Three-dimensional audio-magnetotelluric characterization of the geothermal area in Tucumán basin, Argentina

The main aim of this work is to relate the geoelectrical units defined by the 3D model to the geological units in the southeast of the Tucumán plain, where geothermal manifestations are shown by artesian wells with temperatures between 38 °C and 50 °C. Two field campaigns involving 41 audio-magnetotelluric sites in the frequency range 100,000 to 10 Hz were carried on. Some sites are located near the wells, where the depth from which they bring water to the surface is known. The 3D model allows us to describe characteristics of the electrical resistivity of the different sedimentary formations as well as to correlate it with the structural features present in the region of study. The most remarkable feature of the final model is the high conductivity of the deepest geoelectrical unit associated with a formation of marine origin in which the presence of illite and montmorillonite has been determined. In addition, as some information from the wells is available for the layer taken advantage of, it was possible to validate the resistivity determined by the model with that obtained with Archie's law, finding correspondence.