Ph.D. - Geology and Geophysics

Permanent URI for this collectionhttps://hdl.handle.net/10125/2069

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Olivine as a Probe into the Early Thermal Histories of Solar System Samples
(University of Hawai'i at Manoa, 2023) Nelson, William S.; Hammer, Julia E.; Geology and Geophysics
Clues of our solar system’s history exist in igneous rocks that exist on every terrestrial body in the solar system. Temperature is one of the most important variables to describe and infer the formation and evolution of these rocks. If the temperatures a rock has experienced throughout its formation are known, we can gain a substantial understanding of the processes and conditions behind a rock and its surroundings. This thesis explores the utilization of the heterogeneous distribution of trace elements in olivine to reconstruct the high-temperature thermal histories of igneous rocks. A study of Apollo troctolite 76535 reveals comparatively rapid cooling timescales and demonstrates how one can use diffusive relaxation of heterogeneities to determine the maximum cooling timescales even with minimal constraints on high-temperature cooling rates. This study finds that phosphorus in olivine displays less diffusive relaxation than expected. So, we investigate the diffusive behavior of this element in olivine, both through models and in the lab. We find no evidence of phosphorus heterogeneities diffusively relaxing when reheated. So, we investigate these heterogeneities using nanoscale microscopy. We find these heterogeneities are many orders of magnitude smaller than previously assumed and determine a plausible accommodation mechanism that would explain a lack of diffusive relaxation. Finally, we investigate the relative cooling histories of porphyritic and barred olivine chondrules using a variety of other systems, demonstrating how one can use these methods even when uncertain about the environment, diffusivity of the element, and temperature. Altogether, this dissertation discusses how trace elements behave in olivine and how they can be used to reveal the high-temperature thermal histories of olivine crystals.
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 Geophysics
The 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.
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 Geophysics
Strike-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.
Understanding variations in deformation and seismic behavior at subduction zones
(University of Hawaii at Manoa, 2021) Tilley, Hannah; Moore, Gregory F.; Geology and Geophysics
Subduction 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.
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 Geophysics
The 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 w
Petrogenesis of basaltic rocks from the Mariana Trough
(University of Hawaii at Manoa, 1981) Fryer, Patricia; Geology and Geophysics
The 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 retrie
Tectonic history of the Fiji Plateau
(University of Hawaii at Manoa, 1979) Halunen, Arlie John; Geology and Geophysics
Marine 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 m
Age and tectonic relationships among volcanic chains on the Pacific plate
(University of Hawaii at Manoa, 1978) Epp, David.; Geology and Geophysics
The 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 t
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 Geophysics
Body-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-wave
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 Geophysics
The 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
Paleomagnetism of western equatorial Pacific sediment cores
(University of Hawaii at Manoa, 1974) Hammond, Stephen Randolph.; Geology and Geophysics
Stable, detrital paleomagnetism measured in samples from 78 deep-sea sediment cores from the western equatorial Pacific provides the basis for a regional comparison of sediment magnetic characteristics and determination of area-wide patterns of Pliocene-P
The Jurassic Meteorite Flux: A Record from Extraterrestrial Chrome-Spinels
(University of Hawaii at Manoa, 2020) Caplan, Caroline E.; Huss, Gary R.; Geology and Geophysics
This dissertation focuses on the classification of extraterrestrial chrome-spinels to determine meteorite types and fluxes during the Jurassic time period and the techniques needed to achieve such classifications. We know the relative abundances of meteorite types falling on Earth today, but we do not know what fell in the distant past. Abundances of the past are unknown because meteorites tend to only survive on Earth’s surface for a few tens of thousands of years due to the weathering environment of the Earth. Fortunately, chrome-spinels from disaggregated meteorites and micrometeorites can be preserved in limestone and retain their characteristic compositions. In many instances, the parent meteorite type of each grain can be determined by comparing their chemical compositions and oxygen isotope abundances to those of chrome-spinels from modern day meteorites. The goal of this dissertation is to classify chrome-spinel grains from the Jurassic period, determine the relative abundances of parent meteorite types, and compare these abundances to those of other time periods. This was achieved by ensuring we had a well-characterized database of chrome-spinel compositions from modern meteorites in order to reliably classify each remnant chrome-spinel. We also had to confirm that our chemistry and oxygen-isotope measurements of the Jurassic chrome-spinels were reliable. This was determined, in part, by taking new measurements of chrome-spinels from modern meteorites using the same electron and ion microprobes used for the remnant grains. It was also necessary to understand instrumental artifacts that may affect oxygen isotope abundances during ion probe measurements, such as the crystal orientation of chrome-spinel. We confidently classified the remnant chrome-spinels of the Jurassic using the compiled database, and compared the meteorite abundances to other time periods. However, it was difficult to determine the subgroup for a few of the ordinary-chondrite-like grains using chemistry and isotopes alone. In this event, (scanning) transmission electron microscope techniques were implemented to study the silicate inclusions within these chrome-spinels to help determine their parent meteorite type. Overall, this work supports the use of chemistry, oxygen isotopes, and inclusions to classify remnant chrome-spinels and demonstrates that meteorite populations from the past are different than today.
