The Latin American Association of Volcanology (Asociación Latinoamericana de Volcanología, ALVO), founded in 2010 in Manizales, Colombia, is a non-profit organization dedicated to strengthening volcanology in the region. With more than 2000 members across 26 countries, ALVO is a community-driven association that encompasses a wide diversity of institutions and disciplines, and has progressively become a key facilitator of initiatives aimed at reducing volcanic risk in Latin America. This article provides an updated overview of the association, examining its historical development, organizational structure, and evolution over time. We review the main initiatives developed and supported by the association, including training and mobility programs, scientific meetings, and special issues in peer-reviewed journals, as well as ALVO's efforts to disseminate information and regional volcano science through multiple channels (e.g., social media, website, Gaceta ALVO newsletter). Finally, we offer reflections that frame ALVO's work in a global context and outline future directions that the association aims to explore. The experience of ALVO highlights the role that scientific networks in the Global South can play in strengthening capacity development, fostering collaboration, and addressing shared challenges in volcanic risk reduction. Abstract La Asociación Latinoamericana de Volcanología (ALVO), fundada en 2010 en Manizales, Colombia, es una organización sin fines de lucro dedicada a fortalecer la volcanología en la región. Con más de 2000 miembros en 26 países, ALVO es una asociación gestionada por la propia comunidad que alberga una amplia diversidad de instituciones y disciplinas, y que se ha convertido progresivamente en un facilitador clave de iniciativas orientadas a la reducción del riesgo volcánico en América Latina. Este artículo presenta una actualización detallada de la asociación, examinando su desarrollo histórico, su estructura organizativa y su evolución a lo largo del tiempo. Se describen las principales iniciativas desarrolladas y apoyadas por la asociación, incluyendo programas de formación y movilidad, reuniones científicas y números especiales en revistas con revisión por pares, así como los esfuerzos de ALVO por difundir información y conocimiento volcanológico regional a través de múltiples canales (p. ej., redes sociales, sitio web, Gaceta ALVO). Finalmente, se comparten algunas reflexiones que sitúan el trabajo de ALVO en un contexto global y delinean posibles líneas de acción futura que la asociación busca explorar. La experiencia de ALVO pone de relieve el papel que las redes científicas en el Sur Global pueden desempeñar en el fortalecimiento de capacidades, la promoción de la colaboración y el abordaje de desafíos compartidos en la reducción del riesgo volcánico.

The Cordillera de San Buenaventura is a long-lived Neogene-to-Holocene multifaceted volcanic system located in the southern sector of the Altiplano Puna (NW Argentina). The erupted products span from mafic to high-SiO2 rhyolites, all of which are characterized through time from the same primary assemblage made up of Cpx-Opx-Bt-Hbl-Pl-San-Ol-Mag-Ilm. Recent studies highlighted a common line of descent mainly controlled by amphibole + plagioclase fractionation, and a transcrustal magmatic plumbing system comprising discrete magma storage zones. However, the existing characterization of the anatomy of the magmatic plumbing system derives mainly from inverse mineral-melt thermobarometry models applied to a limited number of the presumed “mineral-melt equilibrium pairs” identified through tests based on Mg-Fe partitioning between phases. In this short communication, we show how the signal of such tests could be misleading due to the multifaceted significance of the mineral-liquid equilibrium in a suprasolidus environment, and therefore how it is preferable the coupling with other inverse thermobarometry model based on the mineral chemistry only. Through this approach, we demonstrate here how the Cordillera the San Buenaventura is vertically distributed along the whole crust, but how major phenocryst phases (Cpx, Opx, Bt, Amp) probably crystallized/fractionated in very limited zones of the plumbing system and then travelled as crystal cargo in the ascending residual liquids.

