18o exchange between steam and carbon dioxide in volcanic and hydrothermal gases implications for the source of water abstract the oxygen isotopic compositions of h 2 o and co 2 from 31 fumaroles from different volcanoes vesuvio campi flegrei vulcano and etna in italy soufriere of guadeloupe in lesser antilles prove that 18 o exchange between co 2 and steam is fast enough in natural gas phases to allow rapid isotopic reequilibration within a wide temperature range 100 1000 c the isotopic composition of h 2 o discharged by volcanic hydrothermal fumaroles is affected by isotopic reequilibration along with cooling of the gas phase and this secondary process must be taken into account when interpreting the origin of the water from isotopic data the use of corrected 18 o values computed considering the overall oxygen isotopic composition of the h 2 o co 2 system is therefore compulsory to overcome interpretative biases as an example we apply this method to 100 600 c fumaroles at vulcano crater whose isotopic composition is reinterpreted considering the effects of 18 o exchange between co 2 and h 2 o in contrast to most previous interpretations the corrected isotopic values for h 2 o clearly show that the vulcano system is fed by a two component mixture of magmatic water with a typical andesitic composition and either 18 o shifted seawater or magmatic steam partly condensed within the volcanic ground with minor contribution of local meteoric water the possible additional effects of isotopic reequilibration involving other o and h bearing gas species in volcanic fluids such as so 2 h 2 s hcl hf and h 2 have been also considered the influence of so 2 upon the isotopic composition of h 2 o is subordinate with respect to that of co 2 whereas significant shifts in deuterium composition are expected from hydrogen isotopic exchanges in the h 2 o h 2 s hcl hf h 2 gas system

hydrothermal hydrocarbon gases in the sediments of the king george basin bransfield strait antarctica thermogenic hydrocarbons formed by the thermal alteration of organic matter are encountered in several piston core stations in the king george basin anatarctica these hemipelagic sediments are being deposited in an area of active hydrothermalism associated with the back arc spreading in the bransfield strait the lateral extent of sediments infiltrated by the hydrothermally influenced interstitial fluids is characterized by basalt diapirix intrusions and is delineated by an acoustically turbid zone in the sediments of the eastern part of the basin iron sulphide bearing veins and fractures cut across the sediment in several cores they appear to be conduits for flow of hydrothermally altered fluids these zones have the highest c2 and ethene contents the thermogenic hydrocarbons have molecular c1 c2 c3 ratios typically 50 and 13ch4 values between 38 and 48 indicating an organic source which has undergone strong thermal stress several sediment cores also have mixed gas signatures which indicate the presence of substantial amounts of bacterial gas predominantly methane hydrocarbon generation in the king george basin is thought to be a local phenomenon resulting from submarine volcanism with temperatures in the range 70 150 c there are no apparent seepages of hydrocarbons into the water column and it is not believed that significant accumulation of thermogenic hydrocarbons reside in the basin

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

geochemistry of some gases in hydrothermal fluids from the southern juan de fuca ridge five samples of hydrothermal fluids from two vent areas on the southern juan de fuca ridge were analyzed for dissolved gases concentrations in the end member hydrothermal fluid of h2 270 527 mol kg ch4 82 118 mol kg and co2 3920 4460 mol kg are well above values in ambient seawater and are similar to concentrations reported for other ridge crest hydrothermal systems the carbon isotopic ratios of the ch4 13c 17 8 to 20 8 and co2 13c 3 6 to 4 7 suggest that at least some of the ch4 and co2 in the fluids is basalt derived the range of 13c values for the basalt derived co2 is 6 8 to 9 7 calculated by assuming conservation of recharge co2 during hydrothermal circulation apparent temperatures of equilibration between the ch4 and the basalt derived co2 range from 640 c to 750 c small amounts of ethane c2h6 ch4 0 9 10 3 2 2 10 3 propane and butane detected in the samples may also have formed in the basalt one sample of almost pure 95 5 hydrothermal fluid contained a significant fraction up to 63 and 74 respectively of the recharge ar and n2 this suggests that the fluid has not undergone extensive vapor liquid phase separation

geochemical and isotopic evidences of magmatic inputs in the hydrothermal reservoir feeding the fumarolic discharges of tacora volcano northern chile abstract tacora volcano is a nearly unknown and understudied 5980 m high volcano located on the northernmost border between chile and peru tacora is characterized by intense fumarolic activity with extensive white colored hydrothermal areas along the nw and w flanks of the volcanic structure the chemical and isotopic features of gas emissions indicate that the hydrothermal reservoir is significantly affected by contributions from magmatic degassing despite relatively low outlet temperatures 82 93 c water and gas isotopic signatures stem from degassing of andesitic magmas produced from the sediment poor subducting slab isotopic data suggests ch 4 co 2 isotopic equilibration occurs at 400 c likely in the deepest portion of the hydrothermal magmatic fluid reservoir the h 2 h 2 o co co 2 h 2 ar ch 4 co 2 and c 2 c 3 alkenes alkanes pairs tend to approach a chemical equilibrium at temperatures between 200 and 320 c when redox conditions are more oxidizing than those determined by the typical feo feo 1 5 rock buffer system boiling occurs at shallow depth at 85 c within a discontinuous thin aquifer enough as thermal buffer but not able to scrub the uprising magmatic related acidic gases

evolution of fluid geochemistry at the turrialba volcano costa rica from 1998 to 2008 turrialba 10 02 n 83 45 w is a 3 349 m high stratovolcano belonging to the holocene cordillera central volcanic belt of costa rica the summit consists of three ew oriented craters east central and west since its last eruptive phase 1864 1866 the central and west craters have displayed modest fumarolic activity with outlet temperatures clustering around 90 c in 2001 seismic swarms ground deformation and increasing fumarolic activity occurred from 2005 to 2008 new fumarolic vents opened between and within the central and west craters and along the western and southwestern outer flanks of the volcanic edifice these physical changes were accompanied by a drastic modification in the gas chemistry that can be divided in three stages 1 hydrothermal from 1998 to autumn 2001 characterized by the presence of h2o co2 h2s and to a very minor extent hcl and hf 2 hydrothermal magmatic autumn 2001 2007 with the appearance of so2 and a significant increase of hcl and hf and 3 magmatic dominated 2007 2008 characterized by increased so2 content so2 h2s 100 and temperatures up to 282 c accordingly gas equilibrium in the co2 ch4 h2 system suggests a progressive evolution of the deep fluid reservoir toward higher temperatures and more oxidizing conditions the chemical physical modifications of turrialba in the last decade can be interpreted as part of a cyclic mechanism controlling the balance between the hydrothermal and the magmatic systems nevertheless the risk of rejuvenation of the volcanic activity cannot be excluded and an appropriate seismic ground deformation and geochemical monitoring program is highly recommended turrialba lies at a distance of 35 and 15 km from san jose and cartago respectively the two largest cities in costa rica

