bluuebunny/crossref_metadata_2025 huggingface dataset:
The Fountain Hills unique CB chondrite: Insights into thermal processes on the CB parent body
Authors: LAURETTA Dante S. , GOREVA Julia S. , HILL Dolores H. , KILLGORE Marvin , BLUE Alyssa R. La , CAMPBELL Andrew , GREENWOOD R. C. , VERCHOVSKY A. B. , FRANCHI Ian A.
Published: January 2010

Abstract— We report the results of an extensive study of the Fountain Hills chondritic meteorite. This meteorite is closely related to the CBa class. Mineral compositions and O‐isotopic ratios are indistinguishable from other members of this group. However, many features of Fountain Hills are distinct from the other CB chondrites. Fountain Hills contains 23 volume percent metal, significantly lower than other members of this class. In addition, Fountain Hills contains porphyritic chondrules, which are extremely rare in other CBa chondrites. Fountain Hills does not appear to have experienced the extensive shock seen in other CB chondrites. The chondrule textures and lack of fine‐grained matrix suggests that Fountain Hills formed in a dust‐poor region of the early solar system by melting of solid precursors. Refractory siderophiles and lithophile elements are present in near‐CI abundances (within a factor of two, related to the enhancement of metal). Moderately volatile and highly volatile elements are significantly depleted in Fountain Hills. The abundances of refractory siderophile trace elements in metal grains are consistent with condensation from a gas that is reduced relative to solar composition and at relatively high pressures (10−3bars). Fountain Hills experienced significant thermal metamorphism on its parent asteroid. Combining results from the chemical gradients in an isolated spinel grain with olivine‐spinel geothermometry suggests a peak temperature of metamorphism between 535 °C and 878 °C, similar to type‐4 ordinary chondrites.
Apollo 17 regolith, 71501,262: A record of impact events and mare volcanism in lunar glasses
Authors: ZELLNER N. E. B. , DELANO J. W. , SWINDLE T. D. , BARRA F. , OLSEN E. , WHITTET D. C. B.
Published: January 2010

Abstract— Thirteen glasses from Apollo 17 regolith 71501,262 have been chemically analyzed by electron microprobe and isotopically dated with the 40Ar/39Ar dating method. We report here the first isotopic age obtained for the Apollo 17 very low titanium (VLT) volcanic glasses, 3630 ± 40 Ma. Twelve impact glasses that span a wide compositional range have been found to record ages ranging from 102 ± 20 Ma to 3740 ± 50 Ma. The compositions of these impact glasses show that some have been produced by impact events within the Apollo 17 region, whereas others appear to be exotic to the landing site. As the data sets that include compositions and ages of lunar impact glasses increase, the impact history in the Earth‐Moon system will become better constrained.
Systematic study of universal‐stage measurements of planar deformation features in shocked quartz: Implications for statistical significance and representation of results
Authors: FERRIÈRE Ludovic , MORROW Jared R. , AMGAA Tsolmon , KOEBERL Christian
Published: January 2010

Abstract— The presence of shocked quartz is one of the key lines of evidence for the impact origin of rocks. Crystallographic orientations of planar deformation feature (PDF) sets in shocked quartz have been used to constrain the peak shock pressure that these grains have experienced. So far no systematic and comparative studies of the various orientation measurement methods and their biases are available. Therefore, three shocked‐quartz‐bearing thin sections from a meta‐greywacke clast in breccia, a biotite‐gneiss, and a sandstone, respectively, were independently analyzed by three operators (two experienced and one inexperienced) using a four‐axis universal‐stage (U‐stage), in order to evaluate the quality, precision, repeatability, and representativeness of U‐stage measurements. Based on the indexing of PDF sets using a new version of the commonly used stereographic projection template, the study of 1751 PDF set orientations in 666 quartz grains in three different shocked rocks shows that differences in abundance and orientation of various PDF sets, as measured by the three separate operators, are rather limited.

The precision of U‐stage measurements depends mainly on the number of PDF sets investigated, as the ability level of the operator (experienced versus inexperienced) is only responsible for minor deviations in the number of unindexed planes. The frequency percent of dominant PDF planes may vary by up to 20 percentage points (pp) or 81% for a given crystallographic orientation when only 25 sets are measured. When 100 PDF sets are measured, however, this deviation in dominant orientations is reduced to about 7 pp or 28%. We recommend the use of a new stereographic projection template, which plots the pole positions of five additional, commonly occurring PDF orientations, as it can allow indexing of up to 12 pp more PDF planes; these are planes that would previously be considered unindexed and potentially regarded as errors of measurement.

Our results suggest that by following a strict measurement procedure, the reproducibility of U‐stage measurements is good and the results of different studies can be readily compared. However, it is critical that published PDF orientation histograms clearly define what type of frequency measurement is used, whether or not unindexed PDF sets are included in the frequency calculations, the numbers of grains and sets analyzed, and the relative proportions of each PDF set population that are combined in the histograms. This information appears to be essential for effectively comparing datasets from different studies.
Elemental and isotope behavior of macromolecular organic matter from CM chondrites during hydrous pyrolysis
Authors: OBA Yasuhiro , NARAOKA Hiroshi
Published: January 2010

