abstract: The hydrothermal chemistry of organic compounds influences many critical geological processes, including the formation of oil and gas reservoirs, the degradation and transport of organic matter in sedimentary basins, metabolic cycles in the deep subsurface biosphere, and possibly prebiotic organic synthesis related to the origin of life. In most previous studies of hydrothermal organic reactions the emphasis has been mainly on determining reaction product distributions, studies that provide detailed mechanistic information or direct evidence for specific reaction intermediates are rare. To develop a better understanding, I performed hydrothermal experiments with model ketone compound dibenzylketone (DBK), which serves as a quite useful tool to probe the bond breaking and forming processes in hydrothermal geochemical transformations. A careful study of reaction kinetics and products of DBK in Chapter 2 of this dissertation reveals reversible and irreversible reaction pathways, and provides evidence for competing ionic and radical reaction mechanisms. The majority of the observed products result from homolytic carbon-carbon and carbon-hydrogen bond cleavage and secondary coupling reactions of the benzyl and related radical intermediates. In the third chapter of the dissertation, a novel hydrothermal photochemical method is studied, which enabled in situ independent generation of the relevant radicals and effectively separated the radical and ionic reactions that occur simultaneously in pure thermal reactions. In the following chapter, I focus on the role of minerals on ketone hydrothermal reactions. Minerals such as quartz and corundum have no detectable effect on DBK, whereas magnetite, hematite, and troilite all increase ketone reactivity to various extents. The influence of these iron-bearing minerals can be attributed to the mineral surface catalysis or the solution chemistry change that is presumably caused by dissolved inorganic species from minerals. In addition, some new discoveries on strong oxidizing effect of copper (II) ion under hydrothermal conditions are described in the latter chapter of the dissertation, where examples of clean and rapid reactions that converted alcohols to aldehyde and aldehydes to carboxylic acids are included. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2014

abstract: The beginning of our Solar System, including events such as the formation of the first solids as well as the accretion and differentiation of planetary bodies, is recorded in meteoritic material. This record can be deciphered using petrographic, geochemical and isotopic investigations of different classes of meteorites and their components. In this dissertation, I have investigated a variety of isotope systematics in chondritic and achondritic meteorites to understand processes that have shaped our Solar System. Specifically, the investigations conducted here are in two main areas: 1) Hydrogen isotope systematics in a meteorite representing the freshest known sample of the martian crust, and 2) Isotopic studies (specifically relating to high resolution chronology, nucleosynthetic anomalies and mass-dependent fractionations) in calcium-aluminum-rich inclusions, which are thought to be the earliest-formed solids in the Solar System. Chapter 1 of this dissertation presents a review of the hydrogen isotopic compositions of various planetary bodies and reservoirs in the Solar System, which could serve as tracers for the volatile sources. Chapter 2 focuses on an investigation of the hydrogen isotopic systematics in the freshest martian meteorite fall, Tissint, using the Cameca IMS-6f secondary ion mass spectrometer (SIMS). These first two chapters comprise the first part of this dissertation. The second part is comprised of chapters 3 through 6 and is focused on isotopic analyses of Calcium-Aluminum-rich Inclusions (CAIs). Chapter 3 is a review of CAIs, which record some of the earliest processes that occurred in the solar nebula. Chapter 4 presents the results of an investigation of the 26Al-26Mg short-lived chronometer (half-life ~0.72 Ma) in two CAIs and their Wark-Lovering (WL) rims from a CV3 carbonaceous chondrite using the Cameca NanoSIMS 50L. Chapter 5 is focused on the results of a study of the Zr isotope compositions of a suite of 15 CAIs from different carbonaceous chondrites using multicollector inductively coupled plasma mass spectrometry (MC-ICPMS), in order to identify nucleosynthetic anomalies in the CAI-forming region. Chapter 6 focuses on the mass-dependent Mg isotopic compositions measured in 11 CAIs from the Allende CV3 carbonaceous chondrite using MC-ICPMS, to evaluate effects of thermal processing on CAIs. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2016

