GNGTS 2014 - Atti del 33° Convegno Nazionale

inside the Ionian accretionary wedge (Polonia et al. , 2011). �������� �� ���������� �� ������ However, as postulated by Govers and Wortel (2005), a STEP fault ���������� ������������ ���� ������� ���������� ��� ��� ����� propagates continuously with shallow expression (in the upper plate) that consist of kilometers scale topography in the landscape and progressive wrenching and structural rotations along its path, all characteristics that have never been reported for the supposed STEPs along the Sicilian-Calabrian collision/subduction system. Recently, high-resolution bathymetry and seismic profiling (Gutscher et al. , 2014) provided evidences for a ~ 90 km long NW-SE oriented strike-slip fault in eastern Sicily offshore. The authors have accounted this as an active STEP segment pointing straight towards the central part of the Etna volcano. In this work, we provide clues for a ������������ ����� ���� ����� ������ ������� ������� lithospheric scale tear fault system ������� ������� slicing through all over the central-eastern portion of the Sicilian Fold and Thrust Belt through a preliminary analysis of large scale geological features, new field investigations and seismological data. Tectonic background. In the central Mediterranean, several crustal compartments of a former paleogeographic configuration have been involved in the long-lived convergence between African and European plates (����� Dewey et al., 1989�� �� ���� ��������� ������ ���� �������� ). In this scenario, blocks with distinct thickness and rheology favoured the setting of collisional/subduction zone with associated accretionary wedges and the development of a complex back-arc/fore-arc/trench system (��������� ����� ���������� ��� ����� ����� ������� ��� ��������� ����� �������� Scandone, 1979; Malinverno and Ryan, 1986; Patacca and Scandone, 1989, Faccenna et al. , 2004�� ��� �������� ������� ��� ���������� ��������� ����� ��� ������ ���������� ������� ��� ). The latter’s include the Tyrrhenian stretched area, the Ionian subduction complex and the orogenic domains, represented by the Sicilian collision zone and by the Calabrian Arc. The occurrence at the same time of collisional, subduction and back-arc extension reflect on the dynamics of this part of central Mediterranean in which different stage of contractional and/or transpressional and extensional deformation took place from early Miocene to recent times. Recent geophysical exploration of the Central Mediterranean (������� Finetti et al. , 2005� ��������� ) highlight that along the southern Tyrrhenian coast, collisional and subduction processes took place contemporaneously. The subduction beneath the Calabrian Arc (���������� ��� ����� ����� Malinverno and Ryan, 1986) and collision to the west resulted in the development of transfer faults, at the plate boundary or along the orogenic hinge, which have accommodated the differential advancement of the unconstrained Calabrian Arc. This regional deformation process took place in the Sicilian collision zone with the nucleation of dextral ������ �������� ������������ ������� ~����� �������� NW–SE trending transcurrent faults. This structural picture is corroborated by the present-day distribution of crustal and shallow seismicity, in which focal mechanisms are mostly characterized by strike–slip, normal and reverse-oblique kinematics compatible with low-dip NNW–SSE to NNE–SSW trending P-axes (����Neri et al. , 2005��). Geological data. Between the Madonie Mts. range and Mt. Etna in eastern Sicily, major NE-SW trending Mio-Pliocene compressive structures (thrust-top and related syncline) are systematically dragged and rotated according to the vertical axis until to assume a hook-shape at their terminations (Fig.1). Although this type of deformation are common in rotational thrust sheets such as the Sicilian Fold and Thrust Belt (SFTB), the geometric setting and the clockwise sense of rotation of such major structures suggests the occurrence of a regional, near 100 km long, dextral bounding fault with a NW-SE direction. Detailed field surveys performed in key sectors revealed that hook-shape geometry is accompanied by strike-slip faulting with right- lateral motion (see Barreca and Monaco, 2013). In the north-western sector (e.g. Madonie Mts.), fault segments show mainly normal-oblique motion and are responsible for the extreme (about 1500 m) down-faulting (zone of Castelbuono town) of the Madonie Mts carbonate units. In the central sector, Neogene thrust and basins formed by the SE-wards migration of the orogenic system are dragged at their NE termination. This process involves three thrust-top basins of the SFTB (the Gangi, Nicosia and Centuripe synclines) with different degree of rotations. The decreasing of the amount of structural rotations toward the SE (see inset in Fig. 1) suggests a progressive tip propagation of the bounding wrench fault. The south-eastern sector of the fault zone (Mt. Judica area, see Fig.1 for location) is characterized by the occurrence of GNGTS 2014 S essione 1.2 129