sulfur diffusion in basaltic melts abstract we measured the diffusion coefficients of sulfur in two different basaltic melts at reduced conditions i e in the sulfide stability field temperatures from 1225 c to 1450 c pressures of 0 5 and 1 gpa and water concentrations of 0 and 3 5 wt although each melt is characterized by slightly different sulfur diffusion coefficients the results can be combined to create a general equation for sulfur diffusion in anhydrous basalts d 2 19 10 4 exp 226 3 58 3 r t where d is the diffusion coefficient in m2s 1 the activation energy is in kj mol 1 r is the gas constant and t is the temperature in k sulfur diffusion in basalts with 3 5 wt water is a factor of three to seven higher than in anhydrous melts and can be described by d 5 91 10 7 exp 130 8 82 6 r t at the conditions of this study the pressure does not measurably affect sulfur diffusion sulfur diffusion in dry basaltic melts is one order of magnitude higher than sulfur diffusion in dry andesitic and dacitic melts whereas sulfur diffusion in hydrous basaltic and andesitic melts is within the same order of magnitude when compared to the diffusivity of other volatile species in nominally dry basaltic melts sulfur diffusion appears to be two times lower than co2 diffusion and two orders of magnitude lower than h2o diffusion

experimental characterization of diffusive and soret isotopic fractionation of sulfur in a reduced anhydrous basaltic melt abstract the diffusivity of isotopes of a given element in magmas can be significantly different leading to observable effects on isotope ratios similarly the soret effect or thermal diffusion can also lead to considerable isotopic fractionations seeking to characterize isotope effects accompanying sulfur diffusion in basaltic melts we conducted experiments involving separately both chemical and thermal diffusion at 1350 1500 c and 1 1 5 gpa in contrast to the isotopes of most elements investigated previously ca li mg fe cl no significant isotope fractionations beyond analytical precision were found for sulfur isotope system 32s 33s 34s and 36s in response to thermal or chemical concentration gradients analysis of our run products by secondary ion mass spectrometry sims reveals a near unity minimum diffusivity ratio for 34s 32s 0 in anhydrous basaltic melt at conditions where sulfide species predominate these results suggest that s isotope fractionations by diffusive processes are not important in basaltic melts and therefore need not be considered when interpreting s isotope signatures however we also report potential soret fractionations as large as approximately 1 for 33s 2 1 for 34s 3 8 for 36s and 40 ppm for elemental s with enrichments of s and its heavier isotopes at the colder ends of the thermal gradients

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

pyrometamorphic processes at the magma hydrothermal system interface of active volcanoes evidence from buchite ejecta of stromboli aeolian islands italy pyrometamorphic ejecta erupted during recent paroxysmal explosions and hydrothermally altered volcanic and subvolcanic rocks from stromboli volcano aeolian islands italy were studied by combined polarizing microscopy electron microprobe scanning electron microscope x ray diffraction transmission electron microscope and whole rock inductively coupled plasma optical emission spectrometry mass spectrometry analysis the pyrometamorphic ejecta are compositionally heterogeneous at the macroand micro scale and are classified as buchites that is glass coupled with a high temperature low pressure modal mineralogy three distinct facies i e cordierite plagioclase mullite plagioclase palisade and tridymite clinopyroxene are recognized among the buchites whose bulk rock chemistry is compatible with aluminousto silica rich protoliths abundant mineral growth e g plagioclase palisades and clinopyroxene coronae occurs at the contact between the ejecta and the crystal rich host shoshonitic basalt which typically coats the pyrometamorphic blocks mineral constraints pseudoporphyritic microstructures plagioclase relict phenocrysts and major and trace element compositions strongly support the origin of the buchite ejecta as hydrothermally altered rocks from thevancori edifice a period of activity spanning 410 kyr which underwent high temperature low pressure contact metamorphism in the uppermost magmatic system of an active island arc volcano such as stromboli volcanic and subvolcanic rocks usually undergo alteration processes induced by acid sulphate hydrothermal systems the circulation of acidic fluids results in leaching of the stromboli rocks in the upper part of the volcano edifice and depending on the ph temperature and exposure time to the hydrothermal fluids production of different alteration facies the hydrothermally altered stromboli rocks show facies consistent with argillic to silicic alteration containing abundant hydrous sulphate and hydroxy sulphate minerals such as the alunite group minerals hexahydrite millosevichite pickeringite and kieserite the hydrothermally altered wall rocks heated by contact with the basaltic magma of the feeder dyke system of stromboli can easily undergo pyrometamorphic processes inducing partial melting and subsolidus crystallization of the volcanic protoliths this results in the development of buchite rocks at the magma hydrothermal system interface

flotation mechanism of sulphide melt on vapour bubbles in partially molten magmatic systems abstract the motion of dense fe rich immiscible sulphide liquids is generally supposed to be dominated by gravitational settling in crustal magma chambers however they may become buoyant by attachment to low density vapour bubbles to form compound drops possibly contributing to the upward transfer of sulphur and transition metals in degassing magma bodies here using numerical models we consider constraints on the flotation of compound drops and find a wide range of morphologies that would be expected to be capable of migrating through magmatic systems including both melt and mush dominated domains but also some situations where the compound drops will spontaneously separate to allow the vapour to rise while the sulphide phase is sequestered in the mush the stability of compound drops is empirically related to a function f b o m v m s m s 1 b o s v s m s m s 1 b o v where m v and s denote silicate melt vapour and sulphide liquid is surface tension n m 1 and bo is the bond number over a range of plausible conditions in magmas f bo must exceed values of 3 to 4 for capillary forces to overcome buoyancy forces tending to pull them apart using published thermodynamic models for vapour and sulphide solubility in silicate melts we show that in many magmas the second boiling of vapour occurs synchronously with the saturation of sulphide liquid increasing the potential for coupling of vapour and sulphide droplets diffusive coarsening produces mm sized bubbles within 100 500 years generating enough buoyancy to trigger the migration of compound drops during compaction driven expulsion of interstitial melt compound drops can pass through constrictions between crystals in mush the flotation of sulphide vapour aggregates is likely to occur in crustal magma reservoirs and provides a feasible mechanism for the removal of sulphide liquid from crystal mushes promoting its ability to participate in the generation of magmatic sulphide and porphyry copper deposits emissions of the metals during volcanic eruptions and even the remobilization of chalcophile metals sequestered in deep arc cumulates to generate porphyry cu au deposits

