GEOTHERMAL TRANSITIONS IN THE CRUST AND UPPER MANTLE ALONG SOUTHERN ROCKY MOUNTAIN TRANSECTS

Heat flow data provide valuable compliments to seismic and gravity studies. The spatial coincidence of thermal anomalies with seismic and gravity anomalies reduces ambiguity as to the cause of the anomalies, supplying evidence of elevated temperature. I consider geothermal data along five profiles crossing from the Colorado Plateau or Great Plains into the high topographic areas of the Southern Rockies. High frequencies in the heat flow and temperature gradient data along the profiles are removed by FFT filtering. The smoothed data are fitted with a sine series for inspection. Because the values along the profiles go from the highest to the lowest values in the regions, estimates of the peak to trough half-width can be made, allowing first-order approximations of anomaly depths. From the sine series coefficients the relative importance of upper mantle and crustal thermal contributions can be appreciated. Depth estimates are non-unique but may lie toward the middle of the range of possibilities.

Heat flow and gravity data are considered along two different profiles from the San Juan Basin to the San Juan Mountains. Both data sets indicate the importance of upper mantle thermal anomalies, consistent with shear wave anomaly studies. Along the western San Juan profile, a significant thermal and gravity crustal anomaly is also noticed, supporting suggestions of a large crustal granitic batholith with elevated radiogenic heat production. A heat flow and gravity profile from the western Piceance Basin to the recently named Aspen Anomaly suggests an upper mantle thermal and gravity anomaly associated with the Aspen Anomaly, consistent with proposed P wave tomography. A north-south profile in the eastern Piceance Basin indicates a thermal and gravity transition in the upper crust. The fifth transect is east-west from the Gore Range, across the Front Range, to Denver. Heat flow and gravity data along this transect suggest crustal heat and gravity anomalies.