THE SARDINIA (ITALY) CENOZOIC GRABEN SYSTEM IN THE FRAMEWORK OF THE WESTERN MEDITERRANEAN GEODYNAMIC EVOLUTION

Field observations, biostratigraphic, geochronologic and paleomagnetic data, and the interpretation of onshore and offshore seismic profiles allow to propose a tectono-sedimentary scenario for the Sardinia (Italy) Cenozoïc graben system. The major structural events are tied to the general geodynamic evolution of the Western Central Mediterranean. The extensional late Oligocene-Aquitanian event, responsible for the formation of the graben system is a consequence of the “Apenninic” westward subduction process with a volcanic arc active from 29-30 to 15-16 my, particularly well exposed in Sardinia. Deposition in the graben system started with continental clastics and was followed by marine deposits since the Aquitanian. The subduction terminated after the opening of the small oceanic Provençal basin accompanied by the rotation of the Sardinia-Corsica block during the Burdigalian- early Langhian (20-21 to 15-16 my). Subduction shifted to the East in the Apennines (Italy) with new crustal extension east of Corsica-Sardinia, conducting to the formation of the small Tyrrhenian oceanic basin. The Messinian compressional event (NE-SW oriented) previously documented by microtectonic data, strongly affected the Oligo-Miocene basin as clearly shown on the seismic data. The superimposed Plio-Quaternary Campidano graben was particularly active during the Middle Pliocene-Pleistocene with the deposition of more than 600 m of fliuvio-deltaic continental sediments. A late alkaline volcanic event began in the Messinian (5.2-5 My) and continued until the Quaternary (0,14 My) with creation of important volcanic massifs in Sardinia.