Salar De Atacama Basin Research Articles

Statistical Exploration of the Salar de Atacama’s: Brine Measurements of the Basin Wells

Abstract In this study, we conduct a statistical analysis using the 4-plot, visibility graph, and horizontal visibility graph methods on brine extraction data from the Salar de Atacama basin in Chile. The 4-plot reveals real trends in the data that could lead model proposals. Conversely, complex networks analysis yields no significant findings, suggesting that the data lacks internal structural features and appears random. This randomness underscores the decision-making processes and highlights areas for potential optimization.

Nuil models for understand crustaceans communities in inland waters in San Pedro de Atacama and Salar de Atacama basin, Antofagasta region, Chile

Nuil models for understand crustaceans communities in inland waters in San Pedro de Atacama and Salar de Atacama basin, Antofagasta region, Chile

Loa-Geo1: A field regional transect to unravel the structure of the western Central Andes

The structure of the Central Andes forearc of northern Chile has been an enigma for many years. Along this region, the preservation of a long pediplain constituted by gravels and unconsolidated sediments has hidden the structure of the region, making it difficult to understand its tectonic evolution. The traditional and regional-scale structural models are mainly supported by outcrop-scale and local observations. To unravel the structure of this Andes region, we carried out a regional-scale study based on local and regional observations, geological mapping, and the elaboration of local and regional balanced cross-sections, thereby illustrating the geometry and distribution of the first-order structural styles. We examined four specific sectors along a regional transect: the Loa and San Salvador rivers (parallel to each other), Sierra de Limón Verde, and Cerros de Tuina. Three structural styles were identified in the hybrid thick- and thin-skinned and doubly verging fold-and-thrust belt. These styles comprise partially inverted Permian to Jurassic normal faults, thick-skinned reverse faults affecting Paleozoic crystalline basement blocks, and shallow and thin-skinned fault-related folds. The shallow and thin-skinned fault-related folds usually result from the propagation of large, thick-skinned thrust ramps into stratigraphic successions. The restoration of a regionally balanced cross section constrained by field data and the previously interpreted two-dimensional (2-D) seismic profiles suggest that much of the crustal shortenings are accommodated by the reverse reactivation of Triassic and Jurassic normal faults bounding half-graben structures. It is also accommodated by blind thrust faults, whose geometry, kinematic, and depth are debatable. However, we have proposed a large, thick-skinned thrust ramp as the structure responsible for the greater shortening in the region, along which a significant thick- to thin-skinned transition occurs. The age of the synorogenic deposits identified here is unknown, specially those exposed at the Loa and San Salvador rives, however, the basal successions exposed at the Tuina sector reported Upper Cretaceous ages, thus suggesting that the orogeny in the forearc could have started during this time spam. Regional correlations with similar synorogenic deposits recognized in neighboring regions (e.g., Salar de Atacama Basin and Coastal Cordillera) also affirm an Upper Cretaceous–Paleocene age for the initiation of the crustal contraction in the region.

Basement-involved tectonism in the western Central Andes: Insights from the eastern Domeyko and Frontal cordilleras, and the Salar de Atacama Basin

Northern Chile is a natural laboratory to understand the relation between different basement-involved structural styles, mechanisms of basement uplift, and the interaction of Pre-Andean rift-related and Andean contractional structures. Field and geophysical data (two-dimensional seismic profiles) are key to understanding the geometry and kinematics of these structures in the subsurface. Herein, we analyzed the basement-involved tectonism in the easternmost part of the Domeyko Cordillera, the southern end of the Salar de Atacama Basin and the Frontal Cordillera in northern Chile based on an updated revision of the structures exposed on the surface and the other ones present in depth. Our results indicate that the Pre-Andean configuration of the region was the first-order factor controlling the basement-involved deformation. Late Permian to Jurassic rift-related, basement rooted, normal faults accommodated much of the shortening in the upper plate, thus triggering their partial and/or full reverse reactivation, situation that in some places was accompanied by purely reverse faulting, thus allowing the exhumation of large Paleozoic basement granitic blocks. This event occurred in a similar manner in the studied regions from Late Cretaceous to Paleocene in an arc-system geological context. The initial distribution of half-grabens, syn-rift and post-rift sequences governed the variations in the basement-involved structural styles ranging from basement-cored anticlines to tectonic wedges, among others. However, the flat-slab process has frequently been invoked as the main process responsible for the basement-involved tectonism in northern Chile. Our results suggest a strong control exerted by inherited stratigraphic and structural features more than variations in slab geometry.

