bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
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.
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.
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.
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.
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.
Iron, calcium, and potassium atom densities in the trails of Leonids and other meteors: Strong evidence for differential ablation
Authors: von ZAHN U. , GERDING M. , HÖFFNER J. , McNEIL W. J. , MURAD Edmond 
Published: February 2010

Abstract— We report on studies of the Fe, Ca, and K atom densities in the trails of meteors. The measurements of the densities were taken simultaneously and in a common volume by three ground‐based lidars. We report and analyze the data obtained during two nights of Leonid showers (1996 and 1998 November 16/17) and of one night five days after the 1998 Leonids. The lidar‐observed trails of Leonids differ from those of other meteor showers in both their mean altitude and in mean metal composition. The Leonid trails show a highly depressed Ca/Fe abundance ratio in comparison to CI meteoritic composition.Our observations are interpreted with the help of a numerical model that describes the ablation processes occurring during the high‐speed entry of meteoroids into the Earth's atmosphere. We conclude that for the lidar‐observed meteoroids, the ablation process occurs differentially for the three elements. This leads to a mixture of metals in the meteor trails, the composition of which is strongly altitude dependent and at any one altitude deviates significantly from a CI meteoritic composition. The model predicts differing altitudes and durations of trail observations for different showers, allowing us to tentatively assign the origin to the observed trails.
Investigation of the Rhabdite/Kamacite Law of Intergrowth in iron meteorites with the aid of the Kossel technique
Authors: HENNIG C. , GEIST V. , HEIDE G. 
Published: February 2010

Abstract— X‐ray microdiffraction measurements based on the Kossel effect have been used for orientation determinations of rhabdite (i.e., small prismatic schreibersite crystals) with respect to the kamacite matrix. For that purpose, polished specimens of the Toluca meteorite have been analyzed after surface etching. Kossel patterns of kamacite and rhabdite have been recorded and simulated. As the law of intergrowth for idiomorphic rhabdite crystals, we confirmed the relations:In comparison with typical line widths, the Kossel lines of kamacite are distinctly broadened. This is found for the meteorite Toluca and a for a second sample, the meteorite Morasko. This behaviour is probably connected with a high dislocation density, as shown by transmission electron microscope investigations.
Mineralogy, petrography, bulk chemical, iodine‐xenon, and oxygen‐isotopic compositions of dark inclusions in the reduced CV3 chondrite Efremovka
Authors: KROT A. N. , BREARLEY A. J. , ULYANOV A. A. , BIRYUKOV V. V. , SWINDLE T. D. , KEIL K. , MITTLEFEHLDT D. W. , SCOTT E. R. D. , CLAYTON R. N. , MAYEDA T. K. 
Published: February 2010

Abstract— 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 Bjurböle 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.
Aspects of the validation of magnetic remanence in meteorites
Authors: WASILEWSKI Peter , DICKINSON Tamara 
Published: February 2010

Abstract— Meteorite magnetic records constitute physical evidence of processes acting during early solar system evolution. Consequently, the validation of these records is important in meteorite research. The first step in the validation process should be the REM value. The REM value is the ratio of natural remanence (NRM) to saturation remanent magnetization imparted by a 1 T magnetic field (SIRM). The REM values range over 3 to 4 orders of magnitude for stony meteorites and for chondrules from Allende (C3V‐S1), Bjurböle (L4‐S1), and Chainpur (LL3‐S1) meteorites.The REM values computed from published NRM and SIRM data identify many orders of magnitude range in the REM values including REM values >100 × 10−3. These data suggest a dependence for the NRM intensity on the curatorial location from which the sample was obtained. Any earth rock acquiring thermoremanent magnetization (TRM) in the geomagnetic field has a restricted range in REM mostly between 5 and 50 × 10−3, the exception being the mineral hematite in the multidomain size range. The only terrestrial samples with REM much greater than 100 × 10−3 are those struck by lightning.The REM value provides a physical basis for recognition between valid records and those that “might be contaminated.” The isothermal remanence acquisition (RA) curve is presented as a contamination curve that allows an indication of the level of magnetic field contamination required to give the computed “REM” (RM/SIRM) value. In the case of the Bjurböle and Chainpur chondrules, with REM values >100 × 10−3, the RA curve indicates that unrealistically large contamination magnetic fields would be required to give REM values greater than 100 × 10−3. This would suggest contamination other than by a hand magnet that is normally available to an experimenter. This would require an explanation that would involve large magnetic fields during chondrule formation, or some extraordinary remanence acquisition mechanism that remains to be described.Magnetic contamination experiments, using ∼80 and ∼40 mT magnets, demonstrate that the “REM” values and extent of modification of the magnetic vector record are mineralogy dependent, and this is mostly related to the amount and characteristics of the mineral tetrataenite. The complexity of the meteorite records suggest validation of the record as a first step. The REM value is the first physical statement that can be made in this validation.
Light noble gases and cosmogenic radionuclides in Estherville, Budulan, and other mesosiderites: Implications for exposure histories and production rates
Authors: ALBRECHT A. , SCHNABEL C. , VOGT S. , XUE S. , HERZOG G. F. , BEGEMANN F. , WEBER H. W. , MIDDLETON R. , FINK D. , KLEIN J. 
Published: February 2010

Abstract—We report measurements of26AI,10Be,41Ca, and36Cl in the silicate and metal phases of 11 mesosiderites, including several specimens each of Budulan and Estherville, of the brecciated meteorite Bencubbin, and of the iron meteorite Udei Station. Average production rate ratios (atom/atom) for metal phase samples from Estherville and Budulan are26Al/10Be = 0.77 ± 0.02;36Cl/10Be = 5.3 ± 0.2. For a larger set of meteorites that includes iron meteorites and other mesosiderites, we find26Al/10Be = 0.72 ± 0.01 and36Cl/10Be = 4.5 ± 0.2. The average41Ca/36Cl production rate ratio is 1.10 ± 0.04 for metal separates from Estherville and four small iron falls. The41Ca activities in dpm/(kg Ca) of various silicate separates from Budulan and Estherville span nearly a factor of 4, from <400 to >1600, indicating preatmospheric radii of >30 cm. After allowance for composition, the activities of26Al and10Be (dpm/kg silicate) are similar to values measured in most ordinary chondrites and appear to depend only weakly on bulk Fe content. Unless shielding effects are larger than suggested by the36Cl and41Ca activities of the metal phases, matrix effects are unimportant for10Be and minor for26Al.Noble gas concentrations and isotopic abundances are reported for samples of Barea, Emery, Mincy, Morristown, and Marjalahti. New estimates of36Cl/36Ar exposure ages for the metal phases agree well with published values. Neon‐21 production rates for mesosiderite silicates calculated from these ages and from measured21Ne contents are consistently higher than predicted for L chondrites despite the fact that the mesosiderite silicates have lower Mg contents than L chondrites. We suggest that the elevation of the21Ne production rate in mesosiderite silicates reflects a “matrix effect,” that is, the influence of the higher Fe content of mesosiderites, which acts to enhance the flux of low‐energy secondary particles and hence the21Ne production from Mg. As10Be production is relatively insensitive to this matrix effect,10Be/21Ne ages give erroneously low production rates and high exposure ages. By coincidence, standard22Ne/21Ne based “shielding” corrections give fairly reliable21Ne production rates in the mesosiderite silicates.