seismicity of the teton southern yellowstone region wyoming abstract epicenter patterns focal depths and focal mechanisms for earthquakes occurring between 1973 and 1981 in the teton jackson hole southern yellowstone region are presented in this study available earthquake information recorded prior to 1980 was combined with the results obtained from two microearthquake surveys operated in 1980 and 1981 earthquakes used in this joint analysis met rigid standards for location accuracy and hence the resulting data set provides the most complete accurate and up to date information on seismicity in this region the majority of earthquakes in the region do not appear to be associated with mapped traces of quaternary faults the teton fault appears to be active at the small earthquake level along some of its segments although several segments including the north central segment which exhibits the greatest prehistoric displacement appear to be quiescent seismicity in the gros ventre range may be related to reactivation of older basement structures fault plane solutions in the region show predominately normal faulting with extension in an east west to northwest southeast direction geologic seismic moment rates of 1 1 10 24 dyne cm yr for the teton region and 4 0 10 23 dyne cm yr for the teton fault were estimated using available geologic information on mapped faults from the limited available data a return period of 130 to 155 yr for a magnitude 6 5 to 7 5 earthquake is predicted for the teton region while the teton fault has a predicted return period of 800 to 1800 yr for a magnitude 7 5 earthquake a regional strain rate of 6 9 10 9 yr is also obtained

volatile emission during the eruption of baitoushan volcano china north korea ca 969 ad magma volume dre 24 5 km3 the main phase ca 95 vol is represented by comenditic tephra deposited dominantly as widespread fallout blankets and proximal ignimbrites the eruption column is estimated to have reached ca 25 km and thus entered the stratosphere a late phase 5 vol is represented by trachyte emplaced chiefly as moderately welded ignimbrites the comendites contain 3 and the trachytes 10 20 vol phenocrysts mainly anorthoclase hedenbergite and fayalite primary glassy melt inclusions with no signs of leakage were found only in phenocrysts in the comenditic tephra whereas those in phenocrysts in the trachytes are devitrified the comendite magma is interpreted to have been generated by fractional crystallization from a trachyte magma represented by melt inclusions in the phenocrysts in the comendite tephra the mass of volatiles emitted to the atmosphere during the eruption was estimated using the petrologic method the average h2o concentration of the comenditic matrix glass is 1 5 wt probably largely secondary and of the corresponding melt inclusions 5 2 wt melt inclusions in feldspar and quartz present the highest halogen concentrations with a calculated average for chlorine of 4762 ppm and for fluorine of 4294 ppm the comenditic matrix glasses are represented by a fluorine rich 3992 ppm f and fluorine poor group 2431 ppm f averaging 3853 ppm for chlorine only 20 of all sulfur analyses of the comenditic matrix glasses and melt inclusions are above the detection limit of 250 ppm s the difference between pre and post eruptive concentration of h2o is at least 3 7 0 6 wt h2o taking into consideration re hydration of the matrix glass and possible leakage of melt inclusions the difference between pre and post eruptive concentrations of the halogens amounts to 909 90 ppm cl and 1863 280 ppm and 302 40 ppm f the difference for s was estimated based on the average of the maximum s concentrations in the melt inclusions 455 ppm s and the detection limit resulting in 205 40 ppm s the calculated mass of volatiles injected into the atmosphere based on the erupted magma volume and volatile data is 1796 453 megatons for h2o 45 10 megatons for chlorine 42 11 megatons for fluorine and 2 0 6 megatons for sulfur the 969 20 ad eruption of baitoushan volcano one of the largest eruptions of the past 2000 years is thought to have had a substantial but possibly short lived effect on climate

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

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

pre eruptive volatile content and degassing history of an evolving peralkaline volcano abstract the volatile contents of melt inclusions trapped within phenocrysts of quartz and feldspar in peralkaline rhyolites from mayor island new zealand have been studied using fourier transform infrared spectroscopy and ion microprobe analyses the glass inclusions analyzed span the 130 ka subaerial eruptive history of the island and come from volcanic deposits representing a wide range of eruptive styles explosive vs effusive magmatic vs phreatomagmatic low vs high discharge rates the water content of all inclusions analysed is uniformly high at 4 4 wt h2o whereas co2 contents are below the limits of detection 50 ppm chlorine in melt inclusions ranges from 2070 to 5200 ppm while coexisting matrix glasses have generally lower cl concentrations of 1700 4200 ppm the apparent bulk distribution coefficient describing cl partitioning between melt and vapor phase cl fluid cl melt during degassing is 5 15 fluorine appears to be less affected by eruptive degassing than is cl and melt inclusion and matrix glass f concentrations show significant overlap 1400 2520 ppm f in inclusions 1550 2890 ppm f in matrix glass the observed invariance of melt inclusion water content with sample age contrasts with ion microprobe data on incompatible trace elements e g zr nb which suggest 35 fractionation between the oldest and youngest samples this along with the cl partitioning behaviour suggests that at least the upper erupting portion of the mayor island magma chamber was water saturated throughout the volcano s 130 ka eruptive history furthermore the large range of eruptive styles observed on mayor island are not due to differences in water concentration of the erupting magma but instead must reflect differences in rates of magma ascent and supply which control the efficiency of non explosive degassing

