Philipp R. Heck^1,2 et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Robert A. Pritzker Center for Meteoritics and Polar Studies, The Field Museum, Chicago, Illinois, USA
²Chicago Center for Cosmochemistry, The University of Chicago, Chicago, Illinois, USA

Atom-probe tomography (APT) is currently the only analytical technique that, due to its spatial resolution and detection efficiency, has the potential to measure the carbon isotope ratios of individual nanodiamonds. We describe three different sample preparation protocols that we developed for the APT analysis of meteoritic nanodiamonds at sub-nm resolution and present carbon isotope peak ratios of meteoritic and synthetic nanodiamonds. The results demonstrate an instrumental bias associated with APT that needs to be quantified and corrected to obtain accurate isotope ratios. After this correction is applied, this technique should allow determination of the distribution of ¹²C/¹³C ratios in individual diamond grains, solving the decades-old question of the origin of meteoritic nanodiamonds: what fraction, if any, formed in the solar system and in presolar environments? Furthermore, APT could help us identify the stellar sources of any presolar nanodiamonds that are detected.

Reference
Heck PR et al. (in press) Atom-probe analyses of nanodiamonds from Allende. Meteoritics & Planetary Science. Meteoritics & Planetary Science
[doi:10.1111/maps.12265]
Published by arrangement with John Wiley & Sons

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J. Gattacceca^1,2, C. Suavet¹, P. Rochette², B. P. Weiss¹, M. Winklhofer³, M. Uehara², Jon M. Friedrich^4,5

¹Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
²CNRS, Aix-Marseille Université, Aix en Provence, France
³Department of Earth and Environmental Sciences, Ludwig-Maximilians-University Munich, Munich, Germany
⁴Department of Chemistry, Fordham University, Bronx, New York, USA
⁵Department of Earth and Planetary Sciences, American Museum of Natural History, New York City, New York, USA

Magnetic properties are sensitive proxies to characterize FeNi metal phases in meteorites. We present a data set of magnetic hysteresis properties of 91 ordinary chondrite falls. We show that hysteresis properties are distinctive of individual meteorites while homogeneous among meteorite subsamples. Except for the most primitive chondrites, these properties can be explained by a mixture of multidomain kamacite that dominates the induced magnetism and tetrataenite (both in the cloudy zone as single-domain grains, and as larger multidomain grains in plessite and in the rim of zoned taenite) dominates the remanent magnetism, in agreement with previous microscopic magnetic observations. The bulk metal contents derived from magnetic measurements are in agreement with those estimated previously from chemical analyses. We evidence a decreasing metal content with increasing petrologic type in ordinary chondrites, compatible with oxidation of metal during thermal metamorphism. Types 5 and 6 ordinary chondrites have higher tetrataenite content than type 4 chondrites. This is compatible with lower cooling rates in the 650–450 °C interval for higher petrographic types (consistent with an onion-shell model), but is more likely the result of the oxidation of ordinary chondrites with increasing metamorphism. In equilibrated chondrites, shock-related transient heating events above approximately 500 °C result in the disordering of tetrataenite and associated drastic change in magnetic properties. As a good indicator of the amount of tetrataenite, hysteresis properties are a very sensitive proxy of the thermal history of ordinary chondrites, revealing low cooling rates during thermal metamorphism and high cooling rates (e.g., following shock reheating or excavation after thermal metamorphism). Our data strengthen the view that the poor magnetic recording properties of multidomain kamacite and the secondary origin of tetrataenite make equilibrated ordinary chondrites challenging targets for paleomagnetic study.

Reference
Beck P et al. (in press) Metal phases in ordinary chondrites: Magnetic hysteresis properties and implications for thermal history. Meteoritics & Planetary Science
[doi:10.1111/maps.12268]
Published by arrangement with John Wiley & Sons

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G. A. Brennecka¹, L. E. Borg¹, M. Wadhwa²

¹Lawrence Livermore National Laboratory, Livermore, California, USA
²School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA

The recent witnessed fall of the meteorite Tissint represents the delivery of a pristine new sample from the surface of Mars. This meteorite provides an unprecedented opportunity to study a variety of aspects about the planet’s evolution. Using the Rb–Sr and Sm–Nd isotopic systems, we determined that Tissint, a depleted shergottite, has a crystallization age of 574 ± 20 Ma, an initial ε¹⁴³Nd = +42.2 ± 0.5, and an initial ⁸⁷Sr/⁸⁶Sr = 0.700760 ± 11. These initial Nd and Sr isotopic compositions suggest that Tissint originated from a mantle source on Mars that is distinct from the source reservoirs of the other Martian meteorites. The known crystallization ages, geochemical characteristics, ejection ages, and ejection dynamics of Tissint and other similarly grouped Martian meteorites suggest that they are likely derived from a source crater up to approximately 90 km in diameter with an age of approximately 1 Ma that is located on terrain that is approximately 600 million years old.

