application of the microboudin method to palaeodifferential stress analysis of deformed impure marbles from syros greece implications for grain size and calcite twin palaeopiezometers abstract microboudinage structures developed within glaucophane are found in the calcite matrix of blueschist facies impure marbles from syros greece the presence of these structures enables the successful application of the microboudin method for palaeodifferential stress analysis which was originally developed for rocks with a quartzose matrix application of the microboudin method reveals that differential stress increased during exhumation of the marble the estimated maximum palaeodifferential stress values are approximately 9 15 mpa an order of magnitude lower than the values estimated using the calcite twin palaeopiezometer this discrepancy reflects the fact that the two methods assess differential stress at different stages in the deformation history differential stresses in the syros samples estimated using three existing equations for grain size palaeopiezometry show a high degree of scatter and no reliable results were obtained by a comparison between the results of the microboudin method and grain size palaeopiezometry

an assessment of dynamically recrystallized grainsize as a palaeopiezometer in quartz bearing mylonite zones abstract recrystallized grainsize has been measured in quartz and in some cases feldspar in about 200 samples from 22 mylonite zones from 3 discrete tectonic settings 1 1 supracrustal low temperature shallow dipping thrusts 2 2 deeper level major 100 km thrusts in high grade metamorphic rocks and 3 3 steeply dipping fault zones in granite within a low grade palaeozoic fold belt the concept of a steady state dynamically recrystallized grainsize largely unaffected by post creep processes e g static grain growth receives strong support especially from the microstructures and the independence of finite strain and grainsize in most mylonite zones however the usefulness of this grainsize for predicting stress magnitudes is limited by the apparently independent influence of metamorphic environment on grainsize the available theoretical and empirical stress grainsize relationships do not account for these effects the concept of a steady state grainsize and the ease of accurate measurement offer a potentially powerful method for predicting stress intensity during deformation predicted deviatoric stresses have been computed using twiss theoretical model for comparison with other crustal stress estimates and most samples fall in the range from 20 to 150 mpa in a few cases where discrete high strain mylonite zones occur within contemporaneously regionally deformed rocks the recrystallized grainsize indicates that stresses were 1 5 to 2 times higher within the zones there is a clear need for improved theoretical and or empirical stress grainsize relationships for quartz and other minerals before extensive further application of this technique

influence of humidity conditions on shear strength of clay rock discontinuities the shear strength of rock discontinuities strongly depends on the water content especially when the rocks contain clay materials to assess the decrease in the mechanical properties of clay infilled discontinuities due to water saturation a series of direct shear tests was performed using an advanced shear box that allows the injection of water into the discontinuity results show that both the friction coefficient and the cohesion decrease when the discontinuity is saturated overall the shear strength of the discontinuity is considerably reduced to approximately 50 of its original value this reduction has to be accounted for when conducting stability analyses of rock slopes dam foundations or underground openings

syntectonic development of a strain independent steady state grain size during mylonitization abstract michibayashi k 1993 syntectonic development of a strain independent steady state grain size during mylonitization tectonophysics 222 151 164 for a distance of greater than 50 km along the median tectonic line japan syntectonic recrystallization of quartz has resulted in the development of a strain independent steady state grain size within the core of the kashio shear zone that is also independent of rock type the mean grain size of quartz in recrystallized aggregates progressively decreases towards the shear zone core becoming stable at around approximately 37 m even though the strain increases within more strongly mylonitized rocks some variation of mean grain sizes may result from secondary effects due to hydrothermal activity associated with the median tectonic line despite the development of a steady state mean grain size individual grains were not stable as revealed by log normal grain size distributions consequently dynamic recrystallization and grain growth were competing processes that achieved a balance and hence resulted in the development of the steady state grain size the actual grain size that resulted probably depended on both the water content and strain rate as well as the flow stress approaching the centre of the shear zone mylonitic fabrics e g s c fabrics mica fish were established well before a steady state grain size was reached a steady state grain shape shape orientation and crystallographic fabrics may not be developed until even more mylonitization had occurred variable grain sizes result from heterogeneous deformation as a consequence of deformation partitioning even under a stable stress prior to the development of a steady state grain size consequently it should be determined whether a steady state grain size has been achieved within a shear zone before the grain size is used as a paleopiezometer

influence of deformation conditions on the development of heterogeneous recrystallization microstructures in experimentally deformed carrara marble recrystallized grains are potentially useful as indicators of palaeostress in naturally deformed rocks providing that well calibrated relationships palaeopiezometers exist between the recrystallized grain size and stress rocks can exhibit microstructures that are heterogeneous that is containing recrystallized as well as deformed grains and showing subgrains within grains that differ in size and character from the grain core to the mantle previous studies on palaeopiezometers only rarely took into account such heterogeneous microstructure we used electron backscattered diffraction ebsd to accurately quantify the heterogeneous microstructures in experimentally deformed carrara marble flow stress 15 85 mpa temperature 700 990 8c and natural strain 0 15 0 90 the sizes of bulges recrystallized grains and deformed grains have been measured we found that the overall character of the microstructures varies as a function of deformation conditions in heterogeneous samples showing core mantle microstructures the sizes of the bulges and recrystallized grains are independent of strain and show an inverse dependency on stress the recrystallized grains have been found to nucleate at grain boundary bulges our study illustrates that very different microstructures may develop in relation to the complexity of the recrystallization mechanisms we therefore suggest that piezometers should be calibrated and applied for a single type of overall microstructure

a modified hoek brown failure criterion for anisotropic intact rock abstract the hoek brown criterion parameters c i m i and s are significantly influenced by the strength anisotropy of intact rock in the present study the criterion was modified by incorporating a new parameter k to account for the effect of strength anisotropy thus being able to determine the strength of intact anisotropic rock under loading in different orientations of the plane of anisotropy the range of the parameter k for the rocks tested has been analytically investigated by carrying out triaxial tests in different orientations of the foliation plane the proposed modification was studied for metamorphic rocks gneiss schist marble but could also be applied to other rock types exhibiting inherent anisotropy e g sedimentary as well as igneous rocks the proposed modified criterion is intended for use for prediction of strength of intact rock but can also be extended to rock masses

true triaxial stresses and the brittle fracture of rock this paper reviews the efforts made in the last 100 years to characterize the effect of the intermediate principal stress 2 on brittle fracture of rocks and on their strength criteria the most common theories of failure in geomechanics such as those of coulomb and mohr disregard 2 and are typically based on triaxial testing of cylindrical rock samples subjected to equal minimum and intermediate principal stresses 3 2 however as early as 1915 boker conducted conventional triaxial extension tests 1 2 on the same carrara marble tested earlier in conventional triaxial compression by von karman that showed a different strength behavior efforts to incorporate the effect of 2 on rock strength continued in the second half of the last century through the work of nadai drucker and prager murrell handin wiebols and cook and others in 1971 mogi designed a high capacity true triaxial testing machine and was the first to obtain complete true triaxial strength criteria for several rocks based on experimental data following his pioneering work several other laboratories developed equipment and conducted true triaxial tests revealing the extent of 2 effect on rock strength e g takahashi and koide michelis smart wawersik testing equipment emulating mogi s but considerably more compact was developed at the university of wisconsin and used for true triaxial testing of some very strong crystalline rocks test results revealed three distinct compressive failure mechanisms depending on loading mode and rock type shear faulting resulting from extensile microcrack localization multiple splitting along the 1 axis and nondilatant shear failure the true triaxial strength criterion for the ktb amphibolite derived from such tests was used in conjunction with logged breakout dimensions to estimate the maximum horizontal in situ stress in the ktb ultra deep scientific hole

