influence of deformation conditions on the development of heterogeneous recrystallization microstructures in experimentally deformed carrara marble recrystallized grains are potentially useful as indicators of palaeostress in naturally deformed rocks providing that well calibrated relationships palaeopiezometers exist between the recrystallized grain size and stress rocks can exhibit microstructures that are heterogeneous that is containing recrystallized as well as deformed grains and showing subgrains within grains that differ in size and character from the grain core to the mantle previous studies on palaeopiezometers only rarely took into account such heterogeneous microstructure we used electron backscattered diffraction ebsd to accurately quantify the heterogeneous microstructures in experimentally deformed carrara marble flow stress 15 85 mpa temperature 700 990 8c and natural strain 0 15 0 90 the sizes of bulges recrystallized grains and deformed grains have been measured we found that the overall character of the microstructures varies as a function of deformation conditions in heterogeneous samples showing core mantle microstructures the sizes of the bulges and recrystallized grains are independent of strain and show an inverse dependency on stress the recrystallized grains have been found to nucleate at grain boundary bulges our study illustrates that very different microstructures may develop in relation to the complexity of the recrystallization mechanisms we therefore suggest that piezometers should be calibrated and applied for a single type of overall microstructure

heterogeneous brittle ductile deformation at shallow crustal levels under high thermal conditions the case of a synkinematic contact aureole in the inner northern apennines southeastern elba island italy abstract we present an example of interaction between magmatism and tectonics at shallow crustal levels in the late miocene the metamorphic units of the eastern elba island northern apennines were intruded at very shallow crustal levels by a large pluton 60 km 2 with the development of an hectometre sized contact aureole defined by growth of low pressure high temperature mineral assemblages p max max 650 c structural data show that the contact aureole is associated with a km sized antiform of the foliation and by several metre to decametre thick high strain domains consisting of strongly foliated rocks containing synkinematic ht lp mineral assemblages and ductile shear zones of variable thickness these shear zones are characterized by a mylonitic foliation variably overprinted by cataclasis quartz microfabrics indicate that the dynamic crystallization processes progressively changed from grain boundary migration associated with the thermal peak of contact metamorphism to subgrain rotation and bulging recrystallization the latter mostly associated with the cataclastic overprint these transitions of recrystallization mechanisms in quartz are related to a progressive decrease of temperature during deformation deformation accompanied the development and cooling of the contact aureole which recorded the switch from high temperature ductile to low temperature brittle conditions the geometry of the studied deformation structures is consistent with the constraints of the regional tectonic evolution and its local interaction with the localized and transient thermal anomaly related to the coeval emplacement of igneous rocks

dynamic implications of discontinuous recrystallization in cold basal ice taylor glacier antarctica crystallographic investigations have been conducted of cold 17 c debris bearing ice from the base of an antarctic outlet glacier taylor glacier the 4 m thick sequence studied has been retrieved from a 20 m long tunnel dug from the glacier snout and has been analyzed with an automatic ice fabric analyzer aifa the top and bottom of the sequence consists of clean meteoric ice englacial facies whereas alternating debris rich and clean bubbly ice layers are found in the middle part stratified facies ice from the englacial facies displays a polygonal texture and a strong c axis clustering toward the vertical denoting recrystallization through subgrain rotation sgr in contrast clean ice from the stratified facies shows sgr fabrics which are delimited at the contact with debris rich layers by large interlocking grains organized in ribbons these two distinct textures within the stratified facies are associated with looser c axis patterns at the scale of single thin sections which is interpreted as resulting from migration recrystallization mr the change from sgr to mr trends marks a clear increase in grain boundary and nucleation kinetics hence the term discontinuous recrystallization and may be associated with strain localization at rheological interfaces during basal ice genesis analogies with bottom ice from deep polar ice sheets where temperature is commonly higher than at the studied site are highlighted two recrystallization scenarios are proposed accounting for the development of both types of fabrics it is shown that by controlling the repartition of stress and strain energy within basal ice the rheology of debris bearing ice layers plays a decisive role in recrystallization dynamics at structural interfaces we also demonstrate how the same recrystallization regimes may occur in cold glaciers and temperate ice sheets provided that strain accumulation has been high enough in the former this challenges the common belief that migration fabrics observed in bottom ice from deep ice sheets are exclusive to warm stagnant annealed ice copyright 2008 by the american geophysical union

