settling and compaction of olivine in basaltic magmas an experimental study on the time scales of cumulate formation a series of centrifuge assisted settling experiments of 30 vol olivine in 70 vol basaltic melt was conducted to elucidate the formation mechanisms and time scales of gravitational cumulates the settling experiments were performed in a centrifuging piston cylinder at 200 1 500g 1 270 1 280 c and 0 8 1 1 gpa on previously annealed and texturally equilibrated samples the mechanical settling of the dense olivine suspension occurs at about 1 6 the speed of simple stokes settling resulting in a sedimentation exponent n 4 1 6 in agreement with predictions from analogue systems the porosity m of the orthocumulate resulting from gravitational settling of crystals is about 54 and formation times of olivine orthocumulates result to 0 1 10 m day 1 for an initial crystal content of the melt of 1 5 and grain sizes of 2 10 mm after mechanical settling olivine grains rest on each other and further compaction occurs through pressure dissolution at grain contacts olivine reprecipitation where olivine is in contact with melt and concomitant expulsion of excess liquid from the cumulate layer with centrifugation at 400g for 50 h porosities as low as 30 3 vol were achieved the olivine content at the bottom of the gravitational cumulate is 1 m log h a t where is the density difference between crystals and melt h the crystal layer thickness a the acceleration and t the time of centrifuging compaction is hence proportional to effective stress integrated over time indicating that pressure dissolution is the dominant mechanism for chemical compaction the compaction limit that is the lowermost porosity to be reached by this mechanism is calculated by equating the lithostatic and hydraulic pressure gradients in the cumulate and results to 3 5 porosity for the experiments crystal size distribution curves and a growth exponent n of 3 1 3 indicate that diffusion controlled ostwald ripening is the dominant crystal growth mechanism the above relationship combined with a linear scaling for grain size as appropriate for reaction controlled pressure solution creep allows calculation of formation times of adcumulates if chemical compaction is dissolution reprecipitation limited then single layers of natural olivine adcumulates of m thickness with 70 75 vol olivine at the base as observed in the rhum layered intrusion would have typical formation times of 0 4 3 years for grain sizes of 2 10 mm this time scale compares favourably with characteristic cooling times of sills if a greater than 20 m thick series of cumulate layers pressurizes a base layer with the porosity still filled by a melt then compaction proceeds to the compaction limit within a few years it can thus be expected that in layered mafic intrusions where cumulates are continuously deposited from a large magma chamber and which characteristic cooling times of more than decades a compaction zone of several tens of metres forms with adcumulates only maintaining porosities in the order of 5 in conclusion gravitational settling and gravitation driven chemical compaction are feasible cumulate forming processes for dense mafic minerals in basaltic magmas and in particular in large layered intrusions

contemporary changes of the channel pattern and braided gravel bed floodplain under rapid small valley glacier recession scott river catchment spitsbergen abstract after the little ice age high latitude proglacial river catchments have been observed to transition to paraglacial conditions through the activation of fluvial processes and changes in the river valley and channel forms this project provides an analysis of contemporary changes in the morphology of the valley bottom and channel development of the proglacial scott river catchment nw part of the wedel jarlsberg land sw spitsbergen based on observations conducted during the 2009 2013 melt seasons almost half of the catchment area of 10 km2 is occupied by a valley glacier currently in the stage of rapid recession the processes driving the development of the glacier free valley floor are determined by 1 long term factors such as geological structure glaciotectonics or the morphogenesis of the terminoglacial zone 2 medium term factors including climatic changes and changes in the extent of the glacial terminus and hydrological regime and 3 short term factors such as weather driven flooding events geological factors determined the development of two valley narrowings and a clear division of the valley floor into three morphological zones the upper gorge in the terminal moraine rampart distinguishes the wide up to 700 m upper section of the valley bottom dominated by an outwash plain where the river system is fed by small tributaries the lower valley gorge dissecting the elevated marine terrace separates the middle section of the braided river floodplain from the mouth section alluvial fan the geomorphological field mapping of the valley floor and riverbed was conducted using geodesic and hydrometric measurements with high resolution survey techniques based on the global positioning system gps the detail measurements of the scott river valley and channel were carried out at representative cross sections and longitudinal profiles in various parts of the catchment because of the dominance of the glacial alimentation regime changes in the discharge rate and bedload transport regime are influenced by the glacial ablation rate which determines the variability of channel morphology and the contemporary development of the valley bottom the upper section of the valley is dominated by a multiple channel braided system fed by sub and supraglacial waters while in the middle section the development pattern changes from a meandering single thread channel to a multiple channel wandering system to a multiple channel braided system the current valley bottom is almost entirely occupied by a braided river floodplain and multiple channel river bed changes in the channel system are related to periods of snowmelt and the related flooding after the retreat of the snow cover the channels are highly stable as their spatial pattern is usually transformed during several days of ablation or ablation precipitation flood flows in the river s mouth section the channel returns to a single thread meandering pattern before transitioning to a multiple channel distribution system and finally to a single thread straight channel the river below the ebb in the storm bank develops a subaqual prodelta

coupled textural and compositional characterization of basaltic scoria insights into the transition from strombolian to fire fountain activity at mount etna italy strombolian and fire fountain activities represent a common expression of explosive basaltic eruptions however the transition between these two eruptive styles and their source mechanisms are still debated we use textural and compositional studies to characterize pyroclastic material from both the strombolian and hawaiian style fire fountain phases of the january june 2000 etna activity we find that basaltic scoria presents distinctive textural and compositional features that reflect different modes of magma vesiculation and crystallization in the two eruptive regimes overall magma that forms strombolian scoria is far more crystallized less vesicular and more evolved indicating strong volatile depletion and longer residence time before being erupted fire fountain scoria indicates a fast rising magma with evidence of moderate syneruptive volatile exsolution the new textural and compositional data set is integrated with previous volcanological and geophysical investigations to provide further insights into the dynamics of fire fountains and to frame the transition from strombolian explosions to fire fountain activity into a model that may apply to future eruptions at mount etna as well as other active basaltic volcanoes

jokulhlaup deposits in proglacial areas abstract this paper discusses the main causes and characteristics of jokulhlaup glacier burst floods and explores the extent to which they generate depositional landform and sediment assemblages that are distinct from those of normal braided river outwash type i outwash two main jokulhlaup outwash environments are identified type ii outwash produced by sudden drainage of ice dammed lakes and type iii associated with drainage during subglacial geothermal activity and distinguished by deposits resulting from high sediment concentrations and hyperconcentrated flows in fluid flows especially ones yielding type ii outwash the most common deposits are large scale expansion bars and locally eddy and pendant bars and mega ripples or dunes both forms normally composed of large scale gravel cobble cross bedding often capped by an imbricated boulder lag a type b2 lithofacies sequence the armour is absent only where runoff decreased too rapidly to allow surface winnowing other jokulhlaup facies include extensive boulder beds type c inverse normally graded cobble beds type ds ice proximal debris flow deposits and deformed bedding containing diamicton clasts types g and h and slack water sediments type a type iii outwash is dominated by massive homogeneous flood surge granules underlain by pre surge gravels and capped by post surge fluid bedforms reflecting deposition during both the rising and falling limbs of the flood hydrograph type e4 the paper demonstrates that jokulhlaups do generate distinctive assemblages of depositional landforms and sediments and concludes with a model of the dominant lithofacies sequences and associated landforms in proglacial environments subject to jokulhlaup drainage

heat flow density measurements in the sediments of three lakes in northern sweden abstract heat flow density measurements in the sediments of three lakes 36 m 73 m and 99 m deep were carried out during a period of 3 5 years the gradient measurements were made from ice during the winter season with a bullard type probe with nine thermistors 0 5 m apart the thermal conductivity was measured in situ corrections were made for the disturbing temperature wave in the horizontally stratified sediments caused by seasonal variations in the bottom water temperature it is clearly shown that the differences in bottom water temperatures between different years can be fully corrected for only by very long time series the heat flow density values obtained are compared with measurements in boreholes and they seem to be correct to within 20 30

