variable parent magmas and recharge regimes of the parinacota magma system n chile revealed by fe mg and sr zoning in plagioclase abstract zoning patterns of an content and fe mg and sr concentrations in plagioclase phenocrysts in andesites from parinacota volcano n chile reflect alternating recharge events with two chemically distinct mafic magmas these magmas are characterized by low and high sr contents similar to two recent mafic flank eruptions one end member basaltic andesite shows large sr enrichment and heavy rare earth depletions and thus equilibrated with lower crustal rocks at depth where plagioclase high sr is unstable and garnet high hree y is stable a second end member magma is lower in sr ba contents and has ree patterns typical for parent magmas elsewhere in the central andes the number of recorded recharge events increases after a catastrophic sector collapse and during the subsequent rebuilding of the stratocone variations of an fe and mg contents and morphology of zones suggest also changes in water pressure including decompression under water under saturated and water saturated conditions evidence for decompression is more present in post collapse samples suggesting that the change in the volcano dynamics involves changes in magma chamber location this shows the importance of the cone collapse event in the volcano s magmatic evolution we propose that both end members are only seen at the surface of parinacota volcano because of the particular dynamics of this volcanic system and that similar processes might occur in other volcanic centres of the central volcanic zone

trace element evidence for plagioclase recycling in calc alkaline magmas abstract trace element zoning in plutonic plagioclase feldspars from the val fredda complex southern adamello massif italy has been measured using secondary ion mass spectrometry sims the studied samples range from hornblende gabbro through diorite to granitoid with an overall range in plagioclase composition from an96 to an15 individual plagioclases display extensive zonation in anorthite through a considerable variety of zoning textures there is equally extensive zoning in trace elements notably sr and ba broadly similar trace element zoning patterns and concentrations are displayed by all plagioclases irrespective of host rock composition using a relationship betweenxan and the distribution coefficientsdsr anddba trace element concentrations in plagioclase are converted to those of the melt which precipitated each crystal zone the calculated variations in ba and sr are greater than can be attributed to changes in pressure or temperature alone indicating that compositional variation in the coexisting melt was the principal cause of zoning the ba sr melt trend for each crystal describes a two stage crystallisation history the calcic cores of all crystals show melt trends of increasing sr and ba which are attributed to mixing and fractionation in parental hydrous picrobasalt magmas in contrast the melt trends recorded by the rims vary from sample to sample but essentially show decreasing sr and ba consistent with fractionation of sodic plagioclase alkali feldspar and or biotite the plagioclase cores are thought to have crystallised in a common magma chamber at 6 10 kbar pressure while the rims crystallised at the emplacement level 1 5 kbar from interstitial melt whose composition is determined by that of the host magma the data suggest that early formed calcic plagioclase was recycled by the magma during fractionation vigorous convection is invoked to both retain relatively dense calcic plagioclase within the evolving magma and to periodically re entrain cumulus crystals into more evolved magmas the occurrence of calcic plagioclase cores in felsic derivative magmas indicates that fractionation from picrobasalt to tonalite occurred on a relatively short time scale

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

petrogenesis of nb ta aplo pegmatites and fine grained granites from the early cretaceous huangshan rare metal granite suite northeast jiangxi province southeast china abstract the early cretaceous ca 130 ma nb rich and ta poor huangshan suite south china includes a series of medium grained granites that contain nb rich mica and very low columbite contents which are indicative of a potential nb resource in addition the huangshan suite contains fine grained granites and aplo pegmatites in which disseminated nb ta columbite is an ore two types of fine grained microcline bearing and albite rich leucogranite sills and dikes were identified sills and dikes of leucogranites and aplo pegmatites intrude the medium grained granites and surrounding hornfels the aplo pegmatites consist of large microcline and quartz crystals that are typically broken and embedded within a foliated albite rich matrix niobium rich and mn poor columbite with ta ta ta nb 0 5 and mn mn mn fe

crystal settling in a vigorously converting magma chamber there has been much debate concerning the mechanism of fractional crystallization in magma chambers the traditional hypothesis of crystal settling has been widely replaced by the concept of in situ crystallization coupled with compositional convection observations from layered intrusions however are equivocal1 4 doubts have been raised about crystal settling on theoretical grounds because convective velocities in magma chambers are often much greater than the crystal settling velocities predicted by stokes law5 but there has been no experimental study of crystal settling in such vigorous convection here we present physical considerations and laboratory experiments which show that the phenomenon of particle settling in these conditions can be accounted for by a simple theory application of this theory to crystal settling in magma chambers suggests that crystal settling may be an efficient differentiation mechanism at least in basaltic magma chambers despite large convective velocities

textural constraints on the kinetics of crystallization of igneous rocks natural systems provide time controlled experiments on scales unreachable in the laboratory and with complexities unapproachable by computer experiments since temperature undercooling cannot be directly scaled with time in situ crystallization experiments provide information unavailable by other means the kinetics of crystallization in simple silicate systems have been studied extensively for glass ceramic systems e g uhlmann 1982 james 1982 but predictive models for nucleation behavior in particular remain inadequate part of the problem in creating models of nucleation lies in the difficulty of experimentally isolating the nucleation process crystal growth measurements are more accessible experimentally and for this reason crystal growth is better understood e g dowty 1980 kirkpatrick 1981 james 1982 baronnet 1984 however predictive models of crystal growth e g lasaga 1982 require accurate models for the temperature and compositional dependence of both the thermodynamic and kinetic driving forces for crystallization information that is currently limited the cse parameterization of the position of ymax as a function of t tl and t suggested by dearnley 1983 provides a potentially useful model that requires further testing similarly application of the adiabatic nucleation model of meyer 1986 to simple systems suggests that the position of tmax relative to tl has an approximately constant value of 0 55 0 60 exceptions are low dsf minerals such as albite and quartz additionally while experimental crystallization rate data is a necessary link between processes in natural melts and numerical models experimental growth rate data is confined to simple systems and conditions of moderately large undercooling while growth rate estimates in complex natural systems suggest that under most conditions undercoolings remain very small quantitative textural studies of dikes suggest a pronounced dependence of growth rate on total crystallization time e g ikeda 1977 which is in turn related to effective undercooling a function of both total dike width and distance from the dike margin by analogy minimum crystallization rates may be estimated from programmed cooling experiments if a temperature interval of crystallization is assumed growth rates determined in this way show the same relationship between growth rate and total crystallization time seen in the dike studies reflecting a systematic relationship between growth rate and cooling rate effective undercooling for plagioclase in basaltic systems while the data are not available for other mineral systems there is no reason to believe that similar patterns would not exist for other silicate minerals i e the similarity in dendritic olivine growth rates estimated by fowler et al 1989 using fractal analysis to the growth rates of plagioclase under conditions of rapid cooling estimated from programmed cooling rate experiments analysis of measured crystal size frequencies provides a means of extracting effective bulk kinetic information from geologic systems that can help to constrain the dynamic feedback between physical models of magmatic systems and rates of chemical change

bulk rock geochemistry and plagioclase zoning in lavas exposed along the northern flank of the western blanco depression northeast pacific insight into open system magma chamber processes abstract the present study is based on a set of lavas and crosscutting dikes collected by dives along detailed vertical transects on the northern flank of the western part of the blanco transform fault northeast pacific the studied area consists of a small basin the western blanco depression wbd extending from the southern end of the juan de fuca ridge to a pseudofault trace 60 km eastward the northern scarp of the wbd comprises a volcanic unit overlying a sheeted dike complex major and trace element data coupled with sr nd isotope ratios reveal a two component mantle source composed by an isotopically depleted matrix variably veined by more enriched material one chemical group ns2 indistinguishable from the other northern scarp samples on the basis of trace element data has an unusually depleted isotopic composition typical of a nearly pure mantle end member some cogenetic samples of the northern scarp have been used to constrain the differentiation modalities anorthite and mgo content profiles in plagioclase xenocrysts and phenocrysts reveal i the existence of h2o bearing evolved melts in the mushy zones and ii the occurrence of mixing process between these melts and anhydrous mafic liquids the hydration is supported by other petrographic features such as high magmatic fo2 values calculated from fe ti oxide pairs and the presence of pyroxene inclusions in plagioclase phenocrysts mixing consistent with the existence of ni rich ferrobasalts is interpreted to be the consequence of the reservoir refilling by mafic liquids mg 70 these petrological and geochemical evidences are combined with the evolution of mg with depth to suggest a periodic open system magma chamber evolution beneath the southern end of the juan de fuca ridge

