Matching Items (14)
Description
The occurrence of exogenic, meteoritic materials on the surface of any world presents opportunities to explore a variety of significant problems in the planetary sciences. In the case of Mars, meteorites found on its surface may help to 1) constrain atmospheric conditions during their time of arrival; 2) provide insights into possible variabilities in meteoroid type sampling between Mars and Earth space environments; 3) aid in our understanding of soil, dust, and sedimentary rock chemistry; 4) assist with the calibration of crater-age dating techniques; and 5) provide witness samples for chemical and mechanical weathering processes. The presence of reduced metallic iron in approximately 88 percent of meteorite falls renders the majority of meteorites particularly sensitive to oxidation by H2O interaction. This makes them excellent markers for H2O occurrence. Several large meteorites have been discovered at Gusev Crater and Meridiani Planum by the Mars Exploration Rovers (MERs). Significant morphologic characteristics interpretable as weathering features in the Meridiani suite of iron meteorites include a 1) large pit lined with delicate iron protrusions suggestive of inclusion removal by corrosive interaction; 2) differentially eroded kamacite and taenite lamellae on three of the meteorites, providing relative timing through cross-cutting relationships with deposition of 3) an iron oxide-rich dark coating; and 4) regmaglypted surfaces testifying to regions of minimal surface modification; with other regions in the same meteorites exhibiting 5) large-scale, cavernous weathering. Iron meteorites found by Mini-TES at both Meridiani Planum and Gusev Crater have prompted laboratory experiments designed to explore elements of reflectivity, dust cover, and potential oxide coatings on their surfaces in the thermal infrared using analog samples. Results show that dust thickness on an iron substrate need be only one tenth as great as that on a silicate rock to obscure its infrared signal. In addition, a database of thermal emission spectra for 46 meteorites was prepared to aid in the on-going detection and interpretation of these valuable rocks on Mars using Mini-TES instruments on both MER spacecraft. Applications to the asteroidal sciences are also relevant and intended for this database.
ContributorsAshley, James Warren (Author) / Christensen, Philip R. (Thesis advisor) / Sharp, Thomas G (Committee member) / Shock, Everett L (Committee member) / Hervig, Richard L (Committee member) / Zolotov, Mikhail Y (Committee member) / Arizona State University (Publisher)
Created2011
Description
Fluorine (F) is a volatile constituent of magmas and hydrous mantle minerals. Compared to other volatile species, F is highly soluble in silicate melts, allowing F to remain in the melt during magma differentiation and rendering F less subject to disturbance during degassing upon magma ascent. Hence, the association between fluorine in basalts and fluorine in the mantle source region is more robust than for other volatile species. The ionic radius of F- is similar to that of OH- and O2-, and F may substitute for hydroxyl and oxygen in silicate minerals and melt. Fluorine is also incorporated at trace levels within nominally anhydrous minerals (NAMs) such as olivine, clinopyroxene, and plagioclase. Investigating the geochemical behavior of F in NAMs provides a means to estimate the pre-eruptive F contents of degassed magmas and to better understand the degassing behavior of H. The partition coefficients of F were determined for clinopyroxene, olivine, plagioclase, and hornblende within melts of olivine-minette, augite-minette, basaltic andesite, and latite compositions. The samples analyzed were run products from previously-published phase-equilibria experiments. Fluorine was measured by secondary ion mass spectrometry (SIMS) using an 16O- primary beam and detection of negative secondary ions (19F-, 18O-, 28Si-). SIMS ion intensities are converted to concentrations by analyzing matrix-matched microanalytical reference materials and constructing calibration curves. For robust F calibration standards, five basaltic glasses (termed Fba glasses) were synthesized in-house using a natural tholeiite mixed with variable amounts of CaF2. The Fba glasses were characterized for F content and homogeneity, using both SIMS and electron-probe microanalysis (EPMA), and used as F standards. The partition coefficients for clinopyroxene (0.04-028) and olivine (0.01-0.16) varied with melt composition such that DF (olivine-minette) < DF (augite-minette) < DF (basaltic andesite) < DF (latite). Crystal chemical controls were found to influence the incorporation of F into clinopyroxene, but none were found that affected olivine. Fluorine partitioning was compared with that of OH within clinopyroxenes, and the alumina content of clinopyroxene was shown to be a strong influence on the incorporation of both anions. Fluorine substitution into both olivine and clinopyroxene was found to be strongly controlled by melt viscosity and degree of melt polymerization.
