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Ditta, M.
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Ditta, M.
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- PublicationRestrictedChanges in fluid geochemistry and physico-chemical conditions of geothermal systems caused by magmatic input: The recent abrupt outgassing off the island of Panarea (Aeolian Islands, Italy)(2005)
; ; ; ; ; ; ; ;Caracausi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Ditta, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Italiano, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Longo, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Nuccio, P. M.; Dipartimento Chimica e Fisica della Terra ed Applicazioni, Via Archirafi 36, 90123 Palermo, Italy ;Paonita, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Rizzo, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; ; ; ; ; ; Hydrothermal systems and related vents can exhibit dramatic changes in their physico-chemical conditions over time as a response to varying activity in the feeding magmatic systems. Massive steam condensation and gas scrubbing processes of thermal fluids during their ascent and cooling cause further compositional changes that mask information regarding the conditions evolving at depth in the hydrothermal system. Here we propose a new stability diagram based on the CO2-CH4-CO-H2 concentrations in vapor, which aims at calculating the temperatures and pressures in hydrothermal reservoirs. To filter gas scrubbing effects, we have also developed a model for selective dissolution of CO2-H2S-N2-CH4-He-Ne mixtures in fresh and/or air-saturated seawater. This methodology has been applied to the recent (November 2002) crisis that affected the geothermal field off the island of Panarea (Italy), where the fluid composition and fluxes have been monitored for the past two decades. The chemical and isotopic compositions of the gases suggest that the volatile elements originate from an active magma, which feeds a boiling saline solution having temperatures of up to 350 C and containing 12 mol CO2 in vapor. The thermal fluids undergo cooling and re-equilibration processes on account of gas-water-rock interactions during their ascent along fracture networks. Furthermore, steam condensation and removal of acidic species, partial dissolution in cold air-saturated seawater and stripping of atmospheric components, affect the composition of the geothermal gases at shallow levels. The observed geochemical variations are consistent with a new input of magmatic fluids that perturbed the geothermal system and caused the unrest event. The present-state evolution shows that this dramatic input of fluids is probably over, and that the system is now tending towards steady-state conditions on a time scale of months.436 100 - PublicationRestrictedHelium and carbon isotopes in the dissolved gases of Friuli Region (NE Italy): Geochemical evidence of CO2 production and degassing over a seismically active area(2009-08)
; ; ; ; ; ;Italiano, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Bonfanti, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Ditta, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Petrini, R.; Dipartimento di Scienze della Terra, University of Trieste ;Slejko, F.; Dipartimento di Scienze della Terra, University of Trieste; ; ; ; The first geochemical data showing the existence of an active degassing activity over a large seismically active sector of the Southern Alps (Friuli Region, NE Italy) are presented. The dissolved gases, helium and carbon isotopic systematics of 46 water samples taken from 13 sites running along E–W and NE–SW faults besides the natural degassing of a 5000 km2 wide area are investigated. The chemical composition of the dissolved gases revealed that a CO2-rich gas phase feeds the local groundwaters. 3He/4He ratios (R) normalized to the atmospheric 3He/4He ratio (Ra=1.39×10−6) and corrected for the atmospheric contamination (R/Rac), range from 0.29 to 1 as a result of a two component (radiogenic and atmospheric) mixing. The δ13C values of total dissolved inorganic carbon (TDIC) ranging from −15.28 to −0.75‰ vs. PDB, show the occurrence of multiple gas–water interactions. The mixing between the atmospheric air and a crustal source and the gas–water interactions occurring at various extents appears to be the main control on the observed He–C systematics. The natural CO2 degassing was evaluated by a soil gas survey carried out by a grid of about 100 measuring sites located over the area that generated destructive seismic sequences (e.g. the Gemona sequence of 1976; main shocks M6.4 of 6th May and M6.1 of 11th and 15th September). The results obtained show that a significant amount of crustal-originated gases are released over the continental area of Eastern Southern Alps. The