zircon a possible indicator of mass transfer in deformation zones a solution for the roffna gneiss controversy suretta nappe switzerland abstract this paper proposes a simple volume mass balancing technique as a means to assess the volume loss and tectonic flattening of mylonitic shear zones the method involves counting the number of zircon crystals in oriented polished thin sections analyzed subsequently in the electron microprobe using the bsei mode and a spectrometer setup for detection of the element zr here we present an application to the roffna gneiss eastern switzerland a porphyritic granite of permian origin which has been metamorphosed and transformed into a phengitic schist under low grade metamorphic conditions mass balances for this material have produced controversial interpretations in that a first analysis of chemical data of wall rock and mylonite suggested an isochoric mylonitic transition event while a dramatic volume loss of some 50 in the course this process was inferred after a re evaluation of the same data electron microscopy of zircon crystals that were retrieved from rocks which had undergone different degrees of deformation revealed only minor alterations and mechanical damage of single grains this stability of zircon justified the use of single crystals and in consequence of the element zr as passive markers in determining volume mass changes during deformation results obtained by this method allow us to confirm that the deformation of the roffna gneiss involved a volume loss of 29 6 accompanied by chemical alterations deformation induced mobility changes of various elements lead to small gains in mg and cr but significant losses si al na ca and sr during the metamorphic event all other elements including the ree underwent no substantial long range transport

electrokinetic experimental study on saturated rock samples zeta potential and surface conductance summary it is important to know the electrokinetic properties of crustal rocks for interpreting the conductivity mechanisms and seismoelectric phenomena during earthquakes and seismoelectric well logging in this study electrokinetic experiments are conducted using a special coreholder by employing an ac lock in technique a series of experiments are conducted on 10 sandstone samples to measure the streaming potentials and streaming currents and the experiments on each sample are done at six different salinities the streaming potential coefficient and streaming current coefficient are calculated from the measured streaming potentials and streaming currents the experimental results show that streaming potential coefficient and streaming current coefficient decrease as the salinity increases the dependence of these two coefficients on permeability and pore radius are analysed and compared with previous works at low salinities the streaming potential coefficient and streaming current coefficient increase with the increasing permeability and pore radius at high salinities the streaming potential coefficient streaming current coefficient almost share a same value for 10 different samples this conclusion indicates that the differences of rock parameters can only be well recognized at lower salinities and the electrokinetic signals are invalid at high salinities which offers a restrictive condition for using the amplitude of electrokinetic signals to estimate rock parameters the zeta potential have also been estimated through combined measurements of streaming potential and streaming current the surface conductivity and its contribution to electrokinetic effects are determined from a comparison of zeta potentials by two different methods and then the validation of the helmholz smoluchowski equation for a capillary tube is tested in rocks we also compare our date with theoretical and experimental works and set up an expression about the relationship between zeta potential and salinity which fits the experimental data well

experimental studies of electrokinetic conversions in fluid saturated borehole models experimental and theoretical studies show that there are electromagnetic em fields generated by seismic waves with two kinds of conversion mechanisms in a fluid saturated porous medium within a homogeneous formation the seismic wave generates a seismoelectric field that exists only in the area disturbed by the seismic wave and whose apparent velocity is that of the seismic wave at an interface between differing formation properties the generated seismoelectric wave is a propagating em wave that can be detected everywhere an electrode used as a receiver on the ground surface can detect the propagating em wave generated at an interface but cannot detect the seismoelectric field generated in a homogeneous formation when the electrode is in a borehole and close to a porous formation it can detect both the em waves and the seismoelectric field in this paper electrokinetic measurements are performed with borehole models made of natural rocks or artificial materials experimental results show that

numerical modeling of frontal and basal accretion at collisional margins 1 we investigate the deformation of orogenic wedges that form in the early stages of continent continent collisions using a two dimensional numerical model limited to the upper lithosphere our models show that deformation at the plate margins is influenced by rheology surface processes and the balance between inward mass flux and outward subduction flux as controlled by the subduction load which represents the effects of slab pull and resistive forces and flexural downbending we find three characteristic deformation modes 1 near pure subduction with little or no accretion 2 frontal accretion with development of an accretionary wedge built up by offscraping of the sediment layer at shallow depth and 3 independent frontal and basal accretion where a retrothrust allows stacking of basement nappes at crustal to mantle depths near pure subduction is enabled for ordinary rheology materials characterized by brittle and viscous material behavior approximating a christmas tree type depth profile and almost zero friction along the subduction shear zone frontal accretion occurs when slightly increased friction along the subduction shear zone allows offscraping of the sediment layer from the subducting plate independent frontal and basal accretion develops in strong rheology models with an almost fully brittle material behavior major surface erosion or a reduction of the subduction load promote the development of large basement nappes frontal accretion is favored by major sedimentation during convergence a large backstop and in the case of a lateral transition from a strong rheology to an ordinary rheology subducting plate our numerical models develop first order characteristics as observed in natural orogenic wedges for example upper crustal nappe stacks frontal and basal accretion or extension in the core of an orogen frontal and basal accretion are interdependent and tend to stabilize the subduction system

shear zone patterns and strain distribution at the scale of a penninic nappe the suretta nappe eastern swiss alps abstract shear zone patterns within the suretta nappe of the swiss alps are studied in order to understand finite strain and bulk tectonic displacements the suretta nappe is chosen for two main reasons the availability of late variscan granites deformed during alpine tectonics only and because of continuous outcrop from bottom to top of the nappe this alpine nappe recorded two major ductile deformation phases which developed under low grade metamorphic conditions the analysis of shear zone patterns in the roffna granite reveals that the first deformation is well developed in the entire nappe the second deformation however is more localized in the lower and upper parts the bulk asymmetry of the shear zone patterns confirms the kinematics recorded by other penninic nappes in this area first a stacking of the nappe towards the nw followed by the top to the e shearing during post thickening extensional tectonics the shear zone patterns and strain distribution allow us to deduce kinematics at the nappe scale

impact of water saturation on seismoelectric transfer functions a laboratory study of coseismic phenomenon s u m m a r y seismic waves propagating in a porous medium under favourable conditions generate measurable electromagnetic fields due to electrokinetic effects it has been proposed following experimental and numerical studies that these so called seismoelectromagnetic couplings depend on pore fluid properties the theoretical frame describing these phenomena are based on the original biot s theory assuming that pores are fluid filled we study here the impact of a partially saturated medium on amplitudes of those seismoelectric couplings by comparing experimental data to an effective fluid model we have built a 1 m length scale experiment designed for imbibition and drainage of an homogeneous silica sand the experimental setup includes a seismic source accelerometers electric dipoles and capacitance probes in order to monitor seismic and seismoelectric fields during water saturation apparent velocities and frequency spectra in the kilohertz range are derived from seismic and electrical measurements during experiments in varying saturation conditions amplitudes of seismic and seismoelectric waves and their ratios i e transfer functions are discussed using a spectral analysis performed by continuous wavelet transform the experiments reveal that amplitude ratios of seismic to coseismic electric signals remain rather constant as a function of the water saturation in the s w 0 2 0 9 range consistently with theoretically predicted transfer functions

modification of streaming potential by precipitation of calcite in a sand water system laboratory measurements in the ph range from 4 to 12 spontaneous potentials associated with volcanic activity are often interpreted by means of the electrokinetic potential which is usually positive in the flow direction i e zeta potential of the rock is negative the water rock interactions in hydrothermal zones alter the primary minerals leading to the formation of secondary minerals this work addresses the study of calcite precipitation in a sand composed of 98 quartz and 2 calcite using streaming potential measurements the precipitation of calcite as a secondary mineral phase inferred by high calcite saturation indices and by a fall in permeability has a significant effect on the electrokinetic behaviour leading to a significant reduction in the zeta potential in absolute value and even a change in sign the measured decrease in zeta potential from 16 mv to 27 4 mv takes place as the ph rises from 4 to 7 while it remains constant at 25 1 mv as the ph increases from 8 to 10 5 for ph higher than 10 5 calcite precipitates and is expected to coat the quartz surface the measured zeta potential vary from 17 to 8 mv for ph ranging from 10 6 to 11 7 depending on the amount of precipitated calcite indicated by the decrease in permeability the observed change in sign of the electrical surface potential rules out the usual qualitative interpretation of sp anomalies in order to determine fluid circulations even at ph lower than 9 if calcite is widely present as a secondary mineral phase since the electrical surface potential of calcite depends also on co2 partial pressure and ca2 therefore sp anomalies as measured in hydrothermal field without mineralogical analyses of hydrothermal deposits and without geochemical fluid survey should be interpreted with caution

the kinematic history of the pennine nappes east of the lepontine dome implications for the tectonic evolution of the central alps the pennine zone of the eastern central alps south middle and north pennine from top to bottom of sequence underwent a complex structural and strain history a first phase d1 is characterized by e w oriented stretching and is of cretaceous lower tertiary age d1 structures affected most but not all of the south and middle pennine units were probably obliterated in the north pennine adula nappe and are absent in the basement nappes underneath the adula nappe further deformation led to n nw directed nappe movement d2 followed by incipient strike slip motion along the periadriatic line late d2 subsequently large scale folding d3 affected mainly the nappe fronts in the adula nappe f3 folds verge towards the foreland whereas the overlying units were backfolded towards the hinterland the d2 d3 events were accompanied by a complex strain pattern that is best seen in the adula nappe and includes plane to prolate strains in the upper frontal part and oblate strains in both the lower frontal part and the interior of the nappe d3 backfolding was associated with the beginning of backthrusting at the periadriatic line and was accompanied and or followed by rapid uplift in the lepontine dome and subsequent unroofing of the latter which led to e ne directed extensional movements d4 in the eastern central alps the d1 event is related to the anticlockwise rotation of the adriatic plate relative to europe this caused dextral transpression between the adriatic and the european plates and partitioning of the deformation into convergence and strike slip it is suggested that the north pennine nappes below the adula nappe were situated along a major strike slip fault and escaped this event d2 resulted from continental collision between adria and europe d2 displacement directions are subperpendicular to the alpine arc and are best approximated by wnw nw oriented motion of adria the structures and the strain pattern of d3 are interpreted as the result of gravitational force late d2 strike slip deformation at the periadriatic line d3 backthrusting at the southern steep belt and the unroofing stage d4 are generally attributed to dextral transpression between adria and europe this approach implies that the alpine evolution of the central alps was largely governed by tangential convergence between the adriatic and the european plates

