hydrothermal alteration and gold mineralization of the awak mas metasedimentary rock hosted gold deposit sulawesi indonesia abstract the awak mas gold deposit is hosted by phyllites and schists indicated and infered resource are around 38 4 mt at 1 41 g t au equaling to total resource of 1 74 moz gold hydrothermal alteration zones proximal to the gold bearing veins are characterized by the mineral assemblage albite ankerite pyrite and marked by elevated na al ratios and depleted 3 k al ratios these changes are manifested by the replacement of muscovite by albite carbonate alteration with ankerite and siderite occured simultaneous to albitization proximal to the veins distal alteration zones are characterized by chlorite albite in phyllites and albite quartz in schists there are two types of au mineralizing veins in the deposit namely quartz albite ankerite veins and quartz ankerite siderite veins gold occurs in pyrite as sub microscopic inclusions and as fracture fillings with a gold fineness of 925 935 and au ag ratios between 12 1 and 14 1 the aqueous ore fluid was co2 poor and of low salinity with homogenization temperatures between 275 and 325 c fluid inclusion leachates have br cl ratios between 1 0 and 2 0 10 3 and i cl ratios of 5 6 to 18 3 10 5 suggesting that the ore fluids were derived from metamorphic dewatering of organic rich marine sedimentary rocks on the other hand br cl ratios between 1 6 and 3 0 10 3 and i cl ratios from 5 1 to 10 6 10 5 in the non mineralized veins indicate an input of magmatic hydrothermal fluids the results of this study show that the awak mas deposit is an epigenetic orogenic gold deposit which developed at the transition between the epizone and the mesozone

halogen behaviour in subduction zones eclogite facies rocks from the western and central alps abstract we examined f cl br and i concentrations and distributions in eclogite facies rocks and minerals from the western and central alpine ophiolitic zone to determine halogen behaviour in subduction zones and to identify potential host phases that may be able to transport halogens to the deeper mantle analysis was carried out on a range of ophiolitic lithologies peridotites serpentinites metagabbros metabasalts and metasediments to assess the distribution of halogens within deeply subducted oceanic crust halogen abundances in individual mineral phases range from below detection 100 ppm to 1900 ppm for f 1 to 3000 ppm for cl 1 to 11 000 ppb for br and from

liquidus phase relationships on the join anorthite forsterite quartz at 10 kbar with applications to basalt petrogenesis liquidus phase relationships determined on the join caal2si2o8 anorthite mg2sio4 forsterite sio2 quartz at 10 kbar show that increasing pressure causes the forsterite and anorthite primary phase fields to shrink and the spinel enstatite and silica fields to expand the boundary line between the enstatite and forsterite fields and that between the enstatite and quartz fields both move away from the sio2 apex as pressure increases therefore simplified source peridotite would yield simplified basaltic partial melts with decreasing silica as pressure increases as has been found in other studies also increasing pressure decreases the amount of silica enrichment in residual liquids produced by fractional crystallization although anorthite is unstable in simplified peridotite above 9 kbar in the system cao mgo al2o3 sio2 it is an important phase in the fractional crystallization of simplified basalts at 10 kbar and probably also in natural basalts

mantle fluid evolution a tale of one diamond abstract microinclusions analyzed in a coated diamond from the diavik mine in canada comprise peridotitic minerals and fluids the fluids span a wide compositional range between a carbonatitic melt and brine the diamond is concentrically zoned the brine microinclusions reside in an inner growth zone and their endmember composition is k19na25ca5mg8fe3ba2si4cl32 mol the carbonatitic melt is found in an outer layer and its endmember composition is k11na21ca11mg26fe7ba2si10al3p2cl5 the transition in inclusion chemistry is accompanied by a change in the carbon isotopic composition of the diamond from 8 5 in the inner zone to 12 1 in the outer zone we suggest that this transition reflects mixing between already evolved brine and a freshly introduced carbonatitic melt of different isotopic composition the compositional range found in diamond on dvk 294 is the widest ever recorded in a single diamond it closes the gap between brine found in cloudy octahedral diamonds from south africa and carbonatitic melt analyzed in cubic diamonds from zaire and botswana thus all microinclusions analyzed to date fall along two arrays connecting the carbonatitic melt composition to either a hydrous silicic endmember or to a brine endmember this connection suggests that many diamonds are formed from fluids derived form a mantle source not significantly influenced by local heterogeneities

a thermodynamic model for silicate melt in cao mgo al2o3 sio2 to 50 kbar and 1800 c a fully thermodynamic model for mafic melt in cao mgo al2o3 sio2 cmas has been calibrated for calculation of melting equilibria in the pressure range 0 50 kbar it is intended as a preliminary step towards a large system melt model suitable for exploring melting melt loss and crystallization processes in a wide range of natural rock compositions calibration was performed with attention to the model s behaviour in its compositional subsystems as a rigorous test of model structure and parameterization the model is consistent with the latest holland powell thermodynamic data set and can therefore be used to calculate phase relations in conjunction with the many solid phase activity composition models written for the data set model calculations successfully reproduce experimental melting reactions in cmas spinel lherzolite and garnet lherzolite assemblages as well as sapphirine and kyanite bearing assemblages at moderate to high pressure thermodynamically sensitive features such as thermal divides are also recovered however some changes to the model structure will be required before the model can describe the full range of mafic and ultramafic melt compositions known from experiment at low pressures

trace element degassing and enrichment in the eruptive plume of the 2000 eruption of hekla volcano iceland during its last eruption in february 2000 hekla volcano iceland emitted a sub plinian plume that was condensed and scavenged down to the ground by heavy snowstorms offering the unique opportunity to study the chemistry of the gaseous plume released during highly explosive eruptions in this paper we present results on trace element and minor volatile species sulfates chlorides and fluorides concentrations in snow samples collected shortly after the beginning of the eruption the goal of this study is to better constrain the degassing and mobility of trace elements in gaseous emissions trace element volatility at hekla is quantified by means of enrichment factors ef relative to be well known volatile trace elements e g transition metals heavy metals and metalloids are considerably enriched in the volcanic plume of hekla their abundances are governed by the primary magmatic degassing of sulfate and or halide compounds which are gaseous at magmatic temperature their volatility is however slightly lower than in basaltic systems most likely because of the lower magma temperature and higher magma viscosity at hekla more surprisingly refractory elements e g ree th ba and y are also significantly enriched in the eruptive plume of hekla where their apparent volatility is two orders of magnitude higher than in mafic systems in addition ree patterns normalized to the hekla 2000 lava composition show a significant enrichment of hree over lree suggesting the presence of ree fluorides in the volcanic plume such enrichments in the most refractory elements and ree fractionation are difficult to reconcile with primary degassing processes since ree fluorides are not gaseous at magma temperature ree enrichments at hekla could be attributed to incongruent dissolution of tephra grains at low temperature by f rich volcanic gases and aerosols within the eruptive plume this view is supported by both leaching experiments performed on hekla tephra and thermodynamic considerations on ree mobility in hydrothermal fluids and modeling of glass dissolution in f rich aqueous solutions tephra dissolution may also explain the observed enrichments in other refractory elements e g th y and ba and could contribute to the degassing mass balance of some volatile trace elements provided they are mobile in f rich fluids it thus appears that both primary magmatic degassing and secondary tephra dissolution processes govern the chemistry of eruptive plumes released during explosive eruptions

evidence for zn isotopic fractionation at merapi volcano abstract fumarolic gases rocks and condensate samples from merapi volcano indonesia have been analyzed by multiple collector inductively coupled plasma mass spectrometry mc icp ms for their zn isotopic compositions the variation observed expressed as 66 zn 66 zn 66 zn 64 zn sample 66 zn 64 zn jmc 3 049l 1 10 3 ranges from 0 05 to 1 68 the overall reproducibility was found to be better than 0 10 2sd the 66 zn of andesitic rock samples are homogeneous with a mean value of 0 24 which is comparable to previously reported basalt data 66 zn in the woro fumerolic field are ranging from 0 05 to 0 85 and 1 48 to 1 68 in fumarolic gases and condensates respectively upon cooling from 590 to 297 c gaseous zn concentrations decrease and become increasingly enriched in the lighter zn isotopes while the condensates become increasingly enriched in the heavier isotopes gas and condensate isotopic compositions can be explained with a rayleigh condensation model with temperature dependent isotope fractionation factor solid vapor over the 574 c to 297 c range of observations 1000 ln solid vapour c 1 c 2 t c 3 t 2 with c 1 0 c 2 0 88 10 3 c 3 1 00 10 6 and t in degrees kelvin which corresponds to solid vapor of 1 00033 to 1 00153 respectively at the indicated temperatures

dehydration of subducting serpentinite implications for halogen mobility in subduction zones and the deep halogen cycle we investigated the halogen cl f br and i chemistry of serpentinites that record progressive dehydration during subduction from shallow oceanic environments via increased pressure and temperature conditions to complete breakdown of antigorite the aim is to evaluate the relevance of serpentinites for halogen recycling in subduction zones and for deep mantle recharge of these elements the halogen compositions of the analyzed samples indicate input from seawater and sedimentary sources during initial serpentinization of either subducting lithospheric mantle during slab bending or forearc mantle by uprising slab fluids during the first dehydration stage antigorite brucite olivine h2o fluids with high br cl and i cl ratios are released resulting in residual serpentinites with lower br cl and i cl ratios veins associated with this event and with the final antigorite breakdown antigorite olivine orthopyroxene h2o show higher halogen ratios compared to their adjacent wall rocks and they are similar to those found in arc volcanoes f cl and i cl between ca 0 083 1 5 and ca 0 00038 0 0013 respectively all measured deserpentinization samples show a narrow range in 37cl values between 0 42 and 0 92 overlapping the 37cl values of seafloor serpentinites and confirming that no significant cl isotope fractionation occurs during subduction dehydration of serpentinites our findings document the conservative behavior of halogens during subduction mass balance constraints reveal that serpentinites strongly control the halogen chemistry of deep subduction zone fluids and that descent of rock residues after deserpentinization strongly affects the halogen budget of the mantle

the characterisation of saharan dusts and nile particulate matter in surface sediments from the levantine basin using sr isotopes abstract the provenance of sediments within the levantine basin of the eastern mediterranean was studied using 87 sr 86 sr isotopic ratios together with major elements measurements were made on the detrital fraction of surface sediments and the two most important sources of detrital matter to the region saharan dust was characterised by an 87 sr 86 sr isotopic ratio in the range 0 7160 0 7192 there was a small systematic decrease in 87 sr 86 sr from west to east which is interpreted as due to a change in the balance of aeolian source material the nile particulate matter had a 87 sr 86 sr isotopic ratio in the range 0 7057 0 7071 87 sr 86 sr isotopic signatures together with sr concentration were used to calculate the contributions made by saharan dust and nile particulate matter to the surface sediments of the levantine basin it was shown that nile derived sediment was dispersed widely across the levantine basin enabling the area affected by retention of sediment behind the aswan dam to be determined

forsterite diopside spinel liquid equilibria in the system cao mgo al2o3 sio2 at 20 kbar and petrological applications liquidus phase relationships in the caalal sio6 mg2sio4 camgsi2o6 caalsi2o8 portion of the simplified basalt tetrahedron in the cao mgo sio2 al2o3 system have been experimentally determined at 20 kbar pressure the fo diss sp li univariant curve that pierces the fo di an join and meets the fo diss enss sp li invariant point in the basalt tetrahedron extends all the way to and pierces the di fo cats join the limit of the simplified basalt tetrahedron toward the silica undersaturated portion

isotopic and elemental evidence for a relationship between kimberlite and zaire cubic diamonds cubic diamonds from zaire contain fluid inclusions which may record the conditions under which the diamonds formed either in the mantle or in the kimberlite magma which transported them to the surface here we present sr isotope ratios for whole cubic diamonds and abundances of rare earth elements k rb sr and ba for both whole cubic diamonds and the leachings from crushed cubic diamonds the 87sr 86sr ratios of the diamonds range from 0 7038 to 0 7052 which is almost identical to that of mbuji mayi kimberlite1 the chondrite normalized elemental abundance patterns of the diamonds roughly resemble that of kimberlite but show more enrichment in incompatible elements the bulk of the impurities are soluble in water the results of the present study support the genesis of fluid inclusions in diamond in the kimberlite or in the source of kimberlite magma

experimentally determined stability of clinopyroxene garnet corundum in the system cao mgo al 2 o 3 sio 2

runoff control of soil degassing at an active volcano the case of piton de la fournaise reunion island abstract airborne atmospheric and in situ soil gas analyses demonstrate that distal gas leaks are non existent at piton de la fournaise pf despite frequent eruptions airborne traverses made at a constant altitude indicated that no detectable large scale co 2 degassing occurs from the volcano in situ soil gas traverses co 2 4 he 222 rn across the active rift zones the summit crater and the caldera rims show both a lack of positive anomalies and evidence of strong depleted concentrations for he and co 2 with respect to air depletions in soil he is explained by intense rain water infiltration a more unexpected result lies in the very low co 2 concentrations down to 92 ppm in bare soils in the summit region such a depletion was not previously reported and is attributed to considerable basalt weathering operating as the result of huge runoff a model has enabled both the runoff and the co 2 consumption occurring within the basaltic layers to be calculated data obtained are consistent with values expected from large scale erosion models and with the local calculated diffusive flux of co 2 in soils the huge runoff together with the basaltic lithology of the volcano are found to be the main factor controlling the soil gas signatures at pf

