mafic and felsic magma interaction in granites the hercynian karkonosze pluton sudetes bohemian massif the hercynian post collisional karkonosze pluton contains several lithologies equigranular and porphyritic granites hybrid quartz diorites and granodiorites microgranular magmatic enclaves and composite and lamprophyre dykes field relationships mineralogy and majorand trace element geochemistry show that 1 the equigranular granite is differentiated and evolved by small degrees of fractional crystallization and that it is free of contamination by mafic magma 2 all other components are affected by mixing the end members of the mixing process were a porphyritic granite and a mafic lamprophyre the degree of mixing varied widely depending on both place and time all of the processes involved are assessed quantitatively with the following conclusions most of the pluton was affected by mixing implying that huge volumes 475 km of mafic magma were available this mafic magma probably supplied the additional heat necessary to initiate crustal melting part of this heat could have also been released as latent heat of crystallization only a very small part of the karkonosze granite escaped interaction with mafic magma specifically the equigranular granite and a subordinate part of the porphyritic granite minerals from these facies are compositionally homogeneous and or normally zoned which together with geochemical modelling indicates that they evolved by small degrees of fractional crystallization 520 accessory minerals played an important role during magmatic differentiation and thus the fractional crystallization history is better recorded by trace rather than by major elements the interactions between mafic and felsic magmas reflect their viscosity contrast with increasing viscosity contrast the magmatic relationships change from homogeneous hybrid quartz diorites granodiorites to rounded magmatic enclaves to composite dykes and finally to dykes with chilled margins these relationships indicate that injection of mafic magma into the granite took place over the whole crystallization history consequently a long lived mafic source coexisted together with the granite magma mafic magmas were derived either directly from the mantle or via one or more crustal storage reservoirs compatible element abundances e g ni show that the mafic magmas that interacted with the granite were progressively poorer in ni in the order hybrid quartz dioritescgranodioritescenclavesccomposite dykes this indicates that the felsic and mafic magmas evolved independently which in the case of the karkonosze granite favours a deep seated magma chamber rather than a continuous flux from mantle two magma sources mantle and crust coexisted and melted almost contemporaneously the two reservoirs evolved independently by fractional crystallization however mafic magma was continuously being intruded into the crystallizing granite with more or less complete mixing several lines of evidence e g magmatic flux structures incorporation of granite feldspars into mafic magma feldspar zoning with fluctuating trace element patterns reflecting rapid changes in magma composition indicate that during its emplacement and crystallization the granite body was affected by strong internal movements these would favour more complete and efficient mixing the systematic spatial temporal association of lamprophyres with crustal magmas is interpreted as indicating that their mantle source is a fertile peridotite possibly enriched metasomatized by earlier subduction processes

timescales of mingling in shallow magmatic reservoirs arrival of magma from depth into shallow reservoirs has been documented as one of the possible processes leading to eruption magma intruding and rising to the surface interacts with the already emplaced degassed magmas residing at shallower depths leaving chemical signatures in the erupted products we performed two dimensional numerical simulations of the arrival of gas rich magmas into shallow reservoirs we solve the fluid dynamics for the two interacting magmas evaluating the space time evolution of the physical properties of the mixture convection and mingling develop quickly into the chamber and feeding conduit dyke leading on longer timescales to a density stratification with the lighter gas richer magma mixed with different proportions of the resident magma rising to the top of the chamber due to buoyancy over timescales of hours the magmas in the reservoir appear to have mingled throughout and convective patterns become harder to identify our simulations have been performed changing the geometry of the shallow reservoir and the gas content of the initial end member magmas horizontally elongated magma chambers as well as higher density contrasts between the two magmas cause faster ascent velocities and also increase the mixing efficiency

the dynamics of magma mixing in a rising magma batch the conditions under which two magmas can become mixed within a rising magma batch are investigated by scaling analyses and fluid dynamical experiments the results of scaling analyses show that the fluid behaviours in a squeezed conduit are determined mainly by the dimensionless number i mu 1 u g delta rho r 2 where 1 is the viscosity of the fluid u is the velocity g is the acceleration due to gravity is the density difference between the two fluids and r is the radius of the tube the parameter i represents a balance between the viscous effects in the uppermost magma which prevent it from being moved off the conduit walls and the buoyancy forces which tend to keep the interface horizontal the experiments are carried out using fluid pairs of various density and viscosity contrasts in a squeezed vinyl tube they show that overturning of the initial density stratification and mixing occur when i order 10 1 the two fluids remain stratified when i order 10 3 transitional states are observed when 10 3 i 10 1 these results are nearly independent of reynolds number re 1 rho 1 ur mu 1 and viscosity ratio mu 1 mu 2 in the range of 10 2 mu 1 mu 2 10 3 and re 1 300 applying these results to magmas shows that silicic to intermediate magmas overlying mafic magma will be prone to mixing in a rising magma batch this mechanism can explain some occurrences of small volume mixed lava flows

behavior of alkalies during diffusive interaction of granitic xenoliths with basaltic magma a series of three experiments was made at 125 c and 10 kbar in which a 1 gram reservoir of molten oceanic tholeiite was maintained in contact with one end of a 6 5 mm diameter cylinder of partially molten fine grained granite detailed microprobe analysis 450 spots total of the quenched samples revealed progressive basalt granite interaction as run duration increased from 0 75 to 8 to 24 hours interdiffusion of melt components is limited for structure controlling species such as si 4 and al 3 and for divalent cations which all mix over a zone less than 0 5 mm wide in 24 hours at run conditions in contrast k and na are extremely mobile resulting in considerable uptake of k by the basalt melt and eventual loss of na from the basalt to the granite by uphill diffusion the chemical diffusivity of k in the basalt can be accurately estimated at 3 times 10 18 cm 2 sec for the specific experimental conditions used although this value is somewhat lower than previous estimates k o

kinematic considerations for mantle mixing recent experimental and computational studies tal and computational mixing studies in highly controlled show that islands u mixedrcgions that donot interactwith flows show that even seemingly inconsequential errors in the surrounding regions are ubiquitous features in chaotically computed velocity field of 3 d or time dependent flows can advecting fluids such is ands uitenaturall account for the geochemically inferred coexistence of apparently distinct long lived geochemical heterogeneity with relatively homo geneous regions of an actively convecting mantle these results also indicate that mixing patterns the set of islands and folds characterizing the large scale material advection are sensitive to small variations in the rheology of the fluid therefore interpretation of numerical simulations of mantle transport and mixing is less straightforward than currently supposed computational studies of analytic flow solutions with systematically introduced and controlled errors indi cate that mantle simulations are unlikely to accurately com pute individual trajectories for even moderate time but that tmjectory ensembles can be accuntely computed for long time significantly computations also indicate that mixing and transport resultsmay not evolve smoothly with increased rheological realism

