did magma ascent rate control the explosive effusive transition at the inyo volcanic chain california rhyolitic eruptions often begin explosively and then shift to extrusions of lava it is widely believed that the style of eruption is dependent on magma flow rate within the conduit fast ascent leading to explosive eruption and slow ascent favoring effusive behavior currently the velocity of rhyolite magma flowing in a conduit is unknown and therefore eruption models remain untested against geologic evidence of magma ascent we show that explosively erupted rhyolite magma from the inyo volcanic chain ascended slowly centimeters per second at same rates as the dome building phases we propose that the explosive effusive transition sub plinian rhyolite eruptions is governed by the alleviation of exsolved volatile pressure in the shallow conduit rather than the magma flow rate

von karman s constant in atmospheric boundary layer flow reevaluated abstract a field experiment has been carried out with the specific objective in mind to determine the value of von karman s constant in atmospheric boundary layer flow and also to investigate its possible dependence on the surface rossby number ro0 data from three field measurement campaigns at marsta sweden were used in the analysis depending on the ground cover deep snow 40 cm plowed field or 15 20 cm high wheat crop the surface roughness in the three campaigns was respectively 1 mm 7 5 mm and 24 mm the corresponding range in ro0 is roughly 2 5 106 6 5 107 in the experiment a turbulence instrument was used the miuu instrument that has been carefully examined for aerodynamic error effects and duly corrected measurements of turbulent fluxes made with this instrument at ca 2 and 6 m above the surface were used together with wind profile measurements data from the measurements with the turbulence instruments were also used to correct the cup anemometers for overspeeding found to be 5

criteria for interpreting kimberlite as coherent insights from the muskox and jericho kimberlites nunavut canada the jurassic muskox and jericho kimberlites northern slave province nunavut canada contain a variety of facies exhibiting different geometries contact relationships internal organisation country rock abundance and olivine shapes although many have similar matrix groundmass mineralogies and textures five facies are examined that either have characteristics consistent with coherent rocks in general i e intrusive and extrusive non fragmental rocks or are mineralogically and texturally similar to kimberlite described as coherent or apparent coherent three facies are interpreted as coherent on the basis of 1 geological setting 2 apparent porphyritic texture 3 sharp contacts with fragmental kimberlite 4 relative abundance of elongate and unbroken olivine crystals and 5 paucity of country rock xenoliths while the remaining two facies are interpreted as fragmental on the basis of 1 the gradational contacts with demonstrably fragmental kimberlite 2 relative abundance and range of sizes of country rock lithic clasts and 3 numerous broken olivine crystals comparisons are made with coherent and apparent coherent kimberlite from the literature our three coherent facies are similar to literature reported coherent kimberlite dykes hosted in country rock ckd in terms of internal organisation low abundance of country rock xenoliths and apparent porphyritic texture conversely our two fragmental facies share attributes with previously described pipe filling coherent and apparent coherent kimberlite ckpf in terms of geometry internal organisation and abundance of country rock xenoliths we conclude that ckd and most ckpf although similar in matrix groundmass mineralogy and texture can be distinguished on the basis of internal organisation country rock lithic clast abundance texture e g apparent porphyritic texture and possibly olivine crystal shapes and suggest that fragmental kimberlite is more common than reported

particle dynamics and aggregation of crystals in a magma chamber with application to kilauea iki olivines abstract crystals settling in relative proximity to each other will settle faster than their respective stokes velocities u s due to their mutual interactions pairs of equant spheres within 100 diameters of each other are accelerated to 1 55 u s modification of han and lawler s han m lawler d f 1991 interactions of two settling spheres settling rates and collision efficiency journal of hydraulic engineering 117 10 1269 1289 equations to include inertia shows that the velocities of a pair of spheres differ and change during descent allowing them to come into contact in quiescent settling experiments with olivine shaped clay prisms the pairs of prisms usually settled faster than their u s the clay prisms aggregated 80 of the time with the pairs of prisms rotating and tumbling as they fall coming into and out of contact size variations in kilauea iki olivines control aggregation during quiescent settling the settling velocities of individual crystals are variable increasing when they are incorporated into aggregates a suspension of olivine crystals more than 0 01 vol in a magma will settle slower than the average stokes velocities except when a buoyant phase is present addition of a buoyant phase such as co 2 bubbles can increase the settling velocity of the olivines when the total concentration olivine plus bubbles e is e 35

size frequency distributions of chondrules and chondrule fragments in ll3 chondrites implications for parent body fragmentation of chondrules we measured the sizes and textural types of 719 intact chondrules and 1322 chondrule fragments in thin sections of semarkona ll3 0 bishunpur ll3 1 krymka ll3 1 piancaldoli ll3 4 and lewis cliff 88175 ll3 8 the mean apparent diameter of chondrules in these ll3 chondrites is 0 80 units or 570 um much smaller than the previous rough estimate of 900 m chondrule fragments in the five ll3 chondrites have a mean apparent cross section of 1 60 phi units or 330 m the smallest fragments are isolated olivine and pyroxene grains these are probably phenocrysts liberated from disrupted porphyritic chondrules all five ll3 chondrites have fragment chondrule number ratios exceeding unity suggesting that substantial numbers of the chondrules in these rocks were shattered most fragmentation probably occurred on the parent asteroid porphyritic chondrules porphyritic olivine porphyritic pyroxene porphyritic olivine pyroxene are more readily broken than droplet chondrules barred olivine radial pyroxene cryptocrystalline the porphyritic fragment chondrule number ratio 2 0 appreciably exceeds that of droplet textured objects 0 9 intact droplet chondrules have a larger mean size than intact porphyritic chondrules implying that large porphyritic chondrules are fragmented preferentially this is consistent with the relatively low percentage of porphyritic chondrules within the set of the largest chondrules 57 compared to that within the set of the smallest chondrules 81 differences in mean size among chondrule textural types may be due mainly to parent body chondrule fragmentation events and not to chondrule formation processes in the solar nebula

a comparison of shear and buoyancy driven planetary boundary layer flows abstract planetary boundary layer pbl flows are known to exhibit fundamental differences depending on the relative combination of wind shear and buoyancy forces these differences are not unexpected in that shear instabilities occur locally while buoyancy force sets up vigorous thermals which result in nonlocal transport of heat and momentum at the same time these two forces can act together to modify the flow field in this study four large eddy simulations less spanning the shear and buoyancy flow regimes were generated two correspond to the extreme cases of shear and buoyancy driven pbls while the other two represent intermediate pbls where both forces are important the extreme cases are used to highlight and quantify the basic differences between shear and convective pbls in 1 flow structures 2 overall statistics and 3 turbulent kinetic energy tke budget distributions results from the two intermediate les cases are used to develop and verify a velocity scaling and a tke budget mode

experimental study of zircon coarsening in quartzite h2o at 1 0 gpa and 1000 c with implications for geochronological studies of high grade metamorphism the rate and mechanism of zircon coarsening in quartzite h 2 o at 1 0 gpa and 1000 c were characterized by performing time series experiments in a piston cylinder apparatus anhydrous experiments show no significant growth of zircon or textural modifications after 24 h in the presence of 1 2 wt h 2 o zircon 2 wt in coarsely powdered quartz recrystallized in the first 8 hours so that mean crystal size decreased relative to the starting material after 8 h zircon grew by ostwald ripening and by coalescence of crystals and maintained its position on quartz grain boundaries even while quartz crystals coarsened by recrystallizing in the fluid fitting the experimental data produced the growth rate equation log n log 2 2 log t to log k n log t to 5 9 where is mean diameter in micrometers the subscript 0 denotes initial value at time zero t is experiment duration in seconds and k n is the growth rate constant with units of m 2 s five experiments r 2 0 988 a value of n 2 suggests that growth is interface controlled with the rate limited by dissolution and precipitation on the crystal surface an equivalent growth rate equation is k 1 n t k 1 n n t 1 n 1 12 x 10 3 m s 1 2 t 1 2 a parabolic rate law equation that can be used to demonstrate that zircon in the presence of h 2 o at 1000 c grows fast enough by ostwald ripening to produce micrometer thick overgrowths in 10 y rapid coarsening of zircon by ostwald ripening will occur during thermal metamorphism when fluid is present addition of fluid and possibly melt greatly increases the rate of coarsening suggesting that most metamorphic rims form nearly instantaneously during fluid influx or anatexis and that u pb rim ages date such events