Lunar Geology Survey With Remote Sensing And Apollo Samples
(University of Hawaii at Manoa, 2020) Sun, Lingzhi; Lucey, Paul; Geology and Geophysics
In this dissertation, I analyze the mineralogy of lunar soil and core samples with spectroscopy. Using these sample data as ground truth, I study the global mineral abundances and Mg# (molar Mg/(Mg+Fe)) distribution through radiative transfermodeling and remotely sensed images. In Chapter 2, I study the major compositional classes of Apollo 15, 16 and 17 samples from the glass-free mineral modes derived by X-ray diffraction (XRD). Using sample data as ground truth, we mapped the global compositional class distributions, and our results suggest that both the lunar highlands and South Pole-Aitken (SPA) basin are enriched with noritic materials. I propose a "two mantles" hypothesis: The noritic composition in highland and SPA basin revealed an low-Ca pyroxene (LCP) rich upper mantle (low in Mg#) that existed before the mantle overturn; while the olivine-rich basin rings trapped the post-overturn upper mantle (high in Mg#). In Chapter 3, I present a model that can unmix mineral abundance and chemistry based on radiative transfer theory. A new set of optical constants for olivine, orthopyroxene and clinopyroxene is reported. I build a spectral library containing mineral mixtures of plagioclase, olivine, low-Ca pyroxene and high-Ca pyroxene and Mg# ranging within 40-90.The accuracy of our model is <3 vol% for olivine, low-Ca pyroxene and high-Ca pyroxene, <6 vol% for plagioclase, and <10 for Mg#. A global Mg# map is produced using our model and the Moon Mineralogy Mapper data, and the Mg# value is consistent with results from Lunar Prospector gamma-ray spectrometer. In Chapter 4, I present the preliminary results of the multiband images and hyperspectral measurements for the first dissection of core 73002. Both multiband images and hyperspectral data show systematic darkening and reddening from bottom to top of the core, indicating an increasing maturity from subsurface to surface soils. FeO and TiO2 abundances suggest the soils within the core have homogeneous compositions, suggesting little contamination from lateral mixing. An optical maturity profile along the core suggests the local vertical regolith reworking depth is about 14 cm, corresponding to a time range around 61 million years. During this time, maturity of surface soils changed from immature to submature.