Reference
Beck P et al. (in press) Insights into the Martian mantle: The age and isotopics of the meteorite fall Tissint. Meteoritics & Planetary Science
[doi:10.1111/maps.12258]
Published by arrangement with John Wiley & Sons

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P. Beck¹ et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, Grenoble, France

Sutter’s Mill is a regolith breccia composed of both heavily altered clasts and more reduced xenoliths. Here, we present a detailed investigation of fragments of SM18 and SM51. We have characterized the water content and the mineralogy by infrared (IR) and thermogravimetric analysis (TGA) and the structure of the organic compounds by Raman spectroscopy, to characterize the secondary history of the clasts, including aqueous alteration and thermal metamorphism. The three methods used in this study suggest that SM18 was significantly heated. The amount of water contained in phyllosilicates derived by TGA is estimated to be approximately 3.2 wt%. This value is quite low compared with other CM chondrites that typically range from 6 to 12 wt%. The infrared transmission spectra of SM18 show that the mineralogy of the sample is dominated by a mixture of phyllosilicate and olivine. SM18 shows an intense peak at 11.2 μm indicative of olivine (Fig. ). If we compare SM18 with other CM and metamorphosed CM chondrites, it shows one of the most intense olivine signatures, and therefore a lower proportion of phyllosilicate minerals. The Raman results tend to support a short-duration heating hypothesis. In the I_D/I_Gversus FWHM-D diagram, SM18 appears to be unusual compared to most CM samples, and close to the metamorphosed CM chondrites Pecora Escarpment (PCA) 91008 and PCA 02012. In the case of SM51, infrared spectroscopy reveals that olivine is less abundant than in SM18 and the 10 μm silicate feature is more similar to that of moderately altered CM chondrites (like Murchison or Queen Alexandra Range [QUE] 97990). Raman spectroscopy does not clearly point to a heating event for SM51 in the I_D/I_G versus FWHM-D diagram. However, TGA analysis suggests that SM51 was slightly dehydrated as the amount of water contained in phyllosilicates is approximately 3.7 wt%, which is higher than SM18, but still lower than phyllosilicate water contents in weakly altered CM chondrites. Altogether, these results confirm that fragments with different secondary histories are present within the Sutter’s Mill fall. The dehydration that is clearly observed for SM18 is attributed to a short-duration heating based on the similarity of its Raman spectra to that of PCA 91008. Because of the brecciated nature of Sutter’s Mill and the presence of adjacent clasts with different thermal histories, impacts that can efficiently fragment and heat porous materials are the preferred heat source.

Reference
Beck P et al. (in press) The secondary history of Sutter’s Mill CM carbonaceous chondrite based on water abundance and the structure of its organic matter from two clasts. Meteoritics & Planetary Science
[doi:10.1111/maps.12273]
Published by arrangement with John Wiley & Sons

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A. Rotundi^1,2 et al. (>10)*
*Find the extensive, full author and affiliation list on the publishers website.

¹Dip. Scienze e Tecnologie, Università degli Studi di Napoli “Parthenope”, Napoli, Italy
²INAF-Istituto di Astrofisica e Planetologia Spaziali, Roma, Italy

We present the analyses results of two bulk Terminal Particles, C2112,7,171,0,0 and C2112,9,171,0,0, derived from the Jupiter-family comet 81P/Wild 2 returned by the Stardust mission. Each particle embedded in a slab of silica aerogel was pressed in a diamond cell. This preparation, as expected, made it difficult to identify the minerals and organic materials present in these particles. This problem was overcome using a combination of three different analytical techniques, viz. FE-SEM/EDS, IR, and Raman microspectroscopy that allowed identifying the minerals and small amounts of amorphous carbon present in both particles. TP2 and TP3 were dominated by Ca-free and low-Ca, Mg-rich, Mg,Fe-olivine. The presence of melilite in both particles is supported by IR microspectroscopy, but is not confirmed by Raman microspectroscopy, possibly because the amounts are too small to be detected. TP2 and TP3 show similar silicate mineral compositions, but Ni-free and low-Ni, subsulfur (Fe,Ni)S grains are present in TP2 only. TP2 contains indigenous amorphous carbon hot spots; no indigenous carbon was identified in TP3. These nonchondritic particles probably originated in a differentiated body. This work found an unanticipated carbon contamination following the FE-SEM/EDS analyses. It is suggested that organic materials in the embedding silica aerogel are irradiated during FE-SEM/EDS analyses creating a carbon gas that develops a strong fluorescence continuum. The combination of the selected analytical techniques can be used to characterize bulk Wild 2 particles without the need of extraction and removal of the encapsulating aerogel. This approach offers a relatively fast sample preparation procedure, but compressing the samples can cause spurious artifacts, viz. silica contamination. Because of the combination of techniques, we account for these artifacts.

