hydrogeochemical conditions and evolution at the aspo hrl sweden abstract the overall hydrogeochemical conditions at and in the near vicinity of the underground experimental aspo hard rock laboratory hrl in se sweden have been investigated groundwater data from more than 400 samples have been compiled and evaluated the groundwater samples represent depths down to 1700 m below sea level and sampling has been performed prior to and during the hrl tunnel excavation episodic events have to a great extent influenced the hydrochemical evolution since the last glaciation which ended some 13 ka ago at that time glacial melt water was flushed under hydraulic pressure down into the fracture system to a depth of at least several hundred metres the next episodic event took place when the baltic freshwater lake transformed into the brackish litorina sea some 7 ka ago at this time aspo was covered by the sea and these denser more saline waters partly replaced the glacial water down to a depth where the density equilibrated with the replacement sea water at some time around 3 4 ka ago aspo started to rise above sea level and meteoric water began to infiltrate the rock the overall trend of increasing salinity with depth may easily be misinterpreted as a fairly simple groundwater system evolving from a two component evolution path between non saline and saline groundwaters however when combining the results from environmental isotopes and the chemical parameters using a new modelling tool named m3 multivariate mixing and mass balance calculations a higher resolution was obtained and a more complex groundwater pattern which reflects the present and paleo hydrogeological events can be recognised the measured groundwater composition was modelled to be a mixture of meteoric past and present baltic seawater glacial or cold climate recharge and brine type of waters the modelling result shows that the processes considered to have a dominating impact on the present aspo groundwater chemistry are mixing both in disturbed and undisturbed systems calcite dissolution and precipitation redox reactions and biological processes the undisturbed groundwater conditions prior to the hrl tunnel construction at aspo consisted of 1 a dominating proportion of meteoric fresh water in the upper 250 m of the aquifer 2 a brackish saline water consisting of mixing proportions of present and ancient baltic sea water and glacial melt water present to a depth of 250 600 m 3 saline water still containing proportions of glacial water which could represent even older glaciations and brines a large portion of which have been stagnant for perhaps millions of years below a depth of 600 m during the hrl tunnel construction there were changes in the composition of the water flowing into the tunnel at different locations although the variation in salinity was relatively small the variations in the mixing proportions of the different water types were substantial

quantification of rock mass damage in underground excavations from microseismic event monitoring abstract rock mass damage assessment is required for many applications in rock engineering practice including support design contamination transport control stope design amongst others while various methods such as displacement measurement seismic refraction and direct observation using borehole camera have been used relatively few efforts have been made to use microseismic monitoring to quantify the rock mass damage from laboratory tests it is well known that microseismic events are indicators of fracturing or rock damage as the rock mass is brought to failure at high stress by capturing the microseismic events underground excavation induced rock mass degradation or damage can be located but can the amount of damage in terms of changes to strength or deformation properties be measured in the present study a method of characterizing rock mass damage near excavations based on microseismic event monitoring is developed and a damage driven numerical model is presented that takes the microseismic data as input to determine the damage state described by fracture density the approach is built on the discovery that a realistic crack size corresponding to a seismic event can be established by applying a tensile cracking model instead of the traditional shear model commonly used in earthquake analysis the rock mass is softened by the introduction of cracks and this is simulated by a micro mechanics based constitutive model the material property input for the model are young s modulus poisson s ratio of the intact rock and information obtained from the monitoring of microseismic events such as the location and the source size of each event calculated from source parameters using data from the atomic energy of canada limited mine by experiment this model has been verified by investigating the linkage between microseismicity rock mass damage and ground deformation it is found that when damage related softening based on microseismic data is considered predicted rock mass displacements are in good agreement with extensometer measurements

hydrochemical disturbances measured in groundwater during the construction and operation of a large scale underground facility in deep crystalline rock in japan changes in the hydrochemical conditions of groundwater were evaluated following the construction of a large scale underground facility at the mizunami underground research laboratory miu japan the facility was constructed to a depth of 500 m in sedimentary and granitic rocks drawdown of the groundwater level in the range of several tens to hundreds of meters was observed up to hundreds of meters away from the shafts during the first ten years of facility construction and operation subsequent changes in groundwater chemistry occurred due to upconing of high salinity groundwater from the deepest part of the shaft and the infiltration of low salinity shallow groundwater we predict that future deep groundwater chemistry in the vicinity of the miu facility will resemble that of the present day shallow groundwater multivariate statistical analysis provides fundamental insights into such a site we found that the extent of hydrochemical variability related to miu construction and operation was dependent on the distance from the facility shafts and galleries and on hydrogeological compartmentalization resulting from lithological boundaries such as permeable conglomerates vs more compact lithological units and other features such as faults or clay layers we conclude that hydrochemical impact assessment of groundwater in low permeability rock is essential prior to the construction of such a facility this should include characterization of hydrogeological structures and compartments to propose suitable location of shafts and galleries

gravity anomalies and segmentation at the east coast usa continental margin summary the free air gravity edge effect anomaly at rifted continental margins has generally been attributed to the transition between thick continental and thin oceanic crust while crustal thinning is a major contributor recent studies suggest that sediment loading and magmatism may significantly modify the edge effect anomaly and cause it at some margins to be highly segmented along their strike in this paper we use a combined 3 d flexural backstripping and gravity anomaly modelling technique to determine the role that sediment loading has played in controlling the segmentation of atlantic type continental margins we focus on the east coast usa since a substantial amount of high quality seismic reflection and refraction gravity and magnetic data already exists for this margin by calculating the gravity anomaly associated with rifting and sediment loading and iteratively comparing it to the observed free air anomaly we have determined the best fit elastic thickness te structure of the margin we show that 0 10 5 a integrated strength of the lithosphere these results imply that weak regions abut strong ones at the east coast usa margin te generally decreases with increase in the amounts of crustal thinning and the flexed basement curvature k suggesting it is controlled at least in part by the mechanical structure of the pre rift lithosphere and yielding due to flexural loading however there is considerable scatter suggesting other factors such as along strike changes in crustal composition irrespective we show that an isostatic anomaly that takes into account the best fit te distribution is significantly reduced in spectral power compared with one which is computed assuming only airy compensation i e te 0 km this is not to imply that rifting and sediment loading completely accounts for the anomalies along strike and across strike the east coast usa margin to the contrary significant isostatic anomaly highs and lows persist especially in inner and middle shelf regions one of the most prominent is an arcuate 670 km long high with flanking lows offshore carolina that we attribute to magmatism during the initial stages of continental break up

nature of the continent ocean transition on the non volcanic rifted margin of the central great australian bight a region of 50 120km width defines the continent ocean transition cot in the central great australian bight it is characterized by a thin apron of post break up sediments overlying complexly deformed sediments and intruded crust bounded landward by a basement ridge complex and oceanward by rough oceanic basement recently acquired deep reflection and refraction seismic data have significantly enhanced understanding of the cot and basement ridge modelled gravity and magnetic data and features interpreted from seismic data are consistent with aspects of extensional and break up models proposed for the west iberia margin many of the features and relationships observed beneath the outer margin of the central great australian bight can be explained by extension within a lithosphere scale pure shear environment involving four layers brittle upper crust and upper mantle and ductile lower crust and lower lithospheric mantle the cot is interpreted to be underlain by extended continental lithosphere thus the continentocean boundary is unequivocally defined between oceanic crust and the cot and appears to be associated with sea floor spreading magnetic anomaly 33 indicating that break up and sea floor spreading did not commence until c 83 ma early carnpanian time later than the currently accepted 95ma age the major part of the basement ridge complex is probably a combination of serpentinized peridotites and mafic intrusions or extrusions derived by mantle upwelling and limited partial melting the magmatic products of this process probably cooled during chron 34 producing a distinctive magnetic anomaly but one that does not relate to break up and sea floor spreading