depth of emplacement fluid provenance and metallogeny in granitic terranes a comparison of western thailand with other tin belts the most important tin mineralization in thailand is associated with the late cretaceous to middle tertiary western thai granite belt a variety of deposit types are present in particular pegmatite vein and greisen styles of mineralization a feature common to most of the deposits is that they are associated with granites that were emplaced into the khang krachan group which consists of poorly sorted carbonaceous pelitic metasediments most of the deposits contain low to moderately saline aqueous fluid inclusions and aqueous carbonic inclusions with variable ch4 co2 ratios low salinity aqueous inclusions represent trapped magmatic fluid in at least one case the nong sua pegmatite based on their occurrence as primary inclusions in magmatic garnet aqueous carbonic inclusions are commonly secondary and neither the co2 nor nacl contents of these inclusions decrease in progressively younger inclusions implying that they are not magmatic in origin reduced carbon is depleted in the metasediments adjacent to granites and the d values greisen muscovites are variable but are as low as 134 per mil indicative of fluid interaction with organic graphitic material this suggests that the aqueous carbonic fluid inclusions represent fluids that were produced at least in part during contact metamorphism metasomatism by comparing the western thai belt with other sn w provinces it is evident that there is a strong correlation between fluid composition and pressure in general low to moderately saline aqueous inclusions and aqueous carbonic inclusions are characteristic of mineralization associated with relatively deep plutonic belts mineralized pegmatites are also typically of deeper plutonic belts and pegmatite hosted deposits may contain cassiterite that is magmatic crystallized from granitic melt or is orthomagmatic hydrothermal crystallized from aqueous or aqueous carbonic fluids in origin the magmatic aqueous fluids those that were exsolved from granitic melts are interpreted to have had low salinities as a consequence of the low salinities tin is partitioned in favour of the melt on vapour saturation thus with a high enough degree of fractionation the crystallization of a magmatic cassiterite or different sn phase such as wodginite is inevitable because tin is not partitioned in favour of the vapour phase upon water saturation of the granitic melts it is proposed that relatively deep vein and greisen systems tend to form by remobilization processes in addition many deeper greisen systems are hosted in part by carbonaceous pelitic metasediments and the reduced nature of the metasediments may play a key role in remobilizing tin sub volcanic systems by contrast are characterized by high temperature high salinity fluids owing to the high chlorinity tin is strongly partitioned in favour of the vapour and cassiterite mineralization can form by of orthomagmatic hydrothermal processes similar relationships between the depth of emplacement and fluid composition also appear to apply to other types of granite hosted deposits such as different types of molybdenum deposits

the probable occurrence of interstitial al in hydrous f bearing and f free aluminosilicate melts experiments carried out on the system sio2 naalsi3o8 kalsi3o8 qz ab or at 1 kbar in the presence of h2o and f show that the quartz alkali feldspar field boundary is progressively displaced towards the feldspar join as f contents increase from 0 to 4 wt f increasing p h 2 o in the absence of f has already been shown to have a similar effect tuttle and bowen 1958 luth jahns and tuttle 1964 the increased size of the quartz field in the f bearing system compared to the hydrous system is believed to be caused by progressive removal of al from the tetrahedral network of the melt by complexing with f the residual network in the melt is thus enriched in si and this stabilizes precipitation of quartz rather than feldspar for certain bulk compositions the common presence of quench cryolite na3alf6 in certain experiments carried out with 4 wt f supports this interpretation and indicates that some al in the melt may be present in six fold coordination with f the effect of h2o in the absence of f may be similar with al being progressively removed from four fold coordination as more h2o is dissolved in the melt although a proportion of al in hydrous melts may occur in six fold coordination dry melts predominantly contain al in four fold coordination this major difference in al complexing may be one of the main causes for differences in the high pressure phase relations of wet and dry albearing silicate systems

