epidote in calcalkaline magmas an experimental study of stability phase relationships and the role of epidote in magmatic evolution experiments on tonalite and granodiorite were performed at conditions ranging from 2 1 to 18 kbar and 550 to 850 c to establish the magmatic stability field of epidote as a function of p t and f02 at water saturated conditions and f02 buffered by nno epidote has a wide magmatic stability field in tonalite at 13 kbar this field extends from the wet solidus at 630 to 790 0c the low pressure intersection of the magmatic epidote crystallization reaction and the h20 saturated tonalite solidus and hence the minimum pressure for magmatic epidote occurs at about 5 kbar the clapeyron slopes of epidote melting reactions are moderately positive in p t space at pressures below the intersection of the epidote melting and the gamet in reactions at 13 kbar 790 c at this intersection epidote reaches its maximal thermal stability 790 c in tonalite h20 in the presence of garnet that is above 14 kbar epidote melting reactions have steep negative clapeyron slopes in p t space at p t conditions near the low pressure intersection of the epidote melting reaction with the water saturated solidus experiments were also performed with f02 buffered by hm at these oxidizing conditions the magmatic stability field of epidote is enlarged down to a pressure of about 3 kbar in granodiorite the stability of epidote has been investigated at pressures from 7 5 to 18 kbar with respect to the tonalite the epidote out reaction is located almost at the same p t conditions at 10 kbar but the maximum thermal stability is about 50 c lower toward higher pressures although few experiments indicate that epidote stability does not increase dramatically with decreasing water activity at present state it is not possible to predict melting and crystallization behavior of epidote at waterundersaturated conditions modal abundances of epidote are low 05 vol in the presence of major 40 vol melt fractions thus epidote in calc alkaline magmatic rocks is not likely to affect major elements strongly by fractional crystallization

reassessment of net surface mass balance in antarctica abstract recent in situ measurements of surface mass balance and improved calculation techniques are used to produce an updated assessment of net surface mass balance over antarctica a new elevation model of antarctica derived from ers 1 satellite altimetry supplemented with conventional data was used to delineate the ice flow drainage basins across antarctica the areas of these basins were calculated using the recent digital descriptions of coastlines and grounding lines the delineation of drainage basins was achieved using an automatic procedure which gave similar results to earlier hand drawn catchment basins more than 1800 published and unpublished in situ measurements of net surface mass balance from antarctica were collated and then interpolated a net surface mass balance map was derived from passive microwave satellite data being employed as a forcing field to control the interpolation of the sparse in situ observations basinwide integrals of net surface mass balance were calculated using t

model experiments on the evolution and stability of ice streams this is the publisher s version also available electronically from http www igsoc org annals 23

growth of greenland ice sheet measurement measurements of ice sheet elevation change by satellite altimetry show that the greenland surface elevation south of 72 degrees north latitude is increasing the vertical velocity of the surface is 0 20 0 06 meters per year from measured changes in surface elevations at 5906 intersections between geosat paths in 1985 and seasat in 1978 and 0 28 0 02 meters per year from 256 694 intersections of geosat paths during a 548 day period of 1985 to 1986

allanite and other ree rich epidote group minerals epidote group minerals rich in rare earth elements ree in particular allanite are common accessory phases in igneous metamorphic metasomatic and sedimentary rocks small amounts of ree are present in most epidote group minerals but in allanite and the related minerals dissakisite ferriallanite dollaseite khristovite and androsite the ree are essential structural constituents an important characteristic of ree rich epidote group minerals is that their octahedrally coordinated m sites contain major amounts of divalent cations this paper summarizes literature data for these minerals and discusses their chemistry occurrence phase relations and petrologic and geologic significance the chapter emphasizes allanite because it is the most common and best studied of the ree rich epidote group minerals epidote group minerals contain isolated silicon tetrahedra and corner sharing groups of two tetrahedra and are thus assigned to the disilicate or sorosilicate structural family for a detailed description of the structure see franz and liebscher 2004 the epidote group structural formula is a2m3 sio4 si2o7 o f oh or in a simplified form a2m3si3o11 o f oh in which a ca sr pb2 mn2 th ree3 and u and m al fe3 fe2 mn3 mn2 mg cr3 and v3 deer et al 1986 there are two structurally different a sites a 1 and a 2 with different coordination numbers and there are three different m sites m 1 m 2 and m 3 which are all octahedrally coordinated ueda 1955 dollase 1971 in epidote group minerals trivalent ree are accommodated in the a sites which in endmember epidote both contain ca the incorporation of ree3 is commonly charge balanced by a divalent cation fe2 mn2 mg substituted for a trivalent one in the m sites table 1

