roman comagmatic province central italy evidence for subduction related magma genesis geochemical data on mafic volcanics show that important affinities exist between the roman and the calc alkaline rocks from the aeolian arc south tyrrhenian sea these affinities together with the close association of calc alkaline and k rich volcanics in the aeolian arc and in the naples area the continuity in the variation of abundances of incompatible elements from calc alkaline to potassic suites and the similarity in terms of major element geochemistry support a genetic relationship of the roman magmatism and the subduction processes that affected the apennines in tertiary time and are still active under the aeolian arc in the genetic model presented here both calc alkaline and k rich magmas were generated within a mantle heterogenously enriched in lil elements composition of the mantle was modified by addition of material probably sediments dragged down by the undergoing slab the geochemical and petrological differences displayed by the calc alkaline and k rich volcanics are accounted for by the different conditions of melting as well as by chemical and isotopic heterogeneities of the source 26 references 3 figures 1 table

monitoring of active but quiescent volcanoes using light hydrocarbon distribution in volcanic gases the results of 4 years of discontinuous monitoring in the campi flegrei italy abstract during the period from january 1991 to january 1994 the 10 yr geochemical monitoring in the campi flegrei southern italy usually performed using the inorganic gas fraction was implemented by discontinuous monitoring of the hydrocarbon gas fraction the measured compositions have revealed the presence of significant amounts of at least 11 hydrocarbon species related to alkane alkene and aromatic classes thermodynamic calculations showed the possible existence of partially independent equilibria within the c1 c2 c3 and c1 c2 c3 c4 alkane systems as well as among alkene alkane pairs at redox conditions controlled by the geothermal feo fe1 5o redox buffer system at temperatures between 200 and 400 c and ph2o controlled by the presence of a saline brine unlike the constancy of the measured and calculated inorganic temperature equilibrium temperature based on organic species has displayed fluctuations and a significant increase starting from the second half of 1993 according to their apparent correlation with other independent observations such as the measured increases of vapor fraction h2s co2 and h2 n2 ratios on the monitored fumarole in addition to a general increase of dissolved co2 in the campi flegrei groundwaters the observed variations of the organic parameters were interpreted as the result of a general increase in acid bearing gas flux throughout the re equilibration zone

fluid geochemistry and geothermometry in the unexploited geothermal field of the vicano cimino volcanic district central italy abstract the vicano cimino volcanic district vcvd is related to the post orogenic magmatic activity of the peri tyrrhenian sector of central italy the chemical and isotopic compositions of 333 water discharges and 25 gas emissions indicate the occurrence of two main sources 1 cold ca hco 3 to ca na k hco 3 type waters from relatively shallow aquifers hosted in volcanic and sedimentary formations and 2 thermal ca so 4 hco 3 type waters located in a deep co 2 pressurized reservoir hosted in carbonate evaporite rocks and separated from the shallow aquifers by thick sequences of low permeability formations carbon dioxide is mainly produced by thermal metamorphic decarbonation within the deepest and hottest parts of the carbonate evaporite reservoir 13 c co 2 from 3 1 to 2 2 vs vpdb likely affected by a mantle rooted co 2 release of co 2 rich gases from the deep aquifer into the overlying shallow aquifers produces high co 2 springs and bubbling pools the spatial distribution of thermal waters and co 2 rich cold discharges is strongly controlled by fractures and faults located in correspondence with buried structural highs stable isotopes d and 18 o suggest that meteoric water feeds both the shallow and deep reservoirs the relatively low r r a values 0 27 1 19 indicate that he is mainly deriving from a crustal source with minor component from the mantle affected by crustal contamination related to the subduction of the adriatic plate consistently relatively high n 2 ar and n 2 3 he ratios and positive 15 n n 2 values from 0 91 to 5 7 vs air characterize the vcvd gas discharges suggesting the occurrence of a significant excess nitrogen isotopic compositions of ch 4 13 c ch 4 and d ch 4 values from 28 9 to 22 1 vs vpdb and from 176 to 138 vs vsmow respectively and composition of light alkanes are indicative of prevalent thermogenic ch 4 although the occurrence of abiogenic ch 4 production cannot be excluded the 34 s h 2 s values from 9 3 to 11 4 vs vcdt are consistent with the hypothesis of h 2 s production from thermogenic reduction of triassic anhydrites gas geothermometry in the h 2 o h 2 ar h 2 s system suggests that the vcvd gases equilibrated in a liquid phase at redox conditions controlled by interactions of fluids with the local mineral assemblage at temperatures lower 2000 m geothermal wells this confirms that secondary processes i e steam condensation gas dissolution in shallow aquifers re equilibration at lower temperature and microbial activity significantly affect the chemistry of the uprising fluids thermal water chemistry supports the occurrence in this area of an anomalous heat flow that coupled with the recent demographic growth makes this site suitable for direct and indirect exploitation of the geothermal resource in agreement with the preliminary surveys carried out in the 1970 s 1990 s for geothermal exploration purposes

excess methane in continental hydrothermal emissions is abiogenic thermogenic hydrocarbons entirely deriving from the thermal degradation of organic matter usually exhibit methane to ethane plus propane ratios smaller than 100 we present hydrocarbon distribution data of continental hydrothermal gases whose methane has been independently identified to derive from the abiogenic reduction of co2 we find that excess amounts of methane with respect to thermogenic hydrocarbon distributions are characteristic for the investigated gases a similar pattern is observed for well discharges whose temperatures are too high to support any microbially mediated methanogenesis these findings strongly suggest that abiogenic methane production in continental hydrothermal systems is a more widespread process than previously assumed the maximum contribution of such emissions to the modern atmospheric ch4 budget is estimated at 1

geochemistry of water and gas discharges from the mt amiata silicic complex and surrounding areas central italy abstract the mt amiata volcano in central italy is intimately related to the post orogenic magmatic activity which started in pliocene times major trace elements and isotopic composition of thermal and cold spring waters and gas manifestations indicate the occurrence of three main reservoir of the thermal and cold waters in the mt amiata region the deepest one is located in an extensive carbonate reservoir buried by thick sequences of low permeability allochthonous and neo autochthonous formations thermal spring waters discharging from this aquifer have a neutral ca so4 composition due to the presence of anhydrite layers at the base of the carbonate series and possibly to absorption of deep derived h2s with subsequent oxidation to so42 in a system where ph is buffered by the calcite anhydrite pair marini and chiodini 1994 isotopic signature of these springs and n2 rich composition of associated gas phases suggest a clear local meteoric origin of the feeding waters and atmospheric o2 may be responsible for the oxidation of h2s the two shallower aquifers have different chemical features one is ca hco3 in composition and located in several sedimentary formations above the mesozoic carbonates the other one has a na cl composition and is hosted in marine sediments filling many post orogenic nw se trending basins strontium ba f and br contents have been used to group waters associated with each aquifer although circulating to some extent in the same carbonate reservoir the deep geothermal fluids at latera and mt amiata and thermal springs discharging from their outcropping areas have different composition na cl and ca so4 type respectively considering the high permeability of the reservoir rock the meteoric origin of thermal springs and the two different composition of the thermal waters self sealed barriers must be present at the boundaries of the geothermal systems the complex hydrology of the reservoir rocks greatly affects the reliability of geothermometers in liquid phase which understimate the real temperatures of the discovered geothermal fields more reliable temperatures are envisaged by using gas composition based geothermometers bulk composition of the 67 gas samples studied seems to be the result of a continuous mixing between a n2 rich component of meteoric origin related to the ca so4 aquifer and a deep co2 rich component rising largely along the boundaries of the geothermal systems nitrogen rich gas samples have nearly atmospheric n2 ar 83 and 15 n 14 n 0 ratios whereas co2 rich samples show anomalously high 15n values up to 6 13 likely related to n2 from metamorphic schists lying below the carbonate formations on the basis of average 13 c 12 c isotopic ratio 13c around 0 co2 seems to originate mainly from thermometamorphic reactions in the carbonate reservoir and or in carbonate layers embedded in the underlying metamorphic basement distribution of 3 he 4 he isotopic ratios indicates a radiogenic origin of helium in a tectonic environment that in spite of the presence of many post orogenic basins and mantle derived magmatics can presently be considered in a compressive phase