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

3d crystal size distributions a case study on quantifying olivine populations in kimberlites abstract new advances in textural analysis and imaging allow the possibility for the true distribution of mineral phases in a rock to be quantified to high resolution also we are able to explore the relations between 2d to 3d datasets more rigorously in this study the application of 2d and 3d textural analysis to the quantification of olivine populations in kimberlites is investigated crystal size distribution studies csd are carried out on two kimberlite samples 1 one from the venetia k2 kimberlite pipe south africa and 2 one from the dutoitspan kimberlite pipe kimberley south africa a 3d x ray ct study is undertaken to investigate the application of this developing technique in kimberlite research and to test the 2d and 3d data sets csd profiles show markedly curved upwards profiles synonymous with fragmented csds supporting an initial crystal population which is modified by fragmentation of crystals on ascent raw plots of 2d area size frequency provide a powerful first estimate of the population 3d statistics in terms of volume size frequency allowing a quick analysis of olivine phases during exploration which can be quality controlled using more detailed 3d studies where necessary the 3d data set provides accurate analysis over a range of 6 0 5 mm below which the separation of grains becomes very difficult additionally the 3d data provides valuable information on crystal shape which can further be used to distinguish different olivine populations both 2d and 3d textural studies using state of the art textural analysis techniques have been successfully tested on complex kimberite textures and will prove useful techniques in the routine quantification of key indicator phases in kimberlite analysis

voluminous lava like precursor to a major ash flow tuff low column pyroclastic eruption of the pagosa peak dacite san juan volcanic field colorado abstract the pagosa peak dacite is an unusual pyroclastic deposit that immediately predated eruption of the enormous fish canyon tuff 5000 km3 from the la garita caldera at 28 ma the pagosa peak dacite is thick to 1 km voluminous 200 km3 and has a high aspect ratio 1 50 similar to those of silicic lava flows it contains a high proportion 40 60 of juvenile clasts to 3 4 m emplaced as viscous magma that was less vesiculated than typical pumice accidental lithic fragments are absent above the basal 5 10 of the unit thick densely welded proximal deposits flowed rheomorphically due to gravitational spreading despite the very high viscosity of the crystal rich magma resulting in a macroscopic appearance similar to flow layered silicic lava although it is a separate depositional unit the pagosa peak dacite is indistinguishable from the overlying fish canyon tuff in bulk rock chemistry phenocryst compositions and 40ar 39ar age the unusual characteristics of this deposit are interpreted as consequences of eruption by low column pyroclastic fountaining and lateral transport as dense poorly inflated pyroclastic flows the inferred eruptive style may be in part related to synchronous disruption of the southern margin of the fish canyon magma chamber by block faulting the pagosa peak eruptive sources are apparently buried in the southern la garita caldera where northerly extensions of observed syneruptive faults served as fissure vents cumulative vent cross sections were large leading to relatively low emission velocities for a given discharge rate many successive pyroclastic flows accumulated sufficiently rapidly to weld densely as a cooling unit up to 1000 m thick and to retain heat adequately to permit rheomorphic flow explosive potential of the magma may have been reduced by degassing during ascent through fissure conduits leading to fracture dominated magma fragmentation at low vesicularity subsequent collapse of the 75 35 km 2 la garita caldera and eruption of the fish canyon tuff were probably triggered by destabilization of the chamber roof as magma was withdrawn during the pagosa peak eruption

primary and secondary fragmentation of crystal bearing intermediate magma abstract crystal rich intermediate magmas are subjected to both primary and secondary fragmentation processes each of which may produce texturally distinct tephra of particular interest for volcanic hazards is the extent to which each process contributes ash to volcanic plumes one way to address this question is by fragmenting pyroclasts under controlled conditions we fragmented pumice samples from soufriere hills volcano shv montserrat by three methods rapid decompression in a shock tube like apparatus impact by a falling piston and milling in a ball mill grain size distributions of the products reveal that all three mechanisms produce fractal breakage patterns and that the fractal dimension increases from a minimum of 2 1 for decompression fragmentation primary fragmentation to a maximum of 2 7 by repeated impact secondary fragmentation to assess the details of the fragmentation process we quantified the shape texture and components of constituent ash particles ash shape analysis shows that the axial ratio increases during milling and that particle convexity increases with repeated impacts we also quantify the extent to which the matrix is separated from the crystals which shows that secondary processes efficiently remove adhering matrix from crystals particularly during milling abrasion furthermore measurements of crystal size distributions before using x ray computed tomography and after by componentry of individual grain size classes decompression driven fragmentation show not only that crystals influence particular size fractions across the total grain size distribution but also that free crystals are smaller in the fragmented material than in the original pumice clast taken together our results confirm previous work showing both the control of initial texture on the primary fragmentation process and the contributions of secondary processes to ash formation critically however our extension of previous analyses to characterisation of shape texture and componentry provides new analytical tools that can be used to assess contributions of secondary processes to ash deposits of uncertain or mixed origin we illustrate this application with examples from shv deposits

microstructures and rheology of hydrous synthetic magmatic suspensions deformed in torsion at high pressure the relationship between magma rheology and characteristic magmatic microstructures was investigated by performing high temperature high pressure deformation experiments on hydrous synthetic magmatic suspensions in the range of 0 to 76 solid fraction alumina grains torsion experiments were conducted at 300 mpa confining pressure temperatures ranging from 475 c to 1000 c and shear strain rates ranging from 2 0 10 5 to 2 1 10 3 s 1 up to total strains of 21 3 flow is newtonian for a solid fraction of s 0 0 0 16 with a log dynamic viscosity 10 3 pa s t 500 c a deviation from newtonian behavior is observed for s 0 16 with an increase in apparent viscosity of about 1 order of magnitude between s 0 16 and 0 54 the shape fabric of the solid phase is characterized by a unimodal orientation that is almost stable and nearly parallel to the shear direction both shape fabric and deviation from newtonian behavior originate from the increase in the number of particle clusters in the suspension the apparent viscosity increases by 1 5 orders of magnitude between s 0 54 and 0 65 and extrapolation of the data suggests a very sharp increase in apparent viscosity for s 0 65 at t 550 c and s 0 54 the solid phase forms an almost entirely connected network composed of two alternating orientation domains at t 550 c and s 0 65 intragranular fracturing and tensile fractures result from high local stresses at contact points between neighboring particles the resulting bulk extensional fabric is almost parallel to the shortening direction

convective boundary layer structure in the presence of wind following swell the marine boundary layer is known to be influenced by fast long ocean swell waves travelling away from their generation area where they were initiated by momentum transferred to the ocean wave field during storms the atmospheric boundary layer during wind following swell and various stability states has been investigated using large eddy simulation les data the dominant energy containing motions in the near neutral atmospheric boundary layer over flat terrain are known to be dominated by near ground shear induced regions of high and low speed flow wind fields and momentum fluxes from les for swell dominated situations have been used to interpret field measurements suggesting that these motions are disrupted by effects related to the underlying wave field in the presence of swell waves statistical analysis and visualization are used to further describe the effects of stratification during swell for convective boundary layer winds and fluxes a mechanism for transport of momentum to the upper levels of the boundary layer is suggested from interpretation of les data coherent detached eddies from the directly wave induced motions near the surface are found to maintain an upward momentum transfer this mechanism is found to strengthen during stronger swell conditions and also during slightly convective conditions in this way it is argued that processes related to both the wave field and surface convection can have a significant influence on the global structure of neutral and convective boundary layers during swell this has implication for the turbulence length scales during wind following swell copyright 2012 royal meteorological society

evolution of crystal sizes in the series of dissolution and precipitation events in open magma systems article i nfo we propose a model that describes the evolution of crystal sizes and crystal size distributions csd of igneous phenocrysts in a sequence of dissolution and crystallization events this model is based on the assumption that crystal dissolution is rate limited by diffusion in melt while crystal growth is controlled by the slower kinetic of new nucleation and growth as a result the dissolution rate is inversely proportional to crystal size coming into effect through the curvature of the crystal s surface but the growth rate does not depend on the crystal size closed form analytical solution of equation for csd is obtained we apply results of modeling to quartz and zircon two prime minerals in silicic igneous systems that are widely used in geochemical and isotopic investigations the time series of multiple solution reprecipitation episodes generate concave downward csds and this result fits well with experimental and natural observations on the abundant concave down csd in silicic igneous rocks we suggest that maturation of crystal populations with sizes above several micrometers can not be caused by a size effect on the solubility of the crystals ostwald ripening but is rather driven by thermal oscillations in experiments and in nature the model predicts that mean crystal size increases with time proportionally to t 0 20 which is very close to the published experimental results for quartz maturation with the exponent of 0 19 0 22 our proposed model gives an opportunity to use natural csds for interpretation of pre eruptive magma history when solubilities and diffusion data are available for constituent elements of the dissolving mineral in particular we present time estimates for maturing zircon populations in large volume ignimbrites and estimate that it takes 100 1000 yrs to mature an initially exponential csd to a lognormal csd

