Abstract

The Rio Grande Rift is known for its diverse geothermal anomalies that are attributed to various types of geologic features, including offsets in range-bounding faults, transition zones, young volcanism, high crustal heat flow and geothermal gradients, possibly associated with blind intrusions in the middle crust. Geothermal areas at the northern and southern ends of the San Luis Basin were selected for geochemical and isotopic studies, and include the vicinities of Poncha Springs, Colorado and Taos, New Mexico. Hydrogen and oxygen isotopes from water samples were used to understand the degree of fluid-rock interactions at these locations, and were compared to other geothermal systems. Helium isotope data suggest mixing between atmospheric, crustal, and mantle helium sources, and high helium-3 to helium-4 (³He/⁴He) ratios for Poncha Hot Springs indicate a mantle-sourced helium signature that could be associated with deep magmatic activity or crustal penetrating faults. Noble gas isotopes suggest that there is a direct and unique relationship between noble gas compositions and structural, magmatic, and tectonic geological features.