Multi-tracer Approaches For Groundwater Discharge And Anthropogenic Pollution In The Pacific
(University of Hawaii at Manoa, 2020) McKenzie, Trista; Dulai, Henrietta; Geology and Geophysics
Submarine groundwater discharge (SGD), or groundwater that flows to the coastal ocean, is a significant source to both water and dissolved chemical budgets. While SGD fluxes frequently rival or exceed those associated with river discharge, it remains poorly characterized along most coastlines. SGD is also a frequently overlooked contaminant flux pathway, despite being a well-documented vector for excess nutrients or other contaminants derived from urban, agricultural, or industrial land-use to reach the coastal ocean. Commonly, local-scale SGD studies consider the coastal ocean in isolation from stream inputs, particularly stream baseflow, despite the direct connection between one another. Wastewater discharge is a common source of poor water quality. Aging wastewater infrastructure (WIS) that often uses antiquated technology leads to leakage to the groundwater that is difficult to detect. Onsite sewage disposal systems (OSDS; e.g., cesspools, septic tanks) are a common alternative to municipal wastewater treatment, while also a frequent source of groundwater pollution. This is particularly the case in areas with a high density of OSDS constructed along the coast, such as in Hawaiʻi. In addition to OSDS, fractured sewer lines are another potential source of wastewater leakage to groundwater. Wastewater discharge to natural waters remains a major issue globally, in part because it can be difficult to isolate the source and cause of the pollution. Contaminants of emerging concern (CECs; e.g., pharmaceuticals, industrial chemicals, pesticides) are pervasive in the environment, but can be used as tracers due to their uniquely anthropogenic source. Sea level rise (SLR) can also indirectly threaten water quality in coastal areas. In addition to surficial flooding, SLR will lead to groundwater inundation (GWI) of WIS and underground tanks or lead to increased salinization of water resources. To date, most SLR impact studies either focus on surface water impacts or are modeling-based studies, meaning few direct observations of GWI and its linkage to water quality decline exist. Chapter 2 of this dissertation links poor coastal water quality and nutrient pollution to total groundwater (stream baseflow + SGD) discharge along the steam-coastal continuum in a watershed with a high density of OSDS (Kāneʻohe, Hawaiʻi) using radon as a groundwater tracer. Additionally, SGD was also compared between perigean spring (king) and spring tides. Increased SGD and nutrient fluxes were observed during the king tide, implying worsening water quality with SLR. Chapter 3 demonstrates that SGD is a source of wastewater contamination to the coastal ocean in a highly urbanized embayment (Sydney Harbour, Australia) using radium isotopes as groundwater tracers and CECs are the primary tracer for for wastewater. Major findings include: (1) SGD is a pathway for CECs to reach the coastal ocean; (2) increasing CEC inventories are related to increasing water residence time; and (3) two of the measured CECs – dioxins and ibuprofen – were in concentrations that pose a risk to the ecosystem. Chapter 4 provides field-based observations of tidally driven GWI of WIS using radon and CECs as tracers during spring tides in Honolulu, Hawaiʻi. Two pathways were studied: (1) direct GWI of coastal WIS that flows to the coastal ocean as SGD, and (2) indirect inundation of WIS through flooded storm drains. For the direct pathway, CEC fluxes increased at high tide, reflecting additional inundation of WIS with rising water levels. In comparison, CEC concentrations decreased at high tide via the indirect pathway, signifying dilution of constantly leaking sewer lines by the rising water table. This chapter demonstrates a tidal connection between groundwater discharge and water quality and has implications for worsening water quality with SLR. This dissertation examined groundwater as a contaminant vector to streams and the coastal ocean using a combination of groundwater (radon and radium) and contaminant (CECs, nutrients, dissolved organic carbon) tracers. Radon was used in two innovative ways in this dissertation: (1) separation of groundwater and surface water along the stream-coastal continuum – leading to a better understanding of contaminant pathways in a polluted watershed; and (2) during spring tides linking GWI of coastal WIS to groundwater discharge to the coastal ocean and storm drains. The results also demonstrate promising use of CECs as wastewater tracers in novel environments and under transient conditions. Future work can build upon this dissertation by conducting further studies that consider groundwater discharge ridge to reef, increasing the number of CECs analyzed as tracers (particularly in groundwater and non-freshwater environments), and running additional studies in coastal areas that add direct evidence for tidally-driven GWI.
Impact Impacts On The Moon, Mercury, And Europa
(University of Hawaii at Manoa, 2020) Costello, Emily S.; Lucey, Paul; Geology and Geophysics
In this work, I reconstitute and improve upon an Apollo-era statistical model of impact gardening (Gault et al. 1974) and validate the model against the gardening implied by remote sensing and analysis of Apollo cores. My major contribution is the modeling and analysis of the influence of secondary crater-forming impacts, which dominate impact gardening. Secondary craters are formed when debris that has been launched by the collision of an object from space with the surface of a body falls back onto the surface with sufficient energy to produce a crater. Interest in secondary craters and their importance in the evolution of the surfaces of Solar System bodies was re-inspired by a study of the secondary craters of Mars’ Zunil crater (McEwen et al. 2005), which shocked many in the cratering community for being so large, far-flung, and numerous. Similarly, studies of Jupiter’s icy moon Europa’s surface showed that most craters that are < 1 km in diameter are secondary craters (Birehaus et al. 2001; 2005). Secondary impacts appear to be significant drivers of changes at the uppermost surface on bodies across the solar system. I apply my model of impact gardening due to secondary impacts to explore the implications of impact gardening on the Moon, Mercury, and Europa, with a specific interest in the implications of impact gardening on the distribution and evolution of water ice resources in the solar system.
