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

sources and petrogenesis of late triassic zhiduo volcanics in the northeast tibet implications for tectonic evolution of the western jinsha paleo tethys ocean abstract the western jinsha suture representing a branch of the paleo tethys makes the junction between the songpan ganzi complex and the north qiangtang block nqb however the triassic tectonic evolution of the western jinsha paleo tethys ocean is poorly constrained this paper shows new la icp ms zircon u pb geochronology major and trace elements and sr nd hf isotopic compositions of the zhiduo dacitic volcanic rocks in the northern margin of the nqb la icp ms zircon u pb dating displays that they erupted between 227 2 and 228 1 ma these rocks exhibit high silica medium k calc alkalic signature and low mgo tio2 p2o5 cr and ni compositions they are enriched in light rare earth elements and large ion lithophile elements with moderate to strong negative eu anomalies eu eu 0 24 0 56 and depleted in heavy rare earth elements and high field strength elements they possess relatively low initial 87sr 86sr ratios 0 7055 0 7084 positive whole rock end t 0 2 to 1 4 and magmatic zircon ehf t values focus on 9 2 2 7 with young nd and hf model ages t2dm nd 885 983 ma t2dm hf 467 1035 ma these features are comparable to those of typical arc volcanic rocks and indicate that they were probably derived from partial melting of a juvenile crust source the eruption of these volcanic rocks could be attributed to southward subduction of the western jinsha paleo tethys ocean in combination with previous studies we propose that the subduction of the western jinsha paleo tethys ocean initiated at the beginning of the late triassic ca 228 ma and closed at the end of the late triassic ca 208 ma in addition there is a universal northeastward younging trend of arc magmas in the northern margin of the nqb which may indicate a model involving the initial shallow subduction and subsequent slab roll back

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

the role of magma mixing in triggering the current eruption at the soufriere hills volcano montserrat west indies the andesite lava currently erupting at the soufriere hills volcano montserrat contains ubiquitous mafic inclusions which show evidence of having been molten when incorporated into the andesite the andesite phenocrysts have a range of textures and zonation patterns which suggest that non uniform reheating of the magma occurred shortly before the current eruption reheating resulted in remobilisation of the resident magma and may have induced eruption

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

source mechanism and surface wave excitation for two earthquakes in northern baja california mexico summary two earthquakes of comparable local magnitude from different regions of northern baja california the 1975 july 17 pino solo earthquake ml 5 1 from the peninsular ranges region and the 1976 december 7 mesa de andrade earthquake ml 5 3 from the colorado river delta region are studied in detail to determine possible causes for the observed stronger excitation of surface waves by earthquakes from the delta region relative to earthquakes of comparable local magnitude in the peninsular ranges region data from distant stations are complemented with data from aftershock studies using local arrays and for the mesa de andrade earthquake with data from two strong motion stations the strong motion records for ihe mesa de andrade earthquake show that it consisted of two events 45 s apart which produced maximum recorded horizontal accelerations of 0 21 and 0 24g respectively at a distance of 18 km from the epicentre synthetic seismograms are used to help determine the depth of these events and their source time functions both events are relatively simple the second event is sharp and impulsive and could be thought of as an aftershock since it has a considerably smaller moment than the first event even though its recorded acceleration was higher comparison of measured parameters shows that while the local magnitude of the mesa de andrade earthquake is only 0 2 units larger than the pino solo earthquake and its source dimension is 2 2 times larger source areas 4 8 times larger its moment is larger by a factor of 6 2 8 5 this is approximately explained by the cy2 scaling law however the near source spectra and accelerations recorded on the strong motion accelerograph at riito at a distance of about 18 km are considerably larger than predicted by the scaling law this is probably a results of high stress drop asperities on the fault surface although near field focusing directivity may also have contributed

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

morphochemistry of patterns produced by mixing of rhyolitic and basaltic melts abstract in this work we present the results of time series experiments performed by mixing basaltic and rhyolitic melts at high temperature using a device recently developed to trigger chaotic dynamics in a mixing system the morphology of mixing patterns is quantified at different times by measuring their fractal dimension and a linear relationship is derived between mixing time and morphological complexity the complexity of mixing patterns is also compared to the degree of homogenization of chemical elements during mixing and empirical relationships are established between the fractal dimension and the temporal variation of concentration variance of elements new concepts and tools to study the magma mixing process unfold from the experimental results presented in this work the first one is that the mixing patterns are fractals and they can be quantified by measuring their fractal dimension this represents a further step in the quantification of the magma mixing process the second outcome is that the relationship between the fractal dimension of the mixing patterns and mixing time is linear this has important volcanological implications as the analyses of the morphology of mixing patterns in volcanic rocks can be complemented by experiments to build a new chronometer to estimate the mixing to eruption time a further result from this work is the relationship between the fractal dimension of mixing patterns and concentration variance of chemical elements this represents the first morphochemical study in igneous petrology bringing with it the potential to infer the relative mobility of chemical elements during the time progression of mixing by analyzing the morphology of mixing patterns in the rocks

steep schlieren and associated enclaves in the vinalhaven granite maine possible indicators for granite rheology schlieren that form above the solidus are potentially diagnostic of the rheology of crystallizing granitic magmas and could provide insights into magma chamber structure here we focus on steep schlieren associated with comagmatic enclaves in the vinalhaven granite steep schlieren extend 1 3 m upward from the sides of enclaves and appear to have steep cylindrical shapes in 3d analyses of schlieren widths and the sizes of associated enclaves suggest that granitic crystal mush in which they occur had a plastic rheology probably characterized by a yield strength the enclaves now enclosed in coarse grained granite must have existed at higher levels in a crystal poor part of a magma chamber and settled downward until reaching material with a yield strength exceeding the buoyancy of the enclaves in addition to constraining the local rheology of the granite their relative positions may indicate vertical rheological variations and possibly the chamber floor

the strain path and emplacement mechanism of lava flows an example from salina southern tyrrhenian sea italy abstract a lava flow from salina southern tyrrhenian sea consists of subcircular to ellipsoidal basaltic enclaves dispersed in a dacitic host a 2d strain and kinematic analysis of the enclaves has been performed in order to determine a the relative contribution of the coaxial and non coaxial components to the bulk flow deformation b the flow vorticity wk c the strain path and d the mechanism of flow emplacement the axial ratio r f and the angle f between the long axis of the enclaves and the transport direction have been measured in 196 sites located at different distances from the vent in the near vent zone whereas further from the vent values were always larger than 1 ranging from 1 6 in the near vent zone to 1 at the front values were between 0 2 at the back and 2 6 at the front wk was between 0 13 and 1 and increased from the back to the front the enclaves result from the injection of basalt into dacite most of the deformation was acquired during the lava flow emplacement and not during the rise in the conduit plug flow the strain path depicted by the enclaves is consistent with that resulting from experimental analogue models and reveals that the lava suffers lateral extension near the vent further from the vent the lava deforms according to an ideal non coaxial model the lava emplacement is mainly controlled by the gravity evidence of deformation induced by the magma pressure is lacking near the vent the lava behaves as a hyperbolic flow whereas at the front it behaves as a simple shear flow the mechanism of flow emplacement is consistent with a mixed viscous gliding spreading transport model at the back and with a viscous gliding model at the front

a felsic mash zone of crustal magmas feedback between granite magma intrusion and in situ crustal anatexis abstract magma mixing and mingling are described from different tectonic environments and are key mechanisms in the evolution of granitoids the literature focuses on the interaction between mafic and felsic magmas with only limited research on the interaction between similar magmas here we investigate instead hybridization processes between felsic magmas formed during the 500 ma delamerian orogeny on the south coast of kangaroo island field relations suggest that a coarse megacrystic granite intruded and interacted with a fine grained diatexite that resulted from combined muscovite dehydration and water fluxed melting of kanmantoo group turbidites the two magmas hybridized during syn magmatic deformation explaining the complexity of relationships and variability of granitoids exposed we suggest that granite intrusion enhanced melting of the turbidites by bringing in heat and h 2 o with rising melt fraction intrusive magmas became increasingly unable to traverse the partially molten terrane creating a positive feedback between intrusion and anatexis this feedback loop generated the exposed mid crustal zone where magmas mixed and homogenized thus the outcrops on kangaroo island represent a crustal and felsic melting assimilation storage homogenization felsic mash zone where instead of having direct mantle magma involvement as originally proposed these processes developed in a purely crustal environment formed by felsic magmas

