Protracted storage of CR chondrules in a region of the disk transparent to galactic cosmic rays

Roth, Antoine S. G.; Metzler, Knut; Baumgartner, Lukas P.; Hofmann, Beda A.; Leya, Ingo (2017). Protracted storage of CR chondrules in a region of the disk transparent to galactic cosmic rays. Meteoritics & planetary science, 52(10), pp. 2166-2177. Meteoritical Society at the University of Arkansas, Dept. of Chemistry and Biochemistry 10.1111/maps.12923

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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 (DIs) from Shişr 033 (CR2). The meteorite was selected based on the absence of implanted solar wind noble gases and an anomalous oxygen isotopic composition of the DIs; the oxygen isotopes match those in CV3 and CO3 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 ³He and 21Ne concentrations up to 4.3 and 7.1 times higher than the DIs, respectively. We derived an average ³He-²¹Ne cosmic ray exposure (CRE) age for Shişr 033 of 2.03 ± 0.20 Ma (2 SD) and excesses in cosmogenic ³He and ²¹Ne in chondrules (relative to the DIs) in the range (in 10 ⁻⁸ cm³STP/g) 3.99–7.76 and 0.94–1.71, respectively. Assuming present-day GCR flux density, the excesses translate into average precompaction ³He-²¹Ne 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 GCRs.

Item Type:

Journal Article (Original Article)

Division/Institute:

08 Faculty of Science > Physics Institute > Space Research and Planetary Sciences

UniBE Contributor:

Leya, Ingo

Subjects:

500 Science > 520 Astronomy
600 Technology > 620 Engineering
500 Science > 530 Physics

ISSN:

1086-9379

Publisher:

Meteoritical Society at the University of Arkansas, Dept. of Chemistry and Biochemistry

Language:

English

Submitter:

Dora Ursula Zimmerer

Date Deposited:

08 Dec 2017 14:12

Last Modified:

08 Dec 2017 14:12

Publisher DOI:

10.1111/maps.12923

BORIS DOI:

10.7892/boris.106989

URI:

https://boris.unibe.ch/id/eprint/106989

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