scrubbing process and chemical equilibria controlling the composition of light hydrocarbons in natural gas discharges an example from the geothermal fields of el salvador 1 the compositional features of fluids from both fumarolic discharges and productive geothermal wells of ahuachapan chipilapa berlin chinameca and san vicente geothermal systems el salvador are described and discussed in order to investigate the complex geochemical interactions involving geothermal fluids within the shallowest part of the hydrothermal circulation pathways our results highlight that secondary processes are able to strongly affect and modify the chemical characteristics of geothermal gases once they discharge to the surface as natural manifestations mainly in relation to the chemical physical properties of each gas species the effects of both gas dissolution in shallow aquifers and gas water rock chemical interactions on gas discharge composition make it difficult to get a correct evaluation of the thermodynamic conditions that characterize the geothermal reservoirs by applying the common geoindicators based on the chemical equilibria of the h2o co2 h2 ch4 co system differently the composition of the c1 c2 c3 alkanes and the c3 and c4 alkane alkene pair established within the geothermal reservoirs under the control of chemical reactions remains stable in samples collected from discharging gas vents these results suggest that the relative abundances of hydrocarbons characterized by similar structure and molecular size seem to be mainly regulated by the diffusion velocity of gases through the liquid dominated system therefore the chemical features of the light organic gas fraction of naturally discharging fluids can be successfully utilized for the evaluation of geothermal reservoir temperatures and redox conditions providing useful indications in terms of geothermal exploration and exploitation on this basis the distribution speciation and relative abundances of light hydrocarbons can also be considered highly promising in geochemical monitoring of active volcanic systems

dissolved potassium in the shallow groundwaters circulating in the volcanic rocks of central southern italy abstract the water rock interaction processes occurring in the low temperature shallow volcanic aquifers of central southern italy were simulated by means of the eq3 6 software package in reaction progress mode in the investigation both the roman magmatic province and monte amiata which belongs to the tuscan magmatic province were included the average k2o content of the volcanic rocks from the two areas is similar but the main k bearing phases are leucite in the roman magmatic province and sanidine at monte amiata computed concentrations of major dissolved components and sio2 are consistent with analytical data suggesting that the results of the eq3 6 runs are reliable simulations of the natural water rock interaction processes hence eq3 6 results can be used to investigate the transfer of k from rocks to water it turns out that the attainment of saturation with sanidine during early stages of rock dissolution limits k concentration in the monte amiata groundwaters to around an average of 2 9 1 3 mg l 1 1sd in the silica undersaturated roman magmatic province saturation with leucite is not attained during the evolution of groundwaters and consequently k concentration reaches comparatively high levels with an average of 24 6 27 1 mg l 1 1sd most of these unusually high k concentrations are due to natural weathering of silicates without any anthropogenic influence

sources and mechanisms of formation of gaseous hydrocarbons in sedimentary rocks abstract accepted concepts of principal stages of hydrocarbon formation fail to satisfactorily explain the accumulation of supergiant gasfields in west siberia u s s r such as for example urengoy which comprise 30 of the proven gas reserves of the world a new mathematical model has been developed which applies the concept of activation energy distribution to the formation of gases characteristic differences in the molecular structure of humic and sapropelic source organic matter are expressed in different activation energy distributions the model allows the calculation of isotope values for different types of organic matter and their dependence on maturity application of the model to west siberia suggests that the supergiant gas accumulations in urengoy are more likely formed from terrestrial organic matter through thermochemical reactions at moderate depths and are not the result of either deep overmature or bacteriogenic processes the new mathematical model suggests that humic organic matter in general has a high methane generating capacity at comparably low maturities of organic matter equivalent to 0 5 0 7 on the vitrinite reflectance scale

structural evolution of the pleistocene cimini trachytic volcanic complex central italy structural geomorphological geophysical and volcanological data have been processed for the implementation of a dedicated gis through which the structural evolution of the pleistocene trachytic cimini volcano central italy has been reconstructed the evolution of the cimini complex includes three main close in time phases 1 intrusion of a shallow laccolith rising along nw and ne trending faults and stagnating at the contact between the mesozoic cenozoic and the pliocene pleistocene sedimentary units constituting the bedrock of the volcano 2 emplacement of lava domes along radial and tangential fractures formed by the swelling induced by the laccolith growth 3 ignimbrite eruptions and final effusion of olivine latitic lavas domes are both of pelean and low lava dome type and their morphology was controlled by the location on the inclined surface of the swelled area some domes show to have uplifted upper pliocene thermally metamorphosed clay sediments suggesting a cryptodome like growth comparison of the top of the mesozoic cenozoic units with the top of the upper pliocene pleistocene sedimentary complex suggests that the laccolith emplaced in a graben of the mesozoic cenozoic sedimentary complex filled by the pliocene pleistocene sediments uplifted by the shallow intrusion stress patterns acting on the cimini area have been deduced analysing the drainage network and the morphotectonic lineaments rose diagrams show a large dispersion of the lineaments reflecting the local presence of radial and tangential fractures the most frequent extensional nw and ne trending lineaments have regional significance and controlled the magma uprise leading to the laccolith emplacement

