Possible Volcanotectonic Controls on High-Temperature Thermal Fluid Upflow in the Valles Caldera, New Mexico

Abstract

Although normal faults and discrete stratigraphic aquifers are important thermal fluid channels in the Valles hydrothermal system, higher order permeability controls may be critical for development of commercial quality geothermal reservoirs in the Valles caldera. All six (of a total 24) commercially producible geothermal wells in the caldera are clustered within a 2 km 2 area coinciding with a prominent subsurface temperature and pressure anomaly defining a major up flow plume. These anomalies occur at the western edge of an inferred central vent zone for initial Plinian eruptions of the Tshirege Member (1.13 Ma) of the Bandelier Tuff: crystal rick tuffs possible ejected from this vent zone thicken dramatically as the zone is approached. We suggest that fractures and faults induced during development of this vent zone could control the current up flow of high temperature thermal fluids, and that future wells targeted closer to the vent zone have an excellent chance of being commercially productive. Other probable major permeability controls in the Valles caldera include intersecting faults sets as well as ring fracture zones around small, concealed, pre Bandelier age calderas.