Silicate melt viscosity is a complex function of composition, temperature and pressure. This dissertation addresses the compositional and pressure dependences of silicate melt viscosity by providing new experimental data on three compositions over a range of pressures. In Chapter 1 I provide critical background, which summarizes the extent of our knowledge of silicate melt viscosity at high pressure, and effectively highlights the outstanding gaps in our knowledge. Each subsequent chapter presents the new experimental data, which are combined with available experimentally determined viscosities, structural information and molecular dynamics simulations, thus linking theory, models and experiments. In Chapter 2 I present a series of experiments on lithium disilicate melt viscosity between 1 and 6 GPa. Using these data I investigate the transition from negative to positive pressure dependence in polymerized systems. Specifically, I address the relationship between composition and the pressure of viscosity minima. Chapter 3 provides extensive details on the falling sphere experimental method. To address the pressure dependence of depolymerized silicate melt viscosities at high pressures I present the viscosities of two komatiites between 1 and 10 GPa. Using these new data I systematize the relationship between pressure and viscosity in depolymerized systems and propose a model that reproduces the observed pressure dependences of viscosity for a range of compositions up to 10 GPa. In Chapter 4 the measured pressure range of molten komatiite viscosities is extended to 13.5 GPa. Based on these new data I develop a new model for depolymerized melts in terms of the fundamental parameter activation volume. This model is used to predict the viscosity of the Earth's magma ocean. Finally, each of the Appendices addresses an experimental detail including pressure and temperature determination, methods for measuring density, and an assessment of the falling sphere technique using numerical simulations.
|Advisor:||Lesher, Charles E.|
|Commitee:||Cooper, Kari M., Kellogg, Louise H.|
|School:||University of California, Davis|
|School Location:||United States -- California|
|Source:||DAI-B 73/10(E), Dissertation Abstracts International|
|Keywords:||Activation volume, Falling sphere, Komatiite, Melt, Silicate, Viscosity|
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