The plutonic rocks of the Paleozoic Isle au Haut Igneous Complex, Maine (424 $\pm$ 1 Ma.), are a trimodal assemblage of granites, diorites, and gabbros. Exposed from the top to the bottom of the pluton, the complex consists of an enclave-bearing granite, a composite layered sequence of alternating gabbroic and dioritic units, a thick and massive gabbroic unit, and a base of an enclave-void granite. The composite layer shows a sequence of ten alternating gabbroic and dioritic units that were liquid or largely liquid contemporaneously. Complex hybridization has taken place between the lower massive gabbroic unit and the underlying granite, while both were liquid or largely liquid contemporaneously. The gabbros are compositionally similar to within-plate tholeiites and they are uniform in average composition throughout the stratigraphic succession. The interlayered dioritic units, on the other hand, change progressively from mafic quartz diorite to quartz monzodiorite with stratigraphic height. A comparison of their respective densities indicates a gravitationally unstable situation if both the gabbroic and dioritic units were simultaneously liquid. I contend that the composite layered sequence represents the successive invasion, or replenishment, of an evolving dioritic chamber by a compositionally uniform gabbroic magma that intruded sill-like between the cumulate floor of the chamber and the overlying melt. Petrography of the individual gabbroic units shows varying degrees of disequilibrium. These include crystals with heterogeneous dissolution textures and mineral assemblages. The hybrid compositions are typically skewed to one side or the other of a linear bulk mixing line between the two proposed end-members. Fractional Crystallization and Assimilation-Fractional Crystallization models are inconsistent with the observed geology, because $>$60-80% crystallization of the gabbroic melt would be required to account for the most silica-rich of the hybrid compositions. Moreover, in element-element comparisons, the hybrids tend to plot away from a linear bulk mixing line in the direction of the experimentally determined, slower diffusing element. The hybrid compositions, on the other hand, can be bounded, on element-element plots, between paths invoking simple diffusion in response to a compositional gradient. Selective contamination and effects of differing rates of diffusion between elements appear to progress in directions consistent with the hybrid samples. Compositionally, the layered dioritic units and the hybrid samples overlap in almost every major, minor, trace, and rare earth element analyses. The composition of the hybrid matrix and the dioritic units does not conform to processes which I examined for the hybrid rocks. Instead, I propose that the compositions of the large-scale dioritic layers are largely controlled by similar diffusion processes which effected the small-scale hybrid compositions. Selective contamination, effects of differing rates of diffusion between elements, and convective transport of those elements at the granite-gabbro contact appear to progress in directions consistent with the hybrid and diorite compositions. Relative diffusivity controlled the composition of a hybrid liquid which formed at both the top and base of the contact of the massive gabbroic unit overlying the granitic unit and collected to produce the composite layers sandwiched between the massive gabbro and the uppermost granite. (Abstract shortened by UMI.)

<p> This dissertation combines field and laboratory work to examine how delta hydrology and sedimentology affects trace element cycling in marsh porewaters. This work was prompted by our lack of understanding of the hydrogeochemistry in the lower Mississippi Delta and how biogeochemical reactions affect fluxes of groundwater constituents to the ocean. In particular, I measured the concentrations of a suite of redox-sensitive trace elements (Fe, Mn, V, As) to determine the dominant geochemical reactions operating in marsh aquifers. </p><p> Because much more is known about As, I first conducted a study comparing V geochemistry along flow paths in a reducing sand aquifer in Texas and an oxidizing bedrock aquifer in Nevada. In agreement with other studies, V concentrations are much higher under oxidizing alkaline conditions. Under the reducing, circumneutral conditions of the Carrizo Sand aquifer, V concentrations are low but relatively constant, owing to complexation with dissolved organic matter. Similar observations regarding V geochemistry are observed in marsh groundwaters. Specifically, in pore waters of organic-rich sediment experiencing sulfate-reducing conditions, V concentrations are high owing to V complexation with organic matter, whereas in coarser-grained sediments, V may be removed from solution by adsorption. Arsenic geochemistry in pore waters varies as a function of depth. In the shallow subsurface, As concentrations are high and stabilized in solution by formation of thioarsenates. At depth, As appears to be sequestered through coprecipitation with pyrite.</p>

<p> Geochemical mixing methods utilizing ²²²Rn and chloride and statistical hydrograph separation techniques were carried out in an attempt to understand baseflow dynamics in a section of the Kern River in the Sierra Nevada of Southern California. ²²²Rn has become a valuable tool for evaluating groundwater inflow to a river, particularly when groundwater and surface water have similar major ion geochemistry. When using geochemical methods it is important to minimize uncertainty through comparison with separate tracers and techniques, though this is complicated in this setting. Snow melt discharge and regulation of natural river flow cause hydrograph-based techniques to suffer from inaccuracies. Geochemical mixing using major ions and stable isotopes are complicated by the chemical similarity between surface water and groundwater. ²²²Rn is a powerful tool to elucidate this relationship in this setting if major uncertainties, like rate of radon degassing and parafluvial and hyporheic radon production can be constrained.</p><p>

Thesis (B. Sc. (Hons.))--University of Adelaide, Dept. of Geology and Geophysics, 1994? / On title page: "National grid reference SH-546737." Includes bibliographical references (leaves 57-60).

Thesis (Ph.D.)--Memorial University of Newfoundland, 1994. / Typescript. Bibliography: leaves 343-375. Also available online.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references. Also available in print.

Thesis (M.Sc.)--Memorial University of Newfoundland. / Bibliography : leaves 183-205. Also available online.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1993. / "June 1993." At head of title: Woods Hole Oceanographic Institution, Massachusetts Institute of Technology, Joint Program in Oceanography/Applied Ocean Science and Engineering. "Doctoral dissertation." Includes bibliographical references.

The Early Proterozoic Agnew Intrusion is a well-preserved leucogabbronoritic to gabbronoritic layered intrusion that is a member of the East Bull Lake suite of layered intrusions (ca. 2490-2470 Ma) occurring in central Ontario. These intrusions are related to the development of the Huronian Rift Zone, which may be part of a much more widespread rifting event that involved the Fennoscandian Shield. Structural data suggest that these intrusions have been subjected to ductile deformation and are erosional remnants of one or more sill-like bodies originally emplaced along the contact between Archaean granitic rocks of the Superior Province and an Early Proterozoic Huronian continental flood basalt sequence in the Southern Province.

The Early Proterozoic Agnew Intrusion is a well-preserved leucogabbronoritic to gabbronoritic layered intrusion that is a member of the East Bull Lake suite of layered intrusions (ca. 2490-2470 Ma) occurring in central Ontario. These intrusions are related to the development of the Huronian Rift Zone, which may be part of a much more widespread rifting event that involved the Fennoscandian Shield. Structural data suggest that these intrusions have been subjected to ductile deformation and are erosional remnants of one or more sill-like bodies originally emplaced along the contact between Archaean granitic rocks of the Superior Province and an Early Proterozoic Huronian continental flood basalt sequence in the Southern Province.