the retreat of a tidewater glacier observations and model calculations on hansbreen spitsbergen based on observations and model calculations the retreat over the last two decades of hansbreen a tidewater glacier in southern spitsbergen svalbard is investigated the observations of the calving front position between 1982 and 1998 show an abrupt retreat in 1990 which is suggested to be related to a depression in the glacier bed the observed seasonal variations of the front position are mainly due to variations of the calving rate the observations of hansbreen further indicate that during periods of slow front position changes melting at the water line may play an important role in triggering the process of calving the evolution of hansbreen between 1982 and 1998 is simulated with a numerical model for the dynamics of tidewater glaciers using a flotation criterion for calving in which for each time step the part of the glacier terminus which is below a critical height above buoyancy is removed we are able to reproduce the observed rapid retreat of hansbreen through the depression in the glacier bed from the observations and model calculations we conclude that the rapid retreat is mainly an effect of basal topography in the terminus region and not a direct response to a change in mass balance

ocean forcing of the greenland ice sheet calving fronts and patterns of retreat identified by automatic satellite monitoring of eastern outlet glaciers 1 we have developed an automatic method to identify changes in the position of calving glacier margins using daily modis imagery application of the method to 32 ocean terminating glaciers in east greenland produced 26 802 margin positions for a 10 year long period 2000 2009 we report these high resolution data and show that the glaciers exhibit seasonal cycles with magnitudes of advance and retreat proportional to glacier width despite similar seasonality there is a distinct difference between the interannual trends of calving front positions north and south of 69 n all glaciers above this latitude showed very limited or no change when seasonality was excluded while glaciers south of 69 n retreated significantly between 2001 and 2005 2 3 km on average approximately 26 of the retreat of southern glaciers was regained by readvance from 2005 to 2009 to explain the latitudinal boundary of glacier dynamics we review basic climatic factors including summer and winter atmospheric forcing sea ice conditions and ocean temperature we conclude that the southern retreats were strongly influenced by warm oceanic conditions associated with increased transport of subtropical waters to the irminger sea and to fjords and coastal regions south of 69 n northern glaciers remained stable despite significant increase in runoff in this region because fjords at latitudes higher than 69 n are less exposed to subtropical waters the southern retreats illustrate sensitive behavior of calving glaciers and we hypothesize that the calving fronts retreated because they were exposed to rapid ice front melting

alteration mineralogy and stable isotope geochemistry of paleoproterozoic basement hosted unconformity type uranium deposits in the athabasca basin canada unconformity type uranium deposits are characterized by mineralization developed along the contact between younger sandstone cover and underlying crystalline basement rocks mineralization may extend up to 400 m into the underlying basement rocks whereas sandstone hosted unconformity type deposits have been well studied deposits hosted primarily in the basement have not this study examines the deposits at rabbit lake dawn lake and mcarthur river in the athabasca basin of canada which are hosted by the metamorphic archean and early paleoproterozoic rocks forming the basement to younger late paleoproterozoic sandstones alteration is similar in the three deposits and is characterized by three distinct paragenetic stages 1 preore alteration involving illitization of plagioclase and amphibole followed by chloritization of biotite and illite which formed at ca 230 c 2 ore stage alteration characterized by uraninite and coarse grained illite which formed at ca 240 c 3 postore alteration comprising spherulitic dravite vein chlorite quartz calcite and fe cu co and pb sulfides which formed at ca 135 c fluid circulation associated with emplacement of later mackenzie dikes initiated partial recrystallization of uraninite a later stage of alteration includes kaolinite and iron hydroxide precipitation formed at much lower temperatures of ca 50 c stable isotope compositions of the alteration minerals in conjunction with their paragenesis indicate that oxidized basinal fluids d 43 to 21 18o 3 8 were derived primarily from evolved seawater and leached uranium from the overlying sandstones of the athabasca formation and transported it into the basement via infiltration along fracture zones associated with reverse faults graphitic units in the basement and preore alteration served as both physical fractured zones and chemical reductants traps for the uranium mineralization the basinal fluids were responsible for the preore illite chlorite synore uraninite illite and the early postore alteration events this differs from many other sandstone hosted deposits where both oxidized basinal and reduced basement derived fluids were responsible for uranium precipitation

measurement of u pb ages of uraninite and davidite by laser ablation hr icp ms laser ablation high resolution inductively coupled plasma mass spectrometry la hr icp ms is a rapid accurate and inexpensive technique for making in situ u pb isotopic measurements of uraninite and davidite the advantages of this method include 1 mineral separation and chemical digestion are not required 2 measurements on complex samples are feasible because significant isobaric interferences can be resolved and 3 accurate u pb and 207pb 206pb dates on 10 25 m spots can be obtained rapidly the la hr icp ms method is applied to u oxide minerals from four deposits and prospects from northern australia and the new dates are compared to previously published conventional thermal ionization mass spectroscopy tims dates and to known ages of geologically important events these comparisons permit us to assess elemental fractionation of u and pb for uraninite and davidite of the new method relative to zircon as well as its geochronological accuracy and precision u pb apparent ages measured previously agree well with our measurements for el sherena palette and mt isa additionally the upper intercept 207pb 206pb dates for adelaide river 701 190 ma 1 and palette 841 94 ma 1 uraninite measured here are similar to those previously obtained for palette 730 ma nabarlek 920 ma and koongarra 870 ma and the upper intercept date for el sherena uraninite 1573 160 ma is within error of that previously determined for ranger 1550 15 and 1472 40 ma such apparent age agreement for uraninite and similarly for davidite indicates that u and pb fractionations are within error of that for zircon whereas the inherent imprecision of our dates and their associated mswd values greater than 2 5 probably indicate that multiple resetting events affected our samples analytically these results demonstrate that the la hr icp ms technique provides excellent spatial resolution while also removing argide phosphide sulfide and halide interferences that can otherwise lead to erroneous data when using quadrupole icp ms geologically the individual 207pb 206pb and upper intercept u pb dates of uraninite from adelaide river and palette are ca 800 ma possibly reflecting recrystallization of uraninite during the break up of rodinia

greenland marine terminating glacier area changes 2000 2010 area changes at 39 of the widest greenland marine terminating glacier outlets are measured in consecutive annual end of melt season moderate resolution imaging spectroradiometer modis scenes spanning ten annual intervals 2000 10 the rates of cumulative area change for glaciers and ice shelves are well represented by linear least squares fits r 0 99 and r 0 94 with average rates of 70 and 65 km 2 a 1 respectively collectively during this decade the 39 glaciers lost a cumulative area of 1368 km 2 more than three quarters of the total area change occurred north of 72 n the largest 11 year area change for a single glacier during the survey period is the 311 km 2 loss at humboldt glacier the largest annual change for a single glacier was extreme compared with the others where petermann glacier retreated 17 km between 3 and 5 august 2010 for the 10 year sample on average the count of glaciers retreating is twice that advancing a larger distinction is evident considering area change with the ratio of retreat and advance on average nine times the gain for glaciers with ice shelves we find no year with collective area gain the area change data from this study are posted at http bprc osu edu jbox data gac

