minor and trace element export from a glacierized alpine headwater catchment haut glacier d arolla switzerland major ion concentrations in meltwaters draining glacial environments have been widely reported however concentrations of minor and trace elements have received scant attention this study presents trace and minor element variations in bulk meltwaters draining haut glacier d arolla switzerland based on twice daily sampling throughout the 1999 ablation season which represents the most detailed meltwater quality dataset to date in order to assess the mode of export from the catchment these elements are partitioned into i dissolved and ii particulate associated minor and trace element components a computer based speciation model phreeqci was applied to the bulk meltwater data suggesting that ba be cd cu li rb and sr exist primarily as mobile monovalent or divalent dissolved cations which may be involved in interactions with suspended sediment surfaces conversely the model predicts the precipitation of fe al mn and cr oxi hydroxides suggesting these species may be predominantly transported as colloids which may remove other minor and trace elements from solution by co precipitation reactions laboratory leaching experiments on suspended sediments and fresh rock powder suggests that minor and trace element concentrations may also be influenced by oxy hydroxide precipitation and adsorption desorption reactions with suspended sediment surfaces the quantity and transport mode of trace and minor elements may influence their bioavailability downstream of glacierized headwater catchments further the enrichment of many dissolved minor and trace elements in meltwaters compared with world stream waters coupled with the timing of water and sediment delivery during the summer months may have implications for downstream aquatic environments copyright 2001 john wiley sons ltd

origin of rhythmic layering in the calamity peak satellite pluton of the harney peak granite south dakota the role of boron abstract the calamity peak satellite granite pluton on the flanks of the harney peak granite south dakota displays prominent mineral and textural layering the latter defined by alternating fine grained and pegmatitic granite superimposed on the fine grained granite layers is a fine scale 0 1 5 cm rhythmic layering defined by modal differences in tourmaline microcline albite and muscovite there is very little variation in the major element mineral compositions in the whole complex analyses by prompt gamma neutron activation gave a b2o3 content of 0 07 in the light layers albite quartz and muscovite and 0 65 in the dark layers tourmaline microcline quartz and albite these contents are essentially proportional to tourmaline abundance in each layer the textural and mineralogic layering is the result of the interplay of tourmaline crystallization and shifts in phase equilibria due to changes in b concentration in the melt initial cotectic crystallization of albite quartz and muscovite increased the activity of fe and mg in the adjacent melt to levels sufficient for tourmaline to form tourmaline crystallization depleted b and decreased the solubility of h2o in the melt causing exsolution of h2o from the melt and further removal of b due to high fluid melt partition coefficient this process also resulted in the precipitation of k feldspar partly at the expense of muscovite and partly due to a slight increase in the solidus temperature once the crystallization front moved to an fe and mg poor region of the melt tourmaline precipitation ceased and the equilibrium shifted back toward quartz muscovite and albite the pegmatitic layers some of which cut across previously formed rhythmic layers and commonly have tourmaline along their borders appear to have crystallized from melt enriched in the exsolved fluid phase

fluid inclusions in the harney peak granite black hills south dakota usa implications for solubility and evolution of magmatic volatiles and crystallization of leucogranite magmas abstract experimental and theoretical studies have shown that magmatic fluids have strong influence on phase equilibria of granitic systems a microthermometric study of fluid inclusions in the proterozoic harney peak granite black hills south dakota usa was undertaken to obtain direct evidence for the composition and evolution of magmatic fluids in a leucogranitic system and to evaluate their effect on liquid lines of descent of leucogranite magmas a previous stable isotopic study has demonstrated that the granite has not interacted with nonmagmatic fluids since its crystallization therefore fluids found in the inclusions are of magmatic origin and present an opportunity to directly sample magmatic fluids trapped during crystallization of a granitic magma and during subsolidus conditions the harney peak granite was emplaced as multiple sills dikes and small intrusions many of which differentiated into coupled aplite pegmatite layers three types of fluid inclusions are found in the granite type 1 consist of variable saline h 2 o c0 2 mixtures with minor ch 4 or other gases inclusions of this type are found in tourmaline and quartz in aplite layers are generally isolated and have negative crystal shapes they are interpreted to be primary there is a general increase in salinity and decrease in isochore temperature with decreasing co 2 h 2 o ratio of the inclusions the trend is ascribed to progressive change in fluid composition with crystallization due to the differential solubility of co 2 and h 2 o in the high silica magma isochores coupled with independently determined crystallization temperatures suggest entrapment pressure 3 5 kbar consistent with geobarometry in the wallrocks type 2 inclusions are carbonic fluids dominated by co 2 whereas type 3 inclusions are saline aqueous fluids without a detected carbonic component both types are mostly found along healed fractures in quartz they are interpreted to be secondary inclusions that formed as a result of unmixing of type 1 inclusions at subsolidus conditions during uplift and cooling of the harney peak granite dome freezing point depressions birefringent daughter crystals phase equilibria considerations and track mapping of b and li distribution in thin sections all indicate that both type 1 and type 3 inclusions contain solutes such as k li and b in addition to nacl using published solubility models for h 2 o and co 2 in granitic melts and the composition of the most co 2 rich type 1 inclusions x co 2 0 55 the initial h 2 o and co 2 concentrations in the harney peak granite magma are deduced to have been 3 5 wt and 1500 ppm respectively the relatively low water concentration is consistent with temperatures of dehydration melting reactions that produced the magma it is suggested that the aplite pegmatite segregations found in parts of the harney peak granite are the result of initial rapid near liquidus crystallization of minerals with high na k ratios including plagioclase and tourmaline along a wide range of increasing h 2 o aplite crystallization was followed by crystallization of relatively potassic residual liquid enriched in fluxing elements under conditions of high h 2 o

contemporary rates of chemical denudation and atmospheric co2 sequestration in glacier basins an arctic perspective this paper presents new estimates of solute fluxes from five high arctic glacier basins in svalbard these estimates are combined with data from two other glacier basins to assess the effectiveness of chemical denudation on svalbard and to estimate rates of temporary or transient co2 drawdown we use a solute provenance model to partition solutes into marine aerosol atmospheric and crustal components and to estimate their annual fluxes crustally derived solute fluxes are equivalent to a mean chemical denudation rate of 350 meq m 2 a 1 for svalbard range 160 560 meq m 2 a 1 which lies within the global range of 94 4200 meq m 2 a 1 for 21 glacier basins in the northern hemisphere and is close to the continental average of 390 meq m 2 a 1 specific annual discharge is the most significant control upon chemical denudation in the glacierized basins and basin lithology is an important secondary control with carbonate rich and basaltic lithologies currently showing the greatest chemical denudation rates estimates of transient co2 drawdown are also directly associated with specific annual discharge and rock type on svalbard transient co2 drawdown lies in the range 110 3000 kg c km 2 a 1 whilst the range is 110 13000 kg c km 2 a 1 for the northern hemisphere glacial data set transient co2 drawdown is therefore usually low in the svalbard basins unless carbonate or basalt rocks are abundant the analysis shows that a large area of uncertainty in the transient co2 drawdown estimates exists due to the non stoichiometric release of solute during silicate hydrolysis silicate hydrolysis is particularly non stoichiometric in basins where the extent of glacierization is high which is most probably an artefact of high flushing rates through ice marginal and subglacial environments where k feldspars are undergoing mechanical comminution copyright 2000 john wiley sons ltd

the effect of inertial accelerations on the higher frequency components of the signal from spring gravimeters summary experimental and theoretical studies have shown that due to the magma gas dynamics in the upper part of a volcano s plumbing system gravity changes can develop over periods between a few tens of seconds and several hours the mass transport implied by certain fast evolving volcanic processes also constitute the source mechanism of seismic waves with frequencies over the lower limit of the seismic band these seismic waves could affect the measuring system of spring gravimeters that are increasingly used as continuously running devices to monitor and study active volcanoes as a consequence under some circumstances the signal from a continuously running spring gravimeter will be the combination of the gravity field component and the inertial acceleration component the latter due to the ground motion in such cases the inertial acceleration must be separated from the gravity signal to assess the amount of mass redistributed during the studied process to achieve this separation the frequency response curve of the spring gravimeter to inertial accelerations must be calculated since it is not supplied by manufacturers in this paper we present a method to retrieve the above curve using simultaneous recordings during the transit of teleseismic waves of a lacoste romberg d gravimeter and a nanometrics trillium 40 broad band seismometer whose frequency response curve to ground acceleration is known ap riori the use of teleseismic waves is particularly useful for our purpose since teleseisms are not associated with a local mass redistribution the gravimeter will thus be affected only by the ground motion making the above calculation possible our results show that because of the instrumental damping the effect of the inertial acceleration is reduced in the output signal from the gravimeter to 0 5 and 0 1 of its original value at frequencies between 0 02 and 0 07 hz respectively the robustness of the calculated frequency response curve is proven using independent simultaneous signals from gravimeter and broad band seismometer

