Earth and Planetary Sciences ETDs

Publication Date

7-26-2004

Abstract

Twenty-six samples from hot springs and fumaroles in Yellowstone National Park (YNP) and 11 in Central America were analyzed for inorganic gases (CO2, SO2, H2S, HCl, Ar, N2, CO, H2, He, 02), methane, and trace volatile light hydrocarbons. Stable isotope analyses of carbon and nitrogen were used in conjunction with the gas geochemistry to determine potential sources of hydrocarbons.

δ13C-CH4 values ranged between -37.6 and-18.2‰ for YNP, from -31.9 to -30.2‰ for El Salvador, and from -38.8 to -23.9‰ for Honduras. δ13C-CO2 values ranged from -4.0 to -1.0‰ and δ15N-N2 values ranged between-3.0 and +5.2 ‰ for YNP. These values support thermogenic breakdown of organic sedimentary material as the major source of volatile light hydrocarbons in YNP and Central America. Abiogenic synthesis may be a minor contributor to observed hydrocarbon concentrations.

Overall hydrocarbon compositions in YNP and Central America are similar, with samples containing light alkanes, alkenes and aromatics. Hydrocarbon concentrations generally decrease with increasing carbon number and are lower in Central America than in YNP. Larger differences in hydrocarbon composition were observed between sites within YNP than between geologic settings (hot spot, arc, back arc).

Three different hydrocarbon distributions are evident in the Yellowstone samples and were used to group the samples. Differential exposure of sedimentary organic material to high temperatures over time can result in the observed differences in hydrocarbon compositions. Some of the samples contain no hydrocarbons higher than methane in the gas phase and are likely derived from organic sedimentary material that is either mature or overmature (Group 1). Decomposition of organic material at low temperatures and over long periods of time leads to alkane-dominated gases (Group 2). Immature fluids that have been rapidly heated to high temperatures can lead to the formation of alkenes (Group 3). Group 3 samples have much lower concentrations and diversity of alkanes, but they contain the alkenes propene and i-butene, the aromatics benzene and toluene, and dimethylsulfide.

Degree Name

Earth and Planetary Sciences

Level of Degree

Masters

Department Name

Department of Earth and Planetary Sciences

First Committee Member (Chair)

Tobias Fischer

Second Committee Member

Zachary Sharp

Third Committee Member

Fraser E. Goff

Project Sponsors

Support for this project was provided by American Chemical Society (ACS PRF #36267) and NSF grants (EAR-0003668 and EAR-0079402 MARGINS) to Tobias Fischer. Additional funding was received from the Department of Earth and Planetary Sciences, University of New Mexico.

Language

English

Document Type

Thesis

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