Regional groundwater flow and accumulation of a massive evaporite deposit at the margin of the Chilean Altiplano

Abstract

Focused groundwater discharge in closed basins provides opportunities to investigate mechanisms for closing hydrologic and solute budgets in arid regions. The Salar de Atacama (SdA), adjacent to the Central Andean Plateau in the hyperarid Atacama Desert, provides an extreme example of halite (>1800 km3) and lithium brine (~5000 ppm) accumulation spanning late Miocene to present. Minimum long‐term water discharge needed to sustain halite accumulation over this timescale at SdA is 9–20 times greater than modern recharge (and double wet‐climate paleorecharge) within the topographic watershed. Closing this imbalance requires sourcing water from recharge on the orogenic plateau in an area over 4 times larger than the topographic watershed. Prolonged water discharge at SdA requires long residence times, deep water tables in recharge zones coupled with persistent near‐surface water tables in discharge areas, and large contributing areas characterized by strong gradients in landscape and climate resulting from plateau uplift.

Imbalance in the modern hydrologic budget of topographic catchments along the western slope of the Andes (21–25 S)

“…Montgomery et al, 2003;Jordan et al, 2015;Rissmann et al, 2015]. Halite accumulation, a proxy for long term average water inflow, confirms the observed hydrologic imbalance over geologically meaningful timescales [up to 10 Myr;Corenthal et al, 2016]. However, recently Munk et al (2018) presented solute fluxes for the surface and shallow sub-surface that account for halite and brine hosted solutes in the uppermost (30 m) on a Myr timescale.…”

“…We define the hydrogeologic watershed as the smallest potential contributing area within which the steady state hydrologic budget closes within reasonable uncertainty bounds (i.e. scenario M in Corenthal et al, [2016]). This conservative scenario has the potential to double count some discharge in both the GW RCH and R terms.…”

“…Previous efforts to balance the water budget of SdA [Dirección General de Aguas, 2013;Rissmann et al, 2015;Corenthal et al, 2016], nearby closed basins [Houston and Hart, 2004], and plateau margins in general [e.g. Andermann et al, 2012] identified large uncertainties in water flux estimates.…”

“…Andermann et al, 2012] identified large uncertainties in water flux estimates. Here, recharge from precipitation is quantified by scaling point measurements to regional satellite datasets including uncertainty, further defining the magnitude and time-scale of the hydrologic imbalance inferred from observations of halite accumulation in SdA [Corenthal et al, 2016]. Unique datasets are integrated to: (1) quantify the area of a regional-scale groundwater catchment necessary to balance modern discharge, and 2approximate the role of late-Pleistocene recharge in modern discharge, and (3) elucidate the mechanisms and process by which water is delivered to the basin.…”

Rapid recharge of fresh water to the halite‐hosted brine aquifer of Salar de Atacama, Chile

“…This neglects the possible addition of water into the salar by migration of the brine/fresh water interface or deeper inflowing waters (Jordan et al , ; Corenthal et al , in press). The change in water level in response to precipitation events multiplied by the S y of the upper several metres of the nucleus provides estimates of direct recharge ( V brine recharge ) envisaged through the mechanisms described in this paper.…”