possible role of superheated magma in the formation of orbicular granitoids orbicular structures in granitoid rocks generally occur in minor intrusions inside or at the edges of larger granitoid plutons some orbs are associated with comb layering at or near pluton margins the orbs typically consist of cores enclaves of various rock types around which are concentric shells of rhythmically precipitated felsic and mafic layers dominated by radial and tangential arrangements of elongate crystals the orbs therefore contrast strongly with the enclosing granitoid rock which has a typical granitoid microstructure with randomly distributed crystals orbicular shells and comb layering have similar features and both require the absence of nuclei in the magma which permits a significant degree of undercooling and forces crystallization to occur only on solid objects superheating is an effective way of destroying nuclei as has been shown experimentally and so orbicular granitoids may have crystallized from formerly superheated magma effective superheating could be caused by engulfment of hydrous felsic or intermediate magma by hot mafic magma or more probably by injection of water into a felsic or intermediate magma the rarity of orbicular granitoids implies that superheating situations are also rare most magmas carrying sufficient nuclei to permit normal crystallization

compositional gradients surrounding spherulites in obsidian and their relationship to spherulite growth and lava cooling spherical masses of crystal fibers spherulites crystalize from rhyolitic melt glass mainly in response to significant undercooling while lava cools spherulite growth should induce compositional gradients in the surrounding glass from expulsion of incompatible constituents and diffusion of those constituents away from the spherulite finite difference numerical modeling of one dimensional diffusion in which diffusivities are allowed to vary with temperature is used to investigate how compositional gradients reflect spherulite growth and lava cooling overall three forms of gradients are identified elements that diffuse quickly are expelled from the spherulite but then migrate away too quickly to become enriched at the boundary of the spherulite elements that diffuse slowly are trapped within the growing spherulite between those endmembers are elements that are not trapped yet diffuse slow enough that they become enriched at the contact their slow diffusion away then elevates their concentrations in the surrounding glass how enriched those elements are at the spherulite matrix interface and how far their enrichments extend outwards into the glass reflect how spherulites grow and thermal conditions during growth concentrations of h2o rb f li cl na k sr cs ba and be were measured in and around spherulites in obsidian from a 4 7 1 km3 rhyolite lava dome erupted from tequila volcano mexico measurable concentration gradients are found for h2o rb and f attributes of those gradients and the behaviors of the other elements are in accord with their experimentally constrained diffusivities spherulites appear to have grown following radial rather than volumetric growth the observed gradients and lack of others are more consistent with growth mainly below the glass transition which would necessitate the dome cooling at ca 10 5 to 10 7 c s 1 such slow cooling is consistent with the relatively large volume of the dome

crystallization of orbicular rocks exemplified by the slattemossa occurrence southeastern sweden the orbicular rock at slattemossa southeastern sweden has a quartz monzodioritic composition the cores of the orbicules crystallized directly from the orbicule forming magma cores made up of xenoliths have not been observed outside the core follow first an inner mafic a felsic and then an outer mafic shell the orbicules occur in a matrix which is similar to the core they grew simultaneously and show an almost perfect parallelism in evolution after initial normal crystallization of the magma superheating probably triggered by a sudden addition of volatiles destroyed earlier formed nuclei and also affected the already crystallized part of the rock cooling caused heterogeneous nucleation and rapid crystallization which formed the inner mafic shell this is enriched in mafic minerals especially biotite compared to the core at the same time the grain size becomes significantly smaller depletion in malic components possibly intensified by a sudden change in physical conditions destabilized biotite and amphibole crystallization causing oversaturation in plagioclase components forming a felsic shell having a sharp boundary with the mafic shell plagioclase is extremely altered mafic minerals were then stabilized probably due to depletion of plagioclase components and an outer mafic shell formed with the return to homogeneous nucleation matrix formation concluded the crystallization orbicules might have moved in the magma causing some squeezing of magma surrounding the orbicules but major movements involved the settling of the whole package of orbicules and matrix in the surrounding non orbicular magma less

growth of megaspherulites in a rhyolitic vitrophyre megaspherulites occur in a rhyolitic vitrophyre near the base of a thick rhyolitic vitrophyre that occupies a late eocene to early oligocene volcanic tectonic basin near silver cliff colorado diameters of the megaspherulites range from 0 3 to over 3 66 m including an alteration layer the megaspherulites are compound spherulites they are holocrystalline very fine to fine grained composed of sanidine and quartz and surrounded by a thin sanidine quartz rind and an alteration layer containing mordenite and 15 a montmorillonite megaspherulite crystallization began soon after the vitrophyre was emplaced as the result of sparse heterogeneous nucleation under highly nonequilibrium conditions spherulite growth proceeded in a diffusion controlled manner under lowered viscosity as a result of a high water content 5 to 7 wt which also contributed to sparse nucleation when nucleation did occur it was at a large t 245 350 c on near critical sized nuclei once the spherulites began to grow continued nucleation was on existing growth cones and new independent spherulites did not form sanidine crystals grew with a fibrous habit which is favored by a large t restricting fibril lengths and diameters between 10 30 and 3 7 m respectively during crystallization these growth cones impinged upon each other resulting in fibril cone free areas these cone free interconal areas consist of coarser fine grained phases dominated by quartz which crystallized from the melt as it accumulated between the crystallizing sanidine fibrils of the cones the anhydrous nature of the sanidine and quartz suggests that their crystallization concentrated a water rich residual fluid enriched in ca mg and fe and depleted in si k and na at the megaspherulite vitrophyre interface this fluid phase enclosed the megaspherulites resulting in the hydrothermal alteration of the vitrophyre forming a hydrothermal alteration layer as indicated by the presence of the minerals mordenite and montmorillonite

microlite orientation in obsidian flow measured by synchrotron x ray diffraction clinopyroxene and plagioclase andesine microlites in an obsidian flow from glass mountain ne california usa display strong alignment synchrotron x ray diffraction coupled with rietveld analysis was used to quantify crystallographic preferred orientation cpo clinopyroxene with a rod shaped morphology shows a strong alignment of 001 in the flow direction and 010 aligned parallel to the inferred flow plane andesine with a platy morphology displays an alignment of 010 platelets in the flow plane some pole densities exceed 90 multiples of random distribution applying a model of rigid ellipsoidal inclusions in a viscous matrix the local pure shear strains are between 2 and 3

spatiotemporal variations of snowmelt in antarctica derived from satellite scanning multichannel microwave radiometer and special sensor microwave imager data 1978 2004 1 we derived the extent onset date end date and duration of snowmelt in antarctica from 1978 to 2004 using satellite passive microwave scanning multichannel microwave radiometer smmr and special sensor microwave imager ssm i data a wavelet transform based method was developed to determine and characterize melt occurrences about 9 12 of the antarctic surface experiences melt annually this is more than twice the surface melt extent measured in greenland seasonally surface melt primarily takes place in december january and february and peaks in early january regression analysis over the 25 year period of study reveals a negative interannual trend in surface melt nevertheless the trend inference is not statistically significant large year to year fluctuations characterize the interannual variability extremely high melt occurred in the 1982 1983 and 1991 1992 summers while extremely weak melt occurred in the 1999 2000 summer a strong correlation with air temperature suggests that the melt index can serve as a diagnostic indicator for regional temperature variations periodic melting has been observed over ross ice shelf ronne filchner ice shelf the west antarctic ice streams and outlet glaciers in the transantarctic mountains the antarctic peninsula west ice shelf shackleton ice shelf amery ice shelf and the ice shelf along the princess ragnhild coast experienced the most persistent and intensive melt and should be closely monitored for their stability in the future given the recent disintegration of the larsen ice shelf a and b

surface melting derived from microwave radiometers a climatic indicator in antarctica this paper aims at presenting a new dataset including the melt events derived from microwave remote sensing occurring in antarctica from summer 1979 80 to 2005 06 the method for detecting melt events and sources of error is presented and then trends in melt duration for every pixel are extracted from the dataset mapped and analyzed the analysis focuses on two particular cases and the main results show that 1 the trends over the period 1980 2006 in the antarctic peninsula match with lengthening of the melt season on the ice shelves and surprisingly shortening of the melt season in the mountainous area of the peninsula and 2 the trends over the period 1996 2006 on the entire continent show a dipolar pattern with the western regions experiencing decreasing melt duration whereas east antarctica and the ross ice shelf experience increasing melt duration this pattern closely mirrors the temperature pattern expected when the southern annular mode is in a decreasing trend as it is over the period 1996 2006 for further analysis and validation the dataset has been made available at http www lgge obs ujf grenoble fr picard melting

diffusion controlled spherulite growth in obsidian inferred from h2o concentration profiles spherulites are spherical clusters of radiating crystals that occur naturally in rhyolitic obsidian the growth of spherulites requires diffusion and uptake of crystal forming components from the host rhyolite melt or glass and rejection of non crystal forming components from the crystallizing region water concentration profiles measured by synchrotron source fourier transform spectroscopy reveal that water is expelled into the surrounding matrix during spherulite growth and that it diffuses outward ahead of the advancing crystalline front we compare these profiles to models of water diffusion in rhyolite to estimate timescales for spherulite growth using a diffusion controlled growth law we find that spherulites can grow on the order of days to months at temperatures above the glass transition the diffusion controlled growth law also accounts for spherulite size distribution spherulite growth below the glass transition and why spherulitic glasses are not completely devitrified

the role of subglacial water in ice sheet mass balance subglacial water can significantly affect the velocity of ice streams and outlet glaciers of ice sheets depending on the geometry and capacity of the subglacial hydrologic system increased surface melting in greenland over the coming decades may influence the ice sheet s mass balance furthermore subglacial lakes in antarctica can modulate ice velocities and act as nucleation points for new fast flowing ice streams in the coming decades significant changes in the polar regions will increase the contribution of ice sheets to global sea level rise under the ice streams and outlet glaciers that deliver ice to the oceans water and deformable wet sediments lubricate the base facilitating fast ice flow the influence of subglacial water on fast ice flow depends on the geometry and capacity of the subglacial hydrologic system water moving rapidly through a well connected system of conduits or channels will have little impact on ice sheet velocities but water injected into a spatially dispersed subglacial system may reduce the effective pressure at the base of the ice sheet and thereby trigger increased ice sheet velocities in greenland the form of the subglacial hydrologic system encountered by increasing surface melt water will determine the influence of changing atmospheric conditions on ice sheet mass balance in antarctica subglacial lakes have the capacity to both modulate velocities in ice streams and outlet glaciers and provide nucleation points for new fast ice flow tributaries climate models of ice sheet responses to global change remain incomplete without a parameterization of subglacial hydrodynamics and ice dynamics

