the 2009 2010 eruption of gaua volcano vanuatu archipelago eruptive dynamics and unsuspected strong halogens source gaua a little known volcano in the northern part of vanuatu archipelago went through a long term eruptive activity between september 2009 and july 2010 the eruption started by a phreatic to phreatomagmatic activity which progressively shifted into a magmatic discharge the first eruptive phase involved the hydrothermal system in place the latter was likely influenced by seawater seepage leading to the formation of anhydrite magma involved hereafter this opening phase is of basaltic andesite and basaltic trachyandesite composition high k calc alkaline series typical of the northern part of the vanuatu archipelago the 2009 2010 activity discharged at least 184 kt of so2 and a significant amount of halogens 72 kt cl and 217 kt f such halogen releases indicate that gaua is a strong source of halogens into the atmosphere high and sustained amount of f discharges are known to induce health issues and should not be ignored on gaua island during this eruption the quiescent and voluminous lake letas was slightly affected by the eruption nevertheless the hydrothermal discharge point into the lake situated on the southeastern part of mt garet appeared to be relatively active at this particular location rock forming elements leached out from volcanic rock by acid fluids released by the new intrusion of magma were discharged along with anions into lake letas this release has triggered localized chemistry changes in the lake we speculate that this discharge has also disturbed the bottom water in a limited perimeter remobilizing reduced fe to the surface and subsequently triggering the change in the water color by fe oxidation

organic molecules formed in a primordial womb primordial organic molecules may have evolved in seafloor hydrothermal systems by mineral catalysis most organic compounds decompose in 300 c vent fluid however we show that smectite type clays can protect and promote development of diverse organic compounds that may be precursors to biomolecules smectite provides a safe haven for the synthesis of organic molecules essentially like a primordial womb our experiments simulated seafloor hydrothermal conditions 300 c 100 mpa and reacted common clays montmorillonite saponite illite with dilute methanol as a source of c montmorillonite reacts under these conditions to illite while the other clays do not change we observed increased organic synthesis over time with montmorillonite during mineralogical reaction approaching equilibrium smectite contracts and organic molecules are expelled organic compounds unstable in hot fluid where the smectite reacts may survive in cooler waters outside the vent

campanian ignimbrite volcanism climate and the final decline of the neanderthals the eruption of the campanian ignimbrite at ca 40 ka coincided with the final decline of neanderthals in europe environmental stress associated with the eruption of the campanian ignimbrite has been invoked as a potential driver for this extinction as well as broader upheaval in paleolithic societies to test the climatic importance of the campanian eruption we used a three dimensional sectional aerosol model to simulate the global aerosol cloud after release of 50 tg and 200 tg so2 we coupled aerosol properties to a comprehensive earth system model under last glacial conditions we find that peak cooling and acid deposition lasted one to two years and that the most intense cooling sidestepped hominin population centers in western europe we conclude that the environmental effects of the campanian ignimbrite eruption alone were insufficient to explain the ultimate demise of neanderthals in europe nonetheless significant volcanic cooling during the years immediately following the eruption could have impacted the viability of already precarious populations and influenced many aspects of daily life for neanderthals and anatomically modern humans

geodynamics of the ogcheon belt south korea abstract the ogcheon belt is a stack of synmetamorphic southeastward verging nappes resulting from the deformation of a volcanosedimentary sequence deposited in an early palaeozoic rift which was affected by polyphase tectonics its pre cretaceous structure results from three main orogenic events the ogcheon late silurian devonian indosinian late permian triassic and yenshanian middle jurassic early cretaceous tectonic phases the external autochthonous or para autochthonous units represent platform zones with shallow water deposits whereas rift facies characterize the internal domain the yeongweol sequence forming an outer shelf on the southeastern margin of the rift displays affinities with the jiangnan basin of south china it is in wrench fault contact with the easternmost duwibong sequence correlated with the north china north korea platform in the internal metamorphic units post cambrian early ordovician pelitic and turbiditic rift metasediments overlie a thin cambrian or cambrian ordovician early platform sequence two subdomains are distinguished the upper units chung ju and pibaryeong units representing the deep axial part of the basin contain distal flyshoids and large olistoliths derived from the northwestern narrow margin the lower units turung san poeun and iwharyeong are related to the wide margin located between the deep rift domain and the stable southeastern platform the latter transitional domain is characterized by thick submarine debris flows and volcanics of alkali or transitional tholeiitic affinity the volcanic activity and mass gravity flow sedimentation are closely related to the crustal thinning and subsequent rifting and tilting lithostratigraphic evidence allows the correlation of the unfossiliferous rift metasediments with the cambrian ordovician platform sequence in one single basin the post middle silurian pre mid carboniferous ogcheon ensialic orogeny resulted in the closure of the rift with relatively minor effects in the platform area it gave rise to an intracontinental fold thrust belt without ophiolites this tectonic event may have been contemporaneous with early palaeozoic tectonism in the quinling belt in central china and in the southeast china fold belt the definitive constitution of the sino korean craton took place before the mid carboniferous and molasse sedimentation was initiated on a single platform located on the western edge of the yakuno oceanic basin of southwest japan in late permian and early triassic times the closure of the oceanic area and the subsequent westward collision of the honshu block are marked in korea by the intracratonic indosinian tectonism since late triassic times predominantly transcurrent movements have occurred along nne ssw faults associated with syntectonic intermontane troughs and important granitization

the fidelity of melt inclusions as records of melt composition a series of experiments created melt inclusions in plagioclase and pyroxene crystals grown from a basaltic melt at 1 150 c 1 0 gpa to investigate diffusive fractionation during melt inclusion formation additionally p diffusion in a basaltic melt was measured at 1 0 gpa melt inclusions and melts within a few 100 microns of plagioclase melt interfaces were analyzed for comparison with melt compositions far from the crystals melt inclusions and melt compositions in the boundary layer close to the crystal melt interface were similar but both differ significantly in incompatible element concentrations from melt found greater than approximately 200 microns away from the crystals the compositional profiles of s cl p fe and al in the boundary layers were successfully reproduced by a two step model of rapid crystal growth followed by diffusive relaxation toward equilibrium after termination of crystal growth applying this model to investigate possible incompatible element enrichment in natural melt inclusions demonstrated that at growth rates high enough to create the conditions for melt inclusion formation 10 9 10 8 m s 1 the concentration of water in the boundary layer near the crystal was similar to that of the bulk melt because of its high diffusion coefficient but sulfur with a diffusivity similar to major elements and co2 was somewhat enriched in the boundary layer melt and phosphorus with its low diffusion coefficient similar to other high field strength elements and rare earth elements was significantly enriched thus the concentrations of sulfur and phosphorus in melt inclusions may over estimate their values in the bulk melt and other elements with similar diffusion coefficients may also be enriched in melt inclusions relative to the bulk melt

the 1995 1998 eruption of the soufriere hills volcano montserrat wi eruption of the soufriere hills volcano began on 18 july 1995 after three years of elevated seismic activity four months of increasingly vigorous phreatic activity culminated in mid november 1995 with the initiation of dome growth growth rates increased unevenly through early march 1996 with fluctuations on time scales from hours to months since march 1996 gravitational collapse of the unstable dome flank has affected an ever increasing area with pyroclastic flows surges and ashfalls major collapse of the eastern flank on 17 september 1996 resulted in a sub plinian explosive eruption later that day by february 1997 the dome had outgrown the confines of the crater and begun to spill into the surrounding valleys a large collapse on 25 june 1997 caused pyroclastic flows and surges on the northern flanks and resulted in the only deaths of the eruption in august september and october 1997 vulcanian explosions followed further collapses on the western and northern flanks the largest event of the eruption occurred on 26 december 1997 with failure of the southwestern flank of the volcano producing a debris avalanche and large dome collapse pyroclastic flows dome growth ceased in early march 1998 but residual volcanic activity has continued and consists of ash venting mild explosions and dome collapse pyroclastic flows

equilibrium and disequilibrium degassing of a phonolitic melt vesuvius ad 79 white pumice simulated by decompression experiments abstract equilibrium and disequilibrium degassing of a volatile phase from a magma of k phonolitic composition was investigated to assess its behavior upon ascent decompression experiments were conducted in ar pressurized externally heated pressure vessels at superliquidus temperature 1050 c in the pressure range 10 200 mpa using pure water as fluid phase all experiments were equilibrated at 200 mpa and then decompressed to lower pressures with rates varying from 0 0028 to 4 8 mpa s isobaric saturation experiments were performed at the same temperature and at 900 950 c to determine the equilibrium water solubility in the pressure range 30 250 mpa the glasses obtained from decompression experiments were analyzed for their dissolved water content vesicularity and bubble size distribution all decompressed samples presented a first event of bubble nucleation at the capsule melt interface homogeneous bubble nucleation in the melt only occurred in fast decompressed experiments 4 8 and 1 7 mpa s for p 100 mpa for these decompression rates high water over saturations were maintained until a rapid exsolution was triggered at p 150 mpa for slower rates 0 0028 0 024 0 17 mpa s the degassing of the melt took place by diffusive growth of the bubbles nucleating at the capsule melt interface this process sensibly reduced water over saturation in the melt preventing homogeneous nucleation to occur for decompression rates of 0 024 and 0 17 mpa s low water over saturations were attained in the melt gradually declining toward equilibrium concentrations at low pressures a near equilibrium degassing path was observed for a decompression rate of 0 0028 mpa s experimental data combined with natural pumice textures suggest that both homogeneous and heterogeneous bubble nucleations occurred in the phonolitic magma during the ad 79 vesuvius plinian event homogeneous bubble nucleation probably occurred at a depth of 3 km in response to a fast decompression of the magma during the ascent

the quantum event of oceanic crustal accretion impacts of diking at mid ocean ridges seafloor diking eruptive events represent the irreducible quantum events of upper oceanic crustal accretion they record events by which a large portion of the oceanic crust has formed through geological history since 1993 the u s navy s real time sound surveillance system has allowed location of ongoing acoustic signatures of dike emplacement and basalt eruptions at ridge crests in the northeast pacific these diking eruptive events trigger a sequence of related rapidly evolving physical chemical and biological processes magmatic volatiles released during these events may provide nutrients for communities of subseafloor microorganisms some of which thrive in high temperature anaerobic environments many of the organisms identified from these systems are archaea if microorganisms can thrive in the water saturated pores and cracks within deep volcanically active portions of our planet other hydrothermally active planets may harbor similar life forms

fluid inclusion and stable isotope studies of gold silver bearing hydrothermal vein deposits yeoju mining district republic of korea the yeoju gold silver mineralized district is located approximately 60 km southeast of seoul within the precambrian gyeonggi metamorphic belt of the korean peninsula mines of the district are located along gold bearing hydrothermal quartz veins that crosscut early proterozoic augen gneiss and mesozoic granites mineralization occurs in three stages i ii and carbonate which fill preexisting fault breccia zones fluid inclusion data suggest that quartz sulfide bearing stages i and ii evolved from initial high temperatures near 350 degrees c to later lower temperatures near 180 degrees c fluid inclusion data from the postore carbonate stage reflect much cooler 220 degrees 190 degrees c more dilute 4 5 equiv wt nacl hydrothermal fluids fluid inclusion and stable isotope evidence show that electrum jalpaite argentite galena and sphalerite were deposited at temperatures between 285 degrees and 185 degrees c from fluids with salinities between 14 0 and 2 6 equiv wt percent nacl fluid inclusion evidence of boiling suggests pressures of less than 100 bars during portions of stage i and ii mineralization corresponding to depths between 500 and 1 250 m assuming lithostatic and hydrostatic loads sulfur isotope compositions of stage i sulfide minerals decrease systematically with paragenetic time from calculated delta 34 s sub h 2 s values of 7 7 to 0 7 per mil a gradual increase in the sulfate sulfide ratio of the fluid likely due to h 2 s loss during boiling coupled with declining temperatures not only resulted in the systematic decrease of delta 34 s sub h 2 s values with time but may also have caused gold deposition by the breakdown of au hs super 2 the h and o isotope values of hydrothermal fluids in the yeoju district are consistent with meteoric water dominance approaching unexchanged meteoric water values comparison of these values with those of other korean au ag deposits reveals a relationship between depth and water to rock ratios jurassic au systems are mesothermal and have ratios of 0 001 to 0 01 whereas cretaceous au ag systems are epithermal with ratios of 0 02 to 0 5

trace elements in magnetite from massive iron oxide apatite deposits indicate a combined formation by igneous and magmatic hydrothermal processes iron oxide apatite ioa deposits are an important source of iron and other elements e g ree p u ag and co vital to modern society however their formation including the namesake kiruna type ioa deposit sweden remains controversial working hypotheses include a purely magmatic origin involving separation of an fe p rich volatile rich oxide melt from a si rich silicate melt and precipitation of magnetite from an aqueous ore fluid which is either of magmatic hydrothermal or non magmatic surface or metamorphic origin in this study we focus on the geochemistry of magnetite from the cretaceous kiruna type los colorados ioa deposit 350 mt fe located in the northern chilean iron belt los colorados has experienced minimal hydrothermal alteration that commonly obscures primary features in ioa deposits laser ablation inductively coupled plasma mass spectroscopy la icp ms transects and electron probe micro analyzer epma wavelength dispersive x ray wdx spectrometry mapping demonstrate distinct chemical zoning in magnetite grains wherein cores are enriched in ti al mn and mg the concentrations of these trace elements in magnetite cores are consistent with igneous magnetite crystallized from a silicate melt whereas magnetite rims show a pronounced depletion in these elements consistent with magnetite grown from an fe rich magmatic hydrothermal aqueous fluid further magnetite grains contain polycrystalline inclusions that re homogenize at magmatic temperatures 850 c smaller inclusions 500 ppm concentrations

