Francesco Italiano

Geochemical evidence of melt intrusions along lithospheric faults of the Southern Apennines, Italy: Geodynamic and seismogenic implications

Several gas emissions, distributed along 200 km of the Southern Apennine axial zone, have been investigated. This portion of the sedimentary chain, which constitutes the accretionary prism of the westward subduction of the Adriatic plate, is subjected to a tensile stress field responsible of high-magnitude earthquakes. The studied emissions are generally CO2-dominated, have 3He/4He ratios in the range of 0.09–2.84 Ra, and display both 3He and 4He outputs in the range of those reported for the Italian active volcanoes Phlegrean Fields and Vulcano. The helium isotope ratios, together with the amount of released gas, indicate that a huge amount of mantle-derived helium is released over all the investigated area. Our geochemical data and the geophysical peculiarities of the region, such as the high heat flow and the low resistivity of rocks below a depth of 15 km, coherently indicate the presence of melt intruded into the crust along lithospheric faults. Magma intrusions along the axial part of the Southern Apennine sedimentary chain are certainly unusual, since volcanism in central and southern Italy is concentrated along the peri-Tyrrhenian margin of the peninsula. We suggest that melt is promoted by adiabatic uprise of the asthenosphere in the mantle wedge beneath the Apennines and it is subsequently intruded along tensile lithospheric faults, strongly affecting the thermal state of the lower crust. An interrelationship between the geodynamics, the melt intrusions, and the genesis of the large earthquakes (up to M = 7.1) in the region is suggested.

Anomalies of mantle-derived helium during the 1997-1998 seismic swarm of Umbria-Marche, Italy

More than 100 ³He/4He isotope ratios were measured in CO2-dominated gas samples collected during the 1997–1998 seismic crisis that shook the Umbria-Marche, Central Apennines, Italy. Although the gas emissions were located in a typical “crustal” environment the measured values delineate variable mixing proportions between mantle-derived and crustal helium. During the monitoring period anomalous ³He/4He ratios were observed, together with a significant increase of fluid outflows. The observed ³He/4He anomalies appear to be driven by stress-induced crustal deformations affecting micro-fracturing and bulk permeability and, in turn, by a seismogenic-induced modification of the crustal permeability of rocks. Since crustal deformations can also occur aseismically, the geochemical anomalies must be considered indicators of processes occurring below the surface, which could eventually help to estimate the probability increase of an impending earthquake, instead of pure empirical precursors.

Mount Etna: Geochemical signals of magma ascent and unusually extensive plumbing system

] FiveyearsofgasmonitoringfromselectedsitessuggestthatMtEtna’splumbingsystemismuchmoreextensivethanpreviously reported. It extends at least 40 km SW from thevolcano’s boundary along the NE-SW regional fault, whereit discharges about 200 tons/day of gas, containing heliumwith mantle-type isotopic composition. Synchronousvariations of

Evidence of a recent input of magmatic gases into the quiescent volcanic edifice of Panarea, Aeolian Islands, Italy

- Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Vesuviano, Naples, Italy. - Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Palermo, Italy. - Dipartimento Chimica e Fisica della Terra ed Applicazioni, Palermo, Italy.

Remote detection of fumarolic gas chemistry at Vulcano, Italy, using an FT-IR spectral radiometer

Abstract An infrared absorption spectroscopy remote sensing technique was used to determine the SO 2 /HCl ratio in fumarolic plumes at Vulcano, Italy. The measurements were made from the southern crater rim of Fossa Grande Crater, about 400 m from the fumarolic area in the crater. Infrared absorption spectra of HCl and SO 2 were observed for four fumaroles a few tens of metres apart using the hot fumarolic surface as an infrared light source. The measured SO 2 /HCl ratios in the FA, F47, FW and lower parti of the F21 fumaroles were 4.5–5.4, 3.5, 9.5–11.2 and 5.8 respectively. The SO 2 /HCl ratio of the FA fumarole was higher than that of the gas collected directly in the fumarolic vent (SO 2 /HCl ratio = 2.9), and was closer to the S (total) /HCl ratio (= 4.6) of the collected gas. Our results show that the SO 2 /HCl ratios of two fumaroles only a few tens of metres apart exhibits differences of about twofold. This suggests that this remote monitoring technique is capable of detecting spatial distribution in the SO 2 /HCl ratios of volcanic plumes. Because temporal variations in S/Cl ratios can provide precursory signals for volcanic eruptions [1–3], this remote sensing technique can used efficiently for evaluation of volcanic activity.

