¹Herbert Palme, ^2,3Dominik C. Hezel, ⁴Denton S. Ebel
¹Forschungsinstitut und Naturmuseum Senckenberg, Senckenberganlage 25, D-60325 Frankfurt am Main, Germany
²Institut für Geologie und Mineralogie, Universität zu Köln, Zülpicherstrasse 55, Germany
³Natural History Museum, Department of Mineralogy, Cromwell Road, SW7 5BD, London, UK
⁴Department of Earth and Planetary Sciences, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024-5192, USA

One of the major unresolved problems in cosmochemistry is the origin of chondrules, once molten, spherical silicate droplets with diameters of 0.2 to 2 mm. Chondrules are an essential component of primitive meteorites and perhaps of all early solar system materials including the terrestrial planets. Numerous hypotheses have been proposed for their origin. Many carbonaceous chondrites are composed of about equal amounts of chondrules and fine-grained matrix. Recent data confirm that matrix in carbonaceous chondrites has high Si/Mg and Fe/Mg ratios when compared to bulk carbonaceous chondrites with solar abundance ratios. Chondrules have the opposite signature, low Si/Mg and Fe/Mg ratios. In some carbonaceous chondrites chondrules have low Al/Ti ratios, matrix has the opposite signature and the bulk is chondritic. It is shown in detail that these complementary relationships cannot have evolved on the parent asteroid(s) of carbonaceous chondrites. They reflect preaccretionary processes. Both chondrules and matrix must have formed from a single, solar-like reservoir. Consequences of complementarity for chondrule formation models are discussed. An independent origin and/or random mixing of chondrules and matrix can be excluded. Hence, complementarity is a strong constraint for all astrophysical–cosmochemical models of chondrule formation. Although chondrules and matrix formed from a single reservoir, the chondrule-matrix system was open to the addition of oxygen and other gaseous components.

Reference
Palme H, Hezel DC, Ebel DS (2014) The origin of chondrules: Constraints from matrix composition and matrix-chondrule complementarity. Earth and Planetary Science Letters (in Press)
Link to Article [doi:10.1016/j.epsl.2014.11.033]

Copyright Elsevier

¹J.C. Bridges,²S.P. Schwenzer,³R. Leveille,⁴F. Westall,⁵R.C. Wiens,⁶N. Mangold,⁷T. Bristow,⁸P. Edwards,⁹G. Berger
¹Space Research Centre, Dept. of Physics and Astronomy, University of Leicester, Leicester, UK
²Dept. of Physical Sciences, The Open University, Milton Keynes, UK
³McGill University, Montreal, Canada
⁴Centre de Biophysique Moléculaire, CNRS, Orléans Cedex 2, France
⁵Space Remote Sensing, Los Alamos National Laboratory, Los Alamos, NM, USA
⁶Laboratoire Planétologie et Géodynamique de Nantes, LPGN/CNRS UMR6112 and Université de Nantes, Nantes, France
⁷Exobiology Branch, NASA Ames Research Center, Moffett Field, CA, USA
⁸Space Research Centre, Dept. of Physics and Astronomy, University of Leicester, Leicester, UK
⁹IRAP (CNRS-Univ. P. Sabatier), Toulouse, France

The Mars Science Laboratory Rover Curiosity found host rocks of basaltic composition and alteration assemblages containing clay minerals at Yellowknife Bay, Gale Crater. On the basis of the observed host rock and alteration minerals, we present results of equilibrium thermochemical modelling of the Sheepbed mudstones of Yellowknife Bay (YKB), in order to constrain formation conditions of its secondary mineral assemblage. Building on conclusions from sedimentary observations by the MSL team, we assume diagenetic, in situ alteration. The modelling shows that the mineral assemblage formed by reaction of a CO2-poor and oxidising, dilute aqueous solution (Gale Portage Water) in an open system with the Fe-rich basaltic-composition sedimentary rocks at 10–50 °C and Water/Rock ratio (mass of rock reacted with the starting fluid) of 100–1000, pH of ~7.5-12. Model alteration assemblages contain predominantly phyllosilicates (Fe-smectite, chlorite) the bulk composition of a mixture of which is close to that of saponite inferred from CheMin data and also to that of saponite observed in the nakhlite martian meteorites and terrestrial analogues. To match the observed clay mineral chemistry, inhomogeneous dissolution dominated by the amorphous phase and olivine is required. We therefore deduce a dissolving composition of approximately 70 % amorphous material, with 20 % olivine, and 10 % whole rock component.

