sulfur isotopes in diamonds reveal differences in continent construction neoproterozoic west african diamonds contain sulfide inclusions with mass independently fractionated mif sulfur isotopes that trace archean surficial signatures into the mantle two episodes of subduction are recorded in these west african sulfide inclusions thickening of the continental lithosphere through horizontal processes around 3 billion years ago and reworking and diamond growth around 650 million years ago we find that the sulfur isotope record in worldwide diamond inclusions is consistent with changes in tectonic processes that formed the continental lithosphere in the archean slave craton diamonds that formed 3 5 billion years ago do not contain any mif sulfur younger diamonds from the kaapvaal zimbabwe and west african cratons do contain mif sulfur which suggests craton construction by advective thickening of mantle lithosphere through conventional subduction style horizontal tectonics

a comparison of three methods of mass balance determination in the tuyuksu glacier region tien shan central asia a photogrammetric survey in 1998 formed the basis for compiling a map of the tuyuksu glacier region in the northern tien shan central asia comparison with a map from 1958 enables calculation of the change in glacier volume over 40 years the results are compared with direct annual measurements carried out continuously since 1956 central tuyuksu glacier shows a mass balance of 12 6 m w e for the geodetic method and 16 8 m for glaciological measurements in view of the high accuracy of the maps the discrepancy can be explained mainly by deficiencies in the glaciological measurements application of the precipitation runoff model hbv eth represents the hydrological method of mass balance determination and delivers specific mass balance losses almost twice those indicated by the geodetic observations this discrepancy is suspected to be caused by erroneous runoff measurements the volume balance derived by the geodetic method is used to calibrate both the glaciological and the hydrological method

quantifying global warming from the retreat of glaciers records of glacier fluctuations compiled by the world glacier monitoring service can be used to derive an independent estimate of global warming during the last 100 years records of different glaciers are made comparable by a two step scaling procedure one allowing for differences in glacier geometry the other for differences in climate sensitivity the retreat of glaciers during the last 100 years appears to be coherent over the globe on the basis of modeling of the climate sensitivity of glaciers the observed glacier retreat can be explained by a linear warming trend of 0 66 kelvin per century

archean crustal evolution of the west african craton example of the amsaga area reguibat rise upb and smnd evidence for crustal growth and recycling abstract new geochronological data u pb and sm nd are used to constrain the archean crustal growth and evolution of the southwestern part of the reguibat rise amsaga area in the west african craton the results are summarized as follows 1 u pb zircon data indicate an emplacement age of 2986 8 ma for the magmatic protolith of a charnockitic pluton in agreement with a whole rock sm nd isochron at 3012 142 ma positive nd 3 0 values ranging between 0 89 and 1 95 and agreement between nd model ages between 3 23 and 3 10 ga and u pb age indicate a juvenile origin for the magmatic protolith and imply a crustal growth event at ca 3 0 ga seven rims of the charnockitic zircons yield discordant 207 pb 206 pb ages ranging from 2979 11 to 2737 11 ma and are interpreted as resulting from growth during the granulitic event 2 whole rock sm nd data on migmatitic orthogneisses that form the central part of the area indicate an archean age for their magmatic protolith t dm ranging from 3 24 to 2 87 ga in agreement with a previous single zircon evaporation age of 2836 16 ma potrel 1994 3 two late tectonic postgranulite plutons both granite and gabbro dated at ca 2 73 ga mark the end of the granulitic event the granite provides a u pb age of 2726 7 ma and the gabbro a mineral sm nd isochron age of 2706 54 ma the t dm ages ranging from 3 1 to 3 2 ga indicate an origin by crustal reworking of the granite and negative nd 2 7 value 0 7 of the gabbro indicate crustal contamination during emplacement these results combined with previous work potrel et al 1996 indicate that the archean reguibat rise formed through a succession of crustal growth events from at least 3 50 3 45 ga until 2 73 ga a major granulitic event took place at ca 2 73 ga and was accompanied by emplacement of crustally derived magmas

a distributed temperature index ice and snowmelt model including potential direct solar radiation hourly melt and discharge of storglaciaren a small glacier in sweden were computed for two melt seasons applying temperature index methods to a 30 m resolution grid for the melt component the classical degree day method yielded a good simulation of the seasonal patient of discharge but the pronounced melt induced daily discharge cycles were not captured modelled degree day factors calculated for every hour and each gridcell from melt obtained from a distributed energy balance model varied substantially both diurnally and spatially a new distributed temperature index model is suggested attempting to capture both the pronounced diurnal melt cycles and the spatial variations in melt due to the effects of surrounding topography this is accomplished by including a radiation index in terms of potential clear sky direct solar radiation and thus without the need for other data besides air temperature this approach improved considerably the simulation of diurnal discharge fluctuations and yielded a more realistic spatial distribution of melt rates the incorporation of measured global radiation to account for the reduction in direct solar radiation due to cloudiness did not lead to additional improvement in model performance

nd and sr isotopes from diamondiferous eclogites udachnaya kimberlite pipe yakutia siberia evidence of differentiation in the early earth nd and sr isotopic data from diamond bearing eclogites found in the udachnaya kimberlite yakutia siberia are interpreted as indicating an early 1 4 ga differentiation event whereby the mantle split into complementary depleted and enriched reservoirs reconstructed whole rock 87sr s6sr ratios present day range from 0 70151 to 0 70315 and are consistent with a mantle origin for these rocks the nd isotopic evolution lines of four samples u 5 u 37 u 41 and u 79 converge at 2 2 2 7 ga sample u 5 is unique in exhibiting the most enriched signature of any of the samples yet analyzed present day end of 20 and this sample points unequivocally to an old enriched component a complementary depleted mantle component is suggested by two of the eclogite samples u 86 and u 25 which yield end values at 2 2 ga of 13 and 7 respectively the two mantle reservoirs possibly formed prior to 4 ga and evolved separately until 2 2 2 7 ga at that time the reservoirs were melted forming eclogites both as residues from the enriched reservoir and as partial melts of peridotite from the depleted reservoir resulting in demonstrably different histories for eclogites from the same locality

instruments and methods glaciological and volumetric mass balance measurements error analysis over 51 years for glacier de sarennes french alps the mass balance of glacier de sarennes french alps has been measured since 1949 using the glaciological method based on core and ablation stake data and area extrapolations to find the overall glacier balance the cumulative balance obtained in this way is very dependent on systematic errors that can increase linearly with the number n of measurement years whereas random errors rise with the volumetric balance method based on aerial photogrammetry provides results whose errors do not depend on the number of years this method was used to test field measurements for the period 1952 2003 and gives a mass balance of 32 30 1 04 m w e compared to 34 89 1 15 m w e based on field data the discrepancy between the two methods is discussed on the basis of a careful error analysis moreover the possibility of using the volumetric method to detect biases in field measurements is evaluated in terms of two types of errors the number and locations of measurement sites required to account for all the spatial and temporal variabilities of the mass balance is discussed by variance analysis methodological implications and recommendations are presented to provide mass balance measurements of the best possible accuracy

on the accuracy of glacier outlines derived from remote sensing data deriving glacier outlines from satellite data has become increasingly popular in the past decade in particular when glacier outlines are used as a base for change assessment it is important to know how accurate they are calculating the accuracy correctly is challenging as appropriate reference data e g from higher resolution sensors are seldom available moreover after the required manual correction of the raw outlines e g for debris cover such a comparison would only reveal the accuracy of the analyst rather than of the algorithm applied here we compare outlines for clean and debris covered glaciers as derived from single and multiple digitizing by different or the same analysts on very high 1 m and medium resolution 30 m remote sensing data against each other and to glacier outlines derived from automated classification of landsat thematic mapper data results show a high variability in the interpretation of debris covered glacier parts largely independent of the spatial resolution area differences were up to 30 and an overall good agreement for clean ice with sufficient contrast to the surrounding terrain differences 5 the differences of the automatically derived outlines from a reference value are as small as the standard deviation of the manual digitizations from several analysts based on these results we conclude that automated mapping of clean ice is preferable to manual digitization and recommend using the latter method only for required corrections of incorrectly mapped glacier parts e g debris cover shadow

gas migration modelling in geological repository module in clay formation and sensitivity analysis abstract corrosion of steel canisters disposed of in a geological repository for high level waste leads to generation and accumulation of hydrogen gas which may significantly affect long term safety of the repository numerical modelling can be used to predict the likely hydraulic evolution of such a disposal facility and to estimate the influence of generated gas on repository safety this article presents a two phase flow not taking into account mechanical coupling gas migration model developed in the original version of the computer code tough2 mp usa an important and new aspect of this model is its capability to introduce a network of very thin interfaces in three dimensional analysis of gas migration this model was verified in the international benchmark exercises in the recent european commission project forge fate of repository gases the analysis was focused on the results of a second benchmark exercise i e hydrogen gas behaviour in a part of a geological repository module situated in clay formation and sensitivity analysis the results showed that the interfaces backfill and excavation disturbed zone are the main migration and accumulation media for gaseous hydrogen in the repository module the peak pressure in the module did not exceed the geological environment pressure at a depth of 500 m and is not sufficient to disturb mechanical stability and functionality of the system of engineered and natural barriers

