microstructure and texture in experimentally folded single layer rock salt abstract buckling experiments on single layers of fine grained artificial polycrystalline rock salt embedded in a plasticine matrix have been performed in the temperature range of 185 200 c under a confining pressure of 10 bars in a plane strain pure shear apparatus strain rates ranged from 2 5 10 7 to 4 7 10 7 layers with an aspect ratio of 7 deformed without buckling but when this ratio was increased to 13 layers deformed by buckling and produced one wavelength of a sinusoidal fold the stress strain and time strain curves indicate that folding is initiated at about 7 to 8 of bulk deformation the layer parallel shortening and thickening continues with progressive folding the changes in the arclength thickness and limb dip show that initially the fold growth is slow and then becomes rapid the inner fold are is characterized by strong preferred dimensional grain orientation with the longer axis normal to the layer surface the axial ratio of grains gradually decreases towards the outer arc the stresses on the outer are have been relieved mainly by the development of tension fractures in the limbs the grains are elongated normal to the layer however close to the surfaces the grains are very fine and exhibit a tendency to elongate along the layer surface the preferred lattice orientation of 100 110 and 111 planes in halite have been determined by x ray texture goniometry and the pole figures are partially comparable to the textures in natural fold from salt domes

modeling and mechanistic interpretation of creep of rock salt below 200 c abstract upper and lower bound estimates of the steady state strain rates of rock salt from five locations are analyzed the measurements were obtained in triaxial creep tests including systematic changes in stress and temperature the various data sets are correlated in activation analyses and fitted by models and combinations of models for power law creep cross slip and dislocation glide to show that a cross slip model yields the best mechanistically most credible fit good fits for cross slip and high power law stress exponents rule out the possibility that pressure solution affected the data in a major way to the lowest recorded strain rates of order 10 10s 1

the effect of material properties on growth rates of folding and boudinage experiments with wax models abstract the growth of unstable structures was studied experimentally in layered wax models the rheological properties of the two wax types were determined independently by a series of cylinder compression tests both waxes enhibited 1 a non newtonian stress vs strain rate relationship 2 strain softening and 3 temperature dependent viscosity the stress strain rate relationships approximated a power law with stress exponents of 5 for the microcrystalline wax and 1 8 for paraffin wax blocks of paraffin with a single embedded layer of microcrystalline wax were deformed in two dimensional pure shear with the layer oriented either parallel to the compressive strain axis so that it shortened and folded or perpendicular to that axis so that it would stretch and boundinage would form the growth rates of tiny initial disturbances were measured the growth rates for folding and boudinage were much higher than could be accounted for by theories assuming newtonian material properties theories taking non newtonian behaviour into account smith r b 1975 bull geol soc am 86 1601 1609 fletcher r c 1974 am j sci 274 1029 1043 better describe the folding growth rates boudinage however grew almost three times faster than would be predicted even by existing non newtonian theory a possible reason for this discrepancy is that the waxes do not exhibit steady state creep as assumed in the theory we therefore extend the theory to include strain softening the crucial step in this theory is the use of a scalar measure of the deformation as a state variable in the constitutive law in this way the isotropic manifestation of strain softening can be taken into account the analysis shows that strain softening can lead to greatly increased boudinage growth rates while having little influence on the growth rates of folds which is in agreement with the experiments

influence of layering and boundary conditions on fault bend and fault propagation folding the influence of heterogeneous layering and boundary conditions on the structural development of fault bend and fault propagation folds has been investigated through petrographic study of nonscaled rock models the models are deformed in a triaxial rock deformation apparatus at room temperature and a 50 mpa confining pressure the models consist of a single layer of sandstone containing a saw cut ramp that is inclined 20 to the layering and an overlying intact thinly layered unit that is composed of limestone interlayered with lead or mica analysis of the fold thrust structures generated in sequentially shortened models with different loading conditions and layer types suggests that the mode of fold thrust interaction activated upon shortening will depend on fault zone drag bending and shearing resistance of the hanging wall shear strength of layer interfaces and loading conditions for the models these parameters may be expressed as a strength ratio describing the resistance to foreland translation relative to the resistance to internal deformation of the thrust system low strength ratios favor fault bend folding high strength ratios favor internal shortening of the sheet isotropic and thick relative to ramp height units above a propagating thrust tip will shorten primarily by faulting whereas thinly layered anisotropic units will shorten by fault propagation folding during both modes of fold thrust interaction the dips of the fold limbs increase interlimb angles decrease and imbricate faults form in the hanging wall or footwall with shortening in one model suite the imbrication is associated with a transition from fault bend folding to fault propagation folding and produces a highly asymmetric ramp anticline similar to a second mode fault bend fold or to a transported fault propagation fold the model data suggest that fault propagation folding in heterogeneously layered rock occurs by the discontinuous formation growth and linkage of faults below the growing fold amplification of the fault propagation fold is affected by the amount of slip transferred out of the deforming region imbrication and buckling the changes in the mode of fold thrust interaction and modifications in the local geometry and strain distribution that occur during shortening result from slip hardening on faults or from rotation or strain induced variations in the strength of the layers

