reconciling heterogeneity in crystal zoning data an application of shared characteristic diagrams at chaos crags lassen volcanic center california isotope trace element and textural crystal zoning patterns record heterogeneity in magmatic systems not resolved by whole rock analyses these zoning data are used to infer crystal residence times magma mixing and other magmatic processes in many magmatic systems we present the shared characteristic diagram scd as an organizational framework for crystal zoning data that compares information from different phases and chemical tracers in a common framework an example from chaos crags in the cascade arc produces three main results 1 anorthite zoning profiles in plagioclase have fewer shared characteristics in mafic inclusions than in the host rhyodacite 2 single crystal 87sr 86sr data from previous studies tepley et al 1999 are consistent with more shared history between crystals than in anorthite profiles this difference reflects a more homogeneous distribution of 87sr 86sr than the intensive parameters controlling plagioclase composition 3 the chaos crags system exhibits a layer of heterogeneity in crystal populations that is not represented in whole rock analyses that indicate only simple binary mixing the inconsistency between 87sr 86sr and anorthite zoning data highlights decoupling between compositionally controlled and temperature water controlled zoning in plagioclase from chaos crags

high resolution quantitative imaging of plagioclase composition using accumulated backscattered electron images new constraints on oscillatory zoning oscillatory zoning in plagioclase is investigated at small scale 10 m using accumulated backscattered electron bse images as high resolution imaging method combined with electron microprobe quantitative analysis gray value profiles across these images can be calibrated for an content with a resolution of 0 5 mol an applied to oscillatory zoned crystals this new application of bse imaging allows better characterization of zoning patterns along a profile and quantification of wavelength amplitude and shape of the oscillations we also obtain high resolution information on the morphology of growth zones boundaries this approach allows us to better classify the different types of oscillations and concentric zoning dissolution is more frequent than usually recognized major resorption surfaces crosscut several growth zones irregular 5 10 m saw tooth zones are delimited by faint wavy dissolution surfaces and must be distinguished from small scale oscillations 1 3 m with straight boundaries this suggests at least two mechanisms for the formation of these zoning patterns faint oscillations are probably caused by local kinetic control whereas wavy dissolution surfaces involve magma chamber dynamics

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

observations of plagioclase zoning using interference imaging abstract interference imaging techniques laser interference microscopy in transmitted light and nomarski differential interference contrast in reflected light have been used to study different types of zoning in magmatic plagioclase crystals samples studied come from a wide range of rock types and geological environments analysis of zoning profiles for individual unit zones shows that a saw tooth pattern in which an initially high an decreases as growth proceeds is the most common type of zoning configuration we recognize 2 major types of zoning type 1 small zones usually less than 10 microns thick with compositional amplitudes up to 10 an and type 2 zones up to50 microns thick with large compositional amplitudes of up to 35 an detailed analysis of zoning patterns shows that oscillatory zoning is not actually oscillatory in the sense of a sine wave it is discontinuous unit zones are characteristically bounded by discontinuities this common pattern is consistent with alternating periods of growth and periods of dissolution reaction and lack of growth or possibly very slow growth our observations firmly establish that dissolution and magmatic reaction involving both growth and dissolution are common during growth of the magmatic plagioclase which we have studied type 1 zonation appears consistent with perturbations of local conditions in a diffusion controlled boundary layer around the growing crystal type 2 zoning is probably due to large scale conditions faceted planar growth surfaces appear to be the rule in magmatic crystallization although in some instances rounded or irregular convolute zonation can occur the repetitive nature of many of the features we have observed is consistent with and suggestive of some form of self organization

the volume and shape of the 1991 1993 lava flow field at mount etna sicily the 1991 1993 lava flow is the most voluminous flow erupted at mount etna sicily in over 300 years estimates of the volume obtained by various methods range from 205 106 m3 tanguy 1996 to over 500 106 m3 barberi et al 1993 this paper describes the results of an electronic distance measurement edm based field survey of the upper surface of the 1991 1993 flow field undertaken in 1995 the results were digitised interpolated and converted into a digital elevation model and then compared with a pre eruption digital elevation model constructed from a 1 25 000 contour map of the area based on 1989 aerial photographs our measurements are the most accurate to date and show that the 1991 1993 lava flow occupies a volume of 231 29 106 m3

