Geologic Framework for Geothermal Energy in the Cascade Range

Abstract

Quaternary volcanoes of the Cascade Range forma 1200 km long belt from northern California to southwest British Columbia and lie above the suduction zone formed as the Juan de Fuca plate is consumed beneath North America. Volcanoes throughout this belt have bee3n active during Quaternary time, and many have erupted within Holocene time. Despite the apparent abundant recent addition of heat into the crust as suggested by intermediate to silicic volcanism, thermal springs are few and inconspicuous. Surface expression of hydrothermal systems possibly is masked by infiltration of abundant rainwater and snowmelt. Deep exploratory boreholes are needed to test this possibility. Several geologic and geophysical features suggest that the Oregon and California parts of the Cascades, where convergence between the Juan de Fuca and North American plates is oblique, are characterized by moderate east west crustal extension; this tectonic regime is one conducive to relatively widespread volcanism and to the formation of normal fault zones of potentially high permeability.