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 (fO 2) 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 fO 2, 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 fO 2s and were used to quantify Eu 3+/(Eu 2++Eu 3+) and Ce 4+/(Ce 3++Ce 4+) in the melt. The partition coefficients of the redox invariant trivalent cations are in excellent agreement with lattice strain theory. The values of D REE are related to those determined for natural samples by the expected dependence on temperature. The incorporation of REE 3+ in zircon was independent of the presence of P. D U/D Th was found to vary systematically with fO 2 indicating the presence of U 4+, U 5+ and U 6+ in the melt at terrestrial conditions. D Ti was independent of fO 2 despite an expectation of significant Ti 3+ in the most reduced experiments.