effect of grain size on the distribution and transport of deep seated fluids and melts because permeability increases with the square of the grain size for a given fluid fraction it is commonly assumed that porous flow of fluids and melts is more effective in coarse grained domains of deep seated rocks this relative behavior is accurate however only as a description of two systems operating in isolation we demonstrate that if coarse and fine grained domains are in chemical communication then equilization of pore wall curvature across the system results in concentration of fluid or melt in domains of finer grain size because of this localization of fluid the permeability of the finer grained domains will match or exceed that of domains with coarser grains fluid focussing due to differences in grain size has potentially important implications for grain scale transport of metamorphic fluids including those released from subducting slabs into the sheared mantle wedge and also for partial melts in the mantle and deep crust

a self consistent model of melting magma migration and buoyancy driven circulation beneath mid ocean ridges numerical modeling and analysis are used to investigate the processes leading to the eruption of mantle derived magma at mid ocean ridges our model includes the following effects melting due to decompression magma migration by percolation and circulation of the mantle driven by both the oceanic plates and the distribution of buoyancy beneath the ridge the distribution of buoyancy is due to both the low density of the liquid and the difference in the density of the residual solids relative to unmelted mantle material the calculation of densities is based on a simple petrological model in which garnet spinel lherzolite melts to form a basaltic liquid and a harzburgite residue we find that the system spontaneously evolves to a state in which a rapid upwelling beneath the ridge axis faster than the plate velocity is confined laterally by stably stratified residual material beneath the newly formed plates this effect is exaggerated if a modest decrease in the shear viscosity of the solid upon melting is included our results provide a simple explanation for the narrowness of the zone of crustal formation at mid ocean ridges the model also predicts a transition from steady state to episodic crustal formation as the spreading velocity is reduced perhaps giving rise to along axis variations in the character of seafloor spreading the narrow rapid upwelling gives rise to substantial porosities at depths that are a large fraction of the depth to the solidus this may allow the liquid at depth to segregate into macroscopic channels which would account for the consensus from experimental petrology that the liquids parental to morb are derived from well below the base of the crust

an approach to estimate the freshwater contribution from glacial melt and precipitation in east greenland shelf waters using colored dissolved organic matter cdom changes in the supply and storage of freshwater in the arctic ocean and its subsequent export to the north atlantic can potentially influence ocean circulation and climate in order to understand how the arctic freshwater budget is changing and the potential impacts it is important to develop and refine empirical approaches for tracing freshwater contributions this in turn can help develop and validate model simulations arctic rivers are an important source of freshwater and stable oxygen isotope measurements are used to separate contributions from meteoric water river glacial and precipitation and sea ice melt we develop this approach further and investigate the use of an additional tracer colored dissolved organic matter cdom which is largely specific to freshwater originating from arctic rivers a robust relationship between the freshwater contribution from meteoric water and cdom is derived from 4 years of measurements in fram strait 2009 2012 combined with measurements from the east greenland shelf and dijmpha sound ne greenland results confirm a high contribution of riverine cdom in arctic halocline waters with salinities 31 5 and indicate the importance of shelf processes riverine input and sea ice formation while previously these waters where thought to be derived from open sea processes cooling and sea ice formation in the northern barents and kara seas in greenlandic coastal waters the meteoric water contribution is influenced by greenland ice sheet meltwater and deviations from the cdom meteoric water relationships found are applied to quantify meltwater contribution along the east greenland shelf waters 0 13

origin of freshwater and polynya water in the arctic ocean halocline in summer 2007 extremely low summer sea ice coverage in the arctic ocean in 2007 allowed extensive sampling and a wide quasi synoptic hydrographic and 18o dataset could be collected in the eurasian basin and the makarov basin up to the alpha ridge and the east siberian continental margin with the aim of determining the origin of freshwater in the halocline fractions of river water and sea ice meltwater in the upper 150 m were quantified by a combination of salinity and 18o in the eurasian basin two methods applying the preformed phosphate concentration po and the nitrate to phosphate ratio n p were compared to further differentiate the marine fraction into atlantic and pacific derived contributions while po based assessments systematically underestimate the contribution of pacific derived waters n p based calculations overestimate pacific derived waters within the transpolar drift due to denitrification in bottom sediments at the laptev sea continental margin within the eurasian basin a west to east oriented front between net melting and production of sea ice is observed outside the atlantic regime dominated by net sea ice melting a pronounced layer influenced by brines released during sea ice formation is present at about 30 to 50 m water depth with a maximum over the lomonosov ridge the geographically distinct definition of this maximum demonstrates the rapid release and transport of signals from the shelf regions in discrete pulses within the transpolar drift the ratio of sea ice derived brine influence and river water is roughly constant within each layer of the arctic ocean halocline the correlation between brine influence and river water reveals two clusters that can be assigned to the two main mechanisms of sea ice formation within the arctic ocean over the open ocean or in polynyas at the continental slope where relatively small amounts of river water are found sea ice formation results in a linear correlation between brine influence and river water at salinities of about 32 to 34 in coastal polynyas in the shallow regions of the laptev sea and southern kara sea sea ice formation transports river water into the shelf s bottom layer due to the close proximity to the river mouths this process therefore results in waters that form a second linear correlation between brine influence and river water at salinities of about 30 to 32 our study indicates which layers of the arctic ocean halocline are primarily influenced by sea ice formation in coastal polynyas and which layers are primarily influenced by sea ice formation over the open ocean accordingly we use the ratio of sea ice derived brine influence and river water to link the maximum in brine influence within the transpolar drift with a pulse of shelf waters from the laptev sea that was likely released in summer 2005

chronosequential changes of selected pedogenic properties in paddy soils as compared with non paddy soils abstract a series of paddy and non paddy soil profiles that are developed in chronosequences from approximately 50 to 1000 years of exposure time on fairly uniform marine deposits under nearly identical landscape and climate conditions were sampled from cixi zhejiang province china where rice has been traditionally grown under water submergence master horizons were identified and sampled selected pedogenic properties such as soil organic carbon soc content clay content fractions of iron total manganese and ph were used to characterize the horizons to compare the differences between paddy and non paddy profiles all paddy profiles are taken as one group and all non paddy profiles as another the measured properties were averaged over 0 100 cm soil depth results showed that paddy group contained significantly p

aqueous fluid connectivity and chemical transport in clinopyroxene rich rocks abstract in order to assess the efficacy of fluid assisted chemical transport in deep seated pyroxene rich rocks two types of experiment involving synthetic clinopyroxenites were performed at 900 950 c and 1 5 gpa 1 annealing of ferrosalite camg 0 4 fe 0 54 mn 0 06 si 2 o 6 or diopside camg 0 94 fe 0 06 si 2 o 6 powder in the presence of aqueous fluids water nacl cacl 2 or co 2 to produce near equilibrium fluid crystal dihedral angles s and 2 diffusion couple experiments in which an h 2 o bearing cylinder of fe rich clinopyroxenite ferrosalite was placed against one of mg rich clinopyroxenite diopside control diffusion experiments on fluid free clinopyroxenite and on single clinopyroxene crystals were also carried out the dihedral angle experiments consistently yielded median apparent values i e in 2d section of 65 69 well above the pinch off value of 60 and independent of additives nacl cacl 2 and co 2 in all cases however the frequency distributions were broad enough to suggest a range of real s on either side of the median the textures were also complicated by frequent crystal faceting at pore margins the diffusion couple experiments carried out with 0 0 6 1 3 2 7 4 0 and 8 0 vol h 2 o at run p and t showed no fe mg interdiffusion for all but the most fluid rich 8 couple this result is consistent with the determinations in showing that for geologically realistic fluid abundances aqueous fluids in clinopyroxenite form isolated noninterconnected pores this conclusion implies that aqueous fluids play no role in larger than grain scale chemical transport in pyroxene rich rocks under conditions of mechanical equilibrium the results also allow the possibility that water can be deeply subducted as a separate but trapped phase beyond the stability limit of amphibole

effect of sea ice melt on inherent optical properties and vertical distribution of solar radiant heating in arctic surface waters the inherent optical properties iops of polar waters pw exiting the arctic ocean in the east greenland current egc and of the inflowing atlantic waters aw in the west spitsbergen current wsc were studied in late summer when surface freshening due to sea ice melt was widespread the absorption and attenuation coefficients in pw were significantly higher than previous observations from the western arctic high concentrations of colored dissolved organic matter cdom resulted in 50 60 more heat deposition in the upper meters relative to clearest natural waters this demonstrates the influence of terrigenous organic material inputs on the optical properties of waters in the eurasian basin sea ice melt in cdom rich pw decreased cdom absorption but an increase in scattering nearly compensated for lower absorption and total attenuation was nearly identical in the sea ice meltwater layer this suggests a source of scattering material associated with sea ice melt relative to the pw in the aw melting sea ice forms a stratified surface layer with lower absorption and attenuation than well mixed aw waters in late summer it is likely that phytoplankton in the surface layer influenced by sea ice melt are nutrient limited the presence of a more transparent surface layer changes the vertical radiant heat absorption profile to greater depths in late summer both in egc and wsc waters shifting accumulation of solar heat to greater depths and thus this heat is not directly available for ice melt during periods of stratification

