Silicic magmas (>65 wt.% SiO2) play an integral role in creating permanent continental crust. Understanding how silicic magmatic systems evolve can help us better understand the processes that control whether silicic magmas remain trapped within Earths crust or ultimately reach Earths surface, culminating in volcanic eruptions. In this study, I use elemental and isotopic compositions of major and accessory minerals from diverse rock types produced by silicic magmatism in southeast Iceland and southwest USA to investigate geochemical relationships between crystals and their associated melt(s). I present an extensive partition coefficient dataset for 8 mineral phases from a high-silica rhyolite, and demonstrate that accessory minerals (zircon, titanite, chevkinite, and apatite) exert a strong control on the distribution of rare earth and high field strength elements in a magma, while major minerals (amphibole, biotite, plagioclase, sanidine) dominantly control large ion lithophile elements. In addition, I offer a mathematical expression to estimate the relative abundances of Eu and Ce in their multivalent states (2+, 3+, and 4+), which may yield insight into the oxidation state of magmas based on the occurrence Ce and Eu anomalies in coexisting mineral phases. I conducted a detailed geochemical study of zircons from Icelandic intrusive rocks, and show that their compositions form a coherent array consistent with the signature of zircons from Icelandic silicic volcanic rocks. I demonstrate that oxygen isotopes and hafnium isotopes (εHf) provide strong evidence for the existence of isotopically diverse magmatic sources in the Icelandic crust, including the influence of meteoric-hydrothermal processes and recycling of highly altered crust as a major contributor to silicic magmas in many Icelandic silicic magmatic systems. The results presented here offer an additional dimension in helping us better understand the accumulation of silicic magmas and subsequent evolution of silicic magmatic systems within the Earths crust.

Silicic magmas pose threats to society in the form of explosive volcanism. Understanding silicic magmatism is thus crucial for evaluating eruption-related risks, but numerous questions are unresolved: How are silicic magmas generated and how do they evolve? Over what timescales? What are the connections between shallow silicic magma reservoirs, their associated volcanic centers, and tectonic setting? This study uses petrography, whole rock and zircon elemental and isotopic geochemistry, and U-Pb zircon geochronology to investigate these questions in ancient silicic volcanic centers of the western U.S. and southern Brazil. The Silver Creek caldera in the Miocene southern Black Mountains volcanic center (SBMVC) of western Arizona produced the 18.8 Ma, ~1000 km3 Peach Spring Tuff (PST) supereruption. The PST was bracketed by 2 million years (19 17 Ma) of compositionally diverse intrusive and volcanic magmatic activity. Analysis of pre- and post-PST SBMVC units reveal that 1) the SBMVC experienced ~200 k.y. (19 18.8 Ma) of localized high-temperature magmatism (≥900 °C), coincident with the PST eruption; 2) SBMVC magmas were derived from Precambrian Mojave crust and enriched lithospheric mantle; 3) pre- and post-PST magmas are isotopically more diverse and have stronger mantle fingerprints than the PST, suggesting they were less homogeneous and less crustal than the PST magma body; and 4) mantle input into the SBMVC increased following the PST eruption. Late Proterozoic to early Cambrian silicic intrusions, lavas, and pyroclastic flows are sporadically exposed for ~1500 km throughout northern Uruguay and southern Brazil and are associated with a series of 600 530 Ma rift-generated basins. Zircon geochemistry and U-Pb geochronology of silicic units associated with the two largest basins, the Camaquã and Itajaí basins, indicate that 1) Neoproterozoic-Cambrian silicic magmatism in the region was episodic, occurring at ~520 Ma in the Itajaí basin and ~540 Ma and ~580 Ma in the Camaquã basin; 2) ~580 Ma magmatism was widespread, extending from the Graciosa region at the northern extent of the magmatic system to the Camaquã basin in the south; and 3) ~580 Ma magmatism is coincident with the proposed widespread rifting event that was responsible for basin development.

