geochemistry of thermal fluids in nw honduras new perspectives for exploitation of geothermal areas in the southern sula graben abstract the results of a geochemical survey on thermal waters and for the first time for this site gas discharges in five geothermal sites azacualpa la cueva rio ulua rio gualcarque el olivar and laguna de agua caliente in nw honduras are here presented and discussed el olivar and laguna de agua caliente in the southern part of the sula graben are very close to a quaternary basaltic field whereas azacualpa la cueva rio ulua and rio gualcarque located to the southwest of the yojoa lake direcly emerge from the cretaceous limestone deposits the measured temperatures range between 37 5 and 104 8 c mature alkaline na so 4 thermal waters discharge from azacualpa la cueva while those from el olivar and laguna de agua caliente are immature and show a na hco 3 composition chemical equilibria of waters and gases from the azacualpa la cueva thermal springs indicate temperatures ranging from 150 to 200 c conversely gas discharges from el olivar and laguna de agua caliente have attained a partial chemical equilibrium in the liquid phase at slightly higher temperatures 200 250 c although gas gas faster reactions involving co seem to be adjusted in an isothermally separated vapor phase unlike azacualpa sio 2 geothermometer at el olivar and laguna de agua caliente indicates equilibrium temperatures for the liquid phase much lower than those calculated for the gas phase 120 c we conclude that thermal waters from the azacualpa area likely represent the direct emergence of a water dominated reservoir having temperatures 150 200 c by contrast at el olivar and laguna de agua caliente hot springs are supplied by a boiling shallow aquifer fed by a vapor phase rising from a steam dominated zone the above geochemical model is consistent with a geothermal reservoir hosted within the cretaceous carbonate sequences of the yojoa group in the whole investigated sites the reservoir extensively crops out in the azacualpa area whereas the geothermal sites of the southern sula graben laguna de agua caliente and el olivar are covered by the oligocene miocene volcano sedimentary sequences of the matagalpa formation possibly acting as efficient impermeable cap rocks these results significantly differ from those reported by previous studies and emphasize that the southern sula graben in particular the el olivar area can represent among the investigated thermal springs the most promising site for the exploitation of a high enthalpy geothermal field

interseismic strain accumulation across the north anatolian fault from envisat insar measurements 1 the north anatolian fault naf is a major feature of middle eastern tectonics and several previous insar studies have measured interseismic deformation across the fault all previous studies however have used sar data acquired from a single line of sight los direction leading to large uncertainties on model parameters and necessitating several modelling assumptions to be made we have measured interseismic deformation across the naf using both ascending and descending sar data for the first time an aim that has previously been limited by the availability of ascending data by using sar data from two look directions we have been able to reduce the range of uncertainties in slip rate and locking depth from previous studies by 60 and by assuming no vertical motion across the fault we estimate both fault normal and fault parallel motion these results support other evidence for predominantly horizontal strike slip motion on the naf our data are consistent with a slip rate of 20 26 mm yr below a locking depth of 13 5 25 km for the naf

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

interseismic strain localization in the san jacinto fault zone we investigate interseismic deformation across the san jacinto fault at anza california where previous geodetic observations have indicated an anomalously high shear strain rate we present an updated set of secular velocities from gps and insar observations that reveal a 2 3 km wide shear zone deforming at a rate that exceeds the background strain rate by more than a factor of two gps occupations of an alignment array installed in 1990 across the fault trace at anza allow us to rule out shallow creep as a possible contributor to the observed strain rate using a dislocation model in a heterogeneous elastic half space we show that a reduction in shear modulus within the fault zone by a factor of 1 2 1 6 as imaged tomographically by allam and ben zion geophys j int 190 1181 1196 2012 can explain about 50 of the observed anomalous strain rate however the best fitting locking depth in this case 10 4 1 3 km is significantly less than the local depth extent of seismicity 14 18 km we show that a deep fault zone with a shear modulus reduction of at least a factor of 2 4 would be required to explain fully the geodetic strain rate assuming the locking depth is 15 km two alternative possibilities include fault creep at a substantial fraction of the long term slip rate within the region of deep microseismicity or a reduced yield strength within the upper fault zone leading to distributed plastic failure during the interseismic period

genesis and evolution of the fumaroles of vulcano aeolian islands italy a geochemical model a geochemical model explaining the presence of fumaroles having different gas composition and temperature at the top of the crater and along the northeastern coast of vulcano island is proposed a pressurized biphase liquid vapor reservoir at the depth of about 2 km is hypothesized energy and mass balance sheets controlp t conditions in the system p t must vary along a boiling curve of brine as liquid is present the co2 content in the steam is governed by the thermodynamic properties of the fluids in the h2 nacl co2 system on the assumption that oxygen fugacity in the system is between the hm fmq oxygen buffers observed so2 h2s co2 co co ch4 ratios in the fumarolic gases at the fossa crater appear in equilibrium with a temperature higher than that observed such as may exist at depth the more reduced gas phases present on the sea side may result from re equilibrium processes in shallower aquifers the suggested model would help in monitoring changes in volcanic activity by analyzing fumarolic gases