Reference
Bridges JC, Schwenzer SP, Leveille R, Westall F, Wiens RC, Mangold N, Bristow T, Edwards P, Berger G (2014) Diagenesis and Clay Mineral Formation at Gale Crater, Mars. Journal of Geophysical Research Planets (in Press)
Link to Article [10.1002/2014JE004757]

Published by Arrangement with John Wiley & Sons

¹Jennifer Whitten, ²James W. Head
¹Center for Earth and Planetary Studies, Smithsonian Institution, Washington DC 20004 USA
²Department of Geological Sciences, Brown University, Providence RI 02912 USA

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Whitten J, Head JW (2014) Lunar cryptomaria: Mineralogy and Composition of Ancient Volcanic Deposits. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2014.11.027]

¹Timothy A. Goudge, ¹John F. Mustard, ¹James W. Head, ²Mark R. Salvatore, ¹Sandra M. Wiseman
¹Department of Earth, Environmental and Planetary Sciences, Brown University, 324 Brook St., Box 1846, Providence, RI 02912
²School of Earth and Space Exploration, Arizona State University, PO Box 876305, Moeur Bldg. Rm. 131, 201 E. Orange Mall, Tempe, AZ 85287-6305

We present morphologic observations and spectral modeling results of a large, kaolin-group mineral-bearing deposit within Kashira crater in the southern highlands of Mars. We employ both non-linear unmixing of Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) visible to near-infrared (VNIR) reflectance data and linear unmixing of Thermal Emission Spectrometer (TES) thermal infrared (TIR) emissivity data to quantitatively analyze the kaolin-group mineral within this deposit. We use a novel approach for quantitative analysis of CRISM data through non-linear unmixing with in-scene, orbitally-derived endmembers combined with laboratory measured endmembers. Results from this approach indicate that the deposit within Kashira crater is best modeled as a combination of surrounding spectral units (i.e., in-scene derived endmembers) with the addition of the kaolin-group mineral halloysite. Linear unmixing of TES data suggest that the deposit contains ∼30% halloysite, a result that is supported by a sensitivity analysis. Potential formation mechanisms for this deposit include hydrothermal alteration, arid-environment pedogenic weathering of a basaltic mound deposit, or pedogenic weathering of a volcanic ash deposit. Our modeling results offer a quantitative reconciliation of the CRISM and TES datasets, and provide a consistent mineralogy from spectral unmixing for an aqueous alteration mineral-bearing deposit on Mars using a combined analysis of both VNIR and TIR hyperspectral data.

Reference
Goudge TA, Mustard JF, Head JW, Salvatore MR, Wiseman SM (2014) Integrating CRISM and TES Hyperspectral Data to Characterize a Halloysite-Bearing Deposit in Kashira Crater, Mars. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2014.11.034]

Copyright Elsevier

¹J. Deckers, ¹J. Teiser
¹Fakultät für Physik, Universität Duisburg-Essen, D-47057 Duisburg, Germany

