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- Creators: Whipple, Kelin
Description
There are many outstanding questions regarding the petrologic processes that give rise to andesitic and basaltic magmas in subduction zones, including the specifics that govern their geographical distribution in a given arc segment. Here I investigate the genesis of calc-alkaline and tholeiitic basalts from the Lassen Volcanic Center in order to determine the pressure, temperature, source composition, and method of melting that lead to the production of melt in the mantle below Lassen. To this aim, a suite of primitive basalts (i.e. SiO2<52 and Mg#>65) are corrected for fractional crystallization by adding minerals back to the bulk rock composition with the goal of returning them to a primary composition in equilibrium with the mantle. Thermobarometry of the primary melt compositions is conducted to determine temperature and pressure of melting, in addition to a forward mantle modeling technique to simulate mantle melting at varying pressures to constrain source composition and method of melting (batch vs. fractional). The results from the two techniques agree on an average depth of melt extraction of 36 km and a source composition similar to that of depleted mantle melted by batch melting. Although attempted for both calc-alkaline and tholeiitic basalts, the fractional crystallization correction and thus the pressure-temperature calculations were only successful for tholeiitic basalts due to the hydrous nature of the calc-alkaline samples. This leaves an opportunity to repeat this study with parameters appropriate for hydrous basalts, allowing for the comparison of calc-alkaline and tholeiitic melting conditions.
ContributorsSheppard, Katherine Davis (Author) / Till, Christy (Thesis director) / Hervig, Richard (Committee member) / Barrett, The Honors College (Contributor) / School of Earth and Space Exploration (Contributor)
Created2015-05
Description
Shallow earthquakes in the upper part of the overriding plate of subduction zones can be devastating due to their proximity to population centers despite the smaller rupture extents than commonly occur on subduction megathrusts that produce the largest earthquakes. Damaging effects can be greater in volcanic arcs like Java because ground shaking is amplified by surficial deposits of uncompacted volcaniclastic sediments. Identifying the upper-plate structures and their potential hazards is key for minimizing the dangers they pose. In particular, the knowledge of the regional stress field and deformation pattern in this region will help us to better understand how subduction and collision affects deformation in this part of the overriding plate. The majority of the upper plate deformation studies have been focused on the deformation in the main thrusts of the fore-arc region. Study of deformation within volcanic arc is limited despite the associated earthquake hazards. In this study, I use maps of active upper-plate structures, earthquake moment tensor data and stress orientation deduced from volcano morphology analysis to characterize the strain field of Java arc. In addition, I use sandbox analog modeling to evaluate the mechanical factors that may be important in controlling deformation. My field- and remotely-based mapping of active faults and folds, supplemented by results from my paleoseismic studies and physical models of the system, suggest that Java’s deformation is distributed over broad areas along small-scale structures. Java is segmented into three main zones based on their distinctive structural patterns and stress orientation. East Java is characterized by NW-SE normal and strike-slip faults, Central Java has E-W folds and thrust faults, and NE-SW strike-slip faults dominate West Java. The sandbox analog models indicate that the strain in response to collision is partitioned into thrusting and strike-slip faulting, with the dominance of margin-normal thrust faulting. My models test the effects of convergence obliquity, geometry, preexisting weaknesses, asperities, and lateral strength contrast. The result suggest that slight variations in convergence obliquity do not affect the deformation pattern significantly, while the margin shape, lateral strength contrast, and perturbation of deformation from asperities each have a greater impact on deformation.
