¹Romain Tartèse, ²Marc Chaussidon, ³Andrey Gurenko, ⁴Frédéric Delarue, ⁵François Robert
Proceedings of the National Academy of Sciences of the United States of America (in Press) Link to Article [DOI:https://doi.org/10.1073/pnas.1808101115]
¹School of Earth and Environmental Sciences, The University of Manchester, Manchester M13 9PL, United Kingdom;
²Institut de Physique du Globe de Paris, Université Sorbonne-Paris-Cité, Université Paris Diderot, CNRS UMR 7154, F-75238 Paris, France;
³Centre de Recherches Pétrographiques et Géochimiques, UMR 7358, Université de Lorraine, F-54501 Vandoeuvre-lès-Nancy, France;
⁴Sorbonne Université, Université Pierre-et-Marie-Curie, CNRS, École Pratique des Hautes Etudes, Paris Sciences et Lettres, UMR 7619 Milieux Environnementaux, Transferts et Interactions dans les Hydrosystèmes et les Sols, F-75005 Paris, France;
⁵Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Muséum National d’Histoire Naturelle, Sorbonne Universités, CNRS, Université Pierre-et-Marie-Curie, and Institut de Recherche pour le Développement, F-75005 Paris, France

Dust grains of organic matter were the main reservoir of C and N in the forming Solar System and are thus considered to be an essential ingredient for the emergence of life. However, the physical environment and the chemical mechanisms at the origin of these organic grains are still highly debated. In this study, we report high-precision triple oxygen isotope composition for insoluble organic matter isolated from three emblematic carbonaceous chondrites, Orgueil, Murchison, and Cold Bokkeveld. These results suggest that the O isotope composition of carbonaceous chondrite insoluble organic matter falls on a slope 1 correlation line in the triple oxygen isotope diagram. The lack of detectable mass-dependent O isotopic fractionation, indicated by the slope 1 line, suggests that the bulk of carbonaceous chondrite organics did not form on asteroidal parent bodies during low-temperature hydrothermal events. On the other hand, these O isotope data, together with the H and N isotope characteristics of insoluble organic matter, may indicate that parent bodies of different carbonaceous chondrite types largely accreted organics formed locally in the protosolar nebula, possibly by photochemical dissociation of C-rich precursors.

¹Brandon Mahan, ^1,2Frédéric Moynier, ^1,2Julien Siebert, ^3,4Bleuenn Gueguen, ³Arnaud Agranier, ^1,5Emily A. Pringle, ⁶Jean Bollard, ⁶James N. Connelly, ^1,6Martin Bizzarro
Proceedings of the National Academy of Sciences of the United States of America (in Press) Link to Article [https://doi.org/10.1073/pnas.1807263115]
¹Institut de Physique du Globe de Paris, Université Paris Diderot, Sorbonne Paris Cité, CNRS UMR 7154, 75238 Paris Cedex 05, France;
²Institut Universitaire de France, 75005 Paris, France;
³Laboratoire Géosciences Océan, UMR CNRS 6538, Université de Bretagne Occidentale et Institut Universitaire Européen de la Mer, 29280 Plouzané, France;
⁴UMS CNRS 3113, Institut Universitaire Européen de la Mer, 29280 Plouzané, France;
⁵Scripps Institution of Oceanography, University of California, San Diego, La Jolla CA 92093;
⁶Center for Star and Planet Formation, University of Copenhagen, DK-1350 Copenhagen, Denmark

Chondrites and their main components, chondrules, are our guides into the evolution of the Solar System. Investigating the history of chondrules, including their volatile element history and the prevailing conditions of their formation, has implications not only for the understanding of chondrule formation and evolution but for that of larger bodies such as the terrestrial planets. Here we have determined the bulk chemical composition—rare earth, refractory, main group, and volatile element contents—of a suite of chondrules previously dated using the Pb−Pb system. The volatile element contents of chondrules increase with time from ∼1 My after Solar System formation, likely the result of mixing with a volatile-enriched component during chondrule recycling. Variations in the Mn/Na ratios signify changes in redox conditions over time, suggestive of decoupled oxygen and volatile element fugacities, and indicating a decrease in oxygen fugacity and a relative increase in the fugacities of in-fluxing volatiles with time. Within the context of terrestrial planet formation via pebble accretion, these observations corroborate the early formation of Mars under relatively oxidizing conditions and the protracted growth of Earth under more reducing conditions, and further suggest that water and volatile elements in the inner Solar System may not have arrived pairwise.

¹Lionel G.Vacher, ¹Yves Marrocchi, ¹Johan Villeneuve, ²Maximilien J.Verdier-Paoletti, ^3,4Matthieu Gounelle
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2018.08.006]
¹CRPG, CNRS, Université de Lorraine, UMR 7358, Vandoeuvre-les-Nancy, F-54501, France
²Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015, USA
³IMPMC, MNHN, Sorbonne Universités, UMR CNRS 7590, 57 rue Cuvier, 75005 Paris, France
⁴Institut Universitaire de France, Maison des Universités, 103 boulevard Saint-Michel, 75005 Paris, France
Copyright Elsevier

Boriskino is a little studied CM2 chondrite composed of millimeter-sized clasts of different lithologies and degrees of alteration. Boriskino thus offers a good opportunity to better understand the preaccretionary alteration history and collisional evolution that took place on the CM parent body. The least altered lithology displays 16O-poor Type 1a calcite and aragonite grains (δ18O ≈ 30-37‰, δ17O ≈ 15-18‰ and Δ17O ≈ -2 to 0‰, SMOW) that precipitated early, before the establishment of the petrofabric, from a fluid whose isotopic composition was established by isotopic exchange between a 16O-poor water and 16O-rich anhydrous silicates. In contrast, the more altered lithologies exhibit 16O-rich Type 2a and veins of calcite (δ18O ≈ 17-23‰, δ17O ≈ 6-9‰ and Δ17O ≈ -4 to -1‰, SMOW) that precipitated after establishment of the deformation, from transported 16O-rich fluid in preexisting fractures. From our petrographic and X-ray tomographic results, we propose that the more altered lithologies of Boriskino were subjected to high intensity impact(s) (10-30 GPa) that produced a petrofabric, fractures and chondrule flattening. Taking all our results together, we propose a scenario for the deformation and alteration history of Boriskino, in which the petrographic and isotopic differences between the lithologies are explained by their separate locations into a single CM parent body. Based on the δ13C-δ18O values of the Boriskino Type 2a calcite (δ13C ≈ 30-71‰, PDB), we propose an alternative δ13C-δ18O model where the precipitation of Type 2a calcite can occurred in an open system environment with the escape of 13C-depleted CH4 produced from the reduction of C-bearing species by H2 released during serpentinization or kamacite corrosion. Assuming a mean precipitation temperature of 110°C, the observed δ13C variability in T2a calcite can be reproduced by the escape of ≈ 15-50% of dissolved carbon into CH4 by Rayleigh distillation.