joint two dimensional dc resistivity and seismic travel time inversion with cross gradients constraints it is now common practice to perform collocated dc resistivity and seismic refraction surveys that complement each other in the search for more accurate characterization of the subsurface although conventional separate dc resistivity and seismic models can be diagnostic we posit that better results can be derived from jointly estimated models we make the assumption that both methods must be sensing the same underlying geology and have developed an innovative resistivity velocity cross gradients relationship to evaluate the structural features common to both methods the cross gradients function is incorporated as a constraint in a nonlinear least squares problem formulation which is solved using the lagrange multiplier method the resultant iterative two dimensional 2 d joint inversion scheme is successfully applied to synthetic data serving as validation tests here and to field data from collocated dc resistivity and seismic refraction profiling experiments and also compared to conventional separate inversion results the joint inversion results are shown to be superior to those from separate 2 d inversions of the respective data sets since our algorithm leads to resistivity and velocity models with remarkable structural agreement

interaction between the deep fluids and the shallow groundwaters on vulcano island italy the aim of this work is to study the interactions processes between the fluids of deep origin and the shallow groundwaters of the vulcano porto area during 1995 13 well waters were sampled three times may july and november and analysed for major and some minor elements b br and nh4 and for dissolved gases the close relationship of these waters with the deep magmatic source is highlighted by the composition of the dissolved gases furthermore the areal distribution of dissolved species is controlled mainly by the gas fluxes from depth and by the presence of a deeper thermal aquifer the distribution of major anomalies in the parameters measured in the groundwaters in fact overlaps the soil gas fluxes distribution that are related to the existence of preferential upflow routes of fumarolic fluids through weak structural lines in the volcanic edifice

chemical and isotopic composition of waters and dissolved gases in some thermal springs of sicily and adjacent volcanic islands italy hydrochemical major and some minor constituents stable isotope open image in new window and open image in new window 13ctdic total dissolved inorganic carbon and dissolved gas composition have been determined on 33 thermal discharges located throughout sicily italy and its adjacent islands on the basis of major ion contents four main water types have been distinguished 1 a na cl type 2 a ca mg na so4 cl type 3 a ca mg hco3 type and 4 a na hco3 type water most waters are meteoric in origin or resulting from mixing between meteoric water and heavy isotope end members in some samples 18o values reflect the effects of equilibrium processes between thermal waters and rocks positive 18o shift or thermal waters and co2 negative 18o shift dissolved gas composition indicates the occurrence of gas water interaction processes in thermal aquifers n2 o2 ratios higher than air saturated water asw suggest the presence of geochemical processes responsible for dissolved oxygen consumption high co2 contents more than 3000 cc litre stp dissolved in the thermal waters indicate the presence of an external source of carbon dioxide rich gas tdic content and 13ctdic show very large ranges from 4 6 to 145 3 mmol kg and from 10 0 and 2 8 respectively calculated values indicate the significant contribution from a deep source of carbon dioxide inorganic in origin interaction with mediterranean magmatic co2 characterized by heavier carbon isotope ratios open image in new window value from 3 to 0 vs v pdb capasso et al 1997 giammanco et al 1998 inguaggiato et al 2000 with respect to morb value and or input of co2 derived from thermal decomposition of marine carbonates have been inferred

fractionation processes affecting the stable carbon isotope signature of thermal waters from hydrothermal volcanic systems the examples of campi flegrei and vulcano island southern italy abstract the carbon isotopic composition of dissolved c bearing species is a powerful tool to discriminate the origin of carbon in thermal waters from volcanic and hydrothermal systems however the 13 c values of dissolved co 2 and tdic total dissolved inorganic carbon are often different with respect to the isotopic signature that characterizes the potential carbon primary sources i e deep hydrothermal reservoirs magmatic gases and organic activity the most commonly invoked explanation for such isotopic values is related to mixing processes between deep and shallow end members nevertheless experimental and empirical investigations demonstrated that isotopic fractionation due to secondary processes acting on the uprising fluids from the hydrothermal reservoirs is able to reproduce the measured isotopic values in this paper we investigated the chemistry of thermal waters collected at campi flegrei and vulcano island southern italy whose origin is related to interaction processes among magmatic gases meteoric water seawater and hosting rocks a special focus was dedicated to the 13 c values of dissolved co 2 13 c co2 aq and total dissolved inorganic carbon 13 c tdic the 13 c co2 aq and 13 c tdic values in the water samples from both these systems ranged from i those measured in fumarolic gases likely directly related to the deep hydrothermal magmatic reservoir and ii those typically characterizing biogenic co 2 i e produced by microbially driven degradation of organic matter a simple mixing model of the two end members apparently explaining these intermediate carbon isotopic values contrasts with the chemical composition of the dissolved gases on the contrary isotopic fractionation due to secondary processes such as calcite precipitation affecting hydrothermal fluids during their underground circulation seems to exhaustively justify both the chemical and isotopic data if not recognized these processes which frequently occur in volcanic and hydrothermal systems may lead to an erroneous interpretation of the carbon source causing an underestimation of the contribution of the hydrothermal magmatic fluids to the dissolved carbon species these results pose extreme caution in the interpretation of intermediate 13 c co2 aq and 13 c tdic values for the assessment of the carbon budget of hydrothermal volcanic systems

total co2 output from vulcano island aeolian islands italy 1 total co2 output from fumaroles soil gas bubbling gas discharges and water dissolved gases discharged from the island was estimated for vulcano island italy the co2 emission from fumaroles from the la fossa summit crater was estimated from the so2 crater output while co2 discharged through diffuse soil emission was quantified on the basis of 730 measurements of co2 fluxes from the soil of the island performed by using the accumulation chamber method the results indicate an overall output of 500 t day 1 of co2 from the island the main contribution to the total co2 output comes from the summit area of the la fossa cone 453 t day 1 with 362 t day 1 from crater fumaroles and 91 t day 1 from crater soil degassing the release of co2 from peripheral areas is 20 t day 1 by soil degassing palizzi and istmo areas mainly an amount comparable to both the contribution of water dissolved co2 6 t day 1 as well as to seawater bubbling co2 4 t day 1 measured in the istmo area presented data september 2007 refer to a period of moderate solphataric activity when the fumaroles temperature were 450 c and gas water molar ratio of fumaroles was up to 0 16 the calculated total co2emission allows the estimation of the mass release and related thermal energy from the volcanic hydrothermal system

water and gas chemistry at lake kivu drc geochemical evidence of vertical and horizontal heterogeneities in a multibasin structure 1 waters and dissolved gases collected along vertical profiles in the five basins main kabuno bay kalehe ishungu and bukavu forming the 485 m deep lake kivu democratic republic of the congo were analyzed to provide a geochemical conceptual model of the several processes controlling lake chemistry the measured horizontal and vertical variations of water and gas compositions suggest that each basin has distinct chemical features produced by 1 different contribution from long circulating fluid system containing magmatic co2 responsible of the huge co2 ch4 rich reservoir hosted within the deep lake water 2 spatial variations of the biomass distribution and or speciation and 3 solutes from water rock interactions the kabuno bay basin is characterized by the highest rate of magmatic fluid input accordingly this basin must be considered the most hazardous site for possible gas outburst that could be triggered by the activity of the nyiragongo and nyamulagira volcanoes located a few kilometers north of the lake

inversion of seismic refraction and wide angle reflection traveltimes for three dimensional layered crustal structure summary we present a method for the determination of crustal structure by simultaneous inversion of seismic refraction and wide angle reflection traveltimes for 3 d interface geometry and layer velocity crustal structure is represented by layers in which velocity varies linearly with depth separated by smooth interfaces with a cubic b spline parametrization lateral variations in structure are therefore represented by variations in interface depth only the model parametrization we have chosen means that ray paths consist of piecewise circular arc segments for which analytic expressions of trajectory and traveltime are calculated the two point problem of finding the first arrival ray path and traveltime of a specified phase between a given source and receiver is solved using a shooting technique a subspace inversion method is used to solve the inverse problem which is formulated as a non linear optimization problem in which we seek to minimize an objective function that consists of a data residual term and a regularization term before performing the inversion each data pick must be assigned as a refraction or reflection from a particular layer or interface since our method represents structure in terms of interfaces fewer parameters would generally be used in a reconstruction compared to an equivalent 3 d variable velocity inversion the method is well suited to wide angle surveys that consist of many sources and relatively few receivers or vice versa such as marine shot lines used in conjunction with land based receivers data coverage in this kind of survey is often sparse and especially if near offset ray paths are unavailable highly variable a 3 d synthetic test with an array consisting of eight sources lying within a three sided square of 79 receivers is described the test model consists of a three interface structure that includes a layer pinch out and the synthetic data set comprises 987 refraction and 930 reflection travel times contaminated with 75 ms of data noise six iterations of an 18 d subspace method demonstrate that the method can produce an accurate reconstruction that satisfies the data from a 1 d starting model we also find that estimates of a posteriori model covariance and resolution obtained from linear theory are useful in analysing solution reliability despite the non linear nature of the problem application of the method to data collected as part of the 1995 tasgo project in tasmania shows that the method can satisfy 1345 refraction and reflection traveltime picks with a geologically reasonable and robust 254 parameter three interface model the inversion results indicate that the moho beneath nw tasmania varies in depth from 27 km near the coast to 37 km near central tasmania with the major increase in depth occurring across the arthur lineament

