Accurate values of the elastic properties of candidate mantle phases are of fundamental importance for placing constraints upon the mineralogy and chemistry of the Earth's interior. Although clinopyroxenes and garnets are essential major constituents of all contemporary models of upper mantle mineralogy, the elastic properties of these minerals are undetermined for many relevant compositions. The overall goal of this research program is to define the effects of chemical composition and crystal structure on the elasticity of geophysically important materials. The PI will determine the elastic properties of clinopyroxene and garnet single crystals under ambient conditions by Brillouin scattering measurements, will initiate an experimental program to determine the elastic properties of minerals at high pressure by Brillouin scattering measurements on samples compressed in a diamond anvil cell. The aim of these experiments is to obtain pressure derivatives of the bulk and shear moduli for the mantle minerals. Extremely few reliable values of such properties are presently available. These results will provide an improved basis for testing mineralogical models of the Earth's upper mantle and transition zone, and will greatly enhance our understanding of how chemical and crystal structural changes affect mineral elasticity within silicate solid solutions.
