anomalously low sodium morb magmas evidence for depleted morb or analytical artifact abstract one common characteristic of quenched natural basaltic glass is the presence of microcrystalline halos surrounding many microphenocrysts spherulites from our investigations of the composition of basaltic grasses in both quenched lavas and in plagioclase hosted melt inclusions we have discovered that quench halo portions of spherulites are over 100 times as susceptible to na loss during microprobe analysis than normal basaltic glass this implies that there may be a significant negative bias in published morb glass na contents this in turn would result in potential systematic errors in existing models of morb petrogenesis that are dependent on those data

non newtonian rheology of igneous melts at high stresses and strain rates experimental results for rhyolite andesite basalt and nephelinite the stress strain rate relationships of four silicate melt compositions high silica rhyolite andesite tholeiitic basalt and nephelinite have been studied using the fiber elongation method measurements were conducted in a stress range of 10 400 mpa and a strain rate range of 10 6 to 10 3 s 1 the stress strain rate relationships for all the melts exhibit newtonian behavior at low strain rates but non newtonian nonlinear stress strain rate behavior at higher strain rates with strain rate increasing faster than the applied stress the decrease in calculated shear viscosity with increasing strain rate precedes brittle failure of the fiber as the applied stress approaches the tensile strength of the melt the decrease in viscosity observed at the high strain rates of the present study ranges from 0 25 to 2 54 log10 pa s the shear relaxation times of these melts have been estimated from the low strain rate newtonian shear viscosity using the maxwell relationship s g non newtonian shear viscosity is observed at strain rates time 1 equivalent to time scales that lie 3 log10 units of time above the calculated relaxation time brittle failure of the fibers occurs 2 log10 units of time above the relaxation time this study illustrates that the occurrence of non newtonian viscous flow in geological melts can be predicted to within a log10 unit of strain rate high silica rhyolite melts involved in ash flow eruptions are expected to undergo a non newtonian phase of deformation immediately prior to brittle failure

rheology of bubble bearing magmas the rheology of bubble bearing suspensions is investigated through a series of three dimensional boundary integral calculations in which the effects of bubble deformation volume fraction and shear rate are considered the behaviour of bubbles in viscous flows is characterized by the capillary number ca the ratio of viscous shear stresses that promote deformation to surface tension stresses that resist bubble deformation estimates of ca in natural lava flows are highly variable reflecting variations in shear rate and melt viscosity in the low capillary number limit e g in carbonatite flows bubbles remain spherical and may contribute greater shear stress to the suspension than in high capillary number flows in which bubble deformation is significant at higher ca deformed bubbles become aligned in the direction of flow and as a result contribute less shear stress to the suspension calculations indicate that the effective shear viscosity of bubbly suspensions at least for ca 0 5 is a weakly increasing function of volume fraction and that suspensions of bubbles are shear thinning field observations and qualitative arguments however suggest that for sufficiently large ca ca greater than about 1 the effective shear viscosity may be less than that of the suspending liquid bubbles reach their quasi steady deformed shapes after strains of order one for shorter times the continuous deformation of the bubbles results in continual changes of rheological properties in particular for small strains the effective shear viscosity of the suspension may be less than that of the liquid phase even for small ca results of this study may help explain previous experimental theoretical and field based observations regarding the effects of bubbles on flow rheology

multi stage growth and fluid evolution of a hydrothermal sulphide chimney in the east pacific ridge 1 2 s hydrothermal field constraints from in situ sulphur isotopesx meng and othersin situ sulphur isotopes of hydrothermal sulphides sulphur isotopes can be used as a powerful tool to trace fluid evolution and explore the formation of chimneys to clarify the in situ s isotopic variations of sulphides at the micro scale we analyzed a sulphide chimney collected from the hydrothermal field in the east pacific rise 1 2 s using a sensitive high mass resolution ion micro probe for stable isotopes shrimp si three mineral zones can be identified in the chimney an external outer wall of porous anhydrite and colloform pyrite an internal middle zone of sub euhedral pyrite and massive chalcopyrite and an inner zone of massive pyrite the 34 s v cdt values of the sulphides fall within the range 1 83 7 51 avg 4 05 n 16 and s isotopic values increase from the core 3 09 n 3 to the middle 3 78 n 11 to the edge 6 99 n 2 these results illustrate mineral crystallization processes and the mixing between seawater derived s and magmatic hydrothermal fluids during the growth of the chimney the zones from the edge to the core are characterized by crystal morphologies of colloform anhedral pyrite to massive pyrite with decreasing 34 s values revealing multi stage mineral deposition and sulphur isotopic fractionation in contrast to the increase in 34 s values from the core to the edge in one profile profile a anomalously low 34 s values in fine grained pyrite relative to chalcopyrite in another profile profile b in the middle zone result from s isotopic exchange between seawater so 4 2 and fluid h 2 s due to different fluid seawater mixing possibly caused by variations in permeability and porosity across the chimney

rheology of bimodal crystals suspensions results from analogue experiments and implications for magma ascent 1 the effect of crystal size of bimodal suspensions on rheology of magmas at strain rates between 0 and 1 s 1 is studied suspensions consist of silicon oil and two populations of natural crystals with size 63 125 and 250 500 m mixed in different proportions the total solid fraction of the mixtures is between 0 25 and 0 5 at 0 4 finer coarser and bimodal suspensions display comparable viscosities at 0 4 the viscosity of the bimodal suspensions is larger than that of the unimodal ones the bimodal suspension made mainly of finer crystals shows a stronger increase of viscosity with the addition of finer crystals to a suspension of coarser ones produces a more pronounced increase of viscosity with respect to suspensions of coarse or fine crystals alone and of finer crystals with added coarser ones the bimodal suspensions of coarser crystals develops yield stress at 0 25 the others at 0 4 it is modeled the ascent velocity in a 20 m wide dike of magmas with bimodal and unimodal populations of crystals of different size for 0 4 the crystal size has not effects on the ascent velocity of magmas for 0 4 the velocity of a magma with growing phenocrystals decreases as increases less than that of a magma with forming microlites and more of a magma with microlites and growing phenocrystals a magma with phenocrystals and forming microlites has the lowest ascent velocity

mechanism of small vulcanian eruptions at suwanosejima volcano japan as inferred from precursor inflations and tremor signals we examine precursory signals of vulcanian eruptions at suwanosejima volcano southwest of japan by deploying seismic and tilt stations close to the active crater to understand the shallow conduit processes just before explosions vulcanian eruptions at suwanosejima for the period from october 2009 to 2011 are often preceded by a sudden cessation of continuous tremor associated with continuous ash emissions the amplitude of continuous tremor decreases within about 10 s and tilt signal starts to show uplift of the active crater then the pause of continuous tremor and uplift continue for about 1 2 min and tilt amplitudes reach a few tens of nanoradians at a distance of 400 m from the active crater as the pause time of continuous tremor before explosion becomes longer the maximum amplitude of explosion earthquake and uplift signal become larger vulcanian eruptions are also observed during periods without continuous tremor in these cases tilt signals capture uplifts of the active crater for about 10 min before explosions and reach a few tens of nanoradians cessations of volcanic gas emissions are observed before some explosions during periods without continuous tremor mori et al 2011 these observations suggest that pressurization in the shallow conduit is caused by an accumulation of volcanic gases and ash through the formation of cap in the conduit possibly composed of stiffened magma due to degassing cooling rheological changes or other mechanisms

multi channel seismic imaging of a crustal magma chamber along the east pacific rise a reflection observed on multi channel seismic profiles along and across the east pacific rise between 8 50 n and 13 30 n is interpreted to arise from the top of a crustal magma chamber located 1 2 2 4 km below the sea floor the magma chamber is quite narrow 4 6 km wide but can be traced as a nearly continuous feature for tens of kilometres along the rise axis

east pacific rise near 13 n geology of new hydrothermal fields abundant massive sulfide deposits are present at the crest of the east pacific rise near 13 north where the opening rate is about 12 centimeters per year large manganese and helium 3 anomalies in seawater samples evidence of intense present day activity of hydrothermal springs indicate that sulfides are still being produced along this segment of the rise massive sulfides also occur on adjacent off axis seamounts

