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Deuterium- and 15N-signatures of organic globules in Murchison and Northwest Africa 801 meteorites

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Title: Deuterium- and 15N-signatures of organic globules in Murchison and Northwest Africa 801 meteorites
Authors: Hashiguchi, Minako Browse this author
Kobayashi, Sachio Browse this author
Yurimoto, Hisayoshi Browse this author →KAKEN DB
Keywords: meteorites
isotope imaging
H and N isotope anomalies
organic matter
aqueous alteration
Issue Date: 2015
Publisher: The Geochemical Society of Japan
Journal Title: Geochemical Journal
Volume: 49
Issue: 4
Start Page: 377
End Page: 391
Publisher DOI: 10.2343/geochemj.2.0363
Abstract: Carbonaceous matter from the matrix of the Murchison (CM2) meteorite and Northwest Africa (NWA) 801 (CR2) meteorite that were extremely rich in deuterium (D) and 15N was studied using in situ isotope imaging. The association of carbon, hydrogen, and nitrogen suggests that the carbonaceous matter was organic in nature, and the maximum magnitudes of D- and 15N-enrichment in the organic matter were δD = 2,880‰ and δ15N = 2,590‰ in Murchison, and δD = 7,500‰ and δ15N = 2,200‰ in NWA 801. The organic matter did not display a simple correlation between the magnitudes of D- and 15N-enrichment, and the isotopically anomalous organic matter was classified into three types based on the H and N isotopic characteristics: extremely 15N-rich without large D-enrichment (15N-rich), extremely D-rich without large 15N-enrichment (D-rich), and highly D- and 15N-rich (D-15N-rich). The occurrence of isotopically anomalous organic matter was attributed to their origin in the molecular clouds and outer solar nebula, ion-molecule reactions at low temperatures, grain surface reactions at low temperatures, and self-shielding effects in gas phase molecules. However, the observed D- and 15N-enrichment of the organic matter is much smaller than predicted by ion-molecule and grain surface reactions. This suggests a secondary modification of the H and N isotopic compositions of the organic matter in the solar nebula and in the parent body. In Murchison, the proportion of D-rich organic matter among the isotopically anomalous organic matter is smaller than in NWA 801, which presumably indicates that the D-enrichments are easily modified by aqueous alteration processes on the parent body. Scanning electron microscopy revealed the morphology of the D- and 15N-rich organic matter as aggregates of globules/particles or non-aggregated globules, where the size of each globule was <1 μm. Although there is no obvious correlation between the morphology of the organic matter and the H and N isotopic compositions, the result that Murchison contains more abundant globule/particle aggregates might suggests formation of aggregated nature due to aqueous activity.
Type: article
Appears in Collections:理学院・理学研究院 (Graduate School of Science / Faculty of Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 圦本 尚義

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