ContributorsGuggino, Steve (Author) / Hervig, Richard L (Thesis advisor) / Donald, Burt M (Committee member) / Amanda, Clarke B (Committee member) / Lynda, Williams B (Committee member) / Stanley, Williams N (Committee member) / Arizona State University (Publisher)
Created2012
Description
Studying natural variations in the isotopic composition of oxygen-sensitive elements in ancient marine sediments is a powerful way to study the geochemical evolution of Earth’s environments in the past. My dissertation focused on two broad aspects of isotope geochemistry: 1) the development of rhenium (Re) isotopes as a paleoredox and nuclear forensics tool, and 2) the application of mercury (Hg) isotopes as a tool to trace Hg mobility in the environment and what this movement means for isotopic changes in sedimentary rocks used to study Earth’s past. Chapter 2 is the first examination of Re isotopes in sedimentary rocks that formed ~2.5 billion years ago during a period of ocean and atmospheric oxygenation prior to the Great Oxidation Event. The data show variations in Re isotope ratios coincide with evidence for changes in oceanic and atmospheric oxygenation, supporting the use of Re isotopes as a tool to track paleoredox conditions throughout Earth's history. Another application of rhenium isotopes is explored in the third chapter on nuclear forensics. Rhenium isotopes in uranium ore concentrates (UOC) from known production locations revealed more than double the range of isotope fractionation previously reported for any natural geologic samples so far. These first Re isotope ratio data indicate that Re is a promising new tool for provenance assessment of UOCs. Chapter 4 focuses on geochemical applications of Hg isotopes. Mercury isotopes in shales are a geochemical tool that can be utilized to study the prevalence of global volcanism and detect oxygen-depleted conditions in the photic zone of ancient oceans. I measured Hg isotope ratio data from a Devonian shale bed in a road cut with varying degrees of weathering that has been well characterized for variations in elemental concentrations and other isotopic ratios. I found significant variation in mass-dependent and mass-independent Hg isotope fractionation in weathered samples. Surprisingly, however, I observed both loss and gain of Hg, when only significant loss was expected based on prior weathering studies. These findings improve the understanding of Hg mobility in nature and indicate that mass-independent fractionation can be modified after deposition in surprising ways.
ContributorsSullivan, Daniel Louis (Author) / Anbar, Ariel D (Thesis advisor) / Gordon, Gwyneth W (Committee member) / Hartnett, Hilairy E (Committee member) / Hervig, Richard L (Committee member) / Zheng, Wang (Committee member) / Arizona State University (Publisher)
Created2023
Description
Planetary surfaces are constantly evolving through a series of endogenic and exogenic processes. Multi-temporal observations enable the detection of these newly formed surface changes. Analysis techniques of these observations require precise image geolocation obtainable only with accurate optical and projection distortion corrections. In this study, the Clementine Ultraviolet-Visible camera is geometrically calibrated, and the spacecraft orientation knowledge is refined, aligning the entire dataset to the reference frame defined by the more recent Lunar Reconnaissance Orbiter mission. This direct registration approach improved the geolocation to within 0.084 pixels (i.e., sub-pixel), enabling new optical maturity and mineral composition maps aligned with the present reference frame.Next, new surface changes on Mercury are discovered with a geometrically calibrated Mercury Dual Imaging Camera suite. Over twenty surface changes varying in size from 450 to 4400 meters are identified that formed between 2011 to 2015. Exogenic impacts do not explain all the surface changes witnessed. Some changes occurred on slopes near prominent tectonic features suggesting a potential tie to seismic activity. A pair of other reflectance changes were identified around hollow formations, meaning the surface feature is still evolving. This temporal dataset provides the first direct evidence of endogenic and exogenic activities of the innermost planet.