fractal structure of heterogeneous ejecta from the me akan volcano eastern hokkaido japan implications for mixing mechanism in a volcanic conduit abstract during the somma building activity about 13 ka of the me akan volcano eastern hokkaido simultaneous eruptions of basaltic andesite andesite and dacite magmas yielded a variety of heterogeneous juvenile ejecta these heterogeneous ejecta ranging from mafic scoria to dacite pumice can be divided into three types based on the morphological structure of the pumicescoria boundary type 1 is characterized by a spot pattern type 2 by a banded pattern containing streaky dense banded and vortical structures and type 3 by irregular lumps with fingering patterns these structures and the eruptive sequence suggest that the basaltic andesite magma was injected into or drawn up with the dacite magma within the volcanic conduit beneath the nakamachineshiri crater a fractal analysis of boundary patterns of the heterogeneous ejecta was performed by a counting method over a length scale of 0 2 mm to 17 mm in order to characterize the mixing mechanism in the conduit the morphological patterns of heterogeneous ejecta have a self similar structure with fractal dimensions of d 0 9 to 1 2 for type 1 d 1 2 to 1 6 for type 2 and of d 1 2 to 1 4 for type 3 the mean value of d 1 37 0 11 for types 2 and 3 ejecta is almost the same as the value measured for fluid turbulence structures such as clouds or jets thus we infer that formation of banded and irregular lump structures was probably produced by turbulent entrainment of dacite magma into basaltic andesite magma in the conduit the lower fractal dimension of type 1 d 1 11 0 08 is due to weakly turbulent or nearly laminar processes homogeneous andesite magma is inferred to result from complete vigorous turbulent mixing

spatial aftershock distribution of the 26 december 2004 great sumatra andaman earthquake in the northern sumatra area 1 in july 2005 about 6 months after the 2004 great sumatra andaman earthquake 20 ocean bottom seismometers were deployed in the northern sumatra area more than 1000 events were identified during the 12 day recording period after relocation the seismicity shows different patterns on each side of the lower splay fault east of this feature and beneath the aceh basin and fore arc the deep earthquakes outline the subduction megathrust fault west of it the aftershocks distribution is strongly influenced by the active n s oceanic fracture zones of the subducted plate two n s trending clusters of 10 to 50 km deep earthquakes observed below the lower wedge are interpreted as reactivated oceanic fracture zones the postseismic activity suggests a significant influence of the n s active fracture zones of the oceanic plate on the toe of the wedge explaining the dextral wrenching of wedge thrusts in the morphology the megathrust fault does not extend to the trench but outcrops east of these active oceanic fractures and seems to merge upward along the lower splay fault where shallow earthquakes are observed

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

hidden dykes detected on ultra long period seismic signals at piton de la fournaise volcano broadband seismic data enable us to test whether ultra long period ulp signals can be used to investigate magma chamber pressure state and to monitor volcanic eruptions by systematically investigating seismic signals at geoscope station rer we find ulp signals associated with volcanic events during the last 2 decades we tentatively propose to interpret these signals as events highlighting the activity of the upper magma feeding system of the piton de la fournaise volcano and as being related to the deep magma chamber some of these unusual signals were previously detected and usually interpreted in term of tilt battaglia j aki k montagner j j p tilt signals derived from a geoscope vbb station on the piton de la fournaise volcano geophys res lett 27 5 2000 605 608 they are detected using sts1 seismometers sensitive in the bandwidth 10 3 to 10 2 hz this alternative model enables to quantify each event in terms of a pressure drop in the upper magma reservoir of the volcano two kinds of seismic waveforms can be associated with two types of fracturing events the first one is related to the fast rise of a magma batch coming from the deep magma chamber and the second is the result of a slow rise in pressure inside a shallow reservoir in both cases we are able to detect these events on very long period seismic data the interpretation of these signals supports the idea of a single magma source at the sea level thus we propose to classify all the eruptions occurring during the last two decades into two groups corresponding to the two primary pressure states of the magma chamber 2007 elsevier b v all rights reserved

role of magma mixing in the pre eruptive dynamics of the aeolian islands volcanoes southern tyrrhenian sea italy abstract we combined literature and experimental data to determine the role of magma mixing in the pre eruptive dynamics of the aeolian islands volcanoes as a first step we systematically reviewed the evidence supporting the hypothesis of mixing triggered eruptions in the aeolian archipelago providing textural chemical and rheological constraints the existing data highlighted the significant role of magma mixing in many eruptions within the aeolian archipelago examples include the upper pollara and porri volcano eruptions at salina monte guardia and the ad 1230 monte pilato eruption at lipari as well as the present day activity at stromboli then we focused on vulcano island chosen as a case study because it represents one of the volcanoes posing the highest risk in the aeolian archipelago at vulcano island we highlighted the role of magma mixing in the ad 1739 and 1888 90 eruptions finally we investigated mixing to eruption timescales for the ad 1739 eruption performing mixing experiments and evaluated the progressive decay of the chemical concentration variance with time results pointed to mixing to eruption timescales of the order of 29 9 h and magma ascent rates ranging between 3 10 2 and 5 10 2 m s 1 we finally emphasized that the presented results may have significant implications in the context of volcanic hazard mitigation and planning of emergency activities

effects of chaotic advection on the timescales of cooling and crystallization of magma bodies at mid crustal levels we numerically define the thermochemical evolution of a subduction related crystal bearing magmatic mass at mid crustal levels 0 7 gpa 20 25 km two main dynamic mechanisms are considered 1 a pure buoyancy driven system where the convective flow is induced by density changes during magma cooling 2 a buoyancy driven convective system governed by chaotic advection the non newtonian rheology of natural magmas is taken into account linking the herschel bulkley formulation with the results of fractional crystallization experiments of magmas with the same composition and at the same conditions of temperature and pressure of the studied system the latent heat of crystallization is also considered in order to address the thermal release in the system induced by the crystallization results indicate that the development of chaotic advection generates a complex thermochemical evolution of the system speeding up the crystallization process and the timing required to reach the jamming condition relative to the pure buoyancy driven convective system nearly 2 times faster our results have important implications for both the rheological history of the magmatic body and the refilling of shallower magmatic systems in particular 1 a time dependent composition ranging from basalt to andesite can be extracted from an initial basaltic magmatic batch 2 at the attainment of the maximum packing fraction i e just before the jamming condition homogeneous andesitic melts can be potentially extracted from the system and 3 the development of chaotic advection within the system allows for the extraction of andesitic melt in shorter times compared to a buoyancy dominated system

sound speed profile characterization by the image source method this paper presents the first results of an imaging technique that measures the geoacoustic structure of a seafloor in shallow water areas the devices used were a broadband 100 hz 6 khz acoustic source towed by a ship and a vertical array among all the acoustic paths existing in the water column two are used the direct one and the seabed reflected one the latter being composed of the reflections from the seafloor s surface as well as that from each buried layer due to the good time resolution of the signal and to the short range configuration the reflected signal can be modeled as a sum of contributions coming from image sources relative to the seabed layers the seabed geometry and the sound speed profile can then be recovered with the detection and localization of these image sources the map of the image sources is obtained by a function that combines back propagation of signals and knowledge of the emitted pulse the thickness and sound speed of each layer is finally obtained by a position analysis of the image sources the results obtained by this data driven algorithm on both at sea and synthetic data are satisfactory

relationships between deformation and mixing processes in lava flows a case study from salina aeolian islands tyrrhenian sea the massive unit of a lava flow from porri volcano salina aeolian islands displays many unusual structures related to the physical interaction between two different magmas the magma a represents approximately 80 of the exposed lava surface it has a crystal content of 51 vol and a dacitic glass composition sio2 63 64 wt the magma b has a basaltic andesite glass composition sio2 54 55 wt and a crystal content of approximately 18 vol it occurs as pillow like enclaves banding boudin like and rolling structures which are hosted in magma a structural analysis suggests that banding and boudin like structures are the result of the deformation of enclaves at different shear strain the linear correlation between strain and stratigraphic height of the measured elements indicates a single mode of deformation we deduce that the component b deformed according to a simple shear model glass analyses of the a b boundary indicate that a and b liquids mix together at high shear strain whereas only mingling occurs at low shear strain this suggests that the amount of deformation i e forced convection plays an important role in the formation of hybrid magmas high shear strain may induce stretching shearing and rolling of fluids which promote both forced convection and dynamical diffusion processes these processes allow mixing of magmas with large differences in their physical properties

