¹Gerrit Budde, ¹Thomas S. Kruijer, ¹Mario Fischer-Gödde, ²Anthony J. Irving, ¹Thorsten Kleine
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm-Straße 10, 48149 Münster, Germany
²Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195, USA

Determining the timescales of the accretion and chemical differentiation of meteorite parent bodies provides some of the most direct constraints on the formation of planetesimals and the earliest stages of planet formation. We present high-precision Hf–W isotope data for a comprehensive set of ureilites, ultramafic mantle restites derived from a partially melted and incompletely differentiated asteroid. All samples are characterized by strong 182W deficits, indicating that silicate melt extraction on the ureilite parent body at 3.3±0.7 Ma3.3±0.7 Ma after CAI formation postdated core formation in iron meteorite parent bodies by ∼2–3 Ma. Thermal modeling of planetesimal heating by 26Al-decay combined with the new Hf–W data indicates that the ureilite parent body accreted at ∼1.6 Ma after CAI formation and, therefore, more than ∼1 Ma later than iron meteorite parent bodies, but more than ∼0.5 Ma earlier that most chondrite parent bodies. Due to its relatively ‘late’ accretion, the ureilite parent body contained too little 26Al to cause complete melting and, therefore, would have probably remained incompletely differentiated even without exhaustion of 26Al by silicate melt segregation. Our results show that both in terms of degree of differentiation and accretion timescale the ureilite parent body is intermediate between fully differentiated and undifferentiated bodies, implying that there is an inverse correlation between extent of melting and metal–silicate separation versus time of accretion and differentiation.

Reference
Budde G, Kruijer TS, Fischer-Gödde M, Irving AJ, Kleine T (2015) Planetesimal differentiation revealed by the Hf–W systematics of ureilites. Earth and Planetary Science Letters 430, 316–325
Link to Article [doi:10.1016/j.epsl.2015.08.034]
Copyright Elsevier

¹S.M. Reddy, ¹T.E. Johnson, ²S. Fischer, ³W.D.A. Rickard,¹R.J.M. Taylor
¹Department of Applied Geology, Institute for Geoscience Research (TIGeR), Curtin University, GPO Box U1987, Perth, WA 6845, Australia
²Department of Earth and Environmental Sciences, University of St Andrews, St Andrews, Fife KY16 9AL, UK
³Department of Imaging and Applied Physics, Curtin University, GPO Box U1987, Perth, WA 6845, Australia

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Reference
Reddy SM, Johnson TE, Fischer S, Rickard WDA, Taylor RJM (2015) Precambrian reidite discovered in shocked zircon from the Stac Fada impactite, Scotland. Geology (in Press)
Link to Article [doi: 10.1130/G37066.1]

^1,2V.V. Svetsov ^1,2V.V. Shuvalov
¹Institute for Dynamics of Geospheres, Leninskiy Prospekt 38-1, Moscow 119334, Russia
²Moscow Institute of Physics and Technology, Institutskiy Per. 9, Dolgoprudny, Moscow Region, 141700, Russia

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Reference
Svetsov VV, Shuvalov VV (2015) Water delivery to the Moon by asteroidal and cometary Impacts. Planetary and Space Science (in Press)
Link to Article [doi:10.1016/j.pss.2015.09.011]

^1,2A. Garenne,^1,2P. Beck,^3,4,5,6G. Montes-Hernandez, ^1,2O. Brissaud, ^1,2B. Schmitt, ^1,2E. Quirico, ^1,2L. Bonal, ⁷C. Beck, ^8,9K.T. Howard
¹Univ. Grenoble Alpes, IPAG, F-38000 Grenoble, France
²CNRS, IPAG, F-38000 Grenoble, France
³Univ. Grenoble Alpes, ISTerre, F-38000 Grenoble, France
⁴CNRS, ISTerre, F-38000 Grenoble, France
⁵IRD, ISTerre, F-38000 Grenoble, France
⁶IFSTTAR, ISTerre, F-38000 Grenoble
⁷Univ. Savoie, ISTerre Science Institue EARTH, 73376, Le Bourget du Lac, France
⁸Kingsborough Community College, 2001 Oriental Blvd., Brooklyn, NewYork, NT 11235, USA
⁹Department of Earth and Planetary Sciences, American Museum of Natural History.

