The deep roots of volcanoes: Models of magma dynamics with applications to subduction zones

In this thesis I present research on the dynamics of the partially molten mantle with applications to magma genesis and transport in subduction zones. Subduction zones are the most complex tectonic setting for magma genesis on Earth. To model and understand them requires a study of the fundamental physics and chemistry of the mantle beneath their associated volcanoes where melting occurs and magma migrates through the pores of the rock toward the surface. These partially molten regions of the mantle control the overall chemical evolution of the Earth as well as the characteristics of the volcanic systems that they feed.; Subduction zones represent the most complex instance of partial melting in a tectonic/volcanic system. Observations of arc volcanoes raise a suite of questions about the dynamics active at depth below them. To address these questions requires comprehensive, self-consistent models of magma genesis and transport in subduction zones. Even a basic model that incorporates fluid and solid flow, reaction and temperature evolution will be complex, challenging to construct, and require advanced computational resources. In Chapter 2 I describe a computational approach for fluid flow in a deforming mantle matrix; in Chapter 3 for modeling mantle flow with highly variable non-Newtonian viscosity; in Chapter 4 for melting systematics of the hydrous magma/mantle system; and in Chapter 5 for temperature-dependent reactive flow of hydrous fluids/magma. Each of these contributes to the development of a comprehensive model of subduction by addressing computational challenges and exposing complex behavior such as sharp viscosity gradients and strong localization phenomena.; The central themes of this thesis are localization phenomena and the effects of complex rheology on the magma-mantle system. Calculations presented here demonstrate that both of these are likely to play an important role in shaping the processes of magma genesis and transport in partially molten regions of the mantle and, particularly, in subduction zones. Many questions are raised by this work, especially regarding the observable signature of predicted localizations. This work represents fundamental progress on understanding the generation and organization of magma in the mantle. (Abstract shortened by UMI.)...