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Six landings were made during the Apollo program and a total of 376 kg of samples was returned. These samples are varied, including basalt, breccia, glass, and unexpected amounts of anorthosite. While much of the returned material remains unstudied in any detail, the basic nature of lunar history has been deciphered. Anorthosite represents the original crust of the Moon, forming at 4.5–4.1 Ga through plagioclase crystallization and flotation from a global magma ocean. Large impacts during this time and lasting until about 3.8 Ga formed large basins all over the Moon. Secondary melting of deeper portions of the crystallized magma ocean resulted in basalts, which erupted and filled many of the basins, resulting in the circular features observable from Earth. Although this volcanism appears to have mainly occurred prior to about 3 Ga, more recent studies indicate that it might have continued at least sporadically to much more recent times.

Isotopic studies of mare basalts have led workers to conclude that their sources are heterogeneous on both large and small scales. Furthermore, these studies have led workers to postulate that depletion within the lunar mantle occurred early in its evolution and was a result of accumulation of mafic minerals from a LREE-enriched magma ocean. High-Ti basalts from the Apollo 1 I and 17 landing sites and ilmenite basalts from Apollo 12 are secondary evidence of this extreme, early depletion event. KREEPy rocks are the complementary enriched component in the Moon. A total of fourteen high-Ti basalts have now been analyzed from the Apollo 11 landing site for neo- dymium and strontium isotopes. A Sm-Nd internal isochron on basalt 10058 yields an age of 3.70 + 0.06 Ga, similar to 40Ar/39Ar ages of other Group B 1 basal@.. A compilation of all previously determined ages on Apollo 11 high-Ti basalts indicates four distinct phases of volcanism at 3.85 + 0.02 Ga (Group B2), 3.71 f 0.02 Ga (Group B3), 3.67 + 0.02 Ga (Group Bl), and 3.59 f 0.04 Ga (Group A). Whole- rock Sm-Nd isotopic data for all Apollo 11 high-Ti basalts form a linear array, which yields the age of the Moon (4.55 f 0.30 Ga). A similar regression of all uncontaminated high-Ti basalts from the Moon (both Apollo 11 and Apollo 17) yields an age of 4.46 + 0.17 Ga. Both arrays are interpreted as average source ages of the high-Ti basalts and are consistent with the formation of these sources by precipitation of cumulates from a magma ocean early in the history of the Moon. These new strontium and neodymium isotopic data, coupled with previously published data, are con- sistent with a two-component model for the upper mantle of the Moon. These two components include mafic adcumulates precipitated from a magma ocean prior to 4.4 Ga and small amounts (~2%) of trapped, KREEPy, late-stage, magma ocean differentiates. The mafic adcumulate evolves from 4.5 Ga, with '47Sm/'44Nd = 0.318 and *'Rb/%r = 0.005 to extremely radiogenic neodymium isotopic ratios and very unradiogenic strontium isotopic ratios. The KREEPy trapped liquid has a 14'Sm/ '44Nd = 0.168 and "Rb/%r = 0.235 and thus, evolves toward very unradiogenic neodymium and radiogenic strontium isotopic ratios. Because the KREEPy trapped liquid is enriched in both rubidium and the REEs by over an order of magnitude compared to the mafic adcumulate, trapping of even small proportions of this liquid in the adcumulate will control the radiogenic isotopic composition of the source. The apparent heterogeneity in the source regions of mare basalts could be caused by trapping of variable, yet small, proportions of this LILE-enriched liquid in the cumulate pile.

Five groups of basalts (A, B1, B2, B3, D) with three principal ages exist at the Apollo 11 site. These range from the low-K, low rare-earth element (REE) Groups B1, B2, and B3 to the low-K, high REE Group D basalts, to the high-K, high-REE Group A basalts. The Group A basalts are the only high-K (>0.2 wt% K2O) basalts, and youngest, with an age of 3.59 ± .02 Ga; Groups B3 and B1 are 3.71 ± .02 and 3.67 ± .02 Ga, respectively; Group B2 basalts are the oldest, at 3.85 ± .02 Ga. Group D basalts have not been dated. Fractionation modelling for major and trace elements indicates that the B1 basalts could have formed from a B3-like parent liquid. The B2 and D basalts can also be related to liquids similar to the B3-B1 composition through the presence of varying amounts of modal whitlockite. Thus, the entirety of low-K high-Ti basalts at Apollo 11 may have formed through melting of the same source region. The Group A basalt compositions are consistent with formation from a different parent liquid, with the composition of Apollo 11 orange glass. Modelling of major- and trace-elements in the Apollo 11 orange glass, indicate that the composition of the Group A basalts is consistent with fractionation of this glass, coupled with some assimilation (~7.5–15%) of an evolved KREEP-like material. However, this component is much younger than primitive KREEP (4.4 Ga). This “neuKREEP” component, similar to the composition of quartz monzodiorites described from the Apollo 15 site, probably represents evolved material formed during plutonism prior to the formation of the Apollo 11 orange glass liquid.