seismic stratigraphy and sediment distribution on the wilkes land and terre adelie margins east antarctica abstract seismic reflection data show the existence of two major sedimentary basins along the continental margin of wilkes land and terre adelie east antarctica that contain more than 5 s twt 9 km of sediments four seismic megasequences are identified ms4 to ms1 that are bounded by basement unconformities of interpreted turonian maastrichtian and early middle eocene age and the seafloor the 4 5 km thick rift and pre rift sediments are concentrated in a margin parallel basin sabrina basin on the basis of seismic correlation with the australian margin this basin is interpreted to be of late jurassic to mid cretaceous age the post rift sediments are generally thick along the margin and in the adjacent deep ocean basin but are particularly thick in a major depocentre off west wilkes land named here the budd coast basin bcb the bcb contains a maximum observed thickness of 5 s twt 9 km of post rift sediments and its location suggests that the sediments were largely derived from a sub glacial basin currently occupied by the totten glacier within the post rift sediments a major regional unconformity is identified that is interpreted to be of early middle eocene age 45 ma while some previous interpretations have suggested that this unconformity marks the onset of the glaciation of east antarctica the unconformity is interpreted here to be the product of the major global plate reorganisation in the middle eocene and the coincident sharp increase in the sea floor spreading rate between australia and antarctica a seismic unconformity that can be correlated with the onset of glaciation is not identified and the position of glacial onset within the sedimentary section can only be estimated through the extrapolation of sedimentation rates from the underlying section and from deep sea drilling project site 269 the post middle eocene section is much thicker than the underlying post rift section and this is interpreted to be largely due to the very high sediment fluxes associated with the period of polythermal glaciation from 34 9 ma sediment isochron and isopach maps derived from a regional seismic grid show that the depocentre of the bcb trends approximately north south beneath the continental slope but is deflected to the east beneath the deep ocean basin this distribution indicates that deep marine processes were important in lateral along margin sediment transport a west to east direction of movement is inferred by the sediment distribution this direction is opposite to the present day marginal currents along the continental slope and rise

thermochronology and the three dimensional cooling pattern of a granitic pluton an example from the toki granite central japan the three dimensional spatial variations in the cooling pattern of the toki granitic body a zoned pluton in central japan have been evaluated quantitatively by thermochronology using cooling age determination based on the different closure temperatures for target mineral species the toki granite has hornblende k ar ages of about 74 3 3 7 ma n 2 closure temperature of 510 25 c biotite k ar ages of 78 5 3 9 to 59 7 1 5 ma n 33 300 50 c and zircon fission track ages of 75 6 3 3 to 52 8 2 6 ma n 44 240 50 c the spatial variation in the biotite k ar age is similar to that in the zircon fission track age in samples collected from 11 boreholes and seven outcrop sites in the toki granite indicating that cooling was effectively from the roof and also from the northwest margin this cooling pattern shows a strong correlation with the alumina saturation index asi distribution of the body larger asi values correspond to earlier and more rapid cooling after emplacement and smaller value to slower cooling toki granite was effectively cooled from the peraluminous regions where assimilation of country sedimentary rock was most extensive

why are marine magnetic anomalies suppressed over sedimented spreading centers the absence of lineated marine magnetic anomalies over sedimented recent spreading centers has been observed in several areas we propose that magnetic anomalies can be suppressed as a result of pervasive hydrothermal reactions underneath thick blankets of sediment the relatively impermeable sediment cover produces comparatively closed hydrothermal systems which increase the residence time of the hot fluids in basaltic layer 2 causing more thorough leaching of the remanence carrying iron titanium oxides and diminishing the marine magnetic anomalies this contrasts with lesser alteration at sparsely or unsedimented zones of extension with more open circulation conversely spreading ridges and oceanic crust characterized by absent or subdued lineated anomalies may signal sites of extensive hydrothermal mineralization this process might also provide an explanation for some magnetic quiet zones such as in the gulf of california the gulf of aden and the northern red sea

on isostasy at atlantic type continental margins cross spectral techniques have been used to analyze the relationship between free air gravity anomalies and topography of approximately 100 profiles over the continental margins of eastern north america southwest africa and the coral sea lord howe rise the resulting admittance functions for these margins have been interpreted in terms of the flexure model of isostasy the relatively young coral sea lord howe rise margin is associated with the lowest value of the effective elastic thickness te 5 km while the relatively old eastern north american margin is associated with the highest value 10 te 20 km thus te appears to increase with the age of the margin these results which are consistent with flexure studies from the major ocean basins have been interpreted in terms of a simple model in which the flexural strength of the lithosphere increases with age the model suggests that a low rigidity plate or airy type model is most applicable early in rifting history while a high rigidity plate is more applicable later in margin evolution thus sediments at a margin initially load a relatively thin and hot plate while sediments later in margin evolution load a relatively thick and cold plate the model explains a number of features of the tectonic stratigraphic evolution of margins these include a change in flexural style from a narrow and deep basin to a broad and shallow basin coastal plain onlap and uplift in the continental interior furthermore the flexure model of isostasy contributes in a major way to observed free air gravity anomalies at continental margins in particular the model explains the existance of airy isostatic gravity anomalies at margins the amplitude and wavelength of these anomalies are a function of the sediment supply the type of mechanisms controlling sediment deposition up building and or out building and the thermal structure history and age of the margin

variations in thickness of layer 3 dominate oceanic crustal structure abstract seismic refraction studies have determined that while much of the crust underlying the world s oceans is about 7 km thick it also occurs in lesser and considerably greater thicknesses here we show that vastly different thicknesses of oceanic crust formed at ridges by seafloor spreading are generally characterized by the two gradient velocity structure recognized as typical of 6 7 km thick oceanic crust adopting a standard we study ninety published seismic velocity structures of oceanic crust ranging in thickness from 2 to 37 km several structures formed in midplate settings ocean islands and seamounts are also considered for comparison regardless of origin ridge or midplate we find that the percentage of the whole crust formed by layer 2 systematically decreases with increasing total crustal thickness while the average velocity of layer 2 varies widely for all crust the average velocity of layer 3 increases systematically with increases in the average whole crustal thickness and velocity crust formed in midplate settings differs in that the thickness of layer 2 velocity crust is generally two to three times that of crust formed at ridges residual depths were calculated for oceanic crust by removing the effects of sediment loading and subsidence due to lithospheric cooling most of the data fall close to a model whereby different crustal thicknesses result from different extents of partial melting of oceanic upper mantle the crustal sections were restored to zero age assuming the average depth of emplacement for 7 km thick oceanic crust is 2 5 km below sea level from this restoration it appears that the depth to the top of layer 3 at the time it was formed is 4 25 1 25 km below sea level regardless of whole crustal thickness or spreading rate these results suggest that the mechanism of construction of oceanic crust is in many ways remarkably uniform despite very large changes in the total thickness of the crust produced very basic questions remain it is for instance not at all clear why layer 2 and layer 3 exist in the proportions they do while neutral buoyancy or melt trapping at the base of a brittle lid may account for local properties of the layer 2 3 boundary they do not seem adequate to account for the global phenomenon

contrasting styles of rifting models and examples from the eastern canadian margin we present the results of a dynamical model of lithospheric rifting and rupture which show that a wide range of crustal thinning patterns across rifted passive margins can be produced by varying the steady state geotherm lithospheric composition dry versus wet materials and strain rate the basic mechanism of continental rupture is assumed to be passive rifting and necking we use a numerical thermomechanical model of lithosphere extension based on a finite element approach when plasticity is significant i e at lower temperatures or for harder materials deformation is unstable and thinning takes place abruptly over a narrow area conversely a progressive thinning across the margin is observed when creep is dominant i e in warm or ductile conditions cooling and associated hardening of the thinned area can occur during extension and cause the locus of extension to migrate laterally in these circumstances rupture is likely to take place asymmetrically along one edge of the thinned area producing a narrow margin and a very wide conjugate the eastern margins of canada and their conjugates across the north atlantic provide examples which cover this range of theoretical profiles the crustal thinning patterns inferred from deep seismic data and the duration of rifting compare well with model results we discuss also the constraints that these geodynamical models provide on such current issues as the seismic reflectivity of the lower crust or the location of the ocean continent boundary in wide areas supposedly underlain by 5 km thin continental crust

geological and hydraulic characterisation of the excavation disturbed zone in the opalinus clay of the mont terri rock laboratory abstract the fracture network in the excavation disturbed zone edz of an argillaceous formation the opalinus clay in the mont terri rock laboratory in northwest switzerland is characterised using structural and hydrogeological techniques sampling of unloading fractures is done by analysing resin injected overcores taken from the edz resulting in a structural data set of fracture orientations frequencies and extent of the edz these parameters are derived in tunnel sections which were excavated by blasting pneumatic hammering and road header techniques pneumatic and hydrogeological tests are subsequently carried out to derive hydraulic parameters such as permeability and transmissivity distributions of the fracture network synthesis of the structural and hydrogeological data led to a conceptual model of the edz in the mont terri rock laboratory which is defined by a 2 m plastically deformed zone around the tunnel this plastic zone is further divided into an inner 1 m zone consisting of an air filled fracture network and an outer zone with mostly saturated and isolated fractures transmissivities in the inner zone are orders of magnitude higher than those of the undisturbed opalinus clay finally a methodology is proposed for the structural and hydrogeological characterisation of the edz this methodology is not site specific and is thus applicable at any argillaceous underground facility