electroseismic and seismoelectric measurements of rock samples in a water tank an electromagnetic em or seismic wave can induce seismic or em waves because of the electrokinetic conversion based on the electric double layer in a fluid saturated porous medium we tested a new method for observing electroseismic and seismoelectric conversions in rock samples our method is designed to overcome the shortcoming of previous attempts to separate signals generated by a continuous electric or seismic source in a small container we first observed acoustic fields around electrodes excited by an electric pulse in a water tank or in a water saturated porous sample in our approach we immersed rock samples in a water tank and measure the seismic or electric responses using electric or acoustic pulses conveyed through the immersed electrodes or hydrophone we measured electroseismic and seismoelectric frequency responses in berea sandstone and westerly granite samples at a frequency range of 15 150 khz the measurements clearly separate the effects of the electric source background noises

alpine and pre alpine subduction events in polycyclic basements of the swiss alps coupling macrostructural and microstructural observation with metamorphic petrology of polymetamorphic mafic rocks occurring in basement rocks of the central alps clearly provides evidence that some part of this basement underwent at least two different and independent events of high pressure metamorphism the older eclogitic event occurred at middle to high temperature and must have been pre alpine because late variscan plutons crosscut the high pressure structures the younger event occurred at high pressure and low temperature conditions and is tertiary in age the separation of alpine from pre alpine eclogite facies events is discussed for several alpine nappes

mechanical model for subduction collision tectonics of alpine type compressional orogens alpine type orogens are characterized by three distinct convergent tectonic phases subduction with deformation that has primarily single vergence a transition from subduction to collision and continental collision with double vergence although the cenozoic history of the european alps has additional complexities a mechanical explanation for these three phases would provide the necessary crustal scale framework in which to develop an understanding of the smaller scale processes we present results from a simple numerical model which explain the mechanics of these three phases as a consequence of the changing buoyancy of the lithosphere subducted beneath the orogen the development and exhumation of a subduction complex suture zone and basement nappe stack piemont suture penninic nappes the presence of a crustal scale back fold and thrust insubric line and uplift of basement on the pro european side of the orogen external basement massifs may be explained as a simple consequence of changing dynamics during the transition from subduction to collision

slab breakoff a model for syncollisional magmatism and tectonics in the alps slab breakoff is the buoyancy driven detachment of subducted oceanic lithosphere from the light continental lithosphere that follows it during continental collision in a recent paper davies and von blanckenburg 1994 have assessed the physical conditions leading to breakoff by quantitative thermomechanical modeling and have predicted various consequences in the evolution of mountain belts breakoff will lead to heating of the overriding lithospheric mantle by upwelling asthenosphere melting of its enriched layers and thus to bimodal magmatism breakoff will also lead to thermal weakening of the subducted crustal lithosphere thereby allowing buoyant rise of released crustal slices from mantle depths in this paper we present a test of this model in the tertiary evolution of the european alps in the alps both basaltic and granitoid magmatism occur between 42 and 25 ma following the closure of oceanic basins by subduction and continental collision the granitoids are now well established to result from mixing of basalt with assimilated continental crust to identify the tectonically crucial origin of the partial mantle melts we have compiled all published geochemical and isotopic data of numerous mafic dykes occurring throughout the whole alpine arc their trace element and isotopic composition suggests that they have been formed by low degree melting of the mechanically stable lithospheric mantle we see no evidence for melting of asthenospheric mantle it was thus not decompressed to depths shallower than 50 km once initiated rapid lateral migration of slab breakoff will result in a linear trace of magmatism in locally thermal weakened crust this explains why all alpine magmatic rocks intruded almost synchronously along a strike slip fault the periadriatic lineament a compilation of ages from penninic high pressure rocks subducted to depths of up to 100 km shows that subduction took place at circa 55 40 ma followed by uplift at 40 35 ma from the short time interval between their uplift and the onset of magmatism we infer that both processes have been induced by the breakoff the slab breakoff model fulfills its predictions in the case of the alps and therefore supports the assumptions made in the theoretical model on a geological basis we believe that the characteristic association of magmatic activity with the return of high pressure rocks to the surface allows the identification of this process in the earth s mountain belts

late stage deformation in a collisional orogen western alps nappe refolding back thrusting or normal faulting nappe refolding back thrusting and normal faulting frequently cause severe late stage overprinting of the architecture of an orogen a combined investigation of nappe stack polarity kinematics of shearing and metamorphic gradients in the western alps develops criteria for distinguishing between these three modes of late stage deformation this distinction is a prerequisite for any retro deformation necessary for understanding the main tectonic and metamorphic evolution of collisional orogens in the case of the western alps overprint was by mega scale nappe refolding in the oligocene this implies exhumation of the hp rocks prior to postnappe folding i e during nappe stacking and by foreland directed ascent within a subduction channel

kaolinite and dickite formation during shale diagenesis isotopic data abstract x ray diffraction scanning electron microscopy and o isotope geochemistry have been used to investigate the origin and possible controls on polymorphic transformation of kaolin minerals filling veins in cretaceous shales from the gibraltar strait area southern spain the mineralogy of the enclosing shales indicates that kaolin minerals formed from smectite dissolution a process that silmultaneously originated i s mixed layers and quartz kaolinite and dickite 18o values suggest that an increase in the water isotopic composition from cretaceous sea water values 1 to values of about 3 occurred parallel to smectite dissolution the intensity of this process being the main factor controlling the isotopic composition of kaolin minerals the minimum formation temperature ranges from 62 c for kaolinite to 86 96 c for dickite indicating that the depth of burial was the main control on polymorph formation this temperature range agrees with that deduced for illite smectite ordering the passage from kaolinite to dickite rich veins was accompanied as deduced from sem examination by a morphologic evolution characterized by the division of large vermiculae dominant in kaolinite samples and the formation of short stacks and platy crystals which are predominant in dickite the mechanism of dickite formation however remains uncertain

experimental measurements of the streaming potential and seismoelectric conversion in berea sandstone the streaming potential across a porous medium is induced by a fluid flow due to an electric double layer between a solid and a fluid when an acoustic wave propagates through a porous medium the wave pressure generates a relative movement between the solid and the fluid the moving charge in the fluid induces an electric field and seismoelectric conversion in order to investigate the streaming potential and the seismoelectric conversion in the same rock sample we conduct measurements with berea sandstone saturated by nacl solutions with different conductivities we measure the electric voltage streaming potential across a cylindrical sample in nacl solutions with different conductivities and under different pressures to determine the dc coupling coefficients we also measure the seismoelectric signals induced by acoustic waves with a berea sandstone plate at different frequencies and solution conductivities the pressures of the acoustic waves are calibrated with a standard hydrophone bruel 8103 at different frequencies 15 120 khz we calculate the quantitative coupling coefficients of the seismoelectric conversion at dc and at high frequencies with samples saturated by solutions with different conductivities when the berea sandstone sample is saturated by the nacl solution with 0 32 ms m in conductivity for example the dc and seismoelectric coupling coefficients at 15 khz are 0 024 v pa and 0 019 v pa respectively the seismoelectric coupling coefficient is an important and helpful parameter for designing a seismoelectric tool more experimental measurements of seismoelectric coupling coefficients in the frequency range of 100 hz to 15 khz are needed in the future

kinematics of austro alpine cover nappes changing translation path due to transpression upper and middle austro alpine nappes of the eastern alps the structural uppermost subunits of the alps suffered two major superposed deformations d1 d2 during the eo alpine cretaceous orogeny d1 is characterized by nw to w directed thrusting and nappe internal rock flow d2 by large scale folding and imbrication toward the north and northeast structures strain metamorphic history microfabrics and stretching trajectories indicate that the superposition of d2 over d1 structures can be interpreted as a progressive deformation it is concluded that the emplacement of the nappes follows a curved translation path a model which emphasizes non coaxial deformation structures explains the detachment of the nappes the configuration of the separating thrust planes and the distribution of intense deformation zones the overall kinematic history of the austro alpine nappes fits a model in which strike slip shearing horizontal shortening and vertical lengthening act together continuously over a finite deformation zone transpressional model this model emphasizing a gradually changing strain regime eliminates the space problems encountered in models which consider simple south over north imbrication during the alpine orogeny the study stresses two interpretations 1 1 stretching lineations indicate nappe transport directions 2 2 transpression may be a common feature of orogenic belts

thermochronometry across the austroalpine pennine boundary central alps switzerland orogen perpendicular normal fault slip on a major overthrust and its implications for orogenesis fifty one new and 309 published thermochronometric ages nine systems with closure temperatures ranging from 450 to 70 c from the graubunden region of the central alps demonstrate that a pronounced thermal mismatch between the austroalpine allochthon alpine orogenic lid and the pennine zone persisted until at least 29 ma and allowably until circa 18 ma the observed mismatch supports previous suggestions that the famous overthrust between the austroalpine allochthon and the pennine zone historically regarded as primarily an eocene top north thrust fault is in fact primarily an oligocene miocene normal fault that has a minimum of 60 km of displacement with top south or top southeast sense of shear two hallmarks of alpine geology deposition of the foredeep molasse and emplacement of the helvetic nappes appear to be coeval peripheral manifestations of crustal thickening via the interposition of the pennine zone as a northward intruding wedge between the austroalpine lid and the european cratonic margin with the helvetic system european margin acting as the floor of the wedge we presume the penninic wedge is driven by the buoyant rise of subducted crust no longer able to remain attached to the descending slab if so emplacement of the pennine wedge could have occurred mainly after adria was juxtaposed against cratonic europe

