Geochemical Patterns of Geothermal Elements in Southern Italian Fumaroles and Thermal Springs in Relation with Mantle Intrusions

Abstract:

The review of published data together with some new data specifically made to fill gaps, to make a database of chemical and isotopic data for thermal emergences (springs, fumaroles and gas vents) in southern Italy, to be used for the publication of a Geothermal Atlas, has hallowed the re-interpretation of all the geochemical data gathered. The main conclusions are as follows. All active volcanic areas (Solfatara, Vesuvius, Ischia Isle, Mt Etna, Aeolian Islands and Pantelleria Isle) have i) high ³He/⁴He rations coupled with ii) high CO₂ emissions and iii) geo-thermometric (isotopic) signatures that suggest the presence of active geothermal systems in all places at shallow depth. In spite of this, no one of these areas, is exploited for geothermal power generation. There are three further Quaternary volcanic areas at: Iblei Mts in Sicily, Vulture volcano in Basilicata region and Logudoro area in Sardinia Island that also have CO₂-rich gas emissions, high in ³He/⁴He ratio, but they are not associated to any relevant thermal emission nearby.

In terms of regional patterns, apart from the Calabria subduction arc area (Calabria region), the stable flat cratonic areas of Apulia in SE Italy, the Iblean Platform in SE Sicily, and most of Sardinia, the latter not involved in the Apennine Orogeny, the remaining southern Italy along the Tyrrhenian sector has huge emission of hydrothermally generated CO₂ crossed, in counterflow, by descending topographically driven N₂ solubilized in recharge meteoric water from the main Apennine belt.

Iso-distribution maps of several of the parameters investigated even more clearly show the sectors of southern Italy affected by the intrusion of mantle magma and therefore the areas where the geothermal heat-flow is maximized by active tectonics.