^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.