first simultaneous mercury and major volatiles characterization of atmospheric hydrothermal emissions at the pisciarelli s fumarolic system campi flegrei italy abstract hydrothermal systems with active surface expressions are important natural source of atmospheric mercury here we report on the first simultaneous assessment of gaseous elemental mercury gem and major volatiles h2s and co2 fluxes from the fumarolic system of pisciarelli currently the most active at the campi flegrei caldera cfc naples italy this was achieved via a gps synchronized lumex and multigas survey which extends similar investigations reported elsewhere gem concentrations measured in the fumarolic emissions were consistently above background air level close to the degassing area mean 8 3 ng m 3 on average and ranged up to 12 000 ng m 3 our data evidenced pulsed sequences of gem increases in the fumarole plume closely matched by temporally consistent increases in co2 and h2s r2 0 9 supporting the idea that major volatiles such as co2 acts as potential carrier in transporting gem within the magmatic hydrothermal systems the slope of the best fit calculated for the dispersion of our data provides a gem co2 molar ratio of 1 1 10 8 and a gem h2s of 5 10 6 respectively these ratios are comparable to those reported for both low 100 c and high t 250 c fumaroles from non explosive volcanic hydrothermal degassing systems elsewhere we adopted an ad hoc method that combines video footages and gas measurements to obtain high precision concentration maps of gas emissions used to estimate the total atmospheric gem co2 and h2s flux of about 0 0113 225059 and 511 t y 1 respectively the human health risk assessment related to the gem emissions at pisciarelli confirms that except for the degassing fumarolic area all the main sites affected by the plume dispersion always remain well below the safe threshold recommended by the health authorities

the geological co2 degassing history of a long lived caldera the majority of the 100 holocene calderas on earth host vigorously active hydrothermal systems the heat and volatile budgets of which are sustained by degassing of deeply stored magma calderas may thus contribute a nontrivial although poorly quantified fraction of the global budget of magmatic volatiles such as co2 here we use original isotopic and petrological results from campi flegrei volcano italy to propose that hydrothermal calcites are natural mineral archives for the magmatic co2 that reacted with reservoir rocks during the geological history of a caldera we show that campi flegrei calcites identified in core samples extracted from 3 km deep geothermal wells formed at isotopic equilibrium with magmatic fluids having 18oh2o of 8 7 to 12 7 and 13cco2 of 1 5 this inferred fossil fluid composition is virtually identical to that of present day fumaroles demonstrating a stable carbon source during the caldera s 40 k y history we use the mass of calcites stored in the hydrothermal system to estimate that 12 gt of magmatic co2 reacted with the campi flegrei rocks during the caldera history this corresponds to a time averaged co2 flux of 800 t d 1 this long term co2 flux the first of its kind in the geological literature is similar to the present day soil co2 degassing flux 1100 200 t d 1 we conclude that the actual magmatic co2 degassing flux from calderas may be severely underestimated if subsurface calcite precipitation is not taken into account

widespread distribution of ascending fluids transporting mantle helium in the fore arc region and their upwelling processes noble gas and major element composition of deep groundwater in the kii peninsula southwest japan abstract chemical and isotopic studies including analyses of noble gases were comprehensively conducted on the groundwater of the entire kii peninsula which is located in the fore arc region of southwest japan groundwater of na cl hco3 na hco3 cl and na cl types was shown to be distributed across the whole area groundwater in the inland central part of the peninsula shows relatively low salinity whereas groundwater from the area along the ene trending median tectonic line mtl on the north side of the peninsula shows high salinity up to 18 800 mg l of cl and the presence of unusual heavy oxygen isotopes this trend is similar to that documented in saline waters from the arima region the so called arima type thermal water high 3he 4he ratios relative to the atmospheric value up to 6 7 ra were recorded throughout the kii peninsula covering a wider area than documented previously the saline groundwater is also strongly depleted in 20ne and heavy noble gases from the wide distribution of high 3he 4he values and the associated 20ne and cl concentrations we infer that aqueous fluids derived from dehydration of the subducting slab are present at depth beneath almost the entire kii peninsula these aqueous fluids may ascend along the major north dipping boundary faults the isotopic composition of groundwater from the southern part of the peninsula suggests that the contribution from these dehydration derived fluids is relatively small in this region however volatile components e g noble gases and co2 in the groundwater of this area may originate from the dehydration derived fluids upwelling of arima type thermal water of the na cl hco3 type is expected to undergo a phase separation of volatile species due to decompression as the fluid ascends the variety of water types documented may be due to this water gas separation and the subsequent incorporation of gaseous species into shallow meteoric groundwater the observed high 3he 4he ratios in the absence of a mantle wedge below the southern part of the kii peninsula may reflect the oblique ascent of these fluids along north dipping boundary faults

carbon dioxide and helium dissolved gases in groundwater at central tenerife island canary islands chemical and isotopic characterization seismic volcanic unrest was detected between 2004 and 2005 in the central and northwest zones of tenerife island canary islands spain with the aim of strengthening the program of geochemical and seismic volcanic surveillance a study of the origin characteristics and spatial distribution of dissolved carbon dioxide co2 and helium he gases in the volcanic aquifer of central tenerife island and around teide volcano was carried out this work also improves the hydrogeological and hydrogeochemical conceptual model of groundwater flow dissolved co2 concentrations in sampled groundwater are several orders of magnitude higher than that of air saturated water asw suggesting a significant contribution of non atmospheric co2 mainly magmatic confirmed through measurement of isotopic compositions 13ctdic and total dissolved inorganic carbon tdic concentrations a vertical stratification of dissolved co2 and 13ctdic values was observed in the volcanic aquifer at the eastern region of las canadas caldera stratification seems to be controlled by both degree of magmatic co2 water interaction and co2 degassing and the original 13cco2 g isotopic composition the highest dissolved helium 4he concentrations in groundwater seem to be related to radiogenic contributions resulting from water rock interactions and increase with residence time instead of with endogenous magmatic inputs isotopic systematics show that the dissolved gases in groundwater of central tenerife are variable mixtures of co2 3he rich fluids of volcanic hydrothermal origin with both organic and atmospheric components the results suggest that the eastern area of las canadas caldera the south volcanic ridge and the teide summit cone are the areas most affected by degassing of the volcanic hydrothermal system and they are therefore the most suitable zones for future geochemical monitoring

geochemistry of bazman thermal springs southeast iran abstract thermal springs of the bazman geothermal field 27 km south of the holocene bazman volcano caldera in makran continental margin se iran were studied for the first time new data on major components selected trace elements li rb cs ba sr fe al water isotopic composition h o and s chemical and isotopic 13c of co2 and ch4 3he 4he and 40ar 36ar composition of dissolved and bubbling gases from the hottest vents are presented four groups of springs with temperature range of 27 44 c discharge na cl waters with total dissolved solids tds of 800 to 7000 mg l from different aquifers composed of diverse type of rocks including granites and limestone only the hottest and most saline springs of the bazman field with low bicarbonate are close to equilibrium with surrounding rocks whereas the others discharge immature waters geothermometry based on sio2 concentrations na k and na k ca mg systems shows low equilibrium temperatures of up to 130 c consist with the temperatures estimated by alumino silicate minerals saturation indices the water isotopic composition 18o and d indicates meteoric origin with a small oxygen isotopic shift measured in the saline waters the 34s values of so4 indicate influence of gypsum and anhydrite dissolution from the host rock dissolved and free gases are n2 rich 95 vol with a high he content 0 5 vol a biogenic origin may be suggested for ch4 and co2 based on their carbon isotopic characteristics 62 and 13 vs v pdb respectively the r ra value of 0 5 indicates a contribution of about 6 of he from the mantle it is suggested that the bazman thermal waters are heated at considerable depth 4 5 km in a deep fault system most probably by the regional heat flow according to the local geothermal gradient

the age of the neapolitan yellow tuff caldera forming eruption campi flegrei caldera italy assessed by 40ar 39ar dating method abstract the neapolitan yellow tuff nyt is the product of the largest known trachytic phreatoplinian eruption it covered an area larger than 1000 km2 with an estimated volume of about 40 km3 of erupted magma during the course of the eruption a caldera collapsed within the previously formed campanian ignimbrite caldera the resulting nested structure strongly influenced the following volcanic activity in the campi flegrei caldera as previous dating of the nyt does not converge toward a unique result a new set of 40ar 39ar age determinations has been carried out to better constrain the age of the eruption two variants of the 40ar 39ar dating method were applied to determine the age of the nyt eruption 1 single crystal total fusion sctf on an individual phenocryst of feldspar and 2 laser incremental heating lih on bulk aliquots of feldspar phenocrysts the results of the sctf analyses show that the overall sample weighted mean age derived from the conventional age calculation is 15 6 0 8 ka a weighted mean of the isochron age is 15 3 1 2 ka 2 and has been assumed as the best indicator of age to be derived from the sctf analyses the lih analyses results show that plateau ages vary from 15 4 0 5 to 14 5 0 5 ka the overall weighted mean age of the isochron results is 14 9 0 4 ka 2 this result has been assumed as the reference age for the nyt eruption and agrees with the sctf age the new age obtained for the nyt deposits is of great relevance for the understanding of the evolution and the present state of the campi flegrei caldera and collocates the nyt in a crucial stratigraphical position to date the climatic oscillations that occurred between the late glacial and the holocene

