Physical Sciences and Mathematics Commons^™

Rheological Bridge Zones: A New Perspective To Explore Strain Localization And Rock Rheological Weakening, He Feng

Electronic Theses and Dissertations

Strain localization, a ubiquitous geological phenomenon, emerges when rock undergoes extensive weakening and accommodates disproportionate deformation. This phenomenon spans from brittle faulting to viscous flow, known as shear zones. Despite its prevalence, discussions on weakening primarily center on highly strained samples, rather than the initial deformation state. This research delves into the evolution of localization and rheology in intact rocks.

Heterogeneous mechanical properties within the lithosphere vary based on mineralogy, microstructure, and environmental conditions. Chapter 2 characterizes microscale structures termed "bridge zones." These zones, observed through optical and electron microscopy, exhibit distinctive morphologies. Comprising fine-grained aggregates, bridge zones link weak …

Investigating Mercer's Paradox: A 10be Chronology Of Moraines Deposited During The Last Glaciation At Soda Lake, Wind River Range, Wyoming, U.S.A., Lauren M. Woods

Electronic Theses and Dissertations

Here I use geomorphic mapping and ¹⁰Be surface-exposure dating to address the paradox that lies within the general understanding of the mechanisms driving ice-age climate and glacial cycles. The long-standing and widely accepted Murphy-Milankovitch hypothesis suggests glacial cycles are controlled by the local intensity of summer-time insolation. By this hypothesis, glacier maxima should be achieved at times of low insolation intensity and asynchronously between the polar hemispheres, a pattern which is inconsistent with the glacial geomorphic record. The ¹⁰Be chronology I have constructed of moraines at Soda Lake, Wind River Range, Wyoming, U.S.A. shows nine glacial advances to …

First-Row Transition Element Distribution Across The Blueschist-Eclogite Transition: A Case Study From New Caledonia, Natalie M. Harmon

Electronic Theses and Dissertations

The first-row transition elements (FRTE), namely Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, are potential redox tracers in the solid Earth due to their general compatibility during crustal processes, and the redox-sensitive nature of certain elements. Despite widespread interest in the FRTEs, their distribution and behavior in subduction zones, particularly across the blueschist-eclogite transition, are still poorly constrained. New Caledonia preserves a prograde subduction zone with largely coherent continuous progression in metamorphic grade. Although the metamorphic sequence has been disrupted to some extent, this is the closest natural example of blueschist and eclogite that was sourced …

Geology And Lithogeochemistry Of The Pickett Mountain Volcanogenic Massive Sulfide Deposit, Northern Maine, Michael J. Mccormick

Electronic Theses and Dissertations

The Pickett Mountain deposit is a volcanogenic massive sulfide (VMS) base-metal deposit located 15 miles north of Patten, ME. The deposit, discovered in 1979, was abandoned in 1989. The deposit remained abandoned until 2017, when Wolfden Mt. Chase LLC purchased the land for further development after Maine mining regulations changed. This project is a collaboration between the University of Maine, the University of Maine – Presque Isle, Wolfden Resources Corp., and the University of New Brunswick to better understand the regional and deposit-scale geology related to the deposit to fill in gaps of the geologic story of northern Maine as …

Sulfur And Trace Metal Cycling At Convergent Margins, Jesse B. Walters

Electronic Theses and Dissertations

Subduction zones are the site of long-term chemical exchange between Earth’s surface and interior geochemical reservoirs. Subducting slabs are progressively depleted in volatiles and other mobile elements through dehydration and melting reactions. These elements are then introduced to the mantle wedge and volcanic arc. One consequence of this cycle is that volcanic arcs produce the most oxidized magmas on Earth. Sulfur, which exhibits a range in valence states from S^2- to S⁶⁺, is one of the few elements in the subducting slab capable of oxidizing the arc and mantle wedge. Sulfides in the slab may also act …

Variations In The Southern Hemisphere Westerlies Over The Last 23,000 Years From Lake Records In The Falkland Islands, Meghan M. Spoth

Electronic Theses and Dissertations

The Southern Hemisphere Westerlies (SHW) are an important driver of climate in the mid-latitudes of the Southern Hemisphere. Abrupt latitudinal migration of this coupled atmospheric-oceanic system is thought to be linked to the onset of the Termination at the end of the last ice age and to subsequent climatic variation through the late-glacial period and Holocene. However, the timing and spatial extent of these shifts, as well as variations in wind intensity, are poorly constrained, hindering our understanding of abrupt climate change in the Southern Hemisphere. In addition, future changes in the position and intensity of the SHW are a …

