Geology Theses and Dissertations

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    PREDICTING THE SEISMIC SIGNATURE OF LAVA TUBES FOR THE EARTH, THE MOON, AND MARS
    (2024) Wike, Linden; Schmerr, Nicholas; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Lava tubes are a type of volcanically-generated subsurface void structure found on Earth, the Moon, and Mars and hold the potential to serve as shelters for crew members, preservation sites of pristine geological samples, and locations of in situ resources. A key question for lava tube science is how to locate them through geophysical methods. Here, we create a workflow that locates and characterizes the geometry of subsurface voids. We build a suite of subsurface synthetic seismic wavefield models that contain lava tube structures and investigate which seismic method best images them. Our models show that the more readily detectable lava tube simulations have a geophone spacing of 0.5 m, variable diameter, and shallow ceiling depth; and reverse-time migration and phase-shift-plus-interpolation migration techniques produce more accurate lava tube reconstructions than the Kirchhoff method. The synthetic modeling serves as a benchmark for understanding seismic wave propagation around lava tubes and helps answer how voids on the Moon and Mars would be imaged through seismology.
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    Safer Grounds: A Study of Landmine Detection using UAV- and Ground-Based Multi-Modal Geophysics
    (2024) Myers, Heidi Patricia; Lekic, Vedran; Lathrop, Daniel; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation addresses the urgent global crisis of landmines, unexploded ordnance (UXO), and explosive remnants of war (ERW) through the lens of multimodal geophysics. Chapter 1 sets the stage by highlighting the humanitarian imperative while underscoring the broader applicability of the developed methods and instruments for shallow critical zone exploration. Unlike conventional engineering-centric approaches, our geoscience-centered methodology offers promising avenues for effectively detecting and characterizing buried hazards. Chapter 2 meticulously examines various geophysical sensors, identifying limitations and proposing innovative solutions. Notably, TetraMag, a novel triaxial magnetic gradiometer, overcomes the deficiencies of single-sensor systems, demonstrating superior sensitivity to small-scale variations in the magnetic field. Chapter 3 delves into the intricate symmetries and invariants of the finite-difference magnetic gradient tensor (FDMGT), elucidating its pivotal role in precise target localization and parameter estimation within the shallow critical zone. The methodology outlined streamlines data processing and interpretation, laying a robust foundation for UAV-based detection systems. Chapter 4 introduces machine learning techniques, particularly convolutional neural networks (CNNs), as robust target detection and parameter estimation tools. By synergizing multiple geophysical modalities, these methods enhance our ability to discern subtle anomalies with high accuracy. Chapter 5 proposes a method to mitigate magnetic self-noise in UAV-mounted gradiometers, enhancing data fidelity and spatial coherence. This approach, applicable to various vehicle platforms, further extends the reach of our detection capabilities. In Chapter 6, we integrate and apply these methodologies to a real-world minefield scenario, successfully detecting and localizing buried targets. While acknowledging limitations such as payload constraints and computational demands, our findings underscore the versatility and robustness of the developed techniques. This dissertation addresses the pressing humanitarian challenge of landmine detection and advances the broader field of shallow critical zone geophysics. The methodologies and technologies presented here hold promise for diverse applications beyond military contexts, ranging from infrastructure mapping to hydrogeological studies.
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    THE CONCENTRATION OF HYDROGEN IN INCOMPLETELY AND WHOLLY MELTED TERRESTRIAL BUILDING BLOCKS
    (2024) Peterson, Liam Donald; Newcombe, Megan E; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Hydrogen (H) is the most abundant element in our solar system and exerts a primary control on the habitability, and geochemical and geodynamic evolution of rocky bodies. Therefore, constraining the source(s), timing of accretion, and abundance of H in the Earth and other bodies is of fundamental importance for understanding how planets evolve. Direct constraints on the source(s) of H and other highly volatile elements (HVEs; e.g., H, C, F, Cl, and S) to the bulk Earth can be provided by analyzing meteorites, which are the remnants of early-formed rocky bodies that were present during the accretion of the terrestrial planets. Such samples either directly sample or provide analogs for terrestrial precursor materials.Rocky solar system materials can be subdivided based upon their nucleosynthetic isotopic compositions (“genetic” tracers; e.g., 50Ti, 54Cr) into two groups, which are thought to correspond to the inner- and outer- solar system. Materials may be further subdivided by their extent