modeling the influence of sinking anhydrite blocks on salt diapirs targeted for hazardous waste disposal due to the low permeability and high ductility of rock salt many salt diapirs such as those in germany and the netherlands are targeted as long term repositories for disposal of high level radioactive and chemical wastes geophysical and subsurface data show that the gorleben salt diapir which is one of the most extensively investigated diapirs in the world and other salt diapirs of the zechstein formation in germany contain large blocks 80 m thick of high density anhydrite inclusions these blocks which were carried upward by the rising salt are considered to be detached segments of intercalated layers that initially were deposited with the salt results of physical and numerical models presented here show that such detached high density blocks which were entrained and carried upward by the diapir at an earlier stage tend to sink in the late stages of diapiric evolution when the rate of diapiric rise slows down during their descent these high density competent blocks deform by folding and create shear zones at the immediate contact with the less competent salt the descending blocks initiate a secondary internal flow within the salt diapirs they descend and they may deform any repository built within such diapirs which would otherwise be considered as tectonically inactive

rheology of rocksalt abstract we review progress in experimental determinations of transient and steady state flow properties and processes of natural rocksalt aggregates focusing primarily on results from avery island louisiana domal salt the steady state flow field established from constant stress and constant strain rate tests at temperatures from 50 to 200 c strain rates from 10 5 to 10 9 s 1 and differential stresses from 20 7 to 2 5 mpa has been separated into two flow regimes each fit by a power law relation at the higher stresses and strain rates this relation is e 1 6 10 4 exp 68 1 rt 10 3 5 3 for which the pre exponential constant is expressed in mpa 5 3 s 1 and the apparent activation energy is in j mol 1 creep rates predicted by equation a do not differ appreciably from those predicted previously the relatively low stress low strain rate data are very well fit by e 8 1 10 5 exp 51 6 rt 10 3 2 4 which is comparable conditions predicts creep rates higher and equivalent viscosities lower than does equation a by two orders of magnitude the change in behavior from a to b is ascribed to a change in rate limiting mechanism from cross slip of screw dislocations to the climb of edge dislocations in this dry material subgrain formation dominates microstructural development during steady state flow of salt and from determinations of average subgrain diameters in crystals from 20 different rocksalt bodies flow stress levels between 0 6 and 1 4 mpa have been estimated these values do not bear directly on arguments concerning the nature of forces initiating salt pillow growth because apparently evidence relating to the early deformational history has been overprinted at that stage fluid assisted grain boundary diffusional processes might dominate dislocation creep leading to a linear stress strain rate mechanical response considering buoyancy forces alone behavior described by equation b rather than a reduces the relief necessary to initiate pillow growth but a 1000 fold amplification is required to produce stress differences near 1 mpa that forces other than buoyancy are important is indicated by the occurrence of these same paleostress levels in bedded salts and in shallow offshore concordant intrusions differential loading generally provides the most plausible initial driving force for the growth of diapiric salt structures

anatomy of mushroom shaped diapirs we produced more than 100 mushroom shaped diapirs in eight centrifuged models under acceleration of 1200 g the modelling results allow natural examples to be recognized mushroom diapirs have an overhanging bulb fringed by one or more skirts which can curl inward to form vortices capable of entraining cover material to various degrees most of the internal folds are downward facing the oldest buoyant unit occurs in the skirt and in the diapiric core younger buoyant units or their immediate cover are infolded in crescentic patterns external mushroom diapirs have skirts that infold cover material with greater maturity the skirts can curl inward to form an external vortex entraining cover in contrast internal mushroom diapirs have skirts confined entirely within the intrusion again with greater maturity these confined skirts may curl inward but they entrain only diapiric material internal mushroom structure results from toroidal circulation confined within the diapir where isoviscosity prevails external mushroom structure results where source and entrained cover have similar effective viscosities entrained inclusions of more permeable country rock threaten the integrity of a mined cavern by creating a plumbing system

deformation experiments on anhydrite rocks of different grain sizes rheology and microfabric miiller w h schmid s m and briegel u 1981 deformation experiments on anhydrite rocks of different grain sizes rheology and microfabric in g s lister h j behr k weber and h zwart editors the effect of deformation on rocks tectonophysics 78 527 543 three anhydrite rocks of different grain size were experimentally deformed in the 20 to 45o c temperature range the strength of the finegrained varieties becomes strongly temperature and strain rate dependent above 3oo c and a flow law of the form 6 a exp h rt sinh o a with an activation energy h of 27 36 kcal mole and a very low value for the exponent n of 1 5 2 was found the course grained rock remains relatively insensitive to strain rate and temperature even at 45o c microstructural and x ray texture analyses suggest that intracrystalline glide and twinning are the major deformation mechanisms the transition from strong work hardening observed at high stresses into steady state flow at low stresses was found to correlate with the onset of dynamic recrystallization by grain boundary migration

