igneous layering through oscillatory nucleation and crystal settling in well mixed magmas oscillatory or competitive nucleation about a binary or perhaps pseudo binary eutectic and ensuing crystal growth and settling is a commonly suggested means of producing layering in magmatic systems a quantitative model is presented of this outwardly relatively simple process of crystal nucleation growth and settling in an otherwise initially crystal free magma avrami style kinetics of crystallization in an always wellmixed body buried in conductive wall rock are coupled to a stokes like formulation of crystal settling in magma whose viscosity depends on temperature and crystallinity two dimensionless numbers se the settling number and av the avrami or kinetic number govern all the results av and se measure the relative importance of crystallization time and settling time respectively relative to the overall cooling time for any value of av which increases strongly with the maximum nucleation and growth rates and cooling time layering is possible only over a range or window of values of se both above and below this window a single layer crystalline below vitric above forms and within this window the number of layers increases systematically with increasing av and se grain size within any single layer generally coarsens upward because the characteristic settling and cooling times both depend on body thickness the lower limit of the settling window is also dependent on sheet thickness within the confines of this model and for nucleation and growth rates set by those observed in natural systems layering is unlikely in sheet like magmas thinner than about 100 m when the body is not always well mixed and crystallization is within inward propagating solidification fronts it is expected that this minimum body thickness will increase

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

crystallization of interstitial liquid and latent heat buffering in solidifying gabbros skaergaard intrusion greenland new compositional profiles across plagioclase grains from the layered series ls marginal border series mbs and upper border series ubs of the skaergaard intrusion are used to understand the mechanisms of cumulate rock solidification and the fate of the interstitial liquid the data show that plagioclase crystals display three types of compositional profile over the whole intrusion as follows 1 grains with normal zoning which dominate the mbs and ubs these are interpreted as having formed at the top of a crystal mush and then buried in the cumulate pile crystallization of the interstitial melt resulted in liquid differentiation and produced normally zoned rims on plagioclase cores 2 unzoned crystals which dominate the upper part of the ls also crystallized at the top of the mush and were then buried in mush with a low interstitial liquid fraction or one experiencing convective movements that kept the liquid to a constant composition 3 crystals with a mantle of decreasing an content followed by a rim of constant composition grains showing this complex zoning mostly occur in the lower parts of the ls depending on the stratigraphic position within the intrusion the composition of the rim can be an56 an51 or an40 in the main magma body these compositions an contents correspond to those of plagioclase primocrysts e g cores at the appearance of cumulus clinopyroxene an56 fe ti oxides an51 and apatite an40 compositional buffering of plagioclase rims is interpreted as being a consequence of enhanced release of latent heat of crystallization at the appearance of new interstitial phases in the crystal mush when a new phase saturates the latent heat contribution to the global enthalpy budget of the system becomes sufficiently high to keep the interstitial melt at its liquidus temperature for a period of time that could exceed thousands of years under these conditions equilibrium adcumulus growth together with diffusion and possibly advection of chemical components result in the formation of plagioclase rims of constant composition an content efficient thermal buffering of the mush liquid depends on the porosity i e fraction of liquid within the mush and the degree of compositional homogeneity of the mush in a heterogeneous and highly porous mush saturation of the new phase occurs in the coldest part of the mush and the enhanced latent heat release at the saturation of this phase is quickly dissipated to the whole volume of liquid including the warmest part that is not yet saturated in a new phase as a consequence no thermal buffering occurs and interstitial crystallization produces grains with normal zoning the distribution of the various types of plagioclase grains throughout the skaergaard intrusion can therefore be used to infer the spatial variability in the physical properties of the crystal mush such as the residual porosity both at an intrusion wide scale and at a millimetre to centimetre scale

the j m platinum palladium reef of the stillwater complex montana ii origin by double diffusive convective magma mixing and implications for the bushveld complex sequences of cumulates form concurrently by downdip accretion from a column of liquid layers that are primarily separated by diffusive interfaces the low cumulates grow in advance of the upper cumulates in accord with their higher crystallization temperatures an important observation is that mixing of the two parent liquids lowers their crystallization temperatures and consequently should produce unsaturated hybrids that could dissolve earlier cumulates the repetition of cyclic units above the j m reef is explained by having periodic additional injections of dense magma beneath the subsiding column of crystallizing liquid layers neither the j m reef nor the bushveld ore zones should ever have been continuous across the floor of their respective magma chambers and for bushveld the circumstances resulted in zones that are actually minable modified journal abstract

the skaergaard layered series part ii magmatic flow and dynamic layering re examination of textural and structural features of the skaergaard intrusion has clarified the process responsible for various forms of layering two general types are distinguished one produced by magmatic flow and another by non dynamic processes such as compaction and varied nucleation and growth of crystals our concern here is mainly with layering of the first type magmatic flow results in contrasting layers and strong foliation accompanied by a linear orientation of elongated minerals it is associated with slumping and cross bedding in a zone near the margins of the intrusion rocks in the interior of the layered series are foliated and commonly layered but have little or no lineation their layering cannot be due solely to deposition from currents the principal structural elements produced by dynamic processes in the magmatic state foliation lineation shear zones folds and current structures define parallel belts mainly around the western and northern margins their distribution suggests that the strongest component of flow was for the western side and that its strength decreased toward the east shear flow trajectories deduced from lineations and kinematic indicators confirm this asymmetry and point to mass movement toward the southeastern part of the floor

