The occurrence of carbonatites in oceanic settings is very rare if compared with their continental counterpart, having been reported only in Cape Verde and Canary Islands. This paper provides an overview of the main geochemical characteristics of oceanic carbonatites, around which many debates still exist regarding their petrogenesis. We present new data on trace elements in minerals and whole-rock, together with the first noble gases isotopic study (He, Ne, Ar) in apatite, calcite, and clinopyroxene from Fuerteventura carbonatites (Canary Islands). Trace elements show a similar trend as Cape Verde carbonatites, almost tracing the same patterns on multi-element and REE abundance diagrams. ³He/⁴He isotopic ratios of Fuerteventura carbonatites reflect a shallow (sub-continental lithospheric mantle, SCLM) He signature in their petrogenesis, and they clearly differ from Cape Verde carbonatites, i.e., fluids from a deep and low degassed mantle with a primitive plume-derived He signature are involved in their petrogenesis.

Aiming at understanding the source of the fluids that mineralizing within seismically active fault zones, we investigate the noble gas isotopes (i.e., helium (He), neon (Ne), and argon (Ar)) in the fluid inclusions (FIs) trapped in the calcite veins sampled along high‐angle fault zones of the Contursi hydrothermal basin, southern Italy. The latter basin lies in close vicinity of the M_W = 6.9, 1980 Irpinia earthquake and exposes numerous fault scarps dissecting Mesozoic shallow‐water carbonates. The analyses of noble gases (He, Ne, Ar) are conducted to identify the origin of the volatiles circulating along the faults at the time of calcite precipitation. Then, outcomes of this discussions are compared with currently outgassing of deep‐sourced CO₂ coupled to mantle‐derived He in that area, whose output is larger than those from some volcanic areas worldwide. The results indicate that He in FIs is dominated by a crustal radiogenic component (⁴He), and by an up to 20% of a mantle‐derived component (³He), with a highest isotopic signature of 1.38 Ra. This value is consistent with the highest percentage of mantle‐derived He associated to high‐flux CO₂ gas emission in the investigated area (1.41 Ra). We propose that the variability of the He isotopic signature measured in primary FIs can result from early trapping of fluid inclusions or post trapping processes and seismic activity that modify the pristine He isotopic signature (i.e., derived from the crust and/or mantle) in groundwater along the faults during periods of background seismicity. Such investigations are fundamental to understand fluid migration in fault systems and the role of fluids in processes of earthquake nucleation.

Among the volcaniclastic products of melilitite–carbonatite eruptions, pelletal lapilli are often found, resulting in them being particularly useful for characterising the interface between the erupting magma and its volatile component. Pelletal lapilli, which were erupted during the most recent melilitite–carbonatite volcanic activity of the Mt. Vulture volcano, are characterised by a predominantly wehrlitic core with CO₂-rich fluid inclusions and a Ca-rich outer portion composed of fine-grained xenocrystic debris of olivine and clinopyroxene, with microcrysts of haüyne and melilite laths (± calcite). The chemical composition of the olivine reflects the interaction with a proto-melilitite–carbonatite melt, which is the main metasomatic agent. The whole-rock analyses of the external portion of pelletal lapilli show values that are comparable with those of extrusive carbonatites. This evidence supports the hypothesis that the primary carbonatite melt was a significant contributor to the CO₂-rich magma source that transported the lapilli to the surface. The modelling of the geometric data of the pelletal lapilli structure, together with inferences regarding the role of the CO₂ gas phase, the main propellant in an ascending gas-dominated medium, allowed for the reconstruction of a possible scenario where the CO₂ expansion and the fluidised spray granulation process are crucial during the volcanic conduit dynamics.

This study provides new mineral chemistry data together with micro‐thermometric measurements on fluid inclusions hosted in ultramafic xenoliths (lherzolite, wehrlite, and dunite) brought to the surface by the last Mt. Vulture volcano activity (140 ka; southern Italy), and fed by melilitite‐carbonatite magmas. Petrographic evidence and mineralogical compositions of Mt. Vulture xenoliths are consistent with an origin in the upper mantle. Fluid inclusions in rock‐forming minerals of lherzolite and wehrlite xenoliths are CO₂‐dominated. The equilibrium temperature calculated by geothermometric estimates ranges from 1039 C (±36°C) to 1142°C (±15°C), and entrapment pressures of fluid inclusions with post‐trapping re‐equilibration correspond to the local crust–mantle boundary (32 km depth), and to a shallow reservoir located at 12–14 km depth. These results contribute to constrain the origin of these xenoliths and the depth of storage of magmas erupted from Mt. Vulture, where carbonatite‐like metasomatism and mantle‐derived CO₂ degassing occur.

This study provides new insights into magma ascent based on mantle xenoliths erupted during the last explosive volcanic activity of Mt. Vulture volcano (southern Italy), combining H diffusion chronometry with fluid-mechanical models. Olivine crystals within lherzolite, wehrlite and dunite xenoliths are Mg-rich (Fo _88-90 ), with NiO contents up to 0.30 wt%. They show hydrogen loss profiles between 0.5 and 2.5 ppm, and the resulting xenolith ascent rates are up to 5 m s ⁻¹ . The fluid mechanical model also generates high magma ascent rates, with values up to three times faster (17 m s ⁻¹ ) than those computed with the H diffusion chronometry. Lag times between the ascent rates of the low-viscosity magma that transported the mantle xenoliths and the xenoliths themselves during the last eruption of Mt. Vulture (140 ka) are constrained to a few tens of minutes. To make the fluid mechanical and the H diffusion chronometry models compatible, a low density contrast between the ascending magma and the surrounding crust (Δϱ = 20–40 kg m ⁻³ ) and a conduit diameter of 2–5 m are required. Our study highlights the importance of using independent models based on multiple parameters to constrain magma ascent rates. This could provide new means for reconstructing the volcanic activity of currently quiescent volcanoes, as carried out here for Mt. Vulture.