ContributorsMarliyani, Gayatri Indah (Author) / Arrowsmith, J Ramon (Thesis advisor) / Clarke, Amanda B (Committee member) / Hartnett, Hilairy (Committee member) / Whipple, Kelin (Committee member) / Garnero, Edward (Committee member) / Arizona State University (Publisher)
Created2016
Description
On Mars, sedimentary deposits reveal a complex history of water- and wind-related geologic processes. Central mounds – kilometer-scale stacks of sediment located within craters – occur across Mars, but the specific processes responsible for mound formation and subsequent modification are still uncertain. A survey of central mounds within large craters was conducted. Mound locations, mound offsets within their host craters, and relative mound heights were used to address various mound formation hypotheses. The results suggest that mound sediments once filled their host craters and were later eroded into the features observed today. Mounds offsets from the center of their host crater imply that wind caused the erosion of central mounds. An in depth study of a single central mound (Mt. Sharp within Gale crater) was also conducted. Thermal Emission Imaging System Visible Imaging Subsystem (THEMIS-VIS) mosaics in grayscale and false color were used to characterize the morphology and color variations in and around Gale crater. One result of this study is that dunes within Gale crater vary in false color composites from blue to purple, and that these color differences may be due to changes in dust cover, grain size, and/or composition. To further investigate dune fields on Mars, albedo variations at eight dune fields were studied based on the hypothesis that a dune’s ripple migration rate is correlated to its albedo. This study concluded that a dune’s minimum albedo does not have a simple correlation with its ripple migration rate. Instead, dust devils remove dust on slow-moving and immobile dunes, whereas saltating sand caused by strong winds removes dust on faster-moving dunes.
On the Moon, explosive volcanic deposits within Oppenheimer crater that were emplaced ballistically were investigated. Lunar Reconnaissance Orbiter (LRO) Diviner Radiometer mid-infrared data, LRO Camera images, and Chandrayaan-1 orbiter Moon Mineralogy Mapper near-infrared spectra were used to test the hypothesis that the pyroclastic deposits in Oppenheimer crater were emplaced via Vulcanian activity by constraining their composition and mineralogy. The mineralogy and iron-content of the pyroclastic deposits vary significantly (including examples of potentially very high iron compositions), which indicates variability in eruption style. These results suggest that localized lunar pyroclastic deposits may have a more complex origin and mode of emplacement than previously thought.
On the Moon, explosive volcanic deposits within Oppenheimer crater that were emplaced ballistically were investigated. Lunar Reconnaissance Orbiter (LRO) Diviner Radiometer mid-infrared data, LRO Camera images, and Chandrayaan-1 orbiter Moon Mineralogy Mapper near-infrared spectra were used to test the hypothesis that the pyroclastic deposits in Oppenheimer crater were emplaced via Vulcanian activity by constraining their composition and mineralogy. The mineralogy and iron-content of the pyroclastic deposits vary significantly (including examples of potentially very high iron compositions), which indicates variability in eruption style. These results suggest that localized lunar pyroclastic deposits may have a more complex origin and mode of emplacement than previously thought.
ContributorsBennett, Kristen Alicia (Author) / Bell, James F. (Thesis advisor) / Christensen, Phillip (Committee member) / Clarke, Amanda (Committee member) / Robinson, Mark (Committee member) / Whipple, Kelin (Committee member) / Arizona State University (Publisher)
Created2016
Description
ABSTRACT
The Spirit landing site in Gusev Crater has been imaged by the Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE) camera more than thirty times since 2006. The breadth of this image set allowed a study of changes to surface features, covering four Mars years.
Small fields of bedforms comprised of dark material, and dark dust devil tracks are among the features revealed in the images. The bedforms are constrained within craters on the plains, and unconstrained in depressions less than 200m wide within the topography of the Columbia Hills, a ~120m-high structure in center of Gusev. Dust devil tracks appear in many images of the bedforms.
Within the Columbia Hills, three bedform fields approximately 180m2 and composed of fine dark basaltic sand were studied, using five HiRISE images taken from 2006 to 2014. Both bedform crests and the dust devil tracks superimposed on them were evaluated for change to azimuth and length, and for correlation between the features. The linear to slightly sinuous transverse crests ranging from less than 1m to 113m in length and two to three meters in wavelength, are primary bedforms. During the study they shifted as much as 33 degrees in azimuth, and individual crests moved on the surface as much as 0.75m. The greatest changes corresponded to a global dust storm in 2007. Average crest movement was documented at the rate of 0.25m per year. Rather than moving progressively, the crests eventually returned to near their original orientation after the storm. The dust devil tracks, reflecting a more complex wind regime, including vortex development during diurnal heating, maintained predominantly NW-SE orientations but also reflected the effects of the storm.
The observed modifications were neither progressive, nor strictly seasonal. The apparent stability of the bedform geometry over four seasons supports the predictions of the Mars Regional Atmospheric Modeling System (MRAMS): low speed (1-7.5 ms-1), daily alternating winds of relatively equal force. Crest profiles were found to be nearly symmetrical, without slipfaces to indicate a preferential wind direction; this finding also is supported by the MRAMS model.