spectroscopic evidence for a lava fountain driven by previously accumulated magmatic gas the eruption of mount etna in 2000 was notable for an exceptional series of 64 periodic lava fountains propelling lava fragments to heights of up to 900 metres it has been difficult to determine which of two suggested sources of power gas release from the magma itself during its rapid ascent or a build up of pressure from gas accumulated at depth is the driving force for these dramatic jets but one of the etna fountains provided volcanologists with the opportunity to use remote sensing not that remote see picture on the following page to determine the infrared spectra of the gas phase this revealed the chemical composition of the gas that powered this fountain as consistent with an origin in an accumulated gas layer lava fountains are spectacular continuous gas jets propelling lava fragments to heights of several hundred metres which occasionally occur during eruptions of low viscosity magmas1 2 3 4 5 whether they are generated by the effervescent disruption of fast rising bubbly melt2 3 4 5 or by the separate ascent of a bubble foam layer accumulated at depth6 7 still remains a matter of debate8 no field measurement has yet allowed firm discrimination between these two models a key insight into the origin of lava fountains may be gained by measuring the chemical composition of the driving gas phase this composition should differ markedly depending on whether the magma degassing occurs before or during eruption9 10 here we report the analysis of magmatic gas during a powerful 250 600 m high lava fountain measured with fourier transform infrared spectroscopy11 12 13 14 on mount etna sicily the abundances of volcanic gas species determined from absorption spectra of lava radiation reveal a fountain gas having higher co2 s and s cl ratios than other etnean emissions14 15 16 17 18 and which cannot derive from syn eruptive bulk degassing of etna basalt19 20 instead its composition suggests violent emptying of a gas bubble layer previously accumulated at about 1 5 km depth below the erupting crater

behavior of halogens during the degassing of felsic magmas 1 residual concentrations of halogens f cl br i and h2o in glass matrix glass and melt inclusions have been determined in a series of volcanic clasts pumice and lava dome fragments of plinian vulcanian and lava dome forming eruptions felsic magmas from calc alkaline trachytic and phonolitic systems have been investigated montagne pelee and soufriere hills of montserrat lesser antilles santa maria santiaguito guatemala fogo azores and vesuvius italy the behavior of halogens during shallow h2o degassing primarily depends on their incompatible character and their partitioning between melt and exsolved h2o vapor however variations in pre eruptive conditions degassing kinetics and syn eruptive melt crystallization induce large variations in the efficiency of halogen extraction in all systems studied cl br and i are not fractionated from each other by differentiation or by degassing processes cl br i ratios in melt remain almost constant from the magma reservoir to the surface the ratios measured in erupted clasts are thus characteristic of pre eruptive magma compositions and may be used to trace deep magmatic processes f behaves as an incompatible element and unlike the other halogens is never significantly extracted by degassing cl br and i are efficiently extracted from melts at high pressure by h2o rich fluids exsolved from magmas or during slow effusive magma degassing but not during rapid explosive degassing because h2o and halogen mobility depends on their speciation which strongly varies with pressure in both silicate melts and exsolved fluids we suggest that the rapid pressure decrease during highly explosive eruptions prevents complete equilibrium between the diverse species of the volatiles and consequently limits their degassing conversely degassing in effusive eruptions is an equilibrium process and leads to significant halogen output in volcanic plumes

the distribution of halogens f cl br in granitoid rocks abstract the halogen contents of granitoid rocks and their distribution between apatite biotite muscovite and amphibole from two different localities german part of the bohemian massif and central aegean greece are investigated in detail whole rock f and cl contents and f cl mass ratios vary systematically with the magmatic halogen bearing mineral assemblage in which biotite and apatite are present in all rock samples muscovite bearing granites are f rich mostly 1100 2000 g g but up to 3100 g g and are relatively cl poor 50 130 g g in contrast amphibole bearing rocks reach high cl contents 50 900 g g and are relatively f poor 500 1400 g g only biotite and apatite bearing granites show intermediate f 750 1100 g g and cl 120 350 g g contents bromine contents of all rock samples are below the detection limit of about 0 6 g g in general f and cl are preferentially incorporated in apatite over biotite and biotite usually contains higher amounts of f and cl than muscovite similarly biotite prefers f over amphibole but the distribution of cl between biotite and amphibole varies between different rock samples bromine contents in muscovite are below the detection limit of 0 4 g g but can reach up to 0 8 g g in biotite and up to 2 5 g g in apatite and amphibole near solidus effects such as fluid exsolution diffusive re equilibration and hydrothermal overprint may change the initial halogen distribution in the rock importantly significant amounts of the whole rock s f up to 60 and cl up to 90 may be accommodated in post magmatic alteration phases fluorite and na k ca bearing sheet silicates and fluid inclusions therefore great care has to be taken when interpreting halogen contents of whole rocks and the influence of post magmatic halogen carriers needs to be taken into account

petrologic constraints on the decompression history of magma prior to vulcanian explosions at the soufriere hills volcano montserrat abstract a series of 88 vulcanian explosions occurred at the soufriere hills volcano montserrat between august and october 1997 conduit conditions conducive to creating these and other vulcanian explosions were explored via analysis of eruptive products and one dimensional numerical modeling of magma ascent through a cylindrical conduit the number densities and textures of plagioclase microlites were documented for twenty three samples from the events the natural samples all show very high number densities of microlites and 50 by number of microlites have areas 2 pre explosion conduit conditions and decompression history have been inferred from these data by comparison with experimental decompressions of similar groundmass compositions our comparisons suggest quench pressures 13 75 mpa each during ascent from chamber to surface values are consistent with field studies of the same events and statistical analysis of explosion time series data the microlite volume number density trend with depth reveals an apparent transition from growth dominated crystallization to nucleation dominated crystallization at pressures of 7 mpa and lower a concurrent sharp increase in bulk density marks the onset of significant open system degassing apparently due to a large increase in system permeability above 70 vesicularity this open system degassing results in a dense plug which eventually seals the conduit and forms conditions favorable to vulcanian explosions the corresponding inferred depth of overpressure at 250 700 m near the base of the dense plug is consistent with depth to center of pressure estimated from deformation measurements here we also illustrate that one dimensional models representing ascent of a degassing crystal rich magma are broadly consistent with conduit profiles constructed via our petrologic analysis the comparison between models and petrologic data suggests that the dense conduit plug forms as a result of high overpressure and open system degassing through conduit walls

magma production and growth of the lava dome of the soufriere hills volcano montserrat west indies november 1995 to december 1997 from november 1995 to december 1997 a total volume of 246 106 dre m of andesite magma erupted partitioned into 93 106 m of the dome 125 106 m of pyroclastic flow deposits and 28 106 m of explosive ejecta in the first 11 weeks magma discharge rate was low 0 5 m s from february 1996 to may 1997 discharge rates have averaged 2 1 m s but have fluctuated significantly and have increased with time three pulses lasting a few months can be recognised with discharge rates reaching 3 to 8 m s short term pulsations in growth lasting a few days reach discharge rates of over 10 m s and there are periods of days to a few weeks when dome growth is 0 5 m s discharge rate increased from may 1997 with an average rate of 7 5 m s to december 1997 the observations indicate an open magmatic system

evidence for a new shallow magma intrusion at la soufriere of guadeloupe lesser antilles insights from long term geochemical monitoring of halogen rich hydrothermal fluids more than three decades of geochemical monitoring of hot springs and fumaroles of la soufriere of guadeloupe allows the construction of a working model of the shallow hydrothermal system this system is delimited by the nested caldera structures inherited from the repeated flank collapse events and the present dome built during the last magmatic eruption 1530 ad and which has been highly fractured by the subsequent phreatic or phreatomagmatic eruptions because it is confined into the low volume highly compartmented and partially sealed upper edifice structure the hydrothermal system is highly reactive to perturbations in the volcanic activity input of deep magmatic fluids the edifice structure sealing and fracturing and meteorology wet tropical regime the current unrest which began with a mild reactivation of fumarolic activity in 1990 increased markedly in 1992 with seismic swarms and an increase of degassing from the summit of the dome in 1997 seismic activity increased further and was accompanied by a sudden high flux hcl rich gas from summit fumaroles we focus on the interpretation of the time series of the chemistry and temperature of fumarolic gases and hot springs as well as the relative behaviours of halogens f cl br and i this extensive geochemical time series shows that the deep magmatic fluids have undergone large changes in composition due to condensation and chemical interaction with shallow groundwater scrubbing it is possible to trace back these processes and the potential contribution of a deep magmatic source using a limited set of geochemical time series t co2 and total s content in fumaroles t and cl in hot springs and the relative fractionations between f cl br and i in both fluids coupling 35 years of geochemical data with meteorological rainfall data and models of ion transport in the hydrothermal aquifers has allowed us to identify a series of magmatic gas pulses into the hydrothermal system since the 1976 1977 crisis the contrasting behaviours of s and cl bearing species in fumarolic gas and in thermal springs suggests that the current activity is the result of a new magma intrusion which was progressively emplaced at shallow depth since 1992 although it might still be evolving the characteristics of this new intrusion indicate that it hasalready reached a magnitude similar to the intrusion that was emplaced during the 1976 1977 eruptive crisis the assessment of potential hazards associated with evolution of the current unrest must consider the implications of recurrent intrusion and further pressurization of the hydrothermal system on the likelihood of renewed phreatic explosive activity moreover the role of hydrothermal pressurization on the basal friction along low strength layers within the upper part of the edifice must be evaluated with regards to partial flank collapse at this stage enhanced monitoring research and data analysis is required to quantify the uncertainties related to future scenarios of renewed eruptive activity and magmatic evolution

an experimental study of bromine behaviour in water saturated silicic melts to assess the effect of the melt composition on bromine concentrations in magmas we have investigated bromide solubility for water saturated iron free silicic melts with variable na k al and si al molar ratios albite haplogranite rhyolite and pantellerite the experiments were performed in rapid quench cold seal autoclaves over a range of pressure 1 1 5 and 2 kbar and temperature 900 1000 and 1080 c with run durations from 5 to 7 days a series of natural volcanic glasses and melt inclusions hosted in magmatic minerals were analysed together with the synthetic glasses by pixe proton induced x ray emission the br concentrations range from 5360 to 7850 ppm for albite from 2800 to 3900 ppm for haplogranite from 4300 to 5900 ppm for rhyolite and from 9745 to 11 250 ppm for pantellerite br concentrations are negatively correlated with pressure in h2o saturated silicic melts and vary with na k al molar ratio with a minimum value at the ratio close to unity br behaves similarly to chlorine for all of these melt compositions the bromide solubility is similar in albitic and rhyolitic melts which implies that df m is nearly the same for both compositions and is applicable for natural rhyolites as suggested in our previous study bureau et al 2000 this means that the volcanic br contribution to the atmosphere may be significant in natural obsidian samples and mi hosted in quartz olivine and leucite the br concentration varies from 3 to 28 ppm with the highest concentrations in pantelleritic melts we attribute the low br concentrations of natural melts to a low initial abundance of this halogen in the earth mantle however because br behaves as an incompatible element before water exsolution our results imply that magmas could contain much more dissolved br before eruption and water degassing than the few ppm usually measured in volcanic rocks br behaviour during magma crystallisation is controlled by its partitioning into the h2o rich fluid phase when this occurs in addition its potential high solubility in silicate melts makes it a very sensitive chemical tracer of magma contamination by seawater and br rich material this infers that the investigation of br behaviour in subduction zone samples may help for a better understanding of volatiles cycling between the earth reservoirs

chlorine variations in the magma of soufriere hills volcano montserrat insights from cl in hornblende and melt inclusions the soufriere hills volcano in montserrat erupts a cl rich porphyritic andesite hcl degassing accompanies eruption and is dependent on the growth rate of the lava dome the magma contains hornblende phenocrysts that show repetitive zoning in most elements including cl on the basis of the zoning data cl oh ratios in the melt calculated from partitioning data increase rimward through each zone indicating that the phenocrysts formed under conditions of varying cl oh m an empirical relationship between a site occupancy in the hornblende and temperature implies that crystallisation of each zone is also accompanied by increasing temperature each zone ends at a resorption horizon and crystallisation recommences at lower temperature and cl oh m melt inclusion h2o and cl contents for the 8th january 2007 explosive eruption can be explained by closed system degassing with dclfl m between 5 and 30 or by open system degassing accompanied by a small amount of crystallisation however neither simple closed system degassing nor convective circulation of magma can explain the positive correlation of cl oh m with temperature we suggest that the zoning can be caused by accumulation of co2 rich vapour in the andesite probably as a result of mafic magma injection into the chamber decreasing h2o fugacity and or increasing clm result in increasing cl oh m while heat transferred with the volatiles causes the rise in temperature intermittently the accumulated fluid is lost to the surface possibly as a result of renewed eruptive activity this model requires the co2 rich fluid to be decoupled from the magma consistent with previous observations of continuous co2 emissions at the surface

experimental investigation of h2o and cl solubilities in f enriched silicate liquids implications for volatile saturation of topaz rhyolite magmas to interpret the degassing of f bearing felsic magmas the solubilities of h2o nacl and kcl in topaz rhyolite liquids have been investigated experimentally at 2000 500 and 1 bar and 700 to 975 c chloride solubility in these liquids increases with decreasing h2o activity increasing pressure increasing f content of the liquid from 0 2 to 1 2 wt f and increasing the molar ratio of al na ca mg si small quantities of cl exert a strong influence on the exsolution of magmatic volatile phases mvps from f bearing topaz rhyolite melts at shallow crustal pressures water and chloride bearing volatile phases such as vapor brine or fluid exsolve from f enriched silicate liquids containing as little as 1 wt h2o and 0 2 to 0 6 wt cl at 2000 bar compared with 5 to 6 wt h2o required for volatile phase exsolution in chloride free liquids the maximum solubility of cl in h2o poor silicate liquids at 500 and 2000 bar is not related to the maximum solubility of h2o in chloride poor liquids by simple linear and negative relationships there are strong positive deviations from ideality in the activities of each volatile in both the silicate liquid and the mvp s plots of h2o versus cl in rhyolite liquids for experiments conducted at 500 bar and 910 930 c show a distinct 90 break in slope pattern that is indicative of coexisting vapor and brine under closed system conditions the presence of two mvps buffers the h2o and cl concentrations of the silicate liquids comparison of these experimentally determined volatile solubilities with the pre eruptive h2o and cl concentrations of five north american topaz and tin rhyolite melts determined from melt inclusion compositions provides evidence for the exsolution of mvps from felsic magmas one of these the cerro el lobo magma appears to have exsolved alkali chloride bearing vapor plus brine or a single supercritical fluid phase prior to entrapment of the melt inclusions and prior to eruption

