The European margin to and from the mantle depth: insights from the Lower Units (Alpine Corsica, France)

In the late Eocene, the peripheral portion of the European margin was involved in the Alpine subduction/exhumation processes. Witnesses of this event are the polyphase deformation and the metamorphism registered by slices of continental crust which compose the Lower Units, i.e. a set of tectonic units placed at the lowest structural level of the Alpine Corsica (France). The pressure- temperature-deformation-time (P-T-d-t) path of one of them named Venaco Unit was traced by using an integrated set of data related to the phyllosilicates which dynamically recrystallized in the metagranitoids and metapelites. Different thermobarometric tools were applied to the chlorite and white mica crystals selected in the microdomains of the metapelites of the Venaco Unit. The 40Ar/39 Ar dating was instead applied on syn-kinematic muscovite sampled from metagranitoids of the Venaco Unit. The results indicates that the Venaco Unit reached the baric peak at ≈ 33 km depth and was exhumed at shallower structural level (i.e., at ≈ 26 km depth) in the middle Priabonian. This retrograde path suggests that the Venaco Unit experienced fast exhumation through the activation of the top-to-W shear zones.