DRUM Collection: Geology Theses and Dissertations

Highly Siderophile Elements and the Rhenium-Osmium System in Chondritic Components

Sun, 01 Jan 2012 00:00:00 GMT

Title: Highly Siderophile Elements and the Rhenium-Osmium System in Chondritic Components Authors: Archer, Gregory Jude Abstract: Chondritic meteorites and their components provide information about the early solar system, as well as processes that affected meteorite parent bodies post-accretion. The rare earth element (REE) abundances, highly siderophile element (HSE) abundances, Re-Os isotope systematics, Re isotopic composition, and Os isotopic composition were investigated in Allende chondritic components in order to: (1) classify several recently separated Allende calcium-aluminum-rich inclusions (CAIs) based on REE abundance patterns, (2) determine the abundances of six HSE (Re, Os, Ir, Ru, Pt, and Pd) in CAIs, chondrules, and matrix, and compare the different chondritic components, (3) further assess the magnitude and characteristics of open-system behavior on the Allende parent body using Re-Os of CAIs, chondrules, and matrix, (4) determine if the Re isotopic composition of CAIs was altered by cosmic ray interactions, and (5) investigate possible nucleosynthetic anomalies in CAIs.

Geochemical and Radiometric Constraints on the Redox History of Late Ediacaran Oceans

Sun, 01 Jan 2012 00:00:00 GMT

Title: Geochemical and Radiometric Constraints on the Redox History of Late Ediacaran Oceans Authors: Peek, Sara Abstract: Over the past decade, significant field and laboratory studies have been devoted to furthering understanding of the chemical conditions that accompanied the origin and diversification of Earth's earliest multicellular animals during the Ediacaran Period (ca. 635-542 Ma). Here, I apply geochemical methods to excellently preserved and exposed sections spanning approximately the last 10 million years of the Ediacaran Period. From Arctic Siberia, hundreds of samples were collected at high stratigraphic resolution, from which carbonate carbon and oxygen profiles have been produced, along with organic carbon and sulfur isotope data. From South China, a carbonate carbon isotope profile has been constructed. Radiometric dates constrain the timing of deposition in our sections. This work uses geochemical data and radiometric dating to inform and improve intra- and inter-basinal correlation, and serves as a preliminary study confirming the suitability of our Siberian sections to the study of oxygenation during the latest Ediacaran Period.

A Study of the Sulfur Isotopic Composition of Martian Meteorites

Sun, 01 Jan 2012 00:00:00 GMT

Title: A Study of the Sulfur Isotopic Composition of Martian Meteorites Authors: Franz, Heather Abstract: ABSTRACT Title of Document: A STUDY OF THE SULFUR ISOTOPIC COMPOSITION OF MARTIAN METEORITES Heather B. Franz, Ph.D., 2012 Directed By: Professor James Farquhar, Department of Geology and ESSIC Sulfur is an important tracer for geochemical processes because it possesses four stable isotopes and forms natural compounds in a range of oxidation states. This element has been shown to undergo mass-independent isotopic fractionation (S-MIF) during laboratory photochemical experiments, which may provide clues to processes that have occurred both in the solar nebula and in planetary atmospheres. The surface of Mars has been found to contain ubiquitous sulfate minerals, marking this planet as an ideal candidate for sulfur isotope study. The shergottites comprise the youngest group of martian meteorites and the most representative of mantle-derived igneous rocks. Extraction and isotopic measurement of sulfur from 30 shergottites yield the first estimate of the juvenile martian sulfur composition, which matches within uncertainties that of Cañon Diablo Troilite. Analysis of martian meteorites spanning a range of ages from the shergottites, as young as ~150 Ma, to the nakhlites, ~1.3 Ga, reveals the presence of sulfur characterized by S-MIF compositions. These findings are interpreted as evidence for cycling of sulfur between an atmospheric reservoir where photochemical processing of sulfur-bearing gases occurred and a surface reservoir in which photochemical products were ultimately deposited. Anomalous sulfur has been detected in both sulfate and sulfide minerals, implying assimilation of sulfur from the martian surface into magmas. Differences in the S-MIF compositions of the nakhlites and shergottites may preserve a record of complementary sulfur formed by a single process or may indicate the operation of multiple photochemical processes at different times or geographical locations. Identification of the photochemical mechanism responsible for producing the anomalous sulfur observed in martian meteorites is important for constraining the atmospheric composition at the time the S-MIF signals were generated. Results of laboratory experiments with pure SO2 gas suggest that self-shielding is insufficient to explain the anomalous sulfur isotopic composition. This implies that an optically thick SO2 column in the martian atmosphere may not have been required for production of the observed signals

The Effect of CO2 on Copper Partitioning in Sulfur- Free and Sulfur-Bearing Felsic Melt-Vapor-Brine Assemblages

Sun, 01 Jan 2012 00:00:00 GMT

Title: The Effect of CO2 on Copper Partitioning in Sulfur- Free and Sulfur-Bearing Felsic Melt-Vapor-Brine Assemblages Authors: Tattitch, Brian Christopher Abstract: Analysis of fluid inclusions from porphyry copper deposits (PCD) reveals that magmatic vapor and/or brine are vital for the removal of copper from arc magmas and its transport to the site of ore formation. Experiments in melt-vapor-brine systems allow for investigating the partitioning of copper between silicate melts and volatile phases under magmatic conditions. The presence of CO₂ affects both the pressure of vapor saturation and the composition of exsolving volatile phases. However, PCD are primarily sulfide ore deposits, and the role of sulfur must also be examined as part of magmatic-hydrothermal experiments. Therefore, the partitioning of copper in CO₂ ± S-bearing experiments was examined in an attempt to provide insights into copper partitioning and the generation of PCD. I present the results from experiments performed at 800 °C and 100 MPa in CO₂-bearing melt-vapor-brine systems with X_CO2 = 0.10 and 0.38. The compositions of vapor and brine inclusions and run-product glasses were used to determine the compositions of the magmatic phases. The partitioning of copper between brine and vapor (D_Cu b/v ±2σ) increases from 25(±6) to 100 (±30) for sulfur-free experiments and increases from 11(±3) to 95(±23) for sulfur-bearing experiments as X_CO2 is increased from 0.10 to 0.38. The partitioning of copper between vapor and melt (D_Cu v/m ±2σ) decreases from 9.6(±3.3) (sulfur-free, HCl-bearing), 18(±8) (sulfur-bearing, HCl-free), and 30(±11) (sulfur-bearing, HCl-bearing) at X_CO2 = 0.10, to 2(±0.8)(HCl-free) at X_CO2 = 0.38, sulfur-free or sulfur-bearing. These data demonstrate that copper partitioning in sulfur-free, CO₂-bearing systems is controlled by the changes in the salinity of the vapor and brine corresponding to changes in X_CO2. Sulfur-bearing experiments demonstrate that magmatic vapors are enriched in copper in the presence of sulfur at low X_CO2. However, the enrichment of copper in the magmatic vapor is suppressed for sulfur-bearing systems at high X_CO2. The MVPart model presented by Candela and Piccoli (1998) was modified to incorporate CO₂ to predict trends in efficiency of removal of copper into exsolving CO₂-bearing magmatic volatile phases. The CO₂-MVPart model predicts two to three times lower efficiency for CO₂-rich (X_CO2 = 0.38) magmatic volatile phases compared to low-CO₂ (X_CO2 ≤ 0.10) systems.