migration of brines in the basement rocks of the athabasca basin through microfracture networks p patch u deposit canada abstract the unconformity type uranium deposits of the athabasca basin saskatchewan canada are hosted near the unconformity between a middle proterozoic intracratonic sedimentary basin and an archean to paleo proterozoic metamorphic and plutonic basement these deposits which are considered to be the richest u deposits in the world are the result of massive basinal fluid migrations in the basement rocks this study shows that basinal brines have strongly penetrated into the basement not only through faults and major pathways but also by way of dense networks of microfractures which favoured the percolation of fluids down to considerable depths hundred metres below the unconformity and their chemical modification salinity increase by interaction with basement lithologies these processes are one of the major causes of uranium mobility within the basement rocks and the formation of unconformity type mineralization microfracture networks which opened during the basinal brine stage ca 1600 1400 ma are interpreted as sets of mode i cracks corresponding to a specific stage of deformation and occur as fluid inclusion planes after healing the stress field at that stage 1 n130 150 e subvertical partly reopened the earlier microcrack networks 1 n80 110 e and n130 150 e subvertical issued from the trans hudson orogeny late retrograde metamorphic stage ca 1795 1720 ma the circulation of the two types of fluids carbonic and brines occurs thus at two distinct events trans hudson orogeny late retrograde metamorphism for carbonic fluids and maximal burial diagenesis for brines but the same main microfissure geometry was used by the fluids this demonstrates the existence of a similar stress field direction acting before and after the basin formation moreover the brine circulations in the basement acted in a wider volume than the clay rich alteration halo surrounding the u ores generally considered as the main envelope of fluid percolation outside the fault systems the data on the chemistry of the fluids and on the geometry of their migration at various scales emphasise the fundamental role of the basement in the chemical evolution of highly saline brines linked to unconformity related uranium mineralization in the athabasca basin

age constraints on the paleoproterozoic tectonometamorphic history of the committee bay region western churchill province canada evidence from zircon and in situ monazite shrimp geochronology in situ u pb sensitive high resolution ion microprobe shrimp analyses of monazite from upper amphibolite facies paragneiss of the committee bay supracrustal belt central rae domain canada reveal three age populations ca 2350 1850 and 1780 ma the ca 1850 ma age also corresponds to growth of low th u zircon as indicated by u pb shrimp analyses of zircon separates from melanosome and leucosome the contextual advantage of the in situ monazite analysis allows evaluation of the geochronological data in terms of the regional structural and metamorphic evolution the region is dominated by a northeast striking s2 s1 fabric axial planar to tight northwest vergent f2 folds early garnet is enveloped by this biotite sillimanite cordierite s2 fabric garneti hosts ca 1850 ma monazite inclusions with ca 2350 ma cores placing a maximum age on garneti growth and s2 development d2 metamorphic conditions progressed through 3 5 kbar 1 kbar 100 mpa and 600 c to near peak conditions of 5 kbar and 675 c a minimum age for s2 is provided by unstrained ca 1820 ma monzogranite that locally and regionally truncates s2 dominantly ca 1780 ma matrix monazite is interpreted to date post s2 garnetii and cordierite which record 5 kbar and 675 c these data indicate that the committee bay region experienced penetrative d2 tectonometamorphism at ca 1850 1820 ma with a subsequent static overprint the absence of a ca 1 85 ga plutonic suite in the region suggests that low pressure metamorphism was a response to thick skinned crustal thickening initiated at ca 1870 ma the new data highlight the importance of paleoproterozoic reworking of the central rae domain in the hinterland of the trans hudson orogen

noble gases ar kr xe and halogens cl br i in fluid inclusions from the athabasca basin canada implications for unconformity related u deposits the formation of unconformity related uranium deposits in the proterozoic athabasca basin canada involved basin scale circulation of u bearing brines during high grade diagenesis 150 200 degrees c at similar to 1 6 1 5 ga the uo2 ores occur both sides of the unconformity and are associated with extensive brecciation and illite sudoite dravite alteration quartz and dolomite cementing veins and breccias are associated with alteration and mineralisation and contain a fairly uniform population of fluid inclusions characterised by variable na ca and salinities of 25 35 wt salts and high u concentrations of up to 600 ppm u in order to further constrain the origin of these u rich brines we analysed the naturally occurring isotopes of ar kr and xe together with halogens cl br and i k ca and u in irradiated quartz and dolomite samples containing representative fluid inclusions this was achieved by the noble gas method for halogen measurement extended ar 40 ar 39 methodology using a combination of noble gas extraction techniques the fluid inclusions opened by crushing quartz and dolomite samples in vacuum have similar molar br cl ratios of 5 8 x 10 3 to 10 4 x 10 3 and molar i cl ratios of 1 8 x 10 6 to 8 2 x 10 6 these compositions lie over the top half of the modern day seawater evaporation trajectory consistent with the fluids deriving the bulk of their salinity by subaerial evaporation of seawater beyond the point of halite saturation the i cl ratios are much lower than is typical of fluids that have interacted with i rich organic matter present in many sedimentary basins or fluid inclusions found in mississippi valley type mvt pb zn ore deposits this is significant because provided the u rich fluid inclusions are representative of the ore stage fluids the low i cl ratios of the fluid inclusions do not favour fluid interaction with organic matter or hydrocarbons as a major process for localising u mineralisation the majority of samples contain fluid inclusions with age corrected ar 40 ar 36 of between the modern atmospheric value of similar to 300 and 450 these values are considered representative of the fluid s initial composition and are typical of upper crustal sedimentary formation waters the fluid inclusions nonradiogenic kr 84 ar 36 and xe 129 ar 36 ratios are slightly enriched in xe 129 relative to air and the fluid inclusions are estimated to contain 0 5 17 3 x 10 10 mol g 1 ar 36 which is up to twenty times the ar 36 concentration of air saturated seawater the data are interpreted to reflect acquisition of atmospheric noble gases from sedimentary rocks and suggest acquisition of radiogenic ar 40 within k rich basement rocks that would have been an important source of excess ar 40 was limited by temperatures of less than 200 degrees c taken together the halogen and noble gas composition of the u bearing fluid inclusions are strongly controlled by subaerial evaporation and subsequent interaction with sedimentary rocks showing that low temperature evaporitic brines dominated the mineralising system mineralisation is unlikely to have been triggered by fluid interaction with organic matter or mixing with voluminous basement derived fluids however the data do not completely preclude a role for volumetrically minor fluid or gas phases introduced by deep seated basement faults preferentially located at the sites of mineralisation

physics and seismic modeling for monitoring co2 storage we present a new petro elastical and numerical simulation methodology to compute synthetic seismograms for reservoirs subject to co2 sequestration the petro elastical equations model the seismic properties of reservoir rocks saturated with co2 methane oil and brine the gas properties are obtained from the van der waals equation and we take into account the absorption of gas by oil and brine as a function of the in situ pore pressure and temperature the dry rock bulk and shear moduli can be obtained either by calibration from real data or by using rock physics models based on the hertz mindlin and hashin shtrikman theories mesoscopic attenuation due to fluids effects is quantified by using white s model of patchy saturation and the wet rock velocities are calculated with gassmann equations by using an effective fluid modulus to describe the velocities predicted by white s model the simulations are performed with a poro viscoelastic modeling code based on biot s theory where viscoelasticity is described by generalizing the solid fluid coupling modulus to a relaxation function using the pseudo spectral method which allows general material variability a complete and accurate characterization of the reservoir can be obtained a simulation that considers the utsira sand of the north sea illustrates the methodology

wave velocities and attenuation of shaley sandstones as a function of pore pressure and partial saturation we obtain the wave velocities and quality factors of clay bearing sandstones as a function of pore pressure frequency and partial saturation the model is based on a biot type three phase theory that considers the coexistence of two solids sand grains and clay particles and a fluid mixture additional attenuation is described with the constant q model and viscodynamic functions to model the high frequency behaviour we apply a uniform gas fluid mixing law that satisfies the wood and voigt averages at low and high frequencies respectively pressure effects are accounted for by using an effective stress law by fitting a permeability model of the kozeny carman type to core data the model is able to predict wave velocity and attenuation from seismic to ultrasonic frequencies including the effects of partial saturation testing of the model with laboratory data shows good agreement between predictions and measurements

