stress tensor determination from the study of e twins in calcite a linear programming method abstract a new method for the determination of the stress tensor from calcite e twin lamellae has been discovered all e planes twinned and untwinned are taken into account to enable derivation of tensor characteristics the basic assumption is that the resolved shear stress a linear function of the unknown stress tensor components is greater respectively lower than the critical resolved shear stress for the twinned respectively untwinned planes the relevant inequality constraints can be solved using linear programming algorithms the application to experimental carrara marble and natural samples a goniatite from morocco has come up against one major difficulty polyphase deformation thus before applying this method it is necessary to operate some selection of the data one procedure based upon linear programming is proposed the results are consistent with those expected both for the experimental and natural cases for the carrara marble an estimate of the critical resolved shear stress t c for twinning gave a value around 300 400 bar the method can give in principle the stress tensor orientation and the relative magnitude of principal stresses simultaneously

displacement of the lewis thrust sheet in southwestern canada new evidence from seismic reflection data seismic reflection data across the rocky mountain trench in the southern canadian cordillera reveal prominent reflections from mesoproterozoic aldridge formation sills that allow a direct stratigraphic correlation across the trench when 10 km of extension is restored trun cated reflections at 11 15 km depth on the west side of the trench are interpreted as a footwall cutoff of the lewis thrust in belt purcell strata that lies 115 km west of the leading edge of the lewis thrust exposed in the waterton area retrodeformation of the lewis sheet requires a minimum of 75 km of transport on the lewis thrust and 40 km of transport by the development of footwall domain duplexes the trench is located above a major change in slope of the top of the north american basement that coincides with a pronounced increase in thickness of lower belt purcell strata in their retrodeformed position this transition may represent part of an ancient margin that was initially established in paleoproterozoic time

the influence of grain size and grain size distribution on methods for estimating paleostresses from twinning in carbonates abstract this study examines the relative differential stresses around a minor thrust fault within the mountain city window tennessee u s a the fault zone developed within dolomite rocks and deformation took place by twinning fracturing pressure solution and the development of fine grained deformation zones grain size reduction is observed from undeformed wall rock to the center of the fault zone and occurred by dynamic recrystallization methods to determine paleostresses in naturally deformed rocks from twinning assume a single coaxial strain inducing event the recrystallization within the center of the fault zone removed the effects of earlier deformation so that the twinning more closely reflects a single coaxial deformation event late in the fault history two methods were used to estimate the relative differential stresses across the fault zone and the results show opposite trends towards the center of the fault zone the different results may be partially explained by the influence of grain size as only one of these methods considers the influence of grain size in addition the grainsize data from this fault zone demonstrate that the tendency for a grain size class to be twinned depends on the grain size distribution the grain size distribution may result in grain to grain stress concentrations that induce twinning thus grain size distribution should also be considered to achieve more accurate estimates of paleostresses

direct observation of microcrack development in marble caused by thermal weathering one of the properties that makes marble such an excellent construction and ornamental material is its low porosity it is very difficult for water or decay agents to penetrate the internal structure of materials with no or few pores so enhancing the durability of these materials however environmental temperature fluctuations bring about significant physical changes in marbles that result in an increase in porosity due to the appearance of new microcracks and the expansion of existing ones these cracks offer new paths into the marble which make it easier for solutions containing pollutants to penetrate the material thermal expansion tests were performed on three different types of marble known as white tranco and yellow macael almeria spain after which an increase in porosity from 17 to 73 depending on marble type was observed mainly due to crack formation the structural changes occurring during thermal expansion tests were more significant in the case of white macael samples a fact that is not only related to its mineralogical composition but also to the morphology of the grains grain boundaries and crystal size our research suggests that thermally weathered white macael marble could be more susceptible to decay by other contaminant agents than tranco or yellow macael the use of hot stage environmental scanning electron microscopy is proposed as a valid tool for observing both in situ and at high magnification changes in the fracture system of building stones induced by thermal stress

