Spatio-Temporal Analyses of Cenozoic Normal Faulting, Graben Basin Sedimentation, and Volcanism around the Snake River Plain, SE Idaho and SW Montana

This dissertation analyzes the spatial distribution and kinematics of the Late Cenozoic Basin and Range (BR) and cross normal fault (CF) systems and their related graben basins around the Snake River Plain (SRP), and investigates the spatio-temporal patterns of lavas that were erupted by the migrating Yellowstone hotspot along the SRP, applying a diverse set of GIS-based spatial statistical techniques. The spatial distribution patterns of the normal fault systems, revealed by the Ripley\u27s K-function, display clustered patterns that correlate with a high linear density, maximum azimuthal variation, and high box-counting fractal dimensions of the fault traces. The extension direction for normal faulting is determined along the major axis of the fractal dimension anisotropy ellipse measured by the modified Cantor dust method and the minor axis of the autocorrelation anisotropy ellipse measured by Ordinary Kriging, and across the linear directional mean (LDM) of the fault traces. Trajectories of the LDMs for the cross faults around each caldera define asymmetric sub-parabolic patterns similar to the reported parabolic distribution of the epicenters, and indicate sub-elliptical extension about each caldera that may mark the shape of hotspot’s thermal doming that formed each generation of cross faults. The decrease in the spatial density of the CFs as a function of distance from the axis of the track of the hotspot (SRP) also suggests the role of the hotspot for the formation of the cross faults. The parallelism of the trend of the exposures of the graben filling Sixmile Creek Formation with the LDM of their bounding cross faults indicates that the grabens were filled during or after the CF event. The global and local Moran’s I analyses of Neogene lava in each caldera along the SRP reveal a higher spatial autocorrelation and clustering of rhyolitic lava than the coeval basaltic lava in the same caldera. The alignment of the major axis of the standard deviational ellipses of lavas with the trend of the eastern SRP, and the successive spatial overlap of older lavas by progressively younger mafic lava, indicate the migration of the centers of eruption as the hotspot moved to the northeast

Spatio-Temporal Analyses of Cenozoic Normal Faulting, Graben Basin Sedimentation, and Volcanism around the Snake River Plain, SE Idaho and SW Montana

This dissertation analyzes the spatial distribution and kinematics of the Late Cenozoic Basin and Range (BR) and cross normal fault (CF) systems and their related graben basins around the Snake River Plain (SRP), and investigates the spatio-temporal patterns of lavas that were erupted by the migrating Yellowstone hotspot along the SRP, applying a diverse set of GIS-based spatial statistical techniques. The spatial distribution patterns of the normal fault systems, revealed by the Ripley\u27s K-function, display clustered patterns that correlate with a high linear density, maximum azimuthal variation, and high box-counting fractal dimensions of the fault traces. The extension direction for normal faulting is determined along the major axis of the fractal dimension anisotropy ellipse measured by the modified Cantor dust method and the minor axis of the autocorrelation anisotropy ellipse measured by Ordinary Kriging, and across the linear directional mean (LDM) of the fault traces. Trajectories of the LDMs for the cross faults around each caldera define asymmetric sub-parabolic patterns similar to the reported parabolic distribution of the epicenters, and indicate sub-elliptical extension about each caldera that may mark the shape of hotspot’s thermal doming that formed each generation of cross faults. The decrease in the spatial density of the CFs as a function of distance from the axis of the track of the hotspot (SRP) also suggests the role of the hotspot for the formation of the cross faults. The parallelism of the trend of the exposures of the graben filling Sixmile Creek Formation with the LDM of their bounding cross faults indicates that the grabens were filled during or after the CF event. The global and local Moran’s I analyses of Neogene lava in each caldera along the SRP reveal a higher spatial autocorrelation and clustering of rhyolitic lava than the coeval basaltic lava in the same caldera. The alignment of the major axis of the standard deviational ellipses of lavas with the trend of the eastern SRP, and the successive spatial overlap of older lavas by progressively younger mafic lava, indicate the migration of the centers of eruption as the hotspot moved to the northeast

The Deschutes Formation: evidence of extension-enhanced explosivity in the early High Cascades