relating vesicle shapes in pyroclasts to eruption styles vesicles in pyroclasts provide a direct record of conduit conditions during explosive volcanic eruptions although their numbers and sizes are used routinely to infer aspects of eruption dynamics vesicle shape remains an underutilized parameter we have quantified vesicle shapes in pyroclasts from fall deposits of seven explosive eruptions of different styles using the dimensionless shape factor omega a measure of the degree of complexity of the bounding surface of an object for each of the seven eruptions we have also estimated the capillary number ca from the magma expansion velocity through coupled diffusive bubble growth and conduit flow modeling we find that omega is smaller for eruptions with rm ca ll 1 than for eruptions with ca gg 1 consistent with previous studies we interpret these results as an expression of the relative importance of structural changes during magma decompression and bubble growth such as coalescence and shape relaxation of bubbles by capillary stresses among the samples analyzed strombolian and hawaiian fire fountain eruptions have rm ca ll 1 in contrast to vulcanian plinian and ultraplinian eruptions interestingly the basaltic plinian eruptions of tarawera volcano new zealand in 1886 and mt etna italy in 122 bc for which the cause of intense explosive activity has been controversial are also characterized by rm ca gg 1 and larger values of omega than strombolian and hawaiian style fire fountain eruptions we interpret this to be the consequence of syn eruptive magma crystallization resulting in high magma viscosity and reduced rates of bubble growth our model results indicate that during these basaltic plinian eruptions buildup of bubble overpressure resulted in brittle magma fragmentation

melt inclusions as indicators of parental magma diversity on the northern east pacific rise the axial plumbing system is recognized as the site of much of the chemical processing that takes place at mid ocean ridges however the extent of that processing and the characteristics of the original parental components are difficult to characterize using the lavas that erupted at the surface alone to better understand the relative roles of different magmatic processes in the formation of axial and off axis magma systems we have studied plagioclase and olivine hosted melt inclusions from two axial segments 10 30 0 n and 11 20 0 n and four seamounts between 5 47 0 n and 9 17 0 n of the northern east pacific rise epr these data are a potential source of information on the characteristics of precursor magmas by comparing the compositions of the inclusions with those of the host lava suite one can discern the nature of the intervening processes the melt inclusions found in these axial and seamount lavas were rehomogenized and analyzed by electron and ion microprobe for major and trace elements the lava groups and their inclusions overlap and contain very similar n morb compatible and incompatible element concentrations with the exception of one n morb host lava which contains both n and e morb inclusions inclusion compositions are co linear with and generally fall at the primitive end of the host lava suites inclusion diversity i e the chemical variation in melt inclusion compositions within a single sample decreases with decreasing mgo probably representing contemporaneous mixing and fractionation seamount lavas differ from axial lavas in that they are more crystalrich and they contain a greater number of inclusions that are generally more primitive in addition they exhibit a larger compositional range in both the incompatible major and trace elements axial and seamount lavas have comparable crystal assemblages and chemistry melt inclusion diversity and range of compositions all these characteristics suggest that axial and seamount magmas are formed in the same mantle melting regime we believe that axial and seamount magmas are created from a single parent magma array derived by the melting of a relatively homogeneous source the parent magmas undergo an initial stage of fractionation and mixing then the axial and seamount magma paths diverge axial lavas continue through the axial magma chamber amc becoming more fractionated and having more phenocrysts removed possibly in the upper melt lens seamount magmas travel to their volcanoes without further significant fractionation and crystal separation the east pacific rise differs from slow and moderate spreading rate ridges amar juan de fuca jdf gorda and seir in its lack of phyric lavas scarcity of inclusions lack of chemical variation between melt inclusions from the same crystal lack of overall compositional variability and absence of e morb inclusions in the majority of the n morb host lavas suggesting that epr must have a fundamentally different axial plumbing system characterized by more extensive fractionation and mixing in the upper mantle and lowermost crust d 2002 published by elsevier science b v

magma production and growth of the lava dome of the soufriere hills volcano montserrat west indies november 1995 to december 1997 from november 1995 to december 1997 a total volume of 246 106 dre m of andesite magma erupted partitioned into 93 106 m of the dome 125 106 m of pyroclastic flow deposits and 28 106 m of explosive ejecta in the first 11 weeks magma discharge rate was low 0 5 m s from february 1996 to may 1997 discharge rates have averaged 2 1 m s but have fluctuated significantly and have increased with time three pulses lasting a few months can be recognised with discharge rates reaching 3 to 8 m s short term pulsations in growth lasting a few days reach discharge rates of over 10 m s and there are periods of days to a few weeks when dome growth is 0 5 m s discharge rate increased from may 1997 with an average rate of 7 5 m s to december 1997 the observations indicate an open magmatic system

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

constraining past seawater δ18o and temperature records developed from foraminiferal geochemistry paired measurements of magnesium to calcium ratios mg ca and the stable oxygen isotopic composition 18o in foraminifera have significantly advanced our knowledge of the climate system by providing information on past temperature and seawater 18o 18osw a proxy for salinity and ice volume however multiple sources of uncertainty exist in transferring these downcore geochemical data into quantitative paleoclimate reconstructions here we develop a computational toolkit entitled paleo seawater uncertainty solver psu solver that performs bootstrap monte carlo simulations to constrain these various sources of uncertainty psu solver calculates temperature and 18osw and their respective confidence intervals using an iterative approach with user defined errors calibrations and sea level curves our probabilistic approach yields reduced uncertainty constraints compared to theoretical considerations and commonly used propagation exercises we demonstrate the applicability of psu solver for published records covering three timescales the late holocene the last deglaciation and the last glacial period we show that the influence of salinity on mg ca can considerably alter the structure and amplitude of change in the resulting reconstruction and can impact the interpretation of paleoceanographic time series we also highlight the sensitivity of the records to various inputs of sea level curves transfer functions and uncertainty constraints psu solver offers an expeditious yet rigorous approach to test the robustness of past climate variability inferred from paired mg ca 18o measurements

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

methods of determining the rheological properties of magmas at sub liquidus temperatures non vesicular basaltic melts behave as newtonian fluids at temperatures above their liquidus and their viscosities can be calculated using a method developed by shaw 1972 and bottinga and weill 1972 because many igneous processes involve the flow of silicates at sub liquidus temperatures numerous attempts have been made to calculate the interactive effects of the crystal phase however current methods are appropriate only for relatively low crystal concentrations and they assume newtonian behaviour we argue that this assumption is invalid when bubble or crystal concentrations exceed 30 at higher concentrations factors other than concentration become increasingly important these include particle shape and size distribution a method which takes these factors into account is tested on a range of suspensions including magmas at sub liquidus temperatures and rheological properties calculated using this method agree closely with the measured values we also demonstrate that an equation which was introduced to explain large differences in measured apparent viscosities during the cooling and crystallisation of mount st helens dacite murase et al 1985 and which is currently used to calculate the rheological properties of crystallising lavas generates viscosities which may be in error by several orders of magnitude this difference is argued to be caused by a combination of factors including the ten orders of magnitude range in the strain rates utilised during the mount st helens measurements causing orders of magnitude difference in the resulting apparent viscosities rheological data on crystallising silicic melts are reinterpreted taking into account the non newtonian rheology of the magmas and changes in activation energy of flow during crystallisation

mineralogic and climatic interpretations of the luochuan loess section china based on diffuse reflectance spectrophotometry we examined the top 135 m that is the entire pleistocene of the classic luochuan section on the chinese loess plateau with a diffuse reflectance spectrophotometer from the near ultraviolet through the visible and into the near infrared from the reflectance data we calculated sample brightness which with some caveats is a reasonable proxy for magnetic susceptibility mineralogic changes were identified by factor analyzing the first derivative of the percent reflectance data and examining samples with high factor scores two factors which explain about 96 of the cumulative variance are distinguished by the relative proportion of hematite and goethite the minerals that are responsible for the color changes in the loess sequence both hematite and goethite are present in both loess and paleosol but goethite dominates in loess whereas hematite dominates in paleosol the goethite factor exhibits an inverse correlation with magnetic susceptibility the hematite factor exhibits a weak positive correlation with susceptibility paleoclimatic interpretations are drawn from comparison of susceptibility to the concentration of spectrally identified hematite based on this comparison paleosols in the early pleistocene wucheng formation are characterized by conditions that are drier than today a dry summer monsoon whereas later pleistocene paleosols are characterized by a wet summer monsoon

