Geochemistry of a high-altitude hypersaline Andean lake and associated carbonate deposits (Laguna del Peinado, Southern Puna Plateau, NW Argentina)

VIGNONI, PAULA ANDREA; JURIKOVA, H.; PLESSEN, B.; TJALLINGII, RIK; CÓRDOBA, FRANCISCO E.; LIEBETRAU, V.; LECOMTE, K.L.; PINKERNEIL, S.; GRUDZINSKA, I; SCHLEICHER, A.; VIOTTO, S.; SANTAMANS, CARLA D.; RAE, J.W.B; BRAUER, ACHIM

Bariloche

Congreso; IAL-IPA Joint Meeting 2022; 2022

The Puna Plateau hosts numerous lakes that are very sensitive to fluctuations in water balance. Laguna del Peinado is a hypersaline lacustrine system located at 3760 m a.s.l. in the Southern Puna of Argentina where wide scale carbonates precipitation occurs. These carbonates comprise a variety of facies including the largest microbialite system in this region and provide promising sensors for studying recent and past environmental and hydrological changes. However, a better understanding of the geochemistry of the contemporary lacustrine system as well as the carbonate formation within is imperative for further application of geochemical proxies and robust reconstructions. To resolve this, we investigated the coupled brine-carbonate chemistry using petrographic (SEM, XRD) and geochemical tools (δ2H, δ18O, δ13C, δ11B, major and minor ion composition), as well as aqueous chemistry modelling (PHREEQC). We found that the main source of water to Laguna del Peinado are hydrothermal springs linked to old meteoric water, which in combination with strong evaporation create distinctive hydro-chemical sub-environments where microbialites (travertines, microbial mounds, microbial mats) and fine-grained calcite mineral precipitates form. In the hot springs, CaCO3 precipitation is triggered by a shift in carbonate equilibrium by hydrothermal CO2 degassing and microbially-driven elevation of local pH at crystallisation. In the Laguna del Peinado lake, CaCO3 precipitation is induced by evaporative supersaturation, CO2 degassing and microbiological processes under apparent equilibrium conditions with the carbonates largely recording the evaporitic enrichment of the parent water. This study provides a detailed account of the hydro-chemistry and functioning of the Laguna del Peinado system, illuminates the intricate processes that drive carbonate formation in a volcanic basin, and contributes to the discussion of fractionation and partitioning of key isotopes and elements in a well-constrained natural brine-carbonate laboratory, with implications for paleoenvironmental and paleoclimatic studies.