tectono metamorphic evolution of a nappe stack a case study of the swiss alps fold and thrust belts are prominent structures that occur at the front of compressional orogens to unravel the tectonic and metamorphic evolution of such complexes kinematic investigations quantitative microstructural analysis and geothermometry calcite graphite calcite dolomite were performed on carbonate mylonites from thrust faults of the helvetic nappe stack in central switzerland paleo isotherms of peak temperature conditions and cooling stages fission track of the nappe pile were reconstructed in a vertical section and linked with the microstructural and kinematic evolution mylonitic microstructures suggest that under metamorphic conditions close to peak temperature strain was highly localized within thrust faults where deformation temperatures spatially continuously increased in both directions from n to s within each nappe and from top down in the nappe stack covering a temperature range of 180 380 c due to the higher metamorphic conditions thrusting of the lowermost nappe the doldenhorn nappe was accompanied by a much more pronounced nappe internal ductile deformation of carbonaceous rock types than was the case for the overlying wildhorn and gellihorn nappes ongoing thrusting brought the doldenhorn nappe closer to the surface the associated cooling resulted in a freezing in of the paleo isotherms of peak metamorphic conditions contemporaneous shearing localized in the basal thrust initially still in the ductile deformation regime and finally as brittle faulting and cataclasis inducing ultimately an inverse metamorphic zonation with ongoing exhumation and the formation of the helvetic antiformal nappe stack a bending of large scale tectonic structures thrusts folds peak temperature isotherms and cooling isotherms occurred while this local bending can directly be attributed to active deformation underneath the section investigated up to times of 2 3 ma a more homogeneous uplift of the entire region is suggested for the very late and still active exhumation stage

geophysical geological transect and tectonic evolution of the swiss italian alps a complete alpine cross section integrates numerous seismic reflection and refraction profiles across and along strike with published and new field data the deepest parts of the profile are constrained by geophysical data only while structural features at intermediate levels are largely depicted according to the results of three dimensional models making use of seismic and field geological data the geometry of the highest structural levels is constrained by classical along strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units because the transect is placed close to the western erosional margin of the austroalpine nappes of the eastern alps it contains all the major tectonic units of the alps a model for the tectonic evolution along the transect is proposed in the form of scaled and area balanced profile sketches shortening within the austroalpine nappes is testimony of a separate cretaceous age orogenic event west directed thrusting in these units is related to westward propagation of a thrust wedge resulting from continental collision along the meliata hallstatt ocean further to the east considerable amounts of oceanic and continental crustal material were subducted during tertiary orogeny which involved some 500 km of n s convergence between europe and apulia consequently only a very small percentage of this crustal material is preserved within the nappes depicted in the transect postcollisional shortening is characterized by the simultaneous activity of gently dipping north directed detachments and steeply inclined south directed detachments both detachments nucleating at the interface between lower and upper crust large scale wedging of the adriatic or apulian lower crust into a gap opening between the subduced european lower crust and the pile of thin upper crustal flakes alpine nappes indicates a relatively strong lower crust and detachment between upper and lower crust

fold axis parallel extension in an arcuate fold and thrust belt the case of the helvetic nappes abstract the helvetic nappes of western switzerland are discussed as an example of an arcuate foreland fold and thrust belt in which active fold axis parallel stretching occurred fold axis parallel extension is recorded by 1 1 incremental strain data from pressure shadow fibres the significance of pressure shadow fibres for the determination of the deformation history of a region is discussed pressure shadows are used to quantify the amount of and to describe the distribution of fold axis parallel extension occurring in the helvetic nappes 2 2 the extension directions of conjugate systems of en echelon veins it is shown that an analysis of the geometry of conjugate vein systems can reveal a regional deformation pattern the relative age of the conjugate en echelon vein systems in the helvetic deformation history can be assessed the geometry of the conjugate sets relative to the local anisotropy plane is described and the significance of the preferred orientation of their extension directions is discussed 3 3 fold axis parallel sections a comparison of the regional distribution of the fold axis parallel strain with the shape of the helvetic nappes in fold axis parallel sections shows that the fold axis parallel strain cannot be related to the footwall topography of the nappes it is concluded that the fold axis parallel extension in the helvetic nappes was induced by a change of direction of overthrust shear this change occurred late in the deformation history and was superposed on the already formed nappes the changing direction of overthrust shear is the expression of an overall anticlockwise rotation going on in the overthrusting alpine nappe pile relative to the european plate a rotation which lead to the arcuate shape of the western alps

duration of the early cambrian u pb ages of volcanic ashes from avalon and gondwana volcanic zircons from three ashes give a u pb date of 511 1 ma on trilobite bearing upper lower cambrian upper branchian series strata of southern new brunswick that correlate into the siberian middle botomian toyonian stage interval this very young age on the late but not latest early cambrian of avalon is consistent both with a 519 1 ma age on the older caerfai bay shales of south wales that are tentatively correlated into strata with the oldest avalonian trilobites lower branchian and with a 517 1 5 ma age on the antatlasia gutta pluviae zone trilobites of morocco determination of a 522 2 ma zircon age on the moroccan subtrilobitic lower cambrian lie de vin formation is consistent with an earlier reported 521 7 ma age from the lie de vin but suggests that a 526 4 ma age on australian trilobite bearing lower cambrian rocks may be too old a 33 ma duration of the avalonian early cambrian and an 8 ma length of the avalonian trilobite bearing lower cambrian support proposals that

