A regional-scale discontinuity in western Sicily revealed by a multidisciplinary approach: A new piece for understanding the geodynamic puzzle of the southern Mediterranean

Abstract

The results of an integrated stratigraphic, structural, geophysical, and geochemical study reveal the presence of a crustal discontinuity in western Sicily that, at present, runs roughly N-S along a band from San Vito Lo Capo to Sciacca. The boundary between the two zones of this discontinuity is nearly orthogonal to the main thrust propagation of the Sicilian thrust-and-fold belt. The different Permian to Tertiary sedimentary evolution recorded by the two zones appears related to this discontinuity, with thick carbonate platforms in the western sector facing deepwater successions in the eastern one. The presence of Upper Triassic reefs, huge megabreccia bodies, and widespread submarine volcanisms along the transition zone suggests the presence of a long-lasting weakness zone. This zone has been reactivated episodically as transpressional and/or transtensional faults in relation to the different geodynamic stress acting in central Mediterranean area in different epochs. We speculate that this transition zone has represented a segment of the passive margin of the Ionian Tethys. During the Maghrebian convergence a different style of deformation has affected the two sectors floored by different sedimentary multilayers. The orthogonal-to-oblique differential convergence between the two sectors has resulted in right-lateral transpressional motions, leading to oblique thrusting of deepwater-derived thrusts onto platform-derived thrusts associated with clockwise rotations. The oblique convergence is still ongoing as demonstrated by the seismicity of the area, by the geothermal field with high mantle-derived helium fluxes and by the GPS measurements collected by different authors.According to Casero and Roure [1994], in western Sicily a NW-SE regional trending shear zone (Segesta Fault) runs across the Sicilian fold-and-thrust belt (SFTB), from San Vito Lo Capo to the Sciacca area. The authors consider the Segesta Fault to be a first-order crustal structure, as it is observed in seismic lines offshore of Sciacca. However, the field evidence of this strike-slip fault is weak.

Relationship between soil CO2 flux and tectonic structures in SW Sicily

“…The DDSs are preferentially elongated along with two perpendicular directions SW-NE and NW-SE respectively. These directions are in agreement with the orientation of the main tectonic structures (white dotted lines) recognized in the area [Barreca et al, 2014;Di Stefano et al, 2015].…”

“…In contrast with such high magnitude earthquakes, the Belice Valley does not display any clear morphological evidence of faults, but it is characterized by smooth reliefs expression of large folds. Even after the 1968 earthquake, no surface ruptures or exposed fault scarps along the epicentral zone were observed [Monaco et al, 1996;Barreca et al, 2014;Di Stefano et al, 2015]. Hence, both the identification of seismogenic structures within the Belice area and more in general, the detection of active deformation evidences in southwestern Sicily, are rather challenging.…”

Crustal deformation, active tectonics and seismic potential in the Sicily Channel (Central Mediterranean), along the Nubia–Eurasia plate boundary

“…The integrated analysis of available morpho-bathymetric data, seismic reflection profiles and gravity maps thus allows identifying a first-order structural feature, whose location, geometry and inferred kinematics, is in good agreement with the spatial distribution of recent volcanism and seismicity, therefore supporting the presence of a sub-vertical lithospheric shear zone favouring magma ascent 26 . Although the nature of this shear zone is poorly established, its deep roots and orientations inferred by gravity data, suggest that it might represent part of inherited Mesozoic discontinuities that cut the basement and formed along the rifted passive margin of the Tethys ocean 54,55 . These structural discontinuities acted as normal or transtensional faults until the Late Miocene, when they underwent transpressional reactivation 39,[56][57][58][59] , but their recent activity seems accommodating the reorganization of the Nubia-Eurasia convergence along this segment of the plate boundary.…”

“…Northward, the inland belt of Sicily is separated by a NNW-striking diffuse deformation zone separating the western and eastern belts. Along this diffuse deformation zone, oblique thrusting associated with clockwise rotations and wrench motions led to a differential shortening during the Neogene accretion of the Sicilian-Maghrebian thrust belt, therefore resulting in major rates in the eastern belts compared to the westernmost ones 55 , 60 . Along this diffuse deformation zone, an advective transfer through buried deep extensional faults linked to the mantle has been inferred on the basis of the occurrence of rising gas and hot waters enriched in mantle elements 61 similarly to what was detected along major transcurrent/transform domains 62 , 63 .…”

Landfill Site Selection for Municipal Solid Waste by Using Ahp Method in Gis Environment: Waste Management Decision-Support in Sicily (Italy)

“…Several municipalities were almost totally damaged and about 300 peoples died. No clear focal mechanisms were available for this seismic sequence, so the seismicity was attributed either to the compressional reactivation of a thrust sheet or to a NW-SE shear band running from the Castellammare gulf to Sciacca (Di Stefano et al, 2015). The epicentral zones of the 1968 seismic sequence was centred southward of the studied area, thus the parameter of peak ground acceleration has to be seriously considered for the assessment of the most suitable sites.…”