texture analysis of volcanic rock samples quantitative study of crystals and vesicles shape preferred orientation from x ray microtomography data abstract in the texture analysis of volcanic rocks the preferred orientation of the constituents can provide useful information for the interpretation of the processes involved in the rock formation we present here a new data analysis technique based on x ray microtomography measurements and on shape preferred orientation analysis to obtain the orientation distribution functions of the constituents of volcanic rocks this procedure proved to be very suitable for volcanic samples where diffraction based techniques developed for crystallographic preferred orientation studies are of limited utilization in addition to the fact that they cannot provide any information about vesicles or bubbles moreover the analysis performed directly in three dimensions 3d overcomes the problems that usually occur when employing stereological methods for the analysis of the images obtained via microscopy based techniques in this study two scoriae from stromboli and etna and a tube pumice from campi flegrei were measured via x ray microtomography and then the resulting volumes were analyzed following the proposed procedure results highlight little preferred orientation for the vesicles in the two scoria samples whereas the pumice shows a marked preferred orientation crystals also divided by mineral species were taken into account as well and in the two scoria samples there is no crystal preferred orientation in contrast with the pumice where crystal preferred orientation features are very similar to the ones found for the vesicles overall we found strong differences in preferred orientation weak for vesicles in scoriae showing an axial symmetry with the axis parallel to the elongation axis of the sample and a stronger and more complex orientation texture in the pumice sample for both crystals and vesicles the promising results obtained suggest that this procedure is potentially very useful for the analysis of preferred orientation in volcanic rocks and geomaterials in general

the 3d quantitative lattice and shape preferred orientation of a mylonitised metagranite from monte rosa western alps combining neutron diffraction texture analysis and synchrotron x ray microtomography abstract two complementary 3d techniques neutron diffraction and synchrotron x ray microtomography sxr ct were used to compare the shape and lattice preferred orientations of a mylonitised metagranite from the monte rosa unit western alps italy the goal of using these techniques was to obtain two different orientation distribution functions although the two functions describe relatively independent characteristics of the rock fabric nonetheless they also exhibit close relationships to macroscopic fabrics and may be complementarily used to quantify rock fabrics and microstructures thereby highlighting 3d features that cannot be obtained with either technique if used independently we describe an approach that can be potentially useful in various disciplines e g structural geology rock mechanics tectonics and geophysics when a complete data set of preferred orientations and size distribution is needed micas display a strong orthorhombic symmetry between mesoscopic lineation and microscopic spo and lpo whereas quartz and feldspars are characterised by a monoclinic symmetry between mesoscopic lineation and lpo these observations suggest a rheological decoupling between the weak phase mica layers and the stronger quartz feldspar layers this mechanical decoupling occurred during the alpine subduction collision when the monte rosa unit was part of the insubric line system and accommodated large vertical strain

effects of site lithology on geochemical signatures of human occupation in archaeological house plans in the netherlands abstract this study presents the application of multi element soil analyses x ray fluorescence spectroscopy and inductively coupled plasma optical emission spectroscopy of 1 m hcl extracts to grid samples from 3 archaeological house plans embedded in sandy clays clays and sands to assess effects of site lithology on geochemical signatures of human occupation the results indicate that this effect is significant and that each house plan is characterized by enhanced concentrations of different sets of elements copper cr sn and nd enrichments were found at all sites and thus represent elements that have no or only a weak relation with lithology depletions of fe and mn were also found to be universal indicators of human occupation in the house plans a combination of off site sampling comparison to regional element background concentrations and the use of bivariate plots al vs selected elements was successfully applied to identify anthropogenic elements verify background element concentrations and element sources and assess element distribution patterns within house plans spatial patterning of several anthropogenic elements suggest the presence of an in house barn at two sites while for another site no spatial patterning of chemical elements was observed for two sites this contrasts with earlier archaeological interpretation our results further suggest that 1 m hcl extractable elements are unreliable indicators of human occupation in clayey and especially calcareous clayey soils

timescales of spherulite crystallization in obsidian inferred from water concentration profiles we determined the kinetics of spherulite growth in obsidians from krafla volcano iceland we measured water concentration profiles around spherulites in obsidian by synchrotron fourier transform infrared spectroscopy the distribution of oh groups surrounding spherulites decreases exponentially away from the spherulite glass border reflecting expulsion of water during crystallization of an anhydrous paragenesis plagioclase sio2 clinopyroxene magnetite this pattern is controlled by a balance between the growth rate of the spherulites and the diffusivity of hydrous solute in the rhyolitic melt we modeled advective and diffusive transport of the water away from the growing spherulites by numerically solving the diffusion equation with a moving boundary numerical models fit the natural data best when a small amount of post growth diffusion is incorporated in the model comparisons between models and data constrain the average spherulite growth rates for different temperatures and highlight size dependent growth among a small population of spherulites

microtexture development during rapid cooling in three rhyolitic lava flows the effects of water concentration and degassing history on the development of spherulites and flow banding were examined in three middle tertiary rhyolitic lava flows from the atascosa mountains of southern arizona the hell s gate lava flow and the atascosa lava flow host spherulites of strongly contrasting texture and neither are flow banded the sycamore canyon lava flow is a flow banded rhyolite that hosts two populations of spherulites spherulites in the hell s gate lava flow consist of two to four generations of bladed radiating alkali feldspar crystals that increase in water concentration along their length needle like radiating feldspar crystals in spherulites in the atascosa and sycamore canyon lava flows are in some cases punctuated by concentric rinds of glass that are reservoirs for water rejected by the feldspar crystals the differences in spherulite crystal morphology between the sycamore canyon and atasocosa flows both needle like and the hell s gate flow bladed may reflect a more rapid cooling rate of the sycamore canyon and atascosa flows thick gray flow bands in the sycamore canyon lava flow host higher water concentrations than thin orange flow bands suggesting that flow bands are zones of greater and lesser volatile concentration deformed by stretching of the flowing magma temperature was uniform across the light and dark flow bands of the sycamore canyon flow indicating that water concentration one of the variables that controls diffusion coefficients rather than temperature controlled spherulite size in this case phenocrysts in the hell s gate lava flow are strongly resorbed probably as a result of magma ascent along a near adiabatic gradient that resulted in exsolution of water from the melt and subsequent dissolution of existing quartz phenocrysts by the water rich melt resumption of crystallization of anhydrous phases such as quartz and feldspar would have further enriched the melt in water facilitating the growth of spherulites spherulites in two of the lava flows sycamore canyon and hell s gate increase in water concentration from core to rim as would be expected in spherulites growing in melt enriched in water rejected by the growing feldspar crystals spherulites in the atascosa rhyolite flow decrease slightly in water concentration from core to rim possibly because the magma degassed during spherulite growth calculation of water concentration profiles in spherulites from all three rhyolite flows on the basis of rayleigh fractionation of water between sanidine and rhyolitic melt shows that the very high water concentrations in spherulites typically 0 6 water concentration in surrounding glass cannot be accounted for by rayleigh fractionation instead it is likely that sanidine incorporated water as fluid inclusions and or as water clusters during rapid crystal growth water concentration profiles in the glass surrounding spherulites do not preserve the high concentration zone at the spherulite boundary that has been observed in younger lava flows so that spherulite growth rates cannot be calculated on the basis of mass balance calculations of distribution of water during spherulite growth rather the water concentration profile in the surrounding glass is a half plateau the height of which is approximately equivalent to the far field water concentration in the surrounding glass indicating that water that accumulated at the spherulite magma boundary diffused sufficiently rapidly to equilibrate with the surrounding magma as the lava flow cooled

spherulites and thundereggs from pitchstones of the deccan traps geology petrochemistry and emplacement environments spherulites and thundereggs are rounded typically spherical polycrystalline objects found in glassy silicic rocks spherulites are dominantly made up of radiating microscopic fibers of alkali feldspar and a silica mineral commonly quartz they form due to heterogeneous nucleation in highly supercooled rhyolitic melts or by devitrification of glass associated features are lithophysae stone bubbles which have an exterior sometimes concentric shells of fine quartz and feldspar and internal cavities left by escaping gas when filled by secondary silica these are termed thundereggs here we describe four distinct occurrences of spherulites and thundereggs in pitchstones mostly rhyolitic some trachytic of the deccan traps india the thundereggs at one locality were previously misidentified as rhyolitic lava bombs and products of pyroclastic extrusive activity we have character ized the thundereggs petrographically and geochemically and have determined low contents of magmatic water 0 21 0 38 wt in them using fourier transform infrared spectros copy we consider that the spherulite bearing outcrops at one of the localities are of lava flows but the other three represent subvolcanic intrusions based on the structural disposition of the deccan sheet intrusions studied here and considerations of regional geology we suggest that they are cone sheets emplaced from a plutonic center now submerged beneath the

crystallization kinetics of alkali feldspars in cooling and decompression induced crystallization experiments in trachytic melt cooling and decompression experiments have been carried out on trachytic melts in order to investigate crystallization kinetics of alkali feldspar the effect of the degree of undercooling t t liquidus t experimental and time on nucleation and crystal growth process this experimental work gives us new data about crystallization kinetics of trachytic melts and it that will be useful to better understand the natural system of campi flegrei volcanoes experiments have been conducted using cold seal pressure vessel apparatus at pressure between 30 and 200 mpa temperature between 750 and 855 c time between 7 200 and 57 600 s and redox condition close to the nno 0 8 buffer these conditions are ideal to reproducing pre and syn eruptive conditions of the campi flegrei volcanoes where the conditions pertain to the complete range of pressures temperatures and time at which the experiments were performed alkali feldspar is the main phase present in this trachyte and its abundance can strongly vary with small changes in pressure temperature and water content in the melt implying appreciable variations in the textures and in the crystallization kinetics the obtained results show that crystallization kinetics are strictly related to t time final pressure superheating t and water content in the melt t is the driving force of the crystallization and it has a strong influence on nucleation and growth processes in fact the growth process dominates crystallization at small t whereas the nucleation dominates crystallization at large t time also is an important variable during crystallization process because long experiment durations involve more nucleation events of alkali feldspar than short experiment durations this is an important aspect to understand magma evolution in the magma chamber and in the conduit which in turn has strong effects on magma rheology

