Oldest immiscible silica-rich melt on the Moon recorded in a ~4.38 Ga zircon

The temporal duration of lunar evolved magmatism is still poorly constrained. In lunar meteorite 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 4382 ± 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 micro-scale 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.