magmatic precursors to the 18 may 1980 eruption of mount st helens usa perhaps the most difficult task facing volcanologists today is that of distinguishing between low level volcanic restlessness and activity that presages a full scale eruption we illustrate these difficulties by reexamining the sequence of events that led to the 18 may 1980 eruption of mount st helens activity that is often presented as a classic example of early phreatic explosions leading to a magmatic eruption this interpretation is problematic however given the known ascent of juvenile magma to within 250 m of the surface prior to the climactic event reexamination of ash samples from several precursory events shows that small amounts of juvenile material were erupted as early as 28 march 1980 just two weeks after the first seismic signals of reawakening and that the juvenile content of the ash had probably increased by early may the magmatic component of these eruptions was not recognized at the time because of the high crystallinity of the juvenile material a signature of extensive degassing induced crystallization during magma ascent identification of juvenile material in the precursory ash from mount st helens has important implications for initiation of eruptive activity

multiple levels of magma storage during the 1980 summer eruptions of mount st helens wa transitions in eruptive style explosive to effusive sustained to pulsatory are a common aspect of volcanic activity and present a major challenge to volcano monitoring efforts a classic example of such transitions is provided by the activity of mount st helens wa during 1980 where a climactic plinian event on may 18 was followed by subplinian and vulcanian eruptions that became increasing pulsatory with time throughout the summer finally progressing to episodic growth of a lava dome here we use variations in the textures glass compositions and volatile contents of melt inclusions preserved in pyroclasts produced by the summer 1980 eruptions to determine conditions of magma ascent and storage that may have led to observed changes in eruptive activity five different pyroclast types identified in pyroclastic flow and fall deposits produced by eruptions in june 12 july 22 and august 7 1980 provide evidence for multiple levels of magma storage prior to each event highly vesicular clasts have h2o rich 4 5 5 5 wt melt inclusions and lack groundmass microlites or hornblende reaction rims characteristics that require magma storage at p 160 mpa until shortly prior to eruption all other clast types have groundmass microlites ph20 estimated from both h2o bearing melt inclusions and textural constraints provided by decompression experiments suggest pre eruptive storage pressures of 75 40 and 10 mpa the distribution of pyroclast types within and between eruptive deposits can be used to place important constraints on eruption mechanisms fall and flow deposits from june 12 1980 lack highly vesicular microlite free pyroclasts this eruption was also preceded by a shallow intrusion on june 3 as evidenced by a seismic crisis and enhanced so2 emissions our constraints suggest that magma intruded to a depth of 4 km beneath the crater floor fed the june eruption in contrast eruptions of july and august although shorter in duration and smaller in volume erupted deep volatile rich magma if modeled as a simple cylinder these data require a step wise decrease in effective conduit diameter from 40 50 m in may and june to 8 12 m in july and august the abundance of vesicular intermediate to deep clast types in july and august further suggests that this change was effected by narrowing the shallower part of the conduit perhaps in response to solidification of intruded magma remaining in the shallow system after the june eruption eruptions from july to october were distinctly pulsatory transitioning between subplinian and vulcanian in character as originally suggested by scandone and malone 1985 a growing mismatch between the rate of magma ascent and magma disruption explains the increasingly pulsatory nature of the eruptions through time recent fragmentation experiments spieler et al 2004 suggest this mismatch may have been aided by the multiple levels at which magma was stored and degassed prior to these events

tracking magma dynamics by laser ablation la icpms trace element analysis of glass in volcanic ash the 1995 activity of mt etna 1 glass fragments in tephra erupted at mt etna from may to december 1995 have been analyzed by laser ablation icpms the trace element compositional variability of ashes deposited during this interval reveals the presence of discrete magma batches with different crystallization degrees in the shallow plumbing system from may to october a highly crystalline magma is predominant within the conduit with only minor sporadic input of fresh and more primitive magma batches after october new and less evolved magma batches become more prevalent and become progressively homogenized within more evolved resident magma in december ashes closely match the chemistry of the volcanics subsequently erupted till february 1996 this study demonstrates that the trace element characterization of ashes has important implications for volcanic monitoring and is a useful tool for the forecasting of paroxysmal events at mt etna

some aspects of the seismicity associated with the 1982 eruption of el chichon volcano chiapas mexico we review the different phases of the seismicity related to the 1982 eruption of el chichon volcano chiapas mexico the pre eruption seismicity was already anomalous by late 1980 became significant by late 1981 and increased towards 28 march 1982 when the first eruptive event occurred a noticeable feature within the 7 day period of unrest is the occurrence of three earthquake swarms before the devastating explosions of 3 and 4 april 1982 local time the periodicity and appearance of the swarms close to the time of maximum tidal strain suggests a large overpressure in the magmatic system and the triggering of the events by the earth tides the post eruption seismicity occurred mostly in a radius 5 km from the crater and a depth range 11 to 15 km suggesting that this region was a deeper reservoir of the erupted magma

magma degassing buffered by vapor flow through brecciated conduit margins obsidian pyroclasts a common component of rhyolitic tephra preserve a range of volatile contents which has been used to infer syneruptive conditions of magmatic degassing here we show that the textures of obsidian pyroclasts provide information on physical mechanisms of magma flow and degassing along conduit margins obsidian clasts often contain xenoliths sheared bands of lithic powder and textures consistent with magma autobrecciation these features suggest that pyroclastic obsidian primarily forms near conduit walls where magma fragments and reanneals during ascent we use these observations to develop a degassing model for pyroclastic obsidian from the a d 1340 mono craters california eruptions we suggest that degassing was buffered by continual flux of vapor through highly permeable brecciated magma along conduit walls continuous reequilibration of magma with vapor of relatively constant composition not only explains the co 2 h 2 o and d h 2 o data from mono craters pyroclastic obsidian but also requires much lower magmatic co 2 values than the commonly accepted model of closed system degassing taken together the chemical and physical evidence suggests that magma brecciation along conduit walls aids the degassing of ascending rhyolite

the behavior of cu zn and pb during magmatic hydrothermal activity at merapi volcano indonesia abstract understanding the behavior of cu zn and pb in magmatic hydrothermal systems is essential in developing models for the genesis of hydrothermal ore deposits in subduction environments a commonly held view is that the metals originate in magmas of intermediate to felsic composition from which they partition directly into exsolving aqueous fluids in this paper we build on the results of an earlier study in which we showed that fe cu co and ni at merapi volcano indonesia were transferred from a mafic melt to an immiscible sulfide melt and then to a magmatic volatile phase which carried them to the surface here we examine the pathways taken by the volatile phase and the behavior of cu zn and pb in the upper part of the magmatic system beneath merapi volcano based on the composition of a suite of silicate melt inclusions and thermodynamic modeling we show that the mafic melt did not hybridize with the resident felsic melt but instead transferred metals to the latter by exsolving a magmatic volatile phase which dissolved the cu rich sulfide melt and then percolated upwards through the felsic melt enriching it in cu and pb it is this fluid which transported the metals to the surface and potentially also to subsurface environments of ore formation

the stability of an evolving atlantic meridional overturning circulation 1 in this study we propose a generalized stability indicator l for a slowly evolving and quasi steady atlantic meridional overturning circulation amoc which represents a feedback related to the amoc and its associated freshwater transport within the atlantic basin as an improvement from previous indicators for the amoc in equilibrium this generalized indicator does not require a divergence free freshwater transport in the atlantic for a collapsed amoc which enables it to correctly monitor the amoc stability through the amoc hysteresis loop in the coupled atmosphere ocean general circulation models from the simulation the indicator l suggests that the amoc is in a stable regime with single equilibrium under the present day and the last glacial maximum lgm climates however under the present day climate a bering strait bs closure will diminish the freshwater outflow from the north atlantic into the arctic as the amoc collapses resulting in a freshwater convergence in the atlantic basin and making the amoc reside in a stable collapsed state i e the amoc exhibits characteristics of multiple equilibria further analysis shows that the bs effect is much reduced under the lgm climate this generalized indicator l has great implications for paleoclimate studies in understanding the abrupt climate change due to the instability of the amoc

