An experimental study of trace element partitioning between zircon and melt as a function of oxygen fugacity

Abstract

The partitioning of P, Sc, Ti, Sr, Y, Nb, the rare earth elements (REE), Hf, Ta, Th and U between zircon and a synthetic andesitic melt was determined as a function of oxygen fugacity (fO2) over a range of fourteen log units, from QFM-8 to QFM+6 (where QFM is the quartz-fayalite-magnetite oxygen buffer) at ∼1300°C and 1atm, using SIMS and LA-ICP-MS. The partition coefficients of Ce and Eu were found to vary systematically with fO2, relative to those of the other REE, producing Ce and Eu anomalies similar to those that are characteristic of natural igneous zircon. These anomalies coexist at terrestrial fO2s and were used to quantify Eu3+/(Eu2++Eu3+) and Ce4+/(Ce3++Ce4+) in the melt. The partition coefficients of the redox invariant trivalent cations are in excellent agreement with lattice strain theory. The values of DREE are related to those determined for natural samples by the expected dependence on temperature. The incorporation of REE3+ in zircon was independent of the presence of P. DU/DTh was found to vary systematically with fO2 indicating the presence of U4+, U5+ and U6+ in the melt at terrestrial conditions. DTi was independent of fO2 despite an expectation of significant Ti3+ in the most reduced experiments. Show more