Introduction to Special Section on the Geological, Geophysical, and Tectonic Setting of the Cascade Range

Abstract

The Cascade Range is an active volcanic arc that is formed by the subduction of the Juan de Fuca plate system beneath North America [Riddihough, 1978]. Knowledge of the Cascade Range, its volcanic rocks, and its tectonic setting is not only of broad scientific interest but also bears directly upon the estimation of geothermal resources and the evaluation of volcanic and seismic hazards.An understanding of the regional aspects of the Cascade Range is at the present time particularly important to the assessment of geothermal resources. Although identified geothermal resources in the Cascade Range are modest [Brook et al., 1979], substantial undiscovered geothermal resources have been inferred [e.g., Brook et al., 1979; Black et al., 1983; Bloomquist et al., 1985], primarily from the favorable volcanic and tectonic setting but also from high regional heat flow along the Cascade Range [Blackwell et al., 1982]. Consequently, a multiyear, multidisciplinary program of studies to refine the geothermal resource estimates of the Cascade Range is a major objective of the U.S. Geological Survey (USGS) Geothermal Research Program [Muffler, 1987]. The smallest and easiest part of this effort is an updated inventory of known hydrothermal convection systems. A much larger and far more difficult task is the estimation of the undiscovered geothermal resources. Existing drill hole information in the Cascade Range is sparse, and under the foreseeable economic climate, direct evaluation of the thermal regime by numerous deep holes is unlikely. However, the magnitude of the undiscovered geothermal resources can be addressed indirectly by an analysis of the tectonic, geophysical, volcanic, and hydrologie setting of the Cascade Range, thus allowing extrapolation of available drill hole data.