on estimating crystal shape for crystal size distribution analysis abstract the accurate determination of three dimensional crystal habit long intermediate short axis is a requirement to enable correct stereological conversion of 2d crystal size measurements to true 3d crystal size distributions csds in this contribution we introduce a database and spreadsheet program which provides an objective estimate of true crystal habit from raw 2d measurements the database compares the sample s 2d measurements with 2d shape curves for random sections through 703 different habits the output gives the five best match curves and corresponding crystal habits based on a least squares fit between sample and database the minimum sample size required to give good shape estimates from 2d data is tested using random runs of sections through known shapes with different population densities at minimum 75 crystal sections are required to robustly determine crystal habit for csd measurements if crystals are tabular in shape with more acicular shapes requiring a minimum of 250 sections suggesting a sample size of 250 sections to be used for shape determination in natural examples where the true 3d shape is unknown the crystal habit of the best match shape can then be used to provide a more robust csd analysis which in turn can be used to investigate magmatic processes with more certainty

particle packing from an earth science viewpoint abstract particle packings are relevant to many aspects of the earth sciences and there is a long history of the study of packings from an earth science viewpoint packings have also been studied in connection with other subjects and disciplines allen 1982 produced a major review which provides a solid base for earth science related studies this review complements allen s work and in particular focuses on advances in the study of random packings over the last ten years transitions from packing to packing may be as important as the packings themselves and possibly easier to model this paper places emphasis on certain neglected works in particular morrow and graves 1969 and the packing transition envelope kahn 1956 and the measurement of packing parameters griffiths 1962 on packings in one dimension and getis and boots 1978 on packings in two dimensions certain packing problems are relevant to current areas of study including structure collapse in loess hydroconsolidation flowslides in very sensitive soils wind erosion jewel quality in opals and the structure and functions of sand dunes the region where interparticle forces become active particles

the spatial distribution of grains and crystals in rocks characterisation and analysis of the spatial distribution pattern sdp of grains or crystals in rocks is potentially a powerful technique which can be used to constrain the processes which operate in the formation of rocks a method to quantify the sdp of grains in thin section is presented the distance betwen the centre of a grain and the centre of its nearest neighbour is calculated for all the grains in the sample area to produce a distribution of distances that characterises the spatial pattern of grains in the rock this distribution is then normalised to a random distribution of points with the same population density to give a descriptive value r values of r for rock samples are plotted against porosity modal abundance of other phases in igneous and metamorphic rocks to characterise the sdp the sdp of randomly packed distributions of equal size spheres varies systematically with porosity producing a line on a porosity versus r plot termed the random sphere distribution line rsdl rocks which plot above the rsdl have an ordered sdp and those that plot below a clustered sdp the effects of variation in grain packing order grain sorting compaction and random crystallisation overgrowth on determined r values were investigated using a combination of 3 d sphere models and 2 d texture models the maximum possible value of r is 2 148 corresponding to a perfect section through hexagonal cubic close packing of grains the minimum value of r is dependent on the proportion of grains in the sample volume and may be as low as 1 2 for a sample volume with 30 grains which are clustered variations in size sorting can cause r to vary by approximately 0 25 mechanical compaction of a loose framework of grains results in a higher packing order and an increase in r continued compaction creates a fabric in the texture and r decreases as cluster patterns are developed perpendicular to the principal stress the overgrowth of grains in a touching framework alters the location of the geometric grain centre as the crystal shape changes leading to an increase in r as porosity decreases results reveal that grain sorting compaction and grain overgrowth produce different r versus porosity relationships which can be identified in and therefore used to constrain the relative importance of these processes in rock samples

multiple ways of producing intermediate and silicic rocks within thingmuli and other icelandic volcanoes major and trace element compositions of rocks and coexisting phenocrysts of the thingmuli volcano suggest a revision of the existing models for the formation of intermediate and silicic melts in iceland the new data define two compositional tholeiitic trends with a significant gap between them a high iron trend hfe contains 6 14 wt total feo in silicic rocks with c 1 wt mgo as well as sodic plagioclase and hedenbergite phenocrysts a low iron trend lfe contains 3 5 wt feo at c 1 wt mgo which is typical of iceland but higher than morb compositions the most evolved phenocrysts of the lfe trend do not reach iron rich end members the hfe trend is interpreted as a result of fractional crystallization numerical modelling using the melts algorithm suggests that crystallization took place under redox conditions constrained to one log unit below the fayalite magnetite quartz oxygen buffer fmq 1 the lfe trend is explained by a combination of mixing between rhyolite and ferrobasalt assimilation of hydrated crust and fractional crystallization under higher redox conditions fmq the two trends and the gap are best defined in a plot of mg versus sio2 that is useful to unravel petrogenetic processes for example intermediate and silicic rocks of the holocene volcanic systems of spreading rifts e g krafla propagating rifts e g hekla and off rifts oraefajokull also fall into high and low iron fields and outline a gap similar to thingmuli the identification of two compositional trends in erupted intermediate and silicic volcanic products shows that processes in the deep roots of single volcanic systems are highly diverse and likely controlled by local variations in the thermal gradients and the extend of hydrothermal alteration generalizations about the relationship between the compositions of intermediate and silicic rocks and plate tectonic setting therefore should be avoided

magma evolution and ascent at volcanic arcs constraining petrogenetic processes through rates and chronologies large 226 ra excesses in a number of mafic arc magmas and geophysical observations of earthquake hypocenters locations indicate that mafic melts can get transferred from source to surface within days to 1 kyr decreasing 226 ra 230 th disequilibria with increasing sio2 in co magmatic suites of individual arc volcanoes suggest that magma differentiation often occurs on timescales of a few thousand years in closed systems or less in open systems however the rapid decrease of global 238 u 230 th disequilibria with increasing sio2 within basaltic andesite compositions suggests that rapid closed system differentiation does not typically produce more evolved compositions from mafic parental magmas with large 238 u excesses in the case of rapid magmatic evolution open system processes are frequently involved in the production of andesites and dacites and the data imply that the open system component is close to 238 u 230 th secular equilibrium melts modeling of magma evolution at santorini in the aegean arc provides corroborating evidence from an individual well studied arc volcano that closed system fractional crystallization fails to produce the more evolved compositions and increasing 87 sr 86 sr ratios with increasing sio2 from andesites to rhyolites suggests assimilation of old crust is involved these observations can be conceptualized through thermal modeling of basaltic sill injections into the lower and upper crust melt production in deep crustal hot zones provides an explanation for low 238 u 230 th disequilibria of the evolved magmatic component as significant accumulation of evolved melts through partial re melting of previously intruded basalts requires n100 kyr incubation time at typical magmatic flux rates thermal modeling also provides a framework for understanding assimilation of old upper crustal rocks in more mature magmatic systems further insights into magmatic evolution can be gained from dating of minerals from mafic intermediate and felsic arc magmas a many u th mineral isochrons in mafic arc magmas yield ages significantly older than those

crystal size distributions of plagioclase in lavas from the july august 2001 mount etna eruption during the 2001 eruption of mount etna two independent vent systems simultaneously erupted two different lavas the upper vents system uv opened between 3100 and 2650 m a s l emitted products that are markedly porphyritic and rich in plagioclase while the lower vents system lv opened at 2100 and 2550 m a s l emitted products that are sparsely porphyritic with scarce plagioclase in this study the crystal size distributions csds of plagioclase were measured for a series of 14 samples collected from all the main flows of the 2001 eruption the coefficient of r 2 determination was used to evaluate the goodness of fit of linear models to the csds and the results are represented as a grid of r 2 values by using a numerical code developed ad hoc r 2 diagrams suggest that the 2001 products can be separated into two main groups with slightly different characteristics plagioclase csds from the uvs can be modeled by three straight lines with different slopes while the plagioclase csds from the lvs are largely concave we have interpreted the csds of the uvs as representing three different populations of plagioclases i the large phenocrysts type i which started to crystallize at lower cooling rate in a deep reservoir from 13 to 8 months before eruption onset ii the phenocrysts type ii which crystallized largely during continuous degassing in a shallow reservoir and iii the microlites which crystallized during magma ascent immediately prior to the eruption the plagioclase csd curves for the lvs lava are interpreted to reflect strong and rapid changes in undercooling induced by strong and sudden degassing