The collision dynamics of dusty bodies are crucial for planetesimal formation. Decimeter agglomerates are especially important in the different formation models. Therefore, in continuation of our experiments on mutual decimeter collisions, we investigate collisions of centimeter onto decimeter dust agglomerates in a small drop tower under vacuum conditions (p lsim 5 × 10–1 mbar) at a mean collision velocity of 6.68 ± 0.67 m s–1. We use quartz dust with irregularly shaped micrometer grains. Centimeter projectiles with different diameters, masses, and heights are used, their typical volume filling factor is Φ p, m = 0.466 ± 0.02. The decimeter agglomerates have a mass of about 1.5 kg, a diameter and height of 12 cm, and a mean filling factor of Φ t, m = 0.44 ± 0.004. At lower collision energies, only the projectile gets destroyed and mass is transferred to the target. The accretion efficiency decreases with increasing obliquity and increasing difference in filling factor, if the projectile is more compact than the target. The accretion efficiency increases with increasing collision energy for collision energies under a certain threshold. Beyond this threshold at 298 ± 25 mJ, catastrophic disruption of the target can be observed. This corresponds to a critical fragmentation strength Q* = 190 ± 16 mJ kg–1, which is a factor of four larger than expected. Analyses of the projectile fragments show a power-law size distribution with an average exponent of –3.8 ± 0.3. The mass distributions suggest that the fraction of smallest fragments increases for higher collision energies. This is interesting for impacts of small particles on large target bodies within protoplanetary disks, as smaller fragments couple better to the surrounding gas and re-accretion by gas drag is more likely.

Reference
Deckers J and Teiser J (2014) Macroscopic Dust in Protoplanetary Disks—from Growth to Destruction. The Astrophysical Journal 796 99.
Link to Article [doi:10.1088/0004-637X/796/2/99]

¹D. A. Oszkiewicz, ¹T. Kwiatkowski, ²T. Tomov, ^3,4M. Birlan, ⁵S. Geier, ⁶A. Penttilä, ¹M. Polińska
¹Astronomical Observatory Institute, Faculty of Physics, A. Mickiewicz University, Słoneczna 36, 60-286 Poznań, Poland
e-mail: dagmara.oszkiewicz@gmail.com
²Nicholaus Copernicus University, ul. Gagarina 11, 87-100 Toruń, Poland
³IMCCE – Paris Observatory – UMR 8028 CNRS 77, av. Denfert-Rochereau, 75014 Paris, France
⁴Astronomical Institute of the Romanian Academy, Strada Cutitul de Argint 5, 040557 Bucureti, Romania
⁵Nordic Optical Telescope, Apartado 474, 38700 Santa Cruz de La Palma, Spain
⁶Division of Geophysics and Astronomy, Department of Physics, PO Box 64, 00014 University of Helsinki, Finland

Context. Asteroid spectroscopy reflects surface mineralogy. There are a few thousand asteroids whose surfaces have been observed spectrally. Determining their surface properties is important for many practical and scientific applications, such as developing impact deflection strategies or studying the history and evolution of the solar system and planet formation.
Aims. The aim of this study is to develop a preselection method that can be used to search for asteroids of any taxonomic complex. The method could then be utilized in multiple applications, such as searching for the missing V-types or looking for primitive asteroids.
Methods. We used the Bayes Naive Classifier combined with observations obtained in the course of the Sloan Digital Sky Survey and the Wide-field Infrared Survey Explorer surveys, as well as a database of asteroid phase curves for asteroids with a known taxonomic type. With this new classification method, we selected a number of possible V-type candidates. Some of the candidates were then spectrally observed at the Nordic Optical Telescope and South African Large Telescope.
Results. We developed and tested the new preselection method. We found three asteroids in the mid-to-outer main belt that probably have differentiated types. Near-infrared observations are still required to confirm this discovery. As in other studies we found that V-type candidates cluster around the Vesta family and are rare in the mid-to-outer main belt.
Conclusions. The new method shows that even largely explored large databases when combined could still be exploited further in, for example, solving the missing dunite problem.