regional groundwater focusing of nitrogen and noble gases into the hugoton panhandle giant gas field usa the hugoton panhandle giant gas field located across sw kansas and the texas and oklahoma panhandles in the usa is the case type example of high nitrogen concentrations in a natural gas being linked with high helium concentrations we collected 31 samples from producing wells in a north south traverse of the 350 km long field the samples reflect the previously observed north south change in 4he n2 with values changing from 0 020 to 0 049 respectively 3he 4he 21ne 22ne and 40ar 36ar vary between 0 14 0 25 ra 0 0373 0 0508 and 818 1156 respectively and are caused by quantifiable contributions from mantle crustal and atmosphere derived sources the atmosphere derived 20ne 36ar ratios are indistinguishable from groundwater values the crustal 4he 21ne and 4he 40ar ratios show a 60 excess of 4he compared to predicted production ratios in the crust and are typical of noble gases released from the shallow crust the mantle 3he n2 and groundwater recharge 36ar n2 ratios enable us to rule out significant magmatic or atmosphere contributions to the gas field n2 which is dominantly crustal in origin correlated 20ne n2 and 4he n2 shows mixing between two distinct crustal n2 components one n2 component n2 is associated with the crustal 4he and groundwater derived 20ne and the other with no resolvable noble gas contribution measured 15nn2 values vary from 2 7 to 9 4 the n2 and non he associated n2 endmembers are inferred to have 15nn2 3 and 13 and contribute from between 25 60 and 75 40 of the nitrogen respectively the non he associated nitrogen is probably derived from relatively mature organic matter in the sedimentary column the 15nn2 value is not compatible with a crystalline or high grade metamorphic source and similar to the 4he is inferred to be from a shallow or low metamorphic grade source rock 4he mass balance requires a regional crustal source its association with significant magmatic 3he pointing to a tectonically active source to the west of the hugoton system the volume of groundwater required to source the 20ne in the gas field demonstrates the viability of the groundwater system in providing the collection transport and focusing mechanism for the 4he and n2 the n2 20ne ratio shows that the n2 transport must be in the aqueous phase and that the degassing mechanism is probably contact between the regional groundwater system and the preexisting reservoir hydrocarbon gas phase

stable isotope geochemistry of cold co2 bearing mineral spring waters daylesford victoria australia sources of gas and water and links with waning volcanism abstract mineral springs in the victorian central highlands australia have high co 2 contents and naturally effervesce 13 c values of co 2 gas and dissolved inorganic carbon are 10 6 to 7 0 and 5 9 to 0 1 respectively with a net 13 c of 8 to 3 the carbon in these waters was derived from a mantle source associated with local pliocene to recent basaltic newer volcanic province rocks previously reported 3 he 4 he 1 2 3 1 relative to air and high he ne ratios are also consistent with the presence of magmatic volatiles silica contents imply that the waters were never heated above 130 c and that the system is not hydrothermal the occurrence of carbonated mineral springs in a relatively small region of the newer volcanics province where volcanic activity ceased several thousands of years ago may be due to the presence of late intrusions combined with deep circulation of water through deeply weathered and fractured ordovician basement a region of low seismic velocity under the daylesford area potentially images those intrusions most spring waters have 18 o and 2 h values of 8 to 6 and 45 to 35 respectively and lie to the left of the local and global meteoric water lines the anomalously low 18 o values results from co 2 exsolution at low temperatures which strongly partitions 18 o into the gas the lack of waters lying to the right of the local meteoric water line also implies that water rock interaction at elevated temperatures did not occur the 2 h values are lower than contemporary meteoric water suggesting that the waters may have recharged under colder climate conditions several thousand years ago the local ordovician rocks are gold bearing the present spring system is cold and would not efficiently transport au however volcanic is waning and the spring systems at the time of volcanism may have been hotter and able to redistribute au

hydrochemistry of two adjacent acid saline lakes in the andes of northern chile numerous closed basins in central andes contain saline lakes and salt crusts salars almost all of them are neutral or alkaline lakes only two lakes out of 84 studied in bolivia and chile are acid lakes they are located in two adjacent intravolcanic basins in northern chile the origin of acidity is due to the juxtaposition of two factors the very strong hydrothermal alteration of volcanic rocks in the drainage basins and the high sulfur content in the whole area primary minerals are replaced by amorphous silica limonite chlorite white mica and elemental sulfur the buffer capacity of the volcanic rocks has been considerably lowered and is no longer sufficient to neutralize the sulfuric acid generated by oxidation of native sulfur dissolution modeling of chlorite white mica and sulfur in a neutral inflow water leads to a composition very much like that of the acid inflows the modeled acid solution is oversaturated with respect to alunite by several orders of magnitude exactly as observed in natural acid inflows some of the alunite reported in the altered zones of the drainage basins could be supergene in origin the simulation of evaporation of acid inflows shows a good agreement between salar brines and computed brines indicating that the acidic brines do not originate in the past hydrothermal activity but result from recent supergene processes the leaching of the severely altered volcanic rocks and the direct evaporation of the resulting acidic waters aluminium shows a conservative behavior in both salars reflecting the drastic lowering of the saturation index of al sulfate minerals in evaporating acid brines which is confirmed by the lack of detection of alunite within both salars

multiple origins of methane in the earth methane occurrences in the earth s crust are predominantly of biogenic origin i e their ultimate source is biologically formed organic matter methane can also form through inorganic reactions and is consequently termed abiogenic biogenic methanes can either form through bacterial or thermogenic processes bacterial processes follow a co2 reduction and or fermentation pathway the fermentation processes are quantitatively more important in recent fresh sediments and swamps methane formed by co2 reduction however is most common in older sediments and commercial gasfields temperature organic substrate and age may be the major factors controlling the relative importance of the two pathways stable isotope concentrations in thermogenic methanes seem to be controlled by the extent of conversion of organic matter the timing of gas expulsion and trapping the different character of methane in individual sedimentary basins may be a result of the geologic history geothermal methanes are most likely derived from pyrolysis of organic matter abiogenic methane occurs in hydrothermal vents and ophiolite complexes inorganic reactions either surficial or deep seated are the likely source of such methanes a uniform mantle origin of methane is not supported by the observed isotope variations in naturally occurring methanes

unravelling abiogenic and biogenic sources of methane in the earth s deep subsurface at four underground sites in precambrian shield rocks in canada and south africa hydrocarbon and hydrogen gases exsolving from saline fracture waters are analyzed for compositional and isotopic signatures dominated by reduced gases such as ch4 h 2 and higher hydrocarbons ethane propane butane the most 13 c enriched methane end members at all four sites show a pattern of carbon and hydrogen isotopic values similar to abiogenic gases produced by water rock interaction that have been identified previously at one site on the precambrian shield in canada the abiogenic nature of these gases was not previously recognized due to mixing with a second methane component produced by microbial processes the microbial methane end member is identified based on carbon and hydrogen isotopic signatures and dna gene amplification pcr data that indicate the presence of methanogens a framework is presented to estimate the relative contribution of abiogenic versus microbial hydrocarbon gases at these sites this approach has important implications for evaluation of potential abiogenic hydrocarbon reservoirs in a wide range of geologic settings including the longstanding controversy concerning the possible contribution of abiogenic gases to economic petroleum hydrocarbon reservoirs the association of high concentrations of h2 with 13 c enriched ch4 end members and h2 depletion in the 13 c depleted methanogenic end members further suggests the possibility that abiogenic gases may support h2 autotrophy linked to methanogenesis in the deep subsurface d 2005 elsevier b v all rights reserved