u series disequilibrium in arc magmas induced by water magma interaction abstract volcanic rocks from subduction zones are widely believed to originate by partial melting of mantle lherzolite modified by the addition of a fluid or melt extracted from the down going slab u series disequilibrium in such magmas is commonly attributed to this particular melting process a detailed study of u series isotopes in the 650 y b p eruptive sequence of mt pelee martinique shows that plinian products are in radioactive equilibrium whereas dome forming products of the same eruption are characterized by 238u 230th disequilibrium the same features apply to other plinian and dome forming products of this volcano and systematically correspond to different eruptive styles we attribute these characteristics to variable superficial interaction of magmas with the hydrothermal system during the final stages of eruption rather than to deep magma genesis processes this conclusion might be generally applicable to arc magmas

the effect of water on the viscosity of a haplogranitic melt under p t x conditions relevant to silicic volcanism the viscosities of hydrous haplogranitic melts synthesized by hydrothermal fusion at 2 kbar pressure and 800 to 1040 c have been measured at temperatures just above the glass transition and at a pressure of 1 bar using micropenetration techniques the micropenetration viscometry has been performed in the viscosity range of 109 pa s to 1012 pa s the samples ranged in water content from 0 4 to 3 5 wt for samples with up to 2 5 wt h2o the water contents have been determined using infrared spectroscopy obtained before and after each viscometry experiment to be constant over the duration of the measurements above this water content a measurable loss of water occurs during the viscometry the viscosity data illustrate an extremely nonlinear decrease in viscosity with added water the viscosity drops drastically with the addition of 0 5 wt of water and then shallows out at water contents of 2 wt an additional viscosity datum point obtained from the analysis of fluid inclusions in a water saturated hpg8 confirms a near invariance of the viscosity with the addition of water between 2 and 6 wt these measurements may be compared directly with the data of hess et al 1995 in press for the effects of excess alkali and alkaline earth oxides on the viscosity of hpg8 also obtained at 1 bar the viscosity of the melts compared on an equivalent molar basis increases in the order h2o li2o na2o k2o rb2o cs2o bao sro cao mgo beo the extraordinary decrease in melt viscosity with added water is poorly reproduced by the calculation scheme of shaw 1972 for the range of water contents investigated here the speciation of water in the quenched glasses can be used to quantify the dependence of the viscosity on hydroxyl content considering only the hydroxyl groups as active fluidizers in the hydrous melts the nonlinearity of the viscosity decrease and the difference with the effects of the alkali oxides becomes larger consequences for degassing calcalkaline rhyolite are discussed

experimental and model constraints on degassing of magma during ascent and eruption surface volcanic gases may reflect volatile budgets of magma and forecast impending eruptions and their release to the atmosphere may affect climate the dynamics of magma degassing is complicated however by differences in the solubility partitioning and diffusion of the various volatiles all of which can vary with pressure temperature and melt composition to constrain possible gas outputs we carried out experiments to determine how cl partitions between water bubbles and silicate melt and decompression experiments to examine how cl behaves during closed and open system degassing we incorporate our findings and those from the literature for co2 and s into a steady isothermal and homogeneous flow model to estimate fluxes of gases at the vent from ascending water rich magma assuming different scenarios for the onset and development of permeability in bubbly magma we find that for given permeability scenarios total gas fluxes vary with magma flux but ratios of gas species do not change the s cl and so2 co2 ratios do change however depending on whether the magma is oxidized or reduced after magma fragments into a plinian eruption column gases continue to escape from cooling pumice in the plume but here the rate of gas release is controlled by diffusion which varies with temperature degassing of pumice and ash was modeled by linking a steady state plume model which gives the vertical variation of mean temperature and velocity of particles inside the plume to a conductive cooling model of pumices which controls diffusion of cl co2 and s in pumice we find that gas loss increases with column height mass flux and initial temperature because in both cases pumices cool over a longer time period allowing more gas to diffuse out of the matrix glass the amount of gas released also depends on the size distribution of particles in the erupting mixture with less being released for a finely skewed distribution

methane rich fluids in the oceanic crust analyses of fluid inclusions in plutonic rocks recovered from the slow spreading southwest indian ridge swir record ch4 concentrations of 15 40 times those of hydrothermal vent fluids and of basalt hosted volcanic gases and provide the first direct sampling of co2 ch4 h2o h2 c bearing fluids in the oceanic crust compositional thermal and spatial analyses of these fluids are used to model the evolution of volatiles during the crystallization and cooling of mid ocean ridge magma chambers and to assess the potential importance of carbon bearing fluids in geochemical processes in the lower crustal component of hydrothermal systems results from these analyses show that the earliest fluids to be exsolved from the melts are dominated by co2 rich vapors which with progressive fractionation evolved to more h2o rich compositions these later fluids were most likely exsolved under immiscible conditions and involved the development of co2 h2o rich vapors and co2 h2o nacl brines that were trapped during mineral growth as well as during later high temperature fracturing events co2 ch4 h2o rich fluids in olivine and plagioclase minerals that contain up to 30 50 mol co2 and 33 mol ch4 may reflect respeciation of magmatic co2 during cooling and attendant graphite precipitation phase equilibria suggest that these fluids reequilibrated at 500 600 c and at fo2 s 3 log units below to close to qfm conditions alternatively the inclusions may record respeciation of magmatic fluids attendant with the inward diffusion of h2 into the inclusions and reduction of entrapped co2 during degassing and cooling of the gabbros throughout the subsolidus regime subsequent seawater reaction at minimum temperatures of 400 c with mafic rich layers within the gabbroic rocks or with ultramafic material that underlies the plutonic sequence resulted in the formation of ch4 h2o fluids that contain up to 40 mol ch4 molecular h2 and graphite daughter minerals these data provide strong evidence that the ch4 h2o rich fluids produced during serpentinization reactions were trapped under equilibrium conditions in the presence of graphite at very near to qfm conditions the ubiquitous occurrence of ch4 rich fluids in oceanic crustal layer 3 rocks from the swir indicates that these fluids may be a significant and previously unrecognized source for these volatile species in some hydrothermal systems venting on the seafloor and that the deep seated fluids most likely play an important role in the transfer of carbon from the lithosphere to the hydrosphere

vapor phase cristobalite as a durable indicator of magmatic pore structure and halogen degassing an example from white island volcano new zealand vesicles in volcanic rocks are physical records of magmatic degassing however the interpretation of their textures is complicated by resorption coalescence and collapse we discuss the textural significance of vesicle hosted vapor phase cristobalite high t low p sio2 polymorph and its utility as a complement to textural assessments of magmatic degassing using a representative dacite bomb erupted from white island volcano new zealand in 1999 imaging in 2d sem and 3d ct shows the bomb to have 56 bulk porosity almost all of which is connected 99 and devoid of sio2 phases the remaining 1 of porosity is in isolated sub spherical vesicles that have corroded walls and contain small 30 m across prismatic vapor phase cristobalite crystals 98 4 0 4 wt sio2 with diagnostic laser raman spectra halogen degassing models show vapor phase cristobalite to be indicative of closed system chlorine and fluorine partitioning into h2o rich fluid in isolated pores at white island this occurred during shallow 100s of meters ascent and extensive 50 groundmass crystallization associated with slow cooling in a volcanic plug pristine textures in this white island bomb demonstrate the link between pore isolation and vapor phase cristobalite deposition we suggest that because these crystals have higher preservation potential than the bubbles in which they form they can serve as durable qualitative textural indicators of halogen degassing and pre quench bubble morphologies in slowly cooled volcanic rocks e g lava flows and domes even where emplacement mechanisms have overprinted original bubble textures

enriched h2 ch4 and 3he concentrations in hydrothermal plumes associated with the 1996 gorda ridge eruptive event abstract the rapid field response in march and april 1996 to diking eruptive events on the northern gorda ridge allowed the first detailed co measurement of 3 he h 2 and ch 4 in plumes associated with a submarine eruption and examination of the chemical transformation of these volatile species during aging of the plumes the diking eruptive event generated extensive event plumes with a low 3 he heat ratio of 0 4 10 12 cm 3 stp gm 1 c 1 while chronic plumes had 3 he heat ratios of 2 1 6 2 10 12 cm 3 stp gm 1 c 1 hydrogen concentrations in the initial event plume ep96a reached a maximum value of 47 nm 235 times that of ocean background concentration 0 2 nm in contrast roughly one month later h 2 concentrations although still elevated had drastically dropped to 40 times background values methane concentrations in both event and chronic plume fluids were also elevated and similar to stable hydrothermal systems in unsedimented ridge environments reaching a maximum value of 7 nm the intense rapid interaction at very high temperatures of hydrothermal fluids with the host rock during dike intrusion or with seawater during extrusion of the basalt likely generated high localized concentrations of h 2 the data indicate however that maximum rates of h 2 production during event plume formation could have lasted a few days at most

gold rich mesothermal vein deposits of the republic of korea geochemical studies of the jungwon gold area gold vein deposits of the jungwon area are among the first documented examples of mesothermal gold deposition in the republic of korea the deposits are composed of massive quartz veins up to 1 0 m wide which occupy fault planes in precambrian gneiss k ar dating of alteration sericite 146 156 m y indicates a late jurassic age for ore mineralization similar to that of a nearby granodiorite the veins are gold rich and sulfide poor with ore shoots up to 200 m in horizontal and vertical extent ore grades average 10 2 g ton gold with an average gold silver production ratio of 6 1 fluid inclusion data indicate that gold was deposited between 375 degrees and 290 degrees c from relatively dilute fluids asymp 4 equiv wt nacl containing asymp 15 to 25 mole percent co 2 evidence of fluid unmixing co 2 effervescence indicates pressures of 1 200 to 1 500 bars gold deposition was likely a result of decrease of sulfur activity caused by sulfide deposition and or h 2 s loss accompanying fluid unmixing measured and calculated compositions of ore fluids in the jungwon area delta 18 o 5 0 to 7 7ppm delta d 78 to 113ppm indicate that gold was deposited from a highly evolved meteoric water that underwent extreme 18 o enrichment and moderate d enrichment mineralogy and ore fluid chemistry of the jungwon area deposits are similar to those of mesothermal gold vein deposits of the canadian cordillera canadian archcan greenstone belts and the mother lode district of california the diversity of host rocks in these deposits indicates that host rock petrology is not a controlling factor in the formation of mesothermal gold vein deposits these observations together with our geochemical studies of korean deposits may validate a more general application of meteoric water models for the formation of mesothermal gold vein deposits

the volatile component of some pumice forming alkaline magmas from the azores and canary islands the abundances of pre eruptive magmatic volatile species in the system h o s may be determined by application of thermodynamic methods to phenocryst assemblages commonly found in volcanic rocks as demonstrated by rutherford and heming 1978 these methods are applied to alkaline pumice deposits of airfall and ignimbrite type from tenerife canary islands sao miguel and faial azores it is argued that reliable temperature and fo2 buffering mechanisms found in rhyolitic magmas appear not to operate in more alkaline liquids fh2o is estimated using biotite the high values found are shown to be compatible with the violently explosive nature of the magmas concerned fs2 is estimated from pyrrhotite composition fh2 fh2s fso2 fso3 are calculated from gas equilibria water fugacity may be very roughly estimated for non biotite bearing samples from data on the sulphur species abundances of these species are similar in alkaline and calc alkaline salic magmas volcanological implications relating to the release of volatiles during explosive eruptions are considered

andesitic magma degassing investigated through h2o vapour melt partitioning of halogens at soufriere hills volcano montserrat lesser antilles magma degassing at soufriere hills volcano shv is characterised by an almost permanent so2 flux and a hcl production rate which mainly depends on dome growth rate degassing processes have been studied through textural h2o and halogen analyses of clasts collected between 1995 and 2006 on the dome and in pyroclastic flows and vulcanian eruption deposits cl br and i are strongly depleted in melts during h2o degassing with no significant cl br i fractionation whereas f is almost unaffected all magmas erupted at shv have followed a multi step degassing path from the magma chamber up to a shallow depth 1 km p 20 mpa from that depth however effusive and explosive paths are distinct vulcanian eruptions are the result of closed system degassing csd while effusive dome growth is the result of csd up to a very shallow depth 200 m p 5 2 mpa followed by open system degassing osd csd is modelled using the h2o solubility law the perfect gas law and partition coefficients of halogens between a rhyolitic melt and h2o vapour dv li gas loss characteristic of osd is modelled using a rayleigh law degassing induced crystallisation is introduced through the ratio of crystallisation and degassing rates which ranges from 150 500 dv lcl for osd ranges between 50 300 increasing with melt cl content for csd the lower effective dv lcl 20 is attributed to kinetic effects dome forming activity has a greater impact on atmospheric chemistry than vulcanian eruptions because osd is much more efficient at extracting halogens the model shows that hcl flux is a good proxy for the dome forming eruption rate comparison between model and measured gas compositions suggests a high hbr bro conversion rate bro total br 1 3 in the shv gas plume the degassing behaviour of cl br and i implies similar cl br 160 and br i 90 in initial melts volcanic clasts and high temperature gases the low cl br at shv compared to other island arcs 250 300 is attributed to a shallow pre eruptive br enrichment the almost permanent dome extrusion at shv since 1995 has likely had a significant regional atmospheric impact because of the very efficient effusive degassing and the high conversion rate of halogens into reactive species within the gas plume