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

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

effects of crystal shape and size modality on magma rheology erupting magma often contains crystals over a wide range of sizes and shapes potentially affecting magma viscosity over many orders of magnitude a robust relation between viscosity and the modality of crystal sizes and shapes remains lacking principally because of the dimensional complexity and size of the governing parameter space we have performed a suite of shear viscosity measurements on liquid particle suspensions of dynamical similarity to crystal bearing magma our experiments encompass five suspension types each consisting of unique mixtures of two different particle sizes and shapes the experiments span two orthogonal subspaces of particle concentration as well as particle size and shape for each suspension type thereby providing insight into the topology of parameter space for each suspension type we determined the dry maximum packing fraction and measured shear rates across a range of applied shear stresses the results were fitted using a herschel bulkley model and augment existing predictive capabilities we demonstrate that our results are consistent with previous work including friction based constitutive laws for granular materials we conclude that predictions for ascent rates of crystal rich magmas must take the shear rate dependence of viscosity into account shear rate dependence depends first and foremost on the volume fraction of crystals relative to the maximum packing fraction which in turn depends on crystal size and shape distribution

magmatic fabric acquisition mechanisms in a syenite results of a combined anisotropy of magnetic susceptibility and image analysis study the structural significance of the anisotropy of magnetic susceptibility ams and acquisition mechanisms of silicate and ferrimagnetic mineral fabrics are investigated in the archean lebel syenite intrusion ontario canada bulk mineral subfabrics are determined by intercept counting of mineral phases in classified digital images of thin sections cut parallel to the principal planes of the magnetic fabric ellipsoids of the samples intensities shapes and principal direction orientations of the resulting intercept ellipsoids are generally similar to the corresponding ams ellipsoids differences are due mainly to bimodal distribution of mineral fabrics observed on foliation planes of some samples showing pre full crystallization textures and structural overprinting in samples deformed after crystallization subfabrics of clinopyroxene and magnetite in samples showing pre full crystallization microstructure are investigated by measuring inertia tensors of individual grain shapes the resulting inertia tensor ellipsoids indicate that magnetic fabrics in these rocks are strongly correlated to the shape preferred orientation of magnetite which is similar to the overall petrofabric of the samples crystal size distributions of clinopyroxene and magnetite indicate that they formed during in situ crystallization and that magnetite probably appeared late in the crystallization and flow history of the magma analysis of preferred orientations of these grains suggests that the petrofabrics of the samples were acquired during flow with strongly interacting grains analogous to a logjam in a river the final characteristics of the ams and silicate petrofabric are the end points of a continuous crystallization and flow history in the magma rather than transient late features

percolation threshold and permeability of crystallizing igneous rocks the importance of textural equilibrium the permeability of a crystal mush fundamentally controls the ability of its melt to migrate or segregate with respect to the solid phase and thus controls the extent to which compaction and porous media convection can occur in crystallizing igneous cumulates in particular the existence of a percolation threshold which defines the porosity at which a crystallizing rock becomes impermeable can limit the effectiveness of these processes we present three dimensional numerical models of the topology of porosity in both texturally equilibrated and nonequilibrated crystal melt systems these models enable porosity vs permeability relationships and hence percolation thresholds to be calculated the permeability of the nonequilibrated models was calculated using a network simulation method these models confirm that there is no percolation threshold for a perfectly texturally equilibrated rock with dihedral angles of 20 these results suggest that the volume of trapped melt in an igneous cumulate may be controlled by the ability of the crystallizing crystal melt system to reach textural equilibrium

crystalmom a new model for the evolution of crystal size distributions in magmas with the quadrature based method of moments nucleation and growth of crystals and the resulting crystal size distribution play a fundamental role in controlling the physical properties of magmas and consequently the dynamics of the eruptions in the past decades laboratory experiments demonstrated that size and shape of crystals strongly control the physical properties of magma and lava additionally natural and experimental samples are usually characterized in terms of their crystal size distribution to link it with physical processes that are not directly observable such as cooling or decompression mechanisms in this paper we present crystalmom a new predictive model based on the quadrature based method of moments developed for studying the kinetic of crystallization in volcanic systems the quadrature based method of moments well established in the field of chemical engineering represents a mesoscale modelling approach that rigorously simulates the space time evolution of a distribution of particles by considering its moments the method is applied here for the first time for studying the equilibrium disequilibrium crystallization in magma modelling the temporal evolution of the moments of a crystal size distribution the model verified against numerical and experimental data represents a valuable tool to infer the cooling and decompression rates from the crystal size distribution observed in natural samples

the role of crystal frameworks in the preservation of enclaves during magma mixing abstract the dacitic lava flows of nea kameni santorini greece contain a variety of partially crystalline mafic enclaves each enclave type is derived from the break up of a layer of replenishing magma emplaced in the dacite chamber prior to eruption crystallisation induced vesiculation of this layer driven by the temperature contrast between the two magmas was sufficient to drive upwelling and overturn of the layer resulting in the formation of mafic enclaves within the host the replenishing magmas are preserved as enclaves due to the presence of a plagioclase crystal framework spatial distribution pattern sdp analysis and melting experiments demonstrate that the plagioclase crystallinity and crystal aspect ratios observed in the kameni enclaves are sufficient to form a touching framework of crystals observations on the coherence of the framework during exsolution of volatiles and enclave transport suggest that the morphology of the dominant framework forming phase places a significant control on the strength and viscosity of the crystal framework which in turn determines the extent to which the replenishing magmas will fragment and mix with the dacite host frameworks composed of high aspect ratio crystals are weak and respond to rapid vesicle expansion in a brittle manner the replenishing magma then disaggregates to become a source of crystals dispersed throughout the host magma in contrast low aspect ratio crystals form strong crystal frameworks that are more resistant to rapid vesicle expansion resulting in preservation of the replenishing magma as vesicular enclaves

magmatic emulsion texture formed by mixing during extrusion rauðafell composite complex breiðdalur volcano eastern iceland the rau afell composite complex is part of the neogene brei dalur volcano eastern iceland and is composed of a composite feeder dyke a vent structure and a composite flow the two end members of the composite complex are rhyolite and basalt and both are rich in plagioclase macrocrysts bytownite in basalt and oligoclase in rhyolite the rhyolite also includes ferroaugite macrocrysts the mixed rocks are separated in three textural groups related to mixing proportions when the basaltic end member is dominant a hybrid texture with a homogeneous matrix is observed and the only evidence of mixing is the presence of antecrysts of both end members when the basaltic end member represents c 65 to 30 of the mixture we observe emulsion textures composed of finely co mingled basalt and rhyolite the difference between these two textural expressions of mixing is due to effects of diffusion the third texture shows mafic enclaves suspended in a rhyolitic matrix in these rocks the proportion of the basaltic end member is inferior to 30 implying that the basalt froze solid in contact with the rhyolite zoning of plagioclase shows that the mixing processes are driven initially by highly efficient micro mingling the emulsification is possibly a result of compositional gradient stresses korteweg stress between miscible basalt and rhyolite this is followed by chemical diffusion hybridisation and tend to protect antecrysts from reaction with the primitive magmas when antecrysts originated in the evolved magma they undergo dissolution due to thermal disequilibrium during mingling and chemical disequilibrium during hybridisation we argue that such mixing processes are important in producing intermediate rocks in iceland and elsewhere that shows only the chemical attributes of an origin by mixing the preservation of emulsion textures is rare and highly dependent on cooling history

combining csd and isotopic microanalysis magma supply and mixing processes at stromboli volcano aeolian islands italy integrating isotopic microanalysis with other analytical techniques creates powerful new methodologies for understanding the evolution of rock samples at the sub grain scale here we present crystal size distribution csd data for a 26 000 year old sample from stromboli volcano and accompanying isotopic microanalysis of the phenocrysts a technique called the icsd plot is introduced which given stated assumptions allows the integration of both sets of data to generate timelines of isotopic evolution through the volcanic system the combined approach is powerful allowing investigation of the magma supply mixing crystallisation and contamination processes prior to eruption of a volcanic sample for stromboli volcano the combined analysis suggests that the change in magma type following a cone collapse took roughly five years to complete similar to the timescale of changes seen in recent decades

magmatic history and parental melt composition of olivine phyric shergottite lar 06319 importance of magmatic degassing and olivine antecrysts in martian magmatism several olivine phyric shergottites contain enough olivine that they could conceivably represent the products of closed system crystallization of primary melts derived from partial melting of the martian mantle larkman nunatak lar 06319 has been suggested to represent a close approach to a martian primary liquid composition based on approximate equilibrium between its olivine and groundmass to better understand the olivine melt relationship and the evolution of this meteorite we report the results of new petrographic and chemical analyses we find that olivine megacryst cores are generally not in equilibrium with the groundmass but rather have been homogenized by diffusion to mg 72 we have identified two unique grain types an olivine glomerocryst and an olivine grain preserving a primary magmatic boundary that constrains the time scale of eruption to be on the order of hours we also report the presence of trace oxide phases and phosphate compositions that suggest that the melt contained approximately 1 1 h2o and lost volatiles during cooling also associated with an increase in oxygen fugacity upon degassing we additionally report in situ rare earth element measurements of the various mineral phases in lar 06319 based on these reported trace element abundances we estimate the oxygen fugacity in the lar 06319 parent melt early in its crystallization sequence i e at the time of crystallization of the low ca and high ca pyroxenes the rare earth element composition of the parent melt and those of melts in equilibrium with later formed phases we suggest that lar 06319 represents the product of closed system crystallization within a shallow magma chamber with additional olivine accumulated from a cumulate pile we infer that the olivine megacrysts are antecrysts derived from a single magma chamber but not directly related to the host magma and suggest that mixing of antecrysts within magma chambers may be a common process in martian magmatic systems

