Isotopic and compositional constraints on the source of basalt collected from the lunar farside

Volcanism on the Moon has produced surface basalt deposits, which record lunar interior processes. The Chang’e-6 mission retrieved samples from the South Pole–Aitken basin (SPA) on the Moon’s far side. We analyzed basalt fragments collected by Chang’e-6 and found that their composition resembles that of low-titanium basalts previously sampled by the Apollo missions. Uranium-lead (U-Pb) dating indicated a basalt age of 2823.0 ± 5.9 million years and a source 238 U/ 204 Pb ratio (μ-value) of 480 ± 56. This high μ-value indicates that the source contained materials that formed during the late stages of lunar magma ocean (LMO) crystallization. The results are consistent with the LMO model, but the Chang’e-6 basalt deviates from the trend in Apollo mission samples of younger basalts having higher μ-values. We suggest that this indicates post-LMO modification of the mantle by the SPA impact.