| Knowledge of elastic properties of the phases constituting the Earth's mantle are of extreme importance for determination of Earth's chemical composition, the distribution of phases and the processes that result in such distribution. Data on elasticity of these constituent phases are critical not only for interpreting seismic observations, but are also essential for geochemical and geodynamical modeling. This dissertation is mainly devoted to determination of the elasticity and stability of stishovite, the high-pressure silica polymorph, as a major constituent of the MORB layer of subducting lithospheric slabs. These thin (∼10km thick) layers subducted into the Earth mantle create regions of thermal, compositional and, hence, rheological heterogeneity. Being a key component of the mantle convection system, subducting slabs may counteract compositional stratification of the Earth by acting to remix differentiated lithospheric material. In addition, there has recently been great interest in subducting slabs as possible carriers of volatiles - mainly water - back to the lower mantle. Stishovite is likely the primary water-bearing phase. The elastic properties and thermodynamic stability of water-bearing stishovite, and the effect of other impurities on these properties, is the main focus of this work. An important related issue I addressed is the establishment of a self-consistent (absolute) equation of state for the B2 phase of sodium chloride (NaCl). NaCl is a commonly-used pressure transmitting medium in high-pressure devices. Accurate knowledge of the NaCl equation of state therefore reduces errors in pressure determination resulting from the use of the secondary pressure calibrants. In order to perform these tasks I used Brillouin scattering and Raman spectroscopy, combined with synchrotron x-ray diffraction at standard conditions, and at high pressures and temperatures in the diamond anvil cell. Experiments were performed in Merrill-Bassett and piston-cylinder types of diamond anvil cells with Ne, KBr, NaCl, Ar, N2, silicone oil, and a ethanol-methanol-water mixture as pressure transmitting media up to 78 GPa at 300K. |
