Structural Evolution of the Crotone Basin: Successive Shortening and Extension Episodes Parallel to the Calabrian Forearc (South Italy)

At 10-12 Ma, the continental fragment of Calabria separated from Sardinia and became the crystalline core of a forearc in a NW-directed subduction system that is being consuming the Mesozoic (Neo-Tethys) oceanic lithosphere. The southeastward rollback of this arc has left in its wake the Tyrrhenian Sea by back-arc spreading. This system is confined between the continental margins of Africa and its Apulian promontory and created matching oblique-collision orogens (Sicilian Maghrebides and Apennines, respectively) along the margins. These progressive collisions shortened the arc because the gap between the margins narrowed to the SE. However, the arc is now lengthening after passing the point of closest approach of Sicily and Apulia, probably in the Quaternary. We seek evidence of this and other neotectonic episodes in the evolution of the forearc in the Crotone basin, which is situated on the accretionary E side of Calabria. A widespread unconformity correlated with the onset of rollback marks a regional foundering controlled by multidirectional extensional growth faults. These faults are consistently capped by the Messinian evaporite sequence. This sequence ends with a widespread unconformity that marks the final desiccation of the Ionian Sea ~5Ma. Mechanical changes due to drop in pore pressure and backward tilting of the accretionary wedge due to flexural unloading may be responsible for the landward emplacement of an accretionary mélange on the NE side of the Crotone Basin and the deposition of a characteristic conglomerate that locally caps the evaporites. After a well known mid-Pliocene basin-forming extensional event, we find evidence for a basin-wide contraction affecting the entire Neogene sequence up to the mid-to-late Pliocene. Vergence ranges from N to NW from east to west across the basin and is consistent with longitudinal shortening of the forearc. The shortening structures are cut or reactivated(?) by extensional faulting which we associate with Late(?) Quaternary longitudinal extension manifested by several transverse basins across the Calabrian forearc.