the lower zone critical zone transition of the bushveld complex a quantitative textural study the lower zone critical zone boundary of the bushveld complex is an intrusion wide major stratigraphic transition from ultramafic harzburgite and pyroxenite in the lower zone to increasingly plagioclase richpyroxenitesandnoritesinthecriticalzone quantitative textural and compositional data for 29 samples through this transition show the following lower zone orthopyroxene grains are larger have higher aspect ratios are better foliated and have a lower trapped liquid component than those of the critical zone the larger grain size of the lower zone results in crystal size distribution plots that are rotated to lower slopes and intercepts relative to those in the critical zone although all rocks show differing amountsoffoliation mineral lineations are weak to absent these data are consistent with significant compaction driven recrystallization in the study section numerical modeling of concurrent compaction and crystallization provides a quantitative model of how the lower zone critical zone transition may have formed plagioclase is rare in the lower zone because compaction removes interstitial liquid before it reaches plagioclasesaturation however asthecrystalpilegrows plagioclase saturation is reached in the interstitial liquid before compaction is complete in more evolved pyroxenites producing more abundant but still modest amounts of plagioclase characteristic of the lower critical zone it is concluded that both the textures and the modal mineralogy are largely controlled by compaction and compactiondriven recrystallization primary magmatic textures are not preserved

bubble migration in a compacting crystal liquid mush recent theoretical models have suggested that bubbles are unlikely to undergo significant migration in a compaction crystal mush by capillary invasion while the system remains partly molten to test this experiments of bubble migration during compaction in a crystal liquid mush were modeled using deformable foam crystals in corn syrup in a volumetric burette compacted with rods of varying weights a bubble source was provided by sodium bicarbonate alka seltzer large bubbles several crystal sizes are pinched by the compacting matrix and become overpressured and deformed as the bubbles experience a load change from hydrostatic to lithostatic once they begin to move they move much faster than the compaction driven liquid bubbles that are about the same size as the crystals but larger than the narrower pore throats move by deformation or breaking into smaller bubbles as they are forced through pore restrictions bubbles that are less than the typical pore diameter generally move with the liquid the liquid bubble mixture behaves as a single phase with a lower density than the bubble free liquid and as a consequence it rises faster than bubble free liquid and allows for faster compaction the overpressure required to force a bubble through the matrix max grain size 5 mm is modest about 5 and it is estimated that for a grain size of 1 mm the required overpressure would be about 25 using apatite distribution in a stillwater olivine gabbro as an analog for bubble nucleation and growth it is suggested that relatively large bubbles initially nucleate and grow in liquid rich channels that develop late in the compaction history overpressure from compaction allows bubbles to rise higher into hotter parts of the crystal pile where they redissolve and increase the volatile content of the liquid over what it would have without the bubble migration leading to progressively earlier vapor saturation during crystallization of the interstitial liquid bubbles can also move rapidly by surfing on porosity waves that can develop in a compacting mush

investigations of the stillwater complex part v apatites as indicators of evolving fluid composition variations in the f cl and oh contents of apatite are not constrained by crystal chemical factors in contrast to micas and amphiboles and thus changes in the abundance of these components provide an indicator of halogen fugacity variations and insights into the degassing history of igneous rocks microprobe analysis of intercumulus apatites from the stillwater complex reveal that cl rich apatites typically containing 6 0 wt cl occur throughout the lower 1 3 of the complex excluding the basal series a change from cl rich to more f rich apatite occurs within olivine bearing zone i ob i of the banded series the host zone of the platiniferous j m reef although apatite compositions are somewhat variable above the j m reef more f rich apatites predominante and typically contain 1 2 wt f and 3 0 wt cl the most f rich apatites occur in the uppermost exposed cumulates pristine apatites from coeval sills and dikes from below the complex and from the basal series are similarly f rich in all apatites the cl and f contents are lower in rocks affected by later metamorphic fluids rare earth element ree concentrations in chlorapatites show a marked peak in the olivine rich rocks of the j m reef and contain up to 2 wt ce2o3 la2o3 the trend of first increasing then decreasing cl f ratios with stratigraphic height is modeled by a vapor driven zone refining process occurring within the cumulate pile causing cl enrichment in the interstitial melt accompanied by degassing at the top of the magma chamber causing overall loss of cl from the magma as crystallization proceeded the abrupt change from cl rich to more f rich apatites within ob i is interpreted as the result of a breakdown of the cl rich zone refining front and mixing with cl poor supernatant melt any high temperature fluids that exsolved and circulated through the lower 1 3 of the complex must have been enriched in cl and could have transported ree and trace metals

discordant bodies from olivine bearing zones iii and iv of the stillwater complex montana evidence for postcumulus fluid migration and reaction in layered intrusions mineralogically zoned and unzoned discordant bodies composed predominately of plagioclase with up to 35 olivine occur at three different levels in olivine bearing zones iii and iv of the middle banded series of the stillwater complex the discordant bodies are elongate perpendicular to the layering of the host cumulates with slender concordant apophyses although the host olivine gabbros are foliated with tabular plagioclase the discordant bodies lack a discernible fabric and have blocky plagioclase average olivine in the host rocks is slightly more magnesian than that of the discordant bodies mg 75 8 0 7 versus mg 74 6 0 3 respectively but plagioclase compositions are indistinguishable an77 6 2 0 versus an76 6 4 3 average host and discordant bodies respectively whole rock major and trace element compositions of the discordant bodies are generally indistinguishable from cumulates with similar modal abundance however bulk compositions of anorthositic cores from the discordant bodies are enriched in k na ba sr and p we conclude that the discordant bodies formed when cooler volatile fluids or fluid rich silicate liquids moved upward and encountered a hotter undersaturated solid plus liquid assemblage continued liquid fluid fluxing increased the permeability along the flow path and focused the flow allowing the original bulk compositions to be modified and leaving plagioclase rich troctolites and anorthosites the shapes of the discordant bodies suggest that the cumulus pile had anisotropic permeability during late stage liquid fluid flow chemical and mineralogical evidence from other parts of olivine bearing zones iii and iv suggests that the processes that formed the discordant bodies may have influenced other cumulates in fact it appears that the same processes that formed the discordant bodies operated within an anorthositic layer strongly modifying the chemistry of the rock but leaving no mineralogical or textural evidence

compaction of igneous cumulates when initially deposited mafic igneous cumulates consist of a solid matrix of mineral phases plus 50 60 interstitial liquid due to its greater density the matrix compacts squeezing the interstitial liquid upward a numerical fluid mechanical model of this process indicates that if the cumulate deposition rate is constant compaction occurs in one of two distinct models for rapid deposition the system is permeability controlled with compaction occurring only at the base of the cumulate pile for slowly deposited cumulates an additional compaction zone that is partially viscosity controlled develops at the top of the pile if the extent of compaction and thickness of this zone are known for a real system the model can be used to estimate the permeability and effective viscosity of the compacting cumulates such calculations yield a permeability of 1 5 times 10 3 a 2 f 3 1 f 2 for olivine cumulates in the muskox intrusion reliable viscosity estimates await an empirical law relating ma

dynamics and energetics of bubble growth in magmas analytical formulation and numerical modeling we have developed a model of diffusive and decompressive growth of a bubble in a finite region of melt which accounts for the energetics of volatile degassing and melt deformation as well as the interactions between magmatic system parameters such as viscosity volatile concentration and diffusivity on the basis of our formulation we constructed a numerical model of bubble growth in volcanic systems we conducted a parametric study in which a saturated magma is instantaneously decompressed to one bar and the sensitivity of the system to variations in various parameters is examined variations of each of seven parameters over practical ranges of magmatic conditions can change bubble growth rates by 2 4 orders of magnitude our numerical formulation allows determination of the relative importance of each parameter controlling bubble growth for a given or evolving set of magmatic conditions an analysis of the modeling results reveals that the commonly invoked parabolic law for bubble growth dynamics r t1 2 is not applicable to magma degassing at low pressures or high water oversaturation but that a logarithmic relationship r log t is more appropriate during active bubble growth under certain conditions a second aspect of our study involved a constant decompression bubble growth model in which an initially saturated magma was subjected to a constant rate of decompression model results for degassing of initially water saturated rhyolitic magma with a constant decompression rate show that oversaturation at the vent depends on the initial depth of magma ascent on the basis of decompression history explosive eruptions of silicic magmas are expected for magmas rising from chambers deeper than 2 km for ascent rates 1 5 m s 1

