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

Abstract

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.

Active Degassing of Deeply Sourced Fluids in Central Europe: New Evidences From a Geochemical Study in Serbia

“…4 He/ 20 Ne ratios are >1,000 for crust and mantle and 0.318 for air respectively (Sano et al, 1985). Because of these different end-member compositions, He isotopes in natural fluids, coupled with their 4 He/ 20 Ne ratios, can be used to resolve the relative He contributions from the three sources (e.g., Caracausi & Sulli, 2019;Sano & Wakita, 1985;Sano et al, 1997, and references therein). Using the approach proposed in Sano et al (1997), and assuming that all 20 Ne is atmospheric, we estimate low atmospheric contributions (<3%, Table 1) for all samples, except those collected from the hyperalkaline waters, and mantle helium fractions of 1% to ∼20%, with the highest fractions calculated for the CO 2 -dominated samples (Figure 4).…”

“…4 He/ 20 Ne ratios are >1,000 for crust and mantle and 0.318 for air respectively (Sano et al., 1985). Because of these different end‐member compositions, He isotopes in natural fluids, coupled with their 4 He/ 20 Ne ratios, can be used to resolve the relative He contributions from the three sources (e.g., Caracausi & Sulli, 2019; Sano & Wakita, 1985; Sano et al., 1997, and references therein). Using the approach proposed in Sano et al.…”

Neotectonics of the Sea of Galilee (northeast Israel): implication for geodynamics and seismicity along the Dead Sea Fault system

“…He and Ne isotopic composition was determined at the National Institute of Geophysics and Volcanology (INGV), Italy. 3 He, 4 He and 20 Ne were determined by injecting He into a split flight tube mass spectrometer (model GVI-Helix SFT ) and Ne into a multi-collector mass spectrometer (model Thermo-Helix MC plus ), after standard purification procedures 69 . The results have an analytical error generally less than 1%.…”

Mantle-Derived Helium Emission near the Pohang EGS Site, South Korea: Implications for Active Fault Distribution

“…, and Jamyeong faults (PH19-07). Reference data from San Andreas Fault Zone (SAFZ, [50]), North Anatolian Fault [50], Alpine Fault [46], Eastern Morogongo basin [56], North-Central Sicilly thermal basin (NCStb) [57], extensive tectonics settings [22], and Northern Taiwan [51]. 12 Geofluids CO 2 /CH 4 and concentration of 4 He plot.…”