Abstract— A new insight into carbon and hydrogen isotope variations of insoluble organic matter (IOM) is provided from seven CM chondrites, including Murchison and six Antarctic meteorites (Y‐791198, Y‐793321, A‐881280, A‐881334, A‐881458 and B‐7904) as well as Murchison IOM residues after hydrous pyrolysis at 270–330 °C for 72 h. Isotopic compositions of bulk carbon (δ13Cbulk) and hydrogen (δD) of the seven IOMs vary widely, ranging from −15.1 to −7.6%0 and +133 to +986%0, respectively. Intramolecular carboxyl carbon (δ13CCOOH) is more enriched in 13C by 7.5. 11%0 than bulk carbon. After hydrous pyrolysis of Murchison IOM at 330 °C, H/C ratio, δ13Cbulk, δ13CCOOH, and δD values decrease by up to 0.31, 3.5%0, 5.5%0, and 961%0, respectively. The O/C ratio increases from 0.22 to 0.46 at 270 °C and to 0.25 at 300 °C, and decreases to 0.10 at 330 °C. δ13Cbulk‐δD cross plot of Murchison IOM and its pyrolysis residues shows an isotopic sequence. Of the six Antarctic IOMs, A‐881280, A‐881458, Y‐791198 and B‐7904 lie on or near the isotopic sequence depending on the degree of hydrous and/or thermal alteration, while A‐881334 and Y‐793321 consist of another distinct isotope group. A δ13Cbulk‐δ13CCOOH cross‐plot of IOMs, including Murchison pyrolysis residues, has a positive correlation between them, implying that the oxidation process to produce carboxyls is similar among all IOMs. These isotope distributions reflect various degree of alteration on the meteorite parent bodies and/or difference in original isotopic compositions before the parent body processes.
Geochemical identification of impactor for Lonar crater, India
Authors: MISRA Saumitra , NEWSOM Horton E. , PRASAD M. SHYAM , GEISSMAN John W. , DUBE Anand , SENGUPTA Debashish
Published: January 2010

Abstract— The only well‐known terrestrial analogue of impact craters in basaltic crusts of the rocky planets is the Lonar crater, India. For the first time, evidence of the impactor that formed the crater has been identified within the impact spherules, which are ?0.3 to 1 mm in size and of different aerodynamic shapes including spheres, teardrops, cylinders, dumbbells and spindles. They were found in ejecta on the rim of the crater. The spherules have high magnetic susceptibility (from 0.31 to 0.02 SI‐mass) and natural remanent magnetization (NRM) intensity. Both NRM and saturation isothermal remanent magnetization (SIRM) intensity are ?2 Am2/Kg. Demagnetization response by the NRM suggests a complicated history of remanence acquisition. The spherules show schlieren structure described by chains of tiny dendritic and octahedral‐shaped magnetite crystals indicating their quenching from liquid droplets. Microprobe analyses show that, relative to the target basalt compositions, the spherules have relatively high average Fe2O3 (by ?1.5 wt%), MgO (?1 wt%), Mn (?200 ppm), Cr (?200 ppm), Co (?50 ppm), Ni (?1000 ppm) and Zn (?70 ppm), and low Na2O (?1 wt%) and P2O5 (?0.2 wt%). Very high Ni contents, up to 14 times the average content of Lonar basalt, require the presence of a meteoritic component in these spherules. We interpret the high Ni, Cr, and Co abundances in these spherules to indicate that the impactor of the Lonar crater was a chondrite, which is present in abundances of 12 to 20 percent by weight in these impact spherules. Relatively high Zn yet low Na2O and P2O5 contents of these spherules indicate exchange of volatiles between the quenching spherule droplets and the impact plume.
Trace element chemistry of Cumulus Ridge 04071 pallasite with implications for main group pallasites
Authors: DANIELSON Lisa R. , RIGHTER Kevin , HUMAYUN Munir
Published: January 2010

Abstract— Pallasites have long been thought to represent samples from the metallic core‐silicate mantle boundary of a small asteroid‐sized body, with as many as ten different parent bodies recognized recently. This report focuses on the description, classification, and petrogenetic history of pallasite Cumulus Ridge (CMS) 04071 using electron microscopy and laser ablation ICP‐MS. Most olivines are angular in CMS 04071, but there are some minor occurrences of small rounded olivines, such as in the Eagle Station pallasite. Olivine, chromite, and metal compositions indicate that CMS 04071 can be classified as a Main Group pallasite. The kamacite/taenite partition coefficients (D) for highly siderophile elements (HSE) are all close to 1, but comparison with previous studies on iron meteorites and pallasites shows that variation of some D values is controlled by the Ni content of taenite. D(HSE)metal/sulfide for Re, Cu, and Cr all are < 1, indicating chalcophile behavior for these three elements, in agreement with experimental Dmetal/sulfide. D(HSE)metal/olivine are variable, which is perhaps due to small metallic inclusions in the olivine that are present to variable extents in different pallasites. All of these data, together with results from previous studies, indicate that the CMS pallasites were likely formed at the core‐mantle boundary of a small asteroid, but not necessarily related to the core that produced the IIIAB irons. In addition, they share a similar volatile element depletion to HEDs that is distinct from other bodies such as Earth, Mars, Angrite Parent Body, and the parent body of the brachinites.
The use of Auger spectroscopy for the in situ elemental characterization of sub‐micrometer presolar grains
Authors: STADERMANN Frank J. , FLOSS Christine , BOSE Maitrayee , LEA A. Scott
Published: January 2010

