Interference between shallow and deep-seated structures in the Sicilian fold and thrust belt.

Abstract

The thrust and fold belt, in Western Sicily, is characterized by the presence and interference of “shallow” and “deep-seated” compressional structures, generated and developed at different structural levels. The “shallow structures” consist of imbricated thrusts and asymmetric folds, with a typical wavelength of 2 km, involving relatively thin deep water units. These units are superposed over thick platform carbonates units, along a wide and originally almost flat floor thrust. The axial trend of the folds is variable, since poli-phased folding often occurs, producing characteristic interference pattern, reflecting continuous variations of the “apparent” transport direction during the emplacement (i.e. rotation of the allochtonous thrust sheets). The “deep-seated structures” consist of large, double-verging pop-up structures, with a typical wavelength of 5-10 km, involving thicker platform carbonates successions. The deep-seated structures are characterized by large folds, with vertical to overturned limbs, accomplished by high-angle, transpressive ramps, which reactivate previous (i.e. Mesozoic) synsedimentary normal or transtensional faults. The floor thrust of the shallow structures is passively deformed by the subsequent growing of the underlying, younger deep-seated structures. Large clockwise rotations of the tectonic units occurred during the compressional deformation, and the amount of rotation is apparently related to the timing and amount of the tectonic transport.