of thermal processing (i.e., unmelted, incompletely melted, and wholly melted). Earths H budget is commonly accounted for by addition of unmelted (i.e., chondritic) materials, namely carbonaceous chondrite-like (CC-like) materials, thought to be derived from the outer solar system, which have high H concentrations (up to ~14 wt. % H2O; total H as H2O equivalents) and similar H isotopic compositions to the bulk Earth. Furthermore, chondrites derived from the inner solar system (e.g., ordinary and enstatite chondrites) are H-poor relative to carbonaceous chondrites. Similarly, all melted planetesimals are commonly assumed to be anhydrous. However, recent analyses of enstatite chondrites (ECs), which are formed in the inner solar system and are the closest match to the nucleosynthetic isotopic composition of the bulk Earth, suggest that ECs have a similar H isotopic composition to the bulk Earth and can account for its entire H budget. Furthermore, recent analyses suggest that melted (i.e., achondritic) bodies may retain considerable amounts of H, potentially enough to account for Earth’s H budget in the case of the enstatite achondrites (i.e., aubrites). However, achondritic materials are predominantly highly H-poor relative to chondritic materials, and it is unclear if the aubrites are an anomaly, and at which stage of planetesimal evolution H and other HVEs are lost. In chapter 2, I re-examine prior bulk analyses of H in aubrites, and by extension ECs, using in situ methods and suggest that nearly all H measured in aubrites by bulk methods reflects pervasive terrestrial contamination and alteration, a result which may extend to concurrent bulk H analyses of ECs. In chapters 3 and 4, I examine the H content of incompletely melted (i.e., primitive achondritic) planetesimals to constrain at what stage of planetesimal evolution H is lost. Chapter 3 characterizes the H contents of the ureilites, a group of C-rich primitive achondrites, and chapter 4 characterizes the H contents of the acapulcoite-lodranite clan which represents the “prototypical” primitive achondritic parent body. I find that primitive achondritic parent bodies are highly H-depleted relative to chondrites, requiring that H is efficiently lost prior to or at the onset of planetesimal melting, and that Earth’s H budget is accounted for by accretion of thermally primitive materials (e.g., chondrites). Within my primitive achondrite data sets, I observe apparent disequilibrium with respect to H between olivine, pyroxene, and feldspar. In chapter 5, I explore whether this apparent disequilibrium is the result of extrapolating high pressure experimental data to low pressures. I conduct olivine–melt H partitioning experiments at low pressures (10 – 200 MPa) and find that the olivine-melt H partition coefficient increases at low pressures, contrary to extrapolation from high pressure data. This observation is best explained by a control of H speciation in the melt on the partitioning of H between olivine and melt.
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    EXPERIMENTAL CONSTRAINTS ON PHYSICAL PROPERTIES OF VOLCANIC ROCKS WITH IMPLICATIONS FOR LUNAR EXPLORATION
    (2023) Braccia, Casey Marie; Zhu, Wenlu; Schmerr, Nicholas; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The lunar subsurface is a primary science target for future missions to the Moon and serves as a potential host location for resources such as water ice, void spaces for astronaut shelter, and important ore bodies for in-situ manufacturing and building materials (Horz, 1985; Coombs and Hawke, 1992; Wendell, 2017). Here we conducted laboratory experiments to investigate how the seismic signature obtained at or near the lunar surface is related to subsurface material properties and structures. A range of analog basaltic samples collected from the San Francisco Volcanic Field (SFVF) in Arizona, Kilbourne Hole (KH) in Southern New Mexico, and Lava Beds National Monument (LBNM) in Northern California are collected and their geophysical properties are measured. The relationships between the seismic wave velocity and porosity of basaltic rocks from different locales are obtained and the measured velocities are compared to local seismic surveys of the sample locale. Using laboratory techniques, the SFVF basalts P-wave and S-wave velocities range from ~5 km/s to ~6 km/s +/- 0.1 km/s and ~2.1 km/s to ~3 km/s +/- 0.1 km/s, respectively. For the KH basalts P-wave and S-wave velocities range from ~3.5 km/s to ~4.4 km/s +/- 0.1 km/s and ~1.8 km/s to ~2.3 km/s +/- 0.1 km/s, respectively. For LBNM basalts P-wave and S-wave velocities range from ~3.1 km/s to ~6 km/s +/- 0.1 km/s and ~1.2 km/s to ~2.4 km/s +/- 0.1 km/s, respectively. A relationship between the porosity and velocity of basalts from these three locations was determined. Using the field seismic data for each study site and the relationship derived from the laboratory seismic data and porosity, the amount of possible large-scale fracturing is derived. Based on these experimental measurements, we estimate the large-scale fractures and voids are ~84 vol% at the SFVF, ~42 vol% at the KH, and ~39 vol% at the LBNM. These results provide quantitative constraints for subsurface exploration in future lunar surface missions.