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

magmatic structures in the krkonose jizera plutonic complex bohemian massif evidence for localized multiphase flow and small scale thermal mechanical instabilities in a granitic magma chamber abstract the present paper examines magmatic structures in the jizera and liberec granites of the krkonose jizera plutonic complex bohemian massif the magmatic structures are here interpreted to preserve direct field evidence for highly localized magma flow and other processes in crystal rich mushes and to capture the evolution of physical processes in an ancient granitic magma chamber we propose that after chamber wide mixing and hybridization as suggested by recent petrological studies laminar magma flow became highly localized to weaker channel like domains within the higher strength crystal framework mafic schlieren formed at flow rims and their formation presumably involved gravitational settling and velocity gradient flow sorting coupled with interstitial melt escape local thermal or compositional convection may have resulted in the formation of vertical schlieren tubes and ladder dikes whereas subhorizontal tubes or channels formed during flow driven by lateral gradients in magma pressure after the cessation or deceleration of channel flow gravity driven processes settling of crystals and enclaves gravitational differentiation development of downward dripping instabilities accompanied by compaction filter pressing and melt segregation dominated in the crystal mush within the flow channels subsequently magmatic folds developed in schlieren layers and the magma chamber recorded complex late magmatic strains at high magma crystallinities late stage magma pulsing into localized submagmatic cracks represents the latest events of magmatic history of the chamber prior to its final crystallization we emphasize that the most favorable environments for the formation and preservation of magmatic structures such as those hosted in the jizera and liberec granites are slowly cooling crystal rich mushes therefore where preserved in plutons these structures may lend strong support for a mush model of magmatic systems

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

kinematic significance of morphological structures generated by mixing of magmas a case study from salina island southern italy morphological features of mixing mingling structures of heterogeneous juveniles from the 13 ka old upper pollara eruption salina island southern italy are studied these heterogeneous rocks result from the mixing between an andesitic and a rhyolitic magma concentration patterns generated by magma mixing are analyzed on digital images and results have been compared with those obtained from numerical simulations of mixing processes coupling chaotic advection and chemical diffusion results show that the upper pollara rocks were produced by mixing 24 49 of andesite and 76 51 of rhyolite multifractal analysis of the mixing structures is performed and the mixing intensity i e the degree of interaction between the two end member magmas has been deduced from the analysis of the singularity spectrum results show that narrower is the multifractal spectrum the higher is the degree of homogenization of magmas reynolds number re during mixing has been estimated from the geometrical analysis of mixing structures by using experimentally defined relationships between shape parameters and re results show that re is between ca 500 and 7000 there is a positive correlation between the estimated initial percentage of mafic magma in the different analyzed samples and re in agreement with the observation that the higher is the percentage of the mafic lower viscosity magma the higher is the turbulence of the mixing system in addition our analysis reveals an unexpected inverse relationship between the calculated re and the degree of magma homogeneity suggesting that energy dissipation may have had a major role in the controlling mixing process because dissipation is inversely proportional to the mixing efficiency results suggest that mixing processes between the andesitic and rhyolitic magmas mainly developed in the conduit it is also suggested that mixing occurred in a shear layer type or pipe type flow

on curved laminae graded layers convection currents and dynamic crystal sorting in the ploumanac h brittany subalkaline granite curved layered objects in a subalkaline potassic intrusive granite are analyzed biotite laminae and cyclic reverse size and modal layers are encountered in an annular zone both cyclic and intermittent layers are observed in rhythmic arrangement truncation the bifurcation curvature of layers with ladle shape represents the action of magmatic currents as would convection cells or fluid dynamic fingers emphasis is put on the bagnold effect related to such currents which would explain the reverse size grading of layers this kind of size sorting hydrodynamic occurs in highly viscous granitic magma simple convection seems more likely than diffusive convection

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

stress heterogeneity in the cerro prieto geothermal field baja california mexico we studied the background seismic activity in the cerro prieto geothermal field cpgf earthquakes were located below the exploitation area of the cpgf between 3 and 12 km deep this activity is located on a horstlike structure below the geothermal field and coincides with the zone of maximum subsidence in the cpgf two earthquake swarms occurred one in november 2000 and the second in february 2001 along the southeast northwest strike of the cerro prieto fault and in the neighborhood of the cerro prieto volcano magnitudes of the located microevents range from 0 3 to 3 5 a v p v s ratio of 1 91 for the region below the volcano suggests a water saturated medium and or a partial melt medium seventy six focal mechanisms of individual microearthquakes reveal significant variation in the orientation of the p and t axes focal mechanism inversions using the gephart 1990 code also reveal significant lateral stress variation of the best fit stresses below the cpgf the orientation of the best fit maximum intermediate and minimum stresses are plunge azimuth 1 66 72 2 6 328 and 3 24 235 for the november 2000 earthquake swarm the best fit principal stress orientations are 1 12 117 2 11 25 and 3 74 253 whereas for the february 2001 earthquake swarm they are 1 36 235 2 24 127 and 3 45 11 the 1 orientations are considerably different from the orientation of the maximum compressive regional stress that lies approximately north south on 1 june and 10 september 1999 two earthquakes of m w 5 2 and 5 3 occurred in the basement at depths of 7 4 and 3 8 km below the cpgf waveform modeling resulted in fault plane geometries given by strike 236 dip 60 slip 58 normal and strike 10 dip 90 slip 159 right lateral strike slip respectively an observed triangular source time function of 0 7 sec and a double source with a total duration of 1 9 sec were used to calculate the synthetics seismograms for these two events static stress drops and seismic moments for the june and september events are 82 5 mpa m 7 65 1016 n m and 31 3 mpa and m 1 27 1017 n m these stress drops are typical of continental events rather than of events originating in spreading centers we concluded from the focal mechanism inversions of the background seismicity and the june and september 1999 events that complex stress heterogeneity exits in the cpgf as a result of the continual thinning of the crust in the cerro prieto basin

geochemical modeling of acid basic magma interaction in the sardinia corsica batholith the case study of sarrabus southeastern sardinia italy abstract the hercynian intrusive rocks outcropping in the sarrabus area southeastern sardinia italy consist of microgranular mafic enclave mme bearing granites 95 associated with coeval stratified gabbroic complexes and basic septa bs

stress drop estimates for some aftershocks of the ometepec guerrero mexico earthquake of june 7 1982 brune s stress drop apparent stress and arms stress drop are estimated at a single station for 25 aftershocks of the ometepec earthquakes ms 6 9 and ms 7 0 the arms stress drops and apparent stresses are systematically smaller than brune s stress drops stress drops from the root mean square of acceleration and apparent stress range from 0 01 to 10 2 bars 1 bar 100 kpa except for two values 21 4 and 33 0 bars on the other hand brune s stress drops range from 0 6 to 239 bars seismic moments ranging from 0 5 1019 to 289 1019 dyn cm 1 dyn cm 10 n cm were estimated for events with coda magnitudes between 0 6 and 2 2 values of radiated seismic energy calculated by integration of the displacement spectra range from 2 5 1012 to 2 3 1016 dyn cm the fmax values lie between 16 and 30 hz seismic coda wave attenuation measured on narrow band pass filtered seismograms show a linear dependence of the seismic quality factor of the form in the range of frequencies from 3 to 24 hz

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

near fault strong ground motions recorded during the morelia normal fault earthquakes of may 2006 in mexicali valley b c mexico by the end of may 2006 a series of earthquakes had occurred in the mexicali valley baja california mexico this activity which included an m w 5 4 event developed in the vicinity of the cerro prieto geothermal field the earthquakes occurred on the morelia fault one of the east dipping normal faults in the mexicali valley cracks and fissures visible on the ground after the stronger earthquake defined two parallel fault segments of 4 and 2 km length the shorter segment being 1 km to the east of the other one down dip displacements of up to 25 30 cm were measured at some places along this surface break zone the ten larger events of the series were recorded by strong motion stations that operate in the epicenter area so that accurate hypocenter locations were obtained on the basis of p wave arrival times from the strong motion recordings the estimated shallow depths combined with the earthquake magnitude explain the strong shaking felt by residents and some damage observed on the cerro prieto geothermal plant the m w 5 4 event produced peak ground accelerations that go from 0 002 g at cuc on rock to 0 5 g at geo on sediments at 13 and 1 7 km from the epicenter respectively the station geo recorded closer to the epicenters and on the hanging wall side of the fault static ground displacements and a predominance of the strike normal over the strike parallel velocity components were determined from the acceleration records of this station these and other ground motion characteristics are also seen on pseudovelocity and absolute acceleration response spectra calculated from data of the larger event altogether the observed ground motion characteristics provide useful insights into the levels of ground shaking that near fault structures in the mexicali valley should be designed to withstand

