Sulfur isotope heterogeneity in Martian shergottites reveals early atmosphere - mantle exchange

The study of sulfur isotopes on Mars provides crucial insights into the planet’s formation, differentiation, and volatile evolution. Primordial sulfur isotope compositions help distinguish Martian sulfur sources, including core-mantle interactions, magmatic outgassing, and atmospheric cycling. While bulk analyses have shown limited mass-independent fractionation (MIF-S), the mechanisms introducing MIF-S into Martian magmas remain poorly understood. Using in situ secondary ion mass spectrometry (SIMS), we analysed sulfides in four shergottites: Yamato 980459, Tissint, Gadamis 001, and NWA 11300, and found extreme heterogeneity in Δ³³S (–1.3 ± 0.48‰ to +1.42 ± 0.64‰) and δ³⁴S (–3.5 ± 0.11‰ to +0.73 ± 0.15‰). Large Δ³³S anomalies are observed in both depleted and enriched samples, indicating that MIF-S sulfur was incorporated into Martian magmatic systems through prolonged mantle-atmosphere exchange. This exchange likely began during magma ocean crystallisation and continued into later magmatic stages through ingassing, crustal assimilation, and/or recycling of crustal sulfur. In situ S isotope analyses of Martian shergottites reveal extreme Δ³³S heterogeneity at the mineral scale, indicating that mass-independent S signatures were incorporated into the mantle early via atmosphere–mantle exchange during magma ocean evolution