Ph.D. - Geology and Geophysics
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Item Olivine as a Probe into the Early Thermal Histories of Solar System Samples(2023) Nelson, William S.; Hammer, Julia E.; Geology and GeophysicsItem Understanding Lunar Volcanic Processes And Mare Surface Age-dating Via Remote Sensing(University of Hawaii at Manoa, 2023) Giguere, Thomas A.; Gillis-Davis, Jeffrey J.; Geology and GeophysicsThe Moon has a long and complex history of volcanism, which shapes the face that we see from Earth to this day. In this dissertation, we use remote sensing to examine multiple locations on the Moon to understand the regional volcanic processes along with their eruption ages. We begin (chapter 2) with the lunar floor-fractured crater Gassendi and surrounding area, which were examined with high-resolution Lunar Reconnaissance Orbiter Camera imagery and other remote-sensing data to characterize and understand the volcanism in the southwestern region. This region exhibits a variety of volcanic features (e.g., cryptomaria deposits, pyroclastic deposits, maria, lava lakes). We confirm the existence of a previously identified cryptomare deposit, identify an additional cryptomare deposit west of Gassendi crater, and a pyroclastic northeast of Gassendi. Spectral and geochemical anomalies associated with dark-haloed impact craters reveal cryptomaria deposits in the western Gassendi crater floor and previously unmapped mare basalt within northeastern Gassendi. We identified three separate lava lakes on the northeast, northwest, and southwest floor of Gassendi crater based on morphology analogous to terrestrial lava lakes, geochemical signatures, and digital terrain data. Crater count (model) age data suggest the lava lakes were active at ~3.6 Ga (300 Ma after floor emplacement). Criteria used to identify lava lakes in Gassendi were applied globally to locate candidate lava lakes within floor-fractured craters. With the identification of lava lake morphology, both in Gassendi crater and in other floor-fractured craters, the current ascent and eruption models should be revised to allow for at least short-term connection between magma supply at depth and surface lava lakes. Hence, this integration of multiple perspectives afforded by recent remote data sets reveals new views about lunar volcanic processes. Next (chapter 3), we examine Northeastern Oceanus Procellarum (NE-OP) study area, which is a patchwork of lava flows that range in model age from 1.4 – 3.5 Ga (average age for all count areas is 2.3 Ga), but whose FeO and TiO2 contents deviate little. The intermediate TiO2 content values (4.0–6.8 wt.%) exhibited by the mare in this region represent material that is underrepresented in the current lunar sample collection. The model ages in the study region are bimodal (~2.2 Ga and ~3.0+ Ga), with eruption of lava flows at the Chang‘E-5 landing site occurring at ~3.0 Ga. By comparison, other investigators estimate the model age of the Chang‘E-5 site to be ~1.2 to 1.6 Ga. We find preliminary evidence that differences in measurement methodology may lead to disparate model ages and explain the difference in predicted model age of the Chang‘E-5 site. We finish (chapter 4) with an examination of three NASA CLPS landing sites in the lunar maria (i.e., Reiner Gamma, Mare Crisium, and Lacus Mortis) and used crater counting techniques to determine the age of the mare (absolute model age). We compare differences in researcher measurement techniques and place the sites in regional context with regards to their lava flow ages. Two researchers performed crater density measurements at the three sites, using identical imagery with the same illumination conditions, and the same software tools. The uniform nature of the analysis environment allowed researchers to use accepted crater counting techniques to determine absolute model ages (AMA), while subsequently allowing the examination of the variations in the personal approaches used by the researchers. Comparisons revealed variations in researcher methodology and resulting AMAs. Landing sites were subdivided into two or more smaller count areas and we determined that all areas have mare basalts that are Imbrian in age. Variations in AMAs between researchers were the result of differences in the number of secondary and degraded craters identified and to a lesser extent crater diameter measurements. Building on the legacy work of the crater counting community, we recommend rigorous secondary crater identification and exclusion, DTM aspect-based diameters to calibrate measurements, high-resolution orbital imagery to improve rimcrest location measurements, and surface imagery to verify rimcrest condition.Item From Faulting On Earth To Faulting On Other Worlds: Modeling The Stress Evolution Of Strike-slip Faulting On The San Andreas Fault System, On Titan, And On Ganymede(University of Hawaii at Manoa, 2022) Burkhard, Liliane ML; Lucey, Paul; Smith-Konter, Bridget R.; Geology and GeophysicsStrike-slip interaction between rigid lithosphere plates causes many of the world's most dangerous earthquakes since plate displacement can be quite large in a single event. Strike-slip tectonism appears to be also widespread throughout the icy ocean worlds in our Solar System, acting as a driver of surface structural evolution and perhaps as a conduit for the exchange of surface and subsurface materials via shear heating processes. Understanding the stress variations of such fault networks can give us an insight into the geologic evolution of planetary bodies throughout the universe. The first study presented in this work models the stress changes of the San Andreas Fault System, analyzing the magnitude and build-up of Coulomb stress along the segments in the area of the Cajon Pass in southern California. As in the past, similar joint ruptures of these segments might occur in the future, and our work suggests that the junction between the San Andreas and San Jacinto faults at the Cajon Pass plays a larger role in seismic hazard in southern California than previously understood because it could function as an ‘earthquake gate’. This research also demonstrates how we can evaluate paleoseismic data sets and comprehend prehistoric and historic fault activity using physics-based models. The second study presented focuses on modeling the possibility of strike-slip faulting on Titan, an icy moon of Saturn, where limited returned data at present hinders the remote exploration of the surface. Titan has stable liquids both on the surface and in the subsurface, and is consequently a prime candidate for astrobiological exploration. We investigate the potential of strike-slip tectonics governed by Coulomb failure laws and tidal