Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item QUANTIFICATION OF MELT DISTRIBUTION, MELT CONNECTIVITY, AND ANISOTROPIC PERMEABILITY OF DEFORMED PARTIALLY MOLTEN ROCKS USING X-RAY MICROTOMOGRAPHY(2024) Bader, James Alexander; Zhu, Wenlu; Montesi, Laurent G.J.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Volcanic activity plays a dominant role in shaping the surface of Earth and other planets. For example, Earth’s ocean floor is created by volcanic activity at mid-ocean ridges. There, magma is sourced from a ~60 km deep, ~100 km wide region of the mantle, from which partial rock ascends and erupts along narrow ridges that run along the middle of Earth’s oceans. Volcanic activity at mid-ocean ridges, the strength of Earth’s mantle, and the geochemical composition of volcanic rocks and ocean water are all influenced by how the melt is distributed in partially molten rocks, and how easily it can flow through the partially molten mantle beneath these ridges. In particular, it is often assumed that most of the melt ascends through isolated channels that direct it towards the mid-ocean ridges, making melt transport localized and anisotropic. A possible origin of these channels is the differential stress induced by upwelling mantle material beneath the ridge, which has been shown in laboratory experiments to localize melt into planar regions named “melt-rich bands.” To date, the development and characteristics of melt-rich bands have been studied principally using theoretical models and two-dimensional (2D) images of sheared partially molten rocks. There has been little experimental research using 3D techniques until now. This thesis uses 3D images of sheared partially molten rocks created in the laboratory, obtained using high-resolution x-ray microtomography (X-ray µCT), to investigate how the distribution of melt, its orientation, its connectivity, and its ability to flow through the rocks changes when stress is applied. This study shows how melt connectivity and, therefore, rock permeability changes as melt changes from being dispersed through a partially molten rock to being localized on well-developed melt-rich bands. This work shows that melt forms melt volumes that are preferentially elongated within the plane of melt-rich bands even before these bands form. This discovery emphasizes the importance of permeability anisotropy at all stages of melt-rich band development. We also measured permeability and melt connectivity at all scales, both inside and outside melt-rich bands. Our results show that melt can hardly flow perpendicular to melt-rich bands over distances larger than a few grains. Additionally, the permeability along the melt-rich bands is also reduced by half compared to that in a partially molten rock that is not subjected to differential stress. This research quantifies the uneven distribution of permeability in a sheared, partially molten rock. It also proposes a scheme to average local permeability estimates, helping us understand and quantify how melt travels along melt-rich bands at various scales. These findings provide valuable insights into how magma flows in the Earth’s mantle, especially at active plate boundaries like mid-ocean ridges. Overall, this research provides the first experimental constraints, based on 3D microtomography images, on the melt network and how melt flows in the presence of stress in partially molten rocks.Item Characterizing 3-dimensional Melt Distribution and Anisotropic Permeability in Sheared Partially Molten Rocks(2020) Bader, James A; Zhu, Wenlu; Montesi, Laurent; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With increasing shear strain, initially homogeneously distributed melt can segregate into an array of melt-rich bands, flanked by melt-poor regions. To address how the formation of these melt-rich bands affects the transport properties of partially molten rocks, I analyzed X-ray synchrotron microtomographic images of an aggregate composed of 10 vol% basaltic melt and 90 vol% olivine that was sheared to a total strain of 13.3. At 0.16 m per pixel, the spatial resolution of the microtomographic dataset is sufficiently high for quantitative characterization of 3-dimensional melt distribution. The results show that the melt distribution is bimodal: in the melt-poor regions, the total melt fractions range from 0.078-0.100, with no interconnected melt; in the melt-rich regions, the total melt fractions range from 0.116 to 0.178, with the interconnected melt fraction ranging from 0.08 to 0.16. The permeability of the sample was calculated using a digital rock physics approach. Along a melt-rich band, permeability (k) as function of melt fraction (ϕ) and grain size (d) can be expressed as k=(ϕ^3.2 d^2)/12.4. Between melt-rich bands, the permeability is negligible. Thus, the permeability of the sheared partially molten rock is highly anisotropic and negligible in the direction perpendicular to the bands. Grain size measurements were obtained through electron backscatter diffraction. After adjusting for grain size, the permeability of a sheared partially molten rock measured along the direction of melt bands is higher than that of its isotropic counterpart with the same bulk melt fraction. The strong anisotropic permeability provides new insight into the effect of melt band formation on melt migration and melt focusing at mid ocean ridges.Item Transport properties and melt distribution of partially molten mantle rocks: insights from micro-computed tomography and virtual rock physics simulations(2015) Miller, Kevin John; Zhu, Wenlu; Montési, Laurent G. J.