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Calcium–aluminum-rich inclusions (CAIs) are primitive objects that formed within the protoplanetary disk surrounding the young Sun. Recent Pb–Pb chronologic studies have demonstrated that CAIs are the oldest solar system solids, crystallizing 4567 Ma ago ( Amelin et al., 2002 , Connelly et al., 2012 ). The isotope systematics of CAIs therefore provide critical insight into the earliest history of the Solar System. Although Sm–Nd and Rb–Sr geochronometers are highly effective tools for investigating cosmochemical evolution in the early Solar System, previous studies of CAIs have revealed evidence for isotopically disturbed systems. Here we report new age data for Allende CAI Al3S4 derived from both the long-lived (147Sm–143Nd) and short-lived (146Sm–142Nd) isotopic systems. The 147Sm–143Nd chronometer yields an age of 4560 ± 34 Ma that is concordant with 207Pb–206Pb ages for CAIs and indicates that the Sm–Nd system was not significantly disturbed by secondary alteration or nucleosynthetic processes. The slope of the 146Sm–142Nd isochron defines the Solar System initial 146Sm/144Sm of 0.00828 ± 0.00044 . This value is significantly different from the value of 0.0094 determined by Kinoshita et al. (2012) . Ages recalculated from all published 146Sm–142Nd isochron data using the traditional 103 Ma half-life and the initial 146Sm/144Sm value determined here closely match Pb–Pb and 147Sm–143Nd ages determined on the same samples. In contrast, ages recalculated using the 68 Ma half-life determined by Kinoshita et al. (2012) and either of the initial 146Sm/144Sm values are often anomalously old. This is particularly true for the youngest samples with 146Sm–142Nd isochron ages that are most sensitive to the choice of 146Sm half-life used in the age calculation. In contrast to the Sm–Nd isotope system, the Rb–Sr system is affected by alteration but yields an apparent isochron with a slope corresponding to a much younger age of 4247 ± 110 Ma . Although the Rb–Sr system in CAIs appears to be disturbed, the initial 87Sr/86Sr value determined from the isochron is 0.698942 ± 0.000008 , and closely approximates estimates of the initial Solar System value. Although this isochron may be a mixing line, it might also record alteration on the Allende parent body in which Rb was added to the Al3S4 CAI that was initially largely devoid of Rb.

To identify the possible anomalous oxygen isotope signature in stratospheric water predicted by model studies, 25 water vapor samples were collected in 2003−2005 at Alert station, Canada (82°30′N), where there is downward transport of stratospheric air to the polar troposphere, and were analyzed for δ 17 O and δ 18 O relative to Chicago local precipitation (CLP). The latter was chosen as a reference because the relatively large evaporative moisture source should erase any possible oxygen isotope anomaly from the stratosphere. A mass-dependent fractionation coefficient for meteoric waters, λ MDF (H 2 O) = 0.529 ± 0.003 [2σ standard error (SE)], was determined from 27 CLP samples collected in 2003−2005. An oxygen isotopic anomaly of Δ 17 O = 76 ± 16 ppm (2σ SE) was found in water vapor samples from Alert relative to CLP. We propose that the positive oxygen isotope anomalies observed at Alert originated from stratospheric ozone, were transferred to water in the stratosphere, and subsequently mixed with tropospheric water at high latitudes as the stratospheric air descended into the troposphere. On the basis of this ground signal, the average Δ 17 O in stratospheric water vapor predicted by a steady-state box model is ∼40‰. Seven ice core samples (1930−1991) from Dasuopu glacier (Himalayas, China) and Standard Light Antarctic Precipitation did not show an obvious oxygen isotope anomaly, and Vienna Standard Mean Ocean Water exhibited a negative Δ 17 O relative to CLP. Six Alert snow samples collected in March 2011 and measured at Laboratoire des Sciences du Climat et de l'Environnement, Gif sur Yvette, France, had 17 O excess of 45 ± 5 ppm (2σ SE) relative to Vienna Standard Mean Ocean Water.

Dhofar (Dho) 225 and Dho 735 are carbonaceous chondrites found in a hot desert and having affinities to Belgica-like Antarctic chondrites (Belgica [B-] 7904 and Yamato [Y-] 86720). Texturally they resemble CM2 chondrites, but differ in mineralogy, bulk chemistry and oxygen isotopic compositions. The texture and main mineralogy of Dho 225 and Dho 735 are similar to the CM2 chondrites, but unlike CM2 chondrites they do not contain any (P, Cr)-sulfides, nor tochilinite 6Fe0.9S*5(Fe,Mg)(OH)2. H2O-contents of Dho 225 and Dho 735 (1.76 and 1.06 wt%) are lower than those of CM2 chondrites (2-18 wt%), but similar to those in the metamorphosed carbonaceous chondrites of the Belgica-like group. Bulk compositions of Dho 225 and Dho 735, as well as their matrices, have low Fe and S and low Fe/Si ratios relative to CM2 chondrites. X-ray powder diffraction patterns of the Dho 225 and Dho 735 matrices showed similarities to laboratory-heated Murchison CM2 chondrite and the transformation of serpentine to olivine. Dho 225 and 735's oxygen isotopic compositions are in the high 18O range on the oxygen diagram, close to the Belgica-like meteorites. This differs from the oxygen isotopic compositions of typical CM2 chondrites. Experimental results showed that the oxygen isotopic compositions of Dho 225 and Dhofar 725, could not be derived from those of typical CM2 chondrites via dehydration caused by thermal metamorphism. Dho 225 and Dho 735 may represent a group of chondrites whose primary material was different from typical CM2 chondrites and the Belgica-like meteorites, but they formed in an oxygen reservoir similar to that of the Belgica-like meteorites.

Synchrotron X-ray fluorescence was used in this study for the first time to measure trace element abundances in single presolar grains. The abundances of Zr and Nb were determined in SiC grains of the KJF size-separate. These grains are most likely from C-rich asymptotic giant branch stars (mainstream grains). Comparison of the data with s-process calculations suggests that the relatively short-lived isotope 93Zr (t 1/2 = 1.5 × 106 yr) condensed into the grains. The Nb/Zr ratios of the majority of the grains are higher than the s-process and CI chondrite ratios. This is probably due to grains condensing from stellar gas that was depleted in Zr, potentially because of earlier condensation of ZrC, but not depleted in Nb. However, grain contamination with solar system Nb is possible as well. Upper limits on the initial 93Zr/Zr ratios in the grains agree with the ratios observed in late-type S stars.

Due to exhaustion of the two primary calibration materials, Vienna Standard Mean Ocean Water (VSMOW) and Standard Light Antarctic Precipitation (SLAP), two replacement materials, VSMOW2 and SLAP2, were created with isotopic compositions as close as possible to the original standards in their D/H and 18O/16O ratios. Measurements of the δ17O composition constitute therefore an appropriate independent check of the achieved isotopic adjustment. Aliquots from ampoules of VSMOW, VSMOW2, SLAP, and SLAP2 were fluorinated by BrF5 and analyzed using a dual-inlet Delta E mass spectrometer. VSMOW2 and SLAP2 were found to be indistinguishable from VSMOW and SLAP, respectively, in their δ17O and δ18O values within measurement uncertainties. This result is a confirmation of the successful isotopic matching of VSMOW2 and SLAP2 to their predecessors. Further checks of the δ17O value of SLAP2 seem desirable. Copyright © 2010 John Wiley & Sons, Ltd.