differential stress strain rate and temperatures of mylonitization in the ruby mountains nevada implications for the rate and duration of uplift kno ledge of the m agnitude of the differential stress during the formation of mylonitic rocks provides constramts on mechanical and thermal models for the exhumation of the metamorphosed footwalls of major low angle detachment faults we have analyzed the differential flow stress during the mylonitization of quartzose rocks in the ruby mountains nevada using grain size piezometers and kinetic laws for grain g owth quartzites from mylonitic shear zones in lamoille canyon and secret creek gorge have grain sizes of 91 151 m and 42 64 m respectively the peak temperature during mylonitization was 630 i 50 c and analysis of grain growth kinetics indicates that mylonitization continued during cooling to temperatures s450 c quartz grain size piezometers suggest that the mylonitization occurred under differential stresses crl cr3 of 38 64 mpa or maximum shear stresses of 19 32 mpa extrapolation of quartzite flow laws indicates that the mylonitization occurred at strain rates between 10 10 and 10 13 1 arguments presented m the paper suggest that the likely range of strain rates is 10 11 to 10 12 1 these strain rates are compatible with displacement rates of the order of 23 mm yr l along a 1 5 km thick simple shear zone such a shear zone dipping 15 would produce an uplift rate of 5 8 km m y 1 and a horizontal extensioo rate of 22 km m y l this uplift rate indicates that midcrustal mylonitic rocks could have been lifted up along a 1 5 km thick simple shear zone dipping 15 in 2 6 m y

influence of water content and anisotropy on the strength and deformability of low porosity meta sedimentary rocks under triaxial compression abstract a reduction of uniaxial compressive strength ucs by the presence of water has been ascertained in many sedimentary rocks and even some metamorphic rocks experimentally this paper reports and discusses the influence of water content and anisotropy on the strength and deformability of two meta sedimentary rocks by triaxial compressive tests before conducting the triaxial tests the physical properties of meta siltstone and meta sandstone specimens have been carefully examined the water contents of both tested rocks are very low for instance 0 17 for meta siltstone and 0 10 for meta sandstone the porosities of the tested rocks are analyzed by the technique of mercury intrusion porosimetry mip it shows that the meta sedimentary rocks have very low porosity 0 18 for meta siltstone and 0 53 for meta sandstone on average the thin section analysis reveals that the meta siltstone contains more hydrophilic substances such as clay minerals than the meta sandstone and both two meta sedimentary rocks are characterized by distinct beddings and laminae even though the water contents of two tested rocks are very low they significantly influence the triaxial compressive strength and deformability the reduction of strength by water content is found to be related to a reduction of friction angle in the mohr coulomb failure criterion while a reduction of mi value in the hoek brown failure criterion on the other hand the influence of water on deformability of tested rocks is reflected as a reduction of young s modulus and increase of poisson s ratio which indicates that the wet meta sedimentary rocks will deform more than that of the dry ones under the same stress condition the experimental studies show that the anisotropy associated with bedding in rock specimens plays a weakening effect on the triaxial compressive strength for both tested rocks appearing more severely for meta siltstone in general the triaxial compression strength of rock specimens with transverse bedding planes is higher than the ones with longitudinal bedding planes no matter for meta siltstone or meta sandstone both dry and wet conditions under the same confining stress with regard to the stiffness both the tangent and secant young s moduli of the two tested rocks with transverse bedding are less than the ones with longitudinal bedding appearing more conspicuously for the meta siltstone the paper also discusses the axial strain calibration by two different measurement techniques one by the linear variant difference transducer lvdt technique and the other one by axial strain gages it shows that the axial strain ratio coefficient k elvdt estrain decays with the deviator stress in our present study the secant modulus estrain is usually about 1 4 1 8 times of elvdt at the peak strength point the correlation between mechanical properties and physical properties of the two tested rocks are also discussed in the paper

fracture strength of tourmaline and epidote by three point bending test application to microboudin method for estimating absolute magnitude of palaeodifferential stress abstract three point bending tests are conducted on millimetre scale tourmaline and epidote samples at room temperature and pressure to determine fracture strengths suitable for use with the microboudin method of palaeostress analysis the fracture strength of the samples is obtained from the weibull scale and shape parameters using a size effect model three different size effect models are evaluated and it is found that the effective length model is the most appropriate for describing the fracture strength of tourmaline and epidote based on geological constraints the palaeodifferential stresses determined by this method for samples from wadi tayin sultanate of oman greenbushes australia and four high pressure metamorphic belts in japan are in the range of 10 300 mpa

viscoplasticity of polycrystalline olivine experimentally deformed at high pressure and 900 c abstract we have performed tri axial compression experiments on olivine aggregates at 900 c and at a confining pressure of 300 mpa in a high resolution gas medium mechanical testing apparatus deformation at two different constant strain rates 1 1 10 5 s 1 and 3 4 10 4 s 1 yields continuous hardening reaching maximal differential stresses of 930 and 1076 mpa respectively before sample failure at ca 10 strain the deformed samples were characterized by electron backscatter diffraction ebsd and transmission electron microscopy tem crystallographic preferred orientations cpo are weak but reveal an alignment of the 010 axes around the compression direction and some concentration of 001 and 100 axes normal to it tem observations confirm plastic deformation by dislocation glide with both 001 and 100 burgers vectors electron tomography performed for the first time on deformed fined grained olivine shows that 001 dislocations glide extensively on 110 and 130 planes in complement to the 010 and 100 glide planes often reported at high temperatures 100 dislocations glide mostly on 010 but 011 and 041 planes are also activated the experimental cpo and relative activity of slip systems are well reproduced by viscoplastic self consistent simulations in which all 100 and 001 slip systems have similar strengths they are also consistent with olivine cpo from natural samples deformed at low temperature comparison of the present mechanical results to those obtained for olivine single crystals at similar conditions shows that at low temperature below 1100 c and high stress 300 mpa polycrystalline olivine has a more complex mechanical behavior than single crystals however both datasets advocate for a much weaker dry mantle lithosphere than previously thought

forsterite to wadsleyite phase transformation under shear stress and consequences for the earth s mantle transition zone we have studied the phase transformation of forsterite to wadsleyite under shear stress at the earth s transition zone pressure and temperature conditions two step experiments were performed using a multi anvil press first we hot pressed iron free forsterite at 6 or 11 gpa and 1100 c then we deformed a slab of this starting material using a direct simple shear assembly at 16 gpa and 1400 c for 1 15 35 40 or 60 min both the starting material and the deformed samples were characterized using optical and scanning electron microscopy including measurements of crystal preferred orientations cpo by electron back scattered diffraction ebsd transmission electron microscopy tem and fourier transform infrared spectroscopy ftir the phase transformation occurs very rapidly in less than 1 min and metastable forsterite relics are not observed after deformation the grain size of wadsleyite is slightly smaller than the forsterite starting material the water contents obtained from ftir analyses in forsterite and wadsleyite are 65 124 wt ppm h2o and 114 736 wt ppm h2o respectively which are well below water solubility at similar conditions in the presence of free water wadsleyite aggregates display weak cpo patterns with 1 0 0 axes concentrated at low angle to the shear direction 0 1 0 axes perpendicular to the shear plane and nearly random 0 0 1 axes only a few dislocations were observed in wadsleyite with tem this observation is consistent with the assumption that most dislocations formed during the initial high stress stages of these stress relaxation experiments were consumed in the phase transformation probably enhancing the transformation rate cpo patterns vary as a function of the water content with increasing water content the density of 1 0 0 axes parallel to the shear direction decreases and the density of 0 0 1 axes increases viscoplastic self consistent modeling of cpo evolution using previously reported glide systems for wadsleyite i e 1 0 0 0 k l and 1 2 111 101 cannot reproduce the measured cpo unless the 0 0 1 0 1 0 system for which dislocations have not been observed by tem is also activated in addition wadsleyite grain growth suggests the participation of diffusion assisted processes in deformation calculated anisotropies for p and s waves using measured cpo are always below 1 this very low anisotropy is due to both the low finite strain achieved in the experiments which leads to weak wadsleyite cpo and to the diluting effect of added majorite the present experiments emphasize the importance of stress grain size evolution and water content in the forsterite to wadsleyite phase transformation and subsequent deformation in the transition zone

