bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental rare‐earth‐element partitioning in oldhamite: Implications for the igneous origin of aubritic oldhamite
Authors: DICKINSON Tamara L. , McCOY Timothy J.
Published: February 2010

Abstract— Aubritic oldhamite (CaS) has been the subject of intense study recently because it is the major rare‐earth‐element (REE) carrier in aubrites, has a variety of REE patterns comparable to those in unequilibrated enstatite chondrites and has an extraordinarily high melting point as a pure substance (2525 °C). These latter two facts have caused some authors to assert that much of the aubritic oldhamite is an unmelted nebular relict, rather than of igneous origin. We have conducted REE partitioning experiments between oldhamite and silicate melt using an aubritic bulk composition at 1200 °C and 1300 °C and subsolidus annealing experiments. All experiments produced crystalline oldhamite, with a range of compositions, glass and Fe metal, as well as enstatite, SiO2, diopside and troilite in some charges. Rare‐earth‐element partitioning is strongly dependent on oldhamite composition and temperature. Subsolidus annealing results in larger partition coefficients for some oldhamite grains, particularly those in contact with troilite. All experimental oldhamite/silicate melt partition coefficients are <20 and the vast majority are <5, which is similar to those reported in the literature and is two orders of magnitude less than those inferred for natural aubritic oldhamite. These partition coefficients preclude a simple igneous model, since REE abundances in aubritic oldhamite are greater than would be predicted on the basis of the experimental partition coefficients. Our experimental partition coefficients are consistent with a relict nebular origin for aubritic oldhamite, although experimental evidence that suggests melting of oldhamite at temperatures lower than that reached on the aubrite parent body are clearly inconsistent with the nebular model. Our experiments are consistent also with a complex igneous history. Oldhamite REE patterns may reflect a complex process of partial melting, melt removal, fractional crystallization and subsolidus annealing and exsolution. These mechanisms (primarily fractional crystallization and subsolidus annealing) can produce a wide range of REE patterns in aubritic oldhamite, as well as elevated (100–1000 × CI) REE abundances observed in aubritic oldhamite.
The porosity and permeability of chondritic meteorites and interplanetary dust particles
Authors: CORRIGAN Catherine M. , ZOLENSKY Michael E. , DAHL Jason , LONG Michael , WEIR Joseph , SAPP Clyde , BURKETT Patti Jo
Published: February 2010

Abstract— We have investigated the porosity of a large number of chondritic interplanetary dust particles (IDPs) and meteorites by three techniques: standard liquid/gas flow techniques, a new, noninvasive ultrasonic technique, and image processing of backscattered images. The latter technique is obviously best‐suited to sub‐kilogram sized samples. We have also measured the gas and liquid permeabilities of some chondrites by two techniques: standard liquid/gas flow techniques, and a new, nondestructive pressure release technique. We find that chondritic IDPs have a somewhat bimodal porosity distribution. Peaks are present at 0 and 4% porosity; a tail then extends to 53%. Type 1–3 chondrite matrix porosities range up to 30%, with a peak at 2%. The bulk porosities for type 1–3 chondrites have the same approximate range as exhibited by the matrix, which indicates that other components of the bulk meteorites (including chondrules and aggregates) have the same average porosity as the matrix. These results reveal that the porosities of primitive materials at scales ranging from nanogram to kilogram are similar, which implies that similar accretion dynamics operated through 12 orders of size magnitude. Permeabilities of the investigated chondrites vary by several orders of magnitude, and there appears to be no simple dependence of permeability with degree of aqueous alteration, chondrite type or porosity.
Suevite breccia of the Ries impact crater, Germany: Petrography, chemistry and shock metamorphism of crystalline rock clasts
Authors: von ENGELHARDT Wolf
Published: February 2010

Abstract— Clasts of deep‐seated crystalline basement rocks in suevites of the Ries crater, Germany, were catalogued lithologically and classified with regard to their degree of shock metamorphism. The sample suite consisted of 806 clasts from 10 outcrops in fallout suevites and 447 clasts from drill cores encountering crater suevite in the crater interior. These clasts can be grouped into seven types of metamorphic and nine types of igneous rocks. One hundred forty‐three clasts, representing these lithologies, were analyzed for major element bulk composition.

The fallout suevite contains on average 4 vol% of crystalline basement clasts, 0.4 vol% of sedimentary rocks, 16 vol% of glass bodies (some of them aerodynamically shaped), and 79 vol% of groundmass. On average, 52% of all crystalline clasts are from metamorphic sources and 42% are of igneous origin. Using the shock classification of Stöffler (1974), 8% of all crystalline clasts appear unshocked (<10 Gpa), and 34, 30 and 27% of clasts are shocked to stages I (10–35 Gpa), II (35–45 GPa) and III (45–60 GPa), respectively. The bulk composition of suevite glasses is consistent with the modal proportions of crystalline rock types observed in the clast populations. This indicates that the glasses originate by shock‐fusion of a similarly composed basement.

The crater suevite contains the same crystalline rock types that occur in the fallout suevites. The bore hole “Nördlingen 1973” yields an average of 62 vol% metamorphic and 38 vol% igneous rocks. The crater suevite differs from fallout suevites by a higher clast/glass ratio, by preponderance (65–95%) of clasts shocked to stage I only, and by the absence of aerodynamically shaped glass bodies.