lithium in tektites and impact glasses implications for sources histories and large impacts abstract lithium li abundances and isotope compositions were determined in a representative suite of tektites moldavites muong nong type tektites and an australite ivory coast tektites and bediasites impact related glasses libyan desert glass zhamanshinites and irghizites a glass fragment embedded in the suevite from the ries impact crater and sedimentary materials in order to test a possible susceptibility of li to fractionation during hypervelocity impact events and to de convolve links to their potential parental sources the overall data show a large spread in li abundance 4 7 58 ppm li and 7 li values 3 2 to 26 0 but individual groups of tektites and impact glasses have distinctive li compositions most importantly any significant high temperature li isotope fractionation can be excluded by comparing sedimentary lithologies from central europe with moldavites instead we suggest that li isotope compositions in tektites and impact related glasses are probably diagnostic of the precursor materials and their pre impact geological histories the muong nong type tektites and australite specimen are identical in terms of li concentrations and 7 li and we tentatively endorse their common origin in a single impact event evidence for low temperature rayleigh fractionation which must have operated prior to impact induced melting and solidification is provided for a subset of muong nong type tektites although li isotope variations in most tektites are broadly similar to those of the upper continental crust libyan desert glass carries high 7 li 24 7 which appears to mirror the previous fluvial history of parental material that was perhaps deposited in lacustrine environment or coastal seawater lithium isotopes in impact related glasses from the zhamanshin crater define a group distinct from all other samples and point to melting of chemically less evolved mafic lithologies which is also consistent with their major and trace element patterns extreme shock pressures and the related extreme post shock temperatures alone appear not to have any effect on the li isotope systematics therefore useful information on parental lithologies and magmatic processes may be retrieved from analyses of martian and lunar meteorites moreover lack of significant li depletion in tektites provides further constraints on the loss of moderately volatile elements during the moon forming impact

magmatic hydrothermal evolution and devolatilization beneath merapi volcano indonesia abstract at merapi volcano indonesia explosive eruptions lasting several months result from injections of reduced mafic magmas and are interspersed by periods of lava dome growth and collapse quiescent degassing assimilation of wall rock and fractional crystallization lasting a few years silicate melt inclusions and volcanic gases were analyzed to study processes of magmatic volatile exsolution and volcanic degassing during periods of quiescent degassing at merapi volcanic gases were sampled at merapi in 1994 during a phase of quiescent degassing and in 2006 at the end of a dome growth and collapse explosive eruption silicate melt inclusions were collected and analyzed from lavas and scorias for their major element and volatile components solubility relationships between h 2 o and co 2 in melt inclusions demonstrate that melt was being trapped beneath merapi to depths reaching 19 km host amphibole geobarometry indicates crystallization pressures reaching up to 26 km hence there is evidence of deep pooling and crystallization of magma beneath merapi at appreciable depths using a mass balance model of magmatic volatile exsolution we demonstrate that the magma degassing from 19 km to the surface approaches closed system behavior compared to the bulk magmatic volatiles analyzed in melt inclusions volcanic gases had similar amounts of co 2 were enriched in h 2 o and s and depleted in cl and f we thus propose that the magmatic volatile phase was initially exsolved from the magma as a supercritical fluid and that it subsequently exsolved into a h 2 o cl f rich brine and co 2 s rich vapor according to the h 2 o nacl model brine vapor exsolution occurred at 5 km in depth for a 5 wt nacl 900 c to 1000 c fluid although the presence of h 2 s so 2 and co 2 may cause the supercritical fluid to unmix at greater depths magma at shallower depths exsolved a brine and a vapor directly from the melt the volcanic gases at merapi thus represent the vapor fraction of a magmatic volatile phase as brine ponded below the surface we further suggest that carbon dioxide liberated by the magmatic assimilation of limestone as proposed by other studies fluxed the melt thereby promoting co 2 enrichment of the melt and h 2 o degassing finally we propose that merapi volcanic gases are enriched in sulfur compared to the modeled volatile phase composition because deep reduced mafic magma supplies sulfur to the shallow magmatic plumbing system

210pb 230th and 10be in central indian basin seamount sediments signatures of degassing and hydrothermal alteration of recent origin 1 isotopic 210pb 238u 230th 10be major and trace elements and micromorphological and microchemical data were used to identify recent 100 yrs hydrothermal alteration of a 200 kyr sedimentary record from the flank of a seamount in the central indian basin located at the edge of the 75 30 e fracture zone alteration effects are also reflected in 1 the depleted sedimentary organic carbon 2 dissolution features of radiolarian skeletons 3 the presence of altered minerals such as smectite and zeolites and 4 distinctly different magnetic properties in the altered sediments we interpret a predominant influence of neutral chloride type hydrothermal fluids this is the first report of recently occurring sediment alteration by shallow circulating sub surface fluids along the indian ocean intra plate seamount environment

groundmass crystallization of mount st helens dacite 1980 1986 a tool for interpreting shallow magmatic processes the 1980 1986 eruption of mount st helens volcano provides an unprecedented opportunity to observe the evolution of a silicic magma system over a short time scale groundmass plagioclase size measurements are coupled with measured changes in matrix glass plagioclase and fe ti oxide chemistry to document increasing groundmass crystallinity and thus to better constrain proposed physical models of the post may 18 1980 magmatic reservoir measurements of plagioclase microlite and microphenocryst sizes demonstrate that relatively rapid growth approximately 10 9 cm s of groundmass plagioclase occurred immediately subsequent to may 18 relatively rapid plagioclase growth continued through the end of 1980 at an average rate of 3x10 11 cm s plagioclase growth rates then decreased to 1x10 11 cm s through 1986 changes in groundmass crystallinity are reflected in changes in both matrix glass and plagioclase microphenocryst rim chemistry although the matrix glass composition appears to have remained approximately constant from 1981 1986 after a rapid compositional change from may 18 until the end of 1980 plagioclase microphenocrysts show increasingly more complex zoning patterns with time microphenocryst core compositions are commonly positively correlated with crystal size both of these observations indicate continuous groundmass plagioclase growth through 1986 magmatic temperatures estimated from fe ti oxide pairs are approximately constant through 1981 at eruption temperatures of 930 c and at log fo2 of 10 8 by 1985 1986 oxide temperatures decreased to 870 c chemical and textural changes can be explained by 1 rapid degassing and crystallization in response to the intrusion of magma into a shallow 4 5 km reservoir toward the end of the may 18 1980 eruption 2 continued crystallization at a much reduced rate through 1986 due to slow cooling of the shallow magma reservoir growth rates and consequent chemical changes appear to decrease at the end of 1980 this is coincident with the change in eruption style from explosive eruptions sometimes followed by dome growth to solely extrusive dome building events and can be explained by the expected viscosity increase of both degassing and increasing crystallinity the model of twostage crystallization of magma in a shallow reservoir is consistent with conclusions from gas studies casadevall et al 1983 gerlach and casadevall 1986 a b patterns of crater deformation chadwkck et al 1988 and post 1980 seismicity endo et al 1990 although it does not explain the experimental data of hill and rutherford 1989 on the growth rate of amphibole reaction rims textural measurements on mount st helens dacite can also be used to evaluate crystallization kinetics in silicic magmas systems for which experimental data is almost non existent plagioclase growth rates are 5 10 times slower than estimated plagioclase growth rates in basaltic systems a result consistent with the higher viscosity of a more silicic melt furthermore patterns of textural change both average crystal size and number density are similar to those observed during the 1984 mauna loa eruption by lipman and banks 1987 suggesting that the only modification to the crystallization behavior of plagioclase required in extrapolation from basaltic systems is a moderate decrease in rates such that the rate of crystallization scales with the melt viscosity