paleoproterozoic basement cover infolding and thick skinned thrusting in hearne domain nunavut canada intracratonic response to trans hudson orogen enveloped by orogenic belts during the assembly of laurentia 2 0 1 7 ga the rae and hearne domains of the western churchill province experienced a complex sequence of tectonic events historically referred to as the hudsonian orogeny in hearne domain diverse thick skinned intraplate structures developed in response to accretionary processes in trans hudson orogen these structures include infolds of archean basement and paleoproterozoic cover and broken foreland thrusts in central hearne domain an intracratonic basin succession of continental to shallow marine strata hurwitz group 2 45 1 91 ga is exposed in outliers that constitute the keels of doubly plunging basement cover synclinoria defining a fold train with wavelengths of 35 45 km with the exception of local out of syncline shear zones basement and hurwitz group are welded formed under greenschist facies conditions the basement cover infolds are open concentric and commonly display complex structures in their interiors in the poorfish windy outlier southwestern hearne domain continental rift deposits of the kiyuk group unconformably overlie the hurwitz group in contrast to basement cover infolding to the north and east archean basement the hurwitz group and the kiyuk group are imbricated by thick skinned northwest vergent thrusts and folds thrusting in the poorfish windy belt was completed by 1815 10 ma as indicated by new u pb data from hydrothermal metamorphic titanite recovered from recrystallized cements at the top of the kiyuk group we interpret that shortening from shallow level basement cover infolding is balanced at depth by intrabasement faulting and distributed ductile strain and that the geometric link between central hearne basement cover infolding and poorfish windy thrusting is via intrabasement faults that cut to the surface the main controls on thick skinned deformation were the high competency of the lower hurwitz group previous thermal weakening basement heterogeneities and possibly shallow subduction preceding terminal collision in trans hudson orogen 2002 elsevier science b v all rights reserved

early proterozoic evolution of the saskatchewan craton and its allochthonous cover trans hudson orogen the composition chronology and structural relations of the saskatchewan craton and enveloping mylonitic rocks exposed in basement windows of the glennie domain trans hudson orogen have been determined by geochemical geochronologic and structural studies accompanying detailed field mapping basement windows lie along the hinge zone of a regional crustal culmination and consist mostly of 2 4 2 5 ga felsic plutonic rocks enveloped by the nistowiak thrust the nistowiak thrust is a folded 1 2 km thick upper amphibolite facies mylonite zone formed during emplacement of the flin flon glennie complex across the saskatchewan craton it is likely correlative to the pelican thrust which envelops basement windows in the hanson lake block 100 km to the east an internal high strain zone within the overlying nappe pile the guncoat thrust is composed primarily of mylonitized porphyroclastic pelitic and psammitic migmatites u pb geochronological results suggest calc alkaline plutonism from 1889 1837 ma thr

structural development of the snow lake allochthon and its role in the evolution of the southeastern trans hudson orogen in manitoba central canada the snow lake allochthon is a zone of tectonic interleaving of sedimentary rocks of an inverted marginal basin kisseynew domain with island arc and oceanic rocks it is located in the southeaster

timing constraints of orogeny to cratonization thermochronology of the paleoproterozoic trans hudson orogen manitoba and saskatchewan canada abstract a comprehensive thermochronometric investigation across a 600 km transect of the paleoproterozoic trans hudson orogen tho in canada has resolved two first order thermal events 1 widespread peak metamorphism at 1 82 1 79 ga associated with terrane amalgamation and 2 a late collisional metamorphic episode at ca 1 77 ga that is characterized by significant strike slip deformation and rapid cooling geophysical observations of the lithosphere beneath the tho reveal crust that is markedly different on either side of the crustal scale tabbernor sturgeon weir tsw strike slip fault system which offsets lower crustal reflectors the tho east of the fault system records u pb titanite and total pb monazite domain ages that are relatively indistinguishable from 40ar 39ar hornblende and mica cooling ages indicating rapid cooling and perhaps exhumation following 1 77 ga metamorphism seismic imaging indicates the eastern orogen is an irregular package of stacked crustal blocks and our thermochronometric data demonstrate it behaved as a single coherent element shortly 20 30 m y following cessation of convergence in contrast rocks located west of the tsw fault system cooled distinctly later preserving 40ar 39ar muscovite and biotite ages between 1 74 and 1 72 ga this crustal architecture delineated from seismic surveys illustrates a more homogeneous slightly 5 km thinner crust in the case of this orogen apparent stabilization and cratonization occurred ca 100 m y after peak terrane amalgamation and notably the orogen was likely cratonized as two blocks east and west of the tsw fault system

the cora lake shear zone athabasca granulite terrane an intraplate response to far field orogenic processes during the amalgamation of laurentia the cora lake shear zone clsz is a 4 6 km wide localized high strain zone that bisects the polydeformed athabasca granulite terrane northern saskatchewan it also coincides with the geophysical trace of the snowbird tectonic zone the clsz represents a major lithotectonic and thermobarometric discontinuity within the exposure of 20 000 km2 of high pressure granulites most rocks have a strong mineral lineation plunging moderately to the southwest the northwestern subdomain hangingwall is characterized by ca 2 6 ga plutonic rocks that contain an early subhorizontal gneissic layering ca 2 57 ga that was overprinted by large amplitude folds and a partitioned but pervasive axial planar dextral shear fabric at ca 1 9 ga thermobarometry suggests metamorphic conditions of 0 9 gpa and 750 c during both of the phases of tectonism the footwall is predominantly underlain by the ca 3 3 3 0 ga chipman tonalite layers of intercalated mafic and felsic granulite and the widespread 1 9 ga chipman

magmatic and metamorphic uraninite mineralization in the western margin of the trans hudson orogen saskatchewan canada a uranium source for unconformity related uranium deposits the genetic model for the giant unconformity related uranium deposits of the athabasca basin is still being debated with one of the main issues being the source of the uranium concentrated by mesoproterozoic era ca 1 60 1 00 ga diagenetic hydrothermal events at the interface between the athabasca basin and the underlying archean paleoproterozoic basement rocks currently accessory minerals like monazite zircon and or apatite from the sedimentary basin and basement rocks are proposed as the primary uranium source for these high grade uranium deposits numerous occurrences of u mineralization of hudsonian age have been documented for decades all around the athabasca basin however so far these have not been regarded as viable u sources here a systematic and detailed study of two areas of basement rocks near the eastern part of the athabasca basin is presented i e the way lake property lying outside the current margin of the basin and the moore lakes property currently covered by the basin this study highlights the significant and widespread occurrence of hudsonian ca 1 81 1 76 ga uranium oxide uo2 mineralization in these zones two types of mineralization are identified and documented here magmatic uranium oxides related to granitic pegmatites and leucogranites which are more common and high temperature vein hosted uranium oxides which have the highest grades the two types were formed during the peak 1 82 1 81 ga and or postthermal peak 1 81 1 72 ga events related to the evolution of the trans hudson orogeny the magmatic uranium oxides formed by partial melting of wollaston group metasedimentary rocks the origin of the vein type occurrences is unclear but their high thorium and rare earth element ree contents suggest a high temperature process associated with ca and or na metasomatism the uranium oxides are associated with other u th and reebearing accessory minerals like u rich thorite thorite zircon and or monazite adding to the exceptional u contents 100 2 460 ppm of these uo2 bearing rocks up to 200 times more primarily enriched in u than other basement or basin rock types a 3 d model of a 1 300 630 200 m basement zone from the way lake property indicates that uraninite bearing granitic pegmatites and leucogranites represent 7 of the total volume of crystalline rock within this rock volume are approximately 8 121 assuming a mean u content of 250 ppm to 16 242 assuming a mean u content of 500 ppm tonnes u the u tonnage of this limited rock volume contained mainly by the hudsonian age uo2 corresponds to between 4 for mcarthur river and 103 for rabbit lake of the u tonnage of known unconformity related u deposits of the basin some of the studied rock samples even macroscopically fresh and located far away from any known unconformity related u deposit present clear evidence of alteration including clay minerals aluminophosphatesulfate aps minerals and uo2 dissolution indicating the percolation of the brines associated with the formation of unconformity related uranium deposits when the basin was far more geographically extensive due to geologic similarities between the studied zones and the basement domains from the eastern part of the athabasca basin i e the hearne province it is proposed that these domains hosted widespread hudsonianage uranium oxide protores these protores provided easily leachable uranium for the metal enrichment of basinal brines during their percolation within the basement and the formation of the unconformity related u deposits these observations bring new insight to the debate about the genetic model of unconformity related u deposits and reinforce the metal source potential of the basement compared to that of the sedimentary basin