strength characteristics of the r f and c slip systems in calcite abstract numerical modelling of crystallographic preferred orientation or texture development in plastically deformed materials requires specification of all potential slip and twinning systems and their relative strengths or critical resolved shear stresses crrs it is widely believed that the most important intracrystalline deformation systems in calcite are twinning on e 1 018 40 4 1 slip on r 10 1 4 2 021 and slip on f 1 012 2 2 01 the superscripted signs indicating slip sense it is these systems which have been used in modelling texture development in calcite polycrystals to date however modelling has been limited by insufficient and partly conflicting data on the relative strengths of the various slip and twinning systems in calcite deformation experiments on calcite single crystals performed by us in recent years taken together provide new data for a more complete and consistent quantification of the strength properties of the calcite glide systems in our experiments single crystals of calcite were compressed in both the 4041 and 2243 orientations at temperatures and constant strain rates in the range 300 800 c and 3 10 4 3 10 8 s 1 respectively the stress strain curves obtained mostly show two yield points slip line analysis shows that these yield points are related to the onset of macroscopically observable slip first on an r 2 021 system and then on an f 10 1 1 or c a system the latter two systems dominate at higher temperature 600 c at strain rate 3 10 5 s 1 and have not been taken into account in any texture modelling so far with increasing absolute temperature tabs calculated crss values c for the r f and c systems decrease in a manner which can be described by empirical power law functions of the type c a tabs b where b r 2 021 and f 10 1 1 systems the yield stresses for r 2 021 and f 10 1 1 slip were found to be rather insensitive to strain rate with conventional power law stress exponents 12 comparing the present results with previous data we conclude that two regimes of slip system activity exist namely a low temperature regime involving e twinning slip on r 2 021 and on f 2 2 01 positive direction not reported and a high temperature regime with r 2 021 f 10 1 1 and c a slip this slip system transition occurs at t 400 c at strain rate 10 4 10 5 s 1 and is expected to be associated with one or more texture transitions the results point to a clear need for renewed texture modelling of calcite polycrystals

influence of stress temperature and strain on calcite twins constrained by deformation experiments abstract a series of low strain triaxial compression and high strain torsion experiments were performed on marble and limestone samples to examine the influence of stress temperature and strain on the evolution of twin density the percentage of grains with 1 2 or 3 twin sets and the twin width all parameters that have been suggested as either paleopiezometers or paleothermometers cylindrical and dog bone shaped samples were deformed in the semibrittle regime between 20 c and 350 c under confining pressures of 50 400 mpa and at strain rates of 10 4 10 6 s 1 the samples sustained shear stresses up to 280 mpa failing when deformed to shear strains 1 the mean width of calcite twins increased with both temperature and strain and thus measurement of twin width provides only a rough estimation of peak temperature unless additional constraints on deformation are known in carrara marble the twin density nl no of twins mm increased as the rock hardened with strain and was approximately related to the peak differential stress mpa by the relation 19 5 9 8 n l dislocation tangles occurred along twin boundaries resulting in a complicated cell structure which also evolved with stress as previously established the square root of dislocation density observed after quench also correlated with peak stress apparently both twin density and dislocation cell structure are important state variables for describing the strength of these rocks

a stress inversion procedure for polyphase calcite twin and fault slip data sets in rocks that are polydeformed an approach which separates faults prior to stress inversion is more appropriate the traditional stress inversion approach involving the concept of the best fit stress tensor e g a tensor which minimises the misfit between calculated and measured fault striae data often risks computing artificial stress tensors that are some form of average of mixed sets of real stress tensors a new approach is proposed in which fault data are pre processed to group the faults on the basis of their response to all possible orientations and magnitudes of applied stress a computer method is described which utilises cluster analysis based on the right dihedra method to divide dynamically mixed fault populations to monophase subsets this division is based on the ranked similarity coefficients of each fault pair from the raw data set the data clusters form dynamically homogeneous subsets which are used for the composite right dihedra solution this solution is re computed for the reduced stress tensor defined by the orientation of principal stress axes and the ratio of their magnitudes

distribution of non plane strain in experimental compression of short cylinders of solnhofen limestone axi symmetric compression experiments on short cylinders radiusolength have great potential for the investigation of different nonplane strain geometries in such experiments strain geometry and intensity are heterogeneously distributed throughout the specimens due to the effects of friction at the contact surface between the pistons and the specimen we ran a series of tests on solnhofen limestone at constant confining pressure 200 mpa temperature 600 8c and displacement rate 5 2 10 k6 ms k1 conditions at which this material deforms predominantly by crystal plasticity using shape and crystallographic preferred orientation spo and cpo patterns of calcite grains the latter measured by electron back scattered diffraction techniques ebsd we can discriminate areas in the deformed specimens with distinct non plane strain geometries spo and cpo patterns record differences in the orientation of the finite stretching direction with respect to the external reference frame it is radial in the vicinities of the rigid loading pistons but circumferential outside the periphery of the pistons as shortening progressed the middle part of the specimen was extruded with respect to the contacts with the rigid end pieces imparting a noncoaxial component to the flow with a circumferential vorticity axis in both upper and lower halves of the specimen this component was recorded in the microstructure as an asymmetric cpo the aim of the experiments is to improve the interpretation of naturally deformed rock bodies when strain departs from plane strain conditions by using the cpo as a 3d kinematic indicator providing not only shearing direction but also information about the shape in 3d of the strain ellipsoid q 2005 elsevier ltd all rights reserved