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

fumarolic activity of avachinsky and koryaksky volcanoes kamchatka from 1993 to 1994 volcanic gas and condensate samples were collected in 1993 1994 from fumaroles of koryaksky and avachinsky basaltic andesite volcanoes on the kamchatka peninsula near petropavlovsk kamchatsky the highest temperature fumarolic discharges 220 c at koryaksky and 473 c at avachinsky are water rich 940 985 mmol mol of h2o and have chemical and isotopic characteristics typical of kamchatka kurile high and medium temperature volcanic gases the temperature and chemical and water isotopic compositions of the koryaksky gases have not changed during the past 11 years they represent an approximate 2 1 mixture of magmatic and meteoric end members low temperature near boiling point discharges of avachinsky volcano are water poor 880 mmol mol their compositions have not changed since the 1991 eruption and are suggested to be derived from partially condensed magmatic gases at shallow depth based on a simple model involving mixing and single step steam separation low water and high co2 contents as well as the observed cl concentration and water isotopic composition in low temperature discharges are the result of near surface boiling of a brine composed of the almost pure condensed magmatic gas high methane content in low temperature avachinsky gases and the 220 c koryaksky fumarole low c isotopic ratio in co2 at koryaksky 11 8 and water isotope data suggest that the meteoric end member contains considerable amounts of the regional methane rich thermal water discovered in the vicinity of both volcanoes

middle cretaceous calcareous nannofossil biogeography and preservation in the atlantic and indian oceans implications for paleoceanography abstract the quantitative study of calcareous nannofossil preservation and biogeographic distribution puts constraints on paleoceanographic models for the atlantic and indian oceans during the middle cretaceous we establish a dissolution ranking of middle cretaceous calcareous nannofossils based on susceptibility to dissolution a positive correlation of organic carbon content of the sediments and the relative abundance of watznaueria indicates that much of the carbonate dissolution was caused by the release of carbon dioxide during oxidation of organic matter the depth distribution of the most dissolution resistant species watznaueria barnesae shows relative abundance maxima at the deepest sites and a maximum where intermediate waters impinge on slopes this reflects stagnant oxygen poor bottom waters and possibly a mid water oxygen minimum zone with increased deposition and catabolic breakdown of organic matter factor analyses are performed on various data sets for three different time slices ranging in age from late aptian to early albian middle albian and late albian to cenomanian the resulting factors can be related to paleoceanographic conditions such as colder water at high latitudes high fertility upwelling conditions and neritic conditions for all three time intervals a wide tropical to subtropical zone was flanked by boreal and austral zones upwelling conditions probably existed along the north african margin and over the falkland plateau zonal upwelling is tentatively postulated for the northwestern and northeastern margin of the north atlantic in the middle albian and for the eastern margin of the north atlantic off western europe for the late albian to cenomanian we speculate on surface water current patterns location of upwelling regions and haline driven deep circulation for the middle cretaceous

the magmatic and hydrothermal dominated fumarolic system at the active crater of lascar volcano northern chile low to high temperature fumaroles discharging from the active crater of lascar volcano northern chile have been collected in november 2002 may 2005 and october 2006 for chemical and isotopic analysis to provide the first geochemical survey on the magmatic hydrothermal system of this active volcano chemical and isotopic gas composition shows direct addition of high temperature fluids from magmatic degassing mainly testified by the very high contents of so2 hcl and hf up to 87 800 29 500 and 2 900 mol mol and the high r ra values up to 7 29 contributions from a hydrothermal source mainly in gas discharges of the active crater rim has also been detected significant variations in fluid chemistry mainly consisting of a general decrease of magmatic related compounds i e so2 have affected the fumarolic system during the period of observation indicating an increase of the influence of the hydrothermal system surrounding the ascending deep fluids the chemical composition of active crater fumaroles has been used to build up a geochemical model describing the main processes that regulate the fluid circulation system of lascar volcano to be utilized in volcanic surveillance

recurring taiga forest steppe habitats in the carpathian basin in the upper weichselian many loess pro les some lake sediments and archaeological sites in di erent parts of the carpathian basin were analysed in respect of their geology sedimentology molluscs and macro charcoal remains radiocarbon dating was also carried out on charcoal remains as well as on molluscan shells the loess pro les prove to have been formed during the last glacial period between ca 70 000 and 15 000 years bp two well developed and a weakly developed charcoal layer can be found at the sites dating from that period all rest on the top of a palaeosol on the basis of palaeoecological investigations of these charcoal layers and the molluscs found within the loess it is concluded that recurring boreal forest steppe habitats characterised the carpathian basin the woodlands mostly consisting of picea trees in the north and pinus sylvestris in the south as well as six other arboreal species by reference to the subsequent charcoal layers reforestation occurred every 2000 5000 years with the same composition although their density may have varied these forests thus recur in the same places after extensive forest res how often and why these reforestation events took place and how much time was needed for the forests steppes to redevelop needs further clari cation 2001 published by elsevier science ltd