nature of assean lake ancient crust manitoba a combined shrimp id tims u pb geochronology and sm nd isotope study abstract the assean lake crustal complex alcc located at the northwest periphery of the superior province in northern manitoba canada hosts an ancient assembly of rocks that record a complex and prolonged crustal history spanning more than two billion years from 3 9 to 1 8 ga a supracrustal assemblage consisting of amphibolite grade greywacke quartz arenite arkose mafic to intermediate volcanics and to a lesser extent iron formation dominates the alcc and likely formed in a shallow marine arc back arc setting the supracrustal rocks are intruded by amphibolite grade calc alkaline tonalite to granite orthogneiss nd model ages for felsic para and orthogneisses range from 3 5 to 4 2 ga and suggest that paleoarchean basement may be preserved at assean lake shrimp u pb zircon ages and id tims conventional u pb zircon and monazite ages show that felsic magmatism occurred at 3 1 3 2 ga whereas a record extending back to at least 3 9 ga is preserved in detritus in paragneiss that may have a depositional age of 3 2 ga orthogneiss was metamorphosed at 2 68 ga whereas local migmatisation of paragneiss occurred at 2 61 ga monazite growth events at 2 6 2 45 and 1 8 ga might represent episodes of accretion of archean crustal segments including the alcc and possibly the sask craton trans hudson basement along the northwest superior province margin at present matching segments of the exotic alcc are unknown but remnants may exist in parts of the sask craton

metal rich fluid inclusions provide new insights into unconformity related u deposits athabasca basin and basement canada the paleoproterozoic athabasca basin canada hosts numerous giant unconformity related uranium deposits the scope of this study is to establish the pressure temperature and composition p t x conditions of the brines that circulated at the base of the athabasca basin and in its crystalline basement before during and after uo2 deposition these brines are commonly sampled as fluid inclusions in quartz and dolomite cementing veins and breccias associated with alteration and u mineralization microthermometry and laser ablation inductively coupled plasma mass spectrometry la icp ms data from five deposits rabbit lake p patch eagle point millennium and shea creek complement previously published data for the mcarthur river deposit in all of the deposits investigated fluid inclusion salinity is between 25 and 40 wt nacl equiv with compositions displaying a continuum between a nacl rich brine end member cl na ca mg k and a cacl2 rich brine end member cl ca mg na k the cacl2 rich brine has the highest salinity and shows evidence for halite saturation at the time of trapping the continuum of compositions between the nacl rich brine and the cacl2 rich brine end members combined with p t reconstructions suggest anisothermal mixing of the two brines nacl rich brine 180 30 c and 800 400 bars cacl2 rich brine 120 30 c and 600 300 bars that occurred under fluctuating pressure conditions hydrostatic to supra hydrostatic however because the two brines were u bearing and therefore oxidized brine mixing was probably not the driving force for uo2 deposition several scenarios are put forward to account for the cl na ca mg k composition of the brines involving combinations of seawater evaporation halite dissolution mixing with a halite dissolution brine mg ca exchange by dolomitization na ca exchange by albitization of plagioclase na k exchange by albitization of k feldspar and mg loss by mg rich alteration finally the metal concentrations in the nacl rich and cacl2 rich brines are among the highest recorded compared to present day sedimentary formation waters and fluid inclusions from basin hosted base metal deposits up to 600 ppm u 3000 ppm mn 4000 ppm zn 6000 ppm cu 8000 ppm pb and 10 000 ppm fe the cacl2 rich brine carries up to one order of magnitude more metal than the nacl rich brine though the exact origin of major cations and metals of the two brines remains uncertain their contrasting compositions indicate that the two brines had distinct flow paths and fluid rock interactions large scale circulation of the brines in the athabasca basin and basement was therefore a key parameter for metal mobility including u and formation of unconformity related u deposits

neoarchean arc magmatism and subsequent collisional orogenesis along the eastern rae domain western churchill province implications for the early growth of laurentia abstract the athabasca granulite terrane on the eastern margin of the rae domain of the western churchill province contains a well exposed record of neoarchean magmatism deformation and metamorphism circa 2 63 2 60 ga plutonic rocks range from 58 01 to 73 71 sio2 and vary from ferroan to magnesian they form shallow linear trends on modified alkali lime index diagram plotting largely in the calc alkaline field on tectonic discrimination diagrams all samples plot in the volcanic arc field samples are lree enriched and contain relatively steep negative slopes and flat depleted hree profiles when normalized to chondrites the entire neoarchean plutonic complex independent of lithology contains strong enrichments in the liles and pb and depletions in hfses monazite u th total pb results from a migmatitic paragneiss suggest that partial melting occurred at ca 2 57 ga within the chipman subdomain monazite results from the adjacent northwestern subdomain suggest that deformation occurred at ca 2 57 ga in sims and icp ms zircon u pb geochronology corroborates these conclusions although the region is dominated by paleoproterozoic localized shear zones internal to each subdomain is evidence of a widespread tectonothermal event during the neoarchean that involved arc plutonism crustal thickening lower crustal flow at pressures exceeding 1 0 gpa and extensive partial melting of the lower continental crust we interpret this sequence of magmatic deformational and anatectic processes to reflect the transition from a continental arc to a collisional tectonic setting the recognized series of events presented herein is likely correlative to the 2 60 2 50 ga macquoid orogen which has been recognized further to the northeast and likely parallels the eastern margin of the rae domain of the western churchill province these data support an important component of modern style plate tectonics during continental magmatism and accretion in the neoarchean

origin of the archean sask craton and its extent within the trans hudson orogen evidence from pb and nd isotopic compositions of basement rocks and post orogenic intrusions u pb zircon ages from the exposed sask craton are 2450 3100 ma from the peter lake domain 2575 2640 ma and from rocks of the trans hudson orogen 1840 1880 ma u pb monazite and zircon ages of post orogenic pegmatites and aplites are 1770 1800 ma common pb and sm nd isotopic compositions of post orogenic intrusions as probes of crust beneath the orogen were compared to sask craton rocks and ca 1850 ma orogenic rocks to infer the origin and subsurface distribution of the sask craton within the internides of the trans hudson orogen results show that post orogenic intrusions within most of the glennie domain and hanson lake block were derived at least in part from archean source materials demonstrating that the sask craton lies beneath paleoproterozoic orogenic rocks present at the surface in contrast common pb and sm nd isotopic compositions from pegmatites and aplites of the la ronge domain are essentially identical with those of the paleoproterozoic orogenic rocks into which they are intruded indicating derivation by partial melting of similar rocks thus if the sask craton extended to the west beneath the la ronge domain it was beneath the zone of melting that produced the post orogenic intrusions making it unlikely that the sask craton is a detached part of the hearne craton many samples from the sask craton have elevated pb 208 pb 204 ratios unlike superior craton or hearne craton rocks suggesting that the sask craton was derived from an exotic source such as the wyoming craton which shares similar elevated pb 208 pb 204 ratios

seismic attenuation due to wave induced flow analytical expressions for three p wave attenuation mechanisms in sedimentary rocks are given a unified theoretical framework two of the models concern wave induced flow due to heterogeneity in the elastic moduli at mesoscopic scales scales greater than grain sizes but smaller than wavelengths in the first model the heterogeneity is due to lithological variations e g mixtures of sands and clays with a single fluid saturating all the pores in the second model a single uniform lithology is saturated in mesoscopic patches by two immiscible fluids e g air and water in the third model the heterogeneity is at microscopic grain scales broken grain contacts and or micro cracks in the grains and the associated fluid response corresponds to squirt flow the model of squirt flow derived here reduces to proper limits as any of the fluid bulk modulus crack porosity and or frequency is reduced to zero it is shown that squirt flow is incapable of explaining the measured level of loss 10 sup 2 q sup 1 10 sup 1 within the seismic band of frequencies 1 to 10 sup 4 hz however either of the two mesoscopic scale models easily produce enough attenuation to explain the field data

finite difference calculation of travel times the travel times of the first arriving seismic waves through any velocity structure can be rapidly computed on a two or three dimensional numerical grid by finite difference extrapolation from point to point wavefronts rather than the traditional rays are tracked head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 03 per cent are found between the results of this technique and raytracing for a complex two dimensional model this scheme is useful for the windowing of finite difference calculations to increase computing speed and promises to aid in earthquake location tomographic inversion and kirchhoff migration in structures that have strong lateral velocity gradients

significant groundwater contribution to antarctic ice streams hydrologic budget satellite observations have revealed active hydrologic systems beneath antarctic ice streams but sources and sinks of water within these systems are uncertain here we use numerical simulations of ice streams to estimate the generation flux and budget of water beneath five ice streams on the siple coast we estimate that 47 of the total hydrologic input 0 98 km3 yr 1 to whillans wis mercer mis and kamb kis ice streams comes from the ice sheet interior and that only 8 forms by local basal melting the remaining 45 comes from a groundwater reservoir an overlooked source in which depletion significantly exceeds recharge of the total input to bindschadler bis and macayeal macis ice streams 0 56 km3 yr 1 72 comes from the interior 19 from groundwater and 9 from local melting this contrasting hydrologic setting modulates the ice streams flow and has important implications for the search for life in subglacial lakes