simulation of the borehole quasistatic electric field excited by the acoustic wave during logging while drilling due to electrokinetic effect acoustic logging while drilling lwd is an important commercial technology for oil and gas exploration however the collar wave in the full waveform has been found to interfere with signals from the formation making it difficult to obtain formation compressional and shear velocities from acoustic lwd signals we investigated seismoelectric lwd to solve this problem we focused on the feasibility of obtaining the formation acoustic compressional and shear velocities from electric signals that go with acoustic waves near the borehole due to the electrokinetic effect the theoretical full waveform of the seismoelectric lwd was simulated by one way conversion approximation the full waveform of acoustic pressure was simulated first with a viscoelastic formation medium the pore pressure was then estimated by confining pressure the electric field excited by the elastic wave was seen as quasistatic and was simulated by solving the poisson equation under the borehole conditions with an inhomogeneous term generated by the acoustic disturbance in the full waveform of the synthesized electric field there was a signal traveling with the collar wave speed as well as signals accompanying compressional shear and similar guided wave groups the converted electric collar wave signal was weaker than its acoustic counterpart in terms of their amplitudes relative to other wave groups in their respective full waveforms

two subduction events in a polycyclic basement alpine and pre alpine high pressure metamorphism in the suretta nappe swiss eastern alps this study is essentially based on coupling macrostructures microstructures and metamorphic petrology in polymetamorphic mafic rocks from the swiss eastern alps suretta nappe penninic domain petrographic criteria are used in conjunction with structural analysis and microprobe work to define crystallization deformation relationships and to establish a relative but precise sequence of tectono metamorphic events a first eclogite facies overprint and related exhumation occurred before emplacement of late palaeozoic intrusives during the alpine cycle the suretta nappe was part of the thinned european continental margin the tertiary burial due to subduction and collision is responsible for d1 ductile thrusting and blueschist facies metamorphism late deformation phases related to exhumation are responsible for the development of extensional structures under greenschist facies conditions quantitative metamorphic petrology based on gibbs free energy minimization domino by de capitani gives a constraint on the p t conditions during the polymetamorphic and polycyclic evolution the first high p metamorphic event related to pre alpine structures occurred at c 700 c and at least 2 0 gpa these conditions are compatible with pre alpine high p re equilibration already described in several alpine units the alpine high p metamorphism occurred under blueschist facies conditions at c 400 450 c and 1 0 gpa similar high p low t conditions have already been described in the mesozoic and permian rock types the two high p events are clearly related to two different geothermal regimes and geodynamic environments

fast inversion of formation permeability from stoneley wave logs using a simplified biot rosenbaum model this paper describes a fast algorithm for estimating formation permeability from stoneley wave logs the procedure uses a simplified biot rosenbaum model formulation the input to the inversion is the stoneley wave spectral amplitudes at each receiver position the bore hole fluid properties velocity and density the borehole caliper log the formation density and porosity from log data and the compressional and shear velocities for the interval of interest the model uses the borehole caliper and elastic properties to compute the stoneley wave excitation that is predicted amplitude without permeability effects as a function of frequency and the porosity and permeability to compute the fluid flow amplitude reduction this method also uses a reference depth of known permeability and compares amplitude variations at other depths relative to the reference depth the permeability value obtained from the inversion represents the best fit over all receivers and all relevant frequencies a processing example is shown to demonstrate the ability of this technique to extract formation permeability from stoneley wave logs

initiation and development of the pennine basal thrust swiss alps a structural and geochronological study of an exhumed megathrust abstract the pennine basal thrust pbt is an exhumed megathrust developed during continental collision from late eocene to miocene to trace its evolution five samples with indications for up to three microstructurally diachronous white mica generations were investigated by laser in situ and step heating 40 ar 39 ar dating three deformation related crystallization ages can be distinguished 1 d 1 characterized in the pbt hanging wall by an s 1 foliation defined by white mica chloritoid began at or before 38 0 ma 2 d 2 formed a pervasive s 2 cleavage and synchronous white mica rich veins dated at 27 ma 3 d 3 produced an s 3 crenulation cleavage and chlorite white mica veins dated at 23 ma older ages of 96 ma footwall and 115 ma hanging wall are interpreted as minimum ages for the detrital component finally discrete faulting produced fault gouge with an illite k ar age of 19 ma a simplified back restored reconstruction provides a tectonic context for the dated structures in this framework d 1 occurred during middle to late eocene tectonic accretion after late eocene initiation of continental collision d 2 reflects oligocene top to nw shearing with both in and out of sequence thrusting d 3 then developed from 23 to 19 ma during the progressive deactivation of the pbt

strain accumulation during basal accretion in continental collision a case study from the suretta nappe eastern swiss alps abstract stacked crystalline basement nappes are a typical feature in the core of many orogens the suretta nappe exposed in eastern switzerland consists of briancon derived crustal slices which were assembled in a south dipping subduction zone during the alpine orogenic cycle the nappe contains post variscan rocks of the rofna porphyry complex rpc and permo mesozoic cover sequences which are ideal to study the strain evolution during alpine nappe formation we present new structural cross sections finite strain analyses and a retrodeformation for the frontal part of the suretta nappe the overall geometry of the suretta nappe is the result of two main deformation phases 1 eocene top to the nnw directed thrusting and folding ferrera phase which is overprinted by 2 backfolding and backshearing niemet beverin phase we suspect that this backshearing was caused by the buoyant rise of light continental crust beneath the suretta nappe and by frictional resistance at the top contact of the suretta nappe which had been accreted to the upper plate in the course of nappe stacking in the lower and interior parts of the suretta nappe weakly to undeformed boudins are generally surrounded by l tectonites indicating wsw ene stretching foliated equivalents reveal a plane strain deformation state the upper part of the suretta nappe which was strongly affected by backshearing shows flattening strain strain data were used to reconstruct the palinspastic evolution of the suretta nappe at two distinct time slots prior to niemet beverin backfolding the suretta nappe is characterized by thrust faults and large scale detachment folds before the onset of ferrera phase nappe stacking jurassic normal faults and the rpc intrusion shape trigger the localization of subsequent deformation our structural study confirms a complex polyphase evolution for the suretta nappe which might be characteristic for crystalline basement nappes in continental collision zones elsewhere

diagenetic stabilization of aragonite and low mg calcite ii stable isotopes in rudists abstract cretaceous rudists having thick multilayered bimineralic aragonite and low mg calcite shells have been studied for the effects of phreatic vadose meteoric diagenesis on their microstructural and isotopic attributes rudist skeletal components with preserved original mineralogy of aragonite and low mg calcite and with preserved microstructures have isotopic signatures analogous to holocene marine bivalves this similarity argues for a comparable isotopic composition of the cretaceous and holocene seawater as well as for a similar mode of incorporation of stable isotopes into their shells diagenetic stabilization of rudist shells appears to have been a two stage process with low mg calcite diagenetic calcite lmc dlmc and particularly aragonite diagenetic calcite a dlmc transformation as the first step and cementation as a later development the direct a dlmc mineralogical transformation calcitization results in initial depletion in 18o of 2 and the subsequent diagenetic precipitation of ferroan calcite spar causes depletion in 13c as well as an additional decrease in 18o the former due to introduction of organically derived co2 into the diagenetic aquifer in contrast 13o and 13c isotopic depletions in the originally lmc skeletal components are both related to the precipitation of the late diagenetic ferroan sparry calcite cement the earlier calcitization stage being of subordinate importance only

bayesian inversion of joint sh seismic and seismoelectric data to infer glacier system properties abstract in glacial studies properties such as glacier thickness and the basement permeability and porosity are key to understand the hydrological and mechanical behaviour of the system the seismoelectric method could potentially be used to determine key properties of glacial environments here we analytically model the generation of seismic and seismoelectric signals by means of a shear horizontal seismic wave source on top of a glacier overlying a porous basement considering a one dimensional setting we compute the seismic waves and the electrokinetically induced electric field we then analyse the sensitivity of the seismic and electromagnetic data to relevant model parameters namely depth of the glacier bottom porosity permeability shear modulus and saturating water salinity of the glacier basement moreover we study the possibility of inferring these key parameters from a set of very low noise synthetic data adopting a bayesian framework to pay particular attention to the uncertainty of the model parameters mentioned above we tackle the resolution of the probabilistic inverse problem with two strategies 1 we compute the marginal posterior distributions of each model parameter solving multidimensional integrals numerically and 2 we use a markov chain monte carlo algorithm to retrieve a collection of model parameters that follows the posterior probability density function of the model parameters given the synthetic data set both methodologies are able to obtain the marginal distributions of the parameters and estimate their mean and standard deviation the markov chain monte carlo algorithm performs better in terms of numerical stability and number of iterations needed to characterize the distributions the inversion of seismic data alone is not able to constrain the values of porosity and permeability further than the prior distribution in turn the inversion of the electric data alone and the joint inversion of seismic and electric data are useful to constrain these parameters as well as other glacial system properties furthermore the joint inversion reduces the uncertainty of the model parameters estimates and provides more accurate results

detection of fluid flow variations at the nankai trough by electric and magnetic measurements in boreholes or at the seafloor detection of changes in the flow rate of expelled fluids in accretionary prisms by monitoring of electric and magnetic fields is discussed a numerical model of the electric and magnetic fields associated with fluid flow variations at the nankai trough is presented which gives a numerical solution of the coupled system of electric convection currents and conduction currents that directly determines the magnetic anomaly itself measurements in a borehole located between two vents are shown to be well adapted to detection of fluid flow variations using the vertical gradient of the electric potential and the horizontal magnetic field the vertical electric field is about 10 mv km up to 500 m depth where there is a lithologic reflector and about 50 mv km below this reflector the horizontal gradient of the magnetic field is 2 nt km at the seafloor modelization with a lower fault conductivity and a larger decollement thickness has also been modeled the vertical gradient of the horizontal magnetic field is 5 to 15 nt km a variation of 3 mv and 1 5 to 3 nt at 600 m depth in a borehole could reveal a fluid flow rate variation of 20 which is a reasonable fluid flow change based on some observations at short scale time since a 1 5 to 3 nt anomaly seems easier to detect than a 3 mv anomaly it is likely that the variation of the magnetic field would more sensitively reveal fluid flow variations when monitoring the magnetic field at the seafloor a change of 0 4 nt km in the horizontal gradient could reveal a fluid flow rate variation of 20