geochemical influences on the design construction and operation of a nuclear waste vault abstract the design construction and operation of a vault for used nuclear fuel in crystalline rock may be influenced by a number of geochemical factors during the period when a site is being selected information is needed regarding the rock type heterogeneities in its composition and the mineralogy of permeable zones because these will cause variations in thermal conductivity strength and radionuclide sorptive properties of the rock these factors may affect decisions regarding depth of vault construction tunnel dimensions and spacing of panels and waste containers during site characterization borehole drilling from the surface and subsequent hydraulic testing will introduce both chemical and microbiological contaminants that may further influence this decision during vault construction the geochemistry of the rock may cause changes to the design and construction methods used high salinity fluids in the rock matrix could limit the ability of radar surveys to detect fractures in the surrounding rock and may also cause unacceptably high total dissolved solids loadings in water discharged from the facility the presence of toxic corrosive or radioactive constituents in inflowing groundwater may require grouting or development of treatment facilities both above and below ground the use of explosives will cause high organic and nitrate loadings in service water as well as the possible impregnation of these chemicals in the disturbed wall rock surrounding an excavation these chemicals may remain despite cleaning efforts and act as nutrients to promote microbial activity in the post closure phase in the operational phase inflow of increasingly saline groundwater may affect predicted container corrosion rates and buffer and grout stabilities following vault resaturation and increase in temperature this in turn may affect designs for container materials and spacing salt accumulations and microbial growths on vault walls may extend into the rock mass and require skimming of wall rock before closure this paper describes geochemical influences that might be anticipated in the disposal of nuclear waste with examples from the construction and operation of canada s underground research laboratory manitoba in a granitic batholith on the canadian shield

total tectonic subsidence a parameter for distinguishing crust type at the u s atlantic continental margin total tectonic subsidence tts is the difference between the prerifting continental crust elevation and the present sediment unloaded basement depth in a sedimentary basin tts is calculated using observations of bathymetry and basement depth and assumptions about sediment density and the loading response of the lithosphere i use the extensional model for sedimentary basin formation to interpret the tts of a passive continental margin that model predicts that the tts on an old margin should define the major crust type boundaries and indicate the lateral distribution of extension within the extended continental crust tts analysis of the u s atlantic continental margin indicates that the boundary between extended continental and oceanic crusts lies along the east coast magnetic anomaly ecma to the north of the blake spur fracture zone bsfz and along the blake escarpment to the south there is no tts anomaly associated with the blake spur magnetic anomaly which seems to be underlain by normal oceanic crust the ecma appears to be associated with a tts minimum but i attribute that to artificially shallow estimates of depth to magnetic basement under the ecma tts estimates of extended continental crust thickness agree well with gravity models except where the problem with magnetic basement depth estimates interferes the amount of crust extension prior to seafloor spreading varies along the strike of the margin the most abrupt change is at the bsfz across the bsfz the amount of extension varies by 160 km but the volume of continental material does not vary the extension variation may be caused by lateral changes in the gross rheology of the continental lithosphere in the case of the bsfz it would be the suture of more ductile pre late paleozoic african craton with more brittle north american craton that could cause the abrupt change

sediment loading on the western platform of the new zealand continent implications for the strength of a continental margin abstract mechanical properties of the new zealand lithosphere are determined by forward modelling the gravity and isostatic response of a plio pleistocene sediment loaded shelf margin the giant foreset formation on the western platform of new zealand is a 2 km thick 250 km long and 100 km wide sediment package both the downward flexed pliocene miocene boundary beneath the package and a 35 50 mgal peak to trough gravity anomaly over the sediment package are best matched with a flexural rigidity in the region of 5 6 10 22 1 5 10 23 n m effective elastic thickness t e 20 28 km the giant foresets are a particularly important load to model because unlike most sediment loaded passive margins there is a time gap of about 70 80 ma between rifting and subsequent deposition of the sedimentary load furthermore the width of the giant foreset load is sufficiently small to afford a reasonable resolution of t e

tectonic framework of the indus and shyok suture zones in eastern ladakh northwest himalaya abstract three different phases of plutonic volcanic activity viz 1 1 cretaceous volcanics of the dras and luzarmu formations 2 2 early tertiary granitoids of the ladakh plutonic complex 3 3 oligocene acid volcanics and dykes of the khardung formation have been recognised in the ladakh magmatic arc the dras formation of the indus suture zone and the luzarmu formation of the shyok suture zone were one stratigraphic unit into which granitoids of the ladakh plutonic complex intruded the rocks of the shyok suture zone are interpreted to represent the tectonised remainder of a marginal back arc basin the closure of the marginal basin occurred at the eocene oligocene time boundary and crustal shortening was responsible for generation of neogene 2 mica granites of the karakoram plutonic complex and regional metamorphism of the pangong tso group

gravity anomalies crustal structure and flexure of the lithosphere at the baltimore canyon trough seismic and gravity anomaly data have been used to examine the long term mechanical properties of the lithosphere beneath the baltimore canyon trough a 15 km deep sedimentary basin in the rifted u s atlantic margin seismic data constrain the crustal structure at the time of rifting as well as the amount of sedimentation and erosion that has occurred the gravity effect of the initial crustal structure sedimentary loading and erosional unloading have been computed and compared to the observed free air gravity anomaly the best fitting model is one in which the elastic thickness of the lithosphere te changes at the east coast magnetic anomaly landward of the anomaly te is significantly smaller than previously reported values for continental or oceanic lithosphere of the same thermal age seaward of the anomaly however te follows the depth to the 450 c oceanic isotherm which also describes the response of oceanic lithosphere to seamount and oceanic island loads these results are interpreted as indicating that the shelf part of the trough is underlain by continental lithosphere which following rifting did not acquire any significant long term strength

relative importance of strain rate and rheology for the mode of continental extension summary both extension rate and rheology have been shown to influence the style of continental rifting so far their effect on the dynamics of extension has been discussed separately in the literature leading to diverging conclusions the rate of extension mostly affects the dynamics of rifting through the occurrence of syn rift cooling at low extension rates this cooling results in an increase of strength if the lithosphere has a temperature dependent rheology england 1983 first suggested that this effect will limit the amount of extension that an area may undergo kusznir park 1987 argued more generally that it will induce a widening of the rift and concluded that extension rate is the major control on wide versus narrow rifting later studies bassi 1991 bassi keen potter 1993 however have demonstrated the importance of rheological layering within the lithosphere for the mode of continental extension by showing that a plasticity dominated rheology will lead to rapid and narrow necking while a creep dominated rheology results in wider rifts and margins gravitational stresses arising from density anomalies due to lithosphere thinning also affect the style of rifting buck 1991 in this paper we examine the combined effect of these different parameters in order to reconcile earlier studies and assess the importance of syn rift cooling for the process of lithospheric necking the approach introduced in a previous study bassi 1991 uses a finite element technique to simulate extension of a vertical cross section of the lithosphere the effect of cooling on the necking pattern depends strongly on the rheology of the thinned lithosphere when it starts to cool if heat diffusion always induces strengthening and delays rupture in time it only modifies significantly the geometry of the rift when the upper mantle is weak and viscous in this case the locus of maximum strain rate migrates laterally once the central area starts to cool and harden as hypothesized by kusznir park 1987 eventually strain concentrates at the transition between deformed and undeformed lithosphere we predict that this pattern will induce asymmetric breakup and produce a very narrow margin and a wide uniformly thinned conjugate margin in all other cases i e when the upper mantle is initially in the low plasticity regime or if it reaches the yield stress during extension the rate of extension appears to have little effect on the rifting pattern

evidence for unusually thin oceanic crust and strong mantle beneath the amazon fan we used seismic and gravity data to determine the structure of the crust and mantle beneath the amazon fan seismic data suggest that the crust is of oceanic type and is unusually thin 4 km compared to elsewhere in the atlantic we attribute the thin crust to ultraslow seafloor spreading following the breakup of south america and africa during the early cretaceous gravity data suggest that the fan was emplaced on lithosphere that in creased its elastic thickness te and hence strength following rift ing the increase from 10 km to 40 km is greater however than would be expected if te were determined by a single controlling isotherm based on a cooling plate model hence we conclude that the amazon fan has been emplaced on and is supported by un usually thin oceanic crust and strong mantle

