rapid eocene extension in the chapedony metamorphic core complex central iran constraints from 40ar 39ar dating abstract the neybaz chatak detachment system accommodated nne directed extension along the southwest central iranian plateau during eocene time the detachment is mainly exposed as southeast and north west dipping low angle normal fault for more than 100 km along strike of a ne trending structural dome structural data and abundant migmatite granite and diorite show features typical for a mantled gneiss dome coupled with peak p t conditions of ca 3 kbar and 650 750 c new hornblende muscovite biotite and k feldspar 40ar 39ar ages together with published u pb zircon and u th he apatite and zircon ages imply rapid cooling from ca 750 c to 60 c of the chapedony complex between 49 and 30 ma the neybaz chatak detachment comprises low grade hydrous mylonites with 40ar 39ar white mica ages of ca 43 ma interpreted to date activity along the shear zone ca 20 100 m thick cataclasites and hydrothermal chlorite breccias separate the footwall from the overlying hangingwall unit the documentation of eocene coeval compression in the neotethyan suture and extension in central iranian plateau has important implications for the understanding of the dynamics of collisional orogenesis

the limitations of three dimensional kinematic vorticity analysis abstract the kinematic vorticity number wk can be calculated for three dimensional as well as two dimensional geologic deformations for steady state deformations wk can be correlated to and analyzed in terms of finite strains the analysis shows that assumptions commonly made for two dimensional deformations are not applicable to three dimensional deformations a single wk describes an infinite number of three dimensional deformations further even knowledge of flow apophyses orientation instantaneous stretching axes orientation and or wk are not sufficient to describe deformation three dimensional deformations also require knowledge of the deformation type or boundary conditions of deformation e g transpression hence in addition to being difficult to estimate the value of knowing wk for three dimensional deformations is greatly reduced compared with plane strain the most useful methods of determining wk from naturally deformed rocks are presented

two stage collision related extrusion of the western dabie hp uhp metamorphic terranes central china evidence from quartz c axis fabrics and structures abstract the western dabie orogen also known as the hong an block forms the western part of the dabie sulu hp uhp belt central china rocks of this orogen have been subjected to pervasive ductile deformation and include numerous quartz schists and felsic mylonites cropping out in ductile shear zones quartz textures in these mylonites contain important clues for understanding the movement sense of late collisional extrusion and exhumation of high pressure ultrahigh pressure hp uhp rocks from the lower crustal level to the upper crustal level during middle triassic and early jurassic the orientation and distribution of quartz crystallographic axes were used to confirm the regional shear sense across the orogen the asymmetry of c axis patterns consistently indicates top to the southeast thrusting across the orogen in early structural stages later stages of deformation show different senses of movement in northern and southern parts of the orogen with top to the northwest sinistral shearing recorded in rocks north of the xinxian hp uhp eclogite facies belt and top to the southeast dextral shearing south of the same unit based on our study on quartz c axis fabrics and marco to micro scale structures simultaneous southeastward shearing within a large part of the orogen and normal faulting north of the xinxian hp uhp unit is explained by upward extrusion in early stages of deformation the extrusion process has been attributed to syn and late collisional processes accounting for some earlier deformation in the western dabie orogen such as metamorphic sequences around the core of the xinxian hp uhp eclogite facies unit much higher pressure of deformation is also indicated in the aligned glaucophane and omphacite from blueschist and eclogite in the field an orogen parallel eastward extrusion of the xinxian hp uhp eclogite facies unit however occurred diachronously in later stages of deformation therefore a tectonic model combining an early upward extrusion with a later eastward extrusion is presented two different stages and types of extrusion for exhumation of hp uhp rocks are suitable to all of east central china geochronological data shows that the first upward extrusion occurred during middle triassic the second eastward extrusion occurred during late triassic to early jurassic these two extrusions are correlative with two stages of rapid exhumation of the dabie hp uhp rocks respectively these two stage late collisional middle triassic to early jurassic extrusion events bridge the gap between syn collisional early to middle triassic vertical extrusion and post collisional cretaceous eastward directed lateral escape and provide vital clues to understanding the more detailed processes of exhumation of hp uhp rocks

fabric transitions in the saxony granulite terrain abstract quartz fabric transitions reported from the saxony granulite terrain and from the nearby ore mountains are interesting because of the changes in the pattern types and the variation in the opening angles of the fabric skeletons a short summary is presented of salient features in research documented in the east german literature between 1961 and 1978 the changes in fabric skeleton with decreasing metamorphic grade are proposed as mainly consequent to the deactivation of prism c glide systems as temperature decreases fabrics indicative of the appearance of the c burgers vector might be diagnostic for deformation in regimes of comparatively high temperatures or low strainrates or for deformation under conditions such that there is a relatively high kinetically effective hydroxyl content in the quartz structure

microstructures and quartz lattice preferred orientations in the eclogite bearing migmatitic gneisses of the d entrecasteaux islands papua new guinea 1 lattice preferred orientations lpo of quartz in gneiss domes of the d entrecasteaux islands woodlark rift shed insight into exhumation of the world s youngest 5 7 ma eclogite bearing terrane at cm yr rates we focus on deformation that affected the terrane as it transited between lower crustal depths and the surface including 1 grain scale deformation mechanisms and 2 style of flow and mode of emplacement of the domes electron backscatter diffraction was used to analyze microstructure and lpos of 37 quartzofeldspathic gneiss samples that enclose meter scale mafic blocks preserving original eclogite facies assemblages during exhumation of the ultrahigh pressure uhp terrane gneisses were retrogressed in the amphibolite facies at lower crustal depths the lpos change from dome cores to carapaces consistent with decreasing deformational temperatures in the relatively chilled outer carapaces of the domes the quartz lpos consist of mostly crossed girdle c axis patterns with some cleft girdle and small circle lpos and record dislocation creep accommodated by mixed slip in the cores of the migmatitic domes a chessboard pattern of subgrains is common and quartz lpos primarily record prism c slip probably at 630 c other microstructures indicate recovery by high temperature grain boundary migration grain boundary mobility was anisotropic leading to strong grain shape fabrics oblique to foliation but not obviously relatable to shear sense evidence for melt present deformation is abundant and microstructures including partially dissolved feldspar grains indicate some deformation by fluid assisted grain boundary diffusion creep lpos in carapace rocks are symmetrical recording flow that was dominantly coaxial we interpret the gneiss domes to have been emplaced into the rift as partially molten diapirs

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

modes of continental lithospheric extension experimental verification of strain localization processes abstract three modes of continental lithospheric extension narrow rift wide rift and core complex were studied by means of analogue experiments the experimental method is based on models which simulate an idealized lithospheric strength profile and are scaled for gravity various styles of lithospheric extension were induced by systematic variation of brittle upper crustal thicknesses narrow rifting occurs during stable lithospheric extension when the resistance of the brittle upper crust dominates the deformation process wide rifting results from unstable lithospheric extension when the brittle upper crust is thin and ductile flow in the lower crust allows expansion of the deformation zone periodic instabilities with two wavelengths dominate wide rifting core complex mode extension is transitional between unstable and stable lithospheric extension it begins as a distributed zone of unstable extension due to thin upper brittle crust but lower crustal flow induced by the gravity force causes a relocalization of strain into narrow zones transitions between the three modes of extension are characterized in terms of competition between the strength of lithosphere and gravity forces as well as between stable and unstable deformation processes

heterogeneous sub simple deformation in the gol e gohar shear zone zagros sw iran insights from microstructural and crystal fabric analyses petrofabrics and microstructural characteristics of the quartz rich mylonites were investigated in the nw se trending gol e gohar shear zone with length of ca 25 km within the zagros transpression zone sw iran the semi quantitative vorticity analysis using quartz c axis fabric rxz method and rigid porphyroclast geometry rigid grain net method reveals that mean kinematic vorticity number wm increases towards the baghat thrust fault displaying the occurrence of spatial and temporal variations of flow during progressive deformation the wm values show pure shear dominated flow progressively was changed to a simple shear dominated flow toward to the late stages of ductile deformation implying that the accelerating flow path was accompanied with progressive cooling and strain localization at the lower parts of the zone the measured vertical thinning dip parallel elongation suggests that thrust emplacement and metamorphic rock extrusion likely occurred by a combination of simple shear with a pure shear component of deformation i e general shear the estimated deformation temperatures based on the quartz c axis fabric patterns and their opening angles highlight greenschist to amphibolite facies conditions

p t d histories from quartz a case study of the application of the titaniq thermobarometer to progressive fabric development in metapelites 1 this study investigates the ability of quartz to record segments of the pressure temperature deformation p t d path in poly deformed metamorphic terranes and the associated application of the ti in quartz thermobarometer titaniq metapelites from the strafford dome eastern vermont were selected for this study because they record progressive fabric development during prograde metamorphism and have well constrained p t d histories from previous work results of this investigation are in agreement with previous studies and demonstrate that quartz in these samples records additional distinct intervals of the p t d path six preserved quartz equilibration events include 1 early prograde growth during burial 2 kyanite in quartz producing reactions 3 prenappe emplacement equilibration during isobaric heating 4 precipitation of quartz in quartz feldspar domains during crenulation cleavage development due to solution transfer 5 quartz producing chlorite out reactions during heating postnappe emplacement and 6 retrograde quartz overgrowths from an influx of siliceous fluids modeling quartz volume allows for the identification of quartz producing reactions in p t space the same may be done for ti phases to better constrain activities during reequilibration events an integration of cathodoluminescence imaging microstructural and petrographic investigation isochemical forward stability modeling and thermobarometry allows identification and interpretation of zoning patterns in quartz to unravel histories that would otherwise not be obtainable

