Thesis (Ph. D.)--Open University. BLDSC no. DXN024724.

Thesis (M.S.)--Miami University, Dept. of Geology, 2003. / Title from first page of PDF document. Document formatted into pages; contains viii, 105 p. : ill. Includes bibliographical references (p. 83-91).

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 167-178). Available also in a digital version from Dissertation Abstracts.

Thesis--M. Phil., University of Hong Kong. / Typescript.

A Cl stable isotope fractionation factor between amphibole and fluid has been determined at 700 °C and 0.2 GPa. Rates of isotope exchange between pargasite and water at 600-800 °C were slow; therefore synthesis of amphibole in the presence of a fluid was necessary to facilitate the incorporation of Cl into amphibole. Hastingsite was synthesized from an oxide mixture and reacted with a NaCl-bearing supercritical fluid for periods of 3 to 14 days, approximately at the wüstite-magnetite buffer. Based on these synthesis-reaction experiments, the fractionation between hastingsite and a NaCl-bearing solution (~20000 ppm Cl) at 700 °C is 103lnαamphibole-fluid = 0.19‰ ± 0.23‰. These data display near zero fractionation at 700 °C, but suggest that amphibole is slightly enriched in 37Cl relative to the fluid, in agreement with empirical and theoretical results. / text

This study addresses the influences on ridge basalt chemistry, through analysis of their major and trace element and isotopic composition at scales ranging from individual ridge segments to the entire length of the ridge system. Local-scale studies of basalts along the Mid-Atlantic Ridge shed light on crustal accretion at slow-spreading ridges, and on the nature of plume-ridge interaction in this region. We show that segments must have multiple supplies of magma delivered along their length, but with preferential delivery of magma to segment centers. Plume-ridge interaction near the Azores is not simple two- component mixing between “plume” mantle and “depleted” mantle as previously argued. The elevated highly incompatible trace element ratios possessed by basalts well south of the plume are the definitive sign of a low-degree melt, which can fractionate highly incompatible element ratios. We show that a low-degree melt of plume mantle acts to metasomatize ambient depleted mantle, creating a mixed source that melts to produce the enriched basalts south of the Azores. This metasomatized source is the enriched mixing component that produces the observed geochemical gradient, rather than bulk plume mantle. The latter half of this study is global in scope, involving a carefully compiled ridge basalt geochemical database. This database is unparalleled in size and coverage – including data from portions of the Gakkel and Southwest Indian Ridges and Lau basin that were unavailable in prior data compilations. It includes a catalog of 771 global ridge segments, enabling the calculation of mean MORB by averaging the “segment means”, including weighting on segment length and spreading rate and a quantitative treatment of errors. We show that the mean composition of ocean ridge basalts is more enriched than previously suggested, and argue for a re-definition of “normal MORB”. Segment basalt compositions are individually corrected for crystal fractionation, arriving at parental magma compositions that can be interpreted in terms of mantle processes. The fractionation-corrected mean segment compositions correlate with ridge depth, and with each other, in a manner that is consistent with control by mantle temperature variations. Mantle compositional heterogeneity is also seen, but appears to be a second-order effect. / Earth and Planetary Sciences

General control of atoms and molecules has long been a goal for atomic physicists and physical chemists. Techniques such as laser cooling have been a huge breakthrough in studying ultra cold atoms and BECs. Although laser cooling has been a remarkable tool, it is limited to small group of atoms on the periodic table. A general technique to control and manipulate the entire periodic table has been out of reach until now. In this thesis I describe two methods of general control of atoms in the contexts of stopping supersonic beams and of isotope separation. Both these methods take advantage of high flux supersonic beams and the fact that every atom has a magnetic moment in the ground state or a long-lived excited state which can be manipulated using magnetic field gradients. The first method uses a series of pulsed electomagnetic coils to slow and stop a supersonic beam of paramagnetic atoms and molecules. We have demonstrated the slowing of metastable neon and molecular oxygen using 64 coils from 446.5 m/s to 55.8 m/s for metastable neon, and from 389 m/s to 83 m/s for molecular oxygen respectively. The second method is a novel and efficient approach to isotope separation which utilizes the concept of Maxwell's Demon. We call this technique Single-Photon Atomic Sorting as it is closely related to Single-Photon Cooling, a cooling technique developed in our laboratory. Our method uses a laser beam to change the magnetic moment to mass ratio in such a way that the desired isotopes are guided through a multi-pole magnetic field and collected. We show simulation results for various test cases which highlight the general applicability of this method. / text

