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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. [ABSTRACT FROM AUTHOR]

• The study area is located in the region defined as Central Puna Energy Hub. • The gravity and magnetic of the area were conducted in an attempt to delineate geological structures controlling the circulation of the fluids and estimate the geothermal field extent. • The low density and susceptibility contrast can be related to a combination of high temperatures and steam versus liquid-filled pores and fractures. • 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. • 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. 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. [ABSTRACT FROM AUTHOR]

This work presents the first carbon dioxide diffuse degassing survey carried out in the Cerro Blanco Geothermal System (CBGS; Southern Puna plateau, NW Argentina) with the aim to estimate the thermal energy release. The survey was divided into (i) a prospecting stage of the degassing sites within the CBGS and (ii) mapping of the selected diffuse degassing sites. The purpose of the prospecting stage was to elaborate two transects, crosscutting the nested caldera of Cerro Blanco Volcanic Complex (CBVC) and Los Hornitos thermal site, both belonging to CBGS. More than 60 soil diffuse CO 2 flux and soil temperature measurements were carried out in the 16-km and 1-km long transects. Significant soil diffuse emissions were only found within the Cerro Blanco caldera, where a detailed mapping of CO 2 flux was produced. In this site, named CBa, a single diffuse degassing structure releasing 22.44 kg d−1 of deep-sourced CO 2 into the atmosphere was identified. Any other geologic feature of the CBVC and Los Hornitos hydrothermal site presented very low CO 2 flux values. According to statistical and geochemical analyses, soil diffuse CO 2 degassing is fed by a deep-seated (hydrothermal) and a soil respiration source, which mix each other at different degree. The thermal energy release associated with the diffuse degassing process at CBa is estimated to be ~2.4 kJ/s. This low magnitude thermal energy release is probably a consequence of an efficient cap-rock that likely buffer the surficial expressions of the geothermal resource potentially occurring at depth. • Cerro Blanco Geothermal System emits diffuse carbon dioxide through a single diffuse degassing structure. • The diffuse emission and the thermal is significantly low if compared with other volcanic and geothermal Andean areas. • Background CO 2 fluxes can be partitioned into biotic and abiotic components. [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]