interseismic fault movement of xianshuihe fault zone based on across fault deformation data and insar tectonic movement is closely related to earthquake preparation across fault sites and insar data are applied to reveal crust deformation from different precision different temporal scale and different spatial scale in this paper xianshuihe fault zone is taken as an example dislocation model in near fault field is derived from screw dislocation model proposed by savage and burford 1973 which can reveal the locking information of the across fault site using baseline data locking depth of each across fault site on xianshuihe fault zone is calculated using baseline data which indicates that the locking depth of laoqianning across fault site is about 18 km and the locking depth of other sites is shallow time series analysis of sbas insar is used to study interseismic tectonic deformation deformation field from insar reveals the left lateral slip property of xianshuihe fault zone the average locking depth is about 2 4 km calculated by the pixels slip rate around in near fault field which indicates that locking depth is shallow and consistent using insar data as well as across fault data screw model is used to obtain the best fitting result of fault locking depth and slip rate layered dislocation model is put forward to explain shallow locking depth of fault zone according to the theory of fault slip deficit and seismic moment equilibrium accumulative seismic moments caused by fault slip and the release amount of ms 5 0 earthquakes are calculated to estimate seismic risk of study area all results indicate that qianning segment of xianshuihe fault zone is the future danger area with strong earthquakes

the effect of variations in rainfall on the chemical composition of vulcano fumaroles italy analytical data for samples collected over a period of 17 months at the crater fumaroles of vulcano are given

variations in surface manifestations at vulcano aeolian islands italy as a possible evidence of deep processes five years of geochemical surveillance at vulcano have shown interesting changes in the physico chemical characters of the fumaroles at the crater and of the phreatic waters in the surrounding area in particular 1 the maximum temperature of the fumaroles which had been of about 200 c for at least 30 years rose suddenly to above 300 c after a period of rather constant values a decreasing trend has recently been observed 2 an increase of co2 s compounds and hf with respect to hcl b br occurred in the gas composition contemporaneous to the rise in temperature this increase is now gradually declining 3 higher concentrations of sulphate ion and silica in phreatic waters accompanied the thermal changes observed at the fumaroles according to a model previously proposed martini et al 1980 the increase in the above mentioned factors would reflect an increasing magmatic contribution to the volcanic system which might be due to an increased permeability to fluids at depth because a sensible seismic shock occurred in the area a few months after the first chemical and thermal variations had been observed such variations may be regarded as forerunners of the seismic event and may be used to forecast some months in advance changes occurring at depth

the hydrothermal volcanic system of rincon de la vieja volcano costa rica a combined inorganic and organic geochemical approach to understanding the origin of the fluid discharges and its possible application to volcanic surveillance abstract in the period 1998 2002 thermal spring discharges of rincon de la vieja volcano nw costa rica have been sampled and analyzed for major trace and isotopic 18 o 16 o and d h in waters and 3 he 4 he and 13 c 12 c in co 2 in gases composition the boiling pools hosted inside the summit crater active crater are characterized by high contents of magmatic related compounds so 2 hcl and hf that strongly affect the chemistry of the crater lake these chemical features are not shown by the thermal discharges seeping out in the surrounding area of the volcano here the shallow aquifer apparently masks any possible clues related to the magmatic system this suggests that the fluid vents located inside the active crater are likely to represent the most appropriate sampling sites for geochemical surveillance purposes although the high gas discharge rate from the lake may occasionally prevent any fluid sampling alternatively as already suggested by recent studies on the behavior of light hydrocarbons in different volcanic environments the compositional features of the organic gas fraction in the more accessible outer flank thermal discharges could usefully be utilized at least to assess the thermodynamic conditions of the volcanic hydrothermal system since these compounds are affected by secondary processes only at limited extent