automatic grain boundary detection and grain size analysis using polarization micrographs or orientation images abstract a simple procedure for creating grain boundary maps from petrographic thin sections termed the lazy grain boundary lgb method has been devised it is based on a set of macro commands programmed for nih image a public domain image processing software the grain boundary detection is based on gradient filtering the procedure makes use of multiple input images sets of regular polarized micrographs or where possible orientation misorientation images on each image of a given input set only the most significant grain boundaries are detected and by combining those a single grain boundary map is obtained image models and criteria for grain boundary identification are discussed briefly the principal aim of the lgb method is to facilitate the production of large grain boundary maps containing several thousand cross sectional areas to provide statistically valid samples for grain size analysis a section of black hills quartzite was used to test the lgb method five different input sets were prepared and used for automatic lgb analysis one set was additionally used for an interactive analysis and for a manual tracing from all seven grain boundary maps the 2 and 3 d grain size distributions were calculated the results are compared and the different image sets and procedures are rated for precision over and undersegmentation and speed of preparation

water absorption process effect on strength of ayazini tuff such as the uniaxial compressive strength ucs flexural strength and freeze and thaw effect tuffs have been used as a construction material possibly since ancient times in afyonkarahisar turkey there are numerous buildings constructed by tuff tuff has been a local construction material during the roman seljuk and ottoman periods even though tuffs have relatively low durability and low strength values compared to marble etc they have survived with no major deterioration failures on many historical buildings it has also been preferred because of its high porous texture lightweight and easy shaping and process properties in the building sector naturally it would be easily affected by water and humidity because of its porous structure however having this kind of structure leads to poor durability properties due to keeping water in it the main objective of this study was to evaluate the physical and mechanical properties of the tuff quarried from the region and possible water effect which may lead to degradation of its strength and durability of the material thereby shortening the life span of the building structure used samples which were tested after exposing to water and the freeze and thaw effects were measured at a certain time in this study uniaxial compressive strength and flexural strength tests were conducted on test samples the test results indicate that water may deteriorate the tuff s strength properties and durability of the materials in due time

influence of large scale initial oceanic mixed layer depth on tropical cyclones abstract the influence of spatial variations of the oceanic mixed layer depth omld on tropical cyclones tcs is investigated using a coupled atmosphere ocean model the model consists of a version of the naval research laboratory limited area weather prediction model coupled to a simple 2 layer ocean model interactions between the tc and the ocean are represented by wind induced turbulent mixing in the upper ocean and latent and sensible heat fluxes across the air sea interface four numerical experiments are conducted with different spatial variations of the unperturbed omld representing idealizations of broad scale patterns observed in the north atlantic and north pacific oceans during the tropical cyclone season in each the coupled model is integrated for 96 h with an atmospheric vortex initially of tropical storm intensity embedded in an easterly mean flow of 5 m s 1 and located over an oceanic mixed layer that is locally 40 m deep the numerical solutions reveal that the rate of intensificatio

dissolution solution transfer diffusion versus fluid flow and volume loss during deformation metamorphism dissolution and solution transfer during deformation metamorphism are controlled by the partitioning of deformation into progressive shearing and shortening components progressive shearing is readily accommodated by slip on the planar crystal structure of phyllosilicates and graphite without accumulating dislocation density gradients across grain boundaries progressive shortening is accommodated by the cores of most other minerals including sulphides these minerals develop strain and hence dislocation density gradients on their rims due to progressive shearing along grain boundaries these gradients are particularly large when the mineral abuts phyllosilicate or graphite the resulting chemical potential gradients between the core and rim drive dissolution causing removal of the highly strained grain margins removal of dissolved material by solution transfer is aided by the geometry of shearing of phyllosilicates and graphite around other grains in an active anastomosing foliation interlayers and interfaces on boundaries lying at a low angle to the direction of shearing and oriented relative to the sense of shear such that they can open gape by small amounts water present in these interlayer spaces becomes destructured considerably enhancing diffusion rates along the foliation penetrative volume loss especially in deforming metamorphosing pelitic rocks is large at all metamorphic grades increasing and becoming more penetrative with depth to at least the transition into granulite and eclogite facies transference of material by fluid flow from deep to high levels in the earth s crust is precluded because thousands to tens of thousands of rock volumes of fluid are required necessitating continual recirculation of fluid from shallow to deep crustal levels in one large or several small sets of cells unless some extremely large scale form of fluid channelling is possible reassessment of diffusion mechanisms and hence rates during deformation and pervasive foliation generation in large volumes of rock where fluid channeling cannot provide enough fluid indicates that diffusion can proceed with sufficient rapidity that massive recirculation of fluid is no longer required the amount of fluid can be reduced sufficiently to allow large volume losses by a one way flow of fluid to the earth s surface in deforming metamorphosing environments where the fluid pressure equals or exceeds the hydrostatic pressure deformation partitioning controlled dissolution progressively changes the bulk chemistry of a rock containing phyllosilicates or graphite during deformation metamorphism because matrix minerals other than phyllosilicates and graphite are preferentially removed the large size of porphyroblasts if present tends to preserve them from dissolution hence the bulk chemistry operative during subsequent porphyroblast growth can have changed considerably from that operative when the first porphyroblasts grew in rocks in which bedding is still well preserved

influence of water content on the strength of rock water content is one of the most important factors influencing rock strength considerable research has been carried out to investigate rock strength under both dry and water saturated conditions according to these results the petrophysical properties of rocks decrease with increasing moisture and this can result in an increase in the mechanical compliance in some cases in several cases the strength decrease is remarkable after only 1 water saturation for rock mechanics and rock engineering projects it is strongly recommended that the dry uniaxial compressive strength is used for the purposes of strength classification while for the actual engineering design it is essential to establish the wet strength and ideally the water sensitivity of the rock in order to asses their potential change in strength and deformability the goal of this paper is to show a method for estimating the sensitivity of sandstone rocks to water content using the published data

matrix deformation mechanisms in hp lt tectonic melanges microstructural record of jadeite blueschist from the franciscan complex california abstract exhumed high pressure low temperature metamorphic melanges of tectonic origin are believed to reflect high strain accumulated in large scale interplate shear zones during subduction rigid blocks of widely varying size are embedded in a weak matrix which takes up the deformation and controls the rheology of the composite the microfabrics of a highly deformed jadeite blueschist from the franciscan complex california are investigated to help understand deformation mechanisms at depth the specimen shows a transposed foliation with dismembered fold hinges and boudinage structures several generations of open fractures have been sealed to become veins at high pressure metamorphic conditions the shape of these veins frequently restricted to specific layers indicates distributed host rock deformation during and after sealing small cracks in jadeite and lawsonite are healed with tiny quartz inclusions aligned along the former fracture surface large jadeite porphyroblasts show strain caps and strain shadows open fractures are sealed by quartz and new jadeite epitactically grown on the broken host monophase glaucophane aggregates consist of undeformed needles with a diameter between 0 1 and 2 m grown after formation of isoclinal folds only quartz microfabrics indicate some stage of crystal plastic deformation followed by annealing and grain growth aragonite in the latest vein generation shows retrogression to calcite along its rims the entire deformation happened under hp lt metamorphic conditions in the stability field of jadeite and quartz at temperatures between 300 and 450 c and pressures exceeding 1 1 4 gpa the microfabrics indicate that dissolution precipitation creep was the predominant deformation mechanism accompanied by brittle failure and vein formation at quasi lithostatic pore fluid pressure this indicates low flow strength and combined with high strain rates expected for localized deformation between the plates a very low viscosity of material in the interplate shear zone at a depth 30 45 km

dilatancy brittle strength and anisotropy of foliated rocks experimental deformation and micromechanical modeling 1 triaxial compression experiments were performed on the four mile gneiss the biotite foliation in the four mile gneiss results in dilatancy and strength anisotropies which become more pronounced with increasing confining pressure microstructural observations indicate that when there is high resolved shear stress on the macroscopic foliation dilatancy arises from extensile microcracks nucleated by frictional slip on biotite grains evolution of crack geometry and coalescence are also influenced by the biotite foliation motivated by these observations a damage mechanics model based on sliding wing cracks was adopted to analyze the anisotropic development of dilatancy and brittle fracture frictional coefficients for the sliding cracks are inferred to be comparable to those of cleavage surfaces of biotite the strength anisotropy data of the four mile gneiss can be explained by the variation of the initial damage with the foliation angle the damage derives from a set of preexisting microcracks with random orientation and a set of cleavage cracks in mica grains preferentially oriented along the foliation angle hence the initial damage is higher for the intermediate angles and consequently the strength is somewhat lower the observation that the mechanical strengths of a variety of foliated rocks decrease with increasing mica content can be explained by the same model with the implication that the initial damage and mica content are linearly related the mechanical and microstructural data show that dilatancy anisotropy may significantly influence the progressive development of borehole breakout and strain localization