chemical and isotopic features of cold and thermal fluids discharged in the southern volcanic zone between 32 5 s and 36 s insights into the physical and chemical processes controlling fluid geochemistry in geothermal systems of central chile abstract the principal cordillera of central chile is characterized by two belts of different ages and lithologies i an eastern mesozoic belt consisting of limestone and gypsum rich sedimentary rocks at the border between central chile and argentina where the active volcanic arc occurs and ii a western belt of cenozoic age containing basaltic to andesitic volcanic and volcanoclastic sequences this distinctive geological setting controls water chemistry of cold and thermal springs in the region which are fed by meteoric water that circulates through deep regional structures in the western sector of principal cordillera water rock interaction processes produce low tds slightly alkaline hco3 dominated waters although dissolution of underlying mesozoic evaporitic rocks occasionally causes so42 and cl enrichments in this area few na hco3 and na so42 waters occurred being likely produced by a ca2 na exchange during water rock interactions differently the chemical features of ca2 cl waters was likely related to an albitization chloritization process affecting basaltic to andesitic rocks outcropping in this area addition of na cl brines uprising from the eastern sector through the west verging thrust faults cannot be excluded as suggested by the occurrence of mantle he 19 in dissolved gases in contrast in the eastern sector of the study region mainly characterized by the occurrence of evaporitic sequences and relatively high heat flow mature na cl waters were recognized the latter being likely related to promising geothermal reservoirs as supported by the chemical composition of the associated bubbling and fumarolic gases their relatively low 3he 4he ratios up to 3 9 ra measured in the fumaroles on this area evidenced a significant crustal contamination by radiogenic 4he the latter was likely due to i degassing from 4he rich magma batches residing in the crust and or ii addition of fluids interacting with sedimentary rocks this interpretation is consistent with the measured 13c co2 values from 13 2 to 5 72 vs v pdb and the co2 3he ratios up to 14 6 1010 which suggest that co2 mostly originates from the limestone rich basement and recycling of subducted sediments with an important addition of sedimentary organic derived carbon whereas mantle degassing contributes at a minor extent according to geothermometric estimations based on the na k mg2 and ca2 contents the mature na cl rich waters approached a chemical equilibrium with calcite dolomite anhydrite fluorite albite k feldspar and ca and mg saponites at a broad range of temperatures up to 300 c in the associated gas phase equilibria of chemical reactions characterized by slow kinetics e g sabatier reaction suggested significant contributions from hot and oxidizing magmatic gases this hypothesis is consistent with the 13c co2 rc ra co2 3he values of the fumarolic gases accordingly the isotopic signatures of the fumarolic steam is similar to that of fluids discharged from the summit craters of the two active volcanoes in the study area tupungatito and planchon peteroa these results encourage the development of further geochemical and geophysical surveys aimed to provide an exhaustive evaluation of the geothermal potential of these volcanic hydrothermal systems

the link between volcanism and tectonics in the southern volcanic zone of the chilean andes a review abstract the nature of the interplay between tectonics and volcanism is a major question in continental margin tectonics the southern andes volcanic zone svz located at the obliquely convergent nazca south america plate margin between 33 s and 46 s offers a unique opportunity to address this question because of along strike changes in crustal thickness tectonic style and well constrained long term and short term kinematic history the complex interaction between tectonic and magmatic processes is evidenced by both the architecture and geochemical signature of volcanic systems main first order factors accounting for the along strike variations in the nature and composition of volcanism are crustal thickness and the existence of a major intra arc fault system the liquine ofqui fault zone lofz second order factors include the local nature of the volcanic arc basement two main categories of volcano tectonic associations have been identified according to the spatial distribution and internal organization of individual volcanoes and clusters of volcanoes with respect to both the overall strike of the volcanic arc and the first and second order active inactive basement faults kinematically coupled associations those that are directly related to the current dextral transpressional tectonic regime include ne trending volcanic alignments of stratovolcanoes and or monogenetic cones kinematically uncoupled associations in which coupling with the current regime is not required include stratovolcanoes built on top of ancient reverse and strike slip faults of the volcanic arc basement and monogenetic cones lying along master faults of the lofz whereas mostly primitive magmas are found in the first category more evolved terms can occur genetically associated with the second category we propose a simplified three dimensional model for the magma plumbing system along and across the svz that integrates kinematically coupled and kinematically uncoupled volcano tectonic associations within the framework of first and second order geological and structural constraints

tectonic control on sediment accretion and subduction off south central chile implications for coseismic rupture processes of the 1960 and 2010 megathrust earthquakes based on a compilation of published and new seismic refraction and multichannel seismic reflection data along the south central chile margin 33 46 s we study the processes of sediment accretion and subduction and their implications on megathrust seismicity in terms of the frontal accretionary prism fap size the marine south central chile fore arc can be divided in two main segments 1 the maule segment south of the juan fernandez ridge and north of the mocha block characterized by a relative large fap 20 40 km wide and 2 the chiloe segment south of the mocha block and north of the nazca antarctic south america plates junction characterized by a small fap 10 km wide in addition the maule and chiloe segments correlate with a thin 1 km thick and thick 1 5 km thick subduction channel respectively the mocha block lies between 37 5 and 40 s and is configured by the chile trench mocha and valdivia fracture zones this region separates young 0 25 ma oceanic lithosphere in the south from old 30 35 ma oceanic lithosphere in the north and it represents a fundamental tectonic boundary separating two different styles of sediment accretion and subduction respectively a process responsible for this segmentation could be related to differences in initial angles of subduction which in turn depend on the amplitude of the down deflected oceanic lithosphere under trench sediment loading on the other hand a small fap along the chiloe segment is coincident with the rupture area of the trans pacific tsunamigenic 1960 earthquake mw 9 5 while a relatively large fap along the maule segment is coincident with the rupture area of the 2010 earthquake mw 8 8 differences in earthquake and tsunami magnitudes between these events can be explained in terms of the fap size along the chiloe and maule segments that control the location of the updip limit of the seismogenic zone the rupture area of the 1960 event also correlates with a thick subduction channel chiloe segment that may provide enough smoothness at the subduction interface allowing long lateral earthquake rupture propagation

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

coseismic changes in the chemical composition of volcanic gases from the owakudani geothermal area on hakone volcano japan the chemical and isotopic compositions of volcanic gases at a borehole and a natural fumarole in the owakudani geothermal area hakone volcano japan have been repeatedly measured since 2001 when a seismic swarm occurred in the area the co2 h2o and co2 h2s ratios were high in 2001 it increased in 2006 and again in 2008 when seismic swarms occurred beneath the geothermal area the observed increases suggest the injection of co2 and so2 rich magmatic gas into the underlying hydrothermal reservoir implying that the magmatic gas was episodically supplied to the hydrothermal system in 2006 and 2008 the earthquake swarms probably resulted from the injection of gas through the shallow crust accompanying the break of the sealing zone

