Interface partition coefficients of trace elements in carbonate-silicate parental media for diamonds and paragenetic inclusions (experiments at 7.0-8.5 GPa)

Interface partition coefficients KD of a representative set of trace elements (TE) in the partly molten diamond-forming peridotite-eclogite- carbonatite system are experimentally determined at 7.0-8.5 GPa. The experimental data evidence that trace-element partition does not depend on the melt composition, with heavy rare-earth elements (HREE) concentrating mainly in garnet. Model TE partition coefficients for the natural diamond-producing carbonatite melts of mantle chambers are calculated based on TE concentrations in minerals of peridotite and eclogite parageneses of diamond inclusions, on the one hand, and on the experimental KD coefficients, on the other. The results show that the TE of the parental media are mostly the mantle peridotite components, with the parental media being depleted in medium (Ba, La, Ce, Pr, Nd, Sm, Eu, Gd) and heavy (Tb, Dy, Ho, Er, Yb, Lu, Hf) rare-earth elements relative to the primitive peridotite. The elevated contents of Sr, Nb, and Ce in the completely miscible carbonate-silicate melts might be due to the participation of “metasomatic agents” in the formation of chambers of diamond-forming carbonatite magmas.