dawsonite formation in the beier sag hailar basin ne china tuff a natural analog for mineral carbon storage abstract we determined the rock types the authigenic minerals the paragenetic sequence and the origin of dawsonite in pyroclastic rocks from the yimin formation of beier sag in the hailar basin china dawsonite a diagenetic mineral is thought to result from a large influx of co 2 and therefore this system represents a natural analogue for in situ mineral carbon storage the studied host rocks are mainly tuffs tuffaceous sandstones which now contain up to 70 vol authigenic carbonates including dawsonite ankerite and siderite the initial alteration of the tuffs yielded minor siderite kaolinite illite and mixed illite smectite then formed as product phases dawsonite and quartz subsequently precipitated in response to co 2 influx apparently coupled to feldspar and perhaps kaolinte dissolution dawsonite reaches a maximum 25 vol of the bulk rock mass balance suggests that this co 2 influx was coupled to the external import of sodium and export of sio 2 ankerite and additional siderite precipitated during the late stage alkaline diagenesis the carbon isotope values of the dawsonite are in the range 4 1 to 2 2 indicating the magmatic origin of the co 2 vitrinite reflectance and thermal gradient constraints suggest that the dawsonite at this location formed at a temperature of 75 c

geochemical effects of co2 sequestration in sandstones under simulated in situ conditions of deep saline aquifers abstract the geochemical effects of brine and supercritical co 2 scco 2 on reservoir rocks from deep 1500 2000 m saline aquifers were examined via experimental simulation at in situ conditions dry sandstone samples were mounted in a triaxial cell and autoclave system evacuated and saturated with 1 m nacl solution the brine rock system was allowed to react at 30 mpa confining pressure 15 mpa pore fluid pressure and 60 c while scco 2 was injected at a pressure gradient of 1 2 mpa the experiment was conducted for a period of 1496 h during which fluids were periodically sampled and analyzed the ph measured in partially degassed fluid samples at 25 c decreased from a starting value of 7 0 4 3 9 days and finally 5 1 after saturation with scco 2 fluid analyses indicate that most of the major e g ca mg fe mn and trace elements e g sr ba pb of the sandstone increase in concentration during the reaction with brine and scco 2 these results are supported by scanning electron microscopy which indicates dissolution of dolomite cement k feldspar and albite in addition to dissolution reactions the formation of montmorillonite was observed by adjusting surface area and reaction rates of dissolution and precipitation geochemical modeling of the experiments could reproduce long term trends in solution chemistry and indicated limited rates of dissolution as the system remained strongly undersaturated with most minerals including carbonates the geochemical models could not account for decreases in concentration of some elements changes in solution composition resulting from changes in imposed pressure gradient and the observed ca mg and si al ratios in solution

a fresh approach to investigating co2 storage experimental co2 water rock interactions in a low salinity reservoir system the interactions between co2 water and rock in low salinity host formations remain largely unexplored for conditions relevant to co2 injection and storage core samples and sub plugs from five jurassic aged surat basin sandstones and siltstones of varying mineralogy have been experimentally reacted in low salinity water with supercritical co2 at simulated in situ reservoir conditions p 12mpa and t 60 c for 16days 384h with a view to characterising potential co2 water rock interactions in fresh or low salinity potential siliclastic co2 storage targets located in queensland australia co2 water rock reactions were coupled with detailed mineral and porosity characterisation obtained prior to and following reaction to identify changes in the mineralogy and porosity of selected reservoir and seal rocks during simulated co2 injection aqueous element concentrations were measured from fluid extracts obtained periodically throughout the experiments to infer fluid rock reactions over time fluid analyses show an evolution of dissolved concentration over time with most major e g ca fe si mg mn and minor e g s sr ba zn components increasing in concentration during reaction with co2 similar trends between elements reflect shared sources and or similar release mechanisms such as dissolution and desorption with decreasing ph small decreases in concentration of selected elements were observed towards the end of some experiments however no precipitation of minerals was directly observed in petrography sample characterisation on a fine scale allowed direct scrutiny of mineralogical and porosity changes by comparing pre and post reaction observations scanning electron microscopy and registered 3d images from micro computed tomography micro ct indicate dissolution of minerals including carbonates chlorite biotite members and to a lesser extent feldspars quantitative mineral mapping of sub plugs identified dissolution of calcite from carbonate cemented core with a decrease in calcite content from 17vol to 15vol following reaction and a subsequent increase in porosity of 1 1vol kinetic geochemical modelling of the co2 water rock experiments successfully reproduced the general trends observed in aqueous geochemistry for the investigated major elements after coupling experimental geochemistry with detailed sample characterisation and numerical modelling expected initial reactions in the near well region include partial dissolution and desorption of calcite mixed carbonates chloritic clays and annite due to ph decrease followed in the longer term by dissolution of additional silicates such as feldspars dissolution of carbonates is predicted to improve injectivity in the near well environment and contribute to the eventual re precipitation of carbonates in the far field

experimental study on water rock interactions during co2 flooding in the tensleep formation wyoming usa abstract the conditions for mineral alteration and formation damage during co2 treatment of tensleep sandstone reservoirs in northern wyoming usa were examined through core flooding laboratory experiments carried out under simulated reservoir conditions 80 c and 166 bars subsurface cores from the tensleep sandstone which were cemented by dolomite and anhydrite and synthetic brines were used the brines used were ca mg na so4 nacl solution 9 69 g l total dissolved solids for run 1 and a 0 25 mol l nacl solution for run 2 the solution used in run 1 was saturated with respect to anhydrite at run conditions which is characteristic of tensleep formation waters three major reactions took place during flooding including 1 dissolution of dolomite 2 alteration of k feldspar to form kaolinite and 3 precipitation in run 1 or dissolution in run 2 of anhydrite all sample solutions remained undersaturated with respect to carbonates the permeability of all the cores except one used in run 2 decreased during the experiments despite the dissolution of authigenic cement kaolinite crystal growth occurring in pore throats likely reduced the permeability application of the experimental results to reservoirs in the tensleep formation indicates that an injection solution will obtain saturation with respect to dolomite and anhydrite in the immediate vicinity of the injection well the injection of nacl type water which can be obtained from other formations causes a greater increase in porosity than the injection of tensleep formation waters because of the dissolution of both dolomite and anhydrite cements

compositional and dynamic controls on mafic silicic magma interactions at continental arc volcanoes evidence from cordon el guadal tatara san pedro complex chile

wavelet based correlation wbc of zoned crystal populations and magma mixing magma mixing is a common process and yet the rates kinematics and numbers of events are difficult to establish one expression of mixing is the major trace element and isotopic zoning in crystals which provides a sequential but non monotonic record of the creation and dissipation of volumes of distinct chemical potential we demonstrate a wavelet based correlation wbc technique that uses this zoning for the recognition of the minimum number of mixing or open system events and the criteria for identifying populations of crystals that have previously shared a mixing event when combined with field observations of the spatial distribution of crystal populations wbc provides a statistical link between the time varying thermodynamic and fluid dynamic history of the magmatic system wbc can also be used as a data mining utility to reveal open system events where outcrop is sparse an analysis of zoned plagioclase from the tuolumne intrusive suite provides a proof of principle for wbc 1 2002 elsevier science b v all rights reserved

influence of localised igneous activity on cleat dawsonite formation in late permian coal measures upper hunter valley australia abstract stable 13 c and 18 o and radiogenic 87 sr 86 sr isotopic data have been used to investigate the origin of cleat dawsonite naalco 3 oh 2 in the late permian wittingham coal measures of the upper hunter region in the sydney basin new south wales the 13 c pdb values have a narrow range 1 7 to 2 4 with an average of 0 3 suggesting a magmatic source for the carbon in contrast 18 o smow values have a wide range 13 6 to 19 8 and decrease systematically with decreasing distance from a major intrusion this systematic variation reflects establishment of localised hydrothermal cells water rock interaction between fluids associated with these hydrothermal cells and rb poor volcaniclastic detritus in the coal measures produced mantle like 87 sr 86 sr 0 705032 to 0 706464 in the dawsonite

precursory dike propagation control of viscous magma eruptions plinian eruptions of phenocryst rich viscous silicic magmas have been reported and in several cases the climactic eruptions were preceded by a small eruption of the magmas formed by mixing with more mafic magmas the eruptive sequence suggests that the less viscous mixed magmas formed a dike prior to the climactic eruption of the viscous silicic magmas the viscosities of seven sets of precursory and climactic magmas were investigated all the climactic silicic magmas had viscosities 10 6 pa s in contrast to the precursory mixed magmas which had viscosities one to five orders of magnitude smaller these viscosity contrasts can be interpreted by adopting a hypothesis of dike propagation limit for magma viscosity above which the magmas are too viscous to form dikes without freezing the dike propagation limit estimated by the dike propagation model of rubin and the maximum excess pressure retained by the tensile strength of a chamber9s wall rock are consistent with the observation of the threshold viscosity of 10 5 10 7 pa s between the precursory and climactic magmas the consistency of the seven examples with the physical model suggests that precursory dike formation by less viscous mixed magma is one of the effective mechanisms for tapping silicic viscous magma chambers

co2 percolation experiment through chlorite zeolite rich sandstone pretty hill formation otway basin australia underground co2 sequestration is highly recommended as an effective means of significantly decreasing co2 concentration in the atmosphere mineral storage is the more secure technology but requires the presence of high concentration of divalent cations in the pore fluid results from co2 percolation experiments through chlorite zeolite rich sandstone samples from the pretty hill formation otway basin australia are presented the dissolution of the laumontite 7 wt and chamosite 7 wt are the potential sources of calcium iron and magnesium required for carbonate precipitation the percolation experiment was setup to reproduce at laboratory scale the in situ temperature and pressure conditions t 95 degrees c and p 10 mpa the fluid injected at constant flow rate is a rock equilibrated brine subsequently enriched in co2 up to partial pressure of 6 mpa we observe feldspars laumontite and chamosite dissolution kaolinite and silica precipitation and a noticeable sink of co2 in the sample which is attributed to the precipitation of both amorphous carbon due to the reduction of co2 and fe rich carbonate permeability decreases of about one order of magnitude due to the localization of the kaolinite precipitation in the main flow paths while porosity increases the high reactivity of this sandstone makes this reservoir a valuable target for co2 mineralization but the associated permeability decrease may limit the injection rate and the spreading of the co2 in the reservoir