Lastly, the color and photometric properties of newly formed impact craters are explored using hundreds of observations acquired before and post-impact. These observations reveal new details about the distal surface changes associated with the impact process. Phase ratio imaging enables a measurement of the phase curve slope, including near opposition (phase ~ 0°). While the entire proximal ejecta blanket shows an increase in the optical surface roughness properties, the region adjacent to the crater rim (1.0 to 1.25 crater radii from the center) expresses a broadening of the opposition surge consistent with the presence of fine-scale surface particles and rocks. Finally, Hapke parameters and color maps are also derived for the entire region before and after the impact event to quantify changes in surface properties and the maturity state of the regolith. This work provides new insight into the broad extent of surface modifications around newly formed craters.
ContributorsSpeyerer, Emerson (Author) / Robinson, Mark S (Thesis advisor) / Bell, James F (Committee member) / Hervig, Richard L (Committee member) / Scowen, Paul A (Committee member) / Zolotov, Mikhail Y (Committee member) / Arizona State University (Publisher)
Created2023
Description
Oxygen fugacity (ƒO2) is a thermodynamic variable used to represent the redox state of a material or a system. It is equivalent to the partial pressure of oxygen in a particular environment corrected for the non-ideal behavior of the gas. ƒO2 is often used to indicate the potential for iron to occur in a more oxidized or reduced state at a particular temperature and pressure in a natural system. Secondary ion mass spectrometry (SIMS) is a powerful analytical instrument that can be used to analyze elemental and isotopic compositional information about microscopic features within solid materials. SIMS analyses of the secondary ion energy distribution of semi-pure metals demonstrate that the energy spectrum of individual mass lines can provide information about alterations in its surface environment.
The application of high-resolution (see Appendix C) energy spectrum calibrations to natural ilmenite led to the investigation of zirconium (90Zr+) and niobium (93Nb+) as potential indicators of sample ƒO2. Energy spectrum measurements were performed on an array of ilmenite crystals from the earth’s upper mantle retrieved from kimberlites and from a reduced meteorite. In all studied materials, variability in the peak shape and width of the energy spectra has been correlated with inferred sample ƒO2. The best descriptor of this relationship is the full-width at half-maximum (FWHM; see Appendix C) of the energy spectra for each sample. It has been estimated that a 1eV change in the FWHM of 93Nb+ energy spectra is roughly equivalent to 1 log unit ƒO2. Simple estimates of precision suggest the FWHM values can be trusted to 1eV and sample ƒO2 can be predicted to ±1 log unit, assuming the temperature of formation is known.
The work of this thesis also explores the applicability of this technique beyond analysis of semi-pure metals and ilmenite crystals from kimberlites. This technique was applied to titanium oxides experimentally formed at known ƒO2 as well as an ilmenite crystal that showed compositional variations across the grain (i.e., core to rim chemical variations). Analyses of titanium oxides formed at known ƒO2 agree with the estimation that 1 eV change in the FWHM of 93Nb+ is equivalent to ~1 log unit ƒO2 (in all cases but one); this is also true for analyses of a natural ilmenite crystal with compositional variations across the grain.
The application of high-resolution (see Appendix C) energy spectrum calibrations to natural ilmenite led to the investigation of zirconium (90Zr+) and niobium (93Nb+) as potential indicators of sample ƒO2. Energy spectrum measurements were performed on an array of ilmenite crystals from the earth’s upper mantle retrieved from kimberlites and from a reduced meteorite. In all studied materials, variability in the peak shape and width of the energy spectra has been correlated with inferred sample ƒO2. The best descriptor of this relationship is the full-width at half-maximum (FWHM; see Appendix C) of the energy spectra for each sample. It has been estimated that a 1eV change in the FWHM of 93Nb+ energy spectra is roughly equivalent to 1 log unit ƒO2. Simple estimates of precision suggest the FWHM values can be trusted to 1eV and sample ƒO2 can be predicted to ±1 log unit, assuming the temperature of formation is known.