geoelectric structure of the northeastern williston basin and underlying precambrian lithosphereearth science sector ess contribution 20080509 magnetotelluric mt measurements were made in southern manitoba canada as part of the portable observatories for lithosphere analysis and research investigating seismicity polaris project to image the northeastern part of the williston basin and underlying precambrian lithosphere data collected at 21 sites along a 400 km east west profile at 49 5 n and a 300 km north south profile at 100 w were analyzed using robust spectral analysis tensor decomposition and two dimensional inversion the resulting resistivity models allow subdivision of the williston basin into three layers an upper layer of 1 5 m corresponding to mesozoic and upper paleozoic rocks a 20 50 m layer corresponding to lower paleozoic carbonate rocks and a 2 3 m layer corresponding to the ordovician winnipeg formation deeper penetrating mt responses interpreted with other mt data reveal a region in the westernmost superior craton with a southwest northeast geoelectric fabric that is oblique to subprovince boundaries the

seismic low frequency effects in monitoring fluid saturated reservoirs there is a complex relationship between seismic attributes including the frequency dependence of reflections and fluid saturation in a reservoir observations in both laboratory and field data indicate that reflections from a fluid saturated layer have an increased amplitude and delayed traveltime at low frequencies when compared with reflections from a gas saturated layer comparison of laboratory modeling results with a diffusive viscous theory model show that low 5 values of the quality factor q can explain the observations of frequency dependence at the field scale conventional processing of time lapse vsp data found minimal changes in seismic response of a gas storage reservoir when the reservoir fluid changed from gas to water lowfrequency analysis found significant seismic reflectionattribute variation in the range of 15 50 hz the field observations agree with effects seen in laboratory data and predicted by the diffusive viscous theory one explanation is that very low values of q are the result of internal diffusive losses caused by fluid flow this explanation needs further theoretical investigation the frequencydependent amplitude and phase reflection properties presented in this paper can be used for detecting and monitoring fluid saturated layers

paleoproterozoic arc magmatism imposed on an older backarc basin implications for the tectonic evolution of the trans hudson orogen canada compositional data from 72 granitoids and associated mafic rocks in the paleoproterozoic kisseynew domain trans hudson orogen canada were used to evaluate the tectonic setting of magma generation between 1840 and 1820 ma these data thus provide insights into the development of the trans hudson orogen just prior to amphibolite grade metamorphism and the final stages of continental collision the granitoid rocks are hornblende or orthopyroxene bearing medium to high k calc alkalic and weakly peraluminous the trends on harker variation diagrams are consistent with crystal fractionation processes although the range in values is related to the temporal and spatial distribution of samples the extent of lree light rare earth element enrichment increases with increasing sio 2 as does variability in hree heavy rare earth element fractionation and magnitude of eu anomalies most samples have gd yb n 10 suite ia although five have gd yb n 17 24 suggesting the presence of garnet residua suite ib the range in rock types calc alkalic character and negative nb and ti anomalies are all characteristic of arc environments magma generation within the trans hudson orogen including the kisseynew domain between 1 84 and 1 82 ga was related to interaction between the sask craton and the flin flon glennie complex a decrease in subduction angle likely resulted from northward directed subduction of more buoyant crust with associated changes in thermal conditions leading to melting over a wide area most magmas formed in a slab dehydration dominated regime although localized slab melts may have been generated ultimately subduction ceased and the slab foundered into the mantle potentially resulting in the generation of alkalic and potassic magmas within the rae and hearne cratons

paleoproterozoic rocks of central colorado accreted arcs or extended older crust paleoproterozoic 1770 1735 ma bimodal volcanic rocks in central colorado have been considered to represent southward growth of laurentia by arc accretion although the bimodality of these rocks suggests an extensional continental setting rather than continental or oceanic arcs there has been little evidence for pre 1800 ma crust south of the wyoming craton other than the 1840 1 ma elves chasm pluton in the upper granite gorge of the grand canyon arizona we report shrimp u pb ages of inherited zircons from metarhyolites and plutons in central colorado that are latest archean earliest proterozoic 2520 2000 ma and trans hudson penokean 1878 1814 ma associated quartzites contain detrital zircons with mean ages of 1735 ma indicating only local derivation a meta arkose however contains detrital zircons of trans hudson penokean and archean ages we believe it likely that the 1900 1800 ma trans hudson penokean orogens including archean enclaves extended farther south and west than is currently thought and were the source of the bimodal volcanic rocks and associated plutons during the period 1770 1700 ma

on the propagation of a disturbance in a heterogeneous deformable porous medium saturated with two fluid phases the coupled modeling of the flow of two immiscible fluid phases in a heterogeneous elastic porous material is formulated in a manner analogous to that for a single fluid phase an asymptotic technique valid when the heterogeneity is smoothly varying is used to derive equations for the phase velocities of the various modes of propagation a cubic equation is associated with the phase velocities of the longitudinal modes the coefficients of the cubic equation are expressed in terms of sums of the determinants of 3 3 matrices whose elements are the parameters found in the governing equations in addition to the three longitudinal modes there is a transverse mode of propagation a generalization of the elastic shear wave estimates of the phase velocities for a homogeneous medium based upon the formulas in this paper agree with previous studies furthermore predictions of longitudinal and transverse phase velocities made for the massilon sandstone containing varying amounts of air and water are compatible with laboratory observations

grain growth in polar ice i theory many observations regarding grain growth in ice sheets are glaciologically interesting but imperfectly understood here we develop the theory of grain growth in ice that is not deforming rapidly and in the succeeding paper we use this theory to explain observations from glacial ice in the absence of significant strain energy the driving force for grain growth arises from grain boundary curvature grain growth is slowed by the interaction of grain boundaries with extrinsic materials microparticles bubbles and dissolved impurities if the driving force for growth is not large enough to cause boundaries to separate from an extrinsic material then the grain boundary velocity is determined by the velocity characteristic of the extrinsic material low velocity regime if the driving force is large enough to cause separation then boundaries migrate more rapidly than the extrinsic material high velocity regime but the net driving force is reduced through transient pinning by the extrinsic material polar ice is typically in the low velocity regime relative to dissolved impurities and the high velocity regime relative to microparticles and bubbles cross sectional area of grains is predicted to increase linearly with time under most but not all circumstances

pressure and fluid saturation prediction in a multicomponent reservoir using combined seismic and electromagnetic imaging this paper presents a method for combining seismic and electromagnetic em measurements to predict changes in water saturation pressure and co2 gas oil ratio in a reservoir undergoing co2 flood crosswell seismic and em data sets taken before and during co2 flooding of an oil reservoir are inverted to produce crosswell images of the change in compressional velocity shear velocity and electrical conductivity during a co2 injection pilot study a rock properties model is developed using measured log porosity fluid saturations pressure temperature bulk density sonic velocity and electrical conductivity the parameters of the rock properties model are found by an l1 norm simplex minimization of predicted and observed differences in compressional velocity and density a separate minimization using archie s law provides parameters for modeling the relations between water saturation porosity and electrical conductivity the rock properties model is used to generate relationships between changes in

impact of fluid saturation on the reflection coefficient of a poroelastic layer the impact of changes in saturation on the frequencydependent reflection coefficient of a partially saturated layer was studied seismic attenuation and velocity dispersion in partially saturated i e patchy saturated poroelastic media were accounted for by using the analytical solution of the 1d white s model for wave induced fluid flow white s solution was applied in combination with an analytical solution for the normal incidence reflection coefficient of an attenuating layer embedded in an elastic or attenuating background medium to investigate the effects of attenuation velocity dispersion and tuning on the reflection coefficient approximations for the frequency dependent quality factor its minimum value and the frequency at which the minimum value of the quality factor occurs were derived the approximations are valid for any two alternating sets of petrophysical parameters an approximation for the normal incidence reflection coefficient of an attenuating thin compared to the wavelength layer was also derived this approximation gives insight into the influence of contrasts in acoustic impedance and or attenuation on the reflectivity of a thin layer laboratory data for reflections from a water saturated sand layer and from a dry sand layer were further fit with petrophysical parameters for unconsolidated sand partially saturated with water and air the results showed that wave induced fluid flow can explain low frequency reflection anomalies which are related to fluid saturation and can be observed in seismic field data the results further indicate that reflection coefficients of partially saturated layers e g hydrocarbon reservoirs can vary significantly with frequency especially at low seismic frequencies where partial saturation may often cause high attenuation

a pressure sintering model for the densification of polar firn and glacier ice on presente les predictions de la theorie de frittage pression pour la glace pure et on les compare avec les mesures d indlandsis au groenland et en antarctique

