Evaporation and crystallization experiments of CAI melt in Mg-Si-O-H gas

Abstract

Calcium-aluminum-rich inclusions (CAIs), found in chondrites, are the oldest materials formed in the Solar System and record the early stage of the evolution of the Solar System. Evaporation and crystallization experiments of type B CAI analog melt in hydrogen gas showed that mantle structures of melilite (Ca₂Al₂SiO₇-Ca₂MgSi₂O₇) formed at higher P_H2 than about 1Pa. However, the evaporation of Mg and Si at P_H2 of about 1Pa could result in the excessive depletion of Mg and Si. The formation of grossite (CaAl₄O₇) in hydrogen gas, which is rare in natural type B CAIs, has also been identified. In this study, we placed enstatite (MgSiO₃) below the melt and conducted evaporation and crystallization experiments of CAI melt in the presence of Mg-, Si-bearing gases. As a result, it was confirmed that Mg-, Si-bearing gases contributed to the reduction of evaporative losses and the suppression of the grossite formation.