characteristics of colored dissolved organic matter cdom in the arctic outflow in the fram strait assessing the changes and fate of terrigenous cdom in the arctic ocean absorption coefficients of colored dissolved organic matter cdom were measured together with salinity delta o 18 and inorganic nutrients across the fram strait a pronounced cdom absorption maximum between 30 and 120 m depth was associated with river and sea ice brine enriched water characteristic of the arctic mixed layer and upper halocline waters in the east greenland current egc the lowest cdom concentrations were found in the atlantic inflow we show that the salinity cdom relationship is not suitable for evaluating conservative mixing of cdom the strong correlation between meteoric water and cdom is indicative of the riverine terrigenous origin of cdom in the egc based on cdom absorption in polar water and comparison with an arctic river discharge weighted mean we estimate that a 49 59 integrated loss of cdom absorption across 250 600 nm has occurred a preferential removal of absorption at longer wavelengths reflects the loss of high molecular weight material in contrast cdom fluxes through the fram strait using september velocity fields from a high resolution ocean sea ice model indicate that the net southward transport of terrigenous cdom through the fram strait equals up to 50 of the total riverine cdom input this suggests that the fram strait export is a major sink of cdom these contrasting results indicate that we have to constrain the c dom budgets for the arctic ocean much better and examine uncertainties related to using tracers to assess conservative mixing in polar waters citation granskog m a c a stedmon p a dodd r m w amon a k pavlov l de steur and e hansen 2012 characteristics of colored dissolved organic matter cdom in the arctic outflow in the fram strait assessing the changes and fate of terrigenous cdom in the arctic ocean j geophys res 117 c12021 doi 10 1029 2012jc008075

aqueous fluid connectivity in pyrope aggregates water transport into the deep mantle by a subducted oceanic crust without any hydrous minerals abstract the effect of pressure and temperature on the dihedral angles of aqueous fluid in a pyrope matrix was investigated experiments were performed on an h 2 o pyrope system in a multianvil apparatus over the pressure and temperature ranges of 4 13 gpa and 900 1200 c respectively the dihedral angle of the fluid in contact with the pyrope exhibited a significant change at pressures around 8 9 gpa the dihedral angles increased with increasing pressure up to 9 gpa at pressures above 9 gpa the dihedral angles were greater than 60 at temperatures below 1000 c therefore the efficient percolation of aqueous fluid in a pyrope matrix is not feasible in the upper mantle and the transition zone the fluid released from the breakdown reactions of the hydrous minerals lawsonite and phengite exists in the oceanic crust which mainly consists of garnet in the upper mantle and transition zone we conclude that a part of the aqueous fluid released from the hydrous minerals may be retained in the subducted oceanic crust and transferred into the deep mantle by the subduction process

thermohaline circulation hysteresis a model intercomparison we present results from an intercomparison of 11 different climate models of intermediate complexity in which the north atlantic ocean was subjected to slowly varying changes in freshwater input all models show a characteristic hysteresis response of the thermohaline circulation to the freshwater forcing which can be explained by stommel s salt advection feedback the width of the hysteresis curves varies between 0 2 and 0 5 sv in the models major differences are found in the location of present day climate on the hysteresis diagram in seven of the models present day climate for standard parameter choices is found in the bi stable regime in four models this climate is in the mono stable regime the proximity of the present day climate to the stommel bifurcation point beyond which north atlantic deep water formation cannot be sustained varies from less than 0 1 sv to over 0 5 sv

the effect of different second phase particle regimes on grain growth in two phase aggregates insights from in situ rock analogue experiments the aim of the study was to investigate the effect of rigid second phases on grain growth of a matrix phase for this purpose variable mixtures of norcamphor as the matrix phase with glass beads 0 08 0 51 volume fraction as second phase were used to perform see through rock analogue experiments under static conditions at constant temperatures 50 c irrespective of the second phase content grain size evolution of all mixtures can be subdivided into a stage of continuous grain growth a transient stage and a stage of a finally stabilized grain size on the grain scale the second phases affect the migrating grain boundaries either by pinning by single particles by multiple particles or even by particle clusters summed up over the entire aggregate these pinning regimes affect the average bulk grain size of the matrix grains such that the changes in matrix grain size directly correlate with the amount of second phases their dispersion and their degree of clustering in this way the matrix grain size decreases with increasing second phase content which can be expressed as a zener relationship originating from the modification of an ordinary grain growth law a new mathematical expression is defined which allows the calculation of changes in the matrix grain size as a function of different second phase volume fractions and particle sizes such models will be helpful in the future to predict microstructural changes in polymineralic rocks at depth

assessing parent material uniformity of a red and black soil complex in the landscapes abstract the distribution of red and black soil xeralfs xerolls associations in the monarto area south australia is complex and their genesis either being derived from a uniform parent material or a lithologic discontinuity is not known the objectives of this study were i to assess zr and ti bearing grains as minerals resistant to chemical weathering prior to employing zr and ti in determining parent material uniformity and ii to confirm whether pedological processes or a lithologic discontinuity may be responsible for the textural contrast within the red and black soil profiles scanning electron microscopy sem and energy dispersive x ray analysis edax were used to study chemical weathering and elemental composition of surfaces of zr and ti bearing grains x ray fluorescence xrf analysis was used to determine elemental concentrations in various soil fractions results showed that zr bearing grains consisted of only zircon having smooth clean surfaces which are characteristic of a mineral resistant to chemical weathering edax spectra confirmed that zr was a specific element to represent zircon suggesting its reliability to be used in assessing parent material uniformity on the other hand ti derived not only from minerals rutile anatase resistant but also from minerals ilmenite pseudorutile biotite susceptible to chemical weathering this limited the usefulness of ti as an index mineral for soil development studies except for zr ti ratio all other indicators of parent material uniformity i e depth distribution curves of zr and y in various fractions and y zr ratio showed no considerable inflection and variation with depth in a xeralf red soil this indicated the xeralf derived from a uniform parent material mica schists thereby texture contrast within a profile is due to pedological processes on the other hand depth distribution curves showed clear inflection and variation in xerolls black soils indicating soils developed from lithologic discontinuities so different trends in particle size fractions between 0 48 cm for ma5 and 0 59 cm for ma3 profiles compared to the underlying layers are due to parent material differences and not pedogenesis the presence of complex red and black soil association in the landscape is attributed to the difference in parent materials where the red soil developed from mica schist and the black soils from calcareous deposits

grain scale permeabilities of synthetic quartzite with volumetrically minor phlogopite corundum or aluminosilicate abstract in order to examine grain scale permeabilities in materials that are microstructurally similar to those of the lower crust and upper mantle we produced porous synthetic quartzites with small fractions of an additional minor mineral powdered quartz was mixed with minor amounts of either corundum or phlogopite and run in ag capsules at 800 850 c and 1 4 gpa for 5 to 10 days the resulting quartzites generally exhibited microstructural equilibrium and contained phlogopite corundum or aluminosilicate the minor mineral in all runs typically resided along quartz grain boundaries at low volume fractions x but increasingly occurred as porous clusters within corner pores at higher x in all polished sections the smallest quartz bound pores appeared free of the minor mineral pore geometry of all materials differed from that observed in pure synthetic quartzite pores exhibited an increased number of facets a small decrease in the dihedral angle and partial filling of larger pores by the minor phase measurements of permeability k were both higher and lower than those of monomineralic quartzite with similar with k decreasing as a function of x this decrease is likely the result of pore throat reduction either through fluid redistribution or obstruction of fluid pathways

effect of pore geometry on vp vs from equilibrium geometry to crack seismic wave velocities of melt or aqueous fluid containing systems are studied over a wide range of pore shapes including oblate spheroids tubes cracks and an equilibrium geometry controlled by a dihedral angle the relative role of liquid compressibility and pore geometry on the v p v s velocity ratio is clarified the result clearly indicates that p and s velocity structures determined by seismic tomography can be used to verify whether interfacial energy controlled melt or fluid geometry equilibrium geometry is achieved relationships between the diverse models are clearly established by relating each model to the oblate spheroid model in terms of the equivalent aspect ratio as a function of the aspect ratio a significant effect of pore geometry on d in v s d in v p the ratio of the fractional changes in v s and v p is shown equilibrium geometry of the partially molten rocks characterized by a dihedral angle of 20 40 corresponds to an aspect ratio of 0 1 0 15 the value of d in v s d in v p expected for the texturally equilibrated partially molten rocks is shown to be 1 1 5 which is much smaller than that expected for cracks and dikes with an aspect ratio of 10 2 10 3 in the upper mantle low velocity regions the seismologically obtained value of d in v s d in v p is within this range beneath the bolivian andes 1 1 1 4 but is as high as 2 beneath iceland 1 7 2 3 and beneath northeastern japan 2 0 the former region can be regarded as a region where equilibrium geometry is achieved and the latter regions can be regarded as regions where dikes and veins typical of a system far from the textural equilibrium dominate

stratification of parent material in european volcanic and related soils studied by laser diffraction grain sizing and chemical analysis abstract sedimentary stratification identified by field descriptions of 12 soils derived wholly or partly from volcanic materials was compared with results obtained by chemical analyses contents and ratios of lithogenic elements contents of heavy metals and detailed grain size data after removal of organic matter and amorphous fractions the finest sedimentary stratification was indicated by cluster analysis of ratios of lithogenic elements and by the grain size analyses sedimentary stratification in the field is difficult to determine or describe when 1 the deposits are strongly weathered 2 soil horizon boundaries coincide with stratification boundaries or 3 stratification is very fine nevertheless field descriptions are a reasonably good way of differentiating parent materials though they often underestimate the number of sedimentary layers

