Exhumation of a Variscan orogenic complex: insights into the composite granulitic–amphibolitic metamorphic basement of south-east Corsica (France).

A structural, petrological and geochronological (U-Th-Pb of zircon and monazite) study reveals that the lower crust sequences of the Variscan high-grade basement cropping out between Solenzara and Porto Vecchio, south-east Corsica (France) have been tectonically juxtaposed along with middle crustal rocks during the extrusion of the orogenic root of the Variscan chain. We propose that a system of high-temperature, orogen-parallel shear zones that developed under a transpressive dextral tectonic regime caused the exhumation of the entire sequence. This tectonic complex is thus made up of rocks having undergone different P–T conditions (eclogite-?, high-pressure granulite facies and amphibolite facies) at different times, reflecting the progressive foreland migration of the orogenic front. The Solenzara granulites were derived from burial of continental crust to high-pressure (1.8–1.4 GPa) and high- to ultrahigh-temperature conditions (900–1000 °C) during the Variscan convergence: U–Pb ELA-ICPMS zircon dating constrained the timing of this metamorphism at c. 360 Ma. The gneisses cropping out at Porto Vecchio are middle crustal-level rocks that reached their peak temperature conditions (700–750 °C at <1.0 GPa) at c. 340 Ma. The diachronism of the metamorphic events, the foliation patterns and their geometry suggest that the granulites were exhumed to middle crustal levels through channel flow tectonics under continuous compression. The amphibolite facies gneisses of Porto Vecchio and the granulites of Solenzara were accreted through the development of a major dextral mylonitic zone forming under amphibolite facies conditions: in situ monazite isotope dating (ELA-ICPMS) revealed that this deformation occurred at c. 320 Ma and was accompanied by the emplacement of syntectonic high-K melts. A final HTLP static overprint, constrained at 312–308 Ma by monazite U-Th-Pb isotope dating, is related to the emplacement of the igneous products of the Sardinia-Corsica batholith and marks the transition from the Variscan orogenic event to the Permian extension. [ABSTRACT FROM AUTHOR]