SOLUBILITY OF CARBON-MONOXIDE IN SILICATE MELTS AT HIGH-PRESSURES AND ITS EFFECT ON SILICATE PHASE-RELATIONS

The solubility of CO-CO2 vapors in equilibrium with graphite has been measured in several silicate melts at pressures to 30 kbar and temperatures to 1700°C. The vapors contain 30-40% CO, by thermodynamic calculation. The CO-CO2 vapors are slightly more soluble than CO2 alone in melts investigated at near-liquidus temperatures. The temperature dependence of the solubility of CO is apparently negative, in contrast to the positive temperature dependence of CO2. As a result, the solubility of CO-CO2 at superliquidus temperatures is less than that of CO2. Infrared spectra of quenched glasses containing CO and CO2 essentially show only a CO32- absorption band. The depressions of the liquidi of two compositions by CO-CO2 vapor were found to be slightly greater than the depressions by CO2 vapor. These phase relations imply that melting points are depressed more by CO than by CO2 and that CO/(CO + CO2) is somewhat greater in the liquid than in the vapor. The temperatures and pressures at which the liquidus phase of a peridotitic composition changes from olivine to orthopyroxene have been determined. These determinations suggest that melts containing CO and CO2 are nearly as polymerized as melts containing only CO2. These melts are significantly more polymerized than volatile-absent melts. Melting relations of peridotite in the presence of CO-CO2 will be similar, accordingly, to melting in the presence of CO2. © 1979.