microstructures and c axis fabrics indicative of quartz dissolution in sheared quartzites and phyllonites abstract quartzites sheared in low metamorphic grade shear zones that extend along the contact with migmatitic gneissic complexes in the quadrilatere ferifero region southeastern brazil show quartz microstructures indicating deformation by dissolution dissolution occurred adjacent to the foliation planes preferentially in quartz porphyroclasts oriented with their 0001 planes parallel to the foliation dissolution worked as an efficient mechanism to remove porphyroclast edges smoothing foliations and enabling strain accommodation both dissolution and crystal plasticity were competitive crystallographically controlled processes operating in different domains of the evolving microstructure dissolution occurred along the foliation planes while isovolume crystal plasticity and accompanying recrystallization operated essentially in the quartzose domains between folia phyllonites formed in the most strained domains of the shear zones fine grained quartz grains in phyllonites show uncommon c axis fabrics c axis oriented at low angles to the stretching lineation which were interpreted to form either by direct reprecipitation or by residual concentration of grains unfavourably orientated to undergo dissolution domainal c axis fabrics reflect a deformation partitioning path with increasing participation of solution transfer strengthening c axis maxima at low angles with the stretching lineation at the expense of crystal plastic processes during progressive phyllonitization

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

quartz c axis fabric differences between porphyroclasts and recrystallized grains discussion recently kirschner teyssier 1991 identified differences between quartz c axis fabrics of porphyroclasts and recrystallized grains in mylonitic quartzites heavitree quartzites and interpreted these differences as indicating a change in the kinematic framework during the deformation history in this discussion we suggest an alternative interpretation of such fabrics derived from our current research on sheared granitoids see the appendix for a description from the archean bonfim metamorphic complex in the quadrilatero ferrifero southeast brazil in these rocks differences between c axis fabrics shown by old and new grains resulted from the heterogeneous disappearance of porphyroclasts with increasing recrystallization the porphyroclasts that disappeared faster were ones more favourably oriented to undergo dynamic recrystallization by subgrain rotation heterogeneous disappearance of porphyroclasts gradually altered the deformation fabric initially shown by porphyroclasts by reinforcing the orientations most resistant to recrystallization in the most recrystallized samples it is suggested that the porphyroclast fabrics displayed by kirschner teyssier 1991 have a similar origin before we deal with kirschner and teyssier s paper itself a brief comment on both selective recrystallization and residual fabric is necessary as these are the keys to our reinterpretation of the heavitree quartzite fabrics the concept of residual fabric expected firstly in the strength and distribution of the maxima and then in the fabric skeleton itself thus a fabric that portrays the orientation of the porphyroclast relicts most resistant to recrystallization the residue of the recrystallization might be gradually displayed in this discussion it is called the residual fabric unfortunately residual fabrics have not received attention in studies on quartz microfabric probably because they are more noticeable when the amount of porphyroclasts is relatively low commonly there are insufficient porphyroclasts in a single thin section to permit the construction of fabric diagrams in these cases two or more thin sections of the same sample are required to obtain a representative plot

using incremental elongation and shearing to unravel the kinematics of a complex transpressional zone abstract this study presents in depth geometric and kinematic analyses of a complex transpressional shear zone fellos shear zone fsz that integrates structural mapping with microstructural and quartz crystallographic texture data the fsz strikes ne sw and formed in the short limb of a map scale antiform the foliation pattern within the zone indicates dextral shearing whereas the macroscopic object lineation is dispersed over a half great circle girdle along the mean mylonitic foliation based on this deformation pattern the fsz could be interpreted as a dextral ne directed triclinic transpressional zone however the integration of field based with microtectonic data reveal a more complicate kinematic history we show that the elongation trend is dispersed along an entire great circle girdle when we take into account the trends of incremental elongations recorded by fabrics with different strain memories mapping of incremental shear directions implies that the fsz initiated as a ne directed dextral transpressional shear zone and progressively evolved into a nw directed dextral zone the passage from ne to nw directed shearing was accompanied by transpression whilst local transtension likely occurred during the last stages of ductile deformation deformation in the fsz ended up at semi ductile conditions with localized ne directed dextral shearing our study demonstrates that the integration of field observations and fabrics microstructures that have different strain memories is a powerful tool for unravelling the complex kinematics of high strain zones

