26Al–26Mg chronology of high-temperature condensate hibonite in a fine-grained, Ca-Al-rich inclusion from reduced CV chondrite

1Noriyuki KAWASAKI,2Daiki YAMAMOTO,3Sohei WADA,1Changkun PARK,3Hwayoung KIM,4Naoya SAKAMOTO,1,4Hisayoshi YURIMOTO
Meteoritics & Planetary Science (in Press) Link to Article [doi: 10.1111/maps.13989]
1Department of Natural History Sciences, Hokkaido University, Sapporo, Japan
2Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan
3Division of Earth-System Sciences, Korea Polar Research Institute, Incheon, Republic of Korea
4Isotope Imaging Laboratory, Creative Research Institution, Hokkaido University, Sapporo, Japan
Published by arrangement with John Wiley & Sons

Al–Mg mineral isochron studies using secondary ion mass spectrometry (SIMS)have revealed the initial26Al/27Al ratios, (26Al/27Al)0, for individual Ca-Al-rich inclusions(CAIs) in meteorites. We find that the relative sensitivity factors of27Al/24Mg ratio forSIMS analysis of hibonite, one of the major constituent minerals of CAIs, exhibit variationsbased on their chemical compositions. This underscores the critical need for usingappropriate hibonite standards to obtain accurate Al-Mg data. We measured the AlMgmineral isochron for hibonite in a fine-grained CAI (FGI) from the Northwest Africa 8613reduced CV chondrite by SIMS using synthesized hibonite standards with27Al/24Mg of~30,~100, and~400. The obtained mineral isochron of hibonite in the FGI yields (26Al/27Al)0of(4.730.09)9105, which is identical to that previously obtained from the mineralisochron of spinel and melilite in the same FGI (Kawasaki et al., 2020). The uncertainties of(26Al/27Al)0indicate that the constituent minerals in the FGI formed within~0.02 Myr inthe earliest solar system. The disequilibrium O-isotope distributions of the minerals in theFGI suggest that the O-isotope compositions of the nebular gas from which they condensedunderwent a transitional change from16O-rich to16O-poor within~0.02 Myr in the earliestsolar system. Once formed, the FGI may have been removed from the forming regionwithin~0.02 Myr and transported to the accretion region of the parent body.


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