deformation temperatures and flow vorticities near the base of the greater himalayan series sutlej valley and shimla klippe nw india abstract we report new deformation temperature and flow vorticity data from the base of the greater himalayan series ghs exposed in the sutlej valley and shimla klippe of nw india we focus on three groups of transects across the hanging wall of the main central thrust mct in order of relative foreland hinterland positions they are the shimla klippe western and eastern sutlej transects deformation temperatures indicated by quartz c axis fabric opening angles increase both from foreland to hinterland at a given structural distance above the mct and up structural section from the mct within individual transects deformation temperatures in the immediate hanging wall to the mct are estimated at 510 535 535 550 and 610 c on the shimla western sutlej and eastern sutlej transects respectively the steepest inferred field gradients in deformation temperatures are recorded adjacent to the mct and progressively decrease up structural section following a power law relationship comparison with temperature estimates based on multi mineral phase equilibria data suggests that penetrative shearing occurred at close to peak metamorphic conditions vorticity analyses indicate that shearing along the base of the ghs occurred under sub simple shear conditions wm values of 0 9 1 0 with a minor component of pure shear

regional stratigraphy of the zagros fold thrust belt of iran and its proforeland evolution the latest neoproterozoic through phanerozoic stratigraphy of the zagros fold thrust belt of iran has been revised in the light of recent investigations the revised stratigraphy consists of four groups of rocks each composed of a number of unconformity bounded megasequences representing various tectonosedimentary settings in the lowest group ranging in age from latest precambrian to devonian the uppermost neoproterozoic to middle cambrian rocks constitute a megasequence of evaporites siliciclastic deposits and interlayered carbonates which were deposited in pull apart basins that developed by the najd strike slip fault system this megasequence is overlain by a second one middle to late cambrian in age which consists of shallow marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform the overlying shales siltstones and partly volcanogenic sandstones of ordovician silurian and devonian age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities the second group consists of two megasequences one permian and the other triassic composed of widespread transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial epi pangean very shallow platformal sea the third group is composed of four megasequences formed of shallow and deep water carbonates with some siliciclastic and evaporite deposits which accumulated on a neo tethyan continental shelf during earliest jurassic through late turonian time the fourth group comprises siliciclastic and carbonate deposits of a largely underfilled nw to se trending forward and backward migrating late cretaceous to recent proforeland basin which has evolved as an integral part of the zagros orogen this last group consists of three megasequences ix x and xi with distinctive lateral and vertical facies variations which reflect specific tectonic events megasequence ix comprises uppermost turonian to middle maastrichtian prograding and retrograding siliciclastic and carbonate deposits whose accumulations reflect emplacement obduction of ophiolite slivers and subsequent collisional events in the zagros orogen megasequence x consists of uppermost maastrichtian to upper eocene siliciclastic and carbonate rocks which deposited first progradationally in front of the zagros orogenic wedge with reduced contractional tectonic activity and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen megasequence xi consists of oligocene and lower miocene carbonate strata deposited retrogradationally shortly after a period of intensified late eocene thrust faulting in the deformational wedge and an overlying succession of upward coarsening northeasterly derived siliciclastic deposits of lower miocene to recent age which are composed of erosional byproducts of the southwest vergent zagros thrust sheets

cenozoic evolution of neotethys and implications for the causes of plate motions africa north america eurasia plate circuit rotations combined with red sea rotations and new estimates of crustal shortening in iran define the cenozoic history of the neotethyan ocean between arabia and eurasia the new constraints indicate that arabia eurasia convergence has been fairly constant at 2 to 3 cm yr since 56 ma with slowing of africa eurasia motion to 1 cm yr near 25 ma coeval with the opening of the red sea ocean closure occurred no later than 10 ma and could have occurred prior to this time only if a large amount of continental lithosphere was subducted suggesting that slowing of africa significantly predated the arabia eurasia collision these kinematics imply that africa s disconnection with the negative buoyancy of the downgoing slab of lithosphere beneath southern eurasia slowed its motion the slow steady rate of northward subduction since 56 ma contrasts with strongly variable rates of magma production in the urumieh dokhtar arc implying magma production rate in continental arcs is not linked to subduction rate

cooling history of the chapedony metamorphic core complex central iran implications for the eurasia arabia collision abstract new apatite and zircon u th he thermochronometry is used to constrain the late stage cooling history of the chapedony metamorphic core complex in the saghand region of central iran providing new constraints on the cenozoic tectonic evolution of this segment of the euro arabian collision zone zircon and apatite he ages from the footwall indicate that it cooled to near surface temperatures by 30 ma combined with previous high temperature thermochronology the new data require that the chapedony metamorphic core complex cooled from 750 c to 60 c in less than 20 million years at 80 c myr cooling of the complex occurred through tectonic exhumation at a rate of 1 2 1 5 km myr exhumation of the core complex occurred during the main phase of subduction of the distal arabian margin beneath the central iranian plate at 49 to 30 ma zircon he ages from the hangingwall units of the complex suggest an earlier pulse of exhumation in middle late cretaceous apatite he ages from the hangingwall 22 30 ma are significantly younger than the core complex exhumation but is consistent with the regional timing of initial eurasia arabia collision

experimental deformation of a quartz mylonite abstract samples of a pure quartz mylonite have been axially shortened up to 60 in nickel capsules with water at temperatures of 600 900 c strain rates of 10 5 10 7 s 1 and a confining pressure of 1 64 gpa in a solid medium deformation apparatus the mylonite was loaded in four orientations relative to the initial foliation and lineation psl parallel to the foliation and lineation 45sl 45 to the foliation and lineation nsl normal to the foliation and lineation and psnl parallel to the foliation normal to the lineation the strength of the mylonite varies with the orientation of the specimen with respect to the loading direction as well as with temperature and strain rate specimens deformed psl are weakest with those deformed 45sl slightly stronger while specimens deformed nsl and psnl are generally 200 400 mpa stronger all experiments exhibit strain softening at strains greater than 15 strongly flattened grains with sub basal deformation lamellae are developed in all specimens with the amount of recrystallization increasing as temperature is increased and or strain rate is decreased the initial c axis preferred orientation typical of quartz mylonites is an asymmetric girdle normal to the mylonitic foliation and lineation in specimens deformed nsl and psnl strengthening of the c axis maximum parallel to the shortening direction is the major change in preferred orientation the c axes in these specimens are inferred to be in stable orientations with respect to the shortening direction in specimens deformed psl a new girdle develops parallel to the initial foliation with subsidiary girdles running from the shortening direction to a position normal to the initial foliation and lineation more complex fabrics observed in specimens deformed 45sl are associated with the triclinic symmetry of the overall deformation the fabrics develop by initial kinking of grains which have c axes at high angles to the shortening direction causing them to rotate into orientations more suitable for dislocation slip slip occurs on both basal and prism planes rhomb slip may have a minor influence in all cases slip parallel to a is consistent with the observed fabrics the complexity of the fabrics indicates that even at these high strains 60 quartz can still show a memory for fabrics developed in previous deformations

the 3d quantitative lattice and shape preferred orientation of a mylonitised metagranite from monte rosa western alps combining neutron diffraction texture analysis and synchrotron x ray microtomography abstract two complementary 3d techniques neutron diffraction and synchrotron x ray microtomography sxr ct were used to compare the shape and lattice preferred orientations of a mylonitised metagranite from the monte rosa unit western alps italy the goal of using these techniques was to obtain two different orientation distribution functions although the two functions describe relatively independent characteristics of the rock fabric nonetheless they also exhibit close relationships to macroscopic fabrics and may be complementarily used to quantify rock fabrics and microstructures thereby highlighting 3d features that cannot be obtained with either technique if used independently we describe an approach that can be potentially useful in various disciplines e g structural geology rock mechanics tectonics and geophysics when a complete data set of preferred orientations and size distribution is needed micas display a strong orthorhombic symmetry between mesoscopic lineation and microscopic spo and lpo whereas quartz and feldspars are characterised by a monoclinic symmetry between mesoscopic lineation and lpo these observations suggest a rheological decoupling between the weak phase mica layers and the stronger quartz feldspar layers this mechanical decoupling occurred during the alpine subduction collision when the monte rosa unit was part of the insubric line system and accommodated large vertical strain

tectonometamorphic evolution of the koralm complex eastern alps constraints from microstructures and textures of the plattengneis shear zone abstract lattice preferred orientations lpo of quartz have been investigated along a south north oriented section across the plattengneis of the koralm complex eastern alps the plattengneis forms an important shear zone within the austroalpine nappe complex of the eastern alps which has developed during the cretaceous evolution of the alpine orogen the quartz c axes form small circle distributions in the southernmost parts of the koralm complex which represent the uppermost structural level of the plattengneis further to the north two maxima between the y and z directions of the finite strain can be interpreted in terms of preferred slip on the rhomb planes these fabrics continuously grade into type i and type ii crossed girdle distributions in a northward direction a strong maximum near the y axis with the tendency to be distributed along a single girdle with three corresponding maxima of a axes near the margin of the pole figure can be observed in the central and northern parts such lpo are characteristic for both high grade metamorphic conditions and high finite strain the microstructures display that the deformation within the plattengneis shear zone was synmetamorphic a continuous increase of peak temperatures and pressure from approximately 550 c to approximately 750 c from the south to the central parts can be inferred from geothermometric calculations the temperatures then decrease to approximately 650 c from the central parts to the north the related pressures increase from 8 to 16 kbar and then decrease to 10 kbar the lpo changes that have been observed in the study area are best interpreted in terms of temperature dependence of the activation of glide systems within quartz aggregates the temperature and pressure evolution may indicate that the central parts of the koralm complex have been exhumed by larger amounts than the northern and southern parts this is also documented by the lpo evolution therefore we assume that the plattengneis shear zone formed during the exhumation of the koralm complex and is related to the exhumation of high pressure units in the footwall of this shear zone accordingly the kinematics of the plattengneis shear zone is rather extensional than thrust related the implications for the structural evolution of the eastern alps are shortly discussed