strain and shape fabric variations associated with ductile shear zones abstract the foliated and compositionally banded granitic orthogneisses in the central core of the maggia nappe a lower pennine basement nappe of the central swiss alps are shown to be the sheared equivalent of late hercynian age granitic intrusions these ductile shear zones show mineral assemblages in amphibolite facies are alpine in age and form an anastomosing network enclosing remnant lozenge shaped pods of relatively undeformed rock the foliation developed within the shear zones concomitantly with a change in shape of quartz grain aggregates from initially equidimensional through tear drop shapes to ribbon like aggregates these shape changes occurred by intracrystalline glide together with intercrystalline slip on deformation induced planar surfaces

multi approach stability analyses of large caverns excavated in low angled bedded sedimentary rock masses in singapore abstract the first commercial underground rock caverns for hydrocarbon storage in south east asia the jurong rock caverns project jrc project have recently been completed in singapore the storage capacity of 5 caverns is 1 47 million cubic meters and 3 5 million cubic meters of rocks were excavated in this project geologically it was excavated in low angled bedded meta sedimentary mudstone pyroclastic rocks and sandstone although traditional arch roofed style excavations are typical for tunnel and cavern for stability condition flat roofed profiles tend to form in low angle stratified sedimentary rock mass in this study the stability of such flat roofed tunnel and cavern with structurally controlled stability was analyzed using geotechnical classification systems including the stability graph method analytical voussoir techniques and numerical models accordingly and once presented the main features of the project characterization of the rock masses is presented some classification system approaches providing a convenient but probably over estimated support and reinforcement recommendation are illustrated then basic wedge stability analysis is briefly illustrated voussoir analogue techniques are applied to unsupported cavern profiles showing instability but clear stability for the supported case discontinuous models of the final designed cavities are presented showing a good agreement with indicative measurements on place and stress distributions associated with the excavation sections are analyzed using examine2d to show that abutment relaxation was unlikely to occur in jrc project the study shows that classification systems are useful tools but application of analytical techniques and numerical models contribute to a better understanding of the excavation and reinforcement process

effect of fluid pressure on rock compressive failure in a nearly impermeable crystalline rock implication on mechanism of borehole breakouts abstract we conducted laboratory true triaxial experiments in the nearly impermeable pohang rhyolite to investigate failure mechanisms under dry and wet rock conditions under dry conditions prismatic specimens were jacketed all around to prevent confining fluid penetration under wet conditions one pair of the specimen faces was left unjacketed and in direct contact with the confining fluid kerosene applying the least principal stress in an attempt to simulate the case of an unlined borehole wall in both testing setups the true triaxial compressive strength for a given least principal stress increases significantly as the intermediate principal stress rises the unjacketed rhyolite strength is however only 60 to 85 of the strength under dry conditions depending on the magnitude of the intermediate principal stress in dry rhyolite the failure process begins upon dilatancy onset followed by microcrack localization and ending in a steeply dipping shear fracture on the other hand brittle fracture in wet specimens occurs almost immediately after the onset of dilatancy by the development of one or more through going extensile fractures subparallel and adjacent to one of the unjacketed faces resembling the extensile cracks leading to borehole breakouts in crystalline rocks we infer that upon dilatancy the confining fluid intrudes and quickly propagates newly opened stress induced microcracks subparallel to the unjacketed faces leading to early failure

flow stresses from microstructures in mylonitic quartzites of the moine thrust zone assynt area scotland recrystallized grain sizes subgrain sizes and dislocation densities of quartz grains in quartzose mylonitic rocks have been examined using optical and transmission electron microscopy tem the samples come from the moine thrust zone in the assynt district scotland they had been studied previously and described in detail with respect to their structural position in relation to the various thrusts in the region and to their preferred orientation stresses were derived from these samples using empirical and theoretical equations relating flow stress to the scale of the microstructures the stresses determined 43 244 mpa from recrystallized grain size 9 13 mpa from etched subgrain size 50 95 mpa from tem scale subgrain size and 75 147 mpa from dislocation density are not constant in individual samples simultaneous formation of the quartz fabrics and of the dynamically recrystallized grains during the period of mylonitization may have occurred under flow stresses ranging from 43 to 244 mpa a later dynamic recovery event reset subgrain sizes and dislocation densities to a constant value for each microstructure throughout the area there is insufficient empirical information available on the flow stress subgrain size relationship and on the effects of annealing recovery and annealing recrystallization to allow for a more detailed interpretation recrystallized grain size is still the most easily measured microstructural feature and the relationship of recrystallized grain size to flow stress has a sounder experimental basis than subgrain size or dislocation density the effect of chemical environment on the behaviour of all the microstructures is still unknown

progress in microboudin method for palaeo stress analysis of metamorphic tectonites application of mathematically refined expression abstract the microboudin method for palaeo stress analysis is mathematically refined by incorporating the recently proposed shear lag model which describes the relationship between stress distribution along a fibre embedded within an elastic matrix and the far field differential stress applied to the matrix the refined probability density function of fractured fibres g with respect to the aspect ratio of the fibre r and the stress parameter is given by g r 1 exp m 1 m r m e f e q m 1 1 e q e f 1 cosh ar m where eq and ef are the elastic constants of the matrix and fibre m is the weibull modulus of the fibre material and a is a constant the stress parameter is defined as 0 s where 0 is the far field differential stress applied to the matrix and s is the modal fracture strength of the fibre material at r 1 this method is applied to tourmaline and piemontite boudins in quartzose rocks from six areas and it is revealed that the probability density function adequately models the proportion of boudinaged tourmaline and piemontite grains the value of is determined for each sample allowing 0 to be determined by this method when s is known

the role of stress in ductile deformation abstract the concept of progressive ductile deformation has previously been discussed mainly in kinematic terms little attention has been paid to the principal stresses that control the formation of ductile deformation patterns many deformation patterns of rocks may have been created in a stress field of stable orientation an equation derived here directly links the orientation of the major axis of deviatoric stress to the stretch and rotation components of plane isochoric deformation in isotropic rocks estimations of rotation and stretch of finite strain ellipsoids may therefore aid the recovery of palaeostress axes using a nomogram introduced here the inclination of the major principal deviatoric stress axis with respect to a reference plane controls both the particle movement paths and mode of progressive deformation the deformation tensor obtained by integrating the rate of displacement or velocity gradient equations is first expressed in time dependent terms comprising only the normal and shear components of the strain rate tensor mohr s equations of stress can then be used to link strain rates to the major principal stress responsible for them the rate of progressive deformation is determined by the rheology of the deforming rocks and the magnitude of the deviatoric stress this derivation yields a time dependent deformation tensor which is expressed in terms of the dynamic viscosity and the magnitude and orientation of the major deviatoric stress with respect to a reference plane the significance of this deformation tensor is illustrated by forward modelling using computer graphics these allow the progressive deformation of a unit volume of rock in response to deviatoric stresses of various stable orientations to be visualized

effect of layer orientation on the failure of layered sandstone under brazilian test conditions abstract the experimental research in this paper focuses at macro scale on the effect of the layer orientation on failure strength and fractures induced by the brazilian tensile test for one particular sandstone sandstone from modave in the south of belgium the variation in the strength the applied energy and the failure pattern are examined as a function of the inclination angle between the layer plane and the loading direction for each sample the length of fractures parallel to the layers as well as corresponding to other directions is measured for the layered sandstone in this study the transition angle range is determined whereby the relative importance of both types of fractures switches

