Syn-convergence exhumation of continental crust: evidence from structural and metamorphic analysis of the Monte Cecu area, Alpine Corsica (Northern Corsica, France).

In the Corsica island, a stack of metamorphic continental units is thrust over a pre-alpine basement. The Piedigriggio-Prato Unit is representative of these units, all regarded as fragments of the european continental margin involved in the convergence-related processes during the Late Eocene-Early Miocene time span. The tectono-metamorphic history of the Piedigriggio-Prato Unit has been reconstructed by an integrated approach, ranging from map- to meso- and microscale analyses. This unit is characterized by a polyphase deformation history that consists of three deformation phases developed under retrograde metamorphism ranging from blueschist to greenschist and sub-greenschist metamorphic P/T conditions. At the map-scale, the Piedigriggio-Prato Unit is characterized by km-size isoclinal antiforms and sinforms that are deformed by open to close folds showing sub-horizontal axial planes. The features of the deformations and the P/T conditions of the metamorphism suggest that the first two phases were acquired during exhumation by extrusion tectonics. The following third phase produced the last exhumation up to surface of the Piedigriggio-Prato Unit before the Early Miocene. On the whole, the Piedigriggio-Prato Unit can be regarded as representative for the exhumation history of a continental fragments during the transition of the continental subduction to continental collision.