the disappearance of glaciers in the tien shan mountains in central asia at the end of pleistocene glaciers in central asia are among the largest ice masses in the eurasian continent and have supplied vital water to local inhabitants for thousands of years the glaciers in this region are generally believed to be remnants of the last deglaciation however glacier variability in the central asian mountains since the last glacial maximum lgm has not been well documented here we report an 86 87 m deep ice core record drilled on an ice cap in the tien shan mountains of central asia radiocarbon dating of organic soil from the bottom of the ice core borehole showed that the age of the soil was 12 656 e 12 434 cal years before present coincident with the beginning of the younger dryas cold period yd this result indicates that the ice cap did not exist in the bolling allerod period ba which was the warm period before the yd and that the ba climate was significantly warmer than at present it also indicates that the ice cap has never entirely disappeared in any warm periods throughout the holocene we estimated that during the ba its extent was 43 or less of the present glacier coverage in the mountains our results suggest that this region at the end of pleistocene was considerably warmer than at present and that most of the present glaciers in this region are not relics of the last glacial period but are composed of ice formed during the yd and holocene 2014 the authors published by elsevier ltd this is an open access article under the cc by nc nd license http creativecommons org licenses by nc nd 3 0

re evaluation of leonian and liberian events in the geodynamical evolution of the man leo shield west african craton abstract the leonian 3400 3100 ma and liberian 2850 2700 ma events are important magmatic and tectono metamorphic events in the archean domain of the man leo shield in the southern west africa craton the older leonian event was associated with crust formation which was variably reworked during the younger liberian event in the man domain of western cote d ivoire zircon in situ dating by la icpms of granulitic grey gneisses gggs the mangouin charnockite and the lagoulale augen orthogneiss allows for the re evaluation of magmatic and metamorphic activity related to the leonian and liberian events we report here our findings that the gggs represent the oldest rocks in the study area and formed during the leonian event the ages recorded in the gggs in the man area are 3156 24 3098 19 3093 49 and 3019 53 ma the ages of 3156 24 and 3098 19 ma represent leonian juvenile magmatism while those of 3093 49 and 3019 53 ma represent leonian metamorphism the ages of the mangouin charnockite and the lagoulale augen orthogneiss are 2798 8 ma and 2795 9 ma respectively and are interpreted to record peak metamorphic conditions during the liberian event zircon from the augen orthogneiss includes an inherited core with an age of 3121 37 ma which corresponds to leonian ggg ages this inheritance indicates that the mangouin charnockite and the lagoulale augen orthogneiss were derived either partially or completely from leonian formations a previously constrained sm nd model age of 3250 ma for the charnockite and augen orthogneiss agrees with such a process the majority of th u is higher indicating a magmatic origin for most zircons the leonian and liberian events are proposed as two distinct events in man leo shield

effect of precipitation seasonality on climatic sensitivity of glacier mass balance abstract numerical calculations are described aimed at evaluating the influence of precipitation seasonality and seasonality concentration on climatic sensitivity of glacier mass balance equilibrium line altitudes elas are modeled using idealized meteorological variables and then a warming test 1 c is performed which revealed that the effects of latitude and the annual precipitation amount are less than those of precipitation seasonality and its concentration calculation shows higher sensitivities for the glaciers located in a summer precipitation climate than for those located within a winter precipitation climate difference due to seasonality is enhanced with the seasonality concentration the present study suggests that the earlier parameterization of glacier mass balance with annual precipitation amount is insufficient to describe the response of glaciers to climate change distribution of precipitation seasonality and its concentration suggest that many parts of the world have a summer precipitation climate but their seasonality concentration is not significant worldwide on the other hand an extensive region of asia and part of the andes are located in the highly concentrated summer precipitation climate this suggests the high sensitivity of glacier mass balance in these regions to climate change

glacier changes in the central and northern tien shan during the last 140 years based on surface and remote sensing data this research presents a precise evaluation of the recession of akshiirak and ala archa glaciers tien shan central asia based on data of geodetic surveys from 1861 69 aerial photographs from 1943 1963 1977 and 1981 1 25 000 scale topographic maps and srtm and aster data from 2000 03 the akshiirak glacierized massif in the central tien shan contains 178 glaciers covering 371 6 km 2 and the ala archa glacier basin in the northern tien shan contains 48 glaciers covering 36 31 km 2 the tien shan glaciers retreated as much as 3 km from the 1860s to 2003 area shrinkage of akshiirak and ala archa was 4 2 and 5 1 respectively from 1943 to 1977 and 8 7 and 10 6 respectively from 1977 to 2003 the volume of the akshiirak glaciers was reduced by 3 566 km 3 from 1943 to 1977 and 6 145 km 3 from 1977 to 2000 the total reduction of the tien shan glaciers is 14 2 during the last 60 years 1943 2003 the northern and central tien shan have not experienced a significant precipitation increase during the last 100 years but they have experienced an increase in summer air temperatures especially observable since the 1970s which accelerated the recession of the tien shan glaciers

mass balance observations and reconstruction for haxilegen glacier no 51 eastern tien shan from 1999 to 2015 haxilegen glacier no 51 43 731 n 84 391 e cn5y741c0051 is located in the kuytun river basin erenharbirga range eastern tien shan this study presents the annual mass balance of haxilegen glacier no 51 for 7 hydrological years and uses a temperature index and an accumulation model to reconstruct the annual mass balance from 1999 to 2015 the model is calibrated against annual altitudinal mass balance measurements and then applied to the period with no measurements we find an accumulated mass balance of 6 06 0 88 m w e a 1 over the period of 16 hydrological years with an average annual value of 0 32 0 22 m w e a 1 the mean glacier wide annual summer and winter balances for 1999 to 2015 are 0 37 0 54 and 0 16 0 22 m w e a 1 respectively with a high correlation coefficient r 0 95 p 0 001 between annual balance and summer balance the calculated mass balance sensitivity of the glacier to temperature is 0 51 m w e a 1 c 1 and to precipitation is 0 08 m w e a 1 for a 10 increase the sensitivity of seasonal mass balance indicates that temperature during the melt season may august and annual precipitation are the major contributors to mass balance fluctuation

a study of caprock hydromechanical changes associated with co2 injection into a brine formation a numerical study of hydromechanical changes during a deep underground injection of supercritical co2 in a hypothetical brine aquifer caprock system is conducted the injection process is simulated using a newly developed computer model for multi phase analysis of co2 and brine water flow coupled with heat transfer and rock deformations in this modeling co2 is injected at a constant rate over a 10 year period at a depth of 1 300 1 500 m the injection zone is overlain by a 100 m thick caprock located at 1 200 1 300 m which in one of the studied cases is intersected by a vertical fault the hydraulic mechanical as well as hydromechanical responses caused by the injection are studied this includes the spread of the co2 plume effective stress changes ground surface uplift stress induced permeability changes and mechanical failure analysis the analysis shows that most hydromechanical changes are induced in the lower part of the caprock near its contact with the injection zone whereas the sealing mechanism of the upper part may remain intact despite an injection pressure close to the lithostratic stress value

homogenization of long term mass balance time series the re analysis of long term mass balance time series is important to provide bias corrected mass balance data for climate change impact studies a method to homogenize time series of compre hensive mass balance monitoring programmes is presented and applied to the nearly 50 year mass balance records of griesgletscher and silvrettagletscher switzerland using a distributed mass balance model in daily resolution we correct the mass balance data for varying observation dates direct point measurements are combined with independent geodetic mass changes a prerequisite for a thorough homogenization of mass balance records differences between mass balance evaluated in the hydro logical year or according to the measurement period and the stratigraphic system are analyzed and may be up to 0 5 m w e a 1 cumulative mass balance of both glaciers based on the glaciological method generally agrees well with geodetic mass change on the investigated glaciers however for silvretta gletscher a significant bias of 0 37 m w e a 1 has been detected and corrected for since 1994

modelling of the hydro mechanical response of sedimentary rocks of southern ontario to past glaciations abstract glaciation is considered as one of the main natural processes that can have a significant impact on the long term performance of a deep geological nuclear waste repository dgr located in the northern hemisphere the northern part of the american continent has been subjected to a series of strong glaciation and deglaciation events over the past million years the last glacial cycle in the northern hemisphere started approximately 110 000 year ago during that cycle southern ontario was buried under a continental ice sheet with a maximum thickness of up to 3000 m at about 20 000 years ago the ice cap retreated approximately 10 000 years ago however field data from deep boreholes in sedimentary rocks of southern ontario show anomalous pore water pressure including underpressure and overpressure zones in this paper a large scale coupled hydro mechanical hm model is developed to investigate the hydro mechanical hm response of the sedimentary rocks of southern ontario to past glacial cycles particular emphasis has been placed on the evolution of pore water pressures and surface displacements the hm model is verified using analytical solutions the results of the large scale hm modeling study shows that the past glaciation particularly the second cycle 22 000 apb had significant impact on the pore water pressure gradient and effective stress distribution in the sedimentary rocks of southern ontario furthermore good agreement between the large scale modeling results and anomalous pressures leads us to the conclusion that these anomalies could be glacially induced the results of this research can provide information that will contribute to a better understanding of the impact of future glaciations on the long term performance of drgs in sedimentary rocks

