¹Aaron P. Wilson,¹Matthew J. Genge,²Agata M. Krzesińska,⁴Andrew G. Tomkins
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13360]
¹Department of Earth Science and Engineering, Imperial College London, Exhibition Road, London, SW7 2AZ UK
²Centre for Earth Evolution and Dynamics, University of Oslo, Sem Sælands vei 2A, Oslo, 0371 Norway
³School of Earth, Atmosphere and Environment, Monash University, Melbourne, Victoria, 3800 Australia
Published by arrangement with John Wiley & Sons

The atmospheric entry heating of micrometeorites (MMs) can significantly alter their pre‐existing mineralogy, texture, and organic material. The degree of heating depends predominantly on the gravity and atmospheric density of the planet on which they fall. For particles falling on Earth, the alteration can be significant, leading to the destruction of much of the pre‐entry organics; however, the weaker gravity and thinner atmosphere of Mars enhance the survival of MMs and increase the fraction of particles that preserve organic material. This paper investigates the entry heating of MMs on the Earth and Mars in order to examine the MM population on each planet and give insights into the survival of extraterrestrial organic material. The results show that particles reaching the surface of Mars experience a lower peak temperature compared to Earth and, therefore, experience less evaporative mass loss. Of the particles which reach the surface, 68.2% remain unmelted on Mars compared to only 22.8% on Earth. Due to evaporative mass loss, unmelted particles that reach the surface of Earth are restricted to sizes <70 μm whereas particles >475 μm survive unmelted on Mars. Approximately 10% of particles experience temperatures below ~800 K, that is, the sublimation temperature of refractory organics found in MMs. On Earth, this fraction is significantly lower with less than 1% expected to remain below this temperature. Lower peak temperatures coupled with the larger sizes of particles surviving without significant heating on Mars suggest a much higher fraction of organic material surviving to the Martian surface.

¹Houda El Kerni et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13347]
¹ of Sciences Ain Chock, GAIA Laboratory, Hassan II University of Casablanca, km 8 Route d’El Jadida, 20150 Casablanca, Morocco
Published by arrangement with John Wiley & Sons

Since the discovery of shatter cones (SCs) near the village of Agoudal (Morocco, Central High Atlas Mountains) in 2013, the absence of one or several associated circular structures led to speculation about the age of the impact event, the number, and the size of the impact crater or craters. Additional constraints on the crater size, age, and erosion rates are obtained here from geological, structural, and geophysical mapping and from cosmogenic nuclide data. Our geological maps of the Agoudal impact site at the scales of 1:30,000 (6 km2) and 1:15,000 (2.25 km2) include all known occurrences of SCs in target rocks, breccias, and vertical to overturned strata. Considering that strata surrounding the impact site are subhorizontal, we argue that disturbed strata are related to the impact event. Three types of breccias have been observed. Two of them (br1‐2 and br2) could be produced by erosion–sedimentation–consolidation processes, with no evidence for impact breccias, while breccia (br1) might be impact related. The most probable center of the structure is estimated at 31°59′13.73ʺN, 5°30′55.14ʺW using the concentric deviation method applied to the orientation of strata over the disturbed area. Despite the absence of a morphological expression, the ground magnetic and electromagnetic surveys reveal anomalies spatially associated with disturbed strata and SC occurrences. The geophysical data, the structural observations, and the area of occurrence of SCs in target rocks are all consistent with an original size of 1.4–4.2 km in diameter. Cosmogenic nuclide data (36Cl) constrain the local erosion rates between 220 ± 22 m Ma−1 and 430 ± 43 m Ma−1. These erosion rates may remove the topographic expression of such a crater and its ejecta in a time period of about 0.3–1.9 Ma. This age is older than the Agoudal iron meteorite age (105 ± 40 kyr). This new age constraint excludes the possibility of a genetic relationship between the Agoudal iron meteorite fall and the formation of the Agoudal impact site. A chronolgy chart including the Atlas orogeny, the alternation of sedimentation and erosion periods, and the meteoritic impacts is presented based on all obtained and combined data.

^1,2W. Fujiya,³P. Hoppe,⁴T. Ushikubo,^2,5K. Fukuda,⁶P. Lindgren,⁷M. R. Lee,^8,9M. Koike,^8,10K. Shirai,⁸Y. Sano
Nature Astronomy (in Press) Link to Article [https://doi.org/10.1038/s41550-019-0801-4]
¹Faculty of Science, Ibaraki University, Mito, Japan
²Department of Geoscience, University of Wisconsin-Madison, Madison, WI, USA
³Max Planck Institute for Chemistry, Mainz, Germany
⁴Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Nankoku, Japan
⁵Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
⁶Department of Geology, Lund University, Lund, Sweden
⁷School of Geographical and Earth Sciences, University of Glasgow, Glasgow, UK
⁸Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Japan
⁹Department of Solar System Science, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan
¹⁰International Coastal Research Center, Atmosphere and Ocean Research Institute, The University of Tokyo, Otsuchi, Japan