using quantitative textural analysis to understand the emplacement of shallow level rhyolitic laccoliths a case study from the halle volcanic complex germany received february 1 2002 accepted november 8 2002in qualitatively homogeneous magmatic bodies quantitativetextural analysis such as crystal size distribution modalabundance and spatial distribution pattern analyses allowstheir internal heterogeneity to be measured and interpreted inthis study these methods are applied to samples from a 300mdrill core through one of the porphyritic rhyolitic laccoliths petersberg unit of the 300ma halle volcanic complex germany qualitatively thegeochemicallyhomogeneouspetersbergunit does not show much textural variation quantitatively however the crystal size distributions of the three most commonphenocryst phases orthoclase plagioclase and quartz suggestcontinuouscrystalgrowthduringmagmaascentandemplacement but different growth histories of the phenocryst phases throughoutthe genesis of the laccolith in situ cooling did not affect thephenocryst population size distributions of the phenocrysts varyon a centimetre to decimetre scale but are similar on the scale ofthe laccolith the modal abundance of the phenocryst phases isvery similar throughout the drill core quantification of thespatial distribution of phenocrysts however reveals a trend forclusteringtowardstheinteriororupperpartofthelaccolith whichis attributed to flow and shear processes during emplacement anddiscontinuities in the interior relating to the intrusion of differentmagmapulses circularstatisticsoftheorientationoflongaxesofcrystals reveala weakalignment oftheorthoclaseand plagioclasephenocrystsonthesamplescaleasaresultofflowinthemagmainspite of little acicularity in general laccoliths can be fedby several pulses of magma without major cooling betweenbatches

zoned orthopyroxenes in the ni co sulfide ore bearing xiarihamu mafic ultramafic intrusion in northern tibetan plateau china implications for multiple magma replenishments abstract the xiarihamu mafic ultramafic intrusion is situated in the east kunlun orogenic belt e kob northern tibetan plateau china with ni co sulfide mineralization mainly in orthopyroxenite and olivine orthopyroxenite whole rock and mineral compositions show cyclic variations in drill hole intersections through the xiarihamu mafic ultramafic intrusion microbeam x ray fluorescence xrf mapping shows reverse zoning cr poor core cr rich rim and oscillatory zoning cr poor core cr rich mantle and cr poor rim in orthopyroxene of olivine orthopyroxenite and orthopyroxenite zoned orthopyroxenes are euhedral or subhedral and there are relatively sharp interfaces between zones with distinct cr contents crystal size distribution csd curves of orthopyroxenes in olivine orthopyroxenite show concave upward curvature at size larger than 3 0 mm and larger orthopyroxenes commonly display zoning implying a secondary recrystallization and grain growth of larger orthopyroxenes quantitative analyses show that cr and enstatite contents of cores are relatively lower but incompatible element e g ti zr ga and sr contents of cores are higher than rims in reverse zoned orthopyroxenes and chemical profiles of unzoned orthopyroxenes resemble those of rims but different from those of cores in reverse zoned orthopyroxenes chemical profiles of orthopyroxenes indicate that cr zoning is not due to the change in cr partitioning behavior between orthopyroxene and silicate melt which shows significant temperature and redox dependence textural feature and crystal size distribution of orthopyroxenes suggest the formation of cr rich zones attests to the multi stage growth in the process of magma replenishment rather than a reactive liquid flow model or in situ trapped liquid overgrowth orthopyroxene zoning together with compositional variation and intrusive relationship between olivine orthopyroxenite and orthopyroxenite imply that the xiarihamu mafic ultramafic intrusion was formed by multiple magma replenishments with magma varying roughly from a more evolved to a more primitive composition

a tephrochronologic method based on apatite trace element chemistry geochemical correlation of ash fall beds with conventional tephrochronologic methods is not feasible when original glass composition is altered thus alternative correlation methods may be required initial studies of heavily altered paleozoic tephra k bentonites have suggested the potential for employing trace element concentrations in apatite as ash fall bed discriminators to further test the utility of apatite trace element tephrochronology we analyzed apatite phenocrysts from unaltered volcanic rocks with an electron microprobe nine samples from rocks erupted during the quaternary and one sample from a rock erupted during the paleogene the resulting apatite trace element data provide unique bed discriminators despite within crystal variability each of the volcanic rocks studied possesses unique trends in mg cl mn fe ce and y concentrations in apatite the results from this study establish an important tephrochronologic method that can be applied to nearly all portions of the phanerozoic stratigraphic record and greatly assist development of an advanced timescale in addition to establishing a fingerprint for a particular eruption apatite chemistry provides useful information about the source magma

on the identification of textural equilibrium in rocks using dihedral angle measurements three dimensional numerical simulations have been constructed to investigate the distributions of apparent dihedral angles expected in unequilibrated rock textures for comparison with those expected in equilibrated rock textures for unequilibrated fully crystallized monomineralic rocks the simulation shows that the distribution of apparent dihedral angles is nonrandom and similar to that expected from an equilibrated rock and is largely independent of crystal shape and crystal nuclei distribution this new distribution together with the one previously derived for an equilibrated texture defines a pair of apparent dihedral angle curves which encompass curves corresponding to any degree of textural equilibrium within a monomineralic rock the location of a measured curve within this range allows a quantitative assessment of the degree of textural equilibrium within that rock the simulations also show that unequilibrated partially crystallized rocks generate apparent dihedral angle distributions for closed triangular pores that depending on crystal shape may mimic equilibrated dihedral angle distributions they also indicate that unless a rock is in complete equilibrium different dihedral angle distributions are produced by measuring the apparent dihedral angles of closed triangular or open nontriangular pores an important conclusion of this work is that apparent dihedral angle curves for unequilibrated textures are similar to those for equilibrated textures therefore care must be taken when interpreting textural equilibrium from apparent dihedral angle curves

quantitative petrological evidence for the origin of k feldspar megacrysts in dacites from taapaca volcano chile k feldspar megacrysts are common in granitoids but relatively rare in chemically equivalent volcanic rocks dacites from taapaca volcano have euhedral sanidine megacrysts up to 5 cm long small crystals where present are rounded growth of the megacrysts engulfed plagioclase and amphibole crystals crystal size distributions csd of sanidine megacrysts are hump shaped all these data show that megacrysts developed from the host magma by coarsening this was enabled by the cycling of magma temperature around the sanidine liquidus temperature in response to injections of more mafic magma and subsequent magmatic overturns plagioclase crystals enclosed in the megacrysts are small and have short steep straight csds which contrasts with the csds of plagioclase in the groundmass which are shallower and extend to larger sizes this shows that plagioclase was also coarsened approximately synchronously with sanidine in response to the same temperature conditions

textural analysis of magmatic enclaves from the kameni islands santorini greece abstract the kameni islands have been the focus of historic volcanic activity on santorini greece the islands comprise a series of dacite lavas the erupted compositions of which have remained approximately constant for the last 2200 years the dacite lava flows of nea kameni contain a variety of mafic enclaves distinguished by differences in texture composition and mechanical behaviour the mafic enclaves represent chilled fragments of mafic magma that crystallised rapidly on contact with the cooler more silicic host magma the absence of chilled margins on the enclaves suggests that the replenishing magma initially formed a dense layer at the base of the chamber groundmass textures are interpreted as an indication of the degree of undercooling between the enclaves and the host groundmass textural information obtained from the enclaves has been used to determine the relative volumes of replenishing magmas injected into the host magma before eruption which indicates that the volume of erupted magma is directly proportional to the volume of replenishing magma emplaced in the chamber prior to eruption which thus may act as a potential eruption trigger the variety of replenishing magmas implies the existence of a complex conduit and chamber system beneath santorini volcano andesitic enclaves with linear crystal size distributions are thought to have originated as an aphyric andesitic melt expelled from a crystal mush by filter pressing disequilibrium phenocryst assemblages in the lavas and phenocryst bearing enclaves provide evidence for the entrainment and recycling of older phenocryst populations

