experimental pressure solution in halite the effect of grain interphase boundary structure to investigate the mechanisms and kinetics of pressure solution we measured deformation at contacts between polished convex lenses of halite and polished flat lenses of either halite or fused silica in saturated brine at 50 2 0 2 c and fluid pressures of 0 1 mpa loads applied using small springs ranged from 0 1 4 2 n mean effective normal stresses within the contact zone ranged from 1 14 mpa the geometry and diametric growth rate of the contact spot neck growth and the rate at which the lenses approached one another convergence were monitored during deformation using transmitted and reflected light photomicrography time dependent convergence did not occur at measurable rates when two halite lenses were pressed together in saturated brine but did occur when halite and fused silica lenses were pressed together in brine convergence rates in the halite silica experiments were 0 01 0 05 m day although the initial deformation during loading involved elastic and plastic processes control experiments without brine showed no time dependent convergence indicating that dislocation creep did not contribute to the observed rates no undercutting or cataclasis was observed in any experiments residual fluid inclusions were formed along grain boundaries between two halite lenses loaded in brine indicating non zero wetting angles

flow laws for rocks containing two non linear viscous phases a phenomenological approach abstract mylonitic rocks and rock analogue materials reveal two basic types of structure 1 a load bearing framework lbf of strong phase contains isolated pockets of weak phase 2 interconnected layers of weak phase iwl separate boudins and clasts of strong phase aggregates with the lbf microstructure are characterized by nearly uniform strain rate stress is concentrated in the load bearing framework in aggregates with an iwl microstructure strain rate and sometimes also stress are higher in the interconnected weak phase than in the boudins and clasts of strong phase the degree of stress and strain partitioning depends strongly on the viscous strength contrast and on the relative amounts of the constituent mineral phases based on these observations the rheology of two phase rock is modelled with separate functions for lbf and iwl microstructures a new flow law is derived for rock with iwl structure in which two phases undergo dislocation creep the flow law expresses composite creep strength in terms of temperature bulk strain rate and the volume proportions and creep parameters of the minerals in the rock strain rate and stress are averaged in the constituent phases and slip along phase boundaries maintains strain compatibility within the aggregate composite strengths predicted with the iwl flow law fall well within the uniform stress and uniform strain rate bounds and are generally consistent with the viscous strengths of experimentally deformed bimineralic aggregates a hypothesis of viscous strain energy minimization is used to determine the relative stability of the lbf and iwl microstructures during steady state creep the iwl microstructure is predicted to be stable over a broad range of two phase compositions and mineral strength contrasts whereas the lbf microstructure is stable only in rocks with low volume proportions of weak phase and low to moderate mineral strength contrasts the iwl flow law indicates that rheological stratification in the lithosphere depends strongly on rock composition especially in rocks with low volume proportions of a weak phase and high mineral strength contrasts

the interaction of fluid inclusions and migrating grain boundaries in a rock analogue deformation and annealing of polycrystalline camphor ethanol mixtures the results of deformation and annealing experiments using a rock analogue containing a liquid phase as observed in transmitted light microscopy are presented samples were made of camphor ethanol mixtures with the polycrystalline solid being a rhombohedral phase and the liquid a saturated solution of camphor in ethanol results show the in situ pore fluid morphology during grain boundary migration recrystallization samples were deformed at high homologous temperatures th 0 7 and strain rates of 1 10 6 to 9 10 4 s 1 for grain boundary migration rates ranging from 10 10 to 10 6 ms 1 zener pinning not only the drag and drop of fluid inclusions by migrating grain boundaries but also the passage of grain boundaries over fluid inclusions without noticeable interaction was observed the drag limiting migration rate is three times lower for post kinematic annealing than for dynamic recrystallization and shows a weak dependence on fluid inclusion size a detailed description is presented of fluid inclusion grain boundary interaction with respect to fluid inclusion sizes and grain boundary migration rates fluid inclusions show up to 39 reduction in diameter after passage of a grain boundary indicating fluid flow along the mobile grain boundary

deformation of partially molten granite a review and comparison of experimental and natural case studies experimental and natural investigations of partially molten granite are compared and reviewed experiments suggest that deformation of partially molten granite with low viscosity melt 104 pa s exhibits a rheological critical melt percentage rcmp in case of high viscosity melts 108 pa s however the relationship between melt fraction and log viscosity of the partially molten granite may be linear considerations about viscosity rheological thresholds and segregation of natural melts suggest that low viscosity melt experiments simulate natural conditions more realistically therefore an rcmp is to be expected under natural conditions both diffusion creep and dislocation creep may occur under natural conditions whereas cataclastic flow is only observed under experimental conditions a melt induced transition from dislocation creep to diffusion creep occurs under experimental and natural conditions melt topology is controlled by the magnitude of differential stress under experimental conditions if differential stress is higher than 100 150 mpa melt pockets are elongate and oriented at a low angle to the maximum compressive stress in contrast in nature melt pockets tend to be oriented subparallel to the foliation plane i e presumably at a high angle to the maximum compressive stress

deformation mechanisms of deeply buried and surface piercing late pre cambrian to early cambrian ara salt from interior oman we compared microstructures of late pre cambrian to early cambrian ara salt diapirs from the deep subsurface 3 5 5 km of the south oman salt basin and from surface piercing salt domes of the ghaba salt basin laterally these basins are approximately 500 km apart but belong to the same tectono sedimentary system the excellent data situation from both wells and outcrops allows a unique quantification of formation and deformation mechanisms spanning from sedimentation to deep burial and via re activated diapir rise to surface piercement microstructures of gamma irradiated and etched thin sections indicate dislocation creep and fluid assisted grain boundary migration as the main deformation mechanisms operating in the deep subsurface microstructures from the surface are characterised by large old subgrain rich crystals these old grains are partly replaced by new subgrain free and subgrain poor crystals which show gamma irradiation decorated growth bands and fibrous microstructures indicative of pressure solution creep and static recrystallisation most likely due to surface piercement and exposure using subgrain size piezometry the maximum differential stresses for the subsurface salt is 1 7 mpa and those for the surface piercing salt is 3 4 mpa the latter value displaying the high stress conditions in the diapir stem as the salt rises on its way to the surface

weakening of rock salt by water during long term creep the rheological properties of rock salt are of fundamental importance in predicting the long term evolution of salt based radioactive waste repositories and strategic storage caverns and in modelling the formation of salt diapirs and associated oil traps1 2 the short term high stress rheology of rock salt is well known from laboratory experiments however extrapolation to appropriately low stresses fails to predict the rapid flow seen in certain natural structures furthermore experiments have failed to reproduce the recrystallized microstructure of naturally deformed salt here we report experiments indicating that the above discrepancies can be explained by taking into account the influence of trace amounts of brine trace brine is always present in natural salt but sometimes escapes during experiments our tests on dry dilated salt show more or less conventional dislocation creep behaviour but brine bearing samples show marked weakening at low strain rates this is associated with dynamic recrystallization and a change of deformation mechanism to solution transfer creep because natural rock salt always contains some brine these results cast substantial doubt on the validity of presently accepted dislocation creep laws for predicting the long term rheological behaviour of salt in nature