At first, a brief history of the origins of volcanology, giving special attention to its development in Latin America, is presented. There follows a description of this process in Argentina as well as the impact of different volcanic eruptions that affected the Argentina territory in the last 100 years and the reaction of the population to these phenomena. It is remarked that the Andean Volcanic Chain hosts the highest volcanoes in the world and their eruptions have had global effects, such as Huaynaputina eruption in 1600. For the purpose of geological risk, it is pointed out that due to wind circulation, ashes are preferentially deposited towards to the east, affecting people's life in the foreland, as well as providing the long-term benefit of soil fertility. It is remarked that modern volcanology in Argentina began with the scientific studies carried out after the great eruption of Quizapu in 1932, with the pioneering work of E. Kittl. From then on, studies focused on petrological, geochemical and geochronological aspects. Around 1980, work began on large volcanic structures, such as Caldera del Galan, using satellite images, as well as the study of Antarctic volcanism. In the 1990s, with the eruptions of Hudson, Peteroa and Lascar volcanoes, the issue of volcanic risk became of interest again. Therefore, numerous scientific teams, which have been working since then throughout the country on the composition and effects of volcanism, are described. This culminated with the enactment of Law 27.287 in 2016, which created the National System of Integrated Risk Management and Civil Protection (SINAGIR). Finally, the role of different Argentine volcanologists in national and international institutions is highlighted.

The long-lived Neogene-Holocene Cordillera de San Buenaventura (CSB) volcanic system in Southern Puna (NW Argentina), represents a valuable archive of information for the understanding of eruptive behaviors and magma dynamics and to decipher the anatomy of the trans-crustal plumbing system from the depth of the reservoir to the subsurface magmatic plexus. The CSB is characterized by cyclic mafic-intermediate eruptive styles, spanning from lava flows to caldera-forming events with a nearly continuous compositional series of erupted material from basaltic trachyandesites to high-silica rhyolites. For this reason, the CSB has recently been the focus of petrological studies through a general approach integrating textural observation and conventional thermobarometric models. However, due to intrinsic limits of the formulations, conventional models are not able to define either the P-T conditions of the solidus reaction nor the extent of the pre-eruptive supra-solidus environment. Moreover, conventional models cannot reconstruct either the amount or composition of the residual liquids at given pre-eruptive P-T values. Consequently, the published reconstructions and conceptual models that focus on the pre-eruptive state of the magmatic system are poorly constrained. To address this, the application of forward modelling thermobarometry based on the P-T-X pseudosection methods could represent an effective approach to better-constrain the pre-eruptive supra-solidus environment, to independently assess the effectiveness of thermobaric estimates from conventional modelling, and to evaluate if the modelled raw whole-rock composition is representative or not of the relic pre-eruptive magmatic equilibrium.

