fabric transitions in the saxony granulite terrain abstract quartz fabric transitions reported from the saxony granulite terrain and from the nearby ore mountains are interesting because of the changes in the pattern types and the variation in the opening angles of the fabric skeletons a short summary is presented of salient features in research documented in the east german literature between 1961 and 1978 the changes in fabric skeleton with decreasing metamorphic grade are proposed as mainly consequent to the deactivation of prism c glide systems as temperature decreases fabrics indicative of the appearance of the c burgers vector might be diagnostic for deformation in regimes of comparatively high temperatures or low strainrates or for deformation under conditions such that there is a relatively high kinetically effective hydroxyl content in the quartz structure

a particle based conditional sampling scheme for the simulation of transport in fractured rock with diffusion into stagnant water and rock matrix in situ experiments and field scale characterization studies have pointed out that in fractured crystalline media groundwater flow is highly channelized this implies that at the scale of a sing

models for the assessment of transport of naturally occurring nuclides in fractured media abstract in fractured media naturally occurring nuclides are produced by the decay of the natural uranium and thorium present in the rock matrix back diffusion from the matrix into the water bearing fractures and advection along these fractures leads to nuclide concentration values that are representative of groundwater flow and transport processes hence interpretation of measured levels of naturally occurring nuclides might provide valuable information about these underlying processes here we have provided mathematical models for the simulation of generation and transport of naturally occurring nuclides in fractured media the proposed analytical solutions have been applied to study 4 he generation and migration in realistic transport pathways the results of these simulations have shown that in fractured crystalline media steady state conditions are attained after thousands to tens of thousands of years one of the developed analytical solution have also been used to infer typical values of transport resistance i e the ratio between the groundwater residence time and the fracture half aperture in the shallow bedrock at olkiluoto finland the results of this analysis have pointed out the very strong retention capacity of the considered fractured system

strike slip orogens an explanation for the hercynides the nature of oblique plate interactions is not yet well understood the oblique interaction of pacific and n american plates has resulted in large scale migration rotation and accretion of microplates intervening basins are ephemeral individually filled and deformed oblique motion results in zones of both compression and extension the latter may be sufficient to generate new oceanic crust and the former to obduct it both subduction and collision are restricted in time and space the resulting orogen is extraordinarily complex in detail the far more complicated hercynides are the result of dextral interaction between continental plates europe and africa the lateral variability of the orogen the major and long lived strike slip faults the bimodal volcanism and related ore deposits of the european trough the lizard ophiolite and its melanges the nw spanish ophiolites and the iberian pyrite belt are all explained using an oblique collision model in particular the generation deformation and obduction of ophiolites in oblique slip mobile zones is discussed

geological interpretation of dekorp 2 s a deep seismic reflection profile across the saxothuringian and possible implications for the late variscan structural evolution of central europe abstract a 250 km long deep seismic section the first of its kind in west germany s dekorp project is interpreted in terms of late variscan collisional tectonics the structural model used is based on the intracontinental thrust tectonics concept of modern collision orogens the crustal profile across the saxothuringian zone seems to indicate north facing ramps antiformal stacks and culminations within the crystalline basement of the internal mid european variscides that have been only partially overprinted by permo mesozoic crustal stretching

u pb investigations on zircons from pre variscan gneisses i a study from the schwarzwald west germany abstract field observations in the schwarzwald indicate that pre variscan rocks were formed by the following events 1 1 intrusion of granitic to granodioritic magma into sediments 2 2 a sequence of two anatectic events with an intervening regional metamorphism and development of a gneissic schistosity the absolute chronology of these older gneisses and migmatites has not yet been satisfactorily resolved we collected several samples of a coarse grained homogeneous orthogneiss of granodioritic composition and one sample of a metasedimentary source rock related to this orthogneiss body in the einetwald forest north of steinach kinzig valley the metasedimentary rock corresponds to the biotitepoor paragneisses in the schwarzwald the zircons in the latter sample are detrital and only very small specimens 45 m are euhedral the zircons from the orthogneiss samples are euhedral some are zoned and some have dark inclusions analyses of the three coarser fractions of the paragneiss form a linear array on a concordia diagram with upper and lower intercepts of about 2000 myr and 524 20 myr respectively the 2000 myr value is interpreted as the average age of the sedimentary source rocks for this material the 524 myr intercept defines an event responsible for most of the lead loss in the zircons as well as new zircon growth analyses of the zircons from the orthogneiss samples do not show a linear array on the concordia diagram because of inclusions of older inherited zircons stepwise leaching of two zircon fractions shows newly grown u rich zircon rims around old cores a 207 pb 206 pb age of 517 15 myr was found for the first dissolution steps about 50 of the zircons dissolved in subsequent steps with progressive dissolution of the residue 207 pb 206 pb age increased to 950 myr the u pb zircon data for the paragneiss and the orthogneiss establish an age of 520 15 myr for the magma intrusion