lithogic partitioning of fluids and melts under conditions of mechanical equilibrium the grain scale distribution of fluid or melt in a lithologically complex system is governed by the relative energies of the mineral fluid interfaces and the grain boundaries accordingly spatial changes in mineralogy imply accompanying changes in the connectivity and even the amount of fluid or melt present at equilibrium the hypothesized phenomenon of local variation in fluid or melt abundance with spatial changes in mineralogy is referred to here as lithologic partitioning of fluid or melt the phenomenon is potentially important because it could lead to the existence of highly permeable or impermeable zones in lithologically complex regions of the crust and upper mantle to verify and evaluate the concept of lithologic partitioning of aqueous fluid experiments were conducted in simple analog systems by annealing juxtaposed cylinders of two different rock types at 700 925 degrees c and 1 0 1 5 gpa these polycrystalline fluid partition couples included the following rock pairs calcite fluorite quartz fluorite and quartz clinopyroxene with overall aqueous fluid volume fractions phi ranging from approximately 0 015 to 0 10 in calcite fluorite couples fluid is partitioned by a factor of approximately 1 5 5 into the fluorite the actual value depends upon the chemical purity of the fluorite in fluorite quartz couples the fluid is partitioned into the quartz by a factor of 2 5 and in quartz clinopyroxene couples it is enriched in the clinopyroxene by a factor of approximately 3 similar experiments were done in a partially molten mantle system by juxtaposing peridotite and orthopyroxenite cylinders in the presence of approximately 6 basaltic melt in this case however no preference of the melt for one host rock relative to the other could be verified in general lithologic partitioning is a factor to be reckoned with as we seek understanding of fluid related petrologic and geochemical phenomena the effect is clearly capable of rapid and significant re distribution and localization of fluids in mineralogically variable systems

freshwater balance and the sources of deep and bottom waters in the arctic ocean inferred from the distribution of h218o data from sections across the eurasian basin of the arctic ocean occupied in 1987 and 1991 are used to derive information on the freshwater balance of the arctic ocean and on sources of the deep waters of the nansen amundsen and makarov basins using salinity h218o and mass balances we estimate the river runoff and the sea ice melt water fractions contained in the upper waters of the arctic ocean and infer pathways of the river runoff signal from the shelf seas across the central arctic ocean to fram strait the average mean residence time of the river runoff fraction contained in the arctic ocean halocline is determined to be about 11 to 14 years pacific water entering through bering strait is traced using silicate and its influence on the halocline waters of the canadian basin is estimated water column inventories of river runoff and sea ice melt water are calculated for a section just north of fram strait and implications of these inventories for sea ice export through fram strait are discussed comparison of the 18o 16o ratios of shelf water atlantic water and the deep waters of the arctic ocean indicate that the sources of the deep and bottom waters of the eurasian basin are located in the barents and kara seas

what controls partial melting in migmatites the layers of six stromatic migmatites from northern western and central europe display small but systematic chemical and mineralogical differences at least five of these migmatites do not show any signs of largescale metamorphic differentiation metasomatism or segregation of melts it is concluded therefore that the compositional layering observed in most of the investigated migmatites is due to compositional differences inherited from the parent rocks almost isochemical partial melting seems to be the most probable process transforming layered paragneisses metavolcanics or schists into migmatites the formation of neosomes is believed to be caused by higher amounts of partial melts formed due to higher amounts of water moving into these layers the neosomes have less biotite and more k feldspar if k feldspar is present at all than the adjacent mesosomes these differences are small but systematic and seem to control the access of different amounts of water to the various rock portions petrographical observations chemical data and theoretical considerations indicate a close relationship between rock composition rock deformation transport of water partial melting and formation of layered migmatites

the behaviour of so called immobile elements in hydrothermally altered rocks associated with volcanogenic submarine exhalative ore deposits evidence is available that some elements notably zr tio2 y sc ce and nb are largely immobile during the alteration of volcanic rocks owing to metamorphism hydrothermal events and weathering e g floyd and winchester 1978 however it is shown by reference to analyses of rocks from the environment of five volcanogenic massive sulphide bodies that while zr tio2 and ce are mostly immobile even during intense hydrothermal alteration y and particularly sc and nb may be extremely mobile when elements are removed by solution in a hydrothermal fluid it seems that reaction rates are such that these elements are almost totally removed from the rock therefore of the so called immobile trace elements only zr and tio2 may be used with any reliability to identify the degree of magmatic differentiation in an hydrothermally altered rock however if an element has been mobile it is usually readily identified as having moved

soluble chromophores in marine snow seawater sea ice and frost flowers near barrow alaska 1 we measured light absorption in 42 marine snow sea ice seawater brine and frost flower samples collected during the oasis field campaign between february 27 and april 15 2009 samples represented multiple sites between landfast ice and open pack ice in coastal areas approximately 5 km west of barrow alaska the chromophores that are most commonly measured in snow h2o2 no3 and no2 on average account for less than 1 of sunlight absorption in our samples instead light absorption is dominated by unidentified residual species likely organic compounds light absorption coefficients for the frost flowers on first year sea ice are on average 40 times larger than values for terrestrial snow samples at barrow suggesting very large rates of photochemical reactions in frost flowers for our marine samples the calculated rates of sunlight absorption and oh production from known chromophores are 0 1 1 4 1014 photons cm 3 s 1 and 5 70 10 12 mol l 1 s 1 respectively our residual spectra are similar to spectra of marine chromophoric dissolved organic matter cdom suggesting that cdom is the dominant chromophore in our samples based on our light absorption measurements we estimate dissolved organic carbon doc concentrations in barrow seawater and frost flowers as approximately 130 and 360 m c respectively we expect that cdom is a major source of oh in our marine samples and it is likely to have other significant photochemistry as well

water contents of silicic to intermediate magmas silicic to intermediate magmas have water contents that range from 1 wt to around 7 wt depending on the character and depth of the magma source type of melting reaction and the degree of differentiation the condition of water saturation is rare implying that crustal magma genesis generally takes place under fluid absent conditions or that any fluid present must contain volatile species other than h2o the source and quantity of water present during partial melting profoundly affect the types of melting reactions residues and magmas as well as subsequent magma evolution for s type granitic magmas melting reactions involving muscovite breakdown in pelites yield low temperature wet melts that form veins pockets and small plutons in regional metamorphic terranes biotite breakdown in pelites near the amphibolite granulite facies transition yields hotter magmas with variable water contents these are emplaced at medium to high levels under granulite facies conditions biotite breakdown in quartzofeld spathic rocks yields high temperature dry magmas emplaced as subvolcanic batholiths and volcanics

p t x effects on equilibrium carbonate h 2 o co 2 nacl dihedral angles constraints on carbonate permeability and the role of deformation during fluid infiltration fluid solid solid dihedral angles in the nacl h2o co2 calcite dolomite magnesite system have been determined at pressures ranging from 0 5 to 7 kbar and temperatures from 450 c to 750 c at 1 kbar and 650 c both dolomite and magnesite exhibit a dihedral angle minimum for intermediate h2o co2 fluids similar to that previously determined by the present authors for calcite but the depth of the minimum is smaller being above the critical value of 60 for both dolomite and magnesite for all fluid compositions calcite calcite brine dihedral angles at 650 c have been determined in the pressure range 1 5 kbar angles decrease with increasing salt content of the fluid tending towards a constant value of about 65 for strong brines at pressures above 2 kbar there is a general increase of angle with increasing pressure which is most marked for strong brines a positive correlation of angle with pressure is also observed in calcite h2o co2 fluids the position of the minimum moving towards higher angles and towards h2o rich fluids with increasing pressure the permeability window previously observed by the present authors at 1 kbar and intermediate fluid compositions closes at about 1 5 kbar the results demonstrate that the permeability of carbonates to grain edge fluid flow is only possible at low pressures and for fluids of restricted h2o co2 nacl compositions however geochemical evidence from metamorphic terrains suggests that pervasive infiltration does occur under conditions where impermeability is predicted from examination of published studies of infiltrated carbonates we conclude that deformation plays a critical role in enhancing carbonate permeability possible mechanisms for this include shear enhanced dilatancy micro cracking fluid inclusion drag by deformation controlled grain boundary migration and dynamically maintained transient grain boundary fluid films

observed increases in bering strait oceanic fluxes from the pacific to the arctic from 2001 to 2011 and their impacts on the arctic ocean water column 1 mooring data indicate the bering strait throughflow increases 50 from 2001 0 7 sv to 2011 1 1 sv driving heat and freshwater flux increases increase in the pacific arctic pressure head explains two thirds of the change the rest being attributable to weaker local winds the 2011 heat flux 5 1020j approaches the previous record high 2007 due to transport increases and warmer lower layer ll temperatures despite surface temperature sst cooling in the last decade warmer ll waters arrive earlier 1 6 1 1 days yr though winds and sst are typical for recent decades maximum summer salinities likely set in the bering sea remain remarkably constant 33 1 psu over the decade elucidating the stable salinity of the western arctic cold halocline despite this freshwater flux variability strongly driven by transport exceeds variability in other arctic freshwater sources remote data winds sst prove insufficient for quantifying variability indicating interannual change can still only be assessed by in situ year round measurements

contrasting rock permeability in the aureole of the ballachulish igneous complex scottish highlands the influence of surface energy the ballachulish igneous complex in the scottish highlands part of a widespread group of late caledonian calcalkaline intrusions was emplaced at a depth of 10 km into dalradian metasediments resulting in melting of the country rocks near the intrusive contact the greatest extent of melting occurred in the leven schist in the 400 m wide so called chaotic zone which experienced infiltration of aqueous fluids from the pluton in contrast adjacent to the chaotic zone the feldspar bearing appin quartzite underwent significant melting only within a few metres of the intrusion despite both being in contact with the same fluid source as the leven schist and having a similar wet melting point the permeability of the appin quartzite and quartz horizons in the leven schist to pervasive grain edge infiltration of aqueous fluids was determined by measuring the equilibrium quartz h2o dihedral angle for the p t conditions of contact metamorphism addition of powdered samples of both rock types to the pure quartz h2o system results in a linear decrease of the quartz h2o dihedral angle with increasing temperature the rate of this decrease for the leven schist is greater than that for the appin quartzite and the angle decreases below 60 some 30 c below the wet solidus 670 c at 0 3 gpa charges bearing appin quartzite had dihedral angles greater than 60 at all temperatures below the wet solidus 690 c at 0 3 gpa these results demonstrate that quartz rich horizons in the leven schist would have been permeable to infiltration of aqueous fluids close to the solidus permitting extensive h2o fluxed melting to occur the appin quartzite would have remained impermeable to grain edge flow consistent with the observed differences in the extent of partial melting of the two lithologies