The exploration of novel geothermal systems, particularly those promising for electrical power generation, plays a fundamental role in incorporating new renewable sources into the energy matrix. Geothermal systems associated with volcanic calderas are considered ideal targets for exploration. This study focuses on the geochemical features of fluids from the Cerro Gal & aacute;n hydrothermal system, which is hosted within a major resurgent caldera with >3.5 Myr of magmatic evolution situated on the Southern Puna (Central Volcanic Zone of the Andes, NW Argentina). The main aim is constructing the first geochemical conceptual model and provide information on the geothermal potential of this interesting resource. The main hydrothermal reservoir consists of a NaCl aquifer with estimated temperatures up to 187 degrees C at depth. This reservoir is likely hosted within the fractured pre-caldera basement rocks, mainly including Miocene-Pliocene volcanic rocks and Proterozoic-Cambrian igneous and metamorphic rocks. The confinement of the deep reservoir is attributed to the deposits of the Toconquis Group and Cueva Negra Ignimbrite, along with the basal section of the Cerro Gal & aacute;n Ignimbrite, which exhibit low permeability due to hydrothermal alteration. The presence of a phreatic explosion crater near one of the hot spring-rich areas is likely indicating past over-pressurization of the hydrothermal aquifer, resulting from efficient sealing. Furthermore, the absence of anomalous soil CO2 flux values on the top of the reservoir, except where the thermal spring discharges are located, can be explained by an effective cap-rock layer. Deep circulation of meteoric water, enriched with atmospheric gases, receives inputs of magmatic fluids (similar to 11% of primordial helium), leading to the development of the hydrothermal NaCl aquifer. However, this deep fluid contribution might be underestimated due to significant crustal assimilation (up to 50%) involved in the magma genesis of the Cerro Gal & aacute;n Volcanic Complex, a process which modifies the He isotopic signature of the magmatic endmember. The hot springs, characterized by high flow rate (up to 459 m(3)/h) are positioned at the intersection between the caldera margins and the NNE-SSW oriented tectonic structures, suggesting favorable permeability conditions. The preliminary geothermal gradient for the Cerro Gal & aacute;n area is estimated at around 98-101 degrees C/km. Such a high gradient can be attributed to the considerable heat flux generated by the transcrustal plumbing system of the Cerro Gal & aacute;n caldera, which includes the shallow crystal mush reservoir (<4 km depth). The preliminary geothermal potential of this giant caldera was performed using the volumetric method along with Monte Carlo simulations. The results indicate a probable power production capacity of 2.09 MWe and 10.85 MWe at 90 and 50% confidence level, respectively. The results presented in this work constitute a foundational knowledge base to promote a more advanced exploration phase for the geothermal resource. Additionally to the local energy demand, lithium and other metal mining operations, which are operating independently from the National Interconnected System, could potentially be interested in power generation through binary cycles.

Here, we present new gravity and airborne magnetic geophysical data from a preliminary exploration along the western sector of the NW-striking Calama-Olacapato-Toro fault system. This area is located in the back-arc region of the Central Andes (NW, Argentina) and is considered as a high potential geothermal area within the Central Puna Energy Hub. The gravity and magnetic modelling was carried out with the aim of delineating geological structures that control the geothermal manifestations and estimate the geothermal field extent. Gravity data were separated into regional and residual components. Then, a 2-D gravity and magnetic modelling was carried out through the 2-D GM-SYS -Oasis Montaj software in order to build an inversion model that adjusts the residual gravimetric and magnetic anomalies observed on the surface. The resultant model was also fitted taking into consideration previous electrical resistivity studies, surface manifestations, geology, and geological structures. Bouguer anomalies are negative in the range of-411 to-304 mGal, while magnetic anomalies have a range of -127 to 15 nT, in the central part of the study area. Hot springs correlate with low residual Bouguer and magnetic anomalies located on the Calama-Olacapato-Toro lineament, and are related to the alteration zone and the main damage zone. Gravity and magnetic inversion show low density and susceptibility contrast of rocks associated with volcano-sedimentary rocks filling a volcano-tectonic depression, limited by the Antuco and Pompeya N-S thrust faults, westward and eastward respectively. The low density and susceptibility contrast can be related to a combination of high temperatures and steam versus liquid-filled pores and fractures. Hence, this geological conceptual model based on the 2-D forward modelling of geophysical data, allows better knowledge and comprehension of hydrothermal fluids circulation in the middle of the Central Puna, in northwest Argentina.

We applied a new thermobarometric model based solely on biotite composition to the trachyandesitic to rhyolitic volcanic rocks of the Cordillera de San Buenaventura, a long-lived magma plumbing system (spanning from the Late Miocene to the Holocene) in the Southern Puna plateau (Central Volcanic Zone of the Andean Cordillera). Within these rocks, biotite is a widespread mineral phase found in association with amphibole, as either glomerocrysts, mutual inclusions, or free phenocrysts. This allowed us to compare the biotite-only model with other thermobarometric estimates that rely on amphibole, mineral-melt, and mineral-mineral composition. Our goal was to determine the conditions of formation for biotite and its petrogenetic significance in the evolution of the Cordillera de San Buenaventura magma system. The results indicate that biotite crystallization occurred mainly at middle-to upper-crustal depths (2.1-5.1 kbar) with temperatures below 1000 degrees C (763-919 degrees C). The biotite-only T-P estimates for individual lithologies are consistent with those obtained using the amphibole-only model, and this is particularly true for the thermometer. Furthermore, our findings align with the existing petrogenetic models, which suggest extensive fractional crystallization, and with the analyses of mineral textures, that indicates events of magma replenishment. Therefore, our results support the validity of the biotiteonly model and its ability to elucidate magmatic processes, including magma differentiation via fractional crystallization, magma ascent and cooling, and magma replenishment and/or mixing events.