h2o and halogen f cl br behaviour during shallow magma degassing processes abstract degassing paths of silicic h2o rich magmas during explosive plinian and dome forming eruptions may be represented in simple evolution diagrams relating the residual volatile content of the melt to the volume ratio of gas over melt vg vl these parameters are measurable in erupted magma fragments they are used for interpreting the h2o and halogen contents determined in a series of variously degassed volcanic clasts from the 650 y b p eruption at mt pelee martinique fwi which is characterized by the succession of a dome extrusion and a plinian activity h2o degassing of plinian pumice clasts are modeled by an equilibrium closed system evolution which allows to calculate the partition coefficients of halogen between the aqueous fluid and the rhyolitic melt d v l i 1 for f 10 1 5 for cl and 3 7 1 for br at around 900 c the strong increase of the dv li values of cl and br during dome extrusion is explained by an open system degassing model with a simultaneous crystallization of the melt some significant br enrichments relative to cl in dome fragments are attributed to interactions with an hydrothermal fluid close to seawater in composition the models allow calculation of cl and br contents of aqueous fluids generated by the different degassing paths cl contents are 0 5 mol l for closed system evolution and vary between 0 2 and 1 mol l during open system evolutions these fluids are able to extract significant amounts of chloride complexed metals and silica from the magma during dome forming eruptions they also may generate mineralization of the wall rocks or the rising dome itself e g silica precipitation which may seal the volcanic system and be responsible for the dome explosivity and the transition from dome forming to plinian eruptive style the cl br ratio of initial melts of p1 eruption 250 is much lower than the basaltic and exospheric ratios 400 suggesting that strong cl br fractionation may occur during the production or the differentiation of subduction related magmas

the source of uranium within hydrothermal uranium deposits of the motianling mining district guangxi south china abstract uranium deposits are diverse as a result of their formation in a wide variety of geological environments however the source of the uranium within these deposits is difficult to identify and as a result it is usually poorly understood this study focuses on the hydrothermal sanqiliu and sanqisi uranium deposits both of which formed within ne sw striking shear zones that cross cut the sanfang batholith and low grade metasedimentary rocks of the motianling district southern china the deposits contain vein hosted pitchblende quartz pyrite chlorite mica orebodies fluid inclusions within quartz in the orebodies in the district homogenize at temperatures between 205 c and 222 c indicating the deposit formed as a result of low to intermediate temperature hydrothermal activity pitchblende associated hydrothermal pyrite within the sanqiliu and sanqisi deposits has 34s values from 24 7 to 19 7 and from 6 0 to 13 6 respectively quartz separates from the sanqiliu deposit yield 18o values of 1 4 11 5 mean of 5 8 for syn ore hydrothermal fluids these stable isotope data indicate that the fluids that formed these deposits were derived from the sanfang granites sediments of the sibao group and meteoric sources in addition uraninite from the host sanfang granite yields u pb ages of ca 732 773 ma combining these data with the geology of the ore deposits in this region suggests that these deposits were generated from deeply circulating meteoric water and the uraninite within the highly fractionated sanfang granite is the source of the uranium within the sanqiliu and sanqisi uranium deposits

microanalysis of cl br and i in apatite scapolite and silicate glass by la icp ms constraining the abundance and distribution of halogens in geological materials has the potential to provide novel insights into a broad range of earth system processes e g metasomatism melting volatile cycling and ore formation in this contribution we develop analytical protocols for the in situ measurement of cl br and i in widely distributed standard reference materials apatite scapolite silicate glass using readily available laser ablation icp ms instrumentation ablations were performed at a range of square spot sizes 30 80 m using a high repetition rate 25 hz and extended analyte dwell times up to 250 ms to improve sensitivity and signal stability a comparison of la icp ms results with published halogen data was used to calculate the following theoretical limits of quantification cl 360 g g br 8 g g i 0 75 g g a detailed assessment of raw signal intensities for different matrices with known halogen contents combined with high resolution mass scans provides new constraints on the origin of apparent halogen signals on mass cl signal excesses are likely ooh and or oo br is influenced by peak shoulder overlap from arar a diargon cation ar and a matrix based interference tb for samples with br tb 0 6 i signals are similar for all but the highest i materials analysed here suggesting the presence of ubiquitous gas based interferences the observation that false positive halogen signals only occur during sample ablation suggests that they are either matrix derived or related to the process of sample introduction during ablation matrix loading may reduce plasma energy resulting in a greater proportion of polyatomic interferences in the system for cl we provide a new time dependent excess apparent cl spline correction defined by analysis of halogen free olivine via a modified version of the iolite data reduction scheme x trace elements is the correction improves the limit of linearity to 100 g g for cl in glasses down to a 38 m spot size we test our methodology on apatite from permian alkaline lamprophyres in the pyrenees spain and quartz hosted melt inclusions from rhyolitic deposits at the taupo volcanic zone new zealand obtaining results comparable to electron microprobe and sims data we provide recommendations for analytical best practice and highlight the need for well characterised matrix matched srms spanning a broad range of concentrations to allow for the identification and removal of non analyte related contributions to measured signals

volcanic degassing of bromine and iodine experimental fluid melt partitioning data and applications to stratospheric chemistry abstract in order to understand the degassing behavior of heavy halogens in volcanic processes we experimentally studied the distribution of cl br and i between albite melt and hydrous fluids containing 0 01 2 wt of nacl nabr or nai respectively all experiments were carried out at 2 kbar and 900 c in rapid quench cold seal autoclaves with a run duration of 7 days the major element compositions and cl contents of the glassy run products were measured by electron microprobe bromine and iodine were measured by proton induced x ray emission fluid compositions were obtained by mass balance all halogens investigated were found to partition strongly into the fluid phase over the range of concentrations studied the halogen contents in the melt are proportional to the concentrations in the fluid the fluid melt partition coefficients df m are 8 1 0 2 for cl 17 5 0 6 for br and 104 7 for i the logarithm of df m is linearly correlated with the ionic radius of the halogenide ion on the basis of our experimental data we estimate the amount of bromine injected into the stratosphere by major volcanic explosions for the 1991 mount pinatubo eruption we obtain br yields of 11 25 kt as minimum estimates these numbers are comparable to the total annual influx of bromine into the stratosphere from all other natural and anthropogenic sources about 100 kt year since bromine is much more efficient in destroying stratospheric ozone than chlorine it could at least be partially responsible for the massive ozone depletion observed after the 1991 mount pinatubo eruption

new boron isotopic evidence for sedimentary and magmatic fluid influence in the shallow hydrothermal vent system of milos island aegean sea greece abstract magmatic sources may contribute a significant amount of volatiles in geothermal springs however their role is poorly understood in submarine hydrothermal systems worldwide in this study new results of b and 11 b in 41 hydrothermal vent waters collected from the shallow hydrothermal system of milos island in the aegean sea were combined with previously published data from other tectonic settings and laboratory experiments to quantify the effects of phase separation fluid sediment interaction and magmatic contribution two cl extreme solutions were identified high cl waters cl as high as 2000 mm and low cl waters cl 3 mol mol and extremely low 11 b 1 4 6 3 except for the waters with mg content of near the seawater value and 11 b 10 3 17 4 these high cl waters with high b cl and low 11 b plot close to the vent waters in sediment hosted hydrothermal system i e okinawa trough or fumarole condensates from on land volcanoes implying b addition from sediment or magmatic fluids plays an important role this is in agreement with fluid sediment interactions resulting in the observed b and 11 b as well as previously reported br i cl ratios supporting a scenario of slab derived fluid addition with elevated b 11 b rich and low br cl and i cl which is derived from the dehydration of subducted sediments the slab fluid becomes subsequently mixed with the parent magma of milos the deep brine reservoir is partially affected by injections of magmatic fluid gases during degassing the results presented here are crucial for deciphering the evolution of the brine reservoirs involved in phase separation fluid sediment interaction and magmatic contribution in the deep reaction zone of the milos hydrothermal system they also have implications in the understanding of the formation of metallic vein mineralization

the influence of hydrothermal fluid composition and advection rates on black smoker chimney mineralogy insights from modeling transport and reaction abstract a detailed study of black smoker chimneys was carried out by drawing together mineralogical observations and measured fluid compositions the modeling technique which establishes a link between vent fluid chemistry and vent deposit mineralogy is used to examine the influence of the physical environment on transport across short length scales centimeters which are subject to steep thermal 350 c and chemical gradients and to predict saturation states of minerals as functions of position within chimney walls owing to short length scales steep gradients and constancy of bounding fluid compositions concentration profiles are controlled by transport the effect of reaction rates on profiles is assumed to be negligible precipitation at points within the chimney wall is thus kinetically controlled local equilibrium does not apply and precipitation must be suppressed when calculating distributions of species and saturation states of minerals model calculations are performed in a series of four steps the first is speciation of measured fluid compositions at in situ temperature and pressure conditions results of calculations are plotted on stability diagrams of log fo2 log f s2 and log fo2 log a fe 2 a cu 2 to examine how closely the predicted saturation states fit with observations of minerals coexisting with the hydrothermal fluid at the vent sites the second step is calculation of heat and mass transport across the chimney wall the third is speciation of the pore fluid compositions calculated to exist in the wall subsequent to transport and the fourth is comparison of calculated mineral saturation states to observations of naturally occurring chimney samples application of the modeling technique to five vent sites which exhibit distinct fluid compositions allows reproduction of observed mineralogy model results demonstrate the sensitivity of geochemical processes to the physical environment porosity tortuosity permeability mineral composition to rates of advection of seawater inward or hydrothermal fluid outward across chimney walls and to endmember fluid composition

reactive halogens bro and oclo detected in the plume of soufriere hills volcano during an eruption hiatus volcanic plumes are sites of dynamic chemistry involving halogen gases here we present new data on the relative abundances of so2 bro and oclo gases emitted from soufriere hills volcano shv they were collected during an eruptive hiatus but during sustained degassing at this halogen rich volcano by comparison with data from a previous study during an eruptive phase and application of the data and modeling of villemant et al 2008 we suggest that after consideration of errors either the rate of hbr conversion to bro is variable ranging from 30 to 15 and or the relative partitioning of cl and br into the gas phase from the melt changes according to eruptive activity we examine the potential implications of this for fluid melt partitioning and compare our results with data from the experimental literature our work contributes toward understanding the controls on the bro so2 ratio for volcano monitoring purposes the changes in plume chemistry with regard to bromine at the onset of lava extrusion may be large and rapid oclo was detected in the plume at shv for the first time this species has only previously been detected in emissions from mount etna using ground based methods and from puyehue cordon caulle using satellite based methods no hcho or noy species were detected in the spectra

40ar 39ar ages and residual volatile contents in degassed subaerial and subglacial glassy volcanic rocks from iceland abstract major volatile contents h 2 o co 2 f cl and s and 40 ar 39 ar ages have been determined in variably degassed rhyolite obsidians from pleistocene holocene aged subaerial and subglacial eruption environments from the torfajokull volcanic center and the monogenetic volcano at prestahnukur iceland icelandic subglacial rhyolites preserve residual h 2 o contents of 0 08 0 69 wt undetectable co 2 840 1780 ppm f 430 2000 ppm cl and 6 45 ppm s most subglacial obsidians have degassed volatile signatures at the time of their eruption under ice one eruption blahnukur torfajokull showed h 2 o contents which exceed those expected for quenching at atmospheric pressures up to 0 69 wt h 2 o and are consistent with eruption at 40 kbar of pressure or equivalent to under 450 m of ice altered and microcrystalline groundmass in some subglacial rhyolites yield variable volatile contents that are likely the result of micro scale variability and the presence of alteration products two subaerial rhyolite obsidians gave low volatile contents consistent with quenching at the surface new 40 ar 39 ar ages were determined on the subglacially erupted rhyolites and provide broad constraints on the timing and frequency of glacio volcanism during the pleistocene three subglacial eruptions at torfajokull yielded ages of 108 22 ka blahnukur 255 20 ka habarmur and 236 7 ka hasker ingur which fit into a range of previously determined ages at torfajokull of 67 384 ka a new age of 132 19 ka was determined for the monogenetic subglacial eruption at prestahnukur holocene aged subaerial volcanic glass produced no ages due to large amounts of air derived 40 ar 84 93 preliminary apparent 40 ar 39 ar ages from the limited feldspar phenocrysts available in these crystal poor samples yield erroneous apparent plateau ages far older than eruption ages suggesting a homogenously distributed excess ar component disturbances to the 40 ar 39 ar geochronometer are correlated with a heterogeneous distribution of volatiles in glass and linked to hydration e g kaldaklofsfjoll mild alteration e g habarmur and alteration and or recrystallization of glass e g blahnukur our observations indicate however that unaltered subglacially erupted glasses that are partially to wholly degassed are promising materials for the application of the 40 ar 39 ar geochronometer the precision to which we can date these young glassy samples currently limits the use of 40 ar 39 ar geochronometer as a tool for understanding the exact timing and duration of glaciovolcanism in the recent past

