Browsing by Author "Hansen, Samantha E."
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Item Are the mantle lithosphere and lower crust preferentially thinned during continental rifting?(University of Alabama Libraries, 2018) Tew, Kalyn J.; Goodliffe, Andrew M.; University of Alabama TuscaloosaWorldwide, estimates of extension in rift zones vary greatly depending on the method used to calculate the extension. This variability is the result of the discrepancy between different methodologies and may be the result of polyphase faulting, subresolution faulting, and/or depth-dependent extension. Such inconsistency between estimates has been noted in the Woodlark Basin, an active transition zone between continental rifting and seafloor spreading. Previous work in the basin, where seafloor spreading has not initiated, calculated extension by summing fault heaves, calculating subsidence, and determining plate motion from Euler pole kinematics, yielding estimates of 111 km (23) from brittle extension, 115 km (47) from subsidence, and 200 km (40) from Euler pole kinematics (Kington and Goodliffe, 2008). By incorporating polyphase and subresolution faulting into the brittle extension estimate, Kington and Goodliffe (2008) resolved the discrepancy between estimates of extension derived from brittle faulting and subsidence. The third method used to estimate extension, Euler pole kinematics, produced a large discrepancy. Kington and Goodliffe (2008) interpreted this to be the result of preferential extension of the lower crust and mantle lithosphere during the rifting phase and proposed that uniform extension would occur throughout the lithosphere after seafloor spreading initiation. The current study explores potential errors in previous work in the basin and determines if the results are applicable to other portions of the basin. In contrast to Kington and Goodliffe (2008), the current study determines extension where seafloor spreading initiated at ~0.8 Ma. Using the methods and associated errors from Kington and Goodliffe (2008), Euler pole extension estimates (~202 to 238 km) are ~2 times higher than brittle (~69 to 90 km) and subsidence (~60 to 79 km) extension estimates, consistent with the previously seen discrepancy. When taking into account other sources of error not considered by Kington and Goodliffe (2008), the current study shows the previous methods lack the constraints necessary to produce conclusive results. This would also render the results of the previous study by Kington and Goodliffe (2008) inconclusive. Therefore, it is not necessary to invoke the Kington and Goodliffe (2008) model to explain rifting in the western Woodlark Basin.Item Crustal structure beneath the Northern Transantarctic Mountains and Wilkes Subglacial Basin: Implications for tectonic origins(American Geophysical Union, 2016-02-13) Hansen, Samantha E.; Kenyon, Lindsey M.; Graw, Jordan H.; Park, Yongcheol; Nyblade, Andrew A.; University of Alabama Tuscaloosa; Korea Institute of Ocean Science & Technology (KIOST); Korea Polar Research Institute (KOPRI); Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University ParkThe Transantarctic Mountains (TAMs) are the largest noncollisional mountain range on Earth. Their origin, as well as the origin of the Wilkes Subglacial Basin (WSB) along the inland side of the TAMs, has been widely debated, and a key constraint to distinguish between competing models is the underlying crustal structure. Previous investigations have examined this structure but have primarily focused on a small region of the central TAMs near Ross Island, providing little along-strike constraint. In this study, we use data from the new Transantarctic Mountains Northern Network and from five stations operated by the Korea Polar Research Institute to investigate the crustal structure beneath a previously unexplored portion of the TAMs. Using S wave receiver functions and Rayleigh wave phase velocities, crustal thickness and average crustal shear velocity ((V)overbar(s)) are resolved within 4km and 0.1km/s, respectively. The crust thickens from similar to 20km near the Ross Sea coast to similar to 46km beneath the northern TAMs, which is somewhat thicker than that imaged in previous studies beneath the central TAMs. The crust thins to similar to 41km beneath the WSB. (V)overbar(s) ranges from similar to 3.1-3.9km/s, with slower velocities near the coast. Our findings are consistent with a flexural origin for the TAMs and WSB, where these features result from broad flexure of the East Antarctic lithosphere and uplift along its western edge due to thermal conduction from hotter mantle beneath West Antarctica. Locally, thicker crust may explain the similar to 1km of additional topography in the northern TAMs compared to the central TAMs.Item Determining crustal thickness beneath the Transantarctic Mountains and the Wilkes Subglacial Basin using S-wave receiver functions(University of Alabama Libraries, 2014) Kenyon, Lindsey M.; Hansen, Samantha E.; University of Alabama TuscaloosaThe Transantarctic Mountains (TAMs) are a ~4,000 km long mountain range, with elevations up to 4,500 m, which separate East and West Antarctica. Given the lack of compressional structures in the TAMs, the origin for these mountains is unclear, and many possible uplift mechanisms have been suggested. The formation of the Wilkes Subglacial Basin (WSB), which is situated inland and parallel to the TAMs, has also been widely debated. A key characteristic to distinguish between different origin models for the TAMs and the WSB is the thickness of the crust beneath these areas. A new 15-station