Large scale mapping in Prosser Township has revealed an entirely felsic subaqueous volcanic sequence containing both pyroclastic and effusive high silica rhyolites which are exceptionally well preserved. The eruption sequence alternates between thin coulees and tuffaceous units, all of which are covered by two distinct units, a pumice- and spatter-rich tuff breccia and a quartz porphyritic rhyolite. Aphyric coulees are well preserved, having flow banding, perlite, and hyaloclastite, which are indicative of a glassy protolith. In the coulee interior there is no evidence of sea-floor clay alteration; the former glass has been isochemically recrystallized to an inter-grown mixture of quartz and plagioclase during metamorphism. These formerly glassy rhyolites formed thin flows by normal effusive eruption without the intervention of high temperatures or volatile depolymerising agents. The crystal-poor rocks were not erupted near their liquidus temperatures (ca. 980°C) as suggested by earlier work using zircon saturation thermometry, but instead the Ti-in-zircon thermometer demonstrates they were erupted around 830°C. Detailed petrography has allowed the robust determination of a protolith composition which is used to assess mobility of the rare earth and high field strength elements. The rare earth elements are shown to be considerably mobile, approximately by a factor of three within a single, 6 m thick coulee. In contrast the HFSE, with the exception of Pb and Y, have only been mobilized up to 10%, largely as a result of sericitization and chloritization. The Nb/Zr vs. Al2O3/TiO2 diagram reliably discriminates between aphyric and quartz porphyritic rhyolite units which respectively correlate with the Lower and Upper members of the nearby Kidd Creek deposit. Furthermore the Hf-Th-Ta diagram shows a clear magmatic evolutionary trend towards the Hf apex. This is consistent with observed zircon abundances within the aphyric rhyolite coulees. The volcanological, textural and lithogeochemical work allows for the correlation of the Prosser Township rocks to the adjacent Kidd Creek mine stratigraphic sequence. However, the Middle member at the mine, a volcanoclastic unit which separates aphyric and quartz porphyritic lavas, is found as a pyroclastic pumice- and spatter-rich tuff breccia at Prosser Township that has not been previously described in the area. As such it may provide a suitable host rock for hydrothermal massive sulphide mineralization.

Subduction zones recycle material from Earth’s surface into the mantle, and are an important means of continent building. The subduction system serves as a stamp, imprinting the distinct chemical characteristics of our planet’s geological reservoirs, and distinguishing it within the solar system. As such, the elemental exchanges mediated by this system are a long-standing focus of geochemical and geophysical research. Advances in geochemical techniques and improved geophysical models of subduction have illuminated the processes which give rise to arc volcanism. Great strides have been made in answering the question of what goes down, and what comes back up, though much remains unknown. Arc volcanoes provide a valuable window into the complex subduction environment, and so a comprehensive understanding of arc magma petrogenesis provides a means to resolve significant outstanding questions. The processes that regulate the compositions of erupted arc magmas are complicated, however. In order to use arc magmas as a tool for constraining elemental fluxes across large-scale geochemical reservoirs, we must trace the path of lavas sampled on Earth’s surface back down through the lithosphere. Once we reach the asthenosphere, we require constraints on the conditions from which the magma was generated – a mantle source, fluxed by some hydrous material originating from the subducting plate. We can determine which elements have been added to the mantle at this point only if we know the composition of the mantle before the hydrous addition. None of these processes are likely to be identical from one volcano to the next (or, indeed, at a single volcano over time). Instead, these processes will vary dependent on the physical conditions present. Thus, this work requires an understanding of the physical conditions across the earth, as well as their effects of physical processes on elemental transfer within the system. Chapter 1 of this dissertation addresses the question of how magma ascent through the crust can vary on short timescales (~50 years) at a single location, specifically at Bezymianny Volcano, in Kamchatka, Russia. This project was conducted following two field seasons at Bezymianny. Field experience provided an on-the-ground understanding of this volcano’s unique magma system, and fostered multi-disciplinary interactions with geophysicists and seismologists that informed the interpretation of its geochemistry. Bezymianny often erupts multiple times per year. The sample set used in this study was collected by several different volcanologists over five decades, and provides unprecedented temporal resolution of sampling for