New conceptual model for the Tocomar geothermal system (Central Puna, NW Argentina): insights from geological, structural and geochemical data.

FILIPOVICH, RUBEN; INVERNIZZI, CHIARA; AHUMADA, MARIA FLORENCIA; CHIODI, AGOSTINA; BÁEZ, WALTER; ALDEGA, LUCA; BIGI, SABINA; CORRADO, SVEVA; CARICCHI, CHIARA; DE ASTIS, GIANFILIPPO; DE BENEDETTI, ARNALDO; GROPELLI, GIANLUCA; NORINI, GIANLUCA; TAVIANI, SARA; TASSI, FRANCO; VIRAMONTE, JOSE GERMAN; GIORDANO, GUIDO

Catania

Congreso; Geosciences for the environment, natural hazard and cultural heritage; 2018

Società Geologica Italiana

geothermal exploration since these schemes are by farthe most effective cost-benefit tool. While analogue models of geothermalfields provide an overall picture of reservoirs, they do not help planningexploration programs as each area of geothermal interest is a function ofsite-specific variables. Thus, reconstructing  stratigraphic andstructural framework is fundamental for i) understanding the relationship amongcap rocks, reservoirs and fluid circulation, ii) geothermal potential, and iii)planning  resource exploitation. Limited geothermal resource assessment inArgentina is based on weak exploration approaches as anomaly hunting or anomalystacking, more than on realistic conceptual models generated from detailedgeological information. In this sense, a new conceptual model for the TocomarGeothermal System (TGS) based on geological, structural and geochemical dataalong with the available geophysical data is presented. The TGS is located inthe Central Puna (Central Andes, NW Argentina), related to the 0.57 Ma Tocomarvolcanic center (TVC) emplaced in a small extensional basin ?Tocomar basin(TB)? linked to the active NW?SE trans-Andean tectonic lineament known asCalama?Olacapato?Toro (COT) fault system. The pre-basin succession is made oflow-grade metamorphic and sedimentary lower Paleozoic rocks, Cretaceouscontinental rift-related deposits and ignimbrites from the Aguas CalientesCaldera (10-17 Ma). The basin infill consists of a thick alluvial depositformed by polymictic conglomerates and sandstones that evolve upwards toseveral pyroclastic deposits.The updated conceptual model for the TGS consists of aheat source related to the 0.57 Ma rhyolitic magmatic activity of the TVC. Thegeothermal reservoir has a NW-SE geometry elongated along the COT-likeChorrillos fault, with a minimum area of ca. 6 km2. The averagedepth of the top of the reservoir is 1,000-1,400 mbgs, probably hosted inCretaceous sedimentary rocks. The primary permeability is enhanced by intensedeformation along the COT. Both the interbedded fine-grained Cretaceous faciesand a hydrothermal clay cap (argillic alteration) act as seal rocks. Hotsprings occur in association with deep N30-N60 fractures related to the COT.They show a Na-Cl composition, with pH values of 5.84 to 6.87, and outlettemperatures ranging from 30.3°C to 70.2°C. Temperature estimation using theNA-K geothermometer indicates reservoir temperatures of 184-230°C. Estimatedlocal geothermal gradient for the TB is ~150 °C/km and the minimum stored heatin the geothermal reservoir is of about 3.21x1015 kJ.