eruptive history of the late quaternary ciomadul csomad volcano east carpathians part i timing of lava dome activity located at the southern tip of the intra carpathian volcanic range in romania and composed of a dozen dacitic lava domes the ciomadul csomad volcanic complex is the youngest eruptive centre of the carpatho pannonian region whereas in the last decade the explosive history of ciomadul since 50 ka has been well constrained by numerous studies the chronology of the dome sequence still lacks robust chronological constraints and an extended analysis of all available data here we apply a detailed k ar dating approach to refine the chronology of the lava dome eruptions using the unspiked k ar cassignol gillot technique our dating focused on the most voluminous central part of the lava dome complex new eruption ages were determined following a strict separation of 10 g of groundmass from about 3 kg of unaltered sample rocks thereby isolating material whose cooling was contemporaneous with the eruption the newly applied methodology mainly consisting of a double full preparation first at larger grain size 0 4 mm and then at 100 m provides an appropriate procedure to separate suitable material to obtain the k ar age of the eruption i e the sample s groundmass in which there is no risk of the presence of older inherited crystals our new geochronological data set gives an improved insight into the temporal construction of the ciomadul volcanic complex where due to the method applied here all ages are younger than those from previous studies that used whole rock k ar ages our new results show that ciomadul s volcanic activity began with the construction of the south eastern peripheral domes from ca 850 ka to 440 ka after a ca 250 ky long repose period the activity resumed in the northern part at around 200 ka with subsequent domes emplaced between 200 and 130 ka aligned roughly north south in the western central part of the complex following a 30 ky long quiescence period the eastern central domes formed between 100 and 60 ka in addition to the chronological history of lava dome volcanism we also investigated the sequence of crystallization of mineral phases present in the lavas with respect to the modification of eruption ages ages obtained on pure minerals plagioclase amphibole and biotite are systematically older than those obtained on groundmass showing that most of them formed up to 1 85 myr before eruption in a long lived pre ciomadul magmatic system crystal size distribution csd data support the age contrasts between juvenile groundmass and older inherited minerals after injection of new magma and convective mixing with crystal clots ascent of the resulting mixture led to eruptions of material representing contrasting ages

continuous mixing of crystal mush and replenished magma in the ongoing unzen eruption zoning profiles of magnetite phenocrysts in the successively effused dacite of the ongoing unzen eruption from 1991 wereanalyzed to estimate the time scale of magma mixing the dacite was formed by mixing of relatively high and low temperature t end member magmas the magnetite phenocrysts derived from the low t magma are reversely zoned by the mixing with high t magma a diffusion calculation for reequilibration of the reverse zonings gives the time interval from magma mixing to quenching for the mixed dacite erupted from may 1991 to may 1993 the typical diffusion time was estimated to be a few months regardless of the effused sequence for 2 yr this indicates that the mixing was continuous during the effusion the invariability of the other mixing signatures such as the thickness of reaction rims around biotite phenocrysts also supports the continuous mixing model low t end member magma is estimated by mass balance calculation to be a crystal rich mush of dacitic composition these observations lead to a model wherein the highly crystallized remnant magma of the preceding activity has been mixed with the newly injected hot magma of similar bulk composition just prior to the effusion the proposed mechanism implies that this type of magma mixing is an inevitable process in periodically erupting polygenetic volcanoes

equilibration scales in silicic to intermediate magmas implications for experimental studies experimental phase equilibrium studies are increasingly being used for the determination of intensive variables p t fh2o fo2 in silicic to intermediate magmas in contrast silicic igneous bodies are now perceived as open periodically recharged systems involving only limited chemical equilibration thus the use of laboratory determined crystal liquid equilibrium data needs clarification here we review the field petrological and geochemical evidence concerning states and scales of chemical equilibrium in silicic magma bodies it is concluded that total chemical equilibrium is generally not the rule however a subsystem in local equilibrium the reactive magma can be identified equilibration scales in silicic magmas are rate limited either by diffusive flux in crystals dicl regime or by diffusive flux in the melt md regime the recognition that equilibrium in magmas is limited to a reactive subsystem requires phase equilibrium studies to be chemically scaled experiments either of total or partial equilibrium type should aim at a close reproduction of equilibrium states specific to natural systems the laboratory reconstruction of the natural equilibrium states guarantees a precise determination of the pre eruptive parameters and a reliable application of the experimental data to active volcanic systems

time scales of recent phlegrean fields eruptions inferred from the application of a diffusive fractionation model of trace elements the variation of chemical element compositions in two pyroclastic sequences astroni 6 and averno 2 phlegrean fields italy is studied both sequences are compositionally zoned indicating a variability of melt compositions in the magma chamber prior to eruption a clear dichotomy between the behaviour of major vs trace elements is also observed in both sequences with major elements displaying nearly linear inter elemental trends and trace elements showing a variable scattered behaviour together with previous petrological investigations these observations are consistent with the hypothesis that magma mixing processes played a key role in the evolution of these two magmatic systems recently it has been suggested that mixing processes in igneous systems may strongly influence the mobility of trace elements inducing a diffusive fractionation phenomenon whose extent depends on the mixing time scale here we merge information from 1 numerical simulations of magma mixing and 2 magma mixing experiments using as end members natural compositions from phlegrean fields to derive a relationship relating the degree of diffusive fractionation to the mixing time scales application of the diffusive fractionation model to the two studied pyroclastic sequences allowed us to apply the relationship derived by numerical simulations and experiments to estimate the mixing time scales for these two magmatic systems results indicate that mixing processes in astroni 6 and averno 2 systems lasted for approximately 2 and 9 days respectively prior to eruption

illite and hydrocarbon exploration illite is a general term for the dioctahedral mica like clay mineral common in sedimentary rocks especially shales illite is of interest to the petroleum industry because it can provide a k ar isotope date that constrains the timing of basin heating events it is critical to establish that hydrocarbon formation and migration occurred after the formation of the trap anticline etc that is to hold the oil illite also may precipitate in the pores of sandstone reservoirs impeding fluid flow illite in shales is a mixture of detrital mica and its weathering products with diagenetic illite formed by reaction with pore fluids during burial k ar ages are apparent ages of mixtures of detrital and diagenetic end members and what we need are the ages of the end members themselves this paper describes a methodology based on mineralogy and crystallography for interpreting the k ar ages from illites in sedimentary rocks and for estimating the ages of the end members

buoyant replenishment in silicic magma reservoirs experimental approach and implications for magma dynamics crystal mush remobilization and eruption 1 we present new experiments on replenishment of rhyolite magma chambers by rhyolite magma using corn syrup water solutions we emphasize small density contrasts and show that buoyancy is the key controlling factor for whether injections will rise to the top if buoyant or pond at the base if denser during emplacement we observe little or no mixing of the injected liquid with the reservoir liquid as predicted by the fact that our injections have low reynolds numbers 10 typically at later stages the low buoyancy 1 kg m 3 injected liquid which has accumulated at the top of the reservoir undergoes mixing with the reservoir liquid which may originate by the gravitational destabilization of a thin layer of denser resident liquid trapped above the injected liquid layer the presence of a basal crystal mush modeled by acrylic beads in a corn syrup water solution matrix is also considered slightly buoyant injections entrain a small fraction of mush particles to the top of the overlying liquid layer entrainment efficiency increases dramatically for high buoyancy injections we hypothesize that the injected liquid can entrain a maximum quantity of mush particles which corresponds to the amount required for the injected liquid mush particle suspension to attain neutral buoyancy in the resident liquid hence for silicic systems a replenishing melt can entrain up to 12 5 crystals during its ascent through the mush our results have implications for rhyolites bearing crystals with disequilibrium features as they may represent mush crystals remobilized by a replenishing silicic magma

preeruptive magma viscosity an important measure of magma eruptibility 1 using a compilation of melt compositions meltwater contents temperatures and phenocryst contents the preeruptive viscosities under magma reservoir conditions are calculated for 83 erupted magmas the basaltic to rhyolitic magmas have preeruptive viscosities over the range 101 to 108 pa s although bulk sio2 content has often been used as a qualitative measure of preeruptive magma viscosity the bulk sio2 content shows a weak correlation with magma viscosity correlation coefficient r 0 5 because of a wide range of phenocryst contents from 0 to 50 vol andesitic magmas have viscosities ranging from 102 to 107 pa s which are lower or higher than those of phenocryst poor rhyolitic magmas with 105 to 106 pa s focusing on andesitic to rhyolitic magmas the r between bulk sio2 contents and magma viscosities changes to 0 1 in contrast the melt only sio2 content from a basaltic to rhyolitic melt shows a good linear correlation with melt only viscosity r 0 9 although most of the calculated viscosities of erupted magmas fall below 106 pa s as consistent with the previous compilation study this paper describes 20 examples of highly viscous magmas with 106 pa s in most cases composed of mixtures of high silica rhyolitic melt 75 79 wt sio2 and abundant phenocrysts 30 55 vol in these highly viscous magmas 9 examples have erupted following the precursory eruption of less viscous magma suggesting that precursory dike propagation and conduit formation by the less viscous magma with 106 pa s induced the following eruption of less eruptible highly viscous magmas

distribution and compositions of magmatic inclusions in the mount helen dome lassen volcanic center california insights into magma chamber processes abstract variations in spatial abundances compositions and textures of undercooled magmatic inclusions were determined in a glaciated pleistocene lava dome mt helen 0 6 km3 at the lassen volcanic center lvc southernmost cascades spatial variations were determined by point counting at 86 locations separated by 100 m on the dome major and trace element compositions of host rocks and inclusions at 12 locations along the flow length of the dome were obtained important results include the following 1 inclusion abundances range from 3 19 vol with the highest values generally located along the little eroded northwestern margin and flow front of the dome 2 host rock compositions are markedly uniform across the dome 65 4 0 4 wt sio2 indicating that the degree of inclusion disaggregation was uniform despite large spatial variations in inclusion abundances 3 inclusion sizes range from a maximum of 1 m across to mm sized crystal clots of phenocrysts plus adhering ca rich plagioclase microphenocrysts 4 inclusions have variable macroscopic textures indicating that partial undercooling both prior to and following entrapment in cooler dacitic host magma were important processes 5 inclusions are variably fractionated magmas with large variations in ni 79 11 ppm and cr 87 7 ppm contents that are lower than presumed mantle derived melts furthermore large ranges in incompatible trace elements indicate that inclusion compositions also reflect deep processes involving either melting of variable mantle source rocks or assimilation fractional crystallization 6 inclusions are variably mixed magmas 56 61 wt sio2 that contain up to 50 host dacitic magma 7 correlations between ni and cr contents in hosts and inclusions from individual outcrops indicate that the effect of inclusion disaggregation and magma mingling on host dacitic magma was local e g these features are interpreted to reflect protracted recharge of diverse composition mafic magmas into the base of a shallow magma reservoir containing a lower layer of compositionally evolving hybrid mafic magma and an upper layer of rhyodacitic magma complex interactions among magmas in the upper and lower layers resulted in formation of mafic inclusions by both pre and post entrapment undercooling mechanisms followed by buoyant rise and accumulation near the roof of the reservoir the main stage of inclusion disaggregation probably occurred in the conduit during eruptive ascent and largely ceased upon surface eruption we infer that endogenous growth concentrated inclusions along the margins and top of the dome as more inclusion poor dacite was progressively tapped from deeper regions of the reservoir

evaluation of the impact of co2 co contaminant gas aqueous fluid and reservoir rock interactions on the geologic sequestration of co2 lowering the costs of front end processes e g separation in the geologic sequestration of co2 can dramatically lower the overall costs one possible approach is to sequester less pure co2 waste streams that are less expensive or require less energy to separate from flue gas or a coal gasification process etc the objective of this research is to evaluate the impacts of co2 itself as well as an impure co2 waste stream on geologic sequestration using reaction progress models reactive transport simulators and analogous reactive transport experiments run in a plug flow reactor specifically we are investigating the potential for co injecting the sox nox and h2s present in coal fired waste streams along with the co2 we present here the results of reactive transport simulations made to investigate the long term impact of dissolved co2 h2s and so2 on carbon sequestration in the frio fm tx the results suggest that addition of relatively large amounts of h2s to a co2 injection should not adversely impact injectivity or sequestration compared to the injection of co2 alone the co injection of so2 however could produce significantly different results if conditions are such that so2 can oxidize to sulfate in the long term the simulations suggest that carbonate mineral formation can sequester a significant fraction of the injected carbon through the formation of calcite magnesite and dawsonite

