¹Dian Ji, ¹Rajdeep Dasgupta
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.02.019]
¹Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005, United States of America
Copyright Elsevier

Assessing whether the lunar mantle retains sulfide, through episodes of magmatism, is important in tracking the origin and evolution of sulfur and other volatile and chalcophile elements on the Moon. To determine sulfur concentrations at sulfide saturation (SCSS) in the mantle conditions of young Chang’e-5 (CE-5) mare basalts, we conducted experiments with three possible CE-5 parental melt compositions and Fe ± Ni-S sulfide at 1.0–3.0 GPa and 1250–1550 °C. We doped excess Fe metal in a subset of experiments in order to generate sulfide of various metal/sulfur molar ratio (M/S; 1.0–2.1), and thus investigate the effect of sulfide composition on SCSS under different oxygen fugacities (fO2s). Our experimental results indicate that SCSS is sensitive to temperature, pressure, silicate melt, sulfide compositions, and fO2. Using our new and literature data, we developed a new thermodynamic SCSS model and utilized the model to calculate the SCSS for scenarios that the CE-5 parental melt is in equilibrium with pure FeS, high Fe/S ratio sulfide, as well as high M/S Ni-bearing sulfide. All results suggest predictive SCSS values are higher than the S concentration in CE-5 parental magma, indicating the CE-5 mantle residue was likely sulfide-absent, unless an extremely S-poor and Ni-rich, Fe-alloy was the chief S-bearing accessory phase. We further reconstruct the S abundance in the CE-5 mantle source. Compared with the mantle of Apollo mare basalts, the ∼ 2 Gyrs lunar mantle has much lower S abundances, suggesting sulfur extraction by mantle melting over the magmatic history of the Moon, or S distribution heterogeneity in the lunar interior.