Deep structure of the north-western Mediterranean Basin: Results of a two-ship seismic survey

Abstract

Data from thirty-two Expanding-Spread Profiles carried out in the Gulf of Lions and Ligurian Sea in September 1981 were used to study the deep structure of Western Mediterranean Basin. P-refractions and precritical reflections were observed, down to the Mohorovicic discontinuity, despite the presence of a halokinetic Messinian salt layer, and they have been used in the x—t domain to derive the velocity structure of both sedimentary cover and crust. Three different geological domains are distinguished: a thick continental domain, with a velocity of 6.2 km s −1 and a crustal thickness of more than 20 km, that is continued seawards by a thinned continental domain with a crustal thickness of 5–7 km only, and then in the center of the basin, a double-layered crust with velocities of 5.8 and 6.9 km s −1 and total thickness of about 5 km, interpreted as an oceanic domain, with basement at about 10 km below sea level. The Gulf of Lions margin and the Ligurian Sea are two contrasting areas: the thinned continental domain is very wide in the Gulf of Lions (100 km) and considerably reduced in the Ligurian Sea. A paleo-oceanic ridge appears to be present in the Gulf of Lions. The two basins are separated by a major fracture zone. Ante-rift sediments are observed in the Gulf of Lions.