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Pyroclastic density currents (PDCs) are one of the most dangerous volcanic phenomena. The correct interpretation and mapping of PDC deposits in the volcano record is important to establish the eruptive style and play a fundamental role in hazard assessment and risk management. The Copahue volcano is an active intermediate volcano of the Southern Volcanic Zone of the Andes (Argentina-Chile) that presents fragmentary evidence of explosive activity during its evolution, with unusual minor PDC deposits. The recorded historic eruptions were mainly phreatomagmatic due to the presence of a crater lake. In this study, four key deposits previously interpreted as PDC products corresponding to different stages of the Copahue volcano evolution (Pleistocene, Holocene, and Historic times) are analyzed and this origin is discussed: (i) A Pleistocene reddish succession located in the northeast flank of the volcano formed by stretched bombs in a coherent lava is interpreted as clastogenic lavas; (ii) a series of proximal bedded volcaniclastics deposits of Pleistocene age are interpreted as redeposition of hyaloclastic fragments from syn-eruptive subglacial meltwater flows associated with subglacial eruptions; (iii) a distal Holocene deposit located ~12 km east of the active crater consist mainly in fine-sized clasts forming aggregates is reinterpreted as a sedimentary (lacustrine) deposit with volcaniclastic input; and, (iv) a historic whitish-grey clastic deposit located on the eastern flank is considered a product of a mixed avalanche generated during the 1992–1995 activity. Consequently, the PDC occurrence during the Copahue volcano evolution is less than previously thought. Large PDCs are unlikely in the future and their influence area would be reduced near the active crater as observed in recent eruptions. Flows triggered by the melting of snow/ice during volcanic activity and sudden drainage of the crater lake appear to be a more likely potential hazard that should be considered during risk assessment. • Reinterpretation of four deposits previously interpreted as PDCs-products. • Clastogenic lavas, subglacial flows, lacustrine deposits, and mixed avalanches. • Overestimation of the PDCs occurrence in the Copahue volcano. • Melting of snow and sudden drainage of the crater lake are potential hazard. [ABSTRACT FROM AUTHOR]

Establishing the factors that control the pathways of magma ascent is an important issue in the study of monogenic mafic volcanism since it provides information about the relationship between the source of the ascending magma and the regional and local tectonic frameworks. We have quantitatively analyzed the spatial distribution of the volcanic centers in the monogenic volcanic fields (MVFs) of the Southern Puna using Nearest-Neighbor Analysis to assess the degree of randomness between individual centers. We also performed alignment analysis which highlights the structural weaknesses that magmas use to ascend. We integrate these novel data with published structural, petrologic, and geophysical data to propose a source-to-surface model which explains the spatial distribution of monogenic mafic centers of the Southern Puna. We find that MVFs display two distinct spatial patterns related to different magmatic production rates. Specifically, in those areas where the magmatic production is long-lasting and relatively high, the magma exerts strain rates suffciently high to reactivate pre-exisiting discontinuities with random orientations with respect to the current local stress conditions. As a result the volcanic centers are arranged with a clustered spatial distribution. We define these as MVFs controlled by magmatism or high flux fields (MVFs-M). On the other hand, low magmatic production rates tend to produce areas where mafic centers display a Poisson distribution, because strain rates are only sufficient to reactivate pre-existing discontinuities that are nearly parallel to the maximum compressive stress. This latter group is defined as MVFs controlled by tectonism or low flux fields (MVFs-T). Available petrological and geophysical data indicate that both groups are fed by a complex lower crustal MASH zone where magma production is associated with lithospheric foundering and subduction-related mantle melting. Spatial distribution of the MVFs in the Southern Puna are also affected by the development of upper crustal magma storage zones. • Bivariate Gauss-kernels Density allow to define the number of MVF in the Southern Puna. • Nearest-Neighbor and Two-Azimuth quantitative methods reveal the spatial distribution of the MVFs. • Two main types of MVFs were identified: dominated by magmatism and dominated by tectonism. • Both groups are feed by a complex source related to lithospheric foundering and subduction. • Spatial distribution is later affected by lithospheric processes. [ABSTRACT FROM AUTHOR]

• An integrated conceptual model of the Tocomar Geothermal system is presented. • Compositional data of thermal fluids along with structural, Raman spectroscopic, and in-situ permeability data from the Tocomar Geothermal area are reported. • Cation geothermometers indicates reservoir temperatures up to 235 °C. • The structural control on flow pathways and fluids-rock interaction processes are discussed. • The geothermal electric potential is stochastically assessed. The Argentinean Andean region hosts a vast geothermal resource clustered by active magmatic and tectonic activity. One of the most studied geothermal areas is the Tuzgle-Tocomar geothermal system in Central Puna (NW Argentina). However, despite the existence of several studies since the 1970′s highlighting the geothermal potential of the area, only highly schematic and dissimilar conceptual models have been proposed for the Tocomar Geothermal System. This study presents new detailed geological-structural and hydrogeochemical data, together with in-situ permeability analysis of fault zones and Raman spectroscopic characterization of hydrothermal-alteration minerals. The electrical generating capacity has also been evaluated using the volumetric method and a stochastic approach. A new comprehensive conceptual model of the studied area was constructed highlighting the role of the Calama-Olacapato-El Toro (COT) fault-system in the circulation of hydrothermal fluids. The reservoir of the Tocomar geothermal system has a Na+-Clˉ(HCO 3)ˉ composition and an estimated temperature of ∼235 °C. Such a reservoir is hosted in fractured Ordovician rocks and controlled by the COT-like Chorrillos transpressive fault at 1000–1500 m depth b.g.l. The water isotopic data and hydrological features indicate a regional recharge beyond the Tocomar sub-basin boundaries (>5000 m a.s.l.). Additionally, the main hydrothermal reservoir receives inputs of magmatic fluids from the degassing of the intra-crustal rhyolitic magma chamber of the Tocomar volcanic center. The Monte Carlo simulations suggest that the Tocomar geothermal system has a probable power production capacity above 1.23 MWe (P90), 6.18 MWe (P50) and 11.67 MWe (P10) at different confidence levels. All calculations were biased towards minimum values, thus a tighter definition of the resource size and fracture porosity would significantly impact on the predictions. Notwithstanding, the strategic position of the Tocomar geothermal field encourages move forward towards more in-depth exploration phases. [ABSTRACT FROM AUTHOR]