seismic array deployed in the northern TAMs, called the Transantarctic Mountains Northern Network (TAMNNET), as well as 5 stations operated by the Korean Polar Research Institute (KOPRI), are used to investigate the crustal structure beneath a previously unexplored portion of the TAMs and the WSB. Data from the combined TAMNNET and KOPRI networks are analyzed using S-wave receiver functions (SRFs) to estimate the crustal thicknesses. Using both the timing of the conversion from the crust-mantle interface obtained with the SRFs and Rayleigh wave phase velocities, a grid search procedure is used to determine the crustal thickness and velocity beneath each station. Results indicate that the crust is 12-27 km thick near the Ross Sea coast, increasing to a maximum thickness of ~47 km beneath some portions of the TAMs. Further inland, beneath the East Antarctic craton and the WSB, the crust has an average thickness of ~42 km. Average crustal S-wave velocities range from 3.3-3.8 km/s, with the slowest velocities near the coast. These results support a flexural origin model, which jointly explains the uplift of the TAMs and the down-warp of the WSB. Small variations in the crustal thickness may contribute to locally high topography, but crustal isostasy does not appear to play a major role in the overall support of the TAMs.Item Determining the upper mantle seismic structure beneath the northern transantarctic mountains, Antarctica, form regional p- and s-wave tomography(University of Alabama Libraries, 2016) Brenn, Gregory; Hansen, Samantha E.; University of Alabama TuscaloosaStretching ~3,500 km across Antarctica, with peak elevations up to 4,500 m, the Transantarctic Mountains (TAMs) are the largest non-compressional continental mountain range on Earth and represent a tectonic boundary between the East Antarctica (EA) craton and the West Antarctic Rift System. The origin and uplift mechanism associated with the TAMs is controversial, and multiple models have been proposed. Seismic investigations of the TAM’s subsurface structure can provide key constraints to help evaluate these models, but previous studies have been primarily focused only on the central TAMs near Ross Island. Using data from the new 15-station Transantarctic Mountain Northern Network as well as data from several smaller networks, this study investigates the upper mantle velocity structure beneath a previously unexplored portion of the northern TAMs through regional body wave tomography. Relative travel-times were calculated for 11,182 P-wave and 8,285 S-wave arrivals from 790 and 581 Mw ≥ 5.5 events, respectively, using multi-channel cross correlation, and these data were then inverted for models of the upper mantle seismic structure. Resulting P- and S-wave tomography images reveal two focused low velocity anomalies beneath Ross Island (RI; δVP ≈ -2.0%; δVS ≈ -1.5% to -4.0%) and Terra Nova Bay (TNB; δVP ≈ -1.5% to -2.0%; δVS ≈ -1.0% to -4.0%) that extend to depths of ~200 and ~150 km, respectively. The RI and TNB slow anomalies also extend ~50-100 km laterally beneath the TAMs front and sharply abut fast velocities beneath the EA craton (δVP ≈ 0.5% to 2%; δVS ≈ 1.5% to 4.0%). A low velocity region (δVP ≈ -1.5%), centered at ~150 km depth beneath the Terror Rift (TR) and primarily constrained within the Victoria Land Basin, connects the RI and TNB anomalies. The focused low velocities are interpreted as regions of partial melt and buoyancy-driven upwelling, connected by a broad region of slow (presumably warm) upper mantle associated with Cenozoic extension along the TR. Dynamic topography estimates based on the imaged S-wave velocity perturbations are consistent with observed surface topography in the central and northern TAMs, thereby providing support for uplift models that advocate for thermal loading and a flexural origin for the mountain range.Item Double-Array Stacking of Pcp Waveforms: an Application to the Investigation of Ultra-Low Velocity Zones (ULVZs) in the Southern Hemisphere(University of Alabama Libraries, 2023) Agboola, Kayode Johnson; Hansen, Samantha E.Ultra-low velocity zones (ULVZs) are one of the most anomalous features in the Earth's interior. Located just above the core-mantle boundary (CMB), ULVZs are generally associated with decreased seismic velocities and increased density compared to the surrounding mantle; however, previously reported ULVZ properties span a wide range of values, which has made ULVZ origins a topic of debate. Limited seismic sampling of the Earth's lowermost mantle, especially beneath the southern hemisphere, further compounds the uncertainties associated with ULVZs. In this study, I examine core-reflected PcP waveforms recorded by stations in Antarctica to investigate ULVZs beneath the southern hemisphere. The Historical Interstation Pattern Referencing approach is applied to generate event and station weights, which are then incorporated into a double-array stacking procedure to generate high quality PcP waveform stacks. If a ULVZ is present, pre-cursory PcP signals caused by reflections from the mantle-ULVZ interface are expected. Such signals are further characterized using 1-D synthetic modeling, though in some cases, multiple pre-cursory signals are observed, which may indicate more complex ULVZs. My results show that there is widespread ULVZ structure with variable thickness across the southern hemisphere. Given that the study region is not located in a particularly hot portion of the lowermost mantle, the results support a compositional origin for the ULVZs. One plausible explanation is that the ULVZs are associated with