¹Giovanna Serventi, ²Cristian Carli
Icarus (in Press) Link to Article [http://doi.org/10.1016/j.icarus.2017.04.018]
¹Department of Chemistry, Life Sciences and Environmental Sustainability, University of Parma, Viale delle Scienze 157/A Parma 43124, Italy
²IAPS-Inaf, Viale Fosso del Cavaliere Tor Vergata, Roma, 00133 Italy
Copyright Elsevier

The lunar surface consists of a regolith layer that covers the underlying bedrocks, and is generally characterized by particulates

The coarsest sizes of the regolith are chemically and mineralogically similar, while the finest fractions are more feldspathic, probably due to easier fracturing of plagioclase than mafic minerals.

Due to the more feldspathic nature of the very fine lunar soils, in this paper, we quantitatively investigate the influence of very fine (

(1) fine sizes act principally on reflectance and on spectral contrast (with the former increasing and the latter decreasing); (2) very fine plagioclase has a blue slope in the Near Infrared and very shallow 1250 nm band depth, close to zero; (3) consequently, the plagioclase band is always shallower than mafic bands; (4) in mixtures with olivine, the composite band center always shows the typical olivine value, differently from coarser mixtures; and (5) mafic materials have a blue slope in the Short Wavelength Infrared Region, a more V-shaped 1µm pyroxene absorption and the 1µm mafic band centers are shifted by ca. 40 nm vs. coarse sizes, reflecting a different weight within the crystal field absorption of the mafic component in very fine size. We also evidenced that a coarse plagioclase could be overestimated, while a very fine one could be underestimated if compared with the 63-125µm size.

¹Pierrick Roperch, ²Jérôme Gattacceca, ³Millarca Valenzuela, ²Bertrand Devouard, ⁴Jean-Pierre Lorand, ⁵Cesar Arriagada, ²Pierre Rochette,^6,7Claudio Latorre, ⁸Pierre Beck
Earth and Planetary Science Letters 469, 15-26 Link to Article [http://doi.org/10.1016/j.epsl.2017.04.009]
¹Géosciences Rennes, CNRS–INSU, Université de Rennes 1, Rennes, France
²CNRS, Aix Marseille Univ., IRD, Coll France, CEREGE, Aix-en-Provence, France
³Instituto de Astrofísica, P. Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile
⁴Laboratoire de Planétologie et Géodynamique, CNRS UMR 6112, Université de Nantes, 2 Rue la Houssinière, 44322, Nantes, France
⁵Departamento de Geología, Facultad de Ciencas Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile
⁶Centro UC del Desierto de Atacama and Departamento de Ecología, Pontificia Universidad Católica de Chile, Alameda 340, Santiago, Chile
⁷Institute of Ecology & Biodiversity (IEB), Santiago, Chile
⁸Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 414, Rue de la Piscine, Domaine Universitaire, 38400 St-Martin d’Hères, France
Copyright Elsevier

We describe extended occurrences of unusual silicate glass surface layers from the Atacama Desert (Chile). These glasses, found near the town of Pica at four localities separated by up to 70 km, are neither fulgurites, nor volcanic glasses, nor metallurgical slags related to anthropic activity, but show close similarities to other glasses that have been previously attributed to large airbursts created by meteoroids entering the Earth’s atmosphere. The glasses are restricted to specific Late Pleistocene terrains: paleo-wetlands and soils rich in organic matter with SiO2-rich plant remains, salts and carbonates. 14C dating and paleomagnetic data indicate that the glasses were formed during at least two distinct periods. This rules out the hypothesis of a single large airburst as the cause of surface melting. Instead, burning of organic-rich soils in dried-out grassy wetlands during climate oscillations between wet and dry periods can account for the formation of the Pica glasses. Large oases did indeed form in the hyperarid Atacama Desert due to elevated groundwater tables and increased surface discharge during the Central Andean Pluvial Event (roughly coeval with the Mystery interval and Younger Dryas). Finally, we discuss the implications of our results for the other surface glasses previously attributed to extraterrestrial events.