Reference
Oszkiewicz DA, Kwiatkowski T, Tomov T, Birlan M, Geier S, Penttilä A, Polińska M (2014) Selecting asteroids for a targeted spectroscopic Survey. Astronomy&Astrophysics (in Press)
Link to Article [http://dx.doi.org/10.1051/0004-6361/201323250]

Reproduced with permission ©ESO

¹Hikaru Yabuta et al. (>10)*
¹Department of Earth and Space Science, Osaka University, 1-1 Machikaneyama, Toyonaka 560-0043, Osaka, Japan
*Find the extensive, full author and affiliation list on the publishers website

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

Reference
Yabuta H et al. (2014) X-ray absorption near edge structure spectroscopic study of Hayabusa category 3 carbonaceous particles. Earth, Planets and Space 66, 156
Link to Article [doi:10.1186/s40623-014-0156-0]

^1,2Emily A. Pringle, ^1,3Frédéric Moynier, ^1,2,4Paul S. Savage, ^1,5James Badro,⁶Jean-Alix Barrat
¹Institut de Physique du Globe de Paris, Université Paris Diderot, Sorbonne Paris Cité, 75005 Paris, France;
²Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO 63130;
³Institut Universitaire de France, 75005 Paris, France;
⁴Department of Earth Sciences, Science Labs, Durham University, Durham DH1 3LE, United Kingdom;
⁵Earth and Planetary Sciences Laboratory, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland; and
⁶Université de Brest, Institut Universitaire Européen de la Mer, 29280 Plouzané, France

Inner solar system bodies, including the Earth, Moon, and asteroids, are depleted in volatile elements relative to chondrites. Hypotheses for this volatile element depletion include incomplete condensation from the solar nebula and volatile loss during energetic impacts. These processes are expected to each produce characteristic stable isotope signatures. However, processes of planetary differentiation may also modify the isotopic composition of geochemical reservoirs. Angrites are rare meteorites that crystallized only a few million years after calcium–aluminum-rich inclusions and exhibit extreme depletions in volatile elements relative to chondrites, making them ideal samples with which to study volatile element depletion in the early solar system. Here we present high-precision Si isotope data that show angrites are enriched in the heavy isotopes of Si relative to chondritic meteorites by 50–100 ppm/amu. Silicon is sufficiently volatile such that it may be isotopically fractionated during incomplete condensation or evaporative mass loss, but theoretical calculations and experimental results also predict isotope fractionation under specific conditions of metal–silicate differentiation. We show that the Si isotope composition of angrites cannot be explained by any plausible core formation scenario, but rather reflects isotope fractionation during impact-induced evaporation. Our results indicate planetesimals initially formed from volatile-rich material and were subsequently depleted in volatile elements during accretion.

Reference
Pringle EA, Moynier F, Savage PS, Badro J, Barrat J-A (2014) Silicon isotopes in angrites and volatile loss in planetesimals. Proceedings of the National Academy of Sciences 111, 17029–17032
Link to Article [doi: 10.1073/pnas.1418889111]

¹Erwin Dehouck,¹Scott M. McLennan,²Pierre-Yves Meslin,³Agnès Cousin
¹Department of Geosciences, State University of New York at Stony Brook, Stony Brook, NY, USA
²Institut de Recherche en Astrophysique et Planétologie, CNRS/Université Paul Sabatier, Toulouse, France
³Los Alamos National Laboratory, Los Alamos, NM, USA

X-ray diffraction patterns of the three samples analyzed by Curiosity’s CheMin instrument during the first year of the Mars Science Laboratory mission – the Rocknest sand; and the John Klein and Cumberland drill fines, both extracted from the Sheepbed mudstone – show evidence for a significant amorphous component of unclear origin. We developed a mass balance calculation program that determines the range of possible chemical compositions of the crystalline and amorphous components of these samples within the uncertainties of mineral abundances derived from CheMin data. In turn, the chemistry constrains the minimum abundance of amorphous component required to have realistic compositions (all oxides ≥0 wt%): 21—22 wt% for Rocknest and 15—20 wt% for Cumberland, in good agreement with estimates derived from the diffraction patterns (~27 and ~31 wt%, respectively). Despite obvious differences between the Rocknest sand and the Sheepbed mudstone, the amorphous components of the two sites are chemically very similar, having comparable concentrations of SiO2, TiO2, Al2O3, Cr2O3, FeOT, CaO, Na2O, K2O and P2O5. MgO tends to be lower in Rocknest, although it may also be comparable between the two samples depending on the exact composition of the smectite in Sheepbed. The only unambiguous difference is the SO3 content, which is always higher in Rocknest. The observed similarity suggests that the two amorphous components share a common origin or formation process. The individual phases possibly present within the amorphous components include: volcanic (or impact) glass, hisingerite (or silica + ferrihydrite), amorphous sulfates (or adsorbed SO42−) and nanophase ferric oxides.