Oxygen isotope and trace element data for 13 samples of the Kaidun chondritic breccia reaffirm the complex polymict nature of this unique meteorite. Bulk Kaidun samples most closely resemble CR chondrites, but the matrix is CI-like. Two separated clasts are CR-like but have some properties that resemble CM, two clasts are enstatite chondrites (one EL and one EH), one clast is an aubrite-like metal-rich impact melt, and one clast is a unique layered olivine-bearing pyroxenite with the isotopic composition of an aubrite. Yet, although each clast resembles a known meteorite group, all deviate in some respect from the norms for those groups. Collectively, Kaidun has sampled materials not yet represented in the world meteorite collections and which greatly extend the definitions of known meteorite groups. Phyllosilicates in Kaidun span a very wide range in composition and vary from clast to clast, suggesting that the aqueous alteration experienced by the clasts predated assembly of the Kaidun parent body.

Laboratory studies of vacuum dehydration of Mg-O-H units in minerals and rocks reveal large kinetic isotope effects in oxygen, with light-isotope enrichment in the liberated water, and concomitant heavy-isotope enrichment in the residual solids. Application of the same techniques to a meteorite assemblage including hydrous magnesium silicates shows a much more complex behavior, probably due to isotopic heterogeneity inherited from processes on the meteorite parent body. Measurements of both the 17 O/ 16 O variations and the 18 O/ 16 O variations confirm theoretical predictions that slopes of three-isotope correlation lines are systematically larger for equilibrium isotope effects than for kinetic isotope effects.

Kalahari 008 and 009 are two lunar meteorites that were found close to each other in Botswana. Kalahari 008 is a typical lunar anorthositic breccia; Kalahari 009 a monomict breccia with basaltic composition and mineralogy. Based on minor and trace elements Kalahari 009 is classified as VLT (very-low-Ti) mare basalt with extremely low contents of incompatible elements, including the REE. The Lu–Hf data define an age of 4286 ± 95 Ma indicating that Kalahari 009 is one of the oldest known basalt samples from the Moon. It provides evidence for lunar basalt volcanism prior to 4.1 Ga (pre-Nectarian) and may represent the first sample from a cryptomare. The very radiogenic initial 176Hf/177Hf (eHf = +12.9 ± 4.6), the low REE, Th and Ti concentrations indicate that Kalahari 009 formed from re-melting of mantle material that had undergone strong incompatible trace element depletion early in lunar history. This unusually depleted composition points toward a hitherto unsampled basalt source region for the lunar interior that may represent a new depleted endmember source for low-Ti mare basalt volcanism. Apparently, the Moon became chemically very heterogeneous at an early stage in its history and different cumulate sources are responsible for the diverse mare basalt types. Evidence that Kalahari 008 and 009 may be paired includes the similar fayalite content of their olivine, the identical initial Hf isotope composition, the exceptionally low exposure ages of both rocks and the fact that they were found close to each other. Since cryptomaria are covered by highland ejecta, it is possible that these rocks are from the boundary area, where basalt deposits are covered by highland ejecta. The concentrations of cosmogenic radionuclides and trapped noble gases are unusually low in both rocks, although Kalahari 008 contains slightly higher concentrations. A likely reason for this difference is that Kalahari 008 is a polymict breccia containing a briefly exposed regolith, while Kalahari 009 is a monomict brecciated rock that may never have been at the surface of the Moon. Altogether, the compositions of Kalahari 008 and 009 permit new insight into early lunar evolution, as both meteorites sample lunar reservoirs hitherto unsampled by spacecraft missions. The very low Th and REE content of Kalahari 009 as well as the depletion in Sm and the lack of a KREEP-like signature in Kalahari 008 point to a possible source far from the influence of the Procellarum-KREEP Terrane, possibly the lunar farside.

Bulk chemical and O-, Mg- and Si-isotopic compositions were measured for each of 17 Types A and B refractory inclusions from CV3 chondrites. After bulk chemical compositions were corrected for non-representative sampling in the laboratory, the Mg- and Si-isotopic compositions of each inclusion were used to calculate its original chemical composition assuming that the heavy-isotope enrichments of these elements are due to Rayleigh fractionation that accompanied their evaporation from CMAS liquids. The resulting pre-evaporation chemical compositions are consistent with those predicted by equilibrium thermodynamic calculations for high-temperature nebular condensates, but only if different inclusions condensed from nebular regions that ranged in total pressure from 10−6 to 10−1 bar, regardless of whether they formed in a system of solar composition or in one enriched in dust of ordinary chondrite composition relative to gas by a factor of 10 compared to solar composition. This is similar to the range of total pressures predicted by dynamic models of the solar nebula for regions whose temperatures are in the range of silicate condensation temperatures. Alternatively, if departure from equilibrium condensation and/or non-representative sampling of condensates in the nebula occurred, the inferred range of total pressure could be smaller. Simple kinetic modeling of evaporation successfully reproduces observed chemical compositions of most inclusions from their inferred pre-evaporation compositions, suggesting that closed-system isotopic exchange processes did not have a significant effect on their isotopic compositions. Comparison of pre-evaporation compositions with observed ones indicates that 80% of the enrichment in refractory CaO + Al2O3 relative to more volatile MgO + SiO2 is due to initial condensation and 20% due to subsequent evaporation for both Types A and B inclusions.

Recent models attempting to explain non-mass-dependent oxygen isotopic anomalies in meteorites and planets posit that they may have originated within the gas phase of the solar nebula, which suggests the potential for correlations of non-mass-dependent oxygen isotopic anomalies with other chemical fractionations generated during cooling and condensation of the nebula. We have examined three specific issues: possible correlations of Δ17O with (i) oxidation state; (ii) bulk chondrite chemistry; and (iii) bulk planetary properties. Isolated grains and chondrules from several carbonaceous chondrite groups exhibit good to weak positive correlations between Δ17O and olivine fayalite content, and whole rock ureilite samples show a positive correlation of Δ17O with olivine fayalite content. These are consistent with oxidation of Fe metal by 17O-, 18O-enriched oxygen in the precursor materials that formed these objects. In contrast, oxygen isotopic and major element compositions of ferromagnesian phases in ordinary chondrite chondrules, and in bulk chondrites do not show a correlation. Thus, there is no compelling evidence that oxidation of nebular materials was tightly linked to gas species carrying anomalous O. Using average chondrite group compositions, we demonstrate that significant negative correlations of refractory lithophile element/Mg and refractory siderophile element/Ni with Δ17O exist. Refractory inclusions (CAIs and AOAs) are modally rare in many chondrite types that exhibit substantial range in Δ17O. Thus, the refractory component in these chondrites must occur in a crypto-component, e.g. material dissolved in chondrule melts during chondrule formation. Significant positive correlations of moderately volatile elements/Mg with Δ17O are not simply explained by incomplete mixing of 16O-enriched refractory grains, but are broadly consistent with nebula-based mechanisms of non-mass-dependent oxygen isotope fractionation. The estimated compositions of the primitive mantles of the Earth, Mars and 4 Vesta have some compositional, redox and isotopic properties that vary with heliocentric distance. However, Δ17O does not vary monotonically in this sequence, indicating a decoupling of planetary O isotopic composition from other compositional characteristics.

The first suggestion for the use of oxygen isotopes in cosmochemistry was that of H. C. Urey and colleagues in 1934, but appropriate instrumentation had not yet been developed. The modern era of oxygen isotope cosmochemistry began with the study of Apollo lunar samples in 1969 and of Allende refractory inclusions in 1973. The large (>5%) variations in 17O/16O and 18O/16O ratios, and small variations in 17O/18O were first interpreted as nucleosynthetic effects, but are now recognized to be the result of chemical processes early in Solar System history. Thus oxygen isotopes provide natural tracers for processes of formation of solid bodies in the inner Solar System. In particular, oxygen isotopes are very useful in recognizing genetic associations among meteorite groups. They also have been valuable in the study of parent body processes, such as metamorphism and aqueous alteration. There is conjecture that the ultimate cause of the oxygen isotope effects may be isotope-selective photodissociation of CO, which will be tested by isotopic measurement of solar oxygen and nitrogen collected in the NASA Genesis mission.