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

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

hindered settling of sand grains the sedimentation rate of sand grains in the hindered settling regime has been considered to assess particle shape effects the behaviour of various particulate systems involving sand has been compared with the widely used richardson zaki expression the general form of the expression is found to hold in as much as remaining as a suitable means to describe the hindered settling of irregular particles the sedimentation exponent n in the richardson zaki expression is found to be significantly larger for natural sand grains than for regular particles the hindered settling effect is therefore greater leading to lower concentration gradients than expected the effect becomes more pronounced with increasing particle irregularity at concentrations around 0 4 the hindered settling velocity of fine and medium natural sands reduces to about 70 of the value predicted using existing empirical expressions for n using appropriate expressions for the fluidization velocity and the clear water settling velocity a simple method is discussed to evaluate the sedimentation exponent and to determine the hindered settling effect for sands of various shapes

experimental compaction of quartz sand at low effective stress and temperature conditions experiments have been carried out on dry and fluid saturated quartz sands to investigate the behaviour during compaction under diagenetic conditions and to evaluate the importance of stress induced solution transfer 9pressure solution9 as a compaction mechanism the experiments were performed at temperatures t in the range 150 350 c applied effective stresses e up to 20 7 mpa and pore fluid pressures p 1 of 12 5 and 15 5 mpa using material with a grain size d in the range 20 100 m and an initial porosity of 45 52 dry quartz sands underwent significant compac tion during the loading stage but showed very little compaction creep once full load was achieved i e essentially time independent compaction in contrast fluid saturated material at constant applied effective stress showed substantial time dependent compaction i e creep with increasing temperature there is a decreasing number of grains in the wet compacted sand which show intragranular cracks and an increasing number of grains which show dissolution features at contacts with adjacent grains in addition there is a decreasing dependence of the volumetric strain rate on e with both increasing volumetric strain e v and increasing e and a decreasing dependence of on e v with increasing temperature these observations suggest that for wet quartz sand a gradual change might occur from compaction creep controlled by time dependent microcracking at t 250 300 c to compaction creep controlled by stress induced intergranular solution transfer at t 300 350 c

significant effect of grain size distribution on compaction rates in granular aggregates we investigate the role of pressure solution in deformation of upper to mid crustal rocks using aggregates of halite as a room temperature analog for fluid assisted deformation processes in the earth s crust experiments evaluate the effects of initial grain size distribution on macroscopic pressure solution rate of the aggregate and compare the results to theoretical models for pressure solution we find that the grain size exponent deviates significantly from the theoretical value of 3 for diffusion controlled pressure solution models typically assume mono dispersed spherical particles in pseudo regular packing we infer that the discrepancy between experimentally determined grain size exponents and the theoretical values are a result of deviation of experimental and natural samples from regular packs of mono dispersed spherical particles moreover we find that compaction rates can vary by up to one order of magnitude as a function of the width of the grain size distribution for a given mean grain size wider size distributions allow for higher initial compaction rates increasing the macroscopic compaction rate with respect to more narrow grain size distributions grain sizes in rocks fault gouges and hydrocarbon reservoirs are typically log normal or power law distributed and therefore pressure solution rates may significantly exceed theoretical predictions spatiotemporal variations in pressure solution rates due to variations in grain size may cause the formation of low porosity zones which could potentially focus deformation in these zones and produce pockets of high pore pressures promoting nucleation of frictional instability and earthquake rupture

trapped liquid paleo porosity and formation time scale of a chromitite ortho pyroxenite cumulate section bushveld south africa to evaluate compaction and interstitial melt expulsion during cumulate formation a 20 m cumulate section including the ug2 and ug3 chromitites from a 264 m drill core through the upper critical zone of the bushveld complex south africa has been studied the cumulates in the studied section are as follows 3 m plagioclase pyroxenite to pyroxenite pegmatoid footwall pyroxenite at the lower contact to ug2 0 7 m ug2 chromitite 6 8 m pyroxenite 0 24 m ug3 chromitite 2 0 m plagioclase rich pyroxenite changing locally to norite the two 5 cm leader stringers ug3a and ug3b and 7 m total of olivine pyroxenites grading into plagioclase pyroxenites all pyroxenites are dominated by orthopyroxene opx and the cumulate sequence is topped by mottled anorthosite grading into norite stratigraphic concentrations of major and trace elements of 52 bulk rock samples were determined bulk rock mg numbers are 0 79 0 81 throughout the silicate cumulate units and 0 40 0 46 in the chromitite layers the stratigraphic distribution of six incompatible trace elements k rb ba cs zr and th has been used to determine the amount of trapped liquid ftl or paleo porosity in the cumulate rocks final porosities volume fractions based on averages from the six trace elements are 0 06 0 33 in the pyroxenites in chromitite layers trapped melt fractions of 0 12 0 36 are calculated from incompatible trace element concentrations but bulk sio2 concentrations and x ray tomography yield 0 04 0 17 higher porosities hence the bulk silicate fraction in the chromitites may not necessarily correspond to the trapped liquid fraction as poikilitic opx was crystallizing while the silicate melt still equilibrated using a previously derived experiment based model for compaction time scales gravitationally driven chemical compaction in the ug2 ug3 pyroxenite section is calculated to occur within 1 10 years this time frame corresponds to the times necessary to cool a 20 m layer by 10 50 c the temperature interval argued to encompass the liquidus and almost complete solidification compaction within a decade can in fact easily develop the paleo porosities indirectly observed today and is probably stopped by crystallization of the interstitial liquid contrary to previous assertions melt expulsion from the cumulate pile does not hinder compaction calculated permeabilities would allow for the migration of an order of magnitude higher amount of melt than has to be expelled from the 20 m pile of cumulate the pegmatoid zones in the chromitite footwalls enriched in incompatible trace elements are consistent with a collection of interstitial melts expelling from the underlying compacting pyroxenites their entrapment below the chromitite layers suggests that these act as permeability barriers this is in part due to their finer grain size compared with the pyroxenites but is mainly due to the crystallization of large poikilitic opx during compaction

