Single-Crystal Elasticity of San Carlos Olivine in the Earth’s Mantle

Abstract:

Olivine is the most abundant mineral in the Earth’s upper mantle. Studies on the elasticity of olivine attracted extensive research interests in the past few decades and have provided important constraints on the composition and structure of the Earth’s upper mantle. Of particular importance is the single-crystal elasticity of olivine which is essential for understanding the anisotropy structure of the upper mantle. However, previous experimental studies on the single-crystal elasticity of olivine are limited to high pressure and ambient temperature or high temperature and ambient pressure. Much of our current knowledge on the velocity and anisotropy structures of the upper mantle heavily relies on extrapolations of limited experimental results. Here, we have studied the single-crystal elasticity of San Carlos olivine, [(Mg_0.9Fe_0.1)₂SiO₄], up to 20 GPa and 900 K using Brillouin spectroscopy and X-ray diffraction in an externally-heated diamond anvil cell at GSECARS of the Advanced Photon Source, Argonne National Laboratory. The simultaneously high pressure-temperature experiments allow us to investigate the combined effect of pressure and temperature on the velocity and anisotropy of olivine. 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 upper mantle. Comparing the modeling results with seismic observations allow us to have a more comprehensive understanding on the velocity and anisotropy structure of the Earth’s upper mantle.