[S-IT20] Property and role of liquids inside terrestrial planets

[SIT20-01] Ultrahigh pressure structure change in SiO₂ glass with coordination number >6

★Invited Papers

*Yoshio Kono¹, Yu Shu², Curtis Kenney-Benson², Yanbin Wang³, Guoyin Shen² (1.Geodynamics Research Center, Ehime University, 2.Argonne National Laboratory, 3.The University of Chicago)

Keywords:high pressure, SiO2 glass, magma, core-mantle boundary

Possible existence of ultrahigh pressure structural change in silicate magma with the Si-O coordination number (CN) larger than 6 is one of the most important issues in understanding nature of silicate magmas at the Earth’s core-mantle boundary. However, structure of silicate magmas at the ultrahigh pressure conditions of the core-mantle boundary remain poorly understood, because of experimental challenges. Efforts have been made to investigate structure and/or properties of silicate glasses, as an analogue of silicate magma, at ultrahigh pressure conditions. Pioneering work by Murakami and Bass (2010) discovered a kink in the pressure dependence of shear-wave velocity in SiO₂ glass around 140 GPa, which was interpreted as evidence of ultrahigh pressure structural transition with the CN>6. However, no structural information is available under such ultrahigh pressure conditions. Our recent development of double-stage large volume cell combined with multi-angle energy dispersive X-ray diffraction opened a new way to investigate structure of oxide glasses under ultrahigh pressure conditions of >100 GPa. The new experiment revealed existence of ultrahigh pressure polyamorphism in GeO₂ glass with CN>6 (Kono et al., 2016). Our latest development further enhanced the structure measurement capability and we succeeded to measure structure of SiO₂ glass up to 120 GPa. Here we will show ultrahigh-pressure structural change in SiO₂ glass at the pressure conditions near the Earth’s core-mantle boundary.



Kono Y, et al. (2016) Ultrahigh-pressure polyamorphism in GeO₂ glass with coordination number> 6. Proceedings of the National Academy of Sciences 113(13):3436-3441.

Murakami, M., & Bass, J. D. (2010). Spectroscopic evidence for ultrahigh-pressure polymorphism in SiO₂ glass. Physical review letters, 104(2), 025504.