experimental and modeled chlorine solubilities in aluminosilicate melts at 1 to 7000 bars and 700 to 1250 c applications to magmas of augustine volcano alaska hydrothermal experiments were conducted at ca 1 to 7000 bars and 700 to 1250 c in 121 rhyolitic to basaltic systems to determine cl solubility in silicate melts i e the maximum cl concentration in melts that are saturated in a hydrosaline liquid with or without an aqueous or aqueous carbonic vapor the cl concentration of melts increases with the cl contents of the fluid unless the melt coexists with vapor plus hydrosaline liquid at fixed pressure and temperature this phase assemblage buffers the cl content of each phase with increasing cl in the system the cl content of fluid s saturated melts is independent of the co 2 concentration of the saline liquid vapor with up to 21 wt co 2 in the fluid s the experiments show that cl dissolution in aluminosilicate melts increases with temperature and pressure chlorine solubility is also a function of melt composition it increases with the molar al 1 2 ca 1 2 mg 1 2 na si of the melt these experimental data have been integrated with results involving 41 other experiments webster and de vivo 2002 to develop a broadly expanded model that supports calculation of cl solubility in 163 aluminosilicate melts this empirical model applies to cl dissolution in melts of most silicate magmas at depths as great as 25 km it determines the exsolution of hydrosaline liquid with or without a coexisting vapor as magmas ascend from depth cool crystallize and differentiate from mafic to felsic compositions in combination with h 2 o solubility models our model supports determination of h 2 o cl solubility relations for most aluminosilicate magmas and is useful for barometric estimations based on silicate melt inclusions containing low co 2 and moderate to high cl concentrations the model is applied to the phase relations of fluids in volatile enriched magmas of augustine volcano alaska the cl and h 2 o concentrations of melt inclusions from 14 basaltic to dacitic eruptive units are compared with modeled solubilities of cl and h 2 o in augustine melts the majority of these eruptions involved magmas that first exsolved aqueous to aqueous carbonic vapors when the melts were dacitic in composition i e before the residual melts in these magmas had evolved to felsic compositions and well prior to the eruptions hydrosaline liquid with or without a vapor phase exsolved from other more felsic fractions of augustine melts at low near surface pressures of several tens of bars

the geochemical signature of fluid saturated magma determined from silicate melt inclusions in ascension island granite xenoliths abstract silicate glasses in crystal free to crystal poor melt inclusions from two coarse grained granite xenoliths in alkaline volcanic rocks of ascension island were analyzed for 29 major minor and trace elements for most constituents the glass compositions are similar to those of the volcanic whole rocks and the xenoliths we interpret the glasses to be chemically representative of granite melt the melt inclusions are silicic alkaline contain low s and p abundances and are enriched in h 2 o cl f and na relative to k inclusions from one xenolith contain 1 3 wt f on average whereas those from the other xenolith contain half that amount the melt inclusion compositions allow investigation of the means and extent of granite magma evolution the presence of magmatic fluid inclusions in close proximity to melt inclusions in the phenocrysts indicates that the granite melt was saturated in one or more volatile phases roedder and coombs 1967 the cl and h 2 o contents of the melt inclusions are consistent with the exsolution of volatile phase s at pressures of 3000 to 2000 bars the glasses also show trends involving the cl h 2 o ratio and the incompatible trace elements in melt that are indicative of melt evolution via crystal fractionation of volatile phase saturated melt these trends should be useful for recognizing volatile phase saturation in other cl enriched melts

k and cl concentrations on the martian surface determined by the mars odyssey gamma ray spectrometer implications for bulk halogen abundances in mars 1 orbital gamma ray spectrometry shows that the martian surface has a mean cl k ratio of 1 3 0 2 indistinguishable from the ratio in ci chondrites 1 28 although cl and k fractionate by magma degassing and aqueous processing during igneous partial melting both elements are highly incompatible thus if the surface cl k reflects the bulk crustal value then the mantle hence primitive silicate mars also has a roughly ci ratio martian meteorite data indicate that cl br is also approximately chondritic suggesting that elements that condensed in the nebula between 1000 k k and cl to 500 k br are uniformly depleted in mars at about 0 6 ci chondrite concentrations mars clearly does not contain 0 6 ci levels of h2o which would be 6 wt indicating that mars was constructed by planetesimals rich in volatile elements but not in water