new insights into the processes controlling compositional zoning in plagioclase abstract although plagioclase is the most abundant mineral in crustal rocks the factors that control the magnitude of compositional zoning in plagioclase remain poorly constrained the composition of magmatic plagioclase depends upon physical parameters such as temperature t and total pressure p as well as the full range of compositional controls including the water content of the melt wt h 2 o the changes in these physical parameters can be quantified using available numerical phase equilibria models for various differentiation scenarios and the magnitude of these effects on plagioclase zoning can be calculated the role of temperature total pressure and water content on plagioclase zoning has been experimentally investigated previously in a pure albite anorthite ab an system in this study we use the melts algorithm to quantify the effects of p t and water content of the melt on compositional zoning in plagioclase in a basaltic system our first two simulations are designed to evaluate the magnitude of compositional changes that may be attributable to specific system changes exclusive of assimilation and recharge the first scenario involves a two step crystallization process in the first step magma rises from a deeper to a shallower chamber while crystallizing plagioclase at successively lower pressures in the second step the magma pools in the shallower magma chamber and continues to crystallize isobarically if these two steps are repeated the result is the development of reverse normal and oscillatory zoning in plagioclase the second scenario involves plagioclase zoning in a large convecting magma chamber where plagioclase crystallizes as the magma convects resulting in oscillatory zoning the third scenario involves a two step process where crystallization is interrupted by multiple recharge events in this case magma crystallizes isobarically as a new batch of primitive magma is injected periodically to the magma chamber and crystallization continues after mixing during the repetition of these two steps plagioclase develops normal and reverse zoning based on our results we interpret zoning in plagioclase in terms of the partitioning of na 2 o and cao between the melt and plagioclase and the changes in the total volume during dissolution reactions of albite vab dissolution and anorthite van dissolution components for the first two scenarios our calculations show that as pressure decreases vab dissolution and van dissolution decrease while as pressure increases both of them increase vab dissolution always being larger than van dissolution controls the zoning in plagioclase by compensating the larger volume change in the melt either by albite component dissolving into its oxides or by oxides reacting to produce albite component therefore at a given temperature with decreasing pressure na 2 o partitions increasingly into the melt compared to cao making the coexisting plagioclase more an rich thus ascent of magma from a deeper to a shallower chamber isentropically or convection of a magma in a large chamber polybaricaly results in the development of reverse zoning in plagioclase the magnitude of the effects is on the order of 3 mol an per kbar for both decompression driven crystallization and isothermal polybaric convection

decoding whole rock plagioclase zircon and apatite isotopic and geochemical signatures from variably contaminated dioritic magmas zircon and apatite grains from three types of variably contaminated quartz diorite were analyzed in the gesiniec intrusion sw poland the zircon isotopic compositions ehf300 5 5 0 and 18o 5 6 9 3 are consistent with contamination processes zircon is characterized by an increase in u th pb and ree from the least to the most evolved quartz diorite type apatite is characterized by ranges in trace element concentrations and with the progress of contamination its composition evolves from those typical for i type granites toward those typical for s type isotopic and trace element variations in zircon and apatite correlate with sr isotopic composition of plagioclase 87sr 86sr300 0 7069 0 7084 pietranik and waight 2008 however both sr isotopic composition of plagioclase and trace element composition of apatite could be homogenized by late stage resorption leaving zircon as the only record of contamination processes that predate resorption comparison between plagioclase and zircon isotopic composition is consistent with both plagioclase cores and zircons recording similar stages of magma contamination comparison between plagioclase and apatite composition indicates that crystallization of apatite was contemporaneous with crystallization of plagioclase rims the preferred interpretation of isotopic and trace element variations observed in different grains is a two stage contamination by crustally derived magmas early contamination was probably dominated by material typical of the lower crust i e with none or only small amounts of a sedimentary component as indicated by low 18o in zircon 5 6 6 5 in both the least and the most contaminated types later contamination was dominated by crustally derived magmas containing more than 20 of a sedimentary component as the most contaminated sample includes zircon with 18o up to 9 3 partial melts generated from an s type granite source are the most probable contaminant for this second stage contamination as indicated by apatite trace element composition in general isotopic and chemical composition of plagioclase zircon and apatite provides complementary information on magmatic processes but records a longer time span than a single mineral only due to their diachronous crystallization histories

crustal differentiation processes at krakatau volcano indonesia anak krakatau is a basaltic andesite cone that has grown following the famous caldera forming 1883 eruption of krakatau it breached sea level in 1927 and since the 1950s has been growing at an average rate of similar to 8 cm a week we present new major and trace element data combined with whole rock delta o 18 sr and nd isotope data for 1883 1993 and 2002 krakatau eruptive products and the surrounding crust bombs erupted from anak krakatau during 2002 contain frothy metasedimentary and plutonic xenoliths that show variable degrees of thermal metamorphism plastic deformation and partial melting contact metamorphic minerals such as cordierite and tridymite in metasedimentary xenoliths are consistent with high temperature metamorphism and incorporation at mid to upper crustal depth energy constrained assimilation and fractional crystallization modelling of whole rock data suggests that the anak krakatau magmas have a genetic relationship with the 1883 eruption products the geochemical impact of crustal contaminants on whole rock compositions is apparently small and we conclude that low levels of assimilation of a quartzo feldspathic sediment are recorded in anak krakatau magmas plagioclase phenocrysts from the 2002 eruption exhibit disequilibrium textures and complex compositional zoning however and are also isotopically variable with a total range in sr 87 sr 86 of 0 center dot 7043 0 center dot 7048 as determined by in situ laser ablation inductively coupled plasma mass spectrometry this suggests that although shallow crustal assimilation appears to have had a limited effect on whole rock chemistry a complex late stage differentiation history is recorded within the magma s cargo of crystals and xenoliths

minor and trace element zoning in plagioclase implications for magma chamber processes at parinacota volcano northern chile textural and compositional zoning in plagioclase phenocrysts in a sample from parinacota volcano chile was investigated using backscattered electron images and electron microprobe analysis of major and trace elements large 2 mm oscillatory zoned crystals type i with resorption surfaces of moderate an discontinuities 10 an and decreasing trace element contents sr mg ti towards the rim reflect melt differentiation and turbulent convection in the main magma body early recharge with a low sr mafic magma is seen in the core small scale sr variations in the core indicate limited diffusion and thus residence and differentiation times of the magma shorter than a few thousand years smaller crystals type ii with low trace element an ratio reflect the influence of an h2o rich melt probably from a differentiated boundary layer closed system in situ crystallisation mafic magma recharge and the role of a water rich differentiated boundary layer can be distinguished from the an trace element relationships crystals apparently move relatively freely between different parts and regimes in the magma chamber evidence for convective crystal dispersion high sr type ii crystals indicate an earlier input of sr rich mafic magma recharge of two distinct mafic magma types is thus identified high sr and low sr which must have been present at increasing recharge rates with time in the plumbing system throughout the volcano s history

