| Title | The Pyramid Lake Paiute Reservation, Western Nevada (USA): Exploration for Blind Geothermal Systems in a Transtensional Displacement Transfer Zone |
|---|---|
| Authors | James Faulds, Peter Drakos, Garrett Vice, Brett Mayhew, Donna Noel |
| Year | 2011 |
| Conference | New Zealand Geothermal Workshop |
| Keywords | Nevada, geothermal system, structural controls, Walker Lane, Pyramid Lake |
| Abstract | The Walker Lane belt (WL) is a zone of dextral shear that accommodates ~20% (~1 cm/yr) of the Pacific – North America plate motion, with the bulk of strain taken up by the San Andreas fault. As the WL terminates northwestward in northeast California, dextral shear is transferred into WNW-directed extension in the northwestern Basin and Range, which accentuates dilation on normal faults and generates a broad region of high geothermal potential in the northwestern Great Basin. The major dextral faults in the northern WL form a left-stepping en echelon pattern, with each dextral fault terminating in arrays of N- to NNE- striking normal faults. We refer to these areas of strain transfer as transtensional displacement transfer zones. The Pyramid Lake region occupies a major displacement transfer zone, as the NW-striking right-lateral Pyramid Lake fault (PLF) ends northward and transfers strain to a major west-dipping normal fault system. Offset of an Oligocene paleovalley suggests ~10 km of dextral displacement on the PLF just south of its terminus. Cumulative normal displacement on west-dipping normal faults in the region is ~10.7-12.6 km, which is sufficient to have accommodated transfer of most of the dextral slip on the PLF. Enhanced extension results in high geothermal potential in the Pyramid Lake region. However, known high-enthalpy systems occur in culturally sensitive areas in the reservation and thus cannot be developed. We have therefore embarked on a broad exploration program aimed at discovering blind geothermal systems within the reservation. This multi-disciplinary analysis includes identifying surficial features indicative of past geothermal activity (e.g., tufa towers) and favorable structural settings (e.g., relay ramps and fault intersections). The Astor Pass area directly northwest of Pyramid Lake was initially selected, because it contains two linear trends of tufa towers that mark a major fault intersection. Temperatures of 94oC were observed at 70 m depth proximal to the central tufa tower, but deeper drilling (>1 km) nearby has yet to yield higher temperatures despite promising geothermometry. Another promising area is a major step-over or relay ramp directly northeast of Pyramid Lake between the W-dipping range front faults of the Lake and Fox Ranges. Integrated geologic and geophysical studies will be employed to identify additional areas with high geothermal potential. |