Chromium Isotopic Evidence for an Early Formation of Chondrules from the Ornans CO Chondrite

Ke Zhu, Jia Liu, Frédéric Moynier, Liping Qin, Conel M.O.D. Alexander, Yongsheng He

Research output: Contribution to journalArticle (Academic Journal)peer-review

31 Citations (Scopus)

Abstract

Chondrules are the main components of primitive meteorites and possibly the building blocks of planetary embryos and terrestrial planets. However, their ages and modes of formation are still highly debated. Here, we present high-precision Cr isotope data of nine chondrules from one of the more primitive chondrites, the CO3 chondrite Ornans. These chondrules define an external 53 Mn- 53 Cr isochron, with an initial 53 Mn/ 55 Mn of (7.1 ± 1.6) ×10 -6 , corresponding to an age of 4567.6 ±1.3 Ma when anchored to the angrite D'Orbigny (U-corrected). This age is within error of the age of formation of calcium-aluminum-rich inclusions (CAIs). All chondrules show a wide range of ϵ 54 Cr values (+0.20 to +1.22) and a positive correlation between ϵ 53 Cr and ϵ 54 Cr values, suggesting mixing of different isotopic sources in the protoplanetary disk. This could reflect that silicate materials from the CAI-forming region (with complementary compositions to CAIs, i.e., low Mn/Cr and ϵ 54 Cr) were transported to the accretion region of the CO chondrite parent body and mixed with CI-like material (high-Mn/Cr and ϵ 54 Cr) during chondrule formation. Such mixing must have occurred prior to the formation of chondrule precursors. Furthermore, chondrules from chondrites with more CAIs (CV and CO) exhibit greater variability in ϵ 54 Cr than chondrules from chondrites formed later with fewer CAIs (e.g., CB and CR), suggesting that the accretion regions of the former received more material transported from the inner solar system than the latter. This dichotomy may indicate the CB and CR chondrites accreted at greater orbital distances than other chondrites.

Original languageEnglish
Article number82
JournalAstrophysical Journal
Volume873
Issue number1
DOIs
Publication statusPublished - 2019

Bibliographical note

Funding Information:
This work was funded by Strategic Priority Research Program (B) (No. XDB18000000) and the Key Research Program (No. XDPB11) of Chinese Academy of Sciences, National Natural Science Foundation of China (Nos. 41625013, 41473066, 41773060), and the “111” project. We greatly appreciate Jiuxing Xia and Paolo A. Sossi for their helpful discussions. We would like to thank the Natural History Museum, London for supplying the sample of Ornans used in this study. We also appreciate the comments by an anonymous reviewer, which greatly improved the quality of this paper. K.Z. acknowledges the Ph.D. fellowship from China Scholarship Council (No. 201706340161).

Publisher Copyright:
© 2019. The American Astronomical Society. All rights reserved.

Keywords

  • astrochemistry
  • meteorites, meteors, meteoroids
  • nuclear reactions, nucleosynthesis, abundances

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