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    LONGITUDINAL STREAM SYNOPTIC (LSS) MONITORING TO EVALUATE WATER QUALITY IN RESTORED STREAMS
    (2023) Malin, Joseph Thomas; Kaushal, Sujay S; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Many kilometers of streams are being restored in the Chesapeake Bay watershed and elsewhere in efforts to stabilize streambanks, protect infrastructure, and improve water quality. Urban development and impervious surface cover increase peak flows, which degrade streams. Restoration strategies often employ engineering approaches to enhance stream-floodplain reconnection, dissipate erosive forces from urban runoff, and enhance contaminant retention. In this study, longitudinal stream synoptic (LSS) monitoring (sampling multiple points along flowpaths across both space and time) was conducted to assess the effectiveness of different forms of stream restoration in attenuating pollutants downstream. Spatial and temporal monitoring of carbon, nutrients, salt ions, and metals were conducted across five watersheds experiencing varying levels of stream-floodplain reconnection and stormwater management within the Chesapeake Bay region. Study sites included Sligo Creek (minimal floodplain reconnection), Paint Branch (streambank stabilization without significant reconnection), Scotts Level Branch (engineered stream-floodplain reconnection), Little Paint Branch (natural floodplain reconnection from sedimentation), and Campus Creek (regenerative stormwater conveyance with engineered floodplain reconnection). We investigated: (1) whether changes in water chemistry can be detected along longitudinal flowpaths in response to stream-floodplain reconnection, and (2) which monitoring scales across space and time can provide useful information regarding the effectiveness of restoration. Results from this work suggest that longitudinal synoptic monitoring can track the fate and transport of multiple contaminants and evaluate restoration strategies across high spatial-resolution scales. Along all five watersheds, stream water chemistry varied substantially across finer spatial scales (sometimes within hundreds of meters) in response to changes in landscapes, restoration features, or local hydrology. There were significant declining concentrations (p<0.05) or stable concentrations of nutrients, salts, and metals as streams flowed through restoration features. There were significant increasing trends in chemical concentrations (e.g. Na+, Ca2+, K+) in unrestored stream reaches with increasing impervious surface cover. Principal component analysis (PCA) also indicated that there were changes in the chemical compositions of mixtures of salts, metals, and nutrients in response to restoration projects, storm events, and seasons. Interestingly, dissolved Fe and Mn concentrations showed significant increasing trends along some stream reaches with hydrologically connected floodplains. Fe and Mn also showed significant decreasing trends along some unrestored stream reaches surrounded by increasing impervious surfaces. Increased concentrations of dissolved Fe and Mn may have been an indicator of increased hydrologic connectivity between groundwater and surface water and decreased redox potentials. Overall, longitudinal water quality changes over meters and kilometers can be useful in detecting effects of stream restoration on water quality at the watershed scale. Results suggest that water quality in urban streams can change locally in response to restoration projects for multiple chemicals, but the incremental changes associated with different forms of stream restoration and riparian conservation can also be overwhelmed across broader watershed spatial scales and during storm events.
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    Characterizing Chemical Signatures of Life via Mass Spectrometry
    (2023) Ni, Ziqin; Arevalo Jr., Ricardo; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The search for signs of life beyond Earth has been fueled by a natural curiosity about whether we are alone in the universe. Organic molecules, as the primary chemical components of terrestrial living organisms, are major targets in life detection missions. However, organic compounds have also been found in abundance in meteorites. They can be synthesized via abiotic processes such as lightning strikes, and naturally degraded with time. Searching for chemical signatures of life requires analog experiments to constrain chances of false positive detection and advancement of instrumentation to reduce possibilities of false negative measurements. The capacity to synthesize organics via abiotic mechanisms is influenced strongly by the redox condition. In this dissertation, the redox state of early Earth is estimated using trace element systematics in zircon grains. The Earth's surface is found to have reached a habitable redox condition as early as 4 billion years ago, coinciding with a time when Earth was still routinely bombarded by meteorites. Simulations of such high-speed impacts using high-power laser beams demonstrate the feasibility of synthesizing simple organic compounds from carbonates and nitrogen salts. Laboratory experiments and numerical modeling suggest that crater-forming impacts could have synthesized a considerable concentration of organics on the surface of Earth, Mars, and Ceres. The detection and characterization of organic molecules requires sophisticated analytical instrumentation. Laser desorption mass spectrometry (LDMS) and OrbitrapTM mass analysis are examples of next-generation techniques under development for conducting comprehensive chemical investigations in space. Although a combination of these two techniques enables the determination of the atomic composition of organic molecules, even complex polymers such as peptides, such an approach fails to recognize the 3D structure and sequencing of polymers. To facilitate the ionization and sequencing capability of peptides via LDMS, silicon nanoparticles are incorporated in the substrate as an alternative to conventional organic matrices but with reduced risk of forward contamination. The simultaneous measurement of mass to charge ratio and collision cross-section via Orbitrap mass analysis allows for rapid separation of organic molecules by their class, structure, and composition in sample mixtures. The techniques developed here are valuable for astrobiological exploration beyond Earth.
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    No change in ENSO hydroclimate variability after the industrial revolution as recorded in ?18O of Tectona grandis L.F. from Southeast Sulawesi, Indonesia
    (2023) Herho, Sandy Hardian Susanto; Evans, Michael MNE; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    El Niño-Southern Oscillation (ENSO) is a quasi-periodic interannual oscillation of the ocean-atmosphere system in the tropical Pacific which greatly influences global climate variability. However, the long-term response to greenhouse gas forcing is still controversial. In this study, we measured the oxygen isotopic composition of ?-cellulose samples at intraannual resolution from independently crossdated teak cores (Tectona grandis L. f.) collected at Muna, Indonesia (5.3ºS, 123ºE, elev. 10m). The site and observation has been previously shown to provide an indirect measure of ENSO activity via local precipitation amount variations associated with ENSO. We created an ensembled composite of the interannual variability for the period 1680-2005 (316 years) using empirical high pass filtering and random sampling of intra-annual resolution measurements. In processing this time series composite, we used Singular Spectrum Analysis (SSA) to high pass filter the data for the interannual variability associated with ENSO. The annually-resolved composite time series of ?18O that we constructed has a higher resolution than other studies that have been conducted to reconstruct ENSO-hydroclimate activities in the western tropical Pacific region over this period. Using this ?18O composite, we compared the distribution of events in the period before and after the industrial revolution using the two-sample Kolmogorov-Smirnov(KS) test. We found no statistically significant change in the distribution of ?18O anomalies. The same statistical test was applied to the Niño 3.4 reconstruction from the Last Millennium Reanalysis (LMR). The results of this study suggest that if there is indeed a forced response of ENSO, it is as yet indetectable. This may be because the forcing is not yet large enough or the forced response is small relative to the unforced variability. Additional factors that might explain this result in the ?18O composite include its observational and interpretational uncertainty, and in the LMR reconstruction, the scarcity of tropical observational constraints and systematic error in the representation of ENSO in climate simulations.
