Temperature and compostitional dependence of trace element partitioning in silicate systems

Trace element partitioning between divine and melt, and between orthopyroxene and melt, have been determined by microprobe analysis of synthetic divine, orthopyroxene, and quenched basaltic glass equilibrated in latm gas mixing furnaces. Experiments were conducted in several compositional systems at temperatures ranging from 1180°C to 1420°C. Partitioning values are determined for- the elements Eu, Ca, Mn, Fe, Ni, Sm, Gd, Y, Yb, Sc, Al, Zr, and Ti.

Equations expressing the temperature and compositional dependence of trace element partitioning are derived based on an evaluation of the substitution reaction between crystal and melt and the lattice energies of the trace element components. The lattice energies are modeled assuming that the crystals are ionically bonded. The derived expressions permit the prediction of trace element partitioning for compositions and temperatures not directly measured. The relation of enthalpies and entropies of exchange to cation size permits prediction of the partitioning of elements not experimentally investigated.

Based on these trace element partition coefficients and known phase equilibria for major elements, continuous fractional crystallization is not completely successful in modeling selected basaltic suites. Though major elements are modeled by fractional crystallization, Ni is better modeled by assuming all Ni has reequilibrated to the conditions of the lower temperature members of the suite. This suggests an olivine accumulation or olivine re-mixing model may be a more realistic portrayal of the genetic relations of the Hawaiian suites investigated.