the application of high resolution x ray computed tomography on naturally deformed rock salt multi scale investigations of the structural inventory abstract x ray computed tomography ct represents a useful technique providing new perspectives and insights for the structural investigation of naturally deformed rock salt several samples of permian rock salt from gorleben asse and teutschenthal germany were investigated by exploiting the non destructive nature of ct and nct techniques particularly for salt rocks ct imaging enabled the visualization and quantification of anhydrite impurities pore space and fluid phases located along grain boundaries or trapped as intracrystalline inclusions disseminated grains and aggregates of anhydrite in rock salt of the gorleben salt dome have been visualized and quantified by ct for the first time in order to portray their spatial occurrence the visualization of anhydrite aggregates and pore space shows no correlation between their spatial distributions this independence excludes the anhydrite to be responsible for elevated porosity 0 87 0 07 vol high resolution nct scans 1 m voxel size of single intracrystalline and grain boundary fluid inclusions from gorleben and asse rock salt allowed the visualization and quantification of their various phase components a major achievement is the detailed description of the morphology and shape of the fluid inclusions and of their phase components which has not been conducted in rock salt research by high resolution x ray ct imaging before

outcrop scale tomography insights into the 3d structure of multiphase boudins abstract we analyze the 3d geomorphology of a boudinaged amphibolite layer encased in marble using meter scale tomography by serial sectioning high resolution imaging and 3d reconstruction of a 2 m block from a quarry in the high grade core of the naxos core complex local uncertainties in the model are resolved by dissolution of marble in selected slabs yielding a large highly accurate 3d model results show five generations of brittle extension of the amphibolite in ductile marble although examination of the boudinaged layer on the outside of the block only suggested one generation most prominent are the rotated domino boudins where part of the dilatancy between domino boudins can be shown to be due to later reactivation shear fractures between domino boudins have relatively large throw gradients indicating ductile rupture layer parallel stretch as measured by reconstruction of domino boudins decreases with amphibolite layer thickness although the layer has undergone the same bulk stretch everywhere this suggests that with decreasing layer thickness deformation becomes delocalized offering tantalizing glimpses of rheology under metamorphic conditions

single layer buckle folding in non linear materials i experimental study of fold development from an isolated initial perturbation abstract scale model experiments involving pure shear compression of a single layer embedded in a weaker matrix were carried out to study the influence of a pre existing isolated perturbation in the shape of an otherwise planar layer on the location and shape of folds different grades of paraffin wax were used as analogues for rocks with power law rheology the wax used for the matrix flows in steady state with a stress exponent of about 3 8 the layer has a stress exponent of about 3 and strain softens viscosity ratios considered at yield stress for the layer and matrix of 30 1 and 8 1 were used bell shaped perturbations were introduced into the layer with initial average wavelengths of 8 16 and 32 times layer thickness and corresponding initial limb dips of 12 5 and 3 respectively the fold packet develops at the site of the introduced perturbation and spreads slowly along the layer with increasing shortening the shape of the initial perturbation strongly influences the fold geometry broader initial perturbations develop broader folds undergo more layer parallel shortening and develop a wider zone of contact strain the influence of the introduced perturbation shape is most marked when its average wavelength component is larger than the dominant wavelength i e the wavelength of maximum growth rate the degree of bonding between layer and matrix also influences fold development folds with welded layer matrix boundaries amplify much more slowly with a greater proportion of layer parallel shortening than folds where slip between layer and matrix is promoted

experimental folding and boudinage under pure constrictional conditions abstract constrictional folds are characterized by true fold axis parallel extension if the rock volume does not vary during deformation studies of such folds in experiments using plasticine layers of different apparent viscosity and power law exponent clearly indicate that fold axis parallel stretch may be accompanied by plastic elongation as well as boudinage of the competent layer characteristic aspects of the experimentally folded competent layers are 1 coeval development of folds and boudins 2 layer thickness not changing during deformation 3 layer parallel shortening in sections perpendicular to the fold stretching axis 4 enlargement of the initial thickness of the competent layer results in increasing fold wavelength and decreasing number of boudins the ratio of dominant wavelength to layer thickness of the constrictional folds can be described mathematically approximately by the equation developed for plane strain folding of power law materials

