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- All Subjects: Geochemistry
- Genre: Academic theses
- Creators: Hartnett, Hilairy E
- Creators: Hervig, Richard L
- Member of: ASU Electronic Theses and Dissertations
Description
Boron concentrations and isotopic composition of phlogopite mica, amphibole, and selected coexisting anhydrous phases in mantle-derived xenoliths from the Kaapvaal Craton were measured by secondary ion mass spectrometry in an effort to better understand the B isotope geochemistry of the subcontinental lithospheric mantle (SCLM) and its implications for the global geochemical cycle of B in the mantle. These samples display a wide, and previously unrecognized, range in their boron contents and isotopic compositions reflecting a complex history involving melt depletion and metasomatism by subduction- and plume-derived components, as well as late stage isotopic exchange related to kimberlite emplacements. Micas from ancient lithospheric harzburgite metasomatized by slab-derived fluids suggest extensive B-depletion during subduction, resulting in low-B, isotopically light compositions whereas kimberlite-related metasomatic products and a sample from the 2 Ga Palabora carbonatite have boron isotopic compositions similar to proposed primitive mantle. The results suggest that subduction of oceanic lithosphere plays a limited role in the B geochemistry of the convecting mantle.
ContributorsGuild, Meghan R (Author) / Hervig, Richard L (Thesis advisor) / Bell, David R. (Committee member) / Mcnamara, Allen (Committee member) / Arizona State University (Publisher)
Created2014
Description
The focus of this thesis is to study dissolved organic carbon composition and reactivity along the Colorado and Green Rivers. Dissolved organic carbon (DOC) in large-scale, managed rivers is relatively poorly studied as most literature has focused on pristine unmanaged rivers. The Colorado River System is the 7th largest in the North America; there are seventeen large dams along the Colorado and Green River. DOC in rivers and in the lakes formed by dams (reservoirs) undergo photo-chemical and bio-degradation. DOC concentration and composition in these systems were investigated using bulk concentration, optical properties, and fluorescence spectroscopy. The riverine DOC concentration decreased from upstream to downstream but there was no change in the specific ultraviolet absorbance at 254 nm (SUVA254). Total fluorescence also decreased along the river. In general, the fluorescence index (FI) increased slightly, the humification index (HIX) decreased, and the freshness index (β/α) increased from upstream to downstream. Photo-oxidation and biodegradation experiments were used to determine if the observed changes in DOC composition along the river could be driven by these biogeochemical alteration processes.
In two-week natural sunlight photo-oxidation experiments the DOC concentration did not change, while the SUVA254 and TF decreased. In addition, the FI and ‘freshness’ increased and HIX decreased during photo-oxidation. Photo-oxidation can explain the upstream to downstream trends for TF, FI, HIX, and freshness observed in river water. Serial photo-oxidation and biodegradation experiments were performed on water collected from three sites along the Colorado River. Bulk DOC concentration in all samples decreased during the biodegradation portion of the study, but DOC bioavailability was lower in samples that were photo-oxidized prior to the bioavailability study.
The upstream to downstream trends in DOC concentration and composition along the river can be explained by a combination of photo-chemical and microbial degradation. The bulk DOC concentration change is primarily driven by microbial degradation, while the changes in the composition of the fluorescent DOC are driven by photo-oxidation.
In two-week natural sunlight photo-oxidation experiments the DOC concentration did not change, while the SUVA254 and TF decreased. In addition, the FI and ‘freshness’ increased and HIX decreased during photo-oxidation. Photo-oxidation can explain the upstream to downstream trends for TF, FI, HIX, and freshness observed in river water. Serial photo-oxidation and biodegradation experiments were performed on water collected from three sites along the Colorado River. Bulk DOC concentration in all samples decreased during the biodegradation portion of the study, but DOC bioavailability was lower in samples that were photo-oxidized prior to the bioavailability study.
The upstream to downstream trends in DOC concentration and composition along the river can be explained by a combination of photo-chemical and microbial degradation. The bulk DOC concentration change is primarily driven by microbial degradation, while the changes in the composition of the fluorescent DOC are driven by photo-oxidation.