the magma mixing origin of mantled feldspars the key to mantled feldspar genesis is epitaxial nucleation of plagioclase on k feldspar or k feldspar on plagioclase once this nucleation takes place there is a relatively straightforward process of crystal growth yielding rapakivi and antirapikivi textures the most common mantling is plagioclase on k feldspar which occurs in both volcanic and plutonic environments in the volcanic environment the morphology of the plagioclase overgrowth typically is dendritic though in subvolcanic and shallow plutonic environments dendritic growth is followed by a more or less continuous non cellular shell of plagioclase in the plutonic environment early stages of plagioclase overgrowth also tend to be dendritic although with coarser grained characteristics dendritic morphology is thus a common denominator in rapakivi genesis since growth of dendritic plagioclase is clearly related to marked undercooling in silicate melt systems its occurrence in many volcanic rocks is to be expected equivalent quenching in the plutonic environment requires a cooling mechanism independent of conductive heat transfer to wallrock and also independent of effective cooling related to sudden loss of volatile phases that could only occur late in the crystallization of most magmas and therefore after much dendritic plagioclase had already formed internal quenching of portions of magma systems must occur if mafic magma is abruptly mixed with felsic magma such magma mixing yields a heterogeneous system at first one that is in a drastic state of disequilibrium and tending to force nucleation of one feldspar type on the surface of another resulting in epitaxial crystallization of dendritic plagioclase on k feldspar mantling of one feldspar type by another during magma mixing is paralleled by dendritic growth zones in coexisting plagioclase crystals

magma evolution and open system processes at shiveluch volcano insights from phenocryst zoning phenocryst zoning patterns are used to identify open system magmatic processes in the products of the 2001 eruption of shiveluch volcano kamchatka the lavas and pumices studied are hornblende plagioclase andesites with average pre eruptive temperatures of 840c and fo2 of 1 5 2 1 log units above nickel nickel oxide nno plagioclase zoning includes oscillatory and patchy zonation and sieve textures hornblendes are commonly unzoned but some show simple multiple or patchy zoning apatite microphenocrysts display normal and reverse zoning of sulphur the textural similarity of patchy hornblende and plagioclase together with ba sr systematics in patchy plagioclase indicate that the cores of these crystals were derived from cumulate material plagioclase liquid equilibria suggest that the patchy texture develops by resorption during h2o undersaturated decompression when h2o saturated crystallization recommences at lower pressure reduced ph2o results in lower xan in plagioclase causing more al rich hornblende to crystallize plagioclase cores with diffuse oscillatory zoning and unzoned hornblende crystals probably represent a population of crystals resident in the magma chamber for long periods of time in contrast oscillatory zoning in the rims of plagioclase phenocrysts may reflect eruption dynamics during decompression crystallization increasing fe al in oscillatory zoned rims suggests oxidation as a result of degassing of h2o during decompression a general lack of textural overlap between phenocryst types suggests that different phenocryst populations were spatially or temporally isolated during crystallization we present evidence that the host andesite has mixed with both more felsic and more mafic magmas olivine and orthopyroxene xenocrysts with reaction or overgrowth rims and strong normal zoning indicate mixing with basalt sieve textured plagioclase resulted from mixing of a more felsic magma with the host andesite the mineralogy and mineral compositions of a mafic andesite enclave are identical to those of the host magma which implies efficient thermal quenching and thus small volumes of intruding magma mixing of this magma with the host andesite results in phenocryst zoning because of differences in dissolved volatile contents we suggest that small magma pulses differentiated at depth and ascended intermittently into the growing magma chamber producing incremental variations in whole rock compositions

low pressure crystallization paths of h2o saturated basaltic hawaiitic melts from mt etna implications for open system degassing of basaltic volcanoes melt inclusions indicate that the basaltic hawaiitic magmas from mt etna sicily contained up to 2 3 wt h2o dissolved in the melt prior to eruption the effect of h2o degassing during magma ascent has been experimentally constrained between 1135 and 1009 c for ph2o ptotal varying from 800 to 270 bars the starting material was a primitive hawaiitic lava sample mgo 7 1 wt representative of the less evolved lava emitted at mt etna experiments were conducted in tzm pressure vessels with ag70pd30 capsules in order to minimize the feo loss at temperatures of 1135 1090 c ph2o 800 bars with ninio and fmq buffers olivine fo83 80 is the liquidus phase in equilibrium with a residual hawaiitic melt mg 0 60 0 57 cao al2o3 0 82 salitic pyroxene begins to crystallize at 1075 c plagioclase at 1025 c and at 1009 c the magma is 33 5 crystallized with olivine ca rich pyroxene and plagioclase 16 60 24 at ph2o 270 bars fmq buffer olivine fo79 3 80 and salitic pyroxene are the main liquidus phases between 1100 and 1090 c they are in equilibrium with hawaiitic melts mg 0 51 cao al2o3 0 73 at 1070 c the experimental charges are highly crystallized 51 5 with olivine fo70 salite and plagioclase an78 4 76 3 in 14 44 42 relative proportions increasing the water content of hawaiitic basaltic magmas expands the stability field of the olivine relative to the other phases lowers the crystallization temperatures of pyroxene and plagioclase and results in the development of a more an rich plagioclase when compared to the natural samples these results support a model of early and moderate crystallization of olivine from etnean primitive hawaiitic magmas containing close to 2 5 wt h2o with nno oxygen buffering conditions at low pressure ph2o ptotal we propose a model of crystallization driven by decompression and water degassing during the emplacement of magma in the volcanic pile itself and possibly concomitant with the opening of fractures