experimental deformation of partially molten westerly granite under fluid absent conditions with implications for the extraction of granitic magmas the mechanical behavior of partially molten westerly granite was investigated in the temperature range 800 1100 c 250 mpa confining pressure by means of constant strain rate creep and stress relaxation tests the only water in the samples came from the breakdown of hydrous phases biotite minor chlorite and muscovite and alteration products of feldspars thus the amount of melt was controlled by the test temperature and ranged from 3 at 800 c to 50 at 1100 c over that temperature range strength decreased from 500 mpa to less than 1 mpa and a preliminary constitutive flow law for the partially molten rock was obtained to allow extrapolation to low strain rates the comparative viscosity of the melt alone was estimated at 950 and 1000 c from the distance it could be made to penetrate into a porous sand under a known pressure gradient under all conditions deformation of the matrix of solid grains was by brittle fracture only samples containing up to 10 vol melt failed with the formation of a shear fault zone at higher melt fractions melt filled pores collapsed by shear enhanced compaction squeezing the melt into axial cracks above 40 vol melt unfractured solid grains were carried about passively in the flowing liquid there was no evidence of a rheologically critical melt percentage in this system by analogy with the uniaxial compaction of water saturated soils a simple model is erected to describe a two stage process for the extraction of granitic melts from their protoliths with the aid of nonhydrostatic stress shear enhanced compaction is inferred to drive melt into a network of melt filled veins whereupon porous flow through the high permeability vein network allows rapid drainage of melt to higher crustal levels

vertical extrusion and horizontal channel flow of orogenic lower crust key exhumation mechanisms in large hot orogens a large database of structural geochronological and petrological data combined with a bouguer anomaly map is used to develop a two stage exhumation model of deep seated rocks in the eastern sector of the variscan belt an early sub vertical fabric developed in the orogenic lower and middle crust during intracrustal folding followed by the vertical extrusion of the lower crustal rocks these events were responsible for exhumation of the orogenic lower crust from depths equivalent to 18 20 kbar to depths equivalent to 8 10 kbar and for coeval burial of upper crustal rocks to depths equivalent to 8 9 kbar following the folding and vertical extrusion event sub horizontal fabrics developed at medium to low pressure in the orogenic lower and middle crust during vertical shortening fabrics that record the early vertical extrusion originated between 350 and 340 ma during building of an orogenic root in response to se directed saxothuringian continental subduction fabrics that record the later sub horizontal exhumation event relate to an eastern promontory of the brunia continent indenting into the rheologically weaker rocks of the orogenic root indentation initiated thrusting or flow of the orogenic crust over the brunia continent in a north directed sub horizontal channel this sub horizontal flow operated between 330 and 325 ma and was responsible for a heterogeneous mixing of blocks and boudins of lower and middle crustal rocks and for their progressive thermal re equilibration the erosion depth as well as the degree of reworking decreases from south to north pointing to an outflow of lower crustal material to the surface which was subsequently eroded and deposited in a foreland basin indentation by the brunia continental promontory was highly noncoaxial with respect to the se oriented saxothuringian continental subduction in the early visean suggesting a major switch of plate configuration during the middle to late visean

composition of plagioclase feldspar in modern deep sea sands relationship to tectonic setting microprobe analysis of plagioclase in deep sea sands from various tectonic settings gives averages ranging from 19 an for trailing edge continental margins to 56 an for basins on the ocean side of an island arc for each setting except island arcs anomalously high amounts of pure albite are found these albitic grains may be recycled from pre existing sedimentary rocks potassium rich plagioclase thought to be indicative of a volcanic provenance is less abundant than would be expected from the proportion of volcanic rock fragments perhaps such high k plagioclases are less resistant to weathering than low k plagioclase

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

karst aquifer evolution in fractured porous rocks the evolution of flow in a fractured porous karst aquifer is studied by means of the finite element method on a two dimensional mesh of irregularly spaced nodal points flow within the karst aquifer is driven by surface recharge from the entire region simulating a precipitation pattern and is directed toward an entrenched river as a base level during the early phase of karstification both the permeable rock matrix modeled as triangular elements and fractures within the rock matrix modeled as linear elements carry the flow as the fractures are enlarged with time by chemical dissolution within the system calcite carbon dioxide water flow becomes more confined to the fractures this selective enlargement of fractures increases the fracture conductivity by several orders of magnitude during the early phase of karstification thus flow characteristics change from more homogeneous pore controlled flow to strongly heterogeneous fracture controlled flow we study several scenarios for pure limestone aquifers mixed sandstone limestone aquifers and various surface recharge conditions as well as the effect of faulting on the aquifer evolution our results are sensitive to initial fracture width faulting of the region and recharge rate

evolution of dilatancy and permeability in rock salt during hydrostatic compaction and triaxial deformation combined gas permeability and p and s wave velocity measurements were carried out on rock salt samples from the gorleben salt dome and the morsleben salt mine under hydrostatic and triaxial loading condions mostly at room temperature permeabilities in the as received samples vary between 10 16 and 2x10 20 m 2 the initial permeability is primarily due to decompaction induced by drilling core retrieval and sample preparation hydrostatic loading gives rise to a marked decrease of permeability and a coeval significant increase of p and s wave velocities due to progressive closure of grain boundary cracks tending to approach the in situ matrix permeability 18 mpa differential stress at 10 mpa confining pressure to similar to 30 mpa at confining pressures above similar to 70 mpa dilatancy is due to the opening of grain boundary and 100 cleavage cracks and depends on the applied confining pressure the orientation of the open cracks is primarily controlled by the loading geometry system compression extension as a consequence permeability increases dramatically with progressive dilatancy followed by a period of plus minus constant permeability during strain hardening up to 10 axial strain or even more this suggests that the evolution of permeability is not only a function of dilatancy but also of microcrack linkage importantly the anisotropic crack array within the samples causes a strong directional dependence of permeability

early development of karst systems 2 turbulent flow a simulation model developed to explore patterns of fracture enlargement within incipient limestone karst aquifers has been extended to turbulent flow in contrast to the highly selective passage enlargement that occurs early in cave network development under laminar flow the transition to turbulent flow results in more general passage enlargement leading to maze networks when initial fractures are large and hydraulic gradients are high these results support previously published hypotheses for the development of maze patterns including formation within structural settings that have created initially large fractures or within flow systems periodically inundated by flooding maze development is also favored under turbulent flow when passages are entirely water filled and where the groundwater flow system is long lived by contrast branched patterns are most common when passages become free surface subterranean streams because depression of the piezometric surface along main passages downcutting along main passages and possible infilling with sediment of side passages limit the sharing of discharge among interconnected fractures or bedding planes that promote maze development