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

plagioclase zonation styles in hornblende gabbro inclusions from little glass mountain medicine lake volcano california implications for fractionation mechanisms and the formation of composition gaps the rhyolite of little glass mountain 73 74 sio2 is a single eruptive unit that contains inclusions of quenched andesite liquid 54 61 sio2 and partially crystalline cumulate hornblende gabbro 53 55 sio2 based on previous studies the quenched andesite inclusions and host rhyolite lava are related to one another through fractional crystallization and represent an example of a fractionation generated composition gap the hornblende gabbros represent the cumulate residue associated with the rhyolite producing and composition gap forming fractionation event this study combines textural nomarski differential interference contrast ndic imaging major element an content and trace element mg fe sr k ti ba data on the style of zonation of plagioclase crystals from representative andesite and gabbro inclusions to assess the physical environment in which the fractionation event and composition gap formation took place the andesite inclusions 54 61 sio2 are sparsely phyric with phenocrysts of plagioclase augite and fe oxide olivine orthopyroxene hornblende set within a glassy to crystalline matrix the gabbro cumulates 53 55 sio2 consist of an interconnected framework of plagioclase augite olivine orthopyroxene hornblende and fe oxide along with highly vesicular interstitial glass 70 74 sio2 the gabbros record a two stage crystallization history of plagioclase olivine augite stage i followed by plagioclase orthopyroxene hornblende fe oxide stage ii texturally the plagioclase crystals in the andesite inclusions are characterized by complex fine scale oscillatory zonation and abundant dissolution surfaces compositionally an content the crystals are essentially unzoned from core to rim these features indicate growth within a dynamic convecting reservoir of andesite magma in contrast the plagioclase crystals in the gabbros are texturally smooth and featureless with strong normal zonation from an74 at the core to around an30 k and ba abundances increase and mg abundances decrease steadily towards the rim ti fe and sr abundances increase and then decrease towards the rim the trace element variations are fully consistent with the two stage crystallization sequence inferred from the gabbro mineralogy these results indicate progressive closed system in situ crystallization in a quiescent magmatic boundary layer environment located along the margins of the andesite magma body the fractional crystallization that generated the host rhyolite lava is one of inward solidification of a crystallizing boundary layer followed by melt extraction and accumulation of highly evolved interstitial liquid this mechanism explains the formation of the composition gap between parental andesite and rhyolite magma compositions

neo tethyan evolution in southeastern extension of tibet constraints from early paleocene to early eocene granitic rocks with associated enclaves in tengchong block abstract the granite is one of most widely distribution rocks in crust and its petrogenesis is crucial to advance our knowledge of thermal condition in continental crust the long time tectonic evolution of crust in the active continental margin could be recorded by multi stages of granitic assemblage in order to reveal the subduction of neo tethys and initial collision of indian asian continents in eastern tibetan plateau we selected the early paleocene to early eocene granitic rocks with associated enclaves in tengchong block southeastern extension of gangdese magmatic belt to clarify their different derivation regimes using geochemical and isotopic compositions mineral compositional variation the zircon data show that early paleocene granites formed at 64 ma and early eocene granitic rocks formed at 54 ma combing with the field contact relationship the similar and enriched sr nd pb and zircon hf isotopic compositions indicate that the two stages of granitic rocks have a common and ancient lower crustal source the enclaves in early paleocene granites could represent crystallization of coeval and cognate magmas at margin of magmatic conduit but the enclaves in early eocene granitic rocks are products of magma mixing between mafic and felsic magma according to rock assemblages and geochemical signatures of granitic rocks during early paleocene to early eocene in tengchong block we propose that early paleocene granitic rocks are derived from partial melting of lower crustal rocks induced by long lived heat accumulation with no or minimal basalt flux during the neo tethyan subduction whereas early eocene granitic rocks are derived from melting of crustal materials resulted from high mafic magma flux during indian asian continental collision the initial collision occurred at ca 55 ma

the nevados de payachata volcanic region 18 s 69 w n chile subduction related volcanism in the nevados de payachata region of the central andes at 18 s comprises two temporally and geochemically distinct phases an older period of magmatism is represented by glaciated stratocones and ignimbrite sheets of late miocene age the pleistocene to recent phase 0 3 ma includes the twin stratovolcanoes volcan pomerape and volcan parinacota the nevados de payachata volcanic group and two small centers to the west i e caquena and vilacollo both stratovolcanoes consist of an older dome and flow series capped by an andesitic cone the younger cone i e v parinacota suffered a postglacial cone collapse producing a widespread debris avalanche deposit subsequently the cone reformed during a brief second volcanic episode a number of small relatively mafic satellitic cinder cones and associated flows were produced during the most recent activity at v parinacota at the older cone i e v pomerape an early dome sequence with an overlying isolated mafic spatter cone and the cone forming andesitic dacitic phase mostly flows have been recognized the two nevados de payachata stratovolcanoes display continuous major and trace element trends from high k2o basaltic andesites through rhyolites 53 76 sio2 that are well defined and distinct from those of the older volcanic centers petrography chemical composition and eruptive styles at v parinacota differ between pre and post debris avalanche lavas precollapse flows have abundant amphibole at sio2 59 wt and lower mg numbers than postcollapse lavas which are generally less silicic and more restricted in composition compositional variations indicate that the magmas of the nevados de payachata volcanic group evolved through a combination of fractional crystallization crustal assimilation and intratrend magma mixing isotope compositions exhibit only minor variations pb isotope ratios are relatively low 206pb 204pb 17 95 18 20 and208pb 204pb 38 2 38 5 87sr 86sr ratios range 0 70612 0 70707 143nd 144nd ratios range 0 51238 0 51230 and 18osmow values range from 6 8 o to 7 6 o smow a comparison with other central volcanic zone centers shows that the nevados de payachata magmas are unusually rich in ba up to 1800 ppm and sr up to 1700 ppm and thus represent an unusual chemical signature in the andean arc these chemical and isotope variations suggest a complex petrogenetic evolution involving at least three distinct components primary mantle derived melts which are similar to those generated by subduction processes throughout the andean arc are modified by deep crustal interactions to produce magmas that are parental to those erupted at the surface these magmas subsequently evolve at shallower levels through assimilation crystallization processes involving upper crust and intratrend magma mixing which in both cases were restricted to end members of low isotopic contrast

plagioclase zoning as an indicator of magma processes at bezymianny volcano kamchatka back scattered electron bse derived zoning patterns of plagioclase phenocrysts are used to identify magma processes at bezymianny volcano kamchatka based on the 2000 2007 sequence of eruptive products the erupted magmas are two pyroxene andesites which last equilibrated at 915 c temperature 77 87 mpa pressure and a water content of 1 4 wt textural and compositional zoning of individual plagioclase phenocrysts typically includes a repeated core to rim sequence of oscillatory zoning an50 60 truncated by a dissolution surface followed by an abrupt increase in an content up to an85 which then gradually decreases rimward this zoning pattern is interpreted to be the result of frequent replenishments of the magma chamber which cause both thermal and chemical interaction between resident and recharge magmas the outermost 70 to 150 m wide zoning patterns of plagioclase phenocrysts are composed of dissolution surface with a subsequent increase in an and fe contents zoning patterns of the rims exhibit correlation among plagioclase phenocrysts within one eruption rims are interpreted as a result of crystallization of a batch of magma in the conduit after recharge event

strontium diffusion kinetics in plagioclase feldspars abstract a pronounced systematic variation by a factor of 104 in strontium tracer diffusion kinetics has been measured in four feldspar specimens that span the range of plagioclase compositions the experiments were carried out in air using isotopically enriched 86sr and analyzed with an ion microprobe the arrhenius relations for strontium diffusion are plagioclase ab d 0 m 2 s q kj g atom sr temperature range c albite 98 1 05e 279 550 1080 oligoclase 73 7 4e 7 261 750 1100 labradorite 36 1 1e 6 295 800 1300 anorthite 4 5 7e 9 267 900 1300 no difference was found within the measurement uncertainty between these results and those for albite under hydrothermal conditions at one kbar 100 mpa strontium diffusion rates parallel to and normal to the albite twin lamellae are the same there is no effect on the strontium diffusion rate in albite between an oxygen partial pressure of 0 2 bar air and 10 19 bar graphite buffer a relation is developed that permits calculation of the strontium diffusion arrhenius parameters for any normal plagioclase composition the large variation in diffusion rate with composition has a major effect on the ease of strontium isotope exchange at high temperatures between plagioclases and coexisting phases in rocks which may prove useful in determining thermal histories

magma mixing recharge and eruption histories recorded in plagioclase phenocrysts from el chichon volcano mexico operative throughout the 200 ky history of the el chichon magma consistent core to rim decreases of sr sr ratios and coincident system increases in sr concentrations in plagioclase phenocrysts of varying size 1 cm to 2 mm are reported from samples of the 1982 and pre 1982 200 ka eruptions of el chichon volcano maximum sr sr ratios of 0 7054 significantly higher than the wholerock isotopic ratios 0 7040 0 7045 are found in the cores