damage and recovery of calcite rocks deformed in the cataclastic regime compressional and shear wave velocities have been measured during the experimental deformation of carrara marble and solnhofen limestone in the cataclastic regime both in dry and wet conditions at room temperature measurements were performed under hydrostatic conditions up to 260 mpa confining pressure and 10 mpa pore pressure during triaxial loading at the constant strain rate of 10 s as well as during differential stress relaxation during a full cycle our results show that the seismic velocities first increase as effective mean stress increases however when the stress onset of cataclastic deformation was reached elastic velocities showed rapid decrease due to stress induced damage in the rock during stress relaxation tests we observed an increase of elastic velocities with time which suggested a fast recovery of the microstructure a substantial and rapid drop in the velocities occurred when reloading suggesting that the previous recovery was only transient subsequent relaxation tests showed other marked increases in velocities these experimental results suggest that during the deformation of low porosity calcite rich rocks dilatant crack opening and frictional sliding and compaction micromechanism pore closure compete evolutions of elastic properties mainly sensitive to crack density and macroscopic volumetric strain more sensitive to porosity are therefore not systematically correlated and depend on the strain rate the solid stress conditions and the

the effect of experimental and microstructural parameters on the transition from brittle failure to cataclastic flow of carbonate rocks abstract triaxial compression tests were conducted on cold pressed calcite aragonite and limestone aggregates and on solnhofen limestone specimens to study the effect of experimental and microstructural parameters on the transition from brittle failure to cataclastic flow the tests were performed at confining pressures up to 195 mpa and at strain rates between 5 10 4 s 1 and 5 10 6 s 1 axial as well as volumetric strain were measured samples were produced by cold pressing powders of crushed calcite and aragonite crystals and of crushed solnhofen limestone sample porosity ranged between 5 and 25 and the average grain size varied between 5 and 400 m for both the cold pressed aggregates and the intact limestone specimens the confining pressure at the transition from localized brittle failure to non localized cataclastic flow decreases with increasing porosity and grain size the transition is characterized by a zero work hardening coefficient by dilation for low porosity and compaction for high porosity rocks by a constant ratio between axial stress and confining pressure and by decreasing yield strength for increasing confining pressure the experimental results disagree with the critical state concept over most of the porosity range investigated and indicate non associated material behaviour these properties of the brittle ductile transition are addressed on the basis of continuum mechanics or by models suggested for granular materials the problems discussed and the results obtained are of fundamental interest to rock deformation and structural geology

determination of deviatoric stress tensors based on inversion of calcite twin data from experimentally deformed monophase samples preliminary results abstract following previous successful paleo stress determinations from numerically generated aggregates and naturally deformed samples preliminary results about stress reconstructions based on inversion of calcite twin data from experimentally deformed monophase samples are reported this new study carried out on samples of carrara marble and crinoidic limestone from eastern france provides a test of the validity of stress reconstructions using inverse methods which had not been properly calibrated before the percentages of correlated twins are discussed for each stress tesnor and the range of uncertainties on the determination of stress orientations and differential stress magnitudes is evaluated

lattice strain measurements on sandstones under load using neutron diffraction abstract neutron diffraction methods both time of flight and angle dispersive diffraction are applied to intracrystalline strain measurements on geological samples undergoing uniaxial increasing compressional load the experiments were carried out on cretaceous sandstones from the elbezone east germany consisting of 95 quartz which are bedded but without crystallographic preferred orientation of quartz from the stress strain relation the young s modulus for our quartz sample was determined to be 72 2 2 9 gpa using results of the neutron time of flight method the influence of different kinds of bedding in sandstones laminated and convolute bedding could be determined we observed differences of factor 2 convolute bedding and 3 laminated bedding for the elastic stiffness determined with angle dispersive neutron diffraction crystallographic strain and with strain gauges mechanical strain the data indicate which geological conditions may influence the stress strain behaviour of geological materials the influence of bedding on the stress strain behaviour of a laminated bedded sandstone was indicated by direct residual stress measurements using neutron time of flight diffraction the measurements were carried out six days after unloading the sample residual strain was measured for three positions from the centre to the periphery and within two radial directions of the cylinder we observed that residual strain changes from extension to compression in a different manner for two perpendicular directions of the bedding plane