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

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

early development of karst aquifers on percolation networks of fractures in limestone we have modeled flow and dissolution processes within percolation networks representing stochastic primary fracture systems in limestone at the beginning of karstification flow is evenly distributed on all fractures available as the system develops by dissolutional widening of the fractures preferred flow pathways evolve which attract more and more flow until at breakthrough the total flow rate increases dramatically these breakthrough times have been investigated with regard to their dependence on the initial fracture aperture width the dimension of the evolving karst aquifer hydraulic gradients connectivity of the percolation network and the chemical parameters such as higher order rate constants and exponents and equilibrium concentration they exhibit a behavior similar to that of breakthrough times for one dimensional conduits dreybrodt 1996 our results show that the structure of the evolving karst aquifer is determined by the initial geological setting however the final conduits are selected from competing pathways with potential breakthrough times close to each other whereby the details of the distribution of undersaturation with respect to calcite play an important role

distribution of brine in grain boundaries during static recrystallization in wet synthetic halite insight from broad ion beam sectioning and sem observation at cryogenic temperature we report observations from room temperature static recrystallization experiments annealing times from minutes to year of cold pressed synthetic coarse grained wet sodium chloride prepared by broad ion beam polishing and sem observations at cryogenic temperature to observe directly the brine in grain boundaries at all stages of annealing the majority of the brine in the samples is connected in 2d sections along grain boundaries another part of the brine is in isolated brine inclusion arrays along grain boundaries and in brine inclusions left behind by migrating brine filled grain boundaries most of these boundaries are mobile because the aggregate is coarsening we interpret that the boundaries without observable brine films 15 nm and brine inclusion arrays are healed and immobile evolution of grain boundary structure involves three major processes first dissolution on one side of the grain boundary and precipitation on the other side result ing in grain boundary migration second the development of facets formed by low index crystallographic planes of the grains bounding the grain boundary brine when both sides of a grain boundary are able to develop low index facets in a thick brine film the resulting impingement boundary is interpreted to be immobile and may prevent the new grain from migrating into a deformed neighbor when one side of a faceted boundary consists of low index crystallographic planes and the other side passively follows this faceted shape along irrational surfaces the boundary is mobile third the healing of grain boundary brine films producing solid solid grain boundaries without resolvable brine films

power law distributions of discharge mass and energy in river basins river networks constitute dissipative systems with many spatial degrees of freedom previous work by mandelbrot 1983 and bak et al 1987 1988 1990 suggests that such systems will follow power law distributions in their mass and energy characteristics it is shown that this is the case for river networks where the exponent in the distribution p x x x is approximately equal to 0 45 and 0 90 for discharge and energy respectively in the case of several networks analyzed in north america when these variables are calculated for each individual link throughout the drainage network an explanation of the values of is offered based on the fractal structure of rivers and on principles of energy expenditure in river basins

fractal structures as least energy patterns the case of river networks natural drainage networks like river basins exhibit fractal and multifractal properties this work shows that these properties evolve from arbitrary initial conditions by minimizing the local and global rates of energy expenditure in the system this suggests that many fractal structures may arise as a natural consequence of least energy dissipation requirements

experimental investigation of melt topology in partially molten quartzo feldspathic aggregates under hydrostatic and non hydrostatic stress continental collision results in deep burial of crustal rocks and their subsequent partial melting field relations of melt along zones of intense deformation suggest that partially molten rocks may play an important role in regional tectonics however subsequent deformation may erase the microstructures produced by the earlier deformation mechanisms inhibiting our understanding of the rheology of partially molten crustal rocks thus in this paper we report the results of an experimental study of the distribution of 2 5 vol melt in quartzo feldspathic aggregates of various grain sizes 2 5 5 10 10 16 and 26 31 m three types of samples were examined all with the composition of 60 wt albite 25 wt potassium feldspar 10 wt quartz and 5 wt biotite the first group included mineral powders annealed at 1000 c 1 0 gpa for c 100 h the second group included commercially hot pressed mineral powders which yielded c 25 vol glass cores of this material were also annealed at 1000 c 1 0 gpa for c 100 h the third group included cores of hot pressed material that were annealed at 1000 c 1 0 gpa for c 45 h then deformed all samples were quenched rapidly in order to examine the melt distribution wetting angles are very similar in both the hydrostatically annealed and the deformed samples analysis of melt pool orientations reveal that melt migrates away from grain boundaries normal to the maximum compressive stress direction in response to the applied non hydrostatic stress this response is easily seen in the coarser grained samples in which melt pools elongated parallel to the maximum compressive stress direction formed during deformation if these results extrapolate to naturally deformed rocks it will be important to consider the orientation of the state of stress in a region during syn magmatic deformation because of its effect on the melt distribution

a model for intergranular pressure solution in open systems abstract intergranular pressure solution ips represents a well known mechanism of bulk deformation and pore volume change especially in sedimentary rocks which has been documented in the field and reproduced in laboratory experiments theoretical descriptions of the process in terms of simple pressure solution creep laws can explain features such as grain size dependence of creep rates but have typically remained restricted to closed system conditions with negligible long range transport in the fluid phase and somewhat biased toward grain boundary diffusion controlled creep the recasting of the classical weyl rutter model of ips considered in this paper emphasizes open system conditions and the competition between diffusion and dissolution reaction rate processes the thermodynamic force which drives ips is expressed in terms of an effective grain boundary normal traction and a solute supersaturation this suggests the occurrence of a transition from ips to grain boundary healing at a certain level of supersaturation of the pore fluid although the process of healing is not studied here the explicit appearance of the solute concentration in the driving force highlights the coupling of the ips deformation process to the long range transport of dissolved material and the need to model the diagenesis of compacting sedimentary sequences accordingly the conceptual grain boundary model used in this paper is that of a fluid invaded grain to grain contact zone which is visualized to remain in a roughened state during continued ips the use of simple linear phenomenological rate laws for dissolution and grain boundary diffusion allows the ranges of rate control by dissolution or diffusion to be succinctly characterized in terms of the ratio of corresponding time constants the associated compaction behaviour is explored quantitatively in this paper by presenting solutions for the uniaxial and isotropic compaction creep strain vs time for a simple cubic packing of spheres

modeling three dimensional karst aquifer evolution using different matrix flow contributions summary we have developed the program package karstaquifer which simulates flow and transport in a three dimensional transient karst aquifer consisting of fractures and matrix elements the fractures can be enlarged by chemical dissolution of calcite increasing the secondary permeability of the karst aquifer boundary conditions for our model setup are guided by published benchmark models for karst aquifer evolution in two dimensions length and width with a 100 m high hydraulic head difference across the model domain responsible for relatively fast evolution of the aquifer we are interested in the effect of the third dimension on the evolution of the karst aquifer especially the effect of matrix flow with a matrix defined either as porous medium or as fine fracture system or both we first discuss our model results using a pseudo 3d setup to be able to directly compare results to the 2d benchmark scenarios published we then discuss real 3d models with a prominent fault located in the central part of the aquifer connecting input and output regions finally we replace the prominent fault with a statistical fracture diameter distribution our results compare well with existing 2d scenarios and the additional third dimension offers new insights into the evolution of karst aquifers especially the role of matrix flow under fixed head boundary conditions in their early phases can be studied in more detail

detrital modes of recent deep sea sands and their relation to tectonic setting a first approximation complete petrographic analyses of modern deep sea sands are surprisingly rare but are needed if problems such as the influence of tectonics on petrology or changes in petrology due to diagenesis are to be understood in ancient sandstones this paper is a first attempt using data from our own study of 80 sands plus data from the literature to establish a baseline for modern deep sea sands with which ancient sandstones can be compared we assigned sands to five plate tectonic categories each of which has a distinct average petrologic composition 1 basins associated with trailing edge continental margins q62f26l12 2 with leading edge continental margins either subduction q16f53l31 or 3 strike slip q34f39l27 4 back arc basins q20f29l51 5 fore arc basins q8f17l75 the amount and type of lithic fragments and the type of feldspar are particularly important discriminators the amount of quartz less so trailing edge and fore arc basins have quite distinctive compositions but back arc basins and basins near the two types of leading edge margins show some overlap and thus may be hard to differentiate in ancient sandstones