the early archaean itsaq gneiss complex of southern west greenland the importance of field observations in interpreting age and isotopic constraints for early terrestrial evolution geochemical and isotopic studies of small volumes of variably preserved 3600 ma rocks in gneiss complexes are crucial for documenting early earth history in the itsaq gneiss complex of the nuuk region west greenland there is dispute whether the granitic sensu lato orthogneisses dominating it are mainly products of a single ca 3650 ma crust formation super event or whether they formed in several unrelated events between ca 3850 and 3560 ma which of these interpretations of the dates is correct has major implications regarding what the whole rock radiogenic isotopic record pb pb sm nd rb sr reveals about continental crust formation and early terrestrial differentiation there is also debate whether some west greenland metasedimentary rocks with 12c 13c data interpreted as evidence for life are 3850 ma or only 3650 ma old establishing the correct age for these rocks is important for debates concerning early surficial environments and origin of life controversies have arisen because of different approaches taken by different workers specifically with respect to how much emphasis is placed on field geology in interpreting dates and isotopic data in this paper field observations and sampling from low strain zones where the origin and geological context of the rocks are best preserved and understood are closely integrated with u pb zircon dates and cathodoluminescence cl imagery of the zircons this approach shows that most single phase well preserved meta granitoid samples have simple zircon populations dominated by oscillatory zoned prismatic grains formed when their host magmas crystallized on the other hand migmatites and some strongly deformed banded gneisses have much more complex zircon populations the combined field evidence and zircon geochronology on the itsaq gneiss complex demonstrate that 1 some areas contain exposed orthogneisses formed during multiple magmatic thermal events between ca 3850 and 3560 ma and are not as suggested by kamber and moorbath 1998 dominated by ca 3650 ma granitoids containing abundant 3650 ma zircons inherited from cryptic unexposed older rocks 2 abundant 3750 ma granitoids are present which are locally well preserved 3 some water lain sediments reported as showing c isotope evidence for life were deposited as early as 3850 ma 4 the whole rock sm nd isochron approach fails to distinguish with any confidence 3650 ma from 3800 ma rocks 5 however it reinforces previous indications for markedly depleted 2 5 nd domains in the pre 3750 ma mantle

reos and upb geochronological constraints on the eclogite tonalite connection in the archean man shield west africa abstract mantle derived eclogite xenoliths and tonalite trondhjemite granodiorites ttg that occur in the man shield west africa sample different levels of archean lithosphere chemical and oxygen isotope systematics indicate that low mgo eclogites from the koidu kimberlite are ancient remnants of subducted oceanic crust that may have been involved in regional archean crust formation re os whole rock isotopic data for these eclogites scatter about a line with slope corresponding to an archean age of 3 44 0 76 ga 2 with re os model ages ranging from 1 4 to 3 9 ga this wide range of model ages overlaps with the age range for crust formation and metamorphism in the man shield in situ u pb ages of zircons from crustal rocks have been measured by laser ablation icp ms a tonalitic gneiss has discordant zircons with rare old cores 3 6 ga and an upper concordia intercept at 2890 9 ma 2 zircons from a mafic lower crustal granulite xenolith are concordant at 2686 32 ma our results together with previously published ages for man shield rocks indicate an early archean crust formation event followed by major crustal growth at 2 9 3 0 ga and a last major metamorphic event at 2 7 ga these data show that the eclogites and the continental crust of the west african craton overlap in time of formation but only at the very broad age uncertainty provided by the eclogite re os results they are permissive of archean crustal growth by melting of the protoliths of the materials now sampled as the koidu eclogite xenoliths if so this suggests that archean crustal growth in the man shield occurred in a convergent margin setting

new rb sr age determinations on the archaean basement of eastern sierra leone abstract the archean basement of sierra leone is a typical example of granite greenstone terrains found in ancient continental nucleii reconnaissance field mapping showed that the area can be subdivided into old gneiss which predates the greenstone belts and young granite which is later than the greenstone belts new rb sr whole rock age determinations on two suites of old tonalitic gneiss yield ages of 2786 49 ma and 2770 137 ma which either reflect the time of formation of the original tonalites or their metamorphism three new rb sr whole rock age determination on young granites yield ages of 2786 143 ma 2780 79 ma and 2770 50 ma which are interpreted as the time of emplacement the widespread occurrence of similar young granites throughout the archaean of west africa suggests that these results date a major event in the evolution of this segment of the crust a published pb pb age of the old gneiss and the new ages of the young granite bracket the age of the greenstone belts to 3000 2770 ma however if the rb sr ages of the old gneiss reported in this paper reflect the time of their formation the age of the greenstone belts is tightly bracketed to ca 2770 ma there is no isotopic evidence for rocks substantially older than 3000 ma in the west african archaean

estimating glacier snow accumulation from backward calculation of melt and snowline tracking estimating precipitation to determine accumulation is challenging we present a method that combines melt modelling and snowline tracking to determine winter glacier snow accumulation along snowlines the method assumes that the net accumulation is zero on the transient snowlines and the maximum winter accumulation at the snowline can be calculated backwards with a temperature index melt model to verify the method the accumulation model is applied for the year 2004 on storglaciaren sweden for which extensive meteorological and mass balance data are available the measured mean snowline accumulation is 0 94 0 10 m w e for 2004 modelled accumulation using backward melt modelling at the same snowlines is 0 82 0 25 m w e the accumulation model is also compared with an often used linear regression accumulation model which yields a mean snowline accumulation of 1 02 0 38 m w e the reduction in standard error from 0 38 m w e to 0 25 m w e shows that the backward melt modelling applied at snowlines can provide a better spatial representation of the accumulation pattern than the regression model importantly the applied method requires no field measurements of accumulation during the winter and snowlines can be readily traced in remotely sensed images

snow accumulation distribution inferred from time lapse photography and simple modelling the spatial and temporal distribution of snow accumulation is complex and significantly influences the hydrological characteristics of mountain catchments many snow redistribution processes such as avalanching slushflow or wind drift are controlled by topography but their modelling remains challenging in situ measurements of snow accumulation are laborious and generally have a coarse spatial or temporal resolution in this respect time lapse photography shows itself as a powerful tool for collecting information at relatively low cost and without the need for direct field access in this paper the snow accumulation distribution of an alpine catchment is inferred by adjusting a simple snow accumulation model combined with a temperature index melt model to match the modelled melt out pattern evolution to the pattern monitored during an ablation season through terrestrial oblique photography the comparison of the resulting end of winter snow water equivalent distribution with direct measurements shows that the achieved accuracy is comparable with that obtained with an inverse distance interpolation of the point measurements on average over the ablation season the observed melt out pattern can be reproduced correctly in 93 of the area visible from the fixed camera the relations between inferred snow accumulation distribution and topographic variables indicate large scatter however a significant correlation with local slope is found and terrain curvature is detected as a factor limiting the maximal snow accumulation copyright 2010 john wiley sons ltd

a 3 5 ga granite gneiss basement in guinea further evidence for early archean accretion within the west african craton abstract a granite gneiss formation guelemata orthogneiss was mapped on the northern and western slopes of the mount nimba hill range in guinea the original rocks were high al low yb medium to high k granites similar to most archean ttg analyses of u and pb isotopes in zircons using an ion microprobe shrimp gave ages of 3542 and 3535 ma respectively for the granite gneiss and a neighbouring granulitic metagabbro these are the oldest ages so far reported from the archean kenema man domain of west africa partial melting of an unfractionated basalt under eclogite facies conditions appears to be a suitable model for the origin of the granite gneiss

influence of precipitation seasonality on glacier mass balance and its sensitivity to climate change numerical calculations are described aimed at evaluating the influence of precipitation seasonality summer and winter on glacier mass balance first equilibrium line altitudes elas are modeled using idealized meteorological variables modeled climatic conditions summer mean temperature and annual precipitation at the ela of glaciers located within a winter accumulation pattern confirm the observational results of earlier studies however the ela of glaciers located within a summer accumulation climate pattern locates in a colder environment than that of glaciers located within a winter accumulation climate pattern this difference is mainly due to the annual snow accumulation and the surface albedo a warming test 1k reveals higher sensitivities for the glaciers located within a summer accumulation pattern than for the glaciers located within a winter accumulation pattern in a humid environment a significant decrease in snow accumulation on the glaciers located within a summer accumulation pattern directly causes higher sensitivities in an arid environment on the other hand the decreased summer snow induces accelerated melting by lowering the surface albedo and thus increasing absorption of solar radiation on the glaciers located within a summer accumulation pattern both influences are due to significant differences in summer precipitation this study shows the importance of precipitation seasonality on the climatic sensitivity of glacier mass balance which in previous studies has been linked only with annual precipitation

geochemistry of adakites from neoarchaean active continental margin of shimoga schist belt western dharwar craton india implications for the genesis of ttg abstract adakites are identified for the first time from a neoarchaean active continental margin acm preserved in the eastern part of the shimoga schist belt near ranibennur western dharwar craton india these adakites consists mainly of quartz plagioclase and minor amphiboles and are interlayered with the turbidites they exhibit typical adakitic low y 8 35 14 70 ppm and yb 0 85 1 47 ppm may be classified as high sio2 and low mg ni and cr type adakites other constituents such as na2o k2o nb zr lree and hree and their ratios such as na2o k2o zr sm nb la la yb n gd yb n and th u also closely resemble with the high silica adakites hsa of martin et al martin h smithies r h rapp r moyen j f champion d 2005 an overview of adakite tonalite trondhjemite granodiorite ttg and sanukitoid relationships and some implications for crustal evolution lithos 79 1 24 sr y values are moderate generally lower than the high sr low silica cenozoic adakites but within the range of archaean adakites the negative nb ta and ti anomalies characteristic of cenozoic adakites are found in ranibennur adakites also zr zr and hf hf ratios are also similar to hsa these adakites further depict compositional similarities with meso and neoarchaean tonalite trondhjemite granodiorites ttgs such types of adakites have been experimentally generated by the partial melting of hydrous basalts that are similar to adakitic glass veins low mgo cao cr and ni found in peridotite xenoliths of kamchatka arc xiong x l xia b xu j f niu h c xiao w s 2006 na depletion in modern adakites via melt rock reaction within the sub arc mantle chem geol 229 273 292 since archaean had higher geothermal regime subduction of the basaltic slab was most probably shallow and significant mantle wedge was not available to react with adakitic melt hence archaean adakites in general and particularly from ranibennur are relatively depleted in the peridotiitic mantle wedge components their identification from an archaean acm and their compositional similarities with the paleo meso archaean ttgs suggest the possibility of identical origin i e the melting of a shallow hydrous basaltic slab this mechanism during archaean was widespread and rapid resulted in faster continental crustal growth during the early history of the earth identification of archaean adakites in association with island arc turbidites from a greenstone belt sequence supports the rapid subduction mechanism for the crustal growth that coincides with 2 7 ga peak episode of almost all geological processes

