wind and thermodynamic retrieval from single doppler measurements of a gust front observed during phoenix ii abstract the adjoint method to retrieve the three dimensional wind and thermodynamic fields is applied to single doppler observations of a gust front measured during the phoenix ii experiment this method uses a fluid dynamics model and its adjoint and combines the retrieval with data assimilation into the prediction model the wind and thermodynamic variables are determined by minimizing the difference between the model solution and the observations experiments are conducted first with radial velocity alone and then with both radial velocity and reflectivity to examine the quality of the retrieval with respect to radar location boundary conditions length of assimilation data filtering smoothing enforced by penalty functions and model accuracy verification of these experiments is provided by a dual doppler analysis test results show that the adjoint method is able to retrieve the wind and thermodynamic fields of the gust front the retrieved horizontal wind agrees very well with the dual doppler

preferred orientation of plagioclase neutron diffraction and u stage data abstract pole figures of anorthosite mylonite an 65 from san juan bautista california were determined with neutron diffraction using a 23 position sensitive detector this novel technique enables us to deconvolute the complex diffraction spectrum of this triclinic mineral into fifteen separate peaks hkl which are measured simultaneously all pole figures display strong preferred orientation with complicated triclinic distributions from which it appears that 001 poles are concentrated normal to the schistosity plane of the specimen the triclinic mineral is well suited to discuss some fundamental issues of texture representation if crystals are measured individually e g on the u stage positive and negative ends of directions can be unequivocally identified and the whole sphere rather than a hemisphere is necessary to represent the distribution of positive axes this is illustrated for a plagioclase rich amphibolite from orno huvud sweden

microstructural deformation record of an orogen parallel extension in the vepor unit west carpathians abstract deformation microstructures of quartzo feldspathic rocks have been used to analyse the orogen parallel stretching of the vepor unit in the west carpathians during cretaceous convergence this process occurs contemporaneously with the burial of the vepor basement related to the overthrusting palaeozoic volcano sedimentary sequences of the gemer unit the microstructures develop along a metamorphic gradient indicating an increase of pressure and temperature towards the structural footwall the recrystallization of quartz occurs in the field of subgrain rotation recrystallization sgr while the plagioclase and k feldspar disintegrate into a neocrystallized muscovite albite matrix palaeopiezometry of the recrystallized quartz in conjunction with p t estimates yield strain rates of 9 10 12 to 6 10 14 s 1 depending on temperature 380 480 c and choice of piezometer and flow law calibration strain analysis of the recrystallized quartz aggregates and quartz texture analysis indicate an overprint of the variscan magmatic and high grade fabrics by a cretaceous plane strain deformation resulting in vertical shortening and horizontal orogen parallel east west stretching spatial distribution and conflicting sense of shear of the asymmetrical quartz lattice preferred orientation patterns indicate that the large scale pure shear deformation of the vepor unit is locally accommodated by simple shear zones observed metamorphic gradients across the vepor unit are interpreted to result from later large scale folding and heterogeneous exhumation of the orogen parallel deformation fabric

quantification of the microstructural evolution of polycrystalline fabrics using fame application to in situ deformation of ice abstract in geology glaciology and material science new technological advances result in an ever increasing amount of data and datasets in particular when in situ experiments are conducted rapid rigorous and reliable statistical treatment is needed to allow researchers to access these large datasets for further analysis here we present fame fabric analyser based microstructure evaluation a suite of matlab scripts that utilize the matlab open source toolboxes mtex and polylx optional for rapid quantification of thin section data the data has been collected using an automated fabric analyser at a spatial resolution of 5 m pixel from the dataset grain maps are reconstructed and grain and grain boundary statistics are determined the same scripts calculate orientation density distribution diagrams and eigenvalues of the orientation tensor in the case of 2d in situ plane strain deformation experiments on polycrystalline heavy water d2o a matlab script based batch analysis for each deformation step was performed fame offers the possibility to generate movie files that combine optical data with c axes orientation data and grain statistics application of the presented scripts to analyse in situ deformation experiments of polycrystalline ice shows the value of rigorous quantification of the microstructural evolution data for process oriented research

quartz vein fabrics coupled to elevated fluid pressures in the stawell gold deposit south eastern australia shear and extensional veins formed during the reactivation of the magdala shear system at stawell in western victoria australia contribute to the formation of the auriferous central and basalt contact lodes within this shear system is a range of fault rocks accompanied by steep dipping 65 quartz rich laminated shear veins and relatively flat lying extensional veins both vein sets appear to have been a primary source for the host rock permeability during fluid flow in a regime of significant deviatoric stresses the macro and microstructures suggest that the dilatancy that produced mineralized veins formed under conditions of overpressure generated by fluid infiltration late in a tectonic regime a new microfabric analysis technique is used to investigate the quartz rich veins which allows rapid integration of the microstructure with the crystallographic preferred orientations cpos both the shear and extensional quartz veins have a random cpo with 120 dihedral angles between the quartz quartz grains which is typical of a metamorphic equilibrium microfabric the microstructures indicate that the quartz has undergone extensive grain adjustment in the solid state with grain shape and size affected by interfacial solution pressure solution effects these features are consistent with inferences from experimental rock deformation studies where grain boundary migration is enhanced in a water rich environment the onset of solution transfer processes pressure solution developed as the quartz microfabric stabilized and continued to modify the cpo and microstructure significantly it is concluded that grain growth and pressure solution are coupled diffusive mass transfer processes related to fluctuations in pore fluid pressures in a region undergoing deformation at near lithostatic pressures

natural deformation fabrics of plagioclase implications for slip systems and seismic anisotropy abstract the optical and tem microstructures and fabrics of twelve naturally deformed plagioclase containing rocks of compositions from an0 an80 have been studied with a view to determining the deformation mechanisms the optical indicatrix fabrics have been recorded in all samples with respect to the foliation and lineation in general and form a girdle in the foliation plane with a high concentration of normal to the foliation in some cases the orientation of 010 and 001 cleavages or albite and pericline twins has allowed the construction of pole figures in all cases 010 has been shown to be the dominant slip plane with either 001 or 100 the dominant slip direction tem shows that the dominant slip system is 010 001 with secondary 010 100 the seismic p wave anisotropy has been calculated for the first time from the lpo data of plagioclase the anisotropy coefficient is high at around 15 the minimum p velocity is normal to the lineation in the foliation plane and the maximum is sub parallel to the foliation normal the combined information on deformation kinematics and seismic anisotropy is valuable for interpretations of deep crustal seismic sections