¹Matthias M. M. Meier,²Kees C. Welten,^1,3My E. I. Riebe,^4,5Marc W. Caffee,^6,7,8Maria Gritsevich,¹Colin Maden,¹Henner Busemann
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12874]
¹ETH Zurich, Institute of Geochemistry and Petrology, Zurich, Switzerland
²Space Sciences Laboratory, University of California, Berkeley, California, USA
³Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC, USA
⁴Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana, USA
⁵Department of Earth, Atmospheric and Planetary Sciences, Purdue University, West Lafayette, Indiana, USA
⁶Department of Physics, University of Helsinki, Helsinki, Finland
⁷Finnish Geospatial Research Institute, Masala, Finland
⁸Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russia
Published by arrangement with John Wiley & Sons

The Park Forest (L5) meteorite fell in a suburb of Chicago, Illinois (USA) on March 26, 2003. It is one of the currently 25 meteorites for which photographic documentation of the fireball enabled the reconstruction of the meteoroid orbit. The combination of orbits with pre-atmospheric sizes, cosmic-ray exposure (CRE), and radiogenic gas retention ages (“cosmic histories”) is significant because they can be used to constrain the meteoroid’s “birth region,” and test models of meteoroid delivery. Using He, Ne, Ar, 10Be, and 26Al, as well as a dynamical model, we show that the Park Forest meteoroid had a pre-atmospheric size close to 180 g cm−2, 0–40% porosity, and a pre-atmospheric mass range of ~2–6 tons. It has a CRE age of 14 ± 2 Ma, and (U, Th)-He and K-Ar ages of 430 ± 90 and 490 ± 70 Ma, respectively. Of the meteorites with photographic orbits, Park Forest is the second (after Novato) that was shocked during the L chondrite parent body (LCPB) break-up event approximately 470 Ma ago. The suggested association of this event with the formation of the Gefion family of asteroids has recently been challenged and we suggest the Ino family as a potential alternative source for the shocked L chondrites. The location of the LCPB break-up event close to the 5:2 resonance also allows us to put some constraints on the possible orbital migration paths of the Park Forest meteoroid.

¹Addi Bischoff, ²Gerhard Wurm, ³Marc Chaussidon, ¹Marian Horstmann, ¹Knut Metzler, ⁴Mona Weyrauch, ¹Julia Weinauer
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12833]
¹Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Münster, Germany
²Fakultät für Physik, Universität Duisburg-Essen, Duisburg, Germany
³Institut de Physique du Globe, Sorbonne Paris Cité, UMR CNRS 7154, Université Paris Diderot, Paris Cedex 05, France
⁴Institut für Mineralogie, Leibniz-Universität Hannover, Hannover, Germany
Published by arrangement with John Wiley & Sons

In Allende, a very complex compound chondrule (Allende compound chondrule; ACC) was found consisting of at least 16 subchondrules (14 siblings and 2 independents). Its overall texture can roughly be described as a barred olivine object (BO). The BO texture is similar in all siblings, but does not exist in the two independents, which appear as relatively compact olivine-rich units. Because of secondary alteration of pristine Allende components and the ACC in particular, only limited predictions can be made concerning the original compositions of the colliding melt droplets. Based on textural and mineralogical characteristics, the siblings must have been formed on a very short time scale in a dense, local environment. This is also supported by oxygen isotope systematics showing similar compositions for all 16 subchondrules. Furthermore, the ACC subchondrules are isotopically distinct from typical Allende chondrules, indicating formation in or reaction with a more 16O-poor reservoir. We modeled constraints on the particle density required at the ACC formation location, using textural, mineral-chemical, and isotopic observations on this multicompound chondrule to define melt droplet collision conditions. In this context, we discuss the possible relationship between the formation of complex chondrules and the formation of macrochondrules and cluster chondrites. While macrochondrules may have formed under similar or related conditions as complex chondrules, cluster chondrites certainly require different formation conditions. Cluster chondrites represent a mixture of viscously deformed, seemingly young chondrules of different chemical and textural types and a population of older chondrules. Concerning the formation of ACC calculations suggest the existence of very local, kilometer-sized, and super-dense chondrule-forming regions with extremely high solid-to-gas mass ratios of 1000 or more.

