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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

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
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Description

The Star Planet Activity Research CubeSat (SPARCS) will be a 6U CubeSat devoted to photometric monitoring of M dwarfs in the far-ultraviolet (FUV) and near-ultraviolet (NUV) (160 and 280 nm respectively), measuring the time-dependent spectral slope, intensity and evolution of M dwarf stellar UV radiation. The delta-doped detectors baselined for

The Star Planet Activity Research CubeSat (SPARCS) will be a 6U CubeSat devoted to photometric monitoring of M dwarfs in the far-ultraviolet (FUV) and near-ultraviolet (NUV) (160 and 280 nm respectively), measuring the time-dependent spectral slope, intensity and evolution of M dwarf stellar UV radiation. The delta-doped detectors baselined for SPARCS have demonstrated more than five times the in-band quantum efficiency of the detectors of GALEX. Given that red:UV photon emission from cool, low-mass stars can be million:one, UV observation of thes stars are susceptible to red light contamination. In addition to the high efficiency delta-doped detectors, SPARCS will include red-rejection filters to help minimize red leak. Even so, careful red-rejection and photometric calibration is needed. As was done for GALEX, white dwarfs are used for photometric calibration in the UV. We find that the use of white dwarfs to calibrate the observations of red stars leads to significant errors in the reported flux, due to the differences in white dwarf and red dwarf spectra. Here we discuss the planned SPARCS calibration model and the color correction, and demonstrate the importance of this correction when recording UV measurements of M stars taken by SPARCS.

ContributorsOsby, Ella (Author) / Shkolnik, Evgenya (Thesis director) / Ardila, David (Committee member) / School of Earth and Space Exploration (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
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Description
Cinder cones are common volcanic structures that occur in fields, and on the flanks of shield volcanoes, stratovolcanoes, and calderas. Because they are common structures, they have a significant possibility of impacting humans and human environments. As such, there is a need to analyze cinder cones to get a better

Cinder cones are common volcanic structures that occur in fields, and on the flanks of shield volcanoes, stratovolcanoes, and calderas. Because they are common structures, they have a significant possibility of impacting humans and human environments. As such, there is a need to analyze cinder cones to get a better understanding of their eruptions and associated hazards. I will approach this analysis by focusing on volcanic bombs and ballistics, which are large clots of lava that are launched from the volcanic vent, follow ballistic trajectories, and can travel meters to a few kilometers from their source (e.g. Fagents and Wilson 1993; Waitt et al. 1995).
Tecolote Volcano in the Pinacate Volcanic Field in Mexico contains multiple vents within a horseshoe-shaped crater that have all produced various ejecta (Zawacki et al. 2019). The objectives of this research are to map ballistic distribution to understand the relationship between the source vent or vents and the bombs and ballistics that litter the region around Tecolote, and interpret the eruption conditions that ejected those bombs by using their distributions, morphologies, and fine-scale textures.
The findings of this work are that these bombs are apparently from the last stages of the eruption, succeeding the final lava flows. The interiors and exteriors of the bombs display different cooling rates which can are indicated by the fabric found within. Using this, certain characteristics of the bombs during eruption were extrapolated. The ‘cow pie’ bombs were determined to be the least viscous or contained a higher gas content at the time of eruption. Whereas the ribbon/rope bombs were determined to be the most viscous or contained a lesser gas content. Looking at the Southern Bomb Field site, it is dominated by large bombs that were during flight were molded into aerodynamic shapes. The Eastern Rim site is dominated by smaller bombs that appeared to be more liquid during the eruption. This difference in the two sites is a probable indication of at least two different eruptive events of different degrees of explosivity. Overall, aerodynamic bombs are more common and extend to greater distances from the presumed vent (up to 800 m), while very fluidal bombs are uncommon beyond 500 meters. Fluidal bombs (‘cow pie’, ‘ribbon’, ‘rope/spindle’) show a clear trend in decreasing size with distance from vent, whereas the size-distance trend is less dramatic for the aerodynamic bombs.
ContributorsWest, Jacob Alexander (Co-author) / West, Jacob (Co-author) / Clarke, Amanda (Thesis director) / Arrowsmith, Ramon (Committee member) / Roggensack, Kurt (Committee member) / School of Earth and Space Exploration (Contributor, Contributor) / Barrett, The Honors College (Contributor)
Created2020-05
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Description
Volcanic eruptions are serious geological hazards; the aftermath of the explosive eruptions produced at high-silica volcanic systems often results in long-term threats to climate, travel, farming, and human life. To construct models for eruption forecasting, the timescales of events leading up to eruption must be accurately quantified. In the field

Volcanic eruptions are serious geological hazards; the aftermath of the explosive eruptions produced at high-silica volcanic systems often results in long-term threats to climate, travel, farming, and human life. To construct models for eruption forecasting, the timescales of events leading up to eruption must be accurately quantified. In the field of igneous petrology, the timing of these events (e.g. periods of magma formation, duration of recharge events) and their influence on eruptive timescales are still poorly constrained.

In this dissertation, I discuss how the new tools and methods I have developed are helping to improve our understanding of these magmatic events. I have developed a method to calculate more accurate timescales for these events from the diffusive relaxation of chemical zoning in individual mineral crystals (i.e., diffusion chronometry), and I use this technique to compare the times recorded by different minerals from the same Yellowstone lava flow, the Scaup Lake rhyolite.

I have also derived a new geothermometer to calculate magma temperature from the compositions of the mineral clinopyroxene and the surrounding liquid. This empirically-derived geothermometer is calibrated for the high FeOtot (Mg# = 56) and low Al2O3 (0.53–0.73 wt%) clinopyroxene found in the Scaup Lake rhyolite and other high-silica igneous systems. A determination of accurate mineral temperatures is crucial to calculate magmatic heat budgets and to use methods such as diffusion chronometry. Together, these tools allow me to paint a more accurate picture of the conditions and tempo of events inside a magma body in the millennia to months leading up to eruption.

Additionally, I conducted petrological experiments to determine the composition of hypothetical exoplanet partial mantle melts, which could become these planets’ new crust, and therefore new surface. Understanding the composition of an exoplanet’s crust is the first step to understanding chemical weathering, surface-atmosphere chemical interactions, the volcanic contribution to any atmosphere present, and biological processes, as life depends on these surfaces for nutrients. The data I have produced can be used to predict differences in crust compositions of exoplanets with similar bulk compositions to those explored herein, as well as to calibrate future exoplanet petrologic models.
ContributorsBrugman, Karalee (Author) / Till, Christy B. (Thesis advisor) / Bose, Maitrayee (Committee member) / Desch, Steven J (Committee member) / Hervig, Richard L (Committee member) / Shock, Everett L (Committee member) / Arizona State University (Publisher)
Created2020