early development of karst systems 1 preferential flow path enlargement under laminar flow modeling of flow and solutional processes within networks of interconnected conduits in limestone aquifers indicates that enlargement occurs very selectively during the early stages of karst aquifer development under laminar flow if initial flow paths are uniform in size almost all enlargement occurs along a single set of connected conduits that lie along a direct path between recharge and discharge locations and are aligned along the hydraulic gradient with a sufficiently large variation in initial aperture widths enlargement occurs along the flow path offering the least resistance to flow but since flow rates in laminar flow are proportional to the fourth power of diameter but only linearly proportional to hydraulic gradient the preferentially enlarged set of fractures may follow an indirect path results disfavor earlier suggestions that nonselective cave patterns result from artesian flows at least under laminar flow conditions and that all passages should be competitive until the onset of turbulent flow

transient discontinuities revisited pseudotachylyte plastic instability and the influence of low pore fluid pressure on deformation processes in the mid crust abstract occurrences of pseudotachylyte cyclically introduced as melts into the outer hebrides thrust are demonstrably synkinematic with crystal plastic mylonites classical interpretations of these rock types as respectively products of pressure dependent frictional melting and thermally activated intracrystalline deformation create a paradox in that these processes are to a large extent mutually exclusive detailed microstructural and microcompositional analyses of host mylonites and primary and deformed pseudotachylyte were carried out by light and electron microscopy the ambient shear zone environment in which pseudotachylyte formed was determined to comprise temperatures in the order of 500 c and stresses of 140 210 mpa on which were imposed much higher transient stresses in response to heterogeneous non uniform flow the latter conditions are sufficient for the development of plastic instabilities in feldspar rich crust if pore fluid pressures are sufficiently low the latter is consistent with the absence of hydration during exhumation observed in the rocks under study low pore fluid pressure during thrust exhumation of deep crust enables activation of high strength ductile processes dominated by dislocation glide which may be a prerequisite to instability whereas other studies have demonstrated the possible occurrence of such melt generating instabilities it is believed that this study provides the first example in which the calculated potential for instability formation is consistent with the deformation microstructures and estimated pressure temperature conditions grain size reduction to produce ultramylonites dominated by grainsize sensitive flow is achieved by both deformation induced dynamic recrystallization and crystallization of instability generated melts

intrusion of lamprophyre dyke and related deformation effects in the host rock salt a case study from the loule diapir portugal abstract a rock salt lamprophyre dyke contact zone sub vertical ne sw strike was investigated for its petrographic mechanic and physical properties by means of anisotropy of magnetic susceptibility ams and rock magnetic properties coupled with quantitative microstructural analysis and thermal mathematical modelling the quantitative microstructural analysis of halite texture and solid inclusions revealed good spatial correlation with ams and halite fabrics the fabrics of both lamprophyre and rock salt record the magmatic intrusion plastic flow and regional deformation characterized by a nw se trending steep foliation ams and microstructural analysis revealed two deformation fabrics in the rock salt 1 the deformation fabrics in rock salt on the nw side of the dyke are associated with high temperature and high fluid activity attributed to the dyke emplacement 2 on the opposite side of the dyke the emplacement related fabric is reworked by localized tectonic deformation the paleomagnetic results suggest significant rotation of the whole dyke probably during the diapir ascent and or the regional tertiary to quaternary deformation

karst aquifer evolution in fractured rocks we study the large scale evolution and flow in a fractured karst aquifer by means of a newly developed numerical method a karst aquifer is discretized into a set of irregularly spaced nodal points which are connected to their set of natural neighbors to simulate a network of interconnected conduits in two dimensions the conduits are allowed to enlarge by solutional widening the geometric flexibility of this method along with a simplified model for the dissolution kinetics within the system water carbon dioxide calcite enables us to study both laminar and turbulent flow in a karst aquifer during its early phase of evolution a sensitivity analysis is conducted for parameters such as conduit diameter hydraulic pressure differences and recharge conditions along the surface of the aquifer and shows that passage evolution depends strongly on the recharge condition and the amount of water available under fixed hydraulic head boundary conditions an early single passage system develops under laminar conditions and is transformed into a maze like passage system after the onset of turbulence fixed recharge boundary conditions are more likely to result in a branchwork like passage system although the addition of distributed recharge may lead to a maze like system of secondary passages

microfabrics and 3d grain shape of gorleben rock salt constraints on deformation mechanisms and paleodifferential stress abstract the permian knauel and streifensalz formations z2hs1 and z2hs2 are main constituents of the gorleben salt dome northern germany and show different amounts and distributions of anhydrite the reconstruction of 3d halite grain shape ellipsoids reveals small grain size 3 4 0 6 mm and heterogeneous grain shapes in both formations the latter attributed to the polyphase deformation of the rock salt during diapirism the halite microfabrics of both formations indicate that strain induced grain boundary migration was active during deformation crystal plastic deformation of halite is further documented by lattice bending subgrain formation and minor subgrain rotation evidence for pressure solution of halite has not been found but cannot be excluded because of the small grain size the lack of lpo and the low differential stress 1 1 1 3 mpa as deduced from subgrain size piezometry anhydrite has been deformed in the brittle ductile regime by solution precipitation creep minor dislocation creep and brittle boudinage no continuous anhydrite layers are preserved and halite has acted as a sealing matrix embedding the disrupted anhydrite fragments prohibiting any potential migration pathways for fluids thus anhydrite should not have a negative effect on the barrier properties of the gorleben rock salts investigated in this study

structural changes during microstructural development in natural salt samples abstract this paper presents the microstructural and structural properties of two natural salt samples from iran and portugal their strength ductility behavior is explored by uniaxial compression experiments that demonstrate that the observed differences lie not only in the inhomogeneous composition of the samples and their different grain sizes but also in their internal microstructural inhomogeneities microstructural inhomogeneities and substructural changes were observed with the sem method scanning electron microscopy the thin section microscope investigations and the exafs extended x ray absorption fine structure spectroscopy ebsd electron backscattered diffraction analyses show maximum in the 100 or 110 directions in the inverse pole figure this demonstrates that recrystallization and grain growth processes took place together a weak 111 texture sometimes observed nearby indicates that residual stress is still present in the recrystallized sample comparison of the textural and structural results show that local structural rearrangements take place during textural development this is attributed to different orientations influencing the deformation and recrystallization of adjacent grains influencing the bulk final texture

experimental deformation of coarse grained rock salt to high strain the processes and deformation mechanisms e g dislocation creep pressure solution grain boundary sliding and recrystallization of rock salt are still a matter of debate in order to fill this gap high strain constriction experiments at 345 c atmospheric pressure and a strain rate of 10 7 s 1 have been conducted on natural halite cuboids 60 60 45 mm from the morsleben mine of northern germany most samples were almost single crystals and contain a small amount of smaller grains 10 26 the grain boundaries are decorated with fluid inclusions the experiments were stopped at different final strains ey z of 10 20 30 and 40 corresponding to a maximum strain ex range of 20 170 the halite is deformed by dislocation creep and the size of developed subgrains corresponds to the applied stress the combined schmid factor and subgrain boundary analysis indicate that slip was largely accommodated by the 110 slip systems with possible minor contribution by slip on the 100 slip systems some of the deformed samples show evidence of grain boundary migration in addition subgrains with small misorientations form that result in large cumulative misorientations within a single grain 40 however no subgrain rotation recrystallization is observed i e misorientation angles are 10 all the experiments show strain hardening suggesting that recrystallization by grain boundary migration was not extensive and did not reset the microstructure the experiments show that high finite strain in coarse grained relatively dry rock salt can be accommodated by dislocation creep without extensive dynamic recrystallization