temperature and strain rate dependent microfabric evolution in monomineralic mylonite evidence from in situ deformation of norcamphor norcamphor c7h10o was subjected to plane strain simple shear in a see through deformation rig at four different strain rate and temperature conditions two transient stages in the microfabric evolution to steady state are distinguished the grain scale mechanisms associated with the microstructural and textural evolution vary with the applied temperature strain rate and strain in high temperature low strain rate experiments computer integrated polarization microscopy reveals that the texture evolution is closely related to the crystallographic rotation paths and rotation rates of individual grains high c axis rotation rates at low to intermediate shear strains are related to the development of a symmetrical c axis cross girdle by the end of the first transient stage 1 5 to 2 during the second transient stage 1 5 to 6 the cross girdle yields to an oblique c axis single girdle as c axis rotation rates decrease and the relative activity of grain boundary migration recrystallization increases steady state 8 is characterized by a stable end orientation of the sample texture and the cyclic growth rotation and consumption of individual grains within the aggregate

deformation induced silica redistribution in banded iron formation hamersley province australia abstract the formation of banded iron formations bif remains controversial despite their potential to provide key information on precambrian atmospheres and hydrospheres it is widely agreed that bif are chemical sedimentary rocks comprising alternating layers of iron oxides and chert formed from poorly known precursor phases many models address the chemical transformation of such precursor iron oxide phases into bif during compaction and diagenesis however the formation of chert and the influence of physical forces in this process have received less attention microstructural analysis of bif from the hamersley province western australia reveals that significant amounts of silica were redistributed by dissolution precipitation creep during both diagenesis and regional scale deformation this physicochemical process led to silica remobilisation and volume loss by stress induced dissolution of microcrystalline quartz in an aqueous fluid the dissolved solid phase was transported by diffusion and fluid flow along grain boundaries or within available porosity and then reprecipitated in low pressure zones leading to local volume increase these processes were further enhanced by rheological contrasts between different minerals resulting in significant variations of chert band thickness microstructural observations combined with quantitative microfabric analysis reveal domains of crystallographic preferred orientations cpo in quartz grains within chert layers the cpo fabrics record strain regimes e g pure and simple shear extension and shortening that modified quartz aggregates by dissolution precipitation creep providing new insights into the metamorphic and deformation history of bif we document microstructures that indicate that non coaxial deformation was active during diagenesis and subsequent deformation of the hamersley province bif further relatively undeformed chert layers may have been similarly affected by significant amounts of dissolution precipitation creep providing a possible explanation for the destruction of primary features we show that different generations of chert alternate on a micro scale suggesting that the role of deformation has been underestimated in many aspects of bif research the discovery of dissolution precipitation creep in low grade metamorphic bif provides a potential link between the physical and chemical processes that occur within these rocks after deposition in the hamersley province dissolution precipitation creep was active from the compaction or diagenesis stage and probably operated during all major extensional and compressional deformation events we also suggest that chert layers without cpo record the least overprint by diagenesis and as the most pristine form of bif should be targeted for future paleo environmental research

the influence of crystallographic orientation and grain boundary migration on microstructural and textural evolution in an s c mylonite abstract the analysis of the subgrain and dislocation sub structure present in grains in different crystallographic orientations within a domainal s c mylonite is reported the study reveals a range in subgrain size and development which is related to the crystal orientation of the host grain in the mylonite subgrains in grains with easy slip orientations contain large subgrains while grains in more complex slip orientations contain small subgrains the dislocation densities preserved in the mylonite are extremely variable even within individual subgrains and may be the result of a late stress pulse the analysis indicates that grain boundary migration was an important process in the microstructural evolution initiating the selective removal of some orientations and thus influencing the final crystallographic preferred orientation present in different domains the data collected is also used to assess the potential stability and preservation of microstructures during the non steady state deformation expected at the end of a deformation event

influence of deformation and fluids on ar retention in white mica dating the dover fault newfoundland appalachians abstract white mica 40ar 39ar analyses may provide useful constraints on the timing of tectonic processes but complex geological and thermal histories can perturb ar systematics in a variety of ways ductile shear zones represent excellent case studies for exploring the link s between dynamic re neo crystallization of white mica and coeval enhanced fluid flow and their effect on 40ar 39ar dates white mica 40ar 39ar dates were collected from compositionally similar granites that record different episodes of deformation with proximity to the dover fault a terrane bounding strike slip shear zone in the appalachian orogen newfoundland canada 40ar 39ar data were collected in situ by laser ablation and by step heating single crystals results were compared to each other and against complementary u pb zircon and monazite and k ar fault gouge analysis although step heat 40ar 39ar is a widely applied method in orogenic settings this dataset shows that relatively flat step heat 40ar 39ar spectra are in contradiction with wide spreads in in situ 40ar 39ar dates from the same samples and that plateau dates in some cases yielded mixed dates of equivocal geological significance this result indicates that the step wise release of ar from white mica likely homogenizes and obscures spatially controlled ar isotope reservoirs in white mica from sheared rocks in contrast in situ laser ablation 40ar 39ar analysis preserves the spatial resolution of 40ar reservoirs that have been variably reset by deformation and fluid interaction this study therefore suggests that laser ablation is the best method for dating the timing of deformation recorded by white mica final interpretation of results should be guided by microstructural analysis estimation of deformation temperature chemical characterization of white mica and complementary chronometers overall the dataset shows that granitic protoliths were emplaced between 430 and 422 ma u pb zircon high strain deformation along the wing pond shear zone occurred between ca 422 405 ma u pb monazite and 40ar 39ar subsequent patchy ar loss in white mica occurred locally during low t shear

intracrystalline vorticity record of flow kinematics during shear zone reactivation abstract the vorticity axis of deformation of a shear zone is a rotational axis controlled by the relative movement of its boundaries when characterized it is a reliable tool to determine the ductile flow geometry monoclinic general monoclinic transpressive or triclinic and an asset to identify the kinematics of complex oblique collisions advancements in analysis of electron backscattered diffraction ebsd maps now permit inference of vorticity axes known as crystallographic vorticity axes cvas from the intragranular lattice orientation dispersion of strain bearing minerals however natural shear zones may preserve a record of multiple shear events with contrasting kinematics and it is not understood to which extent the quartz lattice may preserve a kinematic record through multiple deformation events herein we characterize the finite flow kinematic record produced during reactivation of the eastern highlands shear zone ehsz in an oblique collision within the canadian appalachians we integrate field and thin section observations quartz lattice preferred orientations ebsd maps and grain classification leading to a new method to determine and compare cva within relict and recrystallized quartz grains using this method we were able to conclude that the ehsz was reactivated in an heterogenous monoclinic flow environment