the northeast kingdom batholith vermont magmatic evolution and geochemical constraints on the origin of acadian granitic rocks five devonian plutons west charleston echo pond nulhegan derby and willoughby that constitute the northeast kingdom batholith in vermont show wide ranges in elemental abundances and ratios consistent with major crustal contributions during their evolution the batholith consists of metaluminous quartz gabbro diorite and quartz monzodiorite peraluminous granodiorite and granite and strongly peraluminous leucogranite contents of major elements vary systematically with increasingsio 40 and have small negative eu anomalies the strongly peraluminous willoughby leucogranite has unique trace element abundances and ratios relative to the rest of the batholith including low contents of hf zr sr and ba low values of k rb 80 164 th ta 9 rb cs 7 40 k cs 0 1 0 5 ce pb 0 5 4 high values of rb sr 1 18 low to moderate ree contents and light ree enriched patterns with small negative eu anomalies flat ree patterns with large negative eu anomalies are found in a small hydrothermally altered area characterized by high abundances of sn up to 26 ppm rb up to 670 ppm li up to 310 ppm ta up to 13 1 ppm and u up to 10 ppm there is no single mixing trend fractional crystallization assemblage or assimilationscheme that accounts for all trace elementvariations from quartz gabbro to granite in the northeast kingdom batholith the plutons originated by mixing mantle derived components and crustal melts generated at different levels in the heterogeneous lithosphere in a continental collisional environment hybrid rocks in the batholith evolved by fractional crystallization and assimilation of country rocks 50 by mass and some of the leucogranitic rocks were subsequently disturbed by a mild hydrothermal event that resulted in the deposition of small amounts of sulfide minerals

is the antarctic ice sheet growing a common public perception is that global warming will accelerate the melting of polar ice sheets causing sea level to rise a common scientific position is that the volume of grounded antarctic ice is slowly growing and will damp future sea level rise at present studies supporting recent shrinkage or growth depend on limited measurements that are subject to high temporal and regional variability and it is too early to say how the antarctic ice sheet will behave in a warmer world

different ers altimeter measurements between ascending and descending tracks caused by wind induced features over ice sheets the ers1 satellite provides a high resolution radar altimeter measurement up to 81 5 latitude for polar cap studies here we examine one particular effect of the interaction between the radar wave and the snowpack surface on height measurements measurements from ascending and descending tracks show systematic differences as large as 1 m such an artifact to be removed if it can be estimated the difference appears to be related to the way the altimeter perceives wind induced sculpting of the snowpack differences in the volume echo weight between ascending and descending passes appear to be the explanation seasat scatterometer allowed us to estimate independently the signal that could be inferred by wind features our results yield a map of the effect of wind on radar altimetric measurement finally we consider the possibility of long term variations in altimeter measurements caused by climatic changes

the joint gravity model 3 an improved earth geopotential model complete to spherical harmonic degree and order 70 has been determined by combining the joint gravity model 1 jgm 1 geopotential coefficients and their associated error covariance with new information from slr doris and gps tracking of topex poseidon laser tracking of lageos 1 lageos 2 and stella and additional doris tracking of spot 2 the resulting field jgm 3 which has been adopted for the topex poseidon altimeter data rerelease yields improved orbit accuracies as demonstrated by better fits to withheld tracking data and substantially reduced geographically correlated orbit error methods for analyzing the performance of the gravity field using high precision tracking station positioning were applied geodetic results including station coordinates and earth orientation parameters are significantly improved with the jgm 3 model sea surface topography solutions from topex poseidon altimetry indicate that the ocean geoid has been improved subset solutions performed by withholding either the gps data or the slr doris data were computed to demonstrate the effect of these particular data sets on the gravity model used for topex poseidon orbit determination