Salt marsh food webs are complex systems, with high levels of in situ primary production supporting a wealth of resident and migratory species. In this study, we use stable isotopes as a tool to trace organic matter utilization within the Nueces Marsh food web. Specifically, we were interested in (1) the use of treated wastewater as a ¹⁵N tracer, and (2) seasonal and interannual variation in food web structure. We hypothesized that treated wastewater would selectively label detrital resourse use within the food web, allowing us to trace grazing vs. detrital pathways within the marsh system. We also hypothesized that marsh consumers would exhibit distinct differences in isotopic composition between summer and winter, and between different years. We found that the Nueces Marsh food web consists of 3.5 consumer trophic levels. The [delta]¹³C values of consumer organisms were similar across the spatial extent of the low marsh, regardless of proximity to wastewater inflow. However, a majority of the organisms collected from the wastewater channel were significantly (p<0.05) enriched in ¹⁵N compared to their reference counterparts. We propose that ¹⁵N-enriched nitrogen is entering the Nueces Marsh food web through detrital rather than grazing-based pathways, making wastewater effluent an effective tracer of detrital integration into a marsh food web system. Hydrologic data indicate that isotopic shifts between seasons and between years reflected larger scale shifts between drought and wet years. During drought years, decreased production by phytoplankton and emergent plants led consumers to rely more heavily on ¹³C-enriched cyanobacterial carbon. In contrast, wet years encourage phytoplankton and emergent plant production, making cyanobacterial carbon relatively less exploited. While the Nueces Marsh food web is supported by a stable detrital carbon pool, it may still be susceptible to larger scale hydrologic events. / text

Uranium-series isotopes are an emerging tool to characterize weathering and soil forming processes in the Critical Zone, the dynamic region of earth's surface where bedrock, water, soil, and life chemically and physically interact to support ecosystems. Understanding controls on the U-series composition of soils across a range of lithologies and climate is critical to applying existing mass balance models of U-series isotopes to calculate soil formation rates in these systems. This study seeks to understand the behavior of U-series isotopes in soil profiles in the semi-arid complex volcanic terrain of the Valles Caldera, NM. (²³⁴U/²³⁸U) measured in soils ranged from 0.90 to 1.56 and (²³⁰Th/²³⁸U) values ranged from 0.48 to 1.39. Significant ²³⁰Th enrichment in upper soil profiles was interpreted as evidence of mixing with ²³⁰Th-enriched volcanic ash and significant ²³⁴U enrichment in one soil profile was interpreted as evidence of addition of U to soils from ²³⁴U-enriched soil solutions. A simple U isotope mass balance model was applied to estimate soil residence time based on U addition, which yielded a minimum residence time of ~10ka. Evidence of past episodic mixing of volcanic ash in these soils suggests modeling soil formation using a mass balance approach is problematic, and future applications of existing models in other heterogeneous volcanic soils should be applied cautiously. U-series isotopes have also shown promise as a tracer of residence time in shallow groundwater and streams. In this study, (²³⁴U/²³⁸U) in dissolved U is used to trace seasonal variation in source water contributions to streamflow in a small (3.29km²), headwater catchment in the Jemez River Basin Critical Zone Observatory within the Valles Caldera. Systematically lower (²³⁴U/²³⁸U) values in dissolved U were observed in spring and stream waters in conjunction with greater contributions of longer residence time waters during snowmelt ((²³⁴U/²³⁸U) ranged 1.7 to 2.8) vs. dry seasons ((²³⁴U/²³⁸U) ranged 1.9 to 3.1). The lower (²³⁴U/²³⁸U) values in longer residence time waters were attributed to progressive depletion of easily-weathered ²³⁴U with increasing duration of water rock interaction. Further studies with more quantitative age tracers, such as ³H, could help to establish (²³⁴U/²³⁸U) values as a powerful tracer of water sources and residence time in streamwaters at the catchment scale.

The Middle San Pedro Basin in southeastern Arizona is a typical alluvial basin in the semi-arid southwestern United States with a rapidly growing population that is dependent upon groundwater resources for water supply. This study investigated recharge areas, compartmentalization and potential mixing of water sources, and travel times of groundwater throughout the basin using variations in major ion chemistry (water type, Ca/Sr ratios, SO4/Cl ratios) and isotope ratios (18O, 2H, 3H, 34S, 13C, 14C) of groundwaters, surface waters and precipitation in conjunction with hydrogeologic data (e.g. hydraulic head and hydrostratigraphy). Recent recharge (<50 years) has occurred within mountain systems along the basin margins, and in shallow floodplain aquifers adjacent to the San Pedro River. Groundwaters in confined aquifers in the central basin were recharged at high elevation in the fractured bedrock and have been extensively modified by water-rock reactions over long timescales (up to 34,600 years). These results can be used to constrain physical assumptions of future groundwater flow models designed to help make improved water management decisions.