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

evolution of high temperature hydrothermal fluids associated with greisenization and feldspathic alteration of a tin mineralized granite northeast queensland greisenization albitization and k feldspathization occur as pervasive background alteration and fracture controlled selvage style alteration in the go sam granite in the herberton mount garnet tin fields of northeast queensland optical sem and microthermometric investigations of fluid inclusions principally from vug filling minerals in selvage style alteration permit interpretation of the nature and evolution of hydrothermal fluids responsible for alteration of the granite saline hydrothermal fluids are dominated by na k ca fe chloride solutions with mg mn zn si al th ce and la relatively minor but important components salinities of up to 70 wt percent total dissolved salts have been calculated using the phase volume method indicated trapping temperatures of 600 degrees to 650 degrees c for many saline inclusions in vug filling minerals from feldspathic rocks record minimum temperatures for feldspathic alteration inferred temperatures for greisenization are similar and slightly lower 450 degrees 525 degrees c trapping temperatures and the composition of fluids in saline inclusions suggest late magmatic to early postmagmatic alteration of the granite by predominantly magmatic fluids inclusions containing relatively dilute fluids of possible meteoric origin homogenize between 100 degrees and 400 degrees c salinities as low as 2 equiv wt percent nacl are indicated and significant co super 2 3 hco super 3 or so super 2 4 may be present associated vapor rich inclusions indicate that the dilute fluids were probably boiling between 300 degrees and 400 degrees c a continuous range of salinities from dilute fluids to saline fluids has been found in the inclusions investigated dilution of very saline high temperature fluids could have occurred by separation of dissolved components as the fluid cooled and by mixing with dilute fluids below 400 degrees c data from fluid inclusions in magmatic quartz from the go sam granite are similar to those obtained from vug filling minerals in fracture controlled metasomatic rocks they suggest that pervasive alteration and fracture controlled alteration occurred contemporaneously and as a result of interaction with the same fluids consistently high temperatures inferred for the formation of all feldspathic rocks and associated greisens do not fit an established soviet model which emphasizes falling temperatures for the origin of comparable rocks a tentative model which emphasizes high temperature evolution of hydrothermal fluids due to changes in chemical parameters ph salinity na k f sub f 2 and confining pressures is discussed

magma mixing and gold mineralization in the maevatanana gold deposit madagascar abstract the maevatanana gold deposit in madagascar is hosted by archean metamorphic rocks in quartz sulfide veins that are structurally controlled by nnw sse trending shear zones fluid inclusion data show that the trapping conditions in quartz range from 0 87 to 2 58 kbar at temperatures of 269 362 c laser raman spectroscopy confirms that these inclusions consist of co 2 so 2 and h 2 o the 34 s values of the pyrites range from 1 7 to 3 6 with an average of 2 25 supporting a magmatic origin noble gases he ne ar ke xe are chemically inert thus will not be involved in chemical reactions during geological processes also due to the low concentration of he in the atmosphere and the low solubility of he in aqueous fluids the atmosphere derived he is unlikely to significantly affect he abundances and isotopic ratios of crustal fluids ensures that he production should have the typical crust 3 he 4 he ratios the 3 he 4 he ratios of fluid inclusions in pyrite from the deposit range from 0 06 to 0 12 ra while the 40 ar 36 ar ratios range from 6631 to 11441 we infer that the ore forming fluids could have been exsolved from a granitic magma the oxygen and hydrogen isotope compositions of the ore forming fluids 1 5 18 o h2o 7 8 72 d 117 indicate they were derived from a granitic magma four pyrite samples from the gold deposit yield a precise re os isochron age of 534 13 ma given that the post collisional granites in northern and central madagascar were derived by melting of sub continental lithospheric mantle and formed between 537 and 522 ma we can state that the gold metallogenesis was coeval with the crystallization age of these parental magmas these data could be accounted for the formation of the maevatanana gold deposit first the shear zones hosting the deposit formed around 2 5 ga when the madagascan micro continental blocks collided with other continental blocks triggering large scale tectono magmatic activity and forming nnw sse trending shear zones the gold mineralization at maevatanana is coeval with the crystallization age of the cambrian post collisional a type granitoid plutons in northern and central madagascar implying that this deposit is associated with extensional collapse of the east african orogen this extension in turn induced asthenospheric upwelling melting of sub continental lithospheric mantle these magmas underplated the lower crust generating voluminous granitic magmas by partial melting of the lower crust the mixing magma during tectono thermal reactivation of the east african orogen produced large volumes of volatiles that extracted gold from the granitic magma and produced au s complexes e g au hso 3 2 the shear zones which were then placed under extensional collapse of the east african orogen in the cambrian formed favorable pathways for the magmatic ore forming fluids these fluids then precipitated gold sulfides that form the maevatanana gold deposit

cl br and i in igneous standard rocks abstract radiochemical neutron activation analysis rnaa and isotope dilution mass spectrometry idms are applied to the determination of cl br and i in igneous standard rocks seventeen different standard samples of igneous rocks distributed by the geological survey of japan gsj and by the association national de la recherche technique anrt in france were investigated the cl contents range from 10 to 1000 ppm br from 0 05 to 2 5 ppm and i from 5 to 100 ppb in this study four standard samples for cl eight for br and six for i were newly determined the analytical results between rnaa and idms are in good agreement within one standard deviation the halogen contents are found to be well correlated for cl and br but less clearly for i halogens generally are enriched in rhyolites in the volcanic rock series while they are depleted in plutonic rock series especially in granite