differentiation and compaction in the skaergaard intrusion igneous differentiation processes are constrained from bulk compositions densities and mineral modes of 116 cumulate gabbro samples in a new reference profile through the layered series of the skaergaard intrusion east greenland the stratigraphic distribution of p u and rb in cumulates and residual magma modeled by rayleigh fractionation constrains the final porosities or trapped liquid contents to 30 52 in lza troctolites decreasing to 4 12 at the top of lzb olivine gabbros and remaining low 1 13 4 middle dot 6 on average in the oxide gabbros of lzc mz and uz local variations in trapped liquid content are associated with modal layering leucocratic low density rocks have higher proportions of trapped melt than adjacent melanocratic high density rocks these observations are explained by varying degrees of compaction compaction was most important after the onset of fe ti oxide crystallization because of the high densities of the crystal matrix here computed rates of compaction exceed the rate of crystal accumulation in layers that are metres to a few tens of metres thick in the basal section lza the crystal pile was too thin and the density of the crystal matrix too low to drive the rate of compaction above the high rate of crystal accumulation promoted by initial cooling through the intrusion floor in the overlying section lzb the efficiency of compaction gradually increased as a result of thickening of the crystal pile and lowering of the rate of crystal accumulation the modeling constrains the p2o5 content of the residual magma to 1 middle dot 7 wt at the level of apatite in suggesting that the magma contained 49 wt sio2 and followed a trend of iron enrichment compaction of the uppermost metres to tens of metres of crystal mush at the top of the cumulate pile was an efficient means of differentiation and resulted in layers with variable final porosities and trace element contents depending on the mineralogy and density of the crystal matrix

heat flow measurement in lacustrine or oceanic sediments without recording bottom temperature variations water bottom temperature variations btv introduce many uncertainties into heat flow density hfd values determined from the temperature depth t z plot from a one time probe insertion into the top few meters of sediments the btv have to be carefully monitored for a number of years up to the date of the probe measurements this makes the method time consuming and economically unattractive in this paper we present the theory for a promising new technique the method does not require monitoring of the btv but does require at least two t z profiles separated in time by only a few months a generalized inversion of the btv history using the separated t z data and any other a priori information that is available is then performed in the frequency domain to give the most probable bayesian estimates of various parameters and their error bounds numerical examples show that the inversion can resolve not only the hfd but also the mean sediment surface temperature and gives information on the longer term trend as well as details of the btv over the previous year these together with thermal properties structure are the factors that contribute most to the shape of the time dependent t z profiles used in a typical situation where a uniform half space with a background hfd 60 mw m 2 has been perturbed by complex btv with a maximum variation of 1 8 k using a misguessed hfd of 90 100 mw m 2 in the inversion of two t z profiles taken 3 months apart over a 2 to 5 m section results in a posteriori hfd of 58 11 m w m 2 although the technique gives an optimally determined mean hfd its principal value lies in the ability to place reliable error bounds on the mean

compaction of density stratified cumulates effect on trapped liquid distribution igneous rocks formed by the accumulation of crystals from a cooling magma body compose a significant fraction of both the terrestrial oceanic crust and the lunar crust and mantle here we report the results of numerical simulations of compaction of accumulating crystals for which the bulk density is not constant the simulations are designed to provide insight into the behavior of interstitial liquid during compaction when a sharp drop in the density of the cumulus minerals is encountered e g at the ultramafic mafic boundary in a layered intrusion the simulations provide an explanation for trapped liquid distributions associated with sharp mineral density transitions density transition in the mineral assemblage is a feature common to many layered intrusions and the oceanic crust this process does not require external mechanisms such as injections of new and different magmas and has important implications for the formation of pt ores found at ultramafic mafic transitions the model also has implic

the halogen geochemistry of the bushveld complex republic of south africa implications for chalcophile element distribution in the lower and critical zones solidification of the interstitial liquid the stratigraphic distribution halogen bearing minerals especially apatite are minor but ubiof s cu and the pge in the critical zone cannot readily be quitous phases throughout the bushveld complex interstitial apatite explained either by precipitation of sulfide as a cotectic phase or as is near end member chlorapatite below the merensky reef lower a function of trapped liquid abundance evidence from potholes and and critical zones and has increasingly fluorian compositions with the pge rich driekop pipe of the bushveld complex imply that increasing structural height above the reef main and upper zones migrating cl rich fluids mobilized the base and precious metal cl f variations in biotite are more limited owing to crystal chemical sulfides we suggest that the distribution of sulfide minerals and controls on halogen substitution but are also consistent with a the chalcophile elements in the lower and critical zones reflects a decrease in the cl f ratio with structural height in the complex general process of vapor refining and chromatographic separation of a detailed section of the upper lower zone to the critical zone is these elements during the evolution and migration of a metalliferous characterized by an upward decrease in sulfide mode from 0 01 cl rich fluid phase 0 1 to trace 0 001 cu tends to correlate with other incompatible elements in most samples whereas the platinum group elements pge can behave independently particularly in the critical zone the decrease in the cl f ratio of apatite in the

relationships between the petrophysical properties density seismic velocity heat generation and mineralogical constitution the petrophysical properties density p compressional wave velocity v p and heat generation a exhibit considerable variation with rock type to characterize a given rock quantitatively a single parameter the cation fraction expressed by the k value has been found to be suited best 100 crystalline rocks have been sampled to cover the widest possible range in k value from silicic types like granophyres and granites through granodiorites tonalites diorites gabbros amphibolites hornblendites pyroxenites to ultrabasic rocks p k a and v p were determined experimentally the latter at 0 5 kbar 50 mpa the interrelations between these properties were established by regression analysis the relation k and v p k show a linear dependence whereas a k a and a v p follow exponential laws in a w m 3 12 20 230 5 k mole cm 3 in a 22 5 8 15 g cm 3 and in a 16 5 2 74 v p km s all correlation coefficients are better than 0 9

genesis of compositional characteristics of stillwater an i and an ii thick anorthosite units a single 10 m 10 m outcrop of stillwater anorthosite unit an ii was mapped for pyroxene mode on a decimeter scale and samples from each range of pyroxene proportion were analyzed for major and trace elements distinct one to several square meter regions of different pyroxene mode were observed samples from regions with 10 pyroxene showed strong elemental correlations and anticorrelations with mgo concentrations that can be interpreted in terms of the following scheme for development of the stillwater anorthosites aggregates containing 50 to 80 cumulus plagioclase average 67 formed stable frameworks in a crystal mush of complexly zoned plagioclase the interstices among the plagioclase grains in these frameworks filled in part with pyroxene and plagioclase that were produced in equilibrium with the bulk melt and in part with pyroxene and plagioclase derived by crystallization of trapped intercumulus liquid the proportions of these three types of materials were mutually constrained in a manner that gave rise to lines instead of fields on two element variation diagrams samples richest in cumulus plagioclase are also richest in intercumulus plagioclase and pyroxene regions of the outcrop with 10 original pyroxene underwent substantial alteration by hydrous fluids that produced variations in fe2o3 tio2 loi and most incompatible trace elements

crystal mush compaction and the origin of pegmatitic segregation sheets in a thick flood basalt flow in the mesozoic hartford basin connecticut

