Geoquímica de ríos de montaña en las Sierras pampeanas: II. El río Los Reartes, Sierra de Comechingones, provincia de Córdoba, Argentina.

PASQUINI, A.I.; LECOMTE, K.L.; DEPETRIS, P.J.

Revista de la Asociación Geológica Argentina

Asociación Geológica Argentina

Lugar: Buenos Aires; Año: 2004 vol. 59 p. 129 - 140

0004-4822

Abstract We analyze the hydrochemistry of Los Reartes River, a typical high-altitude, mountainous drainage basin in the Sierras Pampeanas of Córdoba, Argentina. The dominant rocks are granites and gneisses of the crystalline basement. Maximum and minimum altitudes are 2400 m, and 670 m above the sea level, respectively. The slopes decrease from 20% in the headwaters down to 6% at the outfall. Climate is high-altitude semiarid with most of the rainfall concentrated during the southern summer. The water pH oscillates between 6.9 and 9.1 and most total dissolved solids (TDS) determinations are in the 17 ? 114 mg/l range. The major chemical composition is characterized by HCO3-  > Cl- + SO42-, and by Na+ + Ca2+ > K+ + Mg2+. TDS, pH, and alkalinity increase downstream, evolving from HCO3-- Na+- K+-type to HCO3-- Ca2+-type. Dissolved trace elements reach concentrations 10-3 to 10-7 times lower than the upper continental crust. The more soluble elements (Ca, Na, K, Mg, Ba, Sr) exhibit the highest concentrations whereas the less mobile are the least concentrated. As a result of pH and adsorption processes, REE show extremely low concentrations in the dissolved phases (between 30 and 319 ng/l). The irregular distribution of rainfall exerts a seasonal control over REE concentrations; moreover, the chemistry of these waters evidences the joint control of rocks and climate. The prevailing semiarid condition determines an incipient alteration in the silicates and the natures of the dominant rocks in the drainage govern a common chemical signature in the waters of the region.