strain path partitioning within thrust sheets microstructural and petrofabric evidence from the moine thrust zone at loch eriboll northwest scotland abstract quartz c axis fabrics and microstructures have been investigated within a suite of quartzites collected from the loch eriboll area of the moine thrust zone and are used to interpret the detailed processes involved in fabric evolution the intensity of quartz c axis fabrics is directly proportional to the calculated strain magnitude a correlation is also established between the pattern of c axis fabrics and the calculated strain symmetry two kinematic domains are recognized within one of the studied thrust sheets which outcrops immediately beneath the moine thrust within the upper and central levels of the thrust sheet coaxial deformation is indicated by conjugate mutually interfering shear bands globular low strain detrital quartz grains whose c axes are aligned sub parallel to the principal finite shortening direction z and quartz c axis fabrics which are symmetric both in terms of skeletal outline and intensity distribution with respect to mylonitic foliation and lineation non coaxial deformation is indicated within the more intensely deformed and recrystallized quartzites located near the base of the thrust sheet by single sets of shear bands and c axis fabrics which are asymmetric with respect to foliation and lineation tectonic models offering possible explanations for the presence of kinematic strain path domains within thrust sheets are considered

an interlinked system of folds and ductile shear zones late stage svecokarelian deformation in the central fennoscandian shield finland abstract the svecokarelian deformation of the karelian and svecofennian provinces in finland involved four main phases isoclinal folding and associated thrusting were the main processes of d 1 which was followed by more open folding in d 2 subsequent deformation was localized during d 3 and d 4 this paper focuses on the late stage d 4 svecokarelian deformation that created most of the ductile shear zones in the central fennoscandian shield and was the last penetrative deformational event to affect the entire palaeoproterozoic domain deformation during d 4 occurred approximately from 1 85 1 80 ga and left a greater imprint in the rocks than has commonly been supposed the shear zones formed during d 4 are referred to collectively as the finlandia shear system the karelian province is composed of archaean basement and its autochthonous allochthonous palaeoproterozoic sedimentary cover svecokarelian tectonics split the basement into separate complexes the rheological properties of which differed markedly from those of the adjacent proterozoic supracrustal units on the northern and southern margins of the archaean complexes folding with steep e w trending axial surfaces was the main response to d 4 deformation whereas on the eastern and western margins of the complexes the response to d 4 was the development of sinistral and dextral shear zones trending ne sw and nw se respectively on a large scale these areas of folding and of shearing form an interlinked system the changes from one style of deformation to the other being gradual the principal d 4 elements in the area of juvenile svecofennian crust are folds with e w trending axial surfaces

subsurface structural interpretation by applying trishear algorithm an example from the lenghu5 fold and thrust belt qaidam basin northern tibetan plateau abstract the application of trishear algorithm in which deformation occurs in a triangle zone in front of a propagating fault tip is often used to understand fault related folding in comparison to kink band methods a key characteristic of trishear algorithm is that non uniform deformation within the triangle zone allows the layer thickness and horizon length to change during deformation which is commonly observed in natural structures an example from the lenghu5 fold and thrust belt qaidam basin northern tibetan plateau is interpreted to help understand how to employ trishear forward modelling to improve the accuracy of seismic interpretation high resolution fieldwork data including high angle dips dragging structures thinning hanging wall and thickening footwall are used to determined best fit trishear model to explain the deformation happened to the lenghu5 fold and thrust belt we also consider the factors that increase the complexity of trishear models including a fault dip changes and b pre existing faults we integrate fault dip change and pre existing faults to predict subsurface structures that are apparently under seismic resolution the analogue analysis by trishear models indicates that the lenghu5 fold and thrust belt is controlled by an upward steepening reverse fault above a pre existing opposite thrusting fault in deeper subsurface the validity of the trishear model is confirmed by the high accordance between the model and the high resolution fieldwork the validated trishear forward model provides geometric constraints to the faults and horizons in the seismic section e g fault cutoffs and fault tip position faults intersecting relationship and horizon fault cross cutting relationship the subsurface prediction using trishear algorithm can significantly increase the accuracy of seismic interpretation particularly in seismic sections with low signal noise ratio