settling and compaction of chromite cumulates employing a centrifuging piston cylinder and application to layered mafic intrusions the time scales and mechanics of gravitationally driven crystal settling and compaction is investigated through high temperature 1 280 1 500 c centrifuge assisted experiments on a chromite basalt melt system at 100 1 500g 0 5 gpa subsequently the feasibility of this process for the formation of dense chromite cumulate layers in large layered mafic intrusions lmis is assessed centrifugation leads to a single cumulate layer formed at the gravitational bottom of the capsule the experimentally observed mechanical settling velocity of a suspension of 24 vol chromite is calculated to be about half 0 53 of the stokes settling velocity with a sedimentation exponent n of 2 35 3 gravitational settling leads to an orthocumulate layer with a porosity of 0 52 all porosities as fraction formation times for such a layer from a magma with initial chromite contents of 0 1 1 vol are 140 3 5 days equal to a growth rate of 0 007 0 3 m day for grain sizes of 1 2 mm more compacted chromite layers form with increasing centrifugation time and acceleration through chemical compaction an increase of grain contact areas and grain sizes together with a decrease in porosity is best explained by pressure dissolution at grain contacts reprecipitation and grain growth into the intergranular space and a concomitant expulsion of intergranular melt the relation between the porosity in the cumulate pile and effective pressure integrated over time h a t is best fit with a logarithmic function in fact confirming that a pressure dissolution reprecipitation process is the dominant mechanism of compaction the experimentally derived equation allows calculating compaction times 70 80 chromite at the bottom of a 1 m thick chromite layer are reached after 9 250 years whereas equivalent compaction times are 0 2 0 9 years for olivine both for 2 mm grain size the experiments allow to determine the bulk viscosities of chromite and olivine cumulates to be of magnitude 109 pa s much lower than previously reported as long as melt escape from the compacting cumulate remains homogeneous fluidization does not play any role however channelized melt flow may lead to suspension and upward movement of cumulate crystals in lmis chromitite layers are typically part of a sequence with layers of mafic minerals compaction occurs under the additional weight of the overlying layers and can be achieved in a few years to decades

descent and modification of the overflow plume in the denmark strait bulk properties of the denmark strait overflow dso plume observed in velocity and hydrography surveys undertaken in 1997 and 1998 are described despite the presence of considerable short term variability it is found that the pathway and evolution of the plume density anomaly are remarkably steady bottom stress measurements show that the pathway of the plume core matches well with a rate of descent controlled by friction the estimated entrainment rate diagnosed from the rate of plume dilution with distance shows a marked increase in entrainment at approximately 125 km from the sill leading to a net dilution consistent with previous reports of a doubling of overflow transport measured by current meter arrays the entrainment rate increase is likely related to the increased topographic slopes in the region compounded by a decrease in interface stratification as the plume is diluted and enters a denser background

pressure solution in sedimentary basins effect of temperature gradient abstract pressure solution is an important process in sedimentary basins and its behaviour depends mainly on the sediment rheology and temperature distribution the compaction relation of pressure solution is typically assumed to be a viscous one and is often written as a relationship between effective stress and strain rate a new derivation of viscous compaction relation is formulated based on more realistic boundary conditions at grain contacts a non linear diffusion problem with a moving boundary is solved numerically and a simple asymptotic solution is given to compare with numerical simulations pressure solution is significantly influenced by the temperature gradient porosity reduction due to pressure solution is enhanced in an environment with a higher thermal gradient while porosity decreases much slowly in the region where the thermal gradient is small pressure solution tends to complete more quickly at shallower depths and earlier time in higher temperature environment than that in a low one these features of pressure solution in porous sediments are analysed using a perturbation method to get a solution for the steady state comparison with real data shows a reasonably very good agreement

pressure solution and viscous compaction in sedimentary basins mathematical models of compaction in sedimentary basins typically assume a relationship between effective pressure pand porosity which is of a non linear type that is p p d however at depths greater than a kilometer pressure solution becomes important and this relationship approaches a viscous one we derive a mathematical model for viscous compaction in sedimentary basins and show how the model suggests different styles of behavior in the limits of slow nd fst compaction the initial pore pressure will be lithostatic over time the sediments compact and the resultant expulsion of pore water allows the pore pressure to approach a hy drostatic limit and in so doing the porosity is reduced at depths up to about a kilometer this compaction is elastic and due to the rearrangement of sediment particles at greater depths cementation and pressure solution occur and the latter causes further compac tion we call compaction by pressure solution viscous compaction and it forms the subject of the present pa per one of the interesting features of overpressuring is that it typically occurs suddenly at depths in excess of 3000 meters hunt 1990 and is often associated