distinguishing magmatic from subsolidus epidote laser probe oxygen isotope compositions epidote occurs in four textural varieties in the mount lowe intrusion of southern california euhedra anhedra intergrowths and cross cutting veins of these conspicuous elongate euhedra which range up to 3 cm in length meet most of the established textural criteria for magmatic epidote equant anhedral grains which are 5 mm in diameter are texturally ambiguous although rare allanite cores are suggestive of a magmatic origin epidote intergrowths with hornblende and biotite also meet certain textural criteria for crystallization from a magma notably euhedral faces against biotite finally late stage veins of epidote cross cut all phases in the rock and are likely subsolidus oxygen isotopic compositions of these four textural varieties of epidote determined using the laser probe indicate that the use of textural criteria alone in establishing epidote parageneses can be misleading intracrystalline 18o variations in the euhedra document both magmatic and subsolidus compositions oxygen isotope compositions are bimodal averaging 5 36 0 13 n 11 and 4 66 0 23 n 21 these data combined with plagioclase and zircon 18o values are interpreted to indicate that magmatic oxygen isotopic compositions have been preserved where epidote 18o is greater than 5 significant portions of each euhedral crystal have been affected by subsolidus exchange and are characterized by epidote 18o values less than 5 intracrystalline 18o values of epidote anhedra range from 4 50 to 6 08 and thus also document both magmatic and subsolidus compositions subsolidus exchange is volumetrically less significant in the anhedra than in the euhedra values of 18o for intergrowths and late stage cross cutting veins of epidote average 3 81 0 22 and document clearly subsolidus growth the data confirm that in the mount lowe intrusion large euhedra of epidote are magmatic in origin consistent with textural evidence the data also indicate that equant anhedra of epidote are also magmatic in origin and thus the absence of good crystal faces does not necessarily indicate subsolidus growth the subsolidus origin of intergrowths of epidote with euhedral faces against biotite indicates that well developed crystal faces do not require growth from a magma finally the subsolidus origin of the vein epidote is consistent with textural evidence the increased resolution available with laser based oxygen isotope measurements offers an important test for documenting whether epidote is of magmatic or subsolidus origin given the barometric significance of magmatic epidote oxygen isotope compositions can be used to aid in the interpretation of epidote bearing plutons

an algorithm for time series analysis of ice sheet surface elevations from satellite altimetry a new method to derive the seasonal elevation signal from a continuous time series of altimeter crossover data is presented the method utilizes the complete set of intrasatellite crossover data to provide fine temporal resolution and to significantly reduce random measurement errors this is an improvement over the standard time series method that only uses those data referenced to a single time period at the beginning of the satellite mission

recent increase in south pole snow accumulation this paper summarizes the 37 year history of net accumulation measurements at the geographic south pole obtained by numerous investigators using a variety of techniques these data lead to the conclusion that annual net snow accumulation has increased in the vicinity of south pole station sps since 1955 the records were examined for evidence of a station effect and it is concluded that not all of the observed increase can be attributed to snow drift associated with the presence of the station furthermore the accumulation increase at the south pole appears consistent with increases observed at other locations on the east antarctic plateau and in the peninsula region as well these data suggest that the recent accumulation increase at sps may be regionally extensive over the east antarctic plateau

rapid thinning of parts of the southern greenland ice sheet aircraft laser altimeter surveys over southern greenland in 1993 and 1998 show three areas of thickening by more than 10 centimeters per year in the southern part of the region and large areas of thinning particularly in the east above 2000 meters elevation the ice sheet is in balance but thinning predominates at lower elevations with rates exceeding 1 meter per year on east coast outlet glaciers these high thinning rates occur at different latitudes and at elevations up to 1500 meters which suggests that they are caused by increased rates of creep thinning rather than by excessive melting taken as a whole the surveyed region is in negative balance