towards remote monitoring of sub seasonal glacier mass balance this study presents a method that allows continuous monitoring of mass balance for remote or inaccessible glaciers based on repeated oblique photography hourly to daily pictures from two automatic cameras overlooking two large valley glaciers in the swiss alps are available for eight ablation seasons 2004 11 in total we determine the fraction of snow covered glacier surface from orthorectified and georeferenced images and combine this information with simple accumulation and melt modelling using meteorological data by applying this approach the evolution of glacier wide mass balance throughout the ablation period can be directly calculated based on terrestrial remote sensing data validation against independent in situ mass balance observations indicates good agreement our methodology has considerable potential for the remote determination of mountain glacier mass balance at high temporal resolution and could be applied using both repeated terrestrial and air spaceborne observations

methodological approaches to infer end of winter snow distribution on alpine glaciers snow accumulation is an important component of the mass balance of alpine glaciers to improve our understanding of the processes related to accumulation and their representation in state of the art mass balance models extensive field measurements are required we present measurements of snow accumulation distribution on findelengletscher switzerland for april 2010 using 1 in situ snow probings 2 airborne ground penetrating radar gpr and 3 differencing of two airborne light detection and ranging lidar digital elevation models dems calculating high resolution snow depth from dem differencing requires careful correction for vertical ice flow velocity and densification in the accumulation area all three methods reveal a general increase in snow depth with elevation but also a significant small scale spatial variability lidar differencing and in situ snow probings show good agreement for the mean specific winter balance 0 72 and 0 78 m w e respectively the lidar derived distributed snow depth reveals significant zonal correlations with elevation slope and curvature in a multiple linear regression model unlike lidar differencing gpr derived snow depth is not affected by glacier dynamics or firn compaction but to a smaller degree by snow density and liquid water content it is thus a valuable independent data source for validation the simultaneous availability of the three datasets facilitates the comparison of the methods and contributes to a better understanding of processes that govern winter accumulation distribution on alpine glaciers

superimposed ice in glacier mass balance on the tibetan plateau the relations betw een mass bal ance and meltwater refre ezing were examined on the basis of glac iolo gical obse rvations carried out in summer 1993 on xiao dongkemadi glacier tanggula mountai ns central tibetan plateau on this glacier a part of melt water refreezes at the snovv ice int erface as superimp osed ice the amount of supe rimp osed ice formation was determ ined by both meltw ater supply and temperat ure condit ion of the glaci er snow lay er thic kness on the glacier ice body is less than 2 m even in the higher accu mulat ion zone about 60 of meltw ater generate d in the accumula tion zone for the period v1ay september was trapped at the snow ice interface by refre ezing and was not dis charged out of the glacie r about 26 of accumulated snow to the glacier surface was repl aced on the snow ice interface by refreez ing in the accumulation zone these facts indicate that superim posed ice formation is quit e signifi cant for water retention in glaciers unde r low pre cipitation conditions

massive collapse of two glaciers in western tibet in 2016 after surge like instability surges and glacier avalanches are expressions of glacier instability and among the most dramatic phenomena in the mountain cryosphere until now the catastrophic collapse of a glacier combining the large volume of surges and mobility of ice avalanches has been reported only for the 2002 130 106 m3 detachment of kolka glacier caucasus mountains which has been considered a globally singular event here we report on the similar detachment of the entire lower parts of two adjacent glaciers in western tibet in july and september 2016 leading to an unprecedented pair of giant low angle ice avalanches with volumes of 68 2 106 m3 and 83 2 106 m3 on the basis of satellite remote sensing numerical modelling and field investigations we find that the twin collapses were caused by climate and weather driven external forcing acting on specific polythermal and soft bed glacier properties these factors converged to produce surge like enhancement of driving stresses and massively reduced basal friction connected to subglacial water and fine grained bed lithology to eventually exceed collapse thresholds in resisting forces of the tongues frozen to their bed our findings show that large catastrophic instabilities of low angle glaciers can happen under rare circumstances without historical precedent two catastrophic glacier collapse events in western tibet in 2016 were caused by a convergence of weather and glacier bed conditions according to an analysis of observations and modelling

an insight into the surface velocity of inylchek glacier and its effect on lake merzbacher during 2006 2016 with landsat time series imagery mountain glacier is one of the extremely sensitive indicators for climate change and its surface motion distribution and corresponding variation are valuable information for understanding ice mass exchange and glacier dynamics this paper presents the long term ice velocity distributions of inylchek glacier in the tianshan region by pixel tracking algorithm with time series landsat imagery acquired during 2006 2016 then the monitored ice motion fields of inylchek glacier were carefully analyzed and revealed a generally similar spatial distribution characteristic most of the ice of the north inylchek glacier remains in a stagnant state except for the upstream part but a relatively high velocity of 20 40 cm day with an rmse of 3 cm day was observed on most part of the south inylchek glacier except for the slow moving glacier terminus we also state the glacier dynamics around lake merzbacher and their possible effect on its glacier lake outburst flood glof risk besides the surface velocity distribution on south inylchek glacier surface during the ablation period from 2014 to 2016 was also established and also compared with annual velocity the corresponding difference yields that there is a positive relation between ice motion and temperature variation therefore the time series ice surface motion yielded by the landsat imagery thus could provide us an efficient and low cost way to analyze the current state and changes in glaciers thanks to the continuous and regular spaceborne observations provided by the landsat satellites

a reconciled estimate of glacier contributions to sea level rise 2003 to 2009 glaciers distinct from the greenland and antarctic ice sheets are losing large amounts of water to the world s oceans however estimates of their contribution to sea level rise disagree we provide a consensus estimate by standardizing existing and creating new mass budget estimates from satellite gravimetry and altimetry and from local glaciological records in many regions local measurements are more negative than satellite based estimates all regions lost mass during 2003 2009 with the largest losses from arctic canada alaska coastal greenland the southern andes and high mountain asia but there was little loss from glaciers in antarctica over this period the global mass budget was 259 28 gigatons per year equivalent to the combined loss from both ice sheets and accounting for 29 13 of the observed sea level rise

rapid decrease of observed mass balance in the urumqi glacier no 1 tianshan mountains central asia the mass balance of urumqi glacier no 1 located in tianshan mountains of central asia has been monitored since 1959 based on the long term climate and glacier mass balance observation data for the period 1959 2010 analyses show that the glacier mass balance has decreased rapidly the equilibrium line altitude ela has ascended significantly and the glacier terminus has retreated continuously in response to climate change the cumulative mass balance was 14 883 mm w e equivalent to glacier thinning of 16 5 m with a mean value of 0 32 m y the ela showed a significant ascending trend ascending about 90 m the averaged ela was 4067 m a s l and analysis shows the steady state ela ela 0 was 4018 m a s l with the mass balance gradient alpha 5 9 mm m the glacier terminus retreated by 199 3 m at the east branch and 241 3 m at the west branch linear regression analysis results suggest that 1 c degrees summer temperature increases leads to 440 6 mm mass balance decrease mass balance increases by 120 mm when annual precipitation increases by 100 mm mass balance decrease was controlled mainly by summer temperature if such increased warming continues in the future the glacier mass balance will form a strongly negative balance the glacier will shrink and the glacier terminus will continue to retreat c 2013 elsevier ltd and inqua all rights reserved

heterogeneous mass loss of glaciers in the aksu tarim catchment central tien shan revealed by 1976 kh 9 hexagon and 2009 spot 5 stereo imagery the meltwater released by the glaciers in the aksu tarim catchment south of tomur peak central tien shan feeds the tarim river which is the main artery for the oases at the northern margin of the taklamakan desert the correct modeling of the contribution of the glaciers meltwater to the total runoff of the tarim river is hampered by the lack of mass balance data multi temporal digital terrain models dtms allow the determination of volume changes for large samples of glacier here we present the mass changes for 12 glaciers using 1976 kh 9 hexagon 2000 srtm3 and 2009 spot 5 datasets the results show that most of the glaciers have been losing mass since 1976 the largest glaciers koxkar and west qongterang lost 0 27 0 15 m w e a 1 and 0 43 0 15 m w e a 1 between 1976 and 2009 despite thick debris cover however some smaller glaciers show mass gain at their tongues indicating glacier surges using srtm3 data the volume gain of qinbingtan glacier no 74 could be dated to the time period 1999 2009 the overall mass budget of 0 33 0 15 m w e a 1 for 1976 2009 of the investigated glaciers is within the variability range of the global average however in the recent years 1999 2009 a slightly decelerated mass loss of 0 23 0 19 m w e a 1 could be observed c 2012 elsevier inc all rights reserved

carbon isotope composition of graphite in mantle eclogites the carbon isotope composition 13c of primary graphite from 28 mantle derived eclogite xenoliths from kimberlites in southern africa and usa range from 14 31 to 2 84 pdb with a mean value of 6 2 both group i and group ii eclogites are represented by anomalously low carbon isotope ratios there is no simple correlation between isotopic composition and depth of origin demonstrating carbon isotopic heterogeneity in the shallow upper mantle not previously recognized but known from the deeper eclogite diamond population interpreted in the light of recent geochemical evidence supporting a subduction origin for some mantle eclogites and their diamonds low 13c graphite bearing eclogites could represent some of the earliest material emplaced beneath the cratons by subduction