the axial summit graben and cross sectional shape of the east pacific rise as indicators of axial magma chambers and recent volcanic eruptions abstract the axis of the east pacific rise epr undulates up and down hundreds of meters over distances of 30 200 km along strike the deep areas occurring at transform faults and other ridge axis discontinuities such as overlapping spreading centers oscs we have suggested that systematic variations in depth and cross sectional shape of the rise are indicators of the changes in the local axial magmatic budget along a given ridge segment 1 a comparison of recently collected multichannel seismic mcs data 2 with our sea beam and seamarc ii data have allowed us to test and advance this hypothesis along the epr from 9 to 13 n there is an excellent correlation between three parameters that are all directly related to the phase of a magmatic cycle along a given ridge segment the cross sectional shape of the rise the presence or absence of an axial summit graben and the presence or absence of a shallow axial magma chamber as interpreted from mcs data where the axial magma chamber is present the cross sectional shape of the ridge is broad and an axial summit graben is recognized along the axis in contrast where the cross sectional shape of the rise is narrow and triangular an axial magma chamber is not detected and an axial summit graben is absent these ridge axis characteristics tend to occur along deeper portions of a given ridge segment often near ridge axis discontinuities we suggest that these systematic variations in ridge axis morphology cross sectional shape and structure presence or absence of an axial graben reflect spatial and temporal variations in the magmatic budget of the ridge axis where the magmatic budget is waxing shallow level magma reservoirs in the crust and underlying upper mantle swell creating a broad axial bulge with a summit graben where the magmatic budget is diminished the crustal magma chamber is small this proposed correlation of shape structure and magmatic parameters fails along only two short portions of the ridge in these areas there is evidence for an axial magma chamber and the rise has a broad cross sectional shape but there is no summit graben bottom photographs and submersible results however show that in these areas the rise crest is covered with very fresh lavas undisrupted by faulting suggesting that the summit graben has been recently filled in by lava flows and the development of a summit graben or a linear caldera by volcano tectonic collapse has not yet occurred

oscillatory rheology measurements of particle and bubble bearing fluids solid like behavior of a crystal rich basaltic magma the rheology of crystal and bubble bearing magmas governs the propagation of seismic waves as well as eruption dynamics here rheology includes viscous and elastic components and their ratio known as attenuation we perform an oscillatory rheology measurements which provide storage elastic component and loss viscous component moduli and attenuation with frequency dependence using particle and bubble bearing fluids whose liquid viscosity is in the range of that of a basaltic melt we find that both the storage and loss moduli dramatically increase with the particle fraction but weakly depend on the bubble fraction solid like behavior equivalent to attenuation 40 vol the shallow conduit of stromboli volcano filled by a crystal rich and low viscosity basaltic magma may be an example where shear waves propagate and brittle fractures occur to cause explosive eruptions because of its high crystallinity

rheology of crystal bearing silicate melts an experimental study at high viscosities the viscosity of partially crystallized mg3al2si3o12 melts has been measured under uniaxial compression in the interval 1010 1013 poise as a function of the volume fraction of crystals these inclusions are well rounded spherulites of aluminous enstatite having the same composition as the melt and whose growth rate is negligible at the temperature of the measurements the viscosity increases by less than 1 order of magnitude for crystal fractions of 40 vol and remains newtonian up to the maximum stress exerted namely 1 kbar the einstein roscoe equation 0 1 m n provides very good fits to the measurements only if either the m or n parameter is allowed to depend on temperature for modeling of magmatic processes however the widely recommended constant values m 0 6 and n 2 5 should be adequate the rheology changes abruptly when the clustered spherulites begin to oppose shear deformation at a crystal fraction of about 40 vol the viscosity becomes non newtonian with yield strengths of a few tens of bars at temperatures at which the viscosity of the melt is higher than 1010 poise as long as the crystal fraction remains lower than 70 vol the deformation proceeds in an irregular manner with a nonuniform distribution of crystals and melt the deformation becomes again regular at low stresses with lower melt fractions but samples undergo extensive fracturation along the direction of uniaxial stress similar rheology changes have been observed during the isothermal crystallization of li2si2o5 melts which produces small ellipsoidal inclusions these results suggest that the influence of solid suspensions on the rheology of magmas is primarily determined by the crystal fraction even though additional measurements would be useful to determine the possible influence of other factors such as the size distribution or the shape of the inclusions

the effects of shape on crystal settling and on the rheology of magmas the effects of the shape of phenocrysts on their settling velocity and on the rheology of magmas are discussed spherical crystals fall at a velocity given by stokes law and need to be present in large concentrations before they have a marked effect on the viscosity of a suspension elongate crystals fall at a much smaller velocity which may be determined from the formulas and graphs given herein such elongate crystals can have a dramatic effect on the viscosity of a suspension even at low volume fractions suspended crystals and bubbles will not impart a yield stress to the magma unless they form a touching network across the entire suspension it is suggested therefore that most previous inferences of a yield stress in subliquidus magmas are erroneous measurements of the subliquidus rheology of magmas need to be accompanied by careful characterization of the microstructure and distribution of the solid phase on which such rheologies critically depend

steady and non steady state magma chambers below the east pacific rise volcanic rocks collected on flowline traverses on the flanks of the east pacific rise epr document changes in axial magma chemistry with time providing a record of the thermal history of axial magma chambers amc we present data for a sample set of closely spaced 1 2 km samples along epr flowlines at three localities out to 800 ka showing both steady constant average temperature and non steady state behavior of magma chambers on time scales of 200 500 ka though based on only three symmetrical traverses so far it appears that magmatically robust ridge locations 11 20 n and 9 30 n have steady state chambers whereas a magmatically starved axis 10 30 n shows large temperature changes with time these observations provide a new petrologic perspective to the ongoing debate regarding the significance and causes of morphologic variations along the axis of the east pacific rise

on the mechanical effects of poroelastic crystal mush in classical magma chamber models author posting american geophysical union 2018 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research solid earth 123 11 2018 9376 9406 doi 10 1029 2018jb015985

rheological tests of polyurethane foam undergoing vesiculation deformation solidification as a magma analogue abstract in this study we examined the rheology of polyurethane foam puf as an analogue system of magma undergoing vesiculation deformation and solidification solid puf was formed by mixing two polymeric liquids followed by chemical reactions of foaming and curing the transient rheology during the processes was investigated using an instrument based on a stress controlled rheometer first the oscillatory rheology was measured applying small amplitude oscillations with cyclic frequency sweeps in the foaming stage the frequency dependence of the rheology depends on the dynamic capillary number in a similar way to the existing bubbly flow model in the curing stage the viscoelasticity of the liquid becomes dominant and the rheology of puf shows maxwell type viscoelasticity with relaxation time exponentially increasing with time when the reaction is rapid because of high temperature the viscoelasticity during curing is not scaled by the single relaxation time instead puf passes through a condition called gelation which is characterized by a power law relaxation spectrum next we examined the relationship between the dynamic viscosity measured by the small strain oscillation and the shear viscosity measured with a fixed shear rate at a large strain we found that puf obeys the cox merz rule which states that the two viscosities are equivalent when the shear rate and the angular frequency are equal specifically the shear viscosity tends to be smaller than the dynamic viscosity by a few tens of percent the difference was shown to be in the range expected for bubbly fluid in the foaming stage while it went beyond what can be explained by the bubbly fluid model when the viscoelasticity of the liquid becomes significant x ray computed tomography analyses revealed that samples in these cases contained large bubbles indicating bubble coalescence we infer that the difference is caused by bubble coalescence as well as non newtonian rheology during solidification including gelation all these processes might occur in actual magma during eruptions we show that the ranges of the capillary number comparing the deformation time and the bubble shape relaxation time and deborah number comparing the deformation time and the viscoelastic relaxation time in our experiments are comparable with their ranges expected for magma ascending in an eruptive conduit the characteristic time of viscosity increase of puf was also shown to be realizable for magma in natural volcanoes we conclude that puf is useful for simulating magma processes in eruptive conduits

verification of ideal semi logarithmic lognormal or fractal crystal size distributions from 2d datasets crystal size distributions can follow any function provided the total crystal content is less than 100 however many theories suggest that they approximate a number of ideal distribution models the most widely adopted model for igneous rocks produces a straight line on a classic csd diagram of ln population density versus size lognormal by size distributions have been proposed for igneous and metamorphic rocks and materials that crystallise at low temperatures lognormal models are difficult to prove with simple linear frequency histograms or on a classic csd diagram instead it is better to use a normalized cumulative distribution function diagram which gives a straight line for lognormal distributions similarly fractal size distributions can best be verified simply by using a bi logarithmic diagram statistical measures can be used to invalidate a null hypothesis but with much caution for real data especially those derived from two dimensional measurements and with a limited range in sizes these methods are applied to csds of plagioclase in three igneous rock samples to illustrate the pitfalls of model fitting a simple nomenclature is proposed for ideal csd shapes