unusual lapilli tuff ejecta erupted at stromboli during the 15 march 2007 explosion shed light on the nature and thermal state of rocks forming the crater system of the volcano abstract textural and mineralogical study of high temperature angular blocks erupted during the stromboli explosion of 15 march 2007 was used to make inferences on the nature and thermal state of rocks forming the subsurface of the volcano summit crater terrace the studied ejecta consist of lapilli tuff that formed as a result of the transformation and high temperature induration sintering of the basaltic scoriae lapilli and ash originally accumulated as loose tephra during the current activity of the volcano the main processes leading to the tephra transformation were investigated through microstructural observations mineral and glass analyses sem eds and emp analyses investigations revealed that subsolidus reactions and partial melting of the tephra occurred at temperatures higher than 600 c and under variable fo 2 conditions from qfm to hm buffering curves in some blocks evidence of high t reheating and partial melting at the expense of secondary hydrothermal minerals was also observed in order to track the subsolidus reheating history of the basaltic pyroclasts a detailed study of the pseudomorphic phases and reactions after olivine driven by iron oxidation under high t conditions was performed the observed mineralogical transformation suggests that the lapilli tuff material originating from the burial of tephra routinely accumulated by persistent strombolian explosions within the crater terrace were in some cases altered by the circulation of acidic fluids and were in any case reheated due to isotherm rise forced by high heat flux and gas streaming delivered by the underlying magma system it is worth noting that the ejection of these unusual volcanic lithotypes was possible because a few days before the 15 march 2007 event the craters were clogged with lapilli tuff material that slid into the crater bottom between 7 and 9 march findings of this study suggest that the scattered permanently active vents and shallow conduits of stromboli are surrounded sideways and underneath the crater terrace by a fairly large volume of high temperature rocks with variable degree of compaction sintering up to partially melted such a spectrum of rock types is in good agreement with the conceptual model of prominent thermal zoning all around sideway and upwards the active magmatic system we speculate that continuous migration upwards of isotherms led to transformation and partial melting of the normal strombolian tephra

dark inclusions in allende leoville and vigarano evidence for nebular oxidation of cv3 constituents dark lithic inclusions are known to occur in several cv3 chondrites we report petrologic chemical and oxygen isotopic data on examples from allende leoville and vigarano the allende inclusions comprise a petrographic sequence ranging from a type which contains chondrules and refractory inclusions and resembles cv3 or co3 chondrites to a type which contains porous aggregates of iron rich olivine oxygen isotopic compositions correlate with the sequence chondrule rich inclusions have compositions similar to the host meteorite bulk values whereas olivine aggregate rich inclusions have more 16o depleted compositions chemical compositions on the other hand do not correlate with the petrographic sequence the dark inclusions are all systematically enriched in iron and depleted in potassium and sodium relative to their host meteorites the inclusions appear to be fragments of cv3 parent bodies which were processed to different degrees prior to their incorporation as clasts into allende leoville and vigarano the processing homogenized olivine compositions presumably through heating and also involved oxygen exchange with 16o poorer surroundings either parent body metamorphism or nebular heating might have produced the petrographic and isotopic sequences however the most 16o depleted inclusions also have layered silicate rims surrounding them which are better attributed to gas solid reactions than parent body processes in particular andradite is abundant in the rims which implies that the rims grew under conditions significantly more oxidizing than those likely to have occurred on a cv3 parent body at least part of the processing therefore appears to have taken place prior to final accumulation of the material when the fragments were dispersed in the nebula the evidence for coupled oxidation and 16o depletion in the nebula suggests that other features of the cv3 group such as the oxidized and reduced subgroups ferrous rims on forsteritic olivines and coarse grained rims on chondrules may have been established by similar gas solid reactions prior to the final assembly of the meteorites

the structure dynamics and chemical composition of noneruptive plumes from mount st helens 1980 1988 abstract from may 1980 to september 1988 more than 1000 fixed wing aircraft flights were made with a correlation spectrometer to measure the sulfur dioxide flux from mount st helens volcano these flights also provided valuable data on the structure and dynamics of noneruptive plumes emanating from mount st helens during 1980 and part of 1981 an infrared spectrometer was also used to measure carbon dioxide emission rates at distances up to 25 km from mount st helens plume widths can range up to 20 km or more with width thickness ratios from 3 to about 30 maximum sulfur dioxide concentrations in these plumes depend on wind speed and are typically under 5 ppm and usually 1 ppm or less close examination of the plume data reveals that the characteristics of quiescent plumes from mount st helens are strongly affected by certain meteorological conditions such as thermal and wind stratification in the troposphere as well as by the topography of the volcano

insights into the dynamics of mafic magmatic hydromagmatic eruptions from volatile degassing behaviour the hverfjall fires iceland abstract the style and intensity of hydromagmatic activity is governed by a complex interplay between the relative volumes of magma and water that interact their relative viscosities the depth of subsurface explosions the substrate properties and the vent geometry fundamental questions remain however regarding the role of magmatic vesiculation in determining the dynamics of magma water interaction mwi petrological reconstructions of magmatic degassing histories are commonly employed to interpret the pre and syn eruptive conditions during dry magmatic eruptions but the application of similar techniques to hydromagmatic activity has not yet been fully explored in this study we integrate glass volatile measurements s cl h2o and co2 with field observations and microtextural measurements to examine the relationship between degassing and eruptive style during the hverfjall fires fissure eruption iceland here coeval fissure vents produced both dry magmatic jar ba sholar scoria cone complex and variably wet hydromagmatic hverfjall tuff ring activity generating physically distinct pyroclastic deposits with contrasting volatile signatures matrix glass volatile concentrations in hydromagmatic ash 883 172 1 ppm s 0 45 0 03 1 wt h2o 20 ppm co2 are consistently elevated relative to magmatic ash and scoria lapilli 418 93 1 ppm s 0 12 0 48 1 wt h2o co2 below detection and overlap with the range for co erupted phenocryst hosted melt inclusions 1522 127 1 ppm s 165 27 1 ppm cl measurements of hydromagmatic glasses indicate that the magma has degassed between 17 and 70 of its initial sulfur prior to premature quenching at variably elevated confining pressures by comparing volatile saturation pressures for both magmatic and hydromagmatic glasses and how these vary through the eruptive stratigraphy we place constraints on the conditions of mwi crucially our data demonstrate that the magma was already vesiculating when it encountered groundwater at depths of 100 200 m and that the external water supply was sufficient to maintain mwi throughout the eruption with no significant vertical or lateral migration of the fragmentation surface we propose that development of an in vent water sediment slurry provides a mechanism through which the elevated confining pressures of 1 6 2 6 mpa or up to 6 mpa accounting for uncertainty in co2 below analytical detection could be maintained and buffered throughout the eruption whilst enabling vertical mixing and ejection of fragmented juvenile and lithic material from a range of depths importantly these results demonstrate that the volatile contents of hydromagmatic deposits provide valuable records of 1 the environment of mwi e g groundwater versus surface water vertical migration of the fragmentation level and 2 the state of the magma at the time of fragmentation and quenching we further suggest that the volatile content of tephra glasses provides a reliable alternative or additional indicator of a hydromagmatic origin particularly for reduced ocean island basalts where late stage volatile saturation and degassing s h2o occurs over a pressure range relevant to typical mwi environments