a coupled hydro mechanical model for simulation of gas migration in host sedimentary rocks for nuclear waste repositories abstract in a deep geological repository dgr for nuclear wastes several mechanisms such as waste form degradation and corrosion could lead to gas generation the produced gas can potentially overpressurize the repository alter the hydraulic and mechanical properties of the host rock and affect the long term containment function of the natural host rock and engineered barriers thus the understanding of the gas migration within the host rock and engineered barriers and the associated potential impacts on their integrity is important for the safety assessment of a dgr in this paper a coupled hydro mechanical model for predicting and simulating the gas migration in sedimentary host rock is presented a detailed formulation coupling moisture liquid water and water vapor and gas transfer in a deformable porous medium is given the model takes into account the damage controlled fluid gas water flow as well as the coupling of hydraulic and mechanical processes e g stress deformation the model also considers the coupling of the diffusion coefficient with mechanical deformation as well as considers the modification of capillary pressure due to the variation of permeability and porosity the prediction capability of the developed model is tested against laboratory scale and in situ experiments conducted on potential host sedimentary rocks for nuclear waste disposal the model predictions are in good agreement with the experimental results the numerical simulations of the laboratory and field gas injection tests provide a better understanding of the mechanisms of gas migration and the potential effects of excessive gas pressure on the host sedimentary rocks this research work has allowed us to identify key features related to gas generation and migration that are considered important in the long term safety assessment of a dgr in sedimentary host formations

quantifying the effects of climate and surface change on glacier mass balance when a mass balance is computed using an outdated map that computation does not reveal the actual mass change but older maps often must be used for practical reasons we present a method by which with a few additional measurements each year a mass balance computed with an outdated map can be transformed into an actual mass change this is done by taking into account the influence of changes in areal extent and changes in the surface elevation of the glacier since the map was made this method is applied to south cascade glacier washington u s a as an example the computed cumulative mass balance from 1970 to 1997 would have been 16 too negative if the 1970 map had not been updated while the actual volume change of a glacier is relevant to hydrological studies the change that would have occurred on a constant or static surface is more relevant to certain glacier dynamics problems and most climate problems we term this the reference surface balance and propose that such a balance which deliberately omits the influence of changes in area and surface elevation is better correlated to climatic variations than the conventional one which incorporates those influences

internal structures of zircons from archaean granites from the darling range batholith implications for zircon stability and the interpretation of zircon u pb ages internal structures in zircons from granitoids from the late archaean darling range batholith show secondary features revealed by hf etching which record reconstitution of the zircons and modification of the distribution of trace elements during post crystallisation cooling of the granitoid zircons from the granites commonly contain unzoned to weakly zoned cores surrounded by rims showing oscillatory zoning which has been modified by recrystallisation the most striking feature is the development of high trace element concentration areas found in zircons from a number of granites these structures range from enhanced trace element concentrations in primary zones to a single accumulation of most trace elements in one band about half way between the outer edge and the centre of the zircon in any zircon the extent of the concentration of trace elements towards the formation of a single trace element band appears to be inversely related to the fading and broadening of primary oscillatory zones in the outer rim this suggests that the trace element bands formed by migration of trace elements from the outer primary zones to new concentration sites on an inner set of primary zones this explanation is supported by the formation of multiple curved trace element bands that transgress primary zoning and the determination of younger shrimp ages on depleted zircon outer rims compared to remnant primary oscillatory zoned areas of the zircon and unzoned centres also observed in some granite zircons is a finely convoluted zoning which overprints oscillatory zoning in parts of a zoned zircon and in rare cases occurs throughout the zircon this structure is explained in terms of secondary migration and reconcentration of trace elements in curved bands all structures can be transgressed by generally rounded lobes and patches of low u weakly nebulously zoned zircon this is interpreted as a late stage interaction between the zircon and fluids formed during cooling and crystallisation of the granitoid resulting in recrystallisation of affected parts of the zircon with accompanying loss of trace elements from the zircon

dating the lower crust by ion microprobe ion microprobe uthpb ages of zircons from granulite facies lower crustal xenoliths from north queensland australia correlate well with the ages of major orogenic episodes manifest at the earth s surface about half of the xenoliths contain proterozoic zircons which are similar in age to the episodes of high grade metamorphism of the older surface rocks all the xenoliths contain late paleozoic zircons which show a real 100 ma range in206pb238 u ages from 320 to 220 ma which is attributed to granulite facies metamorphism followed by slow cooling in the deep crust the paleozoic zircon ages coincide in time with the prolonged episode of eruption of voluminous felsic ash flows and intrusion of high level granites in this region 320 270 ma mineral and melt inclusions in the zircons provide clues to the origin of some of the xenoliths and coupled with the age information can be used to infer the geological processes operating in the lower crust the zircons from two mafic xenoliths contain felsic and intermediate melt inclusions implying at least a two stage history for these rocks involving either partial melting of a more felsic protolith or crystal accumulation from an evolved melt some of the zircons from the felsic xenoliths contain co2 rich fluid inclusions indicating that those zircons grew during high grade metamorphism the isotopic and chemical data for the whole rock xenoliths show that they originate from a segment of the lower crust which is a heterogeneous mixture of supracrustal and mafic mantle derived lithologies the major orogenic event responsible for the formation of that crust occurred in the late paleozoic when proterozoic supracrustal rocks were emplaced into the lower crust possibly along thin skinned thrust slices this was accompanied by intrusion of high temperature mantle derived melts which caused partial melting of pre existing crust the most likely setting for such tectonism is a continental margin subduction zone

effect of summer accumulation on glacier mass balance on the tibetan plateau revealed by mass balance model the characteristics and sensitivities of a cold based glacier on the tibetan plateau where the summer monsoon provides most of the mass input to glaciers are discussed using an energy balance model incorporating the process of water refreezing the model accurately represents the observational results related to the mass balance of xiao dongkemadi glacier on the central plateau during 1992 93 our data revealed that the mass balance of cold glaciers cannot simply be described by the surface mass heat balances because about 20 of infiltrated water is refrozen and thus does not run off from the glacier model calculations demonstrate that glaciers in an arid environment can maintain their mass since the monsoon provides precipitation during the melting season snowfall in summer keeps surface albedo high and largely restrains ablation nevertheless the calculations also make clear that glaciers on the plateau are more vulnerable than those of other regions because of summer accumulation in the monsoon climate warming would cause not only a decrease in accumulation but also a drastic increase in ablation in combination with surface albedo lowering therefore although glaciers on and around the plateau can be sustained by summer accumulation they are more vulnerable to warming than winter accumulation type glaciers

full scale 3d modelling of a nuclear waste repository in the callovo oxfordian clay part 1 thermo hydraulic two phase transport of water and hydrogen

archaean crustal evolution in west africa a new synthesis of the archaean geology in sierra leone liberia guinea and ivory coast abstract a new synthesis of the geology and geochronology of the little known archaean rocks in sierra leone liberia guinea and ivory coast is presented in order to better understand the processes of archaean crustal evolution in this region and to attempt to interpret these data in the light of our current understanding of archaean crustal evolution in addition this study seeks to identify those aspects of archaean crustal evolution which are currently not known in this area and which need to become the subject of future studies given the economic importance of this region in terms of the mineral deposits hosted in the archaean rocks these include greenstone belt hosted iron ore lode gold chromite and columbite tantalite and younger diamondiferous kimberlites intrusive into archaean felsic gneisses the new results show that this cratonic nucleus comprises of four main geological units 1 the oldest crust is made up of 3 5 3 6 ga ttg tonalite trondhjemite granodiorite gneisses these only outcrop in the east of the craton in guinea but their presence is indicated elsewhere in the central part of the craton though xenocrystic zircon cores in younger rocks 2 the major rock type found throughout the craton is 3 26 2 85 ga ttg gneiss in detail these magmas are thought to have formed in two episodes one between 3 05 3 26 ga and the other between 2 85 2 96 ga the presence of inherited zircons in the younger suite indicate that this event represents the partial reworking of the older gneisses 3 4 ga eclogite xenoliths in kimberlite derived from the sub continental lithospheric mantle are thought to be the restite after the partial melting of a basaltic protolith in the production of the ttg magmas 3 supracrustal rocks form linear belts infolded into the ttg gneisses and metamorphosed to amphibolite and granulite grade they are of different sizes contain a variety of lithological sequences and may be of several different ages the larger supracrustal belts in sierra leone contain a thick basalt komatiite sequence derived by the partial melting of two different mantle sources unconformably overlain by a sedimentary formation they are seen as an important resource for gold iron ore chromite and columbite tantalite 4 a suite of late archaean granitoids formed by the partial melting of the ttg gneisses in a craton wide deformation metamorphic partial melting event at 2800 20 ma this thermal event is thought to be responsible for the stabilisation of the craton this new synthesis highlights major geological and geochronological similarities between the archaean rocks of sierra leone liberia guinea and ivory coast and those in the reguibat shield in the northern part of the west african craton suggesting that the two regions were once more closely related

thermohydromechanics of partially saturated geological media governing equations and formulation of four finite element models this paper presents the general governing equations for coupled thermohydromechanical thm processes in saturated and unsaturated geologic formations and reviews four finite element codes for modeling of such system three of the codes are developed for the special purpose of analyzing coupled thm processes in unsaturated porous and fractured geological media and the fourth is a commercial code that has been used in its standard version with a few adaptations for this specialized problem the basic assumptions and fundamental equations for coupled thm processes in unsaturated porous fractured rock are presented and formulations of the four finite element models are compared