diagenesis of the aphebian mistassini regolith quebec canada abstract a well developed regolith is preserved beneath early proterozoic aphebian rocks of the otish and mistassini groups in central quebec canada the regolith is covered by fluviatile clastic rocks otish group in the north and by a thick sequence of stromatolitic and sandy dolomite mistassini group in the south where preserved beneath clastic rocks the regolith exhibits the structures and textures of its crystalline parent rocks tonalite gneiss and amphibolite despite the alteration of feldspars to clay minerals and the partial oxidation of biotite a later event recrystallized the clay minerals to muscovite while conserving the original outline of the feldspars beneath the dolomite the regolith was largely replaced by dolomite but retains many original textures dolomite replaced first the clay minerals then quartz and unaltered feldspars and finally biotite repeated crustifications of dolomite with intervals of chert and minor anthraxolite surround unaltered blocks of crystalline rock within the regolith profile and similar complex veins fill many master joints these veins are identical in composition to vug fillings throughout the overlying carbonate formations clasts of partly dolomitized regolith included in non dolomitic sands filling channels and scours dug deep into the profile suggest that dolomitization commenced very early possibly related to a sabkha environment developed during the transgression

recent glacier mass changes in the gulf of alaska region from grace mascon solutions the mass changes of the gulf of alaska goa glaciers are computed from the gravity recovery and climate experiment grace inter satellite range rate data for the period april 2003 september 2007 through the application of unique processing techniques and a surface mass concentration mascon parameterization the mass variations in the goa glacier regions have been estimated at high temporal 10 day and spatial 2 2 arc degrees resolution the mascon solutions are directly estimated from a reduction of the grace k band inter satellite range rate data and unlike previous grace solutions for the goa glaciers do not exhibit contamination by leakage from mass change occurring outside the region of interest the mascon solutions reveal considerable temporal and spatial variation within the goa glacier region with the largest negative mass balances observed in the st elias mountains including the yakutat and glacier bay regions the most rapid losses occurred during the 2004 melt season due to record temperatures in alaska during that year the total mass balance of the goa glacier region was 84 5 gt a 1 contributing 0 23 0 01 mm a 1 to global sea level rise from april 2003 through march 2007 highlighting the large seasonal and interannual variability of the goa glaciers the rate determined over the period april 2003 march 2006 is 102 5 gt a 1 which includes the anomalously high temperatures of 2004 and does not include the large 2007 winter balance year snowfall the mascon solutions agree well with regional patterns of glacier mass loss determined from aircraft altimetry and in situ measurements

a review of the superior province of the canadian shield a product of archean accretion abstract the superior province consists of northern and southern high grade gneiss subprovinces and a central region of alternating granite greenstone and metasedimentary belts subprovinces are commonly fault bounded and display contrasting lithological assemblages metamorphic and structural styles geophysical characteristics and ages they are comparable to phanerozoic suspect terranes the middle and late archean rocks of the superior province are of mantle and juvenile crustal origin with little evidence of inheritance of components older than ca 3 1 ga high grade gneiss subprovinces are mainly deeper level equivalents of the supracrustal rich belts but one minnesota river valley is part of an older ca 3 6 ga terrane that was juxtaposed late in the tectonic history granite greenstone terranes are characterized by low grade volcano sedimentary sequences tholeiitic komatiitic submarine lava plain tholeiitic calc alkalic submarine to subaerial central complexes early platform type quartz arenite stromatolitic carbonate late timiskaming type shoshonitic alkalic volcanic fluvial sediment that range in age from ca 3 0 ga to 2 7 ga the volcanics represent oceanic island arc and continental arc volcanism the quartz arenite carbonate sequences deposition on relatively stable early formed ca 3 0 ga crust and the timiskaming type sequences deposition in pull apart basins developed along strike slip faults late archean ca 2 75 2 70 ga greenstone sequences occur throughout the superior province middle archean ca 3 0 2 8 ga sequences are common in northern and central superior province rare or absent in the south volcanism was accompanied by mafic to trondhjemitic plutonism the metasedimentary belts consist of variably metamorphosed volcanogenic turbidites with detrital zircons ranging in age from ca 3 0 ga to 2 7 ga the metasediments were deposited after major volcanism and probably represent accretionary prisms late archean orogenesis accompanied and followed by calc alkalic plutonism youngs southward from about 2 73 2 72 ga to 2 70 2 68 ga it involved large scale north south compression and dextral transpression and displays thin to thick skinned transitions the contemporaneity of events along the lengths of the belts and their southward younging coupled with the evidence of major compression are consistent with subduction driven oblique accretion of oceanic and continental volcanic arcs accretionary sedimentary wedges older microcontinental fragments etc in a convergent margin setting analogous to parts of the pacific rim differences eg abundance of komatiites and tonalitic plutonic suites are attributable to a hotter archean mantle

buoyant flexure and basal crevassing in dynamic mass loss at helheim glacier despite the role that calving plays in greenland mass loss the mechanisms of calving are poorly constrained observations of greenland s helheim glacier suggest that buoyant flexure at the glacier terminus leads to the propagation of basal crevasses and iceberg calving

analysis of time series of glacier speed columbia glacier alaska during the summers of 1984 and 1985 laser measurements were made of the distance from a reference location to markers on the surface of the lower reach of columbia glacier alaska the data have numerous gaps mostly because of inclement weather the laser measurements were corrected for variations in atmospheric temperature and pressure and for the trajectory of the marker the marker speed was calculated by using a combination of cubic splines and digital filters to arrive at a data set with 1 hour time intervals the speed varies from 7 to 15 m d and has three noteworthy components 1 a low frequency perturbation in speed with a time scale of days related to increased precipitation 2 semidiurnal and diurnal variations related to sea tides and 3 diurnal variations related to glacier surface melt the low frequency and tidal period variations are separated by low pass filtering and subtracting the filtered data from the original data the variations from melt runoff and tides have the same frequency range and are examined using harmonic analysis and multiple regression with the various forcing functions the high frequency portion of the ice speed signal is dominated by tidal influences and to a lesser extent by meltwater influences the low frequency portion of the signal is dominated by the effects of precipitation

age and tectonic implications of paleoproterozoic mafic dyke swarms for the origin of 2 2 ga enriched lithosphere beneath the ungava peninsula canada abstract mafic dyke swarms represent short lived magmatic events that carry important temporal and chemical constraints for the evolution of the lithospheric mantle five baddeleyite u pb isotopic analyses of paleoproterozoic mafic dyke swarms intruding the ungava peninsula yielded ages of 2508 6 2220 1 2212 3 2199 5 and 2149 3 ma these ages fall within the 2 5 2 0 ga period previously defined by five other swarms which together comprise a magmatic record of more than 500 ma the similar age composition and surface area of two 2 51 ga swarms along with the lack of coeval supracrustal rocks suggest they correspond to failed rifts an important magmatic hiatus of 280 ma follows but ends with the intrusion of numerous dykes between 2 23 and 2 20 ga in the thinnest lithosphere of the northern ungava peninsula these dykes exhibit chemical signatures that vary from enriched older 2229 2212 ma dykes nd t 4 to relatively depleted 2209 2199 ma voluminous younger dykes nd t 1 4 la yb ca 2 21 2 20 ga later dykes emplaced ca 2 17 ga within a rejuvenated paleoproterozoic lithosphere also have depleted chemical compositions and map the extent of rifting coeval with the emplacement of early basalts in the labrador trough dykes emplaced in the 2 15 2 00 ga period further to the south are proximal to coeval continental basalts with which they share enriched isotopic compositions nd t 1 5 to 7 and a positive correlation between la yb and zr nb la yb 4 10 zr nb 7 20 that suggest assimilation of an archean crustal component a progressive decrease in the nd t values of these magmas with decreasing age further implies increasing contamination until the archean lithosphere failed ca 2 0 ga and permitted the eruption of isotopically depleted basalts the ca 2 2 ga depleted northern dykes and the 2 1 1 9 ga povungnituk basalts of the cape smith foldbelt share a negative correlation between zr nb and la yb that is expected for the incorporation of an enriched lithospheric component this component is represented by the alkaline rocks comprised in the circum ungava supracrustal belts carbonatites lamprophyric lavas alkaline basalts and by the lac aigneau lamprophyric dykes 1941 3 ma intruding the ungava peninsula these alkaline magmas collectively have 2 2 2 1 ga depleted mantle nd model ages t dm similar to a 2 15 ga sm nd isochron defined by the basaltic rocks of the supracrustal belts although these nd t dm ages and isochron are 100 300 ma older than magmatic ages they are identical with the ca 2 2 ga mafic dykes of the ungava peninsula this time correlation along with the similar chemical signature of the northern dykes and younger povungnituk basalts suggest that the composition of younger lavas and alkaline magmas was influenced by an enriched component associated with the pervasive metasomatism of the lithosphere coeval with the emplacement of the many ca 2 2 ga dykes