In this study, we measured bidirectional reflectance spectra (0.5-4.0 μm) of 24 CMs, five CRs, one CI, one CV, and one C2 carbonaceous chondrites. These meteorites are known to have experienced an important variability in their relative degrees of aqueous alteration degree (Rubin et al., 2007 and Howard et al., 2009; 2011; Alexander et al., 2013). These measurements were performed on meteorite powders inside an environmental cell under a primary vacuum and heated at 60°C in order to minimize adsorbed terrestrial water. This protocol allows controlling of atmospheric conditions (i.e. humidity) in order to avoid contamination by terrestrial water. We discuss various spectral metrics (e.g. reflectance, band depth, single-scattering albedo, …) in the light of recent bulk composition characterization (Howard et al., 2009, Howard et al., 2015, Alexander et al., 2012, Beck et al., 2014 and Garenne et al., 2014). This study reveals variability of reflectance among meteorite groups. The reflectance is not correlated with carbon or hydrogen abundance neither with measured grain size distribution. We suggest that it is rather controlled by the nature of accreted components, in particular the initial matrix/chondrule proportion. Band depth, integrated band depth, mean optical path length, normalized optical path length, effective single–particle absorption thickness were calculated on the so called 3-μm band for reflectance spectra and for single scattering albedo spectra. They were compared with hydrated phase proportions from previous study on the same meteorites by thermogravimetric analyses and infrared spectroscopy in transmission. We find that normalized optical path length (NOPL) is the most appropriate to quantify water abundance, with an absolute error of about 5 wt.%. These datasets also reveal a variability of the band shape between 2.8 and 2.9 μm, which is interpreted as reflecting variation in the chemical composition and structure of phyllosilicates. This chemical variation could also be used to quantify the aqueous alteration degree between meteorite groups. The combination of reflectance at 2 μm and the depth of 3-μm band can be combined, to classify carbonaceous chondrites in reflectance in term of primary composition (e.g. matrix/chondrule ratio, carbon content) and secondary processes (e.g. aqueous alteration, thermal metamorphism). This could be used to decipher the nature of aqueous alteration in C-complex asteroids.

Reference
Garenne A, Beck P, Montes-Hernandez G, Brissaud O, Schmitt B, Quirico E, Bonal L, Beck C, Howard KT (2015) Bidirectional reflectance spectroscopy of carbonaceous chondrites: Implications for water quantification and primary composition. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.09.005]
Copyright Elsevier

¹H.M. Kaluna, ²J.R. Masiero, ¹K.J. Meech
¹Institute for Astronomy, University of Hawaii, 2680 Woodlawn Dr., Honolulu-HI-96822, USA
²Jet Propulsion Laboratory/Caltech, Pasadena, CA, USA

We present visible spectroscopic and albedo data of the 2.3 Gyr old Themis family and the 15 km) and small (⩽⩽15 km) Themis members suggest these phyllosilicate feature and albedo trends result from regolith variations as a function of diameter. Observations of the Beagle asteroids show a small, but notable fraction of members with phyllosilicate features. The presence of phyllosilicates and the dynamical association of the main-belt comet 133P/Elst-Pizarro with the Beagle family imply the Beagle parent body was a heterogenous mixture of ice and aqueously altered minerals.

Reference
Kaluna HM, Masiero JR, Meech KJ (2015) Space Weathering Trends Among Carbonaceous Asteroids. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.09.007]
Copyright Elsevier

¹Romy D. Hanna,¹Richard A. Ketcham,²Mike Zolensky,¹Whitney Behr
¹Jackson School of Geosciences, University of Texas, Austin TX 78712, USA
²Astromaterials Research and Exploration Science, NASA Johnson Space Center, Houston, TX 77058, USA

X-ray computed tomographic scanning of a 44 g Murchison stone (USNM 5487) reveals a preferred alignment of deformed, partially altered chondrules, which define a prominent foliation and weak lineation in 3D. The presence of a lineation and evidence for a component of rotational, noncoaxial shear suggest that the deformation was caused by impact. Olivine optical extinction indicates that the sample can be classified as shock stage S1, and electron backscatter diffraction (EBSD) and electron microscopy reveal that plastic deformation within the chondrules was minimal and that brittle deformation in the form of fracturing, cataclasis, and grain boundary sliding was the dominant microstructural strain-accommodating mechanism. Textural evidence such as serpentine veins parallel to the foliation fabric and crosscutting alteration veins strongly suggest that some aqueous alteration post-dated or was contemporaneous with the deformation and that multiple episodes of fracturing and mineralization occurred. Finally, using the deformed shape of the chondrules we estimate that the strain experienced by Murchison was 17-43%. This combined with the current measured porosity of Murchison suggests that the original bulk porosity of Murchison prior to its deformation was 32.2 – 53.4% and likely at the upper end of this range due to chondrule compressibility, providing a unique estimate of pre-deformation porosity for a carbonaceous chondrite. Our findings suggest that significant porosity loss, deformation, and compaction from impact can occur on chondrite parent bodies whose samples may record only a low level of shock, and that significant chondrule deformation resulting in a chondrite foliation fabric can occur primarily through brittle processes and does not require plastic deformation of grains.