the role of h 2 o in rapid emplacement and crystallization of granite pegmatites resolving the paradox of large crystals in highly undercooled melts granite pegmatite sheets in the continental crust are characterized by very large crystals there has been a shift in viewing pegmatites as products of very slow cooling of granite melts to viewing them as products of crystal growth in undercooled liquids with this shift there has been a renewed debate about the role of h2o in the petrogenesis of pegmatites based on data on nucleation of minerals and new viscosity models for hydrous granite melts it is argued that h2o is the essential component in the petrogenesis of granite pegmatites h2o is key to reducing the viscosity of granite melts which enhances their transport within the crust it also dramatically reduces the glass transition temperature which permits crystallization of melts at hundreds of degrees below the thermodynamic solidus which has been demonstrated by fluid inclusion studies and other geothermometers published experimental data show that because h2o drastically reduces the nucleation rates of silicate minerals the minerals may not be able to nucleate until melt is substantially undercooled in a rapidly cooling intrusion nucleation starts at its highly undercooled margins followed by inward crystal growth towards its slower cooling hotter core delay in nucleation may be caused by competition for crystallization by several minerals in the near eutectic melts and by the very different structures of minerals and the highly hydrated melts once a mineral nucleates however it may grow rapidly to a size that is determined by the distance between the site of nucleation and the point in the magma at which the temperature is approximately that of the mineral s liquidus assuming components necessary for mineral growth are available along the growth path granite pegmatites are apparently able to retain h2o during most of their crystallization histories within the confinement of their wall rocks pegmatitic texture is a consequence of delayed nucleation and rapid growth at large undercooling both of which are facilitated by high h2o li b f and p contents in granite pegmatite melts without retention of h2o the conditions for pegmatitic textural growth may be difficult to achieve loss of h2o due to decompression and venting leads to microcrystalline texture and potentially glass during rapid cooling as seen in rhyolites in contrast slow cooling within a large magma chamber promotes continuous exsolution of h2o from crystallizing magma growth of equant crystals and final solidification at the thermodynamic solidus these are the characteristics of normal granites that distinguish them from pegmatites

rates of chemical denudation and co2 drawdown in a glacier covered alpine catchment solute fluxes from a glacier covered alpine catchment are partitioned into components derived from sea salt acid aerosol dissolution of atmospheric co2 and crustal weathering the bulk of solute is crustally derived coupled sulfide oxidation and carbonate dissolution so cd and carbonation of carbonate minerals generate approximately equal amounts of solute chemical denudation constitutes 1 5 of solid denudation but is significantly higher than the continental average co2 drawdown by weathering reactions varies directly with discharge and suspended sediment load and inversely with meltwater p co2 if it is generally true that flushing rates control co2 drawdown in glacier covered catchments then glacially driven chemical weathering could be a significant factor in carbon cycling and climate change on glacial interglacial time scales

geometry bed topography and drainage system structure of the haut glacier d arolla switzerland as part of an integrated study of the hydrology meltwater quality and dynamics of the haut glacier d arolla switzerland the glacier s drainage network structure was determined from patterns of dye recovery in 342 injection experiments conducted from 47 moulins distributed widely across the glacier this structure was compared with theoretical predictions based upon reconstructed patterns of water flow governed by a the subglacial hydraulic potential surface and b the subglacial bedrock surface these reconstructions were based on measurements of ice surface and bedrock topography obtained by a combination of ground survey and radio echo sounding techniques the two reconstructions simulate the drainage system structures expected for a closed channels in which water is pressurized by the overlying ice and b gravity driven open channel flow the closed channel model provides the best fit to the observed structure even though theoretical calculations suggest that under summer discharge conditions open channel flow may be widespread beneath the glacier possible reasons for this apparent discrepancy are discussed

petrogenetic relationships between pegmatite and granite based on geochemistry of muscovite in pegmatite wall zones black hills south dakota usa abstract the compositions of large samples of granitic pegmatite wall zones have been determined for a suite of ten pegmatites of diverse geochemical character and degree of compositional evolution in the keystone area of the black hills whole rock compositions are strongly peraluminous and they deviate substantially from the granite minimum composition in quartz albite orthoclase normalized components showing considerably more scatter than harney peak granite whole rocks wall zone minerals are commonly coarsely segregated leading to large modal variability among whole rocks these features make whole rock samples of wall zones unsuitable for the determination of initial pegmatite bulk compositions trace and minor element compositions of muscovite separates from the wall zones were thus determined to eliminate the effects of modal variability on trace element concentrations so that geochemical differences between pegmatites could be modeled estimates of initial pegmatite melt trace element concentrations range from 800 4000 ppm rb 100 1000 ppm cs 200 2000 ppm li and 1 50 ppm ba trace element concentrations of muscovite from a given pegmatite generally cluster together although several show considerable intra pegmatite scatter and there are large overlaps among different pegmatites the geochemical characteristics of samples from the etta pegmatite indicate mixing with and assimilation of country rocks exceptionally low rb cs ratios of muscovite from the etta pegmatite are similar to those of muscovite from k feldspar rich assemblages of other pegmatites where the rb concentration of melt may have been buffered by crystallizing assemblages that had bulk rb distribution coefficients close to 1 the large degree of scatter of geochemical parameters among these pegmatites precludes derivation of the entire suite by either single stage crystallization or partial melting processes nor can the pegmatites be satisfactorily related by any fractionation trajectory from a single starting composition fractional crystallization is difficult to model due to an apparent geochemical decoupling that exists among several of these elements in different pegmatites e g rb from cs or li from rb cs and nonsystematic variation of ba concentrations however the magnitude of observed rare element enrichments could be achieved by 75 90 fractional crystallization of melts that crystallized harney peak granite in nearby exposures the inter pegmatite scatter and apparent geochemical decoupling that characterize the suite indicate an origin by partial melting of a heterogeneous source rock or rock sequence followed by an intermediate episode of fractional crystallization prior to final emplacement of the pegmatite melts additional compositional variations among samples from the wall zones of individual pegmatites were caused by processes during or after emplacement including local interaction with host metamorphic rocks and fractionation during internal evolution of the pegmatites as they crystallized

a petrologic assessment of internal zonation in granitic pegmatites abstract cameron et al 1949 devised the nomenclature and delineated the patterns of internal zonation within granitic pegmatites that are in use today zonation in pegmatites is manifested both in mineralogy and in fabric mineral habits and rock texture although internal zonation is a conspicuous and distinctive attribute of pegmatites there has been no thorough effort to explain that mineralogical and textural evolution in relation to the zoning sequence presented by cameron et al 1949 or in terms of the comprehensive petrogenesis of pegmatite bodies pressure temperature and whole rock composition this overview of internal zonation within granitic pegmatites consists of four principal parts 1 a historic review of the subject 2 a summary of the current understanding of the pegmatite forming environment 3 the processes that determine mineralogical and textural zonation in pegmatites and 4 the applications of those processes to each of the major zones of pegmatites based on the concepts presented in london 2008 the fundamental determinates of the internal evolution of pegmatite zones are 1 the bulk composition of melt 2 the magnitude of liquidus undercooling prior to the onset of crystallization 3 subsolidus isothermal fractional crystallization by which eutectic or minimum melts fractionate by sequential non eutectic crystallization 4 constitutional zone refining via the creation of a boundary layer liquid chemically distinct from but continuous with the bulk melt at the crystallization front and 5 far field chemical diffusion the long range and coordinated diffusion of ions particularly of alkalis and alkaline earths through melt

phosphorus and the rare earth elements in felsic magmas an assessment of the role of apatite abstract the solubility of fluorapatite in 17 silica rich melts in the system na 2 o k 2 o al 2 o 3 sio 2 with and without cao or caf 2 was determined at 1 kbar water pressure and 750 900 c apatite saturation occurs at levels of dissolved p 2 o 5 ranging between 0 04 0 02 and 0 28 0 13 wt with only 4 values outside the 0 09 0 20 wt range the results demonstrate not only that apatite is a common liquidus phase in felsic melts but also that under most circumstances it remains in the residue during episodes of partial fusion of the crust given a solubility limit of 0 14 wt dissolved p 2 o 5 the mean of the experimental values a source containing as little as 0 05 p 2 o 5 must be 35 melted before apatite is lost from the residue and no longer buffers the melt p 2 o 5 concentration at the saturation value higher abundances of p 2 o 5 in the source postpone the loss of residual apatite to still higher degrees of melting and if the source p 2 o 5 content exceeds 0 14 wt apatite must be residual for all degrees of melting increasing in abundance as melting proceeds the generally secondary influence of apatite on the rare earth element ree patterns of melt and residue is most apparent when garnet and or amphibole is minor or lacking in the residue fractional crystallization of intermediate e g andesitic magmas toward felsic compositions invariably results in saturation in apatite and some consequent depletion of ree in the melt

climate versus geological controls on glacial meltwater micronutrient production in southern greenland abstract low concentrations of micronutrients in subarctic north atlantic surface waters limit phytoplankton growth iron phosphorous and silicon are all potentially bio limiting nutrients iron is the most well documented in the subarctic north atlantic manganese nickel copper and zinc are also essential trace metals for phytoplankton cell function however the spatial and temporal variability in the flux of these elements to the subarctic north atlantic is undercharacterized here we show new data from the meltseason peak in 2013 indicating that glacial meltwater from the southern tip of greenland has elevated dissolved major and trace metal concentrations compared to glacial meltwater draining shorter melt season glacial catchments to the north fe concentrations range from 0 13 to 6 97 m zn from 4 to 95 m and si from 4 to 36 m all higher than the depleted surface waters of the subarctic north atlantic measured hydrochemical data modeled by phreeqc indicates meltwater is undersaturated in pyrite and silicate phases but supersaturated with respect to oxyhydroxides hematite and goethite all phases that precipitate fe as colloids of which the nanoparticle phases should remain biologically available the variability in geologic units between the sites indicates that subglacial lithology is a minor but not the dominant control on meltwater chemistry the disparity in concentrations is directly correlated with climate and an extended melt season suggesting that future warming in greenland will lead to increased trace element and potential micronutrient flux to the subarctic north atlantic surface waters

