MELTING EXPERIMENTS ON KOMATIITE ANALOG COMPOSITIONS AT 5 GPA

The results of multi-anvil melting experiments are reported for a wide range of komatiite analog mixes with compositions in the system CaO-M gO-FeO-Fe2O3+/-Fe-0-Al2O3-SiO2 at 5 GPa (CMAS and CMFAS+/-Fe-0). The l iquidus crystallization fields for olivine, orthopyroxene, clinopyroxe ne, and garnet were mapped out, as were their intersections at various cotectics and invariant points. For the assemblage L+Ol+Opx+Cpx+Gt, t he compositions of liquids at the invariant point in CMAS and at sever al pseudoinvariant points in CMFAS were determined to within +/-0.50 w t% (1 sigma). The effect of FeO is to expand the liquidus crystallizat ion fields in the following relative ways: garnet at the expense of al l other crystallizing phases, pyroxenes at the expense of olivine, and clinopyroxene at the expense of orthopyroxene. The results reported h ere are in excellent agreement with previous determinations (Fujii et al. 1989; Herzberg 1992; Tronnes et al. 1992), but the uncertainties a re much lower. It is demonstrated that the multi-anvil apparatus is ca pable of yielding crystal-liquid phase-equilibrium information at 5 Cp a with an accuracy that is comparable to those at lower pressures.