Elasticity of the Earth’s Mantle Minerals at High Pressure and Temperature
Jung-Fu Lin1,2
1. Department of Geological Science, The University of Texas at Austin
2. Center for High Pressure Science & Technology Advanced Research (HPSTAR)
Seismic wave observations of the Earth’s interior provide the primary constrains on the
physics and chemistry of the Earth’s interior. Seismic variations in the Earth’s interior can be
used to derive temperature and compositional heterogeneities of the region, while seismic
compressional and shear wave splitting anisotropies can be used to infer potential petrological
layering and/or mineralogical texturing that carry significant information in understanding the
geodynamics of the planet. Laboratory investigations on the elasticity (e.g, sound velocities and
elastic constants) of the candidate materials at the relevant pressure-temperature conditions of the
planet is needed to provide critical information in understanding seismic profiles and velocity
anisotropies, in building reliable compositional and mineralogical models, and in deciphering
geodynamic processes of the Earth’s interior. However, measuring Vp and Vs velocities and
solving for full elastic constants of the mantle minerals at relevant conditions have been very
challenging. In this presentation, I will discuss recent advances in high-pressure laser and X-ray
spectroscopies in measuring elasticity of candidate mantle minerals at high pressures and
temperatures. Specifically, the combination of Impulsive Stimulated Light Scattering (ISLS) and
Brillouin Light Scattering (BLS) results has been be used to solve for full elastic constants of the
mantle minerals such as ferropericlase and silicate perovskite at relevant lower mantle pressures.
Measured compressional and shear wave velocities of ferropericlase simultaneously along [100]
and [110] crystallographic axes up to megabar pressures permit the derivation of reliable full
elastic constants and the modeling of the elastic and seismic properties across the spin transition.
These results show that the compressional wave velocities exhibit significant softening, while
shear wave velocities are only slightly affected by the spin transition. I will discuss the effects of
the spin transition on elastic constants, sound velocities, elastic anisotropies, and seismic
parameters of ferropericlase at lower-mantle pressure-temperature conditions. We have also
derived full elastic constants of single-crystal silicate perovskite (C11, C22, C33, C44, C55, C66, C12,
C23 and C13) under high pressures via measuring both Vp and Vs sound velocities as a function
of azimuthal angle in single-crystal pervoskite under lower mantle pressures. These results have
been applied to model the velocity structure, Vp and Vs anisotropy, Vp/Vs ratio, and Poisson’s
ratio of the Earth’s lower mantle. These results are compared with seismic observations of the
deep lower mantle in order to better understand seismic signatures and mineralogical models of
the lower mantle.