We measured nickel isotopes via multicollector inductively coupled plasma mass spectrometry (MC-ICPMS) in the bulk metal from 36 meteorites, including chondrites, pallasites, and irons (magmatic and non-magmatic). The Ni isotopes in these meteorites are mass fractionated; the fractionation spans an overall range of ≈0.4 amu^(-1). The ranges of Ni isotopic compositions (relative to the SRM 986 Ni isotopic standard) in metal from iron meteorites (≈0.0 to ≈0.3 amu^(-1)) and chondrites (≈0.0 to ≈0.2 amu^(-1)) are similar, whereas the range in pallasite metal (≈-0.1 to 0.0 amu^(-1)) appears distinct. The fractionation of Ni isotopes within a suite of fourteen IIIAB irons (≈0.0 to ≈0.3 amu^(-1)) spans the entire range measured in all magmatic irons. However, the degree of Ni isotopic fractionation in these samples does not correlate with their Ni content, suggesting that core crystallization did not fractionate Ni isotopes in a systematic way. We also measured the Ni and Fe isotopes in adjacent kamacite and taenite from the Toluca IAB iron meteorite. Nickel isotopes show clearly resolvable fractionation between these two phases; kamacite is heavier relative to taenite by ≈0.4 amu^(-1). In contrast, the Fe isotopes do not show a resolvable fractionation between kamacite and taenite. The observed isotopic compositions of kamacite and taenite can be understood in terms of kinetic fractionation due to diffusion of Ni during cooling of the Fe-Ni alloy and the development of the Widmansttten pattern.

We have critically reevaluated equilibrium iron isotope fractionation factors for oxide and sulfide minerals using recently acquired data obtained by Mossbauer spectroscopy and inelastic nuclear resonant X-ray scattering (INRXS) synchrotron radiation. Good agreement was observed in the iron b-factors of metallic iron (a-Fe) and hematite calculated using both Mossbauer- and INRXS-derived data, which supports the validity and reliability of the calculations. Based on this excellent agreement, we suggest the use of the present data on the iron b-factors of hematite as a reference. The previous Mossbauer-derived iron b-factor for magnetite has been modified significantly based on the Fe-sublattice density of states obtained from the INRXS experiments. This resolves the disagreement between naturally observed iron iso- tope fractionation factors for mineral pairs involving magnetite and those obtained from the calculated b-factors. The cor- rectness of iron b-factor for pyrite has been corroborated by the good agreement with experimental data of sulfur isotope geothermometers of pyrite-galena and pyrite-sphalerite. A good correlation between the potential energy of the cation site, the oxidation state of iron and the iron b-factor value has been established. Specifically, ferric compounds, which have a high- er potential energy of iron than ferrous compounds, have higher b-factors. A similar dependence of b-factors on the oxidation state and potential energy could be extended to other transition metals. Extremely low values of INRXS-derived iron b-fac- tors for troilite and Fe3S significantly widen the range of iron b-factors for covalently bonded compounds. � 2007 Elsevier Ltd. All rights reserved.

Experimental and theoretical aspects of oxygen isotope fractionation in the system calcite–water at low temperatures were critically examined. Contrary to the claim made by Zhou and Zheng [Zhou G.-T., and Zheng Y.-F. (2003) An experimental study of oxygen isotope fractionation between inorganically precipitated aragonite and water at low temperatures. Geochim. Cosmochim. Acta 67 , 387–399], there is excellent agreement between fractionation factors that were experimentally determined by means of slow, inorganic precipitation of calcite from solutions and those obtained largely from theoretical, statistical–mechanical calculations of the reduced partition function ratios. This agreement strongly suggests that calcite was precipitated from a solution very close to isotopic equilibrium. However, recently Zhou and Zheng [Zhou G.-T., and Zheng Y.-F. (2005) Effect of polymorphic transition on oxygen isotope fractionation between aragonite, calcite and water: a low-temperature experimental study. Am. Miner. 90 , 1121–1130] presented, without any explanation, conclusions on these major aspects that contradict the previous statements of Zhou and Zheng (2003). The apparent discrepancy in calcite–water oxygen isotope fractionation between experimental and theoretical studies discussed by Zhou and Zheng (2003) originates from the “mineral–water interaction” term in the modified increment method, which was developed by one of the authors (Y.-F. Zheng). We call for evidence for the theoretical nature of the modified increment method, which has never been presented in any of Zheng’s papers. Without such evidence, great caution must be exercised in using fractionation factors derived from the modified increment method.

Isotopic compositions of up to three elements (Mo, Zr, Ba) were measured on 55 presolar SiC grains from the Murchison meteorite, allowing identification of grains potentially contaminated with solar system material. The range of compositions of uncontaminated grains may constrain the amount of 13C produced in parent AGB stars to a narrow range around the amount required to explain solar system s-process abundances.

A method of determination of the reduced isotopic partition function ratio (β-factor) from the partial density of state (PDOS) obtained by inelastic nuclear resonant X-ray scattering (INRXS) in synchrotron radiation experiments has been established. The method has been demonstrated by the example of tin isotopes. The tin β-factors for CaSnO3, SnO2, SnO have been computed from the INRXS-derived PDOSs. ln ⁡ β Sn 122 / 116 = ( 0.390 ± 0.0076 ) x − ( 0.00160 ± 0.0000242 ) x 2 + ( 1.099 ± 0.0573 ) ⋅ 10 − 5 x 3 ) for SnO ln ⁡ β Sn 122 / 116 = ( 0.771 ± 0.0150 ) x − ( 0.00392 ± 0.000061 ) x 2 + ( 3.548 ± 0.287 ) ⋅ 10 − 5 x 3 for SnO 2 ln ⁡ β Sn 122 / 116 = ( 0.776 ± 0.0157 ) x − ( 0.00334 ± 0.000064 ) x 2 + ( 2.561 ± 0.157 ) ⋅ 10 − 5 x 3 for CaSnO 3 Equilibrium 122/116Sn isotope fractionation between di- and tetravalent tin compounds is about 0.4‰ at 1000 K and about 4.1‰ at room temperature and can be measured by modern multicollector inductively-coupled plasma mass-spectrometers. Tin β-factors reveal dependence on oxidation state previously detected for iron isotopes. A comparison of the tin β-factors for SnO2 obtained on the basis of the INRXS-derived PDOS with those obtained by the Mossbauer spectroscopy method shows that both methods give similar results, but application of synchrotron radiation provides more accurate and reliable data. Equilibrium stable isotope fractionation of transition metals between different oxidation state compounds is not negligible even for elements as heavy as tin.

Direct oxygen isotope fractionation between cassiterite and calcite has been investigated experimentally at 15 kbar with temperature ranging from 800 to 1000°C. Combined with the quartz-calcite fractionation measured with the same technique ( Clayton et al., 1989 ), the calcite-cassiterite and quartz-cassiterite oxygen isotope fractionations can be expressed as: Δ CaCO 3 − SnO 2 = 4.14 × 10 6 T − 2 Δ SiO 2 − SnO 2 = 4.52 × 10 6 T − 2 at temperatures higher than 600°C. These calibrations are in good agreement with those obtained from heat capacity and X-ray resonant data. The theory of using X-ray resonant data to calculate the reduced partition function ratios of transition elements that have at least one Mossbauer-sensitive isotope is evaluated with the current experimental result.

