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Sister species that live in sympatry provide the possibility to analyse the level of divergence in their ecological, physiological and life-history traits and how they can coexist without out-competing each other. We studied the thermal sensitivity of locomotor performance in the sympatric lizards Phymaturus querque and Phymaturus zapalensis from Patagonia, Argentina. We measured morphological traits relevant to locomotor performance and the running speed at different body temperatures, and we estimated the critical thermal minimum (CTmin) and maximum (CTmax) at which running performance equals zero. We obtained the maximum speeds, the temperature at which the performance is maximized (optimal temperature, T o) and the temperature range over which an individual performs 50% and 80% of their maximal performance (B 50 and B 80). Also, we recorded the availability of thermal microenvironments for thermoregulation (operative temperatures) and calculated two indices of vulnerability to global warming. Phymaturus zapalensis and P. querque exhibited differences in most of the morphological traits relevant to locomotor performance. Both species presented similar values of T o, CTmin and CTmax, but B 50 and B 80 were broader in P. zapalensis. During the warmest month, the environmental temperatures are already higher than the physiological optimal temperature, indicating that populations could currently be facing challenges in the context of global warming. [ABSTRACT FROM AUTHOR]

Current assessments of organismal vulnerability to global warming are focusing on physiological trait‐based indices that may allow biologically sounding estimates of heating risk at the local scale. However, intraspecific variability in both exposure and physiological performance may determine large heterogeneity in the distribution of heating risks through the overall species range compromising whole species risk assessments. We examine intra‐ and interspecific variability in two vulnerability indexes: warming tolerances (WT), or the extent that maximum temperatures (Tmax) reaching upper thermal tolerances (CTmax); and thermal safety margin (TSM), or the magnitude that average environmental temperatures (Tmean) exceeding the selected or preferred temperatures (Tsel), in a subtropical warm amphibian tadpole community, at the Monte Desert ecoregion, Argentina. Tadpole populations breeds in temporary ponds and permanent streams that exhibit high thermal heterogeneity. Those populations and species living in hot water bodies, although exhibiting higher CTmax, have lower WT and are more prone to suffer acute heat impacts, thus confirming the prediction of higher thermal risk in ectotherms exposed to higher temperatures. However, these hot pond breeders, although living closer to their CTmax, also preferred high temperatures, showing higher TSMs and being actually exposed to a lower proportion of stressful temperatures than cool selecting populations. Both WT and TSM indexes have significant interpopulational variation. Thus, our findings suggest that attempts to build mechanistic models to forecast species vulnerability to heat stress due to climate change have to include physiological variation among populations. [ABSTRACT FROM AUTHOR]

Jurassic siliceous hot-spring (sinter) deposits from Argentine Patagonia were evaluated to determine the distribution and preservation quality of their entombed microbial fabrics. Detailed study showed that the Claudia palaeo-geothermal field hosts the best-preserved sinter apron in the Deseado Massif geological province, where we also found hot-spring silica–biotic interactions extending into hydrothermally influenced fluvial and lacustrine settings. Carbonaceous material was identified by petrography and Raman spectroscopy mapping; it is inter-laminated with silica across proximal vent to distal marsh facies. The ubiquitous presence of microbial biosignatures has application to studies of hydrothermal settings of early life on Earth and potentially Mars. [ABSTRACT FROM AUTHOR]

