Experimental Determination of the Redox Potential of Rock-Water Systems. 3. Basalt-Water and Dunite-Water Systems at 400 deg C, 1 kbar. General Conclusion

摘要

Hydrogen fugacity was determined experimentally in rock-water systems (where the rock was granite, basalt, or dunite) at 400-450 deg C and 1 kbar from the activity of HCl~°produced in Ag/AgCl, aqeous solution/rock powder + water cells (the cell is divided by a Pt membrane/permeable to hydrogen). The experiments lasted for 12 days, which was sufficient to attain equilibrium from both sides. The equlibrium HCl concentration in the Pt ampoule with Ag/AgCl was determined potentiometrically (pH) after quenching. The cell was calibrated using the Ni/NiO buffer, for which the hydrogen fugacity was calculated from the Gibbs energy for reaction with water. At a total pressure of 1000 bar, the hydrogen fugacity was 0.69 at 400 deg C and 1.07 bar at 450 deg C. The hydrogen fugacities experimentally determined for the rock power + water mixtures confirm the results of physicochemical computer simulation under experimenal conditions. The reduction of the pore fluids was noted to increase in the succession acid rocks -mafic rocks -> ultramafic rocks.