palaeostress estimation using calcite twinning experimental calibration and application to nature abstract by means of high temperature deformation experiments on calcite rocks of different grain sizes we have established the relationships between differential stress and twinning incidence twin density and volume fraction and the way that these relationships depend on grain size both twinning incidence and volume fraction increase with grain size at a constant level of differential stress log twin density is proportional to stress but is independent of grain size at a given grain size volume fraction of twinning increases non linearly with differential stress twinning activity measured by twinning incidence increases linearly with stress the behaviour of each of these parameters is independent of temperature strain and strain rate these relationships can be used as a basis for the estimation of palaeostress values in naturally deformed calcite rocks this is illustrated by a study of twinning activity in limestones close to thrust faults in the cantabrian zone of the variscan orogenic belt in northwestern spain high peak differential stresses were measured ranging from 150 to 250 mpa using the turner dynamic analysis technique however it is clear that shear stresses resolved parallel to the fault planes were very low the attainment of high stress differences when the resistance to faulting was low is attributed either to bending forces induced during the motion of the non planar surfaces relative to each other or to the stress peak being attained prior to the localization of deformation onto the fault surfaces

using neutron diffraction to investigate the elastic properties of anisotropic rocks results from an olivine orthopyroxene mylonite 1 the penetrating power of neutrons means that neutron diffraction may be employed to determine the lattice parameters of mineral phases within samples over 1 cm in size we have exploited this fact to obtain high resolution measurements of the elastic strains experienced by olivine and orthopyroxene during room temperature uniaxial deformation experiments performed in a neutron beam line on a mylonite from the oman ophiolite specimens were loaded in three orthogonal directions with respect to the macroscopic fabric of the rock in each case the average olivine and orthopyroxene strains were the same even though the elastic stiffnesses of the two phases were different in comparison with the strains expected from the single crystal elastic stiffness tensors the average strains in the different lattice directions for each phase were found to be greater in the stiffer directions and lesser in the more compliant directions the overall effect of this tendency toward strain homogenization was for the measured elastic anisotropy of the rock to be significantly lesser than that given by voigt reuss averaging of the single crystal elastic properties according to the lattice preferred orientations of each phase the technique used to derive these conclusions potentially provides an important experimental method for the quantitative examination of nonfracture related controls on the elastic anisotropy of geological materials

coastal erosion and recovery from a cascadia subduction zone earthquake and tsunami abstract tsunamis generated by great earthquakes threaten coastal infrastructure development and human life earlier work has documented the inland extent and frequency of past tsunamis but little is known about the magnitude of material eroded during prehistoric tsunamis and how erosion and coastal recovery are recorded in coastal stratigraphy in this study we use high resolution ground penetrating radar gpr to image and quantify coastal erosion experienced during a late holocene 900 cal bp cascadia subduction zone earthquake and tsunami along the northern california coast the gpr profiles illustrate three stratigraphic signatures created during co seismic subsidence and tsunami erosion and coastal recovery the first is erosional truncation of the underlying seaward dipping reflections created by pre tsunami normal beach progradation the second is a series of landward dipping flat lying and channelized reflections marking the filling of erosional topography and coastal reworking of the irregular shoreline following inundation and erosion the third is an abrupt landward termination of the stratigraphic unit marking coastal straightening and post tsunami rejuvenation of normal coastal progradation erosion from the 900 cal bp earthquake and tsunami extended 110 m inland of the contemporary shoreline and removed reworked 225 000 28 000 m3 of sand from a 1 7 km stretch of the coast far exceeding anything experienced during historical el ninos along the pacific coast of north america this study provides the first quantitative estimate of the amount of coastal erosion from a pre historic earthquake and tsunami and outlines a strategy for estimating erosion during similar events elsewhere