magma ascent rates from amphibole breakdown an experimental study applied to the 1980 1986 mount st helens eruptions recent 1980 1986 mount st helens dacites contain the phenocryst assemblage plagioclase amphibole low ca pyroxene magnetite ilmenite and rare high ca pyroxene which indicates that they all originated from an 8 km deep reservoir at 900 20 c with xh2o 0 67 in fluid according to experimental data iron titanium oxide phenocryst compositions indicate that all post may 18 dacitic magmas erupted at 900 20 c except for the final lava extrusion in october 1986 the magma reservoir may have cooled to 866 c by october 1986 amphiboles in the post may 18 1980 magma contain one or more amphibole populations characterized by reaction rims of different thicknesses the development of the amphibole reaction rims in these rocks is a response to water loss from the coexisting melt during an approximately adiabatic ascent from a deep reservoir constant p and t and isothermal decompression experiments show that during a 900 c constant rate decompression from 8 km to the surface no reaction rim develops on amphibole in 4 days a 10 m rim develops in 10 days and a 35 m rim develops in 20 days these experimental data and histograms of rim widths in 1980 1986 mount st helens dacites show that post may 18 eruptions are composed in large part of magma represented by a population of thin rimmed amphiboles magma which ascended from the deep 8 km reservoir in 6 to 10 days the remainder of each sample consists of magma containing amphiboles with reaction rims ranging from 14 to 60 m magma which apparently spent from 8 to 25 days along the conduit margins before being mixed thoroughly millimeter scale into the erupting magma the mixing in a viscous slowly ascending dacite may be enhanced by its flow through partially crystallized magma emplaced earlier and by the evolution and loss of a large vesicle population the experimental calibration of amphibole reaction rim width versus decompression time yields average ascent velocities for post may 18 dacites of about 15 30 m h for magma represented by the thick rimmed amphiboles and from 35 to 50 m hr for magma represented by the thin rimmed crystals an ascent rate of 66 m h is indicated for the may 18 1980 eruption which contains amphiboles with no reaction rims the volume of endogenous dome growth which preceded extrusion of magma newly derived from the deep source region suggests that the effective conduit volume beneath mount st helens in 1981 1982 was equivalent to a cylinder 8 km long and 8 9 m in radius

preliminary experimental determination of the partitioning of lithium between plagioclase crystals of different anorthite contents abstract the role of plagioclase anorthite content in controlling the partitioning of li has been investigated experimentally plagioclase crystals of different anorthite contents were equilibrated with a single plagioclase powder at 1000 c the results show that the partition coefficient of lithium is a strong function of the anorthite content of the plagioclase decreasing by a factor of 3 5 from an 60 to an 80 this has important implications for the interpretation of the distribution of li in plagioclase in natural samples an example of the importance of considering the change in partition coefficient with plagioclase anorthite content is given using published plagioclase li contents in the products of the soufriere hills volcano it is shown that the distribution of li in these plagioclase phenocrysts can be reproduced using a model in which li diffuses into and out of the plagioclase crystals if the change in partition coefficient with an content is accounted for because li diffusion in plagioclase is very rapid the distribution of li in plagioclase crystal rims can record changing conditions during eruption and pyroclastic flow emplacement second to minute timescales

vapor transfer prior to the october 2004 eruption of mount st helens washington dome lavas from the 2004 eruption of mount st helens show elevated li contents in plagioclase phenocrysts at the onset of dome growth in october 2004 these cannot be explained by variations in plagioclase melt partitioning but require elevated li contents in coexisting melt a fact confirmed by measurements of li contents as high as 207 g g in coexisting melt inclusions similar li enrichment has been observed in material erupted prior to and during the climactic may 1980 eruption and is likewise best explained via pre eruptive transfer of an exsolved alkali rich vapor phase derived from deeper within the magma transport system unlike 1980 however high li samples from 2004 show no evidence of excess 210pb 226ra implying that measurable li enrichments may occur despite significant differences in the timing and or extent of magmatic degassing diffusion modeling shows that li enrichment occurred within 1 yr before eruption and that magma remained li enriched until immediately before eruption and cooling this short flux time and the very high li contents in ash produced by phreatomagmatic activity prior to the onset of dome extrusion suggest that vapor transfer and accumulation were associated with initiation of the current eruption overall observation of a high li signature in both 1980 and 2004 dacites indicates that li enrichment may be a relatively common phenomenon and may prove useful for petrologic monitoring of mount st helens and other silicic volcanoes lithium diffusion is also sufficiently rapid to constrain vapor transfer on similar time scales to short lived radionuclides

in situ measurements of plagioclase growth using sims depth profiles of 7li 30si a means to acquire crystallization rates during short duration decompression events numerous petrologic studies have attempted to determine crystal growth rates in volcanic systems through several methods including analyses of crystal size distributions in natural samples and decompression experiments on hydrous magmas experiments have revealed that rim growth on existing crystals will occur under a wide range of decompression conditions and is favored under conditions of low to moderate undercoolings over microlite nucleation which has typically been the focus of decompression induced crystallization studies for this study samples of eruptive clasts were collected from a vulcanian explosion that occurred following the july 12 13 2003 dome collapse of soufriere hills volcano montserrat plagioclase phenocrysts were extracted and examined with secondary ion mass spectrometry sims depth profiling lithium inflection depths within the profiles along with the observed time interval between the peak in the collapse decompression and the explosion that ejected the examined samples were used to calculate the growth rates as a result of magma devolatilization with an average of 8 3 x 10 8 mm s anorthite content of the plagioclase rim growth indicates an average decompression magnitude of 40 mpa inducing an undercooling of 45 c that favors crystal growth over microlite nucleation however variability in the final anorthite contents suggests that not all phenocrysts recorded an equilibrium composition reflecting accurate pressure conditions in such events occurring over short timescales 10 h lithium is a more reliable indicator of decompression induced growth than changing anorthite content due to lithium s rapid diffusivity

using amphibole phenocrysts to track vapor transfer during magma crystallization and transport an example from mount st helens washington abstract in order to evaluate and further constrain models for volatile movement and vapor enrichment of magma stored at shallow levels amphibole phenocrysts from 2004 2005 mount st helens dacite were analyzed for major and selected trace elements li cu zn mn and ree and li isotopes several recent studies have examined fluid mobile trace element abundances in phencryst phases and melt inclusions as a means of tracking volatile movement within subvolcanic magmatic systems and high li contents in plagioclase phenocrysts from 1980 and 2004 mount st helens dacites have been interpreted as evidence that shallow magma was fluxed by a li bearing vapor phase prior to eruption in amphibole phenocrysts zn and mn behave compatibly correlating to feo and al 2 o 3 and show no systematic change with time in contrast li and cu abundances in amphibole vary by up to 3 orders of magnitude 7 6 1140 g g and 1 7 to 94 g g respectively and do not generally correlate with either major or trace elements however they do correlate moderately well r 2 0 54 95 confidence with each other and show systematic temporal variations that are opposite to those observed for plagioclase precluding a simple 1 step diffusion model for li enrichment we propose a diffusion crystallization multi stage dcms model to explain the temporal variations and co variations of li and cu in early erupted dacite october december 2004 profiles of li isotopes in conjunction with measured 7 li intensities and core to rim increases in li concentration are characteristic of li diffusion into the amphiboles consistent with prior models of plagioclase enrichment in amphiboles from 2005 dacite average li and cu concentrations are high 260 660 g g and 29 45 g g respectively and in contrast to amphiboles from earlier erupted dacite correlate weakly with al 2 o 3 wt amphibole al 2 o 3 concentrations are an indicator of pressure with high al amphiboles crystallizing at higher pressures and we suggest that li and cu are partitioned into a fluid phase during ascent and crystallization of the magma so that amphiboles crystallizing at lower pressure have correspondingly lower li and cu concentrations however low li and cu in amphiboles from the dacite at the start of the eruption also require crystallization from a low li cu bearing melt or residence times long enough for amphiboles to re equilibrate with a li cu depleted melt estimated residence times suggest that amphiboles in early dacite could have been present since the end of the 1980 1986 eruptive episode at mount st helens

the diffusion behavior of hydrogen in plagioclase feldspar at 800 1000 c implications for re equilibration of hydroxyl in volcanic phenocrysts to use structural hydroxyl oh concentrations preserved in volcanic phenocrysts to constrain magmatic water contents prior to eruption it is first necessary to understand the diffusive behavior of hydrogen in plagioclase in this study diffusion coefficients for a natural oh bearing plagioclase feldspar ab 66 an 31 or 3 are determined from a series of integrated loss heating experiments performed at 800 1000 c and 1 atm under air nitrogen gas and a co 2 h 2 mixture at the fmq oxygen buffer hydrogen diffusion is found to be isotropic within analytical error using a one dimensional diffusive loss model for an infinite slab the diffusion behavior for hydrogen in plagioclase is described by the diffusion parameters log d 0 1 62 0 31 m 2 s and e a 266 77 kj mol and log d 0 0 97 0 35 m 2 s and e a 278 90 kj mol for experiments only conducted under nitrogen gas nearly complete 83 97 loss of oh from the andesine was achieved in 900 and 1000 c heating series except for the 900 c fmq buffer experiment in which only 64 of the total oh was lost after 21 6 days of cumulative heating the diffusion rates of hydrogen in the plagioclase after 800 1000 c are similar to interpolated diffusion rates for sodium diffusion in an 30 feldspar implying that na and h both diffuse via frenkel defects involving the large cation sites and interstitial ions the diffusion coefficient d values for hydrogen in plagioclase are lower than most reported diffusion data for hydrogen in nominally anhydrous minerals and are most similar to d reported for pure forsterite unaffected by iron redox reactions based on the hydrogen diffusion parameters in this study a 1 mm spherical plagioclase phenocryst experiencing dehydration under lowered water activity during ascent and eruption at 800 c retains 50 of its initial oh concentration after 34 days at 900 and 1000 c a 1 mm phenocryst retains 50 of its initial oh concentration after only 1 3 days and 0 25 day respectively oh concentrations in plagioclase are therefore most indicative of magmatic water contents during the latest stages of ascent and eruption

