Magmatic Signature in Submarine Hydrothermal Fluids Vented Offshore Ventotene and Zannone Islands (Pontine Archipelago, Central Italy)

Figure 6

Helium isotopic ratios (as R/Ra) and ⁴He/²⁰Ne relationships. The theoretical black lines represent binary mixing trends for atmospheric helium with helium from crust and mantle sources. The assumed end-members are ASSW (yellow star) with and ; crust with and ; MORB-type mantle with and ; contaminated mantle by crustal fluids due to subduction of continental crust having and . Data for bubbling gases from Panarea and Basiluzzo [16], Stromboli [60], Vulsini [61], and Alban Hills [62] are plotted for comparison.