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

mineral assisted production of benzene under hydrothermal conditions insights from experimental studies on c6 cyclic hydrocarbons abstract volatile organic compounds vocs are ubiquitously present at low but detectable concentrations in hydrothermal fluids from volcanic and geothermal systems although their behavior is strictly controlled by physical and chemical parameters the mechanisms responsible for the production of most vocs in natural environments are poorly understood among them benzene whose abundances were found to be relatively high in hydrothermal gases can theoretically be originated from reversible catalytic reforming processes i e multi step dehydrogenation reactions involving saturated hydrocarbons however this hypothesis and other hypotheses are difficult to definitively prove on the basis of compositional data obtained by natural gas discharges only in this study therefore laboratory experiments were carried out to investigate the production of benzene from cyclic hydrocarbons at hydrothermal conditions specifically 300 c and 85 bar the results of experiments carried out in the presence of water and selected powdered minerals suggest that cyclohexane undergoes dehydrogenation to form benzene with cyclohexene and cyclohexadiene as by products and also as likely reaction intermediates this reaction is slow when carried out in water alone and competes with isomerization and hydration pathways however benzene formation was increased compared to these competing reactions in the presence of sulfide sphalerite and pyrite and iron oxide magnetite and hematite minerals whereas no enhancement of any reaction products was observed in the presence of quartz the production of thiols was observed in experiments involving sphalerite and pyrite suggesting that sulfide minerals may act both to enhance reactivity and also as reactants after dissolution these experiments demonstrate that benzene can be effectively produced at hydrothermal conditions through dehydrogenation of saturated cyclic organic structures and highlight the crucial role played by minerals in this process

origin of the fumarolic fluids of vulcano island italy and implications for volcanic surveillance variations in d and 18o values with h2o contents and outlet temperatures indicate that the fumaroles of la fossa crater have discharged mixtures of magmatic water and marine hydrothermal water since 1979 the contribution of meteoric water was low in the period 1979 1982 and very low afterwards the 18o values of the marine hydrothermal component of 5 to 7 2 are due to isotopic exchange with the 18o rich silicates of the rocks under high temperature and low permeability conditions the 18o value of the magmatic end member is generally 3 5 to 4 3 although values as high as 5 5 to 6 5 were reached in the summer of 1988 when magma degassing appears to have extended into the core of the magma body the d values of the end member were close to 20 typical of andesitic waters both the isotopic values and chemical data strongly support a dry model consisting of a central magmatic gas column and a surrounding hydrothermal envelope in which marine hydrothermal brines move along limited fracture zones to undergo total evaporation on approaching the conduits of magmatic fluids the vents at the eastern and western boundaries of the fumarolic field are fed by fluids whose pressure is governed by the coexistence of vapor liquid and halite giving rise to a high risk of phreato magmatic explosions should magma penetrate into these wet environments most la fossa eruptions were triggered by an initial hydrothermal blast and continued with a series of phreatomagmatic explosions the fluids discharged by the forgia vecchia fumaroles are mixed with meteoric water which is largely evaporated although subordinate loss of condensed steam may be responsible for scrubbing most of the acidic gas species the temperatures and pressures and the risk of a sudden pressure increase are low a boiling hydrothermal aquifer at 230 c is present underneath the baia di levante beach this area has a minor risk of hydrothermal explosions

interseismic slip rate of the northwestern xianshuihe fault from insar data 1 the xianshuihe fault is a highly active strike slip fault system near the eastern margin of the tibetan plateau we use a multi interferogram method to construct a map of line of sight deformation rate due to interseismic strain accumulation on the northwestern xianshuihe fault from a decade of sar data acquired by the ers 1 2 and envisat satellites the rate map shows a clear deformation gradient associated with the fault but slightly offset to the northeast from the surface trace joint inversion of insar rate map and gps data using monte carlo method we estimate a slip rate of 9 12 mm yr with a locking depth of 3 6 km at the 90 confidence level the slip rate agrees with the holocene fault slip rate and the historical earthquakes our results also suggest no significant across fault extension in the future insar data from both ascending and descending orbits may further constrain the 3 d fault slip rate on this fault

line of sight displacement from alos 2 interferometry mw 7 8 gorkha earthquake and mw 7 3 aftershock interferometric synthetic aperture radar insar is a key tool for the analysis of displacement and stress changes caused by large crustal earthquakes particularly in remote areas a challenge for traditional insar has been its limited spatial and temporal coverage especially for very large events whose dimensions exceed the typical swath width of 70 100 km this problem is addressed by the alos 2 satellite whose palsar 2 instrument operates in scansar mode enabling a repeat time of 2 weeks and a swath width of 350 km here we present insar line of sight displacement data from alos 2 palsar 2 observations covering the mw 7 8 gorkha nepal earthquake and its mw 7 3 aftershock that were acquired within 1 week of each event the data are made freely available and we encourage their use in models of the fault slip and associated stress changes the mw 7 3 aftershock not only extended the rupture area of the main shock toward the east but also left a 20 km gap where the fault has little or no coseismic slip we estimate this unslipped fault patch has the potential to generate a mw 6 9 event