pacific freshwater river water and sea ice meltwater across arctic ocean basins results from the 2005 beringia expedition 1 pacific water sea ice meltwater and river water are the primary sources of freshwater in the arctic ocean we have determined their relative fractions on a transect across the arctic ocean section 2005 expedition onboard ib oden which took place from 21 august to 23 september 2005 the transect began north of alaska continued through the central canada basin to the alpha ridge and into the makarov basin and ended in amundsen basin pacific freshwater and river water were the major sources of freshwater throughout the central canada basin and into makarov basin with river water fractions sometimes considerably higher than pacific water in the top 50 m pacific freshwater extended to depths of about 200 m pacific water found over the alpha ridge and in the amundsen basin is suggested to have been transported there in the transpolar drift the inventories of pacific freshwater and river water were roughly constant along the section through most of the canada and makarov basins river water fractions were greater than those of pacific freshwater in the amundsen basin sea ice meltwater fractions were negative reflecting net ice formation or near zero throughout most of the section a comparison of freshwater inventories with those at stations occupied during expeditions in 1991 1994 and 1996 indicated an increase in river water inventories in the makarov and amundsen basins on the eurasian side of the arctic ocean

distribution of atlantic and pacific waters in the upper arctic ocean implications for circulation the atlantic and pacific oceans provide source waters for the arctic ocean that can be distinguished by their differing nitrate and phosphate concentration relationships using these relationships we estimate the amount of atlantic and pacific waters in the surface layer top 30 m of the arctic ocean atlantic source water is dominant in most of the eurasian basin and is present in significant amounts in the makarov basin north of the east siberian sea pacific source water is dominant in most of the canadian basin and is present in significant amounts in the amundsen basin north of greenland we deduce circulation patterns from the distributions of atlantic and pacific source waters in the surface layer of the arctic ocean and conclude that the flow within the surface layer differs from ice drift along the north american and european boundaries of the polar basin

organic carbon accumulation in a 2000 year chronosequence of paddy soil evolution considerable amounts of soil organic matter som are stabilized in paddy soils and thus a large proportion of the terrestrial carbon is conserved in wetland rice soils nonetheless the mechanisms for stabilization of organic carbon oc in paddy soils are largely unknown based on a chronosequence derived from marine sediments the objectives of this study are to investigate the accumulation of oc and the concurrent loss of inorganic carbon ic and to identify the role of the soil fractions for the stabilization of oc with increasing duration of paddy soil management a chronosequence of six age groups of paddy soil formation was chosen in the zhejiang province pr china ranging from 50 to 2000 years yrs of paddy management soil samples obtained from horizontal sampling of three soil profiles within each age group were analyzed for bulk density bd oc as well as ic concentrations oc stocks of bulk soil and the oc contributions to the bulk soil of the particle size fractions paddy soils are characterized by relatively low bulk densities in the puddled topsoil horizons 1 0 and 1 2 g cm 3 and high values in the plow pan 1 6 g cm 3 our results demonstrate a substantial loss of carbonates during soil formation as the upper 20 cm were free of carbonates in 100 year old paddy soils but carbonate removal from the entire soil profile required almost 700 yrs of rice cultivation we observed an increase of topsoil oc stocks from 2 5 to 4 4 kg m 2 during 50 to 2000 yrs of paddy management the oc accumulation in the bulk soil was dominated by the silt and clay sized fractions the silt fraction showed a high accretion of oc and seems to be an important long term oc sink during soil evolution fine clay in the puddled topsoil horizon was already saturated and the highest storage capacity for oc was calculated for coarse clay with longer paddy management the fractions 20 m showed an increasing actual oc saturation level but did not reach the calculated potential storage capacity

freshwater composition of the waters off southeast greenland and their link to the arctic ocean 1 the freshwater composition of waters on the southeast greenland shelf and slope are described using a set of high resolution transects occupied in summer 2004 which included hydrographic velocity nutrient and chemical tracer measurements the nutrient and tracer data are used to quantify the fractions of pacific water sea ice melt and meteoric water present in the upper layers of the east greenland current egc and east greenland coastal current egcc the egc egcc system dominates the circulation of this region and strongly influences the observed distribution of the three freshwater types sea ice melt and meteoric water fractions are surface intensified reflecting their sources and generally increase southward from denmark strait to cape farewell as well as shoreward significant fractions of pacific water are found in the subsurface layers of the egcc supporting the idea that this inner shelf branch is directly linked to the egc and thus to the arctic ocean a set of historical sections is examined to investigate the variability of pacific water content in the egc and egcc from 1984 to 2004 in the vicinity of denmark strait the fraction of pacific water increased substantially in the late 1990s and subsequently declined to low levels in 2002 and 2004 mirroring the reduction in pacific water content reported previously at fram strait this variability is found to correlate significantly with the arctic oscillation index lagged by 9 years suggesting that the arctic ocean circulation patterns bring varying amounts of pacific water to the north atlantic via the egc egcc

natural constraints on metamorphic reaction rates abstract quantitative constraints on the rates at which metamorphic reactions proceed in nature are now available from several sources most common are predictions made on the basis of laboratory kinetic data however the applicability of such laboratory based predictions has long been questioned and many observations in the field now suggest much slower rates here published quantitative field based constraints on high temperature 400 c reaction rates are assembled from a variety of sources reaction rates attending regional metamorphism are four to seven orders of magnitude slower than most laboratory based predictions a general rate law for regional metamorphism has been derived which best describes these field based data log 10 r net 0 0029 t 9 6 1 where r net is the net reaction rate g cm 2 a and t is temperature c at the same time natural reaction rates attending contact metamorphism differ from laboratory based predictions by less than two orders of magnitude and are in close agreement at higher temperatures thus while existing laboratory based kinetic data may be judiciously applied to some contact metamorphic systems laboratory based kinetic predictions clearly misrepresent regional metamorphism to explain this kinetic discrepancy regional metamorphic reaction rates may be limited by slow intergranular transport due to comparatively limited or transient availability of aqueous fluid in the intergranular medium the general field based rate law may be applied to regional metamorphic and other environments i e ultrahigh pressure or ultrahigh temperature metamorphism if similar system characteristics mainly low aqueous fluid content can be inferred

grain growth in synthetic marbles with added mica and water evolution of grain size in synthetic marbles was traced from compaction of unconsolidated powder through primary recrystallization and normal grain growth to a size stabilized by second phases to form the marbles reagent grade caco3 was mixed with 0 1 and 5 volume mica and heat treated under pressure with added water densification with negligible recrystallization occurred within one hour at 500 c and 500 mpa confining pressure primary recrystallization occurred at 500 550 c causing increases of grain size of factors of 2 5 resulting samples had uniform grain size gently curved grain boundaries and near equilibrium triple junctions they were used subsequently for normal grain growth studies normal grain growth occurred above 550 c at 800 c grain size d increased from 7 m d0 to 65 m in 24 hours growth rates fit the equation d n d 0 n kt where k is a constant and n 2 6 minor amounts of pores or mica particles inhibit normal grain growth and lead to a stabilized grain size dmax which depends on the size of the second phases and the inverse of their volume fraction raised to a power between 0 3 and 1 once dmax is reached normal growth continues only if second phases are mobile or coarsen or if new driving forces are introduced that cause unpinning of boundaries normal grain growth in solnhofen limestone was significantly slower than in pure synthetic marble suggesting that migration is also inhibited by second phases in the limestone

dilution of the northern north atlantic ocean in recent decades declining salinities signify that large amounts of fresh water have been added to the northern north atlantic ocean since the mid 1960s we estimate that the nordic seas and subpolar basins were diluted by an extra 19 000 5000 cubic kilometers of freshwater input between 1965 and 1995 fully half of that additional fresh water about 10 000 cubic kilometers infiltrated the system in the late 1960s at an approximate rate of 2000 cubic kilometers per year patterns of freshwater accumulation observed in the nordic seas suggest a century time scale to reach freshening thresholds critical to that portion of the atlantic meridional overturning circulation

differentiating fluvial components of upper canada basin waters on the basis of measurements of dissolved barium combined with other physical and chemical tracers 1 the utility of dissolved barium ba as a quasi conservative tracer of arctic water masses has been demonstrated previously here we report distributions of salinity temperature and ba in the upper 200 m of the canada basin and adjacent areas observed during cruises conducted in 2003 2004 as part of the joint western arctic climate study and beaufort gyre exploration project a salinity oxygen isotope mass balance is used to calculate the relative contributions from sea ice melt meteoric and saline end members and ba measurements are incorporated to resolve the meteoric fraction into separate contributions from north american and eurasian sources of runoff large fractions of eurasian runoff as high as 15 5 were observed in the surface layer throughout the canada basin but significant amounts of north american runoff in the surface layer were only observed at the southernmost station occupied in the canada basin in 2004 nearest to the mouth of the mackenzie river smaller contributions from both eurasian and north american runoff were evident in the summer and winter pacific derived water masses that comprise the underlying upper halocline layer in the canada basin significant amounts of eurasian and north american runoff were observed throughout the water column at a station occupied in amundsen gulf in 2004 this suggests the export of runoff from both sources through the passages of the canadian arctic archipelago

