Experimental determination of rare earth element partitioning between hydrous silicate melt, amphibole and garnet peridotite minerals at upper mantle pressures and temperatures

Abstract

Partition coefficients of Ce, Sm and Tm involving garnet peridotite minerals, amphibole and hydrous silicate melt have been determined experimentally in the temperature and pressure ranges 950–1075°C and 10–25 kbar. Only several parts per million to several tens of parts per million of rare earth element (REE) can dissolve in the minerals before the crystal-liquid partition coefficients begin to vary as a function of REE content. The concentration ranges of constant partition coefficient increase with increasing temperature and are also positively correlated with the magnitude of the crystal-liquid partition coefficients. The upper concentration limits of constant partition coefficient and the value of the crystal-liquid partition coefficient for REE decrease in the order garnet > clinopyroxene > amphibole > orthopyroxene > olivine. Partition coefficients may vary by at least an order of magnitude as a function of bulk composition of the liquid phase (e.g. changing from basaltic to andesitic). The approximate ranges of the values of the partition coefficients as a function of bulk liquid composition are as follows: Ce Sm Tm K ga-liq 0.01–0.1 0.3–3.4 1–10 K cpx-liq 0.05–0.4 0.09–0.7 0.04–0.4 K amph-liq 0.04–0.4 0.08–0.8 0.07–0.7 K opx-liq 0.04–0.1 0.05–0.1 0.08–0.1 K ol-liq 0.01–0.02 0.01–0.02 0.01–0.02 where the values increase with increasing acidity of the melt.