Outgassing of Mantle Volatiles in Compressional Tectonic Regime Away From Volcanism: The Role of Continental Delamination

In this study we discuss the occurrence of mantle‐derived heat and volatiles (i.e., helium and
CO2) feeding hydrothermal systems in a seismically active margin between two convergent plates
(African and European) without any signals of volcanism. The helium (He) isotopes clearly indicate a
mantle‐derived component in the outgassing volatiles. The estimated mantle‐derived He fluxes are up to two
to three orders of magnitude greater than those in a stable continental area. Such high He fluxes cannot be
provided by a long‐lasting diffusion, thereby implying a more efficient transport (i.e., advective transport
through faults). He data coupled to heat‐He relationship suggest the occurrence of active degassing of
magmatic intrusions in this area of continental collisional. Geophysical data indicate the presence of a hot
mantle wedge below the outgassing of mantle volatiles and a system of faults cutting the continental crust
down to the hot mantle wedge. Here we discuss the hot mantle wedge and possible associated magmatic
intrusions as the source of the mantle‐derived volatiles outgassing in the region. We also assessed the output
of mantle‐derived CO2 from the investigated hydrothermal basins. The possible occurrence of magma at
depth as well as the geometry of the thick‐skinned deformed wedge unambiguously indicates delamination
processes that are related to continental subduction. Hence, we show that delamination processes can really
produce magma at depth without evidences of volcanism at the surface. Finally, we have also provided
the fault systems that work as a network of pathways and actively sustain the advective transfer of the
mantle fluids toward the surface.