mount dutton volcano alaska aleutian arc analog to unzen volcano japan abstract holocene eruptions from mount dutton a small late quaternary volcano near the tip of the alaska peninsula bear strong physical and petrologic similarities to the 1990 1995 unzen fugendake eruption in japan the volcano had a protracted phase of effusive calcalkaline andesitic 54 59 wt sio 2 cone building in the late pleistocene followed by an abrupt switch to more silicic 65 wt sio 2 lavas emplaced as a central summit cluster of steep sided domes beginning in the early holocene the flanks of the volcano are mantled by pyroclastic flows debris flows and talus formed as a result of gravitational dome collapse disequilibrium mineral assemblages including coexisting quartz and olivine in eruptive episodes ranging from the initial cone building basaltic andesite lavas to the latest holocene dacite domes suggest extensive magma mixing in addition up to meter sized pillow like cognate mafic enclaves of hornblende plagioclase glass are common in the latest of the summit dacite domes mineralogical evidence and bulk chemical data indicate the enclaves represent a high alumina basalt parent with variable and subordinate reservoir contaminant and the host lava is reservoir magma with variable and subordinate basaltic contaminant mount dutton s history and petrology can be interpreted as reflecting the monotonous repetitive intrusion of mantle derived mafic magma into a silicic crystal rich crustal reservoir during the holocene these injections resulted in the extrusion of partially crystallized viscous sticky central domes which typically failed by collapse resulting in small volume merapi type flowage deposits we speculate that slow introduction of mafic magma into the silicic chamber leads both to enclave formation and to the effusive eruption style mount dutton volcano experienced severe shallow earthquake swarms in 1984 1988 and to a lesser extent in 1991 although none of these swarms resulted in an eruption their epicenter distribution and volcanic tectonic character indicate they recorded the movement of magma at shallow depth beneath the volcano the lessons of unzen and montserrat suggest that despite limited tephra production these small volcanic centers with central dome complexes present a serious hazard to life and property

experimental identification of co2 oil brine rock interactions implications for co2 sequestration after termination of a co2 eor project abstract carbon dioxide enhanced oil recovery co 2 eor has been widely applied to the process of carbon capture utilization and storage ccus here we investigate co 2 oil water rock interactions under reservoir conditions 100 c and 24 mpa in order to understand the fluid rock interactions following termination of a co 2 eor project our experimental results show that co 2 rich fluid remained the active fluid controlling the dissolution precipitation processes in an oil undersaturated sandstone reservoir e g the dissolution of feldspar and calcite and the precipitation of kaolinite as well as solid phases comprising o si al na c and ti mineral dissolution rates were reduced in the case that mineral surfaces were coated by oil mineral wettability and composition and oil saturation were the main controls on the exposed surface area of grains and mineral wettability in particular led to selective dissolution in addition the permeability of the reservoir decreased substantially due to the precipitation of kaolinite and solid phase particles and due to the clogging of less soluble mineral particles released by the dissolution of k feldspar and carbonate cement whereas porosity increased the results provide insight into potential formation damage resulting from co 2 eor projects

dynamics of the ca 4965 yr 14c bp ochre pumice plinian eruption of popocatepetl volcano mexico abstract the ochre pumice op plinian fallout was produced by popocatepetl volcano in central mexico during a major plinian eruption that occurred 4965 65 14 c yr bp 3700 bc the op is part of the ochre pumice sequence ops that consists of surge fall and pyroclastic flow deposits the op plinian fallout shows a bimodal grain size distribution with poor to moderate sorting that improves progressively towards the upper beds the juvenile component is mainly pumice 83 wt whereas the accidental components consist of igneous sedimentary and metamorphic clasts from the walls of the magma chamber and or conduit the vesicularity of the pumice decreases from bottom to top of the stratigraphic sequence while the crystal and glass contents increase this suggests increasing magma degassing prior and during the eruption the chemical composition of the pumice varies insignificantly at the base it is less evolved sio 2 61 wt and it becomes slightly more silicic towards the top sio 2 63 wt pumice clasts have a crystallinity index that ranges between 10 and 25 vol and display a seriate texture with phenocrysts of euhedral plagioclase pl clinopyroxene cpx orthopyroxene opx olivine ol oxide ox apatite ap the size of the maximum lithic 2 5 cm at a horizontal distance of 19 km indicates an eruption column height of 37 41 km the isopach map allows the recognition of a dispersal axis that points towards the nne where an area of 300 km 2 was covered by 6 cm of pumice and ash a minimum volume for the op plinian fallout deposit was calculated using a minimum thickness of 6 cm found at distal outcrops and was estimated at 4 9 km 3 which corresponds to 2 km 3 of dense rock equivalent dre stratigraphic relations indicate that the entire ops was emplaced during a short time interval of a few days to weeks and consisted of three main different phases phreato magmatic plinian and vulcanian it started violently with the emplacement of surges and then culminated with the eruption of the op fallout deposit as the eruption advanced discharge rates became more intermittent and the height of the column fluctuated and finally collapsed generating pumice and ash flows that were emplaced around the volcano this short but intense activity was followed during subsequent years by the growth of domes in the crater and the emplacement of block and ash flows generated by vulcanian explosions

plate force due to bending at subduction zones 1 bending of the lithosphere at subduction zones generates stresses that contribute to the force balance on plates we determine the net horizontal force on subducting plates by imposing a simple kinematic description of strain in the equations that govern the mechanical equilibrium of a thin viscous sheet the magnitude of the force depends on the velocity thickness and curvature of the subducting plate using representative values for old oceanic lithosphere we obtain an effective horizontal force that is nearly 40 of the buoyancy force due to slabs in the upper mantle

experimental petrology of the 1991 1995 unzen dacite japan part ii cl oh partitioning between hornblende and melt and its implications for the origin of oscillatory zoning of hornblende phenocrysts high temperature pressure experiments were carried out to determine the chlorine hydroxyl exchange partition coefficient between hornblende and melt in the 1992 unzen dacite cl in hornblende and melt was analyzed by electron microprobe whereas oh in hornblende and melt was calculated assuming anion stoichiometry of hornblende and utilizing the dissociation reaction constant for h2o o 1 4 2 oh in water saturated melt respectively the partition coefficient strongly depends on the mg mg fe ratio of hornblende and is expressed as ln k1 1 4 cl oh hb cl oh melt 1 4 2 37 4 6 mg mg fe hb at 2 3 kbar and 800 850 c the twofold variation in cl content in the oscillatory zoned cores of hornblende phenocrysts in the 1991 1995 dacite cannot be explained by the dependence of the cl oh partition coefficient on the mg mg fe hb ratio and requires c 80 variation of the cl oh ratio of the coexisting melt available experimental data at 200 mpa on cl oh fractionation between fluid and melt suggest that c 1 2 1 8 wt degassing of water from the magma can explain the required 80 variation in the cl oh ratio of the melt the negative correlation between al content and mg mg fe ratio in the oscillatory zoned cores of the hornblende phenocrysts is consistent with repeated influx and convective degassing of the fluid phase in the magma chamber

amphibole perspective to unravel pre eruptive processes and conditions in volcanic plumbing systems beneath intermediate arc volcanoes a case study from ciomadul volcano se carpathians ciomadul is the youngest volcano in the carpathian pannonian region produced crystal rich high k dacites that contain abundant amphibole phenocrysts the amphiboles in the studied dacites are characterized by large variety of zoning patterns textures and a wide range of compositions e g 6 4 15 wt al2o3 79 821 ppm sr often in thin section scale and even in single crystals two amphibole populations were observed in the dacite low al hornblendes represent a cold 900 c mafic magma amphibole thermobarometry suggests that the silicic crystal mush was stored in an upper crustal storage 8 12 km this was also the place where the erupted dacitic magma was formed during the remobilization of upper crustal silicic crystal mush body by hot mafic magma indicated by simple zoned and composite amphiboles this includes reheating by 200 c and partial remelting of different parts of the crystal mush followed by intensive crystallization of the second mineral population including pargasites breakdown textures of amphiboles imply that they were formed by reheating in case of hornblendes suggesting that pre eruptive heating and mixing could take place within days or weeks before the eruption the decompression rim of pargasites suggests around 12 days of magma ascent in the conduit several arc volcanoes produce mixed intermediate magmas with similar bimodal amphibole cargo as the ciomadul but in our dacite the two amphibole population can be found even in a single crystal composite amphiboles our study indicates that high al pargasites form as a second generation in these magmas after the mafic replenishment into a silicic capture zone thus they cannot unambiguously indicate a deeper mafic storage zone beneath these volcanoes the simple zoned and composite amphiboles provide direct evidence that significant compositional variations of amphiboles do not necessarily mean variation in the pressure of crystallization even if the al tschermak substitution can be recognized suggesting that amphibole barometers that consider only amphibole composition may often yield unrealistic pressure variation

experimental simulation of magma mixing at high pressure abstract magma mixing features are observed in many plutonic and volcanic environments they result from the juxtaposition of two chemically contrasted magmas usually not only during the replenishment of a magmatic reservoir but also syn eruptively within the conduit despite its ubiquity only a few experimental studies have explored mixing between magmas existing data have been mostly acquired at atmospheric pressure and high shear rates 10 1 s 1 which differ from those accompanying magma mixing in reservoirs to fill this gap we performed high pressure mixing experiments at strain rates ranging from 4 10 4 to 1 10 3 s 1 layers of a synthetic crystal free haplotonalite and a natural partially molten basalt were juxtaposed in a paterson apparatus at 300 mpa and deformed between 900 and 1200 c the experiments shed light on the first stages of magma mixing and illustrate the role and behaviour of crystals either pre existing or newly grown experiments evidence a rheological threshold for mafic material disruption which sets in abruptly as its melt fraction exceeds 50 which in the experiments occurs in the narrow temperature interval 1160 1170 c below this threshold plagioclase crystals in the mafic magma form a rigid touching network and all the deformations are accommodated by the less viscous felsic layer above it the crystal network collapses allowing typical mingling mixing features to appear altogether such as enclaves melt filaments and single xenocrysts isolated into the felsic end member coexisting with newly grown phases plagioclase and pyroxene whose compositions spread out over considerable ranges the pre existing fabric of the mafic magma is only slightly affected by deformation altogether providing few clues on either the regime or geometry of applied deformation during the magmatic stage