thermomechanics of an extensional shear zone raft river metamorphic core complex nw utah abstract a detailed structural and microstructural analysis of the miocene raft river detachment shear zone nw utah provides insight into the thermomechanical evolution of the continental crust during extension associated with the exhumation of metamorphic core complexes combined microstructural electron backscattered diffraction strain and vorticity analysis of the very well exposed quartzite mylonite show an increase in intensity of the rock fabrics from west to east along the transport direction compatible with observed finite strain markers and a model of necking of the shear zone microstructural evidence quartz microstructures and deformation lamellae suggests that the detachment shear zone evolved at its peak strength close to the dislocation creep exponential creep transition where meteoric fluids played an important role on strain hardening embrittlement and eventually seismic failure empirically calibrated paleopiezometers based on quartz recrystallized grain size and deformation lamellae spacing show very similar results indicate that the shear zone developed under stress ranging from 40 mpa to 60 mpa using a quartzite dislocation creep flow law we further estimate that the detachment shear zone quartzite mylonite developed at a strain rates between 10 12 and 10 14 s 1 we suggest that a compressed geothermal gradient across this detachment which was produced by a combination of ductile shearing heat advection and cooling by meteoric fluids may have triggered mechanical instabilities and strongly influenced the rheology of the detachment shear zone

the eigenvalues of steady flow in mohr space abstract the eigenvalues of the velocity gradients tensor and of the position gradients tensor describing instantaneous flow or incremental deformations are easily determined in mohr space as the points of intersection between a mohr circle and the horizontal mohr axis intersections occur only if the tensor has real eigenvalues eigenvectors associated with the eigenvalues are directions of no rotation a line of material particles under an eigenvector does not rotate during steady flow although the line is instantaneously stretching at a rate equal to its corresponding eigenvalue for non spinning steady sub simple shearing there will always be two eigenvectors the angle between the eigenvectors is dependent on the ratio of pure to simple shearing rates this angle decreases as the pure shearing component decreases relative to the simple shearing component superimposed increments of pure shear and simple shear produce an equivalent set of non rotated material lines but the deformation histories of these lines are rotational the influence of eigendirections on geological structures is constrained by the rheology of a rock during deformation in homogenous steady flow no influence may be obvious spatially periodic material softening along eigenvectors during bulk hardening may result in a complex fabric of intersecting shear zones the geometry of the fabric elements provides important information on the bulk deformation of the rock particularly on the bulk shear sense

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

quartz preferred orientation in naturally deformed mylonitic rocks montalto shear zone italy a comparison of results by different techniques their advantages and limitations in the geologic record the quartz c axis patterns are widely adopted in the investigation of crystallographic preferred orientations cpo of naturally deformed rocks to this aim in the present work four different methods for measuring quartz c axis orientations in naturally sheared rocks were applied and compared the classical universal stage technique the computer integrated polarization microscopy method cip the time of flight tof neutron diffraction analysis and the electron backscatter diffraction ebsd microstructural analysis and cpo patterns of quartz together with the ones obtained for feldspars and micas in mylonitic granitoid rocks have been then considered to solve structural and geological questions related to the montalto crustal scale shear zone calabria southern italy results obtained by applying the different techniques are discussed and the advantages as well as limitations of each method are highlighted importantly our findings suggest that patterns obtained by means of different techniques are quite similar in particular for such mylonites a subsimple shear 40 simple shear vs 60 pure shear by shape analysis of porphyroclasts was inferred a general tendency of an asymmetric c maximum near to the z direction normal to foliation suggesting dominant basal slip consistent with fabric patterns related to dynamically recrystallization under greenschist facies is recognized rhombohedral slip was likely active as documented by pole figures of positive and negative rhombs tof which reveal also potential mechanical dauphine twinning results showed that the most complete cpo characterization on deformed rocks is given by the tof from which also other quartz crystallographic axes can be obtained as well as various mineral phases may be investigated however this use is restricted by the fact that a there are very few tof facilities around the world and b there is loss of any domainal reference since tof is a bulk type analysis ebsd is a widely used technique which allows an excellent microstructural control of the user covering a good amount of investigated grains cip and us are not expensive techniques with respect the other kind of investigations and even if they might be considered obsolete and or time consuming they have the advantage to provide a fine and grain by grain first round inspection on the investigated rock fabric

thermometry of quartz mylonites importance of dynamic recrystallization on ti in quartz reequilibration quartz mylonites from the tonale fault zone in the alps northern italy have been investigated by the ti in quartz geothermometer titaniq in order to test its applicability to measure deformation temperatures the eastern part of the tonale fault zone was contact metamorphosed by the synkinematic intrusion of the adamello pluton forming an 800 m wide mylonitic shear zone with a synkinematic temperature gradient from 280 c at the frictional viscous transition to 700 c at the pluton contact as derived from metamorphic mineral assemblages deformation microstructures from quartz mylonite samples systematically collected across the mylonitic shear zone display the entire range of dynamic recrystallization in quartz which comprise bulging recrystallization blg subgrain rotation recrystallization sgr and grain boundary migration recrystallization gbm titaniq geothermometry yields the near peak deformation temperature for quartz mylonites deformed at metamorphic temperatures above 540 c in the zone of gbm however for mylonites formed under lower temperatures in the zones of sgr and blg the preexisting ti concentrations were not reset it is suggested that this is due to the sluggish ti volume diffusion rates below 500 c and the short duration of contact metamorphism and deformation even in the higher temperature samples the reequilibration of ti in quartz content was achieved by grain boundary migration rather than by volume diffusion hence our results show that gbm is crucial for the reequilibration of ti in quartz while quartz mylonites deformed by either blg or sgr which predominate in natural shear zones at greenschist facies metamorphic conditions most likely yield inherited temperatures

kinematics of rock flow in a crustal scale shear zone implication for the orogenic evolution of the southwestern hellenides combined shear sense criteria finite strain data and vorticity analyses were used to study the deformation path in a curved crustal scale shear zone phyllite quartzite series of the southwestern hellenides the results are combined with data on the structural evolution of a cover nappe pindos thrust belt to provide new insights into the orogenic evolution of this region ductile deformation within the phyllite quartzite series was associated with a top to the west southwest shearing and was partitioned into two structural domains a root zone and a frontal domain the root zone is characterized by vertical coaxial stretching high strain and upward movement of the material while the frontal domain comprises simple shear deformation at the base and pure shear at the top this pattern suggests superposition of pure shear on simple shear deformation and implies tectonic extrusion of the material from the root zone the initiation of brittle deformation in the pindos thrust belt was associated with westward translation above the sub horizontal pindos thrust later as the mountain range elevated normal faulting at high altitudes and migration of thrusting to the west occurred while east directed folding and thrusting in the belt started to the east according to the proposed model crustal thickening was taking place throughout the oligocene and early miocene including the subduction of the apulian beneath the pelagonian microcontinent and the intracontinental subduction of the phyllite quartzite series during the lower miocene vertical buoyancy forces led to the successive steepening of the shear zone and the simultaneous duplexing of its basement facilitating tectonic extrusion of the material from its root zone finally an indentation process caused vertical expulsion of the orogenic wedge and gravity collapse in the brittle crust

geology and thermochronology of tertiary cordilleran style metamorphic core complexes in the saghand region of central iran an 100 km long north south belt of metamorphic core complexes is localized along the boundary between the yazd and tabas tectonic blocks of the central iranian micro continent between the towns of saghand and posht e badam amphibolite facies mylonitic gneisses are structurally overlain by east tilted supracrustal rocks including thick 1 km steeply dipping nonmarine siliciclastic and volcanic strata near the detachment the neybaz chatak fault the gneisses are generally overprinted by chlorite brecciation crosscutting relationships along with u pb zircon and 40 ar 39 ar age data indicate that migmatization mylonitic deformation volcanism and sedimentation all occurred in the middle eocene between ca 49 and 41 ma the westernmost portion of the tabas block immediately east of the complexes is an east tilted crustal section of neoproterozoic cambrian crystalline rocks and metasedi mentary strata 10 km thick the 40 ar 39 ar biotite ages of 150 160 ma from structurally deep parts of the section contrast with ages of 218 295 ma from shallower parts and suggest late jurassic tilting of the crustal section these results define three events 1 a late jurassic period of upper crustal cooling of the western tabas block that corresponds to regional jurassic cretaceous tectonism and erosion recorded by a strong angular unconformity below mid cretaceous strata throughout central iran 2 profound approximately east west middle eocene crustal extension plutonism and volcanism ca 44 40 ma and 3 2 3 km of early miocene ca 20 ma erosional exhumation of both core complex and tabas block assemblages at uppermost crustal levels resulting from significant north south shortening the discovery of these and other complexes within the mid tertiary magmatic arcs of iran demonstrates that cordilleran style core complexes are an important tectonic element in all major segments of the alpine himalayan orogenic system