case studies of plagioclase growth and residence times in island arc lavas from tonga and the lesser antilles and a model to reconcile discordant age information abstract the time scales of crystal growth and residence in magmas have received much attention because such information can constrain the physical processes involved however crystals and liquids can have different ages leading to apparently contradictory information from different dating methods two case studies are presented from island arc lavas that highlight such dichotomies plagioclase crystal size distributions and u th ra isotope data are presented for lavas from late and metis shoal in tonga and from soufriere st vincent in the lesser antilles in all three lavas mineral data yield apparent u th ages of 30 50 kyr yet 226 ra excesses are preserved in both the minerals and the whole rocks the crystal size distributions suggest crystal growth over 100s of years but also frequently indicate the presence of mixed crystal populations furthermore a cumulate from soufriere yields the same u th age as its host lava on 226 ra ba versus time evolution diagrams curves for melts in equilibrium with plagioclase provide apparent ages of 1700 3300 yr for tonga but for soufriere they are displaced below that of the whole rock our interpretation is that the phenocrysts from all three lavas are zoned in both composition and age the apparent u th ages reflect mixtures of old cores and young rims and indicate a volume integrated age of 10s of kyr for the time for initial crystal growth crystal liquid segregation the time of storage as a cumulate plus the time spent during entrainment and growth in the new magma prior to eruption the 226 ra excesses were imparted to overgrowths on the old cumulate cores during entrainment by subsequent injections of new magma because crystal growth segregation and entrainment can all appear to occur in 100s to a few thousand years at most the bulk of the u th time scale is inferred to record storage in cumulates which are then incorporated into new magma batches plagioclase growth rates of 3 9 10 13 cm s 1 would reconcile the combined ra th and crystal size distribution data magma differentiation time scales and eruptive periodicity are one to three orders of magnitude shorter than the inferred cumulate storage times indicating complex phenocryst liquid behaviour beneath island arc volcanoes

the record of magma chamber processes in plagioclase phenocrysts at thera volcano aegean volcanic arc greece lavas and pyroclastic rocks throughout the volcanic stratigraphy of the tertiary quaternary volcanic complex of thera in the aegean island arc display inhomogenous plagioclase populations and phenocryst resorption textures interpreted as indicative of magma mixing plagioclase zoning characteristics studied by nomarski and laser interferometry techniques establish three main categories of plagioclase i inherited plagioclase nucleated in endmember prior to initial mixing event ii in situ plagioclase nucleated in mixed or hybrid magma and iii xenocrystic plagioclase nomarski contrast images and linearized compositional zoning profiles reveal striking differences between calcic and sodic plagioclases depending on the composition of the lava in which they are hosted these differences reflect the contrasting effects of changes in physical chemical parameters in basic vis a vis more acidic melts during magma mixing and or influx of new magma into the subvolcanic magma chamber as well as the influence of magma chamber dynamics on plagioclase equilibration variations in bulk major and trace element abundances of thera volcanic products reflect the dominant overprint of crystal fractionation but decoupling between major and trace element fractionation models and variations in incompatible trace element distributions are all indicative of magma mixing processes consistent with compositional and textural zoning in plagioclases

on the structure of mare basalt lava flows from textural analysis of the lapaz icefield and northwest africa 032 lunar meteorites quantitative textural data for northwest africa nwa 032 and the lapaz lap mare basalt meteorites lap 02205 lap 02224 lap 02226 and lap 02436 provide constraints on their crystallization and mineral growth histories in conjunction with whole rock and mineral chemistry textural analysis provides powerful evidence for meteorite pairing petrographic observations and crystal size distribution csd measurements of nwa 032 indicate a mixed population of slowly cooled phenocrysts and faster cooled matrix lapaz basalt crystal populations are consistent with a single phase of nucleation and growth spatial distribution patterns sdp of minerals in the meteorites highlight the importance of clumping and formation of clustered crystal frameworks in their melts succeeded by continued nucleation and growth of crystals this process resulted in increasingly poor sorting during competition for growth as the melt crystallized based on csd and sdp data we suggest a potential lava flow geometry model to explain the different crystal populations for nwa 032 and the lapaz basalts this model involves crystallization of early formed phenocrysts at hypabyssal depths in the lunar crust followed by eruption and flow differentiation on the lunar surface lava flow differentiation would allow for formation of a cumulate base and facilitate variable cooling within the stratigraphy explaining the varied textures and modal mineralogies of mare basalt meteorites the model may also provide insight into the relative relationships of some apollo mare basalt suites shallow level crystal fractionation processes and the nature of mare basalt volcanism over lunar history

quantitative 3d petrography using x ray tomography application to bishop tuff pumice clasts abstract textures are traditionally studied using the petrographic microscope which limits observations to 2d sections of 3d objects given the difficulty in retrieving information on shapes sizes and spatial distribution of objects in 3d from random sections a method that can yield observations in 3d is highly desirable x ray tomography yields a 3d map of the linear x ray attenuation coefficient which is a function of the atomic number and density of the material and the x ray energy used based on the compositional contrasts between different phases various phases can be identified in a rock pumice clasts characterized by isolated crystals surrounded by a low density matrix are ideal for the application of this technique we present our first results obtained using x ray tomography for pumice clasts from the bishop tuff samples studied are from units f7 and f8 and are representative of the variability in density and crystal contents observed in the early erupted bishop tuff data were collected on the geosoilenvironcars beamline at the advanced photon source argonne national laboratory using a 22 kev monochromatic x ray beam image analysis was performed using the software blob3d brightness contrasts in the resulting images allow the separation of magnetite sanidine quartz including minor plagioclase glass and vesicles crystals smaller than 5 voxels in diameter cannot be quantified properly mostly due to noise in the images this constrains the spatial resolution of the resulting images such that there is a trade off between sample size and spatial resolution we employed two runs with samples of varying sizes 5 and 10 mm to obtain adequate resolution voxel sizes ca 8 and 17 m we have previously studied quartz size distributions in bishop pumice clasts using a crushing sieving and winnowing procedure the agreement between our new and previous results is excellent quartz size distributions obtained using the tomography data are concave upward on population density vs size plots and resemble the size distributions for all quartz crystals including both whole crystals and fragments these size distributions were probably generated by fragmentation through which large crystals were converted in a larger number of small crystals petrographic observations suggest fragmentation occurred mostly under magmatic conditions sanidine size distributions are similar to those observed for quartz magnetite size distributions are typically linear indicating a simple magmatic history in contrast with the tektosilicates

caldera formation on santorini and the physiography of the islands in the late bronze age the caldera of santorini is a composite structure with a subsidence history extending over 100 ka or more geomorphological mapping shows that the present day caldera wall is a complex assemblage of cliff surfaces of different ages and that collapse at santorini has repeatedly exhumed earlier caldera cliffs and unconformities cliffs bounding the southern southeastern and northwestern rims of the caldera are morphologically fresh and probably formed during or soon after the minoan eruption in the late bronze age the well scalloped shape of these cliffs is attributed to large scale rotational landslip around the margins of the minoan caldera the deposit from one landslip is preserved subaerially minoan landslips in southeast santorini detached along the basement unconformity exposing a cliff of the prevolcanic island the caldera wall in the north northeast and east preserves evidence for three generations of cliff those of minoan age and two earlier generations of caldera wall the two early calderas can be dated relative to a well established statigraphy of lavas and tuffs the presence of in situ minoan tephra plastered onto the present day caldera wall provides evidence that these ancient caldera cliffs had already been exhumed prior to the minoan eruption field relationships permit reconstruction of the physiography of bronze age santorini immediately before the minoan eruption the reconstruction differs from some previously published versions and is believed to be the most accurate to date bronze age sa ntorini had a large flooded caldera formed 21 ka ago this caldera must have acted as an excellent harbour for the bronze age inhabitants of the island the 3 6 ka minoan eruption deepened and widened the extant caldera the volume of minoan collapse 25 km3 is in good agreement with published estimates for the volume of discharged magma if between 5 and 8 km3 of minoan ignimbrite ponded as intracaldera tuff

new equations for swelling characteristics of bentonite based buffer materials compacted bentonite and sand bentonite mixtures are attracting greater attention as buffer material for repositories of high level nuclear waste this buffer material is expected to fill up the space between the canisters containing the waste and the surrounding ground by swelling to produce the specifications such as dry density sand bentonite mass ratio and dimensions of the buffer material the swelling characteristics of compacted bentonite and sand bentonite mixtures must be evaluated quantitatively new equations for evaluating the swelling behavior of compacted bentonite and sand bentonite mixtures are presented that can accommodate the influences of the sand bentonite mass ratio and the exchangeable cation composition of bentonite the new method for predicting swelling characteristics is presented by combining the new equations with the theoretical equations of the gouy chapman diffuse double layer theory and of the van der waals force which can evaluate the repulsive and attractive forces