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

the other isotopes research avenues based on 36ar 37ar and 38ar the earliest publications on 40 ar 39 ar dating recognized the usefulness of 39 ar 37 ar in providing chemical clues to the species releasing argon during stepped heating while 37 ar measurements are required for interference corrections aside from these essential roles 36 ar 37 ar and 38 ar have other useful applications the dominance of ca as the target nucleus for the production of 38 ar and 36 ar from spallation by cosmic rays has led to the determination of cosmic ray exposure ages from 38 ar 37 ar 38 ar production from cl has an important role in the study of ore minerals containing saline fluid inclusions both in dating and in understanding theirgenesis combining 38 ar 36 arratioswith micro thermometricdeterminations ofsalinity pro vides a way to determine absolute concentrations of noble gases in ore fluids absorption of cosmic ray produced secondary neutrons by 35 cl and 37 cl provides another means to study cosmic ray exposure of meteorites 36 s excesses in meteoritic sodalite provide evidence of now extinct 36 cl in the early solar system surprisingly there is little or no evidence of excess 36 ar beyond what can be accounted for by secondary neutron exposure we have recently devised a method to identify monoisotopic 36 ar from 36 cl decay

age and isotopic relationships among the angrites lewis cliff 86010 and angra dos reis results of a wide ranging isotopic investigation of the unique antarctican angrite lew 86010 lew are presented together with a reassessment of the type angrite angra dos reis ador the principal objectives of this study are to obtain precise radiometric ages initial sr isotopic compositions and to search for the erstwhile presence of the short lived nuclei 146sm and 26al via their daughter products the isotopic compositions of sm u ca and ti were also measured this allows a detailed appraisal to be made of the relations between and the geneology of these two angrites lew proves to be severely contaminated with modern terrestrial pb which is shown to result from terrestrial weathering nevertheless concordant pb pb model ages of pyroxene separates were obtained 2 4 55784 52 ga for lew and 4 55780 42 ga for ador uranium isotopic compositions are normal within error the inferred initial pb isotopic composition is within error of primordial pb as defined by canon diablo troilite because of the extreme upb ratios of both angrites this places an upper limit of 2 ma on the time between volatile element loss of the angrite parent body or its precursor planetesimals and the final crystallization of the angrites as differentiates initial 87sr86sr ratios were found to be indistinguishable in lew ador and the cumulate eucrite moore county the derived initial 87sr86sr for all three meteorites is 0 698970 15 2 a 147sm 143nd isochron for lew was obtained yielding an age of 4 553 34 ga with an initial 143nd144nd of 0 506682 49 2 146sm142nd isotope systematics were also measured anomalies on 142nd arising from extinct 146sm were clearly resolved resulting in an initial 146sm144sm of 0 0071 17 with nd142 2 57 0 62 at the time of isotopic closure both of these sm nd methods imply derivation of lew from a reservoir with chondritic smnd ratio they are also quite consistent with the previously reported systematics for ador overall the age and isotopic similarities between lew and ador are striking it suggests almost simultaneous production on the same asteroid even though recent experimental studies imply that the two are not comagmatic calcium and titanium do not exhibit enrichments in the n rich isotopes in contrast to cais making it unlikely that the angrite parent body is inherently rich in early condensates from the solar nebula no evidence was found for live 26al in lew when combined with the pb pb age and initial 87sr86sr data this firmly excludes 26al being an important heat source in the early solar system heat supplied for for example 1 the differentiation of the angrite and eucrite parent bodies and 2 metamorphism of the chondrite parent bodies must come from some other source the debate over live vs extinct 26al in the earliest solar system remains unresolved by this new data from lew however both the angrite and eucrite parent bodies have extremely low rbsr and high upb ratios compared to the solar nebula therefore the common initial 87sr86sr of 0 698970 can be firmly associated with the u pb angrite age above and the formation of both bodies this enables an absolute chronology of the early solar system to be established based upon 87sr86sr differences the oldest cais are a minimum of 11 4 ma older than the angrites i e 4 569 5 ga the age and isotopic constraints are discussed with respect to current collapse condensation and accretion timescales calculated for the solar nebula

volcanological and petrological evolution of vulcano island aeolian arc southern tyrrhenian sea petrological and geochemical data are reported for volcanic rocks from vulcano island the subaerial volcanism 120 ka to present built up a nw se elongated composite structure affected by two intersecting multistage calderas volcanics older than 20 ka consist mostly of high k calc alkaline hkca to shoshonitic sho mafic rocks these magmas interacted significantly with the continental crust which generated variable sr isotopic ratios 0 70412 0 70520 however a major role was also played by input of parental liquids into the magma chamber which prevented further evolution of the magmas hkca sho and potassic ks rocks formed from 20 to 8 ka display a much larger range of sio2 from shoshonites to rhyolites and higher concentrations of incompatible elements with respect to the previous stage sr isotopic ratios show small variations 0 70448 0 70486 mixing of silicic and mafic liquids and fractional crystallization processes fc were the main evolutionary processes during this stage volcanics younger than 8 ka consist of sho and leucite bearing ks mafic rocks with abundant intermediate and silicic products mafic and intermediate rocks display similar incompatible element abundances and sr isotopic ratios as the previous stage volcanics whereas higher 87sr 86sr 0 70494 0 70583 are observed in some rhyolites these products originated from a complex interplay of fc crustal assimilation and magma mixing processes the most mafic rocks show increasing incompatible element abundances rb sr rb ba mg al mg ca and a decrease in large ion lithophile to high field strength element ratios passing from older hkca sho to the younger sho ks volcanics these variations suggest a shifting of magma sources from a slightly metasomatized asthenosphere fertile peridotite to a more strongly metasomatized lithospheric mantle residual peridotite time related petrological and geochemical variations have been used to develop a model for the evolution of the vulcano plumbing system

acid alteration in the fumarolic environment of usu volcano hokkaido japan abstract the last eruptive activity of usu volcano in 1977 78 involved the development of high temperature 550 710 c fumaroles the gases emitted were h2o rich 95 99 mol with cl s 0 05 0 9 f cl 0 3 0 2 and with rh 2 5 close to the rock buffer feo feo1 5 cooling and oxidation of the high temperature gases resulted in the formation of acidic condensates ph 1 6 that interacted with the wall rock complete leaching of the cations ca na mg al and fe from the primary minerals and matrix glass occurred leaving in place only silica these mobilized cations precipitated as secondary minerals from acidic fluids that circulated in microcracks sem study shows mineral associations reflecting increasing fluid oxidation a al fluorides such as ralstonite namgalf6 h2o pyrite and anhydrite gypsum b an al hydroxide hematite gypsum and amorphous silica or cristobalite c al sulfates such as hydronium alunite h3o al3 so4 2 oh 6 alunite kal3 so4 2 oh 6 amorphous silica cristobalite hematite and anhydrite gypsum d al sulfates al fluorides amorphous silica cristobalite pyrite and anhydrite gypsum a ti oxide a fe mg sulfate and barite are present in minor amounts clay minerals are absent from the observed assemblages primary phenocrysts and matrix glass undergo a complete transformation to silica enriched in fluorine 1 7 wt this fluorine enrichment in the silicified parts of silicates and in silica incrustations suggests that f may play a role in silica mobilization modeling of the cooling of the high temperature gases was performed with the program gasworks the calculations suggest that 66 of the total sulfur from the gases may be lost by deposition as native sulfur at temperatures below 160 c thermochemical modeling of condensate rock interaction using chiller indicates that the cooling of gases was the source of the altering solutions oxidation by atmospheric o2 of the sulfur reduced species in the volcanic gas condensates resulted in their extreme acidification condensate rock interactions produce supersaturation with respect to the following mineral assemblages at 95 c 1 pyrite native sulfur cristobalite barite anhydrite diaspore log m h 2 s aq 2 32 2 cristobalite anhydrite hematite alunite diaspore log m h 2 s aq gypsum replaces anhydrite at t 25 c the calculated mineral assemblages are in agreement with those observed in the field

modelling the growth of natural diamonds abstract in the following article we have reviewed the mineralogical chemical physical and isotopic evidence concerning the growth of coated diamonds and have combined it to produce a comprehensive model for their formation we suggest that the coatings formed during a period of metasomatic activity which preceded the eruption of their host kimberlites ultrapotassic co21bh2o rich fluids resulted from the crystallisation of diamond free kimberlitic magmas intruded into the deep lithosphere the kimberlite magmas were derived from an asthenospheric source which was globally quite uniform in terms of the isotopic composition of carbon and nitrogen 13c and 15n both being close to 5 the fluids produced during crystallisation invaded overlying diamondiferous lithosphere in which different regions could contain diamond populations with different mineralogical isotopic and physical characteristics depending on the history of their source region either intrinsic to their formation or due to reaction with reduced lithosphere the fluids were super saturated with carbon although not to such an extent as to allow for the nucleation of new diamonds when these super saturated fluids encountered older diamonds new and fibrous diamond growth commenced immediately this period of metasomatic activity was followed rapidly by one or more successful kimberlite eruptions which transported the now coated diamonds to the surface in the crust carbonates within hypabyssal facies kimberlites will have 13c values which reflect the deep seated source 5 whereas those within diatreme facies may be more variable due to outgassing of co2 during eruption finally we consider isotope fractionation related to growth we suggest that approaches based on equilibrium are not appropriate to diamonds but rather that it is better to consider the nature and kinetics of the surface reactions leading to growth where diamond growth is very rapid as may be the case for fibrous diamond we propose that there will be no difference in isotopic composition between the fluid and diamond and not the 3 4 13c depletion in the latter predicted by theoretical treatments octahedral diamonds are more problematic since far less is known about their growth conditions however we show in principle how the content and perhaps isotopic composition of nitrogen within a diamond may be controlled by its growth rate we are uncertain whether 13 c would be affected

a noble gas study of cubic diamonds from zaire constraints on their mantle source cubic diamonds are known to contain fluid in submicrometer inclusions which are thought to originate from the mantle beneath the continental crust noble gas elemental and isotopic compositions of sixteen cubic diamonds from zaire are noticeably different from those in morb the 3he 4he ratios observed in the diamonds are 5 12 10 6 and lower than the typical morb value of 1 10 5 the 20ne 22ne ratios 11 and the 21ne 22ne ratios 0 06 show a rough linear correlation and have a slope that is lower than that defined for morb the excess 21ne responsible for the shallower slope may be produced by nuclear reactions either in the source mantle or in the fluid trapped in the diamonds a nucleogenic origin for excess 21ne in the cubic diamonds relative to morb is consistent with their lower 3he 4he ratios positively correlated excesses of 129xe and 131 136xe of up to 10 relative to the atmospheric xe ratios are also observed they are attributed to the decay of extinct 129i and to spontaneous fission of extinct 244pu and or extant 238u respectively xenon isotopic data for the cubic diamonds lie on the same correlation line as that defined for morb in the three isotope diagram of 136xe 130xe vs 129xe 130xe very high 40ar 36ar ratios of up to 35000 are found and are similar to the expected value for the morb source mantle from the 3he 4he and 40ar 36ar ratios some constraints can be made on the origin of cubic diamonds the observed ratios can be explained if the cubic diamonds crystallized in a fluid which separated from a mantle source previously enriched in incompatible elements this is consistent with the previously suggested model for the origin of fluid bearing diamonds the 38ar 36ar ratios in the cubic diamonds are slightly but significantly higher than the atmospheric ratio this high 38ar 36ar ratio may represent the primordial isotopic ratio preserved in the mantle alternatively the observed excess 38ar may be attributed to the nuclear reaction 35cl p 38ar in the fluid phase if the production rate of nucleogenic 38ar is about ten times higher than the previously reported value and the age of the fluid inclusions is quite old 109 yr