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

deformation thermometry based on quartz c axis fabrics and recrystallization microstructures a review abstract for quartz rich tectonites two types of deformation thermometer are currently commonly employed 1 the quartz c axis fabric opening angle thermometer that provides an estimate of deformation temperatures when fabrics were locked in during dislocation creep and dynamic recrystallization 2 the quartz recrystallization thermometer that indicates a range of likely deformation temperatures based on observed microstructures and inferred mechanisms of dynamic recrystallization a critically important caveat in applying both thermometers is the assumption that deformation temperature is the primary controlling factor in recrystallization mechanisms and fabric development however fabric opening angles and recrystallization mechanisms are also sensitive to other variables such as strain rate and water weakening in this paper the development of these thermometers is reviewed and their potential sensitivities to competing factors such as temperature strain rate water weakening and in the case of opening angles 3d strain type are discussed examples of the application of these potential thermometers to naturally deformed quartz rich rocks are given and case studies of correlations between deformation temperatures estimated by these thermometers and temperatures of synkinematic metamorphism determined by petrology based thermobarometers are highlighted in the review attention is focused on problems associated with applying these thermometers to natural deformation and examples of such problems are discussed

transpressional deformations within the sanandaj sirjan metamorphic belt zagros mountains iran abstract polyphase deformation structures of the sanandaj sirjan metamorphic belt in the neyriz area zagros mountains iran are consistent with dextral transpressional deformation which is related to the oblique collision between the african arabian continent and the iranian microcontinent the collision started in the late cretaceous and is continuing to the present day quantitative kinematic analyses quartz textures suggest localized shear zones deformed with a significant pure shear component spatial orientation of lineation and semi quantitative kinematic indicators indicate shear zone parallel stretching and shear zone perpendicular shortening the occurrence of a horizontal stretching component parallel to the deformation zone boundary allows a kinematic model of combined transpression and lateral extrusion for this part of the zagros orogeny

petrogenesis of cretaceous adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china implications for geodynamics and cu au mineralization both adakitic and shoshonitic igneous rocks in the luzong area anhui province eastern china are associated with cretaceous cu au mineralization the shaxi quartz diorite porphyrites exhibit adakite like geochemical features such as light rare earth element lree enrichment heavy ree hree depletion high al2o3 mgo sr sr y and la yb values and low y and yb contents they have low end t values 3 46 to 6 28 and high 87sr 86sr i ratios 0 7051 0 7057 sensitive high resolution ion microprobe shrimp zircon analyses indicate a crystallization age of 136 3 ma for the adakitic rocks most volcanic rocks and the majority of monzonites and syenites in the luzong area are k rich or shoshonitic and were also produced during the cretaceous 140 125 ma they are enriched in lree and large ion lithophile elements and depleted in ti and nb and ba and exhibit relatively lower end t values ranging from 4 65 to 7 03 and relatively higher 87sr 86sr i ratios varying between 0 7057 and 0 7062 the shoshonitic and adakitic rocks in the luzong area have similar pb isotopic compositions 206pb 204pb 17 90 18 83 207pb 204pb 15 45 15 62 and 208pb 204pb 38 07 38 80 geological data from the luzong area suggest that the cretaceous igneous rocks are distributed along ne fault zones e g tanlu and yangtze river fault zones in eastern china and were likely formed in an extensional setting within the yangtze block the shaxi adakitic rocks were probably derived by the partial melting of delaminated lower crust at pressures equivalent to crustal thickness of 50 km i e 1 5 gpa possibly leaving rutile bearing eclogitic residue the shoshonitic magmas in contrast originated mainly from an enriched mantle metasomatized by subducted oceanic sediments they underwent early high pressure 1 5 gpa fractional crystallization at the boundary between thickened 50 km lower crust and lithospheric mantle and late low pressure 1 5 gpa fractional crystallization in the shallow 50 km crust the adakitic and shoshonitic rocks appear to be linked to an intra continental extensional setting where partial melting of enriched mantle and delaminated lower crust was probably controlled by lithospheric thinning and upwelling of hot asthenosphere along ne fault zones e g tanlu and yangtze river fault zones in eastern china both the shoshonitic and adakitic magmas were fertile with respect to cu au mineralization

fold controlled quartz textures in the pennine mischabel backfold near zermatt switzerland abstract quartz fabric analyses along the basal thrust of the dent blanche nappe and in the footfall pennine units indicate south directed thrusting for the last stage of austro alpine pennine nappe emplacement quartz fabrics in particular those from the pennine mischabel backfold imply complex spatial and temporal texture developments with crystallographic preferred orientations cpo that are commonly in disagreement with mesoscopic grain shape lineations in consequence kinematic directions inferred by quartz textures do not necessarily coincide with those predicted by mesoscopic structural elements such as grain shape lineations in our particular case orientation of grain shape lineations is rather complex in the study area while principal axes inferred from the quartz textures remain geographically constant and exhibit a simple geometric relationship to the mischabel backfold it is suggested that the grain shape lineations correspond to the total accommodated finite strain whereas the quartz fabrics reflect late increments of deformation quartz cpos in the hinge of the mischabel fold are similar to those along the thrust revealing asymmetric single girdles to c axes point maxima subgrain rotation is the predominant recrystallization mechanism suggesting steady state conditions in fabric development during progressive rotational deformation in contrast asymmetric cross girdles dominate the upper limb and uneven small circle c axes distributions characterize the lower limb although recrystallization in both limbs is characterized by grain boundary migration this clear separation of quartz textures and recrystallization deformation mechanism conflicts with the common view on heterogeneous deformation patterns in folds where the major component of rotational shear is expected in the fold limbs our study suggests that fabric development in the limbs of the recumbent mischabel fold was reset during progressive deformation shortly prior to the transition from an active buckling to passive fold amplification while the hinge suffered continuous bulk deformation provided by the back thrusting of the dent blanche nappe

electron backscatter diffraction analysis to determine the mechanisms that operated during dynamic recrystallisation of quartz rich rocks abstract determination of the controlling nucleation and recrystallisation mechanisms from a samples microstructure are essential for understanding how the microstructure formed and evolved through time the aim of our research was to apply a quantified analytical approach to the identification of the controlling nucleation recrystallisation and microstructural modification mechanisms we used electron backscatter diffraction to quantify the microstructures of naturally deformed quartz rich rocks which were deformed at various temperature and pressure conditions our results show that ratios of the recrystallised grain size to the subgrain size with values less than 1 0 5 0 7 in the data presented here suggest bulge nucleation whereas ratios of 1 suggest subgrain rotation nucleation other supporting evidence for subgrain rotation nucleation is an increase in misorientation from the centre of an original protolith parent grain to the edge all samples show evidence for modification of the microstructure due to grain boundary sliding including increased misorientation angles between grains and movement of recrystallised grains between parent grains by systematically analysing sample microstructures it is possible to separate out evidence to determine the controlling nucleation and recrystallisation mechanisms as well as being able to identify microstructure modification mechanisms using microstructural quantification via ebsd allows a systematic methodology to analyse samples from any location from an objective viewpoint

electron microprobe petrochronology the term petrochronology has increasingly appeared in publications and presentations over the past decade the term has been defined in a somewhat narrow sense as the interpretation of isotopic dates in the light of complementary elemental or isotopic information from the same mineral s kylander clark et al 2013 although complementary isotopic and elementary information are certainly a central and critical part of most if not all petrochronology studies the range of recent studies that might use the term covers a much broader scope the term petrochronology might alternatively be defined as the detailed incorporation of chronometer phases into the petrologic and tectonic evolution of their host rocks in order to place direct age constraints on petrologic and structural processes as noted by kylander clark et al 2013 the linkage between geochronology and petrology can involve a variety of data including mineral textures and fabrics the distribution of mineral modes or volume proportions compositional zoning mineral inclusion relationships and certainly major element trace element and isotopic composition of the chronometer and all other phases electron probe micro analysis epma has a central and critical role to play in establishing the linkage between chronometer phases and their host assemblage the basic instrument is an electron microscope which can be used in either scanning or fixed beam modes with integrated wavelength dispersive spectrometers wds energy dispersive spectrometers eds electron detectors to image secondary and backscattered signals a light optical system and optionally cathodoluminescence cl detection the electron microprobe is used to investigate the distribution composition and compositional zonation of all mineral phases the data that underpin thermobarometric analysis and modeling of p t histories the microprobe with m scale spatial resolution can also characterize compositional zonation in very small accessory phases including monazite xenotime zircon allanite titanite apatite and others this as discussed below can be a

the lateral boundary of a metamorphic core complex the moutsounas shear zone on naxos cyclades greece we describe the structure microstructures texture and paleopiezometry of quartz rich phyllites and marbles along n trending moutsounas shear zone at the eastern margin of the naxos metamorphic core complex mcc fabrics consistently indicate a top to the nne non coaxial shear and formed during the main stage of updoming and exhumation between ca 14 and 11 ma of the naxos mcc the main stage of exhumation postdates the deposition of overlying miocene sedimentary successions and predates the overlying upper miocene pliocene conglomerates detailed microstructural and textural analysis reveals that the movement along the moutsounas shear zone is associated with a retrograde greenschist to subgreenschist facies overprint of the early higher temperature rocks paleopiezometry on recrystallized quartz and calcite yields differential stresses of 20 77 mpa and a strain rate of 10 15 10 13 s 1 at 350 c for quartz and ca 300 c for calcite chlorite geothermometry of the shear zone yields two temperature regimes 300 360 c and 200 250 c the lower temperature group is interpreted to result from late stage hydrothermal overprint