Abstract— Presolar grains are small samples of stardust that can be found at low abundances in some of the most unaltered types of extraterrestrial materials. While earlier laboratory studies of stardust mainly focused on grain types that can be extracted from bulk meteorites by acid dissolution techniques, such as silicon carbide and graphite, recent analyses of presolar silicates rely on isotope imaging searches for locating these grains in situ. Since presolar silicates are generally less than a micrometer in diameter and represent at best only a few hundred ppm of their host materials (e.g., primitive meteorites or interplanetary dust particles), locating and studying these particles can be analytically challenging. Recently, we began using scanning Auger spectroscopy for the in situ elemental characterization of presolar silicate grains as a complement to NanoSIMS isotopic studies for obtaining spatially matched compositional data. Auger spectroscopy is a well‐established analytical technique for elemental characterizations in the material sciences, but has not been widely used in geological applications. We discuss the application of this technique to sub‐micrometer sized silicate grains and address practical issues such as sample preparation, measurement settings, spatial resolution, data processing, and elemental quantification.
Multiple fluvial reworking of impact ejecta—A case study from the Ries crater, southern Germany
Authors: BUCHNER Elmar , SCHMIEDER Martin
Published: January 2010

Abstract— Impact ejecta eroded and transported by gravity flows, tsunamis, or glaciers have been reported from a number of impact structures on Earth. Impact ejecta reworked by fluvial processes, however, are sparsely mentioned in the literature. This suggests that shocked mineral grains and impact glasses are unstable when eroded and transported in a fluvial system. As a case study, we here present a report of impact ejecta affected by multiple fluvial reworking including rounded quartz grains with planar deformation features and diaplectic quartz and feldspar glass in pebbles of fluvial sandstones from the “Monheimer Höhensande” ?10 km east of the Ries crater in southern Germany.
Cosmogenic nuclides in stony meteorites revisited
Authors: LEYA Ingo , MASARIK Jozef
Published: January 2010

Abstract— We present new model calculations for depth and size dependent cosmogenic production rates in ordinary and carbonaceous chondrites by galactic cosmic rays. This model, essentially that of Leya et al. (2000a), folds together particle spectra and cross sections for the relevant nuclear reactions, but has been significantly improved due to major improvements in the neutron cross section database and better Monte Carlo modeling of the primary and the secondary particle spectra. The data presented here replace (and extend) the results of our earlier model predictions. Here we give for ordinary and carbonaceous chondrites elemental production rates for the cosmogenic radionuclides 10Be, 14C, 26Al, 36Cl, 41Ca, 53Mn, 60Fe, and 129I as well as for the noble gas isotopes 3He, 4He, 20Ne, 21Ne, 22Ne, 36Ar, and 38Ar. Using the new data and expressing size and depth scales to the unit [g/cm2], we are able to demonstrate that the matrix effect for both chondrite types is negligible for all target product combinations, except for those which are dominated by thermal or very low energy neutron reactions. Based on the new model predictions, we present a variety of elemental and isotopic production rate ratios allowing for a reliable determination of preatmospheric sizes, shielding depths, cosmic‐ray exposure ages, and diffusive losses.
Hydrodynamic modelling of cometary particles captured in aerogel and the Earth's atmosphere
Authors: Coulson S. G.
Published: January 2010

Abstract— The capture of cometary fragments in aerogel by the Stardust mission is analogous to the process of meteoroid deceleration in the Earth's atmosphere. We present a simplified model for the formation of the tracks formed in aerogel by hypervelocity impacts of cometary material. Using a hydrodynamic approach to model this class of problem overcomes some of the errors associated with previous semi‐analytical models for track formation (Coulson 2009). The hydrodynamic models developed allow the particle velocity, temperature and pressure to be calculated as a function of track length within aerogel. A qualative description of how this model can be extended to the formation of bulbous cavities using the Chapman‐Jouquet theory is provided.
Time evolution and temperatures of hypervelocity impact‐generated tracks in aerogel
Authors: Dominguez Gerardo
Published: January 2010

Abstract— Aerogel collectors have been used to capture cometary, interplanetary, and interstellar dust grains by NASA's Stardust mission, highlighting their importance as a scientific instrument. Due to the fragile and heterogeneous nature of cometary dust grains, their fragments are found along the walls of tracks that are formed during the capture process. These fragments appear to experience a wide range of thermal alteration and the causes of this variation are not well understood at a theoretical level as physical models of track formation are not well developed. Here, a general model of track formation that allows for the existence of partially and completely vaporized aerogel material in tracks is developed. It is shown that under certain conditions, this general track model reduces to the kinetic “snowplow” model that has previously been proposed. It is also shown, based on energetic considerations, that track formation is dominated by an expansion that is snowplow‐like in the later stages of track formation. The equation of motion for this snowplow‐like stage can be solved analytically, thus placing constraints on the amount of heating experienced by cometary dust fragments embedded in track walls. It is found that the heating of these fragments, for a given impact velocity, is expected to be greater for those embedded in larger tracks. Given the expected future use of aerogels for sample return missions, the results presented here imply that the choice of aerogel compositions can have a significant effect on the modification of samples captured and retrieved by these collectors.
Interpretation of Wild 2 dust fine structure: Comparison of Stardust aluminum foil craters to the three‐dimensional shape of experimental impacts by artificial aggregate particles and meteorite powders
Authors: Kearsley A. T. , Burchell M. J. , Price M. C. , Graham G. A. , Wozniakiewicz P. J. , Cole M. J. , Foster N. J. , Teslich N.
Published: January 2010