The source of crystalline clasts and melt particles of suevites is a volume of rocks, located deep in the crystalline basement, to which the projectile transmittted most of its energy so that only rocks of the basement were shocked by pressures exceeding 10 GPa (deep‐burst impact model). Fallout suevites were ejected, propelled by an expanding plume of vaporized rock, and withdrew preferentially from this volume melt and highly shocked clasts, leaving in the transient cavity the crater suevite with more clasts of modest shock levels and less melt.
Presolar silicon carbide from the Indarch (EH4) meteorite: Comparison with silicon carbide populations from other meteorite classes
Authors: RUSSELL SARA S. , OTT ULRICH , ALEXANDER CONEL M. O'D. , ZINNER ERNST K. , ARDEN JOHN W. , PILLINGER C. T.
Published: February 2010

Abstract— Presolar SiC from the Indarch (EH4) meteorite was studied by scanning electron microscopy (SEM), by ion probe analysis for C and Si isotopic compositions, and by static source mass spectrometry for noble gas and C isotopic compositions. The data obtained are compared to SiC data from other meteorites, especially from Murchison (CM2), for which there is the most information available. The isotopic compositions of the major elements in SiC from Indarch and Murchison are similar. Stepped combustion data suggest a mean δ13C for SiC from both meteorites of ∼+1430%o. Silicon isotopes in Indarch and Murchison SiC also compare well. In some other important respects, however, SiC in the two meteorites are different. Morphologically, SiC from Indarch appears finer grained than SiC from Murchison and is entirely composed of submicron grains. The finer‐grained nature of Indarch SiC is confirmed by its noble gas characteristics. The mean Ne‐E/Xe‐S ratio for bulk Indarch SiC is significantly lower than the same ratio in Murchison (625 ± 47 vs. ∼3500) but is similar to that of the finest grain‐size fractions (<1 μm) in Murchison.

A comparison of noble gas data from SiC from several different meteorites suggests that it might be Murchison SiC, rather than Indarch SiC, that is unusual. The grain‐size disparities in SiC between meteorites are difficult to explain by residue processing differences or differing parent body processing. Instead, we speculate that a grain‐size sorting mechanism for SiC may have operated in the solar nebula.
Automated energy dispersive spectrometer modal analysis applied to the diogenites
Authors: BOWMAN L. E. , SPILDE M. N. , PAPIKE J. J.
Published: February 2010

Abstract— We have analyzed the modal abundances of 23 of the known 24 diogenites in 31 thin sections using an energy dispersive spectrometer (EDS) and automated phase distribution analysis software. Orthopyroxene is predictably the most abundant phase, ranging from 27.7 vol% to 99.8 vol% in these samples. The grand average mode of all the analyzed diogenites includes the “olivine diogenites” but not ALH 85015, a probable howardite, and ALHA81208, a sample with an abundant silica phase. The grand average of these 21 diogenites is: orthopyroxene 92.2 vol%, olivine 4.2 vol%, clinopyroxene 1.2 vol%, chromite 0.9 vol%, plagioclase 0.4 vol%, FeNi metal 0.1 vol%, troilite 0.6 vol%, and silica phase 0.4 vol%. Plagioclase feldspar is extremely depleted in all samples, with modal abundance from none detected to 4.6 vol% in range. Such a low volume of plagioclase may indicate that the diogenite parental melts originated in a source region depleted in Al (Warren, 1985; Stolper, 1975), which is consistent with crystallization from a melt derived from material that had previously experienced extraction of a eucrite‐type melt.
The Meteoritical Bulletin, No. 81, 1997 Jul
Authors: Grossman Jeffrey n.
Published: February 2010

Abstract— Meteoritical Bulletin, No. 81 lists 181 new meteorites. Noteworthy among these are a new lunar meteorite (Dar al Gani 262), four observed falls (Dong Ujimqin Qi, Galkiv, Mount Tazerzait, and Piplia Kalan), four irons (Albion, Great Sand Sea 003, Hot Springs, and Mont Dieu), two mesosiderites (Dong Ujimqin Qi and Lamont), an acapulcoite (FRO 95029), a eucrite (Piplia Kalan), two probably‐paired ureilites (Dar al Gani 164 and 165), an R chondrite (Hammadah al Hamra 119), an ungrouped type‐3 chondrite (Hammadah al Hamra 180), a highly unequilibrated ordinary chondrite (Wells, LL3.3), and a variety of carbonaceous and unequilibrated ordinary chondrites from Libya and Antarctica. All italicized abbreviations refer to addresses listed in the appendix.
The porosities of ordinary chondrites: Models and interpretation
Authors: CONSOLMAGNO S.J. G. J. , BRITT D. T. , STOLL C. P.
Published: February 2010

Abstract— Densities and porosities for 285 ordinary chondrites have been assembled and analyzed. Measured chondrite porosities are bimodal; finds have an average porosity of <3%, whereas fall porosities average 7% but range from zero to >30%. We conclude that mild degrees of weathering fill pore spaces, lowering grain densities and porosities without significantly changing the bulk size or mass of the sample. By assuming an original pristine grain density (as a function of the meteorite's mineralogy—determined by its class), we can derive model pristine porosities. These model porosities cluster around an average value of 10% for all classes of ordinary chondrites.

Ordinary chondrites do not show any correlation of porosity (model or measured) with petrographic grade or sample size (over a range from 0.2 g to 2 kg). However, we do see a correlation between shock state and porosity. Shock‐blackened meteorites are less porous than other meteorites. Furthermore, less severely shocked meteorites show a much broader range of porosities, with the maximum porosity seen among meteorites of a given shock class falling linearly as a function of that shock class. This is consistent with the idea that shock compresses and closes pore space.