coeval folding and boudinage in four dimensions scaled analogue experiments have been carried out incrementally to demonstrate the growth of constrictional folds and boudins through space and time pure constriction acted on a single stiff layer that was embedded in a weak matrix with the layer trending parallel to the x axis of the constrictional strain ellipsoid the viscosity ratio between non linear viscous layer and matrix was set at ca 13 three dimensional images of the incrementally deformed layer have been obtained using computer tomography they yielded clear evidence that d1 folds and d1 boudins show striking interactions when growing simultaneously at low to moderate finite strain the axes of d1 folds are subparallel and the axes of d1 boudins are subperpendicular to the x axis of the constrictional strain ellipsoid the normalized wavelengths of d1 folds and d1 boudins and the amplitudes of d1 folds are fixed already at low finite strain 5 and do not significantly change as deformation proceeds the normalized wavelength of both structures is not so in line as suggested by theoretical studies at higher degrees of finite strain d1 boudins are affected by d2 folds and rotated limbs of the latter show d2 boudinage resulting in complex deformation patterns that are difficult to identify in the field the model results are important for the analysis and interpretation of deformation structures in rheologically stratified rocks undergoing dislocation creep under bulk constriction tectonic settings where constrictional folds and boudins may develop simultaneously are stems of salt diapirs subduction zones or thermal plumes

interfering folds in constrictional deformation abstract experiments on buckle folding indicate that in pure constriction 2 3 2 3 there is an association of domes and basins with nonplane noncylindrical folds the areas of domes and basins are reduced with increasing deformation there is a dominant fold trend perpendicular to 3 with a less dominant trend perpendicular to 3 folds at an angle to these two sets may also occur the divergent folds link up in smooth arcs or join up at a dome or a basin over a relatively large domain the interference pattern produced by general constriction can be recognized by the association of domes and basins with nonplane noncylindrical folds by occurrence of hair pin bends of hinge lines of open folds by occurrence of amoeboid outcrop patterns and by absence of a consistent overprinting relation among different sets of folds layers subparallel to the 3 axis of general constriction may give rise to two or more sets of coaxial cylindrical folds with orthogonal axial surfaces

a deformation apparatus for three dimensional coaxial deformation and its application to rheologically stratified analogue material abstract a new apparatus is described that supports all types of three dimensional coaxial deformation from pure constriction to pure flattening up to 78 shortening is possible at strain rates ranging from 4 10 6 to 1 10 2 s 1 the apparatus has been used to study the influence of the deformation regime on the geometry of a deforming stiff layer embedded in a weak matrix layer and matrix consist of plasticine the apparent viscosity and stress exponent n of which vary from 2 10 6 to 2 10 7 pa s and 6 9 respectively first results suggest a considerable influence of the deformation regime on the geometry of the deformed layer including its thickness if the viscosity ratio between layer and matrix is small 2 1 5 folding is restricted to the flattening and plane strain regime the latter if the layer is initially oriented perpendicular to the long axis x of the finite strain ellipsoid if the layer is oriented perpendicular to the intermediate y axis under plane and constrictional strain low viscosity ratios result in boudinage but folding is hardly developed however simultaneous growth of folds and boudins is possible under pure constriction at a viscosity ratio of 10 three dimensional images based on computer tomography suggest a strong interaction between such coeval folds and boudins resulting in characteristic deformation patterns that should not occur if both structures form in sequence during polyphase deformation

internal kinematics of salt diapirs the internal structure of intrusive and extrusive salt bodies elucidates their external shape and the mechanism and history of diapiric emplacement information relevant to petroleum exploration trace amounts of brine can act like heat to weaken salt and promote geologic creep by solution transfer mechanisms we compare natural strain markers in salt with the artificial markers used by fluid dynamicists stream lines are the smooth flow paths followed by fluid particles stream surfaces separate flow laminae and contain the stream lines grain shape fabrics in salt anneal readily and have strain memories so short that lineations map the stream lines and foliations map the stream surfaces of the last stages of deformation by contrast larger structures like folded beddi g have much longer strain memories as a result multiple generations of tonguelike recumbent flow folds formed by unsteady flow in the mother source layer rotate to upright sheath folds or spines in the stems of diapirs here they are constricted and refolded into steep curtain folds to form crescentic and other interference patterns visible in the roofs of salt mines mature diapirs can form crestal bulbs which may be balloon or mushroom shaped and which potentially form larger petroleum traps than previously supposed screens of country rock may be entrained between the stem and peripheral overhanging lobes caused by episodic sedimentation