geochemical data as indicators of environmental change and human impact in sediments derived from downstream marshes of an ephemeral river northeast china recent sedimentary history of natural environmental change and anthropogenic influence in an ephemeral river catchment has been reconstructed using selected major and trace elements element ratios and their different geochemical phases tessier sequential extraction methods pollen and grain size combined with 210pb and 137cs dating method in marsh sedimentary cores attempts were made to use selected element ratios with different geochemical phases residual phase of ti al v cr ni rb k sr and ba mobile sr and ba combined with 210pb and 137cs chronology to interpret certain time information of environmental changes saved within the marsh sediments results indicate that there were two marked humid periods during 1850 1860 ad and 1890 1920 ad and sand storm activities prevailed during 1920 1930 ad after about 1900 ad soil erosion has increased with the extensive agricultural activities in the huolin river catchments and further intensified after 1950s after 1980 soil erosion has become even more intense which is consistent with the reinforcement of human activities the drastic loss of vegetation cover in the upstream lands especially the exploitation of the open cast coalmine in the upstream of huolin river at that time influenced by the inundation of the huolin river the heavy metal pollution historical trends in xianghai marsh wetland could be roughly divided into three periods by analysis of sediment enrichment factor ksef and the index of geoaccumulation igeo 1760 1880 ad 1880 1980 ad and 1980 now human activities accelerate the inputs of heavy metal which leads to degradation of the marsh this study also investigated on source of marsh sediments by ti al redox condition by v cr and v v ni and salinization indicators by sr ba and rb k the results demonstrate that sources of sediments and redox conditions were partly similar for both riparian and depressional marshes besides some differences in degree of salinization between two types of marsh were also identified especially after 1880

seasonal reorganization of subglacial drainage inferred from measurements in boreholes the effect of the formation of a major subglacial drainage channel on the behaviour of the subglacial drainage system of haut glacier d arolla switzerland was investigated using measurements of borehole water level and the electrical conductivity and turbidity of basal meltwaters electrical conductivity profiles were also measured within borehole water columns to identify the water sources driving water level changes and to determine patterns of water circulation in boreholes prior to channel formation boreholes showed idiosyncratic and poorly coordinated behaviour diurnal water level fluctuations were small and driven by supraglacial englacial water inputs even when boreholes were connected to a subglacial drainage system this system appeared to consist of hydraulically impermeable patches interspersed with storage spaces and transmitted a very low water flux drainage reorganization which occurred around 31 july 1993 in response to rapidly rising meltwater and rainfall inputs seems to have involved the creation of a connection between an incipient channel and a well established channelized system located further down glacier once a major channel existed within the area of the borehole array borehole water level fluctuations were forced by discharge related changes in channel water pressure although a diversity of responses was observed these included i synchronous ii damped and lagged iii inverse and iv alternating inverse lagged responses synchronous responses occurred in boreholes connected directly to the channel while damped and lagged responses occurred in boreholes connected to it by a more resistive drainage system pressure variations within the channel resulted in diurnal transfer of mechanical support for the ice overburden between connected and unconnected areas of the bed producing inverse and alternating patterns of water level response 1998 john wiley sons ltd

cooling rates and crystallization dynamics of shallow level pegmatite aplite dikes san diego county california pegmatites of the pala and mesa grande pegmatite districts san diego county california are typically thin sheet like composite pegmatite aplite dikes aplitic portions of many dikes display pronounced mineralogical layering referred to as line rock characterized by fine grained garnet rich bands alternating with albite and quartz rich bands thermal modeling was performed for four dikes in san diego county including the 1 m thick himalaya dike the 2 m thick mission dike the 8 m thick george ashley dike and the 25 m thick stewart dike calculations were based on conductive cooling equations accounting for latent heat of crystallization a melt emplacement temperature of 650 c into 150 c fractured gabbroic country rock at a depth of 5 km and an estimated 3 wt initial h 2o content in the melt cooling to 550 c at the center of each dike occurred in 9 years for the stewart dike 340 days for the george ashley dike 22 days for the mission dike and 5 days for the himalaya dike based on these calculations growth rates for large pegmatitic minerals such as the 10 cm long himalaya hanging wall tourmaline crystals may have been on the order of 10 5 cm s crystal size distribution csd studies of garnet from layered aplites suggest growth rates of about 10 6 cm s these results indicate that the dikes cooled and crystallized rapidly with variable nucleation rates but high overall crystal growth rates initial high nucleation rates coincident with emplacement and strong undercooling can account for the millimeter size aplite grains lower nucleation rates coupled with high growth rates can explain the decimeter size minerals in the hanging walls cores and miarolitic cavities of the pegmatites the presence of tourmaline and or lepidolite throughout these dikes suggests that although the melts were initially h 2o undersaturated high melt concentrations of incompatible or fluxing components such as b f and li h 2o aided in the development of large pegmatitic crystals that grew rapidly in the short times suggested by the conductive cooling models

correlations of suspended sediment size with bedrock lithology and glacier dynamics the hypothesized link between glacier surging and bedrock geology motivates this study of the suspended sediment size distributions sssd from surge type and non surge type glaciers we analyze sssds from proglacial streams in 20 individual basins comprising various fractions of metasedimentary ms and felsic plutonic rocks we compare the size distributions by performing tests of significance on the distribution statistics and a principal component analysis on discrete grain sizes we find that surge type and non surge type glaciers underlain solely by ms rocks have significantly different sssds while surge type glaciers as a whole have remarkably similar sssds regardless of the underlying bedrock geology these observations hint at a relationship between sediment characteristics and glacier surging though causation in either direction cannot be established without additional data

neutralization of atmospheric acidity by chemical weathering in an alpine drainage basin in the north cascade mountains the most important weathering reaction that neutralizes incoming atmospheric acidity in the south cascade lake basin is weathering of calcite which occurs in trace amounts in veins on joint surfaces and as a subglacial surficial deposit although the basin is underlain by igneous and high grade metamorphic rocks weathering of plagioclase is quantitatively negligible the principal silicate weathering reaction is alteration of biotite to vermiculite these conclusions are based on mass balance calculations involving runoff compositions and on mineralogical observations for predictive modeling of the effects of increased acid deposition it is essential to identify the relevant weathering reactions feldspar weathering is commonly not an important source of solutes in alpine basins underlain by granitic rocks 30 references 2 figures 1 table

textural and chemical evolution of a fractionated granitic system the podlesi stock czech republic the podlesigranite stock czech republic is a fractionated peraluminous f li and p rich and sn w nb ta bearing rare metal granite system its magmatic evolution involved processes typical of intrusions related to porphyry type deposits explosive breccia comb layers rare metal granites stockscheider and rare metal pegmatites extreme f p li enrichment nb ta sn minerals layering geological textural and mineralogical data suggest that the podlesigranites evolved from fractionated granitic melt progressively enriched in h2o f p li etc quartz k feldspar fe li mica and topaz bear evidence of multistage crystallization that alternated with episodes of resorption changes in chemical composition between individual crystal zones and or populations provide evidence of chemical evolution of the melt variations in rock textures mirror changes in the pressure and temperature conditions of crystallization equilibrium crystallization was interrupted several times by opening of the system and the consequent adiabatic decrease of pressure and temperature resulted in episodes of nonequilibrium crystallization the podlesigranites demonstrate that adiabatic fluctuation of pressure bswinging eutecticq and boundary layer crystallization of undercooled melt can explain magmatic layering and unidirectional solidification textures usts in highly fractionated granites d 2004 elsevier b v all rights reserved

velocity discharge relationships derived from dye tracer experiments in glacial meltwaters implications for subglacial flow conditions repeated dye tracer tests were undertaken from individual moulins at haut glacier d arolla switzerland over a number of diurnal discharge cycles during the summers of 1989 1991 it was hoped to use the concepts of at a station hydraulic geometry to infer flow conditions in subglacial channels from the form of the velocity discharge relationships derived from these tests the results however displayed both clockwise and anticlockwise velocity discharge hysteresis in addition to the simple power function relationship assumed in the hydraulic geometry approach clockwise hysteresis seems to indicate that a moulin drains into a small tributary channel rather than directly into an arterial channel and that discharges in the two channels vary out of phase with each other anticlockwise hysteresis is accompanied by strong diurnal variations in the value of dispersivity derived from the dye breakthrough curve and is best explained by hydraulic damming of moulins or sub englacial passageways despite the complex velocity discharge relationships observed some indication of subglacial flow conditions may be obtained if tributary channels comprise only a small fraction of the drainage path and power function velocity discharge relationships are derived from dye injections conducted during periods when the supraglacial discharge entering the moulin and the bulk discharge vary in phase analyses based on this premise suggest that both open and closed channel flow occur beneath haut glacier d arolla and that flow conditions are highly variable at and between sites

internal differentiation of rare element pegmatites effects of boron phosphorus and fluorine lithium rich rare element pegmatites are characterized by high concentrations of b p and f the interactions of these components with h2o and rare alkalis lower liquidas and solidus temperatures enhance silicate liquid h2o miscibility and control partitioning and concentration of group i elements and higher field strength cations boron f and perhaps p may form peralkaline na and li species that promote early saturation in mica quartz activities of f p and especially b are largely unbuffered throughout crystallization concentration of these components through fractional crystallization involving muscovite generates a peralkaline na aluminosilicate rich melt or vapor from which albitites rich in tourmaline phosphates f rich micas beryl zircon and nb ta sn oxides crystallize phase equilibrium experiments with peraluminous b p f rich rhyolite obsidian macusanite simulate many features of rare element pegmatites especially at h2o undersaturated conditions