Arc magmatism plays a key-role in the growth and differentiation of continental crust. In particular, the prolonged magmatic flux events control the genesis of deep crustal hot zones where magma accumulation and fractionation favour the continental arc crust evolution and geochemical stratification. In this view long-lived magmatic systems located in arc domains, with their erupted products spanning from basalts to rhyolites are formidable archive for the understanding the evolution of transcrustal magmatic plumbing systems and the construction of a stratified continental crust. This study focuses on the long-lived (ca. 9 Ma) Miocene-Holocene Cordillera de San Buenaventura volcanic system in the Southern Puna Plateau (NW Argentina), a unique natural laboratory where exploring the building up of MASH-zones (or deep crustal 'hot zones') and related sustained volcanism. Synthesis of new and published data, together with new thermobarometry and fractional crystallization modelling, indicates a cyclic scenario with mantle melts undergoing fractional crystallization dominated incipient and waning stages alternate to major mafic magma recharge events during the building up phase of the MASH-zone. This magmatic scenario is also discussed in the light of the coeval geodynamic framework dominated by the subduction of the Nazca plate and the eastward migration of the frontal arc magmatism.

The Tocomar Geothermal System is located in the Puna Plateau (NW Argentina), within the Central Puna Energy Hub, and is considered one of the most promising places to harness potential alternative of power and heat sources in the Central Andean Volcanic Zone (16-28 degrees S). It is related to the Calama-Olacapato-Toro lineament and to the Quaternary Tocomar volcanic centre. Moreover, it is surrounded by active and fossil geothermal manifestations, like hot-springs, travertines and siliceous sinter deposits. Despite some geological studies in the area, no geophysical investigations have targeted the geothermal fields along the Central Puna. In this work we present a 3-D inversion of audio-magnetotelluric data around the Tocomar Geothermal System. These data was obtained in the frequency range of 1000-0.1 Hz to map the main elements of the geothermal system (clay cap and potential reservoir) at depths of approximately 1000 m. To achieve this goal, previous geoelectrical studies, the local geology and the trend of the main structures were also considered. For the 3-D inversion process the ModEM code was used. The model shows a low-resistivity layer (less than 10 Omega m) at least 300 m thick, at a depth of about 200-500 m, aligned with both the strike of the Calama-Olacapato-Toro lineament and the local superficial geothermal manifestations (hot-springs and hydrothermally altered rocks). This low-resistivity layer is linked with the clay cap at the shallow depth of the geothermal reservoir. At depths greater than 800 m, a gradual increase in resistivity is observed related to a potential reservoir within the fractured Ordovician basement. The final 3-D resistivity model highly correlates with the conceptual models of high-temperature volcanic geothermal systems.

Methodology, calculations, and data analysis.

