geochemistry of gold quartz vein walls from jales northern portugal abstract the long hydrothermal quartz veins from campo de jales northern portugal have been exploited for au and form the main portuguese au deposit au and electrum occur included in sulfides sulfosalts and quartz and in thin veinlets along fractures with sulfides while ag occurs in electrum argentite galena and most of the sulfosalts the campo gold quartz vein cuts mainly the hercynian peraluminous medium to coarse grained porphyritic seriate two mica granite and also the pre ordovician biotite muscovite andalusite schist with sillimanite at 1 0 5 m from the vein the granite is altered into a porphyritic muscovite biotite granite while adjacent to the vein up to 0 5 m it is a muscovite granite at 3 m from the vein the mica schist shows some metasomatic effects but it is transformed into a biotite muscovite brunsvigite schist at 2 m from the vein and into a mica schist enriched in muscovite and sulfides adjacent to the vein in a zone of 0 1 0 5 m up to 1 m from the vein there are progressive increases in sio2 fe2o3 k2o h2o s as sn sb cu pb rb au a negative eu anomaly and progressive decreases in tio2 feo mgo cao cl li sr th and all ree with increasing degree of hydrothermal alteration of granite k2o f s rb and cs progressively increase while feo cao zr and sr progressively decrease with increasing degree of hydrothermal alteration of mica schist at the direct contact with the vein the granite and mica schist show enrichment in k2o fe2o3 h2o sn rb s as zn sb cu pb and au and impoverishment in tio2 mgo feo cao na2o cl cr v nb li ni and zr which gives information on the ore forming fluids the hydrothermal alteration of granite increases with depth but seems to decrease with increasing distance from the granite schist contact the mineral data are used to show the evolution of hydrothermal alteration at the vein walls and to write the representative reactions of hydrothermal alteration the unaltered granite was emplaced at 3 kbar and 690 c and fo2 of 10 18 bar but was completely crystallized at 460 600 c it was hydrothermally altered at 200 400 c and log f h 2 o f hf and log f hcl f hf increase and log f h 2 o f hcl decreases during the alteration the mica schist was hydrothermally altered at log f h 2 o f hf and log f hcl f hf

the evolution of climatically driven weathering inputs into the western arctic ocean since the late miocene radiogenic isotope evidence highlights seawater hf nd pb isotopic evolution in the deep arctic ocean of the past 7 myr climatically driven changes in weathering inputs since 4 ma north american laurentide ice sheet runoff controlled the isotopic budget in the canada basin more congruent hf release due to glacial weathering conditions past arctic ocean water masses show larger isotopic differences than today abstract we present the first continuous records of dissolved radiogenic neodymium hafnium and lead isotope compositions of deep waters in the western arctic ocean spanning the time from the late miocene to the present the data were obtained from three hydrogenetic ferromanganese fe mn crusts recovered from seamounts along the northernmost edge of the northwind ridge in the canada basin from water depths of 2200 2400 and 3600 m dating the crusts using cosmogenic 10be documents undisturbed present day growth surfaces and yields growth rates between 27 and 2 2 mm myr the nd hf isotope time series of the three crusts show similar evolutions from endend ehf ehf of 8 5 4 in the oldest parts to 11 5 4 at the surfaces and a pronounced trend to less radiogenic values starting at 4 ma this coincided with a trend of the pb isotope evolution towards more radiogenic 206pb 204pb 207pb 204pb and 208pb 204pb it is inferred that climatically controlled changes in weathering regime and sediment transport along the north american continent were responsible for the major change of the radiogenic isotope composition of the arctic deep water adw in the canada basin based on these records we conclude that weathering inputs from the north american continent linked to enhanced glacial conditions started to increase and to influence the radiogenic isotope composition of adw 4 million years ago and were further intensified at 1 ma these new time series differ markedly from the radiogenic isotope evolution of arctic intermediate water recorded on the lomonosov ridge and suggest that much larger isotopic differences between the water masses of the arctic ocean than today prevailed in the past

geochemistry of s type granitic rocks from the reversely zoned castelo branco pluton central portugal abstract the zoned pluton from castelo branco consists of variscan peraluminous s type granitic rocks a muscovite biotite granite in the pluton s core is surrounded successively by biotite muscovite granodiorite porphyritic biotite muscovite granodiorite grading to biotite muscovite granite and finally by muscovite biotite granite id tims u pb ages for zircon and monazite indicate that all phases of the pluton formed at 310 1 ma whole rock analyses show slight variation in 87 sr 86 sr 310 ma between 0 708 and 0 712 nd 310 ma values between 1 and 4 and 18 o values between 12 2 and 13 6 these geological mineralogical geochemical and isotopic data indicate a crustal origin of the suite probably from partial melting of heterogeneous early paleozoic pelitic country rock in detail there is evidence for derivation from different sources but also fractional crystallization linking some of internal plutonic phases least squares analysis of major elements and modelling of trace elements indicate that the porphyritic granodiorite and biotite muscovite granite were derived from the granodiorite magma by fractional crystallization of plagioclase quartz biotite and ilmenite by contrast variation diagrams of major and trace elements in biotite and muscovite the behaviours of ba in microcline and whole rock 18 o the ree patterns of rocks and isotopic data indicate that both muscovite dominant granites were probably originated by two distinct pulses of granite magma

peak last glacial weathering intensity on the north american continent recorded by the authigenic hf isotope composition of north atlantic deep sea sediments we have retrieved radiogenic hafnium hf isotope compositions hf from authigenic fe mn oxyhydroxides of deep northwest atlantic sediments deposited over the past 26 ka to investigate the oceanic evidence of changes in dissolved weathering inputs from ne america during the last deglaciation the extraction of seawater derived hf isotopic compositions from fe mn oxyhydroxides is not a standard procedure comparisons between the al hf ratios and hf isotopic compositions of the chemically extracted authigenic phase on the one hand and those of the corresponding detrital fractions on the other provide evidence that the composition of past seawater has been reliably obtained for most sampled depths with our leaching procedures this is endorsed most strongly by data for a sediment core from 4250 m water depth at the deeper blake ridge for which consistent replicates were produced throughout the hf isotopic composition of the most recent sample in this core also closely matches that of nearby present day central north atlantic seawater comparison with previously published seawater nd and pb isotope compositions obtained on the same cores shows that both hf and pb were released incongruently during incipient chemical weathering but responded differently to the deglacial retreat of the laurentide ice sheet hafnium was released more congruently during peak glacial conditions of the last glacial maximum lgm and changed to typical incongruent interglacial hf signatures either during or shortly after the lgm this indicates that some zircon derived hf was released to seawater during the lgm conversely there is no clear evidence for an increase in the influence of weathering of lu rich mineral phases during deglaciation possibly since relatively unradiogenic hf contributions from feldspar weathering were superimposed while the authigenic pb isotope signal in the same marine sediment samples traced peak chemical weathering rates on continental north america during the transition to the holocene a similar incongruent excursion is notably absent in the hf isotope record the early change towards more radiogenic hf in relation to the lgm may provide direct evidence for the transition from a cold based to a warm based laurentide ice sheet on the atlantic sector of north america

the hafnium neodymium isotopic composition of atlantic seawater the first full water column hafnium isotopic compositions of atlantic seawater have been obtained at seven locations from the labrador sea to the drake passage despite subpicomolar concentrations in seawater a precision of the hf isotopic measurements of 03 epsilon hf units was achieved an overall epsilon hf range between 3 1 in the labrador sea and 4 4 in antarctic bottom water was determined the distribution of which broadly reflects continental weathering inputs within particular water column profiles significant differences of up to 4 epsilon hf units occur combined with nd isotope data of the same samples it is evident that the hf isotopic composition of seawater is too radiogenic for a given nd isotopic composition and that the largest difference between expected and measured hf isotopic compositions in seawater occurs near the oldest continental crust in the labrador sea this corroborates the previous proposition which was mainly based on ferromanganese crust data that the hf isotopic composition of seawater is controlled by incongruent weathering of continental crust and possibly to some extent by hydrothermal contributions hafnium concentrations in the ocean do not increase along the deep ocean conveyer indicating an oceanic residence time of only a few hundred years which is significantly shorter than previously assumed the hf isotopic composition of past seawater can therefore serve as a proxy for short distance basin scale mixing processes and the regime and intensity of nearby continental weathering processes c 2009 elsevier b v all rights reserved

the hafnium and neodymium isotope composition of seawater in the atlantic sector of the southern ocean we present the first combined dissolved hafnium hf and neodymium nd concentrations and isotope compositions of deep water masses from the atlantic sector of the southern ocean eight full depth profiles were analyzed for hf and twelve for nd hafnium concentrations are generally depleted in the upper few hundred meters ranging between 0 2 pmol kg and 0 4 pmol kg and increase to relatively constant values of around 0 6 pmol kg in the deeper water column at the stations north of the polar front pf nd concentrations increase linearly from about 10 pmol kg at depths of 200 m to up to 31 pmol kg close to the bottom indicating particle scavenging and release within the weddell gyre wg however nd concentrations are essentially constant at 25 pmol kg at depths greater than 1000 m the distributions of both elements show a positive correlation with dissolved silicon implying a close linkage to diatom biogeochemistry hafnium essentially shows invariant isotope compositions with values averaging at ehf 4 6 whereas nd isotopes mark distinct differences between water masses such as modified north atlantic deep water nadw end 11 to 10 and antarctic bottom water aabw end 8 6 to 9 6 but also waters locally advected via the agulhas current can be identified by their unradiogenic nd isotope compositions mixing calculations suggest that a small fraction of nd is removed by particle scavenging during mixing of water masses north of the pf nevertheless the nd isotope composition has apparently not been significantly affected by uptake and release of nd from particles as indicated by mixing calculations a mixing envelope of an approximated north pacific and a north atlantic end member shows that nd isotope and concentration patterns in the lower circumpolar deep water lcdw can be fully explained by 30 70 percentage contributions of these respective end members

metalliferous sediments and the scavenging residence time of nd near hydrothermal vents the isotopic composition of nd is uniform in metalliferous sediments formed at distances varying from 1000 km to within 10 km of the east pacific rise epr palaeoridge these data indicate that hydrothermal vent fluids despite having concentrations more than 500 times greater have no effect on the nd isotopic composition of seawater this implicates efficient scavenging of hydrothermal nd by particulates resulting in extremely short residence times 1 year close to the hydrothermal vents therefore nd isotopic studies of ancient seawater precipitates particularly metalliferous sediments cannot be used to delimit the magnitude of past hydrothermal circulation without independent constraints on local scavenging rates or residence times relative to those of modern oceans

the control of weathering processes on riverine and seawater hafnium isotope ratios hafnium 176 hf 177 hf isotope ratio variations in marine records are thought to reflect changes in continental weathering through time but the behavior of hf in rivers and during weathering is not well understood here we present 176 hf 177 hf data for rivers bedrock soils and leaching experiments for the moselle basin vosges france these data strongly suggest that the 176 hf 177 hf composition of river waters is controlled by prefer ential dissolution of accessory phases i e apatite sphene versus more resistant minerals e g k feldspar and linked to the intensity of silicate weathering estimates for the global isotopic composition of riverine hf suggest that the ocean hf budget may be dominated by river input and variations seen in marine records can be directly related to changes in silicate weathering intensity