microstructural evolution and rheological behaviour of marbles deformed at different crustal levels abstract microstructures from naturally deformed marbles were investigated from a nappe pile with inverted barrovian metamorphic zones detailed microstructural and textural work combined with existing pt data allows us to correlate microstructural types with tectonic events type 1 microstructure related to d1 continental underthrusting shows highly asymmetrical grain boundaries increasing grain size and increasing intensity of lattice preferred orientation with increasing metamorphic grade these characteristics suggest that dislocation creep with concommitant grain boundary migration operated during the simple shear dominated underthrusting regime paleopiezometric and strain rate estimates show a decrease of flow stress with increasing metamorphic temperature and a strain rate of around 10 14 s 1 thrust related microstructure type 2 is developed in upper and lower nappes and is characterised by grain size reduction increase of grain boundary symmetry and weaker textures microstructural and textural studies indicate dislocation creep with possible contribution of grain boundary sliding sub grain rotation paleopiezometry and strain rate estimates show a decrease in flow stress with respect to the type 1 microstructure and strain rate increase to around 10 12 to 10 13 s 1 type 3 microstructure is developed in thrust related shear zones in the parautochthon and syn convergent extensional zones in the top of the nappe pile this microstructure shows a high contribution of diffusion creep indicating low values of flow stress and significant weakening of marble layers the general feature of studied area is the localisation of deformation into marbles during thrusting in low metamorphic grades while in higher grades marbles are not exploited as lubricating layers

c slip in quartz from subsolidus deformed granite abstract the slip behaviour of quartz from a granite and granitic veins during subsolidus high temperature conditions 700 800 c of deformation is studied by lattice preferred orientation lpo and microstructural techniques lpos with a point maximum of c axes parallel to the shear direction which is close to the stretching lineation are presented and interpreted with the aid of light and electron microscopy in terms of c as the dominant slip direction during plastic deformation microscopy of such samples reveals the presence of 0001 tilt boundaries and free 0001 burgers vector dislocations in edge orientations a change in lpo in a decreasing temperature environment from c axes parallel to the shear direction to c axes normal to the shear direction documents a fabric transition from the rare c slip to the more common a slip fabric it is concluded that conditions of high temperature and partial pressure of water are required to initiate dominant c slip during deformation at geological strain rates

development of crystallographic preferred orientations by nucleation and growth of new grains in experimentally deformed quartz single crystals abstract deformation experiments have been carried out to investigate the effect of dynamic recrystallisation on crystallographic preferred orientation cpo development cylindrical samples of natural single crystals of quartz were axially deformed together with 1 vol of added water and 20 mg of mn2o3 powder in a griggs solid medium deformation apparatus in different crystallographic orientations with compression direction i parallel to ii at 45 to and 45 to and iii parallel to the experiments were performed at a temperature of 800 c a confining pressure of 1 2 gpa a strain rate of 10 6 s 1 to bulk finite strains of 14 36 the deformed samples were analysed in detail using optical microscopy electron backscatter diffraction ebsd and transmission electron microscopy tem two different microstructural domains were distinguished in the deformed samples i domains with undulatory extinction and deformation lamellae and ii domains with new recrystallised grains within the domains of undulatory extinction crystal plastic deformation caused gradual rotations of the crystal lattice up to 30 away from the host orientation new recrystallised grains show a strong cpo with c axis maxima at 45 to the compression direction this is the case in all experiments irrespective of the initial crystallographic orientation the results show that c axes are not continuously rotated towards the new maxima the new grains thus developed through a mechanism different from subgrain rotation recrystallisation new grains have a subeuhedral shape and numerous microcavities voids fluid channels and fluid inclusions at their grain boundaries no host control is recorded in misorientation axes across their large angle grain boundaries new grains might have been created by nucleation from solution in the m scale voids and microfractures the cpo most likely developed due to preferred growth of the freshly precipitated grains with orientations suitable for intracrystalline deformation at the imposed experimental conditions

comparison of neutron and x ray diffraction in texture analysis of deformed carbonate rocks the paper compares pole figure determinations with neutron diffraction and x ray diffraction on experimentally deformed carbonate rocks a coarse grained marble and fine grained limestone neutron diffraction enables determination of complete pole figures on a single spherical specimen and is advantageous for coarse grained materials results obtained with both diffraction techniques agree satisfactorily although uncertainties introduced by counting statistics are more serious for neutrons than for x rays continuous detectors add new possibilities which are still little explored

fabric development in experimentally sheared quartzites abstract a fine grained quartzite was deformed under a combination of simple shear and axial compression to varying amounts of shear strain 1 3 to 2 9 the experiments were conducted at 800 c 1500 mpa and an axial strain rate of 10 6 s in the dislocation creep regime shear zone boundaries were oriented at 45 or 30 to the compressior axis the progressive development of deformation microstructures including planar fabrics and c axis preferred orientations was studied as a function of increasing shear strain elongate original grains define a foliation s which rotates from 45 to 0 to the shear zone boundary with increasing strain producing a sigmoidal foliation in a single shear zone a second foliation invariant in orientation is defined by elongate recrystallized grains which lie at about 30 40 to the shear zone boundaries no c surfaces parallel to the shear zone boundaries were observed however extensional crenulation cleavages c defined by parallel zones of recrystallized grains as well as impurity and melt segregations were observed even at low strain lying at approximately 30 to the shear zone boundaries and these could easily be mistaken for c surfaces c axis preferred orientations of original grains define symmetric type i crossed circle girdles at low strain 2 with the greater concentration of c axes in the direction of shear these features are very similar to those observed in natural ductile shear zones

midcrustal discontinuities and the assembly of the himalayan midcrust detailed quartz lattice preferred orientation lpo data define two structural discontinuities in the exhumed high grade metamorphic core of the himalaya exposed in the upper tama kosi region of east central nepal the structures are marked by abrupt breaks in a general trend of up structural section increasing quartz lpo defined deformation temperatures deformation associated with the upper structural discontinuity which occurs within sillimanite grade rocks is postpeak metamorphism in both the hanging wall and the footwall new geochronologic data constrain the timing of metamorphism in the hanging wall of the upper discontinuity to between 24 and 16 ma indistinguishable from previously published ages for the footwall movement across this structure represents early miocene strain localization and thickening in the himalayan midcrust movement across the lower discontinuity which occurs between staurolite and kyanite grade rocks appears to be synmetamorphic with material in its footwall at approximately 10 ma but postpeak metamorphism for material in its hanging wall this movement is interpreted to reflect the underplating and incorporation of material into the metamorphic core the recognition of two thrust sense discontinuities in the exhumed himalayan core in the tama kosi region is consistent with other similar structures recognized along the himalaya the widespread nature of these structures reinforces that they are important to our understanding of the evolution of the kinematics of large hot orogens