strain investigations on calcite marbles using neutron time of flight diffraction in order to describe and explain the effect of bowing of marble facade panels neutron time of flight diffraction was applied to determine residual macro and microstrain on the calcite mineral phase the measurements were combined with investigations of the crystallographic preferred orientation texture measurements by neutron diffraction macroscopic measuring of the bowing on marble building stones as well as microfabric analyses three samples were investigated to explain the bowing effect a fresh broken sample a good conditioned facade panel and a strongly deformed facade panel residual intracrystalline strain was detected in all investigated samples which differed in the degree of bowing for the first time the preferred orientation and the residual strain were found to be related the results show that different strain magnitudes are reflected by residual strains which differ significantly in magnitude and direction furthermore different bragg peak widths have been detected as an indication of microscopic strain the observed residual strain values in the samples are related with the grain shape and texture properties

using neutron diffraction to examine the onset of mechanical twinning in calcite rocks experimental calibration of the calcite twin piezometer is complicated by the difficulty of establishing the stresses at which the twins observed in the final deformation microstructures actually formed in principle this difficulty may be circumvented if the deformation experiments are performed in a polychromatic neutron beam line because this allows the elastic strain and hence stress in differently oriented grains to be simultaneously monitored from diffraction patterns collected as the experiment is proceeding to test this idea small strain 0 3 uniaxial compression experiments have been performed on carrara marble grain size 150 m and solnhofen limestone 5 m at temperatures of 20 600 c using the engin x instrument at the isis neutron facility uk at the lowest temperatures 25 c carrara 200 c solnhofen the deformation response was purely elastic up to the greatest stresses applied 60 mpa carrara 175 mpa solnhofen the sign of the calcite elastic stiffness component c14 is confirmed to be positive when the obverse setting of the calcite rhombohedral lattice in hexagonal axes is used in the carrara marble samples deformed at higher temperatures elastic twinning was initiated at small stresses 15 mpa in grains oriented such that the schmid factor for twinning was positive on more than one e twin system at greater stresses 65 mpa at 200 c decreasing to 41 mpa at 500 c there was an abrupt onset of permanent twinning in grains with large schmid factors for twinning on any one e twin system no twinning was observed in the solnhofen limestone samples deformed at 200 or 400 c at applied stresses of 180 mpa these results highlight the potential of this approach for detecting the onset of twinning and provide through experiments on samples with different microstructures a strategy for systematically investigating the effects of microstructural variables on crystallographically controlled inelastic processes

precision and accuracy of the calcite strain gage technique the twinned calcite strain gage technique allows the determination of strain magnitude and direction in mildly deformed sedimentary rocks in that the measurements required for the calculation are rather time consuming it is important to know the minimum number required to obtain a precision that is comparable with the accuracy of the result this paper documents a series of tests on three different limestones having different textures and porosities in order to determine the precision and accuracy of the technique as a function of the number of measurements and the number of perpendicular thin sections the tests show that for most purposes the best measurement strategy will be to make 25 measurements on each of two perpendicular thin sections the best determined principal strain axis is the one having a magnitude that is opposite in sign from the other two over the range of zero to 11 shortening the magnitude of the odd signed strain axis will than have a precision and accuracy of about 11 in magnitude and a precision and accuracy of about 6 to 8 in orientation differences in texture and porosity do not appear to have significant effects upon precision and accuracy

calcite twinning and determination of paleostress orientations three methods compared the classic turner 1953 method of determining 1 and 3 from an analysis of calcite twins is compared with a graphical method modified after dietrich and song 1984 and a newly devised method which treats calcite twin glide directions and twin planes in an analogous way to slickensides on fault planes all three methods provide similar positions for 1 but none gives a reliable position for 3 if a c axes preferred orientation exists 3 can most successfully be identified as the axis of a girdle of turner compression axes computer assisted adaptations of the turner method are recommended as the most rapid and internally consistent means of determining 1 and 3 the manual graphical method provides a useful check on turner determinations of 1 and a means of cleaning data

dilatancy during rock deformation at high temperatures and pressures the dilatancy during deformation at high pressure and temperature and at various pore pressures has been measured in carrara marble solnhofen limestone and gosford sandstone the method consists of monitoring the volume of pore fluid argon that flows into or out of the specimen at constant pore pressure the confining pressure was 300 mpa temperatures were up to 873 k and pore pressure ranged from 30 to 280 mpa positive dilatancy was observed in some cases in all three rocks in the ductile regime up to the highest temperature provided the difference between confining pressure and pore pressure was relatively small thus indicating the occurrence of microcracking even under these conditions however the behavior was complicated by the collapse of initial porosity in the limestone and sandstone and by microcracking due to intergranular thermal stresses upon heating especially in the marble the dilatancy observations have important implications for kinetics of fluid rock interactions under geological conditions

