New data for lunar meteorites and a synthesis of literature data have significant implications for the interpretation of global Th data and for the Moons bulk composition. As presently calibrated (Prettyman et al. 2002), the Lunar Prospector gamma-ray data imply that the average global surface Th = 1.58 micrograms/g. However, that calibration yields implausibly high concentrations for the three most Th-poor documented sampling sites, it extrapolates to a nonzero Lunar Prospector Th, ~0.7 micrograms/g, at zero sample Th, and it results in a misfit toward too-high Th when compared with the global regolith Th spectrum as constrained using mainly lunaite regolith breccias. Another problem is manifested by Th versus K systematics. Ground truth data plot consistently to the high-Th/K side of the Prospector data trend, offset by a factor of 1.2. A new calibration is proposed that represents a compromise between the Th levels indicated by ground truth constraints and the Prettyman et al. (2002) calibration. Conservatively assuming that the Th versus K issue is mostly a K problem, the average global surface Th is estimated to be ~1.35 micrograms/g. The Moons remarkable global asymmetry in KREEP abundance is even more pronounced than previously supposed. The surface Th concentration ratio between the hemisphere antipodal to the Procellarum basin and the hemisphere centered on Procellarum is reduced to 0.24 in the new calibration. This extreme disparity is most simply interpreted as a consequence of Procellarums origin at a time when the Moon still contained at least a thin residual layer of a global magma ocean. Allowing for diminution of Th with depth, the extrapolated bulk crustal Th is ~0.73 micrograms/g. Further extrapolation to bulk Moon Th yields ~0.07 micrograms/g, which is nearly identical to the consensus estimate for Earths primitive mantle. Assuming chondritic proportionality among refractory lithophile elements implies Al2O3 of approximately 3.8 wt%. The Moons bulk mantle mg ratio is only weakly constrained by seismic and mare-basaltic data. KREEPand mare-free lunaite regolith samples, other thoroughly polymict lunar meteorites, and a few KREEP-free Apollo highland samples manifest a remarkable anticorrelation on a plot of Al2O3 versus mg. This trend implies that an important component of the Moon is highly magnesian. The bulk Moon is inferred to have an Earth-like oxide mg ratio of ~87-88 mol%. The close resemblance between the bulk Moon and Earths primitive mantle extends to moderately volatile elements, most clearly Mn. Unless major proportions of Cr and V are sequestered into deep mantle spinel, remarkably Earth-like depletions (versus chondrites) are also inferred for bulk Moon Cr and V.

A large (7 mm in diameter) Allende type B inclusion has a typical bulk composition and a unique structure: a fassaite-rich mantle enclosing a melilite-rich core. The core and mantle have sharply contrasting textures. In the mantle, coarse (~1 mm across), subhedral fassaite crystals enclose radially oriented melilite laths about 500 micrometers long that occur at the inclusion rim. The core consists of blocky melilite grains 20-50 micrometers across and poikilitically enclosed in anhedral fassaite grains that are optically continuous over ~1 mm. Another unique feature of this inclusion is that melilite laths also extend from the core into the mantle. Fassaite in both the core and mantle is very rich in fine-grained (1-10 micrometer) spinel. The rim laths are normally zoned (Åk 30-70) inward from the rim of the inclusion with reverse zoning over the last ~200 micrometers to crystallize. A very wide range of melilite compositions is found in the core of the inclusion, where gehlenitic grains (Åk 5-12) occur. These grains are enclosed in strongly zoned (Åk 15-70) overgrowths. The gehlenitic cores and innermost parts of the overgrowths are Na2O-free, but the outer parts of the overgrowths are not. In the laths at the rim, Na2O decreases inward from the rim, then increases. Fassaite in the core has the same range of Ti contents as that in the mantle: 29 wt% TiO2 + Ti2O3. Two melting events are required to account for the features of this inclusion. In the first event, the precursor assemblage is heated to ~1400 degrees C and melts except for gehlenitic (Åk 5-12) melilite and some spinel. These grains become concentrated in the core. During cooling, Na2O-free melilite nucleates at the rim of the inclusion and on the relict grains in the core. After open system secondary alteration, the inclusion is heated again, but only to ~1260 degrees C. Melilite more gehlenitic than Åk40 does not melt. During cooling, Na2O-bearing melilite crystallizes as small, blocky grains and laths in the core and as overgrowths on relict grains in the core and at the rim. Eventually melilite co-crystallizes with fassaite, leading to the reverse zoning observed in the laths. The coexistence in this inclusion of Na-free and Na-bearing melilite, plus a positive correlation between Na2O and ååkermanite contents in melilite in an inclusion with a bulk Mg isotopic composition that is mass-fractionated in favor of the heavy isotopes, are both consistent with at least two melting events. Several other recently described coarse-grained inclusions also have features consistent with a sequence of early, high-temperature melting, secondary alteration, and remelting at a lower temperature, suggesting that remelting of refractory inclusions was a common occurrence in the solar nebula.

