Elastic anisotropy of forsterite, wadsleysite, ringwoodite at high pressure and temperature and its geophysical significances

The transition zone has always been critical for us to understand the dynamics of Earth's mantle. The elastic anisotropy in the Earth's mantle transition zone which between 410 and 660 km plays an important role to understand the convection from the upper mantle and the low mantle. The three polymorphs of Mg2SiO4, forsterite, wadsleysite, and ringwoodite (α, β and γ phases, respectively), are the most abundant minerals in the Earth's upper mantle and transition zone. We have determined from first-principles thermal elastic constant tensor and obtain the elastic anisotropy of the three polymorphs of Mg2SiO4 at pressure-temperature conditions of the mantle transition zone. Our results show that the elastic anisotropy of the three polymorphs of Mg2SiO4 is sensitive to temperature at the upper mantle pressure. The mantle transition zone anisotropy may originate from the lattice preferred orientation of the three polymorphs anisotropic materials. Our results can therefore be used to important constrain on mantle deformation mechanisms.