Episodic and short-lived granitic pulses in a post-collisional setting: evidence from precise U–Pb zircon dating through a crustal cross-section in Corsica

In western Corsica, a large granitoid batholith was emplaced during Carboniferous and Permian times. These rocks display an evolution through time from high Mg–K calc-alkaline, to calc-alkaline, then alkaline affinities. Moreover, the magmatic processes can be observed at different crustal levels. New and precise Isotope Dilution and Thermo-Ionisation Mass Spectrometry (ID-TIMS) U–Pb dating suggests that granite magmatism in Corsica did not simply reflect the continuous thermal evolution of a thickened crust. A precise timing for the post-collisional magmatism is documented with four distinct short-lived episodes, respectively at 345, 338, 305 and 280 Ma, separated by periods of inactivity. These four magma pulses display variable Nd isotopic signatures related to mantle–crust interactions. Granite magma generation and emplacement is strongly connected to the thermal and tectonic activity of the lithosphere. An increasing contribution of a depleted mantle to the magmatic processes is documented for the last igneous event. This is interpreted to reflect the emplacement of depleted mantle materials in the lower crust, which enhanced heat flow and triggered partial melting of previously underplated mafic rocks. This increasing contribution of mantle materials marks the onset of a new geodynamic cycle characterised by an extensional tectonic regime, preluding to the opening of the Alpine orogenic tract.