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

high resolution geoacoustic inversion in shallow water a joint time and frequency domain technique high resolution geoacoustic data are required for accurate predictions of acoustic propagation and scattering in shallow water since direct measurement of geoacoustic data is difficult time consuming and expensive inversion of acoustic data is a promising alternative however the main problem encountered in geoacoustic inversion is the problem of uniqueness i e many diverse geoacoustic models can be made to fit the same data set a key and perhaps unique aspect of this approach is the combination of data analysis in both the space time and the space frequency domains this combination attempts to ameliorate the uniqueness problem by exploiting as much independent data as possible in order to meet the stringent requirements of high spatial resolution and uniqueness an entire method has been developed including a new measurement technique processing analysis technique and inversion strategy these techniques are described and then illustrated with a shallow water data set sound speed gradients in the upper few meters of the sub bottom appear to be much higher one order of magnitude than generally assumed and although often ignored a large density gradient was observed in the top layer that played an acoustically significant role

time scales of crystal mixing in magma mushes magma mixing is widely recognized as a means of producing compositional diversity and preconditioning magmas for eruption however the processes and associated time scales that produce the commonly observed expressions of magma mixing are poorly understood especially under crystal rich conditions here we introduce and exemplify a parameterized method to predict the characteristic mixing time of crystals in a crystal rich magma mush that is subject to open system reintrusion events our approach includes novel numerical simulations that resolve multiphase particle fluid interactions it also quantifies the crystal mixing by calculating both the local and system wide progressive loss of the spatial correlation of individual crystals throughout the mixing region both inertial and viscous time scales for bulk mixing are introduced estimated mixing times are compared to natural examples and the time for basaltic mush systems to become well mixed can be on the order of 10 days

petrographic classification of crystal morphology the terms euhedral subhedral and anhedral have limited value as an expression of crystal morphology relating to conditions of crystal formation and rock forming processes the basis of this traditional nomenclature is the presence or absence of crystal faces implying that if a crystal has faces its overall shape is likely to reflect crystal structure experimental reproduction of growth dissolution and melting textures along with an ever increasing awareness of the importance of incomplete and malformed crystals in natural systems is the impetus for presentation here of a more detailed morphological classification of crystals at the petrographic scale the classification is binary based on the degree to which crystals are an expression of crystal structure and on the degree of completeness unlike the traditional scheme the proposed classification is sensitive to faceted crystals that do not have ideal shape and to incomplete crystals variously described as skeletal dendritic cellular

range dependent sediment sound speed profile measurements using the image source method this paper presents a range dependent sediment sound speed profile measurement obtained using the image source method this technique is based on the analysis of the seafloor reflected acoustic wave as a collection of image sources which positions are linked with the thick nesses and the sound speed of the sediment stack the data used were acquired by the nurc in 2009 during the clutter09 experiment the equipment used was an autonomous undersea vehicle towing a 1600 3500 hz frequency band source and a 32 m horizontal line array of 32 hydrophones at 12 m above the seabed under the assumption of locally range independent seabed properties the moving horizontal array provides successive range independent sediment sound speed profiles along a track to obtain the range and depth dependent structure of the seafloor two key steps include recovery of the time varying unknown array shape from the data and spatial filtering of the successive sound speed profiles a comparison of the image source method result and seismic data along nearly the same 14 km track indicates that the seabed stratigraphy is correctly mapped by this method

magma mixing by convective entrainment recent studies of volcanic eruptions have brought to light a puzzling sequence the ejection of dense and mixed liquids followed by a larger volume of unmixed less dense liquid1 4 although these studies have shown that the mixing is associated with the injection of basaltic liquid into a more silicic magma chamber a paradox remains basaltic magma is denser than silicic magma and should flow along the floor of the magma chamber this configuration impedes mixing of the two liquids and appears incompatible with the early eruption of basaltic liquid from the top of the chamber previously proposed mixing processes explain neither the eruption sequence nor the eruption of dense liquid during the time of lowest eruption rate1 8 we report here fluid mechanical experiments that suggest a solution a thermal plume forms over the replenishment inlet dragging basaltic liquid upward by viscous coupling and producing mixing only in a localized area without affecting the bulk of the chamber

dynamics and time evolution of a shallow plumbing system the 1739 and 1888 90 eruptions vulcano island italy abstract in this work we analyze the morphology of latitic enclaves occurring in the rhyolitic lava flow of pietre cotte island of vulcano italy we show that enclave morphology is a feature inherited from the shallow plumbing system of the volcano during the invasion of the latitic magma into the rhyolitic magma the complexity of enclave morphology is quantified by fractal analyses using the empirical relationship given by perugini et al 2005 relating the fractal dimension and viscosity ratio the range of viscosity ratios that developed during the injection of the latitic magma into the rhyolitic one is estimated thermodynamical and rheological modeling indicates that the most plausible scenario to explain the variability of observed viscosity ratios is represented by a plumbing system where a large volume of latitic magma intruded a smaller volume of rhyolitic magma the comparison of volume proportions of magmas on the outcrop with those estimated by the modeling allows us to infer that most of the latitic magma remained in the plumbing system after the ending of the 1739 eruptive cycle the strong similarity of compositions from the pietre cotte lava flow and products erupted during the last volcanic activity of vulcano 1888 1890 is interpreted as the reactivation of the latitic magma that possibly evolved through fractional crystallization to produce trachy rhyolitic compositions during the 1888 1890 eruptive cycle we suggest that the methodological approach presented here can represent a further tool for hazard mitigation in volcanic areas in particular it allows obtaining information about the dynamics of plumbing systems of active volcanoes and their time evolution

the mixing of magmas in plutonic and volcanic environments analogies and differences abstract magma mixing processes have been widely recognized in both the plutonic and volcanic environments but the quality and quantity of information that can be extracted from the two environments are substantially different understanding the advantages and limits associated with the study of plutonic and volcanic rocks is essential to establish precise methodological approaches to build the most complete conceptual model by merging information from these two complementary igneous environments in this work we review magmatic interaction processes in the plutonic and volcanic environments by considering several aspects of these geological phenomena in particular we first briefly report on the structural and geochemical evidence for magma mixing in both plutonic and volcanic rocks with the aim to provide a general picture of this natural phenomenon successively we discuss some recent results about magma mixing achieved using the concepts from chaos theory and discuss their potential impact on magma differentiation finally we attempt to build a general picture of this igneous process by merging present day information from both the plutonic and volcanic environments it emerges from the general picture that the time spent by the magmatic system in the molten or partially molten state is the crucial factor for the preservation of the fingerprints of magma mixing in the two environments we propose a conceptual model that may be useful to understand what kind of information we can obtain from volcanic and plutonic rocks and ultimately to maximize our knowledge about magma mixing

exponential decay of concentration variance during magma mixing robustness of a volcanic chronometer and implications for the homogenization of chemical heterogeneities in magmatic systems abstract the mixing of magmas is a fundamental process in the earth system causing extreme compositional variations in igneous rocks this process can develop with different intensities both in space and time making the interpretation of compositional patterns in igneous rocks a petrological challenge as a time dependent process magma mixing has been suggested to preserve information about the time elapsed between the injection of a new magma into sub volcanic magma chambers and eruptions this allowed the use of magma mixing as an additional volcanological tool to infer the mixing to eruption timescales in spite of the potential of magma mixing processes to provide information about the timing of volcanic eruptions its statistical robustness is not yet established this represents a prerequisite to apply reliably this conceptual model here new chaotic magma mixing experiments were performed at different times using natural melts the degree of reproducibility of experimental results was tested repeating one experiment at the same starting conditions and comparing the compositional variability we further tested the robustness of the statistical analysis by randomly removing from the analysed dataset a progressively increasing number of samples results highlight the robustness of the method to derive empirical relationships linking the efficiency of chemical exchanges and mixing time these empirical relationships remain valid by removing up to 80 of the analytical determinations experimental results were applied to constrain the homogenization time of chemical heterogeneities in natural magmatic system during mixing the calculations show that when the mixing dynamics generate millimetre thick filaments homogenization timescales of the order of a few minutes are to be expected

