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Major ion and stable isotopic compositions of a saline lake linked to the SW margin of Laguna Mar Chiquita, Argentina (30°55′ S, 62°51′ W) were studied. The groundwater inflow into the Laguna del Plata was quantified for the first time using a stable isotope mass balance. Shallow groundwater inflow is expected in the Laguna Mar Chiquita system since it represents the terminal water body of the catchment. Lake waters are alkaline and exhibit total dissolved solids contents >30 g L−1. The cationic relative abundance is Na+ ≫ Mg2+ > Ca2+ > K+, whereas that of major anions is Cl− ≫ SO42− > HCO3− + CO32−, which are mainly present as free aqueous ions. PHREEQC simulations indicate that lake waters are oversaturated in Ca2+ and Mg2+ carbonates (calcite, huntite, aragonite, dolomite, magnesite), which are expected to be the first minerals to precipitate due to evaporation processes. The main tributary of the lake (Suquia River) and the phreatic aquifer exhibit δ18O and δ2H values consistent with the isotopic signature of rainfall, whereas lake waters define an evaporation line (δ2H (‰) = 5.4 δ18O (‰) + 1.8). The confined aquifer shows a more depleted isotopic composition, reflecting an allochthonous recharge from the mountain ranges (Sierras Pampeanas). The δ18O mass balance indicates a groundwater inflow of ~4.7 m year−1 to the lake, confirming the hydrological conceptual model for the catchment. However, the groundwater contributions do not affect the chemical composition of lake waters, which mainly results from the evaporation processes as shown by the Spencer diagram.

Metamorphic rocks, granitic rocks, and sediments from the Eastern Sierras Pampanas, Argentina, were analyzed for major and trace element concentrations, including rare earth elements (REE). Parental rocks exhibit distinctive REE normalized diagram patterns and elemental ratios, and some elemental ratios reveal significant differences between rock sources. For example, ratios such as Th/Sc, Cr/Th, and La/Cr have a mean value of 0.7, 8.4 and 0.4 in metamorphic rocks, whereas granitic rocks exhibit means of 1.4, 0.7 and 4.9, respectively. These ratios are also useful in linking detrital materials with the corresponding parental rocks. Metamorphic sources yield sediments with lower Th/Sc and La/Cr, and higher Cr/Th ratios than sediments derived from granitic sources. REE and other elements are enriched in the silt-size fraction, whereas they are diluted by quartz in the sand-size fraction. The size of the Eu/Eu* anomaly can be used as a stratigraphical correlation tool in the sedimentary record: Cretaceous rocks show a mean value of 0.9±0.1, whereas Tertiary rocks have a mean value of 2.9±0.3. The Eu anomaly in Quaternary and modern sediments ranges from 0.5 to 0.8.