interaction between fumarolic gases and thermal groundwaters at vulcano island italy evidences from chemical composition of dissolved gases in waters abstract the chemical composition of some gaseous species dissolved in thermal groundwaters from vulcano island was determined directly in the field the determinations were made using a methodology based on the equilibrium partitioning of gases between a liquid and a gaseous phase the analyses were performed with a portable gas chromatograph using a simple analytical procedure lasting 70 s he and co 2 partial pressures are notably higher than those of waters in equilibrium with the atmosphere confirming an interaction between volcanic gases and groundwaters the highest co 2 values were recorded in wells located in areas of anomalous co 2 and he exhalations related to the active volcano tectonic structures on the island the temporal variations in co 2 concentrations both in the crater fumarolic gases and in the dissolved gases of some wells showed a very similar pattern lastly the lowering of the he contents in the dissolved gases that occurred in 1996 1997 was probably due to a decreased interaction between the main degassing system crater fumaroles and the thermal groundwaters

chemical features and isotopic composition of gaseous manifestations on vulcano island aeolian islands italy an interpretative model of fluid circulation abstract between 1987 and 1995 gases were sampled from various manifestations on vulcano island including various fumaroles at la fossa crater and baia di levante and diffuse soil gas emissions in several areas which are characterized by high c02 fluxes since the end of 1987 volcanic activity has increased considerably showing a marked rise in temperature 300 c in 1987 to 670 c in december 1992 and in output of steam from crater fumaroles in addition variations have been observed in the chemical and isotopic compositions of gases and thermal waters which can be attributed to an increased inflow of deeper fluids the isotopic composition of fumarolec steam seems to be the result of mixing processes between a positive endmember of deep origin d 10 15 18o 6 8 and two endmembers of meteoric origin with different oxygen shifts variations observed in the c02 isotopic composition suggest that all sampled manifestations are fed by a single deep source which may be magmatic such a source would be characterized by the 613cco2 values of high temperature fumaroles 13cco2 0 these values are noticeably more positive than those generally attributed to magmatic gases 13cco2 5 8 implying crustal contamination processes of the magma the observed decrease in 18oco2 values of the crater fumaroles from 20 in 1978 to between 12 and 15 in 1993 1994 was probably caused by two different processes the first is a reduction of the enrichment factor between c02 and h2o which is related to the increased temperature of the gases and the second is a mixing with more negative waters of meteoric origin finally c02 addition or removal processes caused by interactions between deep gases and shallow hydrothermal waters are likely to be responsible for the different chemical and isotopic compositions of gaseous emissions in the vulcano porto area and the crater fumaroles

effects of steam heating processes on a stratified volcanic aquifer stable isotopes and dissolved gases in thermal waters of vulcano island aeolian archipelago we report on a comprehensive study of major ion chemistry dissolved gases and stable isotopes measured in water wells at vulcano island since 1988 the work focuses on a quantitative model describing steam condensation and boiling phenomena in shallow water bodies the model is based on the differences in partition coefficients between liquid water and vapor characterizing oxygen and hydrogen isotopes as well as volcanic gases co2 s species and hcl based on both physical conditions of aquifers identified during drilling campaigns and the composition of the volcanic vapor mass and enthalpy balances are applied in a multistep process of steam separation and condensation in shallower aquifers by comparing the model results with measured data we infer that i strong isotope enrichment observed in some shallow thermal waters can result from an increasing mass rate of condensing deep vapor even in water meteoric in origin ii the high co2 content measured in the fumarolic vapor during 1988 1993 affected the 18o value of the steam heated water due to co2 h2o isotope exchange iii the high pco2 measured in the coldest and peripheral waters are explained by the progressive enrichment of this gas in the vapor phase during multistep boiling and iv the high cl and so42 contents in the hottest waters can be attributed to the direct condensation single step of volcanic vapor the model also takes into account both the mass fluxes and the compositions of the involved endmembers steam and shallow groundwater which provides important inferences on the modifications observed or expected during periods of increasing mass and heat input from depth

carbon dioxide earth degassing and seismogenesis in central and southern italy 1 we present the first regional map of co2 earth degassing from a large area most of central and south italy derived from the carbon of deep provenance dissolved in the main springs of the region the investigation shows that a globally significant amount of deeply derived co2 10 of the estimated global co2 emitted from subaerial volcanoes is released by two large areas located in western italy the anomalous flux of co2 suddenly disappears in the apennine in correspondence to a narrow band where most of seismicity concentrates here at depth the gas accumulates in crustal traps generating co2 overpressurized reservoirs which induce seismicity

chemical and isotopic characterization of the gases of mount etna italy abstract in the period 1990 1995 43 samples of dissolved gases in groundwaters wells springs and drainage galleries and 64 samples of free gases fumaroles bubbling and soil gases from the mount etna area were collected and analysed isotopic analyses were also carried out of both the carbon of the co 2 in free gases and dissolved inorganic carbon dic in the waters the chemical composition of the gases depends on the relative abundances of three interacting components these are gases of 1 atmospheric origin enriched in o 2 and n 2 present almost exclusively in dissolved gases 2 deep origin enriched in co 2 prevalent in the majority of cases and 3 more superficial origin enriched in ch 4 prevailing in peripheral areas the isotopic composition of co 2 carbon confirms its mantle origin with either thermometamorphic co 2 contributions or modifications due to interaction with hot waters

hydrogeochemistry of the campania region in southern italy abstract a geochemical study of thermal springs cold springs stream waters and natural gas emissions has been carried out in the campania region of southern italy this region hosts four quaternary volcanic areas and thermal springs and gas emissions occur in three of them most thermal springs discharge na cl composition waters of connate origin derived from post orogenic volcanic and sedimentary formations although high enthalpy systems are present in two of the four volcanic areas there appear to be no magmatic contributions to the thermal springs solute geothermometers are unreliable as spring waters are strongly affected by mixing with shallow brines before discharging thermal springs and gas emissions also occur in non volcanic areas where an extensive carbonate unit acts as a regional aquifer for cold low salinity bicarbonate waters thermal features in these areas occur in fractured zones associated with active faults their compositions are determined only by the type of rock encountered by solutions before surface discharge as in other areas of north central italy the widespread occurrence of hot and cold co2 rich springs and gas emissions in both volcanic and non volcanic zones suggests a deep origin for the co2

chemical and isotopic compositions of minerals and waters from the campi flegrei volcanic system naples italy abstract based on their 34 s signature sulfate minerals and native sulfur around fumaroles and hot water pools from the campi flegrei volcanic area derive from supergenic oxidation of volcanic h 2 s their mean 34 s value 0 2 1 7 matches with that of fumarolic h 2 s at solfatara 0 3 0 3 as well as with the 34 s of 1 4 obtained for total sulfur in fresh trachyte from the area all 34 s values indicate a mostly deep seated origin for sulfur thermal waters were analysed for major and minor chemistry and for oxygen hydrogen and sulfur isotope compositions pools at pisciarelli are filled with evaporated meteoric water heated by rising magmatic gases the water 18 o 3 8 1 3 and 2 h 6 5 2 2 values in these steam heated waters are controlled by mixing and evaporation effects and the 34 s value of dissolved sulfate 1 3 0 3 basically agrees with supergenic oxidation of deep seated h 2 s as the major source of sulfur instead water from thermal springs and wells elsewhere in the campi flegrei appears to be a mixture between dilute meteoric and saline marine components the latter may be local seawater from the bay of pozzuoli the 18 o and 2 h values of waters sampled during 1993 1994 range from 5 6 to 0 3 and from 33 to 3 4 respectively the 34 s values of dissolved sulfate range between 0 1 and 19 5 in general sulfate is probably derived essentially from two sources both within the volcanic cover i e oxidation dissolution of pyrite and anhydrite and marine water an occasional source of water and sulfate is represented by magmatic gases which directly interact with shallow meteoric water as in the case of the hotel tennis well yielding steam heated water with 18 o 1 5 0 2 2 h 17 1 and 34 s 0 1

first observations of the fumarolic gas output from a restless caldera implications for the current period of unrest 2005 2013 at campi flegrei 1 the fumarolic gas output has not been quantified for any of the currently deforming calderas worldwide due to the lack of suitable gas flux sensing techniques in view of resumption of ground uplift since 2005 and the associated variations in gas chemistry campi flegrei in southern italy is one of the restless calderas where gas flux observations are especially necessary here we report the first ever obtained estimate of the campi flegrei fumarolic gas output based on a set of multigas surveys performed in 2012 and 2013 with an ad hoc designed measurement setup we estimate that the current campi flegrei fumarolic sulphur s flux is low on the order of 1 5 2 2 tons day suggesting substantial scrubbing of magmatic s by the hydrothermal system however the fumarolic carbon dioxide co2 output is 460 160 tons day mean sd which is surprisingly high for a dormant volcano in the hydrothermal stage of activity and results in a combined fumaroles soil co2 output of 1560 tons day assuming magma to be the predominant source we propose that the current co2 output can be supplied by either i a large 0 6 4 6 km3 deeply stored 7 km magmatic source with low co2 contents 0 05 0 1 wt or ii by a small to medium sized 0 01 0 1 km3 but co2 rich 2 wt magma possibly stored at pressures of 100 to 120 mpa independent geophysical evidence e g inferred from geodetic and gravity data is needed to distinguish between these two possibilities