The Spirit landing site in Gusev Crater has been imaged by the Mars Reconnaissance Orbiter High Resolution Imaging Science Experiment (HiRISE) camera more than thirty times since 2006. The breadth of this image set allowed a study of changes to surface features, covering four Mars years.
Small fields of bedforms comprised of dark material, and dark dust devil tracks are among the features revealed in the images. The bedforms are constrained within craters on the plains, and unconstrained in depressions less than 200m wide within the topography of the Columbia Hills, a ~120m-high structure in center of Gusev. Dust devil tracks appear in many images of the bedforms.
Within the Columbia Hills, three bedform fields approximately 180m2 and composed of fine dark basaltic sand were studied, using five HiRISE images taken from 2006 to 2014. Both bedform crests and the dust devil tracks superimposed on them were evaluated for change to azimuth and length, and for correlation between the features. The linear to slightly sinuous transverse crests ranging from less than 1m to 113m in length and two to three meters in wavelength, are primary bedforms. During the study they shifted as much as 33 degrees in azimuth, and individual crests moved on the surface as much as 0.75m. The greatest changes corresponded to a global dust storm in 2007. Average crest movement was documented at the rate of 0.25m per year. Rather than moving progressively, the crests eventually returned to near their original orientation after the storm. The dust devil tracks, reflecting a more complex wind regime, including vortex development during diurnal heating, maintained predominantly NW-SE orientations but also reflected the effects of the storm.
The observed modifications were neither progressive, nor strictly seasonal. The apparent stability of the bedform geometry over four seasons supports the predictions of the Mars Regional Atmospheric Modeling System (MRAMS): low speed (1-7.5 ms-1), daily alternating winds of relatively equal force. Crest profiles were found to be nearly symmetrical, without slipfaces to indicate a preferential wind direction; this finding also is supported by the MRAMS model.
ContributorsPendleton-Hoffer, Mary C (Author) / Christensen, Philip R. (Philip Russel) (Thesis advisor) / Whipple, Kelin (Committee member) / Knauth, Paul (Committee member) / Arizona State University (Publisher)
Created2016
Description
Many shallow craters near the Spirit Mars Exploration Rover landing site contain asymmetric deposits of windblown sediments which could indicate the predominant local wind direction at the time of deposition or redistribution. Wind tunnel simulations and field studies of terrestrial craters were used to determine trends in deposition as a function of crater morphometry and wind direction. Terrestrial analog field work at the Amboy lava field, Mojave Desert, California, included real-time wind measurements and assessments of active sediment deposition in four small (<100 m) craters. Preliminary results indicate that reverse flow or stagnant wind and deposition on the upwind side of the crater floor occurs in craters with depth-to-diameter (d/D) ratios ≥0.05. Measurements taken within a crater of d/D of ~0.02 do not indicate reverse flow. Therefore, reverse flow is expected to cease within a d/D range of 0.02 to 0.05, resulting in wind movement directly over the crater floor in the downwind direction with no asymmetric sediment deposition. Wind tunnel simulations using six crater models, including a scaled model of a crater from the Amboy lava field, were completed to assess the wind flow in and around craters as a function of crater morphometry (depth, diameter). Reverse flow occurred in craters with d/D ratios ≥0.033, resulting in sediment deposition in the upwind portion of the crater floor. Visual observations of a crater with a d/D of ~0.020 did not indicate reverse flow, similar to the results of field studies; therefore, reverse flow appears to cease within a d/D range of 0.020 to 0.033. Craters with asymmetric aeolian deposits near the Mars Spirit landing site have d/D ratios of 0.034 to 0.076, suggesting that reverse flow occurs in these craters. Thus, the position of windblown sediments in the northwest parts of the crater floors would indicate prevailing winds from the northwest to the southeast, consistent with late afternoon winds as predicted by the Mars Regional Atmospheric Modeling System (MRAMS) circulation model.
ContributorsKienenberger, Rebekah (Author) / Greeley, Ronald (Thesis advisor) / Christensen, Philip R. (Philip Russel) (Committee member) / Whipple, Kelin (Committee member) / Arizona State University (Publisher)
Created2011