numerical modelling of rise and fall of a dense layer in salt diapirs this thesis uses results of systematic numerical models to argue that externally inactive salt structures which are potential targets for radioactive waste disposal might be internally active due to the presence of dense layers or blocks within a salt layer the three papers that support this thesis use the gorleben salt diapir nw germany which was targeted as a future final repository for high grade radioactive waste as a general guideline the first two papers present systematic studies of the parameters that control the development of a salt diapir and how it entrains a dense anhydrite layer results from these numerical models show that the entrainment of a dense anhydrite layer within a salt diapir depends on four parameters sedimentation rate viscosity of salt perturbation width and the stratigraphic location of the dense layer the combined effect of these four parameters which has a direct impact on the rate of salt supply volume area of the salt that is supplied to the diapir with time shape a diapir and the mode of entrainment salt diapirs down built with sedimentary units of high viscosity can potentially grow with an embedded anhydrite layer and deplete their source layer salt supply ceases however when salt supply decreases dramatically or ceases entirely the entrained anhydrite layer segments start to sink within the diapir in inactive diapirs sinking of the entrained anhydrite layer is inevitable and strongly depends on the rheology of the salt which is in direct contact with the anhydrite layer during the post depositional stage if the effective viscosity of salt falls below the threshold value of around 1018 1019 pa s the mobility of anhydrite blocks might influence any repository within the diapir however the internal deformation of the salt diapir by the descending blocks decreases with increase in effective viscosity of salt the results presented in this thesis suggest that it is highly likely that salt structures where dense and viscous layer blocks are present undergo an internal deformation processes when these dense blocks start sinking within the diapir depending on size and orientation of these blocks deformation pattern is significantly different within the diapir furthermore model results applied to the gorleben diapir show that the rate of descent of the entrained anhydrite blocks differs on different sides of the diapir this suggests that if the anhydrite blocks descent within the gorleben diapir they initiate an asymmetric internal flow within it

creep of rocksalt abstract a review is presented of the fundamental flow properties and processes in experimentally deformed natural and synthetic halite single crystals and polycrystalline aggregates included in the summary are discussions of a microstructures induced during steady state creep b creep rupture of rocksalt c experiments associated with project salt vault and more recent field studies and d brine migration a representative steady state flow law determined for natural aggregates and maximum natural deviatoric stresses deduced from subgrain sizes are applied briefly to considerations of creep in waste repositories and of salt dome dynamics while the mechanical behavior of rocksalt is probably better understood than for all other rock types further investigations especially on load path stress history and creep rupture are clearly mandated furthermore additional investigations of brine migration and of bench and field scale deformations are needed the latter incorporating realistic rocksalt flow properties into numerical simulations of natural rock mass response

experimental deformation of a single layer anhydrite in halite matrix under bulk constriction part 1 geometric and kinematic aspects a new deformation apparatus has been used to model the internal kinematics of salt diapirs composite natural samples consisting of a single layer of anhydrite embedded in halite matrix were constrictionally deformed at temperature t 345 c strain rate 10 7 s 1 maximum viscosity 2 1013 pa s and maximum finite strain ex 122 the anhydrite layer oriented parallel to the major stretching axis x was deformed by fracturing whereas halite behaved viscously at advanced state of constriction ex 90 a strong increase in strain hardening of halite led to a transient tension fracture that healed up and was shortened by folding during the final phase of viscous deformation tiny prismatic anhydrite inclusions disseminated inside the halite matrix were reoriented during constriction resulting in a linear grain shape fabric 3d images of the anhydrite layer based on computer tomography revealed rare kink folds with axes subparallel to x and boudins which result from tension fracture with increasing layer thickness hi the width of boudins wa increases linearly wa 0 3 1 3 hi the normalized width of boudins wd wa hi is almost constant at 1 5 1 0 these geometrical parameters can be used to reveal fracture boudinage under bulk constriction the oblique orientation of most of the boudins with respect to the principal strain axes results from folding of the boudins by a second generation of folds the latter with axes subperpendicular to the layer

texture development of polycrystalline anhydrite experimentally deformed in torsion a polycrystalline aggregate of anhydrite was deformed in torsion to a maximum shear strain of 8 1 at 700 c and a maximum shear strain rate of 5 10 3 s 1 the crystallographic preferred orientation cpo or texture was investigated as a function of shear strain shear strain rate in a radial profile from the centre to the edge of the sample a deformation texture developed at shear strains of 1 5 2 corresponding to shear strain rates of 1 to 1 3 10 3 s 1 and reached a stable position relative to the kinematic frame at a shear strain of 3 7 2 3 10 3 s 1 further shear strain only led to a small increase in texture strength but no change in the orientation relative to the kinematic frame the cpo is very similar to naturally observed textures and can be explained by the activity of the 001 and 012 slip systems although independent mechanical data indicate that a change of mechanism from dislocation to diffusion controlled creep occurred at a shear strain of approximately 1 5 the texture does not weaken but rather increases in strength with higher shear strains