age and emplacement of late variscan granites of the western bohemian massif with main focus on the hauzenberg granitoids european variscides germany abstract the variscan hauzenberg pluton consists of granite and granodiorite that intruded late to postkinematically into ht metamorphic rocks of the moldanubian unit at the southwestern margin of the bohemian massif passauer wald u pb dating of zircon single grains and monazite fractions separated from medium to coarse grained biotite muscovite granite hauzenberg granite ii yielded concordant ages of 320 3 and 329 7 ma interpreted as emplacement age zircons extracted from the younger hauzenberg granodiorite yielded a 207 pb 206 pb mean age of 318 6 4 1 ma the hauzenberg granite i has not been dated the pressure during solidification of the hauzenberg granite ii was estimated at 4 6 0 6 kbar using phengite barometry on magmatic muscovite corresponding to an emplacement depth of 16 18 km the new data are compatible with pre existing cooling ages of biotite and muscovite which indicate the hauzenberg pluton to have cooled below t 250 400 c in upper carboniferous times a compilation of age data from magmatic and metamorphic rocks of the western margin of the bohemian massif suggests a west to northwestward shift of magmatism and ht lp metamorphism with time both processes started at 325 ma within the south bohemian pluton and magmatism ceased at ca 310 ma in the bavarian oberpfalz the slight different timing of ht metamorphism in northern austria and the bavarian forest is interpreted as being the result of partial delamination of mantle lithosphere or removal of the thermal boundary layer

hafnium isotope fractionation during continental weathering implications for the generation of the seawater nd hf isotope relationships to investigate the mechanisms of the offset of seawater radiogenic nd hf isotope compositions from those of the upper continental crust rocks combined nd hf isotope compositions of desert and loess samples from northern china which integrate a wide range of lithologies and ages of continental rocks are presented in this study the results show significant and systematic fractionation of hf isotopes between finegrained detritals leachates 5 mm and coarser fractions 75 mm of the same samples a small but systematic difference of nd isotope compositions between leachates and detrital silicates is also revealed overall the leaching data either plot along or slightly above the nd hf seawater array providing strong direct support that the seawater nd hf isotope relationship is predominantly generated by weathering of upper continental crust our study supports the application of dissolved hf isotopes as a proxy for different modes of weathering regimes rather than for continental source provenances

in situ behaviour of a stiff layered clay subject to thermal loading observations and interpretation the paper presents an interpretation of an in situ heating test carried out on opalinus clay in the mont terri underground laboratory opalinus clay is a stiff strongly bedded mesozoic clay of marine origin when subjected to thermal loading saturated stiff clays exhibit a strong pore pressure response that significantly affects the hydraulic and mechanical behaviour of the material the observations gathered in the in situ test have provided an opportunity to examine the integrated thermo hydro mechanical thm response of this sedimentary clay coupled thm numerical analyses have been carried out to provide a structured framework for interpretation and to enhance understanding of thm clay behaviour numerical analyses have been based on a coupled theoretical formulation that incorporates a constitutive law especially developed for this type of material the law includes degradation of bonding by damage by performing three dimensional computations it has been possible to incorporate anisotropy of m

mechanisms controlling the silicon isotopic compositions of river waters it has been proposed that silicon si isotopes are fractionated during weathering and biological activity leading to heavy dissolved riverine compositions in this study the first seasonal variations of stable isotope compositions of dissolved riverine si are reported and compared with concomitant changes in water chemistry four different rivers in switzerland were sampled between march 2004 and july 2005 the unique high resolution multi collector icp ms nu1700 has been used to provide simultaneous interference free measurements of 28si 29si and 30si abundances with an average limiting precision of 0 04 on 30si this precision facilitates the clarification of small temporal variations in isotope composition the average of all the data for the 40 samples is 30si 0 84 0 19 1 sd despite significant differences in catchment lithologies biomass climate total dissolved solids and weathering fluxes the averaged isotopic composition of dissolved si in each river is strikingly similar with means of 0 70 0 12 for the birs 0 95 0 22 for the saane 0 93 0 12 for the ticino and 0 79 0 19 for the verzasca however the 30si undergoes seasonal variations of up to 0 6 comparisons between 30si and physico chemical parameters such as the concentration of dissolved si and other cations the discharge of the rivers and the resulting weathering fluxes permits an understanding of the processes that control the si budget and the fate of dissolved si within these rivers the main mechanism controlling the si isotope composition of the mountainous verzasca river appears to be a two component mixing between the seepage of soil ground waters with heavier si produced by clay formation and superficial runoff associated with lighter si during high discharge events a biologically mediated fractionation can be excluded in this particular river system the other rivers display increasing complexity with increases in the proportion of forested and cultivated landscapes as well as carbonate rocks in the catchment in these instances it is impossible to resolve the extent of the isotopic fractionation and contributed flux of si contributed by biological processes as opposed to abiotic weathering the presence of seasonal variations in si isotope composition in mountainous rivers provides evidence that extreme changes in climate affect the overall composition of dissolved si delivered to the oceans the oceanic si isotope composition is very sensitive to even small changes in the riverine si isotope composition and this parameter appears to be more critical than plausible changes in the si flux therefore concurrent changes in weathering style may need to be considered when using the si isotopic compositions of diatoms sponges and radiolaria as paleoproductivity proxies

hafnium and neodymium isotopes in seawater and in ferromanganese crusts the element perspective abstract hafnium and nd isotopes are increasingly used as paleoceanographic proxies comparing the mantle crust array and the seawater array in plots of e hf vs e nd it has been observed that for a given e nd value the corresponding e hf value is higher for seawater than it is for terrestrial rocks while this difference had initially been explained by significant hydrothermal input of mantle hf into seawater the currently favoured explanation is incongruent weathering of continental rocks producing radiogenic riverine hf input we here address this topic from the perspective of the behaviour of these two elements in seawater and in ferromanganese fe mn crusts we distinguish between a truly dissolved and a dissolved hf and nd pool the latter being comprised of truly dissolved and colloid bound colloidal hf and nd while there exists a hydrothermal pathway for colloid bound dissolved mantle hf into the oceans there is in marked contrast to nd no important riverine pathway for colloidal or truly dissolved continental hf owing to their respective chemical speciation in seawater there exists truly dissolved nd in the ocean while the amount of truly dissolved hf is insignificant neodymium is in exchange equilibrium between local seawater and both the hydrous fe and mn oxides hydrogenetic fe mn crusts are composed of due to continuous ad and desorption there is continuous isotopic re equilibration and the isotopic composition of nd in a fe mn crust reflects that of truly dissolved nd in local ambient seawater in contrast hf is only associated with the hydrous fe oxides on which it forms surface precipitates that do not exchange with seawater due to this lack of isotopic re equilibration the isotopic composition of hf in a fe mn crust is the average of that of all the hf scavenged during the lifetime of the hydrous fe oxide particles since the hf bearing hydrous fe oxides in a fe mn crust do not form from local ambient seawater at the crust s growth site but are advected as colloids or fine particles their hf isotopic composition depends on the origin and migration pathway of these colloids hence while nd isotopes in fe mn crusts provide reliable information on truly dissolved nd in local ambient seawater hf isotopes rather indicate the origin and pathway of hydrous fe oxide colloids and might differ from truly dissolved hf in local ambient seawater this may explain the occasional decoupling of nd and hf isotopes in fe mn crusts and supports the notion of a significant hydrothermal mantle signal of hf in seawater

the hafnium isotope composition of pacific ocean water the first hf isotope data for seawater are reported for a series of stations in the northwestern pacific and define a range from epsilon hf 3 5 1 4 to 8 6 1 6 most samples have values within error of the average of epsilon hf 5 9 but significant variations are found in intermediate waters at a depth of 600 m as well as in deep waters the nd and hf isotope compositions of the deep waters fall within the range of values found for surfaces of hydrogenetic ferromanganese crusts in the region confirming that hf in the fe mn crusts has been derived from the overlying water column which thus provide an archive of past seawater compositions although the seawater samples are generally close to the global epsilon nd epsilon hf correlation obtained from ferromanganese crusts there are significant deviations from this correlation indicating that there is some additional decoupling between nd and hf isotope signals most likely caused by local water mass mixing and differences in residence times this is not resolved in the crust samples which integrate seawater signals over 10 4 years the combined use of these two isotope systems in seawater therefore provides an additional dimension for tracing water masses in the oceans studies of the distribution of oceanic hf isotope compositions that have been confined to deep water and boundary waters as recorded in seafloor ferromanganese crusts can now be extended and aimed at characterising the entire present day water column average hf concentrations measured in this study are somewhat lower than previously reported suggesting a shorter residence time for hf in the global oceans although the uncertainty in the extent of hf removal from the water column during estuarine mixing as well as a lack of data on hydrothermal and dust inputs remains a limit on how well the residence time can be defined c 2008 elsevier ltd all rights reserved

weathering versus circulation controlled changes in radiogenic isotope tracer composition of the labrador sea and north atlantic deep water geological reconstructions and general circulation models suggest that the onset of both northern hemisphere glaciation 2 7 myr ago and convection of labrador sea water lsw were caused by the closure of the panama gateway 4 5 myr ago time series data that have been obtained from studies of ferromanganese crusts from the northwestern atlantic suggest that radiogenic isotopes of intermediate ocean residence time pb and nd can serve as suitable tracers to reconstruct these events however it has been unclear until now as to whether the changes that have been observed in isotope composition at this time are the result of increased thermohaline circulation or due to the effects of increased glacial weathering in this paper we adopt a box model approach to demonstrate that the shifts in radiogenic isotope compositions are unlikely to be due to changes in convection in lsw but can be explained in terms of increases of erosion levels due to the glaciation of greenland and canada furthermore we provide experimental evidence for the incongruent release of a labile fraction of strongly radiogenic pb and nonradiogenic nd from continental detritus eroding into the labrador sea this can be attributed to the glacial weathering of old continents and accounts for the paradox that one of the areas of the world most deficient in radiogenic pb should provide such a rich supply of radiogenic pb to the oceans an important general conclusion is that the compositions of radiogenic isotopes in seawater are not always a reflection of their continental sources perhaps more importantly the transition from chemical weathering to mechanical erosion is likely to result in significant variations in radiogenic tracers in seawater

hf and nd isotopes in marine sediments constraints on global silicate weathering the combined use of lu hf and sm nd isotope systems potentially offers a unique perspective for investigating continental erosion but little is known about whether and to what extent the hf nd isotope composition of sediments is related to silicate weathering intensity in this study hf and nd elemental and isotope data are reported for marine muds leached fe oxide fractions and zircon rich turbidite sands collected off the congo river mouth and from other parts of the se atlantic ocean all studied samples from the congo fan muds fe hydroxides sands exhibit indistinguishable nd isotopic composition end 16 indicating that fe hydroxides leached from these sediments correspond to continental oxides precipitated within the congo basin in marked contrast hf isotope compositions for the same samples exhibit significant variations leached fe hydroxide fractions are characterized by ehf values from 1 1 to 1 3 far more radiogenic than associated sediments from 7 1 to 12 0 and turbidite sands from 27 2 to 31 6 ehf values for congo fan sediments correlate very well with al k i e a well known index for the intensity of chemical weathering in central africa taken together these results indicate that 1 silicate weathering on continents leads to erosion products having very distinctive hf isotope signatures and 2 a direct relationship exists between ehf of secondary clay minerals and chemical weathering intensity these results combined with data from the literature have global implications for understanding the hf nd isotope variability in marine precipitates and sediments leached fe hydroxides from congo fan sediments plot remarkably well on an extension of the seawater array i e the correlation defined by deep sea fe mn precipitates providing additional support to the suggestion that the ocean hf budget is dominated by continental inputs fine grained sediments define a diffuse trend between that for igneous rocks and the seawater array which we refer to as the zircon free sediment array ehf 0 91 end 3 10 finally we show that the hf nd arrays for seawater unweathered igneous rocks zircon free and zircon bearing sediments ehf 1 80 end 2 35 can all be reconciled using monte carlo simulations with a simple weathering model of the continental crust

