconstructions has been compiled. This shows the evolution of the South China Sea area from the Late Triassic to the Pliocene. The reconstructions illustrate amongst other things: (1), the convergent continental margin setting of the North Palawan block during much of the Jurassic and Cretaceous(2) the Late Cretaceous inception of the Philippine island arc system(3) the subsequent anticlockwise rotation of the arc system from the Late Eocene onwards(4) the Palaeocene to Mid-Miocene opening of the South China Sea, and (5) the Early to Mid-Miocene colIision between the North Palawan block and the Palawan subduction system