Doctor of Philosophy(PhD) / Mid-ocean ridges are a fundamental but insufficiently understood component of the global plate tectonic system. Mid-ocean ridges control the landscape of the Earth's ocean basins through seafloor spreading and influence the evolution of overriding plate margins during midocean ridge subduction. The majority of new crust created at the surface of the Earth is formed at mid-ocean ridges and the accretion process strongly influences the morphology of the seafloor, which interacts with ocean currents and mixing to influence ocean circulation and regional and global climate. Seafloor spreading rates are well known to influence oceanic basement topography. However, I show that parameters such as mantle conditions and spreading obliquity also play significant roles in modulating seafloor topography. I find that high mantle temperatures are associated with smooth oceanic basement, while cold and/or depleted mantle is associated with rough basement topography. In addition spreading obliquities greater than > 45° lead to extreme seafloor roughness. These results provide a predictive framework for reconstructing the seafloor of ancient oceans, a fundamental input required for modelling ocean-mixing in palaeoclimate studies. The importance of being able to accurately predict the morphology of vanished ocean floor is demonstrated by a regional analysis of the Adare Trough, which shows through an analysis of seismic stratigraphy how a relatively rough bathymetric feature can strongly influence the flow of ocean bottom currents. As well as seafloor, mid-ocean ridges influence the composition and morphology of overriding plate margins as they are consumed by subduction, with implications for landscape and natural resources development. Mid-ocean ridge subduction also effects the morphology and composition of the overriding plate margin by influencing the tectonic regime experienced by the overriding plate margin and impacting on the volume, composition and timing of arc-volcanism. Investigation of the Wharton Ridge slab window that formed beneath Sundaland between 70 Ma and 43 Ma reveals that although the relative motion of an overriding plate margin is the dominant force effecting tectonic regime on the overriding plate margin, this can be overridden by extension caused by the underlying slab window. Mid-ocean ridge subduction can also affect the balance of global plate motions. A longstanding controversy in global tectonics concerns the ultimate driving forces that cause periodic plate reorganisations. I find strong evidence supporting the hypothesis that the plates themselves drive instabilities in the plate-mantle system rather than major mantle overturns being the driving mechanism. I find that rapid sub-parallel subduction of the Izanagi mid-ocean ridge and subsequent catastrophic slab break o_ likely precipitated a global plate reorganisation event that formed the Emperor-Hawaii bend, and the change in relative plate motion between Australia and Antarctica at approximately 50 Ma