evolution of light hydrocarbon gases in subsurface processes constraints from chemical equilibrium abstract the behaviour of ch 4 c 2 h 6 and c 3 h 8 in subsurface processes such as magma intrusion volcanic gas discharge and natural gas generation have been examined from the viewpoint of chemical equilibrium it seems that equilibrium among these three hydrocarbons is attainable at about 200 c when a system at high temperatures is cooled re equilibration is continued until a low temperature is reached the rate at which re equilibration is achieved however steadily diminishes and below 200 c the reaction between the hydrocarbons stops and the gas composition at this time is frozen in and it remains unchanged in a metastable state for a long period of geological time natural gas compositions from various fields have shown that when a hydrocarbon system out of chemical equilibrium is heated it gradually approaches equilibrium above 150 c on the way towards equilibration compositions of thermogenic gases apparently temporarily show a thermodynamic equilibrium constant at a temperature that is higher than the real equilibrium temperature expected from the ambient temperature of the samples in contrast biogenic gases indicate a lower temperature in lower temperature regions kinetic effects probably control the gas composition the compositions are essentially subjected to genetic processes operating on the gases such as pyrolysis of organic material and bacterial activity and they fluctuate substantially examination of volcanic gases and pyrolysis experimental data however have suggested that the equilibration rate of these hydrocarbons is sluggish in comparison with that of reactive inorganic species such as h 2 s and so 2 the view presented in this study will be helpful in understanding the genetic processes that create oil and gas and the migration of these hydrocarbons and in interpreting the origins of magmatic gases

isotopic composition of natural thermal discharges on vulcano island southern italy this paper reviews the isotopic 18o16o and d h ratios reported in the literature for phreatic waters in the plain of vulcano island off sicily and condensates from high temperature fumaroles at the top of the summit crater the vulcano phreatic waters have a rather high average annual temperature greater than 30 dgc but do not seem to be heated directly by mixture with condensates of fumarolic steam they seem to originate from rainwater and to undergo high evaporation particularly in summer owing to high conductive heat flow in the island by comparing the 18o16o and d h ratios with cl as hcl content it is estimated that 75 of the steam from the high temperature fumaroles comes from seawater and 25 from low salinity waters the latter however do not seem to come directly from the shallow aquifer of vulcano because the steam from the fumaroles does not contain radiogenic tritium this mixing model and the lack of steam condensation in the vulcano aquifer implies indirectly that there are no steam losses during the rise of deep fluids and that some observed variations in the outlet temperatures without accompanying variations in the composition of the associated gas phase may be due to increased or decreased extent of fracturation in the volcanic edifice as a result for instance of tectonic movements which cause more or less vaporization of low salinity fresh water into the volcanic ducts as well as faster or slower outflow of deep gases

isotopic variation of the hydrothermal system on vulcano island italy the isotopic and chemical composition of thermal waters and the isotopic composition of high temperature fumarolic steam at vulcano island indicate an evolution of the hydrothermal system from its magmatic origin through interaction with rocks and mixing with meteoric water seawater is not a component in this system the isotopic values of the fumaroles indicate a local magmatic composition of 7 to 8 18o and 5 to 15 d the high d values of this vapor may reflect contamination of the magma by connate water the isotopic and chemical composition of water from well w2 indicates the existence of geothermal fluid formed by mixing of hcl and so2 bearing condensates of volcanic origin with groundwater with subsequent evolution via water rock interaction the estimated isotopic composition of the geothermal water is 18o 1 and d 5 local shallow seismic events result in a temporary increase in fracture permeability enabling the mixing of magmatic vapor with groundwater or geothermal water tectonic activity associated with deep structures appears to increase the contribution of magmatic vapor to the fumaroles

volcanic steam output directly measured in fumaroles the observed variations at vulcano island italy between 1983 and 1987 the mass of steam emitted by the fumaroles of the crater of vulcano aeolian islands italy was evaluated by using a direct measuring method measurements were effected with this method between 1983 and 1987 in nine field campaigns the results of which are given in this paper the steam flux measurements were performed by an instrument expressly designed for steam condensation the estimates of the thermal energy transported daily by the steam gave values of up to 10e12 j the sharp variations in the total mass outputs recorded in 1984 and 1985 are here interpreted as being a consequence of the probable accumulation of fluid pressure at depth during the evolution of volcanic activity the different results obtained from the various areas of the fumarolic field during the evolutionary phases have led to the hypothesis that different subsystems exist that feed the fumaroles and that their activity is triggered by volcano tectonics this method can be applied in the evaluation of both fumarolic steam and thermal energy outputs and therefore it is particularly useful in geothermal exploration in the evaluation of the environmental impact of volcanic degassing and in the forecasting of volcanic eruptions the evaluation of the steam output is also useful for quantifying the release of other gaseous species and giving univocal interpretations regarding their variations in concentrations furthermore this direct method provides a new way of calibrating the flux estimates effected by other telemetric techniques lidar cospec etc