Understanding the Composition and Evolution of the Lunar Surface Through Laboratory Space Weathering Simulations and Remote Sensing
(University of Hawaii at Manoa, 2019) Corley, Laura Michelle; Gillis-Davis, Jeffrey J.; Geology and Geophysics
Without an atmosphere, the lunar surface is vulnerable to space weathering, a process by which solar wind, galactic rays, and micrometeoroids bombard a planetary body and alter the surface’s physical, chemical, and spectral properties. The most well studied spectral changes are in the visible to near-infrared wavelengths, where increasing exposures to space weathering results in decreased reflectance, spectral reddening, and subdued absorption bands. Thus, mineralogical and compositional analyses of planetary bodies via spectral reflectance measurements are complicated by the space weathering process. The first part of this dissertation investigates sites on the lunar surface that contain olivine, a mineral that is relatively sparse in the crust and is critical to understanding the magmatic history of the Moon. We examine both known and previously unidentified olivine exposures using hyperspectral visible to near-infrared data from the Moon Mineralogy Mapper. In an effort to determine the origins and transport mechanisms that led to these individual exposures, we estimate crustal thicknesses using the Gravity Recovery and Interior Laboratory, investigate geologic settings using images from the Lunar Reconnaissance Orbiter Camera, and estimate mineral abundances using radiative transfer modeling. Our combined geophysical and spectral investigation allows for the identification of both volcanic and mantle-derived olivine. The second part of this dissertation characterizes space weathering effects in order to improve compositional and mineralogical analyses of spectral data in the future. We simulate space weathering (i.e., micrometeoroid bombardment) in the laboratory via kinetic impact, laser irradiation, and a combination of the two methods on lunar analog material to understand the various physical and spectral changes produced by each method and determine which method produces the most accurate lunar space weathering effects. We conclude that a combination of the two methods best replicates lunar-like space weathering, in part because subsequent laser irradiation of the analog that was first weathered by kinetic impacts enhances darkening of the material and produces more submicroscopic iron. This effect is likely due to the lower melting/vaporization temperature of the glass relative to minerals, which allows iron to be extracted from the glass more easily than from a crystalline structure. We also examine how space weathering affects regoliths in cold environments. We perform laser irradiation when minerals are held at two different temperatures, 85 K and 295 K. With equal amounts of irradiation, we find that the olivine and pyroxene irradiated at 85 K have higher reflectance than those irradiated at 295 K. Analyses of our samples using Scanning Transmission Electron Microscopy suggest that space weathering of low-temperature regolith produces less melting and less submicroscopic iron. Our results help to quantify the effects of space weathering on low-temperature regolith, which needs to be considered when interpreting spectral measurements at different latitudes, geologic settings, and distance from the Sun.