origin of carbon in fumarolic gas from island arcs abstract we have measured 3 he 4 he ratios 13c values and co 2 3 he ratios of fumaroles and hot spring gases in three volcanic areas in japan the 3 he 4 he ratios 13c values and co 2 3 he ratios vary from 02 05 ratm 9 7 to 2 7 and from 7 74 109 to 1 18 1011 respectively based on these data and those in the literature we present the first quantitative estimates of the upper mantle sediment and limestone including slab components in co2 of volcanic and hydrothermal fluids from subduction zones taking compiled c isotopic data of limestone and organic sediment assuming that the co 2 3 he ratio and 13c value of mid ocean ridge basalt morb are representative of the upper mantle component and that later isotopic and elemental fractionations are minimal it is possible to deconvole each fraction of c on the basis of simple mixing equations up to 20 of the carbon in high temperature volcanic gases in subduction zones is derived from a morb type source while the major fraction of the gases is attributable to co2 produced by decarbonation of subducted marine limestone and slab carbonate

fluid geochemistry and geothermometry in the western sector of the sabatini volcanic district and the tolfa mountains central italy abstract a geochemical survey of 197 fluid discharges cold and thermal waters and bubbling pools and 15 gas emissions from the western sector of the sabatini volcanic district and the tolfa mountains latium central italy was carried out in 2007 2008 the chemical and isotopic compositions of the fluid discharges indicate the occurrence of two main sources 1 relatively shallow aquifers with ca na k hco 3 and ca mg hco 3 compositions when trapped in volcanic and sedimentary formations respectively and 2 a deep reservoir which is hosted in the mesozoic carbonate sequence rich in co 2 and having a ca so 4 hco 3 composition dissolution of a co 2 rich gas phase into the shallow aquifers produces high tds and high pco 2 cold waters while oxidation of deep derived h 2 s to so 4 2 generates low ph the 13 c co 2 values for gas emissions from 2 8 to 2 7 vs vpdb suggest that the origin of co 2 associated with the deep fluids is mainly related to thermo metamorphic reactions within the carbonate reservoir although significant mantle contribution may also occur however r r a values 0 37 0 62 indicate that he is mainly produced by a crustal source with a minor component from a crust contaminated mantle on the basis of the 13 c ch 4 and d ch 4 values from 25 7 to 19 5 vs vpdb and from 152 to 93 4 vs vsmow respectively ch 4 production is associated with thermogenic processes possibly related to abiogenic co 2 reduction within the carbonate reservoir the 34 s h 2 s values from 9 3 to 10 4 vs vcdt are consistent with the hypothesis of a sedimentary source of sulfur from thermogenic reduction of triassic sulfates geothermometric evaluations based on chemical equilibria co 2 ch 4 and separately h 2 s suggest that the reservoir equilibrium temperature is up to 300 c the d and 18 o data indicate that water recharging both the shallow and deep aquifers has a meteoric origin fluid geochemistry coupled with gravimetric data and tectonic lineaments supports the idea that significant contributions from a deep seated geothermal brine are present in the stigliano thermal fluid discharges exploration surveys investigated this area during 70 s 90 s for geothermal purposes nevertheless presently the area is still under exploited the presence of thermal waters and anomalous heat flow together with the demographic growth of the last years makes this site a suitable location for direct applications of the geothermal resource

sulfur and oxygen isotopes in italian marine sulfates of permian and triassic ages evaporitic sulfates of permian and triassic ages from italian occurrences were analyzed for sulfur and oxygen isotopes in order to supplement the corresponding isotope age curves and to use isotopic data to trace the origin of the sulfate in hydrologic systems the sulfur isotopic composition age relationships obtained in this study generally agree with those found throughout the world in two cases i e in samples from the carniola di bovegno formation bergamo and brescia alps and from the lower part of the gracilis formation recoaro vicenza sulfur isotopes suggest different ages for the rocks than the formerly ascribed ones oxygen isotopic compositions show the same range from 10 5 to 18 5 without any consistent relationship with sulfur these ranges of values are almost identical to those published previously for sulfates of permian and triassic ages from other locations

distribution of ammonium in minerals of metamorphic and granitic rocks abstract sixty nine analyses are given for nh4 in minerals of metamorphic and granitic rocks mostly from the ryoke belt japan the distribution of nh4 in coexisting minerals is quite systematic suggesting that nh4 is one of the stable geochemical components in high temperature processes biotite has the highest content of nh4 followed by muscovite k feldspar and plagioclase pure quartz is almost free from nh4 calcic plagioclase contains less nh4 than does sodic plagioclase the partition coefficients d pl bi d kf bi and d kf bi are on the average 0 11 0 38 and 0 43 respectively the fractionation of nh4 in these minerals is quite similar to that of rb but much smaller than that of cs distribution of nh4 as well as those of rb and cs appears to be explained by its ionic radius and the shortest cation o distances in alkali positions of minerals

hydrogeochemistry of the volcanic district in the tolfa and sabatini mountains in central italy abstract a geochemical study on 26 thermal springs and 5 samples from thermal wells t 20 c 19 cold springs 11 cold gas pools and 14 stream samples from the tolfa and sabatini mountains volcanic district about 1300 km2 has clarified their genesis and evolution meteoric waters infiltrate the more permeable exposed rocks carbonates and or volcanites and percolate down into two main aquifers one is deep and located in mesozoic anhydritic carbonate formations and is the regional geothermal reservoir that feeds springs that emerge at the margins of the carbonate series either exposed or barely covered its waters display typical bicarbonate sulfate alkaline earth composition the other aquifer s is shallower consisting of waters that circulate primarily in volcanic deposits the chemical characteristics of these shallow waters are heavily influenced by lithology and by a gas phase mainly co2 originating at depth temperature estimates obtained with sio2 and gas geothermometers which seem to be the most reliable under these conditions indicate the widespread occurrence of deep fluids at temperatures higher than 110 c under the area covered by the sabatini volcanites in some areas manziana trevignano nepi and cesano the subsurface waters reach temperatures within the range characteristic of medium to high enthalpy systems 120 160 c

depth dependent seismic attenuation in western greece abstract coda q estimates for the seismically active region of western greece are obtained by analyzing earthquakes occurring within the borders of the recently established patras seismological network the data set is composed of 97 low magnitude local events coda q values obtained show a clear dependence of frequency according to the relation q q 0 f n where n ranges from 0 77 to 0 82 the data fit indicated an increase of q 0 with increasing lapse time which is interpreted as being due to attenuation variation with depth

tracing nitrogen in volcanic and geothermal volatiles from the nicaraguan volcanic front we report new chemical and isotopic data from 26 volcanic and geothermal gases vapor condensates and thermal water samples collected along the nicaraguan volcanic front the samples were analyzed for chemical abundances and stable isotope compositions with a focus on nitrogen abundances and isotope ratios these data are used to evaluate samples for volatile contributions from magma air air saturated water and the crust samples devoid of crustal contamination based upon he isotope composition but slightly contaminated by air or air saturated water are corrected using n2 ar ratios in order to obtain primary magmatic values composed of contributions from upper mantle and subducted hemipelagic sediment on the down going plate using a mantle endmember with d 15 n 5 and n2 he 100 and a subducted sediment component with d 15 n 7 and n2 he 10 500 the average sediment contribution to nicaraguan volcanic and geothermal gases was determined to be 71 most of the gases were dominated by sediment de