geochemistry of dendritic anorthosites and associated pegmatites in the skaergaard intrusion east greenland evidence for metasomatism by a chlorine rich fluid abstract in the upper zone uza of the skaergaard intrusion dendritic anorthosites and pegmatites are found in a zone of deformed gabbro along the flank of a trough banded structure apatite biotite some having over 2 wt c1 and amphibole have higher chlorine contents than those found in the surrounding rocks and indicate the presence of a high temperature aqueous fluid having a high hcl hf fugacity ratio the fluid must have been derived locally by exsolution of magmatic volatiles because hydrous minerals in nearby hydrothermal veins have low chlorine contents and the structures are far from the margin of the intrusion apatite and quartz in the pegmatites have abundant fluid inclusions containing cubic halide crystals giving evidence for a separate aqueous fluid coexisting with an evolved residual melt the pegmatites are also characterized by mafic and felsic clots with compositions similar to immiscible silicate liquids dendritic anorthosites have equal or higher abundances of zr hf ta and rare earth elements than the surrounding gabbros yet they contain little pyroxene or fe ti oxides the unusual trace element enrichment patterns and the associated rare assemblage of zirconolite zircon baddeleyite and allanite suggest that the chlorine rich fluid was enriched in trace elements derived from the residual melt and the reacted mafic minerals deformation of the magma at a crystallinity below the critical melt fraction resulted in localized exsolution and channeling of a magmatic aqueous fluid and an evolved residual melt dissolution of pyroxene olivine and fe ti oxides allowed for further deformation and expulsion of the mafic melt leaving a plagioclase rich residue these structures are the product of enhanced reaction locally of an aqueous fluid which may have moved upward as a nearly planar reactive front throughout the lower crystallization zone in addition to the transport of trace elements migration of a high temperature fluid through the zone of crystallization could aid in the compaction of igneous cumulates and the development of layering this study presents the first evidence for a high temperature chlorine rich aqueous fluid in the layered series of the skaergaard intrusion and illustrates the important effect of such fluids on the physical and chemical evolution of layered intrusions

channel pattern of proglacial rivers topographic forcing due to glacier retreat this is the peer reviewed version of the following article marren p m toomath s c 2014 channel pattern of proglacial rivers topographic forcing due to glacier retreat earth surface processes and landforms 39 7 943 951 doi 10 1002 esp 3545 which has been published in final form at http onlinelibrary wiley com doi 10 1002 esp 3545 abstract this article may be used for non commercial purposes in accordance with wiley terms and conditions for self archiving

metamorphism in basement rocks and the implications for the tectonic evolution nasafjall window scandinavian caledonides the rocks of the nasafjall window comprise proterozoic granitoids with a metasedimentary cover of late precambrian to ordovician age the mierkenis group the metamorphic grade in the window varies from greenschist facies in the eastern part of the window to amphibolite facies in the western part the metamorphic maximum is syn to post kinematic in relation to the formation of the thrust related pervasive foliation this suggests a rapid basement heating in response to the late silurian to early devonian nappe emplacement the caledonian metamorphism terminated in middle devonian times and the retrograde phase was characterized by decompression this implies that the later stage of the thrusting was not associated with an increase in thickness of the nappe pile above the rocks of the nasafjall window

plagioclase chain networks in slowly cooled basaltic magma plagioclase crystals in the slowly cooled interior of the thick holyoke flood basalt flow of connecticut linked to form monomineralic chains at an early crystallization stage partial melting experiments reveal that when the quartz tholeiite was only 25 crystallized the chains had already linked to form a continuous 3 d network at such an early stage of crystallization the network was weak highly permeable and easily deformed consequently the mush of plagioclase chains and interstitial pyroxene crystals underwent compaction in the lower third of the flow with the expelled liquid rising to the center of the flow where it crystallized to form coarse grained sheets of fractionated basalt plagioclase chains are most easily seen in the basalt after it has been partly melted and the late crystallizing minerals converted to glass the chains are several crystals wide the crystals which are approximately 0 5 mm long are attached together randomly normal zoning patterns indicate crystals had a brief period of growth before linking together the chains branch every few millimeters to form the 3 d network which was mapped using serial polished sections and x ray ct scans the chain frequency measured along vertical and horizontal traverses decreases toward the center of the flow in the compaction zone the frequency in the vertical direction is greater than in the horizontal making the reasonable assumption that these frequencies were initially the same the difference is used to calculate the degree of compaction the resulting pattern through the flow matches almost exactly the pattern indicated by variations in the incompatible elements plagioclase chains are also found in some coarser grained plutonic rocks if they are common their fabric may provide a new direct means of measuring the degree of compaction in crystal mushes

control of early formed vesicle cylinders on upper crustal prismatic jointing in compound pāhoehoe lavas of elephanta island western deccan traps india upper crustal prismatic joints and vesicle cylinders common in p hoehoe lava flows form early and late respectively and are therefore independent features however small scale compound p hoehoe lava lobes on elephanta island western deccan traps india which resemble s type spongy p hoehoe in some aspects contain vesicle cylinders which apparently controlled the locations of upper crustal prismatic joints the lobes are decimeters thick did not experience inflation after emplacement and solidified rapidly they have meter scale areas that are exceptionally rich in vesicle cylinders up to 68 cylinders in 1 m2 with a mean spacing of 12 1 cm separated by cylinder free areas and pervasive upper crustal prismatic jointing with t curved t and quadruple joint intersections a majority 76 5 of the cylinders are located exactly on joints or at joint intersections and were not simply captured by downward growing joints as the cylinders show no deflection in vertical section we suggest that large numbers of cylinders originated in a layer of bubble rich residual liquid at the top of a basal diktytaxitic crystal mush zone which was formed very early probably within the first few minutes of the emplacement history the locations where the rising cylinders breached the crust provided weak points or mechanical flaws towards which any existing joints formed by thermal contraction propagated new joints may also have propagated outwards from the cylinders and linked up laterally some cylinders breached the crust between the joints and thus formed a little later than most others the elephanta island example reveals that whereas thermal contraction is undoubtedly valid as a standard mechanism for forming upper crustal prismatic joints abundant mechanical flaws such as large concentrations of early formed crust breaching vesicle cylinders can also control the joint formation process

lithospheric thermal structure in the baltic shield summary steady state heat conduction modelling was carried out to calculate the crustal temperature field and thermal lithosphere thickness in the baltic shield the radiogenic sources at the surface were fixed depending on the age of the crust below the uppermost 10 kilometres a relationship between heat generation and p wave velocity was applied and seismic structure was used to define individual crustal blocks of specific thermal parameters small scale surface heat flow density anomalies are interpreted as lateral variations of heat generation within the upper part of the crust whereas the large anomaly in the southern part of the shield is attributed to an anomalously high mantle heat flow density the results are shown on maps outlining mantle heat flow density moho temperature and thermal lithosphere thickness a relationship between subcrustal temperature and moho depth was found except for southern sweden the lithospheric thickness is found to exceed 200 km in the bothnian gulf northern central finland and part of the kola peninsula where temperatures at the moho are less than 500 c the temperature gradient at the top of the mantle has on the average a value of 7 5 mk m and the mantle heat flow density varies from 19 to 25mwm 2 towards the south the lithospheric thickness decreases until it attains a value lower than 100km under southern sweden in this latter area the moho temperature and mantle heat flow density are remarkably high 700 900 c and 30 45 mw m 2 respectively as well as the temperature gradient which amounts to 10 mk m

