Abstract

Heat-flow values within the western Snake River Plain average about 1.7 µcal/cm2 sec, but even higher values are measured in granitic rocks along the margins of the Snake River Plain (2.5 µcal/cm2 sec or higher). The heat-flow distribution is related to the combined effects of crustal thermal refraction and a large, transient crustal heat source. A regional model consistent with the heat-flow pattern and other geophysical and geological data is described which assumes the emplacement of a large heat source (mafic intrusion?) under the western Snake River Plain about 10 to 15 m.y. ago. An anomaly of about 0.3 µcal/cm2 sec is predicted over the center of the heat source at the present time. The timing of the emplacement of the heat source corresponds with the age of voluminous silicic volcanism in the western Snake River Plain. A time-progressive thermal model is presented for the Snake River Plain which is consistent with the time progression of silicic volcanism. Based on the model, higher regional heat-flow values are predicted for the eastern Snake River Plain. Confirmation of the high regional heat-flow values is not possible in the bore holes available (200± m deep) because of regional circulation of cold ground water in the Snake Plain Aquifer. However, a close correlation between integrated crustal and upper mantle temperature and observed elevation changes along the axis of the Snake River Plain is strong support for the heat-flow model. The possibility of high heat flow in the eastern part of the Snake River Plain implies that the area may have significant geothermal potential in spite of the low surface heat flow. The regional aseismic warping observed in the eastern Snake River Plain can be interpreted as a thermal contraction phenomenon involving the crust and upper mantle.

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