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

on the rheologically critical melt fraction abstract with increasing melt fraction the strength of partially molten granite decreases from a value characteristic of solid competent rock to a value nearly equal to that of the melt previously published mechanical and microstructural data indicate that deformation in partially molten rocks often involves brittle processes thus the pressure in the melt is expected to be important in determining strength when the volume changes during deformation strength and fluid flow will be coupled by such parameters as permeability k storage capacity per unit volume or storativity s melt compressibility f grain size d fluid viscosity and strain rate experiments on brittle rock at low temperatures show that the strain rate at which the internal fluid pressure can be maintained constant is approximately proportional to k s an evaluation of published experimental data suggests that this relation also holds for partially molten granites indicating that the strength of these rocks depends on their transport properties since the permeability is related to below a critical melt fraction rcmf the melt pressure will change if deformation is not iso volumetric by assuming a power law relationship between k and we estimate that rcmf f d m 1 n 1 where m and n relate permeability to grain size and respectively

fluid distribution in grain boundaries of natural fine grained rock salt deformed at low differential stress qom kuh salt fountain central iran implications for rheology and transport properties we used a combination of broad ion beam cross sectioning and cryogenic sem to image polished surfaces and corresponding pairs of fractured grain boundaries in an investigation of grain boundary microstructures and fluid distribution in naturally deformed halite from the qom kuh salt glacier central iran at the scale of observations four types of fluid filled grain boundary can be distinguished by morphology from straight to wavy thickness from 5000 to 50 nm and the presence of fluid inclusions the mobility of the brine is shown after cutting the inclusions by broad ion beam bib in vacuum and fine grained halite forms efflorescence and precipitates on internal walls of inclusions at cryogenic temperature grain boundary brine is shown either as continuous film or in isolated inclusions the halite halite grain boundary between isolated fluid inclusions is interpreted to have formed by fluid assisted grain boundary healing preliminary experiments on the samples at shear stress conditions of natural salt glacier show very slow strain rates 7 4 10 10 s 1 and 1 10 9 s 1 which are less than expected for pressure solution creep both microstructures and deformation experiments suggest interfacial energy driven grain boundary healing and therefore rendering inactive the pressure solution creep in our samples this result disagrees with previous microstructural studies of the same sample which showed microstructural evidence for pressure solution and dislocation creep different explanations are discussed which imply that both healing and reactivation of grain boundaries are important in salt glaciers leading to heterogeneous distribution of deformation mechanisms and strain rates in both space and time

microstructural evolution of deformation modified primary halite from the middle triassic rot formation at hengelo the netherlands the microstructure of halite from the subhorizontal bedded main rot evaporite member at hengelo the netherlands akzo well 382 depth interval of 420 460 m was studied by transmitted and reflected light microscopy of gamma irradiation decorated samples primary microstructures compare favourably with those found in recent ephemeral salt pans large blocky fluid inclusion poor halite grains and elongated chevrons are interpreted to have formed in the saline lake stage while void filling clear halite is interpreted to have formed during the desiccation stage of the salt pan in addition in all layers the grains are rich in deformation related substructures such as slip bands and subgrains indicating strains of a few percent the study of gamma irradiation decorated thin sections shows that the main recrystallization mechanism is grain boundary migration grain boundary migration removes primary fluid inclusions and produces clear strain free new grains differential stresses as determined by subgrain size piezometry were 0 45 0 97 mpa the deformation of the salt layers is probably related to cretaceous inversion in the area

solution precipitation creep and fluid flow in halite a case study of zechstein z1 rocksalt from neuhof salt mine germany zechstein z1 rocksalt from the fulda basin from the immediate vicinity of the hessen potash bed is folded into tight to isoclinal folds which are cut by an undeformed 1 cm thick coarse grained halite vein microstructures were investigated in etched gamma irradiated thin sections from both the wall rock and the vein the lack of synsedimentary dissolution structures and the widespread occurrence of plate shaped and hopper grains in the wall rock suggests that the sedimentary environment was perennial lake deformation microstructures are in good agreement with solution precipitation creep process and salt flow under very low differential stress strength contrast between anhydrite rich and anhydrite poor layers caused the small scale folding in the halite beds the vein is completely sealed and composed mainly of euhedral to subhedral halite grains which often overgrow the wall rock grains those microstructures together with the presence of occasional fluid inclusion bands suggest that the crystals grew into a solution filled open space based on considerations on the maximum value of in situ differential stress the dilatancy criteria the amount of released fluids from the potash bed during metamorphism and the volume change it is proposed that the crack was generated by hydrofracturing of the rocksalt due to the presence of the salt metamorphic fluid at near lithostatic pressure

the orogenic superstructure infrastructure concept revisited quantified and revived the historical superstructure infrastructure concept s i expressed contrasts in structural style and metamorphic grade between shallow and deep orogenic levels two dimensional thermal mechanical models provide a quantitative explanation in terms of progressive crustal shortening and thickening phase 1 thermal relaxation and rheological weakening phase 2 and ductile flow at depth phase 3 results predict an upper crustal superstructure dominated by early steep structures separated across a subhorizontal high strain zone from a ductile infrastructure with late gently dipping structures this is consistent with observations from the western superior province these models can account for contrasts in structural style metamorphic grade seismic reflectivity and age between upper and lower crustal levels in contrast to conventional thrust tectonics models the revived s i model shows how young structures can form beneath older ones during progressive convergence thereby encouraging reassessment of standard seismic reflection interpretations

large strain shearing of halite experimental and theoretical evidence for dynamic texture changes abstract we report results from torsion experiments on polycrystalline halite nacl to shear strains 8 and observe a very complex texture evolution the same behavior was reproduced with polycrystal plasticity simulations suggesting that we capture the underlying mechanisms while crystal shapes gradually rotate into the shear plane crystal orientations change continuously and dynamic texture patterns evolve with increasing shear this is highly significant for ultra large deformation as for example implied from geodynamic modeling for the deep earth where seismic anisotropy patterns may develop and locally disappear again as material is deformed during convection the study also suggests that caution is required when interpreting deformation mechanisms from simple shear preferred orientation patterns

diffusion creep in feldspar aggregates experimental evidence a combination of mechanical and microstructural results for experimentally deformed albite aggregates of 2 10 m grain size indicates a regime of grain boundary diffusion creep that depends upon the presence of water temperature and strain rate at 900 c and 10 5 s 1 deformation occurs dominantly by recrystallization accommodated dislocation creep when the aggregates contain 0 2 wt water but by grain boundary diffusion creep when the aggregates contain 0 9 wt water experiments at other temperatures and strain rates indicate that fine grained aggregates with added water may go directly from cataclastic flow to grain boundary diffusion creep with increasing temperature or decreasing strain rate bypassing the field of dislocation creep microstructural evidence for grain boundary diffusion creep in the wet fine grained aggregates includes the development of rectangular grains rather than polygonal grains grain growth a very low average dislocation density open grain boundaries including pores and channels and the presence of overgrowths of a different composition on grains in a two plagioclase an1 and an79 aggregate additional evidence for diffusion creep in the wet fine grained aggregates is indicated by their similar microstructures and strengths when deformed at 600 and 1500 mpa in contrast dry feldspar aggregates deforming by dislocation creep show an increase in strength and a transition to semi brittle behavior at lower confining pressures grain boundary diffusion creep of feldspars may be common in naturally deformed rocks due to the ease of grain size reduction by both cataclasis and dynamic recrystallization