Icelands great abundance of silicic rock (10-13% of subaerial exposures), coupled with the unusual thickness of the islands crust, hints at continental nucleation and permanent crust construction in an oceanic environment. This phenomenon is rare on modern Earth, but it is often postulated that Icelandic magmatism is a modern analogue for ancient (Hadean) crustal construction. Understanding the processes that form abundant, juvenile, silicic crust in oceanic Iceland has important implications for understanding Earths early, and ongoing, history. The Icelandic crust is juvenile; there is neither ancient nor appreciable felsic crust nor sediments to complicate the magmatic history. Investigations into the origins of Icelandic silicic magma are therefore more focused than the global approach to the issue. Despite this, the issue remains highly contentions and hotly debated. Studies of zircon have elsewhere underpinned understanding of silicic magma processes and crustal evolution, but no such research has been carried out in Iceland until now. This investigation into the origins and evolution of Icelands silicic crust is the first comprehensive study of Icelandic zircons. Elemental and isotopic geochemistry and U-Th-Pb geochronology of zircon from intrusive and extrusive rocks and sediments, coupled with supporting bulk-rock elemental and isotope geochemistry and petrography, reveal that: (1) very low 18O/16O supports partial melting of crust hydrothermally altered by meteoric water as a primary driver of Icelandic felsic petrogenesis; (2) uniformity of O isotopic compositions demonstrates neither a change in magmatic processes nor a change in the meteoric-water composition imprinted on magmas throughout Icelands history, despite extreme climate variability; (3) increased variability in Hf isotope ratios suggest changes to Icelands mantle source with time, (4) Iceland is not an appropriate modern analogue for the Hadean, as their zircon records are quite distinct; (5) zircons reflect tens of thousands of years of activity preceding individual rhyolitic eruptions, and indicate the longevity of silicic magma systems at individual central volcanoes may reach three million years; (6) Icelandic zircons form a compositional category that is distinguishable from typical continental and oceanic zircon populations.

Climate change mitigation will require extensive decarbonization of the electricity sector. This thesis addresses both large-scale wind integration (Papers 1-3) and development of new energy technologies (Paper 4) in service of this goal. Compressed air energy storage (CAES) could be paired with a wind farm to provide firm, dispatchable baseload power, or serve as a peaking plant and capture upswings in electricity prices. Paper 1 presents a firm-level engineering-economic analysis of a wind/CAES system with a wind farm in central Texas, load in either Dallas or Houston, and a CAES plant whose location is profit-optimized. Of a range of market scenarios considered, the CAES plant is found to be profitable only given the existence of large and infrequent price spikes. Social benefits of wind/CAES include avoided construction of new generation capacity, improved air quality during peak demand, and increased economic surplus, but may not outweigh the private cost of the CAES system nor justify a subsidy. Like CAES, pumped hydropower storage (PHS) ramps quickly enough to smooth wind power and could profit from arbitrage on short-term price fluctuations exacerbated by large-scale wind. Germany has aggressive plans for wind power expansion, and Paper 2 analyzes an investment opportunity in a PHS facility in Norway that practices arbitrage in the German spot market. Price forecasts given increased wind capacity are used to calculate profit-maximizing production schedules and annual revenue streams. Real options theory is used to value the investment opportunity, since unlike net present value, it accounts for uncertainty and intertemporal choice. Results show that the optimal investment strategy under the base scenario is to wait approximately eight years then invest in the largest available plant. Paper 3 examines long-distance interconnection as an alternate method of wind power smoothing. Frequency-domain analysis indicates that interconnection of aggregate regional wind plants across much of the western and mid-western U.S. would not result in significantly greater smoothing than interconnection within a single region. Time-domain analysis shows that interconnection across regions reduces the magnitude of low-probability step changes and doubles firm power output (capacity available at least 92 % of the time) compared with a single region. An approximate cost analysis indicates that despite these benefits, balancing wind and providing firm power with local natural gas turbines would be more cost-effective than with transmission interconnection. Papers 1 and 3 demonstrate the need for further RD&D (research, development, and deployment) of low-carbon energy technologies. Energy technology development is highly uncertain but most often modeled as deterministic, which neglects the ability both to adapt RD&D strategy to changing conditions and to invest in initially high-cost technologies with small breakthrough probabilities. Paper 4 develops an analytical stochastic dynamic programming framework in which RD&D spending decreases the expected value of the stochastic cost of a technology. Results for a two-factor cost model (which separates RD&D into R&D and learning-by-doing) applied to carbon capture and sequestration (CCS) indicate that given 15 years until large-scale deployment, investment in the RD&D program is optimal over a very broad range of initial mitigation costs ($10-$380/tCO2). While the NPV of the program is zero if initial mitigation cost is $100/tCO2, under uncertainty the program is worth about $7 billion. If initial mitigation cost is high, the program is worth most if cost reductions exogenous to the program (e.g. due to private sector activity) are also high. Factors that promote R&D spending over learning-by-doing include more imminent deployment, high initial cost, lower exogenous cost reductions, and lower program funds available.

