GEOCHEMISTRY OF THE GALÁPAGOS ARCHIPELAGO: UNRAVELING DEEP MANTLE SIGNATURES FROM THE INFLUENCE OF SHALLOW LEVEL PROCESSES

Peterson, Mary E.

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Year:: 2015
Contributor:: Peterson, Mary E (creator); Saal, Alberto (Director); Kurz, M (Reader); Parman, Stephen (Reader); Forsyth, Donald (Reader); Cooper, Reid (Reader); Brown University. Geological Sciences (sponsor)
Genre:: theses
Subject:: Galapagos; hotspot; mantle; volatile elements; lead isotopes; oxygen isotopes; oxygen fugacity; oxidation state; shallow level process; Lead--Isotopes; Oxygen--Isotopes; Galapagos Islands
Extent:: xiii, 313 p.
DOI: https://doi.org/10.7301/Z0WH2NCV

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Abstract:: In this dissertation, I present a large geochemical data set of submarine glass, melt inclusions and whole rock collected from across the Galapagos Archipelago to explore the influence of shallow level processes on lavas erupted at the surface and to isolate deep mantle signatures of the plume. The first chapter examines the ghost plagioclase signature using Pb isotope analyses of melt inclusions collected from the Islands of Fernandina and Santiago [published in Journal of Petrology. 55(11), 2193-2216]. The measurement of Pb-isotopes on melt-inclusions from Fernandina and Santiago show the ghost plagioclase signature is best explained by contamination in the present-day crust, over an ancient recycled mantle source. The second chapter measures 118 submarine glasses from across the Galapagos Archipelago for major, trace, isotopic and volatile contents [manuscript submitted to Journal of Petrology April 2015]. After evaluating the effects of shallow level processes, H2O/Ce and F/Nd were found to best distinguish different isotopic end-members. The Fernandina end-member possesses a higher water content than the depleted upper mantle, as well as high C/3He ratios, showing this end-member to be carbonated as well as wet. The third chapter uses μ-XANES measurements of Fe+3/ΣFe (a proxy for fO2) on a subset of samples characterized in Chapter 2. Crystal fractionation and assimilation increases, while S degassing decreases Fe+3/ΣFe ratios. After accounting for these shallow level processes, the Fernandina component is found to be the most oxidized isotopic end-member in the Galapagos. The fourth chapter presents new stable oxygen isotope analyses for olivines collected across the Galapagos Archipelago. Variations in δ18O (~ +4.7‰ – +5.4‰) fall outside the expected value for the upper mantle. However, the δ18O values of the isotopic end-members are within error of the upper mantle range. This shows the homogeneity in δ18O of the Galapagos plume mantle and indicates variations outside this value are due to assimilation of shallow level material. This is consistent with observed correlations between δ18O values and Sr/Sr* and Ba/Nb ratios.
Notes:: Thesis (Ph.D. -- Brown University (2015)

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Peterson, Mary E., "GEOCHEMISTRY OF THE GALÁPAGOS ARCHIPELAGO: UNRAVELING DEEP MANTLE SIGNATURES FROM THE INFLUENCE OF SHALLOW LEVEL PROCESSES" (2015). Earth, Environmental and Planetary Sciences Theses and Dissertations. Brown Digital Repository. Brown University Library. https://doi.org/10.7301/Z0WH2NCV

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Theses and Dissertations for the Earth, Environmental and Planetary Sciences department.
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