fragmentation phenomena in populations of magmatic crystals fragmentation of crystals is an important mechanism and a component of particle dynamics in igneous and metamorphic rocks that has received surprisingly little attention recent advances in textural analysis extraction techniques digital imaging and computer assisted measurements enable rapid accumulation of 3d data on particle shapes and size distributions this paper reviews fragment size distributions fsd that result from fragmentation lognormal fractal loggamma and weibull discusses their genesis mechanisms and presents relevant examples of fragmentation from experimental physics next the paper considers fsds of feldspars on digitized images of thin sections and on published images and quartz extracted from vesicular pumice by acid from eight well known large volume eruptive units the acid solution of pumice enables examination of volume abundance 3d shapes proportions of fragmented crystals and measurements of their csds and fsds fsds were also measured in samples of welded tuff and a granite disaggregated by electric pulse products of syneruptive shock wave fragmentation and fragmentation by an electric pulse are found to be fractal with large breakage probabilities branching ratios and fractal dimensions of 2 to 3 in contrast most quartz fragments in pumice obey a lognormal distribution and fragmentation is driven by a melt inclusion decrepitation mechanism which results in low breakage probability and small number 2 3 of fragments per breakage cycle these results are consistent with one atmosphere heating experiments of quartz phenocrysts that led to melt inclusion decrepitation and caused quartz to break up into several smaller pieces collectively having lognormal fsd measured melt inclusion size distributions suggest decrepitation of outermost melt inclusions and low survival rate for large inclusions and inclusions with large radius crystal size ratio the modeling of periodic fragmentation of crystals with melt inclusions due to overheating and or decompression which may occur many times during the lifetime of a long lived magma body may explain concave down lognormal csds abundant in igneous rocks the genesis of lognormality can be explained by the fragmentation algorithm of kolmogorov 1941 other algorithms may generate lognormal like loggamma distributions fragmentation serves as an important size limiting factor a nucleation aid and it facilitates isotopic and trace elemental exchange

shallow water bathymetry derived from an analysis of x band marine radar images of waves image sequences of surface gravity waves are readily produced by standard marine x band radars these image sequences contain a great deal of information regarding wave parameters and their variation over an area by approaching the analysis of such data using image analysis techniques it is possible to map the variations in wave behaviour in a shallow water area wave celerity and direction can be mapped and inversion algorithms based on linear wave theory used to infer the underlying bathymetry knowledge of the period of the waves is necessary for the analysis and this can also be calculated from the radar data although there is some discrepancy between the figures derived from radar data and from an offshore s4dw instrument these discrepancies are investigated and the results presented three days of data from the holderness ii deployment during 1995 have been analysed and estimates of the bathymetry produced the calculated depths show a mean water level comparable to that read off an admiralty chart for the area and a tidal signal is also clearly superimposed on the data giving confidence in the water depths derived using this technique

wave driven wind jets in the marine atmospheric boundary layer abstract the interaction between ocean surface waves and the overlying wind leads to a transfer of momentum across the air sea interface atmospheric and oceanic models typically allow for momentum transfer to be directed only downward from the atmosphere to the ocean recent observations have suggested that momentum can also be transferred upward when long wavelength waves characteristic of remotely generated swell propagate faster than the wind speed the effect of upward momentum transfer on the marine atmospheric boundary layer is investigated here using idealized models that solve the momentum budget above the ocean surface a variant of the classical ekman model that accounts for the wave induced stress demonstrates that although the momentum flux due to the waves penetrates only a small fraction of the depth of the boundary layer the wind profile is profoundly changed through its whole depth when the upward momentum transfer from surface waves sufficiently exceeds the downward turbulent momen

constraints on cooling rates and permeabilities of pumice in an explosive eruption jet from colour and magnetic mineralogy abstract in explosive volcanic eruptions vesicular magma droplets produced by fragmentation are propelled into the atmosphere where they are chilled to form pumices the thermal history of droplets and the permeability of their internal bubble networks determine how much they are deformed in the eruption jet and hence what information pumices record about the state of the magma at fragmentation we study these aspects of the minoan plinian eruption of santorini volcano by quantifying the rate of oxidation reactions that took place when air entered the hot magma fragments in our experiments white minoan pumices were heated for minutes to hours between 600 and 850 c either in air or in an atmosphere with an oxygen fugacity at the ni nio buffer pumices were unchanged by heating at ni nio those heated in air often became pink to dark pink depending on heating time and their curie temperatures as determined by magnetic susceptibility measurements increased we use oxidation rates deduced from these experiments in conjunction with calculations of the rate of conductive cooling and of the rate at which air can enter a pumice to constrain the conditions experienced by pumices during the eruption natural minoan pumices less than about 5 cm in radius are white whereas larger ones often have white rims and pink interiors with curie temperatures higher than those of white material we infer that small pumices were cooled before being oxidized and that oxidation of the interiors of large clasts mostly took place during flight at temperatures within a few tens of degrees of magmatic values white rims of large pumices despite being permeable were cooled before oxidation could occur permeability developed in the liquid state but did not develop early enough with respect to cooling or was not large enough to allow extreme oxidation we give measurements of pumice permeabilities that should be close to magmatic values

crystallization stages of the bishop tuff magma body recorded in crystal textures in pumice clasts the bishop tuff is a giant silicic ignimbrite erupted at 0 76 ma in eastern california usa five pumice clasts from the late erupted bishop tuff aeolian buttes were studied in an effort to better understand the pre and syn eruptive history of the bishop magma body and place constraints on the timescales of its existence this study complements and expands on a previous study that focused on early erupted bishop tuff pumice clasts bulk densities of pumice clasts were measured using an immersion method and phenocryst crystal contents were determined using a sieving and winnowing procedure x ray tomography was used to obtain qualitative and quantitative textural information particularly crystal size distributions csds we have determined csds for crystals ranging in size from approx 10 to approx 1000 micro m for three groups of mineral phases magnetite ilmenite pyroxene biotite quartz feldspar similar to early erupted pumice late erupted pumice bulk density and crystal contents are positively correlated and comparison of crystal fraction vs size trends suggests that the proportion of large crystals is the primary control on crystallinity porosity is negatively correlated with crystal content which is difficult to reconcile with closed system crystallization magnetite and pyroxene biotite size distributions are fractal in nature often attributedmore to fragmentation however crystals are mostly whole and euhedral such that an alternative mechanism is necessary to explain these distributions quartz feldspar size distributions are kinked with a shallow sloped log linear section describing large crystals 140 micro m and a steep sloped log linear section describing small crystals 140 micro m we interpret these two crystal populations as resulting from a shift in crystallization regime we suggest that the shallow sloped section describes a pre eruptive quartz feldspar growth dominated regime whereas the steep sloped section represents a population that grew during a nucleation dominated regime that began as a result of decompression at the onset of eruption timescales of quartz growth calculated from the slopes of these two segments of the size distributions indicate that the pre eruptive crystal population grew on timescales on the order of millennia and may describe the timescale of crystallization of the bishop magma body the syn eruptive population gives timescales of 1 2 years but possibly much less and probably marks the onset of eruptive decompression less

a practical petrological method for the determination of volume proportions of magma chamber refilling abstract a method is described for determining the proportion of the volume of a magma chamber refilled by new pulses of hot primitive melts this method is based on the changes is crystal contents and in phenocryst zoning resulting from temperature equilibration study of phenocryst zoning and the composition of interstitial glasses from various chilled magmatic inclusions and mafic bands in hybrid rocks supports the idea that equilibration of temperatures between two magmas is reached before their physical mixing if the magmas are genetically related for example magma fractionate and initial hot melt this leads to equilibration of the compositions of residual melts and phenocrysts rims intervals of reverse zoning in minerals resulting from temperature increases and intervals of normal zoning caused by cooling along with the changes in modal mineral contents enable estimation of the amounts of released and adsorbed heat and therefore assessment of the proportion of the volume of each magma application of the method to some hybrid volcanic series of the kurile kamchatka island arc shows that the proportion of mafic magma intruded into a siliceous magma chamber reservoir never exceeds 10 of the volume of the host magma based upon thermal considerations however the observed degree of compositional mingling requres 25 50 of the mafic end member it is shown that this contradiction is related to flotation of vesiculated magmatic inclusions towards the chamber roof where they become concentrated near the exit and are further mingled with the host during the eruption forced convection

