Reproduction Experiments of Radial Pyroxene Chondrules Using a Gas-jet Levitation System under Reduced Conditions

Reproduction experiments of radial pyroxene (RP) chondrules were carried out using an Ar-H2 or Ar gas-jet levitation system in a reducing atmosphere in order to simulate chondrule formation in the protoplanetary disk. The experiments reproduced RP-chondrule textures, consisting of sets of thin pyroxene crystals and mesostasis glass between crystals. However, iron partition coefficients between pyroxene and glassy mesostasis (DFe =Fe mol%pyroxene/Fe mol%mesostasis) in natural RP chondrules were much higher than that in the experimentally reproduced RP chondrules. The high DFe in natural RP chondrules suggests that iron was removed from the mesostasis melt at high temperatures after the growth of pyroxene crystals. We found that many small iron-metal inclusions had formed in the mesostasis glass, indicating that FeO in the high-temperature melt of mesostasis was reduced to metallic iron, and iron in the mesostasis diffused into the newly formed metal inclusions. The formation of the iron-metal inclusions in the mesostasis was reproduced by our experiments in a reducing atmosphere, confirming that DFe in natural RP chondrules increased after the growth of RP crystals. Therefore, the DFe of RP chondrules can be an indicator to constrain cooling rates and redox states during chondrule formation.