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

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

on convection in a volatile saturated magma when a saturated basaltic magma cools and crystallises in a shallow magma reservoir gas bubbles may be exsolved from solution thereby influencing the density convective mixing and pressure evolution of the melt in wet basaltic magmas saturated with h2o the production of small bubbles may dominate the density evolution of the mixture causing a gradual decrease of the bulk density with cooling cool upper boundaries of the chamber may therefore become stable to convection while vigorous convection may develop as the bubbly mixture rises from cold lower boundaries the intensity of such bubble driven convection may be an order of magnitude greater than purely thermal or compositional convection which arises in unsaturated melt new laboratory experiments of such bubble driven convection suggest that after a transient an equilibrium bubble concentration is attained and subsequently bubble magma separation leads to build up of a layer of bubbles above the well mixed bubble laden melt 1 these results have some important implications for mixing when a volatile rich mafic magma is intruded below an evolved less dense body of silicic magma when the mafic magma becomes volatile saturated then owing to cooling at its upper boundary the bulk density in the upper boundary layer of the mafic magma will decrease owing to the exsolution of gas if the density falls below that of the overlying silicic magma then small plumes of buoyant bubble rich mafic magma may rise from the boundary into the upper silicic layer in addition on saturation of the mafic magma cooling at the lower boundary will begin to drive convection of bubble rich melt the mafic magma may eventually reach an equilibrium bubble concentration and subsequently the bubbles produced at the base of the layer will be supplied to the interface between the silicic and mafic layers large scale overturn of the mafic and silicic magmas can therefore only occur if at the equilibrium bubble concentration the bulk density of the bubbly mafic magma is smaller than that of the overlying magma otherwise mixing continues through small plumes of vesicular mafic melt rising from the upper boundary layer for basaltic magma in which co2 is the dominant volatile phase the generation of bubbles does not typically dominate the density evolution and the convective flows are similar to those in an unsaturated melt

time evolution of chemical exchanges during mixing of rhyolitic and basaltic melts we present the first set of chaotic mixing experiments performed using natural basaltic and rhyolitic melts the mixing process is triggered by a recently developed apparatus that generates chaotic streamlines in the melts mimicking the development of magma mixing in nature the study of the interplay of physical dynamics and chemical exchanges between melts is carried out performing time series mixing experiments under controlled chaotic dynamic conditions the variation of major and trace elements is studied in detail by electron microprobe and laser ablation icp ms the mobility of each element during mixing is estimated by calculating the decrease in the concentration variance in time both major and trace element variances decay exponentially with the value of exponent of the exponential function quantifying the element mobility our results confirm and quantify how different chemical elements homogenize in the melt at differing rates the differential mobility of elements in the mixing system is considered to be responsible for the highly variable degree of correlation linear nonlinear or scattered of chemical elements in many published inter elemental plots elements with similar mobility tend to be linearly correlated whereas as the difference in mobility increases the plots become progressively more nonlinear and or scattered the results from this study indicate that the decay of concentration variance is in fact a robust tool for obtaining new insights into chemical exchanges during mixing of silicate melts concentration variance is in a single measure an expression of the influence of all possible factors e g viscosity composition and fluid dynamic regime controlling the mobility of chemical elements and thus can be an additional petrologic tool to address the great complexity characterizing magma mixing processes

frictional melt homogenisation during fault slip geochemical textural and rheological fingerprints abstract volcanic environments often represent structurally active settings where strain localisation can promote faulting frictional deformation and subsequent melting along fault planes such frictional melting is thermodynamically a disequilibrium process initiated by selective melting of individual mineral phases and softening of volcanic glass at its glass transition as a response to rapid frictional heating the formation of a thin melt layer on a fault plane surface can drastically accelerate or terminate slip during fault motion a comprehensive understanding of the physical and chemical properties of the frictional melt is required for a full assessment of slip mechanisms as frictional rheology depends on the contributions from selectively melted mineral and glass phases as well as the physical effects of restite fragments suspended in the frictional melt here we experimentally investigate the impact of host rock mineralogy on the compositional and textural evolution of a frictional melt during slip high velocity rotary shear hvr experiments were performed under controlled volcanically relevant coseismic conditions 1 m s 1 slip rate and 1 mpa normal stress using three intermediate dome lavas with contrasting mineral assemblages sampled from volcanic systems where fault friction is evident 1 an amphibole bearing andesite soufriere hills volcano montserrat 2 an amphibole poor dacite santiaguito dome complex guatemala and 3 an amphibole free andesite volcan de colima mexico for each sample five hvr experiments were terminated at different stages of frictional melt evolution namely 1 at the onset of melting 2 upon formation of a steady state melt layer and 3 after 5 m 4 10 m and 5 15 m of slip at steady state conditions progressive mixing and homogenisation of selective single phase melts within the frictional melt layer through double diffusion convection demonstrates the control of melt composition on slip behaviour amphiboles melted preferentially leading to consistently lower shear stress 1 mpa less than amphibole poor samples and pronounced shear weakening during the frictional melting of amphibole bearing lavas the results highlight the implications of mineral assemblages on fault slip including conduit flow processes which may influence the style of eruptions and run out distances of rapid granular flows

interactions between dioritic and granodioritic magmas in mingling zones plagioclase record of mixing mingling and subsolidus interactions in the gesiniec intrusion ne bohemian massif sw poland dioritic and granodioritic rocks coexist in the gesiniec intrusion in sw poland showing typical relationships in many mafic felsic mingling zones worldwide such as dioritic syn putonic dykes and microgranular enclaves within granodioritic host plagioclase zonation from granodioritic rocks suggests late stage mixing probably with dioritic magma whereas no magma mixing is recorded in plagioclase from dioritic rocks the diorites seem to show effects of interaction with evolved leucocratic melts derived from granodiorite not with the granodioritic melt itself we conclude that the diorites compositions were modified after their emplacement within the granodioritic host when the diorites were essentially solidified and injection of evolved melt from granodiorite did not involve marked modification of plagioclase composition compositional zoning patterns of plagioclase in diorites can be modeled by closed system fractional crystallization interrupted by resorption induced probably by decompression granodioritic plagioclase seems to be affected by the same resorption event plagioclase that crystallized in dioritic magma before the resorption does not record interaction between dioritic and granodioritic magmas suggesting that both magmas evolved separately