In an attempt to understand the phase equilibria and petrogenesis of MORB anorthitic plagioclase, Cr-spinel commonly hosted within anorthitic plagioclase has been investigated petrographically and compositionally. Based on spinel-anorthite relationships from three samples of plagioclase ultra-phyric basalt (PUB; Southeast Indian Ridge, Axial Seamount and West Valley Segment, Juan de Fuca Ridge) our work finds that Cr-spinel hosted within anorthitic megacrysts consistently exhibit rounded, partially dissolved morphologies. In addition, spinel included in anorthitic plagioclase are often accompanied by melt in a composite 2 phase inclusion. Cr-spinel compositionally exhibits collinear negative correlations in Mg# (Mg/Mg+Fe; 0.6-0.73) and Cr# (Cr/Cr+Al; 0.2-0.6), and positive correlations of Cr# and Fe�����# (Fe�����/ Fe�����+Cr+Al; <0.1) with TiO��� wt% (0.3-0.8). Additionally, all spinel appear to exhibit mantle affinity (Fe�����#<0.1; Barnes and Roedder, 2001). Based on historical interpretations of Cr-spinel (Dick and Bullen, 1984), we conclude that Cr-spinel hosted within MORB anorthitic plagioclase preserve melt-mantle reaction signatures. Such reactions, potentially forming dunite, result when ascending low-a[subscript silica] primitive melts interact and consume upper mantle silicates (i.e. clinopyroxene), and include Cr,Al-rich spinel. Thus, both Al and Ca are released into the derivative melt stabilizing anorthitic plagioclase. Given that olivine has never been found in contact with plagioclase >An������, we propose that anorthitic plagioclase precipitates from the derivative liquid prior to olivine. Recently, studies have used the trace element signatures of MORB anorthitic plagioclase as probes of early differentiation processes beneath MOR (Adams et al., 2011; Weinsteiger et al., in review). However, these studies have outlined the need to decipher the geochemical signals of individual anorthitic plagioclase so that population trends may be interpreted. In response, this thesis also reports detailed trace element profiles of individual anorthitic plagioclase crystals and population trends from two samples of PUB (Southeast Indian Ridge [SEIR] sample, Axial Seamount sample). Profiles can be categorized as dominantly stochastic since correlations between trace elements and trace and major elements are largely not found; potentially precluding a role for diffusive re-equilibration. We propose that trace element heterogeneities found within individual crystals reflect the degree of trace element variability present within upper mantle and lower crust conduits. However, by observing population data specific processes may be seen. Similarities in Axial Seamount plagioclase trace elements suggest a relatively uniform source that was evolving largely as a result of plagioclase only fractionation. In contrast, the array of trace element concentrations of SEIR plagioclase positively correlates with major element variations. This suggests a complex process of melt aggregation of increasing percent melts concurrently with anorthitic plagioclase precipitation. Further process related signatures can be derived by viewing plots combining trace and major elements from both samples. In this format, each samples data suggest that similar large scale processes occur in conduits within the upper mantle where these anorthite populations' form. Although plagioclase only fractionation appears to frame the trend, the correlation is diffuse and potentially reflects additional magmatic processes (i.e. AFC, % melt, and melt aggregation). Calculated equilibrium liquids based on Axial Seamount and SEIR plagioclase are considerably depleted relative to their host glass and natural glasses documented to occur near the sampled site. The differentiation processes linking these melt compositions is currently unknown. / Graduation date: 2013

