New insights on the structural configuration and evolution of the deepwater offshore margin of Sabah, Borneo

Offshore Borneo in the South China Sea has a complicated structural setting resulting from complex regional geodynamics, marginal basins subductions and openings. Here we present a model for the tectonic evolution of the deepwater offshore Sabah region, North-West Borneo, based on recent observations on seismic and integration of multiphysics data in the Sabah trough (also called Nansha trough) and the Dangerous Grounds. In this work we look at the basin architecture, structural style, and evolution of the margin and well as discussing the nature of the crust in the study area.

The area of interest experienced rifting from Palaeocene-early Eocene to the Oligocene when the South China Sea starts opening. We look at the early configuration of the basin, the rifting style and fault systems involved in the rifting stages. At the end of the rifting there is evidence of volcanic activity across the margin, then starts a sag phase and the buildup of carbonate mounds on topographic highs. Subsidence continues in the Sabah trough during the Miocene, which causes carbonate mounds, which are at the edge of the trough, to be drowned and a more siliciclastic sedimentation takes the relay. A fold-and-thrust belt starts forming to the South-East and puts the trough in a position of foreland basin.

The reason and modalities for the presence of compressional structures West of Borneo are still debated and various tectonic models exist. Nonetheless, recent paleomagnetic studies have proposed that Borneo started to rotate anticlockwise since the late Eocene and this results in compressional features on the west margin of Borneo. We investigate the possible scenarios of crustal configurations associated with the structures visible on seismic. The integration of magnetotelluric (MT) data to seismic, gravity and magnetic data allows us to draw a new picture of this part of the margin, showing crustal thickness variations and nature, and the implications for the regional tectonics.