element zoning trends in olivine phenocrysts from a supposed primary high magnesian andesite an electron and ion microprobe study electron and ion probe microanalysis have been used to obtain zoning profiles for major and trace elements in olivine phenocrysts from a high magnesian andesite from shodo shima island southwest japan this rock was previously thought to represent undifferentiated primary magma some crystals have unzoned cores while others show cores which are reversely zoned with respect to mg mg fe ni mn and cr in addition some ni profiles show a normally zoned hump at the most central portions of the reversely zoned crystals all crystals show normally zoned rims the li concentrations are constant throughout the cores of all crystals studied but rise sharply by a factor of up to at least six in the rims the ca and co concentrations are essentially constant throughout all the crystals mechanisms for producing the observed zoning profiles are discussed and it is concluded that the reverse zoning was produced by the introduction of crystals into a less differentiated magma than that in which they grew the reversely zoned crystals could therefore represent xenocrysts which were introduced into an undifferentiated magma or phenocrysts introduced into a more primitive magma by a magma mixing process the ni profiles are used to estimate the residence time of these crystals in the more primitive magma the following trace element partition co efficients have been estimated for the olivine groundmass system in this rock dni 16 dmn 1 1 dco 4 2 dca 0 02 dti 0 005 dv 0 05 dsc 0 2 dna 0 0002 studies of trace element zoning will become increasingly important as the new generation of trace element microprobes become available but a larger database of experimentally determined values for trace element partition coefficients and diffusion coefficients in crystals and magmas and a better understanding of other disequilibrium processes are required to fully exploit the new data

feeding system and magma storage beneath mt etna as revealed by recent inflation deflation cycles 1 ground deformation at mt etna detected by three gps surveys carried out in 2004 2005 and 2006 is analyzed the data set encompasses the 2004 2005 eruptions and foreruns those of 2006 a wide deflation of the entire volcano was detected from 2004 to 2005 accompanying the 2004 2005 eruption conversely an evident inflation phase from 2005 to 2006 followed this eruption and preceded the 2006 one in both cases the deflation inflation cycle was accompanied by a continuous seaward motion of the eastern flank we inverted both data sets 2004 2005 deflation and 2005 2006 inflation using an optimization algorithm based on the genetic algorithm ga in order to detect the ground deformation sources the wide contraction measured during the eruption reveals the drainage of a sill shaped magma reservoir located by data inversions at a depth of about 4 5 km b s l the pressurizing source modeled for the 2005 2006 time interval indicates a refilling of the shallower near vertical plumbing system of the volcano this could indicate a change in the geometry of the feeding system active after the 2004 2005 eruption with a new and shallower magma storage that could have enabled the resumption of volcanic activity that was observed at summit craters in 2006 these results improve the imaging of the plumbing system of mt etna volcano

effects of magma storage and ascent on the kinetics of crystal growth the size distributions of crystals of olivine plagioclase and oxides of the 1991 93 eruption at mt etna italy are analyzed the simultaneous collection of this information for different minerals gives precious insight into the cooling history of lavas three distinct episodes are detectable a storage of the magma in a deep reservoir characterized by nearly constant and low nucleation and growth rates near to equilibrium an ascent phase with an ever increasing nucleation rate related to volatile exsolution and finally a quenching phase in addition to geochemical and geophysical evidence the similarity of the crystal size distributions of the present eruption with those of previous ones of this century makes it possible to exclude that crystal size distributions of etnean lavas are due to mixing of different populations this strongly suggests that the main features of the volcano feeding system have not changed despite observed variations in the magma output rates