how tightly does calcite e twin constrain stress abstract mechanical twinning along calcite e planes has been used for paleostress analyses since the twinning has a critical resolved shear stress at 10 mpa not only principal stress axes but also differential stress can be determined from the twins in this article five dimensional stress space used in plasticity theory was introduced to describe the yield loci of calcite e twinning the constraints to paleostress from twin and untwin data and from calcite grains twinned on 0 1 2 and 3 e planes were quantified by using their information contents which were defined in the stress space the orientations of twinned and untwinned e planes are known to constrain not only stress axes but also differential stress d but they loose the resolution of d if the twin lamellae were formed at d greater than 50 100 mpa on the other hand it is difficult to observe twin lamellae subparallel to a thin section the stochastic modeling of this effect showed that 20 25 of twin lamellae can be overlooked the degradation of the constraints by this sampling bias can be serious especially for the determination of d

dynamics of ice mass deformation linking processes to rheology texture and microstructure 1 prediction of glacier and polar ice sheet dynamics is a major challenge especially in view of changing climate the flow behavior of an ice mass is fundamentally linked to processes at the grain and subgrain scale however our understanding of ice rheology and microstructure evolution based on conventional deformation experiments where samples are analyzed before and after deformation remains incomplete to close this gap we combine deformation experiments with in situ neutron diffraction textural and grain analysis that allows continuous monitoring of the evolution of rheology texture and microstructure we prepared ice samples from deuterium water as hydrogen in water ice has a high incoherent neutron scattering rendering it unsuitable for neutron diffraction analysis we report experimental results from deformation of initially randomly oriented polycrystalline ice at three different constant strain rates results show a dynamic system where steady state rheology is not necessarily coupled to microstructural and textural stability textures change from a weak single central c axis maxima to a strong girdle distribution at 35 to the compression axis attributed to dominance of basal slip followed by basal combined with pyramidal slip dislocation related hardening accompanies this switch and is followed by weakening due to new grain nucleation and grain boundary migration with decreasing strain rate grain boundary migration becomes increasingly dominant and texture more pronounced our observations highlight the link between the dynamics of processes competition and rheological and textural behavior this link needs to be taken into account to improve ice mass deformation modeling critical for climate change predictions

reliability of selected procedures of stress inversion and data separation for inhomogeneous populations of calcite twins and striated faults insights from numerical experiments in the course of numerical experiments selected algorithms for stress tensor inversion and separation of heterogeneous populations of calcite twins and striated faults were tested artificial data sets were created in a manner simulating natural processes they were composed of data dynamically compatible with one or two stress tensors and chaotic noise imitating natural imperfections for calcite twins the classical inversion procedure is considered valid with restrictions regarding a high proportion of chaotic data when shape ratio of the stress tensor is poorly constrained the algorithm of etchecopar 1984 fide tourneret and laurent in tectonophysics 180 287 302 1990 devised originally for calcite twins has been modified and applied to fault slip data facilitating a rejection of incompatible outliers two main classes of data separation procedures were tested separation contemporary with inversion and separation prior to inversion utilising hierarchical clustering the separation contemporary with inversion performs moderately but often fails with complex calcite twin sets the performance of hierarchical clustering is high but only with a 1 orientation as a similarity criterion the new strategy introduced in this contribution for fault slip data the hierarchical clustering with the right dihedra construction as the similarity criterion nemcok et al 1999 is satisfactory additionally a new approach is proposed for fault slip data utilising principles of the classical algorithm for heterogeneous populations of calcite twins validated algorithms for striated faults were successfully applied to a natural data set from the holy cross mts central poland