Abstract— New experimental results show that Stardust crater morphology is consistent with interpretation of many larger Wild 2 dust grains being aggregates, albeit most of low porosity and therefore relatively high density. The majority of large Stardust grains (i.e. those carrying most of the cometary dust mass) probably had density of 2.4 g cm−3 (similar to soda‐lime glass used in earlier calibration experiments) or greater, and porosity of 25% or less, akin to consolidated carbonaceous chondrite meteorites, and much lower than the 80% suggested for fractal dust aggregates. Although better size calibration is required for interpretation of the very smallest impacting grains, we suggest that aggregates could have dense components dominated by μm‐scale and smaller sub‐grains. If porosity of the Wild 2 nucleus is high, with similar bulk density to other comets, much of the pore space may be at a scale of tens of micrometers, between coarser, denser grains.

Successful demonstration of aggregate projectile impacts in the laboratory now opens the possibility of experiments to further constrain the conditions for creation of bulbous (Type C) tracks in aerogel, which we have observed in recent shots. We are also using mixed mineral aggregates to document differential survival of pristine composition and crystalline structure in diverse finegrained components of aggregate cometary dust analogues, impacted onto both foil and aerogel under Stardust encounter conditions.
In situ analysis of residues resulting from laboratory impacts into aluminum 1100 foil: Implications for Stardust crater analyses
Authors: Wozniakiewicz P. J. , Kearsley A. T. , Burchell M. J. , Foster N. J. , Cole M. J. , Bland P. A. , Russell S. S.
Published: January 2010

Abstract— The encounter between the Stardust spacecraft and particles from comet 81P/Wild 2 gave impacts at a relative velocity of 6.1 km s−1 and near perpendicular incidence to the collector surface. Such conditions are well within the performance limits of light gas gun laboratory simulations. For this study, two series of shots were conducted at the University of Kent, firing magnesium silicates (Mg end‐member forsterite, enstatite, diopside and lizardite), followed by a suite of increasingly Ferich olivines (through to Fe end‐member fayalite) into Stardust flight‐spare foils. Preserved residues were analysed using scanning electron microscopy combined with energy dispersive X‐ray analyses (SEM/EDX). X‐ray count integrals show that mineral compositions remain distinct from one another after impact, although they do show increased scatter. However, there is a small but systematic increase in Mg relative to Si for all residues when compared to projectile compositions. While some changes in Mg: Si may be due to complex analytical geometries in craters, there appears to be some preferential loss of Si. In practice, EDX analyses in craters on Stardust Al 1100 foil inevitably include contributions from Fe‐ and Si‐rich alloy inclusions, leading to further scattering of element ratios. Such inclusions have complicated Mg: Fe data interpretation. Compositional heterogeneity in the synthetic olivine projectiles also introduces data spread. Nevertheless, even with the preceding caveats, we find that the main groups of mafic silicates can be easily and reliably distinguished in EDX analyses performed in rapid surveys of foil craters, enabling access to a valuable additional collection of cometary materials.
Connection between micrometeorites and Wild 2 particles: From Antarctic snow to cometary ices
Authors: Dobricǎ E. , Engrand C. , Duprat J. , Gounelle M. , Leroux H. , Quirico E. , Rouzaud J.‐N.
Published: January 2010

Abstract— We discuss the relationship between large cosmic dust that represents the main source of extraterrestrial matter presently accreted by the Earth and samples from comet 81P/Wild 2 returned by the Stardust mission in January 2006. Prior examinations of the Stardust samples have shown that Wild 2 cometary dust particles contain a large diversity of components, formed at various heliocentric distances. These analyses suggest large‐scale radial mixing mechanism(s) in the early solar nebula and the existence of a continuum between primitive asteroidal and cometary matter. The recent collection of CONCORDIA Antarctic micrometeorites recovered from ultra‐clean snow close to Dome C provides the most unbiased collection of large cosmic dust available for analyses in the laboratory. Many similarities can be found between Antarctic micrometeorites and Wild 2 samples, in terms of chemical, mineralogical, and isotopic compositions, and in the structure and composition of their carbonaceous matter. Cosmic dust in the form of CONCORDIA Antarctic micrometeorites and primitive IDPs are preferred samples to study the asteroid‐comet continuum.
Dynamics of high‐temperature materials delivered by jets to the outer solar nebula
Authors: Ciesla Fred J.
Published: January 2010

Abstract— The presence of high‐temperature materials in the Stardust collection that are isotopically similar to those seen in chondritic meteorites argues for the outward transport of materials from the hot, inner region of the solar nebula to the region where comets formed. A number of mechanisms have been proposed to be responsible for this transport, with a number of models being developed to show that such outward transport is possible. However, these models have not examined in detail how these grains are transported after they have been delivered to the comet formation region or how they may be distributed in the cometary nuclei that form. Here, the dynamical evolution of crystalline silicates injected onto the surface of the solar nebula as proposed by jet models for radial transport is considered. It is generally found that crystalline grains should be heterogeneously distributed within the population of comets and within individual cometary nuclei. In order to achieve a homogeneous distribution of such grains, turbulence must be effective at mixing the crystalline silicates with native, amorphous grains on fine scales. However, this turbulent mixing would serve to dilute the crystalline silicates as it would redistribute them over large radial distances. These results suggest that it is difficult to infer the bulk properties of Wild 2 from the Stardust samples, and that the abundance of crystalline grains in these samples cannot alone be used to rule out or in favor of any of the different radial transport models that have been proposed.
Nebular mixing constrained by the Stardust samples
Authors: Ogliore R. C. , Westphal A. J. , Gainsforth Z. , Butterworth A. L. , Fakra S. C. , Marcus M. A.
Published: January 2010