ice stream retreat and ice shelf history in marguerite trough antarctic peninsula sedimentological and foraminiferal signatures the timing nature and causes of grounded ice sheet retreat following the last glacial maximum lgm in marguerite trough west antarctic peninsula and subsequent early holocene ice shelf decay are presented in this paper we use sedimentological foraminiferal geotechnical and accelerator mass spectrometer ams radiocarbon data from marine cores from the mid continental shelf together with previously published ams dates to establish a sedimentological and chronological model initial ice sheet retreat through the outer and mid shelf sectors of marguerite trough was under way by ca 14 ka b p was rapid and coincided with the sea level rise of meltwater pulse 1a an ice shelf formed during this retreat and fine grained laminated muds reflecting meltwater derived suspension settling and or tidal pumping were deposited during this time the ice sheet remained grounded on the inner shelf ice shelf breakup and retreat of the calving front from ca 13 2 to 12 5 ka b p was slow 100 m a 1 across the outer and mid shelf with calving bay conditions remaining for at least 3 5 ka we interpret this ice shelf decay to have been driven by an incursion of weddell sea transitional water onto the shelf in contrast grounding line and ice shelf retreat in the inner bay occurred from ca 9 3 ka b p and was driven by circumpolar warm deep water encroaching onto the continental shelf at this time the mid shelf was an open marine environment characterized by hemipelagic deposition these findings highlight the importance of oceanographic controls in the breakup of antarctic peninsula ice shelves during the holocene

rapid ice discharge from southeast greenland glaciers interferometric synthetic aperture radar insar observations of southeast greenland glaciers acquired by the earth remote sensing satellites ers 1 2 in 1996 were combined with ice sounding radar data collected in the late 1990s to estimate a total discharge of 46 3 km 3 ice per year between 62 n and 66 n which is significantly lower than a mass input of 29 3 km 3 ice per year calculated from a recent compilation of snow accumulation data further north helheim glacier discharges 23 1 km 3 yr vs 30 3 km 3 yr accumulation kangerdlugssuaq glacier discharges 29 2 km 3 yr vs 23 km 3 yr and daugaard jensen glacier discharges 10 5 0 6 km 3 yr vs 10 5 1 km 3 yr the mass balance of east greenland glaciers is therefore dominated by the negative mass balance of southeast greenland glaciers 17 4 km 3 yr equivalent to a sea level rise of 0 04 0 01 mm yr warmer and drier conditions cannot explain the imbalance which we attribute to longterm changes in ice dynamics copyright 2004 by the american geophysical union

calving processes and the dynamics of calving glaciers abstract calving of icebergs is an important component of mass loss from the polar ice sheets and glaciers in many parts of the world calving rates can increase dramatically in response to increases in velocity and or retreat of the glacier margin with important implications for sea level change despite their importance calving and related dynamic processes are poorly represented in the current generation of ice sheet models this is largely because understanding the calving problem involves several other long standing problems in glaciology combined with the difficulties and dangers of field data collection in this paper we systematically review different aspects of the calving problem and outline a new framework for representing calving processes in ice sheet models we define a hierarchy of calving processes to distinguish those that exert a fundamental control on the position of the ice margin from more localised processes responsible for individual calving events the first order control on calving is the strain rate arising from spatial variations in velocity particularly sliding speed which determines the location and depth of surface crevasses superimposed on this first order process are second order processes that can further erode the ice margin these include fracture propagation in response to local stress imbalances in the immediate vicinity of the glacier front undercutting of the glacier terminus by melting at or below the waterline and bending at the junction between grounded and buoyant parts of an ice tongue calving of projecting submerged ice feet can be regarded as a third order process because it is paced by first or second order calving above the waterline first order calving can be represented in glacier models using a calving criterion based on crevasse depth which is a function of longitudinal strain rate modelling changes in terminus position and calving rates thus reduces to the problem of determining the ice geometry and velocity distribution realistic solutions to the problem of modelling ice flow therefore depend critically on an appropriate choice of sliding law models that assume that basal velocities are controlled by basal drag can replicate much of the observed behaviour of calving glaciers with grounded termini but an important limitation is that they cannot be used to model floating glacier termini or ice shelves alternative sliding laws that parameterise drag from the glacier margins provide more flexible and robust ways of representing calving in ice sheet models such models can explain a remarkable range of observed phenomena within a simple unifying framework including downglacier increases in velocity and strain rates where basal and or lateral drag diminishes flow acceleration in response to thinning through time the tendency for glaciers to stabilise at pinning points in relatively shallow water or fjord narrowings the constraints on ice shelf stability and the contrasts in calving rates between tidewater and freshwater calving glaciers many unresolved issues remain however including the role played by the removal of backstress in the acceleration of retreating calving glaciers and the controls on melting at and below the waterline

basin evolution and unconformity related uranium mineralization the camie river u prospect paleoproterozoic otish basin quebec the paleoproterozoic otish basin quebec hosts several uranium prospects that until recently remained underexplored and poorly understood in this study the camie river u prospect which shows similar charac teristics to high grade unconformity related u deposits is the focus of an integrated basin analysis in the western otish basin conglomerate and sandstone of the indicator formation which were deposited in at least six depositional sequences were affected by insignificant early diagenetic compaction and cementation this allowed the for mation of regional peak diagenetic aquifers which became muscovite altered due to interaction with fluids having 18 o and 2h values similar to those of seawater influenced basinal brines at 250 c u mineralization at camie river occurred at 1721 20 ma based on a 207 pb 206 pb date obtained by laser ablation of uraninite which coincides with a phase of the otish gabbro intrusion that has been dated at ca 1730 ma the intrusive event promoted circulation of u bearing basinal brines triggering u mineralization at several locations in the western otish basin interaction of basinal brines with the otish gabbro produced coarse grained chlorite tourmaline and phengitic muscovite which decreased the fluid conducting capabilities of diagenetic aquifers and resulted in fault zone and fracture dominated fluid flow subsequent fluid alteration events produced limited u remobilization sulfides sudoite and siderite between ca 1670 and 1410 ma based on mineral paragenesis and 40 ar 39 ar dates of muscovite metamorphic fluids having high 18 o values and temperatures around 300 c accompanied 1 2 to 1 0 ga grenville orogene sis and subgreenschist grade metamorphism in the otish basin but were present at low water rock ratios at camie river and therefore produced little alteration post grenville uplift of the otish basin likely produced late low temperature alteration minerals that have been influenced by recent meteoric water suggesting that the fault zones and fractures the minerals occupy remain as preferential fluid flow pathways to the present day radiogenic pb and the characteristic trace elements mo w nb have also preferentially dispersed from the mineralization along fault zones fractures and depositional sequence boundaries and can be used to explore for camie river style u mineralization