Hydrothermal systems at oceanic spreading centers play an important role in the composition of seawater, the formation of ore deposits, the support of microbial and macrofaunal ecosystems, and even for the development of life on early earth. These circulation systems are driven by heat transport from the underlying magma chamber, where latent heat of crystallization and sensible heat from cooling are transferred by vigorous, high Rayleigh number convection through a thin conductive boundary layer. The traditional study of magmatic-hydrothermal systems is primarily based on the time-series observation, which takes the form of repeat visits, continuous offline monitoring by autonomous instruments, or continuous online monitoring by instruments with satellite or cable links to shore. Although a number of studies have deployed autonomous monitoring instruments at vents and around mid-ocean ridges to investigate geophysical and hydrothermal processes, the data are still rather limited and a comprehensive understanding of magma-hydrothermal processes at oceanic spreading centers is lacking. Numerical modeling needs to be employed to elucidate the dynamic behavior of magmatic hydrothermal systems and for testing completing hypotheses in these complex, data-poor environments. In this dissertation, I develop a mathematical framework for investigating heat transport from a vigorously convecting, crystallizing, cooling, and replenished magma chamber to an overlying hydrothermal system at an oceanic spreading center. The resulting equations are solved numerically using MATLAB. The simulations proceed step-by-step to investigate several different aspects of the system. First, I consider a hydrothermal system driven by convection, cooling and crystallization in a ~ 100 m thick basaltic magma sill representing an axial magma chamber (AMC) at an oceanic spreading center. I investigate two different crystallization scenarios, crystal-suspended and crystal-settling, and consider both un-replenished and replenished AMCs. In cases without magma replenishment, the simulation results for crystals-suspended models show that heat output and the hydrothermal temperature decrease rapidly and crystallinity reaches 60% in less than ten years. In crystals-settling models, magma convection may last for decades, but decreasing heat output and hydrothermal temperatures still occur on decadal timescales. When magma replenishment is included, the magmatic heat flux approaches steady state on decadal timescales, while the magma body grows to double its original size. The rate of magma replenishment needed ranges between 5 x 10⁵ and 5 x 10⁶ m³/yr, which is somewhat faster than required for seafloor spreading, but less than fluxes to some terrestrial and subseafloor volcanoes on similar timescales. The heat output from a convecting, crystallizing, replenished magma body that is needed to drive observed high-temperature hydrothermal systems is consistent, with gabbro glacier models of crustal production at mid-ocean ridges. Secondly, I study the heat transfer model from a parametric perspective and examine the effects of both initial magma chamber thickness and magma replenishment rate on the hydrothermal heat output. The initial rate of convective heat transfer is independent of the initial sill thickness; but without magma replenishment, the rate of decay of the heat output varies linearly with thickness, resulting in short convective lifetimes and decaying hydrothermal temperatures for sills up to ~ 100m thick. When magma replenishment is included in crystals settling scenarios at constant or exponentially decreasing rates of ~ 10⁻⁸ m/s to the base of the sill, growth of the sill results in stabilized heat output and hydrothermal temperature on decadal timescales and a relatively constant to increasing thickness of the liquid layer. Sills initially ~ 10 m thick can grow, in principal, to ~ 10 times their initial size with stable heat output and a final melt thickness less than 100m. Seismic data provides evidence of AMC thickness, but it can not discriminate whether it denotes initial magma thickness or is a result of replenishment. These results suggest that magma replenishment might not be seismically detectable on decadal time scales. Periodic replenishment may also result in quasi-stable heat output, but the magnitude of the heat output may vary considerably in crystals suspended models at low frequencies; compared to crystals settling models. In these models the direct coupling between magmatic and hydrothermal heat output suggests that heat output fluctuations might be recorded in hydrothermal vents; but if damping effects of the basal conductive boundary layer and the upflow zone are taken into account, it seems unlikely that heat output fluctuations on a time scale of years would be recorded in hydrothermal vent temperatures or heat output. Thirdly, I extend the work to the binary system motivated by the fact that the real magmas are multi-component fluids. I focus on the extensively studied binary system, diopside-anorthite (Di-An), and investigate the effects of convection of a two-component magma system on the hydrothermal circulation system through the dynamic modeling of both temperature and heat output. I model the melt temperature and viscosity as a function of Di concentration, and incorporate these relations in the modeling of the heat flux. Simulations comparing the effects of different initial Di concentrations indicate that magmas with higher initial Di concentrations convect more vigorously, which results in faster heat transfer, more rapid removal of Di from the melt and growth of crystals on the floor. With magma replenishment, I assume that the magma chamber grows either horizontally or vertically. In either case magma replenishment at a constant rate of ~ 10⁻⁸ m³/a can maintain relatively stable heat output of 10⁷-10⁹ Watts and reasonable hydrothermal vent temperatures for decades. The final stabilized heat flux increases with increasing Di content of the added magma. Periodic replenishment with a 10 year period results in temperature perturbations within the magma that also increase as a function of increasing Di. With the simple magma model used here, one can not discern conclusively whether the decrease in magma temperature between the 1991/1992 and the 2005/2006 eruptions at EPR 9°50'N involved replenishment with more or less evolved magmas. Fourthly, I investigate a high-silica magma chamber as the hydrothermal circulation driver. I construct viscosity models for andesite and dacite melts as a function of temperature and water content and incorporate these expressions into a numerical model of thermal convective heat transport from a high Rayleigh number, well-mixed, crystallizing and replenished magma sill beneath a hydrothermal circulation system. Simulations comparing the time dependent heat flux from basalt, 0.1wt.% andesite, 3wt.% andesite, and 4wt.% dacite, indicate that higher viscosity magmas convect less vigorously, which results not only in lower heat transport and hydrothermal vent temperatures, but also in a lower decay rate of the vent temperature. Though somewhat colder, hydrothermal systems driven by unreplenished high-silica melts tend to have a longer lifetime than those driven by basalts, assuming a heat output cutoff of 10⁷ Watts. As in the basaltic case, magma replenishment at a rate of ~ 3 x 10⁵ - 3 x 10⁶ m³/a can maintain relatively stable heat output of 10⁷-10⁹ Watts and hydrothermal vent temperatures for decades. Idealized models of porous flow through the lower crust suggest such replenishment rates are not likely to occur, especially for high-viscosity magmas such as andesite and dacite. Long term stability of hydrothermal systems driven by these magmas requires an alternate means of magma replenishment. Finally, the dissertation concludes by discussing some avenues for future work. Most important of these are to: (1) couple magma convection with more realistic hydrothermal models and (2) link magma chamber processes to better physical models of replenishment and eruption.

