The Ionian and Alfeo-Etna fault zones: New segments of an evolving plate boundary in the central Mediterranean Sea?

The Calabrian Arc is a narrowsubduction–rollback systemresulting from Africa/Eurasia plate convergence. Whilecrustal shortening is taken up in the accretionary wedge, transtensive deformation accounts for margin segmentationalong transverse lithospheric faults. One of these structures is the NNW–SSE transtensive fault system connecting the Alfeo seamount and the Etna volcano (Alfeo–Etna Fault, AEF). A second, NW–SE crustal discontinuity,the Ionian Fault (IF), separates two lobes of the CA subduction complex (Western and Eastern Lobes) and impinges on the Sicilian coasts south of the Messina Straits. Analysis of multichannel seismic reflection profiles shows that: 1) the IF and the AEF are transfer crustal tectonic features bounding a complex deformation zone, which produces the downthrown of the Western lobe along a set of transtensive fault strands; 2) during Pleistocene times, transtensive faulting reactivated structural boundaries inherited fromthe Mesozoic Tethyan domainwhich acted as thrust faults during the Messinian and Pliocene; and 3) the IF and the AEF, and locally the Malta escarpment, accommodate a recent tectonic event coeval and possibly linked to the Mt. Etna formation. Regional geodynamic models show that, whereas AEF and IF are neighboring fault systems, their individual rolesare different. Faulting primarily resulting fromthe ESE retreat of the Ionian slab is expressed in the northwestern part of the IF. The AEF, on the other hand, is part of the overall dextral shear deformation, resulting from differencesin Africa–Eurasia motion between the western and eastern sectors of the Tyrrhenian margin of northern Sicily, and accommodating diverging motions in the adjacent compartments, which results in rifting processeswithin the Western Lobe of the Calabrian Arc accretionary wedge. As such, it is primarily associated with Africa–Eurasia relative motion.