phase relationships of gabbro tonalite granite water at 15 kbar with applications to differentiation and anatexis phase relationships have been determined at 15 kbar with variable h 2o contents for three rocks a gabbro a tonalite and a muscovite granite representing the compositional trend of the calc alkaline rock series experiments were conducted in 0 5 in piston cylinder apparatus using ag pd or pt capsules the results obtained are acceptable representations of the phase relationships for elucidation of petrological processes selected runs with 5 h 2o were completed using au capsules to overcome the problem of iron loss up to the temperature limit of au for reliable electron microprobe analyses of glass garnet clinopyroxene amphibole and plagioclase no glasses could be analyzed in the gabbro the data provide k d values as a function of temperature for pairs of coexisting minerals and liquid the chemical variations are used to evaluate 1 the fractionation trends in hydrous magmas at 55 km in thickened continental crust or uppermost mantle and 2 the products of anatexis of the thickened crust at this depth fractionation of hydrous basalt or anatexis of gabbro and tonalite or their metamorphosed equivalents appears to produce liquids diverging from the calc alkaline trend anatexis of granite produces a liquid less siliceous than itself with some chemical characteristics of syenite

a petrological and rbsr isotopic study of an early archean fertile granite pegmatite system the sinceni pluton in swaziland abstract the sinceni pluton in the eastern kaapvaal craton of swaziland is one of the world s earliest examples of a fertile granite with associated rare metal pegmatites the rb sr isochron age of the pluton is 2990 43 ma 87 sr 86 sr i 0 711 7 95 confidence limit errors cogenetic rare metal lct type pegmatites yield k feldspar and muscovite rb sr ages of 3000 100 ma the sinceni pluton is asymetrically zoned in chemical and mineralogical composition and the sinceni pegmatite field occurs at the most differentiated southern end of the pluton geochemical modelling shows that the internal differentiation of the pluton is consistent with 25 35 fractional crystallization and that over 90 99 fractional crystallization would produce the observed rb sr ba and cs contents of the pegmatites the geochemically primitive pre 3000 ma archean crust in swaziland is unlikely to constitute a direct source of the sinceni pluton according to the sr isotopic and age data the origin of the pluton can best be explained as a late differentiate from a large volume of granitic magma which formed penecontemporaneous batholiths

inter and intra crystal ree variations in apatite from the bob ingersoll pegmatite black hills south dakota abstract concentrations of rare earth elements ree have been measured on a suite of apatite crystals from an internally zoned granitic pegmatite enriched in li b be f nb ta sn and u with a cameca ims 3f ion microprobe using energy filtering an apatite specimen from the tin mountain pegmatite analyzed previously by isotope dilution was used as a standard the chondrite normalized pattern determined with the ion microprobe closely matches the pattern determined by isotope dilution with maxima at sm and dy and minima at nd and er apatite samples from the bob ingersoll pegmatite show a large range of ree patterns and concentrations in one case apatite crystals within millimeters show differences in ree concentrations and pattern shapes including a switch from positive to negative eu anomalies samples from several mineral assemblages show patchy individual crystal zoning with respect to the ree that is not mirrored by major element zoning this indicates disequilibrium conditions on a small scale consistent with rapid growth from a melt fluid system that was either of locally heterogeneous melt structure or in which the melt structure fluctuated rapidly as volatile rich minerals such as tourmaline crystallized these effects may be coupled with non ideal partitioning of ree in a heterogeneous mixture of melt aqueous fluid and crystals ree concentrations in apatite samples from the different pegmatite zones indicate a large variation in outer zones 10 500x chondrite high concentrations 100 1000x chondrite near the pegmatite core and very low concentration in the core 2 20x chondrite patterns are flat to slightly inclined ce yb 1 to 5 and most samples have positive eu anomalies the magnitude of positive eu anomalies decreases with inward position in the pegmatite possibly indicating a progressive increase in o 2 and a sharp increase may be indicated by systematic ce depletion in apatite from the pegmatite core ree specific volatile complexes may contribute to variations including unusual kinks observed in ree patterns of apatite from mineral assemblages in upper parts of the pegmatite

the geochemical differentiation of s type pegmatites constraints from major trace element and li b isotopic composition of muscovite and tourmaline pegmatites often exhibit regional as well as internal zonation in this study we use major and trace element and li b isotopic composition of muscovite and tourmaline from internally zoned and un zoned s type pegmatites and their host granites to characterize the geochemical and isotopic fractionation associated with their formation the internally zoned pegmatites comprise three distinct textural zones namely wall intermediate and core muscovite and tourmaline occur in all the zones of these pegmatites the trace element concentrations ratios of muscovite from the three zones form well defined differentiation trends marked by enrichment of incompatible elements such as rb cs sr b zn nb ta p and the depletion of ni co v sc ti ba from the wall zone through the intermediate zone to the core zone this is suggestive of a strong role of fractional crystallization in producing the compositional diversity in the internally zoned pegmatites alkali element ratios such k rb and k cs in muscovite exhibit near exponential decline from the wall to the core zone which is suggestive of rayleigh type fractional crystallization fractional crystallization modelling reveals that the formation of the wall zone requires 69 crystallization the intermediate zone 85 95 and the core zone ca 99 crystallization leading to extreme enrichment of rb and cs and other incompatible elements muscovites and tourmaline from the un zoned pegmatites display similar compositional trends as the internally zoned ones but with a significant compositional gap between the host granite and the pegmatite lithium isotopic composition of muscovites and b isotopic composition of tourmalines become progressively lighter from wall to core zone of the internally zoned pegmatite and from the granite to the pegmatite for the un zoned pegmatites this is suggestive of an important role of vapour exsolution in the formation of the pegmatites taken together the geochemical and isotopic trends in the pegmatites can be explained by rayleigh fractional crystallization operating in tandem with vapour exsolution

crystallization conditions and evolution of magmatic fluids in the harney peak granite and associated pegmatites black hills south dakota evidence from fluid inclusions abstract a microthermometric study of inclusions in granites and pegmatites in the proterozoic harney peak granite system identified four types of inclusions type 1 inclusions are mixtures of co2 and h2o and have low salinities on average 3 5 wt nacleq type 2 inclusions are aqueous solutions of variable salinities from 0 to 40 wt nacleq type 3 inclusions are carbonic dominated by co2 with no detectable water and type 4 inclusions consist of 20 to 100 solids with the remaining volume occupied by a co2 h2o fluid many inclusions have a secondary character however a primary character can be unambiguously established in several occurrences of the type 1 inclusions these inclusions were trapped above the solidus and represent the exsolved magmatic fluid the secondary populations of types 1 2 and 3 probably formed as a result of reequilibration and unmixing of the type 1 fluid that progressively changed composition and density with decreasing temperature and pressure and was finally trapped along healed microfractures under subsolidus conditions type 4 inclusions are primary and are interpreted to be trapped fluid bearing complex silicate melts that subsequently solidified or underwent other posttrapping changes it is demonstrated that primary type 1 fluid inclusions that coexist with crystallized melt inclusions in the complex li bearing tin mountain pegmatite were trapped along the two fluid phase boundary in the system co2 h2o nacleq consequently the temperature and pressure conditions of trapping are identical to the bulk homogenization conditions on average 340 c and 2 7 kbar these conditions indicate that this li cs rb p and b rich pegmatite crystallized at some of the lowest known temperatures for a silicate melt in the crust an internally consistent empirical solvus surface in p t xco2 coordinates was generated for the pseudobinary co2 h2o 4 3 wt nacleq pegmatite fluid system distribution coefficients for the major species co2 h2o nacl and ch4 between the immiscible co2 rich and h2o rich fluid phases as a function of pressure and temperature were extracted from data for the two cogenetic fluid inclusions types

the role of diffusion controlled oscillatory nucleation in the formation of line rock in pegmatite plite dikes the george ashley block gab located in the pala pegmatite introduction district san diego county california is a composite pegmatite modal or phase layering is a phenomenon that is seen aplite dike of 8 m thickness displaying striking mineralogical layering in plutonic igneous rocks of all compositions from highin the aplite portion of the dike referred to as line rock rhythmic temperature low viscosity mafic complexes to low temlayering is characterized by garnet rich bands alternating with perature high viscosity felsic complexes the sizes of albite quartz muscovite rich bands cumulus textures are notably such plutonic bodies can range from the large layered absent from the layered portion of the dike elongated quartz intrusive complexes such as the 3000 m thick skaergaard megacrysts are oriented perpendicular to the garnet rich layers and complex down to dikes a few meters wide there is poikilitically include garnet albite and muscovite calculated however no consensus as to the origin of the layering crystal free magma viscosity with 3 h2o is 10 pa s and the modal layering that results from the gravitational settling calculated settling velocity for garnet is 0 51 cm year conductive of crystals from a magma is a model often invoked to cooling calculations based on emplacement of a 650 c dike into explain the layering in mafic magmatic systems this is 150 c fractured gabbroic country rock at 1 5 kbar and accounting more problematic in granitic systems because of the for latent heat of crystallization demonstrate that the line rock higher viscosities of the melts and the smaller density portion of the dike cools to 550 c in about 1 year crystal difference between crystals and melt size distribution studies also suggest very rapid nucleation and this paper presents a temperature crystallization crystallization diffusion controlled gel crystallization experiments model for the george ashley composite pegmatite aplite yield textures virtually identical to those observed in the layered dike which displays well developed rhythmic layering aplite including rhythmic banding colloform layering and band line rock in the aplite portion of the dike kleck 1996 discontinuities thus observed textures and calculated magmatic proposed that the layering in the george ashley block parameters suggest that mineralogical layering in the gab results gab a float slide block from this dike could be exfrom an in situ diffusion controlled process of oscillatory nucleation plained by the gravitational settling of garnet and albite and crystallization we propose that any event that promotes from the melt and that many of the textural features strong undercooling has the potential to initiate rapid heterogeneous which characterize the line rock such as offsets in the nucleation and oscillatory crystal growth leading to the development layers formed as a result of soft sediment deformation of a layer of excluded components in front of the crystallization of a crystal liquid mush the purpose of this investigation front and the formation of line rock was to evaluate crystal settling as a possible mechanism