this time period. The compositions of Bezymianny magmas varied regularly throughout the eruptive cycle. Using whole rock trace element compositions and thermobarometry from amphiboles, it was possible to characterize magma mixing at Bezymianny that varied in proportions from three separate crustal reservoirs -- each positioned at a different depth within the crust. A comparison is then drawn between the magma plumbing systems of Bezymianny and other volcanoes with similar surface features. This analysis demonstrates that the form of a volcano on the surface does not necessarily reflect the structure of its roots. Chapters 2 and 3 were motivated by Chapter 4, rather than the other way around. Chapter 4 is a regional investigation of chemical variability along the Chilean Southern Volcanic Zone (SVZ). The SVZ is a classic study area for igneous chemistry, in which the compositions of erupted magmas vary along and across the strike of the volcanic arc. Along with magma chemistry, multiple physical parameters that may influence the subduction system (or simply, “subduction parameters”), also vary along-strike. From south to north within the SVZ the crust becomes thicker, while the depth of the slab increases significantly. In addition, there is a decrease in the angle of the slab beneath the arc front. To resolve whether the magma variability in the SVZ is due to variation of subduction parameters within the overriding plate or the subducting slab (or both) is non-trivial. In part, this is because variations in the flux from the slab, the melting processes, and in intra-crustal processing, can have similar chemical consequences. This ambiguity motivated a re-examination of the relationships between subduction parameters and global magma chemistry. In many ways this project builds upon the study of Plank and Langmuir (1988), but also utilizes the extensive literature database that has been developed in the interim. The new data enable assessment of not only major elemental variation, but also trace elements and isotopes. Chapter 2 presents the systematics of a global dataset, which includes several new observations of global correlations between trace elements and trace element ratios. The global correlations with magma chemistry also extend to correlations with crustal thickness. There are strong correlations among incompatible elements that are typically separated into groups. The ratio Dy/Yb also correlates with incompatible elements, suggesting involvement of garnet. In Chapter 2, this dataset is used to investigate whether the global trends might arise from intra-crustal processes. This possibility is supported by the correlations between chemical parameters and the thickness of the crust. The main crustal processes considered are high-pressure crystal fractionation and mixing between primary magmas and an enriched crustal component. High-pressure fractionation trends are not found to be more abundant at arcs with thick crust, however, and the composition of the hypothetical global contaminant is unlikely to exist in nature. The global magma variation is therefore most plausibly primary in nature, arising from processes in the slab or mantle, rather than the crust. Chapter 3 investigates whether variable slab fluxes or melting processes are responsible for the global correlations in magma chemistry. The correlations with crustal thickness, if not produced by processes within the crust itself, are suggestive of a melting process. The chemical parameters also correlate, however, with the slab “thermal parameter,” implicating processes within the downgoing plate. In addition to the arc front chemical systematics, it is shown that rear-arc volcanic compositions, after filtration to minimize the effects of slab input, have strong correlations between Sr and Nd isotopes. Rear-arc Nd isotopes also correlate well with the Nd isotope values of the arc front. To constrain the potential effects of slab and mantle processes, quantitative models are developed for two different scenarios: In one scenario, global chemical diversity is produced by a variable slab flux, while the mantle thermal structure is held constant. In a second scenario, global chemical diversity is produced by a variable mantle thermal structure, while slab flux is relatively constant. Both models are able to reproduce the global trends, though the observed correlations between filtered rear-arc and arc front Nd isotopes are difficult to reconcile with potentially large fluxes of slab material to the mantle wedge. Both models have implications as well for the flux of H2O, both from the slab to the mantle, and from the mantle back to the exosphere. Finally, in Chapter 4, we apply this global modeling framework back to the problem of the SVZ. It is demonstrated that the systematics of the SVZ mimic those of the global system in a remarkable way. The correlations between elements within the global dataset are also