The Velay granite pluton (Massif Central, France) is the youngest (304 ± 5 Ma) and largest (∼6,900 km²) of the major Massif Central monzogranites/granodiorites and was formed nearly 50 Ma after the cessation of Hercynian continental collision (Pin & Duthou 1990). It is a highly heterogeneous pluton consisting of I-type, high-Sr granites (Sr= 500–900 ppm) with low ε_Sr(304) (+35 to +41) and high ε_Nd(304) (−3 to −5), at its centre, grading into S-type and mixed I–S-type heterogeneous granites of more normal Sr content (100–420 ppm) and higher ε_Sr(304) (+40 to +210) and lower ε_Nd(304) (−3·8 to −7.3) at its margins.

The metasedimentary lower crust of the Massif Central was underplated/intruded by mafic mantle-derived magmas between 360 Ma and 300 Ma. From 300–280 Ma (Downes et al. 1991) underplating led to partial melting and granulite facies metamorphism of the material (represented by felsic and mafic meta-igneous lower crustal xenoliths, ε_Sr(304) = −11 to + 112, ε_Nd(304) = +2·2 to 8·2, Downes et al 1990). The partial melts assimilated mainly schist but also felsic gneiss and older granite country rock material (ε_Sr(304) = +100 to +300, ε_Nd(304) = −5 to −9) to produce the heterogeneous granites. Plagioclase and biotite were accumulated at the base of the intrusion which was intruded to high levels to form the high-Sr granites.