experimental investigations of the weathering of suspended sediment by alpine glacial meltwater the magnitude and processes of solute acquisition by dilute meltwater in contact with suspended sediment in the channelized component of the hydroglacial system have been investigated through a suite of controlled laboratory experiments constrained by field data from haut glacier d arolla valais switzerland the effects of the water to rock ratio particle size crushing repeated wetting and the availability of protons on the rate of solute acquisition are demonstrated these free drift experiments suggest that the rock flour is extremely geochemically reactive and that dilute quickflow waters are certain to acquire solute from suspended sediment these data have important implications for hydrological interpretations based on the solute content of glacial meltwater mixing model calculations geochemical denudation rates and solute provenance studies

the ubiquitous nature of accessory calcite in granitoid rocks implications for weathering solute evolution and petrogenesis calcite is frequently cited as a source of excess ca sr and alkalinity in solutes discharging from silicate terrains yet no previous effort has been made to assess systematically the overall abundance composition and petrogenesis of accessory calcite in granitoid rocks this study addresses this issue by analyzing a worldwide distribution of more than 100 granitoid rocks calcite is found to be universally present in a concentration range between 0 028 to 18 8 g kg 1 mean 2 52 g kg 1 calcite occurrences include small to large isolated anhedral grains fracture and cavity infillings and sericitized cores of plagioclase no correlation exists between the amount of calcite present and major rock oxide compositions including cao ion microprobe analyses of in situ calcite grains indicate relatively low sr 120 to 660 ppm negligible rb and 87sr 86sr ratios equal to or higher than those of coexisting plagioclase solutes including ca and alkalinity produced by batch leaching of the granitoid rocks 5 co2 in di water for 75 d at 25 c are dominated by the dissolution of calcite relative to silicate minerals the correlation of these parameters with higher calcite concentrations decreases as leachates approach thermodynamic saturation in longer term column experiments 1 5 yr reactive calcite becomes exhausted solute ca and sr become controlled by feldspar dissolution and 87sr 86sr by biotite oxidation some accessory calcite in granitoid rocks is related to intrusion into carbonate wall rock or produced by later hydrothermal alteration however the ubiquitous occurrence of calcite also suggests formation during late stage subsolidus magmatic processes this conclusion is supported by petrographic observations and 87sr 86sr analyses a review of thermodynamic data indicates that at moderate pressures and reasonable co2 fugacities calcite is a stable phase at temperatures of 400 to 700 c

solubility of excess alumina in hydrous granitic melts in equilibrium with peraluminous minerals at 700 800 c and 200 mpa and applications of the aluminum saturation index we have studied the controls on the alumi num saturation index asi molec al2o3 cao na2o k2o and the concentration of normative corundum of granitic liquids saturated in alumina by equilibrating peraluminous minerals with initially meta luminous haplogranitic minimum composition liquids at 700 800 c and 200 mpa at and below h2o saturation the asi and normative corundum increase with increasing h2o concentration in the melt 0 04 to 0 10 moles excess al2o3 per mole of h2o temperature and with addition of the non haplogranitic components fe mg and b the asi parameter and concentration of normative corundum cannot be used to monitor aal2o3 between different mineral assemblages and melt because other components that affect the solubility of alumina including h2o fe mg and b do not appear in their formulations asi and normative corundum however provide petrogenetic information about magmas gener ated by partial melting of strongly peraluminous proto liths by virtue of their regular and predictable variation with melt composition e g h2o concentration and temperature for the application of these data to natural rocks it is necessary to choose as an analogue system the asi solubility or normative corundum solubility relations of the most chemically complex peraluminous mineral present in the rock comparison of asi values of anatectic leucosomes and allochthonous leucogranites with experimentally predicted values suggests low h2o concentrations in melt during crustal partial melting rapid melt segregation before equilibration with restitic peraluminous phases is also suggested in some cases

minor and trace elements as indicators of solute provenance and flow routing in a subglacial hydrological system mitchell a c brown g h fuge r 2006 minor and trace elements as indicators of solute provenance and flow routing in a subglacial hydrological system hydrological processes 20 4 877 897 sponsorship university of wales aberystwyth studentship am university of wales aberystwyth research grants 56 95 and 36 96 ghb and rf and nerc grant no gr3 11216

petrologic and geochemical links between the post collisional proterozoic harney peak leucogranite south dakota usa and its source rocks abstract the proterozoic terrane of the black hills south dakota includes the composite harney peak leucogranite and associated pegmatites that were emplaced into metamorphosed pelites and graywackes available dates indicate that granite generation post dated regional metamorphism and deformation that have been attributed to collision of the wyoming and superior cratons at 1760 ma previous radiogenic and stable isotope work indicates that the exposed metasedimentary rocks are equivalent to sources of the leucogranites in this study whole rock and mineral compositions of the metasedimentary rocks were used to calculate the likely average residue mineralogies and melt fractions that would be generated by muscovite dehydration melting of the rocks these were then used to model observed trace element compositions of the granites using published mineral melt distribution coefficients model trace element melt compositions using pelitic and graywacke protoliths yield similar results the models reproduce well the observed depletion of transition metals and ba in the granites relative to metasedimentary protoliths the depletion is due mainly to high proportion of biotite with variable amounts of k feldspar in the model residue sr is also depleted in the granites compared to source rocks but to a lesser relative extent than ba this is because of the low biotite melt distribution coefficient for sr and because high proportion of plagioclase in the residue is compensated by high sr concentrations in protoliths rubidium cs and ta behaved as slightly compatible to incompatible elements and therefore were not strongly fractionated during melting of the considered elements only b appears to have been highly incompatible relative to residue during melting the protoliths had sufficient b to allow tourmaline crystallization in those parts of the harney peak granite in which ti concentration was sufficiently low not to enhance crystallization of biotite the reproducibility of observed trace element concentrations in the harney peak granite by the models supports the often made proposition that metapelites and metagraywackes are common sources for leucogranites this argues against mass input from the mantle into metagraywacke and metapelitic crustal sources or melting of amphibolites to generate the post collisional harney peak and other similar peraluminous granite suites

the generation and crystallization conditions of the proterozoic harney peak leucogranite black hills south dakota usa petrologic and geochemical constraints the mineralogy petrology and geochemistry of the proterozoic harney peak granite black hills south dakota were examined in view of experimentally determined phase equilibria applicable to granitic systems in order to place constraints on the progenesis of peraluminous leucogranites and commonly associated rare element pegmatites the granite was emplaced at 3 4 kbar as multiple sills and dikes into quartz mica schists at the culmination of a regional high temperature low pressure metamorphic event principally along the periphery of the main pluton and in satellite intrusions the sills segregated into granite pegmatite couplets the major minerals include quartz k feldspar sodic plagioclase and muscovite biotite mg no molar mgo mgo feo 0 32 0 38 is the predominant ferromagnesian mineral in the granite s core whereas at the periphery of the main pluton and in the satellite intrusions tourmaline mg no 0 18 0 48 is the dominant ferromagnesian phase almandine spessartine garnet is also found in the outer intrusions there is virtually a complete overlap in the wide concentration ranges of sio2 cao mgo feo sr zr w of the biotite and tourmaline bearing granite suites with no discernable differentiation trends on harker diagrams precluding the derivation of one suite from the other by differentiation following emplacement this is consistent with the oxygen isotope compositions which are 11 5 0 6 for the biotite granites and 13 2 0 8 for the tourmaline granites suggesting derivation from different sources the concentrations of tio2 and possibly ba are higher and of mno and b are lower in the biotite granites the normative orthoclase albite ratio is extremely variable ranging from 0 26 to 1 65 in the biotite granites to 0 01 1 75 in the tourmaline granites very few sample compositions fall near the high pressure watersaturated haplogranite minima eutectic trend indicating that the granites for the most part are not minimum melts generated under conditions with a text h text 2 text o 1 instead most biotite granites are more potassic than the water saturated minima and eutectics and in analogy with experimentally produced granitic melts they are best explained by melting at 6 kbar a text h text 2 text o 1 and temperatures 800 c such high temperatures are also indicated by oxygen isotope equilibration among the constituent minerals nabelek et al 1992 several of the tourmaline granite samples contain virtually no k feldspar and have oxygen isotope equilibration temperatures 716 775 c therefore they must represent high temperature accumulations of liquidus minerals crystallized under equilibrium conditions from melts more sodic than the water saturated haplogranite minima or during fractionation of intruded melts into granite pegmatite couplets accompanied by volatile aided differentiation of the alkali elements the indicated high temperatures a text h text 2 text o 1 the relatively high tio2 and ba concentrations and the relatively low partial 18 text o values of the biotite granites suggest that they were generated by high extent biotite dehydration melting of an immature archean metasedimentary source the ascent of the hot melts may have triggered low extent muscovite dehydration melting of schists higher in the crust producing the high b low ti melts comprising the periphery of the main pluton and the satellite intrusions alternatively the different granite types may be the result of melting of a vertical section of the crust in response to the ascent of a thermal pulse with the low partial 18 text o biotite granites generated at a deeper hotter region and the high partial 18 text o tourmaline granites at a higher cooler region of the crust the low ti and high b concentrations in the high partial 18 text o melts resulted in the crystallization of tourmaline rather than biotite which promoted the observed differentiation of the melts into the granitic and pegmatitic layers found along the periphery of the main pluton and the satellite intrusions