An Inside Sun: Lickanantay Volcanology in the Salar de Atacama

The need of establishing more substantive dialogs between the mainstream and Indigenous knowledge on volcanoes has been increasingly recognized. To contribute to this endeavor, in this article we present the basic volcanological understandings of the Lickanantay people in the Salar de Atacama Basin. The Salar de Atacama Basin is an active volcanic territory within the Central Volcanic Zone of the Andes (CVZA). From the El Tatio geothermal field to Socompa volcano, more than 19 active volcanoes surround the territory that the Lickanantay (Atacameño) people have inhabited for more than 11,000 years. Living around and with the geological dynamism of the CVZA for millennia, the Lickanantay communities have accumulated rich observational and ceremonial data on volcanoes and volcanism. Paradoxically, however, while the Atacameño people have thoroughly characterized the CVZA, the volcanology community has not been properly introduced to the ancestral knowledge articulated in the territory. In order to make traditional Atacameño perspectives on volcanoes, volcanic risk, and geo-cosmic interdependence more amply available to the volcanology community, in this article, we present a basic description of what we call Atacameño volcanology. By Atacameño volcanology, we understand the ancestral principles by which volcanoes are known and understood as partaking in larger processes of a cosmo-ecological formation. Specifically, we describe the basic volcanological notions arising from the Lickanantay ancestral knowledge—volcanic formation, functions, and behavior. Second, we focus on the El Tatio geothermal field to offer a situated example. Finally, we delineate some relevant elements of human–volcano interactions and volcanic risk management from an Atacameño perspective. In our conclusions we suggest that volcanology, particularly in the context of the Andes, needs to engage more substantially with the Atacameño or other ancestral systems of knowledge production to expand volcanological insights and respond to the call for decolonizing science.

Evaluating the role of stratigraphy and inherited basement structures on the evolution of thick and thin-skinned related folds: Insights from the Salar de Atacama Basin in the Central Andes

We investigated the role of pre-existing basement normal faults, and ductile layers present within post-rift sequences on the final geometry and kinematics of hybrid (thick and thin-skinned) fold and thrust belts that result of tectonic inversion, using as an example the northern region of the Salar de Atacama Basin in the Central Andes. The study was developed integrating field data consisting of regional and local observations and geological mapping, and the seismic and structural interpretation of 2-D industrial seismic profiles to understand the current structure of the basin. A regional-scale balanced cross-section was constructed and restored to validate our interpretations and determine the pre-shortening tectonic configuration of the basin. Our results suggest that low angle normal faults result in favorable structures for the development of thick-skinned thrust ramps from their full tectonic inversion during the growth of fold and thrust belts. In the Salar de Atacama Basin, these structures allowed for the uplift and exhumation of large Paleozoic stratified and crystalline rock on its western section. The existence of ductile strata within post-rift sequences commonly facilitates the transition from thick to thin-skinned structural style during the progressive tectonic inversion of pre-existing half-graben structures. This mechanism allowed for the creation of prominent east-verging basement cored anticlines and doubly verging and narrow, shallow thin-skinned folds and thrusts at the northernmost part of the Salar de Atacama Basin. Pieces of evidence from the basin suggest that the initial areal extension (length) of the post-rift ductile strata exert a fundamental role in the lateral extension of thin-skinned thrusts. Finally, the existence or not of important ductile strata in the overburden stratigraphy conditions the progression of hybrid fold and thrust belts after pre-existing normal faults are reactivated.

