Light noble gas records and cosmic ray exposure histories of recent ordinary chondrite falls

1Thomas Smith,1,2,3Huaiyu He,4Shijie Li,1P. M. Ranjith,1,2Fei Su,5Jérôme Gattacceca,5Régis Braucher,5ASTER-Team
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13760]
1State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029 China
2Institutions of Earth Science, Chinese Academy of Sciences, Beijing, 100029 China
3College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, 100049 China
4Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, 550081 China
5Centre Européen de Recherche et d’Enseignement de Géosciences de l’Environnement (CEREGE), CNRS, Aix-Marseille University, IRD, INRAE, Aix-en-Provence, France
Published by arrangement with John Wiley

We measured noble gas concentrations and isotopic ratios (He, Ne, and Ar isotopes) in six recent ordinary chondrite falls: Mangui (L6), Viñales (L6), Ozerki (L6), Tamdakht (H5), Kheneg Ljouâd (LL5/6), and Katol (L6). Among them, the three L6 chondrites Mangui, Viñales, and Ozerki fell in only a few months interval; their apparent similar petrographic and mineralogic characteristics might indicate source crater pairing. To test this hypothesis, we have investigated those meteorites for their cosmic ray exposure (CRE) histories, using the cosmogenic noble gases 3He, 21Ne, and 38Ar. We systematically (re)calculated the CRE ages as well as the gas retention ages of these meteorites. The CRE age of the Mangui is, based on noble gases, <1 Ma, which is unusually short for an L chondrite. Indeed, the range of exposure ages for L chondrites is generally distributed between ˜1 and ˜60 Ma, with major peaks occurring around ˜5, ˜30, and ˜40 Ma. In addition, the cosmogenic 3Hecos data of two Mangui duplicates are consistent with a remarkably high loss of helium by diffusion due to heating by solar radiation. Such a short parent body-Earth transfer time (<1 Ma) can be explained by a delivery from an Earth-crossing object. Regarding the other L6 chondrites, Viñales has a nominal CRE age of ˜9.4 Ma, whereas the Ozerki meteorite has a nominal CRE age of ˜1.2 Ma, which is consistent with Korochantseva et al. (2019). Based on their CRE ages as well as on their gas retention ages, it appears that none of these three recent L6 chondrite falls are source crater paired, and therefore, all three originate from different meteoroids. The nominal exposure ages of Tamdakht, Kheneg Ljouâd, and Katol are ˜3.2, ˜11, and ˜30 Ma, respectively, and are consistent with identified age peaks on the exposure age histogram of H, LL, and L chondrites, respectively. The nominal CRE age of Tamdakht is consistent with previous observations for H chondrites and implies that they are dominated by small impact events occurring in several parent bodies.

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