AN EXPERIMENTAL-STUDY ON THE EFFECT OF TEMPERATURE AND MELT COMPOSITION ON THE PARTITIONING OF NICKEL BETWEEN OLIVINE AND SILICATE MELT

Experiments in the simple system CaO-MgO-Al2O3-SiO2-Na2O-FeO were carried out to investigate the control of temperature and melt composition on the partitioning of nickel between olivine and silicate melt (Doliv/liqNi). Eleven experiments determine the influence of changing forsterite (Fo) content on Doliv/liqNi in this simple system. The equation of Hart and Davis (1978) that accounts for the variation of Doliv/liqNi in terms of MgO content of the silicate liquid is tested using experimental data from ironbearing simple and natural systems and found to be inadequate to explain the observed variation of Doliv/liqNi (±39% relative average error of prediction). Two different equations are formulated to describe the partitioning behavior of Ni between olivine and silicate melt. The first is similar to that of Hart and Davis (1978) and uses an expression for Ni-Mg exchange between olivine and silicate melt. The second uses an expression for the Ni-olivine formation reaction. The Ni-Mg exchange equation for Doliv/liqNi depends on the forsterite content of the olivine and the mole fraction MgOliq, and predicts the experimentally determined values within ±13% relative average error. The Ni-olivine formation reaction equation for Doliv/liqNi depends on temperature, mole fraction SiOliq2, and melt compositional terms that arise from a symmetric, binary, Margules formulation of the activity coefficients for NiOliq and SiOliq2. This equation predicts the experimentally determined values within ±9% relative average error. © 1990.