crustal thickening by tectonic wedging of the ganderian rocks southern new england usa evidence from cataclastic zircon microstructures and u pb ages abstract zircon grains in granites from avalonian and ganderian rocks in southern new england host brittle internal structures that are interpreted here to show the host rocks to be allochthonous significant among these structures are inherited cores that are commonly fractured and even dismembered this intense fracturing is interpreted as reflecting an important cataclastic event the maximum age of fracturing is constrained to be younger than the age of the youngest broken magmatic core 360 4 ma the minimum age must be older than the oldest zircon rim that heals these fractures that is early permian the occurrence of cataclastic zircon requires that these rocks were relatively cold i e in the upper crust during the carboniferous and therefore were not involved in the pervasive high grade acadian metamorphism the present map pattern of inter tonguing high grade and low grade slices of peri gondwanan rocks shows that they were assembled by crustal scale tectonic wedging the consequent thickening ultimately led to anatexis in the lower slices during the permian thus evidence for cataclasis of zircon grains from the avalon and gander terranes of southern new england suggests that these peri gondwanan terranes remained outboard of laurentia during the well documented early devonian acadian orogeny and were first fully accreted to north america during the alleghanian permian orogeny

s c mylonites two types of foliations are commonly developed in mylonites and mylonitic rocks a s surfaces related to the accumulation of finite strain and b c surfaces related to displacement discontinuities or zones of relatively high shear strain there are two types of s c mylonites type i s c mylonites described by berthe et al typically occur in deformed granitoids they involve narrow zones of intense shear strain which cut across mylonitic foliation type ii s c mylonites described here have widespread occurrence in quartz mica rocks involved in zones of intense non coaxial laminar flow the c surfaces are defined by trails of mica fish formed as the result of microscopic displacement discontinuities or zones of very high shear strain the s surfaces are defined by oblique foliations in the adjacent quartz aggregates formed as the result of dynamic recrystallization which periodically resets the finite strain clock these oblique foliations are characterized by grain elongations alignments of segments of the grain boundary enveloping surfaces and by trails of grains with similar c axis orientations examples of this aspect of foliation development in mylonitic rocks are so widespread that we suggest the creation of a broad class of s c tectonites and a deviation from the general tradition of purely geometric analysis of foliation and time relationships kinematic indicators such as those discussed here allow the recognition of kilometre scale zones of intense non coaxial laminar flow in crustal rocks and unambiguous determination of the sense of shear

kinematics of rock flow and fabric development associated with shear deformation within the zagros transpression zone iran this paper presents quantitative data on the finite strain quartz crystal fabric geometry of flow and deformation temperatures in deformed quartzite samples to characterize the ductile deformation along the thrust sheets constituting the sanandaj sirjan metamorphic belt within the zagros mountains of iran the results of this study emphasize the heterogeneous nature of deformation in this belt showing a spatial variation in strain magnitude and in degree of non coaxiality a dominant top to the se sense of shear is indicated by the asymmetry of microstructures and quartz c axis fabrics quartz c axis opening angles suggest deformation temperatures range between 435 50 c and 510 50 c which yield greenschist to amphibolite facies conditions during the ductile deformation mean kinematic vorticity number w m measured in the quartzite samples ranges between 0 6 and 0 9 with an average of 0 76 which indicates that extrusion of the metamorphic rocks of the region was facilitated by a significant component of pure shear strain traced towards the basal thrust of the zagros thrust system from northeast to southwest the quartz grain fabrics change from asymmetric cross girdle fabrics in the internal part of the deformation zone to an asymmetric single girdle fabric at distances close to the basal thrust this variation may depend on the structural depth and on the geometry of the ductile deformation zone the observed increase in strain and vorticity within the study area is comparable with patterns recorded within metamorphic rock extrusions within other orogens in the world

some seismological and geometric features of intraplate earthquakes to understand the nature and cause of intraplate earthquakes we carried out a systematic search for common features associated with them various geological geophysical and seismic data were analyzed and geometric and seismic parameters were compared for 29 intraplate events m 4 5 occurring worldwide the results suggest that intraplate earthquakes occur by the reactivation of pre existing zones of weakness in a compressional stress regime which is generally oriented parallel to the absolute direction of plate motion two styles of faulting were observed for type a earthquakes observed in the eastern united states eastern china western europe and west africa deformation occurs by strike slip motion on steeply dipping faults type b events are usually associated with thrust or normal faulting and were observed in eastern canada fennoscandia australia and peninsular india focal depths did not explain the differences between type a and type b earthquakes rather the differences are due to the perturbation of a regional stress field by a local stress field the regional stress field for type a events is primarily due to ridge push forces the method of stress perturbation varied from region to region the earthquakes in the type b category were further divided into three subcategories type b1 occurring in eastern canada and fennoscandia type b2 occurring in australia peninsular india and central brazil and type b3 occurring in the gulf coast of the u s the inferred causes of the perturbing stresses are deglaciation intracontinental resistive forces resulting from the collision of plates and the deposition of a large thickness of sediments respectively type a events were found to be associated with intersecting faults and generally supported the intersection model of talwani 1988 and had analogs in plate boundary events

a new estimate of the conditions for transition from basal a to prism c slip in naturally deformed quartz abstract quartz c axis fabrics of naturally deformed quartz in metacherts from the ryoke metamorphic belt in the yanai district southwestern japan suggest that the prism c prism a and basal a slip systems were activated during the plastic deformation under high temperature metamorphic conditions with increasing temperature quartz c axis fabric patterns change from girdle type through x maximum with a faint crossed girdle to x maximum the dominant orientation of subgrain boundaries in the quartz also changes from prism to basal with increasing temperature closely correlated with the change in quartz c axis fabric the fabric transition is also accompanied by an abrupt increase of recrystallized quartz grain size moreover observations with transmission electron microscopy tem clearly identify the dominant activation of c slip through the presence of basal subgrain boundaries and free dislocations with the 0001 burgers vector in the quartz from the metachert samples exhibiting x maximum c axis fabric based on these observations it is concluded that the mechanism switch from basal a to prism c slip systems occurred with increasing temperature in the metacherts the transition temperature is petrologically estimated to be ca 550 600 c at the natural strain rate

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

late cenozoic and modern stress fields in the western fars iran implications for the tectonic and kinematic evolution of central zagros 1 the zagros iran developed during mio pliocene times in response to arabia eurasia convergence the western fars highlights a major bend of the deformation front and displays a remarkable set of nearly n s right lateral strike slip faults the kazerun borazjan karebass sabz pushan sarvestan faults oblique at high angle to the belt the region likely plays a major kinematic role by accommodating the change in shortening modes from partitioned in the western central zagros to nonpartitioned in the eastern zagros the inversion of focal mechanisms from small and moderate earthquakes shows a consistent n020 030 compression with a low ratio between differential stresses this regime accounts for the combination of strike slip and thrust type mechanisms through likely 2 3 permutations fault slip analysis reveals two successive late cenozoic regional compressional trends ne sw then n020 the latter is in good agreement with the present day stress the significance of the ne sw compression is discussed alternatively in terms of stress deviations or block rotations in relation to the strike slip fault system fieldwork and satellite imagery suggest that these faults behave first as transfer faults during folding of the cover and later as strike slip faults in agreement with the succession of stress regimes and the evolution of the dominant deformation style from thin skinned to thick skinned the first order stability of the collision related state of stress since 5 ma supports that the arabia eurasia convergence did not give rise to partitioning in the western fars but rather was and is still accommodated by distributed deformation involving both shortening and strike slip motion throughout the cover and the basement

kinematic analysis of rock flow and deformation temperature of the sirjan thrust sheet zagros orogen iran microstructural finite strain and vorticity analyses of quartz rich mylonites were used in order to investigate kinematics of rock flow and deformation temperature in the sirjan thrust sheet exposed in a structural window within the sanandaj sirjan high pressure low temperature hp lt metamorphic belt that forms part of the hinterland of the zagros orogenic belt of iran a dominant top to the sw sense of shear in the study area is indicated by several shear sense indicators such as asymmetric boudins rotated porphyroclasts mica fish and s c fabrics quantitative analyses reveal approximately plane strain deformation conditions with r xz values ranging from 2 5 to 4 3 and increasing towards the sirjan thrust opening angles of quartz c axis fabrics and recrystallization regimes suggest deformation temperatures vary from 430 to 625 50 c in the hanging wall rocks oblique grain shape and quartz c axis fabrics were used to estimate the degree of non coaxiality during deformation the obtained vorticity profile indicates a down section increase in kinematic vorticity number w m from 0 6 to 0 89 this range of vorticity numbers confirms contributions of both simple 41 68 and pure shear 32 59 deformation components the structural characteristics of the study area ultimately were controlled by oblique motion of the afro arabian plate relative to the iranian plate

characterizing a middle to upper crustal shear zone microstructures quartz c axis fabrics deformation temperatures and flow vorticity analysis of the northern ailao shan red river shear zone china abstract structural and microstructural characteristics deformation temperatures and flow vorticities of the northern ailao shan als high grade metamorphic belt provide significant information regarding the nature and tectonic evolution of the ailao shan red river asrr shear zone mineral deformation mechanisms quartz lattice preferred orientation lpo patterns and the opening angles of quartz c axis fabrics of samples from the gasa section indicate that the northern als high grade metamorphic belt has experienced progressive shear deformation the early stage shearing is characterized by a gradual decrease of deformation temperatures from 650 c at the northeastern unit to ca 300 c at the southwestern unit that results in the formation of migmatites mylonitic gneisses thin bedded mylonites mylonitic schists and phyllonites from the ne to sw across the strike of the shear zone the late stage low temperature 300 400 c shearing is superimposed on the early deformation throughout the belt with the formation of discrete small scale shear zones especially in the thin banded mylonitic rocks along both margins the kinematic vorticity values estimated by rotated rigid porphyroclast method and oblique grain shaped quartz c axis fabric method imply that the general shear dominated flow 0 49 0 77 progressively changed to a simple shear dominated flow 0 77 1 toward the late stage of ductile deformation the two stages of shearing are consistent with early shortening dominated and late extrusion controlled regional tectonic processes the transition between them occurred at ca 27 ma in the als high grade metamorphic belt along the asrr shear zone the large amount of strike slip displacement along the asrr shear zone is predominantly attributed to accelerated flow along the shear zone during the late extrusion controlled tectonic process