Oxygen isotope equilibrium fractionation constants (β18O-factors) of cassiterite were evaluated on the basis of heat capacity and X-ray resonant (Mossbauer spectroscopy and X-ray inelastic scattering) data. The low-temperature heat capacity of cassiterite was measured in the range from 13 to 340 K using an adiabatic calorimeter. Results of measurements of two samples agree very closely but deviate more than 5% from previous heat capacity data used for calculation of thermodynamic functions. The temperature dependence of heat capacity was treated using the modern version of the Thirring expansion, and the appropriate temperature dependence of the vibrational kinetic energy was found. Measurements of temperature-dependent Mossbauer parameters of cassiterite were conducted in the range from 300 to 900 K. The attempt to describe Mossbauer fraction and the second order Doppler (SOD) shift on the basis of the Debye model failed. The first term of the Thirring expansion of the Mossbauer SOD shift agrees with that calculated from the Sn sublattice vibration density of states (VDOS) obtained via synchrotron X-ray scattering. Based on this agreement we calculated the kinetic energy of the cassiterite Sn sublattice from VDOS. From the kinetic energy of the total cassiterite crystalline lattice and its Sn sublattice, β18O-factors of cassiterite were computed in the temperature range 300–1500 K by the method of Polyakov and Mineev (2000). Appropriate polynomials, which are valid at temperatures above 400 K, are the following: 103ln⁡βSnO2=(7.176±0.252)x − (0.07369±0.00089)x2 +(0.0008026±0.0001022)x3, x = 106/T2;103ln⁡αCaCO3−SnO2=4.607x − 0.3463x2 + 0.01500x3, x = 106/T2;103ln⁡αSiO2−SnO2=4.942x − 0.2963x2 + 0.01150x3, x = 106/T2. The evaluated cassiterite isotope fractionation factors are significantly different from those obtained by synthesis, increment and empirical methods. To resolve the differences, laboratory direct exchange experiments are needed.

The heat capacity of tin dioxide was measured at low temperatures by the adiabatic calorimeter technique. The measurements were conducted for two samples of tin dioxide. The discrepancy between two sets of the measurements does not exceed experimental error. However, a large disagreement (more than 5%) was observed between this study and data previously used for thermodynamic calculations. Using non-linear least-square method (LSM), the equation approximating and smoothing experimental data was derived. Thermodynamic functions at 298.15 K (heat capacity, entropy and enthalpy increment) values calculated from experimental data are as follows: C p, m 0 =55.24±0.03 J mol −1 K −1 , Δ 0 298 S m 0 =51.82±0.07 J mol −1 K −1 , Δ 0 298 H m 0 =8.806±0.005 kJ mol −1 . These values of the thermodynamic functions are about 5% larger than those used in reference books elsewhere.

On the night of March 26, 2003, a large meteorite broke up and fell upon the south suburbs of Chicago. The name Park Forest, for the village that is at the center of the strewnfield, has been approved by the nomenclature committee of the Meteoritical Society. Satellite data indicate that the bolide traveled from the southwest toward the northeast. The strewnfield has a southeast-northwest trend; however, this is probably due to the effects of strong westerly winds at high altitudes. Its very low 56Co and very high 60Co activities indicate that Park Forest had a preatmospheric mass that was at least ~900 kg and could have been as large as ~7 x 10^3 kg, of which only ~30 kg have been recovered. The average compositions of olivine and low-Ca pyroxene, Fa24.7 ± 1.1 and Fs20.8 ± 0.7, respectively, and its bulk oxygen isotopic composition, δ18O = +4.68‰, δ17O = +3.44‰, show that Park Forest is an L chondrite. The ferromagnesian minerals are well equilibrated, chondrules are easily recognized, and maskelynite is mostly ≤50 μm across. Based on these observations, we classify Park Forest as type 5. The meteorite has been strongly shocked, and based on the presence of maskelynite, mosaicism and planar deformation features in olivine, undulatory extinction in pyroxene, and glassy veins, the shock stage is S5. The meteorite is a monomict breccia, consisting of light-colored, angular to rounded clasts in a very dark host. The light and dark lithologies have essentially identical mineral and oxygen isotopic compositions. Their striking difference in appearance is due to the presence of a fine, pervasive network of sulfide veins in the dark lithology, resulting in very short optical path lengths. The dark lithology probably formed from the light lithology in an impact that formed a sulfide-rich melt and injected it into cracks.

D'Orbigny is the sixth and by far the largest angrite known. Its bulk chemical and mineral chemical compositions, rare gas abundances and oxygen and rare gas isotope compositions fit the composi- tional ranges known from other angrites. It is, however, peculiar with respect to three features: the abundance of hollow shells, the presence of abundant open druses and the abundant presence of glasses. The shape, structure and texture of D'Orbigny and its mineral and bulk chemical compositions indicate an unusual genesis under changing redox conditions. In our view, data and observations are incompatible with an igneous origin of this rock but are suggestive of a complex growth and metasomatism scenario. The sequence of events apparently began with the formation of spheres of a phase which later vanished and therefore is unknown but could have been CaS. On top of these spheres (sizes from 1-30 mm) olivine-anorthite intergrowths precipitated forming compact shells and fluffy protrusions. Aggregation of these objects plus occasional large plates made of the same intergrowths led to formation of a highly porous object with abundant large open space between the olivine-anorthite intergrowths. The aggregate also included previously formed olivines, olivinite rocks and Al-spinels. The latter carry highly porous decomposition rims of Cr-enriched Al-spinel and record mildly oxidizing conditions prevailing very early in D'Orbigny's history. Conditions changed (with falling T?) and became oxidizing causing the phase(s) that constituted the spheres to become unstable. Their breakdown liberated large amounts of Ca and trace elements which at least in part re-precipitated by reacting with Si and Mg from the vapor to form augites that grew into the open space thus forming augite druses. Also, some of the preexisting olivine was converted into augite, which is very rich in refractory lithophile trace elements (abundances 10 CI). Augites grew mainly under oxidizing conditions leading to atomic Fe/(FeMg) ratios of about 0.44. Finally, conditions became highly oxidizing and strongly mobilized Ca from a source that apparently became unstable. The high partial pressures of Ca and Fe (and also Ti) led to precipitation of Ca-olivine and kirschsteinite (Fo1La20 and Fo1La33, respectively) and of titaniferous aluminous hedenbergite—atomic Fe/(FeMg) 0.97. Ulvospinel and sulfides were also precip- itated. Because the original phase(s) forming the early spheres vanished during these oxidizing events, the shells remained empty. In this scenario, D'Orbigny provides us with a record of changing conditions ranging from extremely reducing to highly oxidizing and with a record of the formation of an achondritic rock from a chondritic source. Angrites bear many similarities with CAIs, texturally, mineralogically and chemically. Possibly, they can be seen as CAIs, which grew larger 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. They reproduce most of the textures and structures of CAIs: crystallized liquids (Asuka 881371, LEW 87051), metasomatic granoblastic rocks (LEW 86010, Angra dos Reis?) and aggregates (D'Orbigny). In addition, all angrites record metasomatic alterations, subsolidus processing after formation, also similar to what is recorded by most CAIs. Obviously, they missed the alkali metasomatic event recorded by many CAIs but they record a siderophile— lithophile element separation event that is not recorded by CAIs. Copyright © 2004 Elsevier Ltd