Abstract— Using X‐ray microprobe analysis of samples from comet Wild 2 returned by the Stardust mission, we determine that the crystalline Fe‐bearing silicate fraction in this Jupiter‐family comet is greater than 0.5. Assuming this mixture is a composite of crystalline inner solar system material and amorphous cold molecular cloud material, we deduce that more than half of Wild 2 has been processed in the inner solar system. Several models exist that explain the presence of crystalline materials in comets. We explore some of these models in light of our results.
The mineralogy of the Yaringie Hill meteorite—A new H5 chondrite from South Australia
Authors: Tappert Ralf , Foden John , Pring Allan
Published: January 2010

Abstract— The Yaringie Hill meteorite is a new H5 ordinary chondrite found in the Gawler Ranges, South Australia. The meteorite, which shows only minor signs of terrestrial weathering, is predominantly composed of olivine (Fa17.2), orthopyroxene (Fs15.1Wo1.1), and three distinct phases of nickeliferous iron metal (kamacite, taenite, tetrataenite). Other minerals include troilite, plagioclase (Ab81An16Or3), clinopyroxene (En52Wo42Fs6), chlorapatite, merrillite, ilmenite, and native copper. Three types of spinel with distinctive textures (coarse, skeletal aggregates, rounded aggregates) and with compositions close to the join MgAl2O4‐FeCr2O4 are also present. Chondrules within the Yaringie Hill meteorite, which often have poorly defined boundaries, are placed in a recrystallized matrix. Shock indicators suggest that the meteorite experienced only weak shock metamorphism (S3).
Stardust glass: Indigenous and modified comet Wild 2 particles
Authors: Rietmeijer Frans J. M.
Published: January 2010

Abstract— Does comet 81P/Wild 2 have indigenous glass? Glass is used here to include all types of amorphous materials that could be either indigenous or modified comet Wild 2 grains, and all amorphous phases in chondritic aggregate interplanetary dust particles (IDPs). The answer is that it probably does, but very little is known of their compositions to allow a definitive answer to be given. There is no evidence among the collected comet dust for interstellar glass with embedded metals and sulfides. There is, however, ample evidence for melting of the smallest, sub‐micrometer comet particles of nanometer‐scale grains similar to those in the matrix of chondritic aggregate IDPs, including pyrrhotite. Massive patches of Mg‐SiO, Al‐SiO, or Ca‐Si‐O glass are incorporated in the familiar, vesicular Si‐rich glass are melted Wild 2 silicates. Magnesiosilica glass has a deep metastable eutectic smectite‐dehydroxylate composition. It indicates that very high temperatures well above the liquidus temperatures of forsterite were achieved very rapidly and were followed but ultra‐rapid quenching. This predictable and systematic response is not limited to Mg‐silicates, and recognizing this phenomenon among massive glass will provide a means to complete the reconstruction of this comet's original minerals, as well as constrain the physiochemical environment created during aerogel melting and evaporation.
The comparative behavior of apatite‐zircon U‐Pb systems in Apollo 14 breccias: Implications for the thermal history of the Fra Mauro Formation
Authors: Nemchin A. A. , Pidgeon R. T. , Healy D. , Grange M. L. , Whitehouse M. J. , Vaughan J.
Published: January 2010

Abstract— We report secondary ion mass spectrometry (SIMS) U‐Pb analyses of zircon and apatite from four breccia samples from the Apollo 14 landing site. The zircon and apatite grains occur as cogenetic minerals in lithic clasts in two of the breccias and as unrelated mineral clasts in the matrices of the other two. SIMS U‐Pb analyses show that the ages of zircon grains range from 4023 ± 24 Ma to 4342 ± 5 Ma, whereas all apatite grains define an isochron corresponding to an age of 3926 ± 3 Ma. The disparity in the ages of cogenetic apatite and zircon demonstrates that the apatite U‐Pb systems have been completely reset at 3926 ± 3 Ma, whereas the U‐Pb system of zircon has not been noticeably disturbed at this time. The apatite U‐Pb age is slightly older than the ages determined by other methods on Apollo 14 materials highlighting need to reconcile decay constants used for the U‐Pb, Ar‐Ar and Rb‐Sr systems. We interpret the apatite age as a time of formation of the Fra Mauro Formation. If the interpretation of this Formation as an Imbrium ejecta is correct, apatite also determines the timing of Imbrium impact. The contrast in the Pb loss behavior of apatite and zircon places constraints on the temperature history of the Apollo 14 breccias and we estimate, from the experimentally determined Pb diffusion constants and an approximation of the original depth of the excavated samples in the Fra Mauro Formation, that the breccias experienced an initial temperature of about 1300–1100 °C, but cooled within the first five to ten years.
Vesta and the HED meteorites: Mid‐infrared modeling of minerals and their abundances
Authors: Hanna Kerri Donaldson , Sprague Ann L.
Published: January 2010