Abstract The Copahue volcano host one of the most attractive geothermal resources of Argentina. Several studies focused on both the volcanic activity and the related geothermal manifestations, including a feasibility report during the '90s. However, limited, unclear and usually contradictory structural interpretations are found in the literature, and the role of the main faults over the geothermal system remains thus unsolved. This paper provides the first structural characterization and role assessment of the faults over the fluid flow and the reservoir geometry. A 3D structural model has been constructed to achieve this goal, and a fault-plane striations survey has been carried out at Anfiteatro, Termas and Maquinitas hydrothermal zones. Using this dataset, a slip and dilation tendency analysis over the main structures have been performed. The 3D structural model indicates that the Copahue geothermal field is bounded by an N60°-trending fault set and constrained to the north by the Trolope fault and to the south by the Chancho-Co fault, both with WNW-ESE trend. The collected fault-plain striations data was inverted to obtain the paleostress tensor related to the formation of the Copahue village fault system (CVFS), the structure that controls the hydrothermal areas. The subvertical maximum principal stress axis obtained defines a well constrained tensional regime, with a subhorizontal NW-SE minimum principal stress, consistent in all the surveyed locations. Both the 3D model and the inverted paleostress tensor indicate that the geothermal field, and probably the entire northeastern slope of the volcano, is subjected to an extensional faulting regime. Our analysis shows that the N°60-trending fault set is critically stressed for dilation and probably behaves as an active hydrological fault system, whereas the N105° and N135° fault sets have intermediate and low dilation tendency, respectively. These tendencies might lead to a northeast-trend fluid path between the Chancho-co and the N135° faults and might define the extension of the steam cap. We propose a compartmentalized reservoir model made up by three fault segmented blocks. While a steam cap over a deeper reservoir controlled by the CVFS characterizes the central segment, a pressurized liquid-dominated reservoir could prevail to the west of Termas and the east of Maquinas hydrothermal zones. This model explains the differences between the fumaroles inside the CVFS (i.e., Termas to Maquinas fumaroles) and outside this structural system (i.e., Anfiteatro), is consistent with the steam cap identified by the exploration boreholes and is consistent with the 3D structural framework proposed. Also, the model suggests that the collapse of the eastern slope of the Chancho-co hill might constitute the initial state of the current configuration of the geothermal system. Additional studies are needed to verify the proposed reservoir model before defining deep exploration targets, including magnetotellurics, discrete fracture network analysis, and preliminary thermodynamical models. Highlights • Geothermal field subjected to extensional stress regime(NW-SE Sh min) • N60°, N105°, and N135°-trending faults have respectively high, medium and low dilation tendency • Compartmentalized reservoir explains isotopic differences between fumaroles • Steam cap is related to the Copahue village extensional fault system [ABSTRACT FROM AUTHOR]

Cap rock characterization of geothermal systems is often neglected despite fracturing may reduce its efficiency and favours fluid migration. We investigated the siliciclastic cap rock of Rosario de La Frontera geothermal system (NW Argentina) in order to assess its quality as a function of fracture patterns and related thermal alteration. Paleothermal investigations (XRD on fine-grained fraction of sediments, organic matter optical analysis and fluid inclusions on veins) and 1D thermal modelling allowed us to distinguish the thermal fingerprint associated to sedimentary burial from that related to fluid migration. The geothermal system is hosted in a Neogene N-S anticline dissected by high angle NNW- and ENE-striking faults. Its cap rock can be grouped into two quality categories: • rocks acting as good insulators, deformed by NNW–SSE and E–W shear fractures, NNE-SSW gypsum- and N-S-striking calcite-filled veins that developed during the initial stage of anticline growth. Maximum paleo-temperatures (< 60 °C) were experienced during deposition to folding phases. • rocks acting as bad insulators, deformed by NNW-SSE fault planes and NNW- and WNW-striking sets of fractures associated to late transpressive kinematics. Maximum paleo-temperatures higher than about 115 °C are linked to fluid migration from the reservoir to surface (with a reservoir top at maximum depths of 2.5 km) along fault damage zones. This multi-method approach turned out to be particularly useful to trace the main pathways of hot fluids and can be applied in blind geothermal systems where either subsurface data are scarce or surface thermal anomalies are lacking. [ABSTRACT FROM AUTHOR]

The Andean broken foreland in west-central Argentina, located 400-800 km from the Peru-Chile Trench, is associated with flat sub-duction linked to collision of the oceanic Juan Fernandez Ridge. While the conditions associated with flat subduction would be expected to produce increases in rock uplift and exhumation, where thrusting and dynamic forces work together, a prevalence of pre-Cenozoic apatite fission track (AFT) cooling ages suggests that there is no such link. The lack of Cenozoic cooling ages is at odds with structural reconstructions and basin studies along the foreland that show several kilometers of exhumation. This paradox can be reconciled by taking into account the thermal effects of flat subduction that removed the mantle wedge, and a significant source of heat flow into the crust. Reinterpretation of published AFT exhumation data (>320 ages) using more realistic lower geothermal gradient values allows for substantial exhumation and explains the lack of Cenozoic exhumation ages across the foreland region. [ABSTRACT FROM AUTHOR]