magma storage ascent and recharge history prior to the 1991 eruption at avachinsky volcano kamchatka russia inferences on the plumbing system geometry article i nfo textural and compositional features of plagioclase phenocrysts of the 1991 eruption lavas at avachinsky volcano kamchatka russia were used to investigate the feeding system processes volcanics are porphyritic basaltic andesites and andesites with low k affinity a fractionation modeling for both major and trace elements was per formed to justify the development of these evolved compositions the occurrence of other magma chamber pro cesses was verified through high contrast bse images and core to rim compositional profiles an and feo wt on plagioclase crystals textural types include small and large scale oscillation patterns disequilibrium textures at the crystal core patchy zoning coarse sieve textures dissolved cores disequilibrium textures at the crystal rim sieve textures melt inclusion alignments at the rim disequilibrium textures at the cores may testify episodes of destabilization at various decompression rates under water undersaturated conditions which suggests different pathways of magma ascent at depth at shallower water saturated conditions plagioclase crystallization continues in a system not affected by important chemical physical perturbations oscillatory zoning develops strongly sieve textured rims along with an increase at rather constant feo are evidence of mixing before the 1991 eruption between a residing magma and a hotter and volatile richer one the textural evidence implies that crystals underwent common histories at shallow levels supporting the existence of a large magma reservoir whose top is at 5 5 km of depth distinct textures at the outer rims in a hand size sample are evidence that crys

petrogenesis of dongguashan skarn porphyry cu au deposit related intrusion in the tongling district eastern china geochronological mineralogical geochemical and hf isotopic evidence the dongguashan skarn porphyry cu au deposit located in the tongling district of the middle lower yangtze river valley metallogenic belt mlyb consists of skarn ore bodies in the upper part and porphyry ore bodies in the lower part both of which are hosted in quartz diorite and quartz monzodiorite zircon u pb age and geochemical studies show that the quartz diorite of the dongguashan intrusion formed at 140 3 2 0 ma mswd 0 19 and belongs to the high potassium calc alkaline series it is enriched in large ion lithophile elements lile and light rare earth elements lree depleted in high field strength elements hfse and heavy rare earth elements hree and has a slightly negative eu anomaly 176hf 177hf values of the rims of zircons show a variable range 0 282087 0 282391 corresponding with calculated ehf t values of 10 72 to 21 46 plagioclases in the quartz diorite have unbalanced structure characterized by bright andesine and labradorite an 37 0 65 5 cores with higher contents of fe and sr and are corroded by dark oligoclase an 13 8 27 6 rim major elements trace elements hf isotope and the composition of plagioclases indicate that the parental magma of the dongguashan intrusion was produced by the mixing of underplating mafic magma and felsic magma formed by remelting of paleoproterozoic and neoarchean crustal rocks neoproterozoic crust may also provide some material to the felsic magma mafic magma played a key role and made the parental magma rich in water sulfur metals cu au and gave it a high oxygen fugacity during its magmatic evolution the parental magma underwent fractional crystallization of hornblende apatite sphene and other mafic minerals some quartz diorite and quartz monzodiorite samples that show adakitic signatures may result from injection of mafic magma some inherited zircons of the quartz diorite in the dongguashan intrusion gave ages of 2 40 2 50 ga 1 95 2 05 ga and 0 74 0 81 ga coming from ultramafic mafic and andesitic igneous rocks and this indicates that there may have been three periods 2 4 2 0 and 0 8 ga of magmatic activity in the tongling district

textural and chemical variation in plagioclase phenocrysts from the 1980 eruptions of mount st helens usa this study presents major and trace element chemistry of plagioclase phenocrysts from the 1980 eruptions of mount st helens volcano despite the considerable variation in textures and composition of plagioclase phenocrysts distinct segments have been cross correlated between crystals the variation of sr and ba concentration in the melt as calculated from the concentration in the phenocrysts using partition coefficients suggests the cores and rims crystallised from compositionally different melts offset by the plagioclase crystallisation vector in both of these melts sr and ba are correlated despite the abundance of plagioclase in the 1980 dacites we propose that rapid crystallisation of plagioclase upon magma ascent caused a shift in melt composition towards lower sr and higher ba as documented in the rims of the phenocrysts although the cores of the phenocrysts crystallised at relatively shallow depths they preserve the sr and ba of the deep seated melts as they ascended from a deeper region further magma ascent resulted in microlite nucleation which is responsible for a similar shift to even lower sr concentration as observed in the groundmass of post 18 may 1980 samples

resistivity survey of the subsurface conditions in the estuary of the rio de la plata an electrical resistivity survey was performed at the estuary of the rio de la plata as part of more comprehensive geotechnical investigations of the subsurface conditions the studies were required for the emplacement of a 3 5 m diameter conduit proposed for the discharge of the treated wastewater of the city of buenos aires the soil profile at the site consists mainly of clays and silts underlain by a layer of dense sand the dense sand layer is a confined aquifer and the project required that the depth to the sand layer be perfectly determined previous geophysical surveys at the site and the general geotechnical conditions showed the inadequacy of seismic methods which are usually adopted in similar environments the resistivity method was determined to be a reliable alternative even though there has been little experience in surveying shallow depth water for geotechnical investigations the four electrode schlumberger electrode array was adopted for the resistivity survey some of the test devices were developed especially for the purpose of this project calibration of the method was achieved with data obtained from boreholes the results show that the resistivity technique performed satisfactorily to the 40 m depth required in this project as a result of the survey the next geotechnical investigation was focused on a more reduced area and the required number of boreholes was reduced substantially

coupled caal nasi diffusion in plagioclase feldspar experiments and applications to cooling rate speedometry abstract the rate of caal nasi interdiffusion in plagioclase feldspar was determined under 1 atm anhydrous conditions over the temperature range 1400 to 1000 c in calcic plagioclase an80 81 by homogenizing coherent exsolution lamellae the dependence of the average interdiffusion coefficient on temperature is given by the expression d 10 99 cm 2 sec exp 123 4 kcal mol rt t in k this value is for diffusion perpendicular to the 03 1 interface of the lamellae caal nasi interdiffusion is 4 to 5 orders of magnitude slower than oxygen diffusion in the temperature range 1400 to 1200 c and possibly 10 orders of magnitude slower at subsolidus temperatures the large differences in diffusion rates explain the apparent contradiction posed by the plagioclases of large layered intrusions e g the skaergaard which retain delicate ca na compositional zoning profiles on the micron scale but have undergone complete oxygen isotopic exchange with heated meteoric groundwater from the surrounding wall rocks caal nasi diffusion is slow the closure temperature is high within the solidus liquidus interval and ca na zoning is preserved oxygen diffusion is faster the closure temperature is lower 350 400 c and the feldspars exchange oxygen with the low temperature hydrothermal fluids the complex micron scale oscillatory zones in plagioclase can also be used as cooling rate speedometers for volcanic and plutonic plagioclase cooling histories typical of large mafic intrusions e g the stillwater are slow begin at high initial temperatures 1200 c and result in homogenization of oscillatory zones on the scale of 10 microns the oscillatory zones found in the plagioclase of granodioritic plutons are preserved because cooling is initiated at a lower temperature 1000 c limiting diffusion to submicron length scales despite the slow cooling rate of the intrusion

isotopic equilibration during partial melting an experimental test of the behaviour of sr abstract experiments using isotopically enriched sr doped minerals designed to test for isotopic equilibrium between source and melt during partial melting reveal that 87 sr 86 sr ratios of the liquids are primarily determined by the proportions of minerals consumed and vary with the advancement of the melting reaction the experiments were performed at 1 atm on model crustal assemblages composed of pairs of natural plagioclase an 68 87 sr 86 sr 0 701 and synthetic fluorphlogopite doped with 90 ppm sr having 87 sr 86 sr 4 2 sims traverses showed that during the initial stages of the reaction liquids are isotopically zoned all the analyzed melts have 87 sr 86 sr markedly higher than that of the bulk starting assemblage i e the source because of the faster melting rate of fluorphlogopite at 1200 c and 1250 c melting occurs above a critical temperature wherein the dissolution rates of the crystals are controlled by diffusion of species in the melt and reactants and reaction products are out of isotopic equilibrium this is due to faster melt crystal boundary migration when compared to sr diffusion in the crystals equilibration is possible only if melting stops calculations show that total equilibration between melt and residue by sr tracer diffusion in the crystals takes 10 4 10 6 yr for temperature and grain size ranging respectively from 800 c to 1000 c and 0 1 to 1 cm when compared to the proposed residence time of crustal magmas at their sources this result strongly suggests that magmas that do not reflect the bulk isotopic characteristics of their source regions can be produced

