¹Kang Liu, ¹Li Zhang, ¹Hesan Wu, ¹Wan-Cai Li, ^1,2Huaiwei Ni
Geochimica et Cosmochimica Acta (in Press), Link to Article [DOI: 10.1016/j.gca.2026.08.028]
¹State Key Laboratory of Lithospheric and Environmental Coevolution, School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China
²Deep Space Exploration Laboratory, Hefei 230088, China
Copyright Elsevier

Lunar volcanic glass beads preserve records of sulfur evolution in primitive lunar magmas and provide important constraints on the sulfur inventory of the lunar interior. Reconstruction of their pre-eruptive sulfur contents requires sulfur diffusivity data for lunar melts, which have remained largely unavailable. Here we experimentally determined sulfur diffusivities in three synthetic lunar basaltic melts, spanning compositions from Apollo green (low TiO₂, 0.52 wt%) and orange (intermediate TiO₂, 8.58 wt%) to red (high TiO₂, 13.93 wt%), with SiO₂ decreasing from 45.35 to 35.92 wt% and MgO from 16.00 to 11.00 wt%, using diffusion-couple experiments at 0.5 GPa and 1674–1876 K in a piston cylinder apparatus. Sulfur diffusivity increases systematically from green to orange to red glass compositions, with NBO/T rising from 1.76 to 2.49 to 2.82, respectively. At 1673 K, sulfur diffusivity in lunar melts is 6–13 times higher than that in terrestrial basaltic melts (NBO/T = 0.61–0.79), primarily owing to the more depolymerized structure of lunar melts. Combining these results with published experimental data, we develop a general parameterization for sulfur diffusivity in anhydrous lunar and terrestrial silicate melts under reduced conditions as a function of temperature (T) and melt composition (X_Si+Al, expressed by the combined mole fraction of Si + Al), which reproduces nearly all available experimental data within a factor of 2. Applying our new sulfur diffusivity data to Apollo green and orange glass beads yields revised pre-eruptive sulfur concentrations of 282–311 and 331 μg/g, corresponding to mantle source sulfur abundances of 9–28 and 27–63 μg/g, respectively. These estimates differ substantially from values previously inferred for Apollo and Chang’e mare basalts, indicating significant sulfur heterogeneity within the lunar interior, likely inherited from lunar magma ocean differentiation and subsequent mantle overturn.