constraints on the age and halogen composition of mantle fluids in siberian coated diamonds extension of the ar ar stepped heating technique has been used to characterise the ar halogen cl br i ca and k components in seven coated diamonds from the aikhal kimberlite siberia at least three components have been identified with different ar isotope compositions the major component is characterised by high 40ar 36ar 11 000 and constant 40ar cl 527 22 10 6 br cl 1 74 0 18 10 3 and i cl 22 0 3 4 10 6 indicative of a mantle fluid phase this component is widespread in coated diamonds having been previously reported in samples from africa and canada estimates of halogen abundances in the sub continental mantle based on data from african and siberian coated diamonds are 3 ppm cl 11 ppb br and 0 4 ppb i these low abundances which are in good agreement with values derived for the depleted asthenospheric mantle derived from morb data imply that the upper mantle is 90 degassed of its halogens a second ar component in coated stones is most simply understood by in situ decay of 40k and is consistent with the coat forming event occurring close to the time of host kimberlite eruption 350 380 ma ago a third ar component has a low 40ar 36ar ratio 300 is unassociated with release of k or halogens and is most likely to be atmospheric blank

iridium bearing sublimates at a hot spot volcano piton de la fournaise indian ocean sublimates and incrustations derived upon the cooling of volcanic gases have been collected on various sites piton de la fournaise poas momotombo etna ardoukoba and erta ale they have been analysed for ir and other volatile elements se as cu au ag pb tl by means of instrumental neutron activation analysis inaa and proton induced x ray emission pixe among the investigated volcanoes only piton de la fournaise is found to release detectable amounts of iridium ir in piton de la fournaise sublimates is associated with f minerals this confirms its gaseous transport as a volatile fluoride compound iridium seems to be preferentialy released by hot spot type volcanoes and its detection in piton de la fournaise sublimates provides a positive argument in favour of a volcanic hypothesis to explain the ktb events

the siberian lithosphere traverse mantle terranes and the assembly of the siberian craton abstract the kimberlite fields scattered across the ne part of the siberian craton have been used to map the subcontinental lithospheric mantle sclm as it existed during devonian to late jurassic time along a 1000 km traverse ne sw across the archean magan and anabar provinces and into the proterozoic olenek province 4100 garnets and 260 chromites from 65 kimberlites have been analysed by electron probe major elements and proton microprobe trace elements these data and radiometric ages on the kimberlites have been used to estimate the position of the local paleo geotherm and the thickness of the lithosphere and to map the detailed distribution of specific rock types and mantle processes in space and time a low geotherm corresponding approximately to the 35 mw m2 conductive model of pollack and chapman tectonophysics 38 279 296 1977 characterised the devonian lithosphere beneath the magan and anabar crustal provinces the devonian geotherm beneath the northern part of the area was higher rising to near a 40 mw m2 conductive model areas intruded by mesozoic kimberlites are generally characterised by this higher but still cratonic geotherm lithosphere thickness at the time of kimberlite intrusion varied from ca 190 to ca 240 km beneath the archean magan and anabar provinces but was less 150 180 km beneath the proterozoic olenek province already in devonian time thinner devonian lithosphere 140 km in parts of this area may be related to riphean rifting near the northern end of the traverse differences in geotherm lithosphere thickness and composition between the devonian toluopka area and the nearby mesozoic kimberlite fields suggest thinning of the lithosphere by ca 50 60 km related to devonian rifting and triassic magmatism a major conclusion of this study is that the crustal terrane boundaries defined by geological mapping and geophysical data extended from outcrops in the anabar shield represent major lithospheric sutures which continue through the upper mantle and juxtapose lithospheric domains that differ significantly in composition and rock type distribution between 100 and 250 km depth the presence of significant proportions of harzburgitic and depleted lherzolitic garnets beneath the magan and anabar provinces is concordant with their archean surface geology the lack of harzburgitic garnets and the chemistry of the lherzolitic garnets beneath most of the other fields are consistent with the proterozoic surface rocks mantle sections for different terranes within the archean portion of the craton show pronounced differences in bulk composition rock type distribution metasomatic overprint and lithospheric thickness these observations suggest that individual crustal terranes of both archean and proterozoic age had developed their own lithospheric roots and that these differences were preserved during the proterozoic assembly of the craton data from kimberlite fields near the main archean proterozoic suture the billyakh shear zone suggest that reworking and mixing of archean and proterozoic mantle was limited to a zone less than 100 km wide

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

volatile composition of microinclusions in diamonds from the panda kimberlite canada implications for chemical and isotopic heterogeneity in the mantle abstract in order to better investigate the compositions and the origins of fluids associated with diamond growth we have carried out combined noble gas he and ar c and n isotope k ca and halogen cl br i determinations on fragments of individual microinclusion bearing diamonds from the panda kimberlite north west territories canada the fluid concentrations of halogens and noble gases in panda diamonds are enriched by several orders of magnitude over typical upper mantle abundances however noble gas c and n isotopic ratios 3he 4he 4 6 ra 40ar 36ar 20 000 30 000 13c 4 5 to 6 9 and 15n 1 2 to 8 8 are within the worldwide range determined for fibrous diamonds and similar to the mid ocean ridge basalt morb source value the high 36ar content of the diamonds 1 10 9 cm3 g is at least an order of magnitude higher than any previously reported mantle sample and enables the 36ar content of the subcontinental lithospheric mantle to be estimated at 0 6 10 12 cm3 g again similar to estimates for the morb source three fluid types distinguished on the basis of ca k cl compositions are consistent with carbonatitic silicic and saline end members identified in previous studies of diamonds from worldwide sources these fluid end members also have distinct halogen ratios br cl and i cl the role of subducted seawater derived halogens originally invoked to explain some of the halogen ratio variations in diamonds is not considered an essential component in the formation of the fluids in contrast it is considered that large halogen fractionation of a primitive mantle ratio occurs during fluid melt partitioning in forming silicic fluids and during separation of an immiscible saline fluid

petrochronology and hygrochronology of tectono metamorphic events abstract u th pb petrochronology is based on the incontrovertible fact that the diffusion of radiogenic pb is negligibly small relative to retrograde reaction rates multi element maps demonstrate that patchy textures tightly correspond to u th pb age variations requiring that fluid induced dissolution reprecipitation is the principal cause of pb mobility attempts to model intracrystalline core rim pb zonations as diffusive transport are not legitimate unless genuine bell shaped diffusion profiles in minerals can be documented which happens only exceptionally monazite and zircon intra grain age maps confirm that coupled dissolution reprecipitation and retrogression reactions assisted by fluids control th u pb ages not temperature the chemical zonations observed in many th u bearing mineral chronometers e g monazite allanite xenotime zircon provide petrological constraints linking petrology with textures and the isotope record allows reconstructing entire segments of the p t a x d t history of a rock and its geodynamic environment the dearth of mathematically sound diffusion profiles equally applies to the isotope records of micas and feldspars the tight link between petrology microtextures chemical composition and geochronology also pertains to rb sr and k ar overdetermined multi mineral rb sr isochrons with excess scatter and spatially resolved stepwise release 39ar 40ar results demonstrate ubiquitous correspondence between relict phases and isotopic inheritance many rock forming minerals are highly retentive of sr and ar unless they are obliterated by retrograde reactions the rates of dissolution in fluid controlled reactions are several orders of magnitude faster at upper and mid crustal levels than diffusive reequilibration rates thus as a rule rb sr and k ar chronometers date their own formation accurately establishing p t paths of monometamorphic rocks requires assessing petrologic equilibrium using multivariate thermodynamic software dating complex parageneses of polymetamorphic unequilibrated rocks requires labor intensive disentangling by i qualitative identification of relicts retrogression reactions and chemically open systems by imaging techniques e g cathodoluminescence element maps etc ii microchemical analyses at the m scale quantifying heterochemical disequilibrium phases and assigning them to a p t a x segment iii spatially resolved stepwise release relating the chemical signature of the analyzed mineral to its age k ar and rb sr usually provide a different perspective on the p t evolution of a rock than does th u pb as k rb rich minerals phyllosilicates and especially feldspars mostly form later and react dissolve faster in the retrograde path than u rich accessory phases the present paper reviews these general principles by means of well understood examples both successful and unsuccessful in matching the independently known external constraints

the april 2007 eruption and the dolomieu crater collapse two major events at piton de la fournaise la reunion island indian ocean abstract after 10 years of high activity and 24 eruptions piton de la fournaise pdf produced on april 2 to may 1 2007 one of its most voluminous and intense eruption since at least one century the eruption focused at 590 m elevation in the grand brule on the south east flank of piton de la fournaise 7 km away from summit it was located close to the southern cliff of the grand brule volcano tectonic collapse the rempart du tremblet and to the nearby village called le tremblet and it highly rattled and incommoded the inhabitants there eleven hours after the beginning of the eruption the lava flows reached the sea and created 0 45 km 2 of new land until the end of eruption in the night of april 5 the rock column beneath dolomieu crater started to collapse with a piston like mechanism into the magma chamber forming within less than 24 h the most recent and well documented caldera we report in this paper the chronology of these two related major events in the recent activity of pdf seen by the scientific networks of the volcanological observatory ovpf ipgp and field observations which allowed to back up the scenario of the caldera formation and to quantify these two exceptional episodes

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

volatilization transport and sublimation of metallic and non metallic elements in high temperature gases at merapi volcano indonesia abstract condensates silica tube sublimates and incrustations were sampled from 500 800 c fumaroles and lava samples were collected at merapi volcano indonesia in jan feb 1984 with respect to the magma merapi gases are enriched by factors greater than 105 in se re bi and cd 104 105 in au br in pb and w 103 104 in mo cl cs s sn and ag 102 103 in as zn f and rb and 1 102 in cu k na sb ni ga v fe mn and li the fumaroles are transporting more than 106 grams day g d of s cl and f 104 106 g d of al br zn fe k and mg 103 104 g d of pb as mo mn v w and sr and less than 103 g d of ni cu cr ga sb bi cd li co and u with decreasing temperature 800 500 c there were five sublimate zones found in silica tubes 1 cristobalite and magnetite first deposition of si fe and al 2 k ca sulfate acmite halite sylvite and pyrite maximum deposition of cl na k si s fe mo br al rb cs mn w p ca re ag au and co 3 aphthitalite k na sulfate sphalerite galena and cs k sulfate maximum deposition of zn bi cd se and in higher deposition of pb and sn 4 pb k chloride and na k fe sulfate maximum deposition of pb sn and cu and 5 zn cu and k pb sulfates maximum deposition of pb sn ti as and sb the incrustations surrounding the fumaroles are also chemically zoned bi cd pb w mo zn cu k na v fe and mn are concentrated most in or very close to the vent as expected with cooling atmospheric contamination and dispersion the highly volatile elements br cl as and sb are transported primarily away from high temperature vents ba si p al ca and cr are derived from wall rock reactions incomplete degassing of shallow magma at 915 c is the origin of most of the elements in the merapi volcanic gas although it is partly contaminated by particles or wall rock reactions the metals are transported predominantly as chloride species as the gas cools in the fumarolic environment it becomes saturated with sublimate phases that fractionate from the gas in the order of their equilibrium saturation temperatures devolatilization of a cooling batholith could transport enough acids and metals to a hydrothermal system to play a significant role in forming an ore deposit however sublimation from a high temperature high velocity carrier gas is not efficient enough to form a large ore deposit re se cd and bi could be used as supporting evidence for magmatic fluid transport in an ore deposit

