[P-PS08] 太陽系物質進化

[PPS08-P19] A newfound ²⁶Al-poor Ca-Al-rich inclusion with nucleosynthetic Si isotope anomaly

*Yung-Hsin Liu¹、Der-Chuen Lee¹、Yu-Hsuan Liang¹、Yoshiyuki Iizuka¹、Hao-Yang Lee ¹、Hsien Shang² (1.Institute of Earth Sciences, Academia Sinica, Taiwan、2.NanoSIMS Laboratory, Institute of Astronomy and Astrophysics, Academia Sinica, Taiwan)

キーワード：Ca-Al-rich inclusions, Mass-independent isotopic anomaly, Si isotope

Two ²⁶Al-poor Ca-Al-rich inclusions (CAIs) were identified among 2000 grains using our established laser-based Mg isotope ratio measurement technique. One sample (A2-35-6) also showed Si mass-independent isotopic anomaly. The intense fluid metasomatism affected these fine-grained CAIs to form high abundant secondary minerals. This late-stage process could minimize the extent of Mg and Si anomalies, and cause heterogeneous values of δ²⁶Mg in sample A2-17-1, which has higher amount of hendenburgite. The oxygen isotope ratios of hendenburgite and parts of ferroan olivine were in equilibrium with fluids. These could inferred a fluid composition with similar Δ¹⁷O but higher δ¹⁸O values compared to the Allende fluid compositions reported by Krot et al. (2019, 2021). The oxygen isotopic exchange in spinel, diopside, and Mg-rich olivine were not attained equilibrium during metasomatism. Duo to the slow diffusivities, these minerals was most likely condensates to preserve the pristine Mg, Si, and O isotopic signatures. Compiled the results of published and our newfound Si-MIF CAIs, their negative δ²⁶Mg and δ³⁰Si values were resulted from involvement of the ²⁵Mg-rich and normal Group 1 presolar silicates during CAI precursor formation. The population of Si-MIF CAIs is very scarce, probably because of intense thermal processing such as reaction with gaseous SiO in the protoplanetary disk or addition of Si during metasomatism.