subsidence history crustal structure and thermal evolution of the valencia trough a young extensional basin in the western mediterranean the valencia trough is an extensional basin that began rifting during the late oligoceneearly miocene yet it is located within a region of compression between the european and african plates seismic reflection seismic refraction well gravity and geoid data have been used to determine the relative importance of extensional and compressional processes in controlling the structure and evolution of the trough although the trough appears symmetric on bathymetric maps seismic and gravity and geoid data indicate a fundamental asymmetry in its deep crustal and upper mantle structure two dimensional flexural backstripping techniques have been used to estimate the total amount of crustal stretching along a transect of the trough between the catalan coastal ranges and mallorca there is good agreement between the predicted depth to the mono based on a stretching model and the seismically constrained depth beneath the catalan margin but poor agreement beneath mallorca the seismic moho beneath mallorca can be explained by a model in which the crust was modified by the flexural effects of thrust fold loading geoid data suggest that the differences in the crustal structure between the two margins extend into the upper mantle the catalan margin is characterized by a thermal and mechanical boundary which marks the transition between cold unstretched lithosphere and hot thin lithosphere while mallorca is located above a broad region of lithospheric thinning the subsidence history and amount of crustal thinning in the catalan margin resemble that of typical atlantic type nonvolcanic margin however a narrow transition zone 60 km the lack of any evidence for a conjugate margin and the absence of oceanic crust suggest fundamental differences in the way that extensional processes may occur in convergent plate settings

a marine geophysical study of the wilkes land rifted continental margin antarctica summary the wilkes land margin of east antarctica conjugate to the southern australian margin is a non volcanic rifted margin that formed during the late cretaceous during 2000 01 and 2001 02 geoscience australia acquired 10 000 line km of seismic reflection and refraction magnetic anomaly and gravity anomaly data over the margin we have used the seismic data to estimate the sediment thickness along the margin the data reveal a deep 11 km rift basin that contains over 9 km of sediments seaward of the totten glacier western wilkes land the limits of oceanic and continental crust that underlies the thick post rift and the significantly thinner pre and syn rift sediments are equivocal seismic reflection data suggest a 30 100 km wide continent ocean transition zone cotz along the margin the cotz extends over 400 km seaward of the shelf break off the eastern wilkes land terre ad elie sector

a transect across australia s southern margin in the otway basin region crustal architecture and the nature of rifting from wide angle seismic profiling abstract the otway basin in southeastern australia formed on a triangular shaped area of extended continental lithosphere during two extensional episodes in cretaceous to miocene times which ultimately led to the separation of australia and antarctica the velocity structure and crustal architecture of the otway continental margin has been interpreted from offshore onshore wide angle seismic profiling data along a transect extending from near the northern otway basin margin with palaeozoic outcrop to the deep ocean basin under the southern ocean along this transect the otway continental margin ocm transect the onshore half graben geometry of early cretaceous deposition gives way to a 5 km thick basin sequence p wave velocity 2 2 4 6 km s extending down the continental slope offshore to at least 60 km from the shoreline at 120 km from the nearest shore sonobuoy data indicate a 4 5 km sedimentary sequence overlying 7 km of crustal basement rocks above the moho at 15 km depth water depth 4220 m conspicuous strong moho reflections are evident under the continental slope at about 10 2 s twt basement is interpreted to be attenuated faulted palaeozoic rocks of the delamerian and lachlan orogens intruded with jurassic volcanics that thin from 16 km onshore to about 3 5 km at 120 km from the nearest shore these rocks comprise a 3 km section that has a velocity of 5 5 5 7 km s overlying deeper basement with a velocity of 6 15 6 35 km s over the same distance the moho shallows from a depth of 30 km onshore to 15 km depth at 120 km from the nearest shore and then to about 12 km in the deep ocean at the limits of the profile water depth 5200 m the continent ocean boundary cob is interpreted to be at a prominent topographic inflection point at the bottom of the continental slope in 4800 m of water p wave velocities in the lower crust are 6 4 6 8 km s above a transition to the moho with an upper mantle velocity of 8 05 km s there is no evidence of massive high velocity 7 km s intrusives underplate material in the lower crust nor any syn rift or early post rift subaerial volcanics indicating that the otway continental margin can be considered a non volcanic margin similar in many respects to some parts of the atlantic ocean margins e g the nova scotia newfoundland margin off canada and the galicia bank off the iberian peninsula

characterization of rare earth elements rees associated with suspended particles in deep granitic groundwater and their post closure behavior from a simulated underground facility abstract understanding radionuclide transport processes deep underground is indispensable for safety assessments of the geological disposal of radioactive wastes this study investigated the behavior of rare earth elements rees associated with suspended particles in deep granitic groundwater and in a sealed drift at a depth of 500 m in the mizunami underground research laboratory url in japan as an analogue study of radionuclide behavior around an underground waste disposal facility particles suspended in natural groundwater consist of silicate minerals including clays and iron hydroxide calcite sulfide and organic substances approximately 10 60 of rees in groundwater are associated with suspended particles furthermore sequential chemical extraction analyses of the suspended materials trapped on membrane filters suggests that rees are primarily sorbed onto carbonate particles in deep granitic groundwater carbonate particles in groundwater are most likely derived from in situ precipitation of supersaturated carbonate minerals such as calcite the concentration of lanthanum associated with suspended particles as an example is highest when the calcite saturation index shows equilibrium si 0 and decreases as the calcite saturation index increase because deep granitic groundwater is generally in equilibrium with the saturated condition for calcite the results of this study suggest that calcite particles inevitably exist in groundwater and preferentially sorb rees the ree concentrations in the water and suspended particles from the closed drift are significantly lower compared with concentrations in the surrounding groundwater thermodynamic calculations show that the dissolved ree carbonate complexes in the closed drift decreased in the drift closure period these complexes may have been absorbed or co precipitated within the shotcrete on the drift wall in the closed drift zns particles and large amounts of organic suspensions as artificial suspended particles were observed in addition to the particles observed in natural groundwater a sequential chemical extraction analysis indicates that rees are primarily sorbed onto the carbonate particles and not on the large quantity of organic particles there may be little ree adsorption onto organic suspensions or rees may have preferentially adsorbed onto calcite particles or shotcrete rather than organic matter the occurrence of calcite particles under the cementitious conditions of the closed drift changes from the large suspended particles to aggregates of relatively small particles with time precipitation of carbonate particle borne rees is probably one of reasons for the decrease in the suspended rees concentrations the usage of cement based materials would generate environmental conditions in which rees are fundamentally immobile in and around the underground facilities

in situ experiments on an excavation disturbed zone induced by mechanical excavation in neogene sedimentary rock at tono mine central japan abstract the excavation disturbed zone edz is defined as the rock zone where rock properties and conditions have been changed due to the processes induced by excavation such as fracturing stress redistribution and desaturation based on our results of the in situ blasting excavation disturbance experiment at the tono mines the rock mass around the drift behaved elastically and the excavation damage induced by blasting was considered to be a primary factor in causing a change in rock properties the excavation damage was considered to depend on the excavation method so we performed an excavation disturbance experiment with mechanical excavation using a boom header in the neogene sedimentary soft rock to compare the rock property change and width of the edz induced by blasting geological observation rock mass displacement and vibration measurement were performed during the drift excavation seismic refraction and tomographic surveys borehole expansion test and hydraulic test were performed before and after the drift excavation a low seismic velocity layer of the edz with a width of ca 0 3 m and a seismic velocity of 65 70 of the intact rock was detected by a seismic refraction survey along the drift wall deformability and hydraulic conductivity were not changed in the rock mass up to 0 3 m from the drift wall the change in rock properties and width of the edz was shown to depend on the excavation method in this geological setting the mechanical excavation method is more effective in limiting the extent of the edz and change in rock mass properties

assessment of seawater intrusion into underground oil storage cavern and prediction of its sustainability operation of underground oil gas storage cavern in coastal area can induce seawater intrusion because excavation of underground storage cavern causes the groundwater level decrease of coastal aquifer seawater intrusion has the potential to cause the corrosion of underground cavern facility and leakage of gas and oil from the storage caverns therefore seawater intrusion into the underground storage caverns should be evaluated carefully to avoid unexpected operation problems in this study the extent of seawater intrusion into underground oil storage cavern in yeosu korea was assessed through field monitoring and numerical modeling to evaluate the storage cavern sustainability against seawater intrusion the mean values of seawater mixing ratios of seepage water in each cavern estimated through modeling range from 0 01 to 8 70 which are less than the measured mixing ratio 2 3 12 8 based on the cl concentrations this result indicates that other source of cl may have contributed to the observed salinity in the cavern seepage water spatial and temporal variations in monitoring data and numerical modeling demonstrate that the location of storage seepage water flow rate and the fracture zones are important factors controlling seawater mixing ratio seawater intrusion barrier wells located along the coastline were shown to be important to prevent seawater intrusion into the storage caverns significantly the predicted seawater mixing ratio after 100 years of cavern operation is 0 06 12 7 varying depending on the caverns location

flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension we suggest that the uplift of rift flanks results from mechanical unloading of the lithosphere during extension and consequent isostatic rebound this mechanism is presented as an alternative to explanations for rift flank uplift involving thermal or dynamic processes and magmatic thickening of the crust our hypothesis is based on two critical concepts first the lithosphere retains finite mechanical strength or flexural rigidity during extension second isostatic rebound uplift of the lithosphere follows when the kinematics of extension produces a surface topographic depression that is deeper than the level to which the surface of the extended lithosphere would subside assuming local isostatic compensation we develop and analyze two kinematic models for instantaneous extension of the lithosphere to show that flexural rebound is a viable explanation for the uplift of rift flanks we first investigate the isostatic consequences of finite simple slip on an initially planar dipping normal fault cutting the entire lithosphere when the lithosphere retains flexural rigidity during extension the topography resulting from this model resembles a half graben and the footwall rift flank is flexurally uplifted this simple normal faulting model explains free air gravity anomalies and topography observed at rift flanks in oceanic lithosphere such as broken ridge in the eastern indian ocean the caroline ridges sorol trough in the western equatorial pacific and the coriolis trough behind the new hebrides island arc we then investigate a general kinematic model for lithospheric extension where simple slip on a surface of arbitrary shape is accompanied by pure shear extension in the upper and lower plates when the simple slip component is not zero or the distribution of pure shear in the upper and lower plates is not identical the surface of slip can be regarded as a detachment by simplification our general model accounts for pure shear extension of the lithosphere that is uniform with depth in this case detachments have no meaning in the geologic sense however the kinematics of depth independent pure shear may nevertheless be described in terms of a surface which we term a kinematic reference surface at some depth in the lithosphere we speculate that the depth of this surface may be rheologically controlled the magnitude of rift flank uplift by flexure depends critically on the depth of this reference surface in contrast if local isostasy is assumed when the lithosphere undergoes a given amount of depth independent pure shear the resulting topography will be the same regardless of how the kinematics of that extension are formulated the basin and rift flank topography and free air gravity anomaly over young continental rifts such as the rhine graben can be satisfied using our general extensional model with a small amount 5 km of extension along a listric shaped detachment soling into the crust mantle boundary because the flexural rebound mechanism explains the observed topography and gravity anomaly over both oceanic and continental extensional domains we suggest that rheological differences between the two lithospheric types may not be important in their overall response to extension

factors controlling the style of continental rifting insights from numerical modelling passive continental margins similarly formed by lithospheric stretching and rifting can differ significantly in terms of width ranging from 50 to 400 km or subsidence history our interest lies in determining what properties of the lithosphere and what stress and strain boundary conditions control this regional variability and the siting of rupture continental breakup occurs probably as the result of a stretching instability which develops in a zone of material or geometrical heterogeneity to analyze the factors controlling these instabilities we use a numerical thermo mechanical model of lithosphere extension based on a finite element program the particular program was chosen because it combines constitutive models appropriate to our knowledge of lithosphere rheology elasticity plasticity and nonlinear temperature dependent creep with a kinematic formulation for large inelastic strain we choose to weaken the plate by locally increasing the crustal thickness by a very small amount and examine how this defect or perturbation acts to localize the deformation we compare the geometry and timing of necking for relatively wet versus dry rheology cold versus warm geotherm and fast versus slow strain rate we examine as well how the width and amplitude of the perturbation itself affects the deformation history since a velocity boundary condition is applied the required extensional forces are evaluated and compared to estimates of plate driving forces conditions that favor deformation by plasticity rather than creep cold geotherms dry rheologies lead to a more localized extension and rapid rupture but the forces involved 1013 n m are larger than typical plate driving forces increasing the amplitude of the defect i e crustal thickness contrasts accelerates necking as well cooling of the thinned area becomes significant at low extension rates depending on the initial rheology cooling simply delays the moment when deformation becomes unstable or conversely inhibits necking

on the evolution of rifted continental margins comparison of models and observations for the nova scotian margin summary a model for the formation and evolution of rifted continental margins based on lithospheric extension during rifting and its thermal and mechanical consequences is proposed model predictions are then compared with geological and geophysical observations from a transect of the 185 ma old rifted margin off nova scotia through the scotian basin three kinematic models of the rifting process are discussed these are 1 the uniform extension model in which the amount of extension is uniform with depth but varies with position across the margin 2 the uniform extension and melt segregation model which has similar properties but also provides an explanation for the properties of the extended continental crust and its transition to oceanic crust by postulating that basaltic melt segregates from the asthenosphere and migrates to the crust and 3 the depth dependent extension model in which the first order consequences of rapidly changing rheological properties with depth in the lithosphere are included by decoupling the lithosphere into two zones with depth each of which undergoes differing amounts of extension these rift models predict the form of crustal and lithospheric thinning subsidence and temperature change once the amount of extension has been determined this is estimated from seismic measurements of present crustal thickness on the assumption that the crust had a uniform thickness equal to that currently measured in the adjacent continental region before rifting occurred rifting is also considered to occur instantaneously a time stepping thermo mechanical model is used to predict the cooling of rifted margin additional thermal contraction subsidence and its amplification by water and sediment loading thermal aspects are calculated using a finite difference model of time dependent conductive heat transport whereas regional isostatic response to loading is calculated by a finite element model the models are coupled because the temperature distribution is used to define a rheological lithosphere an elastic region with thickness that varies in time and space as the model evolves for flexural calculations in the mechanical model secondary coupling occurs through perturbations to the temperature field by sedimentary thermal blanketing and advection of heat during isostatic adjustment the model predictions of 1 sedimentary basin stratigraphy 2 moho position 3 free air gravity anomaly 4 age depth relations for deep exploratory wells and 5 subsidence and temperature histories agree well with observations from the scotian basin additional effects due to sedimentary and crustal radiogenic heat production lateral heat transport and the possible existence of a near surface brittle listric faulted region created during rifting are also considered it is concluded that a model in which rifting occurred by depth dependent extension and which includes a finite thickness for the rheological lithosphere radiogenic heat production in the sediments and crust and a brittle listric faulted crustal layer affords an accurate description of the first order processes that occur during rifting and evolution of this margin

a geophysical transect of the adelie margin east antarctica abstract in 1982 a geophysical survey of the antarctic margin including multichannel seismic gravity magnetic and bathymetric surveying was carried out off adelie coast wilkes land and in the eastern ross sea of the 5000 km of lines recorded 3000 km were in the adelie coast area lines atc 101 102 approximately following meridian 138 e show the first complete transect of the adelie coast margin from the southeast indian abyssal plain at dsdp site 269 to the continental shelf these lines reveal a thick sedimentary series divided into three main acoustic units by two major unconformities considered to be upper eocene 42 ma and late oligocene 25 ma oceanic or continental basement can be traced under the whole area and the ocean continent boundary clearly lies beneath the lower continental slope a deep high amplitude low frequency horizon extending under the oceanic basement for over 300 km of line is considered to be the moho our interpretation supports a recent revision be cande and mutter proposing an early upper cretaceous opening between australia and east antarctica

antarctic tectonics constraints from an ers 1 satellite marine gravity field a high resolution gravity field of poorly charted and ice covered ocean near west antarctica from the ross sea east to the weddell sea has been derived with the use of satellite altimetry including ers 1 geodetic phase wave form data this gravity field reveals regional tectonic fabric such as gravity lineations which are the expression of fracture zones left by early 65 to 83 million years ago pacific antarctic sea floor spreading that separated the campbell plateau and new zealand continent from west antarctica these lineations constrain plate motion history and confirm the hypothesis that antarctica behaved as two distinct plates separated from each other by an extensional bellingshausen plate boundary active in the amundsen sea before about 61 million years ago

hydrochemical baseline condition of groundwater at the mizunami underground research laboratory miu abstract hydrochemical conditions up to depths of 1000 m below ground level around the mizunami underground research laboratory were investigated to construct a baseline condition model describing the undisturbed hydrochemical environment prior to excavation of the underground facilities at mizunami gifu japan groundwater chemistry in this area was classified into a na ca hco 3 type of groundwater in the upper part of sedimentary rock sequence and a na ca cl type of groundwater in the deeper part of the sedimentary rock sequence and basement granite the residence time of the groundwaters was estimated from their 14 c contents to be approximately 9 3 ka in the middle part of the sedimentary rock and older than 50 ka in the deep part of the granite the evolution processes of these groundwaters were inferred to be water rock interactions such as weathering of plagioclase dissolution of marine sulphate sulphide minerals and carbonate minerals in the na ca hco 3 type of groundwater and mixing between low salinity water in the shallow part and higher salinity water in the deeper part of the granite in the na ca cl type of groundwater the source of salinity in the deeper part of the granite was possibly a palaeo hydrothermal water or a fossil seawater that recharged in the miocene subsequently being modified by long term water rock interaction the cl depth trend in granitic groundwater changes at a depth of 400 m below sea level the hydrogeological properties controlling the groundwater flow and or mixing processes such as advection and diffusion were inferred to be different at this depth in the granite this hydrochemical conceptual model is indispensable not only when constructing the numerical model for evaluating the hydrochemical disturbance during construction and operation of the miu facility but also when confirming a hydrogeological model

