Abstract
Geochemical investigations carried out on submarine hydrothermal fluids vented offshore the Pontine Islands (Tyrrhenian Sea) revealed the existence of gas vents to the W of Zannone Island and SW of Ventotene Island. The geochemical features of the CO2-rich gas samples show a clear mantle-derived signature with3He/4He of 3.72-3.75 Ra and 1.33 Ra at Zannone and Ventotene, respectively. Gas geochemistry denotes how CO2-rich gases undergo fractionation processes due to CO2dissolution to a variable extent favoring enrichment in the less soluble gas species, i.e., CH4, N2, and He. The carbon isotope composition of CO2, expressed asδ13C vs. V-PDB, ranges from -0.71 and -6.16‰ at Zannone to 1.93‰ at Ventotene. Preliminary geothermometric and geobarometric estimations indicate equilibrium temperatures in the range of 150-200°C at Zannone and >200°C at Ventotene besides H2O pressures in the range of 5 bar and 20 bar at Zannone and Ventotene, respectively. Although the latest volcanic activity at the Pontine Archipelago is dated Middle Pleistocene, the combination of the new geochemical information along with geothermometric estimations indicates that cooling magmas are likely releasing enough thermal energy to form an efficient hydrothermal system.
Highlights
The Central Mediterranean Sea and the Italian Peninsula have been affected by intense Neogene and Quaternary Volcanism
The igneous activity of the Tyrrhenian Sea and its eastern margin triggers the development of several geothermal systems
Hydrothermal fields in the Southern Tyrrhenian Sea are present around seamounts [13,14,15], in the Aeolian Archipelago [16,17,18,19], in front of Capo Vaticano [20, 21], along the coast of Ischia Island
Summary
In this sector, the geodynamic processes, framed in the Alpine Orogeny, are expressed by the subduction of the Adriatic microplate under the Eurasian plate and by the opening of the Tyrrhenian back-arc basin [1,2,3,4]. Hydrothermal fields in the Southern Tyrrhenian Sea are present around seamounts [13,14,15], in the Aeolian Archipelago [16,17,18,19], in front of Capo Vaticano [20, 21], along the coast of Ischia Island [17], and in the Bay of Naples [22, 23] All these zones are characterized by CO2-rich emissions and are commonly associated with the occurrence of magmatic bodies underneath the seafloor. Geochemical features of the thermal fluids provide important information on both the current status of cooling magma batches intruding the upper crust and interaction processes taking place between rising fluids and hosting rocks
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