ABSTRACT: A New Look at Geothermal Energy Potential of the Eastern Snake River Plain, Idaho
Richard P. Smith, William R. Hackett, David D. Faulder, Suzette M. Jackson
Passage of the Yellowstone plume beneath the Eastern Snake River Plain (ESRP) left a wake of silicic batholiths and associated 4 to 6 Ma rhyolitic tufts, a 1 km thick sequence of post 4 Ma basalt lava flows, and high heat flow comparable to that of the Basin-and-Range province. U.S.G.S. Circular 790 estimates that accessible resources are one-third larger than those of the Cascades, but geothermal exploration and research activities on the ESRP have quietly perished. We believe that the ESRP merits further attention as a geothermal exploration target. In this article, the first of several by our group, we identify relevant geological and geophysical features of the ESRP, the first step toward a meaningful exploration strategy.
Although exploration is hindered by the heat-sapping effects of the overlying SRP aquifer, several geological features of the ESRP suggest that viable exploration targets exist beneath the aquifer: (1) the fracture zones of buried, Neogene silicic calderas; (2) Quaternary basaltic rift zones (several NW-trending ones and an axial one), which have been persistent zones of fissuring, minor faulting, and magma transport; (3) high-angle faults and fractures around the margin of the downwarped ESRP, including NW-trending basin-and-range faults and NE-trending marginal faults; and (4) fractured or brecciated zones near Pleistocene rhyolite domes and silicic intrusions.
Existing geophysical data also constrain exploration targets. Aeromagnetic surveys show NW-trending highs that intersect a NE-trending axial high; rhyolite domes and youthful basaltic volcanism are localized along the highs and at intersections. Although the ESRP is remarkably aseismic, recently installed local seismic networks have identified contemporary microearthquakes that could preserve fracture permeability to depths of several kilometers.
The geologic features of several developed geothermal regions are similar to those of the ESRP. The Puna and Krafla areas occur in active basaltic rift zones. Beowawe, Nevada, is a possible analogy to the basin-and-range, fault-related geothermal systems that may exist along the margins of the ESRP. Steamboat Springs, Nevada, is associated with Pleistocene silicic magmatism, and is a possible analog to geothermal systems that might occur near silicic domes and intrusions of the ESRP axis.
AAPG Search and Discovery Article #90097©1990 Fifth Circum-Pacific Energy and Mineral Resources Conference, Honolulu, Hawaii, July 29-August 3, 1990