Mindoro: a rifted microcontinent in collision with the Philippines volcanic arc; basin evolution and hydrocarbon potential

The Mindoro area is the easternmost part of the Palawan-Mindoro microcontinent which rifted away from the South China margin during the Early Oligocene. Sea floor spreading carried it southwards until the Late Miocene, when collision with the Philippines Arc in the east, and other terranes to the south began. This paper considers the collision tectonics which operated at the eastern end of the microcontinent, which resulted in the inversion and thrusting of its rifted margin. These processes are documented by seismic data and field outcrop. The syn- and post-rift sedimentary sequences contain prospective source and reservoir intervals. Subsequent burial and deformation have resulted in the generation of hydrocarbons, as proved by the existence of several oil seeps on Mindoro Island, and by hydrocarbon shows recorded in offshore exploration wells. The structural history of the area since the Eocene is divided into four phases: The unconformities which separate these stratigraphic sequences can be identified on seismic data. The sequences show characteristic differences in stratigraphy and structure, which control their prospectivity. The Syn-Rift Sequence consists of non-marine arkosic sandstones at the base, becoming marine towards the top and including platform and reefal limestones. The Drift Sequence records an overall regression, beginning with the deposition of marine shales, sandstones and detrital limestones and passes upwards into deltaic sands, shales and coals. This sequence contains reservoir quality sandstones and several potential source horizons. On Mindoro Island, the Collision/Transpression Sequence interval is dominated by coarse clastics derived from the uplifted collision zone. In offshore areas to the south and west, away from the collision zone with the arc, a more uniform blanket of parallel bedded shale and calcaeous siltstones was deposited. These form a regional seal to structural traps which may contain significant volumes of hydrocarbons