temperature dependent viscoelastic compaction and compartmentalization in sedimentary basins the near surface compaction regime of most sedimentary basins is characterized by hydrostatic fluid pressures and is therefore determined entirely by sediment matrix rheology within this regime compaction is initially well described by a pseudoelastic rheological model with increasing depth precipitation dissolution processes lead to thermally activated viscous deformation the steady state porosity profile of the viscous regime is a function of two length scales the viscous e fold length related to the compaction activation energy and a scale determined by the remaining parameters of the sedimentary process overpressure development is weakly dependent on the second scale for activation energies 20 kj mol application of the steady state model to pannonian basin shales and sandstones indicates a dominant role for viscous compaction in these lithologies at porosities below 10 and 25 respectively activation energies and shear viscosities derived from the profiles are 20 40 kj mol and 1020 1021 pa s at 3 km depth the analytical formulation of the compaction model provides a simple method of predicting both the depth at which permeability limits compaction resulting in top seal formation and the amount of fluid trapped beneath the top seal fluid flow during hydraulically limited compaction is unstable such that sedimentation rate perturbations or devolatilization cause nucleation of porosity waves on the viscous e fold length scale 0 5 1 5 km the porosity waves are characterized by fluid overpressure with a hydrostatic fluid pressure gradient and propagate through creation of secondary porosity in response to the mean stress gradient the waves are a mechanism of episodic fluid expulsion that can be significantly more eycient than uniform darcyian fluid flow but upward wave propagation is constrained by the compaction front so that the waves evolve into essentially static domains of high porosity following cessation of sedimentation yielding mechanisms do not appreciably alter the time and length scale of episodic fluid flow because fluid expulsion is ultimately controlled by compaction the flow instabilities inherent in viscous compaction are similar to and a possible explanation for fluid compartments 2000 elsevier science b v all rights reserved

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

syn tectonic magmatism and the development of compositional layering ungava orogen northern quebec canada abstract layer and foliation parallel emplacement of granitic veins was an important process in the regional development of compositional layering in now exhumed middle crustal sections of both archean and paleoproterozoic age in the northern ungava peninsula quebec canada in the archean superior province diorite and tonalite plutons were penetratively deformed and metamorphosed at granulite facies conditions coeval with voluminous granitic magmatism the paleoproterozoic narsajuaq arc contains evidence for contemporaneous magmatism transpressional deformation and granulite facies metamorphism prior to its collision with the superior province basement in both plutonic domains regional compositional layering is defined by 1 metre to kilometre scale alternation of generally well foliated tonalite and quartz diorite bodies and 2 centimetre to kilometre scale variably deformed granitic veins and sheets that lie parallel to layering tectonic foliation in the host rocks syn tectonic intrusion of a substantial portion of the veins along extension fractures sub parallel to layering foliation i e at high angle to the regional shortening direction is interpreted to have occurred due to the combination of a strong anisotropy and high magma pressures compositional layering generated and or enhanced by this process may contribute to the overall seismic reflectivity of the middle and lower crust

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

porosity reduction by pressure solution a theoretical model for quartz arenites pressure solution and the subsequent precipitation of the dissolved material may play an important role in the lithification of sandstones and limestones this paper presents a one dimensional model for a well sorted quartz arenite sequence undergoing diagenesis the sedimentary sequence is treated as a saturated porous medium in which pressure solution occurs at individual grain contacts quartz dissolved at grain contacts precipitates on free surfaces of adjacent grains this solution and precipitation process reduces porosity and forces the migration of pore fluid permeability decreases with porosity hindering fluid migration and excess fluid pressures are generated distributions of porosity pore pressure and fluid flow rates are given for several sedimentation rates and thermal gradients complete reduction of the primary intergranular porosity was accomplished in all cases examined by a depth of 3 5 km

thermodynamic modeling for an incrementally fractionated granite magma system implications for the origin of igneous charnockite abstract understanding fractionation of silicic magma is crucial to advance our knowledge of differentiation of continental crust enrichment of elements of economic interest and plutonic volcanic connection microstructural records afford critical appraisals for silicic magma fractionation yet are rarely reported in granite plutons here we combine detailed microstructural observations and thermodynamic modeling to quantify the components and the conditions of silicic magma fractionation using the peraluminous jiuzhou pluton south china as an example the pluton shows compositional gradients from primitive orthopyroxene bearing granite charnockite at stratigraphically low levels to relatively evolved orthopyroxene free granite at stratigraphically high levels deviation of whole rock compositions from metasediment sourced experimental melts and step zoned plagioclase and alkali feldspar crystals in the exposed rocks suggest open system fractionation by melt extraction partial dissolution and subsequent crystallization from trapped minimum melt crystal cluster and chain fabrics and viscous deformation are more abundant in the charnockites than in the overlying orthopyroxene free granites suggesting that gravitational compaction driven fractionation increased towards the bottom of the pluton field observations thermodynamic modeling and petrographic studies further demonstrate that gravitational compaction reduces the trapped melt fraction of a crystal mush with thickness of 100 m from 30 wt at the upper level to 10 wt at the lower level of the pluton significant melt extraction restricted back reaction with high temperature phases during progressive crystallization which preserved orthopyroxene during the solidification of granitic magma the compositional mineralogical and textural zoning of the jiuzhou pluton suggests that incremental fractionation of granite systems may be an important process that produces compositionally zoned cumulate incremental fractionation may occur in many zoned granite plutons worldwide causing their whole rock composition to deviate from their primary melt composition detailed microstructural examination for these granite plutons may provide insights into the mechanism s for melt extraction and crystal accumulation of silicic magma providing key insights towards quantifying fractionation of magma systems

