Geodynamic significance of early orogenic high-K crustal and mantle melts: example of the Corsica Batholith

Early post-collision Variscan magmatism in Corsica, France was characterised by high-K granitic intrusions of Namurian age. They consist of quartz-monzonites, monzogranites and leuco-monzogranites associated with vaugnerite (meladiorites or hornblende–biotite diorites) intrusive stocks and enclaves. The composition of the vaugnerites shows that they originated from slowly cooled syn-magmatically amphibolitized lamprophyric magmas probably derived from enriched mantle melts that were injected into the lower crust and contributed to its extensive anatexis giving the high-K granitic melts. Deep-seated interactions between felsic and mafic magmas were responsible for the common characteristics of both magma suites. The granitoid suite is characterised by: high K and Mg contents; relatively high concentrations of Th, Rb, Sr and Ba; (La/Yb)N from 10 to 20; LREE enrichments (LaN≈100–300); Sri≈0.707; δ18O≈6; εNd≈−3.5 to −2.5. The Mg-rich minerals of the high-K plutonic suite and the vaugnerites constrain emplacement conditions to: 270±100 MPa (Al-in-hornblende geobarometer), 675±25 °C (solidus temperature), logfO2≈−16 and H2O contents in the range 3–4 wt.%. K-rich magmatism of Carboniferous age mostly occurs in two parallel belts in the high grade zones of the Variscan orogen. It is interpreted as resulting from continental crust–mantle interactions under high-pressure conditions (≈1.5 GPa). The chemical evolution of post-collision plutonism is explained in terms of mantle–crust interactions at decreasing depths during post-orogenic extension.