subsidence history of australia s southern margin constraints on basin models the subsidence history of australia s southern margin is shown to consist of two distinct tectonic phases and has important implications for models of sedimentary basin formation the first phase is characterized by rapid tectonic subsidence about 50 m m y which lasted for about 25 30 m y during the early cretaceous the period of rapid subsidence represents the rifting phase of margin development this early stage is correlated with associated rifting phenomena faulting and extension of the brittle upper crust formation of grabens and half grabens and the rapid accumulation of volcanogenic detritus otway group the amount of extension 20 50 is estimated from a comparison of observed and modeled tectonic subsidence at several exploratory wells along the margin the model includes uniform extension and thinning of the continental lithosphere a prolonged extensional event followed by simple cooling horizontal and vertical conduction of heat and radioactive heat production by the crust the rift phase may have begun earlier but the most rapid and widespread subsidence occurred during the early cretaceous the end of rapid and widespread subsidence occurred during the early cretaceous the end of rapid subsidence coincides closely with the age of the oldest sea floor spreading magnetic anomaly about 90 ma adjacent to the continent ocean boundary cob the second stage of margin development is the post rift or drift phase a period of much slower rates of subsidence and relative tectonic quiescence subsidence during the post rift stage is modeled as cooling and contraction of extended continental lithosphere estimates of extension and thinning from subsidence modeling agree with seismic refraction measurements of the thickness of continental crust near the cob estimates of extension from the geometry of basement blocks near the cob do not agree with the analysis from subsidence modeling upper crustal extension seems to record only a small proportion of total lithospheric extension alternative or supplementary mechanisms of extension are explored with emphasis on implications from a model that includes localized shear along a lithospheric detachment system

structure and variability of oceanic crust on the flanks of the east pacific rise between 11 and 13 n we use over 500 seismograms collected by five ocean bottom seismometers to examine the structure and variability of 0 5 m y old crust in the rivera ocean seismic experiment rose area of the east pacific rise between 11 and 13 n there are no significant differences among the first arrival travel times for 10 independent refraction line segments along the isochron amplitude patterns recorded on the individual lines however suggest that structural boundaries within the upper crust vary by hundreds of meters in depth over lateral distances of tens of kilometers within this 200 km segment of lithosphere on the basis of the modeling of amplitude patterns at ranges of 5 10 km and of comparisons with the upper crust sampled at deep sea drilling project hole 504b and in ophiolite complexes layer 2 can be divided into three units 2a corresponds to extrusive volcanics with a steep velocity gradient 2b to extrusives with a near zero velocity gradient and 2c to a complex region of transition from extrusives to sheeted dikes the total thickness of layer 2 varies by about 0 7 km over the length of the line another amplitude peak which varies in range between 14 and 21 km may be related to the downward transition from sheeted dikes to isotropic gabbros within layer 3 the variability of these two amplitude patterns provides direct evidence that the along strike structure of oceanic crust in the rose area is definably heterogeneous and that the process of crustal accretion is likewise variable on the scale resolved by amplitude and travel time information

gravity anomalies sediment loading and lithospheric flexure associated with the krishna godavari basin eastern continental margin of india abstract gravity anomalies constrained by seismic data have been used to examine the long term mechanical properties of the lithosphere beneath the krishna godavari basin a deltaic sedimentary basin on the eastern continental margin of india the gravity effect of the rift crust sedimentary loading and erosional unloading have been computed and the sum effect of these when compared with the observed gravity anomalies gives a best fitting te of 30 km at the margin the results suggest that the lithosphere which was weak during the early rifting stage has gained strength during sedimentation the onshore dipping doublet gravity anomaly at the margin reflects a weak rifted continental lithosphere abutting a strong oceanic lithosphere comparison with the results of similar investigations for the bengal basin in the north and cauvery basin in the south suggests increasing strength for the lithosphere from north to south

the mont terri rock laboratory a new international research project in a mesozoic shale formation in switzerland abstract in many countries argillaceous formations are being considered as potential host rocks for repositories of radioactive waste therefore in 1995 several organisations decided to start an international research project in the reconnaissance gallery of the mont terri motorway tunnel in north western switzerland in a mesozoic shale formation the opalinus clay aalenian this project is under the patronage of the swiss national hydrological and geological survey the following organisations are also partners in the project andra and ipsn france bgr germany enresa spain nagra switzerland jnc and obayashi japan sckcen belgium the aims of the project are to analyse the hydrogeological geochemical and rock mechanical properties of an argillaceous formation the changes of these properties induced by the excavation of galleries and to evaluate and improve appropriate investigation techniques in january 1996 eight niches were excavated for the project and 15 experiments were started in boreholes of no more than 30 m in length in the winter of 1997 1998 a new research gallery was excavated to host further experiments different excavation drilling and investigation techniques have been tested and improved significant results of the different experiments are already available some of those dealing with hydrochemistry porewater pressure measurements and the evolution of the excavation disturbed zone edz are reported in this paper

large scale intrusion of shallow water into a vertical fracture zone in crystalline bedrock initial hydrochemical perturbation during tunnel construction at the aspo hard rock laboratory southeastern sweden on march 13 1991 construction of the entrance tunnel to the aspo hard rock laboratory opened a vertical fracture zone at a depth of 70 m this provides an opportunity to study geochemical changes resulting from shallow water inflow into a crystalline bedrock aquifer as anticipated during construction and operation of a deep repository for spent nuclear fuel chloride ion is a natural conservative tracer for mixing between the dilute cl 10 mg l 1 shallow groundwater and the saline cl 5000 mg l 1 native groundwater of the fracture zone a sharp dilution front corresponding to 80 dilution of the native groundwater indicated arrival of shallow groundwater in the entrance tunnel after 3 weeks in spite of this large input of shallow water the fracture zone remains predominantly anoxic major element hydrochemistry and carbon and oxygen stable isotope data indicate large inputs of alkalinity and biogenic co2 g input of organic carbon with shallow groundwater provides a possible energy and carbon source for anaerobic respiration there is no evidence for sulfate reduction and fe iii oxyhydroxide fracture minerals are the only other dominant electron acceptor observed

geohydromechanical processes in the excavation damaged zone in crystalline rock rock salt and indurated and plastic clays in the context of radioactive waste disposal abstract the creation of an excavation disturbed zone edz or excavation damaged zone edz is expected around all man made openings in geologic formations macro and micro fracturing and in general a redistribution of in situ stresses and rearrangement of rock structures will occur in this zone resulting in drastic changes of permeability to flow mainly through the fractures and cracks induced by excavation the edz may have significant implications for the operation and long term performance of an underground nuclear waste repository various issues of concern need to be evaluated such as processes creating fractures in the edz the degree of permeability increase and the potential for sealing or healing with permeability reduction in the zone in recent years efforts along these lines have been made for a potential repository in four rock types crystalline rock salt indurated clay and plastic clay and these efforts have involved field laboratory and theoretical studies the present work involves a synthesis of the ideas and issues that emerged from presentations and discussions on edz in these four rock types at a cluster conference and workshop held in luxembourg in november 2003 first definitions of excavation disturbed and edzs that may be applicable to all four rock types are proposed then an approach is suggested for the synthesis and intercomparison of geohydromechanical processes in the edz for crystalline rock salt indurated clay and plastic clay comparison tables of relevant processes associated factors and modelling and testing techniques are developed a discussion of the general state of the art and outstanding issues is also presented a substantial bibliography of relevant papers on the subject is supplied at the end of the paper

australian antarctic depression from the mid ocean ridge to adjacent continents a morphotectonic depression some 15 106 km2 in area and centred on the australia antarctic discordance1 extends across the southern half of australia through the south east indian ocean to wilkes land in antarctica fig 1a b the depression is co extensive with a negative satellite free air gravity anomaly2 which suggests that the region is underlain by downward convecting asthenosphere here i outline the depression and explore its age in a pre breakup 55 myr reconstruction fig 1c the eastern highlands of australia and the transantarctic mountains are colinear because the eastern highlands were notably high during the late cretaceous and shared with the transantarctic mountains a history of volcanism in the jurassic both highlands probably constituted the eastern flank of the past depression in the centre of which thick 8 km late cretaceous sediment in the ceduna saddle3 and a possible mirror image in offshore antarctica mark its depocentre a broad area of late carboniferous marine sediments in southern australia4 may represent the earliest sign of the depression

