New Mexico Geological Society Annual Spring Meeting — Abstracts

Most convective geothermal systems in the Rio Grande rift have fractured Precambrian, Paleozoic, or lower Mesozoic reservoir hosts and the discharge for most systems occurs where regional Mesozoic and Tertiary aquitards are tectonically or erosionally stripped to form hydrogeologic windows. A spatial affinity to Laramide or older structural highs is apparent when the systems are plotted on a Tertiary subcrop map. A closer examination shows that many overlie the vergent margins of Laramide basement-cored, north- and northwest-striking uplifts. Geothermal systems at Montezuma Hot Springs, Salado Warm Springs, TorC, Derry Warm Springs, Lake Valley, Rincon, San Diego Mountain, and Radium Springs are examples. Elsewhere, core drilling of the geothermal system at McGregor Range encountered a thrust fault slicing a large overturned fold that has either late Paleozoic or Laramide affinity. The Lightning Dock system straddles a major west-northwest striking zone that shows evidence for tectonic inversion of a Jurassic extensional fault zone during Laramide compression. Confirmed reservoir temperatures and aqueous chemical geothermometry imply typical water circulation depths greater than 3 km. Considering the temperatures and high mass flow rates for some of the systems, a very deeply penetrating and extensive fracture permeability network is required. Forelimb domain deformation in the hanging wall of a large-scale basement-cored reverse fault and fold structure would provide the shattered volume and depth penetration necessary to create geothermal system plumbing. Any contemporaneous Laramide transpression components and later mid-Tertiary volcanotectonic features and Neogene rift faults act to enhance and sustain the older permeability. Impermeable reverse fault cores or gouge zones and folded aquitards on the footwall would direct flow vertically in the fractured domain and facilitate discharge or recharge.