deformation and recrystallization mechanisms in actively extruding salt fountain microstructural evidence for a switch in deformation mechanisms with increased availability of meteoric water and decreased grain size qum kuh central iran microstructural study of rocksalt samples from an active salt fountain qum kuh central iran enabled to identify the relative contribution of different deformation mechanisms on extrusive salt flow the microstructural study combined reflected and transmitted light microscopy of gamma irradiated thin sections textural analysis of digitized microstructures and electron back scattered diffraction ebsd deformation microstructures record the strongly variable deformation conditions of salt flow in the diapiric system from the diapiric stem towards the distal part of the mature viscous fountain high stress deformation conditions typical for diapiric stems are recorded in the small subgrains within the porphyroclasts of all documented samples recovery and recrystallization due to divergent and decelerating flow associated with differential stress drop in the salt extrusion above the diapiric orifice is reflected by abundant growth band microstructures this study reveals also evidence for penetration of rainwater into the salt mass and documents the switch from the dominant dislocation creep into dominant solution precipitation creep from the upper part to the distal part of the fountain this deformation mechanism switch is provided by influx of meteoric water and grain size decrease likely controlled by subgrain rotation and grain boundary migration recrystallization

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

rheology of fine grained siliciclastic rocks in the middle crust evidence from structural and numerical analysis constitutive models to describe the rheology of the crust are based on a combination of indirect methods and many aspects are still unknown and controversial here we present a new method to quantify the rheology of fine grained siliciclastic rocks which are common in the middle crust and deform by solution precipitation processes we use a combination of structural analysis at different scales and a geomechanical model to develop a parameter estimation scheme to calculate rheological parameters at 350 400 8c and geologic strain rates the results of this study demonstrate that fine grained siliciclastic rocks in the middle crust have a newtonian viscous rheology approximately 10 times weaker than wet quartz this is in agreement with observed microstructures our results imply that the strength of polyphase quartz rich rocks located in the middle crust is much lower than predicted by conventional models based on flow laws for dislocation creep because fine grained siliciclastic rocks control the rheology of the middle crust in many sedimentary basins our results provide new quantitative parameters for geodynamic modelling in settings where dissolution precipitation creep is important d 2005 elsevier b v all rights reserved

spreading of tracer plumes through confined telogenetic karst aquifers a model summary to calculate spreading of a tracer or contaminant through an aquifer all details of the aquifer e g distribution of hydraulic parameters must be known this is not possible in nature to study the spreading of plumes through karst we have used a digital model of a confined karst aquifer at different stages of early karstification in these models all details such as fracture aperture widths their lengths and widths and the hydraulic boundary conditions are known therefore the flow velocity of water can be calculated in each fracture using this information a particle tracking method is employed to calculate the propagation and spreading of a plume caused by an instantaneous input pulse into selected regions of the aquifer from this information the time dependence of the outflow of particles from any selected region is obtained this function represents the transfer response function for an instantaneous dirac function input two digital karst models are designed in the first homogeneous one the aperture widths of the fractures are statistically distributed but of similar width in the second a coarse percolating net of prominent fractures with larger constant aperture width is embedded into the dense net of narrow fissures propagation of the plumes and the transfer response function are presented at the onset of karstification and at different times of karst evolution if particles are injected at the entrance of evolving karst channels propagating towards the output boundary tracer breakthrough times increase with increasing time of karst evolution until shortly before breakthrough of the karst conduit they drop to half of their maximal value with increasing evolution of the karst aquifer the hydraulic heads are redistributed and regions of low hydraulic gradients in the upstream side of the aquifer are created particles injected into fractures which have stopped dissolutional widening of their aperture widths and are located in regions of low gradient are kept in these regions for long times in the order of 100 years until they have propagated towards regions of high hydraulic heads where a fan like plume develops along the pathway of steepest gradient

rheological behaviour of synthetic rocksalt the interplay between water dynamic recrystallization and deformation mechanisms abstract the ductile deformation of rocks in nature can be greatly enhanced by the presence of water part of the water induced weakening of rocks at depth may come from fluid assisted deformation or recrystallization mechanisms that are absent in dry rocks in this study we investigate the effect of water on the rheological behaviour of rocksalt we focus on quantification of the contribution of individual deformation and recrystallization mechanisms to deformation we also aim to calibrate a flow law that incorporates the effect of all the relevant microphysical processes and hence more accurately describes the flow of rocksalt in nature for this purpose the mechanical behaviour and microstructural evolution of synthetic rocksalt samples that are similar except for differences in water content determined using ftir analysis are investigated the samples are deformed to natural strains of 0 07 0 46 at 50 mpa confining pressure strain rates of 5 10 7 1 10 4 s 1 and temperatures of 75 240 c resulting in flow stresses of 7 22 mpa the flow stress of samples with a water content below 5 ppm dry is higher than that of samples with a water content of 9 46 ppm wet at all strains under the investigated conditions the difference in flow stress can be explained as due to the operation of only work hardening dislocation creep without dynamic recrystallization in the dry material versus combined dislocation and solution precipitation creep plus fluid assisted grain boundary migration in the wet material the results allow us to calibrate a flow law for wet rocksalt that incorporates the effects of solution precipitation creep and fluid assisted grain boundary migration the results also suggest that strain localization in natural rocksalt is more likely to be localized due to fluid infiltration and associated rheological weakening than due to progressive removal of strain hardening substructure by grain boundary migration

deformation and recrystallization mechanisms in mylonitic shear zones in naturally deformed extrusive eocene oligocene rocksalt from eyvanekey plateau and garmsar hills central iran abstract microstructural processes in mylonitic shear zones from extrusions of eocene oligocene rocksalts from garmsar hills and eyvanekey plateau central iran are described and analyzed the halite samples were studied by transmitted light microscopy of gamma irradiated thin sections subgrain size palaeopiezometry of polished and chemically etched samples and texture measurements by electron backscatter diffraction ebsd the studied shear zones are thin using published flow laws the strain rate in the fine grained mylonites is about 10 10 l s which is in a good agreement with earlier in situ measurements on glacier salt flow rate

use of solution mined caverns in salt for oil and gas storage and toxic waste disposal in germany abstract the need for storage caverns for oil and gas and repositories for toxic chemical waste is increasing world wide rock salt formations are particularly suitable for the construction of cavities for such purposes owing to its favourable geomechanical properties rock salt remains stable over long periods of time without support and it can be shown that the geological barrier of the host rock remains intact for a remarkably long time safety analysis must be made for each proposed site based on site specific data the methods of doing this are well known and related technical recommendations exist in germany these recommendations apply to the planning construction operation and post operational management of salt caverns used for the underground disposal of hazardous wastes in particular geotechnical site specific safety verification as required by the government s technical regulations on wastes ta abfall under the section underground disposal is required this safety verification must cover the entire system comprising the waste the cavern and the surrounding rocks for this purpose geomechanical models have to be developed the steps which must be taken when carrying out geological engineering site explorations and when determining geotechnical parameters are discussed in addition recommendations are made for the design and construction of underground repositories for liquid filled caverns long term sealing from the biosphere is of particular interest in this instance it must be shown that the natural increase in pressure in the closed cavity due to long term convergence does not exceed the fracture pressure a special filled test scale 1 1 has been performed to study this

