Condensation of cometary silicate dust using an induction thermal plasma system

1S. Enju,2H. Kawano,3,4,5A. Tsuchiyama,6T. H. Kim, A.7Takigawa,3J. Matsuno,8H. Komaki
Astronomy & Astrophysics 661, A121 Link to Article [DOI
1Earth’s Evolution and Environment Course, Department of Mathematics, Physics, and Earth Science, Ehime University, 2-5 Bunkyocho, Matsuyama, Ehime, 790-8577, Japan
2Division of Earth and Planetary Sciences, Kyoto University, Kyoto 606-8502, Japan
3Research Organization of Science and Technology, Ritsumeikan University, Shiga 525-8577, Japan
4CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (CAS), Guangzhou 510640, PR China
5CAS Center for Excellence in Deep Earth Science, Guangzhou 510640, PR China
6Department of Chemical Engineering, Wonkwang University, 460 Iksan-daero, Iksan 54538, Republic of Korea
7Department of Earth and Planetary Science, The University of Tokyo, Tokyo 113-0033, Japan
8JEOL Ltd., Tokyo 196-8558, Japan
Reproduced with permission (C) ESO

Glass with embedded metal and sulfides (GEMS), the major components of chondritic-porous interplanetary dust particles (CP-IDPs), is one of the most primitive materials in the Solar System and may be analogous to the amorphous silicate dust observed in various astronomical environments. Mineralogical characteristics of GEMS should reflect their formation process and condition. In this study, synthetic experiments in the sulfur-bearing system of Fe–Mg–Si–O–S were performed with a systematic change in redox conditions using thermal plasma systems to reproduce the mineralogy and textures of GEMS. The resulting condensates were composed of amorphous silicates with Fe-bearing nano-inclusions. The Fe content and texture in the amorphous silicates as well as the mineral phases of the nanoparticles correlate with redox conditions. Fe dissolved in the amorphous silicate as FeO in oxidizing conditions formed Fe-metal nanoparticles in intermediate redox conditions, and gupeiite (Fe3 Si) nanoparticles in reducing conditions. In intermediate to reducing redox conditions, Fe-poor amorphous silicate formed a biphasic texture with Mg- and Si-rich regions, indicating liquid immiscibility during the melt phase. Most Fe-metal particles were surrounded by FeS and formed on the surface of amorphous silicate grains. Condensates produced in intermediate to slightly reducing redox conditions resemble GEMS in that they have similar mineral assemblages and chemical compositions to amorphous silicate, except that the Fe-metal grains are absent from the interior of the amorphous silicate grains. This textural difference can be explained by the sulfidation at high temperatures in this study, in contrast to sulfidation occurring at low temperatures in the presence of H2 in natural GEMS formation. Based on the two-liquid structures observed in the experimental products and in GEMS, also recognized in infrared spectra, we propose that GEMS condensed as silicate melt under limited redox conditions followed by incorporation of multiple metal grains into the silicate melt or by aggregation of coreshell structured grains before sulfidation of the metallic iron. Condensates produced in oxidizing conditions are similar to GEMS-like material in the matrices of primitive carbonaceous chondrite meteorites, indicating the possibility that they form by direct condensation from nebula gas in relatively oxidizing conditions compared to GEMS.


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