short term flow dynamics of a retreating tidewater glacier leconte glacier alaska u s a an analysis of motion in the terminus region of leconte glacier alaska u s a delineates mechanisms that are important to tidewater glacier stability this glacier is undergoing rapid retreat since 1995 it has retreated 2 km and thinned 125 m at the present location of the terminus ice velocities in this region are quite high at the terminus they exceed 27 m d 1 our analysis reveals that fluctuations in speed and surface elevation are forced by ocean tides surface melt and precipitation the near terminus ice speed is 180 out of phase with the tide such that high tide corresponds to low speed smaller melt forced diurnal variations in speed are present throughout the lowermost 7 km speed ups in excess of 10 of the mean often occur after rainstorms as a result of increased basal water pressure and storage but the relation is not simple the velocity does not vary over the spring and summer seasons

an empirical oxygen and hydrogen isotope geothermometer for quartz tourmaline and tourmaline water abstract oxygen isotope equilibration temperatures of coexisting quartz muscovite illite chlorite and biotite from a variety of geologic environments have been used in conjunction with the 18o and d values of associated tourmaline to formulate empirical quartz tourmaline and tourmaline water isotope fractionation factors over temperatures from 200 to 600 c the fractionation factors determined using this method are as follows 1 1 1000 in quartz tourmaline 1 0 0 17 10 6 t 2 0 39 0 44 oxygen 2 2 1000 in tourmaline water 27 2 4 4 10 6 t 2 28 1 9 8 hydrogen 350 600 c the isotopic properties of tourmaline are nearly identical to those of muscovite and illite despite the significant differences in their crystal structures similarities in the oxygen and hydrogen isotope systematics of tourmalines and micas imply that the dominant controls on the isotopic properties of these minerals are the vibrational energies of the al si o and si o bonds however the bo3 groups in the tourmalines may have some effect on oxygen isotopic properties as there are minor differences between the 18o values of coexisting tourmalines and micas d values of coexisting tourmalines and micas are generally concordant to within 10 chemical compositions indicate that varying fe mg ratios in the tourmalines appear to have only a minor control on their d values there is a discontinuity in the 1000 in tourmaline water values for hydrogen at temperatures between 200 c and 300 c suggesting that the hydroxl groups in tourmaline are affected by hydrogen bonding and changes in the properties of water near its critical point as are some other hydrous minerals

the importance of pressurized subglacial water in separation and sliding at the glacier bed l effet de l eau sous glaciaire sous pression sur le processus de glissement est examine a partir d un parametre appele indice de decollement du lit qui exprime les contraintes perpendiculaires au lit et la pression d eau les donnees proviennent de trois glaciers de formes differentes une loi puissance du type de weertman avec un exposant voisin de 3 modifiee pour tenir compte de l effet de la pression des eaux sous glaciaires apparait comme etant la meilleure

subglacial discharge at tidewater glaciers revealed by seismic tremor subglacial discharge influences glacier basal motion and erodes and redeposits sediment at tidewater glacier termini discharge drives submarine terminus melting affects fjord circulation and is a central component of proglacial marine ecosystems however our present inability to track subglacial discharge and its variability significantly hinders our understanding of these processes here we report observations of hourly to seasonal variations in 1 5 10 hz seismic tremor that strongly correlate with subglacial discharge but not with basal motion weather or discrete icequakes our data demonstrate that vigorous discharge occurs from tidewater glaciers during summer in spite of fast basal motion that could limit the formation of subglacial conduits and then abates during winter furthermore tremor observations and a melt model demonstrate that drainage efficiency of tidewater glaciers evolves seasonally glaciohydraulic tremor provides a means by which to quantify subglacial discharge variations and offers a promising window into otherwise obscured glacierized environments

the distribution and flow characteristics of surge type glaciers in the canadian high arctic a systematic review of 1959 60 aerial photography and 1999 2000 landsat 7 imagery has identified 51 surge type polythermal glaciers in the canadian high arctic these were identified from the presence of features such as looped medial moraines intense folding visible at the surface rapid terminus advance heavy surface crevassing and high surface velocities these observations suggest that surging glaciers are much more common than previously believed in the canadian high arctic where only six surge type glaciers have previously been described of the 51 surge type glaciers identified in this study 15 were observed in the active phase in the 1959 60 and or 1999 2000 imagery the most dramatic advances have occurred on western axel heiberg island where iceberg good friday bay and airdrop glaciers have all advanced by 4 7 km between1959 and 1999 for glaciers with repeat landsat 7 coverage from 1999 and 2000 image correlation software was used to determine the magnitude and spatial distribution of surge velocities for example mittie glacier on manson icefield was moving at a rate of up to 1 kma over a distance of at least 25 km back from its terminus the terminus of this glacier has advanced by at least 4 km since 1959 and the glacier was observed to be heavily crevassed during overflights in april 2000 with clear signs of surface lowering of 10 25 m indicated by a strandline

neoglacial fluctuations and sedimentation of an iceberg calving glacier resolved with tree rings kenai fjords national park alaska abstract the mccarty fjord iceberg calving glacier and its land terminating tributaries have fluctuated with some asynchroneity during the past two millennia during advance mccarty glacier shed outwash along the fjord and into ice dammed tributaries inundating forests a radioacarbon framework has revealed at least two major late holocene glacial advances that occurred following a poorly documented expansion about 3600 bp these two later advances are resolved within this fjord with tree ring dating of in situ and transported tree trunks the first event was an early medieval expansion of the mccarty trunk glacier beyond midfjord about 596 a d this followed an interval of tree growth of at least 206 years tributary glaciers probably also advanced at this time however continuous tree growth occurred in the distal southern tributary valleys during this advance while northern tributaries were being dammed by the advancing trunk glacier the down valley extent of this expansion is thus constrained to a position within 12 km of the present contracted ice margin the tree ring refined chronology shows that a second mccarty ice expansion began in the 9th century and reached midfjord by 900 a d and continued to advance through the little ice age in contrast expansions of land terminating glaciers here began after 1300 a d in concert with mountain glaciers worldwide a log from a diamict cross dated with a living tree ring chronology shows that mccarty glacier was advancing within a kilometer of its little ice age maximum at 1790 a d since about 1905 a d dramatic ice retreat has uncovered more than 20 km of mccarty fjord

the tectonic significance of some basic dyke swarms in the canadian superior province with special reference to the geochemistry and paleomagnetism of the mistassini swarm quebec canada the mistassini dykes extend northwest from the mistassini embayment and comprise both tholeiitic and komatiitic suites they are probably 2000 ma old and yield two major paleomagnetic components one of these with a pole at 131 w 13 s is thought to be an overprint related to the elsonian disturbance 1400 1500 ma ago a very steeply down and reversed component may be primary and has a pole at 080 w 50 n these spacial chemical and age relationships between the mistassini molson marathon and payne river dyke swarms and the aphebian supracrustal fold belts on the perimeter of the superior province suggest a genetic relationship between the dyke swarms and the fold belts the supracrustal belts are evidence of the opening and closing of oceans and the dyke swarms are evidence of early stage failed arms related to these openings more rarely for example the payne river dykes early stage dyke swarms are developed and preserved parallel to the edges of newly developed spreading plate boundaries

