Estimation of oxygen diffusivity from anion porosity in minerals

An empirical model for predicting oxygen diffusivity from anion porosity is presented for a wide range of minerals. It is based on the examination of experimental diffusion data under anhydrous and hydrothermal conditions. The relationship between activation energies and pre-exponential factors in all minerals is assumed to obey a common compensation law regardless of diffusion medium (H2O, OH-, CO2 or O-2). However, the H2O molecules and OH-groups are relatively small in volume and thus can migrate within mineral structures with given anion porosities easier than the CO2 and O-2. As a result, the rates of oxygen diffusion in minerals under hydrothermal conditions are greater than those under anhydrous conditions. The Arrhenius parameters for oxygen diffusion in about 130 minerals have been estimated for the anhydrous and hydrothermal conditions, respectively. The empirical results on oxygen diffusivity are internally consistent for the minerals of geochemical interest and thus can be applicable to oxygen isotope geospeedometry during cooling of high-temperature mineral assemblages.