the ultimate fate of a synmagmatic shear zone interplay between rupturing and ductile flow in a cooling granite pluton abstract the neoarchean cundimurra pluton yilgarn craton western australia was emplaced incrementally along the transpressional cundimurra shear zone during syndeformational cooling discrete networks of cataclasites and ultramylonites developed in the narrowest segment of the shear zone showing the same kinematics as the earlier synmagmatic structures lithological boundaries between aplite pegmatite veins and host granitic gneiss show more intense pre cataclasite fabrics than homogeneous material and these boundaries later became the preferred sites of shear rupture and cataclasite nucleation transient ductile instabilities established along lithological boundaries culminated in shear rupture at relatively high temperature 500 600 c here tensile fractures at high angles from the fault plane formed asymmetrically on one side of the fault indicating development during seismic rupture establishing the oldest documented earthquake on earth tourmaline veins were emplaced during brittle shearing but fluid pressure probably played a minor role in brittle failure as cataclasites are in places tourmaline free subsequent ductile deformation localized in the rheologically weak tourmaline rich aggregates forming ultramylonites that deformed by grain size sensitive creep the shape and width of the pluton shear zone and the regime of strain partitioning induced by melt present deformation and established during pluton emplacement played a key role in controlling the local distribution of brittle and then ductile subsolidus structures

texture analysis of a muscovite bearing quartzite a comparison of some currently used techniques abstract four well established techniques were applied to determine the mineral textures of a muscovite bearing quartzite 1 directional measurements on an optical u stage 2 x ray 3 neutron and 4 electron diffraction ebsd techniques 1 and 4 are of the single grain type and techniques 2 and 3 of the statistical or volume type experimental pole density diagrams were compared by means of the construction of pole figure differences difference pole figures which led to the observation that ebsd and u stage derived pole figures agree well even in detail in contrast pole figures derived from x ray and neutron diffraction are clearly different from pole figures derived from the single grain techniques visible as pronounced preferred orientation in the difference pole figures specific properties of the applied techniques may be responsible for the observed differences such as 1 missing proportionality to the grain volume in the single grain methods 2 the accessible sample volume 3 erroneous data correction or 4 statistical errors also the method of data treatment which is basically different for the single grain and statistical methods should be considered when pole figures are evaluated apart from purely economical constraints and availibility of equipment the decision on the most suitable method for a texture determination should be based on the scientific goals and specific properties of particular techniques texture measurements of the statistical type are well suited for determination of bulk textures of rocks e g as required for the calculation of anisotropic physical properties of rocks whereas single grain measurements are advantageous for the investigation of local textures and texture forming mechanisms

fabric and kinematic study of the bites orthogneiss southwestern moravia result of large scale northeastward shearing parallel to the moldanubian moravian boundary abstract the body of the bites orthogneiss bo in southwestern moravia was affected by ductile shear deformation of probably late variscan age north to northeast directed shearing is indicated by the orientation of sheath fold axes s c fabric strong asymmetrical c axis preferred orientation and ne dipping shear bands deformational structures stretching lineation mylonitic foliation and sheath folds associated with thrust wrench tectonics are connected with lower amphibolite to green schist facies metamorphism a strain study shows complex fabric development from the core to the boundaries of the bo thrust sheet fabrics in the core of the bo body are characterized by oblate strain ellipsoids low strain intensity and quartz c axis fabrics that can be approximated to small circle girdles centred around the z axis of finite strain strain ellipsoids near the boundaries of the bo thrust sheet are mostly prolate with high strain intensity and quartz diagrams show single or incomplete crossed girdles highly asymmetrical with respect to the structural framework the coaxial strain history in the core and the noncoaxial history which prevails at the boundaries of the bo thrust sheet are interpreted as a result of different strain paths in the framework of a crustal scale shear zone

refining the structural framework of the khimti khola region east central nepal himalaya using quartz textures and c axis fabrics abstract new quartz texture and c axis fabric data from across the paleoproterozoic ulleri phaplu melung orthogneiss in the khimti khola region of east central nepal provide new constraints on the internal structural framework of the himalaya that help shed light on the convergence accommodation processes active in the upper portion of the crust during orogenesis these data outline a strain history that varies across the unit deformation near the base of the unit occurred at 605 50 c with evidence of significant static recrystallization and recovery preserved in quartz whereas deformation near the top of the unit occurred at 540 50 c with quartz characterized by dynamic recrystallization mechanisms the strength of the quartz c axis fabrics follows a similar spatial pattern with those from near the top of the unit recording stronger fabrics than those measured from lower in the unit together these data are interpreted to indicate strain localization possibly at progressively lower temperature near the top of the ulleri phaplu melung orthogneiss this interpretation is consistent with cooling ages that indicate the upper boundary of the unit coincides with an out of sequence shear zone this study not only provides a structural characterization of the shear zone helping to refine the kinematic framework of this portion of the himalaya but also confirms the utility of fabric strength analysis in deciphering strain localization within pervasively deformed rocks

ebsd measured lattice preferred orientations and seismic properties of eclogites we investigated the deformation mechanisms and the seismic properties of 10 eclogite samples from different localities alps norway mali and eastern china through the analysis of their microstructures and lattice preferred orientations lpo these samples are representative of various types and intensity of deformation under eclogitic metamorphic conditions omphacite and garnet lpo were determined from electron backscatter diffraction ebsd technique garnet appears to be almost randomly oriented whereas omphacite develops strong lpo characterized by the 001 axes concentrated sub parallel to the lineation and the 010 poles concentrated sub perpendicular to the foliation in order to analyze the deformation mechanisms that produced such omphacite lpo we compare our observations to lpo simulated by viscoplastic self consistent numerical models a good fit to the measured lpo is obtained for models in which the dominant slip systems are 1 2h110i 11 0 001 110 and 001 100 dominant activation of these slip systems is in agreement with tem studies of naturally deformed omphacite seismic properties of eclogite are calculated by combining the measured lpo and the single crystal elastic constants of omphacite and garnet although eclogite seismic anisotropies are very weak less than 3 for both p and s wave they are generally characterized by a maximum p wave velocity sub parallel to the lineation and by a minimum velocity approximately normal to foliation the mean p and s wave velocities are high respectively 8 6 and 4 9 km s the s wave anisotropy pattern displays complex relationships with the structural frame but the fast polarization plane generally tends to be parallel to the foliation calculated reflection coefficients show that an eclogite crust interface is generally a good reflector rc 0 1 whereas an eclogite body embedded in the upper mantle would be hardly detectable