cooling induced strain localization in carbonate mylonites within a large scale shear zone glarus thrust switzerland abstract the glarus thrust switzerland offers a great field example of strain localization under retrograde conditions along the thrust mylonitic microfabrics are characterized by a temperature stress controlled balance of grain size reducing mechanisms and grain growth consequently mean grain sizes decrease along the thrust with decreasing metamorphic conditions and towards the thrust contact in an opposite manner calcite twin densities increase towards the contact cpos are strongest between 0 5 and 15 m away from the thrust but become generally weaker in the last centimeters where also cataclasites occur the cpo weakening and grain size reduction towards the shear zone point to a change from predominant dislocation creep to granular flow finally ending in cataclastic deformation the microfabric changes correlate with a decrease in 13c and 18o towards the thrust contact indicating the presence of fluids during cycles of brittle and plastic deformation based on the microfabric changes variations in stable isotopes and cross cut relationships a subdivision into a low and high temperature shear zone can be made the microfabric modifications resulted from changes in deformation conditions due to ongoing thrusting and exhumation induced cooling promoting further strain localization of an existing high strain shear zone

very low grade metamorphism of the taveyanne greywacke glarus alps switzerland detailed textural and chemical data for mineral assemblages on a regional scale are presented for the metaandesitic eocene oligocene taveyanne greywacke of the glarus alps eastern switzerland presented data indicate an increase of metamorphic grade from zeolite facies to prehnite pumpellyite and pumpellyite actinolite facies low grade outcrops contain laumontite minor corrensite and pumpellyite assemblage type 1 whereas outcrops of higher metamorphic grade contain prehnite and two populations of pumpellyite type 2 prehnite pumpellyite al white mica type 3 a single outcrop shows pumpellyite actinolite facies type 4 from the zeolite to prehnite pumpellyite pumpellyite actinolite facies there are indications for an increase of the chemical equilibrium domain size for the critical paragenesis from a single detrital grain 1 mm in type 1 to a few millimetres in type 2 and to a whole thin section in type 3 metamorphic p t conditions were determined by a combination of chlorite thermometry fluid inclusion and vitrinite reflectance data peak temperatures range from 170 190d c for zeolite facies to 270 310d c for prehnite pumpellyite and pumpellyite actinolite facies for the higher temperature range pressures of 2 3 kbar are derived indicating a geothermal gradient of 24 32d c km 1 the well constrained temperature estimations derived for the assemblages provide a useful test of the different empirical calibrations of chlorite thermometers recently proposed the best correspondence to the temperatures determined here is for the cathelineau calibration in addition in the lower grade samples differences in textures and calculated temperatures provide a mean to distinguish between detrital and newly formed chlorites

simple shear experiments on calcite rocks rheology and microfabric ideal simple shearing of carrara marble and solnhofen limestone was achieved by inserting calcite rock slices into sandstone cylinders precut at 35 the experiments covered a wide range in temperatures 25 900 c at confining pressures of 200 and 250 mpa and at strain rates between 10 3 and 10 5 s 1 shear strains of up 2 7 were achieved the stress strain data for simple shear favourably compare with predictions on the basis of existing flow laws established in coaxial testing this comparison demonstrates that the simple shear experiments covered most of the previously established flow regimes for calcite rocks at the highest temperatures carrara marble exhibited substantial work softening after high shear strains a complete texture analysis was carried out with the u stage and a texture goniometer the following four distinct microfabric regimes were found 1 twinning regime an oblique c axis maximum deflected from the pole to the flattening plane towards 1 and against the imposed sense of shear results directly from e twinning extensive twinning some grains are completely twinned rapidly rotates the c axes into near parallelism with 1 this regime was observed for carrara marble deformed at temperatures below 700 c and for solnhofen limestone at room temperature 2 intracrystalline slip regime three c axis maxima were observed in both rock types at more elevated temperatures and in the absence of twinning these c axis orientations result from an alignment of slip planes and slip directions into parallelism with the shear zone boundary and the shear direction respectively this finding supports the idea of an orientation for easy slip resulting from simple shearing in addition to r and f glide basal glide is inferred to have been operative 3 grain boundary sliding regime a great circle distribution of c axes approximately perpendicular to the direction of finite shortening is observed this texture is weaker compared to the other regimes it is interpreted to result from minor contributions of f slip towards total strain this regime is restricted to fine grained solnhofen limestone deformed at the highest temperatures 4 grain boundary migration regime only in carrara marble deformed at the highest temperatures is there substantial grain boundary migration recrystallization the texture consists of a dominant c axis maximum oriented perpendicular to the shear zone boundary this single maximum corresponds to an orientation for easy slip for basal slip grain boundary migration assists rapid lattice reorientation and leads to geometrical work softening quantitative analysis of grain boundary surface orientations gave the following results within the twinning and the intracrystalline slip regimes the characteristic grain shape is elliptical for both rock types the strain ellipses derived from this analysis closely correspond to the known finite strain at the lowest temperatures at intermediate temperatures and especially in carrara marble there is a consistent trend for the aspect ratios to indicate too little flattening and for the angles between the long axis of the strain ellipse and the shear zone boundary to be too small in the absence of grain boundary migration recrystallization this finding indicates minor translations of grains with respect to one another grain boundary sliding or translations accommodated in the mantle regions of grains at the highest temperatures where extensive grain boundary migration occurs in carrara marble grain boundary migration regime two preferred orientations of grain boundaries are observed 1 parallel to the shear zone boundary and 2 parallel to an oblique direction deflected 20 away from the normal to the shear zone boundary in the sense of the imposed shear the same pattern of grain boundary alignment is observed in solnhofen limestone deformed in the grain boundary sliding regime the geological applications of this experimental work are discussed in terms of calcite tectonites in particular and sheared rocks in general

