Uranium–lead systematics of phosphates in lunar basaltic regolith breccia, Meteorite Hills 01210

摘要

Chronological studies of brecciated lunar meteorites have proved difficult, because they are mixtures of materials from various sources and the radiometric “clocks” are sometimes affected by the subsequent impact events on the Moon. Here, we report the in-situ U–Pb dating of phosphates in lunar meteorite, Meteorite Hills (MET) 01210, which is a regolith breccia consisting of low-Ti mare basalt clasts and mineral fragments with a minor anorthositic component. In-situ analyses of four merrillite and four apatite grains in MET 01210, which are resistant to secondary events, resulted in a 207Pb/206Pb–204Pb/206Pb isochron age of 3904 ± 85 Ma (95% confidence limit). This phosphate formation age, when considered as the crystallisation age of this low-Ti basalt, is similar to crystallization ages of 3.8–3.9 Ga for unbrecciated low-Ti basalt meteorites, Asuka 881757 and Yamato 793169. This result reinforces the hypothesis that all these three meteorites originated from the same area on the Moon and were launched by a single impact event, consistent with the similarity of launch ages, mineralogical and geochemical signatures.