evolution of quartz microstructure and c axis crystallographic preferred orientation within ductilely deformed granitoids arolla unit western alps abstract we have studied quartz microstructures and the c axis crystallographic preferred orientations cpos in four granitoid samples representative of increasing ductile shear deformation from a weakly deformed granitoid stage 1 to a mylonitic granitoid stage 4 the quartz c axis cpo measured in the mylonitic granitoid has been compared with the one observed in a fully recrystallized quartz mylonite from the same area all the samples belong to the austroalpine arolla unit western alps and were deformed at greenschist facies conditions the quartz c axis cpo was analyzed using a u stage and the optical orientation imaging technique the magmatic plagioclase forming more than 50 of the volume of the granitoid is extensively replaced by a mica rich aggregate even in weakly deformed samples of stage 1 these aggregates flow to form an interconnected weak matrix with increasing deformation wrapping relatively less strained quartz grains that undergo dominantly coaxial strain recrystallization of quartz ranges from less than 1 in the weakly deformed granitoid to up to 85 in the mylonitic granitoid with average grain strain of 41 and 64 respectively with increasing strain and recrystallization quartz grains in the granitoids show a sequence of transient microstructures and cpos crystal plastic deformation is initially accomplished by dislocation glide with limited recovery and at 50 grain strain it results in a cpo consistent with dominantly basal a slip at 60 grain strain recrystallization is preferentially localized along shear bands which appear to develop along former intragranular cracks and the recrystallized grains develop a strong c axis cpo with maxima orthogonal to the shear band boundaries and independent of the host grain orientation within the granitoid mylonite at an average quartz grain strain of 64 recrystallization is extensive and the c axis cpo of new grains displays maxima overlapping the host c axis orientation and therefore unrelated to the bulk sense of shear the host controlled cpo is inferred to reflect pervasive recrystallization by progressive subgrain rotation the switch from shear band control to host control on c axis cpo occurred between 40 and 70 of recrystallization in the quartz mylonite the quartz c axis cpo develops an asymmetric single girdle consistent with the bulk sense of shear and the synkinematic greenschist facies conditions this study indicates that the cpo evolution of quartz may significantly differ in cases of polymineralic vs monomineralic rocks under the same deformation conditions if quartz in the polymineralic rock behaves as a strong phase

origin of migmatites by deformation enhanced melt infiltration of orthogneiss a new model based on quantitative microstructural analysis a detailed field study reveals a gradual transition from high grade solid state banded orthogneiss via stromatic migmatite and schlieren migmatite to irregular foliation parallel bodies of nebulitic migmatite within the eastern part of the gfohl unit moldanubian domain bohemian massif the orthogneiss to nebulitic migmatite sequence is characterized by progressive destruction of well equilibrated banded microstructure by crystallization of new interstitial phases kfs pl and qtz along feldspar boundaries and by resorption of relict feldspar and biotite the grain size of all felsic phases decreases continuously whereas the population density of new phases increases the new phases preferentially nucleate along high energy like like boundaries causing the development of a regular distribution of individual phases this evolutionary trend is accompanied by a decrease in grain shape preferred orientation of all felsic phases to explain these data a new petrogenetic model is proposed for the origin of felsic migmatites by melt infiltration from an external source into banded orthogneiss during deformation in this model infiltrating melt passes pervasively along grain boundaries through the whole rock volume and changes completely its macro and microscopic appearance it is suggested that the individual migmatite types represent different degrees of equilibration between the host rock and migrating melt during exhumation the melt topology mimicked by feldspar in banded orthogneiss forms elongate pockets oriented at a high angle to the compositional banding indicating that the melt distribution was controlled by the deformation of the solid framework the microstructure exhibits features compatible with a combination of dislocation creep and grain boundary sliding deformation mechanisms the migmatite microstructures developed by granular flow accompanied by melt enhanced diffusion and or melt flow however an ams study and quartz microfabrics suggest that the amount of melt present did not exceed a critical threshold during the deformation to allow free movements of grains

quartz c axes orientation determination using the rotating polarizer microscope abstract a fast and accurate optical method to calculate quartz c axis orientations using the rotating polarizer stage and standard thin sections is presented c axis orientations are calculated for each pixel and achsenverteilungsanalyse ava can easily be constructed to study problems that would normally require a prohibitive amount of tedious work the computer controlled rotating polarizer stage replaces the polarizer and analyzer of the standard petrographic microscope and allows a thin section to remain fixed while the polarizing filters are rotated by stepper motors data are collected by stepping the polarizers through a 180 rotation capturing a frame at each step and extracting information on the intensity of the pixel and position of the polarizers the position data are used to calculate the trend or trend 180 of the quartz c axes while a simple mathematical relationship between intensity and plunge is derived which allows the plunges of c axes to be calculated

the role of dynamic recrystallization in the development of lattice preferred orientations in experimentally deformed quartz aggregates abstract experiments on coaxially deformed quartz aggregates show that when dynamic recrystallization involves grain size reduction the lattice preferred orientation lpo of the recrystallized grains depends on the recrystallization mechanism at low temperatures and fast strain rates strain induced grain boundary migration recrystallization favors growth of grains oriented poorly for slip on the basal and prism planes resulting in an lpo of c axes parallel to the 1 direction at higher temperatures or slower strain rates progressive subgrain rotation produces recrystallized grains which inherit the small circle girdle lpo of their deformed host grains and which continue to re orient by slip at even higher temperatures and slower strain rates progressive subgrain rotation is accompanied by rapid grain boundary migration which does not favor grains of any particular orientation thus the lpo is again similar to that of non recrystallized grains in contrast when dynamic recrystallization involves grain growth driven by surface energy reduction a strong lpo of c axes parallel to 1 develops during grain growth but then evolves with increasing strain toward a small circle girdle the correlation of lpos with recrystallization mechanisms has important implications for the assumption of homogeneous strain in theoretical models of lpos and for interpreting natural lpos in recrystallized rocks

analysis of submerged bar nourishment strategies in a wave dominated environment using a 2dv process based model the present study aims to analyze the effects of different submerged bars nourishment strategies using a 2dv process based morphodynamical model a two barred beach profile typical of the french mediterranean micro tidal storm dominated coastline is chosen as a reference profile two different kinds of modified beach profiles are considered i only the outer bar is nourished the inner bar being unchanged ii both bars are nourished three typical wave forcing regimes are considered the behavior of the natural profile is first investigated under the 3 wave forcing regimes then the behavior of the various nourished profiles is analyzed in terms of wave dynamics and bars behavior on the basis of the model results the outer bar only nourishment strategy appears to be preferable