a model for the rheology of particle bearing suspensions and partially molten rocks an edited version of this paper was published by agu copyright 2009 american geophysical union

experimental investigation of magma rheology at 300 mpa from pure hydrous melt to 76 vol of crystals the rheological behaviour of synthetic crystal bearing magmas containing up to 75 vol of crystals 0 s 0 75 has been investigated experimentally at a confining pressure of 300 mpa and temperatures between 475 and 600 c at shear rates between 10 4 and 2x10 3 s 1 starting hydrated crystal bearing glasses were synthesized from a dry haplogranitic glass qz36ab39or29 and 2 5 wt water mixed with 0 pure hydrous melt 16 34 54 65 or 75 vol of al2o3 sieved 45 o 90 m crystals shear viscosity measurements were performed in torsion in a paterson gas medium apparatus for each composition the rheological data were fitted to a power law of the form 1 where is shear rate is shear stress t is temperature r is the gas constant and a n and q are empirical parameters defined as the preexponential term the stress exponent and the activation energy respectively the rheology is found to be newtonian n 1 for pure hydrated melt and 16 vol of crystals at higher crystal contents the magmas behave as pseudoplastic materials and exhibit shear thinning behaviour with stress exponents of 1 3 1 9 and 2 8 for 34 54 and 65 vol of crystals respectively the activation energy seems to be nearly independent of crystal fraction and has a mean value of 231 kj mol 1 the einstein roscoe equation adequately estimates viscosities of the crystal bearing magmas at low crystal contents s 0 25 but progressively deviates from the measured viscosities with increasing crystal content as the rheological behaviour becomes non newtonian a modified power law formulation incorporating crystal content as a variable allows a fit to the experimental data set over the whole range of conditions

the rheology of two phase magmas a review and analysis abstract we consider the current state of our understanding of the rheology of two phase magmas that is suspensions of either bubbles or crystals in a viscous silicate melt the discussion is restricted to strain rates at which the suspending melt can be considered newtonian we start by considering the range of textures found in magmas and the bubble deformation and particle motions caused by shearing we then review proposed models for suspensions focussing on those functions of the form r f or f that have been most widely used to describe magmatic systems r is the relative apparent viscosity of the suspension is the volume fraction of the suspended phase is the driving stress and is the strain rate both theoretical and empirical methods are presented and then compared against the available analogue i e non magmatic and magmatic data the paper contains new data and significant re analysis of previously published data we present a new semi empirical constitutive model for bubble bearing magmas that is valid for steady and unsteady flow and large strains and strain rates this equation utilises a new parameter the capillarity cx that encapsulates the combined effect of shearing and unsteadiness on bubble suspensions we also present a new scheme for dealing with polydispersivity of bubble suspensions new data on the rheology of particle suspensions undergoing forced oscillations are presented these data show that the cox merz rule only holds for dilute particle suspensions 0 25 a re analysis of all available experimental data that relate rheology to particle aspect ratio provides distinct curves of maximum packing as a function of aspect ratio for smooth and rough particles with magmatic data lying on the curve appropriate for rough particles we analyse several rheological datasets of crystal bearing basaltic magmas and find that they are in good agreement with the constitutive equations derived from analogue data by contrast the same equations do not agree well with data for high viscosity haplogranitic melts this may be an effect of fracturing or viscous dissipation within these samples the paper concludes with a practical rheological recipes section giving a step by step method for calculating a constitutive equation for a two phase magmatic suspension and assessing its likely accuracy

collision of manihiki plateau fragments to accretional margins of northern andes and antarctic peninsula the manihiki plateau a large igneous province lip was emplaced in the early cretaceous as a single plateau together with the ontong java plateau and the hikurangi plateau additional to the present manihiki plateau fragments to its northeast and east have been formed plate kinematic reconstructions suggest the capturing of these fragments by the farallon plate and the phoenix plate respectively by tracing these fragments we report a paleocene collision of the northeastern manihiki plateau fragment with the northern south american craton the northern andes exhibit multiple terranes of lip origin we infer based on geophysical petrological and geochemical data that the pinon formation consists of crustal units of the former manihiki plateau an early cretaceous collision of the eastern manihiki plateau fragment is reconstructed for west antarctica the subduction of this fragment in the palmer land region can be associated with the so called palmer land event and a flattening of the subduction slab by reconstructing the dispersal of the fragments of the manihiki plateau we provide a deeper insight in the possible subduction scenarios and buildup of the accretional margins of the northern andes and the antarctic peninsula

geologic form and setting of a hydrothermal vent field at lat 10 56 n east pacific rise a detailed study using angus and alvin a hydrothermal vent field here called the feather duster site occurs on the eastern marginal high near the edge of a narrow 95 m and shallow 15 20 m axial graben within an area dominated by sheet flows and collapse features the sheet flows are intermediate in relative age between younger fluid flow lavas on the floor of the axial graben and older pillow constructional lavas on the marginal highs hydrothermal activity occurs in two zones within a 65 by 45 m area the main zone is located where a fissure system and sulfide sulfate chimneys vent warm 9 47 sup 0 c and hot 347 sup 0 c hydrothermal fluids here two mounds of massive sulfide totaling about 200 t are forming one occurs at the base of a 3 m high scarp which is the wall of a drained lava lake the other is perched on top of the scarp 19 references 4 figures

bubble nucleation growth and coalescence during the 1997 vulcanian explosions of soufriere hills volcano montserrat abstract soufriere hills volcano had two periods of repetitive vulcanian activity in 1997 each explosion discharged the contents of the upper 0 5 2 km of the conduit as pyroclastic flows and fallout frothy pumices from a deep gas rich zone lava and breadcrust bombs from a degassed lava plug and dense pumices from a transition zone vesicles constitute 1 66 vol of breadcrust bombs and 24 79 of pumices all those larger than a few tens of m being interconnected small vesicles few hundreds of m in pumices are interpreted as pre dating explosion implying pre explosive conduit porosities up to 55 about a sixth of large vesicles in pumices and all those in breadcrust bombs are angular voids formed by syn explosive fracturing of amphibole phenocrysts an intermediate sized vesicle population formed by coalescence of the small syn explosive bubbles bubble nucleation took place heterogeneously on titanomagnetite number densities of which greatly exceed those of vesicles and growth took place mainly by decompression development of pyroclast vesicle textures was controlled by the time interval between the onset of explosion decompression and surface quench in contact with air lava plug fragments entered the air quickly after fragmentation 10 s so the interiors continued to vesiculate once the rinds had quenched forming breadcrust bombs deeper gas rich magma took longer 50 s to reach the surface and vesiculation of resulting pumice clasts was essentially complete prior to surface quench this accounts for the absence of breadcrusting on pumice clasts and for the textural similarity between pyroclastic flow and fallout pumices despite different thermal histories after leaving the vent it also allowed syn explosive coalescence to proceed further in the pumices than in the breadcrust bombs uniaxial boudinage of amphibole phenocrysts in pumices implies significant syn explosive vesiculation even prior to magma fragmentation probably in a zone of steep pressure gradient beneath the descending fragmentation front syn explosive decompression rates estimated from vesicle number densities 0 3 6 5 mpa s 1 are consistent with those predicted by previously published numerical models