theories and applicability of grain size piezometers the role of dynamic recrystallization mechanisms abstract the average grain size d arising from dynamic recrystallization drx is often used as an indicator of flow stress however a theoretical basis for the scaling relation between d and has yet to be well established in this paper theories for the development of recrystallized grain size are reviewed and their applicability is examined special attention is paid to the dependence of the d relation on drx mechanisms steady state drx is classified into discontinuous drx with bulging blg nucleation grain boundary migration gbm and continuous drx with subgrain rotation sgr nucleation gbm the nucleation and growth model derived from derby ashby theory describes the former case whereas that derived from shimizu theory applies to the latter a static energy balance model derived from twiss theory is applicable to subgrain size but not to recrystallized grain size the lower limit of grain size is possibly constrained by a change in deformation mechanism from dislocation creep to diffusion creep because deformation induced grain size reduction ceases in the diffusion creep field scaling relations determined in the laboratory support the shimizu model in the case of sgr gbm the theoretical piezometer calibrated for quartz suggests significant temperature effects under low temperature metamorphic conditions

paleowattmeters a scaling relation for dynamically recrystallized grain size during dislocation creep mineral grains often evolve to a stable size dictated by the deformation conditions we suggest that grain size evolution during deformation is determined by the rate of mechanical work provided that other elements of microstructure have achieved steady state and that the dissipation rate is roughly constant then changes in internal energy will be proportional to changes in grain boundary area if normal grain growth and dynamic grain size reduction occur simultaneously then the steady state grain size is determined by the balance of those rates a scaling model using these assumptions and published grain growth and mechanical relations matches stress grain size relations for quartz and olivine rocks with no fitting for marbles the model also explains scatter not rationalized by assuming that recrystallized grain size is a function of stress alone when extrapolated to conditions typical for natural mylonites the model is consistent with field constraints on stresses and strain rates

insights into the post emplacement history of the saunstein granitic dyke showing heterogeneous deformation and inconsistent shear sense indicators bavarian forest germany the recent mapping survey undertaken in the bavarian forest led to the discovery of several eew trending sinistral shear zones usually affecting granitic dykes or areas intruded by dykes we studied a granitic dyke affected by one of these shear zones the deformation in the dyke as well as in other dykes of the region is not homogeneous and concentrates mainly next to the contact to the country rock the differences in mineralogy between dyke and host probably controlled the distribution of strain favoring the deformation of the lithology richer in quartz i e the granite dyke next to a rheological boundary i e the contact to the host rock as inferred from microfabrics and quartz textures quartz deformation occurred by dislocation creep accommodated by grain boundary migration and subgrain rotation recrystallization intracrystalline glide on prism planes in the direction indicate a temperature of w500e550 c only in the most strained fine grained bands was deformation achieved by grain boundary sliding a late shear sense reversal after the principal sinistral deformation in the dyke led to the development of a dextral quartz shape fabric this reflects on the one hand how quartz is able to record late low strain overprints and on the other hand how oblique quartz foliations may lead to wrong interpretations when being used without corroboration of other shear sense indicators

experimental research on creep properties of limestone under fluid solid coupling water is one of the important factors influencing the long term stability of underground construction water becomes a huge threat to the safe operation of underground construction because of the increasing hydraulic pressure in deep stratum in the present study compression creep tests of limestone not covered by rubber jacket under different hydraulic confining pressures were carried out by using the self developed ysl 200 multi channel rock creep testing system based on the analysis of test data the creep properties of limestone under fluid solid coupling were studied then the effect of water and hydraulic confining pressure on the failure mechanism and creep properties were discussed the results show that the hydraulic confining pressure has a significant influence on the rock creep properties compared with the confining pressure in conventional triaxial creep test under the long term effect of hydraulic confining pressure water seeps into the rock through fissures or cracks and applies splitting effects on the crack surface which promotes crack propagation increases the damage of rock and accelerates the rock failure process both the value of strain and the creep strain rate increase with the increasing of hydraulic confining pressure but the increase magnitude of the creep strain rate is much smaller the results can provide a reference for the study of long term stability of underground structure under fluid solid coupling

variscan shear zone deformation of late precambrian basement in sw iberia implications for circum atlantic pre mesozoic tectonics abstract polyphase deformation and metamorphism in the badajoz cordoba shear belt sw spain relate to a poly orogenic evolution involving two major tectonothermal episodes the accretion of mid and lower crust tectonic slices in an orogenic wedge complex during pre variscan times and the development of an intracontinental ductile shear zone during the late palaeozoic structural analysis of zones with different intensities of shear dominated variscan deformation allows a recognition of the poly deformed nature of most units of the belt identification of varying deformation mechanisms and a description of the geometry of early structures the implications for the regional tectonics of this area of the southern iberian massif are discussed in the light of the geodynamic evolution of the ibero armorican arc during the variscan orogeny and the reconstruction of the late precambrian cadomian avalonian panafrican orogen of the circum atlantic region

energy evolution characteristics of hard rock during triaxial failure with different loading and unloading paths abstract triaxial compression tests were conducted on fine to medium grained granite specimens with initial confining pressures of 10 20 40 and 60 mpa under various loading and unloading stress paths the energy evolution characteristics of granite specimens from a quarry in miluo city china were studied in the triaxial deformation and failure process of the rocks the results show that the time history curves of the total strain energy elastic strain energy and dissipative strain energy exhibit significant stage features in particular the ratio of the dissipative strain energy to the total strain energy can be used to describe the deformation and degree of damage to rock specimens during the triaxial loading and unloading processes under the same initial confining pressure the maximum values of the total strain energy elastic strain energy and dissipative strain energy occur in the conventional triaxial compressive testing of group i and the minimum values occur in test group ii with constant axial stress and decreasing confining pressure the total strain energy elastic strain energy and circumferential strain energy all increase as the initial confining pressure increases whereas the dissipative strain energy does not during the process of unloading the confining pressure the increase of the circumferential strain is considerably larger than that of the axial strain under unloading conditions rock bursts may occur more easily for hard rocks than under conventional triaxial loading conditions especially under the conditions of test group iii with increasing axial stress and decreasing confining pressure the micro difference in the granite micro cracks was identified using a scanning electron microscope sem combined with an energy dispersive spectrometer eds shear failure characteristics were observed in a conventional triaxial test and the combined tension and shear failure was identified through unloading confining pressure tests the tensile failure characteristics of the granite in group iii are more pronounced than those of group ii this indicates that the triaxial failure of rock results from the development of micro extension cracks and volumetric expansion in the granite specimen under unloading confining pressure tests

rock mechanics observations pertinent to the rheology of the continental lithosphere and the localization of strain along shear zones emphasized in this paper are the deformation processes and rheologies of rocks at high temperatures and high effective pressures conditions that are presumably appropriate to the lower crust and upper mantle in continental collision zones much recent progress has been made in understanding the flexure of the oceanic lithosphere using rock mechanics based yield criteria for the inelastic deformations at the top and base at mid plate depths stresses are likely to be supported elastically because bending strains and elastic stresses are low the collisional tectonic regime however is far more complex because very large permanent strains are sustained at mid plate depths and this requires us to include the broad transition between brittle and ductile flow moreover important changes in the ductile flow mechanisms occur at the intermediate temperatures found at mid plate depths two specific contributions of laboratory rock rheology research are considered in this paper first the high temperature steady state flow mechanisms and rheology of mafic and ultramafic rocks are reviewed with special emphasis on olivine and crystalline rocks rock strength decreases very markedly with increases in temperature and it is the onset of flow by high temperature ductile mechanisms that defines the base of the lithosphere the thickness of the continental lithosphere can therefore be defined by the depth to a particular isotherm tc above which at geologic strain rates the high temperature ductile strength falls below some arbitrary strength isobar e g 100 mpa for olivine tc is about 700 800 c but for other crustal silicates tc may be as low as 400 600 c suggesting that substantial decoupling may take place within thick continental crust and that strength may increase with depth at the moho as suggested by a number of workers on independent grounds put another way the moho is a rheological discontinuity a second class of laboratory observations pertains to the general phenomenon of ductile faulting in which ductile strains are localized into shear zones ductile faults have been produced in experiments of five different rock types and is generally expressed as strain softening in constant strain rate tests or as an accelerating creep rate stage at constant differential stress a number of physical mechanisms have been identified that may be responsible for ductile faulting including the onset of dynamic recrystallization phase changes hydrothermal alteration and hydrolytic weakening microscopic evidence for these processes as well as larger scale geological and geophysical observations suggest that ductile faulting in the middle to lower crust and upper mantle may greatly influence the distribution and magnitudes of differential stresses and the style of deformation in the overlying upper continental lithosphere