internal structure of piton de la fournaise volcano from seismic wave propagation and earthquake distribution abstract arrival times of seismic waves from local earthquakes are inverted for both locating the source and defining the 3 d velocity heterogeneity of piton de la fournaise the lateral heterogeneity of the 2632 m high edifice is resolved as a high velocity plug 1 5 km in diameter surrounded by a low velocity ring which may be interpreted as due to the construction of fournaise on the flank of the older volcano piton des neiges wave mode conversion detected on three component seismograms provides evidence for boundaries of contrasted velocities pre eruptive swarm earthquakes cluster in the high velocity zone under the dolomieu summit crater low strength and cohesion of the surrounding material account for the lack of seismicity for the final 1 3 km radial flow of magma to the vents in enclos fouque beneath the high velocity plug the existence of a body with low velocity for p and even for s waves is well constrained however the walls and base are poorly defined because of the lack of deep earthquakes for sampling the few earthquakes that are located in this depth region usually occur at a depth of around 1 5 km below sea level in the region of the cone this can be considered providing the upper constraint on the lower limit of the aseismic part of the low velocity body the coincidence in time of their occurrence with the swarms above sea level and the eruptions suggests magmatic activation of the low velocity aseismic volume 1 5 km below sea level under the high velocity plug of the cone further down the concentration of seismicity in two swarms between 2 and 4 km under the eastern flank does not allow the structure to be sampled effectively

a sr isotopic comparison between thermal waters rocks and hydrothermal calcites long valley caldera california abstract the 87 sr 86 sr values of thermal waters and hydrothermal calcites of the long valley caldera geothermal system are more radiogenic than those of young intracaldera volcanic rocks five thermal waters display 87 sr 86 sr of 0 7081 0 7078 but show systematically lighter values from west to east in the direction of lateral flow we believe the decrease in ratio from west to east signifies increased interaction of deeply circulating thermal water with relatively fresh volcanic rocks filling the caldera depression all types of pre syn and post caldera volcanic rocks in the west and central caldera have 87 sr 86 sr m between about 0 7060 and 0 7072 and values for sierra nevada granodiorites adjacent to the caldera are similar sierran pre intrusive metavolcanic and metasedimentary rocks can have considerably higher sr isotope ratios 0 7061 0 7246 and 0 7090 0 7250 respectively hydrothermally altered volcanic rocks inside the caldera have 87 sr 86 sr m slightly heavier than their fresh volcanic equivalents and hydrothermal calcites 0 7068 0 7105 occupy a midrange of values between the volcanic plutonic rocks and the sierran metamorphic rocks these data indicate that the long valley geothermal reservoir is first equilibrated in a basement complex that contains at least some metasedimentary rocks reequilibration of sr isotope ratios to lower values occurs in thermal waters as convecting geothermal fluids flow through the isotopically lighter volcanic rocks of the caldera fill

magma transport and storage at piton de la fournaise la reunion between 1972 and 2007 a review of geophysical and geochemical data abstract since the middle of the 20th century improvement in volcano monitoring techniques has provided large data sets that can be used to evaluate the evolution of magma plumbing systems at piton de la fournaise volcano abundant eruptive activity and a dense monitoring network are especially conducive to such research analysis of the extensive set of geophysical and geochemical data associated with the last 35 years of activity provides new insights into magma transport and storage at piton de la fournaise two periods of frequent eruptions separated by 6 years of inactivity can be distinguished 1972 1992 and 1998 2007 considering these two periods we show evidence of major changes in the shallow plumbing system in 2000 during 1972 1992 and 1998 2000 lava compositions and weak long term eruptive precursors lasting few days to three weeks characterized by no significant summit inflation and about ten volcano tectonic earthquakes per day suggest that eruptions were fed by the progressive drainage of an occasionally recharged shallow magma reservoir geophysical evidence of shallow magma reservoir recharge was only recorded in 1986 and 1998 in contrast from 2000 to 2007 geophysical data highlight the appearance of long term precursors 1 to 5 months of summit inflation and strong seismicity up to one hundred events per day preceding cycles of successive eruptions each cycle of eruptions was characterized by a sequence 3 to 10 months in duration of summit and near summit proximal eruptions and ended with a distal low altitude oceanite olivine abundances 20 vol eruption on the eastern flank of the volcano within each of these eruptive cycles lavas became progressively more magnesian over time the preferential motion of the eastern flank caused by continuous recharging of the shallow reservoir since 2000 would favour the occurrence of distal eruptions towards this flank at the end of a cycle

boron sr o and h isotope geochemistry of groundwaters from mt etna sicily hydrologic implications combined b o h and sr isotopic studies of groundwaters from mt etna provide new constraints on their origin and the consequences of fluid rock interaction within this hydrologic system variations in d 18 o 29 7 to 27 2 and d d 262 to 223 mainly lie along the regional meteoric water line and suggest that most waters originated as local precipitation however small shifts in d 18 o and variable 87 sr 86 sr 0 70355 to 0 70879 and d 11 b 25 2 to 125 8 indicate that subsequent interactions occurred between the fluids and local rocks high b cl ratios in all samples seemingly preclude direct involvement of seawater in the hydrologic system despite the proximity to the coast and in some samples elevated 87 sr 86 sr and d 11 b two general end member water types are recognized on the basis of their chemistry these apparently are produced by interactions of local meteoric waters with the dominant reservoir rocks either basaltic lavas of etna or the underlying sediments respectively high d 11 b in the sediment hosted end member points to a significant marine carbonate contribution subsequent mixing between these or similar end members produced a range of intermediate composition groundwaters certain anomalous water compositions require the presence locally of a distinct component with high b and moderate d 11 b ca 110 but relatively low 87 sr 86 sr an anthropogenic source for this component is plausible one unusual sample has b and sr isotopic compositions similar to the other volcanic rock hosted waters but anomalously high cl content that likely reflects local magmatic outgassing near this sampling locality in general this study indicates that groundwater b and sr isotopic compositions are rock dominated these data provide useful constraints on the origin and evolution of groundwaters copyright 2000 elsevier science ltd

geographic control on pb isotope distribution and sources in indian ocean fe mn deposits abstract high precision pb isotope data have been obtained on indian ocean fe mn deposits with a large geographic coverage these data reveal a strong geographic control on the distribution of pb isotopes as well as sources of pb within this basin the provinciality of pb isotopes at the scale of the whole indian ocean as well as that of individual basins broadly matches the pattern of deepwater flow the existence of several sources of pb is best illustrated by the presence of three well defined pb isotopic arrays each of which is confined to clear cut geographic domains these arrays imply a dominance of binary mixing of pb sources within each of these domains the domains consist of the north indian n indian north of 20 s southwest indian sw indian 20 s to 50 s west of 45 e south indian s indian 20 s to 50 s east of 45 e and antarctic indian a indian south of 50 s and clearly exhibit a strong control by latitude the s indian domain and mozambique channel samples form a cluster suggesting that there are more than just two sources contributing in these regions we show that the n indian is dominated by sources of pb derived from the high himalayas and the trans himalayan complex and most likely inherited from interaction at the water interface with bengal and indus fan sediments the sw indian and a indian domains share a common unradiogenic component represented by circumpolar waters derived from the pacific ocean and flowing through the drake passage into the atlantic and indian oceans however the radiogenic sources of pb in these two domains are clearly distinct in the sw indian the radiogenic pb signal reflects the tongue of north atlantic deep water flowing around the tip of south africa while in the a indian the source of radiogenic pb is less certain but quite probably originates in the weddell sea region these data illustrate the complexity of the spatial pb isotopic distribution and pb sources within a single ocean basin at the present day which should be borne in mind when interpreting long term radiogenic isotope paleorecords from fe mn crusts

halogen cycling and precious metal enrichment in sub volcanic magmatic systems insights from the rum layered intrusion scotland abstract the cycling of the halogens in sub volcanic systems may play an important role in magmatic ore deposit formation and the emission of climate altering gases via volcanic outgassing however the mobile and reactive nature of the halogens as well as their typically low abundances in most intrusive igneous rocks means that their behaviour in shallow crustal level magmatic systems is difficult to constrain we present data from the 60 ma rum layered suite nw scotland utilising the neutron irradiation noble gas mass spectrometry ni ngms technique to provide insight into the provenance and behaviour of cl br and i in magma chamber and precious metal enrichment processes as a well characterised and superbly exposed example of an open system sub volcanic magmatic body the rum intrusion is an ideal locality to investigate halogen behaviour in this context our data reveal concentrations of

condensation of volatile elements in high temperature gases of mount st helens abstract the cooling of high temperature 675 650 c volcanic gases in silica tubes produces successive condensation of volatile elements as solids on the inner walls of the tubes the chemistry of the solid phases obtained by these reactions varies along the temperature gradient 675 400 c fe3o4 and sio2 occur above 570 c mos2 and fewo4 are mainly enriched between 570 and 480 c nacl and kcl occur in the range 550 450 c and cds occurs at 520 450 c pb and bi sulfides are typical of the low temperature zone 480 400 c thermodynamic calculations performed to define the nature of the stable solid phases in equilibrium with the oxygen sulfur and chlorine fugacities of the gas phase show that the observed solid phases reflect a formation in a low o2 fugacity environment the chemistry of fumarolic incrustations collected around high temperature vents 300 c 5 15 cm below the surface reveals that condensation processes similar to those observed in the tubes occur naturally in the ground these incrustations show marked differences with those generally collected at the outlet of fumarolic vents where reactions with atmospheric gases and wall rocks are the major processes leading to the formation of these incrustations

vapor deposition of trace elements from degassed basaltic lava piton de la fournaise volcano reunion island abstract silica tube sublimates resulting from the cooling of high temperature volcanic gases from degassed lava in lava tunnels have been sampled at piton de la fournaise volcano mineral phases deposited in the tube are mainly halides na k and cu chlorides si and k fluorides the distribution of most of the chemical elements as a function of the temperature is mainly controlled by their volatility volatile elements such as rb cs se pb and tl are associated with low temperature deposits whereas refractory elements such as r e e alkaline earth sc ta hf th and zr are not detected the mineral assemblages are characterized by the lack of sulfides sulfates native sulfur and oxides in the same way numerous transition and semi metallic elements are lacking this is interpreted as the result of the magma transport in surface lava tunnels leading to extensive degassing upstream of the collection site

nucleosynthetic nd isotope anomalies in primitive enstatite chondrites abstract we carried out stepwise dissolutions of four primitive enstatite chondrites ec belonging to the eh subgroup large nd isotope anomalies are found in the most refractory phases dissolved using strong acids residues are characterized by excesses in 142nd and deficits in 145nd 148nd and 150nd isotopes the nd anomalies measured in the alha77295 residue are even greater than those measured in the murchison carbonaceous chondrite cc using a similar analytical technique qin et al 2011 once corrected for a common sm nd evolution the 142nd excess in the alha77295 residue is equal to 700 ppm relative to the terrestrial standard value the nd isotope patterns measured in ec and cc residues can be adjusted to coincide by adding a small amount of an s process rich carrier phase such as sic and 0 075 is required to fit the alha7795 residue small isotope differences still persist between these residues even if they can be considered similar within error in enstatite chondrites residues have a deficit in 150nd similar to or smaller than that measured in 148nd whereas in sic extracted from carbonaceous chondrites or in whole rock the deficit in 150nd is always greater than that in 148nd moreover in a binary 142nd 148nd diagram the best fit lines obtained for leachates and residues from carbonaceous chondrites and enstatite chondrites have slightly different slopes for the same 148nd 144nd ratio the anomalous component in an enstatite chondrite has a higher 142nd 144nd ratio compared to carbonaceous chondrites a feature already observed at the whole rock scale our results suggest that different chondrite groups sample different reservoirs of presolar grains formed in different environments assuming that the carrier of this anomalous component measured in residues of enstatite chondrites are sic our results may suggest that different meteorite parent bodies sample reservoirs of presolar sic formed in different stellar environments this could explain why alha77295 the sample which is the most enriched in presolar grains has a bulk 142nd isotope composition similar to the terrestrial value further investigation of enstatite chondrites is needed to test whether the isotope composition of the most refractory phases is similar to that measured in carbonaceous chondrites and in particular the 144sm that is a p process isotope only finally this study highlights the difficulty of interpreting the 142nd excess in terrestrial samples relative to chondrites since incomplete mixing of nucleosynthetic material in the solar nebula creates significant 142nd variation as shown by alha77295