geochemical and seismological investigations at vulcano aeolian islands during 1978 1989 both geochemical and geophysical evidence indicates that the activity of the fumarolic system of the fossa crater can be divided into two periods from 1978 to 1983 such activity has been mainly controlled by two competing processes which affect the permeability of the fumarolic system at deep levels 1 rock fracturing induced by faulting and 2 mineral deposition alteration the latter which causes a slow decrease of the permeability at deep levels through clogging of fractures and voids prevailed at the end of this period determining a fluid pressure increment in the deep parts of the system from 1984 to 1989 fluid pressure at deep levels remained persistently high triggering local microseismic swarms furthermore pt conditions much higher than before were attained in the zones where hydrothermal fluids seep into the conduits from lateral aquifers owing to an uprising of the isotherms a deepening of these seeping zones or both

evolution of the fossa cone vulcano abstract in decreasing order of abundance the principal emplacement mechanisms for deposits of the fossa edifice of vulcano include dry surge wet surge pyroclastic fall lahar lava flow pyroclastic flow and epiclastic processes most samples from pyroclastic beds on fossa contain two grain size populations the coarser mode at 0 5 1 5 resulted from modified ballistic transport whereas the finer mode at 2 5 3 5 is related to surge transport reconstruction of the entire stratigraphy of the cone permits the beds to be grouped into five principal eruptive cycles all of which postdate the lower pilato ash of lipari dated at 11 000 to 8 500 y b p pte nere cycle palizzi cycle commenda cycle pietre cotte cycle and the modern cycle additional cycles may be present but exposures on the cone are insufficient for their adequate definition all cycles follow a similar stochastic pattern starting with surge eruptions and ending with effusion of lava from the crater rim the frequency of pyroclastic fall events increases with time throughout each cycle this progressive decrease in the efficiency of water melt interaction through the duration of each cycle may be due to a gradual rise of each new magma column coupled with an increase in magmatic volatiles tectonism and magma mixing both play a role in triggering eruptions on fossa the present crater lies at the intersection of two prominent tectonic trends a nnw fracture system parallels the main eruptive centers and an ene set aligns with the migration of minor vents the silicic lavas of fossa contain a mixture of two components xenocrysts of plagioclase augite and olivine surrounded by a dark glass are intimately dispersed into an evolved rhyolitic matrix

geogenic and atmospheric sources for volatile organic compounds in fumarolic emissions from mt etna and vulcano island sicily italy 1 in this paper fluid source s and processes controlling the chemical composition of volatile organic compounds vocs in gas discharges from mt etna and vulcano island sicily italy were investigated the main composition of the etnean and volcano gas emissions is produced by mixing to various degrees of magmatic and hydrothermal components vocs are dominated by alkanes alkenes and aromatics with minor though significant concentrations of o s and cl f substituted compounds the main mechanism for the production of alkanes is likely related to pyrolysis of organic matter bearing sediments that interact with the ascending magmatic fluids alkanes are then converted to alkene and aromatic compounds via catalytic reactions dehydrogenation and dehydroaromatization respectively nevertheless an abiogenic origin for the light hydrocarbons cannot be ruled out oxidative processes of hydrocarbons at relatively high temperatures and oxidizing conditions typical of these volcanic hydrothermal fluids may explain the production of alcohols esters aldehydes as well as o and s bearing heterocycles by comparing the concentrations of hydrochlorofluorocarbons hcfcs in the fumarolic discharges with respect to those of background air it is possible to highlight that they have a geogenic origin likely due to halogenation of both methane and alkenes finally chlorofluorocarbon cfc abundances appear to be consistent with background air although the strong air contamination that affects the mt etna fumaroles may mask a possible geogenic contribution for these compounds on the other hand no cfcs were detected in the vulcano gases which are characterized by low air contribution nevertheless a geogenic source for these compounds cannot be excluded on the basis of the present data

evolution of fumarolic gases boundary conditions set by measured parameters case study at vulcano italy physical chemical and isotopic parameters were measured in fumaroles at the vulcano crater and in drowned fumaroles near the beach the data were used to define boundary conditions for possible conceptual models of the system crater fumaroles time variations of co2 and so2 concentrations indicate mixing of saline gas rich water with local fresh water cl br ratios of 300 400 favour sea water as a major source for cl brand part of the water in the fumaroles cl concentrations and d values revealed independently amixing of 0 75 sea water with 0 25 local freshwaterin furmarole f 5 during september 1982 patterns of parameter correlation and mass balances reveal that co2 s nh3 and b originate from sources other than sea water the co2 value of 13c 2 o favours at least partial origin from decomposition of sedimentary rocks rather than mantle derived material radiogenic4he 1 3 lo 3 ccstp g water and radiogenic40ar 10 6 10 4 ccstp g water are observed 4he 40ar radiogenic 1 2 well in the range of values observed in geothermal systems drowned fumaroles strongly bubbling gas at a pond and at the beachappears to have the same origin and initial compositionas the crater fumaroles 2 km away the fumarolic gas is modified by depletion of the reactive gases caused by dissolution in shallow water atmospheric ne ar kr and xe are addeden route some radiogenic he and ar are maintained the vulcano system seems to be strongly influenced by the contribution of sea water and decomposition of sedimentary rocks evidence of magmatic contributions is mainly derived from heat