the hf isotopic composition of ferromanganese nodules and crusts and hydrothermal manganese deposits implications for seawater hf we present hf and pb isotopic data and chemical compositions of the outermost layers of marine ferromanganese deposits of different types hydrogenous and hydrothermal with a worldwide distribution the hf isotopic compositions display a broad range and refine previously reported regional differences as follows atlantic ocean hf 4to 2 indian ocean hf 2to 4 pacific ocean hf 3to 10 the most radiogenic hf isotopic compositions in the pacific samples are for hydrothermal manganese deposits that also have low 207pb204pb demonstrating that this signature reflects a contribution from hydrothermal venting of hf leached from oceanic volcanic rocks rather than from riverine inputs volcanic ash or eolian dust hafnium concentrations in the deposits increase from 20 ppb to 20 ppm with decreasing hf the hf and pb isotopic compositions for ferromanganese crusts define an apparent mixing trend between literature values of average continental crust and morb the range in hf for ferromanganese crusts is narrower than it is for 206pb204pb compared to the differences in isotopic composition of the sources of hf and pb this is consistent with hf having a longer residence time than pb the concentration of hf in ferromanganese crusts has been found to co vary with growth rate and inversely correlates with hf isotopic compositions hf isotope ratios may be used to determine not only the source of hf but possibly the source of fe and mn measurements of hf and hf concentrations in nodule tops bottoms and associated sediments show that the hf of nodules is sensitive to sedimentary oxic and sub oxic diagenetic processes and thus most nodules may not reliably reflect the isotopic composition of hf in seawater

impact of glacial activity on the weathering of hf isotopes observations from southwest greenland abstract data for the modern oceans and their authigenic precipitates suggest incongruent release of hafnium hf isotopes by chemical weathering of the continents the fact that weathering during recent glacial periods is associated with more congruent release of hf isotopes has led to the hypothesis that the incongruency may be controlled by retention of unradiogenic hf by zircons and that glacial grinding enhances release of hf from zircons here we study the relationship between glacial weathering processes and hf isotope compositions released to rivers fed by land terminating glaciers of the greenland ice sheet as well as neighbouring non glacial streams the weathered source rocks in the studied area mostly consist of gneisses but also include amphibolites of the same age 1 9 ga hafnium and neodymium isotope compositions in catchment sediments and in the riverine suspended load are consistent with a predominantly gneissic source containing variable trace amounts of zircon and different abundances of hornblende garnet and titanite glacially sourced rivers and non glacial streams fed by precipitation and lakes show very unradiogenic nd isotopic compositions in a narrow range nd 42 8 to 37 9 hafnium isotopes on the other hand are much more radiogenic and variable with hf between 18 3 and 0 9 in glacial rivers and even more radiogenic values of 15 8 to 46 3 in non glacial streams although relatively unradiogenic hf is released by glacial weathering glacial rivers actually fall close to the seawater array in hf nd isotope space and are not distinctly unradiogenic based on their abundance in rocks and sediments and their isotope compositions different minerals contribute to the radiogenic hf in solution with a decreasing relevance from garnet to titanite hornblende and apatite neodymium isotopes preclude a much stronger representation of titanite hornblende and apatite in solution such as might result from differences in dissolution rates than estimated from mineral abundance the strong contrast in hf isotope compositions between glacial rivers and non glacial streams results mostly from different contributions from garnet and zircon where zircon weathering is more efficient in the subglacial environment a key difference between glacial and non glacial waters is the water rock interaction time while glacial rivers receive continuous contributions from long residence time waters of distributed subglacial drainage systems non glacial streams are characterized by fast superficial drainage above the permafrost horizon therefore the increased congruency in hf isotope weathering in glacial systems could simply reflect the hydrological conditions at the base of the ice sheet and glaciers with zircon weathering contributions increasing with water rock interaction time

rare earth element geochemistry of late devonian reefal carbonates canning basin western australia confirmation of a seawater ree proxy in ancient limestones rare earth element and yttrium ree y concentrations were determined in 49 late devonian reefal carbonates from the lennard shelf canning basin western australia shale normalized sn ree y patterns of the late devonian samples display features consistent with the geochemistry of well oxygenated shallow seawater a variety of different ancient limestone components including microbialites some skeletal carbonates stromatoporoids and cements record seawater like ree y signatures contamination associated with phosphate fe oxides and shale was tested quantitatively and can be discounted as the source of the ree y patterns co occurring carbonate components that presumably precipitated from the same seawater have different relative ree concentrations but consistent ree y patterns clean devonian early marine cements n 3 display ree y signatures most like that of modern open ocean seawater and the highest y ho ratios e g 59 and greatest light ree lree depletion average nd sn yb sn 0 413 sd 0 076 however synsedimentary cements have the lowest ree concentrations e g 405 ppb non contaminated devonian microbialite samples containing a mixture of the calcimicrobe renalcis and micritic thrombolite aggregates in early marine cement n 11 have the highest relative ree concentrations of tested carbonates average total ree 11 3 ppm stromatoporoid skeletons unlike modern corals algae and molluscs also contain well developed seawater like ree patterns samples from an estuarine fringing reef have very different ree y patterns with lree enrichment nd sn yb sn 1 possibly reflecting inclusion of estuarine colloidal material that contained preferentially scavenged lree from a nearby riverine input source hence devonian limestones provide a proxy for marine ree geochemistry and allow the differentiation of co occurring water masses on the ancient lennard shelf although appropriate partition coefficients for quantification of devonian seawater ree concentrations from out data are unknown hypothetical devonian canning basin seawater ree patterns were obtained with coefficients derived from modern natural proxies and experimental values resulting devonian seawater patterns are slightly enriched in lree compared to most modem seawaters and suggest higher overall ree concentrations but are very similar to seawaters from regions with high terrigenous inputs our results suggest that most limestones should record important aspects of the ree geochemistry of the waters in which they precipitated provided they are relatively free of terrigenous contamination and major diagenetic alteration from fluids with high non seawater like ree contents hence we expect that many other ancient limestones will serve as seawater ree proxies and thereby provide information on paleoceanography paleogeography and geochemical evolution of the oceans copyright c 2004 elsevier ltd

environmental hf nd isotopic decoupling in world river clays abstract the hafnium and neodymium radiogenic isotope systems behave differently during earth surface processes causing a wide dispersion of hf and nd isotopic compositions in sediments and other sedimentary rocks the decoupling between hf and nd isotopes in sediments is generally attributed to a combination of preferential sorting of zircon during sediment transport and incongruent weathering processes on continents in this study we analysed size fractions of sediment samples collected near the mouth of 53 rivers worldwide to better understand the factors controlling the distribution of hf and nd isotopes in sediments our results for rivers draining old cratonic areas and volcanic provinces demonstrate that both granite and basalt weathering can lead to significant grain size dependent hf isotopic variability while silt size fractions mainly plot along the terrestrial array world river clays are systematically shifted towards more radiogenic hf isotopic compositions defining together with published data a new clay array e hf 0 78 e nd 5 23 the hf nd isotope decoupling observed in volcanogenic sediments is best explained by selective alteration of lu rich mineral phases e g olivine and preferential enrichment of resistant unradiogenic minerals such as spinel and ilmenite in silt fractions we also show that the extent to which world river clays deviate from the clay array e hf clay is not linked to the presence of zircons instead it correlates positively with weathering indices and climatic parameters temperature rainfall of the corresponding drainage basins overall these findings demonstrate that the distribution of hf nd isotopes in clay size sediments is related to a large extent to weathering conditions on continents although the precise mechanisms controlling this relationship remain unclear we finally propose that the hf nd isotope pair proxy could be used in palaeoenvironmental studies to provide semi quantitative information on past climates

major and trace elements of river borne material the congo basin the congo river basin is the second largest drainage basin in the world after the amazon the materials carried by its main rivers provide the opportunity to study the products of denudation of a large fraction of the upper continental crust of the african continent this paper presents the chemical composition of the different phases carried in the congo rivers and is followed by a companion paper devoted to the modelling of major and trace elements the congo river between bangui and brazzaville as well as its main tributaries including a few organic rich rivers also called black rivers were sampled during the 1989 high water stage the three main phases suspended load dissolved load and bedload were analysed for twenty five major and trace elements concentrations normalized to the upper continental crust show that in each river suspended sediments and dissolved load are chemical complements for the most soluble elements ca na sr k ba rb and u while these elements are enriched in the dissolved loads they are considerably depleted in the corresponding suspended sediments this is consistent with their high mobility during weathering another type of complementarity is observed for zr and hf between suspended sediments and bedload related to the differential velocity of suspended sediments and zircons which are concentrated in bedloads compared to other rivers absolute dissolved concentrations of ca na sr k ba rb and u are remarkably low surprisingly high dissolved concentrations are found in the congo waters for other trace elements e g rees especially in the black rivers on a world scale these concentrations are among the highest measured in rivers and are shown to be ph dependent for a number of dissolved trace elements the dissolved loads are systematically normalized to the suspended loads for each river in order to remove the variations of the element abundances owing to source rock variations normalized diagrams for rees are presented and extended to the other elements they strongly support the argument that the apparent higher solubility of trace elements in the congo waters is due to the presence in the dissolved load of a colloidal phase as a result of 0 2 m filtration an important result is that these colloids are strongly depleted in fe and al with respect to the other elements finally the comparison of the dissolved suspended and sandy transport fluxes of each element in the congo basin rivers shows that although the proportions of for example the rees in the dissolved loads of the majority of the congo basin rivers is close to 10 of the total transport flux up to 80 of the rees are transported by the so called dissolved load in the black rivers

temporal variations in the fractionation of the rare earth elements in a boreal river the role of colloidal particles rare earth element ree data from weekly sampling of the filtered 0 45 m and suspended particulate phase during 18 months in the kalix river northern sweden are presented together with data on colloidal particles and the solution fraction 3 kda the filtered ree concentration show large seasonal and temporal variations in the river lanthanum varied between approximately 300 and 2100 pm high ree concentration in the filter passing fraction is related to increased water discharge and there is a strong correlation between the ree concentration organic carbon al and fe physical erosion of detrital particles plays a minor role for the yearly transport of particulate ree in this boreal river system the suspended particulate fraction which is dominated by non detrital fractions accounted for only 35 of the yearly total transport of la in the river approximately 10 of the ree were transported in detrital particles during winter at spring flood in may about 30 of the lree and up to 60 of the hree where hosted in detrital particles ultrafiltration of river water during spring flood shows that colloidal particles dominate the transport of filter passing ree less than 5 of the filtered ree are found in the fraction smaller than 3 kda the colloidal fraction shows a flat to slightly lree enriched pattern whereas the solution fraction 3 kda show an hree enriched pattern compared with till in the catchment suspended particles show a lree enriched pattern data indicate that the ree are associated with two phases in the colloidal and particulate fraction an organic rich phase with associated al fe and an fe rich fe oxyhydroxide inorganic phase the ce anomaly in the suspended particulate fraction in the river shows systematic variations and can be used to interpret fractionation processes of the ree during weathering and transport there was no anomaly at maximum spring flood but during the ice covered period the anomaly became more and more negative the temporal and seasonal variations of the ce anomaly in the suspended particulate phase reflect transport of ree c al fe enriched colloids from the upper section of the till and or from mires to the river at storm events