A suite of samples, including kaersutite and ilmenite megacrysts, spinel peridotites, garnet pyroxenites, and the alkali basalts that host them, have been studied in an effort to better constrain the mineralogy and chemistry of the subcontinental mantle beneath the central portion of the Arabian plate. Kaersutite megacrysts are classified as Type-A high-pressure precipitates of the alkali basalt host, which transported these xenoliths to the surface and extruded them during formation of the Tell-Danun volcano, southwestern Syria. Ilmenite megacrysts are classified as Type-B megacrysts and could not have precipitated from the alkali basalts presently sampled. Instead, they were derived from a magma that was enriched in the rare-earth elements (REE) by ca. four times and depleted in Zr and Hf, compared to the alkali basalts. Garnet pyroxenites from the Tell-Danun volcanic field yield temperatures and pressures of 946-1045° C and 8-10 kbar, respectively. These xenoliths likely were precipitated as dikes or a...

Major-element and REE compositions of 14 diamondiferous eclogites from the Udachnaya kimberlite in Yakutia, Siberia have been determined by electron microprobe and secondary ion mass spectrometer (SIMS). Based on previous clinopyroxene classification schemes (e.g., Taylor and Neal 1989), all of these eclogite xenoliths belong to Group B/C, although some of the garnet compositions and mineral REE abundances are inconsistent with the indicated groups. This demonstrates the inadequacy of the classification scheme based on African eclogites for application to Siberian samples. Because of the coarse grain size of the Udachnaya nodules, meaningful modal abundances could not be obtained. However, reconstructed REE compositions using various garnet: clinopyroxene ratios demonstrate relative insensitivity to changes in mode for common eclogitic assemblages. Many of these reconstructed REE compositions show LREE depletions. Some depletions are consistent with an origin (either directly or through partial melting) as “normal” or Type-I ocean floor basalt. Others, however, require material of eclogitic or pyroxenitic affinities to undergo partial melting; this facilitates the depletion of LREE while leaving the HREE at nearly original levels. Many of the eclogites of South Africa are consistent with a protolith of “anomalous” or Type II ocean floor basalt. This fundamental difference between the two regions is the likely cause of the inconsistencies with the chemicallybased classification.

Results of elemental analyses, performed either by instrumental neutron activation analysis (NAA) or radiochemical NAA, of 19 lunar rock samples obtained by the Apollo 15, 17, and 12 missions are presented. Two of the samples are most extraordinary: 'large' (1 g) felsite from Apollo 12 and a pristine ferroan anorthosite from Apollo 15. The felsite is mainly a graphic intergrowth of K-feldspar and a silica phase, with about 6 pct plagioclase and 1 pct each of ferroaugite, ilmenite, and fayalitic olivine. The Fe-metal content of ferroan anorthosite is 1.2 wt pct in the thin section studied (but, based on mass balance for Co and Ni, must have been lower in the chip used for bulk-rock analysis); the measured bulk-rock concentrations of siderophile elements Re, Os, and Ir are far higher than previously observed among pristine lunar anorthosites. These results underscore the uncertainty associated with any attempt to estimate the overall siderophile element contents of the moon's crust.

Seven 5-cm basaltic pebbles from the Vaca Muerta mesosiderite were studied by neutron activation and electron microprobe analysis, and three additional pebbles were studied petrographically. The cumulate pebbles had low REE concentrations and high Eu/Sm ratios, indicating the absence of intercumulus liquid. Siderophile interelement ratios were similar to those found in Vaca Muerta metal except for anomalously low Ir concentrations. The presence of 20 percent impact-melt breccias among the pebbles and 35-40 percent melt breccias among the mesosiderite whole-rocks suggests that the mesosiderites were more extensively impact melted than the howardites. Three alternative models to explain this greater proportion of impact-melted material among the mesosiderites are proposed.

Two gabbroic pebbles and one pebble with basaltic textural affinities from the Vaca Muerta mesosiderite were analyzed by instrumental neutron activation analysis and electron microprobe. These analyses plus literature data reveal remarkable compositional differences between basaltic and gabbroic clasts in mesosiderites. On average, basaltic clasts have small (15%) depletions in light relative to heavy rare earth elements (REEs) and moderate positive Eu anomalies (i.e., H-chondrite-normalizedLa/Lu= 0.85;Eu/Sm= 1.30). The meanLa/Lu andEu/Sm abundance ratios of gabbroic clasts are at least 3.3 × smaller and 28 × greater, respectively. Intense meteoroid bombardment probably persisted until after the mesosiderite parent body had differentiated. Near-surface mixtures of major amounts of basalt and lesser amounts of cumulate eucritic rocks were essentially totally melted and rapidly cooled, accounting for the moderately fractionated REE patterns of most basaltic clasts. At greater depths, impact-heating partially melted cumulate gabbros; incompatible-element-rich eutectic liquids drained away, creating large REE fractionations in the residual rocks. These rocks cooled slowly and developed gabbroic textures.