fold controlled quartz textures in the pennine mischabel backfold near zermatt switzerland abstract quartz fabric analyses along the basal thrust of the dent blanche nappe and in the footfall pennine units indicate south directed thrusting for the last stage of austro alpine pennine nappe emplacement quartz fabrics in particular those from the pennine mischabel backfold imply complex spatial and temporal texture developments with crystallographic preferred orientations cpo that are commonly in disagreement with mesoscopic grain shape lineations in consequence kinematic directions inferred by quartz textures do not necessarily coincide with those predicted by mesoscopic structural elements such as grain shape lineations in our particular case orientation of grain shape lineations is rather complex in the study area while principal axes inferred from the quartz textures remain geographically constant and exhibit a simple geometric relationship to the mischabel backfold it is suggested that the grain shape lineations correspond to the total accommodated finite strain whereas the quartz fabrics reflect late increments of deformation quartz cpos in the hinge of the mischabel fold are similar to those along the thrust revealing asymmetric single girdles to c axes point maxima subgrain rotation is the predominant recrystallization mechanism suggesting steady state conditions in fabric development during progressive rotational deformation in contrast asymmetric cross girdles dominate the upper limb and uneven small circle c axes distributions characterize the lower limb although recrystallization in both limbs is characterized by grain boundary migration this clear separation of quartz textures and recrystallization deformation mechanism conflicts with the common view on heterogeneous deformation patterns in folds where the major component of rotational shear is expected in the fold limbs our study suggests that fabric development in the limbs of the recumbent mischabel fold was reset during progressive deformation shortly prior to the transition from an active buckling to passive fold amplification while the hinge suffered continuous bulk deformation provided by the back thrusting of the dent blanche nappe

the fry method applied to an augen orthogneiss problems and results the application of the fry method to measure strain in deformed porphyritic granites is discussed this method requires that the distribution of markers has to satisfy at least two conditions it has to be homogeneous and isotropic statistics on point distribution with the help of a morishita diagram can easily test homogeneity isotropy can be checked with a cumulative histogram of angles between points application of these tests to undeformed mte capanne granite elba and to deformed randa orthogneiss alps of switzerland porphyritic granite reveals that their k feldspars phenocrysts both satisfy these conditions and can be used as strain markers with the fry method other problems are also examined one is the possible distribution of deformation on discrete shear bands providing several tests are met we conclude that the fry method can be used to estimate strain in deformed porphyritic granites

processes that control mineral and element abundances in shales abstract a shale s composition can be used to infer physical chemical and biological processes that have acted on it over its life history and this knowledge is used to surmise conditions at the time when each process was active this review lists the most important processes that control shale mineral and element abundances during each of the five stages of its life history 1 during weathering transport and deposition the most important processes are chemical weathering hydraulic sorting and mixing adsorption reverse weathering and incorporation of organic matter and biominerals 2 during early diagenesis the most important processes are exchange across the water sediment interface compaction microbial respiration mineral transformations and concretion formation 3 during burial diagenesis the most important processes are compaction catagenesis and metagenesis and mineral transformations 4 during exhumation the most important processes are decompaction brine invasion groundwater penetration and microbial respiration 5 during weathering the most important processes are organic matter oxidation mineral oxidation and hydrolysis groundwater transport and disaggregation this classification of processes provides a way to envision how concurrent and consecutive processes that occurred over a shale s life history have affected its mineralogy and chemical composition

deformation of granitic rocks across the brittle ductile transition abstract a microstructural analysis has been carried out on mylonites and mylonitic gneisses of the eastern peninsular ranges mylonite zone which were formed over a range of metamorphic conditions from lower greenschist to amphibolite facies composite planar fabrics in the form of c and s planes are found at all metamorphic grades fractured feldspars kinked biotites and ductile deformation of quartz characterize the lower greenschist facies mylonites at mid upper greenschist grade orthoclase grains show dynamic recrystallization textures whereas plagioclase exhibits low temperature plasticity with only minor recovery biotite ribbons form by progressive rotation and coalescence of kink band segments to produce chevron fold patterns at epidote amphibolite grade and above recovery processes and annealing recrystallization predominate in all minerals residual orthoclase porphyroclasts show strain related myrmekite formation along those sides of the grains that face the instantaneous shortening direction myrmekite formation due to replacement reactions cannot explain this geometry it is proposed that the myrmekites formed due to a combination of exsolution replacement and strain enhanced diffusion

deformation of granitoids at low metamorphic grade i reactions and grain size reduction abstract deformation and chemical reaction in granitoids at greenschist facies conditions were investigated in samples from three shear zones two from the alps corvatsch granodiorite and aiguilles rouges granite switzerland and one from eastern australia wyangala granite when examined by light and electron microscopy all show similar features of deformation that progressed from coarse parent rock through to fine grained mylonite quartz deformed plastically while both k feldspar and plagioclase fractured and recrystallized in conjunction with chemical change which had as its end point an assemblage albite quartz white mica caal silicates k feldspar and calcic plagioclase depending on fluid chemistry from the parent rock were unstable at low metamorphic grades in the presence of aqueous fluid since ca bearing plagioclase was not stable in these environments myrmekite did not replace k feldspar in any of the rocks examined recrystallization of feldspar which should perhaps be termed neocrystallization was initiated predominantly at clast margins or along microfractures that are marked by fluid inclusions and twin offsets in old feldspar grains particularly in plagioclases dislocations exist in wall like structures that are commonly associated with voids suggesting origins in microfractures these dislocations had severely limited mobility and subgrain rotation does not appear to have contributed to recrystallization we conclude that recrystallization mainly occurred via a classical nucleation mechanism with minor contributions from twin boundary migration we argue that the 450 550 c lower limit for recrystallization of feldspar referenced throughout the literature is not applicable to the rock systems under investigation and should be discarded as a universal limit microfracturing microboudinage and reaction are seen as the prerequisites for mylonite formation from coarse grained granitic rocks at low metamorphic grades see part ii of this paper neocrystallization fluid access and nucleation appear to have accompanied or immediately followed the first deformation increments and were primarily responsible for continued grain size reduction transgranular fracture was comparatively important only at the onset of deformation since the formation of shear zones in granitoids commonly takes place under conditions of low metamorphic grade in the presence of aqueous fluids in the earth s crust breakdown reactions and nucleation recrystallization in feldspars may be important influences upon localization of deformation in granitoids

libyan desert glass new field and fourier transform infrared data results are presented of new geological observations and laboratory analyses on libyan desert glass ldg a unique kind of impact glass found in egypt probably 28 5 29 4 million years in age a new ldg occurrence has been discovered some 50 kilometers southward of the main ldg occurrences in the great sand sea from fourier transform infrared ftir analysis the molecular structure of ldg is refined and significant differences are shown between ldg specimens and other pure silica glasses fulgurite industrial fused quartz and amorphous biogenic silica that are related to differences in their structures the slight variations observed here for the mean si o si angle between the different glasses are attributed to their thermal histories with regard to the other glasses analyzed the ldg infrared spectral parameters point to a higher ratio of discontinuities and defects in the tetrahedral sio4 network the quantitative mineralogical constitutions of sandstones and quartzites from the ldg geological setting were analyzed by ftir cretaceous sandstones have a specific composition about 90 wt quartz 10 dickite clearly different from the palaeozoic ones about 90 wt quartz but 7 kaolinite it is shown that the reddish silts bearing the ldg are constituted mainly by microquartz enriched with dickite whose particle size distribution is characteristic of fluvio lacustrine deposits probably oligocene to miocene in age the target rocks most probably quartz sand resulted from the weathering loss of the cementing microquartz of the cretaceous sandstones from the gilf khebir plateau with deposition in a high energy environment

influence of the mineralogical composition on the self potential response to advection of kcl concentration fronts through sand 1 we measured the self potential sp response to advective transport of kcl concentration fronts through two laboratory scale sand bodies with different mineralogical composition in pure quartz sand the amplitude and polarity of the sp signals agreed with a previously published model in sand containing 3 potassic feldspars and 1 micas and clays the shape of the sp response differed significantly the amplitude was much larger than the model prediction and a change in polarity occurred after the passage of the front furthermore the kcl concentration in the effluent was strongly reduced we suggest that the minor mineral phases reacted with the k ions trapping them during the front passage and releasing them later even though the reactions involved are not fully identified to date this study demonstrates that even small amounts of chemically active mineral phases such as micas or clays can significantly influence the sp signals

basement cover relationships in the tambo nappe central alps switzerland geometry structure and kinematics in the pennine zone of the central alps the tambo nappe forms a thin crystalline sliver embedded in the mesozoic cover four tertiary alpine deformations are observed the d1 ductile deformation is linked to the progressive eocene stacking of the nappes towards the northwest during d1 basement deformation is governed by imbricate tectonics whereas cover is thin skinned and intensively folded these different structures reflect the original strong rheological contrast between basement and cover during the heterogeneous and ductile d2 deformation the behaviour of the basement and cover became similar the strong vertical d2 shortening associated with a top to the east shear led to the folding of the prior se dipping structures developing se vergent folds with axes close to the e w l2 stretching lineation d2 corresponds to post collisional crustal thinning following d2 crustal thickening the d3 and d4 deformations occurred under retrograde conditions and can be correlated with uplift and late dextral movement on the insubric line respectively

kaolinite transformation into dickite during burial diagenesis the mechanism of kaolinite transformation into dickite has been investigating using 13 samples from the froy and rind oil fields broad fourteens basin north sea 3 kaolinite specimens with different crystal order kga 2 kaolinite api 17 keokuk kaolinite and 2 dickite rich samples natural history museum collection detailed analysis of xrd thermal analysis and sem data show that 1 as dickite content increases there is also an increase of the crystal order of kaolinite 2 in dickite rich specimens kaolinite and dickite have crystals or xrd coherent domains of the same size 3 there is no specific dehydroxylation temperature for each polytype rather particle size and crystal order control dehydroxylation temperature independently of polytype 4 with progressive dickite content the development of both particle size and the size of the coherent crystal domains within particles is greater in the c direction than in the a b plane 5 the growth of defect free segments in the c direction is not connected with the growth in the a and b directions as would be expected in crystallization from solution 6 textural features indicate coalescence of kaolin plates with burial 7 there is a very weak positive correlation between particle dimensions and relative kaolinite dickite content these results are interpreted as resulting from a double reaction taking place in the solid state with burial some kaolinite domains grow in size and crystal order while other domains are transformed into dickite presumably also the dickite domains formed early in the transformation grow in crystal order the transformation into dickite stops at 90 95 dickite because the remaining kaolinite domains are so large and stable that the stability increase produced by the polytype transformation would be negligible

