Heat Flow and Hydrothermal Circulation in the Cascade Range, North-Central Oregon

In north-central Oregon a large area of near-zero near-surface conductive heat flow occurs in young volcanic rocks of the Cascade Range. Recent advective heat flux measurements and a heat-budget analysis suggest that ground-water circulation sweeps sufficient heat out of areas where rocks younger than 6 Ma (million years ago) are exposed to account for the anomalously high advective and conductive heat discharge measured in older rocks at lower elevations. Earlier workers have proposed that an extensive midcrustal magmatic heat source is responsible for this anomalously high heat flow. Instead, high heat flow in the older rocks may be a relatively shallow phenomenon caused by regional ground-water flow. Any deeper anomaly may be relatively narrow, spatially variable, and essentially confined to the Quaternary (less than 2 Ma) arc. Magmatic intrusion at a rate of 9 to 33 cubic kilometers per kilometer of arc length per million years can account for the total heat flow anomaly. Deep drilling in the areas of high heat flow in the older rocks could indicate which model is more appropriate for the near-surface heat flow data.