HEAT FLOW STUDIES AND GEOTHERMAL EXPLORATION IN WESTERN TRANS-PECOS TEXAS

Trans-Pecos Texas is a zone of transition between the Basin and Range and the Great Plains tectonic provinces. The continuation or termination of the Rio Grande Rift may also occur in this region. The first part of this study presents a new heat flow map which delineates the transition in thermal terms. The eastern part of the area displays heat flows typical of the Great Plains, namely about 1.1 H.F.U., whilst higher values (2.0 to 2.8 H.F.U.) occur in the west. This is taken to indicate a possible extension of the Rio Grande Rift. Interest in alternative energy has encouraged the definition of possible geothermal resources in Trans-Pecos Texas, and to this end a geothermal gradient map of the region is presented, based on nearly 200 temperature and gradient measurements. Several areas of high thermal gradient are located, notably in Presidio County, where several hot springs and wells exist. Possible mechanisms for the high gradients (and heat flow) here are discussed as a basis for further, more detailed, examination of the area. A small high gradient area is also indicated in northeast El Paso County, and the second part of the study describes a geophysical investigation of this prospect. The proximity to the city of El Paso made this a prime target for resource evaluation. Geophysical methods employed include gravity, self-potential and electrical resistivity, the surveys culminating in a shallow drilling programme to define the areal extent of the anomaly