¹Shun Ichimura, ¹Yusuke Seto, ¹Kazushige Tomeoka
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://doi.org/10.1016/j.gca.2017.04.025]
¹Department of Planetology, Graduate School of Science, Kobe University, Nada, Kobe 657-8501, Japan
Copyright Elsevier

Nepheline is present as fine grains mainly in refractory inclusions and chondrules in CV and CO carbonaceous chondrites. The nepheline has been formed primarily by replacement of melilite and plagioclase in refractory inclusions and plagioclase and glass in chondrules. The nepheline formation is thought to have occurred during aqueous alteration and thermal metamorphism in the meteorite parent bodies. To verify this hypothesis, we performed the following experiments.

Hydrothermal experiments of gehlenite (Al-rich melilite) and plagioclase (An48) were carried out at 200 °C and ∼15 bar for 168 h using solutions of pH 0, 7, 13, and 14 with a uniform Na concentration. In the gehlenite experiments, various amounts of SiO2 were added. The results revealed that a Na zeolite, analcime, was produced from 10/3 and 10/6 mixtures of gehlenite/SiO2 at pH 7, 13, and14, and from a 10/10 mixture of gehlenite/SiO2 and plagioclase at pH 13 and 14. In particular, at pH 14, in addition to analcime, significant amounts of two other zeolites, fabriesite and hydroxycancrinite, were produced from the 10/6 mixture of gehlenite/SiO2, and fabriesite from plagioclase.

Isothermal heating experiments for 24 h showed that fabriesite, hydroxycancrinite, and analcime transform to nepheline at 600–650, 550–600, and 750–800 °C, respectively. Differential thermal analysis of these zeolites revealed that fabriesite and hydroxycancrinite exhibit exothermic peaks, which correspond to transformation to nepheline, and that the temperatures of those peaks decrease steadily with decreasing heating rate. Kinetic analysis using these data revealed that fabriesite and hydroxycancrinite transform to nepheline at temperatures more than 50–100 degrees lower than determined by the isothermal experiments if heated for durations > 102 and ∼ 1 yr, respectively. Analcime heated non-isothermally at a rate of 1 °C/min transformed to nepheline at temperature higher than that determined by the isothermal experiments, suggesting that its transformation temperature also decreases if it is heated for a much longer duration. From these experiments and analyses, we conclude that fabriesite, hydroxycancrinite, and possibly analcime are capable of transforming to nepheline by heating in meteorite parent bodies.

From our results, we propose that the nepheline in refractory inclusions and chondrules in meteorites formed by a two-stage alteration process: (1) formation of the Na zeolites from melilite, plagioclase, and glass by hydrothermal alteration at low temperature (probably

^1,2,3Hao Sun, ⁴Min Yi, ^1,24Zhigang Shen, ^1,2Xiaojing Zhang, ^1,2Shulin Ma
Planetary and Space Science (in Press) Link to Article [http://doi.org/10.1016/j.pss.2017.04.010]
¹School of Aeronautic Science and Engineering, Beihang University, Beijing 100191, China
²Beijing Key Laboratory for Powder Technology Research and Development, Beijing 100191, China
³Honors College of Beihang University, Beijing 100191, China
⁴Institute of Materials Science, Technische Universität Darmstadt, Darmstadt 64287, Germany

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²Archana M. Nair, ¹George Mathewa
Planetary and Space Science (in Press) Link to Article [http://doi.org/10.1016/j.pss.2017.04.009]
¹Department of Earth Sciences, Indian Institute of Technology (IIT) Bombay, Powai, Mumbai- 400 076
²Department of Civil Engineering, Indian Institute of Technology (IIT) Guwahati, Guwahati -781039

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Benjamin P. Weiss et al. (>10)*
Earth and Planetary Science Letters (in Press) Link to Article [http://doi.org/10.1016/j.epsl.2017.03.026]
¹Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
Copyright Elsevier

Paleomagnetic studies of meteorites have shown that the solar nebula was likely magnetized and that many early planetary bodies generated dynamo magnetic fields in their advecting metallic cores. The surface fields on these bodies were recorded by a diversity of chondrites and achondrites, ranging in intensity from several μT to several hundred μT. In fact, an achondrite parent body without evidence for paleomagnetic fields has yet to be confidently identified, hinting that early solar system field generation and the dynamo process in particular may have been common. Here we present paleomagnetic measurements of the ungrouped achondrite NWA 7325 indicating that it last cooled in a near-zero field (<∼1.7 μT), estimated to have occurred at 4563.09±0.264563.09±0.26 million years ago (Ma) from Al–Mg chronometry. Because NWA 7325 is highly depleted in siderophile elements, its parent body nevertheless underwent large-scale metal-silicate differentiation and likely formed a metallic core. This makes NWA 7325 the first recognized example of an essentially unmagnetized igneous rock from a differentiated early solar system body. These results indicate that all magnetic fields, including those from any core dynamo on the NWA 7325 parent body, the solar nebula, young Sun, and solar wind, were <1.7 μT at the location of NWA 7325 at 4563 Ma. This supports a recent conclusion that the solar nebula had dissipated by ∼4 million years after solar system formation. NWA 7325 also serves as an experimental control that gives greater confidence in the positive identification of remanent magnetization in other achondrites.

¹C.M.O’D. Alexander, ²R.C. Greenwood, ³R. Bowden, ²J.M. Gibson, ⁴K.T. Howard, ²I.A. Franchi
Geochimica et Cosmochimica Acta (in Press) Link to Article [http://doi.org/10.1016/j.gca.2017.04.021]
¹Dept. Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington DC 20015, USA
²Planetary and Space Sciences, Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
³Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington DC 20015, USA
⁴Physical Sciences Department, Kingsborough Community College, City University of New York, 2001 Oriental Blvd., Brooklyn, New York, NY 11235, USA
Copyright Elsevier

As part of a study to identify the most primitive COs and to look for weakly altered CMs amongst the COs, we have conducted a multi-technique study of 16 Antarctic meteorites that had been classified as primitive COs. For this study, we have determined: (1) the bulk H, C and N abundances and isotopes, (2) bulk O isotopic compositions, (3) bulk modal mineralogies, and (4) for some selected samples the abundances and compositions of their insoluble organic matter (IOM). Two of the 16 meteorites do appear to be CMs – BUC 10943 seems to be a fairly typical CM, while MIL 090073 has probably been heated. Of the COs, DOM 08006 appears to be the most primitive CO identified to date and is quite distinct from the other members of its pairing group. The other COs fall into two groups that are less primitive than DOM 08006 and ALH 77307, the previously most primitive CO. The first group is composed of members of the DOM 08004 pairing group, except DOM 08006. The second group is composed of meteorites belonging to the MIL 03377 and MIL 07099 pairing groups. These two pairing groups should probably be combined. There is a dichotomy in the bulk O isotopes between the primitive (all Antarctic finds) and the more metamorphosed COs (mostly falls). This dichotomy can only partly be explained by the terrestrial weathering experienced by the primitive Antarctic samples. It seems that the more equilibrated samples interacted to a greater extent with 16O-poor material, probably water, than the more primitive meteorites.

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.