Geochemical evidence for the existence of high-temperature hydrothermal brines at Vesuvio volcano, Italy

Chiodini, Giovanni; Marini, Luigi; Russo, Mario Salvatore

doi:10.1016/s0016-7037(01)00583-x

Cited by 154 publications

(201 citation statements)

References 64 publications

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“…The presence of CO 2 -rich gas discharges, characterized by d 13 C-CO 2 values slightly lower than À1‰ V-PDB (Table 7), certainly suggests the presence of a deep-seated source feeding these gas vents. Such values are indeed similar to those found in the fumarolic gas discharges from the Island of Volcano (e.g., Paonita et al, 2002) and Solfatara, Somma-Vesuvius and related submarine emissions (e.g., Chiodini et al, 2001;Caliro et al, 2007;Vaselli et al, 2011;Passaro et al, 2016) and many gas vents distributed along the peri-Tyrrhenian strip (e.g., Minissale et al, 1997) of the Italian peninsula. The origin of the periTyrrhenian vents is mainly related to thermometamorphic processes of marine limestone, although small contributions from a magmatic source cannot be excluded.…”

Section: Isotopic Composition Of Carbonates and Origin Of Mineralizinsupporting

confidence: 83%

Authigenic minerals from the Paola Ridge (southern Tyrrhenian Sea): Evidences of episodic methane seepage

Franchi

Rovere

Gamberi

et al. 2017

Marine and Petroleum Geology

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a b s t r a c tPaola Ridge, along the NW Calabrian margin (southern Tyrrhenian Sea), is one of the few reported deep sea sites of precipitation of authigenic carbonates in the Tyrrhenian Sea. Here, the changing composition of the seeping fluids and the dynamic nature of the seepage induced the precipitation of pyrite, siderite and other carbonate phases. The occurrence of this array of authigenic precipitates is thought to be related to fluctuation of the sulfate-methane transition zone (SMTZ).Concretions of authigenic minerals formed in the near sub-bottom sediments of the Paola Ridge were investigated for their geochemical and isotopic composition. These concretions were collected in an area characterized by the presence of two alleged mud volcanoes and three mud diapirs. The mud diapirs are dotted by pockmarks and dissected by normal faults, and are known for having been a site of fluid seepage for at least the past 40 kyrs. Present-day venting activity occurs alongside the two alleged mud volcanoes and is dominated by CO 2 -rich discharging fluids. This discover led us to question the hypothesis of the mud volcanoes and investigate the origin of the fluids in each different domed structure of the study area.In this study, we used stable isotopes (carbon and oxygen) of carbonates coupled with rare earth element (REE) composition of different carbonate and non-carbonate phases for tracing fluid composition and early diagenesis of authigenic precipitates. The analyses on authigenic precipitates were coupled with chemical investigation of venting gas and sea-water.Authigenic calcite/aragonite concretions, from surficial sediments on diapiric structures, have depleted values. The siderite REE pattern shows consistent LREE (light REE) fractionation, MREE (medium REE) enrichment and positive Gd and La anomalies. As shown by the REE distribution, the 13 C-depleted composition and their association with chemosymbiotic fauna, calcite/aragonite precipitated at time of moderate to high methane flux close to the seafloor, under the influence of bottom seawater. Authigenic siderite, on the other hand, formed in the subseafloor, during periods of lower gas discharges under prolonged anoxic conditions within sediments in equilibrium with 13 C-rich dissolved inorganic carbon (DIC) and 18 O-rich water, likely related to methanogenesis and intermittent venting of deep-sourced CO 2 .

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Section: Isotopic Composition Of Carbonates and Origin Of Mineralizinsupporting

confidence: 83%

Authigenic minerals from the Paola Ridge (southern Tyrrhenian Sea): Evidences of episodic methane seepage

Franchi

Rovere

Gamberi

et al. 2017

Marine and Petroleum Geology

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“…Viscosity, volatile content and temperature was experimentally calculated for the 1631 phonolitic melt portion [47,51,52]. We calculated similar values for the main 1631 rock-types and crystal settling velocity using Stokes' law (Table 4).…”