dating slate belts using 40 ar 39 ar geochronology and zircon ages from crosscutting plutons a case study from east central maine usa abstract we report the ages of cleavage development in a normally intractable lower greenschist facies slate belt the central maine aroostook matapedia belt in east central maine we have attacked this problem by identifying the minimum ages of muscovite in a regional acadian cleavage s 1 and in a local ductile fault zone cleavage s 2 using 40 ar 39 ar geochronology and the ages of crosscutting plutons our success stems from the regional low grade metamorphism of the rocks in which each crystallization event preserves a 40 ar 39 ar crystallization age and not a cooling age evidence for recrystallization via a pressure solution mechanism comes from truncations of detrital authigenic and in some rocks s 1 muscovite and chlorite grains by new cleavage forming muscovite and chlorite grains low blank furnace age spectra from meta arkosic and slaty rocks climb from moderate temperature devonian age steps dominated by cleavage forming muscovite to ordovician age steps dominated by a detrital muscovite component s 1 and s 2 cleaved rocks were hornfelsed by granitoids of 407 and 377 ma respectively the combination of these minimum ages with the maximum metamorphic crystallization ages establishes narrow constraints on the timing of these two cleavage forming events 410 ma s 1 and 380 ma s 2 these two events coincide in time with a change in the plate convergence kinematics from the arrival of the avalon terrane acadian orogeny to a right lateral transpression arrival of the meguma terrane in the neoacadian orogeny

forceful emplacement of the eureka valley joshua flat beer creek composite pluton into a structural basin in eastern california internal structure and wall rock deformation abstract anisotropy of magnetic susceptibility parameters have been analyzed at 311 locations in the eureka valley joshua flat beer creek ejb pluton of eastern california the large amount of data has allowed for the ams parameters to be contoured using techniques that both reveal map scale trends and emphasize small scale differences the contour maps suggest that magnetic susceptibility is dominantly controlled by composition of the magma but may also be affected by emplacement related strain as the magma chamber inflated and forced the wall rocks outward pluton construction involved two major pulses of different composition magmas that were emplaced sequentially but with overlapping periods of crystallization the magmas initially intruded as sill like bodies into a structural basin the magnetic foliation of the pluton cuts across internal magmatic contacts on the map scale and is parallel to local contacts between the pluton and surrounding metasedimentary wall rocks the magnetic fabric is similar in orientation and symmetry to intense flattening strains recorded in the aureole rocks the metasedimentary wall rocks have been shortened between 60 and 70 and this strain magnitude is approximately equal on the west south and east margins of the pluton strain in the wall rocks is dominantly flattening and concentrated into a narrow 1 km wide inner aureole mapping of bedding cleavage intersection lineations south of the pluton indicates that the magma made room for itself by translating the wall rocks outward and rotating the already inward dipping wall rocks of the structural basin to sub vertical stretching of the inner aureole around an expanding magma chamber was responsible for the intense shortening limited data on the marble canyon pluton to the south of the ejb pluton indicates a very similar emplacement process

the deformation matrix for simultaneous simple shearing pure shearing and volume change and its application to transpression transtension tectonics simultaneous simple shearing and pure shearing with or without additional volume change can be combined into a single upper triangular deformation matrix the off diagonal term is named the effective shear strain and is a simple function of the pure shearing and simple shearing components a three dimensional deformation matrix for the simultaneous combination of coaxial deformation with or without additional volume change and up to three simple shearing systems with mutually orthogonal shear planes is also presented by using this matrix one can easily extract the various properties of incremental as well as finite strain and the progressive as well as finite rotation of passive markers during deformation the case of transpression transtension is revised using the unified deformation matrix the orientation of the major axis of the strain ellipsoid 1 is always horizontal if the deformation is transtensional switches from horizontal to vertical during transpressional wrenching 1 wk 0 81 for constant vorticity deformations and is always vertical for highly transpressional deformations wk 0 81 for transpression material lines initially rotate towards the horizontal shearing direction but generally turn to rotate towards the vertical axis after a certain strain for transtension all material lines rotate towards a direction in the horizontal plane which is oblique to the shearing direction

tectonic implication of quantitative micro fabric analyses of quartz c axis development within the tutak gneiss dome zagros hinterland fold and thrust belt quartz c axis fabrics finite strain and kinematic vorticity number analyses were used to investigate deformation characteristics of the tutak gneiss dome located in the eastern edge of the basement involved zagros hinterland fold and thrust belt the opening angle of the quartz c axis fabric patterns was used to estimate deformation temperatures which suggest greenschist to amphibolite facies conditions 430 50 c to 660 50 c the kinematic vorticity number varies from 0 6 to 0 95 mean kinematic vorticity number of 0 81 which indicates that the metamorphic rocks of the tutak gneiss dome experienced a sub simple shear regime by contribution of both pure shear 39 and simple shear 61 deformation components nw se striking foliations have commonly sw and ne dips accompanied by mostly nw se plunging and subordinate ne sw plunging stretching lineations these indicate more extension along the nw se trend to produce a prolate elliptical wedge shape in map view structural and vorticity analysis suggests that the tutak gneiss dome has experienced earlier dome formation followed by thrust stacking rather than the two deformations occurring synchronously and a protracted progressive deformation through a decreasing temperature regime

exhumation of the west central alborz mountains iran caspian subsidence and collision related tectonics crystallization and thermal histories of two plutons in the west central alborz also elburz elburs mountains northern iran are combined with crosscutting relations and kinematic data from nearby faults to determine the cenozoic tectonic evolution of this segment of the youthful euro arabian collision zone u pb 40 ar 39 ar and u th he data were obtained from zircon biotite k feldspar and apatite the akapol pluton intruded at 56 2 ma cooled to 150 c by ca 40 ma and stayed near that temperature until at least 25 ma the nearby alam kuh granite intruded at 6 8 0 1 ma and cooled rapidly to 70 c by ca 6 ma these results imply tectonic stability of the west central alborz from late eocene to late miocene time consistent with miocene sedimentation patterns in central iran elevation correlated u th he ages from the akapol suite indicate 0 7 km m y exhumation between 6 and 4 ma and imply 10 km of alborz uplift that was nearly synchronous with rapid south caspian subsidence suggesting a causal relation uplift south caspian subsidence and subsequent folding reversal of alborz strike slip from dextral to sinistral and eastward extrusion of central iran coarse zagros molasse deposition dead sea transform reorganization red sea oceanic spreading and north and east anatolian fault slip all apparently began ca 5 2 ma suggesting a widespread tectonic event that we infer was a response to buoyant arabian lithosphere choking the neo tethyan subduction zone

quartz c axis fabric development associated with shear deformation along an extensional detachment shear zone chapedony metamorphic core complex central east iranian microcontinent abstract lattice preferred orientations lpos of quartz were used to establish differences in deformation geometry finite strain and temperature across an extensional detachment shear zone within the chapedony metamorphic core complex in the central east iranian microcontinent along the northern flank of gondwana quartz c axis data show a continuous evolution across the core complex from asymmetric type i crossed girdles at the southwest margin to broken asymmetric type i crossed girdle and single girdle with a large concentration of axes plotted in the center of the stereoplot at the central parts of the core complex and small circle girdle pattern at the northeast margin these variations in quartz c axis patterns imply change in strain geometry during deformation from plane strain to general flattening and pure flattening integrating analyses of quartz c axis opening angles quartz c axis patterns and recrystalization regimes of quartz and feldspar suggests deformation temperatures range between less than 400 c and 650 c which yield greenschist to amphibolite facies conditions mean kinematic vorticity number wm measured in the mylonite samples ranges between 0 67 and 0 71 which indicates that exhumation of the metamorphic rocks of the cmcc was facilitated by a significant component of pure shear strain within a general shear regime

vorticity analysis in a metachert from the sanbagawa belt sw japan abstract common tectonic features of deformed metachert include both sets of extended and shortened veins and quartz c axis preferred orientation patterns in such rocks information is also commonly available on the orientation and magnitude of the finite strain these features can be used to derive two independent estimates of the degree of non coaxiality during deformation in an example from the sanbagawa belt sw japan the two methods give consistent results and show that deformation was intermediate between simple and pure shear such types of progressive deformation distributed over a broad region could cause substantial subvertical thinning and be a significant factor in the exhumation of high p t rocks in the region

mesozoic to eocene ductile deformation of western central iran from cimmerian collisional orogeny to eocene exhumation abstract to advance our understanding of the mesozoic to eocene tectonics and kinematics of basement units exposed in the south western central iran plateau this paper presents new structural and thermochronological data from the chapedony metamorphic core complex and hangingwall units particularly from the posht e badam complex the overall paleogene structural characteristics of the area are related to an oblique convergent zone the saghand area represents part of a deformation zone between the arabian and eurasian plates and can be interpreted to result from the central iran intracontinental deformation acting as a weak zone during mesozoic to paleogene times field and microstructural evidence reveal that the metamorphic and igneous rocks suffered a ductile shear deformation including mylonitization at the hangingwall boundary of the eocene chapedony metamorphic core complex comparison of deformation features in the mylonites and other structural features within the footwall unit leads to the conclusion that the mylonites were formed in a subhorizontal shear zone by ne sw stretching during middle to late eocene extensional tectonics the chapedony metamorphic core complex is characterized by amphibolite facies metamorphism and development of s and s l tectonic fabrics the posht e badam complex was deformed by two stages during cimmerian tectonic processes forming the paleo tethyan suture