borehole electrokinetic responses in fracture dominated hydraulically conductive zones electrokinetic borehole logging experiments conducted in fracture dominated devonian metasediments and carboniferous limestone boreholes containing dissolu tion discontinuities indicate a strong relative amplitude correlation between a downhole electrokinetic response and previously obtained hydrogeological data for the respective boreholes voltages in the range 0 2 1 5 volt were recorded per mpa of gauge pressure induced in the borehole fluid a relationship between fracture aperture and the frequency content of the electrical data has also been observed

deformation of granitoids at low metamorphic grade ii granular flow in albite rich mylonites abstract the high strain deformation at low metamorphic grades of three investigated granitoids is dominated by the granular flow of albite rich polyphase aggregates these aggregates formed by retrograde breakdown reactions from intermediate plagioclase and k feldspar the predominant deformation mechanism changes in granitoids as the grain size is reduced coarse grained low strain examples are deformed by a combination of intracrystalline plasticity quartz and fracturing feldspar in the mylonites intracrystalline plasticity of quartz plays only a minor role and the dominant deformation mechanism is a non cataclastic granular flow of polyphase aggregates consisting largely of albite and quartz deformation appears to be stable probably because grain growth in albite quartz mixtures is inhibited these fine grained aggregates are mechanically weaker than pure quartz aggregates thus the change in deformation mechanism mainly due to feldspar breakdown reactions appears to be important for the localization of high shear strain deformation at low metamorphic grades in granitoids and other lithologies modally dominated by feldspar the rheological behaviour of albite dominated mineral aggregates may have two consequences for middle to upper crustal deformation of modally feldspar dominated lithologies 1 feldspar in the presence of aqueous fluids can be an important mineral controlling the rheology at low metamorphic grades that is below amphibolite facies p t conditions 2 the occurrence of granular flow of fine grained polyphase aggregates in low grade granitoids is probably common and calls for great care in the modelling of middle to upper crustal rheology based on flow laws for intracrystalline plasticity of single minerals such as quartz

measurement of streaming potential coupling coefficient in sandstones saturated with high salinity nacl brine 1 we present measurements of the streaming potential coupling coefficient in intact sandstone samples saturated with nacl brines at concentrations up to 5 5 moll 1 the values we record at low salinity are consistent with those reported previously as brine salinity increases the coupling coefficient decreases in magnitude but is still measureable up to the saturated concentration limit the magnitude of the zeta potential also decreases with increasing salinity but approaches a constant value at high salinity this behaviour is not captured by current models of the electrical double layer our results suggest that streaming potential measurements may be used to monitor flow in saline subsurface environments such as deep saline aquifers and hydrocarbon reservoirs however they were obtained at laboratory temperature future work will focus on the effect of elevated temperatures at high salinity

magnetization carriers of grey to red deep water limestones in the gssp of the givetian frasnian boundary puech de la suque france signals influenced by moderate diagenetic overprinting limestones at the puech de la suque global boundary stratotype section and point gssp of the givetian frasnian boundary show a drastic change towards much higher magnetic susceptibility values in the givetian rocks different rock magnetic parameters indicate that ferromagnetic minerals are the main controlling factor the ferromagnetic fraction is composed of low magnetite type and high coercivity hematite and goethite phases confirmed by the spectral reflectance high coercivity minerals are fluctuating along the section with a higher abundance in the basal frasnian these phases may be of secondary origin and produced during burial stage the magnetite type phase contains two different grain size populations the identified that stable single domain superparamagnetic ssd sp particles are of diagenetic origin and their amount decreases slightly upwards a second group of magnetite grains correspond to coarse grained particles identified using the squareness v coercive force plot it is tentatively suggested here that these particles present throughout the section are of primary origin on the contrary the paramagnetic minerals underwent a clear diagenetic overprinting and may represent secondary minerals the presence of a primary ferromagnetic carrier allowed the use of spectral analyses leading to the detection of spectral peaks at 1 25 and 4 cycles m which can be interpreted as the result of 405 kyr and 100 kyr eccentricity forcing respectively

sequence and style of major post nappe structures simplon pennine alps abstract in the upper pennine nappe complex of the simplon pennine alps switzerland and italy at least three phases of major post nappe folding in places associated with thrusting can be distinguished these are superimposed on an earlier formed partly chaotic complex of tectonic units including the bernhard and monte rosa continental flakes and the zermatt saas and antrona ophiolite complexes the earliest post nappe folds were essentially isoclinal throughout the whole region and were accompanied by a strong schistosity which is the main foliation in most areas later two successive phases of back folding led to the present overall structure both phases typically show rapid variations in style from open folds lacking axial planar schistosity to very tight structures with complete foliation transposition this has been demonstrated by systematically mapping the major axial traces over the whole region successively removing the major structures in reverse order shows that the ophiolite complexes were originally part of a continuous unit marking an important suture between the bernhard and monte rosa nappes

dependence of seismoelectric amplitudes on water content summary the expectation behind seismoelectric field measurements is to achieve a combination of the sensitivity of electrical properties to water content and permeability and the high spatial resolution of seismic surveys a better understanding of the physical processes and a reliable quantification of the conversion between seismic energy and electric energy are necessary and need to take into account the effect of water content especially for shallow subsurface investigations we performed a field survey to quantify the seismoelectric signals as the water content changed we measured seismoelectric signals induced by seismic wave propagation by repeating the observations on the same two profiles during several months the electrical resistivity was monitored to take into account the water content variations weshowthatthehorizontalcomponentoftheseismoelectricfield normalizedwithrespectto the horizontal component of the seismic acceleration is inversely proportional to the electrical resistivity 0 42 0 25 assuming that the observed resistivity changes depend only on the water content this result implies that the electrokinetic coefficient should increase with increasing water saturation taking into account the water saturation and combining our results with the archie law for the resistivity in non saturated conditions the normalized seismoelectric field is a power law of the effective saturation with the exponent 0 42 0 25 n where n is archie s saturation exponent

crosshole seismoelectric measurements in borehole models with fractures laboratory experiments are performed in crossborehole models with fractures to investigate seismoelectric conversions in the fractures using an electrode in a borehole we measure the electric field induced by an acoustic wave and we investigate the relationship between the electric signal and the fracture aperture using ultrasonic fracture borehole models the experimental results confirm that a radiating electromagnetic em wave is induced by a guide wave at a fracture between an acoustic source and electric receiver boreholes the position of a vertical or inclined fracture between two boreholes can be determined using the arrival times of the em wave and the formation velocity by placing the acoustic source at a different depth and recording electric signals with real or synthetic arrays of acoustic and electric receivers in the second borehole crosshole seismoelectric measurements might be a technique for investigating fractures between boreholes more directly than traditional acoustic measurements

hydrogen and oxygen isotopic compositions of sedimentary kaolin deposits egypt paleoclimatic implications abstract the clay fractions of sedimentary kaolin deposits representing different ages carboniferous and cretaceous types pisolitic flint and plastic and localities sinai and aswan from egypt were analyzed for their h and o isotopic compositions to examine the paleoclimate conditions during their formation the d values of the carboniferous deposits in sinai range between 67 and 88 while the values for the cretaceous deposits in sinai range between 59 and 75 the 18 o values of the carboniferous deposits range from 17 9 to 19 4 and the values for the cretaceous deposits range between 19 2 and 20 4 the relatively low d and 18 o values of the carboniferous deposit at the abu natash area 67 and 17 9 respectively compared to other carboniferous deposits averages of 83 3 and 18 8 for d and 18 o respectively could be due to isotopic exchange between this deposit and the adjacent dolomite and or the enclosed hydrothermally formed mn ores of the carboniferous um bogma formation the d and 18 o values of the cretaceous pisolitic flint kaolin deposit from aswan averages of 65 and 20 3 respectively and plastic kaolin from the same area averages of 66 and 19 5 respectively are almost identical the differences in the 18 o values between the clay fractions of the pisolitic flint kaolin 20 3 and the previously analyzed bulk kaolin of the same deposit average of 17 5 suggest a significant effect of non clay minerals on the isotopic compositions of the kaolin deposits the h and o isotopic compositions plot close to the kaolinite line that marks the isotopic composition of kaolinite in equilibrium with meteoric water at 20 c this indicates that the kaolinite from both the carboniferous and cretaceous deposits in egypt formed by meteoric water weathering of the source rock s the d and 18 o values also suggest that kaolinite of these deposits formed under warm temperate to tropical conditions the slight deviations of some samples from the kaolinite line suggest post depositional modifications of the isotopic compositions of studied deposits probably due to the interaction between earlier formed kaolinite and downward percolating meteoric water the d and 18 o values of the cretaceous and carboniferous deposits from all localities suggest that both deposits formed under similar climatic conditions due to the location of egypt at almost the same distance from the equator either to the south during the carboniferous or to the north during the cretaceous

anatomy of a seismoelectric conversion measurements and conceptual modeling in boreholes penetrating a sandy aquifer 1 conversions of compressional seismic waves to electric fields have been measured in two boreholes drilled in an unconfined sandy aquifer on the gnangara mound near perth australia the seismoelectric conversions at both field sites occurred in the vicinity of the water table at 13 m depth and yielded maximum amplitudes of 1 v m using a sledgehammer source on surface partially cemented layers inferred from geological and geophysical logs straddle the water table and may play a role in generating the conversion and influencing its amplitude distribution the dense vertical sampling used in these borehole experiments reveals spatial and temporal polarity reversals of the interfacial signal which provide new evidence in support of the conceptual model for seismoelectric conversions at interfaces we demonstrate that the growth rate of the source zone and its maximum vertical extent below the water table are encoded in the polarity of the interfacial signal these experiments confirm that vertical seismoelectric profiling can be used to gain further insight into seismoelectric conversions and characteristics of interfaces that makes them amenable to detection