spinel inclusions in olivine and plagioclase crystals in a layered gabbro a marker and a tracer for primary phenocrysts in a differentiating magma reservoir the problem of whether cumulate rocks were formed by crystal settling or by in situ crystallization after magma emplacement is an important issue concerning the mechanisms of magmatic differentiation however it is hard to distinguish these two processes for plutonic rocks because the primary texture and chemical composition have generally been modified by postcumulus processes to contribute this problem we studied the distribution and compositions of cr spinel inclusions hosted in olivine and plagioclase in the murotomisaki gabbroic intrusion mgi sw japan it is shown that the olivine hosted inclusions are restricted to specific horizons where accumulation of olivine phenocrysts is thought to have occurred and that the compositional variations of the cr spinel are explained by a secondary compositional modification that probably took place after the magma emplacement it is also shown that the cr spinel inclusions in a chilled margin have suffered the least compositional modification and nearly retains the primary composition those in the interior of the intrusion on the contrary have been significantly modified by re equilibration with residual melt driven by cation diffusions through the host phases those in plagioclase have been less modified it is shown that all the spinel inclusions had primarily the same and common composition at the time of magma emplacement this implies that all the inclusion bearing crystals olivine and plagioclase represent primary phenocrysts that had already existed in the emplaced magma in this way spinel inclusion in the mgi may be regarded to be a useful petrographic marker for identifying intratelluric phenocrysts and also as a tracer to trace the motion of the primary phenocrysts after the magma emplacement

the skaergaard layered series part iii non dynamic layering layering in the skaergaard intrusion has been divided into two introduction general types one produced by magmatic flow and another by recent studies of the structural and textural features of processes resulting from variations of rates of nucleation and crysthe skaergaard intrusion mcbirney nicolas 1997 tallization and in the case of the layered series by compactionhave distinguished two broad types of layering one related processes modal variations caused by shifts of cotectic produced by the dynamic effects of magmatic flow and proportions produce thick layers which in the layered and upper another by processes that operate in situ such as varied border series are diffuse and normally lack strong foliation and nucleation and growth of crystals recrystallization or by lineation in the marginal border series the layers are thinner and compaction related mechanisms we refer to layering sharper possibly because the rate of accumulation was slower formed by these latter processes as non dynamic to oscillatory nucleation may have played a role in producing fineemphasize that it is not the result of fluid dynamic scale cyclic layers but it was less important than solution and processes although most layering combines elements of reprecipitation during slow cooling and ostwald ripening evidence more than one process the contribution of each mechfor compaction is found in deformed plagioclase laths and a relative anism can usually be recognized from its distinctive form deficiency of incompatible elements in rocks formed on the floor and setting layering related to compaction becomes sharper with increasing the distinguishing features of dynamic magmatic layheight in the layered series until it suddenly disappears above the ering have been described in part ii of this series mcbirtrough horizon near the base of upper zone b mechanical sorting ney nicolas 1997 they are best seen near the steep during compaction may have produced crude layering but if it did margins of the layered series in what wager brown the evidence has long since been destroyed by the superimposed effects 1968 referred to as the cross bedded zone where the of solution and reprecipitation when interstitial liquid rose through layering is disrupted by slumping and channeling and the overlying crystals and re equilibrated with them numerical the rocks have a marked foliation and lineation simulations illustrate how small differences of surface energy caused layering not associated with magmatic flow takes a by variations of grain size textural dependence of solubility and variety of forms but we can distinguish two general pressure solution can cause segregation of minerals into layers during end members each of which has a distinct origin and solution and reprecipitation characteristics the first results from varied rates of

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

hydraulic estimates of denmark strait overflow 1 upper bounds of the denmark strait deep water overflow from the nordic seas into the north atlantic are estimated using rotating hydraulic theory the calculations are made for the real bottom topography of the strait and are based on hydrographic sections surveyed during a dedicated field experiment in the area results are presented for zero as well as finite but constant potential vorticity and it is shown that the differences in outcome between these two approaches are only minor the calculated interface configurations are found to be in good agreement with those observed and the theoretically obtained transports conform with earlier estimates

topographic control of oceanic flows in deep passages and straits saddle points between neighboring deep ocean basins are the sites of unidirectional flow from one basin to the next depending on the source of bottom water flow in these sites appears to be topographically controlled so the interface between the bottom water and the water above adjusts itself to permit bottom water flow from the basin that contains a source of bottom water into the next examples in the atlantic include flow in the romanche fracture zone the vema channel the ceara abyssal plain the anegada jungfern passage and the discovery gap but there are many more theoretical predictions of volume flux using a method that requires only conductivity temperature depth data archives and detailed knowledge of bathymetry near the saddle point are compared with volume flux estimates using current meters and or geostrophic estimates for seven cases the ratio of prediction to volume flux estimate ranges from 1 0 to 2 7 some ocean straits that separate adjacent seas are also found to critically control bidirectional flows between basins theory of the influence of rotation on such critical flows is reviewed predictions of volume flux in eight cases are compared with ocean estimates of volume flux from traditional methods