Effusion rate estimation based on solidified lava flows: Implications for volcanic hazard assessment in the Negros de Aras monogenetic volcanic field, northern Chile

Effusion rate is the instantaneous lava flow output by a vent. It is one of the most important factors that govern the emplacement and dynamics of lava flows and can be determined by direct measurements or estimated through modeling. The Negros de Aras monogenetic volcanic field, located in the Central Volcanic Zone of the Andes, is the largest volcanic field in northern Chile. It is situated north of the active Socompa volcano and south of the Salar de Atacama basin, consisting of scoria cones and lava flows. Here, we estimate the effusion rates of three overlapping and representative solidified lava flows from this volcanic field applying an iterative procedure using the Q-LavHA GIS plugin, where the effusion rate is treated as an unknown parameter and the solution is reached by comparing the simulated results with the real extension of the flows. The pre-eruptive surface was reconstructed using the 12 m resolution TanDEM-X digital elevation model. Other required input parameters for the modeling (e.g., channel ratio, viscosity, temperature) were estimated through geomorphometric, petrographic, and geochemical analysis. The estimated effusion rates vary between 14 and 113 m3/s, comparable with rates measured elsewhere. The method was validated by applying it to two directly measured (Nyamuragira 2006; Mount Etna 2001) and one calculated effusion rate (Lentiscal 2450 BP, Canary Islands). The estimated effusion rates gave an average underestimation of 10%. Considering this percentage of adjustment, the effusion rates for the three studied lava flows from the Negros de Aras monogenetic volcanic field vary from 15 m3/s to 124 m3/s. Our results provide valuable information for mitigating volcanic risk in the event of future lava flow eruptions, which could affect nearby villages and mining operations.

Characterization of precipitation and recharge in the peripheral aquifer of the Salar de Atacama

To reduce uncertainty in the identification of the recharge areas in the Peripheral Aquifer of the Salar de Atacama (SdA), a few studies have investigated the isotopic characteristics and moisture sources of precipitation in the SdA basin. In the present study, the seasonal cycle of meteorological parameters and the relationships of this cycle with sea surface temperature anomalies are shown, the sources of humidity are identified, and the types of clouds producing precipitation are defined. Finally, the isotopic compositions of precipitation, surface water and groundwater in the SdA basin and the Altiplano-Puna Plateau basins are analysed to identify the area recharging the northern, eastern and southern subbasins of the SdA. In summer, when the highest temperature, relative humidity and precipitation values of the year are recorded, the precipitation is due to deep convection. The trajectories of the arriving air masses can be classified into three groups: from the North Atlantic Ocean across the Amazon basin, from the South Atlantic Ocean across the La Plata River basin and the Gran Chaco, and from the Pacific Ocean. In winter, when the temperature, relative humidity and precipitation are lower, the moisture masses come from the Pacific Ocean. Winter precipitation is more depleted in heavy isotopes than summer precipitation. The isotopic analysis of precipitation, surface water and groundwater shows that recharge of the eastern subbasins of the SdA occurs by diffuse infiltration of precipitation and concentrated infiltration of surface water, both within the hydrographic basin of the SdA. The meteoric source of the waters in the Altiplano-Puna Plateau basins is isotopically lighter than the waters found in the side basins of the SdA, so there is no significant water quantity transfer to the peripheral aquifers of the SdA from outside the hydrographic basin.

Magnetotelluric image of the Chilean subduction zone in the Salar de Atacama region (23°-24°S): Insights into factors controlling the distribution of volcanic arc magmatism.