the squirt flow mechanism macroscopic description we introduce a poroelasticity model that incorporates the two most important mechanisms of solid fluid interaction in rocks the biot mechanism and the squirt flow mechanism this combined biot squirt bisq model relates compressional velocity and attenuation to the elastic constants of the drained skeleton and of the solid phase porosity permeability saturation fluid viscosity and compressibility and the characteristic squirt flow length squirt flow length is a fundamental rock property that does not depend on frequency fluid viscosity or compressibility and is determined experimentally we find that the viscoelastic response of many sandstones is dominated by the squirt flow component of the bisq mechanism and that the viscoelastic properties of these rocks can be expressed through a single dimensionless parameter omega r 2 kappa where omega is angular frequency r is the characteristic squirt flow length and kappa is hydraulic diffusivity the biot mechanism alone does not give an adequate explanation of the observed velocity dispersion and attenuation and the viscoelastic behavior of many sandstones

geochronological constraints on the trans hudsonian tectono metamorphic evolution of the pre athabasca basement within the wollaston mudjatik transition zone saskatchewan the hudsonian pressure temperature deformation time p t d t evolution of the pre athabasca crystalline basement 1700 ma of the wollaston mudjatik transition zone wmtz highlights two major tectono metamorphic events m1 d1 and m2 d2 the ages of these two event have been obtained by in situ la icpms u th pb dating of monazite from grt crd bearing pelitic gneiss and u pb analyses performed on zircons from pegmatites using both exposed basement and drill cores from the wolly mcclean exploration drilling project the m1 d1 event interpreted as the burial of the thinned hearne margin via southward thrusting to pressures varying from 10 to 6 kbar occurred between ca 1840 and 1813 ma the m2 d2 event producing the northeast structural trend of the wmtz was formed in a sinistral transpressional tectonic regime during the late stage of the hudsonian oblique collision between ca 1813 and 1770 ma thermobarometric estimates on the m2 d2 assemblages show that the entire studied area was reequilibrated at about 5 kbar and 750 825 c trans hudsonian pegmatites are viewed as the main proto ore of the uranium rich athabasca unconformity type deposits formation transfer and differenciation of these trans hudsonian pegmatites are replaced in this p t d t evolution during the 1840 1813 ma m1 d1 partial melting event the first batches of melt produced in the deep crust are the most likely enriched in uranium then these melts were transferred upwards to the upper crustal levels owing to the development of crustal scale steeply dipping d2 shear zones and finally were differentiated to form uranium enriched pegmatites between 1813 and 1770 ma some monazite and zircon grains within retrogressed migmatites recorded a later event at ca 1720 ma interpreted as the terminal cooling event down to 300 400 c responsible for partial retrogression of metamorphic assemblages this age provides new insights into the timing of the onset of the athabasca sedimentation that should therefore be at least 1710 ma old or younger

basal hydraulic system of a west antarctic ice stream constraints from borehole observations pressure and tracer measurements in boreholes drilled to the bottom of ice stream b west antarctica are used to obtain information about the basal water conduit system in which high water pressures are developed these high pressures presumably make possible the rapid movement of the ice stream pressure in the system is indicated by the borehole water level once connection to the conduit system is made on initial connection here also called breakthrough to the basal water system the water level drops in a few minutes to an initial depth in the range 96 117 m below the surface these water levels are near but mostly somewhat deeper than the flotation level of about 100m depth water level at which basal water pressure and ice overburden pressure are equal which is calculated from depth density profiles and is measured in one borehole the conduit system can be modelled as a continuous or somewhat discontinuous gap between ice and bed the thickness of the gap has to be about 2 mm to account for the water level drop on breakthrough and about 4 mm to fit the results of a salt tracer experiment indicating downstream transport at a speed of 7 5 mm s 1 the above gap conduit model is however ruled out by the way a pressure pulse injected into the basal water system at breakthrough propagates outward from the injection hole and also by the large hole to hole variation in measured basal pressure which if present in a gap conduit system with 2 or 4 mm would result in unacceptably large local water fluxes an alternative model that avoids the e objections called the gap opening model involves opening a gap as injection proceeds starting with a thin film the injection of water under pressure lifts the ice mass a round the borehole creating a gap 3 or 4 mm wide at the ice bed interface evaluated quantitatively the gap opening model accounts for the volume of water that the basal watery system accepts on breakthrough which obviates the gap conduit model in order to transport basal meltwater from upstream it is then necessary for the complete hydraulic model to contain also a network of relatively large conduits of which the most promising type is the canal conduit proposed theoretically by walder and fowler 1994 flat low conduits incised into the till 0 1 m deep and perhaps 1 m wide with a flat ice roof the basal water pressure data suggest that the canals are spaced 50 300 m apart much closer than r tunnel would be the deepest observed water level 117 m i the most likely to reflect the actual water pressure in the canals corresponding to a basal effective pressure of 1 6 bar in this interpretation the shallower water levels are affected by loss of hydraulic head in the narrow passageway s that connect along the bed from borehole to canal s once a borehole has frozen up and any passageways connecting with canals have become closed a pressure sensor in contact with the unfrozen till that underlies the ice will measure the pore pressure in the till given enough time for pressure equilibration this pressure varies considerably with time over the equivalent water level range from 100 to 113 m basal pressure sensors 500 m apart report uncorrelated variations whereas sensors in boreholes 25 m apart report mostly but not entirely well correlated variations of unknown origin in part of the record remarkable anticorrelated variations are interspersed with positively correlated one and there are rare abrupt excursions to extreme water levels as deep as 125m and as shallow as 74 m a diurnal pressure fluctuation intermittently observed may possibly be caused by the ocean tide in the ross sea the lack of any observed variation in ice stream motion when large percentagewise variations in basal effective pressure were occurring according to our data suggests that the observed pressure variations are sufficiently local and so randomly variable from place to place that they are averaged out in the process by which the basal motion of the ice stream is determined by an integration over a large area of the bed

tectonics and surface effects of the supercontinent columbia abstract assembly of the supercontinent columbia at about 1 85 1 90 ga coincided with several events that affected the entire earth the oldest worldwide network of orogenic belts formed at the same time although some granite granodiorite gg suites had formed earlier the gg suites became common in the 1 8 1 9 ga orogenic belts these suites succeeded the older tonalite trondhjemite granodiorite ttg suites which were not produced after 1 8 ga changes on the earth s surface at 1 8 1 9 ga include rapid increase in the concentration of oxygen in the atmosphere and oceans and probably the evolution of eukaryotes all of these surface changes occurred as columbia accreted and the assembly of columbia may have contributed to the drastic changes in the earth s surface environment as well as to the evolution of primitive life forms

basal sliding of ice stream b west antarctica a tethered stake apparatus is used to measure basal sliding in a borehole on ice stream b west antarctica about 300 km upstream east from its grounding line near the head of the ross ice shelf a metal stake emplaced at the top of a layer of unfrozen till underlying the ice is connected by a tether line to a metering unit that measures the tether line as it is pulled out from the borehole by the stake as a result of basal sliding the measured sliding motion includes any actual slip across the ice till interface and may include in addition a possible contribution from shear deformation of till within about 3 cm of the interface this 3 cm figure follows from a qualitative model of the movements of the stake in the course of the experiment based on features of the record of apparent sliding alternative but less likely models would increase the figure from 3 cm to 10 cm or 25 cm in any case it is small compared to the seismically inferred till thickness of 9 m measured apparent sliding averages 69 of the total motion of 1 2 m d 1 over 26 days of observation if a 3 5 day period of slow apparent sliding 8 of the total motion is included in the average the occurrence of the slow period raises the possibility that the sliding motion switches back and forth between c 80 and c 8 of the total motion on a time scale of a few days however it is likely that the period of slow apparent sliding represents instead a period when the stake got caught on the ice sole if the slow period is therefore omitted the indicated average basal sliding rate is 83 of the total motion in either case basal sliding predominates as the cause of the rapid ice stream motion in the last 2 days of observation the average apparent sliding rate reached 1 17 m d 1 essentially 100 of the motion of the ice stream if till deformation contributes significantly to the ice stream motion the contribution is concentrated in a shear zone 3 cm to possibly 25 cm thick at the top of the 9 m thick till layer these observations if applicable to the west antarctic ice sheet in general pose complications in modeling the rapid ice streaming motion