taking the pulse of volcanic eruptions using plagioclase glomerocrysts abstract crystallization timescales in subvolcanic systems and the consequences of interaction between ascending magmas and gases remain largely unconstrained as do links between these processes and monitoring signals at restless volcanoes we apply diffusion chronometry to radially oriented plagioclase and associated olivine in a glomerocryst from tolbachik volcano kamchatka russia to elucidate such processes we show that cm size glomerocrysts grow in a few days prior to or during eruption melt inclusions from these glomerocrysts show no compositional evolution during crystallization implying growth in a melt rich and dynamic environment volatile elements in melt inclusions show significant variability with increasing co2 as h2o decreases this behaviour is inconsistent with normal degassing processes and more likely reflects co2 fluxing on the basis of short residence timescales of glomerocrysts and sharp changes in melt inclusion volatile abundances we propose that rapid pre eruptive crystallization is controlled by rhythmic fluxing of magmatic h2o and co2 through the sub volcanic conduit this implies that compositional zoning in plagioclase from resorption textures to oscillatory zoning record short term co2 and h2o fluxing episodes consistent with strombolian eruption dynamics we propose that volcanic glomerocrysts represent the counterpart of vertical igneous layering or comb layering in shallow plutons magmatic layering and glomerocrysts dominated by radial plagioclase offer novel ways of targeting short term crystallization and degassing processes in subvolcanic systems

crystallization history of obsidian dome inyo domes california samples obtained by u s department of energy research drilling at the 600 year old obsidian dome volcano provide the rare opportunity to examine the transition from volcanic dome to plutonic intrusion textures in a silicic magma system textures in the lavas from obsidian dome record multiple periods of crystallization initiated in response to changes in undercooling t related to variable degassing in the mag ma phenocr ysts formed first at low t a drastic increase in t related to loss of a vapor phase during initial stages of eruption caused nucleation of microlites all of the lavas thus contain phenocrysts and microlites extrusion and subsequent devitrification of the dry 0 1 wt h2o magma crystallized spherulites and fine grained rhyolite at high t a granophyric texture representing crystallization at a moderate t formed in the intrusions beneath obsidian dome textures in the intrusion apparently represent crystallization of hydrous 1 2 wt h2o rhyolitic magma at shallow depths

deleterious reactions of aggregate with alkalis in concrete concrete in the built environment the word concrete is derived from the latin concretus compact condensed representing a conjunction of con together and the past participle of cresco to grow compare crescendo thus concrete could be liberally translated as grown solid together alluding to the consolidation of a particulate aggregate material with a cement binder of some sort concrete containing aggregate has been used in construction by the ancient greek and romans possibly as a further development of clay initially used by the assyrians and babylonians as a binder later superseded by burnt lime and gypsum by the egyptians as a construction material concrete allows architects and engineers to design a structure with only minimal constraints to its form a complicated shape requiring great effort to chisel out from a piece of stone can simply be poured in a mold and reproduced as often as desired also ex situ both the invention of ordinary portland cement opc first patented by british bricklayer joseph aspdin in 1824 and of reinforced concrete first patented by parisian gardener joseph monier in 1867 for making durable flower pots contributed to the development of mechanically stronger concrete allowing yet slimmer and taller structures to be built today concrete is the most popular building and construction material with an annual production volume exceeding 7 5 km3 or about 20 billion tonne concrete is the prime ingredient in the world s largest and most prominent structures and landmark edifices including hydropower dams e g three gorges dam yichang cn also see charlwood and solymar 1995 coastal defense works e g delta works nl telecommunication e g cn tower toronto ca office skyscrapers e g burj khalifa dubai uae theatres e g opera house sydney au hotels and casinos e g marina bay area singapore sg nuclear power plants oil and gas drilling and productions rigs e g sakhalin ru sea ports and harbors e g

primary clinopyroxene spherulites in basaltic lavas from the pacific antarctic ridge fresh glassy basaltic andesite samples recovered from the northern part of the pacific antarctic ridge contain abundant spherulites consisting of arrays of closely packed clinopyroxene fibers the spherulites frequently enclose elongated vesicles that are tear drop shaped or tailed the long axes of the elongated vesicles were found to be always parallel to the orientation of the surrounding crystal fibers in several cases elongated vesicles having different orientations are hosted by a single spherulite the existence of elongated vesicles provides unequivocal evidence that a significant proportion of the clinopyroxene fibers must have crystallized directly from a supercooled liquid at temperatures above the glass transition moreover the absence of fractures within the spherulites and the surrounding glass as well as the observed nucleation of clinopyroxene fibers at vesicle walls are interpreted to be consistent with a primary origin of the clinopyroxene spherulites based on these textural observations it has to be concluded that spherulites do not represent a diagnostic texture for the devitrification of volcanic glass that occurs below the glass transition temperature

extent and duration of antarctic surface melting the extent and duration of surface melting on the antarctic ice shelves and margins of the antarctic ice sheet are derived from satellite passive microwave data for 1978 87 the occurrence of surface melting in daily maps of t b is indicated by a marked increase in microwave brightness temperature t b which is caused by moisture in the near surface firn t b increases of more than 30 deg above the annual mean t b are chosen to indicate melting most antarctic surface melting occurs during december and january the observed melting is correlated with regional air temperatures but some melt patterns also appear to be related to katabatic wind effects the correlations suggest that the surface melting in antarctica increases about 3 5 10 6 d km 2 per degree of summer temperature increase the surface melt index duration times area of melting calculated for antarctica is 24 10 6 d km 2 averaged over nine summers the observed inter annual and regional variability is large surface melting was most extensive during the 1982 83 summer 36 10 6 d km 2 and least extensive during the 1985 86 summer 15 10 6 d km 2 the data indicate a decline in surface melting over the 9 years but meaningful inferences regarding trends in surface melting are precluded by the large inter annual variability

genesis of megaspherulites in el viejo rhyolitic coulee pleistocene southern puna argentina crystalline domains in rhyolitic domes and coulees are commonly characterized by spherulites and lithophysae spherulites typically range from microscopic to a few centimeters in diameter larger spherulites termed megaspherulites are rare but have been reported in the usa and mexico the uncommon nature of such structures supports the need for a study to explore the factors and special conditions that allow them to reach such a large size in the southern puna of argentina el viejo coulee includes megaspherulites up to 4 m in diameter we present observations from field work petrography scanning electron microscopy bulk geochemistry and fourier transform infrared spectroscopy the megaspherulites occur in obsidian lenses that differ in phenocryst content and composition from the foliated coherent facies that forms the rest of the coulee the obsidian lacks vesicles and microlites and is unaltered the megaspherulites comprise growth cones consisting of micropoikilitic texture where quartz encloses potassium feldspar the growth cones are separated by interconal areas composed of lithophysae we propose that the megaspherulites were formed above the glass transition temperature tg and are the product of primary crystallization of rhyolitic melt the exceptionally large size of the megaspherulites implies high diffusion rates which are favored by temperatures above tg during crystallization the large size also suggests scarcity of nucleation sites which is consistent with the megaspherulites being hosted by unaltered microlite and vesicle free glass the position of the obsidian lens at the base of the coulee may have played a critical role in maintaining the temperature above the tg long enough to allow the crystallization of the megaspherulites these conditions also favored crystallization in the most advanced stage where micropoikilitic texture replaced the fans of crystal fibers typical of spherulites crystallization of anhydrous quartz and feldspar in the growth cones led to the concentration of volatiles in the melt in the interconal areas resulting in volatile exsolution and formation of vesicles that became nucleation sites for lithophysae the study advances our understanding of some of the special processes that are involved in the cooling and solidification of rhyolitic magmas fundamentally we find that the position of the obsidian at the base of the coulee was critically important because this position favored maintenance of the temperature above the tg which in turn favored high diffusion rates also the scarcity of nucleation sites in the obsidian melt allowed only a small number of spherulites to nucleate those that nucleated therefore grew very large the meter scale megaspherulites may have taken 55 years to create

insignificant change in antarctic snowmelt volume since 1979 1 surface snowmelt is widespread in coastal antarctica satellite based microwave sensors have been observing melt area and duration for over three decades however these observations do not reveal the total volume of meltwater produced on the ice sheet here we present an antarctic melt volume climatology for the period 1979 2010 obtained using a regional climate model equipped with realistic snow physics we find that mean continent wide meltwater volume 1979 2010 amounts to 89 gt y 1 with large interannual variability 41 gt y 1 of this amount 57 gt y 1 64 is produced on the floating ice shelves extending from the grounded ice sheet and 71 gt y 1in west antarctica including the antarctic peninsula we find no statistically significant trend in either continent wide or regional meltwater volume for the 31 year period 1979 2010

ion microprobe analyses of trace elements in anorthoclase hedenbergite aenigmatite quartz apatite and glass in pantellerite evidence for high water contents in pantellerite melt

effusive silicic volcanism in the parana magmatic province south brazil evidence for locally fed lava flows and domes from detailed field work abstract lava flows and dome complexes of silicic composition were identified in the lower cretaceous parana magmatic province pmp at rio grande do sul state southern brazil detailed mapping and image analysis reveals significant volumes of effusive deposits aligned according to main lineaments likely representing the fissural systems that fed the three palmas type silicic units different structures indicative of effusive emplacement lava domes lobated flows sheet flows and autobreccias are very common in the study area and are probably also more abundant than previously thought in whole pmp silicic magmatism in fact effusive deposits seem predominant in the three distinct silicic units identified in the area since no remnants of pyroclastic components have been identified the vitreous dacites that make up the upper flows of the basaltic andesite to dacite barros cassal sequence are clearly effusive as indicated by their occurrence as thin sheet flows the much thicker early caxias do sul dacites occur mostly as lava flow lobes and pancake like of low to moderate viscosity and lava domes the younger high sio2 santa maria rhyolite unit shows unequivocal examples of effusive deposits at its lower portion as lobated flows formed by vesicle rich obsidian in spite of higher viscosities relative to the previous units 106 pa s it is probable that the very low h2o contents 1 wt of these rhyolite melts associated with high discharge rates resulted in an effusive nature in most to this unit

