Elastic behavior of (Mg xFe 1− x) 2SiO 4 olivine at high pressure from first-principles simulations

Abstract

The elastic properties of Fe 2SiO 4 (Fa), (Mg 0.875Fe 0.125) 2SiO 4 (Fa 12.5) and Mg 2SiO 4 (Fo) crystals at high pressures were investigated using first-principles calculations. Incorporation of Fe in the α-phase forsterite crystals results in increasing bulk modulus, but reducing shear modulus. Compared with the forsterite (Fo), the compressional wave velocity ( V P ) of Fa 12.5 decreases by 3.0% and 3.1% at 0 and 20 GPa, respectively, and the shear wave velocity ( V S ) by 4.9% and 5.8%. For Fa, V P values decrease by 20.5% and 20.6% at 0 and 15 GPa, respectively, and V S by 30.3% and 30.9%. These results demonstrate that the elasticity of olivine strongly depends on the chemical compositions, which has implications on the origin of low-velocity zones in the mantle.