Direct evidence of middle oligocene extension in the Calabria-Peloritani terrane from co-seismic faulting: the pseudotachylyte-bearing shear zones of Palmi (southern Calabria, Italy).

The Variscan crystalline basement of the Calabria-Peloritani terrane (CPT) in southern Italy was partly reworked by ductile and brittle shear zones throughout the Alpine tectonic evolution (from thickening to exhumation). Although evidence of extensional tectonics in the CPT has already been found and roughly constrained to the Oligocene onward, no attempt has ever been made to directly date brittle fault movements. Structural (meso- and micro-scale), kinematic and petrographic analyses and 40Ar-39Ar laser experiments reveal that the pseudotachylyte-bearing shear zones of the Palmi area in southern Calabria formed in response to extensional shearing 33.5 Ma ago and overprinted compressional tectonic structures. Results provide the first direct evidence of Middle Oligocene co-seismic faulting in the area and confirm the role of extensional tectonics in promoting the Oligocene exhumation of the Calabria basement.