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

experimental evidence for mobility of zr and other trace elements in soils a soxhlet extraction was carried out over a period of 27 d on a column comprising 3 cm of quartz overlain by 4 cm of soil from the b horizon and then 1 cm of soil from the a horizon of a granitic podzol major and trace elements were leached from the column and accumulated in a reservoir at the base of the column total loss of elements from the soil over the course of the experiment ranged from 0 002 to 1 wt with major elements and the light and heavy rare earth elements ree showing the largest percentage losses zirconium 0 002 and then al 0 008 showed the lowest percentage loss the light ree were leached out of the soil preferentially to the mid ree all elements showed accumulation by a factor of 2 to 11 in the quartz layers at the base of the column particularly in the upper first 1 cm of the quartz major elements were leached from the column at a rate of 0 02 to 0 59 mol h 1 whereas zr nd sm gd dy rb and sr were leached at the rate of 0 5 to 30 10 6 mol h 1 concentrations of other ree in the reservoir increased over the duration of the experiment but they were poorly correlated with time so leaching rates were not calculated normalization of the major element leaching rates to take into account the constant flushing of water through the column the average annual rainfall in the allt a mharcaidh catchment in scotland from where the soil was sampled and the cross sectional area of the soil in the column together with the temperature of the soil in the column 70 c compared with the average annual temperature of the allt a mharcaidh catchment 5 7 c gave major element release rates from the soil of 0 002 to 0 97 meq m 2 yr 1 depending on the choice of ea the dissolution activation energy which are generally less than those measured in the field of 0 1 to 40 9 meq m 2 yr 1 calculations showed that despite the redistribution and loss of zr from the column assumptions of zr mobility would have had a negligible effect on calculated element release rates of na ca fe and mg however significant underestimates of the release of k 5 ti 57 al 5 and si 10 as well as some trace elements e g nd 23 rb 54 sr 24 would have occurred concentrations of ca and sr leached from the column correlated well rsq 0 93 p 0 01 supporting the idea of the use of sr release as a proxy for ca release in weathering rate calculations the release rates and percentage loss of ree from the soil varied between elements indicating that ree distribution patterns of rocks and soils may not be preserved in drainage waters

sources and distribution of fresh water in the east greenland current abstract fresh water flowing from the arctic ocean via the east greenland current influences deep water formation in the nordic seas as well as the salinity of the surface and deep waters flowing from there this fresh water has three sources pacific water relatively fresh cf atlantic water river runoff and sea ice meltwater to determine the relative amounts of the three sources of fresh water in may 2002 we collected water samples across the east greenland current in sections from 81 5 n to the irminger sea south of denmark strait we used nitrate phosphate relationships to distinguish pacific waters from atlantic waters salinity to obtain the sum of sea ice melt water and river runoff water and total alkalinity to distinguish the latter river runoff contributed the largest part of the total fresh water component in some regions with some inventories exceeding 12 m pacific fresh water pacific source water s 32 cf atlantic source water s 34 9 typically provided about 1 3 of the river runoff contribution sea ice meltwater was very nearly non existent in the surface waters of all sections likely at least in part as a result of the samples being collected before the onset of the melt season the fresh water from the arctic ocean was strongly confined to near the greenland coast we thus conjecture that the main source of fresh water from the arctic ocean most strongly impacting deep convection in the nordic seas would be sea ice as opposed to fresh water in the liquid phase i e river runoff pacific fresh water and sea ice meltwater

melting and diffusion processes in closed system migmatization estimated variations in mineral concentrations across leucosomes suggest that leucosomes are generated during anatexis by a diffusive exchange between the leucosome and the mesosome and not by the migration of melt from the mesosome however the presence of melt is a precondition for the diffusive exchange to take place initially a crack is formed due to shear stress the formation of a crack allows a diffusive exchange to take place through the melt which causes melting of minerals situated near the crack the diffusive exchange of material is less efficient in the mesosome where the melt is isolated at grain corners and edges the microcline enrichment of some granitic leucosomes is thought to be due to the diffusive depletion of the mesosome caused by growth of alkali feldspar during the consolidation of the migmatite in general it seems unnecessary to invoke concentrations of water in the leucosome or the intrusion of external fluids or magmas for migmatite formation

freshwater budget of the canada basin arctic ocean from salinity δ18o and nutrients 1 the contribution of freshwater components e g meteoric sea ice and pacific water in the canada basin is quantified using salinity 18o and nutrient data collected in 2003 and 2004 the penetration depth of sea ice meltwater is limited to the upper 30 m and brine rejected during sea ice formation is observed from 30 to 250 m depth the fraction of meteoric water is high in the upper 50 m and decreases with depth pacific water entering via bering strait is the main source of freshwater below 50 m depth bering strait throughflow which transports pacific water with salinity 32 5 together with meteoric water supplied upstream of the bering strait contributes up to 75 of freshwater input 3200 km3 a 1 to the canada basin the mean residence time of pacific water in the canada basin is estimated to be 11 years precipitation and river runoff from both north american and eurasian continents add 800 km3 a 1 and sea ice formation removes 900 km3 a 1 0 6 m a 1 of fresh water the export of ice and liquid fresh water from the canada basin contributes 40 of the freshwater flux from the arctic ocean to the north atlantic ocean

effects of water on dynamically recrystallized grain size of olivine abstract recrystallized grain size versus stress relationship for olivine has been determined under water poor and water rich conditions we found that when the water content in olivine exceeds 800 ppm h si the size of recrystallized grains is about two to three times larger than under water poor conditions compared at the same stress level microstructural observations of deformed samples show that the ratio of recrystallized grain size to that of subgrains increases significantly with water content and that the volume fraction of grains containing subgrain boundaries is smaller under water rich conditions than under water poor conditions these observations suggest that the enhancement of grain boundary mobility by water is more significant than that of dislocation recovery leading to a larger size of recrystallized grains under water rich conditions

response of vertisols andosols and alisols to paddy management abstract interchanging submergence and drainage in paddy soils induce alternating redox conditions it is known that this causes changes in organic carbon stocks in amounts and crystallinity of fe oxides as well as transformation of clay minerals and subsequent changes in cation exchange capacity cec however the influence of the initial soil type on the extent of these changes is not yet well understood therefore we studied paddy soils that derived from three different soil types vertisols andosols alisols on volcanic parent material in java indonesia to account for the variability in parent materials we additionally sampled sandstone derived alisols in china adjacent non paddy soils were sampled as references samples were analyzed for texture bulk density clay mineral composition total element content ph cec phosphorus retention organic carbon oc and acid oxalate feox and dithionite citrate bicarbonate extractable fe fedcb only the alisol derived paddy soil in china showed textural changes compared to the non paddy soil evidence for paddy management induced ferrolysis was not found the smaller topsoil clay content in the paddy soil is most probable caused by clay migration only minor differences in clay minerals were found topsoils of andosol derived paddy soils however tend to be less desilicated indicating phytolith accumulation except for vertisols paddy management caused significant depletion in fe oxides in the topsoils puddled layer and plow pan due to redox processes the extent to which the reduced fe was leached or re oxidized as short range ordered fe oxides depended on the soil texture andosols and sandy alisols facilitated leaching clayey alisols re oxidation in either case the stocks of crystalline fe oxides diminished causing increased proportions of short range ordered fe oxides retention of phosphorus was directly related to changes in the absolute amounts of short range ordered fe oxides an accumulation of fe oxides in paddy subsoils was not found lateral transport with drainage water might be a reason in highly permeable soils with large vertical water fluxes e g andosols under paddy management colloidal transport might also play a role despite losses in potential oc storage capacity i e fe oxides clay minerals allophane paddy soils derived from andosols and sandy alisols in china had larger oc concentrations in the puddled topsoil whereby the other soils showed no increase in oc under paddy management therefore paddy management does not necessarily enhance carbon sequestration rather differences in organic matter input between non paddy and paddy soils seem to determine whether oc is accumulated under paddy management or not effects of paddy management on cec were little and mainly due to oc accumulation and fe oxide coating removal from clay minerals overall paddy management induced changes were partly influenced by the original soil and the parent material in turn the main characteristics of the initial soil type were preserved and not overridden by paddy management

sources to the east greenland current and its contribution to the denmark strait overflow data from the east greenland current in 2002 are evaluated using optimum multiparameter analysis the current is followed from north of fram strait to the denmark strait sill and the contributions of different source waters in mass fractions are deduced from the results it can be concluded that at least in spring 2002 the east greenland current was the main source for the waters found at the denmark strait sill contributing to the overflow into the north atlantic the east greenland current carried water masses from different source regions in the arctic ocean the west spitsbergen current and the greenland sea the results agree well with the known circulation of the western nordic seas but also add knowledge both to the quantification and to the mixing processes showing the importance of the locally formed greenland sea arctic intermediate water for the east greenland current and the denmark strait

the freshwater composition of the fram strait outflow derived from a decade of tracer measurements the composition of the fram strait freshwater outflow is investigated by comparing 10 sections of concurrent salinity 18o nitrate and phosphate measurements collected between 1997 and 2011 the largest inventories of net sea ice meltwater are found in 2009 2010 and 2011 the 2009 2011 sections are also the first to show positive fractions of sea ice meltwater at the surface near the core of the egc sections from september 2009 2011 show an increased input of sea ice meltwater at the surface relative to older september sections this suggests that more sea ice now melts back into the surface in late summer than previously comparison of april july and september sections reveals seasonal variations in the inventory of positive sea ice meltwater with maximum inventories in september sections the time series of sections reveals a strong anti correlation between meteoric water and net sea ice meltwater inventories suggesting that meteoric water and brine may be delivered to fram strait together from a common source we find that the freshwater outflow at fram strait exhibits a similar meteoric water to net sea ice meltwater ratio as the central arctic ocean and siberian shelves suggesting that much of the sea ice meltwater and meteoric water at fram strait may originate from these regions however we also find that the ratio of meteoric water to sea ice meltwater inventories at fram strait is decreasing with time due to an increased surface input of sea ice meltwater in recent sections

