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Data are presented for the O isotopic composition of clinopyroxene and garnet, the C isotopic composition of diamond, and the OH- content of garnet from eclogite xenoliths brought to the surface by the Udachnaya kimberlite pipe, Yakutia, Siberia. Radiogenic isotopic data suggest that the eclogites could have been derived from an ultradepleted mantle at approximately 2.9 Ga (Pearson et al., 1995; Snyder et al., in preparation). O isotopic compositions generally show equilibration between the eclogitic minerals (Δ_(cpx-Grt) = 0.11-0.41‰) and have δ^(18)O_(SMOW) for both garnet and clinopyroxene that lie near the range of accepted mantle values of 5.7±0.7‰. However, several eclogites indicate significant deviations from this range, at higher values of 6.8-7.0‰. Also, two eclogites lie at the lower end of the mantle range, at values of 4.8 and 5.0‰ (all in clinopyroxene). C isotopic compositions of diamonds all have δ^(13)C_(PDB) in the range of -1 to -7‰ and are centered at approximately -5‰, also within the range of accepted mantle values. The OH- contents of the garnet are generally between 0 and 22 ppm (as H_(2)0), although two samples exceed 70 ppm. This range of OH- is similar to eclogitic garnet from the Kaapvaal craton of southern Africa. The mantle C isotopic values of associated diamonds, the majority of O isotopic data, and the low OH- content of the minerals, although suggesting a general lack of crustal participation in the formation of the Udachnaya eclogites, do not rule out the participation of some ancient crustal material. That these eclogites include both ^(18)O-enriched and ^(18)O-depleted types suggests that the protoliths may have been overprinted by both low- and high-temperature hydrothermal events (cf. Jacob et aI., 1994). A positive correlation between δ^(18)O and ^(87)Sr/^(86)Sr allows the interpretation of these eclogites as representing a cross section of an Archean ophiolite. However, the lack of a single coherent grouping on a plot of δ^(18)O vs. ^(87)Sr/^(86)Sr suggests that, if the Udachnaya eclogites were derived from oceanic crust, they cannot be cogenetic and must represent at least two separate ophiolite sequences. Conversely, if the eclogites are found to be cogenetic, then a totally different process affected their formation and a probable metasomatic mechanism was operative. Because of the total lack of correlation of δ^(18)O with other geochemical parameters, we find no compelling evidence that all eclogites are derived ultimately from oceanic crust.

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.

Nd and Sr isotopic data from diamond-bearing eclogites found in the Udachnaya kimberlite, Yakutia, Siberia, are interpreted as indicating an early (>1 4 Ga) differentiation event, whereby the mantle split into complementary depleted and enriched reservoirs. Reconstructed whole-rock 87Sr/S6Sr ratios (present-day) range from 0.70151 to 0.70315 and are consistent with a mantle origin for these rocks. The Nd isotopic evolution lines of four samples (U-5, U-37, U-41 and U-79) converge at 2.2-2.7 Ga. Sample U-5 is unique in exhibiting the most enriched signature of any of the samples yet analyzed (present-day end of --20), and this sample points unequivocally to an old, enriched component. A complementary depleted mantle component is suggested by two of the eclogite samples, U-86 and U-25, which yield ENd values (at 2.2 Ga) of + 13 and + 7, respectively. The two mantle reservoirs possibly formed prior to 4 Ga and evolved separately until 2.2-2.7 Ga. At that time, the reservoirs were melted forming eclogites both as residues (from the enriched reservoir) and as partial melts of peridotite (from the depleted reservoir), resulting in demonstrably different histories for eclogites from the same locality.

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.

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.

Bulk compositions of 21 Apollo regolith breccias were determined using an INAA procedure modified from that of Kallemeyn et al. (1989). With one major exception, namely, the 14076,1 sample, the regolith breccias analyzed were found to be not significantly different from the surfaces from which they were collected. In contrast, the 14076,1 sample from the Fra Mauro (Apollo 14) region is a highly anorthositic regolith breccia from a site where anorthosites are extremely scarce. The sample's composition resembles soils from the Descartes (Apollo 16) highlands. However, the low statistical probability for long-distance horizontal transport by impact cratering, together with the relatively high contents of imcompatible elements in 14076,1 suggest that this regolith breccia originated within a few hundred kilometers of the Apollo 14 site. Its compositional resemblance to ferroan anorthosite strengthens the hypothesis that ferroan anorthosite originated as the flotation crust of a global magmasphere.

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.

Concentrations of 14 elements in the metal of 38 iron meteorites and a pallasite are reported. Three samples are paired with previously classified irons, raising the number of well-classified, independent iron meteorites to 598. Several of the new irons are from Antarctica. Of 24 independent irons from Antarctica, eight are ungrouped, a much higher fraction than that among all classified irons. The difference is probably related to the fact that the median mass of Antarctic irons is about two orders of magnitude smaller than that of non-Antarctic irons. Smaller meteoroids may tend to sample a larger number of asteroidal source regions, perhaps because small meteoroids tend to have higher ejection velocities or because they have random-walked a greater increment of orbital semimajor axis away from that of the parent body.

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.

The composition and structure of the Guin ungrouped iron meteorite inclusions have been investigated experimentally. The structural characteristics of polished and etched slabs of the meteorite were studied microscopically in reflected light. Modal abundances of troilite nodules and silicate inclusions were determined by weighing paper traces. The bulk composition of the silicate inclusions was calculated by combining modal phase abundances and mineral compositions. It is found that the largest silicate inclusion (2 x 4 cm) consists mostly of a shock-melted plagioclase-rich matrix surrounding large, partly melted augite grains. The oxygen isotopic composition of the inclusion is near that of LL chondrites. The inclusion is found to be similar in composition to selected melt pocket glasses in ordinary chondrites produced in situ by preferential melting of plagioclase rock due to shock compression. It is suggested that the Guin assemblage was formed by impact melting on a chondritic parent body. Silicate inclusions in IIE irons share many of the compositional and petrological characteristics of the Guin inclusions, indicating that IIE irons also formed by impact-melting of chondritic materials. Black and white photomicrographs of the silicate inclusions are provided.

Data for 10 siderophile elements in all of the known lunar meteorites except for Y793274 are reported. Bulk compositional data for Ni, Ge, Cd, Re, Os, Ir, and Au were obtained from radiochemical neutron activation analysis (Warren et al., 1986). Data for Fe, Co, and Zn, and additional data for Ni, Ir, and Au were obtained by instrumental neutron activation analysis (Kallemeyn et al., 1988). Except for the case of Au in Y791197, there was good agreement between the results obtained by the two methods. The differences observed between the lunar-meteoritic regolith samples and central nearside highlands regolith samples are discussed.

Compositional (by INAA) and petrographic studies were performed among the smaller rocks (not analyzed previously) from the Apollo 14, 16, and 17 sites as part of a search for regolith samples exotic to the small traverse areas associated with these missions. Of the 40 samples studied, 31 were regolith breccias. Among these, three of the Apollo 14 samples proved to be compositionally unique, particularly the 14315 sample, which is radically different from all other Apollo 14 regolith materials (lower Mg and Fe, far higher Al and far lower REE abundances), and is probably exotic to the Apollo 14 traverse area. Among 10 samples from Apollo 17, all but one proved to be typical Apollo 17 regolith breccia. However, the 72504,10 sample is more than 99 percent pure pyroclastic glass, compositionally identical to the Apollo 17 orange glass obtained at a location 4 km away, attesting to the widespread distribution of orange glass deposits.