Electrochemical measurements and thermodynamic calculations of redox equilibria in pallasite meteorites - Implications for the eucrite parent body

The intrinsic oxygen fugacity (IOF) of olivine separates from the Salta, Springwater, and Eagle Station pallasites was measured between 850 and 1150 C using oxygen-specific solid zirconia electrolytes at 100,000 Pa. Thermodynamic calculations of redox equilibria involving equalibrium pallasite assemblages are in good agreement with the experimental results and provide a lower limit to pallasite redox stability; others involving disequilibrium assemblages, suggest that pallasites experienced localized, late-stage oxidation and reduction effects. Consideration of the redox buffer metal-olivine-orthopyroxene utilizing calculated Eucrite Parent Body (EPB) mantle phase compositions indicates that small redox gradients may have existed in the EPB. Such gradients may have produced strong compositional variation within the EPB. In addition, there is apparently significant redox heterogeneity in the source area of Eagle Station Trio pallasites and Bocaiuva iron meteorites.