anorogenic gross spitzkoppe granite stock in central western namibia part ii structures and textures indicating crystallization from undercooled melt the anorogenic cretaceous gross spitzkoppe granite stock and associated bimodal dike swarms are related to continental rifting which led to separation of africa from south america the stock is composed of highly evolved topaz bearing a type granites subhorizontal 20m wide aplite dikes and thinner aplite pegmatite dikes cut the granites the contact of the stock and the upper contacts of subhorizontal microgranite aplite dikes are marked by stockscheiders composed of layered aplites and pegmatites the layering is characterized by rhythmic variations in grain size grain morphology and mineral composition regular orientation of columnar alkali feldspar crystals or plumose alkali feldspar quartz intergrowths and dendritic biotite indicate unidirectional crystal growth against the heat flow in the marginal stockscheider toward the stock in the upper parts of the subhorizontal aplite dikes downward and in some steeply dipping aplite pegmatite dikes from both margins inward these structures and textures are interpreted to result from diffusion controlled oscillatory nucleation and rapid growth from undercooled melt coupled with changes in vapor pressure crystal growth from undercooled melt with sparse alkali feldspar megacrysts acting as a substrate for the growing crystals is indicated also by an irregular dike of orbicular granite cutting the marginal granite of the stock

phase relations of tourmaline leucogranites and the significance of tourmaline in silicic magmas by means of melting and recrystallization tourmaline seeded experiments phase relations of two natural tourmaline bearing fe rich members of the schorl dravite series leucogranites have been determined between 1 and 3 kbar under h2o saturation with fo2 close to ni nio the presence of tourmaline slightly lowers the solidus temperatures of both samples from 5 to 20 c compared to the corresponding tourmaline free solidus quartz k feldspar and plagioclase phase relations are not significantly dependent on the presence of tourmaline tourmaline is the last major phase to disappear for both samples and a demonstrated liquidus phase exists for one in the recrystallization experiments the compositions of the tourmalines growing from the melt change from more mg rich at high temperatures to more fe rich at lower temperatures the tourmalines are always richer in mg than the melt is but fe and mg are not especially partitioned between crystallizing tourmaline and melt melt compositions do not depart

elevated stream trace and minor element concentrations in the foreland of receding tropical glaciers globally the ongoing retreat of mountain glaciers will ultimately diminish fresh water supplies this has already begun in watersheds with greatly reduced glacial coverage still unknown are the affects of glacial retreat on downstream water quality including the threats to human and ecosystem health in the cordillera blanca retreating glaciers have exposed sulfide rich rock outcrops negatively affecting the quality of the glacial meltwater this study has evaluated glacial melt stream hydrogeochemistry in the sulfide bearing rio quilcay watershed 927 0 s 7722 0 w during the 2008 dry season surface water samples were collected from the upper 12 km of the watershed during the 2008 dry season dissolved 0 4 lm and unfiltered acidified ph 2 al co cu fe ni mn pb zn and dissolved major ions and organic c doc concentrations were quantified and ph and temperature were measured in the field twenty of 22 stream samples had ph values below 4 generating significantly p 0 01 a 0 05 greater cation denudation normalized to discharge than other worldwide glacier fed streams additionally dissolved trace and minor element concentrations were comparable to acid mine drainage non conservative dissolved element behaviors resulted from adsorption desorption reactions in tributary mixing zones at low ph values hydrous fe oxides acted as the dominant sorption surfaces the poor water quality observed in cordillera blanca headwaters coupled with the likely exposure of additional sulfide rich outcrops from ongoing glacial retreat may pose water quality challenges

comments on the use of chemically based mixing models in glacier hydrology the assumptions involved in the use of chemically based mixing models for analysis of flow routing of meltwaters in glacierized basins are critically evaluated the assumption that glacial drainage systems consist of only two primary flow components is arbitrary and must be supported by independent evidence recent studies of the processes by which meltwaters acquire solute indicate that the assumption that flow components have unique and constant chemical compositions is unlikely to lie correct source water composition and weathering potential will vary over the course of a melt season and the extent of subglacial weathering is strongly dependent upon such factors as meltwater residence time and the availability of reactive sediment both of which are known to vary on diurnal to seasonal time scales mixing of flow components does not appear to be confined to the terminal regions of glaciers and is therefore unlikely to be conservative as assumed a multi parameter mixing model is applied to the analysis of data on the chemistry of waters sampled from bureholes drilled through haut glacier d arolla switzerland to demonstrate the range of dissolved species for which the assumption of conservative mixing is violated the consequences of this violation for quantitative hydrograph separation are shown to be highly significant the utility of mixing models as a tool for the investigation of glacier hydrological systems is questionable and the results of previous studies are unreliable

stable isotope evidence for the petrogenesis and fluid evolution in the proterozoic harney peak leucogranite black hills south dakota abstract oxygen and hydrogen isotope systematics of the proterozoic harney peak granite black hills south dakota were examined in order to constrain its petrogenesis and to examine the role of fluids in a peraluminous granite pegmatite magmatic system the leucogranite and its satellite intrusions were emplaced as hundreds of sills and dikes which are texturally heterogeneous ranging from aplitic to pegmatitic the dominant ferromagnesian mineral in the core of the granite is biotite while along its perimeter and in satellite intrusions it is tourmaline biotite and tourmaline are for the most part mutually exclusive oxygen isotopes among minerals in non pegmatitic rocks from throughout the pluton equilibrated for the most part at magmatic temperatures between 800 to 650 c in the pegmatitic samples quartzfeldspar oxygen isotope fractionations point to disequilibrium probably a result of the sequential crystallization of these minerals the isotopic composition of most pegmatites suggests local derivation by differentiation of emplaced batches of magma the whole rock 18 o values of the granites are heterogeneous ranging from 10 4 to 14 3 however there is a pronounced difference in the isotopic composition of the biotite containing granites from the core of the pluton 11 5 0 6 and the tourmaline rich granites from its perimeter and the satellite intrusions 13 2 0 8 the average oxygen isotopic composition of the surrounding schists is identical to that of the latter granites biotite muscovite and tourmaline muscovite d values vary from 20 to 10 and from 0 to 10 respectively although these values differ from theoretical values the narrow ranges suggest that the minerals are in isotopic equilibrium and that their isotopic compositions record the composition of the magmatic fluid the calculated d value of the magmatic fluid is 67 to 58 well within the magmatic water range however somewhat elevated mineral d values in the southern part of the harney peak granite where the metasediments reached the second sillimanite isograd suggest that limited interaction with fluids derived from the dehydrating metasediments may have occurred alternatively the elevated values could reflect a hydrogen isotope heterogeneity in the source or interaction with another magmatic system to the south of the harney peak granite it is shown that fractional crystallization or subsolidus interaction of the harney peak granite with the magmatic fluid or a fluid derived from the schist cannot explain the difference between the 18 o values of the core and perimeter granites although some oxygen isotope heterogeneity in the granite could be explained by assimilation of the country rocks assimilation cannot explain all of the difference between the two granite types instead it is proposed that intrusion of the magma which led to the biotite granites in the core of the pluton at the culmination of regional metamorphism initiated melting of the schists at a depth somewhat greater than the present level of erosion the melts were emplaced into the overlying schist and differentiated into the many tourmaline rich granite pegmatite sills and dikes comprising much of the perimeter of the harney peak granite and its satellite plutons alternatively the different melts may have resulted from melting along an isotopically heterogeneous vertical section of the crust in response to the ascent of a thermal pulse

gravity steps at mt etna volcano italy instrumental effects or evidences of earthquake triggered magma density changes 1 on two occasions sudden gravity changes occurred simultaneously at two summit etna s stations during local low magnitude earthquakes a systematic coupling between earthquakes inducing comparable maximum acceleration and displacement at the observation points and gravity steps is missing implying 1 the non instrumental nature of the steps and 2 the need for particular underlying conditions for the triggering mechanism s to activate we review some of the volcanological processes that could induce fast underground mass redistributions resulting in gravity changes at the surface these processes involve bubbles and crystals present in the magma and require particular conditions in order to be effective as mass redistributing processes the gravity steps could be a geophysical evidence of the dynamical stress transfer between tectonic and magmatic systems at a local scale given the implications that these transfers may have on the volcanic activity routine volcano monitoring should include the observation of fast gravity changes

trace element and major ion concentrations and dynamics in glacier snow and melt eliot glacier oregon cascades we present concentrations of environmentally available unfiltered acidified 2 v v hno3 as cu cd pb v sr and major ions including ca2 cl and so42 in a july 2005 and a march 2006 shallow snow profile from the lower eliot glacier mount hood oregon and its proglacial stream eliot creek low enrichment factors ef with respect to crustal averages suggests that in fresh march 2006 snow environmentally available elements are derived primarily from lithogenic sources soluble salts occurred in lower and less variable concentrations in july 2005 snow than march 2006 conversely environmentally available trace elements occurred in greater and more variable concentrations in july 2005 than march 2006 snow unlike major solutes particulate associated trace elements are not readily eluted during the melt season additionally elevated surface concentrations suggest that they are likely added throughout the year via dry deposition in a 1 h stream sampling ratios of dissolved 0 45 m v cl sr cl and cu cl are enriched in the eliot stream with respect to their environmentally available trace element to cl ratios in eliot glacier snow suggesting chemical weathering additions in the stream waters dissolved pb cl is depleted in the eliot stream with respect to the ratio of environmentally available pb to cl in snow corresponding to greater adsorption onto particles at greater ph values copyright 2009 john wiley sons ltd

