The Exhumation of Continental Crust in Collisional Belts: Insights from the Deep Structure of Alpine Corsica in the Cima Pedani Area

Abstract

In northern Corsica, the Cima Pedani area is characterized by a stack of continental and oceanic units belonging to Alpine Corsica. The base of the unit stack consists of three metamorphic continental units (Canavaggia, Pedani, and Scoltola) that are overthrust by the Schistes Lustrés Complex, represented by oceanic units. The continental units are metamorphic fragments of the European continental margin. They include a Paleozoic basement intruded by Permo-Carboniferous metagranitoids covered by Permian metavolcanites and a Triassic-Jurassic metacarbonatic sequence, unconformably covered by metabreccias and metasandstones of Eocene age. These units are affected by a polyphased tectonometamorphic history acquired in a time frame from the Priabonian to the Aquitanian. The reconstructed pressure-temperature (P-T) paths and the related deformations describe a retrograde history acquired during their progressive exhumation, whereas no trace of the older prograde history has been preserved. In all the reconstructed P-T paths, the P peak (1.04–1.35 GPa) corresponds to the maximum depth reached by these units, whereas the subsequent history includes a progressive P decrease associated with a coeval T increase. The deformation history related to exhumation includes three deformation phases. In particular, the D2 phase is characterized by noncoaxial ductile structures parallel to the boundaries of the units observed in the Cima Pedani tectonic window. The sense of shear of these shear zones is generally top-to-the-W (i.e., toward the Alpine foreland). The collected data provide evidence that the continental units were deformed and metamorphosed during the exhumation following their ascent path along the plate boundary interface. The geodynamic mechanism we propose for the exhumation of the Cima Pedani units is the subduction channel, in which high-pressure units arise between the down-going plate and the former accretionary wedge built up during the oceanic subduction, represented by the Schistes Lustrés Complex.