Nagaoka, and 4 co-authors, reported in 2013 that the lunar meteorite Northwest Africa (NWA) 2200 is a regolith breccia with a ferroan feldspathic bulk composition (Al2O3 ¼ 30.1 wt.%; Mg# ¼ molar 100 Mg/(Mg þ Fe) ¼ 59.2) and low Th content (0.42 mg/g). Lithologically, NWA 2200 is a diverse mixture of lithic and glassy clasts, mineral fragments, and impact glass spherules, all embedded in a dark glassy matrix.
NWA 2200 contains some feldspathic brecciated rock components (ferroan anorthositic granulitic breccia, poikiloblastic granulitic breccia, and glassy melt breccia with an intersertal texture). The bulk compositions of these brecciated components indicate they are derived from ferroan troctolitic or noritic anorthosite lithologies (bulk Al2O3 ¼ 26e30 wt.%; bulk FeO/MgO > 1.0).
The bulk composition of NWA 2200 is more ferroan and feldspathic than the Apollo feldspathic regolith samples and feldspathic lunar regolith meteorites, and is also more depleted in incompatible elements (e.g., rare earth elements) than Apollo 16 feldspathic regolith samples. We conclude that NWA 2200 originated from a location different to the Apollo landing sites, and may have been sourced from the ferroan KREEP-poor highlands, “KREEP” materials are enriched in such elements as potassium (K), rare earth elements (REE), phosphorus (P).
The authors concluded that the bulk composition of NWA 2200 is more ferroan and Al-rich than Apollo mission samples of feldspathic regolith and lunar meteorite regolith samples, as evidenced by the absence of mafic impact melt breccias as observed in the Apollo 16 regolith samples and magnesian troctolitic granulites.
Incompatible element (e.g., REE and Th) abundances in NWA 2200 are consistent with mean values of feldspathic lunar meteorites, and lower than average
typical Apollo 16 mature regolith samples. Most regolith samples from the Apollo 16 landing site were contaminated with KREEP materials from the PKT
region. NWA 2200 may have originated from the ferroan KREEP-poor highlands.
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