fluid flow pathways along the glarus overthrust derived from stable and sr isotope patterns the glarus thrust of the eastern helvetic alps has been proposed as a major pathway for metamorphic fluids expelled from the footwall during alpine deformation and prograde metamorphism the stable isotope composition of calcite in a thin continuous calc mylonite layer and gradients into the overlying verrucano siltstones and underlying flysch or carbonate are analyzed in detail a regional scale map of the 18 o composition of the calc mylonite covering 25 kilometers east west by 15 kilometers north south is interpolated from 35 sampling sites with a total of over 700 samples this map reveals a steep northward increase in 18 o from 11 to 18 permil smow interpreted as an isotopic front within the southernmost 6 kilometers and leveling out at about 20 permil farther north vertical profiles across the sharp thrust contact show significantly different isotopic fronts in the south where the verrucano formation is thrust upon marine carbonates and in northern sites where it rests on tertiary flysch southern sites display steep continuous isotopic gradients over about 1 meter above the thrust where both 18 o and 13 c decrease to background verrucano formation values of 10 to 11 permil 18 o smow and 6 permil 13 c pdb respectively footwall carbonates are significantly depleted from their original value of about 26 permil within a zone of less than 10 meters below the thrust contact the front geometry of 13 c increasing from 2t o2 permil downward within about 1 meter is much steeper than the one defined by 18 o northern sites in contrast display distended isotopic alteration fronts upward into the verrucano hangingwall where higher than background values in 18 o and 13 c are found up to 15 meters and 6 meters above the thrust contact respectively no isotopic alterations could be detected within the footwall flysch up to the thrust contact the 87 sr 86 sr systematics has been observed on the centimeter to millimeter scale in vertical profiles across the calc mylonite in three southern sites in each sample slab a topmost zone of slightly enriched homogeneous 87 sr 86 sr values 0 709 to 0 712 is found within a zone of highly sheared and dynamically recrystallized yellow veins alternating with dark stylolite seams on the sub millimeter scale in two slabs smooth vertical downward gradients to marine carbonate values 0 708 could be observed on the centimeter scale regional and local isotopic gradients are explained as exchange between the different rock reservoirs through the advection diffusion dispersion of fluids interact ing in a regime of brittle ductile deformation associated with 30 kilometers north ward thrust translation different scenarios of fluid flow along and or across the thrust plane are modeled using transport theory coupled with isotopic exchange reactions at an assumed temperature of 300 c considerable amounts of externally derived 18 o depleted basement derived fluids are required to explain the isotopic characteristics in the southern part of the thrust a time integrated fluid flux tiff of 4500 to 9100 m 3 m 2 is calculated for the channelized flow component along the thrust far exceeding any cross thrust compo nent of downward fluid infiltration of 3 45 to 5 7 m 3 m 2 in northern sites however any potential thrust parallel fluid flow is obscured by a dominant component of upward cross thrust flow of fluids derived from compaction dehydration of flysch units in the immediate footwall these calcite saturated fluids left their imprint in the

fluid migration through thrust faults in the helvetic nappes western swiss alps the 18o 13c and 87sr 86sr values of calcite and organic matter were measured for carbonate mylonites from numerous thrusts in the helvetic alps carbonate mylonites in most of the thrusts retain essentially unaltered protolith 18o and 13c values consistent with there having been little to no advection of isotopically distinct fluid through these faults only carbonate mylonites from the basal thrusts of the largest nappes have 18o and or 13c values that differ from those of their protoliths the zone of isotopic alteration exchange is confined to c 10 to 20 meters of these fault contacts we propose the fluids that migrated through these faults contained variable amounts of organically derived carbon and radiogenic strontium and were probably derived from dewatering of the sedimentary rocks and prograde metamorphic reactions in the nappes root zones apart from the basal thrusts of the largest nappes that behaved as narrow laterally extensive conduits for fluids there is little isotopic evidence that large quantities of fluids passed through most of the carbonate hosted thrusts in the helvetic alps