anisotropic strength and deformational behavior of himalayan schists abstract anisotropy which is characteristic of metamorphic rocks such as schists is due to a process of metamorphic differentiation preferred orientation of minerals like mica and chlorite in response to tectonic stresses makes schistose rocks foliated as a result their engineering properties vary with the direction of loading the influence of transverse anisotropy on strength and deformational responses of four schistose rocks obtained from the foundation of two underground powerhouse sites in the himalayas has been critically examined specimens at different orientation of the foliations varying from 0 to 90 with respect to the axial stress 1 in the unconfined state and also in the confined states up to 100 mpa of confining pressure were tested to evaluate the applicability of the non linear strength criterion for the prediction of triaxial compressive strength and modulus based on the analysis of large experimental results it has been possible to predict strength and modulus with minimum pre evaluation experimental data i e only with three uniaxial compressive strength tests at 0 30 and 90 and two triaxial compression tests conducted at convenient confining pressures at 90 orientation predicted non linear stress strain curves using predicted values of strength and modulus have been found to match well with the experimental stress strain curves even at higher confining pressures

large strain deformation studies using polycrystalline magnesium as a rock analogue part i grain size paleopiezometry in mylonite zones abstract the results of large strain deformation studies of polycrystalline magnesium are reported shear zones develop at temperatures below 0 65 tm for strain rates between 10 4 10 5 s 1 the zones are characterised by small recrystallised grains and are analogues of mylonite zones in crustal and mantle rocks their development is marked by a stress drop but the recrystallised grains in the zones do not re equilibrate and remain equilibrated to the peak stress however the recrystallised grains in the areas bordering the shear zones undergo a strain dependent coarsening and their sizes re equilibrate to the relaxed stresses at natural strains of 1 the geological implications of these results are discussed

frictional viscous flow in mylonite with varied bimineralic composition and its effect on lithospheric strength abstract a theoretical composite flow law is presented for mylonite containing interconnected layers of a weak mineral undergoing power law creep and porphyroclasts of a stronger mineral undergoing fracture and frictional sliding such mylonite termed clastomylonite is said to undergo frictional viscous fv mylonitic flow its bulk strength is expressed as a function of bimineralic composition temperature effective pressure and shear strain rate as well as the material parameters for the constituent minerals the fv flow law predicts that the rheology of clastomylonite is predominantly non linear viscous and only slightly pressure sensitive for most bimineralic compositions fv mylonitic flow is shown to occupy a depth interval between cataclastic flow involving adhesive wear in the upper crust and fully viscous mylonitic flow at greater depths the transition from adhesive wear to fv mylonitic flow is related to the onset of dislocation creep glide plus climb in the weakest phase and is inferred to coincide with a crustal strength maximum a peak strength of about 80 mpa is calculated with a combination of byerlee s constants for frictional sliding of granite and the fv flow law for granitic clastomylonite 30 vol quartz at elevated fluid pressures this value falls within the range of flow stresses independently obtained from quartz palaeopiezometry in many greenschist facies granitic mylonite zones

calcite and quartz microstructural geothermometry of low grade metasedimentary rocks northern range trinidad abstract the northern range of trinidad is a mountainous exposure of deformed metasedimentary rocks with mesozoic depositional ages and tertiary metamorphic ages located in the caribbean south american plate boundary zone these rocks lack precise mineralogical indicators of metamorphic grade using temperature sensitive quartz and calcite microstructures and fission track data we identify describe quantify and map a nearly continuous spectrum of relatively low l50 c to relatively high 250 400 c deformation temperatures from east to west across the range average estimated rock exhumation rates also increase systematically along this trend the analysis illuminates a sharp east west trending major thermal discontinuity i e a fault along the southern boundary of the range kinematic analysis of faults and shear bands adjacent to this boundary and modeling indicate that the fault probably dips southward at 80 85 and accommodated normal dip slip at rates that decreased from west to east earlier experimental studies at high strain rates illustrated a strong strain rate dependency for quartz microstructural transitions our work indicates a possible strong temperature control for quartz microstructural transitions at natural strain rates

microboudin structures of piemontite along the sambagawa metamorphic belt japan implications for lateral variation of differential stress during regional metamorphism evidence is presented of a lateral variation in differential stress during metamorphism along a regional metamorphic belt on the basis of the proportion of microboudinaged piemontite grains p in a quartz matrix in metacherts it is proposed that p is a practical indicator of relative differential stress analysis of 123 metacherts from the 800 km long sambagawa metamorphic belt japan reveals that p values range from 0 01 to 0 7 in this region most samples from wakayama in the mid belt area have p values of 0 4 0 6 whereas those from western shikoku have p values of 0 1 this difference cannot be explained by variations in metamorphic temperature and is instead attributed to a regional lateral variation in differential stress during metamorphism

a new perspective on paleopiezometry dynamically recrystallized grain size distributions indicate mechanism changes the dynamically recrystallized grain size is a material parameter associated with dislocation creep of crystalline solids that is especially important as a flow stress indicator via piezometer calibrations grain sizes have been measured in many studies of deformed rocks as well as metals and ceramics but global analyses of the frequency distribution of dynamically recrystallized grain sizes are lacking here we present the first systematic investigation of the recrystallized grain size distribution for quartz the grain diameters compiled from 555 samples of 31 studies of quartz mylonites deformed over a wide range of conditions extend from 3 m to 3 mm with distinct maxima at 10 20 m and 70 80 m and minima at 35 40 m and 120 m the frequency maxima correlate with distinct microstructures and the minima with the transitions between these microstructures which we interpret to result from the dominance of the recrystallization mechanisms of bulging subgrain rotation and grain boundary migration recrystallization these results demonstrate the necessity of distinct piezometer calibrations for different recrystallization mechanisms and highlight the importance of the recrystallized grain size for theoretical models of dynamic recrystallization

quantitative characterization of textures in mantle spinel peridotite xenoliths a method for quantitative characterization of grain size in thin sections has been established for mantle spinel peridotite xenoliths using optical scanning of large areas of thin sections skeletonization of grain section outlines and computerized measurement of individual grain section areas measurements range from 218 for the coarsest example to more than 3000 in the finest grained variability of the samples has been examined in relation to size and number of grain section areas measured by using multiple and orthogonal sections from several xenoliths the results show a linear relationship of arithmetic mean against additive standard deviation including data from coarse grained protogranular through porphyroclastic to the finer grained equigranular examples this suggests that peridotite textures form a continuous series rather than discrete groups as suggested by qualitative subjective assessment the observed distributions of grain section areas have been explored in relation to their description and possible mechanistic origin by direct measurement and comparison of cumulative number and area distribution curves we show that qualitatively assessed typical grain sizes are influenced by a small number of larger grain sections although the arithmetic mean and standard deviation provide a convenient method for comparison in practice grain section area distributions show marked positive skewness more consistent with log normal or power law functions linear log probability curves also support the existence of a continuous series of peridotite textures suggesting that the shallow lithospheric mantle has been subject to processes of comminution and or grain growth dependent on the law of proportionate effect the geological society of london 2010