origin of light hydrocarbons in gases from mud volcanoes and ch4 rich emissions abstract this paper presents new chemical data of hydrocarbon rich gases discharged from mud volcanoes and ch4 rich emissions located in different areas of italy northern apennines and sicily the determination of c5 c10 alkanes cyclics and aromatics was carried out by gc ms while the main gas species and c1 c4 hydrocarbons were analyzed by gc tdc and gc fid respectively methane is by far the most abundant component of all the investigated gas emissions with the exception of part of those discharging close to mt etna volcano which are co2 rich the gas samples collected from the emilia apennine and sicily show d ch4 and 13c ch4 values typical of thermogenic gases most gases from the romagna apennine discharge methane with a biogenic isotopic signature non methane hydrocarbons of biogenic gases are almost exclusively c2 c4 alkanes with minor amounts fraction of mol mol of c4 compounds including few aromatics and cyclics likely deriving from minor thermogenic contribution not evidenced by the 13c ch4 and d ch4 values the etnean gases whose r ra and 13c co2 values indicate a strong contribution from a hydrothermal fluid source related to the nearby volcanic system show a significant enrichment of aromatics compounds up to 36 of the non methane organic gas fraction which is likely produced by catalytic reforming processes such as dehydrocyclization of alkanes the thermogenic gases from the apennines and southwestern sicily are characterized by the presence of more than 20 different cyclic compounds with concentrations up to several mol mol cyclic compounds are likely formed by i thermal cracking and ii uncompleted aromatization of alkanes occurring at depth 3 km and temperatures not exceeding 120 150 c

constraints on water depth of massive sulfide formation evidence from modern seafloor hydrothermal systems in arc related settings the results of three decades of seafloor research provide the most reliable information on the importance of water depth in massive sulfide formation available data from over 130 occurrences show that water depths of seafloor vent sites vary with plate tectonic setting and the regional magmatic and volcanic environment the shallowest hydrothermal systems in subduction related settings are hosted by arc volcanoes these shallow vent sites have a number of features in common with subaerial epithermal systems massive sulfide occurrences in arc related rifts the most likely setting for many ancient analogs are generally restricted to water depths from 700 to 2 000 m with rifts developing within old arc crust at the deeper end of this range back arc spreading centers proximal to arcs host massive sulfide deposits at depths of 1 500 to 2 000 m the deepest hydrothermal systems occur along mature back arc spreading centers distal to volcanic arcs where water depths range from 2 000 to 3 700 m these deeper vent sites probably represent the best modern analogues of ophiolite hosted massive sulfide deposits boiling of the hydrothermal fluids is common at volcanic arcs and in arc related rifts in these environments elevated magmatic gas contents of the hydrothermal fluids can contribute to the widespread occurrence of phase separation and associated gas loss by contrast the high ambient pressures in deep marine hydrothermal systems along mature back arc spreading centers prevent fluids from boiling during their ascent to the seafloor boiling controls the maximum temperature at which hydrothermal fluids discharge at the seafloor and therefore influences the metal content of seafloor sulfide deposits copper rich massive sulfides typically occur at water depths exceeding 1 000 m whereas zn and pb rich occurrences may form at any water depth boiling can be an important control on ag and au grades but is not the only factor controlling precious metal enrichment in massive sulfides shallow marine hot spring deposits can be highly enriched in trace metals such as as hg and sb submarine volcanic arc and back arc settings are geologically complex and significant variations in water depth can occur over short distances paleoenvironmental reconstruction of these environments in ancient volcanic terranes is hampered by the lack of unequivocal volcanological or sedimentological criteria that indicate water depth the relationships established here using modern seafloor observations provide important constraints on the paleoenvironmental setting of ancient volcanic hosted massive sulfide deposits

multiple hazards and paths to eruptions a review of the volcanic system of vulcano aeolian islands italy abstract vulcano is one of the 7 volcanic islands and 6 seamounts forming the aeolian volcanic district italy vulcano has a long eruptive record and its last eruption 1888 90 originated the definition of the vulcanian eruptive style like most volcanic islands vulcano generates many potentially interconnected hazards determining a potentially high risk here we review the state of knowledge on its geology eruptive activity historical accounts structural setting geophysical and geochemical surveillance and available hazard quantifications in order to have an updated picture of the state knowledge on volcanic hazard we follow a prototypal reviewing scheme based on three standardized steps i review of the volcanic system ii review of available eruptive and non eruptive hazard quantifications iii development of a conceptual interpretative model we find that while a rather vast literature is dedicated to the volcanic system of vulcano and the reconstruction of past events few quantitative hazard assessments exist in addition the range of natural variability considered for each hazard is potentially underestimated e g limited range of considered eruption magnitude and style and of vent position as it is the potential effect of multi hazard impact the developed conceptual model for the feeding system provides a synthetic picture of the present knowledge about the system as emerged from the review in addition it allows for the identification of potential paths to eruption and provides a first order link among the main hazards this review provides an up to date snapshot of existing knowledge on volcanic hazard at vulcano on which to build future hazard quantifications as well as to support present and future decision making

