ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
In addition to the electronic theses found in the ASU Digital Repository, ASU Theses and Dissertations can be found in the ASU Library Catalog.
Dissertations and Theses granted by Arizona State University are archived and made available through a joint effort of the ASU Graduate College and the ASU Libraries. For more information or questions about this collection contact or visit the Digital Repository ETD Library Guide or contact the ASU Graduate College at gradformat@asu.edu.
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- All Subjects: geology
Description
Earthquake faulting and the dynamics of subducting lithosphere are among the frontiers of geophysics. Exploring the nature, cause, and implications of geophysical phenomena requires multidisciplinary investigations focused at a range of spatial scales. Within this dissertation, I present studies of micro-scale processes using observational seismology and experimental mineral physics to provide important constraints on models for a range of large-scale geophysical phenomena within the crust and mantle.
The Great Basin (GB) in the western U.S. is part of the diffuse North American-Pacific plate boundary. The interior of the GB occasionally produces large earthquakes, yet the current distribution of regional seismic networks poorly samples it. The EarthScope USArray Transportable Array provides unprecedented station density and data quality for the central GB. I use this dataset to develop an earthquake catalog for the region that is complete to M 1.5. The catalog contains small-magnitude seismicity throughout the interior of the GB. The spatial distribution of earthquakes is consistent with recent regional geodetic studies, confirming that the interior of the GB is actively deforming everywhere and all the time. Additionally, improved event detection thresholds reveal that swarms of temporally-clustered repeating earthquakes occur throughout the GB. The swarms are not associated with active volcanism or other swarm triggering mechanisms, and therefore, may represent a common fault behavior.
Enstatite (Mg,Fe)SiO3 is the second most abundant mineral within subducting lithosphere. Previous studies suggest that metastable enstatite within subducting slabs may persist to the base of the mantle transition zone (MTZ) before transforming to high-pressure polymorphs. The metastable persistence of enstatite has been proposed as a potential cause for both deep-focus earthquakes and the stagnation of slabs at the base of the MTZ. I show that natural Al- and Fe-bearing enstatite reacts more readily than previous studies and by multiple transformation mechanisms at conditions as low as 1200°C and 18 GPa. Metastable enstatite is thus unlikely to survive to the base of the MTZ. Additionally, coherent growth of akimotoite and other high-pressure phases along polysynthetic twin boundaries provides a mechanism for the inheritance of crystallographic preferred orientation from previously deformed enstatite-bearing rocks within subducting slabs.
The Great Basin (GB) in the western U.S. is part of the diffuse North American-Pacific plate boundary. The interior of the GB occasionally produces large earthquakes, yet the current distribution of regional seismic networks poorly samples it. The EarthScope USArray Transportable Array provides unprecedented station density and data quality for the central GB. I use this dataset to develop an earthquake catalog for the region that is complete to M 1.5. The catalog contains small-magnitude seismicity throughout the interior of the GB. The spatial distribution of earthquakes is consistent with recent regional geodetic studies, confirming that the interior of the GB is actively deforming everywhere and all the time. Additionally, improved event detection thresholds reveal that swarms of temporally-clustered repeating earthquakes occur throughout the GB. The swarms are not associated with active volcanism or other swarm triggering mechanisms, and therefore, may represent a common fault behavior.
Enstatite (Mg,Fe)SiO3 is the second most abundant mineral within subducting lithosphere. Previous studies suggest that metastable enstatite within subducting slabs may persist to the base of the mantle transition zone (MTZ) before transforming to high-pressure polymorphs. The metastable persistence of enstatite has been proposed as a potential cause for both deep-focus earthquakes and the stagnation of slabs at the base of the MTZ. I show that natural Al- and Fe-bearing enstatite reacts more readily than previous studies and by multiple transformation mechanisms at conditions as low as 1200°C and 18 GPa. Metastable enstatite is thus unlikely to survive to the base of the MTZ. Additionally, coherent growth of akimotoite and other high-pressure phases along polysynthetic twin boundaries provides a mechanism for the inheritance of crystallographic preferred orientation from previously deformed enstatite-bearing rocks within subducting slabs.
