Do Magmatic-Related Geothermal Energy Resources Exist in Southeast Idaho?

Abstract

This paper assesses the possibility that magmatically related geothermal systems occur as blind geothermal resources in southeast Idaho. A brief summary is provided of the robust late- Pleistocene-Holocene structural, thermal and volcanic evolution of southeast Idaho, and contrasts that with the relative paucity of surficial manifestations of geothermal activity in the area. The paper presents and evaluates three hypotheses for the paucity of surficial expressions of magmatic-geothermal activity: 1. Accessible magma-related heat does not exist in the region. 2. Accessible magmatic heat exists but the hot rock bodies have not generated significant circulation of high-temperature geothermal fluids. 3. Magmatic geothermal systems exist in the region, but their surficial geothermal expression is diverted and/or muted owing to external factors (i.e. they exist as blind resources). Each hypothesis is examined in light of documented features of the regional geology, petrogenesis of late-Pleistocene-Holocene volcanics and hydrogeology. Arguments are presented which suggest that the first two hypotheses are unlikely. The paper concludes that magmatic-related geothermal systems are likely to exist in southeast Idaho, and it proposes that those systems are masked by the combined effects of a distinctive shallow hydrogeologic conditions and deeper crustal anisotropy that controls fluid pathways at depth.