accumulations of subducted materials in the lowermost mantle. Their variable thickness may result from mantle flow advecting the subducted materials along the CMB, thereby leading to different concentrations. More complex ULVZs could also be associated with localized regions of partial melt. My finding could also indicate that ULVZs are ubiquitous along the CMB and that areas where ULVZs were not imaged by prior studies might denote locations where the ULVZ thickness is lower than seismic detection thresholds.Item Estimating nonlinear source parameters of volcano deformation: an application of FEM-based inverse methods and InSAR(University of Alabama Libraries, 2011) Stone, Jonathan; Masterlark, Timothy; University of Alabama TuscaloosaMigration of magma within an active volcano produces a deformation signature at the Earth's surface. The internal structure of a volcano and specific movements of the magma control the actual deformation that is observed. Relatively simple models that simulate magma injection as a pressurized body embedded in a homogeneous elastic half-space (e.g., Mogi) can predict the characteristic radially-symmetric deformation patterns that are commonly observed for episodes of volcano inflation or deflation. Inverse methods, based on half-space models, can precisely and efficiently estimate the non-linear parameters that describe the geometry (position and shape) of the deformation source, as well as the linear parameter that describes the strength (pressure) of the deformation source. However, although such models can accurately predict the observed deformation, actual volcanoes have internal structures that are not compatible with the elastic half-space assumptions inherent to Mogi-type models. This incompatibility translates to errors in source parameter estimations. Alternatively, Finite Element Models (FEMs) can simulate a pressurized body embedded in a problem domain having an arbitrary distribution of material properties that better corresponds to the internal structure of an active volcano. FEMs can be used in inverse methods for estimating linear deformation source parameters, such as the source pressure. However, perturbations of the non-linear parameters that describe the geometry of the source require automated re-meshing of the problem domain - a significant obstacle to implementing FEM-based nonlinear inverse methods in volcano deformation studies. I present a parametric executable (C++ source code), which automatically generates FEMs that simulate a pressurized ellipsoid embedded in an axisymmetric problem domain, having an a priori distribution of material properties. I demonstrate this executable by analyzing Interferometric Synthetic Aperture Radar (InSAR) deformation data of the 1997 eruption of Okmok Volcano, Alaska as an example. This executable facilitates an inverse analysis that estimates the non-linear parameters that describe the depth and radius of the spherical source, as well as the linear strength parameter that best accounts for the InSAR data. The strong radial symmetry and high signal-to-noise ratio of the InSAR data, along with known seismic tomography data, provide robust constraints for estimated parameters and sensitivity analyses.Item Exploring Girl Scouts' self-perceptions as geoscientists using a feminist standpoint lens and transformative mixed methods(University of Alabama Libraries, 2015) Renz, Heather Fowler; Nichols, Sharon E.; Goldston, M. Jenice; University of Alabama TuscaloosaCurrently in the United States jobs abound in science, technology, engineering and math (STEM). Yet, women remain an underrepresented demographic both in university STEM degrees and careers. This study sought to understand constraints to the participation of young women in geoscience learning. Twenty-one girls in the sixth through eighth grades participated in a six-week study, which featured informal geoscience experiences. Three research questions guided the study: (1) What are girls' standpoints on "science"? (2) How might the Girl Scouts offer an alternative environment for learning and doing science while at the same time allowing them to be scientists? (3) How might this Girl Scout experience transform the ways girls engage with geoscience? The study employed a transformative mixed method approach involving quantitative and qualitative data generation tools including the CLES, the DAST, autobiographical writing, photonarratives, and researcher analytic memos. The study results are reported through three key phases of data generation. Phase 1 categorizes the girls as those having positive, negative and neutral science perceptions. Phase 2 explores the girls underlying science stories. Phase 3 highlights the girls' transformative narratives. Results of this study contribute significant insights about the subtle stances of young girls in [geo]science learning and how engaging their voices to critique their science learning experiences can open up their agentic possibilities to take up participation in science.Item A geophysical characterization of stratigraphy in the Eastern Black Warrior Basin underlying Gorgas Power Generation Plant, Walker County, Alabama(University of Alabama Libraries, 2012) Rutter, Rachael S.; Goodliffe, Andrew M.; University of Alabama TuscaloosaThe Black Warrior Basin is a triangular shaped foreland basin located in the southeastern United States between the Appalachian and Ouachita fold and thrust belts. The basin has the potential to provide geologic carbon sinks into multiple stacked saline reservoirs over a large area. CO_2 storage potential of saline aquifers and oil and gas