fractal analysis of mingled mixed magmas an example from the upper pollara eruption salina island southern tyrrhenian sea italy abstract upper pollara eruption products 13 ka salina island italy include both homogeneous and heterogeneous pumices resulting from mixing mingling processes between an hk andesite and a high sio2 rhyolite representative samples of heterogeneous pumices are collected and analyzed in order to check the correspondence between glass composition and morphological features of the mingling mixing structures image analysis techniques are applied and eight grey color ranges classes are extracted from high resolution scans of pumice class 1 lighter colors and class 8 darker colors show end member glass compositions i e hk andesite and high sio2 rhyolite respectively these two classes show spot to cluster like morphological structures intermediate classes show an hk dacitic to rhyolitic composition and a banding to fold like morphology fractal analysis by box counting of the boundary pattern of eight grey classified images is performed over a length scale of 0 028 1 8 cm fractal dimension d is between 1 01 and 1 84 coupled fractal analysis and geochemical data reveal that d increases as the degree of magma interaction homogenization increases this feature well fits the results from numerical models on the convective mixing of fluids driven by thermal convection we conclude that the increase of d observed in the upper pollara samples reflects the transition from fractal mixing to homogenization end member magmas hk andesite and high sio2 rhyolite represent isolated mixing regions while homogenized magmas represent active mixing regions in the analyzed pumices isolated and active mixing regions coexist at scales between 10 4 and 10 2 m morphological and compositional features of the upper pollara pumices result from turbulence

morphometric analysis of magmatic enclaves a tool for understanding magma vesiculation and ascent abstract the extent of deformation of magmatic enclaves that occur in different portions of the khaggiar endogenous lava dome island of pantelleria italy has been quantified using two morphometric techniques thin plate splines and fractals deformation of enclaves decreases from the outer portions of the dome to the more internal portions defining two exponential trends the amount and distribution of vesicles have also been quantified using image analysis of digital images obtained by a scanning electron microscope the variation of deformation of enclaves correlates with the variation of their vesicle content suggesting that deformation and vesiculation are related we envisaged a continuous feedback system between vesiculation of enclaves and radial forces exerted by the surrounding host magma during the growth of the dome these relationships are used as dynamic markers to infer the eruptive style of the endogenous dome in particular it is suggested that the variation of vesicularity of enclaves is related to the pressure exerted by magma on the extrusion vent this resulted in enclaves being more vesicular and more deformed in the outer portions of the dome that emplaced first and at lower pressure and less vesicular and less deformed in the more internal portions that emplaced later and at higher pressure we interpret the occurrence of the two trends in the variation of deformation and porosity as related to two main eruptive pulses of dome growth

silica rich melts in quartz xenoliths from vulcano island and their bearing on processes of crustal anatexis and crust magma interaction beneath the aeolian arc southern italy o 3 6 wt contents two types of inclusions can be distin guishedbasedontheirtimeofentrapmentandincompatibletraceelement ite concentrations one type late ite enrichedinclusions has trace element characteristics that resemble thoseof the metamorphic rocks of the calabro peloritano basement ofthe adjacent mainland other inclusions early ite depleted have variable ba rb sr and cs and low nb zr and rareearth element ree contents their ree patterns areunfractionated with a marked positive eu anomaly geochem ical modelling suggests that the ite depleted inclusions cannotbe derived from equilibrium melting of calabro peloritanometamorphic rocks ite enriched inclusions can be modelledby large degrees 480 of melting of basement gneisses andschists leaving a quartz rich residue represented by the quartz rich xenoliths glass inclusions in quartz rich xenoliths repre sent potential contaminants of aeolian arc magmas interactionbetweencalc alkalinemagmasandcrustalanatecticmeltswithacomposition similar to the analysed inclusions may generatesignificant enrichment in potassium in the magmas however ite contents of the melt inclusions are comparable with orlower than those of vulcano calc alkaline and potassic rocks this precludes the possibility that potassic magmas in theaeolian arc may originate from calc alkaline parents throughdifferent degrees of incorporation of crustal melts

venus concentrations of radar reflective minerals by wind abstract areas of high radar reflectivity and low emissivity on venus may be covered with windblown material rich in fe and ti such as ilmenite a mineral common in some basaltic lava flows experiments under venus like conditions show that dense mineral grains become concentrated on the surfaces of windblown sediments when subjected to the low winds typical for venus

