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We report Li–Be–B and Al–Mg isotopic compositions of Ca-Al-rich inclusions (CAIs) in Sayh al Uhaymir 290 (CH) and Isheyevo (CH/CB) metal-rich carbonaceous chondrites. All CAIs studied here do not show resolvable excesses in 26Mg, a decay product of the short-lived radionuclide 26Al, which suggests their formation occurred prior to the injection of 26Al into the solar system from a nearby stellar source. The inferred initial 10Be/9Be ratios obtained for these CAIs range from 0.17 × 10−3 to 6.1 × 10−3, which tend to be much higher and more variable than those of CAIs in CV3 chondrites. The high 10Be/9Be ratios suggest that 10Be was most likely synthesized through solar cosmic-ray irradiation. The lithium isotopic compositions of these CAIs are nearly chondritic, independent of their initial 10Be/9Be ratios. This can be explained by the irradiation targets being of chondritic composition; in other words, targets were most likely not solid CAI themselves, but their precursors in solar composition. The larger variations in 10Be/9Be ratios observed in CH and CH/CB CAIs than in CV CAIs may reflect more variable cosmic-ray fluxes from the earlier, more active Sun at an earlier evolutionary stage (class 0-I) for the former, and a later, less active stage of the Sun (class II) for the latter. If this is the case, our new Be–B and Al–Mg data set implies that the earliest formed CAIs tend to be transported into the outer part of the solar protoplanetary disk, where the parent bodies of metal-rich chondrites likely accreted. [ABSTRACT FROM AUTHOR]

We report mineral assemblages from three clasts in the Northwest Africa 801 CR chondrite. The clasts, 1-3 mm in size, are ellipsoidal to irregular shaped, and show similar granular texture. The constituent minerals in the clasts are omphacite-rich clinopyroxene and pyrope-rich garnet, in addition to olivine and orthopyroxene. The omphacite contains jadeite (34 mol%) and diopside-hedenbergite (37%), and a significant amount of an enstatite-ferrosilite component (19%), which distinguishes it from terrestrial omphacite. The omphacite has a disordered C2/c structure. Graphite, phlogopite, chlorapatite, Fe-Ni metal, troilite, and pentlandite are present as minor minerals in the clasts. The minerals commonly found in chondrites, such as plagioclase and spinel group minerals, are not found in these clasts. Aluminum and sodium in the clasts are completely partitioned into omphacite and garnet. The mineral assemblages and compositions of the clasts are similar to those in terrestrial eclogite, except for the occurrence of olivine and some mineral chemistry, and this is the first discovery of an extraterrestrial eclogitic mineral assemblage. The clasts formed under high-pressure conditions, 2.8-4.2 GPa and 940-1080 °C, as estimated from a set of conventional geothermobarometers, indicative of formation in a large parent body. Another possibility is impact-induced origin, although the formation conditions would have been different from those for known shock veins. Meteorites usually consist of minerals that formed under low-pressure conditions, except for ultrahigh-pressure minerals found in shock veins. However, this study suggests that the pressure conditions for meteorite formation vary much wider than previously understood. [ABSTRACT FROM AUTHOR]

Abstract: We found a unique hibonite (CaAl12O19) inclusion Kz1–2 from the Kainsaz (CO3) chondrite, which exhibits evidence for a strong link between “normal” CAIs and FUN inclusions. Kz1–2 shows strongly fractionated isotopic compositions of O, Ca, and Ti preferring heavy isotopes and a characteristic REE abundance pattern similar to those of FUN (or HAL-type hibonite) inclusions, suggesting an intensive distillation process in the formation of this inclusion. Unlike FUN inclusions, however, Kz1–2 shows large excesses in 26Mg and possibly in 41K most likely from the decays of now-extinct nuclides 26Al and 41Ca with the inferred initial ratios of (26Al/27Al)0 ∼5.3×10−5 and (41Ca/40Ca)0 ∼1.1×10−8, respectively, and no detectable mass-independent isotopic anomalies in Ca and Ti, both of which are characteristic of “normal” CAIs. These observations suggest that the distillation process which produced isotopic fractionation in Kz1–2 occurred as early as the formation of “normal” CAIs. It is also inferred that the formation process of FUN inclusions is closely related to that of “normal” CAIs. [Copyright &y& Elsevier]

Focuses on excesses in olivine-rich inclusions in Yamato-86009 and Murchison chondrites. Their relation to calcium-aluminium-rich inclusions, most commonly observed in carbonaceous chondrite groups; Details of results of situ ion microprobe analyses of oxygen isotopes; Conclusion that oxygen isotopic anomalies were more extensive in the early solar system than was previously thought and that their origin may be attributed to a nebular chemical process.

We have performed in situ analyses of C and O isotopic compositions, trace element concentrations, and cathodoluminescence (CL) intensities on calcite in Murchison, a weakly altered CM chondrite. We found that the trace element (Mg, Mn, and Fe) concentrations are heterogeneous within single calcite grains. Grain to grain heterogeneity is even more pronounced. The analyzed calcite grains can be separated into two distinct types with respect to their C isotopic ratios, trace element concentrations, and CL characteristics: Calcite grains with higher δ 13 C PDB values (∼75‰) have low trace element concentrations and uniformly dark CL, while grains with lower δ 13 C values (∼35‰) have higher trace element concentrations and CL zoning. In contrast to the C isotopic ratios, O isotopic ratios are similar for both types of calcites (δ 18 O SMOW ∼ 34‰). The O isotopic ratios, trace element concentrations, and CL characteristics provide no evidence for C-isotope evolution in fluids from a single C reservoir by Rayleigh-type isotope fractionation (i.e., removal of C-bearing gaseous species). Also, it seems difficult to explain the O and C isotopic compositions of the two types of calcites by their formation at different temperatures from a single fluid. Instead, the δ 13 C variation suggests the presence of at least two C reservoirs with different isotopic ratios in the aqueous fluids from which the calcites precipitated. The C reservoirs with lower δ 13 C values are likely to be organic matter. The same holds for the C reservoirs with higher δ 13 C values which might have significant contributions from the 13 C-enriched grains identified in meteoritic insoluble organic matter. Thermodynamic calculations show that calcite with lower Fe concentrations formed under more reduced conditions than calcite with higher Fe concentrations. If this is the case, the 13 C-rich organic grains may have been destroyed and dissolved in the fluids under more reduced conditions than other organic components. The fact that the two types of calcites were found in different domains in the same thin section suggests that microenvironments with diverse physicochemical conditions such as redox states were present at scales of 100’s μm. [ABSTRACT FROM AUTHOR]