miocene to holocene exhumation of metamorphic crustal wedges in the nw himalaya evidence for tectonic extrusion coupled to fluvial erosion the himalayan crystalline core zone exposed along the sutlej valley india is composed of two high grade metamorphic gneiss sheets that were successively underthrusted and tectonically extruded as a consequence of the foreland directed propagation of crustal deformation in the indian plate margin the high himalayan crystalline sequence hhcs is composed of amphibolite facies to migmatitic paragneisses metamorphosed at temperatures up to 750 c at 30 km depth between eocene and early miocene during early miocene combined thrusting along the main central thrust mct and extension along the sangla detachment induced the rapid exhumation and cooling of the hhcs whereas exhumation was mainly controlled by erosion since middle miocene the lesser himalayan crystalline sequence lhcs is composed of amphibolite facies para and orthogneisses metamorphosed at temperatures up to 700 c during underthrusting down to 30 km depth beneath the mct the lhcs cooled very rapidly since late miocene as a consequence of exhumation controlled by thrusting along the munsiari thrust and extension in the mct hanging wall this renewed phase of tectonic extrusion at the himalayan front is still active as indicated by the present day regional seismicity and by hydrothermal circulation linked to elevated near surface geothermal gradients in the lhcs as recently evidenced in the himalayan syntaxes active exhumation of deep crustal rocks along the sutlej valley is spatially correlated with the high erosional potential of this major trans himalayan river this correlation supports the emerging view of a positive feedback during continental collision between crustal scale tectono thermal reworking and efficient erosion along major river systems

thermodynamics of organic transformations in hydrothermal fluids hydrothermal fluids obtain organic compounds through diverse pathways in submarine systems organic compounds are already dissolved in seawater that is heated and transformed into hydrothermal fluids through water rock reactions microbes inhabiting hydrothermal systems produce metabolites that enter the fluids and cells can be carried into the reaction zones by circulating fluids and pyrolyzed analogous sources of organic compounds can be anticipated in continental systems with the possible addition of novel plant and soil derived organic compounds from the surface in addition hydrothermal systems possess large potentials for abiotic organic synthesis that may add a novel suite of compounds when sedimentary rocks are present ancient biogenic organic matter can be mobilized or transformed by hot fluids these transformations accompany the generation of petroleum coal and other fossil fuels suggesting that expectations for hydrothermal transformations can be built on those that occur in sedimentary basins likewise some types of ore deposition are accompanied by transformations of organic compounds and metal organic complexes may be involved in enhancing the transport of metals in ore forming and other crustal fluids with these thoughts in mind this review starts with an inventory of the types of organic compounds found in hydrothermal systems and some ways that hydrothermal organic compounds are transformed methane can be generated biotically and abiotically from organic or inorganic reactants and since it lacks a carbon carbon bond some researchers would not consider it to be an organic compound nevertheless more data exist for methane in hydrothermal fluids than for any organic compound that fits the definition methane has been quantified in continental and submarine hydrothermal fluids fumarolic gases associated with hydrothermal systems oil field brines deep fluids in sedimentary basins and igneous basement rocks fluids associated with active serpentinization and fluid inclusions in minerals from ore deposits sedimentary basins and deep crustal settings recent examples include

