A study of crystallization process of CAI using Sr and Ba as tracers

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Ca, Al-rich inclusions (CAI) in the primitive meteorite are believed to be one of the oldest solid material in the solar system. We have experimentally synthesized CAI analogues to investigate the process of formation of the CAIs. We first synthesized CAIs adding minor amounts of Sr and Ba as tracers, and investigated the order of crystallization of minerals by determining the distribution of Sr and Ba in the samples. It is found that the plot of Sr/Ca vs Ba/Ca ratios as parameters is very useful in describing the process of crystallization of CAIs.Based on the heterogeneous distribution of Oxygen isotopes among the minerals in the CAIs, it is suggested that CAIs cannot have been produced by a single sequence of cooling from a molten state. It is suggested that the heterogeneous distribution observed for CAIs are explained by repeated rapid heating and cooling in the gaseous environment with changing Oxygen isotopeRatios while partially melted. We have performed experiments in which the synthetic CAIs with no Sr and Ba tracers were inserted in a tracer doped Ca, Al-rich melt and cooled to investigate the process of remelting-recrystallization process by determining the distribution of Sr and Ba in the solid products. The plot of Sr/Ca vs Ba/Ca ratios as parameters is found to be a useful tool to describing the remelting-recrystalli-zation processes in this case again.Melilite is a major component mineral of the CAIs and is a solid solution of two end-members, gehlenite( Ca_2Al_2SiO_7) and akermanite (Ca_2MgSi_2O_7). When heated to a temperature between solidus and liquidus, is it expected to separate in to small crystals of solidus composition and the liquid of liquidus composition. We heated synthetic melilite crystals to such a temperature and found that a mosaic structure composed of tiny crystals of gehlenitic melilite and akermanitic glass was produced.