crystal chemical controls on rare earth element partitioning between epidote group minerals and melts an experimental and theoretical study we have experimentally determined the partitioning of ree rare earth elements between zoisite and hydrous silicate melt at 1 100 c and 3 gpa all ree behave moderately compatible in zoisite with respect to the melt and all d ree zo melt show a smooth parabolic dependence on ionic radius the partitioning parabola peaks at nd left d nd zo melt 4 9 right and the compatibility slightly decreases towards la left d la zo melt 3 9 right and decreases by half an order of magnitude towards yb left d yb zo melt 1 1 right application of the elastic strain model of blundy and wood 1994 to the available zoisite and allanite ree mineral melt partitioning data and comparison with partitioning pattern calculated from a combination of structural and physical data taken from the literature with the elastic strain model suggest that in zoisite ree prefer the a1 site and that only la and ce are incorporated into the a2 site in significant amounts in contrast in allanite all ree are preferentially incorporated into the large and highly co ordinated a2 site as a result zoisite fractionates the mree effectively from the hree and moderately from the lree while allanite fractionates the lree very effectively from the mree and hree consequently the presence of either zoisite or allanite during slab melting will lead to quite different ree pattern in the produced melt

improved elevation change measurement of the southern greenland ice sheet from satellite radar altimetry a new analysis of seasat and geosat satellite radar altimeter measurements over the greenland ice sheet was performed to determine surface elevation change the new analysis includes twice as many measurements and has 50 greater spatial coverage than the authors previous study in addition a precise global ocean reference network created from four years of topex poseidon altimeter data is used to obtain improved estimates of altimeter orbit errors and measurement system biases the results show that the average elevation change of the southern greenland ice sheet above 2000 m from 1978 to 1988 is not significantly different than zero this contradicts earlier and even more recent studies that reported positive ice sheet growth rates and suggested increased precipitation due to a warmer polar climate

metamorphic and stratigraphic constraints on the evolution of the santa catalina mountains metamorphic core complex arizona contact metamorphic mineral assemblages in the santa catalina mountains metamorphic core complex constrain the emplacement depth of the metaluminous late cretaceous leatherwood quartz diorite to between 7 5 and 14 km 2 3 8 kbar the peraluminous eocene wilderness granite is constrained to have been emplaced at depths of less than 14 km stratigraphic and tectonic considerations are consistent with emplacement of both the leatherwood quartz diorite and wilderness granite at upper crustal levels published igneous thermobarometry anderson et al 1988 although in approximate agreement with the metamorphic and tectonostratigraphic estimates for the depth of emplacement of the wilderness granite suggests that the leatherwood quartz diortite was emplaced at depths of 21 km 5 6 kbar or greater the discrepancy between the different emplacement estimates may reflect ambiguities associated with interpretations of the results from each technique igneous barometric assemblages may reflect conditions experienced during a period of crystallization during ascent of the magma through the crust i e ponding of the magma alternatively emplacement of the voluminous wilderness granite and associated plutons may have entirely overprinted earlier leatherwood related contact metamorphism the proposed upper crustal emplacement of the leatherwood quartz diorite is consistent with the observation that lararrade age crustal thickening in southeast arizona probably did not exceed 8 km

bed topography and surges in ice streams 1 extensive bed topography at the scale of the ice thickness occurs frequently in the form of drumlins by analogy with hard bed sliding ice flow over this type of topography leads to the generation of drag on the ice particularly when ice flow is rapid a crucial difference with classical nye kamb sliding is that the upper free surface of the ice has a significant effect on the sliding process through the formation of a standing wave using a theoretical model we demonstrate that the presence of this wave introduces a non linearity into the sliding motion which can lead to multiple sliding velocities for the same large scale ice stream geometry and that switches between these velocities can cause surging behavior