microfabric study on the deformational and thermal history of the alpi apuane marbles carrara marbles italy marbles from different geometrical and structural positions within the alpi apuane metamorphic complex show a large variability in microfabric types as indicated by microstructure c axis orientation and temperature analysis statically recrystallized samples showing a granoblastic microstructure and polygonal grain boundaries are characterized by a grain size variation from east to west from 80 100 m to 250 300 m this is correlated with an equilibration calcite dolomite temperature from 360 380 c to 420 430 c two kinds of dynamically recrystallized microstructures have been investigated a first one exhibiting coarse grains 150 200 m with lobate grain boundaries and a strong shape preferred orientation and a second one characterized by a smaller grain size 40 50 m and predominantly straight grain boundaries these microstructural types associated with localized post thermal peak shear zones and meter to kilometer scale folds are interpreted as related to high strain and high temperature crystal plastic deformation mechanisms dislocation creep associated with predominant grain boundary migration type b1 or subgrain rotation recrystallization type b2 these differences in dynamically recrystallized microstructures are related to equilibration temperatures higher in type b1 390 c than in type b2 370 340 c we have been able to relate the development of the different microfabric types to the successive stages of deformation of the alpi apuane metamorphic complex

post deformational annealing of calcite rocks abstract the evolution of microstructure and crystallographic preferred orientation cpo during post deformational annealing was studied on three calcite rock types differing in purity and grain size carrara marble 98 calcite mean grain size of 115 m solnhofen limestone 96 5 m and synthetic calcite aggregates 99 7 m samples were first deformed in torsion at 727 c at a shear strain rate of 3 10 4 s 1 to a shear strain of 5 and subsequently heat treated at 727 c for various durations between 0 and 24 h microstructures and cpos were analysed by optical microscopy image analysis and electron backscatter diffraction ebsd all rock types deformed in the dislocation creep field at the same applied conditions but their microstructures and cpos after deformation and after annealing differed depending on starting grain size and material composition in carrara marble and in the synthetic calcite aggregate a strong cpo developed during deformation accompanied by dynamic recrystallisation with significant changes in grain size during annealing widespread grain growth and subtle changes of cpo occurred and equilibrated foam microstructures were approached after long annealing times the cpo is the only feature in annealed samples indicating an earlier deformation phase although it is not always identical to the cpo formed during deformation in the more impure solnhofen limestone secondary phases on grain boundaries suppressed grain boundary mobility and prevented both the formation of a recrystallisation cpo during deformation and grain size modification during deformation and annealing

calcite mylonites in the central alpine root zone abstract north of the insubric line in the central alpine root zone carbonate rocks are concentrated in very narrow zones and have been metamorphosed under amphibolite facies conditions by the tertiary lepontine metamorphism grain size 1 mm post metamorphic deformation under greenschist facies conditions produced calcite mylonite bands a few millimeters to tens of meters wide in these marble zones microstructural development begins with twin formation bending of twin boundaries grain and twin boundary migration and recrystallization in high stress regions progressive mylonitization by dynamic recrystallization results in a microstructure with elongated calcite crystals long axis 20 50 m axial ration 1 4 in this fine grained matrix porphyroclasts of calcite quartz white mica biotite diopside tremolite scapolite and plagioclase are preserved ultra mylonite bands in pure calcite rocks show an even finer grain size of 5 10 m lattice preferred orientation is not present in the undeformed marbles but it develops during mylonitization the c axis orientation in the mylonites forms an asymmetric point maximum in the ultra mylonite no preferred orientation is left it is concluded from microstructural and textural aspects that during mylonitization dislocation creep accompanied by dynamic recrystallization were the most important processes whilst grain boundary sliding was the dominant mechanism during the formation of the ultra mylonites shear sense determinations indicate a horizontal right lateral strike slip shear system this is in good agreement with evidence regarding other movements along the insubric line which can be observed in ductile and brittle shear zones

grain coarsening maps for polymineralic carbonate mylonites a calibration based on data from different helvetic nappes switzerland abstract microstructures of carbonate mylonites with 0 40 vol second phase particles from different helvetic nappes switzerland have been analyzed while the mean calcite grain size dcc increases with temperature t second phases pin calcite grain boundaries two types of second phases can be distinguished small second phases included in calcite grains and larger second phases at calcite grain boundaries both coarsening with volume fraction and t these trends are controlled by an interaction of different processes during deformation including diffusion dynamic recrystallization grain growth and pinning in terms of dcc t dependencies the microstructures of the investigated nappes are similar the relationship between dcc and t differs for high t and low t these observations can be explained by a change in the simultaneous activity of dominant mechanisms e g diffusion and dislocation creep as a function of t and second phase content in contrast the relation log dp 1 t dp second phase grain size is linear with constant slope for all nappes indicating that growth processes of second phases are identical despite differences in fluid activity and strain rate between individual nappes the microstructural relationships of dcc second phases and t remain similar therefore grain coarsening maps of second phase and recrystallization controlled calcite aggregates are a representative tool to predict deformation conditions and mechanisms for other shear zones developed under similar physical conditions

experimental study of the influence of stress temperature and strain on the dynamic recrystallization of carrara marble carrara marble has been deformed experimentally at temperatures ranging between 500 and 1000 c at confining pressures of 200 and 300 mpa and up to very large strains in extension and compression in order to study the microstructural and mechanical property changes associated with dynamic recrystallization microstructural studies were made by optical microscopy on ultrathin sections and automatic grain size measurement techniques were used when the temperature is sufficiently high 600 c and the stresses are high enough for deformation twinning to occur twin boundary migration is a powerful recrystallization mechanism that does not modify the grain size at stress levels too low to activate twinning recrystallization occurs in two stages the formation of nuclei by grain boundary bulging and subgrain rotation recrystallization in the grain boundary regions followed by a second stage of grain boundary migration recrystallization to a larger grain size that eventually overprints the entire rock volume the recrystallization process requires larger prestrains at the lower temperatures the size to which migration recrystallized grains grow seems to be limited by the stress and grain size dependent twinning field boundary or by the boundary between the dislocation creep and grain size sensitive flow mechanisms within the range of experimental observations dynamically recrystallized grain size does not depend on strain rate or temperature separate empirical stress versus grain size relations are presented for rotation and migration recrystallization that may be used for palaeopiezometry no unequivocal experimental evidence of weakening resulting from recrystallization to finer grain sizes at laboratory strain rates was found however extrapolation of the experimental data to low natural strain rates suggests that weakening following recrystallization may occur in nature

