An imbrication model for the Rajang Accretionary Complex in Sarawak, Borneo

The structural framework of the Rajang Accretionary Complex is interpreted on the basis of field surveys conducted around the Lupar Fault Zone in southwestern Sarawak. Bedding dips in the Rajang Accretionary Complex are generally southward, while the complex as a whole becomes younger northward. The complex is interpreted as a series of thrust slices formed by accretion at a subduction trench. Each slice forms a unit 10 to 15 km in width. Thrust slices of this order of this order of magnitude are consistent with those formed by accretion processes at modern subduction trenches. It is suggested that accretion of Late Jurassic to Cretaceous oceanic crust occurred initially from the Pacific (eastern) side of Borneo in the Late Cretaceous, forming part of an arc system extending all along the eastern margin of Asia from Japan to Kalimantan. Subsequently, in the Early Tertiary, due to bending of the southern end of the arc system in Borneo, the direction of subduction changed, so that accretion occurred from the north.