geochemistry of large river suspended sediments silicate weathering or recycling tracer this study focuses on the major and trace element composition of suspended sediments transported by the world s largest rivers its main purpose is to answer the following question is the degree of weathering of modern river borne particles consistent with the estimated river dissolved loads derived from silicate weathering in agreement with the well known mobility of elements during weathering of continental rocks we confirm that river sediments are systematically depleted in na k ba with respect to the upper continental crust for each of these mobile elements a systematics of weathering indexes of river borne solids is attempted a global consistency is found between all these indexes important variations in weathering intensities exist a clear dependence of weathering intensities with climate is observed for the rivers draining mostly lowlands however no global correlation exists between weathering intensities and climatic or relief parameters because the trend observed for lowlands is obscured by rivers draining orogenic zones an inverse correlation between weathering intensities and suspended sediment concentrations is observed showing that the regions having the highest rates of physical denudation produce the least weathered sediments finally chemical and physical weathering are compared through the use of a simple steady state model we show that the weathering intensities of large river suspended sediments can only be reconciled with the silicate derived dissolved load of rivers by admitting that most of the continental rocks submitted to weathering in large river basins have already suffered previous weathering cycles a simple graphical method is proposed for calculating the proportion of sedimentary recycling in large river basins finally even if orogenic zones produce weakly weathered sediments we emphasize the fact that silicate chemical weathering rates and hence co2 consumption rates by silicate weathering are greatly enhanced in mountains simply because the sediment yields in orogenic drainage basins are higher hence the parameters that control chemical weathering rates would be those that control physical denudation rates

radiometric constraints on hydrothermal circulation in cooling granite plutons improved precision of radiometric dating of ore deposits can provide information about the thermal history of hydrothermal circulation in cooling plutons in jales a hercynian porphyritic two mica granite and pre ordovician mica schists are cut and intensely altered by the campo gold quartz vein the unaltered granite must be younger than 320 6 ma and gives mica rb sr ages of 308 5 2 4 1 ma muscovite and 294 5 1 1 ma biotite alteration muscovites from the granite give a weighted mean rb sr age of 308 1 1 5 ma and a mean 39ar 40ar age of 300 7 2 8 ma alteration muscovites from the mica schists give similar 39ar 40ar ages averaging 303 0 2 8 ma the results suggest that circulation of the campo mineralising fluids took place no more than 2 4 ma after the granite cooled through the muscovite rb sr closure temperature about 500 c and that subsequent cooling to biotite closure at about 300 c took place at less than 14 c ma the mean cooling rate following emplacement was 15 to 25 c ma the most detailed comparable published data for the cornubian ore field imply much faster cooling rates

petrogenesis of tourmaline granites and topaz granites the contribution of experimental data abstract fluorine and boron are generally only minor components of granitic rocks but may be found highly concentrated in certain tourmaline granites and topaz granites up to 1 wt b2o3 and 3 2 wt f respectively studies of various examples of these granite types which occur as small bodies emplaced at shallow levels p lithostatic textural and petrographic data indicate that the tourmaline and topaz granite magmas crystallized at low to moderate temperatures below 700 c and that a fluid phase may have been present during the crystallization interval both granites varieties are peraluminous co up to 5 characterized by the presence of white micas lithium micas or muscovite aluminium silicates and other al rich minerals garnet cordierite boron and fluorine are hosted by tourmaline schorl rich member of the schorl dravite series topaz and mica respectively these granites have low ca fe mg and ti contents each the crystallization of tourmaline granite and topaz granite magmas is discussed using experimental data derived from studies of granitic systems with added boron and fluorine both elements act as a flux enabling boron and fluorine enriched melts to persist to temperatures as low as 650 c at 1 kbar in addition the effect of increasing fluorine content displaces the minimum in q ab or at ph2o 1 kbar toward the albite apex plots of fluorine rich topaz granites coincide with this trend suggesting that the role of fluorine in magmatic processes may have affected the rock composition as well as crystallization temperatures boron rich granites plot near the low ph2o minima in qz ab or suggesting that boron has less of an influence on minimum melt compositions the low temperatures of crystallization permits phases such as muscovite or andalusite topaz and two alkali feldspars to crystallize directly from f and b enriched melts at low pressures in addition the limited available experimental data are used to compare the effects of fluorine and boron on major and trace element distribution during melt vapour interaction

glacial weathering and the hafnium isotope composition of seawater the hf isotope composition of seawater does not match that expected from dissolution of bulk continental crust this mismatch is generally considered to be due to retention of unradiogenic hf in resistant zircons during incomplete weathering of continental crust during periods of intense glacial weathering zircons should break down more efficiently resulting in the release of highly unradiogenic hf to the oceans we test this hypothesis by comparing nd and hf isotope time series obtained from nw atlantic ferromanganese crusts both isotope systems show a decrease associated with the onset of northern hemisphere glaciation the observed changes display distinct trajectories in nd hf space which differ from previously reported arrays of bulk terrestrial material and seawater such patterns are consistent with the release of highly unradiogenic hf from very old zircons facilitated by enhanced mechanical weathering

zircon effect alone insufficient to generate seawater nd hf isotope relationships 1 many studies have suggested that continental weathering inputs have controlled the dissolved oceanic budget of hafnium hf however whether the offset of seawater nd hf isotope compositions from the terrestrial array can be fully generated by incongruent weathering of continental rocks the zircon effect is still not well constrained in recent years an increasing amount of combined u pb ages and hf isotopic compositions of riverine detrital zircons have been published here a new model of the nd hf isotopic compositions of the weathered zircon free part of the upper continental crust is presented which is based on published hf isotope compositions and formation ages of modern riverine detrital zircons combined with nd isotopic compositions of rocks from the upper continental crust our model results indicate that the nd hf isotopic composition of the weathered zircon free part of the upper continental crust is not consistent with the seawater isotopic compositions this suggests that the elevated seawater hf isotope compositions for given nd isotope compositions cannot be fully explained by incongruent zircon weathering of the continents which is also supported by a recent study demonstrating incongruent weathering of other minerals than zircon

estuarine distributions of zr hf and ag in the hudson river and the implications for their continental and anthropogenic sources to seawater 1 zirconium and hf in seawater are derived from continental weathering and are transported to the oceans by rivers but the modification of this flux with estuaries is largely unknown furthermore there is no information as to whether there is a pollutant source of these metals that might affect their budget calculations in the modern ocean to address the riverine flux and potential anthropogenic sources the distributions of dissolved zr and hf have been measured in surface and bottom water through the hudson river estuary the distribution of ag is included because it is sensitive to urban sources and has partial similarities in its distribution to those of zr and hf there is about 50 removal of zr and hf in surface water relative to their freshwater end member concentrations of 243 and 3 1 pmol kg as salinity starts to increase but an urban source of these metals midestuary may obscure greater removal silver concentrations in surface water are below the detection limit until salinity of 3 5 is reached the concentrations of zr and hf 0 5 m above the bottom are 1 5 to 3 times higher than their surface water concentrations throughout the estuary and may result from input of groundwater diffusion from pore fluids or inclusion of colloidal phases in our analyses downstream of the turbidity maximum bottom water ag concentrations are high due to release from particles that originally formed within the estuary and were moved inland following the spring freshet this process may also affect zr and hf the increase in the freshwater atomic zr hf ratio from 70 to 80 characteristic of terrestrial rocks to the elevated zr hf 110 ratio of seawater takes place at middle to high salinity due to enhanced release of zr from resuspended particles and slower removal rates compared to hf a main implication of this study is that estuaries are a sink for zr and hf the reduction of the predicted export of continental zr and hf to the oceans increases their previously calculated seawater residence by as much as 2 to 4 times assuming rivers dominate the supply of zr and hf to seawater

contrasting geochemical cycling of hafnium and neodymium in the central baltic sea the central baltic sea is a marginal brackish basin which comprises anoxic bottom waters and is surrounded by geological source terrains with a wide variety of compositions and ages this allows the investigation of water mass mixing using radiogenic isotope compositions of nd and hf as well as their geochemical cycling across varying redox conditions in the water column in this study we present the distribution of nd and hf concentrations and their isotopic compositions for 6 depth profiles and 3 surface water sites obtained during a cruise in the central baltic sea onboard the rv oceania as a part of the international geotraces program the results obtained indicate that nd isotopes effectively trace the mixing between more radiogenic saline waters from the south and unradiogenic fresh waters from the north which helps to understand the reliability of nd isotopes as water mass tracer in the open ocean in surface waters nd shows higher concentrations and less radiogenic isotope compositions at the northern stations which are progressively diluted and become more radiogenic to the south consistent with the counterclockwise circulation pattern of central baltic sea surface waters in contrast to the variable nd concentrations hf shows much less variability at the gotland deep station the nd concentrations of the euxinic waters are higher by a factor 10 than those of the overlying oxygen depleted waters whereas hf only shows small concentration variations this indicates faster removal of hf from the water column than nd moreover the dissolved hf isotope signatures document great variability but no consistent mixing trends our explanation is that hf has a lower residence time than nd and also that the hf isotope signatures of the sources are highly heterogeneous which is attributed to their differing magmatic and tectonic histories as well as incongruent post glacial weathering around the central baltic sea

rare earth elements and sr and nd isotopic compositions of dissolved and suspended loads from small river systems in the vosges mountains france the river rhine and groundwater abstract the aim of this study is to characterize the evolution of the rare earth elements ree in non mature streams from small catchment areas in the vosges mountains downstream to more mature plain rivers including the river rhine the dissolved load ree distribution patterns of the low ph vosges streams are very different from those of high ph plain rivers indicating that different physico chemical parameters control ree transport in these different water systems the plain rivers and groundwater show similar ree distribution patterns with a strong negative ce anomaly and heavy rare earth element hree enrichment in addition the river rhine has a positive gd anomaly which is of anthropogenic origin similar to the world s major rivers the light rare earth element lree enrichment in the plain rivers is mainly ph controlled their sm nd and 143 nd 144 nd isotope ratios are close to average continental crust values this is not the case for the less evolved non mature and low ph vosges streams their high sm nd and 143 nd 144 nd ratios but low 87 sr 86 sr ratios suggest that chemical alteration of accessory middle rare earth element mree enriched minerals such as apatites from rocks in the catchment area control the ree abundances of these waters a comparison of the dissolved load ree distribution patterns with those of the principal lithologies in the corresponding drainage basins illustrates that especially the eu anomalies of the vosges streamlets are strongly lithology dependent leaching experiments indicate that the suspended load is isotopically very inhomogeneous the ree distribution patterns of the suspended load leachates have no similarities with those of the corresponding dissolved load indicating that the leachable reservoir not only contains adsorbed ree but also ree from leachable mineral phases their 143 nd 144 nd sm nd and 87 sr 86 sr ratios support this suggestion being always higher and lower respectively than those of their corresponding dissolved loads they rather point to the presence of relic primary apatite in the leachable portion of the suspended load the flat paas normalized ree distribution patterns the high 87 sr 86 sr and low 143 nd 144 nd isotopic ratios of the corresponding residues suggest secondary silicate phases such as clay minerals in the residual phase of the suspended load leachates and corresponding residual phases define alignments in the sm nd isochron diagram whose slopes define ages ranging between 200 and 390 ma indicating that the mineral phases in the suspended load retain some memory of their primary precursor minerals in the hercynian granitic source rocks