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

quantifying three dimensional silicate fabrics in cumulates using cumulative distribution functions we present a new method for quantifying three dimensional silicate fabrics and the associated uncertainties from grain orientation data on three orthogonal sections our technique is applied to the orientation of crystallographic features and hence yields a fabric related to the lattice preferred orientation although the method could be applied to shape preferred orientations or strain analysis based on passive linear markers the orientation data for each section are represented by their cumulative distribution function and an iterative procedure is used to find the symmetric second rank strain tensor that will simultaneously satisfy the cumulative distribution functions observed on each section for samples with well developed fabrics this technique provides a much closer match to the sectional data than do previous techniques based on eigenparameter analysis of two dimensional orientation data robust uncertainty estimates are derived from a non parametric bootstrap resampling scheme the method is applied to two cumulates one with a well developed fabric and the other with a weak fabric from the stillwater complex montana the silicate petrofabric orientations obtained for these samples compare favorably with independent direct estimates of the volume fabric from electron backscatter diffraction and magnetic techniques

igneous microstructures from kinetic models of crystallization during crystallization a variety of competing kinetic processes determine the evolution of the igneous microstructure yet the relative contribution of each process remains elusive to this end a stochastic algorithm is developed to yield a detailed spatial representation of the igneous microstructure during progressive crystallization this algorithm is used to test a variety of kinetic models for nucleation and crystal growth that yield realistic igneous microstructures the algorithm itself relies on a theoretical model of crystallization the avrami method and can therefore be internally validated in addition to being verified against natural microstructures using crystal size distributions csds the most realistic simulated igneous microstructure in which the csds remain approximately log linear throughout the crystallization interval is produced using a kinetic model involving exponential nucleation rate and constant growth rate an extension of the algorithm is used to simulate multiply saturated mineral growth emulating basalt crystallization through simultaneous nucleation and growth of plagioclase and clinopyroxene a fundamentally important feature of this procedure is the numerical production of detailed 3d representations of the microstructure that can be interrogated to study many physical and chemical processes for example the critical crystallinity necessary for the onset of a finite yield strength and the interstitial melt flow within the igneous microstructure depend on the percolation of the solid and melt phases respectively bounds on the percolation thresholds the critical crystallinity at which the phase of interest is connected or contiguous such that it extends across the full microstructure from one face to the opposite face are determined for the simulated igneous microstructure and are comparable with previously published results for the percolation threshold of both the melt phase and solid network the simulated igneous microstructure can also be used as input into other physical models to ascertain the physical properties of partially molten magmas that are otherwise difficult to estimate by experiment in a real sense these computed microstructures are equivalent to 3d microtomographic images of partially molten basalt within a solidification front

high resolution la icp ms trace element mapping of igneous minerals in search of magma histories we report experiments on optimisation of la icp ms mapping as a tool for visualising and quantifying internal structure of trace element concentration in igneous minerals the experimental design was refined with maps on clinopyroxene and amphibole macrocrysts mainly antecrysts from a porphyritic lamprophyre in ne spain as well as on a high precision metal wire grid in terms of spatial resolution we demonstrate with scanning electron microscope and white light interferometry that a full ablation removes between 0 4 and 0 7 mu m of material depending on ablation parameters maps were produced with square laser beam spots of 12 and 24 mu m it was found that complexities can be resolved in the sample even though they are smaller than the beam diameter e g 7 10 mu m discontinuities using 12 mu m laser beam resolution in x and y was found to be identical probably reflecting the fast washout of the two volume ablation cell and the short total dwell time of the analyte menu selected due to the excellent stage reproducibility and the limited ablation depth it is feasible to re ablate the identical map area many times employing different instrument parameters or analyte menus on the magmatic crystals la icp ms maps define very sharp compositional zoning in trace elements highlighting complex crystallisation histories where normal magmatic fractionation is not the only process events of mafic recharge are easily recognised as zones enriched in compatible metals such as cr ni or sc further trace element maps reveal complexities in mineral zoning previously undetectable with petrography or major element data these include resorbed primitive cores and oscillatory zoning within apparently homogeneous mineral zones therefore la icp ms mapping opens a new window of opportunity for analysis of magmatic histories the wide combination of instrumental parameters such as laser beam size scan speed and repetition rate make it possible to carry out experiments at different levels of detail we recommend a two step approach to mapping the initial step involves rapid maps to gain an overview of potential complexities in the sample this enhances representativeness of the analysed materials as a large number of crystals and trace elements can be tested in little time subsequently detailed maps can be carried out on areas of interest an additional functionality is to create 1d profiles from 2d maps the potential of the technique to unveil compositional complexities efficiently and at greater detail than traditional microanalysis will help to improve our understanding of processes in the magmatic environment and beyond c 2015 elsevier b v all rights reserved

crystal size distribution csd in rocks and the kinetics and dynamics of crystallization ii makaopuhi lava lake crystal size distribution csd theory has been applied to drill core samples from makaopuhi lava lake kilauea volcano hawaii plagioclase and fe ti oxide size distribution spectra were measured and population densities n were calculated and analyzed using a steady state crystal population balance equation n n0 exp l g slopes on ln n versus crystal size l plots determine the parameter g a product of average crystal growth rate g and average crystal growth time the intercept is j g where j is nucleation rate known temperature depth distributions for the lava lake provide an estimate of effective growth time allowing nucleation and growth rates to be determined that are independent of any kinetic model plagioclase growth rates decrease with increasing crystallinity 9 9 5 4 10 11 cm s as do plagioclase nucleation rates 33 9 1 6 10 3 cm3 s ilmenite growth and nucleation rates also decrease with increasing crystallinity 4 9 3 4 10 10 cm s and 15 2 2 10 3 cm3 s respectively magnetite growth and nucleation rates are also estimated from the one sample collected below the magnetite liquidus g 2 9 10 10 cm s j 7 6 10 2 cm3 s moments of the population density function were used to examine the change in crystallization rates with time preliminary results suggest that total crystal volume increases approximately linearly with time after 50 crystallization a more complete set of samples is needed for material with 50 crystals to define the entire crystallization history comparisons of calculated crystallization rates with experimental data suggests that crystallization in the lava lake occurred at very small values of undercooling this interpretation is consistent with proposed thermal models of magmatic cooling where heat loss is balanced by latent heat production to maintain equilibrium cooling

what can crystal size distributions and olivine compositions tell us about magma solidification processes inside kilauea iki lava lake hawaii abstract lava lakes offer the opportunity to investigate magma solidification and can be considered as a proxy for small magma chambers here we present olivine compositions and crystal size distributions csds from scoria and drill core samples from kilauea iki lava lake which formed during the 1959 eruption of kilauea volcano hawaii three chemically distinct olivine populations were distinguished in the basis of their forsterite fo content 1 a high fo population fo86 90 2 an intermediate fo population fo78 82 and 3 a minor low fo population fo74 78 populations 1 and 2 both have deformed and undeformed crystals the third population may be the result of rejuvenation olivine in the lower 60 m of lake has a less fo rich composition and more crystals are deformed the csd analysis yields estimates of the average olivine residence time 1 60 years the shape of the olivine csds is fairly uniform with respect to depth curved csds are considered to be evidence of hybrid populations partly or totally involving crystal or magma mixing the turndown at the smallest sizes of most foundered crust and lake csds may be the result of coarsening making this process active both before and after eruption our csd modelling does not support significant crystal settling and overall convection in the lava lake although small advective currents are known to have occurred the olivine vertical stratification cannot be an original feature which is consistent with supposed strong stirring of the lake magma due to intense activity over the 17 eruptive phases it is also possible that independent basal feeding of the lake during the eruption may be needed to explain fully features of the chemical and mineralogical stratification

permeability and melt flow in simulated and natural partially molten basaltic magmas abstract a lattice boltzmann method is used to calculate grain scale low reynolds number single phase interstitial porous melt flow in two independent igneous microstructures 1 a microstructure simulated using a stochastic algorithm for progressive crystallization and 2 a natural microstructure obtained through x ray computed tomography ct of a partially melted basalt in both cases the error in the calculated flow field due to finite discretization and domain size has been estimated or demonstrated to be insignificant visually the porous melt flow tends to localize into high flux channels especially with increasing crystallinity and this impression is quantitatively confirmed by increasing skewness of the velocity distribution in the direction parallel to the imposed pressure gradient driving the flow a change from uniform to localized melt flow in naturally occurring situations may have a profound effect on the distribution of trace elements and if the melt is reactive the chemical and structural evolution of the igneous microstructure through localized phase change permeabilities of both microstructures are determined from the calculated steady flow field the permeabilities are then fitted to two different correlation models which are based on the rumpf gupte and carman kozeny relations in these models we express permeability as functions of melt fraction and either the mean crystal length or specific surface area extrapolated permeability to higher melt fractions using both correlation models for the partially melted basalt is shown to be within a factor of four of experimentally determined permeability of a similar sample we determine permeability estimates in the relatively unexplored melt fraction range of 30 80 and find consistency with previous work for permeability estimates in the melt fraction range of 20 30

