Publication Type:Journal Article
Source:Chemical GeologyChemical Geology, Elsevier, Amsterdam, Netherlands, Volume 396, p.164-181 (2015)
Keywords:alkaline earth metals, Alkalinity, Andes, Antofagasta Chile, aquifers, arid environment, Atacama Desert, brines, C-13/C-12, carbon, carbon dioxide, chemical composition, chemically precipitated rocks, Chile, D/H, evaporites, ground water, hydrogen, hydrothermal conditions, ICP mass spectra, isotope ratios, Isotopes, major elements, mass spectra, metals, multivariate analysis, O-18/O-16, oxygen, pH, recharge, S-34/S-32, Sedimentary rocks, Socompa, solutes, South America, spectra, Sr-87/Sr-86, Stable isotopes, statistical analysis, strontium, sulfur, terrestrial environment, theoretical models, thermal waters, Trace elements, volatiles, Volcanoes, water-rock interaction
This paper investigates the origin of solutes within the groundwaters of the Monturaqui-Negrillar-Tilopozo (MNT) aquifer system within the high Andes of the Atacama Desert that discharges into the Salar de Atacama. Key questions include the relative significance of volcanic hydrothermal processes and evaporitic brine recycling over solute supply as well as the pathways of solute ingress to the MNT aquifer system. Groundwaters were analysed for elemental (major, minor and trace) and isotopic (delta (super 18) O/delta (super 2) H; delta (super 13) C-DIC; delta (super 34) S-SO (sub 4) ; (super 87) Sr/ (super 86) Sr) constituents to which various hydrochemical and multivariate statistical methods have been applied. Groundwaters are all classified as thermal and show increasing temperatures (27-35 degrees C) and concentrations of HCO (sub 3) (4.4-10.4 mmol L (super - 1) dissolved inorganic carbon [DIC]) with increasing proximity to Volcano Socompa resulting from an increasing mass flux of steam and magmatic CO (sub 2) (pCO (sub 2) = 0.016 to 0.10 atm; delta (super 13) C-CO (sub 2) = - 9.3 to - 3.6 ppm (V-PDB)) boiled off a deep hydrothermal reservoir. Superimposed upon this gradational and relatively smooth spatial increase in heat and mass flow is a sharp, structurally controlled, increase in TDS (826-3632 mg l (super - 1) ) and a concomitant change in delta (super 34) S-SO (sub 4) (+ 0.79 to 4.9 ppm (V-CDT)) and (super 87) Sr/ (super 86) Sr values (0.707375-0.706859) associated with the inflow of evaporitic solutes. Evaporitic inputs are chemically and isotopically distinct from localised secondary hydrothermally derived solutes with major, minor and trace element data suggesting an origin within a highly oxidising, alkaline, evaporitic lake receiving dilute inflows enriched in volcanic/fumarolic sulfur mineralisation probably from volcanoes Socompa, Salin or Pular that delimit the eastern topographic extent of the aquifer system. The conceptual model presented in this paper proposes that basal leakage of evaporitic brines from active salar(s), within the high altiplano/volcanic arc, are actively entrained by sub-regional groundwater flow and conveyed to the MNT aquifer system where they mix with solutes derived from localised secondary hydrothermal gas-water-rock interaction. This work provides detail on the origin and processes controlling the solute composition of groundwater inflows to the Salar de Atacama within the volcanically active and hyperarid Atacama Desert and may be of significance to conceptual models of evaporitic brine evolution, recycling of evaporitic brines and hydrothermalism in arid regions. Abstract Copyright (2015) Elsevier, B.V.
GeoRef, Copyright 2018, American Geological Institute.<br/>2015-041849<br/>Atacama salt lake<br/>Monturaqui Basin<br/>Monturaqui-Negrillar-Tilopozo aquifer system<br/>Pular<br/>Salar de Atacama<br/>Salin