Geochemistry and isotope geochemistry of the Monfalcone thermal waters (northern Italy): inference on the deep geothermal reservoir

Geochemical investigations were carried out to define the origin of the low- to moderate-temperature thermal waters feeding the Monfalcone springs in northern Italy. Chemical data indicate that waters approach the composition of seawater. Mixing processes with cold low-salinity waters are highlighted. The δ18O and δD values are in the range −5.0 to −6.4 ‰, and −33 to −40 ‰, respectively, suggesting the dilution of the saline reservoir by karst-type freshwaters. A surplus of Ca2+ and Sr2+ ions with respect to a conservative mixing is ascribed to diagenetic reactions of the thermal waters with Cretaceous carbonates at depth. The measured Sr isotopic composition (87Sr/86Sr ratio) ranges between 0.70803 and 0.70814; after correction for the surplus Sr, a 87Sr/86Sr ratio indicating Miocene paleo-seawater is obtained. The dissolved gases indicate long-lasting gas–water interactions with a deep-originated gas phase of crustal origin, dominated by CO2 and marked by a water TDIC isotopic composition in the range −5.9 to−8.8 and helium signature with 0.08 < R/Ra < 0.27, which is a typical range for the crust. A possible scenario for the Monfalcone thermal reservoir consists of Miocene marine paleowaters which infiltrated through the karstic voids formed within the prevalently Cretaceous carbonates during the upper Eocene emersion of the platform, and which were entrapped by the progressive burial by terrigenous sediments.RésuméDes investigations géochimiques ont été effectuées pour définir l’origine des températures basses à modérées des eaux thermales qui alimentent les sources de Monfalcone dans le Nord de l’Italie. Les données chimiques indiquent que les eaux approchent la composition de l’eau de mer. Les processus de mélange avec de l’eau froide de faible salinité sont mis en lumière. Les valeurs de δ18O et δD varient de −5.0 à −6.4 ‰, et −33 à −40 ‰, respectivement, suggérant une dilution du réservoir salé par de l’eau douce de type karstique. Un excédent d’ions Ca2+ et Sr2+ par rapport à un mélange conservatif est attribué aux réactions diagénétiques des eaux thermales avec les carbonates du Crétacé en profondeur. La composition isotopique mesurée du Sr (rapport 87Sr/86Sr ) s’étend entre 0.70803 et 0.70814; Après correction pour l’excédent de Sr, un rapport 87Sr/86Sr représentatif d’une paléo eau de mer Miocène est obtenu. Les gaz dissous indiquent des interactions eau-gaz de longue durée avec un phase gazeuse d’origine profonde (crustale), dominée par le CO2 et marquée par une composition isotopique TDIC de −5.9 à −8.8 et une signature hélium avec 0.08 < R/Ra < 0.27, qui est typique de la croute. Un scénario possible pour le réservoir thermal de Monfalcone considère des eaux anciennes marines miocènes qui se sont infiltrées par les vides karstiques formés dans les carbonates crétacés durant l’emersion éocene de la plateforme, et qui ont été rendues prisonnières du fait de l’ensevelissement progressif par les sédiments terrigènes.ResumenSe llevaron a cabo investigaciones geoquímicas para definir el origen de la baja a moderada temperatura de aguas termales que alimentan a los manantiales de Monfalcone en el norte de Italia, Los datos químicos indican que las aguas se aproximan a la composición del agua de mar. Se destacan los procesos de mezcla con aguas frías de baja salinidad. Los valores de δ18O y δD están en el rango de −5.0 a −6.4 ‰, y −33 a −40 ‰, respectivamente, sugiriendo la dilución del reservorio salino por agua dulces de tipo kárstico. Un exceso de los iones Ca2+ y Sr2+ con respecto a una mezcla conservativa se atribuye a reacciones diagenéticas de las agua termales con carbonatos del Cretácico en profundidad. La composición medida del isótopo Sr (relación 87Sr/86Sr) varía entre 0.70803 y 0.70814; después de haber corregido por los excesos de Sr, relación 87Sr/86Sr obtenida indica paleoaguas marinas del Mioceno. La presencia de gases disueltos indica las interacciones gas – agua de larga duración con una fase gaseosa originada en profundidad de origen cortical, dominada por CO2 y marcada por una composición isotópica del agua TDIC en el rango de −5.9 a −8.8 y vestigios de helio con 0.08 < R/Ra < 0.27, que es un intervalo típico para la corteza. Un escenario posible para el reservorio termal de Monfalcone consiste en paleoaguas marinas del Mioceno las cuales se infiltraron a través de huecos kárstico formados dentro de los carbonatos prevalentes del Cretácico durante la emersión de la plataforma en el Eoceno superior, y que fueron entrampados por un enterramiento progresivo debido a sedimentos terrígenos.摘要地球化学调查界定了意大利北部Monfalcone(蒙法尔科内)低-中温温泉水的来源。化学数据显示,水的成分与海水相同。