Thesis (Ph.D.)--University of Wyoming, 2008. / Title from PDF title page (viewed on Mar. 8, 2010). Includes bibliographical references.

Microwave scattering from sea ice ridges is poorly understood. This thesis aims to improve the current knowledge on in situ C-band microwave scattering from first-year sea ice (FYI) pressure ridges during winter, and how C-band backscatter can vary with changes to radar and target parameters. Remotely sensed data of ridged ice were collected at a sea ice mesocosm using a LiDAR laser scanner and a fully-polarimetric C-band scatterometer. Thesis results indicate that using an incidence angle between 30 and 50° and HV polarization will best enable distinguishing between smooth and ridged ice, while using an incidence angle of 40° and HV or HH polarization will best enable detecting variations in ridge height. Overall results indicate that a significant proportion of the variance in FYI snow-free ridge C-band backscatter can be explained by incidence angle, polarization, and ridge height, with almost 88% of the variability in backscatter attributed to ridge height.

Tire bales have become an innovative and cost effective fill material that can be used for the construction of geotechnical structures, like embankments for highway projects. The mechanical and physical properties they present allow them to be suitable for this type of structures, as long as they are provided with an appropriate drainage system. Stability of these structures is controlled by the interface shear strength existing in the contact surfaces between the bales. However, the tire bale has a jagged, uneven and highly variable surface and it presents a number of irregular tire ridges with random dimensions that are difficult to quantify. Due to the flexibility of these ridges, deformation of the interface occurs when a horizontal shear load is applied, and following this deformation the actual displacement of the interface takes place. Freilich (2009) performed large scale tests in the field and in the laboratory to observe the behavior of the whole tire bale structure, which is composed of the tire bale mass and the tire bale interface. Due to the irregular and highly variable surface of the tire bale, the deformations that occur on the ridges along the interface cannot be directly measured and quantified. Following similar concepts of some rock mechanic models, Freilich characterized the tire ridge interface using three parameters and came up with a model. Using these parameters, an ideal interface was constructed where the variability was reduced by incorporating a known geometry, and it can still be characterized in the same manner as that for the tire bale interface. Loads, deformations and displacements occurring along the interface were measured and recorded. From this data, shear strength parameters are defined and incorporated into Freilich’s tire ridge interface model that is used to predict the geometric and mechanical behavior of the irregular ridges controlling the interface shear strength. The behavior predicted from the model is then compared to the recorded data representing the actual geometric and mechanical behavior of the interface with known geometry, where the deformations on the asperities are approximated. This comparison verifies that the consideration of the flexibility from the tire ridges is not entirely described by the tire ridge interface model. Therefore a possible modification, based on the observations recorded, could be found. / text