ContributorsBowman, Margaret (Author) / Hartnett, Hilairy E (Thesis advisor) / Hayes, Mark A. (Committee member) / Herckes, Pierre (Committee member) / Arizona State University (Publisher)
Created2015
Description
This dissertation examines two topics of emerging interest in the field of organic geochemistry. The topic of the first portion of the dissertation is cold organic geochemistry on Saturn's moon Titan. Titan has an atmosphere and surface that are rich in organic compounds. Liquid hydrocarbons exist on the surface, most famously as lakes. Photochemical reactions produce solid organics in Titan's atmosphere, and these materials settle onto the surface. At the surface, liquids can interact with solids, and geochemical processes can occur. To better understand these processes, I developed a thermodynamic model that can be used to calculate the solubilities of gases and solids in liquid hydrocarbons at cryogenic temperatures. The model was parameterized using experimental data, and provides a good fit to the data. Application of the model to Titan reveals that the equilibrium composition of surface liquids depends on the abundance of methane in the local atmosphere. The model also indicates that solid acetylene should be quite soluble in surface liquids, which implies that acetylene-rich rocks should be susceptible to chemical erosion, and acetylene evaporites may form on Titan. In the latter half of this dissertation, I focus on hot organic geochemistry below the surface of the Earth. Organic compounds are common in sediments. Burial of sediments leads to changes in physical and chemical conditions, promoting organic reactions. An important organic reaction in subsurface environments is decarboxylation, which generates hydrocarbons and carbon dioxide from simple organic acids. Fundamental knowledge about decarboxylation is required to better understand how the organic and inorganic compositions of sediments evolve in response to changing geochemical conditions. I performed experiments with the model compound phenylacetic acid to obtain information about mechanisms of decarboxylation in hydrothermal fluids. Patterns in rates of decarboxylation of substituted phenylacetic acids point to a mechanism that proceeds through a ring-protonated zwitterion of phenylacetic acid. In contrast, substituted sodium phenylacetates exhibit a different kinetic pattern, one that is consistent with the formation of the benzyl anion as an intermediate. Results from experiments with added hydrochloric acid or sodium hydroxide, and deuterated water agree with these interpretations. Thus, speciation dictates mechanism of decarboxylation.
ContributorsGlein, Christopher R (Author) / Shock, Everett L (Thesis advisor) / Hartnett, Hilairy E (Committee member) / Zolotov, Mikhail Y (Committee member) / Williams, Lynda B (Committee member) / Gould, Ian R (Committee member) / Arizona State University (Publisher)
Created2012
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
In many natural systems aqueous geochemical conditions dictate the reaction pathways of organic compounds. Geologic settings that span wide ranges in temperature, pressure, and composition vastly alter relative reaction rates and resulting organic abundances. The dependence of organic reactions on these variables contributes to planetary-scale nutrient cycling, and suggests that relative abundances of organic compounds can reveal information about inaccessible geologic environments, whether from the terrestrial subsurface, remote planetary settings, or even the distant past (if organic abundances are well preserved). Despite their relevance to planetary modeling and exploration, organic reactions remain poorly characterized under geochemically relevant conditions, especially in terms of their reaction kinetics, mechanisms, and equilibria.
In order to better understand organic transformations in natural systems, the reactivities of oxygen- and nitrogen-bearing organic functional groups were investigated under experimental hydrothermal conditions, at 250°C and 40 bar. The model compounds benzylamine and α-methylbenzylamine were used as analogs to environmentally relevant amines, ultimately elucidating two dominant deamination mechanisms for benzylamine, SN1 and SN2, and a single SN1 mechanism for deamination of α-methylbenzylamine. The presence of unimolecular and bimolecular mechanisms has implications for temperature dependent kinetics, indicating that Arrhenius rate extrapolation is currently unreliable for deamination.
Hydrothermal experiments with benzyl alcohol, benzylamine, dibenzylamine, or tribenzylamine as the starting material indicate that substitution reactions between these compounds (and others) are reversible and approach metastable equilibrium after 72 hours. These findings suggest that relative ratios of organic compounds capable of substitution reactions could be targeted as tracers of inaccessible geochemical conditions.
Metastable equilibria for organic reactions were investigated in a natural low-temperature serpentinizing continental system. Serpentinization is a water-rock reaction which generates hyperalkaline, reducing conditions. Thermodynamic calculations were performed for reactions between dissolved inorganic carbon and hydrogen to produce methane, formate, and acetate. Quantifying conditions that satisfy equilibrium for these reactions allows subsurface conditions to be predicted. These calculations also lead to hypotheses regarding active microbial processes during serpentinization.
In order to better understand organic transformations in natural systems, the reactivities of oxygen- and nitrogen-bearing organic functional groups were investigated under experimental hydrothermal conditions, at 250°C and 40 bar. The model compounds benzylamine and α-methylbenzylamine were used as analogs to environmentally relevant amines, ultimately elucidating two dominant deamination mechanisms for benzylamine, SN1 and SN2, and a single SN1 mechanism for deamination of α-methylbenzylamine. The presence of unimolecular and bimolecular mechanisms has implications for temperature dependent kinetics, indicating that Arrhenius rate extrapolation is currently unreliable for deamination.
Hydrothermal experiments with benzyl alcohol, benzylamine, dibenzylamine, or tribenzylamine as the starting material indicate that substitution reactions between these compounds (and others) are reversible and approach metastable equilibrium after 72 hours. These findings suggest that relative ratios of organic compounds capable of substitution reactions could be targeted as tracers of inaccessible geochemical conditions.