waveforms and spectra of preshocks and aftershocks of the 1979 imperial valley california earthquake evidence for fault heterogeneity we have compared digitally recorded waveforms of m l 2 0 2 8 earthquakes that occurred in two small areas along the imperial fault before and after it broke in the ml 6 6 imperial valley earthquake on october 15 1979 eight preshocks 1977 1979 from a 4 by 1 km area centered 4 km se of the mainshock epicenter have strikingly similar waveforms over the entire record length 30 s with an average peak cross correlation between seismograms of 0 74 the seismograms are well correlated at frequencies up to at least 4 hz this implies similar source mechanisms and hypocenters within of the 4 hz wavelengths i e 200 400 m five aftershocks from the same area show an average peak cross correlation between seismograms of only 0 23 any associated changes in mechanism must be small because they are not reflected in the first motion data analysis of frequency content of these events using bandpass filtering techniques showed no systematic temporal changes in spectral shape ten preshocks and 24 aftershocks from a 1 by 2 km source area centered along the fault 16 km nw of the mainshock epicenter were also studied first motion data suggest that all of the aftershocks and a swarm of six preshocks on december 7 9 1978 were associated with the main fault but that four earlier preshocks were not the six preshocks on december 7 9 1978 were tightly clustered as evidenced by the strong similarity of the waveforms most peak cross correlations 0 6 during this swarm the 8 to 16 hz spectral amplitude increased relative to the 1 to 2 hz spectral amplitude over the whole record length by about a factor of 3 suggesting a systematic increase in stress drop groups of like events are also present among the aftershocks in this data set the average peak correlation for pairs of aftershocks 0 43 is almost the same as that for pairs of preshocks 0 45 if all 10 preshocks are included however several sources appear to have been active simultaneously during the aftershock period so that no more than two to three consecutive aftershocks have maximum cross correlations 0 6 the highly localized sources characterized by waveform similarity may represent fault asperities or clusters of asperities our observations are consistent with a decrease in the number of these asperities as the weaker ones fail under increasing stress during the intervals between large earthquakes

two mw 4 8 cerro prieto baja california mexico earthquakes on 1 june and 10 september 1999 strong motion observations we analyzed the strong motion records of two m w 4 8 normal fault earthquakes that occurred in june and september 1999 in the sedimentary environment of the mexicali valley peak ground accelerations of up to 0 452 g were recorded for these events at distances between 2 and 37 km we found that peak amplitudes recorded at the shorter distances tend to match the attenuation functions for southern california however as the distance from the epicenter increases the cerro prieto peak amplitudes decay at a significantly higher rate we also show that acceleration data from other small to moderate size earthquakes of the area decay with the same attenuation pattern thus as the sediments of the mexicali valley rapidly attenuate the intensity of the ground motion the potential of the earthquakes to cause damage at distance is reduced too although the higher accelerations were recorded at the station geo located in the yard of the cerro prieto geothermal plant the damage caused to the plant was minimal in this study we also explored the possibility of nonlinear behavior of the sediments beneath the station geo in the cerro prieto earthquakes for this a set of geo acceleration records from smaller magnitude earthquakes of the area was studied first to gain an understanding of the response of sediments to less intense ground motions horizontal to vertical component ratios of shear wave spectra indicated very similar ground amplifications for 17 earthquakes with magnitudes between 2 2 and 4 0 this result suggested that the sediments at geo behave linearly during earthquakes in this range of magnitude the mean site amplification from the smaller magnitude earthquakes was then compared to the ground amplifications from the two stronger events relative to this weak motion amplification only a light nonlinear response of the sediments for the june event was inferred for the september event however the comparison showed a clear reduction in the site amplification such deamplification of motion suggests nonlinear behavior of the sediments during the more intense ground shaking of this event furthermore a well defined peak of resonance in the weak motion amplification was clearly absent in the response of the two stronger events as has been reported in other studies of nonlinear response of sediments

analysis of peak ground motion in terms of a model of inhomogeneous faulting measurements of peak ground velocity v and acceleration a for earthquakes and mine tremors with local magnitudes ranging from 0 8 to 6 4 have been analyzed in terms of a model of inhomogeneous faulting the fault model involves the failure of a circular asperity of radius ri surrounded by a previously faulted annular region of outer radius r0 the failure of the asperity results in seismic radiation with a characteristic frequency proportional to 1 ri followed by lower frequency radiation proportional to 1 r0 as static equilibrium is regained over the larger region for r0 ri 1 both v and a are associated primarily with the failure of the asperity but also depend on the large scale source parameters specifically v r0 r 0 10 r0 ri 0 15 and a r 0 30 r0 ri 2 0 45 where is the shear wave velocity is the overall stress drop is the modulus of rigidity and is density the terms involving r0 ri correspond to the high frequency radiation associated with the failure of the asperity and the other terms indicate the peak parameters due to the broad scale readjustment observations of peak ground motion for events with seismic moments ranging from 5 1016 to 1026 dyn cm indicate that r0 ri is normally in the range of 1 10 and appears to be independent of earthquake size the inhomogeneous fault model also yields convenient expressions for the small scale displacement and stress drop of the asperity failure as well as for the level of regional stress available to cause slip

mixing and compositional stratification produced by natural convection 1 experiments and their application to earth s core and mantle an extensive series of laboratory experiments is used to quantify the circumstances under which fluids can be mixed by natural convection at high flux rayleigh number a compositionally buoyant fluid was injected at a fixed rate into an overlying layer of ambient fluid from a planar horizontally uniform source the nature of the resulting compositional convection was found to depend on two key dimensionless parameters a reynolds number re and the ratio u of the ambient fluid viscosity to the input fluid viscosity increasing the reynolds number corresponded to increasing the vigor of the convection while the viscosity ratio was found to determine the spacing between plumes and whether buoyant fluid rose as sheets u 1 from measurements of the final density profile in the fluid after the experiments we quantified the extent to which buoyant liquid was mixed in terms of a thermodynamic mixing efficiency e the mixing efficiency was found to be high e 0 9 when either the reynolds number was large re 100 or the viscosity ratio was small u 200 the amount of mixing was related to whether ascending plumes generated a large scale circulation in the ambient fluid when our results are applied to the differentiation of the earth s core we suggest that the convection resulting from the release of buoyant residual liquid into the liquid outer core due to crystallization at the boundary between the inner and the outer core will probably lead to nearly complete mixing in the dynamically very different context of the mantle mantle plumes are predicted to ascend through the mantle and pond beneath the lithosphere whereas convection driven by the subduction of oceanic lithosphere is expected to produce moderate to extensive mixing of the mantle when the competing plate and plume modes of mantle convection are considered together we find that owing to a larger driving buoyancy flux the plate scale flow will destroy any stratification at the top of the mantle produced by mantle plumes applying our results to the stagnant lid style of thermal convection predicted to occur in the mantles of the moon mercury mars venus and pre archean earth we expect the respective flows to produce minor thermal stratification at the respective core mantle boundaries in part 2 of this study jellinek and kerr this issue we apply our results to the differentiation of magma chambers and komatiite lava flows

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

magma flow within the tavares pluton northeastern brazil compositional and thermal convection crystallization coupled with gravity removal of depleted interstitial melt has long been recognized as a mechanism of magma differentiation similarly heat released by synplutonic basaltic magma intrusions has long been recognized as capable of driving convection in granite chambers direct evidence of these processes has seldom been described in granites in the tavares pluton we mapped a number of melt extraction structures from pores of a crystal liquid mush an effectively solid magma where crystals form an interconnected skeleton and a variety of flow structures such as 1 meter scale tear or mushroom shaped blobs representing within chamber diapirs 2 meter scale ellipsoids representing frozen thermal plumes of granite driven by heat released from disrupted diorite intrusions and 3 ladder dikes and snail structures representing cross sections of several superposed cylindrical magma channels possibly feeders of diapirs and plume heads a fundamental feature of the structures in the tavares pluton is that they are well delineated by mafic schlieren developed at active channel margins we postulate a new model for the origin of marginal schlieren which combines shear flow sorting and melt escape from the flowing magma into an effectively solid surrounding mush extraction structures representing melt extraction from mush pores into melt pockets and schlieren representing regions where melt escaped into surrounding mush pores are both favored by magmas that form an interconnected solid framework at low crystal fractions 50 because these mushes are ductile and permeable favorable magmas are those with a high wetting angle between melt and solid 60 and a propitious crystal size and shape distribution we propose a model of compositional and thermal convection that accounts for all described structures

basalt triggering of the c ad 1305 kaharoa rhyolite eruption tarawera volcanic complex new zealand abstract the ad 1305 kaharoa eruption episode of tarawera volcanic complex was the largest 4 km3 magma eruption in new zealand in the last 1000 years high silica 76 sio2 rhyolite was erupted from seven vents along an 8 km linear zone to form pumiceous pyroclastic deposits and lava domes initial vent clearing explosions were followed by a series of plinian pumice eruptions that spread tephra downwind and pyroclastic density current deposits over the volcano slopes the early pyroclastic eruptions were followed by extrusion of a dome in the summit vent and the migration of further plinian activity to adjacent vents the episode finished with the extrusion of three summit lava domes accompanied by block and ash flows two main types of rhyolite were erupted 1 a low zr low sr high rb type comprising the early plinian pyroclastics and 2 a high zr high sr low rb type comprising the late eruptives including the summit domes basaltic material basalt and basaltic andesite is commonly present as free clasts within the kaharoa pyroclastic deposits along with rare clasts of granodiorite diorite gabbro and olivine clinopyroxenite the basaltic clasts are often veneered by kaharoa rhyolite basaltic material is also common as inclusions within rhyolite pumices along with olivine and augite xenocrysts derived from the basalt the basaltic clasts and inclusions contain complexly zoned plagioclase and corroded olivine commonly with a reaction rim consistent with disequilibrium caused by magma mixing some basaltic clasts and inclusions are hornblende free others contain groundmass hornblende plumes of brown glass often extend from hornblende bearing basaltic inclusions into the surrounding rhyolite these plumes demonstrate magma mixing as does the presence of rhyolitic glass and quartz xenocrysts in some basaltic inclusions most basaltic inclusions have crenulate boundaries suggesting they were fluidal when coming into contact with the rhyolite magma diorite gabbro and olivine clinopyroxenite clasts have mineralogy similar to the basalts commonly contain patches of fine grained basaltic material and are considered co magmatic with the basalts intrusion of basalt magma into the base of the rhyolite magma chamber appears to have occurred for some time before the kaharoa eruptions began allowing considerable mixing with the rhyolite magma transfer of water to some basalt inclusions and formation of hornblende in their groundmass conversely the hornblende free basalt inclusions did not have time to react with the rhyolite magma and must have been intruded shortly before the start of the eruption intrusion of this hornblende free basalt appears to have triggered the kaharoa eruption after the magma chamber had been primed by the earlier intrusions

