GNGTS 2013 - Atti del 32° Convegno Nazionale

ESE oriented right-lateral shear zones that disjointed the SE-verging orogenic belt (Finetti et al. , 1996; Lentini et al. , 1996). These processes have been linked to the differential roll back between continental crust of the northern termination of the Nubia plate, facing the Sicilian collision zone, and the adjacent less resistant oceanic crust of the Ionian slab, sub-ducting beneath the Calabrian Arc. Starting from about 600 ka B.P. the whole NE Sicily has been characterized by a huge tectonic uplift, disengaging from the surrounding domains. The main fault systems that define the PMB have been partially identified, someone of which has been thoroughly studied. To the east, the PMB is bordered by a relevant off-shore NE-SW oriented faults (Taormina Fault) belonging to the SCRZ (Catalano et al. , 2008), the whose effects of activity are already recognizable along the near Ionian on-shore. The south-western margin of PMB , as also evidenced by geodetic data (Hollenstein et al. , 2003; D’Agostino and Selvaggi, 2004) (Fig. 1a), corresponds to a narrow NW-SE oriented fault belt at the Nebrodi-Peloritani boundary (Fig. 1b), represented by a set of normal fault segments showing morpho-structural evidences of Holocene activity (Pavano et al. , 2012). Except for some seismic profile, carried out in the Tyrrhenian off-shore, and some seismological data, the location of the north-eastern and north- western edges of the mobile block is quite uncertain. Recently (June-September 2011) the area around Longi and Galati Mamertino villages has been affected by a swarm of medium-low magnitude seismic events. The main event (M = 4.1 – ISIDe Working Group, 2011) provided a focal mechanism showing a NNE-SSW oriented extension (Fig. 1b), according to the geodetic data. The linkage between this seismic swarm and the fault-controlled south-western border of the mobile block, has been hypothesized. A meso-scale structural field investigation has been carried out in order to analyse and kinematically define several normal fault segments. The segments located to the south of Naso village, near Capo d’Orlando ( NFZ in Fig. 1b), are characterised by a 2 m high scarp, clearly displacing the Recent (Holocene) talus. Further well defined rejuvenated fault scarps have been recognized between S. Marco d’Alunzio and Galati Mamertino villages (Fig. 1b), belonging to a 8.5 km-long fault zone (San Marco d’Alunzio Fault Zone – SFZ , Fig. 1b; Pavano et al. , 2012). These are charcterized by 3-5 m high, SW facing fresh bedrock scarp, marked by a basal light coloured strip as an evidence of their Holocene activity (Benedetti et al. , 2002; Palumbo et al. , 2004). Kinematic markers with pitch of 80° observed on the fault plane, constrain a normal sense of motion. Normal movement indicators (pitch 80°), superimposing on ancient dextral kinematic striations (Pitch 160°), has been found along the fault plane of an associated 3 m-high, 2 km-long antithetic segment. More to the southeast, further fault segments, showing 2-3 m-high fresh bedrock scarps, have been recognised (Fig. 1b). In the surrounding area of Tortorici, an antithetic 1600 m long, N140° oriented, rejuvenated fault scarp shows clear rests of welded fault breccias along its 3 m high fault plane, as a further evidence of recent activity. Kinematic indicators measured along this latter indicate a normal sense of the deformation (pitch 90°). Finally, in the same area two measurement sites have been located along a N10 directed, E-dipping, more than 1500 m long fresh bedrock scarp. On these sites striations and accretion and fracture steps indicate both dextral (pitch= 30°) and more recent normal (70-80°) motions. Morphostructural analysis. The tectonic uplift involving the PMB is evidenced in NE Sicily by the presence, around the coastal area, of a marine terraces flight assigned to the Oxygen Isotope Stage (OIS) from 15 (570 ka) to 3 (60 ka) (Catalano and Di Stefano, 1997). Along the Tyrrhenian coast, from Capo d’Orlando to Capo Rasocolmo (Catalano and Cinque, 1995; Catalano and Di Stefano, 1997), the ancient NW-SE and NNW-SSE oriented dextral faults are crossed without interruption, strongly indicating an almost uniform elevation of strandlines around the PMB . In contrast, along the Ionian side of PMB the elevation of the Late Quaternary marine terraces is extremely variable, due to the huge faulting-related deformation at the footwall of the Taormina Fault. 177 GNGTS 2013 S essione 1.2