on the distribution and separation of crystals in convecting magma abstract fractionation of crystals from magma stands squarely as the central principle of igneous petrology and the critical balance is the competition between crystal settling or rising velocity and magmatic convective velocity a ratio we call s the convective velocity is intimately related to the rate of heat transfer from the system although the theory of sediment distribution in rivers establishes the critical parametric balance and it has been often applied to igneous systems this method turns out to be valid only for small concentrations of crystals and it is not clear if it is accurate for other than turbulent flows where the prandtl number is near unity a generalized theory of particle crystal or bubble behavior is presented scaling of the generalized result shows for the magmatic conditions of small crystallinities small particle reynolds number and newtonian viscosity that the exact distribution of crystals in a convecting magma can be found analytically regardless of the flow field critical retention occurs only for 0 s s 0 for sinking crystals retention is centered in the region of maximum updraft for floating particles retention occurs in regions of downflow which for a simple cellular convective pattern produces a torus shaped retention region against the walls about the midsection of the body for a stack of flattened convective cells which in the crudest sense is analogous to double diffusive convection the zones of retention form depending on the exact flow field either a stack or staggered stack of pillows through the central region crystals settling from top to bottom around this stack take a tortuous path and may exhibit a complex but regular compositional zoning additional effects of fluids possessing a yield strength turbulence particle shape and wall and particle dispersive effects are more qualitatively evaluated for each flow field the amount of retention and the effective settling velocity of all crystals is found as a function of s the critical parameter s controlling retention can be estimated from a parametric representation involving stokes s law and the rayleigh number this shows that some retention probably occurs in all magmas and it increases with approach of the magma to the earth s surface although both crystal settling rate and convection decrease with increasing magmatic viscosity the overall effect is to increase retention decrease s magmas having a viscosity near and beyond about 10 4 poise and chambered in the nearsurface environment should show large degrees of crystal retention retention is however never complete for magmas and the flux of settling crystals leading to differentiation varies as a function of crystallinity this flux or flux probability p f is zero both at the liquidus and the point of maximum packing of crystals which for basalts is about 60 the importance of differentiation is regulated by the amount of time spent in the high crystal flux state and a relative measure of this time is given by the thermal probability p t introduced previously thus the probability of differentiation p d is given by the product p f p t which shows that differentiation must occur over a restricted range of crystallinities from about 20 to 45 for basalts and from about 10 to 30 for rhyolitic magmas the most basic lessons learned here are that the full range of crystallinities is not equally accessible to crystal fractionation and the most fundamental information describing the dynamic state and behavior of magma may well be the distribution of crystal sizes found in lavas

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

numerical simulations of crystallization processes of plagioclase in complex melts the origin of major and oscillatory zoning in plagioclase numerical simulations of the growth of a large crystal face of plagioclase in response to an instantaneous undercooling below the equilibrium temperature are presented for model granodiorite and basalt melts with varying water contents the simulations suggest that the anorthite content of plagioclase decreases uniformly from the composition in equilibrium with the bulk melt as undercooling is increased and that the water content in the melt has little influence on this result comparison of the simulations with sharp compositional changes in natural profiles suggests that undercoolings of tens of degrees c can be rapidly imposed on plutonic phenocrysts large changes of undercooling most likely result from chilling of the magma and local convection around growing crystals the observation in experiments that growth rate does not increase rapidly with increasing water content in the starting melting composition can be attributed to the concentration of water at the crystal face during growth the action of water to reduce liquidus temperature and undercooling has a greater effect on growth rate than its action to increase transport rates even at large undercooling there is no significant increase in temperature at the interface caused by the release of heat of crystallization

laser interferometry study of oscillatory zoning in plagioclase the record of magma mixing and phenocryst recycling in calc alkaline magma chambers iztaccihuatl volcano mexico

a temporal record of magma accumulation and evolution beneath nevado de toluca mexico preserved in plagioclase phenocrysts plagioclase crystals from the 8 km 10 5 ka upper toluca pumice utp eruption from nevado detoluca provide a detailed temporal record of pre eruptive magmatic processes the crystals display a range of textures and major and trace element concentrations a distinct feature of the crystals is the presence of several sharp increases in mgo feo andtio2 which occur at some of the numerous resorption horizons and coincide with increases in xan and in some cases ce and la these abrupt compositional peaks and the associated textural variations reflect recharge events of more mafic melt three distinct recharge events can be recognized the general compositional trends suggest that crystallization occurred within a common chamber however the crystal cores display a range of textures and a wide range of compositions suggesting that they are relics of earlier crystallization episodes within the upper crust the temporal record of sr and ba melt contents recorded by the crystals calculated using partition coefficients fluctuates significantly within single crystals overall two trends of sr ba variation in the melt are apparent the first trend involves decreasing sr and slightly increasing ba consistent with plagioclase crystallization the second trend involves an increase in both sr and ba that is not consistent with crystallization of plagioclase alone this trend is ascribed to chemical variations within the deeper magma reservoirs from which the various magma batches entering the utp shallow reservoir were ultimately sourced the magmatic system under nevado de toluca was open and received intermittent but relatively small pulses of magma from a deeper source dacite was the predominant recharge composition although some pulses were distinctly more mafic and hotter these processes led to the accumulation of a large volume of dacitic magma in the upper crust one of the more mafic pulses appears to have triggered the eruption

boundary layer crystallization in a basaltic magma chamber evidence from rishiri volcano northern japan the evolution of basaltic magma by mushy boundary layer processes introduction in a magma chamber is documented for an alkali basalt kutsugata the evolution of magma chambers is of major petrologic lava from rishiri volcano northern japan on the basis of zoning interest and has been studied extensively experimental patterns of plagioclase phenocrysts and their spatial distribution in and theoretical studies that have investigated the cooling the lava plagioclase phenocrysts with complex zoning patterns can of magma chambers have demonstrated that a magma be divided into four types type 1 is characterized by an extremely chamber solidifies through formation of a mushy boundan rich core an71 90 which is commonly corroded and filled with ary layer composed of crystals and interstitial melt along sodic plagioclase type 2 has an ab rich core surrounded by a calcic the chamber walls e g brandeis jaupart 1986 turner mantle characteristic of partial dissolution type 3 is characterized by et al 1986 marsh 1988 tait jaupart 1992 layered igneous complexes e g morse 1969 shirley 1987 an ab rich core that is commonly surrounded by a reversely zoned mcbirney 1996 provide useful information on how slightly calcic mantle type 4 has an ab rich core without a calcic mafic magma chambers evolve and consolidate but they mantle the an rich cores of the type 1 plagioclase are too calcic do not offer much insight into the instantaneous state of to have crystallized from a liquid represented by any whole rock a chamber because those intrusions integrate processes composition at the estimated temperatures of the kutsugata magma that occurred over long solidification times mcbirney system the an rich cores are inferred to have been formed in a noyes 1979 tait 1988 volcanic products such as mushy boundary layer along the wall of a magma chamber where lava flows and tephra deposits can sample the inthe magma was relatively cool and rich in water because of significant stantaneous state of a magma chamber there are a few olivine fractionation and possibly because of addition of water studies along this line of approach tait 1988 de silva expelled from the chilled margin and or groundwater from the 1989 nakada et al 1994 these studies focused on surrounding crust the ab rich cores of types 2 4 plagioclase crystal aggregates in volcanic products and concluded phenocrysts are interpreted to have crystallized in the main magma that the crystal formation in a mushy boundary layer body of the reservoir the types 2 and 3 ab rich cores were brought plays a dominant role in magmatic evolution in a magma to the mushy layer by convection the temporal and spatial variations reservoir however these studies were mostly on silicic of zoning patterns of plagioclase phenocrysts in basaltic lava flows magmas and there are significant differences in physical give useful information on the evolution of mafic magma chambers and chemical features between silicic and mafic magma chambers in this paper the magmatic evolution of an alkali basalt kutsugata lava from rishiri volcano northern japan is studied the kutsugata lava is divided into three lava flows on the basis of whole rock chemical

