New Mexico Geological Society Annual Spring Meeting — Abstracts

Heat flow and subsurface temperature gradient data are considered along with seismic and gravity studies for several large regions with geothermal resource potential. In the north central and north eastern San Juan Basin heat flows and geothermal gradients become elevated approaching the San Juan Volcanic Field and the associated large scale negative Bouguer gravity anomaly. These geothermal data are near the perimeter of a regional upper mantle low shear wave velocity centered at Alamosa, Colorado, having a diameter of several hundred km. Just south of Alamosa, a slow P wave anomaly at 100 km depth extends southward for 60 km along the Rio Grande rift in southern Colorado and northern New Mexico. Two nearby heat flow values just to the south-southwest of this anomaly are elevated. P wave tomography at 100 km depth indicates a large slow velocity region of the order of 100 km on a side associated with the Jemez Caldera. Preliminary geothermal gradient data suggest a change in very elevated gradients to normal gradients over a distance of ~ 20-40 km, implying observable geothermal resources are in the uppermost crust. In the Datil-Mogollon volcanic field a large slow P wave anomaly at 100 km coincides with a relatively large negative Bouguer gravity anomaly and estimated high geothermal gradients. Large batholiths modeled in the San Juan and Datil-Mogollon volcanic fields would have dissipated their heat over the past ~ 25-35 my since caldera eruptions. This and the above data imply thermal source replenishment over time. Temperature gradients near the San Juan and Datil-Mogollon volcanic fields are as elevated as higher gradients along the Rio Grande rift.