structural style deformation mechanisms and paleodifferential stress along an exposed crustal section constraints on the rheology of quartzofeldspathic rocks at supra and infrastructural levels bohemian massif abstract investigations of variscan shortening of quartzofeldspathic rocks have been carried out along an exposed crustal section located in the western part of the tepla barrandian unit bohemian massif the study focuses on determining differential stress deformation mechanisms and geometry of cadomian metagreywackes and cambrian granitoids which show different grade of variscan barrovian type metamorphism ranging from the greenschist subgreenschist facies boundary semibrittle deformation regime to the high grade amphibolite facies the semibrittle deformation regime t ca 300 c is characterized by large scale thrusting within a folding environment and by similar intensities of cataclasis diffusive mass transfer and crystal plasticity of quartz the latter including low temperature migration recrystallization within cadomian quartz veins of the greenschist facies part dislocation creep of quartz operated at differential stresses ranging from ca 70 mpa in the lowermost greenschist facies to ca 20 mpa in the uppermost greenschist facies these values have been derived by paleopiezometry using the grain size of recrystallized quartz they are interpreted as upper bounds for the bulk stress because of intense diffusive mass transfer within the adjacent metagreywackes a marking increase in recrystallized grain size of quartz occurs within the lower greenschist facies where low temperature grain boundary migration is replaced by subgrain rotation thus causion is needed when applying the recrystallized grain size paleopiezometer to this crustal level pressure solution of quartz and development of discrete crenulation cleavage was common in fine grained metagreywackes of the lower greenschist facies whereas the upper greenschist facies t ca 500 570 c is characterized by increasing intensity of metamorphic reactions grain coarsening and development of a schistosity the entire greenschist facies level forms a suprastructure where viscosity contrasts between mica and quartz rich layers were sufficiently high for buckle folding strain protected intercalated metagranitoids on the other hand do not show pervasive deformation fabrics the amphibolite facies part forms an infrastructure characterized by pervasive mylonitic shearing of both cambrian granitoids and metagreywackes it is suggested that the combination of the following processes has contributed to weaken the amphibolite facies level making nonlocalized flow possible 1 increased recrystallization of feldspar 2 crystal plastic softening of quartz due to high temperature grain boundary migration and activity of prism slip and 3 enhanced diffusive mass transfer in the form of metamorphic reactions the structural breaks at the semibrittle crustal level and at the greenschist amphibolite facies boundary supports the view that rheological boundaries are prone to form major detachment horizons in the continental crust

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

influence of plastic shear strain and confinement dependent rock dilation on rock failure and displacement near an excavation boundary abstract excavation induced rock failure and displacement near an underground opening boundary is closely associated with rock mass dilation a better understanding of rock mass dilation around the excavation helps us to predict or anticipate displacements and extent and shape of the failed zone and subsequently assist design of proper ground support systems a calibrated cohesion weakening and frictional strengthening cwfs model with a constant dilation angle can capture the stress induced brittle failure shape in hard rocks however the use of a constant dilation angle in either cwfs mohr coulomb perfectly elasto plastic or mohr coulomb strain softening models cannot simulate the displacement distribution near the excavation reasonably in the present study numerical simulations are performed to study excavation induced displacement around tunnels located in different rock mass types i e coarse grained hard rock medium grained hard rock fine medium grained soft rock and fine grained soft rock using a mobilized dilation angle model that depends on both confining stress and plastic shear strain it is illustrated from a few examples that displacement distributions obtained from the dilation angle model are more reasonable when compared with the general trend measured underground

a spherical electron channelling pattern map for use in quartz petrofabric analysis electron channelling patterns ecp s are formed in the scanning electron microscope sem by the interaction between the incident electrons and the lattice of crystalline specimens the patterns are unique for a particular crystallographic orientation and are therefore of considerable potential in petrofabric studies provided they can be accurately indexed indexing requires an ecp map of the crystallographic stereogram or unit triangle covering all possible orientations and hence ecp patterns due to the presence of long range distortions in planar ecp maps it is more convenient to construct the maps over a spherical surface this also facilitates the indexing of individual ecp s a spherical ecp map for quartz is presented together with an example of its use in petrofabric analysis

ultrafine grained quartz mylonites from high grade shear zones evidence for strong dry middle to lower crust creep strength of the crust depends upon the rheology of the most common mineral usually quartz recrystallized quartz grains in many high grade shear zones from the middle to lower crust are typically large millimeter sized implying active grain boundary migration but equivalents from old polymetamorphic and water deficient basement sheared at similar crustal depths can be very small for the latter strong crystallographic preferred orientation cpo of quartz with c axes aligned close to y progressive misorientation of crystals subgrain and dislocation development and core mantle structures with recrystallized grains of 2 8 m size all point to dislocation glide dominantly on the prism a system with recrystallization by subgrain rotation recrystallized grain size piezometry of such quartz indicates high flow stress in fine grained shear zones while the synkinematic metamorphic mineral assemblage and the cpo are typical of amphibolite facies conditions this is evidence that middle to lower crust is not inevitably weak due to its high temperature water content also has an important influence

the role of intragranular fracturing on grain size reduction in feldspar during mylonitization abstract measurements of the size shape and orientation of k feldspar and plagioclase grains within a granitic mylonite in the kashio shear zone central honshu japan revealed that grain size was the most effective parameter controlling development of intragranular fracturing during mylonitization intragranular fractures are dominantly located near the centre of each grain and form preferentially along the 001 cleavage the grain size distribution of both feldspars is log normal with an average of 760 m the proportion of fractured grains expands dramatically to 100 as the grain size increases whereas few feldspar grains smaller than 300 m have been fractured during the mylonitization indicating that the fractures have preferentially developed in coarser grains furthermore the shape and shape preferred orientation of feldspar grains also affects the development of fractures the proportion of fractured grains not only increases up to 20 towards the extension direction but also rises slightly as the aspect ratio of feldspar grains increases it is therefore suggested that feldspar grains lying perpendicular to the extension direction may resist fracturing regardless of grain size unless their shape preferred orientations became sub parallel to the extension direction due to rotation or modification of their grain shapes during mylonitization the development of intragranular fractures could be statistically explained in terms of a fibre loading model although individual fractures may result from various fracture mechanisms

the development of discrete shear zones in a granite stress strain and changes in deformation mechanisms abstract the development of millimetre scale continuous shear zones in the sidi ali bou nab algeria granite and their progressive transformation into discrete shear zones are presented increases in strain stress and strain rate magnitudes as well as changes of deformation mechanisms are suggested by an evolution of the microstructure across these narrow shear zones temperatures are assumed to be constant from boundaries to core the most striking aspects of this evolution are 1 1 a decrease in the angle between the foliation and the shear zone 2 2 a decrease in the recrystallized grain size of quartz together with the development of a crystallographic orientation characterized by a strong concentration of c axes around the y axis of the finite strain ellipsoid 3 3 the development of very fine grained feldspathic aggregates or layers probably through dynamic recrystallization of original large crystals and 4 4 the replacement of original biotite by muscovite and a new generation of biotite in the continuous shear zones the deformation is controlled by the behaviour of quartz this mineral undergoes extensive dynamic recrystallization which probably favours a higher strain rate and a change in the active slip system from a dominant basal one in the outermost part of the structures to a dominant prismatic one in its core paleopiezometry and strain computations show a shear strain up to 10 and an inferred steady state differential stress to 100 130 mpa respectively the high stress level is suspect because the estimates are derived from recrystallized grain size which may be sensitive to strain and variations of chemical environment discrete shear zones develop in relation with dynamic recrystallization of feldspars in the core of continuous shear zones dynamic recrystallization of feldspars produces very fine grained aggregates grain size of 6 7 m which coalesce and form a continuous layer at the central part of the shear zones this fabric may result from 1 1 a change in the driving flow mechanism from dislocation creep of quartz to dislocation creep or and grain boundary sliding of feldspar neoblasts and 2 2 a large strain softening that would favour strain concentration in the fine grained matrix and the development of sharp shear zone boundaries

contrast in stress strain history during exhumation between high and ultrahigh pressure metamorphic units in the western alps microboudinage analysis of piemontite in metacherts abstract our analyses of microboudinage structures of piemontite grains embedded within six samples of metachert one collected from an ultrahigh pressure uhp metamorphic unit at lago di cignana in italy of the western alps and the other five from surrounding high pressure hp metamorphic units in italy and france have revealed that the structures are all symmetrical in type and were presumably produced in coaxial strain fields stress strain analyses of the microboudinaged grains revealed significant contrasts in the stress and strain histories of the uhp and hp metamorphic units with the differential stress recorded by the uhp sample being unequivocally lower than that recorded by the five hp samples in addition our analyses showed that the uhp sample underwent stress relaxation during microboudinage whereas the five hp samples did not on the basis of these observations and analyses we discuss the mechanical decoupling of the uhp and hp units that led to different histories in differential stress between the units during exhumation of the western alps