glacier change in norway since the 1960s an overview of mass balance area length and surface elevation changes in this paper we give an overview of changes in area length surface elevation and mass balance of glaciers in mainland norway since the 1960s frontal advances have been recorded in all regions except the northernmost glaciers in troms and finnmark storsteinsfjellbreen lyngen and langfjordjokelen more than half of the observed glaciers 27 of 49 had marked advances in the 1990s the glaciological mass balance values for the period 1962 2018 where 43 glaciers have been measured show great inter annual variability the results reveal accelerated deficit since 2000 the most negative decade being 2001 2010 some years with a positive mass balance or less negative after 2010s can be attributed to variations in large scale atmospheric circulation a surface elevation change and geodetic mass balance were calculated for a sample of 131 glaciers covering 817 km 2 in the 1960s and 734 km 2 in the 2010s giving an area reduction of 84 km 2 or 10 the sample covers many of the largest glaciers in norway and they had an overall change in surface elevation of 15 5 m for the 50 year period converted to a geodetic mass balance this gives a mean mass balance of 0 27 0 05 m w e a 1

mass balance reconstruction for glacier no 354 tien shan from 2003 to 2014 this study presents a reconstruction of the seasonal mass balance of glacier no 354 located in the akshiirak range kyrgyzstan from 2003 to 2014 we use a distributed accumulation and temperature index melt model driven by daily air temperature and precipitation from a nearby meteorological station the model is calibrated with in situ measurements of the annual mass balance collected from 2011 to 2014 the snow cover depletion pattern observed using satellite imagery provides additional information on the dynamics of mass change throughout the melting season two digital elevation models derived from high resolution satellite stereo images acquired in 2003 and 2012 are used to calculate glacier volume change for the corresponding period the geodetic mass change thus derived is used to validate the modelled cumulative glacier wide balance for the period 2003 12 we find a cumulative mass balance of 0 40 10mw e a 1 this result agrees well with the geodetic balance of 0 48 0 07mw e a 1 over the same period

hydrological cycles on the north and south peripheries of mountain glacial basins of central asia four high mountain glacial basins of the northern and southern periphery of central asia were studied to determine their interaction with the external hydrological cycle over the eurasian continent two of them located in the northern periphery are closed drainage basins with continental climate and the other two are open basins located in the southern periphery calculations of mass energy exchange glacial runoff and components of the hydrological cycles were conducted for glaciers with a continental climate the calculations of snow ice melt and runoff were based on solar parameters for glaciers with a marine climate regime glacier melt and runoff were based on air temperature the relative errors of simulated annual flows were on average 8 14 the components of the regional hydrological cycles precipitation condensation runoff and evaporation were quantified for each glacial system and their share in total atmospheric moisture was determined the closed basins of the northern periphery in central asia stored annually about 0 1 2 4 of the total external atmospheric moisture in the aralo caspian and tarim hydrographic systems about 0 22 0 24 of the external water cycle is transferred annually in open glacial basins of the southern periphery the glaciers of these regions return 0 25 0 30 of the external water cycle per year to the pacific and indian oceans 0 03 and 0 06 of this external moisture is taken from the glacial resources of the gongga and xixibangma glaciers

eclogites of the snowbird tectonic zone petrological and u pb geochronological evidence for paleoproterozoic high pressure metamorphism in the western canadian shield eclogite occurs within the southern domain of the east athabasca mylonite triangle in northern saskatchewan situated at the boundary between the archean rae and hearne provinces of the western canadian shield the east athabasca mylonite triangle is a fundamental exposure of the 3 000 km long snowbird tectonic zone the eclogite occurs in association with a variety of lower crustal high pressure granulites that record a complex metamorphic history from 2 6 to 1 9 ga temperatures of the eclogite facies metamorphism are constrained by garnet clinopyroxene exchange thermometry at 920 1 000 c minimum pressure conditions are recorded by the jadeite quartz albite geobarometer at 1 8 2 0 gpa a near isothermal decompression path to granulite facies conditions is inferred from retrograde reaction textures involving the formation of granulite facies assemblages such as orthopyroxene plagioclase and pargasite plagioclase u pb idtims zircon geochronology of the eclogite yields a weighted mean 207pb 206pb date of 1 904 0 0 3 ma which we interpret as the time of peak eclogite facies metamorphism shrimp in situ analyses of metamorphic zircons included within omphacitic clinopyroxene support this interpretation with a weighted mean 207pb 206pb date of 1 905 19 ma inclusion suites of high pressure phases and the petrographic setting of zircon are a direct link between zircon growth and eclogite facies metamorphism zircon from one eclogite sample has older cores that are 2 54 ga which is a minimum age for the emplacement or earliest metamorphism of the gabbroic protolith u pb rutile data indicate slow cooling at 1 c ma below 500 c from 1 88 to 1 85 ga the formation and exhumation of the eclogites at ca 1 9 ga has important implications for the tectonic significance of the snowbird tectonic zone during the paleoproterozoic the eclogites described here are consistent with transport of continental crust to mantle depths during the paleoproterozoic followed by rapid buoyancy driven exhumation to normal lower crustal depths

geochronological evidence for reworking of archean terrains during the early proterozoic 2 1 ga in the western coˆte d ivoire man rise west african craton abstract a period of accretion of continental crust is recognized during the archean at ca 3 2 3 3 ga on the basis of wholerock nd model ages and pb ages on detrital zircons from various gneisses of the man area in co te d ivoire there is no significant evidence of any older event such as the 3 5 3 6 ga accretion episode recognized in the archean of the reguibat rise in mauritania the earliest magmatic events recorded in the northern domain of the man area correspond to tonalitic grey gneisses of a minimum age ca 3 05 ga leonian event a subsequent major phase of igneous and metamorphic activity around 2 8 ga liberian event is recorded in the entire archean terrain without any evidence of new accretion this second event began at 2830 7 ma its climax is indicated by charnockitic intrusions followed by granodioritic magmas at ca 2800 10 pb pb and u pb ages on monazite and zircon cooling after the liberian event occurred ca 2 75 ga ago k feldspar whole rock garnet sm nd ages paleoproterozoic reworking is mainly found in the southern part of the archean terrain of the man area zircon monazite sphene and garnet geochronometers all indicate an important thermal effect during the birimian event i e 2 1 ga the earliest influence of this event is recorded in a range of 2250 40 70 ma with a major event ca 2 1 ga partial to total resetting of u pb and sm nd geochronometers indicate that high temperature conditions were reached during the birimian event this metamorphic overprint and the diapiric emplacement of coeval paleoproterozoic juvenile magmas at 2 1 ga in the southern domain toule pleu massif suggest that the 2 1 ga overprint could be related to major underplating processes under the archean basement the thermal flow related to the differentiation and the accretion of these juvenile birimian magmas may account for the reworking of the surrounding archean domain which had been possibly thinned during underplating these results suggest close proximity between the archean continents and an accretion zone associated with juvenile magmatism 2 1 ga ago

compilation of west african mineral deposits spatial distribution and mineral endowment abstract the west african craton is highly endowed in minerals and their spatial and temporal distribution varies from single to multi phase mineralization events they are broadly related to three major tectono metallogenic elements and formed during distinct mineral epochs 1 in both archean shields kenema man and reguibat and paleoproterozoic domains baoule mossi eglab these are characterized by giant iron ore deposits that formed between ca 2 5 2 3 ga nearly all gold porphyry copper lead zinc and sedimentary manganese ore that developed between 2 2 and 2 1 ga and primary diamonds that formed between two intervals at ca 2 2 2 0 ga and in the mesozoic 2 across pan african and variscan belts these are distinguished by major precambrian iocg s copper gold that formed at ca 2 1 ga and approximately 680 ma and neoproterozoic sedimentary iron ore and phosphate deposits 3 within intracratonic and coastal basins these include the development of cenozoic lateritic bauxites over mesozoic dolerites tertiary quaternary mineral sands deposits oolitic iron ore and sedimentary phosphate deposits geological spatial and temporal correlations using the multi commodity west african mineral deposit database highlight that gold and non gold commodities formed in multiple phases this commenced in the liberian orogeny 2 9 2 8 ga with the enrichment of iron ore nickel sulphides diamonds and gold in the earth s crust the pre eburnean or tangaean eoeburnean eburnean i event yielded gold and the major eburnean orogeny yielded gold iron ore manganese diamonds magmatic nickel sulphides copper gold lead zinc and ree minerals throughout the pan african event sedimentary manganese deposits lead zinc ree minerals sedimentary phosphates and again gold were formed primary diamonds and magmatic nickel sulphides are related to the break up of gondwana followed by an intense lateritic weathering period that formed bauxite deposits along the craton margin

the mechanical behaviour of weak mudstone opalinus clay at low stresses abstract over the last 10 years argillaceous rocks mudrocks such as the jurassic claystone opalinus clay have gained acceptance as a potential host formation for geological disposal of nuclear waste observations from tunnels in opalinus clay at the mont terri rock laboratory switzerland suggest that the excavation induced response is not linear elastic the micro structure of the opalinus clay has been identified as a source for this response it has been demonstrated that diagenetic processes over the last 180 ma have been responsible for the formation of strong diagenetic bonds locking latent strain energy into the micro structure of opalinus clay a conceptual model of the micro structure including the effects of diagenetic processes has been developed as a framework to interpret the mechanical behaviour of the opalinus clay samples recovered at mont terri rock laboratory have been subjected to processes that have resulted in bond breakage and the release of locked in latent strain energy this tends to reduce the strength and deformation properties of samples and induces low stiffness non linearity of the stress strain curve at low stress levels numerical modelling of the sampling stress path at mont terri rock laboratory shows that unloading was the dominant factor resulting in this response as a result samples can shed light on the unloading response of the rockmass to excavation this non linear behaviour has been quantified by means of routine laboratory compressive tests

