Reprocessing of lunar crust at ∼4.3 Ga inferred from in situ U-Pb isotopic and trace element investigation of Northwest Africa 11479
Jingyou Chen, Shaolin Li, Shiyong Liao, Jian Chen, Alexander Nemchin, Katherine H. Joy, Xiaochao Che, Weibiao Hsu, Menghua Zhu
Geochimica et Cosmochimica Acta, In Press, Journal Pre-proof, Available online 11 January 2026
“The increasing identification of magnesian anorthosites (MAN) in lunar meteorites, along with inferences from remote sensing techniques, has intensified research interest in understanding their role in lunar crust formation. However, the lack of robust geochronological constraints for MAN impeded our comprehension of the timeline of crustal evolution. The lunar feldspathic breccia meteorite, Northwest Africa (NWA) 11479, is composed primarily of Mg-rich, KREEP-poor (K, rare earth elements, and P) highland lithic fragments, predominantly consisting of magnesian anorthositic lithologies (including anorthosite noritic/troctolitic anorthosites, and the associated magnesian granulites). The close chemical match between the bulk rock and lunar remote sensing data supports a farside origin, providing evidence for the presence of MAN in the Feldspathic Highlands Terrane (FHT).
Zircon and apatite grains have been discovered within the small Mg-rich anorthositic clasts in NWA 11479. Notably, the occurrence of these highly evolved accessory minerals contrasts with the depletion of incompatible trace elements in the coexisting silicates, suggesting their formation via interactions between the anorthositic crust and a later-stage KREEPy metasomatic melt. In-situ U-Pb isotopic analysis of the zircon and apatite yields a well-defined discordia line, with an upper intercept date of 4328 ± 9 Ma (2σ), and a lower intercept date of 140 ± 64 Ma (2σ). The younger age likely reflects a more recent impact event, whereas the upper intercept is consistent with both the concordant U-Pb zircon date (4327 ± 12 Ma, 2σ) and the weighted average 207Pb/206Pb date of the zircon and apatite (4326 ± 8 Ma, 2σ). This ∼ 4.33 Ga age is interpreted as the timing of metasomatism responsible for the formation of the zircon and apatite, or an impact event. Importantly, this age obtained from the putative-origin meteorite coincides with the period (4.3–4.35 Ga) of the active secondary magmatism recorded in nearside-collected Apollo samples, the proposed formation age of the giant South Pole–Aitken (SPA) basin. These temporal correlations suggest that this epoch represents a major phase of global reworking of the primordial lunar crust, likely driven by the overturn of mantle cumulates and further intensified by basin‑scale impact events, or both”
