TRANSITION FROM TYRRHENIAN BASIN EXTENSION TO COLLISIONAL TECTONICS -EVIDENCE OF N-S COMPRESSION DURING THE RECENT QUATERNARY AT USTICA (SOUTHERN TYRRHENIAN-SEA, ITALY)

Compressive deformations (reverse and/or transcurrent faults from kilo metre to metre scale, indicating N-S shortening) cut the Middle and Up per quaternary volcanic and sedimentary terrains of Ustica. They follo wed an episode of extension that deformed the old volcanics of the bas e of the island. The alternation of extension and compression, probabl y repeated, is in agreement with the magmatic evolution of the island, and is then followed by a further extensive episode (NW-SE extension) and, finally, by the cessation of volcanic activity. This neotectonic evolution indicates the substitution between Sardinia and Sicily, of the Neogene tectonic extension, linked to the opening of the oceanic T yrrhenian basin, by collisional tectonics.