James Biemiller (Advisors: Luc Lavier / Laura Wallace)
Title: The influence of tectonic inheritance on crustal extension style: Applications to metamorphic core complexes in Papua New Guinea
Abstract: The structural, mechanical and geometric evolution of rifted continental crust depends on the lithospheric conditions in the region prior to the onset of extension. In areas where tectonic activity preceded rift initiation, structural and physical properties of the previous tectonic regime may be inherited by the rift and influence its development. Many continental rifts form and expose metamorphic core complexes (MCCs), coherent exposures of deep crustal rocks typically exhumed as arched or domed structures. MCCs are exhumed in regions where the faulted upper crust is displaced laterally from upwelling ductile material along a weak detachment fault. Some MCCs form during extensional inversion of a subduction thrust following failed subduction of continental crust, but the degree to which lithospheric conditions inherited from the preceding subduction phase control the extensional style in these systems remains unclear. For example, the Dayman Dome in Southeastern Papua New Guinea exposes prehnite-pumpellyite to greenschist facies rocks in a smooth 2.5 km-high, 20-25 km-wavelength dome exhumed along one main low-angle detachment normal fault, the Maiiu Fault. The extension driving the exhumation of Dayman Dome is associated with the cessation of northward subduction of Australian continental crust beneath the oceanic lithosphere of the Woodlark Plate.
Kris Darnell (Advisor: Peter Flemings)
Title: Simulations of fluid flow and phase behavior in multi-component hydrate systems
Abstract: Hydrates, or hydrate clathrates, are non-stoichiometric, ice-like solid compounds of water and gas molecules that form at low temperatures and high pressures. Since hydrates are dense, immobile solids, they provide ideal storage of gas molecules. For example, massive deposits of naturally occurring methane hydrates sequester methane with an energy density exceeding that of a gaseous phase for a suite of pressure-temperature conditions. One potential strategy to exploit the energy density of hydrates is to produce natural methane hydrates in shallow sub-marine or sub-permafrost reservoirs by an injection of carbon dioxide mixtures such that the carbon dioxide is left behind and stored as hydrate within the reservoir. This serves the purpose of recovering methane, while simultaneously providing geological storage of carbon dioxide. However, the optimal injection mixture and the ensuing reservoir dynamics of such a strategy are still poorly understood. Here, I present one-dimensional, multi-phase flow model results for injections of carbon dioxide and nitrogen mixtures, or flue gas, into methane hydrate bearing reservoirs. This flow model is coupled to a thermodynamic simulator that predicts phase stabilities as a function of composition, so multiple phases can appear, disappear, or change composition as the injection invades the reservoir. I show that the coupling of multi-phase fluid flow with phase behavior causes preferential phase fractionation in which each component flows through the reservoir at different speeds and in different phases. This behavior is qualitatively similar to the dynamics present in enhanced oil recovery or enhanced coalbed methane recovery. These results explain why the inclusion of nitrogen in mixed gas injection into methane hydrate reservoirs has been far more successful at producing methane than pure carbon dioxide injections. These results also provide a test for the validity of equilibrium thermodynamics in transport-dominated multi-component hydrate systems that can be validated by laboratory-scale flow-through experiments.
Denis Felikson (Advisor: Ginny Catania)
Title: Greenland Ice Sheet thinning: How far inland can it reach?
Abstract: Greenland's contribution to sea level rise over the next century remains uncertain, in part because of poorly understood marine-terminating outlet glaciers, where most of the observed dynamic thinning occurs. By modeling terminus-initiated thinning perturbations as kinematic waves, we have developed an easily-calculable metric that predicts the inland extent of dynamic thinning. We survey 185 marine-terminating glaciers around the ice sheet and, using our metric, determine each glacier's susceptibility to future mass loss. We find that in Northwest Greenland, glaciers are particularly susceptible to dynamic thinning extending far inland. However, though they are large contributors to dynamic ice sheet mass loss over the last 15 years, glaciers in East Greenland do not allow the diffusion of dynamic thinning very far inland. Differences in the behavior of glaciers in the Northwest and East are due to differences in bed topography, which is more mountainous in East Greenland than in the Northwest. Our glacier susceptibility ranking can help focus future monitoring and modeling efforts on the most vulnerable parts of the ice sheet.