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

deformation of two phase systems with contrasting rheologies abstract rheological model experiments are used as analogues for foliation development in quartz mica rocks in a regime of pure shear in situ observations involving ice containing varying proportions and distributions of naphthalene and camphor illustrated two contrasting types of behaviour a matrix controlled versus a particle controlled deformation the matrix controlled deformation accommodates shortening predominantly by intracrystalline slip in the ice accompanied by some recrystallization while the more rigid naphthalene plates undergo rotation and mechanical alignment where shortening is normal to an initial platelet preferred orientation the foliation is enhanced and the matrix material aggregates between the rigid plates whereas a conjugate foliation is produced during shortening parallel to an initial platelet preferred orientation during particle controlled deformation strain is localized in particle concentrates the matrix areas and particles isolated in the matrix show little deformation at shortenings 10 dissolution of selected particles is achieved through an artificial fluid transport mechanism to create voids further shortening does not create closure of the fluid filled holes where shape is supported by the rigid matrix

deformation inside a paleosubduction channel insights from microstructures and crystallographic preferred orientations of eclogites and metasediments from the tauern window austria the eclogite zone of the tauern window is an exhumed subduction channel comprising eclogites with different grades of retrogression in a matrix of high pressure metasediments the rocks were exposed to 600 c and 20 25 kbars and then retrogressed during their exhumation first under blueschist facies and later under amphibolite facies metamorphism to gain insights into the deformation within the subduction channel during subduction and exhumation both fresh and retrogressed eclogites as well as the surrounding metasediments were investigated with respect to their deformation microstructures and crystallographic preferred orientations cpos pristine and retrogressed eclogites show grain boundary migration and subgrain rotation recrystallization microstructures in omphacite a misorientation axes analysis reveals the activity of complementary deformation mechanisms including grain boundary sliding and dislocation creep the omphacite cpos of the eclogites correspond to dominant sl fabrics characteristic of plane strain deformation though there are local variations towards flattening or constriction within the paleosubduction channel the glaucophane cpos in retrogressed eclogites match those of omphacite suggesting that a constant strain geometry persisted during exhumation at blueschist facies conditions plastic deformation of the host high pressure metasediments outlasted that of the eclogites as indicated by white mica fabrics and quartz cpo the latter is consistently asymmetric pointing to the operation of non coaxial deformation the microstructures and cpo data indicate a continuous plastic deformation cycle with eclogite and blueschist facies metamorphism related to subduction and exhumation of the different rock units

two early holocene rock avalanches in the bernese alps rinderhorn switzerland abstract large rock avalanches constitute a critical process modulating the evolution of alpine landscapes however the relatively infrequent occurrence of these high magnitude events makes identifying underlying process controls challenging here we describe two rock avalanches in the rinderhorn area of the bernese alps switzerland providing new mapping of rock avalanche source areas and deposits refined volume estimates for each event runout modeling back analyses and absolute age constraint from cosmogenic 36 cl surface exposure dating results reveal that the daubensee rock avalanche released 4 million m 3 of limestone sliding from the western crest of the rinderhorn debris ran out across a lateglacial moraine before reaching the valley bottom and spreading leaving thin on average 7 m deposits across a broad area the runout resulted in a fahrboschung angle of 21 part of the deposit now lies beneath lake daubensee the klein rinderhorn rock avalanche released 37 million m 3 of limestone along a dip slope sliding plane with a maximum runout distance of 4 3 km and estimated fahrboschung angle of 14 deposits bulked to 47 million m 3 running up the opposing slope with distinct hummocky morphology in the proximal area and a distal longitudinal flow ridge these deposits were later modified and partly obscured by ice avalanches from the nearby altels peak cosmogenic 36 cl surface exposure dating revealed nearly coincident ages for both rock avalanches of 9 8 0 5 ka the large lag time between local deglaciation and failure suggests that the events were not directly triggered by deglaciation rather the concurrent exposure ages also coinciding with the nearby kander valley rock avalanche as well as paleoseismic records from nearby lakes strongly suggest seismic triggering