The eruptive history of the Quaternary Cascades arc has been relatively well characterized. However, much less is known about the frequency and sizes of explosive eruptions produced by earlier stages of the arc. The Late Neogene Deschutes Formation of Central Oregon preserves a remarkable record of heightened pyroclastic activity during the initial stages of High Cascades volcanism, following an eastward shift in volcanic activity ~7.5 Ma. Extensive fieldwork, 40Ar 39Ar geochronology, and geochemical analyses allow us to reconstruct this unusually explosive phase of the earliest Central Oregon High Cascades.Plagioclase 40Ar 39Ar ages for eight laterally-extensive marker ignimbrites that stratigraphically bracket the many pyroclastic deposits exposed within the Deschutes Formation, indicate that almost all of these explosive eruptions occurred within only ~800 k.y., between 6.25± 0.07 and 5.45± 0.04 Ma. Combining these age data with multivariate statistical tephra correlation methods, I establish a comprehensive tephrostratigraphy of the Deschutes Formation. These correlations suggest that at least 67 distinct explosive eruptions (possibly as many as 120) occurred within the 800 k.y. explosive pulse.Using a new ArcGIS-based method that I developed for calculating ignimbrite volumes, I find that a total volume of 82 km3 (62 km3 DRE) for just 26 of the ignimbrites deposited distally into the Deschutes Basin. If these ignimbrites also deposited an equal volume to the west and had a tephra fall:flow ratio of betweenii0.5:1 and 1.9:1 (similar to Mount Pinatubo and Valley of Ten Thousand Smokes), the total volume of all 26 eruptions was likely between 246 and 475 km3, or a rate of 6-12 km3 m.y. km. This rate is approximately 2-8 times higher than the production rate of all compositions over the entire Quaternary Cascades and is the highest rate in Oregon over at least the last 17 Ma.The unique timing and location of this pulse, approximately 1 m.y. after an eastward shift of the arc axis, and in a region undergoing extension, may explain the anomalous explosivity recorded in the Deschutes Formation. I suggest that such extension allowed for penetration of hot, low-K tholeiitic basalt magmas into shallow levels of the crust, which induced a period of enhanced shallow crustal melting and the production of large volumes of hot-dry-reduced rhyolites (high Fe, Na, Y, MREE, and low Eu Eu* and Sr). Thus, the anomalously high production of silicic magma and rate of explosive volcanism recorded in the Deschutes Formation is mirrored by the unusual geochemistry of the eruptive products, and are together indicative of magmatic processes driven by extension, that no longer operate during the Quaternary.In addition to constraining changes in geochemistry and style of volcanism through time, I used rigorous statistical methodology to assess the geochemical variability along-arc for the Quaternary Cascades. To do this, I compiled a dataset of over 11,000 samples and utilized a Monte Carlo approach with weighted bootstrap resampling to reduce the bias that over-sampled volcanoes have on overall trends. In in doing so, I assessed regional, rather than local processes. Our study develops a novel approach to assessing along-arc geochemical variability using entirely objective and statistically-based methodology. Using this new approach, I separated the Cascades arc into 5 segments such that the geochemical differences between each is maximized. This new segmentation scheme, which includes the North, Washington, Graben, Mazama, and South Segments is more statistically robust than previous segmentation schemes. By separating the arc into the most statistically distinct regions, one can better assess the spatially disparate processes that lead to geochemical heterogeneity. This, in turn, provides a better understanding of the fundamental processes involved in arc magma generation.Keywords: Cascades Arc, Explosive volcanism, Volcanology, Geochemistry, Tephrochronology, Igneous Petrolog

Reconstructing species responses to past climatic changes using niche modeling and genetic data

Glacial – interglacial cycles have a pronounced impact on species distributions and genetic structure. Many species shift their distributions to lower latitudes and altitudes during the colder glacial periods and expand northwards and up the elevation during warmer interglacial periods. Some species however are capable of adapting to changing environment which allows them to persist in place despite climatic changes. I explored how climatic changes after the last glacial maximum (LGM) effected two species inhabiting the deserts of western North America: one mammal (Chisel-toothed Kangaroo Rat, Dipodomys microps) and one reptile (Desert Horned Lizard, Phrynosoma platyrhinos). I used a methodology of transferal modeling which is commonly used to predict species responses to future climatic changes. I approximated the species current and LGM distribution by modeling their current climatic niches, which I then projected onto the climatic conditions of the LGM. The accuracy of the transferal models, however, is dependent on several conceptual and algorithmic assumptions. Therefore, I compared the models with the phylogeographic structure of each species as phylogeographic signals imprinted in species genomes can inform us about species past geographic and demographic processes. The transferal models predicted that the northern parts of the species current ranges were unsuitable during the LGM and that both species could have persisted only within the more southern deserts where climatic conditions remained suitable. The phylogeographic analyses, however, suggested that D. microps did not experience large scale distributional changes in response to the warming climate after the LGM as suggested by the models and instead persisted in place throughout most of its current range. Phrynosoma platyrhinos expanded its range northwards after the LGM but was able to expand further than indicated by models, into colder and wetter areas than those experienced during the LGM. My results indicate that the two species responded to the warming climate after the LGM in an idiosyncratic fashion and that the transferal models did not correctly predict the species response to the climate change. These results motivated me to explore in the last chapter several high-priority challenges in transferal modeling through theoretical background and sets of experiments. I demonstrated how these challenges can affect resulting models and, when possible, offered suggestions on how uncertainties might be diminished