source parameters of the ensenada bay earthquake swarm baja california mexico seismic data collected from the ensenada bay earthquake swarm of late 1981 were used to calculate the spectra of ground displacement data from the stations of ensenada enx and cerro bola cbx

trace element mobility during magma mixing preliminary experimental results abstract magma mixing tests have been performed experimentally in a taylor couette like experimental setting the variation of trace element concentrations along transects crossing the resultant melt column has been measured results indicate a strongly variable mobility of the different trace elements in the same mixing system such a different behaviour of trace elements tends to be enhanced as the mixing time increases leading to the production of highly heterogeneous volumes of melts in which depletion and enrichment of trace elements occurred depending on their potential of spreading across the magma mixing system the results presented here offer new insights into the complexity of processes expected to be operating during mixing of magmas it is demonstrated that on short mixing times also the trace elements may become highly non correlated this is due to the development of chaotic advection diffusion processes in the system these results indicate that the onset of diffusive fractionation processes may strongly influence the patterns of data on inter elemental diagrams depending on the relative mobility of the different elements

simulations of strong ground motion for earthquakes in the mexicali imperial valley region summary in this paper computer modelling is used to test simple approximations for simulating strong ground motions for moderate and large earthquakes in the mexicali imperial valley region initially we represent an earthquake rupture process as a series of many independent small earthquakes distributed in a somewhat random manner in both space and time along the rupture surface by summing real seismograms for small earthquakes used as empirical green s functions strong ground motions at specific sites near a fault are calculated alternatively theoretical green s functions that include frequencies up to 20 hz are used in essentially similar simulations the model uses random numbers to emulate some of the non deterministic irregularities associated with real earthquakes due either to complexities in the rupture process itself and or strong variations in the material properties of the medium simulations of the 1980 june 9 victoria baja california earthquake ml 6 1 approximately agree with the duration of shaking the maximum ground acceleration and the frequency content of strong ground motion records obtained at distances of up to 35 km for this moderate earthquake in the initial stages of modelling we do not introduce any scaling of spectral shape with magnitude in order to see at what stage the data require it surprisingly such scaling is not critical in going from m 4 5 events to the m 6 1 victoria earthquake however it is clearly required by the el centro accelerogram for the imperial valley 1940 earthquake which had a much higher moment ms 7 we derive the spectral modification function for this event the resulting model for this magnitude 7 earthquake is then used to predict the ground motions at short distances from the fault predicted peak horizontal accelerations for the m 7 event are about 25 50 per cent higher than those observed for the m 6 1 victoria event

strange attractors in magmas evidence from lava flows abstract magma mixing structures from three different lava flows salina vulcano and lesbos are studied in order to assess the possible chaotic origin of magma mixing processes structures are analysed using a new technique based on image analysis procedures that extract time series that are representative of the relative change in composition through the structures these time series are then used to reconstruct the attractors underlying the magma mixing process and to calculate the fractal dimension of the attractors results show that attractors exist and possess fractional dimensions this evidence suggests that the mixing of magmas is a chaotic process governed by a low number of degrees of freedom in addition fractal dimension analyses allows us to discriminate between different regimes of mixing in the three lava flows in particular our analyses suggest that the lava flow of salina underwent more turbulent mixing than the lava flows of lesbos and vulcano

eruption triggered mixing of extra caldera basalt and rhyolite complexes along the east gallatin washburn fault zone yellowstone national park wy usa abstract though mixing and commingling of magmas is common mixing between rhyolite and basalt magmas is not commonly preserved in volcanic rocks the presence of at least four mixed magma complexes at yellowstone national park suggests that mingling is not due to random intersections of feeder dikes geochemical analyses also show that though these magmas appear to be commingled there is mixing between the two disparate end members our model combines previous work on the grizzly lake gardner river crystal spring and appolinaris spring mixed magma complexes with results from new analyses recent mixing experiments and regional structural geology coeval extensional tectonism as seen in the east gallatin washburn fault zone is also present in other areas of basalt and rhyolite mixing mingling e g iceland the central portions or core of the complexes contain increased concentrations of emulsion rock occasional basaltic pillows in a rhyolite matrix net veining and mixed magma with highly variable geochemistry sio 2 ranges from 50 to 78 wt phenocrysts have been transferred between mafic and felsic portions of the complexes and suggest that these mixed magmas did not have enough time or energy e g heat to thoroughly mix into complete hybrid intermediate magmas this implies that mixing occurred during eruption furthermore analyses at the micron scale suggest that zones of chaotic mixing between basalt and high silica rhyolites may be more complete than previously thought during mixing of high silica rhyolites and basalts with greater than 4 wt mgo the temperature of the rhyolitic magmas was approximately 850 c with a viscosity between 1 10 6 and 3 10 6 pas the basalt was approximately 1070 c with a viscosity of 2 10 2 to 9 10 3 pas prior to mixing mixing of these two extreme end members may have required decompression of the lower basaltic magma chamber during eruption of the overlying rhyolitic magma chamber into through structurally weakened zones of the upper crust the decompression induced mixing was facilitated by coeval extensional tectonics and structures in the norris mammoth corridor extra caldera rhyolites are some of the first volcanics following the collapse of the current caldera and also some of the youngest volcanics in the yellowstone plateau and require further understanding of volcanism in the yellowstone plateau

strong motion seismology strong motion seismology is concerned with earthquake ground motion in the amplitude range that poses the threat of human injury or property damage because the occurrence of strong motion cannot be predicted in advance and because the time between significant events at any one place may range from tens to thousands of years strong motion data is recorded on triggered instruments that typically must be maintained in readiness for years between periods of significant recording as a consequence the strong motion data set is sparse because of the engineering need for estimates of future ground motion the scope of the field of strong motion seismology encompasses seismic source theory and any other aspect of seismology that can provide insights helpful in making the best possible estimates given the limited data this relationship with the rest of seismology is a reciprocal one in that strong motion data gives perhaps the best information available on earthquake source processes

petrogenesis of early cretaceous granites and associated microgranular enclaves in the xiabie co area central tibet crust derived magma mixing and melt extraction abstract multiple petrogenesis models have been proposed for granitic rocks and the mafic microgranular enclaves mmes hosted in them the mantle and crust derived magma mixing mingling process was widely suggested for the formation of mmes or the host granitoids however whether the mixing between magmas derived from different crustal sources may also form microgranular enclaves mes not restricted to mafic or the host granites remain unclear here we report petrological geochemical and zircon in situ hf o isotopic data for mes and their host granites in the northern nyima area southern qiangtang terrane sqt central tibet the host granitic rocks consist of amphibole bearing biotite granites and syenogranite minor granodiorite and aplite veins and mes comprising diorite and granodiorite host rocks and mes are contemporaneous and were generated in the early cretaceous 120 ma host granitoid samples are high k calc alkaline rocks and have high sio2 66 78 wt and low mgo 5 wt high zr 500 ppm with zr hf ratios 45 and high ba 400 ppm implying biotite and zircon concentrations combining this information with embayed feldspars curved biotites and closely spaced feldspar grains we suggest that liquid loss resulted from crystal compaction or filter pressing both the fine grained syenogranites and aplite veins exhibit high sio2 and rb sr ratios in addition to low zr hf ratios and zr and ba concentrations with remarkably negative eu anomalies indicating that they are highly differentiated melts extracted from felsic crystal mush such a crystal mush is possibly represented by the biotite granites gradual contact relationships between variable granitic phases indicate that melt extraction and crystal concentration were coeval residual melt extraction from the crystal mush was facilitated by mush remobilization resulting from magma replenishment we suggest that for the host rocks the biotite granites were mainly derived by partial melting of ancient crust and the granodiorites most likely resulted from the magma mixing mingling that might be accompanied with the loss of melts the fine grained syenogranites and aplites represent highly evolved residual melts mes are geochemically characterized by intermediate to felsic compositions sio2 56 3 67 8 wt with low mgo

the space and time complexity of chaotic mixing of silicate melts implications for igneous petrology abstract we present new experimental results on the study of the space and time modulation of compositional fields during chaotic mixing between mafic and felsic silicate melts the experimental strategy was planned using numerical simulations performed using the experimental geometry these mixing experiments were performed using a recently developed experimental apparatus which is capable of mixing high viscosity silicate melts at high temperatures and under precisely controlled conditions of fluid dynamics and strain the compositional variability produced by the mixing process was investigated both along linear analytical transects and on high resolution 2d x ray maps covering the mixing patterns our results indicate that chaotic flow fields represent very powerful dynamics to blend silicate melts even under laminar fluid dynamic conditions reynolds number ca 10 7 and for dissimilar melts with high viscosity ratios on the order of 103 the repetition of stretching and folding processes between the two melts induced a strong increase of contact interfaces thus favoring efficient chemical exchanges as a result the initial mafic composition is no longer detectable in the mixing system after ca 2 h i e the duration of the experiment a further important result is the observation of highly non linear patterns in inter elemental plots produced by the onset of diffusive fractionation processes this is contrary to common thinking that magma mixing should always produce linear trends between pairs of chemical elements a new measure the concentration variance is proposed to quantify chemical element mobility during the mixing process this measure is statistically robust and can be quantitatively used to measure chemical element mobility independently of the geometry in which the compositional variation i e transects areas etc is embedded or the local strain history of the mingling our results highlight concentration variance as a robust probe of the as yet poorly understood processes involved in the common petrological process of magma mixing

