Geology Theses and Dissertations
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Item Pressure-Temperature-time-Deformation (P-T-t-D) History of High-Grade Gneisses of the Port aux Basque Area, Southwest Newfoundland, Canada(1994) Burgess, Jerry Lee; Brown, Michael; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)A polyphase deformation history (D1-D4) and upper amphibolite facies metamorphism characterize the Port aux Basques Gneisses. Late-D1 to early D2 kyanite porphyroblasts each contain inclusion trails that preserve S1. Reaction out of muscovite, staurolite and kyanite in favor of sillimanite + garnet + alkali feldspar-bearing assemblages in the matapelitic gneisses record syn- to late- D2 peak metamorphic conditions. Isograd surfaces related to syn-D2 metamorphism were probably subhorizontal to inclined but not their metamorphism were probably subhorizontal to incline but now their map pattern reflects subsequent deformation by D3. Fluid-present melting initiated in the kyanite zone and continued into the sillimanite zone. Metamorphic conditions increase to the southeast with 'peak' temperatures of c. 700-750° at 8-9 kbar associated with the D2/M2 thermal regime. A Pb207/Pb206 date of c. 417 Ma was obtained from titanite in high-grade rocks of the Harbour le Cou Group. This date provides a minimum contraint for the M2 event. Hornblende from a nearby amphibolite yields an 40Ar/39Ar isotope correlation date of c. 419 Ma. Muscovite at the same locality records a 40Ar/39Ar plateau date of 391 Ma. Hornblende and muscovite separates from rocks of the Port aux Basques Complex yield similar 40Ar/39Ar dates. Calculations indicate that post- D3 cooling rates of approximately 8-1°C/Ma are required for the area. They kyanite to sillimanite transition and D2 structures suggest a clockwise trajectory in P-T space as a result of Silurian orogenesis.Item The Kinetics and Mechanism of Sedimentary Iron Sulfide Formation(1976) Pyzik, Albert John; Sommer, Sheldon E.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The reaction between goethite, ∝-FeOOH, and aqueous bisulfide ion, HS, was studied under conditions representative of estuarine sediments. The concentration-time curves of the following species were determined by spectrophotometric methods: total sulfide, dissolved sulfide, precipitated sulfide, thiosulfate ion, sulfite ion, elemental sulfur , and dissolved (<0.1μ) iron. Polysulfides were monitored by ultraviolet absorbance measurements, while the hydrogen ion concentration was determined with a pH electrode. Elemental sulfur, both as free and polysulfide sulfur was found to be the major sulfide oxidation product. Thiosulfate ion comprised about 14±8% (electron balance-wise) of the oxidation products. Concentration-time curves of precipitated sulfide sulfur were analyzed by the initial rate method to determine the rate expression. The rate expression for the reaction between ∝-FeOOH and HS- is d [FeS]/dt = k [HS-]i^97 (H+)i^82 A1.1FeOOHi where d [FeS]/dt is the rate of precipitated iron sulfide formation, (H+)i is the initial hydrogen ion activity, AFeOOHi is the initial geothite surface are in m^2/1, and k is the rate constant with the value 31±10 M^-1 1^-1 m^-2 min ^-1. 0.97, 0.82, and 1.1 are the reaction orders for the species bisulfide ion, hydrogen ion, and goethite surface area respectively. A combination of hydrogen balance and electron transfer balance and stoichiometric reactions were studied in view of the rate expression to yield a mechanism. The multistep mechanism consisted of several parallel and consecutive reactions: (1) the protonation reaction of the goethite surface, (2) the parallel reduction reactions of ferric iron to yield elemental sulfur and thiosulfate as oxidation products, (3) the dissolution of the ferrous hydroxide, and (4) the precipitation reaction of dissolved ferrous species and aqueous bisulfide ion. The rate determining step in the reaction sequence was the dissolution step. Results of this study indicate that the oxidation of sulfide species by ferric iron may be a significant source of elemental sulfur in the sediment. Elemental sulfur is necessary for the formation of pyrite (FeS2), the thermodynamically stable iron sulfide. In addition, the previous studies of the interstitial waters of anoxic sediments showed an excess of "dissolved" iron which was greater than calculated from equilibrium solubility products. It is suggested from particle size studies of the precipitated iron sulfide that these high concentration are a result of the submicron particles of ferrous sulfide (<0.1μ). These particles would obviously pass through the .45μ filters which are traditionally used as the dividing line for dissolved and particulate species.Item Impact of Isotopic Heterogeneity in Shallow Systems on Modeling of Stormflow Generation(1993) Kendall, Carol; Candela, Philip A.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)A major uncertainty in hydrologic and geochemical modeling of stormflow generation in watersheds has been quantification of the contributions of water and solutes from different sources and hydrologic pathways to streamwater. Isotopic techniques have recently gained widespread acceptance as useful tools in the investigation of sources of stream flow, but considerable debate still surrounds the question of whether the spatial and temporal variations in the isotopic and chemical compositions of water components are negligible. At Panola Mountain, Georgia, a 2-year study of temporal and spatial variability in rain and throughfall has determined that average throughfall is enriched by 0.5% in 0^18O and 3.0% in 0D relative to rain; site-specific differences in canopy cause up to 1.2 % variation in 0^18O among collectors for the same storm; and throughfall ^18O enrichment takes place throughout the storm, not just at the beginning. Evaporative losses are greater and