The Salar de Atacama region (23°-24°S) in the Central Andes of northern Chile represents an anomalous segment of the Andes, where a very large forearc basin is present (Salar de Atacama) and the axis of the active volcanic chain is deflected to the east from its regional trend. Here we used magnetotelluric (MT) data to infer the distribution of partial melts and hydrothermal fluids in order to better understand the mechanism controlling the magmatism in this subduction zone.Our 3-D inversion model shows a complex electrical resistivity structure, with several mid crustal conductors (<5 Ωm) imaged around the Salar de Atacama basin (SdAb). Although the forearc is dominated by high resistivities (>1000 Ωm), conductors were imaged below the Precordillera and in the northern SdAb, where major trench-parallel and transverse fault systems are present. We interpret these forearc conductors as evidence of active and fossil hydrothermal systems hosted by the Precordillera Fault System and the Calama-Olacapato-El Toro transverse fault. Conductors found along the arc are spatially coincident with active volcanoes likely representing partial melting in the continental crust. A large conductor was imaged in the backarc, indicating the presence of a significant volume of partial melts below the Altiplano-Puna plateau, as many previous geophysical studies have suggested. The model shows that the mid-lower crust and subcontinental mantle (i.e., >15 km depth) below the SdAb is dominated by resistivity values >100 Ωm., suggesting the presence of a relatively poorly hydrated continental crust and mantle wedge in this segment of the northern Chile subduction zone. These results, together with petrophysical interpretations derived from previous seismic and gravimetric studies, suggest that the lithosphere below the SdAb represents an impermeable block, which inhibits the upward flow of fluids and melts derived from deeper parts of the subduction system.

Evolution of a magmatic to a phreatomagmatic volcanic system: The birth of a monogenetic volcanic field, Tilocálar volcanoes, northern Chile

The Tilocálar volcanic complex comprises four monogenetic volcanoes located at the southeastern edge of the Salar de Atacama Basin, northern Chile. These monogenetic volcanic centers are the Tilocálar Norte lava, the El Maní dome, the Tilocálar Sur small–lava shield, and the Tilocálar Sur maar, respectively, and were formed between 460 ± 50 ka to < 1 Ma ago along the north–south-striking Tilomonte ridge that underlies the Tucúcaro Ignimbrite (3.2 ± 0.3 Ma). Their formation is the result of an intermediate magma rising to the surface during a local transtensional regime, which is observed at El Maní, under a dominantly compressional tectonic setting. The Tilocálar monogenetic centers provide a rare opportunity to examine the variability from individual and small–volume magma batches to the development of a monogenetic volcanic field. These volcanoes and the control on their eruption styles were studied by geological mapping and stratigraphic considerations, morphometric analysis, textural studies (density and vesicularity), petrographic observations, and geochemical analyzes. The Tilocálar Norte lavas have an intermediate composition (mostly andesite, 62.02 wt.% SiO2) that reach a maximum distance of 3.9 km to the north and 1.2 km to the southwest from their vent, with a dense–rock equivalent (DRE) volume of 8.73×107 m3. The El Maní lava dome is small (covering 750 m2 area and consisting of 1.06×103 m3 DRE volume) that presents mingled mafic (63.89 wt.% SiO2) and felsic (73.73 wt.% SiO2) products of the original magma source, related to shallow crustal melts. The Tilocálar Sur small lava–shield is characterized by a pyroclastic fall deposit and lavas. The pyroclastic fall deposit is characterized by agglutinated andesite scoria–spatter fall units, covering 2.81 km2 and consisting of 7.75×105 m3 DRE volume. In contrast, the lavas are characterized by an andesitic composition (57.64 wt.% SiO2), which is 1.8 km in length to the northwest and 1.4 km to the east of their source. These lavas cover an area of 3.78 km2 with 9.15×107 m3 DRE volume. Tilocálar Sur maar crater has an elliptical shape in map view (363 m diameter east–west and 288 m diameter north–south), surrounded by individual conglomerates, sandstones, granitoids, and tuff fragments that lie on the present–day surface around the crater rim. The Tilocálar volcanic complex is interpreted as a small monogenetic volcanic field that shows an eruption history defined by a spectrum of eruptive processes determined by internal and external parameters at any given time from the four independent volcanic centers.

