Terrestrial-like zircon in a clast from an Apollo 14 breccia

A felsite clast in lunar breccia Apollo sample 14321, which has been interpreted as Imbrium ejecta, has petrographic and chemical features that are consistent with formation conditions commonly assigned to both lunar and terrestrial environments. A simple model of Imbrium impact ejecta presented here indicates a pre-impact depth of 30–70 km, i.e. near the base of the lunar crust. Results from Secondary Ion Mass Spectrometry trace element analyses indicate that zircon grains recovered from this clast have positive Ce/Ce⁎ anomalies corresponding to an oxygen fugacity +2 to +4 log units higher than that of the lunar mantle, with crystallization temperatures of 771±88 to 810 ± 37°C (2σ) that are unusually low for lunar magmas. Additionally, Ti-in-quartz and zircon calculations indicate a pressure of crystallization of 6.9±1.2 kbar, corresponding to a depth of crystallization of 167±27 km on the Moon, contradicting ejecta modelling results. Such low-T, high-fO2, and high-P have not been observed for any other lunar clasts, are not known to exist on the Moon, and are broadly similar to those found in terrestrial magmas.