isotopic study of the origin of sulfur and carbon in solfatara fumaroles campi flegrei caldera abstract isotopic study of the origin of sulfur and carbon in the hottest solfatara fumaroles of campi flegrei caldera southern italy was carried out on gas samples collected between 1983 and 1988 i e during and after the 1982 1984 seismo volcanic crisis the results for sulfur h2s the first ever reported on these gases indicate a mean 34 s of 0 3 0 3 range 0 7 to 0 1 versus canyon diablo troilite standard consistent with an igneous derivation of this element from either active magma degassing or and leaching of reduced sulfur bearing minerals in the volcanic layers the lack of peculiar 34s variation during and after the crisis suggests that the chemical variation of h2s and s c ratio in the fumaroles increase and then decrease by a factor 3 were not due to a changing origin of sulfur the mean 13c of carbon co2 over the period of survey 1 6 0 2 range 1 9 to 1 3 versus pdb standard is similar to the values obtained before the crisis since 1970 such an isotopic constancy requires a large and stable source of carbon feeding the fumaroles the measured 13c values are much higher than those typical of primary mantle magmatic carbon 6 2 and plot within the 13c range for marine carbonates 0 2 such high values may reflect either a 13c fractionation during degassing of co2 from the underlying 5 km depth magma chamber or b the contribution of heavy co2 of sedimentary origin derived from either thermometamorphism of mesozoic limestone series embedding the magma chamber or possibly past contamination of the local mantle by subducted sediments various arguments among which volcanological evidence of an isolated and cooling magma reservoir which would have been extensively degassed and so depleted in 13c along with time the low 3he 4he ratios and the broad 13c enrichment of volcanic fluids in the region and geochemical evidence of crust magma fluid interactions suggest that a considerable fraction 60 of co2 in solfatara fumaroles derives from carbonate sediments in the basement the contribution of magma derived co2 may be higher within the central part of the caldera including solfatara crater than toward its western margin where fumarolic and geothermal well gases exhibit lower 3he 4he ratios and still higher 13c values such a geochemical pattern is consistent with the central distribution of ground deformation and seismicity during the 1982 1984 crisis and with the idea of a residual magma body confined beneath the central part of the structure alternatively higher 13c and lower 3he 4he ratios toward the western margin may result from dilution of solfatara type gas during progressively deeper water boiling finally accepting that solfatara co2 derives from simple crustal mixing between magmatic and sedimentary carbon its constant isotopic composition together with the constant he isotope ratio would restrict the possibility of magma intrusion and or higher magmatic gas input as mechanisms responsible for the 1982 1984 events however this conclusion would no more hold true if the magma itself or even its mantle source were previously contaminated by crustal carbon

helium and carbon isotopes in the dissolved gases of friuli region ne italy geochemical evidence of co2 production and degassing over a seismically active area abstract 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 km 2 wide area are investigated the chemical composition of the dissolved gases revealed that a co 2 rich gas phase feeds the local groundwaters 3 he 4 he ratios r normalized to the atmospheric 3 he 4 he ratio ra 1 39 10 6 and corrected for the atmospheric contamination r ra c range from 0 29 to 1 as a result of a two component radiogenic and atmospheric mixing the 13 c 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 co 2 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 co 2 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

impact of depositional facies on the distribution of diagenetic alterations in the devonian shoreface sandstone reservoirs southern ghadamis basin libya abstract the middle devonian shoreface quartz arenites present day burial depths 2833 2786 m are important oil and gas reservoirs in the ghadamis basin western libya this integrated petrographic and geochemical study aims to unravel the impact of depositional facies on distribution of diagenetic alterations and consequently related reservoir quality and heterogeneity of the sandstones eogenetic alterations include the formation of kaolinite pseudomatrix and pyrite the mesogenetic alterations include cementation by quartz overgrowths fe dolomite ankerite and illite transformation of kaolinite to dickite illitization of smectite intergranular quartz dissolution and stylolitization and albitization of feldspar the higher energy of deposition of the coarser grained upper shoreface sandstones combined with less extensive chemical compaction and smaller amounts of quartz overgrowths account for their better primary reservoir quality compared to the finer grained middle lower shoreface sandstones the formation of kaolin in the upper and middle shoreface sandstones is attributed to a greater flux of meteoric water more abundant quartz overgrowths in the middle and lower shoreface is attributed to a greater extent of stylolitization which was promoted by more abundant illitic clays this study demonstrated that linking the distribution of diagenetic alterations to depositional facies of shoreface sandstones leads to a better understanding of the impact of these alterations on the spatial and temporal variation in quality and heterogeneity of the reservoirs

variation in the total dissolved carbon isotope composition of thermal waters of the island of ischia italy and its implications for volcanic surveillance abstract during surveys conducted in 1997 30 thermal waters for a total of 39 analysis were collected from shallow wells utilised for resort spas on the island of ischia well temperatures ranged from 25 to 82 c and their depths from 30 to 150 m pools with temperatures of 26 to 67 c were also sampled on the northern flank of the mt epomeo the samples were analysed for bulk chemical composition as well as h o and c isotope composition isotopic analyses of water samples showed wide variations in both deuterium and oxygen 18 which ranged from 37 4 to 8 1 and 6 8 to 1 1 respectively overall 13 c in total dissolved carbon tdc ranged from 11 5 to 2 3 and computed 13 c of co 2 g results ranged from 18 5 to 1 72 water samples with co 2 content of up to about 1 bar partial pressure exhibited 13 c co 2 ranging from 4 to 1 water samples varied chemically from low salinity hco 3 well waters 1 4 g l of essentially meteoric origin to high salinity cl waters up to 40 g l mixing processes from local groundwater seawater and evaporated waters have also been identified models for the chemical and isotopic data on the thermal manifestations have been developed for low and high pressure conditions in order to assess the isotopic composition of deep co 2 assuming that this component is continuously added to the solutions until degassing occurs at shallow depths or at the surface constraints due to the reaction of water with volcanic glass have been taken into account for in the computations in addition to those relative to the carbon components participating in the carbonate equilibria results from such simulations indicate that deep co 2 added to the shallow waters probably has a carbon isotope composition 2 which most likely stems from a mixed magmatic sedimentary origin

geochemical monitoring of the thermal waters of the phlegraean fields abstract thermal waters from the phlegraean fields pf caldera area have been periodically sampled and analysed during the period 1990 1999 for major chemical constituents and chemico physical parameters to define the most useful variables for geochemical surveillance the variations observed in waters from different locations were compared with ground movements and microseismic events recorded at the time of observation the discontinuous monitoring of the hydrothermal system of the pf has given indications about the geochemical variations brought about by changes in the chemical and physical characteristics of the deep aquifers because of the complexity of the pf geothermal system in each sampling location different variations have been observed and then evaluated on the basis of the different kinds and degrees of deep fluid supply characterising waters sampled in the different zones in some cases a good correspondence between vertical soil movements and chemical changes in the waters has been observed in particular in pools and wells located around the solfatara crater interesting variations in some chemical parameters ph ammonia and or so 4 2 cl ratios have been recorded variations can be observed in all of the sampling locations but pools and wells located near the solfatara crater are the best sites for detecting changes occurring in the deep hydrothermal system and possibly in the activity of the underlying magma chamber

mantle vs crustal fluid sources in the gas discharges from lesser caucasus and talysh mountains azerbaijan in relation to the regional geotectonic setting abstract azerbaijan is famous for the impressive phenomenon of mud volcanism that dominates the landscape of the central sector of the country the gases released are here strongly ch4 enriched conversely the lesser caucasus to the nw host numerous thermo mineral springs into which co2 rich gas are bubbling in the talysh area located to se at the border with iran ch4 n2 and co2 rich gases are discharged the chemical and isotopic composition of the free gases from the lesser caucasus and talysh was investigated to define their origin in a particularly complex geodynamical and geological setting the co2 in the lesser caucasus was apparently associated with thermometamorphic processes affecting the jurassic and cretaceous limestones at which a minor contribution by a mantle component helium was also recognized likely related to oceanic subduction and or fluid interactions with the accreted ophiolite complex the fold zone of talysh which represents the northern extension of the iranian alborz chain produced the early and middle eocene to pleistocene volcanism that was invoked to explain the distinct chemical and isotopic composition of the discharged gases the co2 rich gases at buludul showed helium and carbon isotopic ratios that suggested mixing processes between i a crustal component produced by hydrolysis of limestones and interaction with volcano sedimentary complexes rich in organic material and ii tectonically driven mantle derived fluids the relatively high rc ra values 6 are indeed comparable with those recorded in the active volcanoes of the region indicating the presence of degassing magmas at depth finally typical hydrothermal gas compounds e g co and h2s were not detected in both the study areas unless secondary processes at shallow depth are occurring the presence of developed hydrothermal systems at regional scale is unlikely