transition to chaos and implications for time scales of magma hybridization during mixing processes in magma chambers abstract in this contribution numerical simulations of magma mixing are carried out with the aim of understanding the physico chemical conditions that trigger the development of chaotic mixing dynamics in detail the mixing process is simulated in a magma chamber where a less evolved magma underplates a more evolved magma the chaoticity of this system is quantitatively estimated via computed finite time lyapunov exponents it is shown that magma chamber dynamics are strongly controlled by the rayleigh number ra whereas other parameters such as buoyancy ratio and viscosity ratio play a subordinate role results indicate that magma chambers with ra of the order of 10 6 are dominated by non chaotic behaviour increasing ra shifts the system towards an increasing chaotic state and in particular above ra 10 7 chaotic dynamics are fully developed in the magma chamber estimates of possible time scales of hybridization of magmas during chaotic mixing suggest for example that a blob of mafic magma with an initial diameter of 100 m within a magma chamber with a width of 1000 m is stretched to a filament like structure with a thickness of 15 m after 320 years and after 1900 years its thickness is reduced to 4 0 mm using typical chemical diffusion coefficients for magmas of the order of 10 14 m 2 s it can be calculated that a 4 0 mm thick filament would homogenize by diffusion in 10 years such homogenization time scales are orders of magnitude lower that typical life times estimated for magma chambers even in the volcanic environment indicating that fast hybridization of magmas can be rapidly achieved when chaotic dynamics govern the evolution of the magmatic system

high resolution geochemistry of volcanic ash highlights complex magma dynamics during the eyjafjallajokull 2010 eruption the april to may 2010 eruption of eyjafjallajokull iceland volcano was characterized by a large compositional variability of erupted products to contribute to the understanding of the plumbing system dynamics of this volcano we present new empa and la icp ms data on groundmass glasses of ash particles and minerals erupted between april 15 and 22 the occurrence of disequilibrium textures in minerals such as resorption and inverse zoning indicate that open system processes were involved in determining the observed compositional variability the variation of major and trace element data of glasses corroborates this hypothesis indicating that mixing between magma batches with different compositions interacted throughout the whole duration of the eruption in particular the arrival of new basaltic magma into the plumbing system of the volcano destabilized and remobilized magma batches of trachyandesite and rhyolite compositions that according to geophysical data might have intruded as sills over the past 20 years beneath the eyjafjallajokull edifice two mixing processes are envisaged to explain the time variation of the compositions recorded by the erupted tephra the first occurred between basaltic and trachyandesitic end members the second occurred between trachyandesite and rhyolites least squares modeling of major elements supports this hypothesis furthermore investigation of compositional histograms of trace elements allows us to estimate the initial proportions of melts that interacted to generate the compositional variability triggered by mixing of trachyandesites and rhyolites

diffusive fractionation of trace elements by chaotic mixing of magmas abstract recent research on magma mixing systems has shown that the mixing process is governed by chaotic dynamics and that this process is responsible for the generation of fractal structures that propagate within the magmatic mass from the meter to the micrometer length scale laser ablation icp ms trace element analyses have been performed on rock samples with evidence of chaotic mixing phenomena results indicate that trace elements with similar values of diffusion coefficient display good correlations in inter elemental plots whereas as the difference between diffusion coefficients increases the correlation is progressively lost in addition a large variability of ree patterns is observed with the remarkable feature of the presence of positive and negative eu anomalies occurring at short length scale of the order of few mm given the chaotic nature of magma mixing structures the mixing process has been simulated by coupling a chaotic advection and a chemical diffusion numerical scheme by considering several trace elements with variable diffusivities simulations indicate that such a model explains with good approximation the variable correlations among trace elements observed in natural samples in addition the same patterns of ree observed in natural samples including the occurrence of positive and negative eu anomalies at short length scale are observed indicating that a chaotic advection diffusion dynamic system is a suitable model to explain natural data results presented in this contribution indicate that at the micrometric length scale small volumes of magmas are strongly influenced by the coupled action of chemical diffusion and chaotic flow fields and hence they do not represent magmas de facto present in the magmatic system because their compositions may have experienced a diffusive fractionation process these results may have important petrogenetic implications for instance if such melts were trapped as melt inclusions they would provide misleading information about melt compositions it is suggested that the approach of studying the degree of correlation among trace elements may be a possible method to test if melt inclusion compositions commonly used as petrogenetic indicators display evidence of such a diffusive fractionation process

isotopic evolution of the mantle the role of magma mixing trace element and isotopic data for magmas from the two major mantle reservoirs appear to be inconsistent the incompatible elements and sr and nd isotopes show that abyssal tholeiities morb are form a reservoir that has current and time integrated depletions of the elements that are fractionated into a melt morb however have206pb 204pb and207pb 204pb ratios suggesting long term enrichment in u pb i e future single stage ages alkali basalts and tholeiities from continents and oceanic islands are derived from lile and u pb enriched reservoirs sr and nd isotopic ratios however appear to indicate that some of these basalts are derived from unfractionated reservoirs and others from reservoirs with time integrated depletions the apparent stages of the mantle reservoirs are much younger than the ages of continental shields these inconsistencies can be reconciled by assuming that oceanic and continental basalts are mixtures of magmas from depleted and enriched reservoirs morb are slightly contaminated depleted magmas while ocean island and continental basalts are mixtures of morb or a depleted picritic parent magma and an enriched end member having trace element patterns similar to high k magmas such as kimberlites or nephelinites the mixing relations are such that mixtures can be enriched in u pb rb sr nd sm 206pb 204pb relative to primitive mantle yet appear to have time integrated depletions in143nd 144nd and87sr 86sr a small amount of contamination by material from an enriched reservoir can explain the pb results for morb depleted basalts are more sensitive to pb than to rb or nd contamination the238u 204pb of uncontaminated morb may be about 7 compared to 7 9 for the primary growth curve and 10 for the enriched reservoirs similarly continental and ocean island basalts may represent mixtures of enriched and depleted magmas if so the ages of mantle reservoirs have been underestimated we propose that both of the major mantle magmas source are in the upper mantle and that both are global in extent the shallower one 200 km depth is inhomogenous having been enriched metasomatised at various time by fluids from the depleting layer it may also be the sink of subducted sediments and hydrothermally altered oceanic crust the deeper source 220 670 km depth is more homogenous more garnet rich and provides depleted magmas which however become contaminated as they rise through the shallow encriched layer partial melting and diapiric ascent originated in the thermal boundary layer between the two chemically distinct layers magma mixing prior to eruption is an inevitable consequence of a chemically layered mantle with depleted magmas rising through an enriched uppermost mantle this allows quantification of the heretofore nebolous concept of mantle metasomatism

open system dynamics and mixing in magma mushes magma in earth s crust is in a crystal rich mushy state yet must be fluidized before eruptions numerical simulations show that rapid injection of new magma into a reservoir creates a mixing bowl of fluid and crystals that are able to erupt

tomographic inversion of geoacoustic properties in a range dependent shallow water environment this paper presents a matched field tomographic method to estimate the geoacoustic properties of the ocean bottom for a range dependent medium in shallow water the inversion method has been developed in order to interpret experimental data from the haro strait primer sea trial this experiment was carried out in june 96 and used low frequency broadband signals that were received on three vertical line arrays inversion of the data is particularly difficult because of the complex bathymetry of the haro strait experimental site for this inversion a range dependent ray code was developed to solve the forward problem allowing an arbitrarily layered bottom environment the inversion scheme is based on modeling the propagation time and the amplitude of the recorded data and a simple new cost function is proposed the signal ray paths are identified automatically using a simple process that compares calculated and measured travel times data from multiple source positions are used to invert the range dependence of the geoacoustic model the environment is separated into segments and within each segment the inversion is carried out layer by layer for a multilayer geoacoustic model starting with the topmost layer the range dependent thickness and sound speed are estimated via a monte carlo method inversion results are presented for synthetic and experimental data from the haro strait sea trial

