Rates of dehydration in hydrous, high-Fo, magmatic olivines

Natural olivine from the Etna Fall Stratified eruption (3930 BP) was dehydrated to determine hydrogen diffusivity. Dehydration was carried out in several time-steps, from 0.5 to 40 cumulative hours, in a 1 atm. furnace at 810 and 1000 °C. This starting material has high H2O concentration (∼50 ppm), high forsterite (Fo ∼ 90 %), and high fO2 (∼NNO + 1.2), reflecting characteristics of its host magma. H2O concentration was measured using Fourier transform infrared spectroscopy after each heating step. Spectral peaks were fit with Gaussian curves to determine the contribution from each H+ defect. Zonation profiles along each crystallographic direction were modelled using the ‘whole-block’ method to determine bulk and defect-specific H+ diffusivity.