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ID 57730
著者
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
抄録
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.
キーワード
Lithium
Oxygen
Chondrule
Chondrite
Asteroid
Allende
Igneous rim
SIMS
備考
This fulltext will be available in Mar 2021
発行日
2019-05-01
出版物タイトル
Geochimica et Cosmochimica Acta
252巻
出版者
PERGAMON-ELSEVIER SCIENCE
開始ページ
107
終了ページ
125
ISSN
0016-7037
NCID
AA00655038
資料タイプ
学術雑誌論文
言語
English
OAI-PMH Set
岡山大学
論文のバージョン
author
DOI
Web of Science KeyUT
関連URL
isVersionOf https://doi.org/1010.1016/j.gca.2019.02.038
ライセンス
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.
助成機関名
文部科学省