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

aluminous granite as a source magma of hydrothermal ore deposits an experimental study partition ratios of zinc and lead between synthetic granitic melts and aqueous phase were determined at 800 degrees c and under p sub h 2 o 3 5 or 0 25 kb two starting glasses in the system sio 2 al 2 o 3 cao na 2 o were prepared their bulk chemical compositions are similar i e sio 2 content of 75 65 percent in glass 1 and of 74 68 percent in glass 2 glass 1 is prepared to be slightly alkaline with 1 89 percent normative wollastonite and glass 2 is slightly aluminous with 2 42 percent normative corundum the partition ratio of sodium between aqueous fluid and melt k p na can be expressed by the following equation over the whole range of chloride concentrations in the aqueous solution m v cl mole kg regardless of the normative composition of the melt k p na 0 468 x m v cl however the partition ratio of zinc k p zn for the aluminous melt is more than two orders of magnitude larger than that for the alkaline melt k p zn varies with the square of the chloride concentration in the aqueous phase and is satisfied by the following two equations k p zn 9 40 x m v cl 2 aluminous melt 2 and k p zn 0 0833 x m v cl 2 alkaline melt 1 a similar contrast was also observed in the partition ratios of lead between aqueous phase and melts k p pb 2 26 x m v cl 2 aluminous melt 2 and k p pb 0 0474 x m v cl 2 alkaline melt 1 the log of the partition ratio shows an excellent inversely proportional relation with the ph at 25 degrees c of the aqueous solution which was equilibrated with granitic melts and quenched a slope of 2 is obtained for alkaline melt and is reasonably explained by the equation pbo melt 2h super vapor 2cl super vapor pbcl sub 2 vapor h 2 o the slope for the aluminous melt 1 2 may be explained only by complex reactions involving silicate ligands in the melt the results indicate that only aluminous granite is capable of producing hydrothermal fluids which would contain a significant amount of ore metals in other words aluminous granite can be ore bearing by postmagmatic processes this is likely to happen when a granitie magma which originally was slightly alkaline changed its composition to slightly aluminous during diapiric uplift by assimilation of pelitic sediments if this compositional evolution happened then granitic magma would tend to store up base metals during the early stages of its evolution and release them very efficiently in the later stages to form a hydrothermal ore solution

magmatic co 2 and saline melts from the sybille monzosyenite laramie anorthosite complex wyoming there are three populations of fluid inclusions in quartz from the sybille monzosyenite early co2 secondary co2 and rare secondary brines the oldest consist of low density co2 0 70 inclusions that appear to be co magmatic the densities of these inclusions are consistent with the inferred crystallization conditions of the sybille monzosyenite namely 3 kilobars and 950 1000 c the other types of inclusions are secondary they contain co2 0 50 and secondary brine inclusions that form trains radiating out from a decrepitated inclusion the sites of these decrepitated inclusions are now marked by irregularly shaped fluid inclusions and solid inclusions of salt and carbonate rather than fluid inclusions feldspar contain abundant solid inclusions these consist of magmatic minerals hedenbergite hornblende ilmenite apatite and graphite intimately associated with k na chlorides we interpret these relations as follows the sybille monzosyenite formed from a magma that contained immiscible droplets of a halide rich melt along with a co2 vapor phase the salt was trapped along with the other obvious magmatic minerals during growth of the feldspars co2 may have also been included in the feldspars but it probably leaked later during exsolution of the feldspars and was not preserved both the saline melt and the co2 vapor were trapped in the quartz the melt inclusions in the quartz later decrepitated perhaps due to progressive exsolution of fluids to produce the secondary h2o and co2 inclusions these observations indicate that the sybille monzosyenite which is a markedly anhydrous rock was actually vapor saturated rather than being h2o however the vapor was co2 rich and possibly related to an immiscible chloride rich melt

geological 3 d model of the larger altensalzwedel area germany for temperature prognosis and reservoir simulation in the framework of the german r d programme clean co2 large scale enhanced gas recovery in the altmark natural gas field the geological structure of an area encompassing the altensalzwedel sub field and its surrounding was analysed in detail a 3 d model was developed that contains the major geological formations and their general lithology including the natural gas reservoir in the permian rotliegend the immediate cap rock permian zechstein of the reservoir and its overburden based on this geological model a 3 d steady state thermal model was generated as part of a shared earth model the parameterisation of the geological model layers with thermal rock properties is based on laboratory and well log data the model shows temperature changes in dependence of geological structure and of different rock thermal conductivity the calculated surface heat flow is high 80 mw m 2 for most of the area which is in accordance to measured surface heat flow temperature on top of the rotliegend reservoir is variable ranging from 110 to 150 c the quantification of temperature changes versus depth as well as laterally in the reservoir are valuable input data for modelling the dynamic processes of co2 injection within clean