Analysis of meteorite porosity provides a lower bound to the fine‐scale porosity of asteroids. Our densities, even with 10% primordial porosity, are significantly higher than inferred densities of possible asteroid parent bodies. These asteroids are probably loose piles of rubble.
Thermally metamorphosed carbonaceous chondrites from data for thermally mobile trace elements
Authors: WANG MING‐SHENG , LIPSCHUTZ MICHAEL E.
Published: February 2010

Abstract—We report radiochemical neutron activation analysis (RNAA) data for U, Co, Au, Sb, Ga, Rb, Cs, Se, Ag, Te, Zn, In, Bi, Tl, and Cd (ordered by increasing ease of vaporization and loss from the Murchison CM2 chondrite during open‐system heating) in nine Antarctic C2 and C3 chondrites. These meteorites exhibit properties (obtained by reflectance spectroscopy, O isotopic mass spectrometry and/or mineralogy‐petrology) suggesting thermal metamorphism in their parent bodies.

Five of these meteorites (Asuka (A) 881655, Yamato (Y) 793495, Y‐790992, Pecora Escarpment (PCA) 91008, and Y‐86789—paired with Y‐86720) exhibit significant depletion of the most thermally mobile 1–5 trace elements, which is consistent with open‐system loss during extended parent‐body heating (under conditions duplicated by week‐long heating of the Murchison C2 chondrite, heated at 500–700 °C in a low‐pressure (initially 10−5atm) H2atmosphere). From earlier data, three other C3 chondrites—Allan Hills (ALH) 81003, ALH 85003, and Lewis Cliffs (LEW) 85332—show significant Cd depletion. Nine additional C2 and C3 chondrites show no evidence of mobile trace element depletion—including Y‐793321, which by all other criteria was mildly metamorphosed thermally. Either metamorphism of these nine meteorites occurred under closed conditions and/or alteration took place under such mild conditions that even Cd could not be lost.

The RNAA data suggest that 10 of the 46 Antarctic carbonaceous chondrites (including 4 of 37 from Victoria Land and 6 of 9 from Queen Maud Land) exhibit open‐system loss of at least some thermally mobile trace elements by heating in their parent bodies, whereas none of the 25 non‐Antarctic falls experienced this. These results are consistent with the idea that the Antarctic sampling of near‐Earth material differs from that being sampled today.
The Campos Sales meteorite from Brazil: A lightly shocked L5 chondrite fall
Authors: SCORZELLI R. B. , MICHEL‐LÉVY M. CHRISTOPHE , GILABERT E. , LAVIELLE B. , AZEVEDO I. SOUZA , VIEIRA V. W. , COSTA T. V. V. , ARAÚJO M. A. B.
Published: February 2010

Abstract— The Campos Sales meteorite fell close to the town of Campos Sales in the northeastern Brazilian state of Ceará (7°2′ S, 40°10′ W) on 1991 January 31 at 10:00 P.M. (local time). Several fragments were recovered from an area estimated to be 1 × 3 km. The stone is an ordinary L5 chondrite (Fa25.0 and FS21.6) and is lightly shocked (S1). Metal phases present are kamacite, tetrataenite, and antitaenite. Noble gases He, Ne, Ar, Kr, and Xe have been analyzed in two bulk samples of Campos Sales. All exposure ages based on determination of cosmogenic 3He, 21Ne, 38Ar, 83Kr, and 126Xe abundances and on the cosmogenic 81Kr/83Kr ratio agree well, which suggests no gas loss during cosmic‐ray exposure. The cosmic‐ray exposure age is 23.3 ± 1.0 Ma, which falls in the range observed for L5 chondrites (20–30 Ma). The gas‐retention ages indicate He loss that must have occurred prior to or during ejection from the L‐chondrite parent body.
Mineralogy of Antarctic basaltic shergottite Queen Alexandra Range 94201: Similarities to Elephant Moraine A79001 (Lithology B) martian meteorite
Authors: MIKOUCHI TAKASHI , MIYAMOTO MASAMICHI , McKAY GORDON A.
Published: February 2010

Abstract— Antarctic meteorite QUE 94201 is a new basaltic shergottite that is mainly composed of subequal amounts of maskelynite and pyroxenes (pigeonite and augite) plus abundant merrillite and accessory phases. It also contains impact melt. Complex zoning patterns in QUE 94201 pyroxenes revealed by elemental map analyses using an electron microprobe suggest a crystallization sequence from Mg‐rich pigeonite (En62Fss30Wog) to extremely Fe‐rich pigeonite (En5Fs81Wo14) via {110} Mg‐rich augite bands (En44Fs20Wo36) in a single crystal. These textures, along with the abundant plagioclase (maskelynite), indicates single‐stage rapid cooling (>5 °C/year) of this rock from a supercooled magma. Transition from Mg‐rich augite to Fe‐rich pigeonite reflects the onset of plagioclase crystallization. Enrichment of late‐stage phases in QUE 94201 implies crystallization from an evolved magma and suggests a different parent magma composition from the other basaltic shergottites. Lithology B of EETA79001 basaltic shergottite contains pyroxenes that show complex zoning with augite bands similar to those in QUE 94201 pyroxene, which suggests similar one‐stage rapid cooling. Lithology B of EETA79001 also resembles QUE 94201 in its coarse‐grained texture of silicates and its high abundance of maskelynite, although QUE 94201 probably crystallized from a more fractionated magma. We also note that some Apollo lunar mare basalts (e.g., 12020 and 12021) have similar mineralogy and petrology to QUE 94201, especially in pyroxene zoning. All these basaltic rocks with complex pyroxene zoning suggest rapid metastable crystallization from supercooled magmas.
Formation of carbides and hydrocarbons in chondritic interplanetary dust particles: A laboratory study
Authors: LLORCA JORDI , CASANOVA IGNASI
Published: February 2010