epidote phenocrysts in dacitic dikes boulder county colorado epidote ps21 crystallized early as elongate phenocrysts in late cretaceous rhyodacitic dikes in the vicinity of ward boulder county colorado other unusual phenocryst phases are garnet gr17 24 and muscovite in a xenolith containing kyanite corundum biotite and plagioclase magmatic garnet grew as a rim around xenocrystic pyrope rich py37 garnet the xenolith was derived from a granulite facies zone not represented at the present day erosion surface which is composed of upper amphibolite facies cordierite and sillimanite bearing gneisses the dike magmas were fed not from an immediately underlying batholith but from a magma chamber at a depth corresponding to a pressure of 8 13 kilobars phenocrysts cystallized in the temperature range 800 to 700 c under h2o and o2 activities greater than normal for silicic magmas this occurrence shows convincingly not only that epidote can be magmatic but that it is a possible early crystallization phase in silicic magmas

growth of the southern greenland ice sheet the principal conclusion of c h davis et al 1 1 that the elevation of the southern greenland ice sheet increased at a smaller rate than the 23 cm year we previously reported 2 2 3 3 is in qualitative agreement with our new analysis their statement however that surface

antarctic elevation change from 1992 to 1996 satellite radar altimeter measurements show that the average elevation of the antarctic ice sheet interior fell by 0 9 0 5 centimeters per year from 1992 to 1996 if the variability of snowfall observed in antarctic ice cores is allowed for the mass imbalance of the interior this century is only 0 06 0 08 of the mean mass accumulation rate

changes in greenland ice sheet elevation attributed primarily to snow accumulation variability the response of grounded ice sheets to a changing climate critically influences possible future changes in sea level recent satellite surveys over southern greenland show little overall elevation change at higher elevations but large spatial variability using satellite studies alone it is not possible to determine the geophysical processes responsible for the observed elevation changes and to decide if recent rates of change exceed the natural variability here we derive changes in ice sheet elevation in southern greenland for the years 1978 88 using a physically based model of firn densification and records of annual snow accumulation reconstructed from 12 ice cores at high elevation our patterns of accumulation driven elevation change agree closely with contemporaneous satellite measurements of ice sheet elevation change and we therefore attribute the changes observed in 1978 88 to variability in snow accumulation similar analyses of longer ice core records show that in this decade the greenland ice sheet exhibited typical variability at high elevations well within the long term natural variability our results indicate that a better understanding of ice sheet mass changes will require long term measurements of both surface elevation and snow accumulation

elevation change measurement of the east antarctic ice sheet 1978 to 1988 from satellite radar altimetry seasat and geosat satellite radar altimeter measurements over the east antarctic ice sheet eais are analyzed to determine surface elevation change over the period from 1978 to 1988 the results show that the average elevation change over 1 7 spl times 10 sup 6 km sup 2 of the eais is 0 4 spl plusmn 1 8 cm yr and is therefore not significantly different than zero this result is in very good agreement with ers 1 2 radar altimeter estimates of eais elevation change from 1992 to 1996 the combined results suggest that the eais has been close to a state of balance for two decades this further reduces the likelihood that recent changes in snow accumulation have masked a long term mass imbalance in the eais

using the temporal variability of satellite radar altimetric observations to map surface properties of the antarctic ice sheet the problem of measuring surface height and snowpack characteristics from satellite radar altimeter echoes is investigated in this paper we perform an analysis of the ers1 altimeter dataset acquired during a 3 day repeat orbit the analysis reveals that there are temporal variations in shapes of the radar altimeter echo and that these variations are linked to meteorological phenomena the time and space scales over which these variations apply are a few to tens of days and a few hundred kilometres respectively this phenomenon if not accounted for can create error in the height measurement a numerical echo model is used to recover snowpack characteristics by taking advantage of the temporal variations of the radar echoes a map of penetration depth of the radar waves in the ku band over the antarctic continent is obtained and suggests that grain size produces the dominant effect on radar extinction in the snowpack at this frequency finally a procedure is proposed to correct the height measurement within the context of ice sheet mass balance survey