a few remarks on the kinetics of static grain growth in rocks static grain growth is a relatively simple transformation in which grain size increases under driving forces caused by grain and interphase boundary curvature given the relative simplicity of the protocol for grain growth experiments measurements of grain boundary mobility show surprising variations boundary mobilities during grain growth are affected by solute and impurity chemistry chemical fugacity of trace and major elements pore size and number pore fluid chemistry the presence of melts and the presence of solid second phases as well as temperature and pressure all of these factors may exert influence on grain growth of rocks in natural situations and many are also present during the laboratory experiments provided that the necessary kinetics parameters are known bounds may be placed on the interface mobility when pores partial melts or solutes are present to predict the rate of grain growth in natural situations will require improved laboratory data and careful consideration of the thermodynamic conditions likely to be encountered in nature

differences in grain growth of calcite a field based modeling approach normal grain growth of calcite was investigated by combining grain size analysis of calcite across the contact aureole of the adamello pluton and grain growth modeling based on a thermal model of the surroundings of the pluton in an unbiased model system i e location dependent variations in temperature time path 2 3 and 1 3 of grain growth occurs during pro and retrograde metamorphism at all locations respectively in contrast to this idealized situation in the field example three groups can be distinguished which are characterized by variations in their grain size versus temperature relationships group i occurs at low temperatures and the grain size remains constant because nano scale second phase particles of organic origin inhibit grain growth in the calcite aggregates under these conditions in the presence of an aqueous fluid these second phases decay at a temperature of about 350 c enabling the onset of grain growth in calcite in the following growth period fluid enhanced group ii and slower group iii growth occurs for group ii a continuous and intense grain size increase with t is typical while the grain growth decreases with t for group iii none of the observed trends correlate with experimentally based grain growth kinetics probably due to differences between nature and experiment which have not yet been investigated e g porosity second phases therefore grain growth modeling was used to iteratively improve the correlation between measured and modeled grain sizes by optimizing activation energy q pre exponential factor k0 and grain size exponent n for n 2 q of 350 kj mol k0 of 1 7 1021 mns 1 and q of 35 kj mol k0 of 2 5 10 5 mns 1 were obtained for group ii and iii respectively with respect to future work field data based grain growth modeling might be a promising tool for investigating the influences of secondary effects like porosity and second phases on grain growth in nature and to unravel differences between nature and experiment

the concept of steady state foliation abstract a steady state foliation is thought of as a foliation with constant orientation and intensity in a rock undergoing steady state flow the problem discussed is whether such straininsensitive foliations exist in rocks and how they might be distinguished from the more familiar strain sensitive foliations steady state foliations would be useful indicators of stress or of strain rate yet misleading if used as indicators of finite strain one requirement for maintenance of steady state foliations is operation of processes that locally weaken grain shape preferred orientation or reduce grain aspect ratios or destroy lithological layering during flow these are the inverses of the processes normally discussed in connection with foliation development many such processes are known though the details of how and when they operate efficiently enough to stabilize a foliation are unknown there is however a tendency for some of them to operate more efficiently at high strains high temperatures and in flow regimes with high vorticity natural and experimental high temperature shear zones are accordingly one environment in which steadystate foliations may be encountered an experiment is described in which a thin specimen of para dichlorobenzene was given a large shearing deformation at 90 of its absolute melting point a steady state foliation was not produced but the technique is a promising one for further microstructural studies where in situ observation of material undergoing large deformations is desirable

grain coarsening in contact metamorphic carbonates effects of second phase particles fluid flow and thermal perturbations under contact metamorphic conditions carbonate rocks in the direct vicinity of the adamello pluton reflect a temperature induced grain coarsening despite this large scale trend a considerable grain size scatter occurs on the outcrop scale indicating local influence of second order effects such as thermal perturbations fluid flow and second phase particles second phase particles whose sizes range from nano to the micron scale induce the most pronounced data scatter resulting in grain sizes too small by up to a factor of 10 compared with theoretical grain growth in a pure system such values are restricted to relatively impure samples consisting of up to 10 vol micron scale second phase particles or to samples containing a large number of nano scale particles the obtained data set suggests that the second phases induce a temperature controlled reduction on calcite grain growth the mean calcite grain size can therefore be expressed in the form d 1 4 c2 eq rt dp fp m where c2 is a constant q is an activation energy t the temperature and m the exponent of the ratio dp fp i e of the average size of the second phases divided by their volume fraction however more data are needed to obtain reliable values for c2 and q besides variations in the average grain size the presence of second phase particles generates crystal size distribution csd shapes characterized by lognormal distributions which differ from the gaussian type distributions of the pure samples in contrast fluid enhanced grain growth does not change the shape of the csds but due to enhanced transport properties the average grain sizes increase by a factor of 2 and the variance of the distribution increases stable d18o and d13c isotope ratios in fluid affected zones only deviate slightly from the host rock values suggesting low fluid rock ratios grain growth modelling indicates that the fluid induced grain size variations can develop within several ka as inferred from a combination of thermal and grain growth modelling dykes with widths of up to 1 m have only a restricted influence on grain size deviations smaller than a factor of 1 1 to summarize considerable grain size variations of up to one order of magnitude can locally result from second order effects such effects require special attention when comparing experimentally derived grain growth kinetics with field studies

