A Mossbauer-based XANES calibration for hydrous basalt glasses reveals radiation-induced oxidation of Fe

Oxygen fugacity (f(O2)) exerts first-order control on the geochemical evolution of planetary interiors, and the Fe3+/Sigma Fe ratios of silicate glasses provide a useful proxy for f(O2). Fe K-edge micro-X-ray absorption near-edge structure (XANES) spectroscopy allows researchers to micro-analytically determine the Fe3+/Sigma Fe ratios of silicate glasses with high precision. In this study we characterize hydrous and anhydrous basalt glass standards with Mossbauer and XANES spectroscopy and show that synchrotron radiation causes progressive changes to the XANES spectra of hydrous glasses as a function of radiation dose (here defined as total photons delivered per square micrometer), water concentration, and initial Fe3+/Sigma Fe ratio.