adakite ttg connection and fate of mesoarchaean basaltic crust of holenarsipur nucleus dharwar craton india abstract holenarsipur nucleus hn is one of the oldest part 3 5 3 1 ga of the continental crust of india it is made up of mafic ultramafic komatitic 3 35 ga greenstone belts migmatitic ttg tonalite trondhjemite granodiorite 3 3 ga and diapiric trondhjemites 3 1 ga new major trace and ree data on these rocks presented here provide constraints on adakite ttg connection model and petrogenesis of these rocks of hn in addition to recycling of the early mesoarchaean basaltic crust and evolution of mesoarchaean continental crust although of two different ages the chemical characteristics of the migmatitic ttgs and diapiric trondhjemites of the hn resemble with the archaean and cenozoic high silica adakites hsa and the adakites from two neoarchaean greenstone belts of dharwar craton they also display similarities with the early mesoarchaean ttgs from different cratons based on the compositional variations observed in ttg and diapiric trondhjemites of hn we propose that plume fed basaltic and or basaltic komatiitic oceanic crust slab flatly shallow angle subducted and melted under high archaean geothermal regime to produce ttgs identification of hsa in 2 7 ga old greenstone belt subduction complexes that are compositionally similar to ttg suggests the possibility of continuation of this process into neoarchaean and supports a genetic connection between ttg and adakites

damage induced permeability changes in granite a case example at the url in canada abstract this paper concerns both in situ measurements of permeability and numerical modelling of changes in permeability induced by microcrack growth hydraulic experiments including pulse tests with the seppi probe are in progress these tests are a part of the tunnel sealing experiment tsx at the 420 m level of canada s underground research laboratory whose aim is to estimate the in situ hydraulic properties of lac du bonnet granite based on laboratory investigations the anisotropic damage model developed by homand et al comput geotech 22 1998 135 and recently reviewed by shao et al int j rock mech min sci 36 1999 1001 has been extended in order to account for changes in permeability induced by microcrack growth we have implemented this extension in the three dimensional code flac 3 d triaxial compression tests with permeability measurements carried out on two different granites provide a verification of the numerical implementation with a good agreement between experiments and predictions comparison between in situ measurements of permeability and predictions indicates that both the results of numerical modelling and observations are globally in agreement finally numerical modelling as well as the in situ measurements indicate that a depth of 50 70 cm is a good estimation of the extent of excavation disturbed zone in the tsx tunnel

measurement of in situ stress in weak rocks at mont terri rock laboratory switzerland in situ stress measurements in weak rocks such as clay shales that respond strongly to environmental changes are particularly difficult an extensive in situ stress measurement program has been conducted at the mont terri rock laboratory in northwestern switzerland hydraulic fracturing undercoring around a 600 mm diameter borehole using csiro triaxial strain cells and the borehole slotter were used to establish the state of stress for the opalinus clay at this location conflicting orientations and magnitudes resulted from the measurement programs three dimensional elastic modelling was used in conjunction with tunnel and borehole observations to establish the most likely stress tensor a stress measurement program using a borehole deformation gauge is currently underway to check the stress tensor resulting from the observational modelling

limitations in identifying the equilibrium line altitude from the optical remote sensing derived snowline in the tien shan china optical remote sensing derived end of summer snowline altitude sla has long been employed on glaciers as an indicator of the equilibrium line altitude ela in the tien shan northwest china both accumulation and ablation of glaciers occur mainly in the warm season making it difficult to obtain the representative snowline highest snowline in the area the high spatio temporal resolution of hj 1 satellite images enables the highest snowline to be acquired in this paper we compare image derived sla and measured in situ ela for two adjacent glaciers in the tien shan over the period 2009 10 results indicate that 1 in 2009 there was a substantial difference between sla and ela on one glacier suggesting inconsistent applicability in using sla to identify ela over a large area and 2 in 2010 an intense ablation year the field data derived ela surpassed the glacier peak in this situation there is no theoretical relationship between sla and ela and the image derived snowline actually indicates the boundary between ice and firn from previous years in summary errors will arise from the discrepancies between individual glaciers and from intensive ablation when using sla to identify ela over a large area

geochronology of polygenetic monazites constrained by in situ electron microprobe th u total lead determination implications for lead behaviour in monazite abstract monazite grains are generally concordant and with an electron microprobe give th u total pb isochron ages in agreement with conventional u pb data monazites from four samples of post archean migmatite from the ivory coast record two main ages an archean age at 2 80 ga partly overprinted by a late migmatization event at 2 03 ga the in situ electron microprobe determination has also shown a third event that systematically appears at 2 72 ga for all the monazites from two of the four studied rocks the three events at 2 80 2 72 and 2 03 ga recorded by the th u total pb system in monazite were each obtained on independent homogeneous parts of a single grain with no sign of pb diffusion thus the oldest monazite remained closed during a high grade resetting migmatization at a temperature estimated at around 700 c and also remained closed during the growth of secondary monazite conventional u pb data isotope dilution on monazite from the same rocks did not allow precise age determinations because the representative points were highly up to 83 discordant and did not fit well along a chord in the concordia diagram the u pb isotope dilution method gave a lower intercept age of 2029 25 ma in agreement with the electron microprobe age although with an unusually high uncertainty due to a poor fit of the data the pb evaporation method gave an old archean age at 2830 7 ma and proterozoic ages ranging from 2417 10 to 2074 7 ma thus although the oldest archean age obtained with the pb evaporation and electron microprobe methods is similar within the analytical error the proterozoic ages obtained by the pb evaporation method are significantly older than the th u total pb proterozoic age obtained with the electron microprobe this discrepancy is presumed to be due to the influence in the pb evaporation method of radiogenic lead contained within archean zones of the monazite grains in other words it means that migmatization took place later than 2074 7 ma and probably around 2030 ma the second archean event at 2 72 ga revealed by high spatial resolution of the electron microprobe could not be determined by other methods the th u total pb method appears to be an inexpensive alternative method for dating simple monazites with a precision close to 20 ma even if the u pb isotopic dilution technique remains the reference method moreover owing to the very high spatial resolution 1 m of the electron microprobe it appears to have no competitor for dating complex polygenetic monazites especially when more than two events are recorded homogeneous zones of different ages coexist in a single grain with no major indication of lead diffusion a procedure for age and error calculations is defined

archaean re os age for siberian eclogites and constraints on archaean tectonics considerable uncertainty surrounds the nature and evolution of the earth s mantle in archaean times 2 5 gyr ago mantle derived eclogite xenoliths erupted by kimberlites provide important clues in this regard because their basaltic composition suggests that they may be remnants of an early 4 gyr magma ocean1 2 subducted archaean oceanic crust3 5 or crystallized high pressure mantle melts6 9 better constraints on the age and origin of mantle eclogites are thus important for our understanding of early earth processes here we present rhenium osmium isotope data for diamond bearing eclogites from the udachnaya kimberlite pipe in siberia which indicate formation in the archaean 2 9 0 4 gyr this age is too young for the eclogites to be remnants of early earth differentiation but overlaps the age range for crust generation and craton stabilization on both the aldan and anabar shields of the siberian craton 2 85 3 2 gyr 10 11 these data together with 3 1 gyr re os model ages for diamond bearing udachnaya peridotites12 show that the siberian craton lithosphere was at least 150 km thick the minimum required for diamond stability by the mid archaean

four zircon ages from one rock the history of a 3930 ma old granulite from mount sones enderby land antarctica ion microprobe u th pb analyses of zircons from a granulite grade orthogneiss from mount sones enderby land antarctica record the ages of four principal events in the history of the gneiss three of which already have been recognized through previous isotopic dating of other samples the structure of the zircons indicates at least four different stages of growth the several zircon ages were obtained by grouping the analyses according to the stage they represented in the observed stratigraphic succession of growth and thereby defining separate u pb discordance patterns for each stage the stratigraphically oldest zircon rare discrete cores is indistinguishable in age from the most common euhedrally zoned zircon both crystallized when the tonalitic precursor of the orthogneiss was emplaced into the crust 3927 10 ma ago making the orthogneiss currently the oldest known terrestrial rock the outer parts of most grains and some whole grains recrystallized at 2948 31 17 ma during or immediately after possibly 100 ma of high granulite grade metamorphism the recrystallized zircon was isotopically disturbed by tectonism associated with reactivation of the southern margin of the napier complex at 1000 ma in the intervening time at 2479 23 ma the cores and zoned zircon suffered a major isotopic disturbance involving movement of radiogenic pb which left most of the crystals with radiogenic pb deficiencies but produced local radiogenic pb excesses in others a new generation of zircon characterized by very high th u and low u grew at that time that event deformation and possibly a minor rise in temperature produced widespread perturbations of other isotopic systems throughout the napier complex