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    THE METAMORPHIC HISTORY OF A SUBDUCTED SLAB: NEW INSIGHTS FROM THE CATALINA SCHIST
    (2023) Taylor, Alexander Theodore; Penniston-Dorland, Sarah C.; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Rocks exhumed from ancient subduction zone interfaces often contain both coherent terranes and block-in-matrix mélanges, but the relationship between these two endmembers and its implications for underplating have not been closely examined. The Catalina Schist is a Cretaceous paleosubduction complex on Santa Catalina Island (California) that contains an amphibolite facies mélange with an underlying unit of coherent amphibolite. In this thesis, I present a metamorphic history of the coherent amphibolite that is based on field and petrographic evidence and pressure-temperature estimates from Raman elastic barometry and trace element thermometry. Rocks from the coherent amphibolite record peak metamorphic conditions of 1.20 to 1.29 GPa and 665 to 691 °C. This is consistent with several amphibolite mélange blocks, but the range of block conditions suggests that some upwards movement of the coherent amphibolite may have occurred at the subduction interface prior to the current juxtaposition of the two units.
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    MOBILIZATION OF CHEMICAL COCKTAILS BY FRESHWATER SALINIZATION SYNDROME IN THE CHESAPEAKE BAY WATERSHED
    (2023) Galella, Joseph George; Kaushal, Sujay S; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Increasing trends in base cations, pH, and salinity of urbanizing freshwaters have been documented in U.S. streams for over 50 years. These patterns, collectively known as Freshwater Salinization Syndrome (FSS), are driven by multiple processes, including applications of road salt and human-accelerated weathering of impervious surfaces, reductions in acid rain, and other anthropogenic legacies of change. FSS mobilizes chemical cocktails of distinct elemental mixtures via ion exchange, and other biogeochemical processes. Urban streams in temperate areas experience chronic salinization throughout the year punctuated by acute salinization during winter storms with associated road salting. My research analyzed impacts of FSS on stream water chemistry in the field with routine bi-weekly and targeted high frequency sampling during road salting events. Field sites were proximal to USGS stream sensors using multiparameter datasondes, allowing for additional parameters to be monitored at 5-15 minute resolution. In the laboratory incubation analyses were also conducted using sediment and water samples to assess the function of stormwater best management practices (BMPs) during road salting events. Acute FSS associated with road salting was found to mobilize chemical cocktails of metals (Mn, Cu, Sr²⁺), base cations (Na+, Ca²⁺, Mg²⁺, K⁺), nutrients (TDN), and organic matter (NPOC). Regression relationships were developed among specific conductance and major ion and trace metal concentrations. These linear relationships were statistically significant in most of the urban streams studied (e.g., R2 = 0.62 and 0.43 for Mn and Cu, respectively), and showed that specific conductance could be used as a proxy to predict concentrations of major ions and trace metals. Principal component analysis (PCA) showed co-mobilization (i.e., correlations among combinations of specific conductance, Mn, Cu, Sr²⁺, and all base cations during certain times of year and hydrologic conditions). Co-mobilization of metals and base cations was strongest during peak snow events but could continue over 24 hours after specific conductance peaked, suggesting ongoing cation exchange in soils and stream sediments. Increased salt concentrations of all three major road salts (NaCl, CaCl₂, and MgCl₂) had profound effects on major and trace element mobilization, with all three salts showing significant positive relationships across nearly all elements analyzed. Salt type showed preferential mobilization of certain elements. NaCl mobilized Cu, a potent toxicant to aquatic biota, at rates over an order of magnitude greater than both CaCl₂ and MgCl₂. Hourly mass fluxes of TDN in streams were also found to be elevated during winter months with peaks coinciding with road salting events. Targeted winter snow event sampling and high-frequency sensor data suggested plateaus in NO₃⁻ / NO₂⁻ and TDN concentrations at the highest peak levels of SC during road salt events between 1,000 and 2,000 μS/cm, which possibly indicated source limitation of TDN after extraction and mobilization of watershed nitrogen reservoirs by road salt ions. My results may help guide future regulations on road salt usage as there are currently no federally enforceable limits. NaCl is the most commonly used deicer in the United States, largely because it is often the least expensive option. Other technologies such as brines and other more efficient deicers (CaCl₂ and MgCl₂) should be considered in order to lessen the deleterious effects of FSS.