throughfall is generally slightly enriched in ^18O in conifer forests relative to deciduous forests. However, throughfall shows little evidence of evaporative fractionation; instead, the high deuterium-excess values suggest considerable exchange with re-evaporated waters. A 490-m^2 artificial catchment in China was used to investigate the effects of temporal variations in rain composition, and temporal and spatial variations in dominant water flowpath, on the development of isotopic and chemical heterogeneity in soil waters and groundwater. In response to changes in storm intensity, variability in the amounts of water transported via piston versus macropore flow caused a 4% range in 0^18O of groundwaters. Selective storage of early rain in shallow soils makes characterization of the isotopic composition of infiltrating rain water problematic. Seasonal and hydrologic differences in the sources of alkalinity were investigated at four watersheds at Catoctin Mountain, Maryland, by analyzing the dissolved inorganic carbon in streamwater for 0^13C. Because of short residence times, the isotopic signatures of the two primary carbon sources, calcite and soil-derived carbonic acid, do not appear to be appreciably overprinted by exchange reactions, biological recycling, or degassing; hence, 0^13C seems to be a useful semi-conservative tracer of water flowpaths and carbon sources.Item CONSTRAINTS ON THE DEPOSITIONAL AGES OF LESSER HIMALAYAN ROCKS IN CENTRAL NEPAL AND THEIR STRUCTURAL IMPLICATIONS(2009) Burgy, Katherine Diane; Martin, Aaron; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The lack of good exposures and paucity of datable horizons in central Nepal has hindered the ability of geologists to piece together a relatively cohesive and straightforward stratigraphic succession within the Lesser Himalaya. U-Pb isotopic analyses of detrital zircons from the Modi Khola valley indicates maximum depositional ages of ~1875 Ma for the Kuncha Formation, ~1800 Ma for the Fagfog Formation, and ~ 1780 Ma for the Kushma Formation. The intrusive 1831 ± 17 Ma Ulleri augen gneiss provides a minimum depositional age bound for the Kuncha. Combined, these data suggest the Kuncha Formation is the oldest member of the Lesser Himalayan series in central Nepal. Additionally, 13C data suggest the Malekhu Formation of the Lakharpata Group was deposited before ca. 1250 Ma. A field mapping comparison based on the redefined stratigraphy indicates the Ramgarh thrust is located >10 km farther south than previously mapped, potentially reducing regional shortening estimates.Item EFFECTS OF BAR FORMATION ON CHANNEL STABILITY AND SEDIMENT LOADS IN AN URBAN WATERSHED(2009) Blanchet, Zachary; Prestegaard, Karen L; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study investigates channel adjustment due to urbanization in the Little Paint Branch creek of the Anacostia River watershed. In the past 15 years, large gravel bars have formed in the channels, more than doubling the active channel width of some reaches. Field data was collected to analyze downstream hydraulic geometry and the effects of gravel bars on shear stress, turbidity, and morphological change. The watershed was gauged at three locations to document the contributions of discharge and sediment to the downstream Anacostia Estuary. The results indicate that Little Paint Branch Creek generates proportionally more runoff per basin area than the watershed does as a whole, even though the impervious surface area is lower in the upstream tributaries, like Little Paint Branch Creek. Bar formation induces channel widening, which decreases flow depth and thus shear stress for bankfull and higher stages. This shoaling limits bed transport and will eventually limit bank erosion.Item Advection-Diffusion Controlled Lithium Isotopic Distribution in Contact Aureoles: A Case Study from the Florence County Pegmatites, Wisconsin(2009) Liu, Xiaoming; Hier-Majumder, Saswata; Rudnick, Roberta L; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Stable isotopes are useful tracers of fluid-rock interactions in contact aureole settings. To date, only a few case studies have used Li isotopes to study fluid-rock interactions in contact aureole settings. These studies highlight the very large Li isotopic fractionation that can be generated in these settings via diffusion of Li from the pluton into the country rocks, but none of these studies have generated a complete and detailed section of the contact aureole needed to understand the Li distributions. Here, I report the results from a combination of Li isotope analyses and 2-D advection-diffusion modeling for two detailed profiles through country rocks adjacent to Li-rich pegmatite dikes in the Florence County pegmatite field. The results show that the Li concentration and isotopic distribution in the two contact profiles is consistent with fluid infiltration and diffusion of Li through a grain boundary fluid from the pegmatites into their country rocks.Item Highly Siderophile Element and Tungsten Systematics of Hawaiian Picrites(2009) Ireland, Thomas James; Walker, Richard J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A suite of Hawaiian picrites (MgO > 13 wt.