fluid inclusion evidence for magmatic silicate saline co2 immiscibility and geochemistry of alkaline xenoliths from ventotene island italy abstract fluid and melt inclusions and geochemical features of alkali syenite mafic and ultramafic cumulate xenoliths in the last ignimbritic event volcanism up to 300 ky b p at the island of ventotene in the pontine archipelago gaeta gulf were investigated to establish the genesis and evolution of the fluids trapped in the inclusions ranges in lead isotopic compositions of the xenoliths as a group are narrow 206pb 204pb 18 778 18 864 207pb 204pb 15 641 15 701 208pb 204pb 38 858 39 090 the values overlap among the groups implying that the xenoliths are closely related the xenoliths straddle the best fit line describing the regional nw se variation of values for uranogenic pb in volcanic rocks from the roman alkaline province the similarity between the xenoliths and volcanic rocks permits the interpretation that the xenoliths are representative of the source region of the volcanic rocks residues after partial melting of the source region or fractional crystallization of the volcanic rocks or even that the xenoliths represent assimilants obtained during the evolution of the magmas that produced the volcanic rocks xenoliths belonging to the ultramafic mafic cumulate group contain only silicate melt inclusions vapor bubble droplets of an opaque phase and rarely some co2 trapped in silicate melt inclusions xenoliths in the alkali syenite group have three types of fluid inclusions 1 single phase vapor and silicate melt inclusions 2 two phase silicate melt salt silicate melt co2 v aqueous l v and silicate melt vapor inclusions and 3 three phase and multiphase inclusions co2 l co2 v h2o silicate melt saline melt h2o birefringent or opaque trapped minerals h2o salt silicate glass birefringent trapped minerals during heating experiments melting of salt occurs at temperatures from 565 to 815 c depending on the water content of the inclusions homogenization of the vapor bubble occurs from 850 1160 c and complete melting of the silicate glass at about 950 c the highly variable proportions of the individual phases in the silicate melt salt h2o inclusions and the coexistence of silicate melt co2 inclusions indicates immiscibility during the crystallization of the magma primary and secondary co2 inclusions in the alkali syenite suite indicate lower densities from 0 10 to 0 22 g cm3 than those resulting from primary co2 inclusions in the gabbroic suite from 0 34 to 0 42 g cm3 the p t trajectory of the probable fluid evolution path shows that the crystallization of gabbro occurred between 1 and 1 4 kbars whereas alkali syenite crystallized between 200 and 400 bars the secondary h2o inclusions in alkali syenite were trapped in the later stages of the hydrothermal process and at much lower temperatures 130 290 c but at pressures relatively close to those of alkali syenite crystallization the almost isobaric conditions during the final stage of the fluid evolution path are explained by the very shallow emplacement of the alkali syenite intrusive body

gas saturation and evolution of volatile and light lithophile elements in the bandelier magma chamber between two caldera forming eruptions we have studied the distribution of light and volatile elements li be b h2o f cl in matrix glasses and melt inclusions in quartz and sanidine phenocrysts from tephras of the cerro toledo rhyolite which were erupted from the bandelier magma chamber between two caldera forming eruptions at 1 608 ma and 1 225 ma since the small volume tephras of the cerro toledo rhyolite record chemical evolution of the upper parts of the magma chamber during this 383 kyr period we can track volatile evolution in the magma during its differentiation specifically the development of a separate fluid phase from the magma the partitioning of volatile and light elements between this fluid and the magma and the timing of the second caldera eruption at 1 225 ma the melt inclusion data reveal that li be and b were progressively enriched with time at the top of the magma chamber showing a similar three fold enrichment by contrast f cl and f2o show more variable behavior f was enriched 3 6 times in the magma and cl increased 2 5 times while water concentrations remained constant evidence for a separate fluid phase includes 1 comparatively small magmatic enrichment factors for cl and h2o elements which are known to partition into fluid 2 decline of the cl be and cl b ratios in melt inclusions with time indicating preferential loss of cl and 3 maximum cl contents of 2900 3000 ppm in melt inclusions which are concentrations at or close to the saturation limit for cl in a two phase gas saturated magma the lack of temporal h2o enrichment in the magma suggests that it became gas saturated at an early stage the cl fluid magma partition coefficient was initially low due to the presence of a low salinity single phase vapor the fluid is calculated to have increased its salinity from 0 76 wt equivalent nacl to 3 1 wt nacl by crystallization and cl enrichment in the magma consequently the fluid was transformed to two immiscible phases as a result the cl partition coefficient increased and the cl content in the magma was buffered at 2900 3000 ppm overpressures in the magma chamber have been modeled as a function of crystallization total pressure and depth h2o solubility in rhyolite resurgence crystallization contraction and initial fluid mass for the large amounts of crystallization 40 70 required by the geochemical relations unrealistically large overpressures 75 mpa are indicated unless 1 the magma existed as a foam or 2 the chamber was able to degas passively and thus buffer the buildup of pressure to maintain realistic overpressures in the magma chamber 50 mpa an equilibrium was required between gas buildup by crystallization and volatile loss by passive degassing the change from a one phase vapor to a two phase immiscible fluid before the upper bandelier tuff eruption may have promoted partial or complete sealing of the magmatic hydrothermal system permitting significant overpressures to develop the result could have been a cataclysmic caldera forming eruption

