Spatial And Temporal Distribution Of Hydrothermal Minerals And Sources Of Hydrothermal Fluids Inferred From Light Stable Isotopes Keweenaw Peninsula Native Copper District Michigan

Author : Jeffrey Todd Cullen
Publisher :
ISBN 13 :
Total Pages : 430 pages
Book Rating : 4.:/5 (15 download)

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Download or read book Water-rhyolite Interaction in the Yellowstone Hydrothermal System written by Jeffrey Todd Cullen and published by . This book was released on 2018 with total page 430 pages. Available in PDF, EPUB and Kindle. Book excerpt: In caldera-hosted rhyolitic hydrothermal systems, thermal waters, which are expelled to the surface through geysers and hot springs, provide a window into the conditions of water-rock interaction and element source/transport pathways of the dissolved components. By conducting hydrothermal experiments, we can constrain element behaviors during water-rock (W-R) interaction which enhances our ability to accurately interpret natural thermal waters and thus gain insights into processes occurring at depth in the hydrothermal system. This dissertation focuses on constraining elemental and isotopic behaviors during water rock interactions under conditions appropriate of continental, rhyolitic-caldera-hosted hydrothermal systems; more specifically the Yellowstone Hydrothermal System. In Chapter 2, I conduct water-rhyolite experiments over a temperature range of 150°C-350°C to constrain element leaching behaviors at each temperature, the secondary minerals formed, and how the secondary minerals control the concentrations of certain essential proxy fluid-mobile trace elements (Cl, F, Br, Li, and B). The experiments show rhyolite obsidian is stable at T ≤ 250°C. No alteration occurs and F is mobilized readily out of the rock by hydration exchange reactions. Cl and B are not leached from the rock. At T ≥ 275 °C, the rhyolite is completely broken down and recrystallized to the zeolite, ferrierite. Fluorine has affinity for the zeolite and is removed from solution into this phase, whereas Cl and B are completely leached from the rock and remain in solution. Li is moderately fluid mobile over the entire temperature range. In Chapter 3, I investigate the Cl, Li, and B stable isotope behaviors of the experimental materials in order to determine whether these isotopes fractionate during water rock interaction. The experimental results are compared with natural Yellowstone thermal waters from Upper Geyser Basin (UGB). The results indicate that Cl and B isotopes fractionate negligibly during leaching and during precipitation of ferrierite at T ≥ 275 °C. 7Li is only preferentially released into solution during leaching at T ≤ 250°C. The Cl, Li, and B isotope compositions of Upper Geyser Basin (UGB) waters reflect the leaching from host rhyolites with little to no fractionation. Elemental ratios suggest a small fraction of Cl and perhaps Li are derived from a magmatic source. In Chapter 4, I generate aqueous geochemical data from an extensive suite of Yellowstone thermal waters we collected between 2014 and 2016 (n = 141) from 11 separate geyser basins/thermal areas in the Yellowstone Hydrothermal System to uncover chemical correlations between thermal areas and water types across the entire system. Data are in good agreement with the experimental results. delta37Cl, values are relatively uniform throughout, and indicate leaching from host rhyolites. In alkaline-chloride dominant thermal areas, delta7Li, and delta11B values indicate leaching of host rhyolites with minimal fractionation and/or interaction with preciously altered rhyolites. In acid-SO4 and mixed SO4-Cl areas, delta7Li, and delta11B values are consistent with fractionation due to interaction with secondary clay minerals. Higher resolution investigation of UGB thermal waters reveals spatial correlations with compositions and inferred reservoir equilibrium temperatures.