Collision, rotation, and the initiation of subduction in the evolution of Sulawesi, Indonesia

Abstract

The island of Sulawesi, Indonesia, has been shaped and deformed as a result of collision with the Sula platform, a sliver of continental material from the northern margin of Australia‐New Guinea. The collision has resulted in rotation of the north volcanic arm of Sulawesi and the development of the accretionary wedge of the North Sulawesi trench. The North Sulawesi trench changes laterally from a zone of no active deformation in the eastern part to a wide accretionary wedge in the west. Early stages of thrusting produce a steep frontal slope (8°–16°), indicative of relatively high basal shear stress, whereas the more advanced (western) zone of thrusting produces a gentle (2°) slope, consistent with low basal shear stress. Reported paleomagnetic data suggest post late Eocene counter‐clockwise rotation of the North Arm, and the offshore geophysics are explained by a pivot of the North Arm with respect to the Celebes basin about the eastern end of the arc. Convergence between the north Banda basin and Southeast Sulawesi is documented by the presence of the Tolo thrust. Its outcrop is strongly arcuate and its accretionary wedge varies in width from a minimum of a few kilometers at each end to a maximum of 30–40 km in the central part. The northern end transforms to the leftlateral Matano fault, with a reported offset of 20 km. The southern end of the thrust projects toward the deformed rocks of Buton, but the structural relations there are not clear. The Matano fault zone appears to connect westward with the Palu fault, which forms the western transform of the North Sulawesi trench. The Palu‐Matano fault system acts as a trench‐trench transform between the North Sulawesi trench and the Tolo thrust, and this system is described by the same rotation pole as that for the Sulawesi North Arm.

Collisional model for rapid fore‐arc block rotations, arc curvature, and episodic back‐arc rifting in subduction settings

“…Bathymetry from ETOPO5. by Silver et al [1983a], but we suggest that the intersection of the Sangihe arc with the North Sulawesi trench has modified the kinematics of the Sula block, by causing it to pivot about a nearby pole of rotation.…”

The subduction initiation stage of the Wilson cycle

“…Ophiolites in East Sulawesi (Kündig 1956;Silver et al 1983), derived from the ocean north of the Sula Spur, were thrust southwards onto the continental crust of the Sula Spur in East Sulawesi beneath the North Sulawesi forearc. After this collision, continued northwards movement of Australia was absorbed in several ways, including the subduction of oceanic crust at the Java trench, the broad nonrigid counter-clockwise rotation of SE Asia (Borneo, West Sulawesi, Java) and contraction and uplift in East and SE Sulawesi.…”

“…Hamilton 1979;Cardwell et al 1980). The Tolo trough has been recognized as a thrust (Silver 1981;Silver et al 1983;Hinschberger et al 2000Hinschberger et al , 2003, but not identified as an incipient subduction zone. The Sula deep has not been discussed before.…”

Neogene Tectonic Evolution of the Celebes-Sulu Basins: New Insights from Leg 124 Drilling

“…The island of Sulawesi appears to be a major suture zone along which a large oceanic basin (probably the Neotethys) was subducted (Hamilton, 1979;Silver et al, 1983aSilver et al, , 1983b. Along this suture zone, the Banda and Celebes-Sulu blocks were welded together in middle Miocene time (Kundig, 1956).…”