Primordial and cosmogenic noble gases in the Sutter’s Mill CM chondrite

1Ryuji Okazaki, 2,3Keisuke Nagao
Meteoritics & Planetary Science (in Press) Link to Article [DOI: 10.1111/maps.12819]
1Faculty of Sciences, Department of Earth and Planetary Sciences, Kyushu University, Nishi-ku, Fukuoka, Japan
2Graduate School of Science, Geochemical Research Center, University of Tokyo, Hongo, Bunkyo-ku, Tokyo, Japan
3Korea Polar Research Institute, Incheon, Yeonsu-gu, South Korea
Published by arrangement with John Wiley & Sons

The Sutter’s Mill (SM) CM chondrite fell in California in 2012. The CM chondrite group is one of the most primitive, consisting of unequilibrated minerals, but some of them have experienced complex processes occurring on their parent body, such as aqueous alteration, thermal metamorphism, brecciation, and solar wind implantation. We have determined noble gas concentrations and isotopic compositions for SM samples using a stepped heating gas extraction method, in addition to mineralogical observation of the specimens. The primordial noble gas abundances, especially the P3 component trapped in presolar diamonds, confirm the classification of SM as a CM chondrite. The mineralogical features of SM indicate that it experienced mild thermal alteration after aqueous alteration. The heating temperature is estimated to be 500 °C. The variation in the heating temperature of thermal alteration is consistent with the texture as a breccia. The heterogeneous distribution of solar wind noble gases is also consistent with it. The cosmic-ray exposure (CRE) age for SM is calculated to be 0.059 ± 0.023 Myr based on cosmogenic 21Ne by considering trapped noble gases as solar wind, the terrestrial atmosphere, P1 (or Q), P3, A2, and G components. The CRE age lies at the shorter end of the CRE age distribution of the CM chondrite group.

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