present in the SVZ, and these trends overlap. An extensive dataset of rear arc SVZ samples is used to demonstrate control of Nd isotopes and other compositional features by variable mantle heterogeneity, rather than variable slab flux. The along-strike chemical trends of the SVZ are consistent with the scenario of variable mantle thermal structure, but not with the scenario of variable slab flux. This conclusion is quantitatively tested using a model in which both mantle heterogeneity and mantle thermal structure are varied along the arc. The model is successful in reproducing the observed chemical variations. Because the SVZ and global systematics are so similar, it is likely that conclusions drawn from this region can be extrapolated back to the global framework. / Earth and Planetary Sciences

There is no direct geologic record of the level of free oxygen in the atmosphere over Earth history. Indirect proxy records have led to a canonical view of atmospheric pO2, according to which the atmosphere has passed through three stages. During the first of these periods, corresponding roughly to the Archean eon, pO2 was less than 0.001% present atmospheric levels (PAL). Oxygen levels rose abruptly around 2.4 billion years ago, a transition referred to as the “Great Oxidation Event” (GOE). This event marks the beginning of the second phase in the history of oxygen, corresponding roughly to the Proterozoic eon, during which pO2 was in the range of 1% to 10% PAL. Between the latest Neoproterozoic and the early Phanerozoic eon, oxygen rose again, beginning the final stage in the history of oxygen, characterized by essentially modern levels of pO2. The processes governing this evolution of the atmosphere are poorly understood. The bio geochemical cycles of redox-sensitive species in the ocean and atmosphere, including oxygen, carbon, iron, and sulfur, must somehow stabilize pO2 on billion-year time scales, much longer than the residence time of the individual species, and yet also allow pO2 to achieve equilib- rium at widely divergent levels at different points in time. Only with a clear understanding of these steady-state processes can we understand how pO2 will respond to the changes in biogeochemical cycling that may have driven the two major oxidation events. In this thesis we use a model of biogeochemical cycling and laboratory experiments to explore the processes that stabilize pO2 at different levels over Earth history. We find that a suite of negative feedbacks, including the oxygen-sensitivity of organic carbon burial, allow the stability of oxygen at modern levels. These feedbacks leave pO2 very insensitive to most aspects of the biogeochemical system, such that stable, Proterozoic levels of pO2 can only be explained by a smaller supply of phosphorus to the biosphere at that time. Experimental results show that inorganic scavenging processes, which compete with biology for phosphorus, may be more effective in low-oxygen environments due to differences in iron-redox cycling. We explore redox dynamics in the Archean by coupling our biogeochemical model to a hydrogen escape calculation that incorporates the effects of changing oxygen levels on thermosphere composition and temperature. We find that the Archean was characterized by several different steady states of oxygen, each corresponding to a different stage in the evolution of life. Furthermore, interactions between the cycles of carbon, oxygen, iron and calcium give rise to a previously unrecognized positive feedback. Our model results show that this feedback allows Archean pO2 to increase rapidly to a new steady state at Proterozoic levels, given a large enough perturbation. The high levels of atmospheric carbon dioxide following a Snowball Earth glacial event do act as such a trigger in our simulations, providing a hypothesis for the apparent synchronicity between the GOE and the Paleoproterozoic Snowball glacials. / Earth and Planetary Sciences

No description available.

The Murdock Creek intrusion, immediately southwest of Kirkland Lake, Ontario, in the southern part of the Abitibi belt, is a member of a suite of late Archean ($\approx$2680 Ma) syenitic intrusions located within and adjacent to the Kirkland Lake-Larder Lake fault zone (KLF), which host virtually all of the gold mineralization in the Kirkland Lake camp. An early crystallizing mafic margin consisting of clinopyroxenite, meladiorite, melamonzodiorite, and melasyenite encloses an extensive felsic core of alkali-feldspar syenite. A coeval hornblendite unit with lamprophyric affinities, intrudes throughout the pluton and most closely approximates the mantel-derived liquids which differentiated to produce the suite of syenitic intrusions and possibly potassic alkaline extrusive rocks of the Timiskaming Group. The intrinsically oxidized nature of the pluton suggests a genetic link with gold mineralization in the Kirkland Lake camp. (Abstract shortened by UMI.)