composition age and origin of granitoid rocks in the davin lake area rottenstone domain trans hudson orogen northern saskatchewan the rottenstone domain of the trans hudson orogen is a 25 km wide granitic migmatitic belt lying between the la ronge volcanic plutonic island arc 1890 1830 ma to the southeast and the ensialic wathaman batholith 1855 ma to the northwest the rottenstone domain consists of three lithotectonic belts parallel to the orogen i southeast gently folded migmatized quartzo feldspathic metasedimentary and mafic metavolcanic rocks intruded by small concordant and discordant white tonalite monzogranite bodies ii central intensely folded and migmatized metasedimentary rocks and minor metavolcanic rocks intruded by largely discordant xenolith rich pink aplite pegmatite monzogranite bodies and iii northwest steeply folded migmatized metasedimentary rocks cut by subvertical white tonalite monzogranite sheets emplacement of granitoid rocks consists predominantly of contiguous orogen parallel steeply dipping syntectonic and post tectonic sheets with prominent magmatic schlieren bands overprinted by parallel solid state deformation features the white granitoid rocks have a cnk mol al2o3 mol cao na2 o k 2o 1 14 1 22 k rb 500 ree sum of rare earth elements 1 87 sr 86 sri 0 7032 and endi 2 the pink monzogranites have a cnk 1 11 1 16 k rb 500 ree 90 ppm eu eu 1 87 sr 86 sri 0 7031 and endi 2 the white granitoid rocks show a wider compositional range and more compositional scatter than the pink monzogranites reflecting some combination of smaller volume melts less homogenization and less control by crystal melt equilibria all metavolcanic metasedimentary and granitic rocks in the rottenstone domain have the distinctive geochemical signatures of an arc environment new sensitive high resolution ion microprobe shrimp u pb geochronology on the rottenstone granitoid rocks reveals complex growth histories for monazite and zircon variably controlled by inheritance magmatism and high grade meta morphism monazite ages for the granitoid bodies and migmatites cluster at 1834 and 1814 ma whereas zircon ages range from 2480 ma rare cores to 1900 1830 ma cores and mantles but also 1818 1814 ma for low th u recrystallized rims overgrowths and rare discrete euhedral prisms these results demonstrate that at least some source material for the granitic magmas included earliest paleoproterozoic crust sask craton or its derived sediments and that rottenstone granitic magmatism postdated plutonism in the bounding la ronge arc and wathaman batholith we estimate the age of terminal metamorphism in the davin lake area to be 1815 ma petrogenetically the rottenstone migmatites and granitoid rocks appear for the most part locally derived from their metasedimentary and metavolcanic host rocks shed from the la ronge arc sask craton and possibly the hearne craton the rottenstone domain was the least competent member in the overthrust stack and probably underwent a combination of fluid present melting and fluid absent decompression melting resulting in largely syntectonic granitoid magmatism 1835 1815 ma analogous to granite production in the high himalayan gneiss belt

u redox fronts and kaolinisation in basement hosted unconformity related u ores of the athabasca basin canada late u remobilisation by meteoric fluids proterozoic basement hosted unconformity related uranium deposits of the athabasca basin saskatchewan canada were affected by significant uranium redistribution along oxidation reduction redox fronts related to cold and late meteoric fluid infiltration these redox fronts exhibit the same mineralogical and geochemical features as the well studied uranium roll front deposits in siliclastic rocks the primary hydrothermal uranium mineralisation 1 6 1 3 ga of basement hosted deposits is strongly reworked to new disseminated ores comprising three distinctly coloured zones a white green zone corresponding to the previous clay rich alteration halo contemporaneous with hydrothermal ores a uranium front corresponding to the uranium deposition zone of the redox front brownish zone rich in goethite and a hematite rich red zone marking the front progression the three zones directly reflect the mineralogical zonation related to uranium oxides pitchblende sulphides iron minerals hematite and goethite and alumino phosphate sulphate aps minerals the zoning can be explained by processes of dissolution precipitation along a redox interface and was produced by the infiltration of cold 50 c meteoric fluids to the hydrothermally altered areas u fe ca pb s ree v y w mo and se were the main mobile elements in this process and their distribution within the three zones was for most of them directly dependent on their redox potential the elements concentrated in the redox fronts were sourced by the alteration of previously crystallised hydrothermal minerals such as uranium oxides and light rare earth element lree rich aps the uranium oxides from the redox front are characterised by lree enriched patterns which differ from those of unconformity related ores and clearly demonstrate their distinct conditions of formation uranium redox front formation is thought to be linked to fluid circulation episodes initiated during the 400 300 ma period during uplift and erosion of the athabasca basin when it was near the equator and to have been still active during the last million years a major kaolinisation event was caused by changes in the fluid circulation regime reworking the primary uranium redox fronts and causing the redistribution of elements originally concentrated in the uranium enriched meteoric related redox fronts

archean rocks in the southern rottenstone domain significance for the evolution of the trans hudson orogen an augened strongly flasered and multiply folded monzonitic gneiss occurs in a structural dome in the black bear island lake region of northern saskatchewan within the ca 1850 ma paleoproterozoic southern rottenstone domain of the trans hudson orogen tho a sample of this rock has yielded thermal ionization mass spectrometry tims and sensitive high resolution ion microprobe shrimp zircon data consistent with a formation age of at least 2500 ma zircons also show somewhat younger ca 2380 ma overgrowths indicating a complex history the nd model age tdm of 2726 ma also confirms the late archean age of the rock as does the isotopic composition of common pb from a k feldspar sample u pb analyses of titanites yield ages of ca 1800 ma indicating recrystallization during terminal closure of the tho it is unlikely that the archean rocks are a part of the archean sask craton in the glennie domain for lithoprobe seismic sections indicate that the sask craton dips westward beneath the la ronge a

lyon mountain ferroan leucogranite suite magmatic response to extensional thinning of overthickened crust in the core of the grenville orogen

insights into the late cenozoic configuration of the laurentide ice sheet from 40ar 39ar dating of glacially transported minerals in midcontinent tills glacial sedimentary sequences in the north central united states record multiple advances of the laurentide ice sheet lis since 2 ma although the tills found in these sequences were deposited by southward flowing glacial lobes little information is available on the geometry of flow lines in the interior of the lis during any one glaciation and the provenance of glacial deposits older than the last ice advance is largely unknown systematic changes in the composition of midcontinent tills and other paleogeographic considerations however raise the possibility of significant shifts in the trajectory of flow lines feeding the lobes of the southwestern lis margin here we constrain till provenance using 40ar 39ar ages of individual hornblende and feldspar grains retrieved from tills representing several glaciations since 2 ma hornblende grains show 40ar 39ar ages that indicate erosion of paleoproterozoic 1 7 2 0 ga and late archean 2 5 ga rock sources whereas feldspar grains show a broad range of paleoproterozoic ages 1 4 2 4 ga dating of hornblende and feldspar minerals in single pebbles suggests that this latter distribution of ages is related to the greater sensitivity of feldspars to thermal resetting during minor tectonic events accordingly the range of 40ar 39ar ages for the predominant population of paleoproterozoic hornblende and feldspar grains in our samples is consistent with a source from terrains forming the churchill province of the canadian shield while the small population of archean age grains likely reflects a source from the southwestern tip of the archean superior province that crops out near the study area these results indicate that midcontinent tills were deposited by ice derived from the northwestern keewatin sector of the lis the nearly identical distribution of hornblende and feldspar ages in the till samples identifies the keewatin ice dome and the related ice flow to the midcontinent as long standing features of the lis throughout the late pliocene pleistocene glaciations

an evaporated seawater origin for the ore forming brines in unconformity related uranium deposits athabasca basin canada cl br and δ37cl analysis of fluid inclusions abstract analyses of halogen concentration and stable chlorine isotope composition of fluid inclusions from hydrothermal quartz and carbonate veins spatially and temporally associated with giant unconformity related uranium deposits from the paleoproterozoic athabasca basin canada were performed in order to determine the origin of chloride in the ore forming brines microthermometric analyses show that samples contain variable amounts of a nacl rich brine cl concentration between 120 000 and 180 000 ppm and a cacl2 rich brine cl concentration between 160 000 and 220 000 ppm molar cl br ratios of fluid inclusion leachates range from 100 to 900 with most values between 150 and 350 cl br ratios below 650 seawater value indicate that the high salinities were acquired by evaporation of seawater most 37cl values are between 0 6 and 0 seawater value which is also compatible with a common evaporated seawater origin for both nacl and cacl2 rich brines slight discrepancies between the cl concentration cl br 37cl data and seawater evaporation trends indicate that the evaporated seawater underwent secondary minor modification of its composition by i mixing with a minor amount of halite dissolution brine or re equilibration with halite during burial ii dilution in a maximum of 30 of connate and or formation waters during its migration towards the base of the athabasca sandstones iii leaching of chloride from biotites within basement rocks and iv water loss by hydration reactions in alteration haloes linked to uranium deposition the chloride in uranium ore forming brines of the athabasca basin has an unambiguous dominantly marine origin and has required large scale seawater evaporation and evaporite deposition although the direct evidence for evaporative environments in the athabasca basin are lacking due to the erosion of 80 of the sedimentary pile cl br ratios and 37cl values of brines have behaved conservatively at the basin scale and throughout basin history

