Interpretations of the Central Oregon Cascades Heat Flow Anomaly

Abstract

In 1979-80 the Oregon Department of Geology and Mineral Industries completed a 21 hole drilling program (152 m nominal depth) which confirmed the transition from low heat flow in the Willamette Valley and most the Western Cascade physiographic provinces to high heat flow in the extreme eastern portion of the Western Cascade province and the High Cascade province. Modeling of the surface heat flow data predicts temperatures as high as 700°C at depths of less than 10km. An alternative model suggests that high heat flow values measured in holes west of the High Cascades axis result from the lateral transfer of heat in moderate temperature (100-200°C) aquifers at depths on the order of 1 km. Although final resolution of the differing models will await publication of deep drill hole data, several other geophysical studies (i.e. gravity, aeromagnetic, teleseismic residual, and magentometelluric surveys) either suggest or are permissive of the presence of high temperature, possibly molten, rock at depths on the order of 10km.