constraining the recent plumbing system of vulcano aeolian arc italy by textural petrological and fractal analysis the 1739 a d pietre cotte lava flow 1 the 1739 a d pietre cotte lava flow is part of a sequence of low explosive to weak effusion events occurred at la fossa cone the active vent on vulcano island aeolian arc italy this lava is rhyolitic texturally heterogeneous and contains lati trachytic enclaves these compositions are recurrent in the la fossa volcanic products and are representative of the recent vulcano plumbing system the host lava is vesicular relatively phenocryst free and locally contains microlites and millimeter sized spherulites the enclaves are up to 10 cm in size display angular to spherical shapes and can form the core of spherulites enclaves mostly consist of plagioclase and augitic phenocrysts set in a weakly vesicular groundmass characterized by variable abundance of glass and feldspar microlites field textural and fractal data allow us to constrain the rheological features of the rhyolitic and lati trachytic magmas in situ major trace and volatile element analyses provide evidence for heterogeneities in the glassy matrix and zoning of phenocrysts processes of magma evolution have been quantitatively constrained by using the apparent distribution ratios of trace elements measured between mineral phases and glassy matrices the collected data in combination with petrological and fluid inclusion data from the literature provides evidence for 1 a genetic relationship between the two magmas through assimilation fractional crystallization process 2 a mingling mechanism between an uprising rhyolitic magma and a shallower partly crystallized lati trachytic magma plug 3 the desegregation enclaves at variable scales of the lati trachyte within the rhyolite and 4 the possible eruptive scenarios consequent to a future magmatic unrest

enhancement of magma mixing efficiency by chaotic dynamics an experimental study magma mixing is common in the earth understanding the dynamics of the mixing process is necessary for dealing with the likely consequences of mixing events in the petrogenesis of igneous rocks and the physics of volcanic eruptive triggers here a new apparatus has been developed in order to perform chaotic mixing experiments in systems of melts with high viscosity contrast the apparatus consists of an outer and an inner cylinder which can be independently rotated at finite strains to generate chaotic streamlines the two cylinder axes are offset experiments have been performed for ca 2 h at 1 400 c under laminar fluid dynamic conditions re 10 7 two end member silicate melt compositions were synthesized 1 a peralkaline haplogranite and 2 a haplobasalt the viscosity ratio between these two melts was of the order of 103 optical analysis of post experimental samples reveals a complex pattern of mingled filaments forming a scale invariant i e fractal distribution down to the m scale as commonly observed in natural samples this is due to the development in space and time of stretching and folding of the two melts chemical analysis shows strong non linear correlations in inter elemental plots the original end member compositions have nearly entirely disappeared from the filaments the generation of thin layers of widely compositionally contrasting interfaces strongly enhances chemical diffusion producing a remarkable modulation of compositional fields over a short length scale notably diffusive fractionation generates highly heterogeneous pockets of melt in which depletion or enrichment of chemical elements occur depending on their potential to spread via chemical diffusion within the magma mixing system results presented in this work offer new insights into the complexity of processes expected to be operating during magma mixing and may have important petrological implications in particular 1 it is shown that in contrast with current thinking rheologically contrasting magmas can mix i e with large proportions of felsic magmas and high viscosity ratios thus extending significantly the spectrum of geological conditions under which magma mixing processes can occur efficiently 2 the mixing process cannot be modeled using the classical linear two end member mixing model and 3 the chemical compositions on short length scales represent snapshots within the process of mixing and therefore may not reflect the final composition of the magmatic system this study implies that microanalysis on short length scales may provide misleading information on the parental composition of magmas

compositional variations and magma mixing in the 1991 eruptions of hudson volcano chile the august 1991 eruptions of hudson volcano produced 2 7 km3 dense rock equivalent dre of basaltic to trachyandesitic pyroclastic deposits making it one of the largest historical eruptions in south america phase 1 of the eruption p1 april 8 involved both lava flows and a phreatomagmatic eruption from a fissure located in the nw corner of the caldera the paroxysmal phase p2 began several days later april 12 with a plinian style eruption from a different vent 4 km to the south southeast tephra from the 1991 eruption ranges in composition from basalt phase 1 to trachyandesite phase 2 with a distinct gap between the two erupted phases from 54 60 wt sio2 a trend of decreasing sio2 is evident from the earliest part of the phase 2 eruption unit a 63 65 wt sio2 to the end unit d 60 63 wt sio2 melt inclusion data and textures suggest that mixing occurred in magmas from both eruptive phases the basaltic and trachyandesitic magmas can be genetically related through both magma mixing and fractional crystallization processes a combination of observed phase assemblages inferred water content crystallinity and geothermometry estimates suggest pre eruptive storage of the phase 2 trachyandesite at pressures between 50 100 megapascal mpa at 972 26 c under water saturated conditions log fo2 10 33 0 2 it is proposed that rising p1 basaltic magma intersected the lower part of the p2 magma storage region between 2 and 3 km depth subsequent mixing between the two magmas preferentially hybridized the lower part of the chamber basaltic magma continued advancing towards the surface as a dyke to eventually be erupted in the northwestern part of the hudson caldera the presence of tachylite in the p1 products suggests that some of the magma was stalled close to the surface 0 5 km prior to eruption seismicity related to magma movement and the p1 eruption combined with chamber overpressure associated with basalt injection may have created a pathway to the surface for the trachyandesite magma and subsequent p2 eruption at a different vent 4 km to the south southeast

resolving meso scale seabed variability using reflection measurements from an autonomous underwater vehicle seabed geoacoustic variability is driven by geological processes that occur over a wide spectrum of space time scales while the acoustics community has some understanding of horizontal fine scale geoacoustic variability less than o 100 m and large scale variability greater than o 103 m there is a paucity of data resolving the geoacoustic meso scale o 100 103 m measurements of the meso scale along an ostensibly benign portion of the outer shelf reveal three classes of variability the first class was expected and is due to horizontal variability of layer thicknesses this was the only class that could be directly tied to seismic reflection data the second class is due to rapid changes in layer properties and or boundaries occurring over scales of meters to hundreds of meters the third class was observed as rapid variations of the angle frequency dependent reflection coefficient within a single observation and is suggestive of variability at scales of meter or less though generally assumed to be negligible in acoustic modeling the second and third classes are indicative of strong horizontal geoacoustic variability within a given layer the observations give early insight into possible effects of horizontal geoacoustic variability on long range acoustic propagation and reverberation

silicic magma chambers as traps for basaltic magmas the cadillac mountain intrusive complex mount desert island maine the cadillac mountain intrusive complex located on mount desert island maine provides a superb record of episodic invasion of a floored silicic magma chamber by many pulses of basaltic magma the complex consists of three units the cadillac mountain granite cmg the somesville granite sg and gabbro diorite g d basaltic magmas were emplaced before during and after the emplacement and crystallization of the granitic plutons and the chambers of silicic magma acted as traps for basaltic magma basaltic magma emplaced into the surrounding country rocks crystallized as homogeneous diabase and gabbro while basaltic magma emplaced within the perimeter of the granite displays abundant evidence for commingling with silicic magma the g d unit about 1 5 km thick consists of interlayered gabbroic dioritic and granitic rocks although thin 1 m thick gabbroic layers in the g d unit are typically chilled on all margins thicker layers of gabbro commonly form the lower parts of macrorhythmic units