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

near axis seamounts on the flanks of the east pacific rise 8 n to 17 n with complete seabeam and seamarcii bathymetry and nearly complete seamarcii side scan coverage of the northern east pacific rise and its flanks from 8 to 17 n we characterize the entire population of seamounts on young seafloor 0 to 2 ma formed along this fast spreading center there are 179 seamounts in this area taller than 200 m most of which belong to one of 21 seamount chains these chains are oriented between the relative and absolute plate motion directions of the pacific and cocos plates and most of the larger chains are more voluminous near their centers than near their ends several of the seamount chains contain bends in orientation which are not coincident with each other the two largest seamount chains at 9 55 n lamont seamounts and 15 40 n are aligned with portions of the east pacific rise crest which are among the shallowest and broadest of this area overall the maximum abundance and size of seamounts increase with shallower and broader ridge axes no near axis seamounts form on the summit of the axial ridge nonetheless within 15 km 0 3 ma of the axis the abundance of seamounts achieves its overall average observations of the numbers and cumulative volume of seamount edifices versus distance from the axis are consistent with a model where the majority of near axis seamounts are formed in a narrow zone on crust aged 0 1 0 3 ma 5 15 km from the axis with significant growth in a zone several times wider side scan sonar reflectivity and seamount magnetization analyses are largely consistent with the predictions of this model two exceptions to this model however are seamount chains at 15 40 n and 8 25 n which show evidence for activity over a broader region this may be due to the presence of fracture zones within about 30 km of these chains a compilation of seamount counts from a wide range of spreading centers indicates that seamounts taller than 400 m are more abundant at greater spreading rates and with transitions from a rift valley to an axial ridge the variations with spreading rate of melt availability and of lithosphere penetrability probably combine to produce the observed results although these influences cannot be distinguished in this analysis

cooling and crystallization of lava in open channels and the transition of pāhoehoe lava to a ā samples collected from a lava channel active at kilauea volcano during may 1997 are used to con strain rates of lava cooling and crystallization during early stages of flow lava erupted at near liquidus tem peratures f1150 7c cooled and crystallized rapidly in upper parts of the channel glass geothermometry indi cates cooling by 12 14 7c over the first 2 km of trans port at flow velocities of 1 2 m s this translates to cooling rates of 22 50 7c h cooling rates this high can be explained by radiative cooling of a well stirred flow consistent with observations of non steady flow in proximal regions of the channel crystallization of plag ioclase and pyroxene microlites occurred in response to cooling with crystallization rates of 20 50 per hour crystallization proceeded primarily by nucleation of new crystals and nucleation rates of f10 4 cm 3 s are similar to those measured in the 1984 open channel flow from mauna loa volcano there is no evidence for the large nucleation delays commonly assumed for plagioclase crystallization in basaltic melts possibly a reflection of enhanced nucleation due to stirring of the flow the transition of the flow surface morphology from pahoehoe to a aoccurred at a distance of 1 9 km from the vent at this point the flow was thermally stratified with an interior temperature of f1137 7c and crystallinity of f15 and a flow surface tempera ture of f1100 7c and crystallinity of f45 a afor mation initiated along channel margins where crust was continuously disrupted and involved tearing and clotting of the flow surface both observations suggest that the transition involved crossing of a rheological threshold we suggest this threshold to be the develop ment of a lava yield strength sufficient to prevent vis cous flow of lava at the channel margin we use this concept to propose that a aformation in open chan nels requires both sufficiently high strain rates for con tinued disruption of surface crusts and sufficient groundmass crystallinity to generate a yield strength equivalent to the imposed stress in hawai i where lava is typically microlite poor on eruption these combined requirements help to explain two common observations on a aformation a a aflow fields are generated when effusion rates are high thus promoting crustal disruption and b under most eruption conditions lava issues from the vent as pahoehoe and changes to a aonly after flowing some distance thus permitting sufficient crystallization

the rheology of crystal bearing basaltic magmas from stromboli and etna abstract our ability to forecast volcanic hazards at active volcanoes stems from our knowledge of parameters affecting eruption dynamics persistent activity displayed by basaltic volcanic systems such as etna and stromboli is governed mainly by the textural evolution and rheological properties of eruptive products here we investigate the high temperature 1131 c

interpretation of open system petrogenetic processes phase equilibria constraints on magma evolution we have used a computer model traces to simulate low pressure differentiation of natural basaltic magmas in an attempt to investigate the chemical dynamics of open system magmatic processes our results in the form of simulated liquid lines of descent and the calculated equilibrium mineralogy were determined for perfect fractional crystallization fractionation paired with recharge and eruption prf fractionation paired with assimilation afc and fractionation paired with recharge eruption and assimilation fear these simulations were calculated in an attempt to assess the effects of combinations of petrogenetic processes on major and trace element evolution of natural systems and to test techniques that have been used to decipher the relative roles of these processes if the results of prf calculations are interpreted in terms of a mass balance based fractionation model e g bryan et al 1969 it is possible to generate low residuals even if one assumes that fractional crystallization was the only active process in effect the chemical consequences of recharge are invisible to mass balance models pearce element ratio analyses however can effectively discern the effects of prf versus simple fractionation the fractionating mineral proportions and therefore bulk distribution coefficients d of a differentiating system are dependent on the recharge or assimilation rate comparison of the results of simulations assuming constant d with the results calculated by traces show that the steady state liquid concentrations of some elements can differ by a factor of 2 to 5 if the prf simulation is periodic with episodes of mixing separated by intervals of fractionation parallel liquidus mineral control lines are produced most of these control lines do not project back to the parental composition this must be an important consideration when attempting to calculate a potential parental magma for any natural suite where magma chamber recharge has occurred most basaltic magmas cannot evolve to high silica compositions without magnetite fractionation small amounts of rhyolite assimilation assimilation fractionation 0 1 however can drive evolving basalts to more silica rich compositions if mass balance models are used to interpret these synthetic afc data low residuals are obtained if magnetite is added to the crystallizing assemblage this approach works even for cases where magnetite was not a fractionating phase thus the mass balance results are mathematically correct but are geologically irrelevant

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

low pressure phase equilibria of anhydrous anorthite bearing mafic magmas 1 one of the most persistent questions regarding the phase equilibria of mid ocean ridge basalts morb pertains to the petrogenesis of the anorthitic plagioclase phenocrysts an90 that are characteristic of the more primitive members of such suites anorthitic phenocrysts are present in many if not most morb suites in spite of the fact that no naturally occurring morb glasses have ever been discovered to be in equilibrium with plagioclase more calcic than an85 we have addressed this paradox by attempting to saturate natural basalts with anorthite in a series of 1 atm experiments using three different natural basaltic starting compositions an n morb an e morb and a continental high alumina basalt to ensure duplication of the olivine and anorthite saturation observed in natural anorthite bearing basalt the experiments were run in an93 6 capsules with fo92 olivine added to the starting glass the compositions of experimental liquids are generally colinear with the trends observed in the lava suites used as the source material for the starting glasses significantly aluminous spinel al2o3 contents of 61 68 wt was produced at 1290 c in all compositions and chromites al2o3 contents of 33 42 wt at lower temperatures in n morb derived liquids despite no spinel having been added to the starting mixture in addition the experiments produced basaltic liquid in equilibrium with both fo89 olivine and an85 feldspar at temperatures of 1230 and 1210 these liquids have compositions with mg at mg mg fet 100 that range from 63 to 85 the tio2 mgo correlation indicates large 16 23 amounts of crystallization for each percent decrease in mgo these results suggest the possibility that dry anorthite bearing basaltic magmas are the product of the interaction between primary melt and al spinel bearing upper mantle in addition the results indicate that morb magmas can undergo a large amount 50 of crystallization prior to reaching 8 mgo further although anorthite bearing magmas have characteristics consistent with their being a significant volumetric component of morb parent magmas the reaction mechanism suggested for their petrogenesis indicates that they are not necessarily primary magmas

non newtonian behavior of plagioclase bearing basaltic magma subliquidus viscosity measurement of the 1707 basalt of fuji volcano japan abstract laboratory measurements of viscosity were done for basalt erupted in 1707 ad from fuji volcano japan using a concentric cylinder rotational viscometer at temperatures of 1297 1157 c 1 atm pressure and fo 2 near the ni nio buffer on cooling elongated plagioclase crystals with a mean length width ratio of ca 8 5 appeared at 1237 c followed by olivine at 1157 c at progressively lower temperatures the total crystal volume fraction increased monotonously to ca 0 25 viscosity increased from 38 9 to 765 pa s at a shear strain rate of 1 s 1 this basalt magma behaves as a newtonian fluid at temperatures greater than 1217 c but shear thinning behavior occurs at temperatures less than 1197 c because of the suspended plagioclase crystals this behavior is well approximated as a power law fluid at the onset of shear thinning the crystal volume fraction was between 0 06 and 0 13 which is attributed to the pronounced lath shape of plagioclase crystals the relative viscosity increases monotonously with increase of crystal volume fraction at a constant shear strain rate and with decrease of shear strain rate at a constant crystal volume fraction a modified form of the krieger dougherty equation is introduced herein it enables us to describe the dependencies of relative viscosity on both the crystal volume fraction and shear strain rate and consequently the onset of shear thinning behavior