alpine deformation on naxos greece a detailed structural study of naxos attic cycladic massif greece reveals two major deformation events the first one is associated with large scale thrusting and high pressure low temperature metamorphism during an early alpine subduction episode the second event occurred during continental extension and the associated development of localized thermal domes where lower crustal rocks were brought into contact with upper crustal units along a major shallow dipping shear zone we agree with a model of naxos as a cordilleran type metamorphic core complex however our observations show that the sense of shear was upper plate moving north during the second event calling for a reinterpretation of existing tectonic models of the cyclades

grain coarsening maps a new tool to predict microfabric evolution of polymineralic rocks polymineralic rocks undergo grain coarsening with increasing temperature in both static and deformational environments as long as no mineral reactions occur the grain coarsening in such rocks is complex because the different phases influence each other and it is this interaction that controls the rate of grain coarsening of the entire aggregate we present a mathematical approach to investigate coupled grain coarsening using a set of microstructural parameters including grain size and volume fraction of both second phases and matrix mineral in combination with temperature information based on samples from polymineralic carbonate mylonites that were deformed at different temperatures we demonstrate how the mathematical relation can be calibrated for this natural system using such data sets for other lithologies grain coarsening maps can be generated which allow the prediction of microstructural evolution in polymineralic rocks such predictions are crucial for all subdisciplines in the earth sciences that require fundamental knowledge about microstructural changes and rheology of an orogen at different depths such as structural geology geophysics geodynamics and metamorphic petrology

granular flow in polymineralic rocks bearing sheet silicates new evidence from natural examples abstract natural deformation in carbonate mylonites bearing sheet silicates occurs via a complex interaction of granular flow and solution transfer processes and involves continuous cycles of dissolution grain boundary diffusion nucleation and growth in this way new sheet silicates a nucleate within voids formed by grain boundary sliding of calcite grains b grow and c rotate towards the shear plane as a consequence small mica grains show a wide range of orientations with respect to the shear plane but moderate to large grains are subparallel both to each other and to the shear plane increases of average grain sizes with increasing temperature of sheet silicates in mica rich layers is more pronounced than in mica poor layers in the calcitic matrix however sheet silicates can only grow via solution precipitation and mass transfer processes therefore the observed grain size variability indicates drastic differences in mass transfer behavior between the individual layers which might be related to differences in the fluid flux based on these observations a conceptual model for the microfabric evolution in sheet silicate bearing mylonites is presented

oxygen isotope thermometry of quartz calcite veins unraveling the thermal tectonic history of the subgreenschist facies morcles nappe swiss alps combined structural analysis and oxygen isotope thermometry of syntectonic quartz calcite fibrous veins can be used to correlate the thermal history of deformed rocks with specific structural and tectonic events results are presented for the morcles nappe in the western helvetic alps switzerland where mineral parageneses illite crystallinity and fluid inclusion chemistry record an apparent peak metamorphic temperature gradient that increased across the morcles nappe from anchizonal conditions in the foreland to epizonal conditions in its hinterland root zone twenty seven quartz calcite veins were analyzed in this study in order to determine the temperatures of veining during formation and deformation of the nappe peak metamorphic temperatures ranged from 260 to 290 c in the shallower foreland localities and to 330 to 350 c in the deeper more hinterland localities at the end of s1 foliation formation related to large scale folding temperatures gradually decreased throughout the nappe during subsequent development of the s2 foliation and s3 crenulation cleavage uplift and erosion of the overlying nappe pile resulted in slow cooling of the morcles nappe during the waning stages of the alpine orogeny the dominant foliation forming deformation of the morcles nappe occurred at elevated temperatures over the course of 10 to 15 ma combined structure oxygen isotope analyses of quartz calcite veins yield better temperature and temporal constraints on the thermal histories of subgreenschist vein bearing tectonites than do other geothermometers

thermally induced grain growth of calcite marbles on naxos island greece the island of naxos is composed of an elliptically shaped structural and thermal dome of miocene age peak metamorphic temperatures within the central migmatite complex exceeded 700 c decreasing to about 300 c at the most distant exposures on the island equigranular calcite marbles which outcrop together with metapelites and metabasites over the whole island show a systematic pattern of increasing grain size towards the central migmatite complex with a significant discontinuity in the pattern corresponding approximately with the 500 c isotherm the microstructures and grain size distributions in the marbles are consistent with normal grain growth the variation of grain size with peak temperature attained can be explained equally well by the assumptions that a a maximum grainsize had developed particularly at higher temperatures or that b the grain size had been frozen in by a combination of cooling and coarsening both of which combine to reduce the rate of grain growth