¹Isabella Pignatelli, ¹Yves Marrocchi, ^2,3Enrico Mugnaioli, ⁴Franck Bourdelle, ⁵Matthieu Gounelle
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://doi.org/10.1016/j.gca.2017.04.017]
¹CRPG, UMR 7358, CNRS – Université de Lorraine, 54500 Vandoeuvre-lès-Nancy, France
²Dipartimento di Scienze Fisiche, della Terre e dell’Ambiente, Università degli Studi di Siena, Via Laterino 8, 53100 Siena, Italy
³Center for Nanotechnology Innovation@NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127, Pisa, Italy
⁴LGCgE, Université de Lille 1, SN 5, 59655 Villeneuve d’Ascq, France
⁵IMPMC, MNHN, UPMC, UMR CNRS 7590, 61 rue Buffon, 75005 Paris, France
⁶InstitutUniversitaire de France, Maison des Universités, 103 bd. Saint-Michel, 75005 Paris
Copyright Elsevier

The CM chondrites represent the largest group of hydrated meteorites and span a wide range of conditions, from less altered (i.e., CM2) down to heavily altered (i.e., CM 1). The Paris chondrite is considered the least altered CM and thus enables the earliest stages of aqueous alteration processes to be deciphered. Here, we report results from a nanoscale study of tochilinite/cronstedtite intergrowths (TCIs) in Paris —TCIs being the emblematic secondary mineral assemblages of CM chondrites, formed from the alteration of Fe-Ni metal beads (type-I TCIs) and anhydrous silicates (type-II TCIs). We combined high-resolution transmission electron microscopy, scanning transmission X-ray microscopy and electron diffraction tomography to characterize the crystal structure, crystal chemistry and redox state of TCIs. The data obtained are useful to reconstruct the alteration conditions of Paris and to compare them with those of other meteorites. Our results show that tochilinite in Paris is characterized by a high hydroxide layer content (n = 2.1-2.2) regardless of the silicate precursors. When examined alongside other CMs, it appears that the hydroxide layer and iron contents of tochilinites correlate with the degree of alteration experienced by the chondrites. The Fe3+/ΣFe ratios of TCIs are high: 8-15% in tochilinite, 33-60% in cronstedtite and 70-80% in hydroxides. These observations suggest that alteration of CM chondrites took place under oxidizing conditions that could have been induced by significant H2 release during serpentinization. Similar results were recently reported in CR chondrites (Le Guillou et al., 2015), suggesting that the process(es) controlling the redox state of the secondary mineral assemblages were quite similar in the CM and CR parent bodies despite the different alteration conditions.

According to our mineralogical and crystallographic survey, the formation of TCIs in Paris occurred at temperatures lower than 100°C, under neutral, slightly alkaline conditions that favored the formation of both tochilinite and cronstedtite. During the course of alteration, the reduction in sulphur activity and/or the decrease of temperature prevented tochilinite crystallization and favoured the formation of cronstedtite and iron hydroxides. We suggest that iron hydroxides probably formed as ferrihydrite and then progressively converted to goethite between 50° and 80°C, a temperature range that is also favourable for cronstedtite formation. The presence of cronstedtite plays a key role in the reconstruction of the alteration history, demonstrating that the alteration of Paris took place by way of serpentinization processes similar to those described on the Earth.