remobilization of andesite magma by intrusion of mafic magma at the soufriere hills volcano montserrat west indies the 1995 1999 eruption of the soufriere hills volcano montintroduction serrat has produced a crystal rich andesite containing quenchthe soufriere hills volcano montserrat located in the textured mafic inclusions which show evidence of having been molten lesser antilles island arc in the west indies began to when incorporated into the host magma individual crystals in the erupt on 18 july 1995 after about 350 years of dormancy andesite record diverse histories amphibole phenocrysts vary from young et al 1998b the eruption was preceded by a pristine and unaltered to strongly oxidized and pseudomorphed by period of seismic swarms which began in january 1992 anhydrous reaction products plagioclase phenocrysts are commonly previous earthquake crises have occurred on montserrat reverse zoned often with dusty sieve textures reverse zoned rims are in 1896 1897 1932 1935 and 1966 1967 powell 1938 also common on orthopyroxene phenocrysts pyroxene geothermometry shepherd et al 1971 initial phreatic and phregives an average temperature of 858 20 c for orthopyroxene atomagmatic activity was followed by extrusion of an phenocryst cores whereas reverse zoned rims record temperatures andesitic lava dome in november 1995 pyroclastic flows from about 880 to 1050 c the heterogeneity in mineral rim generated by gravitational collapse of the unstable dome compositions zoning patterns and textures is interpreted as reflecting have been the dominant form of activity throughout the non uniform reheating and remobilization of the resident magma eruption but periods of explosive activity producing body by intrusion of hotter mafic magma convective remobilization pumice flows and falls have also occurred robertson et results in mixing together of phenocrysts that have experienced al 1998 young et al 1998b dome growth ceased different thermal histories depending on proximity to the intruding suddenly in march 1998 and further activity up to may mafic magma the low temperature and high crystallinity are 1999 has mainly involved gravitational collapses of the interpreted as reflecting the presence of a cool highly crystalline dome and periods of ash venting with some small scale magma body beneath the soufriere hills volcano the petrological vulcanian explosive events observations in combination with data on seismicity extrusion rate the soufriere hills volcano is the only active centre and so2 fluxes indicate that the current eruption was triggered by on montserrat the volcano is a composite of at least recent influx of hot mafic magma five andesitic lava domes flanked by pyroclastic deposits rea 1974 identified four other volcanic centres all

non linear deformation and break up of enclaves in a rhyolitic magma a case study from lipari island southern italy 1 a dome from lipari island southern italy consists of 12 vol of circular elongated and folded latitic enclaves hosted in a rhyolitic matrix the dm to cm scale enclaves are more deformed than the mm scale blobs the critical value of the ratio between the viscous forces which allow deformation and eventually break up blobs of latitic magma and the interfacial tension forces is larger than 0 29 the reynolds number is 5 3 the equivalent radius and the axial ratio of the enclaves follow power law distributions this feature suggests that the break up and stretching of magmas are non linear scale invariant probably cyclic processes the coexistence of enclaves of different shape and the self similar size distributions suggest that chaotic advection plays a major role in the formation of mingled magmas caution must be used when measuring the finite strain from enclave shapes because they may break apart during the deformation

the episodic and abrupt geochemical changes at la fossa fumaroles vulcano island italy and related constraints on the dynamics structure and compositions of the magmatic system abstract herein we report on the chemical and isotopic c h o and he compositions of the fluids from la fossa crater fumaroles of vulcano from 1999 to 2010 consistent with records obtained since the end of the 1980s our data show that the geochemical features of the fumarole system have experienced several episodes of remarkable change each lasting no more than a few months typical signatures of these short term anomalies are large increments in co 2 n 2 and he concentrations coupled to increased 13 c 12 c isotopic ratios but their meaning remains widely debated within a model of fumarolic fluids based on mixing between hydrothermal and magmatic endmembers we have developed a novel approach to constrain chemical he co 2 and n 2 he and isotopic 13 c 12 c d h and 3 he 4 he ratios of the magmatic endmember during the short term anomalies although much of the geochemical variability in fumaroles results from changes in mixing proportions the magmatic fluid unquestionably shows significant variations in time the magmatic he co 2 n 2 he 13 c 12 c and 3 he 4 he values throughout 1988 1996 differed from those feeding the anomaly at the end of 2004 early clues of the new magmatic fluid appeared in 1998 1999 far from any short term anomaly whereas new and old magmatic fluids coexisted after 2004 we quantitatively prove that the detected geochemical changes are consistent with the degassing path of a magma having a latitic composition and suggest the presence of two magma ponding levels at slightly different pressures where bubble melt decoupling can occur the different he isotope compositions at these levels suggest low hydraulic connectivity typical of a complex reservoir with dike and sill structures in this framework the short term geochemical anomalies are probably due to gas accumulation at the top of magma bodies followed by massive escape or activation of new degassing levels in the reservoir for which the stress field almost certainly plays a key role such a scenario explains the observed increases in both fumarole output and shallow high frequency seismicity due to increased pore pressure during the anomalies while being consistent with the concomitant absence of any deep seismicity or ground deformation eventually related to magma movement

