Paris vs. Murchison: Impact of hydrothermal alteration on organic matter in CM chondrites

1V. Vinogradoff, 2C. Le Guillou, 3S. Bernarda, L. Binet, 4P. Cartigny, 5A.J. Brearley, 1L. Remusat
Geochmica et Cosmochimica Acta (in Press) Link to Article []
1Institut de minéralogie, de physique des matériaux et de cosmochimie (IMPMC), Sorbonne Universités, UMR CNRS 7590, MNHN, UPMC, UMR IRD 206, CP 52, 57 rue Cuvier, 75005 Paris, France
2Unité matériaux et transformation (UMET), CNRS UMR 8207, Université Lille 1, France
3PSL Research University, Chimie-ParisTech, Institut de Recherche de Chimie-Paris, 11 rue Pierre et Marie Curie, 75005 Paris, France
4Institut de physique du globe de Paris (IPGP), Sorbonne Paris Cité, Université Paris Diderot, UMR CNRS 7154, 1 rue Jussieu, 75238 Paris cedex 05, France
5Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, USA
Copyright Elsevier

Unravelling the origin of organic compounds that were accreted into asteroids requires better constraining the impact of asteroidal hydrothermal alteration on their isotopic signatures, molecular structures, and spatial distribution. Here, we conducted a multi-scale/multi-technique comparative study of the organic matter (OM) from two CM chondrites (that originate from the same parent body or from identical parent bodies that accreted the same mixture of precursors) and underwent a different degree of hydrothermal alteration: Paris (a weakly altered CM chondrite – CM 2.8) and Murchison (a more altered one – CM 2.5). The Paris insoluble organic matter (IOM) shows a higher aliphatic/aromatic carbon ratio, a higher radical abundance and a lower oxygen content than the Murchison IOM. Analysis of the OM in situ shows that two texturally distinct populations of organic compounds are present within the Paris matrix: sub-micrometric individual OM particles and diffuse OM finely distributed within phyllosilicates and amorphous silicates. These results indicate that hydrothermal alteration on the CM parent body induced aromatization and oxidation of the IOM, as well as a decrease in radical and nitrogen contents. Some of these observations were also reported by studies of variably altered fragment of Tagish Lake (C2), although the hydrothermal alteration of the OM in Tagish Lake was apparently much more severe. Finally, comparison with data available in the literature suggests that the parent bodies of other chondrite petrologic groups could have accreted a mixture of organic precursors different from that accreted by the parent body of CMs.


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