^1,2K.E. Miller, ^1,2D.S. Lauretta, ^2,3,4,5H.C. Connolly Jr., ⁶E.L. Berger, ⁷K. Nagashima, ²K. Domanik
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://doi.org/10.1016/j.gca.2017.04.009]
¹Space Sciences Division, Southwest Research Institute, San Antonio, TX 78238
²Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA
³Department of Geology, School of Earth and the Environment, Rowan University, 201 Mullica Hill Road, Glassboro, N. J. 08028 USA
⁴Earth and Environmental Sciences, The Graduate Center of the City University of New York, Brooklyn, NY 10016, USA
⁵Earth and Planetary Science, American Museum of Natural History, Central Park West, New York, NY 10024, USA
⁶GeoControl Systems Inc. – Jacobs JETS – NASA Johnson Space Center, Houston, TX 77058, USA
⁷Hawai’i Institute of Geophysics and Planetology, University of Hawai’i at Manoa, Honolulu, HI 96822, USA
Copyright Elsevier

Sulfide assemblages are commonly found in chondritic meteorites as small inclusions in the matrix or in association with chondrules. These assemblages are widely hypothesized to form through pre-accretionary corrosion of metal by H2S gas or through parent body processes. We report here on two unequilibrated R chondrite samples that contain large, chondrule-sized sulfide nodules in the matrix. Both samples are from Mount Prestrud (PRE) 95404. Chemical maps and spot and broad-beam electron microprobe analyses (EMPA) were used to assess the distribution, stoichiometry, and bulk composition of sulfide nodules and silicate chondrules in the clasts. Oxygen isotope data were collected via secondary ion mass spectrometry (SIMS) to assess the relationship of chondrules to other chondrite groups. Scanning electron microscopy (SEM), focused ion beam (FIB), and transmission electron microscopy (TEM) analyses were used to assess fine-scale features and identify crystal structures in sulfide assemblages. Thermodynamic models were used to assess the temperature, sulfur fugacity (fS2), total pressure, dust-to-gas ratio, and oxygen fugacity (fO2) conditions during sulfide nodule and chondrule formation.

The unequilibrated clasts include a mixture of type I and type II chondrules, as well as non-porphyritic chondrules. Chondrule oxygen isotopes overlap with ordinary-chondrite chondrules. Sulfide nodules average 200 µm in diameter, have rounded shapes, and are primarily composed of pyrrhotite, pentlandite, and magnetite. Some are deformed around chondrules in a petrologic relationship similar in appearance to compound chondrules. Both nodules and sulfides in chondrules include phosphate inclusions and Cu-rich lamellae, which suggests a genetic relationship between sulfides in chondrules and in the matrix. Ni/Co ratios for matrix and chondrule sulfides are solar, while Fe and Ni are non-solar and inversely related.

We hypothesize that sulfide nodules formed via pre-accretionary melt processes. During chondrule formation, precursors composed of a mixture of silicate and sulfide material were heated to form immiscible melt droplets, which separated and cooled to form Si-rich chondrules and S-rich nodules. Sulfide melt was stabilized by a high total pressure (∼1 atm) in a dust- or ice-enriched environment. Heating of this material contributed to a high fS2 (2 × 10-3 atm at 1138 °C), and high fO2 (IW – 1 to IW – 4), in an environment with peak temperatures between 1539 °C and 1750 °C. Oxygen isotopic compositions in this region were similar to those recorded by the LL-chondrite chondrules.

¹Raphael J. Baumgartner, ¹Marco L. Fiorentini, ²Jean-Pierre Lorand, ^3,4David Baratoux, ⁵Federica Zaccarini, ⁶Ludovic Ferrière, ⁷Marko K. Prašek,⁸Kerim Sener
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://doi.org/10.1016/j.gca.2017.04.011]
¹Centre for Exploration Targeting, School of Earth Sciences, ARC Centre of Excellence for Core to Crust Fluid Systems, University of Western Australia, 6009 Crawley, Australia
²Laboratoire de Planétologie et Géodynamique de Nantes, Université de Nantes and Centre National de la Recherche Scientifique, UMR 6112 44322 Nantes, France
³Géosciences Environnement Toulouse, CNRS, IRD and University of Toulouse, 31400 Toulouse, France
⁴Institut Fondamental d’Afrique Noire Cheikh Anta Diop, 5005 Dakar, Senegal
⁵Department of Applied Geological Sciences and Geophysics, University of Leoben, 8700 Leoben, Austria
⁶Natural History Museum Vienna, 1010 Vienna, Austria
⁷McGill University, Department of Earth and Planetary Sciences, H3A 0E8, Montreal, Canada
⁸Matrix Exploration Pty Ltd, 6112 Armadale, Australia
Copyright Elsevier

