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

Abstract

Reproduction experiments of radial pyroxene (RP) chondrules were carried out using an Ar–H _2 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 (D _Fe =Fe mol% _pyroxene /Fe mol% _mesostasis ) in natural RP chondrules were much higher than that in the experimentally reproduced RP chondrules. The high D _Fe 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 D _Fe in natural RP chondrules increased after the growth of RP crystals. Therefore, the D _Fe of RP chondrules can be an indicator to constrain cooling rates and redox states during chondrule formation.

Keywords

• Chondrules
• Chondrites
• Experimental techniques
• Protoplanetary disks