Abstract— The reaction between kamacite grains and H2 + CO gas mixture has been tested in the laboratory under experimental conditions presumed for interplanetary dust particle (IDP) formation in a nebular‐type environment (H2:CO = 250:1; 5 × 10−4 atm total pressure, and 473 K). Carbon deposition, hydrocarbon production in the C1–C4 range, and the formation of an ɛ‐carbide phase occur when well‐defined model FeNi bcc alloy (kamacite) particles are exposed to a mixture of H2 + CO during 103 h. These results strongly support the idea that gas‐solid reactions in the solar nebula during CO hydrogenation represent a plausible scenario for the formation of carbides and carbonaceous materials in IDPs, as well as for the production of hydrocarbons through Fischer‐Tropsch‐type reactions.
The age of the Kara impact structure, Russia
Authors: TRIELOFF MARIO , DEUTSCH ALEXANDER , JESSBERGER ELMAR K.
Published: February 2010

Abstract— For the ∼65 km sized Kara impact structure close to the polar Ural, we report an age of 70.3 ± 2.2 Ma (2s̀), defined by the mean of 40Ar‐39Ar plateau ages for three glassy or crystalline impact melt rocks cleaned from mineral and rock clasts. The fine structure of the age spectra of these samples can quantitatively be simulated by modeling taking into account 39Ar recoil effects, without assuming the presence of excess Ar. The calculations corroborate our age results by showing that 39Ar recoil does not affect the plateau fractions. Previously, Kara has been proposed as a probable K/T impact site or was related to the Campanian‐Maastrichtian boundary at 73 Ma. At the 2s̀ level, both suggestions are ruled out by the well‐constrained age for the Kara impact structure.
Correlated petrologic and geochemical characteristics of CO3 chondrites
Authors: RUBIN ALAN E.
Published: February 2010

Abstract— Many properties of CO3 chondrites have been shown previously to have resulted from thermal metamorphism; petrologic subtypes 3.0–3.7 have been assigned to members of the group. Additional properties that correlate with the metamorphic sequence but seem to have resulted from hydrothermal alteration include the modal abundance of amoeboid olivine inclusions (AOI), chondrule size, the types of refractory inclusions and whole rock O isotopic composition. The percentage of rimmed AOI increases with petrologic subtype. The rims most likely formed during hydrothermal alteration. The previously reported correlation between AOI abundance and chondrite subtype is probably an artifact due to the difficulty in recognizing small unrimmed AOI in the least metamorphosed CO3 chondrites. Because large (≥ 200 μm size) porphyritic chondrules have nearly the same mean size in all CO3 chondrites, it seems likely that the correlation between chondrule size and subtype is due to alteration of the smallest chondrules to the point of unrecogizability as complete objects in the more metamorphosed CO3 chondrites. The previously reported decrease in the proportion of melilite‐rich refractory inclusions with increasing petrologic subtype may have resulted from more extensive hydrothermal alteration in CO3.4–3.7 chondrites that converted primary melilite into Ca‐pyroxene, andradite and nepheline. Alteration probably caused the preferential occurrence of 16O‐poor oxygen isotopes in the more metamorphosed whole rock samples.
Nitrogen components in primitive ordinary chondrites
Authors: SUGIURA NAOJI , KIYOTA KAORU , HASHIZUME KO
Published: February 2010

Abstract— Nitrogen and Ar in more than 20 primitive ordinary chondrites were studied by a stepped combustion method. Several N carriers that are characterized by N isotopic composition, N release pattern and trapped Ar release pattern are recognized in the primitive ordinary chondrites. Large fractions of anomalous N and associated Ar are removed by acid treatment in most cases. The N isotopic anomalies cannot be explained by known presolar grains (with a possible exception of graphite), and some of the N isotopic anomalies may be due to unknown presolar grains. There is no specific relationship between the type of N carriers contained in an ordinary chondrite and the chemical type (H, L, or LL) of the chondrite. It is likely that as a result of impacts, the carriers of isotopically anomalous N were mixed in various parent bodies as rock fragments rather than as individual fine particles. The presence of distinctive N isotopic anomalies in primitive meteorites indicates that the primitive solar nebula may have been heterogeneous either spatially or temporally.
Rhenium‐187—osmium‐187 in iron meteorites and the strange origin of the Kodaïkanal meteorite
Authors: BIRCK J. L. , ALLÈGRE C. J.
Published: February 2010

Abstract— A set of iron meteorites was investigated for Re‐Os isotopes and provides a well‐defined isochron age of 4.624 ± 0.017 Ba and an initial 187Os/188Os ratio of 0.095636 ± 0.00009. Actual ages may be a few percent lower due to uncertainty on the 187Re decay constant. Within the small sample number presented here, there is no evidence for age differences between classes. A more detailed study of the meteorite Kodaïkanal shows that the metal reservoir of this meteorite formed approximately at the same time as the other iron meteorites, in contrast with the silicate inclusions which display a formation age of 3.67 Ba with all other chronometers. A collisional origin is in agreement with the data on this meteorite. Major secondary events do not affect the Re‐Os system at the bulk rock scale in metal as it is the sole significant reservoir of these two elements. A Re‐Os and Rb‐Sr investigation of meteoritic troilite exhibits disturbed chronometric systems, which we attribute to the terrestrial history of the meteorite.
The igneous crystallization history of an ancient Martian meteorite from rare earth element microdistributions
Authors: WADHWA MEENAKSHI , CROZAZ GHISLAINE
Published: February 2010