fractal analysis of enclaves as a new tool for estimating rheological properties of magmas during mixing the case of montana reventada tenerife canary islands the volcanic unit of montana reventada on the island of tenerife canary islands spain is an example of magma mingling and mixing in which the eruptive process was triggered by an intrusion of basanite into a phonolite magma chamber the eruption started with emplacement of a basanitic scoria deposit followed by emplacement of a phonolitic lava flow characterized by the presence of mafic enclaves these enclaves represent approximately 1 of the outcrop and are basanitic phono tephritic and tephri phonolitic in composition the morphology of each enclave is different varying from rounded to complex finger like structures usually with cuspate terminations in this study we quantified textural heterogeneity related to the enclaves generated by the mixing process and thus provided a new perspective on the 1100 ad montana reventada eruption the textural study was performed by use of fractal geometry methods and the results show that the logarithm of the viscosity ratio between the phonolitic magma and the enclaves ranges between 0 39 and 0 81 with a mode at 0 49 this enables us to infer the water content is 2 2 5 wt for the phonolitic magma and 1 5 2 wt for the basanitic magma and the enclaves

viscous fingering during replenishment of felsic magma chambers by continuous inputs of mafic magmas field evidence and fluid mechanics experiments vegetation island outcrops terra nova intrusive complex antarctica offer a unique example of the replenishment of a felsic magma chamber fossilized at the initial stages of intrusion of a mafic magma the morphology of interfaces between the mafic and the felsic magma ranges from rounded to finger like and their quantification by means of fractal dimension indicates a wide variability of morphological complexity fluid mechanics experiments of viscous fingering have been performed by injecting water glycerin solutions with different viscosity ratios into pure glycerin using the hele shaw cell the fact that interface morphologies between the injected and the host fluid are identical to those observed on outcrops indicates that the latter shows the development of viscous fingering processes during the initial stages of intrusion of the mafic magma into the felsic magma chamber the fractal dimension of the simulated structures was measured and a very good exponential empirical relationship between the logarithm of viscosity ratio and fractal dimension has been derived the empirical relationship is used to estimate viscosity ratios of natural structures by using measured values of fractal dimension results indicate that in the same magmatic system a wide range of viscosity ratio existed between the two magmas these results are used to reconstruct the mechanism of replenishment of the felsic magma chamber as characterized by continuous heating of the resident felsic magma by continuous inputs of the mafic magma

assessment of a shallow magmatic system the 1888 90 eruption vulcano island italy the magmatic system feeding the last eruption of the volcano la fossa vulcano island italy was studied the petrogenetic mechanisms controlling the differentiation of erupted rocks were investigated through petrography mineral chemistry major trace and rare earth element and sr nd and pb isotopic geochemistry in addition melt inclusion and fluid inclusion data were collected on both juvenile material and xenolithic partially melted metamorphic clasts to quantify the p t conditions of the magma chamber feeding the eruption a regular and continuous chemical zoning has been highlighted rhyolites are the first erupted products followed by trachytes and latites whereas rhyolitic compositions were also found in the upper part of the sequence the chemical and isotopic composition of the rhyolites indicates that they originated by fractional crystallization from latitic magmas plus the assimilation of crustal material the trachytes represent hybrid magmas resulting from the mixing of latites and rhyolites contaminated in the shallow magmatic system the erupted products primarily compositionally zoned from latites to rhyolites are heterogeneous due to syn eruptive mingling the occurrence of magmacrust interaction processes evidenced by isotopic variations 87sr 86sr 0 70474 3 to 0 70511 3 143nd 144nd 0 512550 6 to 0 512614 8 206pb 204pb 19 318 19 489 207pb 204pb 15 642 15 782 208pb 204pb 39 175 39 613 is confirmed by the presence of partially melted metamorphic xenoliths with 87sr 86sr 0 71633 6 to 0 72505 2 and 143nd 144nd 0 51229 7 in rhyolites and trachytes afc calculations indicate a few percentage contribution of crustal material to the differentiating magmas thermometric measurements on melt inclusions indicate that the crystallization temperatures of the latites and trachytes were in the range of 1050 1100 c whereas the temperature of the rhyolites appears to have been around 1000 c at the time of the eruption compositional data on melt inclusions reveal that the magmas involved in the eruption contained about 1 1 5 wt dissolved h2o in pre eruptive conditions secondary fluid inclusions found in metamorphic xenoliths give low equilibration pressure data 30 60 mpa giving the location of the higher portions of the chamber at around 1500 2000 m of depth

experimental mixing of hydrous magmas deformation experiments involving hydrous magmas of different compositions basalt and haplotonalite have been performed in a paterson press at 300 mpa in the temperature range 600 c 1020 c with water saturated melts during 2 4 h prior to deformation the two end member magmas were annealed at either 950 c or 1000 c yielding magmas with crystal contents in the range 31 53 wt and 2 sets of viscosity contrasts under the experimental conditions investigated i e moderate shear rates 950 c in the temperature range 950 985 c a few mixing and mingling textures occur though both end members essentially retain their physical integrity it is only at or above 1000 c that a dramatic jump in mingling efficiency happens corresponding to a crystal fraction of 45 vol textures include entrainment of mafic crystals into the felsic magma mafic felsic banding enclave formation and diffusion induced interface the latter only over limited distances 300 m due to the short run durations in the most strained parcels of interacting magmas complex mixing mingling textures were produced similar to those observed in volcanic and plutonic rocks in arc settings the experiments show that mixing between hydrous felsic and mafic magmas takes place at around 1000 c a temperature which is almost 200 c lower than mixing under dry conditions magma mixing is commonly invoked as a trigger for volcanic eruptions our experiments suggest that such eruptions can be driven by small 15 c temperature fluctuation in the reservoir our results also suggest that slow replenishment of a felsic reservoir by mafic inputs will likely result in stratification between end members rather than in a homogeneous mixture

chaotic three dimensional distribution of ba rb and sr in feldspar megacrysts grown in an open magmatic system as has been demonstrated in recent years the heterogeneities of coeval magmas can be more successfully revealed by zoned megacrysts rather than by analysis of the whole rocks hosting them here the geochemical heterogeneities of feldspar megacrysts from the karkonosze granite poland are investigated by la icp ms the crystals are the product of migration and growth in regions of poorly mixed magmas 3d modeling of the ba sr and rb distributions emphasizes the importance of micro domain growth morphologies two models of element behavior a relative concentration model and a composition gradient model provide a potentially effective tool for tracking the mixing process on a microscale measured concentrations of elements of different mobilities do not agree with what might be expected from the mixing of two end member magmas if mixing was the only process occurring linear correlations between the concentrations of any two elements should be observed this however is not the case for combinations of any two of the three elements modeling reveals differing non linear correlations between concentrations the megacryst heterogeneities provide an insight into how mixing magmas are chaotically advected to growing crystals and the degree of inter magma element exchange between the magmas

