Neogene kinematics and structural evolution of the eastern Southern Alps (Giudicarie Belt, Northern Italy)

The eastern Southern Alps formed as a retro-wedge of the Alpine orogen and shortening is partitioned into three kinematically linked fold-and-fault systems: (1) the Giudicarie Bel; (2) the Valsugana Thrust System; and (3) the external orogenic front, including the strike-slip Schio-Vicenza Fault. Here, we present closely spaced geological cross-sections from the Northern Giudicarie Fault to the South Alpine orogenic front to assess the amount of Neogene shortening and better understand deformation of the Adriatic indenter in Mio-Pliocene time. The amount of Neogene, NNW-SSE shortening varies from 8 km in the vicinity of the Adige embayment to 25 km further to the northeast, with most shortening (18-22 km) accommodated within the Giudicarie Belt and Valsugana Thrust System. Shortening estimates vary on either side of the Trento-Cles, Schio-Vicenza and Ballino-Garda strike-slip faults. These faults coincide with major Permian-Mesozoic paleogeographic boundaries across which the stratigraphic thickness and rheological properties of rock units significantly change. We interpret these to be responsible for strain partitioning in the eastern Southern Alps. Moreover, balancing and forward modelling of the cross-sections with MOVE Suite Software indicate that the depth of the detachments within the Pre-Permian basement is no greater than 20km. The Northern Giudicarie Fault has recorded 75 km of Neogene sinistral offset, of which 40 km was accommodated by shortening along the Val Trompia fold-and-thrust belt and 35 km by shortening along the Giudicarie/Valsugana domain east of the Trento-Cles Fault. Additional Neogene shortening may have occurred within a decoupled lower crustal Adriatic wedge beneath the Tauern Window.