The coupling of high-pressure oceanic and continental units in Alpine Corsica: Evidence for syn-exhumation tectonic erosion at the roof of the plate interface

Abstract

The subduction of continental crust is now a matter of fact but which are the mechanisms and the factors controlling the exhumation of continental units and their coupling with oceanic units are still a matter of debate. We herein present the tectono-metamorphic study of selected continental units belonging to the Alpine Corsica (Corte area, Central Corsica, France). The tectonic pile in the study area features thin slices of oceanic units (i.e. Schistes Lustrés Complex) tectonically stacked between the continental units (i.e. the Lower Units), which record a pressure–temperature-deformation (P-T-d) evolution related to their burial, down to P-T-peak conditions in the blueschist facies and subsequent exhumation during the Late Cretaceous – Early Oligocene time span. The metamorphic conditions were calculated crossing the results of three different thermobarometers based on the HP-LT metapelites. The continental units only recorded the P-peak conditions of 1.2 GPa-250 °C, up to the T-peak conditions of 0.8 GPa-400 °C, and the retrograde path up to LP-LT conditions. The metamorphic record of the oceanic units includes part of the prograde path occurring before the peak conditions reached at 1.0 GPa-250 °C followed by the last metamorphic event related to LP-LT conditions. The results indicate that each unit experienced a multistage independent pressure–temperature-deformation (P-T-d) evolution and suggest that the oceanic and continental units were coupled during the rising of the last ones at about 10 km of depth, where the oceanic units were stored at the base of the wedge. Subsequently they were deformed together by the last ductile deformation event during exhumation. We propose a mechanism of tectonic erosion at the base of the wedge, by which slices of Schistes Lustrés Complex were removed at the roof of the plate interface during the exhumation of the Lower Units.