helium isotopes in alpine regions abstract the isotopic composition of helium has been determined for a variety of groundwaters from springs and boreholes in the alps and adjacent regions the main alpine block in france italy switzerland and austria is characterized by a virtual absence of mantle derived 3he in near surface groundwaters in contrast adjacent areas where crust has been thinned by extension to the west in the rhone valley and ardeche to the north in the rhine valley and to the east in the vienna and pannonian basins mantle derived helium is clearly identified helium and undoubtedly other gases are introduced by melts whose generation is associated with crustal thinning however the surface distribution of mantle helium covers a much larger than that of associated surface volcanics this probably results from the dispersion of helium following its solution in groundwaters the po and the molasse neogene sedimentary basins developing by loading on the south and the north sides of the alps respectively have helium with typical crustal composition and a mantle component cannot be resolved these results clearly indicate the control of tectonics on the distribution of helium isotopes in the alpine regions

geothermometry on fluids circulating in a carbonate reservoir in north central italy the peri tyrrhenian belt of north central italy is a site of large scale fluid circulation in mesozoic carbonate anhydritic formations of thermal waters with ca sulfate composition these carbonate formations are the principal geothermal reservoir of the known italian geothermal fields owing to differences in the regional structure these carbonate rocks may have an intrinsic high or low hydraulic continuity the ca sulfate springs that surface at the periphery of these formations have circulated in the unconfined parts of the carbonate aquifer the high salinity na chloride geothermal fluids discharge from the confined parts of the same reservoir rocks these fluids are somewhat separated from fluids generated in the unconfined parts by possible barriers of low permeability they are also diluted with the ca sulfate waters and have re equilibrated at lower temperature because of these conditions the assessment of the deep reservoir temperatures cannot be made using rapidly re equilibrating geothermometers such as the sio2 geothermometer the latter reveals the temperature of the unconfined aquifer at best the study of the geohydrological nature of the reservoir rocks the composition of liquid and gas phases and the statistical behavior of the main chemical geothermometers applied to the shallow cold waters of the principal italian geothermal areas has shown that the geothermometer based on nali ratio seems to be the most reliable to evaluate the deep temperatures inside the confined parts of the carbonate reservoir

gas blowout from shallow boreholes at fiumicino rome induced hazard and evidence of deep co2 degassing on the tyrrhenian margin of central italy abstract a borehole drilled at fiumicino rome down to only 27 m depth in a zone where no gas emission at the surface was known caused a gas blowout from a pressurized gas pocket confined beneath a clay cover gas slowly diffused from the borehole within superficial permeable sand seven persons living in three ground floor flats of a near building had to be hospitalized due to co2 exposure all the houses in the proximity were evacuated at the request of the fire brigade two additional boreholes were drilled nearby hoping that this could rapidly exhaust the gas stored underground to the contrary the soil gas flux near houses increased and indoor co2 air concentration rapidly rose to lethal values 15 to 30 vol as a remediation we suggested to restore the continuity of the impervious gas cover by squeezing quick setting cement into the formation through new boreholes to be drilled near the existing ones although the first cement squeeze reduced drastically the co2 soil flux and indoor concentration six additional squeezes had to be carried out in order to lower the gas emission below the gas hazard threshold the gas was mostly made of co2 98 vol with minor n2 and ch4 its chemical and isotopic composition 13cco2 1 55 3he 4he 0 314 ra is similar to that of the gas manifestations of mts sabatini and alban hills volcanic areas though being somewhat contaminated by crustal and shallow organic volatiles these gases likely have a component originated in the mantle that beneath the volcanic roman comagmatic province is probably deeply contaminated with crustal material the fiumicino gas blowout indicates that the area of central italy characterized by strong co2 degassing extends westerly to include the tyrrhenian coast

carbon dioxide degassing and thermal energy release in the monte amiata volcanic geothermal area italy abstract the quaternary volcanic complex of mount amiata is located in southern tuscany italy and represents the most recent manifestation of the tuscan magmatic province the region is characterised by a large thermal anomaly and by the presence of numerous co2 rich gas emissions and geothermal features mainly located at the periphery of the volcanic complex two geothermal systems are located at increasing depths in the carbonate and metamorphic formations beneath the volcanic complex the shallow volcanic aquifer is separated from the deep geothermal systems by a low permeability unit ligurian unit a measured co2 discharge through soils of 1 8 109 mol a 1 shows that large amounts of co2 move from the deep reservoir to the surface a large range in 13ctdic 21 07 to 3 65 characterises the waters circulating in the aquifers of the region and the mass and isotopic balance of tdic allows distinguishing a discharge of 0 3 109 mol a 1 of deeply sourced co2 in spring waters the total natural co2 discharge 2 1 109 mol a 1 is slightly less than minimum co2 output estimated by an indirect method 2 8 109 mol a 1 but present day release of 5 8 109 mol a 1 co2 from deep geothermal wells may have reduced natural co2 discharge the heat transported by groundwater computed considering the increase in temperature from the infiltration area to the discharge from springs is of the same order of magnitude or higher than the regional conductive heat flow 200 mw m 2 and reaches extremely high values up to 2700 mw m 2 in the north eastern part of the study area heat transfer occurs mainly by conductive heating in the volcanic aquifer and by uprising gas and vapor along fault zones and in those areas where low permeability cover is lacking the comparison of co2 flux heat flow and geological setting shows that near surface geology and hydrogeological setting play a central role in determining co2 degassing and heat transfer patterns

temperature pressure and redox conditions governing the composition of the cold co2 gases discharged in north latium central italy abstract gases rich in co2 are produced over the northern latium area by metamorphic reactions involving carbonate formations or by magma degassing the gas migrates towards the surface and accumulates in sedimentary permeable structures which act as gas traps in that environment the pco2 is a variable externally fixed and the redox conditions at which the gases equilibrate are governed by the c co2 buffer temperature in the interval 100 180 c and pco2 from few bar to tens of bar have been estimated by means of the ratios between the redox sensitive gas species and co2 the composition of gases from two geothermal wells located in the study area and of other hydrothermal fluids suggest that the redox potential of low medium temperature carbonate hosted hydrothermal systems may be fixed by the c co2 buffer

helium strontium isotope constraints on mantle evolution beneath the roman comagmatic province italy european social fund scottish universities carnegie trust for the universities of scotland