water solubility and chlorine partitioning in cl rich granitic systems effects of melt composition at 2 kbar and 800 c abstract experiments have been conducted in the system na2o k2o al2o3 sio2 h2o cl2o 1 at 2 kbar and 800 c to determine the effects of melt composition on the solubility of water in haplogranite melt and on the distribution of cl between aqueous fluid and haplogranite melt the melts studied include peraluminous subaluminous and peralkaline haplogranites and quartz albite and quartz orthoclase compositions the solubility of water at 2 kbar and 800 c in water saturated haplogranite melts varies strongly as a function of melt composition water solubility in melt decreases in the order strongly peralkaline haplogranite quartz albite composition moderately peralkaline haplogranite peraluminous haplogranite subaluminous haplogranite quartz orthoclase composition d cl wt cl in fluid wt cl in melt is a strong function of system composition d cl increases as the concentration of cl in the system increases a comparison of the distribution of cl between haplogranite melts of subaluminous peraluminous and peralkaline compositions and aqueous fluids shows that with similar concentrations of cl in the system d cl is largest for subaluminous melts a nk 1 having relatively high k2o concentrations as the a nk of melt increases or decreases from 1 or as the n nk of the melt increases both d cl and the concentration of cl in the fluid decrease the experimental data imply that complexes involving cl and na in hydrous subaluminous granite melts are dominant furthermore the data imply that in hydrous peraluminous granite melts cl complexes with network modifying a13 and in hydrous peralkaline granite melts cl complexes with network modifying na k on a molar basis cl apparently complexes with network modifying a13 in peraluminous melts as strongly as it does with na and k in peralkaline melts experimental studies of cl partitioning in granitic systems suggest that the strongest enrichment of magmatic hydrothermal fluids in cl and ore metals complexed with cl will most likely occur in fluids exsolved from subaluminous granite magmas that are relatively enriched in k2o sio2 and cl and relatively depleted in f co2 and na2o

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

magma storage conditions of large plinian eruptions of santorini volcano greece the intensive variables of dacitic rhyodacitic magmas prior to four large plinian eruptions of santorini volcano over the last 200 kyr minoan cape riva lower pumice 2 and lower pumice 1 were determined by combining crystallization experiments with study of the natural products including the volatile contents of melt inclusions trapped in phenocrysts phase equilibria of the silicic magmas were determined at pressures of 1 2 and 4 kbar temperatures of 850 900 c fluid h2o co2 saturation xh2o molar h2o h2o co2 between 0 6 and 1 melt h2o contents of 2 10 wt and redox conditions of fmq fayalite magnetite quartz buffer or nno 1 where nno is ni nio buffer experiments were generally successful in reproducing the phenocryst assemblage of the natural products the phase relationships vary significantly among the investigated compositions revealing a sensitivity to small variations in whole rock compositions our results show that the pre eruptive storage conditions of the four silicic magmas were all very similar the magmas were stored at t 850 900 c and p 2 kbar under moderately reduced conditions nno 0 9 to 0 1 and were poor in fluorine 500 800 ppm and sulphur 100 ppm but rich in water and chlorine 5 6 wt and 2500 3500 ppm respectively in all cases the melts were slightly undersaturated with respect to h2o but most probably saturated with respect to h2o cl co2 and a brine the santorini magma plumbing system appears to be dominated by a large long lived 200 kyr predominantly silicic magma storage region situated at 8 km depth from which crystal poor melt batches were extracted during the largest caldera forming eruptions of the volcanic system

gold solubility in oxidized and reduced water saturated mafic melt abstract we have performed experiments to evaluate au solubility in natural water saturated basaltic melts as a function of oxygen fugacity experiments were carried out at 1000 c and 200 mpa and oxygen fugacity was controlled at the fayalite magnetite quartz fmq oxygen fugacity buffer and fmq 4 all experiments were saturated with a metal chloride aqueous solution loaded initially as a 10 wt nacl eq fluid the stable phase assemblage at fmq consists of basalt melt olivine clinopyroxene a single phase aqueous fluid and metallic au the stable phase assemblage at fmq 4 consists of basalt melt clinopyroxene magnetite spinel solid solution a single phase aqueous fluid and metallic au silicate glasses i e quenched melt and their contained crystalline material were analyzed by using both electron probe microanalysis epma and laser ablation inductively coupled plasma mass spectrometry la icp ms measured au concentrations in the quenched melt range from 4 8 g g 1 to 0 64 g g 1 at fmq 4 and 0 54 g g 1 to 0 1 g g 1 at fmq the measured solubility of au in olivine and clinopyroxene was consistently below the la icp ms limit of detection i e 0 1 g g 1 these melt solubility data place important limitations on the dissolved au content of water saturated cl and s bearing basaltic liquids at geologically relevant fo2 values the new data are compared to published experimentally determined values for au solubility in dry and hydrous silicate liquids spanning the compositional range from basalt to rhyolite and the effects of melt composition oxygen fugacity pressure and temperature are discussed