diversity of channeling flow in heterogeneous aperture distribution inferred from integrated experimental numerical analysis on flow through shear fracture in granite 1 shear mode ii fractures with shear displacements of 1 and 5 mm were generated by direct shear on granite under normal stresses of 1 20 and 60 mpa fracture surface mapping showed that the surface roughnesses of the shear fractures decreased with increasing shear displacement and normal stress and were smaller than those of tensile fractures reported in our previous study fluid flow experiments on the shear fractures provided fracture permeabilities at a wide range of confining pressures of 10 100 mpa nonmonotonic permeability was usually observed to decrease with increasing confining pressure however the permeability changes were different between the shear fractures generated at the normal stress of 20 and 60 mpa in addition obvious permeability changes with shear displacement were observed for 60 mpa whereas no significant difference was observed for 20 mpa comparing the shear fractures with the tensile fractures having shear displacements revealed clear differences even for equivalent shear displacements numerical models that were constructed using the data of the fracture surface mapping by matching their permeabilities with the experimentally evaluated fracture permeabilities revealed the development of preferential flow paths i e channeling flows for the shear fractures providing a diversity of channeling flow in heterogeneous aperture distributions of rock fractures in the earth s crust

thin skinned tectonics in the northern rhenish massif germany a network of profiles in the hercynian mountain system geo traverse rhenoherzynikum is needed to determine details of the geological structure and find the reasons for tectonic movements outstanding features within the mountain system such as the large fault zone along the southern boundary of the hunsruck1 and the left flank of the rhinegraben have already been investigated by reflection seismology2 3 we describe here a new reflection refraction experiment carried out in 1978 in the most northern part of the rhenish massif across the stavelot venn massif near aachen fig 1 while layers in the lower crust dip to the nnw a strong upper reflector at 3 4 km depth shows a slight dip to the sse and indicates a prominent fault zone near aachen known in belgium as the faille du midi here a comparable and apparently identical reflector was found some 100 and 175 km to the west of our profile we interpreted this reflector as a prominent and well lubricated thrust fault along which a huge horizontal nappe displacement took place during the last stages of the variscan orogeny

paleomagnetic constraints on the assembly of the old red continent abstract a model is proposed on the basis of paleomagnetic and geological arguments for the assembly of the old red continent which in the devonian comprised north america the baltic shield and russian platform as well as a third element called armorica the latter is thought to have included most of hercynian europe and southern england and wales as well as possibly the avalonian terranes of northeastern north america and perhaps some parts of the atlas ranges and moroccan meseta the model envisions a late ordovician taconic collision of north america and armorica which are joined in the late silurian by the baltic shield and russian platform not until the late early carboniferous did gondwana join the old red continent in a collision responsible for a large internal megashear parallel to the caledonian orogenic belt as well as the hercynian alleghenian orogeny subduction of the large siluro devonian ocean between gondwana and the old red continent is held responsible for the mid devonian acadian orogeny

datation u pb sur zircons de l eclogite de la borie haut allier france et consequences sur l evolution ante hercynienne de l europe occidentale a crystallization age of 432 10 20 ma has been determined for the la borie eclogite haut allier france by u pb dating on zircons this age is yielded by the upper intercept with the concordia curve in agreement with recent dates obtained in the southern part of the massif central in brittany and in vendee these data indicate that the high pressure high temperature metamorphic phase representative of the pre variscan evolution of the western europe took place at the silurian ordovician boundary this high pressure high temperature metamorphism could be significant of subduction processes more or less synchronous preceding the main continental collision responsible of the variscan belt s s