the alpine geodynamic evolution of penninic nappes in the eastern central alps the eastern central alps consist of several pennine nappes with different tectonometamorphic histories the tectonically uppermost units oceanic avers bundnerschiefer continental suretta and tambo nappes oceanic vals bundnerschiefer show cretaceous early tertiary w directed thrusting with associated blueschist facies metamorphism related to subduction of the pennine units beneath the austroalpine continental crust this event caused eclogite facies metamorphism in the underlying continental adula nappe the gross effect was crustal thickening the tectonically lower continental simano nappe is devoid of any imprint from this event in the course of continent continent collision high t metamorphism and n directed movements occurred both affected the whole nappe pile more or less continuously from amphibolite to greenschist facies conditions crustal thinning commenced during the regional temperature peak a final phase is related to differential uplift under retrograde p t conditions further thinning of the crust was accommodated by e to ne directed extensional deformation

electrical properties of zeolitized volcaniclastic materials 1 the interpretation of electromagnetic anomalies associated with volcanic activity requires a good understanding of two rock properties the electrical conductivity and the streaming potential coupling coefficient we measured these properties on 22 consolidated tuff samples containing clays and zeolites typically found in hydrothermal systems or in other areas of high water rock interactions associated with active volcanic areas these rocks exhibit unusually high surface conductivity and electrical cementation exponent 2 5 3 3 these features are explained by the highly complex texture of these rocks due to hydration dissolution processes of the volcanic glass and the formation of clay minerals and zeolites as alteration products at a pore fluid conductivity of 1 0 0 2 s m 1 the streaming potential coupling coefficient ranges from 3 55 to 10 7 mv mpa 1 the zeta potential a key electrochemical property of the pore water mineral interface determined from these measurements at t0 20 c and ph 6 7 and corrected for surface conductivity is 28 8 mv at 0 1 m nacl two clay free samples exhibit a zeta potential 16 5 mv a value associated with zeolites clinoptilolite the temperature dependence of the potential is rather strong with t t0 1 t t0 where 4 2 10 2 c 1 in the temperature range 20 60 c these data are applied to the understanding of large scale self potential anomalies located at the ground surface of miyake jima volcano

high selenium in the carboniferous coal measures of northumberland north east england the carboniferous lower and middle coal measures coals of the northumberland coalfield are anomalously rich in selenium se content up to 62 ppm compared to the averages for the common uk and worldwide coals as well as posing an environmental toxicity threat se is now regarded as an important resource for alloys photovoltaic products and nanotechnologies and high se coals in north east england offer an opportunity to assess the se means of occurrence origins transport mechanisms and enrichment in coals at least two generations of pyrite host high se in the sampled coal seams microbial formed disseminated pyrite both cubic and framboidal in habit and later cleat filling pyrite identified by petrographic observations laser ablation methods and sulphur isotope compositions there is a notable se enrichment of up to 250 ppm in later formed cleat filling pyrite trace element enrichment may have been sourced and influenced by seawater distribution during diagenesis and localised dykes and deformation may have acted as an enrichment mechanism for sampled seams in the region the high se coals in northumberland may provide a potential e tech element source and should be considered and carefully managed as coal mining and production are reduced in the area the study also highlights the nature of se enrichment in pyritic coals affected by cleat formation and multiple episodes of mineralisation important as critical element demand continues to increase worldwide

mechanical decoupling of high pressure crustal units during continental subduction the mechanics of the transition from continental subduction toward upper crustal nappe stacking is still poorly understood and is studied here through a 2d thermal and strength numerical modelling of a subducted passive margin geological observations in the core of most mountain belts show the piling up of several hp lt upper crustal units that are most likely related to the detachment of upper crustal units from the subducted continental margin and to the subsequent stacking of the detached units at depths the adula unit lepontine dome central alps switzerland is a long and thin upper crustal unit and is used here as a natural case study as it provides a well documented example of these units 2d thermal modeling shows that two steps successive in time characterized the burial history of the passive margin undergoing continental subduction 1 an increase in the margin strength due to an increase in the confining pressure during the first million years of the margin subduction and 2 the progressive heating of the subducted margin from the overlying lithosphere leads to a decrease in the margin strength due to thermal weakening which progressively counter balances the increase in confining pressure two strength gradients develop within the subducted lithosphere 1 along the slab the strength decreases with increasing burial depth and 2 perpendicular to the slab the strength increases with depth due to an inverse temperature distribution the detachment of hp lt continental units from the subducted margin could occur when the slab strength becomes lower than the applied net stress this allows the detachment of ductile weakened thin and long upper crustal units the thickness and length of the detached crustal units are controlled by the following parameters in order of their importance subduction dip angle crustal rheology mantle heat flux and subduction velocity the comparison of our model results with the geometry and pt conditions of the adula unit yields an estimate of the alpine subduction dip angle at the time of deformation and metamorphism

seismoelectric wave propagation numerical modelling in partially saturated materials to better understand and interpret seismoelectric measurements acquired over vadose environments both the existing theory and the wave propagation modelling programmes available for saturated materials should be extended to partial saturation conditions we propose here an extension of pride s equations aiming to take into account partially saturated materials in the case of a water air mixture this new set of equations was incorporated into an existing seismoelectric wave propagation modelling code originally designed for stratified saturated media this extension concerns both the mechanical part using a generalization of the biot gassmann theory and the electromagnetic part for which dielectric permittivity and electrical conductivity were expressed against water saturation the dynamic seismoelectric coupling was written as a function of the streaming potential coefficient which depends on saturation using four different relations derived from recent laboratory or theoretical studies in a second part this extended programme was used to synthesize the seismoelectric response for a layered medium consisting of a partially saturated sand overburden on top of a saturated sandstone half space subsequent analysis of the modelled amplitudes suggests that the typically very weak interface response ir may be best recovered when the shallow layer exhibits low saturation we also use our programme to compute the seismoelectric response of a capillary fringe between a vadose sand overburden and a saturated sand half space our first modelling results suggest that the study of the seismoelectric ir may help to detect a sharp saturation contrast better than a smooth saturation transition in our example a saturation contrast of 50 per cent between a fully saturated sand half space and a partially saturated shallow sand layer yields a stronger ir than a stepwise decrease in saturation

seismoelectric measurements in a porous quartz sand sample with anisotropic permeability seismoelectric coupling coefficients are difficult to predict theoretically because they depend on a large numbers of rock properties including porosity permeability tortuosity etc the dependence of the coupling coefficient on rock properties such as permeability requires experimental data in this study we carry out a set of laboratory measurements to determine the dependence of seismoelectric coupling coefficient on permeability we use both an artificial porous sandstone sample with cracks built using quartz sand and berea sandstone samples the artificial sample is a cube with 39 porosity its permeability levels are anisotropic 14 7 d 13 8 d and 8 3 d in the x y and z directions respectively seismoelectric measurements are performed in a water tank in the frequency range of 20 khz 90 khz a piezoelectric p wave source is used to generate an acoustic wave that propagates through the sample from the three different x y and z directions the amplitudes of the seismoelectric signal induced by the acoustic waves vary with the direction the highest signal is in the direction of the highest permeability and the lowest signal is in the direction of the lowest permeability since the porosity of the sample is constant the results directly show the dependence of seismoelectric coefficients on permeability seismoelectric measurements with natural rocks are performed using berea sandstone 500 and 100 samples because the berea samples are nearly isotropic in permeability the amplitudes of the seismoelectric signals induced in the different directions are the same within the measurement error because the permeability of berea 500 is higher than that of berea 100 the amplitude of the seismoelectric signals induced in berea 500 is higher than those in berea 100 to determine the relative contributions of porosity and permeability on seismoelectric conversion we carried out an analysis using pride 1994 formulation and kozeny carman relationship the normalized amplitudes of seismoelectric coupling coefficients in three directions are calculated and compared with the experimental results the results show that the seismoelectric conversion is related to permeability in the frequency range of measurements this is an encouraging result since it opens the possibility of determining the permeability of a formation from seismoelectric measurements

structural evolution of orogenic wedges interplay between erosion and weak decollements orogenic wedges commonly display an inner wedge where crystalline units have been exhumed and an outer wedge formed by imbricated sedimentary units detached from the basement analog experiments have shown that similar structures can emerge naturally in the presence of weak decollements due to the interplay between erosion and deformation in this study we further investigate this hypothesis using two dimensional visco elasto plastic numerical models our experiments assume a basal and an intermediate decollement within the wedge experiments with a frictional strength of the basal decollement lower or equal to that of the intermediate decollement show a structural evolution of fold and thrust belts dominated by out of sequence thrusting conversely when the intermediate decollement is weaker than the basal decollement distinct outer and inner wedges are formed this process leads to episodic migration of midcrustal ramps tectonic underplating and antiformal stacking facilitated by erosion comparison between our models and the himalayan wedge suggests a low effective friction 0 10 which is probably due to dynamic weakening during large m8 himalayan earthquakes the deeper decollement along which the lower plate thrusts beneath the high himalaya must be a thermally activated ductile shear zone with an apparent friction of 0 18 fold and thrust belts worldwide exhibit various architectures in which different decollement levels might be activated thus our study provides a framework to help assess under which conditions a variety of structures observed in orogenic systems can arise

streaming potential properties of westerly granite with applications this paper reports on laboratory measurements of the streaming potential properties of common minerals and in particular of westerly granite data are presented for these solids in contact with simple electrolytic solutions and in one case for temperature variation in the range 5 70 c for 1 1 electrolytes the ratio of the streaming potential coupling coefficient to fluid resistivity was approximately 4 mv atm m and for 2 1 electrolytes 2 mv atm m the effect of temperature was small 0 05 mv c temperature increase and indicates that the zeta potential was independent of temperature preliminary experimental results using mixed electrolytic solutions nacl cacl2 and two phase fluid flow are also described two phase flow can enhance streaming potentials by as much as a factor of 3 or 4 the laboratory data are used to interpret streaming potentials in geological problems such as earthquake prediction geothermal prospecting using the self potential method and surface conductivity contribution to the electrical resistivity of rocks