Abstract— Rare earth element (REE) and other selected trace and minor element concentrations were measured in individual grains of orthopyroxene, feldspathic glass (of plagioclase composition) and merrillite of the ALH 84001 Martian meteorite. Unlike in other Martian meteorites, phosphate is not the main REE carrier in ALH 84001. The REE pattern of ALH 84001 bulk rock is dependent on the modal abundances of three REE‐bearing phases, namely, orthopyroxene, which contains most of the heavy rare earth elements (HREEs); feldspathic glass, which dominates the Eu abundances; and merrillite, which contains the majority of the light rare earth elements (LREEs). Variations in the REE abundances previously observed in different splits of ALH 84001 can easily be explained in terms of small variations in the modal abundances of these three minerals without the need to invoke extensive redistribution of LREEs. At least some orthopyroxenes (i.e., those away from contacts with feldspathic glass) in ALH 84001 appear to have preserved their original REE zonation from igneous fractionation. An estimate of the ALH 84001 parent magma composition from that of the unaltered orthopyroxene “core” (i.e., zoned orthopyroxene with the lowest REE abundances) indicates that it is LREE depleted. This implies that the Martian mantle was already partly depleted within ∼100 Ma of solar system formation, which is consistent with rapid accretion and differentiation of Mars. Although equilibration and exchange of REEs between phases (in particular, transport of LREEs into the interstitial phases, feldspathic glass and merrillite) cannot be ruled out, our data suggest that the LREE enrichment in melts “in equilibrium” with these interstitial phases is most likely the result of late‐stage infiltration of the cumulate pile by a LREE‐enriched melt.
Spectroscopic analysis of Martian meteorite Allan Hills 84001 powder and applications for spectral identification of minerals and other soil components on Mars
Authors: BISHOP JANICE L. , PIETERS CARLÉ M. , HIROI TAKAHIRO , MUSTARD JOHN F.
Published: February 2010

Abstract— Spectroscopic measurement and analysis of Martian meteorites provide important information about the mineralogy of Mars, as well as necessary ground‐truths for deconvolving remote sensing spectra of the Martian surface rocks. The spectroscopic properties of particulate ALH 84001 from 0.3 to 25 μm correctly identify low‐Ca pyroxene as the dominant mineralogy. Absorption bands due to electronic transitions of ferrous iron are observed at 0.94 and 1.97 μm that are typical for low‐Ca pyroxene. A strong, broad water band is observed near 3 μm that is characteristic of the water band typically associated with pyroxenes. Weaker features near 4.8, 5.2 and 6.2 μm are characteristic of particulate low‐Ca pyroxene and can be distinguished readily from the features due to high‐Ca pyroxene and other silicate minerals. The reflectance minimum occurs near 8.6 μm for the ALH 84001 powder, which is more consistent with high‐Ca pyroxene and augite than low‐Ca pyroxene. The dominant mid‐infrared (IR) spectral features for the ALH 84001 powder are observed near 9 and 19.5 μm; however, there are multiple features in this region. These mid‐IR features are generally characteristic of low‐Ca pyroxene but cannot be explained by low‐Ca pyroxene alone.

Spectral features from 2.5–5 μm are typically associated with water, organics and carbonates and have been studied in spectra of the ALH 84001, split 92 powder and ALH 84001, splits 92 and 271 chip surfaces. Weak features have been identified near 3.5 and 4 μm that are assigned to organic material and carbonates. Another feature is observed at 4.27 μm in many surface spots and in the powder but has not yet been uniquely identified. Spectroscopic identification of minor organic and carbonate components in this probable piece of Mars suggests that detection of small amounts of organics and carbonates in the Martian surface regolith would also be possible using visible‐infrared hyperspectral analyses. Laboratory spectroscopic analysis of Martian meteorites provides a unique opportunity to identify the spectral features of minerals and other components while they are embedded in their natural medium.
Cation diffusion in calcite: Determining closure temperatures and the thermal history for the Allan Hills 84001 meteorite
Authors: FISLER DIANA K. , CYGAN RANDALL T.
Published: February 2010

Abstract— The presence of zoned Fe, Mg, Ca, and Mn in the carbonate phases associated with the cracks and inclusions of the Allan Hills (ALH) 84001 meteorite provides evidence for constraining the thermal history of the meteorite. Using self‐ and tracer‐diffusion coefficients obtained from laboratory experiments on natural calcite, cooling rates are calculated for various temperatures and diffusion distances to assist in the evaluation of the compositional zoning associated with the carbonate phases in ALH 84001. The closure temperature model provides the average temperature below which compositional zoning will be preserved for a given cooling rate, that is, the temperature at which diffusion will be ineffective in homogenizing the phase. The validity of various theories for the formation of the carbonate globules may be examined, therefore, in view of the diffusion‐limited kinetic constraints. Experiments using a thin film‐mineral diffusion couple and ion microprobe for depth profiling analysis were performed for the temperature range of 550–800 °C to determine self‐ and tracer‐diffusion coefficients for Ca and Mg and in calcite. The resulting activation energies for Ca (Ea(Ca) = 271 ± 80 kJ/mol) and for Mg (Ea(Mg) = 284 ± 74 kJ/mol) were used then to calculate a series of cooling rate, grain size, and closure temperature curves. The data indicate, for example, that by the diffusion of Mg in calcite, a 10 μm compositional zone would be completely homogenized at a temperature of 300 °C for cooling rates <100 K/Ma. These data provide no constraint on formation models that propose a low‐temperature fluid precipitation mechanism; however, they indicate that the carbonate globules were not exposed to a high‐temperature environment for long time scales following formation.
The Burnwell, Kentucky, low iron oxide chondrite fall: Description, classification and origin
Authors: RUSSELL SARA S. , McCOY TIMOTHY J. , JAROSEWICH EUGENE , ASH RICHARD D.
Published: February 2010