breadcrust bombs as indicators of vulcanian eruption dynamics at guagua pichincha volcano ecuador vulcanian eruptions are common at many volcanoes around the world vulcanian activity occurs as either isolated sequences of eruptions or as precursors to sustained explosive events and is interpreted as clearing of shallow plugs from volcanic conduits breadcrust bombs characteristic of vulcanian eruptions represent samples of different parts of these plugs and preserve information that can be used to infer parameters of pre eruption magma ascent the morphology and preserved volatile contents of breadcrust bombs erupted in 1999 from guagua pichincha volcano ecuador thus allow us to constrain the physical processes responsible for vulcanian eruption sequences of this volcano morphologically breadcrust bombs differ in the thickness of glassy surface rinds and in the orientation and density of crack networks thick rinds fracture to create deep widely spaced cracks that form large rectangular domains of surface crust in contrast thin rinds form polygonal networks of closely spaced shallow cracks rind thickness in turn is inversely correlated with matrix glass water content in the rind assuming that all rinds cooled at the same rate this correlation suggests increasing bubble nucleation delay times with decreasing pre fragmentation water content of the melt a critical bubble nucleation threshold of 0 4 0 9 wt water exists below which bubble nucleation does not occur and resultant bombs are dense at pre fragmentation melt h2o contents of 0 9 wt only glassy rinds are dense and bomb interiors vesiculate after fragmentation for matrix glass h2o contents of 1 4 wt rinds are thin and vesicular instead of thick and non vesicular a maximum measured h2o content of 3 1 wt establishes the maxi mum pressure 63 mpa and depth 2 5 km of magma that may have been tapped during a single eruptive event more common h2o contents of 1 5 wt suggest that most eruptions involved evacuation of 1 5 km of the conduit as we expect that substantial overpressures existed in the conduit prior to eruption these depth estimates based on magmastatic pressure are maxima moreover the presence of measurable co2 17 ppm in quenched glass of highly degassed magma is inconsistent with simple models of either open or closed system degassing and leads us instead to suggest re equilibration of the melt with gas derived from a deeper magmatic source together these observations suggest a model for the repeated vulcanian eruptions that includes 1 evacuation of the shallow conduit during an individual eruption 2 depressurization of magma remaining in the conduit accompanied by open system degassing through permeable bubble networks 3 rapid conduit re filling and 4 dome formation prior to the subsequent explosion an important part of this process is densification of upper conduit magma to allow repressur ization between explosions at a critical overpressure trapped pressurized gas fragments the nascent impermeable cap to repeat the process

little ice age catastrophic storms and the destruction of a shetland island community abstract subarctic communities are useful bellwethers of human adaptability to climate change previous studies have compared the socio ecological adaptations of culturally comparable but geographically separated communities such as medieval greenland and iceland in the shetland islands during the little ice age lia unusual storminess in the 16th and 17th centuries deposited wind driven sand in the township of broo dunrosssness and on its surrounding estates documents historical records and optically stimulated luminescence osl dated sand layers show the history of deposition and reveal two episodes of sand movement one from the mid 16th century the second from the late 17th or early 18th century artifacts records and stratigraphy suggest broo s inhabitants successfully resisted the 16th century sand incursion but were driven from their homes by the early 18th century adjacent communities embedded in the same socio economic culture survived the same events and remain viable settlements to the present day wind simulations demonstrate that storm conditions are likely to produce markedly lower wind velocities in the area around broo than over the surrounding landscape making it singularly vulnerable to sand inundation in this instance human ingenuity and resilience could not counter the misfortune of location we conclude that in this marginal environment small geographical differences had profound and lasting impact on survivability during an episode of catastrophic environmental change

geochemical evidence for mixing between fluids exsolved at different depths in the magmatic system of mt etna italy abstract a 4 year geochemical survey of some fumaroles at the voragine summit crater of mt etna was performed in combination with synchronous monitoring of peripheral gas emissions at the base of the volcano this was the first geochemical study at mt etna to have included the abundances of ar he and c isotopes once the effects of postmagmatic shallow processes were identified and quantitatively removed the he ar co 2 systematics of the voragine crater fumaroles and peripheral gas emissions described the same degassing path combining the carbon isotope composition with information about noble gases provided evidence that the crater fumaroles are fed from a two endmember mixture composed of a deep member coming from pressures between 200 and 400 mpa depending on time and a shallower one exsolved at 130 mpa similar mixing processes probably also occur in gases from peripheral vents the simultaneous assessment of 13 c co2 and he ar values of crater fumaroles over time has identified simple changes in the mixing proportion between the two endmembers and moreover periods during which the exsolution pressure of the deep fluid increased these periods seem to be linked to pre eruptive phases of the volcano the identified open system degassing processes are indicative of efficient bubble melt decoupling at depth whereas the mixing process requires a convective transfer of the deeply exsolved fluids toward shallower levels of magma where further vapor is exsolved in agreement with the most recent geophysical and petrological data from mt etna these observations allow inferences about a deep portion of the plumbing system 5 to 12 km b s l comprising sill like reservoirs connected by small vertical structures and a main reservoir at 2 3 km b s l that is probably fluxed by magmatic volatiles

lithium isotope fractionation during magma degassing constraints from silicic differentiates and natural gas condensates from piton de la fournaise volcano reunion island abstract recent volcanic products from the piton de la fournaise volcano reunion show pronounced depletion or enrichment in lithium and significant isotopic fractionation related to degassing 1 trachytic pumices from the april 2007 eruption show extreme li depletion 90 and isotopic fractionation 7 li of 21 the depletion of water and volatiles cl f b cs in these samples suggests that li loss occurred in response to degassing which most likely occurred as the small isolated volume of magma underwent extensive differentiation near the surface because the pre degassing composition is relatively well known the composition of the degassed pumice constrains the partition coefficient to 60 v m v m to 1 010 at magmatic temperatures unlike d v m v m does not depend on whether crystallization and degassing occurred successively or concomitantly 2 basaltic samples from the interior wall of the long lived 1998 piton kapor were extensively altered by acidic gas they also show extreme li depletion but barely significant isotopic fractionation 7 li 4 5 suggesting that high temperature leaching of li by volcanic gas does not significantly fractionate li isotopes 3 high temperature 400 325 c gas condensates formed during degassing of the thick lava flow of april 2007 display high li contents 50 100 ppm which are consistent with li being as volatile as zn and sn their isotopically light li signature average of 1 7 is consistent with their derivation from isotopically heavy vapor 13 5 if the factor of isotopic fractionation between condensate and vapor is less than 0 985 a degassing crystallization model accounts for the evolution of trace species which like lithium are volatile but also moderately incompatible

amphibole clinopyroxene and plagioclase melt partitioning of trace and economic metals in halogen bearing rhyodacitic melts