the solubility of h_ 2 o in melts in the system sio_ 2 al_ 2 o_ 3 na_ 2 o k_ 2 o at 1 to 2 kbars the solubilities of water in six melts in the system k 2 o na 2 o al 2 o 3 sio 2 were determined at 970 1630 bars and 800 c melts were synthesized hydrothermally in pt capsules in cold seal vessels and then quenched isobarically the solubilities were determined by micromanometric measurement of h 2 o evolved during vacuum fusion of vesicle free glass wafers and are reproducible to 2 8 2 s d of the concentration the solubilities at 970 bars for the granitic and phonolitic minimum melts are 2 88 pm 0 10 wt and 5 01 pm 0 14 wt respectively both peralkaline and peraluminous granitic melts have higher h 2 o solubilities than the 1 kbar p h 2 o minimum melt and indicate the existence of minima in solubilities at molar na k al 1 along joins of constant sio 2 two melts at constant sio 2 and na k al ratio but varying in na na k 0 57 0 69 molar have the same solubility 2 88 pm 0 10 2 74 pm 0 10 wt the compositional depend

chlorine rich pyrometamorphic magma at white island volcano new zealand abstract the 25 january 1987 phreatomagmatic eruption of congress vent on white island volcano ejected paralava bombs derived from pockets of pyrometamorphic magma the current white island magmas are calc alkaline basaltic andesite andesite but the paralavas are mostly highly peralkaline with molar na 2 o k 2 o al 2 o 3 ratios from 1 to 22 recorded in matrix glasses the glass compositions are highly variable though quench crystals of tridymite wollastonite and green clinopyroxene are ubiquitous while albite occurs only in the least peralkaline samples all have high alkali contents na 2 o k 2 o 10 and chlorine mostly 1 and up to 1 7 the paralava glasses represent the most cl rich volcanic melts yet discovered they display a strong positive correlation between cl and total fe but a negative correlation between cl and normative alkali feldspar content it is likely that the fe content of melts was the dominant control over cl solubility not their alumina alkali systematics possible parent rocks for the pyrometamorphic magmas include halite cemented crater lake sediments and acid sulfate hydrothermally altered vent breccias and tuffs as found in the eruption deposits together with the paralava bombs fusion probably occurred at temperatures between 830 and 1000 c and at a pressure below 5 mpa in a regime where silicate melts were buffered by immiscible nacl saturated aqueous vapor and hydrosaline melt the conditions required to form the paralava bombs appear to be uncommon but it is likely that similar pyrometamorphic melts could be generated at many volcanoes where shallow magma penetrates a hydrothermal system

fluid immiscibility in volcanic environments volatile components enter the atmosphere oceans and other surface waters through pre syn and post eruptive volcanic processes that involve a variety of fluids aluminosilicate poor fluids include aqueous or carbonic to sulfide sulfate chloride fluoride carbonate and phosphate rich compositions in volcanic environments but other more complex combinations of these constituents may be involved giggenbach 1977 roedder 1984 1992 lowenstern 1995 other rare gases and dissolved constituents e g h2 n2 he ar h3bo3 hg ch4 and other hydrocarbon compounds metals and metalloids are also present but in general they are not sufficiently concentrated to form their own phases or control bulk fluid composition and volcanic processes as a result of their diverse compositions volcanic fluids ranging from vapor to liquid exhibit widely different densities and show strong distinctions in heat capacity dielectric behavior viscosity and other chemical and physical characteristics geiger et al 2006a the density of a saline liquid in the system nacl h2o at 50 mpa and 800 c for example is more than 7 times that of the coexisting aqueous vapor e g 0 2 gm cm3 henley and mcnabb 1978 multiple fluids move mix and or unmix in magma chambers and volcanic conduits in the root zone of fumaroles and in the convective hydrothermal systems that are ubiquitous to volcanic environments hydrothermal systems are typically centered on magmatic intrusions and may include crater lakes at the top of eruptive conduits hydrothermal processes involving two or more fluid phases operate through a variety of geologically relevant shallow crustal pressure temperature composition conditions volcanic fluids occur at supersolidus to subsolidus conditions meaning that the dense aluminosilicate melt that is common to volcanism may or may not be present this chapter addresses the evidence for and occurrence of two or more low density aluminosilicate poor fluids

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