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Abstract-The meteorite Northwest Africa 773 (NWA 773) is a lunar sample with implications for the evolution of mafic magmas on the moon. A combination of key parameters including whole-rock oxygen isotopic composition, Fe/Mn ratios in mafic silicates, noble gas concentrations, a KREEP-like rare earth element pattern, and the presence of regolith agglutinate fragments indicate a lunar origin for NWA 773. Partial maskelynitization of feldspar and occasional twinning of pyroxene are attributed to shock deformation. Terrestrial weathering has caused fracturing and precipitation of Carich carbonates and sulfates in the fractures, but lunar minerals appear fresh and unoxidized. The meteorite is composed of two distinct lithologies: a two-pyroxene olivine gabbro with cumulate texture, and a polymict, fragmental regolith breccia. The olivine gabbro is dominated by cumulate olivine with pigeonite, augite, and interstitial plagioclase feldspar. The breccia consists of several types of clasts but is dominated by clasts from the gabbro and more FeO-rich derivatives. Variations in clast mineral assemblage and pyroxene Mg/(Mg + Fe) and Ti/(Ti + Cr) record an igneous Fe-enrichment trend that culminated in crystallization of fayalite + silica + hedenbergitebearing symplectites.The Fe-enrichment trend and cumulate textures observed in NWA 773 are similar to features of terrestrial ponded lava flows and shallow-level mafic intrusives, indicating that NWA 773 may be from a layered mafic intrusion or a thick, differentiated lava flow. NWA 773 and several other mafic lunar meteorites have LREE-enriched patters distinct from Apollo and Luna mare basalts, which tend to be LREE-depleted. This is somewhat surprising in light of remote sensing data that indicates that the Apollo and Luna missions sampled a portion of the moon that was enriched in incompatible heatproducing elements.

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(Part of a series ofpapers dedicated to the memory of Paul Barringer)Abstract-A large hand sample and numerous polished thin sections, made from the hand sample, of the Kapoeta howardite and its many diverse lithic clasts were studied in detail by optical microscopy and electron microprobe techniques in an attempt to understand the surface processes that operated on the howarditeeucrite-diogenite (HED) parent body (most likely the asteroid 4 Vesta). Four unique, unusually large clasts, designated A (mafic breccia), B (granoblastic eucrite), D (howardite) and H (melt-coated breccia), were selected for detailed study (modal analysis, mineral microprobe analysis, and noble gas measurements). Petrographic studies reveal that Kapoeta consists of a fine-grained matrix made mostly of minute pyroxene and plagioclase fragments, into which are embedded numerous different lithic and mineral clasts of highly variable sizes. The lithic clasts include pyroxene-plagioclase (eucrite), orthopyroxenite (diogenite), howardite, impact-melt, metal-sulfide-rich, and carbonaceous chondrite clasts. The howardite clasts include examples of lithic clasts that constitute breccias-within-breccias, suggesting that at least two regolith generations are represented in the Kapoeta sample we studied. The clast assemblage suggests that repeated shock lithification was an important process during regolith evolution. Noble gas analyses of clast samples fall into two populations: (a) solar-gas-rich clasts H (rim only) and D and (b) clasts A and B, which are essentially free of solar gases. The concentrations of solar noble gases in the two matrix samples differ by a factor of -40. It appears that clast D is a true regolith breccia within the Kapoeta howardite (breccia-within-breccia), while clast H is a regolith breccia that has been significantly impact reworked. Our data indicate that the Kapoeta howardite is an extraordinarily heterogeneous rock in modal mineral and lithic clast abundances, grain size distributions, solar-wind noble gas concentrations and cosmic-ray exposure ages. These results illustrate the repetitive nature of impact comminution and lithification in the regolith of the HED parent body.

Bulk compositionspetrology and mineralogy of > 0.5 mm Luna 16 aluminous mare basalt particles are described. The data rule out any close genetic relationships between Luna 16 and other major types of lunar mare basalts. Compared to high‐Ti mare basaltsthe Luna 16 basalts contain lower TiO2 (5.1 wt %) and Ta (∼ 0.8 ppm) and higher Al2O3 (13.3 wt %) and REE (∼ 30‐70X chondrites) abundancessuggesting that the Luna 16 source rocks crystallized later than (i.e. stratigraphically above) the ilmenite‐bearing high‐Ti basalt cumulate source rocks. The REE pattern for the Luna 16 basalts requires that the source material from which they were derived crystallized from a light REE enriched magma.