finite strain patterns in some alpine nappes abstract the patterns of finite strain in some alpine nappes and thrust sheets are reviewed together with their tectonic evolution glarus nappe the finite strain pattern approximately that of heterogeneous simple shear was acquired during upper oligocene times when the helvetic thrust block was deformed together with its infrastructure and basement the glarus thrust was formed during miocene times and modified by pliocene to recent differential uplift morcles nappe this large recumbent fold nappe overrode the aiguilles rouges massif and its cover towards the northwest the finite strain pattern resulted from successive diagenetic compaction multilayer buckling and heterogeneous simple shear high strains occur along the inverted limb of the nappe and fold hinges are oriented subperpendicular to the nw stretching lineation final emplacement of the nappe during the miocene was perhaps a later event chartreuse massif 33 e w shortening was developed across this fold and thrust belt during post helvetian times by decollement along the oxfordian shales in response to thrusting and uplift in the belledonne basement the oxfordian shales had earlier accommodated a pre helvetian probably oligocene deformation in the basement and its trias bajocian cover when n030 trending subhorizontal folds cleavage and a stretching lineation 18 n030 stretching were developed digne nappe detached along the keuper evaporites the cover was displaced westwards in two stages 1 late oligocene with folding cleavage development formation of the frontal slices and an overall e w shortening of 20 and 2 late miocene pliocene after emplacement of the embrunais nappes in the east producing the digne thrust it is concluded that for these alpine nappes geological criteria must be used to establish their evolution if the internal deformation can then be assigned to part of this evolution the pattern of finite strain can be used to quantify and elucidate that part a maximum of information is gained if the incremental deformation history can also be obtained from study of syntectonic fibres

microfabrics in carbonate mylonites along a large scale shear zone helvetic alps abstract carbonate mylonites with varying proportions of second phase minerals were collected at positions of increasing metamorphic grade along the basal thrust of the morcles nappe helvetic nappes switzerland variations of temperature stress and strain rate changes in chemistry of solid and fluid phases and differing degrees of strain localization and annealing were tracked by measuring the shapes mean sizes and size distributions of both matrix and second phase grains as well as crystal preferred orientation cpo of the matrix field structures suggest that strain rate was constant along the fault the mean and distribution of the calcite grain sizes were affected most profoundly by temperature increased temperature presumably accompanied by decreased stress correlated with larger mean sizes and wider size distributions at a given location the matrix grains in mylonites with more second phase particles are on average smaller have narrower size distributions and have more elongate shapes for example mylonites with 50 vol of second phases have matrix grain sizes half that of pure mylonites changes in calcite chemistry and the presence of synkinematic fluids seemed to influence microfabric only weakly temporal variations in conditions such as exhumation induced cooling apparently provoke changes in temperature stress and strain rate along the nappe these changes result in further strain localization during retrograde conditions and cause the grain size to be reduced by an additional 50 the matrix cpo strengthens with increasing temperature or strain but weakens and rotates with increasing second phase content these fabric changes suggest differing rates of grain growth grain size reduction and development of cpo owing to variations in the deformation conditions and perhaps mechanisms to interpret natural mylonite structures or to extrapolate mechanical data to natural situations requires careful characterization of the microfabric and in particular second phase minerals

composite flow laws for crystalline materials with log normally distributed grain size theory and application to olivine abstract conventional steady state flow laws describing combined grain size insensitive dislocation creep and grain size sensitive diffusion creep incorporate grain size as a single mean value however rocks exhibit distributed grain size and variations in the shape of the distribution such as its width will accordingly affect rheological behavior to evaluate this effect we have derived composite dislocation diffusion flow laws describing upper and lower bounds on the rate of deformation of materials showing a grain size distribution of the commonly observed log normal type the upper and lower bound flow laws obtained allow systematic investigation of the influence of the grain size distribution parameters i e the median and standard deviation on composite rheology the results demonstrate major effects of distribution width as well as median value application to polycrystalline olivine deforming by coble creep and power law dislocation creep reveals significant implications for interpreting deformation experiments and modeling flow in the earth s mantle the flow laws also provide an improved basis for modeling the deformation of rocks during geological processes in the crust and mantle

a new technique to automatically quantify microstructures of fine grained carbonate mylonites two step etching combined with sem imaging and image analysis a two step etching technique for fine grained calcite mylonites using 0 37 hydrochloric and 0 1 acetic acid produces a topographic relief which reflects the grain boundary geometry with this technique calcite grain boundaries become more intensely dissolved than their grain interiors but second phase minerals like dolomite quartz feldspars apatite hematite and pyrite are not affected by the acid and therefore form topographic peaks based on digital backscatter electron images and element distribution maps acquired on a scanning electron microscope the geometry of calcite and the second phase minerals can be automatically quantified using image analysis software for research on fine grained carbonate rocks e g dolomite calcite mixtures this low cost approach is an attractive alternative to the generation of manual grain boundary maps based on photographs from ultra thin sections or orientation contrast images