neogene extension and volcanism in the kunlun fault zone northern tibet new constraints on the age of the kunlun fault 1 the geology of the jingyu basin north tibet provides constraints on the relationship between localized e w extension in the qiangtang block and strike slip motion along the kunlun fault eocene to oligocene sw ne compression formed topographic relief in the present western kunlun shan pull apart basins started forming in the western kunlun ranges around 15 ma possibly coincident with the initiation of subduction of the tarim qaidam lithosphere under the kunlun shan extensional tectonism is still active and the jingyu basin is extending as a normal fault connected with the kunlun fault was recently active localized extension allows tertiary and quaternary shoshonitic magmas to reach the surface from crustal depths of 50 to 60 km miocene strike slip faulting indicates that the initiation of the kunlun strike slip fault is early neogene in age and that the total amount of horizontal movement that occurred along the fault has to be reconsidered

domainal and fabric heterogeneities in the cap de creus quartz mylonites abstract a characteristic domainal configuration is reported for both micro structures and c axis fabrics in the cap de creus pure quartz mylonites as displayed in 50 samples from the centres of different shear zones three types of domains are found a b and c each domain has a distinct c axis orientation pattern these three fabric elements also labelled a b and c make up the total fabric c axis fabrics are symmetric or asymmetric with respect to the main mylonitic foliation depending on the presence or absence of the b domain and its fabric element the boundaries of the domains are parallel to the main mylonitic foliation two domain types a and b display an internal foliation defined by preferred grain boundary alignment parallel to the direction of optical orientation within the domain the internal foliations are oblique to the main mylonitic foliation in two different senses giving the sample a herring bone appearance these internal foliations are shown to be related to extensional crenulations domains are not produced by host controlled recrystallization the fabric elements and corresponding domains are the expression of kinematic heterogeneities on the scale of the thin section

sense of nappe emplacement from quartz c axis fabrics an example from the betic cordilleras spain preferred crystallographic orientation patterns fabrics in zones of ductile deformation beneath nappes are a potentially useful indicator of the sense of nappe translation quartz c axis fabrics from a shear zone beneath the pile of higher betic nappes in the betic cordilleras spain have distinctly asymmetric topologies revealed by constructing a fabric skeleton these skeletons closely resemble those produced by computer simulations of quartz fabric development basedon taylor bishop hill theory the fabric asymmetry indicates a northerly sense of transport for the nappes consistent with field evidence from the same area analyses of both c and a axis fabrics based on asymmetric intensity distributions within the fabric give equivocal results and may reflect the presence of earlier preferred orientation patterns predating nappe emplacement

scandium bearing carbonates of the tarr albitite complex southeast sinai unusually high sc concentrations 30 to 150 ppm were found in the carbonate minerals dolomite breunnerite calcite of the tarr albitite complex scandium is probably part of the carbonate crystal structure substituting for mg fe2 scandium is considered to have originated from a source of mantle affinity thus supporting an earlier suggestion that the tarr albitite complex is related to an ophiolite at depth

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

heterogeneous constrictional deformation in a ductile shear zone resulting from the transposition of a lineation parallel fold abstract we use new micro structural petrofabric strain and vorticity data to analyze the deformation path in a mesoscopic quartz mylonite zone the mylonite zone resulted from the complete transposition of a stretching lineation parallel isoclinal fold symmetric cleft girdle quartz c axis fabrics were recorded in the middle domain which occupies the inner limbs of the precursor isoclinal fold while asymmetric cleft and crossed girdle fabrics were observed in the upper and lower domains that represent the outer limbs constrictional strain with increasing k values towards the middle domain is inferred from petrofabric and 3d strain data oblique grain shape fabrics yield vorticity estimates of 0 72 0 90 in the zone however in the middle domain pure shear dominated deformation is suggested by orthorhombic crystallographic fabrics strain rate is constant throughout the zone a strain decrease towards the zone center implies that deformation ceased earlier in the middle domain the data indicates that fold transposition and subsequent mylonitization started as pure shear dominated constrictional deformation and progressively changed to simple shear dominated plane strain during this flow path the asymmetric quartz c axis fabrics likely developed by depopulation of cleft girdle maxima rather than from the synthetic rotation of fabric maxima itself

