Slab-melting during Alpine orogeny: evidence from mafic cumulates of the Adamello batholith (Central Alps, Italy)

Oxygen isotope compositions of mineral separates have been determined by laser fluorination. δ18O values of brown and green amphiboles (+5.4 to +5.7‰) and of titanite (+4.0‰) indicate that crustal contamination played a negligible role in the origin of parental melts of both parageneses. The peculiar trace element signature of the liquids in equilibrium with the second paragenesis (e.g., extremely high Th/Nb and La/Yb values) has been attributed to slab-derived melts with a high sediment component. Equilibration of the ascending slab melts with the peridotitic mantle wedge would explain the observed low δO18 of amphibole and their relatively high Mg contents.