diurnal dynamics of minor and trace elements in stream water draining dongkemadi glacier on the tibetan plateau and its environmental implications abstract global warming has resulted in rapid glacier retreat on the tibetan plateau tp and the impacts of glacier melting on downstream ecosystems remain largely unknown minor and trace elements in stream water draining dongkemadi glacier dg were examined during the ablation season of 2013 dominant ions and elements are hco 3 ca 2 fe and sr water chemistry is controlled by the weathering of calcite oxidation of pyrite and dissolution of evaporites correlations suggests the hydrological e g meltwater generation and routing water residence time and physicochemical e g sorption precipitation oversaturation controls on species concentrations the distribution of metals is featured by the mixture of soluble metal and non metal ligand complexes and free monovalent and divalent ions downstream increased concentrations and or fluxes of some metals and metalloid e g cr cu and as suggest potential environmental impacts discharge normalized cation denudation rate 372 meq m 3 in the dg basin is larger than those from alpine and polar glaciers suggesting a stronger weathering of carbonate with greater abundance on the tp in comparison to other mountain and polar glacial catchments the maximum fe concentration exceeds the usepa guideline and al zn and pb are close to or of the same order of magnitude as liminal values this implies that the tp may face a challenge of ecosystem health and environmental issue in a warming climate

geochemical weathering at the bed of haut glacier d arolla switzerland a new model waters were sampled from 17 boreholes at haut glacier d arolla during the 1993 and 1994 ablation seasons three types of concentrated subglacial water were identified based on the relative proportions of ca 2c h co 3 and so4 2 to si type a waters are the most solute rich and have the lowest relative proportion of si they are believed to form in hydrologically inefficient areas of a distributed drainage system most solute is obtained from coupled sulphide oxidation and carbonate dissolution so cd it is possible that there is a subglacial source of o2 perhaps from gas bubbles released during regelation because the high so4 2 levels found up to 1200 eq l are greater than could be achieved if sulphides are oxidized by oxygen in saturated water at 0 c c 414 eq l a more likely alternative is that sulphide is oxidized by fe 3c in anoxic environments if this is the case exchange reactions involving fe iii and fe ii from silicates are possible these have the potential to generate relatively high concentrations of hco3 with respect to so4 2 formation of secondary weathering products such as clays may explain the low si concentrations of type a waters type b waters were the most frequently sampled subglacial water they are believed to be representative of waters flowing in more efficient parts of a distributed drainage system residence time and reaction kinetics help determine the solute composition of these waters the initial water rock reactions are carbonate and silicate hydrolysis and there is exchange of divalent cations from solution for monovalent cations held on surface exchange sites hydrolysis is followed by so cd the so4 2 concentrations usually are 414 eq l although some range up to 580 eq l which suggests that elements of the distributed drainage system may become anoxic type c waters were the most dilute yet they were very turbid their chemical composition is characterized by low so4 2 h co3 ratios and high ph type c waters were usually artefacts of the borehole chemical weathering environment true type c waters are believed to flow through sulphide poor basal debris particularly in the channel marginal zone the composition of bulk runoff was most similar to diluted type b waters at high discharge and was similar to a mixture of type b and c waters at lower discharge these observations suggest that some supraglacial meltwaters input to the bed are stored temporarily in the channel marginal zone during rising discharge and are released during declining flow little of the subglacial chemical weathering we infer is associated with the sequestration of atmospheric co2 t he progression of reactions is from carbonate and silicate hydrolysis through sulphide oxidation by first oxygen and then fe iii which drives further carbonate and silicate weathering a crude estimate of the ratio of carbonate to silicate weathering following hydrolysis is 4 1 we speculate that microbial oxidation of organic carbon also may occur both sulphide oxidation and microbial oxidation of organic carbon are likely to drive the bed towards suboxic conditions hence we believe that subglacial chemical weathering does not sequester significant quantities of atmospheric co2 and that one of the key controls on the rate and magnitude of solute acquisition is microbial activity which catalyses the reduction of fe iii and the oxidation of fes2 copyright 2002 john wiley sons ltd

hydrochemistry of carbonate terrains in alpine glacial settings nearly 200 analyses of meltwaters ice and snow from three alpine glacial sites in carbonate terrain are summarized and discussed in terms of sources of solutes and kinetic controls on the progress of weathering reactions most data derive from the swiss glacier de tsanfleuron which is based on cretaceous and tertiary pure and impure limestones two other sites marmolada italian dolomites and the saskatchewan glacier alberta are based on a mixed calcitic dolomitic substrate most solutes originate from carbonate dissolution moreover where pyrite is present its oxidation supplies significant sulphate and forces more dissolution of carbonate the ratios sr2 ca2 and mg2 ca2 are much higher in tsanfleuron melt waters than local bedrock a phenomenon that can be reproduced in the laboratory at small percentages of dissolution these anomalous ratios are attributed to incongruent dissolution of traces of the metastable carbonates mg calcite and aragonite these phases also provide na to solution k is argued to originate mainly by ion exchange on clays with solute ca2 quartz and very minor feldspar dissolution are also inferred locally enhanced input from atmospheric sources is recognized by high cl and associated na the progress of weathering reactions has been evaluated by the trends in the data computer modelling and some simple laboratory experiments the most dilute samples show a trend towards removal of co2 to low partial pressures c 10 5 5 atmospheres reflecting initially rapid carbonate dissolution and relatively slow dissolution of gaseous co2 later addition of atmospheric co2 or acid from pyrite oxidation allows further carbonate dissolution but solutions show a wide range of saturations and co2 pressures as high as 10 2 2 where pyrite oxidation is important in a carbonate terrain measurement of electroconductivity corrected to 25 c and alkalinity in the field allows the following preliminary deductions where meq stands for milliequivalents formula presented where s is the minimum meq ca2 mg2 produced by simple dissolution of carbonate unconnected with pyrite oxidation as with any proxy method these deductions do not remove the need for chemical analysis of waters in a given study area copyright 1994 john wiley sons ltd

distribution of boron in the tip top pegmatite black hills south dakota experimental evidence has shown the importance of boron on the crystallization behavior of granitic systems however the intercrystalline and intracrystalline distribution of boron in mineral phases crystallizing from granitic systems is not well documented the distribution of boron between coexisting phases in the tip top pegmatite south dakota is as follows beryl ca quartz ca triphylite ca montebrasite ca potassium feldspar biotite albite muscovite spodumene tourmaline the bulk boron content of the tip top pegmatite decreases significantly with the termination of tourmaline crystallization the significant decrease in boron in the inner zones of the pegmatite is consistent with the depletion of boron in the granite melt by either the crystallization of tourmaline from the granitic melt or the partitioning of boron into an exsolved aqueous solutions 35 references

variability in the chemical composition of in situ subglacial meltwaters meltwaters collected from boreholes drilled to the base of the haut glacier d arolla switzerland have chemical compositions that can be classified into three main groups the first group is dilute whereas the second group is similar to though generally less concentrated in major ions than contemporaneous bulk glacial runoff the third group is more concentrated than any observed bulk runoff including periods of flow recession waters of the first group are believed to represent supraglacial meltwater and ice melted during drilling limited solutes may be derived from interactions with debris in the borehole the spatial pattern of borehole water levels and borehole water column stratification combined with the chemical composition of the different groups suggest that the second group represent samples of subglacial waters that exchange with channel water on a diurnal basis and that the third group represent samples of water draining through a distributed subglacial hydraulic system high no 3 concentrations in the third group suggest that snowmelt may provide a significant proportion of the waters and that the residence time of the waters at the bed in this particular section of the distributed system is of the order of a few months the high no 3 concentrations also suggest that some snowmelt is routed along different subglacial flowpaths to those used by icemelt the average so2 4 hco 3 so2 4 ratio of the third group of meltwaters is 0 3 suggesting that sulphide oxidation and carbonate dissolution which gives rise to a ratio of 0 5 cannot provide all the hco 3 to solution hence carbonate hydrolysis may be occurring before sulphide oxidation or there may be subglacial sources of co2 perhaps arising from microbial oxidation of organic c in bedrock air bubbles in glacier ice or pockets of air trapped in subglacial cavities the channel marginal zone is identified as an area that may influence the composition of bulk meltwater during periods of recession flow and low diurnal discharge regimes 1997 by john wiley sons ltd

diurnal hydrological physicochemical controls and sampling methods for minor and trace elements in an alpine glacial hydrological system summary we present diurnal i 0 45 and 0 1 m pore size filtered and ii operationally defined labile particulate associated major minor and trace element concentrations and fluxes in glacial outflow waters draining haut glacier d arolla switzerland we use speciation modelling phreeqci and water suspended sediment interaction experiments are utilised under conditions analogous to the subglacial channellised hydrological system in order to assess controls on and the most suitable sampling methods to investigate short term variations in the mode of major minor and trace element species export from a glacierised headwater catchment 0 45 m pore size filtered major ions sr and u are exported in glacial outflow waters predominately as mobile monovalent or divalent ions or as carbonate complexes and are controlled by hydrological variations over diurnal cycles exhibiting an inverse concentration with increasing meltwater discharge conversely 0 45 m pore size filtered concentrations of most minor and trace elements e g fe mn co ba and pb exhibit variations that are not strongly inter correlated with meltwater discharge or suspended sediment concentrations ssc over diurnal periods the use of 0 45 and 0 1 m pore size filter membranes indicates that significant colloidal material is not passing through the 0 45 m pore size filters and these unsystematic variations are not a result of colloid measurement speciation modelling applied to meltwaters and observations during water rock interaction experiments suggest that these unsystematic temporal variations reflect physicochemical controls this includes sorption and the oversaturation and precipitation of fe and al oxi hydroxides and the co precipitation of other species diurnal ph variations appear important in controlling such short term physicochemical controls which limits such species use for hydrological investigations the percentage of total elemental fluxes exported as the labile particulate associated flux paf for each minor and trace element changes dramatically between and during the diurnal cycles reflecting species specific sensitivity to hydrological and physicochemical controls hydrological interpretations of hydrochemical data must be made carefully when using chemical determinations by icp ms since we demonstrate that measurements will comprise of any material that passes through the filter this can lead to higher concentration measurements than if determined by ion chromatography which measures truly ionic dissolved species