understanding crystal populations and their significance through the magma plumbing system crystals are rarely composed of a single crystal population that have grown solely from the batch of magma in which they are resident on emplacement either by eruption or shallow intrusion close investigation of the majority of crystal populations reveal that they comprise up to four main components phenocrysts crystals co genetic with their magmatic host xenocrysts crystals wholly or in part foreign to the magmatic host and magma system antecrysts crystals which are recycled one or several times before inclusion in the host magma but have an origin within the magmatic system and microlites which represent small co genetic crystals which nucleate and grow rapidly on decompression and eruption textural analysis techniques are employed to quantify key aspects of the crystal population including crystal shape crystal size distributions spatial distribution patterns and textural modification using dihedral angles santorini provides a case study of an active volcanic system where a combined textural analysis study has been developed highlighting how the crystal population is being continuously modified by a series of replenishment and mixing events developing textural and microgeochemical techniques provides the next stage in the interrogation of crystal populations linking textures to isotopic heterogeneities and providing fingerprints of where crystals are sourced and re cycled

crystal size distributions csd in three dimensions insights from the 3d reconstruction of a highly porphyritic rhyolite growth histories and residence times of crystals in magmatic systems can be revealed by studying crystal sizes size distributions and shapes in this contribution serial sectioning has been employed on a sample of porphyritic rhyolite from a permo carboniferous laccolith from the halle volcanic complex germany to reconstruct the distribution of felsic phenocrysts in three dimensions in order to determine their true shapes sizes and three dimensional size distributions a model of all three phenocryst phases quartz plagioclase k feldspar with 217 crystals and a larger model containing 1599 k feldspar crystals was reconstructed in three dimensions the first model revealed a non touching framework of crystals in three dimensions suggesting that individual crystals grew freely in the melt prior to quenching of the texture however crystal shapes are complex and show large variation on a zingg diagram intermediate over long axis plotted against short over intermediate axis they often do not resemble the crystallographic shapes expected for phenocrysts growing unhindered from a melt indicating complex growth histories in contrast the three dimensional size distribution is a simple straight line with a negative slope stereologically corrected size distributions from individual sections compare well with stereologically corrected size distributions obtained previously from the same sample however crystal size distribution csd data from individual sections scatter considerably it is shown that csds can be robustly reproduced with a sampling size of greater than 200 crystals the kind of shape assumed in stereological correction of csds however has a large influence on the calculation and estimation of crystal residence times

dynamic triggering of creep events in the salton trough southern california by regional m 5 4 earthquakes constrained by geodetic observations and numerical simulations abstract since a regional earthquake in 1951 shallow creep events on strike slip faults within the salton trough southern california have been triggered at least 10 times by m 5 4 earthquakes within 200 km the high earthquake and creep activity and the long history of digital recording within the salton trough region provide a unique opportunity to study the mechanism of creep event triggering by nearby earthquakes here we document the history of fault creep events on the superstition hills fault based on data from creepmeters insar and field surveys since 1988 we focus on a subset of these creep events that were triggered by significant nearby earthquakes we model these events by adding realistic static and dynamic perturbations to a theoretical fault model based on rate and state dependent friction we find that the static stress changes from the causal earthquakes are less than 0 1 mpa and too small to instantaneously trigger creep events in contrast we can reproduce the characteristics of triggered slip with dynamic perturbations alone the instantaneous triggering of creep events depends on the peak and the time integrated amplitudes of the dynamic coulomb stress change based on observations and simulations the stress change amplitude required to trigger a creep event of a 0 01 mm surface slip is about 0 6 mpa this threshold is at least an order of magnitude larger than the reported triggering threshold of non volcanic tremors 2 60 kpa and earthquakes in geothermal fields 5 kpa and near shale gas production sites 0 2 0 4 kpa which may result from differences in effective normal stress fault friction the density of nucleation sites in these systems or triggering mechanisms we conclude that shallow frictional heterogeneity can explain both the spontaneous and dynamically triggered creep events on the superstition hills fault

the pilot knob magnetite deposit in the proterozoic st francois mountains terrane southeast missouri usa a magmatic and hydrothermal replacement iron deposit abstract the pilot knob magnetite deposit is located in southeast missouri within the 1380 1480 ma st francois mountains terrane rhyolitic trachytic volcanic rocks the deposit is tabular dips about 45 and is sill like in nature being approximately parallel to the bedding in the host tuffs the deposit was uncovered by erosion and exposed to weathering in the late proterozoic and is overlain in angular unconformity by the cambrian lamotte sandstone this proterozoic weathering cycle apparently had little effect on the deposit with only the updip edge being converted to hematite textural and mineralogical features of the deposit suggest a combined magmatic and hydrothermal replacement origin the magnetite rich ores that make up the bulk of the deposit are interpreted as having crystallized from an iron rich magma and a surrounding envelope of lower to moderate grade ores where magnetite has clearly replaced the tuffaceous host rocks are interpreted as hydrothermal in origin after the development of the higher grade magnetite ores and the envelope of lower to moderate grade ores late hydrothermal minerals were deposited as cross cutting veins and breccia fill the two most abundant minerals in the higher grade portions of the deposit are magnetite and albitic plagioclase and petrologically the higher grade ores could be described as a magnetite sodic syenite the most abundant gangue mineral within the lower grade impregnated envelope of ores around the higher grade ores is k feldspar apparently relict from the rhyolites trachytes thin lenses within the higher grade ores contain calcite as a matrix mineral to the magnetite and are considered to indicate carbonatitic affinity rare earth elements are elevated in one of five whole rock chemical analyses of the ores and the ree bearing mineral ferriallanite has been identified minor portions of the deposit below the proterozoic weathering cap consist of high grade hematite ores having equilibrium textures at depth the deposit is intruded by the shepherd mountain gabbro a 120 m thick near horizontal dike which resulted in minor contact metamorphism of the ore

magma dynamics beneath kameni volcano thera greece as revealed by crystal size and shape measurements size distributions of plagioclase crystals in series of recent porphyritic dacite lavas from kameni volcano greece can be modelled by mixing two populations of crystals each with overlapping linear crystal size distributions csd termed microlites and megacrysts the magmas bearing the microlites and megacrysts started to crystallise 6 13 and 24 96 years respectively before each eruption the dates of initiation of crystallisation of the megacrysts indicate that they are left overs of earlier injections of new magma into a shallow chamber some magma remains after each eruption and continues to crystallise new magma with few or no crystals is then introduced and the microlites crystallise from the mixed magma eruption followed 6 13 years after mixing such a model would suggest that some porphyritic magmas are products of a shallow magma chamber that is never completely emptied just topped up from time to time

wetting behavior of partial melts during crustal anatexis the distribution of hydrous silicic melts in polycrystalline aggregates of quartz the equilibrium distribution of hydrous silicic melts in polycrystalline aggregates of quartz was characterized in a series of partial melting and melt distribution experiments in the systems quartz albite orthoclase h2o and quartz anorthite h2o at 650 to 1000 mpa and 800 to 900 c near equilibrium textures in these experiments are characterized by very low quartz quartz melt wetting angles and by a substantial number of thin melt films along grain boundaries wetting angles in the h2o saturated experiments are as follows 18 at 800 c 1000 mpa and 12 at 900 c 1000 mpa in the granitic system 18 at 850 c 650 mpa 15 at 900 c 650 mpa and 15 at 900 c 1000 mpa in the quartzanorthite system in the granitic system at 900 c 1000 mpa a decrease of h2o content in melt from 17 wt at saturation to 6 wt results in a slight increase of wetting angle from 12 to 16 these low wetting angles and the observation that many grain boundaries are wetted by melt films indicate that the ratio of quartz quartz to quartz melt interfacial energies ss s1 is high 2 secondary electron imaging of fracture surfaces of melt poor samples provided a three dimensional insight into the geometry of melt at low melt fraction melt forms an interconnected network of channels along grain edges as predicted for isotropic systems with wetting angles below 60 this high permeability geometry suggests that the segregation of granitic melts is not as sluggish as previously anticipated simple compaction calculations for a permeability range of 10 12 to 10 9 m2 indicate that segregation may operate at low to moderate melt fractions below 30 vol within relatively short time scales i e 105 to 106 years quartzmelt textures show significant deviations from the equilibrium geometries predicted for isotropic partially molten systems the most consistent deviation is the pervasive development of crystallographically controlled planar faces of quartz these faces provide definitive evidence for non isotropic quartz melt surface energy for most silicates other than quartz the grain scale distribution of partial melts deviates even more significantly from equilibrium distributions in isotropic systems accordingly in order to describe adequately melt distributions in most natural source regions the equilibrium model should be modified to account for anisotropy of solid liquid interfacial energy

discovery of llandovery silurian graptolites and probable devonian corals in the southalpine metamorphic basement of the eastern alps agordo ne italy we report the discovery of aeronian middle llandovery graptolites and corals of probable devonian age in boudins hosted by greenschists within the southalpine metamorphic basement these discoveries provide key constraints to the depositional age range of the protoliths this remarkable occurrence of almost undeformed graptolites and compound corals in boudins within a metamorphic shear zone indicates very marked local strain partitioning

