First-principles determination of elastic anisotropy and wave velocities of MgO at lower mantle conditions

The individual elastic constants of magnesium oxide (MgO) have been determined throughout Earth's lower mantle (LM) pressure-temperature regime with density functional perturbation theory. It is shown that temperature effects on seismic observables (density, velocities, and anisotropy) are monotonically suppressed with increasing pressure. Therefore, at realistic LM conditions, the isotropic wave velocities of MgO remain comparable to seismic velocities, as previously noticed in athermal high-pressure calculations. Also, the predicted strong pressure-induced anisotropy is preserved toward the bottom of the LM, so lattice-preferred orientations in MgO may contribute substantially to the observed seismic anisotropy in the D" layer.

[1]  O. Anderson,et al.  Measured elastic moduli of single-crystal MgO up to 1800 K , 1989 .

[2]  Y. Fei.  Effects of temperature and composition on the bulk modulus of (Mg,Fe)O , 1999 .

[3]  L. Stixrude,et al.  Seismic velocities of major silicate and oxide phases of the lower mantle , 1999 .

[4]  Raymond Jeanloz,et al.  Phase transitions and mantle discontinuities , 1983 .

[5]  G. Peckham,et al.  Lattice dynamics of magnesium oxide , 1970 .

[6]  S. Saxena,et al.  Equation of state of MgSiO3 with the perovskite structure based on experimental measurement , 1999 .

[7]  D. L. Anderson,et al.  Seismic velocities in mantle minerals and the mineralogy of the upper mantle , 1989 .

[8]  M. Mehl,et al.  Calculated elastic and thermal properties of MGO at high pressures and temperatures , 1990 .

[9]  Mrinal K. Sen,et al.  Evidence for anisotropy in the deep mantle beneath Alaska , 1996 .

[10]  J. Crain,et al.  Elastic properties of orthorhombic MgSiO3 perovskite at lower mantle pressures , 1997 .

[11]  A. Ringwood.  Composition and petrology of the earth's mantle , 1975 .

[12]  Duffy,et al.  Equation of state and shear strength at multimegabar pressures: Magnesium oxide to 227 GPa. , 1995, Physical review letters.

[13]  Thorne Lay,et al.  The core–mantle boundary layer and deep Earth dynamics , 1998, Nature.

[14]  O. Anderson,et al.  The relationship between shear and compressional velocities at high pressures: Reconciliation of seismic tomography and mineral physics , 1992 .

[15]  Graeme Ackland,et al.  Structure and elasticity of MgO at high pressure , 1997 .

[16]  Y. S. Touloukian.  Thermophysical properties of matter , 1970 .

[17]  S. Grand.  Mantle shear structure beneath the Americas and surrounding oceans , 1994 .

[18]  Price,et al.  Ab initio molecular dynamics with variable cell shape: Application to MgSiO3. , 1993, Physical review letters.

[19]  S. Karato,et al.  Importance of anelasticity in the interpretation of seismic tomography , 1993 .

[20]  D. L. Anderson,et al.  Preliminary reference earth model , 1981 .

[21]  H. Mao,et al.  Brillouin scattering and X-ray diffraction of San Carlos olivine: direct pressure determination to 32 GPa , 1998 .

[22]  Stefano de Gironcoli,et al.  Ab initio calculation of phonon dispersions in semiconductors. , 1991, Physical review. B, Condensed matter.

[23]  T. Lay,et al.  Lateral variations in lowermost mantle shear wave anisotropy beneath the north Pacific and Alaska , 1997 .

[24]  M. Kunz,et al.  P-V-T EQUATION OF STATE OF MGSIO3 PEROVSKITE , 1998 .

[25]  Weidner,et al.  Elasticity of single-crystal MgO to 8 gigapascals and 1600 kelvin , 1998, Science.

[26]  T. Ahrens,et al.  Thermal expansion of mantle and core materials at very high pressures , 1993 .

[27]  S. Karato.  Some remarks on the origin of seismic anisotropy in the D” layer , 1998 .

[28]  H. Spetzler,et al.  Equation of State of Polycrystalline and Single‐Crystal MgO to 8 Kilobars and 800°K , 1970 .

[29]  Testa,et al.  Green's-function approach to linear response in solids. , 1987, Physical review letters.

[30]  A. Dziewoński,et al.  Global Images of the Earth's Interior , 1987, Science.