The Taltson magmatic zone is a north-trending belt of Early Proterozoic granitoids exposed over an area exceeding 18,000 km$\sp2$ in the Northwest Territories. Three petrologically and chronologically distinct intrusive suites comprise the Taltson zone. These are the 1986 Ma Deskenatlata suite, the 1955 to 1925 Ma Slave suite and the 1935 Ma Konth suite. The Deskenatlata suite is composed of a biotite-hornblende diorite to granite suite whose major and trace element chemistry supports derivation by arc magmatism. The Slave and Konth suites are leucocratic granitoids which contain numerous xenoliths of dominantly pelitic high grade paragneiss and display S-type granite mineralogy which commonly duplicates that of the pelitic gneisses. Bulk rock chemistry for the Konth suite is consistent with a homogeneous crustal magma source whereas the Slave suite is compositionally more heterogeneous. The Deskenatlata suite is considered as continental arc-derived granitoids resulting from eastward subduction of oceanic lithosphere beneath the Churchill Province. The Slave suite is regarded as the result of melting of various segments of heterogeneous Archean crust whereas the Konth may have evolved exclusively from melting of pelitic metasediments. (Abstract shortened by UMI.)

An increase in the degree of post-depositional alteration of Belt limestones is reflected in a diminution of Sr and Mg content, increase in Mn and by depletion in $\sp $C and $\sp $O. $\delta\sb1\sp8$O of limestones ranges from +13.4 to +22.9$\perthous$ SMOW and $\delta\sp $C from $-$5.6 to +2.4$\perthous$ PDB. Two diagenetic trends can be resolved for the limestones. One, affecting the presumed originally aragonite-rich sediments, comprises the Newland, Libby and perhaps the Snowslip Formations. The other trend is confined to the Middle Belt Carbonate and may have been controlled by high-Mg calcitic sediments. A regional westward depletion in $\sp $O of 8$\perthous$ and $\sp $C of 2.5$\perthous$ reflects a higher temperature of alteration (300$\sp\circ$C) and an increased contribution from CO$\sb2$ derived from thermal cracking of hydrocarbons in the western Belt basin. The $\delta\sp $O and $\delta\sp $C compositions of the Belt limestones are within the ranges of the values reported for coeval Proterozoic basins. If compared to the modern ocean, the $\delta\sp $O of the Belt sea may have been lighter by perhaps 7$\perthous$. $\delta\sp $C averages close to 2$\perthous$, similar to modern values. Dolostones in the Belt basin are dominantly micritic, with good preservation of depositional textures. $\delta\sp $O of dolomite ranges from 18.1 to 27.9$\perthous$ SMOW and $\delta\sp $C from $-$2.2 to 1.9$\perthous$ PDB. Post-depositional alteration of dolostone is indexed by a decrease in Sr and Na contents, increase in Mn and by depletion in $\sp $O and $\sp $C. Dolostones of the Mt. Shields and Altyn Formations have low Sr and heavy $\delta\sp $O and $\delta\sp $C (if compared to the bulk of Belt samples), show pervasive and destructive dolomitization and may have formed in a mixed water zone of the Dorag type. The remainder of the Belt dolostones resemble typical 'early' diagenetic micritic dolostones in their high Sr content and may have formed in an evaporative setting. Carbonates of mixed dolomite and calcite composition show depletion in $\sp $O and $\sp $C and increase in Mn content with progressive diagenetic alteration. Secular variations in $\delta\sp $C are superimposed on diagenetic trends in this population, showing that carbonates of the Spokane/Greyson, Libby and Newland Formations are $\approx$2$\perthous$ heavier than those of the Middle Belt Carbonate. $\sp‡$Sr/$\sp†$Sr of Belt carbonates range between 0.70484 and 0.74991. Progressive diagenesis, as indexed by decreasing elemental Sr and depletion in $\sp $O and $\sp $C, results in an increase in $\sp‡$Sr/$\sp†$Sr values. $\sp‡$Sr/$\sp†$Sr is better preserved in dolomitized rocks and rocks with initially high Sr content (the Newland and Greyson/Spokane Formations). The 'best', that is the least radiogenic values, are similar to those for previously published coeval Proterozoic carbonates and they are more radiogenic than the contemporaneous mantle. A comparison of $\sp‡$Sr/$\sp†$Sr for the dissolved vs. the suspended load of the Belt basin indicates that the rivers supplying strontium to the basin did not exclusively drain young volcanic or plutonic terrain, but this terrain must have contained a significant source of Sr with marine isotopic composition. Alternatively, the source of nonradiogenic Sr might have been marine waters. (Abstract shortened by UMI.)