impact of communal irrigation on the 2018 palu earthquake triggered landslides anthropogenic changes to the environment can enhance earthquake triggered landslides yet their role in earthquake disasters is often overlooked co seismic landslides frequently involve liquefaction of granular materials a process that reduces shear strength and facilitates downslope motion even on gentle slopes irrigation systems can increase liquefaction susceptibility and compromise otherwise stable slopes here we investigate devastating landslides that affected palu indonesia during the 28 september 2018 earthquake of moment magnitude 7 5 we document fields and buildings translated over 1 km down slopes of 2 and show that landslides were limited to irrigated ground a liquefied detachment was rooted upslope in a conveyance canal that supplied water to the irrigation network a strong correlation between landslide displacement irrigation infrastructure and the highest slopes 1 5 suggests a causative mechanism that should provoke urgent assessment of gently sloping irrigated terrain elsewhere in sulawesi and in tectonically active areas worldwide landslides triggered during the palu 2018 earthquake correlate spatially with the presence of irrigation systems according to satellite analyses suggesting that liquefaction of alluvial fans played a role

deformation of chromite s e m investigations abstract the scannning electron microscope operated in the back scattered electron mode has been applied in a microstructural analysis of chromites samples from the oman vourinos greece and tiebaghi new caledonia ophiolites displaying a variety of mantle flow and emplacement structures have been examined and compared with undeformed chromite from the bushveld intrusion and deformed chromite from the high grade metamorphic fiskenaesset complex channelling contrast and electron channelling patterns provide information on grain boundaries subgrains inclusions and cracks as well as defects in the chromite lattice these microstructures suggest that dislocation mechanisms are active in chromite deforming under mantle conditions recovery is quick whereas nucleation is slow and accordingly recrystallization of chromite occurs by migration of grain boundaries driven either by strain energy or by interfacial energy increasing the grain size during deformation dislocation mechanisms however only provide a secondary mode of deformation compared to brittle fracturing and passive rotation of chromite grains and fragments in the weaker silicate matrix diffusion accommodated flow may also be significant

comments on the interpretation of deformation textures in rocks abstract in rocks that undergo ductile deformation preferred orientation develops as a result of intracrystalline slip and mechanical twinning the orientation distribution is a consequence of the microscopic mechanisms and of the strain path it can be used to get some insight into the deformation history however it is never unique the interpretation relies largely on polycrystal plasticity theory the concepts of stress equilibrium and strain compatibility which are two extreme assumptions made to model deformation are discussed new approaches such as the viscoplastic self consistent theory are a compromise and may be applicable to mineral systems which display a high degree of plastic anisotropy important extensions allow for heterogeneous deformation in the polycrystal from grain to grain and even within grains in correspondence with microstructural observations all these theories defy the popular notion which is becoming entrenched in the geological literature that the microscopic slip plane normal aligns with the axis of maximum principal compressive stress and that in simple shear the crystallographic slip plane rotates into the macroscopic shear plane and the slip direction into the macroscopic shear direction an orientation referred to by geologists as easy glide it is emphasized that future work on texture development of rocks should be based on rigorous physics rather than ingenious intuition in accordance with an old recommendation of walter schmidt

dynamic recrystallization of quartz under greenschist conditions abstract the sem electron channelling technique has been used to investigate the dynamic recrystallization of three quartz grains representative of optical textures observed in quartzite deformed under greenschist facies conditions the degree of recrystallization has been determined at 10 20 50 and 100 respectively we demonstrate that dynamic recrystallization is a sequential process involving subgrain grain rotation and grainboundary migration it initiates via subgrain polygonization on a single crystal slip system and continues via subgrain and neoblast rotation on several slip systems in the early stages of recrystallization

deformation of crystalline materials in thin section a method applicable to weak low melting point model materials permits observation through a petrographic microscope of large simple shearing deformation of samples as thin as ordinary thin sections examples of ductile brittle and intermediate behavior can be studied the method lends itself to teaching and may also prove valuable in research