Reference
Rotundi A et al. (in press) Two refractory Wild 2 terminal particles from a carrot-shaped track characterized combining MIR/FIR/Raman microspectroscopy and FE-SEM/EDS analyses. Meteoritics & Planetary Science
[doi:10.1111/maps.12274]
Published by arrangement with John Wiley & Sons

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Maria Gritsevich^1,2,3, Vladimir Vinnikov², Tomáš Kohout^4,5, Juraj Tóth⁶, Jouni Peltoniemi^1,4, Leonid Turchak², Jenni Virtanen¹

¹Finnish Geodetic Institute, Masala, Finland
²Department of Computational Physics, Dorodnicyn Computing Centre, Russian Academy of Sciences, Moscow, Russia
³Institute of Mechanics, Lomonosov Moscow State University, Moscow, Russia
⁴Department of Physics, University of Helsinki, Helsinki, Finland
⁵Institute of Geology, Academy of Sciences of the Czech Republic, Prague 6, Czech Republic
⁶Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia

In this study, we conduct a detailed analysis of the Košice meteorite fall (February 28, 2010), to derive a reliable law describing the mass distribution among the recovered fragments. In total, 218 fragments of the Košice meteorite, with a total mass of 11.285 kg, were analyzed. Bimodal Weibull, bimodal Grady, and bimodal lognormal distributions are found to be the most appropriate for describing the Košice fragmentation process. Based on the assumption of bimodal lognormal, bimodal Grady, bimodal sequential, and bimodal Weibull fragmentation distributions, we suggest that, prior to further extensive fragmentation in the lower atmosphere, the Košice meteoroid was initially represented by two independent pieces with cumulative residual masses of approximately 2 and 9 kg, respectively. The smaller piece produced about 2 kg of multiple lightweight meteorite fragments with the mean around 12 g. The larger one resulted in 9 kg of meteorite fragments, recovered on the ground, including the two heaviest pieces of 2.374 kg and 2.167 kg with the mean around 140 g. Based on our investigations, we conclude that two to three larger fragments of 500–1000 g each should exist, but were either not recovered or not reported by illegal meteorite hunters.

Reference
Gritsevich M, Vinnikov V, Kohout T, Tóth J, Peltoniemi J, Turchak L and Virtanen J (in press) A comprehensive study of distribution laws for the fragments of Košice meteorite. Meteoritics & Planetary Science
[doi:10.1111/maps.12252]
Published by arrangement with John Wiley & Sons

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Deon van Niekerk¹, Klaus Keil¹, Munir Humayun²

¹Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Manoa, Honolulu, Hawai‘i, USA
²National High Magnetic Field Laboratory, Department of Earth, Ocean & Atmospheric Science, Florida State University, Tallahassee, Florida, USA

Queen Alexandra Range (QUE) meteorite 94204 is an anomalous enstatite meteorite whose petrogenesis has been ascribed to either partial melting or impact melting. We studied the meteorite pairs QUE 94204, 97289/97348, 99059/99122/99157/99158/99387, and Yamato (Y)-793225; these were previously suggested to represent a new grouplet. We present new data for mineral abundances, mineral chemistries, and siderophile trace element compositions (of Fe,Ni metal) in these meteorites. We find that the texture and composition of Y-793225 are related to EL6, and that this meteorite is unrelated to the QUEs. The mineralogy and siderophile element compositions of the QUEs are consistent with petrogenesis from an enstatite chondrite precursor. We caution that potential re-equilibration during melting and recrystallization of enstatite chondrite melt-rocks make it unreliable to use mineral chemistries to assign a specific parent body affinity (i.e., EH or EL). The QUEs have similar mineral chemistries among themselves, while slight variations in texture and modal abundances exist between them. They are dominated by inclusion-bearing millimeter-sized enstatite (average En_99.1–99.5) with interstitial spaces filled predominantly by oligoclase feldspar (sometimes zoned), kamacite (Si approximately 2.4 wt%), troilite (≤2.4 wt% Ti), and cristobalite. Siderophile elements that partition compatibly between solid metal and liquid metal are not enriched like in partial melt residues Itqiy and Northwest Africa (NWA) 2526. We find that the modal compositions of the QUEs are broadly unfractionated with respect to enstatite chondrites. We conclude that a petrogenesis by impact melting, not partial melting, is most consistent with our observations.