%), and associated basalts, that represent some of the most primitive melts from the Hawaiian mantle source regions were analyzed for their W, highly siderophile element (HSE: Os, Ir, Ru, Pt, Pd and Re) and 186Os-187Os isotope systematics. These picritic samples are among the most primitive samples produced from the Hawaiian main-shield stage volcanoes. As such, they may preserve considerable information about the mantle source regions from which they were derived. Hawaii is of particular interest because there is geochemical and geophysical evidence that suggest that the Hawaiian plume may originate at the core-mantle boundary. If any outer core material is incorporated into plume lavas, it could carry important geochemical information. The primary goal of this study is to improve our understanding of the processes and materials that may affect the mantle source regions of the Hawaiian volcanoes. Abundances of HSE and W, as well as Os isotopes, are useful tools for evaluating the mantle source regions of ocean island basalts because their absolute and relative abundances may be affected by various mantle processes, including the recycling of oceanic crust and sediment, mantle metasomatism, and other forms of crystal-liquid fractionation. In addition, these elements may be suitable for addressing the question of core-mantle interaction, because the core is highly concentrated in both the moderately siderophile and highly siderophile elements, and may have a distinct Os isotopic composition relative to the mantle. The collected data imply that W abundances in the Hawaiian mantle sources are similar for all volcanic centers, and enriched relative to depleted MORB mantle. This suggests that W may be controlled by a primary source component that is less depleted in incompatible elements than the depleted mantle. HSE abundances in the picrites are controlled predominantly by crystal-liquid fractionation processes, and may reflect the presence of residual sulfides in the mantle sources. Lastly, the 187Os/188Os variations are consistent with some proportion of a recycled oceanic crust component; however, variations in 186Os/188Os require another process, such as the incorporation of variable Pt-enriched base-metal sulfides, or mixing with an 186Os-187Os enriched reservoir.Item Scales of Bank Roughness and Their Relationship to Bank Erosion Processes(2009) Hankin, Erik Ravnholt; Prestegaard, Karen L; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Stream bank erosion rates and the stabilization of channel width are poorly understood processes. There have been two distinct approaches to the study and prediction of bank erosion rates in natural streams. In order to predict bank shear stresses, scientists either define a reach as being meandering or straight, even though most river channels are neither meandering nor straight but a combination of the two. This thesis aims to determine if river segments can be divided into straight reaches and curved reaches with different bank erosion prediction approaches applied to each as well as investigating the role of bank roughness element size and spacing in bank erosion. The results show that straight reaches are affected by upstream curvature and that large isolated bank protrusions that are widely spaced generate erosion-causing, stable, macroturbulent eddies. The thesis has implications for stream restoration practices regarding bank stability and erosion.Item An empirical re-evaluation of the boron isotope/pH proxy in marine carbonates(2009) Klochko, Kateryna; Kaufman, Alan J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The boron isotopic composition measured in marine carbonates is considered to be a tracer of seawater pH. However, an accurate application of this proxy has been hampered by our lack of intimate understanding of chemical kinetics and thermodynamic isotope exchange between the two dominant boron-bearing species in seawater: boric acid B(OH)3o and borate ions B(OH)4-, as well as their subsequent partitioning into a carbonate lattice. In this dissertation I have taken on a task of a systematic empirical re-evaluation of the fundamental parameters and assumptions on which the boron isotope paleo-pH proxy is based. As a result of this research strikingly different values of the boron isotope exchange constant in solution (Klochko et al., 2006) and boron speciation and partitioning in carbonates (Klochko et al., 2009) were determined, suggesting that the most parameters and assumptions that were believed to be previously constrained and have been widely applied to the 11B-pH reconstructions were incorrect. Recognizing that both biological and inorganic processes may potentially affect boron speciation and isotopic composition in carbonates, to isolate purely inorganic effects on the boron isotope co-precipitation with carbonates, we have designed a series of pH-controlled 11B calibration experiments of inorganic calcite and inorganic aragonite. Results to date reveal that precipitates from our experiments at pH = 8.7 fall exactly along the borate ion 11B curve predicted by our empirically determined boron isotope fractionation factor (Byrne et al., 2005; Klochko et al., 2006). Extending these experiments to wider range of pH conditions will provide the necessary inorganic baseline for paleo-studies of inorganic carbonate and future investigations of the purely biological effects on the boron isotope distributions in carbonates.Item Topographic signatures in the Himalaya: A geospatial survey of the interaction between tectonics and erosion in the Modi Khola valley, central Nepal(2009) Walsh, Lisa Schleicher; Martin, Aaron J; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Spurred by the recognition that lithologic resistivity to erosion influences the steepness of terrain, the purpose of this study is to enhance our understanding of feedbacks between erosion and tectonics in the Himalaya. Using spatial statistics, within a Geographic Information Systems (GIS) framework, this study extracts steepness and curvature values from the terrain to identify the unique spatial signature of lithologic units in the Annapurna Range. The spatial relationship of faults and significant changes in river steepness (ksn) and concavity (θ) are examined in this project using high resolution digital elevation models (DEMs), derived from a variety of interpolation methods. Through these quantifications, I explore the possibility of a new model for tectonic activity in central Nepal, in an effort to improve our understanding of how surface processes sculpt the landscape.