gas geochemistry of the magmatic hydrothermal fluid reservoir in the copahue caviahue volcanic complex argentina abstract copahue volcano is part of the caviahue copahue volcanic complex ccvc which is located in the southwestern sector of the caviahue volcano tectonic depression argentina chile this depression is a pull apart basin accommodating stresses between the southern liquine ofqui strike slip and the northern copahue antinir compressive fault systems in a back arc setting with respect to the southern andean volcanic zone in this study we present chemical inorganic and organic and isotope compositions 13c co2 15n 3he 4he 40ar 36ar 13c ch4 d ch4 and d h2o and 18o h2o of fumaroles and bubbling gases of thermal springs located at the foot of copahue volcano sampled in 2006 2007 and 2012 helium isotope ratios the highest observed for a southern american volcano r ra up to 7 94 indicate a non classic arc like setting but rather an extensional regime subdued to asthenospheric thinning 13c co2 values from 8 8 to 6 8 vs v pdb 15n values 5 3 to 5 5 vs air and co2 3he ratios from 1 4 to 8 8 109 suggest that the magmatic source is significantly affected by contamination of subducted sediments gases discharged from the northern sector of the ccvc show contribution of 3he poor fluids likely permeating through local fault systems despite the clear mantle isotope signature in the ccvc gases the acidic gas species have suffered scrubbing processes by a hydrothermal system mainly recharged by meteoric water gas geothermometry in the h2o co2 ch4 co h2 system suggests that co and h2 re equilibrate in a separated vapor phase at 200 220 c on the contrary rock fluid interactions controlling co2 ch4 production from sabatier reaction and c3h8 dehydrogenation seem to occur within the hydrothermal reservoir at temperatures ranging from 250 to 300 c fumarole gases sampled in 2006 2007 show relatively low n2 he and n2 ar ratios and high r ra values with respect to those measured in 2012 such compositional and isotope variations were likely related to injection of mafic magma that likely triggered the 2000 eruption therefore changes affecting the magmatic system had a delayed effect on the chemistry of the ccvc gases due to the presence of the hydrothermal reservoir however geochemical monitoring activities mainly focused on the behavior of inert gas compounds n2 and he should be increased to investigate the mechanism at the origin of the unrest started in 2011

field study of a highly active fault zone the xianshuihe fault of southwestern china the xianshuihe fault of western sichuan province china is one of the world s most active faults having produced 4 earthquakes during this century of magnitude 7 along a 350 km length of the fault at least 8 such events have occurred since 1725 in the more limited 150 km long segment including luhuo and daofu major earthquakes in 1904 1923 1973 and 1981 m 7 7 7 6 6 9 were associated with overlapping surficial fault ruptures and with individual left lateral displacements as large as 3 6 m field studies indicate that this high degree of activity is typical of the fault s longer term history the holocene left lateral slip rate on the north western segment of the fault has been 15 5 mm yr decreasing to about 5 mm yr on its southeastern segment based on radiometrically dated offset stream channel and terrace deposits and on offset glacial moraines physiographic features of active faulting are fully as diagrammatic as those of california s san andreas fault mainly because of high altitude preservation and the absence of cultural modification on this eastern margin of the tibetan plateau detailed en echelon tensional and pushup features resulting from surface ruptures in 1973 1955 1923 and 1893 can still be recognized today and new data have been collected bearing on the offsets and fault rupture lengths during these and other events the locations and magnitudes of historic earthquakes suggest that the characteristic earthquake model may apply to the xianshuihe fault obvious geometric segmentation of the fault has controlled the initiation and termination of ruptures in some events whereas segmentation control for others remains obscure based on the historic record repeat times estimated from slip rates and current seismic gaps two segments are particularly likely sites for m 7 earthquakes in the near future the 65 km long segment between daofu and qianning and the 135 km long segment bracketing kangding continuing creep has been documented along some segments of the fault and this together with the high degree of activity and other unique attributes makes the xianshuihe fault one of the most promising sites in the world for earthquake prediction and hazard evaluation studies

active shortening within the himalayan orogenic wedge implied by the 2015 gorkha earthquake the himalaya grow as the indian plate is thrust beneath tibet analysis of surface deformation caused by the 2015 gorkha earthquake suggests slip on smaller scale faults at the foot of the high himalaya help build earth s highest peaks

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

lower edge of locked main himalayan thrust unzipped by the 2015 gorkha earthquake faults are unlocked by earthquakes analysis of seismic data from the 2015 nepal earthquake shows that only part of the main himalayan thrust fault was unzipped by the quake leaving much of the fault locked and ready to slip in a future event

light hydrocarbons in hydrothermal and magmatic fumaroles hints of catalytic and thermal reactions volcanic gaseous mixtures emitted from active volcanoes frequently show variable amounts of saturated alkanes unsaturated alkenes and aromatic volatile hydrocarbons three major patterns of distributions can be recognized apparently related to the chemical physical environment of formation of the gas exhalations alkane rich low temperature gas emissions from recently active volcanic areas aromatic rich hydrothermal manifestations and alkene rich magmatic fumaroles on active volcanoes thermodynamic data together with theoretical and practical findings from the petroleum industry point to two main types of reactions occurring in these volcanic environments cracking and reforming cracking processes mainly caused by thermal effects occur when hydrocarbon bearing hydrothermal fluids enter and mix with a hot and dry rapidly rising magmatic gas phase the most probable products are light alkenes with carbon numbers decreasing with increasing reaction temperatures the presence of aromatic species in hydrothermal fluids can be linked to reforming processes catalysed by several possible agents such as smectites and zeolites generally present in the hydrothermally altered volcanic terranes and facilitated by long residence times in a hydrothermal envelope

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

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

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