monitoring in situ stress strain behaviour during plastic yielding in polymineralic rocks using neutron diffraction abstract attempts to use rock deformation experiments to examine the elastic and plastic behaviour of polymineralic rocks are hampered by the fact that usually only whole sample properties can be monitored as opposed to the separate contribution of each phase to circumvent this difficulty room temperature uniaxial compression experiments were performed in a neutron beam line on a suite of calcite halite samples with different phase volume proportions by collecting diffraction data during loading the elastic strain and hence stress in each phase was determined as a function of load to bulk strains of 1 2 in all cases the calcite behaved elastically while the halite underwent plastic yielding during the fully elastic part of the deformation the composite elastic properties and the within phase stresses are well described both by recent shear lag models and by analyses based on eshelby s solution for the elastic field around an ellipsoidal inclusion in a homogeneous medium after the onset of yielding the halite in situ stress total strain curve may be reconstructed using the rule of mixtures at calcite contents of greater than 30 the in situ halite response may be significantly weaker or stronger than that obtained at lesser calcite contents the results highlight the potential that such techniques offer for developing an explicitly experimental approach for determining the influence of microstructural variables on the mechanical properties of polymineralic rocks

calcite fabrics in a natural shear environment the helvetic nappes of western switzerland the aim of this contribution is to describe and interpret the crystallographic orientations and microstructures of calcite in the upper jurassic limestones of the helvetic nappes between the mont blanc and aar massifs over a distance along strike of about 180 km the c axis preferred orientation pattern which could be inferred is regionally very constant the c axis point maxima are everywhere subperpendicular to the regional strike of the chain there is an obliquity between the orientation of the macroscopically dominant cleavage and the microscopically visible long axes of individual grains the c axis maxima in most specimens are parallel to the axis of shortening of the microscopic grain shape fabric this fabric geometry indicates either continuous shear deformation or alternatively a two stage deformation history the obliquity of the grain shape fabric may be due to the fact that the flattening plane of the individual grains reflects only the last increment of a continuous shear process or it may represent a later finite deformation which has led to the formation of a regionally developed second cleavage there is a systematic relationship between the direction of these late shear movements and the main overthrust direction as given by the finite strain pattern this suggests that the microfabric of the rocks was acquired during a progressive rotation with time of the main overthrust direction the observed pattern of preferred orientation has been correlated by several authors with intracrystalline deformation mechanisms a combination of slip on r and twinning on e however the e twinning observed in the specimens investigated is younger than the development of the crystallographic fabric a new method for stress determination from e twinning is proposed

intraplate paleostresses reconstructed with calcite twinning and faulting improved method and application to the eastern paris basin lorraine france this study deals with the reconstruction of intraplate paleostresses calcite twinning inversion provides paleostress directions and differential values even in poorly outcropping areas however existing methods are not well adapted to multiphase deformation cases and the calculation of stress values provides unreliable estimates modifications were brought to a calcite twinning inverse method and to the processing of results in a new twin data separation process the whole set of data is used to calculate each tensor the variability of yield stress value for twinning with strain hardening is taken into consideration a first order yield stress calcite grain size dependence function has been established with a sample showing various grain sizes this modified method of calcite twinning inversion was applied in the eastern paris basin lorraine france in this platform area measured fractures are preferentially trending ne sw and nw se at all scales the meso cenozoic paleostress succession reconstructed with fault slips is complex jurassic sedimentation occurred during the tethys rifting a mainly strike slip phase with r1 successively striking nnw and nne is attributed to the tertiary pyrenean orogenesis and is followed by wnw extension in the oligocene after local ene compression wnw compression was probably due to the alpine late miocene collision the calcite twinning inversion has confirmed these tectonic events and their succession order and the directions of stress axes were specified using grain size and strain rate sensitive yield stress values the differential stresses can be estimated with an uncertainty of few mpa they range between 20 and 30 mpa depending on the tectonic event the oligocene paleodepths of the sampled calcite estimated using differential stress values are structurally sensible thus the original calcite twinning inverse method has been improved complex paleostress successions such as in platform areas may be deciphered by combination with fault slip inversion even if additional improvement is possible this calcite twinning inverse method opens new ways to determine stress distributions in tectonic plates d 2004 published by elsevier b v

constraining the pressure threshold of impact induced calcite twinning implications for the deformation history of aqueously altered carbonaceous chondrite parent bodies calcite twinning in carbonaceous chondrite meteorites can be used to reconstruct the deformation history and the parent body environment during and or after aqueous alteration but the shock pressure threshold at which the twins develop is unknown accordingly the aim of this study is to determine the magnitude of shock pressure that is needed to generate calcite twins this was done by measuring the depths of twinning beneath the resulting craters from experimental impacts in six calcite targets combined with hydrocode modelling of the peak pressures at the corresponding depths within the targets brecciation fracturing and calcite e twinning occur below the floors of all the craters and results from the hydrocode modelling show that the twins start to form at shock pressures of 110 to 480 mpa which is at least a factor of ten higher than the 10 mpa that is considered to be required to produce calcite twins in low strain rate terrestrial settings these pressures are equivalent to shock stage s1 as determined by olivine microstructures and consistent with calcite twinning in carbonaceous chondrites being a result of impact gardening in shallow levels of their asteroidal parent bodies