polymineralic orientation analysis of magmatic rocks using electron back scatter diffraction implications for igneous fabric origin and evolution abstract electron back scatter diffraction ebsd which provides an easy way of acquiring large numbers of individual crystallographic orientation data from different phases has been applied to the study of magmatic fabrics using this technique the crystallographic preferred orientation cpo of plagioclase biotite orthopyroxene hornblende and quartz in natural tonalites and quartzdiorites from the santa olalla igneous complex sw iberia deformed during the magmatic stage have been determined plagioclase is the coarser phase defining the main fabric in each sample whereas biotite can display either the same fabric as plagioclase or a completely different one the differences between these two phases occur because 1 smaller phases interact with the larger ones to produce more random orientations 2 under simple shear finer phases can completely rotate giving a girdle included in the xz plane 3 finer phases can more easily preserve relict fabrics while the coarser phases are completely reoriented by the last stress tensor the last phases to crystallize show weak to completely random cpos hornblende or completely random distributions quartz the study was completed with a shape preferred orientation analysis using the intercept method in order to detect weak magmatic lineations and numerical modelling simulations of theoretically equivalent simple shear situations for each sample

evolution of c axis pole figures and grain size during dynamic recrystallization results from experimentally sheared quartzite 1 quartzite samples experimentally sheared at conditions where subgrain rotation and grain boundary migration recrystallization are active show a striking change in the c axis crystallographic preferred orientation cpo with increasing shear strain up to 8 and degree of recrystallization up to 100 we used optical methods to determine the c axis cpo for the bulk samples and for porphyroclasts and recrystallized grains separately and to track the strengths of the cpos in five different orientation domains with increasing the c axis pole figure evolves from a broad peripheral maximum indicative of basal a slip to an inclined single girdle with two maxima indicative of rhomb a slip and finally an elongate single maximum at the girdle center indicative of prism a slip throughout this sequence the fabric skeleton rotates with the sense of shear the bulk preferred c axis orientation results from growth and shrinkage of differently oriented crystallographic domains grain boundary density analysis indicates that the size of prism a recrystallized grains is 1 5 times that of average and 2 times that of rhomb grains indicating that prism a slip is significantly easier at our experimental conditions this inference is supported by autocorrelation function analysis of the various orientation domains and how they evolve with strain similar progressive changes in c axis cpo are observed in quartzites naturally sheared at conditions where grain boundary migration recrystallization operates these results indicate that achievement of microstructural and mechanical steady state requires high strain and complete recrystallization

prism and basal plane parallel subgrain boundaries in quartz a microstructural geothermobarometer empirical data on quartz subgrain patterns from various metamorphic rocks show that at least up to 10 kbar in the stability field of low quartz prismatic subgrain boundaries are dominant whereas basal subgrain boundaries are not developed in the high quartz stability field both prismatic and basal subgrain boundaries occur and form typical rectangular chessboard patterns the likely reason behind the different occurrence of these subgrain patterns is that in high quartz prismatic glide becomes as easy as or probably even easier than basal glide the two types of subgrain patterns can be clearly distinguished by optical microscopy consequently the occurrence of chessboard subgrain patterns in quartz represents a practicable geothermobarometer the possibilities of its application are far reaching and include the specification of deformation conditions at high grade metamorphism the recognition of syntectonic intrusions and the distinction between pluton emplacement at lower and at higher crustal levels

dynamic recrystallization near the brittle plastic transition in naturally and experimentally deformed quartz aggregates the electron backscattering diffraction technique ebsd was used to analyze bulging recrystallization microstructures from naturally and experimentally deformed quartz aggregates both of which are characterized by porphyroclasts with finely serrated grain boundaries and grain boundary bulges set in a matrix of very fine recrystallized grains for the tonale mylonites we investigated a temperature range of 300 380 c 0 25 gpa confining pressure a flow stress range of 0 1 0 2 gpa and a strain rate of 10 13 s 1 were estimated experimental samples of black hills quartzite were analyzed which had been deformed in axial compression at 700 c 1 2 1 5 gpa confining pressure a flow stress of 0 3 0 4 gpa a strain rate of 10 6 s 1 and to 44 to 73 axial shortening using orientation imaging we investigated the dynamic recrystallization microstructures and discuss which processes may contribute to their development our results suggest that several deformation processes are important for the dismantling of the porphyroclasts and the formation of recrystallized grains grain boundary bulges are not only formed by local grain boundary migration but they also display a lattice misorientation indicative of subgrain rotation dynamic recrystallization affects especially the rims of host porphyroclasts with a hard orientation i e with an orientation unsuitable for easy basal slip in addition dauphine twins within porphyroclasts are preferred sites for recrystallization we interpret large misorientation angles in the experimental samples which increase with increasing strain as formed by the activity of fluid assisted grain boundary sliding

evaluating quartz crystallographic preferred orientations and the role of deformation partitioning using ebsd and fabric analyser techniques quartz crystallographic preferred orientations cpo from three distinct orthogneisses using both the electron back scatter diffraction ebsd and fabric analyser fa techniques reveal a clear trend from basal and rhomb slip for high p t conditions 670 20 degrees c 9 kbar rhomb and basal slip for medium p t 590 15 degrees c 6 kbar and a dominance of prism slip for lower p t conditions 570 degrees c 4 5 kbar the textural variations are interpreted in terms of a temperature field gradient and microscale strain partitioning controlled by a weak feldspar matrix that can locally invert the expected slip system sequences locally quartz cpus are different within one thin section and in comparison to bulk orientation measurements both ebsd and the fabric analyser techniques are ideal to determine such textural heterogeneities while the ebsd is a powerful technique to determine the full cpo measurements from similar locations inside several quartz grains from the orthogneisses and an annealed and undeformed quartzite show that the fa is an accurate tool to determine cpus of c axis orientations in uniaxial materials in a cpo focussed study the fa is a cheap alternative to ebsd as the analysis of whole thin section can be accomplished in a very short time with minimal sample preparation with the fa it is possible to evaluate the cpus of several samples quickly with an accuracy that allows identification of the main slip systems and their homogeneity

high temperature microstructures and rheology of deformed granite erzgebirge bohemian massif abstract three stages of granite deformation were recognized in porphyric granitoids sheared under amphibolite facies conditions in the erzgebirge mts 1 weakly deformed granite in lozenge shaped pods 2 s c orthogneiss and 3 thin zones of banded mylonites weakly deformed granite forms a load bearing framework lbf structure in which quartz and feldspar aggregates exhibit similar strain intensities and shapes k feldspar deforms by fracturing and onset of dynamic recrystallization along clast margins plagioclase recrystallizes completely and quartz shows effects of grain boundary migration recrystallization and activity of basal a slip s c orthogneiss is interpreted as an interconnected weak layer iwl structure with high viscosity contrast between quartz and both feldspars concentration of deformation into thin quartz layers is indicated by intense strain of quartz grain size variations of recrystallized quartz and dominant prism a slip feldspars show well annealed structures and slip on 010 001 banded mylonite is marked by similar strain intensity of quartz and feldspar aggregates and low viscosity contrast between constituent phases quartz shows evidence for grain size increase and rhomb a c slip fully recrystallized feldspars show evidence for 010 100 slip the whole microstructural sequence and the transitions from lbf structure to iwl structures show the dependence of microstructural evolution of different materials on the bulk strain intensity