Abstract— We demonstrate that the use of an established spectral deconvolution algorithm with mid‐infrared spectral libraries of mineral separates of varying grain sizes is capable of identifying the known mineral compositions and abundances of a selection of howardite, eucrite, and diogenite (HED) meteorite samples. In addition, we apply the same technique to mid‐infrared spectral emissivity measurements of Vesta that have been obtained from Cornell's Mid‐Infrared Asteroid Spectroscopy (MIDAS) Survey and the Infrared Space Observatory (ISO). Each Vesta measurement was made over a different range of longitudes. Our spectral deconvolution results to the Vesta spectra corroborate that Vesta's surface is howardite or eucrite‐like in composition and heterogeneous across its surface. The spectral fits produced by the linear deconvolution algorithm yields good results for the HED samples of known composition, thus giving us a high degree of confidence that our results for Vesta are valid.
Interpreting the I‐Xe system in individual silicate grains from Toluca IAB
Authors: Pravdivtseva O. V. , Meshik A. P. , Hohenberg C. M. , Petaev M.
Published: January 2010

Abstract— Detailed isotopic and mineralogical studies of silicate inclusions separated from a troilite nodule of the Toluca IAB iron meteorite reveal the presence of radiogenic 129Xe in chlorapatite, plagioclase, perryite, and pyroxene grains. Subsequent I‐Xe studies of 32 neutron‐irradiated pyroxene grains indicate that high‐Mg and low‐Mg pyroxenes have distinctive I‐Xe signatures. The I‐Xe system in high‐Mg pyroxenes closed at 4560.5 ± 2.4 Ma, probably reflecting exsolution of silicates from the melt, while the low‐Mg pyroxenes closed at 4552.0 ± 3.7 Ma, 8.5 Ma later, providing a means for determining the cooling rate at the time of exsolution. If the host Toluca graphite‐troilite‐rich inclusion formed after the breakup and reassembly of the IAB parent body as has been suggested, the I‐Xe ages of the high‐Mg pyroxenes separated from this inclusions indicate that this catastrophic impact occurred not later than 4560.5 Ma, 6.7 Ma after formation of CAIs. The cooling rate at the time of silicates exsolution in Toluca is 14.5 ± 10.0 °C/Ma.
Shocked quartz grains in the polymict breccia of the Granby structure, Sweden–‐Verification of an impact
Authors: Alwmark Carl
Published: January 2010

Abstract— The Middle Ordovician Granby structure in Sweden is generally considered the result of an asteroidal or cometary collision with Earth, although no hard evidence, i.e., shock metamorphic features or traces of the impactor, have been presented to date. In this study, drill core samples of a sedimentary breccia from the Granby structure have been investigated for microscopic shock metamorphic evidence in an attempt to verify the impact genesis of the structure. The finding of multiple sets of decorated planar deformation features (PDFs) in quartz grains in these samples provides unambiguous evidence that the structure is impact derived. Furthermore, the orientation of the PDFs, e.g., ω {101

}, π {101

} and r, z {101

}, is characteristic for impact deformation. The fact that a majority of the PDFs are decorated implies a water‐bearing target. The shocked quartz grains can be divided into two groups; rounded grains found in the breccia matrix likely originated from mature sandstone, and angular grains in fragments from crystalline target rocks. The absence of melt particles provides an estimated maximum shock pressure for the sedimentary derived quartz of 15–20 GPa and the frequency distribution of PDF orientations in the bedrock quartz implies pressures of the order of 10 GPa.
Estimate of the magnetic field of Mars based on the magnetic characteristics of the Yamato 000593 nakhlite
Authors: Funaki Minoru , Hoffmann Viktor , Imae Naoya
Published: January 2010

Abstract— Yamato 000593, a nakhlite, was analyzed in terms of its magnetic record and magnetomineralogy. The natural remanent magnetization (NRM: 3.55–6.07 times 10−5 Am2/kg) was thermally demagnetized at ∼320 °C, and it was unstable against alternating field demagnetization. Based on analyses of thermomagnetic curves, the temperature dependence of hysteresis parameters, and microscopic observations, the magnetic minerals mainly consist of magnetite (0.68 wt% of the sample, including ∼5% Fe2TiO4) of less than 100 μm in size, associated with minor amounts of monoclinic pyrrhotite (<0.069 wt% of the sample) and goethite. Thermal demagnetization of NRM at ∼330 °C is explained due to an offset of magnetization of antipodal NRM components of magnetite, whereas it is not due to a pyrrhotite Curie point. Large magnetite grains show exsolution texture with ilmenite laths, and are cut by silicate (including goethite) veins that formed along cracks. Numerous single‐domain (SD) and pseudo‐single‐domain (PSD) magnetite grains are scattered in the mesostasis and adjacent olivine grains. Moderate coercive forces of HC = 6.8 mT and HRC = 31.1 mT suggest that Yamato 000593 is fundamentally able to carry a stable NRM; however, NRM was found to be unstable. Accordingly, the meteorite was possibly crystallized at 1.3 Ga under an extremely weak or absent magnetic field, or was demagnetized by impact shock at 12 Ma (ejection age) on Mars. This finding differs from the results of previous paleomagnetic studies of SNC (shergottites, nakhlites, chassignites, and orthopyroxenite) Martian meteorites. The significant dipole magnetic field resulting from the molten metallic core was probably absent during the Amazonian Epoch (after 1.8 Ga) on Mars.
Identification of the Bloody Creek structure, a possible impact crater in southwestern Nova Scotia, Canada
Authors: Spooner Ian , Stevens George , Morrow Jared , Pufahl Peir , Grieve Richard , Raeside Rob , Pilon Jean , Stanley Cliff , Barr Sandra , McMullin David
Published: January 2010

Abstract— An approximately 0.4 km diameter elliptical structure formed in Devonian granite in southwestern Nova Scotia, herein named the Bloody Creek structure (BCS), is identified as a possible impact crater. Evidence for an impact origin is based on integrated geomorphic, geophysical, and petrographic data. A near‐continuous geomorphic rim and a 10 m deep crater that is infilled with lacustrine sediments and peat define the BCS. Ground penetrating radar shows that the crater has a depressed inner floor that is sharply ringed by a 1 m high buried scarp. Heterogeneous material under the floor, interpreted as deposits from collapse of the transient cavity walls, is overlain by stratified and faulted lacustrine and wetland sediments.

