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Geophysical Modeling of the Dixie Meadows Geothermal Prospect: Dual Analysis of Gravity and Magnetic Data towards Identifying Structural Controls
AdvisorKarlin, Robert E
Geological Sciences and Engineering
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The northern Great Basin has abundant geothermal systems. Studies have shown these systems are structurally controlled by extensional faults. The faults, and sometimes systems themselves, often have little or no surface expression and must therefore be characterized by geophysical methods. The Dixie Meadows geothermal prospect, located within the Humboldt Structural Zone in central Dixie Valley, Nevada, was investigated in this study in order to delineate basin and fault structure that likely control hydrothermal fluid flow in the subsurface. The study focused on dual interpretation and modeling of gravity and magnetic geophysical data, but was also supported by geological reconnaissance and assessment of surficial hydrothermal expressions. Results indicate a concealed piedmont fault zone separates a deep basin from a relatively shallow intra-basin adjacent to the rangefront. Geophysically delineated faults are located in the intra-basin and piedmont fault zones, and have little or no surface expressions. Rangefront, intra-basin, and piedmont faults are interpreted to be moderately- to steeply-dipping. Faults strike in multiple directions, revealing a network of interlinking and interacting faults. Interpreted structural, geophysical, and hydrothermal patterns along the intrabasin and rangefront demarcate a primary geothermal target area and two secondary targets. The primary target area is characterized by advanced argillic alteration at the surface and upflow indicated by two fumarole zones. Fault intersection appears to be the key structural pattern controlling upflow in the target areas, but fault splaying and step-over are also contributing factors. Integration of dual gravity and magnetic models with geological observations indicates three discrete phases of extension have occurred in Cenozoic time. The superposition of normal faults from these extensional phases appears to be a key component in generating the fault patterns that are controlling hydrothermal fluid flow in the subsurface. The findings of this study are intended to influence further exploration and potential development of the Dixie Meadows geothermal prospect, as well as exemplifying approaches that may aid in discovery, exploration, and development of other prospects in the Humboldt Structural Zone and the Great Basin.