Isotopic and chemical studies of groundwater in the Llanura Tucumana geothermal area; Tucuman, Argentina

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 geophysical studies (Pomposiello, et al., 1991, 2000; Favetto et al. 2000). It is bounded to the west by the Nevados del Aconquija (5500m) and the Sierra de Guasayan (600m) at east. Both ranges are part of the Sierras Pampeanas System. The southern part of this plain is an important thermal area, which is known through surface manifestations and drilled wells. There are a great quantity of artesian wells with discharge water at temperatures that oscillate between 30oC and 50oC. The Aconquija System is a climatic barrier for the humid east winds. The precipitation is torrential with intense and short time storms, mainly in summer. The rain amount decreases gradually to the SE, from 1200 to 800mm and it is 600mm near the Rio Hondo Dam area. The mean January temperature is 26.7oC and the coldest month is July with 12.9oC. This paper presents the isotopic and chemical results and a first approach for the origin and circulation pattern of water (au)