comparative 40ar 39ar and k ar dating of illite type clay minerals a tentative explanation for age identities and differences abstract the 40 k 40 ar k ar and 40 ar 39 ar dating methods are applied here to the same very small micrometric illite type particles that crystallized under low temperature 5 9 ma the same size fractions dated by the 40 ar 39 ar method give total gas ages ranging from 173 3 2 0 to 228 8 1 6 ma nearly all 40 ar 39 ar total gas ages are slightly older which cannot be explained by the recoil effect only the impact of which being amplified by the inhomogeneous shape of the clay minerals and their crystallographic characteristics with varied crystallinity indices and a particle width about 10 times large than thickness the 40 ar 39 ar data outline some advantages such as the plateaus obtained by incremental step heating of the various size fractions even if not translatable straight as ages of the illite populations they allow identification of two generations of authigenic illite that formed at about 200 and 175 ma and one detrital generation however 40 ar 39 ar dating of clay minerals remains challenging as technical factors such as the non standardized encapsulation may have potential unexpected effects both dating methods have their limitations 1 k ar dating requires relatively large samples ca 10 20 mg incurring potential sample homogeneity problems with two aliquots required for k and ar analysis for an age determination also inducing a higher analytical uncertainty 2 an identified drawback of 40 ar 39 ar dating is ar recoil and therefore potential loss that occurs during neutronic creation of 39 ar from 39 k mostly in the finer mineral particles if all the recoiled 39 ar is redistributed into adjacent grains minerals the final 40 ar 39 ar age of the analyzed size fraction remains theoretically identical but it is not systematic in clay type material the finest grain sizes e g 39 ar recoil and are therefore only datable by the 40 ar 39 ar method using an encapsulation technique that still needs to be technically evaluated in this study 39 ar recoil during irradiation was quantified by encapsulation it ranged from about 20 of the total 39 ar for the 39 ar recoil confirms that grain size increasing minimizes the recoil effect but how it proceeds has still to be explained despite recent developments in 40 ar 39 ar dating the conventional k ar method is still a valuable tool for clay dating due to a convenient and straightforward use supported by a standardized and well controlled technical approach the present comparison of the two ar dating methods as applied to clay material shows that neither method is presently outdated and that they are even of reciprocal use both methods have distinct application fields in clay geochronology and complementary application fields in clay crystallography

the 1996 eruption of karymsky volcano kamchatka historical record of basaltic replenishment of an andesite reservoir the simultaneous eruption in 1996 of andesite from karymsky volcano and of basalt from the academy nauk vent 6km away appears to provide a case of mafic recharge of an andesite reservoir for which the time of recharge is exactly known and direct samples of the recharging magma are available the explosive phreato magmatic eruption of basalt was terminated in less than 24h whereas andesite erupted continuously during the following 4 years detailed petrological study of volcanic ash bombs and lavas of karymsky andesite erupted during the period 1996 1999 provides evidence for basaltic replenishment at the beginning of the eruptive cycle as well as a record of compositional variations within the karymsky magma reservoir induced by basaltic recharge shortly after the beginning of the eruption the composition of the matrix glass of the karymsky tephra became more mafic and then within 2 months gradually returned to its original state and remained almost constant for the following 3 years further evidence for basaltic replenishment is provided by the presence of xenocrysts of basaltic origin in the andesite of karymsky a conspicuous portion of the plagioclase phenocrysts in the karymsky andesite has calcic cores with compositions and textures resembling those of plagioclases in the academy nauk basalt similarly the earlier portion of the andesite of the eruption sequence contains rare olivines which occur as resorbed cores in pyroxenes the composition of the olivine matches that of olivines in the academy nauk basalt the sequence of events appears to be 1 injection of basaltic magma into the karymsky chamber with immediate compensating expulsion of pre existing chamber magma from the karymsky central vent 2 direct mixing of basaltic and andesitic magmas with dispersal of phenocrysts associated with the basalt throughout the andesite so that newly mixed magma appeared at the vent within 2 months 3 re establishment of thermal and chemical equilibrium within the reservoir involving crystallization in the new hybrid liquid which returned the melt composition to normal formed rims on inherited calcic plagioclase and caused the resorption of dispersed olivine xenocrysts taken together these findings indicate that the karymsky magma reservoir was recharged by basalt at the onset of the 1996 eruptive cycle the rapidity and thoroughness of mixing of the basalt with the preexisting andesite probably reflects the modest contrast in temperature viscosity and density between the two magmas

dawsonite cement in the triassic lam formation shabwa basin yemen a natural analogue for a potential mineral product of subsurface co2 storage for greenhouse gas reduction abstract the origin and permeability effects of carbonate cement blamed for poor reservoir quality in the upper triassic turbidite sandstones of the lam formation in yemen have been investigated using petrography x ray diffraction stable isotopes fluid inclusions and thermodynamic modelling in order of growth in the sandstone the carbonate cements include ferroan calcite dawsonite naalco3 oh 2 ferroan dolomite and siderite ferroan dolomite is the most abundant cement there is an inverse correlation between permeability and total carbonate cement volume supporting the earlier assertion that carbonate cements are the main control on reservoir quality in these sandstones ferroan calcite replaced and was sourced by marine limestone rock fragments that are abundant in the turbidite sandstone the later cements were probably also at least partly sourced from the marine limestone rock fragments stable isotope data from ferroan calcite ferroan dolomite and siderite show that diagenesis occurred in formation water with oxygen isotopes typical of closed system diagenesis and that only minor organic derived carbon dioxide was involved in diagenesis dawsonite while not common as a diagenetic mineral in sandstones has recently been suspected of being a routine consequence of co2 storage in the subsurface for greenhouse gas reduction in the lam formation dawsonite found at concentrations of up to 8 vol of the rock grew at the expense of detrital feldspar minerals under conditions of elevated partial pressure of carbon dioxide isotopic data show that dawsonite grew in the presence of carbon dioxide with a 13c value of about 4 to 2 this is distinctly different from the carbon isotope ratio of the gas phase carbon dioxide now present in the sandstone 27 which had an organic source rock origin the dawsonite 13c data probably represent a mixture between carbonate from detrital marine limestone rock fragments and carbon dioxide from a moderately negative source possibly of magmatic or basement origins dawsonite may thus be the result of a mass influx of deep e g magmatic carbon dioxide that pushed the lam formation into the dawsonite stability field at the expense of albite

constraints on crystal storage timescales in mixed magmas uranium series disequilibria in plagioclase from holocene magmas at mount hood oregon abstract uranium series crystal ages interpreted within a textural and geochemical framework can provide insight into crystal storage timescales especially in cases where crystals may derive from multiple sources we report here 230 th 226 ra model ages of two distinct populations of plagioclase from low silica dacites from mount hood oregon a volcano where previous studies show that the compositions of erupted magmas are controlled by magma recharge mixing and incorporation of plagioclase derived from mafic and silicic end member magmas we have measured trace element concentrations and 238 u 230 th 226 ra disequilibria in four plagioclase size fractions from the timberline 1500 a and old maid 215 a eruptive sequences after correction for groundmass and apatite contamination average 230 th 226 ra model ages of large 500 m plagioclase are 4 5 ka timberline and 5 5 ka old maid with ages of cores that are 10 ka in each case indicating that plagioclase derived from silicic magmas crystallized thousands of years before eruptions these model ages are longer than timescales of repose between eruptions indicating that these crystals resided in the sub surface over multiple eruptions likely stored in a silicic crystal mush zone that periodically interacts with mafic recharge magmas remobilizing a fraction of the large plagioclase crystals during each eruptive event after correction for large plagioclase contamination small 226 ra ba relative to equilibrium with liquid proxies groundmass and mafic inclusion leading to 230 th 226 ra model ages that are 230 th 226 ra disequilibria require that the majority of crystals in the separate are young 226 ra ba could potentially be explained by rapid crystallization immediately prior to and or during mixing events consistent with evidence of rapid crystallization of rims rapid crystallization of mafic intrusions may trigger eruption at mount hood by producing a partially crystalline mafic magma capable of mixing with a reheated silicic crystal mush

reaction of plagioclase feldspars with co2 under hydrothermal conditions abstract geological storage of co 2 in plagioclase bearing sediments granitic rocks and fractured basalts is expected to have a variety of geochemical and geomechanical effects including mineral trapping and porosity permeability changes the amount of co 2 trapped by mineralisation and the extent of any changes in host rock transport or mechanical properties depend on rock composition to date studies of mineralisation have mainly been based on dissolution and precipitation experiments performed at ambient surface conditions or at slightly elevated temperature and pressure however the reactions that occur under in situ conditions are poorly constrained in an attempt to determine the secondary phases formed in the plagioclase co 2 water system under such conditions we performed a set of batch experiments at temperatures in the range 200 300 c using carbon dioxide pressures from 0 4 to 15 mpa we investigated reaction of anorthite and albite which are expected to precipitate calcite and kaolinite and dawsonite and quartz respectively however in most of our experiments reactions precipitating clays kaolinite and smectite or illite boehmite and a mg ni fe hydrotalcite like phase dominated the nickel being derived from the reaction vessel little or no carbonate and no dawsonite were detected additional feldspar free control experiments employing mg rich brine showed that carbonates would be preserved in our feldspar experiments if formed but that a carbonate substrate is needed to promote precipitation since the secondary phases formed in our plagioclase experiments are stable under a wide range of conditions we expect that they will also form under co 2 storage systems with suitable fluid rock composition from our results we conclude that clay precipitation can proceed or accompany carbonate precipitation depending on the availability of carbonate substrate though an artefact in our experiments in the context of subsurface alkaline waste injection hydrotalcite may play a positive role here by immobilising heavy metals while carbonates will mineralise the co 2

rejuvenation of crustal magma mush a tale of multiply nested processes and timescales some relatively crystal rich silicic volcanic deposits including large volume ignimbrites preserve evidence of a history where a rheologically locked high crystallinity magma was rejuvenated unlocked through enthalpy mass exchange with newly injected recharge magma of higher specific enthalpy this is one event in a possible complex history that is the volcanic product of an eruption reflects an array of sequential and nested processes including melt formation and segregation ascent cooling crystallization crustal assimilation magma recharge unlocking shallow ascent fluid exsolution and eruption deconvolution of these these nested processes and concomitant timescales is complicated and relies on a multidisciplinary approach studies that do not clearly associate process and correlated timescale have the potential to provide misleading timescale information we report the results of thermodynamic and heat transfer calculations that document mass energy and phase equilibria constraints for the unlocking of near solidus rhyolite mush via magma mingling heat exchange only with basaltic recharge magma of higher specific enthalpy to achieve unlocking defined as the transition from near solidus to 50 percent melt of the host silicic magma phase equilibria computations provide 1 the enthalpy required to unlock mush 2 the mass ratio of recharge magma to mush mr mm when the two magmas achieve thermal equilibrium and 3 the changes in melt mineral and fluid phase masses compositions and temperatures during the approach to unlocking the behavior of trace elements is computed with knowledge of mineral fluid and melt proportions and solid fluid and solid melt partition coefficients evaluation of unlocking for relatively dry 0 5 wt h2o and wet 3 9 wt h2o rhyolitic mushy locked magma by basaltic recharge at upper crustal pressures indicates minimum values of mr mm can be significantly less than 1 assuming the mingling process is isenthalpic with no waste heat for active volcanic systems estimates of mr may be tested using geodetic data wet mush has lower energy requirements for unlocking and thus requires lower mr mm than dry mush wet rejuvenated magmas therefore may be more abundant in the volcanic rock record and unlocked dry mushes may be restricted to extensional tectonic settings with high recharge flux temperature changes in dry mush as it unlocks are pronounced greater than 150 c compared to those in wet mush which are smaller than the resolution of classical geothermometry 15 c phase equilibria calculations show that as required the net volume of crystals decreases during unlocking interestingly calculations also indicate reactive crystal growth by chemical re equilibration at the crystal size scale during unlocking may also take place in either dissolution by unidirectional resorption or reactive dissolution new growth the chemical signatures of unlocking potentially preserved in crystals or parts of crystals for example rims are predictable and hence testable independent of unlocking thermodynamics the phase equilibria and elemental consequences of isentropic magma ascent a transport event that follows unlocking can also be predicted detailed examination of several canonical cases reveals a marked contrast with isenthalpic unlocking thereby providing a means of process deconvolution unlocking timescales are estimated by two methods one that calculates the time to reach thermal equilibrium for recharge magma dispersed in mush as clumps of fixed size and the second where the required volume of recharge magma is initially a single clump and evolves to smaller size through clump stretching and folding for a range of magma volumes from 0 1 to 5000 km3 unlocking times range from 10 2 to 106 years the shorter timescales for any magma volume requires a large number of relatively small clumps n 106 which implies that large volumes of mush purported to unlock over short timescales 102 103 years and less should preserve and exhibit evidence of intimate magma mingling the key result of our analysis is that multiple timescales are operative during the potentially long and complex history of silicic mush formation rejuvenation and ascent to correctly ascribe timescales to unlocking requires a holistic understanding of the myriad processes that affect the magma before during and after enthalpy exchange in the absence of this context unlocking timescales may be incorrectly constrained which in turn may hinder eruption forecasting and associated hazard mitigation