reservoirs in the Black Warrior Basin has yet to be fully assessed. This study evaluates saline reservoirs on the eastern edge of the basin underlying William C. Gorgas Power Plant (Plant Gorgas), Walker County, Alabama. Key reservoirs include the Pennsylvanian Boyles Sandstone, the Mississippian Hartselle Sandstone and Tuscumbia Limestone, and the Ordovician Stones River Group. Data include two post-stack time-migrated seismic reflection profiles, geophysical logs collected in a 1498 m (4915 ft) stratigraphic test well, and a zero-offset vertical seismic profile (ZVSP). Interpretations of key seismic reflectors in the Black Warrior Basin are presented based on a synthetic seismogram, check-shots, a zero-offset VSP, and a well-constrained well-seismic tie. Units in the velocity model are based on lithologic boundaries interpreted as seismic horizons and well tops. An investigation of geologic structures and the lateral extent of saline aquifers in the area surrounding Plant Gorgas is based on depth converted seismic data. Volumetric calculations for the Boyles and Hartselle sandstones, and the Tuscumbia and Stones River Group limestones were calculated to demonstrate the potential to store substantial amounts of carbon dioxide in the Black Warrior Basin. The volumetric estimations that are listed below show the effects of injecting 10% of Plant Gorgas's emissions (0.75 Megatons of CO_2 /year) over a thirty-year period. The Lower Boyles Sandstone CO_2 plume would extend to a radius of 3.6 km (2.25 miles) ± 0.22 km (0.14 miles) around the borehole; 5.2 km (3.23 miles) ± 0.35 km (0.22 miles) in the Hartselle Sandstone; 4.7 km (2.92 miles) ± 0.07 km (0.04 miles) in the Tuscumbia Limestone; and 7.2 km (4.47 miles) ± 0.065 km (0.04 miles) in the Stones River Formation.Item Globally distributed subducted materials along the Earth's core-mantle boundary: Implications for ultralow velocity zones(American Association for the Advancement of Science, 2023) Hansen, Samantha E.; Garnero, Edward J.; Li, Mingming; Shim, Sang-Heon; Rost, Sebastian; University of Alabama Tuscaloosa; Arizona State University; Arizona State University-Tempe; University of LeedsUltralow velocity zones (ULVZs) are the most anomalous structures within the Earth's interior; however, given the wide range of associated characteristics (thickness and composition) reported by previous studies, the origins of ULVZs have been debated for decades. Using a recently developed seismic analysis approach, we find widespread, variable ULVZs along the core-mantle boundary (CMB) beneath a largely unsampled portion of the Southern Hemisphere. Our study region is not beneath current or recent subduction zones, but our mantle convection simulations demonstrate how heterogeneous accumulations of previously subducted materials could form on the CMB and explain our seismic observations. We further show that subducted materials can be globally distributed throughout the lowermost mantle with variable concentrations. These subducted materials, advected along the CMB, can provide an explanation for the distribution and range of reported ULVZ properties.Item Investigating the P wave velocity structure beneath Harrat Lunayyir, northwestern Saudi Arabia, using double-difference tomography and earthquakes from the 2009 seismic swarm(American Geophysical Union, 2013-09-12) Hansen, Samantha E.; DeShon, Heather R.; Moore-Driskell, Melissa M.; Al-Amri, Abdullah M. S.; University of Alabama Tuscaloosa; Southern Methodist University; King Saud UniversityIn 2009, a swarm of more than 30,000 earthquakes occurred beneath the Harrat Lunayyir lava field in northwest Saudi Arabia. This event was just one of several seismic swarms to occur in this region over the past decade. Surface deformation associated with the seismicity, modeled in previous studies using Interferometric Synthetic Aperture Radar (InSAR) data, is best attributed to the intrusion of a 10kmlong dyke. However, little is known about the velocity structure beneath Harrat Lunayyir, making assessment of future seismic and volcanic hazards difficult. In this study, we use local double-difference tomography to generate a P wave velocity model beneath Harrat Lunayyir and to more precisely locate earthquakes from the 2009 seismic swarm. A pronounced fast velocity anomaly, centered at similar to 15km depth with a shallower extension to the N-NW, is interpreted as an area of repeated magmatic intrusion. The crust surrounding the fast intrusion is slower than that suggested by broader-scale models for the Arabian Shield. The largest magnitude events occurred early in the swarm, concentrated at shallow depths (similar to 2-8km) beneath northern Harrat Lunayyir, and these events are associated with the dyke intrusion. Later, deep earthquakes (similar to 15km) beneath the southern end of the study region as well as a group of intermediate-depth events connecting the shallow and deep regions of seismicity occurred. These later events likely represent responses to the local stress conditions following the intrusion. Our results are unique since harrat magma systems are rarely imaged, and our observations, coupled with the seismic history in this region, suggest that future volcanic intrusions beneath Harrat Lunayyir are likely.Item Investigating ultra-low velocity zones at the core-mantle boundary beneath the Southern Hemisphere using an Antarctic dataset(University of Alabama Libraries, 2018) Carson, Sarah; Hansen, Samantha E.; University of Alabama TuscaloosaThe core-mantle boundary (CMB) represents the largest absolute density contrast on our planet, and it is associated with