Gas Leakage From Shallow Ponding Magma and Trapdoor Faulting at Sierra Negra Volcano (Isabela Island, Galápagos)

We report on new volcanic gas composition results acquired in October 2017 at Minas de Azufre, a persistent fumarolic field topping the resurgent Sierra Negra caldera, Galápagos archipelago. Our indicate that Azufre fumaroles are moderately hydrous (52–64 mol.% H2O) and rich CO2 (35–46 mol.%), with total sulfur (ST) being 21–35 times less abundant than CO2. SO2, most S species, is released an average rate of 19 ± 9 tons/day. Using volatile saturation model provides magmatic gases equilibrium western basaltic melt (48 wt. % SiO2) 400–0.1 MPa pressure range, we infer emissions consist mixture (a) magma-derived coexisting ∼50–60 (b) shallow meteoric water. thus propose supplied by outgassing magma stored ∼2 km deep sill-like reservoir underneath caldera floor, trapdoor fault system margin block acts as preferential pathway for ascent surface discharge. suggest that, contrast to majority volcano-hosted hydrothermal systems worldwide, releases relatively pristine gas.