global neodymium hafnium isotope systematics revisited global nd hf isotope systematics can be mainly described with two linear arrays the global silicate earth array the terrestrial array and the global ferromanganese crust and nodule array the seawater array the offset between these two arrays provides evidence for the sources and mechanisms by which these elements are added to ocean water however the reason for this offset is under debate with the two preferred hypotheses being i incongruent release of hf during continental weathering and ii hydrothermal contribution of hf to the seawater budget here we present new nd and hf isotope data on glacio marine core top sediments from around the perimeter of the antarctic continent the results range from ehf 30 0 to ehf 3 9 and end 21 3 to end 0 9 reflecting the large range of basement ages and lithologies around the antarctic continent in nd hf isotope space they confirm the systematic correlations found in rocks from other parts around the world and provide valuable insights into the previously underrepresented group of sediments with very old provenance in this paper we revisit the cause for the offset of the seawater array from the terrestrial array using simple mass balance considerations we use these calculations to test to what degree the seawater array could be a product of preferential weathering of non zircon portions of the upper continental crust implying retention of zircons in the solid residue of weathering lutetium hf and sm nd evolution and mixing calculations show that the global seawater array can be generated with continental sources only on the other hand a predominantly hydrothermal origin of hf in the ocean is not possible because the seawater hf isotopic composition is significantly less radiogenic than hydrothermal sources and requires a minimum fraction of 50 continental hf while hydrothermal sources may contribute some hf to seawater continental contributions are required to balance the budget

ree fractionation during granite weathering and removal by waters and suspended loads sr and nd isotopic evidence very few studies deal with ree rare earth element mobility within the system soil soil solution streamwater in this article we try to characterize the fractionation and the migration of the ree in a granite derived soil system located in a small catchment of the vosges mountains icp ms and tims measurements were performed on both solid samples fresh granite soil and suspended load of the stream and waters soil solutions springwater and streamwater to determine their respective ree concentrations and sr and nd isotopic compositions the paas normalized ree pattern of the bedrock is characterized by a strong depletion in hree heavy ree and a negative eu anomaly 0 46 similarly the granite normalized ree distribution patterns of the soil samples show hree depletions that become more important with decreasing depth the correlative behavior between p2o5 th and ree with depth indicates that besides apatite other phosphate minerals such as monazite are the most important phases controlling the th and ree budget in the soil profile on the other hand at greater depth zircon seems to be another important mineral phase controlling especially the hree enrichment as shown by the positive relationship between zr content and the yb ho ratio different grain size fractions show similar ree distribution patterns and are only weakly fractionated compared with bulk soil sample however the finest fraction 0 20 m is more enriched in sr and ree suggesting a stronger concentration of ree carrying minerals in this fraction the suspended and dissolved load of the stream show as a whole an enrichment in hree if compared with the granite or with the different soil samples however compared with the uppermost soil samples the suspended load is significantly more enriched in hree its ree distribution pattern is more similar to that of the finest fraction of the deeper soil sample and to the fresh granite thus most probably the ree of the suspended load originated from a source with ree characteristics found in the deep soil horizons this source might have been situated in the uppermost soil profile which is actually ree depleted the weathering process can be compared with a leaching experiment where the waters correspond to the leachate and the soil to the residual phase of the granite the sr isotope data indicate that the suspended load originates from the finest soil fraction the sr and nd isotopic data of the suspended load suggest that it contains up to 3 sr and nd from apatite and up to 97 from feldspar most of the sr and nd in the waters originate from apatite leaching or dissolution

u pb zircon and monazite geochronology of variscan magmatism related to syn convergence extension in central northern portugal abstract the viseu area is located in the central iberian zone of the iberian variscan belt and hosts numerous post thickening collision related granitoids intruded into upper and middle crustal levels the present paper reports high precision u pb zircon and monazite ages for four plutons of the viseu area the syn kinematic granitoids of maceira 314 5 ma casal vasco 311 1 ma and junqueira 307 8 0 7 ma and the late kinematic biotite monzogranites of cota 306 9 ma this points to a synchronous emplacement of the different syn kinematic plutons shortly followed by the intrusion of the late kinematic granites and shows that the upper carboniferous plutonism occurred within a short time span of ca 10 million years the ascent of granite magmas took place after an extensional tectonic event d 2 and is coeval with dextral and sinistral crustal scale transcurrent shearing d 3 field and petrographical evidence suggest a narrow time span between peak t metamorphic conditions and the intrusion of granitic melts which implies very fast uplift rates accommodated through active tectonic exhumation magma compositions evolve through time reflecting an increasing involvement of mid crustal sources and the underplating effect of an upwelling asthenospheric mantle at the base of a thinning and stretching continental crust

a full scale in situ heating test for high level nuclear waste disposal observations analysis and interpretation the paper describes the performance observations and interpretation of a large scale in situ heating test that simulates a disposal concept for heat emitting high level nuclear waste in the experiment heaters are emplaced in the axis of a tunnel excavated in granite to simulate the heat production of radioactive waste the test is fully instrumented and attention is focused on the thermo hydro mechanical thm behaviour of the near field region constituted by the compacted bentonite barrier surrounding the heater and the immediately adjacent rock interpretation of the test is assisted by the performance of a coupled numerical analysis based on a formulation that incorporates the relevant thm phenomena initial and boundary conditions for the analysis as well as material parameters are determined from an extensive programme of field and laboratory experiments the paper presents and discusses the thermal hydraulic and mechanical observations in the bentonite barrier and in the host rock special attention is paid to the progress of hydration in the barrier to the effects of heating and vapour transport and to the development of swelling pressures in the barrier after five years of heating one of the heaters was switched off and the experiment was partially dismantled allowing the final state of the barrier to be observed directly the numerical analysis performed has proved able to represent the progress of the experiment very satisfactorily in addition predictions concerning the final state of the clay barrier are very close to the observations obtained during dismantling the performance and analysis of the in situ test have significantly enhanced the understanding of a complex thm problem and have proved the capability of the numerical formulation to provide adequate predictive capacity

geochemical and isotopic constraints on the petrogenesis of early ordovician granodiorite and variscan two mica granites from the gouveia area central portugal abstract a biotite granodiorite and seven sn bearing two mica granites crop out in the gouveia area central portugal a shrimp u th pb zircon age from the granodiorite and monazite ages from four of the two mica granites show that they are of early ordovician 480 ma and permo carboniferous i e variscan 305 and 290 ma age respectively the variscan two mica granites are late and post d3 major and trace element variation in the granitic rocks and their biotite and muscovite indicate mainly individual fractionation trends the granitic rocks are mostly depleted in hree relative to lree the biotite granodiorite is probably derived from igneous lower crust as evidenced by low initial 87 sr 86 sr 0 7036 high e nd t 2 5 and moderate 18 o 8 8 the two mica granites are probably derived by partial melting of heterogeneous mid crustal metasediments mainly metapelite and some metagraywacke as evidenced by their high initial 87 sr 86 sr 0 7076 0 7174 18 o 10 7 13 4 and major element compositions however variation diagrams for major and trace elements from two of the muscovite biotite granites and their micas define fractionation trends rb sr whole rock analyses from the two granites are perfectly fitted to a single isochron and the rocks have sub parallel ree patterns the younger granite is derived from the older by fractional crystallization of quartz plagioclase biotite and ilmenite tested by modelling major and trace elements most of the sn bearing granites are derived from distinct magma batches they result from partial melting of a heterogeneous mid crustal metasediment they do not represent a crustal anomaly in tin fractional crystallization is responsible for the increase in the sn contents of the granites and their micas muscovite has a higher sn content than coexisting biotite and is the principal host mineral for sn in these rocks

decoupled hf and nd isotopes in suspended particles and in the dissolved load of late archean seawater abstract it is generally agreed that decoupling of the hf and nd isotope systems in modern aqueous systems is a result of incongruent release of hf during terrestrial weathering of the continental crust although the mechanism s behind this process are not yet fully understood we here present hf nd isotope data for the neoarchean krivoy rog banded iron formation bifs ukraine and combine observations on modern aqueous environments with those of the early earth to further evaluate the mechanism s behind hf nd isotope decoupling in aqueous systems the pure late archean krivoy rog chemical sediment endmember representing the dissolved pool of ancient seawater shows decoupled end2 60ga ehf2 60ga values of 2 3 and 9 48 respectively and suggests that decoupled hf nd isotopes had been a global rather than a local phenomenon in neoarchean seawater this further reveals that incongruent hf release via terrestrial weathering and erosion of emerged and evolved continental landmasses were widespread geological processes by late archean time impure krivoy rog bif samples composed of a mixture of seawater derived and detrital nd and hf show systematically more positive end2 60ga values but still reveal decoupled end ehf values relative to an associated schist that plots slightly below the terrestrial array this suggests that mineral sorting between a zircon bearing sand sized fraction and fine grained sediment particles occurred on in late archean continents rivers and oceans and had significant impact on the chemical compositions of the suspended and dissolved element loads of late archean seawater less radiogenic hf isotope compositions in the krivoy rog seawater relative to detritus contaminated bifs further suggest a pathway for high temperature hydrothermal hf into anoxic archean seawater that diluted the even more radiogenic hf isotopic composition of continental run off created by the mineralogical composition of the continental hinterland and the zircon effect alternatively the less pronounced decoupling of ehf end in late archean seawater may be related to a shorter residence time of hf relative to nd furthermore systematically more positive initial end values in detritus contaminated archean bifs relative to respective dissolved seawater loads suggest that weathered and eroded material of ultra mafic rock suites had significant impact on the suspended and dissolved fractions in archean seawater

a routine high precision method for lu hf isotope geochemistry and chronology a method for chemical separation of lu and hf from rock meteorite and mineral samples is described together with a much improved mass spectrometric running technique for hf this allows i geo and cosmochronology using the176lu 176hf decay scheme and ii geochemical studies of planetary processes in the earth and moon chemical yields for the three stage ion exchange column procedure average 90 for hf chemical blanks are 0 2 ng for lu and hf from 1 g of hf a total ion current of 0 5 10 11 ampere can be maintained for 3 5 h yielding 0 01 0 03 precision on the ratio176hf 177hf normalisation to179hf 177hf 0 7325 is used extensive results for the johnson matthey hf standard jmc 475 are presented and this sample is urged as an international mass spectrometric standard suitable aliquots prepared from a single batch of jmc 475 are available from denver lu hf analyses of the standard rocks bcr 1 and jb 1 are given the potential of the lu hf method in isotope geochemistry is assessed

geochemical constraints on the genesis of hercynian two mica leucogranites from the massif central france abstract late hercynian two mica leucogranites dated at 340 280 3a old occur across the entire massif central france and form dykes and stocks up to 130 km in length they are peraluminous molecular al 2 o 3 na 2 o k 2 o cao asi 1 16 1 25 and have low initial nd 8 2 to 6 1 indicating derivation from the metasedimentary lower crust as sampled in crustal xenoliths nd 340 8 6 to 4 3 nd 280 9 0 to 4 8 their high sio 2 70 78 wt p 2 o 5 up to 0 5 rb and ga and low ba sr and ree are mainly a result of partial melting processes rather than fractionation partial melting was initiated by underplating of the lower crust by mantle derived basic magmas between 360 and 270 ma and was intensified by granulite facies metamorphism between 300 and 280 ma from this model there is little similarity between the genesis of two mica leucogranite in the massif central and that in the himalaya with which it has previously been compared

swelling phenomena and effective stress in compacted expansive clays the central aim of this paper is to discuss the applicability of the effective stress principle as defined by terzaghi total stress minus pore water pressure to predict the behaviour of expansive