gas driven filter pressing in magmas insights into in situ melt segregation from crystal mushes gas driven filter pressing is the process of melt expulsion from a volatile saturated crystal mush induced by the buildup and subsequent release of gas pressure filter pressing is inferred to play a major role in magma fractionation at shallow depths 10 km by moving melt and gas relative to the solid crystalline framework however the magmatic conditions at which this process operates remain poorly constrained we present novel experimental data that illustrate how the crystal content of the mush affects the ability of gas driven filter pressing to segregate melt hydrous haplogranite 2 1 wt water in the melt and dacite 4 2 wt water in the melt crystal mushes with a wide range of crystallinities 34 80 vol crystals were investigated using in situ high temperature 500 800 c synchrotron x ray tomographic microscopy with high spatial 3 m pixel and temporal resolution 8 s per three dimensional data set our experimental results show that gas driven filter pressing operates only below the maximum packing of bubbles and crystals 74 vol above this threshold the mush tends to fracture and gas escapes via fractures therefore the efficiency of gas driven filter pressing is promoted close to the percolation threshold and in situations where a mush inflates slowly relative to build up of pressure and expulsion of melt such observations offer a likely explanation for the production of eruptible crystal poor magmas within earth s crust

numerical study of nucleation and growth of bubbles in viscous magmas the nucleation and growth processes of bubbles in viscous magmas with a constant decompression rate have been numerically investigated based on a formation which accounts for effects of viscosity as well as diffusivity interfacial tension and decompression rate the numerical solutions show two regimes in the nucleation and growth process a diffusion controlled regime and a viscosity controlled regime mainly depending on the decompression rate initial saturation pressure and viscosity the basic mechanism common to both regimes is that growth governs nucleation through depletion of degassing components in basaltic eruptions the vesiculation is essentially controlled by diffusion and the viscosity controlled regime is limited to very high decompression rate and very small water content when andesitic magma saturated by water at 10 mpa is decompressed through the propagation of rarefraction wave induced by a landslide as took place in the mount st helens 1980 eruption the vesiculation is controlled by the viscosity up to 100 m depth on the other hand in a rhyolitic magma for the same situation vesiculation is controlled by the viscosity over the whole depth of the magma column in the viscosity controlled regime the vesicularity may be 90 or less as seen in silicic pumice whereas in the diffusion controlledmore regime the vesicularity equals or exceeds 98 such as in reticulite in hawaiian basalt an observed variation of the number density of bubbles by several orders of magnitude in plinian eruptions and the correlation with the sio2 content can be attributed approximately to the dependence of diffusivity of viscosity on sio2 content and temperature assuming the apparent correlation between sio2 content and temperature of magma less

regional trends in the platinum group mineralogy of the critical zone of the bushveld complex south africa a wealth of quantitative data on the types volume distribution and mode of occurrence of the platinum group minerals residing in the merensky reef the ug 2 chromitite layer and platreef has been obtained over a twelve year period with the result that general platinum group mineral types for unexplored areas can perhaps now be predicted the platinum group minerals of the ug 2 and overlying merensky layers although locally different in composition mode of occurrence and size show close ties when viewed on a regional scale especially with regard to their pt pd sulfide and pt fe alloy contents thus if in one particular area the merensky reef contains pt pd sulfides as the predominant platinum group minerals then it can be safely inferred that pt pd sulfides will be a significant component of the ug 2 layer in that area the occurrence of pt fe alloy also follows this principle the distribution of pt fe alloy is in fact a major factor in differentiating the ores in the vicinity north and south of the pilansberg alkaline complex from those of the same layers farther along the arcuate strike northeastern and southeastern horns of the western bushveld and has led to an overall concept relating platinum group mineral types to postulated centers of increased volatile activity or perhaps feeder sites of the complex the mineralogy of reef disturbances such as potholes is discussed the mode of occurrence of the platinum group minerals varies between base metal sulfide silicate and chromite associations and the size of platinum group minerals in the various reefs is given solid solution or lattice substitutions of platinum group elements in the base metal sulfides account for the very important latent fraction of the total platinum group elements as distinct from platinum group minerals of the bushveld complex rhodium in the merensky reef occurs almost wholly in solid solution within pentlandite whereas rh minerals occur in the ug 2 layer chromite tends to host microscopic to submicroscopic inclusions of laurite and does not appear to take ru into the crystal lattice the probability of solid solution of platinum group elements in silicate and other oxide phases is discussed

petrogenesis of the contact metamorphic rocks beneath the stillwater complex montana the stillwater gabbroic complex was emplaced at about 2700 ma in a metasedimentary section consisting of pelitic schist iron formation and quartzite contact metamorphism resulted in the development of a 500 1000 m hypersthene hornfels zone at the contact and a 500 1500 m cordierite cummingtonite hornfels zone farther from the contact weakly foliated biotite schist occurs beyond the hornfels pelitic rocks are poor in potassium generally lack muscovite and typically contain the assemblage garnet staurolite gedrite chlorite cordierite biotite plagioclase ilmenite quartz the diagnostic hornfels assemblage is cordierite cummingtonite biotite plagioclase ilmenite quartz cummingtonite is replaced by hypersthene near the contact the assemblages in the biotite schist formed during a low pressure regional metamorphism temperature ranged from 450 625 c in biotite schist to 650 800 c in hypersthene hornfels pressure estimates range from 100 250 mpa in biotite schist to 50 300 mpa in hypersthene hornfels the alpha h 2 o in the hypersthene zone is estimated to have been 0 27 orthoamphibole in the biotite schist has compositions that fall on a well defined linear trend from fe 3 5 mg 3 5 si 8 o 22 oh 2 to na 0 7 fe 3 5 mg 1 4 al 2 0 al 2 5 si 5 5 o 22 oh 2 there is no evidence for any immiscibility between anthophyllite and gedrite at the pressure of metamorphism orthoamphibole was replaced by clinoamphibole with increasing grade the petrogenetic grid calculated from estimates of thermodynamic data for the observed compositions of minerals indicates that most reactions in biotite schist occur in the temperature range 525 550 c at 200 mpa the formation of the assemblage cordierite cummingtonite occurs at 600 c and hypersthene is stable above 700 c the net reaction during formation of cordierite cummingtonite hornfels from biotite schist indicates little loss of h 2 o and a small increase in solid volume the pressure and temperature of metamorphism are consistent with subvolcanic emplacement of the complex at a depth of 6 7 km in metasedimentary country rock following a period of regional metamorphism

high silica granites terminal porosity and crystal settling in shallow magma chambers abstract high silica 70 wt sio2 granites hsgs are important carriers of highly incompatible elements thus understanding their origin is relevant to understanding how the composition of the continental crust evolves we examined a large scale geochemical study of plutons in the peninsular ranges batholith in southern california usa to better understand the petrogenetic relationships between hsgs and the batholith using highly incompatible and compatible elements we show that hsgs represent residual liquids within a felsic 69 72 wt sio2 magmatic crystal mush at crystal fractions of 50 60 and residual liquid fractions of 40 50 trace element systematics show that separation of the hsg liquid from the crystal mush is inefficient such that no more than 70 80 of the hsg is fully extracted and the remaining greater than 20 30 remains trapped in cumulate mush we find little evidence of more efficient liquid crystal segregation which suggests that compaction induced segregation may be too slow to be important on a large scale instead the terminal porosity of 20 30 coincides with theoretical maximum packing fraction of unimodal particles settled out of suspension 0 74 which may indicate that crystal settling perhaps in the form of hindered settling drives segregation of viscous silicic melts and crystals unlike compaction settling operates on timescales of 1 10 ky fast enough to generate large volumes of hsg and complementary cumulates with trapped melt before magma chambers freeze many felsic plutons may thus be cumulates but because of trapped melt they are difficult to geochemically distinguish from plutons whose compositions fall along liquid lines of descent the approach here using a combination of highly incompatible and compatible elements provides a way of identifying and quantifying trapped melt fractions finally we show that hsgs appear to form only in the shallow crust

