Energetics, equation of state, and elasticity of NAL phase: Potential host for alkali and aluminum in the lower mantle
Article first published online: 12 OCT 2012
©2012. American Geophysical Union. All Rights Reserved.
Geophysical Research Letters
Volume 39, Issue 19, 16 October 2012
How to Cite
2012), Energetics, equation of state, and elasticity of NAL phase: Potential host for alkali and aluminum in the lower mantle, Geophys. Res. Lett., 39, L19306, doi:10.1029/2012GL053682., , , and (
- Issue published online: 12 OCT 2012
- Article first published online: 12 OCT 2012
- Manuscript Accepted: 5 SEP 2012
- Manuscript Received: 24 AUG 2012
- aluminous phases;
- high pressure;
- mantle heterogeneity;
 The new aluminous (NAL) phase and aluminous phase with calcium ferrite (CF) structure constitutes more than 25 volume % of the deeply subducted crust at lower mantle depths. Using first principle simulations, we calculate the energetics, equation of state, and elasticity of NAL phase with a widely varying composition including CaMg2Al6O12, NaNa2Al3Si3O12 and KNa2Al3Si3O12. Our calculations indicate the relative stability of NAL and CF phases is a sensitive function of pressure, temperature, and composition, with increasing pressure tending to favor the CF phase, and increasing temperature, Mg-content and alkali-content tending to favor the NAL phase. The sound wave velocities of the NAL phase is significantly lower than CF phases and other major lower mantle phases. In deeply subducted MORB and CC, the faster sound velocity of silica (SiO2) and its high-pressure polymorphic phase is likely to be compensated with the slower sound wave velocities of NAL phase.