critical re evaluation of differential stress estimates from calcite twins in coarse grained limestone abstract comparison of two techniques to estimate differential stress magnitude based on calcite twinning reveals significantly different calculated values of differential stress for limestone experimentally and naturally deformed at low temperature this inequality may be due to fundamental differences between the rock type marble versus limestone and deformation temperatures above and below 200 c for samples used in technique calibration versus samples used in testing and application a technique that was empirically derived from marble experimentally deformed at 200 800 c yields values of differential stress that are factors of 2 to 9 times larger than maximum differential stress measured during experimental deformation of limestone at low temperature

rheological and microstructural evolution of carrara marble with high shear strain results from high temperature torsion experiments abstract this study investigated the rheological and microstructural evolution of carrara marble deformed to large shear strain to understand how dynamic recrystallization and lattice preferred orientation lpo are related to strain softening processes solid cylinders of carrara marble were deformed in torsion up to a shear strain of 11 at constant twist rates which correspond to a shear strain rate of 3 10 4 s 1 at the outer surface and at temperatures of 1000 and 1200 k 727 and 927 c respectively for the initial grain size of 150 m these conditions are within the dislocation creep regime substantial changes in both rheology and microstructure were observed as the marble deformed to high shear strain at 1000 k 1200 k a peak stress was reached at about 1 0 5 followed by moderate strain weakening an apparent steady state flow stress was obtained at high shear strain of 5 2 the stress exponent n decreased slowly with strain from 10 1 to 6 9 at 1000 k but it remained approximately constant at 1200 k n around 10 at the maximum reached shear strain of 11 8 5 the marble had almost completely recrystallized to a fine grain size of about 10 m 20 m a secondary foliation developed in the recrystallized matrix which is at a large oblique angle to the shear zone boundary szb lpo was measured by electron backscatter diffraction ebsd for both temperatures the lpo evolved from an oblique deformation texture to a very sharp and symmetric single orientation component with r 1014 parallel to the shear plane and a 1210 parallel to the shear direction it is concluded that strain weakening was associated with the development of a strong lpo during dynamic recrystallization to a finer grain size mechanical and microstructural steady state is only reached at large shear strain the steady state lattice and grain shape fabrics can hardly be used as shear sense indicators in such recrystallized calcite mylonites

determination of deviatoric stress tensors based on inversion of calcite twin data from experimentally deformed monophase samples part ii axial and triaxial stress experiments three samples of a bioclastic bajocian limestone from burgundy france were experimentally deformed under axial and triaxial conditions at 200 and 300 c in each sample a series of three mutually orthogonal thin sections were studied using a u stage the intracrystalline deformation of the calcite grains involved mainly twinning on the e planes precise measurement of the e twin lamellae combined with the etchecopar inverse method 1984 allowed the calculation of the four parameters of the reduced stress tensor responsible for the twinning as the principal differential stress values of the experimental deviatoric stress tensors were known the critical resolved shear stress crss values tau s for twinning on the e planes were then determined in each case at 200 c and 4 8 strain tau s is close to 15 mpa at 300 c and at 8 7 and 9 4 strain the calculated tau s values are close to 10 1 and 13 4 mpa respectively when compared with the data published by turner et al 1954 turner and heard 1965 and lacombe and laurent 1996 our results confirm that the crss values are more or less dependent on both the temperature and the bulk amount of strain consequences for the estimation of the actual principal differential stress values sigma 1 sigma 3 are described particularly for very weakly deformed cover rocks in the forelands of mountain chains

determination of principal stress magnitudes using calcite twins and rock mechanics data abstract this paper proposes a new method for determining principal stress magnitudes based on the use of the deviatoric stress tensor determined from computer inversion of calcite twin data additional evaluation of the vertical stress weight of overburden or of the mean stress is enough to calculate the complete stress tensor we emphasize that the best reasoning consists of combining calcite twin analysis with rock mechanics data failure friction criteria because the determination of the six parameters of the absolute stress tensor is overconstrained