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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.

The hypabyssal rocks associated with the Keweenawan (1.1 Ga) Midcontinent Rift along the Minnesota shore of Lake Superior are a distinct suite within the rock associations of this region. These rocks are found predominantly as ophitic diabase dikes and sills of various sizes, ranging from a few meters to several hundred meters across. Chilled margins were sampled and analyzed by neutron activation analysis and microprobe fused-bead techniques for bulk chemistry. Mineral compositions were obtained by electron microprobe. Variations in composition were found that are consistent with fractionation. Major-element modeling of fractionation indicates that the majority of the hypabyssal rocks formed at moderate pressures ({approximately}6 kbar), although a number show evidence of fractionation at near-surface levels, and some deeper ({approximately}10 kbar). Resorption features seen in plagioclase phenocrysts are evidence for magmatic evolution at varying levels in the crust. It is possible to relate the varied hypabyssal rocks to a single primary parent through polybaric fractionation. This parent is a high-Al primitive olivine tholeiite--a magma composition common among the volcanic rocks associated with the Midcontinent Rift. Trace-element modeling with this same parent composition yields results consistent with the formation of some hypabyssal rocks as products of a periodically tapped and replenished, constantlymore » fractionating magma chamber, which can decouple the behavior of major and trace elements.« less

Two of the most well-preserved igneous bodies in the early Preeambrian White Sea complex— the Severnyy and Yuzhnyy massifs on Pezhostrov Island—have been studied in order to gain a better understanding of ultramafic-mafic magmatism in the Belomorian tectonic block. These massifs represent portions of a single, differentiated pluton, ranging in composition from lherzolite to gabbronorite to anorthosite. Mineral-chemical and trace-element compositions of chill margins from this pluton were used to model the differentiation in this ancient magma chamber. Major-element compositions of minerals suggest that plagioclase in these rocks is not in equilibrium with the mafic minerals. This possibly is the result of suspension of less dense, early-formed plagioclase in more dense, early residual liquids. Later, as the liquid density decreased because of precipitation of mafic phases, plagioclase began to precipitate. We speculate that the liquid density did not decrease to a point where plagioclase would settle, unt...

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...

Eclogite xenoliths from the mantle have experienced a wide variety of processes and P-T conditions, many of which are recorded in the mineral compositions and textures. Exsolution of garnet from clinopyroxene is one such texture, occurring in a minority of mantle eclogites. New analyses of clinopyroxene and garnet of eclogite xenoliths from kimberlites at Bellsbank (South Africa) and Obnazhennaya (Yakutia, Russia) are presented here, and these are combined with data from the literature. Exsolution of garnet from clinopyroxene is generally lamellar, although lens-shaped garnets are also present. Major- and trace-element characteristics show a wide range of compositions and include eclogite Groups A, B, and C. Rare-earth element (REE) concentrations of garnet and pyroxene were determined by SIMS, and the REE patterns are subtly different from those in “ordinary” eclogites. Differences include the absence of prominent Eu anomalies in samples of this study and differences in the slopes of chondrite-normalized REE patterns. It is possible that these “signatures” are unique to exsolved eclogites, a result of subsolidus elemental partitioning during exsolution. Some reconstructed whole-rock compositions are aluminuous; comparison with ordinary eclogites shows only minor differences, implying a similar origin. If the immediate precursor to the exsolved eclogites was a monomineralic pyroxenite, the excess aluminium was tied up in Tschermak's molecule, although the occasional presence of kyanite exsolution lamellae is indicative of a Ca-Eskola component. Reconstructed “pyroxenes” from kyanite- and corundum-rich samples contain unrealistic amounts of aluminium for mantle pyroxenes. A protolith (or parental pyroxene) “threshold” of ∼24% Al2O3 may exist, above which (as in a plagioclase cumulate) the final assemblage is kyanite- and/or corundum-bearing.

The new bulk-rock analyses reported for the ALHA81001, Lakangaon and Nuevo Laredo eucritic meteorites indicate that the first of these resembles Ibitira in possessing lower Na concentrations than any other eucrite, while the other two are the lowest-Mg/Fe of all eucrites. The present data and those seen in the literature suggest that most of the ostensible Main Group eucrites actually belong to the Nuevo Laredo Trend, which is characterized by limited variations of incompatible element contents despite considerable variations in Mg/(Mg+Fe) ratio and V content.

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.