Effect of Al on the sharpness of the MgSiO3 perovskite to post-perovskite phase transition

Details Effect of Al on the sharpness of the MgSiO3 perovskite to post-perovskite phase transition Effect of Al on the sharpness of the MgSiO3 perovskite to post-perovskite phase transition

Jul 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005georl..3214303a&link_type=abstract

Geophysical Research Letters, Volume 32, Issue 14, CiteID L14303

Physics

21

Mineralogy And Petrology: Reactions And Phase Equilibria (1012, 8412), Mineral Physics, Mineral Physics: High-Pressure Behavior, Mineral Physics: Equations Of State

Scientific paper

By means of static ab-initio computations we investigate the influence of Al on the recently discovered perovskite to post-perovskite phase transition in MgSiO3. We examine three substitution mechanisms for Al in the two structures: MgSi -> AlAl; SiSiO -> AlAl□ and Si -> AlH. The substitutions introducing oxygen vacancies (highly unfavorable, energetically) and water (favorable) both lower the 0 Kelvin transition pressure, whereas charge coupled substitution increases it relative to 105 GPa for pure MgSiO3. From the transition pressures for 0, 6.25, and 100 mol% charge coupled Al2O3 incorporation and simple solution theories, we estimate the phase diagram of Al-bearing MgSiO3 at low Al concentrations. Assuming the Clapeyron slope is independent of Al concentration, we find the perovskite-to-post-perovskite transition region to span 127-140 GPa, at 6.25 mol% Al2O3. When the upper pressure limit is bounded by the core-mantle boundary, the phase coexistence region has width 150 km.

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