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

evidence of thermal driven processes triggering the 2005 2014 unrest at campi flegrei caldera abstract an accelerating process of ground deformation that began 10 years ago is currently affecting the campi flegrei caldera the deformation pattern is here explained with the overlapping of two processes short time pulses that are caused by injection of magmatic fluids into the hydrothermal system and a long time process of heating of the rock the short pulses are highlighted by comparison of the residuals of ground deformation fitted with an accelerating polynomial function with the fumarolic co 2 ch 4 and he ch 4 ratios which are good geochemical indicators of the arrival of magmatic gases the two independent datasets show the same sequence of five peaks with a delay of 200 days of the geochemical signal with respect to the geodetic signal the heating of the hydrothermal system which parallels the long period accelerating curve is inferred by temperature pressure gas geoindicators referring to a recent interpretation that relates variations in the fumarolic inert gas species to open system magma degassing we infer that the heating is caused by enrichment in water of the magmatic fluids and by an increment in their flux heating of the rock caused by magmatic fluids can be a central factor in triggering unrest at calderas

geophysical modeling via simultaneous joint inversion of seismic gravity and electromagnetic data application to prestack depth imaging geophysical modeling of multiple geophysical parameters can take place reliably through the simultaneous joint inversion of the different geophysical domains the desired objective is the derivation of a model expressing different geophysical properties of the earth but at the same time showing consistency among the parameters this concept generally referred to as data integration is widespread in geophysics but the way of achieving it is not obvious several authors have proposed different approaches where data interpretation and experience all contributed to the task the result is that no general workflows could be defined that left ample margins for uncertainties and personal judgment

volcanological and petrological evolution of vulcano island aeolian arc southern tyrrhenian sea petrological and geochemical data are reported for volcanic rocks from vulcano island the subaerial volcanism 120 ka to present built up a nw se elongated composite structure affected by two intersecting multistage calderas volcanics older than 20 ka consist mostly of high k calc alkaline hkca to shoshonitic sho mafic rocks these magmas interacted significantly with the continental crust which generated variable sr isotopic ratios 0 70412 0 70520 however a major role was also played by input of parental liquids into the magma chamber which prevented further evolution of the magmas hkca sho and potassic ks rocks formed from 20 to 8 ka display a much larger range of sio2 from shoshonites to rhyolites and higher concentrations of incompatible elements with respect to the previous stage sr isotopic ratios show small variations 0 70448 0 70486 mixing of silicic and mafic liquids and fractional crystallization processes fc were the main evolutionary processes during this stage volcanics younger than 8 ka consist of sho and leucite bearing ks mafic rocks with abundant intermediate and silicic products mafic and intermediate rocks display similar incompatible element abundances and sr isotopic ratios as the previous stage volcanics whereas higher 87sr 86sr 0 70494 0 70583 are observed in some rhyolites these products originated from a complex interplay of fc crustal assimilation and magma mixing processes the most mafic rocks show increasing incompatible element abundances rb sr rb ba mg al mg ca and a decrease in large ion lithophile to high field strength element ratios passing from older hkca sho to the younger sho ks volcanics these variations suggest a shifting of magma sources from a slightly metasomatized asthenosphere fertile peridotite to a more strongly metasomatized lithospheric mantle residual peridotite time related petrological and geochemical variations have been used to develop a model for the evolution of the vulcano plumbing system

monitoring and modelling hydrothermal fluid emission at la solfatara phlegrean fields italy an interdisciplinary approach to the study of diffuse degassing discharge of hydrothermal fluids at la solfatara is one of the many pieces of evidence testifying to the level of activity and the potential danger characterizing the volcanic complex of the phlegrean fields recent measurements of diffuse degassing shed light on the unexpected magnitude of this process and prompted further research to improve our understanding of the hydrothermal system feeding the surface phenomenon at la solfatara in this work we first present new data on co2 diffuse degassing that were collected during a campaign in july 2000 and confirm previous measurements of the degassing rate these data together with other information on subsurface structures and conditions provided the necessary constraints to perform physical modelling of the hydrothermal fluid circulation at la solfatara numerical simulations describe the ascent and evolution of a hot multi phase and multi component fluid composed of water and carbon dioxide through a homogeneous porous medium when certain system properties and conditions are used this model reproduces some of the main features which characterize the natural system including the energy budget associated with the ascent and condensation of hot fluids and the development of a single phase gas region whose existence was inferred from independent chemical data further simulations investigated the effects associated with changes in rock properties and fluid injection rates results showed that an increase in the permeability at shallow depth may have an important influence on the system conditions and fluid discharge they imply that surface phenomena accompanied by very high temperatures at shallow depths may survive long after deep feeding has ceased

water and dissolved gas geochemistry at coatepeque ilopango and chanmico volcanic lakes el salvador central america abstract coatepeque on the e slope of santa ana volcano ilopango inside ilopango caldera and chanmico associated with san salvador volcano are volcanic lakes in el salvador showing a thermocline at a relatively shallow depth from 30 to 40 m from 20 to 40 m and from 5 to 15 m depth respectively and anoxic conditions below 33 24 and 4 m depth respectively the na cl composition of the coatepeque and ilopango lakes displaying tds values up to 1226 and 1216 mg l respectively is likely due to hydrothermal fluids that feed these two lakes as also confirmed by cl br molar ratios 650 high as b li and si contents and cl so42 ratio 1 the mg2 hco3 water composition of lake chanmico whose tds values were between 566 and 856 mg l suggests water rock interaction processes with mafic ultramafic rocks variably affected by serpentinization processes which produced high mg2 si and b concentrations waters at depth were characterized by the presence of co2 from an extra lacustrine source as suggested by 13c co2 values significantly less negative than those typically related to biogenic processes albeit this gas was found in smaller quantities when compared to those recorded in other meromictic lakes hosted in quiescent volcanic systems e g lake kivu in drc monticchio albano and averno lakes in italy hule and rio cuarto lakes in costa rica lake pavin in france the occurrence of ch4 whose concentrations in lake chanmico were up to two orders of magnitude higher than those recorded in coatepeque and ilopango lakes suggests bacterial methanogenesis

source processes of the thermal waters from the phlegraean fields naples italy by means of the study of selected minor and trace elements distribution abstract the geochemical characteristics of hydrothermal waters from the phlegraean fields p f naples italy were analysed for minor and trace elements selectively mobilised in hydrothermal systems such as b f hg as pb and tl the water samples collected from a shallow aquifer likely to be fed by deeper fluids showed various geochemical features resulting from the mixing of three components 1 surface waters of meteoric origin 2 hot deep waters deriving from water rock interaction and including deep waters of marine origin 3 magmatic fluids rising from the local magma chamber lying a few kilometres below the town of pozzuoli this setting although very complex provides a reliable means of studying the distribution of the investigated trace elements in particular within the phlegraean area high contents of b 0 1 48 mg l f 0 5 8 mg l as 16 6050 g l and hg 0 7 232 g l were observed the levels of thallium in the springs close to solfatara about 7 g l were in line with those normally recorded in hydrothermal areas whereas high levels of this element up to 23 3 g l were identified in other wells of the study area lead 1 3 to 29 1 g l appears to be anomalous with respect to its normal content in groundwater about 1 g l owing to the presence of high density brines at depth which enhance the solubility of pb in volcanic rocks under hydrothermal conditions the distribution of the investigated trace elements in the phlegraean fields thermal area is probably related to the different ascent pathways of the fluids clearly apart from the influence exerted by anomalous thermal conditions each element shows a different behaviour depending on its geochemical affinity with mineral phases and as a consequence of the different enthalpy values which determine ion partitioning in gaseous phases based on geochemical evidences and on the distribution of minor and trace elements the source processes of the investigated hydrothermal waters were defined five main groups were identified 1 acid sulphate waters resulting from mixing of meteoric water with magmatic gases mainly h 2 s 2 high sulphate chloride waters from a deep reservoir located in the major upflow zone 3 waters associated with significant degassing of magmatic co 2 4 waters from a deep geothermal neutral chloride reservoir resulting from heating of marine water modified by water rock interaction processes 5 cold waters from the inner area influenced by low temperature water rock interaction processes

chemical and isotopic signatures of the basement rocks from the campi flegrei geothermal field naples southern italy inferences about the origin and evolution of its hydrothermal fluids abstract the campi flegrei naples campanian plain southern italy geothermal system is hosted by quaternary volcanic rocks erupted before during and after the formation of the caldera that represents one of the major structural features in the neapolitan area the volcanic products rest on a mesozoic carbonate basement cropping out north east and south of the area chemical major minor and trace elements and stable isotope c h o analyses were conducted on drill core samples recovered from geothermal wells mf 1 mf 5 sv 1 and sv 3 at depths of 1100 to 2900 m the study was complemented by petrographic and sem examination of thin sections the water which feeds the system is both marine and meteoric in origin mineral zonation typical of a high temperature geothermal system exists in all the geothermal wells measured temperatures in wells are as high as 400 c the chemical composition of the waters suggests the existence of two reservoirs a shallow reservoir depth 2000 m of hypersaline water the drill cores are mainly hydrothermally altered volcanics of trachy latitic affinity but some altered pelites and limestones are also present published na mg and k concentrations of selected geothermal waters indicate that the hydrothermal fluids are in equilibrium with their host rocks with respect to k feldspar albite sericite and chlorite the measured 18 o smow values of rocks range from 4 3 to 16 5 the measured d smow values range from 79 to 46 the calculated isotopic composition of the fluids at equilibrium with the samples vary from 1 to 8 3 18 o and from 52 to 1 d the estimated isotopic composition of the waters at equilibrium with the studied samples confirmed the existence of two distinct fluid types circulating in the geothermal system the shallower has a marine water signature while the deeper water has a signature consistent both with magmatic and meteoric origins in the latter case the recharge of this aquifer likely occurs at the outcrop of the mesozoic limestones surrounding the campanian plain after infiltration the water percolates through evaporitic layers becoming hypersaline and d depleted

seismic attenuation imaging of campi flegrei evidence of gas reservoirs hydrothermal basins and feeding systems 1 passive high resolution attenuation tomography is used here to image the geological structure in the first upper 4 km of the shallow crust beneath the campi flegrei caldera southern italy the inverse q was estimated for each source receiver path using the coda normalization method s waves and the slope decay method p waves and s waves inversion was performed using a multi resolution method which ensures a minimum cell size resolution of 500 m the study of the resolution matrix as well as the synthetic tests guarantee an optimal reproduction of the input anomalies in the center of the caldera between 0 and 3 5 km in depth high attenuation vertical structures are connected at the surface with the main volcanological features e g the solfatara and mofete fumarole fields and depict vertical q contrast imaging important geological structures such as the la starza fault these high attenuation volumes extend between the surface and a depth of about 3 km where a hard rock layer is imaged by the sharp contrast of the quality factors the retrieved image of the campi flegrei has been jointly interpreted taking into account evidence from seismological geological volcanological and geochemical investigations this analysis has allowed an unprecedented view of the feeding systems in this area and in particular it recognizes the vertically extending high attenuation structures that correspond to gas or fluid reservoirs beneath pozzuoli solfatara solfatara mofete mt nuovo and agnano this high attenuation system is possibly connected with the magma sill revealed at about 7 km in depth by passive travel time tomography

