¹S. P. Aithala,¹R. A. Lange,¹M. M. Hirschmann
Journal of Geophysical Research: Planets (in Press) Open Access Link to Article [https://doi.org/10.1029/2025JE009148]
¹Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN, USA, 2Department ofEarth and Environmental Sciences, University of Michigan, Ann Arbor, MI, USA
Published by arrangement with John Wiley & Sons

To elucidate the relationship between oxygen fugacities (f_O2) recorded in martian basalts and redox processes in the martian interior, superliquidus 100-kPa furnace experiments on a composition similar to Humphrey (Adirondack basalt) were conducted at variable f_O2 and temperature. Quenched glasses were analyzed by EPMA, Mössbauer spectroscopy, colorimetric wet chemistry, and microbeam X-ray absorption near edge structure (XANES) spectroscopy. The experiments reveal Mössbauer and wet chemical determinations of silicate glass Fe³⁺/Fe^T agreeing within uncertainty, supporting the accuracy of extended-Voigt-based fitting of Mössbauer spectra when recoil-free fraction is considered. Fe³⁺/Fe^T ratios determined from Mössbauer spectroscopy from Humphrey and previously studied martian-relevant glass compositions are combined to calibrate models that characterize the relationship between Fe³⁺/Fe^T, f_O2, temperature, and composition in martian silicate liquids. The models demonstrate, similar to previously investigated silicate liquids, that the correlation between $$ and log f_O2 in martian magmas has a slope less than the value (0.25) expected if ferric and ferrous iron oxide mixed ideally. Martian magma Fe³⁺/Fe^T ratios are more temperature-sensitive compared to non-martian compositions, suggesting that temperature variations may contribute to comparatively large f_O2 variations in martian basalt. The models are applied to demonstrate that the Fe³⁺/Fe^T increases required to explain multiple-log unit changes in f_O2 in shergottite magma would not increase terrestrial magma f_O2 as effectively. To aid in future investigations of martian magma redox, a XANES technique that allows for non-destructive, microanalytical characterization of Fe³⁺/Fe^T in natural martian materials and martian-relevant experiments is introduced.