old magma and a new intrusive trigger using diffusion chronometry to understand the rapid onset calbuco eruption april 2015 southern chile in april 2015 an unpredicted rapid onset eruption occurred at calbuco volcano southern andes of chile this event consisted of two sub plinian eruptions separated by a few hours by analysis of fe ti exchange between ilmenite and titanomagnetite crystals in samples of erupted material we determine timescales of pre eruptive heating experienced at the partially solidified chamber base and constrain the magma residence time for the bulk of the carrier magma analysis of the fe ti oxide pairs from a sample retrieved from a pyroclastic density current deposit cal 160 shows that it was affected by a significant heating event recording 70 220 c of heating while other collected samples did not record this late heating this sample is interpreted to represent a piece of crystal mush located at the bottom of a prolate ellipsoidal mush reservoir mobilised 4 days before the eruption by a triggering pulse of mafic magma considerably hotter than the typical magmatic temperature of the reservoir another two fall deposit samples lapillus cal 149tb and cal 155 of the eruption are interpreted to represent resident eruptible magmas that did not interact with any magma recharge immediately prior to or during the eruption we infer that these magmas had been at eruption temperature for some years based on their extensively equilibrated fe ti oxides

heat source of the 2014 phreatic eruption of mount ontake japan we present petrological evidence of the shallow magmatic processes that may have supplied heat and gas to the eruption of mount ontake japan on 27 september 2014 which resulted in 63 fatalities ash from the eruption comprises primarily hydrothermally altered white toned rock fragments however the ash contains trace amounts 0 7 wt of vitreous less altered particles laps which are only altered on their surfaces suggesting rapid ascent through the hydrothermal system the laps are classified into two categories glassy and crystalline glassy laps comprise high silica rhyolitic glass 74 83 wt sio2 with rounded quartz chalcedony free vesicles and reversely zoned plagioclase cores 47 mol an rims 70 mol an indicating magma re heating crystalline laps have a groundmass like texture that suggests eutectic crystallization at shallow depths thermodynamic calculations indicate that the pre eruptive temperatures of the glassy and crystalline laps were 700 1300 c and 700 c respectively and that the storage depth was 4 km pressure 100 mpa the observed petrological features suggest that the laps were sourced from a magma recently intruded at shallow depths although crustal deformation i e the volume change associated with magmatic intrusion was insignificant prior to the 2014 eruption a clear signature of crustal deformation was observed in 2007 the source of which was located 3 km below the summit we suggest that the magma that was intruded 3 km below the summit in 2007 supplied the heat and gas for the 2014 phreatic eruption

experiments on upward migration of a liquid rich layer in a granular medium implications for a crystalline magma chamber 1 we perform a series of experiments to investigate the situation in which a melt rich layer formed by a magma intrusion ascends through a crystalline magma chamber the initial condition is such that a heavier granular layer overlies a liquid layer the particles consisting the upper granular layer are in a jammed state and only the particles near the interface can move to form a dilated boundary layer the dilated layer detaches from the upper granular layer and forms downwelling plumes which drive a cellular convection within the liquid rich layer the convection erodes the upper granular layer and the liquid rich layer migrates upwards with time this upward migration of the liquid rich layer differs from the previously known mechanisms of liquid transport permeable flow in which the liquid migrates at the darcy velocity the stokes settling in which the individual particle settles and diapirs formed by the rayleigh taylor instability we find that the velocity of the upward migration of the liquid rich layer can be scaled by the volumetric flux of the liquid ascending through the narrow channel between the particles the upward migration of the liquid rich layer is faster than the darcy velocity in a mushy magma chamber whose crystals are in a jammed state neither the stokes settling nor the rayleigh taylor instability can occur we propose that the upward migration of the melt rich layer observed in our experiments can become an efficient mechanism of melt transport in a crystalline magma chamber

viscosity of andesite melts and its implication for magma mixing prior to unzen 1991 1995 eruption abstract the viscosity of an iron bearing melt with composition similar to unzen andesite was determined experimentally in the high 10 9 10 10 5 pa s and low 5 1000 pa s viscosity range using a parallel plate viscometer and the falling sphere method respectively falling sphere experiments were carried out in an internally heated argon pressure vessel and in a piston cylinder apparatus at 1323 to 1573 k and 200 to 2000 mpa creep experiments were performed in the temperature range of 747 845 k at 300 mpa the water content of the melt varies from nominally dry to 6 2 wt h 2 o the fe 2 fe tot ratio was determined for each sample in the quenched glass using a colorimetric method pressure has minor influence on the viscosity compared with the effect of temperature water content main compositional parameter controlling the viscosity or with the fe 2 fe tot ratio especially important at low water content of the melt based on our new viscosity data and literature data with measured fe 2 fe tot ratio we propose a new empirical equation to estimate the viscosity in pa s of andesitic melts as a function of temperature t in k water content w in wt and fe 2 fe tot ratio the derived relationship reproduces the experimental data 87 in total in the viscosity range from 10 0 5 to 10 13 pa s with a 1 standard deviation of 0 17 log units however application of this calculation model is limited to fe 2 fe tot fe tot 0 3 and to temperatures above t g moreover in the high viscosity range the variation of viscosity with water content is constrained only by few experimental data and needs verification by additional measurements the viscosity data are used to interpret mixing processes in the unzen magma chamber prior to 1991 1995 eruption we demonstrate that the viscosities of the rhyolite and andesite melts from the two end member magmas are nearly identical prior and during mixing enabling efficient magma mixing

the redox state of pinatubo dacite and the ilmenite hematite solvus the oxidation state of the 1991 pinatubo dacite and many other oxidized silicic arc volcanic rocks has been overestimated we reproduce the compositions of magnetite and ferrian ilmenite found in pinatubo dacite by doing crystallization experiments at 780 degrees c 2 2 kbar and nno 1 7 or 0 2 log units the extra components in igneous ilmenite notably geikielite expand the solvus in a way that is not correctly accommodated in current formulations of the iron titanium oxide thermobarometer

dynamics and thermodynamics of magma mixing insights from a simple exploratory model the mixing of magmas of distinct temperature bulk composition mineralogy and physical properties plays a central role in explaining the diversity of magma types on earth and in explaining the growth of continental and oceanic crust magma mixing is also of practical importance for example the mixing of distinct magmas has been cited as an important process in creation of economically important horizons in layered intrusions as well as a triggering mechanism for initiation of volcanic eruptions the motivation for better quantifying the dynamics and thermodynamics of magma mixing and its attendant plutonic and volcanic products is clear the degree of magma mixing which spans a continuum from mingling to complete hybridization depends upon initial and boundary conditions magma properties driving forces and time available for mixing magma mingling produces a heterogeneous mixture of discrete clumps of the end member magmas whereas complete hybridization involves the thermodynamic equilibration of two distinct magmas to form a third qualitatively mixing occurs via reduction in the size of compositional heterogeneities i e clumps through stretching and folding by viscous flow followed by homogenization once shear has reduced the size of compositional anomalies to diffusive length scales quantification of this process relies on two statistical measures the linear scale of segregation defined as the spatial integral of the compositional correlation function related to the size distribution of the segregated clumps within the mixture and the intensity of segregation i a measure that quantifies how much the composition at each location differs from the average the mixing dynamics of a layered system are analyzed in terms of the parameters governing mixing rayleigh lewis and buoyancy numbers and viscosity ratio to estimate how the timescale for magma hybridization h compares to solidification recharge diffusive and assimilation timescales this analysis illustrates that hybridization times can be shorter than or comparable to thermal solidification and replenishment timescales thus formation of hybridized or nearly hybridized magmas is one anticipated outcome of mixing the machinery of thermodynamics can be used to compute the hybrid magma state an exploratory model for the thermochemistry of hybridization is developed based on binary eutectic phase relations and thermodynamics eight thermodynamic parameters define the phase diagram and associated energetics and six parameters initial temperatures compositions mass ratio of mixing magmas and an enthalpy parameter are necessary and sufficient to determine the state of hybrid magma uniquely while relevant combinations of 14 thermodynamic and mixing parameters might suggest that the number of mixing outcomes i e products is too high to systematize monte carlo simulations using the exploratory model document how millions of arbitrary initial states evolve into five possible final mixed states such an analysis implies that a magma mixing taxonomy that defines possible mixed product states can be developed and tied to petrologic indicators of mixing additional insights gained from this exploratory model that are supported by independent results from a multicomponent multiphase thermodynamic model of magma mixing magma chamber simulator include 1 the proclivity of invariant point hybrid states which may explain some instances of compositionally monotonous melts associated with mixed magma eruptions 2 a surprising thermal effect such that the temperature of hybridized magma can be significantly less than the initial temperature of either of the mixing magmas this type of magma mixing may result in crystal resorption thus invalidating an assumption that resorption textures in crystals are typically the result of a magma heating event 3 illustration of the differing effects of stoped block temperature and composition on hybrid magma temperature and phase state and 4 illustration of a cessation of crystallization effect that may pertain to the morb pyroxene paradox differences between adiabatic or r hybridization and diabatic or rfc hybridization are also explored the model can be used to elucidate the thermodynamic principles underlying magma mixing in the hybridization limit these principles are of general applicability and carry over to more compositionally complicated systems

mantle wedge infiltrated with saline fluids from dehydration and decarbonation of subducting slab slab derived fluids play an important role in heat and material transfer in subduction zones dehydration and decarbonation reactions of minerals in the subducting slab have been investigated using phase equilibria and modeling of fluid flow nevertheless direct observations of the fluid chemistry and pressure temperature conditions of fluids are few this report describes co2 bearing saline fluid inclusions in spinel harzburgite xenoliths collected from the 1991 pinatubo pumice deposits the fluid inclusions are filled with saline solutions with 5 1 1 0 wt nacl equivalent magnesite crystals co2 bearing vapor bubbles and a talc and or chrysotile layer on the walls the xenoliths contain tremolite amphibole which is stable in temperatures lower than 830 c at the uppermost mantle the pinatubo volcano is located at the volcanic front of the luzon arc associated with subduction of warm oceanic plate the present observation suggests hydration of forearc mantle and the uppermost mantle by slab derived co2 bearing saline fluids dehydration and decarbonation take place and seawater like saline fluids migrate from the subducting slab to the mantle wedge the presence of saline fluids is important because they can dissolve more metals than pure h2o and affect the chemical evolution of the mantle wedge

