Deep fluid circulation within crystalline basement rocks and the role of hydrologic windows in the formation of the Truth or Consequences, New Mexico low‐temperature geothermal system. Issue 1 (7th October 2014)

• Record Type: Journal Article
• Authors: Pepin, J.; Person, M.; Phillips, F.; Kelley, S.; Timmons, S.; Owens, L.; Witcher, J.; Gable, C.
• Is Part Of: Geofluids. Volume 15:Issue 1/2(2015)
• Page Start: 139
• Page End: 160
• Publication Date: 2014-10-07
• Subjects: Hydrogeology -- Periodicals; Sedimentary basins -- Periodicals; Fluids -- Migration -- Periodicals; Groundwater flow -- Periodicals; Geothermal resources -- Periodicals; Fluid dynamics -- Periodicals; Earth -- Crust -- Periodicals; 551.49
• DOI: 10.1111/gfl.12111
• Languages: English
• ISSNs: 1468-8115

Abstract

<abstract abstract-type="main" id="gfl12111-abs-0001"> <title>Abstract</title> <p>Hot springs can occur in amagmatic settings, but the mechanisms of heating are often obscure. We have investigated the origin of the Truth or Consequences, New Mexico low‐temperature (approximately 41°C) hot springs in the southern Rio Grande Rift. We tested two hypotheses that could account for this amagmatic geothermal anomaly: lateral forced convection in a gently dipping carbonate aquifer and circulation through high‐permeability crystalline basement rocks to depths of 8 km that is then focused through an overlying faulted hydrologic window. These hypotheses were tested using a regional two‐dimensional hydrothermal model. Model parameters were constrained by calibrating to measured temperatures, specific discharge rates, and groundwater residence times. We collected 16 temperature profiles, 11 geochemistry samples, and 6 carbon‐14 samples within the study area. The geothermal waters are Na<sup>+</sup>/Cl<sup>−</sup>‐dominated and have apparent groundwater ages ranging from 5500 to 11 500 years. Hot‐spring geochemistry is consistent with water/rock interaction in a silicate geothermal reservoir, rather than a carbonate system. Peclet number analysis of temperature profiles suggests that specific discharge rates beneath Truth or Consequences range from 2 to 4 m year<sup>−1</sup>. Geothermometry indicates maximum reservoir temperatures are around 170°C. Observed measurements were reasonably reproduced using the deep circulation permeable‐basement modeling scenario (10<sup>−12</sup> m<sup>2</sup>) but not the lateral forced‐convection carbonate‐aquifer scenario. Focused geothermal discharge is the result of localized faulting, which has created a hydrologic window through a regional confining unit. In tectonically active areas, such as the Rio Grande Rift, deep groundwater circulation within fractured crystalline basement may play a more prominent role in the formation of geothermal systems than has generally been acknowledged.</p> </abstract>