A Groundwater Flow Model To Aid In Water Resource Management For The Carraipia Basin In The Coastal Semi-Arid Region Of La Guajira State (Colombia), Efren D. Gomez Arevalo

Electronic Theses and Dissertations

About 160,000 inhabitants live in the 1,600 square kilometers Carraipia River Basin located in northeastern Colombia and northwestern Venezuela. Historically, water has been supplied to the inhabitants in this arid coastal region by shallow dug wells. Water supplied by these wells is frequently of poor quality due to high concentrations of total dissolved solids (TDS). Recently, due to the increasing demand for water, numerous deep wells have been drilled in the region to supply water to rural and urban areas from deep aquifers. Colombian agencies seek more quantitative information on groundwater resources, driven by increasingly severe water shortages over the …

Fractures, Fluids, And Metamorphism: Shear Zone Initiation In The Marcy Anorthosite Massif, Adirondacks, New York, Usa, James Hodge

Electronic Theses and Dissertations

Localized shear zones are important rheological features that influence deformation behavior throughout the Earth’s middle-to-lower crust. Therefore, the processes through which shear zones initiate and localize remains an important geologic question. The study of strain localization and shear zone initiation is made difficult due to continued deformation overprinting the microstructures which lead to initiation and obfuscating the context in which localization occurred. The Marcy anorthosite in the Adirondack Highlands, New York, is a nominally granulite-facies, plagioclase-rich massif cut by centimeter-to-meter scale shear zones which provides a natural example of shear zone localization within the middle-to-lower crust. My work focuses on …

Investigations Into The Advancement Of Cryptotephra Geochemical Fingerprinting, Laura Hartman

Electronic Theses and Dissertations

The primary purpose of this work is to advance new sample preparation and analytical methods for ice core tephrochronology. When a volcanic source can be accurately identified using volcanic glass particle geochemistry, it may provide a robust time reference for the ice core’s timescale. The presence of an identifiable tephra layer may also suggest atmospheric pathways at the time of deposition, or assist in reconstructing volcanic forcing of climactic state for a specific event. One of the perpetual challenges in ice core based tephrochronological work is measuring the geochemical composition of ultra-fine particles (<10 >μm). Not only is it difficult …

Three-Dimensional Bedrock Channel Evolution With Smoothed Particle Hydrodynamics, Nick Richmond

Electronic Theses and Dissertations

Bedrock channels are responsible for balancing and communicating tectonic and climatic signals across landscapes, but it is difficult and dangerous to observe and measure the flows responsible for removing weakly-attached blocks of bedrock from the channel boundary. Consequently, quantitative descriptions of the dynamics of bedrock removal are scarce. Detailed numerical simulation of violent flows in three dimensions has been historically challenging due to technological limitations, but advances in computational fluid dynamics aided by high-performance computing have made it practical to generate approximate solutions to the governing equations of fluid dynamics. From these numerical solutions we gain detailed knowledge of the …

Utilizing Ground-Penetrating Radar In The Delineation And Cultural Resource Management Of Eroding Maine Coastal Shell Middens, Jacquelynn F. Miller

Electronic Theses and Dissertations

Shell middens along the Maine coast archive up to 5000 years of cultural and climatic change, but the record is continually and rapidly lost to the sea through climate-driven coastal erosion and sea-level rise. These sites were constructed by the ancestors of Maine Tribes, and are composed of centimeters to meters of clam (Mya arenaria) and/or oyster (Crassostrea virginica) shells, other faunal remains, and cultural materials. Shell middens record human interaction with the environment and early coastal occupation and adaptation. The faunal remains reflect paleoenvironmental conditions and the distribution of extinct and extant forage-species along the western Gulf of Maine. …

In Situ Dating Of Multiple Events In Granulite-Facies Rocks Of The Larsemann Hills, Prydz Bay, East Antarctica Using Electron Microprobe Analysis Of Monazite, Steven K. Spreitzer

Electronic Theses and Dissertations

The metamorphic rocks exposed along the southeast coast of Prydz Bay were affected by several metamorphic and plutonic events associated with collision in the Neoproterozoic and Cambrian. Critical units exposed in the Larsemann Hills and nearby ice-free areas include (1) basement Søstrene Orthogneiss, (2) cover sequence Brattstrand Paragneiss and (3) anatectic pegmatites intrusive into the Brattstrand Paragneiss. Zircon U-Pb data from previous studies yielded a maximum depositional age of 1023 ± 19 Ma for the Brattstrand Paragneiss, but only approximate ca. 900 Ma to ca. 1000 Ma and ca. 530 Ma ages for two metamorphic events. In order to constrain …

