Insights into the origin of carbonaceous chondrite organics from their triple oxygen isotope composition

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.

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