the migration of fluid filled grain boundaries in recrystallizing synthetic bischofite first results of in situ high pressure high temperature deformation experiments in transmitted light the effect of fluids on recrystallization behaviour is well known however the detailed microscale distribution of fluid in grain boundaries and the influence of fluid on grain boundary migration are still unresolved in this study in situ deformation experiments in transmitted light microscopy were undertaken as this allows continuous and direct observation of the whole range of processes involved in fluid assisted grain boundary migration a new see through deformation apparatus was developed to enable the control of fluid pressure bischofite containing small amounts of aqueous fluid was deformed at temperatures between 50 and 90 c over a range of fluid pressure from 0 5 to 1 mpa and strain rates of 5 10 6 to 1 10 4 s 1 the rates of grain boundary migration were measured at different temperatures and strain rates detailed observations during and after the deformation illustrate the evolution of migrating fluid filled grain boundaries and show that the incorporation of fluids from inclusions as well as their pinch off is dependent on the grain boundary velocity the thickness of the grain boundary and the size and shape of the inclusions direct evidence is presented for the contraction of the grain boundary fluids into isolated inclusions after equilibrium conditions are attained

deformation and recrystallization mechanisms inferred from microstructures of naturally deformed rock salt from the diapiric stem and surface glaciers of a salt diapir in southern iran abstract microstructures of three naturally deformed rocksalt samples from the deh kuyeh salt fountain in south iran were studied by electron backscatter diffraction to constrain deformation and recrystallization processes two samples came from the upper salt fountain glaciers and one from the diapiric stem lattice distortion and low angle boundaries in salt grains have intra crystalline misorientations described by rotations around low order crystallographic axes and are inferred to relate to dislocation creep and recovery misorientation analysis suggests that both easy and hard slip systems are responsible for grain distortions small grains have similar dimensions to subgrains which we interpret to mean that subgrain rotation recrystallization sgr is important many boundaries are quite lobate consistent with grain boundary migration gbm also being active bulges off of some large grains are related to the host by a tilt or twist boundary suggesting that gbm and sgr interacted to facilitate a bulge nucleation process idiomorphic grains occur particularly in the upper fountain surface glaciers samples and are less deformed internally than neighboring grains the grain and subgrain sizes in the sample from the diapiric stem are smaller than those in the upper salt fountain subgrain sizes suggest differential stresses were twice as large 2 mpa during deformation in the diapiric stem compared to the upper fountain the diapiric stem sample has greater intragranular distortion compared to the fountain samples furthermore the diapiric stem sample has a continuous grain boundary hierarchy suggesting a dominance of sgr whereas the upper fountain samples have different boundary hierarchy characteristics for boundary misorientations above and below 7 suggesting that gbm is limiting the sgr process grains are consumed by gbm before boundaries with misorientations 7 developed by sgr the increased importance of gbm relative to sgr in the upper fountain compared to the diapiric stem is consistent with the change in balance of the different recrystallization mechanisms expected as a function of lower stress magnitude in the upper fountain

simulation of the development of karst aquifers using a coupled continuum pipe flow model 1 this paper is intended to provide insight into the controlling mechanisms of karst genesis based on an advanced modeling approach covering the characteristic hydraulics in karst systems the dissolution kinetics and the associated temporal decrease in flow resistance karst water hydraulics is strongly governed by the interaction between a highly conductive low storage conduit network and a low conductive high storage rock matrix under variable boundary conditions only if this coupling of flow mechanisms is considered can an appropriate representation of other relevant processes be achieved e g carbonate dissolution transport of dissolved solids and limited groundwater recharge here a parameter study performed with the numerical model carbonate aquifer void evolution cave is presented which allows the simulation of the genesis of karst aquifers during geologic time periods cave integrates several important features relevant for different scenarios of karst evolution 1 the complex hydraulic interplay between flow in the karst conduits and in the small fissures of the rock matrix 2 laminar as well as turbulent flow conditions 3 time dependent and nonuniform recharge to both flow systems 4 the widening of the conduits accounting for appropriate physicochemical relationships governing calcite dissolution kinetics this is achieved by predefining an initial network of karst conduits protoconduits which are allowed to grow according to the amount of aggressive water available due to hydraulic boundary conditions the increase in conduit transmissivity is associated with an increase in conduit diameters while the conductivity of the fissured system is assumed to be constant in time the importance of various parameters controlling karst genesis is demonstrated in a parameter study covering the recharge distribution the upgradient boundary conditions for the conduit system and the hydraulic coupling between the conduit network and the rock matrix in particular it is shown that conduit diameters increase in downgradient or upgradient direction depending on the spatial distribution local versus uniform of the recharge component which directly enters the conduit system

structural micro structural and kinematic analyses of channel flow in the karmostaj salt diapir in the zagros foreland folded belt fars province iran abstract one of the main characteristic of the zagros foreland fold and thrust belt and the zagros foreland folded belt are wide distributions of surface extrusion from the hormuz salt diapirs this study examines the structure and kinematic of channel flow in the karmostaj salt diapir in the southwestern part of the zagros foreland folded belt this diapir has reached the surface as a result of the channel flow mechanism and has extruded in the southern limb of the kuh gach anticline which is an asymmetric decollement fold with convergence to the south structural and microstructural studies and quantitative finite strain rs and kinematic vorticity number wk analyses were carried out within this salt diapir and its namakier this was in order to investigate the structural evolution in the salt diapiric system the characteristics and mechanism of the salt flow and the distribution of flow regimes within the salt diapir and interaction of regional tectonics and salt diaprism the extruded salt has developed a flow foliation sub parallel to the remnant bedding recorded by different colors a variety of internal folds including symmetrical and asymmetrical folds and interference fold patterns shear zones and boudins these structures were used to analyze mechanisms and history of diapiric flow and extrusion the microstructures reveal various deformation mechanisms in various parts of salt diapir the measurements of finite strain show that rs values in the margin of salt diapir are higher than within its namakier which is consistent with the results of structural studies mean kinematic vorticity number wm measured in steady state deformation of diapir and namakier is wm 0 45 0 48 0 13 the estimated mean finite deformation wm values indicate that 67 8 pure shear and 32 2 simple shear deformation were involved the implications of which are discussed the vorticity of flow indicates that in the early stage of growth poiseuille flow was the dominate mechanism especially in the core of diapir with higher pure shear component relative to simple shear component whilst a couette flow at the margins of diapir is the dominate mechanism with higher simple shear component relative to pure shear component the obtained kinematic vorticity number reflects spatial partitioning of dominantly poiseuille flow in core and couette flow along edges of diapir these two mechanisms reflect a persistent flow governed by a simultaneous combination of pure shear and simple shear in a hybrid poiseuille coutte flow

geology and models of salt extrusion at qum kuh central iran profiles through the summit of a small nearly axisymmetric extrusion of oligocene and miocene salt and simple analogue models of it simulate the profiles of piles of ductile nappes extruded from convergent orogens the salt extrudes from a reactive diapir along a major strike slip fault at about 82 mm a 1 and rises 315 m above the central plateau of iran the salt has the distinctive smooth profile of a viscous fountain in which an asymmetric apron of allochthonous salt gravity spreads over its surroundings from a summit dome curtain folds developed in the source layer extrude from the diapir and are refolded by major recumbent folds with circumferential axes that simulate nappes minor flow folds with circumferential axes refold major folds in the top 10 50 m of surficial salt master joints 100 m long indicate brittle failure of dilated salt by regional stress fields tuned to the dimensions of qum kuh analytical and analogue models of viscous extrusions constrain the dynamic salt budget and a time of extrusion of at least 42 000 years new analogue models suggest that the number amplitude and spacing of major recumbent folds within the extruded salt and ductile nappe piles record the number amount and relative timing of fluctuations in the driving forces