Rhyolitic volcanism can provide important information about the mechanisms by which highly-evolved crystal-poor melts can be extracted from silicic crystal-mush reservoirs. In the Altiplano-Puna plateau (Central Andes), rhyolites are volumetrically less abundant than the high-volume, crystal-rich intermediate products emitted during the ignimbritic flare-up (ca. 10–1 Ma), and their geological and temporal relation with the widespread, upper crustal, dacitic mush systems is not well constrained. We studied the isotopic (UPb ages), trace (U, Th, Hf, Y, Ti, P) and rare earth element compositions of zircon contained in the rhyolitic products of the Ramadas Volcanic Centre (late Miocene), which erupted extremely-aphyric, garnet-bearing tubular pumice during a single Plinian event (Corte Blanco Tuff; northern Puna plateau). Results reveal a complex pre-eruptive magmatic history characterized by variable crystallization conditions existing at different times within an upper-crustal crystal-mush reservoir. The unmixing model applied to magmatic zircon sharing textural and geochemical features (oscillatory texture, Th/U = 0.2–0.6; Eu/Eu* = 0.1–0.7) indicates the existence of at least two mush-related crystallization events, which are separated by a protracted hiatus (ca. 2 Ma), and are supported by independent isotopic ages. An episode of zircon crystallization (average disequilibrium-corrected 206Pb/238U age of 9.06 ± 0.19 Ma) coincides with the ages determined for accessory phases associated with garnet in pumice samples (9.163 ± 0.037 Ma, UPb age determination on zircon; 8.70 ± 0.23 Ma, U-Th-Pb age determination on monazite). A further zircon crystallization event is recorded at ca. 6.64 ± 0.12 Ma, which is concordant with published radiometric ages dating the eruption at 6.3 ± 0.3 Ma (average 40Ar/39Ar age of glass shards from distal locations) and at 6.63 ± 0.28 Ma (fission track age of proximal obsidian). The existence of a late-stage to hydrothermal crystallization event is evident from another zircon population with low Th/U ratios (< 0.1) and a 206Pb/238U age of 6.514 ± 0.058 Ma, which crystallized in cold and highly-evolved parts of the reservoir resulting in negative Eu/Eu* and Ti depletion in zircon before these crystals were recycled into the erupting magma. The extreme aphyric character of the rhyolitic products and the nearly-complete lack of phenocrysts and glomerocrysts despite their evolved composition indicate that the Plinian eruption was preceded by effective extraction of crystal-poor melts from the mush zone, during which only micrometric antecrystic minerals (≤ 200 μm) were incorporated. Gas filter-pressing, combined with a compressional local stress field, likely contributed to melt-crystal separation, which was favoured by high volatile contents (H2Omelt 3–5 wt%) and shallow emplacement levels (< 10 km). Finally, the distribution of the U-Pb ages of zircon antecrysts suggests a correlation between the evolution of the Ramadas magmatic system and the fluctuating pattern characterizing the Altiplano-Puna Volcanic Complex flare-up activity, highlighting a possible geological and temporal connection between rhyolitic volcanism and the widespread dacitic mush systems in this sector of the Puna plateau.

The Pleistocene-Holocene Cerro Blanco Volcanic Complex (CBVC), one of the youngest caldera complexes in the Southern Central Andes, is the source of possibly one of largest Holocene eruptions on Earth, the 4.2 ka, Cerro Blanco eruption. This caldera forming eruption is the younger of two major explosive events from the CBVC. Previous work has estimated the range from VEI 6 to 7, yet to date there is no detailed study of the stratigraphy and volcanology of the proximal deposits and dynamics of the Cerro Blanco eruption. Here we present the first detailed analysis of the eruptive products of the Holocene Cerro Blanco eruption that reveal the eruptive sequence highlighting the flow dynamics of the related pyroclastic density currents (PDCs). The PDCs were mainly inertia-dominated, however, channelization of parental PDCs into deep valleys resulted in the flow transformation to forced convection-dominated flows. In addition, topographic constriction in valleys enhanced the sedimentation rate producing regressive bed forms and ultimately the avulsion of the main path of the PDCs resulting in flooding of secondary valleys. A model is presented whereby simultaneous convective and collapsing eruptive column dynamics were established and sustained throughout the eruption. Towards its end, instabilities of the column occurred in response to the climax of a protracted incremental caldera collapse. This eruptive sequence is similar to those observed in well-documented small collapse calderas. An important unresolved issue for the CB eruption is it volume. The currently estimated volume of 83 km(3) (DRE) by Femando-Turiel et al. (2019) is inconsistent with the size of the Cerro Blanco caldera and to date the over thickening of the distal ash by local rework is poor assessed. Further work is needed to fully evaluate this mismatch and accurately estimate the volume of this important Holocene eruption.