partitioning of cl and f between fluid and hydrous phonolitic melt of mt vesuvius at 850 1000 c and 200 mpa abstract the solubilities of cl and or f bearing fluids in phonolitic melts of vesuvius volcano have been determined experimentally at temperatures of 845 865 c and 1000 c and pressure of 200 mpa at 845 865 c the maximum cl concentration in the melt m cl coexisting with cl rich 35 5 wt fl cl and f free fluid is about 0 5 wt an addition of f to the system increases the cl content of the melt up to 0 7 wt at 39 wt cl and 13 wt f in the fluid s the relationship between m cl and fl cl indicates that low density vapor and dense brine phases might have coexisted in some experiments the relationship between m cl and fl cl at 1000 c is similar to that determined at 845 865 c implying that variations of temperature in the range 850 1000 c have no significant effect on the partitioning of cl between fluid and phonolitic melt the concentration of f in phonolitic melt coexisting with f rich fluid s reaches at least 0 9 wt at 845 865 c and 1 3 wt at 1000 c the comparison of data from experiments conducted in au and pt capsules indicates that f may react with au which influences the quality of the experimental results the partition coefficients of f between bulk fluid and melt fl m d f are higher than 1 in all experiments indicating that fluorine is preferentially incorporated into the fluid phase in phonolitic systems in contrast to fl m d f values determined in rhyolitic systems the influence of cl on fl m d f is not detectable at the conditions of our experiments the experimental data imply that mt somma vesuvius phonolitic magmas from the eruptions between a d 79 and a d 1944 may have coexisted with cl rich and f rich fluid phase s prior to eruption

chlorine isotope and cl br fractionation in fluids of poas volcano costa rica insight into an active volcanic hydrothermal system abstract halogen rich volcanic fluids issued at the surface carry information on properties and processes operating in shallow hydrothermal systems this paper reports a long term record of cl br concentrations and 37cl signatures of lake water and fumaroles from the active crater of poas volcano costa rica where surface expressions of magmatic hydrothermal activity have shown substantial periodic changes over the last decades both the hyperacid water of its crater lake laguna caliente and subaerial fumaroles show significant temporal variability in cl br concentrations br cl ratios and 37cl reflecting variations in the mode and magnitude of volatile transfer the 37cl signatures of the lake covering the period 1985 2012 show fluctuations between 0 02 0 06 and 1 15 0 09 condensate samples from adjacent fumaroles on the southern shore collected during the interval 2010 2012 with strong changes in gas temperature 107 763 c display a much larger range from 0 43 0 09 to 14 09 0 08 most of the variations in cl isotope br cl and concentration signals can be attributed to interaction between magma derived gas and liquid water in the volcanic hydrothermal system below the crater the 37cl were lowest and closest to magmatic values in 1 fumarolic gas that experienced little or no interaction with subsurface water and followed a relatively dry pathway and 2 water that captured the bulk of magmatic halogen output so that no phase separation could induce fractionation in contrast elevated 37cl can be explained by partial scavenging and fractionation during subsurface gas liquid interaction hence strong cl isotope fractionation leading to very high 37cl in poas fumaroles indicates that they followed a wet pathway highest 37cl values in the lake water were found mostly in periods when it received a significant input from subaqueous fumaroles or when high temperatures and low ph caused hcl evaporation it is concluded that combined monitoring of 37cl and br cl in laguna caliente and adjacent fumaroles provides valuable information on activity in the subsurface hydrothermal system with significant relevance for volcanic surveillance of poas

transition from dome forming to plinian eruptive styles controlled by h2o and cl degassing the transition from a plinian pumice to an effusive dome forming eruptive style is frequently observed in volcanic systems and is generally attributed to the progressive loss of volatiles from magma stored in a superficial reservoir this explosive effusive transition has been explained by the evolution from a closed to an open system of degassing1 2 3 4 but in this context an eruption at mt pelee martinique french west indies dated at 650 years ago which exhibited a rarely observed5 6 succession from dome forming to plinian activity in a short interval of time7 is at odds with such an explanation in this eruption near surface explosions of the dome produced two peleean turbulent pyroclastic flows whose deposits are similar to those of the effusive 1902 eruption and then plinian activity produced pumice fallouts and flows the reconstruction of the degassing paths of both eruptive regimes using the densities and the h2o and cl contents of the clasts shows that the interaction of rising magma with hydrothermal fluids at shallow depth may play a critical role in determining eruptive style

fragmentation of magma during plinian volcanic eruptions the ratio of the volume of vesicles gas to that of glass liquid in pumice clasts v g v l reflects the degassing and dynamic history experienced by a magma during an explosive eruption v g v l in pumices from a large number of plinian eruption deposits is shown here to vary by two orders of magnitude even between pumices at a given level in a deposit these variations in v g v l do not correlate with crystallinity or initial water content of the magmas or their eruptive intensities despite large ranges in these variables gas volume ratios of pumices do however vary systematically with magma viscosity estimated at the point of fragmentation and we infer that pumices do not quench at the level of fragmentation but undergo some post fragmentary evolution on the timescale of plinian eruptions pumices with viscosities 109 pa s can expand after fragmentation as long as their bubbles retain gas at a rate inversely proportional to their viscosity once the bubbles connect to form a permeable network and lose their gas expansion halts and pumices with viscosities 105 pa s can collapse under the action of surface tension textural evidence from bubble sizes and shapes in pumices indicates that both expansion and collapse have taken place the magnitudes of expansion and collapse therefore depend critically on the timing of bubble connectivity relative to the final moment of quenching we propose that bubbles in different pumices become connected at different times throughout the time span between fragmentation and quenching after accounting for these effects we derive new information on the fragmentation process from two characteristics of pumices the most important is a relatively constant minimum value of v g v l of 1 78 64 vol vesicularity in all samples with viscosities 105 pa s this value is independent of magma composition and thus reflects a property of the eruptive mechanism the other characteristic is that highly expanded pumices 85 vol vesicularities are common which argues against overpressure in bubbles as a mechanism for fragmenting magma we suggest that magma fragments when it reaches a vesicularity of 64 vol but only if sheared sufficiently strongly the intensity of shear varies as a function of velocity in the conduit which is related to overpressure in the chamber so that changes in overpressure with time are important in controlling the common progression from explosive to effusive activity at volcanoes

halogens in volcanic systems the transport degassing and atmospheric release of halogens from active volcanism on earth have been the focus of increasing interest over the last few decades and have recently been the subject of the 1st workshop on halogens in volcanic systems and their environmental impacts that was held in december of 2007 at yosemite lodge in yosemite national park california as an introduction to this chemical geology special issue collecting contributions from many of the participants at the workshop we review here recent advances in this field including experimental and theoretical investigations of halogen behaviour in volcanic and related magmatic systems we discuss previous research on several aspects of halogen geochemistry including halogen abundances in the mantle and magmas on earth the effects of halogens on phase equilibria and melt viscosities their partitioning between melt and fluid phase s upon decompression cooling and crystallisation of magmas in the earth s crust and their final atmospheric release as volcanic gases the role of halogens in the genesis of hydrothermal systems and in the transport of ore forming metals is also reviewed and we discuss our current understanding of atmospheric processing of volcanic halogens in both the troposphere and stratosphere and their consequent impacts in spite of these recent advancements our current understanding of halogen geochemistry at active volcanoes is still far too fragmentary and the key questions that require answers from future research are summarised in our conclusions

a comparison of temperatures estimated from the electrum sphalerite pyrite argentite assemblage and filling temperatures of fluid inclusions from epithermal au ag vein type deposits in japan the assemblage electrum sphalerite pyrite argentite is common in epithermal au ag vein type deposits in japan on the basis of the iron content of sphalerite and the silver content of electrum in this assemblage the precipitation temperatures were estimated the electrum sphalerite temperatures were compared with the filling temperatures of fluid inclusions in quartz which was considered to have grown nearly simultaneously with this mineral assemblage almost all electrum sphalerite temperatures are within or 30 degrees c of the filling temperatures showing a reasonably good agreement this agreement indicates that 1 the f sub s 2 temperature relations in the au ag s and fe zn s systems can be extrapolated to temperatures below 200 degrees c from or 300 degrees c experimental data 2 the electrum sphalerite pyrite argentite assemblage probably formed at close to an equilibrium condition and 3 the pressure corrections to filling temperatures of fluid inclusions necessary to obtain formation temperatures are relatively small 30 degrees c in contrast to the precipitation temperatures for the electrum sphalerite pyrite argentite assemblage the temperatures for the electrum sphalerite pyrite ag se te mineral naumannite aguilarite hessitc assemblage are not in good agreement with the filling temperatures of fluid inclusions a less than unity activity of ag 2 s in ag se te minerals may explain this disagreement

carbon isotope composition of organic compounds produced by abiotic synthesis under hydrothermal conditions although it is widely believed that production of organic compounds by fischer tropsch synthesis and related processes occurs in many geologic environments unambiguous identification of compounds with an abiotic origin in natural samples has been hampered by a lack of means to discriminate between abiotic compounds and organic matter from biological sources while isotopic compositions might provide a means to discriminate between biologic and non biologic sources of organic matter there are few data presently available to constrain the isotopic composition of compounds produced by abiotic processes in geologic systems here we report results of laboratory experiments conducted to evaluate the isotopic composition of organic compounds synthesized abiotically under hydrothermal conditions we find the organic products are depleted in 13c to a degree typically ascribed to biological processes indicating that carbon isotopic composition may not be a particularly effective diagnostic means to differentiate between biologic and non biologic sources furthermore our results suggest that the isotopic compositions of reduced carbon compounds found in many ancient rocks that have heretofore been attributed to biological sources could be consistent with an abiotic origin in a hydrothermal setting

the explosive eruption of soufriere hills volcano montserrat west indies 17 september 1996 on 17 september 1996 the soufriere hills volcano started a 9 hour period of dome collapse involving 11 7 106 m dre of lava after 2 5 hours of quiescence a sustained explosive eruption began estimated eruption parameters are plume height at least 11 3 km and a maximum of 15 km 180 m s for launch velocities of ballistic clasts peak explosion pressure of 27 5 mpa magma water contents of 2 5 5 magma discharge rates from 2300 to 4300 m s ejecta volume of 3 2 0 9 106 m dre ejecta consists of pumice 1160 kg m higher density vesiculated ejecta 1300 to 2000 kg m dense glassy clasts 2600 kg m breccias cut by tuffisite veins and hydrothermally altered lithics the ejecta are interpreted as a conduit assemblage with evacuation of the conduit down to depths of about 3 to 5 km the eruption was triggered by unloading of a gas pressurised conduit due to dome collapse

chlorine partitioning between a basaltic melt and h2o co2 fluids at mount etna abstract partitioning experiments between a basaltic melt from mt etna and a low density hydrous fluid or vapor containing h 2 o or h 2 o co 2 were performed at 1200 1260 c at pressures between 1 and 200 mpa either near the nickel nickel oxide nno buffer or at two log units above it nno 2 and with different chloride concentrations most of the experiments were done at chloride brine undersaturated conditions although at the highest cl concentrations explored brine saturation might have been reached the average partition coefficients d cl fluid melt over the range of cl concentrations were derived on a weight basis by plotting the calculated concentrations of cl in the fluid phase versus the measured ones in the melt for h 2 o cl experiments in which the cl concentration in the melt was 0 4 wt a negative dependence between d cl f m and pressure is observed d cl fluid melt in h 2 o cl bearing experiments ranges between 11 14 at 1 and 25 mpa to 6 at 200 mpa at nno and between 4 at 50 mpa and 13 at 100 mpa at nno 2 addition of co 2 at nno yields lower partition coefficients than in co 2 free conditions over the pressure range investigated the negative pressure dependence observed for h 2 o cl experiments disappears when co 2 is present in the system overall once co 2 is introduced in the system cl fugacity in the silicate melt tends to increase thus resulting in a decrease of d cl f m application to mt etna shows that the composition of the volcanic plume in terms of cl records very shallow pressures of magma equilibration with its exsolved fluid

abiogenic methanogenesis in crystalline rocks isotopically anomalous ch4 rich gas deposits are found in mining sites on both the canadian and fennoscandian shields with 13cch4 values from 22 4 to 48 5 and dch4 values from 133 to 372 these methane deposits cannot be accounted for by conventional processes of bacterial or thermogenic methanogenesis compositionally the gases are similar to other ch4 rich gas occurrences found in canadian and fennoscandian shield rocks sherwood lollar et al 1993 however the isotopically anomalous gases of this study are characterized by unexpectedly high concentrations of h2 gas ranging from several volume percent up to 30 vol the h2 gases are consistently depleted in the heavy isotope with dh2 values of 619 to 659 3h 4he ratios in the range of 0 4 10 8 to 4 4 sx 10 8 indicate that there is no resolvable component of mantle derived he in these deposits based on these results a mantle derived source for the c bearing gases is unlikely several lines of evidence support an alternative abiogenic origin for the gases from sudbury canada and juuka and pori finland the d depleted h2 gas and calculated d ch4 h2 equilibration temperatures of 110 170 c at all three sites are in good agreement with results obtained for abiogenically produced ch4 and h2 in ophiolite sequences in oman and the philippines serpentinization and the hydration of ultramafic rocks are the proposed mechanisms for ch4 and h2 production in these ophiolite sequences the widespread occurrence of serpentinized and altered ultramafic rocks at juuka and at a number of other sites in both canada and finland implies that similar mechanisms may be involved in gas production at at least three sites on the shields the origin of the gases at the remaining shield sites is discussed alternative hypothesis include 1 production of the rest of the shield gases by mixing between abiogenic endmembers and bacterially generated hydrocarbon gas such as identified elsewhere on the canadian and fennoscandian shields sherwood lollar et al 1993 and 2 production of a series of isotopically distinct abiogenic ch4 endmembers at each site due to variability in the isotopic composition of available carbon sources we cannot conclusively distinguish between the alternative scenarios based on existing data however the evidence for an abiogenic ch4 endmember at at least three sites emphasizes the need for substantial revision of current theories of methanogenesis abiogenic processes of ch4 production may be considerably more widespread than previously anticipated

