Geothermal studies in the San Juan Basin and the Four Corners area of the Colorado Plateau I. Terrestrial heat-flow measurements

Abstract

Twenty-five new heat-flow measurements are presented for the San Juan Basin and the Four Corners area of the Colorado Plateau in the southwestern United States. Temperature gradients at most sites are calculated from temperature logs at depths between 1 km and 2 km. Resulting heat-flow values appear to be locally less variable than shallower data. These new data develop smooth, uniform trends consistent with the regional geology. As such, it is reasonable to suggest that these data may be somewhat less influenced by near surface perturbations to heat flow than are shallower data in the area; i.e., local hydrologie movement, weathered conductivity samples, topographic variations, and paleoclimate effects. Heat-flow increases going from the Four Corners area into the northern San Juan Basin; a trend consistent with other geophysical studies. Heat flow also increases as the San Juan Basin is traversed south to north, approaching the San Juan volcanic field. This observation suggests a unique thermal anomaly associated with the San Juan volcanics. Heat flow in areas of the San Juan Basin, quite away from extensive volcanics, is 70 mW/m 2; suggesting a small but statistically valid difference between regional heat flow in the non-volcanic regions of the San Juan Basin and in some of the other non-volcanic regions of the Colorado Plateau where the mean heat flow is 65 mW/m 2. Again, this conclusion seems consistent with other geophysical data.