Cerro Blanco Volcanic Complex (CBVC) is one of the youngest caldera complexes in the Southern Central Andes. Subsidence registered at CBVC has shown a slowdown in deformation velocity since 1992 (2.6 cm/yr) to 2010 (0.87 cm/yr). We update the deformation state of this caldera system by processing DInSAR data between 2003 and 2020 and GPS as a complementary tool. Results showed a circular deformation pattern of about 12 km diameter related to subsidence centered at CBVC throughout the entire period under analysis. Deformation rate decreased from 1 cm/yr for 2003-2009 period (Envisat data) to 0.7 cm for the 2012-2020 period (COSMO-SkyMed and Sentinel-1 data). Rate values were confirmed with GPS measurements during 2004 and 2013-2015. Analytical inverse modelling was used to infer the main characteristic of the source responsible for the measured displacement. Best-fitting solution corresponded to a spherical source located between 9 and 14 km from the surface with a volume decrease of about 0.013 km(3)/yr for the entire period. We propose that a combination of magmatic and geothermal dynamic as the origin of the continuous and slow subsidence observed in the CBVC as a consequence of the last eruption that occurred ca. 4 ka ago.

The rhyolitic Campo de la Piedra Pomez ignimbrite crops out in the Southern Puna of NW Argentina and it is related to the youngest caldera-complex (Cerro Blanco caldera complex) of the Central Andes (73 - 4 kyr). The presence of rhyolitic pumice and mafic enclaves with different compositional and textural features, which variability can be observed within a single juvenile class (multiple-banded pumice), characterized these deposits. The enclaves are associated with hybrid (trachydacitic) pumice and sporadic remnants of rhyolitic material included in the trachydacite. To unravel the possible role of the mafic recharge as eruption trigger, the occurrence of mixing events and the mechanisms of enclave formation, we studied the enclaves and silicic pumice material (petrography, whole rock analyses, mineral and glass chemistry) to decipher the magmatic interaction between the host rhyolitic melt and the enclave-forming magmas. Results allowed recognizing two main mafic recharge events. During the first episode, the mixing of the rhyolite with the injecting magma generated sporadic dacitic products. Mixing was favored by the relatively high temperature of both the injecting magma and the rhyolitic melt, as revealed by clinopyroxene-liquid, plagioclase-liquid and two-pyroxene geothermometers (>= 875 degrees C). The second mafic recharge event involved magma that remained confined at the bottom of the reservoir and crystallized with differential cooling rates. At the interface with the silicic host, the magma generated sub-millimetric mineral assemblage in which amphibole has normally zoned rims. Differently, within the body of the mafic intrusion, crystallization proceeded with a lower undercooling degree, generating a coarser crystalline assemblage in which amphibole crystals do not display zoning. The convergence of different thermobarometric models (applied to the rhyolite, trachydacite, and enclaves) suggests that these magmas interacted at a crustal depth of ca. 2.7 Kbar, here interpreted as the base of the Campo de la Piedra Pornez rhyolitic reservoir (similar to 10 Km b.s.l.). A time lapse occurred between the last mafic recharge and the eruptive events, where the felsic magma cooled down to similar to 800 degrees C and the amphibole re-equilibration took place.