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¹Elishevah Kootenvan,^1,2Frédéric Moynier
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.07.022]
¹Université de Paris, Institut de Physique du Globe de Paris, CNRS UMR 7154, 1 rue Jussieu, 75238 Paris, France
²Institut Universitaire de France, Paris, France
Copyright Elsevier

The potential complementarity between chondrules and matrix of chondrites, the Solar System’s building blocks, is still a highly debated subject. Complementary superchrondritic compositions of chondrite matrices and subchondritic chondrules may point to formation of these components within the same reservoir or, alternatively, to mobilization of elements during secondary alteration on chondrite parent bodies. Zinc isotope fractionation through evaporation during chondrule formation may play an important role in identifying complementary relationships between chondrules and matrix and is additionally a mobile element during hydrothermal processes. In an effort to distinguish between primary Zn isotope fractionation during chondrule formation and secondary alteration, we here report the Zn isotope data of five chondrule cores, five corresponding igneous rims and two matrices of the relatively unaltered Leoville CV3.1 chondrite. The detail required for these analyses necessitated the development of an adjusted Zn isotope analyses protocol outlined in this study. This method allows for the measurement of 5 ng Zn fractions, for which we have analyzed the isotope composition with an external reproducibility of 120 ppm. We demonstrate that we measure primary Zn isotope signatures within the sampled fractions of Leoville, which show negative δ66Zn values for the chondrule cores (δ66Zn = –0.43±0.14 ‰‰), more positive values for the igneous rims (δ66Zn = –0.01±0.30 ‰‰) and chondritic values for the matrix (δ66Zn = 0.19±0.14 ‰‰). In combination with elemental compositions and petrology of these chondrite fractions, we argue that chondrule cores, igneous rims and matrix could have formed within the same reservoir in the protoplanetary disk. The required formation mechanism involves Zn isotope fractionation through sulfide loss during chondrule core formation and concurrent thermal processing of matrix material. Depleted olivine-bearing grains representing this processed matrix would have accreted to the depleted chondrule cores and subsequently reabsorbed material (including 66Zn-rich) from a complementary volatile-rich gas, thereby forming the igneous rims. This would have allowed the rims to move towards an isotopically chondritic composition, similar to the non-processed matrix in Leoville. We note that Zn isotope analyses of components in other chondrites (f.e., CM, CO, EC) are necessary to identify if this complementarity relationship is generic or unique for each chondrite group. The development of a Zn isotope protocol for singularly small samples is a step forward in that direction.

¹Laurent Remusat,^2,3Jean-Yves Bonnet,¹Sylvain Bernard,⁴Arnaud Buch,³Eric Quirico
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.07.013]
¹Institut de Minéralogie, Physique des Matériaux et Cosmochimie (IMPMC), UMR CNRS 7590, Sorbonne Université, Muséum National d’Histoire Naturelle, 57 rue Cuvier, Case 52, 75231 Paris Cedex 5, France
²LATMOS-IPSL, Université Versailles St-Quentin, Sorbonne Université, CNRS UMR 8190, 78280 Guyancourt, France
³Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), UMR CNRS 5274, Université Grenoble Alpes, 38041 Grenoble, France
⁴Laboratoire Génie des Procédés et Matériaux (LGPM) CentraleSupelec, 8-10 rue Joliot-Curie 91190 Gif-sur-Yvette, France
Copyright Elsevier

Organic matter contained in carbonaceous chondrites may have evolved due to aqueous and/or thermal evolution on the parent body. The thermal behavior of the insoluble organic matter (IOM) of the Orgueil meteorite was investigated. The evolutions of structural and molecular properties were assessed by Raman, infrared and XANES spectroscopies, the H- and N-isotopic compositions by NanoSIMS. The starting IOM is a disordered organic macromolecule presenting a high degree of cross-linking. Hydrogen and Nitrogen isotope distributions are heterogeneous with the occurrence of numerous micron-sized hot spots enriched in heavy isotopes of H or N. After 1 hour at 300°C, there is subtle modification of the structural ordering and the isotopic compositions. After 1 hour at 500°C, the structure evolves toward condensation. Indeed, FTIR and XANES data are consistent with a continuous evolution of the molecular structure toward an increase of aromatization, starting at 300°C and becoming more intense at 500°C. The bulk D-enrichment is significantly reduced and D-rich hot spots are lost at 500°C. The experimental evolution of the δD is consistent with observations of IOM isolated from lightly altered carbonaceous chondrites. In contrast, the ¹⁵N-rich hot spots seem insensitive to high temperature up to 500°C and bulk δ¹⁵N remains constant. The thermal evolution of H- and N- isotopes is decoupled, indicating that the D-rich and ¹⁵N-rich moieties exhibit different thermal recalcitrance.