A novel thermoacidophilic archaeal strain has been isolated from three geothermal acidic hot springs in Copahue, Argentina. One of the most striking characteristic of ALE1 isolate is its metabolic versatility. It grows on sulphur, tetrathionate, iron (II) and sucrose under aerobic conditions, but it can also develop under anaerobic conditions using iron (III) or sulphur as electron acceptors and sulphur or hydrogen as electron donors autotrophically. A temperature of 75 °C and a pH between 2.5 and 3.0 are strain ALE1 optimal growth conditions, but it is able to oxidise iron (II) even at pH 1.0. Cells are irregular cocci surrounded by a regularly arrayed glycoprotein layer (S-layer). Phylogenetic analysis shows that strain ALE1 belongs to the family Sulfolobaceae in the class Thermoprotei, within the phylum Crenarchaeota. Based on 16S rRNA gene sequence similarity on NCBI database, ALE1 does not have closely related relatives, neither in culture nor uncultured, which is more surprising. Its closest related species are strains of Acidianus hospitalis (91 % of sequence similarity), Acidianus infernus (90 %), Acidianus ambivalens (90 %) and Acidianus manzanensis (90 %). Its DNA base composition of 34.5 % mol C + G is higher than that reported for other Acidianus species. Considering physiological and phylogenetic characteristics of strain ALE1, we considered it to represent a novel species of the genus Acidianus ( candidatus ' Acidianus copahuensis'). The aim of this study is to physiologically characterise this novel archaea in order to understand its role in iron and sulphur geochemical cycles in the Copahue geothermal area and to evaluate its potential applications in bioleaching and biooxidation. [ABSTRACT FROM AUTHOR]

The thermal ecology of the endemic lizard Liolaemus eleodori was studied at the San Guillermo National Park, Province of San Juan, Argentina. Data were collected during December 2004 and February 2005. Cloacal (Tc), substrate (Ts) and air (Ta) temperatures were registered using a quick reading thermometer. Liolaemus eleodori exhibited a thermo-conformist thermoregulatory strategy with a unimodal pattern of activity, showing a marked preference for a naked ground microhabitat (completely free of vegetation). Our data suggest that the thermoregulatory strategy and use of space and time is strictly related to the harsh climatic conditions of the study site. [ABSTRACT FROM AUTHOR]

J uáárez ÁÁ.B., V éélez C.G., I ññiguez A.R., M artíínez D.E., R odrííguez M.C., V igna M.S. and R ííos de M olina M.C. 2011. A (Trebouxiophyceae, Chlorophyta) strain from an extremely acidic geothermal pond in Argentina. 50: 413--421. DOI: 10.2216/10-79.1 Acidic geothermal environments are rare and very few organisms can thrive in them. or -like species have been described in a variety of environments but their presence in extremely acidic waters have rarely been reported. A -like alga (strain BAFC CA10) was isolated from Laguna Verde, a volcanic mesothermal acidic pond from northern Patagonia (Argentina). Applying a multimethod approach including microscopic, ultrastructural, chemical and phylogenetic analyses, the acidotolerant strain BAFC CA10 was identified as ( == ) on the basis of comparisons with the authentic strain SAG 211-11g. Our results confirmed the initial characterization of the Laguna Verde strain as , but since this species was transferred to the new genus , strain BAFC CA10 should be designated as . Histochemical staining and sugar composition of the cell-wall amorphous and fibrillar matrix, together with transmission electron microscopy of the cells, showed the distinctive characters of the species: (1) glucosamine was the exclusive component of the fibrillar cell wall; (2) rhamnose, galactose, glucose and xylose together with minor quantities of arabinose, mannose and fucose were present in the cell-wall hemicellulose matrix; (3) there was a single parietal chloroplast surrounding the entire cell with a small aperture (''mantel-shaped''); (4) there was one pyrenoid in the thickening of the chloroplast surrounded by two starch granules and bisected by two thylakoids; and (5) the cell wall was an electron-transparent homogeneous structure 60--80 nm thick. Phylogenetic analyses of concatenated small-subunit and internal transcribed sequence ribosomal DNA sequences of coccoid green algae within the and the clades of the Chlorellaceae confirmed that strain BAFC CA10 is unequivocally related to the strains. Our results suggest that should be added to the list of species capable of adapting to live in extremely acidic environments. [ABSTRACT FROM AUTHOR]

