GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 1.2 139 Morphometric, geodetic and geophysical surveys of mud volcanoes: evidence of tectonic control in the Sicilian collisional belt G. De Guidi 1 , F. Carnemolla 1 , G. Barreca 1 , F. Brighenti 1 , C. Monaco 1 , A. Di Pietro 1 , S. Marchese 1 , D. Messina 1 , L. Scarfì 2 , A. Vecchio 1 1 Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Sezione di Scienze della Terra, Università di Catania, Italy 2 Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, Catania, Italy Introduction. The Sicilian belt is part of the complex collisional boundary between African and Europe convergent plates. The thrust system is characterized by the underplated African- Pelagian continental crust and by the overlying imbricated tectonic units of the Apenninic- Maghrebian chain, this latter originated by deformation of Meso-Cenozoic sedimentary sequences belonging both to the oceanic crust-type sector (Alpine Tethys and Ionian basin) and to the African paleo-margin. Neogene-Quaternary sedimentary top-thrust sequences have recorded the recent geodynamic evolution of the Sicilian orogeny (Lentini and Carbone, 2014). The surficial landscape of the largest thrust-top basin in central-southern Sicily is influenced by morphostructural evidences of south-southeast foreland-verging fold and thrust belt in which consequent and subsequent drainage patterns dissect and contour the geological structures in relation to their space-time evolution and rheological proprieties. In particular, some features linked to fluvial processes (v-shape section valley, overflowing and trellis patterns) indicate recent derangements of basins evolution characterised by recent variations of base level and suggest recent and active vertical deformation of folds and thrusts. Although NNW-SSE compressive regime in Sicily is mostly accommodated by aseismic folding at the front of the chain, the earthquakes distribution shows a clear trend of the seismic events deepening from very shallow hypocenters down to a depth of about 40÷50 km, towards the NNW, below the chain, where the “Sicilian Basal Thrust” has been previously recognized (De Guidi et al. , 2015; Lavecchia et al. , 2007). Therefore, we used earthquake focal localizations and local mechanism solutions to relate deep thrusts with surface structures as well as stress directions and geodetic surveying to evaluate surficial horizontal and vertical GNSS velocity (IGMI 92_ networks, discrete UNICT_NET in operation since 2016). The solution and inversion of all data sets allowed us to reconstruct the relations between deeper and surficial orientations of both stress and strain fields. Moreover, the morpho-structural study of mud volcanoes distributed along the frontal sector of the Sicilian collisional belt (San Biagio, Santa Barbara and Aragona villages) (Fig. 1) (Imposa et al. , 2016; Madonia et al. , 2011) also represents a clue that could be used as a proxy for supplementary stress and strain indicators. In fact, on a regional scale, mud volcanoes in active fold-and-thrust belts may occur over wider areas or may cluster along discrete structures, where the generation of overpressures is expected to establish a positive feedback loop allowing for fault movement and mud volcanism. Geological framework. The center-south sector of Sicily consists of four groups of terrain, three of which represent tectonic complexes, while the latter consists of piggy-back structures superimposed at rear of the three tectonic complexes. The three tectonic complexes represent, from the bottom upwards: the Western extension of the Hyblean Foreland, partly deformed, consisting mainly of meso-pliocenic carbonate successions, which in this area fell below the Sicilian chain. A group of tectonic units deriving from the deformation of the sican domain, arranged tectonically according to prevalent duplex geometries. A group of tectonic units, largely outcropping in the study area, consisting of predominantly clayey, conglomerate and arenitic successions, which are indicated by the authors “Falda di Gela”. The tectonic-stratigraphic succession emerging in the nissena area is made up of tectonic units of the lower Cretaceous-Miocene ages belonging to the outer edges of the Sicilide Tettonic Units. These units are covered by several neogenic-quaternary sedimentary cycles that have