| Abstract |
The Paipa geothermal system, located in the Eastern Cordillera of Colombian Andes, 150 km north of Bogotá, is an area of great interest because it may be related to volcanic bodies emplaced on a sedimentary and orogenic environment, about 400 km away from the main volcanic arc located at the Central Cordillera. Geological, geophysical and geochemical investigations, most of them developed by the Geological Survey of Colombia (formerly INGEOMINAS) have identified the presence of a caldera rim generated by the collapse of a volcanic structure, its associated deposits, the later emplacement of domes of Pleistocene age, besides other sub-volcanic bodies. On surface, the discharge zone of the geothermal system includes steam vents and, perhaps the most important element due to the intense recreational use and its economic revenues, hot springs with temperatures up to 74° Celsius. Those hot springs show hydrochemical evidence of mixing with a shallow sodium sulfate source that masks the chemical and isotope composition of the geothermal reservoir and prevents the application of geothermometers and other geochemical tools. As a result of those investigations, a conceptual model of the geothermal system were formulated that includes potential recharge areas, heat sources, circulation mechanisms and zones of fluid mixture with shallow sources. This investigation provides the resistivity-modeling of the sub-surface structure beneath the Paipa geothermal area by the acquisition, processing and 2D modeling of 69 sites of AMT and AMT/MT magnetotelluric soundings, from which structures and other aspects potentially related to a geothermal system, like three well differentiate resistivity zones correlated with basement, sedimentary sequence and high conductive layer, low resistivity zones product of hydrothermal alteration (cap seal) or the influence of a saline source. The deep structure Paipa-Toca Fault, with no surface expression, is related to the possible conduct of fluids (magma and geothermal fluid) ascent. |