Abstract— The Burnwell, Kentucky, meteorite fell as a single stone on 1990 September 4. The Burnwell meteorite has lower Fa in olivine (15.8 mol%), Fs in orthopyroxene (13.4 mol%), Co in kamacite (0.36 wt%), FeO from bulk chemical analysis (9.43 wt%), and Δ17O (0.51 ± 0.02%), and higher Fe, Ni, Co metal (19.75 wt% from bulk wet chemical analysis) than observed in H chondrites. The Burnwell meteorite plots on extensions of H‐L‐LL chondrite trends for each of these properties towards more reducing compositions than in H chondrites. Extensions of this trend have been previously suggested in the case of other low‐FeO chondrites or silicate inclusions in the HE iron Netschaëvo, but interpretation of the evidence in these meteorites is complicated by terrestrial weathering, chemical disequilibrium or reduction. In contrast, the Burn‐well meteorite is an equilibrated fall that exhibits no evidence for reduction. As such, it provides the first definitive evidence for extension of the H‐L‐LL ordinary chondrite trend beyond typical H values towards more reducing compositions.
Multiple nitrogen isotopic components coexisting in ureilites
Authors: YAMAMOTO TOMOKO , HASHIZUME KO , MATSUDA JUN‐ICHI , KASE TOMOHIKO
Published: February 2010

Abstract— Nitrogen and noble gas isotopic compositions and C abundance of ureilites were analyzed using a stepwise combustion technique. Four Antarctic ureilites, ALHA77257, Asuka 881931, Yamato 791538 and Yamato 790981 were analyzed. Multiple N isotopic components were observed in these ureilites. The δ15N values of these N components ranged from +160 to −120%. The minimum δ15N values of typically −120% were observed at combustion temperatures at 700–900 °C where large amounts of C were released. A heavy N component was observed in only two ureilites, ALHA77257 and Asuka 881931. Silicate‐enriched fractions and C‐concentrated fractions were prepared for these two ureilites. We conclude that both the light N and the heavy N are trapped in the carbonaceous vein minerals. The lack of correction between the N/C ratio and the 36Ar/C ratio suggests that the primary carrier phase of the light N does not correspond to that of the planetary noble gases. We consider that the isotopically heavy N, which was observed in this study, is related to the heavy N observed among polymict ureilites. Small amounts (<0.5 ppm) of light N with the minimum δ15N value of −120% were observed among the silicate fractions at the highest combustion temperature of 1200 °C, although the exact carrier phase of this light N is not known. We consider that the currently observed ureilites were produced by injection of several volatile‐rich objects into volatile‐poor ureilitic silicates.
Laser argon‐40‐argon‐39 age determinations of Luna 24 mare basalts
Authors: BURGESS RAY , TURNER GRENVILLE
Published: February 2010

Abstract— The ages of seven rock fragments from the soil fraction of the Luna 24 core have been determined using a laser 40Ar‐39Ar stepped heating technique. The investigated lithologies include fragments of fine‐grained ophitic basalt, coarse‐grained basalt, metabasalts and a regolith breccia. Most of the samples contain nonradiogenic Ar components of variable 36Ar/40Ar composition. These surface‐correlated trapped components are predominantly released at low temperature and can be distinguished from volume‐correlated radiogenic and cosmogenic components released at higher temperature during stepped heating. Binary mixtures of radiogenic and cosmogenic Ar components give linear correlations on 36Art/40Ar‐39Ar/40Ar diagrams from which the age and 36Ar/40Ar value of trapped Ar can be determined. The ages obtained span a narrow range between 3.18‐3.28 Ga with an average of 3.22 ± 0.04 Ga. This is interpreted as being the age of the basalts at the Luna 24 sampling site. Systematic age differences between lithologies were not detected; however, a single age of 2.93 Ga obtained from a coarse‐grained basalt hints at the possibility of younger volcanism. The results of this work effectively triple the chronological information available for Mare Crisium and are within the range of radiometric age measurements of Luna 24 mare basalts obtained previously.
Carbon, nitrogen, argon and helium study of impact diamonds from Ebeliakh alluvial deposits and Popigai crater
Authors: SHELKOV D. A. , VERCHOVSKY A. B. , MILLEDGE H. J. , KAMINSKY F. V. , PILLINGER C. T.
Published: February 2010

Abstract— Nineteen diamond aggregate specimens (1–2 mm in size) from impactites of Popigai crater and five diamond samples (5–7 mm in size) from Ebeliakh river placers were studied. Our investigations indicate that samples from Ebeliakh were formed in an impact event with the exception of one specimen (Y7).

The carbon isotopic composition of diamonds from Popigai varies within the previously reported limits (δ13C, −8 to −22%); whereas, diamonds from Ebeliakh placers show heavier values of δ13C (−7 to −10%). All the specimens studied contain very low amounts of N, mostly <20 ppm, but a few contained up to 60 ppm. For specimens, where the quantity of N allowed reliable analysis, δ15N values were found to be in the range of −3.9 to +11.9%. On the basis of combined Ar and N study, it was concluded that impact diamonds studied here can be a mixture of at least two types of gas carriers (e.g., different diamond components). A possible explanation would be involvement of a carbon vapour deposition (CVD) process or diamond growth in the impact melt in addition to the direct graphite‐diamond shock transformation. The δ13C distributions and different N/36Ar correlations have indicated a difference between impact diamonds from Ebeliakh and diamonds extracted from Popigai crater. This could be explained by the existence of different diamond populations formed during the Popigai impact event. On the other hand, Ebeliakh diamonds could have resulted from a separate impact event to Popigai and an alternative crater is yet to be found.
A halite‐siderite‐anhydrite‐chlorapatite assemblage in Nakhla: Mineralogical evidence for evaporites on Mars
Authors: BRIDGES J. C. , GRADY M. M.
Published: February 2010