experimental constraints on metal transport in fumarolic gases abstract metals are efficiently transported in a gas phase and the gas composition strongly affects transport rates of these metals in the gas phase here we present a new approach to systematically investigate metal transport and deposition from volcanic gases of different compositions we test the effect of sulfur and chlorine on the volatilization of 30 metal oxides and the phases deposited along a temperature gradient of 1250 300 c in evacuated silica glass tubes in water free systems in total we observe 30 different deposited phases including oxides sulfides and chlorides the experimental results are compared with closed system and open system thermochemical equilibrium calculations the closed system calculations provide insights into the metal speciation in the gas phase and the open system calculations provide thermodynamic predictions of the temperature ranges over which metals deposited from the gas phase both approaches only partially reproduce the experimental observations of the deposited phases in the silica glass tubes however when we compare our experimental results with records from fumaroles on three different volcanoes kudriavy volcano russia la fossa crater on vulcano italy and momotombo nicaragua we find that our experiments agree very well with natural observations we suggest that similar experimental investigations are powerful tools in the study of metal transport in ore forming systems involving gas phases and results may be applied to various processes in terrestrial and planetary environments

climatic fluctuations and sea surface water circulation patterns at the end of the cretaceous era calcareous nannofossil evidence abstract new paleoecological data are presented for late maastrichtian calcareous nannofossil assemblages of the indian ocean and the boreal epicontinental chalk sea these data are compiled with recent results in the tropical atlantic pacific and tethys oceans in order to characterize environmental changes by the end of the cretaceous era the paleobiogeographic distribution of the warm water species micula murus is updated and indicates the existence of major sea surface currents in the late maastrichtian atlantic ocean similar to the present day the end maastrichtian greenhouse warming is characterized at tropical and subtropical latitudes by an increase in abundance of m murus and the temporary disappearance of the high fertility marker biscutum constans in the boreal realm the greenhouse episode is marked by a contemporaneous acme of watznaueria barnesiae coincident with very rare occurrences of m murus and other tropical nannofossil species which have never been reported before at boreal latitudes a review of cyclostratigraphic and calcareous nannofossil data in the atlantic pacific indian and tethys oceans points to the following evolution of sea surface paleotemperatures for the last ca 350 380 kyr of the cretaceous the end maastrichtian greenhouse warming lasted on average a little more than 200 kyr and was followed by a ca 100 120 kyr cooling in the tethys a 30 40 kyr additional pulse of warming is highlighted immediately below the cretaceous paleogene boundary these findings indicate an important instability of the climate system at the end of the maastrichtian most likely caused by deccan volcanism the calcareous nannofossil species richness dropped during the end maastrichtian greenhouse warming which may indicate environmental stress and or ocean acidification however nannoplankton diversity returned rapidly to higher values after this climatic episode and remained high up to the cretaceous paleogene boundary no significant extinction is recorded in this biotic group prior to the boundary clay

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

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

the hydrothermal system of the domuyo volcanic complex argentina a conceptual model based on new geochemical and isotopic evidences abstract the domuyo volcanic complex neuquen province argentina hosts one of the most promising geothermal systems of patagonia giving rise to thermal manifestations discharging hot and cl rich fluids this study reports a complete geochemical dataset of gas and water samples collected in three years 2013 2014 and 2015 from the main fluid discharges of this area the chemical and isotopic composition d h 2 o and 18 o h 2 o of waters indicates that rainwater and snow melting are the primary recharge of a hydrothermal reservoir located at relative shallow depth 400 600 m possibly connected to a second deeper 2 3 km reservoir reactive magmatic gases are completely scrubbed by the hydrothermal aquifer s whereas interaction of meteoric waters at the surface causes a significant air contamination and dilution of the fluid discharges located along the creeks at the foothill of the cerro domuyo edifice thermal discharges located at relatively high altitude 3150 m a s l namely bramadora are less affected by this process as also shown by their relatively high r ra values up to 6 91 pointing to the occurrence of an actively degassing magma batch located at an unknown depth gas and solute geothermometry suggests equilibrium temperatures up to 220 240 c likely referred to the shallower hydrothermal reservoir these results confirming the promising indications of the preliminary surveys carried out in the 1980 s provide useful information for a reliable estimation of the geothermal potential of this extinct volcanic system although a detailed geophysical measurements is required for the correct estimation of depth and dimensions of the fluid reservoir s

geochemistry of the magmatic hydrothermal system of kawah ijen volcano east java indonesia samples from kawah ijen crater lake spring and fumarole discharges were collected between 1990 and 1996 for chemical and isotopic analysis an extremely low ph 0 3 lake contains so 4 cl waters produced during absorption of magmatic volatiles into shallow ground water the acidic waters dissolve the rock isochemically to produce immature solutions the strong d and 18 o enrichment of the lake is mainly due to enhanced evaporation at elevated temperature but involvement of a magmatic component with heavy isotopic ratios also modifies the lake d and 18 o content the large so4 s d 23 8 26 4 measured in the lake suggest that dissolved so 4 forms during disproportionation of magmatic so 2 in the hydrothermal conduit at temperatures of 250 280 c the lake 18 o so4 and 18 o h2o values may reflect equilibration during subsurface circulation of the water at temperatures near 150 c significant variations in the lake s bulk composition from 1990 to 1996 were not detected however we interpret a change in the distribution and concentration of polythionate species in 1996 as a result of increased so 2 rich gas input to the lake system thermal springs at kawah ijen consist of acidic so 4 cl waters on the lakeshore and neutral ph hco 3 so 4 cl na waters in blawan village 17 km from the crater the cation contents of these discharges are diluted compared to the crater lake but still do not represent equilibrium with the rock the so 4 cl ratios and water and sulfur isotopic compositions support the idea that these springs are mixtures of summit acidic so 4 cl water and ground water the lakeshore fumarole discharges t 170 245 c have both a magmatic and a hydrothermal component and are supersaturated with respect to elemental sulfur the apparent equilibrium temperature of the gas is 260 c the proportions of the oxidized so 2 dominated magmatic vapor anti of the reduced h 2 s dominated hydrothermal vapor in the fumaroles varied between 1979 and 1996 this may be the result of interaction of so 2 bearing magmatic vapors with the summit acidic hydrothermal reservoir this idea is supported by the lower h 2 s so 2 ratio deduced for the gas producing the so 4 cl reservoir feeding the lake compared with that observed in the subaerial gas discharges the condensing gas may have equilibrated in a liquid vapor zone at about 350 c elemental sulfur occurs in the crater lake environment as banded sediments exposed on the lakeshore and as a subaqueous molten body on the crater floor the sediments were precipitated in the past during inorganic oxidation of h 2 s in the lake water this process was not continuous but was interrupted by periods of massive silica poorly crystallized precipitation similar to the present day lake conditions we suggest that the factor controlling the type of deposition is related to whether h 2 s or silica rich volcanic discharges enter the lake this could depend on the efficiency with which the lake water circulates in the hydrothermal cell beneath the crater quenched liquid sulfur products show 34 s values similar to those found in the banded deposits suggesting that the subaqueous molten body simply consists of melted sediments previously accumulated at the lake bottom