grain growth in the forsterite diopside system abstract grain growth experiments in dunite clinopyroxenite and wehrlites with various forsterite diopside ratios were performed to investigate the effect of modal composition on grain growth kinetics in the earth s uppermost mantle the experiments were conducted using a piston cylinder apparatus at 1200 c and 1 2 gpa for 2 763 h under dry conditions normal grain growth ngg occurred in dunite clinopyroxenite and relatively forsterite poor wehrlites 70 vol of forsterite grain growth rates of forsterite and diopside in relatively forsterite poor wehrlites were much slower than those in dunite and clinopyroxenite in the forsterite rich wehrlites 80 vol of forsterite ngg of diopside and abnormal grain growth agg of forsterite occurred the growth rate of diopside was significantly slower than that in clinopyroxenite while the growth rate of forsterite by agg was found to be similar to that by ngg in dunite the presence of 20 vol diopside had the effect of inhibiting the forsterite grain growth during the initial stage resulting in agg of forsterite thus overtaking the growth rate in dunite our experimental results suggest that there would be a significant difference in grain growth rate and consequently in effective viscosity between olivine rich peridotites depleted mantle and relatively olivine poor peridotites fertile mantle in the case of grain size sensitive creep variation of mean grain sizes in the upper mantle would result not only from differences in temperature and phase assemblage but also from the variation of modal compositions

arctic ocean water mass balance from isotope data the distributions of the oxygen 18 and tritium isotopes and of salinity yield a residence time of 10 years for the surface and halocline waters of the arctic basin we find a yearly net production of 0 59 m of sea ice and an input of 1 16 m of freshwater from continental river runoff local precipitation and bering strait salinity deficiency using the basin area value with these numbers gives long term average total net production and transport rates of 0 15 sv of ice and 0 18 sv of meteoric component bering strait water not included if in addition a reasonable depth profile of relative current velocity is assumed for the outflow a yearly input of 2 8 sv of atlantic and bering strait water is needed to replenish the upper and halocline waters these numbers should be good to 20 and are multiyear averages the isotope data clearly indicate that the barents sea is an inflow area for atlantic water to the basin but that net export of ice occurs there

tracer derived freshwater composition of the siberian continental shelf and slope following the extreme arctic summer of 2007 we investigate the freshwater composition of the shelf and slope of the arctic ocean north of the new siberian islands using geochemical tracer data 18o ba and po 4 collected following the extreme summer of 2007 we find that the anomalous wind patterns that partly explained the sea ice minimum at this time also led to significant quantities of pacific derived surface water in the westernmost part of the makarov basin we also find larger quantities of meteoric water near lomonosov ridge than were found in 1995 dissolved barium is depleted in the upper layers in one region of our study area probably as a result of biological activity in open waters increasingly ice free conditions compromise the quantitative use of barium as a tracer of river water in the arctic ocean

beginning of melting in the granite system qz or ab an h2o the beginning of melting in the system qz or ab an h2 o was experimentally reversed in the pressure range p text h text 2 text o 2 15 kbar using starting materials made up of mixtures of quartz and synthetic feldspars with increasing pressure the melting temperature decreases from 690 c at 2 kbar to 630 c at 17 kbar in the an free alkalifeldspar granite system qz or ab h2o in the granite system qz or ab an h2o the increase of the solidus temperature with increasing an content is only very small in comparison to the alkalifeldspar granite system the solidus temperature increases by 3 c 7 c if albite is replaced by plagioclase an 20 an 40 the difference between the solidus temperatures of the alkalifeldspar granite system and of quartz anorthite sanidine assemblages system qz or an h2o is approximately 50 c

distribution of partial melt in a felsic system the importance of surface energy the texture distribution and infiltration tendency of a quartz albite melt in equilibrium with a synthetic texturally equilibrated quartzite was examined in a series of distribution and infiltration experiments at 1 250 c and 8 kbar hydrostatic pressure wetting angle measurements from melt distribution experiments show a dihedral angle of 60 degrees implying a quartz quartz interfacial energy approximately 1 7 times the quartz melt value because of this specific relationship between interfacial energies the system can achieve its lowest surface free energy state with the melt either in pools or along grain edge intersections possibly forming some interconnected channels stability of melt in pockets and along grain edge intersections was observed in a fourteen day dispersed melt experiment yet melt pools failed to disperse into the quartzite during infiltration experiments comparison of the observed dihedral angle with previously measured surface energy values for the melt and quartz shows excellent agreement and also demonstrates that an aggregate of randomly orientated anisotropic grains acts approximately isotropically

fluid absent melting and the roles of fluids in the lithosphere a slanted summary abstract the presence or absence nature and compositions of lithospheric fluids are crucial factors in the evolution of igneous and metamorphic rocks despite this confusion still surrounds perceptions of the degrees of fluid involvement in many geological settings however experimental and field investigations constrain these roles and we are able to make some valid generalizations studies of prograde metamorphism have highlighted the spatial heterogeneity of fluid concentrations in many crustal environments this commonly indicates internal lithological control of volatile activities under fluid present conditions crustal fluids do not appear to mix readily fluid flow is generally structurally or lithologically controlled the transition from amphibolite to granulite facies is characterized by a decrease in ah2o as well as a temperature increase in many terranes these phenomena correlate with the appearance of migmatites some granulites are not migmatitic but have chemical and mineralogical characteristics of melt depleted restites this indicates efficient extraction of melts incongruent melting reactions involving the breakdown of crystalline hydrates in crustal rocks produce granitoid melts plus denser restites that are nearly or actually anhydrous experimental and theoretical treatments of fluid absent melting show that micas and amphiboles decompose at 700 to 900 c for mid to lower crustal pressures the melts resemble the compositions of s and i type granitoids pervasive aqueous fluids could not generally have been present during this melting since exposed granulite terranes are not characterized by high melt proportions and the magmas themselves are water undersaturated likewise the general presence of very h2o poor pervasive fluids is unlikely since this would allow only subsolidus dehydration at normally attainable crustal temperatures in this case the amphibolite granulite transition is possible at relatively low temperatures and the resultant rocks would not contain evidence of in situ melting the granulite granite connexion and effective crustal differentiation seem viable only during high temperature fluid absent metamorphism data on continental geotherms show that the lower crust is not entirely granulitic granulites are produced in regions of anomalously high heat flow the mantle connexion thus inferences on the nature of the lower crust should not be entirely based on studies of exposed granulite terranes mineral assemblages in eclogites also indicate widespread internal buffering of volatile activities and probable fluid absent conditions mantle derived basaltic magmas too are volatile bearing and it is plausible that volatile fixing phases also occur in the mantle volatiles may largely be introduced into the mantle through subduction processes and only released during the melting attending the breakdown of hydrous minerals as in the crust

equilibrium dihedral angles in the system h2o co2 nacl calcite and implications for fluid flow during metamorphism fluid calcite calcite dihedral angles have been measured for fluids in the system h2o co2 nacl between 1 and 2 kbar and 550 750 c it is found that the calcite calcite h2o dihedral angle decreases steadily with addition of nacl from a value of about 80 pure water to 44 60 wt nacl the co2 h2o system displays a well defined minimum at x co 2 0 5 with a dihedral angle of 50 in contrast to those of pure co2 and h2o which are 90 and 80 respectively experiments containing fluids which are immiscible at run conditions showed a bimodal distribution of dihedral angles in the co2 h2o nacl system which can be approximately correlated with the compositions of the two fluid phases such bimodality was only observed for immiscible fluids in the h2o nacl system if the quench rate exceeded about 200 c per min this is probably due to the extremely rapid establishment of the single phase dihedral angle on quenching the fluid phase topology in devolatilising marbles will only be a connected network for very saline brines and fluids with x co 2 close to 0 5 fluids trapped in fluid inclusions in calcite grains in marbles may be predominantly h2o rich or co2 rich and of low salinity all other fluid compositions in the h2o co2 nacl calcite system will occupy isolated pores the largest of which will grow at the expense of the smallest escape of fluid produced during devolatilisation reactions under such conditions will occur by fluid overpressuring and hydrofracture in contrast previous experimental studies of quartz fluid dihedral angles between 950 and 1100 c watson and brenan 1987 predict that quartz dominated lithologies will permit pervasive flow of h2o nacl fluids but not of h2o co2 fluids documented geological examples of differences in permeability and fluid flow mechanism between metamorphic argillites psammites and limestones which support the results of the experimental studies are discussed