This paper presents a detailed geological map at the 1:20,000 scale of the Tocomar basin in the Central Puna (north-western Argentina), which extends over an area of about 80 km2 and displays the spatial distribution of the Quaternary deposits and the structures that cover the Ordovician basement and the Tertiary sedimentary and volcanic units. The new dataset includes litho-facies descriptions, stratigraphic and structural data and new 234U/230Th ages for travertine rocks. The new reconstructed stratigraphic framework, along with the structural analysis, has revealed the complex evolution of a small extensional basin including a period of prolonged volcanic activity with different eruptive centres and styles. The geological map improves the knowledge of the geology of the Tocomar basin and the local interplay between orogen-parallel thrusts and orogen-oblique fault systems. This contribution represents a fundamental support for in depth research and also for encouraging geothermal exploration and exploitation in the Puna Plateau region.

ATLAS-1.0 (ATmospheric LAgrangian diSpersion) is a new atmospheric dispersion and sedimentation Lagrangian model tailored to volcanic tephra/ash. The model solves the Advection–Diffusion–Sedimentation equation across multiple scales (from regional to global) and can be driven off-line by different numerical weather prediction models in combination. For example, meteorological data from the mesoscale Weather Research Forecast (WRF) model can be combined with data from the Global Forecast System (GFS) so that ATLAS automatically selects the highest resolution data available in any part of the computational domain. ATLAS can be used in forward mode to forecast ash dispersal from a volcano (or from extended sources) or in backward mode to integrate trajectories backwards in time and constrain unknown source term characteristics. Multiple source terms can be defined, e.g. to simulate several eruption phases with different granulometric characteristics on a single model execution. We validate the implementation of the model using the 2011 Cordón Caulle and the 2015 Calbuco eruptions and compare the results with previous simulations performed with the FALL3D model. The code has been designed from scratch to facilitate future parallelization, inclusion of ash resuspension schemes, and ensemble-based probabilistic forecast assimilating data from satellite retrievals.

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+-Cl-(HCO3)(-) composition with estimated temperatures >= 135 degrees 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 (delta O-18 and delta D) 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 hydro thermal 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 H2S, CH4 and H-2. Considering the high geothermal gradient of this area (similar to 104 degrees C/km) and the relatively high fraction of mantle He (similar to 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*10(18) 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.

One of the most outstanding features of the Southern Puna is the occurrence of a widespread monogenetic mafic volcanism during Neogene-Quaternary. Despite a number of published papers focusing on the petrogenesis of this back-arc volcanism, works aimed on its physical volcanology are scarce. This paper presents the characterization of the monogenetic mafic volcanism in the Pasto Ventura region, located in the southeast edge of the Southern Puna. The results show that in the Pasto Ventura region there is a low density of small-volume eruptive centers aligned with regional tectonic structures and a significant variability in eruptive styles (effusive, strombolian, hawaiian, violent strombolian and phreatomagmatic) and typology of volcanic structures (domes, scoria cones, maars and tuff rings). The first of these features is explained by a limited magma flow rate from the deep source and the use of favorable tectonic structures (oriented obliquely to the regional maximum compression direction) for the ascent of small volumes of magma through the upper crust. The variability of eruptive styles responds to the complex interaction of different endogenous and exogenous factors. The occurrence of effusive or explosive eruptions depends on the differences in magma ascent rates including periods of stagnation in the upper crust, which in turn control the efficiency of degassing and ultimately the occurrence of fragmentation. On the other hand, the more humid local climatic conditions (~150 mm/year), which are related to the geographical position of the Pasto Ventura region in the eastern edge of the Puna, favor the occurrence of phreatomagmatic activity. Phreatomagmatic activity also varies according to the topography, substrate typology and depth at which water-magma interaction occurs.