numerical models for the control of inherited basin geometries on structures and emplacement of the klippen nappe swiss prealps cover nappes commonly deform above a shallow basal detachment surface located above rigid crystalline basement rocks inherited basin geometries are presumed to control the kinematic evolution and detachment of cover nappes in an accretionary wedge we compare results from two dimensional finite element modelling with the structural style of a natural cover nappe the klippen nappe which was detached from its basement along an evaporitic detachment horizon and thrust over a distance of roughly 100 km first order characteristics of the klippen nappe paleo basin include a complex distribution of weak detachment rocks and various changes in the sediment composition and layer thicknesses two types of structural style can be distinguished an imbricate fan at the rear end of the nappe prealpes medianes rigides and a fold dominated region at the front prealpes medianes plastiques the model results resemble the first order characteristics of the klippen nappe the model experiments suggest that the formation of imbricates and fault related folds are controlled by the discontinuity of detachment horizons discontinuities are locations where thrust ramps are triggered and layer heterogeneities control the locations for the initiation of detachment folds basement horsts may lead to the formation of recumbent folds which develop a melange zone on the highly sheared inverted limb the experiments also suggest that the thickness of the basal detachment horizon of the medianes plastiques decreases gradually from the foreland to the hinterland

permeability and borehole stoneley waves comparison between experiment and theory we performed laboratory experiments to evaluate theoretical models of borehole stoneley wave propagation in permeable materials a berea sandstone and synthetic samples made of cemented glass beads were saturated with silicone oils we measured both velocity and attenuation over a frequency band from 10 khz to 90 khz our theoretical modeling incorporated biot theory and deresiewicz skalak boundary conditions into a cylindrical geometry and included frequency dependent permeability by varying the viscosity of the saturating pore fluid we were able to study both low frequency and high frequency regions of biot theory as well as the intermediate transition zone in both low frequency and high frequency regions of the theory we obtained excellent agreement between experimental observations and theoretical predictions velocity and attenuation 1 q are frequency dependent especially at low frequencies also at low frequencies velocity decreases and attenuation increases with increasing fluid mobility permeability viscosity more complicated behavior is observed at high frequencies these results support recent observations from the oil field suggesting that stoneley wave velocity and attenuation may be indicative of formation permeability

argillization processes at the el berrocal analogue granitic system spain mineralogy isotopic study and implications for the performance assessment of radwaste geological disposal abstract the el berrocal granite u bearing quartz vein uqv system has been studied as a natural analogue of a high level radioactive waste repository the main objective was to understand the geochemical behaviour of natural nuclides under different physicochemical conditions within this framework the argillization processes related to fracturing and formation of the uranium quartz vein were studied from a mineralogical and isotopic standpoint in order to establish their temperatures of formation and thus complete the geothermal history of the system for this purpose 18 o values were determined for pure mineral from the unaltered granite and quartz from the uranium quartz vein as well as for mixture samples from the hydrothermally altered granite sericitised granite and clayey samples from fracture fillings including the clayey walls of the uranium quartz vein the isotopic signature of quartz from the uranium quartz vein and the monophasic nature of its fluid inclusions led us to conclude that the isotopic signature of water in equilibrium with quartz was approximately in the range from 8 3 to 5 7 v smov its temperature of formation being around 85 120 c the 18 o values of pure sericite from the hydrothermally altered granite calculated by means of the oxygen fraction molar method indicate that its temperature of formation in equilibrium with the aforementioned waters is also in the range from 70 c to approximately 120 c clays from fracture fillings and clayey walls of the uranium quartz vein are usually mixtures in different proportions of illite approximately formed between 70 and 125 c two generations of kaolinite formed at approximately 90 130 c and at around 25 c respectively smectite formed at 25 c and occasionally palygorskite formed either between 30 and 45 c or 19 and 32 c depending on the fractionation equation used these data suggest that sericite from the hydrothermally altered granite quartz from the uranium quartz vein illite and the first generation of kaolinite from the fracture fillings resulted from the same hydrothermal process affecting the el berrocal granite in relation to fracturing under certain physicochemical conditions t 100 c ph 8 and log h 4 sio 4 between 4 and 3 illite and kaolinite can be paragenetic as a result of weathering processes smectite was formed from hydrothermal illite and inherited albite under alkaline weathering while the second generation of kaolinite was formed from smectite under acid conditions and close to the sulphide rich uranium quartz vein palygorskite is an occasional mineral formed probably either during the thermal tail of the above described hydrothermal process or during weathering processes in both cases palygorskite must have formed from alkaline si mg rich solutions finally these data and processes are discussed in terms of natural analogue processes drawing some implications for the performance assessment of a deep geological radwaste repository dgrr

geophysical applications of electrokinetic conversion in volume 1 of geophysics 1936 r r thompson of humble oil and refining company proposed that the coupling of seismic and electrical energy can be used as an exploration tool subsequent efforts were directed toward using electric field antennas as geophones small scale studies concluded that antennas are not as sensitive as conventional geophones and their response is highly variable depending on the local soil conditions by 1959 martner and sparks of pan american petroleum reported in geophysics a systematic study of seismoelectric coupling using explosives at various depths their results were the first to show that the conversion of seismic to electromagnetic energy at the water table could be detected using surface antennas no studies have systematically explored the full potential of electroseismic methods using the same level of experimental sophistication used in seismic exploration

permeability inversion from low frequency seismoelectric logs in fluid saturated porous formations in this paper a method is proposed to invert permeability from seismoelectric logs in fluid saturated porous formations from the analysis of both the amplitude and the phase of simulated seismoelectric logs we find that the stoneley wave amplitude of the ratio of the converted electric field to the pressure rep is sensitive to porosity rather than permeability while the tangent of the rep s phase is sensitive to permeability the rep s phase reflects the phase discrepancy between the electric field and the pressure at the same location in the borehole we theoretically derive the frequency dependent expression of the rep of the low frequency stoneley wave and find that the tangent of the rep s argument is approximately in inverse proportion to permeability we obtain an inversion formula and present the permeability inversion method by using the tangent of the rep s phase to test this method the permeabilities of different sandstones are inverted from the synthetic full waveform data of seismoelectric logs a modified inversion process is proposed based on the analysis of inversion errors by which the relative errors are controlled below 25 and they are smaller than those of the permeability inversion from the stoneley wave of acoustic logs

using borehole electroseismic measurements to detect and characterize fractured permeable zones in 1996 we measured stoneley wave induced electrical fields in an uncased water well drilled in fractured granite and diorite near hamilton massachusetts stoneley waves generated by sledgehammer blows to the surface casing produced a flow of pore fluid in permeable zones intersected by the borehole in turn this flow induced a streaming electrical field even though these electrical signals were very small tens of microvolts we were able to detect them using electrodes placed in the borehole after power line and telluric signals were canceled by remote referencing and notch filtering amplitude analysis of the electrical fields confirmed that they were induced by fluid flow in the fractured formation the normalized amplitudes of these electrical fields correlate with the fracture density log and agree with the theoretical model for this electroseismic phenomenon our biot theory based model predicts that borehole electroseismic measurements can be used to characterize permeable zones according t

episodic and long lasting paleozoic felsic magmatism in the pre alpine basement of the suretta nappe eastern swiss alps the suretta nappe of eastern switzerland contains a series of meta igneous rocks with the rofna porphyry complex rpc being the most prominent member we present la icp ms u pb zircon data from 12 samples representing a broad spectrum of meta igneous rocks within the suretta nappe in order to unravel the pre alpine magmatic history of this basement unit fine grained porphyries and coarse grained augengneisses from the rpc give crystallization ages between 284 and 271 ma which either represent distinct magma pulses or long lasting magmatic activity in a complex magma chamber there is also evidence for an earlier variscan magmatic event at 320 310 ma mylonites at the base of the suretta nappe are probably derived from either the rpc augengneisses or another unknown carboniferous permian magmatic protolith with a crystallization age between 320 and 290 ma two polymetamorphic orthogneisses from the southern suretta nappe yield crystallization ages of 490 ma inherited zircon cores are mainly of late neoproterozoic age with minor neo to paleoproterozoic sources we interpret the suretta nappe as mainly representing a gondwana derived crustal unit which was subsequently intruded by minor cambrian ordovician and major carboniferous permian magmatic rocks finally the suretta nappe was thrust into its present position during the alpine orogeny which hardly affected the u pb system in zircon

upper crustal deformation in continent continent collision a case study from the bernard nappe complex valais switzerland 1 the penninic nappes in the swiss alps formed during continental collision between the adriatic and european plates in cenozoic times although intensely studied the finite geometry of the basement bearing penninic nappes in western switzerland has remained a matter of debate for decades e g siviez mischabel dilemma and the paleogeographic origin of various nappes has been disputed here we present new structural data for the central part of the penninic bernard nappe complex which contains pre permian basement and permo mesozoic metasedimentary units our lithological and structural observations indicate that the discrepancy between the different structural models proposed for the bernard nappe complex can be explained by a lateral discontinuity in the west the presence of a permian graben caused complex isoclinal folding whereas in the east the absence of such a graben resulted mainly in imbricate thrusting the overall geometry of the bernard nappe complex is the result of three main deformation phases 1 detachment of mesozoic cover sediments along triassic evaporites evolene phase during the early stages of collision 2 eocene top to the n nw nappe stacking anniviers phase and 3 subsequent backfolding and backshearing mischabel phase the southward localized backshearing is key to understand the structural position and paleogeographic origin of units such as the frilihorn and cimes blanches nappes and the antrona ophiolites based on these observations we present a new tectonic model for the entire penninic region of western switzerland and discuss this model in terms of continental collision zone processes

seismoelectric and seismomagnetic measurements in fractured borehole models seismoelectric and seismomagnetic fields generated by seismic waves in fluid saturated fractured borehole models are experimentally investigated with an electrode and a hall effect sensor in a borehole with a horizontal fracture the stoneley and flexural waves induce seismoelectric and seismomagnetic fields on the borehole wall and an electromagnetic wave propagating at light speed at the horizontal fracture in a borehole with a vertical fracture the acoustic field generated by a monopole or dipole source is similar to that in a borehole without a vertical fracture however the acoustic wave propagating along the vertical fracture induces seismoelectric and seismomagnetic fields whose apparent velocities are equal to that of a stoneley wave experimental results show that two different kinds of electric and magnetic fields are generated by acoustic waves in borehole models with horizontal and or vertical fractures one is an electromagnetic wave propagating with light speed the second is a stationary or localized seismoelectric and seismomagnetic field seismoelectric and seismomagnetic measurements might be a new logging technique for exploring fractures in a borehole