ocean circulation and freshwater pathways in the arctic mediterranean based on a combined nd isotope ree and oxygen isotope section across fram strait the water masses passing the fram strait are mainly responsible for the exchange of heat and freshwater between the nordic seas and the arctic ocean the arctic mediterranean am disentangling their exact sources distribution and mixing however is complex this work provides new insights based on a detailed geochemical tracer inventory including dissolved nd isotope end rare earth element ree and stable oxygen isotope 18o data along a full water depth section across fram strait we find that nd isotope and ree distributions in the open am primarily reflect lateral advection of water masses and their mixing seawater particle interactions exert important control only above the shelf regions as observed above the ne greenland shelf advection of northward flowing warm atlantic water aw is clearly reflected by an end signature of 11 7 and a nd concentration nd of 16 pmol kg in the upper 500 m of the eastern and central fram strait freshening and cooling of the aw on its way trough the am are accompanied by a continuous change towards more radiogenic end signatures e g 10 4 of dense arctic atlantic water this mainly reflects mixing with intermediate waters but also admixture of dense kara sea waters and pacific derived waters the more radiogenic end signatures of the intermediate and deep waters reaching 9 5 are mainly acquired in the sw nordic seas through exchange with basaltic formations of iceland and se greenland inputs of nd from svalbard are not observed and surface waters and nd on the svalbard shelf originate from the barents sea shallow southward flowing arctic derived waters 200 m form the core of the east greenland current above the greenland slope and can be traced by their relatively radiogenic end reaching 8 8 and elevated nd 21 to 29 pmol kg these properties are used together with 18o and standard hydrographic tracers to define the proportions of pacific derived 30 based on nd isotopes and atlantic derived waters as well as of river waters 8 shallow waters 150 m on the ne greenland shelf share some characteristics of arctic derived waters but exhibit less radiogenic end values reaching 12 4 and higher nd up to 38 pmol kg in the upper 100 m this suggests local addition of greenland freshwater of up to 6 in addition to these observations this study shows that the pronounced gradients in end signatures and ree characteristics in the upper water column provide a reliable basis for assessments of shallow hydrological changes within the am

electrical conductivity of albite quartz water and albite water nacl systems and its implication to the high conductivity anomalies in the continental crust abstract the electrical conductivities of albite water albite quartz water and albite water nacl systems have been measured in terms of impedance spectroscopy at 1 gpa and 400 1000 k the relationship between electrical conductivity and temperature in the albite quartz water system cannot be expressed by the arrhenian formula whereas that in the brine bearing system follow the arrhenian law showing small temperature dependence the electrical conductivity of the albite quartz water samples decreased with decreasing temperature from 1000 to 800 k then increased rapidly upon further cooling from 800 to around 550 k the bulk conductivities of the albite quartz water system are consistent with variation of the total concentration of the dissolved electric charge carriers of h oh na alo 2 and hsio 3 in aqueous fluid with temperature based on the thermal dynamic calibration there is a small negative dependence of bulk conductivity on aqueous fluid fraction electrical conductivity of the albite water nacl samples is higher than that of the albite quartz water samples which shows the following features 1 small dependence of conductivity on the temperature 2 increase of electrical conductivity with the fluid fraction and the salinity our results suggest that the high conductivity anomalies of 10 1 s m typically observed in the continental crust can be explained by the presence of albite and quartz with fluid fraction as low as 0 014 at temperatures lower than 650 k in the case that the geotherm is higher than 650 k the observed value of 10 1 s m can be explained by the brine bearing albite with a fluid fraction of 1 vol if the salinity is similar to the seawater

melt segregation in migmatites anatectic stromatic migmatites have a symmetrical layered structure with a low ratio of thickness to length and a periodicity features that have not been explained satisfactorily but which are related to physical processes of melt segregation we evaluate the compaction model for segregation as it applies to migmatites and develop models for melt segregation based upon convection driven by volume change and upon advection down pressure gradients that result from applied differential stress acting on an anisotropic multilayer protolith compaction by gravity driven two phase flow results in asymmetric separation yields calculated segregation times that are slow or geologically unreasonable and yields relative volumes that are not consistent with the abundance of leucosome seen in natural migmatites although calculated segregation times for very wet granite might allow segregation by compaction some driving force in addition to gravity is needed to cause widespread melt segregation in the crust for segregation at low volume fraction of melt we develop a two dimensional two phase matrix and fluid viscous flow cell model length much greater than thickness with phase changes which predicts either expansion or contraction convection depending on whether volume change vr is positive or negative convection leads to melt segregation to form a stromatic structure in a geologically reasonable timescale at moderate volume fraction of melt segregation may occur by filter pressing in compositionally layered rocks in response to applied differential stress melt migration is by porous medium flow driven by differences in mean normal stress between the layers as a consequence of differences in rheology and shear enhanced matrix collapse calculated segregation rates are fast and the model yields adequate volume of leucosome the positive vr for volatile phase absent melting reactions under crustal pressures promotes melt escape unless extensional deformation facilitates melt accumulation if the rate of melt production exceeds the rate of melt escape then the increase in melt pressure may lead to melt enhanced embrittlement and fracture and melt may migrate out of the system in contrast water rich volatile phase present melt producing reactions have a negative vr which promotes melt retention after segregation unless deformation generates melt escape pathways evolution of stromatic structure through anatectic erosion of mesosome by increasing the melt fraction in situ may lead to breakdown of the solid matrix and will lead to instability due to buoyancy and magma may become mobile and entrain residual material restite

effect of grain growth on cation exchange between dunite and fluid implications for chemical homogenization in the upper mantle the effect of grain growth on the cation exchange between synthesized forsterite aggregates i e dunite and nickel rich aqueous fluid was evaluated experimentally at 1 2 gpa and 1 200 c the grain boundary gb migration caused nickel enrichment in the area swept by the gbs in a fashion similar to that reported for stable isotope exchange in the quartz aggregates the progress of the grain growth resulted in an increase in the average nickel concentration in the dunites of up to 80 times that was calculated for a system having stationary gbs the overall diffusivity of the nickel along the wet gbs and interconnected fluid networks was found to be 6 5 10 19 6 7 10 18 m3 s which is 4 5 orders of magnitude higher than the grain boundary diffusivity in the dry dunite these results show that the grain growth rate is a fundamental factor in the evaluation of the time scale of chemical homogenization in the upper mantle

grain growth in the system forsterite diopside water abstract grain growth experiments in dunite clinopyroxenite and wehrlites having various forsterite diopside ratios under water saturated conditions were performed to investigate the effect of water on grain growth kinetics in the earth s upper mantle the experiments were conducted at 1200 c and 1 2 gpa for 1 5 763 h using a piston cylinder apparatus both normal grain growth ngg and abnormal grain growth agg proceeded in the rocks the addition of water to the rocks resulted in the inhibition of ngg in dunite and clinopyroxenite whereas it resulted in the acceleration of ngg of both forsterite and diopside in wehrlites agg of the first phase in the rocks tended to be promoted by increasing the amount of water added the values of the growth exponent n for forsterite and diopside in wehrlites were in the range 1 8 4 8 and 1 8 4 5 respectively the n values for the first phase in wehrlites tended to show low values 1 8 2 5 whereas higher n values 3 have been reported under dry conditions this suggests that faster ngg of the first phase with n 2 can proceed in peridotites under water saturated conditions whereas much slower ngg of the first phase with n 3 proceeds under dry conditions this could have the consequences that the effective viscosity of the water saturated peridotites can be higher than that under dry conditions in the earth s upper mantle when the creep mechanism is grain size sensitive creep

the influence of partial melting on the electrical behavior of crustal rocks laboratory examinations model calculations and geological interpretations abstract the complex electrical impedance of a granulite has been determined over the frequency range 10 1 to 105 hz at temperatures between 600 and 1200 c at normal pressure and different oxygen fugacities in the stability field of magnetite the impedance spectroscopic is measurements are compared with the results of melting experiments performed under the same experimental conditions and with the same rock sample as the is measurements a strong increase in the electrical conductivity of about one and a half orders of magnitude is observed during partial melting this increase is explained by the formation of an interconnected network of melt the wetting of the grain surfaces starts slightly above the solidus however complete interconnection of the network is detected at higher temperatures 1070 c and hence higher melt fractions 10 vol this is explained by deviations from the equilibrium fabric of the partially molten sample with a modified brick layer model mblm the electrical conductivity is calculated as a function of the observed melt portion this model is valid if the melt forms a complete interconnected network at the grain boundaries the electrical conductivity at different temperatures was modeled using the results of the melting experiments and the mblm melt 10 s m with ea melt 1 ev solid 0 01 s m with ea solid 1 4 ev the results of the laboratory examinations were applied to different crustal regions where partially molten rocks are assumed to exist the same mblm is used to estimate the melt fraction that is necessary to explain the high conducting zones hczs observed in the crust beneath the andean orogen the pyrenees and the tibetan plateau at least 14 4 and 4 vol of interconnected melt are necessary to produce the observed conductivity respectively the actual amount of melt should be higher due to perturbation problems and melt trapped in pockets

the effect of feldspar on quartz h 2 o co 2 dihedral angles at 4 kbar with consequences for the behaviour of aqueous fluids in migmatites an investigation was made of the effect of trace amounts of feldspar na and or k on dihedral angles in the quartz h2o co2 system at 4 kbar and 450 1050 c quartz quartz h2o dihedral angles in feldspar bearing quartz aggregates are observed to be the same as those in pure quartz aggregates at temperatures below 500 c above this temperature they decrease with increasing temperature until the solidus the final angle at the inception of melting is about 65 for microcline quartz h2o and microcline albite quartz h2o and much less than 60 the critical value for formation of grain edge fluid channels in an isotropic system for the albite quartz h2o system co2 was observed to produce a constant quartz quartz fluid dihedral angle of 97 in feldspar bearing quartz aggregates at all temperatures studied also examined were the dihedral angles for the two co existing supersolidus fluids in quartz aggregates in all systems the quartz volatile fluid angle is greater than 60 whereas the quartz melt angle is lower than 60 both supersolidus angles decrease with increasing temperature the transition from nonconnected to connected porosity with increasing temperature observed in the quartz albite h2o system some tens of degrees below the solidus termed a permeability transition if a common feature of rocks near their melting points will play an important role in controlling the permeability of high grade rocks to aqueous fluids

