Deep Terrestrial Heat-Flow Studies in Southwestern United States: ABSTRACT

Abstract

End_Page 771------------------------------Deep geothermal gradient measurements yielding good heat-flow data are necessary to accurately predict lithospheric and asthenospheric temperatures and relate thermal conditions in the lithosphere and asthenosphere to fundamental tectonic processes such as vertical movements in the earth. Many heat-flow measurements are calculated from temperature gradients taken at depths less than 1 km. In some places, groundwater perturbation of these temperature gradients precludes basic appreciation of regional lithospheric or local geothermal conditions. Previous heat-flow data suggest the Colorado Plateau is an area of low heat flow (~1.2 HFU) whereas new deeper heat-flow measurements show the Colorado Plateau has intermediate heat flow (~1.6 HFU). These new data are in keeping with other geoph sical measurements. As such, the gradual uplift component of vertical movement over the western United States since the Eocene may relate to lithospheric reheating (thermal expansion) as North America drifted over hotter asthenosphere. New deep data in the southern Basin and Range province indicate regional heat flow of 1.95 HFU suggesting 0.3 to 0.4 HFU difference between the Basin and Range and Colorado Plateau. Different lithospheric responses to asthenospheric anomalies may allow widespread magma intrusion in the Basin and Range with only modest intrusion in the Colorado Plateau. Both large scale and local geothermal anomalies are also significantly perturbed by groundwater movement, e.g., the Rio Grande rift and the San Francisco Mountains. High quality heat-flow data extending alon profiles from mountainous areas will allow appreciation of thermal conditions in mountain blocks and magma bodies, such as profiles from the southern Rockies and the San Juan Mountains. End_of_Article - Last_Page 772------------