ContributorsLockridge, Jeffrey Steven (Author) / Sharp, Thomas (Thesis advisor) / Arrowsmith, Ramon (Thesis advisor) / Shim, Sang-Heon (Committee member) / Garnero, Edward (Committee member) / Leinenweber, Kurt (Committee member) / Arizona State University (Publisher)
Created2015
Description
The transport of hydrogen to the Earth’s deep interior remains uncertain. The upper mantle minerals have very low hydrogen solubilities (hundreds of ppm). The hydrogen storage capability in the transition zone minerals (2 wt%) is high compared to those of the upper mantle. The hydrogen storage in the lower mantle is not well known. The main minerals in the lower mantle bridgmanite and ferropericlase have very low hydrogen storage capacities (less than 20 ppm). In order to further understand the hydrogen storage in the lower mantle, a series of experiments had been conducted to simulate the environment similar to the Earth’s mantle. The experiments with hydrous Mg2SiO4 ringwoodite (Rw) show that it converts to crystalline dense hydrous silica, stishovite (Stv) or CaCl2-type SiO2(mStv), containing ∼1 wt% H2O together with bridgmanite (Brd) and MgO at the pressure-temperature conditions expected for lower mantle depths between approximately 660 to 1600 km. Brd would break down partially to dense hydrous silica (6–25 mol%) and(Mg,Fe)O in mid-mantle regions with 0.05–0.27 wt% H2O. The hydrous stishovite has a CaCl2 structure, which is common among hydrous minerals in the lower mantle. Based on this observation, I hypothesize the existence of hydrous phases in the lower mantle. The experiments found a new hexagonal iron hydroxide (η-Fe12O18+x/2Hx) between the stability fields of the epsilon and pyrite-type FeOOH at 60–80 GPa and high temperature. The new phase contains less H2O, limiting the H2O transport from the shallow to the deep mantle in the Fe–O–H system. Possible hydrogen storage in Ca-perovskite was studied. CaPv could contain 0.5–1 wt% water and the water in CaPv could distort the crystal structure of CaPv from cubic to tetragonal structure. In conclusion, hydrogen can be stored in hydrous stishovite in the shallower depth of the lower mantle. At greater depth, the new η phase and pyrite-type phase would take over the hydrogen storage. The role of CaPv in deep water storage needs to be considered in future studies.
ContributorsChen, Huawei (Author) / Shim, Sang-Heon (Thesis advisor) / Garnero, Edward (Committee member) / Bose, Maitrayee (Committee member) / Li, Mingming (Committee member) / Leinenweber, Kurt (Committee member) / Arizona State University (Publisher)
Created2019
Description
The redox conditions of Earth have been changing since proto-Earth’s accretion from the solar nebula. These changes have influenced the distribution and partitioning of volatile elements between the atmosphere and the mantle (Righter et al., 2020; Stagno and Fei, 2020. Though oxygen fugacity fO2 is arguably not the main factor for phase stability at certain pressure-temperature conditions (McCammon, 2005), it can influence which phases are stable, especially within a closed system such as the ones presented in this study. Despite the importance of controlling fO2 for interpreting the history of planetary bodies, there have been no methods to control the redox conditions in the laser-heated diamond anvil cell (LHDAC). This thesis has examined the feasibility for controlling redox conditions in the LHDAC using a mixture of Ar and H2 for insulation media. The experiments of this study were carried out at the GSECARS sector of the Advanced Photon Source at Argonne National Laboratory. In this study, α-Fe2O3 (hematite), ε-FeOOH (CaCl2-type), and Fe3O4 (magnetite) starting materials were used for probing changes of redox conditions. Experiments were also conducted with a pure Ar-medium for ε-FeOOH at the same pressure-temperature conditions of the hydrogen-bearing medium in order to provide a reference point for data which has uncontrolled redox conditions for an initially Fe(2+)-free material. The results for the ε-FeOOH starting material in Ar show transformation to ι-Fe2O3 (Rh2O3(II)-type) at 30.0 GPa and 1900 K, while in Ar + H2 it transformed to Fe5O7 with minor FeH (dhcp) at 30.0 GPa and 1850 K. For α-Fe2O3 in Ar + H2, it was found to convert to ε-FeOOH, Fe5O7, Fe5O6, and FeH (dhcp) at 36.5 GPa and 1800 K. For Fe3O4 in Ar + H2, it was found to convert to Fe4O5 (CaFe3O5-type), Fe5O6, and minor FeH (fcc) at 26.0 GPa and 1800 K. These results demonstrate that H in an Ar medium can promote the conversion of some Fe(3+) to Fe(2+) and Fe(0). However, the formation of ε-FeOOH in the α-Fe2O3 starting material suggests that H may participate in the chemical reaction of iron oxides.
ContributorsKulka, Britany Lynn (Author) / Shim, Sang-Heon (Thesis advisor) / Sharp, Thomas (Committee member) / Leinenweber, Kurt (Committee member) / Hervig, Richard (Committee member) / Arizona State University (Publisher)
Created2021