variability in ice motion at a land terminating greenlandic outlet glacier the role of channelized and distributed drainage systems we use a combination of field observations and hydrological modelling to examine the mechanisms through which variability in meltwater input affects ice motion at a land terminating greenlandic outlet glacier we find a close agreement between horizontal ice velocity vertical ice velocity and modelled subglacial water pressure over the course of a melt season on this basis we argue that variation in horizontal and vertical ice velocity primarily reflects the displacement of basal ice during periods of cavity expansion and contraction a process itself driven by fluctuations in basal water pressure originating in subglacial channels this process is not captured by traditional sliding laws linking water pressure and basal velocity which may hinder the simulation of realistic diurnal to seasonal variability in ice velocity in coupled models of glacial hydrology and dynamics

mobilization and agglomeration of uraninite nanoparticles a nano mineralogical study of samples from the matoush uranium ore deposit the occurrence of uraninite nanoparticles in the alteration zones of uranium ore deposits suggests potential mobilization of u iv under reducing conditions which is important for understanding the mobility of uranium in contaminated sites and potential repositories for nuclear waste this study investigates the occurrence of uraninite nanoparticles in the outer alteration zone of the matoush uranium ore deposit quebec canada selected samples with finely disseminated uraninite from the outer alteration zone of the deposit are examined by x ray fluorescence spectroscopy scanning electron microscopy and high resolution transmission electron microscopy on specimens prepared using the focused ion beam milling technique uraninite nanoparticles occur as single particles in clusters and in larger aggregates in close association with the cr rich phases chromceladonite cr rich mica ideally kmgcr 3 si 4 o 10 oh 2 eskolaite ideally cr 2 3 o 3 bracewellite cr 3 ooh and an amorphous cr rich oxide matrix as well as with fluorapatite and galena nanoparticles on the surface and in the outer rim of single uraninite crystals indicate the growth of larger uraninite crystals via crystallization through particle attachment and oswald ripening the flow texture of the uraninite nanoparticles in the amorphous cr rich oxide matrix their aggregation on the surface of nanocrystals of bracewellite the absence of products of a redox reaction involving u vi and fe ii and the occurrence of amorphous fe depleted alteration layers between uraninite and eskolaite and uraninite and cr rich mica indicate that the uraninite nanoparticles have been mobilized under reducing conditions leaching of fe 2 from the alteration layer at low t amorphous character of the alteration layer after the main mineralization event from the center of the mineralization to the outer parts of the matoush dike complex these results indicate that fluids can mobilize u iv under reducing conditions in the form of uraninite nanoparticles albeit over limited distances the potential mobilization of these nanoparticles may also explain the occurrence of proximal mineralized zones in u ore deposits that lack common products resulting from the reduction of u vi by fe 2 e g hematite and other fe 3 phases

formation and evolution of the centennial unconformity related uranium deposit in the south central athabasca basin canada the centennial u deposit is situated in the south central athabasca basin canada and straddles the unconformity between early paleoproterozoic to archean metasedimentary and metavolcanic rocks and granitoids and the clastic sediments of the paleoproterozoic athabasca group although it has most characteristics of an unconformity related uranium deposit the centennial deposit is atypical in that it is not directly associated with an electromagnetic conductor there is a paucity of graphite in the basement or with a major reverse fault zone it is distal from a major fluid conduit ca 300 to 400 m from the dufferin lake fault has low ni cu co zn and pb contents and contains an unusually large amount up to 5 of secondary uranyl minerals additionally a network of diabase dikes and sills is observed at centennial seemingly intruding the main u mineralization of massive uraninite based on the relatively sharp contacts between the diabase dike and the high grade u mineralization the pre u alteration assemblage at centennial includes kaolinite illite and sudoite which have been formed by fluids with isotopic and chemical compositions that are comparable with those from other sandstone hosted unconformity type u deposits in the athabasca basin pre u illite related fluids have 18o of ca 3 and d of ca 40 whereas pre u chlorite related fluids have 18o between 1 7 and 4 3 and d between 18 and 1 laser ablation inductively coupled plasma mass spectrometry la icp ms u pb dating of the various u phases indicates that initial mineralization represented by disseminated uraninite found directly to the north northeast of the centennial deposit occurred at ca 1 6 ga the main u mineralization represented by massive and strongly altered uraninite followed at an unknown time a minor 5 unaltered uraninite formed from the local remobilization of the main massive uraninite at ca 380 ma the main uranyl mineral uranophane formed last at ca 2 ma the recurrence of local u remobilization might have been facilitated by the persisting high permeability of the sandstones in the area due to the nearby dufferin lake fault and to the emplacement of the diabase dikes the usefulness of pb isotopes for exploration is demonstrated at the centennial deposit with strongly radiogenic pb isotope signatures close to the deposit and a common pb signature observed at a distance of a few km from the deposit

mass balance in the glacier bay area of alaska usa and british columbia canada 1995 2011 using airborne laser altimetry the glacier bay region of southeast alaska usa and british columbia canada has undergone major glacier retreat since the little ice age lia we used airborne laser altimetry elevation data acquired between 1995 and 2011 to estimate the mass loss of the glacier bay region over four time periods 1995 2000 2000 05 2005 09 2009 11 for each glacier we extrapolated from center line profiles to the entire glacier to estimate glacier wide mass balance and then averaged these results over the entire region using three difference methods normalized elevation area weighted method and simple average we found that there was large interannual variability of the mass loss since 1995 compared with the long term post lia average for the full period 1995 2011 the average mass loss was 3 93 0 89 gt a 1 0 6 0 1 m w e a 1 compared with 17 8 gt a 1 for the post lia 1770 1948 rate our mass loss rate is consistent with grace gravity signal changes for the 2003 10 period our results also show that there is a lower bias due to center line profiling than was previously found by a digital elevation model difference method

the transition from dyke to sill in the otish mountains quebec relations to host rock characteristics the otish gabbro sills intrude aphebian clastic rocks lying uncanformably on the archean rocks of the superior province close to its juncture with the grenville province the sills are undated but by inference may be ca 1750 ma two dyke swarms are known in the vicinity the 1950 ma northwest trending mistassini dykes and a northeast trending swarm of unknown age extending 600 km from senneterre to the otish mountains and possibly another 300 km to the northeast the trends of feeder dykes to the otish sills are physically compatible with the dominant northeast dykes which are therefore considered to be the feeders and should be called the otish dykes the otish sills appear to be a unique occurrence along the 900 km dyke trend possibly but not entirely because of the chances of preservation the general form of the otish sill complex is a triangle bounded on the north by the east west lip of the sedimentary basin on the southwest by a northwest trending otish feeder dyke and on the southeast by the

vanadio oxy chromium dravite nav3 cr4mg2 si6o18 bo3 3 oh 3o a new mineral species of the tourmaline supergroup vanadio oxy chromium dravite nav3 cr4mg2 si6o18 bo3 3 oh 3o a new mineral species of the tourmaline supergroup