chemical variation in hercynian basalts relative to plate tectonics the geochemistry of hercynian basalts is reviewed with special reference to sw england hercynian basalts have the following chemical features 1 relative enrichment in incompatible elements 2 fractionated rare earth element ree patterns ranging from mild to strongly light ree enriched and 3 generally low large ion lithophile lil high field strength hfs element ratios high and variable alkali contents and k rb ratios are indicative of low grade alteration basalts are predominantly tholeiites although alkali basalts may be developed on some trough margins basalts from different sedimentary troughs within the main hercynian tectonic zones are characterized by specific incompatible element abundances and ratios these variations are interpreted in terms of variable fractional crystallization partial melting and mantle heterogeneity hercynian volcanism was typically bimodal with basic and acid products characterizing the rheno hercynian and saxo thuringian zones activity in the moldanubian zone was more variable with a high proportion of calc alkali andesites two systematic chemical changes throughout the devonian and carboniferous have been recognized with both light heavy ree and lil hfs element ratios increasing with time these features may relate to the introduction of lil enriched fluids derived by dehydration of subducted lithosphere that caused progressive metasomatism of the overlying mantle wedge chemical discrimination of tectonic setting demonstrates that most of the basalts typify the continental intra plate environment although early devonian basalts produced in the initial stages of continent rifting have some of the chemical features of incompatible element enriched oceanic basalts an ensialic back arc basin model underlain by a shallow northward dipping subduction zone provides a possible explanation for the spatial and temporal variation in the hercynian volcanic rocks

shear enhanced nonlinear flow in rough walled rock fractures abstract nonlinear flow in 3d rough walled rock fractures is simulated by solving the navier stokes equations the emphasis is on the impact of shear caused aperture changes variable apertures and asperity contacts and flow conditions inertial term upon nonlinear flow behavior in order to compare shear effects two 3d fracture models with and without shear were established with identical initial rough walled surfaces topographies of a realistic rock sample five groups of simulations with different inflow boundary conditions of flowrates reynolds numbers re were conducted to demonstrate shear enhanced nonlinearity of flow fields and limitations of local cubic law lcl approach the flow results clearly show channeling flow along the preferential paths transverse flow around the contact spots and eddy flows behind contact spots with increasing re which cannot be observed in 2d models the effective transmissivity of the 3d fracture model was calculated from the modeling results of velocity and pressure fields the results showed that the effective transmissivity is a function of local apertures with important uncertainties even when re is small i e re 0 4 in this study thus the validity of the transmissivity evaluation using lcl approach for nonlinear flow in 3d rough walled rock fractures is questionable

palaeomagnetism of the ibero armorican arc and the hercynian orogeny in western europe van der voo1 has pointed out that further advances in the understanding of the hercynian orogeny require palaeomagnetic data from well studied orogenic areas we report here palaeomagnetic results of palaeozoic rocks taken in brittany portugal and spain in the ibero armorican arc iaa a large geological feature considered to be a key area for the hercynian orogeny in western europe they show evidence that the iaa formed in two stages extending results obtained in spain by ries et al 2 giving precise constraints for the former shape of the arc we can use pre hercynian palaeomagnetic directions found in spain and portugal to follow its evolution during palaeozoic times this megastructure linking brittany to iberia squeezed between gondwana and the northern continents during the carboniferous did break away from the former block during ordovician times

a large scale flow and tracer experiment in granite 2 results and interpretation water and tracer flow has been monitored in a specially excavated drift in the stripa mine several new experimental techniques and equipment were developed and used the whole ceiling and the upper part of the walls were covered with 375 individual plastic sheets where the water flow into the drift could be collected eleven different tracers were injected at distances between 11 and 50 m from the ceiling of the drift the flow rate and tracer monitoring was kept up for more than 2 years the tracer breakthrough curves and flow rate distributions were used to study the flow paths velocities hydraulic conductivities dispersivities and channeling effects in the rock in a companion paper the experimental design and performed experiments are described the present paper describes the interpretation of flow and tracer movement in the rock outside the drift the tracer movement was measured by the more than 160 individual tracer curves the tracer experiments have permitted the flow porosity and dispersion to be studied the possible effects of channeling and the diffusion of tracers into stagnant waters in the rock matrix and in stagnant waters in the fractures have also been addressed