evaluation of a relaxation geospeedometer for volcanic glasses abstract the cooling of silicate melts influences the character of volcanic processes primarily through the effect of temperature on melt viscosity but also through the derivative thermal properties expansivity and heat capacity if the cooling rates of volcanic facies can be established then the undoubtedly complex processes of erupting cooling and degassing magmas can be more readily understood the frozen structure of every glass volcanic or synthetic is influenced by the previous cooling history moreover the relaxation of the glass structure back to equilibrium during reheating across the glass transition is also dependent on the quenched in structure and thus can be used to determine the cooling rate history in this study differential scanning calorimetry dsc measurements have been used to determine the enthalpic relaxation of four volcanic glasses each glass has been heated at known heating rates in the calorimeter to temperatures above the glass transition interval the first heating of the glass involves the relaxation of the structure frozen in during the volcanic cooling subsequent controlled heating and cooling in the calorimeter enables the determination of a set of kinetic parameters which can be used to model the heat capacity curves by modeling the transient values of heat capacity across the glass transition interval the relaxation of enthalpy and the volcanic cooling rate across the glass transition interval can be obtained from our study we can demonstrate four different cooling rates for volcanic glasses over a range of three orders of magnitude from 4 c min 1 to 2 c day 1 we propose that the enthalpic relaxation of silicate melts can be applied as a geospeedometer to the study of volcanic rocks from a variety of occurrences

review of the evolution of geochemical monitoring networks and methodologies applied to the volcanoes of the aeolian arc italy abstract fluids discharged from volcanic systems are the direct surface manifestation of magma degassing at depth and provide primary insights for evaluating the state of volcanic activity we review the geochemical best practice in volcanic surveillance based to a huge amount of monitoring data collected at different active volcanoes using both continuous and discontinuous approaches the targeted volcanoes belong to the aeolian arc located in the tyrrhenian sea italy and they have exhibited different activity states during the monitoring activities reported here la fossa cone on vulcano island has been in an uninterrupted quiescent stage characterized by variable solfataric activity in contrast stromboli island has shown a persistent mild explosive activity episodically interrupted by effusive eruptions in 1985 2002 2007 and 2014 panarea island which is the summit of a seamount rising from the seafloor of the southern tyrrhenian sea showed only undersea fluid release the only observable clues of active volcanism at panarea island have been impulsive changes in the undersea fluid release with the last submarine gas burst event being observed in november 2002 the geochemical monitoring and observations at each of these volcanoes has directly involved the volcanic plume and or the fumarole vents thermal waters and diffuse soil degassing depending on the type of manifestations and the level of activity encountered through direct access to the magmatic samples when possible and the collection of as much observable data related to the fluid release as possible the aim has been i to verify the thermodynamic equilibrium condition ii to discern among the possible hydrothermal magmatic marine and meteoric sources in the fluid mixtures iii to develop models of the fluid circulation supported by data iv to follow the evolution of these natural systems by long term monitoring and v to support surveillance actions related to defining the volcanic risk and the evaluation and possible mitigation of related hazards the examples provided in this review article show the close relationships among data analysis interpretation and modeling we particularly focus on describing the fieldwork procedures since any theoretical approach must always be verified and supported by field data rather than just by experiments controlled in laboratory indeed the natural systems involve many variables producing effects that cannot be neglected the monitored volcanic systems have been regarded as natural laboratories and all of the activities have focused on both volcanological research and surveillance purposes in order to ensure that these two goals have overlapped an appendix is also included that explains the scientific approach to the systematic activities regarding geochemical monitoring of volcanic activity

rheology of granitic magmas during ascent and emplacement flow abstract considerable progress has been made over the past decade in under standing the static rheological properties of granitic magmas in the continental crust changes in h2o content co2 content and oxidation state of the interstitial melt phase have been identified as important compositional factors governing the rheodynamic behavior of the solid fluid mixture although the strengths of granitic magmas over the crystallization interval are still poorly constrained theoretical investigations suggest that during magma ascent yield strengths of the order of 9 kpa are required to com pletely retard the upward flow in meter wide conduits in low bagnold number magma suspensions with moderate crystal contents solidosities 0 1 0 3 viscous fluc tuations may lead to flow differentiation by shear enhanced diffusion ams and mi crostructural studies support the idea that granite plutons are intruded as crystal poor liquids 50 with fabric and foliation development restricted to the final stages of emplacement if so then these fabrics contain no information on the ascent verti cal transport history of the magma deformation of a magmatic mush during pluton emplacement can enhance significantly the pressure gradient in the melt resulting in a range of local macroscopic flow structures including layering crystal alignment and other mechanical instabilities such as shear zones as the suspension viscosity varies with stress rate it is not clear how the timing of proposed rheological transitions formulated from simple equations for static magma suspensions applies to mixtures undergoing shear new theories of magmas as multiphase flows are required if the full complexity of granitic magma rheology is to be resolved