hydrogen isotope investigation of amphibole and glass in dacite magmas erupted in 1980 1986 and 2005 at mount st helens washington in active shallow sub volcanic magma conduits the extent of the dehydrogenation oxidation reaction in amphibole phenocrysts is controlled by energetic processes that cause crystal lattice damage or conditions that increase hydrogen diffusivity in magmatic phases amphibole phenocrysts separated from dacitic volcanic rocks erupted from 1980 to 1986 and in 2005 at mount st helens msh were analyzed for dd water content and fe3 fe2 and fragments of glassy groundmass were analyzed for dd and water content changes in amphibole dd values through time are evaluated within the context of carefully observed volcanic eruption behavior and published petrological and geochemical investigations driving forces for amphibole dehydrogenation include increase in magma oxygen fugacity decrease in amphibole hydrogen fugacity or both the phenocryst amphibole dd value c 57o and 2 wt h2o in the white fallout pumice of the may 18 1980 plinian eruptive phase is probably little modified during rapid magma ascent up an 7 km conduit younger volcanic rocks incorporate some shallowly degassed dacitic magma from earlier pulses based on amphibole phenocryst populations that exhibit varying degrees of dehydrogenation pyroclastic rocks from explosive eruptions in june october 1980 have elevated abundances of mottled amphibole phenocrysts peaking in some pyroclastic rocks erupted on july 22 1980 and extensive amphibole dehydrogenation is linked to crystal damage from vesiculation and pyroclastic fountain collapse that increased effective hydrogen diffusion in amphibole multiple amphibole dd populations in many 1980 pyroclastic rocks combined with their groundmass characteristics e g mixed pumice textures support models of shallow mixing prior to or during eruption as new volatile rich magma pulses blended with more oxidized degassed magma amphibole dehydrogenation is quenched at the top surface of msh dacite lava lobes but the diversity in the ddamph populations in original fresh lava flow surfaces may occur from blending magma domains with different ascent histories in the sub volcanic environment immediately before eruption multi stage open system magma degassing operated in each parcel of magma rising toward the surface whereas the magma below 7 km was a relatively closed system at least to the october 1986 eruption based on the large population of minimally dehydrogenated rim free amphibole in the lavas magma degassing and possibly h isotope exchange with low dd fluids around the roof zone may have accompanied the 1 5 km upward migration of the 1980 magma body the low ddamph c 188 to 122o oxy amphibole phenocrysts in lava spines extruded in may 2005 reflect dehydrogenation as ascending viscous magma degassed and crystallized and fractures that admitted oxygen into the hot solidified lava spine interior facilitated additional iron oxidation

evidence for degassing of fresh magma during the 2004 2008 eruption of mount st helens subtle signals from the hydrothermal system abstract results from chemical and isotopic analyses of water and gas collected between 2002 and 2016 from sites on and around mount st helens are used to assess magmatic degassing related to the 2004 2008 eruption during 2005 the chemistry of hot springs in the breach of mount st helens showed no obvious response to the eruption and over the next few years changes were subtle giving only slight indications of perturbations in the system by 2010 however water chemistry temperatures and isotope compositions d and 18o clearly indicated some inputs of volatiles and heat associated with the eruption but the changes were such that they could be attributed to a pre existing gas depleted magma an increase of 1 5 in the 13c values of dissolved carbon in the springs was noted in 2006 and continued through 2009 a change that was mirrored by a similar shift in 13c co2 in bubble gas emissions these changes require input of a new source of carbon to the hydrothermal system and provide clear evidence of co2 from an undegassed body of magma rising trends in 3he 4he ratios in gas also accompanied the increases in 13c since 2011 maximum rc ra values are 6 4 and are distinctly higher than 5 samples collected between 1986 and 2002 and provide additional evidence for some involvement of new magma as early as 2006 and possibly earlier given the unknown time needed for co2 and he to traverse the system and arrive at the springs

degassing crystallization and eruption dynamics at stromboli trace element and lithium isotopic evidence from 2003 ashes during its 1800 year long persistent activity the stromboli volcano has erupted a highly porphyritic hp volatile poor scoriaceous magma and a low porphyritic lp volatile rich pumiceous magma the hp magma is erupted during normal strombolian explosions and lava effusions while the lp one is related to more energetic paroxysms during the march april 2003 explosive activity stromboli ejected two typologies of juvenile glassy ashes namely highly vesicular lp shards and volatile poor hp shards their textural and in situ chemical characteristics are used to unravel mutual relationships between hp and lp magmas as well as magma dynamics within the shallow plumbing system the mantle normalized trace element patterns of both ash types show the typical arc lava pattern however hp glasses possess incompatible element concentrations higher than lp glasses along with sr and eu negative anomalies hp shards are generally characterized by higher li contents to 20 ppm and lower 7li values 1 2 to 3 8 with respect to lp shards li contents of 7 14 ppm and 7li ranging between 4 6 and 0 9 fractional crystallization models based on major and trace element compositions combined with a degassing model based on open system rayleigh distillation and on the assumption that melt fluiddli 1 show that abundant 30 plagioclase precipitation and variable degrees of degassing can lead the more primitive lp magma to evolve toward a differentiated isotopically lighter hp magma ponding in the upper conduit and undergoing slow continuous degassing induced crystallization this study also evidences that in march 2003 stromboli volcano poured out a small early volume of lp magma that traveled slower within the conduit with respect to later and larger volumes of fast ascending lp magma erupted during the april 5 paroxysm the different ascent rates and cooling rates of the two lp magma batches i e pre and post paroxysm resulted in small but detectable differences in their chemical signatures finally this study highlights the high potential of in situ investigations of juvenile glassy ashes in petrologic and geochemical monitoring the volcanic activity and of li isotopes as tracers of degassing processes within the shallow plumbing system

a 210pb 226ra 230th 238u study of klyuchevskoy and bezymianny volcanoes kamchatka abstract lavas from klyuchevskoy and bezymianny volcanoes kamchatka appear to show a link between the extent of partial melting in their mantle source region and the subsequent degree of fractionation suffered by the magmas during passage through the crust this fractionation may have occurred on timescales significantly less than 1000 years if observed 226 ra excesses largely reflect variable residual porosity in the source melting region unlike most arc lavas those with the highest mgo contents and ba th ratios have the lowest 226 ra excess forward models suggest that those portions of the source which had undergone the greatest addition of u by fluids from the subducting plate also underwent the greatest extents of partial melting at the highest residual porosity at kluchevskoy a change from eruption of high mgo to high al 2 o 3 basaltic andesites around 1945 is reflected in an increase in size of 226 ra excess which seems to require a simultaneous decrease in residual porosity and suggests a rapid changes in the melting regime the eruption of andesites at bezyminanny simultaneous with the eruption of basaltic andesites at klyuchevskoy further suggests that different degree melts produced at differing residual porosity can be formed and extracted from the melt region at the same time thus the melting processes beneath klyuchevskoy and bezyminanny are demonstrably complex they have clearly been influenced by both fluid addition from the subducting plate and extension and decompression beneath the central kamchatka depression finally the 210 pb data are with one or two exceptions in equilibrium with 226 ra suggesting that there was restricted relative magma gas movement in this highly productive magmatic system

textural and chemical variation in plagioclase phenocrysts from the 1980 eruptions of mount st helens usa this study presents major and trace element chemistry of plagioclase phenocrysts from the 1980 eruptions of mount st helens volcano despite the considerable variation in textures and composition of plagioclase phenocrysts distinct segments have been cross correlated between crystals the variation of sr and ba concentration in the melt as calculated from the concentration in the phenocrysts using partition coefficients suggests the cores and rims crystallised from compositionally different melts offset by the plagioclase crystallisation vector in both of these melts sr and ba are correlated despite the abundance of plagioclase in the 1980 dacites we propose that rapid crystallisation of plagioclase upon magma ascent caused a shift in melt composition towards lower sr and higher ba as documented in the rims of the phenocrysts although the cores of the phenocrysts crystallised at relatively shallow depths they preserve the sr and ba of the deep seated melts as they ascended from a deeper region further magma ascent resulted in microlite nucleation which is responsible for a similar shift to even lower sr concentration as observed in the groundmass of post 18 may 1980 samples

geochemical precursors to volcanic activity at mount st helens usa the importance of the interplay between degassing and crystallization before and after the eruption of mount st helens washington usa in 1980 is well established here we show that degassing occurred over a period of decades to days before eruptions and that the manner of degassing as deduced from geochemical signatures within the magma was characteristic of the eruptive style trace element lithium and short lived radioactive isotope lead 210 and radium 226 data show that ascending magma stalled within the conduit leading to the accumulation of volatiles and the formation of lead 210 excesses which signals the presence of degassing magma at depth