structure and evolution of upheaval dome a pinched off salt diapir upheaval dome canyonlands national park utah is an enigmatic structure previously attributed to underlying salt doming cryptovolcanic explosion fluid escape or meteoritic impact we propose that an overhanging diapir of partly extrusive salt was pinched off from its stem and subsequently eroded many features support this inference especially synsedimentary structures that indicate jurassic growth of the dome over at least 20 m y conversely evidence favoring other hypotheses seems sparse and equivocal in the rim syncline strata were thinned by circumferentially striking low angle extensional faults verging both inward toward the center of the dome and outward near the dome s core radial shortening produced constrictional bulk strain forming an inward verging thrust duplex and tight to isoclinal circumferentially trending folds farther inward circumferential shortening predominated radially trending growth folds and imbricate thrusts pass inward into steep clastic dikes in the dome s core we infer that abortive salt glaciers spread from a passive salt stock during late triassic and early jurassic time during middle jurassic time the allochthonous salt spread into a pancake shaped glacier inferred to be 3 km in diameter diapiric pinch off may have involved inward gravitational collapse of the country rocks which intensely constricted the center of the dome sediments in the axial shear zone beneath the glacier steepened to near vertical the central uplift is inferred to be the toe of the convergent gravity spreading system

effect of confining pressure on dilatation recrystallization and flow of rock salt at 150 c microstructural evidence for fluid assisted dynamic recrystallization fadrx is widespread in naturally deformed rock salt however the principal experimental evidence for fadrx in salt has been obtained from stress relaxation experiments and it is unclear whether the process occurs during steady state dislocation creep and what its effect might be here we report deformation experiments performed on natural rock salt at a constant strain rate of 3 5 10 7 s 1 150 c and confining pressures pc of 3 30 mpa samples deformed at pc 3 mpa showed continuous work hardening and minor dilatation microstructurally they exhibited intergranular cracking plus slip band and subgrain structures indicative of dislocation glide creep electron backscatter diffraction analysis revealed a high frequency of boundaries with low angle misorientations in the range 5 10 in contrast samples deformed at pc 6 5 mpa showed work hardening followed by steady state flow at strains 6 7 these samples compacted slightly and crystal plastic deformation was accompanied by extensive fadrx with a predominance of high angle boundaries 30 50 over low angle boundaries we infer that fadrx is suppressed by dilatation at low pressures as a result of grain boundary disruption at pressures high enough to prevent dilatation however fadrx acts as a recovery mechanism counteracting work hardening the results offer a possible explanation for rheological variability seen in previous experiments conducted at pressures up to 30 mpa a simple rate model for diffusion and interface controlled fadrx indicates that fadrx should become increasingly important toward natural halokinetic conditions although the effect on flow stresses is likely to be small

geometry of torn boudin an indicator of relative viscosity abstract the present study determines the role of viscosity on the development of rectangular torn boudin and its various types defined by the curvature of their exterior and face margins numerical modeling was performed with the help of finite element method considering maxwell visco elastic materials in commercial code ansys seven different viscosities were used and interchanged among the boudin inter boudin and matrix materials to understand the effect of viscosity ratios specifically of relative viscosity of inter boudin material results show that the viscosity of inter boudin material has significant control on the shape of torn boudins apart from the viscosity ratio of boudin to matrix material bone shaped boudin develops only when the inter boudin is more competent than boudin and it becomes more prominent when matrix is also competent than boudin but incompetent than inter boudin when boudins are stiffer than inter boudin barrel shaped and fish head boudins with concave faces develop exterior or face margins remain almost straight when boudin is relatively rigid compared to its surrounding matrix materials or when there is no or very little viscosity contrast between boudin and inter boudin material even in case of large boudin matrix viscosity contrast therefore the relative viscosity among the boudin inter boudin and matrix materials can be estimated qualitatively by studying the shape of boudin in the field

quantification of the geometrical parameters of non cylindrical folds abstract the geometrical parameters of natural folds are used by structural geologists to estimate finite strain and rheological properties of deformed rocks the relation between geometry and rheology is well understood in cases of cylindrical folds but is still limited for non cylindrical folds although the latter are frequent in nature the sparsity of quantitative geometrical data of non cylindrical folds can be explained by the small number of 3d exposures and by the lack of robust methods to quantify their geometrical parameters in 3d space we present a new workflow which can be used to quantify geometrical parameters of non cylindrical folds 3d fold geometry is described using fold wavelength arc length l and amplitude a as most natural folds do not show ideal shapes but are affected by various types of discontinuities the new procedure is not fully automatic but requires the manual selection of measuring profiles along which the geometrical parameters are constrained the new workflow is tested using natural and experimentally produced non cylindrical folds the geometric parameters obtained can be used to improve our understanding of fold kinematics and fold mechanics and should assist the quantitative analysis of non cylindrical folds present in gneiss and salt domes and in rocks containing reservoirs of hydrocarbons and minerals deposits