zoning of phosphorus in igneous olivine we describe p zoning in olivines from terrestrial basalts andesites dacites and komatiites and from a martian meteorite p2o5 contents of olivines vary from below the detection limit 0 01 wt to 0 2 0 4 wt over a few microns with no correlated variations in fo content zoning patterns include p rich crystal cores with skeletal hopper or euhedral shapes oscillatory zoning structures suggesting replacement of p rich zones by p poor olivine and sector zoning melt inclusions in olivines are usually located near p rich regions but in direct contact with low p olivine crystallization experiments on basaltic compositions at constant cooling rates 15 30 c h reproduce many of these features we infer that p rich zones in experimental and natural olivines reflect incorporation of p in excess of equilibrium partitioning during rapid growth and zoning patterns primarily record crystal growth rate variations occurrences of high p phenocryst cores may reflect pulses of rapid crystal growth following delayed nucleation due to undercooling most cases of oscillatory zoning in p likely reflect internal factors whereby oscillating growth rates occur without external forcings but some p zoning in natural olivines may reflect external forcings e g magma mixing events eruption that result in variable crystal growth rates and or p contents in the magma in experimental and some natural olivines al cr and p concentrations are roughly linearly and positively correlated suggesting coupled substitutions but in natural phenocrysts cr zoning is usually less intense than p zoning and al zoning weak to absent we propose that olivines grow from basic and ultrabasic magmas with correlated zoning in p cr and al superimposed on normal zoning in fe mg rapidly diffusing divalent cations homogenize during residence in hot magma al and cr only partially homogenize and delicate p zoning is preserved because p diffuses very slowly this interpretation is consistent with the fact that zoning is largely preserved not only in p but also in al cr and divalent cations in olivines with short residence times at high temperature e g experimentally grown olivines komatiitic olivines groundmass olivines and the rims of olivine phenocrysts grown during eruption p zoning is widespread in magmatic olivine revealing details of crystal growth and intra crystal stratigraphy in what otherwise appear to be relatively featureless crystals since it is preserved in early formed olivines with prolonged residence times in magmas at high temperatures p zoning has promise as an archive of information about an otherwise largely inaccessible stage of a magma s history study of such features should be a valuable supplement to routine petrographic investigations of basic and ultrabasic rocks especially because these features can be observed with standard electron microprobe techniques

so2 flux measurements at mount etna sicily since 1987 over 220 measurements of the so2 flux at mount etna have been carried out using a correlation spectrometer cospec with different measuring techniques mainly with cospec mounted on a ground based vehicle this paper reports and analyzes the data obtained between october 1987 and december 1991 during this period three distinct time intervals characterized by particular so2 emission patterns were identified the first interval a showed a mean so2 flux of 5500 t d associated with relatively quiet summit crater eruptive activity the second interval b included two eruptive periods september october 1989 and january february 1990 associated with high fluxes reaching 10 000 25 000 t d the third interval c started in concert with a regional earthquake december 13 1990 and showed first a decrease and then an increase of so2 emissions before the onset of the major 1991 1993 flank eruption analysis of the data reveals a cyclic pattern to the so2 emissions over prolonged periods a nearly constant supply of so2 from the volcano s main feeder system especially evident in the long term a two to fivefold increase above mean flux values from 10 000 to 25 000 t d when occurring with paroxysmal eruptive activity and minimal flux values 1000 t d about 1 month prior to important eruptive events

the horizontal velocity field in the deforming aegean sea region determined from the moment tensors of earthquakes we use the spatial distribution of seismic moment tensors of earthquakes in the aegean region over the time interval 1909 1983 to recover a continuous horizontal velocity field that describes the overall deformation of the lithosphere at large length scales the calculated velocity field is dominated by two effects 1 an e w right lateral shear of the eastern aegean related to motion on the north anatolian fault becoming distributed as it enters the aegean and 2 a n s extension probably related to the sinking of the slab in the hellenic trench the southern part of the central aegean is found to be moving in a sw direction relative to europe at a rate of about 30 mm yr probably a lower bound with an error of around 10 mm yr and rotating clockwise in the seismogenic upper crust this velocity field is accommodated by right lateral strike slip faults in the eastern aegean and by normal faults that rotate clockwise in central greece a comparison of paleomagnetic declination data with the expected rotation of rigid elongate inclusions in the velocity field shows in most places an agreement in sense and approximate agreement in rate of rotation expected rotation rates of line elements are sometimes too low probably because our derived velocity field is smoothed and unable to match locally high strain rates there is only one part of the region where line elements are predicted to rotate in either clockwise or counterclockwise directions depending on their orientation this is in western turkey which coincident ally is the only place where paleomagnetic rotations in both directions have been observed this coincidence in particular suggests to us that the analogy of rigid elongate inclusions in the velocity field responding to forces on their bases may be useful in predicting the senses and approximate rates of rotation of crustal blocks in deforming continental regions the velocity field we obtain preserves the strike directions of the major faults as directions of zero length change in spite of considerable smoothing we use this observation to speculate that the interaction between the upper crust and the rest of the lithosphere beneath it may involve an interplay of effects on one hand the variation of strength with direction in the crust may control the strike directions of faults that form or become reactivated and may also limit the velocity fields that are allowable on the other hand the fault bounded blocks may rotate in the velocity field in response to forces on their bases which would require the velocity field to change with time if the directions of zero length change are fixed to the blocks