origins of calcite in a boiling geothermal system the formation of hydrothermal calcite relates to the movement of carbon dioxide in a geothermal system as governed by boiling dilution and condensation in this paper we show how these processes control the occurrence distribution and stable isotope composition of calcite based on a study at broadlands ohaaki the two principal calcite occurrences in the broadlands ohaaki geothermal system are 1 as replacement of rock forming minerals and volcanic glass and 2 as platy crystals infilling voids both are stable over a broad temperature range from 160 degrees c to 300 degrees c replacement calcite is widespread and forms through hydrolysis reactions involving calcium alumino silicates and sub boiling liquids that contain 0 3 to 0 75 m co 2 platy calcite in contrast forms over a restricted vertical interval of a few hundred meters within the upflow zone it precipitates from boiling fluids through exsolution of carbon dioxide as indicated by coeval liquid rich and vapor rich fluid inclusions and its formation in the two phase zone fluid inclusion data help to define the boiling paths of fluids from which platy calcite formed homogenization temperatures range from 160 degrees c to 310 degrees c and are consistent within the present geothermal regime ice melting temperatures range from 0 0 to 1 0 degrees c and indicate the presence of up to 0 5 m dissolved carbon dioxide model boiling curves calculated to match these data show how the concentration of dissolved carbon dioxide in the preboiled fluid dictates the depth of first boiling most fluid inclusion data lie along a model boiling path characteristic of the centre of the upflow zone in which the rising fluid initially containing 0 75 m co 2 begins to boil at approximately 320 degrees c and approximately 2000 m depth data from well br 18 instead matches a curve in which the rising fluid initially containing 0 53 m co 2 begins boiling at approximately 245 degrees c and approximately 900 m depth the shallowing of the depth of first boiling likely results from dilution of dissolved carbon dioxide in the parent chloride water as it rises and mixes with marginal waters calcite precipitates from both shallow formed steam headed groundwater and deeply derived chloride water and these waters are isotopically distinct at broadlands ohaaki the delta 18 0 values of calcite at 200 degrees c range from 0 5 to 7 5 per mil whereas delta 18 0 values of calcite at 200 degrees c range from 4 to 10 per mil taking appropriate temperature dependent fractionation factors into account these data indicate equilibration with chloride water delta 18 0 h2o 4 5 per mil and steam heated groundwater delta 18 o h2o 7 0 per mil respectively oxygen isotopes of hydrothermal calcites in the nearby wairakei and waiotapu geothermal systems show similar patterns consistent with the occurrence of both chloride and steam heated waters there calcite formation is explained by a model that describes the distribution of two phase conditions and aqueous carbon dioxide concentrations in a column of hydrothermal fluid rising through a rock matrix of isotropic permeability in this ideal situation platy calcite forms along the inner margin of the two phase zone having the shape of an inverted cone whereas replacement calcite mostly forms in the surrounding one phase liquid only zone the sparse occurrence of calcite at less than or equal to 800 m depth in the central upflow of the ohaaki sector at broadlands ohaaki is compatible with this model and appears related to the exsolution of dissolved carbon dioxide through boiling deeper in the system

constrained resistivity inversion using seismic data summary in this paper we describe and apply a method for constraining structure in anisotropic electrical resistivity inversion structural constraints are routinely used to achieve improved model inversion here a second order curvature based regularization tensor model covariance is used to build structure in the model this structure could be obtained from other imaging methods such as seismic tomography core samples or otherwise known structure in the model our method allows the incorporation of existing geophysical data into the inversion in a general form that does not rely on any one to one correlation between data sets or material properties ambiguities in the resistivity distribution from electrical inversion and in particular anisotropic inversion may be reduced with this approach to demonstrate the approach we invert a synthetic data set showing the regularization tensor explicitly in different locations we then apply the method to field data where we have some knowledge of the subsurface from seismic imaging our results show that it is possible to achieve a high level of convergence while using spatially varying structural constraints common problems associated with resistivity inversion such as source receiver effects and false imaging of strongly resistive or conductive zones may also be reduced as part of the inversion method we show how the magnitude of the constraints in the form of penalty parameters appropriate to an inversion may be estimated reducing the computational expense of resistivity inversion

measurements of volcanic so2 and co2 fluxes by combined doas multi gas and ftir observations a case study from turrialba and telica volcanoes over the past few decades substantial progress has been made to overcome the technical difficulties of continuously measuring volcanic so2 emissions however measurements of co2 emissions still present many difficulties partly due to the lack of instruments that can directly measure co2 emissions and partly due to its strong atmospheric background in order to overcome these difficulties a commonly taken approach is to combine differential optical absorption spectroscopy doas by using novac scan doas instruments for continuous measurements of crateric so2 emissions and electrochemical ndir multi component gas analyser system multi gas instruments for measuring co2 so2 ratios of excerpts of the volcanic plume this study aims to quantify the representativeness of excerpts of co2 so2 ratios measured by multi gas as a fraction of the whole plume composition by comparison with simultaneously measured co2 so2 ratios using cross crater fourier transform infrared spectroscopy ftir two study cases are presented telica volcano nicaragua with a homogenous plume quiescent degassing from a deep source and ambient temperature and turrialba volcano costa rica which has a non homogeneous plume from three main sources with different compositions and temperatures our comparison shows that in our easier case telica ftir and multi gas co2 so2 ratios agree within a factor about 3 in our complicated case turrialba multi gas and ftir yield co2 so2 ratios differing by approximately 13 25 at most these results suggest that a fair estimation of volcanic co2 emissions can be provided by the combination of doas and multi gas instruments for volcanoes with similar degassing conditions as telica or turrialba based on the results of this comparison we report that by the time our measurements were made telica and turrialba were emitting approximately 100 and 1 000 t day 1 of co2 respectively

regional variations in the chemical and helium carbon isotope composition of geothermal fluids across tunisia abstract tunisia has numerous thermo mineral springs previous studies have shown that their chemical composition and occurrence are strongly influenced by the regional geology however little work has been done so far to study the isotopic composition of volatiles associated with these geothermal manifestations here we report on the results of an extensive survey of both natural hot springs and production wells across tunisia aimed at investigating the spatial distribution of thermal fluids geochemical characteristics and he c isotopic composition the chemistry of the analyzed samples highlights the heterogeneity of the water mineralization processes in tunisia as a consequence of the complex geological and tectonic setting of the country in terms of chemical composition we are able to conclude however that dissolution of halite and gypsum plays a key control on groundwater chemistry helium and carbon isotope systematics confirm the prevalently crustal origin of the volatiles interacting with the aquifer systems consistent with the absence of any recent magmatism most samples are characterized by crustal type helium 3 he 4 he in the range 0 02 ra 0 4 ra associated with a co 2 predominantly metamorphic in origin with the exception of the saharan platform where the carbon content is low and mostly organically derived in eastern tunisia however a few samples have he c isotope compositions which suggest at least partial mantle derivation of the dissolved gas phase the 3 he 4 he ratio reaches 2 4 ra corresponding to 30 of mantle derived helium at the ain garci site a co 2 rich mineral spring located some 30 km south of the city of zaghouan this mantle signature is consistent with the fact that the pelagian block to which eastern tunisia belongs has been deeply affected by extensional and transtensional tectonics since the opening of the tethys a process which is still ongoing in the sicily channel pantelleria rift as a whole however our results show that the italian mantle gas anomaly only marginally extends to northwestern africa

the origin of the fumaroles of la solfatara campi flegrei south italy abstract the analysis of gaseous compositions from solfatara campi flegrei south italy fumaroles since the early 1980s clearly reveals a double thermobarometric signature a first signature at temperatures of about 360 c was inferred by methane based chemical isotopic geoindicators and by the h2 ar geothermometer these high temperatures close to the critical point of water are representative of a deep zone where magmatic gases flash the hydrothermal liquid forming a gas plume a second signature was found to be at around 200 240 c at these temperatures the kinetically fast reactive species h2 and co re equilibrate in a pure vapor phase during the rise of the plume a combination of these observations with an original interpretation of the oxygen isotopic composition of the two dominant species i e h2o and co2 shed light on the origin of fumarolic fluids by showing that effluents are mixture between fluids degassed from a magma body and the vapor generated at about 360 c by the vaporization of hydrothermal liquids a typical andesitic water type d 20 18o 10 and a co2 rich composition x co 2 0 4 has been inferred for the magmatic fluids while for the hydrothermal component a meteoric origin and a co2 fugacity fixed by fluid rock reaction at high temperatures have been estimated in the time the fraction of magmatic fluids in the fumaroles increased up to 0 5 at each seismic and ground uplift crisis bradyseism which occurred at campi flegrei suggesting that bradyseismic crises are triggered by periodic injections of co2 rich magmatic fluids at the bottom of the hydrothermal system

local earthquake le tomography with joint inversion for p and s wave velocities using structural constraints local earthquake le tomography with joint inversion for p and s wave velocities using structural constraints