significant heterogeneities. The CMB structure focused on in this study are ultra-low velocity zones (ULVZs), laterally-varying, 5-50 km thick isolated patches seen in some locations just above the CMB that are associated with increased density and reduced seismic wave velocities. The variable characteristics associated with ULVZs have led to many questions regarding their origins, but only about 17% of the CMB has been surveyed for the presence of ULVZs given limited seismic coverage of the lowermost mantle. Therefore, investigations that sample the CMB with new geometries are critical to further our understanding of ULVZs and their potential connection to other deep Earth processes. The Transantarctic Mountains Northern Network (TAMNNET), a 15-station seismic array that was deployed in Antarctica from 2012-2015, provides a unique dataset to further study ULVZ structure with new and unique path geometry. Core-reflected ScP phases recorded by TAMNNET well sample the CMB in the vicinity of New Zealand in the southwestern Pacific, providing coverage between an area to the northeast where ULVZ structure has been previously identified and another region to the south, where ULVZ evidence is inconclusive. This area is of particular interest because the data sample across the boundary of the Pacific Large Low Shear Velocity Province (LLSVP). The Weddell Sea region near Antarctica is also well sampled in this study, providing new information on this area that has not been previously studied. By identifying and modeling energy associated with the ScP waveform, new portions of the CMB have been explored and evidence for ULVZs in both regions has been found. A correlative scheme between 1-D synthetic seismograms and observed data demonstrate that ULVZs are required in the study regions, but modeling uncertainties limit the ability to definitively define ULVZ characteristics. Given that ULVZs are detected within, along the edge of, and far from the Pacific LLSVP, the results support the hypothesis that ULVZs are compositionally distinct from the surrounding mantle, and thus may be ubiquitous along the CMB; however, they may be thinner than can be resolved by seismic detection in some locations. Mantle convection currents may sweep the ULVZs into thicker piles in some areas and may push these anomalies toward the boundaries of LLSVPs.Item Nonmarine stratigraphic successions in the Yidun Terrane: a record of Mesozoic and early Cenozoic deformation and deposition in the Eastern Tibetan Plateau(University of Alabama Libraries, 2017) Jackson, William Thomas; Robinson, D. M.; University of Alabama TuscaloosaThe Tibetan Plateau is the largest and highest plateau on Earth, covering > 2,500,000 km2 with an average elevation > 4,500 m. The plateau’s present crustal configuration is a product of the Early Cenozoic India-Asia collision as well as similar Mesozoic collisions along the southern margin of Eurasia. The spatial and temporal relationship of Mesozoic and Early Cenozoic deformation resulting from collisions are required parameters to advance understanding of the plateau’s rise and outgrowth evolution. Nonmarine strata in interior parts of the plateau provide records of this deformation; however, in the eastern Tibetan Plateau these strata remain unexplored. This dissertation presents structural and sedimentological field data, detrital zircon U-Pb geochronology and Hf isotope geochemistry, as well as petrology data from the Mula basin, west Ganzi basin, east Ganzi basin, and Ganzi-Litang suture to determine the stratigraphic age, sedimentary provenance, and tectonic setting of the nonmarine strata in the Yidun terrane, eastern Tibetan Plateau. Weighted mean averages from the youngest detrital zircon age populations suggest that the Mula basin and nonmarine strata in the Ganzi-Litang suture are Early Cenozoic, while the west Ganzi basin and east Ganzi basin are Mesozoic. Sedimentary provenance analyses show that Early Cenozoic strata were sourced locally, whereas Mesozoic strata indicate regional sourcing. Basin-bounding fault characteristics demonstrate that deformation and nonmarine deposition were associated with compressional tectonic settings for both the Mesozoic and Cenozoic basins. Integration of data from this dissertation illustrates that a fold-thrust belt developed in Mesozoic and Early Cenozoic time near the Late Triassic Ganzi-Litang suture throughout the eastern Yidun terrane. The Late Triassic Ganzi-Litang suture was structurally reactivated by subsequent Mesozoic and Cenozoic collisions along the southern margin of Eurasia, suggesting that the spatial evolution of deformation in the eastern Tibetan Plateau was controlled by the presence of crustal weaknesses. In addition, this dissertation establishes the stratigraphic architecture for nonmarine strata in the Yidun terrane, providing the stimulus for regional correlations that further clarify the timing and style of deformation throughout the eastern Tibetan Plateau.Item Rayleigh wave constraints on the structure and tectonic history of the Gamburtsev Subglacial Mountains, East Antarctica(American Geophysical Union, 2013-05-10) Heeszel, David S.; Wiens, Douglas A.; Nyblade, Andrew A.; Hansen, Samantha E.; Kanao, Masaki; An, Meijan; Zhao, Yue; Washington University (WUSTL); University of California System; University of California San Diego; Scripps Institution of Oceanography; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; University of Alabama Tuscaloosa; Research Organization of Information & Systems (ROIS); National Institute of Polar Research (NIPR) - Japan; Chinese Academy of Geological