SOMUN CURA FRESH WATER ISOTOPIC AND CHEMISTRY FEATURES

PARICA, CLAUDIO A.; DAPEÑA, CRISTINA; REMESAL, MARCELA B.

Heidelberg

Otro; The 23rd Latin American Colloquium on Earth Sciences GAEA; 2014

Germany Research Foundation (DFG), LAK

Somun Cura Plateau was developed in the centre north of the Argentinean Patagonia. It is a large plateau of 25.000 km2 of tertiary basaltic lava flows in a first stage and several post plateau events represented by post plateau events of alkaline composition (Ardolino et al 1999). Located in the provinces of Río Negro and Chubut, has a desert environment with high speed winds from the west, with extreme temperatures day and night and Summer Winter too. Rain regime is extremely limited to Spring and Autumn (100/170 mm). The hydrology in the plateau is controlled by the morphology and the structures with lagoons sited in depressions developed by wind erosive processes and under washing (piping). Small streams and creeks are also developed, mainly with a structural pattern. Some natural springs are located on the flanks of the plateau with particular features, one the most important features is the temperature, with highest up to 45°C, all of them on the northern area (Parica et al, 2012), meanwhile on the South (Chubut Province), the maximum temperature determined was 22°C. The difference between both areas are interpreted because the residence time inside the basaltic plateau, which would be the source of the temperature, long in the northern, short in the south. As a common feature for the water flow in the plateau, the water provenance is located in the highest areas where snow is deposited. Water isotopic analyses, δ18O and δ2H (made by laser spectroscopy following Lis et al 2008) made on local rainfalls and snowfalls show poor or non evaporation processes, which means fast entrance of water into the fractures system in the plateau, mainly radial with flux between different lava flows. Piper, Schöller Berkaloff diagrams and RAS index were the tools used for chemistry classification. According Piper Diagram and Schöller-Berkaloff water samples are Na-Ca bicarbonated to chlorinated, with pH between 5 to 8 with 7 as dominant. The RAS index shows samples grouped in c2-s1 and c3-s1. Most of samples are representative of drinkable water; just a few are non drinkable water coming from closed lagoons.