geothermal structure of the tyrrhenian sea over 200 heat flow measurements have been carried out in the tyrrhenian sea mostly since 1977 as part of the heat flow map for italy and surrounding seas italian program as well as part of the french italian tyrrhenia program all data have been corrected for the influence of the plio quaternary sedimentation measured heat flow values were evaluated according to the sedimentary environment following criteria outlined by sclater et al 1980 in this way areas affected mainly by shallow thermal effects in the zones with maximum density of data have been displayed filtering out these shallow contributions the major regional geothermal trends were obtained the tyrrhenian basin can be divided in two distinct regions with different geothermal characteristics the northern part of the basin appears to be connected with the continental structures involved in the interaction between the corsica and tuscan margins the maximum heat flow area located offshore civitavecchia is related to the tensile structures of the tuscan geothermal province the most important thermal features of the central and southern part are located along the central belt trending nw se the lowest heat flow values are located in the peri tyrrhenian areas and are related to the continental margins of the basin while the maxima are connected with the stretched and thinned area localized in the bathyal plain taking into account the heat flow data as well as other geological and geophysical information an evolutionary model for the tyrrhenian sea is presented suggesting a generalized stretching of an initially continental crust accompanied by intensive rifting phases which may have favoured the onset of oceanic type crust

ammonium concentration and nitrogen isotope composition in metasedimentary rocks from different tectonometamorphic units of the european variscan belt the content and isotopic composition of ammonium nh4 were measured by using kjeldahl distillation for 63 samples of predominantly metasedimentary rocks from two different geological settings of the european variscides i e the erzgebirge and the zone of erbendorf vohenstrauss in germany the studied erzgebirge schists represent an early paleozoic passive margin sequence that reappears in different deep subducted metamorphic units this allows an efficient examination of nitrogen loss and isotope fractionation during prograde metamorphism ammonium is found to be progressively depleted accompanied by a shift in 15n from the low grade units 2 kbar 300 c with 638 124 ppm and 15n 2 2 0 6 to the garnet phyllite unit 9 kbar 470 c with 621 190 ppm and 15n 3 5 0 9 the mica schist eclogite unit 12 kbar 550 c with 394 113 ppm and 15n 3 9 0 8 and to the gneiss eclogite unit 12 kbar 730 c with 99 32 ppm and 15n 7 7 2 0 using equilibrium models for rayleigh distillation and batch volatilization suggest that the nitrogen depletion took place by ammonia release only for the mica schists this isotope fractionation can be explained by the loss of molecular nitrogen in comparison with the early paleozoic schists the proterozoic ortho and paragneisses of the erzgebirge gneiss unit 6 8 kbar 650 c contain significantly lower amounts of ammonium 70 ppm and reach relatively low 15n values 2 5 to 3 6 the paragneisses from the zone of erbendorf vohenstrauss zev sampled from the ktb pilot hole represents a separate tectonometamorphic unit that has undergone polyphase metamorphic conditions with the major imprint being amphibolite facies 7 kbar 650 700 c the metagraywackes have nh4 contents of 80 ppm and 15n of approximately 6 gneisses in the vicinity of a late cataclastic shear zone at 2000 m depth are characterized by a shift in nh4 250 ppm and 15n up to 12 which suggest late fluid rock interactions with a nitrogen and 15n enriched fluid

geologic volcanologic and tectonic setting of the vico cimino area italy abstract although the cimino and vico volcanic complexes are located close to each other in a structural low they belong to two different provinces cimino is connected to the tuscan roman anatectic magmatic province and vico to the roman campanian potassic alkaline province barberi et al 1971 marinelli 1975 the two volcanic centers lie on a basement formed by clays and sands of a miocene pliocene aged sedimentary cycle the mount cimino complex forms a central volcano composed of a series of rhyodacitic domes it was emplaced along a nw se trending fracture zone which can be followed for about 16 km cimino volcano was active from 1 4 m y to 0 95 m y ago eruption of rhyodacitic ignimbrites were preceded and followed by the emplacement of domes of the same composition fluid lavas of latitic and olivine latitic composition were emitted from the central volcano during the final phase of activity vico is a central volcano mainly composed of lava with a composite summit caldera it was emplaced along a ne sw trending fracture system the vico stratovolcano is formed by lavas of various compositions including phonolitic tephrites tephritic phonolites and slightly undersaturated trachytes the construction of the stratovolcano the most ancient exposed products of which have an age of 0 4 m y was followed by the eruption of four pyroclastic flows totalling several cubic kilometers which are dated at 0 3 0 15 m y the collapse of the caldera is most likely connected to the eruption of these pyroclastic flows the ring fractures of the caldera are associated with the emplacement of a pyroclastic unit most of which erupted along the inner northeast and north rim of the caldera post caldera activity is characterized by the emission of tephritic phonolitic and tephritic products that form the intra caldera stratovolcano named mount venere the vico cimino area northern latium located between the apennine chain and the tyrrhenian sea lies along the circum tyrrhenian belt that extends from northern tuscany to campania this zone has experienced post orogenic tensional movements since the middle miocene the teconic evolution of the tyrrhenian basin is closely associated with acid anatectic and potassic alkaline volcanism along the tyrrhenian margin of the apennines the age composition and geographic position of the volcanoes are controlled by different magnitudes of tensional tectonics and crustal thinning processes of the western margin of the apennine chain

origin of nitrogen rich natural gases in the california great valley evidence from helium carbon and nitrogen isotope ratios abstract dry natural gases produced from the sacramento and northern san joaquin basins contain up to 87 nitrogen 15n measurements for gases with n2 8 vary from 0 9 to 3 5 methane 13c values vary from 61 to 15 3 he 4 he ratios indicate the presence of mantle derived helium in addition to radiogenic crustal helium and suggest that the gases may originate from mixing between three principal components a hydrocarbon rich gas with 3 he 4 he 0 1r a derived from the microbial and thermogenic alteration of sedimentary organic matter a hydrocarbonrich gas with 3 he 4 he 2 75r a derived from the localized pyrolysis of sediments by magmatic volatiles and a nitrogenrich gas with 3 he 4 he 1r a the nitrogen rich component is characterized by methane 13c less negative than 25 and n 2 ar ratios as high as 22 000 nitrogen concentrations tend to increase towards the basement along the shallow eastern margin of the valley suggesting that the nitrogen rich component is derived from metasedimentary rocks deep within the crust the coast ranges fraciscan complex which was thrust well beneath the great valley during late mesozoic and early cenozoic subduction appears to be the most likely source

