Trace element partitioning between perovskite and kimberlite to carbonatite melt: New experimental constraints

We present experimentally determined trace element partition coefficients (D) between perovskite (CaTiO3) and several different silicate and carbonate melt compositions. Our data indicate that perovskite is able to strongly fractionate trace elements during the evolution of SiO2-undersaturated magmas. In silicate magmas, perovskite efficiently fractionates Zr and Hf from Nb and Ta, with D-Zr and D-Hf coefficients below and D-Nb and D-Ta, significantly above unity, respectively. All trace element partition coefficients between perovskite and the diverse silicate melts, which primarily differ in their CaO and SiO2 contents, are fairly similar within propagated uncertainties. We find that D perovskite/silicate melt for the high field strength elements is much lower than corresponding perovskite/carbonate melt partition coefficients for the same elements. Another key difference between perovskite/melt trace element partitioning in silicate and carbonate systems is the relative behavior of U and Th. Whereas all silicate system experiments show that D-Th > D-U, the relationship is different in the carbonatite experiment. This implies that perovskite may fractionate U and Th in silicate magmas whereas perovskite cannot fractionate U and Th in carbonate magmas. The Th/U ratio of magmatic perovskite may, therefore, provide a tool for a better understanding of the evolution of hybrid carbonate-silicate magmatic systems. The rare earth elements (REE) show similar perovskite/melt partitioning in the silicate and carbonate systems investigated. Our data indicate that the REE are highly compatible in perovskite in both silicate and carbonatite compositions, which explains the high rare earth element concentrations in naturally occurring magmatic perovskites. In particular, our new trace element partition coefficients help to better understand and to quantify the strong control of perovskite on the bulk REE budget of kimberlites and related rocks. (c) 2012 Elsevier B.V. All rights reserved.