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    Thermal Control on the Location of the Volcanic Arc at Subduction Zones
    (2023) Ha, Goeun; Montesi, Laurent G.J.; Zhu, Wenlu; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    At subduction zones, where oceanic plates are recycled into the Earth’s interior, water released by the subducting plate initiates partial melts that form volcanic arcs. Partial melts can be present in a broad melting zone below a narrow volcanic arc. The second melting zone can be formed by mantle upwelling induced by active extension behind the arc and subsequent decompression melting. In this dissertation, I explain the locations of the arc in global using a temperature-dependent melt focusing mechanism. I present a simple geometrical model to explain the observed correlation between the location of the arc and the back-arc spreading center (BASC) at five subduction zones. Lastly, I discuss the thermal influence of the BASC on the arc location. The melts rise vertically through the pore spaces in the mantle rock until they encounter a low permeability barrier formed at a temperature where the crystallization rate is maximum. As the melt trajectory is deflected laterally, the melts are focused at the apex of the permeability barrier and the volcano is more likely to form immediately above the magma pool. In the subduction zones without back-arc spreading, the projection of the apex of the barrier-forming isotherm shows good agreement with the observed arc locations. The arc and the BASC location are negatively correlated with the slab dip at five subduction zones. The decoupling depth between the slab and the overlying mantle defines the closest approach of the nose of the isotherm. The horizontal distance from the trench to the decoupling depth is controlled by the slab dip, which produces the negative correlation. The back-arc extension is related to the trench retreat and the slab anchoring at 660 km discontinuity, which results in a decrease in the slab dip. The relation between the slab anchoring depth and the slab dip generates the observed negative correlation. When the BASC develops near the trench, the thermal structure is disrupted by the mantle upwelling and thereby the predicted arc location moves toward the spreading center.
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    Rapid destabilization of deep, superhydrous magma prior to the largest known Plinian eruption of Cerro Machin volcano, Colombia
    (2022) Castilla Montagut , Silvia Camila; Newcombe, Megan; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A detailed stratigraphy of the pyroclastic fall deposits associated with Cerro Machin volcano (CMV) is presented following a previously defined categorization of the different eruptive units: El Espartillal, P0, P1, El Guaico, P2 and El Anillo. For the largest Plinian eruption in the sequence (P1), two lithofacies were distinguished on the basis of sedimentary features, grain size and componentry analysis. Early stages of the eruption could have been associated with vulcanian-type phases characterized by conduit/plug clearing explosions, producing a monolithologic lithic-rich laminated basal layer. The climactic event is represented by a white to grey, clast-supported, reverse to normally graded pumice-rich lapilli layer formed by a sustained eruptive column that gradually waned towards the end of the eruption. Associated deposits were identified up to 40 km from the vent. Pumice clasts from the most explosive phase were sampled along thedeposit layer in order to characterize storage conditions and ascent rates for the magma erupted. Pumice samples were classified as medium-K, calc-alkaline dacites (63-67 wt.% SiO2). The mineral assemblage includes plagioclase+amphibole+biotite+quartz and olivine and orthopyroxene (Fo 89-92) as accessory phases with amphibole overgrowths. Geothermobarometry of unzoned amphiboles, cores of reversely zoned crystals and rims of normally zoned crystals indicate a temperature range from 825±17°C and 913±45°C, a pressure range from 270±75 MPa to 1000±320 MPa indicating crystallization depths of 8-29 km. Thermobarometry of minor populations of unzoned amphibole crystals, cores of normally zoned crystals and rims of reversely zoned amphiboles show the same crystallization pressures as the dominant amphibole populations, but higher temperatures between 850±17°C and 978±29°C. The presence of these small populations of high-temperature amphiboles suggests a minor recharge event that did not drastically change the average crystallization conditions of the main dacitic reservoir but that could have been the trigger mechanism for the explosive eruption. CMV dacites display several geochemical signatures of adakites (low Y < 14 ppm, high Sr >700ppm, high Al2O3 > 16 wt.%, low MgO < 3 wt.%) which suggest that CMV magmas are produced by fractional crystallization of primitive hydrous magmas at the Moho boundary. The primitive magmas could have been the result of the interaction between Ba-enriched fluids dehydrated from the subducted slab with mantle peridotite in the mantle wedge. Three lines of evidence support the presence of superhydrous magma (containing >~8 wt% H2O) beneath Cerro Machin: 1) water concentrations of 2–11 wt% measured in plagioclase- and quartz-hosted melt inclusions; 2) the presence of Fo89-92 olivine rimmed by high Mg# amphibole; and 3) measurements of ~100–167 ppm H2O in plagioclase phenocrysts. Assuming a partition coefficient of 0.002, measured plagioclase crystals crystallized in a melt with 5-8 wt% H2O. Water-diffusion modelling in plagioclase crystals indicates a minimum time of 1 day for the magma to ascend from shallow depth (<250 MPa, ~5 km) before the eruption. Rapid ascent times are also suggested by the absence of breakdown rims in amphibole crystals which indicate a magma ascent timescale of <4 days from 8 km to the surface (Rutherford & Hill, 1993). Results from this study indicate that the 3600 yr BP eruption was preceded by rapid mobilization and ascent of superhydrous dacitic magma from mid- to deep-crustal storage regions beneath Cerro Machin. This thesis comprises eight appendices (A-H), Appendix A contains fieldwork information including: map of locations, a description of sample labels and schematic stratigraphic columns. In Appendix B, descriptions of componentry analysis are presented as well as pictures of the different grains identified under binocular observations. Appendix C is conformed by ten petrographic forms in which petrographic observations are detailed. This is followed by Appendix D in which whole rock chemistry of five samples is listed. In Appendix E, water measurements in melt inclusions are presented. In Appendix F, measurements of water in feldspar are detailed while in Appendix G, glass, melt inclusions, mineral chemistry and pictures of each crystal are presented, it also contains plagioclase-melt and amphibole-melt equilibrium tests and geothermobarometry calculations. Finally, Appendix H contains the link with the repository of the Matlab code used for volatile diffusion modelling in feldspar.