the relationship between potassic and calc alkaline post orogenic magmatism at vico volcano central italy abstract post orogenic magmatism in italy took place during the plio pleistocene alkaline ultrapotassic magmas and sub alkaline magmas were erupted from closely spaced volcanoes throughout the central part of italy therefore central italy is one of the best site to study the relationship between calc alkaline and alkaline magmatism in complex tectonic regimes activity at vico volcano developed in three periods between 0 419 ma and 0 095 ma vico products overlie leucite free volcanic rocks of monte cimino volcano that have a variable affinity from high potassium calc alkaline to ultrapotassic most of the vico rocks are leucite bearing roman type ultrapotassic however during the first period leucite free silicic rocks are interbedded with leucite bearing products the early erupted vico magmas are isotopically distinct from the youngest magmas age corrected sr sr i 0 71110 0 71149 and nd nd i 0 51210 0 51211 isotope ratios fall within the gap between roman type including younger vico and monte cimino rocks some leucite free vico rocks contain orthopyroxene crystals and al contents in clinopyroxenes are lower than those in clinopyroxenes from roman type rocks these characteristics are however also found in monte cimino rocks at the beginning of the first period leucite free latites to trachytes and rhyolites with high sr i 0 71127 0 71149 were erupted trachytes and leucite bearing latites with lower sr i 0 71110 0 71138 were erupted later the younger trachytes have higher rb and lre element contents than older leucite free rocks with similar sio 2 contents furthermore the onset of leucite crystallization is marked by a change in 87 sr 86 sr and sio 2 sr isotope ratios and their time related variations as well as the presence of two different trends in some trace element variation diagrams define two distinct modes of magma differentiation magmas evolved along a stratigraphically lower trend at the beginning of the activity whereas they evolved differently along a stratigraphically upper trend later in the volcanic history modelling of geochemical and sr isotope variations indicates that along the lower trend fractional crystallisation was the main evolutionary process whereas along the upper trend mixing between a leucite free magma and a leucite bearing magma occurred during crystallisation the sr isotope compositions of rocks from the early stage of activity at vico suggest mixing between magmas having different petrological affinities a leucite bearing roman type magma and a high potassium calc alkaline magma

fault controlled geothermal fluids of the northern trans mexican volcanic belt a geochemical and isotopic study of the los geysers field valley of queretaro mexico abstract this study focuses on the geochemical and isotopic composition of natural spring waters and gases discharging at los geysers thermal area northern trans mexican volcanic belt tmvb and its relations to the regional tectonic framework water is of na hco3 type and samples were collected at temperatures ranging from 48 c to 98 c and ph from 6 8 to 9 3 stable isotope compositions 10 0 to 8 0 for 18o and 75 6 to 69 7 for d deviate from the global and local meteoric lines suggesting fractionation by steam loss the 87sr 86sr values of the thermal waters range from 0 70664 to 0 70698 indicating that most of the strontium comes from the dissolution of carbonate belonging to the late berriasian to early valanginian in the guanajuato conglomerate group and a minor component of less radiogenic sr from paleogene neogene volcano sedimentary and volcanic rocks solute geothermometers reveal a reservoir temperature around 164 c a mixture between air and hydrothermal co2 composes the bubbling gases helium isotopes data r ra 0 96 1 71 and 4he 20ne ratios 0 53 9 41 reveal that helium is dominated by a radiogenic component with a considerable mantle he contribution up to 20 8 since there is no active volcanism at the northern tmvb mantle he is best explained by transport of volatiles along active faults reaching the crust mantle boundary the conceptual hydrogeochemical model involves a thermal aquifer at 1000 m depth which is recharged by regional meteoric water flow a high thermal gradient 153 c km and fast fluid upflow to the surface along discontinuities related to regional horst and graben tectonics

rate of diffuse carbon dioxide earth degassing estimated from carbon balance of regional aquifers the case of central apennine italy central italy is characterized by an anomalous flux of deeply derived co2 in the western tyrrhenian sector of central italy co2 degassing occurs mainly from focused emissions vents and strong diffuse degassing and thermal springs whereas in the eastern apennine area deep co2 is dissolved in cold groundwaters of regional aquifers hosted by mesozoic carbonate evaporite formations influx of deep co2 into 12 carbonate aquifers 12 500 km2 of the central apennine is computed through a carbon mass balance that couples aquifer geochemistry with isotopic and hydrogeological data mass balance calculations estimate that 6 5 1010 mol yr 1 of inorganic carbon are dissolved in the studied aquifers approximately 23 of this amount derives from biological sources active during the infiltration of the recharge waters 36 comes from carbonate dissolution while 41 is representative of deep carbon sources characterized by a common isotopic signature 13c 3 the calculated deep co2 influx rate ranges from 105 to 107 mol yr 1 km 2 increasing regionally from east to west in the study area

karst springs as natural pluviometers constraints on the isotopic composition of rainfall in the apennines of central italy abstract this paper describes an indirect method to calculate the isotopic composition of rainfall by using the isotopic composition of karst springs fed by waters circulating in the most important regional aquifer of central italy i e the mesozoic limestone sequence that forms the backbone of the apennines by using 18o and d data and the 18o and or d average gradient for elevation evaluated through the use of literature rainfall data and new measurements from a typical alpine valley in northern italy the altitude of precipitation of their parent water has been re calculated vertical descents of more than 2000 m from recharge to discharge have been assessed in some high flow rate cold springs in the morphologically steep adriatic sector of central italy a clear correlation between the vertical descents and more negative isotopic compositions at their relative emergence elevations is highlighted in contrast in the tyrrhenian sector lower karstic drops generally lower than 500 m correlate with less negative isotopic composition of recharge areas the 18o iso contour map of the recalculated parent rainfall in central italy is more detailed than any possible isotopic map of rainfall made using pluviometers unless large number of rainfall collectors were deployed on mountaintops the data also show that the isotopic composition of rainfall depends on the source of the storm water in particular precipitation is isotopically heavier when originating in the mediterranean sea and lighter when formed in the atlantic ocean consequently the collision between air masses with such a different isotopic signature results in a relatively small latitudinal fractionation effect the peninsular part of central italy is very narrow with several mountains and massifs more that 2000 m high and any latitudinal variation in the isotopic composition between rainfall sourced in the atlantic ocean and in the mediterranean sea is much lower than that due to the isotopic fractionation due to elevation

systematic review of geochemical data from thermal springs gas vents and fumaroles of southern italy for geothermal favourability mapping abstract in recent years two research projects specifically conceived by italian institutions of research to promote the implementation of the use of geothermal energy in southern italy has allowed the review of most data on chemical and isotopic compositions of natural thermal manifestations in the territory of italy two large databases one for thermal springs and co2 rich springs and a second one for fumarolic condensates and associated gas phase have been produced and are available on line with data spanning in time from the early 70 s to the present we have used those data after careful evaluation of the quality and reliability of them to produce correlation diagrams and isodistribution maps of some relevant geochemical geothermal parameters such as pco2 in thermal springs co2 and 13c in co2 of gas phases 3he 4he ratio and he in this way we have been able to delimit the areal patterns of thermal anomalies potentially related with geothermal reservoirs the cross correlation among the many parameters 40 selected has allowed the overview on the circulation of fluids at shallow crust in one of the most active tectonic boundary of the earth between the african and the eurasian continents shallow circulation of hot fluids is particularly active in the roman comagmatic province the neapolitan area and sicily both at etna aeolian archipelago and pantelleria island in the sicily channel where active geothermal systems are already known whose areal extension is probably much larger than what envisaged at present the geothermometric evaluation of data has not allowed to clearly identity new areas apart from those already known but nevertheless some areas in the inner apennines as well as sicily and sardinia have shown anomalous 3he 4he values that point to the presence of mantle fluids located inside the crust being most of active volcanic islands likely much smaller than the thermal anomaly they are associated with a futuristic perspective of utilizing geothermal fluids off shore is suggested moreover the database and the proposed maps can be a useful tool both scientific community and stakeholders to perform geothermal favourability maps and to identify potential new areas interesting from a geothermal perspective