significance of fracture rim zone heterogeneity for tracer transport in crystalline rock 1 conducting fractures of crystalline rock are typically altered over long periods of time the fracture rim zone a result of these alterations will as a rule have different physical and chemical properties from the unaltered fresh rock depending on various microscopic and macroscopic factors of the alterations in this paper we study the impact of rim zone heterogeneity exemplified by a decreasing porosity trend as inferred from the aspo hard rock laboratory site sweden on short and long term tracer transport our main finding is that this particular rim zone structure will have a dominant effect on transport of moderately to strongly sorbing tracers on experimental time scales and a notable effect on application time scales the findings of this work lend further support to the interpretation of the relatively strong retention reported by cvetkovic et al the fracture rim zone porosity structure may provide an additional safety margin for sorbing radionuclides in crystalline rock at sites where fracture alteration is prevalent

channeling with diffusion into stagnant water and into a matrix in series numerous field observations show that most water flow in fractured rocks takes place in only a small part of the fractures we call these channels solutes in the flowing water can diffuse in and out of stagnant water in the porous rock matrix that the flowing water contacts via the so called flow wetted surface fws in addition the solutes can diffuse into stagnant water in the fractures themselves and from this water further into the rock matrix for narrow channels with small fws the transport via the stagnant water in the fracture can considerably add to the exchange of solutes between flowing water and matrix water for sorbing solutes that interact with the micropore surfaces in the matrix the effect can be very strong some models that account for these processes are developed and solved using laplace transforms some examples are presented that show the effects of first diffusion into stagnant waters in fractures with subsequent diffusion into the rock matrix effects of slit like and tube like channels are considered as well as the presence of intersecting fractures the solutions are especially useful to model solute transport in complex three dimensional channels networks where wide and narrow or even tube like channels with widely varying flow rates combine into a multitude of different paths

the variscan belt in central europe main structures geodynamic implications open questions abstract the variscan belt of europe originated from the confrontation of northern europe and gondwana with intervening pre variscan blocks cadomian and older armorica tepla barrandean moravo silesian though a strike slip component cannot be excluded geological evidence suggests a subduction collision process newly discovered features include basaltic rocks with morb affinities high pressure metamorphic rocks trench deposits and large scale allochthonism which also affects the pre variscan basement and has often led to an inversion of the metamorphic isogrades large scale thrusting is evident at all crustal levels and is also observable by geophysical methods the structure of the variscan crust is best described as horizontal tectonic layering late ordovician through carboniferous convergence closed one rhenohercynian and one saxo thuringian basin to the north and at least one mediterranean basin to the south of the pre variscan blocks subduction occurred from the north as well as from the south down under the dorsal core region the exact timing and the driving mechanism of this bilateral activity remains a problem likewise uncertain are the exact limination of the pre variscan blocks and the existence and width of oceanic areas in the saxothuringian zone and in the south facing part of the moldanubian zone there is good evidence of early palaeozoic rifting and of late ordovician through carboniferous plate convergence palaeomagnetic and palaeoclimatic constraints however suggest only a limited extent of oceanic basins in these areas while they appear to allow a wider ocean at the rhenohercynian saxothuringian boundary which is relatively unobtrusive from the geological point of view research during the past decade has produced a wealth of information on the variscan fold belt in europe the resulting geodynamic models however are extremely diverging evidently it is not the time yet for definitive statements the present paper intends to review the state of knowledge to deduce such basic items of a geodynamic model as appear reasonably well documented and to point out the most urgent open questions stress will be laid on central europe which offers a complete cross section through the northern flank of the variscan belt and where we have carried out most of our studies during the last years