the control of lava flow during the 1991 1992 eruption of mt etna abstract all the actions carried out in 1992 to protect the village of zafferana etnea from being invaded by lava are described an earthen barrier 234 m long and 21 m high was firstly built in january 1992 by accumulating with mechanical escavators 370 000 m 3 of earth scoriae and stones this embankment contained the lava for about one month and was overflowed by april 9 1992 three additional smaller earthen barriers lenght 90 160 m height 6 12 m were built in april to gain time while the lava front was descending towards zafferana from the overflowed first embankment the major effort of the 1992 operation consisted of several attempts at stopping the lava front advance by diverting the flow out from the natural and extensively tunnelled channel through a skylight near the vent the main intervention point was located in valle del bove at an elevation of 2000 m at 8 km from zafferana in a zone almost unaccessible from land helicopters were hence extensively used during the whole operation initial interventions called for attempts at plugging a tunnel by dumping into it linked concrete blocks hedgehogs and blasted portions of the solid levee each intervention caused the partial obstruction of the tunnelled channel which determined major increases of lava overflow in valle del bove and the consequent halt of the most advanced fronts however benefits were of brief duration at the most two weeks of respite before new lava fronts approached again and again the outskirts of zafferana the final successful intervention was carried out on may 27 29 an artificial channel was dug departing from the natural one the solid separation levee was thinned to 3 m and blasted by 7000 kg of explosives after the explosion 2 3 of the lava flowed spontaneously in the artificial channel and then the total diversion was obtained the tunnel being plugged by dumping into the natural flow 230 m 3 of lava boulders as a consequence of the intervention the active natural lava front that on may 27 was only 850 m from zafferana came to an halt as did the entire flow downhill from the diversion point bringing back the situation as it was five months earlier a few days after the beginning of the eruption with the new front of the diverted flow at 6 7 km from zafferana in june 1992 the effusion rate halved from 30 to 15 m 3 s and with this reduced thrust the lava was no longer capable of covering long distances five months after the conclusive intervention the diverted lava continues to flow over its initial natural field but remaining confined in the upper valle del bove without any new threat to zafferana

magmatic residence times of zoned phenocrysts introduction and application of the binary element diffusion modelling bedm technique this paper describes a general technique binary element diffusion modelling bedm for determining single crystal residence times in magmas that relies on modelling the diffusion of two or more elements in the crystal bedm has the advantage over other diffusion based models in that it does not need a precisely defined initial compositional profile for the crystal at zero time and instead requires that the concentrations of the two elements are correlated during crystallisation any differences subsequently observed between the two elements are caused by intracrystalline diffusion during residence in hot magma these differences are removed by artificially ageing the slower diffusing of the two elements and the amount of time taken to undo the difference between the elements is simply related to the crystal residence time decoupling time at high temperatures the bedm principle is demonstrated using artificial data and is then applied to literature data for sr and ba in a zoned sanidine crystal from the bishop tuff anderson et al in j petrol 41 3 449 473 2000 for this crystal the method gives a residence time estimate of 114 ka at 800 c which is then compared with estimates from other methods in theory the method can be further expanded for use as a geothermometer as well as geochronometer however this is not easily possible with the diffusivity data currently available

plagioclase residence times at two island arc volcanoes kameni islands santorini and soufriere st vincent determined by sr diffusion systematics the diffusive relaxation of trace element profiles in plagioclase phenocrysts may provide important constraints on magma residence times in crustal magma chambers initial trace element profiles in plagioclase phenocrysts are governed by variations in the concentration of a trace element in the melt and by the plagioclase melt partition coefficient trace element diffusion will subsequently act to modify this initial profile and given enough time produce a profile that is in equilibrium with the anorthite variations within the crystal we argue that the trace element partition coefficient da b between two parts a and b of a plagioclase crystal of variable anorthite content is equal to the ratio of their crystal liquid partition coefficients and that the equilibrium profile of the crystal can be calculated the time required to establish diffusive equilibrium is dependent on the wavelength and amplitude of the initial trace element concentration range and on the diffusivity of the trace element in plagioclase strontium plagioclase melt partition coefficients and diffusivities are calculated for a range of magmatic temperatures and plagioclase compositions a one dimensional diffusion model is developed that describes the diffusive destruction of oscillatory trace element zoning with time and allows the calculation of upper limits for plagioclase crystal residence times in a magma reservoir the model is tested using major and trace element concentrations measured along crystal traverses of plagioclase phenocrysts from the kameni island dacites santorini and from the 1979 soufriere andesite st vincent three out of eight plagioclase phenocrysts have sr concentration profiles that are not in diffusive equilibrium for these the diffusion model is employed to calculate maximum crystal residence times from incomplete diffusive equilibration of trace element zoning in plagioclase maximum crystal residence times range from 100 to 450 years this is in good agreement with estimates from crystal size distribution and from ra th disequilibrium studies for the kameni islands for soufriere however such short residence times are incompatible with u th mineral errorchron data that suggest residence times of 40 ka in a thermally buffered magma reservoir to reconcile these apparently different ages we invoke a more complicated magmatic history for soufriere where an initially buffered magma reservoir is disturbed by magma mixing and suffers limited additional crystal fractionation prior to eruption