textural characterization major and volatile element quantification and ar ar systematics of spherulites in the rocche rosse obsidian flow lipari aeolian islands a temperature continuum growth model spherulitic textures in the rocche rosse obsidian flow lipari aeolian islands italy have been characterized through petrographic crystal size distribution csd and in situ major and volatile elemental analyses to assess the mode temperature and timescales of spherulite formation bulk glass chemistry and spherulite chemistry analyzed along transects across the spherulite growth front glass boundary reveal major oxide and volatile h2o co2 f cl and s chemical variations and heterogeneities at a 5 m scale numerous bulk volatile data in non vesicular glass spatially removed from spherulitic textures reveal homogenous distributions of volatile concentrations h2o 0 089 0 012 wt f 950 40 ppm and cl 4 100 330 ppm with co2 and s consistently below detection limits suggesting either complete degassing of these volatiles or an originally volatile poor melt volatile concentrations across the spherulite boundary and within the spherulitic textures are highly variable these observations are consistent with diffusive expulsion of volatiles into melt leaving a volatile poor rim advancing ahead of anhydrous crystallite growth which is envisaged to have had a pronounced effect on spherulite crystallization dynamics argon concentrations dissolved in the glass and spherulites differ by a factor of 20 with ar sequestered preferentially in the glass phase petrographic observation csd analysis volatile and ar data as well as diffusion modeling support continuous spherulite nucleation and growth starting at magmatic emplacement temperatures of 790 825 c and progressing through the glass transition temperature range tg 750 620 c being further modified in the solid state we propose that nucleation and growth rate are isothermally constant but vary between differing stages of spherulite growth with continued cooling from magmatic temperatures such that there is an evolution from a high to a low rate of crystallization and low to high crystal nucleation based on the diffusion of h2o across these temperature ranges 800 300 c timescales of spherulite crystallization occur on a timescale of 4 days with further modification up to 400 years growth is prohibitively slow 400 c and would become diffusion reliant selective deformation of spherulites supports a down temperature continuum of spherulite formation in the rocche rosse obsidian indeed petrographic evidence suggests that high strain zones may have catalyzed progressive nucleation and growth of further generations of spherulites during syn and post emplacement cooling

calculating anisotropic physical properties from texture data using the mtex open source package this paper presents the background for the calculation of physical properties of an aggregate from constituent crystal properties and the texture of the aggregate in a coherent manner emphasis is placed on the important tensor properties of 2nd and 4th rank with applications in rock deformation structural geology geodynamics and geophysics we cover texture information that comes from pole figure diffraction and single orientation measurements electron backscattered diffraction or ebsd electron channelling pattern laue pattern optical microscope universal stage in particular we provide explicit formulae for the calculation of the averaged tensor from individual orientations or from an orientation distribution function odf for the latter we consider numerical integration and an approach based on the expansion into spherical harmonics this paper also serves as a reference paper for the mathematical tensor capabilities of the texture analysis software mtex which is a comprehensive freely available matlab toolbox that covers a wide range of problems in quantitative texture analysis for example odf modelling pole figure to odf inversion ebsd data analysis and grain detection mtex offers a programming interface which allows the processing of involved research problems as well as highly customizable visualization capabilities mtex is therefore ideal for presentations publications and teaching demonstrations

deciphering the upper famennian hangenberg black shale depositional environments based on multi proxy record abstract presented for the first time in this paper are the results of a detailed multi proxy investigation conducted on the hangenberg black shale hbs from the polish part of the laurussian shelf which provide details about the environmental conditions in existence during deposition of the shale and the role played by anoxic conditions in the mass extinction events that occurred at the end of the devonian times inorganic and organic redox indicators indicate that bottom water redox conditions changed periodically from being mainly anoxic euxinic to oxic or being partially depleted in oxygen u th values above 1 25 ni co values above 7 and v v ni values above 0 8 recorded from the lower part of the hbs all point to anoxic euxinic conditions being present as do high total organic carbon contents toc above 10 and degree of pyritisation dop values around 0 75 however the presence of benthic fauna over the lower part of the hbs attests to opportunistic colonisation of the seafloor during oxic episodes evidence for similar episodes has also been recognised over the middle part of the hbs e g u th values below 1 25 ni co values below 4 v v ni values below 0 8 toc values of 3 to 5 5 and dop values of 0 4 to 0 75 plus the common occurrence of benthic fauna anoxic conditions returned during the deposition of the upper part of the hsb though they were not as well developed as when the lower part of the shale was laid down of interest is the presence of small pyrite framboids and isorenieratene biomarkers in all the analysed samples which suggest that euxinic conditions persisted in the photic zone of the water column a twenty centimetre thick layer of volcanogenic deposits tuffites is present in the middle part of the hbs the geochemical characteristics of which are typical of ocean floor basalts the occurrence of volcanogenic material below and within the hbs together with an absence of calcium carbonate over its upper part the presence of abundant tetrads just above the black shale and a drastic decrease in faunal frequency in the upper part of the hbs imply that volcanism may have caused oceanic acidification or hypercapnia that in turn potentially may have influenced the hangenberg mass extinction event

evidence of recent climatic warming on the eastern antarctic peninsula air temperatures at the stations marambio esperanza and matienzo have been analysed to investigate recent climate change on the eastern part of the antarctic peninsula the data are compared with the station orcadas on the south orkney islands the longest record available in antarctica and with faraday on the western coast of the peninsula though the interannual variability is comparatively high and the stations are located in different climatic regimes a pronounced warming trend shows up in all records at marambio a temperature increase of 1 5 c has been observed since the beginning of the record in 1971 this is of similar magnitude as the increase at the station faraday on the west coast with 2 5 c for the longer period since 1945 the steady retreat and collapse of the northern larsen ice shelf coincided with this warming trend of particular importance for the ice shelf mass balance in this region are the summer temperatures which show a statistically significant warming trend at the stations marambio and esperanza the representativity of the summer temperatures of marambio for northern larsen ice shelf is confirmed by intercomparison with the parallel measurements at matienzo which is located on the ice shelf

variations in snowpack melt on the greenland ice sheet based on passive microwave measurements a simple microwave emission model is used to simulate 37 ghz brightness temperatures associated with snowpack melt conditions for locations across the greenland ice sheet the simulated values are utilized as threshold values and compared to daily gridded smmr and ssm i passive microwave data in order to reveal regions experiencing melt the spatial extent of the area classified as melting is examined on a daily monthly and seasonal may august basis for 1979 91 the typical seasonal cycle of melt coverage shows melt beginning in late april a rapid increase in the melting area from mid may to mid july a rapid decrease in melt extent from late july through mid august and cessation of melt in late september seasonal averages of the daily melt extents demonstrate an apparent increase in melt coverage over the 13 year period of approximately 3 8 annually significant at the 95 confidence interval this increase is dominated by statistically significant positive trends in melt coverage during july and august in the west and southwest of the ice sheet we find that a linear correlation between microwave derived melt extent and a surface measure of ablation rate is significant in june and july but not august so caution must be exercised in using the microwave derived melt extents in august nevertheless knowledge of the variability of snowpack melt on the greenland ice sheet as derived from microwave data should prove useful in detecting climate change in the arctic and examining the impact of climate change on the ice sheet

orbicular volcanic rocks of cerro panizos their origin and implications for orb formation orbs which are a rare occurrence in granitoid rocks are present in a 5 m thick stratum within the cerro panizos ignimbrite and in two post ignimbrite lava flows orbs in volcanic host rocks are extremely rare and have not been described in detail previously the orbs consist of two to five crystalline rings surrounding a xenolithic or orthopyroxene core the rings alternate between bands of large radially oriented plagioclase and orthopyroxene crystals and bands of small tangentially or radially oriented biotite and ilmenite crystals the ignimbrite orbs are associated with two types of pumice 1 a coarsely porphyritic biotite quartz plagioclase dacite with 35 40 crystals found throughout the ignimbrite and 2 a finely porphyritic biotite plagioclase quartz dacite with 75 80 crystals found only in association with the orbs the major and trace element and isotopic compositions of the two pumice types are identical bronzite and quartz megacrysts are also found with the ignimbrite orbs and rarely occur in the overlying sequence plagioclase and orthopyroxene compositions in orb associated rocks exhibit large variations the orb inner rings and finely porphyritic pumice have the most mafic compositions an81 92 and en60 77 coarsely porphyritic pumice and lavas have the most felsic compositions mostly an45 63 and en42 50 and the outer rings of the orbs span the entire gap between the two groups an67 77 and en50 66 the orbs formed in a water rich cupola along the roof of the magma body where the magma was superheated and most crystals were resorbed pressure release related to eruption caused exsolution of water leading to large degrees of undercooling orbs formed rapidly around the few available nuclei as limited mixing with the surrounding coarsely porphyritic magma occurred heterogeneous nucleation in the supercooled magma began forming the abundant small crystals seen in the finely porphyritic pumice eruption of the orbicular dacite occurred when a ring vent conduit tapped the magma in the cupola similar processes may form orbs in plutonic rocks with pressure release related to either eruption or intrusion to higher levels in the crust

the effects of heterogeneity in magma water concentration on the development of flow banding and spherulites in rhyolitic lava abstract this study focuses on the origin of flow banded rhyolites that consist of compositionally similar darker and lighter flow bands of contrasting texture and color infrared radiation was used to obtain fourier transform infrared ftir spectra from which water concentrations were calculated and to map variations in water concentrations across zones of spherulites and glass from the 23 million year old sycamore canyon lava flow of southern arizona lighter colored thicker flow bands consist of gray glass fine grained quartz and large 1 0 to 1 5 mm spherulites darker colored thinner flow bands consist of orange glass and smaller 0 1 to 0 2 mm spherulites the centers of both large and small spherulites are occupied by either 1 a quartz or sanidine crystal 2 a granophyric intergrowth or 3 a vesicle mapping of water concentration dominantly oh in glass and oh and h2o in sanidine crystals illustrates fluctuating water availability during quenching of the host melt textures of large spherulites in the lighter gray bands in some cases indicate complex quenching histories that suggest that local water concentration controlled the generation of glass versus crystals small spherulites in darker orange bands have only one generation of radiating crystal growth both the glass surrounding spherulites and the crystals in the spherulites contain more water in the gray flow bands than in the orange flow bands flow banding in the sycamore canyon lava flow may have originated by the stretching of a magma that contained pre existing zones vesicles or proto vesicles of contrasting water concentration as the magma flowed in the conduit and on the surface variation in the original water concentration in the alternating layers is interpreted to have resulted in differences in undercooling textures in spherulites in the lighter compared to the darker flow bands