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

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 monte guardia eruption lipari aeolian islands an example of a reversely zoned magma mixing sequence the monte guardia rhyolitic eruption 22 ka lipari aeolian islands italy produced a sequence of pyroclastic deposits followed by the emplacement of lava domes the total volume of dense magma erupted was nearly 0 5 km3 the juvenile clasts in the pyroclastic deposits display a variety of magma mixing evidence mafic magmatic enclaves streaky pumices mineral disequilibria and heterogeneous glass composition petrographic mineralogical and geochemical investigations and melt inclusion studies were carried out on the juvenile clasts in order to reconstruct the mixing process and to assess the pre eruptive chemico physical magmatic conditions the results suggest that the different mingling and mixing textures were generated during a single mixing event between a latitic and a rhyolitic end member a denser mixed magma was first erupted followed by a larger volume of an unmixed lighter rhyolitic one this compositional sequence is the reverse of what would be expected from the tapping of a zoned magma chamber the monte guardia rhyolitic magma stored below 200 mpa was volatile rich and fluid saturated or very close to this despite its relatively low explosivity in contrast to previous interpretations there exists the possibility that the rhyolite could rise and erupt without the trigger of a mafic input the entire data collected are compatible with two possible mechanisms that would generate a reversely zoned sequence 1 the occurrence of thermal instabilities in a density stratified salic to mafic magma chamber and 2 the intrusion of rising rhyolite into a shallower mafic sill dike

relative rheological evolution of chemically contrasted coeval magmas example of the tichka plutonic complex morocco the tichka plutonic complex presents many unusual structures related to physical interaction between mafic and felsic coeval magmas in this paper a rheological approach is used to attempt to understand the various observed structures after a general presentation of rheological laws and a discussion about the present state of our understanding of the rheology of suspensions we analyse the main steps of rheological evolution of magmas during crystallization taking into account the effect of cooling increase of silica content and increase of crystallinity on viscosity during thermal evolution of magma a general rheological diagram is presented two main rheological thresholds at about 35 crystallinity th1 and about 65 70 th2 allow us to distinguish three major steps in the rheological behaviour of magmas during cooling comparative study of evolution curves for viscosity of coeval mafic m and felsic f magmas shows that an inversion temperature ti exists at which viscosities of both magmas are the same this point has major petrologic significance because the viscosity ratio m f inverses during cooling when the temperature of magma falls below the ti point a model for the evolution of the tichka magmas during cooling has been derived from the knowledge of the chemical and mineralogical composition of the different rocks representing the original m and f magmas as well as some hybrid and differentiated samples viscosities and crystal fractions of magmas as functions of temperature have been calculated from chemical and mineralogical data curves representing the evolution of apparent viscosity of the three initial magmas of the complex are presented from these vicosity temperature curves and from the calculted temperatures corresponding to rheological thresholds th1 and th2 for the different coeval magmas five main evolution stages are defined the different structures observed at the contracts between m and f magmas are developed throughout the entire cooling history of the pluton each structure being related to one of the main evolution stages

clinopyroxene liquid trace element partitioning in natural trachyte trachyphonolite systems insights from campi flegrei southern italy trace element partition coefficients between clinopyroxenes and associated glassy matrix cpx l d have been determined for 13 ree hfse4 5 u th sr pb sc and v from combined la icp ms emp analyses in selected trachytes and trachyphonolites from campi flegrei composition of clinopyroxene and glass is pretty homogeneous in the trachyphonolites pointing to an overall attainment of the equilibrium conditions in trachytes conversely phases show some compositional heterogeneity due to the presence of clinopyroxene xenocrysts that requested a more careful petrographic and geochemical inspection of the samples to assess the equilibrium clinopyroxene composition in the trachyte clinopyroxenes ree are compatible from nd to lu cpx l d up to 2 9 like y ti sc and v the cpx l d for eu is lower than those of the adjacent ree highlighting eu2 contribution high d values are also shown by u th pb zr hf nb and ta relatively to basaltic and andesitic systems whereas the d sr is roughly similar to that found for less evolved magmas trachyphonolites are characterized by an overall decrease of the cpx l d for highly charged cations with the exception of v and by a slight increase of d sr ree are still compatible from nd to lu cpx l d up to 2 1 like ti y sc and v this variation is also predicted for ree and y by models based on the elastic strain theory being consistent with the slightly lower polymerization degree estimated for the trachyphonolites however the observed cpx l d ree y are matched by the modelled ones only considering very low t 825 c which are believed unlikely this mismatch cannot be attributed to effects induced by the water rich composition of the trachyte trachyphonolite suite since they would lower the observed cpx l d ree y moreover the anomalous inflections of measured cpx l d for hree suggests some crystal chemical control such as the entrance of these elements in a site distinct from m2 it is concluded that the large cpx l d determined for trachytes and trachyphonolites are likely induced by hitherto unconstrained changes of the z3 activities related to the composition of melt and or solid all these considerations strongly highlight the importance of a direct characterization of trace element partitioning in natural samples from magmatic systems poorly characterized by experimental studies

