Effects of minerals on metamorphism of organic matter during thermal processes in meteorite parent bodies

1Naoki Hirakawa,1Yoko Kebukawa,1Kensei Kobayashi,2Hideyuki Nakano
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2020.114167]
1Graduate School of Engineering Science, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan
2Faculty of Culture and Sport Policy, Toin University of Yokohama, 1614 Kurogane-cho, Aoba-ku, Yokohama 225-8503, Japan
Copyright Elsevier

Molecular structures and chemical compositions of organic matter in primitive meteorites reflect the conditions of the parent bodies, as well as the preaccretional history. During the parent body processing, co-existing minerals could have effects on structural changes of organics, in addition to temperature and redox state. Here, we performed heating experiments of a primordial organic matter analog with and without minerals to understand the effects of minerals on organic matter in conditions simulating metamorphism in thermally metamorphosed type 3 chondrites. The primordial analog materials were heated up to 400 °C, and the experimental products were analyzed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and gas chromatography mass spectrometry (GC/MS). Montmorillonite and olivine, particularly montmorillonite, enhanced decomposition of oxygen containing species due to decarboxylation and/or cracking, while olivine enhanced esterification at lower temperature. Our results further imply that the variations of insoluble organic matter in CV, CO, and type 3 ordinary chondrites could be partially due to different mineral compositions. We also tested the effects of pressure on the degradation of the organic matter at 400 °C up to 268 atm, however no significant pressure effects were observed by FTIR and GC/MS.

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