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Noble gases in individual chondrules of the Allende CV 3 chondrite
Author(s) -
Miura Yayoi N.,
Nagao Keisuke,
Kimura Makoto
Publication year - 2014
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/maps.12313
Subject(s) - chondrule , allende meteorite , radiogenic nuclide , chondrite , olivine , geology , nuclide , meteorite , geochemistry , astrobiology , physics , nuclear physics , mantle (geology)
We analyzed noble gases in nine individual chondrules, an assemblage of small chondrules, and four whole‐rock samples of the Allende CV 3 chondrite. Major elements were also determined for five chondrules. The cosmic ray exposure ages are calculated from cosmogenic 3 He to be 5.17 ± 0.38 and 5.15 ± 0.25 Myr for the averages of the chondrules and whole rocks, respectively, showing no significant pre‐exposure evidence for the studied chondrules. Large amounts of 36 Ar, 80,82 Kr, and 128 Xe produced by neutron capture are observed in most samples; the abundances of these nuclides are correlated among the samples. The epithermal neutron flux and neutron slowing down density are calculated based on [ 80 Kr] n , from which a sample depth of about 30 cm can be calculated. The measured chondrules contain variable amounts of radiogenic 129 Xe. The abundance ratios of radiogenic 129 Xe to neutron capture–produced 128 Xe are rather constant among the studied chondrules; four chondrules give more precise ratios at the high‐temperature fractions, ranging from 1920 ± 80 to 2280 ± 140, which corresponds to a time difference of 3.9 ± 2.4 Myr. It is noticeable that most chondrules also contain 244 Pu‐derived fission Xe. The average 244 Pu/ 238 U ratio for nine chondrules is 0.0069 ± 0.0018, which agrees well with the preferred ratio reported for chondrites.