an experimental study of ostwald ripening of olivine and plagioclase in silicate melts implications for the growth and size of crystals in magmas we carried out an experimental study to characterize the kinetics of ostwald ripening in the forsterite basalt system and in the plagioclase an65 andesite system eight experiments were done in each system to monitor the evolution of mean grain size and crystal size distribution csd with time t the experiments were performed in a 1 atmosphere quench furnace at 1 250 c for plagioclase and 1 300 c for olivine very contrasted coarsening kinetics were observed in the two series in the plagioclase series the mean grain size increased as log t from 3 m to only 8 7 m in 336 h the kinetic law in log t means that ostwald ripening was rate limited by surface nucleation at plagioclase liquid interfaces in the olivine series the mean grain size increased as t1 3 from 3 m to 23 2 m in 496 h a kinetic law in t1 3 is expected when ostwald ripening is rate limited either by diffusion in the liquid or by grain growth dissolution controlled by a screw dislocation mechanism the shape of olivine csds in particular their positive skewness indicates that grain coarsening in the olivine experiments was controlled by a screw dislocation mechanism not by diffusion as the degrees of undercooling t or supersaturation involved in ostwald ripening are essentially 1 c the mechanisms of crystal growth identified in our experiments are expected to be those prevailing during the slow crystallisation of large magma chambers we extrapolated our experimental data to geological time scales to estimate the effect of ostwald ripening on the size of crystals in magmas in the case of plagioclase ostwald ripening is only efficient for mean grain sizes of a few microns to 20 m even for a time scale of 105 years it can however result in a significant decrease of the number of small crystals per unit volume and contribute to the development of convex upwards csds for olivine the mean grain size increases from 2 3 m to 70 m in 1 year and 700 m in 103 years a mean grain size of 3 mm is reached in 105 years accordingly the rate of grain size dependent processes such as compaction of olivine rich cumulates or melt extraction from partially molten peridotites may significantly be enhanced by textural coarsening

synthetic fluid inclusions vi quantitative evaluation of the decrepitation behaviour of fluid inclusions in quartz at one atmosphere confining pressure the decrepitation behaviour of fluid inclusions in quartz at one atmosphere confining pressure has been evaluated using pure h2o synthetic inclusions formed by healing fractures in natural quartz three different modes of non elastic deformation referred to as stretching leakage or partial decrepitation and total decrepitation have been observed the internal pressure required to initiate non elastic deformation is inversely related to inclusion size according to the equation internal pressure kbar 4 26 d 0 423 where d is the inclusion diameter in microns regularly shaped inclusions require a higher internal pressure to initiate non elastic deformation than do irregularly shaped inclusions of similar size heating inclusions through the quartz inversion results in mechanical instability in the quartz crystal and leads to mass decrepitation of inclusions owing to structural mismatches generated by pressure gradients in the quartz around each inclusion long term heating experiments 2 years suggest that the internal pressure required to initiate non elastic deformation does not decrease significantly with time and indicates that short lived thermal fluctuations in natural systems should not alter the inclusion density and homogenization temperature inclusions that do exhibit decreased density higher homogenization temperature are however always accompanied by a change in shape from irregular to that of a negative crystal observations of this study are consistent with elasticity theory related to fracture generation and propagation around inclusions in minerals these results indicate that an inclusion will not be influenced by a neighbouring inclusion or other defect in the host phase as long as the distance between the two is 2 4 diameters of the larger of the two inclusions

crystal sizes in evolving silicic magma chambers crystal size distributions csds of quartz and zircon phenocrysts in individual pumice clasts from several voluminous ash flow tuffs provide a quenched snapshot view of conditions in preclimactic magma chambers a common feature of these csds is a concave down lognormal shape in contrast to the reported linear csds in more mafic systems this feature is interpreted to be a general result of surface controlled size dependent growth by a layer nucleation in silicic magmas at low supersaturation specific csds may be important for interpreting nucleation and crystal growth conditions and mechanisms in magmas erupted as large ash flow tuffs and smaller volume volcanic units and for fingerprinting different magma batches layers in products of the same eruption

energetics of glass fragmentation experiments on synthetic and natural glasses 1 natural silicate glasses are an essential component of many volcanic rock types including coherent and pyroclastic rocks they span a wide range of compositions occur in diverse environments and form under a variety of pressure temperature conditions in subsurface volcanic environments e g conduits and feeders melts intersect the thermodynamically defined glass transition temperature to form glasses at elevated confining pressures and under differential stresses we present a series of room temperature experiments designed to explore the fundamental mechanical and fragmentation behavior of natural obsidian and synthetic glasses pyrex under confining pressures of 0 1 100 mpa in each experiment glass cores are driven to brittle failure under compressive triaxial stress analysis of the load displacement response curves is used to quantify the storage of energy in samples prior to failure the brittle release of elastic energy at failure and the residual energy stored in the post failure material we then establish a relationship between the energy density within the sample at failure and the grain size distributions d values of the experimental products the relationship between d values and energy density for compressive fragmentation is significantly different from relationships established by previous workers for decompressive fragmentation compressive fragmentation is found to have lower fragmentation efficiency than fragmentation through decompression i e a smaller change in d value with increasing energy density we further show that the stress storage capacity of natural glasses can be enhanced approaching synthetic glasses through heat treatment

phenocryst fragments in rhyolitic lavas and lava domes although rhyolitic lavas and lava domes are characterised by evenly porphyritic textures not all the phenocrysts are whole euhedra we undertook image analysis of 46 rhyolitic lava and lava dome samples to determine the abundance and shape of quartz and feldspar phenocryst fragments phenocryst fragments were identified in nearly all samples on average fragments amount to approximately 5 of the total phenocryst population or approximately 0 5 modal the abundance of fragments in lavas and lava domes is not related to the groundmass texture whether vesicular flow banded massive glassy or crystalline nor to distance from source fragments are however more abundant in samples with higher phenocryst contents the phenocryst fragments in rhyolitic lavas and lava domes are mainly medium to large 0 5 3 5 mm almost euhedral crystals with only a small portion removed or chunky equant subhedral fragments and occur in near jigsaw fit or clast rotated pairs or groups the fragments probably formed in response to decompression of large melt inclusions shear during laminar flow then dismembered the phenocrysts continued laminar shear separated and rotated the fragments fractures probably formed preferentially along weaknesses in the phenocrysts such as zones of melt inclusions cleavage planes and twin composition planes rare splintery fragments are also present especially within devitrified domains splinters are attributed to comminution of solid lava adjacent to fractures that were later healed for comparison we measured crystal abundance in a further 12 rhyolite samples that include block and ash flow deposits and ignimbrite phenocryst fragments within clasts in the block and ash flow samples showed similar shapes and abundances to those fragments within the lava and lava domes crystal fragments are much more abundant in ignimbrite exceeding 67 of the crystal population however and dominated by small equant anhedral chunks or splinters the larger crystals in the ignimbrite are subrounded the phenocrysts within ignimbrite pumice lapilli are also more intensely fractured than those in lavas and lava domes thus in deformed and altered volcanic successions data on crystal fragment abundance and shape can help discriminate lavas from pyroclastic facies

a case study of air sea interaction during swell conditions air sea interaction data from a situation with pronounced unidirectional swell have been analyzed measurements of turbulence at three levels 10 18 and 26 m above mean sea level together with directional wave buoy data from the site ostergarnsholm in the baltic sea were used the situation which lasted for 48 hours appeared in the aftermath of a gale the wind direction during the swell situation turned slowly within a 90 sector both during the gale phase and the swell phase the over water fetch was 150 km the wind speed during the swell phase was typically 4 m s 1 during the swell phase a wind maximum near or below the lowest wind speed measuring level 10 m was observed the net momentum flux was very small resulting in cd values 0 7 10 3 throughout the lowest 26 m covered by the tower measurements turbulence intensities in all three components remained high despite the low value of the kinematic momentum flux u w resulting in a reduction of the correlation coefficient for the longitudinal and vertical velocity from its typical value around 0 35 to between 0 2 and 0 and with some positive values at the higher measuring levels appearing abruptly at wave age c0 u10 equal to 1 2 turbulence spectra of the horizontal components were shown not to scale with height above the water surface in contrast to vertical velocity spectra for which such a variation was observed in the low frequency range in addition spectral peaks in the horizontal wind spectra were found at a frequency as low as 10 3 hz from a comparison with results from a previous study it was concluded that this turbulence is of the inactive kind being brought down from the upper parts of the boundary layer by pressure transport

