| Abstract |
The MacFarlane geothermal system is located ~85 km west of Winnemucca on the eastern margin of the Black Rock Desert, in Humboldt County, Nevada. An E-trending travertine mound, ~180 m long, and up to ~2 m tall and ~5 m wide, has a central fissure ridge along its long axis and an active hot springs flowing out of its west end. Reservoir temperatures were estimated at 80° ? 140° C (Sibbett et al, 1982). Detailed geologic mapping, structural analysis and two-meter temperature data analysis integrated with previous datasets suggest the structural controls of the MacFarlane geothermal system, which include a NS-striking, west-dipping Tertiary fault east of MacFarlane hot springs, a NNE-striking, west-dipping Quaternary fault set directly surrounding the hot springs and a ENE-striking fault mapped just north of the hot springs by Sibbett et al. (1982). Although the highest temperature gradient is found at a proposed intersection between the Tertiary and Quaternary fault sets (Sibbett et al, 1982; Swanberg et al, 1982), other scenarios involving the geometry of the Quaternary faults and/or a combination of structural scenarios need to be considered. MacFarlane hot springs and the travertine mound lie between two Quaternary faults, in a dextral step-over or relay ramp zone. The controls on the anomalously orientated travertine fissure ridges might be due to perturbations in the stress field during relay ramp formation, perturbations in the stress field related to a single fault termination, or a buried EW-striking fault. Many of these faults are covered in Quaternary sediments, so a geophysical survey and more detailed Quaternary mapping are in progress to resolve the specific structural setting here. |