heat flow measurements in 17 perialpine lakes thirty eight heat flow measurements were carried out in 17 perialpine lakes to supplement the scanty information concerning the thermal conditions in the crust underlying central europe a probe of the corer type was built which allowed the measurement of 11 temperatures at equally spaced subbottom intervals to a maximum penetration of 10 5 m measurements of this type were made in lake constance greifensee lake zurich lake zug lake lucerne baldeggersee lake biel lake murten lake neuch tel lake geneva lac d9annecy lac de bourget lago maggiore lago di lugano lago di como lago d9iseo and lago di garda after retrieval of the probe a sediment core was collected for samples on which thermal conductivity was measured with the needle probe method after treating the material to remove exsolved gas pubbles continuous seismic reflection and reflection profiles in all of these lakes provided a set of parameters for gradient correction due to heat flow refraction additional corrections were applied on the basis of palynologically determined sedimentation rates and for the influence of the last period of glaciation final heat flow values obtained in this manner are given the lesser values are generally found in the more western lakes north of the alps the higher values are found in the more eastern lakes north and south of the alps the higher values are partially confirmed by earlier measurements in lakes but show considerable discrepancy with measurements from the central alps this could be explained by the underthrusting of a cold wedge under the aar and gotthard massif in the late miocene and early pliocene which then would lower the temperature gradient in the central alps

sub bottom temperature perturbations due to temperature variations at the boundary of inhomogeneous lake or oceanic sediments abstract for many years continental heat flow data were obtained from temperature gradients measured in boreholes and conductivity measurements made on representative cores because of the difficulty of obtaining deep holes in suitable regions increasing use is being made of measurements made in the top few meters of the sediments at the bottom of continental lakes for reliable heat flow results two conditions must be met first an accurate record of the temperature history at the top of the sediment should be available preferably over a time span of 4 or 5 years second if the thermal properties are not constant with depth then the depth dependence should be known errors that may arise if either or both of these conditions cannot be met can be serious using various surface thermal histories we compare results from models assuming constant diffusivity a diffusivity changing exponentially with depth and a layered medium all being structures based upon observed variations near the sediment water interface where conductivity may change by a factor of two over 2 or 3 m in some situations errors as large as several hundred percents may occur but in such cases it should be possible to deduce from the data that something has occurred to make the data unreliable more realistically there are occasions where a temperature depth plot which is linear within normally acceptable limits of accuracy and with a gradient that is within the range of expectations may be as much as 100 in error

compositions of pegmatoids beneath the j m reef of the stillwater complex montana u s a abstract pegmatoids sporadically occur in the cumulates of the ultramafic series and norite zone i and gabbronorite zone i the lower banded series below the level of the platiniferous j m reef of the stillwater complex but are less common in norite zone ii and gabbronorite zone ii above the reef the pegmatoids are composed of the same minerals plagioclase orthopyroxene and clinopyroxene as the host cumulates and in approximately the same proportions but with grains that may be in excess of several tens of centimeters in length whole rock compositions show the pegmatoids to be modestly enriched in lithophile incompatible major and trace elements relative to the host cumulates whereas average host cumulates of norite zone i and gabbronorite zone i have a whole rock molar mg mg fe ratio of 81 1 5 and a normative an content of 85 1 5 almost all pegmatoid samples have lower values with mg mg fe ratios as low as 71 and normative an content as low as 58 these results are confirmed by electron microprobe analyses ratios of soluble insoluble lithophile trace elements e g ba zr show inconsistent trends excess sulfide in some pegmatoids strongly affects chalcophile element abundance if it is accepted that the pegmatoids define pods where late stage volatile rich fluids were locally enriched or channel ways by which fluids migrated up through the cumulate sequence then it is clear that such fluids differ from the host assemblages only in that the fluids were in equilibrium with a slightly more evolved bulk rock compositions calculated fluid compositions are relatively rich in fe and na and poor in ca and mg and are consistent with the compositional features of the pegmatoids the lack of significant difference in the ratios of soluble insoluble lithophile trace elements between the pegmatoids and the host cumulates suggests that it could be difficult to detect geochemical signatures for the former presence of igneous fluid in nonpegmatoidal cumulate rocks using these elements alone

continuous measurements of bedload transport rates in a small glacial river catchment in the summer season spitsbergen abstract the study on bedload transport was conducted on the gravel bed scott river catchment with a glacial alimentation regime located in the nw part of the wedel jarlsberg land spitsbergen with subpolar climatic conditions in the melt season of 2010 bedload transport rate was continuously monitored at 24 hour intervals by means of four river bedload trap devices aligned across the width of the channel the maximum bedload transport rate varied strongly at portions of the cross section from 16 to 152 kg m 1 d 1 in cross profile i c p i and 4 to 125 kg m 1 d 1 in cross profile ii c p ii the maximum channel mean bedload transport rate qa amounted to 54 kg m 1 d 1 c p i and 35 kg m 1 d 1 c p ii mean daily bedload discharge qb was estimated at a level of 97 kg day 1 c p i and 35 kg m 1 d 1 c p ii and the total bedload yield was determined at approx 4345 kg in the measurement period 2086 kg c p i 2203 kg c p ii from 13 07 to 10 08 the analysis of the relationship between channel mean bedload transport rate and water velocity or shear stress revealed a significant value of the correlation coefficient r2 0 6 discharge and rate of bedload transport were dependent on the weather and number of days with flood discharge approx 58 of the entire discharged bedload was transported during 3 violent ablation precipitation floods bedload grain size distribution was right skewed and showed moderate sorting

textural effects of steady state behaviour of the stromboli feeding system abstract the exceptionally persistent activity of stromboli volcano has lasted for at least 1400 years the normal strombolian activity is periodically interrupted by more energetic explosions 1 2 per year and by sporadic effusive episodes every 10 20 years normal activity and effusive episodes are characterized by crystal rich high k to shoshonitic basalts issuing from a volatile poor shallow system crystal poor pumice are emitted only during more violent explosions and are thought to derive from deep pulses of volatile rich magma shallow level degassing induces massive crystallization of deep pulses of feeding magma that continuously mixing with the resident one produces the crystal rich shoshonite of the persistent activity we examined the crystallization history of the crystal rich shallow reservoir using plagioclase crystal size distribution csd analysis of scoriae and lavas emitted in the past twenty years csds show a linear dependence from crystal size in the size interval 0 06 1 2 mm number density of larger crystals is biased by right hand truncation effects csds slopes and intercepts are quite constant during the whole considered time span revealing a system that is close to the equilibrium also from a kinetic point of view the linear crystal size distribution are reached by the system through episodes of growth and resorption respectively occurring in the degassed and undegassed magma during the continuous mixing in the feeding system plagioclase net growth rate 2 10 11 cm s results from a balance of growth 10 10 cm s and resorption episodes which induce spectacular zoning and resorption textures in crystals larger than 200 m csds of mafic phases cannot be accurately acquired on each single sample due to poor counting statistics the evaluation of pyroxene and olivine csd on the whole data set however confirms the conclusions acquired from plagioclase csds

using apatite to dispel the trapped liquid concept and to understand the loss of interstitial liquid by compaction in mafic cumulates an example from the stillwater complex montana the size paragenetic setting distribution and composition of apatite grains in 16 thin sections from one sample of an olivine gabbro from the stillwater complex montana were documented to determine whether they grew from trapped interstitial liquid or in an open system the grains show extreme variability in cross sectional area ranging from 300 000 m2 the apatite grains are not associated with quartz fe ti oxides or evolved overgrowths on cumulus grains as expected for the crystallization of a trapped liquid which suggests that they grew in an open system the grains are very irregularly distributed with a single cluster comprising almost 25 of the cumulative apatite cross sectional area from all 16 slides the spatial patterns of the apatite indicate that the interstitial liquid moved in tubular channels during the final stages of compaction the trace element composition of liquids calculated from apatite and silicate mineral compositions are similar indicating that the apatite crystallized from liquids that were not dramatically enriched in incompatible elements we conclude that the interstitial liquid never actually became trapped that liquid was lost in an open system to essentially zero porosity and that the model of cumulates as a combination of cumulus grains and trapped liquid should be discarded