water enhanced interdiffusion of major elements between natural shoshonite and high k rhyolite melts abstract the interdiffusion of six major elements si ti fe mg ca k between natural shoshonite and a high k rhyolite vulcano island aeolian archipelago italy has been experimentally measured by the diffusion couple technique at 1200 c pressures from 50 to 500 mpa and water contents from 0 3 nominally dry to 2 wt the experiments were carried out in an internally heated pressure vessel and major element profiles were later acquired by electron probe microanalysis the concentration distance profiles are evaluated using a concentration dependent diffusivity approach effective binary diffusion coefficients for four intermediate silica contents are obtained by the sauer freise modified boltzmann matano method at the experimental temperature and pressures the diffusivity of all studied elements notably increases with dissolved h 2 o content particularly diffusion is up to 1 4 orders of magnitude faster in a melt containing 2 wt h 2 o than in nominally dry melts this effect is slightly enhanced in the more mafic compositions uphill diffusion was observed for al while all other elements can be described by the concept of effective binary interdiffusion ti is the slowest diffusing element through all experimental conditions and compositions followed by si fe mg ca and k diffuse at similar rates but always more rapidly than si and ti this trend suggests a strong coupling between melt components since effects of composition including water content are dominant a pressure effect on diffusion cannot be clearly resolved in the experimental pressure range

microgranitic enclave shapes and magmatic strain histories constraints from drop deformation theory microgranitic mafic enclaves are common components of plutonic bodies and may represent the result of mingling of mafic and felsic magmas these enclaves are often ellipsoidal or elongate in shape in order to constrain the conditions under which such enclaves were generated and deformed by their host pluton we apply drop deformation theory to model their distortion our model takes into account the change in viscosity of both the host and enclave with temperature composition and the amount of suspended solids in enclave host systems and it assumes that simple shear flow predominates in the plutonic system we focus on the deformational history of enclaves over the time period in which they remain liquid and are either more or less viscous than their granitic host we find that the most stable enclaves with respect to being broken up by their entraining flow are generally the most mafic enclaves those with silica contents near those of the host granite are highly unstable this is in reasonable accord with field observations of the abundance of enclaves of different chemistry most deformation of microgranitic enclaves is likely to occur at relatively high temperatures probably between 950 c and 1050 c and therefore the enclaves record magmatic strain of the host over only a limited temperature time range in the host s cooling history furthermore the observation of apparent deformation of these enclaves in a liquid regime coupled with our calculated dependences of enclave deformation on flow velocity implies that magmatic flow velocities are likely to be below 10 m yr in enclave bearing plutonic systems

insights into magma chamber processes from the analysis of size distribution of enclaves in lava flows a case study from vulcano island southern italy the size distribution of latitic enclaves dispersed in a rhyolitic lava flow is studied enclave size distribution is self similar a feature that can be explained by a fractal fragmentation process and estimated fractal dimension of fragmentation is 2 50 fragment size distribution of enclaves generated by disruption of viscous fingering structures in granitoid rocks is analyzed it is shown that this distribution is fractal with a value of fractal dimension of fragmentation of 2 55 in close agreement with the value estimated for enclaves in the lava flow it is suggested that the fragmentation process producing the size distribution of enclaves in the lava flow may have occurred in response to the disruption of viscous fingering morphologies generated by the injection of the more mafic magma into the felsic one accordingly the size distribution of enclaves dispersed in the lava flow is considered a feature inherited from deep magma chamber processes and gives insights into magma chamber dynamics

controls on conduit magma flow dynamics during lava dome building eruptions 1 lava dome eruptions commonly display fairly regular alternations between periods of high and low or no activity with timescales typically of weeks to years and sudden transitions between effusive and explosive activity we develop a transient model of the magma flow in a volcanic conduit from an open system magma chamber with continuous replenishment the model incorporates gas exsolution bubble growth gas escape through the magma and decompression induced crystallization and considers variations in magma temperature water content conduit diameter phenocryst size chamber volume and magma rheology calculations show the presence of periodic variations in discharge rate due to the transition from a stable regime when discharge rate is low and crystals grow efficiently leading to high magma viscosity to another stable state when discharge rate is high and crystallization is negligible the difference in discharge rates between these regimes can be several orders of magnitude periods are similar to the observed timescales and mainly depend on the chamber volume the system shows strongly nonlinear responses to the variation of governing parameters if magma has a bingham rheology pauses in discharge rate occur between peaks of discharge and the peaks are much higher than for the case of newtonian rheology large changes in discharge rate and eruptive behavior can occur as the consequence of small changes in magma temperature water content phenocryst size distribution or conduit diameter the system can fluctuate between low and high discharge rates with transitions to explosive activity

