Rupture and accretion of the Celebes Sea crustrelated to the North–Sulawesi subduction: combinedinterpretation of reflection and refraction seismicmeasurements

Abstract

A number of different models have been developed for the tectonic processes and theevolution of the marginal basins in Southeast Asia. Due to their complex setting at the triplejunction of three major converging plates, a definite tectonic concept has not yet been establishedfor most of the basins. In particular, the formation and history of the Celebes Sea basin is stillambiguous.New seismic wide-angle recordings along the North–Sulawesi subduction zone provideinsight into the deep structure of the accretionary wedge and the Celebes Sea crust, particularly inconjunction with multichannel reflection data. Based on the reflection seismic lines, we previouslyinterpreted prominent block structures within the accretionary wedge to be of ophiolitic character,but in most cases refraction seismic modelling could not confirm crystalline velocities; even in thedeeper parts of the wedge the velocities are relatively low. Therefore a sedimentary origin seemsmore plausible.The Celebes Sea is underlain by typical oceanic crust, except for an unusual crustalthickening from about 7 to 12 km beneath the accretionary wedge. This is observed on all threeprofiles and could represent tectonic thickening of the crust, induced by a collision of thesouthward subducting Celebes Sea plate with another slab subducting northward underNorth–Sulawesi (the still active Molucca Sea slab or the northern part of the Sula platform, thatonce subducted beneath the Celebes Sea).