the physics of bubbles in surficial soft cohesive sediments abstract this paper reviews current understanding of the physics of bubbles in soft unlithified cohesive sediments certainly in the top 100 m from the sediment water interface but likely much deeper experimental evidence primarily ct scans and internal pressure records indicate that near surface bubbles grow by elastically compressing and fracturing these sediments which results in thin irregular disks of gas these data do not suggest either plastic or fluid behavior on the part of the bulk sediment in addition there is no hint of capillary invasion of gas into the pores of fine grained sediments the growth rate of an elastic fracturing disk shaped bubble can vastly exceed that of a spherical bubble depending on the eccentricity of the bubble this effect results from the far more favorable surface to volume ratio of flattened bubbles the initial rate of rise of bubbles in cohesive sediments also appears to be governed by a fracture process which is driven by pseudo buoyancy the rate of bubble rise could be controlled by various possible mechanisms but only the predictions from a visco elastic fracture propagation model seem to produce rise velocities that are not ballistic experimental evidence demonstrates that a rising bubble can deviate from its path to the surface if it encounters a zone of sediment with lower lateral fracture toughness such a bubble will begin to move in a lateral direction but stall because pseudo buoyancy is no longer operative subsequent bubbles will do the same and accumulate in the low fracture toughness zone this explains the occurrence of shallow sub seafloor domes of gas and modeling of this process predicts only modest over pressures in such structures

compaction of igneous cumulates part ii compaction and the development of igneous foliations quantitative petrofabric analysis of 66 samples from olivine bearing zones iii and iv of the middle banded series of the stillwater complex montana was conducted to allow direct comparison among textural and chemical variations systematic variations in foliations with stratigraphic height are observed in both zones statistical analysis of the orientations of inequant grains was used to calculate an alignment factor af corresponding to the extent of the development of the foliation both petrofabric and petrographic evidence indicates that the foliation is best explained by compaction of the crystal pile comparison of afs with estimates of the amount of compaction based on whole rock compositions shows approximate agreement variations in mole fraction cl of interstitial apatite mimic the observed trends in the af indicating that local concentrations of fluids exsolved from interstitial liquid were important in the development of strong foliations we conclude that 1 differing amounts of co

a physical model for metal extraction and transport in shallow magmatic systems 1 the highest concentrations of metals e g cu au ag mo in the earth s crust are found in porphyry type deposits the metals are ultimately sourced from magmas and appear to be concentrated hundred to thousand fold from typical magmatic contents ppm ppb in the exsolved volatile phase to better quantify the purging and transport of metals we develop a physical model of volatile evolution in an incrementally built upper crustal magma reservoirs that considers 1 partitioning of metals from the melt to an exsolved volatile phase and 2 advection of the buoyant volatile phase using a single dimensionless parameter the peclet number pe ratio of advection rate over diffusion rate we propose that metal extraction and segregation from magmas can occur in 3 stages with different pe 1 during exsolution of the magmatic volatile phase in shallow crystal poor magma bodies slow volatile advection pe 1 2 during the growth of volatile channels that develop in the reservoir as crystallinity increases pe 1 and 3 during advection in connected channels rapid volatile advection high pe 1 for each stage a metal enrichment factor can be calculated allowing insight into the optimal conditions to maximize metal mass flux into the overlying hydrothermal system the model predicts that the most efficient purging of metals occurs for magmas with intermediate volatile contents and is enhanced during late stage magmatic activity as the reservoirs reach high crystallinity and are not disturbed by volcanic venting in agreement with natural observations suggesting that ore formation post dates volcanic activity

estimation of ground surface temperatures from borehole temperature data to infer past climatic changes from temperatures measured in boreholes one must obtain reliable estimates of ground surface temperature gst histories from these data this paper presents a method that uses a bayesian inverse technique to estimate the gst in the fourier frequency domain by assuming the a priori gst to be stationary with a prescribed standard deviation and a cutoff period the time series is constrained to be bounded and smooth because accounting for conductivity variations with depth is crucial to the estimation of gst a layered earth medium has been used for which the forward analytical solution of one dimensional heat conduction is available borehole data from flin flon and lac dufault in canada are inverted with this method the flin flon hole logged to a depth of 2900 m provides an opportunity to study long term gst variations and the estimated gst from this hole shows some effects of deglaciation at the end of pleistocene at lac dufault similar gsts were obtained independently from three holes ranging from 550 to 900 m and hence the results are considered more reliable in the lac dufault gsts there is a warm period centered about 1000 years bp and a cold period about 400 years b p confirming the presence of the little climatic optimum and the little ice age respectively the flin flon result does not show the little climatic optimum and the little ice age occurs about 100 200 years earlier however in both locations the gsts show another brief cold period around the turn of the century followed by rapid warming until 1940 1950 in good agreement with the trend of northern hemisphere surface air temperatures

inversion of temperature measurements in lake sediment summary the problem of determining heat flow density hfd from temperature data obtained in lake sediments is formulated using an iterated linear inverse theory with numerical results presented in the forms of probability density function and sensitivity coefficient the galerkin finite element method and a weighted finite difference scheme are used in the spatial and temporal domains respectively to allow for layered structure in the sediments and for transient disturbances arising from lake bottom temperature variation btv with time when a record of btv is lacking inversion of temperature data from a single probe penetration gives an unreliable estimate of hfd this difficulty is alleviated by using multiple probe measurements which if taken at intervals of several months prove adequate for a reliable estimation of the hfd and the most recent part of btv thermal properties of the sediments however must be accurately known a priori because a simultaneous estimation of hfd btv and the thermal properties remains unattainable in a practical case hfd is usually resolved to the same extent that thermal conductivity is known a priori

thrust related metamorphism in basement windows of the central scandinavian caledonides the late caledonian metamorphic evolution of the basement beneath the caledonian allochthons of the central scandes has been determined by studying mafic schists and phyllonites of the crystalline basement and the overlying vendian and or cambrian sedimentary rocks the studied rocks occur along the caledonian front and in tectonic windows within the scandinavian caledonides a gradual westwards increase in metamorphic grade is recorded which varies from upper diagenetic conditions in the autochthonous rocks along the eastern thrust front of the caledonides to middle amphibolite facies in the western parts of the nasafjall and tomeras windows locally strain related deviations from this pattern occur further west the grade of caledonian metamorphism of the basement increases and reaches the eclogite and granulite facies the scandian metamorphic conditions in the basement rocks studied prevailed in the mid to late silurian at pressures of 8 2 kbar and temperatures of 550 50 c in the tommeras window and 7 2 kbar at 550 50 c in the nasafjall window uplift and cooling followed thereafter continuing into the devonian the final retrograde metamorphism was characterized by temperatures of 450 50 c at pressures of about 3 kbar in the nasafjall and tommeras windows the occurence of syn schistosity amphibolite facies assemblages implies heating of the basement rocks during nappe emplacement available time constraints suggest that this was a relatively rapid process in late silurian to early devonian the prograde phase was followed by uplift and erosion the metamorphic evolution also demonstrates that early devonian thrust movements were associated with a decrease in the thickness of the nappe pile

sr and pb isotopic disequilibrium between coexisting plagioclase and orthopyroxene in the bushveld complex south africa microdrilling and progressive leaching evidence for sub liquidus contamination within a crystal mush progressive leaching of plagioclase for sr iso topes and microdrilling for sr and pb isotopes from grains of plagioclase and orthopyroxene from the critical zone and the lower zone indicates that these minerals are not in isotopic equilibrium leaching suggests critical zone plagioclase either lost rb or had a more radiogenic sri rim relative to the core whereas plagioclase from an upper zone sample is isotopically homogeneous for sri microdrilling analyses of plagioclase from the lower and critical zones consistently have a higher initial 87 sr 86 sr sri and a less radiogenic modeled 238 u 204 pb composition l2 than coexisting ortho pyroxene the range of calculated sri for plagioclase and orthopyroxene is 0 70506 0 70662 34 and 0 70290 0 70654 36 respectively the average difference in sri between mineral pairs was 0 00095 the range of calculated l2 for plagioclase and orthopyroxene is 9 42 10 30 average 9 7 and 9 83 15 75 average 10 1 respectively the range of measured 208 pb 206 pb for plagioclase and orthopyroxene is 34 757 36 439 33 and 36 669 41 845 85 respectively one orthopyroxenite without evidence for more than one population of crystal size distribution nonetheless had sri 0 70654 36 with calculated l2 of 10 32 for larger grains as compared with sri 0 70290 32 and calculated l2 of 9 97 for smaller grain size fractions isotopic results from this study demonstrate that whole rock isotopic data may not provide the appropriate level of detail necessary to address some processes in the bushveld complex however systematic changes have the potential to elucidate the timing of contamination with regard to other processes crystal aging compaction driven recrystallization and mineral exsolution occurring within a slowly cooled crystal liquid vapor mush system