Constraining The Spatial Extent Of Strain Localization At The Base Of The Seismogenic Zone: A Case Study From The Sandhill Corner Shear Zone, Maine, Usa, Erik Kristian Anderson

Electronic Theses and Dissertations

Knowledge of the structure and processes of strain localization at the base of the seismogenic zone can provide constraints on the rheologic evolution of shear zones at depth and the spatial extent that seismicity influences the surrounding rock. Such knowledge is hindered by limitations of borehole measurements from such depths and a lack of structural/mineralogical preservation of original rock fabric. The Sandhill Corner Shear Zone, Maine, USA provides an opportunity to study well-preserved structures relating to strain localization along major faults exhumed from seismogenic depths. In south-central Maine, this shear zone juxtaposes two rock types: the Cape Elizabeth Formation and …

Microstructural Analysis Of Thermoelastic Response, Nonlinear Creep, And Pervasive Cracking In Heterogeneous Materials, Alden C. Cook

Electronic Theses and Dissertations

This dissertation is concerned with the development of robust numerical solution procedures for the generalized micromechanical analysis of linear and nonlinear constitutive behavior in heterogeneous materials. Although the methods developed are applicable in many engineering, geological, and materials science fields, three main areas are explored in this work. First, a numerical methodology is presented for the thermomechanical analysis of heterogeneous materials with a special focus on real polycrystalline microstructures obtained using electron backscatter diffraction techniques. Asymptotic expansion homogenization and finite element analysis are employed for micromechanical analysis of polycrystalline materials. Effective thermoelastic properties of polycrystalline materials are determined and compared …

Processes Leading To The Formation Of Deep Granitic Shear Zones In The Grenville Front Tectonic Zone, Ontario, Canada, Deborah J. Shulman

Electronic Theses and Dissertations

The rheology of the deep crust influences the transmission of mantle stresses to the surface as well as the topographic relief of orogenic terrains. Since deformation in the deep crust is often localized in shear zones, we investigate the mechanical processes associated with strain localization to understand the rheology of the deep crust. Strain localizes due to a strength heterogeneity, which can be created by the activation of one or more weakening factors. Studying the mechanical processes and weakening factors that sustain strain localization in the deep crust is becoming increasingly important as geodynamic models become more computationally robust, and …

Los Morteros: Early Monumentality And Environmental Change In The Lower Chao Valley, Northern Peruvian Coast, Ana Cecilia Mauricio Llonto

Electronic Theses and Dissertations

This doctoral dissertation presents the results of archaeological and geoarchaeological studies carried out at the site of Los Morteros and the Archaeological Complex of Pampa de las Salinas, lower Chao Valley, North Coast of Peru, between September 2012 and July 2014. This research focuses on the study of the mound-shaped site of Los Morteros and the environmental contexts in which this site developed. Previous excavations at the site considered Los Morteros as a “stabilized dune” whose top was used as cemetery for pre-pottery people around cal. 5000 B.P (Cardenas 1995, 1999). However, geo-radar explorations of the mound in 2006 and …

Topographic Signatures Of Geodynamics, Samuel G. Roy

Electronic Theses and Dissertations

The surface of the Earth retains an imperfect memory of the diverse geodynamic, climatic, and surface transport processes that cooperatively drive the evolution of Earth. In this thesis I explore the potential of using topographic analysis and landscape evolution models to unlock past and/or present evidence for geodynamic activity. I explore the potential isolated effects of geodynamics on landscape evolution, particularly focusing on two byproducts of tectonic strain: rock displacement and damage. Field evidence supports a strong correlation between rock damage and erodibility, and a numerical sensitivity analysis supports the hypothesis that an order of magnitude weakening in rock, well …

Structure And Rheology Of The Sandhill Corner Shear Zone, Norumbega Fault System, Maine: A Study Of A Fault From The Base Of The Seismogenic Zone, Nancy Ann Price

Electronic Theses and Dissertations

Determining the structure and rheology of a seismogenic fault at frictional-to-viscous transition (FVT) depths is vital for understanding its strength and behavior. Few studies describe a fault from within this depth level, so the architecture of a shear zone at these depths as well as the effect of transient coseismic and postseismic deformation on the rheology of the shear zone is poorly-understood. The Sandhill Corner strand of the Paleozoic Norumbega fault system of Maine is the one of the few known examples of a subvertical, strike-slip fault exhumed from FVT depths. Using a suite of samples collected from the Sandhill …