evidence that carbon dioxide is associated with radiogenic-type helium denotes the lack of the mantle as primary energy and degassing source, highlighting the possibility that CO2 is produced by thermo-mechanical processes occurring at seismogenic depth. The information provided here may be used to start up a long-term geochemical monitoring of this seismically active area and could be able to detect the modifications occurring to the circulating fluids to gain a better insight on the relationships between the fluids' geochemistry and the activity of the local seismogenic faults.745 21 - PublicationOpen AccessInferences on physico-chemical conditions and gas-water interaction by new quantitative approaches: The case of Panarea (Italy)(2004-06-05)
; ; ; ; ; ; ; ;Caracausi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Ditta, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Italiano, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Longo, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Maugeri, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Nuccio, P. M.; DCFTA-Univ. Palermo ;Paonita, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; ; ; ; ; ; ; ; ; ;Arnorsson, S.Svensen, E.We have developed two new quantitative approaches to calculate temperatures in hydrothermal reservoirs by using the CO2-CH4-CO-H2 gaseous system and to model selective dissolution of CO2-H2S-N2-CH4-He-Ne mixtures in fresh and/or air saturated seawater. The anomalous outgassing starting November 2003 from the submarine exhalative system offshore Panarea island (Italy), was the occasion to apply such approaches to the extensive collection of volcanic gases. Gas geothermometry suggest the presence of a deep geothermal system at temperature up to 350°C and about 12 mol% CO2 in the vapor, which feeds the submarine emissions. Based on the fractional dissolution model, the rising geothermal vapor interacts with air-saturated seawater at low depths, dissolving 30-40% CO2 and even more H2S, modifying the pH of the aqueous solution and stripping the dissolved atmospheric volatiles (N2, Ne). Interaction of the liquid phase of the thermal fluids with country rocks, as well extensive mixing with seawater, have been also recognized and quantified. The measured output of hydrothermal fluids from Panarea exhalative field [1] accounts for the involvement of volatiles from an active degassing magma, nonetheless the climax of the investigated phenomenon is probably overcome and the system is new tending towards a steady-state. Our quantitative approaches allow us to monitor the geochemical indicators of the geothermal physico-chemical conditions and their potential evolution towards phreatic events or massive gas releases, which certainly are the main hazards to be expected in the area. The event at Panarea has in fact highlighted how hydrothermal systems can exhibit dramatic and sudden changes of their physico-chemical conditions and rate of fluid release, as a response to variable activity of feeding magmatic systems.180 110 - PublicationRestrictedEvidence of a recent input of magmatic gases into the quiescent volcanic edifice of Panarea, Aeolian Islands, Italy(2004)
; ; ; ; ; ; ; ; ; ; ;Caliro, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Caracausi, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Chiodini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Ditta, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Italiano, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Longo, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Minopoli, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Nuccio, P. M.; Dipartimento Chimica e Fisica della Terra ed Applicazioni, Palermo, Italy ;Paonita, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Rizzo, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; ; ; ; ; ; ; ; ; On 2nd/3rd November 2002, a huge amount of gas, mainly composed of CO2, was suddenly released from the sea bottom off the coast of Panarea, producing a ‘‘crater’’20 by 10 meters wide and 7 meters deep. The gas output was estimated to be 109 l/d, two orders of magnitude higher than that measured in the 1980s. The anomalous degassing rate lasted for some weeks, slowly decreasing to an almost constant rate of about 4 x 107 l/d after two months. The geothermo- barometric estimations revealed an increase of both the temperature and pressure in the geothermal system feeding the sampled vents. The 3He/4He ratios were similar to those measured in nearby Stromboli. We have monitored the area for the last two decades, and based on our intensive and extensive geochemical measurements, have ascertained that the geothermal reservoir has lost its steady state. We maintain that a new magmatic input caused these phenomena.294 99 - PublicationOpen AccessThe Porretta thermal springs (Northern Apennines): seismogenic structures and long-term geochemical monitoring(2007-08)