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    Freshwater salinization syndrome limits management efforts to improve water quality
    (2022) Maas, Carly Marcella; Kaushal, Sujay S; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Freshwater Salinization Syndrome (FSS) refers to the interactive effects of salt ions on the degradation of the natural, built, and social systems. FSS can mobilize chemical mixtures, termed ‘chemical cocktails’, in watersheds. The formation of chemical cocktails across space and time depends on the amounts and types of salt pollution, the surrounding land use including conservation and restoration areas, and the location along the flowpath in the watershed. We investigated (1) the formation of chemical cocktails temporally and spatially and (2) the natural capacity of watersheds and streams to attenuate salt ions along flowpaths with conservation and restoration efforts. We monitored high-frequency temporal and longitudinal spatial chemical changes in stream water in response to different pollution events (i.e., road salt, stormwater runoff, wastewater effluent, and baseflow conditions) and several types of watershed management efforts (i.e., national parks, regional parks, and floodplain reconnection) in six urban watersheds in the Chesapeake Bay region. There were significant relationships between watershed impervious surface cover and mean concentrations of salt ions (Ca2+, K+, Mg2+), metals (Fe, Mn, Sr2+), and nutrients (total dissolved nitrogen) (p < 0.05). Principal component analysis (PCA) indicates that chemical cocktails which formed along flowpaths in response to winter road salt applications were enriched in salts and metals (e.g., Na+, Mn, and Cu). During most baseflow and stormflow conditions, chemical cocktails that were less enriched in salt ions and trace metals were attenuated downstream. There was also downstream attenuation of FSS ions during baseflow conditions through management efforts including a regional park, national park, and floodplain restoration. Conversely, chemical cocktails that formed in response to multiple road salt applications or prolonged road salt exposure did not show patterns of attenuation downstream. The spatial patterns were quite variable, with increasing, plateauing, or decreasing patterns based on the magnitude, timing, duration of road salt loading, and extent of management efforts. Our results suggest that FSS can mobilize multiple contaminants along watershed flowpaths, however, the capacity of current watershed management strategies such as restoration and conservation areas to attenuate FSS is limited.
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    GENETICS, AGES, AND CHEMICAL COMPOSITIONS OF THE GROUP IIIE IRON METEORITES AND THE IRON METEORITE LIEKSA
    (2022) Chiappe, Emily; Walker, Richard; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Siderophile element concentrations, genetic isotopic data, and chronological data for ten group IIIE iron meteorites and the recently found iron meteorite Lieksa were determined. The modeling of siderophile element abundances shows that the IIIE irons can be related to one another through a common fractional crystallization process. Highly siderophile element data, however, indicate that the anomalous IIIE iron meteorite Aletai does not sample the same crystallization sequence as the bona fide IIIE irons. The bulk chemical characteristics of Lieksa are distinct from that of the established iron meteorite groups, indicating that, if it is an iron meteorite, it should be classified as an ungrouped iron meteorite. Isotopic data shows that, while the IIIE iron meteorites, Lieksa, and Aletai exhibit different HSE abundances, they exhibit similar genetic characteristics, indicating that they likely originated from the same nebular reservoir. Additionally, isotopic data indicate that all irons analyzed here sample parent bodies that differentiated within the first ~2 Myr of solar system history, which is consistent with other NC-type bodies.
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    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.
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    Deciphering Core Records of Carbon and Nitrogen in Typha-Dominated Freshwater Wetlands
    (2022) Ravi, Rumya; Prestegaard, Karen; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    I conducted decomposition experiments and examined soil characteristics in restored and natural freshwater marsh platform sites to decipher core records of soil C and N. Carbon loss rates and changes in ẟ13C and ẟ15N were obtained from decomposition experiments. Core samples at each site were analyzed for bulk density, weight %C, %N, ẟ13C, and ẟ15N. Typha C loss rates were similar among sites, and there was little change in ẟ13C composition, suggesting that DOC leaching is significant. Core carbon storage is higher in natural wetland sites. Initial Typha %N and ẟ15N reflect local N concentrations and sources to each wetland. ẟ15N increases between decomposed vegetation and upper cores in the tidal wetlands, possibly indicating denitrification. In N-rich wetlands, core %N and ẟ15N reflect differences in N sources and changes in N sources over time. In a wetland limited by N transport, core %N and ẟ15N may reflect vegetation N uptake.