viscosity measurements of subliquidus magmas alkali olivine basalt from the higashi matsuura district southwest japan abstract we carried out viscosity measurements and sampling of a crystal suspension derived from alkali olivine basalt from the matsuura district sw japan at subliquidus temperatures from 1230 c to 1140 c under 1 atm with nno oxygen buffered conditions viscosity increased from 31 to 1235 pa s with a decrease in temperature from 1230 to 1140 c on cooling olivine first appeared at 1210 c followed by plagioclase at 1170 c the crystal content of the sample attained 31 vol at 1140 c plagioclase 22 olivine 9 non newtonian behaviors including thixotropy and shear thinning were pronounced in the presence of tabular plagioclase crystals the cause of such behavior is discussed in relation to shear induced changes in melt crystal textures relative viscosities r s m where s and m are the viscosities of the suspension and the melt respectively were obtained by calculating melt viscosities from the melt composition and temperature at 1 atm using the equation proposed by giordano and dingwell giordano d dingwell d b 2003 non arrhenian multicomponent melt viscosity a model earth and planetary science letters 208 337 349 the obtained relative viscosities are generally consistent with the einstein roscoe relation which represents r for suspensions that contain equant and equigranular crystals even though the crystal suspension analyzed in the present experiments contained tabular plagioclase and granular olivine of various grain sizes this consistency is attributed to the fact that the effect of crystal shape was counterbalanced by the effect of the dispersion of crystal size the applicability of the einstein roscoe equation with respect to crystal shape is discussed on the basis of the present experimental results our experiments and those of sato sato h 2005 viscosity measurement of subliquidus magmas 1707 basalt of fuji volcano journal of mineralogical and petrological sciences 100 133 142 show that the relationship between relative viscosity and crystal fraction is consistent with the einstein roscoe relationship for axial ratios that are smaller than the critical value of 4 6 5 but discrepancies occur for higher ratios

the yield strength of subliquidus basalts experimental results yield strength is an important property of particle fluid suspensions in basaltic lavas that crystallize during flow emplacement the onset of yield strength may result in threshold transitions in flow behavior and flow surface morphology however yield strength crystallinity relations are poorly known particularly in geologic suspensions where difficulties of experimental and field measurements have limited data acquisition in the subliquidus temperature range here we describe two complementary experimental approaches designed to examine the effect of particle shape on the low shear yield strength of subliquidus basalts the first involves melting cubes of holocrystalline basalt samples with different initial textures to determine the temperature crystallinity at which these samples lose their cubic form these experiments provide information on the minimum crystal volume fractions 0 20 0 35 required to maintain the structual integrity of the cube the second set of experiments uses suspensions of corn syrup and neutrally buoyant particles to isolate the effect of particle shape on yield strength development from these experiments we conclude that the shape is important in determining the volume fraction range over which suspensions exhibit a finite yield strength as anisotropic particles may orient during flow the effect of particle shape will be controlled by the orientation distribution of the constituent particles we find that the so called excluded volume can be used to relate results of experiments on anisotropic particles to those of suspensions of spherical particles recent measurements of yield strength onset in basaltic melts at crystal volume fractions near 0 25 are consistent with our observations that crystal frameworks develop at low to moderate crystal volume fractions when crystals are anisotropic e g plagioclase we further suggest that conditions leading to yield strength onset at low crystallinities include rapid cooling increased crystal anisotropy heterogeneous nucleation which promotes extensive crystal clustering and large cluster anisotropy and static conditions random crystal orientations

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

the effect of particle shape on suspension viscosity and implications for magmatic flows 1 the rheology of crystal bearing magma and lava depends on both the shape and volume fraction of the suspended crystals we present the results of analogue rheometric experiments on monodisperse suspensions of solid particles in a newtonian liquid in which particle volume fraction and aspect ratio rp are varied systematically we find that the effect of on viscosity is well captured by the maron pierce model and that this model is valid across the range of particle aspect ratios investigated 0 04 rp 22 i e strongly oblate to strongly prolate when the maximum packing fraction m is treated as a fitting parameter the value of m derived from fitting to our experimental data depends strongly and systematically on particle aspect ratio hence m represents an effective proxy for the influence of particle shape on suspension rheology we present a simple relationship for m rp which allows the viscosity of a suspension to be calculated as a function of and rp only we investigate the impact of accounting for crystal shape when modelling volcanic flows by simulating the eruption of magma carrying crystals of different aspect ratio and conclude that the effect of crystal shape should not be neglected

crystallization kinetics and rheology of leucite bearing tephriphonolite magmas from the colli albani volcano italy abstract we have investigated the rheology of liquid and crystal bearing tephriphonolite magmas from the colli albani volcanic district high 1124 1569 c and low 690 800 c temperature anhydrous liquid viscosities were determined by a combination of concentric cylinder 101 0 to 103 6 pa s and micropenetration 109 2 to 1012 1 pa s viscometry comparison with literature data reveals that at high temperatures viscosity seems to be related to the melts degree of polymerization nbo t while at low temperatures the dependency is not linear with values of viscosity higher than expected subliquidus isothermal crystallization experiments and viscosity determinations were carried out at high temperature 1150 1240 c in air using a concentric cylinder apparatus at constant shear strain rate 0 1 s 1 the overall crystal fraction varies between 0 06 at 1240 c leucite and 0 34 at 1150 c leucite 0 32 plagioclase 0 02 with a direct linear increase of crystal content with decreasing temperature which parallels the viscosity increase the inspection of products quenched at the end of the crystallization stage defined when viscosity reaches a constant value reveals strong evidence of leucite clustering after the first segment of the experiment performed at a constant shear rate a second stage of experiments at variable shear rate was performed comprised of an up ramp 0 1 s 1 0 9 s 1 and a down ramp 0 9 s 1 0 1 s 1 segment at the end of the down ramp leucite crystals appear sub spherical and unclustered for the same applied shear rate the viscosity values of the up ramp are not recovered within the experimental time scale indicating strain and strain rate dependent rheology for these suspensions while the down ramp viscosity data are shown to be in perfect agreement with literature models discrepancies between the up ramp data and pre existing predicting models have been observed we suggest that this complex behavior is related to the clustering of leucite crystals during the crystallization process and their breakage during the higher shear rate viscosity measurements the kinetics of crystallization in terms of nucleation and growth rates seems to be strongly affected by the degree of undercooling and dynamic stirring conditions we conclude that any modeling of tephriphonolite magma flow either in conduit or subaerial should take into account the effects of strain strain rate and internal textures i e clustering

non newtonian rheological law for highly crystalline dome lavas volcanic eruption models are hampered by the lack of multiphase magmatic flow laws most rheological models estimate the viscosity of multiphase lavas via the einstein roscoe equation but this simplification cannot be used for high crystallinity and it does not consider the non newtonian strain rate dependence of viscosity we carried out parallel plate experiments on natural samples to simulate multiphase lava deformation under various stresses and strain rates multiphase lavas exhibit an important component of shear thinning and appear to invalidate the adequacy of einstein roscoe based formulations for highly crystalline lava rheology the remarkable singular dependence of viscosity on strain rate yields a novel universal rheology law at eruptive temperatures t i e log 0 993 8974 t 0 543 log our work reveals the importance of considering microcracking and viscous dissipation at very high strain rate 10 3 s 1 explaining the occurrence of seismic swarms along the conduit margins and consequently supporting plug like magma ascent models

the effect of particle size on the rheology of liquid solid mixtures with application to lava flows results from analogue experiments 1 we investigate the effect of crystal size on the rheology of basaltic magmas by means of a rheometer and suspensions of silicon oil with natural magmatic crystals of variable size from 63 to 0 5 mm and volume fraction from 0 03 to 0 6 at constant finer suspensions display higher viscosities than coarser ones shear thinning flow index n 0 1 0 2 and is more pronounced stronger departure from the newtonian behavior in finer suspensions maximum packing and average crystal size displays a nonlinear positive correlation while yield stress develops at 0 2 0 3 irrespective of the crystal size we incorporate our results into physical models for flow of lava and show that with respect to lava flows containing coarser crystals those with smaller crystals are expected to 1 flow at lower velocity 2 have a lower velocity gradient and 3 be more prone to develop a region of plug flow our experimental results explain the observation that phenocryst bearing and microlite bearing lavas at etna volcano italy show smooth pahoehoe and rough aa surfaces respectively