triaxial stress state deep in orogenic belts an example from turkey abstract a rare metachert pebble containing amphibole grains with microboudin structures in a wide range of orientations provides an opportunity to perform stress analysis in two orthogonal orientations on the foliation surface the sample was analysed by the microboudin method to infer the triaxial stress state during microboudinage stress parameters proportional to the far field differential stress were determined for sodic amphibole grains in the two orientations the ratio of the stresses in the two orthogonal orientations 1 2 1 3 was calculated to be 0 64 indicating that 2 lies closer to the midpoint between 1 and 3 than to 3

microstructures of olivine and stresses in the upper mantle beneath eastern china abstract we have examined the microstructure of spinel and garnet peridotite xenoliths from eleven basalt localities in eastern china the dislocation substructures of olivine in all of the specimens are similar to those reported previously from other areas of the world and are strongly reminiscent of the substructures produced in laboratory deformation of polycrystals at high temperature and pressure extensive measurements of 100 and 001 subgrain dimensions demonstrate that in almost all cases the frequency of subgrain spacing follows a lognormal distribution with geometric mean spacings of 30 60 m in one locality mingxi two xenoliths show significantly narrower spacings of 15 20 m indicating a much higher stress while others from the same locality have the normal wider spacing and one specimen has a mixed distribution indicating that the strain produced at higher stress was not sufficient to re equilibrate the microstructure even higher stresses but probably trivial strains are suggested by 110 slip bands sporadically superposed on the normal microstructure which presumably were produced during extraction of the xenoliths by the magma the general correspondence between these results and those of previous studies conducted elsewhere in the world suggests that the general level of lithospheric stress of c 10 50 mpa has been essentially constant since the middle tertiary or that the dynamic process of magma generation and or extraction always leads to similar microstructures

mylonitization in the lower plate of the buckskin rawhide detachment fault west central arizona implications for the geometric evolution of metamorphic core complexes abstract in metamorphic core complexes it is commonly unclear whether lower plate mylonites formed as the down dip continuation of a detachment fault or whether they represent a subhorizontal shear zone that was captured by a more steeply dipping detachment fault detailed microstructural fabric and strain data from mylonites in the buckskin rawhide metamorphic core complex west central arizona constrain the structural development of the lower plate shear zone widespread exposures of 22 21 ma granitoids of the swansea plutonic suite enable us to separate miocene strain coeval with core complex extension from older deformation mylonites across the lower plate consistently record top to the ne directed shear miocene quartz and feldspar deformation recrystallization mechanisms indicate 450 500 c mylonitization temperatures that were relatively uniform across a distance of 35 km in the extension direction quartz dynamically recrystallized grain sizes do not systematically vary in the extension direction strain recorded in the swansea plutonic suite is also relatively uniform in the extension direction which is incompatible with models in which lower plate mylonites form as the ductile root of a major detachment fault altogether these data suggest the mylonitic shear zone initiated with a 4 dip and was unroofed by a more steeply dipping detachment fault system lower plate mylonites in the buckskin rawhide metamorphic core complex thus represent a captured subhorizontal shear zone rather than the down dip continuation of a detachment fault

water deficient mylonite zones an example from the pyrenees abstract some mylonite zones which operate at retrograde conditions in metamorphic rocks have a low water content of the metamorphic fluid resulting in an incomplete reequilibration of the mineral assemblages recognition of such zones is important for a correct assessment of p t conditions of deformation especially where these data are used for reconstructing palaeogeometry of exhumed normal fault and thrust zones an example of a water deficient mylonite zone from the pyrenees is characterized by incomplete breakdown of sillimanite orthoclase in the stability field of muscovite quartz pure co 2 fluid inclusions limited postkinematic grain growth and high differential stresses during the deformation as indicated by recrystallized quartz grain size

the influence of the water saturation on the strength of volcanic tuffs used as building stones moisture content is one of the most important factors influencing the strength of building stones ayazini and seydiler afyonkarahisar turkey tuffs were investigated with the goal to determine the influence of the water on their strength mercury porosimetry was used to determine the pore size distribution ayazini tuffs have pore sizes ranging from about 200 000 to 10 nm and seydiler tuffs ranging from about 7000 to 10 nm the tuff samples are immersed in water with different time periods of 1 6 24 and 48 h the following physico mechanical properties were measured for all the samples both in dry and saturated condition compressive strength and flexural strength test results were indicated by simple regression analysis good correlations were found between physico mechanical properties with dry and saturated tuff samples the results had shown their mechanical strength decreases in wet conditions for dry samples tested had 22 21 mpa uniaxial compression strength while 1 h immersed samples had 15 11 mpa which indicates a decrease of 31 96 after the 48 h water immersion time period the value of compression strength decreases by 43 99 and becomes 12 44 mpa

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

magnitude of σ1 σ2 and σ3 at mid crustal levels in an orogenic belt microboudin method applied to an impure metachert from turkey abstract we revised an equation for estimating palaeostress magnitude using the microboudin technique by incorporating the influence of time on the fracture strength of minerals the equation was used to estimate triaxial palaeostresses from a rare sample of metachert from turkey that contains microboudinaged columnar tourmaline grains in a wide range of orientations within the foliation plane the estimated principal palaeostresses are 1 605 mpa 2 598 mpa and 3 597 mpa as the microboudinage is considered to have occurred immediately before the rock encountered the brittle plastic transition during exhumation these stress values correspond to conditions at approximately 18 km depth and 300 c within a cretaceous orogenic belt

shearing during progressive retrogression in granitoids abrupt grain size reduction of quartz at the plastic brittle transition for feldspar the kashio shear zone chubu district japan affects the southeast margins of the ryoke granitic plutons as well as the ryoke metasedimentary rocks and is truncated by the median tectonic line near the shear zone centre coarse quartz grains within the granitic rocks have been dynamically recrystallized to quartz aggregates towards the pluton margins the grain size data show an abrupt reduction from various sizes 59 148 m to a steady state size around 35 m at approximately 400 m from the boundary of the granitic plutons without any tectonic boundary such as a fault being present this abrupt grain size reduction accompanies brittle deformation in feldspar that overprints earlier plastic deformation and develops strong mylonitic fabrics in contrast feldspar away from the pluton margins contains only weak microstructural evidence for plastic deformation and still locally preserves magmatic polycrystal structures amongst the inhomogeneously recrystallized quartz grains these features combined with an isochronological study suggest that the kashio shear zone began at high temperature 450 c as a ductile event that affected relatively wide regions in the ryoke granitic plutons before rapid cooling by ca 70 ma at this latter stage strong mylonitization at lower temperatures 300 c in a semiductile regime occurred in a narrow zone towards the shear zone centre here recrystallized quartz aggregates reached a steady state grain size by ca 60 ma that is cooling within the granitic plutons resulted in strain localization with the abrupt grain size reduction of quartz aggregates correlating with the plastic brittle transition of feldspar

experimental and theoretical study of the anisotropic properties of shale abstract the effect of bedding plane orientations on shear strength and failure mechanisms of shale is investigated with an emphasis on the shear parameters of the bedding planes this study is based on direct shear tests conducted on directional shale samples obtained from formations which exhibit well developed stratification the tested cylindrical specimens were prepared by coring at 30 intervals from the direction of the bedding planes the results indicate that the anisotropy of the shear strength of shale can be readily observed due to the anisotropic effects of bedding plane orientation and normal stress the shear parameters such as strength cohesion and internal friction angle reach their maximum and the minimum values at 60 and 0 respectively where is the angle between the bedding planes and the coring orientation which is also the direction of normal stress during the laboratory tests it is demonstrated that the bedding planes are weak not only with regards to cementing strength but also with regards to friction three different shear failure modes were built up depending on the shearing angle 1 sliding failure across the bedding planes 2 sliding failure along the bedding planes and 3 sliding failure across the bedding planes combined with tensile splitting along the bedding planes an expression of the shear stress concentration factor of the direct shear model is derived to evaluate the anisotropy of shear strength