c and n isotopic composition and the infrared absorption spectra of coated diamonds evidence for the regional uniformity of co2h2o rich fluids in lithospheric mantle abstract the 13 c and 15 n values nitrogen abundances and nitrogen aggregation states of coated diamonds from botswana angola sierra leone and siberia have been determined a single cubic micro diamond from the northern territory australia was also analysed the cubic coats of the diamonds and the cubic diamond from australia had a restricted range in isotope composition 13 c 7 2 to 4 1 15 n 8 7 to 1 7 in contrast the cores of the coated diamonds were found to be highly variable 13 c 21 1 to 1 9 and 15 n 2 8 to 12 1 with the majority being positive all of the coats gave the type iaa absorption spectra together with others due to micro inclusions dominated by h 2 o and co 2 whereas the cores contained nitrogen that was more highly aggregated the results suggest that coated diamonds were formed following the influx of co 2 h 2 o rich fluids into diamond bearing lithosphere pre existing diamonds acted as seeds for renewed growth and these are now the cores of the diamonds these cores may be very variable in terms of morphology isotopic composition age nitrogen aggregation state and crystallinity depending on the particular history of the source regions and the conditions of diamond growth it is believed that the influx of volatiles and the growth of the coats was linked to kimberlite magmatism the 13 c and 15 n results for the coats indicate that in terms of c and n isotope composition the source of co 2 h 2 o rich fluids is globally quite homogeneous it is probably located beneath continental lithosphere and in addition may have characteristics similar to the source of the ocean island basalts

distribution patterns of the elements in the ocean a synthesis the observed partition patterns of elements between a marine solid phase e g pelagic clays deep sea manganese nodules seamount manganese crusts and plankton and seawater can be to the first approximation explained by the james and healy adsorption model except for ce co mn pb and tl which are concentrated in the solid phase through oxidative uptake processes in other words the composition of seawater is mainly controlled by the compositions of source materials i e the crustal igneous rocks and primary magmatic volatiles and the physicochemical principles regulating the adsorption processes of various chemical species in seawater onto oceanic pelagic clays

he ar and c isotopes in coated and polycrystalline diamonds helium ar and c isotopic measurements have been undertaken on different qualities of industrial grade and polycrystalline diamond from localities in africa and brazil these include coated and cloudy diamonds which contain abundant volatile rich micro inclusions and framesites and carbonados which consist of aggregates of micron sized diamond crystals interspersed with mineral inclusions in an attempt to release selectively the primary trapped he from the diamonds they were analysed using an in vacuo crushing technique the he data are combined with ar k and u data obtained from 40ar 39ar stepped heating studies of irradiated fractions of the diamonds and bulk carbon isotope data obtained from the crushed residues results indicate that coated and cloudy diamonds best preserve a mantle signature with 3he 4he values of 1 7 ra and 13c of 5 to 6 coated diamonds have uniformly high he and ar concentrations of 10 6 10 5 cm3 g 1 framesites have lower 3he 4he values 0 1 3 ra and bimodal 13c values with modes at 6 and 20 carbonados show both the lowest 13c values 25 and 3he 4he of 0 1 ra u and k concentrations show a progressive increase from coats framesites carbonados while it is tempting to attribute low 13c low 3he 4he and high u to the influence of subducted crustal material it is likely that implantation of 4he by u th rich minerals adjacent to the micro diamonds is also a possible cause of the low he isotope ratios

new constraints on fluid sources in orogenic gold deposits victoria australia fluid inclusion microthermometry raman spectroscopy and noble gas plus halogen geochemistry complemented by published stable isotope data have been used to assess the origin of gold rich fluids in the lachlan fold belt of central victoria south eastern australia victorian gold deposits vary from large turbidite hosted orogenic lode and disseminated stockwork gold only deposits formed close to the metamorphic peak to smaller polymetallic gold deposits temporally associated with later post orogenic granite intrusions despite the differences in relative timing metal association and the size of these deposits fluid inclusion microthermometry indicates that all deposits are genetically associated with similar low salinity aqueous co2 bearing fluids the majority of these fluid inclusions also have similar 40ar 36ar values of less than 1500 and 36ar concentrations of 2 6 58 ppb by mass that are equal to or much greater than air saturation levels 1 3 2 7 ppb limited amounts of nitrogen rich fluids are present at a local scale and have the highest measured 40ar 36ar values of up to 5 700 suggesting an external or distinct source compared to the aqueous fluids the predominance of low salinity aqueous carbonic fluids with low 40ar 36ar values in both orogenic and intrusion related gold deposits is attributed to fluid production from common basement volcano sedimentary sequences and fluid interaction with sedimentary cover rocks turbidites aqueous fluid inclusions in the stawell magdala deposit of western victoria including those associated with n2 preserve mantle like br cl and i cl values in contrast fluid inclusions in deposits in the eastern structural zones which contain more abundant shales have elevated molar i cl ratios with maximum values of 5 170 10 6 in the melbourne zone br i ratios in this zone range from 0 5 to 3 0 that are characteristic of fluid interaction with organic rich sediments the maximum i cl and characteristic br i ratios provide evidence for organic br and i released during metamorphism of the shales therefore the regional data provide strong evidence for the involvement of sedimentary components in gold mineralisation but are consistent with deeper metamorphic fluid sources from basement volcano sedimentary rocks the overlying sediments are probably involved in gold mineralisation via fluid rock interaction

first evidence of hydrous silicic fluid films around solid inclusions in gem quality diamonds abstract diamonds form from fluids or melts circulating at depth in the earth s mantle analysis of these fluids is possible if they remain entrapped in the diamond during its growth but this is rarely observed in gem quality stones we provide the first evidence that typical mineral inclusions in gem quality diamonds from the siberian and kaapvaal cratons are surrounded by a thin film of hydrous silicic fluid of maximum thickness 1 5 m the fluid contains si 2 o oh 6 si oh 4 and molecular h 2 o and was identified using confocal micro raman spectroscopy and synchrotron based x ray tomographic microscopy as the solid mineral inclusions have both peridotitic and eclogitic affinities and occur in two cratonic regions our results demonstrate the strong connection between water rich fluids and the growth of gem quality lithospheric diamonds the presence of the fluid films should be taken into account for a proper evaluation of h 2 o contents in the mantle based on h 2 o contents in solid inclusions and for a robust assessment of diamond formation pressures based on the residual pressures of the inclusions

antiquity of peridotitic diamonds from the siberian craton diamonds erupted by kimberlites traversing ancient continental tectosphere 1 provide a window into the evolution of continents and their mantle keels however the vintage of this window that is the timing of crystallization of peridotitic mineral inclusion bearing diamonds beneath different cratons has proved controversial because of the model age arguments involved 2 12 isochron age data for peridotitic garnets in combination with nitrogen aggregation data for host diamonds from the udachnaya kimberlite on the siberian craton show that such diamonds are ancient and could not have crystallized as recently 70 ka before eruption as proposed 10 12 the garnets yield a smnd isochron age of 2 0 ga and the diamonds display nitrogen aggregation characteristics requiring lithospheric mantle storage at temperatures of 1100 1200 c for a comparable period the crystallization age of these peridotitic diamonds is similar to that of equivalent diamonds from the premier kimberlite on the kaapvaal craton which postdate the massive 2 05 ga old bushveld complex and represent a diamond generation unrelated to craton keel stabilization 3 2 ga ago 3 9 10

characteristics of djerfisherite from fluid rich metasomatized alkaline intrusive environments and anhydrous enstatite chondrites and achondrites djerfisherite is a k cl bearing sulfide that is present in both ultra reduced extraterrestrial enstatite meteorites enstatite chondrites or achondrites and reduced terrestrial alkaline intrusions kimberlites ore deposits and skarns major element chemistry of two terrestrial occurrences of djerfisherite from the ilimaussaq and khibina alkaline igneous suites and three extraterrestrial examples of djerfisherite have been determined and combined with petrographic characterization and element mapping to unravel three discrete modes of djerfisherite formation high fe cu is characteristic of extraterrestrial djerfisherite and low fe cu is typical of terrestrial djerfisherite ilimaussaq djerfisherite which has high fe contents 55 wt is the exception low ni contents are typical of terrestrial djerfisherite due to preferential incorporation of fe and or cu over ni but ni contents of up to 2 2 wt are measured in extraterrestrial djerfisherite extensive interchange between k and na is evident in extraterrestrial samples though na is limited

mid crustal fluid mixing in a proterozoic fe oxide cu au deposit ernest henry australia evidence from ar kr xe cl br and i fluid inclusions in six quartz veins associated with cu au mineralisation at the giant ernest henry iron oxide copper gold deposit 167 mt 1 1 cu 0 54 ppm au in northwest queensland have been analysed for naturally occurring and neutron produced noble gas isotopes of ar kr and xe a combination of thermal and mechanical decrepitation methods enables distinction between four types of fluid inclusion ultra high salinity 30 to 70 wt nacl eq fluid inclusions have compositions that define two end members that are variably mixed in different samples the first end member has a 40 ar 36 ar value of 29 000 a 40 are cl value of 3 10 3 and mantle like br cl and i cl values of 1 2 10 3 and 11 10 6 respectively the second end member has a much lower 40 ar 36 ar value of less than 2500 a 40 are cl value of 10 6 low br cl values of 0 4 10 3 and i cl values of 1 2 10 6 all ratios are molar carbon dioxide and later lower salinity liquid vapour fluid inclusions have similar 40 ar 36 ar values of less than 2500 in all samples these data are compatible with genetic models in which cu au mineralisation formed at a depth of 6 10 km from circulation of magmatic fluids derived from regionally abundant a type granites and a high salinity halite dissolution brine generated from sedimentary formation waters in the upper crust the largest source of co2 was probably carbonate rich lithologies in the midcrust later lower salinity fluids with a surficial origin diluted the mineralising brines and are preserved in the latest secondary fluid inclusions these data provide insight on the composition of crustal fluids during the proterozoic furthermore the magmatic fluid endmember derived from melts generated by re melting lower crustal paleoproterozoic igneous rocks with a mantle source preserves mantle like br cl and i cl these geochemical characteristics are interpreted to provide insight on i recycling at subduction zones and the composition of seawater in the paleoproterozoic 2007 elsevier b v all rights reserved

fumarole distribution morphology and encrustation mineralogy associated with the 1986 eruptive deposits of mount st augustine alaska numerous rootless fumaroles were developed on pyroclastic flows and a lava flow generated during the march 1986 eruptive cycle of mount st augustine gases issued from fumarole vents with four different shapes fissure phreatic explosion crater single multiple ovoid opening and diffuse multiple opening fumarole distribution and morphology were controlled by preeruption drainage and topography as well as by the thickness compaction and settling of the flow deposits fumarole temperatures measured in june and july 1986 ranged from 75 394 c varying amounts of colorful and often roughly zoned encrustations are associated with all fumarole vent shapes only six types of crystalline phases were detected by x ray diffraction with gypsum the most abundant mineral followed by anhydrite sulfur tridymite halite and soda alum scanning electron microscopy and energy dispersive x ray analysis revealed a number of amorphous phases mainly halogen rich as well as other minor crystalline phases the mineral assemblages in the encrustations suggest formation conditions for these deposits within a general range of 25 250 c in an oxidizing environment many of the amorphous phases are metastable and upon cooling of the fumarole lose nonstructural water and crystallize to more stable forms the high halogen contents of the fumarole condensates and the mineralogy chemistry and morphology of the encrustations support leaching of the andesitic ash and lava flow by condensed acid vapors as the primary source for the chemical components contained in the encrustations comparison of traceelement sr ba v co ni and cr contents in unaltered and altered ash suggests that trace element distribution follows a pattern of isomorphic substitution in the encrustation phases

helium isotopic ratio in vulcano island fumaroles temporal variations in shallow level mixing and deep magmatic supply intensive gas emanations occur throughout the island of vulcano italy sharp fluctuations recorded in the crater gas composition suggest the presence of two separate volcanic reservoirs and continuous mixing with another source crustal waters this mixing differs between the beach and crater fumaroles gas samples from three crater fumaroles with temperatures ranging from 200 to 550 c were sampled repeatedly over a one year period during the same interval of time six samples from submarine and subaerial beach fumaroles and water well gases were also sampled gases from one crater fumarole f5 showed variations of 3he4he fumarole to 3he4he air between 5 and 6 correlated with variations of several chemical species high 3he4he ratios for the beach fluids similar to those of crater fluids suggest the existence of a unique large magmatic reservoir at depth feeding both the crater and beach intermediate reservoirs however temporal changes clearly indicate variable degrees of fluids mixing and the geographic distribution of the 3he4he ratios as well as the chemical composition of the fluids suggest the existence between the magma reservoir and the surface of two intermediate different reservoirs independently related to crater and to beach fumaroles