Reference
Dehouck E, McLennan SM, Meslin P-Y, Cousin A (2014) Constraints on abundance, composition and nature of X-ray amorphous components of soils and rocks at Gale crater, Mars. Journal of Geophysical Research Planets (in Press)
Link to Article [DOI: 10.1002/2014JE004716]

Published by arrangement with John Wiley&Sons

¹Svetoslav V. Georgiev, ^1,2Holly J. Stein, ^1,2Judith L. Hannah, ³Charles M. Henderson,
^4,5Thomas J. Algeo
¹AIRIE Program, Colorado State University, Fort Collins, 80523-1482 CO, USA
²CEED (Centre for Earth Evolution and Dynamics), University of Oslo, 0316 Oslo, Norway
³Department of Geoscience, University of Calgary, Calgary, Alberta T2N 1N4, Canada
⁴Department of Geology, University of Cincinnati, Cincinnati, 45221-0013 OH, USA
⁵State Key Laboratories of BGEG and GPMR, China University of Geosciences, Wuhan 430074, China

The geochemical record for the Permian-Triassic boundary in northern latitudes is essential to evaluation of global changes associated with the most profound extinction of life on Earth. We present inorganic and organic geochemical data, and Re-Os isotope systematics in a critical stratigraphic interval of pre- and post-extinction Upper Permian-Lower Triassic sediments from Opal Creek, western Canada (paleolatitude of ∼30°N). We document significant and long-lived changes in Panthalassa seawater chemistry that were initiated during the first of four magmatic or meteoritic inputs to Late Permian seawater, evidenced by notable decreases of Os isotopic ratios upsection.

Geochemical signals indicate establishment of anoxic bottom waters shortly after regional transgression reinitiated sedimentation in the Late Permian. Euxinic signals are most prominent in the Upper Permian sediments with low organic carbon and high sulfur contents, and gradually wane in the Lower Triassic. The observed features may have been generated in a strongly euxinic ocean in which high bacterioplankton productivity sustained prolific microbial sulfate reduction in the sediment and/or water column, providing hydrogen sulfide to form pyrite. This scenario requires nearlycomplete anaerobic decomposition of predominantly labile marine organic matter (OM) without the necessity for a complete collapse of primary marine productivity. Similar geochemical variations could have been achieved by widespread oxidation of methane by sulfate reducers after a methanogenic burst in the Late Permian. Both scenarios could have provided similar kill mechanisms for the latest Permian mass extinction.

Despite the moderate thermal maturity of the section, OM in all studied samples is dominantly terrestrial and/or continentally derived, recycled and refractory ancient OM. We argue that, as such, the quantity of the OM in the section mainly reflects changes in terrestrial vegetation and/or weathering, and not in marine productivity. At Opal Creek, a pyrite layer and <20-cm-thick siltstones that are lean in OM mark dramatic and long-lived inorganic geochemical and stable isotope changes. Initial Os isotope ratios decline markedly toward values of ∼0.35 in the pyrite interval, indicating a mantle-sourced or meteoritic trigger for the intensification and expansion of latest Permian anoxia. Subsequent and stronger magmatic or meteoritic pulses recorded by low initial Os isotopes followed the main extinction.

Reference
Georgiev SV, Holly J. Stein HJ, Judith L. Hannah JL, Charles M. Henderson CM, Thomas J. Algeo TJ (2014)Enhanced recycling of organic matter and Os-isotopic evidence for multiple magmatic or meteoritic inputs to the Late Permian Panthalassic Ocean, Opal Creek, Canada. Geochimica et Cosmochimica (in Press)
Link to Article [doi:10.1016/j.gca.2014.11.019]

Copyright Elsevier