a methodology to interpret cross hole tests in a granite block water flow through low permeability fractured media is often concentrated in a small number of fractures this fractures need to be characterized in order to simulate accurately the hydraulic behaviour of such media we present a methodology to identify the most significant water conductive fractures the method is based on the interpretation of cross hole tests and is supported by geology geophysics and hydraulic data the methodology has been applied to the hydrogeological characterization of a granitic block around the febex experiment at the grimsel underground laboratory switzerland geology and geophysics are used for identifying candidates to flow controlling fractures single borehole hydraulic tests help in neglecting those with low transmissivity but the only means to assess connectivity consists of performing cross hole tests the resulting geometry is later implemented into a 3d finite element mesh where the fractures are simulated as 2d elements embedded into a 3d porous medium the latter includes the effect of minor fracturing and can be heterogeneous and anisotropic the resulting model is calibrated to obtain an integrated model this methodology has proven capable of reproducing single hole and cross hole tests and steady state heads and also of quantifying groundwater flow to the experimental area of the febex tunnel

seismic waves velocities and anisotropy in serpentinized peridotites from xigaze ophiolite abundance of serpentine in slow spreading ridge the effect of serpentinization on seismic wave velocity and anisotropy has been analysed in 6 peridotite samples of the xigaze ophiolite having harzburgitic composition and a degree of serpentinization ranging from 3 to 70 we found i p and s wave velocities are linearly correlated with serpentine content ii anisotropy of p and s waves decreases with increasing serpentinization while in fresh peridotites anisotropy is of the order of 6 for 70 of serpentinization it drops to 1 for p waves and to 2 for s waves comparison of published laboratory velocity data in oceanic lithologies like gabbros and dolerites with serpentinized peridotite data shows the difficulty of distinguishing between gabbros and peridotites having a percentage of serpentine between 10 and 40 by seismic waves velocities only this comparison suggests that seismic velocity data are consistent with the existence of partialy serpentinized peridotites up to 40 of serpentinization in the oceanic crust formed at slow spreading ridges in accordance with geological observation

deep structure of the ocean continent transition in the southern iberia abyssal plain from seismic refraction profiles the iam 9 transect at 40 20 n we present a crust and mantle velocity structure for the west iberia passive continental margin derived from a 320 km long wide angle seismic profile acquired in the southern iberia abyssal plain we observe a 170 km wide ocean continent transition zone which includes a pair of overlapping peridotite ridges and is bounded by oceanic crust and landward by fault bounded blocks of continental crust the profile lies 40 km south of the transect sampled by ocean drilling program odp legs 149 and 173 the transition zone structure can be divided into an upper layer 2 4 km thick with velocities of between 4 5 and 7 0 km s 1 and generally a high velocity gradient 1 s 1 and a lower layer up to 4 km thick with a velocity of 7 6 km s 1 and a low velocity gradient a weak moho reflection in this zone was seen only on wide angle profiles at an offset of 30 km the upper layer has a distinctly lower velocity than thinned continental crust adjacent to the continental slope conversely the lower layer has too high a velocity to be magmatically intruded or underplated lower continental crust on the coincident seismic reflection profile fault bounded crustal blocks identified in unequivocal extended continental crust are not observed in the transition zone the upper layer has velocity bounds and gradient similar to oceanic layer 2 observed west of the peridotite ridges but no oceanic layer 3 velocity structure is present while magnetic anomalies have been identified within the transition zone they have not been modeled successfully as seafloor spreading magnetic anomalies nor do they generally form long linear margin parallel features finally odp boreholes 40 km north of our profile and within the interpreted transition zone have recovered up to 140 m thick sections of serpentinite and serpentinized peridotites with little evidence of mafic igneous material we conclude that the transition zone cannot be dominantly composed of either extended continental crust or oceanic crust although current melting models predict a considerably thicker crust of decompression melt products we interpret this region as exposed upper mantle peridotite with little or no synrift extrusive material and limited amounts of synrift material intruded within the serpentinized peridotite

three dimensional subsidence analysis and gravity modelling of the continental margin offshore namibia summary seismic re ection pro les and gravity anomaly data have been used to determine the structure and evolution of the namibian continental margin in comparison to other margins the gravity anomaly at the namibian margin shows a number of distinctive features it lacks an oishore gravity low and despite the presence of up to 9 km of sediments the gravity high is displaced landwards of the maximum sediment thickness in an attempt to explain these features the early cretaceous recent stratigraphic record is analysed using a combined 3 d backstripping and gravity modelling technique that enables constraints to be placed on the long term mechanical properties of the lithosphere a neutral depth of necking and a relatively high exural rigidity or equivalent elastic thickness te o f 25 km can explain part of the anomaly at least in the south of the margin however large residual anomalies exist that can be reduced by the presence of pre rift low density sediments within the zone of maximum stretching south of 22 0 s high density volcanic material at the eastern pinch out of the lower rift sequence and a lateral sediment density variation across the shelf slope and rise in addition the presence of a magmatic body at the base of the crust provided that the exural strength of the margin is high signi cantly improves the t between observed and calculated gravity anomalies recovered stretching factors enable predictions of the geometry of the moho to be made palaeobathymetry is estimated along the entire margin through time by comparing the subsidence determined from backstripping to that predicted by simple models of rifting these estimates are within the errors of observed palaeowater depths where well control exists the requirement of high te rather than te that increases with time suggests that stretched continental crust extends oishore for some distance and the continent ocean boundary occurs in relatively deep water near magnetic anomaly m4 reconstruction of the gravity eld of the south atlantic at 100 ma illustrates that in terms of their gravity signature the south atlantic margins are asymmetric

are buoyancy forces important during the formation of rifted margins summary profiles of crustal thickness across rifted continental margins are examined in an attempt to understand the key observations and controlling parameters crustal stretching factor profiles from rifted continental margins supplemented by isochron data for early seafloor spreading have been used to determine a correlation between strain rate e and stretching factor despite the different methods assumptions and data sources our e relationship for rifted margins is consistent with that observed by newman and white for intracontinental rift basins the e relationship we derive is also consistent with the dynamic models of newman and white which include thermorheological strain hardening and strain softening but omit crustal buoyancy forces generated by lateral crustal thickness variations whilst crustal buoyancy forces are not included in the above dynamic models the e data do not necessarily preclude their importance simple numerical models of buoyancy force evolution show that for the first 30 myr after rifting the thermally derived buoyancy forces within the lithosphere that assist extension are larger than the crustal buoyancy forces that oppose extension this rift push force acts as a positive feedback mechanism is of the order of 3 10 12 nm 1 and dominates over the opposing crustal buoyancy forces immediately after rifting it is therefore clear that the delocalising effects of the crustal buoyancy force are dominant over a restricted range of conditions namely at low strain rate and at long times after rifting histograms of the lateral pressure gradients derived from crustal thinning factors along rifted margins show a dominant peak at 0 05 0 3 kpa m 1 and a significant secondary peak at 0 8 0 3 kpa m 1 the lower lateral pressure gradient peak corresponds to thinned parts of the continental crust which is adjacent to unstretched continental crust and may define the edge of a zone of thermal strain softening independent observations show that narrow margins are associated with rapid strain rates and are consistent with thermal strain softening predicted by thermorheological models however the dominant near zero pressure gradient peak is consistent with the operation of crustal buoyancy force processes during rifting which attempt to remove variations in crustal thickness

basin forming processes and the deep structure of the campos basin offshore brazil abstract this paper discusses a worldwide dataset of deep seismic reflection profiles that help the understanding of crustal behaviour and the genetic processes that are involved in the formation of sedimentary basins the events observed in seismic reflection data at lower crustal depths correspond to impedance contrasts associated with one or a combination of the following factors shear zones thin layers of intrusive rocks underplated material gneissic banding fluids and heterogeneities in the crust and mantle several types of sedimentary basins have been recognized with the aid of deep seismic reflection data basins formed along active master faults basins formed along inactive faults basins with no fault control basins formed by low angle detachment faults and basins formed by pervasive pure shear or an approximately pure shear where the lower crust has been locally extended by a different amount than the upper crust the mechanisms of basin forming processes recognized in deep seismic profiles are a simple shear along low angle detachment faults extending to the lower crust and maybe the upper mantle b thinning of the lower crust and mantle by ductile processes convective mechanisms or flow in the mantle and the upper crust by faulting resulting in an overall pure shear and c thinning of the lower crust associated with phase changes in the mantle or non conservation of mass two end member models of basin formation involving lithospheric stretching may be recognized in the south atlantic simple shear stretching where only the upper crust is involved in the process and mantle uplift is offset relative to the basin and pure shear stretching where uplift of the mantle vertically balances the basin fill the first mechanism has been suggested for the onshore tucano basin the data obtained for the offshore campos basin suggests regional lithospheric stretching and crustal thinning with moho uplift compensating for sediment accumulation in the basin depocentre complex relationships between sediment accumulation and crustal thinning are obtained in the western limit of the campos basin