magmatic lineations inferred from anisotropy of magnetic susceptibility fabrics in units 8 9 and 10 of the rum eastern layered series nw scotland the eastern layered series of the rum layered suite nw scotland comprises a sequence of sixteen 30 150 m thick cyclic units the upper troctolite olivine gabbro parts of each of these units exhibit small scale modal layering and a pervasive layerparallel mineral lamination that is often associated with soft sediment deformation structures a sporadic macroscopic magmatic lineation measurable on mineral lamination surfaces is also observed in places anisotropy of magnetic susceptibility ams fabrics were studied in three of these cyclic units 8 9 and 10 in the northern part of the eastern layered series magnetic fabrics measured in the troctolites and gabbros yield one dominant trend in which magnetic foliations parallel magmatic layering and magnetic lineations trend nw se and plunge gently magnetic fabrics measured for two detailed traverses through unit 10 on the northern side of hallival also yield one dominant trend similar to that measured elsewhere in the eastern layered series however toward the centre of unit 10 in each traverse magnetic lineations sometimes plunge approximately downdip sw on the magnetic foliation planes the implications of these results are discussed with reference to previous textural and fabric observations on rum a model is suggested in which weak linear arrangements of cumulus olivine and plagioclase crystals are developed due to slumping and soft sediment deformation of unconsolidated crystal mushes during central sagging of the rum layered suite 2007 elsevier b v all rights reserved

variation of cooling rate with depth in lower crust formed at an oceanic spreading ridge plagioclase crystal size distributions in gabbros from the oman ophiolite 1 analysis of crystal size distributions csd of plagioclase in gabbros from the oman ophiolite indicates that cooling rates in the lower crust beneath a medium to fast spreading oceanic ridge did not vary smoothly with depth cooling rates in the upper half of the gabbro section were approximately 1 5 2 times faster than in the lower half of the gabbro section during igneous crystallization and or high temperature grain growth processes our results are inconsistent with thermal models for oceanic spreading ridges that approximate the effect of hydrothermal convection by using an enhanced thermal conductivity together with a conductive heat transfer mechanism instead the oman csd data are consistent with recent seismic and modeling studies that suggest that hydrothermal convection leads to closely spaced near vertical isotherms in the upper half of the plutonic section within a few kilometers of the ridge axis

magma solidification processes beneath kilauea volcano hawaii a quantitative textural and geochemical study of the 1969 1974 mauna ulu lavas sents a late magma component formed in the summit magma storage region our results are consistent with the hypothesis that the components of the mu magmas followed two different routes the deformed olivine bearing magma moved along the deep basal

recycling of k feldspar antecrysts in the baishiya porphyritic granodiorite east kunlun orogenic belt northern tibet plateau implications for magma differentiation in a crystal mush reservoir abstract it is popular in geochemical models to assume that chemical differentiation occurs by crystal fractionation from high melt fraction magma reservoirs however a crystal mush reservoir characterized by low melt fraction has been gradually accepted in the past decade magma differentiation in this scenario remains poorly understand located in the east kunlun orogenic belt northern tibet plateau the baishiya granodiorite is an ideal example to investigate magma reservoir processes although major elements of the baishiya granodiorite are relatively homogeneous there is a distinct variation of magmatic texture trace elements concentrations and isotopic ratios from top to bottom the textural and geochemical signatures above cannot be explained by assimilation fractionation crystallization magma mixing or convective self mixing alone within the concept model of crystal mush we propose a multistage formation process of the studied granodiorite first a rhyolitic mushy reservoir once existed it was replenished by episodic basaltic melts from below resulting in the textural coarsening of k feldspar when the heat and or melts injection was high enough the crystal mush could be gradually rejuvenated and subsequently stirred some k feldspar antecrysts would be partly recycled to form mantled plagioclase through convective self mixing thus the evolved and buoyancy melts exhibited an equilibrated geochemical signature with plagioclase and ultimately formed the porphyry phase on the top moreover recycling of k feldspar antecrysts contributed to a depletion of heavy rare earth elements and y contents as well as an elevation of cr concentrations and eu eu ratios in the residual crystal mush and finally formed the porphyritic granodiorite due to a continuous injection and convective self mixing the overall magma reservoir became more mafic gradually until it reached a granodioritic composition within a waning intensity of magma flux the magma reservoir would be locked again the injected melts would go through a rapid crystallization and subsequently form microlites such as the dioritic enclaves and the ground mass of the studied granodiorite consequently traditional mechanisms that are based on low crystallinity magmas may be a specific part of the protracted history rather than the whole story of the magma reservoir geochemical index of granitoid rocks should be used with caution due to this inherited affinity it should be prerequisite to investigate crystal genesis carefully before utilizing geochemical diagrams

ominelite fe mg al3bsio9 fe2 analogue of grandidierite a new mineral from porphyritic granite in japan ominelite fe mg al3bsio9 is the fe2 analog of grandidierite the mineral occurs as elongated and euhedral to equant and anhedral grains in close association with sekaninaite fe dominant analogue of cordierite garnet biotite andalusite topaz alkali feldspar plagioclase muscovite quartz dumortierite schorl zircon ilmenite apatite monazite and pyrite in a porphyritic granite of miocene age exposed along the misen river in tenkawa yoshino nara prefecture japan 34 12 40 n 135 53 40 e temperatures r major lines in the powder pattern d in a i hkl are 5 57 m 020 5 21 vs 200 3 73 m 121 3 51 m 130 2 97 s 101 2 79 s 040 2 18 s 150 421 312 space group is pbnm lattice parameters are a 10 343 2 b 11 095 1 c 5 7601 8 a and v 661 0 2 a3 z 4 d calc 3 169 g cm3 refinement of the structure confirms that ominelite is isostructural with grandidierite with no detectable substitution of al by fe3

quantifying the building blocks of igneous rocks are clustered crystal frameworks the foundation most phenocryst populations in volcanic rocks and those preserved in shallow level igneous intrusions are clustered variously referred to as clots clumps or glomerocrysts these clusters of crystals are the building blocks that accumulate to form the high porosity touching crystal frameworks from which igneous cumulates form examination of touching crystal frameworks in olivine komatiite cumulates and experimental charges and plagioclase dominant crystal populations holyoke flood basalt connecticut usa reveal complex high porosity clustered crystal arrangements olivine touching frameworks in komatiite flows are interpreted to form in hundreds of days plagioclase frameworks are calculated to have formed in less than 17 years for a crystal growth rate of 1 x 10 10 mm s to less than 3 years for a growth rate of 5 x 10 10 mm s based on crystal size distributions the origin of crystal clusters is likely to involve either or a combination of heterogeneous nucleation remobilization of cumulate mushes or crystals sticking together during settling and or flow the spatial distribution pattern of clustered crystal frameworks from both natural and experimental examples constrains fields on spatial packing diagrams that allow the identification of touching and non touching crystal populations and further improve our understanding of crystal packing arrangements and cluster size distributions

crystal size distributions derived from 3d datasets sample size versus uncertainties crystal size distributions csd are the most commonly studied character in quantitative textural investigations of igneous rocks the quality of csd depends fundamentally on the sample size i e total number of crystals here we use 3d x ray tomographic datasets of two early erupted bishop tuff pumice clasts comprising 849 and 446 quartz crystals to investigate the effect of sample size on the quality of the quartz size distributions because csd are obtained using a counting procedure uncertainties related to counting statistics can be used as minimum estimates of error given that most natural samples are characterized by a decreasing number of crystals with increasing crystal size uncertainties tend to increase markedly with crystal size and the number of small crystals to be counted grows very quickly with increasing sample size accordingly with as few as 100 crystals in total it is possible to properly estimate the population densities for small size bins 20 80mm however to obtain meaningful estimates across four bin sizes 20 320mm at least 250 crystals but preferably 400 crystals are needed to minimize the total number of crystals counted and keep the uncertainties on the larger size ranges within reasonable values it becomes necessary to study multiple volumes at variable spatial resolution

on the cluster analysis of grains and crystals in rocks cluster analysis has the potential to quantify the size and characteristics of groups or clusters of grains and crystals within a rock texture we present two techniques 1 the complete linkage hierarchical cluster analysis clhca technique that we use to analyze grain center distributions and 2 the density linkage cluster analysis dlca technique that we use to analyze grain boundary distributions clhca applies a cluster algorithm to the distance matrix calculated from grain center coordinates this produces a hierarchical cluster distribution that is characteristic of the spatial pattern of the texture this cluster distribution is normalized to that of a random distribution of points to identify clustered and ordered patterns in the data the technique successfully identified 3 d cluster sizes from 2 d sections of a modal data set in the application to real rock textures the clhca of a komatiite cumulate identified a glomerocryst population with cluster sizes in the range of 0 3 2 5 mm and also a variation of cluster patterns up through the cumulate pile the clhca of a polymodal texture from a pyroxene scapolite sphene granulite indicated a clustered distribution for the sphene which was restricted in growth pattern by the pyroxene and scapolite in the texture dlca computes a single solution of clusters that conforms to the search criteria input into the algorithm dlca performed poorly when used to identify distributions of large randomly packed clusters of small spheres mainly identifying smaller cluster patterns within each large cluster application of dlca to the komatiite cumulate example indicated cluster lengths of 0 72 0 80 mm similar to the clhca results and an average aspect ratio of 1 52