the origin of early archean banded iron formations and of continental crust isua southern west greenland abstract a long standing geological debate is whether the fe component of precambrian banded iron formations bifs was derived from continental sources or had its origin in hydrothermal alteration of the oceanic crust recent ree and nd and fe isotope studies of iron rich layers in bifs have provided strong supporting evidence for the hydrothermal origin of the fe component pillow basalts from the 3800 3700 ma isua greenstone belt west greenland underwent significant enrichment of fe up to 21 wt fe2o3 and some chalcophile elements e g pb 5 4 7 2 ppm prior to a late archean tectonothermal metamorphic event recorded in the region published and new pb pb isotopic data from the isua pillow basalts and the spatially associated bifs suggest that the enrichment of fe and pb and deposition of the bifs took place between 3800 and 3600 ma similar pb isotopic compositions in pillow basalts and bifs are consistent with a common source of pb for both supracrustal rocks iron and pb were probably scavenged from the oceanic crust and were re deposited on the ocean floor by hydrothermal fluids suggesting that high temperature hydrothermal alteration of early archean oceanic crust played an important role in the deposition of the isua bifs geochemical lithological and structural data from the isua greenstone belt are all collectively consistent with a convergent margin geodynamic setting the isua bifs are spatially and temporally associated with boninitic and island arc picritic pillow basalts given the observations that cenozoic boninites and picrites tend to form in an intra oceanic arc forearc setting we suggest that the isua bif boninite and bif picrite associations were also deposited in a similar geodynamic setting the original pillow basalt bif stratigraphy was dismembered and transposed throughout the belt during early to late archean tectonothermal events the high temperature hydrothermal alteration of the oceanic crust produced significant hydrothermal discharge with large quantities of fe necessary to contribute to the deposition of the isua bifs the hydrothermal alteration may have resulted from the opening of an asthenospheric window developed as a consequence of ridge subduction beneath an early archean arc forearc region the ridge subduction model can also explain the origin of the contemporaneous tonalite trondhjemite granodiorite ttg intrusions in the isua region partial melting of laterally accreted and thickened oceanic crust under amphibolite to eclogite metamorphic conditions by upwelling of asthenospheric windows may have produced ttg melts the diapirically upwelling ttg melts formed the early archean continental crust and the complementary eclogitic residues contributed to the sub continental lithospheric mantle

an enhanced temperature index glacier melt model including the shortwave radiation balance development and testing for haut glacier d arolla switzerland an enhanced temperature index glacier melt model incorporating incoming shortwave radiation and albedo is presented the model is an attempt to combine the high temporal resolution and accuracy of physically based melt models with the lower data requirements and computational simplicity of empirical melt models represented by the degree day method and its variants the model is run with both measured and modelled radiation data to test its applicability to glaciers with differing data availability five automatic weather stations were established on haut glacier d arolla switzerland between may and september 2001 reference surface melt rates were calculated using a physically based energy balance melt model the performance of the enhanced temperature index model was tested at each of the four validation stations by comparing predicted hourly melt rates with reference melt rates predictions made with three other temperature index models were evaluated in the same way for comparison the enhanced temperature index model offers significant improvements over the other temperature index models and accounts for 90 95 of the variation in the reference melt rate the improvement is lower but still significant when the model is forced by modelled shortwave radiation data thus offering a better alternative to existing models that require only temperature data input

extraction of pb with artificially too old ages during stepwise dissolution experiments on archean zircon abstract stepwise hf dissolution experiments on five archean zircon populations reveal very systematic patterns of pb discrimination releasing at one point pb with artificially too old 207 pb 206 pb ages the experiments involved a first hf dissolution step for 1 h at room temperature and evaporation on a hot plate that produces pb with young 207 pb 206 pb ages followed by a 4 1 2 h hf dissolution step in an oven at 190 c that liberates the excessively old pb the final residue yields in most cases u pb data that are consistent with the results obtained by the normal selection abrasion and total dissolution procedure in these examples the too old ages cannot be easily explained by the presence of an inherited core component but are more likely to indicate segregation of pb in zircon sub domains during thermal annealing episodes early in its history as has been proposed by other workers aside from shedding light on these particular aspects of zircon u pb systematics the combined results also provide geologically relevant information concerning the regional evolution of the western superior province in ontario an age of 2718 3 ma for a gabbroic unit from the quetico subprovince shows that this was coeval to 2722 2718 ma ultramafic to felsic igneous rocks in the adjacent shebandowan greenstone belt including a gabbro body dated in this study at 2725 17 11 ma these age relationships suggest that volcanic units of the shebandowan greenstone belt were tectonically imbricated in younger sedimentary rocks of the quetico basin during late archean convergence the other three samples represent felsic intrusive units from geraldton in the wabigoon subprovince an age of 2699 1 ma for an au mineralized feldspar porphyry dyke and identical ages of 2690 1 ma for two phases of the syn tectonic croll lake stock put constraints on the timing of major deformation and hydrothermal activity in the belt

shrimp u pb geochronological constraints on the timing of the intra alcudian cadomian angular unconformity in the central iberian zone iberian massif spain new shrimp u pb ages of detrital zircons from neoproterozoic low grade metasandstones of the schist graywacke complex central iberian zone iberian massif sampled just below and above the intra alcudian unconformity at two selected locations contribute to reconstruct the geodynamic evolution of iberia during the cadomian orogeny in the north gondwana margin the youngest zircons i e maximum depositional age in the lower alcudian are c 580 576 ma while those in the upper alcudian are c 555 552 ma the obtained remarkable time gap of about 21 ma supports the existence of a tectonic event in between this event resulted in moderate folding without related foliation metamorphism that verticalized the lower alcudian previous to the deposition of the upper alcudian additional evidence of late cadomian tectonothermal events elsewhere in iberia also fit in the interval c 560 550 ma combined with other geological data the most probable maximum depositional ages are c 580 560 ma for the lower alcudian previous to the late cadomian folding event and c 550 540 ma for the upper alcudian previous to the deposition of the overlying pusian group and lower cambrian sandstones and limestones a comparison of the new zircon age spectra with possible source areas verifies recent studies that point to the cadomian foreland in the north gondwana continent affected by the pan african orogeny the west african craton and or the saharan metacraton furthermore ongoing cadomian arc related magmatism in iberia c 605 545 ma could have contributed as a local zircon source the end of the cadomian activity is marked by a transient stage ephemeral lower cambrian platform which preceded widespread cambro ordovician rifting of north gondwana

integrated monitoring of mountain glaciers as key indicators of global climate change the european alps the internationally recommended multi level strategy for monitoring mountain glaciers is illustrated using the example of the european alps where especially dense information has been available through historical times this strategy combines in situ measurements mass balance length change with remote sensing inventories and numerical modelling it helps to bridge the gap between detailed local process oriented studies and global coverage since the 1980s mass balances have become increasingly negative with values close to 1 m w e a 1 during the first 5 years of the 21st century the hot dry summer of 2003 alone caused a record mean loss of 2 45 m w e roughly 50 above the previous record loss in 1998 more than three times the average between 1980 and 2000 and an order of magnitude more than characteristic long term averages since the end of the little ice age and other extended periods of glacier shrinkage during the past 2000 years it can be estimated that glaciers in the european alps lost about half their total volume roughly 0 5 a 1 between 1850 and around 1975 another 25 or 1 a 1 of the remaining amount between 1975 and 2000 and an additional 10 15 or 2 3 a 1 in the first 5 years of this century

late twentieth century changes in glacier extent in the ak shirak range central asia determined from historical data and aster imagery 1 global analysis of glacier regimes reveals widespread wastage since the late 1970s with a marked acceleration in the late 1980s we investigate changes in the heavily glacierized ak shirak range central tien shan plateau 43 n 75 e using air photo mapping surveys 1943 and 1977 an aster imagery 2001 and long term glaciological and meteorological observations the wasting of the ak shirak glacier system features a decrease in average glacier size and an increase in the area of outcrops a small shrinkage during 1943 1977 was followed by a greater than 20 reduction during 1977 2001 in response to increases in summer and annual air temperature and decreases in annual precipitation

archean emplacement of eclogitic components into the lithospheric mantle during formation of the kaapvaal craton re os data for selected whole rock eclogites and eclogitic sulfide inclusions in diamonds from seven kimberlites on the kaapvaal zimbabwe cratons yield ages around 3 ga the presence of such old eclogitic components in the subcontinental lithospheric mantle is more common than previously thought overlap of these ages with those of many cratonic peridotites demonstrates that incorporation of eclogitic materials accompanied or closely followed cratonic lithosphere stabilization many of these eclogitic components have fractionated c n o and s isotopic compositions which could have been created at low temperatures implying that some style of archean subduction involving emplacement of oceanic lithosphere was part of craton keel development

strong spatial variability of snow accumulation observed with helicopter borne gpr on two adjacent alpine glaciers the spatial distribution of snow accumulation plays an essential role for the mass balancedistribution on alpine glaciers traditional point measurements snow pits and probes are labour intensive and interpolation in between the points causes uncertainties airborne radar measurements have already been used for snow mapping innon glacierized terrain but not on alpine glaciers to enhance our understanding ofthe spatial distribution of accumulation and pin down reasons for observed variations we have conducted high resolution helicopter borne radar measurements on the temperatedglacier findel and neighbouring adler glacier in southwestern switzerland the radar sensor was mounted underneath a helicopter and operated at a centre frequencyof 500 mhz with a bandwidth of 400 mhz the results were validated withextensive ground based profiling of the snow cover the radar data allows a clearrecognition of the snow cover 6 of the total profile length of 10 km did not allowinterpretation due to missing or disturbed layering and agreed well with the groundbased measurements r2 0 85 reduced accumulation has been observed in allcrevassed zones statistical analysis of the correlation between observed accumulationand terrain characteristics have been performed in a gis environment revealing differingaccumulation patterns on the lower part of findel glacier accumulation showsa clear altitudinal trend while the upper part is dominated by strongly varying snowdepth without an altitudinal trend the accumulation characteristic on adler glacieris similar to the upper part of findel glacier but despite of their close vicinity accumulationis reduced by 40 compared to the same elevation on findel glacier thisstudy reveals a large potential of helicopter borne snow profiling for measurements ofaccumulation distribution on alpine glaciers