Backthrusts and passive roof duplexes in fold-and-thrust belts: The case of Central-Western Sicily based on seismic reflection data

Abstract

Seismic reflection profiles crossing the area bounded by the M. Kumeta Ridge and the M. Maranfusa-M. Galiello-Rocca Busambra morphostructural feature (central-western Sicily) were used to constrain the deep structural setting of the Sicilian–Maghrebian fold-and-thrust belt (FTB). By integrating seismic, field and well data, we attempted to correlate outcropping and deep-seated contractional structures, shedding light on the internal geometries of the thrust system. Results of the new seismostratigraphic analysis presented in this paper reveal structural variations along the tectonic edifice. This suggests dividing the study area into two sectors: the western sector is characterized by foreland-verging thrusts comparable to the already known structural model of the chain, conversely in the easternmost sector duplexes and hinterland-verging structures, here highlighted for the first time, prevail. In fact, the main carbonate relief of this area (Rocca Busambra Ridge) appears as the outcropping part of a thick tectonic pile bounded on its northern side by a high-angle backthrust, while at depth a blind southern verging (i.e. forelandward) thrust can been recognized; this structural setting suggests that underthrusting of the buried S-verging carbonate body induced the N-verging (i.e. hinterlandward) dislocation of the overlying units. On the whole, this structure can be interpreted as a triangle zone, where the outcropping relief represents a passive-roof duplex bounded, on its northern side, by the high-angle backthrust deeply connected with a low-angle décollement layer. The recognized backthrust appears as the product of a deep-seated tectonic activity, that played a key role for the upper thrust-sheet emplacement.