A PROCEDURE FOR CALCULATING THE EQUILIBRIUM DISTRIBUTION OF TRACE-ELEMENTS AMONG THE MINERALS OF CUMULATE ROCKS, AND THE CONCENTRATION OF TRACE-ELEMENTS IN THE COEXISTING LIQUIDS

Whole-rock trace-element analyses can be used in conjunction with partition coefficients and mineral modes to calculate a liquidus-temperature equilibrium distribution of trace elements among the constituent minerals of cumulate rocks. Once the concentration of a trace element in a given mineral phase is known, then the trace-element concentration in the liquid that was in equilibrium with this mineral can be calculated if certain assumptions are made about the temperature and major-element chemistry of the liquid. The effects of a trapped melt fraction (TMF) are accounted for by: (1) including in the calculation a phase (the trapped melt) with a mineral/ melt partition coefficient of 1; and (2) adjusting the rock's mode to reflect removal of the TMF. The method yields results comparable to those given by mineral separation or in situ analysis for trace elements.