telkibanya lava domes lithofacies architecture of a miocene rhyolite field tokaj mountains carpathian pannonian region hungary abstract this work focuses on the miocene telkibanya lava dome field tokaj mountains hungary proposed as an example of poorly investigated lithofacies architecture of old silicic lava dome fields a detailed fieldwork combined with petrographic and radiometric k ar dating analyses allows us the redefinition of the volcano stratigraphy of a 25 km2 area and the recognition of two temporary different generation of domes that grew in a subaerial environment 12 cohesive and autoclastic lithofacies are identified and grouped together to document the internal variability of the domes as well as the erosional phases that affected the lithofacies architecture furthermore stratigraphy lithofacies association and morphology allow recognizing the areal distribution of 5 lithosomes lava flows coulees or domes all these findings represent a major breakthrough in the identification and interpretation of the volcanic processes that control the growth of silicic lava domes and their products in late miocene environment of carpathian pannonian region

cummingtonite and the evolution of the mount st helens washington magma system an experimental study hydrothermal experiments have been conducted on the 3 5 ka cummingtonite bearing yn tephra from mount st helens washington to determine the stability field of cummingtonite in volcanic rocks and to gather additional data on the evolutionary history of the mount st helens magmatic system cummingtonite is not stable in experiments conducted at or above 810 c at pressures 2 o analyses of melt inclusions that yield preeruption melt h 2 o contents of 6 4 wt the yn tephra belongs to a series of cummingtonite bearing dacites that erupted early in the history of mount st helens these early dacites have relatively homogeneous compositions and are characterized by low temperature 800 c high water pressure and high oxygen fugacity nno 1 phenocryst crystallization silicic magmas that erupted after eruption of basaltic andesite at mount st helens 2 3 ka are more heterogeneous in composition and last equilibrated under higher temperatures 900 c lower water pressures and lower oxygen fugacities than the early dacites these changes in the magma chamber conditions appear to have been related to the intrusion of mafic magma into an upper crustal dacitic magma chamber

spherulites and lithophysae 200 years of investigation on high temperature crystallization domains in silica rich volcanic rocks high temperature crystallization domains htcds including spherulites and lithophysae form during cooling of silica rich lava and welded ignimbrites spherulites grow in silicate melts or hot glass and they display a radiating or microcrystalline texture typically consisting of cristobalite tridymite and sanidine lithophysae are htcds comprising one or more cavities this contribution reviews the research and discussions on htcds carried out over the last 200 years the emphasis here is on lithophysae and summarizes current knowledge of their formation a number of parameters influence the initiation and growth of lithophysae as well as their shapes and internal textures the most likely cause of cavity formation is transient tensional stress that produces a mechanical opening and widening at the interface between the crystallization front and the host melt e g where t tg cavity growth and expansion forced by rising vapor pressure is considered less important in some cases further growth of htcd cavities results from vapor phase corrosion and brecciation

spherulitic aphyric pillow lobe metatholeiitic dacite lava of the timmins area ontario canada a new archean facies formed from superheated melts fragmental rocks of the v10 units of the vipond formation of the tisdale assemblage previously have been identified as pillow basalts but many samples are shown to be intermediate to felsic in character likely tholeiitic dacite in composition specifically the v10b unit is mapped as a pillow lobe dacite aside from being more geochemically evolved in terms of their immobile trace elements these rocks differ from typical pillow basalts in that they have more abundant primary breccia and hyaloclastite the pillow lobes are contorted having been folded in a plastic state and are zoned typically having a spherulite rich core moreover the flows are aphyric interpreted to mean that they were erupted in a superheated state this along with their pillow lobe nature demonstrates that they were erupted as relatively low viscosity melts for such silicic compositions interaction with water quenched the outer pillow lobe and contributed to the formation of the abundant breccia the fact that the melt was crystal and microlite free inhibited crystal growth such that the bulk of the lobes were quenched to crystal free glass nucleation occurred only in the cores where cooling rates were lower in comparison to the medial and exterior areas of the pillow lobes although in the cores crystal growth rates were high so that abundant spherulite formation took place the flows are exposed over a strike length of more than 10 km and are interpreted to be continuous and to have resulted from fissure eruptions the resulting porous permeable high fe mg high surface area glassy rocks may have been ideal for channeling and reacting with gold bearing hydrothermal solutions descriptions of most other archean subaqueous felsic lobes document that the lavas were phyric and that spherulites formed near the external lobe margin the distinctly different zoning of the v10b pillow lobes suggests that they constitute a new archean facies formed from superheated melts

paleo pedological record of the rocourt pedosequence at veldwezelt hezerwater belgian pleistocene loess belt part 2 soil formation abstract as the environment influences soil formation quaternary loess paleosols provide an important yet complex source on former climate and vegetation conditions this study revises the paleopedological record of the rocourt complex the pedostratigraphic marker for the eemian and early weichselian in the belgian loess belt depth functions were established from an exceptionally well preserved in situ sequence based on soil micromorphological features total element contents iron fractions and carbon content a reconstruction was made of the polygenetic formation of the rocourt soil results indicate that only by combining multiple soil features consistent information could be obtained furthermore this study shows that cryogenic processes transport of colloids iron dynamics redox conditions organic matter formation and biological activity were major soil forming processes the hypothesis of six major stages of soil formation under varying climatic conditions was most supported by the data during the warm to temperate oceanic climate of the eemian a strongly weathered argic horizon was formed this horizon was later disrupted by reticulate ice segregation and stagnogley during the severe and prolonged cold conditions of the first cold stadial following the eemian weak soil formation during the relatively short continental st germain i interstadial subsequently formed cambic soil properties and a humiferous horizon in a mixture of local and new sediments these soils were disrupted by fragipan formation with its associated cryogenic structure banded eluviation and redoxfront during the succeeding stadial with periglacial conditions during the st germain ii another a horizon formed in new calcareous material during more stable climatic conditions allowing organic matter build up eluviation of smectite and formation of pedogenetic iron during the evolution from this warmer climate with forest or forested steppe to eventually periglacial open tundra an accretionary humiferous soil concluded the last episode of soil formation before the onset of pleniglacial weichselian conditions

δd and δ18o variations of the magmatic system beneath deception island volcano antarctica implications for magma ascent and eruption forecasting abstract geochemistry of volatiles in active volcanoes provides insights into the magmatic processes and evolution at depth such as magma evolution and degassing which can be implemented into volcanic hazards assessment deception island is one of the most active volcanoes in antarctica with more than twenty explosive eruptions documented over the past two centuries hydrogen and oxygen isotopic variations in the volatiles trapped in the deception island rocks glass and melt inclusions in phenocrysts provide essential information on the mechanisms controlling the eruptive history in this volcanic suite thus understanding the petrological and related isotopic variations in the island has the potential to foresee the possible occurrence and its main eruptive features of a future eruption the new isotopic results of this study combined with exhaustive petrologic knowledge reveal in deception island i fast ascent and quenching of most magmas preserving pre eruptive magmatic signal of water contents and isotopic ratios with local modification by rehydration due to glass exposition to seawater and by meteoric and fumarolic waters ii a plumbing system s variable with time and currently dominated by closed system degassing leading to explosive eruptions iii control on the interactions of ascending magmas with the surface waters producing hydrovolcanic activity throughout the two main fault systems in deception island and at different magma stagnation depths these results can be considered in further studies of volcanic monitoring to improve the capability to interpret geophysical data and signals recorded during volcanic unrest episodes and hence forecast volcanic eruptions and related hazards

experimental quantification of plagioclase crystal size distribution during cooling of a basaltic liquid an experimental study has been conducted to constrain how thermal history controls crystal size distribution csd of plagioclase in cooling basalts data from all experiments are dominated by a log linear segment of decreasing number density with increasing crystal size consistent with observations in many natural rocks the slope of the csd is found to be a function of cooling rate faster cooling leading to greater slopes at constant cooling rate the csds flatten as temperature decreases and are sometimes kinked characteristics consistent with independent textural observations that crystal agglomeration contributes significantly to crystal growth a downturn is observed toward small size which suggests ostwald ripening furthermore we find that thermal history above the liquidus has a major influence on csds and on the temperatures of phase appearance we conclude that near the liquidus heterogeneous nucleation typically dominates

new data on magmatic h 2 o contents of pantellerites with implications for petrogenesis and eruptive dynamics at pantelleria infrared spectroscopic analyses of melt inclusions in quartz phenocrysts from pantellerites erupted at pantelleria italy show that the magmas contained moderate pre eruptive h2o contents ranging from 1 4 to 2 1 wt melt h2o concentrations increase linearly with incompatible elements demonstrating that h2o contents were not buffered significantly during fractionation by any crystalline or vapor phase the relatively low h2o contents of pantellerites are consistent with an origin by partial melting of alkali gabbros rather than fractional crystallization of basalt preeruptive h2o concentrations do not correlate with the volume or explosivity of pantellerite eruptions decompression history is critical in determining the style of pantellerite and other eruptions

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

hydrothermal synthesis of hematite spherules and jarosite implications for diagenesis and hematite spherule formation in sulfate outcrops at meridiani planum mars we synthesized hematite spherules whose mineralogic chemical and crystallographic properties are strikingly similar to those for the hematite rich spherules in lag deposits on the surface and embedded in outcrops at meridiani planum mars the spherules were synthesized in the laboratory along with hydronium jarosite and minor hydronium alunite from fe al mg s cl acid sulfate solutions under hydrothermal conditions the reaction sequence was 1 precipitation of hydronium jarosite 2 jarosite dissolution and precipitation of hematite spherules and 3 precipitation of hydronium alunite upon depletion of hydronium jarosite the spherules exhibit a radial growth texture with the crystallographic c axis aligned along the radial direction so that thermal emission spectra have no hematite emissivity minimum at 390 cm 1 our experiments show that hydrothermal acid sulfate solutions are a pathway for formation of jarosite and the hematite spherules at meridiani planum mars