Lithium extractivism and water injustices in the Salar de Atacama, Chile: The colonial shadow of green electromobility

This paper analyzes the linkages and feedback between green electromobility, lithium extractivism, and water injustices affecting the Atacameño's indigenous communities in the Salar de Atacama basin (Atacama Salt Flats). Currently, lithium is in high demand in the international markets as a strategic resource for the green electromobility industry, which represents part of the Global North policies established by the Paris Agreement to mitigate climate change's effects. Using both documentary and ethnographic methods based mainly on semi-structured interviews conducted with Atacameño people, public officials, and lithium companies' representatives and workers, we propose a decolonial interpretation of lithium extractivism in brine mining through the lens of Latin American political ecology combined with a decolonial and water justice approach. The results demonstrate how the linkages and feedback between global and local dynamics of lithium mining in the Salar de Atacama constitute a form of green extractivism that further replicates the historical inequalities between the Northern and Southern hemispheres and especially affects the indigenous Andean territories and the water ecosystems in the Global South. We call this phenomenon the colonial shadow of green electromobility. We conclude by exposing the need to rethink global proposals addressing climate change by reducing the commodity demand and aiming for water justice at global and local levels.

Imbalance in the modern hydrologic budget of topographic catchments along the western slope of the Andes (21–25°S): implications for groundwater recharge assessment

Modern rates of water discharge often exceed groundwater recharge in arid catchments. This apparent mass imbalance within a catchment may be reconciled through either groundwater flow between topographic drainages and/or the draining of stored groundwater recharged during pluvial periods. This study investigates discrepancies in the modern hydrologic budget of catchments along the west flank of the Andes in northern Chile (21–25° S), focusing on the endorheic Salar de Atacama basin and adjacent basins. Uncertainty-bounded estimates of modern recharge rates are presented, which do not come close to balancing observed modern groundwater discharge within topographic catchments. Two conceptualizations of hydrogeologic catchments discharging to Salar de Atacama were explored with a simplified two-dimensional groundwater model. Results from the models support the interpretation that subsurface interbasin flow and transient drainage of groundwater from storage are required to balance water budgets along the plateau margin. The models further examine whether this system is still responding to climatic forcing (on paleoclimatic time scales) from pluvial periods and highlight general characteristics for similar plateau margin systems including: (1) water level changes at the plateau margin that are highly sensitive to long-term (100–1,000 years) changes in recharge on the plateau, (2) extent and magnitude of the changes in water table, which are controlled by the distribution of hydraulic conductivity at the margin, and (3) the contributing area to the lower-elevation catchment, which is itself dynamic and not coincident with the topographic boundary.

Multi-proxy insights into the structure and geometry of the tectonic boundary at the Cordillera de Domeyko-Salar de Atacama border: An example of the interplay between basement and foreland basins

The study of the Cordillera de Domeyko and the Salar de Atacama Basin in northern Chile has been critical to understand the generation of the Andean Cordillera and the migration of the deformation front eastwards. However, the relation between the uplift of the range, its temporal pattern, and the formation of the Preandean Depression have not been fully understood. In this article, we forward modeled two gravimetry surveys, consisting in 185 stations crossing the boundary between the Salar de Atacama Basin and Cordillera de Domeyko, with the goal of understanding the physical traits of each domain and the variations in basin geometry. We interpreted two seismic reflection profiles, along with log data from one well in the basin center, and additionally, we analyzed an inversion of the magnetic anomaly for both lines. The results of the analysis show the segmentation of physical properties into two domains. The first is interpreted as basement (Triassic-older) units, while the other shows the presence of gravity lows correlated with late Mesozoic-Cenozoic units cropping out along the western edge of the basin. The magnetic anomalies identified were correlated with variations within the basement and outcrops of crystalline intrusives. Within the sedimentary units, the Late Cretaceous-Paleogene Purilactis Group and Paleogene-Eocene formations were distinguished from the evaporite-rich Oligocene-Miocene Paciencia Group. The latter was deposited after a compressive event (Incaic Event) which thrusted basement units eastwards, inverted Mesozoic extensional faults, and generated the accommodation space required for its deposition. The basin then experienced renewed compression during the Miocene. This interplay between basement uplift and thrusting, along with fault inversion and basin generation, is a characteristic found in other parts of the Salar de Atacama Basin and the orogen, suggesting that this tectonic style might be prevalent in other basins comprising the Preandean Depression and along the Central Andes.