the development of shear zones in polycrystalline camphor urai j l and humphreys f j 1981 the development of shear zones in polycrystalline camphor in g s lister h j behr k weber and h j zwart editors the effect of deformation on rocks tectonophysics 78 677 685 thin polycrystalline specimens of rhombohedral camphor have been deformed in pure shear in the temperature range 283 343k the deformation processes dynamic recrystallization and the development of microstructure were followed by transmission polarized light microscopy when the stress distribution in the specimens was favourable shear zones were initiated the development of microstructure changed drastically above 310320k the shape of the dynamically recrystallized grains which was equiaxed below this temperature became strongly elongated this change probably due to the development of a marked anisotropy in grain boundary mobilities and the activation of new slip systems made the development of shear zones a more frequently occurring phenomenon above 310 320k

breakdown of feldspar volume gain and lateral mass transfer during mylonitization of granitoid in a low metamorphic grade shear zone abstract in a low metamorphic grade shear zone from quadrilatero ferrifero southeastern brazil granitoid rocks have been transformed into phyllonites and mylonites via activation of crystal plastic processes in quartz and fluid assisted reaction softening in feldspars quartz deformed by basal a and prism a slip with concurrent subgrain rotation recrystallization breakdown of matrix plagioclase an 22 35 via mica producing softening reactions required cationic exchanges between ca na and k forming replacement perthites in the k feldspar megacrysts which occupy around 60 of the original rock volume subsequent breakdown of the perthitic plagioclase an 12 15 led to disruption of the megacrysts enabling strain accommodation that localized the mylonite and phyllonite zones domainal volume and mass balance calculations based on major and minor elements indicate only small positive changes in mass and volume around 15 in the whole system however accentuated differences ranging from mass and volume losses of 25 and 35 at the margins to gains of 85 and 95 in the centre respectively exist between the individual longitudinal subzones occupied by the different tectonite types this scenario indicates that deformation proceeded as a nearly isochemical process although with lateral mobility of major elements principally si al and k within the shear zone these results are different from those previously reported for other granitic mylonites most of them indicating volume losses in compressional tectonic settings it is suggested that the extensional tectonic framework attributed to the moeda bonfim shear zone where mass volume losses are in principle not required enhanced the access of fluid and consequent transport of components into the shear zone principally fe si and k producing the small gains of mass and volume observed

some new aspects of kinematic vorticity analysis in naturally deformed quartzites abstract two vorticity methods have been proposed to estimate kinematic vorticity number in naturally deformed quartzites these combine the degree of quartz c axis fabric asymmetry either with the strain ratio in the xz plane of finite strain r xz or with the angle between the oblique grain shape fabric and the main foliation here it is suggested that the incorporation of r xz data with angle values can also serve as an additional method of vorticity analysis the use of a new nomogram that provides a rapid means of evaluating the consistency of vorticity estimates obtained by the three methods is also discussed a comparison of vorticity estimates from low grade test samples using all methods yields that three methods may record different parts of deformation history this hypothesis was then used to discuss the spatial and temporal variation of kinematic vorticity in a crustal scale shear zone this natural example showed that the new method is able to record late stage changes in the flow regime which are slightly or not detectable by previous methods also it is noteworthy that vertical vorticity profiles based on results of rigid porphyroclast analysis tend to average profiles obtained by the estimates of quartz based methods

quartz c axis fabric differences between porphyroclasts and recrystallized grains abstract observed differences in c axis fabrics between quartz porphyroclasts and recrystallized quartz from the same quartzite samples suggest some changes in the fabric forming parameters during deformation the fabric patterns are consistent with a change in the incremental strain history from flattening to constriction during duplex development which is supported by the observed overprinting of structures in the field

local variations in quartz c axis orientations in non coaxial regimes and their significance for the mechanics of s c fabrics abstract the quartz c axis orientations of quartz bearing s c mylonites vary on the mm scale two specimens from different tectonic settings the variscan schwarzwald west germany and the eastern alps austria are investigated in the first specimen prism glide along a predominates and in the second specimen basal glide along a predominates in both specimens the pattern of c axis variations is similar it is suggested to be characteristic of s c mylonites on the local scale there are two patterns of preferred orientation 1 a crossed girdle type i which is inclined in a sense opposite to the inferred overall sense of shear this occurs in moderately strained domains 2 a single girdle which is slightly inclined in the same sense as the inferred overall sense of shear this occurs in domains that suffered higher strain both types are considered to reflect stable orientations of the easy glide direction crystallographic a direction at different stages of the deformational history two kinematic interpretations are discussed quartz c axis fabric variations reflect a spatial and possibly also temporal partitioning in flow path between domains that underwent either 1 spinning coaxial flow and non spinning non coaxial flow or 2 spinning non coaxial flow and non spinning non coaxial flow associated with variations in parameters of the deformation such as magnitude of strain and strain rate and perhaps also rate of recrystallization and recovery in either interpretation in moderately strained domains oblique c axis girdles are generated that cannot be used as shear sense indicators