permeability impairment of a limestone reservoir triggered by heterogeneous dissolution and particles migration during co2 rich injection 1 a co2 rich brine core flood experiment in calcite limestone for conditions representative of underground storage p 12 mpa and t 100 c was performed in order to explore the dissolution mechanisms arising at moderate co2 partial pressure 0 3 mpa an increase of the total porosity t accompanied by a persistent permeability k decrease was measured the mechanisms controlling this atypical anticorrelated k t relationship were investigated from the analysis of high resolution x ray microtomography images of the sample acquired before and after the experiment all the evidences converge to the conclusion that the ubiquitous decrease of permeability measured during the 44 h of dissolution is due to the clogging of a fraction of the macroporosity by microporous material triggered by the rearrangement of the detached undissolved particles this mechanism results in the development of low permeability zones bridging the macroporosity

volcanism mineralization and metamorphism at the xitieshan pb zn deposit nw china insights from zircon geochronology and geochemistry abstract the footwall volcanic rocks of the ordovician tanjianshan group in the world class xitieshan pb zn deposit have experienced prolonged arc volcanism followed by strong metamorphism and deformation this has resulted in a complex thermal history and led to ambiguity in interpretation of zircon geochronological results an integrated study involving textural characterization cl imaging trace element analysis ti in zircon thermometry and la icpms u pb dating has provided tight constraints on the age and genesis of the zircon groups in the volcanic rocks the temperature of metamorphism and deformation indicated by metacryst minerals and micro structures in the volcanic rocks ranges from 550 to 650 c which partially overlaps with the lower temperature range of zircon crystallization 600 750 c calculated using the ti in zircon thermometer cathodoluminescence images and trace element compositions confirm a magmatic origin for the zircons which have also been variably altered by metamorphic fluids two ranges of u pb ages 475 470 ma and 460 450 ma have been obtained on typical magmatic zircons and are interpreted to represent pre mineralization arc volcanism in the xitieshan deposit a younger age group of 440 430 ma for the fluid modified zircons is considered to record post ore metamorphism during the north qadaim orogeny thus we propose that the original exhalative ores at the xitieshan pb zn deposit formed at 450 440 ma

petrology and isotopic geochemistry of dawsonite bearing sandstones in hailaer basin northeastern china abstract the co2 gas reservoir sandstones in the hailaer basin contain abundant dawsonite and provide an ideal laboratory to study whether any genetic relationship exists between dawsonite and the modern gas phase of co2 the origins of dawsonite and co2 in these sandstones were studied by petrographic and isotopic analysis according to the paragenetic sequence of the sandstones dawsonite grew later than co2 charging at 110 85 ma the dawsonite 18o value is 7 4 smow and the calculated 18o values of the water present during dawsonite growth are from 11 4 to 9 2 smow this combined with the nahco3 dominated water linked to dawsonite growth suggests meteoric water being responsible for dawsonite growth the 13c values of gas phase co2 and the ratios of 3he 4he of the associated he suggest a mantle magmatic origin of co2 rich natural gas in hailaer basin dawsonite 13c values are 5 3 to 1 5 average 3 4 and the calculated 13c values of co2 gas in isotopic equilibrium with dawsonite are 11 4 to 7 3 these c isotopic values are ambiguous for the dawsonite c source from the geological context the timing of events together with formation water conditions for dawsonite growth dawsonite possibly grew in meteoric derived water atmospherically derived co2 maybe or at least the dominant c source for dawsonite it seems that there are few relationships between dawsonite and the modern gas phase of co2 in the hailaer basin

continental scale magmatic carbon dioxide seepage recorded by dawsonite in the bowen gunnedah sydney basin system eastern australia abstract dawsonite naalco3 oh 2 is widespread as a cement replacement and cavity filling in permo triassic sedimentary rocks of the bowen gunnedah sydney basin system eastern australia the origin of dawsonite in these rocks was studied by petrographic and stable isotope analysis dawsonite d13c pdb values range from 4 0 to 4 1 and are remarkably consistent throughout the bowen gunnedah sydney basin system these values indicate either a marine carbonate or magmatic source for carbon in the dawsonite a magmatic carbon source is considered more likely on the basis that 1 evidence of and the cause for widespread marine carbonate dissolution in the sedimentary successions are not apparen 2 dawsonite is widespread in both marine and nonmarine facies 3 the region has been the site of major igneous activity 4 other dawsonite deposits of similar carbon isotopic composition are linked to igneous activity and 5 magmatic co2 accumulations are known in parts of the bowen gunnedah sydney basin system the timing of igneous activity in the bowen basin constrains the timing of dawsonite formation in the bowen gunnedah sydney basin system to the tertiary consistent with textural relationships which indicate that dawsonite formed late during the burial history of the permo triassic sequences the distribution and interpreted origin of dawsonite implies magmatic co2 seepage in the bowen gunnedah sydney basin system on a continental scale

remobilization of highly crystalline felsic magma by injection of mafic magma constraints from the middle sixth century eruption at haruna volcano honshu japan the latest eruption of haruna volcano at futatsudake took place in the middle of the sixth century starting with a plinian fall followed by pyroclastic flows and ending with lava dome formation gray pumices found in the first plinian phase lower fall and the dome lavas are the products of mixing between felsic andesitic magma having 50 vol phenocrysts and mafic magma the mafic magma was aphyric in the initial phase whereas it was relatively phyric during the final phase the aphyric magma is chemically equivalent to the melt part of the phyric mafic magma and probably resulted from the separation of phenocrysts at their storage depth of 15 km the major part of the felsic magma erupted as white pumice without mixing and heating prior to the eruption after the mixed magma gray pumice and heated felsic magma white pumice of the lower fall deposit although the mafic magma was injected into the felsic magma reservoir at 7 km depth part of the product lower fall ejecta preceded eruption of the felsic reservoir magma as a consequence of upward dragging by the convecting reservoir of felsic magma the mafic magma injection made the nearly rigid felsic magma erupt letting low viscosity mixed and heated magmas open the conduit and vent indeed the lower fall white pumices preserve a record of syneruptive slow ascent of magma to 2 km depth probably associated with conduit formation

co2 wettability of seal and reservoir rocks and the implications for carbon geo sequestration we review the literature data published on the topic of co2 wettability of storage and seal rocks we first introduce the concept of wettability and explain why it is important in the context of carbon geo sequestration cgs projects and review how it is measured this is done to raise awareness of this parameter in the cgs community which as we show later on in this text may have a dramatic impact on structural and residual trapping of co2 these two trapping mechanisms would be severely and negatively affected in case of co2 wet storage and or seal rock overall at the current state of the art a substantial amount of work has been completed and we find that sandstone and limestone plus pure minerals such as quartz calcite feldspar and mica are strongly water wet in a co2 water system oil wet limestone oil wet quartz or coal is intermediate wet or co2 wet in a co2 water system the contact angle alone is insufficient for predicting capillary pressures in reservoir or seal rocks the current contact angle data have a large uncertainty solid theoretical understanding on a molecular level of rock co2 brine interactions is currently limited in an ideal scenario all seal and storage rocks in cgs formations are tested for their co2 wettability achieving representative subsurface conditions especially in terms of the rock surface in the laboratory is of key importance but also very challenging

the prevalence of plagioclase antecrysts and xenocrysts in andesite magma exemplified by lavas of the tongariro volcanic complex new zealand beneath subduction zone volcanoes the parental magmas are thoroughly blended during temporary storage in the crust via repeated heating and mixing from new inputs of magma to obtain a clearer picture of magma assembly we employed a sub crystal scale sr isotope analysis coupled with textural and geochemical data on plagioclase phenocrysts in basaltic andesite and andesite erupted from the tongariro volcanic complex new zealand deposits from two neighbouring vents were examined 1 0 3 3 4 ka lava flows of the polygenetic red crater volcano and 2 26 ka pyroclastics of the monogenetic pukeonake scoria cone despite the differences in eruptive styles and history of the two volcanoes the plagioclase growth histories are similar one common phenocryst type comprises of a resorbed core zone variously an50 70 surrounded by a sieve textured mantle rim of higher an 80 fe and mg contents other phenocrysts have resorbed calcic cores an70 90 in situ 87sr 86sr analyses reveal a wide isotopic range 0 7044 0 7060 for pre 1 8 ka red crater 0 7044 7057 for post 1 8 ka red crater 0 7047 0 7055 for pukeonake most of the values are higher than that of the host bulk rock 87sr 86sr 0 7049 0 7051 for pre 1 8 ka red crater 0 7045 0 7046 for post 1 8 ka red crater 0 7048 for pukeonake the variation within some individual phenocrysts is comparable to that of the entire population the higher 87sr 86sr ratios are related relic phenocryst cores indicating that their parental source was more radiogenic than the host magma in contrast their sieve textured mantle rim zones have lower 87sr 86sr ratios 0 7045 0 7049 similar that of their host rock these features record magma mixing less than 10 of phenocryst interiors are cognate autocrysts with the host rock based on their high 87sr 86sr ratio some phenocrysts are likely to be xenocrysts derived from the disintegration of deep crustal meta igneous rocks however based on textures consistent with growth from a melt the majority are antecrysts from intrusive forerunners and or crystal mush zones entrained during eruption or storage overall the andesites are a product of crystal poor magmas of mantle or lower crustal origin carrying phenocrysts from mostly crustal sources the magma system likely comprised of a series of semi isolated melt pods or crystal mush zones in a larger network of intrusions of various ages and states of solidification possibly hosted in country rock of various compositions resorption of the sieve textured mantle zones on the phenocrysts and growth of a normally zoned outermost rim represents a final period of fractional crystallization in the newly homogenised melt following the ascent and intrusion of mafic magma hence the final tipping point to eruption may have involved crystallization induced volatile exsolution and degassing

the temporal evolution of chemical and physical properties of magmatic systems exactly 100 years ago the great canadian born petrologist n l bowen published two seminal works on the chemical differentiation of magmas in which he posed the basis for a physico chemical understanding of the fractionation of crystals from melts in molten rock a subsequent century of research and technological advances has enhanced our understanding of the physics and chemistry of magmatic systems and their temporal evolution the image of sub volcanic magmatic systems has evolved greatly in that time from a simple boiling vat concept of molten rock in which bubbles crystals and melt separate gravitationally to a recognition that magma vats are relatively rare and that most magmatic systems spend much of their lifetime in a partially molten or mushy state real magmatic systems appear to be organized into a series of storage regions periodically connected by feeding structures transferring magma and heat at different fluxes magma fluxes between the different portions of this plumbing system and the variation of the chemical and physical properties of magma as it rises through the crust exert essential controls on the eruptive modalities of volcanoes and the geochemistry of their products this book presents a collection of contributions that use petrology geochemistry geochronology and numerical modelling to identify the processes operating at different depths within magmatic systems and to characterize the fluxes of magma between them