Transition from small-volume ephemeral lava emission to explosive hydrovolcanism: The case of Cerro Tujle maar, northern Chile

Cerro Tujle is an isolated Quaternary maar located 21 km south-east of the Salar de Atacama basin. It is situated at 3,554 m a.s.l., on the top of the Cordón de Tujle ridge forming a north-south striking morphological element in the Central Volcanic Zone of the Andes, in northern Chile. The material erupted at Cerro Tujle lies over the Tucúcaro Ignimbrite (3.2 ± 0.3 Ma), covering the whole area. The origin of the magma source, as well as the evolution and control of the volcanic eruptive styles, were determined by fieldwork, stratigraphic, morphometric, textural (density and vesicularity), petrographic, and geochemical analyses. The Cerro Tujle maar features an elliptical crater (333 × 279 m wide in east-west and north-south directions, respectively) surrounded by lava flow and tephra deposits. The total Dense Rock Equivalent volume of the products was calculated in 1.53 × 105 m3, and mainly correspond to andesites (58.62–59.80 wt% of SiO2). The lava flow can be categorized in at least two types: i) brown-red and green-to-gray andesites located on the north-northwestern flank of the crater, and ii) black andesites with felsic rock clasts distributed around the crater underlying the other lavas. In contrast, the pyroclastic deposit displays breccias of juvenile pyroclasts with xenoliths of rhyolitic composition. These felsic clasts suggest magma assimilation with a shallow magma reservoir during a relatively fast ascent of the magma. This is evidenced by disequilibrium textures in mineral levels, such as reaction rim, and skeletal and sieve textures of the phenocrysts. The field evidence and results of the different analyses suggest a change in the eruptive style from effusive to explosive. This transition is associated with a decrease of the magma flux and a withdrawal of magma below the groundwater table, which has produced a phreatomagmatic eruption by magma-water interaction.

East-vergent thrusts and inversion structures: An updated tectonic model to understand the Domeyko Cordillera and the Salar de Atacama Basin transition in the western Central Andes

The tectonic evolution of the Andean forearc in northern Chile has commonly been related to superimposed deformational events associated with different tectonic settings. The eastern Domeyko Cordillera and the Salar de Atacama Basin on the inner Andean forearc, have been widely investigated, and several alternative tectonic models including extensional and/or contractional deformation are proposed to explain its evolution. Nevertheless, when trying to determine the role of Paleozoic and Mesozoic inherited-basement extensional structures during the Andean orogeny an evolutionary model is still not clear. Therefore, the aim of this research is to improve the understanding of these aspects. Based on the interpretation of a regional 2-D seismic grid and new structural data from outcrops, we propose that the main mechanisms of contractional deformation and uplift are related to: (1) the propagation of east-vergent basement-involved thrust faults, (2) the tectonic inversion of pre-existing normal faults and (3) the activation of shallow thin-skinned thrusts. Additionally, the resultant geometry of the structural styles is frequently controlled by three factors: (i) the initial geometry of inherited major faults, (ii) the rheology of the deformed rocks, and (iii) the rate of accumulation of the Upper Cretaceous-Cenozoic syn-tectonic deposits. Finally, we interpreted that the tectonic transition between the Domeyko Cordillera and the Salar de Atacama Basin is marked by the interaction between east-vergent thick-skinned thrusts and west-vergent inverted normal faults.

Staphylococcus sciuri Strain LCHXa is a Free-Living Lithium-Tolerant Bacterium Isolated from Salar de Atacama, Chile.