Metastable equilibria for organic reactions were investigated in a natural low-temperature serpentinizing continental system. Serpentinization is a water-rock reaction which generates hyperalkaline, reducing conditions. Thermodynamic calculations were performed for reactions between dissolved inorganic carbon and hydrogen to produce methane, formate, and acetate. Quantifying conditions that satisfy equilibrium for these reactions allows subsurface conditions to be predicted. These calculations also lead to hypotheses regarding active microbial processes during serpentinization.
ContributorsRobinson, Kirtland J (Author) / Shock, Everett L (Thesis advisor) / Herckes, Pierre (Committee member) / Hartnett, Hilairy E (Committee member) / Anbar, Ariel D (Committee member) / Arizona State University (Publisher)
Created2017
Description
Atmospheric deposition of iron (Fe) can limit primary productivity and carbon dioxide uptake in some marine ecosystems. Recent modeling studies suggest that biomass burning aerosols may contribute a significant amount of soluble Fe to the surface ocean. Existing studies of burn-induced trace element mobilization have often collected both entrained soil particles along with material from biomass burning, making it difficult to determine the actual source of aerosolized trace metals.
In order to better constrain the importance of biomass versus entrained soil as a source of trace metals in burn aerosols, small-scale burn experiments were conducted using soil-free foliage representative of a variety of fire-impacted ecosystems. The resulting burn aerosols were collected in two stages (PM > 2.5 μm and PM < 2.5 μm) on cellulose filters using a high-volume air sampler equipped with an all-Teflon impactor. Unburned foliage and burn aerosols were analyzed for Fe and other trace metals using inductively coupled plasma mass spectrometry (ICP-MS).
Results of this analysis show that less than 2% of Fe in plant biomass is likely mobilized as atmospheric aerosols during biomass burning events. The results of this study and estimates of annual global wildfire area were used to estimate the impact of biomass burning aerosols on total atmospheric Fe flux to the ocean. I estimate that foliage-derived Fe contributes 114 ± 57 Gg annually. Prior studies, which implicitly include both biomass and soil-derived Fe, concluded that biomass burning contributes approximately 690 Gg of Fe. Together, these studies suggest that fire-entrained soil particles contribute 83% (576 Gg) of Fe in biomass burning emissions, while plant derived iron only accounts for at most 17%.
In order to better constrain the importance of biomass versus entrained soil as a source of trace metals in burn aerosols, small-scale burn experiments were conducted using soil-free foliage representative of a variety of fire-impacted ecosystems. The resulting burn aerosols were collected in two stages (PM > 2.5 μm and PM < 2.5 μm) on cellulose filters using a high-volume air sampler equipped with an all-Teflon impactor. Unburned foliage and burn aerosols were analyzed for Fe and other trace metals using inductively coupled plasma mass spectrometry (ICP-MS).
Results of this analysis show that less than 2% of Fe in plant biomass is likely mobilized as atmospheric aerosols during biomass burning events. The results of this study and estimates of annual global wildfire area were used to estimate the impact of biomass burning aerosols on total atmospheric Fe flux to the ocean. I estimate that foliage-derived Fe contributes 114 ± 57 Gg annually. Prior studies, which implicitly include both biomass and soil-derived Fe, concluded that biomass burning contributes approximately 690 Gg of Fe. Together, these studies suggest that fire-entrained soil particles contribute 83% (576 Gg) of Fe in biomass burning emissions, while plant derived iron only accounts for at most 17%.
ContributorsSherry, Alyssa M (Author) / Anbar, Ariel D (Thesis advisor) / Herckes, Pierre (Thesis advisor) / Hartnett, Hilairy E (Committee member) / Fraser, Matthew (Committee member) / Arizona State University (Publisher)
Created2019
Description
Organic reactions in natural hydrothermal settings have relevance toward the deep carbon cycle, petroleum formation, the ecology of deep microbial communities, and potentially the origin of life. Many reaction pathways involving organic compounds under geochemically relevant hydrothermal conditions have now been characterized, but their mechanisms, in particular those involving mineral surface catalysis, are largely unknown. The overall goal of this work is to describe these mechanisms so that predictive models of reactivity can be developed and so that applications of these reactions beyond geochemistry can be explored. The focus of this dissertation is the mechanisms of hydrothermal dehydration and catalytic hydrogenation reactions. Kinetic and structure/activity relationships show that elimination occurs mainly by the E1 mechanism for simple alcohols via homogeneous catalysis. Stereochemical probes show that hydrogenation on nickel occurs on the metal surface. By combining dehydration with and catalytic reduction, effective deoxygenation of organic structures with various functional groups such as alkenes, polyols, ketones, and carboxylic acids can be accomplished under hydrothermal conditions, using either nickel or copper-zinc alloy. These geomimetic reactions can potentially be used in biomass reduction to generate useful fuels and other high value chemicals. Through the use of earth-abundant metal catalysts, and water as the solvent, the reactions presented in this dissertation are a green alternative to current biomass deoxygenation/reduction methods, which often use exotic, rare-metal catalysts, and organic solvents.