很明显,与寒冷的低盐度水的混合过程十分明显。δ18O 和 δD值分别在–5.0至-6.4‰ 和–33到40‰。这一现象表明地下卡斯特淡水河对盐水储层的稀释作用。剩余的Ca2+ 和 Sr2+离子归因于热水域与白垩纪碳酸盐在深度的成岩反应的结果。检测到的Sr 同位素成分(87Sr/86Sr 比率) 在0.70803和0.70814之间。修正后,剩余的Sr, 87Sr/86Sr的比率现实出来自中新世的古海水。溶解的气体显示,持续的源于地壳的二氧化碳与水的相互作用,主要由水中的TDIC 同位素成分在-5.9到-8.8和氦0.08 < R/Ra < 0.27。这是典型的源于地壳数值。蒙法尔科内热储层极有可能是由中新世的古海水渗入在上始新世形成的碳酸盐平台,被连续的陆源沉积物截流形成的。SažetakGeokemijska istraživanja provedena su kako bi se utvrdilo porijeklo termalnih voda niskih do srednjih temperatura koje napajaju Monfalconske izvore u sjevernoj Italiji. Kemijski podatci pokazuju da se sastav voda približava sastavu morske vode. Istaknuti su procesi miješanja sa hladnim vodama niskog saliniteta. Vrijednosti δ18O i δD u rasponu su od −5.0 do −6.4 ‰ odnosno −33 to −40 ‰, sugerirajući razrjeđivanje slanog rezervoara slatkim vodama krškog tipa. Višak iona Ca2+ i Sr2+ s obzirom na konzervativno miješanje pripisuje se diagenetičkim reakcijama termalnih voda s krednim karbonatima u dubini. Izmjereni izotopni sasatav (omjer 87Sr/86Sr) varira između 0.70803 i 0.70814, nakon ispravka za suvišan Sr, pokazujući paleo morsku vodu iz Miocena. Otopljeni plinovi pokazuju dugoročne interakcije plinova i voda s plinovitom fazom dubokog krustalnog porijetla s dominirajućim CO2 i istaknutim izotopnom kompozicijom TDIC-a u rasponu −5.9 do −8.8 i helija sa 0.08 < R/Ra < 0.27, što je tipičan raspon za koru. Mogući scenarij za Monfalkonski termalni spremnik sastoji se od miocenskih morskih paleo voda koje prodiru kroz krške šupljine formirane u pretežno krednim karbonatima tijekom izdizanja platforme u gornjem Eocenu koje su zatočene od strane progresivnog pokopavanje terestičkim sedimenatima.ResumoRealizaram-se investigações geoquímicas com o fim de identificar a origem de águas termais de baixa a moderada temperatura que alimentam as nascentes de Monfalcone, no norte de Itália. Os dados químicos indicam que a água tem composição próxima da água do mar. Salienta-se a existência de processos de mistura com águas de baixas temperatura e salinidade. Os valores de δ18O e δD apresentam-se entre −5.0 a −6.4 ‰ e −33 a −40 ‰, respetivamente, o que sugere a diluição das águas marinhas por águas continentais de origem cársica. Um excesso de iões de Ca2+ e Sr2+ relativamente a uma mistura conservativa é atribuída a reações diagenéticas com águas termais cretácicas profundas. As composições isotópicas analisadas de Sr (relação 87Sr/86Sr) variam entre 0.70803 e 0.70814; no entanto, após a correção do excesso de Sr, a relação 87Sr/86Sr aponta para a presença de uma água fóssil de idade miocénica. Os gases dissolvidos indiciam um longo período de interações gás-água, com uma fase gasosa de origem crustal profunda dominada por CO2 e marcada por uma água com valores de carbono inorgânico dissolvido total entre −5.9 e −8.8 e uma assinatura de hélio com 0.08 < R/Ra < 0.27, a qual corresponde a um intervalo típico de origem crustal. Um cenário possível para o reservatório termal de Monfalcone consiste em paleoáguas marinhas miocénicas infiltradas através de cavidades cársicas formadas no seio das rochas carbonatadas do Cretácico durante a emersão da plataforma no Eocénico superior, as quais foram aprisionadas pelo progressivo preenchimento das cavidades por sedimentos terrígenos.IzvlečekNa termalnih vodah izvira pri Tržiču v severni Italiji, ki imajo od nizke do zmerne temperature, so bile opravljene geokemijske preiskave za določitev njihovega izvora. Kemijski podatki te termalne vode kažejo značilnosti, ki so podobne tistim morske vode. Poudarjeni so tudi procesi mešanja s hladno vodo nizke slanosti. Vrednosti δ18O in δD so v intervalu od −5.0 do −6.4 ‰ prve in od −33 do −40 ‰ druge in kažejo torej na redčenje slanega rezervoarja s sladkimi vodami kraškega značaja. Diagenetske reakcije in interakcije s karbonatno matriko so povzročile presežek ionov Ca2 + in Sr2 + v primerjavi z binarnim konzervativnim postopkom mešanja, kar kaže na globoke procese interakcije s karbonati iz obdobja Krede. Izmerjena izotopska sestava Sr ( razmerje 87Sr/86Sr ) se giblje med 0.70803 and 0.70814; po korekciji za presežek Sr, razmerje 87Sr/86Sr nakazuje paleo-morsko vodo iz Miocena. Raztopljeni plini nakazujejo dolgotrajne interakcije plin-voda s plinsko komponento globokega izvora v zemeljski skorji. V komponenti prevladuje CO2, vrednosti izotopske sestave vode TDIC so v intervalu od −5.9 do −8.8 in helij je med 0.08 < R/Ra < 0.27, kar je tipično v zemeljski skorji. Možni scenarij za termalni rezervoar v Tržiču je torej prisotnost paleo-morske vode iz Miocena, ki je prodrla skozi kraške votline, ki so predhodno nastale v karbonatih iz pretežno obdobja Krede, v času nastajanja celine v Zgornjem Eocenu in ki je bila ujeta in zaprta v karbonatih od naknadnega prekritja s terigeni sedimenti.