shallow magma pathway geometry at mt etna volcano 1 a fundamental goal of volcano seismology is to understand the dynamics of active magmatic systems in order to assess eruptive behavior and the associated hazard imaging of magma conduits quantification of magma transport and investigation of long period seismic sources together with their temporal variations are crucial for the comprehension of eruption triggering mechanisms at mt etna volcano several intense episodes of tremor activity were recorded during 2007 in association with strombolian activity and or intense fire fountaining episodes occurring from the south east crater sec the locations of the tremor sources and of the long period seismic events are used here to constrain both the area and the depth range of magma degassing highlighting the geometry of the shallow conduits feeding sec the imaged conduits consist of two connected resonating dike like bodies nnw sse and nw se oriented extending from sea level to the surface in addition we show how tremor long period lp and very long period vlp event locations and signatures reflect pressure fluctuations in the plumbing system associated with the ascent discharge of gas rich magma linked to the lava fountains the evidence here reported also corroborated by ground deformation variations can help develop a better prediction and early warning system for those eruptions effusive or explosive that apparently manifest no clear precursors

numerical simulation of convection and mixing in magma chambers replenished with co2 rich magma 1 magma convection and mixing and periodic refilling commonly occur in magma chambers we show here that the presence of co2 in the refilling magma is a very efficient mean of inducing buoyant driven plume rise and large scale convection numerical simulations performed with an appositely developed code for the transient 2d dynamics of multicomponent compressible to incompressible fluids reveal several features of the processes of plume rise convection and mixing in magma chambers associated with chamber refilling a parametric study on co2 abundance in the refilling magma shows that progressively larger amounts of this volatile produce a shift from simple plume rise and spreading near the chamber top to complex patterns of flow circulation and large scale vorticity and mixing lower chamber depth and lower magma viscosity largely enhance the efficiency of mixing and convection favoring the formation of multiple vortexes migrating with time

borehole water level variations and the structure of the subglacial hydrological system of haut glacier d arolla valais switzerland late summer subglacial water pressures have been measured in a dense array of boreholes in the ablation area of haut glacier d arolla switzerland interpolated surfaces of minimum diurnal water pressure and diurnal water pressure variation suggest the presence of a subglacial channel within a more widespread distributed drainage system the channel flows along the centre of a variable pressure axis vpa some tens of metres wide that is characterized by low minimum diurnal water pressures frequently atmospheric and high diurnal water pressure variations these characteristics are transitional over a lateral distance of c 70 m to higher and more stable subglacial water pressures in the adjacent distributed system water pressure variations recorded in boreholes located close to the centre of the vpa reflect the delivery of surface derived meltwater to the glacier bed and result in a diurnally reversing transverse hydraulic gradient that drives water out from the channel into the distributed system during the afternoon and back to the channel overnight subglacial observations suggest that such flow occurs through a vertically confined sediment layer borehole turbidity records indicate that the resulting diurnal water flows are responsible for the mobilization and transport of fine debris in suspension analysis of the propagation velocity and amplitude attenuation of the diurnal pressure waves suggests that the hydraulic conductivity of the sediment layer decreases exponentially with distance from the channel falling from c 10 4 m s 1 at the channel boundary to c 10 7 ms 1 70m away these apparent hydraulic conductivities are consistent with darcian flow through clean sand and typical glacial till respectively we suggest that fine material is systematically flushed from basal sediments located adjacent to large melt season drainage channels beneath warm based glaciers this process may have important implications for patterns of glacier erosion hydrochemistry and dynamics

trace element constraints on pegmatite genesis tin mountain pegmatite black hills south dakota the tin mountain pegmatite is a small zoned granitic body that is extremely enriched in rb and li but has moderate concentrations of sr and ba these trace elements are modelled using granitic distribution coefficients in order to test the potentials of partial melting of metasedimentary rocks and fractionation of a less evolved granitic melt to have produced the parental liquid to the tin mountain pegmatite batch melting of any reasonable metasedimentary source rock would likely have yielded melts that were either insufficiently enriched in rb and li to be the parental liquid or that had sr and ba concentrations that were much higher than those estimated for the parental liquid the modelling of simple fractional crystallization and equilibrium crystallization of a granitic melt within the compositional range of the spatially associated harney peak granite gives calculated melt compositions with either lower sr and ba concentrations or inadequate rb and li enrichments to be the parent liquid of the pegmatite at least two variants from simple crystal liquid fractionation models can however successfully account for the derivation of the parent liquid 1 generation of a rb li ba and sr rich granitic melt outside of the compositional range of the sampled portions of the harney peak granite complex by low degrees of partial melting of metasedimentary rocks found in the black hills followed by moderate extents of fractional or equilibrium crystallization 2 derivation from harney peak granite via a complex multi stage crystal liquid fractionation process such as progressive equilibrium crystallization

glacier meltwater hydrochemistry abstract glacierised areas present an ideal environment in which to study water rock interaction since chemical weathering rates are high and anthropogenic impacts are often minimal detailed investigations of meltwater quality variations have suggested the importance of these environments in estimates of terrestrial chemical erosion and global biogeochemical cycles most notably the role of meltwaters in co2 sequestration during episodes of deglaciation has attracted considerable attention since this may impact on climate at glacial interglacial timescales however there is still considerable uncertainty surrounding estimates of co2 drawdown by meltwaters which remains to be resolved water flow through glaciers exerts an important control on ice mass dynamics and influences the quantity and quality of water delivered to environments downstream of glacierised basins thus the study of the configuration and dynamics of subglacial drainage systems is important not only to enhance scientific understanding but also to allow effective water resource utilisation in glacierised headwater catchments bulk meltwater quality characteristics draining terrestrial ice masses also offer the potential to provide unique information on hydrological and hydrochemical processes operating in the inaccessible subglacial environment here significant advances have been made in understanding the controls on chemical weathering reactions based on the identification of key dissolved indicator species this has allowed water quality variations to be exploited as a tool for both subglacial hydrochemical and hydrological investigations as a result this area of glaciology has received considerable attention in recent years utilising an increasing range of dissolved ions and integrating field and laboratory studies however uncertainty still surrounds certain areas of meltwater quality science including the role of microorganisms in a system which to date has largely been viewed as abiotic a better understanding of the processes and rates of chemical weathering in glacierised environments has the potential to enhance our understanding of the environment and to facilitate the exploitation of water quality variations for both scientific and applied objectives in this paper the development and current state of meltwater quality science as a tool for investigating subglacial hydrology and geochemistry is detailed and problems and future directions identified this will hopefully stimulate wider interest in an important area of aquatic chemistry with significant applied implications

boron geochemistry of the lower crust evidence from granulite terranes and deep crustal xenoliths abstract boron contents are uniformly low in more than 100 granulites from exposed terranes in india norway and scotland and from xenolith suites in the western usa averages for the terranes 2 5 ppm and for xenoliths 1 2 ppm suggest maximum b contents of about 2 1 ppm for the lower crust abundance distributions from exposed terranes are skewed to higher values as b has been added to some samples via retrograde fluids during decompression the samples studied include mafic to felsic lithologies of both igneous and sedimentary origin there is no correlation of b content with bulk composition or with protolith type in any of the suites studied boron is apparently depleted in all granulite protoliths during prograde metamorphism and dehydration similar depletions of b and other fluid mobile elements e g u cs with respect to rare earth elements ree zr ba rb and k 2 o are seemingly inconsistent with origin of granulites primarily via extraction of silicate melts these distinctive geochemical features are attributed to selective element transport in fluids released by devolatilization reactions anatexis is not necessarily precluded but dehydration of the subsolidus protolith normally would precede melting and lead to depletion of the fluid mobile elements compositions of any melts and restites eventually formed would reflect the effects of this antecedent process the systematic depletion of b and cs in granulites contrasts with the highly variable contents of most other incompatible elements determined for this reason the estimated lower crust abundance for b is relatively well constrained whereas abundance estimates for many other elements are model dependent have large uncertainties and are unlikely to be globally representative

chemical models of solute acquisition in glacial melt waters chemical models for the evolution of bulk melt waters can be constructed by assuming that rock mineral weathering and solute acquisition are controlled by carbonate equilibria different open and closed system models are defined by variations in the rates of weathering relative to the rate of hydrogen ion supply by the dissolution and dissociation of co2 and can be recognized by characteristic ph and relationships the observed and inferred compositions of englacial and subglacial melt suggest that mixing is unlikely to be conservative and that closed system conditions result where post mixing weathering reactions occur the final composition of bulk melt waters is determined by the mixing ratio between englacial and subglacial melt the extent of post mixing evolution and opportunity for mixing with ground waters or re equilibration with the atmosphere