genetic environment of germanium bearing gold silver vein ores from the wolyu mine republic of korea the wolyu mine is one of the largest vein type gold silver bearing epithermal systems in the youngdong district and is the first gold silver deposit in korea found to contain significant germanium in the form of argyrodite ag8ges6 mineralized veins 78 9 1 2 ma crosscutting late cretaceous hostrock tuff and quartz porphyry 81 5 1 8 ma consist of three stages of quartz and carbonates the first of which contains pyrite basemetal sulfides and au ag minerals stage i au ag ge mineralized veins show a systematic variation of mineral assemblage with time 1 quartz pyrite 2 quartz pyrite sphalerite electrum argentite 3 carbonate quartz sphalerite electrum argentite 4 carbonate native silver argentite ag sulfosalts argyrodite sphalerite calculated values of temperature and sulfur activity are assemblage 1 360 280 c and 10 7 10 10 2 280 210 c and 10 10 10 14 3 210 180 c and 10 14 10 16 4 180 155 c and 10 17 10 18 these data the frequent association of gold with sulfides and the abundance of pyrite in alteration zones indicate that decreasing sulfur activity and cooling were important in triggering gold deposition hydrogen and oxygen isotope compositions of ore fluids display a systematic variation with increasing time within the main ag au ge mineralization d and 18o values decrease with the transition from quartz to carbonate deposition from 78 and 2 8 to 90 and 8 7 respectively indicating increasing involvement mixing of less evolved meteoric water which resulted in progressive cooling and dilution of ore fluids in the shallow 370 600 m wolyu epithermal system

temporal trends in lava dome extrusion at santiaguito 1922 2000 we present a means of extracting lava dome extrusion rates from data provided by the thematic mapper and enhanced thematic mapper plus instruments flown on the landsat satellites extrusion rates derived from the landsat data for santiaguito dome complex guatemala during november 1987 and january 2000 of 0 72 0 08 and 0 48 0 09 m3 s 1 compare favorably with ground based estimates of 0 63 0 28 and 0 48 0 17 m3 s 1 a satellite data derived set of 18 extrusion rate estimates between 1987 and 2000 along with ground based volume estimates prior to 1987 allow us to infer volumes of magma erupted since 1922 these data reveal cyclic extrusion at santiaguito each cycle begins with a 3 6 year long phase of high extrusion rate 0 5 2 1 m3 s 1 followed by a longer 3 11 years phase of low extrusion rate 0 2 m3 s 1 the 8th cycle began in 1996 and was still in its high extrusion rate phase during january 2000 with time however the durations of the low extrusion rate phases have increased peak extrusion and time averaged extrusion rates for each cycle have decreased and the difference between extrusion rates during the high and low extrusion rate phases of each cycle has decreased these trends may be the result of depressurization and exhaustion of the source in this case the current eruption may be expected to end around 2020 alternatively santiaguito may be entering a period of persistent activity maintained by a stable magma supply in this case we may expect extrusion to become less cyclic and to stabilize at 0 2 0 4 m3 s 1 however a 2 wt decrease in sio2 content of erupted products since 1970 appears to be consistent with chamber exhaustion as well as an increase in block lava flow lengths during 1970 2000

organic synthesis during fluid mixing in hydrothermal systems hydrothermal circulation can lead to fluid mixing on any planet with liquid water and a source of heat aqueous fluids with differing compositions especially different oxidation states are likely to be far from thermodynamic equilibrium when they mix and provide a source of free energy that can drive organic synthesis from co 2 and h 2 and or supply a source of geochemical energy to chemolithoautotrophic organisms results are presented that quantify the potential for organic synthesis during unbuffered fluid mixing in present submarine hydrothermal svstems as well as hypothetical systems that may have existed on the early earth and mars dissolved hydrogen present in submarine hydrothermal fluids owing to the high temperature reduction of h 2 o as seawater reacts with oceanic crustal rocks provides the reduction potential and the thermodynamic drive for organic synthesis from co 2 or bicarbonate as hydrothermal fluids mix with seawater the potential for organic synthesis is a strong function of the h 2 content of the hydrothermal fluid which is in turn a function of the prevailing oxidation state controlled by the composition of the rock that hosts the hydrothermal system hydrothermal fluids with initial oxidation states at or below those set by the fayalite magnetite quartz mineral assemblage show the greatest potential for driving organic synthesis these calculations show that it is thermodynamically possible for 100 of the carbon in the mixed fluid to be reduced to a mixture of carboxylic acids alcohols and ketones in the range 250 50 c as cold seawater mixes with the hydrothermal fluid as the temperature drops larger organic molecules are favored which implies that fluid mixing could drive the geochemical equivalent of a metaholic system this enormous reduction potential probably drives a large portion of the primary productivity around present seafloor hydrothermal vents and would have been present in hydrothermal systems on the early earth or mars the single largest control on the potential for organic synthesis is the composition of the rock that hosts the hydrothermal system

experimental studies in model fluid systems numerous observations provide strong evidence that fluid fluid coexistence is a widespread phenomenon in many geological processes i oceanic hydrothermal fluids display a wide range in salinity which clearly indicates fluid phase separation of the circulating seawater see foustoukos and seyfried 2007a ii selective enrichment of certain elements and coeval entrapped inclusions of different co existing fluids highlight the role immiscible fluids play in ore formation see heinrich 2007a iii trace element and stable isotope characteristic as well as equilibrium mineral assemblages in contact aureoles prove immiscible fluids to be a ubiquitous feature in most contact metamorphism see heinrich 2007b iv small scale fluid heterogeneity in eclogitic rocks indicate fluid immiscibility to occur in metamorphic rocks up to high or even ultra high pressure see heinrich 2007b unfortunately fluids are principally non quenchable phases and direct quantitative information on fluid properties at p and t is in most cases not available experimental studies are thus central in studying geologic fluids in general and co existing fluids in particular they are still the primary source of quantitative information on physicochemical properties of co existing crustal fluids they allow e g determine i fluid phase relations as function of p t and x ii physical fluid properties like density and viscosity and iii trace element and isotope fractionation between co existing fluids but also between co existing fluids and solids the experimental data can then be used as input in forward modeling approaches the results and or predictions of which may then be tested in natural systems see driesner and geiger 2007 experimental data on co existing fluids in systems of geological relevance already date back to the flrst half of last century e g keevil 1942 since the 1960ies numerous systematic experimental studies on fluid fluid phase relations at crustal p and t conditions were performed e g sourirajan and kennedy

bromine and chlorine emissions from plinian eruptions along the central american volcanic arc from source to atmosphere highlights data set of br and cl emissions from 29 large cava eruptions vei 5 melt inclusions are strongly enriched in chlorine and bromine compared to their respective matrix glasses fluid partitioning is 4 to 68 times more efficient for br than for cl subducted calcareous sediments are the major control on the arc magmatic bromine contents average cava eruption would add 368 eesc of recent annual loading to stratosphere abstract large explosive volcanic eruptions inject gases aerosols and fine ashes into the stratosphere potentially influencing climate and atmosphere composition on a global scale although the potential climate effect of chlorine cl and bromine br injections into the stratosphere is known the global mass fluxes are poorly constrained in this study we focus on the magmatic degassing systematics and budgets of br and cl and on constraining the major sources of br in a subduction setting we therefore present a regional time series of br and cl emissions from 29 highly explosive eruptions throughout the central american volcanic arc cava covering the last 200 ka and a range of magmatic compositions and eruption magnitudes we have measured br and cl in matrix glasses and melt inclusions using synchrotron radiation micro x ray fluorescence spectrometry sr micro xrf and electron microprobe respectively melt inclusions of the cava tephras generally have higher br 0 9 to 17 9 ppm and cl 770 to 3800 ppm contents than the matrix glasses 0 39 to 1 5 ppm br 600 to 2800 ppm cl moreover the difference between maximum and minimum concentrations observed in melt inclusions of a given sample ranges between 9 and 90 of the maximum observed concentration for br and between 2 and 40 for cl such intra sample variations arise from variable pre eruptive degassing of these halogens into a magmatic fluid phase the relative loss of br from the melt is 4 to 68 times higher than that of cl the masses of br 2 1100 kt and cl 0 1 to 800 mt emitted by the eruptions generate instantaneous additions to the stratosphere potentially amounting to 6 5600 of the present day stratospheric annual global loading of equivalent effective stratospheric chlorine as the size of the stratospheric impact is primarily a function of eruption magnitude we use magnitude frequency relationships to estimate that eruptions adding 10 to resident eesc loading would occur every 40 years while every 200 years an eruption would double the eesc loading comparing the variations in br and cl concentrations and particularly minimum cl br ratios in melt inclusions with geochemical trace element proxies e g u la ba th and lead isotope compositions which change along the arc in response to changing subduction conditions we suggest that subducted calcareous sediment is a major source of magmatic br but also infer an important role of fluids expelled from serpentinized subducted mantle extrapolation of cava volcanic br emissions to the global subduction system thus needs to consider variations in the nature of subducted lithologies

insights into the behaviour of s f and cl at santiaguito volcano guatemala from apatite and glass abstract the mineral apatite can incorporate all of the major magmatic volatile species into its structure where melt inclusions are not available magmatic apatite may therefore represent an opportunity to quantify volatile concentrations in the pre eruptive melt we analysed apatites and matrix glasses from andesites and dacites erupted from santiaguito volcano guatemala between the 1920s and 2002 x ray mapping shows complex zoning of sulphur in the apatite grains but typically with sulphur rich cores and sulphur poor rims apatite microphenocrysts are enriched in f and depleted in cl relative to inclusions matrix glasses are dacite to rhyolite and contain low f but up to 2400 ppm cl overall the data are consistent with progressive depletion of cl in the most evolved melts due to crystallisation and degassing in the absence of pristine melt inclusions we used apatite together with published partitioning data to reconstruct the likely volatile contents of the pre eruptive melt and hence estimate long term average gas emissions of so 2 hf and hcl for the ongoing eruption the data indicate time averaged so 2 emissions of up to 157 tonnes day hcl of 74 1382 tonnes day and up to 196 tonnes day hf apatite may provide a useful measure of long term volatile emissions at volcanoes where direct emissions measurements are unavailable or for comparison with intermittent gas sampling methods however significant uncertainty remains regarding volatile distribution coefficients for apatite and their variations with temperature and pressure

tracing the evolution and distribution of f and cl in plutonic systems from volatile bearing minerals a case study from the liujiawa pluton dabie orogen china fluorine and chlorine play an important role in magmatic differentiation hydrothermal alteration and related mineralization processes but tracing their evolution in magmatic and especially plutonic systems is not an easy task the f and cl in melts can be estimated from f and cl concentrations in minerals provided that partitioning between minerals and melts are constrained based on available partitioning models between mineral melt mineral fluid and melt fluid a set of equations has been derived to determine f and cl concentrations in melts from the compositions of amphibole biotite and apatite the new calculation procedure has been applied to a plutonic system the liujiawa pluton eastern dabie orogen china cl and f concentrations in amphiboles biotites and apatites from different rock types gabbronorite two pyroxene diorite clinopyroxene diorite and hornblende gabbro have been determined by electron microprobe most amphiboles show a negative correlation between log cl oh and mg number and a positive correlation between log f oh and a site occupation biotites from the gabbronorite and two pyroxene diorite show a slight positive correlation between log cl oh and mg which is however not the case for the clinopyroxene diorite apatites from all the samples are rich in f and show negative correlations between cl and f concentrations in our case study we demonstrate that the cl concentration in melt remains approximately constant at 1 000 2 000 ppm over the major crystallization interval but decreases strongly at near solidus temperatures as a result of fluid exsolution the f concentration in melt remains nearly constant at ca 2 000 3 000 ppm at high temperatures as well as near solidus conditions indicating that it is not largely affected by fluid exsolution because of its strongly preferred incorporation into melt interestingly the evolution of cl and f concentrations in melt with magmatic differentiation is similar to that determined in volcanic systems suggesting that the evolution of cl and f in melts during crystallization and late magmatic stages at depth plutonic systems is similar to that observed in volcanic systems during decompression and degassing

exsolution of immiscible vapor and liquid phases from a crystallizing silicate melt implications for chlorine and metal transport abstract the compositional variation of a cl bearing aqueous fluid exsolving from a crystallizing silicate melt is evaluated for the system haplogranitic melt na k c1 h 2 o with attention to the effect of vaporliquid immiscibility on the aqueous fluid above critical pressures for the aqueous fluid p 1 5 kb at 800 c where the fluid is single phase the cl concentration in the aqueous fluid c cl aq gradually decreases with crystallization of a silicate melt under rayleigh fractionation as demonstrated by previous studies however the variation of ca is quite different below critical pressures where vapor liquid immiscibility occurs in particular at low pressures p cl h 2 o ratio in a melt is small and ca will increase with crystallization a high cl h 2 o ratio at low pressure results in liquid exsolution and decreasing ca with crystallization eventually both vapor and liquid phases will exsolve simultaneously regardless of the initial exsolving phase during this simultaneous exsolution the composition of the exsolving vapor and liquid phases the mass ratio of these phases and the cl concentration of the silicate melt will all remain constant comparison of the model and published experimental data indicates that the simultaneous exsolution of vapor and liquid may occur from a normal rhyolite crystallized at pressures below the critical pressure for the aqueous fluid therefore simultaneous exsolution of the immiscible aqueous phases is likely to be a common phenomenon in magmatic hydrothermal systems at conditions for the vapor liquid immiscibility model calculations at 0 6 and 1 2 kb indicate that major amounts of cl in the system will be distributed to the liquid phase particularly at the lower pressure this suggests that the majority of chloridecomplexed metals exsolving from a magma may be transported in the liquid phase under shallow crustal conditions