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

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

the seismic spectrum radiated energy and the savage and wood inequality for complex earthquakes abstract we have integrated velocity squared spectra in order to determine the seismic energy radiated during fault rupture the high frequency spectral fall off and the shape of the spectrum at the corner frequency are critical to the energy calculation high frequency spectral fall offs of 2 beyond the corner frequency in a brune 1970 source model return radiated energies approximately equal to that of an orowan 1960 type fault failure where the final stress level is equal to the dynamic frictional stress any spectra with an extended intermediate slope of 1 would therefore result in higher radiated energies savage and wood 1971 proposed a model in which the final stress level was less than the dynamic stress level and that this was the result of overshoot they based their model on the observation that the ratio of twice the apparent stress to the stress drop was typically around 0 3 we show that for such a ratio to exist high frequency spectral fall offs of 3 would be required composite spectra have been constructed for several moderate to large earthquakes these spectra have been compared to that predicted by the haskell 1966 model and velocity squared spectra have been integrated to determine the radiated energy in all cases this ratio twice the apparent stress to the stress drop is greater than or equal to one violating the savage and wood 1971 inequality and provides evidence against overshoot as a source model

the fracturing in volcanic edifice before an eruption the june july 1998 high frequency earthquake swarm at volcan de colima mexico the recent eruption of volcan de colima mexico began in november 1998 and was preceded by a 12 month period of seismic activity which consisted from a few swarms of numerous microeathquakes we study the source characteristics of earthquakes that occurred during june july 1998 swarm within the edifice of volcan de colima which consists of the dormant nevado de colima and active volcan de fuego a three component digital seismic station added to the one component seismic network of five stations during this period allowed us to analyze s wave spectra for our study thirty two microearthquakes with hypocentral distances up to 7 km and magnitudes mw between 0 5 and 1 8 were analyzed in the frame of brune s model these events were characterized by high frequency radiation with corner frequencies from 3 9 to 9 0 hz their seismic moments varied from 0 9 1010 to and stress drops were obtained in the range between 0 05 and 13 bars we found three groups of events with different corner frequencies that may reflect the presence of three fracture zones with distinct characteristic lengths of fissures formed by the subsurface dike intrusion before the eruption the first stage from june 16 to july 3 of swarm development was characterized by simultaneous fracturing within two fracture zones the first zone was represented by a system of fractures with length of about 80 90 m and was situated below nevada de colima the second zone was represented by a system of fractures with length of about 130 150 m and was situated below the crater zone of volcan de fuego the second stage from july 4 to 6 of swarm development was characterized by simultaneous fracturing within three fracture zones a third zone was added to the first two zones with the fracture length of intermediate size about 110 m the majority of foci that occurred from june 16 to july 3 were situated along the se slope of nevado de colima the events of july 4 to 6 occurred mainly below the crater zone of volcan de fuego the fracturing in the volcanic edifice occurred within a system of fractures of ene direction tracing by epicenters and coinciding with the general trend of tamazula regional fault that intersects the volcanic structure we suggested that this development of the earthquake swarm reflects either 1 the migration of dike to the active crater of volcan de colima or 2 the growth of branches of the dike swarm tree within the volcanic edifice

strange attractors in plagioclase oscillatory zoning petrological implications oscillatory zoning in plagioclase crystals from different mixed lava flows cropping out on the island of capraia italy has been investigated an calibrated profiles from back scattered electron images are used as compositional time series of oscillatory zoning they are analyzed by a qualitative visual method that allows to appreciate at first sight the global structure of the time series and by a quantitative method to reconstruct the attractors associated to the oscillatory patterns and to calculate the fractal dimension of attractors results show that attractors have fractional dimensions indicating that series are chaotic in addition it is evidenced that there is a wide variation in oscillatory zoning in crystals from the same lava flow and that plagioclase populations from the different lava flows differ in the shape of frequency histograms of attractor dimension the development of oscillatory zoning is simulated by considering a chemically inhomogeneous magmatic mass governed by chaotic flow fields coupled with chemical diffusion in which plagioclase crystals grow according to the availability of nutrients in their neighborhoods results show that in such a dynamical system plagioclase crystals develop chaotic zoning patterns analogous to those observed in natural plagioclases this approach allows us to explain the differences observed in plagioclase crystals from the same lava flow and the differences in the shape of frequency histograms of attractor dimensions in the four lava flows

static stress drop associated with brittle slip events on exhumed faults 1 we estimate the static stress drop on small exhumed strike slip faults in the lake edison granodiorite of the central sierra nevada california the subvertical strike slip faults were exhumed from 4 to 15 km depth and were chosen because they are exposed in outcrop along their entire tip to tip lengths of 8 12 m slip nucleated on joints and accumulated by crystal plastic shearing forming quartz mylonites from early quartz vein filling in joints and successive brittle faulting forming epidote bearing cataclasites the occurrence of thin 300 m wide pseudotachylytes along some small faults throughout the study area suggests that some if not all of the brittle slip on the study area faults may have been seismic we suggest that the contribution of brittle cataclastic slip to the total slip along the studied cataclasite bearing small faults may be estimated by the length of epidote filled rhombohedral dilatational jogs rhombochasms distributed quasi periodically along the length of the faults the interpretation that slip recorded by rhombochasms occurred in single events is based on evidence that 1 epidote crystals are randomly oriented and undeformed within the rhombochasm 2 cataclasite in principal slip zones does not include clasts of previous cataclasite and 3 rhombochasm lengths vary systematically along the length of the faults with slip maximum occurring near the fault center tapering to the fault tips we thereby constrain both the rupture length and slip on the basis of these measurements we calculate stress drops ranging over 90 250 mpa i e one to two orders of magnitude larger than typical seismological estimates for earthquakes but similar in magnitude to seismological estimates of small m2 earthquakes from the san andreas fault observatory at depth safod the slip events described in the present study occurred along small deep seated faults and given the calculated stress drops and observations that brittle faults exploited joints sealed by quartz bearing mylonite we conclude that these were strong faults

trace element diffusion in jadeite and diopside melts at high pressures and its geochemical implication abstract diffusivities of geochemically important trace elements eleven rare earth elements ree rb sr ba and y in jadeite and diopside melts and those of zr nb th and u in jadeite melt have been measured at pressures between 7 5 and 20 kbar and at temperatures 50 200 above the liquidus using diffusion couples and ion microprobe analysis the concentrations of these elements in the experimental charges are close to those in natural igneous rocks in the jadeite melt which is nearly fully polymerized nbo t 0 1 diffusivities of ree increase with increasing ionic radii 2 diffusivities of tri and tetravalent elements increase with increasing pressure at constant temperature whereas those of mono and divalent elements do not change significantly with pressure and 3 diffusivities of these elements decrease with increasing their ionic charge at constant pressure and temperature in the diopside melt which is considerably less polymerized nbo t 2 1 diffusivities of these trace elements depend mainly on their ionic radii rather than ionic charges the diffusivities of mono and divalent ions decrease with increasing ionic radii at constant pressure and temperature and 2 diffusivities of ree are nearly the same as that of ca and decrease with increasing pressure at constant temperature the behavior of these trace elements is correlated with that of major elements in the jadeite melt tri and tetravalent elements behave similarly to network forming cations al and si whereas mono and divalent elements behave as network modifying cations similarly to na in the diopside melt the diffusion behavior of all these trace elements is similar to that of network modifying cations ca and mg the results of the present experiments suggest that the abundance of some trace elements in igneous rocks may have been affected by diffusion process at the magmatic stage in the case of ree for example if two different magmas with high and low ree concentrations become in contact one another by multiple intrusion and a zoned magma chamber is formed diffusion begins to take place between them and near the interface the ree enriched magma will become more light ree depleted whereas ree depleted magma will become more light ree enriched and in addition if magmas are reduced the former will show a negative eu anomaly whereas the latter will show a positive eu anomaly