Reference
Hanna RD, Ketcham RA, Zolensky M, Behr W (2015) Impact-induced brittle deformation, porosity loss, and aqueous alteration in the Murchison CM chondrite. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.09.005]
Copyright Elsevier

¹Frans J. M. Rietmeijer
¹Department of Earth and Planetary Sciences, MSC 03-2040, 1-University of New Mexico, Albuquerque, New Mexico, USA

The bulbous Stardust track #80 (C2092,3,80,0,0) is a huge cavity. Allocations C2092,2,80,46,1 nearest the entry hole and C2092,2,80,47,6 about 0.8 mm beneath the entry hole provide evidence of highly chaotic conditions during capture. They are dominated by nonvesicular low-Mg silica glass instead of highly vesicular glass found deeper into this track which is consistent with the escape of magnesiosilica vapors generated from the smallest comet grains. The survival of delicate (Mg,Al,Ca)-bearing silica glass structures is unique to the entry hole. Both allocations show a dearth of surviving comet dust except for a small enstatite, a low-Ca hypersthene grain, and a Ti-oxide fragment. Finding scattered TiO2 fragments in the silica glass could support, but not prove, TiO2 grain fragmentation during hypervelocity capture. The here reported dearth in mineral species is in marked contrast to the wealth of surviving silicate and oxide minerals deeper into the bulb. Both allocations show Fe-Ni-S nanograins dispersed throughout the low-Mg silica glass matrix. It is noted that neither comet Halley nor Wild 2 had a CI bulk composition for the smallest grains. Using the analogs of interplanetary dust particles (IDPs) and cluster IDPs it is argued that a CI chondritic composition requires the mixing of nonchondritic components in the appropriate proportions. So far, the fine-grained Wild 2 dust is biased toward nonchondritic ferromagnesiosilica materials and lacking contributions of nonchondritic components with Mg-Fe-Ni-S[Si-O] compositions. To be specific, “Where are the GEMS”? The GEMS look-alike found in this study suggests that evidence of GEMS in comet Wild 2 may still be found in the Stardust glass.

Reference
Rietmeijer FJM (2015) The smallest comet 81P/Wild 2 dust dances around the CI composition. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12510]
Published by arrangement with John Wiley&Sons

¹James M. D. Day, ¹Christopher A. Corder, ²Douglas Rumble III, ³Nelly Assayag, ³Pierre Cartigny,⁴Lawrence A. Taylor
¹Geosciences Research Division, Scripps Institution of Oceanography, La Jolla, California, USA
²Geophysical Laboratory, Carnegie Institution of Washington, Washington, District of Columbia, USA
³Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ. Paris Diderot, UMR 7154 CNRS, Paris, France
⁴Department of Earth and Planetary Sciences, Planetary Geosciences Institute, University of Tennessee, Knoxville, Tennessee, USA

Olivine-dominated (70–80 modal %) achondrite meteorite Lewis Cliff (LEW) 88763 originated from metamorphism and limited partial melting of a FeO-rich parent body. The meteorite experienced some alteration on Earth, evident from subchondritic Re/Os, and redistribution of rhenium within the sample. LEW 88763 is texturally similar to winonaites, has a Δ17O value of −1.19 ± 0.10‰, and low bulk-rock Mg/(Mg+Fe) (0.39), similar to the FeO-rich cumulate achondrite Northwest Africa (NWA) 6693. The similar bulk-rock major-, minor-, and trace-element abundances of LEW 88763, relative to some carbonaceous chondrites, including ratios of Pd/Os, Pt/Os, Ir/Os, and 187Os/188Os (0.1262), implies a FeO- and volatile-rich precursor composition. Lack of fractionation of the rare earth elements, but a factor of approximately two lower highly siderophile element abundances in LEW 88763, compared with chondrites, implies limited loss of Fe-Ni-S melts during metamorphism and anatexis. These results support the generation of high Fe/Mg, sulfide, and/or metal-rich partial melts from FeO-rich parent bodies during partial melting. In detail, however, LEW 88763 cannot be a parent composition to any other meteorite sample, due to highly limited silicate melt loss (0 to <<5%). As such, LEW 88763 represents the least-modified FeO-rich achondrite source composition recognized to date and is distinct from all other meteorites. LEW 88763 should be reclassified as an anomalous achondrite that experienced limited Fe,Ni-FeS melt loss. Lewis Cliff 88763, combined with a growing collection of FeO-rich meteorites, such as brachinites, brachinite-like achondrites, the Graves Nunataks (GRA) 06128/9 meteorites, NWA 6693, and Tafassasset, has important implications for understanding the initiation of planetary differentiation. Specifically, regardless of precursor compositions, partial melting and differentiation processes appear to be similar on asteroidal bodies spanning a range of initial oxidation states and volatile contents.

