Collision and strike-slip faulting in the northern Molucca Sea (Philippines and Indonesia): preliminary results of a morphotectonic study

Abstract

A swath mapping, gravity and single channel seismic survey was carried out in the northern Molucca Sea with RV. L'Atnlnnfe. Preliminary interpretation of these data reveals the presence of an almost complete Sangihe arc and forearc. The Mangas-Pujada-Talaud ridge in the cenaal part of the Molucca Sea appears to be a backstop within the Sangihe forearc. East of the ridge very contrasting terranes arc'separated by a major NW-SE crustal discontinuity interpreted as a left-lateral strike-slip fault. North of 6N the Philippine Trench inner wall is dissected by NW-SE trending left-lateral strike-slip faults, resulting from the dominantly oblique convergence between colliding ans. South of 6N the westward subduction of the buoyant Sneliius volcanic plateau, a fragment of the Halmahera arc terrant. has induced the formation of a new plate boundary, the Philippine Trench along what is interpreted as a former strike-slip fault zone. East of the Miangas-Pujada-Talaud ridge there is a wide sedimentay wedge separated from the Snellius Ridge to the south by the major NW-SE crustal discontinuity. The thickness of this wedge cannot be explained by subduction along the very young Philippine Trench. It could be either an accretionary wedge developed at the deformed leading edge of the Sangihe forearc or be part of a former intra-arc basin which was part ofthe colliding Halmahera arc terrane. There is no clear evidence for accreted oceanic c ~ s f belonging to the recently subducted Molucca Sea The Mangas-Pujada-Talaud ridge is part of the San,gihe forearc, and the ophiolites could represent its basement, u p i i d along the outer arc ridge. The dog-leg-shaped Philippine Trench is propagating southward a m s s the fragmented Halmahera arc tenane and its southern segment could reactivate a former strike-slip fault zone. -