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

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

centrifuge modeling and numerical analysis on seismic site response of deep offshore clay deposits abstract nonlinear site response of deep offshore clay deposit plays an important role in changing the characteristics of ground motions when subjected to strong shaking especially when different amplification behaviors of acceleration and displacement are considered the paper describes a series of centrifuge shaking table tests and numerical simulations to investigate the behavior of deep offshore clay deposits subjected to earthquake loadings the centrifuge model tests were performed on a slightly overconsolidated clay deposit at uc davis a suite of shaking tests were conducted including impulse step wave testing frequency sweeps a small elastic earthquake event and a ductility level large earthquake event accelerations displacements and pore pressures were measured in the soils free field throughout the test program for the elastic level excitations about a 33 amplification was observed between the input acceleration at the base and the measured accelerations near the top of the clay deposit however for the ductility level earthquake excitation which had peak input acceleration at the base of 0 46g acceleration near the top of the deposit was reduced to 0 07g these observations are correctly simulated by deepsoil with proper soil models and parameters back analyzed from the centrifuge model test then systematic 1 d site response analyses are performed on synthetic clay deposit models with 30 to 120 m depths using the validated deepsoil program and the amplification characteristics of acceleration and deformation induced by base excitation with different intensities and frequencies are analyzed in both time and frequency domains the results reveal that for deep soft offshore clay deposits subjected to large earthquakes significant acceleration attenuation may occur near the top of deposit due to soil nonlinearity and even local shear failure however significant amplification of displacement at low frequencies is expected regardless of the intensities of base motions which suggests that for displacement sensitive offshore foundations and structures such amplified low frequency displacement response will play an important role in seismic design

decadal time gaps between mafic intrusion and silicic eruption obtained from chemical zoning patterns in olivine abstract intrusion of mafic magma in a silicic crustal reservoir has been reported in numerous studies of subduction related volcanoes and is considered a main process for triggering explosive eruptions and for transferring geochemical signatures from the mantle to the crust here we determine the timescales between mafic silicic encounters and eruption by exploiting the fact that during such interactions magmas exchange crystals and their mineral compositions will strive to equilibrate to the new environmental conditions specifically we model the fe mg zoning patterns of olivine found in the dacites andesite and quenched mafic inclusions of the holocene zoned eruption of volcan san pedro 36 s chilean andes the san pedro eruption is an example where mixing between silicic and mafic magmas produced intermediate compositions e g andesite at depth in the magma reservoir for modeling the compositional profiles we took into account the anisotropy of fe mg diffusion in olivine and also the effects of diffusion in multiple dimensions aspects that have been largely neglected in previous works the retrieved timescales for olivine melt equilibration by diffusion display an array ranging from 1 year for the most silica rich dacite to 50 years for the andesite this array of timescales rather than a single value provides new insight into the details of mafic silicic mixing at depth they reveal processes that occur on a longer timescale than the days to weeks time gap for cases where the mafic intrusion triggered the eruption and they might be associated with the instances where seismic activity or significant inflation of the volcanic edifice was not immediately followed by eruption on the other hand the year to decade timescales that we report for producing magmas of intermediate composition e g andesites are much shorter than the 10 3 10 5 years inferred from u series disequilibria data for igneous differentiation by closed system fractionation to produce similar magma compositions at subduction zones

shape and microstructure of microgranitoid enclaves indicators of magma mingling and flow abstract at tarandore point 328 km south of sydney new south wales australia two tonalite phases are in contact with a gabbroic diorite all belonging to the moruya batholith lobate to crenulate contacts pillowing of the more mafic phase in the more felsic phase net veining of the more mafic phase by the more felsic local chilling of the more mafic phase against the more felsic and an abundance of rounded to elongate microgranitoid enclaves all suggest mingling of magmas at the site of emplacement therefore all phases were emplaced before the others solidified and an order of intrusion cannot be determined the variety of microgranitoid enclaves suggests that repeated magma mingling has occurred linear geochemical trends indicate either magma mixing or restite unmixing as a prime cause of variation in the members of the moruya suite of granitoids direct evidence of mixing is not present but evidence that the magmas were substantially liquid at the time of emplacement sugests that mixing is possible restite unmixing is unlikely to be the prime process because near minimum melts which would occur in all granitoid phases according to that model should mix easily rather than mingling in fact mingling has occurred between tonalite phases of very similar composition which would not be expected if the liquid parts of enclaves were minimum melts available experimental and theoretical data on mixing in both magma chambers and conduits cannot be applied directly to the occurrence at tarandore point owing to inadequately constrained parameters but mixing generally should be favoured by higher temperatures which is consistent with our inference that relatively high proportions of melt were present in the granitoid phases at the time of emplacement conduit mixing may be reflected in a local zone of strong to extreme elongation of enclaves in which the distortion has been accomplished by magmatic flow without solid state deformation as evidenced by strong dimensional preferred orientations coupled with a lack of microstructural evidence of intragranular plastic strain this suggests that elongate enclaves should not be used as indicators of solid state deformation or as tectonic strain markers without microstructural evidence that suitably strong intracrystalline plastic deformation has taken place

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

chaotic flow patterns from a deep plutonic environment a case study on natural magma mixing this work focuses on the mixing between basalt and granite in a deep plutonic environment the description of mixing patterns and measurements of fractal dimensions and the evaluation of geochemical data from a cambro ordovician granitic pluton are summarized and discussed different morphologic domains within the pluton reveal concentric fragmented and or folded layers of granite in a gabbro granite mixed matrix this stands in contrast to two predominantly regular gabbroic regions these regular regions are separated by tightly stretched filament areas in which mixing is enhanced sharp and gradational contacts between granitic and gabbroic domains depict the interplay among frozen flows mingling and convection enhanced diffusion processes mixing measurements of fractal dimensions at different scales and analysis of normalized concentration variance for major elements point towards magma mixing the compositional variability and flow patterns of the studied pluton have been greatly controlled by a natural chaotic mixing process between a granitic and a basaltic end member during the mixing process coeval fractional crystallization no doubt contributed to increasing the complexity of the system however since flow and therefore mixing stops with temperature decrease flow patterns must have retained the predominant morphology and composition of the moment at which both contrasting magmas came together and froze flow patterns have been preserved with further temperature decrease fractional crystallization took over and hybrid rocks were generated from the fractionation of magmas previously mixed in different proportions

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

experiments on magma mixing 1 the arrival of a new hot batch of magma changes the thermal and the chemical state of a volcanic plumbing system formation of hybrid magma by chemical dilution liquid miscibility model of different magma batches is generally accepted observations of drop like domains of less evolved newer magma in more evolved host magma point to the contribution of a mechanical mixing process liquid immiscibility the interplay of both mechanisms seems to control the time scale from the dormant to the active state of a volcano we carried out laboratory experiments using melts from natural volcanic rock compositions with the aim to validate model calculations for shear rate dependent domain sizes the results confirmed the model and also the importance of hydro mechanically mixing for chemical dilution the key process however that is able to change the state of a magma reservoir on a critical time scale is hydrodynamic magma mixing

time scales of hybridisation of magmatic enclaves in regular and chaotic flow fields petrologic and volcanologic implications this paper describes numerical models of advection diffusion between enclaves and host magmas applied with the aim of estimating time scales during which enclaves can be homogenised in particular advection was simulated using a numerical system consisting of regular and chaotic regions results indicate that the homogenisation time of enclaves in chaotic regions is several orders of magnitude faster than in regular regions for instance an enclave with a diameter of 100 cm may be homogenised in the chaotic region in 380 years assuming an advection velocity of 10 cm year whereas in the regular region it would require 6 5 105 years for complete homogenisation this implies that in the same magmatic system large differences in the degree of homogenisation may co exist generating magmatic masses with large spatial and temporal inhomogeneities

the fluid dynamics of a basaltic magma chamber replenished by influx of hot dense ultrabasic magma this paper describes a fluid dynamical investigation of the influx of hot dense ultrabasic magma into a reservoir containing lighter fractionated basaltic magma this situation is compared with that which develops when hot salty water is introduced under cold fresh water theoretical and empirical models for salt water systems are adapted to develop a model for magmatic systems a feature of the model is that the ultrabasic melt does not immediately mix with the basalt but spreads out over the floor of the chamber forming an independent layer a non turbulent interface forms between this layer and the overlying magma layer across which heat and mass are transferred by the process of molecular diffusion both layers convect vigorously as heat is transferred to the upper layer at a rate which greatly exceeds the heat lost to the surrounding country rock the convection continues until the two layers have almost the same temperature the compositions of the layers remain distinct due to the low diffusivity of mass compared to heat the temperatures of the layers as functions of time and their cooling rate depend on their viscosities their thermal properties the density difference between the layers and their thicknesses for a layer of ultrabasic melt 18 mgo a few tens of metres thick at the base of a basaltic 10 mgo magma chamber a few kilometres thick the temperature of the layers will become nearly identical over a period of between a few months and a few years during this time the turbulent convective velocities in the ultrabasic layer are far larger than the settling velocity of olivines which crystallise within the layer during cooling olivines only settle after the two layers have nearly reached thermal equilibrium at this stage residual basaltic melt segregates as the olivines sediment in the lower layer depending on its density the released basalt can either mix convectively with the overlying basalt layer or can continue as a separate layer the model provides an explanation for large scale cyclic layering in basic and ultrabasic intrusions the model also suggests reasons for the restriction of erupted basaltic liquids to compositions with mgo 10 and the formation of some quench textures in layered igneous rocks