Alteration features found only in rim rocks include common grain comminution, polymict lithic microbreccias, kink‐banded feldspar and biotite, single and multiple sets of closely spaced planar microstructures (PMs) in quartz and feldspar, and quartz mosaicism, rare reduced mineral birefringence, and chlorite showing plastic deformation and flow microtextures. Based on their form and crystallographic orientations, the quartz PMs consist of planar deformation features that document shock‐metamorphic pressures ≤25 GPa.

The age of the BCS is not determined. The low depth to diameter ratio of the crater, coupled with anomalously high shock‐metamorphic pressures recorded at its exposed rim, may be a result of significant post‐impact erosion. Alternatively, impact onto glacier ice during the waning stages of Wisconsinian deglaciation (about 12 ka BP) may have resulted in dissipation of much impact energy into the ice, resulting in the present morphology of the BCS.
A combined ToF‐SIMS and EMP/SEM study of a three‐phase symplectite in the Los Angeles basaltic shergottite
Authors: Rost Detlef , Stephan Thomas , Greshake Ansgar , Fritz Jörg , Weber Iris , Jessberger Elmar K. , Stöffler Dieter
Published: January 2010

Abstract— A rare three‐phase symplectite consisting of Ca‐rich pyroxene, Fe‐rich olivine, and a silica phase is frequently found rimming pyroxene in the Martian meteorite Los Angeles. This assemblage is usually interpreted as the breakdown product of metastable pyroxferroite, a very rare pyroxenoid mineral itself. However, its origin is not entirely understood, mainly because the extremely small average size of the constituent phases represents a challenge for precise high‐resolution analysis. In addition to electron microbeam methods, the present study uses time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) to overcome the limits of spatial resolution and to comprehensively study this mineral assemblage. The prevailing breakdown hypothesis is supported by the following results: (1) The three symplectite phases are very homogenous in composition from 100 μm down to the micrometer scale. (2) The silica phase could be shown to be almost pure SiO2. (3) The symplectite bulk composition is consistent with pyroxferroite. Sub‐micrometer sized Ti‐oxide grains are found within the symplectite (but not within the Ca‐rich pyroxene) and probably represent a minor breakdown phase in addition to the three main phases.
Petrography, mineralogy, and trace element geochemistry of lunar meteorite Dhofar 1180
Authors: Zhang Aicheng , Hsu Weibiao
Published: January 2010

Abstract— Here we report the petrography, mineralogy, and trace element geochemistry of the Dhofar 1180 lunar meteorite. Dhofar 1180 is predominantly composed of fine‐grained matrix with abundant mineral fragments and a few lithic and glassy clasts. Lithic clasts show a variety of textures including cataclastic, gabbroic, granulitic, ophitic/subophitic, and microporphyritic. Both feldspathic and mafic lithic clasts are present. Most feldspathic lithic clasts have a strong affinity to ferroan anorthositic suite rocks and one to magnesian suite rocks. Mafic lithic clasts are moderately to extremely Fe‐rich. The Ti/[Ti+Cr]‐Fe/[Fe+Mg] compositional trend of pyroxenes in mafic lithic clasts is consistent with that of low‐Ti mare basalts. Glasses display a wide chemical variation from mafic to feldspathic. Some glasses are very similar to those from Apollo 16 soils. KREEP components are essentially absent in Dhofar 1180. One glassy clast is rich in K, REE and P, but its Mg/[Mg+Fe] is very low (0.25). It is probably a last‐stage differentiation product of mare basalt. Molar Fe/Mn ratios of both olivine and pyroxene are essentially consistent with a lunar origin.

Dhofar 1180 has a LREE‐enriched (La 18 × CI, Sm 14 × CI) pattern with a small positive Eu anomaly (Eu 15 × CI). Th concentration is 0.7 ppm in Dhofar 1180. Petrography, mineralogy, and trace element geochemistry of Dhofar 1180 are different from those of other lunar meteorites, indicating that Dhofar 1180 represents a unique mingled lunar breccia derived from an area on the lunar nearside but far away from the center of the Imbrium Basin.
Compositional and lithological diversity among brecciated lunar meteorites of intermediate iron concentration
Authors: Korotev Randy L. , Zeigler Ryan A. , Jolliff Bradley L. , Irvin Anthony J. , Bunch Theodore E.
Published: January 2010

