Review of Metamorphic Mixed-Volatile (H,O-CO,) Equilibria

The slopes and curvatures of various types of mixed-volatile (H"O-COr) equilibria on T-X diagrams can be readily interpreted by considering the change in chemical potentials of volatile components as a function of activity.?-X equitibria can be extrapolated with sufficient accuracy from a narrow experimental bracket, using an equation assuming constant AfI " and account-ing for non-ideal mixing in the fluid phase. Positive deviations from ideal mixing in the fluid, as measured experimentally, will flatten the extrapolated T-X curves of various types of mixed-volatile equilibria in comparison to the curves for ideal mixing. Addition of CH. to the fluid, as with graphite-bearing systems, would alter the T-X projections of most types of mixed-volatile reactions. Mixed-volatile equilibria can also be analyzed with isobaric, isothermal pE,p- pco2 (or log f"p- log lm,) diagrams. The main advantage of such diagrams over T-X plots is that vapor-deficient systems can be investigated. Critical evaluation of experimental data on mixed-volatile e4uilibria must include an esti-mate of the sensitivity of the experimental technique, the amount of reaction which occuned