a transient method for measuring the dc streaming potential coefficient of porous and fractured rocks high quality streaming potential coupling coefficient measurements have been carried out using a newly designed cell with both a steady state methodology and a new pressure transient approach the pressure transient approach has shown itself to be particularly good at providing high quality streaming potential coefficient measurements as each transient increase or decrease allows thousands of measurements to be made at different pressures to which a good linear regression can be fitted nevertheless the transient method can be up to 5 times as fast as the conventional measurement approaches because data from all flow rates are taken in the same transient measurement rather than separately test measurements have been made on samples of berea and boise sandstone as a function of salinity approximately 18 salinities between 10 5 mol dm3 and 2 mol dm3 the data have also been inverted to obtain the zeta potential the streaming potential coefficient becomes greater more negative for fluids with lower salinities which is consistent with existing measurements our measurements are also consistent with the high salinity streaming potential coefficient measurements made by vinogradov et al 2010 both the streaming potential coefficient and the zeta potential have also been modeled using the theoretical approach of glover 2012 this modeling allows the microstructural electrochemical and fluid properties of the saturated rock to be taken into account in order to provide a relationship that is unique to each particular rock sample in all cases we found that the experimental data were a good match to the theoretical model

influence of water pressure dynamics and fluid flow on the streaming potential response for unsaturated conditions streaming potentials are produced by electrokinetic effects in relation to fluid flow and are used for geophysical prospecting the aim of this study is to model streaming potential measurements for unsaturated conditions using an empirical approach a conceptual model is applied to streaming potential measurements obtained from two drainage experiments in sand the streaming potential data presented here show a non monotonous behaviour with increasing water saturation following a pattern that cannot be predicted by existing models a model involving quasi static and dynamic components is proposed to reproduce the streaming potential measurements the dynamic component is based on the first time derivative of the driving pore pressure the influence of this component is investigated with respect to fluid velocity which is very different between the two experiments the results demonstrate that the dynamic component is predominant at the onset of drainage in experiments with the slowest water flow on the other hand its influence appears to vanish with increasing drainage velocity our results suggest that fluid flow and water distribution at the pore scale have an important influence on the streaming potential response for unsaturated conditions we propose to explain this specific streaming potential response in terms of the behaviour of both rock water interface and water air interfaces created during desaturation processes the water air interfaces are negatively charged as also observed in the case of water rock interfaces both the surface area and the flow velocity across these interfaces are thought to contribute to the non monotonous behaviour of the streaming potential coefficient as well as the variations in its amplitude the non monotonous behaviour of air water interfaces created during the flow was highlighted as it was measured and modelled by studies published in the literature the streaming potential coefficient can increase to about 10 to 40 when water saturation decreases such an increase is possible if the amount of water air interfaces is increased in sufficient amount which can be the case

oxygen and hydrogen isotope geochemistry of cretaceous bentonites and shales from the disturbed belt montana the mineralogy o18 and d of the 0 1 m fraction of 22 cretaceous bentonites and the mineralogy and o18 of the 0 1 m fraction of 14 adjacent shales collected from outcrops in the sweetgrass arch and disturbed belt montana have been determined mixed layer illite smectite i s is the dominant mineral in the bulk bentonite and usually the only mineral in the 0 1 m fraction i s is also the major clay mineral in the shales the diagenetic grade in bentonite is qualitatively given by the percentage of illite layers in i s which varies from 2 to 25 sweetgrass arch to as high as 95 disturbed belt o18 of 0 1 m bentonite generally decreases from about 20 to about 13 with increasing diagenetic grade on a plot of d versus o18 data for the 0 1 m bentonite define a field that generally parallels but falls on the meteoric water line side of the smectite water line savin and epstein 1970 o18 of bulk bentonite is 1 to 3 more negative than the o18 of the 0 1 m fraction due to the presence of volcanic quartz and feldspar o18 of several size fractions of clay sized quartz separated from the bentonite varies from 11 to 24 and in a given bentonite generally increases with decreasing grain size among the different bentonites the o18 range of the different grain sizes decreases as the percentage of illite layers in the coexisting i s increases the o18 of 0 1 0 5 m shale quartz is generally 1 to 4 more positive than clay sized quartz from an adjacent bentonite and the o18 of 0 1 m i s concentrate of shales is generally 1 to 4 more negative than the 0 1 m i s from an adjacent bentonite isotopic temperatures interpreted to be maximum burial temperatures range between about 160 c shale to about 250 c bentonite the isotopic data can be interpreted using the stages 1 1 deposition of volcanic glassy ash containing some quartz and feldspar 2 2 devitrification into mostly 100 expandable smectite with a o18 of about 20 and d of 60 to 80 3 3 tectonic burial beneath thrust sheets in the disturbed belt region which induced elevated temperatures that allowed oxygen and hydrogen isotope reequilibration as the percentage of illite layers in i s increased and diagenetic quartz formed and 4 4 exhumation of the strata with preservation of o18o16 and d h attained during burial

experimental measurements of seismoelectric signals in borehole models s u m m a r y an experimental system is built for the electrokinetic measurements with a small scaled seismoelectric detector and a high resolution digitizer 1 ms s 1 22 bits the acoustic and seismoelectric experiments are carried out in different boreholemodels at the high frequency of 90 khz in the laboratory all the localized seismoelectric signals that accompany compressional wave shear wave and stoneley wave are first clearly observed with a monopole source in sandstone boreholes that are saturated by tap water the amplitudes of these signals are measured in the range of 1 120 v which is useful for designing the seismoelectric logging instruments then the amplitude ratio of electric signal to acoustic pressure rep for each of the three waves is calculated and compared with the theoretical simulations based on the experimental data we find that seismoelectric logging signals as well as rep become stronger at the more permeable borehole model we also find that seismoelectric logging signals are more sensitive to permeability and porosity comparedwith acoustic logging signals therefore this study verifies the feasibility of seismoelectric well logging and further indicates that the seismoelectric logging technique might be a preferable method to estimate formation parameters in the field measurements

basement involved thin skinned and thick skinned tectonics in the alps the deformation of continental crust during continental collision by folding and thrusting follows three types of structural styles 1 in a true thin skinned style only cover rocks are involved 2 in the case of a thin skinned basement involved style thin slabs of crystalline basement rocks are piled up into a nappe stack 3 in a true thick skinned style the entire upper crust is involved in the deformation in the alps all three styles can be recognized the helvetic nappes and parts of the penninic nappes exhibit true thin skinned style tectonics triassic evaporites jurassic shales and cretaceous marls acted as detachment horizons basement involved thin skinned tectonics is typical for the penninic nappes in the core of the orogen the thickness of the basement thrust sheets is controlled by the effects of mesozoic rifting by deep burial and heating of the subducting crust and by the presence of late palaeozoic structures thick skinned style is observed in the more external parts of the orogen the external massifs and the southalpine nappe system it occurred in the late phase of collision and involved the entire upper crust the basal detachment occurred possibly along phyllonites generated by the breakdown of load bearing feldspar considering the alpine orogen as a whole the lower crust deformed seemingly independently from the upper crust the detachment of the cover units by thin skinned tectonics occurred prior to thrusting related to basement involved thin skinned tectonics thrust faults of both types were overprinted by post nappe folding

streaming potential and permeability of saturated sandstones under triaxial stress consequences for electrotelluric anomalies prior to earthquakes the streaming potential due to fluid circulation in rock was measured on saturated sediments fontainebleau sandstones the electrokinetic coupling coefficient which is the ratio of the streaming potential and the excess pore pressure is proportional to the fluid resistivity additionally for a fluid conductivity of 10 3 s m the electrokinetic coupling coefficient varies from 10 to 6642 mv 0 1 mpa for sample permeability in the range of permeabilities from 0 15 10 15 to 1220 10 15 m2 the different values of the electrokinetic coupling coefficient have been explained by the effect of increasing surface conductivity which becomes nonnegligible compared to fluid conductivity for low permeability when the sample is deformed under triaxial stress up to failure the vertical permeability along the principal stress drops by about 0 20 0 1 mpa when failure occurs the typical variation of the electrokinetic coupling coefficient is a large increase beginning with the onset of the localization of the shear band at about 75 of the yield stress and stopping at the failure this increase of the electrokinetic coupling coefficient is due to an increase of potential in the shear zone when new surfaces are created and connected possible consequences of our results are given concerning the electrical fields which could appear during the preparation of an earthquake it is shown that in some cases self potential anomalies reported in the deformed zone preceding an earthquake occurrence could be due to an increase of the electrokinetic coupling coefficient from 75 of the yield stress to rupture in the vicinity of one of the electrodes any variation of fluid resistivity or permeability in the vicinity of one electrode could change the electrokinetic coupling coefficient inducing a surface electrokinetic potential anomaly in regard to the interpretation of the electrokinetic effect which occurs at large distance from the epicenter a larger electrokinetic potential anomaly could be measured between electrodes situated along a vertical fluid flow for instance in a shallow borehole an electrokinetic potential anomaly up to 30 mv for a fluid conductivity of 0 01 s m and a rock permeability of 10 12 m2 could be observed with a change of the underground water table level as slight as 50 cm 50 mbar moreover if the permeability between the electrodes is increased by a factor of 8 103 the electrokinetic coupling coefficient could be enhanced by a factor up to 650

a purely structural restoration of the nfp20 east cross section and potential tectonic overpressure in the adula nappe central alps common extrusion type models for the high to ultrahigh pressure adula nappe require a major normal fault along the top of this unit which is not conveyed in the structural record this implies that such a normal fault existed but was completely erased during later deformational stages however there is evidence that decompression occurred during top to the foreland thrusting we performed a new purely structural kinematic restoration of the central part of the nfp20 east cross section in order to estimate the burial depths of individual units without converting petrological pressure data into depth under the assumption that pressures were lithostatic the results show that pressures within most of the units were close to but somewhat higher than lithostatic for several stages of the tectono metamorphic history only for the maximum burial stage of the adula nappe we estimate local tectonic overpressures of 40 to 80 of the lithostatic pressures accepting such an amount of overpressure which is moderate compared to values theoretically possible the adula nappe was probably not subducted to subcrustal depth we propose that the structural record of the penninic nappe stack is quite complete and suggest that the decay of tectonic overpressure is a feasible explanation for decompression from eclogite to amphibolite facies conditions during thrusting consequently exhumation and convergence rates of the eocene to oligocene alps may be smaller than previously assumed