The influence of NaCl, CaCl2, and dissolved minerals on the oxygen isotope fractionation in mineral-water systems at high pressure and high temperature was studied experimentally. The salt effects of NaCl (up to 37 molal) and 5-molal CaCl2 on the oxygen isotope fractionation between quartz and water and between calcite and water were measured at 5 and 15 kbar at temperatures from 300 to 750°C. CaCl2 has a larger influence than NaCl on the isotopic fractionation between quartz and water. Although NaCl systematically changes the isotopic fractionation between quartz and water, it has no influence on the isotopic fractionation between calcite and water. This difference in the apparent oxygen isotope salt effects of NaCl must relate to the use of different minerals as reference phases. The term oxygen isotope salt effect is expanded here to encompass the effects of dissolved minerals on the fractionations between minerals and aqueous fluids. The oxygen isotope salt effects of dissolved quartz, calcite, and phlogopite at 15 kbar and 750°C were measured in the three-phase systems quartz-calcite-water and phlogopite-calcite-water. Under these conditions, the oxygen isotope salt effects of the three dissolved minerals range from ∼0.7 to 2.1‰. In both three-phase hydrothermal systems, the equilibrium fractionation factors between the pairs of minerals are the same as those obtained by anhydrous direct exchange between each pair of minerals, proving that the use of carbonate as exchange medium provides correct isotopic fractionations for a mineral pair. When the oxygen isotope salt effects of two minerals are different, the use of water as an indirect exchange medium will give erroneous fractionations between the two minerals. The isotope salt effect of a dissolved mineral is also the main reason for the observation that the experimentally calibrated oxygen isotope fractionations between a mineral and water are systematically 1.5 to 2‰ more positive than the results of theoretical calculations. Dissolved minerals greatly affect the isotopic fractionation in mineral-water systems at high pressure and high temperature. If the presence of a solute changes the solubility of a mineral, the real oxygen isotope salt effect of the solute at high pressure and high temperature cannot be correctly derived by using the mineral as reference phase.

Gujba is a coarse-grained meteorite fall composed of 41 vol% large kamacite globules, 20 vol% large light-colored silicate globules with cryptocrystalline, barred pyroxene and barred olivine textures, 39 vol% dark-colored, silicate-rich matrix, and rare refractory inclusions. Gujba resembles Bencubbin and Weatherford in texture, oxygen-isotopic composition and in having high bulk delta N-15 values (approximately +685%0). The He-3 cosmic-ray exposure age of Gujba (26 +/- 7 Ma) is essentially identical to that of Bencubbin, suggesting that they were both reduced to meter-size fragments in the same parent-body collision. The Gujba metal globules exhibit metal-troilite quench textures and vary in their abundances of troilite and volatile siderophile elements. We suggest that the metal globules formed as liquid droplets either via condensation in an impact-generated vapor plume or by evaporation of preexisting metal particles in a plume. The lower the abundance of volatile elements in the metal globules, the higher the globule quench temperature. We infer that the large silicate globules also formed from completely molten droplets; their low volatile-element abundances indicate that they also formed at high temperatures, probably by processes analogous to those that formed the metal globules. The coarse-grained Bencubbin-Weatherford-Gujba meteorites may represent a depositional component from the vapor cloud enriched in coarse and dense particles. A second class of Bencubbin-like meteorites (represented by Hammadah a1 Hamra 237 and QUE 94411) may be a finer fraction derived from the same vapor cloud

Barium isotopic compositions of single 2.3–5.3 μm presolar SiC grains from the Murchison meteorite were measured by resonant ionization mass spectrometry. Mainstream SiC grains are enriched in s-process barium and show a spread in isotopic composition from solar to dominantly s-process. In the relatively coarse grain size fraction analyzed, there are large grain-to-grain variations of barium isotopic composition. Comparison of single grain data with models of nucleosynthesis in asymptotic giant branch (AGB) stars indicates that the grains most likely come from low mass carbon-rich AGB stars (1.5 to 3 solar masses) of about solar metallicity and with approximately solar initial proportions of r- and s-process isotopes. Measurements of single grains imply a wide variety of neutron-to-seed ratios, in agreement with previous measurements of strontium, zirconium and molybdenum isotopic compositions of single presolar SiC grains.

The meteorite Northwest Africa 773 (NWA 773) is a lunar sample with implications for the evolution of mafic magmas on the moon. A combination of key parameters including whole-rock oxygen isotopic composition, Fe/Mn ratios in mafic silicates, noble gas concentrations, a KREEP-like rare earth element pattern, and the presence of regolith agglutinate fragments indicate a lunar origin for NWA 773. Partial maskelynitization of feldspar and occasional twinning of pyroxene are attributed to shock deformation. Terrestrial weathering has caused fracturing and precipitation of Carich carbonates and sulfates in the fractures, but lunar minerals appear fresh and unoxidized. The meteorite is composed of two distinct lithologies: a two-pyroxene olivine gabbro with cumulate texture, and a polymict, fragmental regolith breccia. The olivine gabbro is dominated by cumulate olivine with pigeonite, augite, and interstitial plagioclase feldspar. The breccia consists of several types of clasts but is dominated by clasts from the gabbro and more FeO-rich derivatives. Variations in clast mineral assemblage and pyroxene Mg/(Mg + Fe) and Ti/(Ti + Cr) record an igneous Fe-enrichment trend that culminated in crystallization of fayalite + silica + hedenbergitebearing symplectites. The Fe-enrichment trend and cumulate textures observed in NWA 773 are similar to features of terrestrial ponded lava flows and shallow-level mafic intrusives, indicating that NWA 773 may be from a layered mafic intrusion or a thick, differentiated lava flow. NWA 773 and several other mafic lunar meteorites have LREE-enriched patters distinct from Apollo and Luna mare basalts, which tend to be LREE-depleted. This is somewhat surprising in light of remote sensing data that indicates that the Apollo and Luna missions sampled a portion of the moon that was enriched in incompatible heatproducing elements.

Variations in the isotopic ratios of volatile elements in different reservoirs on the terrestrial planets carry information about processes that operated on the planets since their formation. Comparisons between primordial planetary compositions, to the extent they can be determined, may help us understand the planetary formation process. This working group report summarizes our knowledge of terrestrial planet volatile inventories.

The oxygen three-isotope system has major advantages over the two-isotope systems of hydrogen, carbon, and nitrogen because different fractionation laws govern intraplanetary and interplanetary processes. This permits discriminating between solar nebular processes and parent-body processes. Oxygen isotopes also serve as a sensitive natural tracer for meteorite classification.

In this paper we report petrological and chemical data of the unusual chondritic meteorites Yamato (Y)-792947, Y-93408 and Y-82038. The three meteorites are very similar in texture and chemical composition, suggesting that they are pieces of a single fall. The whole-rock oxygen isotopes and the chemical compositions are indicative ofH chondrites. In addition, the mineralogy, and the abundances of chondrule types, opaque minerals and matrices suggest that these meteorites are H3 chondrites. They were hardly affected by thermal and shock metamorphism. The degree of weathering is very low. We conclude that these are the most primitive H chondrites, H3.2-3.4 (SI), known to date. On the other hand, these chondrites contain extraordinarily high amounts of refractory inclusions, intermediate between those of ordinary and carbonaceous chondrites. The distribution of the inclusions may have been highly heterogeneous in the primitive solar nebula. The mineralogy, chemistry and oxygen isotopic compositions of inclusions studied here are similar to those in CO and E chondrites.