experimental study of chlorine behavior in hydrous silicic melts chlorine solubility in silicate melts has been investigated at 830 850 plus minus 5c and at pressures ranging from 50 to 200 mpa using both natural pantellerite rhyolite phonolite and synthetic sio sub 2 al sub 2 o sub 3 k sub 2 o na sub 2 o compositions and a stated h sub 2 o nacl kcl fluid phase near 4 molal at 100 mpa cl contents in pantelleritic melts reach a solubility plateau at initial aqueous phase molality near 2 this plateau coincides with a large immiscibility gap between aqueous and chloride rich fluids with the coexisting cl saturated aqueous phase cl ranges from 2 720 plus minus 120 ppm in rhyolite to 8 960 plus minus 85 ppm in pantellerite and reaches 6 270 plus minus 170 ppm in phonolite at 100 mpa between 50 and 200 mpa the cl content in pantelleritic melt decreases from 9 640 plus minus 200 ppm to 5 040 plus minus 150 ppm although cl solubility increases with increasing feo sup in high sio sub 2 melts it is mainly controlled by the al si and na k al molar ratios of the melt with a minimum at na k al 1 in a series of synthetic rhyolitic to pantelleritic melts the experimental results suggest that chlorine occurs as alkali chloride complexes in high sio sub 2 more melts they also indicate that cl is concentrated in the aqueous fluids in equilibrium with sio sub 2 rich melts the exact value of d depending on melt composition and melt chlorine concentration volcanic degassing will create chlorine rich hydrothermal fluids and decrease chlorine melt content less

reduction of co2 during serpentinization of olivine at 300 c and 500 bar co 2 reduction processes occurring during experimental serpentinization of olivine at 300 c and 500 bar confirm that ultramafic rocks can play an important role in the generation of abiogenic hydrocarbon gas data reveal that conversion of fe ii in olivine to fe iii in magnetite during serpentinization leads to production of h 2 and conversion of dissolved co 2 to reduced c species including methane ethane propane and an amorphous carbonaceous phase hydrocarbon gases generated in the process fit a schulz flory distribution consistent with catalysis by mineral reactants or products magnetite is inferred to be the catalyst for methanization during serpentinization because it has been previously shown to accelerate fischer tropsch synthesis of methane in industrial applications involving mixtures of h 2 and co 2 the carbonaceous phase was predominantly aliphatic but had a significant aromatic component although this phase should ultimately be converted to hydrocarbon gases and graphite if full thermodynamic equilibrium were established its formation in these experiments indicates that the pathway for reduction of co 2 during serpentinization processes is complex and involves a series of metastable intermediates

h2o in rhyolitic glasses and melts measurement speciation solubility and diffusion dissolved h2o in silicate melts and glasses plays a crucial role in volcanic eruptions on terrestrial planets and affects glass properties and magma evolution in this paper major progress on several aspects of the h2o melt or glass system is reviewed consistency among a variety of data is investigated discrepancies are evaluated and confusion is clarified on the infrared measurement of total h2o and species concentrations calibration for a variety of glasses has been carried out at room temperature the measurements for h2o in rhyolitic glasses have undergone the most scrutiny resulting in the realization that absorptivities for the near infrared bands depend on total h2o content although the variation of the absorptivities does not seem to significantly affect the determination of total h2o it does affect the determination of molecular h2o and oh species concentrations calibration of the infrared technique for h2o in rhyolitic glasses still needs much improvement especially at high total h2o furthermore it is now almost certain that the molar absorptivities also depend on the measurement temperature in in situ studies hence it will be necessary to carry out calibrations in situ at high temperatures on h2o speciation results from two experimental approaches the quench technique and the in situ technique are very different leading to controversy in our understanding of true speciation a solution is presented to reconcile this controversy it is almost certain that the quench technique does not suffer from a quench problem but interpretation of in situ results suffered from ignoring the dependence of the molar absorptivities on measurement temperature accurate calibration at high temperatures is necessary for the quantitative application of the in situ technique to h2o speciation in silicate melts and glasses on h2o solubility in silicate melts recent experimental work has significantly expanded the t p range of solubility measurements and recent solubility models fill a gap for predicting solubility for a wide range of melt compositions i present a solubility model for rhyolitic and quasi rhyolitic melts over a wide range of t and p 500 1350 c 0 8 kbar by incorporating the role of speciation the solubility model is able to recover the experimental solubility data and has extrapolative value although the partial molar volume of h2o derived from the solubility model differs from that derived from density measurements on h2o diffusion recent studies on h2o diffusion in a quasi rhyolitic melt at 800 1200 c 0 5 5 kbar and up to 7 total h2o not only provide important new diffusion data but are also challenging earlier understanding of h2o diffusion based on data in rhyolitic glasses at 400 550 c 1 bar and 0 2 1 8 total h2o a comparison between the earlier model and recent data is made the recent high temperature diffusivities at total h2o 2 can be predicted by the earlier model however at higher total h2o the earlier model fails new work is under way to understand the diffusion mechanisms at high h2o contents

the biological potential of mars the early earth and europa the potential biomass that could have existed on mars is constrained by the total amount of energy available to construct it from an inventory of the available geochemical sources of energy we estimate that from the time of the onset of the visible geologic record 4 b y ago to the present as much as 20 g cm 2 of biota could have been created this is the same amount that could have been constructed on the early earth in only 100 million years this indicates that there likely was sufficient energy available to support an origin of life on mars but not sufficient energy to create a ubiquitous and lush biosphere similar calculations for europa suggest that even less geochemical energy would have been available there

the source of halogens in geothermal fluids from the taupo volcanic zone north island new zealand abstract forty seven samples of deep geothermal well fluids and hot springs from 14 geothermal sites in the taupo volcanic zone tvz north island new zealand were analyzed for cl br and li concentrations and 37cl 7li 18o and d values the main purpose of this study was to identify the sources of salinity in the tvz fluids and to assess the processes that control stable chlorine isotopic fractionation in the geothermal waters the samples were obtained from deep wells in the mokai ohaaki wairakei rotokawa kawerau ngatamariki and tauhara geothermal fields and from the hot springs at rotorua waiotapu lake taupo waimangu waikite orakei korako and tokaanu two main meteoric recharge areas were identified in the central tvz one located to the ne with 18o and d values of 5 5 and 35 respectively and the other to the sw with a 18o value of 6 7 and d value of 43 water rock interactions in most of the geothermal fluids resulted in a 18o shift to more positive values up to 1 for mokai and over 3 for kawerau the 7li values range from 2 9 to 2 0 and suggest that the deep geothermal fluids have interacted with rocks with low 7li values the highest 7li values 1 4 in the reservoir fluids were found at kawerau where the low quartz content of the greywacke may result in the depletion of 6li the 37cl values of the samples ranged from 1 0 to 0 8 the 37cl values of 0 2 0 1 and 0 0 were measured in samples from orakei korako waiotapu and waimangu respectively and these are interpreted to have been affected by surface evaporation and distillation processes excluding these data most waters with high cl br ratios had positive 37cl values the cl br molar ratios in well samples ranged from 659 to 1664 and the 37cl values from 1 0 to 0 8 the hot springs had cl br molar ratios ranging from 858 to 1611and 37cl values from 0 8 to 0 7 overall the cl br molar ratios of the fluids are comparable with published data on basaltic magmas and these magmas are inferred to be the main source of halogens in the geothermal fluids however the geothermal fluids can be separated into two main groups one associated with rhyolitic magmas characterized by positive 37cl values and high cl br molar ratios and other related to andesitic magmas with negative 37cl values and lower cl br molar ratios we suggest therefore that the isotopic fractionation of the stable cl isotopes is related to the difference in water contents of andesitic and rhyolitic magmas and that the fluid phase is enriched in 37cl during magmatic evolution there is no evidence of isotopic fractionation during the transit of the geothermal fluids from the reservoir to the surface but evaporation and distillation processes at the surface can affect the 37cl values

degassing of cl f li and be during extrusion and crystallization of the rhyolite dome at volcan chaiten chile during 2008 and 2009 we investigated the distribution of cl f li and be in pumices obsidians and crystallized dome rocks at chaiten volcano in 2008 2009 in order to explore the behavior of these elements during explosive and effusive volcanic activity electron and ion microprobe analyses of matrix and inclusion glasses from pumice obsidian and microlite rich dome rock indicate that cl and other elements were lost primarily during crystallization of the rhyolitic dome after it had approached the surface glass in pumice and microlite free obsidian has 888 121 ppm cl whereas residual glass in evolved microlite rich dome rock generally retains less cl as low as 0 7 mt cl with a potential maximum of 1 8 mt for the entire 0 8 km3 dome elemental variations reflect an integrated bulk distribution ratio for cl 1 7 1 7 times more cl was degassed or incorporated into crystals than remained in the melt because cl is lost dominantly as the very last h2o is degassed and cl is minimally if at all partitioned into microlites the integrated vapor melt distribution ratio for cl exceeds 200 200 times more cl in the evolved vapor than in the melt cl is likely lost as hcl which is readily partitioned into magmatic vapor at low pressure cl loss is accelerated by the change in the composition of the residual melt due to microlite growth cl loss also may be affected by open system gas fluxing integrated vapor melt distribution ratios for li f and be all exceed 1 000 on degassing an unknown fraction of these volatiles could be immediately dissolved in rainwater

direct observation of the evolution of a seafloor black smoker from vapor to brine a single hydrothermal vent f vent occurring on very young crust at 9 16 8 n east pacific rise was sampled in 1991 and 1994 in 1991 at the measured temperature of 388 c and seafloor pressure of 258 bar the fluids from this vent were on the two phase curve for seawater these fluids were very low in chlorinity and other dissolved species and high in gases compared to seawater and most sampled seafloor hydrothermal vent fluids in 1994 when this vent was next sampled it had cooled to 351 c and was venting fluids 1 5 times seawater chlorinity this is the first reported example of a single seafloor hydrothermal vent evolving from vapor to brine the 1991 and 1994 fluids sampled from this vent are compositionally conjugate pairs to one another these results support the hypothesis that vapor phase fluids vent in the early period following a volcanic eruption and that the liquid phase brines are stored within the oceanic crust and vent at a later time in this case 3 years these results demonstrate that the venting of brines can occur in the same location in fact from the same sulfide edifice where the vapor phase fluids vented previously

geochemistry of hydrothermal fluids from axial seamount hydrothermal emissions study vent field juan de fuca ridge subseafloor boiling and subsequent fluid rock interaction hydrothermal fluids collected from the ashes vent field in 1986 1987 and 1988 exhibit a very wide range of chemical composition over a small area 60 m in diameter compositions range from a 300 c gas enriched 285 mmol kg co2 low chlorinity 33 of seawater fluid to a 328 c relatively gas depleted 50 mmol kg co2 high chlorinity 116 of seawater fluid the entire range of measured compositions at ashes is best explained by a single hydrothermal fluid undergoing phase separation while rising through the ocean crust followed by partial segregation of the vapor and brine phases other mechanisms proposed to produce chlorinity variations in hydrothermal fluids precipitation dissolution of a chloride bearing mineral or crustal hydration cannot produce the covariation of chlorinity and gas content observed at ashes there is good agreement of the measured fluid compositions with compositions generated by a simple model of phase separation in which gases are partitioned according to henry s law and all salt remains in the liquid phase significant enrichments in silica lithium and boron in the low chlorinity fluids over levels predicted by the model are attributed to fluid rock interaction in the upflow zone depletions in iron and calcium suggest that these elements have been removed by iron sulfide and anhydrite precipitation at some time in the history of the low chlorinity fluids the distribution of low and high chlorinity venting is consistent with mechanisms of phase segregation based on differential buoyancy or relative permeability the relatively shallow depth of the seafloor 1540 m and the observed chemistry of ashes fluids are consistent with phase separation in the sub critical or near critical region

assessment of the ore forming process of the gejiu tin district south china abstract the gejiu tin district of southern china is the largest tin polymetallic ore district in the world even though the mining operation has lasted more than 2000 years in this area the metallogenic mechanism of this gigantic tin mineralization is still controversial based on petrographic geochemical and zirconological information from this study we present a particular model of the magma evolution and tin mineralization for the gejiu tin district the ore forming processes involved both a batholithic biotite monzogranite bmg emplaced at 94 ma and a satellitic muscovite alkali feldspar granite mag emplaced at 72 ma the bmg and the mag were produced from a long lived magma chamber by two stages of magmatic activity during intracontinental orogeny in the youjiang block the hiatus between the two magmatic stages indicates that the deep seated magma chamber persisted during the dominant phase of the orogeny progressive fractional crystallization of the magma caused the extreme enrichment of incompatible elements which include ore forming components such as tin aqueous fluids and other volatiles in the residual magma when the regional tectonic environment evolved into the extensional regime at 72 ma the highly fractionated residual magma ascended and once emplaced it formed the highly evolved mag with a mean zircon crystallization age of 71 8 1 2 ma the mag is temporally and spatially associated with cassiterite bearing quartz vein cqv with a mean zircon crystallization age of 72 6 1 6 ma this metallogenic model of the bmg mag cqv association is generally applicable to other granite related metallic deposits in south china southeast asia and elsewhere australia bolivia brazil usa etc the recognition of this bmg mag cqv association in regional geological survey may facilitate the future exploration for this type of deposit

sources of nutrients and energy for a deep biosphere on mars hydrothermal vents appear to be the tip of the subsurface biosphere in the ocean crust the primary prducers in this biosphere are prokaryotes that tolerate a wide variety of physical and chemical conditions and are versatile in their use of inorganic compounds to drive metabolism a synthesis of chemical and mineralogical data from martian meteorites and measurements of the martian surface suggest that conditions similar to those that make life possible in earth s oceanic crust namely water carbon nutrients appropriate temperatures and gradients in redox conditions also occur within mars chemolithoautotrophic microorganisms capable of living below the seafloor on earth would probably survive in some regions of the martian subsurface

