GNGTS 2013 - Atti del 32° Convegno Nazionale

A first geochemical survey was conducted in May 2012, in the area of Lamezia Terme (Calabria) for a total of 48 groundwaters sampled (Fig. 1) and then, in July 2012 the area of Contursi Terme (Campania) with a total of 24 sites (Fig. 1). During this time, new geochemical data on groundwater were acquired, interpreted and modelled. These data provide an overview of the possible use of geothermal potential in the studied areas; in order to obtain useful information, thermal and cold waters were sampled in the last year. Methods. Physical parameters (temperature, pH, Eh and electrical conductivity) and alkalinity (titration with 0.05 N HCl) were determined in situ. Water samples were filtered (0.45 µm) and stored in high-density polyethylene flacons for laboratory analysis. Major anions and cations were analyzed by ion-chromatography (analytical error was < 5); minor and trace elements were determined by ICP–MS (analytical error was 10%). The analysis of the chemical composition of dissolved gases (He, H 2 , O 2 , N 2 , CH 4 , CO 2 ) was carried out by using a gas chromatograph equipped with TCD, with argon as carrier gas (analytical error was < 5%). Dissolved 222 Rn was stripped from water and adsorbed into the activated charcoal layer hosted in Active Charcoal Collectors (ACC) by using a Radon Degassing Unit; ACC were analyzed through γ-spectrometry (Mancini et al. , 2000). Analytical error was < 5%. The 18 O/ 16 O ad 2 H/ 1 H isotopic ratios (expressed as δ 18 O and δD ‰ vs. VSMOW) were determined by a mass spectrometer. The analytical precision is 0.1 ‰ for δ 18 O and 1 ‰ for δD. The carbon isotopic ratio of TDIC (Total Dissolved Inorganic Carbon), expressed as δ 13 C ‰ vs. VPDB, was analyzed by mass spectrometry following the procedure described by Favara et al. (2002). Geological setting. The following main tectonic-stratigraphic units crop out in the Lamezia Terme area, briefly described from bottom to top (Tansi et al. , 2007): i ) Slate and metapelite Unit , made up by dominantly foliated slates, black metapelites and metasilts, interbedded with quartzite strata (Paleozoic); ii ) Orthogneiss Unit , made of mylonitic augen-gneiss, micaschist, and subordinately thick granitoid sheets (Paleozoic); iii ) Paragneiss Unit made of high-grade metamorphic rocks (biotite-sillimanite-garnet gneiss), intruded by plutonic bodies (Paleozoic); iv ) Mesozoic carbonate complex , made up by dolostone and metalimestone Unit (Late Triassic- Liassic), locally outcropping in “tectonic windows” of the Apennine chain, as in the Caronte area. A transgressive Late Miocene conglomerate-calcarenite-clay-evaporite succession, and an Early Pliocene conglomerate-sand-clay succession unconformably overlie the above-mentioned tectonic units. Middle Pliocene to Middle Pleistocene deposits, made of thick conglomerate- sand-sandstone-clay marine successions, represent the basin-fill deposits of the main tectonic depression (Catanzaro Trough). Locally, Late Pleistocene fluvial terraced deposits, marine terraces and Late Pleistocene-Holocene alluvial fans crop out. The tectonic of the area in its northern sector is dominated by the Lamezia-Catanzaro Fault (LCF, Tansi et al. , 2007), a 50-60 km long left-lateral strike-slip fault, separating the Plio- quaternary Catanzaro Trough from the southern edge of the Sila Massif. Contursi Terme area is a tectonic depression bounded by the Mt. Polveracchio – Mt. Cervialto to the north-west and the Mt. Marzano – Mt. Ogna to the south-east. In the study area, the following main stratigraphic-structural units crop out, briefly described from top to bottom (Celico et al. , 1979; Polselli, 2004): i) Continental deposits mainly consisting of pebbles and sand. This complex is characterized by a variable permeability in relation to the lithology and the grain size of the sediments; ii) Irpinian Unit outcropping in small patches in the northern part of the valley and consist of alternation of conglomerates, sandstones and clays unconformable on the limestone and clays of the Campania-Lucania platform; iii) Varicolored shales consist of alternations of clay, limestones, calcilutites, micaceous sandstones and marls; iv) Apennine carbonate platform consist of Triassic dolomite (with a thickness of about 1000- 1200 m), typically tectonised. Follows, in stratigraphic continuity, a stretch of calcareous series (thickness equal to about 2500 m) which present, in the lower part, dolomite and limestone- dolomite. These units represent the most productive aquifers of the study area. 258 GNGTS 2013 S essione 1.3