Rupture and accretion of the Celebes Sea crust related to the North-Sulawesi subduction: combined interpretation of reflection and refraction seismicmeasurements

A number of different models have been developed for the tectonic processes and the evolution of the marginal basins in Southeast Asia. Due to their c omplex setting at the triple junction of three major converging plates, a d efinite tectonic concept has not yet been established for most of the basin s. In particular, the formation and history of the Celebes Sea basin is sti ll ambiguous. New seismic wide-angle recordings along the North-Sulawesi subduction zone provide insight into the deep structure of the accretionary wedge and the C elebes Sea crust, particularly in conjunction with multichannel reflection data. Based on the reflection seismic lines, we previously interpreted prom inent block structures within the accretionary wedge to be of ophiolitic ch aracter, but in most cases refraction seismic modelling could not confirm c rystalline velocities; even in the deeper parts of the wedge the velocities are relatively low. Therefore a sedimentary origin seems more plausible. The Celebes Sea is underlain by typical oceanic crust, except for an unusua l crustal thickening from about 7 to 12 km beneath the accretionary wedge. This is observed on all three profiles and could represent tectonic thicken ing of the crust, induced by a collision of the southward subducting Celebe s Sea plate with another slab subducting northward under North-Sulawesi (th e still active Molucca Sea slab or the northern part of the Sula platform, that once subducted beneath the Celebes Sea). (C) 1999 Elsevier Science Ltd . All rights reserved.