Carbon in deep Earth from high-pressure and high-temperature studies of the Fe-C system
(University of Hawaii at Manoa, 2019) Lai, Xiaojing; Chen, Bin; Geology and Geophysics
Carbon in deep Earth, as well as the nature and extent of deep carbon cycles, is essential for understanding the physical and chemical evolution of habitable planets. This dissertation includes three projects to address carbon in the Earth’s deep interior from the perspectives of high-pressure mineral physics. The first project (Chapter 3) comprises experimental and computational results on the structural evolution of iron-nickel liquids alloyed with carbon at high pressures. Our X-ray diffraction experiments up to 7.3 gigapascals (GPa) demonstrate that Fe90Ni10 liquids alloyed with 3 and 5 wt.% carbon undergo a polyamorphic liquid structure transition at approximately 5 GPa. Corroborating the experimental observations, our first-principles molecular dynamic calculations reveal that the structural transitions result from the marked prevalence of three-atom face-sharing polyhedral connections in the liquids at >5 GPa. The structure and polyamorphic transitions of liquid iron-nickel-carbon alloys govern their physical and chemical properties and may thus cast fresh light on the chemical evolution of terrestrial planets and moons. The second project (Chapter 4) concerns the high-pressure thermoelastic properties of one of the Earth’s inner core candidates, iron carbide, Fe7C3. In this study, we performed synchrotron-based single-crystal X-ray diffraction experiments using an externally-heated diamond anvil cell to determine the crystal structure and thermoelastic properties of Fe7C3 up to 80 GPa and 800K. Our diffraction data indicate that Fe7C3 adopts an orthorhombic structure under the experimentally investigated conditions. The pressure-volume-temperature relations of Fe7C3 were obtained by fitting the high-temperature Birch-Murnaghan equation of state. We also observed an anisotropic elastic response to changes in pressure and temperature along the different crystallographic directions. Fe7C3 has strong anisotropic compressibilities with the linear moduli Ma > Mc > Mb from zero pressure to core pressures at 300K, revealing the b axis to be the most compressible. The thermal expansion of c3 is approximately four times larger than that of a3 and b3 at 600K and 700K, implying that high temperature may significantly influence the elastic anisotropy of Fe7C3. Therefore, the effect of high temperature needs to be considered when using Fe7C3 to explain the anisotropy of the Earth’s inner core. The third project (Chapter 5) examines the high-pressure phase stability and melting behavior of the Fe-C-(H) system by both multi-anvil press and diamond anvil cell experiments. Metallic iron reacted with an organic C-H compound, which served as carbon and hydrogen source, under conditions of high pressure and temperature. With excess C-H compound, Fe carbide and molecular hydrogen formed first from the reaction at high pressures and relatively low temperature. With increasing temperature, Fe hydride and diamond were found to form. With excess Fe, by contrast, the presence of hydrogen depressed the melting temperature of the Fe-C system, such that the eutectic melting temperatures for both the Fe-C and Fe-C-H systems are below the mantle geotherm. Those Fe-rich melts may facilitate the cycling of subducted carbon and hydrogen in the deep mantle. These melts may provide a necessary melt environment for the growth of macro diamonds in deep mantle; they could also serve as a potential reservoir for both carbon and hydrogen in the mantle.
Tectonic Influences On Surficial Processes And Deformation Along The Nankai Accretionary Prism, Southwest Japan
(University of Hawaii at Manoa, 2019) Lackey, Jason; Moore, Gregory F.; Geology and Geophysics
This dissertation presents interpretations of new, high-resolution multibeam bathymetric data, reprocessed 3D seismic data and drill cores from the southern Kumano Basin and Nankai accretionary prism off southwest Japan. These combined data sets show a widely variable surface morphology and provide insight into: 1) the distribution of landsliding along the prism, 2) a nested series of moderately-sized mass transport deposits (MTDs) along the seaward side of the forearc basin, 3) and record ~2.87 million years of structural and depositional history of a trench slope basin. We mapped and cataloged 718 individual landslide scars, 56% of which are part of complex (multi-slide) structures. One of the more prominent complexes in the forearc basin is completely contained within the 3D seismic volume and dates to ~0.3 – 0.9 Ma. A kinematic investigation revealed 10 individual landslides that originate from the same prominent scar as a likely result of earthquake cycle related faulting along a regional out-of-sequence thrust (megasplay fault). Fault related landsliding also occurs within a trench slope basin seaward of the outer ridge. The 3D seismic volume and drill core data permit a kinematic reconstruction of the basin since ~2.4 Ma. In the NE, deformation is accommodated by the main megasplay while deformation in the SW is along break-backward imbricate branches of the megasplay. We suggest that these differences are caused by subsurface geometry and seamount subduction and directly influence the depth and surface morphology of the trench slope basin via landsliding.
