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

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 analyze basalt fragments collected by Chang’e-6, finding their composition resembles low-Ti basalts previously sampled by the Apollo missions. U-Pb dating indicates a basalt age of 2823.0 ± 5.9 Ma 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 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 this indicates post-LMO modification of the mantle by the SPA impact.