evolution of a vent hosted hydrothermal system beneath ruapehu crater lake new zealand a two year chemical monitoring program of ruapehu crater lake shows that it has evolved considerably since the volcano s more active eruptive periods in the early 1970s the present ph 20 c of 0 6 is about one half unit more acid than the baseline values in the 1970s whereas s cl ratios have increased markedly owing in part to declining hcl inputs into the lake but also to absolute increases in so4 levels which now stand at the highest values ever recorded increases in k mg and na mg ratios over the 20 year period are attributed to hydrothermal reaction processes in the vent which are presently causing dissolution of previously formed alteration phases such as natroalunite these observations combined with results of a recent heat budget analysis of the lake have led to the development of hydrothermal convection model for the upper portion of the vent possible vent lake chemical reaction processes between end member reactants have been modelled with the computer code chiller the results are consistent with the view that variations in lake chemistry which are initiated by the introduction of fresh magmatic material into the vent reflect the extent of dissolution reaction progress on the magmatic material and or its alteration products the results also provide insights into the role of such vent processes in the formation of high sulfidation type ore deposits

late cenozoic tectonics of the southern chile trench marine geophysical data from off shore of southern chile are used to define the interaction between the chile ridge and chile trench during late cenozoic time we identify three distinct ridge trench collision events between 14 and 10 ma a 700 km long nearly continuous section of the chile ridge was sub ducted between 55 s and 48 s shorter sections of the ridge offset by large transform faults were subducted at 6 and 3 ma between 48 s and 47 s at the present day triple junction the subduction of the ridge has a strong influence on the chile trench in this region the landward trench slope has undergone a recent episode of subduction driven tectonic erosion the trench slope is narrower and steeper than along other sectors of the margin and the trench axis has migrated shoreward evidence exists for late neogene and quaternary uplift and plutonism on the adjacent continental margin south of 48 s where collision took place between 10 and 14 ma the effects of collision are much less pronounced in particular the landward trench slope does not appear to have been subjected to extensive tectonic erosion we conclude that the configuration of the spreading centers and transform faults on the chile rise is the chief factor controlling ridge trench tectonic interaction tectonic erosion of the landward trench slope and tectonic activity in the adjacent continental margin are much greater when short sections of ridge offset by large transform faults are subducted a major sub marine channel leads along the trench axis south ward from the triple junction this channel cuts across the outer trench rise and carries sediment westward to the mornington abyssal plain the paleogene tectonic history of the southern chile trench includes a southward migrating ridge trench collision involving the farallon aluk spreading center in eocene time

calcareous nannofossils and milankovitch cycles the example of the albian gault clay formation southern england a quantitative study of calcareous nannofossil assemblages was carried out on the albian gault clay formation england this unit consists of grey marly claystones and marlstones with phosphatic nodules and glauconitic layers as minor lithologies two cores were analyzed in detail to focus on changes in nannofloral assemblages and consider their significance preservation of calcareous nannofossils is excellent and therefore diagenesis cannot be invoked to explain not even partially the changes registered in assemblages fast fourier spectral analysis was performed on percentages of selected nannofossil species fluctuations in abundance of both biscutum constans and watznaueria barnesae regarded as fertility and non fertility indices respectively appear to be orbitally driven because spectral analysis showed periodicities of approximately 41 kyr obliquity cycle and 100 kyr short eccentricity cycle in all the spectra the axial obliquityc cycle is a strong signal as expected at these high latitude sites from the boreal realm the same pattern was observed in another fertility controlled taxon zygodiscus cf erectus but cross correlation shows that its abundance plot is displaced with respect to that of b constans orbital perturbations induce variations in climate and ocean circulation because they influence the earth s insolation and seasonality during times of high seasonality strong gradients cause vigorous oceanic circulation a better cycling of nutrients and higher fertility whereas during times of low seasonality low gradients induce more sluggish circulation and lower fertility the carbonate content of the gault clay cores is not correlatable to the higher fertility indices as the abundance curves of b constans w barnesae and z cf erectus are displaced with respect to caco3 content variations this also means that cyclicity in nannofossil assemblages is not a result of diagenesis but an original signal abundance fluctuations of repagulum parvidentatum and combined parhabdolithus asper p splendens colder and warmer water indicators respectively provide evidence for orbital periodicities suggesting that also cyclic variations of surface water temperature might have influenced the nannofossil assemblage patterns within the gault clay

tectonic inheritance and pliocene pleistocene inversion of the algerian margin around algiers insights from multibeam and seismic reflection data 1 the algerian margin has originated from the opening of the algerian basin about 25 30 ma ago the central margin provides evidence for large scale normal faults of oligo miocene age whereas transcurrent tectonics characterizes the western margin a set of nw se oriented dextral transform faults was active during basin opening and divided the 600 km long central margin into segments of 120 150 km the upper miocene plio quaternary and present day tectonic setting is however compressional and supports the occurrence of a margin inversion a process still poorly documented worldwide we show that the central algerian margin represents a rare example of inverted margin where the process of subduction inception is particularly well expressed and helps understand how extensional and transtensive structures are involved in margin shortening using multibeam bathymetry and multichannel seismic reflection sections from the maradja 2003 and 2005 cruises we evidence pliocene pleistocene shortening with contrasting styles along the margin between west khayr al din bank and east boumerdes dellys margin of algiers pre miocene structures such as basement highs and transform faults appear to control changes of the deformation pattern along this part of the margin resulting in different widths geometries and relative positions of folds and faults plio quaternary and active blind thrust faults do not reuse oligo miocene normal and transform faults during inversion but instead grow within the continental margin as testified for instance by the 21 may 2003 mw 6 8 boumerdes zemmouri earthquake at the foot of the continental slope and at the northern sides of basement highs interpreted as stretched continental blocks of the rifted margin the inherited structures of the margin appear therefore to determine this deformation pattern and ultimately the earthquake and tsunami sizes offshore the complex geometry of the fault system along the algerian margin suggests a process of initiation of subduction in its central and eastern parts