recharge in volcanic systems evidence from isotope profiles of phenocrysts strontium isotope ratios measured from core to rim across plagioclase feldspar crystals can be used to monitor changes in the isotope composition of the magma from which they grew in samples from three magma systems from convergent margin volcanoes sudden changes in major element composition petrographic features and strontium isotope composition were found to correspond to discrete magmatic events most likely repeated recharge of more mafic magma with lower ratios of strontium 87 to strontium 86 into a crustally contaminated magma

sr isotope zoning in plagioclase from parinacota volcano northern chile quantifying magma mixing and crustal contamination we present analyses of sr isotope zoning by microdrilling and thermal ionization mass spectrometry in plagioclase crystals from parinacota volcano central volcanic zone northern chile which were analysed for major and minor element zoning in a previous study although the isotopic range of the bulk rock samples is small at this volcano 0 7067 0 7070 except for one flow of mafic andesite at 0 7061 significant variations are seen 0 70649 0 70700 within and between plagioclase crystals a general negative correlation is observed between sr isotope composition and sr concentration in the liquid in equilibrium with each plagioclase zone as calculated from chemical zoning data and partition coefficients additional scatter is superimposed on this general trend indicating a decoupling between isotopic and chemical variations for sr in one dacite sample a detailed isotopic profile shows increasing contamination during crystal growth except for an abrupt decrease correlated with a dissolution surface and interpreted as a recharge event we apply energy constrained recharge assimilation and fractional crystallization modelling to the melt evolution recorded in the chemical and isotopic zoning in this crystal results suggest 20 assimilation of the local wall rock gneiss at high initial temperatures the isotopic data confirm the involvement of two contrasting mafic magmas which are sampled at flank cinder cone vents one lower ajata has a low sr content with high 87sr 86sr the other upper ajata has a high sr content with lower 87sr 86sr in some samples from parinacota the isotopic composition of plagioclase crystal rims or groundmass crystals is significantly higher than that of the high 87sr 86sr mafic magma in others where chemical zoning profiles suggest that recharge was from the low 87sr 86sr magma the 87sr 86sr of the groundmass and crystal rims is higher than expected this indicates either additional parent magmas to the two previously identified or further crustal assimilation either at lower crustal depths before crystallization of plagioclase or just after the last recharge our results illustrate the complexity of magma crust interaction beneath parinacota which is likely to be representative of many other central andean volcanoes formed on thick crust such complex interactions can be revealed by combined study of chemical and isotopic zoning in plagioclase in a textural petrographic context despite a small whole rock isotopic range the distinct contamination patterns of various samples suggest an important role for the geometry location and evolution of the magma plumbing system and in general variations of the thermal and compositional structure of the crust underneath the volcano

three years 2011 2013 of eruptive activity at mt etna working modes and timescales of the modern volcano plumbing system from micro analytical studies of crystals abstract tracking magma dynamics at active volcanoes by using the compositional and textural records of minerals is becoming an important aspect of modern volcanology to solve key issues such as temporal relationships between magma recharge and eruption duration of magma storage and final ascent upward to the surface these issues are relevant at mt etna where the style of volcanic activity during the last years showed drastic variations in duration and intensity the paroxysmal activity between 2011 and 2013 at the volcano summit has given the opportunity to investigate the chemical physical processes driving the activity and to fix their spatial temporal relationships into the plumbing system an extensive compositional dataset of plagioclase and olivine crystals from lavas emitted between the 2011 and 2013 at mt etna has been used to constrain modes and timescales of magma storage and transfer to the surface plagioclase crystals display either near equilibrium or disequilibrium textures at the core and rim that indicate complex histories of magma crystallization under variable chemical and physical conditions crystals with different textures have been characterized for major an minor fe and mg and trace elements sr ba textural relationships at the plagioclase cores support the idea that crystals undergo variable decompression rates in the deep parts of the plumbing system fe and mg zoning vs anorthite in correspondence of plagioclase sieve textures at the rim suggest that processes of gas flushing have a dominant role in triggering paroxysmal eruptions determining a sudden intensification of the eruptive activity up to the fountaining phase the sr ba ratio in oscillatory zoned plagioclase revealed the dominant presence into the plumbing system of high sr magma volumes coexisting with low sr magma batches that preserve a geochemical signature similar to that of magmas feeding the pre 1971 activity through sr diffusion modeling in plagioclase the maximum time of magma storage during the considered eruptive period has been evaluated timescales of crystal residence in the plumbing system are short five years to three decades suggesting limited magma storage and faster transfer dynamics to the surface chemical zoning of olivine crystals highlights processes of multi step magma transfer and residence at different levels of the plumbing system the upward migration of magmas occurred primarily through multiple episodes of injection and mixing between five compositionally distinct magmatic environments m i whose p t o 2 characteristics and concentrations in dissolved volatiles were constrained by thermodynamic modeling on the basis of the forsterite contents found at the olivine cores from a deepest reservoir located at depth of 600 mpa the most primitive magma m00 fo 84 moved along dominant pathways intercepting the m0 fo 80 82 at 390 mpa and or m1a fo 78 250 mpa m1b fo 75 140 mpa and finally the shallow m2 fo 70 73 40 mpa storage zones for some eruptive episodes olivine zoning highlights a preferential route of transfer connecting the m00 and m2 storage zones that facilitated the fast migration of primitive magma at shallow depth fe mg diffusion modeling on olivine normal and reverse zoning defines the timescales of magma transfer and storage across these magmatic environments which vary from 1 to 18 months whereas intrusion and mixing by more basic magma into the shallowest reservoir occurred always within 5 months before the eruption relevance of this study mainly relies on the quantification of volcanic processes at depth that may have considerable consequences in development of unusual high energy eruptions at basaltic volcanoes generally acknowledged for their weak to mild explosive activity

crystallization and resorption in plutonic plagioclase implications on the evolution of granodiorite magma gesiniec granodiorite strzelin crystalline massif sw poland abstract granodiorite from the gesiniec intrusion strzelin crystalline massif sw poland contains complexly zoned plagioclases five chemically and structurally distinct zones can be correlated among crystals cores 25 35 an inner mantles 40 45 an outer mantles 40 25 an resorption zones 35 50 an and rims 35 30 an good structural and chemical major and trace elements correlation of zones between crystals indicates that zonation was produced by changes in conditions of crystallization on a magma chamber scale plagioclase being the liquidus phase records a time span from the beginning of crystallization to emplacement and rapid cooling of granodiorite as thin dykes crystallization began with the formation of inner mantles the paucity and different sizes of inner mantles suggests slow crystallization in high temperature magma normally zoned inner mantles were formed under increasing undercooling compositional trends in mantles suggest closed system crystallization the major resorption zones were caused by injection of less evolved magma as indicated by the strontium increase in plagioclase the injection triggered a rapid rise of magma and plagioclase crystals facilitating mixing but also inducing fast kinetically controlled growth of complex multiple oscillatory zonation within resorption zones the ascent of magma caused decompression melting of plagioclase and produced melt inclusions within inner mantles the cores the decompression range is estimated at a minimum of 2 kbar emplacement of granodiorite as thin dykes allow rapid cooling and preservation of magmatic zonation in plagioclases melt inclusions crystallized completely during post magmatic cooling the zonation styles of plutonic plagioclase differ markedly from volcanic ones suggesting different magma evolution zones in plutonic plagioclase are well correlated indicating crystallization in quiescent magma where crystals accumulation and compositional magma stratification may occur crystals probably did not travel between different regimes resorption occurred but as single albeit complex episodes good correlation of zones in plutonic plagioclases allows a distinction between the main processes controlling zonation and superimposed kinetic effects

entrainment from a bed of particles by thermal convection differentiation in magma chambers in the earth s core and in the partially molten early earth is a competitive process between sedimentation and re entrainment of crystals in the presence of convection previous studies show that the particles suspended in convective layers eventually settle and do so almost as fast as in the absence of convection however the nature and magnitude of the competing entrainment has remained unclear here we provide a simple theory and experimental evidence showing that entrainment occurs at the crests of dunes created in the particle bed at the base of a convecting fluid in both laminar and turbulent regimes the dune formation and entrainment are driven by viscous stresses produced by thermal plumes at sufficiently high rayleigh numbers the particles are probably entrained by reynolds stresses entrainment in the earth s core is hardly possible because it requires unreasonably small crystals entrainment of 10 2 10 1 cm diameter crystals is very likely in magma oceans for magma chambers entrainment requires large viscosities 10 6 p and even when it occurs the total amount of the suspended solid fraction is very small