extreme ductile deformation of fine grained salt by coupled solution precipitation creep and microcracking microstructural evidence from perennial zechstein sequence neuhof salt mine germany abstract microstructural study revealed that the ductile flow of intensely folded fine grained salt exposed in an underground mine zechstein werra salt sequence neuhof mine germany was accommodated by coupled activity of solution precipitation sp creep and microcracking of the halite grains the grain cores of the halite aggregates contain remnants of sedimentary microstructures with straight and chevron shaped fluid inclusion trails fits and are surrounded by two concentric mantles reflecting different events of salt precipitation numerous intra granular or transgranular microcracks originate at the tips of fits and propagate preferentially along the interface between sedimentary cores and the surrounding mantle of reprecipitated halite these microcracks are interpreted as tensional griffith cracks microcracks starting at grain boundary triple junctions or grain boundary ledges form due to stress concentrations generated by grain boundary sliding gbs solid or fluid inclusions frequently alter the course of the propagating microcracks or the cracks terminate at these inclusions because the inner mantle containing the microcracks is corroded and is surrounded by microcrack free outer mantle microcracking is interpreted to reflect transient failure of the aggregate microcracking is argued to play a fundamental role in the continuation and enhancement of the sp gbs creep during halokinesis of the werra salt because the transgranular cracks 1 provide the ingress of additional fluid in the grain boundary network when cross cutting the fits and 2 decrease grain size by splitting the grains more over the ingress of additional fluids into grain boundaries is also provided by non conservative grain boundary migration that advanced into fits bearing cores of grains described readjustments of the microstructure and mechanical and chemical feedbacks for the grain boundary diffusion flow in halite brine system are proposed to be comparable to other rock fluid or rock melt aggregates deforming by the grain boundary sliding gbs coupled deformation mechanisms

impact of solid second phases on deformation mechanisms of naturally deformed salt rocks kuh e namak dashti iran and rheological stratification of the hormuz salt formation abstract viscosity contrasts displayed in flow structures of a mountain namakier kuh e namak dashti between weak second phase bearing rock salt and strong pure rock salt types are studied for deformation mechanisms using detailed quantitative microstructural study while the solid inclusions rich dirty rock salts contain disaggregated siltstone and dolomite interlayers clean salts reveal microscopic hematite and remnants of abundant fluid inclusions in non recrystallized cores of porphyroclasts although the flow in both the recrystallized dirty and clean salt types is accommodated by combined mechanisms of pressure solution creep ps grain boundary sliding gbs transgranular microcracking and dislocation creep accommodated grain boundary migration gbm their viscosity contrasts observed in the field outcrops are explained by 1 enhanced ductility of dirty salts due to increased diffusion rates along the solid inclusion halite contacts than along halite halite contacts and 2 slow rates of intergranular diffusion due to dissolved iron and inhibited dislocation creep due to hematite inclusions for clean salt types rheological contrasts inferred by microstructural analysis between both salt rock classes apply in general for the dirty salt forming lower hormuz and the clean salt forming the upper hormuz of the hormuz formation and imply strain rate gradients or decoupling along horizons of mobilized salt types of different composition and microstructure

deformation related recrystallization processes abstract recrystallization is a common microstructural transformation that occurs during deformation metamorphism and diagenesis of rocks studies on minerals and rock analogues have demonstrated that a wide range of recrystallization mechanisms can occur the range of mechanisms is related to the various ways in which two basic processes grain boundary migration and new grain boundary formation combine to transform the microstructure two recent papers drury et al 1985 urai et al 1986 have proposed different schemes for the description of recrystallization mechanisms the purpose of this paper is to provide a unified framework for the description of mechanisms recrystallization mechanisms are divided into three main types rotation mechanisms which principally involve the formation of new grain boundaries migration mechanisms which principally involve grain boundary migration and general mechanisms which involve both basic processes a further distinction is made on the basis of the continuity of the microstructural transformation with respect to time each of the three main types of mechanism can be divided into a number of sub types depending on whether the processes of grain boundary migration new grain boundary formation and new grain formation occur in a discontinuous or continuous manner with respect to time as the terms continuous and discontinuous have been used in the metallurgical literature to signify the spatial continuity of the microstructural transformation the terms discontinuai and continual are used to refer to the temporal continuity of the transformation it is recommended that the following aspects should be specified if possible in a general description of recrystallization mechanisms 1 1 how do the basic processes combine to transform the microstructure 2 2 if new grain development occurs what is the development mechanism and does new grain formation occur in a continual or discontinuai manner 3 3 if grain boundary migration is involved in the transformation what is the migration mechanism i e fast solute escape migration slow solute loaded migration fluid assisted migration etc and is migration a continual or discontinuai process the application of the unified scheme is illustrated by reviewing studies that have provided detailed information on the recrystallization mechanisms involved the complicating effects of solid solution impurities dispersed second phase particles and grain boundary fluid films are also considered and it is demonstrated that variations in content of these types of impurity can significantly effect the types of recrystallization that occur in a given material

microcracks in rocks a review abstract in the past decade the number of studies about microcracks in rocks has rapidly increased this review of recent work concentrates on microcracks in rock as separate entities emphasizing microcrack morphogenesis kinematics dynamics population statistics and observational techniques cracks are produced when the local stress exceeds the local strength the local stress may be augmented by twin lamellae interactions kink bands and deformation lamellae stress concentrations at grain boundary contacts and around intracrystalline cavities local strength may be reduced along cleavage planes along grain boundaries and along any internal surface as a result of corrosion by chemically active fluids dislocations appear not to be a significant factor for crack nucleation below about 500 c in silicates spatial and temporal changes in temperature can also induce microcracking as a result of differential thermal expansion between grains with different thermoelastic moduli and thermal conductivities the amount of quartz in the rock has a significant effect on thermally induced microcracks because of its large and variable thermal expansivity the application of hydrostatic pressure between 100 and 200 mpa effectively closes most cracks but the closure may not be uniform if crack wall asperities exist hydrostatic pressure appears to stabilize cracks and make crack growth more difficult the number and average size of mechanically induced microcracks is greater in rock deformed at higher pressures the application of a deviatoric stress field on the boundaries of a rock mass results on a microscopic scale in a very complex stress system which greatly affects nucleation and propagation paths the relative amount of intragranular and intergranular cracking appears to depend upon mineralogy rock type and stress state the vast majority of stress induced microcracks in rocks appear to be extensional statistically they are predominantly oriented within 30 of the macroscopic maximum stress direction crack densities increase as macroscopic deviatoric stress increases above a threshold level crack size distributions may be either lognormal or exponential fracture in rock under compressive boundary loads is a result of the coalescence of many microcracks not the growth of a single crack some crack configurations are more favorable for coalescence than others as deviatoric stress increases and rock failure is approached the microcrack population changes spatially from random to locally intense zones of cracking away from the fault the crack density dies off rapidly to the background level a few grains away under lesser deviatoric stresses slow subcritical microcrack growth can occur as a result of stress aided corrosion at the crack tip the rate governing mechanism may be either the chemical reaction rate or the rate at which water can get to the crack tip important details still remain to be worked out