implications of basement rock alteration in the nankai trough japan for subduction megathrust slip behavior abstract the nankai trough is an exceptionally well studied convergent margin known to host damaging megathrust earthquakes as well as various forms of slow fault slip outcrop studies of exhumed analogues for the modern subduction thrust as well as seismic reflection images of the active subduction zone suggest that the basaltic basement participates in plate boundary shearing at depths of a few km and greater we obtained altered basaltic upper basement from the modern nankai trough seaward of the trench recovered by drilling on iodp expedition 333 we performed laboratory friction experiments on bare surfaces and gouge powders of this material in addition to and in combination with other materials for comparison the altered basalt exhibits predominantly velocity strengthening frictional behavior indicating a tendency for stable slip for bare surface experiments few instances of velocity weakening friction occur and are restricted to slip rates of

light hydrocarbons as redox and temperature indicators in the geothermal field of el tatio northern chile abstract el tatio northern chile one of the largest geothermal fields of south america is presently undergoing a new program of geothermal exploration after the failure of the first exploration phase in the early 1970s the geochemical features of the fluid discharges characterizing this system mainly consist of boiling pools and fumaroles and represent the result of a complex mixing process involving 3 main components i hydrothermal ii atmospheric iii magmatic chemical reactions involving light hydrocarbons equilibrate at higher temperature than those directly measured in the geothermal wells and calculated on the basis of the composition of the inorganic gas species this suggests that in the deeper parts of the hydrothermal system temperatures higher than 300 c may be achieved such results can have a strong impact for the evaluation of the potential resources of this geothermal system moreover the chemical characteristics of the organic gas fraction allow the assessment of the chemical physical conditions governing the geochemical processes acting on geothermal fluids at depth

isotopic composition of precipitation in italy a first overall map abstract composite monthly samples of atmospheric precipitation were collected over different periods of time ranging from one to seven years at 77 different locations throughout italy these samples were measured for their oxygen and hydrogen isotopic composition to obtain basic information for hydrological and meteorological studies in this area on the basis of the results obtained a first map of the isotopic composition of precipitations in italy has been drawn up the main features of this map are the following 1 no isotopic latitudinal gradient has been found along the tyrrhenian coast from sicily to the italian french border despite the considerable range of latitude 2 a minor latitudinal gradient is found in the southeasternmost section of the country apulia partially favored by the local morphology 3 a marked shadow effect of the apennines is apparent along the southern section of the po valley and along the central section of the adriatic coast 4 the contribution of water vapor from the northernmost section of the adriatic sea affects the eastern and central sections of the po plain 5 the shadow effect of the alps is considerably smaller than expected 6 the isotopic vertical gradients calculated in nine different areas and based on groups of two to five different stations vary but are essentially close to about 0 2 100 m 7 when mean monthly temperature values were available their relationship with the isotopic composition of precipitation was found to be on average very poor 8 the relationship between mean 18o and mean d calculated for the collection locations shows shifts of both the slope and the deuterium excess when compared to the global meteoric water line these shifts are different for northern central and southern italy 9 in a few cases anomalously low monthly values suggest the existence of pronounced amount effects

dissolved helium isotope ratios in ground waters a new technique based on gas water re equilibration and its application to stromboli volcanic system here a new technique for the determination of dissolved he isotope ratios in ground waters is presented this method is based on the extraction and subsequent equilibrium of dissolved gases in an added host gas phase ultra pure n2 is placed in glass flasks 250 cc containing water samples that were hermetically sealed after their collection after shaking in an ultrasonic bath for 10 min an aliquot of the separated gas phase was removed from the flask for ms analysis 3he 4he ratios are measured by using a modified double collector mass spectrometer vg 5400 tft helium and ne concentrations are calculated by comparing the partial pressures of masses 4 and 20 of the samples with those of the air standard measured by a quadrupole mass spectrometer qms vg quartz using he and ne equilibrium partitioning coefficients it is possible to calculate the amount of gas originally dissolved in the water the technique was tested on both air saturated waters asw and thermal waters from stromboli aeolian islands south italy the results of which confirmed good reproducibility 5 and accuracy 3 of the data the method was then applied to three thermal water samples collected from the same volcanic area and the results compared with those of a fumarolic and a soil gas the isotope ratios for dissolved he gave values of 4 06 4 23 ra which are significantly higher than those previously reported in the literature 3 0 3 5 and 2 9 ra and that measured at the fumarole 3 09 ra suggesting a newer and higher isotopic signature for the volcanic system the proposed method appears to be a useful tool in the determination of 3he 4he ratios in ground water systems especially when free gases are not available or are dangerous to collect

origins of methane discharging from volcanic hydrothermal geothermal and cold emissions in italy abstract we have addressed the origins of methane in fumarolic thermal and cold emissions discharging from a diversity of geological settings spread all over the italian peninsula and at panarea and pantelleria islands fluid discharges from the main geothermal systems of the peri tyrrhenian area including mt amiata larderello latera and manziana show 13c ch4 and d ch4 values 28 v pdb and 160 v smow respectively and c1 c2 concentration ratios 1000 these patterns suggest that ch4 discharged from these systems is primarily generated by abiogenic reduction of co2 and or co methane seems to have at least partially a different origin than the higher hydrocarbons that might be entirely related to the thermal decomposition of organic matter or alternatively to methane polymerization fumaroles from the volcanic systems of solfatara vesuvio panarea and pantelleria have c1 c2 concentration ratios in a wide range from 17 to 4300 but 13c ch4 and d ch4 values 21 v pdb and 120 v smow respectively such isotopic values are very similar to those reported for ch4 discharging from ultramafic hydrothermal systems in agreement with recent evidence provided for solfatara and pantelleria we therefore infer that the ch4 in the volcanic fumaroles is mainly abiogenic too the 13c ch4 from 21 6 to 36 9 v pdb and d ch4 from 113 to 164 v smow values as well as the c1 c2 concentration ratios from 19 to 2240 in the co2 rich fluid discharges located between the geothermal volcanic systems and the apennine sedimentary chain tend to decrease eastwards as the temperatures of the fluid reservoirs progressively diminish suggesting that the ch4 production is mainly related to thermogenic processes according to this general trend the ch4 dominated fluids from mud volcanoes located eastwards of the co2 rich emissions are fed by an almost pure thermogenic source the easternmost fluid discharges from the po valley and the adriatic coast where organic matter evolves at relatively shallow depths in the presence of a low geothermal gradient record the lowest 13c ch4 and d ch4 values i e as low as 69 v pdb and