¹Mancuso, S.,^1,2Taricco, C.,²Colombetti, P.,^1,2Rubinetti, S.,³Sinha, N.,⁴Bhandari, N.,
^1,2Barghini, D.,¹Gardiol, D.
Nuovo Cimento della Societa Italiana di Fisica C 42, Article number Y Link to Article [DOI: 10.1393/ncc/i2019-19043-8]
¹Istituto Nazionale di Astrofisica, Osservatorio Astrofisico di Torino – Strada Osservatorio 20, Pino Torinese, 10025, Italy
²Dipartimento di Fisica, Università di Torino -, Via P. Giuria 1, Torino, 10125, Italy
³Wentworth Institute of Technology, Boston, MA, United States

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^1,2Litasov, K.D.,³Ishikawa, A.,⁴Kopylova, A.G.,
¹Podgornykh, N.M.,¹Pokhilenko, N.P.
Doklady Earth Sciences 485, 381-385 Link to Article [DOI: 10.1134/S1028334X19040068]
¹Sobolev Institute of Geology and Mineralogy, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090, Russian Federation
²Novosibirsk State University, Novosibirsk, 630090, Russian Federation
³Tokyo Institute of Technology, Tokyo, 152-8550, Japan

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¹Ouknine, L.,¹Khiri, F.,¹Ibhi, A.,²Heikal, M.T.S.,³Saint-Gerant, T.,³Medjkane, M.
Journal of African Earth Sciences 158, 103551 Link to Article [DOI: 10.1016/j.jafrearsci.2019.103551]
¹Petrology, Metallogeny and Meteorites Team, Faculty of Sciences, Ibn Zohr University, Agadir, Morocco
²Geology Department, Faculty of Science, Tanta University, Egypt
³Identité et Différenciation Des Espaces, de L’environnement et des Sociétés (IDEES), Université de Caen, France

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¹Akira Yamaguchi,¹Makoto Kimura,^2,3Jean‐Alix Barrat,⁴Richard Greenwood
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13351]
¹National Institute of Polar Research, Tachikawa, Tokyo, 190‐8518 Japan
²Université Européenne de Bretagne, Lorient, France
³CNRS, UMR 6538 (Domaines Océaniques), U.B.O.‐I.U.E.M., Place Nicolas Copernic, 29280 Plouzané Cedex, France
⁴Planetary and Space Sciences, Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA UK
Published by arrangement with John Wiley & Sons

We performed a petrologic, geochemical, and oxygen isotopic study of the lowest FeO ordinary chondrite (OC), Yamato (Y) 982717. Y 982717 shows a chondritic texture composed of chondrules and chondrule fragments, and mineral fragments set in a finer grained, clastic matrix, similar to H4 chondrites. The composition of olivine (Fa_{11.17 ± 0.48 (1σ)}) and low‐Ca pyroxene (Fs_{11.07 ± 0.98 (1σ)}Wo_{0.90 ± 0.71(1σ)}) is significantly more magnesian than those of typical H chondrites (Fa_16.0‐20, Fs_14.5‐18.0), as well as other known low‐FeO OCs (Fa_12.8‐16.7; Fs_13‐16). However, the bulk chemical composition of Y 982717, in particular lithophile and moderately volatile elements, is within the range of OCs. The bulk siderophile element composition (Ni, Co) is within the range of H chondrites and distinguishable from L chondrites. The O‐isotopic composition is also within the range of H chondrites. The lack of reduction textures indicates that the low olivine Fa content and low‐Ca pyroxene Fs content are characteristics of the precursor materials, rather than the result of reduction during thermal metamorphism. We suggest that the H chondrites are more compositionally diverse than has been previously recognized.

¹Chi Ma,²Oliver Tschauner,^3,4Luca Bindi,¹John R. Beckett,^5,6Xiande Xie
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13349]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, 91125 USA
²Department of Geoscience, University of Nevada, Las Vegas, Nevada, 89154 USA
³Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via G. La Pira 4, I‐50121 Firenze, Italy
⁴CNR, Istituto di Geoscienze e Georisorse, Sezione di Firenze, Via G. La Pira 4, I‐50121 Firenze, Florence, Italy
⁵Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640 China
⁶Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Chinese Academy of Sciences, Guangzhou, 510640 China
Published by arrangement with John Wiley & Sons

A new high‐pressure silicate, (Mg,Fe,Si)2(Si,□)O4 with a tetragonal spinelloid structure, was discovered within shock melt veins in the Tenham and Suizhou meteorites, two highly shocked L6 ordinary chondrites. Relative to ringwoodite, this phase exhibits an inversion of Si coupled with intrinsic vacancies and a consequent reduction of symmetry. Most notably, the spinelloid makes up about 30–40 vol% of the matrix of shock veins with the remainder composed of a vitrified (Mg,Fe)SiO3 phase (in Tenham) or (Mg,Fe)SiO3‐rich clinopyroxene (in Suizhou); these phase assemblages constitute the bulk of the matrix in the shock veins. Previous assessments of the melt matrices concluded that majorite and akimotoite were the major phases. Our contrasting result requires revision of inferred conditions during shock melt cooling of the Tenham and Suizhou meteorites, revealing in particular a much higher quench rate (at least 5 × 103 K s−1) for veins of 100–500 μm diameter, thus overriding formation of the stable phase assemblage majoritic garnet plus periclase.