Compressional Behavior Of Hydrogen-bonded Crystals: Anhydrous Comparisons And Polymorphism
(University of Hawaii at Manoa, 2018-12) Shelton, Hannah Laura; Dera, Przemyslaw; Geology and Geophysics
Hydrogen, despite its ubiquity, remains a little-understood factor in high pressure mineral physics and material science. Hydrogen in the solid state can profoundly affect the structure and behavior of crystal, often as hydrogen bonding interactions. In a geological setting, the addition of hydrogen – typically as water – drastically changes the material properties of mantle minerals, including the rheology, electrical conductivity, elasticity, and phase transition conditions. However, the degree of influence that hydrogen exerts is often variable, which makes the determination of structural and thermoelastic information at high pressures more difficult. To better understand its role in crystal structures, analogue materials have been used to explore the influence of hydrogen in crystal structures at high pressure. In this dissertation, several high pressure crystal structures with relevance to planetary and materials science have been examined in the context of hydrous and anhydrous analogues. Chapter 3 describes the high pressure behavior of the mineral β-behoite (Be(OH)2) as a hydrous analogue structure to α-cristobalite, a high-temperature polymorph of SiO2. The low-pressure structures β-behoite and α-cristobalite are topologically identical, but differ by the added presence of O-H···O hydrogen bonds, which add structural rigidity and resist distortion of the structure. As a result, behoite does not follow cristobalite’s phase transition pathway to higher coordination states. This pathway is discussed in detail within Chapter 4, where the change in Si ion coordination at high pressures creates a polymorph called cristobalite X-I. This phase is the only known octahedrally coordinated phase of SiO2 that cannot be returned to ambient pressures, and represents a bridge in the densification process of SiO2 that occurs within the Earth. Additionally, cristobalite X-I is discussed as an analogue structure for six-coordinated CO2, which may occur in the interiors of giant planets. Lastly, Chapter 5 examines high-pressure hydrogen bonding and polymorphism in melamine, an aromatic organic molecule derived from s-triazine that forms an extensive network of hydrogen bonds. These hydrogen bonds inhibit reactivity and polymorphism when compared to non-hydrogen bonded organic crystals like s-triazine and benzene, and may act as a stabilizer in the formation of co-crystals relevant to molecular materials and organic minerals.
Multi-Decadal Space-Based Observations of Basaltic Effusive Eruptions from MODIS Infrared Data
(University of Hawaii at Manoa, 2018-08) Bonny, Estelle S.; Geology and Geophysics
Lava discharge rate, the volume of lava emitted from a vent at any given time, is a critical parameter that volcanologists use to study effusive eruptions. It not only gives us information about the eruption dynamics but also is a key control on how far lava can flow. Thermal infrared satellite remote sensing has shown advantages for deriving lava discharge rate and monitoring temporal changes during an eruption, with a higher temporal resolution than in-situ measurements. In this dissertation, I use NASA’s MODIS (Moderate Resolution Imaging Spectroradiometer) sensor to study 104 basaltic effusive eruptions over a 15-year time period, to retrieve time-averaged discharge rates (TADR). I first show that the theoretical asymmetrical shape of TADR time-series can be used to predict the end of lava flow-forming eruptions from space. Then, I investigate the 2014-2015 Holuhraun eruption, Iceland, the country’s largest basaltic effusive eruption in the past 200 years. I compared the satellite- and ground-based TADR for this exceptional six month-long eruption. Final flow volumes estimated from both techniques were in good agreement. However, systematic differences between satellite and field TADR estimates the first 30 days of the eruption indicated that the satellite-derived method, and some of the assumptions on which it is based, need to be revised to reconcile these differences for lava flows that are areally extensive and highly radiant. Finally, I tested three different thermal satellite-based methods to retrieve TADR (Harris et al., 1997a; Wright et al., 2001a; and Coppola et al., 2012) to determine whether they yield comparable results, and assess the absolute accuracy of these approaches. I used the global TADR time-series database of basaltic effusive eruptions to estimate final flow volumes (by integrating the TADR time-series), which can be very well constrained at the end of an eruption unlike instantaneous discharge rates. Using final flow volumes from the literature and inferred volumes from satellite images, we demonstrated that the Harris et al. (1997a) method yields TADR closer to reality. However, we showed that the accuracy of TADR could be improved by updating the coefficient method (Wright et al., 2001a) with our eruption database.

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