The work of this thesis also explores the applicability of this technique beyond analysis of semi-pure metals and ilmenite crystals from kimberlites. This technique was applied to titanium oxides experimentally formed at known ƒO2 as well as an ilmenite crystal that showed compositional variations across the grain (i.e., core to rim chemical variations). Analyses of titanium oxides formed at known ƒO2 agree with the estimation that 1 eV change in the FWHM of 93Nb+ is equivalent to ~1 log unit ƒO2 (in all cases but one); this is also true for analyses of a natural ilmenite crystal with compositional variations across the grain.
ContributorsDillon, Sarah Marie (Author) / Hervig, Richard L (Thesis advisor) / Shim, Sang-Heon (Committee member) / Williams, Peter (Committee member) / Arizona State University (Publisher)
Created2019
Description
Volcanic devolatilization is one of the major processes in the global nitrogen cycle. Past studies have often estimated the magnitude of this flux using volcanic emission measurements, which are limited to currently active systems and sensitive to atmospheric contamination. A different methodological approach requires appropriate analytical parameters for nitrogen analysis in silicate glasses by secondary ion mass spectrometry (SIMS), which have not yet been established. To this end, we analyze various ion implanted basaltic and rhyolitic glasses by SIMS. We demonstrate that water content significantly affects the ion yields of 14N+ and 14N16O−, as well as the background intensity of 14N+ and 12C+. Application of implant-derived calibrations to natural samples provide the first reported concentrations of nitrogen in melt inclusions. These measurements are from samples from the Bishop Tuff in California, the Huckleberry Ridge Tuff of the Yellowstone Volcanic Center, and material from the Okaia and Oruanui eruptions in the Taupo Volcanic Center. In all studied material, we find maximum nitrogen contents of less than 45 ppm and that nitrogen concentration varies positively with CO2 concentration, which is interpreted to reflect partial degassing trend. Using the maximum measured nitrogen contents for each eruption, we find that the Bishop released >3.6 x 1013 g of nitrogen, the Huckleberry Ridge released >1.3 x 1014 g, the Okaia released >1.1 x 1011 g of nitrogen, the Oruanui released >4.7 x 1013 g of nitrogen. Simple calculations suggest that with concentrations such as these, rhyolitic eruptions may ephemerally increase the nitrogen flux to the atmosphere, but are insignificant compared to the 4 x 1021 g of nitrogen stored in the atmosphere.
ContributorsRegier, Margo Elaine (Author) / Hervig, Richard L (Thesis advisor) / Roggensack, Kurt (Committee member) / Till, Christy B. (Committee member) / Arizona State University (Publisher)
Created2016
Description
Impact cratering has played a key role in the evolution of the solid surfaces of Solar System bodies. While much of Earth’s impact record has been erased, its Moon preserves an extensive history of bombardment. Quantifying the timing of lunar impact events is crucial to understanding how impacts have shaped the evolution of early Earth, and provides the basis for estimating the ages of other cratered surfaces in the Solar System.
Many lunar impact melt rocks are complex mixtures of glassy and crystalline “melt” materials and inherited clasts of pre-impact minerals and rocks. If analyzed in bulk, these samples can yield complicated incremental release 40Ar/39Ar spectra, making it challenging to uniquely interpret impact ages. Here, I have used a combination of high-spatial resolution 40Ar/39Ar geochronology and thermal-kinetic modeling to gain new insights into the impact histories recorded by such lunar samples.
