In situ Sr-Nd-Pb isotopes of lunar basaltic meteorite NWA 14526: Implications for the generation of young mare basalts

Abstract

This study presents a comprehensive analysis of the mineralogical, geochemical properties, and in situ Sr-Nd-Pb isotopic systematics of a newly discovered unbrecciated lunar basaltic meteorite NWA 14526 (NWA refers to northwest Africa). Bulk composition derived through both mineral modes and impact melt vein classifies NWA 14526 as a low-Ti, low-Al, and low-K mare basalt. In situ Pb isotopic analyses define a Pb–Pb isochron yielding an age of 3009 ± 43 Ma, representing the meteorite's crystallization age. In situ Rb-Sr isotopic analyses of plagioclase and maskelynite provide an initial ⁸⁷Sr/⁸⁶Sr ratio of 0.69969 ± 0.00024 (2σ), while phosphate and mesostasis in situ Sm-Nd analyses yield an initial εNd value of +10.7 ± 2.1 (2σ). Although NWA 14526 shares comparable mineralogical, bulk-rock composition, and Sr isotopic characteristics with contemporaneous lunar basaltic meteorites (NWA 4734, LAP 02205, NWA 14137, and NWA 10597), its significantly elevated εNd values preclude genetic pairing with these specimens. Isotopic modeling indicates minimal KREEP component contribution (<0.5%) in its mantle source. Our compilation of lunar Sr-Nd isotopic data reveals two distinct evolutionary trends corresponding to depleted lunar mantle and urKREEP reservoirs, respectively. Notably, no temporal correlation between basalt source KREEP enrichment and eruption age is observed, suggesting that the KREEP component did not necessarily play a decisive role in driving late-stage lunar magmatism and volcanism.