Evidence of a shallow water submarine hydrothermal field off Zannone Island from morphological and geochemical characterization: implications for Tyrrhenian Sea Quaternary volcanism

Discoveries from multibeam bathymetry and geochemical surveys performed off Zannone Island (western Pontine Archipelago, Tyrrhenian Sea) provide evidence of an undocumented hydrothermal field characterized by ongoing fluid emissions and morphologically complex giant depressions located in shallow water ( 250 m) that host pockmarks, mounds, small cones and active fluid vents, and which are interpreted as complex fluid escape features developed both through vigorous-explosive events and steady seepage. Their spatial distribution suggests that the NE-SW trending faults bounding the Ponza-Zannone structural high and the shallow fractured basement are favorable conditions for the upward migration of hydrothermal fluids. Moreover, we performed a detailed geochemical study to investigate the source of the hydrothermal fluids. The geochemical signature of the collected fluids provides information of active CO2-dominated degassing with a significant contribution of mantle volatiles, with measured 3He/4He values > 3.0 Ra that are similar to those recorded at Stromboli and Panarea volcanoes. The hydrothermal system produces volatiles that may originate from residual magma batches, similar to the Pleistocene trachytes cropping out in the SE sector of Ponza Island, that were probably intruded in the shallow crustal levels and never erupted. The discovery of the Zannone hydrothermal field updates the record of active hydrothermal areas of the Mediterranean Sea. Moreover, the recognition of several giant hydrothermal depressions characterized by a complex morphology is peculiar for the Mediterranean Sea.

Deep submarine gas vents in the aeolian offshore

Abstract Consistent results, concerning the detection of deep submarine hydrothermal vents, were obtained during two cruises (1991 and 1996) offshore from the Aeolian Islands, by CTD profiling from sea surface down to seafloor, and water-sampling casts. In 1991 an echo sounder showed a wide plume at a depth of about 800 m, within which water samples displayed anomalies in He and NH a content, suggesting also the presence of a water-vapour phase. The latter, in 1996, was remarkably observed as a horizontally diffusing plume at about 350 m. Near-plume casts were characterised by high CO2 and CH4 and low O2 concentrations in seawater, disturbed light transmission profiles, and false bottom outputs appearing at ∼300–350 m down to the seafloor from the rosette-mounted altimeter. No significant temperature/salinity anomalies were noted during either events. These preliminary results show the presence of deep hydrothermal activity, over an area where, one century ago, the occurrence of submarine eruptions was detected.

Assessment of the origin and geothermal potential of the thermal waters by hydro-isotope geochemistry: Eskisehir province, Turkey

ABSTRACT The thermal fluids vented over Eskisehir province have been investigated for their origin and to estimate the geothermal potential of the area. Thermal waters as well as bubbling and dissolved gases were collected and analysed for their chemical and isotopic features. Their isotopic composition varies in the range from −11.5 to −7.7 ‰ for δ18O, −84 and −57 ‰ for δ2H, and 0–7.2 TU for tritium. The gases (bubbling and dissolved) are mostly N2-dominated with a significant amount of CO2. The helium isotopic ratios are in the range of 0.2–0.66 R/Rac, indicate remarkable mantle-He contribution ranging between 2 and 10 % in the whole study area. Considering the estimated geothermal gradient about three times higher than the normal gradient, and the reservoir temperatures estimated to be between 50 and 100 °C using quartz and chalcedony geothermometers, a circulation model was built where possible mixing with shallow waters cool down the uprising geothermal fluids.