Pressure effect on hydrogen isotope fractionation between brucite and water at elevated temperatures

Experimental evidence for a pressure effect on isotopic partitioning at elevated temperatures demonstrates that equilibrium deuterium-protium fractionation between the mineral brucite [Mg(OH)₂] and pure water systematically increases by 12.4 per mil as pressure increases from 15 to 800 megapascals at 380°C. A linear relation is observed between the measured fractionation factor and the density of water (0.070 to 1.035 grams per cubic centimeter). The trend of the isotope pressure effect is the same as that of recent theoretical studies, but the magnitude is smaller. The pressure effect must be accounted for in the interpretation of isotopic data of geologic systems involving water (paleotemperature, source of fluids).