textural evolution of synthetic anhydrite halite mylonites the rheology and textural evolution of mylonites for both crustal and mantle rocks are generally poorly understood stress and strain partitioning between shear zones and wall rock foliation development flow mechanisms and constitutive relations are little known to address these problems we have begun an experimental study in which anhydrite and halite aggregates are deformed in simple shear homogeneous mixes at intervals of 10 vol of anhydrite and halite powders of 90 to 180 m grain size comprise the 1 mm thick zone between the 35 precut surfaces in 2 by 4 cm right circular cylinders of anhydrite all specimens are confined under 200 mpa pc and tested at 300 c t producing an aggregate of near zero porosity all specimens are shortened at an axial displacement rate of 5 l0 6 cm s to shear strains of about 2 0 most stress strain curves have a similar form they are characterized by an initial linear response that is followed by a work hardening region that leads to a plateau of constant stress whilst strain continues to accumulate this apparent steady state behavior is followed by a drop in stress to a second apparent steady state stress the strain at this stress drop and the magnitude of the drop increase with increasing anhydrite content the second lower steady state stress for all mixes approaches that of sheared pure halite optical examination of the fabrics shows that straining under the initial apparent steady state is accommodated by both mineral phases a foliation evolves as defined by mineral segregation and grain elongation of halite at 15 to 30 to the shear zone walls anhydrite grains rotate until their 001 010 slip system parallels the foliation the anhydrite also exhibits twin lamellae kinks and microfractures following the stress drop rheologic behavior is dominated by dynamic recovery in halite the recrystallized grain size increasing consistent with the lower stress level

book review the techniques of modern structural geology volume 2 folds and fractures john g ramsay and martin i huber academic press london 1987 xi 309 398 pp price stg17 50 us 34 50 paperback

the tectonometamorphic evolution of high pressure low temperature metamorphic rocks of eastern crete greece constraints from microfabrics strain illite crystallinity and paleodifferential stress abstract analysis of strain paleodifferential stress illite crystallinity and microfabrics of quartz and calcite suggest that multiply alternating late oligocene early miocene n s convergence and n s extension caused significant vertical discontinuities in the grade of high pressure low temperature metamorphism of the phyllite quartzite unit pqu of eastern crete constrictional fabrics and parallelism of d2 stretching lineations and fold axes are attributed to enhanced slab pull forces at greater depth of subduction a major d3 extensional detachment is present in the upper part of the pqu where slates with lowest metamorphic grade diagenesis anchizone transition are resting on top of anchimetamorphic rocks the highest metamorphic grade anchi epizone transition has been determined for skythian rocks on top of pre alpine basement revived n s convergence d4 led to e w trending map scale folds and top to the s directed brittle thrusts there is a clear correlation between d2 related metamorphic grade finite strain differential stress and deformation mechanisms at the anchi epizone transition solution precipitation and dislocation creep of quartz and calcite caused maximum finite strains rxz up to 7 at high strain rates and moderate differential stresses 80 200 mpa at the diagenesis anchizone transition deformation was accommodated by cataclasis dislocation glide and solution precipitation creep resulting in relatively low finite strains rxz

folds with axes parallel to the extension direction an experimental study abstract experimental studies of single and multilayer folding have generally considered shortening of layers oriented perpendicular to the maximum extension direction x i e layers parallel to yz or in a more limited number of cases oblique layers still containing the intermediate y axis few experimental studies have considered the case where the extension direction x lies within the layer itself although in nature folds with axes parallel to x are quite commonly seen these folds have often been ascribed to passive rotation of fold axes during continued shear but it has been shown both theoretically and experimentally that active buckle folds can also develop with axes parallel to x single and multilayer analogue model experiments were performed on planar layers oriented initially perpendicular to the intermediate y axis and with the extension direction x lying within the layer itself all experiments were conducted in plane strain either in pure shear or simple shear paraffin waxes of different melting ranges were used as analogues for rocks with a power law rheology stress exponent around 2 3 with a viscosity ratio of ca 30 1 no measurable fold amplification was discernible for shortening of 36 or shear strain of 3 6 neither domed initial perturbations with circular sections parallel to the layer nor cylindrical perturbations elongate parallel to the initial stretching direction were significantly amplified only at much higher viscosity ratios ca 600 1 did active buckle folding develop this folding at high viscosity ratio was associated with flow of the matrix in the x direction around the layer developing a strong linear fabric parallel to x in the matrix immediately adjacent to the layer the development of this flow discontinuity between matrix and layer may be characteristic of active buckling of layers parallel to xz with fold axes parallel to x

boudinage and two stage folding of oblique single layers under coaxial plane strain layer rotation around the axis of no change y abstract scaled analogue modelling using non linear viscous plasticine as rock analogue has been carried out to investigate the influence of varying layer obliquity on the geometry of single layer folds and boudins under bulk coaxial plane strain two deformation series with different viscosity ratio between layer and matrix m 18 and 82 were carried out the initial angle between shortening axis and competent layer z i was gradually changed from 0 to 90 by multiples of 11 25 shortening at z i 60 because of the high finite strain and related layer rotation these boudins are not asymmetric as expected but symmetric folds and boudins like those produced in the present study occur in salt rocks and in crystalline basement deformed at deeper structural levels