temperature dependence of sulfide and sulfate solubility in olivine saturated basaltic magmas abstract the sulfur concentration at pyrrhotite and anhydrite saturation in primitive hydrous basaltic melt of the 2001 2002 eruption of mt etna was determined at 200 mpa t 1050 1250 c and at log fo2 from fmq to fmq 2 2 fmq is fayalite magnetite quartz oxygen buffer at 1050 c au sample containers were used a double capsule technique using a single crystal olivine sample container closed with an olivine piston embedded in a sealed au80pd20 capsule was developed to perform experiments in s bearing hydrous basaltic systems at t 1050 c pyrrhotite is found to be a stable phase coexisting with melt at fmq fmq 0 3 whereas anhydrite is stable at fmq 1 4 fmq 2 2 the s concentration in the melt increases almost linearly from 0 12 0 01 to 0 39 0 02 wt s at fes saturation and from 0 74 0 01 to 1 08 0 04 wt s at anhydrite saturation with t ranging from 1050 1250 c the relationships between s concentration at pyrrhotite and or anhydrite saturation mgo content of the olivine saturated melt t and log fo2 observed in this study and from previous data are used to develop an empirical model for estimating the magmatic t and fo2 from the s and mgo concentrations of h2o bearing olivine saturated basaltic melts the model can also be used to determine maximum s concentrations if fo2 and mgo content of the melt are known the application of the model to compositions of melt inclusions in olivines from mt etna indicates that the most primitive magmas trapped in inclusions might have been stored at log fo2 slightly higher than fmq 1 and at t 1100 1150 c whereas more evolved melts could have been trapped at t 1100 c these values are in a good agreement with the estimates obtained by other independent methods reported in the literature

illness and elevated human mortality in europe coincident with the laki fissure eruption grattan j durand m taylor s illness and elevated human mortality in europe coincident with the laki fissure eruption in volcanic degassing geological society special publication 213 oppenheimer c pyle d m and barclay j eds geological society london special publications 410 414 2003

correlations between eruption magnitude so2 yield and surface cooling about the book humans have long marvelled at and feared the odorous and colourful manifestations of volcanic emissions and in some cases have harnessed them for their economic value the degassing process responsible for these phenomena is now understood to be one of the key factors influencing the timing and nature of volcanic eruptions moreover the surface emissions of these volatiles can have profound effects on the atmospheric and terrestrial environment and climate even more fundamental are the relationships between the history of planetary outgassing differentiation of the earth s interior chemistry of the atmosphere and hydrosphere and the origin and evolution of life this book provides a compilation of 23 papers that investigate the behaviour of volatiles in magma the feedbacks between degassing and magma dynamics and the composition flux and environmental atmospheric and climatic impacts of volcanic gas emissions

ftir remote sensing of fractional magma degassing at mount etna sicily abstract the chemical composition of volcanic gas emissions from each of the four summit craters of mount etna was measured remotely in may 2001 using a fourier transform infrared ftir spectrometer operated on the upper flanks of the volcano the results reveal constant hci hf ratio but distinct so2 hc1 and so2 hf ratios in the emitted gases which in the light of melt inclusion data for etna basalts can be interpreted in terms of escape of gases from partially and variably degassed magma at different depths beneath the summit gases released from the three main summit craters bocca nuova voragine and northeast had an identical composition controlled by bulk degassing of a single magma body that had previously lost c 25 0 of its original sulphur the similar gas composition at all three main craters suggests that these are connected to a central conduit system that branches at relatively shallow depth measurements of the bulk volcanic plume on the same day c 7 km downwind show that degassing from these craters dominated the total gas output of the volcano and that no significant chemical evolution occurred within the plume over a time scale of c 12 min weaker gas emissions from the southeast crater were comparatively depleted in so2 so2 hc1 and so2 hf ratios a factor of two lower implying that this crater is fed either by a separate conduit or by a branch of the central conduit whose geometry favours solubility controlled volatile fractionation still lower so2 hc1 and so2 hf ratios measured for residual degassing of a lava flow erupted from the southeast crater verify the lower solubility and earlier escape of sulphur compared to halogens at etna fractional magma degassing is also implied by strong chemical contrasts between the bulk volcanic plume and fissure gas emissions measured during the july august 2001 flank eruption these results highlight the ability of ftir spectrometry to detect fine spatial and temporal variations in magma degassing processes and thereby constrain models of shallow plumbing systems introduction magmas contain dissolved volatiles h20 co2 s c1 f etc with differing solubility behaviom which gradually reach a saturation pressure and exsolve into a separate gas phase bubbles during magma ascent and crystallization this volatile phase plays a central role in magmatic and volcanic processes e g anderson 1975 and its chemical composition changes from depth to the surface according to the pressure controlled solubility behaviour of each volatile species but also as a function of the dynamics of magma supply and ascent sparks 2003 this volume in fact gas bubbles may rise with either the same velocity as surrounding magma allowing continuous gas melt equilibration and single step bulk gas emission at the surface or with a higher velocity thereby reaching the surface independently of the parental magma batch e g sparks 1978 vergniolle jaupart 1986 in the latter case chemical equilibrium between gas and magma may be inhibited sustained high gas fluxes in excess of lava production on basaltic volcanoes such as etna and stromboli typically require a separated bubble flow and in the long term convective renewal of volatile rich magma from depth francis