Dhofar 019 is a new martian meteorite found in the desert of Oman. In texture, mineralogy, and major and trace element chemistry, this meteorite is classified as a basaltic shergottite. Olivine megacrysts are set within a groundmass composed of finer grained olivine, pyroxene (pigeonite and augite), and maskelynite. Minor phases are chromite-ulvospinel, ilmenite, silica, K-rich feldspar, merrillite, chlorapatite, and pyrrhotite. Secondary phases of terrestrial origin include calcite, gypsum, celestite, Fe hydroxides, and smectite. Dhofar 019 is most similar to the Elephant Moraine (EETA) 79001 lithology A and Dar al Gani (DaG) 476/489 shergottites. The main features that distinguish Dhofar 019 from other shergottites are lack of orthopyroxene; lower Ni contents of olivine; the heaviest oxygen-isotopic bulk composition; and larger compositional ranges for olivine, maskelynite, and spinel, as well as a wide range for pyroxenes. The large compositional ranges of the minerals are indicative of relatively rapid crystallization. Modeling of olivine chemical zonations yield minimum cooling rates of 0.5-0.8 °C/h. Spinel chemistry suggests that crystallization took place under one of the most reduced conditions for martian meteorites, at an f O2 3 log units below the quartz-fayalite-magnetite (QFM) buffer. The olivine megacrysts are heterogeneously distributed in the rock. Crystal size distribution analysis suggests that they constitute a population formed under steady-state conditions of nucleation and growth, although a few grains may be cumulates. The parent melt is thought to have been derived from partial melting of a light rare earth element- and platinum group element-depleted mantle source. Shergottites, EETA79001 lithology A, DaG 476/489, and Dhofar 019, although of different ages, comprise a particular type of martian rocks. Such rocks could have formed from chemically similar source(s) and parent melt(s), with their bulk compositions affected by olivine accumulation.

Mineralogy, major element compositions of minerals, and elemental and oxygen isotopic compositions of the whole rock attest to a lunar origin of the meteorite Northwest Africa 032 (NWA 032), an unbrecciated basalt found in October 1999. The rock consists predominantly of olivine, pyroxene and chromite phenocrysts, set in a crystalline groundmass of feldspar, pyroxene, ilmenite, troilite and trace metal. Whole-rock shock veins comprise a minor, but ubiquitous portion of the rock. Undulatory to mosaic extinction in olivine and pyroxene phenocrysts and micro-faults in groundmass and phenocrysts also are attributed to shock. Several geochemical signatures taken together indicate unambiguously that NWA 032 originated from the Moon. The most diagnostic criteria include whole-rock oxygen isotopic composition and ratios of Fe:Mn in the whole rock, olivine, and pyroxene. A lunar origin is documented further by the presence of Fe-metal, troilite, and ilmenite; zoning to extremely Fe-rich compositions in pyroxene; the ferrous oxidation state of all Fe in pyroxene; and the rare-earth element pattern with a well-defined negative europium anomaly. This rock is similar in major element chemistry to basalts from Apollo 12 and 15, but is enriched in light rare-earth elements and has an unusually high Th/Sm ratio. Some Apollo 14 basalts yield a closer match to NWA 032 in rare-earth element patterns, but have higher concentrations of Al2O3. Ar-Ar step release results are complex, but yield a whole-rock age of ca. 2.8 Ga, suggesting that NWA 032 was extruded at 2.8 Ga or earlier. This rock may be the youngest sample of mare basalt collected to date. Noble gas concentrations combined with previously collected radionuclide data indicate that the meteorite exposure history is distinct from currently recognized lunar meteorites. In short, the geochemical and petrographic features of NWA 032 are not matched by Apollo or Luna samples, nor by previously identified lunar meteorites, indicating that it originates from a previously unsampled mare deposit. Detailed assessment of petrographic features, olivine zoning, and thermodynamic modelling indicate a relatively simple cooling and crystallization history for NWA 032. Chromite-spinel, olivine, and pyroxene crystallized as phenocrysts while the magma cooled no faster than 2 °C/hr based on the polyhedral morphology of olivine. Comparison of olivine size with crystal growth rates and preserved Fe-Mg diffusion profiles in olivine phenocrysts suggest that olivine was immersed in the melt for no more than 40 days. Plumose textures in groundmass pyroxene, feldspar, and ilmenite, and Fe-rich rims on the phenocrysts formed during rapid crystallization (cooling rates ~ 20 to 60 °C/hr) after eruption.

A new grouplet of primitive, metal-rich chondrites, here called the CB (C, carbonaceous; B, bencubbinite) chondrites, has been recognized. It includes Bencubbin, Weatherford, Hammadah a1 Hamra (HH) 237 and Queen Alexandra Range (QUE) 94411, paired with QUE 94627. Their mineral compositions, as well as their oxygen and nitrogen isotopic compositions, indicate that they are closely related to the CR and CH chondrites, all of which are members of the more inclusive CR clan. CB chondrites have much greater metal/silicate ratios than any other chondrite group, widely increasing the range of metal/silicate fractionation recorded in solar nebular processes. They also have the greatest moderately volatile lithophile element depletions of any chondritic materials. Metal has compositional trends and zoning patterns that suggest a primitive condensation origin, in contrast with metal from other chondrite groups. CB chondrites, as well as other CR clan chondrites, have much heavier nitrogen (higher 15N/14N) than that in other chondrite groups. The primitive characteristics of the CB chondrites suggest that they contain one of the best records of early nebular processes. Another chondrite, Grosvenor Mountains 9555 1, is petrographically similar to the CB chondrites, but its mineral and oxygen and nitrogen isotope compositions indicate that it formed from a different nebular reservoir.

A synthetic material with solar elemental proportions of iron, magnesium, silicon, titanium, calcium, and aluminum oxides and doped with rare earth elements was evaporated in a vacuum furnace at 1800 and 2000°C for different durations to study its chemical and isotopic evolution during the evaporation process. It is demonstrated that kinetic evaporation of solar composition material can produce residues of calcium-, aluminum-rich inclusion bulk chemistry. The evaporation sequence of the main constituents in this solar composition material is iron > silicon ≈ magnesium > titanium. Calcium and aluminum remain unevaporated after evaporation of 95% of the solar composition material. The chemical fractionation between the gas and condensed phase is a function not only of temperature and pressure, but also of the bulk chemical composition of the condensed phase. During the evaporation process, cerium is almost as volatile as iron. The 2,000-fold cerium depletion found in some refractory inclusions in carbonaceous chondrites was reproduced in the evaporation experiment and can be readily explained as a result of evaporation of preexisting meteoritic material. Kinetic isotopic fractionation of magnesium, oxygen, and silicon follows the Rayleigh distillation law during the laboratory evaporation of synthetic solar composition material. This implies that the residue is well mixed during the evaporation process and that the evaporation kinetic processes (both chemical and isotopic) are surface reaction-controlled. The isotopic mass fractionation factors are lower than those predicted from theoretical calculations by using the square root of mass ratios of likely evaporating species. Thus, the surface reaction is more complicated than decomposition into single gas species of each element.

Information about the composition of volatiles in the Martian atmosphere and interior derives from Viking spacecraft and ground-based measurements, and especially from measurements of volatiles trapped in Martian meteorites, which contain several distinct components. One volatile component, found in impact glass in some shergottites, gives the most precise measurement to date of the composition of Martian atmospheric Ar, Kr, and Xe, and also contains significant amounts of atmospheric nitrogen showing elevated 15N/14N. Compared to Viking analyses, the 36Ar/132Xe and 84Kr/132Xe elemental ratios are larger in shergottites, the 129Xe/132Xe ratio is similar, and the 40Ar/36Ar and 36Ar/38Ar ratios are smaller. The isotopic composition of atmospheric Kr is very similar to solar Kr, whereas the isotopes of atmospheric Xe have been strongly mass fractionated in favor of heavier isotopes. The nakhlites and ALH84001 contain an atmospheric component elementally fractionated relative to the recent atmospheric component observed in shergottites. Several Martian meteorites also contain one or more Martian interior components that do not show the mass fractionation observed in atmospheric noble gases and nitrogen. The D/H ratio in the atmosphere is strongly mass fractionated, but meteorites contain a distinct Martian interior hydrogen component. The isotopic composition of Martian atmospheric carbon and oxygen have not been precisely measured, but these elements in meteorites appear to show much less variation in isotopic composition, presumably in part because of buffering of the atmospheric component by larger condensed reservoirs. However, differences in the oxygen isotopic composition between meteorite silicate minerals (on the one hand) and water and carbonates indicate a lack of recycling of these volatiles through the interior. Many models have been presented to explain the observed isotopic fractionation in Martian atmospheric N, H, and noble gases in terms of partial loss of the planetary atmosphere, either very early in Martian history, or over extended geological time. The number of variables in these models is large, and we cannot be certain of their detailed applicability. Evolutionary data based on the radiogenic isotopes (i.e., 40Ar/36Ar, 129Xe/132Xe, and 136Xe/132Xe ratios) are potentially important, but meteorite data do not yet permit their use in detailed chronologies. The sources of Mars’ original volatiles are not well defined. Some Martian components require a solar-like isotopic composition, whereas volatiles other than the noble gases (C, N, and H2O) may have been largely contributed by a carbonaceous (or cometary) veneer late in planet formation. Also, carbonaceous material may have been the source of moderate amounts of water early in Martian history.