the role of disseminated calcite in the chemical weathering of granitoid rocks accessory calcite present at concentrations between 300 and 3000 mg kg 1 occurs in fresh granitoid rocks sampled from the merced watershed in yosemite national park ca usa loch vale in rocky mountain national park co usa the panola watershed ga usa and the rio icacos puerto rico calcite occurs as fillings in microfractures as disseminated grains within the silicate matrix and as replacement of calcic cores in plagioclase flow through column experiments using de ionized water saturated with 0 05 atm co2 produced effluents from the fresh granitoid rocks that were dominated by ca and bicarbonate and thermodynamically saturated with calcite during reactions up to 1 7 yr calcite dissolution progressively decreased and was superceded by steady state dissolution of silicates principally biotite mass balance calculations indicate that most calcite had been removed during this time and accounted for 57 98 of the total ca released from these rocks experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution the lack of excess ca and alkalinity indicated that calcite had been previously removed by natural weathering the extent of ca enrichment in watershed discharge fluxes corresponds to the amounts of calcite exposed in granitoid rocks high ca na ratios relative to plagioclase stoichiometries indicate excess ca in the yosemite loch vale and other alpine watersheds in the sierra nevada and rocky mountains of the western united states this ca enrichment correlates with strong preferential weathering of calcite relative to plagioclase in exfoliated granitoids in glaciated terrains in contrast ca na flux ratios are comparable to or less than the ca na ratios for plagioclase in the subtropical panola and tropical rio icacos watersheds in which deeply weathered regoliths exhibit concurrent losses of calcite and much larger masses of plagioclase during transport limited weathering these results indicate that the weathering of accessory calcite may strongly influence ca and alkalinity fluxes from silicate rocks during and following periods of glaciation and tectonism but is much less important for older stable geomorphic surfaces

mantle and crustal sources in the genesis of late hercynian granitoids nw portugal geochemical and sr nd isotopic constraints abstract large volumes of granitoids were emplaced in the hercynian central iberian zone during the last ductile deformation phase d3 300 320 ma the biotite rich granitoids are the most abundant 1 syn d3 granodiorites monzogranites 313 319 ma with calc alkaline and aluminopotassic affinities 2 late d3 granodiorites monzogranites 306 311 ma related to subalkaline and aluminopotassic series these granitoids are associated with coeval gabbro norite to granodiorite bodies and or mafic microgranular enclaves both granitoids and basic intermediate rocks show petrological geochemical and isotopic evidence of interaction between felsic and mafic magmas the mantle derived melts represented by shoshonitic gabbro norites were probably derived from an enriched and isotopically homogeneous source sr i 0 7049 to 0 7053 e nd 2 1 to 2 5 in some syn and late d3 plutons there are evidences of essentially crustal granites represented by moderately peraluminous monzogranites of aluminopotassic affinity they have similar nd model ages 1 4 ga but different isotopic compositions sr i 0 7089 to 0 7106 e nd 5 6 to 6 8 revealing a heterogeneous crust potential protoliths are metasedimentary immature sediments and or felsic meta igneous lower crust materials large amounts of hybrid magmas were generated by the interaction of these coeval mantle and crust derived liquids giving rise to slightly peraluminous monzogranites granodiorites of calc alkaline and subalkaline affinities which display more depleted isotopic compositions than the crustal end members sr i 0 7064 to 0 7085 e nd 4 4 to 6 2 petrogenetic processes involving mingling and or mixing and fractional crystallization at variable degrees in multiple reservoirs are suggested a major crustal growth event occurred in late hercynian times 305 320 ma related to the input of juvenile mantle magmas and leading to the genesis of composite calc alkaline and subalkaline plutons largely represented in the central iberian zone

the hf isotope composition of global seawater and the evolution of hf isotopes in the deep pacific ocean from fe mn crusts this paper presents a revised chemical purification method of hf for the measurement of hf isotope ratios of fe mn crusts on a new generation of double focusing multiple collector plasma source mass spectrometer mc icp ms by measuring surface scrapings of hydrogenetic fe mn crusts distributed over the three major ocean basins the present day hf isotope distribution of oceanic deep water is assessed in detail the results show an ehf provinciality correlated with those of other radiogenic isotope tracers such as nd and pb in agreement with previous studies this supports the use of hf isotopes as tracer of element source provenance and water masses fe mn crusts display the same present day hf nd isotope array as given before for mn nodules the smaller isotopic variability of hf compared with nd may either be caused by a more efficient mixing of hf than nd in the ocean due to a longer residence time or may be a consequence of a systematically more radiogenic hf than nd isotope signature delivered to the oceans by weathering of continental crust a hf isotope time series was measured on crust va13 2 to assess the hf isotope compositions of the central pacific deep water over the past 26 ma no consistency is observed between the hf and pb isotope time series in contrast hf and nd isotope time series display similar patterns which are however apparently offset by 2 ma prior to 14 ma differential diffusion of hf and nd does not explain this offset the smaller amplitude in the hf isotope variations compared with the nd isotopes rather argues for more efficient mixing of hf in the ocean we suggest that both isotope systems have responded in a similar way to the processes affecting the dissolved radiogenic isotope composition of pacific deep water during this time interval the parallel increase in ehf and end observed between 14 and 3 ma may probably be attributed to the increased inputs of hf and nd into the central pacific ocean derived from the weathering of the pacific islands arcs over the past 3 ma an increased aeolian continental input derived from asia most likely caused negative shifts in end and ehf recorded by va13 2 the fact that hf and nd isotope compositions plot along the present day array for fe mn crusts and mn nodules over the entire past 26 ma suggests that aeolian supply of hf to the pacific ocean has been a long term important feature

neodymium and hafnium boundary contributions to seawater along the west antarctic continental margin highlights nd and hf are released from sediments to the water column in the amundsen sea embayment seawater nd and hf isotope compositions show opposed trends close to the marie byrd seamounts aabw is isotopically distinct in nd between the atlantic and the pacific sectors hf isotope variations occur between the sectors but not with depth in each sector abstract neodymium and hafnium isotopes and elemental concentrations sm nd hf zr have been measured in three water column profiles south of the antarctic circumpolar current in and to the east of the ross sea in conjunction with five bottom water samples from the amundsen sea embayment neodymium and hafnium both appear to be released from sediments in the embayment in the case of nd this is reflected in radiogenic isotope compositions endend up to 5 4 and highly elevated concentrations up to 41 pmol kg hafnium isotopes on the other hand are only very slightly altered relative to the open ocean sites and boundary release is most prominently indicated by elevated concentrations 1 pmol kg versus 0 7 pmol kg there is also a local input of both hf and nd at the marie byrd seamounts which leads to nd isotope compositions as radiogenic as 3 1 and hafnium shifted to less radiogenic compositions in local bottom water a compilation of the new data with literature data reveals a consistent view of the influence of antarctica on the nd isotope composition in lower circumpolar deep water lcdw and antarctic bottom water aabw sector specific nd addition shifts aabw formed in the atlantic sector to less radiogenic isotope compositions average end 9end 9 relative to lcdw average end 8 4end 8 4 whereas aabw in the pacific sector is shifted to more radiogenic values average end 7end 7 the evolution towards more radiogenic endend with depth in lcdw in the pacific sector is likely to reflect admixture of aabw but in addition is also controlled by boundary exchange with the slope as observed at the marie byrd seamounts hafnium isotopes are relatively homogeneous in the data set ranging between ehf 2ehf 2 and 3 8 for most samples excluding less radiogenic compositions in deep waters close to the marie byrd seamounts the hf isotope composition in the pacific sector is however slightly less radiogenic than in the atlantic corresponding to an average of 3 relative to an average of 3 8 this probably reflects unradiogenic hf inputs from antarctica to the pacific sector which are vertically homogenized by reversible scavenging the hf isotope heterogeneity in lcdw between both sectors is likely to indicate a shorter seawater residence time for hf than for nd which is consistent with the dissolved particulate phase partitioning of both elements

mechanical behaviour of heavily compacted bentonite under high suction changes the paper reports the results of an experimental study carried out on a bentonite compacted to a dry density of up to 1 7 mg m3 a high value for this type of soil the soil fabric has been studied using a variety of techniques revealing a clear bimodal pore distribution that corresponds to two distinct structural levels a microstructural one and a macrostructural one the main testing programme has been performed using oedometers especially designed to apply a very large range of suctions by applying the axis translation technique using nitrogen as the gas fluid it has been possible to reach suctions up to 15 mpa the higher suction range has been achieved by applying a controlled atmosphere where the relative humidity has been fixed by a solution of sulphuric acid or salts in this way suctions up to 550 mpa could be reached the maximum vertical stress that could be applied in the apparatus was 10 mpa two types of test have been carried out a tests in which a combination of loading paths at constant suction and drying wetting paths at constant load were applied b swelling tests under constant volume conditions in order to determine the swelling pressure and the stress path followed during wetting the results of the experimental programme are examined taking into account the role of the soil fabric in controlling observed mechanical behaviour in addition the results of the laboratory tests are reproduced and interpreted using a generalised plasticity model that considers explicitly the interaction between macrostructure and microstructure in this way it is possible to achieve a more complete understanding of the mechanisms that underlie observed behaviour and in particular the interplay between the two structural levels

thermodynamic properties of white micas on the basis of high pressure experiments in the systems k2omgoal2o3sio2h2o and k2ofeoal3o3sio2h3o abstract experiments in the piston cylinder apparatus were undertaken to synthesize the assemblage of phengite garnet kyanite and quartz or coesite in the system k2o mgo al2o3 sio2 h2o kmash compositional data of phengite were obtained for 13 experimental runs in the range of 30 to 45 kbar and 850 c to 1100 c the same was achieved for 23 runs in the system k2o feo al2o3 sio2 h2o kfash between 600 c and 900 c and 15 to 55 kbar on the basis of the latter runs and 6 additional synthesis experiments the dependence of the lattice dimensions on the composition of 2m1 phengites in kfash was determined to derive thermodynamic data we evaluated the above experiments and those reported by massonne and schreyer 1987 1989 on kmash phengites coexisting with other assemblages considering simple activity model like ams ms we obtained for the mg al celadonite and fe2 al celadonite theoretical endmembers hf0 5832415 3040 and 5492287 6267 j mol s0 288 527 4 008 and 303 148 6 827 j k mol v0 13 870 0 027 and 13 962 0 067 j bar mol the nonideal behavior of the muscovite ms mg al celadomite series was modelled using an asymmetric margules formalism with the following parameters w12h w21h 0 w12s 58 598 8 804 w21s 15 920 3 393 w12v 0 735 0 118 w21v 0 187 0 026 with units as above for the muscovite fe2 al celadonite series we used a symmetric model with wh 0 ws 24 083 3 088 j k mol and wv 0 3394 0 1120 j bar mol the above data were applied to construct a petrogenetic grid the example chosen is related to the kfash system with potassic white mica quartz and h2o in excess it covers the t range from 150 c to 550 c at a p up to 28 kbar the new thermodynamic data are also discussed in regard to their use in geothermobarometry