In addition to the industrial and biomedical applications of lithium, information on the tolerance of microorganisms to high Li concentrations in natural biological systems is limited. Strain LCHXa is a novel free-living Gram-positive, non-motile bacterium strain isolated from water samples taken at Laguna Chaxa, a non-industrial water body with the highest soluble Li content (33 mM LiCl) within the Salar de Atacama basin in northern Chile. Enrichment was conducted in Luria-Bertani (LB) medium supplemented with 1 M LiCl. Strain LCHXa was a Novobiocin-resistant and coagulase negative Staphylococcus. Phylogenetically, strain LCHXa belongs to the species Staphylococcus sciuri. Strain LCHXa grew optimally in LB medium at pH 6–8 and 37 °C, and it was able to sustain growth at molar Li concentrations at 2 M LiCl, with a decrease in the specific growth rate of 85%. Osmoregulation in strain LCHXa partially involves glycine betaine and glycerol as compatible solutes.

Stable and Radioisotope Systematics Reveal Fossil Water as Fundamental Characteristic of Arid Orogenic‐Scale Groundwater Systems

AbstractIn arid and semiarid regions, persistent hydrological imbalances illuminate the considerable gaps in our spatiotemporal understanding of fundamental catchment‐scale governing mechanisms. The Salar de Atacama basin is the most extreme example of groundwater‐dominated continental basins and therefore is an ideal place to probe these unresolved questions. Geochemical and hydrophysical observations indicate that groundwaters discharging into the basin reflect a large regional system integrated over 102–104 year timescales. The groundwater here, as in other arid regions, is a critical freshwater resource subject to substantial demand from competing interests, particularly as development of its world‐class lithium brine deposit expands. Utilizing a uniquely large and comprehensive set of H and O isotopes in water, we demonstrate that much of the presumed recharge area on the Altiplano‐Puna plateau exhibits isotopic signatures quite distinct from waters presently discharging within the endorheic Salar de Atacama watershed. δ18O values of predicted inflow source waters are 3.6‰ to 5.6‰ higher than modern plateau waters, and 3H data from 87 discrete samples indicate that nearly all of this inflow is composed of premodern recharge (i.e., fossil water). Under plausible conditions, these distinctions cannot be explained solely by natural variability in modern meteoric inputs or by steady state groundwater flow. We present a conceptual model revealing the extensive influence of transient draining of fossil groundwater storage augmented by regional interbasin flow from the Andes. Our analysis provides robust constraints on fundamental mechanisms governing this arid continental groundwater system and a framework within which to address persistent uncertainties in similar systems worldwide.

Geometry and late Mesozoic-Cenozoic evolution of the Salar de Atacama Basin (22°30′-24°30′S) in the northern Central Andes: New constraints from geophysical, geochronological and field data

The late Mesozoic-Cenozoic evolution of the Central Andes of northern Chile consists of a series of events related to changing conditions along the plate margin, leading to different episodes of compression and extension. A long-lasting basin which records these changes corresponds to the Salar de Atacama Basin. Its tectonic history has been blurred by several interpretations of seismic reflection lines and multiple chronostratigraphic correlations between subsurface-surface units. As such, many aspects of its tectonic evolution are still unclear. In this study, we performed an E-W gravimetric profile across the Barros Arana Syncline and the basin. We analyzed interval velocities obtained from seismic reflection studies and reviewed the profiles closest to the gravity survey. Four U-Pb samples for detrital zircon analysis were obtained from Late Cretaceous-Paleogene units. Geophysical data show a segmentation of physical properties within the basin, with denser units and faster interval velocities around the late Mesozoic-early Cenozoic units, and lighter, slower units in the actual salt pan. The main contrast in physical properties is observed in the evaporitic and fine-grained continental deposits of the San Pedro Formation. Geophysical and geological constraints show that its thickness varies between 800 and 1200 m, and that it was deformed during later events. The U-Pb data show that the rocks within the Barros Arana Syncline reach well into the Paleogene, and that they were mainly deformed during the late Eocene Incaic Event, where an east-verging thrust system also involving Permo-Triassic units was developed, establishing the actual structural configuration. The late Oligocene-early Miocene units were then deposited in a post-orogenic setting, with minor compression. A stronger phase around the late Miocene reactivated previous structures and folded these deposits. This continuous, compressive history of the basin, which is mostly a result of the Incaic Event, is in agreement with the regional evolution of the Central Andes.