transient processes in stromboli s shallow basaltic system inferred from dolerite and magmatic breccia blocks erupted during the 5 april 2003 paroxysm we describe the mineralogy geochemistry and mesomicrostructure of fresh subvolcanic blocks erupted during the 5 april 2003 paroxysm of stromboli aeolian islands italy these blocks represent 50 vol of the total erupted ejecta and consist of fine to medium grained basaltic lithotypes ranging from relatively homogeneous dolerites to strongly or poorly welded magmatic breccias the breccia components are represented by angular fragments of dolerites entrapped in a matrix of vesiculated lava like to scoriae crystal rich cr basalt all of the studied blocks are cognates with the cr basalt of the normal strombolian activity or lavas and they are often coated by a few centimeter thick layer of crystal poor cp basaltic pumice erupted during the paroxysm we suggest that they result from the rapid increase of pressure and related subvolcanic rock failure that occurred shortly before the 5 april 2003 explosion when the uppermost portion of the edifice inflated and suffered brecciation as the result of the sudden rise of the gas rich cp basalt that triggered the eruption dolerites and magmatic matrix of the breccias show major and trace element compositions that match those of the cr basalts erupted during normal strombolian activity and effusive events at stromboli volcano dolerites consist of a phenocrysts normally found in the cr basalts and b late stage magmatic minerals such as sanidine an60 28 plagioclase fe mn rich olivines fo68 48 phlogopite apatite and opaque mineral pairs magnetite and ilmenite most of which are never found both in lava flows and scoriae erupted during the persistent explosive activity that characterizes typical strombolian behavior subvolcanic crystallization of the stromboli cr magma leading to slowly cooled equivalents of basalts could result from transient drainage of the magma from the summit craters to lower levels fingering and engulfing of the material that collapsed from the summit crater floor into the shallow basaltic system during the late evening of 28 december 2002 coupled with the short break in the summit persistent explosions between december 2002 and march 2003 permitted the cr magma pockets to solidify as dolerites which were confined to the uppermost portion of the system and thus not involved in the ongoing flank effusive activity crystal size distribution of the basaltic blocks and crystallization of the finer grained 0 1 mm mafic minerals of the dolerites over a time interval of 100 days closely agrees with the above interpretation vesicle filling miarolitic cavities locally found in some dolerites with minerals deposited as vapor phase crystallization is a result of continuous gas percolation through the rocks of the uppermost portion of the volcanic system poorly welded magmatic breccias formed during syn eruptive processes of 5 april 2003 when the paroxysm strongly shattered the shallow subvolcanic system and many dolerite fragments were entrapped in the cr magma in contrast the high degree of welding between the dolerite clasts and the cr basaltic matrix in the strongly welded magmatic breccias provides a snapshot of subvolcanic intrusions of the cr basalt into the dolerite when after a 2 month break in activity cr magmas started to rise again to the summit craters blocks similar to these subvolcanic ejecta of 5 april 2003 were also erupted during previous paroxysms e g 1930 suggesting that changes in the usual strombolian activity e g short breaks in the persistent mild explosions and or flank effusive activity lead to transient crystallization of dolerites in the shallow plumbing system

conditions of magma storage degassing and ascent at stromboli new insights into the volcano plumbing system with inferences on the eruptive dynamics stromboli is known for its persistent degassing and rhythmic strombolian activity occasionally punctuated by paroxysmal eruptions the basaltic pumice and scoria emitted during paroxysms and strombolian activity respectively differ in their textures crystal contents and glass matrix compositions which testify to distinct conditions of crystallization degassing and magma ascent we present here an extensive dataset on major elements and volatiles co2 h2o s and cl in olivine hosted melt inclusions and embayments from pyroclasts emplaced during explosive eruptions of variable magnitude magma saturation pressures were assessed from the dissolved amounts of h2 oa nd co2 taking into account the melt composition evolution both pressures and melt inclusion compositions indicate that 1 ca basaltic melts entrapped in high mg olivines fo89 90 generate stromboli basalts through crystal fractionation and 2 the stromboli plumbing system can be imaged as a succession of magma ponding zones connected by dikes the 7 10 km interval where magmas are stored and differentiate is periodically recharged by new magma batches possibly ranging from ca basalts to basalts with a co2 rich gas phase these deep recharges promote the formation of bubbly basalt blobs which are able to intrude the shallow plumbing system 2 4 km where co2 gas fluxing enhances h2o loss crystallization and generation of crystal rich dense degassed magma chlorine partitioning into the h2o co2 bearing gas phase accounts for its efficient degassing 69 under the open system conditions of strombolian activity paroxysms however are generated through predominantly closed system ascent of basaltic magma batches from the deep storage zone in this situation crystallization is negligible and sulfur exsolution starts at 170 mpa chlorine remains dissolved in the melt until lower pressures only 16 being lost upon eruption finally we propose a continuum in explosive eruption energy from strombolian activity to large paroxysmal events ultimately controlled by variable pressurization of the deep feeding system associated with magma and gas recharges

sulfur diffusion in rhyolite melts diffusion rates for sulfur in rhyolite melt have been measured at temperatures of 800 1100 c water contents of 0 7 3 wt and oxygen fugacities from the quartz fayalite magnetite buffer to air experiments involved dissolution of anhydrite or pyrrhotite into rhyolite melt over time scales of hours to days electron microprobe analysis was used to measure sulfur concentration profiles in the quenched glasses regression of the diffusion data in dry rhyolite melt gives dsulfur 0 05 exp 221 80rt which is one to two orders of magnitude slower than diffusion of other common magmatic volatiles such as h2o co2 and cl diffusion of sulfur in melt with 7 wt dissolved water is 1 5 to 2 orders of magnitude faster than diffusion in the anhydrous melt depending on temperature sulfur is known to dissolve in silicate melts as at least two different species s2 and s6 the proportions of which vary with oxygen fugacity despite this oxygen fugacity does not appear to affect sulfur diffusivity except under extremely oxidizing conditions this result suggests that diffusion of sulfur is controlled by one species over a large range in oxygen fugacity the most likely candidate for the diffusing species is the sulfide ion s2 re equilibration between s2 and s6 in oxidized melts must generally be slow compared to s2 diffusion in order to explain the observed results in a silicic melt undergoing degassing sulfur will tend to be fractionated from other volatile species which diffuse more rapidly this is consistent with analyses of tephra from the 1991 eruption of mount pinatubo philippines and from other high silica volcanic eruptions