hafnium and neodymium isotopes and rey distribution in the truly dissolved nanoparticulate colloidal and suspended loads of rivers in the amazon basin brazil abstract radiogenic isotopes in river sediments and river waters have been widely used in provenance studies as these samples naturally integrate the geology chemistry of the entire catchment while the hf and nd isotope systems are coupled during igneous processes they are decoupled during supergene processes at the earth s surface which is reflected by the isotope composition of riverine sediments we present the first data for both hf and nd isotope compositions of the dissolved 0 2 m filtrates rich in nanoparticles and colloids npcs and the truly dissolved 1 kda ultrafiltrates load of rivers hafnium and nd isotope compositions and concentrations of the rare earths and yttrium rey and hf were determined for suspended particles 0 2 m as well as for the dissolved and the truly dissolved load of the rio solimoes the amazon s largest tributary draining the andes and of the rio negro an organic npc and particle rich river draining the rainforest of northern amazonia we also analyzed the nd isotope compositions of suspended sediments and 0 2 m filtered water samples from the amazon river and its tributaries rio tapajos rio xingu and rio jari our novel results clearly show that the decoupling of the hf and nd isotope systems is related to incongruent weathering processes on the continent as this decoupling can already be observed in the different hf and nd pools i e in the particulate the npc dominated dissolved and the truly dissolved load of rivers in the rio negro and rio solimoes a strong particle size dependent difference in hf isotope composition is observed values of e hf become more radiogenic as filter poresize decreases which can be related to the density and size dependent distribution of hf rich minerals e g zircons and their absence from the truly dissolved pool in contrast the nd isotope composition of amazonian river waters reflects that of their catchment geology tributaries draining the precambrian brazilian and guyana shields show very unradiogenic e nd values of 19 to 25 in their dissolved load whereas the rio solimoes draining the andes yields a more radiogenic e nd signal of only 7 the dissolved nd isotope composition of the amazon is dominated by its andean tributaries and averages at 8 although nd isotope compositions are thought to not being fractionated by earth surface processes significant differences of 1 3 1 9 e units can be observed between the dissolved and suspended loads in the amazon river and its main tributary the rio solimoes in these rivers the dissolved load is more radiogenic than the suspended sediment which is likely due to incongruent weathering and related mineral sorting in the andean headwaters in contrast the organic rich and mineral poor shield rivers do not show a difference between the truly dissolved dissolved and suspended load as the nd in all these pools is controlled by surface and solution complexation and hence isotopically homogenized by continuous exchange and re equilibration

long term experimental evidences of saturation of compacted bentonite under repository conditions abstract this paper summarises the information gathered in the last 15 years on the saturation of compacted bentonite obtained from different laboratory scale tests a large scale mock up test and a real scale in situ test that were performed to simulate the conditions of the bentonite barrier in a high level radioactive waste repository and to better understand the hydration heating processes in all the tests the bentonite used was the spanish febex bentonite the maximum temperature in the system was 100 c and the water used was of the granitic type with low salinity some of the tests were running for more than thirteen years the migration of water vapour in areas affected by the high temperature induced by the radioactive waste decay is very rapid its extent depending on the actual temperature and bentonite porosity the water vapour condensates in cooler areas and this causes water content increases in internal zones of the barrier where the liquid water coming from the host rock has not yet arrived the hydration kinetics is initially quicker when the temperature is high provided no vapour phase is formed nevertheless the major effect of the thermal gradient on saturation is a delaying of it in the inner parts of the barrier which can be very persistent and depends on the actual thermal gradient and consequently on the barrier thickness and boundary conditions during the transient period in which the barrier is saturating important changes in the water content and dry density of the bentonite are generated which induce bentonite density and water content gradients along its thickness these gradients could eventually disappear once the barrier is fully saturated depending on the irreversibility of the deformations the average density of the water in the saturated barrier will be higher than 1 g cm3 due to the predominance of high density interlayer water in the compacted bentonite and consequently more water than expected according to calculations made considering the density of free water would fit in the bentonite pores the rate of hydration of the barrier depends on the bentonite and surrounding media hydraulic properties that is water availability waste temperature and buffer thickness and geometry

modelling the response of lechago earth and rockfill dam lechago dam teruel spain is a 40 m high zoned earth and rockfill dam sitting on soft continental deltaic deposits a relatively narrow central clay core is stabilised by wide rockfill shoulders the dam was well instrumented and continuous records of stress development pore water pressures and vertical displacements are available for the construction period compaction conditions were followed by means of laboratory and in situ control tests core clay material was investigated by means of tests performed on compacted specimens of tertiary clays rockfill samples were excavated in outcrops of highly fractured cambrian quartzitic shale a testing programme on compacted rockfill gravels was conducted under relative humidity control in a large diameter oedometer and triaxial cells a coupled finite element model has been developed to analyse the tests performed and dam behaviour during construction model predictions essentially based on laboratory tests are compared with measurements during constructi

a new tracer density criterion for heterogeneous porous media tracer experiments provide information about aquifer material properties vital for accurate site characterization unfortunately density induced sinking can distort tracer movement leading to an inaccurate assessment of material properties yet existing criteria for selecting appropriate tracer concentrations are based on analysis of homogeneous media instead of media with heterogeneities typical of field sites this work introduces a hydraulic gradient correction for heterogeneous media and applies it to a criterion previously used to indicate density induced instabilities in homogeneous media the modified criterion was tested using a series of two dimensional heterogeneous intermediate scale tracer experiments and data from several detailed field tracer tests the intermediate scale experimental facility 10 0 3 1 2 3 0 06 m included both homogeneous and heterogeneous sln k 2 5 1 22 zones the field tracer tests were less heterogeneous 0 24 sln k 2 0 37 but measurements were sufficient to detect density induced sinking evaluation of the modified criterion using the experiments and field tests demonstrates that the new criterion appears to account for the change in density induced sinking due to heterogeneity the criterion demonstrates the importance of accounting for heterogeneity to predict density induced sinking and differences in the onset of density induced sinking in two and three dimensional systems

hafnium isotopes in arctic ocean water the first isotopic compositions of dissolved hafnium in seawater from across the arctic ocean are reported most samples from the four sub basins of the arctic ocean have values within error of an average of ehf 0 8 combined hf nd isotope compositions do not fall on the well established positive correlation for mantle and crustal rocks instead arctic waters have hf that is more radiogenic than that typically found in rocks with similar nd isotope compositions a feature previously found in ferromanganese crusts and waters from the pacific ocean arctic seawater samples generally fall on the lower part of the ferromanganese crust array reflecting influences of inputs from arctic rivers and interactions of shelf waters with underlying sediments arctic rivers have much higher hf concentrations 7 30 pm than arctic seawater 0 36 4 2 pm water from the mackenzie river has the least radiogenic hf with ehf 7 1 1 7 and plots furthest away from the ferromanganese crust array while waters from the ob yenisey and lena rivers have values that are indistinguishable from most arctic waters in the amundsen makarov and canada basins hf concentrations are highest at the surface and lowest in the deeper waters reflecting the influences of riverine inputs and of waters that have flowed over the extensive siberian continental shelves and have nd and hf characteristics that reflect water sediment interactions this is in contrast to the relatively low near surface hf concentrations reported for locations elsewhere the pacific water layer in the canada basin exhibits the highest value of ehf 6 8 1 8 reflecting the hf isotopic composition of waters entering the arctic from the pacific ocean mixing relationships indicate that a substantial fraction of the hf in the mackenzie river is lost during estuarine mixing the behaviour of hf from other rivers is less constrained

geochemistry of tin bearing granitic rocks abstract the use of rb ba and rb sr ratios as guides to tin mineralization has only local interest because each of the correlations log rb ba log sn and log rb sr log sn of granitic series has a different slope in every area the ternary relation between rb ba and cs is useful to distinguish between sn bearing granitic rocks and non mineralized granitic rocks the sn bearing granitic rocks are late differentiates of anatectic melts s type with primary albite and muscovite and greisenized granites with metasomatic albite and muscovite they have high sn rb contents rb ba and rb sr ratios and low ba and sr contents the portuguese sn bearing muscovite granites aplites pegmatites and hypothermal quartz veins have muscovites richer in sn than those of greisenized granites f and sn of muscovites from portuguese sn bearing granitic rocks are positively correlated cassiterite crystallization seems to be independent of f h 2 o f in hf and favoured by a decrease in fo2

hafnium and neodymium isotope variations in ne atlantic seawater the 176hf 177hf ratio of seawater is measured directly with 143nd 144nd in a composite vertical profile in the ne atlantic the value of hf of intermediate and deep water exhibits little variation and averages 1 0 0 8 surface water shows a wider range 5 7 to 3 3 while intermediate and deep water samples plot on or close to the seawater hf nd isotope array defined by ferromanganese deposits near surface seawater samples plot between the seawater and terrestrial rock hf nd arrays it is likely that the shallow water variability in hf arises from a short residence time of hf in surface water and isotopically heterogeneous inputs the difference between surface and intermediate deep water hf may be maintained by the release of surface scavenged hf at depth from a subset of sinking particles the composition of end at middepths reflects overlying surface water and water advected along isopycnals from areas where they outcrop in winter uniform hf values below 1000 m suggest the residence time of hf may be longer than that of nd the radiogenic isotopic composition of seawater hf relative to nd and terrestrial rocks suggests that minerals with high lu hf ratios may be preferentially weathered providing a source of radiogenic hf to the oceans

thermohydromechanical modelling of the buffer container experiment abstract in order to investigate how heat affects the performance of a dense bentonite sand buffer material a full scale in situ experiment the buffer container experiment bce was conducted by atomic energy of canada limited aecl in the bce an electric heater simulating the heat output of a disposal container of used fuel was installed vertically in a 1 24 m diameter by 5 m deep borehole surrounded by bentonite sand buffer the borehole was drilled in the floor of a room excavated in canadian shield granite on the 240 level of aecl s underground research laboratory url the thermal hydraulic and mechanical responses were monitored in the bentonite sand buffer and in the surrounding rock power was provided to the heater for approximately 896 days in order to get a better understanding of the coupled thermohydromechanical t h m process in the bce numerical simulations were conducted using code bright to model the evolution of the temperature thermally induced pore water pressure and mechanical response in the bentonite sand buffer and the surrounding rock the thermal response in the experiment was successfully modelled the simulated water seepage from the rock to the borehole was compared with measured results for the bce the thermally induced moisture movement in the buffer was also reasonably well simulated the comparison of the simulated pore water pressure in the rock with the measurement indicates that the influence of temperatures on the hydraulic parameters of rock should be further studied the modelled vertical displacements in the rock are also compared with the measured data in the bce and the analysis of the rock displacement suggested that the in situ thermal expansion coefficient of the rock could be much higher than the coefficient determined in the laboratory

experimental evidence for mineral controlled release of radiogenic nd hf and pb isotopes from granitic rocks during progressive chemical weathering the role of accessory minerals in the incongruent release of hf and pb during continental weathering and its implications for the generation of distinct seawater isotope compositions is subject of debate while it has been suggested that radiogenic hf and pb isotope signatures released during the dissolution of rocks are controlled by the relative abundances of minerals with distinct isotope compositions and differences in their resistance to dissolution there has not been a comprehensive experimental investigation of these processes to date we carried out systematic sequential leaching experiments on fresh and partly weathered granitic rock samples as well as separated zircons from the central aar granite in switzerland combined with major and rare earth element concentrations our new quantitative experimental data reveal systematic preferential release of radiogenic nd hf and pb isotopes primarily controlled by dissolution characteristics of the host rock s easily dissolvable accessory and major minerals in particular apatite and sphene during weak chemical weathering moreover pb isotope signatures of incipient weathering conditions contrary to expectations indicate initial congruent release of pb from freshly exposed mineral surfaces that becomes subsequently incongruent during more advanced chemical weathering stages as well as enhanced physical weathering conditions the dissolution of major minerals i e feldspars becomes dominant for nd and pb isotope signatures whereas hf isotopes are still dominated by contributions from highly radiogenic accessories additional leaching experiments of zircon separates were performed to test the specific role of zircons for hf isotope compositions of riverine runoff it is demonstrated that zircon is more efficiently dissolved when physical weathering is enhanced this increased hf release originating from partial dissolution of zircons however is quantitatively not sufficient to explain less radiogenic hf isotope signatures in seawater during episodes of enhanced mechanical erosion alone moreover the observed addition of hf from the more congruent dissolution of the zircon free fractions of the parent rock due to enhanced physical weathering indicate that these minerals also play an important role in controlling hf isotope signatures released under deglacial conditions

