Hydrogen isotope systematics of phase separation in submarine hydrothermal systems: Experimental calibration and theoretical models

Hydrogen isotope fractionation factors were measured for coexisting brines and vapors formed by phase separation of NaCl/H 2O fluids at temperatures ranging from 399–450°C and pressures from 277–397 bars. It was found that brines are depleted in D compared to coexisting vapors at all conditions studied. The magnitude of hydrogen isotope fractionation is dependent on the relative amounts of Cl in the two phases and can be empirically correlated to pressure using the following relationship: 1000 In α (vap-brine) = 2.54(±0.83) + 2.87 (±0.69) × log (Δ P), where α (vap-brine) is the fractionation factor and Δ P is a pressure term representing distance from the critical curve in the NaCl/H 2O system.