Functional traits are those characteristics of organisms that influence the ability of a species to develop in a habitat and persist in the face of environmental changes. The traits are often affected by a multiplicity of species-dependent and external factors. Our objective was to investigate thermal biology of Liolaemus ruibali in a high altitude cold desert at the arid Puna region, Argentina. We address the following question: do sex and seasonal variations in environmental temperature induce changes in the ecophysiological traits? We measured and compared the operative temperatures between fall and spring; and between sexes and seasons, we compared the ecophysiological traits of lizards, microenvironmental temperatures and thermoregulatory behavior. Air and operative temperatures were different between seasons. We found an effect of season-sex interaction on field body temperatures, preferred temperatures, panting threshold and thermal quality. The voluntary and critical temperatures presented seasonal variation in relation to changes in environmental temperatures, suggesting thermal acclimatization. We note behavioral changes between seasons, with the substrate being the main resource for gaining heat in spring. We conclude that Liolaemus ruibali is an efficient thermoregulator; it is a eurythermic lizard and presents phenotypic plasticity in different ecophysiological and behavioral traits induced by sex and seasonality. In addition, we predict that this population could buffer the effects of projected global warming scenarios. • We investigate thermal ecology of Liolaemus ruibali in a high altitude cold desert. • We found an effect of the season-sex interaction in six ecophysiological traits. • We found variations in thermoregulatory behavior regarding to season. • We observe an active thermoregulatory behavior, mainly thigmothermic in spring. • Liolaemus ruibali is an efficient thermoregulatory, which has low thermal plasticity. [ABSTRACT FROM AUTHOR]

• We compare the thermal ecophysiology in P. scapulatus populations at different latitudes in the Puna region. • Both populations has thermal sensitivity in locomotor performance. • P. scapulatus populations adjust optimal temperatures of performance to field body temperatures and preferred temperatures. • Pristidactylus scapulatus is a eurithermic lizard, which has thermal flexibility in the cold. • Thermoregulation effectiveness is better in the population of greater latitude. Reptiles are important models for understanding fundamental aspects of physiological ecology and for assessing how environmental change can impact biodiversity. Abiotic factors (micro-environmental temperatures, operative temperatures, thermal quality) may vary geographically along an altitudinal and latitudinal gradient, and therefore the different thermal resources available for thermoregulation also vary. Comparative analyses among populations provide an opportunity to understand how variation in abiotic factors can affect different ecophysiological traits of a species at different geographical points. Our objective was to carry out a comparative study between two populations of Pristidactylus scapulatus in the Puna region of Argentina, providing the first data available on thermal ecophysiology, thermoregulatory efficiency and locomotor performance of the species. We determined field body temperature, micro-environmental temperatures and operative temperatures. In the laboratory, we measured preferred temperatures and calculated the index of thermoregulatory efficiency. In addition, we recorded critical temperature (minimum and maximum) and we estimated the thermal sensitivity of locomotion by measuring sprint speed at different body temperatures; based on these data we calculated the optimal temperature for performance, the optimal performance breadth and thermal safety margin. Air temperatures and operative temperatures were different between sites. However, we only found differences between populations in the minimum critical temperatures, with these being lower at higher latitude. We note that P. scapulatus populations adjust optimal temperatures of performance to field body temperatures and preferred temperatures, which could reduce the costs of thermoregulation in lizards with limited daily activity and who inhabit sites with variable and unpredictable environment temperatures. We conclude that Pristidactylus scapulatus has thermal sensitivity in locomotor performance, is a moderate thermoregulator with respect to the environment and is a eurithermic lizard, which has thermal flexibility in the cold. [ABSTRACT FROM AUTHOR]