dynamic plumbing system beneath volcanoes revealed by kinetic modeling and the connection to monitoring data an example from mt etna abstract our ability to monitor volcanoes using seismic signals ground deformation gas fluxes or other ground and satellite based observations as well as our understanding of melt reservoirs that feed eruptions have evolved tremendously in recent years the complex plumbing systems that are thought to feed eruptions are however difficult to relate to the monitoring signals here we show that the record preserved in compositional zoning of erupted minerals may be used to reconstruct sections of the plumbing system kinetic modeling of such zoning can yield information on the residence time of magma in different segments of the plumbing systems this allows a more nuanced evaluation of the link between observed monitoring signals or eruption styles and the magmatic processes and movement of batches of melts at depth the approach is illustrated through a study of the compositional zoning recorded in olivine crystals from the 1991 1993 se flank eruption products of mt etna sicily the zoning patterns in crystals reveal that the plumbing system of the volcano consisted of at least three different magmatic environments between which magma was transported and mixed in the year or two preceding the start of eruption quantification of this history indicates that two main pathways of melt migration and three timescales dominated the dynamics of the system combination of this information with the timing of observation of various monitoring signals allows a reconstruction of the dynamic evolution of this section of the plumbing system during the early stages of the 1991 1993 eruption it is seen for example how the migration of melt through the same sections of the plumbing system can cause pre eruptive triggering enhance strombolian activity and through the ensuing eruption cleanse and flush the plumbing system different kinds of mixing occur simultaneously at different sections of the plumbing system on different timescales a few days up to two years

decadal time gaps between mafic intrusion and silicic eruption obtained from chemical zoning patterns in olivine abstract intrusion of mafic magma in a silicic crustal reservoir has been reported in numerous studies of subduction related volcanoes and is considered a main process for triggering explosive eruptions and for transferring geochemical signatures from the mantle to the crust here we determine the timescales between mafic silicic encounters and eruption by exploiting the fact that during such interactions magmas exchange crystals and their mineral compositions will strive to equilibrate to the new environmental conditions specifically we model the fe mg zoning patterns of olivine found in the dacites andesite and quenched mafic inclusions of the holocene zoned eruption of volcan san pedro 36 s chilean andes the san pedro eruption is an example where mixing between silicic and mafic magmas produced intermediate compositions e g andesite at depth in the magma reservoir for modeling the compositional profiles we took into account the anisotropy of fe mg diffusion in olivine and also the effects of diffusion in multiple dimensions aspects that have been largely neglected in previous works the retrieved timescales for olivine melt equilibration by diffusion display an array ranging from 1 year for the most silica rich dacite to 50 years for the andesite this array of timescales rather than a single value provides new insight into the details of mafic silicic mixing at depth they reveal processes that occur on a longer timescale than the days to weeks time gap for cases where the mafic intrusion triggered the eruption and they might be associated with the instances where seismic activity or significant inflation of the volcanic edifice was not immediately followed by eruption on the other hand the year to decade timescales that we report for producing magmas of intermediate composition e g andesites are much shorter than the 10 3 10 5 years inferred from u series disequilibria data for igneous differentiation by closed system fractionation to produce similar magma compositions at subduction zones

geochemical and isotopic monitoring of mt etna 1989 1993 eruptive activity bearing on the shallow feeding system two flank eruptions took place at mt etna during 1989 1993 the former september october 1989 produced lavas among the most primitive of this century while the latter december 1991 march 1993 was unusually long lasting and the largest of the last three centuries alkali basalts of 1989 displayed initial enrichments of rb and k accompanied by an higher value of radiogenic sr and isotopic disequilibrium between host rock and clinopyroxene 0 70364 and 0 70356 respectively subsequently within one week k rb and 87sr86sr ratio decreased to constant values 87sr86sr 0 70355 nd isotopic ratio did not show significant variations these features can be explained by a selective contamination process involving essentially rb k and radiogenic sr the bulk from the 1991 1993 eruption hawaiites were erupted between january and may 1992 in this period lavas here called jml were characterised by uniform geochemical and isotopic compositions and sr isotopic equilibrium between whole rock and pyroxene 0 70355 in other periods december 1991 and june 1992 we observed lower and variable sr isotopic compositions coupled with disequilibria between lavas and their clinopyroxenes 0 70351 in the w r and 0 70345 in the cpx of the sample of 15 december 1991 starting from june 1992 the products seem to reveal fractionation effects as suggested by the continuous rise in concentrations of incompatible elements when the observed variability cannot be ascribed to fractionation effects we are not able to discriminate mixing from selective contamination however lavas erupted during december 1991 evolved towards the isotope composition of jml that was never exceeded moreover the regular behaviour of rb k and radiogenic sr of 1989 lavas was not observed during the 1991 1993 eruption thus we prefer to interpret these variations as mainly due to mixing processes between an end member of jml composition and another one having the same or lower isotopic composition of the clinopyroxene found in the sample of december 1991 several petrogenetic processes are contemporaneously active at mt etna they encompass magma mixing selective contamination and fractional crystallization their relative importance varies according to the original volume of each magma batch and to the status of the shallow feeding system the complexity of these processes acting in the short time span of a few months claims caution about the geochemical representativity of a single lava sample for each eruption

