The role of deformation processes in mantle flow, solid state convection, and melt migration

Understanding the dynamics of the Earth's interior requires an understanding of how rocks deform, since deformation is required for nearly all of the processes occurring within the Earth. For example, mantle convection depends on rocks' ability to flow as a viscous fluid over long time scales. Similarly, the formation of oceanic crust requires that the mantle deforms to pump melt from extraction zones.; Deformation in the Earth is complex, as the manner and rates of deformation depend on a variety of factors. Intrinsic characteristics of rocks, such as their crystalline constituency, major element chemistry, and volatile content, and environmental conditions, such as temperature and pressure, all influence deformation. However, it is the evolution of microstructural properties, such as grain size and texture, which makes the mechanics of rocks significantly more complex than fluids such as air or water. This thesis represents an effort to explore these complexities in studying the dynamics of Earth's interior.; In the first chapter, we used measurements of shear wave splitting to constrain mantle flow kinematics beneath back-arcs of subduction zones. Models which used plate motions analagous to those of the Tonga, southern Kuril, and eastern Aleutian subduction zones produced splitting parameters consistent with most of the observations.; Chapter 2 explores water's role on melt migration. Since water is preferentially sequestered into melts, melting dries the mantle, thereby influencing its viscosity. Our linear stability analysis shows that during the deformation of partially molten rocks undergoing dehydration-induced increases in viscosity, melt localizes with a spacing controlled by the competition between the diffusive and advective transport of water.; The final chapter examines the influence of grain size evolution on convective instability. When grain size evolves during the cooling of boundary layers, rates of grain growth and initial conditions both influence the onset of convection. Grain size evolution leads to large-grained, high viscosity structures where convective stresses are low. Grain size variations induce at least an order of magnitude variation in viscosity, which influences convective dynamics.