constraints on rates of granitic magma transport from epidote dissolution kinetics epidote is stable only at high pressure in granitic magmas but is found in magmas crystallized at shallow crustal levels this observation suggests qualitatively that magma transport is sufficiently rapid to prevent complete epidote resorption experimental measurements of epidote dissolution showed that the presence of epidote implies that magma transport from the deep crust in these systems was rapid and that the transport was by dikes rather than diapirs

mass balance of higher elevation parts of the greenland ice sheet satellite radar and aircraft laser altimeter data and a volume budget comparison of total snow accumulation with total ice discharge give three independent estimates of the recent mass balance of parts of the greenland ice sheet above 2000 m elevation results show the entire region on average to be in balance to within 10 mm yr 1 with very low rates of regional thickness change dh dt in the northeast but high rates with large spatial variability in the south only the volume budget estimates show significant thinning in the northwest but thinning in this area is also inferred from local measurements of ice vertical velocities down boreholes south of latitude 68 n there has been rapid thickening west of the ice divide with equally rapid thinning in the southeast but with large differences between the three estimates of dh dt throughout this region the radar data apply to the period 1978 1988 the laser data are for 1993 1994 1998 1999 and the volume budget calculations represent conditions over at least the last few decades consequently many of the differences between results could be caused by temporal changes particularly in snow accumulation rates that occurred since the 1970s however taken with other information our results suggest long term thickening in the southwest and possibly quite recent onset of rapid thinning in the southeast

flow dynamics of tidewater glaciers a numerical modelling approach the dynamics of grounded tidewater glaciers is investigated with a time dependent numerical flow model which solves the full equations for the stress and velocity fields and includes a water pressure dependent sliding law the calving criterion implemented in the model shifts the calving front at each time step to the position where the frontal ice thickness exceeds flotation height by a prescribed value with this model the linear relation between calving rate and water depth proposed on empirical grounds is qualitatively reproduced for the situation of a slowly retreating or advancing terminus but not for situations of rapid changes length changes of tidewater glaciers i e especially rapid changes are dominantly controlled by the bed topography and are to a minor degree a direct reaction to a mass balance change thus accurate information on the near terminus bed topography is required for reliable prediction of the terminus changes due to climate changes the results also confirm the suggested cycles of slow advance and rapid retreat through a basal depression rapid changes in terminus positions preferably occur in places where the bed slopes upwards in the ice flow direction

paleoproterozoic granitoids of the losevo terrane east european craton age magma source and tectonic implications abstract the losevo terrane lies between the sarmatia and volgo uralia segments of the east european craton and is considered to be part of the east sarmatian orogen eso here we report the results from field petrologic geochemical sm nd isotopic and zircon u pb geochronological studies on a suite of granitoids from the losevo terrane lt the lt granitoids are divided into four types 1 migmatite leucosome from quartz diorite to granodiorite 2 tonalite trondhjemite and granodiorite ttg with high si na sr contents high sr y la yb ratios and low mg k y yb contents 3 trondhjemite granodiorite granite tgg spatially related to the ttg suite but showing higher k negative eu anomalies and flat ree patterns and 4 high k calc alkaline monzogranite and granodiorite of i type the early 2115 ma migmatites occur as lensoid and stromatic layers the ttg and tgg 2100 2075 ma constitute about 20 of the lt and form batholiths 150 540 km 2 and stocks small massifs of the i type granites 2081 12 ma intrude the migmatites the migmatites ttg and tgg contain inherited zircon cores that yield ages between 2130 and 2172 ma the granitic suite shows positive end values ranging from 2 1 to 5 7 for the ttg and tgg and 2 1 and 2 2 for the migmatites suggesting magma derivation from juvenile paleoproterozoic sources model ages 2255 2450 ma in contrast the i type granite shows slightly negative end value of 0 5 suggesting that the magma sources involved a mixture of archean and paleoproterozoic components all the granitoids from lt record varying degrees of fractional crystallization with or without crustal contamination the temperature of parental melts of the granites are estimated to be in the range of 793 33 c to 878 16 c the migmatites were derived mainly from metaigneous sedimentary protoliths under p 5 6 kbar whereas the ttgs were derived from lower crustal metabasites under p 15 kbar the tgg were derived from mid crustal metagreywackes under p