soil co2 degassing on mt etna sicily during the period 1989 1993 discrimination between climatic and volcanic influences wide variations were measured in the diffuse co2 flux through the soils in three selected areas of mt etna between august 1989 and march 1993 degassing of co2 from the area of zafferana etnea s venerina on the eastern slope of the volcano has been determined to be more strongly influenced by meteorological parameters than the other areas the seasonal component found in the data from this area has been excluded using a filtering algorithm based on the best fitting equation calculated from the correlation between co2 flux values and those of air temperature the filtered data appear to have variations temporally coincident with those from the other areas thus suggesting a common and probably deep source of gas the highest fluxes measured in the two most peripheral areas may correlate well with other geophysical and volcanological anomalous signals that preceded the strong eruption of 1991 1993 and that were interpreted as deep pressure increases anomalous decreases in co2 fluxes accompanied the onset and the evolution of that eruption and have been interpreted as a sign of upward migration of the gas source the variations of co2 flux at the 1989 se fracture have also given interesting information on the timing of the magmatic intrusion that has then fed the 1991 1993 eruption

mineral textures and zoning as evidence for open system processes investigations of mineral textures and zoning as evidence for open system processes during magmatic evolution have always been a centerpiece of petrological studies and have provided some of the best evidence for magma mixing and crustal contamination for many decades e g milch 1905 kuno 1936 eichelberger 1975 sato 1975 anderson 1976 in fact evidence from mineral studies was instrumental in the acceptance of magma mixing as important petrological process ever since it was initially proposed by bunsen 1851 in recent years mineral studies are invigorated by the development of high precision high resolution analytical instruments and techniques through which textural information and compositional data are combined e g jerram and davidson 2007 as minerals respond texturally and compositionally to changing magmatic environments they preserve in their crystal growth stratigraphy a wealth of information regarding their past history of magmatic processes and compositions cf ginibre et al 2007 on the other hand magmatic liquids melts are snapshots of current magmatic states and provide less direct evidence of the processes responsible for their evolution in addition liquids may crystallize thereby destroying the direct evidence they provide with an appropriate set of observations and measurements we can correlate textures with mineral compositions and thus produce a richer composite picture of magmatic evolution than compositional data of minerals alone this contribution reviews the zoning and textures of minerals frequently encountered in volcanic rocks many of which apply equally to plutonic rocks and the interpretations ascribed to these features in terms of open system magmatic processes first i will address the analytical tools that are used to acquire textural and compositional data followed by a brief review of open system processes and a summary of the relevant textures from that point on i will address some mineral specific aspects followed by a discussion

magma dynamics in the shallow plumbing system of mt etna as recorded by compositional variations in volcanics of recent summit activity 1995 1999 describe the reactivation and the successive evolution of the shallow plumbing system of mt etna between the end of the largest flank eruption of the last three centuries 1991 1993 and the subterminal eruption from south east crater sec which occurred between february and mid november 1999 our analysis is based on observations of the volcanic activity and petrological studies of the erupted volcanics bulk rock mineral and glass compositions have been determined for more than 80 samples erupted from the four summit craters between october 1995 and february 1999 these data allow us to recognise significant compositional variations among the products of different craters in particular volcanics produced between 1995 and 1999 by bocca nuova bn voragine vor and north east crater nec show limited compositional variations and are similar to those observed during recent eruptions e g 1991 93 more primitive magmas have been produced during the more vigorous fire fountains episodes on the contrary the south east crater produced slightly more differentiated volcanics than those of the other summit craters following its reactivation november 1996 until the end of 1998 whole rock compositions of products from this crater show low cao al 2 o 3 whereas interstitial glasses have lower mgo and higher alkali contents than those from the other craters however since the beginning of 1999 and just before the start of the subterminal eruption from sec the volcanics erupted from this crater progressively changed in composition becoming similar to those of the other craters this trend indicates that within the conduits of the summit craters distinct thermal and fluid dynamical regimes can evolve controlling the cooling and crystallisation of etna magmas

shallow magma pathway geometry at mt etna volcano 1 a fundamental goal of volcano seismology is to understand the dynamics of active magmatic systems in order to assess eruptive behavior and the associated hazard imaging of magma conduits quantification of magma transport and investigation of long period seismic sources together with their temporal variations are crucial for the comprehension of eruption triggering mechanisms at mt etna volcano several intense episodes of tremor activity were recorded during 2007 in association with strombolian activity and or intense fire fountaining episodes occurring from the south east crater sec the locations of the tremor sources and of the long period seismic events are used here to constrain both the area and the depth range of magma degassing highlighting the geometry of the shallow conduits feeding sec the imaged conduits consist of two connected resonating dike like bodies nnw sse and nw se oriented extending from sea level to the surface in addition we show how tremor long period lp and very long period vlp event locations and signatures reflect pressure fluctuations in the plumbing system associated with the ascent discharge of gas rich magma linked to the lava fountains the evidence here reported also corroborated by ground deformation variations can help develop a better prediction and early warning system for those eruptions effusive or explosive that apparently manifest no clear precursors