Spat Stat

Spatial clustering detection has a variety of applications in diverse fields, including identifying infectious disease outbreaks, pinpointing crime hotspots, and identifying clusters of neurons in brain imaging applications. Ripley's K-function is a popular method for detecting clustering (or dispersion) in point process data at specific distances. Ripley's K-function measures the expected number of points within a given distance of any observed point. Clustering can be assessed by comparing the observed value of Ripley's K-function to the expected value under complete spatial randomness. While performing spatial clustering analysis on point process data is common, applications to areal data commonly arise and need to be accurately assessed. Inspired by Ripley's K-function, we develop the | and use it to develop a hypothesis testing procedure for the detection of spatial clustering and dispersion at specific distances in areal data. We compare the performance of the proposed PAPF hypothesis test to that of the global Moran's I statistic, the Getis-Ord general G statistic, and the spatial scan statistic with extensive simulation studies. We then evaluate the real-world performance of our method by using it to detect spatial clustering in land parcels containing conservation easements and US counties with high pediatric overweight/obesity rates.P20 GM130420/GM/NIGMS NIH HHSUnited States/U19 DD001218/DD/NCBDD CDC HHSUnited States

Crustal Structure and Lithospheric Doming: Aspects of Deformation Along an Obliquely Convergent Plate Margin, New Zealand

Lithospheric deformation along and adjacent to the Pacific-Australian Plate boundary through New Zealand has resulted in different expressions in North and South Islands. This thesis investigates some aspects of crustal and upper mantle structure in New Zealand and is divided into two distinct parts. The first examines the structure of the obliquely compressional crustal plate boundary in South Island using seismic techniques; the second focuses on the domed topography of central North Island and its relationship to mantle processes. High density active source, one and three-component, seismic data from a transect across the Southern Alps provides information on the deformation of the crust across the Australia-Pacific plate boundary of South Island. These data show 0-0.08 s ([approximately] 0.25 %) delay times between the radial and transverse directions for shear waves (Sg and SmS phases), with maximum possible delays of 140 ms and the fast direction aligned with the transverse direction (approximately parallel to the plate boundary). The transect is perpendicular to the Alpine Fault, which is slightly oblique to the fast mantle directions determined from SKS phases. The small values of crustal splitting may result from the oblique angle of the ray paths to the actual crustal structure at depth, or the complex nature of the deformation as observed at the surface, which though on a small scale can be strongly anisotropic, may not add constructively over a large region. Poisson's ratio, determined from forward modelling of both P and S phases, shows low values of 0.21 - 0.24 for the crust of South Island. A broad region of low values ([sigma]=0.15) exists at 10-20 km depth under the Southern Alps, which corresponds to a previously identified body of low Vp and high resistivity. The low [sigma] is interpreted as low pore fluid pressure and high silica composition rocks. This contrasts with previous interpretations of iii iv high pore fluid pressure at this depth. The topography of central North Island, New Zealand, describes a 250 km wide and [approximately] 500 m high dome. Exhumation estimates from mudstone porosity measurement indicate an increase in exhumation from [approximately] 500 m at the coast to 2 km in the region of the present topographic high. Combining these values gives an estimate of rock uplift of over 2.5 km for central North Island, since 4 Ma, a rate of 0.6 mm/yr. Tectonic uplift of 1.25 km indicates that [approximately] 50 % of the rock uplift occurs in response to exhumation. An independent local estimation of differential erosion in central North Island gave 300 m of exhumation since at least 500 ka, a rate of [greater than or equal to] 0.6 mm/yr. Using a digital elevation model of New Zealand the fluvial incision of the landscape was calculated and [approximately]169 m of rebound can be attributed to incision. Contouring maximum incision elucidates a region of high incision [approximately] 50 km south of the present centre of domed rock uplift. Using incision as a proxy for rock uplift, it is hypothesised that the incision signal is recent and demonstrates the southward migration of the centre of rock uplift. Rebound of sedimentary basins due to a reduction in plate coupling forces can also account for some of the observed rock uplift. Buoyancy forces required to create the pattern and magnitude of rock uplift are investigated using a 3 D loading model of the lithosphere. Strong upward forces (65 MPa) are required under the Central Volcanic Region, combined with broad uplift (36 MPa) over western North Island, to fit the observed rock uplift. Low Pn velocities under the Central Volcanic Region indicate temperatures 500 [degrees] C hotter than that of normal mantle. This temperature anomaly corresponds to 60 kg/[cubic metre] less dense than normal mantle, which is consistent with the change in density of 66 kg/[cubic metre] estimated from the loading model and aassuming the density change occurs over a 100 km depth range. The southern extent of buoyancy forces does not correspond well to regions of high seismic attenuation in the lithosphere but instead with the region of high incision