Examinando por Autor "Bini, Giulio"

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The Geothermal Resource in the Guanacaste Region (Costa Rica) New Hints From the Geochemistry of Naturally Discharging Fluids
(Frontiers, 2018-06-05) Tassi, Franco; Vaselli, Orlando; Bini, Giulio; Capecchiacci, Francesco; De Moor, J. Marteen; Pecoraino, Giovannella; Venturi, Stefania
The Guanacaste Geothermal Province (GGP) encompasses the three major volcanoes of northern Costa Rica, namely from NW to SE: Rincón de la Vieja, Miravalles, and Tenorio. The dominant occurrence of (i) SO4-rich acidic fluids at Rincón de la Vieja, (ii) Cl-rich mature fluids at Miravalles, and (iii) HCO−3-rich and low-temperature fluids at Tenorio was previously interpreted as due to a north-to-south general flow of thermal waters and a magmatic gas upwelling mostly centered at Rincón de la Vieja, whereas Miravalles volcano was regarded as fed by a typical geothermal reservoir consistingof a highly saline Na-Cl aquifer. The uniformity in chemical and isotopic (R/Ra andδ 34S) compositions of the neutral Cl-rich waters suggested to state that all the thermal discharges in the GGP are linked at depth to a single, regional geothermal system. In thisscenario, the thermal manifestations related to Tenorio volcano were regarded as a distal and diluted fluid outflow. In this study, a new gas geochemical dataset, including both chemical and isotopic (δ 13C-CO2 and R/Ra) parameters of fluid discharges from the three volcanoes, is presented and discussed. Particular attention was devoted to the Tenorio thermal manifestations, since they were poorly studied in the past because this area has been considered of low geothermal potential. The aim is to provide insights into the magmatic-hydrothermal fluid circulation and to verify the spatial distribution of the heat fluid source feeding the fluid manifestations. According to this new dataset, CO2, i.e., the most abundant dry gas in the fluid manifestations, is mostly produced by limestone, whereas the mantle CO2 contribution is ≤3.3%. Strongly acidic gas compounds from magma degassing were absent in the discharged fluids, being scrubbed by secondary processes related to prolonged fluid-rock interactions and mixing with shallow aquifers. Our results only partially confirm the previously depicted model, because the geochemical and isotopic features (e.g., relatively high concentrations of temperature-dependent gases and high R/Ra values) shown by fluids seeping out from the southern sector of Tenorio volcano are more representative of medium-to-high enthalpy volcanic systems than those typically occurring in distal areas. This implies that the geothermal potential in the south of the GGP is higher than previously thought.
The Last Eighteen Years (1998–2014) of Fumarolic Degassing at the Poás Volcano (Costa Rica) and Renewal Activity
(Springer, 2019) Vaselli, Orlando; Tassi, Franco; Fischer, Tobias P; Tardani, Daniele; Fernández, Erick; Martínez, María del Mar; Moor, Marteen de; Bini, Giulio
This chapter reviews the geochemical and isotopic data from the fumarolic gas discharges collected in a discontinuous mode from 1998 to 2014 at Poás volcano. During this period, the “Tico” volcano experienced a renewed phreatic activity that started in 2006 after a couple of decades of relative quiescence. In January 2009, a 6.2 Mw earthquake hit the village of Cinchona, which is located a 4 km to the east of Poás. As the phreatic activity kept evolving, the hyperacidic lake (“Laguna Caliente”) dried out and the high-temperature fumaroles that previously were likely entering the lake were revealed, though not accessible. The pyroclastic dome that formed in the early fifties was destroyed at the beginning of 2017 by several relatively small phreatomagmatic (strombolian and vulcanian type) small-size eruptions. The risk of sudden phreatic and phreato-magmatic events prevented the direct sampling of the fumaroles and as a consequence, no geochemical data were sampled in the last three years. Nevertheless, interesting hints were recorded by the gas geochemistry before the 2006 phreatic activity and the 2009 Cinchona seismic events, mainly based on the temporal variations of the H2S/SO2, H2/H2O, H2/Ar, CO/CO2, CH4/CO2 and HCl/HF ratios. However, in most cases the geochemical record is not complete since the gas discharging vents migrated or stopped their activity and new fumaroles formed up to the recent visual observations.