the nature and occurrence of discrete zoning in plagioclase from recently erupted andesitic volcanic rocks montserrat abstract recently erupted rocks from montserrat lesser antilles were found to be coarsely porphyritic including plagioclase magnesio hornblende orthopyroxene titano magnetite and rare quartz phenocrysts zonations within plagioclase show three distinct periods within the evolution of the andesitic magmas initial steady state oscillatory overgrowths an49 54 represent an early period of growth within a confined andesitic magma chamber interaction with an intruding more mafic hotter magma resulted in thick zones of dissolution features that cut through these early growth layers the dissolution zones and crystal fragments are overgrown by thin calcic an86 plagioclase rims a plagioclase growth rate of 10 7cm s suggests that the calcic plagioclase rims were formed in approximately 10 h consistent with the idea that mineral growth may increase magma viscosity inducing conduit plugging and shallow pressurization resulting in cycles of dome inflation eruption and explosive activity thermodynamic modeling of heating and mixing of the andesitic magma with a basaltic liquid produces plagioclase of composition an79 not the observed composition of the late plagioclase an86 we conclude that the final plagioclase grew under non equilibrium conditions as a result of the mixing event

the nature of volcanic earthquake swarm preceding the 2000 flank eruption at usu volcano hokkaido japan summary the 2000 eruption of usu volcano hokkaido occurred on the northwestern flank of volcano on march 31 at 13 07 local time after about 4 days of intensive seismic activity we study the seismic process prior to the eruption using the routine earthquake catalogue of the japan meteorological agency jma and the digital seismograms of the short period station nbbt jma earthquakes began beneath the summit and southern slope of the volcano then seismic foci clustered along two linear zones intersecting to the south of the initial epicentral zone the majority of earthquakes occurred at depth within the range between 4 and 7 km the magnitude range of located earthquakes varied between 0 8 and 4 4 the earthquake epicentres did not reach the sites of the forthcoming eruption they stopped at a distance of about 1 3 km the eruption began during the ceasing of seismic activity a study of the nature of the swarm was performed for a sample of 303 earthquakes with a magnitude interval from 2 5 to 3 4 that were representative of the swarm visual analysis allowed separating the earthquakes into two groups 286 volcano tectonic vt earthquakes and 17 long period lp earthquakes the spectral analysis of s wave so f274 vt earthquakes in the frame of brune s model showed that the vt earthquakes may be separated into two groups as characterized by high stress drops hsd and low stress drops lsd the swarm began with hsd earthquakes the lsd and lp earthquakes were recorded about 30 40 hr later simultaneously with the beginning of deformation of volcanic edifice and accompanied the hsd earthquakes up to the beginning of eruption we attribute the hsd earthquakes to the probable product of magmatic thermal fracturing of host rocks the relatively long lsd ruptures may be attributed to the slips along the pre existing fractures during magma movement

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

high stress drop events in the victoria baja california earthquake swarm of 1978 march summary the victoria earthquake swarm of 1978 march with magnitudes up to ml 4 8 occurred near the northern end of the cerro prieto fault in northern baja california mexico accurate epicentre locations of a number of earthquakes in the swarm reveal that the activity concentrated in a zone of about 6 km radius projected on the horizontal with earthquakes occuring mostly at depths of around 12 km a composite fault plane solution prepared with data from the larger earthquakes of the swarm indicates right lateral strike slip motion along a vertical plane extending parallel to the cerro prieto fault seismic moment source radius and stress drop are calculated from strong motion records and digital seismograph records obtained at short epicentral distances in most cases less than 10 km from calculated displacement spectra and brune s model stress drops between 1 bar and 1 kbar were estimated for earthquakes with seismic moments in the range 1 4 1019 2 9 1023 dyne cm eighteen events of 44 studied here had stress drops higher than 90 bar a result in striking contrast to lower stress drop results from previous distant station studies of earthquakes in the region results of comparing near source and large distance spectral shapes for two earthquakes in the victoria swarm region indicate that scattering and attenuation are a likely cause of the severe reduction of high frequency energy clearly shown by the larger distance spectra and thus of the resulting lower stress drop determinations at large distances if these events are characteristic of other large events in the region then the low stress drop determinations of thatcher and thatcher hanks for this region may be in doubt very high peak horizontal ground accelerations up to 0 6 g were measured from the near source records which were characterized by short duration bursts of high frequency energy it is suggested here that these high peak accelerations resulted from a combined effect of high stress drop and sediment amplification using a crustal model derived from mcmechan mooney a sedimentary amplification factor of 3 4 is estimated and used as a correction in calculation of the earthquake source parameters four other high stress drop up to 2 5 kbar earthquakes in this area were also analysed the high stress drop values obtained from seismic spectra are corroborated by using the rms root mean square acceleration formulation introduced by hanks

liquid immiscibility and its role at the magmatic hydrothermal transition a summary of experimental studies several types of fluid immiscibility may affect the evolution of volatile rich magmatic systems at the magmatic hydrothermal transition the topology of silicate salt h2o systems implies that three fluid immiscibility silicate melt hydrosaline melt vapour should be stable in a broad range of compositions and p t conditions the most important factor controlling the immiscibility appears to be the coulombic properties electric charges z and ionic radii r of the main network modifying cations and the capacity for immiscibility appears to decrease in the following sequence mg ca sr ba li na k liquid immiscibility is enhanced in peralkaline compositions and in the presence of nonsilicate anions such as f cl co32 and bo33 in volatile rich magmatic systems the h2o is likely to react with the chloride fluoride borate and carbonate species and the chemical effects of high temperature hydrolysis may be greatly enhanced by phase separation in systems with multiple immiscible fluid phases natural granitic magmas can thus exsolve a range of chemically and physically diverse hydrosaline liquids and the role of these fluid phases is likely to be especially significant in pegmatites and li f rare metal granites

bimodal magmatism in the eastern dharwar craton southern india implications for neoarchean crustal evolution abstract archean cratons provide windows to the crustal evolution history in the early earth the dharwar craton is one of the major cratonic blocks in peninsular india and is composed of several ancient microcontinents where multiple continental growth and recycling occurred from 3 8 to 2 5 ga here we investigate a suite of magmatic rocks including granitoids mafic magmatic enclaves ultramafic inclusions and synplutonic mafic dyke from the western margin of the eastern dharwar craton which provide insights on bimodal magmatism in a subduction related arc setting and crustal growth during neoarchean field evidence and geochemical features suggest mixing and mingling of mafic and felsic magmas geochemical features including incompatible and high field strength element features of the enclaves indicate heterogeneous sources involving dominantly enriched mantle reservoirs with minor depleted mantle whereas the host granitoids display depleted to enriched source we present zircon u pb age data from the various rock types and the combined results display unimodal distribution with a single peak of 207pb 206pb age at 2531 ma n 159 suggesting a major neoarchean bimodal magmatic pulse the zircon u pb ages of the mafic enclaves indicate either similar ages or slightly younger ages as compared to their host granitoids implying that enclaves represent late stage injections into crystallizing host granitoid magmas the trace and rare earth element data on zircon from these rocks are consistent with magmatic crystallization zircons from most of the rocks in our study display uniformly positive ehf t 0 3 8 6 suggesting depleted mantle juvenile source for the neoarchean arc building and formation of new crust some of the mafic magmatic and ultramafic enclaves as well as the mafic dyke and charnockite display mixed positive and negative ehf t values 7 0 to 3 8 implying mixed depleted mantle and reworked crustal components of neoarchean to mesoarchean age most of the hf depleted mantle model ages tdm 2520 3115 ma and crustal residence ages tdmc 2507 ma to 3452 ma fall within the region bounding chur and depleted mantle lines suggesting that the dominant magma source involved juvenile depleted mantle components thus latest neoarchean marks a major phase of continent building in the eastern dharwar craton and the results presented in our study suggest that bimodal magmatism in a subduction related setting identical to those in modern convergent margins contributed to crustal growth