Abstract— We report the results of a study of a halite‐siderite‐anhydrite‐chlorapatite assemblage in the Shergotty‐Nakhla‐Chassigny (SNC) Martian meteorite Nakhla. These minerals are found associated with each other in interstitial areas, with halite often being adjacent to or enclosing siderite. We suggest the halite and other minerals are Martian in origin because (1) the conditions of fall preclude significant amounts of terrestrial contamination or weathering having taken place; (2) textures indicate that the minerals within this assemblage crystallized at the same stage as some silicate and oxide minerals within the Nakhla parent; and (3) the association with siderite, which previous studies have shown has C and O‐isotopic compositions incompatible with an origin on the Earth. Siderite has the range of compositions: CaCO3, 0.1–5.7; MgCO3, 2.0–40.9; FeCO3, 23.2–87.0; MnCO3, 1.0–39.9 mol%. There are two compositional groupings: high‐MnCO3 (≥30 mol%) and low‐MnCO3/high‐FeCO3, with a gap identified between the two. This may be a miscibility gap or, alternatively, the two compositional groupings may mark separate generations of carbonate. We have not found any textural evidence for the latter explanation, but acceptance of the presence of a miscibility gap would require independent work on Fe‐Mn carbonates to verify its existence. Trace element abundances have been determined by ion microprobe analysis on three siderite and one anhydrite grains. Siderite has light rare earth elements (2.2–7.3 × C1) greater than heavy rare earth elements (0.32–0.79 × C1) without Ce or Eu anomalies, and the anhydrite has a similar pattern. These abundances reflect the source composition rather than partitioning or complexing controls. They are not typical of hydrothermal signatures which generally do not have such smooth REE abundance patterns. The nature of the mineral assemblage suggests that its source rocks on Mars were evaporites. These may be common in the craters and flood plains of the Martian southern highlands. Two models are suggested in this paper to explain the incorporation of evaporitic material into the Nakhla igneous parent. It may have happened as a low‐temperature process (<200 °C) by crystallisation from an aqueous fluid. An origin at low temperature is compatible with the available experimental data on siderite stability. Alternatively, we suggest evaporitic material may have been incorporated into the Nakhla parent while melt was still present and crystallized ∼800 °C. The latter model can more readily explain the trace element abundances and also the siderite textures that imply intergrowth with residual interstitial melt. Both high‐ and low‐temperature models are consistent with the presence of evaporite sediments on Mars.
Early aqueous alteration, explosive disruption, and reprocessing of asteroids
Authors: WILSON L. , KEIL K. , BROWNING L. B. , KROT A. N. , BOURCIER W.
Published: February 2010

Abstract— Several classes of chondritic meteorites experienced heterogeneous aqueous alteration and subsequent brecciation before agglomeration into the final parent bodies. These processes resulted in intimate mixing of materials altered to various degrees. In the past, this mixing has been attributed solely to impact processes. However, our investigation of the physical consequences of aqueous alteration processes in bodies accreting from a mixture of silicate and ice grains shows that aqueous alteration was commonly accompanied by substantial gas production. The asteroids may have become so internally pressurized by these gases that the sudden onset of gas release led to partial or complete disaggregation of the body. In some cases, fragments may have escaped completely from the parent asteroid and could potentially have been incorporated into other accreting asteroids. In other cases, fragments originating from different parts of the initial body, having various sizes and temperatures and exhibiting varying degrees of alteration, may have re‐accreted into a second‐generation object and undergone further stages of alteration. Such events could have been repeated two or three times during the lifetime of 26Al, the likely heat source for these processes.
Petrology and microstructure of distal impact ejecta from the Flinders Ranges, Australia
Authors: GOSTIN Victor A. , ZBIK Marek
Published: February 2010

Abstract— The Acraman impact ejecta from Bunyeroo Gorge in the central Flinders Ranges consist of clast‐bearing and sandy sublayers set in a shale host rock. A calculated transient crater diameter for the Acraman impact of at least 34 km was obtained from average thicknesses and estimated distances of the ejecta from the impact in the Gawler Ranges.

The ejecta contain numerous grains of quartz and zircon that display impact‐produced features, including one or more sets of decorated planar deformation features. There is also much unshocked material incorporated in the ejecta layer. The coarse‐grained ejecta layer embedded within fine‐grained sediments allowed easy passage for diagenetic fluids that produced a porous honeycomb structure in the clays and enhanced the content of elements such as Cu, Pb, Zn, and U. The clay fraction of the ejecta layers consists of vermiculite and kaolinite, probably formed from alteration and weathering of glassy components. It appears that quartz and zircon grains are the only remnants unaltered by diagenetic processes.
Portales Valley: A meteoritic sample of the brecciated and metal‐veined floor of an impact crater on an H‐chondrite asteroid
Authors: KRING David A. , HILL Dolores H. , GLEASON James D. , BRITT Daniel T. , CONSOLMAGNO Guy J. , FARMER Mike , WILSON Skip , HAAG Robert
Published: February 2010

Abstract—A shower of meteorite fragments fell at ∼0730 h local time on 1998 June 13 near the town of Portales, New Mexico. Thus far, 51 pieces of the Portales Valley (H6) meteorite have been recovered. This meteorite has an unusually large number of metallic veins. Some of these veins are also unusually thick, having widths on the order of centimeters. These wide veins have fine Widmanstätten structure, which is the first time it has been seen in an ordinary chondrite. This structure indicates the metallic veins and the host chondrite cooled slowly. These veins appear to have been produced by shock‐metamorphic processes, which we infer produced a >20 km diameter impact crater on an H‐chondrite planetesimal.
Impact structures of northeastern Eurasia: The territories of Russia and adjacent countries
Authors: MASAITIS V. L.
Published: February 2010