Reference
Day JMD, Corder CA, Rumble III D, Assayag N, Cartigny P, Taylor LA (2015) Differentiation processes in FeO-rich asteroids revealed by the achondrite Lewis Cliff 88763. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12509]

Published by arrangement with John Wiley&Sons

^1,2Vogel, N., ³Bochsler, P., ³Bühler, F., ^4,5Heber, V. S., ³Grimberg, A., ¹Baur, H., ⁵Horstmann, M., ⁵Bischoff, A., ¹Wieler, R.
¹Institute of Geochemistry and Petrology, ETH Zürich, Zürich, Switzerland
²Department of Water Resources and Drinking Water, Eawag, Swiss Federal Institute for Aquatic Research, Dübendorf, Switzerland
³Physikalisches Institut, University of Bern, Bern, Switzerland
⁴Department of Earth, Planetary and Space Sciences, University of California Los Angeles, Los Angeles, California, USA
⁵Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Münster, Germany
⁶Division of Radiation Protection and Safety, Paul Scherrer Institut, OFLC/U103, Villigen PSI, Switzerland

We compare the solar wind (SW) He, Ne, and Ar compositions collected during the Apollo Solar Wind Composition (SWC) experiments (1969–1972; Al- & Pt-foils) and the Genesis mission (2002–2004; so-called DOS targets considered here). While published SW 20Ne/22Ne and 36Ar/38Ar ratios of both data sets agree, differences exist in the 4He/3He, 4He/20Ne, and 20Ne/36Ar ratios. However, 20Ne/36Ar ratios from Apollo-16 Pt-foils, exclusively adopted as SW values by the SWC team, are consistent with the Genesis results. We investigate if the differences indicate a variability of the SW over the course of about 30 yr, or systematic biases of the two data sets, which were collected in different environments and measured several decades apart in different laboratories (University of Bern; ETH Zurich). New measurements of Apollo-15 SWC aluminum foils in Zurich generally agree with the original measurements performed in Bern. Zurich samples show slightly lower 4He concentrations suggesting a few percent of diffusive loss of 4He during storage of the foils. A 3% difference between the He isotopic ratios measured in Bern and in Zurich possibly represents an analytical bias between the laboratories. The low SW 4He/20Ne and 20Ne/36Ar ratios in Apollo-15 Al-foils compared to Genesis data are consistent with a mixture of Genesis-like SW and noble gases from small amounts of lunar dust. Our data suggest that the mean SW He, Ne, and Ar isotopic and elemental compositions have not significantly changed between the overall Apollo and Genesis mission collection periods.

Reference
Vogel N, Bochsler P, Bühler F, Heber VS, Grimberg A, Baur H, Horstmann M, Bischoff A, Wieler R (2015) Similarities and differences between the solar wind light noble gas compositions determined on Apollo 15 SWC foils and on NASA Genesis Targets. Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.12503]

Published by arrangement with John Wiley&Sons

Lidia Pittarello¹, Kitty Baert², Vinciane Debaille³ and Philippe Claeys^1
1Earth System Science, Analytical, Environmental and Geo-Chemistry (AMGC), Vrije Universiteit Brussel, Brussels, Belgium
²Materials and Chemistry, Research Group Electrochemical and Surface Engineering (SURF), Vrije Universiteit Brussel, Brussels, Belgium
³Laboratoire G-Time, Geochemistry: Tracing with isotopes, minerals and elements, Université Libre de Bruxelles, Brussels, Belgium

Classification of ordinary chondrite meteorites generally implies (1) determining the chemical group by the composition in endmembers of olivine and pyroxene, and (2) identifying the petrologic group by microstructural features. The composition of olivine and pyroxene is commonly obtained by microprobe analyses or oil immersion of mineral separates. We propose Raman spectroscopy as an alternative technique to determine the endmember content of olivine and pyroxene in ordinary chondrites, by using the link between the wavelength shift of selected characteristic peaks in the spectra of olivine and pyroxene and the Mg/Fe ratio in these phases. The existing correlation curve has been recalculated from the Raman spectrum of reference minerals of known composition and further refined for the range of chondritic compositions. Although the technique is not as accurate as the microprobe for determining the composition of olivine and pyroxene, for most of the samples the chemical group can be easily determined by Raman spectroscopy. Blind tests with ordinary chondrites of different provenance, weathering, and shock stages have confirmed the potential of the method. Therefore, we suggest that a preliminary screening and the classification of most of the equilibrated ordinary chondrites can be carried out using an optical microscope equipped with a Raman spectrometer.

Reference
Pittarello L, Baert K, Debaille V and Claeys P (2015) Screening and classification of ordinary chondrites by Raman spectroscopy. Meteoritics & Planetary Science (in Press)
Link to Article [http://onlinelibrary.wiley.com/doi/10.1111/maps.12506/abstract]
Published by arrangement with John Wiley & Sons