HR: 10:20h
AN: T22A-01 INVITED     [Abstracts]
TI: Regional and Local Controls on the Distribution of Geothermal Systems in the Great Basin, Western United States
AU: * Coolbaugh, M F
EM: mfc@unr.nevada.edu
AF: University of Nevada, Reno, MS 172, 256 LMR, Reno, NV 89557 United States
AU: Blewitt, G
EM: gblewitt@unr.edu
AF: Nevada Bureau of Mines and Geology, MS 178, SEM 307 University of Nevada, Reno, Reno, NV 89557 United States
AU: Faulds, J E
EM: jfaulds@unr.edu
AF: Nevada Bureau of Mines and Geology, MS 178, SEM 307 University of Nevada, Reno, Reno, NV 89557 United States
AU: Kreemer, C W
EM: kreemer@unr.edu
AF: Nevada Bureau of Mines and Geology, MS 178, SEM 307 University of Nevada, Reno, Reno, NV 89557 United States
AB: In the Great Basin (GB) of the western United States, geothermal systems with reservoir temperatures in excess of 150 C can be classified into two main categories (magmatic and amagmatic) according to the presence or absence of shallow magmatic heat sources. Magmatic systems are restricted to the margins of the GB where they are closely associated with Quaternary silicic volcanic rocks, whereas amagmatic systems occur over a large portion of the Great Basin interior and are not spatially associated with young silicic volcanism. A tabulation of temperature gradients for known geothermal systems in the world confirms research by others indicating that both magmatic and amagmatic systems occur within areas of high temperature gradients and high heat flow. However, high heat flow alone is not sufficient to explain the abundance of high-temperature geothermal activity in the GB interior. While the distribution of favorable host rocks likely plays a role, active crustal tectonics appears instrumental in explaining patterns of geothermal activity. At a detailed scale, Quaternary faults control the location of most geothermal systems in the GB. However, hundreds of Quaternary faults are distributed throughout the GB, and most do not host high-temperature geothermal resources. Spatial statistical analysis demonstrates that high-temperature geothermal systems (more than 150 C) are preferentially associated with NE-striking Quaternary faults, which in turn are oriented roughly perpendicular to the current direction of crustal extension in the western GB. Maps of active crustal extension rates in the GB, derived from Global Positioning System (GPS) velocity measurements and estimated slip rates on Quaternary faults, correlate well with the distribution of high-temperature geothermal systems and help explain why some faults with lower slip rates or unfavorable orientations don't host geothermal activity. Many geothermal systems in the GB occur in a broad transitional region between the transtensional Walker Lane and the more extensional interior of the GB. This pattern of geothermal activity is helping to clarify the tectonic evolution of the northwestern GB, where dextral strike-slip faulting along the Walker Lane is being transferred into a series of extensional structures in the Humboldt structural zone and the central Nevada seismic zone. On-going research at the University of Nevada, Reno is investigating the relationship between active crustal transtension, evolution of the Walker Lane, and the occurrence of high-temperature geothermal resources. One part of this investigation is the setup of a 60-station semi-permanent GPS network with 20km station spacing in western Nevada. Results from this network will be instrumental in further constraining the regional strain rate field.
UR: http://www.unr.edu/geothermal
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 8038 Regional crustal structure
DE: 8130 Heat generation and transport
DE: 9350 North America
SC: Tectonophysics [T]
MN: Fall Meeting 2005