magnetism of al substituted magnetite reduced from al hematite this study was supported by national program on global change and air sea interaction gasi 04 01 02 the national natural science foundation of china grants 41504055 41430962 41374073 and 41025013 and chinese continental shelf deep drilling program gzh201100202 z x j further acknowledges support from the china postdoctoral science foundation a p r and d h acknowledge support from the australian research council grants dp110105419 and dp120103952

distribution of isolated volcanoes on the flanks of the east pacific rise 15 3 s 20 s volcanic constructions not associated with seamount or volcano chains are abundant on the flanks of the east pacific rise epr but are rare along the axial high the distribution of isolated volcanoes based on multibeam bathymetric maps is approximately symmetric about the epr axis this symmetry contrasts with the asymmetries in the distribution of volcano chains more abundant on the west flank the seafloor subsidence rates slower on the west flank and the distribution of plate motion parallel gravity lineaments more prominent on the west flank most of the isolated volcanoes complete their growth within 14 km of the axis on crust younger than 0 2 ma while seamount chain volcanoes continue to be active on older crust volcanic edifices within 6 km of the ridge axis are primarily found adjacent to axial discontinuities suggesting a more sporadic magma supply and stronger lithosphere able to support volcanic constructions near axial discontinuities the volume of isolated near axis volcanoes correlates with ridge axis cross sectional area suggesting a link between the magma budget of the ridge and the eruption of near axis volcanoes within the study area off axis volcanic edifices cover at least 6 of the seafloor and contribute more than 0 2 to the volume of the crust the inferred width of the zone where isolated volcanoes initially form increases with spreading rate for the mid atlantic ridge 4 km northern epr 20 km and southern epr 28 km so that isolated volcanoes form primarily on lithosphere younger than 0 2 ma 4 6 km brittle thickness independent of spreading rate this suggests some form of lithospheric control on the eruption of isolated off axis volcanoes due to brittle thickness increased normal stresses across cracks impeding dike injection or thermal stresses within the newly forming lithosphere

the rheological transition in plagioclase bearing magmas 1 volcanological processes such as melt segregation ascent and eruption are directly dependent on the rheological behavior of magmatic suspensions an increase of the crystal fraction of the suspension leads to the formation of a solid particle network which abruptly increases magma viscosity the crystal fraction at which this rheological transition occurs depends on parameters such as the strain rate and the size shape and sorting of particles to determine the influence of the crystal shape on the rheological transition suspensions of plagioclase a representative anisometric crystal have been investigated at high temperatures and pressures synthetic suspensions with crystal fractions s ranging from 0 38 to 0 75 were deformed both in compression and torsion in a paterson apparatus at 300 mpa 900 c and 800 c and for strain rates between 1 0 10 5 and 1 0 10 3 s 1 all suspensions exhibit a non newtonian shear thinning rheological behavior the experimental results coupled with existing data and models at low crystal fractions s 0 3 allow several rheological domains to be identified from steady state flow to strain weakening each characterized by a specific microstructure in particular a progressive evolution from a pervasive to a strain partitioning fabric is found when increasing the crystal fraction our results highlight the influence of both the strain rate and the shape of crystals on the rheological behavior of magmas during crystallization magmatic suspensions of anisometric minerals such as plagioclase would develop a solid particle network earlier s 0 3 than suspensions of isometric minerals s 0 5 our study shows that localization of strain early in the crystallization history of mushy zones in the magma chamber near the conduit margins and at the base of lava flows would facilitate the mobilization the transfer and the final emplacement at the surface of highly viscous feldspar rich magmas

field and model constraints on silicic melt segregation by compaction hindered settling the role of water and its effect on latent heat release to investigate how large volumes of silicic melts segregate to form granitic plutons we conducted a case study of a zoned pluton in which sio 2 increases from intermediate 69 wt to highly silicic compositions 74 wt toward the contact with metasedimentary wallrock in the outer 25 m of the pluton all other major minor and trace elements vary systematically with sio 2 and indicate that outward increasing sio 2 is due to a decrease in mafic elements and minerals whole rock oxygen isotopes and elemental variation diagrams do not support mixing with wallrock as an explanation for the si rich boundary layer instead mafic enclaves which are common in the pluton also decrease in abundance in the outer 25 m of the pluton suggesting a mechanical origin for the si rich boundary layer the coupling of mechanical and geochemical boundary layers combined with geochemical modeling indicate that the silica rich enclave poor boundary layer formed by hindered settling or compaction of a crystal rich crystal fractions 60 magmatic mush segregation of melts at high crystal fraction is known to be a slow process however petrography and zr based thermometry indicate that the residual si rich liquids were water saturated water decreases melt viscosity which helps expulsion but equally importantly water also delays much of the latent heat release to late in the thermal and crystallization history of a cooling magma we show that the higher the water content the longer the time interval over which a magma chamber resides at the stage when water saturated high silica liquids form allowing sufficient time for exfiltration of silicic liquids before the magma body freezes

kinematics of late cretaceous subduction initiation in the neo tethys ocean reconstructed from ophiolites of turkey cyprus and syria formation of new subduction zones represents one of the cornerstones of plate tectonics yet both the kinematics and geodynamics governing this process remain enigmatic a major subduction initiation event occurred in the late cretaceous within the neo tethys ocean between gondwana and eurasia suprasubduction zone ophiolites i e emerged fragments of ancient oceanic lithosphere formed at suprasubduction spreading centers were generated during this subduction event and are today distributed in the eastern mediterranean region along three e w trending ophiolitic belts several models have been proposed to explain the formation of these ophiolites and the evolution of the associated intra neo tethyan subduction zone here we present new paleospreading directions from six upper cretaceous ophiolites of turkey cyprus and syria calculated by using new and published paleomagnetic data from sheeted dyke complexes our results show that nne ssw subduction zones were formed within the neo tethys during the late cretaceous which we propose were part of a major step shaped subduction system composed of nne ssw and wnw ese segments we infer that this subduction system developed within old triassic lithosphere along fracture zones and perpendicular weakness zones since the neo tethyan spreading ridge formed during gondwana fragmentation would have already been subducted at the pontides subduction zone by the late cretaceous our new results provide an alternative kinematic model of cretaceous neo tethyan subduction initiation and call for future research on the mechanisms of subduction inception within old and cold lithosphere and the formation of metamorphic soles below suprasubduction zone ophiolites in the absence of nearby spreading ridges

rejuvenation of the fish canyon magma body a window into the evolution of large volume silicic magma systems voluminous unzoned phenocryst rich pyroclastic deposits considered as erupted batholiths provide a unique opportunity to investigate magmatic processes in silicic magmas the fish canyon tuff a well documented example of these monotonous ignimbrites displays evidence for simultaneous dissolution of feldspars 1 quartz and crystallization of hydrous phases during gradual near isobaric reheating from 720 to 760 8c these observations along with a high crystallinity 45 and near solidus mineral assemblage suggest that the fish canyon magma cooled to a rigid crystal mush before being partly remelted prior to eruption rejuvenation was triggered by intrusion of water rich mafic magmas at the base of the fish canyon mush but the mechanisms of heat transfer remain poorly understood the growth of amphibole during reheating requires addition of mafic components but the absence of any measurable gradients and the paucity of mafic enclaves in the fish canyon magma rule out a reheating event dominated by convective mixing with a mafic magma closed system processes such as heat conduction and convective self mixing could not account for the transport of externally derived mafic components we performed numerical simulations of upward percolation of a hot low density h2o co2 fluid phase gas sparging through a crystalline framework saturated with rhyolitic melt to assess the efficiency of such a process in rejuvenating silicic mushes in open systems sparging by 20 40 km 3 of gas extracted from 3000 km 3 of mafic magma is capable of reheating 7500 km 3 of silicic crystal mush by 40 8c in 150 200 k y moreover the vertical thermal gradient after 150 k y in most of the mush is small 25 8c in the upper 65 gas sparging also produces an increase in the internal pressure of silicic crystal mushes and may lead to the formation of crystal poor rhyolites by expelling interstitial melt however our simulations predict that filter pressing driven by sparging of externally derived gas could not solely account for the generation of the most voluminous rhyolites