ContributorsBockisch, Christiana (Author) / Gould, Ian R (Thesis advisor) / Hartnett, Hilairy E (Committee member) / Shock, Everett L (Committee member) / Arizona State University (Publisher)
Created2018
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
The present work covers two distinct microanalytical studies that address issues in planetary materials: (1) Genesis Na and K solar wind (SW) measurements, and (2) the effect of water on high-pressure olivine phase transformations.
NASA’s Genesis mission collected SW samples for terrestrial analysis to create a baseline of solar chemical abundances based on direct measurement of solar material. Traditionally, solar abundances are estimated using spectroscopic or meteoritic data. This study measured bulk SW Na and K in two different Genesis SW collector materials (diamond-like carbon (DlC) and silicon) for comparison with these other solar references. Novel techniques were developed for Genesis DlC analysis. Solar wind Na fluence measurements derived from backside depth profiling are generally lower in DlC than Si, despite the use of internal standards. Nevertheless, relative to Mg, the average SW Na and K abundances measured in Genesis wafers are in agreement with solar photospheric and CI chondrite abundances, and with other SW elements with low first ionization potential (within error). The average Genesis SW Na and K fluences are 1.01e11 (+9e09, -2e10) atoms/cm2 and 5.1e09 (+8e08, -8e08) atoms/cm2, respectively. The errors reflect average systematic errors. Results have implications for (1) SW formation models, (2) cosmochemistry based on solar material rather than photospheric measurements or meteorites, and (3) the accurate measurement of solar wind ion abundances in Genesis collectors, particularly DlC and Si.
Deep focus earthquakes have been attributed to rapid transformation of metastable olivine within the mantle transition zone (MTZ). However, the presence of H2O acts to overcome metastability, promoting phase transformation in olivine, so olivine must be relatively anhydrous (<75 ppmw) to remain metastable to depth. A microtextural analysis of olivine phase transformation products was conducted to test the feasibility for subducting olivine to persist metastably to the MTZ. Transformation (as intracrystalline or rim nucleation) shifts from ringwoodite to ringwoodite-wadsleyite nucleation with decreasing H2O content within olivine grains. To provide accurate predictions for olivine metastability at depth, olivine transformation models must reflect how changing H2O distributions lead to complex changes in strain and reaction rates within different parts of a transforming olivine grain.
NASA’s Genesis mission collected SW samples for terrestrial analysis to create a baseline of solar chemical abundances based on direct measurement of solar material. Traditionally, solar abundances are estimated using spectroscopic or meteoritic data. This study measured bulk SW Na and K in two different Genesis SW collector materials (diamond-like carbon (DlC) and silicon) for comparison with these other solar references. Novel techniques were developed for Genesis DlC analysis. Solar wind Na fluence measurements derived from backside depth profiling are generally lower in DlC than Si, despite the use of internal standards. Nevertheless, relative to Mg, the average SW Na and K abundances measured in Genesis wafers are in agreement with solar photospheric and CI chondrite abundances, and with other SW elements with low first ionization potential (within error). The average Genesis SW Na and K fluences are 1.01e11 (+9e09, -2e10) atoms/cm2 and 5.1e09 (+8e08, -8e08) atoms/cm2, respectively. The errors reflect average systematic errors. Results have implications for (1) SW formation models, (2) cosmochemistry based on solar material rather than photospheric measurements or meteorites, and (3) the accurate measurement of solar wind ion abundances in Genesis collectors, particularly DlC and Si.
Deep focus earthquakes have been attributed to rapid transformation of metastable olivine within the mantle transition zone (MTZ). However, the presence of H2O acts to overcome metastability, promoting phase transformation in olivine, so olivine must be relatively anhydrous (<75 ppmw) to remain metastable to depth. A microtextural analysis of olivine phase transformation products was conducted to test the feasibility for subducting olivine to persist metastably to the MTZ. Transformation (as intracrystalline or rim nucleation) shifts from ringwoodite to ringwoodite-wadsleyite nucleation with decreasing H2O content within olivine grains. To provide accurate predictions for olivine metastability at depth, olivine transformation models must reflect how changing H2O distributions lead to complex changes in strain and reaction rates within different parts of a transforming olivine grain.
ContributorsRieck, Karen Dianne (Author) / Hervig, Richard L (Thesis advisor) / Sharp, Thomas G (Thesis advisor) / Jurewicz, Amy J G (Committee member) / Wadhwa, Meenakshi (Committee member) / Williams, Peter (Committee member) / Young, Patrick A (Committee member) / Arizona State University (Publisher)
Created2015