5:15 PM - 6:45 PM
[SIT14-P06] Valence state of iron in (Mg,Fe)SiO3 melts correlated with melt structure
Keywords:iron valence, melt structure, XANES, magma ocean
Understanding the behavior of the valence state of iron in peridotitic melts is important in discussing the redox environment in the Earth's early magma ocean and the speciation of the earliest atmosphere. However, the valence state of iron in peridotitic melts has not been well studied, due to experimental difficulties such as high melting temperature and high reactivity of iron with platinum crucible commonly used in electric furnace. To overcome these difficulties, Sossi et al. (2020) used a laser heating levitation furnace to carry out melting experiments of KLB-1 peridotite melts at very high temperature condition (1900℃), and determined the relationship between the Fe3+/Fe2+ ratio in the peridotite melts and the oxygen fugacity. However, experiment of peridotite melts is still limited to a KLB-1 composition.
This study aims to investigate the effects of chemical composition and the associated changes in the melt structure (NBO/T) on the valence state in (Mg1-x,Fex)SiO3 melts (0≤x=Fe#=Fe/(Fe+Mg)≤0.47). Glass samples (1-2 mm in diameter) of the (Mg1-x,Fex)SiO3 compositions were synthesized by laser heating levitation furnace at 1600–1800℃ for 30 s under air condition. The NBO/T was measured by Raman spectroscopy, and Fe3+/ΣFe was determined by XANES at the BL27SU beamline in SPring-8. Raman measurements showed that Q2 species increased slightly while Q1 and Q3 species remained almost constant with increasing iron content at the Fe#=0.00–0.21. On the other hand, Fe#=0.29–0.47 samples showed increase of Q1 species and decrease of Q3 species with increasing iron content. NBO/T was almost constant (NBO/T≈0.19) regardless of the increase in iron content at the Fe#=0.00–0.21, while it increased to 2.03–2.25 with increasing Fe content at the Fe#=0.29–0.47. Similarly to the Raman measurements, XANES measurements showed a clear difference in the samples between Fe#=0.00–0.21 and Fe#=0.29–0.47. We observed Fe3+/ΣFe of ~0.36 for Fe#=0.10–0.21 samples, while Fe3+/ΣFe of the Fe#=0.29-0.47 samples were ~0.48. These results indicate distinct change in the structure and iron valence of the (Mg1-x,Fex)SiO3 melts at the Fe# between 0.21 and 0.29.
This study aims to investigate the effects of chemical composition and the associated changes in the melt structure (NBO/T) on the valence state in (Mg1-x,Fex)SiO3 melts (0≤x=Fe#=Fe/(Fe+Mg)≤0.47). Glass samples (1-2 mm in diameter) of the (Mg1-x,Fex)SiO3 compositions were synthesized by laser heating levitation furnace at 1600–1800℃ for 30 s under air condition. The NBO/T was measured by Raman spectroscopy, and Fe3+/ΣFe was determined by XANES at the BL27SU beamline in SPring-8. Raman measurements showed that Q2 species increased slightly while Q1 and Q3 species remained almost constant with increasing iron content at the Fe#=0.00–0.21. On the other hand, Fe#=0.29–0.47 samples showed increase of Q1 species and decrease of Q3 species with increasing iron content. NBO/T was almost constant (NBO/T≈0.19) regardless of the increase in iron content at the Fe#=0.00–0.21, while it increased to 2.03–2.25 with increasing Fe content at the Fe#=0.29–0.47. Similarly to the Raman measurements, XANES measurements showed a clear difference in the samples between Fe#=0.00–0.21 and Fe#=0.29–0.47. We observed Fe3+/ΣFe of ~0.36 for Fe#=0.10–0.21 samples, while Fe3+/ΣFe of the Fe#=0.29-0.47 samples were ~0.48. These results indicate distinct change in the structure and iron valence of the (Mg1-x,Fex)SiO3 melts at the Fe# between 0.21 and 0.29.