martian fluid and martian weathering signatures identified in nakhla nwa 998 and mil 03346 by halogen and noble gas analysis we report argon ar noble gas ar ar ages and halogen abundances cl br i of martian nakhlites nakhla nwa 998 and mil 03346 to determine the presence of martian hydrous fluids and weathering products neutron irradiated samples were either crushed and step heated nakhla only or simply step heated using a laser or furnace and analysed for noble gases using an extension of the 40 ar 39 ar technique to determine halogen abundances the data obtained provide the first isotopic evidence for a trapped fluid that is cl rich has a strong correlation with 40 ar xs 40 ar xs 40 ar measured 40 ar radiogenic and displays 40 ar xs 36 ar of 1000 consistent with the martian atmosphere this component was released predominantly in the low temperature and crush experiments which may suggest a fluid inclusion host for the halogens we observe similar br cl and i cl ratios between the nakhlites and terrestrial reservoirs which is surprising given the absence of crustal recycling organic matter and frequent fluid activity on mars in particular br cl ratios in our nakhla samples especially olivine are consistent with previously analysed martian weathering products and both low temperature and crush analyses show a similar trend to the evaporation of seawater this may indicate that surface brines play an important role on mars and on halogen assemblages within martian meteorites and rocks elevated i cl ratios in the low temperature nwa 998 and mil 03346 releases may relate to in situ terrestrial contamination though we are unable to distinguish between low temperature terrestrial or martian components whilst estimates of the amount of water present based on the 36 ar concentrations are too high to be explained by a fluid component alone they are consistent with a mixed phase inclusion gas and fluid or with shock implanted martian atmospheric argon the observed fluid is dilute low salinity but high br cl and i cl ratios contains a martian atmospheric component and may represent a mixture of a shallow fluid with one derived from fluid circulation within the nakhlite cumulate pile with heat for fluid circulation supplied by either the igneous intrusion or by an impact event

thermal surveys of the vulcano fossa fumarole field 1994 1999 evidence for fumarole migration and sealing abstract between 1994 and 1999 we carried out five thermal surveys of the vulcano fossa fumarole field each consisted of 485 1213 vent temperature measurements distributed across the field these show that the field has been cooling and expanding where mean and maximum vent temperatures decreased from 216 to180 c and 541 to 428 c respectively between 1994 and 1997 however expansion of the field resulted in increased heat loss from 45 to 67 mw we suggest that cooling and expansion has been caused by increased gas flux and or permeability where increased flow of fluids of magmatic origin during 1996 is implied by chemical and isotopic data capasso g favara r francofonte s inguaggiato s 1999 chemical and isotopic variations in fumarolic discharge and thermal waters at vulcano island aeolian islands italy during 1996 evidence of resumed volcanic activity j volcanol geotherm res 88 1999 167 175 we propose that the size of the conduit has increased causing the fumarole field to expand and vent temperatures to generally decline as gas and heat losses become distributed over a wider area the increase in exhaling area has outweighed the modulating effect of cooling on total heat losses so that heat loss has increased due to an increased input from the magmatic source and or an increase in system permeability within these field wide trends the rim and then the middle zones have been cooling conversely the lower zone showed evidence of warming during 1994 98 before cooling in 1999 throughout the measurement period a se s thermal migration has been apparent and a new hot zone has developed on the field s southern edge we suggest that sealing of fumaroles by complete boiling of marine fluids on the northern edge of the system and higher permeability on the southern edge may have influenced this expansion direction if vent temperatures drop below 100 c then shallow sulfur sealing will quickly diminish fumarole life expectancy and contribute to the abandonment of vents in cooling zones in our model increased gas flux and or permeability e g due to increased magmatic degassing and or fracturing is the primary mechanism driving observed changes in the field temperature size and location deep and shallow conduit sealing are secondary mechanisms influencing the location of new zones once increased gas and heat fluxes have been triggered

multiple growth events during diamond genesis an integrated study of carbon and nitrogen isotopes and nitrogen aggregation state in coated stones the internal structure and growth history of diamonds have been investigated by the study of carbon isotopes and the abundance isotope composition and aggregation state of nitrogen polished plates of zoned diamonds coated stones were laser sectioned for infrared mapping and isotope profiling nine small cubic and three small octahedral diamonds from zaire and two coated stones and five small cubic diamonds specifically from the mbuji mayi area of that country were also investigated the isotope composition and infrared characteristics of the diamonds of cubic habit including coats were found to be indistinguishable with 13c in the range 5 9 to 7 5 and all the nitrogen being present as the paired structure iaa with a 15n of between 3 1 and 8 0 the diamonds of octahedral habit including the cores of the coated stones were more variable 13c varied from 4 9 to 9 8 infrared spectra of the octahedral diamond exhibited either strong iaa characteristics or a combination of iaa and iab platelets were present in most cases 15n values from octahedral diamonds varied from 5 8 to 13 4 the data suggest that the octahedral diamonds represent a variety of growth events separated in time and or space and that the diamonds resided in the lithosphere for a period sufficient for thermal maturation in the case of the coated stones the octahedral diamonds were later involved in an event which added a component from a single relatively homogeneous reservoir cubic habit diamonds were formed at the same time this latter event is believed to be related to the kimberlite eruption comparison of the data with carbon isotope analyses of cubic diamond from other sources suggests that this reservoir could be widespread

escape of unradiogenic osmium during sub aerial lava degassing evidence from fumarolic deposits piton de la fournaise reunion island abstract this study presents new re os isotope and elemental data in gas condensates and corresponding lavas in order to examine the geochemical behavior of these two elements during magma degassing at piton de la fournaise reunion island gas sublimates formed between 2007 and 2011 at temperature ranging from 400 to ca 100 c include na k sulfate aphthitalite na sulfate thenardite ca cu sulfate e g gypsum ca mg al fe fluoride e g ralstonite and native sulfur the high temperature deposits show trace element typical of volcanic gas with high enrichment in re 24 to 79 ppb almost two order of magnitude higher than the corresponding lavas but with os abundances similar to those of the lavas 14 132 ppt in contrast the os contents of the low temperature fluoride deposits 13 77 ppb are higher than any of the other condensates the fluorides are also enriched in re albeit to lesser extent than os 2 9 15 3 ppb based on high temperature samples the fluid melt partition coefficients estimated for re and os are 100 80 and 1 2 respectively considering 1 of fluid loss these partition coefficients translate into emanation coefficients of 0 50 0 17 0 65 for re and 0 01 0 0 03 for os these results indicate that re unlike os is highly volatile at piton de la fournaise osmium isotopic compositions of samples collected at medium and low temperature 187 os 188 os between 0 130 0 135 and plot within the range of the april 2007 lava flow and the historical lavas of piton de la fournaise i e 0 130 0 137 however the highest temperature condensates na k sulfates with t of 384 400 c yield lower 187 os 188 os ratios i e 0 124 0 129 within the field of mantle signal such unradiogenic compositions are best explained if old mantle sulfides occur in lavas and contribute to volcanic gases within the general frame of osmium mantle geochemistry loss of unradiogenic os during magmas degassing could help to explain osmium isotope disequilibrium between lavas and melting residues

mount st augustine volcano fumarole wall rock alteration mineralogy zoning composition and numerical models of its formation process abstract intensely altered wall rock was collected from high temperature 640 c and low temperature 375 c vents at augustine volcano in july 1989 the high temperature altered rock exhibits distinct mineral zoning differentiated by color bands in order of decreasing temperature the color bands and their mineral assemblages are a white to grey tridymite anhydrite b pink to red tridymite hematite fe hydroxide molysite fecl 3 with minor amounts of anhydrite and halite and c dark green to green anhydrite halite sylvite tridymite with minor amounts of molysite soda and potash alum and other sodium and potassium sulfates the alteration products around the low temperature vents are dominantly cristobalite and amorphous silica with minor potash and soda alum aphthitalite alunogen and anhydrite compared to fresh 1986 augustine lava the altered rocks exhibit enrichments in silica base metals halogens and sulfur and show very strong depletions in al in all alteration zones and in iron alkali and alkaline earth elements in some of the alteration zones to help understand the origins of the mineral assemblages in altered augustine rocks we applied the thermochemical modeling program gasworks in calculations of a reaction of the 1987 and 1989 gases with wall rock at 640 and 375 c b cooling of the 1987 gas from 870 to 100 c with and without mineral fractionation c cooling of the 1989 gas from 757 to 100 c with and without mineral fractionation and d mixing of the 1987 and 1989 gases with air the 640 c gas rock reaction produces an assemblage consisting of silicates tridymite albite diopside sanidine and andalusite oxides magnetite and hercynite and sulfides bornite chalcocite molybdenite and sphalerite the 375 c gas rock reaction produces dominantly silicates quartz albite andalusite microcline cordierite anorthite and tremolite and subordinate amounts of sulfides pyrite chalcocite and wurtzite oxides magnetite sulfates anhydrite and halides halite the cooling calculations produce a anhydrite halite sylvite b cu mo fe and zn sulfides c mg fluoride at high temperature 370 c d chlorides fluorides and sulfates of mn fe zn cu and al at intermediate temperature 170 370 c and e hydrated sulfates liquid sulfur crystalline sulfur hydrated sulfuric acid and water at low temperature

noble gas state of the ancient mantle as deduced from noble gases in coated diamonds cores and coats of five coated diamonds one from botswana and four from zaire were separately analyzed for their noble gases noble gases in the diamonds are essentially of a trapped origin including radio and nucleogenic components such as4he 40ar 21neexcess and excesses in xe isotopes 129 131 136 the fairly precise elemental and isotopic abundances allow us to infer the noble gas state in the ancient mantle 20ne 22ne ratios are fairly constant 11 8 0 4 and very close to that of sep solar energetic particle ne but distinctly different from the atmospheric ratio 21ne 22ne ratios range from 0 028 to 0 06 which is attributed to nucleogenic 21ne from 18o n 21ne and 24mg n 21ne reactions the difference in 20ne 22ne between atmosphere and mantle can be attributed to the hydrodynamic escape of hydrogen from the primitive atmosphere during the very early stage in the earth s history 38ar 36ar and kr isotopic ratios are identical to the atmospheric values within 1 after correction for 238u or 244pu fission xe the 131 136xe abundance ratios are indistinguishable from atmospheric ratios lighter xe isotopes 124 128xe are also likely to be atmospheric but a final conclusion must wait until better data are obtained in a 136xe 130xe 129xe 130xe diagram diamond data lie on the same line as defined for morb the observed identical correlation for both diamonds and morb s appears to suggest that the progenitor of the excess131 136xe is 244pu but not238u though the direct xe isotopic measurements was not precies enough to decide unanimously the progenitor

isotope composition of rain water well water and fumarole steam on the island of vulcano and their implications for volcanic surveillance abstract water samples from eight wells in the vulcano porto area and fumarole steam from the crater of vulcano southern italy were collected at monthly intervals over a two year period from february 1987 to january 1989 samples of bulk precipitation were also collected in three points at vulcano porto and vulcano piano island of vulcano and castroreale tyrrhenian coast of sicily again at monthly intervals the weighted mean isotopic composition of rain water on vulcano is d 32 and d 18 o 6 4 results for well waters tend to support the existence of at least two water bodies one of purely meteoric water and the other of brackish thermal water an intermediate water body probably the result of mixing of the other two was also recognized the isotope composition of fumarolic steam from the crater suggests the mixed contribution of both sea and rain waters although mixing is not the only process occurring the existence of a deep marine brine body is inferred characterized by d and 18o values more positive than those of mediterranean sea water a close relationship indicating common source effects is shown by temporal isotopic variations at some wells and the fumarolic steam wich may be used for volcano survey at distance from the active crater

