Date of Graduation

12-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Geosciences (PhD)

Degree Level

Graduate

Department

Geosciences

Advisor/Mentor

Phillip D. Hays

Committee Member

Matthew D. Covington

Second Committee Member

Kenneth L. Kvamme

Third Committee Member

Benjamin R. K. Runkle

Fourth Committee Member

Kristofer R. Brye

Keywords

carbon dioxide, hydrothermal, isotopes, mixing model, Taupo Volcanic Zone, Valles Caldera

Abstract

Hydrothermal systems constitute an important component of heat and mass transport within Earth’s crust having direct and indirect impacts to society. Investigating contemporary hydrochemical differences and change are critical to evaluating and deconvolving factors that influence geothermal systems through time. In this dissertation, groundwater mixing approaches were used to study hydrochemical differences in two globally significant hydrothermal areas, which included fabrication of a low-cost dissolved CO2 monitoring for dissolved inorganic carbon (DIC). In the Taupo Volcanic Zone (New Zealand), empirical spatial relations were used to derive low-temperature groundwater end-members of Cl and Cl/Br for end-member mixing analysis (EMMA). Using EMMA, mixing ratios exhibited a wide-range of dilutions and Cl/Br ratios between low- and high-temperature groundwater sources. To explain Cl/Br differences in selected hydrothermal surface features, fluid recirculation is inferred. In the Valles Caldera, NM (USA), mixing analysis consisted of DIC and δ13CDIC analyses of surface water along the Jemez River. Results and findings presented dissolved CO2 versus HCO3 concentration, CO2 versus HCO3 loads, and δ13CDIC relations from which four groundwater end-members were interpreted. This corroborated with previous investigations using trace-element chemistry. Analysis of historical DIC data was used to determine seasonal patterns of DIC loads. Seasonal changes in DIC loads were inferred to be controlled by groundwater-climate feedbacks. A low-cost, Arduino-interfaced monitoring platform (LAMP) was also used to monitor dissolved CO2 (CO2-LAMP) at sites in the Valles Caldera and in Northwest Arkansas. The CO2-LAMP demonstrated replicable and accurate measurements compared to reference gases. Also, the platform captured hourly variability of CO2 in cave air, soil atmosphere, and dissolved CO2 in a cave stream. Humid cave air and dissolved CO2 results were found to be within 15% of a more expensive infrared gas analyzer. For dissolved CO2, this range in measurement difference is regularly observed among methods. Formulation of gas analyzer operation found “corrections” currently made to dissolved CO2 measurements using membrane-enclosed infrared gas analyzers are unwarranted. This body of research presented empirical spatial analysis, EMMA, instrumentation development, and DIC and δ13CDIC analyses which provides new inferences as to the nature and extent of hydrothermal fluid circulation in Earth’s crust.

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