dominant simple shear deformation during peak metamorphism for the lower portion of the greater himalayan sequence in west nepal new implications for hybrid channel flow type mechanisms in the dolpo region abstract i conducted new vorticity and deformation temperatures studies to test competing models of the exhumation of the mid crustal rocks exposed in the dolpo region west nepal my results indicate that the main central thrust is located 5 km structurally below the previous mapped locations deformation temperature increasing up structural section from 450 c to 650 c and overlap with peak metamorphic temperature indicating that penetrative shearing was responsible for the exhumation of the ghs occurred at close to peak metamorphic conditions i interpreted the telescoping and the inversion of the paleo isotherms at the base of the ghs as produced mainly by a sub simple shearing wm 0 88 1 pervasively distributed through the lower portion of the ghs my results are consistent with hybrid channel flow type models where the boundary between lower and upper portions of the ghs broadly corresponding to the tectonometamorphic discontinuity recently documented in west nepal represents the limit between buried material affected by dominant simple shearing and exhumed material affected by a general flow dominates by pure shearing this interpretation is consistent with the recent models suggesting the simultaneous operation of channel flow and critical wedge type processes at different structural depth

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

thermal structure and tectonic evolution of the scandian orogenic wedge scottish caledonides integrating geothermometry deformation temperatures and conceptual kinematic thermal models in the caledonides of northwest scotland two independent geothermometers fe mg exchange and quartz c axis fabric opening angle are used to characterize the thermal structure of the lower part of the scandian 435 420 ma orogenic wedge within the moine ben hope and naver sgurr beag thrust sheets traced from west foreland to east hinterland fe mg exchange thermometry yields peak or near peak temperatures ranging from 484 50 c to 524 50 c in the immediate hangingwall of the moine thrust to 601 50 c in the immediate hangingwall of the ben hope thrust to 630 50 c in the naver thrust sheet preserved metamorphic facies and textural relationships are consistent with thermometric estimates deformation temperatures calculated from quartz c axis fabric opening angles across two similar orogen perpendicular transects also yield systematic increases glen golly ben klibreck 520 630 c ullapool contin 465 632 c traced towards the naver and sgurr beag thrusts in addition deformation temperatures show a pronounced increase along the leading edge of the moine thrust sheet moving south towards the assynt window which is interpreted to reflect deeper exhumation of the thrust plane above the assynt footwall imbricate stack because temperatures calculated from metamorphic assemblages are within error of the quartz fabric derived deformation temperatures that are of demonstrably scandian age the metamorphic sequence between the moine and naver sgurr beag thrusts is interpreted to have developed during the scandian orogeny integration of our results with previous 2d thermal mechanical studies allows development of new conceptual thermal kinematic models of scandian orogenesis that may be broadly applicable to other collisional systems furthermore it highlights the critical nature of coupling between orogen kinematic and thermal evolution

a continuum mechanics model for normal faulting using a strain rate softening rheology implications for thermal and rheological controls on continental and oceanic rifting abstract we use a strain rate dependent visco plastic rheology in a finite element model to investigate the effects of crustal rheology and thermal structure on the development of normal faults in 2 d extending lithosphere strain rate softening in the brittle regime is used to simulate the rate dependence of frictional strength observed in laboratory studies results of numerical experiments show that efficient strain rate softening can result in localized zones of high strain rate which develop in response to the rheology and boundary conditions and are not imposed a priori we argue that these zones of localized shearing are analogous to faults and use the calculated deformation field to predict the preferred location of fault formation for a range of thermal and rheologic conditions when no regional temperature gradient is imposed deformation is predicted to be distributed between several sets of conjugate normal faults however in the presence of a horizontally varying temperature field faulting is calculated to focus where the lithosphere is thinnest forming rift like topography model results predict that when crustal thickness is sufficiently small that no ductile layer is present in the lower crust deformation is mantle dominated and rift half width is controlled primarily by the vertical geothermal gradient in contrast when crustal thickness is large enough that the stress accumulation in the upper crust becomes much greater than the stress accumulation in the upper mantle deformation becomes crust dominated and the calculated rift half width is a function of both crustal rheology and the vertical geothermal gradient this implies that deformation in the brittle upper crust does not behave independently of a strong upper mantle even in situations where ductile flow occurs in the lower crust

strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab everest massif tibet this paper presents quantitative data on strain deformation temperatures and vorticity of flow at the top of the greater himalayan slab the data were collected from the tibetan side of the everest massif where two low angle normal faults bound the upper surface of the greater himalayan slab the earlier and structurally lower lhotse detachment and the later and structurally higher qomolangma detachment greenschist to sillimanite grade quartz rich metasedimentary rocks exposed in the rongbuk to north col region of the everest massif are characterized by cross girdle quartz c axis fabrics indicating approximate plane strain conditions fabric opening angles progressively increase with depth beneath the overlying lhotse detachment and indicate progressively rising deformation temperatures of 525 625 50 c at depths of 300 600 m beneath the detachment deformation temperatures of c 450 c are indicated by fabric opening angles in epidote amphibolite facies mylonites located closer to the overlying detachment a top down to the north normal shear sense is indicated by the asymmetry of microstructures and c axis fabrics but the degree of asymmetry is low at distances greater than 400 m beneath the detachment and sillimanite grains are drawn into adjacent conjugate shear bands but still appear pristine indicating that deformation occurred at close to peak metamorphic temperatures these quenched fabrics and microstructures indicate rapid exhumation in agreement with previous isotopic dating studies mean kinematic vorticity numbers w m were independently calculated by three analytical methods calculated w m values range between 0 67 and 0 98 and indicate that although a simple shear component is generally dominant particularly in greenschist facies mylonites located between the lhotse and overlying qomolangma detachments there is also a major component of pure shear in samples located at 400 600 m beneath the lhotse detachment pure and simple shear make equal contributions at w k 0 71 our integrated strain and vorticity data indicate a shortening of 10 30 perpendicular to the upper surface of the greater himalayan slab and confirm that the upper surface of the slab is a stretching fault with estimated down dip stretches of 10 40 assuming plane strain deformation measured parallel to the flow plane transport direction

quartz crystallographic and morphologic fabrics during folding transposition in mylonites abstract quartz grain shape fabrics gsf and c axis lattice preferred orientation lpo were investigated in folded quartz ribbons with variable fold geometry in low metamorphic grade granitic mylonites from northwestern argentina the folds which vary from open to isoclinal show an asymmetric short limb long limb geometry developed simultaneously with the quartz fabrics during progressive simple shear gsf shows a consistent obliquity relative to the bulk shear plane throughout the folded ribbons gsf inclination varies between 25 and 45 oblique to the shear plane indicating that relatively small finite strain increments 1 2 are attained before the gsf regeneration in contrast the c axis preferred orientation varies throughout the folded ribbons unfolded ribbons and long limbs of folds show a typical c axis maximum near the shear plane pole while short limbs of tight and isoclinal folds show a c axis maximum nearly orthogonal to that of long limbs this pattern of domainal lpo is maintained in thickened ribbons derived from folding and transposition this indicates that the gsf regeneration is comparatively much faster than a cycle of folding transposition conversely the lpo regeneration is much slower we conclude that folding transposition is a mechanism for development of domainal quartz lpo in kinematic frameworks with dominant simple shear

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

telescoping of isotherms beneath the south tibetan detachment system mount everest massif abstract petrologic and microstructural crystal fabric data indicate that isotherms recorded in greater himalayan series ghs schists and gneisses in the footwall to the south tibetan detachment system stds have undergone extreme telescoping during penetrative flow associated with southward extrusion of the ghs in the rongbuk valley to the north of mount everest we have made three vertical sampling traverses from the stds down into the ghs and estimated temperatures associated with penetrative deformation using the opening angles of quartz c axis fabrics measured on dynamically recrystallized grains from north to south the deformation temperature data indicate apparent thermal field gradients of 369 385 and 420 c per km for our three traverses traced over a maximum vertical sampling distance of 0 5 km adopting a differential flow path model simple geometric analysis using sections drawn parallel to the local transport direction indicates that detachment parallel transport magnitudes of 25 170 km are needed to explain the extreme telescoping of isotherms in the immediate footwall to the stds depending on assumed original geothermal gradient dip of detachment etc these particle transport estimates are similar to those previously calculated from barometry data of ghs rocks in the everest region and are compatible with channel flow models for extrusion and exhumation of the ghs

vorticity analysis in the zagros orogen shiraz area iran quantitative vorticity analyses in orogenic belts are essential for studying the kinematics of deformation and can be performed using a range of methods the combination of microstructural analysis for vorticity with other methods creates a more rigorous analysis in order to determine the degree of non coaxiality and spatial pattern of vorticity during deformation in the zagros orogenic belt a study area containing the boundary of the zagros folded belt and the zagros fold and thrust belt is selected the study area is situated in the shiraz region of e zagros in iran the kinematic vorticity analysis is carried out using 4 methods based on 1 the degree of asymmetry of the calcite c axis fabric 2 the assumption that the orientation of the long axes of calcite within an oblique stylolite foliation delineates the direction of the instantaneous stretching axis 3 the assumption that the tension gash tips determine the direction of the instantaneous stretching axis and 4 stylolite teeth determine the direction of the instantaneous stretching axis c axis data from calcite give a kinematic vorticity number between 0 68 and 0 83 and the orientation of the long axes of calcite grains yields a range between 0 5 and 0 84 stylolites provide a kinematic vorticity number between 0 5 and 0 79 and tension gashes provide a kinematic vorticity number between 0 56 and 0 81 this range of vorticity numbers confirms the contributions of both simple 33 59 and pure shear 41 67 twining of calcite also reveals that the last stage of deformation occurred at a temperature of 170 200 c spatial analysis reveals an increase in the simple shear component from the sw of the zagros folded belt to the ne of the zagros fold and thrust belt