comments and reply on implications of magmatic epidote bearing plutons on crustal evolution in the accreted terranes of northwestern north america and magmatic epidote and its petrologic significance comment

the origin and longevity of flow stripes on antarctic ice streams flow stripes along the surface of rapidly moving ice streams are shown to be an expected reaction of a viscous medium flowing over an irregular bed whenever the velocity at the bed is large compared to shearing through the thickness the principal features of the process are as follows at high basal speeds the ice acts as a strongly selective band pass filter transmitting basal undulations on spatial scales of a few ice thicknesses very effectively to the surface the decay of the short scale features by diffusion is strongly retarded by horizontal stress gradients consequently localized disturbances at the bed produce topographic effects on the surface that are advected long distances downstream before decaying away this mechanism may explain many of the flow stripes on active ice streams moving by rapid basal motion

a theory of ice sheet surges a simplified model of a two dimensional ice sheet is described it includes basal ice sliding dependent on the basal water pressure which itself is described by a simple theory of basal drainage we show that this simple but sophisticated model predicts surges of the ice mass in realistic circumstances and we describe these surges by solving the problem numerically we also are able to describe some parts of the surge analytically the numerical solution of the model is a delicate matter and highlights pitfalls to be avoided if more complicated models are to be solved successfully

predictions of vertical uplift caused by changing polar ice volumes on a viscoelastic earth measurements of crustal uplift from bedrock around the edges of antarctica or greenland could help constrain the mass balance of those ice caps present day changes in ice could cause vertical displacement rates of several mm yr around antarctica and up to 10 15 mm yr around greenland horizontal displacement rates are likely to be about 1 3 the vertical rates the viscoelastic response of the earth to past changes in ice could cause uplift rates that are several times larger by measuring both gravity and vertical displacements it is possible to remove the viscoelastic effects so that the observations can be used to constrain present day thickness changes

elevation change of the southern greenland ice sheet seasat and geosat satellite altimeter measurements for the greenland ice sheet south of 72 degreesn latitude show that surface elevations above 2000 meters increased at an average rate of only 1 5 0 5 centimeters per year from 1978 to 1988 in contrast elevation changes varied regionally from 15 to 18 centimeters per year seasonally by 15 centimeters and interannually by 8 centimeters the average growth rate is too small to determine if the greenland ice sheet is undergoing a long term change due to a warmer polar climate

stable and radiogenic isotope systematics in epidote group minerals epidote minerals the epidote group together with the orthorhombic polymorph zoisite occur in a wide range of igneous metamorphic and sedimentary lithologies although often present in only small quantities epidote group minerals can nonetheless be used to generate important quantitative constraints on processes such as regional metamorphism deep seated pluton emplacement and uplift hydrothermal fluid flow and sedimentary provenance e g zen and hammarstrom 1984 brandon et al 1996 cartwright et al 1996 keane and morrison 1997 spiegel et al 2002 petrologic studies on epidote group minerals formed by these and other processes are reviewed in bird and spieler 2004 grapes and hoskin 2004 enami et al 2004 and schmidt and poli 2004 in this chapter stable and radiogenic isotope studies of epidote group minerals will be reviewed although stable and or radiogenic isotope data exist for epidote group minerals from a number of different geologic settings such data have produced particularly important insights into 1 fluid flow associated with variable grades of metamorphism particularly ultra high pressure uhp metamorphism 2 intrusion of deep seated plutonic systems 3 the nature of hydrothermal alteration in geothermal systems 4 age relations in hydrothermal systems and 5 sedimentary provenance based on the chemical composition of naturally occurring epidote minerals oxygen hydrogen and chlorine stable isotopes all have the potential to be important petrogenetic indicators in systems involving epidote minerals oxygen is present in epidote minerals bound in isolated to4 tetrahedra t2o7 groups and in the hydroxyl site as both oh and o 2 hydrogen and chlorine are present in the hydroxyl site as oh and cl respectively although cl is present in only very small quantities frei et al 2004 to date oxygen and hydrogen isotope systematics have been studied both