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    ASSESSING FAULT SLIP HAZARD IN TAIWAN USING SPACE GEODESY
    (2022) Robbins, Kathryn Rose; Huang, Mong-Han; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Taiwan is a geologically complex region due to the continuous collision of the Eurasian Plate and the Philippine Sea Plate. This study aimed to quantify the interseismic crustal deformation of Taiwan and detail the island’s seismic hazard potential using space geodesy. Data were collected between 2016 and 2021 through C-band Copernicus Sentinel-1 synthetic aperture radar imagery and continuous GNSS data from Academia Sinica, Taiwan. I excluded major earthquake events within this time period and generated a dataset consisting of interferometric synthetic aperture radar ground motion velocities with GNSS corrections and interpolated GNSS ground motion velocities. Then, utilizing this dataset, I performed a deformation rate analysis and error analysis. Next, I explored block modeling and used a total variation regularization approach to determine the reference block model that best reduced velocity residuals and minimized the number of independently rotating blocks. Results suggested that the Taipei Basin, Ilan Basin, Western Foothills, and Longitudinal Valley were experiencing increased total strain rate accumulation and, therefore, posed increased seismic hazard.
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    Earth's Radiogenic Heat Production and the Composition of the Deep Continental Crust
    (2022) Sammon, Laura Grace; McDonough, William F; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Much of the continental crust, the 40+ km thick plates of rock that make up the outer shell of our planet, is inaccessible to us living on its surface. Thus its composition is a mystery. We lack the technology to sample it directly at depths past 5 km, aside from a few deep (expensive) drill holes, so we must come up with a clever alternative for establishing its composition. The deep crust, the lower two-thirds of the continent, serves as a supporting root. When continents collide, they make mountain ranges, or when pulled apart they make rift valleys and basins. The composition of the deep crust, and specifically its silica, molecular water, and heat producing element (HPE: K, Th, U) contents, directly influence the crust's rheology during tectonic events and its potential for deadly earthquakes. Its chemical makeup is the sum of 4.5 billion years of crustal evolutionary processes that continuously shape and reshape the platform upon which society sits. An accurate description of the deep crust, however, requires careful integration of many different data sources. My research combines geochemistry with thermodynamics, geophysics, mineral-physics, seismology, and even particle physics to produce self-consistent models for the crust’s composition. Using thermodynamic calculations, I generate densities and seismic sound wave speeds from a range of chemical compositions. Matching these forecasted models to Earth’s seismic and gravity data allows me to translate the deep crust's physical properties into chemical compositions on both the regional and the global scale. Importantly, by quantifying not only the compositions, but also the uncertainties and the misfit in these results, I can better define the differences between competing models for crust deformation and evolution. Charting the distribution of Earth's geochemical resources has led to our collaborations with particle physicists, who need our expertise to determine the frequency of radioactive decay and therefore the amount of HPE decay emissions (known as geoneutrinos) in the crust; this geoneutrino flux is the background signal in their nuclear physics experiments. Their global flux measurements constrain our models for heat production and the amount of radiogenic energy that heats the Earth – which provides power to mantle convection, plate tectonics, and the destruction and creation of more continental crust.Our main sources of data are threefold. First, we have critically compiled geochemical analyses of >10,000 rock samples from pre-existing literature (Earthchem.org and affiliates). Second, we use geophysical data provided by sources such as the United States Geological Survey, the Earthscope USArray, and others to determine which of our geochemical samples could produce Earth’s observed seismic and density signals. Third, we partner with particle physicists in the United States, Canada, Italy, Japan, and China to jointly interpret data from three international geoneutrino detectors. By focusing on Earth as a whole system we seek a comprehensive understanding of its natural hazards and resources. Using multidisciplinary constraints, my goal is to build compositional models of the continental crust, with quantifiable uncertainties, that can be applied regionally and at larger scales. These findings will provide predictive insights on the strength and response of the continents when subjected to the dynamic processes of plate tectonics.
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    ANALYZING TIME-VARYING SEISMICITY AND AFTERSHOCK BEHAVIOR IN CENTRAL AND EASTERN UNITED STATES
    (2021) Pearson, Karen M; Lekic, Vedran; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Central and Eastern United States (CEUS) earthquakes are far less common than those in the tectonically active west coast, but the significance is elevated for a few reasons. Due to older, harder, and often denser rocks making up the bedrock geology east of the Rockies, seismic waves can travel much further without losing energy. Poor construction, efficient transmission of seismic waves, and site amplification effects can make even light to moderate earthquakes pose high risk within the CEUS. The CEUS has significant aging infrastructure and some of the highest population densities in the country, which would lead to great economic losses and even the potential for human injury if hazards are not properly identified and communicated. Aftershock sequences are governed by several descriptive statistical “laws,” each with one or more characteristic parameters. These parameters are used to illustrate factors such as the overall productivity, the rate of decay, and the relative frequency of larger and smaller magnitude aftershocks. Variations in these parameters can relate to the geologic region being studied, the tectonic environment, the driving force of seismicity (i.e. induced earthquakes, volcanic, or geothermal-related), and more. This work discusses the aftershock sequences of two unusual CEUS earthquakes from the past five years. The first earthquake I study is a M4.2 earthquake that occurred east of Dover, DE, in late 2017. I continue by studying the aftershocks in the six weeks following a M5.8 earthquake that occurred near Pawnee, OK, in autumn 2016. Both of these earthquakes experienced below-normal aftershock productivities. I explore the challenges of analysis when station coverage is heterogeneous for the period of aftershock analysis. From there, I discuss the limitations of some statistical tests for special cases such as aftershock decay. The work concludes by highlighting additional CEUS earthquakes exceeding M4 that have occurred in the past 20 years and discussing some preliminary analytical findings.
