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arXiv · 1508.01772

Post-stishovite transition in hydrous aluminous SiO2

Koichiro Umemoto·Katsuyuki Kawamura·Kei Hirose·Renata M. Wentzcovitch
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Abstract

Lakshtanov et al. (2007) showed that incorporation of aluminum and some water into SiO2 significantly reduces the post-stishovite transition pressure in SiO2. This discovery suggested that the ferroelastic post-stishovite transition in subducted MORB crust could be the source of reflectors/scatterers with low shear velocities observed in the mid to upper lower mantle. A few years later, a similar effect was observed in anhydrous Al-bearing silica. In this paper, we show using first principles static calculations and molecular dynamics using inter-atomic potentials that hydrogen bonds and hydrogen mobility play a crucial role in lowering the post-stishovite transition pressure. A cooperative redistribution of hydrogen atoms is the main mechanism responsible for the transition pressure reduction in hydrous aluminous stishovite. The effect is enhanced by increasing hydrogen concentration. This perspective suggests a potential relationship between the depth of seismic scatterers and the water content in stishovite.

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Koichiro Umemoto, Katsuyuki Kawamura, Kei Hirose, Renata M. Wentzcovitch. 2015-08-07. Post-stishovite transition in hydrous aluminous SiO2. https://doi.org/10.1016/j.pepi.2016.03.008

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