Geoarchaeological Investigations Along The Tambo-Ilo Coast Of Southern Peru, Louis Fortin

Electronic Theses and Dissertations

The south coast of Peru has had a long history of cultural occupancy from the Preceramic through Chiribaya periods, and into Spanish Colonial / Post-Colonial periods. Procurement and modification of lithic material was an important activity throughout each of these periods but remains an under-explored dataset for late Prehispanic and Colonial populations in the region. Analysis at the Cola de Zorro archaeological site and within the Tambo-Ilo region examined the relation cultures have with their environment through a geoarchaeological analysis of the local geology and the distribution of lithics. Surveys were completed at Cola de Zorro in the quebrada drainage, …

Archaeological Geology And Postglacial Development Of The Central Penobscot River Valley, Maine, Usa, Alice Repsher Kelley

Electronic Theses and Dissertations

The purpose of this interdisciplinary study is to provide a geological and environmental context for the Late Pleistocene and Holocene Native American occupation of the central Penobscot River Valley, Maine. In addition, this work provides a model for the regional synthesis of geological, archaeological, and paleoenvironmental data in order to examine large-scale patterns of archaeological site formation and preservation. The postglacial central Penobscot Valley experienced varied and rapid landscape changes. Withdrawal of the Laurentide Ice Sheet was followed by marine transgression and regression. Subaerial exposure initiated landscape development. The postglacial Penobscot River rapidly excavated a channel through glacial sediments, creating …

Porphyroblast Kinematics And Crenulation Cleavage Development In The Aureole Of The Mooselookmeguntic Pluton, Western Maine, Matthew E. Dupee

Electronic Theses and Dissertations

The porphyroblastic pelitic schists of western Maine are ideal for studying the deformation and metamorphism that accompanies pluton emplacement. A regional lowpressure, high-temperature metamorphic event affected the areally extensive Silurian sediments with the thermal peak occuning ca. 404 Ma. This metamorphism produced the widespread assemblage staurolite + andalusite + biotite +I- garnet, and occurred during the late stages of development of a northeast-trending, steeply-dipping axial-surface foliation. A period of extensive plutonism accompanied and followed this Acadian-aged deformation and metamorphism. This study focuses specifically on the contact aureole of the Mooselookmeguntic pluton emplaced ca. 370 Ma. Contact metamorphism accompanied the development …

A Mass Balance Study Of The West Antarctic Ice Sheet, Vandy Blue Spikes

Electronic Theses and Dissertations

The present state of the West Antarctic ice sheet (WAIS) is a prime concern of science, but its large size and remote location have limited the amount of reliable data that are available for mass balance calculations. The spatial pattern of mass balance for a 100-km² portion of the WAIS is estimated by calculating the residual flux of ice through 1-km grid cells organized into a geographical information system (GIs). The input data used for this estimate include continent-scale compilations of ice thickness and snow accumulation rate measurements, and ground-based measurements of snow accumulation rate and ice velocity. The …

The Characteristics That Control The Stability Of Eroding Coastal Bluffs In Maine, Corinn C. Keblinsky

Electronic Theses and Dissertations

Bluffs of glacigenic sediment exist along 53% of the tidal shoreline of Maine. Under the current regime of rising sea level, waves, groundwater, and sub-aerial processes easily erode these materials. The hazardous nature of the bluffs is not widely recognized by the public, and new homeowners are often shocked to find out that their property is disappearing. To better educate the public, the Maine Geological Survey is mapping the stability of coastal bluffs. This report utilizes that database along with other available data to determine what controls the relative stability of bluffs. A geographic information system (GIs) was used to …

Stable Sulfur Isotope Rations From West Antarctica And The Tien Shan Mountains: Sulfur Cycle Characteristics From Two Environmentally Distinct Areas, Lee Pruett

Electronic Theses and Dissertations

Continuous snow pit and ice core samples from two distinct environments (West Antarctica and the Tien Shan mountains in central Asia) were analyzed for 6 3 4 ~ and used to assess different regional sulfur cycle characteristics. In West Antarctica, 18 continuous samples were obtained from the RIDSA ice core (78.73"S, 116.33"W, 1740 m asl), covering the years 1935 to 1976. Each sample represents from 2 to 3 years of snow deposition, and the combination of summer and winter seasons varies by sample. 6 3 4 ~ values range from 3.1 %O to 9.9%0, and reflect the overall isotopic composition …