The Oak Ridges Moraine, located in south-central Ontario, is recognized for its ecological importance in providing “clean and abundant water resources, healthy and diverse plant and animal habitat, an attractive and distinct landscape, prime agricultural land, and sand and gravel resources” (Ministry of Municipal Affairs and Housing, 2002). It is protected by the Oak Ridges Moraine Conservation Plan (2002). A number of initiatives are ongoing to develop monitoring capabilities across the Oak Ridges Moraine (Monitoring the Moraine Project, 2008; Ontario Ministry of Municipal Affairs, 2008). The purpose of this thesis is to develop and test a multi-party policy monitoring framework to determine if infrastructure environmental assessments on the Oak Ridges Moraine comply with the policies of the Oak Ridges Moraine Conservation Plan (ORMCP) and meet best practices of environmental assessment identified in the literature. The multi-party policy monitoring framework developed for this research has two dimensions: 1. A moraine-wide survey and map of infrastructure environmental assessments contributing to a “governance watch” (Francis, 2006a; Francis, 2006b) perspective of infrastructure; and 2. An evaluation of an infrastructure environmental assessment case study (York Region’s Lower Leslie Street Trunk Sewer and 19th Avenue Interceptor Sewer) against a set of criteria to determine if it complies with the ORMCP and environmental assessment best practices. The results of the environmental assessment map show a distinctive pattern of infrastructure development, concentrated in the eastern half of the moraine, and within designated settlement areas. That being said, infrastructure networks are expanding to connect settlement areas outside the Greater Toronto Area. The environmental assessment map shows the importance of thinking of infrastructure as a networked system, rather than as discrete projects. The results of the case study evaluation showed that the Lower Leslie Street Trunk Sewer and 19th Avenue Interceptor Sewer Environmental Assessment complied with the minimal requirements of Section 41 of the ORMCP, and in some cases went above and beyond the requirements of the ORMCP. The results suggest, however, that some criteria drawn from the literature, would be better addressed by strategic environmental assessment of infrastructure master plans. / Thesis (Master, Urban & Regional Planning) -- Queen's University, 2008-09-28 09:57:19.652

Doctor of Philosophy(PhD) / Mid-ocean ridges are a fundamental but insufficiently understood component of the global plate tectonic system. Mid-ocean ridges control the landscape of the Earth's ocean basins through seafloor spreading and influence the evolution of overriding plate margins during midocean ridge subduction. The majority of new crust created at the surface of the Earth is formed at mid-ocean ridges and the accretion process strongly influences the morphology of the seafloor, which interacts with ocean currents and mixing to influence ocean circulation and regional and global climate. Seafloor spreading rates are well known to influence oceanic basement topography. However, I show that parameters such as mantle conditions and spreading obliquity also play significant roles in modulating seafloor topography. I find that high mantle temperatures are associated with smooth oceanic basement, while cold and/or depleted mantle is associated with rough basement topography. In addition spreading obliquities greater than > 45° lead to extreme seafloor roughness. These results provide a predictive framework for reconstructing the seafloor of ancient oceans, a fundamental input required for modelling ocean-mixing in palaeoclimate studies. The importance of being able to accurately predict the morphology of vanished ocean floor is demonstrated by a regional analysis of the Adare Trough, which shows through an analysis of seismic stratigraphy how a relatively rough bathymetric feature can strongly influence the flow of ocean bottom currents. As well as seafloor, mid-ocean ridges influence the composition and morphology of overriding plate margins as they are consumed by subduction, with implications for landscape and natural resources development. Mid-ocean ridge subduction also effects the morphology and composition of the overriding plate margin by influencing the tectonic regime experienced by the overriding plate margin and impacting on the volume, composition and timing of arc-volcanism. Investigation of the Wharton Ridge slab window that formed beneath Sundaland between 70 Ma and 43 Ma reveals that although the relative motion of an overriding plate margin is the dominant force effecting tectonic regime on the overriding plate margin, this can be overridden by extension caused by the underlying slab window. Mid-ocean ridge subduction can also affect the balance of global plate motions. A longstanding controversy in global tectonics concerns the ultimate driving forces that cause periodic plate reorganisations. I find strong evidence supporting the hypothesis that the plates themselves drive instabilities in the plate-mantle system rather than major mantle overturns being the driving mechanism. I find that rapid sub-parallel subduction of the Izanagi mid-ocean ridge and subsequent catastrophic slab break o_ likely precipitated a global plate reorganisation event that formed the Emperor-Hawaii bend, and the change in relative plate motion between Australia and Antarctica at approximately 50 Ma

Thesis (M.Sc.)--York University, 2006. Graduate Programme in Geography. / Typescript. Includes bibliographical references (leaves 137-144). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR19681

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2007. / "Joint Program in Oceanography/Applied Ocean Science and Engineering"--Cover. Title from Web page (viewed on Mar. 24, 2008). "September 2007". Includes bibliographical references.