High-pressure, temperature elasticity of Fe- and Al-bearing MgSiO3: Implications for the Earth's lower mantle

• Published in: Earth and planetary science letters Vol. 434; no. C; pp. 264 - 273
• Main Authors: Zhang, Shuai, Cottaar, Sanne, Liu, Tao, Stackhouse, Stephen, Militzer, Burkhard
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.01.2016; Elsevier
• Subjects: Aluminum; bridgmanite; Density; Earth; Elastic constants; elastic properties; first principles; Iron; lower mantle; Mantle; Mathematical models; Minerals; post-perovskite; pyrolite; pyrolite; bridgmanite; lower mantle; first principles; post-perovskite; elastic properties
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2015.11.030

Fe and Al are two of the most important rock-forming elements other than Mg, Si, and O. Their presence in the lower mantle's most abundant minerals, MgSiO3 bridgmanite, MgSiO3 post-perovskite and MgO periclase, alters their elastic properties. However, knowledge on the thermoelasticity of Fe- and Al-bearing MgSiO3 bridgmanite, and post-perovskite is scarce. In this study, we perform ab initio molecular dynamics to calculate the elastic and seismic properties of pure, Fe3+- and Fe2+-, and Al3+-bearing MgSiO3 perovskite and post-perovskite, over a wide range of pressures, temperatures, and Fe/Al compositions. Our results show that a mineral assemblage resembling pyrolite fits a 1D seismological model well, down to, at least, a few hundred kilometers above the core–mantle boundary, i.e. the top of the D″ region. In D″, a similar composition is still an excellent fit to the average velocities and fairly approximate to the density. We also implement polycrystal plasticity with a geodynamic model to predict resulting seismic anisotropy, and find post-perovskite with predominant (001) slip across all compositions agrees best with seismic observations in the D″. •We calculated the thermoelasticity of pure, and Fe- and Al-bearing MgSiO3.•Elastic and seismic properties are fitted as functions of P, T, and Fe/Al-content.•We find pyrolite composition matches PREM across the whole lower mantle.•PPv with (001) slip agrees with seismic anisotropy in D″, independent of Fe/Al.