Late Holocene Sea-Level Change Around Newfoundland, Julia Daly

Electronic Theses and Dissertations

Analysis of basal salt-marsh peats and tide-gauge data from several locations around Newfoundland yield high-resolution late Holocene sea-level reconstructions and constrain differential sea-level change. The transition between rising and falling local sea levels and the influence of glacioisostasy on relative sea-level change around Newfoundland through the late Holocene are not well known fiom previous research. The patterns of local relative sea-level change during this time have important implications for constraining numerical models of sea-level change, and therefore inferences about ice sheet thickness and the response of the lithosphere to deglaciation. I investigated the stratigraphy of salt marshes at four locations …

Evolution Of Seabed Pockmarks In Penobscot Bay, Maine, Allen M. Gontz

Electronic Theses and Dissertations

Seafloor depressions, called pockmarks, have been known to exist in Penobscot Bay, Maine since the mid 1980's (Knebel and Scanlon, 1985). Earlier workers (Ostericher, 1965) recognized "channels" on sonoprobe records that are in the sanle area as the pockmarks recognized by Knebel and Scanlon (1985). Their origins and pathways of evolution are unknown. Much speculation about the sources of pore fluids, levels of activity, and evolutionary pathways has occurred since their discovery. Two surveys of Belfast Bay, in 1998 and 1989, have shown differences in the pockmark field population. Over the course of a decade, 36% of the field's 1998 …

Distribution Of Patterned Ground And Surficial Deposits On A Debris-Covered Glacier Surface In Mullins Valley And Upper Beacon Valley, Antarctica, Andrew M. Lorrey

Electronic Theses and Dissertations

Beacon Valley is located in the western Dry Valleys, Antarctica, adjacent to the East Antarctic Ice Sheet (EAIS). The surficial material on the floor of Beacon Valley is segmented into large polygonal landforms separated by trenches. Buried beneath the polygons and surficial material is massive ground ice. One hypothesis is that the buried ice in upper Beacon Valley is glacier ice originating from local debris-covered glaciers. The networks of polygons and trenches form as the buried ice undergoes thermal contraction and sublimation. Contraction cracks that penetrate the surficial material and buried ice in Beacon Valley contain Late Miocene age volcanic …

Surficial Geology And Geomorphology Of The Western Olympus Range, Antarctica: Implications For Ice-Sheet History, Brett Vandenheuvel

Electronic Theses and Dissertations

A widespread erosion surface passes across bedrock and sedimentary deposits in the western Dry Valleys sector of the Transantarctic Mountains (TAM), southern Victoria Land, Antarctica. The surface includes stoss-and-lee slopes, channels, potholes, scoured basins, and corrugated bedrock. These features have been taken to represent subglacial meltwater erosion beneath a greatly expanded East Antarctic Ice Sheet (EAIS) in the mid-Miocene (Denton et al. 1984, Marchant et al. 1993a). Sedimentary deposits that are typically associated with ice-sheet wastage, such as outwash, are not present on the erosion surface. The lack of these deposits indicates that the expanded ice-sheet postulated to be responsible …

Magmatic Enclaves And Evidence For Magma Mixing In The Oak Point Granite, Deer Isle, Maine, Usa, Ben Johnston

Electronic Theses and Dissertations

The Coastal Maine Magmatic Province (CMMP) consists of over 100 post tectonic plutons with ages varying from Silurian to Carboniferous. Predominately, plutons are either felsic or mafic with little intermediate material. Several plutons within the CMMP show evidence for direct interaction of contemporaneous mafic and felsic magmas. These are classified as Mafic and Silicic Layered Intrusions (MASLI), a specific group of plutons with characteristics indicative of mafic magma replenishment into silicic magma chambers. While the Maine coast contains several MASLI type plutons, other plutons in the CMMP contain less definitive, more cryptic evidence that suggests interaction of mafic and silicic …

Evolution Of Sprague Neck Bar, Machias Bay, Maine, Rebecca A. Nestor

Electronic Theses and Dissertations

Sprague Neck Bar is a recurved barrier spit located in Machias Bay, Maine. Principle geomorphic features associated with Sprague Neck Bar include bedrock, coastal bluffs, till in grounding line (the Pond Ridge Moraine) and washboard moraines, mudflats, sand and gravel beaches, and a salt marsh. Sprague Neck Bar is attached to the western end of the Pond Ridge Moraine (Sprague Neck) and extends northward toward the head of Machias Bay for 845 meters before the system recurves to the southeast for 232 meters. The recurve system forms a broad tidal flat with evidence for northward and eastward migration of the …