high frequency variability in the circulation and hydrography of the denmark strait overflow from a high resolution numerical model abstractinitial results are presented from a yearlong high resolution 2 km numerical simulation covering the east greenland shelf and the iceland and irminger seas the model hydrography and circulation in the vicinity of denmark strait show good agreement with available observational datasets this study focuses on the variability of the denmark strait overflow dso by detecting and characterizing boluses and pulses which are the two dominant mesoscale features in the strait the authors estimate that the yearly mean southward volume flux of the dso is about 30 greater in the presence of boluses and pulses on average boluses pulses are 57 1 27 5 h long occur every 3 2 5 5 days and are more frequent during the summer winter boluses pulses increase decrease the overflow cross sectional area and temperatures around the overflow interface are colder warmer by about 2 6 c 1 8 c the lateral extent of the boluses is much greater than that of the pulses in both cases the along stra

kinetic processes for plastic deformation of olivine in the poyi ultramafic intrusion nw china insights from the textural analysis of a 1700 m fully cored succession abstract the ubiquitous presence of undulose extinction and subgrain boundaries in olivine crystals is commonly perceived as originating in the mantle however these plastic deformation features are also well developed in the poyi ultramafic intrusion nw china in this case olivine was deformed through kinetic processes in a crustal magma chamber rather than by deformation processes in the upper mantle moreover accumulation and textural coarsening were critical to the characteristics of crystal size distributions csds of olivines in the poyi intrusion the axial deformational compaction of crystal mush was revealed by virtue of other quantitative textural analyses e g spatial distribution patter alignment factor and aspect ratio additionally based on the contrast of density between crystal matrix and interstitial melt adequate stress was generated by the km scale crystal framework in poyi body 2 11 mpa which triggered the distortion of grain lattice in olivine the deformation mechanisms of olivine primarily are dislocation creep and dislocation accommodated grain boundary sliding disgbs while diffusion creep is subsidiary this study has revealed various kinetic processes in a magmatic system by first demonstrating the genetic relationship between mineral deformation and axial compaction of crystal mush while highlighting the uncertainty of employing the deformation features of olivine in peridotite xenoliths as an indicator for a mantle origin in contrast to the olivine populations of xenocrysts that underwent fragmentation during ascent the deformed primitive olivines in compaction exhibit a distinct shortage of small grains which is conducive to delimiting these two types of deformed grains

significant role of the north icelandic jet in the formation of denmark strait overflow water the largest dense water plume feeding the lower limb of the atlantic meridional overturning circulation from the nordic seas comes from denmark strait overflow water measurements of hydrography and water velocity north of iceland and ocean model simulations indicate that a significant part of this water is supplied by the north icelandic jet

layered intrusions and traffic jams a wide range of explanations has been proposed for the origin of repetitive layering in mafic ultramafic and in per alkaline intrusions here we propose that the interaction of mineral grains that sink and float in the crystallizing magma is an alternative mechanism that can explain many of the features of layered intrusions without the need to invoke extrinsic factors similar to traffic jams on a motorway small perturbations in crystal density develop that impede further ascent or descent of buoyant or heavy minerals respectively these traffic jams separate layers of magma from the rest of the magma chamber the magma in the individual layers further evolves as a largely independent subsystem with gravitational sorting organizing the mineral distribution within each layer layering can develop in the intermediate range between full mineral separation in low viscosity or slowly cooling magma chambers and homogeneous crystallization in high viscosity or fast cooling chambers this self organization mechanism provides a novel explanation for the formation of rhythmic layering in low viscosity magmas for example in the ilimaussaq igneous complex in southwest greenland

atlantic water variability on the se greenland continental shelf and its relationship to sst and bathymetry 1 interaction of warm atlantic origin water aw and colder polar origin water pw advecting southward in the east greenland current egc influences the heat content of water entering greenland s outlet glacial fjords here we use depth and temperature data derived from deep diving seals to map out water mass variability across the continental shelf and to augment existing bathymetric products we compare depths derived from the seal dives with the ibcao version 3 bathymetric database over the shelf and find differences up to 300 m near several large submarine canyons in the vertical temperature structure we find two dominant modes a cold mode with the typical aw pw layering observed in the egc and a warm mode where aw is present throughout the water column the prevalence of these modes varies seasonally and spatially across the continental shelf implying distinct aw pathways in addition we find that satellite sea surface temperatures sst correlate significantly with temperatures in the upper 50 m r 0 54 but this correlation decreases with depth r 0 22 at 200 m and becomes insignificant below 250 m thus care must be taken in using sst as a proxy for heat content as aw mainly resides in these deeper layers sample unit level copyright

high frequency fluctuations in denmark strait transport 1 denmark strait ocean current transport exhibits quasi regular fluctuations immediately south of the sill with periods of 2 4 days the transport variability is similar to the mean transport itself using a circulation model we explore prospects to monitor the fluctuations the model has realistic transport and shows water leaving denmark strait in equivalent barotropic cyclones that are nearly geostrophic and correlate with sea surface height ssh existing satellite altimeter observations of ssh have adequate space time sampling to reconstruct the transport fluctuations using a regression developed from the model results but measurement error overwhelms the signal from the model results the pending surface water and ocean topography swot wide swath altimeter appears accurate enough and with good enough coverage to allow the transport fluctuations to be reconstructed bottom pressure recorders at the exit of the denmark strait can also reproduce the transport variability

