Primordial organic matter in the xenolithic clast in the Zag H chondrite: Possible relation to D/P asteroids

1Yoko Kebukawa,2Michael E.Zolensky,3Motoo Ito,4Nanako O.Ogawa, 4Yoshinori Takano,4 Naohiko Ohkouchi,5Aiko Nakato,6Hiroki Suga,7 Yasuo Takeichi,6Yoshio Takahashi,1Kensei Kobayashi
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.12.012]
1Faculty of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan
2Astromaterials Research and Exploration Science, NASA Johnson Space Center, 2101 NASA Parkway, Houston, TX 77058, USA
3Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, B200 Monobe, Nankoku, Kochi 783-8502, Japan
4Biogeochemistry Program, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-Cho, Yokosuka 237-0061, Japan
5Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Sagamihara 252-5210, Japan
6Department of Earth and Planetary Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
7Institute of Materials Structure Science, High-Energy Accelerator Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan
Copyright Elsevier

Some xenolithic clasts in meteorites may have originated from unique primitive Solar System bodies. These clasts would provide novel insights into the early evolution of the Solar System. We conducted multiple analyses of organic matter (OM) in a CI-like xenolithic clast in the Zag (H5) meteorite including bulk elemental and isotopic analysis, FTIR, STXM/XANES, and NanoSIMS. The bulk C and N abundances in the Zag clast were +5.1 ± 0.4 wt.% and +0.26 ± 0.01 wt.%, respectively, which were the highest observed among various chondrite groups. The bulk δ13C value of the Zag clast was +23.0 ± 4.1 ‰ which was close to the value of the Tagish Lake meteorite; the δ15N value was +300 ± 3 ‰ which was close to the values of CR chondrites and Bells (a unique CM). The δD values of C-rich regions obtained by NanoSIMS were approximately +600 to +2000‰ which were close to the values of IOM from CI, CM and Tagish Lake. Some isotopic “hot spots” were observed with δD values up to ≈ +4000‰ and δ15N values up to ≈ +5500‰. The infrared transmission spectrum of the Zag clast was consistent with the abundant phyllosilicates and carbonates observed in the clast. The STXM showed abundant OM in various forms. C-XANES spectra from the OM were generally similar to CI/CM/CR chondrites. However, some variations existed in the molecular structures. OM in the Zag clast was partially associated with carbonates. The functional group, elemental and isotopic signatures of the OM in the Zag clast support the idea that the Zag clast is unique among known carbonaceous chondrite groups and originated from the outer Solar System such as aqueously-altered D/P type asteroids.

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