petrology and fe ti oxide reequilibration of the 1991 mount unzen mixed magma a dacitic magma 64 5 wt sio2 a mixture of phenocryst rich rhyodacite and an aphyric mafic magma was erupted during the recent 1991 1995 mount unzen eruptive cycle the experimental and analytical results of this study reveal additional details about conditions in the premixing and postmixing magmas and the nature of the mixing process the preeruption rhyodacitic magma was at a temperature of 790 20 c according to fe ti oxide phenocryst cores and at a depth of 6 to 7 km 160 mpa according to al in hornblende geobarometry the mafic magma that mixed with the rhyodacite is found as andesitic 54 to 62 wt sio2 enclaves in the erupted magma and was essentially aphyric when intruded phase equilibria indicate that an aphyric andesite at 160 mpa is 1030 c h2o saturated and possibly as high as 1130 c 2 wt h2o the composition of the rhyodacite which was mixed with the andesite is estimated to lie between 67 and 69 wt sio2 using these compositions and temperatures the temperature of the unzen magma after mixing is estimated to be at least 850 to 870 c the groundmass fe ti oxide microphenocrysts and those in pargasite bearing reaction zones around biotite phenocrysts both give 890 20 c temperatures the oxide oxide contacts give temperatures of 910 20 c the 900 30 c postmixing temperatures are consistent with phase equilibria experiments which show that the magma was not above 930 c at 160 mpa our fe ti oxide reequilibration experiments suggest that the mixing of the two magmas began within a few weeks of the eruption which is a shorter time than is calculated using available diffusion data there is also evidence that some mixing took place much closer to the time of extrusion based on the presence of unrimmed biotite phenocrysts in the magma

petrological architecture of a magmatic shear zone a multidisciplinary investigation of strain localisation during magma ascent at unzen volcano japan shearing of magma during ascent can promote strain localisation near the conduit margins anymechanical and thermal discontinuities associated with such events may alter the chemical physicaland rheological stability of the magma and thus its propensity to erupt lava spines can record suchprocesses preserving a range of macroscopic and microscopic deformation textures attributed toshearing and friction as magma ascends through the viscous brittle transition here we use a multi disciplinary approach combining petrology microstructures crystallography magnetics and experi mentation to assess the evidence role and extent of shearing across a marginal shear zone of the1994 1995 lava spine at unzen volcano japan our results show that crystals can effectively moni tor stress conditions during magma ascent with viscous remobilisation crystal plasticity and com minution all systematically increasing towards the spine margin accompanying this we find anincrease in mineral destabilisation in the form of pargasitic amphibole breakdown displaying tex tural variations across the shear zone from symplectitic to granular rims towards the spine margin in addition the compaction of pores chemical and textural alteration of interstitial glass and mag netic variations all change systematically with shear intensity the strong correlation between thedegree of shearing crystal deformation and disequilibrium features together with distinct magneticproperties implies a localised thermal input due to shear and frictional processes near the conduitmargin during magma ascent this was accompanied by late stage or post emplacement fluid andgas induced alteration of the gouge as well as oxidation and glass devitrification understandingand recognising evidence for strain localisation during magma ascent may therefore be vital whenassessing factors that regulate the style of volcanic eruptions which may provide insights into thecryptic shifts from effusive to explosive activity as observed at many active lava domes

insights into magmatic evolution and recharge history in capraia volcano italy from chemical and isotopic zoning in plagioclase phenocrysts plagioclase phenocrysts in dacites from the high k calc alkaline capraia volcano were investigated for major trace element and sr isotope variations in order to gain better insight into the proposed open system behaviour of the volcano repeated dissolution zones in plagioclases from the early erupted monte castello mc and later monte rucitello mr dacitic units are associated with a sharp increase in an content and variation in isotopic compositions 87sr 86sr 0 70872 0 71004 which argue for repeated magma mixing in particular petrographic and mineralogical evidence suggest that recharge with hot basaltic magma occurred repeatedly during the lifetime of the capraia volcanic system we attempted to correlate shared crystallization and resorption histories using chemical mol an fe and sr isotopic zoning in plagioclase in this correlation framework the observed mismatch between chemical and isotopic data in some phenocrysts is interpreted to reflect either growth of phenocrysts in a separate magma chamber or compositional zoning within a single magma chamber a minor role of crustal contamination is inferred instead the intra crystal variations in isotopic composition in plagioclase reflect the existence of distinct components that may have thoroughly mixed at the end of the mc plagioclase growth history the dominant radiogenic component is similar to lamproites occurring in tuscany recharge with this component occurred throughout the genesis of the mr dacites but was restricted to the early growth history of the mc dacites the mr plagioclases are inferred to have crystallized from separate more differentiated batches of magma that were likely to have evolved at the top of a zoned magma reservoir decrease in the an content after most dissolution zones in all phenocrysts and low temperature estimates from zircon saturation thermometry 800 c also emphasize the importance of crystal fractionation during the evolution of the volcano in agreement with the occurrence of a significant amount of rhyolitic material thus it is inferred that a rather large magma chamber may have existed during the first cycle of eruptive activity

storage conditions and evolution of andesitic magma prior to the 1991 95 eruption of unzen volcano constraints from natural samples and phase equilibria experiments the compositions of homogenized melt inclusions trapped in plagioclase pl microphenocrysts 40 200 m length from mafic enclaves within dacitic rocks erupted at unzen volcano in 1991 95 were investigated the sio2 contents of the melt inclusions vary from 58 to 70 wt and pl anorthite content is an50 70 the stability fields in terms of temperature and water activity of natural pl and coexisting melts from the melt inclusions were estimated from data of phase equilibria experiments performed with a synthetic andesite composition at t 900 1140 c p 200 mpa log fo2 nno 2 nno and water activity of about 0 1 this composition is representative of the average composition of mafic enclaves from the 1991 95 eruption and nearly identical to the composition of andesitic lavas from 1663 unzen eruption the temperatures and h2o melt concentrations calculated using the compositions of coexisting pl and melt inclusions provide an estimation of the conditions of andesitic magma evolution within the mafic enclaves prior to eruption the formation of melt inclusions in plagioclase microphenocrysts occurred at a maximum temperature of 1010 35 c for a melt containing 2 wt h2o and a minimum temperature of 945 c 30 c for a melt with 4 wt dissolved h2o the compositional range of the melt inclusions indicates that the composition of the mafic enclave was not significantly contaminated by the host magma when inclusions were formed the difference between concentrations of dissolved s up to 0 06 wt and cl up to 0 05 wt in melt inclusions in pl of mafic enclaves and concentrations of s 0 005 wt and cl 0 05 0 11 wt in melt inclusions in phenocrysts of the dacitic magma clearly implies that two distinct sources for s and cl in the 1991 95 eruption of unzen volcano need to be considered sulfur degassing was generated by a release of fluids from the high temperature andesitic magma whereas cl was degassed from the low temperature silicic magma the combination of data from melt inclusions and phase equilibria experiments indicates that the mafic end member magma at unzen was already partially crystallized and contained significant proportions 20 to 40 wt of pl and orthopyroxene opx when melt inclusions started to form since clinopyroxene cpx and magnetite mt crystallize after pl and opx the temperatures derived for the mafic end member magma from coexisting opx cpx and ilm mt pairs do not represent temperatures near to the liquidus assuming that the injected mafic magma was nearly aphyric its initial temperature might have been higher than estimated in previous studies

genesis of authigene carbonate minerals in the upper cretaceous reservoir honggang anticline songliao basin a natural analog for mineral trapping of natural co2 storage abstract dawsonite naalco 3 oh 2 as a trace mineral of co 2 is abundant in the upper cretaceous reservoir of the honggang anticline southern songliao basin petrologic and isotopic geochemical characteristics have been investigated by a polarizing microscope a scanning electron microscope sem x ray diffraction xrd cathode luminescence cl fluid inclusions and carbon oxygen isotopic analysis the diagenetic sequence indicated that dawsonite late generation microcrystalline quartz late generation kaolinite late generation calcite and ankerite was formed after co 2 flooding meanwhile as a function of analysis on carbon oxygen isotope the mantle magmatic co 2 provided a carbon source for the precipitation of dawsonite late generation calcite and ankerite the three kinds of carbonate minerals mentioned earlier grew in a progressively evolved condition using a basic thermodynamic fraction equation the total quantity of natural co 2 captured by dawsonite bearing sandstones per cubic meter was calculated to be 99 51 kg

on the interaction of pure and impure supercritical co2 with rock forming minerals in saline aquifers an experimental geochemical approach abstract the aim of this experimental study was to evaluate and compare the geochemical impact of pure and impure co2 on rock forming minerals of possible co2 storage reservoirs this geochemical approach takes into account the incomplete purification of industrial captured co2 and the related effects during injection and provides relevant data for long term storage simulations of this specific greenhouse gas batch experiments were conducted to investigate the interactions of supercritical co2 brine and rock forming mineral concentrates albite microcline kaolinite biotite muscovite calcite dolomite and anhydrite using a newly developed experimental setup after up to 42 day 1000 h experiments using pure and impure supercritical co2 the dissolution and solution characteristics were examined by xrd xrf sem and eds for the solid and icp ms and ic for the fluid reactants respectively experiments with mixtures of supercritical co2 99 5 vol and so2 or no2 impurities 0 5 vol suggest the formation of h2so4 and hno3 reflected in ph values between 1 and 4 for experiments with silicates and anhydrite and between 5 and 6 for experiments with carbonates these acids should be responsible for the general larger amount of cations dissolved from the mineral phases compared to experiments using pure co2 for pure co2 a ph of around 4 was obtained using silicates and anhydrite and 7 8 for carbonates dissolution of carbonates was observed after both pure and impure co2 experiments anhydrite was corroded by approximately 50 wt and gypsum precipitated during experiments with supercritical co2 no2 silicates do not exhibit visible alterations during all experiments but released an increasing amount of cations in the reaction fluid during experiments with impure co2 nonetheless precipitated secondary carbonates could not be identified

an experimental study of co2 brine rock interaction at in situ pressure temperature reservoir conditions abstract a detailed investigation of co 2 brine rock interactions through a core flooding laboratory experiment was carried out under simulated reservoir conditions 100 c and 24 mpa changes in the ionic chemistry of the outlet solution combined with core scanning electron microscopy sem and bulk rock x ray diffraction xrd analysis of the core pre and post experiment reveal new insights into co 2 brine rock interactions minerals such as potassium k feldspar albite calcite and ankerite are variably dissolved after the experiments calcite is the mineral most affected by dissolution followed by ankerite whereas dissolution of feldspar minerals is minimal small amounts of kaolinite and solid phases were generated as a result of the experiment the solid phases are mainly comprised of c o na cl al and si and are presumed to be the transitional products in the formation of carbonate minerals the very low fluid penetration rate in the experiment resulted in significantly reduced contact area between the acidic co 2 fluid and minerals in the cores resulting in low rates of feldspar dissolution core permeability decreased substantially throughout the experiment although core porosity remained unchanged the permeability reduction is the result of precipitation of new mineral phases e g kaolinite and solid phases and potentially also the presence of clay particles released by the dissolution of carbonate cement which have then been transported in the fluid flow path and accumulated at pore throats the results provide new insights into co 2 trapping mechanisms in depleted oil and gas reservoirs and into the potential formation damage that may result from massive injections of co 2 into reservoirs during enhanced oil recovery programs

