Structural elements of the Sulu Sea, Philippines

Abstract

The structure and tectonic history of the Sulu Sea are described on the basis of seismic reflection data combined with the findings of onshore and offshore geological studies, and the results of ODP Leg 124 drilling. Closing of a hypothetical Mesozoic proto-South China Sea associated with the formation of oceanic crustal splinters in the late Eocene followed by southward subduction and, in turn, progressive collision of the north Palawan continental terrane with the micro-continental Borneo plate since the middle Miocene, resulted in the formation of the structurally complex Sulu-Borneo collision belt. The latter comprises north Sabah, southern and central Palawan, and the northwest Sulu basin. Fracturing of the Borneo micro-continental plate into the Sulu and Cagayan ridges initiated the opening of the southeast Sulu basin during the late Oligocene through the early Miocene. Collision of the north Palawan continental terrane with Cagayan Ridge in the late early Miocene and oblique collision of these blocks with the central Philippines resulted in the still ongoing closing of the southeast Sulu basin since the middle or late Miocene. Closing of the southeast Sulu basin began with the formation of an oceanic crustal slab.