numerical and laboratory study of a horizontally evolving convective boundary layer part i transition regimes and development of the mixed layer results are presented from a large eddy simulation les and wind tunnel study of the turbulence regime in a horizontally evolving sheared atmospheric convective boundary layer cbl capped by a temperature inversion the wind tunnel part of the study has been conducted in the thermally stratified tunnel of the university of karlsruhe for the numerical part a modified les procedure that was originally designed for simulation of the horizontally homogeneous atmospheric cbl has been employed the study focuses on the transition between the neutrally buoyant boundary layer in the initial portion of the wind tunnel flow and a quasi homogeneous convectively mixed layer developing downwind the character of the transition between the two boundary layers and the associated changes in the turbulence structure are found to be strongly dependent on the magnitude and distribution of disturbances in the flow at the entrance of the wind tunnel test section for all simulated inflow conditions the transition is preceded by accumulation of potential energy in the premixed cbl the eventual energy release in the transition zone leads to turbulence enhancement that has a form of turbulence outbreak for particular flow configurations the numerically simulated cbl case with temperature fluctuations introduced in the lower portion of the incoming flow appears to be the closest to the basic cbl flow case studied in the wind tunnel second order turbulence statistics derived from the les are shown to be in good agreement with the wind tunnel measurements main features of transition including the turbulence enhancement within the transition zone are successfully reproduced by the les

explosive energy during volcanic eruptions from fractal analysis of pyroclasts abstract despite recent advances by means of experiments and high resolution surveys and the growing understanding of the physical processes before and during volcanic eruptions duration and type of eruptive activity still remain highly unpredictable this uncertainty hinders appropriate hazard and associated risk assessment tremendously in an effort to counter this problem experimentally generated pyroclasts have been studied by fractal statistics with the aim of evaluating possible relationships between eruption energy and fragmentation efficiency rapid decompression experiments have been performed on three differently porous sample sets of the 1990 1995 eruption of unzen volcano japan at 850 c and at initial pressure values above the respective fragmentation threshold u kueppers b scheu o spieler d b dingwell fragmentation efficiency of explosive volcanic eruptions a study of experimentally generated pyroclasts j volcanol geotherm res 153 2006 125 135 o spieler b kennedy u kueppers d b dingwell b scheu j taddeucci the fragmentation threshold of pyroclastic rocks epsl 226 2004 139 148 the size distribution of generated pyroclasts has been studied by fractal fragmentation theory and the fractal dimension of fragmentation df a value quantifying the intensity of fragmentation has been measured for each sample results show that size distribution of pyroclastic fragments follows a fractal law i e power law in the investigated range of fragment sizes indicating that fragmentation of experimental samples reflects a scale invariant mechanism in addition df is correlated positively with the potential energy for fragmentation pef while showing a strong influence of the open porosity of the samples results obtained in this work indicate that fractal fragmentation theory may allow for quantifying fragmentation processes during explosive volcanic eruptions by calculating the fractal dimension of the size distribution of pyroclasts it emerges from this study that fractal dimension may be utilised as a proxy for estimating the explosivity of volcanic eruptions by analysing their natural pyroclastic deposits

combining quantitative textural and geochemical studies to understand the solidification processes of a granite porphyry shanggusi east qinling china igneous rock textures reflect the cooling history of the parental magma combined with chemical data they can provide physical and chemical information about the evolution of a magma body the petrographic textures and chemical compositions of 21 coarse and fine grained granite samples along an 250 m horizontal outcrop of the shanggusi granite porphyry are presented in this case study the coarse grained granite porphyry is an early intrusion and the fine grained granite dykes mostly intruded into the granite porphyry are later intrusions the studied samples have nearly homogeneous major element bulk rock and mineral compositions but show large variations in their trace element compositions and textural characteristics the trace element data suggest the influence of hydrous fluids possibly enriched in co2 f and cl in the evolution of the plutonic body textural analysis of the coarse grained granite porphyry indicates that the crystal size distribution csd slopes intercepts and total numbers of groundmass decrease from the center to the margin of the intrusion in contrast to the maximum diameter of the crystals lmax average length of the four largest quartz crystals for each sample however most fine grained samples and the groundmass of the coarse grained samples show concave down csds indicating textural coarsening quartz csds in the coarse grained samples are kinked with a steep sloped log linear section representing small crystals 5 1mm and a shallow sloped log linear section representing large crystals 4 1mm these two crystal populations are interpreted as resulting from a shift in cooling regime the straight csds of two fine grained samples may be due to a different cooling history in general the spatial variation of the csd patterns can be attributed to various degrees of overgrowth and mechanical compaction the quartz phenocrysts in several coarse grained samples exhibit a high degree of alignment which may be the result of magmatic flow by integrating the field geology geochemistry and quantitative textural data from the horizontal profile of the shanggusi granite porphyry it is suggested that hydrous fluids at the top of the intrusion not only controlled the fractionation of elements but also affected its cooling history fluid migration controlled undercooling can explain the solidification processes in the shanggusi intrusion and may also be prevalent in other fluid rich shallow intrusions quantitative integration of textural and geochemical data for igneous rocks can contribute to our understanding of the relationships between physical and chemical processes in a magma system and provide relatively comprehensive insights into the petrogenesis of granites

origin of broken phenocrysts in ash flow tuffs surprisingly little attention has been devoted to the textural nature of phenocrysts of feldspar and quartz in tuff although many geologists have briefly alluded to broken phenocrysts none have addressed their origin in any detail petrographic study of 117 cooling units in the middle tertiary ash flow province of the great basin united states provides a basis for characterization of the shapes and for interpretation of the origin of felsic phenocrysts in ash flow tuffs although not proven to be wholly ineffective breakage of phenocrysts by mutual impact in the erupting magma and pyroclastic flow is doubtful for at least four reasons first the statistical probability of mutual collision between phenocrysts diminishes exponentially as their proportion to vitroclasts diminishes e g only 1 probability for 10 phenocrysts collision is less likely if pyroclasts move by laminar rather than turbulent flow second the coating of glass and or melt on the phenocrysts provides a cushion that absorbs the impact force third plagioclases broken by impact in the laboratory have unusual shapes unlike those seen in great basin tuffs fourth euhedral phenocrysts of feldspar are commonplace in many great basin tuffs and in some they constitute a significant proportion of the phenocrysts indicating that mutual impact does not modify all intratelluric crystals during explosive eruption the two most populated categories of phenocryst shape in great basin tuffs probably correspond to what has been previously called broken phenocrysts somewhat less than half of the plagioclase and many sanidine phenocrysts are subhedral to anhedral these are similar in shape size and composition to grains in polycrystalline aggregates within the same thin section kindred aggregates and discrete phenocrysts could have been derived from holocrystalline to partly crystalline material in the magma chamber that was disaggregated to varying extents during explosive eruption more than half of the plagioclase and all of the quartz phenocrysts in great basin tuffs consist of irregularly shaped fragments with cuspate embayed outlines resembling pieces of a jigsaw puzzle which we call phenoclasts inclusions of glass are common and are especially evident in larger more or less whole crystals textural features of some phenocrysts in cognate pumice clasts in the tuffs reveal that they broke apart while still in the vesiculating but unfragmented magma as the erupting magma decompressed vesiculation of the melt that was entrapped at higher pressures as inclusions within the phenocrysts blew them apart forming the phenoclasts shapes of felsic phenocrysts in volcanic rocks provide insight into their mode of emplacement euhedral phenocrysts are common in ash flow tuffs as well as lava flows phenoclasts however are diagnostic of ash flow tuffs because they do not occur in plinian ash fall deposits and are rare in lava flows these textural contrasts are useful for interpretation of generally older but in any case altered and recrystallized volcanic rocks in such rocks critical groundmass features and field relations that could provide clues to their origin have been obscured but the shapes of relict phenocrysts are commonly well preserved