40ar 39ar laser probe studies of clinopyroxene inclusions in eclogitic diamonds abstract 40 ar 39 ar laser probe ages are reported for individual clinopyroxene inclusions in thirty two eclogitic diamonds from four localities jwaneng and orapa both in botswana udachnaya siberia and argyle australia ages obtained from cleaved diamonds from jwaneng 244 ma orapa 102 ma and udachnaya 425 ma are similar to those of their host kimberlites however there is considerable variation in age between individual laser extractions obtained from the same inclusion which we suspect is mainly due to partial retention of radiogenic argon that diffused to the inclusion diamond interface while the diamond was in the mantle some of this argon was lost when the diamonds were cleaved as part of the experimental procedure the presence of an ambient mantle 40 ar component trapped in inclusions may be an additional cause of scatter in ages however this cannot be validated with the present data in support of the diffusive loss process the results from an udachnaya inclusion completely enclosed within host diamond with the argon being released by laser drilling yielded an age of 1149 37 ma which is considerably older than the host kimberlite about 340 400 ma likewise the scatter in 40 ar k ratios for eclogitic diamonds from jwaneng and orapa indicates that they too are probably xenocrysts therefore a combination of sample preparation technique and laser drilling can be used to offer a useful extension of the original method enabling both diamond formation from buried inclusions and host rock emplacement ages from cleaved inclusions to be determined argyle clinopyroxenes similarly cleaved to the diamond surface also show a considerable range of inclusion ages 1159 1540 ma only in this case there is a relationship between age and k ca ratio of the inclusions such a relationship is difficult to reconcile in terms of partial loss of 40 ar and instead indicates that there was a protracted period of diamond growth

micrometer scale cavities in fibrous and cloudy diamonds a glance into diamond dissolution events abstract micrometer sized internal cavities in diamonds preserve evidence of diamond dissolution events combining the methods of focused ion beam fib sample preparation and transmission electron microscopy tem enables these features to be studied in detail micrometer scale cavities are found in the inner parts of fibrous and cloudy kimberlitic diamonds their filling consists of amorphous matrix secondary nano crystals volatiles and in some cases larger resorbed crystals trapped minerals include corundum kappa alumina quartz olivine moissanite 6h and ca mg carbonates this is the first observation of kappa alumina in nature secondary nano minerals are observed within the amorphous matrix and include carbonates al oxide fluorite ilmenite and secondary diamond crystals the amorphous matrix is spongy and its composition is dominated by amorphous carbon nitrogen chlorine and also contains water when no crystalline phases are observed the matrix is also enriched in alumina silica and in some cases calcium we propose that micrometer scale cavities in diamonds form during dissolution events induced by the introduction of oxidizing hydrous fluids into the diamond growth area hydrous fluids are the main dissolving agents for most kimberlitic diamonds fedortchouk y canil d semenets e 2007 mechanisms of diamond oxidation and their bearing on the fluid composition in kimberlite magmas am mineral 92 1200 1212 at diamond forming conditions silica and alumina are enriched in hydrous fluids that are in equilibrium with eclogites kessel r ulmer p pettke t schmidt m w thompson a b 2005 the water basalt system at 4 to 6 gpa phase relations and second critical endpoint in a k free eclogite at 700 to 1400 c earth planet sci lett 237 873 892 this is consistent with the increased solubility of alumina with increased pressure and temperature in the na cl bearing fluids manning c e 2006 mobilizing aluminum in crustal and mantle fluids j geochem explor 89 251 253 manning c e 2007 solubility of corundum kyanite in h2o at 700c and 10 kbar evidence for al si complexing at high pressure and temperature geofluids 7 258 269 additionally hydrous fluids may leach grain boundaries that are enriched in alumina in peridotitic environments hiraga t anderson i m kohlstedt d l 2004 grain boundaries as reservoirs of incompatible elements in the earth s mantle nature 427 699 703 wirth r 1996 thin amorphous films 1 2 nm at olivine grain boundaries in mantle xenoliths from san carlos arizona contrib mineral petrol 124 44 54 diamond dissolution will form oxidized carbon species and may decrease the solubility of silica and alumina in the dissolving agent leading to their precipitation diamond forming fluids that are trapped in sub micrometer inclusions in the same fibrous diamonds are the dominant fluid component in the diamond growth area corrosive hydrous fluids are less common and appear as short discrete events followed by the return of the common diamond forming fluids and continued diamond precipitation

lead isotope composition of the sublimates from the fumaroles of vulcano aeolian islands italy inferences on the deep fluid circulation the fumarolic fluids of vulcano aeolian islands italy consist of a mixture of both deep and shallow components the final products the fumarolic gases and the sublimates associated with them provide information on the complex interactions that occur at depth as radiogenic isotopes do not undergo fractionation after they are incorporated in a fumarolic gas they can be used directly to characterize the components that mixed lead isotopes are particularly suitable because seawater which plays an important part in the formation of the fumarolic fluids of vulcano contains only negligible amounts of it 10 12 g g therefore the lead present in the fumarolic gases and sublimates is derived from the magmatic component and a water rock interaction process the lead isotope compositions of the lead sulfosalt sublimates collected from the fossa crater of vulcano in 1924 and between 1989 and 1993 are given the lead isotope ratios of most of the samples are the same within the range of analytical error regardless of their collection date the only samples that display slight variations are those collected in 1993 on the whole the compositional trend of the lead isotopes of the sublimates coincides with that of the latitic rhyolitic activity of fossa and differs substantially from that of the pre fossa trachy basaltic activity the lead composition of the sublimates is very different from that of the calabrian basement rocks the data presented here show that the magma presently degassing at vulcano has the same lead isotopic composition as the products of the recent activity of fossa whereas the fumarolic fluid circulation of vulcano has not involved basement rocks similar to the calabrian metasediments

structural control of collapse events inferred by self potential mapping on the piton de la fournaise volcano la reunion island abstract field surveys were performed on the terminal cone of piton de la fournaise in 2006 and 2008 to precisely map the self potential sp signal and determine the zonation of the hydrothermal activity both on the flanks of the cone and in the summit area including inside the bory and dolomieu craters sp maps inside the craters have been performed 8 months before the 5 7 april 2007 caldera collapse zonations appear both at the scale of the cone and of the summit and allow new interpretation of the electrical signal distribution on the terminal cone of piton de la fournaise superimposed to the sp maxima linked to the rift zones several areas of sp maxima associated with collapse structures have been detected 1 in the summit area the bory and dolomieu craters show the strongest sp values with amplitudes exceeding 2 v with respect to the base of the cone and with a sharp lateral variation to the east corresponding to the inner boundary of the dolomieu caldera collapsed on 5 7 april 2007 and 2 in the paleo pit craters surrounding the summit which show amplitudes similar to the dolomieu bory craters the analysis of the variations of the signal with time evidences a modification of the fluid flow pattern with a higher associated sp signature to the east in 2008 we interpret the amplification of fluid flow to the east in 2008 as a consequence of the eastward motion of the eastern flank of the volcano during the april 2007 eruption the acquisition of sp data during two periods separated by the april 2007 eruption turns out to be a good opportunity to correlate the sp signal to the piton de la fournaise structure and to its evolution in term of hydrothermal and eruptive activity

bromine cycle in subduction zones through in situ br monitoring in diamond anvil cells abstract the geochemical partitioning of bromine between hydrous haplogranitic melts initially enriched with respect to br and aqueous fluids has been continuously monitored in situ during decompression experiments were carried out in diamond anvil cells from 890 c to room temperature and from 1 7 gpa to room pressure typically from high p t conditions corresponding to total miscibility presence of a supercritical fluid br contents were measured in aqueous fluids hydrous melts and supercritical fluids partition coefficients of bromine were characterized at pressure and temperature between fluids hydrous melts and or glasses as appropriate d br fluid melt br fluid br melt ranges from 2 18 to 9 2 0 5 for conditions within the ranges 0 66 1 7 gpa 590 890 c and d br fluid glass br fluid br glass ranges from 60 to 375 at room conditions the results suggest that because high pressure melts and fluids are capable of accepting high concentrations of bromine this element may be efficiently removed from the slab to the mantle source of arc magmas we show that br may be highly concentrated in subduction zone magmas and strongly enriched in subduction related volcanic gases because its mobility is strongly correlated with that of water during magma degassing furthermore our experimental results suggest that a non negligible part of br present in the subducted slab may remain in the down going slab being transported toward the transition zone this indicates that the br cycle in subduction zones is in fact divided in two related but independent parts 1 a shallower one where recycled br may leave the slab with a water and silica bearing fluid leading to enriched arc magmas that return br to the atmosphere 2 a deeper cycle where br may be recycled back to the mantle maybe to the transition zone where it may be present in high pressure water rich metasomatic fluids

boron isotopic variations in fumarolic condensates and thermal waters from vulcano island italy implications for evolution of volcanic fluids abstract temporal variation in the isotopic composition of boron has been monitored in fumarolic condensates collected over an extended time period 1970 1996 from la fossa crater volcano island we also report comparative boron isotopic data for representative vulcano lavas and for shallow hydrologic samples seawater wells thermal springs from the north flank of la fossa combined with concurrent chemical and isotopic 18o d data for the fumaroles these results indicate that the fumarolic fluids record mixing relations between three distinct fluid end members 1 a dominantly magmatic fluid em1 2 a mixture of modified seawater with magmatic fluid em2 and 3 an aqueous fluid produced from seawater by extensive wall rock reaction evaporation and boiling af differences between the latter two end members are most clearly accentuated on the basis of the boron isotopic data long term compositional variations for crater fumaroles were dominated by em1 af mixing between 1979 88 with progressive decrease in em1 contribution with time and by em2 af mixing between 1988 96 the exact spatial distribution of these fluid reservoirs remains unclear but all must have been present throughout the monitoring period to account for the observed variations moreover the combined b o h data seem to preclude important contributions from shallow meteoric reservoirs marked short term variations in 11b closely coincide with episodes of local seismicity which presumably triggered reorganization of hydrothermal circulation patterns gradual variations over periods up to 3 4 years are associated with relatively low seismicity during which fluid circulation was likely influenced by effects of mineral precipitation on permeability of the hydrologic system

first coupled sr and pb isotopic measurements in volcanic gas condensates and groundwaters of vulcano island italy 1 for the first time coupled sr pb concentrations and isotopic compositions have been measured on four crater fumaroles and six groundwaters sampled between 1999 and 2001 at vulcano island southern italy sr concentrations and isotopic compositions of groundwaters show that the sr budget results mainly from the leaching of volcanic rock by groundwaters leaching intensity is controlled by the variable dissolution of volcanic gases into shallow aquifers the data do not reveal any influence of seawater except at one coastal site low pb concentrations together with calculated saturation indexes with respect to mineral phases indicate that pb content in groundwaters is strongly influenced by adsorption and or precipitation processes pb isotopic ratios of two steam heated waters display a clear anthropized meteoric water signature suggesting gas dissolution or wall rock alteration to be a negligible process for this element in this particular context low 0 5 and high 102 103 enrichment factors were calculated for sr and pb respectively indicating their refractory and volatile behavior in volcanic gases most of the gas samples display sr and pb isotopic ratios similar to parent rocks these data suggest that sr is mainly derived from wall rock or particle contamination during gas ascent whereas pb results mainly from magma degassing however two gas condensates collected from two different fumarolic vents and at different periods show a dramatic pb and sr isotopic shift with a clear atmospheric anthropogenic signature episodic permeability variations of the volcanic structure probably arising from microseismicity swarms changes of local stress field and migration of self sealing processes lead to changing interactions between freshly infiltrated meteoric water and volcanic gases that temporarily modify the trace metal signature of the fumarolic gas