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

antarctic surface melting dynamics enhanced perspectives from radar scatterometer data 1 antarctic ice sheet surface melting can regionally influence ice shelf stability mass balance and glacier dynamics in addition to modulating near surface physical and chemical properties over wide areas here we investigate variability in surface melting from 1999 to 2009 using radar backscatter time series from the seawinds scatterometer aboard the quikscat satellite these daily continent wide observations are explored in concert with in situ meteorological records to validate a threshold based melt detection method radar backscatter decreases during melting are significantly correlated with in situ positive degree days as well as meltwater production determined from energy balance modeling at neumayer station east antarctica these results support the use of scatterometer data as a diagnostic indicator of melt intensity i e the relative liquid water production during melting greater spatial and temporal melting detected relative to previous passive microwave based studies is attributed to a higher sensitivity of the scatterometer instrument continental melt intensity variability can be explained in part by the dynamics of the southern annular mode and the southern oscillation index and extreme melting events across the ross ice shelf region may be associated with el nino conditions furthermore we find that the antarctic peninsula accounts for only 20 of antarctic melt extent but greater than 50 of the total antarctic melt intensity over most areas annual melt duration and intensity are proportional however regional and localized distinctions exist where the melt intensity metric provides greater insight into melting dynamics than previously obtainable with other remote sensing techniques

comparison of laser grain size analysis with pipette and sieve analysis a solution for the underestimation of the clay fraction classically the grain size of soil and sediment samples is determined by the sieve method for the coarse fractions and by the pipette method based on the stokes sedimentation rates for the fine fractions results from the two methods are compared with results from laser diffraction size analysis which is based on the forward scattering of monochromatic coherent light from a point of view of laboratory efficiency the laser sizing technique is far superior accuracy and reproducibility are shown by measurements on certified materials it appears that laser grain size measurements of certified materials correspond very well with the certificated measurements tests were also done on a set of randomly selected sediments of fluvial aeolian and lacustrine origin except for the 2 m clay fraction there is a coarsening of the mean diameter of one to two size classes 0 25 caused by the non sphericity of the particles the platy form of the clay particles induces considerable differences eight size classes between pipette and laser measurements the 2 m grain size defined by the pipette method corresponds with a grain size of 8 m defined by the laser particle sizer for the studied sediments using a higher grain size level for the clay fraction when laser analysis is applied enables workers in the geological and environmental field to compare classical pipette analysis with a laser sizing technique

near liquidus growth of feldspar spherulites in trachytic melts 3d morphologies and implications in crystallization mechanisms the nucleation and growth processes of spherulitic alkali feldspar have been investigated in this study through x ray microtomography and electron backscatter diffraction ebsd data here we present the first data on shape preferred orientation spo and crystal preferred orientation cpo of alkali feldspar within spherulites the analysis of synchrotron x ray microtomography and ebsd datasets allowed us to study the morphometric characteristics of spherulites in trachytic melts in quantitative fashion highlighting the three dimensional shape preferred orientation branching of lamellae and crystal twinning providing insights about the nucleation mechanism involved in the crystallization of the spherulites the nucleation starts with a heterogeneous nucleus pre existing crystal or bubble and subsequently it evolves forming bow tie morphologies reaching radially spherulitic shapes in few hours since each lamella within spherulite is also twinned these synthetic spherulites cannot be considered as single nuclei but crystal aggregates originated by heterogeneous nucleation a twin boundary may have a lower energy than general crystal crystal boundaries and many of the twinned grains show evidence of strong local bending which combined with twin plane creates local sites for heterogeneous nucleation this study shows that the growth rates of the lamellae 10 6 10 7 cm s in spherulites are either similar or slightly higher than that for single crystals by up to one order of magnitude furthermore the highest volumetric growth rates 10 11 10 12 cm3 s show that the alkali feldspar within spherulites can grow fast reaching a volumetric size of 10 m3 in 1 s

mountain glaciers and ice caps around antarctica make a large sea level rise contribution the intergovernmental panel on climate change ipcc estimates that the sum of all contributions to sea level rise for the period 1961 2004 was 1 1 0 5 mm a 1 leaving 0 7

ignimbrite correlation using whole rock geochemistry an example from the sulcis sw sardinia italy ignimbrites are useful chronological markers in the geological record at local and regional scales they also provide information on the dynamics of the eruption that produced them making their study of great importance in terms of volcanic hazard assessment however their study is usually hampered by their lateral variation and discontinuity when stratigraphic and lithologic criteria are not sufficient for correlation purposes the use of multiple complementary correlation tools may be necessary to correctly determine their areal extension volume and facies variations whole rock geochemistry is considered one of the less reliable correlation techniques due to the pyroclastic nature of these deposits and their emplacement dynamics these may introduce vertical and horizontal geochemical heterogeneity in the final deposit in addition the occurrence of zoned ignimbrites due to magma supply of changing composition is common in this work we show that if appropriately used whole rock geochemistry can be a valid and highly useful tool for ignimbrite correlation we provide an example from the study of an ignimbrite sequence containing 18 units sensu lato in the sulcis region sw sardinia italy a protocol has been developed for unit recognition based on successive simple binary diagrams where the whole rock composition of a problem sample can be plotted immobile trace elements have been preferentially used to minimize effects of element mobilization associated with alteration and weathering the diagrams provided here are designed for the sulcis but the methodology followed to develop them may be applied to other study areas

crystallization kinetics of rhyolitic melts using oxygen isotope ratios crystals provide themeans to understand igneous systems but natural constraints on crystallization kinetics are rare because thermal conditions and crystallization timescales are typically unknown oxygen isotope ratios in quartz and alkali feldspar crystals in spherulites provide a natural record of the temperature interval of crystallization and crystal growth rates in rhyolitic melts oxygen isotope compositions in both phases change progressively with position from the spherulite core to rim quartz o increases from 5 0 0 3 in the core to 5 6 0 3 at the rims whereas alkali feldspar decreases from 3 7 0 4 in the core to 2 7 0 9 at the rims fractionation therefore increases from 1 3 0 7 in the cores to 2 9 1 1 at the rims oxygen isotope thermometry tracks crystallization temperature with position spherulites nucleate at 578 160 c and continue to grow until 301 88 c the in situ analyses demonstrate that spherulites self contain a record of their thermal history and that of the host lava

experimental determination of liquidus h 2 o contents of haplogranite at deep crustal conditions the liquidus water content of a haplogranite melt at high pressure p and temperature t is important because it is a key parameter for constraining the volume of granite that could be produced by melting of the deep crust previous estimates based on melting experiments at low p 0 5 gpa show substantial scatter when extrapolated to deep crustal p and t 700 1000 c 0 6 1 5 gpa to improve the high p constraints on h2o concentration at the granite liquidus we performed experiments in a piston cylinder apparatus at 1 0 gpa using a range of haplogranite compositions in the albite ab naalsi3o8 orthoclase or kalsi3o8 quartz qz sio2 h2o system we used equal weight fractions of the feldspar components and varied the qz between 20 and 30 wt in each experiment synthetic granitic composition glass h2o was homogenized well above the liquidus t and t was lowered by increments until quartz and alkali feldspar crystalized from the liquid to establish reversed equilibrium we crystallized the homogenized melt at the lower t and then raised t until we found that the crystalline phases were completely resorbed into the liquid the reversed liquidus minimum temperatures at 3 0 4 1 5 8 8 0 and 12 0 wt h2o are 935 985 875 900 775 800 725 775 and 650 675 c respectively quenched charges were analyzed by petrographic microscope scanning electron microscope sem x ray diffraction xrd and electron microprobe analysis empa the equation for the reversed haplogranite liquidus minimum curve for ab36 25or36 25qz27 5 wt basis at 1 0 gpa is t 0 0995 w text h 2 text o 3 5 0242w text h 2 text o 2 88 183 w text h 2 text o 1171 0 for 0 le w text h 2 text o le 17 wt and t is in c we present a revised p t diagram of liquidus minimum h2o isopleths which integrates data from previous determinations of vapor saturated melting and the lower pressure vapor undersaturated melting studies conducted by other workers on the haplogranite system for lower h2o 5 8 wt and higher temperature our results plot on the high end of the extrapolated water contents at liquidus minima when compared to the previous estimates as a consequence amounts of metaluminous granites that can be produced from lower crustal biotite amphibole gneisses by dehydration melting are more restricted than previously thought

spherulite crystallization induces fe redox redistribution in silicic melt rhyolitic obsidians from krafla volcano iceland record the interaction between mobile hydrous species liberated during crystal growth and the reduction of ferric iron in the silicate melt we performed synchrotron ftir and xanes measurements along a transect extending from a spherulite into optically distinct colorless and brown glass zones measurements show that the colorless glass is enriched in oh groups and depleted in ferric iron while the brown glass shows the opposite relationship the color shift between brown and clear glass is sharp suggesting that the colorless glass zone was produced by a redox front that originated from the spherulite margin and moved through surrounding melt during crystallization we conclude that the most likely reducing agent is hydrogen produced by magnetite crystallization within the spherulite the krafla obsidians dramatically capture redox disequilibrium on the micoscale and highlight the importance of hydrous fluid liberation and late stage crystallization to the redox signature of glassy lavas

assessment and development of snowmelt retrieval algorithms over antarctica from k band spaceborne brightness temperature 1979 2008 abstract results from several previously published algorithms for wet snow detection in antarctica from k band spaceborne brightness temperature are compared and evaluated vs estimates of wet snow conditions from ground measurements in addition a new physically driven algorithm in which the detectable liquid water content is assumed constant is proposed and assessed all algorithms are also evaluated by analyzing their results during collapses of ice shelves two algorithms are selected for deriving updated trends of melting index mi the number of melting days times the area subject to melting between 1979 and 2008 over the whole antarctica and at sub continental scales in the first algorithm wet snow is identified when brightness temperature exceeds the mean of winter brightness temperature plus 30 k and the second is the new model based approach described here both negative and positive mi trends are obtained depending on the algorithm used a high number of melting days up to 100 days are detected over the wilkins ice shelf the peninsula and the george vi ice shelf over east antarctica the west and amery ice shelves are subject to melting for a maximum of approximately 50 days positive trends of number of melting days are detected over most of the west antarctica with peak values up to 1 2 days year over the larsen c ice shelf 1 8 days year over the george vi ice shelf and 0 55 days year over the wilkins ice shelf area the correlation between mi values and december january dj averaged air surface temperature over selected locations show values ranging between 0 8 and 0 4 results suggest that a 1 c increase in the monthly averaged dj air surface temperature corresponds to an average mi increase of approximately 2 106 km2 day