origin of anorthosite by textural coarsening quantitative measurements of a natural sequence of textural development the textures of plagioclase crystals within large olivine oikocrysts preserve the sequence of the formation of anorthosite such textures have been quantified in a troctolite anorthosite from the proterozoic lac st jean anorthosite complex canada crystal size distributions csds indicate that initially plagioclase nucleated and grew in an introduction environment of linearly increasing undercooling producing a straight the textures of plutonic rocks are one of their most line csd during this phase latent heat of crystallization was striking aspects but they have been little used to elucidate largely removed by circulation of magma through the porous crystal petrological processes as compared with chemical and mush by about 25 solidification the crystallinity was such that isotopic methods where used discussion has tended it reduced but did not eliminate the circulation of magma resulting to be qualitative in contrast to quantitative chemical in the retention of more latent heat within the crystal pile the methods hence reducing the weight of this approach temperature rose until it was buvered by the solution of plagioclase indeed it is not possible to verify physical models if close to the liquidus temperature of plagioclase nucleation of quantitative data are not available quantitative textural plagioclase was inhibited and conditions were suitable for textural studies of volcanic rocks are becoming more common coarsening of both plagioclase and olivine to occur ostwald and these methods are applied here to the development ripening in this process small crystals were resorbed whereas of anorthosite larger crystals grew from both material recycled by the resorption of quantitative textural studies of plutonic rocks really crystals smaller than the critical size and new material brought in started with jackson s studies of the stillwater complex by the circulating magmatic fluid the results of this process resemble in 1961 jackson 1961 he measured crystal size disthose of high temperature metasomatism but there is no necessity for tributions but did not record the area that he measured a magmatic fluid with a diverent composition the shapes of the hence his data cannot be completely compared with plagioclase csds fit better the communicating neighbours equation of modern data his pioneering work was not really followed textural coarsening rather than the classic lifshitz slyozov wagner up and since then most studies have looked only at equation as do other examples drawn from the literature if olivine average or typical crystal sizes these data are much started to nucleate at a higher temperature than plagioclase then less revealing of petrological processes than crystal size during the textural coarsening phase olivine would have been more distributions partly because they only give one parameter undercooled than plagioclase and would have had a higher maximum for each sample the few existing studies of crystal size growth rate in these conditions olivine would coarsen more rapidly distributions in plutonic rocks have not treated than plagioclase and engulf it hence the order of crystallization plagioclase determined from the textures would be the reverse of the order of one problem especially pertinent to quantitative texfirst nucleation of the two phases from equilibrium phase diagrams tural studies is the way that many igneous petrologists maintenance of the temperature near the plagioclase liquidus may look at rocks they commonly try to reconstruct how a rock has formed by examining the final fully crystallized also inhibit the nucleation and growth of other phases

fragmentation in kimberlite products and intensity of explosive eruption the explosive eruption of kimberlite magma is capable of producing a variety of pyroclast sizes shapes and textures however all pyroclastic deposits of kimberlite comprise two main types of pyroclasts 1 pyroclasts of kimberlite with or without enclosed olivine crystals and 2 olivine crystals which lack coatings of kimberlite here we propose two hypotheses for how kimberlite magmas are modified due to explosive eruption 1 olivine crystals break during kimberlite eruption and 2 kimberlite melt can be efficiently separated from crystals during eruption these ideas are tested against data collected from field study and image analysis of coherent kimberlite and fragmental kimberlite from kimberlite pipes at diavik nt olivines are expected to break because of rapid pressure changes during the explosive eruption disruption of kimberlite magma and pyroclast production is driven by ductile deformation processes rather than by brittle fragmentation the extent to which melt separates from olivine crystals to produce kimberlite free crystals is a direct consequence of the relative proportions of gas melt and crystals lastly the properties of juvenile pyroclasts in deposits of pyroclastic kimberlite are used to index the relative intensity of kimberlite eruptions a fragmentation index is proposed for kimberlite eruption based on a crystal size distributions of olivine and on b ratios of selvage free olivine pyroclasts to pyroclasts of kimberlite with or without olivine crystals

on the fractal dimension of the fallout deposits a case study of the 79 a d plinian eruption at mt vesuvius we investigated the existence of a fractal law power law distribution of size pyroclastic fragments erupted during the fallout phase of the 79 a d plinian eruption at mt vesuvius in particular we performed a particle size distribution analysis on 18 white and grey pumice samples collected in six sites distributed in the sw sector of mt vesuvius our measurements show that the fragmentation of samples in the investigated range from 32 mm to 850 m follows a power law guaranteeing the scale invariance of the process the relationship frequency size distribution of the fragments is verified independently from the nature i e pumices and lithics and stratigraphic height of the considered samples in the pyroclastic deposit therefore the fractal fragmentation theory can be indicated for evaluating the relationship between the intensity of fragmentation fractal dimension d and eruption energy in this way the apparent chaotic distribution of the particles in the fallout deposits hides a self organized complexity revealed by the retrieved power law distribution we further remark that a key aspect of our analysis is the founded evidence that the fractal dimension of the lithics is systematically greater than that of the pumices

observational study of marine atmospheric boundary layer characteristics during swell abstract by combining simultaneous data from an instrumented air sea interaction spar asis buoy and a 30 m tower profiles of wind and turbulence characteristics have been obtained at several heights from about 1 to 30 m above the water surface during swell conditions five cases formed as averages over time periods ranging from 2 5 to 9 5 h representing quasi steady conditions have been selected they represent a range of typical wave age and include wind following swell cases and cross swell cases for relatively large wave age the wind profile exhibits a well defined maximum in the height range 5 10 m for more modest wave age this maximum turns into a sharp knee in the wind profile below the maximum or knee the wind increases rapidly with height above that point the wind is very nearly constant up to the highest measuring level on the tower 30 m analysis of balloon data from one day with swell indicates that the layer with constant wind in fact extends to the top of the boundary layer

dynamics of sheared convective boundary layer entrainment part i methodological background and large eddy simulations abstract the reported study examines the dynamics of entrainment and its effects on the evolution of the dry atmospheric convective boundary layer cbl when wind shear is present the sheared cbl can be studied by means of direct measurements in the atmosphere laboratory studies and numerical techniques the advantages and disadvantages of each technique are discussed in the present paper which also describes the methodological background for studying the dynamics of entrainment in sheared cbls for the reported study large eddy simulation les was chosen as the primary method of convective entrainment investigation twenty four les runs were conducted for cbls growing under varying conditions of surface buoyancy flux free atmospheric stratification and wind shear the simulations were divided into three categories cbl with no mean wind ns cbl with a height constant geostrophic wind of 20 m s 1 gc and cbl with geostrophic wind shear gs in the simulated cases the sheared cbls grew fastes

oxygen isotope study of the long valley magma system california isotope thermometry and convection in large silicic magma bodies products of voluminous pyroclastic eruptions with eruptive draw down of several kilometers provide a snap shot view of batholith scale magma chambers and quench pre eruptive isotopic fractionations i e temperatures between minerals we report analyses of oxygen isotope ratio in individual quartz phenocrysts and concentrates of magnetite pyroxene and zircon from individual pumice clasts of ignimbrite and fall units of caldera forming 0 76 ma bishop tuff bt pre caldera glass mountain 2 1 0 78 ma and post caldera rhyolites 0 65 0 04 ma to characterize the long lived batholith scale magma chamber beneath long valley caldera in california values of 18o show a subtle 1 decrease from the oldest glass mountain lavas to the youngest post caldera rhyolites older glass mountain lavas exhibit larger 1 variability of 18o quartz the youngest domes of glass mountain are similar to bt in 18o quartz values and reflect convective homogenization during formation of bt magma chamber surrounded by extremely heterogeneous country rocks ranging from 2 to 29 oxygen isotope thermometry of bt confirms a temperature gradient between late 815 c and early 715 c bt the 18o quartz values of early and late bt are 8 33 and 8 21 consistent with a constant 18o melt 7 8 0 1 and 100 c temperature difference zircon melt saturation equilibria gives a similar temperature range values of 18o quartz for different stratigraphic units of bt and in pumice clasts ranging in pre eruptive depths from 6 to 11 km based on melt inclusions and document vertical and lateral homogeneity of 18o melt worldwide five other large volume rhyolites lava creek lower bandelier fish canyon cerro galan and toba exhibit equal 18o melt values of earlier and later erupted portions in each of the these climactic caldera forming eruptions we interpret the large scale 18o homogeneity of bt and other large magma chambers as evidence of their longevity 105 years and convection however remaining isotopic zoning in some quartz phenocrysts trace element gradients in feldspars and quartz and zircon crystal size distributions are more consistent with far shorter timescales 102 104 years we propose a sidewall crystallization model that promotes convective homogenization roofward accumulation of more evolved and stagnant volatile rich liquid and develops compositional and temperature gradients in pre climactic magma chamber crystal melt gas bubbles mush near chamber walls of variable 18o gets periodically remobilized in response to chamber refill by new hotter magmas one such episode of chamber refill by high ti sr ba zr and volatile richer magma happened 103 104 years prior to the 0 76 ma caldera collapse that caused magma mixing at the base mush thawing near the roof and walls and downward settling of phenocrysts into this hybrid melt