In this work, we justify our use of Chicago local precipitation (CLP) as a reference and reinforce our confidence in the anomalous oxygen isotope signal in water from the stratosphere, as a response to a recent critique from Miller (1).

Los Angeles is a new martian meteorite that expands the compositional range of basaltic shergottites. Compared to Shergotty, Zagami, QUE94201, and EET79001-B, Los Angeles is more differentiated, with higher concentrations of incompatible elements (e.g., La) and a higher abundance of late-stage phases such as phosphates and K-rich feldspathic glass. The pyroxene crystallization trend starts at compositions more ferroan than in other martian basaits. Trace elements indicate a greater similarity to Shergotty and Zagami than to QUE94201 or EET79001-B, but the Mg/Fe ratio is low even compared to postulated parent melts of Shergotty and Zagami. Pyroxene in Los Angeles has 0.7-4-microns-thick exsolution lamellae, approx. 10 times thicker than those in Shergotty and Zaganii. Opaque oxide compositions suggest a low equilibration temperature at an oxygen fugacity near the fayafite-magnetitequartz buffer. Los Angeles cooled more slowly than Shergotty and Zagami. Slow cooling, coupled with the ferroan bulk composition, produced abundant fine-grained intergrowths of fayalite, hedenbergite, and silica, by the breakdown of pyroxferroite. Shock effects in Los Angeles include maskelynitized plagioclase, pyroxene with mosaic extinction, and rare fault zones. One such fault ruptured a previously decomposed zone of pyroxferroite. Although highly differentiated, the bulk composition of Los Angeles is not close to the low-Ca/Si composition or the globally wind-stirred soil of Mars.

— Two pallasites, Vermillion and Yamato (Y)-8451, have been studied to obtain petrologic, trace element, and O-isotopic data. Both meteorites contain low-Ca and high-Ca pyroxenes (

Single crystals of forsterite were evaporated in a vacuum furnace at temperatures of 1500–1800°C to study evaporation kinetics, magnesium isotopic fractionation, and magnesium diffusion in forsterite. The evaporation of single crystal forsterite revealed that the evaporation process is kinetically hindered, in agreement with the results of Hashimoto (1990) on polycrystalline forsterite. The activation energy of forsterite evaporation obtained from this study is 628 kJ/mole. Forsterite can thus be much more refractory at low temperatures than expected from thermodynamic predictions. The evaporation of solid forsterite supports a model of isotopic fractionation under diffusion-controlled conditions such that isotopic fractionation during the evaporation process is restricted to the vicinity of the evaporating surface. The measured solid-gas fractionation factor of 26Mg/24Mg is smaller than the theoretical prediction, suggesting more complicated gas speciation than a monatomic Mg gas. Diffusion coefficients of forsterite at high temperature (1500–1800°C) were obtained based on measurement of isotopic profiles in the evaporation residues. Mg diffusion in forsterite along its crystallographic a-axis has a very high activation energy (608 kJ/mole).

The carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group, as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula. These isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions. We present a comprehensive set of whole-rock analyses of CV, CO, CK, CM, CR, CH, and CI chondrites, as well as selected components of some of these meteorites. A simple model is developed which describes the isotopic behavior during parent-body aqueous alteration processes. The process of thermal dehydration also produces a recognizable effect in the oxygen isotopic composition.

— We studied the petrography, mineralogy, bulk chemical, I-Xe, and O-isotopic compositions of three dark inclusions (E39, E53, and E80) in the reduced CV3 chondrite Efremovka. They consist of chondrules, calcium-aluminum-rich inclusions (CAIs), and fine-grained matrix. Primary minerals in chondrules and CAIs are pseudomorphed to various degrees by a mixture largely composed of abundant (>95%), fine-grained (>0.2 μm) fayalitic olivine (Fa35–42) and minor amounts of chlorite, poorly-crystalline Si-Al-rich material, and chromite; chondrule and CAI shapes and textures are well-preserved. Secondary Ca-rich minerals (Ti-andradite, kirschsteinite, Fe-diopside) are common in chondrule pseudomorphs and matrices in E39 and E80. The degree of replacement increases from E53 to E39 to E80. Fayalitic olivines are heavily strained and contain abundant voids similar to those in incompletely dehydrated phyllosilicates in metamorphosed CM and CI chondrites. Opaque nodules in chondrules consist of Ni- and Co-rich taenite, Co-rich kamacite, and wairauite; sulfides are rare; magnetite is absent. Bulk O-isotopic compositions of E39 and E53 plot in the field of aqueously altered CM chondrites, close to the terrestrial fractionation line; the more heavily altered E39 is isotopically heavier than the less altered E53. The apparent I-Xe age of E53 is 5.4 Ma earlier than Bjurbole and 5.7 ± 2.0 Ma earlier than E39. The I-Xe data are consistent with the most heavily altered dark inclusion, E39 having experienced either longer or later alteration than E53. Bulk lithophile elements in E39 and E53 most closely match those of CO chondrites, except that Ca is depleted and K and As are enriched. Both inclusions are depleted in Se by factors of 3–5 compared to mean CO, CV, CR, or CK chondrites. Zinc in E39 is lower than the mean of any carbonaceous chondrite groups, but in E53 Zn is similar to the means in CO, CV, and CK chondrites. The Efremovka dark inclusions experienced various degrees of aqueous alteration, followed by low degree thermal metamorphism in an asteroidal environment. These processes resulted in preferential oxidation of Fe from opaque nodules and formation of Ni- and Co-rich metal, metasomatic alteration of primary minerals in chondrules and CAIs, and the formation of fayalitic olivine and secondary Ca-Fe-rich minerals. Based on the observed similarities of the alteration mineralization in the Efremovka and Allende dark inclusions, we infer that the latter may have experienced similar alteration processes.