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Mid-ocean ridges are a fundamental component of plate tectonics on Earth. They are the longest mountain ranges; combined, they stretch over 70,000 km of the Earth’s surface. They are significant sources of volcanism, producing more than 20 km3 of new oceanic crust each year. The volcanism observed at the ridge axis is linked to processes that transport and focus melt in the underlying upper mantle. Typically, upper mantle melt distribution is inferred either through inversion of geophysical data, such as electromagnetic signals, or through geodynamic modeling. Both approaches require robust constitutive relationship between on electrical conductivity, permeability, and porosity. Unfortunately, direct measurements of transport properties of partially molten rock are technically challenging due to the extreme conditions required for melting. This work aims to quantify permeability-porosity and electrical conductivity-porosity relationships of partially molten monomineralic and polymineralic aggregates by simulating fluid flow and direct current within experimentally obtained, high-resolution, three-dimensional (3-D) microstructures of partially molten rocks. In this study, I synthesized rocks containing various proportions of olivine, orthopyroxene (opx), and basaltic melt, common components of the upper mantle. I imaged their 3-D microstructure using high-resolution, synchrotron-based X-ray micro-computed tomography. The resulting 3-D geometries constitute virtual rock samples on which pore morphology, permeability, and electrical conductivity were numerically quantified. This work yields microstructure-based electrical conductivity-porosity and permeability-porosity power laws for olivine-melt and olivine-opx-melt aggregates containing melt fractions of 0.02 to 0.20. By directly comparing the velocity and electrical fields, which are outputs of the fluid flow and direct current simulations, respectively, this study provides strong evidence that fluid and electricity travel through distinctly different pathways within the same rock, due to the stronger dependence of fluid flux on hydraulic radius. This study also provides the first quantitative evidence of lithological melt partitioning, where melt fractions spatially associated with olivine are systematically higher than those with orthopyroxene due to the relatively low surface energy density of olivine-melt interfaces with respect to opx-melt interfaces. The results of this study place important, novel constraints on 3-D melt distribution and transport properties of the partially molten mantle regions beneath mid-ocean ridges.Item Quantification of Permeability-Porosity Relationships in Seafloor Vent Deposits: Dependence on Pore Evolution Processes(2011) Gribbin, Jill Leann; Zhu, Wen-lu; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hydrothermal mineral deposits formed along seafloor spreading centers help regulate the transfer of heat and mass from Earth's interior to the oceans. Aqueous fluids circulate within the seafloor and are emitted through vent deposits, formed from interaction between vent fluids and seawater. These deposits evolve as they react physically and chemically with venting fluids and seawater, therefore changing transport properties, such as permeability and porosity. In this study, measurements of permeability and porosity were used in conjunction with microstructural observations to identify evolution of permeability-porosity relationships (EPPRs) for vent deposits. EPPRs are power-law relationships relating permeability and porosity through an exponent, alpha, which is sensitive to changes in these properties. These relationships are important for understanding pore evolution processes and fluid distribution, in addition to their effects on environmental conditions within vent deposits.Item Keep it the same: Need for closure and the allure of homogeneous groups with impermeable boundaries(2007-07-17) Schultz, Jeremy Michael; Kruglanski, Arie W.; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Need for (cognitive) Closure has been found to predict a "syndrome" of group-centric behaviors in numerous experiments (Kruglanski et al., 2006). This is theorized to be due to a strong desire for social reality, which groups can provide. The present research investigates the requisite conditions in which groups can fulfill this desire for a firm social reality, specifically group boundary impermeability and group homogeneity. It was found that Need for Closure predicted greater liking for the group only when the group was both homogeneous in composition and had impermeable boundaries, but not when only one of these conditions was met. These findings are explained using lay epistemic theory (Kruglanski, 1989).