volcanic tremor and frequency gliding during dike intrusions at kilauea a tale of three eruptions to characterize syneruptive intrusive deviations from background volcanic tremor at kilauea hawai i we analyze the spatial and temporal properties of broadband tremor during dike intrusions into the east rift zone erz in 2007 and 2011 as well as during explosive eruptive activity at kilauea s summit in 2008 background tremor was similar for each event and the 2008 explosions did not affect its properties in contrast the intrusions were accompanied by departures from this background in the form of two phases of seismicity that were separated in space and time in both 2007 and 2011 phase i was characterized by a quick succession of discrete events which were most intense at the onset of intrusion near the presumed locations of the dikes intruding into the erz phase ii marked by continuous broadband tremor around the summit followed 10 14 h later in 2007 phase ii tremor was accompanied by a monotonic downward shift glide of spectral peaks between 0 6 and 1 5 hz over at least 15 h during phase ii in 2011 a gradual upward and subsequent symmetric downward glide between 0 6 and 6 6 hz occurred over 5 10 h respectively the spectra during both phases differed from the background and 2008 as well as from each other indicating different physical mechanisms phase i in 2007 and 2011 is probably related to the mechanics of dike intrusion phase ii tremor may be characteristic for evolving magma bubble dynamics related to the geometry of the plumbing system and the style of magma flow

the role of laboratory experiments in volcanology experiment is central to scienti c methodology within science in general experiments are used for four primary purposes i e as a tool to explore novel phenomena and to provide systematic observations of processes to determine the values of key parameters to test hypotheses and theoretical models and to validate computational models which themselves can be considered as numerical experiments the study of volcanic eruptions and magmatic processes is becoming increasingly systematic quantitative and rigorous the drive is towards providing detailed quantitative descriptions and models of the ow phenomena in terms of fundamental physico chemical processes this is motivated in no small way by an increasing need for reliable and quantitative predictions of volcanic eruptions on which to base rational hazard and risk management decisions during volcanic crises a natural consequence of this development of the scienti c study of volcanic ow phenomena is that rigorous laboratory experimentation is becoming an increasingly important feature within volcanic research the contribution of experimental research to our understanding of volcanic processes is di cult to overstate the determination of the values of key parameters has traditionally taken place in the laboratory however more recently experiments have become much more widely applied to the problem of understanding complex dynamical processes and their underlying mechanisms without models experimental theoretical numerical we are limited to qualitative interpretations of eld observations and remote sensing field data are of course essential and provide the measure against which ultimately the applicability of observations from other sources must be assessed however there are several reasons why the scienti c study of volcanic phenomena cannot rely solely on eld data direct observations of eruption processes in the eld are limited to those parts of an eruption that are accessible this restricts detailed observations to a limited range of above surface processes moreover logistical constraints mean that the systematic collection of data will usually only be possible for volcanic eruptions near an established observatory and for activity for which there has been some forewarning as a result of these constraints direct eld based observations of natural volcanic eruption processes are generally incomplete and uncertain another source of natural data derives from observations made on volcanic deposits in principle processes can be inferred from the features

far field triggering of foreshocks near the nucleation zone of the 5 september 2012 m w 7 6 nicoya peninsula costa rica earthquake abstract on 5 september 2012 a moment magnitude mw 7 6 earthquake occurred directly beneath the nicoya peninsula an area with dense seismic and geodetic network coverage the mainshock ruptured a portion of a previously identified locked patch that was recognized due to a decade long effort to delineate the megathrust seismic and aseismic processes in this area here we conduct a comprehensive study of the seismicity prior to this event utilizing a matched filter analysis that allows us to decrease the magnitude of catalog completeness by 1 unit we observe a statistically significant increase in seismicity rate below the nicoya peninsula following the 27 august 2012 mw 7 3 el salvador earthquake about 450 km to the northwest and 9 days prior to the nicoya earthquake additionally we identify a cluster of small magnitude

crystal size distribution of plagioclase and amphibole from soufriere hills volcano montserrat evidence for dynamic crystallization textural coarsening cycles the crystal size distributions csds of plagioclase and amphibole were determined from andesites of the soufriere hills volcano montserrat plagioclase occurs as separate crystals and as chadocrysts in large amphibole oikocrysts the chadocrysts represent an earlier stage of textural development preserved by growth of the oikocryst seventeen rock and eight chadocryst plagioclase csds are considered together as a series of samples of textural development all are curved concave up and coincident differing only in their maximum crystal size three amphibole csds have a similar shape and behaviour but at a different position from the plagioclase csds a dynamic model is proposed for the origin of textures in these rocks crystallization of plagioclase started following emplacement of andesite magma at a depth of at least 5km a steep straight csd developed by nucleation and growth this process was interrupted by the injection of mafic magma into the chamber or convective overturn of hotter magma the magma temperature rose until it was buffered initially by plagioclase solution and later by crystallization during this period textural coarsening ostwald ripening of plagioclase and amphibole occurred small crystals dissolved simultaneously with the growth of large crystals the csd became less steep and extended to larger crystal sizes early stages of this process are preserved in coarsened amphibole oikocrysts repetitions of this cycle generated the observed family of csds textural coarsening followed the communicating neighbours model hence each crystal has its own unique growth solution history without appealing to mixing of magmas that crystallized in different environments

rheology of magmas with bimodal crystal size and shape distributions insights from analog experiments 1 magmas in volcanic conduits commonly contain microlites in association with preexisting phenocrysts as often indicated by volcanic rock textures in this study we present two different experiments that investigate the flow behavior of these bidisperse systems in the first experiments rotational rheometric methods are used to determine the rheology of monodisperse and polydisperse suspensions consisting of smaller prolate particles microlites and larger equant particles phenocrysts in a bubble free newtonian liquid silicate melt our data show that increasing the relative proportion of prolate microlites to equant phenocrysts in a magma at constant total particle content can increase the relative viscosity by up to three orders of magnitude consequently the rheological effect of particles in magmas cannot be modeled by assuming a monodisperse population of particles we propose a new model that uses interpolated parameters based on the relative proportions of small and large particles and produces a considerably improved fit to the data than earlier models in a second series of experiments we investigate the textures produced by shearing bimodal suspensions in gradually solidifying epoxy resin in a concentric cylinder setup the resulting textures show the prolate particles are aligned with the flow lines and spherical particles are found in well organized strings with sphere depleted shear bands in high shear regions these observations may explain the measured variation in the shear thinning and yield stress behavior with increasing solid fraction and particle aspect ratio the implications for magma flow are discussed and rheological results and textural observations are compared with observations on natural samples

determining flow type shear rate and shear stress in magmas from bubble shapes and orientations we interpret the shear environments that produced bubble textures in obsidian samples using the results of theoretical numerical and experimental studies on the deformation of bubbles in shear flows in particular we use the shapes and orientations of bubbles vesicles in obsidian to estimate shear rates and shear stresses and assess flow type simple vs pure shear this technique can be used to determine shear rates in volcanic conduits the origin of pyroclastic obsidian and the emplacement history and dynamics of obsidian flows a spherical bubble in a viscous fluid subjected to a low reynolds number steady flow field deforms until it reaches a steady shape and orientation bubble deformation is governed by the competing stresses from shearing that deforms and surface tension that rerounds the ratio of these stresses is the capillary number ca because the relationships among ca bubble orientation and shape differ for pure and simple shear we can distinguish between these flow types using preserved bubble geometries furthermore because ca is a function of shear rate we can use relationships between ca and the magnitude of deformation to calculate shear rates when melt viscosity and surface tension are known to demonstrate the potential of the technique we examine three obsidian samples chosen for diversity of origin and texture two of the samples have low crystallinities and banding defined by layers of different vesicularity bubble geometries in a spatter fed obsidian flow sample record deformation by pure shear whereas a juvenile obsidian clast from a pyroclastic fall deposit records predominantly simple shear a third sample from an obsidian flow has banding marked by variable concentrations of microlites and shows bubble deformation most consistent with dominantly simple shear and some bubble relaxation the highest shear rate and shear stress are recorded by the pyroclastic obsidian shear rate 0 01 s 1 shear stress 60 kpa the spatter fed obsidian flow sample deformed by pure shear records the lowest shear stress 4 9 kpa the obsidian flow sample deformed by simple shear records the lowest shear rates 10 6 6 10 6 9 s 1 despite high shear stresses 22 36 kpa because of the high viscosity of the degassed rhyolite 0 13 wt water

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