microstructure evolution of aqueous fluid bearing wehrlites implications for the fluid distribution in polymineralic rocks 1 the microstructure of aqueous fluid bearing wehrlites was experimentally studied in order to investigate the fluid distribution in polymineralic rocks wehrlites of various forsterite diopside ratios were synthesized with 1 0 1 5 wt water at 1200 c and 1 2 gpa for 1 5 668 hours conspicuous grain growth drag and coagulation of pore fluids were observed in the time series experiments the pore fluids were classified into two types those surrounded only by a single phase g type and those surrounded by both forsterite and diopside i type in the short time runs the relative volume fraction of i type pores in all the pores fi agrees well with the value calculated from an ideal pore distribution model in which all the grains are randomly distributed the fi of wehrlites with various forsterite diopside ratios increased with average grain size and reached a steady state value at 80 90 in about 160 163 hours the increase of fi is explained by interphase boundary trapping g type pore fluids move faster than i type and the number of g type becoming i type by being trapped into the interphase boundary per unit time is larger than that of i type pores transforming to g type the experimental results suggest that large fractions of pore fluids might be distributed at the grain junctions surrounded by more than two mineral phases in natural rocks as a result of grain growth the connectivity of the fluid network in polymineralic rocks may be strongly influenced by modal composition of the rocks as well as by the dihedral angles among the fluid and two mineral phases

compressional wave velocity of granite and amphibolite up to melting temperatures at 1 gpa abstract compressional wave velocities vp at above solidus temperatures and at 1 gpa were obtained for a granite and amphibolite which are considered to be major constituents of the continental crust the temperature variation of velocities showed that the vp values of granite decreased with rising temperature but substantially increased beyond the melting temperature 850 900 c such an increase may be caused by the transition of quartz the velocities of amphibolite decreased linearly with increasing temperature and dropped sharply at temperatures above the solidus 700 c indicating that partial melting of amphibolite acts to significantly lower the seismic velocities

barium as a tracer of arctic halocline and river waters dissolved barium ba concentrations are reported for water samples collected during six oceanographic cruises to the arctic in 1993 and during the 1994 arctic ocean section upper arctic 75 nmol ba 1 1 observed in the surface mixed layer of the arctic interior i e beyond the 200 m isobath occurred in the canada basin as a result of the biological removal of ba from surface waters of the chukchi sea and the tendency of the bering inflow to enter the arctic interior at depths below the relatively fresher mixed layer we hypothesize that the mackenzie river is the dominant source of the high ba observed in the surface waters of the canada basin features characterized by local salinity minima and ba maxima in surface waters down to depths of 30 50 m were observed over the arlis plateau and mendeleyev ridge in both 1993 and 1994 and over the makarov basin and lomonosov ridge in 1994 the physical and chemical properties of these waters suggest that they have been significantly influenced by fluvial discharge it could not be determined from available data whether these features arose from offshore transport of eurasian river discharge from the russian arctic seas meanders of the mackenzie river influenced beaufort gyre or a branch of bering inflow that crossed the chukchi shelf and entrained river water from north american and or eurasian sources in both 1993 and 1994 ba concentrations in the upper halocline layer as defined by a core salinity of 33 1 ranged between 42 and 77 nmol ba 1 1 with highest values observed in the canada basin the ba maximum and the related nutrient maxima and oxygen minimum that characterize the upper halocline in the canada basin suggest sources in the chukchi and beaufort seas and that the mechanism by which these waters are formed is linked with the influx of water through the bering strait the ba distributions for 1993 and 1994 delineate the lateral extent of upper halocline waters with canada basin character and show them to be chemically distinct from upper halocline waters in the eurasian basin the front separating these water types ran roughly along the mendeleyev and alpha ridges consistent with reports that the boundary between atlantic and pacific water mass assemblies in the arctic has recently been displaced from its historical position over the lomonosov ridge lateral gradients in both ba and the no parameter were observed within the lower halocline layer defined by an no minimum and core salinity of 34 2 34 4 along the 1994 arctic ocean section indicating that lower halocline waters receive additional inputs as they transit to the canadian basin from their region of formation in the eurasian sector of the arctic

formation and evolution of the surface mixed layer and halocline of the arctic ocean fresh water from summer ice melt and the total freshwater content of the arctic ocean water column above the thermocline are estimated from vertical profiles of temperature and salinity observed on the i b oden 1991 cruise the seasonal ice melt ranges from 0 5 m to slightly above 1 m and is moderately uniform over the observation area regions of lower melting are seen over the morris jesup plateau the freshwater content is calculated relative to the salinity just above the thermocline north of the barents sea the freshwater content increases toward the interior of the arctic ocean showing that fresh water is advected from other regions into the observation area regions of different freshwater content are separated by fronts over the nansen gakkel ridge over the lomonosov ridge and in the western eurasian basin between waters derived from the eurasian and canadian basins denser water homogenized north of the barents sea is recognized by a temperature minimum layer the absence of the temperature minimum near the nansen gakkel ridge indicates that heat is transferred from the atlantic layer over a longer time than the shortest route would allow this observation can be explained if the layer circulates together with the atlantic layer i e toward the east and returns above the nansen gakkel ridge and along the amundsen basin north of the laptev sea this water formed north of the barents sea becomes covered by low salinity shelf water the increased freshwater content limits the winter convection so it no longer reaches the thermocline and an intermediate halocline is formed the halocline in the eurasian basin consists of water originating from winter convection in the arctic ocean north of the barents sea which then circulates around the basin such a formation mechanism also explains the observed distribution of low no water the strong density increase limits vertical exchange and the vertical diffusion coefficient in the halocline is small 1 10 6 m2 s 1 the increased temperature of the halocline shows that the heat lost upward by the atlantic layer mainly by double diffusive convection is trapped below the mixed layer

weathering sequence of soils from volcanic ash involving allophane and halloysite new zealand abstract the clay minerals in a series of soils from rhyolitic ash having the same stratigraphy but different leaching environments were estimated quantitatively by oxalate dissolution infrared spectroscopy differential thermal analysis electron microscopy and x ray diffraction three soils were studied in detail these were the kereone soil mean annual rainfall 1200 mm the ohaupo soil 1400 mm and the mairoa soil 2600 mm the kereone soil contained halloysite as the predominant clay mineral whereas the mairoa soil was mainly allophanic the ohaupo soil contained considerable amounts of both allophane and halloysite thus the allophane content of the soils increased as rainfall increased reflecting a sequence of increased l leaching the si concentration in soil solution decreased as rainfall increased also reflecting increasing leaching of the soils at mairoa si is rapidly removed and allophane al si 2 1 with monomeric silicate is formed whereas at kereone less leaching occurs si levels are higher and halloysite al si 1 1 with polymeric silicate is formed at intermediate sites either allophane or halloysite may form the often reported situation of younger allophanic beds overlying older 10 000 year halloysitic beds may not be due to allophane weathering to halloysite but may result from lower temperature and drier climate during the last glacial maximum between 10 000 and 26 000 years before present bp a new weathering scheme for volcanic ash in new zealand is presented

the multiphase grain control percolation its implication for a partially molten rock a model of percolation process named the multiphase grain control percolation mgcp is proposed in order to estimate the connectivity of the melt phase in a partially molten rock in which spatial melt distribution is determined by the combination of surrounding grain species according to the stability of the melt phase at the grain boundaries three types of percolation model are introduced the corner percolation the edge percolation and the corner edge ce percolation the ce percolation can be reduced to the corner or edge percolation the connectivity of the melt phase is determined as a function of modal composition in a multiphase grain system for various combinations of grain species surrounding the corner or edge occupied by the melt phase we obtain the critical grain fraction at which the connectivity changes abruptly from 0 to 1 the critical grain fraction estimated from the mgcp does not coincide with that from the ordinary percolation model in which random distribution of the melt phase is assumed as a geophysical application of the mgcp we construct the connectivity diagrams modal composition diagram of the connectivity of the melt phase for two partially molten peridotites by using the experimental results of dihedral angle measurements from these diagrams we predict that the melt phase is connected extensively if fraction of olivine exceeds 63 vol for a natural peridotite composed of olivine orthopyroxene and clinopyroxene and 38 vol for a synthetic peridotite composed of olivine and orthopyroxene for the former peridotite we further estimate critical melt fraction it is shown that the melt phase can be connected extensively when the melt fraction exceeds 0 8 vol in the peridotite composed of more than 63 vol olivine

geophysical constraints on partial melt in the upper mantle this paper addresses the conditions under which partial melt can exist in the mantle in order to be observed as a geophysical anomaly typical observed anomalies are high electrical conductivity of the order of 0 1 s m or greater velocity decreases of 7 10 seismic q values less than 100 and a frequency band for seismic effects in the region near 1 hz existing theories of electrical conduction in partial melts and of frequency dependent seismic properties together with recent measurements of melt electrical conductivity viscosity and partial melt texture can be used to establish requirements for melt to be observed by geophysical methods from electrical anomalies mainly sensitive to melt volume and its interconnection one can require a minimum melt fraction of several percent at temperatures close to the solidus 1150 1300 c however seismic models demand only a small volume in very flattened shapes aspect ratio 0 001 melt fraction 0 1 further if melt configuration permits seismic dissipation in bulk that is there exist flattened voids intersecting more or less equant voids then it is possible to infer melt fractions for elastic anomalies that are consistent with the several percent required for electrical anomalies observed equilibrium textures of partly melted peridotite together with inferred melt solid surface energies suggest that melt on a grain size scale in a gravitational field segregates into a strongly anisotropic pattern thus if partial melt causes mantle geophysical anomalies it should exist in a variety of void shapes and probably of sizes while the association of electrical and elastic anomalies with indications of reduced density volcanism and high heat flow makes the hypothesis of partial melting an attractive explanation the minimum physical requirement is for existence of relatively high temperature