isotopic chemical and dissolved gas constraints on spring water from popocatepetl volcano mexico evidence of gas water interaction between magmatic component and shallow fluids abstract geochemical research was carried out on cold and hot springs at popocatepetl popo volcano mexico in 1999 to identify a possible relationship with magmatic activity the chemical and isotopic composition of the fluids is compatible with strong gas water interaction between deep and shallow fluids in fact the isotopic composition of he and dissolved carbon species is consistent with a magmatic origin the presence of a geothermal system having a temperature of 80 100 c was estimated on the basis of liquid geothermometers a large amount of dissolved co 2 in the springs was also detected and associated with high co 2 degassing

electrical resistivity and seismic refraction tomography to detect buried cavities near surface cavities can pose serious hazards to human safety especially in highly urbanized town centres the location of subsurface voids the estimation of their size and the evaluation of the overburden thickness are necessary to assess the risk of collapse in this study electrical resistivity tomography ert and seismic refraction tomography data are integrated in a joint interpretation process for cavity location in the city of rome ert is a well established and widely employed method for cavity detection however additional information provided by seismic refraction tomography is capable of eliminating some potential pitfalls in resistivity data interpretation we propose that the structure of the cavities defined by ert can be used as a base to optimize seismic refraction tomography investigations within the framework of a joint interpretation process data integration and the insertion of a priori information are key issues for reducing the uncertainties associated with the inversion process and for optimizing both acquisition procedures and computation time herein the two geophysical methods are tested on both synthetic and real data and the integration of the results is found to be successful in detecting isolated cavities and in assessing their geometrical characteristics the cavity location inferred by geophysical non invasive methods has been subsequently confirmed by direct inspection

modelling gravity variations consistent with ground deformation in the campi flegrei caldera italy abstract in recent years 1970 72 and 1982 84 two inflation episodes took place in the campi flegrei caldera italy characterized by significant ground uplift and gravity variations an elastic half space model with vertical density stratification is employed to compute the displacement field and the gravity variations produced by the deformation of buried layers following the inflation of a spherically symmetric deformation source contributions to gravity variations are produced by dilation contraction of the medium by the displacements of density interfaces the free surface and subsurface layers and of source boundaries and possibly by new mass input from remote distances into the source volume three cases were examined in detail in case i the magma chamber is identified as the deformation source and volume and pressure increase in the magma chamber is due to input of new magma from remote distances in case ii deformation is due to magma differentiation within the magma chamber deformation source with constant mass in case iii the geothermal system is identified as the deformation source and a pressure increase possibly driven by the exsolution of high temperature and high pressure volatiles in the magma chamber is assumed to play a dominant role from the comparison between measured and computed gravity residuals free air corrected gravity variations we can assess that in case i an inflation source with constant density would predict gravity residuals compatible with observations whereas an expansion at constant mass case ii would predict gravity residuals much lower than observed the resolving power of gravity data however prevents accurate assessment of the density of the emplaced material in case iii the pervasive density increase of the geothermal fluids induced by pressure increase is assumed to be the main source of gravity variations the average porosity value required for this model to match both the ground deformation and the gravity residuals is found to be 10 a value which is compatible with measured porosity values at campi flegrei in deep wells the subsidence phases following both inflation episodes and the gravity residuals during subsidence lead us to consider case iii as more plausible even if a suitable combination of cases i and iii cannot be discarded

assessment of a shallow magmatic system the 1888 90 eruption vulcano island italy the magmatic system feeding the last eruption of the volcano la fossa vulcano island italy was studied the petrogenetic mechanisms controlling the differentiation of erupted rocks were investigated through petrography mineral chemistry major trace and rare earth element and sr nd and pb isotopic geochemistry in addition melt inclusion and fluid inclusion data were collected on both juvenile material and xenolithic partially melted metamorphic clasts to quantify the p t conditions of the magma chamber feeding the eruption a regular and continuous chemical zoning has been highlighted rhyolites are the first erupted products followed by trachytes and latites whereas rhyolitic compositions were also found in the upper part of the sequence the chemical and isotopic composition of the rhyolites indicates that they originated by fractional crystallization from latitic magmas plus the assimilation of crustal material the trachytes represent hybrid magmas resulting from the mixing of latites and rhyolites contaminated in the shallow magmatic system the erupted products primarily compositionally zoned from latites to rhyolites are heterogeneous due to syn eruptive mingling the occurrence of magmacrust interaction processes evidenced by isotopic variations 87sr 86sr 0 70474 3 to 0 70511 3 143nd 144nd 0 512550 6 to 0 512614 8 206pb 204pb 19 318 19 489 207pb 204pb 15 642 15 782 208pb 204pb 39 175 39 613 is confirmed by the presence of partially melted metamorphic xenoliths with 87sr 86sr 0 71633 6 to 0 72505 2 and 143nd 144nd 0 51229 7 in rhyolites and trachytes afc calculations indicate a few percentage contribution of crustal material to the differentiating magmas thermometric measurements on melt inclusions indicate that the crystallization temperatures of the latites and trachytes were in the range of 1050 1100 c whereas the temperature of the rhyolites appears to have been around 1000 c at the time of the eruption compositional data on melt inclusions reveal that the magmas involved in the eruption contained about 1 1 5 wt dissolved h2o in pre eruptive conditions secondary fluid inclusions found in metamorphic xenoliths give low equilibration pressure data 30 60 mpa giving the location of the higher portions of the chamber at around 1500 2000 m of depth

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

diffuse co2 soil degassing and co2 and h2s concentrations in air and related hazards at vulcano island aeolian arc italy ingv dpc programme project v5 diffuse degassing in italy airplane firb project of the italian ministry of the university and research

geochemistry of gas and water discharge from the magmatic hydrothermal system of guallatiri volcano northern chile this work presents the first chemical and isotopic 13c co2 13c ch4 3he 4he 20ne 40ar 36ar 18o and d data for fluid discharges from guallatiri volcano a remote and massive stratovolcano which is considered as the second most active volcano of the central volcanic zone cvz in northern chile fumarolic gases had outlet temperatures of between 80 2 and 265 c and showed a significant magmatic fluid contribution marked by the occurrence of so2 hcl and hf that are partially scrubbed by a hydrothermal aquifer the helium isotope ratios 3 2 were relatively low compared to those of other active volcanoes in cvz possibly due to contamination of the magmatic source by 4he rich crust and or crustal fluid addition to the hydrothermal reservoir geothermometry in the h2o co2 co h2 ch4 system suggests equilibrium temperatures of up to 320 c attained in a vapor phase at redox conditions intermediate between those typical of hydrothermal and magmatic environments thermal springs located 12 km northwest of the volcano s summit had outlet temperatures of up to 50 1 c neutral to slightly basic ph and a sodium bicarbonate composition typical of distal fluid discharges in volcanic systems cold springs at the base of the volcanic edifice showing a calcium sulfate composition were likely produced by interaction of shallow meteoric water with co2 and h2s rich gases a geochemical conceptual model was constructed to graphically represent these results which can be used as an indication for future geochemical monitoring and volcanic hazard assessment

mineralogical geochemical and isotopic features of tuffs from the cfddp drill hole hydrothermal activity in the eastern side of the campi flegrei volcano southern italy abstract a 506 m drill hole has been recently drilled in the framework of the campi flegrei deep drilling project cfddp and the international continental scientific drilling program icdp with the intention of coring the subsurface in the eastern sector of the campi flegrei caldera the borehole located in the western district of the neapolitan city bagnoli plain 3 km to the east of the most active volcanic area and about 5 m above sea level is now targeted for monitoring purposes this paper reports the results obtained from the analysis of two short cores collected at depths of 443 and 506 m below the ground level the cores sampled two pre caldera tuffs observations performed by optical and scanning electron microscopy energy dispersive spectroscopy and powder x ray diffraction were used to achieve data on the primary lithology both primary and secondary mineralogical assemblages and the relationship between texture and secondary mineralization sr isotope ratios were determined on selected primary feldspars whereas 13c and 18o analyses were performed on carbonates from veins and filled voids in tuffs our results provide information on the hydrothermal system in the eastern sector of the caldera that was not among the goals in the previous drilling programs secondary mineralization suggests a saline hydrothermal environment characterized by fluids that progressively evolved from boiling toward more alkaline and cooler conditions a paleo temperature of ca 160 c has been inferred from authigenic mineral occurrences and calculated on the basis of equilibria between cored calcites and fluids presently emitted at the surface by using carbon and oxygen isotope data the temperature measured at the bottom of the drilling is about 80 c

carbon and helium isotopes in thermal springs of la soufriere volcano guadeloupe lesser antilles implications for volcanological monitoring abstract la soufriere guadeloupe lesser antilles is one of the most active and dangerous volcanoes of the lesser antilles arc the renewal of the volcanic activity at la soufriere requires replenishment of the volatile poor andesitic stored magma with more primitive volatile rich basaltic magma this event will trigger early release of large quantities of highly volatile species like co 2 and helium in the hydrothermal system to use these precursors first their baseline abundances and their behaviour in the hydrothermal system must be known during the current phase of dormancy in this study we have combined a previous systematic investigation of noble gases with carbon data of hydrothermal fluids flowing out of la soufriere the results for dissolved gases reveal that an intense interaction between rising magmatic volatiles and groundwaters currently takes place at la soufriere we show that the pristine magmatic composition with a 13 c co2 value of 3 19 0 03 a 3 he 4 he ratio of 8 1 0 2 r a and a co 2 3 he ratio of 1 03 0 18 10 10 may vary during the ascent of magmatic fluids due to either fractionation or mixing processes with meteoric water and or an organic component here we provide a baseline for co 2 and helium isotopes at each monitored spring and describe the superficial processes affecting both elemental and isotopic ratios