detailed record of so2 emissions from pu u o o between episodes 33 and 34 of the 1983 86 erz eruption kilauea hawaii a tripod mounted correlation spectrometer was used to measure so2 emissions from pu u o o vent mid erz kilauea hawaii between episodes 33 and 34 june 13 to july 6 1985 in 24 repose days 906 measurements were collected averaging 38 determinations day measurements reflect 13 of the total 576 hours of the repose and 42 of the bright daylight hours the average so2 emission for the 24 day repose interval is 167 83 t d a total of 4000 tonnes emitted for the entire repose the large standard deviation reflects the puffing character of the plume the overall rate of so2 degassing gently decreased with a zero intercept of 44 58 days and was interrupted by two positive peaks the data are consistent with the gas emanating from a cylindrical conduit of 50 meter diameter and a length of 1700 meters which degasses about 50 of its so2 during 24 days this is in support of the pu u o o model of greenland et al 1987 36 hours before the onset of episode 34 july 5 6 1985 elevated so2 emissions were detected while the magma column was extremely active ultimately spilling over during dome fountaining a mid repose anomaly of so2 emission june 21 22 1985 occurs two days before a sudden increase in the rate of summit inflation on june 24 1985 suggesting magma was simultaneously being injected in both the erz and summit reservoir until july 24 when it was channelled only to the summit reservoir this implies degassing magma is sensitive to perturbations within the rift zone conduit system and may at times reflect these disturbances periods of 7 45 min are detected in the daily so2 emissions which possibly reflect timing of convective overturn in the cylindrical magma body if the 33 34 repose interval is considered representative of other repose periods the erz reposes of jan 1983 jan 1986 erz activity contributed 1 6 105 tonnes of so2 to the atmosphere including summit fuming from non eruptive fumaroles 2 7 105 tonnes so2 28 of the total so2 budget from kilauea between jan 1983 to jan 1986 was contributed by quiescent degassing and the remainder was released during explosive fountaining episodes

water solubility and d h fractionation in the system basaltic andesite h2o at 1250 c and between 0 5 and 3 kbars abstract water solubilities in melt of basaltic andesite composition have been measured in the range 500 to 3000 bars 1200 1250 c the saturation curve obey an empirical relationship very close to the square root of pressure law of hamilton et al hamilton d l burnham c w osborn e f 1964 the solubility of water and effects of oxygen fugacity and water content on crystallisation in mafic magmas j petrol 5 21 39 the best fit is obtained by a power law h 2 o wt ap n p in b where a 0 05 0 01 and n 0 63 the departure from n 0 5 is mainly due to the increasing importance of dissolved molecular water at high pressures hydrogen isotopic fractionation between water vapor and total water dissolved in the melt d v m has been measured at 0 5 2 and 3 kb d v m decreases with pressure from 32 to 20 2 this variation is related to the increase in molecular water proportions relative to hydroxyl group when water solubility increases the variation of the d h ratios in water dissolved in such melts thus appears as a possible indirect measurement of the original oh h 2 o ratio of total dissolved water not subject to variation during quenching as the later is this correlation shows that the d v m isotopic fractionation at very high water vapor pressure tend toward a limit of 16 3 for basic magmas

olivine and sulfur isotopic compositions of the uitkomst ni cu sulfide ore bearing complex south africa evidence for sulfur contamination and multiple magma emplacements the uitkomst complex in northern south africa is host to a ni cu deposit containing a minerable reserve of 2 9 mt massive ore with grades of 2 ni 1 cu and 6 ppm pt pd and an indicated plus inferred resource of 98 mt disseminated ore with grades of 0 6 ni 0 2 cu and 1 ppm pt pd based on similar age and composition to that of the bushveld complex the uitkomst complex is believed by some investigators to be a satellite body of the bushveld complex it has a tubular shape with an exposed surface area of about 0 8 8 km and a thickness of up to 1000 m apparently exploiting the bedding planes of gently dipping footwall sediments that include shale quartzite and dolomite the uikomst complex comprised of stratiform mafic and ultramafic rock units that from base to top include gabbro sulfide mineralized harzburgite unmineralized harzburgite pyroxenite gabbronorite and gabbro the compositions of olivine from different rock units are significantly different olivines from the gabbronorite unit are highly fractionated containing 30 mol fo forsterite mg2sio4 and 300 ppm ni olivines from the underlying pyroxenite and harzburgite units are much more primitive containing 86 91 mol fo abrupt changes in the contents of ni in olivine occur within the pyroxenite unit and between the mineralized and unmineralized harzburgite units the contents of ni in olivine from the unmineralized harzburgite unit are between 2900 and 3600 ppm the contents of ni in olivine from the underlying mineralized harzburgite units are 1500 ppm lower olivines from the lower part of the pyroxenite unit are similar to olivines from the underlying harzburgite unit whereas olivines from the upper part of the pyroxenite unit contain much lower ni 600 ppm numerical modelling suggests that the strikingly different compositions of olivine are related to different parental magmas with different mgo feo ratios and or ni contents the 34s values of the basal gabbro and unmineralized rock units range from 0 9 to 2 6 which are similar to typical mantle values 0 3 in contrast the 34s values of the sulfide ores in the harzburgite units are significantly lower varying between 2 6 and 7 1 the low 34s values of the sulfide ores indicate addition of 34s depleted crustal sulfur the obvious sources of such crustal sulfur are the malmani dolomite and the timebal hill shale that contain pyrite with negative 34s values up to 11 and 18 respectively sulfide saturation in the magma of the mineralized harzburgite units is thought to have resulted from addition of the crustal sulfur the resulting immiscible sulfide liquid droplets were then concentrated in the base of the magma channel some of the sulfide liquid was expelled into the basal gabbro that separated the active magma channel from the footwall quartzite new magma then entered the channel displacing most of the resident magma to form the unmineralized harzburgite the overlying pyroxenite gabbronorite and gabbro units formed either by in situ differentiation of the same magma giving rise to the underlying unmineralized harzburgite or by subsequent emplacement of a more evolved magma

magma decompression rates during explosive eruptions of kīlauea volcano hawaii recorded by melt embayments the decompression rate of magma as it ascends during volcanic eruptions is an important but poorly constrained parameter that controls many of the processes that influence eruptive behavior in this study we quantify decompression rates for basaltic magmas using volatile diffusion in olivine hosted melt tubes embayments for three contrasting eruptions of k lauea volcano hawaii incomplete exsolution of h2o co2 and s from the embayment melts during eruptive ascent creates diffusion profiles that can be measured using microanalytical techniques and then modeled to infer the average decompression rate we obtain average rates of 0 05 0 45 mpa s 1 for eruptions ranging from hawaiian style fountains to basaltic subplinian with the more intense eruptions having higher rates the ascent timescales for these magmas vary from around 5 to 36 min from depths of 2 to 4 km respectively decompression exsolution models based on the embayment data also allow for an estimate of the mass fraction of pre existing exsolved volatiles within the magma body in the eruptions studied this varies from 0 1 to 3 2 wt but does not appear to be the key control on eruptive intensity our results do not support a direct link between the concentration of pre eruptive volatiles and eruptive intensity rather they suggest that for these eruptions decompression rates are proportional to independent estimates of mass discharge rate although the intensity of eruptions is defined by the discharge rate based on the currently available dataset of embayment analyses it does not appear to scale linearly with average decompression rate this study demonstrates the utility of the embayment method for providing quantitative constraints on magma ascent during explosive basaltic eruptions