the grizzly lake complex yellowstone volcano usa mixing between basalt and rhyolite unraveled by microanalysis and x ray microtomography abstract magma mixing is a widespread petrogenetic process it has long been suspected to operate in concert with fractional crystallization and assimilation to produce chemical and temperature gradients in magmas in particular the injection of mafic magmas into felsic magma chambers is widely regarded as a key driver in the sudden triggering of what often become highly explosive volcanic eruptions understanding the mechanistic event chain leading to such hazardous events is a scientific goal of high priority here we investigate a mingling event via the evidence preserved in mingled lavas using a combination of x ray computed microtomographic and electron microprobe analyses to unravel the complex textures and attendant chemical heterogeneities of the mixed basaltic and rhyolitic eruption of grizzly lake in the norris mammoth corridor of the yellowstone plateau volcanic field yvf we observe evidence that both magmatic viscous inter fingering of magmas and disequilibrium crystallization dissolution processes occur furthermore these processes constrain the timescale of interaction between the two magmatic components prior to their eruption x ray microtomography images show variegated textural features involving vesicle and crystal distributions filament morphology the distribution of enclaves and further textural features otherwise obscured in conventional 2d observations and analyses although our central effort was applied to the determination of mixing end members analysis of the hybrid portion has led to the discovery that mixing in the grizzly lake system was also characterized by the disintegration and dissolution of mafic crystals in the rhyolitic magma the presence of mineral phases in both end member for example forsteritic olivine sanidine and quartz and their transport throughout the magmatic mass by a combination of both mixing dynamics and flow imposed by ascent of the magmatic mass and its eruption might have acted as a geometric perturbation of flow fields further fuelling mass exchange between magmas in terms of both chemical diffusion and crystal transfer these results illuminate the complexity of mixing in natural magmatic systems identifying several reaction related textural factors that must be understood more deeply in order to advance our understanding of this igneous process

the interplay between crystallization replenishment and hybridization in large felsic magma chambers abstract while hybridized granitoid magmas are readily identifiable the mechanisms of hybridization in large crustal magma chambers are so not clearly understood characteristic features of hybrid granitoids are 1 both the granitoid and included enclaves are commonly hybrids as shown by mineralogy geochemistry and isotopes 2 mixing seen in zoned plutons and synplutonic dykes and enclaves occurred early 3 zoned plagioclase phenocrysts commonly show very complex life histories of growth and dissolution 4 mafic end members in hybrids are commonly fractionated magmas and 5 stratification in subvolcanic granitoid magma chambers is not uncommon and stratification has been identified in some deeper level plutons hybridization must overcome the tendency to form a stable stratification of dense mafic magma underlying less dense felsic magma experimental work with magma analogues and theoretical considerations reveal very severe thermal rheological and dynamical limitations on mixing only very similar composition temperature magmas are likely to mix to homogeneity and only moderately silicic hybrids are likely to be produced however impossibly silicic hybrids do exist synchronous interactive fractional crystallization and hybridization may provide a mechanism for hybridization of magmas in the following manner a mafic magma intrudes into the base of a stratified felsic magma and is cooled against it crystallization of the upper boundary layer of the mafic magma yields an eventually buoyant residual melt that overturns and mixes with an adjacent stratum of the felsic magma chamber subsequently melt released by crystallization pf this now hybrid zone mixes with adjacent more felsic zones thus a suite of hybrid magmas are progressively formed density inhibitions are overcome by the generation of relatively low density residual melts as crystallization proceeds later injections are preserved as dykes and enclaves composed of hybrid magma in this process only physically adjacent and dynamically thermally similar magmas directly interact and so may mix to homogeneity finally not simply felsic and mafic endmembers mix but a whole suite of intermediate endmembers participate ranging from relatively mafic through to felsic pairs of magmas direct mixing between the primary magmas only occurs at the beginning

chaotic advection fractals and diffusion during mixing of magmas evidence from lava flows structures of magma mixing from three different lava flows have been analyzed and the degree of mingling has been quantified by measuring the contact perimeter between magmas and the fractal dimension of structures in each lava flow the values of these parameters suggest that the magma mixing structures were produced by chaotic dynamics induced by stretching and folding processes between the interacting magmas the mingling of magmas has been simulated using a chaotic dynamical system consisting of repeated stretching and folding processes the simulation shows the same patterns of variation of contact perimeter and fractal dimension as those observed in natural structures and indicates that magma interaction processes acted with different intensities in the three lava flows in response to different magmatic interaction regimes since physical dispersion of one magma inside another through stretching and folding processes and chemical exchanges are closely related we performed coupled numerical simulations of chaotic advection and chemical diffusion the results show a good agreement between the computed and natural structures in particular the occurrence in the same system of well and poorly mixed regions it is shown that magma interaction processes are able to generate magmatic masses having wide spatial heterogenity at many length scales this occurrence can account for the presence of magmatic enclaves inside host rocks showing a variable degree of hybridization in both plutonic and volcanic environments

a model for mixing basaltic and dacitic magmas as deduced from experimental data it has been demonstrated experimentally that basaltic and dacitic magmas can be easily mixed to form both banded dacite and homogeneous andesite in less than a few hours the presence of phenocrysts larger than 0 5 mm increased considerably the efficiency of mixing flow patterns in the experimental system were visualized using pt spheres which indicated that convection occurs in basalt melt but not in dacite melt the reynolds numbers of the basaltic and dacitic melts in the experimental system were calculated to be about 10 3 and 10 6 respectively mixing proceeds initially by mechanical mixing of the two magmas in a large scale but later by coupling interfacial convection and mutual diffusion thus depending on the depth where vesiculation and following disruption of the magma occurs banded pumice homogeneous pumice and homogeneous andesite lava are erupted the observed textures of mixed rocks of plinian type eruption and the limiting occurrence of banded pumice are satisfactorily accounted for on this model

volcanological and petrological evolution of vulcano island aeolian arc southern tyrrhenian sea petrological and geochemical data are reported for volcanic rocks from vulcano island the subaerial volcanism 120 ka to present built up a nw se elongated composite structure affected by two intersecting multistage calderas volcanics older than 20 ka consist mostly of high k calc alkaline hkca to shoshonitic sho mafic rocks these magmas interacted significantly with the continental crust which generated variable sr isotopic ratios 0 70412 0 70520 however a major role was also played by input of parental liquids into the magma chamber which prevented further evolution of the magmas hkca sho and potassic ks rocks formed from 20 to 8 ka display a much larger range of sio2 from shoshonites to rhyolites and higher concentrations of incompatible elements with respect to the previous stage sr isotopic ratios show small variations 0 70448 0 70486 mixing of silicic and mafic liquids and fractional crystallization processes fc were the main evolutionary processes during this stage volcanics younger than 8 ka consist of sho and leucite bearing ks mafic rocks with abundant intermediate and silicic products mafic and intermediate rocks display similar incompatible element abundances and sr isotopic ratios as the previous stage volcanics whereas higher 87sr 86sr 0 70494 0 70583 are observed in some rhyolites these products originated from a complex interplay of fc crustal assimilation and magma mixing processes the most mafic rocks show increasing incompatible element abundances rb sr rb ba mg al mg ca and a decrease in large ion lithophile to high field strength element ratios passing from older hkca sho to the younger sho ks volcanics these variations suggest a shifting of magma sources from a slightly metasomatized asthenosphere fertile peridotite to a more strongly metasomatized lithospheric mantle residual peridotite time related petrological and geochemical variations have been used to develop a model for the evolution of the vulcano plumbing system