Investigation of Geothermal Resource Potential in the Northern Rio Grande Rift, Colorado and New Mexico

Abstract

Geothermal anomalies within the Rio Grande Rift are associated with transfer and scissor faults between successive basins, intrabasin rift faults, where range-front faults are offset in accommodation zones, volcanic complexes, and possibly where blind intrusions of magma have risen to mid-crustal depths. This study is part of the National Geothermal Student Competition sponsored by the National Renewable Energy Laboratory and aims to assess the potential for geothermal resources in the San Luis Basin of southern Colorado and northern New Mexico. A preliminary analysis of existing data was used to identify two areas of interest for field investigations located near zones of structural complexity at Poncha Pass, Colorado and near Taos, New Mexico, representing the northern and southern ends of the basin. A suite of techniques including geological, geophysical, hydrologic, and geochemical applications was used. Geochemical modeling of existing data for the Taos Valley and Valles Caldera in New Mexico simulate the mixing of thermal and groundwater end-members to represent geochemical processes potentially occurring at depth. Noble gas isotope data suggest the presence of mixing in a three end-member model system composed of atmospheric, crustal, and mantle components. Helium isotope data from Poncha Springs, Colorado yields a R/RA value indicative of a mantle-sourced gas signature that may be associated with crustal penetrating faults, ongoing rift activity, and/or the Aspen anomaly. The use of noble gas isotopes for this research implies that there is a direct and unique relationship between noble gas compositions and structural, magmatic, and tectonic geological phenomena. Geophysical data indicate faults that serve as conduits and barriers to upwelling thermal water near Poncha Springs.