a new approach to crystallographic orientation measurement for apatite fission track analysis effects of crystal morphology and implications for automation apatite fission track analysis and in particular computer assisted fission track recognition require the determination of crystallographic orientation crystal morphology cracks fractures and inclusions the selection of a crystal for fission track analysis has largely been based on its surface and track etching characteristics that in conventional fission track dating is performed by the analyst this requires manual scanning of the entire mount for suitable grains which is a very time intensive process during manual fission track counting therefore a computer assisted grain characterisation system is of interest to allow for an automated pre selection of suitable crystals with the use of a fully automated fabric analyser c axis orientations can be measured inside an apatite crystal for each pixel with a spatial resolution of 5 m the results are represented in geometric quality and retardation maps consisting of the c axis orientations for each pixel and two quality values evaluating each orientation these maps allow the determination of the crystallography of the apatite grain as well as its outline in addition most of the crystal morphologies fractures and impurities which can influence automated fission track recognition techniques based on image analysis are determinable using the quality maps on the other hand the method is not sensitive to smaller crystal cracks high fission track densities or coating the quantification of the crystal geometric properties by this method is a step forward to develop a fully automated fission track analysis process

feldspar fabrics in a greenschist facies albite rich mylonite from electron backscatter diffraction abstract the current database of plagioclase cpos in naturally deformed rocks is small and is not supported by cpos from experimentally deformed rocks or by numerical modelling so that the current understanding of plagioclase cpos is limited electron backscatter diffraction ebsd has the potential of measuring the full crystallographic orientation of small domains of any crystalline material including plagioclase we generate and test a file of the relative electron diffraction intensities for lattice planes in the albite structure this enables rapid and accurate individual orientation measurements of albite using ebsd ebsd is used to collect 360 data points from 7 areas across a 2 cm by 1 mm pure albite band in a greenschist facies albite mylonite from a gabbro protolith the cpos are unlike any published the a b and c axes of albite are not symmetrically distributed with respect to the kinematic axes of deformation and do not possess an internal monoclinic or orthorhombic symmetry there is some microstructural evidence for the operation of dislocation creep although this interpretation conflicts with the generally held view that crystal plastic deformation does not occur in plagioclase below about 500 c an alternative mechanism is one of granular flow accommodated by solution transfer however this mechanism would be expected to give a random cpo for either mechanism we need to explain the triclinic nature of the cpo it is possible that the cpo represents the modification by deformation of a pre existing cpo probably defined by a small number of original plagioclase grains

on thrusting regional unconformities and exhumation of high grade greenstones in neoarchean orogens the case of the waroonga shear zone yilgarn craton abstract during the neoarchean the dominant tectonic style progressively changed from an episodic overturn stagnant lid regime to modern style plate tectonics the neoarchean strengthening of continental lithosphere changed the style of deformation of orogenic belts the case study presented here provides insights into how such transition in tectonic style occurred a matter that is generally controversial we present structural and metamorphic data from the c 2660 ma waroonga shear zone wsz in the neoarchean yilgarn orogen western australia the wsz contains a syntectonic pluton and older high grade greenstones the tectonic fabric in the pluton developed during melt present thrusting followed by syn cooling wrench dominated transpression mafic greenstones preserve three metamorphic assemblages the m1 assemblage grt cpx qtz records peak p t conditions of 12 1 kbar and 800 50 c followed by isothermal decompression to 9 kbar m2 these anhydrous assemblages might predate the wsz greenstones then underwent decompression at c 2660 ma 3 4 kbar 600 650 c defined by the amphibole rich m3 assemblage synkinematic with the tectonic fabric in the wsz we show that shearing along the wsz exhumed these greenstones by at least 10 km inducing major uplift and erosion archean accretionary orogens developed on weak lithosphere where deformation suppressed crustal thickening orogenic relief and synorogenic exhumation of orogenic roots however our study indicates a genetic link between i strain localization along contractional structures inducing large scale uplift ii exhumation of high grade greenstones iii development of inverse metamorphic gradients iv establishment of a regional unconformity with clastic sediments fed by the uplifted terrane v incorporation of portions of the newly formed orogenic basins into the footwall of the wsz these features imply that the yilgarn orogenic lithosphere at c 2660 ma was stiff enough to allow tectonic processes analogous to those that dominate modern style orogenic belts representing an intermediate stage between archean and modern type orogens

unusual transition in quartzite dislocation creep regimes and crystal slip systems in the aureole of the eureka valley joshua flat beer creek pluton california a case for anhydrous conditions created by decarbonation reactions abstract microstructures and quartz c axis fabrics were analyzed in five quartzite samples collected across the eastern aureole of the eureka valley joshua flat beer creek composite pluton temperatures of deformation are estimated to be 740 50 c based on a modified c axis opening angle thermometer of kruhl j metamorph geol 16 1998 142 in quartzite layers located closest 140 m to the pluton wall rock contact flattened detrital grains are plastically deformed and partially recrystallized the dominant recrystallization process is subgrain rotation dislocation creep regime 2 of hirth and tullis j struct geol 14 1992 145 although grain boundary migration dislocation creep regime 3 is also evident complete recrystallization occurs in quartzite layers located at a distance of 240 m from the contact and coincides with recrystallization taking place dominantly through grain boundary migration regime 3 within the quartzites strain is calculated to be lowest in the layers closest to the pluton margin based on the aspect ratios of flattened detrital grains the c axis fabrics indicate that a slip operated within the quartzites closest to the pluton wall rock contact and that with distance from the contact the operative slip systems gradually switch to prism c slip the spatial inversion in microstructures and slip systems apparent high temperature deformation and recrystallization further from the pluton contact and apparent low temperature deformation and recrystallization closer to the pluton contact coincides with a change in minor phase mineral content of quartzite samples and also in composition of the surrounding rock units marble and calc silicate assemblages dominate close to the pluton wall rock contact whereas mixed quartzite and pelite assemblages are dominant further from the contact we suggest that a thick marble unit located between the pluton and the quartzite layers acted as a barrier to fluids emanating from the pluton decarbonation reactions in marble layers interbedded with the inner aureole quartzites and calc silicate assemblages in the inner aureole quartzites may have produced high x co 2 water absent fluids during deformation the presence of high x co 2 fluid is inferred from the prograde assemblage of quartz calcite and not wollastonite diopside k feldspar in the inner aureole quartzites we suggest that it was these dry conditions that suppressed prism c slip and regime 3 recrystallization in the inner aureole and resulted in a slip and regime 2 recrystallization which would normally be associated with lower deformation temperatures in contrast the prograde assemblage in the pelite dominated outer part of the aureole is biotite k feldspar these wet pelitic assemblages indicate fluids dominated by water in the outer part of the aureole and promoted prism c slip and regime 3 recrystallization because other variables could also have caused the spatial inversion of c axis fabrics and recrystallization mechanisms we briefly review those variables known to cause a transition in slip systems and dislocation creep regimes in quartz our conclusions are based on a small number of samples and therefore the unusual development of crystal fabrics and microstructures in the aureole to the ejb pluton suggests that further study is needed on the effect of fluid composition on crystal slip system activity and recrystallization mechanisms in naturally deformed rocks