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

halogen diffusion in magmatic systems our current state of knowledge diffusion of halogens has the potential to influence petrogenetic processes in magma chambers and conduit degassing processes this contribution reviews our current state of knowledge concerning halogen diffusion and the influence of halogens on the diffusion of major elements in silicate melts the addition of halogens to silicate melts at common natural concentration levels will have little effect on the diffusion of major elements however the differences between the diffusivity of water the diffusivities of halogens and the diffusivity of sulfur are significant enough that during melt inclusion entrapment or during rapid bubble or crystal growth diffusive fractionation between water and the halogens and between halogens and sulfur are expected to occur and can influence the compositions of melt inclusions crystals and volcanic gases

sulphur release from flood lava eruptions in the veidivotn grimsvotn and katla volcanic systems iceland book description humans have long marvelled at and feared the odorous and colourful manifestations of volcanic emissions and in some cases have harnessed them for their economic value the degassing process responsible for these phenomena is now understood to be one of the key factors influencing the timing and nature of volcanic eruptions moreover the surface emissions of these volatiles can have profound effects on the atmospheric and terrestrial environment and climate even more fundamental are the relationships between the history of planetary outgassing differentiation of the earth s interior chemistry of the atmosphere and hydrosphere and the origin and evolution of life this book provides a compilation of 23 papers that investigate the behaviour of volatiles in magma the feedbacks between degassing and magma dynamics and the composition flux and environmental atmospheric and climatic impacts of volcanic gas emissions

correlations between so2 flux and long period seismicity at galeras volcano the 14 january 1993 eruption of galeras volcano in colombia which killed six scientists and three tourists1 was followed by a larger eruption on 23 march 19932 both eruptions were preceded by episodes of long period seismicity the source of long period seismic events has been modelled extensively3 8 as the resonance within a fluid filled crack induced by pressure transients in the fluid5 7 here we use the so2 flux from galeras volcano measured remotely to infer the degassing history during the episode of long period events preceding the 23 march eruption so2 flux and long period seismicity have been monitored separately elsewhere to forecast volcanic activity9 13 our results show how the combination and correlation of the two methods can be used to interpret the movement of gases from the magma body to the surface and to monitor the pressure buildup leading to an eruption at explosive volcanoes

volatile heavy metal mobility in silicate liquids implications for volcanic degassing and eruption prediction abstract the volatilization of cd re tl pb sb and te from melts in the system cao mgo al 2 o 3 sio 2 cmas and na 2 o mgo al 2 o 3 sio 2 nmas has been investigated at 0 1 mpa and 1200 1350 c experiments were conducted in air using metal doped melts in pt crucibles analysis of quenched glasses by laser ablation inductively coupled plasma mass spectrometry la icp ms normal to the melt gas interface produced concentration profiles for cd re tl pb sb and te to which a semi infinite one dimensional diffusion model could be applied to extract diffusion coefficients d the melt was also doped with cu zn in mo sn and w but concentration profiles for these metals did not develop in the cmas composition at 1300 c the fastest diffusing element was cd having a log d cd 6 5 0 2 the slowest element was re with log d re 7 5 0 3 diffusivities of sb te pb and tl have intermediate values where log d sb 7 1 0 1 log d te 7 2 0 3 log d pb 7 1 0 2 log d tl 7 0 0 2 cm 2 s in the nmas composition log d re 6 5 0 2 log d sb 6 0 0 2 log d pb 6 1 0 1 log d tl 5 8 0 2 cm 2 s values for cd and te were not determined differences in diffusivity of volatile heavy metal ions to a melt gas interface lead to significant fractionation between these metals in magmas during degassing given the observed differences in cd and re diffusivities in the cmas composition we predict an increase in the normalized cd re ratio in the gas phase with increasing bubble growth rate monitoring of the cd re ratios in aerosols from degassing volcanoes may provide a tool for predicting volcanic eruption

diffusion and redox reactions of sulfur in silicate melts although large scale transport in magmas is usually controlled by convection diffusion of sulfur in silicate melts nevertheless plays a crucial role in the kinetics of various magmatic processes the most important process is probably the degassing of magmas and melts initiated by an oversaturation of the melt with respect to dissolved volatiles such oversaturation can be caused in nature i e by decompression when a magma ascends to the earth surface but the degassing of melts is also of major interest for technical applications e g during fining of melts in industrial glass production the kinetics of volcanic eruptions and the fining of glass melts are basically controlled by the dynamics of bubble nucleation and growth and these properties are strongly affected by the diffusion of volatiles from the melt into bubbles nemec 1980a b sparks et al 1994 muller simon 2011 this volume hence understanding the diffusion of volatiles in melts provides a necessary tool for modeling bubble nucleation and growth however the diffusivities of volatiles such as h2o co2 so2 and h2s in the melt do not only affect the degassing rate they may also cause a fractionation of volatiles between gas phase and melt as well due to different diffusivities for instance in hydrous magmas the diffusion of h2o is usually much faster than co2 and sulfur diffusion baker et al 2005 zhang and ni 2010 so rapid disequilibrium removal of bubbles from the melt may cause an artificial enrichment of some components in the bubbles other processes which may be governed by sulfur diffusion in the melts are the dissolution and precipitation of minerals in glass manufacturing crucial problems are the kinetics of dissolution of the raw materials in the melt batch and of