D'Orbigny is an exceptional angrite. Chemically, it resembles other angrites such as Asuka-881371, Sahara 99555, Lewis Cliff (LEW) 87051, and LEW 86010, but its structure and texture are peculiar. It has a compact and porous lithology, abundant glasses, augite-bearing druses, and chemical and mineralogical properties that are highly unusual for igneous rocks. Our previous studies led us to a new view on angrites: they can possibly be considered as CAIs that grew to larger sizes than the ones we know from carbonaceous chondrites. Thus, angrites may bear a record of rare and special conditions in some part of the early solar nebula. Here we report trace element contents of D'Orbigny phases. Trace element data were obtained from both the porous and the compact part of this meteorite. We have confronted our results with the popular igneous genetic model. According to this model, if all phases of D'Orbigny crystallized from the same system, as an igneous origin implies, a record of this genesis should be expressed in the distribution of trace elements among early and late phases. Our results show that the trace element distribution of the two contemporaneous phases olivine and plagioclase, which form the backbone of the rock, seem to require liquids of different composition. Abundances of highly incompatible elements in all olivines, including the megacrysts, indicate disequilibrium with the bulk rock and suggest liquids very rich in these elements (>10,000 x CI), which is much richer than any fractional crystallization could possibly produce. In addition, trace element contents of late phases are incompatible with formation from the bulk systems residual melt. These results add additional severe constraints to the many conflicts that existed previously between an igneous model for the origin of angrites and the mineralogical and chemical observations. This new trace element content data, reported here, corroborate our previous results based on the shape, structure, mineralogy, chemical, and isotopic data of the whole meteorite, as well as on a petrographic and chemical composition study of all types of glasses and give strength to a new genetic model that postulates that D'Orbigny (and possibly all angrites) could have formed in the solar nebula under changing redox conditions, more akin to chondritic constituents (e.g., CAIs) than to planetary differentiated rock.

We have carried out noble gas measurements on graphite from a large graphite-metal inclusion in Canyon Diablo. The Ne data of the low-temperature fractions lie on the mixing line between air and the spallogenic component, but those of high temperatures seem to lie on the mixing line between Ne-HL and the spallogenic component. The Ar isotope data indicate the presence of Q in addition to air, spallogenic component and Ar-HL. As the elemental concentration of Ne in Q is low, we could not detect the Ne-Q from the Ne data. On the other hand, we could not observe Xe-HL in our Xe data. As the Xe concentration and the Xe/Ne ratio in Q is much higher than that in the HL component, it is likely that only the contribution of Q is observed in the Xe data. Xenon isotopic data can be explained as a mixture of Q, air, and "El Taco Xe." The Canyon Diablo graphite contains both HL and Q, very much like carbonaceous chondrites, retaining the signatures of various primordial noble gas components. This indicates that the graphite was formed in a primitive nebular environment and was not heated to high, igneous temperatures. Furthermore, a large excess of 129Xe was observed, which indicates that the graphite was formed at a very early stage of the solar system when 129I was still present. The HL/Q ratios in the graphite in Canyon Diablo are lower than those in carbonaceous chondrites, indicating that some thermal metamorphism occurred on the former. We estimated the temperature of the thermal metamorphism to about 500-600 degrees C from the difference of thermal retentivities of HL and Q. It is also noted that El Taco Xe is commonly observed in many IAB iron meteorites, but its presence in carbonaceous chondrites has not yet been established.

We report on a new angrite, Northwest Africa (NWA) 1296, a fine-grained rock with a magmatic texture of rapid cooling. Dendritic olivine (Fo50) crystallized first in association with anorthite microcrysts (An98100) forming composite chains separated from one another by intergrown Al-Fe diopside-hedenbergite pyroxenes. In addition, some olivines with lower Mg# and increased CaO (up to 12%) are found between the chains as equant microphenocrysts. Pyroxenes and olivines are both normally zoned from Mg# = 0.52 to less than 0.01 in the rims. Ca-rich olivines are surrounded by, intergrown with, or replaced by subcalcic kirschsteinite. They appear after plagioclase crystallization stopped, at the end of the crystallization sequence. Minor phases are pyrrhotite, Fapatite, and titanomagnetite. Pyroxene is the last silicate phase to grow, interstitial to idiomorphic olivine-kirschsteinite. Numerous small vesicles and some channels are filled with microcristalline carbonate. The mode (vol%) is about 28% olivine, 3% kirschsteinite, 32% anorthite, 34% pyroxene, and 3% of the minor phases--close to that reported previously for D'Orbigny and Sahara (SAH) 99555. The bulk chemical composition of NWA 1296 is similar to D'Orbigny and SAH 99555; NWA 1296 differs by its texture and mineralogy, which are interpreted as resulting from rapid crystallization--an evidence of impact melting. Angrites cannot be produced by partial melting of a CV source because segregation of a "planetary" core is necessary to explain the low FeO/MgO ratio of magnesian olivines. Neither the odd Ca/Al ratio nor the very low SiO2 content can be explained by conventional partial melting scenarios. We suggest that carbonate is the key to angrite genesis. This is supported by the striking similarities with terrestrial melilitites (low SiO2, superchondritic Ca/Al ratio, presence of carbonate). The lack of alkalies could be the result of either loss after impact melting or absence of alkalies in the source.