Heat flow in the Oregon Cascade Range and its correlation with regional gravity, Curie point depths

New heat flow data for the Oregon Cascade Range are presented and discussed. Heat flow measurements from several deep wells (up to 2500 m deep), as well as extensive new data from industry exploration efforts in the Breitenbush and the Santiam Pass-Belknap/Foley areas are described. The regional heat flow pattern is similar to that discussed previously. The heat flow is about 100 mW m-2 in the High Cascade Range and at the eastern edge of the Western Cascade Range, It is about 40-50 mW m-2 to the west in the outer arc block of the subduction z e. in the high eat flow zone the heat flow is low at shallow depths in young volcanic rocks due to the high permeability ofthe rocks and the resultant rapid groundwater flow. Below a depth of 200400 m much of the area appears to be dominated by conductive heat transfer at least o 2-2.5 km depth. There are perturbations to the regional heat flow in the vicinity of the hot springs where values are up to twice the background. The gravity field in the Cascade Range has characteristics that can be closely related to the heat flow pattern. The relationship may be causal, and to examine the relationship in more detail, earlier two-dimensional modeling is extended to three dimensions. Consideration of the effects of a midcrustal density anomaly, such as might be associated with a region with at least areas of partial melt, has two major consequences. The first of these is that a high-frequency gravity gradient near the Western Cascade Range/High Cascade Range boundary is explained. Second, the negative gravity anomal