the determination of deep temperatures by means of the co co2 h2 h2o geothermometer an example using fumaroles in the campi flegrei italy chromatographic analyses of fumarolic gases collected in sampling bottles containing an alkaline solution have been carried out using a thermal conductivity detector and a flame ionization detector after catalytic conversion of co and ch4 the latter method enables the concentration of carbon monoxide to be measured with sufficient accuracy for use in a co co2 h2 h2o geothermometer application of this geothermometer to fumaroles in the crater of solfatara in the campi flegrei italy indicates that they are fed from a steam reservoir at 250 15 c and at 10 36 2atm of oxygen on the other hand the ch4 co2 h2 h2o geothermobarometer seems to re equilibrate at superficial temperatures and cannot be used for infering thermodynamic conditions at depth regular sampling of these fumaroles together with a geothermometric interpretation of the gas analyses provides a means of monitoring with comparative accuracy the chemical and thermal evolution of the hydrothermal reservoir below the solfatara crater such monitoring would probably detect an increase in temperature at depth and the injection of magmatic gas into the reservoir

calcareous nannofossil evidence for the existence of the gulf stream during the late maastrichtian 1 upper maastrichtian calcareous nannofossil assemblages from eight cores on the south carolina coastal plain onshore set and three deep sea drilling sites from the continental slope and abyssal hills offshore set were analyzed by correlation and principal component analysis to examine the ancient surface water thermal structure in addition a temperature index derived from independently published paleobiogeographic information was applied to the sample data all three methods indicate a strong separation of the samples into onshore and offshore sets with the offshore data set exhibiting significantly warmer paleotemperatures the great disparity between these two sample sets indicates that there was a strong thermal contrast between the onshore and offshore surface water masses that persisted throughout the late maastrichtian despite evident short term changes in fertility productivity and community structure this suggests the gulf stream was present as a major oceanographic feature during the late maastrichtian

volcanic lake systematics ii chemical constraints abstract a database of 373 lake water analyses from the published literature was compiled and used to explore the geochemical systematics of volcanic lakes binary correlations and principal component analysis indicate strong internal coherence among most chemical parameters compositional variations are influenced by the flux of magmatic volatiles and or deep hydrothermal fluids the chemistry of the fluid entering a lake may be dominated by a high temperature volcanic gas component or by a lower temperature fluid that has interacted extensively with volcanic rocks precipitation of minerals like gypsum and silica can strongly affect the concentrations of ca and si in some lakes a much less concentrated geothermal input fluid provides the mineralized components of some more dilute lakes temporal variations in dilution and evaporation rates ultimately control absolute concentrations of dissolved constituents but not conservative element ratios most volcanic lake waters and presumably their deep hydrothermal fluid inputs classify as immature acid fluids that have not equilibrated with common secondary silicates such as clays or zeolites many such fluids may have equilibrated with secondary minerals earlier in their history but were re acidified by mixing with fresh volcanic fluids we use the concept of degree of neutralization as a new parameter to characterize these acid fluids this leads to a classification of gas dominated versus rock dominated lake waters a further classification is based on a cluster analysis and a hydrothermal speedometer concept which uses the degree of silica equilibration of a fluid during cooling and dilution to evaluate the rate of fluid equilibration in volcano hydrothermal systems

the effects of volatile recycling degassing and crustal contamination on the helium and carbon geochemistry of hydrothermal fluids from the southern volcanic zone of chile abstract we report new helium and carbon isotope 3he 4he 13c and relative abundance co2 3he characteristics of a suite of hydrothermal gases and fluids fumaroles hot springs geothermal wells from 18 localities in the central southern volcanic zone csvz of chile the csvz is characterized by a wide range of 3he 4he ratios from 1 50 to 6 47 ra where ra air 3he 4he 13c co2 values from 2 9 to 17 7 vs pdb and co2 3he ratios which vary over 5 orders of magnitude 3 1 105 to 2 3 1011 one hydrothermal locality aguas calientes has combined he co2 characteristics remarkably similar to other arc related systems worldwide implying that the underlying subduction zone complex and mantle wedge supplies volatiles to the volcanic front with little or no modification en route to the surface the mechanism controlling helium isotope ratios of other hydrothermal systems appears to be mixing between mantle derived helium and a radiogenic component derived from 4he rich country rock the variable he co2 elemental relationships and 13c co2 values at these localities are consistent with gas separation gas samples or temperature dependent calcite precipitation water samples in shallow level hydrothermal systems both processes result in co2 loss which exacerbates the effects of contamination by crustal gases whereas the aguas calientes locality is useful for understanding the role of the underlying mantle wedge and subducting slab in supplying volatiles to the andean volcanic front the value of the majority of hydrothermal samples in the present study lies with discerning the potentially complicating effects of degassing and or crustal contamination on the resulting he co2 record

evolution of volcanic gas composition during repeated culmination of volcanic activity at kuchinoerabujima volcano japan abstract chemical and isotopic compositions of low to medium temperature fumarolic gasses were measured at various fumaroles of kuchinoerabujima volcano from 1993 to 2009 by the combination of fumarolic gas sampling and multi gas measurement of volcanic plumes repeated culmination of the volcanic activity was observed as contemporaneous occurrence of seismic swarms summit inflation and demagnetization almost every two years after 1999 fumarolic activity also increased parallel with these activities new fumarolic fields of low temperature fumaroles at boiling point formed at the southern and western rims of the summit crater in 2003 and intense degassing activity started at medium temperature fumaroles inside the summit crater in 2008 the low temperature fumarolic gasses have peculiar composition with high h2 h2o co co2 and so2 h2s ratios typical features of high temperature volcanic gasses but also with low hcl and total s contents typical features of low temperature gasses these features indicate that the gasses are formed by low temperature differentiation of high temperature gasses variation of h and o isotopic ratios of the low temperature gasses indicates that the gasses are formed by isoenthalpic processes of vapor liquid separation at 100 c of a high temperature gas and meteoric water mixture implying that the high temperature gas was injected into a shallow aquifer without cooling temperatures of the high temperature gasses were estimated as 550 700 c based on the equilibrium temperature calculation with considering the low temperature differentiation the medium temperature fumarolic gasses from the summit crater have typical compositions of high temperature volcanic gasses and are estimated as the source gas of the boiling point fumaroles the h2 h2o and co2 st ratios of the low temperature fumaroles increased from 2004 to 2009 which is interpreted to be caused by the evolution of thermal structure of a shallow gas storage region of a few hundred meters deep increase of magmatic gas supply caused enlargement of a high temperature zone of the gas storage region widening the surrounding temperature transit zone with smaller temperature gradient the enlargement of the high temperature zone also reduces the overlying low temperature aquifer which caused the decrease of co2 st ratio by reduction of sulfur removal reaction the enlargement of the high temperature zone resulted in the leakage of the high temperature gasses directly to the surface as the medium temperature gasses from the summit crater