structure and variability of the denmark strait overflow model and observations we report on a combined modeling and observational effort to understand the denmark strait overflow dso four cruises over the course of 3 years mapped hydrographic properties and velocity fields with high spatial resolution the observations reveal the mean path of the dense water as well as the presence of strong barotropic flows energetic variability and strong bottom friction and entrainment a regional sigma coordinate numerical model of interbasin exchange using realistic bottom topography and an overflow forced only by an upstream reservoir of dense fluid is compared with the observations and used to further investigate these processes the model successfully reproduces the volume transport of dense water at the sill as well as the 1000 m descent of the dense water in the first 200 km from the sill and the intense eddies generated at 1 3 day intervals hydraulic control of the mean flow is indicated by a region supercritical to long gravity waves in the dense layer located approximately 100 km downstream of the sill in both model and observations in addition despite the differences in surface forcing both model and observations exhibit similar transitions from mostly barotropic flow at the sill to a bottom trapped baroclinic flow downstream indicating the dominant role of the overflow in determining the full water column dynamics

included blocks and blocks within blocks in the skaergaard intrusion geologic relations and the origins of rhythmic modally graded layers the early eocene skaergaard intrusion of greenland includes enormous numbers of rocks of both exotic and cognate origins the lower parts of the marginal border series contain abundant fragments of feldspathic peridotite that are possibly autoliths intermixed with occasional xenoliths of precambrian gneiss and metasomatized cretaceous paleocene sediments derived from adjoining country rocks the upper border series includes one exceptionally large block of gneiss several hundred meters across and numerous smaller fragments these originating from the intrusion9s footwalls plus a few pieces of peridotite the layered series contains countless autoliths of troctolite gabbroic anorthosite and oxide magnetite ilmenite gabbro broken from parts of the upper border series that have otherwise been lost to erosion at the upper midlevel of its western half it contains a few xenoliths of basalt derived probably from the now eroded eocene roof of the intrusion a distinctive postintrusion composite basaltic dike at one place contains 40 or more xenoliths of troctolite olivine gabbro and gabbroic anorthosite that may represent parts of the layered series still hidden at depth the layered series autoliths range from fragments a few centimeters on a side to blocks more than 400 m across and they typically are coarser grained than their host cumulates being in this respect more like upper border series rocks the autoliths are spread stratigraphically through the lower 70 of the exposed 2500 m thickness of the layered series and are generally concentrated in three broad stratigraphic zones their physical relationships to their host rocks particularly the way they indent older layers beneath and are covered by younger layers above provide abundant evidence that there was generally a sharp well defined interface between the top of the cumulate pile and the main body of magma in the intrusion while the layered series was forming the distribution of the autoliths between and through the well known rhythmic thin modally graded layers shows that these layers were spread by magmatic currents and their relations to the more extensive macrorhythmic layering suggest that it too was significantly shaped by currents many of the larger autoliths are crudely layered internally and in places it is evident that their stratification existed before they broke loose therefore it must have formed in the upper border series one particularly large block of oxide gabbro exhibits extraordinarily well developed modal and textural layering and includes small troctolitic autoliths of an earlier generation and it provides evidence that currents also spread crystalline materials across the top of the magma body many of the very small autoliths in the layered series are highly anorthositic in composition apparently because they were leached of mafic minerals and some of the larger blocks show local patchy internal replacement by anorthosite most large blocks show little sign of postaccumulation modification and some have thin fine grained augite rich rims or rinds demonstrating that even though they were out of thermal and chemical equilibrium with their host cumulates they still were effectively armored against extensive chemical change also documented is a large block that was cut by several early basaltic dikes before it broke free from the top of the intrusion these early dikes transgress small anorthositic replacement pipes in the block showing that the replacement process also occurred in the upper border environment two mechanisms are described whereby graded cumulate layers can be sorted and deposited by magmatic crystal liquid suspension currents one involving density surge currents has been advocated previously the other is a new concept based on boundary flow separation and reattachment vortex cells the two mechanisms are used in complementary ways to illustrate the formation of 1 some of the principal skaergaard structures involving blocks and layers 2 modally graded layers in the layered series that rhythmically alternate with uniform layers and 3 modally sorted layers in the upper border series featuring underside draping beneath small included blocks explanations are provided for 1 why plagioclase did not float away from the tops of graded layers even though it was less dense than the liquid and 2 how the liquid part of a current was fractionated away from the crystalline materials modal and grain size data from skaergaard intrusion graded layers are shown to be in excellent accord with characteristics predicted for layers sorted by currents a synthesis diagram is presented illustrating how all the above processes may have functioned in concert in the intrusion