fluid melt trace element partitioning behaviour between evolved melts and aqueous fluids experimental constraints on the magmatic hydrothermal transport of metals abstract the fluid melt partition coefficients of ten trace metals li mn cu zn rb sr mo w and pb along with k between hydrous evolved melts and coexisting cl bearing fluid s have been experimentally determined at 850 1050 c 0 6 2 2 kbar and o2 nno 0 5 to nno 2 log units the measured compositions of the quenched fluid phases vary from low salinity 2 wt cl to 19 wt cl with maximum starting fluid concentrations of 21 wt cl the results of 15 partitioning experiments confirm that dmetalfluid melt values depend strongly on the melt and fluid composition with the greatest metal affinities for the fluid phase shown in the experiments with high cl fluids and the most fractionated melts five experiments conducted in au96cu4 capsule alloy show dcufluid melt values ranging from 40 to 80 and a strong correlation with melt feo wt contents at equivalent fluid cl contents in contrast li shows only weak partitioning in favour of coexisting fluids across all melt compositions with dlifluid melt ranging from 0 16 in low salinity fluids to 1 17 in the highest cl fluid 19 15 wt cl a procedure was employed to redissolve and analyse the aluminosilicate precipitates that form during quenching of the experiments this procedure allows for metal contents of the final quench fluids to be constrained by both mass balance and direct measurement by solution icp ms analysis a comparison of the mass balance calculated vs directly measured fluid melt partition coefficients generally gives good agreement within an order of magnitude for most trace elements however discrepancies between these methods arise due to errors inherent in the mass balance calculations for metals with low abundances in the fluids e g sr and especially those showing affinities to alloy with the experiment capsule material e g mo these discrepancies in constraining experimental fluid trace element budgets also suggest that the precious metal capsule alloys cannot always be considered completely inert containers in experimental investigations and semi quantitative la icp ms analysis of the raw capsule alloys confirms the detectable presence of several of the trace elements investigated here integrating these new partitioning data with previous experimental and natural studies confirms that aqueous cl bearing fluids exsolved by hydrous calc alkaline melts stored at mid to upper crustal conditions are capable of efficiently sequestering and transporting some economically important trace metals e g mn cu zn however the new fluid melt li partitioning data in conjunction with evidence of very late post eruptive li modification suggests that li is moderately strongly fluid immobile at depth and suffers from significant post eruptive re equilibration this has implications for deciphering the signatures of volatile fluxing in arc magmas that are preserved in mineral and melt inclusion trace element concentrations and the development of mineralised stockwork regions in porphyry style metal deposits

experimental abiotic synthesis of methanol in seafloor hydrothermal systems during diking events abstract the abiotic synthesis of organic compounds in seafloor hydrothermal systems is one mechanism through which the subsurface environment could be supplied with reduced carbon a flow through fixed bed laboratory reactor vessel the catalytic reactor vessel crv system has been developed to investigate mineral surface promoted organic synthesis at temperatures up to 400 c and pressures up to 30 mpa conditions relevant to seafloor hydrothermal systems here we present evidence that metastable methanol can be directly synthesized from a gas rich co2 h2 h2o mixture in the presence of a mineral substrate experiments have been performed without a substrate with quartz and with a mixture of quartz and magnetite temperatures and pressures in the experiments ranged from 200 c to 350 c and from 15 to 18 mpa respectively maximum conversion of 5 8 10 4 co2 to ch3oh per hour was measured using a mixture of magnetite and quartz in the reactor after passivation of the stainless steel reactor vessel experiments demonstrate that methanol is formed at temperatures up to 350 c in the presence of magnetite and that the formation rate decreases over time the experiments also show a loss of surface reactivity at 310 c and a regeneration of surface reactivity with increased temperature up to 350 c concentrations of co2 and h2 used in the experiments simulate periodic localized and dynamic conditions occurring within the seafloor during and immediately following magmatic diking events high concentrations of co2 and h2 may be generated by dike injection accompanied by exsolution of co2 and reaction of dissolved h2o with feo in the magma to form h2 the experiments described here examine how the ephemeral formation of an h2 co2 rich vapor phase within seafloor hydrothermal systems may supply reactants for abiotic organic synthesis reactions these experiments show that the presence of specific minerals can promote the abiotic synthesis of simple organic molecules from common inorganic reactants such h2o co2 and h2 under geologically realistic conditions

expansion and quenching of vesicular magma fragments in plinian eruptions the conditions of pumice generation in plinian eruptions are studied a physical model describes the behavior of gas bubbles in a magma fragment which is carried upward in a volcanic conduit and an atmospheric eruption column the effects of pressure release and cooling are calculated for a range of eruption conditions the magma fragment expands in the conduit and stops expanding soon after leaving the vent when a thin viscous rind forms against the cold mixture of magmatic gas and air this rind prevents further volume changes pumice vesicularity is a function of the decompression rate in the conduit which depends on ascent velocity and fragmentation depth it is also sensitive to the cooling rate in the atmospheric column which depends on vent radius and mass discharge rate different fragments follow different trajectories in the column and are subjected to different cooling rates this generates a range of vesicularities which reflects the eruptive conditions all else being equal pumice vesicularity increases as magma viscosity decreases these predictions are consistent with observations pumices provide quantitative constraints on conduit flow conditions and mass discharge rate these concepts are applied to two plinian eruptions vesicularity values for the bishop tuff long valley caldera require a mass discharge rate between 108 and 109 kg s 1 vesicularity variations during plinian phase 1 of the minoan eruption santorini are explained by the conduit radius increasing from about 30 m to 120 m both cases require large decompression rates in the eruption conduit suggesting that flow pressures were close to lithostatic values

ascent driven crystallisation of dacite magmas at mount st helens 1980 1986 we introduce a novel scheme that enables natural silicic glasses to be projected into the synthetic system qz ab or h2o in order to relate variations in volcanic glass chemistry to changing pressure p and temperature t conditions in the sub volcanic magma system by this means an important distinction can be made between ascent driven and cooling driven crystallisation under water saturated or undersaturated conditions in samples containing feldspar and a silica phase quartz or tridymite quantitative p t estimates of the conditions of last equilibrium between crystals and melt can be made formation of highly silicic melts i e 77 wt sio2 is a simple consequence of the contraction of the silica phase volume with decreasing pressure such that high silica glasses can only form by crystallisation at low pressure resorption of quartz crystals appears to be a further diagnostic feature of decompression crystallisation groundmass and inclusion glasses in dacites from the 1980 1986 eruption of mount st helens volcano wa span a wide range in sio2 68 80 wt anhydrous the compositions of the least evolved sio2 poor inclusions in amphibole phenocrysts record entrapment of silicic liquids with 5 4 wt water corresponding to a water saturation pressure of 200 mpa at 900 c the compositions of more evolved higher sio2 plagioclase hosted inclusions and groundmass glasses are consistent with extensive ascent driven fractional crystallisation of plagioclase oxide and orthopyroxene phenocrysts and microlites to low pressures during this polybaric crystallisation plagioclase phenocrysts trapped melts with a wide range of dissolved water contents 3 5 5 7 wt magmas erupted during the plinian phase of the 18 may 1980 eruption were derived from a large reservoir at depths of 6 km subsequent magmas ascended to varying depths within the sub volcanic system prior to extraction from glass chemistry and groundmass texture two arrest levels have been identified at depths of 0 5 1 and 2 4 km a single dome sample from february 1983 contains groundmass plagioclase tridymite and quartz testifying to temperatures of at least 885 c at 11 mpa these shallow storage conditions are comparable to those in the cryptodome formed during spring 1980 the corresponding thermal gradient 0 2 c mpa 1 is consistent with near adiabatic magma ascent from 8 km we argue that the crystallisation history of mount st helens dacite magma was largely a consequence of decompression crystallisation of hot magma beyond the point of water saturation this challenges the conventional view that phenocryst crystallisation occurred by cooling in a large magma chamber prior to the 1980 1986 eruption because the crystallisation process is both polybaric and fractional it cannot be simulated directly using isobaric equilibrium crystallisation experiments however calculation of the phase proportions in water saturated 910 15 c experiments by rutherford et al 1985 over the pressure range 220 125 mpa reproduces the crystallisation sequence and phenocryst modes of mount st helens dacites from 18 may 1980 by allowing for the effects of fractional versus equilibrium crystallisation entrained residual source material and small temperature differences between nature and experiment phase compositions can also be matched to the natural samples we conclude that decompression of water saturated magma may be the dominant driving force for crystallisation at many other silicic volcanic centres

combined bromine and chlorine release from large explosive volcanic eruptions a threat to stratospheric ozone large explosive volcanic eruptions inject gases aerosols and fine ashes into the stratosphere potentially influencing climate emissions of chlorine cl and bromine br from such large eruptions play an important role for catalytic destruction of ozone in the stratosphere but hitherto the global effects of simultaneous catastrophic release of volcanic br and cl into the stratosphere have not been investigated the br release from 14 large explosive eruptions throughout nicaragua covering an entire subduction zone segment in the past 70 ka was determined with petrologic methods melt inclusions in volcanic phenocrysts were analyzed using a new optimized synchrotron x ray fluorescence microprobe set up single eruptions produced br outputs of 4 600 kt giving an average br emission of 27 kt per eruption using the assumption that 10 of the emitted halogens reach the stratosphere the average br and cl loading to the stratosphere would be 3 ppt and 1500 ppt respectively which together would account for 185 of the preindustrial equivalent effective stratospheric cl loading we thus conclude that many large tropical volcanic eruptions had and have the potential to substantially deplete ozone on a global scale eventually forming future ozone holes

constraints of hydrothermal and magmatic zircon on the origin of the yaogangxian tungsten deposit southern china abstract the yaogangxian tungsten deposit located in the central nanling range is a well known vein type tungsten deposit and has been mined for centuries this study focuses on the morphology geochronology and geochemistry of zircon crystals from wolframite bearing quartz veins and coexisting alkali feldspar granite to better understand the source of ore forming materials and the exact timing of tungsten mineralization all zircon grains separated from the muscovite alkali feldspar granite and the wolframite bearing quartz veins show core to rim structure the overgrowth rims of the zircon grains from the muscovite alkali feldspar granite and the wolframite bearing quartz veins have crystallization ages of 133 4 1 3 ma and 133 7 1 3 ma whereas the relict cores have ages of 155 3 1 6 ma and 154 8 1 6 ma respectively the ages of the cores are identical to the crystallization age of the hosting yaogangxian biotite monzogranite thus these cores were derived from the biotite monzogranite whereas the overgrowth rims should have crystallized during the intrusion of muscovite alkali feldspar granite and wolframite bearing quartz veins the geochemical consanguinity and similar ages of the muscovite alkali feldspar granite and the ore veins suggest that they were both formed from the highly fractionated granitic magma in an extensional setting this highly fractionated granitic melt might be extracted from the biotite monzogranitic mush in a long surviving deep seated magma chamber

volcanic geology and eruption frequency sao miguel azores six volcanic zones comprise sao miguel the largest island in the azores all are quaternary in age except the last which is partly pliocene from west to east the zones are 1 the trachyte stratovolcano of sete cidades 2 a field of alkali basalt cinder cones and lava flows with minor trachyte 3 the trachyte stratovolcano of agua de pau 4 a field of alkali basalt cinder cones and lava flows with minor trachyte and tristanite 5 the trachyte stratovolcano of furnas and 6 the nordeste shield which includes the povoacao caldera and consists of alkali basalt tristanite and trachyte new radiocarbon and k ar ages augment stratigraphic data obtained during recent geologic mapping of the entire island and provide improved data to interpret eruption frequency average dormant intervals for the past approximately 3000 years in the areas active during that time are about 400 years for sete cidades 145 for zone 2 1150 for agua de pau and 370 for furnas however the average dormant interval at sete cidades increased from 400 to about 680 years before each of the past two eruptions and the interval at furnas decreased from 370 to about 195 years before each of the past four eruptions eruptions in zone 4 occurred about once every 1000 years during latest pleistocene and early holocene time none has occurred for about 3000 years the povoacao caldera truncates part of the nordeste shield and probably formed during the middle to late pleistocene calderas formed during latest pleistocene time at the three younger stratovolcanoes in the sequence outer agua de pau between 46 and 26 5 ka sete cidades about 22 ka inner agua de pau 15 2 ka and furnas about 12 ka normal faults are common but many are buried by holocene trachyte pumice most faults trend northwest or west northwest and are related to the terceira rift whose most active segment on sao miguel passes through sete cidades and zone 2 a major normal fault displaces nordeste lavas 150 250 m and may mark the location of an ancestral terceira rift recent seismicity e g in the 1980s generally has been scattered but some small earthquake swarms have occurred beneath the north eastern flank of agua de pau

the october 1902 plinian eruption of santa maria volcano guatemala abstract the october 1902 eruption of santa maria volcano guatemala was one of the largest this century it was preceded by a great earthquake on april 19 centered at the volcano as well as numerous other major earthquakes the 18 20 hour long plinian eruption on october 25 produced a column at least 28 km high reaching well into the stratosphere the airfall pumice deposit covered more than 1 2 million km2 with a trace of ash and was only two meters thick at the vent white dacitic pumice dark gray scoriaceous basalt with physically and chemically mixed intermediate pumice and loose crystals of plagioclase hornblende hypersthene biotite and magnetite make up the juvenile components of the deposit lithic fragments are of volcanic plutonic and metamorphic origin the plinian deposit is a fine grained crystal rich single pumice fall unit and shows inverse grading mapping of the deposit gives a volume of 8 3 km3 within the one mm isopach crystal concentration studies show that the true volume erupted was at least 20 km3 equivalent to 8 5 km3 of dense dacite and that 90 of the ejecta was less than 2 mm in diameter the plinian volume eruption rate averaged 1 2 105 m3s 1 and the average gas muzzle velocity of the column exceeded 270 ms 1 a total of 8 3 1018 j of energy were released by the eruption a knowledge of both theoretically derived eruption parameters and contemporary information allows a detailed analysis of eruption mechanisms this eruption was the major stratospheric aerosol injection in the 1902 1903 period however mid to low latitude northern hemisphere temperature deviation data for the years following the eruption show no significant temperature decrease this may be explained by the sulfur poor nature of dacite magmas suggesting that volatile composition rather than mass of volatiles is the controlling parameter in climatic response to explosive eruptions