anisotropy and crystalline fabric of whillans ice stream west antarctica inferred from multicomponent seismic data crystal orientation fabric cof describes the intrinsic anisotropic nature of ice and is an important parameter for modeling glacier flow we present the results of three component active source seismic observations from the whillans ice stream wis a fast flowing ice stream in west antarctica surface wave dispersion analysis ray tracing and traveltime inversion of compressional p and shear s waves reveal the presence of transversely isotropic ice with a vertical axis of symmetry vti beneath approximately 65 m of isotropic firn the ice stream is characterized by weak anisotropy involving an average ice thickness of approximately 780 m the analysis indicates that about 95 of the ice mass is anisotropic and the crystalline c axes span within an average broad cone angle of 73 10 with respect to the vertical axis moreover the mean temperature t below the firn estimated from seismic data is 15 5 c these data do not show evidence of englacial seismic reflectivity which indicates the lack of abrupt changes in the cof the presence of azimuthal anisotropy due to transversely compressive flow or fractures aligned along a preferential direction is also excluded we suggest that the observed vti ice structure is typical of large ice streams in regions where basal sliding and bed deformation dominate over internal glacial deformation

tectonic implications of new shrimp and tims u pb geochronology of rocks from the sask craton peter lake domain and hearne margin trans hudson orogen saskatchewan this study reports new sensitive high resolution ion microprobe shrimp and thermal ionization mass spectrometry tims u pb geochronological data for thirteen rocks from the archean to paleoproterozic sask craton the peter lake domain and hearne margin saskatchewan seven samples from the exposed sask craton in both the glennie domain and pelican window record zircon growth between 2425 and 2525 ma and at 1800 ma older precursor material has been identified most notably a refined crystallization age of 3117 ma for a sample of quartzofeldspatic gneiss q gneiss in the pelican window which also experienced ca 2450 ma zircon growth three samples from the peter lake domain and a sample from the linn island inlier of the wollaston domain yield ages of 2575 ma one sample from the peter lake domain is distinctly older yielding an age of 2640 ma but also displays zircon growth at 2575 ma the simplest interpretation of these data is that the peter lake domain is likely a part of the hearne margin

chronology of crustal growth and recycling in the paleoproterozoic amisk collage flin flon belt trans hudson orogen canada u pb zircon ages have been compiled for magmatic and sedimentary rocks from the low metamorphic grade portion of the flin flon greenstone belt now recognized as a paleoproterozoic tectonic collage

griffin gabbro sills 2 11 ga hurwitz basin nunavut canada long distance lateral transport of magmas in western churchill province crust circa 2 11 ga sills and rare dykes herein named the griffin gabbros extend discontinuously across an area 400 by 125 km in the hearne domain of the western churchill province in northern canada sills form poorly connected tongue like tabular bodies primarily within paleoproterozoic intracratonic basin deposits of the lower hurwitz group dykes are restricted to the southern limit of the griffin suite and have not been found in the interior of hurwitz basin or in archean basement incompatible element patterns and low end2111 values 0 1 1 0 indicate an enriched asthenosphere source similar to many modern hotspot related ocean island basalts the gabbros display enrichments in nb and la suggesting a mantle plume origin heavy rare earth element depletions and tio2 values averaging 3 40 wt suggest partial melting of a garnet peridotite source at depths of 70 100 km mgo values averaging 5 20 wt indicate fractionation after melting concentrations of both the incompatible and compatible elements scatter widely with respect to mg number indicating that compositional variation does not represent fractional crystallization from a common parent consistent with derivation from different magma chambers related to the same mantle plume the gabbros fail to show signs of an archean enrichment event recorded by other paleoproterozoic mafic rocks in the hearne domain this together with the absence feeder dykes in basement indicate derivation external to hurwitz basin we interpret that a mantle plume located beyond the present southern margin of the hearne domain was active during 2 1 ga rifting that led to opening of the manikewan ocean the griffin gabbros were likely injected because of the hydraulic head created by topographic doming above this plume analogous to the ferrar sills jurassic in antarctica the gabbros may have been fed by cryptic dykes in which magmas traveled laterally for at least 250 km across the southern hearne domain and then controlled by sedimentary layering spread as sills for hundreds of km within hurwitz basin

isotopic evidence for neoarchean continuity across the snowbird tectonic zone western churchill province canada abstract the snowbird tectonic zone stz the ca 2800 km long boundary between rae and hearne domains of the western canadian shield remains of uncertain tectonic significance but is currently interpreted as a ca 1 9 ga suture the eastern rae domain is well studied and underlain by a 20 000 km2 region of high pressure granulites containing ca 2 60 ga arc rocks and granulite to amphibolite grade structures which formed at ca 2 57 ga d1 m1 and 1 90 ga d2 m2 the 1 85 ga legs lake shear zone juxtaposed the high p granulites of the eastern rae domain structurally above lower amphibolite to greenschist grade supracrustal gneisses of the hearne domain zircon u pb and hf isotopic analyses were acquired from igneous and metasedimentary rocks across the stz and rae hearne boundary to assess the validity of the suture model with specific focus given to the 5 km wide legs lake shear zone results indicate that both 2 60 2 55 ga magmatism and deformation continue unimpeded across the stz and rae hearne boundary furthermore hf isotopic data from igneous zircon from 2 60 ga plutonic rocks across the stz display little variation in ehf indicating that no major crustal break corresponds to the rae hearne boundary or any of the shear zones that parallel the stz on the ground older plutonic rocks show a greater variability in ehf which may indicate a disparate origin grade intensity and timing of paleoproterozoic features vary along the transect and display little continuity across the rae hearne domain boundary in conjunction with existing field and isotopic data we interpret that the rae and hearne domains were together by 2 60 ga and that the stz was host to repeated paleoproterozoic reactivation driven by the latter stages of taltson thelon orogenesis final indentation of the slave craton into the rae domain and accretionary processes on the southern periphery of the hearne domain from 1 93 to 1 84 ga furthermore assessing the viability of major shear zones within high grade terranes as potential sutures is complicated by the lateral and vertical heterogeneity of the crust juxtaposed by them

grain growth in polar ice ii application grain growth observed in polar ice that is not deforming rapidly can be accounted for if concentrations and distributions of extrinsic materials microparticles bubbles and dissolved impurities are characterized fully dissolved impurities segregate to grain boundaries and slow grain growth in all cold glacial ice the high concentration of soluble impurities in wisconsinan ice from the dome c antarctica ice core and perhaps other ice cores probably causes the small grain sizes observed in that ice microparticles have little effect on grain growth in ordinary ice in ice layers that appear dirty owing to concentrations of volcanic tephra such as in the byrd station antarctica ice core or of morainal material micro particles reduce grain growth rates significantly the relatively high vapor pressure of ice allows rapid growth and high mobility of intergranular necks so grain growth in firn is limited by boundary migration rather than by neck growth bubbles formed by pore close off at the firn ice transition are less mobile than grain boundaries causing bubble boundary separation whenever geometric constraints are satisfied however such separation reduces grain growth rates by only about 10 the observed linear increase of grain area with time is thus predicted by theory but the growth rate depends on soluble impurity concentrations as well as on temperature

mixing of sodic and calcic brines and uranium deposition at mcarthur river saskatchewan canada a raman and laser induced breakdown spectroscopic study of fluid inclusions the richest u deposit in saskatchewan canada occurs in the mcarthur river area in the vicinity of the unconformity between the athabasaca sandstones and an archean to lower proterozoic basement paleofluids related to the silicification of the sandstones and the formation of pre and postore cements in breccias were studied using microthermometry raman microspectroscopy and laser induced breakdown spectroscopy libs on individual fluid inclusions a detailed reconstruction of the fluid composition in the system na ca mg cl shows that two types of brines are responsible for the main quartz cements an nacl rich brine 25 wt nacl up to 14 wt cacl 2 and up to 1 wt mgcl 2 which is interpreted as a primary formation water that was expelled from bedded evaporites and a cacl 2 rich brine 5 8 wt nacl 20 wt cacl 2 and up to 11 wt mgcl 2 which is considered to have formed during the interaction between the nacl rich brine and ca rich minerals in the basement and was introduced into the fault system and mixed with the nacl rich brine during the critical stage of u deposition the pressure temperature conditions of formation of the quartz cements are estimated to be 1 200 to1 400 bars and 190 to 235 c for the silicification events during the preore stage and 500 to 900 bars after a pressure decrease from lithostatic conditions and slightly lower temperatures due to the mixing of the nacl rich brine with the cooler approx 140 c cacl 2 rich brine during the main stage of breccia sealing temperature and pressure drops combined with the effects of brine mixing appear to be key factors for the main stages of quartz cementation and u deposition at the mcarthur deposit