— Lunar meteorite Dar al Gani 262 (DG 262)—found in the Libyan part of the Sahara—is a mature, anorthositic regolith breccia with highland affinities. The origin from the Moon is undoubtedly indicated by its bulk chemical composition; radionuclide concentrations; noble gas, N, and O isotopic compositions; and petrographic features. Dar al Gani 262 is a typical anorthositic highland breccia similar in mineralogy and chemical composition to Queen Alexandra Range (QUE) 93069. About 52 vol% of the studied thin sections of Dar al Gani 262 consist of fine-grained(100 μm) constituents, and 48 vol% is mineral and lithic clasts and impact-melt veins. The most abundant clast types are feldspathic fine-grained to microporphyritic crystalline melt breccias (50.2 vol%; includes recrystallized melt breccias), whereas mafic crystalline melt breccias are extremely rare (1.4 vol%). Granulitic lithologies are 12.8 vol%, intragranularly recrystallized anorthosites and cataclastic anorthosites are 8.8 and 8.2 vol%, respectively, and (devitrified) glasses are 2.7 vol%. Impact-melt veins (5.5 vol% of the whole thin sections) cutting across the entire thin section were probably formed subsequent to the lithification process of the bulk rock at pressures below 20 GPa, because the bulk rock never experienced a higher peak shock pressure. Mafic crystalline melt breccias are very rare in Dar al Gani 262 and are similar in abundance to those in QUE 93069. The extremely low abundance of mafic components and the bulk composition may constrain possible areas of the Moon from which the breccia was derived. The source area of Dar al Gani 262 must be a highland terrain lacking significant mafic impact melts or mare components. On the basis of radionuclide activities, an irradiation position of DG 262 on the Moon at a depth of 55–85 g/cm3and a maximum transit time to Earth

Twenty six individual circumstellar SiC grains extracted from the Murchison meteorite were analyzed for their strontium isotopic compositions by resonant ionization mass spectrometry. Large abundance deficits were found for the $p$-process isotope ${}^{84}\mathrm{Sr}$. The measured grains had ${}^{87}\mathrm{Sr}{/}^{86}\mathrm{Sr}$ ratios indistinguishable from the primordial solar value, but several grains differed in their ${}^{88}\mathrm{Sr}{/}^{86}\mathrm{Sr}$ ratios as a consequence of the branch point at ${}^{85}\mathrm{Kr}$. The Sr isotopic data are consistent with $s$-process nucleosynthesis at moderate neutron densities.

We have analyzed 32 individual graphite grains from the Murchison meteorite for their Mo and/or Zr isotopic compositions by resonant ionization mass spectrometry. Enormous isotopic anomalies were observed in some of these grains for both elements. The data for Zr revealed the largest isotopic anomalies, with {sup 96}Zr/{sup 94}Zr ratios ranging from 0.074 times to 10 times the solar value. The isotopic data on Mo show one population of graphite grains with close-to-terrestrial Mo composition in all isotopes and five grains with an {ital s}-process nucleosynthesis signature, i.e., correlated depletions in the {ital p}- and {ital r}-process isotopes. For eight grains we were able to measure both Mo and Zr isotopic compositions. Three of these eight graphite grains have {ital s}-process isotopic characteristics for both Zr and Mo, which suggests low-mass, thermally pulsed asymptotic giant branch stars as their origin. Four grains are puzzling, since they have nearly normal Mo compositions but significant anomalies in Zr, in particular, large depletions or enhancements in the {sup 96}Zr/{sup 94}Zr ratio. Two of these grains have extraordinary enrichments in {sup 96}Zr, with {sup 96}Zr/{sup 94}Zr ratios 10.4 {plus_minus} 1.3 and 2.5 {plus_minus} 0.3 times the solar system value. These enrichments are suggestive ofmore » the {ital r}-process, implying that these grains condensed from the ejecta of core-collapse supernovae, but these enrichments could also be made by the {ital s}-process if the neutron density were unusually high. {copyright} {ital {copyright} 1998.} {ital The American Astronomical Society}« less

Oxygen isotope analyses have been obtained for magnetite and diopside from mafic alkaline volcanic rocks of kamafugitic affinities from Brazil. These rocks are part of the Alto do Paranaiba and Santo Antonio volcanic provinces of Cretaceous age. Based on the clinopyroxene–magnetite pair, the isotopic temperatures obtained for the rocks of the two provinces are: mafitites −1140–920°C; leucitites −920–830°C; kalsilitites −820°C; analcimites (originally leucitites) −1060–1050°C; cumulate pyroxenites 750–690°C. The Mata da Corda (Alto Paranaiba Province) and Santo Antonio da Barra range in δ 18 O coincides with typical values for mantle-derived magmas.

We report the isotopic composition of molybdenum in twenty-three presolar SiC grains from the Murchison meteorite which have been measured by resonant ionization mass spectrometry (RIMS). Relative to terrestrial abundance (and normalized to s-process-only 96Mo), the majority of the analyzed grains show strong depletions in the p-process isotopes 92Mo and 94Mo and the r-process isotope 100Mo. Sixteen of these grains have δ-values

We have characterized the most phyllosilicate-rich members of the CM chondrite group. Based upon petrographic and compositional factors, we conclude that these particular meteorites have experienced pervasive aqueous alteration far beyond that witnessed by typical CMs. The lack of anhydrous silicates, CAI and (except as relicts) chondrules merits the classification of type CMI for three meteorites (EET 83334, ALH 88045, and one Kaidun lithology). Still other CMs, notably ALH 83100, EET 90047, and Yamato 82042, are clearly intermediate between types 1 and 2. Brecciated CM chondrites like Cold Bokkeveld contain all of these varied lithologies. The CM chondrites thus exhibit the complete petrologic range from 2 through 1. Our results show that progressive aqueous alteration on the parent CM asteroid(s) was, locally, accompanied by significant increases in temperature (to a peak of ∼450°C for the Kaidun lithology), fO2, and (locally) degree of chemical leaching, all well beyond the conditions recorded by typical CM2s. The most altered CMs also are commonly deformed, displaying a distinct lineation probably due to static rather than dynamic forces.

The isotopic composition of zirconium in silicon carbide grains from the Murchison meteorite was measured by resonant ionization mass spectrometry of laser-ablated neutral atoms. These grains are condensates from the atmospheres of red giant stars that existed before the formation of our sun and solar system, and they contain records of nucleosynthesis in these stars. The r-process–dominated isotope zirconium-96 was depleted by more than a factor of 2 compared with the s-process–dominated isotopes zirconium-90, zirconium-91, zirconium-92, and zirconium-94, in agreement with expectations for neutron capture nucleosynthesis in asymptotic giant branch stars.

We have conducted petrologic, chemical, and isotopic studies of lodranites in an attempt to constrain their genesis. Lodran, Gibson, Y-791491, Y-791493, Y-74357, Y-8002, Y-75274, MAC 88177, LEW 88280, EET 84302, FRO 90011, and QUE 93148 are classified as lodranites. Lodranites and acapulcoites are indistinguishable on the basis of oxygen isotopic compositions but are distinct in average grain sizes of their mafic silicates, with lodranites being significantly coarser-grained. Lodranites exhibit a diverse range of petrologic and mineralogic features: they range widely in mafic silicate compositions (Fa3–13), plagioclase (0–11.4 vol%), Fe,Ni metal (0.5–20 vol%), and troilite (0.2–5.3 vol%) contents; and shock levels (S1–S4) . They appear to have experienced high peak temperatures and rapid cooling in the temperature range recorded by metallographic cooling rates (i.e., 700-350°C). The only dated lodranite, Gibson, cooled to Ar closure temperatures at 4.49 ± 0.01 Ga. Lodranites formed from chemically and isotopically heterogeneous precursors in which the mineral and oxygen isotopic compositions were correlated. Heating of their parent body to temperatures between ∼ 1050–1200°C resulted in formation of Fe,NiFeS and basaltic partial melts. Depletions of troilite and/ or plagioclase in most lodranites testify to the removal of some of these partial melts, although melt migration was complex. Lodranites appear to have experienced a complex cooling history of slow cooling at high temperatures, followed by rapid cooling at intermediate temperatures, possibly related to breakup of the parent body. Lodranites were liberated from their parent body during 1–3 impact events, with most having cosmic ray exposure ages of 5.5–7 Ma. The acapulcoites are samples from the same parent body but were heated to lower temperatures and, thus, experienced lower degrees of partial melting.