From Permian to rift-inception: new insight from the Western Southern Alps (Varese Area)

The Permian-Triassic tectonic evolution of Western Adria has been variously interpreted either as the first rifting phase that led to the opening of the Alpine Tethys or as the result of continental-scale strike-slip movements. Additionally, a common view on the age of inception of the rifting of the Alpine Tethys, its duration and its relationship with the antecedent Variscan tectonic phases, is still lacking. The European Western Southern Alps expose the basement and cover rocks of Western Adria and therefore represent a key area for understanding and testing the post-Variscan to pre-rifting evolution of this plate. We focus, in particular, on a relatively poorly deformed sector of Northern Italy (Varese Area), where the outcropping Permo-Carboniferous sequence and the overlying Triassic to Early Jurassic units allow to investigate the crosscut relationships between structures that were active during pre-rift and syn-rift tectonic phases. By means of a 3D geological model of the Varese Area, built on a brand-new geological map, firstly we restored Alpine tectonics and then performed a progressive geological restoration of faults, aided by new preliminary thermochronological data. We unveiled a polyphasic strike-slip Permian tectonic phase that switch to an unexpectedly early inception of the rifting.