thermochronological history of the northern canadian shield abstract the northern canadian shield is comprised of multiple archean cratons that were sutured by the late paleoproterozoic to form the canadian component of supercontinent nuna more than 2000 combined k ar and 40ar 39ar cooling ages from across the region reveal a stark contrast in upper and lower plate thermal responses to nuna forming events with the churchill province in particular revealing near complete thermal reworking during the late paleoproterozoic we review the detailed cooling history for five regions that span the churchill province and trans hudson orogen tho thelon tectonic zone south rae reindeer zone south hall peninsula and the cape smith belt the cooling patterns across churchill province are revealed in two 1500 km transects at the plate scale churchill s cooling history is dominated by tho accretionary and collisional events during which it formed the upper plate cooling ages generally young from west to east across both southern and central churchill and latest cooling in the tho is 50 myr older in southernmost churchill reindeer zone compared to eastern churchill hall peninsula indicating diachronous thermal equilibration across 2000 km strike length of the tho churchill exhibits relatively high post terminal tho cooling rates of 4 c myr which support other geological evidence for widespread rapid exhumation of the tho upper plate following terminal collision potentially in response to lithospheric delamination

detectability of petrophysical properties of subsurface co2 saturated aquifer reservoirs using surface geophysical methods the process of capturing carbon dioxide co2 and injecting it into deep saline aquifers is becoming an important method to reduce future atmospheric emissions of co2 key challenges facing carbon capture and storage ccs are the storage reservoir s size and safety the storage size can be addressed by focusing on large saline aquifer reservoirs the safety concern may be lower if co2 is injected into depleted hydrocarbon reservoirs because their cap rock integrity is already proven but such capping systems are generally potentially compromised by poorly cemented abandoned wells and compared to saline aquifers their storage size is small therefore the long term focus of ccs is on saline aquifers to reduce the corresponding risks comprehensive long term monitoring is inevitable

thermotectonic studies in the paleoproterozoic glennie domain trans hudson orogen canada abstract the glennie domain of the trans hudson orogen tho is characterized by paleoproterozoic island arc volcanogenic assemblages and granitoid rocks thrust as sheets over the archean saskatchewan craton prior to terminal collision between the archean rae hearne and superior cratons four discrete deformation events have been recorded in the domain the d1 and d2 events are associated with the southwestward directed imbrication of paleoproterozoic allochthons over the saskatchewan craton while the d3 and d4 events are associated with terminal collision and transpression respectively discernable metamorphic episodes are associated with the d2 and d3 events with peak thermal metamorphism during d3 using inveq thermobarometry metamorphic conditions during d3 in the santoy lake area were ca 655 705 c and 6 1 7 3 kbar and ca 530 595 c and 3 2 4 8 kbar for the brownell lake area 40ar 39ar hornblende and biotite ages suggest the santoy lake area remained above ca 490 c until ca 1720 ma when it underwent rapid cooling through the biotite ar closure temperature of ca 330 c 40ar 39ar biotite ages from the brownell lake area suggest moderate cooling from peak thermal metamorphism at ca 1810 1755 ma when it passed through the ca 310 c biotite ar closure temperature differences between cooling rates for the two areas are interpreted as differential exhumation of smaller lithotectonic blocks bound by domain wide deep crustal faults and shear zones zircon pb evaporation ages of variably deformed granitoid rocks from the santoy lake area show that the d2 event occurred after ca 1857 ma the oldest granitoid in the santoy lake area provides a minimum age of mafic volcanism in the area of ca 1886 ma as well as a significant hiatus ca 50 ma between deposition of the two supracrustal assemblages in the domain

fluvial lacustrine and volcanic sedimentation in the angikuni sub basin and initiation of 1 84 1 79 ga baker lake basin western churchill province nunavut canada abstract continental siliciclastic and volcanogenic deposits of the baker lake group accumulated in numerous sub basins in the interior of the western churchill province between 1 84 and 1 79 ga in the angikuni sub basin on the southeast flank of greater baker lake basin baker lake group rocks outcrop in two segments that extend northeast from angikuni lake they are also exposed in scattered outliers throughout the region at northern angikuni lake in the northern segment conglomerates pebbly sandstones and mudrocks of the angikuni formation unconformably overlie archean basement and are unconformably overlain by ultrapotassic volcanic and siliciclastic rocks of the christopher island formation these rocks record alluvial fan fluvial and sand flat playa deposition in a fault bounded trough formed adjacent to a wedge shaped basement uplift although the angikuni formation was tilted before principal christopher island formation volcanism at northern angikuni lake geochemical and nd isotopic data from mudrocks indicate derivation from earlier or coeval christopher island volcanic like sources the outliers demonstrate that faulting produced significant changes in the structural level of archean basement before christopher island formation volcanism near rack lake in the southern segment angikuni formation conglomerates sandstones and mudrocks define 100 m scale upward fining and upward coarsening to upward fining sequences relative to the northern segment these rocks were deposited in a more distal fine grained sand flat to semi perennial fresh water evaporitic lake setting the angikuni formation at rack lake records deposition between and likely during periods of volcanism as indicated by a conformable angikuni christopher island contact abundant volcanic detritus and local lacustrine chemical sediments that contain magnesite strontianite barite and apatite which reflect the chemistry of the volcanic rocks baker lake basin may have originated during regional uplift and extension within the western churchill province due to terminal collision and post collision processes in trans hudson orogen to the south while the western margin of ancestral north america was a free face

from evaporated seawater to uranium mineralizing brines isotopic and trace element study of quartz dolomite veins in the athabasca system abstract stable isotope o h c radiogenic isotope sr nd and trace element analyses have been applied to quartz dolomite veins and their uranium u bearing fluid inclusions associated with proterozoic unconformity related uo 2 uraninite ores in the athabasca basin canada in order to trace the evolution of pristine evaporated seawater towards u mineralizing brines during their migration through sediments and basement rocks fluid inclusion data show that quartz and dolomite have precipitated from brines of comparable chemistry excepted for relatively small amounts of co 2 found in dolomite hosted fluid inclusions however 18 o values of quartz veins 18 o 11 to 18 and dolomite veins 18 o 13 to 24 clearly indicate isotopic disequilibrium between quartz and dolomite hence it is inferred that this isotopic disequilibrium primarily reflects a decrease in temperature between the quartz stage 180 c and the dolomite stage 120 c the 13 c values of co 2 dissolved in dolomite hosted fluid inclusions 13 c 30 to 4 and the 13 c values of dolomite 13 c 23 5 to 3 5 indicate that the co 2 dissolved in the mineralizing brines originated from brine graphite interactions in the basement the resulting slight increase in the fluid partial pressure of co 2 p co 2 may have triggered dolomite precipitation instead of quartz 18 o values of quartz veins and previously published 18 o values of the main alteration minerals around the u ores illite chlorite and tourmaline show that quartz and alteration minerals were isotopically equilibrated with the same fluid at 180 c the ree concentrations in dolomite produce paas normalized patterns that show some similarities with that of uo 2 and are clearly distinct from that of the other main ree bearing minerals in these environments monazite zircon and aluminum phosphate sulfate aps minerals the radiogenic isotope compositions of dolomite 87 sr 86 sr i 0 7053 to 0 7161 and e nd t 8 8 to 20 3 differ from one deposit to another reflecting both heterogeneity in the basement geology and variable preservation of the original composition of brines the previously published 87 sr 86 sr i and e nd t values of uo 2 compare with the most evolved dolomites i e dolomites precipitated from brines that exchanged the most with the basement this reinforces a close genetic link between dolomites and uo 2 deposition and implies that uo 2 deposition occurred in a cooling system during the transition from quartz to dolomite formation the 18 o and d values of the mineralizing brines 18 o 1 to 8 and d 150 to 50 are considerably shifted from that of their theoretical original values acquired during evaporation of seawater 18 o 3 and d 40 the positive 18 o shift is explained by protracted fluid rock interaction within the basin and basement rocks the negative d shift is attributed to incomplete mixing between the u mineralizing brines and low d water this low d water was likely produced during the abiogenic synthesis of bitumen by fisher tropsch like reactions involving co 2 derived from brine graphite interaction in the basement and radiolytic h 2 the resulting low d brines have been equilibrated with alteration minerals this may explain why some alteration minerals yield anomalously low d values whose significance has long been debated

on the propagation of a disturbance in a smoothly varying heterogeneous porous medium saturated with three fluid phases abstractfrom the equations governing the deformation of a porous medium containing three fluid phases i derive expressions for the phase velocity of the various modes of displacement these expressions are valid for a medium with smoothly varying heterogeneity there is a single mode of transverse displacement similar in nature to an elastic shear wave the four phase velocities of the longitudinal modes of displacement are derived from the solutions of a quartic equation the coefficients of the polynomial equation are written as linear sums of the determinants of 4 4 matrices the matrices contain various combinations of the parameters from the governing equations the three phase expressions are compared to two phase estimates for the case in which one of the fluid saturations vanishes also in a numerical illustration velocity variations of around 10 are associated with the cyclic injection of carbon dioxide and water into an oil saturated reservoir