Investigating the capability for rare earth elements as an environmental proxy during fassaite crystal growth in compact type-A CAI

Abstract

Al-Ti-rich diopside (fassaite) in Ca-Al-rich Inclusion (CAI) can be expected to reflect the environmental change in the protoplanetary disk. Rare Earth Elements (REE)would be used as a redox indicator. However, it has not been reported the signatures of REE during fassaite crystal growth. In this study, we carried out the REE analysis by LA-ICP-MS considering the fassaite crystal growth using Ti contents by EPMA analysis. REE pattern and Sc/Lu ratio show the trend of fractional crystallization from the CAI melt. Y/Ho and Tm/Tm* suggested that this CAI precursor may not be a condensate from fractional gas. On the other hand, although Ce/Ce* and Yb/Yb* cannot be used as redox indicators, Eu/Eu* has a negative correlation with TiO₂ content, suggesting that Eu/Eu* may be used as a redox indicator of CAI melt during fassaite crystal growth.