mt etna volcano modelling of ground deformation patterns of recent eruptions and considerations on the associated precursors abstract the study of the ground deformation associated with the recent eruptions of the etna volcano 1981 1989 1991 93 furnished the opportunity to observe different behaviour relating to the eruptive activity and suggested different feeding and penetration mechanisms inside the volcano edifice in particular the analytical modelling of geodetic data was applied to study the strain sources of these eruptions by the application of single and multiple source models i e composed of two single sources in particular a single tensile dislocation was used to model the se fracture associated with the 1989 eruption a double tensile dislocation was adopted to interpret and model the deformation pattern of the 1981 eruption a double source composed of a tensile dislocation for the final eruptive fracture and a depressuring body for the deflation during the eruption course was considered for the 1991 93 eruption the results of this modelling show that however the final uprising system i e the tensile mechanisms inside the volcano edifice involved the same structure oriented approximately nnw sse this structure was activated by different eruption mechanisms with associated different deformation patterns during these three recent eruptions a review of the methodologies applied and main results obtained in modelling of different sources and mechanisms is presented here the analysis of the deformation data and the performed modelling evidence that the associated precursors can strongly change for the different eruptions in addition the implications both in terms of how the volcano works and in terms of ground deformation precursors are discussed

residence time and crystallization history of nickeliferous olivine phenocrysts from the northern yatsugatake volcanoes central japan application of a growth and diffusion model in the system mg fe ni abstract the chemical zoning of nickeliferous olivine phenocrysts in calc alkaline andesites from the northern yatsugatake volcanoes central japan is examined by a growth and diffusion model in the system mg fe ni nickeliferous olivine phenocrysts are included in the high alumina basaltic end member magma which forms the mixed calc alkaline andesites in the northern yatsugatake volcanoes the olivine phenocrysts can be divided into three types on the basis of chemical composition zoning profile and occurrence type 1 olivine is rich in ca and mg and the zoning profile of type 1 forms a slightly more fe rich trend than the maximum fractionation trend in the nio versus forsterite content fo diagram the most mg and ni rich and mn poor core of type 1 fo 91 5 mol nio 0 40 wt mno 0 13 wt can be in equilibrium with peridotite in the upper mantle by contrast type 2 olivine is ca poor and rich in fe and ni compared to type 1 the zoning patterns of type 2 are more variable the nio content in fe rich type 2 phenocrysts decreases rapidly from core to rim within a narrow range of fo the maximum nio content of type 2 is 0 53 wt the transitional type olivine has an intermediate composition between type 1 and type 2 and a similar zoning profile as that of type 1 type 1 olivine mainly occurs as isolated phenocrysts while fe rich type 2 occurs as crystal clots the growth and diffusion calculation in the system mg fe ni revealed that the composition of normally zoned olivine is enriched in fe by diffusion without a marked depression in the ni content due to a larger fe mg interdiffusion coefficient than the ni tracer diffusion coefficient in olivine the zoning patterns of both type 1 and type 2 can be reproduced by calculation the residence time of type 1 olivine in the magma is estimated to be less than 10 0 5 1 y at 1150 1050 c whereas the residence time of fe enriched type 2 olivine is from ten to one hundred times longer than that of type 1 the long residence time and occurrence as crystal clots suggest that the fe enriched type 2 olivine phenocrysts were captured and crystallized in the crystal mush at the roof and bottom of a magma chamber

diffusion coupling between trace and major elements and a model for calculation of magma residence times using plagioclase residence times of plagioclase crystals in magma reservoirs can be determined by modeling the compositional zoning of trace elements in these crystals we present a formulation to model diffusion of trace elements in plagioclase paying special attention to certain thermodynamic and kinetic aspects in particular we account for the compositional dependence on anorthite content of the chemical potential and diffusion coefficients of trace elements e g mg the choice of suitable boundary conditions and potential effects of diffusion in more than one dimension we show that contrary to intuition diffusive fluxes of trace elements may be coupled to major element concentration gradients and ignoring such coupling can lead to incorrect estimates of timescales we illustrate application of the model using plagioclase crystals from a suite of gabbroic xenoliths from a holocene dacitic lava flow of volcan san pedro chilean andes 36 s the inferred timescale for metasomatism of the xenoliths by evolved liquids is on the order of 100 30 to 148 yr and serves to illustrate how trace element zoning in plagioclase provides a window into timescales of magmatic processes inaccessible by isotopic or other methods