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

fast grain growth of olivine in liquid fe s and the formation of pallasites with rounded olivine grains abstract despite their relatively simple mineralogical composition olivine fe ni metal fes pyroxene the origin of pallasite meteorites remains debated it has been suggested that catastrophic mixing of olivine fragments with fe ni s followed by various degrees of annealing could explain pallasites bearing solely or prevalently fragmented or rounded olivines in order to verify this hypothesis and to quantify the grain growth rate of olivine in a liquid metal matrix we performed a series of annealing experiments on natural olivine plus synthetic fe s mixtures the best explanation for the observed olivine grain size distributions gsd of the experiments are dominant ostwald ripening for small grains followed by random grain boundary migration for larger grains our results indicate that olivine grain growth in molten fe s is significantly faster than in solid sulphur free metal we used the experimentally determined grain growth law to model the coarsening of olivine surrounded by fe s melt in a 100 600 km radius planetesimal in this model an impact is responsible for the mixing of olivine and fe ni s numerical models suggest that annealing at depths of up to 50 km allow for i average grain sizes consistent with the observed rounded olivine in pallasites ii a remnant magnetisation of fe ni olivine inclusions as measured in natural pallasites and iii for the metallographic cooling rates derived from fe ni in pallasites this conclusion is valid even if the impact occurs several millions of years after the differentiation of the target body was completed

a new path for the denmark strait overflow water from the iceland sea to denmark strait 1 denmark strait overflow water dsow is one of the main components of the thermohaline circulation there has been no consensus on where it is formed and by which way it is brought to the denmark strait it is shown here that it is brought to the sill by a hitherto unknown current that is traced from the sill back into the iceland sea north of iceland the transport of this current is sufficient to account for a major part of the transport of dsow as it has been measured at the sill if some entrainment of ambient water is assumed this supports theories suggesting that the iceland sea is the main source for the dsow and this has consequences for the way in which climate change affects the thermohaline circulation

effects of diffusion of water and migration of melts in crustal rocks an experimental study abstract water and melts are crucial in controlling the chemistry architecture and dynamics of the earth s crust however how water and melts influence chemical and textural changes of pervaded rocks during transport and how they chemically react with surrounding minerals remain cryptic we present experimental data illustrating how water undersaturated and potassium rich melt in partially molten felsic granulite or melt lost from such granulite affects the chemistry and texture of an initially nearly anhydrous eclogite at high pressure and high temperature 1 2 gpa 950 c for 20 h the first experiment simulates interaction of eclogite with granulite having a small proportion of melt melt 2 vol solids 98 vol with h2o 0 4 wt in the system granulite melt called in this paper granulite the second experiment simulates interaction of eclogite with melt melt 90 vol solids 10 vol h2o 4 wt in the system granulite melt called in this paper granulite partial melt our results show that during granulite eclogite interaction i the melt in the granulite crystallises as a consequence of water diffusion into the eclogite ii this water causes partial replacement of garnet by plagioclase orthopyroxene magnetite amphibole symplectite whose volumetric proportion correlates with water content in the granulite and iii a small proportion of melt from the granulite 2 vol infiltrates into the eclogite as documented by mineral overgrowths in granulite and by glass pools with increased potassium content in symplectites and along grain boundaries in the eclogite water and melt transfer appears to be effective in causing textural changes but appears to be ineffective in changing the bulk chemistry of the eclogite even if local enrichment in potassium and water occurs such chemically stealthy diffusion of water and migration of limited amount of melt is able to cause major textural changes accompanied by localised chemical changes at grain scale that would not be otherwise observed at the scale of the bulk rock composition

on the use of changes in dihedral angle to decode late stage textural evolution in cumulates the melt filled pore structure in the final stages of solidification of cumulates must lie somewhere between the two end members of impingement in which pore topology is controlled entirely by the juxtaposition of growth faces of adjacent grains and textural equilibrium in which pore topology is controlled by the minimization of internal energies the exact position between these two end members is controlled by the relative rates of crystal growth and textural equilibration for samples in which growth has stopped or is very slow textural equilibrium will prevail a close examination of dihedral angles in natural examples demonstrates that these two end member textures can be distinguished the impingement end member results in a population of apparent solid melt dihedral angles with a median of 60 and a standard deviation of 25 30 whereas the texturally equilibrated end member population has a median of 28 and a standard deviation of 14 for the specific case of cumulates in the rum layered intrusion residual porosity in troctolitic cumulates was close to the impingement end member whereas that in peridotites was close to melt bearing textural equilibrium suites of glass bearing samples from small or frequently disturbed magma systems show modification of initial impingement textures these modifications may be a consequence of textural equilibration or of diffusion limited growth during quenching distinction can be made between these two processes by a consideration of grain shape the geometry of interstitial phases in suites of fully solidified cumulates from the rum layered intrusion shows variable approach to sub solidus textural equilibrium from an initial state inherited by pseudmorphing of the last melt textural equilibration at pore corners occurs as a continuous process with a gradual movement of the entire dihedral angle population towards the equilibrium final state if the initial pseudomorphed state is one of disequilibrium i e a melt present impingement texture this change is accompanied by a reduction in the spread of the population if it is one of equilibrium the change is accompanied by an initial increase in the spread of the population followed by a decrease these observations demonstrate that previously published models of dihedral angle change involving the instantaneous establishment of the equilibrium angle in the immediate vicinity of the pore corner are incorrect

contributions to geotechnique 1948 2008 slope stability and embankment dams the paper reviews the main contributions to geotechnical engineering in the allied fields of slope stability and embankment dams over the past sixty years of geotechnique skempton s rankine lecture is probably the most important single contribution to the science of slope stability engineering through the initial enunciation of the linked ideas of slip surfaces and residual strength embankment dam engineering papers do not have such a single identifiable seminal publication but the contribution of rankine lecturers to the science of embankment dams is equally evident