Modification of crust and mantle in the South Pole Aitken region of the Moon

Current consensus holds that lunar magmas form in mantle reservoirs produced by crystallization of the Lunar Magma Ocean (LMO), which also explains formation of the primary lunar crust. Here we present Pb isotope data from two groups of impact melt fragments in the Chang’e-6 soil sample with ages of 4245 ± 4 Ma and 3876 ± 4 Ma, interpreted as impact remelting of the crust. The fragments show radiogenic initial Pb isotopes and a moderate crustal μ (²³⁸U/²⁰⁴Pb) of 683 ± 140, which cannot be explained by the evolution involving LMO crystallization and do not support a primary origin for this crust. Instead, the data require post-LMO remelting of the crust and underlying mantle, probably triggered by the South Pole–Aitken (SPA) impact. Crystallization of the SPA impact melt produced localized secondary reservoirs with variable μ-values, including secondary crust subsequently sampled by the two fragment groups from Chang’e-6 sample. Pb isotopes from Chang’e-6 impact melt fragments show that the SPA-region crust is not purely a primary product of lunar magma ocean crystallization, but formed through post-LMO remelting and differentiation of crust and upper mantle.