The HP–LT metabasites of the Ile de Groix have Ge, Ga and δ74Ge values typical of basalts. Ge and Ga are only weakly mobile during subduction zone metamorphism. No significant Ge isotopes fractionation during HP dehydration reactions in metabasites. Ge isotopes may fractionate during intensive rehydration reactions in the greenschist facies. Subducted metapelites may generated local Ge isotopic heterogeneities in the mantle wedge.