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Protracted storage of CR chondrules in a region of the disk transparent to galactic cosmic rays
Author(s) -
Roth Antoine S. G.,
Metzler Knut,
Baumgartner Lukas P.,
Hofmann Beda A.,
Leya Ingo
Publication year - 2017
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.12923
Subject(s) - chondrule , cosmic ray , chondrite , meteorite , noble gas , astrophysics , isotopes of oxygen , formation and evolution of the solar system , parent body , carbonaceous chondrite , presolar grains , astrobiology , meteoroid , solar system , breccia , physics , astronomy , geology , geochemistry , atomic physics
Renazzo‐type carbonaceous ( CR ) chondrites are accretionary breccias that formed last. As such they are ideal samples to study precompaction exposures to cosmic rays. Here, we present noble gas data for 24 chondrules and 3 dark inclusion samples ( DI s) from Shişr 033 ( CR 2). The meteorite was selected based on the absence of implanted solar wind noble gases and an anomalous oxygen isotopic composition of the DI s; the oxygen isotopes match those in CV 3 and CO 3 chondrites. Our samples contain variable mixtures of galactic cosmic ray ( GCR )‐produced cosmogenic noble gases and trapped noble gases of presolar origin. Remarkably, all chondrules have cosmogenic 3 He and 21 Ne concentrations up to 4.3 and 7.1 times higher than the DI s, respectively. We derived an average 3 He‐ 21 Ne cosmic ray exposure ( CRE ) age for Shişr 033 of 2.03 ± 0.20 Ma (2 SD ) and excesses in cosmogenic 3 He and 21 Ne in chondrules (relative to the DI s) in the range (in 10 −8 cm 3 STP /g) 3.99–7.76 and 0.94–1.71, respectively. Assuming present‐day GCR flux density, the excesses translate into average precompaction 3 He‐ 21 Ne CRE ages of 3.1–27.3 Ma depending on the exposure geometry. The data can be interpreted assuming a protracted storage of a single chondrule generation prior to the final assembly of the Shişr 033 parent body in a region of the disk transparent to GCR s.