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

using the sr isotope compositions of feldspars and glass to distinguish magma system components and dynamics the individual components of magmatic rocks are being increasingly targeted to gain insight into volcanic systems here we demonstrate the use of sr isotope microsampling to distinguish distinct populations of glass and plagioclase that represent the sources of components liquids and crystals within each erupted magma batch we analyzed glasses and plagioclase feldspar crystal cores to characterize crystal cargoes and host liquids from pumice fall units from the minoan cycle santorini greece using this approach we identify the magmatic components that interacted prior to eruption and formation of pumice clasts allowing us to interpret the magma dynamics associated with each eruption varying degrees of complexity can be identified from relatively simple cases where the crystals are in isotopic equilibrium with the glass to more complex such as the large caldera forming minoan eruption which is characterized by at least two liquid components and three different crystal provenances

local magnitude and source parameters for earthquakes in the peninsular ranges of baja california mexico digital three component seismograms provided by the northwestern mexico seismic network were used to estimate local magnitudes and source parameters for 81 earthquakes located in the peninsular ranges of baja california the magnitude values were estimated from peak amplitudes as measured on equivalent wood anderson seismograms in combination with the attenuation law proposed by richter 1958 for the southern california region the source parameters were determined from spectral analysis based on the seismic source model proposed by brune 1970 1971 a comparison of our local magnitudes mlr with magnitudes reported by the california institute of technology and the u s geological survey shows residuals with a standard deviation of 0 21 concerning the source parameters stress drop determinations yielded values between 1 and 100 bars while the calculated seismic movements range from 2 4 1019 to 7 6 1021 dyne cm least square fits of the moment magnitude data give log m 1 11 0 02 mlr 17 32 0 05 for our data for small earthquakes 2 0 mlr 4 0 and log m 1 63 ml 14 87 for earthquakes in the same area having magnitudes between 4 0 ml 6 8 these two linear relationships intersect at a magnitude of about 4 6

the idea of magma mixing history of a struggle for acceptance abstract in 1851 chemist robert bunsen suggested that the mixing of two magmas one mafic and the other felsic in various proportions might account for the wide range of chemical compositions of igneous rocks based on flaws in several of its secondary provisions the whole hypothesis was rejected by a succession of influential critics and remained in disrepute for a hundred years meanwhile studies of composite dikes and sills indicated that indeed mafic and felsic magmas had coexisted at close quarters and had been emplaced in quick succession this interpretation was also used by some investigators to explain the intimate association of mafic and felsic rock types in the commonly occurring igneous complexes others believed that the mafic components of these complexes were derived from geologically older mafic formations by the early 1900s it had become apparent that mafic magmas crystallized at higher temperatures than felsic magmas this knowledge was not immediately applied to the problem of m

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

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

petrological architecture of a magmatic shear zone a multidisciplinary investigation of strain localisation during magma ascent at unzen volcano japan shearing of magma during ascent can promote strain localisation near the conduit margins anymechanical and thermal discontinuities associated with such events may alter the chemical physicaland rheological stability of the magma and thus its propensity to erupt lava spines can record suchprocesses preserving a range of macroscopic and microscopic deformation textures attributed toshearing and friction as magma ascends through the viscous brittle transition here we use a multi disciplinary approach combining petrology microstructures crystallography magnetics and experi mentation to assess the evidence role and extent of shearing across a marginal shear zone of the1994 1995 lava spine at unzen volcano japan our results show that crystals can effectively moni tor stress conditions during magma ascent with viscous remobilisation crystal plasticity and com minution all systematically increasing towards the spine margin accompanying this we find anincrease in mineral destabilisation in the form of pargasitic amphibole breakdown displaying tex tural variations across the shear zone from symplectitic to granular rims towards the spine margin in addition the compaction of pores chemical and textural alteration of interstitial glass and mag netic variations all change systematically with shear intensity the strong correlation between thedegree of shearing crystal deformation and disequilibrium features together with distinct magneticproperties implies a localised thermal input due to shear and frictional processes near the conduitmargin during magma ascent this was accompanied by late stage or post emplacement fluid andgas induced alteration of the gouge as well as oxidation and glass devitrification understandingand recognising evidence for strain localisation during magma ascent may therefore be vital whenassessing factors that regulate the style of volcanic eruptions which may provide insights into thecryptic shifts from effusive to explosive activity as observed at many active lava domes

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

contrasts between source parameters of m 5 5 earthquakes in northern baja california and southern california summary earthquake source processes are determined for four historic events that occurred in baja california between 1915 and 1954 these results are combined with previous studies of recent and historic seismicity to compare earthquake processes along the san jacinto imperial cerro prieto and northern baja fault systems of southern california and northern mexico observed regional differences in rupture complexity fault rupture lengths and aftershock foreshock activity appear to be related to variations in heat flow and total fault offset there appear to be no systematic variations in stress drop as measured from far field observations between earthquakes along the imperial cerro prieto fault zone and those within the peninsular ranges of northern baja california slip rates estimated from historical seismicity between 1915 and 1992 fall 1 5 cm yr 1 short of the estimated relative plate motion between the pacific plate and north america for this region

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

local magnitude and sediment amplification observations from earthquakes in the northern baja california southern california region abstract the data set that is analyzed in this study consists of strong motion and digital velocity records obtained during the last 6 yr for earthquakes along faults in baja california north and southern california from this set local magnitudes for 60 earthquakes recorded at stations on hard rock and sediments are calculated following the technique proposed by kanamori and jennings 1978 the calculated near source motion magnitudes m lsm are then compared with reported local magnitude values m l which are in the range from 3 to 6 6 from these comparisons it is found that for earthquakes with magnitude m l between 3 and 5 5 almost all the m lsm values estimated from data registered on sediments exceed the m l values by amounts which at the shorter distances less than about 10 km may be as high as an order of magnitude or even higher for a few cases the strong motion records associated with these high m lsm values have highly coherent pulse like s wave signals of very short period and large accelerations similar estimations of local magnitude from more limited data obtained on hard rock were comparable or lower than the standard m l values we conclude that the high m lsm values are the result of a combination of high frequency source spectra and a strong shear wave energy amplification due to the presence of sediments a sediment amplification factor of 3 2 is inferred from the data and is in good agreement with a theoretical factor of 3 4 estimated on the basis of the mcmechan and mooney 1980 velocity model for the imperial valley it is also found from the analyzed data that near source local magnitude decreases between 0 and 10 km indicating that for smaller earthquakes the attenuation function log a 0 richter 1958 used in local magnitude determinations needs to be modified to take into account the characteristics of the seismic energy radiated at short distances near source strong motion data for the 1979 imperial valley m l 6 6 and 1980 victoria m l 6 1 events do not show the strong discrepancy between m lsm and m l observed for the smaller magnitude events factors that might be responsible for this include nonlinear sediment attenuation for larger amplitude waves as well as complex near source spreading out of the waveform resulting from larger source size near source magnitude saturation we give a numerical example using small earthquakes as green9s functions to show that for a complex source function represented as a superposition of smaller earthquakes m lsm and m l for the 1980 victoria earthquake can be explained by the magnitude saturation phenomenon

basaltic pillow mounds in the vinalhaven intrusion maine the vinalhaven intrusion is a dominantly granitic pluton of probable devonian age located on vinalhaven island and adjacent islands maine it consists of four main units coarse grained granite fine grained granite a gabbro diorite unit consisting of interlayered mafic hybrid and granitic rocks and a heterogeneous granitic unit the gabbro diorite unit occurs along the south and east coast of the island as a sheet like body hundreds of meters to more than 1 km thick that dips beneath the central granitic units and rests on heterogeneous granitic rocks that form the base of the intrusion and are exposed on islands to the southeast load cast and pipe structures at the bases of mafic sheets indicate that the gabbro diorite unit represents a sequence of basaltic injections that ponded on crystal rich mush at the base of a silicic magma chamber and variably interacted with overlying crystal poor granitic magma the pluton therefore represents a fossilized silicic magma chamber that was periodically replenished by basaltic magma near the base of the gabbro diorite unit some basaltic injections produced large mounds up to more than 10 m high and 100 m wide of tightly packed meter scale chilled basaltic pillows tubes and sheets in a granitic matrix the mounds appear to represent flow fronts of basaltic injections that entered and ponded on the floor of a silicic magma chamber although physical conditions differ significantly these plutonic pillow mounds appear to share many characteristics with submarine pillow basalts and lava flows

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

on the dynamics of magma mixing by reintrusion implications for pluton assembly processes many plutons have formed by repeated intrusion with complex internal contacts characterized by sharp and diause kinematic and compositional domains we performed numerical experiments of mixing following magma chamber recharge that explicitly considers the fluid dynamics of multiphase mixtures in the limit of zero diausivity of intensive scalar quantities and low stokes number mingling by fluid instability is equivalent to deformation and persistent fluid structures are kinematic attractors three distinct regimes are exemplified and can be described by their multiphase reynolds or grashof number for a reynolds number greater than about 100 an internal intrusive contact will collapse by internal wave breaking and chaotic magma mingling and mixing yield a nearly chamber wide stratification this flow may scour mushy regions at the walls and widely distribute previously crystallized material for reynolds numbers from 10 to 100 the internal wave does not break and the stratification occupies less of the chamber leaving islands of unmixed material for reynolds numbers around 1 internal slumping and folding can occur and is the most likely to be preserved by a mineral fabric internal sub vertical contacts require a high absolute viscosity in the resident magma representing a time break between episodes of reintrusion the shape of perched mafic domains captures the progress of sinking from higher levels into regions of increasing strength and crystallinity 7 2000 elsevier science ltd all rights reserved