quantitative characterization of textures in mantle spinel peridotite xenoliths a method for quantitative characterization of grain size in thin sections has been established for mantle spinel peridotite xenoliths using optical scanning of large areas of thin sections skeletonization of grain section outlines and computerized measurement of individual grain section areas measurements range from 218 for the coarsest example to more than 3000 in the finest grained variability of the samples has been examined in relation to size and number of grain section areas measured by using multiple and orthogonal sections from several xenoliths the results show a linear relationship of arithmetic mean against additive standard deviation including data from coarse grained protogranular through porphyroclastic to the finer grained equigranular examples this suggests that peridotite textures form a continuous series rather than discrete groups as suggested by qualitative subjective assessment the observed distributions of grain section areas have been explored in relation to their description and possible mechanistic origin by direct measurement and comparison of cumulative number and area distribution curves we show that qualitatively assessed typical grain sizes are influenced by a small number of larger grain sections although the arithmetic mean and standard deviation provide a convenient method for comparison in practice grain section area distributions show marked positive skewness more consistent with log normal or power law functions linear log probability curves also support the existence of a continuous series of peridotite textures suggesting that the shallow lithospheric mantle has been subject to processes of comminution and or grain growth dependent on the law of proportionate effect the geological society of london 2010

variations of olivine abundance and grain size in the snap lake kimberlite intrusion northwest territories canada a possible proxy for diamonds abstract the snap lake hypabyssal kimberlite is a 15 inclined intrusion that intrudes archaean rocks of the slave craton mapping has identified two main lithofacies within the intrusion olivine rich kimberlite ork and olivine poor kimberlite opk extensive bulk sampling has demonstrated that diamonds vary in both abundance and size across the intrusion since fresh forsteritic olivine and diamond possess similar densities they can be expected to be hydraulically equivalent this study investigates the local scale variation of olivine grain size and content using image analysis and whether olivine can be used as a proxy for diamond concentration and size direct measurement of diamonds is made difficult by extremely low concentrations of around 0 4 ppm and by the inability of the sampling methodology to sample selectively olivines from the two kimberlite varieties possess distinctly different crystal size distributions and this together with contrasting groundmass textures mineralogy and phlogopite compositions indicates that the opk and ork represent two distinct batches of kimberlite magma the general lack of sorting of olivine grains and the presence of decussate phlogopite textures in the ork indicate that this magma crystallized rapidly but was probably preceded by the opk which had a more complex crystallization history as revealed by complex zoning patterns of its phlogopite grains a methodology for comparing olivine and diamond size distributions has been developed and a strong correlation between diamond and olivine size distributions is demonstrated the correlation is used to demonstrate that diamond size distributions can be predicted from the proportions of opk and ork that comprise each bulk sample it can be concluded that the two textural varieties of kimberlite possess distinctly different olivine and diamond populations and that olivines are a good proxy for understanding diamond distributions at a local scale in the snap lake intrusion

experimental constrains on shear induced crystal breakage in magmas crystal breakage occurs along margins of conduit walls and basal zones of lava flows it is usually interpreted as flow related textures developed at large finite strains and strains rates we have investigated the grain size and shape distributions in an experimentally deformed crystal melt suspension in order to constrain the temperature t the strain and the strain rate r ranges of the crystal breakage process the starting crystal melt suspension is composed of a haplogranitic melt with 54 vol alumina crystals torsion experiments were performed in a gas medium paterson apparatus at 300 mpa confining pressure and subsolidus temperatures crystal size distribution and aspect ratio of alumina grains were measured on polished sections normal to the shear direction i e from the centre to the rim of the deformed cylinders a first minor occurrence of crystal breakage is evidenced in all experiments and low strains it is related to intense stress localisation at some grain contacts in the initially connected solid framework a second intense and penetrative crystal breakage process is observed for t 550 c and r 6 2x10 4 s 1 the evolution of the size distribution as a function of finite strain and the reduced aspect ratios of preserved largest crystals in intensely strained zones support that breakage occurs by abrasion of the larger crystals this abrasion can be attributed to the partial stress propagation over both the melt and partially isolated crystals under visco elastic conditions mechanical data show a transition from slight shear softening at low strain rates and highest temperatures to strain hardening for experiments that produced penetrative crystal breakage the crystal melt suspension exhibits a shear thinning behaviour with a stress exponent larger than 2 06 over the explored strain rate and temperature domain for the experiments without intensive crystal breakage our results are applicable to the interpretation of the crystal breakage often observed at the base of lava flows in domes and near conduit walls this experimental reproduction of a process observed in nature is important because the controls of stress induced breakage we quantified are also key parameters governing magma transport

fractals in petrology abstract a fractal power law distribution is the only statistical distribution applicable to a scale invariant process one of the major problems in petrology is the distribution of trace elements in the earth s crust extreme values of this distribution result in ore deposits there is accumulating observational evidence that tonnage grade statistics of ore deposits are often fractal power law rayleigh distillation and chromatographic models can explain power law fractal distributions for the extreme values of trace element concentrations an alternative fractal approach to problems in petrology is to use self affine fractals the standard approach is to take a fourier transform of a continuous signal an example would be the concentration of a mineral along a linear track if the fourier coefficients scale as a power law of the wavelength the distribution is a self affine fractal many well logs give this result multifractal analyses can also be applied to problems in petrology

causes of fragmented crystals in ignimbrites a case study of the cardones ignimbrite northern chile broken crystals have been documented in many large volume caldera forming ignimbrites and can help to understand the role of crystal fragmentation in both eruption and compaction processes the latter generally overlooked in the literature this study investigates the origin of fragmented crystals in the 1260 km3 crystal rich cardones ignimbrites located in the central andes observations of fragmented crystals in non welded pumice clasts indicate that primary fragmentation includes extensive crystal breakage and an associated ca 5 vol expansion of individual crystals while preserving their original shapes these observations are consistent with the hypothesis that crystals fragment in a brittle response to rapid decompression associated with the eruption additionally we observe that the extent of crystal fragmentation increases with increasing stratigraphic depth in the ignimbrite recording secondary crystal fragmentation during welding and compaction secondary crystal fragmentation aids welding and compaction in two ways first enhanced crystal fragmentation at crystal crystal contacts accommodates compaction along the principal axis of stress second rotation and displacement of individual crystal fragments enhances lateral flow in the direction s of least principal stress this process increases crystal aspect ratios and forms textures that resemble mantled porphyroclasts in shear zones indicating lateral flow adds to processes of compaction and welding alongside bubble collapse in the cardones ignimbrite secondary fragmentation commences at depths of 175 250 m lithostatic pressures 4 6 mpa and is modulated by both the overlying crystal load and the time spent above the glass transition temperature under these conditions the existence of force chains can produce stresses at crystal crystal contacts of a few times the lithostatic pressure we suggest that documenting crystal textures in addition to conventional welding parameters can provide useful information about welding processes in thick crystal rich ignimbrites

zoned quartz phenocrysts from the rhyolitic bishop tuff cathodoluminescence cl reveals growth zones in quartz phenocrysts from the rhyolitic bishop tuff melt inclusions occur in various zones and record the evolving melt composition during zonal growth the zones form an oscillatory pattern between bright and dark cl quartz there are three recognizable patterns of cl zoning in these crystals 1 weakly zoned cores and bright cl rims 2 weakly zoned cores and dark cl rims and 3 no cl intensity difference from core to rim dark cl quartz generally occurs at crystal edges contains most of the melt inclusions and is interpreted as fast growing zones that occur along recognizable crystal edges edge zones are thicker than the same zone on adjacent faces consistent with relatively fast growth of these zones in each successive zone these edge zones decrease in size toward the rim while the zones along the crystal faces increase some of the melt inclusions have bright cl quartz locally associated with them this is interpreted as the postentrapment crystallization of slow growing quartz in the melt inclusions many crystals display zone discordance from the weakly zoned interiors to the rims most of the discordant surfaces are rational and probably are primary growth features pumice clasts from the southern vents are largely compositionally and texturally distinct from those from the northern vents and this distinction is also evident in the quartz cl the crystals that have bright cl rims are all associated with the late erupted northern part of the bishop tuff melt inclusion compositions and cl zoning patterns suggest a common origin for early and middle erupted quartz and the interior zones of late erupted quartz however the bright cl rim on the late erupted quartz indicates an additional stage of crystallization in late erupted magma melt inclusions in individual early erupted crystals have small variations in ba whereas inclusions in late erupted crystals markedly increase in ba toward the rim which is opposite to the normal zoning of sequentially trapped melts expected during closed system crystallization differentiation the quartz zoning features are consistent with the hypothesis of crystal settling in evolving magma that erupted late from northern vents

use of conventional stability parameters during swell the situation with swell is of climatological importance over the baltic sea since swell is present during as much as 40 of the time in this study two periods with unstable and two periods with stable stratification and wind following swell are investigated data are taken at a small flat island in the baltic sea during unstable stratification the turbulent structure shows great resemblance to the free convective boundary layer and scales with the boundary layer height since surface heat flux is too small to support the high levels of turbulence present inactive turbulence is probably the dominating source for the stably stratified layer there are smaller differences between data with and without swell the turbulence is mainly transported upward into the atmosphere with the aid of pressure fluctuations induced by the waves for most of the data with swell the gradients are smaller than for growing sea during unstable conditions the wind gradients are negative indicating the presence of a wave driven wind the gradients increase with increasing height above the surface the drag coefficient is smaller than is usually found for both stable and unstable stratification and varies very little with wind and stratification there are only small variations in the heat transfer coefficients with changing stratification but they are significantly different for stable and unstable stratification

