Geochemical constraints on the genesis of Hercynian two-mica leucogranites from the Massif Central, France

Late Hercynian two-mica leucogranites dated at 340-280 3a old occur across the entire Massif Central, France, and form dykes and stocks up to 130 km in length. They are peraluminous [molecular Al2O3/(Na2O + K2O + CaO), ASI = 1.16–1.25] and have low initial ϵNd (−8.2 to −6.1) indicating derivation from the metasedimentary lower crust as sampled in crustal xenoliths (ϵNd340 = −8.6 to −4.3, ϵNd280 = −9.0 to −4.8). Their high SiO2 (70–78 wt%), P2O5 (up to 0.5%), Rb, and Ga, and low Ba, Sr and ΣREE are mainly a result of partial melting processes rather than fractionation. l melting was initiated by underplating of the lower crust by mantle-derived basic magmas between 360 and 270 Ma and was intensified by granulite-facies metamorphism between 300 and 280 Ma. From this model, there is little similarity between the genesis of two-mica leucogranite in the Massif Central and that in the Himalaya, with which it has previously been compared.