Hydrogen isotope fractionation and hydrogen diffusion in the tourmaline-water system

Abstract

Hydrogen isotope exchange between tourmaline and water has been studied experimentally over the temperature range of 800-350°C. The hydrogen isotope equilibrium fractionation factor between tourmaline and water may be expressed as a function of temperature by the following linear equation: 10 3 ln α tourmaline-water e = −27.9(10 6/ T 2) + 2.3 A study of the kinetics of hydrogen isotope exchange between tourmaline and water indicates that exchange is dominated by hydrogen diffusion. Over the temperature range of 800-450°C, the relation between the hydrogen diffusion coefficient and temperature for the tourmaline-water system is as follows: Cylinder model: log D cyl = −5.96 − 6.68(10 3/ T) Plate model: log D plate = −5.64 − 6.42(10 3/ T) The activation energies for hydrogen diffusion are 128.0 kJ/mol (cylinder model) and 123.1 kJ/mol (plate model), respectively. For the temperature range 800-450 C, the relation of the hydrogen isotope equilibrium fractionation factor to the temperature (10 6/ T 2. chemical composition ( M), and hydroxyl-stretching frequency (ƒ) for systems of nonhydrogen-bonded hydroxyl minerals and water can be expressed as 10 3 ln α mineral-water e = − 14.7 10 3 × f − 3 (10 6/ T 2) + 26.4 + (2 M Al − 4 M Mg − 68 M Fe ) where M represents the mole fraction of designated cation in the mineral.