SciencesThe Gamburtsev Subglacial Mountains (GSM), located near the center of East Antarctica, remain one of the most enigmatic mountain ranges on Earth. A lack of direct geologic samples renders their tectonic history almost totally unconstrained. We utilize teleseismic Rayleigh wave data from a 2 year deployment of broadband seismic stations across the region to image shear velocity structure and analyze the lithospheric age of the GSM and surrounding regions. We solve for 2-D phase velocities and invert these results for 3-D shear velocity structure. We perform a Monte Carlo simulation to improve constraints of crustal thickness and shear velocity structure. Beneath the core of the GSM, we find crustal thickness in excess of 55km. Mantle shear velocities remain faster than global average models to a depth of approximately 250km, indicating a thick lithospheric root. Thinner crust and slower upper mantle velocities are observed beneath the Lambert Rift System and the Polar Subglacial Basin. When compared with phase velocity curves corresponding to specific tectonothermal ages elsewhere in the world, average phase velocity results for the GSM are consistent with regions of Archean-Paleoproterozoic origin. Combined with radiometric ages of detrital zircons found offshore, these results indicate a region of old crust that has undergone repeated periods of uplift and erosion, most recently during the Mesozoic breakup of Gondwana. Lower crustal seismic velocities imply a moderately dense lower crust beneath the core of the GSM, but with lower density than suggested by recent gravity models.Item Reservoir characterization of the Hartselle Sandstone in the vicinity of Gorgas Power Plant, using amplitude variation with offset (avo)(University of Alabama Libraries, 2018) Nguyen, Thu Anh; Goodliffe, Andrew M.; University of Alabama TuscaloosaThe Black Warrior Basin (BWB) contains prolific oil and gas reservoirs, which have been well characterized to the west of two major coal-fired power plants in Alabama. The Mississippian Hartselle Sandstone of the BWB is a major oil sand resource in the United States. A stratigraphic test well, drilled at the William C. Gorgas Power Plant, Walker County, Alabama, revealed light crude oil (40°API) in the Hartselle Sandstone at 2,601.3 ft. (792.9 m) below ground surface. Two 5-mile, 2-D Vibroseis seismic reflection lines, which intersect near the stratigraphic test well, exhibit classic amplitude variation with offset (AVO) responses along the Hartselle Sandstone unit. Using an AVO intercept-gradient analysis along the target horizon (Hartselle Sandstone) across the seismic reflection profiles, the lateral extent of the hydrocarbon resource was mapped up to 1.3 km (0.8 miles) from the test well. The Hartselle Sandstone in the Gorgas area is considered a tight oil sand prospect and is higher impedance than the overlying limestone. The AVO analysis results show a pattern of positive amplitude decreasing with larger offsets consistent with a class I AVO anomaly, typical of high impedance hydrocarbon-saturated sands. The hydrocarbon zone within the Hartselle Sandstone extends a distance of 594 m (1948.82 ft) along line 101 and a distance of 1284 m (4212.60 ft) along line 201. These distances were used to estimate the areal extent of the hydrocarbons along each seismic reflection line, which averages 0.2 km2 (50 acres) for line 101and 0.5 km2 (146 acres) for line 201. In addition to this areal extent estimation, volumetric and risking analysis indicates that the Hartselle Sandstone in the Gorgas area has a large resource potential, with an estimated total volume of hydrocarbons in place ranging from 0.1 to 5.6 million barrels of oil.Item Seismic interpretation and structural analysis of the Alleghanian fold-thrust belt in Central Alabama(University of Alabama Libraries, 2014) Cato, Craig; Robinson, D. M.; University of Alabama TuscaloosaIn the central part of the Alleghanian fold-thrust belt of Alabama, multi-channel seismic and well log data are used to analyze structural elements of the thrust belt. Six horizons were interpreted on the seismic data in two-way travel time and were depth-converted using interval velocities derived from a synthetic seismogram as well as from sonic logs from USS-29-01-09 and COGC-USX #1. The structural interpretation from the depth-converted data shows the thrust belt is a forward-propagating thrust sequence with four main thrust faults branching off of a basal detachment. Basement along the profile is at a minimum depth of 4,700 m in the Black Warrior Basin and a maximum depth of 7,200 m in the Birmingham Graben System, yielding 2,500 m of relief in this Precambrian rift system. The coherent reflectors in this cross-section show no evidence for a ductile duplex; thus, the section was balanced using line length balancing techniques. The balanced cross-section yields a minimum of 30 km or 24% shortening. This value is similar to other balanced cross-sections to the north and south that span the Alleghanian fold-thrust belt in Alabama.Item Seismic investigations of the northern Transantarctic Mountains(University of Alabama Libraries, 2017) Graw, Jordan Hunter; Hansen, Samantha E.; University of Alabama TuscaloosaStretching ~3500 km across Antarctica and reaching elevations of ~4500 m, the Transantarctic Mountains (TAMs) are the largest non-compressional mountain chain on Earth. The TAMs show no evidence of folding or reverse faulting as is typically seen in contractional mountain building, calling the origin of the mountain range into question. Using data from the recent Transantarctic Mountains