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ABSTRACT As the largest and oldest well-preserved impact structure on the Moon, the South Pole–Aitken (SPA) basin on the lunar farside is critical for understanding early solar system dynamics and lunar history, but accurately determining its age remains challenging. Crater-counting chronology and Apollo sample studies propose various SPA-forming ages, which require validation by in situ sampling of the SPA basin. Here, we present the petrology, geochemistry and chronology of norite clasts from the SPA basin that were returned by Chang'e-6. These norites have highly anorthite-rich, rare-earth element-poor plagioclase and magnesium-rich pyroxene, in contrast to Mg-suite norites that were returned from the lunar nearside. Abundant Fe–Ni metals with meteoritic Ni/Co ratios, depletion of volatile elements and variable grain sizes and cooling rates strongly indicate that the norites were crystallized from an impact melt sheet. Precise Pb–Pb ages of zirconium-bearing minerals in the norites yield two distinct impact events at 3.87 and 4.25 Ga. The former represents an impact-resetting event within the basin. The latter finding is most consistent with the age of the SPA impact, providing an initial 4.25-Ga anchor for the older end of the lunar crater chronology and refining the timeline for early lunar evolution.
Su et al. (Thu,) studied this question.