the effect of sulphur on the glass transition temperature in anorthite diopside eutectic glasses the effect of sulfur dissolved in anorthite diopside eutectic ad glasses on the glass transition temperature tg has been investigated via differential scanning calorimetric measurements dsc and thermogravimetric analysis tga under moderately reducing to oxidizing conditions in a series of ad glasses we have measured the change in tg as a function of s content present as so4 2 hs is also identified to a lesser extent and h2o content the ad glasses investigated have s contents ranging from 0 to 7519 ppm and h2o contents ranging from 0 to 5 3 wt in agreement with previous studies increasing h2o content induces a strong exponential decrease in tg volatile free ad glass has a tg at 758 13 c and ad glass with 5 18 0 48 wt h2o has a tg at 450 11 c the change in tg as a function of h2o is wellreproduced with a third order polynomial function and has been used to constrain tg at any h2o content the effect of s on tg is almost inexistent or towards a decrease in tg with increasing s content for instance at 2 4 wt h2o the addition of s induces a change in tg from 585 10 c with 0 ppm s to 523 3 c with 2365 138 ppm s a further increase in s up to 7239 90 ppm s does not induce a dramatic change in tg measured at 529 2 c the limited effect of s on the glass transition temperature contrasts with recent spectroscopic measurements suggesting that s dissolution as so4 2 groups provokes an increase in the polymerization degree we propose an alternative view which reconciles the spectroscopic evidence with the tg measurements the dissolution of s as so4 2 does not induce the formation of si o si molecular bonding through consumption of available non bridging oxygens nbo but instead we suggest that si o s molecular bonds are formed which are not detectable by dsc measurements but mimic the increase in glass polymerization therefore spectroscopic measurements must be used with caution in order to extract melt physical properties

magma and volatile supply to post collapse volcanism and block resurgence in siwi caldera tanna island vanuatu arc v24c 04 allen s r 2005 complex spatterand pumice rich pyroclastic deposits from an andesitic caldera forming eruption the siwi pyroclastic sequence tanna vanuatu bulletin of volcanology 67

effects of open and closed system oxidation on texture and magnetic response of remelted basaltic glass as part of an experimental and observational study of the magnetic response of submarine basaltic glass sbg we have examined using ion backscattering spectrometry rbs transmission and scanning electron microscopy energy dispersive x ray spectrometry and surface x ray diffraction the textures wrought by the controlled open and closed system oxidation of glasses prepared by the controlled environment remelting and quenching of natural sbg initial compositions with 9 wt feo were melted at 1430 c with the oxygen fugacity buffered at fayalite magnetite quartz melts were cooled at a rate of 200 c min 1 near the glass transition tg 680 c in open system experiments where chemical exchange is allowed to occur with the surrounding atmosphere polished pieces of glass were reheated to temperatures both below and above tg for times 1 5000 h undercooled melts were oxidized at 900 c and 1200 c for 18 and 20 h respectively rbs demonstrates unequivocally that the dynamics of open system oxidation involves the outward motion of network modifying cations oxidation results in formation of a fe ca and mg enriched surface layer that consists in part of ti free nanometer scale ferrites a divalent cation depleted layer is observed at depths 1 m specimens annealed oxidized above tg have magnetizations elevated by 1 2 orders of magnitude relative to the as quenched material this does not appear to be related to the surface oxidation quenched glass closed system i e no chemical exchange between sample and atmosphere exhibits very fine scale chemical heterogeneities that coarsen with time under an electron beam this metastable amorphous immiscibility is the potential source for the nucleation of ferrites with a wide range of ti contents ferrites not anticipated from an equilibrium analysis of the bulk basalt composition

degassing of halogens from basaltic volcanism insights from volcanic gas observations abstract the currently available data set of s cl f abundances in volcanic gas plumes and high temperature fumarolic gas samples from basaltic volcanism is reviewed here in the attempt to derive constraints on the modes of halogen degassing from mafic silicate melts apart from large volcano to volcano variations reflecting remarkable differences in volatile abundances in the source magmas each of the explored volcanoes displays large changes of so2 hcl and so2 hf ratios with the style of volcanic activity with hcl hf staying fairly constant halogen abundances are low and so2 hcl and so2 hf are high when fresh volatile rich magmas sustain degassing as during explosive eruptions at the onset of eruptive cycles or shortly before paroxysmal events low so2 hcl and so2 hf ratios are instead characteristic of late stages of volcanic degassing typically being observed in the concluding stages of basaltic eruptions or during periods of reduced magma supply at persistently degassing volcanoes these observations are taken as evidence of halogens being less keen to enter the gas phase relative to s during degassing of basaltic magmas and quantitatively interpreted in light of a rayleigh type open system degassing model the model though simple quantitatively reproduces the range of volcanic gas compositions observed at basaltic volcanoes worldwide and allows prediction of vapour melt partitioning contrasts of factors 9 and 36 for the volatile couples s cl and s f respectively these predictions require validation from appropriately designed experiments of halogen partitioning between magmatic vapours and silicate melts over a range of p t x conditions

species diffusion in clinopyroxene solid solution in the diopside anorthite system the coupled multicomponent diffusion of the species ca2si2o6 caal2sio6 and mg2si2o6 was determined in diopside crystals in the diopside anorthite di an system at temperatures t of 1110 1260 c and oxygen fugacities fo2 between 1 0 log unit below and above the fayalite magnetite quartz equilibrium fmq 1 diffusion couples were prepared by the seed overgrowth technique element concentration profiles were measured perpendicular to the rim core interface by step scanning profiling with a field emission gun scanning electron microscope feg sem the multicomponent diffusion matrix was solved by fitting its eigenvalues and eigenvectors v to the measured concentration profiles the full diffusion matrix d can be recovered by using the formula d p varlambda p 1 resulting in the following equation d text di an left begin array 20 c 1 00 0 67 0 38 1 00 end array right left begin array 20 c lambda 1 left t right 0 0 lambda 2 left t right end array right left begin array 20 c 1 00 0 67 0 38 1 00 end array right 1 the eigenvalues 1 and 2 represent upper limit values and are described by the following arrhenius type equations lambda 1 left text di an right 10 15 98 pm 1 17 times exp left frac 114 4 pm 32 8 text kj mol rt right lambda 2 left text di an right 10 16 23 pm 1 17 times exp left frac 114 4 pm 32 8 text kj mol rt right where 1 and 2 are the first and second eigenvalue of the diffusion matrix in m2 s 1 r is the gas constant and t is the temperature in k the dominant eigenvalue 1 is one quarter order of magnitude larger than the second eigenvalue 2 the eigenvectors are constant for all experiments inferring that the entire d matrix can be described with the eigenvalues as the only t dependent parameter additionally the derived diffusion data and modeling approach were applied to constrain the duration of magmatic processes recorded in zoned clinopyroxene cpx phenocrysts from a basaltic post plutonic dyke of the tertiary adamello batholiths n italy the results reveal residence times of the overgrown cpx prior to final emplacement in the range of 0 25 1 7 years lower limit values testifying that the data and method can be applied to model cpx diffusion profiles in complex natural cpx