hydrothermal evolution of the el teniente deposit chile porphyry cu mo ore deposition from low salinity magmatic fluids the magmatic hydrothermal evolution of the el teniente porphyry cu mo deposit in the central andes in chile is reconstructed based on field relationships scanning electron microscopy cathodoluminescence petrography and fluid inclusion analysis by microthermometry and laser ablation inductively coupled plasma mass spectrometry la icpms three major stages of cu mo mineralization are observed following the barren hydrothermal stage 1 the stage 2 mineralization is characterized by quartz anhydrite stockwork veins and breccias with chalcopyrite bornite and molybdenite both stages 1 and 2 are associated with pervasive potassic alteration quartz anhydrite veins with chalcopyrite bornite and molybdenite associated with phyllic alteration represent stage 3 mineralization stage 4 mineralization linked to the formation of the large braden diatreme is characterized by breccias and rare veins containing a lower temperature assemblage with tourmaline sericite and lesser tennantite bornite and chalcopyrite with late gypsum in local vugs ten fluid types are distinguished in this study based on petrographic and microthermometric criteria such as phase proportions daughter minerals homogenization behavior and salinity the hydrothermal evolution across the stages of cu deposition is characterized by the contraction of a vapor phase originating by phase separation during stage 2 overall cooling of the system at pressures fluctuating around the two phase fluid surface led to a transition from a two phase fluid state dominated by vapor at 410 c and 300 bars in stage 2 to a single phase low salinity fluid derived from cooling and contraction of magmatic vapor to a liquid which dominates during stage 3 mineralization at 350 c and 200 bars copper mineralization mainly formed from the vapor phase and its low salinity liquid derivatives representing a large volume of fluid with an initially high cu content 1 2 0 4 wt cu copper sulfides precipitated upon cooling between 410 and 320 c indicated by a drop of cu na k mn fe ratios of over four orders of magnitude through the evolution of the deposit from stage 2 to stage 4 the highest mo concentrations occur in residual brines resulting from extreme boiling as indicated by concurrent halite saturation recent geochronology cannell 2005 maksaev et al 2004 suggests a relatively long lived magmatic hydrothermal system at el teniente our fluid chemical data show no evidence for major crystal fractionation in a large fluid generating upper crustal magma chamber because cs na k mn fe is constant from pre ore to all syn ore fluids however the initiation of copper mineralization was associated with a 4 to 10 fold increase in the concentration of cu mo li and fe in the inferred main ore forming input fluid compared with pre ore fluids of intermediate salinity and otherwise very similar major and trace element ratios these data indicate that injection from depth of an exceptionally cu mo li and probably also s rich volatile phase into an already actively evolving upper crustal magmatic hydrothermal system triggered the formation of this unusually large and rich copper deposit

two types of volcanic tremor changed with eruption style during 1986 izu oshima eruption volcanic tremor provides clues to magma migration pathways so that tremor source location is expected to be an efficient tool for tracking dynamic behavior of magma in evolution of eruptive activity however clear evidence which connects between temporal variation in volcanic tremor and evolution of eruption style is still lacking we have analyzed volcanic tremors occurred during 1986 izu oshima eruption using recently digitized data the results present a clear link between eruption styles waveform variations and source locations of the tremors moreover precursory activity of the tremors that indicates injection of magma below fissures has been clarified 5 days prior to the fissure eruptions this demonstrates predominance of tremor activity as an adaptive monitoring tool in volcanic eruption

iron and lithium isotope systematics of the hekla volcano iceland evidence for fe isotope fractionation during magma differentiation abstract in this study potential iron isotope fractionation by magmatic processes in the earth s crust was systematically investigated high precision iron isotope analyses by mc icp ms were performed on a suite of rock samples representative for the volcanic evolution of the hekla volcano iceland the whole series of hekla s rocks results from several processes i basaltic magmas rise and induce partial melting of meta basalts in the lower part of the icelandic crust the resulting dacitic magma evolves to rhyolitic composition through crystal fractionation during this differentiation the 56 54feirmm 014 values increase successively from 0 051 0 021 for the primitive dacites to 0 168 0 021 for the rhyolites this increase can be described by a rayleigh fractionation model using a constant bulk fractionation factor between all mineral phases m and the silicate liquid l of 56 54fem l 0 1 ii the basaltic magma itself differentiates by crystal fractionation to basaltic andesite composition no fe isotope fractionation was found in this series all basalts and basaltic andesites have an average 56 54feirmm 014 value of 0 062 0 042 2sd n 9 identical to mean terrestrial basaltic values reported in previous studies this observation is consistent with the limited removal of iron from the remaining silicate melt through crystal fractionation and small mineral melt fe isotope fractionation factors expected at temperatures in excess of 1050 c iii andesites are produced by mixing of basaltic andesite with dacitic melts the iron isotope composition of the andesites is matching that of the basaltic andesites and the less evolved dacites in agreement with a mixing process in the hekla volcanic suite li concentrations are positively correlated with indicators of magma differentiation all hekla rocks have 7li values typical for the upper mantle and demonstrate the absence of resolvable li isotope fractionation during crystal fractionation as a fluid mobile trace element li concentrations and isotopes are a potential tracer of magma fluid interaction at hekla li concentrations and isotope compositions do not indicate any extensive fluid exsolution hence the heavy fe isotope composition of the dacites and rhyolites can be predominately attributed to fractional crystallisation iron isotope analyses on single samples from other icelandic volcanoes torfajokull vestmannaeyjar confirm heavy fe isotope enrichment in evolving magmas our results suggest that the iron isotope composition of highly evolved crust can be slightly modified by magmatic processes

alkali diffusion in plagioclase feldspar tracer diffusion kinetics at 1 atm pressure under dry conditions using 6li 41k and 87rb in four plagioclase feldspars have been determined diffusion profiles were measured using an ion microprobe sims the arrhenius parameters and 2 uncertainties for li k and rb respectively in albite are pre exponential factor log do 3 8 1 0 3 4 1 4 and 5 8 3 8 in m2 s and activation energies 146 14 296 30 and 283 85 kj mol the diffusion rate of k in albite at 700 c and 100 mpa water pressure equals that at 1 atm dry suggesting that diffusion of k is not dependent on water fugacity between 0 004 and 100 mpa the k diffusion rate depends on plagioclase anorthite content and is approximately 20 times slower in labradorite than albite li diffusion rates in albite and anorthite are identical a linear relation between log d for the alkalis measured and their ionic radius squared permits an estimate of cs diffusion kinetics diffusion rates are isotropic or nearly so in albite

partitioning of light lithophile elements during basalt eruptions on earth and application to martian shergottites an enigmatic record of light lithophile element lle zoning in pyroxenes in basaltic shergottite meteorites whereby lle concentrations decrease dramatically from the cores to the rims has been interpreted as being due to partitioning of lle into a hydrous vapor during magma ascent to the surface on mars these trends are used as evidence that martian basaltic melts are water rich mcsween et al 2001 lithium and boron are light lithophile elements lle that partition into volcanic minerals and into vapor from silicate melts making them potential tracers of degassing processes during magma ascent to the surface of earth and of other planets while lle degassing behavior is relatively well understood for silica rich melts where water and lle concentrations are relatively high very little data exists for lle abundance heterogeneity and degassing in basaltic melts the lack of data hampers interpretation of the trends in the shergottite meteorites through a geochemical study of lle volatile and trace elements in olivine hosted melt inclusions from kilauea volcano hawaii it can be demonstrated that lithium behaves similarly to the light to middle rare earth elements during melting magma mixing and fractionation considerable heterogeneity in lithium and boron is inherited from mantle derived primary melts which is dominant over the fractionation and degassing signal lithium and boron are only very weakly volatile in basaltic melt erupted from kilauea volcano with vapor melt partition coefficients 4 wt the observed terrestrial lle partitioning behavior is extrapolated to martian primitive melts through modeling the zoning observed in the shergottite pyroxenes is only consistent with degassing of lle from a martian melt near its liquidus temperature if the vapor melt partition coefficient was an order of magnitude larger than observed on earth the range in lle and trace elements observed in shergottite pyroxenes are instead consistent with concurrent mixing and fractionation of heterogeneous melts from the mantle

