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ID 57730
Author
Kunihiro, Takuya The Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University Kaken ID
Ota, Tsutomu The Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University ORCID Kaken ID publons researchmap
Nakamura, Eizo The Pheasant Memorial Laboratory, Institute for Planetary Materials, Okayama University Kaken ID publons researchmap
Abstract
We report in situ ion-microprobe analyses of Li- and O-isotope compositions for olivine, low-Ca pyroxene, high-Ca pyroxene, and chondrule mesostasis/plagioclase in nine chondrules from the Allende CV3 chondrite. Based on their mineralogy and O-isotope compositions, we infer that the chondrule mesostasis/plagioclase and ferroan olivine rims were extensively modified or formed during metasomatic alteration and metamorphism on the Allende parent asteroid. We excluded these minerals in order to determine the correlations between Li and both O and the chemical compositions of olivines and low-Ca pyroxenes in the chondrules and their igneous rims. Based on the O-isotope composition of the olivines, nine chondrules were divided into three groups. Average Δ17O of olivines (Fo>65) in group 1 and 2 chondrules are −5.3 ± 0.4 and −6.2 ± 0.4‰, respectively. Group 3 chondrules are characterized by the presence of 16O-rich relict grains and the Δ17O of their olivines range from −23.7 to −6.2‰. In group 1 olivines, as Fa content increases, variation of δ7Li becomes smaller and δ7Li approaches the whole-rock value (2.4‰; Seitz et al., 2012), suggesting nearly complete Li-isotope equilibration. In group 2 and 3 olivines, variation of δ7Li is limited even with a significant range of Fa content. We conclude that Li-isotope compositions of olivine in group 1 chondrules were modified not by an asteroidal process but by an igneous-rim formation process, thus chondrule olivines retained Li-isotope compositions acquired in the protosolar nebula. In olivines of the group 3 chondrule PO-8, we observed a correlation between O and Li isotopes: In relict 16O-rich olivine grains with Δ17O of ∼−25 to −20‰, δ7Li ranges from −23 to −3‰; in olivine grains with Δ17O > −20‰, δ7Li is nearly constant (−8 ± 4‰). Based on the Li-isotope composition of low-Ca pyroxenes, which formed from melt during the crystallization of host chondrules and igneous rims, the existence of a gaseous reservoir with a δ7Li ∼ −11‰ is inferred.
Keywords
Lithium
Oxygen
Chondrule
Chondrite
Asteroid
Allende
Igneous rim
SIMS
Note
This fulltext will be available in Mar 2021
Published Date
2019-05-01
Publication Title
Geochimica et Cosmochimica Acta
Volume
volume252
Publisher
PERGAMON-ELSEVIER SCIENCE
Start Page
107
End Page
125
ISSN
0016-7037
NCID
AA00655038
Content Type
Journal Article
language
英語
OAI-PMH Set
岡山大学
File Version
author
DOI
Web of Science KeyUT
Related Url
isVersionOf https://doi.org/1010.1016/j.gca.2019.02.038
License
https://creativecommons.org/licenses/by-nc-nd/4.0/deed.ja
Citation
Tak Kunihiro, Tsutomu Ota, Eizo Nakamura, Lithium- and oxygen-isotope compositions of chondrule constituents in the Allende meteorite, Geochimica et Cosmochimica Acta, Volume 252, 2019, Pages 107-125, ISSN 0016-7037, https://doi.org/10.1016/j.gca.2019.02.038.
Funder Name
Ministry of Education, Culture, Sports, Science and Technology