rare earth elements ree in deep groundwater from granite and fracture filling calcite in the tono area central japan prediction of ree fractionation in paleo to present day groundwater rare earth elements rees combined with yttrium yree in deep groundwater from granite and fracture filling calcite are being studied at the mizunami underground research laboratory miu tono area central japan the groundwater was sampled from cored boreholes drilled from the miu galleries at 200 300 400 and 500 m depths the fracture filling calcite was collected from the same boreholes and dissolved in 1 m nh4 acetate buffer solution ph 4 8 major chemical composition of groundwater changed with depth and the concentrations of some major elements na k ca2 mg2 cl br and b increased with depth while alkalinity so42 and f decreased isotopic compositions of 18o and d indicated that the groundwater originated from meteoric water yree patterns of groundwater also changed with depth with heavy ree hree enrichment in shallow groundwater 200 to 400 m and light ree lree enrichment in deep groundwater 500 m the predominant yree species are yreeco3 and yree co3 2 laco3 65 70 la co3 2 8 27 luco3 20 38 and lu co3 2 53 77 the lree enrichment in the shallow groundwater resulted in preferential scavenging of positively charged yreeco3 by negatively charged bedrock surfaces in slightly alkaline groundwater ph 7 4 8 6 because of the construction and operation of the underground facility the shallow groundwater has been influenced by infiltration of surface water undersaturated in calcite in contrast the deep groundwater was barely affected by the mixing of surface water indicating that the yree originated from yree fractionation by bedrock granite irrespective of depth a negative ce anomaly preserved in the groundwater is probably indicative of paleo oxic conditions during paleo recharge the negative ce anomaly in the groundwater was possibly fractionated from sedimentary calcite with positive ce anomalies during the paleo recharge the yree patterns of the fracture filling calcite were enriched in lree the isotopic variations of 18o and 13c in the fracture filling calcite indicated that it originated from a mixture of sea water and fresh water at a temperature 100 c the yree patterns of paleo groundwater from which the fracture calcite precipitated were calculated using yree abundances in the fracture calcite and distribution coefficient reported in previous laboratory experiments the paleo groundwater was found to be enriched in lree and hree depending on the aqueous yree species our results suggest that changes in the paleo to present day yree fractionation range roughly from that of present day shallow to deep groundwater

a revised identification of the oldest sea floor spreading anomalies between australia and antarctica we propose that magnetic anomalies south of australia and along the conjugate margin of antarctica that were originally identified as anomalies 19 to 22 may be anomalies 20 to 34 the original anomaly identification has two troublesome aspects 1 it does not account for an extra anomaly between anomalies 20 and 21 and 2 it provides no explanation for the rough topography comprising the diamantina zone with our revised identification there is no extra anomaly and the diamantina zone is attributed to a period of very slow spreading 4 5mm yr half rate between 90 and 43 m y the ages bounding the interval of slow spreading 90 and 43 m y correspond to times of global plate reorganizations our revised identification opens up the possibility that part of the magnetic quiet zone south of australia formed during the cretaceous long normal polarity interval breakup of australia and antarctica probably occurred sometime between 110 and 90 m y b p the breakup unconformity identified by falvey in the otway basin may correspond to a eustastic sea level change

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

influence of reaction kinetics and mesh refinement on the numerical modelling of concrete clay interactions large quantities of cements and concretes need to be incorporated in geological disposal facilities for long lived radwaste an alkaline plume diffusing from an aged concrete ph 12 5 through argillite type rocks has been modelled considering feedback of porosity value variations on transport properties using the reactive transport code toughreact the mineralogical composition of the argillite is modified at the interface with the concrete diffusion of cementitious elements leads to rapid and strong porosity occlusion in the argillite numerical results show that both reaction rates and spatial refinement affect mineralogical transformation pathways the variations in porosity and the extension of the zone affected by the alkaline perturbation are compared at different times the major effects of mineral precipitation under kinetic constraints rather than local equilibrium are a delay in the porosity clogging and an increase in the extension of the alkaline perturbation in the clay formation the same time delay rise for the porosity occlusion also appears for the roughest spatial resolutions a simulation as representative as possible of temporal and spatial scales of cementation processes must then be supported by more comparative data such as long term experimental investigations or natural analogues

segmentation and melt supply at the southwest indian ridge the segmentation of mid ocean ridge axes and its variation with spreading rate provide constraints on models of mantle upwelling and the supply of basaltic melt to the crust we present seismic refraction results from three segments of the very slow spreading southwest indian ridge from the absence of oceanic layer 3 beneath segment boundaries and from significant variations in maximum crustal thickness between segments we infer that melt generation and or delivery is focused at segment midpoints and varies between segments anomalously thin crust 2 0 2 5 km beneath the nontransform segment boundaries and 3 5 6 0 km beneath the segment mid points is caused by restricted melt generation resulting from conductive heat loss from the upwelling mantle under the spreading center

hydrology of yucca mountain nevada yucca mountain located in southern nevada in the mojave desert is being considered as a geologic repository for high level radioactive waste although the site is arid previous studies indicate net infiltration rates of 5 10 mm yr 1 under current climate conditions unsaturated flow of water through the mountain generally is vertical and rapid through the fractures of the welded tuffs and slow through the matrix of the nonwelded tuffs the vitric zeolitic boundary of the nonwelded tuffs below the potential repository where it exists causes perching and substantial lateral flow that eventually flows through faults near the eastern edge of the potential repository and recharges the underlying groundwater system fast pathways are located where water flows relatively quickly through the unsaturated zone to the water table for the bulk of the water a large part of the travel time from land surface to the potential repository horizon 300 m below land surface is through the interlayered low fracture density nonwelded tuff where flow is predominately through the matrix the unsaturated zone at yucca mountain is being modeled using a three dimensional dual continuum numerical model to predict the results of measurements and observations in new boreholes and excavations the interaction between experimentalists and modelers is providing confidence in the conceptual model and the numerical model and is providing researchers with the ability to plan further testing and to evaluate the usefulness or necessity of further data collection

magnetic properties of variably serpentinized abyssal peridotites we have compiled new and published data on the magnetic properties of 245 serpentinized abyssal peridotites from seven deep sea drilling project and ocean drilling program sites the magnetic susceptibility k of these samples does not increase linearly with the degree of serpentinization s instead k remains modest in partially serpentinized samples s 75 peridotites in the oceanic crust moderately serpentinized peridotites s 75 have nrm values 5 a m and k 0 05 si low temperature oxidation of magnetite is found to lower the nrm and k values of seafloor samples and of cataclastically deformed drilled samples

dynamic changes in hydrogeochemical conditions caused by tunnel excavation at the aspo hard rock laboratory hrl sweden abstract hydraulic changes caused by tunneling at the aspo hard rock laboratory hrl in sweden have been investigated over a period of 2a using different hydrochemical approaches i e noble gas content isotopic measurements and major ion concentrations the dissolved noble gases 4he and ne contents and the ratio of 3he 4he 40ar 36ar stable isotopes chemical concentrations of major ions and 36cl cl ratios were determined in groundwater samples collected in the tunnel from borehole sections isolated by inflated packers groundwater was categorized into 3 groups based on 4he and cl contents undisturbed groundwater i e prior to tunnel construction with high 4he and cl contents groundwater that has been gradually changed by mixing with baltic seawater and whose 4he and cl contents have gradually increased with increasing depth and groundwater that has been totally changed due to a rapid mixing of baltic seawater and or shallow groundwater and whose 4he and cl contents are extremely low compared with other samples collected at the same surrounding depth the oldest groundwater with a high salinity of more than 14 000 mg l 1 of cl is estimated to be more than 1 8 ma old the groundwater residence time ranges from 0 9 to 900 ka in the mixing zone groundwater in the disturbed zone where rapid mixing has occurred is hard to date reliably and its primary hydrochemical character has already been lost