Section: Petrogenesismentioning

confidence: 99%

Magma evolution inside the 1631 Vesuvius magma chamber and eruption triggering

et al. 2017

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Vesuvius is a high-risk volcano and the 1631 Plinian eruption is a reference event for the next episode of explosive unrest. A complete stratigraphic and petrographic description of 1631 pyroclastics is given in this study. During the 1631 eruption a phonolite was firstly erupted followed by a tephritic phonolite and finally a phonolitic tephrite, indicating a layered magma chamber. We suggest that phonolitic basanite is a good candidate to be the primitive parental-melt of the 1631 eruption. Composition of apatite from the 1631 pyroclastics is different from those of CO 2 -rich melts indicating negligible CO 2 content during magma evolution. Cross checking calculations, using PETROGRAPH and PELE software, accounts for multistage evolution up to phonolite starting from a phonolitic basanite melt similar to the Vesuvius medieval lavas. The model implies crystal settling of clinopyroxene and olivine at 6 kbar and 1220 ∘ C, clinopyroxene plus leucite at a pressure ranging from 2.5 to 0.5 kbar and temperature ranging from 1140 to 940 ∘ C. Inside the phonolitic magma chamber K-feldspar and leucite would coexist at a temperature ranging from from 940 to 840 ∘ C and at a pressure ranging from 2.5 to 0.5 kbar. Thus crystal fractionation is certainly a necessary and probably a sufficient condition to evolve the melt from phono tephritic to phonolitic in the 1631 magma chamber. We speculate that phonolitic tephrite magma refilling from deeper levels destabilised the chamber and triggered the eruption, as testified by the seismic precursor phenomena before 1631 unrest.

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“…A significant difference of H 2 concentration between the NBC (229 µmol/kg) and ESBC (25 µmol/kg) fluids was observed (Table 2). However, the difference is very difficult to explain only by the fluid boiling and the preferential partition of insoluble gas components such as H 2 , CH 4 and He in the Cl-depleted fluids (Chiodini et al, 2001;Takai et al, 2008b) because the CH 4 concentrations were relatively similar between the NBC and ESBC fluids (Table 2). Possible explanations are the microbial H 2 consumption (H 2 depletion) and/or the additional CH 4 input with little H 2 in the subseafloor environments around ESBC site after the phase-separation and -partition process.…”

Section: Gas Geochemistrymentioning

confidence: 99%

Hydrothermal fluid geochemistry at the Iheya North field in the mid-Okinawa Trough: Implication for origin of methane in subseafloor fluid circulation systems

et al. 2011

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Geochemical characteristics of hydrothermal fluids in the Iheya North hydrothermal field, mid-Okinawa Trough, was investigated. Twelve-years observation reveals temporal variation of vent fluid chemistry potentially controlled by temporally varying pattern of the phase-separation and -segregation, while the constant Element/Cl ratios among the periods and chimneys indicate the stable chemical composition of the source hydrothermal fluid prior to undergoing phaseseparation. The high K contents in the estimated source fluid are typical in the arc-backarc hydrothermal systems due to the hydrothermal reaction with the K-enriched felsic rocks. The high I, B and NH 4 contents and alkalinity are derived from decomposition of the sedimentary organic matters.Compositional and isotopic properties of gas species, CH 4 , H 2 , CO 2 , and C 2 H 6 , strongly suggest a dominance of biogenic CH 4 associated with the sedimentary organic matter. Based on the carbon mass balance calculation and the multidisciplinary investigations of the Iheya North hydrothermal system since the discovery, we hypothesized that the microbial methanogenesis occurs not only within the Central Valley where hydrothermal vents exist, but also in the spatially abundant and widespread basin-filling sediments surrounding the Iheya North Knoll, and that the microbially produced CH 4 is recharged together with the source fluid into the deep hydrothermal reaction zone. This "Microbial Methanogenesis at Recharge area in hydrothermal circulation" (MMR) model would be an implication for the generation and incorporation of hydrothermal fluid CH 4 in the deep-sea hydrothermal systems but also for those of cold seep CH 4 and for the presently uncertain hydrothermal fluid paths in the subseafloor environments. In the near future, the IODP drilling will be conducted in the Iheya North hydrothermal system, and give an excellent opportunity to testify our MMR model.

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Geochemical evidence for the existence of high-temperature hydrothermal brines at Vesuvio volcano, Italy

Cited by 154 publications

References 64 publications

Authigenic minerals from the Paola Ridge (southern Tyrrhenian Sea): Evidences of episodic methane seepage

Authigenic minerals from the Paola Ridge (southern Tyrrhenian Sea): Evidences of episodic methane seepage

Magma evolution inside the 1631 Vesuvius magma chamber and eruption triggering

Hydrothermal fluid geochemistry at the Iheya North field in the mid-Okinawa Trough: Implication for origin of methane in subseafloor fluid circulation systems

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