Rheology of olivine at high temperature and high pressure

Two major contributions were accomplished in this dissertation. From the scientific aspect, the rheological properties of olivine at mantle condition were investigated by defining the flow mechanism and quantifying the high-pressure and high temperature flow law for olivine. From the technical development aspect, a breakthrough to measure macroscopic differential stress and strain rate in situ under mantle pressure and temperature condition was recorded in this dissertation. Conventional deformation methods in defining the flow law of olivine have to face factors of large uncertainties of differential stress measurements and/or limited confining pressure for deformation. These two difficulties were overcome by conducting high-temperature (up to 1473 K) deformation experiments of polycrystalline olivine (average grain size <5 micron) at pressure up to 8 GPa using large-volume high-pressure apparatus and synchrotron x-ray radiation. Strain rates of the deformation from x-ray radiograph of the sample itself were measured. Image analysis software for strain rate measurement was developed. Macroscopic differential stress of olivine was measured by monitoring the elastic strain of lattice spacing. The algorithms and programs were developed to convert the elastic strain of samples deformed under uniaxial compression into the macroscopic differential stress. In summary, the flow law for olivine at high temperature and high pressure has been defined as dislocation creep, assisted by dynamic recrystallization. The activation volume is characterized as 0∼5 cm3/mol. The technology developed in the course of this dissertation research opens new possibilities for rheological studies in the future. The accuracy of the results is comparable to the best rheological studies that are carried out in any system at the present.