The role of the inherited Permian-Mesozoic structures during the Neogene convergence in the Central Southern Alps (Northern Italy).

The South-verging chain of the Southern Alps (SA) is a post-collisional chain accreted during the convergence of two continental margins (Europa and Adria) and represent the back-verging transect of the Alps. In the SA realm no metamorphism developed during the alpine tectonic evolution; therefore both the Permian-Mesozoic successions are perfectly preserved and the structural network of the Permian-Mesozoic rifting is today still recognizable. Two principal phases of continental rifting developed in the SA: i) the Permian events which created several fault-bounded volcanic basins over a continental crust builded by the Variscan collisional processes (southalpine crystalline basement); ii) the Mesozoic evolution, especially during Norian to Liassic, related to extensional tectonics of Adria leading to the break-up and drifting in the NeoThetys oceanic realm. During the Neogene convergence the SA were affected by a South-verging in sequence thrust system, according to a main compressional axis oriented NNW-SSE, and the Permian-Mesozoic fault network was reactivated. The extensional Mesozoic Adria margin, mainly trending NNE-SSW, became a sinistral transfer system (Giudicarie Belt), which today divides the Western and Eastern Southern Alps. The transition from Giudicarie to Eastern Southern Alps is marked by a main inherited normal fault (Trento-Cles) which during the Neogene acted both as sinistral and dextral transfer, depending on the alternate activation of the thrusts and different shortenings on the two walls of the fault. Also the Permian normal faults (Calisio, Pinè, Fersina and others) were inverted becoming both transfers and lateral ramps and reverse faults depending on the different attitudes of the Permian faults compared with the direction of the thrusts propagation. The inherited network strongly affected and influenced the architecture of the Central Southern Alps.