where glaciers meet water subaqueous melt and its relevance to glaciers in various settings glacier change is ubiquitous but the fastest and largest magnitude changes occur in glaciers that terminate in water this includes the most rapidly retreating glaciers and also several advancing ones often in similar regional climate settings furthermore water terminating glaciers show a large range in morphology particularly when ice flow into ocean water is compared to that into freshwater lakes all water terminating glaciers share the ability to lose significant volume of ice at the front either through mechanical calving or direct melt from the water in contact here we present a review of the subaqueous melt process we discuss the relevant physics and show how different physical settings can lead to different glacial responses we find that subaqueous melt can be an important trigger for glacier change it can explain many of the morphological differences such as the existence or absence of floating tongues subaqueous melting is influenced by glacial runoff which is largely a function of atmospheric conditions this shows a tight connection between atmosphere oceans and lakes and glaciers subaqueous melt rates even if shown to be large should always be discussed in the context of ice supply to the glacier front to assess its overall relevance we find that melt is often relevant to explain seasonal evolution can be instrumental in shifting a glacier into a different dynamical regime and often forms a large part of a glacier s mass loss on the other hand in some cases melt is a small component of mass loss and does not significantly affect glacier response

ice front change of marine terminating outlet glaciers in northwest and southeast greenland during the 21st century the increasingly negative mass balance of the greenland ice sheet gris over the last 25 years has been associated with enhanced surface melt and increased ice loss from marine terminating outlet glaciers accelerated retreat during 2000 2010 was concentrated in the southeast and northwest sectors of the ice sheet however there was considerable spatial and temporal variability in the timing and magnitude of retreat both within and between these regions this behaviour has yet to be quantified and compared for all glaciers in both regions furthermore it is unclear whether retreat has continued after 2010 in the northwest and whether the documented slowdown in the southeast post 2005 has been sustained here we compare spatial and temporal patterns of frontal change in the northwest and southeast gris for the period 2000 2015 our results show near ubiquitous retreat of outlet glaciers across both regions for the study period however the timing and magnitude of inter annual frontal position change is largely asynchronous we also find that since 2010 there is continued terminus retreat in the northwest which contrasts with considerable inter annual variability in the southeast analysis of the role of glacier specific factors demonstrates that fjord and bed geometry are important controls on the timing and magnitude of glacier retreat

a chlorite solid solution geothermometer the los azufres mexico geothermal system chlorite constitutes a major hydrothermal alteration product of metamorphism of andesites in the active geothermal system of los azufres mexico electron microprobe analyses performed on a set of crystals from each sample show wide variations in composition correlation coefficients among chemical constituents were calculated it is shown that the tetrahedral charge is positively correlated with the octahedral vacancy and negatively with the iron content and there is almost no correlation with the octahedral aluminium and magnesium content a procedure is proposed to select end members and substitution vectors and to give a general formula for these chlorites

calculation of oxygen isotope fractionation in hydroxyl bearing silicates abstract the modified increment method has been applied to the calculation of oxygen isotope fractionation factors for hydroxyl bearing silicate minerals the order of 18o enrichment obtained in common rock forming minerals is pyrophyllite kaolinite tourmaline talc prehnite topaz illite phengite lepidolite muscovite staurolite epidote glaucophane serpentine chlorite tremolite hornblende phlogopite biotite humite norbergite ilvaite hydroxyl bearing silicates are enriched in 18o relative to hydroxyl groups but depleted in 18o relative to anhydrous counterparts three sets of self consistent fractionation factors between quartz and the hydroxyl bearing silicate minerals between calcite and the silicate minerals and between the silicate minerals and water have been calculated for a temperature range of 0 1200 c the fractionation factors calculated for mineral pairs are applicable to isotopic geothermometry in igneous metamorphic and sedimentary petrology they can be used as a test of isotopic equilibrium or disequilibrium in natural mineral assemblages over all temperature ranges of geological interest the difference in oxygen isotope composition between the hydroxyl bearing mineral and the oh group is quantitatively demonstrated to be temperature dependent and therefore can be used as a single mineral geothermometer

tidal flexure of jakobshavns glacier west greenland jakobshavns glacier a floating outlet glacier on the west greenland coast was surveyed during july 1976 the vertical displacements of targets along two profiles perpendicular to the fjord wall bounding the north margin of the glacier were analyzed to determine the effect of flexure caused by tidal oscillations within the fjord an analysis based on the assumption that vertical displacements of the glacier reflected pure elastic bending yielded the conclusion that the effective thickness of the ice i e the thickness which remained unaffected by surface and basal cracking and which behaved as a continuum was 160 m 2 6 km upglacier from the calving front and 110 m 0 6 km from the calving front an analysis based on the more realistic assumption that observed bending reflected elastic and viscoplastic deformation yielded the conclusion that the average effective thickness of the ice was 316 74 m 40 of the estimated 800 m total thickness 2 6 km from the calving front and 160 48 m 21 of the estimated 750 m total 0 6 km from the calving front a constitutive relationship appropriate for hard glide during flexure was used

the jakobshanvs effect the jakobshavns effect may have been a significant factor in hastening the collapse of palaeo ice sheets with the advent of climatic warming after 18 000 years ago and may precipitate partial collapse of the present day greenland and antarctic ice sheets following co2 induced climatic warming in the decades ahead the jakobshavns effect is observed today on jakobshavns glacier which is located at 69 10 n on the west coast of greenland the jakobshavns effect is a group of positive feedback mechanisms which allow jakobshavns glacier to literally pull ice out of the greenland ice sheet at a rate exceeding 7 km a across a floating terminus 800 m thick and 6 km wide the pulling power results from an imbalance of horizontal hydrostatic forces in ice and water columns at the grounding line of the floating terminus positive feedback mechanisms that sustain the rapid ice discharge rate are ubiquitous surface crevassing high summer rates of surface melting extending creep flow progressive basal uncoupling progressive lateral uncoupling and rapid iceberg calving

ice front and flow speed variations of marine terminating outlet glaciers along the coast of prudhoe land northwestern greenland satellite images were analyzed to measure the frontal positions and ice speeds of 19 marine terminating outlet glaciers along the coast of prudhoe land northwestern greenland from 1987 to 2014 all the studied glaciers retreated over the study period at a rate of between 12 and 200 m a 1 with a median mean retreat rate of 30 40 m a 1 the glacier retreat began in the year 2000 which coincided with an increase in summer mean air temperature from 1 4 to 5 5 c between 1996 and 2000 in this region ice speed near the front of the studied glaciers ranged between 20 and 1740 m a 1 in 2014 and many of them accelerated in the early 2000s in general the faster retreat was observed at the glaciers that experienced greater acceleration as represented by tracy glacier which experienced a retreat of 200 m a 1 and a velocity increase of 930 m a 1 during the study period a possible interpretation of this observation is that flow acceleration induced dynamic thinning near the termini resulting in enhanced calving and rapid retreat of the studied glaciers we hypothesize that atmospheric warming conditions in the late 1990s triggered glacier retreat in northwestern greenland since 2000