textural and geophysical characterization of explosive basaltic activity at villarrica volcano 1 villarrica volcano chile is one of the most active volcanoes in south america its activity is currently characterized by continuous degassing from a summit lava lake vent punctuated by explosive events during november 2004 a multidisciplinary experiment was deployed for a 10 d period to define the style of emission and infer shallow conduit dynamics at this basaltic center this involved collection of thermal seismic and infrasonic data to describe the background activity confined inside the crater and use of samples to texturally and chemically characterize the ejecta from more energetic explosions able to attain the crater rim the background activity was characterized by gas bursting with a frequency of 9 events per minute this involved emission of gas puffs fed by bubble bursting with larger bursts emplacing sheets of magma onto the lower crater walls the ejecta population from the more energetic events was characterized by the coexistence of both scoriae and golden pumice these two types of clasts have different textures but identical glass compositions suggesting that they underwent different conduit histories the golden pumice is interpreted as the expanding inner part of a short lived jet fed by a rapidly ascending magma batch the scoria forms the outer portion of the jet and comprises degassed material entrained during passage of the fresh batch through material residing in the upper most portion of the conduit we thus have a largely degassed upper column that feeds persistent bubble bursting through which fresh batches occasionally rise to feed events of relatively higher energy

eulerian measurements of horizontal accelerations in shoaling gravity waves laboratory and field measurements of suspended sediment in the nearshore suggest that fluid accelerations are an important factor in sediment transport by oscillatory waves here eulerian accelerations of the cross shore velocity are calculated from measurements of velocity obtained by an array of bottom mounted electromagnetic flow meters spanning a natural surf zone large shoreward accelerations of brief duration are associated with the steep front faces of both near breaking and breaking waves weaker offshore accelerations of longer duration occur during passage of the more gently sloped rear faces the acceleration field is thus strongly skewed in the shoreward direction power spectra and bispectra indicate as expected that statistics of the acceleration field are significantly influenced by high frequency motions but are rather insensitive to surf beat

bubble mobility in mud and magmatic volcanoes the rheology of particle laden fluids with a yield stress such as mud or crystal rich magmas controls the mobility of bubbles both the size needed to overcome the yield stress and their rise speed we experimentally measured the velocities of bubbles and rigid spheres in mud sampled from the davis schrimpf mud volcanoes adjacent to the salton sea southern california combined with previous measurements in the polymer gel carbopol we obtained an empirical model for the drag coefficient and bounded the conditions under which bubbles overcome the yield stress yield stresses typical of mud and basaltic magmas with sub mm particles can immobilize millimeter to centimeter sized bubbles at stromboli volcano italy a vertical yield stress gradient in the shallow conduit may immobilize bubbles with diameter

initial rise of bubbles in cohesive sediments by a process of viscoelastic fracture 1 an understanding of the mechanics of bubble rise in sediments is essential because of the role of bubbles in releasing methane to the atmosphere and the formation and melting of gas hydrates past models to describe and predict the rise of other buoyant geological bodies through a surrounding solid e g magmas and hydrofractures appear not to be applicable to bubbles in soft sediments and this paper presents a new model for gas bubble rise in soft fine grained cohesive sediments bubbles in such sediments are essentially dry little if any free water and grow through a process of elastic expansion and fracture that can be described using the principles of linear elastic fracture mechanics which assume the existence of a spectrum of flaws within the sediment fabric by extending this theory we predict that bubbles initially rise by preferential propagation of a fracture in a sub vertical direction we present a criterion for initial bubble rise once rise is initiated the speed of rise is controlled by the viscoelastic response of the sediments to stress using this new bubble rise model we estimate rise velocities to be of the order of centimeters per second we again show that capillary pressure plays no substantive role in controlling bubble growth or rise

sediment sources spatiotemporal variability and rates of fluvial bedload transport in glacier connected steep mountain valleys in western norway erdalen and bodalen drainage basins abstract contemporary fluvial bedload transport rates are still very difficult to measure and as a result of this in many sites only quantitative data on suspended and solute transport are included in sediment budget studies carried out for defined drainage basin systems the presented analysis of fluvial bedload dynamics in different defined subsystems of the glacier connected erdalen 79 5 km 2 and bodalen 60 1 km 2 drainage basins in the steep fjord landscape of western norway provides insights into i detectable relevant sediment sources ii instream channel storage of bedload material iii spatiotemporal variability and controls of bedload transport rates and bedload yields and iv the absolute and relative importance of fluvial bedload transport within the sedimentary budgets of these steep cold climate mountain valleys rockfalls snow avalanches stream channel bank erosion and fluvial transfers through small tributaries draining slope systems are relevant sediment sources for fluvial bedload transport in the main stream channels whereas the main outlet glaciers in both drainage basins are not of importance as all bedload material delivered directly from these outlet glaciers is trapped within proglacial lakes narrow valleys within both drainage basin systems are characterized by a higher intensity of slope channel coupling and display higher rates of sediment supply from slopes into the main stream channels than wider valleys snow avalanches are the most important sediment source in erdalen whereas fluvial transfers through small tributaries followed by snow avalanches are most important in bodalen longer term instream channel storage is not of great importance in the steep bodalen drainage basin but currently plays an important role within the erdalen drainage basin which is characterized by a stepped longitudinal main valley bottom profile favoring deposition of bedload material within less steep main channel reaches the mean annual bedload yields 2010 2013 are 2 4 t km 2 y 1 for the entire erdalen and 13 3 t km 2 y 1 for the entire bodalen drainage basin which are comparably low values for steep and partly glacierized drainage basin systems because of supply limited conditions the intensity of fluvial bedload transport is generally much more related to the availability of sediments than to channel discharge fluvial bedload transport accounts for about one third of the total fluvial transport and accordingly plays an important role within the sedimentary budgets of both drainage basin systems

a novel heat flux study of a geothermally active lake lake rotomahana new zealand abstract a new technique for measuring conductive heat flux in a lake was adapted from the marine environment to allow for multiple measurements to be made in areas where bottom sediment cover is sparse or even absent this thermal blanket technique pioneered in the deep ocean for use in volcanic mid ocean rift environments was recently used in the geothermally active lake rotomahana new zealand heat flow from the lake floor propagates into the 0 5 m diameter blanket and establishes a thermal gradient across the known blanket thickness and thereby provides an estimate of the conductive heat flux of the underlying terrain this approach allows conductive heat flux to be measured over a spatially dense set of stations in a relatively short period of time we used 10 blankets and deployed them for 1 day each to complete 110 stations over an 11 day program in the 6 3 km lake results show that lake rotomahana has a total conductive heat flux of about 47 mw averaging 6 w m2 over the geothermally active lake the western half of the lake has two main areas of high heat flux 1 a high heat flux area averaging 21 3 w m2 along the western shoreline which is likely the location of the pre existing geothermal system that fed the famous pink terraces mostly destroyed during the 1886 eruption 2 a region southwest of patiti island with a heat flux averaging 13 1 w m2 that appears to be related to the explosive rift that formed the lake in the 1886 tarawera eruption a small rise in bottom water temperature over the survey period of 0 01 c day suggests the total thermal output of the lake is 112 132 mw and when compared to the conductive heat output suggests that 18 42 of the total thermal energy is by conductive heat transfer