40ar 39ar analyses of clinopyroxene inclusions in african diamonds implications for source ages of detrital diamonds clinopyroxene inclusions in diamond contain elevated potassium contents and can potentially be dated by 40ar 39ar techniques previous 40ar 39ar studies of clinopyroxene inclusions contained in cleaved diamonds have suggested that argon produced from the decay of potassium prior to eruption of the host kimberlite magma diffuses to the diamond clinopyroxene interface under mantle conditions after intrusion and cooling below the closure temperature for argon diffusion radiogenic argon is retained by the clinopyroxene inclusions this behaviour complicates efforts to date diamond crystallisation events however extraction of inclusions from their host diamond should induce loss of all interface argon thus raising the possibility of determining kimberlite emplacement ages this possibility has important implications for constraining the source localities of detrital diamond deposits worldwide with concomitant benefits to diamond exploration to investigate this premise 40ar 39ar laser probe results are presented for single clinopyroxene inclusions extracted from a total of fifteen gem quality diamonds from the mbuji mayi kimberlite in the democratic republic of congo and the jwaneng and orapa kimberlites in botswana initial fusion analyses of clinopyroxene inclusions from mbuji mayi diamonds yielded ages older than the time of host kimberlite intrusion indicating partial retention of extraneous argon by the clinopyroxene inclusions themselves step heating analyses of clinopyroxene inclusions from orapa and jwaneng diamonds produced older apparent ages from lower temperature steps and the rim fragment of one orapa inclusion high temperature fusion analyses yielded younger apparent ages commonly approaching the times of host kimberlite eruption total gas integrated 40ar 39ar ages are mostly intermediate between the times of inferred diamond crystallisation and kimberlite eruption ca k ratios for each sample are uniform across step heating increments indicating that age variations are not due to compositional mineralogical or alteration effects the favoured explanation for these results is partial retention of extraneous argon in primary and or secondary fluid inclusions this component is then preferentially outgassed in lower temperature heating steps yielding older apparent ages the partial retention of extraneous argon by clinopyroxene inclusions clearly restricts efforts to determine source ages for detrital diamond deposits results from individual samples must necessarily be interpreted as maximum source emplacement ages nonetheless step heating analyses of several clinopyroxene inclusions from a detrital diamond deposit may provide reasonable constraints on the ages of source kimberlites lamproites however minor age populations as well as those closely spaced in time may be difficult to resolve it is argued that the majority of older 40ar 39ar ages can be explained in terms of the partial retention of inherited argon produced between the times of diamond crystallisation and kimberlite eruption although the presence of excess argon in some clinopyroxene inclusions cannot be excluded available evidence e g no excess argon in premier eclogitic inclusions or potassium poor inclusions suggests that this is not a factor for most samples three possible mechanistic models are forwarded to account for the uptake of inherited excess argon in fluid inclusions the first envisages negligible interface porosity and diffusion of extraneous argon exclusively to primary fluid inclusions which subsequently partially decrepitated during eruption causing accumulation of argon at the diamond clinopyroxene interface the second model permits diffusive loss of extraneous argon to both the interface region and primary fluid inclusions the third involves diffusion of extraneous argon to the interface region with later entrapment of some interface argon in secondary fluid inclusions produced by fracture annealing processes active during eruption the first model can account for all 40ar 39ar results whereas the latter two mechanisms require the presence of an excess argon component to explain older integrated ages up to 2 9 ga from two jwaneng samples excess argon contamination would compromise efforts to determine diamond genesis ages using the 40ar 39ar dating technique however if the first model is valid then the older 40ar 39ar integrated ages support previous re os age results for the crystallisation of jwaneng diamonds

degassing of metals and metalloids from erupting seamount and mid ocean ridge volcanoes observations and predictions recently it has been reported that the element polonium degasses from mid ocean ridge and seamount volcanoes during eruptions published and new observations on other volatile metal and metalloid elements can also be interpreted as indicating significant degassing of magmatic vapors during submarine eruptions this process potentially plays an important role in the net transfer of chemical elements from erupting volcanoes to seawater in addition to that arising from sea floor hydrothermal systems in this paper a framework is constructed for predicting and assessing semiquantitatively the potential magnitude and chemical fingerprints in the water column of metal and metalloid degassing using 1 predictions from a summary of element volatilities during mafic subaerial volcanism worldwide and 2 limited data from submarine volcanic effusives the latter include analyses of polonium and trace metals in near volcano water masses sampled following a submarine eruption at loihi seamount hawaii 1000 m bsl in 1996 the element volatility predictions and observations show good agreement considering the limited dataset some of the highest volatility main group and transition element enrichments in seawater over loihi are predicted by the degassing mass transfer model i present when expanded to cover all submarine volcanic activity it is predicted that exit fluxes of these elements are up to 102 103 greater by degassing than by normal mor hydrothermalism in contrast mor exit fluxes of low volatility alkali and alkaline earth elements are likely 102 106 greater from hydrothermal inputs degassing inputs to the ocean are probably highly episodic occurring almost entirely during eruptions these are times of enhanced and abnormal hydrothermalism as well although major hydrothermal and degassing events may not be chemically recognizable in real water masses as wholly distinct entities it is nevertheless possible to predict to what extent each process flavors the effluents of the other degassing at mid ocean ridges may explain a variety of observations previously ascribed to complexities occurring during hydrothermal venting and or fluid ascent in the buoyant hydrothermal plumes above ridges

investigation of thallium fluxes from subaerial volcanism implications for the present and past mass balance of thallium in the oceans abstract a suite of 34 volcanic gas condensates and particulates from kilauea hawaii mt etna and vulcano italy mt merapi indonesia white island and mt nguaruhoe new zealand were analysed for both tl isotope compositions and tl pb ratios when considered together with published tl pb abundance data the measurements provide globally representative best estimates of tl pb 0 46 0 25 and e 205 tl 1 7 2 0 for the emissions of subaerial volcanism to the atmosphere and oceans e 205 tl is the deviation of the 205 tl 203 tl isotope ratio from nist srm 997 isotope standard in parts per 10 000 compared to igneous rocks of the crust and mantle volcanic gases were found to have i tl pb ratios that are typically about an order of magnitude higher and ii significantly more variable tl isotope compositions but a mean e 205 tl value that is indistinguishable from estimates for the earth s mantle and continental crust the first observation can be explained by the more volatile nature of tl compared to pb during the production of volcanic gases whilst the second reflects the contrasting and approximately balanced isotope fractionation effects that are generated by partial evaporation of tl during magma degassing and partial tl condensation as a result of the cooling and differentiation of volcanic gases mass balance calculations based on results from this and other recent tl isotope studies were carried out to investigate whether temporal changes in the volcanic tl fluxes could be responsible for the dramatic shift in the e 205 tl value of the oceans at 55 ma which has been inferred from tl isotope time series data for ferromanganese crusts the calculations demonstrate that even large changes in the marine tl input fluxes from volcanism and other sources are unable to significantly alter the tl isotope composition of the oceans based on modelling it is shown that the large inferred change in the e 205 tl value of seawater is best explained if the oceans of the early cenozoic featured significantly larger tl output fluxes to oxic pelagic sediments whilst the sink fluxes to altered ocean crust remained approximately constant

origin of ore fluids in the muruntau gold system constraints from noble gas carbon isotope and halogen data abstract hydrothermal vein minerals directly associated with native gold mineralization in the muruntau vein system uzbekistan have been studied for noble gas carbon isotope and halogen chemistry of the trapped ore related fluids helium trapped in early arsenopyrite 1 which has preserved the original fluid signature better than associated scheelite and quartz indicates a small input from a mantle source 5 of total he however the overwhelming majority of the he in the fluid 95 is from crustal sources the noble gases ne kr and xe in the sample fluids are dominated by gases of atmospheric origin the carbon isotope 13 c 2 1 to 5 3 and halogen characteristics of the fluids log br cl 2 64 to 3 23 lend further support for the activity of juvenile fluids during the main ore stage the high proportion of crustal components in the ore forming fluids may be explained by intense fluid rock interaction and is also supported by previous nd and sr isotope studies the involvement of a juvenile fluid component during the main stage of hydrothermal activity at muruntau 275 ma can be linked to the emplacement of lamprophyric dikes at muruntau due to apparently overlapping ages for high temperature alteration related ore vein formation and intrusion of the dikes the input of mantle derived fluids possibly related to the hercynian collisional event in the western tien shan stimulated intense fluid rock interaction in the crust in this context the mantle derived fluid should be considered as one possible carrier of metals significant amounts of external meteoric fluids circulating in fracture systems are interpreted to have modified the noble gas signature of fluid in quartz mostly during late low temperature fluid circulation

lead isotopes behavior in the fumarolic environment of the piton de la fournaise volcano reunion island abstract the recent activity of the piton de la fournaise volcano offers a rare opportunity to address the issue of pb isotope behavior in volcanic fumaroles as the composition of the degassing source is accurately and precisely known gas sublimates formed between 2007 and 2011 at temperature ranging from 400 to ca 100 c include na k sulfate aphthitalite ca cu sulfate e g gypsum na sulfate thenardite ca mg al fe fluoride e g ralstonite and native sulfur the high temperature deposits show trace element patterns typical of volcanic gas with pb concentration up to 836 ppm while the low temperature deposits are depleted in most volatile elements pb only for low temperature fluoride samples do pb isotope compositions plot significantly outside the field of lavas the isotopic shift is ascribed to leaching ubiquitous unradiogenic phases e g sulfides by acidic gas condensates the similarity in pb isotope signature between lavas and sublimate samples more representative of the gas phase sulfates indicates that the net fractionation of pb isotopes resulting from volatilization and condensation processes is smaller than the precision of pb isotope measurements better than 60 ppm a m u the absence of net fractionation could result from negligible isotope fractionation during pb volatilization followed by extensive condensation of gaseous pb with possibly significant isotopic fractionation at this stage although this scenario has to be refined by more direct measurement of the gas phase and its general applicability tested it suggests that a small fraction resolving very small isotopic differences between magmas and their gaseous products remains an analytical challenge high precision pb isotope measurements rest not only on instrumental performance but also on high yield chemistry as pb isotopes drastically fractionate 800 ppm a m u upon elution on anionic resin for 50 pb recovery the estimated isotopic bias is plus or minus 60 80 ppm a m u depending on which of the early isotopically light or late isotopically heavy pb fraction is lost

rapid passage of a small scale mantle heterogeneity through the melting regions of kilauea and mauna loa volcanoes recent kilauea and mauna loa lavas provide a snapshot of the size shape and distribution of compositional heterogeneities within the hawaiian mantle plume here we present a study of the pb sr and nd isotope ratios of two suites of young prehistoric lavas from these volcanoes 1 kilauea summit lavas erupted from ad 900 to 1400 and 2 14 c dated mauna loa flows erupted from 2580 140 yr before present relative to ad 1950 these lavas display systematic isotopic fluctuations and the kilauea lavas span the pb isotopic divide that was previously thought to exist between these two volcanoes for a brief period from ad 250 to 1400 the 206 pb 204 pb and 87 sr 86 sr isotope ratios and end values of kilauea and mauna loa lavas departed from values typical for each volcano based on historical and other young prehistoric lavas moved towards an intermediate composition and subsequently returned to typical values this is the only known period in the eruptive history of these volcanoes when such a simultaneous convergence of pb sr and nd isotope ratios has occurred the common isotopic composition of lavas erupted from both kilauea and mauna loa during this transient magmatic event was probably caused by the rapid passage of a small scale compositional heterogeneity through the melting regions of both volcanoes this heterogeneity is thought to have been either a single body 35 km long based on the distance between the summits of these volcanoes or the plume matrix itself which would be expected to be present beneath both volcanoes the time scale of this event centuries is much shorter than previously noted for variations in the isotopic composition of hawaiian lavas due to the upwelling of heterogeneities within the plume thousands to tens of thousands of years calculations based on the timing of the isotopic convergence suggest a maximum thickness for the melting region and thus the heterogeneity of 5 10 km the small size of the heterogeneity indicates that melt can be extracted from small regions within the hawaiian plume with minimal subsequent chemical modification beyond the effects of crystal

origin and fate of sulfide liquids in hotspot volcanism la reunion pb isotope constraints from residual fe cu oxides immiscible sulfide liquids in basaltic magmas play an important role in trace metal transport and the sulfur budget of volcanic eruptions however sulfides are transient phases whose origin and fate are poorly constrained we address these issues by analyzing sulfide destabilization products preserved in lavas from la reunion island iron oxide globules and coatings typically 20 80 m in size were found to occur in vesicles of differentiated lavas from piton des neiges and recent pumice samples from piton de la fournaise field and mineralogical evidence indicates that the iron oxides are syn eruptive phases not resulting from hydrothermal processes samples were first studied by scanning electron microscopy the globules were separated whereas the smaller spherules and coatings were concentrated by magnetic sorting and acid leaching and samples were processed through wet chemistry the fe oxide phases comprise 49 74 wt fe 26 40 wt o and up to 6 wt cu 811 ppm ni 140 ppm bi and 8 5 ppm pb compared to the host lava cu ni and bi are enriched by a factor of 101 103 systematic pb isotope disequilibrium between 500 ppm and 2 9 for 206pb 204pb exists between fe oxides and host rocks with fe oxides generally displaying less radiogenic ratios unradiogenic pb is a typical signature of sulfide which tends to concentrate pb but not its parent elements u and th thus both the chemical and isotopic compositions of the vesicle hosted fe oxides suggest that they are more or less direct products of the destabilization of immiscible sulfide liquids although pb dominantly partitions into the gas phase during sulfide breakdown the original pb isotope signature of sulfide is preserved in the residual oxide the composition estimated for the parent sulfides 206pb 204pb 18 20 18 77 207pb 204pb 15 575 and 208pb 204pb 38 2 38 8 precludes a genetic link with the la reunion plume and suggests a lithospheric or crustal origin it is estimated that magma ascent velocities at piton de la fournaise are high enough to counterbalance the settling velocities of millimeter size sulfides despite their high density sulfide liquids are thus transferred upward during eruptions and their destabilization contributes to so2 emanations assimilation of foreign sulfides from the lithosphere can explain why so2 emissions sometimes e g during the april 2007 eruption exceed those predicted from the s content of melt inclusions