radionuclide migration through fractured rock for arbitrary length decay chain analytical solution and global sensitivity analysis summary this study presents an analytical approach to simulate nuclide migration through a channel in a fracture accounting for an arbitrary length decay chain the nuclides are retarded as they diffuse in the porous rock matrix and stagnant zones in the fracture the laplace transform and similarity transform techniques are applied to solve the model the analytical solution to the nuclide concentrations at the fracture outlet is governed by nine parameters representing different mechanisms acting on nuclide transport through a fracture including diffusion into the rock matrices diffusion into the stagnant water zone chain decay and hydrodynamic dispersion furthermore to assess how sensitive the results are to parameter uncertainties the sobol method is applied in variance based global sensitivity analyses of the model output the sobol indices show how uncertainty in the model output is apportioned to the uncertainty in the model input this method takes into account both direct effects and interaction effects between input parameters the simulation results suggest that in the case of pulse injections ignoring the effect of a stagnant water zone can lead to significant errors in the time of first arrival and the peak value of the nuclides likewise neglecting the parent and modeling its daughter as a single stable species can result in a significant overestimation of the peak value of the daughter nuclide it is also found that as the dispersion increases the early arrival time and the peak time of the daughter decrease while the peak value increases more importantly the global sensitivity analysis reveals that for time periods greater than a few thousand years the uncertainty of the model output is more sensitive to the values of the individual parameters than to the interaction between them moreover if one tries to evaluate the true values of the input parameters at the same cost and effort the determination of priorities should follow a certain sequence

palaeomagnetic investigations in the hercynian mountain belt of central europe abstract the palaeomagnetism of sediments and volcanics of middle devonian to early carboniferous age has been studied in the hercynian realm of the vosges harz and franconian forest france and germany after appropriate cleaning characteristic directions of natural remanent magnetization nrm have been determined which are considered to be of pretectonic origin according to rock magnetic and structural geological evidence a mean palaeopole for the devonian rocks in the areas investigated was determined at 29 7 n and 9 0 e the site latitude derived from the devonian rocks agrees very well with that observed in great britain and britanny the significant difference in longitude between our devonian poles and the other european data may be due to an anticlockwise rotation of central europe with respect to the northern hercynian foreland the carboniferous rocks yield a mean palaeopole at 41 7 n and 340 4 e matching the carboniferous part of the european polar wander path a fold test within carboniferous greywackes from the harz mountains proves a pre folding origin of the nrm of these rocks however this stable magnetization direction indicates local or regional tectonic displacement our results do not support any major latitudinal motions of continental segments in central europe during the hercynian orogeny the palaeozoic palaeomagnetic data from the vosges franconian forest harz britanny and central massif can be used to interpret the hercynides in terms of a large scale shear belt

solute transport in fractured rocks with stagnant water zone and rock matrix composed of different geological layers model development and simulations a model is developed to describe solute transport and retention in fractured rocks it accounts for the fact that solutes can not only diffuse directly from the flowing channel into the adjacent ro

temporal variations in seismic event rate and b values from stress corrosion constitutive laws abstract main i g meredith p g and sammonds p r 1992 temporal variations in seismic event rate and b values from stress corrosion constitutive laws in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 233 246 a model is developed to characterise the state of damage for a fractal population of cracks in terms of a mean energy release rate g which depends on the stress the event rate n and the seismic b value n is assumed to be proportional to the total number of potentially active cracks and b to be proportional to the exponent d of the crack length distribution g is then positively correlated with n and negatively correlated with b consistent with experimental observation based on stress intensity as a constitutive variable the model predicts that higher b values are associated either with lower stress intensity or greater material heterogeneity both experiment and theory predict intermediate term seismic quiescence of similar magnitude to that observed in the field 45 90 for only a small simultaneous reduction in stress and stress intensity 2 7 or the equivalent mean energy release rate the theoretical model predicts three different types of quiescence associated with increasing constant or decreasing b value the first two are associated with stable intermediate term quiescence due to a reduction in g and the third is associated with unstable short term quiescence associated with constant or increasing g the theory can be used to infer relative changes in g from acoustic emissions in the laboratory experiments to date show that quiescence of the order 10 can be seen in the laboratory at strain rates of 10 5 s 1 but that this has the characteristics of short term rather than intermediate term quiescence