open path ftir spectroscopy of magma degassing processes during eight lava fountains on mount etna in june july 2001 a series of 16 discrete lava fountain paroxysms occurred at the southeast summit crater sec of mount etna preceding a 28 day long violent flank eruption each paroxysm was preceded by lava effusion growing seismic tremor and a crescendo of strombolian explosive activity culminating into powerful lava fountaining up to 500 m in height during 8 of these 16 events we could measure the chemical composition of the magmatic gas phase h2o co2 so2 hcl hf and co using open path fourier transform infrared op ftir spectrometry at 1 2 km distance from sec and absorption spectra of the radiation emitted by hot lava fragments we show that each fountaining episode was characterized by increasingly co2 rich gas release with co2 so2 and co2 hcl ratios peaking in coincidence with maxima in seismic tremor and fountain height whilst the so2 hcl ratio showed a weak inverse relationship with respect to eruption intensity moreover peak values in both co2 so2 ratio and seismic tremor amplitude for each paroxysm were found to increase linearly in proportion with the repose interval 2 6 days between lava fountains these observations together with a model of volatile degassing at etna support the following driving process prior to and during the june july 2001 lava fountain sequence the shallow 2 km magma reservoir feeding sec received an increasing influx of deeply derived carbon dioxide likely promoted by the deep ascent of volatile rich primitive basalt that produced the subsequent flank eruption this co2 rich gas supply led to gas accumulation and overpressure in sec reservoir generating a bubble foam layer whose periodical collapse powered the successive fountaining events the anti correlation between so2 hcl and eruption intensity is best explained by enhanced syn eruptive degassing of chlorine from finer particles produced during more intense magma fragmentation

volatile sulphur and chlorine major and trace element geochemistry of mafic to intermediate tephras from the chilean southern volcanic zone 33 43 s here we present the first systematic investigation of volatile geochemistry along the southern volcanic zone svz of chile holocene olivine hosted melt inclusions in the most mafic tephras sampled from 16 volcanoes along the volcanic front of the svz between 33 s and 43 s were analysed for pre eruptive sulphur chlorine and major element contents these results are combined with trace element compositions of the host whole rocks the highest fractionation corrected gas contents occur in the least degassed melt inclusions from small monogenetic cones of los hornitos cabeza de vaca and apagado from both the transitional and the southern central svz reaching 3 000 g g s and 1 400 g g cl while the lowest abundances of 1 100 g g s and 600 g g cl were found in the central svz at volcan lonquimay volcan llaima and volcan villarrica chlorine co varies with trace element indicators for the degree of melting and or source enrichment such that the lowest cl contents are found in high degree melts from the most depleted mantle sources the size of the volcanic edifices correlates inversely with cl abundances in the melt this could reflect more extensive degassing during ascent through the complex magma plumbing systems beneath the stratovolcanoes or greater dilution during larger degrees of melting of more depleted sources or a combination of these factors compared to other subduction zones the svz melt inclusions exhibit cl and s abundances in the same range as most of those from the central american and those from the marianas arcs

toward a quantitative model for the formation of gravitational magmatic sulfide deposits abstract a preliminary quantitative model for the formation of magmatic sulfide deposits through gravitational sulfide droplet settling is developed the model incorporates thermodynamic consideration of the oversaturation of sulfide liquid from a silicate melt and the coupled growth kinetics and settling dynamics of sulfide droplets the conditions for the sulfide droplets to have enough time to grow and settle to form a sulfide liquid layer at the bottom of a magma chamber are referred to as the necessary criteria for sulfide ore formation simulations are carried out for dry etna basaltic melt because their melt viscosity and sulfur diffusivity have been measured so that the simulations are more realistic rather than parametric furthermore the effects of empirical nucleation rate and condition and of the variation of solubility viscosity and diffusivity have been parametrically evaluated the simulations show that for a given magma containing about 0 1 to 0 3 wt sulfur sulfide melt layer can form for realistic magma body size with cooling time of 1000 yr or more and realistic solubility viscosity and diffusivity the ability of the sulfide melt to collect ore elements depends critically on the diffusivity of individual ore elements when the diffusivity of an ore element is similar to or greater than that of sulfur near equilibrium partitioning is reached when the diffusivity of an ore element is much smaller than that of sulfur which is often the case for trivalent and tetravalent ions the concentration of the element in the sulfide melt would be far below the equilibrium concentration it is hoped that the model will help both researchers and exploration geologists

diffusion of dissolved carbonate in magmas experimental results and applications the diffusivity of dissolved carbonate in sodium aluminosilicate 60 sio 2 30 na 2 o 10 al 2 o 3 and iron free basalt melts was measured by a 14 c thin source tracer technique at conditions of combined high temperature and high pressure ranging from 800 c to 1350 c and 0 5 to 18 kbar for the simple melt and 1350 to 1500 c at 15 kbar for the haplobasalt melt the two melts have similar dissolved carbonate transport properties expressed for the simple system at 0 5 kbar by d carbonate 3 559exp 46 600 rt the pressure dependence at 1200 c is given by d carbonate 4 13 10 7 exp 11 02p rt the activation energy of 46 6 kcal mole is low relative to expected values for small highly charged cations suggesting that the actual diffusing species is a larger carbonate anion this interpretation is supported by the 11 cm 3 mole activation volume which corresponds to twice the molar volume of oxygen anions because the 14 c diffusion gradients conform quite well to a constant diffusivity thin source model there can be no strong dependence of carbonate diffusivity upon dissolved carbonate content at least in the 0 0 2 wt range represented by the experimental profiles carbonate diffusion is markedly different from previously determined systematics for water being 1 2 orders of magnitude slower in granitic magmas and considerably faster in basalts this difference can result in diffusional fractionation of co 2 and h 2 o in magmas which may be most significant in small scale processes such as growth of vapor bubbles and formation of some types of glass inclusions in phenocrysts the new data also place constraints on the rate at which co 2 dominated fluid bubbles can actually grow under more or less isothermal conditions at 10 kbar the growth rate is on the order of 1 mm day depending upon the degree of supersaturation in co 2 when combined with knowledge of initial co 2 contents of magmas and observed characteristics of dispersed bubbles e g in ocean floor basalt glasses the diffusivity data may expedite the reconstruction of magma decompression paths