late quaternary glacial and deglacial history of eastern vestfirdir iceland using cosmogenic isotope 36cl exposure ages and marine cores the late glacial and deglacial history of vestfirdir nw iceland is interpreted from terrestrial field based evidence and compared with marine cores and seismic studies understanding the timing of deglaciation is complicated by a lack of dateable organic material on land uncertainties associated with interpretation of diamictons and ambiguities in radiocarbon dating new 36cl exposure ages of boulders and bedrock surfaces suggest that at least part of the coastal uplands were ice free by approximately 20 ka deglaciation of the valleys followed boulders from the crest of an end moraine in the sela river valley have a mean 36cl age of 14 6 ka 0 8 ka n 4 and the outermost moraine in the valley adjacent to kaldalonjokull has a mean 36cl age of 11 7 ka 0 9 ka n 2 tephrochronology provides a link between the terrestrial and marine sequences around vestfirdir the vedde ash ca 12 k cal yr bp is present in some offshore cores but it is absent from terrestrial sites suggesting that its distribution provides a constraint on ice extent during the younger dryas the saksunarvatn ash 10 2 0 6 k cal yr bp confirmed by geochemical analyses and radiocarbon dating is present in at least three terrestrial locations on eastern vestfirdir and in many cores from the fjords and shelf which constrains early holocene ice extent copyright 2006 john wiley sons ltd

simulation of the evolution of breidamerkurjokull in the late holocene 1 we have simulated the advance and retreat of breidamerkurjokull a tidewater glacier in iceland by means of a one dimensional numerical ice flow model the calculations were done with two different schemes for iceberg calving the flotation model and the water depth model the model simulates the glacier history by an advance into a lake filled by unlithified sediments without the occurrence of calving followed by a retreat with calving into the excavated lake the results indicate that the flotation model is not capable of producing the observed glacier retreat into deep water well whereas the water depth model provides a glacier evolution similar to the observed retreat the water depth model predicts that breidamerkurjokull will retreat out of the lake after approximately 100 years under the present climatic conditions

widespread acceleration of tidewater glaciers on the antarctic peninsula over the last half century the antarctic peninsula ap has been among the most rapidly warming regions on earth this has led to increased summer snowmelt loss of ice shelves and retreat of 87 of marine and tidewater glacier fronts tidewater glacier flow is sensitive to changes in basal water supply and to thinning of the terminus and faster flow leads directly to sea level rise the flow rates of most ap tidewater glaciers have never been measured however and hence their dynamic response to the recent changes is unknown we present repeated flow rate measurements from over 300 glaciers on the ap west coast through nine summers from 1992 to 2005 we show that the flow rate increased by similar to 12 on average and that this trend is greater than the seasonal variability in flow rate we attribute this widespread acceleration trend not to meltwater enhanced lubrication or increased snowfall but to a dynamic response to frontal thinning we estimate that as a result the annual sea level contribution from this region has increased by 0 047 0 011 mm between 1993 and 2003 this contribution together with previous studies that assessed increased runoff from the area and acceleration of glaciers resulting from the removal of ice shelves implies a combined ap contribution of 0 16 0 06 mm yr 1 this is comparable to the contribution from alaskan glaciers and combined with estimated mass loss from west antarctica is probably large enough to outweigh mass gains in east antarctica and to make the total antarctic sea level contribution positive

rising ela and expanding proglacial lakes indicate impending rapid retreat of brady glacier alaska brady glacier is a large alaskan tidewater glacier that is beginning a period of substantial retreat examination of 27 landsat and modis images from the period 2003 to 2011 indicates that brady glacier has a mean equilibrium line altitude ela of 745 m and accumulation area ratio aar of 0 40 the zero balance ela is 600 m and equilibrium aar 0 65 the negative mass balance associated with the increased ela has triggered thinning of 20 100 m over most of the glacier below the ela from 1948 to 2010 the thinning has caused substantial retreat of seven calving distributary termini of the glacier thinning and retreat have led to an increase in the width of and water depth at the calving fronts in contrast the main terminus has undergone only minor retreat since 1948 in 2010 several small proglacial lakes were evident at the terminus by 2000 a permanent outlet river issuing from trick lake had developed along the western glacier margin initial lake development at the terminus combined with continued mass losses will lead to expansion of the lakes at the main terminus and retreat by calving the glacier bed is likely below sea level along the main axis of brady glacier to the glacier divide retreat of the main terminus in the lake will likely lead to a rapid calving retreat similar to bear excelsior norris portage and yakutat glaciers copyright 2013 john wiley sons ltd

geochemistry of uraniferous bitumen in the southwest athabasca basin saskatchewan canada the sediment hosted unconformity type southwest athabasca uranium mineralization in northern saskatchewan canada contains uraniferous bitumen as observed elsewhere in the athabasca basin uraninite is present either as micron sized grains dispersed in bitumen uraniferous bitumen or as larger grains situated in the pore space between bitumen globules the spatial and textural relationships between uraninite and bitumen suggest that they were co precipitated la icp ms u pb dating of uraniferous bitumen yielded an age of 1575 53 ma similar to that of other unconformity type uranium mineralization in the athabasca basin indicating that the bitumen was formed early in the history of the basin nitrogen carbon and sulfur isotope analyses of uraniferous bitumen indicate that its source material was probably kerogen produced by cyanobacteria in a clastic environment

formation of the enigmatic matoush uranium deposit in the paleoprotozoic otish basin quebec canada the matoush uranium deposit is situated in the paleoproterozoic otish basin northern quebec canada and is hosted by the indicator formation sandstones its sheet like ore bodies are closely associated with the steeply dipping matoush fracture which hosts mafic dykes and minor quartz feldspar tourmaline pegmatites regional diagenesis involving oxidizing basinal fluids 2h 15 18o 8 produced mostly illite and possibly leached u from accessory phases in the indicator formation sandstones the bimodal matoush dyke intruded the indicator formation along the matoush fracture and the related metasomatism produced cr rich dravite and muscovite in both the dyke and the proximal sandstones uraninite formed when u6 in the basinal brine was reduced to u4 in contact with the mafic dyke and by fe2 in cr dravite and cr muscovite and precipitated together with eskolaite and hematite because of its unique characteristics the matoush deposit cannot be easily classified within the generally accepted classification of uranium deposits two of its main characteristics unusual reduction mechanism structural control do not correspond to the sandstone hosted group of deposits unconformity type tabular roll front in spite of uranium being derived from the otish group sandstones

critical geochemical and mineralogical factors for the formation of unconformity related uranium deposits comparison between barren and mineralized systems in the athabasca basin canada the spring point barren alteration system and the maurice bay subeconomic uranium deposit situated on the northwest rim of the athabasca basin northern saskatchewan are hosted by the sandstones and conglomerates of the fair point formation of the athabasca group macroscopic observations indicate two different styles of alteration for the two systems chlorite dominated partly reduced alteration at spring point and illite dominated strongly oxidized alteration at maurice bay the paragenetic sequences developed for each area are similar but the crystal chemistry of the alteration minerals differs markedly indicating that the alteration fluids at spring point were richer in mg and ca than at maurice bay this is consistent with a predominantly basement origin for the former stable isotope analyses of clay alteration minerals indicate that in particular the chlorite related fluids from spring point have a basement signature 18 o 3 5 and d 13 whereas chlorite from maurice bay is more consistent with a mixture of basement and basinal fluids 18 o 5 2 and d 28 the absence of uranium transporting basinal fluids at the critical time when reducing basement fluids were producing chlorite alteration is likely the single most important cause for the lack of uranium mineralization at spring point

