Numerical Simulation of Hydrothermal Circulation in the Cascade Range, North-Central Oregon

Abstract

Alternate conceptual models to explain near surface heat flow observations in the central Oregon Cascade Range involve (1) an extensive mid crustal magmatic heat source underlying both the Quaternary arc and adjacent older rocks or (2) a narrower deep heat source which is flanked by a relatively shallow conductive heat flow anomaly caused by regional groundwater flow (the lateral flow model). Relative to the mid crustal heat source model, the lateral flow model suggests a more limited geothermal resource base, but a better defined exploration target. We simulated groundwater flow and heat transport through two cross sections trending west from the Cascade range crest in order to explore the implications of the two models. The thermal input for the alternate conceptual models was simulated by varying the width and intensity of a basal heat flow anomaly and, in some cases, by introducing shallower heat sources beneath the Quaternary arc. Near surface observations into eh Breitenbush Hot springs area are most readily explained in terms of lateral flow; however, the deep thermal structure still cannot be uniquely inferred. The Sparser thermal data set from the McKenzie River area can be explained with in terms of deep regional groundwater flow or in terms of a conduction dominated system, with groundwater flow essentially confined to Quaternary rocks and fault zones.