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Cluzel, Nicolas
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- PublicationRestrictedDukono, the predominant source of volcanic degassing in Indonesia, sustained by a depleted Indian-MORB(2018)
; ; ; ; ; ; ; ; ; ; ;; ;; ; ; ; ; ;Located on Halmahera island, Dukono is among the least known volcanoes in Indonesia. A compilation of the rare available reports indicates that this remote and hardly accessible volcano has been regularly in eruption since 1933, and has undergone nearly continuous eruptive manifestation over the last decade. The first study of its gas emissions, presented in this work, highlights a huge magmatic volatile contribution into the atmosphere, with an estimated annual output of about 290 kt of SO2, 5000 kt of H2O, 88 kt of CO2, 5 kt of H2S and 7 kt of H2. Assuming these figures are representative of the long-term continuous eruptive activity, then Dukono is the current most prominent volcanic gas discharge point in Indonesia and ranks among the top-ten volcanic SO2 sources on earth. Combining our findings with other recent volcanic SO2 flux results, obtained during periodic campaigns at a number of volcanoes with DOAS and UV-Cameras, the SO2 emission budget for Indonesia is estimated at 540 kt year−1, representing 2–3% of the global volcanic SO2 contribution into the atmosphere. This figure should be considered as minimum as gas emissions from numerous other active volcanoes in Indonesia are yet to be evaluated. This voluminous degassing output from Dukono is sustained by a depleted Indian-MORB (I-MORB) mantle source. This latter is currently undergoing lateral pressure from the steepening of the subducted slab, the downward force from the Philippine Sea plate and the westward motion of a continental fragments along the Sorong fault, leading to high fluid fluxes to the surface. Over the course of Dukono eruptive activity, the magma reservoir has changed from a less differentiated source that fed the past voluminous lava flows to a more evolved melt that sustained the current ongoing explosive activity.318 7 - PublicationEmbargoMagma storage and degassing beneath the youngest volcanoes of the Massif Central (France): Lessons for the monitoring of a dormant volcanic province(2023)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ;Developing appropriate monitoring strategies in long-quiescent volcanic provinces is challenging due to the rarity of recordable geochemical and geophysical signals and the lack of experienced eruptive phenomenology in living memory. This is the case in the Massif Central (France) where the last eruptive sequence formed the Pavin’s Group of Volcanoes, about 7 ka ago. There, current evidence of a mantle activity reminiscence is suggested by the presence of mineral springwaters, mofettes, and soil degassing. It appears fundamental as a prerequisite to decipher the evolution of the gas phase in the magmatic system at the time of the eruptive activity to understand the meaning of current local gas emissions. In this study, we develop an innovative approach coupling CO2 densimetry and geochemistry of fluid inclusions from products erupted by the Pavin’s Group of Volcanoes. 3D imagery by Raman spectroscopy revealed that carbonate forming in fluid inclusions may lead to underestimation of CO2 density in fluid inclusions by up to 50 % and thus to unreliable barometric estimates. Fortunately, we found that this effect may be limited by focusing on fluid inclusions with a small diameter (<4 m) and where no solid phase is detected on Raman spectra. The time evolution of the eruptions of the Pavin’s Group of Volcanoes shows a progressive decrease of the pressure of magma storage (from more than 9 kbar down to 1.5-2 kbar) in parallel to magma differentiation (from basanites at Montcineyre to benmoreites at Pavin). The analysis of the noble gases entrapped in fluid inclusions yielded two main conclusions: (1) the helium isotope signature (Rc/Ra = 6.5-6.8) is in the range of values obtained in fluid inclusions from mantle xenoliths in the Massif Central (Rc/Ra = 5.6±1.1, on average) suggesting partial melting of the subcontinental lithospheric mantle, and (2) magma degassing (4He/40Ar* from 4.0 to 16.2) mirrors magma differentiation and the progressive rise of the magma ponding zones of the Pavin’s Group of Volcanoes. According to our modelling, about 80 % of the initial gas phase would be already exsolved from these magmas, even if stored at mantle depth. Based on the results obtained from fluid inclusions, we propose a model of the evolution of the signature of noble gases and carbon isotopes from mantle depth to crustal levels. In this frame, gas emissions currently emitted in the area (Rc/Ra = 6.1-6.7 and 4He/40Ar* = 1.7) point to an origin in the lithospheric mantle. This study strongly encourages the establishment of a regular sampling of local gas emissions to detect potential geochemical variations that may reflect a change from current steady-state conditions186 2