One of the most outstanding features of the Southern Puna is the occurrence of a widespread monogenetic mafic volcanism during Neogene-Quaternary. Despite a number of published papers focusing on the petrogenesis of this back-arc volcanism, works aimed on its physical volcanology are scarce. This paper presents the characterization of the monogenetic mafic volcanism in the Pasto Ventura region, located in the southeast edge of the Southern Puna. The results show that in the Pasto Ventura region there is a low density of small-volume eruptive centers aligned with regional tectonic structures and a significant variability in eruptive styles (effusive, strombolian, hawaiian, violent strombolian and phreatomagmatic) and typology of volcanic structures (domes, scoria cones, maars and tuff rings). The first of these features is explained by a limited magma flow rate from the deep source and the use of favorable tectonic structures (oriented obliquely to the regional maximum compression direction) for the ascent of small volumes of magma through the upper crust. The variability of eruptive styles responds to the complex interaction of different endogenous and exogenous factors. The occurrence of effusive or explosive eruptions depends on the differences in magma ascent rates including periods of stagnation in the upper crust, which in turn control the efficiency of degassing and ultimately the occurrence of fragmentation. On the other hand, the more humid local climatic conditions (similar to 150 mm/year), which are related to the geographical position of the Pasto Ventura region in the eastern edge of the Puna, favor the occurrence of phreatomagmatic activity. Phreatomagmatic activity also varies according to the topography, substrate typology and depth at which water-magma interaction occurs.

The Ramadas Volcanic Center on the eastern margin of the central Andean Puna plateau along the Olacapato-El Toro lineament in Argentina erupted a rare strongly peraluminous Mn-rich garnet-bearing rhyolitic tuff in the late Miocene. The voluminous ashes from this eruption, which are distinctive in having euhedral spessartine almandine garnets (Alm(70-72)Sps(22-26)Grs(2-4)Prp(0.5-1)) as their only phenocryst, are widely dispersed in the Andean foreland. Among these tuffs are those in the Guanaco Formation foreland basin sediments along the Xibi-Xibi and Los Alisos rivers in the Rio Grande de Jujuy basin and the Metan Valley, some 100-200 km east of the Ramada Volcanic Center. The co-occurrence of tubular to cellular pumice fragments and blocky glass shards in an ash matrix in these tuffs is interpreted as indicating that they erupted in an initial vent-opening event with pulsating pyroclastic surges at the initiation of the strong Plinian eruption of the Ramada Volcanic Center. New Ar/Ar ages from the Guanaco Fm. glass shards agree with fossil ages in placing the eruption at similar to 6.3 +/- 0.3 Ma. A number of distinctive chemical, isotopic and mineralogical features including Mg-rich biotite and Mg-hastingsite xenocrysts of the Guanaco Formation and Ramadas Volcanic Center tuffs are consistent with the melt having been derived by extensive crystallization of a mantle-derived mafic shoshonitic series magma contaminated by assimilation/dehydration melts of metapelitic sediment and the Puna crust. Distinctive chemical features include whole rock SiO2 contents of similar to 75-76% wt%; A/CNK indices >1.2; low Ca, Mg, Ti, and Fe concentrations; steep REE patterns with extreme negative Eu anomalies; low Ba, Sr, LREE and high Cs, Rb, U concentrations; and recalculated initial ratios of Sr-87/Sr-86 at similar to 0.7119 and Nd-143/Nd-144 of similar to 0.5123 at 6.3 Ma. The erupted magma has a transitional chemical character between those of the similar to 11 Ma Mn-rich garnet-bearing Coyaguayma ignimbrites to the north and the similar to 6 Ma Cerro Galan ignimbrites to the south. Unlike these crystal-rich ignimbrites, the Ramadas tuff records the extraction of an extensively fractioned melt from a plagioclase, K-feldspar, quartz and biotite-bearing mush with accessory titanomagnetite and apatite. In line with existing experimental studies on Mn-rich gamets and comparisons with the Coyaguayma ignimbrite, pre-eruption crystallization of the rhyolite segregated from the mush likely occurred at similar to 800 degrees to 720 degrees C at a depth of no <15-12 km as the H2O content increased from similar to 4-5% to similar to 7.5%. Mn-rich garnet was the only phase to be crystallized in the melt extracted from the mush before the eruption, whose rapid rise was facilitated by extension along the Olacapato-El Toro lineament. (C) 2018 Elsevier B.V. All rights reserved.