preliminary magnetostratigraphy of dabusan lake qaidam basin central asia abstract sediment samples from a 528 m deep borehole located about 60 km north of golmud on the northern side of dabusan lake have been used to determine the change in magnetic inclination with depth normal polarity brunhes inclination values are present throughout the section but there are six departures from this value five with negative inclinations and one shallow inclination an attempt has been made to date the core using the magnetic inclination departures together with a limited number of 14c dates

distribution and significance of crystalline perlitic and vesicular textures in the ordovician garth tuff wales diverse spherulitic and granular crystalline fabrics perlitic textures and fabrics related to the growth and migration of vesicles occur in the garth tuff a largely welded ordovician ignimbrite defining the distribution of such textures helps to constrain the ignimbrite s cooling and degassing history suites of spherulitic and perlitic textures closely reflect variation in cooling rates seven facies are defined based on the style and intensity of crystallisation 1 a medium to coarsely crystalline equigranular facies 2 an intensely spherulitic facies 3 a sparsely spherulitic facies 4 a pectinate facies 5 a microcrystalline to cryptocrystalline equigranular facies 6 a lithophysal facies and 7 a transitional perlite pectinate facies textural changes from facies 1 to 5 reflect progressively higher cooling rates facies 1 occurs in proximal settings in the ignimbrite s core facies 2 to 5 successively envelop facies 1 with facies 2 becoming the dominant fabric in the ignimbrite s core in medial settings facies 5 is typically developed in the originally glassy perlitic zones at the ignimbrite s welded margins crystallisation under hydrous conditions is reflected by second boiling textures in the sporadically developed lithophysal facies the seventh facies reflects a subtle interplay between cooling hydration and crystallisation which locally prevented perlitic fracturing the distribution of amygdales reflects patterns of volatile migration and entrapment in the lower levels of the ignimbrite amygdales occur in irregular concentrations or rare subvertical pipe like structures pipe like structures attest to fumarolic activity while the ignimbrite was in a rheomorphic state amygdales are widespread and evenly distributed in the upper levels of the ignimbrite however the top of the welding profile is characterised by a thin poorly vesiculated originally vitrophyric horizon that abruptly caps an intense concentration of amygdales ductile and brittle fabrics developed during the upward migration of gas microscopic drag folds occur around some amygdales jigsaw fit to clast rotated breccias originated through both late stage pneumatic fracturing and autobrecciation vaporisation of water at the flow base provided a significant source of volatiles in addition to gas released during cooling and crystallisation secondary alteration has enhanced or modified some fabrics perlitic zones were susceptible to patchy chlorite sericite carbonate diagenetic alteration diagenesis and metamorphism have contributed to the infilling of vesicles

role of magma mixing during the recent activity of la fossa di vulcano aeolian islands italy abstract relatively homogeneous trachytes have been erupted for approximately 3800 years at la fossa di vulcano from the punte nere eruptive cycle up to the palizzi cycle the products varied little while after the palizzi cycle 1600 1000 a b p to the latest eruption 1888 1890 ad a spectrum of compositions with rhyolite dominating characterized the erupted products a stratigraphic sequence starting with the palizzi lava flow has been studied focussing the attention on lavas and volcanic bombs to define the role that magma mixing processes have played in the recent history of la fossa di vulcano textural and chemical analyses of whole rocks glass groundmass and mineral phases indicate that only the breadcrust bombs erupted during the 1888 1890 show evidence of mixing between trachytic and rhyolitic end members interestingly in the deposits of the same eruption trachytic bombs also occur the lava flows erupted before 1888 1890 display general features suggesting that they entrained crystals and lava fragments during magma ascent during the 1888 1890 eruption the trachytic bombs were erupted before the breadcrust bombs which have a more evolved and hybrid composition these characteristics together with the change of the nature of the products after the palizzi cycle require a complex volcanological model for the recent history of la fossa di vulcano

