Structural evidence for deformation by block rotation in the context of transpressive tectonics, northwestern Sicily (Italy)

This paper presents geological and structural data on a sector of the Apenninic-Maghrebian Chain in northwestern Sicily. The predominantly strike-slip structures are related to the activation of a dextral strike-slip shear zone oriented N120°, which was active between the Late Miocene and the Early Pliocene. This structure (Caccamo Shear Zone) belongs to the Southern Tyrrhenian System that constitutes the southern kinematic junction to the Calabrian Arc. The identification of transpressive structures in the southern Tyrrhenian offshore that were active during the Messinian-Early Pliocene allowed the definition of this sector as transpressive back-stop of the chain. During the transpressive stage dextral transcurrent movements along the Caccamo Shear Zone led to the activation of a multiple set of parallel sinistral faults, conjugate and antithetic to the master fault. The activation of these structures determined a deformation by block rotation which provoked an overall clockwise rotation of 38°. The data show how the rotations observed in the internal sectors of the chain might be caused by the activation of multiple strike-slip fault sets and that the rotational mechanism around vertical axes is connected to transpressive tectonics. The use of kinematic models allow quantification of the blocks rotation due to the combined action of multiple sets of strike-slip faults with modest displacements and to demonstrate that the rotation of blocks and their lateral movement constitute two different, contemporaneous expressions of a single deformational event.