Northern Network seismic deployment, this dissertation integrates Rayleigh wave surface wave tomography, downward continuation and wavefield decomposition, and seismic anisotropy studies to better characterize the structure beneath the northern TAMs and to assess uplift. Surface wave tomographic images indicate a previously unidentified low shear wave velocity anomaly beneath the northern TAMs, with faster seismic velocities behind the TAMs front. The low shear wave velocity anomaly is interpreted as reflect rift-related decompression melting associated with Cenozoic extension. Uplift for the TAMs is attributed to a thermal buoyancy force associated with this anomaly. When trying to assess crustal structure, ice coverage is typically troublesome as reverberations in the ice layer can complicate the P-wave response. Downward continuation and wavefield decomposition removes the effect of ice layers on the P-wave response, resulting in signal that can be directly modeled for Earth structure. Inversion solution models agree well with results from previous studies based on S-wave receiver functions and tomography, confirming relatively thin crust beneath the northern TAMs. Upper mantle structure can also be assessed with seismic anisotropy. I performed shear wave splitting analyses on PKS, SKS, and SKKS phases to obtain the splitting parameters (fast axis directions φ and delay times δt). Behind the TAMs front, the anisotropic signature is interpreted as relict fabric “frozen” into the lithosphere from tectonic processes in the geologic past. Near the Ross Sea coastline, the signature is interpreted as a result from rift-related decompression melting, creating active upper mantle flow. Results highlight heterogeneity in the uplift along the TAMs front. The degree of uplift in the northern TAMs is similar to that in the central TAMs; however, the northern TAMs appear to have a stronger thermal buoyancy component, creating more pronounced topography.Item Seismic velocity structure and depth-dependence of anisotropy in the Red Sea and Arabian shield from surface wave analysis(American Geophysical Union, 2008-10-14) Hansen, Samantha E.; Gaherty, James B.; Schwartz, Susan Y.; Rodgers, Arthur J.; Al-Amri, Abdullah M. S.; King Saud University; Columbia University; United States Department of Energy (DOE); Lawrence Livermore National Laboratory; University of California System; University of California Santa Cruz; University of Alabama TuscaloosaWe investigate the lithospheric and upper mantle shear wave velocity structure and the depth-dependence of anisotropy along the Red Sea and beneath the Arabian Peninsula using receiver function constraints and phase velocities of surface waves traversing two transects of stations from the Saudi Arabian National Digital Seismic Network. Frequency-dependent phase delays of fundamental-mode Love and Rayleigh waves, measured using a cross-correlation procedure, require very slow shear velocities and the presence of anisotropy to depths of at least 180 km in the upper mantle. Linearized inversion of these data produce path-averaged 1D radially anisotropic models with similar to 4% anisotropy in the lithosphere and across the lithosphere-asthenosphere boundary (LAB). Models with reasonable crustal velocities in which the mantle lithosphere is isotropic cannot satisfy the data. The lithosphere, which ranges in thickness from about 70 km near the Red Sea coast to about 90 km beneath the Arabian Shield, is underlain by a pronounced low-velocity zone with shear velocities as low as 4.1 km/s. Forward models of azimuthal anisotropy, which are constructed from previously determined shear wave splitting estimates, can reconcile surface and body wave observations of anisotropy. The low shear velocities extend to greater depth than those observed in other continental rift and oceanic ridge environments. The depth extent of these low velocities combined with the sharp velocity contrast across the LAB may indicate the influence of the Afar hot spot and the presence of partial melt beneath Arabia. The anisotropic signature primarily reflects a combination of plate- and density-driven flow associated with rifting processes in the Red Sea.Item U-Pb zircon and monazite geochronology and hafnium isotopic geochemistry of neoacadian and early alleghanian plutonic rocks in the Alabama Eastern Blue Ridge, Southern Appalachian Mountains(University of Alabama Libraries, 2012) Ingram, Stanton B.; Schwartz, Joshua; University of Alabama TuscaloosaThe Alabama eastern Blue Ridge (EBR) of the Southern Appalachian Mountains hosts a variety of felsic plutonic rocks, which intrude multiply deformed Neoproterozoic to Ordovician metasedimentary rocks. Plutons consist of two distinct suites based on geochemical composition and degree of deformation: pre- to syn-kinematic Neoacadian, low Sr/Y plutons (ca. 380-360 Ma) and late- to post-kinematic, Early Alleghanian high Sr/Y plutons (ca. 350-330 Ma). Here, I report new whole rock geochemistry, U-Pb zircon SHRIMP-RG (Sensitive High Resolution Ion Micro Probe-Reverse Geometry) ages, and Hf isotope data for 6 plutons in the Alabama EBR. Low Sr/Y plutons are predominantly biotite-muscovite granites and granodiorites and include the Rockford Granite (376.6 ± 1.5 Ma) and the Bluff Springs Granite (363.8 ± 2.9 Ma). The Enitachopco trondhjemite dike also displays a Neoacadian age of 366.5 ± 3.5 Ma. Zircon Hf isotope data from the low Sr/Y suite range from -11.2 to +2.0. These plutons are in general strongly deformed, and display geochemical characteristics consistent with mid crustal (<35 km) partial melting of