The Amount of Recycled Crust in Sources of Mantle-Derived Melts

TLDR

Plate tectonic processes introduce basaltic crust (as eclogite) into the peridotitic mantle, but the proportions of these two sources in mantle melts remain poorly understood. Silica‑rich melts derived from eclogite react with peridotite, converting it into olivine‑free pyroxenite. Hybrid pyroxenite melts are enriched in nickel and silicon but depleted in manganese, calcium, and magnesium, and their olivine phenocryst compositions indicate that 2–20 % (up to 28 %) of recycled crust contributes to mantle melting, with 10–30 % in MORBs, >60 % in ocean island and continental basalts, and 20–30 % in komatiites.

Abstract

Plate tectonic processes introduce basaltic crust (as eclogite) into the peridotitic mantle. The proportions of these two sources in mantle melts are poorly understood. Silica-rich melts formed from eclogite react with peridotite, converting it to olivine-free pyroxenite. Partial melts of this hybrid pyroxenite are higher in nickel and silicon but poorer in manganese, calcium, and magnesium than melts of peridotite. Olivine phenocrysts' compositions record these differences and were used to quantify the contributions of pyroxenite-derived melts in mid-ocean ridge basalts (10 to 30%), ocean island and continental basalts (many >60%), and komatiites (20 to 30%). These results imply involvement of 2 to 20% (up to 28%) of recycled crust in mantle melting.