Switching from contractional to extensional tectonics along the Alpine Front: structural and metamorphic evidence from the Balagne area (northern Corsica, France)

Abstract

In the Corsica Island (France), the tectonic boundary along which the units of Alpine Corsica overlap the Hercynian Corsica represents a first-order structure which has not been investigated in depth yet. In this paper, the reconstruction of the Alpine Corsica Front in the Balagne area through the characterization of the deformation history and the associated peak metamorphism for the units of Alpine Corsica and for the Hercynian Corsica is provided. The collected data indicate that a gap in the peak metamorphism between the less metamorphic units located at the top of the unit pile, and those located at lower structural level which registered low-blueschist facies conditions exists. Also, a detailed structural analysis of the shear zones along the Alpine Corsica Front is supplied. The studied N-S trending, E-dipping shear zones documented at the western rim of the Balagne area are characterized by deformation history indicating a top-to-E sense of shear that overprint a former top-to-W kinematics. These findings indicate that the Alpine Corsica Front was affected by extensional tectonics after the shortening, which developed during the top-to-W thrusting of the Alpine Corsica onto the Hercynian Corsica. Framing our results in the regional tectonic setting, we suggest that the extensional tectonics documented in the Balagne area developed during the Oligocene-Early Miocene, i.e., during the transition from the latest stages of orogenic exhumation within the Alpine belt to the post-orogenic rifting stage in the Liguro-Provençal and Tyrrhenian Basins.