antimoniferous vein type mineralization of the berga antiform eastern thuringia germany a fluid inclusion study abstract the antimoniferous vein mineralization in the schleiz and greiz area eastern thuringia are bound to ne sw striking variscan fault zones along the margins of the berga antiform the sb pb zn ores form massive sulfide sulfosalt quartz carbonate veins breccias or stockworks within ordovician and silurian metasedimentary units devonian metabasalts and metagranitoids mineralogical investigations from several sb mines and hard rock quarries near schleiz and greiz germany show that the sb pb zn sulfides are texturally in close association with quartz and carbonates stibnite is the major sb bearing mineral minerals of the sb pb zn sulfide assemblage replace an earlier zn fe as sulfide quartz assemblage quartz i named the ore stage i mineralization stibnite and quartz ii overgrow these early sulfides accounting for the ore stage ii lead dominated sb sulfides e g zinkenite plagionite semseyite represent the ore stage iii phase followed by sphalerite ii galena and quartz iii accounting for ore stage iv fluid inclusion studies on ore and gangue minerals of the different ore stages give insights into the composition and temperature of the mineralizing fluid s primary fluid inclusion assemblages in ore stage ii stibnite and co genetic quartz ii show variable vapor fractions within fluid inclusion assemblages heterogeneous trapping of co2 at constant salinities of fluid inclusions of the same assemblage indicates the influx of a buoyant pure co2 fluid into an aqueous fluid phase the presented data demonstrates the first example of co2 influx into an aqueous fluid identified by fluid inclusion analyses during this ore stage ii a h2o co2 nacl fluid with eq w nacl of 1 to 2 7 at 220 226 c prevails in contrast fluid inclusions in ore stage iii minerals boulangerite contain a homogeneously trapped h2o nacl cacl2 fluid with eq w nacl up to 8 1 at temperatures 146 c ore stage iv minerals sphalerite ii quartz iii contain a homogeneously trapped h2o nacl cacl2 fluid with eq w nacl of 20 and homogenization into the liquid phase at around 120 c fluid inclusion data suggest p t conditions at the onset of mineralization at around 220 c at 0 70 to 0 75 kbar fluid pressure the mechanisms of sb ore precipitation were induced by the influx of co2 fluid cooling quartz ii stibnite boulangerite and late stage mixing with a high salinity fluid resulting in the precipitation of sphalerite ii galena and quartz iii the unique opportunity to analyze fluid inclusions in many different subsequently precipitating ore and gangue minerals enables the reconstruction of the temporal evolution of the sb veins the distinct change of the ore forming processes from the influx of co2 into an aqueous fluid and cooling ore stage i ii to mixing ore stage iii iv as the dominant precipitation mechanisms are also accompanied by a drastic change in the mineralogy from sb sulfides to pb zn sulfides late orogenic granitic intrusions served as a potential heat metal and sulfur source variscan wrench and thrust tectonics and associated metamorphism account for the ore stage i mineralization hydrothermal sb pb zn assemblages ore stages ii iii and iv precipitated during the latest part of the variscan orogeny most likely around the carboniferous permian boundary although fluid composition and formation temperatures of the greiz and schleiz mineralization are on the first view quite similar to those of other variscan sb mineralization the observation of co2 influx and fluid mixing with a high salinity fluid is unique for european sb occurrences

sulphide melt and aqueous fluid saturation in the pge au mineralisation of the skaergaard intrusion evidence from melt inclusions the skaergaard intrusion in east greenland hosts mineralisation of platinum group elements and gold that is characterised by a remarkably low amount of sulphides about 0 02 wt sulphide and a very high metal sulphur ratio here we present the first quantitative analyses of sulphur s copper cu lithium li and other trace elements from melt inclusions in plagioclase to trace their evolution in the magma and to constrain the formation of the mineralisation the concentration of these elements in the melt inclusions varies considerably within each sample the s content in melt inclusions ranges from 165 to 320 ppm in the lower part of the intrusion but increases to 349 512 ppm immediately below the mineralisation interval in the same interval the li content increases from 22 43 to 40 69 ppm and cu ranges from 118 to 1586 ppm with no systematic variations across the mineralisation the li content drops an order of magnitude to 4 7 ppm and s drops to 250 326 ppm we explain these compositional changes as reflecting the magmatic evolution as the result of fractional crystallisation below and coinciding aqueous fluid exsolution and sulphide saturation across the mineralisation normally the s content of basaltic magmas is much higher at sulphide saturation we propose that sulphide saturation is possible nevertheless mostly due to the high cu content and high cu fe in the evolved ferrobasaltic melt resulting in a lowering of the s concentration required for sulphide saturation the relationship between exsolutions of aqueous fluids and sulphides remains unknown

effects of volatile behaviour on dome collapse and resultant pyroclastic surge dynamics gunung merapi 2010 eruption in 2010 gunung merapi central java indonesia generated two violent eruption sequences on 26 october and 5 november culminating in widespread pyroclastic density currents pdcs associated with the destruction of lava domes tephra from pdc deposits were analysed to examine pre dome collapse volatile behaviour and evidence of carbonate assimilation secondary ion mass spectroscopy sims depth profiles of plagioclase phenocrysts reveal that the 7 li 30 si ratios in 26 october products are higher in the glass compared to the crystal indicating a build up of li in the groundmass not observed in the 5 november samples higher li in the groundmass suggests gas accumulation and rapid development of conduit overpressure in the shallow plumbing system prior to the initial 26 october explosion which was only captured through the behaviour of quickly diffusing li and not h 2 o following the explosion induced decompression juvenile magma rapidly ascended in great volume to generate extremely destructive pdcs following subsequent dome collapses particularly on 5 november additionally 26 october tephras contain carbonate grains in the ash component and abundant co 2 within the lava lapilli groundmass glass which supports previous studies indicating assimilation of calc silicate lithologies by the merapi magma at depth in the plumbing system prior to the onset of 2010 activity

isotope fractionation by chemical diffusion between molten basalt and rhyolite abstract experimental diffusion couples were used to study chemical diffusion between molten rhyolite and basalt with special emphasis on the associated fractionation of calcium and lithium isotopes diffusion couples were made by juxtaposing firmly packed powders of a natural basalt suny morb and a natural rhyolite lake county obsidian and then annealing them in a piston cylinder apparatus for times ranging from 0 1 to 15 7 h temperatures of 1350 1450 c and pressures of 1 2 1 3 gpa profiles of the major elements and many trace elements were measured on the recovered quenched glasses the diffusivities of all elements except lithium were found to be remarkably similar while the diffusivity of lithium was two to three orders of magnitude larger than that of any of the other elements measured chemical diffusion of calcium from molten basalt into rhyolite was driven by a concentration ratio of 18 and produced a fractionation of 44ca from 40ca of about 6 because of the relatively low concentration of lithium in the natural starting materials a small amount of spodumene lialsi2o6 was added to the basalt in order to increase the concentration difference between basalt and rhyolite which was expected to increase the magnitude of diffusive isotopic fractionation of lithium the concentration ratio between li doped basalt and natural rhyolite was 15 and the resulting diffusion of lithium into the rhyolite fractionated 7li from 6li by about 40 we anticipate that several other major rock forming elements such as magnesium iron and potassium will also exhibit similarly larger isotopic fractionation whenever they diffuse between natural melts with sufficiently large differences in the abundance of these elements

groundmass crystallisation and cooling rates of lava like ignimbrites the grey s landing ignimbrite southern idaho usa constraining magmatic and eruptive processes is key to understanding how volcanoes operate however reconstructing eruptive and pre eruptive processes requires the ability to see through any post eruptive modification of the deposit the well preserved grey s landing ignimbrite from the central snake river plain provides an opportunity to systematically investigate the post eruptive processes occurring through a single deposit sheet despite overall compositional homogeneity in both bulk and glass compositions the grey s landing ignimbrite does preserve differences in the abundance of li in plagioclase crystals which are strongly associated with the host lithology li abundances in plagioclase from the quickly cooled upper and basal vitrophyres are typically low average 5 ppm n 262 while plagioclase from the microcrystalline interior of the deposit has higher li contents average 33 ppm n 773 given that no other trace elemental parameter in plagioclase varies we interpret the variability in li to reflect a post depositional process groundmass crystallisation of a rhyolite like grey s landing requires 50 crystallisation of sanidine and variable amounts of a silica rich phase quartz tridymite cristobalite and plagioclase to satisfy mass balance we suggest the low affinity of li for sanidine causes migration of groundmass li into plagioclase during crystallisation even within the microcrystalline interior of the deposit the morphology of the groundmass varies the more marginal finer grained regions are dominated by cristobalite as the sio2 rich phase while tridymite and quartz are additionally found in the more slowly cooled coarser grained portions of thick sections of the ignimbrite numerical models of cooling and crystallisation tested against field observations indicate that the groundmass crystallisation occurred relatively rapidly following emplacement a maximum of a few years where the ignimbrite is thickest these numerical models also illustrate that the time at which the potential for rheomorphism ceases either the ignimbrite is a solid glass or 50 crystalline is diachronous across the deposit