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 preservation of δsso434 and δoso418 in carbonate associated sulfate during marine diagenesis a 25 myr test case using marine sediments a 25 million year record of the sulfur and oxygen isotope composition of marine carbonate associated sulfate cas was constructed from 55 nannofossil ooze samples at three different locations we tested the impact of early marine diagenesis on cas by comparing the cas extractions to the sulfur and oxygen isotope composition of the associated pore fluid sulfate to determine the degree of pore fluid incorporation during carbonate recrystallization neither the sulfur nor the oxygen isotope composition of cas are completely overprinted by incorporation of pore fluid sulfate we compare our record to the sulfur and oxygen isotope records of coeval barite the sulfur isotope record is in agreement with the barite record within 2 2 except where very young 2 ma sediments are in the presence of highly evolved pore fluid sulfate view the mathml source s34 70 a simple recrystallization model is used to illustrate the sensitivity of cas view the mathml source sso434 to sedimentation rate and to emphasize that careful sample selection along with an analysis of early diagenetic environmental conditions is crucial when interpreting cas sulfur isotopes oxygen isotopes in cas are more complex and do not reproduce similar values to those of coeval barite we conclude that oxygen isotopes in sulfate may remain a useful proxy but merit closer attention in the future

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

microlite transfer by disaggregation of mafic inclusions following magma mixing at soufriere hills volcano montserrat the soufriere hills volcano on montserrat has for the past 12 years been erupting andesite with basaltic to basaltic andesite inclusions the andesite contains a wide variety of phenocryst textures and strongly zoned microlites analysis of minor elements in both phenocrysts and microlites allows us to put detailed constraints on their origins compositions of clinopyroxene from overgrowth rims on quartz and orthopyroxene and coarse grained breakdown rims on hornblende are identical to those from the mafic inclusions indicating that these rims form during interaction with mafic magma in contrast resorbed quartz and reversely zoned orthopyroxenes form during heating microlites of plagioclase and orthopyroxene are chemically distinct from the phenocrysts being enriched in fe and mg and al and ca respectively however microlites of plagioclase orthopyroxene and clinopyroxene are indistinguishable from the compositions of these phases in the mafic inclusions we infer that the inclusions disaggregated under conditions of high shear stress during ascent in the conduit transferring mafic material into the andesite groundmass the mafic component of the system is therefore greater than previously thought the presence of mafic derived microlites in the andesite groundmass also means that care must be taken when using this as a starting material for phase equilibrium experiments

high k mafic plinian eruptions of volcan de colima mexico the last plinian type eruption of volcan de colima mexico occurred in 1913 this resulted in the removal of the top 100 m of the edifice and the deposition of a tephra layer that blanketed the slopes of the colima volcanic complex cvc road cuts on the flanks of the nearby nevado de colima edifice expose pre 1913 air fall tephra pyroclastic flow and ash rich surge deposits resulting from numerous highly explosive events throughout the holocene the majority of the pumice and scoria fallout deposits are medium k subalkaline basaltic andesite and andesite in composition defining a clear major element differentiation trend in contrast three newly discovered scoria fallout deposits are high k subalkaline transitional to alkaline basaltic andesite in composition and are characterized by the presence of phlogopite these deposits have high mgo up to 7 9 wt k2o up to 2 6 wt and p2o5 up to 0 67 wt contents they are also strongly enriched in fluid and melt mobile large ion lithophile elements lile rb ba k sr and th and light ree lree la ce pr and nd relative to the majority of the colima tephra fallout deposits strontium and nd isotope systematics reveal that the high k mafic scoria have more radiogenic sr 87sr 86sr 0 70365 0 70408 and less radiogenic nd 143nd 144nd 0 51279 0 51294 compared with the majority of the subalkaline tephras 87sr 86sr 0 70338 0 70371 and 143nd 144nd 0 51290 0 51295 two component mixing models using whole rock geochemical data indicate the importance of magma mixing in the petrogenesis of the colima magmas with addition of up to 50 by volume of an alkaline mafic magma component in the most potassic magmas this is supported by mineral chemistry and textural data which reveal multiple episodes of decompression and magma mingling within a shallow crustal magma storage region the presence of these potassic tephra fall deposits among the otherwise prevailing medium k subalkaline stratigraphy indicates that pulses of k rich alkaline mafic magmas periodically enter the cvc plumbing system on timescales of a few thousand years and may trigger plinian explosive eruptions

partition coefficients for iron between plagioclase and basalt as a function of oxygen fugacity implications for archean and lunar anorthosites abstract experimental studies were undertaken to determine d for feot between plagioclase and melt as a function of oxygen fugacity for a basaltic composition that occurs as matrices for plagioclase megacrysts that are similar to those in calcic anorthosites at liquidus conditions the d for feot between calcic plagioclase and tholeiitic basalt changes very little from 0 030 to 0 044 between the very low o 2 of the iron wustite buffer and that of the quartz fayalite magnetite qfm buffer at fugacities above qfm the value for d increases rapidly to 0 14 at the magnetite hematite buffer and 0 36 in air the increase in d results from the fact that nearly all of the fe is in the fe2 state at o 2 below qfm and the fe 3 fe 2 ratio in the melt increases rapidly above qfm causing more fe to enter the plagioclase which accepts fe3 more readily than fe2 there is essentially no change in values of d over cooling rates that vary by two orders of magnitude the d for feot of 0 030 at iron wustite is in good agreement with earlier studies at low o2 terrestrial calcic plagioclase matrix pairs display ds of about 0 043 in excellent agreement with the experimental value of 0 044 at qfm which is the accepted fugacity for terrestrial tholeiitic basalts application of the ds for feot and other components to terrestrial calcic anorthosites indicates that the anorthosites were in equilibrium with nearby coeval tholeiitic basalts at qfm as was expected lunar anorthosites however have anomalously low contents of feot as well as mgo and would be in equilibrium with melts that are several times lower in these components than expected the low values of feot and mgo in the plagioclase of lunar anorthosites are a result of subsolidus reequilibration with pyroxene olivine and other fe mg bearing phases during high temperature metamorphism as is the case in terrestrial anorthosites that have undergone granulite grade metamorphism the ds for k2o mgo and tio2 were determined as 0 21 0 044 and 0 033 respectively and show no variation with o 2 the value for k2o is in good agreement with natural assemblages the values for mgo and tio2 however are lower in natural assemblages but the high degree of mobility of mg and the very low contents of tio2 in plagioclase makes the reliability of the natural values rather low also the d for tio2 may be affected by rate of cooling attempts to determine the d for cr2o3 as a function of o 2 were made difficult by the low levels of cr2o3 300 to 500 ppm in the melt when saturation with a cr spinel occurred because the cr concentrations in plagioclase are nearly 100 times less than those in the melt it was not possible to obtain reliable analyses for plagioclase these uncertainties constrain the d for cr to be less than 0 07 at the qfm buffer

early cretaceous na rich granitoids and their enclaves in the tengchong block sw china magmatism in relation to subduction of the bangong nujiang tethys ocean abstract the na rich intermediate to felsic granitic rocks provide insights into the generation of magmas in subduction zones this paper presents zircon la icp ms u pb ages as well as whole rock geochemical mineral chemical and in situ zircon hf isotopic data on na rich granitic rocks from the tengchong block sw china the granodiorites and associated mafic magmatic enclaves mmes from the menglian batholith yield zircon u pb ages of 116 1 0 8 to 117 8 0 6 ma and 117 7 0 7 ma respectively both host granodiorites and enclaves show calc alkaline and sodium rich nature enrichment in large ion lithophile elements liles and variable depletion in zircon hf isotopic compositions euhedral amphiboles in both granodiorites and associated enclaves are magnesian hornblende with high mg and ca and contain euhedral plagioclase inclusions of labradorite to andesine an36 57 composition the granodiorite was most likely derived through the mixing of partial melts derived from juvenile basaltic lower crust and a minor evolved component of ancient crustal sources the quartz monzodiorite granodiorites and associated mmes from the xiaotang mangdong batholith yield zircon u pb ages of 120 3 1 3 to 122 6 0 8 ma and 120 7 1 5 ma these rocks are also sodium rich and show calc alkaline trend with negative zircon hf isotopic compositions 5 55 to 0 58 the mmes in the host intrusions are monzogabbro with variable and depleted zircon hf isotopic compositions the amphiboles in the both host intrusions and the enclaves show al rich ferro tschermakite composition we infer that the quartz monzodiorite granodiorites were derived from magmas generated by the melting of ancient basaltic rocks in the lower arc crust induced by the underplating of mantle derived mafic magmas the formation of the different types of na rich granitic rocks is correlated to the subduction of bangong nujiang tethyan ocean a comparison with magmatism in the northern magmatic belt suggests that mantle derived magmas played an important role in the genesis of early cretaceous intrusions from tengchong to lhasa blocks although crustal melting is the dominant contributor