Abstract— More than 30 impact structures have been discovered in the last three decades in northeastern Eurasia, which includes Russia, Ukraine, Belarus, Lithuania, Latvia, Estonia, Kazakhstan, and Mongolia. The largest impact events of the twentieth century also occurred here: the Tunguska and Sikhote Alin events in Siberia and Primorye, respectively. Many of these impact structures have been studied in detail. This is particularly the case for the largest examples: Popigai (100 km), Puchezh‐Katunki (80 km), and Kara (65 km). Detailed data and descriptions of the geological characteristics, morphology, and the nature of the impact breccias and impactites (impact‐melt rocks) are to be found in numerous publications published mostly in Russian. As these data and descriptions are not generally available to non‐Russian scientists, this review summarizes the current state of knowledge on these impact structures. It also provides references to the principal publications detailing them.
Accelerator mass spectrometry measurements and model calculations of iron‐60 production rates in meteorites
Authors: KNIE K. , MERCHEL S. , KORSCHINEK G. , FAESTERMANN T. , HERPERS U. , GLORIS M. , MICHEL R.
Published: February 2010

Abstract— The cosmogenic radionuclide 60Fe (T1/2 = 1.49 Ma) was measured in two iron meteorites as well as in the magnetic fractions of a stony‐iron and a stony meteorite by means of accelerator mass spectrometry (AMS).

The measured 60Fe/Fe ratios range from 1.5 × 10‐14 to 6.3 × 10‐14 and show a significant correlation to the respective concentrations of Ni, which is the main target element. The resulting 60Fe specific activities correspond to production rates in meteorites in the order of 1 dpm/kg Ni. In addition, model calculations of depth‐ and size‐dependent 60Fe production rates were performed. Although there are no experimental data for the production cross sections, our measurements are in surprisingly good agreement with the theoretical predictions using production cross sections that were determined by computer model calculations.
Late Eocene microkrystites and microtektites at Maud Rise (Ocean Drilling Project Hole 689B; Southern Ocean) suggest a global extension of the approximately 35.5 Ma Pacific impact ejecta strewn field
Authors: VONHOF H. B. , SMIT J.
Published: February 2010

Abstract— Late Eocene microtektites and microkrystites recovered from Ocean Drilling Project Hole 689B at Maud Rise (Southern Ocean) are stratigraphically and geochemically compared to spherules from the North American and Pacific strewn fields, and to devitrified spherules from the Eocene‐Oligocene global stratotype section and point section in Massignano, Italy.

The ODP 689B microkrystites compare well to the Pacific strewn field microkrystites, which suggests that the geographic extent of the Pacific strewn field was much larger than previously documented.

The elemental composition of microtektites of ODP Hole 689B is comparable to tektites of the North American strewn field. Their 87Sr/86Sr ratio, however, is different. We tentatively interpret this to reflect geochemical heterogeneity within the North American strewn field but can not exclude the option that the chemical discrepancies result from the existence of a third late Eocene impact site.
Extraterrestrial water in micrometeorites and cosmic spherules from Antarctica: An ion microprobe study
Authors: Engrand Cécile , DeLoule Etienne , Robert François , Maurette Michel , Kurat Gero
Published: February 2010

Abstract— The D/H ratios and water contents were measured by ion microprobe analysis in 52 individual Antarctic micrometeorites (AMMs) and 10 Antarctic cosmic spherules (ACSs) containing nuggets of iron hydroxide (COPS phase). In AMMs, δD values vary from −366 to +249%‰ and water contents lie between 0.4‐3.7 wt%. The COPS nuggets in cosmic spherules have high water contents (2 to 8 wt%) and exhibit δD values from −144 to +167%‰, which is indicative of an extraterrestrial origin of their constituent water. The silicate portion of ACSs also contain extraterrestrial H equivalent to ∼0.l to 1.2 wt% water. Deuterium‐exchange experiments were performed with isotopically spiked water. These experiments demonstrate that water in mineral phases of AMMs and ACSs is indigenous and does not result from contamination during residence in Antarctic ice. The frequency distribution of D/H ratios in AMMs allows us to further narrow the relationship between AMMs and carbonaceous chondrites to CM and CI chondrites but contrasts with that of stratospheric interplanetary dust particles (IDPs) of similar sizes (from −10 to 50 μm). The relatively narrow range of D/H ratios measured in AMMs as well as in ACSs (which are more resistant and thus less susceptible to collection biases) suggests that D‐rich IDP‐like particles are very rare in our AMMs collections. This indicates that these D‐rich grains might constitute a minor fraction of the micrometeorite flux in the interplanetary medium and that possible collection biases in Antarctica would not be responsible for their strong depletion in the AMMs collections.
Don't drink the water
Authors: Reed George W.
Published: February 2010

Abstract—If water exists in permanently shadowed terrain on the Moon as suggested by a number of investigators (Watsonet al., 1961; Arnold, 1979; Hodges, 1980; Nozetteet al., 1996; Duke and Whittaker, 1997) and strongly supported by the Lunar Prospector neutron flux measurements (Feldmanet al., 1998), the results of studies on another volatile, namely Hg, are quite relevant. Whereas water has not been positively found, a large number of studies have established the presence of Hg in lunar samples. Its presence and volatile behavior are important when considering water as probably the most importantin situlunar resource. Here we show that the amount of Hg in lunar cold traps may be comparable to the amounts of water.