The globally-deposited clay layer marking the Cretaceous-Tertiary boundary has been studied to determine the mineralogical carrier phases for the anomalously concentrated platinum-group elements, the affinity of these elements for organic complexes in low temperature environments, the degree of terrestrial input to the boundary clay and the usefulness of platinum-group elemental ratios in projectile identification. Grain size separates from marine and terrestrial Cretaceous-Tertiary boundary sites were analyzed for platinum-group elements (Pt, Pd, Ru, Ir, Rh) and gold using sensitive induced coupled plasma mass spectrometry. Detection limits on a five gram sample are 0.05 ppb (Rh, Ru, Ir), 0.1 ppb (Pt, Pd) and 0.2 ppb (Au). Platinum-group elements are concentrated in clay minerals (smectite and illite-smectite clay) formed by the alteration of the original microtektite host. There is also an ubiquitous organic carrier. Ruthenium and Ir were found to be the least susceptible to be fixed in organics. This fact, combined with the geochemical coherence of Ru and Ir makes them more suitable than the other platinum-group elements for estimating the terrestrial platinum-group element input to the boundary clay and for identifying the projectile. The Ru/Ir ratio of marine sections (1.77 $\pm$ 0.53) is statistically different from that of the terrestrial sites (0.92 $\pm$ 0.28), and each represents a relatively coherent group. The marine Ru/Ir ratios are chondritic (1.48 $\pm$ 0.09), but the terrestrial ratios are not. Fractionation of Ru and Ir during condensation from the ejecta cloud may account for the broad differences between marine and terrestrial sites. Post-sedimentary alteration, remobilization or terrestrial PGE input may be responsible for the Ru/Ir ratio variations within the groups of marine and terrestrial sites studied. Modelling indicates that the marine ratios could also be attained if $\approx$15% of the boundary metals were contributed by Deccan Trap emissions. However, volcanic emissions could not have been the principal source of platinum-group elements in the boundary clay because mantle PGE ratios and abundances are inconsistent with those measured in the clay. The Ru/Ir values for pristine Tertiary mantle xenoliths (2.6 $\pm$ 0.48), picrites (4.1 $\pm$ 1.8) and for the Deccan Trap basalt (3.42 $\pm$ 1.96) are all statistically distinct from those measured in the Cretaceous-Tertiary boundary clay. Several Canadian impact craters, believed to have been formed by the impact of chondritic projectiles, were analyzed for platinum-group elements in order to test if the interelement ratios identify the chondrite (i.e., the nature of the impactor). However, the dearth of literature data for various types of meteorites, the overall similarity in their platinum-group element ratios, the unknown fractionation effect upon meteorite volatilization and condensation, and the post-depositional alteration and remobilization of platinum-group elements all hamper application of the technique. Consequently, platinum-group elements cannot be readily utilized for identifying impactors beyond broad groups of meteorites (e.g., chondrite vs. iron). Nevertheless, they can often be used as supporting geochemical evidence, along with other elements (e.g., with Ni, Cr, Co abundance and ratios). This is the case at the K-T boundary, where Ru/Ir ratios, mineralogical and geochemical evidence all support a chondritic nature for the impactor.