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

an unstable kinematic state of the himalayan tectonic wedge evidence from experimental thrust spacing patterns abstract the frontal tectonic wedge in the nw himalayas shows a sequence of imbricate thrusts with increasing spacing in the foreland direction we used analogue model experiments to analyze the thrust pattern in relation to the kinematics of wedge evolution experimental findings reveal two kinematic states of the foreland ward propagation of a wedge unstable state and stable state the unstable state is characterized by continuous vertical growth of the wedge with progressive horizontal contraction on the other hand in the stable state the wedge ceases to grow vertically but propagates laterally in the foreland direction in the experimental runs thrust wedges remained in the unstable state even after large horizontal shortening 50 when the basal friction was high 0 46 our analysis suggests that successive thrusting occurs always with increasing spacing in unstable wedges and the rate of increase is larger for larger basal friction it can maintain uniform spacing only when the wedges turn into the stable state using finite element models we determined the stress distribution in the deforming wedge to find the potential locations of new thrusts in front of a wedge which also show larger spatial distances with increasing vertical thickness of the wedge both physical and numerical models suggest that the tectonic wedge in the nw himalayan frontal belt has evolved in an unstable state

relationships between strain and quartz crystallographic fabrics in the roche maurice quartzites of plougastel western brittany abstract an integrated microstructural and petrofabric study of the plastically deformed and partially recrystallized roche maurice quartzites of plougastel western brittany has revealed a clear correlation between the pattern of c axis fabrics displayed by detrital quartz grains and the symmetry of the calculated strain ellipsoid in specimens with flattening k 0 strains c axes lie on a small circle girdle opening angle 28 42 centred about the principal finite shortening direction z for specimens that exhibit approximate plane strain k 1 cross girdle c axis fabrics consisting of a small circle girdle centred about z and connected through the intermediate principal extension direction y were detected within individual specimens c axis fabrics of syntectonically recrystallized new quartz grains within the matrix are similar to those of detrital quartz grains c axes of new grains located within the relatively undeformed sections of the host detrital grains are commonly orientated at angles between 10 and 40 to the host c axis and are in addition statistically orientated at a higher angle to z than their host c axes these relationships are interpreted as indicating that both host grain control and the local strain and or stress field may have influenced the process of recrystallization the relative influence of these factors is however unknown microstructural and petrofabric studies indicate that the roche maurice quartzites have been subjected to essentially coaxial strain histories the role of syntectonic recrystallization in facilitating continued plastic deformation in quartzites subjected to such strain histories is considered

moine thrust zone mylonites at the stack of glencoul i microstructures strain and influence of recrystallization on quartz crystal fabric development since the early descriptions published by callaway in 1884 the gently dipping mylonites exposed along the moine thrust at the stack of glencoul have drawn generations of geologists to the northern part of the assynt district these mylonites derived from cambrian quartzites footwall and moine pelites and psammites hanging wall have figured prominently in a early research into the influence of crystal plastic deformation and recrystallization on microstructural and crystal fabric evolution b debates on the kinematic interpretation of macro and micro structures and crystal fabrics and c debates on the tectonic significance of such kinematic data in this paper first we briefly review the historical aspects of this research and then using both previously published and unpublished data document the finite strain and quartz fabric development at this classic mylonite locality a tectonic interpretation of these data together with quantitative estimates of flow vorticities associated with mylonite formation at the stack of glencoul are presented in a companion paper by law 2010

