Moon’s volcanic history revealed in glassy spherules from Apollo 17 soil 76501

Rapidly quenched droplets of pyroclastically erupted lava are common in lunar regolith at landing sites proximal to the maria. Here we document the U-Pb chronologies, major element, and trace element compositions of picritic glassy particles from Apollo 17 regolith sample 76501. These particles are dominated by high-Ti compositions similar to those of the established Apollo 17 orange and black pyroclastic deposits (e.g., McIntosh et al., 2024) but the textures of some beads indicate slower cooling and/or equilibration at lower temperatures. Using a new approach to calibrate SIMS U-Pb isotopic analysis of vitrophyric beads, we show that their U-Pb ages are consistent with a single or closely timed multiple eruptions ~50-100 Ma younger than the 3752±9 to 3758±12 Ma crystalline mare basalts collected at this site (Snape et al. 2019). A few picritic beads with Very Low-Ti compositions may be younger, but their ages are not well defined and can be ~3.3-3.6 Ga.