¹Emily A. Pringle, ^1,2Frédéric Moynier, ^2,3Pierre Beck, ⁴Randal Paniello, ^5,6Dominik C. Hezel
Earth and Planetary Science Letters 468. 62-71 Link to Article [http://doi.org/10.1016/j.epsl.2017.04.002]
¹Institut de Physique du Globe de Paris, Université Paris Diderot, Sorbonne Paris Cité, CNRS UMR 7154, 1 rue Jussieu, 75238 Paris, France
²Institut Universitaire de France, Paris, France
³Institut d’Astrophysique et de Planétologie de Grenoble, Université Grenoble Alpes, France
⁴Department of Earth and Planetary Sciences, Washington University in St. Louis, USA
⁵University of Cologne, Department of Geology and Mineralogy, Zülpicher Str. 49b, 50674 Köln, Germany
⁶Department of Mineralogy, Natural History Museum, Cromwell Road, London, SW7 5BD, UK
Copyright Elsevier

¹Ryuji Okazaki, ^2,3Keisuke Nagao
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12819]
¹Faculty of Sciences, Department of Earth and Planetary Sciences, Kyushu University, Nishi-ku, Fukuoka, Japan
²Graduate School of Science, Geochemical Research Center, University of Tokyo, Hongo, Bunkyo-ku, Tokyo, Japan
³Korea Polar Research Institute, Incheon, Yeonsu-gu, South Korea
Published by arrangement with John Wiley & Sons

The Sutter’s Mill (SM) CM chondrite fell in California in 2012. The CM chondrite group is one of the most primitive, consisting of unequilibrated minerals, but some of them have experienced complex processes occurring on their parent body, such as aqueous alteration, thermal metamorphism, brecciation, and solar wind implantation. We have determined noble gas concentrations and isotopic compositions for SM samples using a stepped heating gas extraction method, in addition to mineralogical observation of the specimens. The primordial noble gas abundances, especially the P3 component trapped in presolar diamonds, confirm the classification of SM as a CM chondrite. The mineralogical features of SM indicate that it experienced mild thermal alteration after aqueous alteration. The heating temperature is estimated to be 500 °C. The variation in the heating temperature of thermal alteration is consistent with the texture as a breccia. The heterogeneous distribution of solar wind noble gases is also consistent with it. The cosmic-ray exposure (CRE) age for SM is calculated to be 0.059 ± 0.023 Myr based on cosmogenic 21Ne by considering trapped noble gases as solar wind, the terrestrial atmosphere, P1 (or Q), P3, A2, and G components. The CRE age lies at the shorter end of the CRE age distribution of the CM chondrite group.

^1,2,3Tomáš Kohout et al (>10)*
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12871]
¹Department of Physics, University of Helsinki, Finland
²Institute of Geology, The Czech Academy of Sciences, Praha, Czech Republic
³Finnish Fireball Network, Finland
*Find the extensive, full author and affiliation list on the publishers website
Published by arrangement with John Wiley & Sons

The fall of the Annama meteorite occurred early morning (local time) on April 19, 2014 on the Kola Peninsula (Russia). Based on mineralogy and physical properties, Annama is a typical H chondrite. It has a high Ar-Ar age of 4.4 Ga. Its cosmic ray exposure history is atypical as it is not part of the large group of H chondrites with a prominent 7–8 Ma peak in the exposure age histograms. Instead, its exposure age is within uncertainty of a smaller peak at 30 ± 4 Ma. The results from short-lived radionuclides are compatible with an atmospheric pre-entry radius of 30–40 cm. However, based on noble gas and cosmogenic radionuclide data, Annama must have been part of a larger body (radius >65 cm) for a large part of its cosmic ray exposure history. The 10Be concentration indicates a recent (3–5 Ma) breakup which may be responsible for the Annama parent body size reduction to 30–35 cm pre-entry radius.