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: 103 ln αetourmaline-water = -27.9(106/T2) + 2.3A 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 Dcyl = -5.96 - 6.68(103/T) Plate model: log Dplate = -5.64 - 6.42(103/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 (106/T2), chemical composition (M), and hydroxyl-stretching frequency (f) for systems of nonhydrogen-bonded hydroxyl minerals and water can be expressed as 103 ln αemineral-water = - 14.710-3 x f - 3 (106/T2) + 26.4 + (2MAl - 4MMg - 68MFe) where M represents the mole fraction of designated cation in the mineral.