pre-existing continental crust. By contrast, high Sr/Y plutons are deformed to undeformed, and consist of low-K tonalites and trondhjemites (e.g., Almond trondhjemites and Blakes Ferry pluton) with geochemical characteristics suggestive of deep-crustal partial melting of a garnet amphibole-bearing source. Two samples of the Almond trondhjemite (Wedowee pluton and Almond pluton) yielded ages of 334.6 ± 3.2 Ma and 343.4 ± 3.4 Ma, respectively. An additional peak at 324.4 ± 3.3 may represent a Pb-loss event. Another sample of Almond trondhjemite yielded complex ages with a peak at 349.1 ± 1.8 Ma The undeformed Blakes Ferry pluton also yielded complex results with Grenville-age cores (ca. 1000-1080 Ma), and rim ages ranging from ca. 350 to 330 Ma with peaks at 343.1 ± 3.3 Ma and 331.1 ± 3.8. Igneous monazite yielded an age of 345.9 ± 3.1 Ma supporting a ca. 345 Ma crystallization age. Hf isotope data from the high Sr/Y suite range from -14.6 to +5.6. We propose that the transition from Neoacadian, low Sr/Y, mid-crustal partial melting to Early Alleghanian high Sr/Y deep crustal partial melting reflects thickening of the EBR during Neoacadian deformation. Hf isotope values also transition from crustal values (-εHf) to a mixed signature (+εHf and -εHf), reflecting both mantle and lower crustal melting. This transition may be related to slab break off following Neoacadian deformation.Item Upper mantle seismic anisotropy beneath the Northern Transantarctic Mountains, Antarctica from PKS, SKS, and SKKS splitting analysis(American Geophysical Union, 2017-02-12) Graw, Jordan H.; Hansen, Samantha E.; University of Alabama TuscaloosaUsing data from the new Transantarctic Mountains Northern Network, this study aims to constrain azimuthal anisotropy beneath a previously unexplored portion of the Transantarctic Mountains (TAMs) to assess both past and present deformational processes occurring in this region. Shear-wave splitting parameters have been measured for PKS, SKS, and SKKS phases using the eigenvalue method within the SplitLab software package. Results show two distinct geographic regions of anisotropy within our study area: one behind the TAMs front, with an average fast axis direction of 42638 and an average delay time of 0.960.04 s, and the other within the TAMs near the Ross Sea coastline, with an average fast axis oriented at 51658 and an average delay time of 1.560.08 s. Behind the TAMs front, our results are best explained by a single anisotropic layer that is estimated to be 81-135 km thick, thereby constraining the anisotropic signature within the East Antarctic lithosphere. We interpret the anisotropy behind the TAMs front as relict fabric associated with tectonic episodes occurring early in Antarctica's geologic history. For the coastal stations, our results are best explained by a single anisotropic layer estimated to be 135-225 km thick. This places the anisotropic source within the viscous asthenosphere, which correlates with low seismic velocities along the edge of the West Antarctic Rift System. We interpret the coastal anisotropic signature as resulting from active mantle flow associated with rift-related decompression melting and Cenozoic extension.Item Upper mantle seismic structure beneath central East Antarctica from body wave tomography: Implications for the origin of the Gamburtsev Subglacial Mountains(American Geophysical Union, 2013-04-17) Lloyd, Andrew J.; Nyblade, Andrew A.; Wiens, Douglas A.; Shore, Patrick J.; Hansen, Samantha E.; Kanao, Masaki; Zhao, Dapeng; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; Washington University (WUSTL); University of Alabama Tuscaloosa; Research Organization of Information & Systems (ROIS); National Institute of Polar Research (NIPR) - Japan; Tohoku UniversityThe Gamburtsev Subglacial Mountains (GSM), located near the center of East Antarctica, are the highest feature within the East Antarctic highlands and have been investigated seismically for the first time during the 2007/2008 International Polar Year by the Gamburtsev Mountains Seismic Experiment. Using data from a network of 26 broadband seismic stations and body wave tomography, the P and S wave velocity structure of the upper mantle beneath the GSM and adjacent regions has been examined. Tomographic images produced from teleseismic P and S phases reveal several large-scale, small amplitude anomalies (Vp=1.0%, Vs=2.0%) in the upper 250 km of the mantle. The lateral distributions of these large-scale anomalies are similar in both the P and S wave velocity models and resolution tests show that they are well resolved. Velocity anomalies indicate slower, thinner lithosphere beneath the likely Meso- or Neoproterozoic Polar Subglacial Basin and faster, thicker lithosphere beneath the likely Archean/Paleoproterozoic East Antarctic highlands. Within the region of faster, thicker lithosphere, a lower amplitude (Vp=0.5%, Vs=1.0%) slow to fast velocity pattern is observed beneath the western flank of the GSM, suggesting a suture between two lithospheric blocks possibly of similar age. These findings point to a Precambrian origin for the high topography of the GSM, corroborating other studies invoking a long-lived highland landscape in central East Antarctica, as opposed to uplift caused by Permian/Cretaceous rifting or Cenozoic magmatism. The longevity of the GSM makes them geologically unusual; however, plausible analogs exist, such as the 550 Ma Petermann Ranges in central Australia. Additional uplift may have occurred by the reactivation of pre-existing faults, for example, during the Carboniferous-Permian collision of Gondwana and Laurussia.