Abstract— We present new compositional data for 30 lunar stones representing about 19 meteorites. Most have iron concentrations intermediate to those of the numerous feldspathic lunar meteorites (3–7% FeO) and the basaltic lunar meteorites (17–23% FeO). All but one are polymict breccias. Some, as implied by their intermediate composition, are mainly mixtures of brecciated anorthosite and mare basalt, with low concentrations of incompatible elements such as Sm (1–3 μg/g). These breccias likely originate from points on the Moon where mare basalt has mixed with material of the FHT (Feldspathic Highlands Terrane). Others, however, are not anorthosite‐basalt mixtures. Three (17–75 μ/g Sm) consist mainly of nonmare mafic material from the nearside PKT (Procellarum KREEP Terrane) and a few are ternary mixtures of material from the FHT, PKT, and maria. Some contain mafic, nonmare lithologies like anorthositic norites, norites, gabbronorites, and troctolite. These breccias are largely unlike breccias of the Apollo collection in that they are poor in Sm as well as highly feldspathic anorthosite such as that common at the Apollo 16 site. Several have high Th/Sm compared to Apollo breccias. Dhofar 961, which is olivine gabbronoritic and moderately rich in Sm, has lower Eu/Sm than Apollo samples of similar Sm concentration. This difference indicates that the carrier of rare earth elements is not KREEP, as known from the Apollo missions. On the basis of our present knowledge from remote sensing, among lunar meteorites Dhofar 961 is the one most likely to have originated from South Pole‐Aitken basin on the lunar far side.
Pyroxene mineralogies of near‐Earth vestoids
Authors: Burbine Thomas H. , Buchanan Paul C. , Dolkar Tenzin , Binzel Richard P.
Published: January 2010

Abstract— We have calculated pyroxene mineralogies of seven near‐Earth asteroids (NEAs) with reflectance spectra similar to HEDs (howardites, eucrites, and diogenites). Two different sets of formulas (Gaffey et al. 2002; Burbine et al. 2007) are used to calculate the pyroxene mineralogies of the NEAs from their Band I and II centers. The band centers have been adjusted to compensate for the low temperatures on the asteroid surfaces. All of the derived mineralogies from the Gaffey et al. (2002) formulas and the Burbine et al. (2007) formulas overlap. The derived wollastonite (Wo) contents are very similar with differences being only approximately 1 mol%. The derived ferrosilite (Fs) contents differ by only 3 to 8 mol%. The determined pyroxene mineralogies for all seven near‐Earth vestoids are consistent with eucrites or howardites. None of the objects have pyroxene mineralogies consistent with diogenites. The absence of near‐Earth vestoids with pyroxene mineralogies similar to diogenites may indicate that it is difficult to produce sizeable (km‐sized or larger) bodies that are predominantly composed of diogenitic material, suggesting these objects are rubble piles of mixed ejecta.
Weston: Revised position for a historically significant meteorite fall
Authors: Robson Monty , Pagliaro Frank
Published: January 2010

Abstract— Weston is the first well‐documented meteorite fall in the New World. The fall occurred on December 14, 1807. The Weston event began the study of meteoritics in the United States in the decade that science accepted that stones do, in fact, fall from the sky. It is unfortunate that much of the literature regarding this historically significant fall is erroneous.

This paper will deal with the geographic position of the fall site. One of us (Robson 2007) proposed a new set of coordinates for Weston that was accepted by the Meteoritical Society. At the society's 70th annual meeting, new Weston coordinates were suggested; with the caveat that research was ongoing. However, it was also stated in the presentation that it was unlikely that either coordinate would change by as much as a minute. Further research indicates a final revision is required. Our revised mean fall position of the seven documented fragments of Weston is: 41°16′ N, 73°16′ W (WGS 84 coordinates, to the nearest minute).

A quirk of history is a main factor in the derivation of faulty positions for Weston. The historically changing positions given for the fall are explored. Our methodology is discussed and the newly discovered Weston manuscripts, maps, and communications of Yale's foremost meteoric astronomer, Professor H. A. Newton, support our findings.
Effects of partial miscibility on drop-wall and drop-drop interactions
Authors: Tufano C. , Peters G. W. M. , Meijer H. E. H. , Anderson P. D.
Published: January 2010

The effect of the mutual diffusion of two polymeric phases on the interaction and coalescence of two nearby drops in quiescent conditions is investigated for two partially miscible systems, differing in the miscibility of the components. Transient interfacial tension measurements show that the polybutene (PB)/polydimethylsiloxane (PDMS) system is highly diffusive in terms of diffusing low-molecular weight species, while the polybutadiene (PBD)/PDMS system is less miscible. Drops of the highly diffusive PB/PDMS system at distances closer than their equivalent radius attract each other and coalesce with a rate that, in the last stage of the coalescence process, is the same for all drop combinations. For the slightly diffusive PBD/PDMS system, no coalescence occurs, and, in contrast, repulsion between the drops is observed. These phenomena are qualitatively explained in terms of the overlap of diffuse layers formed at the drop surfaces of two, close enough drops, yielding concentration gradients that cause gradients in the interfacial tension. These gradients yield Marangoni stresses that induce flow leading either to attraction or repulsion. To determine whether Marangoni stresses are strong enough to displace a drop in quiescent conditions, single drops of PB and PBD are placed in a PDMS matrix in the vicinity of a wall. A lateral drop motion toward the wall is observed for the highly diffusive PB/PDMS system only, while PBD drops do not move. The diffuse-interface model is considered as a good candidate to capture these phenomena described since it couples the mutual diffusion of the low-molecular weight component with both drop and matrix, while including hydrodynamic forces. The presented numerical simulations indeed show a diffusion-induced macroscopic motion that qualitatively reproduces the experimental phenomena observed and support our interpretations.