Quantitative Models of Fluid Flow, Chemical Reaction, and Stable Isotopic Fractionation and Their Application to Sediment Diagenesis and Hydrothermal Alteration
Lee, Ming-Kuo
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https://hdl.handle.net/2142/72512
Description
Title
Quantitative Models of Fluid Flow, Chemical Reaction, and Stable Isotopic Fractionation and Their Application to Sediment Diagenesis and Hydrothermal Alteration
Author(s)
Lee, Ming-Kuo
Issue Date
1993
Doctoral Committee Chair(s)
Bethke, Craig M.
Department of Study
Geology
Discipline
Geology
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Geology
Hydrology
Geochemistry
Abstract
In this study, I develop a numerical model to predict dissolution and precipitation reactions by groundwater flow through temperature and pressure gradients in sedimentary basins. I incorporate chemical reaction into a transient model of groundwater flow equations that describes heat transfer and solute transfer. The model is formulated and solved in geologic-time and basin distance scales, and can be therefore applied to study basin-wide diagenesis related to long-distance fluid migration. The model integrates predicted groundwater flow patterns with the reaction path modeling; this approach allows us to predict the rate at which minerals dissolve and precipitate in flow systems of specific interest. Sample calculations of precipitation and dissolution reactions within several flow systems shed light on the rates and patterns of chemical diagenesis that likely accompany fluid migration in sedimentary basins.
I also present a numerical technique that predicts how the stable isotopes $\sp $O, $\sp2$H, $\sp $C, and $\sp{34}$S fractionate among solvent, aqueous species, minerals, and gases over the course of a reaction path model. This model is based on mass balance techniques already presented, but differs from the previous techniques in that it allows minerals to be segregated from isotopic exchange instead of remaining in isotopic equilibrium. Such an approach allows us to simulate isotopic fractionation between rock and fluid resulting solely from mineral dissolution and precipitation. I test this technique by modeling isotopic fractionation during several reaction processes. The results of calculations in which minerals are segregated from isotopic exchange compare well to isotopic trends observed in nature, but differ markedly from calculations that assume isotopic equilibrium.
I combine these hydrologic and geochemical modeling techniques with field and experimental observations to study sediment diagenesis and hydrothermal alteration, including (1) diagenetic alteration in the Lyons sandstone of the Denver basin; (2) brine diagenesis in the deep aquifers of the Illinois basin; and (3) hydrothermal alteration of the Okanagan batholith in southern British Columbia. These case studies illustrate the models' ability to help us better understand the relationship between fluid flow and chemical reactions, as well as how stable isotopes fractionate in reacting geochemical systems.
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