GNGTS 2015 - Atti del 34° Convegno Nazionale

26 GNGTS 2015 S essione 1.1 THE ORIGIN OF THE ACTIVE CRUSTAL STRETCHING AT THE SOUTHERN EDGE OF THE CALABRIA ARC S. Catalano, F. Pavano, G. Romagnoli, G. Tortorici Dip. di Scienze Biologiche, Geologiche e Ambientali, Sezione di Scienze della Terra, Università di Catania, Italy Introduction . In the central Mediterranean the SE-ward migration of the Calabrian arc and the coincident opening of the back-arc Tyrrhenian Basin dominated the post-Tortonian tectonic picture of the region. The current geodynamic models explain both the two processes as the consequence of the roll-back of the oceanic Ionian lithosphere, which drove the forward shifting of the arc with respect to the adjacent Sicily segment of the orogenic belt, colliding with the African continental margin. According to the models, the motions of the Calabrian arc was accommodated, to the west, by the back-arc extension and to the south by dextral motions along NW-SE oriented faults and oblique (righ-lateral) displacements along E-W trending ramps, breaching the previous thrust-nappes of the Sicily collision belt. Whether or not these geodynamics are still active and control the seismicity of the region are still open questions. As a consequence, the seismotectonic models are often contradictive, depending on the adopted reference geodynamic model. A distribution of seismogenic zones mimicking the arcuate shape of the orogeny and marking the separation between the seismogenic extensional features of southern Calabria and eastern Sicily is imposed in the models that start from the evidence of a still active arc migration (Ghisetti and Vezzani, 1982; Meletti and Valensise, 2004). On the other hand, seismotectonic models taking into account the fragmentation of the southern edge of the arc (Monaco and Tortorici, 2000; Catalano et al. , 2008a), in the Straits of Messina area, have been generally related to a recent modification of the geodynamic picture, due to the propagation of an incipient rift zone, extending from southern Calabria to eastern Sicily. This paper aims to summarise the outlines of the Late Quaternary (< 1 Myr) deformation of eastern Sicily, at the southern edge of the Calabrian arc, to frame the active crustal extension of eastern Sicily, responsible for the high level regional seismicity, in the long-term geodynamic evolution of the Calabria arc migration. Active deformation at the southern edge of the Calabrian arc . The active tectonic picture of the southern edge of the Calabrian arc is dominated by an incipient crustal stretching which is well constrained, in the Straits of Messina area, by both GPS data (D’Agostino and Selvaggi, 2004) and by the focal mechanism of the catastrophic 1908 earthquake (Cello et al. , 1982). The geological, structural and morphological data (Monaco and Tortorici, 2000; Catalano and De Guidi, 2003) evidence that the recent faults on the two sides of the Straits of Messina form an antithetic relay ramp, connecting the main west facing normal faults of southern Calabrian (Reggio Calabria and Armo Fault; a and b in Fig. 1) to the east facing Taormina Fault (c in Fig. 1), bounding the Ionian coast of the Peloritani Mountains. The fault belt of the Calabrian side of the Straits originated from the remobilisation of previous extensional features that have also controlled the Plio-Quaternary basins of the peri-Tyrrhenianmargin of the arc. Themorphological features (marine terraces, fault scarps, triangular facets) indicate that the reactivation of the southern Calabria fault belt started at least since 580 kyr B.P. and then progressively propagated to the south, towards the Straits of Messina region (Catalano et al. , 2008a). On the opposite side of the Straits, the off-shore NNE oriented Taormina Fault has controlled the uplift of a discrete segment of the Ionian coast of the Peloritani Mountains since about 125 kyr B.P. (Catalano and De Guidi, 2003). In the Taormina area, a synthetic relay ramp links the southern tip of the Taormina Fault to the on-shore active faults which propagated along the eastern flank of Mt. Etna (d in Fig. 1; Monaco et al. , 1997), in the last 125 kyr (Monaco et al. , 2000; Catalano et al. , 2004). The active faults flanking the Mt. Etna overstep the NNW oriented main extensional fault which was detected in the off-shore from Catania to the Hyblean Plateau (Western Fault of Bianca et al. , 1999; e in Fig. 1). This offshore structure originated from the reactivation of