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

degassing at the soufriere hills volcano montserrat recorded in matrix glass compositions compositions of matrix glasses from the current eruption of soufriere hills volcano indicate that decompression driven crystallization results in 20 70 wt groundmass crystallization during eruption and variable degassing variations in crystallinity and volatile contents water and chlorine of matrix glasses are attributed to variations in extrusion rates and residence times in the lava dome residual water contents in pumice clasts 0 2 0 6 wt indicate minimum pressures of 1 1 3 7 mpa in 1997 vulcanian explosions residual water contents of 1 6 wt in a ballistic block ejected in sub plinian explosive activity on 17 september 1996 imply larger pressure drops similar to20 mpa variable residual water contents in dome samples are consistent with pressure variations of up to 9 mpa in the lava dome interior large variation in chlorine contents between lava blocks compared with explosion pumice clasts indicates that shallow level processes dominate degassing low melt chlorine contents of dome samples cannot be explained by open or closed system degassing especially when crystallization is taken into account instead heterogeneous chlorine leaching by circulation of groundwater vapour in the dome is proposed variable and elevated matrix glass deltad values can also be attributed to interaction with isotopically heavy surface waters hcl emission during the current eruption can be accounted for by cl loss from the melt consistent with the melt being undersaturated in chlorine

crystallization processes in an artificial magma variations in crystal shape growth rate and composition with melt cooling history a large 4 8 m3 1 3x107 g artificial mafic melt with a bulk composition similar to that of a basalt but with a high cao content of 17 wt was generated during a demonstration of in situ vitrification and was allowed to cool naturally during the melting process convection was vigorous resulting in a chemically and thermally homogeneous melt body once heating was complete the cooling rate was rapid with the temperature dropping from 1500 c to 500 c in 6 days within the interior of the 3 m diameter 1 5 m thick body a 20 h period of constant temperature 1140 c observed during colling was the result of latent heat released by widespread crystallization the final crystalline assemblage consists of diopsidic to hedenbergitic pyroxene and anorthitic feldspar with a subordinate amount of potassic feldspar plus a small amount of evolved glass the compositions and proportions of phases agree well with those predicted by the melts thermodynamic model thermal and textural evidence suggest that convection within the melt ceased coincident with formation of the first crystals textural investigation of core samples reveals large up to 1 cm in length acicular diopsidic pyroxenes in a matrix of smaller feldspar and zoned pyroxene crystals 500 m in length crystal shape and pyroxene composition vary as a function of position within the solidified body as a function of cooling rate both crystal size and degree of crystallinity are highest in the central most slowly cooled parts of the rock crystal shape is characterized by tabular equilibrium growth forms in the slowly cooled areas grading to highly skeletal dendritic forms at the rapidly cooled edges of the body the pyroxene crystals are dominantly homogeneous diopside but crystals are characterized by thin fe rich hedenbergitic rims these rims were deposited when mg in the melt was depleted by diopside growth and melt temperature had cooled sufficiently to allow fe rich pyroxene growth crystal growth rates can be calculated based on thermal behavior of the melt reinforced by thermodynamic modelling and are determined to be between 10 7 and 10 8 cm s in the central part of the melt these estimates agree well with growth rates in natural systems with similar cooling rates pyroxene crystals that formed at a higher cooling rates are characterized by higher al and lower mg contents relative to tabular equilibrium crystalline forms presumably as a result of disequilibrium melt compositions at the crystal melt interface

magma mixing at lipari aeolian islands italy insights from textural and compositional features of phenocrysts in southern lipari aeolian islands italy the volcanic activity was exclusively rhyolitic in the last 42 ka but the presence of mafic magmas in the magmatic system is revealed by the occurrence of mingling and mixing textures in the silicic deposits the study of textural and compositional zoning of phenocrysts is a powerful tool to unravel magmatic processes especially when bulk rock data are affected by magma mixing in this work we present the results of detailed petrographic and microanalytical investigations carried out on the rhyolitic products and their mafic enclaves with the aim to improve the knowledge of the lipari magmatic system in recent times trace element profiles on phenocrysts were carried out by laser ablation icp ms on the products of eruptions occurred around 22 ka ago mineral chemistry indicated the formation of different mafic magma batches in that period zoning patterns in clinopyroxene and plagioclase phenocrysts in enclaves record mixing between two different mafic magmas this event preceded of less than a few years the syn eruptive mixing with the rhyolite short residence times less than hundreds of years of plagioclase phenocrysts in the mafic magma prior to mixing with the rhyolite were calculated based on measured sr profiles and diffusion kinetics the results evidence the existence in southern lipari of a composite vertically developed magmatic system storing silicic and mafic magmas as relatively small volume batches interacting with each other

