¹Sophie Benaroya, ¹Christopher D.K. Herd
Earth and Planetary Science Letters 691, 120176 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2026.120176]
¹Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, University of Alberta, Edmonton, AB T6G 2E3, Canada
Copyright Elsevier

Constraining the oxygen fugacity (fO2) of the mantle of Mars is critical for understanding planetary differentiation processes and magmatic evolution. The degree to which the shergottite martian meteorites faithfully record the redox states of their mantle sources remains obscured by several factors. One of these factors is the various methods used to estimate fO2: Fe-based oxybarometers require multiple minerals to be found in chemical equilibrium, which can be challenging to obtain, while previous V-based values rely on estimated parental melt compositions. Here, we present new, mineral-specific V/Sc oxybarometers calibrated for olivine and pyroxene in shergottites using experimentally determined partition coefficients. This method obviates the need for parental melt V concentrations and allows for fO2 determination from single mineral phases, bypassing the equilibrium constraints that limit Fe-oxybarometry. We applied these calibrations to a petrologically diverse suite of geochemically depleted, intermediate, and enriched shergottites. Our results reveal that: (1) basaltic shergottites, previously estimated at fO2 ∼FMQ-1, record a significantly lower initial/magmatic fO2 of ∼FMQ-1.7; (2) the magmatic fO2 of shergottites is correlated with their geochemical enrichment; and (3) all shergottites show oxidation of a magnitude of >0.5 log units with progressive crystallization. The V/Sc oxybarometers provide a robust tool for estimating the magmatic fO2 of shergottites and tracking their redox changes throughout their petrogenetic histories.