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

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

testing the influence of high voltage mineral liberation on grain size shape and yield and on fission track and 40ar 39ar dating mineral liberation and separation are fundamental for modern thermochronology the fragmentation of rocks by high voltage electrical pulses called electrical fragmentation is a new technology only available since the development of a lab sized machine a few years ago the proposed advantages e g disintegration along grain boundaries compete with suspected negative effects of the locally occurring high temperatures up to 104 k on the physical properties of the liberated minerals comparison of electrical fragmentation with conventional mechanical fragmentation jaw crusher revealed similar amounts of liberated apatite and zircon from the same quantity of granite but 45 production of fines 80 m for mechanical fragmentation versus 5 for electrical fragmentation electrical fragmentation yielded larger sized apatite grains 180 250 m compared to 80 125 m for mechanical liberation but no differences in shape factors elongation roundness compactness the liberation of idiomorphic crystals from coarse grained rocks is ameliorated by the new method as shown by the liberation of mm sized idiomorphic biotite crystals from granite degassing curves of 40ar from electrically and mechanically liberated biotites from the same sample are nearly identical maximum difference six percentage points 40ar 39ar ages of biotites from three samples two mechanically one electrically fragmented from the same intrusion are identical within 2 error length measurements of apatite fission tracks gave identical results within 2 error regardless of fragmentation method used in summary the positive aspects of electrical fragmentation have been confirmed in this study while effects negative for thermochronology are not observed

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

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

structure of the entrainment zone capping the convective atmospheric boundary layer the authors use large eddy simulation les to investigate entrainment and structure of the inversion layer of a clear convectively driven planetary boundary layer pbl over a range of bulk richardson numbers ri the les code uses a nested grid technique to achieve fine resolution in all three directions in the inversion layer extensive flow visualization is used to examine the structure of the inversion layer and to illustrate the temporal and spatial interaction of a thermal plume and the overlying inversion it is found that coherent structures in the convective pbl that is thermal plumes are primary instigators of entrainment in the ri range 13 6 ri 43 8 at ri 5 13 6 strong horizontal and downward velocities are generated near the inversion layer because of the plume interface interaction this leads to folding of the interface and hence entrainment of warm inversion air at the plume s edge at ri 5 34 5 the inversion s strong stability prevents folding of the interface but strong horizontal and downward motions near the plume s edge pull down pockets of warm air below the nominal inversion height these pockets of warm air are then scoured off by turbulent motions and entrained into the pbl the structure of the inversion interface from les is in good visual agreement with lidar measurements in the pbl obtained during the lidars in flat terrain field experiment a quadrant analysis of the buoyancy flux shows that net entrainment flux or average minimum buoyancy flux wu min is identified with quadrant iv w2u1 0 motions that is warm air moving downward plumes generate both large negative quadrant ii w1u2 0 and positive quadrant iii w2u2 0 buoyancy fluxes that tend to cancel the maximum vertical gradient in potential temperature at every x y grid point is used to define a local pbl height zi x y a statistical analysis of zi shows that skewness of zi depends on the inversion strength spectra of zi exhibit a sensitivity to grid resolution the normalized entrainment rate we w where we and w are entrainment and convective velocities varies as ari21 with a 0 2 in the range 13 6 ri 43 8 and is in good agreement with convection tank measurements for a clear convective pbl the authors found that the finite thickness of the inversion layer needs to be considered in an entrainment rate parameterization derived from a jump condition

relating the physical properties of volcanic rocks to the characteristics of ash generated by experimental abrasion interactions between clasts in pyroclastic density currents pdcs generate volcanic ash that can be dispersed to the atmosphere in co pdc plumes and due to its small size is far travelled we designed a series of experiments to determine the effects of pyroclast vesicularity and crystal content on the efficiency and type of ash generated by abrasion two different pyroclastic materials were used 1 basaltic andesite pyroclasts from fuego volcano guatemala with 26 46 vesicularity and high groundmass crystallinity and 2 tephri phonolite avellino pumice vesuvius italy with 55 75 vesicularity and low groundmass crystallinity when milled both clast types produced bimodal grain size distributions with fine ash modes between 4 and 5 32 63 m although the vesicular avellino pumice typically generated more ash than the denser fuego pyroclasts the ash generating potential of a single pyroclast was independent of density and instead governed by heterogeneous crystal and vesicle textures one consequence of these heterogeneities was to cause the vesicular avellino clasts to split in addition to abrading which further enhanced abrasion efficiency the matrix characteristics also affected ash shape and componentry which will influence the elutriation and transport properties of ash in the atmosphere the experimental abrasion successfully replicated some of the characteristics of natural co pdc ash samples as shown by similarities in the adherence factor which measures the proportion of attached matrix on phenocrysts of both the experimentally generated ash and natural co pdc ash samples our results support previous studies which have shown that abrasion is an effective mechanism for generating fine ash that is similar in size 5 30 m to that found in co pdc deposits we further show that both the abundance and nature shape density components size distribution of those ash particles are strongly controlled by the matrix properties of the abraded pyroclasts

an introduction to the application of x ray microtomography to the three dimensional study of igneous rocks imaging rocks in three dimensions through x ray microtomography enables routine visualization of structures in samples which can be spatially resolved down to the sub micron scale although x ray tomography has been applied in biomedical research and clinical settings for decades it has only recently been applied to studies of rocks and few geoscientists realize its value and potential this contribution provides an introduction to the principles and techniques of x ray microtomography to the study of igneous rock textures as well as reviewing the current state of the art we hope that this short review will encourage more geoscientists to apply x ray microtomography in their research and that this will lead to new insights into the processes that occur in magmatic as well as other geological systems

large eddy simulations and observations of atmospheric marine boundary layers above nonequilibrium surface waves abstract winds and waves in marine boundary layers are often in an unsettled state when fast running swell generated by distant storms propagates into local regions and modifies the overlying turbulent fields a large eddy simulation les model with the capability to resolve a moving sinusoidal wave at its lower boundary is developed to investigate this low wind fast wave regime it is used to simulate idealized situations with wind following and opposing fast propagating waves swell and stationary bumps les predicts momentum transfer from the ocean to the atmosphere for wind following swell and this can greatly modify the turbulence production mechanism in the marine surface layer in certain circumstances the generation of a low level jet reduces the mean shear between the surface layer and the pbl top resulting in a near collapse of turbulence in the pbl when light winds oppose the propagating swell turbulence levels increase over the depth of the boundary layer and the surface drag increases

comagmatic granophyric granite in the fish canyon tuff colorado implications for magma chamber processes during a large ash flow eruption the 27 8 ma fish canyon tuff a vast ash flow sheet 5000 km 3 of uniform phenocryst rich dacite is representative of monotonous intermediate eruptions from a magma chamber that lacked compositional gradients sparse small fragments of comagmatic granophyre in late erupted tuff and postcaldera lava having mineral compositions indistinguishable from phenocrysts in the tuff and precaldera lava like rocks record complex events in the fish canyon chamber just prior to eruption sanidine phenocrysts in the granophyre preserve zoning evidence of mingling with andesitic magma then shattering by decompression and volatile loss accompanying early fish canyon eruptions before overgrowth by granophyre the textural and chemical disequilibria indicate that the eruption resulted from batholith scale remobilization of a shallow subvolcanic chamber contrary to previous interpretations of magma storage and phenocryst growth in the lower crust

the near neutral marine atmospheric boundary layer with no surface shearing stress a case study abstract data from a marine coastal experiment over the baltic sea comprising airborne measurements and mast measurements have been used to highlight the turbulence dynamics of a case with most unusual flow characteristics the boundary layer had a depth of about 1200 m the thermal stratification was near neutral with small positive heat flux below 300 m and equally small negative heat flux above the entire situation lasted about 6 hours turbulence levels were unexpectedly high in view of the fact that momentum flux was negligible in fact positive in the layers near the surface and buoyancy flux was also small the turbulence was found to scale with the height of the boundary layer giving rise to velocity spectra having the shape of those characteristic of convectively mixed boundary layers analysis of the turbulence budget for the entire planetary boundary layer pbl revealed that energy was produced from shear instability in the uppermost parts of the pbl and was distributed to the lower par