Isotopic and chemical studies of groundwater in the Llanura Tucumana Geothermal Area; Tucumán, Argentina.

DAPEÑA, CRISTINA; POMPOSIELLO, MARIA CRISTINA; PANARELLO, HECTOR; GALINDO, GRISELDA

COMUNICACIONES - DEPARTAMENTO DE GEOLOGIA. FACULTAD DE CIENCIAS FISICAS Y MATEMATICAS. UNIVERSIDAD DE CHILE

Universidad de Chile

Lugar: Santiago, Chile; Año: 2001 vol. 52 p. 102 - 102

0069-357X

The Llanura Tucumana extends along the eastern Andean margin, between 27ºS-28ºS and 64º50´W-65º40´W.It is a structural depression infilled by a thick sedimentary sequence, as shown by the preliminary geophysicalstudies. It is bounded to the west by the Nevados del Aconquija (5500m) and the Sierra de Guasayán (600m) ateast. Both ranges are part of the Sierras Pampeanas System. The southern part of this plain is an important thermalarea, which is known through surface manifestations and drilled wells. There are a great quantity of artesianwells which discharge water at temperatures that oscillate between 30ºC and 50ºC.This geothermal area has been studied by means of hydrochemistry and Isotope Hydrology.The Tertiary aquifer units are the marine Miocene Guasayán Formation and the continental Pliocene LasCañas Formation. The last one has good quality water, although still slightly saline. Overlaying these sediments,the Holocene sequence bears aquifers with high rate of discharge and excellent qualities for mostrequirements.The lack of correlation between the isotopic composition (δ18O, δ2H) and chloride and sulfate ions indicatesthat the salinization mechanism is mainly the leaching of old marine sediments.Like it was observed by others authors, it results very difficult to correlate the different aquifer levels of awell with others neighbor one. This is a consequence of the fact that aquifers are located in sandy lenses presentingvariable thickness and scarce lateral development. These characteristics are proper of the Pliocene andalso Quaternary units. The same conclusion is reached through this isotopic study.As established in previous papers, the system is heterogeneous and it was not possible to find out a systematicpattern that makes possible water typifying.3H and 14C studies are imperative in order to clarify paths and movements of groundwater into the aquiferunits.