Metal pollution is a great concern worldwide and the development of new technologies for more sustainable extraction methods as well as for the remediation of polluted sites is essential. Extremophilic microorganisms are attractive for this purpose since they have poly-resistance mechanisms which make them versatile. In this work, we sampled an acidic river and a hot spring of Caviahue-Copahue volcanic environment. The indigenous microbial communities were exposed to five heavy metals (Cd, Co, Cu, Ni and Zn) in batch-cultures favouring different metabolisms of biotechnological interest. Remarkably, high tolerance values were reached in all the cultures, even though most of the metals studied were not present in the environmental sample. Particularly, outstanding tolerances were exhibited by acidophiles, which grew at concentrations as high as 400 mM of Zn and Ni. High-throughput amplicon sequencing of 16S rRNA gene was used to study the indigenous communities and the resistant consortia. We took three approaches for the analysis: phylotypes, OTUs and amplicon sequence variants (ASVs). Interestingly, similar conclusions were drawn in all three cases. Analysing the phylogenetic structure and functional potential of the adapted consortia, we found that the strongest selection was exerted by the culture media. Notably, there was a poor correlation between alpha diversity and metal stress; furthermore, metal stress did not seem to harm the functional potential of the consortia. All these results reveal a great adaptability and versatility. At the end, 25 metal-resistant extremophilic consortia with potential uses in bioremediation, bioleaching or biomonitoring processes were obtained. Image 1 • An acidic river and a hot spring pond are analysed. • Both microbial communities are highly versatile and adaptative. • The consortia obtained are exceptionally resistant to heavy metals. • Culture media composition exerts greater selection pressure than heavy-metal stress. • Alpha diversity does not correlate with metal resistance and functional capacity. [ABSTRACT FROM AUTHOR]

Thermoregulation in ectotherms may be modulated by climatic variability across geographic gradients. Environmental temperature varies along latitudinal clines resulting in heterogeneous thermal resource availability, which generally induces ectotherms to use compensatory mechanisms to thermoregulate. Lizards can accommodate to ambient temperature changes through a combination of adaptive evolution and behavioral and physiological plasticity. We studied the thermal ecology of the endangered endemic lizard Liolaemus multimaculatus at six different sites distributed from the northern to southern areas of the distribution (700 km) in the Atlantic dune barriers of Argentina, and even including the borders areas of the distribution range. Environmental temperatures and relative humidity showed a strong contrast between northern and southern limits of the distribution range. The northern localities had operative temperatures (T e) above the range of preferred temperatures (T set), instead, the southern localities had large proportion of T es within the T set. Although these different climatic conditions may constrain the thermal biology of L. multimaculatus , individuals from all localities maintained relatively similar field body temperatures (X T b = 34.07 ± 3.02 °C), suggesting that this parameter is conservative. Thermal preference partially reflected latitudinal temperature gradient, since lizards from the two southernmost localities showed the lowest T sel and T set. Thermoregulatory efficiency differed among localities, since E values in the northern localities (E = 0.53–0.69) showed less variability than those of southern localities (E = 0.14–0.67). Although L. multimaculatus employed a strategy of having a conservative T b and being able to acclimatize the thermal preference to copes with latitudinal changes in the thermal environment, other local factors, such as ecological interactions, may also impose limitations to thermoregulation and this may interfered in the interpretation of results at wider spatial scale. • We studied the thermal biology of Liolaemus multimaculatus in a latitudinal gradient. • Field body temperature were constant despite of latitude. • Individuals of different sites used similar thermal patches. • Preferred temperatures decreased up to 3 °C with latitude. • Changes in thermal preferences and behavioral plasticity improve thermoregulation. [ABSTRACT FROM AUTHOR]

The main aim of this work is to relate the geoelectrical units defined by the 3D model to the geological units in the southeast of the Tucumán plain, where geothermal manifestations are shown by artesian wells with temperatures between 38 °C and 50 °C. Two field campaigns involving 41 audio-magnetotelluric sites in the frequency range 100,000 to 10 Hz were carried on. Some sites are located near the wells, where the depth from which they bring water to the surface is known. The 3D model allows us to describe characteristics of the electrical resistivity of the different sedimentary formations as well as to correlate it with the structural features present in the region of study. The most remarkable feature of the final model is the high conductivity of the deepest geoelectrical unit associated with a formation of marine origin in which the presence of illite and montmorillonite has been determined. In addition, as some information from the wells is available for the layer taken advantage of, it was possible to validate the resistivity determined by the model with that obtained with Archie's law, finding correspondence. • The southeast of the Tucumán plain is an area of anomalous geothermal gradient with potential economic interest. • An audio-magnetotelluric (AMT) survey was carried out to characterize the main hydrogeological units. • Prior model and model covariance were parameters investigated for our distribution of AMT sites. • The resistivity of the model is in agreement with that obtained from Archie's law considering the information from the wells. • The model shows correspondence with the geological structures. [ABSTRACT FROM AUTHOR]