mineralogical and geochemical consequences of the long term presence of co2 in natural reservoirs an example from the springerville st johns field arizona and new mexico u s a abstract the springerville st johns co2 field in eastern arizona and western new mexico is one of more than a dozen gas fields developed within the colorado plateau and southern rocky mountain region extensive travertine caco3 deposits record a long history of co2 migration and leakage to the atmosphere the oldest travertine deposits may have formed during the initial filling of the co2 reservoir when groundwaters exsolved co2 upon reaching the surface the youngest travertine deposits are associated with springs on the floor of the little colorado river valley but travertine deposition appears to be insignificant today older deposits occur up to 325 m above the valley floor geologic relationships suggest travertine deposition began in the late pleistocene after volcanic activity ended at 0 3 ma most of the caco3 could have been derived from dissolution of the underlying limestones and dolomites interactions between the reservoir fluids and rocks were observed in core samples from one of the intervals that produced dry gas these reactions resulted in the dissolution of carbonate cements and detrital feldspars and the formation of dawsonite and kaolinite geochemical simulations suggest that the dawsonite could have been deposited when the co2 fugacity reached 20 bars and that the kaolinite formed as the co2 fugacity decreased corrosion of drill pipe by acidic waters and a pronounced hco3 anomaly above the co2 reservoir provide evidence of a continuing flux of co2 from depth co2 storage occurs primarily as dissolved carbonate species and as gas accumulations only a small percentage of the co2 was sequestered in secondary minerals

computer simulation of co2 trapped through mineral precipitation in the rose run sandstone ohio abstract equilibrium path of reaction and kinetic modeling of co2 brine mineral reactions in the rose run sandstone one of ohio s deep saline aquifers was conducted in order to investigate the factors that are likely to influence the capacity of this formation to trap injected co2 as solid carbonate mineral phases equilibrium modeling was applied to investigate the impact of temperature pressure mineralogy brine composition and co2 fugacity on mineral dissolution and precipitation the amount of co2 sequestered and the form of sequestration path of reaction and kinetic modeling were used to evaluate intermediate products and reaction progress as a function of time as well as to investigate the impact of brine to rock ratio the results of equilibrium modeling demonstrate that dissolution of albite k feldspar and glauconite and the precipitation of dawsonite and siderite are potentially very important for mineral trapping of co2 according to the path of reaction and kinetic modelling the stability of carbonate rocks is controlled by the brine to rock ratio the ph of the system the fugacity of co2 and the kinetic rate of dissolution in kinetic modeling with a brine to rock ratio of 1 25 reactive surface area of 10 cm2 g 10 mpa f co 2 and 12 porosity 1 5 2 g of co2 per kg of reacted rock significant quantities 10 40 g of carbonate minerals were precipitated from both the sandstone and mixed rock assemblages the rose run sandstone has the potential to store co2 over millennia as a negatively buoyant aqueous solution and ultimately as immobile carbonate minerals

experimental and textural constraints on mafic enclave formation in volcanic rocks abstract we have used experiments and textural analysis to investigate the process of enclave formation during magma mixing at southwest trident volcano alaska andesite enclaves are present throughout the four dacite lava flows produced by the eruption and resemble mafic enclaves commonly found in other volcanic rocks our experiments replicate the pressure temperature time path taken by enclave forming andesite magma as it is engulfed in dacite during magma mixing pressure and temperature information for the andesite and dacite are from coombs et al contrib mineral petrol 140 2000 99 118 the andesite was annealed at 1000 c and then cooled to 890 c at rates of 110 c h 1 10 c h 1 and 2 c h 1 once cooled to 890 c andesite was held at this lower temperature from times ranging from 1 to 40 h the andesite that was cooled at the slower rates of 2 c h 1 and 10 c h 1 most resembles enclave groundmass texturally and compositionally based on simple thermal calculations these rates are more consistent with cooling of the andesite groundmass below an andesite dacite interface than with cooling of enclave sized spheres if enclaves do crystallize as spheres post crystallization disaggregation must occur calculations using the melts algorithm ghiorso and sack contrib mineral petrol 119 1995 197 212 show that for incoming andesite to become less dense than the dacite 34 volume of its groundmass must crystallize to undergo 18 volume vesiculation these values are similar to those determined for southwest trident enclaves thus such crystallization may lead to flotation of enclaves and be a viable mechanism for enclave formation and dispersal the residual melt in the cooling experiments did not evolve to rhyolitic compositions such as seen in natural enclaves due to a lack of a decompression step in the experiments decompression experiments on southwest trident dacite suggest an average ascent rate for the eruption of 2 3 mpa h 1 an andesite experiment that was cooled and then decompressed at this rate contains melt that matches that of the natural enclaves it is apparent that decompression ascent induced crystallization occurs in enclaves but not in the form of microlites as happens in the dacite host due either to insufficient residence time at chamber temperatures or to the pre existing microphenocrysts which act as sites for new growth

linking fluid dynamics and olivine crystal scale zoning during simulated magma intrusion the compositional zoning styles of natural crystals produced during magma intrusion can be used to investigate the structure of magmatic plumbing systems and its relation to expressions of volcanic unrest seismic deformation volatiles however magma intrusion is a progressive dynamic process and yields non monotonic heterogeneities in physio chemical variables such as complex spatial variations in temperature and liquid composition with time such changes in variables are difficult to incorporate in models of crystal zoning in natural systems here we take another approach by integrating the results of a numerical multiphase simulation of melt arrival in an olivine rich reservoir with models of chemical re equilibration of olivine we evaluate the diversity of chemical zoning styles and the inferred time scales using fe mg diffusion in olivine for a limited range of system geometries and time composition temperature values although our models are still a large simplification of the processes that may occur in natural systems we find several time dependent and systematic relations between variables that can be used to better interpret natural data the proportions of zoned and unzoned crystals the zoning length scales and the calculated diffusion times from the crystals vary with time and the initial position of the crystal in the reservoir these relationships can be used for example to better constrain the plumbing structure and dynamics of mafic eruptions from monogenetic volcanoes by detailed studies of changes in the zoning of the crystal cargo with eruptive sequence moreover we also find that the time scales obtained from modeling of crystals at a single temperature and boundary condition tend to be shorter about 25 than the residence time which could also be tested in natural studies by combining crystal time scale records with monitoring datasets

shift and rotation of composition trends by magma mixing 1983 eruption at miyake jima volcano japan levels of ascent of the fountain in the host andesite magma analysis of compositional zoning in titanomagnetite crystals revealed that the eruption of the 1983 magmas was initiated soon after the replenishment of the basaltic magma in the 1kbar magma chamber

fe mg and fe mn interdiffusion in ilmenite with implications for geospeedometry using oxides the fe mg and fe mn interdiffusion coefficients for ilmenite have been determined as a function of temperature and crystallographic orientation diffusion annealing experiments were conducted at 1 5 gpa between 800 and 1100 circ hbox c for fe mg interdiffusion each diffusion couple consisted of an ilmenite polycrystal and an oriented single crystal of geikielite the activation energy q and pre exponential factor d 0 for fe mg diffusion in the ilmenite polycrystal were found to be q 188 pm 15 hbox kj mol 1 and text log d 0 6 0 pm 0 6 hbox m 2 hbox s 1 for the geikielite single crystal fe mg interdiffusion has q 220 pm 16 hbox kj mol 1 and text log d 0 4 6 pm 0 7 hbox m 2 hbox s 1 our results indicate that crystallographic orientation did not significantly affect diffusion rates for fe mn interdiffusion each diffusion couple consisted of one ilmenite polycrystal and one mn bearing ilmenite polycrystal for fe mn interdiffusion q 264 pm 30 hbox kj mol 1 and text log d 0 2 9 pm 1 3 hbox m 2 hbox s 1 in the ilmenite we did not find a significant concentration dependence for the fe mg and fe mn interdiffusion coefficients in comparing our experimental results for cation diffusion in ilmenite with those previously reported for hematite we have determined that cation diffusion is faster in ilmenite than in hematite at temperatures 1100 circ hbox c at oxygen fugacities near the wustite magnetite buffer fe and mn diffusion rates are similar for ilmenite and titanomagnetite we apply these experimentally determined cation diffusion rates to disequilibrium observed in ilmenites from natural volcanic samples to estimate the time between perturbation and eruption for the bishop tuff fish canyon tuff mt unzen mt st helens and kimberlites when integrated with natural observations of chemically zoned ilmenite and constraints on pre eruptive temperature and grain size our experimentally determined diffusivities for ilmenite can be used to estimate a minimum time between magmatic perturbation and eruption on the timescale of hours to months

petrologic evidence for pre eruptive pressure temperature conditions and recent reheating of andesitic magma erupting at the soufriere hills volcano montserrat w i the recent eruption of the soufriere hills volcano in montserrat july 1995 to present september 1997 has produced an andesitic dome sio 2 59 61 wt the eruption has been caused by invasion of mafic magma into a preexisting andesitic magma storage region p 130 mpa 5 km depth the composition of the andesite has remained essentially constant throughout the eruption but heating by the mafic magma increased the andesite temperature from 830 c to 880 c prior to being heated the stable mineral assemblage in the andesite was plagioclase amphibole orthopyroxene titanomagnetite ilmenite quartz the rise in temperature from 830 c to 880 c fo 2 1 log unit above nno has caused quartz to become unstable and has also caused changes in silicate and fe ti oxide mineral compositions the andesitic magma is likely saturated with an h 2 o rich vapor phase in the upper part of the magma storage region melt h 2 o content is 4 7 wt

comparison of eruptive and intrusive samples from unzen volcano japan effects of contrasting pressure temperature time paths abstract core samples from the conduit of unzen volcano obtained only 9 years after cessation of the 1991 1995 eruption exhibit important differences in physical characteristics and mineralogy and subtle differences in bulk chemistry from erupted samples these differences in the conduit samples reflect emplacement under a confining pressure where about half of the original magmatic water was retained in the melt phase maintenance at hypersolidus temperature for some unknown but significant time span and subsequent subsolidus hydrothermal alteration in contrast magma that extruded as lava underwent decompression to 1 atm with nearly complete loss of magmatic water and cooling at a sufficiently rapid rate to produce glass the resulting hypabyssal texture of the conduit samples while clearly distinct from eruptive rocks is also distinct from plutonic suites given the already low temperature of the conduit less than 200 c nakada s uto k yoshimoto m eichelberger j c shimizu h 2005 scientific results of conduit drilling in the unzen scientific drilling project usdp sci drill 1 18 22 when it was sampled by drilling this texture must have developed within a decade and perhaps within a much shorter time after emplacement the fact that all trace element concentrations of the conduit and the last emplaced lava of the spine 1300 m above it are identical to within analytical uncertainty provides strong evidence that both were produced during the same eruption sequence changes in conduit magma that occurred between emplacement and cooling to the solidus were collapse of vesicles from less than or equal to the equilibrium value of about 50 vol to about 0 1 vol continued resorption of quartz and reaction of biotite phenocrysts due to heating of magma prior to ascent by intruding mafic magma breakdown of hornblende and micro crystallization of rhyolitic melt to feldspar and quartz subsolidus changes were deposition of calcite and pyrite growth of sericite in anorthite rich zones of plagioclase and development of montmorillonite as an alteration product significant changes in bulk composition were depletion of mg fe and na and enrichment in c and s these changes were due mainly to the breakdown of hornblende and plagioclase and addition of carbonate and pyrite respectively the identical concentrations of rees in the conduit and surface lava are consistent with low water to rock ratios during alteration this suggests to us that despite convective hydrothermal removal of heat from the conduit chemical open system effects were limited to early loss of magmatic water and later addition of magmatic co2 and so2 and or h2s streaming up the conduit from deeper levels