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Heterogeneity of oxygen isotopes and chemical compositions in a chondrule rim from carbonaceous chondrite
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| Title: | Heterogeneity of oxygen isotopes and chemical compositions in a chondrule rim from carbonaceous chondrite |
| Other Titles: | 炭素質コンドライト中のコンドリュールリムにおける酸素同位体と化学組成の不均一 |
| Authors: | 松田, 望1 Browse this author |
| Authors(alt): | Matsuda, Nozomi1 |
| Issue Date: | 25-Sep-2019 |
| Publisher: | Hokkaido University |
| Abstract: | Chondrules are surrounded by igneous rims that show evidence of a high degree of melting. Due to their common occurrence in various types of chondrites, igneous rims formed on pre-existing chondrules throughout chondrule-forming regions of the solar nebula. Although igneous rim formation was related to chondrule formation event, the rim formation process is not fully understood. Because igneous rims have experienced extensive alteration on the parent body, primary features of igneous rims could be changed. In this thesis, to reveal the rim formation process, I determined the two-dimensional chemical and oxygen isotopic distributions in an igneous rim of a chondrule within the Northwest Africa 3118 CV3oxA chondrite with sub-micrometer resolution using secondary ion mass spectrometry and scanning electron microscopy.
The chondrule with type I porphyritic texture is completely surrounded by a coarse-grained igneous rim. The igneous rim is mostly dominated by olivine, which has more FeO-rich compositions compared to those within the host chondrule (Fa2–5). The FeO contents show a bimodal distribution: MgO-rich (Fa11–22) and FeO-rich (Fa40-49) compositions. The igneous rim experienced aqueous alteration on the CV parent body. The aqueous alteration resulted in precipitation of the secondary FeO-rich olivine (Fa40–49) and slightly disturbed the Fe-Mg distribution in the MgO-rich olivine phenocrysts (Fa11–22) at about a 1 μm scale. However, no oxygen isotopic disturbances were observed at a scale greater than 100 nm. The MgO-rich olivine, a primary phase of igneous rim formation, has δ17O = −6±3‰ and δ18O = −1±4‰, and some grains contain extreme 16O-rich areas (δ17O, δ18O = ~ −30‰) nearly 10 μm across. I detected oxygen isotopic migration of approximately 1 μm at the boundaries of the extreme 16O-rich areas. Using oxygen self-diffusivity in olivine, the heating time of the igneous rim formation could have continued from several hours to several days at near liquidus temperatures (~2000 K) in the solar nebula suggesting that the rim formed by a similar flash heating event that formed the chondrules. |
| Conffering University: | 北海道大学 |
| Degree Report Number: | 甲第13756号 |
| Degree Level: | 博士 |
| Degree Discipline: | 理学 |
| Examination Committee Members: | (主査) 教授 圦本 尚義, 教授 永井 隆哉, 准教授 山本 順司, 助教 坂本 直哉（創成研究機構） |
| Degree Affiliation: | 理学院（自然史科学専攻） |
| Type: | theses (doctoral) |
| URI: | http://hdl.handle.net/2115/76088 |
| Appears in Collections: | 課程博士 (Doctorate by way of Advanced Course) > 理学院(Graduate School of Science)
学位論文 (Theses) > 博士 （理学）
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