sources and flux of natural gases from mono lake california abstract the ability to identify a formation mechanism for natural gas in a particular environment requires consideration of several geochemical factors when there are multiple sources present four primary sources of methane have been identified in mono lake two of these sources were associated with numerous natural gas seeps which occur at various locations in the lake and extend beyond its present boundary the two other gas sources result from current microbiological processes in the natural gas seeps we observed flow rates as high as 160 moles ch4 day 1 and estimate total lakewide annual seep flux to be 2 1 106 moles ch4 geochemical parameters 13ch4 dch4 ch4 c2h6 c3h8 and 14ch4measurements revealed that most of the seeps originate from a paleo biogenic 13ch4 about 70 natural gas deposit of pleistocene age which underlies the current and former lakebed gas seeps in the vicinity of hot springs had in combination with the biogenic gas a prominent thermogenic gas component resulting from hydrothermal alteration of buried organic matter current microbiological processes responsible for sources of natural gas in the lake included pelagic meth anogenesis and decomposition of terrestrial grasses in the littoral zone methanogenesis in the pelagic sediments resulted in methane saturation 2 3 mm at 50 cm 13ch4 about 85 interstitial sulfate decreased from 133 mm at the surface to 35 mm by 110 cm depth indicating that sulfate reduction and methanogenesis operated concurrently methane diffused out of the sediments resulting in concentrations of about 50 m in the anoxic bottom waters methane oxidation in the oxic anoxic boundry lowered the concentration by 98 but values in surface waters 0 1 1 3 m were supersaturated with respect to the atmosphere the 13ch4 range 21 8 to 71 8 of this unoxidized residual methane was enriched in 13c relative to methane in the bottom water and sediments average outward flux of this methane was 2 77 107 moles yr 1 a fourth but minor source of methane 13ch4 55 2 was associated with the decomposition of terrestrial grasses taking place in the lake s recently expanded littoral zone

origin of fumarolic fluids from tupungatito volcano central chile interplay between magmatic hydrothermal and shallow meteoric sources tupungatito is a poorly known volcano located about 100 km eastward of santiago chile in the northernmost sector of the south volcanic zone this 5 682 m high volcano shows intense fumarolic activity it hosts three crater lakes within the northwestern portion of the summit area chemical compositions of fumarolic gases and isotopic signatures of noble gases 3he 4he and 40ar 36ar are up to 6 09 ra and 461 respectively and steam 18o and d suggest that they are produced by mixing of fluids from a magmatic source rich in acidic gas compounds so2 hcl and hf and meteoric water the magmatic hydrothermal fluids are affected by steam condensation that controls the outlet fumarolic temperatures 200 c and redox conditions are consistent with those inferred by the presence of the so2 h2s redox pair typical of fluids that have attained equilibrium in magmatic environment a comprehensive conceptual geochemical model describing the circulation pattern of the tupungatito hydrothermal magmatic fluids is proposed it includes fluid source regions and re equilibration processes affecting the different gas species due to changing chemical physical conditions as the magmatic hydrothermal fluids rise up toward the surface

physical models of fumarolic flow abstract transport of gas from subsurface magma to the atmosphere is modelled as flow through a narrow rough pipe and through a wider conduit filled with spheres representing flow in a porous pipe macroscopic mass momentum and energy balances are written for a control volume representing a short vertical section of the pipe the balances are solved for a perfect gas with the approximate thermodynamic properties of steam losing heat by steady state radial conduction through the pipe walls with boundary conditions of magmatic temperature at the base of the pipe atmospheric pressure at the surface and an ambient geotherm at a specified distance from the conduit results yield the variation of exit temperature with magmatic source depth conduit radius mass flow rate per unit area distance to ambient temperatures vent porosity and porous particle size two ambient geotherms are used 1 a linear gradient from atmospheric to magmatic temperatures and 2 a hydrothermal geotherm based on water saturation temperatures assuming a hydrostatic pressure gradient because individual vents commonly cluster the porous pipe model is considered to be more realistic than the rough pipe model mainly because the conductive cooling approximation is more likely to remain valid exit temperatures fall as conductive losses increase i e as the source depth increases the conduit narrows the mass flow decreases the distance to ambient temperatures reduces or the ambient geotherm cools the porous pipe model is applied to data from two fumarole fields and indicates magmatic source depths of

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

regional and temporal variations in co2 3he 3he 4he and δ13c along the north anatolian fault zone turkey abstract new he and c relative abundance isotope and concentration results from nine geothermal locations situated along an 800 km transect of the north anatolian fault zone nafz turkey that were monitored during the period november 2001 november 2004 are reported the geothermal waters were collected every 3 6 months to study possible links between temporal geochemical variations and seismic activity along the nafz at the nine sample locations the he isotope ratios range from 0 24 to 2 3 r a 13 c values range from 4 5 to 5 8 and co 2 3 he ratios range from 5 10 9 to 5 10 14 the following geochemical observations are noted 1 the highest 3 he 4 he ratios are found near the galatean volcanic region in the central section of the nafz 2 at each of the nine sample locations the 3 he 4 he ratios are generally constant however co 2 3 he ratios and he contents both show one order of magnitude variability and 13 c values show up to 4 variability and 3 at all locations except resadiye 13 c values show positive correlations with co 2 contents the results indicate that at least three processes are necessary to account for the geochemical variations 1 binary mixing between crustal and mantle derived volatiles can explain the general characteristics of 3 he 4 he ratios 13 c values and co 2 3 he ratios at the nine sample locations 2 preferential degassing of he from the geothermal waters is responsible for variations in co 2 3 he values and he contents at each sample location and 3 co 2 dissolution followed by calcite precipitation is responsible for variations in co 2 contents and 13 c values at most locations for each of the geochemical parameters anomalies are defined in the temporal record by values that fall outside two standard deviations of average values at each specific location geochemical anomalies that may be related to seismic activity are recorded on june 28 2004 at yalova where a m 4 2 earthquake occurred 43 days earlier at 15 km distance from the sample location and on april 7 2003 at efteni where a m 4 0 earthquake occurred 44 days later at a distance of 12 km at both locations the sampling periods containing geochemical anomalies were preceded by an increase in m 3 earthquakes occurring within 60 days and less than 40 km distance