fabric domains in quartz mylonites localized three dimensional analysis of microstructure and texture fabric domains of a quartz vein deformed under greenschist facies conditions arc analysed with domainal x ray texture goniometry optical microscopy computer integrated polarization microscopy cip and shape analysis in two mutually perpendicular sections the analysed domains consist of large non recrystallized deformed clast fragments prolate non recrystallized ribbon grains and prolate recrystallized domains in terms of texture monomaximal and polymaximal domains have been distinguished pronounced partitioning of deformation is observed between these domains this strain partitioning asks for caution when making kinematic inferences for fault zones based on a study of domainal fabrics domains persist as fabric elements up to high strains this emphasizes the often neglected role of a non random initial fabric neighbouring domains with alternating c axis orientations and grain boundary preferred orientations indicating opposing senses of shear occur in both sections the bulk texture is controlled by clast and ribbon domains rather than being strictly deformation induced we infer that prolate elongation of clasts and ribbons is achieved mainly by combined prism and basal slip recrystallized domains are characterized by different textures they are deformed by intracrystalline slip combined with grain boundary migration and sliding inclined preferred grain boundary orientations are continuously maintained by grain boundary migration copyright 0 1996 elsevier science ltd

compaction microstructures in quartz grains and quartz cement in deeply buried reservoir sandstones using combined petrography and ebsd analysis abstract sandstone diagenesis involves porosity loss by mechanical and chemical compaction in this study we have examined relations of diagenesis and microstructures in quartz grains and quartz cement in sandstones from relatively deep burial depths offshore mid norway electron backscatter diffraction analysis ebsd has been combined with optical and cathodoluminescence petrography study of samples with different degrees of compaction and quartz cementation quartz cement is shown to be syntaxial to the nearest host domain grain or subgrain both for monogranular polygranular undeformed and deformed quartz the quartz cement growth may have been initiated at different subgrain surfaces and preserving pre depositional deformation structures ebsd inverse pole figure imaging shows dauphine twins to be common in all samples both in quartz grains and quartz cement the dauphine twins appear in grain grain contacts and in cement crystal boundaries and commonly crossing grain cement boundaries on basis of twin distributions we suggest that both inherited twins from the source area and twins formed by compaction induced grain boundary deformation are present a general problem in sedimentary rocks is to distinguish inherited from sedimentary compaction induced intra grain deformation structures this study shows that the role of ductile deformation mechanisms e g twinning in sediment compaction can be clarified by more comprehensive following up studies using ebsd analysis in combination with other techniques

contrasting styles of deformation during progressive nappe stacking at the southeastern margin of the bohemian massif thaya dome abstract variscan nappe stacking at the southeastern margin of the bohemian massif is a polyphase process implying a progressive modification of the deformation regime from thrusting to wrenching associated change of finite strain axes orientations and progressive downwards migration of thrust or wrench planes a first high temperature deformation phase d 1 is related to nappe stacking of moldanubian units in a nw se direction it is recorded only in these units d 2 corresponds to the piling of the moldanubian units over the moravian ones producing internal nappe stacking of the latter and a first medium temperature mylonitization of thaya basement rocks the main feature of this stage is a switch in finite strain axes orientation and northeastward transpressional shearing strain partitioning is important within the moravian nappes and implies alternation of plane strain oblate and constrictional fabrics d 3 is also a phase connected with strong non coaxial ne directed shearing it is concentrated in zones of weakness and causes reactivation of older structures the structural pattern strongly depends on the position in the nappe pile strike slip tectonics dominate near the resistant eastern cadomian basement border foliation parallel extensional reactivation producing large scale folds is typical in moravian nappes while extensional tectonics prevail in the uppermost gfohl nappe large scale strain partitioning during d 2 stacking of moravian nappes and the extension of the upper part of the nappe pile during d 3 reactivation are mechanically controlled by a lateral ramp basement geometry along the bruno vistulian cadomian foreland

characterization of transpressive deformation in shear zones of the archean north caribou greenstone belt nw superior province and the relationship with regional metamorphism abstract the 2 7 3 0 ga north caribou greenstone belt ncgb host to the musselwhite bif hosted gold deposit possesses abundant shear zones on its northern margins which appear to have formed under amphibolite facies conditions protracted deformation and regional metamorphism are coeval with widespread magmatism and accretion events during crustal amalgamation of the western superior province and are responsible for folding the ore hosting bif and channeling fluids the importance of shear zones in behaving as conduits for fluids during the tectonic evolution of the ncgb is not well known and their relationship with metamorphism is equivocal yet higher grade syn to post tectonic metamorphic minerals seem to correlate with loci of higher strain structural analyses support oblique transpressive collision that produced steeply dipping planar and shallowly plunging linear fabrics with dominant dextral kinematics that trend broadly parallel to the doubly arcuate shape of the belt electron backscatter diffraction analyses were conducted on strategic samples across one shear zone in order to characterize crustal conditions during transpressive deformation the dinnick lake shear zone cuts through mafic metavolcanics and at its core is an l tectonite granite composed of recrystallized quartz whole rock geochemistry shows little variation in ca na mg and k often used as indicators of hydrothermal alteration from surrounding less deformed units suggesting deformation in a dry environment microstructural analysis indicates subgrain rotation recrystallization and deformation by prism a and c slip in quartz as well as aligned hornblende that suggest deformation temperatures above 500 c quartz in mafic rocks along the margins of the shear zone also exhibits a basal a slip component indicating a slight decrease in strain or temperature although the ncgb exhibits some first order evidence of vertical tectonism dome and keel geometries the dominant strain record within shear zones is that of horizontal oblique transpressive displacement this is in agreement with other greenstone belts in the western superior province where vertical tectonism and horizontal tectonism were coeval