Experimentally determined trace and minor element partitioning between clinopyroxene and carbonatite melt under upper mantle conditions

Laser ablation microprobe analyses of clinopyroxenes equilibrated with carbonatite melt at 20–22 kbar and 1050–1100°C are used to calculate partition coefficients for an extensive suite of trace elements. Our experiments were performed on a mixture of peridotite minerals and two types of carbonates with differing trace element contents (natural carbonatite and mixtures of sedimentary carbonates). Although trace element concentrations vary by an order of magnitude between the carbonate mixtures, the partition coefficients are similar. Some, however, differ substantially from previously published values. Most of the measured elements have broadly similar partition coefficients of Dcpxclq = 0.1–0.4, including Pr, Nd, Eu, Dy, Er and Hf, which are reported here for the first time. Considerably higher partition values are found for Ti and V which are compatible in clinopyroxene with Dcpxlq = 1.4 ± 0.6 for Ti and 2.9 ± 0.9 for V (1σ). inopyroxene partitioning data for carbonatite (Dcpxclq) are remarkably similar to published values for silicate melts (Dcpxslq), with significant exceptions for the behaviour of Ti, Ba, Nb and perhaps Ta, whereas values for other silicate minerals differ more strongly between carbonatite and silicate melts. From our results, the most sensitive indicator of mantle metasomatism.by carbonatite melt as opposed to silicate melt infiltration should be low TiEu in metasomatised peridotites assuming closed-system metasomatism. In contrast to suggestions from some studies of metasomatised mantle xenoliths ZrHf ratios appear to remain unchanged during caatite metasomatism. These chemical effects only partly agree with those described from natural mantle rocks interpreted to result from carbonatite metasomatism.