a high resolution marine 187os 188os record for the late maastrichtian distinguishing the chemical fingerprints of deccan volcanism and the kp impact event abstract a composite late maastrichtian 65 5 to 68 5 ma marine osmium os isotope record based on samples from the southern ocean odp site 690 the tropical pacific ocean dsdp site 577 the south atlantic dsdp site 525 and the paleo tethys ocean demonstrates that subaerially exposed pelagic carbonates can record seawater os isotope variations with a fidelity comparable to sediments recovered from the seafloor new results provide robust evidence of a 20 decline in seawater 187os 188os over a period of about 200 kyr early in magnetochron c29r well below the cretaceous paleogene boundary kpb confirming previously reported low resolution data from the south atlantic ocean new results also confirm a second more rapid decline in 187os 188os associated with the kpb that is accompanied by a significant increase in os concentrations complementary platinum pt and iridium ir concentration data indicate that the length scale of diagenetic remobilization of platinum group elements from the kpb is less than 1 m and does not obscure the pre kpb decline in 187os 188os increases in bulk sediment ir concentrations and decreases in bulk carbonate content that coincide with the os isotope shift suggest that carbonate burial flux may have been lower during the initial decline in 187os 188os we speculate that diminished carbonate burial rate may have been the result of ocean acidification caused by deccan volcanism

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

volcanic lake systematics i physical constraints volcanic lakes have a wide range of characteristics and we make an attempt to delineate the limiting physical conditions for several lake classes the ratio between heat input and heat dissipation capacity of a lake constrains the temperature for perfectly mixed steady state volcanic lakes poorly mixed lakes are also conditioned by this ratio but their temperature structure is also strongly influenced by the hydrodynamics resulting from different mechanisms of heat transfer the steady state temperatures of volcanic lakes are largely determined by the magnitude of the volcanic heat influx relative to the surface area of the lake small lakes have only a small capacity for heat dissipation and their temperature rises quickly with only small heat inputs large lakes are buffered against variations in heat input both the heat dissipation and meteoric water input into a lake are functions of lake surface area and therefore each lake water temperature demands a certain precipitation rate for mass conservation independent of lake size the results of energy mass balance modeling shows that under common atmospheric conditions most steady state volcanic lakes are unlikely to maintain a temperature in excess of 45 50 c validation of the volcanic lake model was performed using published data from yugama lake japan and the keli mutu lakes indonesia also the model was applied to 24 natural systems to provide a baseline assessment of energy fluxes under the model assumptions so future work on those systems can identify nuances in individual systems that deviate from the simple model conditions we recommend the model for use in assessing temperature variations and volcanic lake stability in settings with known physical and atmospheric conditions application of the energy mass balance calculations of model lakes provides a genetic classification scheme largely based on physical process parameters

interaction between the chile ridge and chile trench geophysical and geothermal evidence geophysical and geothermal data are examined from the three southernmost sections of the chile ridge starting at 44 s and continuing south to the triple junction of the nazca antarctic and south america plates at 47 s these sections represent three progressively younger stages in a ridge trench collision event corresponding to 3 m y before the collision 1 m y before the collision and culminating in an ongoing collision at the triple junction magnetic and bathymetric data across the chile rise indicate that there is little change in the configuration of the spreading center as the ridge approaches and then collides with the trench in the collision zone a normal looking rift valley can be traced for 40 km before it disappears beneath the toe of the landward trench slope there is no evidence for the complex pattern of ridge jumps and spreading center rotations that occurred when the pacific farallon spreading center collided with north america in contrast the overriding plate is greatly affected by the ridge collision the landward trench slope steepens and narrows as the collision zone is approached at the southern end of the collision zone a ridge associated with the taitao fracture zone is colliding with the trench and may be in the process of being obducted onto the landward trench slope geothermal measurements were made along three transects of the margin corresponding to the time 3 m y before the collision during the collision and 6 m y after the collision the heat flow measurements in the collision zone document a large pulse of heat associated with the subduction of the ridge values as high as 345 mw m2 were recorded on the lower trench slope a prominent bottom simulating reflector bsr observed over a wide area of the landward trench slope north of the triple junction and more locally south of the triple junction is used to expand the grid of heat flow observations excellent agreement is found between measured heat flow and estimates of heat flow based on the depth to the bsr the heat flow measurements compare favorably with a theoretical model assuming conductive heat flow we estimate that the accretionary prism has been substantially removed in the collision zone and conclude that the landward trench slope is undergoing an episode of rapid tectonic erosion periodic ridge collisions in the past may account for the apparent truncation of the andean forearc region

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

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

1980 1990 ten years of geochemical investigation at phlegrean fields italy abstract a systematic geochemical investigation on the thermal manifestations of the volcanic area of phlegrean fields started in 1980 with the aim of obtaining useful information about the changes possibly occurring at the same time of vertical ground movements termed as bradyseismic which frequently interested this area the attention was initially given to the fumaroles and the boiling pools of solfatara and pisciarelli then subsequently extended to thermal springs dug wells and crater lakes analytical data pertaining to a period preceding the last crisis of 1982 1984 were then available as well as other data collected during the previous crisis of 1970 a comprehensive picture of the variations observed before during and after the acceleration of vertical movement has been drawn according to the results obtained the intrusion of a magmatic body as the trigger of the observed ground deformation is considered unrealistic the whole area appears now in a quiet stage and no further perturbation is expected without previous significant tectonic activity chemical precursors appear suitable for an early detection of changes occurring at depth to forecast possible consequences to be expected in the surface environment