Architecture of the Patrimonio Fault System and the Miocene Post-Orogenic Extension in Alpine Corsica (France)

The exhumation of Alpine Corsica is the result of Oligocene-Miocene lithospheric back-arc extension in the wake of the eastward migration of Apenninic subduction. Although the geometry, kinematics and timing of ductile detachments are well constrained, the brittle extension leading to final exhumation of Alpine Corsica is less documented. We integrate structural observations with stable isotope (δ18O–δ13C) geochemistry and U-Pb geochronology of carbonates in fault rocks to constrain the spatial and temporal evolution of the W-dipping Patrimonio Fault System (PFS). The PFS juxtaposes the Low Pressure/Low Temperature Nebbio units and the syn-extensional Miocene sedimentary sequences onto the High Pressure/Low Temperature Schistes Lustrés. The PFS initiated in early Miocene (≥20 Ma), as km-thick top-to-W/WNW brittle–ductile zone with pervasive SCC′ fabric and pseudotachylytes, which exploited inherited contractional-related fabrics on the western limb of the Castagniccia-Cap Corse antiform. Early distributed extension evolved into more localized sinistral transtension, as recorded by lineated slickensides defining the Patrimonio Fault and by cockade-bearing splay faults in the footwall. This stage of sinistral transtension, dated between 20 and 14 Ma, was linked to the anticlockwise rotation of the Sardinia-Corsica block during the opening of the Ligurian-Provençal basin. A later (≤14 Ma) mid- to late-Miocene extensional faulting, driven by Tyrrhenian-related tectonics, produced the mature Patrimonio Fault, characterized by multiple anastomosing strands of foliated gouges and phyllonites accommodating ∼2–3 km of displacement. We show that lithospheric back-arc extension in Alpine Corsica was accommodated by major conjugate E- and W-dipping extensional to transtensional semi-brittle and brittle fault systems during the Miocene.