structures microfabrics and textures of the cordilleran type rechnitz metamorphic core complex eastern alps rechnitz window group represents a cordilleran style metamorphic core complex which is almost entirely located within nearly contemporaneous neogene sediments at the transition zone between the eastern alps and the neogene pannonian basin two tectonic units are distinguished within the rechnitz metamorphic core complex rmcc 1 a lower unit mainly composed of mesozoic metasediments and 2 an upper unit mainly composed of ophiolite remnants both units are metamorphosed within greenschist facies conditions during earliest miocene followed by exhumation and cooling the internal structure of the rmcc is characterized by the following succession of structure forming events 1 blueschist relics of paleocene eocene age formed as a result of subduction d1 2 ductile nappe stacking d2 of an ophiolite nappe over a distant passive margin succession ca e w to wnw ese oriented stretching lineation 3 greenschist facies grade metamorphism annealing dominant in the lower unit and 4 ductile low angle normal faulting d3 with mainly ne sw oriented stretching lineation and 5 ca e to ne vergent folding d4 the microfabrics are related to mostly ductile nappe stacking to ductile low angle normal faulting paleopiezometry in conjunction with p t estimates yield high strain rates of 10 11 to 10 13 s 1 depending on the temperature 400 350 c and choice of piezometer and flow law calibration progressive microstructures and texture analysis indicate an overprint of the high temperature fabrics d2 by the low temperature deformation d3 phengitic mica from the paleocene eocene high pressure metamorphism remained stable during d2 ductile deformation as well as preserved within late stages of final sub greenschist facies shearing chlorite geothermometry yields two temperature groups 376 328 c and 306 132 c chlorite is seemingly accessible to late stage resetting the rmcc underwent an earlier large scale coaxial deformation accommodated by a late non coaxial shear with ductile low angle normal faulting resulting in subvertical thinning in the extensional deformation regime the rmcc was rapidly exhumed during ca 23 18 ma

deformation path partitioning within the transpressional white mountain shear zone california and nevada most numerical simulations of transpression zones predict a change in finite stretching direction from subhorizontal to subvertical for simple shear dominated zones we provide a detailed description of a dextral transpression zone the white mountain shear zone wmsz with a range of lineation orientations and compare these natural data to numerical models the wmsz is characterized by steeply dipping foliations with dominant shallowly plunging lineations and coeval subordinate domains of steeply plunging lineations within shallowly lineated domains foliation geometry shear sense indicators and quartz c axis fabrics indicate a large component of simple shear while microstructural and quartz c axis fabric data from steeply lineated domains indicate a large component of pure shear geometric relationships between foliations and lineations and quartz c axis fabrics demonstrate that lineation orientation has remained constant during much of the deformation history comparison of numerical models with the data collected from wmsz shows that the shear zone geometry and the observed strain path partitioning do not match any of these models we propose a conceptual kinematic model for the wmsz involving stable segregated coeval kinematic domains of simple shear dominated fabrics and pure shear dominated fabrics that accommodate the transcurrent and contractional components of deformation respectively

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

dynamic recrystallization of quartz correlation between natural and experimental conditions quartz veins in the eastern tonale mylonite zone italian alps were deformed in strike slip shear due to the synkinematic emplacement of the adamello pluton a temperature gradient between 280 c and 700 c was effected across this fault zone the resulting dynamic recrystallization microstructures are characteristic of bulging recrystallization subgrain rotation recrystallization and grain boundary migration recrystallization the transitions in recrystallization mechanisms are marked by discrete changes of grain size dependence on temperature differential stresses are calculated from the recrystallized grain size data using paleopiezometric relationships deformation temperatures are obtained from metamorphic reactions in the deformed host rock flow stresses and deformation temperatures are used to determine the strain rate of the tonale mylonites through integration with several published flow laws yielding an average rate of approximately 10 14s 1 to 10 12s 1 the deformation conditions of the natural fault rocks are compared and correlated with three experimental dislocation creep regimes of quartz of hirth tullis linking the microstructures of the naturally and experimentally deformed quartz rocks a recrystallization mechanism map is presented this map permits the derivation of temperature and strain rate for mylonitic fault rocks once the recrystallization mechanism is known

the use of mohr circles to describe non coaxial progressive deformation abstract mohr circles are useful in strain analysis but are also potentially powerful tools to translate geological fabric data into tensors describing the deformation and to reconstruct flow parameters this paper shows how mohr circles can be used to visualize the effects of variable flow parameters such as stretching rate volume change rate and vorticity number on parameters of cumulative deformation as described by the position gradient tensor a mean vorticity number is introduced as a deformation parameter besides finite cumulative strain and volume change

structures and fabrics in a crustal scale shear zone betic cordillera se spain abstract a broad zone of dominantly ductile high strain deformation lies beneath the aguilon nappe in the sierra alhamilla southern spain it forms part of a crustal scale movement zone traceable through much of the betic cordillera which separates the higher betic nappes from the underlying nevado filabride complex the zone is characterized in outcrop by a distinctive platy foliation and a strong nne trending stretching lineation microstructural characteristics include quartz ribbons mica fish augen of feldspar and other minerals in a matrix of dynamically recrystallized quartz and extensional crenulation cleavages narrow bands of ultramylonite and cataclasite occur within and on the margins of the movement zone deformation occurred under lower greenschist facies conditions and was accompanied by retrogression of earlier higher grade mineral assemblages structures in the movement zone developed in a temporal sequence beginning with isoclinal folding and transposition of older foliations this was followed by the formation of extensional crenulation cleavages and the progressive localization of strain into the ultramylonite bands mylonitic foliation in these bands is deformed by syn mylonite folds restricted to the bands all these structures were then deformed by s to se vergent small scale folds restricted to the movement zone as a whole cataclasis associated with alteration is localized along the ultramylonite bands and indicates a transition to late stage brittle deformation the lower boundary of the movement zone is gradational strain decreases recrystallized grainsize and the degree of recrystallization of quartz increases and pressure solution becomes the dominant deformation mechanism in mica schist asymmetric quartz fabrics in the movement zone indicate a nne sense of shear but variations in the degree of asymmetry suggest that flow was partitioned with the ultramylonite bands taking up much of the shear strain and the intervening rocks deforming more slowly and with a lower degree of non coaxiality diffuse fabrics in the fine grained ultramylonite bands may indicate a switch to a grainsize sensitive deformation mechanism and an overall downward increase in the opening angle of crossed girdle fabrics may reflect increased water activity at depth

role of the kazerun fault zone in the formation and deformation of the zagros fold thrust belt iran 1 the kazerun fault is a n s trending fault zone which obliquely truncates the nw se trending zagros fold thrust belt this active fault zone is an ancient structural lineament which has controlled the structure sedimentation and subsidence of the central part of the zagros since the early cambrian and has had an influence on the formation of the hydrocarbon system of the belt the kazerun fault limited the distribution of the cambrian hormuz salt the major decollement horizon that separates the precambrian basement from the thick sedimentary cover to the west its later reactivation with other n s trending fault zones e g the izeh fault zone during the cretaceous resulted in major sedimentary thickness and facies variations along the belt this study presents a new interpretation for the evolution of the kazerun fault zone based on field evidence and a review of various published and unpublished data it is argued that at the surface the fault zone is delineated by four north south trending segments and that marked differences occur in the distribution of deformation on either side of the fault segments in the late tertiary during this time these segments acted as transfer faults lateral ramps linking different segments of the zagros deformation fronts

evolution of the hongzhen metamorphic core complex evidence for early cretaceous extension in the eastern yangtze craton eastern china we conducted structural and geochronological studies on the hongzhen metamorphic core complex in the eastern yangtze craton the hanging wall of the hongzhen metamorphic core complex consists of neoproterozoic to permian unmetamorphosed strata which were folded during nw se shortening in the middle triassic and cretaceous terrestrial basins the exposed paleoproterozoic dongling complex in the footwall is widely overprinted by a detachment ductile shear zone which has consistent sw plunging mineral elongation lineations and top to the sw shear indicators analysis of the mesostructures microstructures and quartz c axis fabrics indicates that they formed within a low angled sw dipping extensional shear zone at midcrustal levels four muscovite grains separated from mylonites within the shear zone yielded 40 ar 39 ar plateau ages ranging from 128 5 1 0 ma to 126 1 1 1 ma they are interpreted as cooling ages of the shear zone associated with the hongzhen metamorphic core complex we propose that the hongzhen metamorphic core complex was initiated as a midcrustal low angle extensional shear zone with top to the sw shear sense at ca 145 ma and the shear zone was then warped and uplifted by the emplacement of the hongzhen granite at 122 ma brittle normal faulting and basin rifting in the hanging wall also developed during the formation of the hongzhen metamorphic core complex but these processes continued until the late cretaceous this study of the hongzhen metamorphic core complex demonstrates that the eastern yangtze craton was also involved in the early cretaceous extension widely occurring in the eastern china continent a ne sw extensional direction during the early cretaceous is indicated by the hongzhen metamorphic core complex