Cretaceous to Middle Cenozoic Exhumation History of the Cordillera de Domeyko and Salar de Atacama Basin, Northern Chile

AbstractSpatiotemporal patterns of deformation and exhumation in the central Andes are key parameters for reconstructing the kinematic history of the orogenic belt. Previous studies of the retroarc thrust belt document overall eastward propagation of deformation since the late Eocene, but the amount and timing of exhumation during the early phase of Andean orogeny remains largely unconstrained, particularly in the modern forearc region. In order to determine the timing and amount of exhumation prior to the late Eocene, we employed a multidating approach combining zircon U‐Pb geochronology with apatite fission track and apatite (U‐Th)/He thermochronology. We focus on the low‐temperature cooling history of the Cordillera de Domeyko thrust belt and synorogenic deposits in the Salar de Atacama basin. Our results show Late Cretaceous to Oligocene cooling and exhumation in the Cordillera de Domeyko. The distribution of cooling ages in the forearc indicates three periods of exhumation: ~86–65, ~65–50, and 50–28 Ma. The amount of cooling was variable in space and time but requires total exhumation of ~2.5–3.3 km of rocks above major structures in the thrust belt. Regional unconformities in the Salar de Atacama basin correlate with periods of eastward migration of the orogenic front at ~65 Ma and ~50–40 Ma. Pulses of deformation at the front of the thrust belt alternated with periods of out‐of‐sequence hinterland deformation and exhumation. Overall, our data show that shortening in the central Andes commenced during the Late Cretaceous (as early as ~86 Ma) and that deformation (shortening) and exhumation were coupled in space and time.

Hydrogeochemical fluxes and processes contributing to the formation of lithium-enriched brines in a hyper-arid continental basin

The accumulation of solutes delivered via shallow groundwater and surface water in arid to hyper-arid closed basins, and the complex hydrogeochemical processes associated with their transport, are key to deciphering mechanisms responsible for the formation of brines and salts in these environments. A rigorous investigation of the hydrogeochemical fluxes and the formation of the Li-enriched brine in the hyper-arid basin of the Salar de Atacama, Chile is presented. Water fluxes within the Salar de Atacama basin range from 0.003 m3/s to 1.50 m3/s with a poor correlation between discharge and drainage basin area. The inflowing waters have major elemental and Li concentrations that are within the same order of magnitude over a period of several decades. The element fluxes indicate, for example, that 58% of the Li in the halite nucleus and brines is derived from the south and southeast parts of the basin. The average δ18Ovsmow and δDvsmow of inflow waters indicate that there are varied sources of recharge corresponding to the defined sub watershed regions. The average water flux-weighted 87Sr/86Sr of inflow waters allows further definition of where in the regional watershed the solutes are derived. The predicted water flux weighted 87Sr/86Sr of the brines (0.70813) compared to the measured average 87Sr/86Sr (0.70801), indicates that there may be unaccounted sources of water and solutes to the basin brines. Elemental accumulation time scales for the volume of halite and brine in the nucleus balance on time frames of 0.5 Ma (Mg), 1.0 Ma (Ca), 1.9 Ma (Li) and 2.2 Ma (K) as compared to 47 Ma (Na) and 53 Ma (Cl), further evidence that Na and Cl require additional sources not accounted for in the modern inflows to the topographic watershed. Dissolved noble gas concentrations of marginal and nucleus brines specify that the brines formed in an atmospheric equilibrated state and have since been isolated below the salt crust. A process-based model is presented to explain the extremely high concentrations of Li in brines which incorporates the δ7Li isotope signatures of waters in the basin to further decipher, on a first order, the contributions of processes such as low temperature weathering and secondary phase formation.