; ; ; ; ;Ciancabilla, N.; ARPA Emilia Romagna ;Ditta, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Italiano, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Martinelli, G.; ARPA Emilia Romagna; ; ; The thermal springs of Porretta are located on a seismically active area of the Northern Apennines. In 19th Century a chemist identified anomalous behaviour of the thermal waters in concomitance with local seismic events. Recent studies assessed the geochemical features of the circulating fluids (e.g., waters carry a dissolved CH4-dominated gas phase with a radiogenic signature of the helium isotopic ratio) and observed anomalous hydrologic and geochemical signals possibly related to crustal strain phenomena due to local seismic events. Long-term geochemical monitoring was carried out from 2001 to 2006 with the aim of detecting the behaviour of the circulating fluids possibly coinciding with seismic activity. The collected data reveal a sensitivity of the thermal waters to the activity of the main fault crossing the village of Porretta and identify a «seismogenic» structure crossing the village.193 335 - PublicationRestrictedPreliminary geochemical and isotopic data on springs along the Fella-Sava fault zone (NE Italy)(2007-12)
; ; ; ; ; ;Slejko, F.; OGS - Trieste ;Petrini, R.; UNI-TS ;Carulli, G. B.; UNI-TS ;Italiano, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Ditta, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; ; ; ; During 2006, a geochemical survey was carried out on three perennial springs discharging along a segment of the Fella-Sava line, a transpressive lineament running in the eastern Southern Alps (Friuli, NE Italy). Waters have both a Ca-bicarbonate and a CaMg(Na)-HCO3SO4 sulfureous character. Oxygen and hydrogen isotopic data indicate a meteoric origin from catchments with different mean topographic elevation. The Sr isotopic composition of the Ca-bicarbonate water is consistent with circulation in Middle Triassic limestones; sulfureous waters have 87Sr/86Sr isotopic ratios which indicate interactions with the Upper Permian dolomite-evaporite layers, the latter representing the preferential decollement horizons during the compressive Alpine cycle. The isotopic data, the negative redox potential and the tritium activity for sulfureous springs suggest a long-lasting flow through different fracture systems. Limited effects of mixing between the deeper and superficial, low-salinity waters are observed. Speciation calculations indicate that sulfureous waters are oversaturated in calcite and silicate minerals, suggesting that cement deposition is an active process along the flowpaths. The formations of diagenetic seals in a compressive regime would contribute to fluid overpressuring in pores at a relatively shallow depth, where part of the seismic activity is concentrated. The SO4, Ca and Mg concentrations, in one of the sulfureous springs, show a marked increase which seems to be related to the seismic events in the area, and is attributed to the expulsion of pore fluids with high concentration of sulphate due to strain changes347 27 - PublicationRestrictedMassive submarine gas output during the volcanic unrest off Panarea Island (Aeolian arc, Italy): Inferences for explosive conditions(2005)
; ; ; ; ; ;Paonita, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Ditta, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Italiano, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Longo, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Nuccio, P. M.; CFTA - Università di Palermo; ; ; ; The possibility of understanding natural processes leading to explosive events in volcanic systems provides advantages for a better management of possible volcanic crises. On account of the possibility of the occurrence of other phenomena, such as tsunamis, the explosions driven by submarine volcanic systems are of particular interest, although little investigated. The recent sudden increase in the degassing activity of the submarine geothermal system of Panarea Island (Aeolian arc), has allowed us to better understand the way in which the quiet degassing activity of a submarine hydrothermal system may develop if new magma or magmatic gases feed it. We focused our investigations on the crater-shaped area where the volcanic crisis started, with the aim of evaluating whether the crater was formed by an explosive event or by sediment erosion due to the intense gas flow rate. The calculated energetic conditions, coupled with the computed physicchemical state of the fluids at the level of the deep reservoir, provided the theoretical boundary conditions of the occurred event, while suggesting that a low-energy explosion was responsible for producing the crater at the sea bottom.188 35