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

magma differentiation rates from 226ra 230th and the size and power output of magma chambers we present a mathematical model for the evolution of the 226ra 230th activity ratio during simultaneous fractional crystallization and ageing of magma the model is applied to published data for four volcanic suites that are independently known to have evolved by fractional crystallization these are tholeiitic basalt from ardoukoba djibouti morb from the east pacific rise alkali basalt to mugearite from vestmannaeyjar iceland and basaltic andesites from miyakejima izu bonin arc in all cases 226ra 230th correlates with indices of fractional crystallization such as th and the data fall close to model curves of constant fractional crystallization rate the best fit rates vary from 2 to 6 10 4 yr 1 consequently the time required to generate moderately evolved magmas f 0 7 is of the order of 500 to 1500 yrs and closed magma chambers will have lifetimes of 1700 to 5000 yrs these rates and timescales are argued to depend principally on the specific power output i e power output per unit volume of the magma chambers that are the sites of fractional crystallization equating the heat flux at the epr to the heat flux from the sub axial magma chamber that evolves at a rate of ca 3 10 4 yr 1 implies that the magma body is a sill of ca 100 m thickness a value which coincides with independent estimates from seismology the similarity of the four inferred differentiation rates suggests that the specific power output of shallow magma chambers in a range of tectonic settings covers a similarly narrow range of ca 10 to 50 mw km 3 their differentiation rates are some two orders of magnitude slower than that of the basaltic makaopuhi lava lake hawaii that cooled to the atmosphere this is consistent with the two orders of magnitude difference in heat flux between makaopuhi and the east pacific rise 226ra 230th data for magma suites related by fractional crystallization allow the magma differentiation rate to be estimated and from this the thermal budget of the magma chamber addressed and where an independent measurement of heat flux exists to place constraints on the size of the magma chamber such results have the potential to constrain the likely timescale and size of future eruptions of evolved magmas

nanoscale characterisation of crystal zoning abstract advances in analytical techniques are fundamental to the enhanced understandings of many geological processes zoned volcanic crystals have been analysed by low 5 kv field emission gun electron probe micro analyser feg epma and nanosims to obtain sub micrometre chemical profiles and compared to time of flight sims tof sims and high 15 20 kv epma profiles plagioclase and orthopyroxene crystals have been analysed by feg epma at accelerating voltages of 5 kv providing a spatial resolution step size of 350 nm the resolution of the lowest energy x ray for orthopyroxene crystals using a 30 nm beam and ca 750 nm for plagioclase crystals which at low voltages are unstable and require a 500 nm defocused beam step sizes are comparable in size to interaction volumes analytical protocols are detailed that permit quantitative major and minor element compositions to be acquired at similar precision and accuracy as traditional epma analyses at 15 20 kv nanosims analysis of the same crystals provides a greater spatial resolution of up to 200 nm and allows the measurement of li also the nanosims profiles however cannot currently be quantified the ability to analyse crystals at sub micrometre scales is demonstrated by the good agreement between nanosims feg epma conventional epma and tof sims data feg epma nanosims and tof sims techniques have broad applications within the earth sciences in petrologic studies for example these methods have the ability to analyse small crystals in experimental charges and provide chemical profiles of crystal zoning at a spatial resolution of ca 200 300 nm such profiles are important in crystal forensics and diffusion chronometry studies the implications for the latter application are that timescales of volcanic processes that occur in the days years immediately prior to the eruption can now be studied

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

new insight into explosive volcanic eruptions connecting crystal scale chemical changes with conduit scale dynamics explosive volcanic eruptions may be triggered by processes in the conduit including p t variations volatile loss and crystal growth these unobserved processes may be inferred via textural and chemical examination of eruptive products juvenile clasts were examined from vulcanian explosions of the soufriere hills volcano here we show that secondary ion mass spectrometry sims depth profiling into plagioclase phenocrysts provides a nearly continuous record of magma ascent from chamber to surface via high resolution 10 nm chemical profiles of decompression induced crystal growth changes in lithium concentration allow quantification of crystal growth rates which range from 2 10 8 mm s to 7 10 8 mm s anorthite variations suggest conduit temperature increases of 50 to 100 c assuming contemporaneous overpressures approaching 20 mpa these data demonstrate a new means of constraining conduit conditions preceding explosive volcanic eruptions

partitioning of lithophile trace elements between h 2 o and h 2 o co 2 fluids and topaz rhyolite melt experiments have been conducted with h 2 o and h 2 o co 2 bearing fluids and melts of a cl f and lithophile trace element enriched vitrophyre associated with topaz rhyolite from spor mountain utah the starting material is mildly peraluminous and contains 1 25 wt percent f and 1 500 ppm cl the experiments were conducted with f sub o 2 controlled near ni nio at pressures of 0 5 to 4 kbars and at temperatures of 770 degrees to 950 degrees c fluid melt trace element distribution coefficients d i were calculated for li be b rb sr y zr nb cs ba ce th and u after ion microprobe analysis of starting material and run product glasses the concentration of element i in the fluid was calculated by mass balance and the fluid melt distribution coefficient d i was calculated as ppm by weight of i in fluid ppm by weight of i in melt the partitioning of li rb sr y nb cs and ce between aqueous fluids and melts of topaz rhyolite composition depends strongly on temperature and pressure at 0 5 kbars li rb sr y nb cs and ce concentrate in the fluid at temperatures or 900 degrees c at 2 kbars this same group of lithophile elements except for sr concentrate in the fluid at t or 900 degrees c be b and ba partition in favor of the melt at 0 5 and 2 kbars and at all temperatures of this study in the presence of co 2 free aqueous fluids at 4 kbars and at temperatures of 770 degrees to 950 degrees c all lithophile elements partition in favor of the melt this behavior for lithophile elements mimics that of published data on the partitioning of pb and zn between rhyolitic melts and cl bearing fluids previous studies have demonstrated an equivalent effect of pressure on the distribution of chalcophile trace elements between granitic melts and cl bearing aqueous fluids fluid melt distribution coefficients for the lithophile trace elements are significantly smaller for topaz rhyolite melts in equilibrium with mixed co 2 h 2 o fluids than for topaz rhyolite melts plus co 2 free aqueous fluids there is no evidence for co 2 complexing with the lithophile trace elements at pressures 6 m the data imply that the alkali elements m dissolve into the fluid as mcl 0 complexes and that ce dissolves into the fluid as a cecl 0 3 complex water saturated magmas of topaz rhyolite composition may become differentiated with respect to li cs and rb or ce y and nb if an aqueous fluid phase is evolved and moves through the magma under the influence of a temperature gradient that has a maximum temperature of at least 850 degrees to 900 degrees c

chemically driven growth and resorption of bubbles in a multivolatile magmatic system abstract a carbon dioxide rich fluid from a deep source fluxes in a water rich shallow stored magma and causes a volatile exchange with the melt we carried out hydrothermal experiments on both bubble free and bearing rhyolitic melts in an h 2 o co 2 system to explore the kinetics of chemical re equilibration between the fluid and the magma in the bubble free experiment a water saturated rhyolitic melt was first synthesized at 800 c and 100 mpa and this interacted with a carbon dioxide rich fluid under the same pt conditions for a period of 3 h the melt temporarily became undersaturated upon the volatile exchange as water quickly diffused out of the melt while dissolution of the carbon dioxide was much slower in the bubble bearing experiments the rhyolitic melt was saturated with h 2 o co 2 fluids at 800 c and 100 mpa decompressed to 50 mpa and then kept for up to 5 56 h water rich bubbles were generated by decompression and initially grew but then dissolved in the melt during the retention time this bubble resorption was attributed to water depletion of the melt upon re equilibration with the carbon dioxide rich surrounding fluid such water depletion and resulting bubble resorption are specific to multivolatile systems such as h 2 o co 2 in which the diffusivity and solubility differ among the end components the bubble resorption occurring in this mechanism may explain the genesis of carbon dioxide rich bubble poor obsidian pyroclasts which are considered to have undergone carbon dioxide rich fluid fluxing we also discuss possible consequences of this effect on the bulk magma density the dissolution of a small amount of carbon dioxide may cause expulsion of a much larger amount of water from the hydrous melt which may increase fluid fraction and thus decrease the bulk density by up to 188 and 104 kg m 3 at 100 and 200 mpa respectively for rhyolitic melts we suggest that such a process has the potential to trigger a volcanic eruption