volatile organic compounds vocs in soil gases from solfatara crater campi flegrei southern italy geogenic source s vs biogeochemical processes the chemical composition of volatile organic compounds vocs in soil gases from the solfatara crater campi flegrei italy was analyzed to investigate the effects of biogeochemical processes on gases discharged from the hydrothermal reservoir and released into the atmosphere through diffuse degassing the chemistry of fluids from fumarolic vents which represent preferential pathways for fluid uprising was also reported for comparison oxidation reduction and hydration dehydration reactions as well as microbial activity strongly affected the composition of c4 c9 alkanes alkenes s bearing compounds and alkylated aromatics especially in those sites where the soil showed relatively low permeability to uprising fluids other endogenous organic compounds such as benzene phenol and hydrofluorocarbons were able to transit through the soil almost undisturbed independently on the gas emission rate products of voc degradation mainly consisted of aldehydes ketones esters ethers and subordinately alcohols cyclic compounds revealed the occurrence of vocs produced within sedimentary formations overlying the hydrothermal reservoir whereas the presence of chlorofluorocarbons cfcs was likely related to air contamination the results of the present study highlighted the strict control of biogeochemical processes on the behavior of hydrothermal vocs that at least at a local scale may have a significant impact on air quality this information could be improved by laboratory experiments conducted at specific chemical physical conditions and in presence of different microbial populations

tectonics and seismicity of the tindari fault system southern italy crustal deformations at the transition between ongoing contractional and extensional domains located above the edge of a subducting slab 1 the tindari fault system southern tyrrhenian sea italy is a regional zone of brittle deformation located at the transition between ongoing contractional and extensional crustal compartments and lying above the western edge of a narrow subducting slab onshore structural data an offshore seismic reflection profile and earthquake data are analyzed to constrain the present geometry of the tindari fault system and its tectonic evolution since neogene including the present seismicity results show that this zone of deformation consists of a broad nnw trending system of faults including sets of right lateral left lateral and extensional faults as well as early strike slip faults reworked under late extension earthquakes and other neotectonic data provide evidence that the tindari fault system is still active in the central and northern sectors and mostly accommodates extensional or right lateral transtensional displacements on a diffuse array of faults from these data a multiphase tectonic history is inferred including an early phase as a right lateral strike slip fault and a late extensional reworking under the influence of the subduction related processes which have led to the formation of the tyrrhenian back arc basin within the present regional geodynamic context the tindari fault system is interpreted as an ongoing accommodation zone between the adjacent contractional and extensional crustal compartments these tectonic compartments relating to the complex processes of plate convergence occurring in the region the tindari fault system might also be included in an incipient oblique extensional transfer zone linking the ongoing contractional belts in the calabrian ionian and southern tyrrhenian compartments

formation processes of thermal waters in green tuff a geochemical study in the hokuriku district central japan abstract thermal waters from green tuff region in the hokuriku district central japan were investigated to reveal formation process of water based on the chemical and isotopic compositions of water and dissolved gases in water the thermal waters of local meteoric origin are typical green tuff type water na ca cl so 4 type or na cl so 4 type which well reacted by water rock interaction and is found to be saturated with calcite and undersaturated with gypsum the green tuff type waters have relatively high 3 he 4 he ratio indicating high contribution of mantle derived helium and have extremely low total carbon 3 he ct 3 he ratio compared with the ratio of morb due to removal of carbon species from waters caused by calcite deposition in contrast a mineral spring water close to an active fault is found to be an immature water with less water rock interaction containing a large amount of gaseous co 2 and is undersaturated with both calcite and gypsum this water has high 3 he 4 he ratio and ct 3 he ratio indicating the high contribution of mantle derived helium and deep seated co 2 and likely provided through the fault we proposed a chemical evolution model considering existence of both chemically immature co 2 gas rich water and mature carbon poor water which well reacted with rocks deep seated co 2 and mantle derived helium are upwelling via faults and are supplied to the groundwater of local meteoric origin and an immature water containing high content of co 2 and mantle derived helium is formed during the circulation of this immature water in the green tuff layers water rock interaction such as ion exchanges with minerals dissolution of gypsum and deposition of calcite occurred at the interaction with rocks deposition of calcite occurs and results in a loss of ca 2 and decrease of ca 2 brings dissolution of gypsum and more calcite deposition consequently almost all the supplied co 2 is eliminated from the water furthermore we made a quantitative evaluation of the chemical evolution of green tuff type water using geochemical modeling code phreeqc taking account of addition of gas components and found the good agreement with observational results this study reveals that the supply of large amounts of co 2 and subsequent water rock interaction are necessary for the formation of green tuff type water with high 3 he 4 he ratio and extremely low ct 3 he ratio

organic and inorganic geochemistry of low temperature gas discharges at the baia di levante beach vulcano island italy abstract discharge from subaereal and submarine gas vents of the baia di levante beach gases from the vulcano island were sampled for major and trace gas components in may and november 1995 chemical compositions and equilibrium calculations suggest three different groups of co 2 rich gas emissions depending on their distance from the la fossa crater 1 gas vents close to the faraglione area are characterised by high h 2 s contents high calculated equilibrium temperatures based on inorganic species and relatively high proportion of alkene compounds 2 gas vents close to vulcanello are characterised by low calculated equilibrium temperatures and low amounts of alkenes and 3 pontile sample has the highest equilibrium co 2 pressure up to 68 bars which may account for the observed absence of benzene the relative large variability of h 2 s in the baia di levante beach gas discharge may be attributed to either different interactions between iron sulphides and weakly acid waters or catalytic effect of elemental sulphur on the de hydrogenation of cyclo hexane thermodynamic calculations suggest that the main inorganic species and ch 4 may have re equilibrated at relatively shallow depth 10 200 m b s l and 30 600 m b s l for a lithostatic and hydrostatic pressure respectively the slow kinetics of reactions in the c n h 2 n c n h 2 n 2 systems with respect to that of ch 4 co co 2 may explain the observed propene propane ratios which can only be reached at reaction temperatures of 300 350 c this low speed of reactions can also explain the observed disequilibrium of c1 c4 alkanes

sealing capacity of clay cap units above the cerro pabellon hidden geothermal system northern chile derived by soil co2 flux and temperature measurements abstract cerro pabellon is a hidden high enthalpy geothermal system reservoir temperature up to 250 c located in the pampa apacheta northern chile where the first geothermal power plant in south america is currently operating a fumarolic field located on the summit of apacheta volcano about 3 5 km w of pampa apacheta is the only evidence of the presence of a degassing magma connected to the surface co 2 soil flux and temperatures on a grid of 400 points were measured to understand the absence of any other thermal manifestations more than 90 of the measured co 2 flux values were below background estimated at 1 35 g m 2 day 1 whereas the associated soil temperatures mean value 19 4 c carried out at 10 cm depth were related at least partially to an endogenous though weak thermal anomaly no spatial correlation was observed between soil co 2 flux and temperature measurements suggesting a minimal role played by the volcano tectonic structures in the circulation of geothermal fluids soil temperature gradients measured on a grid of 85 points in the active fumarolic field where acid waters and magmatic gases are discharged revealed the only strong thermal anomaly temperatures up to 83 c of the area the thick argillic clay cap 300 m located above the geothermal reservoir has a pivotal role in preventing the resurgence of fluids whereas an efficient interaction between the rising magmatic fluids and the liquid dominated reservoir favours acidic gas scrubbing processes thus allowing the ascent of a steam depleted in magmatic compounds this steam interacts with the shallower discontinuous aquifer s below pampa apacheta with the consequent nearly complete dissolution of co 2 and h 2 s and heating of the shallow groundwater this results in low co 2 fluxes and extended slight thermal anomaly at the surface finally an integrated conceptual model using our results and available geological mineralogical geochemical and geophysical data of the cerro pabellon hidden geothermal system is presented with the aim of providing criteria for geothermal exploration of similar high enthalpy geothermal systems in the andes that also exhibit a lack of thermal surface features

two dimensional joint inversion of magnetotelluric and local earthquake data discussion on the contribution to the solution of deep subsurface structures abstract joint inversion of data sets collected by using several geophysical exploration methods has gained importance and associated algorithms have been developed to explore the deep subsurface structures magnetotelluric and local earthquake tomography algorithms are generally used individually due to the usage of natural resources in both methods it is not possible to increase data quality and resolution of model parameters for this reason the solution of the deep structures with the individual usage of the methods cannot be fully attained in this paper we firstly focused on the effects of both magnetotelluric and local earthquake data sets on the solution of deep structures and discussed the results on the basis of the resolving power of the methods the presence of deep focus seismic sources increase the resolution of deep structures moreover conductivity distribution of relatively shallow structures can be solved with high resolution by using mt algorithm therefore we developed a new joint inversion algorithm based on the cross gradient function in order to jointly invert magnetotelluric and local earthquake data sets in the study we added a new regularization parameter into the second term of the parameter correction vector of gallardo and meju 2003 the new regularization parameter is enhancing the stability of the algorithm and controls the contribution of the cross gradient term in the solution the results show that even in cases where resistivity and velocity boundaries are different both methods influence each other positively in addition the region of common structural boundaries of the models are clearly mapped compared with original models furthermore deep structures are identified satisfactorily even with using the minimum number of seismic sources in this paper in order to understand the future studies we discussed joint inversion of magnetotelluric and local earthquake data sets only in two dimensional space in the light of these results and by means of the acceleration on the three dimensional modelling and inversion algorithms it is thought that it may be easier to identify underground structures with high resolution