The geothermal Copahue-Caviahue (GCC) system (Argentina) is an extreme acidic environment, dominated by the activity of Copahue volcano. Environments characterised by low pH values, such as volcanic areas, are of particular interest for the search of acidophilic microorganisms with application in biotechnological processes. In this work, sulfate-reducing microorganisms were investigated in geothermal acidic, anaerobic zones from GCC system. Sediment samples from Agua del Limón (AL1), Las Máquinas (LMa2), Las Maquinitas (LMi) and Baño 9 (B9–2, B9–3) were found to be acidic (pH values 2.1–3.0) to moderate acidic (5.1–5.2), containing small total organic carbon values, and ferric iron precipitates. The organic electron donor added to the enrichment was completely oxidised to CO2. Bacteria related to ' Desulfobacillus acidavidus ' strain CL4 were found to be dominant (67–83% of the total number of clones) in the enrichment cultures, and their presence was confirmed by their isolation on overlay plates. Other bacteria were also detected with lower abundance (6–20% of the total number of clones), with representatives of the genera Acidithiobacillus, Sulfobacillus, Alicyclobacillus and Athalassotoga/Mesoaciditoga. These enrichment and isolates found at low pH confirm the presence of anaerobic activities in the acidic sediments from the geothermal Copahue-Caviahue system. [ABSTRACT FROM AUTHOR]

The Cerro Blanco Caldera (CBC) is the youngest collapse caldera system in the Southern Central Andes (Southern Puna, Argentina). The CBC is subsiding with at an average velocity of 0.87 cm/year and hosts an active geothermal system. A geochemical characterization of emitted fluids was carried out based on the chemical and isotopic compositions of fumaroles, and thermal and cold springs discharged in this volcanic area with the aim of constructing the first hydrogeochemical conceptual model and preliminary estimate the geothermal potential. The main hydrothermal reservoir, likely hosted within the pre-caldera basement rocks, has a Na+-Clˉ(HCO 3)ˉ composition with estimated temperatures ≥135 °C. The unconsolidated, fine-grained Cerro Blanco ignimbrite likely acts as the cap-rock of the hydrothermal system. The presence of phreatic eruption breccias in the surrounding area of the geothermal fumaroles supports the effectiveness of the pyroclastic deposit as sealing rocks. The isotopic data of water (δ18O and δD) indicate a meteoric recharge of the hydrothermal reservoir, suggesting as recharge areas the sectors surrounding the CBC, mainly towards the W and NW where large outcrops of the pre-caldera basement exist. A fault-controlled hydraulic connection between the hot springs and the hydrothermal reservoir is proposed for the Los Hornitos area. The fumaroles show the typical compositional features of hydrothermal fluids, being dominated by water vapor with significant concentrations of H 2 S, CH 4 and H 2. Considering the high geothermal gradient of this area (∼104 °C/km) and the relatively high fraction of mantle He (∼39%) calculated on the basis of the measured R/Ra values, the hydrothermal aquifer likely receives inputs of magmatic fluids from the degassing magma chamber. The preliminary geothermal potential at CBC was evaluated with the Volume Method, calculating up to E = 11.4*1018 J. Both the scarce presence of superficial thermal manifestations and the occurrence of an efficient cap-rock likely contribute to minimize the loss of thermal energy from the reservoir. The results here presented constitute the necessary base of knowledge for further accurate assessment of the geothermal potential and ultimately the implementation of the geothermal resource as a viable energy alternative for small localities or mining facilities isolated from the National Interconnected System due to their remote localization. • Compositional data of thermal fluids from the Cerro Blanco Caldera are reported. • Inputs of magmatic fluids from a degassing magma chamber into the hydrothermal aquifer are inferred. • Silica geothermometers indicates reservoir temperatures ≥135 °C. • The local geothermal gradient for the Cerro Blanco Caldera it would be around ∼104 °C/km. • The preliminary geothermal potential at Cerro Blanco Caldera has been evaluated with the Volume Method, calculating up to E = 11.4*1018 J. [ABSTRACT FROM AUTHOR]

