Strike-slip contractional stepovers in the Southern Alps (northeastern Italy)

Strike-slip pop-ups are seldom recognized because they are sites of rapid uplift and erosion. In addition, they can easily be confused with shortening structures of different age. In the Neogene central-eastern Southern Alps, the western termination of the ENE-trending Valsugana thrust is located at the interference with the suborthogonal Calisio Line, which is an inverted Permian normal fault. Just west of the Calisio Line the Mt. Cornetto di Folgaria (MCF) structural and topographic high is a large-scale pop-up localised at the restraining stepover between the sinistral Calisio and Schio-Vicenza strike-slip faults, which trend at high angle to the thrust belt. The MCF pop-up developed in post-Tortonian times, when the kinematics of these faults changed from dextral to sinistral. At a smaller scale, strike-slip restraining and releasing stepovers of pre-existing steep fault segments show that these inherited faults are kinematically linked and constitute an important mechanical anisotropy responsible for strain partitioning into strike-slip and dip-slip displacements. The analysis of the MCF pop-up and related minor structures suggests that in fold-and-thrust-belts affected by strike-slip faults at high angle to the belt axis, contractional structures related to strike-slip restraining bends and stepovers may be more common than what is usually thought.