To compare my data to those of previous studies, I developed a software tool to account for differences in the decay, isotopic, and monitor age parameters used for different published 40Ar/39Ar datasets. Using an ultraviolet laser ablation microprobe (UVLAMP) system I selectively dated melt and clast components of impact melt rocks collected during the Apollo 16 and 17 missions. UVLAMP 40Ar/39Ar data for samples 77135, 60315, 61015, and 63355 show evidence of open-system behavior, and provide new insights into how to interpret some complexities of published incremental heating 40Ar/39Ar spectra. Samples 77115, 63525, 63549, and 65015 have relatively simple thermal histories, and UVLAMP 40Ar/39Ar data for the melt components of these rocks indicate the timing of impact events—spanning hundreds of millions of years—that influenced the Apollo 16 and 17 sites. My modeling and UVLAMP 40Ar/39Ar data for sample 73217 indicate that some impact melt rocks can quantitatively retain evidence for multiple melt-producing impact events, and imply that such polygenetic rocks should be regarded as high-value sampling opportunities during future exploration missions to cratered planetary surfaces. Collectively, my results complement previous incremental heating 40Ar/39Ar studies, and support interpretations that the Moon experienced a prolonged period of heavy bombardment early in its history.
Many lunar impact melt rocks are complex mixtures of glassy and crystalline “melt” materials and inherited clasts of pre-impact minerals and rocks. If analyzed in bulk, these samples can yield complicated incremental release 40Ar/39Ar spectra, making it challenging to uniquely interpret impact ages. Here, I have used a combination of high-spatial resolution 40Ar/39Ar geochronology and thermal-kinetic modeling to gain new insights into the impact histories recorded by such lunar samples.
To compare my data to those of previous studies, I developed a software tool to account for differences in the decay, isotopic, and monitor age parameters used for different published 40Ar/39Ar datasets. Using an ultraviolet laser ablation microprobe (UVLAMP) system I selectively dated melt and clast components of impact melt rocks collected during the Apollo 16 and 17 missions. UVLAMP 40Ar/39Ar data for samples 77135, 60315, 61015, and 63355 show evidence of open-system behavior, and provide new insights into how to interpret some complexities of published incremental heating 40Ar/39Ar spectra. Samples 77115, 63525, 63549, and 65015 have relatively simple thermal histories, and UVLAMP 40Ar/39Ar data for the melt components of these rocks indicate the timing of impact events—spanning hundreds of millions of years—that influenced the Apollo 16 and 17 sites. My modeling and UVLAMP 40Ar/39Ar data for sample 73217 indicate that some impact melt rocks can quantitatively retain evidence for multiple melt-producing impact events, and imply that such polygenetic rocks should be regarded as high-value sampling opportunities during future exploration missions to cratered planetary surfaces. Collectively, my results complement previous incremental heating 40Ar/39Ar studies, and support interpretations that the Moon experienced a prolonged period of heavy bombardment early in its history.
ContributorsMercer, Cameron Mark (Author) / Hodges, Kip V (Thesis advisor) / Robinson, Mark S (Committee member) / Wadhwa, Meenakshi (Committee member) / Desch, Steven J (Committee member) / Hervig, Richard L (Committee member) / Arizona State University (Publisher)
Created2017
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 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.
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
Description
Isotope ratios of some trace metals have proven useful for tracking Earth’s ocean oxygenation history. As the limitations of some of these isotope systems are realized, it becomes increasingly important to develop new and complementary systems. This dissertation examines the utility of molybdenum (98Mo) and thallium (205Tl) isotope compositions preserved in ancient marine shales to track past ocean oxygenation. My approach is as follows: (1) as an initial exercise, apply the well-established Mo isotope system to a set of ancient shales; (2) validate the use of the newly developed Tl isotope system; and finally (3) examine the potential of applying Mo and Tl isotopes in tandem.
Increasingly heavier 98Mo are found in shales deposited during the Neoarchean (2,800 to 2,500 million years ago, or Ma), which would be a predicted consequence of progressive ocean oxygenation across this timeframe. Increasingly heavier 205Tl across a well-documented Mesozoic Oceanic Anoxic Event (~94 Ma), on the other hand, would be a predicted consequence of progressive ocean de-oxygenation. An anti-correlation in the first combined application of Mo and Tl isotopes in ancient shales provides a strong fingerprint for previously unrecognized levels of ocean oxygenation at ~2,500 Ma. Lastly, neither 98Mo or 205Tl behave as predicted in shales deposited during three Ediacaran Ocean Oxygenation Events (~635 Ma, ~580 Ma, and ~560 Ma). These unexpected trends are due, at least in part, to local-scale overprints that must be taken into consideration when pairing together Mo and Tl isotopes in shales.