Reference
van Niekerk D, Keil K and Humayun M (in press) Petrogenesis of anomalous Queen Alexandra Range enstatite meteorites and their relation to enstatite chondrites, primitive enstatite achondrites, and aubrites. Meteoritics & Planetary Science
[doi:10.1111/maps.12248]
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Jean-Alix Barrat¹ and Akira Yamaguchi^2,3

¹Université de Bretagne Occidentale and Institut Universitaire Européen de la Mer, CNRS UMR 6538, Plouzané Cedex, France
²National Institute of Polar Research, Tachikawa, Tokyo, Japan
³Department of Polar Science, School of Multidisciplinary Science, Graduate University for Advanced Sciences, Tachikawa, Tokyo, Japan

Mandler and Elkins-Tanton () recently proposed an upgraded magma ocean model for the differentiation history of the giant asteroid 4 Vesta. They show that a combination of both equilibrium crystallization and fractional crystallization processes can reproduce the major element compositions of eucritic melts and broadly the range of mineral compositions observed in diogenites. They assert that their model accounts for all the howardites, eucrites, and diogenites (HEDs), and use it to predict the crustal thickness and the proportions of the various lithologies. Here, we show that their model fails to explain the trace element diversity of the diogenites, contrary to their claim. The diversity of the heavy REE enrichment exhibited by the orthopyroxenes in diogenites is inconsistent with crystallization of these cumulates in either shallow magma chambers replenished by melts from a magma ocean or in a magma ocean. Thus, proportions of the various HED lithologies and the crustal thickness predicted from this model are not necessarily valid.

Reference
Barrat J-A and Yamaguchi A (in press) Comment on “The origin of eucrites, diogenites, and olivine diogenites: Magma ocean crystallization and shallow magma processes on Vesta” by B. E. Mandler and L. T. Elkins-Tanton. Meteoritics & Planetary Science
[doi:10.1111/maps.12250]
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A. V. Fisenko¹, A. B. Verchovsky², L. F. Semjonova¹

¹Vernadsky Institute of Geochemistry and Analytical Chemistry RAS, Moscow, Russia
²Department of Physical Sciences, Open University, Milton Keynes, UK

The kinetics of the release of the Xe-P3 component from coarse-grained fractions of Orgueil (CI) meteorite nanodiamonds has been investigated using stepped and isothermal pyrolysis. It has been shown that a first-order chemical reaction diffusion model with a single activation energy cannot provide a satisfactory explanation for the observed retention of Xe-P3 during parent body thermal metamorphism and the kinetics of Xe-P3 release from nanodiamonds during isothermal pyrolysis. Using the activation energy and frequency factor calculated according to this model, it is shown that in the course of thermal metamorphism of the Orgueil meteorite almost the entire Xe-P3 component must have been lost in a very short time (<4 yr at approximately 100 °C). However, the calculated retention of Xe-P3 increases significantly if a diffusion model with a spectrum of activation energies is used. In this case, the model can explain not only a high retention of Xe-P3 in the Orgueil nanodiamonds but also the release pattern of the Xe-P3 from Semarkona and Bishunpur nanodiamonds that have experienced a significant gas loss during parent body metamorphism as well as the release of Xe-P3 during isothermal pyrolysis of the Orgueil nanodiamonds. The energetically complicated Xe-P3 distribution is most likely caused by structural damage to the nanodiamond grains or a complex phase composition of carbon in the surface layer of the diamond grains. It is supposed that the structural damage of the diamond grains can have a radiation origin, while the variations of the carbon phase composition in the grain’s mantle can be caused by the radiation-induced reactions and/or a thermal effect.

Reference
Fisenko AV, Verchovsky AB and Semjonova LF (in press) Kinetics of Xe-P3 release during pyrolysis of the coarse-grained fractions of Orgueil (CI) meteorite nanodiamonds. Meteoritics & Planetary Science
[doi:10.1111/maps.12278]
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Robert W. Hilts¹, Christopher D. K. Herd², Danielle N. Simkus³ and Greg F. Slater³

¹Department of Physical Sciences, MacEwan University, Edmonton, Alberta, Canada
²Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada
³School of Geography and Earth Sciences, McMaster University, Hamilton, Ontario, Canada

The C2 ungrouped Tagish Lake meteorite preserves a range of lithologies, reflecting variable degrees of parent-body aqueous alteration. Here, we report on soluble organic compounds, including aliphatic and aromatic hydrocarbons, monocarboxylic acids, and amino acids, found within specimens representative of the range of aqueous alteration. We find that differences in soluble organic compounds among the lithologies may be explained by oxidative, fluid-assisted alteration, primarily involving the derivation of soluble organic compounds from macromolecular material. In contrast, amino acids probably evolved from precursor molecules, albeit in parallel with other soluble organic compounds. Our results demonstrate the role of parent-body alteration in the modification of organic matter and generation of prebiotic compounds in the early solar system, and have implications for interpretation of the complement of soluble organic compounds in carbonaceous chondrites.

Reference
Hilts RW, Herd CDK, Simkus DN and Slater GF (in press) Soluble organic compounds in the Tagish Lake meteorite. Meteoritics & Planetary Science
[doi:10.1111/maps.12272]
Published by arrangement with John Wiley & Sons

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