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 by first principles static calculations and by 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.
Original language | English (US) |
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Pages (from-to) | 18-26 |
Number of pages | 9 |
Journal | Physics of the Earth and Planetary Interiors |
Volume | 255 |
DOIs | |
State | Published - Jun 1 2016 |
Bibliographical note
Funding Information:The authors thank David Kohlstedt, Justin Revenaugh, and George Helffrich for useful discussions. This work was supported by NSF under Grants EAR-1161023 and EAR-1348066 . Computations were performed at the Minnesota Supercomputing Institute (MSI) and in the Blue Waters system at NCSA.
Keywords
- First principles
- Hydrous aluminous SiO
- Molecular dynamics
- Post-stishovite transition