characteristics and factors controlling reservoir space in the cretaceous volcanic rocks of the hailar basin ne china abstract we discuss the types capacity formation mechanisms and main controlling factors of oil and gas reservoir spaces in early cretaceous acidic volcanic rocks of the hailar basin ne china where asphalt bearing volcanic rocks are exposed at the surface we have made systematic observations and analyses on macroscopic outcrop and microscopic optical microscope sem and fluorescence analyzer scales acidic volcanic reservoirs contain reservoir spaces comprising primary and secondary porosity which are dependent on primary and secondary processes during their formation primary porosity typically accounts for a large contribution to enhanced reservoir quality more importantly it is a prerequisite for migration alteration and filling by inorganic fluids and petroleum which provides a foundation for the development of secondary porosity the development of secondary porosity especially alteration related pores can significantly modify the petrophysical characteristics of a rock in addition to the processes of porosity formation the quality of volcanic reservoirs is influenced by factors such as lithology lithofacies and tectonism lithological differences result in variations in the type and intensity of pore development pyromeride and glassy lava commonly exhibit high reservoir capacities the porosity of different lithofacies typically follows the order of conduit facies extrusive facies effusive facies explosive facies tectonism is necessary for the formation of reservoir spaces and for the migration permeation and accumulation of oil and gas reservoir quality is often positively correlated with the size and density of tectonic fractures

cooling kinetics experiments on different stromboli lavas effects on crystal morphologies and phases composition abstract controlled cooling experiments at atmospheric pressure and fo2 of the nno buffer were performed on three stromboli lavas of calcalkaline ca high k calcalkaline hkca and shoshonitic sho affinities the experiments were conducted at cooling rates of 900 c h fast cooling rate fcr and 1 c h slow cooling rate scr respectively to investigate the kinetic factors governing textural and compositional features such as phase growth morphology phase relations and phase compositions the experiments produced different types of textures as both the cooling rate and the quenching temperatures were varied in general fcr experiments show a decrease of crystal size as well as a change in crystal shape from euhedral to granular to skeletal up to dendritic morphology with decreasing temperatures scr experiments produce less variable crystal size and crystal morphology measurements of plagioclases indicate that the crystal size and calculated crystal growth are functions of cooling rate crystal growth rates are about two orders of magnitude higher in fcr experiments than scr ones such textural responses are in agreement with the empirical calibration based on the plagioclase size dependence on cooling rate developed by cashman 1993 experimental phase relations display three main features of the crystallization process 1 the delay in the crystallization of the liquidus phase in the fcr experiments with respect to the scr ones 2 crystallization controlled by the multiphase cotectic relations plagioclase pyroxenes olivine is more enhanced for fcr experiments compared to that of scr ones at the lowest experimental temperature 1100 c 3 crystallization of augite and pigeonite is sensitive to cooling rate and system compositions pigeonite not found in the natural rocks crystallizes in the ca sample across scr and fcr runs and in the hkca sample just in the scr experiments fcr and scr experiments produce similar liquid lines of descent for both ca and hkca starting materials suggesting that the processes of nucleation and growth play reciprocal roles through mass balance as cooling rate varies this is not true for the sho composition where the trends of melt composition appear to be especially influenced by the different amounts of olivine crystallization at the different cooling rates data on mineral compositions show that plagioclase and clinopyroxene are the phases more strongly affected by the cooling gradients crystals from scr experiments and to a lesser extent from fcr experiments show zoning patterns mainly at the lowest experimental temperature

petrology and geochemistry of the orbicular granitoid of caldera northern chile models and hypotheses on the formation of radial orbicular textures abstract the orbicular granitoid of caldera located at the northern part of the chilean coastal range is a spectacular example of radial textures in orbicular structures the orbicular body crops out as a 375 m 2 tabular to lensoidal intrusive sheet emplaced in the lower jurassic relincho pluton the orbicular structures are 3 7 cm in diameter ellipsoids hosted in a porphyritic matrix the orbicules are comprised by a qtz dioritic core 3 5 cm in diameter composed by pl hbl qtz bt kfs with equiaxial textures and a gabbroic shell 2 3 cm in diameter characterized by feathery and radiate textures with a plagioclase hornblende paragenesis the radial shell crystals are rooted and orthogonally disposed in the irregular contact with the core the radial shell called here inner shell is in contact with the granodioritic equiaxial interorbicular matrix through a 2 3 mm wide poikilitic band around the orbicule outer shell the outer shell and the matrix surrounding the orbicules are characterized by the presence of large hornblende and biotite oikocrystals that include fine grained rounded plagioclase and magnetite the oikocrystals of both the outer shell and the matrix have a circumferential arrangement around the orbicule i e orthogonal to the radial inner shell the coarse grained granodioritic interorbicular matrix present pegmatitic domains with large acicular hornblende and k feldspar megacrysts this work presents a review of the textural characteristics of the orbicules and a complete new mineral and whole rock geochemical study of the different parts of the orbicular granitoid together with thermobarometric and crystallographic data and theoretical modeling of the crystallization and element partitioning processes we propose a model for the formation of the orbicular radial textures consisting of several processes that are suggested to occur fast and consecutively superheating volatile exsolution undercooling geochemical fractionation and columnar and equiaxial crystallization according to the obtained results the formation of the orbicular granitoid of caldera may have initiated 1 during the generation of a magmatic fracture in the crystallization front of the relincho pluton where the water released by the host crystal mush was dissolved in the new batch of dioritic magma 2 the high influx of water rich liquids induced superheating conditions in the newly intruding magma that became a depolymerized liquid where the only solid particules were the small irregular fragments of the host mush dragged from the fracture walls 3 volatile exsolution promoted crystallization under undercooling conditions 4 undercooling and nucleation around the core cold germs involved the physical and geochemical fractionation between two sub systems a gabbroic sub system that comprises the solid paragenesis with a residual water rich liquid and a granodioritic sub system 5 the orbicules including core and inner shell behaved as viscous bodies crystals residual liquid floating in the granodioritic magma 6 higher undercooling rates occurred at the starting stage close to the liquidus promoting columnar crystallization around the cores and formation of the shells conversely in the granodioritic matrix sub system equiaxial crystallization was promoted by low relative crystallization rates 7 the rest of the crystallization process evolved later in the outer shell and the matrix as suggested by the poikilitic textures observed in both sides of the orbicule contact and under conditions close to the solidus of both sub systems shell and matrix the water rich residual liquid expelled during the orbicular shell crystallization was mingled with the partially crystallized matrix magma generating the pegmatitic domains with large kfs megacrysts

climate variability in the amundsen and bellingshausen seas satellite data reveal a 20 decline in sea ice extent in the amundsen and bellingshausen seas in the two decades following 1973 this change is negatively correlated with surface air temperatures on the west side of the antarctic peninsula which have increased 0 58c decade21 since the mid 1940s the recession was strongest during summer when monthly average minima in 1991 92 removed much of the incipient multiyear ice over the continental shelf this would have lowered the regional mean ice thickness impacting snow ice formation brine production and vertical heat flux the northern ice edge contracted by 18 of latitude in all seasons from 1973 79 to 1987 93 returning toward mean conditions in 1993 95 the decline included multiyear cycles of several years in length superimposed on high interannual variability a review of atmospheric forcing shows winds consistent with mean and extreme ice extents and suggests links to larger scale circulation changes in the south pacific historical ocean measurements are sparse in this sector but mixed layer depths and upper pycnoclines beneath the sea ice resemble those in the weddell sea weaker surface currents or changes in the upwelling of circumpolar deep water on the continental shelf could have contributed to the anomaly persistence

heavy metal distribution and environmental status of doon valley soils outer himalaya india doon valley is surrounded by two major river systems ganga and yamuna on either side with a water divide passing nearly across the centre of the valley and is sandwiched between two mountain ranges in the fragile ecological systems of the himalayan foothills in total 398 soil samples were collected from the valley in a grid pattern 1 sample per 2 km2 and investigated for their heavy metal cr cu ni pb and zn abundances that are environmentally sensitive comparison of the heavy metal abundances with the contamination threshold values ctv revealed that most of these elemental abundances in doon valley soils fall well within the range of the uncontaminated to slightly contaminated category in the case of cr and ni a sizeable number of samples exceeded the ctv 250 and 100 mg kg 1 respectively with an overall background value of 109 and 52 mg kg 1 respectively sites of high cr and ni mostly occur in the ganga catchment gc sector that includes even relatively undisturbed forestland the source of this contamination is attributed to geological factors which indicate contribution from the mafic volcanics of the lesser himalaya this is also consistent with the distribution pattern of mn and fe though their abundance levels are not alarming the background concentration of pb is low 22 mg kg 1 in doon valley soils however signs of gradual pb contamination are palpable in and around the centre of the dehra dun city and along the highways aluminium normalized heavy metal ratios were found to exhibit narrow variability in the case of cu ni and cr and had good correlation with al indicating their affinity and association with the clay minerals on the other hand pb and zn seem to be associated with non silicate sources

local background concentrations of trace elements in soils a case study in the grand duchy of luxembourg abstract background concentration values of trace elements were determined for soils in the southern part of the grand duchy of luxembourg which are developed on the bituminous shale bs the so called bifrons shale and the minette m fe oolitic sandstone substrates sampling sites with minimal anthropogenic influence were selected and soil profile samples were analysed for major and trace element contents a clear distinction is seen between the trace element content of the soils developed on the minette sandstone on the one hand and those developed on shales on the other hand for the minette soil samples most elements are present in concentrations exceeding those reported in literature for soils developed upon sandstones with for example values of up to 278 mg kg 1 as median value 123 mg kg 1 287 mg kg 1 cr median value 126 mg kg 1 and 95 mg kg 1 co median value 33 mg kg 1 in the shale soil samples concentrations are generally lower except for cu and mo these elements reach maxima of up to 66 mg kg 1 cu median value 41 mg kg 1 and 59 mg kg 1 mo median value 26 mg kg 1 the results confirm the importance of determining background concentrations locally bivariate analysis shows a linear relationship between fe content and elements such as as co and ni for the minette soils no relationship is found between trace element concentrations and clay or organic carbon oc content but this could be due to the limited variation of these factors among the studied soils a reconnaissance study with regard to the availability of the trace elements in the minette soil samples shows that these elements are quite immobile and hence of minimal threat to the ecosystem