An exhaustive review of the available data related to the reservoir of the volcano-hosted Copahue geothermal system is presented. Reservoir interpretation to date suggests a vapor-dominated nature. However, the review provided reveals the limitations of this model, regarding the transition from shallow argillic to deep propylitic alteration zones, gas geothermometers calibrated to near-neutral pH environment, production tests, and low recharge of the feed zone, among the other features. We propose that a layered model with a shallow vapor zone above a fluid pressurized reservoir better accounts for the known features of the geothermal reservoir. Temperature profiles define the 800-m-thick upper thermal boundary that includes the impermeable clay cap. An argillic alteration layer (smectite + chlorite + illite + kaolinite) with low electric resistivity response, consistent with the presence of smectite, composes the clay cap. A shallow steam cap develops immediately below the impermeable layer. This vapor zone has 200-215 °C, low seismic activity, and high electrical resistivity, and is highlighted by the isothermal segment of the well logs. The bottom part of the reservoir is subjected to controversy because of the lack of direct measurements. The deep liquid-dominated reservoir has a temperature of ~ 280 °C, develops below 1500 m depth under near-neutral pH condition, and probably has a pervasive propylitic alteration, and wairakite + laumontite + chlorite + epidote + prehnite + actinolite is the likely mineral assemblage. Pressure collapse might trigger the development of the shallow steam cap during deflation-inflation volcanic cycles or Pleistocene-to-recent tectonic deformation. This work points out the main weak points of the previous conceptual model, providing an alternative one based on the first comprehensive compilation of data of the Copahue reservoir. Further research, including a deep exploration drilling stage, is required to establish the physicochemical reservoir state precisely and to validate the proposed layered model. [ABSTRACT FROM AUTHOR]

The village of Copahue (Neuquén Province, Argentina) is located in the Andean range, on one of the largest geothermal fields in the country: the Caviahue – Copahue Volcanic Complex (CCVC). Copahue village was conceived and developed as a touristic destination centered on thermal baths and wellness activities. Currently, it receives more than 18,000 visitors per year.Fluid emissions in the CCVC are fed by a hydrothermal reservoir located at 800 m depth, mostly recharged by meteoric water and heated by a magma chamber, located at ~5 km depth. Thermal fluids in Copahue are discharged as fumaroles, diffuse degassing sites, boiling and bubbling pools. Diffuse emissions silently emit more than 100 tons of CO2 per day over the entire area of this town (~0.5 km2). Diffuse CO2 degassing anomalies indicate a strong structural control, with gas rising through fault planes and areas of high structural damage.Recently, members of the community expressed their concern about the increasing presence of fluid discharges nearby and under the foundations of commercial, residential and public buildings. The discharge of these thermal fluids is causing severe damage to buildings and infrastructure, and it constitutes a potential threat for human health. Considering this scenario, the aims of this work are: (i) to identify areas within the town of high fluid flow, (ii) to generate thermal emissions hazard maps and (iii) to assess the impact of volcanic gases on people as well as physical damage to buildings, caused by the thermal fluid discharges. The identification of areas with high fluid flow and the elaboration of hazard maps was carried out by combining multiple map layers (CO2 flux, soil temperature and urban maps) and sets of data points (point-based thermal emissions and damaged buildings within the urban area). The assessment of the physical damage on people and assets was evaluated by performing a visual recognition of the various impacts of hydrothermal gases on buildings, and by collecting audiovisual material along with anecdotal information provided by the Copahue community.The combination of the multiple map layers reveals two main areas of high CO2 release within the village of Copahue, located in the center and in the southern portion of the village. The overlaying of data points on the map layers shows that the damaged buildings are located within the southern-most CO2 diffuse degassing and thermal anomaly area.Numerous buildings present problems caused by outpouring of vapor and gaseous chemicals on floors and walls, infiltrations of fluids in joints and overheated rooms, among other issues. The impact of these geothermal events on human health is yet to be assessed.The results of this work will raise awareness among decision makers and civil protection authorities, and will establish a framework for planning land-use, ultimately fostering a safer coexistence between the population the active volcanic - geothermal field. [ABSTRACT FROM AUTHOR]