Prioritizing the finite resources available to advance research, development and demonstration of the nuclear industry requires a comprehensive evaluation of potential advanced nuclear technologies to inform decision making. A number of advanced nuclear technologies and fuel cycle options present promising improvements that are only realized when deployed and running at steady-state. However, an advanced nuclear fuel cycle will not be implemented all at once. Moreover, there is little work to understand how transitioning to new nuclear energy systems could affect waste management and human health, when compared to the presently deployed, once-through nuclear fuel cycle. A potential transition from the U.S. once-through nuclear fuel cycle to a modified-open nuclear fuel cycle has been modeled, using a phased approach, including reprocessing of both plutonium and uranium within a simplified dynamic energy demand scenario. Low-radioactivity waste generated and worker collective doses were estimated based on data from industry experience and then these metrics were compared to the baseline U.S. once-through nuclear fuel cycle. Overall observations regarding the comparison between the two nuclear fuel cycles were that worker collective doses were not significantly different but a significant amount of radioactive waste was avoided by using recycled uranium and plutonium from used nuclear fuel. Important outcomes of this work were that the once-through nuclear fuel cycle, as implemented in the U.S., is not as simple as depicted in textbooks and fuel cycle evaluations and must be updated to serve as an accurate baseline against which to measure performance of future potential advanced nuclear fuel cycles. It was also concluded that the two major contributions to occupational radiological impacts in the once-through nuclear fuel cycle, from uranium recovery operations through reactor operations, had reversed in recent years; this is different from historical data and conventional wisdom which says that impacts from the front-end of the once-through nuclear fuel cycle are dominant.

Cements blended with industrial byproducts are ubiquitous construction materials widely used in waste management. The use of blended cements as barriers for nuclear waste management necessitates prediction of durability and long-term performance. A key component of durability prediction is mechanistically based reactive transport modeling. This work identifies critical parametric and model uncertainties within three key components of reactive transport modeling for blended cementitious materials: mass transport, mass conservation, and thermodynamic characterization. Studies of electroneutral ionic diffusion and the electrostatic interaction of dissolved ionic species and charged cement pore surfaces suggest that the influence of electrical interaction on transport may be more significant than previously surmised. A novel technique for measuring the elemental composition of reacted cementitious material in mortars compares favorably with established laboratory leaching techniques. Thermodynamic parameters developed for unblended cements are demonstrated to be generally applicable to the description of blended cements in both equilibrium and reactive transport modeling.

<p>Surface chemistry plays an essential role in determining the reactivity, bioaccessibility, bioavailability and toxicity of nanoparticles (NPs) in the environment. Processes such as aggregation, deposition and biouptake are controlled in part by the attachment efficiency, &#945;, between particles and the surfaces they encounter. One premise of this research is that surface hydrophobicity is a pivotal property of NP surfaces that can affect the behavior of NPs in aquatic environment and potentially decide the fate and transport of NPs. However, there are multiple challenges in the characterization of hydrophobicity for NPs. Methods developed for macroscopic surfaces or organic compounds may not be readily applied or interpreted for the case of nano-scale surfaces. This dissertation addresses theoretical basis for applying methods to determining hydrophobicity of NPs. The use of an octanol-water partitioning method analogous to that used for organic compounds was evaluated on the basis of trends anticipated by thermodynamics, and by experimental observations. This work shows that partitioning of NPs in two phases systems, such as water and octanol, is not uniquely determined by hydrophobicity, but also influenced by surface charge and particle size. The water-oil interface rather than the bulk phases becomes the thermodynamically favored location for NP accumulation once NPs are larger than 1-10 nm and/or the surface is amphiphilic. </p><p>Nonetheless, the relative hydrophobicity of selected NPs, as characterized by adsorption of molecular probes (i.e. organic dye and naphthalene), was consistent with the macroscopic contact angle measurements and octanol-water distribution coefficients. The in-situ adsorption of these molecular probes offers the most solid grounds for measurement of hydrophobicity. Other measure of hydrophobicity or hydrophilicity such as water-affinity based methods that measure water vapor adsorption to nanomaterial powders, or immersion microcalorimetry and thermogravimetric analysis, yielded similar results to the molecular probes. However, possible physical or chemical transformations to NP surfaces during characterization by these other methods limited the use of results to infer hydrophobicity based on a rigorous thermodynamic model.</p><p>Column experiments suggested that the attachment efficiency of NPs to biofilm was generally greater for more hydrophobic NPs, though polymeric coatings might stabilize NPs against the attachment. The affinity of NPs for a variety of bacterial surfaces (i.e. different species, planktonic or biofilm, with or without extracellular polymeric substances (EPS)) of different hydrophobicities, which correlated with the quantity of proteins in EPS, was also investigated. It was found that the attachment of hydrophobic NPs increased with the hydrophobicity of bacterial surfaces, but not for hydrophilic NPs. Environmental conditions such as divalent ions and pH influenced the affinity of nanoparticle for bacterial surface by changing the bacterial surface hydrophobicity and electric double layer interaction, respectively.</p> / Dissertation

Thesis (Ph. D.)--Northeastern University, 2008. / Title from title page (viewed Feb. 20, 2009). Graduate School of Engineering, Dept. of Civil & Environmental Engineering. Includes bibliographical references (p. 157-164).

Thesis (Ph.D.)--University of Toronto, 2008. / Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1975. / Typescript. Vita. Description based on print version record. Includes bibliographical references.