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    Petrologic, Geochemical, and Spectral Characteristics of Oxidized Planetary Differentiation
    (2021) Crossley, Samuel Dean; Sunshine, Jessica M; Ash, Richard D; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Meteorites provide evidence that planetary formation occurred across a wide range of oxidation environments in the early Solar System. While the process of differentiation for many reduced, oxygen-poor assemblages has been thoroughly explored, significantly less is known about how differentiation occurred in more oxidized regions of the Solar System. Results from petrologic and geochemical investigations of oxidized chondrites (Rumurutiites) and primitive achondrites (brachinites) reveal that significant mineralogic differences occur with increasing degrees of oxidation. As a consequence, the differentiation pathways of oxidized and reduced assemblages diverge during the earliest stages of partial melting. While reduced materials differentiate to form a basaltic crust, magnesian peridotite mantle, and metallic core, oxidized materials may instead form felsic crusts, ferroan peridotite mantles, and sulfide-dominated cores. These pathways are evident in distinct siderophile trace element systematics for oxidized and reduced endmembers of the brachinite meteorite family. The compositions of olivine between oxidation endmembers are resolvable using remote sensing techniques that are applicable to asteroids. Most olivine-dominated asteroids examined in this work are consistent with having formed in oxidized environments, similar to R chondrites and brachinites, or in even more oxidizing environments not recorded among the meteoritic record. This provides strong evidence that environments capable of supporting oxidized, sulfide-dominated core formation are widespread among asteroidal materials. Several of these asteroids are likely mantle restites, based on their olivine composition and the estimated abundances of pyroxene. The predominance of oxidized over reduced environments among olivine-dominated asteroids is likely related to their respective petrogenetic histories: reduced assemblages must reach and sustain much higher temperatures to fully melt and segregate their pyroxene contents from olivine, which requires larger and earlier-accreted parent bodies. Consequently, sampling reduced mantle restites without significant pyroxene contamination would require catastrophic parent body destruction without mixing crustal and mantle materials. Oxidized materials, in contrast, have much higher initial olivine/pyroxene ratios, and thus are much more prone to producing asteroids dominated by olivine.
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    A prototype miniature mass spectrometer for in situ analysis of trace elements on planetary surfaces
    (2021) Farcy, Benjamin Jacob; Arevalo, Ricardo D; McDonough, William F; Geology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Interrogation of the chemical composition of rocky planets provides a deeper understanding of the history and evolution of the solar system. While laboratory studies of returned samples and remote sensing surveys of planetary surfaces can give insight into planetary history, one technique that has delivered major insights to planetary geology is in situ measurements of a planetary surface via mass spectrometry. Here, a new approach to spaceflight mass spectrometry is discussed, including an overview of the pursued scientific questions, the analytes targeted, and the prototype hardware in development. This effort constitutes the scientific and technological foundation of a landed planetary mission. This dissertation focuses on the history and evolution of the Earth-Moon system as recorded by trace elements. Specifically, the abundance and distribution of the heat producing elements (HPEs: K, Th, U) and their implications for mantle dynamics is considered. The radiogenic heat produced from K, Th, and U drives mantle convection, volcanism, and planetary dynamos. To understand better the chemical dynamics of radiogenic heat distribution in the Earth, the HPE abundance of a series of oceanic basalts was statistically analyzed. This analysis revealed the K/U ratio of the mantle and how it changes due to the enrichment or depletion of incompatible elements. The HPE abundance of the lunar interior was also discussed as a target of a future investigation, along with a series of trace element proxies meant to probe the lunar farside mantle. Further, an analysis of lunar farside craters provides a series of landing sites for an in situ mission, specifically for their surficial exposure of upper mantle material and later emplacement of lunar basalts. To access the trace element systems discussed in this dissertation, a prototype miniature inductively coupled plasma mass spectrometer (ICPMS) was developed to analyze trace elements in situ for landed planetary missions. First, the capability of the plasma to atomize and ionize input material was investigated. A plasma operating at reduced pressure can achieve 99\% ionization efficiency of most elements on the periodic table, with as much as a 50 to 100 times reduction in gas load and forward power compared to commercial systems for both He and Ar based plasma ion sources. The plasma system was integrated with a quadrupole mass spectrometer via a series of DC ion optics and vacuum housing, with its ion current and peak resolution optimized. Quantative data for an analyte spectrum of Kr demonstrates the ability for this instrument to resolve individual mass peaks, which lead to an accuracy and precision measurement of isotope ratios. This effort represents an end-to-end prototype miniature ICPMS, successfully demonstrating a viable instrument for landed planetary missions.