staircase 40 ar39ar spectra of fine grained white mica timing and duration of deformation and empirical constraints on argon diffusion staircase 40 ar 39 ar spectra of 2 to 6 m white micas in ductile carbonate mylonites morcles doldenhorn nappe switzerland record ages between 32 and 13 ma these ages are within independent geochronologic and biostratigraphic time limits for the beginning and ending of deformation of this fold thrust nappe we interpret these data to record protracted white mica neocrystallization and growth during low temperature ductile deformation such that the differences between the maximum and minimum ages in the 40 ar 39 ar spectra record the time span over which mica formed and grew we have modeled the argon concentrations in these micas taking into account the thermal history of the nappe mica growth and diffusional loss of argon our results indicate that available experimental data underestimate the activation energy for argon diffusion in muscovite and that the retentivity of argon in white mica is greater than generally thought

the effect of second phase particles on stable grain size in regionally metamorphosed polyphase calcite marbles samples of the calcite rich shelburne marble collected at the pfizer quarry in adams massachusetts show an order of magnitude variation in grain size calcite grain size ranges from 94 to 1101 m because these calcite marbles share the same pressure temperature and strain histories some other factor must be responsible for the grain size variation grain size appears to be controlled by the concentration of impurity or second phase particles large calcite grain size occurs where the volume fraction of second phase particles is low and grain size decreases as second phase volume fraction increases the relationship between calcite grain size d second phase grain size d and second phase volume fraction f can be described by the power law d d 1 4 f 0 36 a result that is consistent with models based upon short term hours or days laboratory experiments with metals and ceramics and computer simulations of grain growth grain growth appears to be greatly restricted by as little as a few per cent of second phase particles with a transition from highly restricted to almost unrestricted grain growth occurring at 5 volume of second phase particles these results indicate that second phase particles exercise an important control on grain size and can effectively inhibit grain growth in metamorphic rocks the behaviour of second phases in short term laboratory experiments may closely approximate the behaviour of second phases in grain growth lasting several orders of magnitude longer in the metamorphic environment

the role of veining and dissolution in the evolution of fine grained mylonites the mcconnell thrust alberta microstructural observations of the mcconnell thrust fault rocks demonstrate the importance of vein formation and calcite dissolution in the evolution of the mcconnell thrust limestone mylonites the protolith to the mylonite is a micritic limestone the mylonite contains numerous discontinuous bedding parallel calcite veins that range from relatively undeformed except for twinning and undulose extinction to highly sheared the highly sheared veins show evidence for dynamic recrystallization and grain size reduction along grain and twin boundaries that can lead to complete recrystallization to a grain size of approximately 1 3 m the bulk of the calcite matrix within the mcconnell thrust mylonite is interpreted to have formed by dynamical recrystallization of veins the emplacement of relatively coarse grained veins promoted the activation of dislocation creep within the fault rocks of the thrust in the absence of the increase in grain size afforded by vein emplacement it is anticipated that the fine grained protolith would have deformed predominantly by solution transfer with grain boundary sliding and localized brittle shearing the layer parallel calcite veins are found in close proximity to sheared clay seams which are interpreted to represent the insoluble residue left behind after dissolution of calcite these clay seams may have contributed to the build up of high pore fluid pressures which if intermittently reaching lithostatic conditions during displacement would result in transient brittle failure and thrust surface parallel vein emplacement in an otherwise ductilely deforming rock

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

strain partitioning in the helvetic thrust belt of eastern switzerland from the leading edge to the internal zone abstract the strain and strain partitioning in the helvetic thrust belt are analysed in order to determine their variation across the belt from the external thin skinned portion to the internal thick skinned portion and in order to begin the detailed mechanical analysis of the entire fold and thrust belt coarse grained limestones of jurassic and cretaceous age were chosen for analysis because they can be traced from the external to the internal zones the strain within a bed is partitioned into three components transgranular pressure solution microfaults veins twinning granular and intragranular exclusive of twinning crystal plasticity associated with recrystallization transgranular strain was very important in the early history of the helvetic nappes giving way to twinning at a later stage under tectonic burial twinning strain was early in the infrahelvetic complex giving way to intracrystalline deformation at the later stage of burial the transition from transgranular to intragranular dominated strain occurred at a vitrinite reflectance value of 3 5 significantly below the greenschist grade of metamorphism in a large scale fold at the leading edge of the helvetic nappes transgranular strains were associated with the buckling stage of the fold and twinning occurred during fold tightening in more internal parts of the helvetic nappes twinning strains are also late with regard to transgranular strains but here their pattern corresponds to the regional finite strain pattern in the internal zone the infrahelvetic complex twinning seems to have been an early event and records an initial layer parallel shortening followed by regional internal deformation with intragranular strains

influence of rock fragments on the water retention and water percolation in a calcareous soil abstract the water retention properties of a calcareous soil containing rock fragments have been determined in the laboratory thanks to pressure plate measurements done on both the fine earth and the rock fragments from the soil the available water content awc has been calculated from these data we have shown that when the rock fragments are neglected the awc can be overestimated by 39 when we do not neglect their volume but when their hydraulic properties are not considered the awc can be underestimated by 34 by using a reservoir model we have also calculated the effect of rock fragments on water percolation to groundwater depending of the climatic characteristics of the year the underestimation of percolation when we neglect the rock fragments can reach up to 14 9 and the overestimation when we neglect their hydraulic properties can be equal to 15 8 these findings emphasise the role of the rock fragments on the water supply in stony soils