Elasticity of Mg2SiO4 ringwoodite at mantle conditions

The themoelastic properties of Mg2SiO4 ringwoodite at mantle pressure and temperature conditions are reported based on ab initio molecular dynamic simulations. A third-order Birch-Murnaghan equation at a reference temperature of 2000 K is defined by K-0 = 138 GPa, K-0' = 5.2, and V-0(2000 K) = 560 angstrom(3). The Gruneisen parameter is determined to be gamma(V) = gamma(0)(V/V-0(298 K))(q) with gamma(0) = 1.22 and q = 1.44(5), with V-0(298 K) = 524.56 angstrom(3). The thermal expansion is determined to be (alpha/alpha(0)) = (V/V-0(298 K))(delta T) in which alpha(0) = 2.74 x 10(-5) K-1 and delta(T) = 5.2(1). The bulk modulus is temperature independent at constant volume, while the shear moduli vary with temperature at constant volume. Elastic anisotropy decreases with both pressure and temperature becoming isotropic by the bottom of the upper mantle. (c) 2006 Elsevier B.V. All rights reserved.