The ability of the Mo and Tl isotope systems to track changes in past ocean oxygenation is confirmed in this dissertation. Both isotope systems have the potential to track these changes independently, but their combined utility is particularly powerful. Under ideal conditions, their combined application can provide an even more robust fingerprint for changes in past ocean oxygenation. Even under non-ideal conditions, their combined application makes it possible to decipher local-scale overprints from signals of past ocean oxygenation. It is therefore ideal, whenever possible, to measure both 98Mo and 205Tl in the same shale samples to assess past changes in ocean oxygenation.
Increasingly heavier 98Mo are found in shales deposited during the Neoarchean (2,800 to 2,500 million years ago, or Ma), which would be a predicted consequence of progressive ocean oxygenation across this timeframe. Increasingly heavier 205Tl across a well-documented Mesozoic Oceanic Anoxic Event (~94 Ma), on the other hand, would be a predicted consequence of progressive ocean de-oxygenation. An anti-correlation in the first combined application of Mo and Tl isotopes in ancient shales provides a strong fingerprint for previously unrecognized levels of ocean oxygenation at ~2,500 Ma. Lastly, neither 98Mo or 205Tl behave as predicted in shales deposited during three Ediacaran Ocean Oxygenation Events (~635 Ma, ~580 Ma, and ~560 Ma). These unexpected trends are due, at least in part, to local-scale overprints that must be taken into consideration when pairing together Mo and Tl isotopes in shales.
The ability of the Mo and Tl isotope systems to track changes in past ocean oxygenation is confirmed in this dissertation. Both isotope systems have the potential to track these changes independently, but their combined utility is particularly powerful. Under ideal conditions, their combined application can provide an even more robust fingerprint for changes in past ocean oxygenation. Even under non-ideal conditions, their combined application makes it possible to decipher local-scale overprints from signals of past ocean oxygenation. It is therefore ideal, whenever possible, to measure both 98Mo and 205Tl in the same shale samples to assess past changes in ocean oxygenation.
ContributorsOstrander, Chadlin Miles (Author) / Anbar, Ariel D (Thesis advisor) / Till, Christy B. (Committee member) / Wadhwa, Meenakshi (Committee member) / Hervig, Richard L (Committee member) / Mauskopf, Philip D (Committee member) / Arizona State University (Publisher)
Created2020
Description
My dissertation research broadly focuses on the geochemical and physical exchange of materials between the Earth’s crust and mantle at convergent margins, and how this drives the compositional diversity observed on the Earth’s surface. I combine traditional petrologic and geochemical studies of natural and experimental high-pressure mafic rocks, with thermodynamic modeling of high-pressure aqueous fluids and mafic-ultramafic lithologies allowing for more complete understanding of fluid-melt-rock interactions. The results of the research that follows has important implications for: the role of lower crustal foundering in the geochemical origin and evolution of the modern continental crust (Chapter 2; Guild et al., under review), metasomatic processes involving aqueous metal-carbon complexes in high pressure-temperature subduction zone fluids (Chapter 3; Guild & Shock, 2020), natural hydrous mineral stability at the slab-mantle interface (Chapter 4; Guild, et al., in preparation) and water-undersaturated melting in the sub-arc (Chapter 5; Guild & Till, in preparation).
ContributorsGuild, Meghan Rose (Author) / Till, Christy B. (Thesis advisor) / Shock, Everett L (Committee member) / Hervig, Richard L (Committee member) / Hartnett, Hilairy (Committee member) / Clarke, Amanda (Committee member) / Arizona State University (Publisher)
Created2020