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.