Diffusion chronometry is a valuable method for determining the timescales of geological processes, such as the duration of mixing events before eruption. However, these timescales depend on the accuracy of experimentally derived diffusion coefficients (D), assuming pressure and temperature are well constrained. While analytical and modeling techniques are advancing, potential inaccuracies persist in experimental data. For example, diffusion coefficients derived from 'dry' olivine are commonly applied to natural systems, which are typically 'wet'.

The present study focuses on water diffusion in olivine, with experimental diffusivity ranging over several order of magnitude. The diffusion mechanisms of water in forsterite and their impact remain poorly constrained for natural conditions. To address this knowledge gap, a series of experiments were conducted, utilising olivine crystals in graphite and enstatite mix powder, brought at 800-900°C and 1 GPa within a piston cylinder apparatus. Olivine rehydration profiles were measured using high-resolution FTIR spectroscopy. Each of these spectra was deconvoluted into a succession of pseudo-Voigt curves, allowing for the determination of the impact of each crystallographic defect from the rim to the core. This study focused particularly on the 3500-3600 cm-1 band relative to the Ti clinohumite-type defect.