INTERGRANULAR FLUID DISTRIBUTION IN OLIVINE-LIQUID BASALT SYSTEM

The distribution of intergranular fluid in olivine-liquid basalt systems has been investigated at high pressures. Experiments were run from 2 days to 32 days in a piston-cylinder apparatus at temperatures to 1360(DEGREES)C and pressures to 20 kb. Observations of quenched run products using reflected visible light and scanning electron microscopy indicate that surface tension was a dominant force in controlling phase distribution in long-term experiments. The fluid wetting angle, which is determined by the ratio of crystal-liquid surface tension to crystal-crystal surface tension, was always between 20 degrees and 35 degrees.;Observations of run products also show that glass, which represents quenched melt, is located on olivine grain corners and edges, incidating that the melt, forms an interconnected network in three dimensions. Grain faces appear to be fluid-free. Both of these observations are consistent with theoretical predictions that at equilibrium fluid must occur only along grain edges and corners when the wetting angle is greater than 0 degrees and less than 60 degrees.;A model surface topology indicates that total system surface tension energy is a function of melt fraction. For all wetting angles greater than 0 degrees and less than 60 degrees a minimum exists in this function when crystal-liquid interfaces take the form of spherical surfaces. In the model system the value of this critical melt fraction is dependent upon the wetting angle, decreasing from near 20 volume percent at 0 degrees to 0.6 volume percent at 60 degrees. Fluid can only be stabilized by surface tension against removal by buoyancy forces and other nonhydrostatic stresses if its fraction within the assemblage is below the critical amount.