Geothermal Potential of Diverse Volcanotectonic Settings of the Cascade Range, USA

Abstract

Late Quaternary volcanic centers in the Cascade Range comprise four categories that correlate with geothermal potential. Stratovolcanoes: Hydrothermal activity (often transitory) occurs primarily near narrow volcanic conduits, although deep cryptic hydrothermal systems at the more silicic volcanoes cannot be ruled out. (2) Composite centers: Stratovolcanoes with silicic domefields and related young intrusions can support high-temperature hydrothermal systems. (3) Explosive caldera: A caldera at Crater Lake formed at 7700 ka by explosive eruption of -50 of andesite and dacite. Viable heat sources may still remain as the unerupted part of the large magma chamber at 7.5-15 km and as small shallow intrusive bodies associated with pre-caldera magmatism. (4) Shield complexes: Medicine Lake and Newberry volcanoes occur where Basin-and-Range extension impinges on the Cascade Range. Young basalt and rhyolite in shallow intrusive plexuses comprise favorable heat sources. Surface thermal manifestations are very sparse, but promising high-temperature systems have been identified at both volcanoes. Undiscovered hydrothermal resources of the Cascade Range appear to be significantly less than previously estimated.