Elasticity of sing-crystal phase E at high pressure and temperature

Abstract:

Water plays a key role in the dynamic evolution of the Earth due to its significant effects on the physical and chemical properties of minerals, such as partial melting, phase equilibrium and rheology. It could be transported from the surface into the Earth's interior via various hydrous mineral phases in the subducting lithospheric slabs. Although most hydrous minerals in sinking slabs will dehydrate at shallow depths, a few of hydrous phases, including dense hydrous magnesium silicate (DHMS) phases and δ-AlOOH, can survive and remain stable in deep mantle. Phase E, one of DHMS phases, is found to exist up to 21GPa and 1200℃, so it is a potential candidate for water transportation at depth to mantle transition zone. Previous experimental works on phase E mainly focus on its phase stability, lattice dynamics and equation of state, but the experimental investigation of single-crystal elasticity at high pressure and temperature has not been reported yet. The full elasticity information is essential to trace the distribution of phase E and its geophysical consequences using seismology and mineral physics studies. Hence we have measured the full elastic constants of phase E at simultaneous high pressure-temperature conditions with Brillouin scattering and single-crystal X-ray diffraction in an externally-heated diamond anvil. We obtained the compressional and shear bulk modulus, acoustic velocities and elastic anisotropy of phase E along the cold slab geotherm. These results are applied to understand water-bearing subduction slab in the transition zone via comparison with seismic tomographic images.