@article{oai:nipr.repo.nii.ac.jp:00014984,
 author = {Yamanobe, Masakuni and Nakamura, Tomoki and Nakashima, Daisuke},
 journal = {Polar Science},
 month = {Mar},
 note = {To understand oxygen isotope ratios and redox conditions of the chondrule formation environments of the outer rigions of the asteroid belt, we analyzed major element concentrations and oxygen isotope ratios of olivine grains in chondrules, isolated forsterite, and isolated olivine from the WIS 91600 and MET 00432 carbonaceous chondrites, which are thought to have originated from D-type asteroids located in the outer asteroid belt. The oxygen isotope ratios of individual chondrules and isolated grains show a wide variation in δ18O from −9.9‰ to +9.1‰ along the carbonaceous chondrite anhydrous mineral (CCAM) and primitive chondrule mineral (PCM) lines. The Δ17O (= δ17O – 0.52 × δ18O) values of the measured objects increase with decreasing Mg#; i.e., FeO-poor objects (Mg# > 90; type I chondrules and isolated forsterites) mainly have Δ17O values of ca. −6‰, and FeO-rich objects (Mg# < 90; type II chondrules and isolated olivines) have Δ17O values ranging from −3‰ to +2‰. Similar trends are observed for ferromagnesian silicate particles from comet Wild2 and CR chondrite chondrules, particularly in terms of FeO-rich objects with Δ17O values ranging from −3‰ to +2‰. It is suggested that FeO-rich objects formed in the outer regions of the asteroid belt and were transported to the outer solar nebular regions where comet Wild2 formed., 本研究では小惑星帯外縁部（4-5AU）の酸素同位体比を理解するため、同領域に分布するD型小惑星を起源にもつTagish Lake-type隕石中のコンドリュールの酸素同位体比分析を行った。その結果、δ17,18O値は傾き１の直線であるCCAMとPCMラインに沿って分布し、δ18O値の範囲は-9.9‰から+9.1‰であった。またMg# (= molar% MgO/[MgO+FeO])の減少に伴い、δ17O (= δ17O – 0.52 × δ18O)の値が増加する負の相関が確認され、Mg#>90ではΔ17Oは約-6‰を示し、Mg#<90ではΔ17Oは-3‰から+2‰を示した。同様の傾向はWild2彗星中のシリケイトからも確認されており、このことは小惑星帯外縁部で形成したコンドリュールが彗星形成領域である原始惑星系円盤外縁部（現在の冥王星以遠）まで輸送された可能性を示す。},
 pages = {29--38},
 title = {Oxygen isotope reservoirs in the outer asteroid belt inferred from oxygen isotope systematics of chondrule olivines and isolated forsterite and olivine grains in Tagish Lake-type carbonaceous chondrites, WIS 91600 and MET 00432},
 volume = {15},
 year = {2018}
}