basement balancing of rocky mountain foreland uplifts restorable cross sections of foreland basement uplifts must contain faults whose curvatures are consistent with the relative slip and tilt between adjacent basement blocks cylindrical fault surfaces can explain the uniform dip of strata on the back side of foreland uplifts local zones of shortening and extension occur in hinge zones above transitions in fault curvature high curvature fault splays form fault wedges of basement which ease the transition from thrust and reverse faulting of basement blocks to folding in the sedimentary cover 20 references 4 figures

origin of stylolites in upper permian zechstein anhydrite gorleben salt dome germany abstract stylolites in evaporites are very uncommon in the gorleben zechstein salt dome stylolite horizons have been found in the so called banderanhydrit z3ha11 at the top of the zechstein hauptanhydrit main anhydrite these pressure solution features seems to be related to the presence of thin magnesite clay interlayers five principal stylolite morphologies can be distinguished in the core sections studied the orientation of the sutured seams is generally bedding parallel with the stylolite axes vertical to the bedding surface this demonstrates that pressure solution features clearly predate the formation of the salt dome and that there is no relation between their formation and halokinesis solution rates of up to about 26 have been calculated by measuring maximum stylolite amplitudes in certain core intervals considering the bedding parallel occurrence of the stylolites and the fact that the stylolite seams are crosscut by anhydrite crystals that we interpret as pseudomorphs after gypsum it must be concluded that the stylolites formed before the dehydration of gypsum to anhydrite was completed the lower parts of the hauptanhydrit were excluded from these processes because they had already been converted to anhydrite by the overburden of overlying zechstein units and by ascending compaction fluids of the underlying zechstein 2 salt we assume that the dehydration of gypsum to anhydrite was completed before the end of zechstein sedimentation and that the formation of stylolites thus must be attributed to the same time interval

the detection and illustration of regular sedimentary cycles using walsh power spectra and filtering with examples from the lias of switzerland power spectral analysis provides an objective method for the detection of regular cyclicity in data recording some oscillating parameter or time series digitization of measured stratigraphic sections is a convenient method for generating long time series during the examination of pelagic sequences for cyclicity related to orbital variations or milankovitch cycles the application of walsh power spectral analysis to stratigraphic sections is outlined and band pass filtering using the walsh transform introduced it is shown that variations in sedimentation rate hiatuses bioturbation and variations in compaction have the effect of damping or destroying spectral peaks the wavelength ratios of spectral peaks are often used during studies of milankovitch cycles to decide which orbital cycles are involved however in some circumstances hiatuses are able to alter wavelength ratios averaged walsh power spectra were generated for three liassic limestone shale sequences from breggia gorge switzerland the 21 000 year 21 ka precession cycle was detected in all three cases the 100 ka eccentricity cycle in two cases and the 41 ka obliquity cycle in one filtering revealed that the supposed 21 ka sedimentary cycles are grouped into packets of four or five small and large amplitude cycles the packets reflect the 100 ka modulation of the 21 ka precession cycle local disruption of the packaging can be used to locate hiatuses in pelagic strata

the control of salt supply on entrainment of an anhydrite layer within a salt diapir the influence of four parameters sedimentation rate viscosity of salt stratigraphic location of the anhydrite layer within the salt layer and the perturbation width on salt supply to down built diapirs and its entrainment capacity are studied systematically in numerical models model results show that these four parameters affect salt supply and the evolution history of a salt diapir as such these parameters strongly influence the style and the amount of entrainment of dense inclusions into a diapir in active diapirs i e unburied diapirs salt supply increases with increasing sedimentation rate whereas it decreases with an increase in salt viscosity diapirs initiating from wide perturbation provide more salt supply to feed the diapir presence and initial stratigraphic location of any denser layer e g an anhydrite layer within a salt layer also affects salt supply when lateral forces are negligible salt supply into a diapir depends on these four parameters which directly control the entrainment of any embedded anhydrite layer into the diapir

microstructural evolution and grain boundary structure during static recrystallization in synthetic polycrystals of sodium chloride containing saturated brine the effects of brine on recrystallization in halite are well known however properties of brine such as morphology connectivity diffusivity and the resulting influences on deformation mechanisms are still a matter of debate this paper presents a microstructural study of dense statically recrystallizing synthetic polycrystalline halite containing small amounts of brine we used powders of two different grain size classes 10 m and 200 355 m the aggregates were compacted to brine filled porosities less than about 2 and annealed at room temperature without an external stress field