UMD Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/3

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 given thesis/dissertation in DRUM.

More information is available at Theses and Dissertations at University of Maryland Libraries.

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    Anatexis and crustal differentiation: Insights from the Fosdick migmatite-granite complex, West Antarctica
    (2014) Yakymchuk, Christopher; Brown, Michael; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In the Fosdick migmatite-granite complex of West Antarctica, U-Pb geochronology of monazite in migmatites and zircon in granites records two episodes of high-temperature metamorphism, one in the Devonian-Carboniferous and another in the Cretaceous. For the older lower-grade event, whole-rock and zircon isotope geochemistry of granites within the Fosdick complex are interpreted to record crustal reworking during metamorphism associated with continental arc magmatism along the East Gondwana convergent plate margin. By contrast, the geochemistry of correlative granites suites from along and across the same margin indicates a greater proportion of crustal growth. This suggests prominent arc-parallel and arc-normal variations in the mechanisms of crustal reworking versus growth in continental arc systems. Based on garnet Lu-Hf ages, the timing of peak metamorphism in the younger higher-grade event has been determined as c. 116-111 Ma. U-Pb ages of monazite from migmatites and zircon from anatectic granites suggest that exhumation of the complex as a gneiss dome occurred during the interval c. 107-100 Ma. Contemporaneous exhumation of high-grade metamorphic rocks in the Western Province of New Zealand suggests that intracontinental extension preceded the final breakup of New Zealand from West Antarctica by c. 25 Myr. Melt migration through and emplacement within the Fosdick complex during Cretaceous metamorphism was accomplished via a self-organized melt network controlled by the regional stress field and anisotropy of the host rocks. Granites within this network and in sills at shallower crustal levels have microstructures and chemistry consistent with a cumulate origin, and are interpreted to record fractional crystallization during magma ascent and doming related to exhumation. Phase equilibria modeling of open system melting during prograde metamorphism is used to quantify the reduced fertility of source rocks during high-temperature exhumation and later overprinting orogenic events. Quantitative modelling of the dissolution of zircon and monazite during prograde melting demonstrates that accessory minerals are expected to be partially to completely consumed up to the metamorphic peak. New growth of these minerals in migmatite melanosomes is predicted to be limited during cooling, whereas leucosomes and anatectic granites are predicted to contain new zircon and monazite growth.
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    Sediment Biogeochemistry Across the Patuxent River Estuarine Gradient: Geochronology and Fe-S-P Interactions
    (2007-12-21) OKeefe, Jennifer; Cornwell, Jeffrey C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Although salinity and redox gradients are defining features of estuarine biogeochemistry, compositional changes in sediment characteristics associated with these factors are poorly described in U.S. coastal plain estuaries. Understanding the basics of nutrient sources and sinks, in the context of these defining characteristics, is required to make efficient and effective management decisions regarding estuarine eutrophication. In this study, detailed analysis of long-term nutrient burial has been used as a tool to understand the trajectory of nutrient cycling at 7 stations along an oligohaline to mesohaline transect in the Patuxent River estuary. Sediment mass accumulation rates were determined for 3 of the 7 sites. Cores analyzed for total P, total N, organic C, biogenic silica, δ13C, and δ15N did not provide evidence of historical nutrient reduction actions taken in this watershed. Burial rates of Fe-S mineral phases and inorganic P (IP) indicated pyrite formation limited the availability of Fe-oxides for adsorption and retention of IP.