Oldest Immiscible Silica‐rich Melt on the Moon Recorded in a ~4.38 Ga Zircon

Abstract

AbstractThe temporal duration of lunar‐evolved magmatism is still poorly constrained. In lunar meteorite Northwest Africa (NWA) 10049, a melt inclusion‐bearing zircon fragment provides a new tool to understand the composition and age of the melts from which zircon directly crystallized. The studied zircon‐hosted melt inclusions are silica rich and iron poor (e.g., ~80–90 wt% SiO2; <0.5 wt% FeO), compositionally similar with immiscible silica‐rich melts found in Apollo rocks. Nano‐SIMS U–Pb analyses of the zircon yielded a minimum crystallization age of 4,382 ± 40 Ma, older than the ages for Apollo highly evolved alkali suite lithologies (~3.8–4.33 Ga). Our study shows that the melt inclusion‐bearing zircon in NWA 10049 is the oldest microscale evidence for documenting immiscible silica‐rich melts in lunar samples, suggesting that lunar‐evolved silica‐rich melts were prevalent as early as ~4.38 Ga. This work implies that there would be a prolonged silicic magmatism occurred on the Moon.