ABSTRACT

Many studies in the past decade have sought to explore the origin and evolution of water in planetary bodies based on the hydrogen isotopic compositions of apatite. However, no investigation has studied hydrogen diffusivity in apatite. This work reports hydrogen diffusion experiments using a natural Durango fluorapatite carried out under a saturated ²H₂O/O₂ vapor flow at temperatures of 500–700°C. Diffusion depth profiles for ¹H and ²H were measured using secondary ion mass spectrometry (SIMS), indicating that ²H diffusion occurred by an exchange reaction between the original ¹H and ²H during annealing. Hydrogen diffusion coefficients were obtained by the fitting of diffusion profiles of ²H using Fick’s second law; they followed an Arrhenius-type relationship. The temperature dependence of hydrogen diffusion parallel to the c-axis at 500–700°C can be expressed as