the caledonian skerrols thrust sw scotland microstructure and strain abstract strain measurements from quartz grain shapes in deformed jura quartzite around loch skerrols islay sw scotland indicate that a strain gradient is associated with the loch skerrols thrust which separates the jura quartzite from the bowmore sandstone progressive strain is associated with microstructural changes in the form of grain refinement through to dynamic recrystallization the maximum observed ratio of intracrystalline strain is 1 9 1 3 0 4 1 1 the x axis of the finite strain ellipsoid is close to the mesoscopic lineation in quartz mylonites in the thrust belt and the xy plane is sub parallel to the foliation the apparent flattening strain may be explained by superposition of simple shear thrust regime on initial flattening strain associated with the earlier stages of progressive development of the islay anticline this implies that the loch skerrols thrust is comparable to a break thrust strain induced quartz c axis preferred orientation increases in intensity as the thrust is approached at a higher strain the fabric is a type i cross girdle pattern with a point maximum within 20 of z fabric asymmetry both internal and with respect to an external frame defined by the principal strain directions attests to a westward transport of dalradian jura quartzite on the thrust

texture analysis of a recrystallized quartzite using electron diffraction in the scanning electron microscope abstract the microstructure and crystallographic preferred orientation texture of a recrystallized quartzite from the bergell alps was quantitatively investigated using automated indexing of electron backscattered patterns ebsp the results are displayed in orientation maps of the microstructure and orientation as well as misorientation distribution functions the orientation distribution function derived from ebsp compares excellently with texture data derived from independent neutron diffraction experiments the misorientation distribution function of next neighbors reveals strong maxima for small angle grain boundaries subgrain boundaries and the dauphine twin correlation the dauphine twins which are generally not detectable optically are not correlated with specific maxima in the orientation distribution function their origin and their role during recrystallization is discussed during recrystallization no other preferred high angle misorientations developed the frequent occurrence of small angle grain boundaries indicates progressive subgrain rotation as a recrystallization mechanism

deformation conditions and quartz c axis fabric development along nappe boundaries the andrelândia nappe system southern brasilia orogen brazil abstract the liberdade and andrel ndia nappes se brazil record the western gondwana amalgamation in the southern brasilia orogen during the ediacaran the liberdade shear zone acted as the boundary between these two overlapping nappes quartz c axis fabrics and strain data from quartzite samples and petrological data from hosting metapelite rocks were analyzed to investigate the tectonic processes involved in nappe development further constraints were achieved by conducting petrological modeling and geothermobarometry using p t isochemical phase diagram approaches quartz axis plots show consistency with different kinematic criteria verified in the field in meso and macroscale the fabrics are associated to both coaxial deformation and non coaxial deformation quartz microstructures metamorphic assemblages and c axis concentrations primarily around y and x structural directions suggest that deformation was accommodated by grain boundary migration recrystallization under temperature above 500 c disregarding pressure effects the opening angles of quartz c axis fabrics suggest temperatures between 480 and 640 c muscovite quartzite and 650 720 c sillimanite quartzite considering pressure data the opening angles indicate conditions of 550 650 c and 7 10 kbar muscovite quartzite and 600 730 c and 4 7 kbar sillimanite quartzite reflecting primarily distinct baric regimes sillimanite bearing samples estimatives are supported by ubiquitous presence of chessboard subgrain patterns in quartz and by modeled isochemical phase diagrams that constrain conditions of 660 730 c and 6 7 kbar for garnet sillimanite biotite schist samples altogether these results indicate progressive tectonic evolution linked to oblique convergence between tectonic units represented by the andrel ndia and liberdade nappes and the paleoproterozoic basement besides recording distinct thermal and baric regimes the nappes also present different structural styles suggesting that pressure and temperature are important boundary conditions for the nappe structural style

v pull apart microstructures a new shear sense indicator abstract granitoids deformed in a low grade shear zone show conspicuous development of asymmetric pull apart microstructures in feldspars characterized by v shaped gaps between the separated fragments v pull aparts they occur beside active shear planes and result from rigid body rotation of one fragment relative to the other the shear sense in the adjacent flow surface can be easily determined through the asymmetry normally shown by v pull aparts where the fracture wall at a lower angle to the shear plane indicates which fragment has rotated synthetically to the adjacent shearing another diagnostic feature is the foliation deflection that occurs adjacent to the rotated fragment the v shaped gaps are infilled by recrystallized quartz mica aggregates showing quartz c axis patterns indicative of strong participation of crystal plastic processes in these domains evidence of crack seal by precipitation c axes parallel to the direction of separation have also been found the rigid body rotation indicated by these microstructures worked as a mechanism of removal of protruding porphyroclast edges enabling the smoothing of the shear planes rigid body rotation should operate in circumstances where other mechanisms such as dissolution or crystal plasticity did not succeed in eliminating undulations along the shear planes