the effects of undercooling and deformation rates on the crystallization kinetics of stromboli and etna basalts we have investigated the effect of undercooling and deformation on the evolution of the texture and the crystallization kinetics of remelted basaltic material from stromboli pumice from the march 15 2007 paroxysmal eruption and etna 1992 lava flow isothermal crystallization experiments were conducted at different degrees of undercooling and different applied strain rate t 1 157 1 187 c and dot gamma i 4 26 s 1 for stromboli t 1 131 1 182 c and dot gamma i 0 53 s 1 for etna melt viscosity increased due to the decrease in temperature and the increase in crystal content the mineralogical assemblage comprises sp plg dominant cpx with an overall crystal fraction between 0 06 and 0 27 increasing with undercooling and flow conditions both degree of undercooling and deformation rate deeply affect the kinetics of the crystallization process plagioclase nucleation incubation time strongly decreases with increasing t and flow while slow diffusion limited growth characterizes low t low deformation rate experiments both stromboli high strain rate and etna low strain rate plagioclase growth rates g display relative small variations with stromboli showing higher values 4 8 1 9 10 9 m s 1 compared to etna 2 1 1 6 10 9 m s 1 plagioclase average nucleation rates j continuously increase with undercooling from 1 4 106 to 6 7 106 m 3 s 1 for stromboli and from 3 6 104 to 4 0 106 m 3 s 1 for etna the extremely low value of 3 6 104 m 3 s 1 recorded at the lowest undercooling experiment for etna t 20 c indicates that the crystallization process is growth dominated and that possible effects of textural coarsening occur g values obtained in this paper are generally one or two orders of magnitude higher compared to those obtained in the literature for equivalent undercooling conditions stirring of the melt simulating magma flow or convective conditions facilitates nucleation and growth of crystals via mechanical transportation of matter resulting in the higher j and g observed any modeling pertaining to magma dynamics in the conduit e g ascent rate and lava flow emplacement e g flow rate p hoehoe a transition should therefore take the effects of dynamic crystallization into account

ca isotopes record rapid crystal growth in volcanic and subvolcanic systems kinetic calcium isotope effects can be used as growth rate proxies for volcanic and subvolcanic minerals here we analyze ca isotopic compositions in experimental and natural samples and confirm that large kinetic effects 2 can occur during magmatic plagioclase crystallization experiments confirm theoretical predictions that disequilibrium isotope effects depend mainly on the rates for crystal growth relative to liquid phase ca diffusivity r d plagioclase phenocrysts from the 1915 mount lassen rhyodacite eruption the 650 y old deadman creek dome eruption and several mafic subvolcanic orbicules and plagioclase comb layers from northern california have disequilibrium ca isotopic compositions that suggest rapid crystal growth rates 1 cm y to 15 cm y the ca isotope results combined with complementary crystal size distribution analyses suggest that magmatic rejuvenation and eruption events as reflected in crystal growth times can be as short as 10 3 y although mafic systems are predicted to have shorter magmatic rejuvenation periods we find similarly short timescales in both mafic and silicic systems these results are consistent with a growing body of evidence suggesting that dominantly crystalline volcanic magma reservoirs can be rapidly reactivated by the injection of fresh magma prior to eruption by focusing on a common mineral such as plagioclase this approach can be applied across all major magmatic compositions suggesting that ca isotopes can be used as a tool for investigating the dynamics and timing of volcanic eruptions

new reconstruction of antarctic near surface temperatures multidecadal trends and reliability of global reanalyses a reconstruction of antarctic monthly mean near surface temperatures spanning 1958 2012 is presented itsprimarygoalistotakeadvantageofarecentlyrevisedkeytemperaturerecordfromwestantarctica byrd to shed further light on multidecadal temperature changes in this region the spatial interpolation relies on a kriging technique aided by spatiotemporal temperature covariances derived from three global reanalyses the european centre for medium range weather forecasts ecmwf interim re analysis erainterim modern era retrospective analysis for research and applications merra and climate forecast system reanalysis cfsr for 1958 2012 the reconstruction yields statistically significant annual warming in the antarctic peninsula and virtually all of west antarctica but no significant temperature change in east antarctica importantly the warming is of comparable magnitude both in central west antarctica and in most of the peninsula rather than concentrated either in one or the other region as previousreconstructions have suggested the transantarctic mountains act for the temperature trends as a clear dividing line between east and west antarctica reflecting the topographic constraint on warm air advection from the amundsen sea basin the reconstruction also serves to highlight spurious changes in the 1979 2009 time series of the three reanalyses that reduces the reliability of their trends illustrating a longstanding issue in high southern latitudes the study concludes with an examination of the influence of the southern annular mode sam on antarctic temperature trends the results herein suggest that the trend of the sam toward its positive phase in austral summer and fall since the 1950s has had a statistically significant cooling effect not only in east antarctica as already well documented and but also only in fall in west antarctica

geological factors affecting the distribution of trace metals in glacial sediments of central newfoundland in central newfoundland nts 12a 10 15 16 2h 1 as pb and zn concentrations in the clay sized 1000 ppm exceeding levels commonly set for purposes of environmental protection near pb zn mines at buchans geochemical variation with depth reflects the dispersal of detritus from mineralized bedrock and differences in sediment type and provenance there surface sediments are rich in granitic debris derived from the topsails igneous terrane 5 km north of buchans and contain low concentrations of trace metals these sediments are compositionally unrelated to either buchans group volcanic rock or an underlying older till enriched in sulphide minerals and trace metals metal rich till extending up to 10 km southwest of buchans results from combined glacial and debris flow transport related to two distinct geological events trace metals are enriched two to fourfold in the clay sized fraction of till compared to the silt and clay sized and are associated with al and mg bearing minerals that preferentially concentrate in the clay fraction the geochemistry of the silt and clay sized fraction can approximate that of the 2 mm fraction background variations in till illustrate the important role of a geological framework to the interpretation of geochemical surveys and the origins of trace metals in the environment

magma fragmentation in highly explosive basaltic eruptions induced by rapid crystallization basaltic eruptions are the most common form of volcanism on earth and planetary bodies the low viscosity of basaltic magmas inhibits fragmentation which favours effusive and lava fountaining activity yet highly explosive hazardous basaltic eruptions occur the processes that promote fragmentation of basaltic magma remain unclear and are subject to debate here we used a numerical conduit model to show that a rapid magma ascent during explosive eruptions produces a large undercooling in situ experiments revealed that undercooling drives exceptionally rapid in minutes crystallization which induces a step change in viscosity that triggers magma fragmentation the experimentally produced textures are consistent with basaltic plinian eruption products we applied a numerical model to investigate basaltic magma fragmentation over a wide parameter space and found that all basaltic volcanoes have the potential to produce highly explosive eruptions the critical requirements are initial magma temperatures lower than 1 100 c to reach a syn eruptive crystal content of over 30 vol and thus a magma viscosity around 105 pa s which our results suggest is the minimum viscosity required for the fragmentation of fast ascending basaltic magmas these temperature crystal content and viscosity requirements reveal how typically effusive basaltic volcanoes can produce unexpected highly explosive and hazardous eruptions volcanoes that typically erupt effusively can generate highly explosive eruptions of basaltic lava under specific temperature and viscosity conditions suggest crystallization experiments combined with numerical models of magma fragmentation

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

pre eruptive water content of rhyolitic magmas as determined by ion microprobe analyses of melt inclusions in phenocrysts abstract the ion microprobe was used to analyze trapped melt inclusions in phenocrysts from two rhyolitic eruptions for h2o f and incompatible trace elements eleven melt inclusions from phenocrysts in air fall tephra from obsidian dome near long valley usa gave an average of 4 1 1 2 wt h2o and showed large variations in f and incompatible trace elements reflecting a complex history reported to involve mixing of at least two magma types eight inclusions in phenocrysts from the taupo ultraplinian event new zealand gave 4 5 0 8 wt h2o with small variations in the other elements analyzed measured water contents are similar to earlier estimates of the pre eruptive water contents of these and similar rhyolites and major and trace element analyses of inclusions compare closely with bulk analyses suggesting that the analyses of inclusions represent the chemistry of the magma at the time of entrapment

crystallization kinetics in continuous decompression experiments implications for interpreting natural magma ascent processes decompression experiments were performed to study the kinetics of plagioclase crystallization during ascent of hydrous rhyodacite magma these experiments differ from previous studies in that they employ a continuous rather than stepwise pressure time trajectory four series of experiments were performed at rates of 0 5 10mpa h corresponding to ascent rates of 0 007 0 14 m s experiments quenched along each decompression path allow snapshot style monitoring of progressive crystallization as expected rates of plagioclase nucleation and growth depend strongly on decompression rate regardless of decompression rate approximately equal volumes of feldspar crystallize during a given decompression interval even when the observed crystallinity is lower than the equilibrium crystallinity apparently a constant degree of solidification is maintained by a crystallization mechanism striking a shifting balance between nuclei formation and growth of existing crystals other key results pertain to the efficacy with which experimental results allow interpretation of the decompression histories of natural rocks feldspar microlites do not maintain chemical equilibrium with melt they are more anorthite rich than equilibrium plagioclase suggesting that interpretations of magma ascent processes in nature require comparisons with dynamic rather than static phase equilibrium experiments although decompression rate is an important element controlling final textures in volcanic rocks no single compositional or textural parameter uniquely records this rate of the criteria examined microlite number density and morphology are the best indicators of magma decompression rate based on a small number of comparisons between continuous and multi step decompression style at the same time integrated decompression rate 1mpa h decompression path evidently influences crystal texture with stepwise decompression yielding textures correlative with faster decompression than indicated by the time integrated decompression rate thus consideration of magma ascent style in addition to rate will undoubtedly strengthen the interpretive power of experimental studies for constraining natural magma ascent processes

persistent surface snowmelt over antarctica 1987 2006 from 19 35 ghz brightness temperatures 1 persistent melting e g continuing for more than three days or for one consecutive day and night is mapped in antarctica 1987 2006 using night and day time special sensor microwave imager brightness temperatures tb at 19 35 ghz horizontal polarization snowmelt is indicated when tb and relative daily difference exceed threshold values respectively tc and t computed for each pixel and year or when both daytime and nighttime tb exceed tc results from an electromagnetic model suggest that the minimum detectable liquid water content ranges between 0 2 and 0 5 in volume we find that melting areas have been moving inland since 1987 a first time extensive melting 1987 2006 is detected over the transantarctic mountains on january 2005 875 km inland and 2000 m above sea level melting extent and index have been decreasing over antarctica since 1987 although either positive and negative trends are observed from a sub continental scale analysis