enhanced crystal fabric analysis of a lava flow sample by neutron texture diffraction a case study from the castello d ischia dome 1 the crystal fabric of a lava has been analyzed for the first time by neutron texture diffraction in this study we quantitatively investigate the crystallographic preferred orientation of feldspars in the castello d ischia ischia island italy trachytic exogenous dome the crystallographic preferred orientation was measured with the monochromatic neutron texture diffractometer sv7 at the forschungszentrum julich in germany and a rietveld refinement was applied to the sum diffraction pattern the complementary thin section analysis showed that the three dimensional crystal shape and the corresponding shape preferred orientation are in agreement with the quantitative orientation distributions of the neutron texture data the 0k0 crystallographic planes of the feldspars are roughly parallel to the local flow bands whereas the other corresponding pole figures show that a pivotal rotation of the anorthoclase and sanidine crystals was active during the emplacement of this lava dome in combination with scanning electron microscopy investigations electron probe microanalysis xrf and x ray diffraction the rietveld refinement of the neutron diffraction data indicates a slow cooling dynamic on the order of several months during their crystallization under subaerial conditions results attained here demonstrate that neutron texture diffraction is a powerful tool that can be applied to lava flows

on the use of changes in dihedral angle to decode late stage textural evolution in cumulates the melt filled pore structure in the final stages of solidification of cumulates must lie somewhere between the two end members of impingement in which pore topology is controlled entirely by the juxtaposition of growth faces of adjacent grains and textural equilibrium in which pore topology is controlled by the minimization of internal energies the exact position between these two end members is controlled by the relative rates of crystal growth and textural equilibration for samples in which growth has stopped or is very slow textural equilibrium will prevail a close examination of dihedral angles in natural examples demonstrates that these two end member textures can be distinguished the impingement end member results in a population of apparent solid melt dihedral angles with a median of 60 and a standard deviation of 25 30 whereas the texturally equilibrated end member population has a median of 28 and a standard deviation of 14 for the specific case of cumulates in the rum layered intrusion residual porosity in troctolitic cumulates was close to the impingement end member whereas that in peridotites was close to melt bearing textural equilibrium suites of glass bearing samples from small or frequently disturbed magma systems show modification of initial impingement textures these modifications may be a consequence of textural equilibration or of diffusion limited growth during quenching distinction can be made between these two processes by a consideration of grain shape the geometry of interstitial phases in suites of fully solidified cumulates from the rum layered intrusion shows variable approach to sub solidus textural equilibrium from an initial state inherited by pseudmorphing of the last melt textural equilibration at pore corners occurs as a continuous process with a gradual movement of the entire dihedral angle population towards the equilibrium final state if the initial pseudomorphed state is one of disequilibrium i e a melt present impingement texture this change is accompanied by a reduction in the spread of the population if it is one of equilibrium the change is accompanied by an initial increase in the spread of the population followed by a decrease these observations demonstrate that previously published models of dihedral angle change involving the instantaneous establishment of the equilibrium angle in the immediate vicinity of the pore corner are incorrect

correlating tephras and cryptotephras using glass compositional analyses and numerical and statistical methods review and evaluation abstract we define tephras and cryptotephras and their components mainly ash sized particles of glass crystals in distal deposits and summarize the basis of tephrochronology as a chronostratigraphic correlational and dating tool for palaeoenvironmental geological and archaeological research we then document and appraise recent advances in analytical methods used to determine the major minor and trace elements of individual glass shards from tephra or cryptotephra deposits to aid their correlation and application protocols developed recently for the electron probe microanalysis of major elements in individual glass shards help to improve data quality and standardize reporting procedures a narrow electron beam diameter 3 5 m can now be used to analyze smaller glass shards than previously attainable reliable analyses of microshards defined here as glass shards in part 2 of the review we describe critically assess and recommend ways in which tephras or cryptotephras can be correlated in conjunction with other information using numerical or statistical analyses of compositional data statistical methods provide a less subjective means of dealing with analytical data pertaining to tephra components usually glass or crystals phenocrysts than heuristic alternatives they enable a better understanding of relationships among the data from multiple viewpoints to be developed and help quantify the degree of uncertainty in establishing correlations in common with other scientific hypothesis testing it is easier to infer using such analysis that two or more tephras are different rather than the same adding stratigraphic chronological spatial or palaeoenvironmental data i e multiple criteria is usually necessary and allows for more robust correlations to be made a two stage approach is useful the first focussed on differences in the mean composition of samples or their range which can be visualised graphically via scatterplot matrices or bivariate plots coupled with the use of statistical tools such as distance measures similarity coefficients hierarchical cluster analysis informed by distance measures or similarity or cophenetic coefficients and principal components analysis pca some statistical methods cluster analysis discriminant analysis are referred to as machine learning in the computing literature the second stage examines sample variance and the degree of compositional similarity so that sample equivalence or otherwise can be established on a statistical basis this stage may involve discriminant function analysis dfa support vector machines svms canonical variates analysis cva and anova or manova or its two sample special case the hotelling two sample t2 test randomization tests can be used where distributional assumptions such as multivariate normality underlying parametric tests are doubtful compositional data may be transformed and scaled before being subjected to multivariate statistical procedures including calculation of distance matrices hierarchical cluster analysis and pca such transformations may make the assumption of multivariate normality more appropriate a sequential procedure using mahalanobis distance and the hotelling two sample t2 test is illustrated using glass major element data from trachytic to phonolitic kenyan tephras all these methods require a broad range of high quality compositional data which can be used to compare unknowns with reference training sets that are sufficiently complete to account for all possible correlatives including tephras with heterogeneous glasses that contain multiple compositional groups currently incomplete databases are tending to limit correlation efficacy the development of an open online global database to facilitate progress towards integrated high quality tephrostratigraphic frameworks for different regions is encouraged

textural maturity of cumulates a record of chamber filling liquidus assemblage cooling rate and large scale convection in mafic layered intrusions textural maturity describes the extent to which a rock has evolved from the initial reaction controlled texture towards textural equilibrium controlled by the minimization of interfacial energy solidification in a magma chamber results in the formation of an impingement texture by the random juxtaposition of planar sided grains orthocumulates in which the initial melt filled pores are pseudomorphed by later crystallizing phases have an ophitic or intersertal texture immediately after complete solidification which then evolves towards solid state equilibrium by rounding of initially planar grain boundaries and an increase in the median dihedral angle subtended at the junctions of two primocrystic grains with the interstitial phase the bulk of the increase in angle occurs just below the solidus temperature in kilometre scale mafic plutons quantification of textural maturity via measurement of dihedral angle populations in troctolitic and gabbroic cumulates from the rum eastern layered intrusion and the skaergaard intrusion demonstrates that the rocks preserve a record of thermal events related to magma chamber replenishment and the onset of chamber wide convection textural maturity is also a function of the liquidus phase assemblage for systems in which only olivine and plagioclase are liquidus i e cumulus phases in the main magma body above the crystal mush the texture is significantly less mature than that in systems in which clinopyroxene is an additional liquidus phase the difference in textural maturity reflects differences in the cooling and solidification rate and demonstrates directly that the liquidus phase assemblage plays a role in determining the thermal history of plutons

origin of k feldspar megacrysts in rhyolites from the emeishan large igneous province southwest china abstract silicic rocks occur in the uppermost units of the longest volcanic succession 5000 m thick in the binchuan area of the permian emeishan flood basalt province of sw china they are predominantly rhyolites and to a lesser extent trachytes both containing potassium feldspar megacrysts as the dominant phenocryst phase up to approximately 20 mm in size these megacrysts contain domains of albite arranged in vein like networks likely formed by post magmatic alteration crystal size distributions csd suggest that these megacrysts grew in a stable magmatic system consistent with relatively uniform core to rim compositional k 2 o 14 16 wt and isotopic profiles 208 pb 206 pb ratios 2 06 2 08 0 005 both whole rock trace elements and pb isotope ratios of these silicic rocks are similar to the emeishan basalts suggesting a common source for both mafic and felsic units and a limited role of crustal melting in genesis of the felsic units major and trace element models further indicate that these rocks could not have formed exclusively by re melting of old crust or solidified basaltic rock but must have formed through crystal fractionation from the flood basalts or possibly partial melting of basaltic rock followed by fractional crystallization k feldspar bearing rhyolites are also observed in the last stages of other large igneous provinces we suggest that they represent final melt fractions and their appearance in the magmatic system coincides with waning of voluminous magmatic activities

interaction of arc magmas with subvolcanic hydrothermal systems insights from compositions and metasomatic textures of olivine crystals in fresh basalts of daisen and mengameyama western honshu japan