Abstract

Comparison between the sedimentary sequences outcropping in the emerged areas of Sicily and Calabria, and the seismic lines present in the southern Tyrrhenian, has allowed recognition of the morphostructural elements that together constitute a forearc basin. The collapse of the southern Tyrrhenian margin, that has occurred since the Late Pliocene, is due to the roll-back of the African crust recorded in the thrust-belt areas of Sicily and to the contemporary roll-back of the subduction hinge in the Ionian Sea. This new geodynamic setting has caused the SE-ward shifting of the whole forearc/back-arc system and the consequent corresponding extension of the Marsili Basin during the Pleistocene. The segmentation of the forearc basin, and therefore the crustal back-stop of the chain, is linked to some structures that constitute the kinematic junction, that has driven the SE-ward retreat of the slab and the consequent restructuring of the whole system. Extensional fault systems, in some cases seismogenetic, are developed on the "carapace" of the chain, and they overprint the preceding compressive structures of the forearc basin, thus marking the passage from active accretion to extension. The comparison between the geologic data on-land and the seismic lines in the Tyrrhenian off-shore of Sicily and Calabria, has allowed the evolution of the convergent system to be defined. This has produced a complex forearc/back-arc structure, with the consumption of the oceanic crust of the Ionian Sea since the Middle-Late Miocene The contemporaneous emplacement of a wide accretionary wedge, extending from Sicily to the Southern Apennines through the Calabrian Arc, and the opening of the Tyrrhenian back-arc basins occurred in this time span. The recognition of the morphostructural features of the Plio-Pleistocene forearc basin that constitutes the modern southern Tyrrhenian Sea, allows discrimination of the character of the deep crustal structure making up the backstop of the whole chain and establishes some first order structural trends for the understanding of the evolution of this sector of the Mediterranean area.

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