2-SHIP DEEP SEISMIC-SOUNDINGS IN THE BASINS OF THE EASTERN MEDITERRANEAN-SEA (PASIPHAE CRUISE)

New results from a two-ship refraction and oblique reflection deep seismic cruise are presented to discuss the nature of the crust in the Ionian, Sirte and Herodotus abyssal plains. These expanding spread profiles were processed and analysed in both the x-t and tau-p domains. Arrival times of reflected and refracted branches are matched by ray tracing in both domains. In spite of a shallow evaporitic sequence (messinian evaporites) deposited on top of a thick sedimentary pile responsible for velocity inversions on many profiles, we obtain excellent velocity control down to Moho depth. P(m)P and P(n) (8.4-8.6 km s-1) arrivals are observed. The three basins have a relatively thin crust (8 to 11 km) overlain by a thick sedimentary cover, up to 10 km in the Herodotus abyssal plain. The Moho boundary and main crustal units identified in the basins can be followed beneath the Calabrian prism to the west, and beneath the Mediterranean Ridge to the east. The crustal structure is of oceanic type for both the Ionian and Sirte basins, where typical oceanic layer 2 and 3 are recognized. The thin crust of the Herodotus basin may be interpreted either as oceanic or thinned continental crust (about 10 km thick). The top of the crust of the Herodotus basin is much deeper. Therefore, the Herodotus basin is probably significantly older than the Ionian basin, Triassic versus Early Cretaceous in age.