fast tidewater glaciers some iceberg calving outlet glaciers flow continuously at speeds normally associated with surging glaciers arid exhibit dramatic instability scenarios related to those suggested for marine ice sheets no temperate tidewater glaciers are known to have floating termini but many polar and subpolar tidewater glaciers do the fast flow of temperate calving glaciers is almost entirely due to basal sliding and appears to be a function of the effective pressure on the bed which may approach zero and the longitudinal back stress on the terminus the terminus boundary condition the calving relation is imperfectly known yet is vital to the dynamics of these glaciers calving relations for grounded tidewater glaciers have been suggested on empirical grounds but have not been rigorously tested the calving relations for floating termini are virtually unknown this together with the imperfect understanding of basal sliding inhibits confidence in our understanding of the stability of these glaciers columbia glacier alaska is an instructive example because observations have been made on the major changes in its geometry calving rate and dynamics that have occurred in less than 10 years the calving flux has increased more rapidly than the glacier flux causing thinning and retreat as a result the ice velocity has increased markedly the short term velocity changes relate to changes in back pressure ice recession tidal changes and the flux of water injected to the bed these results have relevance to the mechanisms of basal sliding glacier surges and the stability of marine ice streams

age and origin of uranium mineralization in the camie river deposit otish basin quebec canada abstract the camie river uranium deposit is located in the southeastern part of the paleoproterozoic otish basin quebec the uranium mineralization consists of disseminated and vein uraninite and brannerite precipitated close to the unconformity between paleoproterozoic fluviatile pervasively altered sandstones and conglomerates of the matoush formation and the underlying sulfide bearing graphitic schists of the archean hippocampe greenstone belt diagenetic orange pink feldspathic alteration of the matoush formation consists of authigenic albite cement partly replaced by later orthoclase cement with the na2o content of clastic rocks increasing with depth basin wide green muscovite alteration affected both the matoush formation and the top of the basement tichegami group uraninite with minor brannerite is mainly hosted by subvertical reverse faults in basement graphitic metapelites sulfides and overlying sandstones and conglomerates uranium mineralization is associated with chlorite veins and alteration with temperatures near 320 c that are paragenetically late relative to the diagenetic feldspathic and muscovite alterations re os geochronology of molybdenite intergrown with uraninite yields an age of 1724 0 4 9 ma whereas uraninite yields an identical although slightly discordant 1724 29 ma sims u pb age uraninite has high concentrations in ree with flat ree spectra resembling those of uraninite formed from metamorphic fluids rather than the bell shaped patterns typical of unconformity related uraninite paragenesis and geochronology therefore show that the uranium mineralization formed approximately 440 million years after intrusion of the otish gabbro dykes and sills at 2176 ma which constrains the minimum age for the sedimentary host rocks the post diagenetic stage of uraninite after feldspathic and muscovite alterations the paragenetic sequence and the brannerite uraninite assemblage the relatively high temperature for the mineralizing event 320 c following the diagenetic na and k dominated alteration lack of evidence for brines typical of unconformity related u deposits the older age of the otish basin compared to worldwide basins hosting unconformity related uranium deposits the large age difference between basin fill and mineralization the older age of the uranium oxide compared to ages for worldwide unconformity related u deposits and the flat ree spectra of uraninite do not support the previous interpretation that the camie river deposit is an unconformity associated uranium deposit rather the evidence is more consistent with a paleoproterozoic higher temperature hydrothermal event at 1724 ma whose origin remains speculative

application of 3d laser scanner optical transducers and digital image processing techniques in physical modelling of mining related strata movement a physical testing protocol for modelling mining related problems has been presented a new method for monitoring fracture propagation pattern has been introduced laser based and optical devices have been used for physical modelling of subsidence multiple seam subsidence has been measured by photogrammetry dic analysis optoncdt and 3d tls

the sandstone hosted beverley uranium deposit lake frome basin south australia mineralogy geochemistry and a time constrained model for its genesis the sandstone hosted beverley uranium deposit is located in terrestrial sediments in the lake frome basin in the north flinders ranges south australia the deposit is 13 km from the u rich mesoproterozoic basement of the mount painter inlier which is being uplifted 100 to 200 m above the basin by neotectonic activity that probably initiated in the early pliocene the mineralization was deposited mainly in organic matter poor miocene lacustrine sands and partly in the underlying reductive strata comprising organic matter rich clays and silts the bulk of the mineralization consists of coffinite and or uraninite nodules growing around co rich pyrite with an s isotope composition 34 s 1 0 0 3 suggestive of an early diagenetic lacustrine origin in contrast authigenic sulfides in the bulk of the sediments have a negative s isotope signature 34 s ranges from 26 2 to 35 5 indicative of an origin via bacterially mediated sulfate reduction minor amounts of zn bearing native copper and native lead also support the presence of specific reducing microenvironments in the ore zone small amounts of carnotite are associated with the coffinite ore and also occur beneath a paleosoil horizon overlying the uranium deposit provenance studies suggest that the host miocene sediments were derived from the reworking of early cretaceous glacial or glaciolacustrine sediments ultimately derived from paleozoic terranes in eastern australia in contrast the overlying pliocene strata were in part derived from the mesoproterozoic basement inlier mass balance and geochemical data confirm that granites of the mount painter domain were the ultimate source of u and ree at beverley u pb dating of coffinite and carnotite suggest that the u mineralization is pliocene 6 7 3 4 ma the suitability of the beverley deposit for efficient mining via in situ leaching and hence its economic value are determined by the nature of the hosting sand unit which provides the permeability and low reactivity required for high fluid flow and low chemical consumption these favorable sedimentologic and geometrical features result from a complex conjunction of factors including deposition in lacustrine shore environment reworking of angular sands of glacial origin deep pliocene weathering and proximity to an active fault exposing extremely u rich rocks

a model for tidewater glacier undercutting by submarine melting dynamic change at the marine terminating margins of the greenland ice sheet may be initiated by the ocean particularly where subglacial runoff drives vigorous ice marginal plumes and rapid submarine melting here we model submarine melt driven undercutting of tidewater glacier termini simulating a process which is key to understanding ice ocean coupling where runoff emerges from broad subglacial channels we find that undercutting has only a weak impact on local submarine melt rate but increases total ablation by submarine melting due to the larger submerged ice surface area thus the impact of melting is determined not only by the melt rate magnitude but also by the slope of the ice ocean interface we suggest that the most severe undercutting occurs at the maximum height in the fjord reached by the plume likely promoting calving of ice above it remains unclear however whether undercutting proceeds sufficiently rapidly to influence calving at greenland s fastest flowing glaciers

holocene history of hubbard glacier in yakutat bay and russell fiord southern alaska stratigraphic and geomorphic data defined by radiocarbon ages tree ring dates and historical observations provide evidence of three major holocene expansions of hubbard glacier early in each advance the hubbard glacier margin blocked russell fiord to create russell lake raising base level and causing stream beds and fan deltas throughout the russell drainage basin to aggrade each hubbard glacier expansion continued with an ice lobe advancing through disenchantment and yakutat bays in the west and an eastern lobe advancing into russell fiord the earlier two holocene expansions were respectively under way at 7690 and 5600 calibrated yr b p and each advance culminated more than 1 k y later the late holocene advance was under way by 3100 yr ago and reached 13 km farther south in russell fiord than the preceding two expansions late holocene deglaciation of yakutat and disenchantment bays was complete before a d 1791 nunatak glacier flowing from neves east of russell fiord became the primary ice source to the russell fiord lobe at or before this date ice retreat from the southern end of russell fiord began in the late eighteenth century and the penultimate russell lake drained ca a d 1860 the relatively slow advances and more rapid retreats of hubbard glacier are consistent with the model of the iceberg calving glacier cycle hubbard glacier is currently advancing and will likely reestablish russell lake in the near future affecting local fisheries however glacier lobes are unlikely to reach the area of the town of yakutat built on late holocene glacial deposits in the next 1 k y