A ferroan region of the lunar highlands as recorded in meteorites MAC88104 and MAC88105

MacAlpine Hills 88104 and 88105 (MAC88104/5) are paired meteorites of noritic anorthosite composition from the lunar highlands. MAC88105 is a breccia composed mainly of melt-breccia clasts in a fine-grained, fragmental, and partly glassy matrix. The most abundant melt lithologies are feldspathic and are similar in composition to the bulk meteorite. Other melt lithologies include feldspathic melt rocks, mafic melt breccias, and a rare melt breccia relatively enriched in incompatible trace elements. Subordinate lithic clasts are granulitic breccias and ferroan (relatively low Mg [Mg + Fe] ) igneous lithologies, including troctolitic anorthosite, anorthositic norite, gabbronorite, and anorthosite. Igneous clasts having mafic mineral compositions more magnesian than Fo 55 and En 60 were not observed. Rare fragments of glass spheres and shards as well as glass clasts indicate that the meteorite was derived from an immature regolith. The bulk composition of MAC88105 is characterized by a molar Mg (Mg + Fe) ratio of 0.62, at the extreme low end of the range for meteorites from the lunar highlands. Its low concentrations of incompatible trace elements and feldspathic bulk composition (29% Al 2O 3), suggest that it, like the other lunar meteorites, formed at a site far removed from the areas sampled by the Apollo missions. Similarities in mineral compositions among the different lithologies of the breccia (melt-breccia clasts, granulitic breccias, igneous fragments) and the distribution of mineral fragments suggest that most components of the meteorite were derived from a crustal section dominated by material with a noritic anorthosite composition and an affinity to the ferroan suite of plutonic rocks. The mafic melt breccias have roughly peritectic melt compositions, similar to many “low-K Fra Mauro” melt breccias in the Apollo collection but much more ferroan, and represent a source material distinct from the noritic anorthosite. Moderate Ce anomalies, both positive and negative, occur in some separated clasts and to a lesser extent in some small chips dominated by matrix, but not in powder prepared from 20 g of bulk meteorite. These anomalies are almost certainly terrestrial weathering effects. One granulitic breccia clast is rich in siderophile elements as a result of a large amount of Fe-Ni metal. The Au Ir ratio of the clast (0.64, CI-normalized) is distinctly different from that of metal-rich impact melts from Apollo 16 (~3, CI-normalized). The compositional