The Molucca Sea Revisited: Evolution of an Arc-Arc Collision

Abstract

The Molucca Sea is the site of the collision between the opposed Sangihe and Halmahera arcs and is floored by the coalesced accretionary wedges to the two subduction zones. In the north, the sea is bounded by the southern islands of the Philippine Archipelago, while in the south it abuts on the Sula Spur Continental Fragment. Free air and Bouguer anomaly values in its central part are among the lowest recorded offshore anywhere on the globe and provide severe constraints on structural and evolutionary models for the area. Further constraints are provided by the patterns of regional seismicity, which show earthquakes to be virtually confined to the two Benioff zones. Recently obtained geological data from the Halmahera Arc, together with results from the 1988 cruise of the RRS Charles Darwin and reflection seismic data from the southern part of the sea allow refinements to be made to previous interpretations. An understanding of the area is of importance from an exploration point of view because the Mesozoic sediments of the Sula Spur, which are believed to have been laid down at the margin of Gondwanaland, are generally considered to have hydrocarbon potential.