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

magmatic feeding system and crustal magma accumulation beneath vulcano island italy evidence from co2 fluid inclusions in quartz xenoliths 1 pure co2 fluid inclusions are observed in quartz xenoliths from four lava flows in the island of vulcano corresponding to distinct activity stages during the last 120 kyr xenoliths which consist of aggregates of quartz grains are present in lavas of contrasting composition ranging from basaltic andesites to rhyolites two main generations of co2 inclusions are observed early type i inclusions were trapped prior to the ascent of the host xenoliths while type ii inclusions were trapped during the ascent into the host magma fluid inclusions show a bimodal distribution of homogenisation temperatures corresponding to two distinct density intervals 0 89 0 52 g cm 3 type i and 0 42 0 13 g cm 3 type ii type i inclusions indicate pressures of 0 56 0 33 gpa 21 13 km relating to the levels of xenolith entrapment in the host lavas type ii fluid inclusions show considerably lower pressures ranging from 0 14 to 0 03 gpa 5 5 3 km present data suggest ponding of mantle derived magmas in at least two distinct reservoirs located at lower crustal depths and at shallow levels respectively combined fluid inclusion and petrological data suggest that the deep reservoirs were the sites of extensive fractional crystallization mixing with source derived magmas and various degrees of crustal assimilation evolutionary processes also occurred inside shallow magma chambers in which deep magma mixed with residing melts and rested for short periods of time before being erupted to the surface index terms 5480 planetology solid surface planets volcanism 8450 8414 volcanology eruption mechanisms 8434 volcanology magma migration

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

on the deformation and freezing of enclaves during magma mixing abstract mixing of an enclave of hot mafic magma into cooler silicic magma involves the competing effects of heat transfer acting to rigidify the enclave and viscous shearing imposed by a flowing host magma acting to deform and disperse the enclave we model the time required to grow a rigid chilled margin and compare this with the time required to deform the initially hot enclave whether an enclave will deform before it freezes depends on the ratio of the thermal and deformation timescales pe app 3 a 2 s r 2 and the dimensionless rigidification temperature t r t s t m t s where app is the applied shear stress a is the enclave radius is the thermal diffusivity s is the viscosity of the host r is the strength of the chilled rind t r is the temperature at which the enclave attains strength r and t m and t s are the initial temperatures of the mafic enclave and silicic host according to the model small values of pe and large values of promote rapid rigidification the model is verified by laboratory experiments on the flow and freezing of polyglycol wax droplets in cold water geological observations show that correlations between enclave size degree of deformation and local shear stress match the model s predictions studies of enclave size and shape as functions of eruption rate and position within lava flows and minor intrusions offer a new technique for studying magma flow processes during eruptions

petrogenesis of mafic inclusions in rhyolitic lavas from narugo volcano northeastern japan mafic inclusions present in the rhyolitic lavas of narugo volcano japan are vesiculated andesites with diktytaxitic textures mainly composed of quenched acicular plagioclase pyroxenes and interstitial glass when the mafic magma was incorporated into the silicarich host magma the cores of pyroxenes and plagioclase began to crystallize 1000 c in a boundary layer between the mafic and felsic magmas phenocryst rim compositions and interstitial glass compositions average 78 wt sio2 in the mafic inclusions are the same as those of the phenocrysts and groundmass glass in the host rhyolite this suggests that the host felsic melt infiltrated into the incompletely solidified mafic inclusion and that the interstitial melt composition in the inclusions became close to that of the host melt c 850 c infiltration was enhanced by the vesiculation of the mafic magma finally hybridized and density reduced portions of the mafic magma floated up from the boundary layer into the host rhyolite we conclude that the ascent of mafic magma triggered the eruption of the host rhyolitic magma

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

textures water content and degassing of silicic andesites from recent plinian and dome forming eruptions at mount pelee volcano martinique lesser antilles arc previous petrological and phase equilibrium experimental studies on recent silicic andesites from mount pelee volcano have evidenced comparable pre eruptive conditions for plinian and dome forming pelean herein eruptions implying that differences in eruptive style must be primarily controlled by differences in degassing behaviour of the mount pelee magmas during eruption to further investigate the degassing conditions of plinian and pelean magmas of mount pelee we study here the most recent mount pelee s products p1 at 650 years b p 1902 and 1929 eruptions which cover a range of plinian and pelean lithologies for bulk rock vesicularities glass water contents glass inclusions in phenocrysts and matrix glasses and microtextures water contents of glass inclusions are scattered in the plinian pumices but on average compare with the experimentally deduced pre eruptive melt water content i e 5 3 6 3 wt whereas they are much lower in the dominant pelean lithologies crystalline poorly vesicular lithics and dome samples this indicates that the glass inclusions of the pelean products have undergone strong leakage and do not represent pre eruptive water contents the water content of the pyroclast matrix glasses are thought to closely represent the residual water content in the melt at the time of fragmentation determination of the water contents of both the pre eruptive melt and matrix glasses allows the estimation of the amount of water exsolved upon syn eruptive degassing we find the amount of water exsolved during the eruptive process to be higher in the pelean products than in the plinian ones typically 90 100 and 65 70 of the initial water content respectively the vesicularities calculated from the amount of exsolved water compare with the measured vesicularities for the plinian pumices consistent with a closed system near equilibrium degassing up to fragmentation by contrast the low residual water contents low groundmass vesicularities and extensive groundmass crystallization of the pelean products are direct evidence of open system degassing microtextural features including silica bearing and silica free voids in the pelean lithologies may represent a two stage vesiculation