on the long term migration of uranyl in bentonite barrier for high level radioactive waste repositories the effect of different host rocks abstract repositories for high level radioactive waste hosted in argillite or granite with bentonite backfill are the two disposal concepts that been extensively studied a general perception is that granite has very low sorption capacity and therefore is disadvantageous in retarding the migration of radionuclides in comparison with argillite however when there is bentonite backfill does the sorption capacity of granite really matter for the migration of radionuclides how different host rocks would affect the migration of u vi through the bentonite backfill of an engineered barrier system ebs and which properties of the host rocks cause those differences in migration given that migration of radionuclides is a critical measure in assessing the performance of a repository here we present two coupled thermal hydrological and chemical models for the transport of u vi each with an identical setup except for the type of host rock argillite vs granite rock comparisons between our models show that the different host rocks exert their influence on migration of u vi via regulating the chemical conditions in the bentonite which affect the concentration of u vi at the source and the adsorption of u vi in the bentonite the key chemical conditions are ph ca and hco3 concentration in pore water which are strongly affected by soluble carbonate minerals our models also show the occurrence of illitization dissolution of smectite and precipitation of illite in the bentonite which affects the migration of u vi through changing ph and the quantity of adsorbents although generalization of current model results for granite and argillite should be done carefully the simulations highlight the importance of pore water chemistry in host rock as well as bentonite host rock interactions when assessing the performance of a repository in comparison to properties such as thermal conductivity permeability and adsorption capacity properties that have been studied intensively the pore water chemistry of host rocks deserve equal or even more attention because of its strong influence on radionuclide migration

hafnium and neodymium isotopes in surface waters of the eastern atlantic ocean implications for sources and inputs of trace metals to the ocean we present hafnium hf and neodymium nd isotopic compositions and concentrations in surface waters of the eastern atlantic ocean between the coast of spain and south africa these data are complemented by hf and nd isotopic and concentration data as well as rare earth element ree concentrations in saharan dust hafnium concentrations range between a maximum of 0 52 pmol kg in the area of the canary islands and a minimum value of 0 08 pmol kg in the southern angola basin neodymium concentrations also show a local maximum in the area of the canary islands 26 pmol kg but are even higher between 20n and 4n reaching maximum concentrations of 35 pmol kg these elevated concentrations provide evidence of inputs from weathering of the canary islands and from the partial dissolution of dust from the sahara sahel region the inputs from ocean island weathering are also reflected in radiogenic hf and nd isotopes the hf isotopic compositions of dust samples themselves are highly variable ranging between ehf 20 and 0 6 the combined hf and nd isotopic compositions of dust plot close to the terrestrial array during periods of appreciable dust load in the atmosphere during low atmospheric dust loading combined hf and nd isotopic compositions similar to seawater are observed most of the variability can be explained in terms of variable degrees of zircon loss from the dust samples which in turn is linked to sorting during atmospheric transport to the eastern atlantic ocean and possibly presorting by sedimentary redistribution on the continent in addition increasing relative proportions of radiogenic clay minerals with decreasing grain size may contribute to the radiogenic hf isotopic compositions observed while the nd isotopic composition in the surface ocean reflects the nd isotopic composition of the saharan dust adjacent to the sahara sahel region the release of hf from that dust appears to be incongruent and results in surface ocean hf isotopic compositions which are 10 ehf more radiogenic than the bulk dust radiogenic hf appears to be released from clays and possibly from trace apatite rare earth element patterns of dust samples indicate the presence of apatite but provide no evidence for ferromanganese grain coatings suggesting that such coatings are insignificant in the release of hf and nd from saharan dust to the surface ocean the nd isotopic composition of the surface waters becomes less radiogenic south of the equator most likely reflecting the release of nd from congo river sediments the release of hf from saharan dust and the congo river sediments however does not produce distinct hf isotopic signatures in the surface ocean implying that the mobile fraction of hf integrated over large continental areas is isotopically uniform the hf isotopic uniformity in the surface ocean means that the limited variability in deep water isotopic compositions is consistent with a short deep water residence time and reflects homogenous continental inputs rather than efficient deep water homogenization

controls on the incongruent release of hafnium during weathering of metamorphic and sedimentary catchments abstract it is well established that hf weathers incongruently such that the isotopic compositions in seawater are offset from those of nd relative to the correlation defined by bulk lithologies of the continental crust here we study this process in detail with new records of the seasonal variability of isotope compositions and concentrations of hf and nd in four swiss rivers the water has been filtered at a pore size of 0 45 m and therefore represents the truly dissolved and the colloidal pool of both elements the studied rivers drain metamorphic gneissic or sedimentary mixed carbonate siliciclastic lithologies the dissolved isotope data are compared to the isotope compositions and concentrations of the suspended load and different fractions of the actual source rocks in the respective catchments as well as to concomitant changes in the aqueous chemistry of the major elements dissolved nd concentrations span similar ranges for all rivers whereas hf concentrations are one order of magnitude lower in the rivers that drain gneissic catchments compared to those draining sedimentary rocks this primarily results from the retention of most of the hf in the gneissic zircons as indicated by the hf budget of the gneisses whereas hf in the sedimentary catchments is readily weathered from fine detrital silicates large differences are found between the dissolved hf isotope compositions of the rivers and those of the suspended load and the source rocks consistent with the release of hf from a radiogenic rock fraction during weathering in the metamorphic catchments this primarily reflects that fact that zircons are barely accessible for weathering the zircon free portion of the rocks appears to weather congruently as the riverine hf isotope compositions are similar to the zircon free portion of the gneisses rather than being distinctly more radiogenic leaching experiments performed to understand the riverine hf budget in the sedimentary catchments reveal that the carbonate fraction of the sedimentary rocks is extremely radiogenic yielding hf isotope compositions up to ehf of 208 however the hf concentrations in the carbonate fractions are too low to dominate the riverine hf budget which is instead controlled by the weathering of detrital silicate minerals two of the catchments a metamorphic and a sedimentary one show relatively systematic changes towards more radiogenic dissolved hf isotope compositions as discharge increases this suggests that continental runoff conditions could be a relevant parameter for the control of the seawater hf isotope composition whereby more congruent weathering is achieved during low discharge when hf is increasingly derived from weathering resistant unradiogenic minerals

sr nd al36 1997 99 122 hercynian granodiorites and monzogranites massif central france variations in sr nd and pb initial isotope ratios of three large hercynian granitoid massifs of the french massif central are consistent with formation of the granitoids by partial melting of the lower crust the nature of the lower crust of the massif central is known from the granulite facies lower crustal xenoliths brought to the surface by tertiary alkaline volcanics studies of the xenoliths have revealed that during the hercynian orogeny 360 290 ma ago the pre existing metasedimentary and acid metaigneous lower crust was intruded by basic magmas causing anatexis the mantle derived basic magmas mixed with melts from the pre existing lower crust forming the hercynian granitoids the peraluminous gueret and margeride granitoids which are very similar in their major and trace element compositions have 87sr 86sri 0 7089 to 0 7121 and ndi 7 5 to 3 9 values which indicate that they have a high sedimentary component considered to have been derived from lower crustal metasedimentary rocks however the granitoids differ significantly in their initial pb isotope compositions with the gueret granodiorites being less radiogenic indicating the presence of a slightly different crustal source component for the gueret massif in contrast monzogranites from the millevaches massif are less peraluminous and have higher la ybn and lower 87sr 86sri values 0 7064 to 0 7109 these features together with the relatively radiogenic pb isotope compositions of the millevaches granitoids suggest derivation from the acid metaigneous lower crust

the isotopic composition of nd in a boreal river a reflection of selective weathering and colloidal transport in this study the nd concentrations cnd from 18 months of weekly sampling of filtered water 90 dominated by a colloidal phase primarily composed of organic c and fe the end 0 and 147sm 144nd only vary within a narrow range 27 1 to 24 8 and 0 103 to 0 110 respectively with no obvious relationship to cnd and discharge the end 0 and 147sm 144nd in the river water is significantly lower than in the unweathered till and average bedrock in the catchment and show a closer resemblance with the isotopic characteristics found in humic substances and plant material these data show that the isotopic composition of nd exported from a large boreal drainage basin does not directly reflect that of the bulk bedrock in the catchment the isotopic composition is controlled by selective weathering and the nd transport is dominated by organic colloidal particles

changes in erosion and ocean circulation recorded in the hf isotopic compositions of north atlantic and indian ocean ferromanganese crusts abstract high resolution hf isotopic records are presented for hydrogenetic fe mn crusts from the north atlantic and indian oceans bm1969 from the western north atlantic has previously been shown to record systematically decreasing nd isotopic compositions from about 60 to 4 ma at which time both show a rapid decrease to unradiogenic nd composition thought to be related to the increasing influence of nadw or glaciation in the northern hemisphere during the oligocene north atlantic hf became progressively less radiogenic until in the mid miocene 15 ma it reached 1 it then shifted gradually back to an hf value of 3 at 4 ma since when it has decreased rapidly to about 1 at the present day the observed shifts in the hf isotopic composition were probably caused by variation in intensity of erosion as glaciation progressed in the northern hemisphere ferromanganese crusts ss663 and 109d are from about 5500 m depth in the indian ocean and are now separated by 2300 km across the mid indian ridge they display similar trends in hf isotopic composition from 20 to 5 ma with the more northern crust having a composition that is consistently more radiogenic by 2 hf units paradoxically during the last 20 ma the hf isotopic compositions of the two crusts have converged despite increased separation and subsidence relative to the ridge a correlatable negative excursion at 5 ma in the two records may reflect a short term increase in erosion caused by the activation of the himalayan main central thrust changes to unradiogenic hf in the central indian ocean after 5 ma may alternatively have been caused by the expanding influence of nadw into the mid indian basin via circum antarctic deep water or a reduction of pacific flow through the indonesian gateway in either case these results illustrate the utility of the hf isotope system as a tracer of paleoceanographic changes capable of responding to subtle changes in erosional regime not readily resolved using other isotope systems

conceptual uncertainties in modelling the interaction between engineered and natural barriers of nuclear waste repositories in crystalline rocks nuclear waste disposal in geological formations relies on a multi barrier concept that includes engineered components which in many cases include a bentonite buffer surrounding waste packages and the host rock contrasts in materials together with gradients across the interface between the engineered and natural barriers lead to complex interactions between these two subsystems numerical modelling combined with monitoring and testing data can be used to improve our overall understanding of rock bentonite interactions and to predict the performance of this coupled system although established methods exist to examine the prediction uncertainties due to uncertainties in the input parameters the impact of conceptual model decisions on the quantitative and qualitative modelling results is more difficult to assess a swedish nuclear fuel and waste management company task force project facilitated such an assessment in this project 11 teams used different conceptualizations and modelling tools to analyse the bentonite rock interaction experiment brie conducted at the aspo hard rock laboratory in sweden the exercise showed that prior system understanding along with the features implemented in the available simulators affect the processes included in the conceptual model for some of these features sufficient characterization data are available to obtain defensible results and interpretations whereas others are less supported the exercise also helped to identify the conceptual uncertainties that led to different assessments of the relative importance of the engineered and natural barrier subsystems the range of predicted bentonite wetting times encompassed by the ensemble results were considerably larger than the ranges derived from individual models this is a consequence of conceptual uncertainties demonstrating the relevance of using a multi model approach involving alternative conceptualizations