magma evolution revealed by anorthite rich plagioclase cumulate xenoliths from the ontong java plateau insights into lip magma dynamics and melt evolution abstract petrologic studies of igneous rocks often rely on whole rock analyses alone to deduce source and melting histories whole rock compositions represent a mixture of the processes responsible for the final texture and composition of the rock but do not emphasize the evolutionary processes that the rock may have experienced we examine the major minor and trace element compositions of plagioclase phenocrysts and plagioclase rich cumulate xenoliths from a sequence of kwaimbaita pillow basalt and massive flows recovered from ocean drilling program odp site 1183 on the expansive 122 ma ontong java plateau ojp and from subaerial outcrops on the island of malaita solomon islands these data are used to reconstruct equilibrium liquid compositions to understand magma dynamics magma evolution and the distribution basalt types across the ojp results reveal that crystals frequently are out of equilibrium with their host basalt two distinct compositional zones are present in plagioclase phenocrysts and xenolith crystals an80 86 and an65 79 equilibrium magma compositions derived from each of these zones are distinct in relative terms the following distinctions are made an80 86 sr y and eu richer ba and lree depleted higher sr ti lower ba sr and la y an65 79 sr y and eu poorer ba and lree enriched lower sr ti higher ba sr and la y we observed several an65 79 parent magmas with higher la y lower sr and higher lree than the majority of an65 79 zones which suggests that they grew from highly fractionated magmas the an80 86 zones of both xenolith crystals and phenocrysts appear to have crystallized relatively early and are attributed to growth in magmas more primitive than parent magmas of an65 79 zones or the host magma using melts modeling we demonstrate a significant role for h2o is not necessary to form an rich crystals from known ojp magma types these types of zones can instead form when relatively primitive ojp magmas ascend and partially crystallize at low pressures crystal mush layers are rheological elements of multiply saturated solidification fronts and conditions for extreme fractionation are met deep with thermally and mechanically insulated mush solidification fronts conditions in a homogenous magma body alone cannot generate the range of magma compositions and textures recorded in ojp plagioclase crystals we suggest that the ojp magma chamber system consisted of crystal mush dominated regions and liquid dominated regions in a laterally and vertically extensive system of interconnected dikes and sills solidification front disruption was common during magma recharge and transport which freed debris to mix with ojp magmas the volume of crystalline debris from disrupted solidification fronts was small relative to the overall magma volume which leads to little change of bulk magma chemistry this can explain the dominance of the kwaimbaita basalt type across the ojp evidence of solidification front disruption is best preserved as allochthonous crystals both more and less primitive than bulk magma chemistry both of which were observed in ojp basalts coincident with a zone of neutral buoyancy the shallow ojp magma chamber system existed at a depth of 0 7 km the ojp magma chamber system was thinner near the plateau margins which provided less density filtration of magmas this allowed more diverse magma types to reach the surface along the margins it is envisaged that as the ojp formed the zone of neutral buoyancy slowly migrated upward leading to slow yet pervasive assimilation of overlying seawater altered basalt at the base of the lava pile

petrological insights into shifts in eruptive styles at volcan llaima chile tephra and lava pairs from two summit eruptions ad 2008 and 1957 and a flank fissure eruption ad 1850 are compared in terms of textures phenocryst contents and mineral zoning patterns to shed light on processes responsible for the shifts in eruption style during typical eruptive episodes at volcan llaima andean southernvolcanic zone chile the mineralogy and whole rock com positions of tephra and lavas are similar within eruptive episodes suggesting a common magma reservoir for strombolian paroxysms and lava effusion the zoning profiles and textures of plagioclase record successive and discrete intrusions of volatile rich mafic magma accompanied by mixing of these recharge magmas with the resident basaltic andesitic crystal mushes that are commonly present at shallow levels in the llaima system each recharge event destabil izes the plagioclase in equilibrium with the resident crystal mush melt and stabilizes relatively an rich plagioclase as is recorded by the numerous resorption zones lavas typically have 15 20 vol more phenocrysts than the tephra differences in plagioclase and olivine textures and zoning combined with different phenocryst contents indicate that a greater volume fraction of recharge magma is present in the explosively erupted magma than in subsequent effu sively erupted magma we propose that strombolian paroxysms at volcan llaima are triggered by interactions with large volume frac tions of recharge magma which decrease the bulk viscosity and in crease the volatile contents of the erupted magmas leading to the conditions required for the fragmentation of basaltic andesite lava effusion ensues from reduced interactions with the recharge magma after it has partially degassed and crystallized thereby impeding rapid ascent this process could be operating at other steady state basaltic volcanoes wherein shallow reservoirs are periodically re filled by fresh volatile rich magmas

contrasting plagioclase textures and geochemistry in response to magma dynamics in an intra caldera rhyolite system okataina volcano abstract the changing magmatic dynamics of the rhyolite caldera volcano okataina volcanic centre new zealand is revealed in plagioclase growth histories crystals from the 0 7 ka kaharoa eruption are characterized by resorbed cores displaying a cellular texture of high an 40 zones partially replaced by low an 50 20 elevated an fe mg sr and ti follow the resorption surface and display rimward depletion trends accompanied by ba and ree enrichment the zonation is consistent with fractional crystallization and cooling the cores display wide trace element diversity pointing to crystallization in a variety of melts before transport and mixing into a common magma where the rims grew plagioclase from the 36 ka hauparu eruption display several regrowth zones separated by resorption surfaces which surround small resorbed cores with a spongy cellular texture of variable an content an 40 50 the crystals display step wise regrowth of successively higher an fe mg and ti content consistent with progressive mafic recharge two crystal groups are distinguished by trace element chemistry indicating growth in separate melts and co occurrence via magma mingling for plagioclase in both eruption deposits partition coefficients d estimated from crystal rim groundmass glass analyses produce melt compositions similar to the array of rock and glass compositions erupted and are consistent with the processes of fractional crystallization and recharge however d values estimated from some published formulations based on an content and temperature produce unrealistic melts the contrasting zoning patterns in plagioclase correspond to the evolutionary history of magmatism at okataina emptying of the magma reservoir following caldera eruption at 46 ka reduced barriers to mafic magma ascent this is recorded by the frequent resorption and recharge episodes in hauparu crystals subsequent redevelopment of a more silicic reservoir zone post 26 ka dampened thermal and mass perturbations resulting in simpler growth histories of the kaharoa crystals the plagioclase lack features associated with rapid decompression events that are common in andesite systems this reflects the rapid ascent of the rhyolite magmas and lack of precursory eruptions that could decompressed the system

k feldspar phenocrysts in microgranular magmatic enclaves a cathodoluminescence and geochemical study of crystal growth as a marker of magma mingling dynamics abstract the crystallization history of zoned k feldspar phenocrysts in microgranular magmatic enclaves in the karkonosze granite sw poland reveals that the crystals grew in stirred coeval magmas of contrasting compositions the growth mechanism and crystal compositions are investigated using cathodoluminescence and profiling by electron microprobe and laser ablation icp ms these methods provide insight into the crystallization process and the varying compositions of the host melt the phenocrysts show two types of growth patterns with or without resorption interfaces the trace element distribution heterogeneous across different zones and within single phenocryst zones reflects a dynamic process of crystal growth from compositionally heterogeneous magma hybridization is also reflected in the density of structural al o al defects features that relate to coupled ba al incorporation into the crystal structure differences in structural defect densities and crystal composition trace the degree of hybridization in the granitic magma during the growth of the k feldspar phenocrysts