Lunar meteorites from northern Africa

Randy L. Korotev, Anthony J. Irving

Meteoritics & Planetary Science
First Published: 2 February 2021


“We report bulk composition data for 235 stones of ~77 lunar meteorites from northern Africa and 33 lunar meteorites from elsewhere. About 27% of the African meteorites are typical feldspathic lunar rocks, all breccias of similar bulk composition, for example, 3–5% FeO and low concentrations of incompatible elements. Nevertheless, these meteorites have a large range in Mg’ (whole‐rock mole% Mg/[Mg + Fe]), 57–77 (mean: 65.5), and this parameter does not correlate with either albite content of the plagioclase or concentrations of incompatible elements. From this observation, we conclude that feldspathic lunar meteorites do not support the hypotheses that the anorthositic, precursor plutonic rocks of the meteorite breccias all crystallized from a common magma. Among feldspathic lunar meteorites, Mg’ increases with normative olivine abundance but is uncorrelated with normative pyroxene abundance, that is, high‐Mg’ feldspathic rocks of the early lunar crust were troctolitic, not noritic. The NWA 5744 (Northwest Arica) clan of lunar meteorites are anorthositic troctolites (59–75% plagioclase, 15–26% olivine, Fo77–80) with very low concentrations of incompatible elements (2.6 × CI) compared to troctolites in the Apollo collection. They may represent the lower feldspathic crust or differentiated impact melt from portions of the highlands distant from the PKT (Procellarum KREEP Terrane). About 31% of the lunar meteorites from northern Africa, all breccias, are, by lunar standards, moderately mafic (5–13% FeO) but more magnesian than mixtures of typical feldspathic meteorite and mare basalt, implying that they represent moderately mafic regions of the highlands or originate from the South Pole–Aitken basin. With ~6 µg g−1 Th, two NWA meteorites likely originate from the PKT. Including the unique NWA 773 clan, at least six of the northern Africa meteorites are, or are dominated by, unbrecciated basalts and gabbros of mare affinity. We estimate that the ~341 lunar meteorite stones (Africa and elsewhere) for which there are data represent 131–147 terrestrially unpaired meteorites and 109–134 lunar launch sites.”