stresses, and undertake a sensitivity analysis of Titan's shear failure inclinations, given optimal failure circumstances that may occur due to pore fluid interactions. Findings of this study indicate that shear failure is possible at shallow fault depths and for ideally orientated faults under diurnal tidal stress conditions due to such pore fluid pressures, especially in the polar areas. Strike-slip faulting is not only plausible, but it may also be an active deformation process on Titan's surface and subsurface based on interpretation of geologic features observed in radar imagery. On Ganymede, an icy moon of Jupiter, strike-slip faulting has been identified through observational data and studied with tidal stress models, suggesting that a higher past eccentricity and/or nonsynchronous rotation must have existed to generate the stresses needed for fault displacement. In the last study presented in this work, we produce a crater count analysis on Ganymede to verify the published relative ages and shear deformation of tectonic units, investigate a period of higher eccentricity using the previously established methods and raise the hypothesis of impacts producing widespread tectonic features. The unique geodynamics of an ice shell may permit an extensive effect from an impact generated seismic event, causing rapid fault slip and spreading features. The analyzed tectonic features in the Nippur/Philus Sulci region appear to be clustered in age, suggesting three eras of distinct activity: One era was ancient, following the high impact rate that produced the heavily cratered dark terrain, the second intermediate era could be correlated with a period of higher orbital eccentricity, causing fault slip and deformation, and some features in the third and youngest era might be associated in time with the most recent basin-forming impact of Gilgamesh. Taken together, these three studies motivate future research and investigations into strike-slip tectonism and impact craters on icy moons and elsewhere, as they can help uncover the tectonic past and form estimates for the future.Item Understanding variations in deformation and seismic behavior at subduction zones(University of Hawaii at Manoa, 2021) Tilley, Hannah; Moore, Gregory F.; Geology and GeophysicsSubduction zone faults accommodate relative plate motions with spatially varying deformation and seismic behavior. Subducting topography and sediment properties play a key role in modulating the deformation and seismic behavior. We studied two subduction zones, the Nankai Trough and the Hikurangi margin, using new high resolution and 3D seismic data, as well as decades worth of legacy data, to constrain the subduction input and determine the relationship between the sediment and plate characteristics, and variations in deformation and seismic behavior at subduction zones. We found that subducting basement topography is the main driver of upper plate deformation above a site of slow earthquakes at the Hikurangi margin; the upper plate faults responsible for deformation in the mid-slope may be responsible for local microseismicity. We also found that the oceanic basement topography influences the location of contourites and turbidites, which results in highly localized heterogeneities in the porosity and permeability of sediment deposits. Upon subduction, these patchy deposits may result in localized compartments of excess pore pressure, which may pre-condition the plate interface for slow slip behavior. Subducting topography, as well as sediment thickness and lithology, also influences the width of protothrust zones, which form in localized areas seaward of the deformation front. The width of the protothrust zone is important because it influences the style of deformation along the frontal thrust. Our studies show that variations in the sediment characteristics of the incoming plate are highly localized, particularly in areas where there is significant basement topography. As a result, variations in deformation and seismic behavior at convergent margins are also highly localized. This variability needs to be considered at all subduction zones when assessing the seismic hazard potential of margins.Item Seismicity, focal mechanisms and morphology of subducted lithosphere in the Papua New Guinea-Solomon Islands region(University of Hawaii at Manoa, 1985) Cooper, Patricia Ann; Geology and GeophysicsThe Papua New Guinea-Solomon Islands region is a major component of the Western Melanesian Borderlands, the convergent boundary between the northward-moving Inda-Australian Plate and the westwardmoving Pacific Plate (Figure 1.1). The region represents a wItem Petrogenesis of basaltic rocks from the Mariana Trough(University of Hawaii at Manoa, 1981) Fryer, Patricia; Geology and GeophysicsThe Mariana Trough, a young, actively spreading back-arc bas in, 1s very similar tectonically to normal mid-ocean ridges. The major difference 1s proximity of the spreading center 1n the Mariana Trough to an active subduction zone. Basaltic glasses retrieItem Tectonic history of the Fiji Plateau(University of Hawaii at Manoa, 1979) Halunen, Arlie John; Geology and GeophysicsMarine geophysical data collected along 18,600 miles of cruise track significantly augment our knowledge of geotectonics of the Fiji Plateau....The proposed model consists of reversal of a Northwest-trending proto-New Hebrides island arc, and subsequent mItem Age and tectonic relationships among volcanic chains on the Pacific plate(University of Hawaii at Manoa, 1978) Epp, David.; Geology and GeophysicsThe Hawaiian-Emperor volcanic chain is used as a model to predict the ages of other volcanic chains on the Pacific plate. The Hawaiian Emperor chain is assumed to have been formed at a hot spot, and is thus used to approximate the direction of motion of tItem Oceanic mantle phases recorded on hydrophones and seismographs in the northwestern Pacific at distances between 7° and 40°(University of Hawaii at Manoa, 1971) Walker, Daniel A.; Geology and GeophysicsBody-wave data from 60 earthquakes recorded on hydrophones at Midway, Wake, and Eniwetok and from 100 earthquakes recorded on seismographs at Midway, Wake, and Marcus indicate the following for the Northwestern Pacific Basin area: Observed times of P-waveItem Detailed structural interpretations of the Pacific oceanic crust using ASPER and ocean-bottom seismometer methods(University of Hawaii at Manoa, 1972) Hussong, Donald M.; Geology and GeophysicsThe ASPER (Airgun-Sonobuoy-Precision Echo Recorder) seismic refraction exploration technique has provided an inexpensive means of obtaining numerous crustal velocity determinations with greater structural resolution than conventional two-ship explosion me