strain dependent variation of microstructure and texture in naturally deformed carrara marble this study investigates the microstructure and texture variations across a mm scale shear zone in carrara marble of the alpi apuane italy the microstructures have been investigated for grain size texture and shape fabrics textures have been measured with computer integrated polarization microscopy cip and electron back scattered diffraction ebsd separating porphyroclast and recrystallized grains the deformation which post dates an earlier deformation phase and subsequent annealing is strongly localized the microstructures and textures change across the shear strain gradient and are interpreted to preserve a time sequence of progressive stages of deformation the bulk shear strain rate is estimated to be about 10 11 sec 1 at deformation temperatures of approximately 325 c 30 c the protomylonite is characterized by a core mantle structure with a bimodal grain size distribution which changes gradually to a completely dynamically recrystallized microstructure with a unimodal grain size distribution in the mylonitic center of the shear zone core mantlestructures are produced by dominant rotation recrystallization accompanied by some grain boundary migration the microstructural transition from protomylonite to mylonite coincides with a change in texture with increasing strain the single c axis maximum of an earlier inherited texture in the protomylonite is replaced by a similar texture in a different orientation maximum normal to the shear plane which is consistent with dominant basal hai and r h 2201i slip the microstructural and textural variations depend on the proportion of recrystallized grains as dynamic recrystallization progresses with finite strain the texture development is finite strain dependent the comparison of the microstructures and textures to other natural and to experimental examples explains the progressive change of the texture and demonstrates the texture evolution produced by dynamic recrystallization 2006 elsevier ltd all rights reserved

mechanisms and orientation of melt segregation paths during pure shearing of a partially molten rock analog norcamphor benzamide abstract in situ deformation experiments were performed on partially molten analog materials norcamphor in the presence of a benzamide norcamphor melt undergoing pure shearing at a constant melt fraction of 0 13 melt in the samples induces a strain dependent transition from purely dislocation creep to dislocation creep associated with minor intergranular fracturing and grain boundary sliding gbs intergranular fractures drain the melt from initially isotropic melt pockets to grain boundaries along such boundaries grain boundary migration recrystallization is inhibited while gbs occurs intergranular melt pockets occur along grain boundaries oriented subparallel to the shortening direction but melt must have migrated parallel to the elongation direction of the samples as indicated by melt accumulations at both extruding ends of the sample intergranular melt pockets parallel to the elongation direction were only rarely observed because melt was rapidly expelled from these sites nevertheless these grain boundaries are the pathways of melt segregation in the samples

ultra high temperature and subsolidus shear zones examples from the poe mountain anorthosite wyoming abstract ultra high temperature shear zones formed with interstitial melts present during the emplacement of the poe mountain anorthosite wyoming the shear zones are characterized by coarse grained plagioclase with flat extinction and rare deformation microstructures dissected grain microstructures suggest that plagioclase underwent recrystallization by fast grain boundary migration orthopyroxene crystallized from interstitial melts as strain free foliation parallel tablet grains plagioclase has a magmatic petrofabric characterized by poles to 010 normal to the shear foliation and 100 parallel to the foliation and movement direction poles to 001 have a broad distribution with a point maximum roughly parallel to the foliation and normal to the movement direction orthopyroxene petrofabrics result from oriented growth parallel to the shear foliation 100 defines a point maximum perpendicular to the shear foliation and 010 and 001 have great circle distributions approximately parallel to the shear foliation microstructures of the ultra high temperature shear zones contrast with those of granulite grade shear zones cutting across the intrusion the granulite grade shear zones initiated as fractures which evolved into shear zones by dynamic recrystallization deformed primary plagioclase and orthopyroxene recrystallized by grain boundary rotation into smaller polygonal grains

earthquake triggered 2018 palu valley landslides enabled by wet rice cultivation the death toll and economic impact of an earthquake can be greatly exacerbated if seismic ground shaking triggers landslides earthquake triggered landslides typically occur in two different contexts localized failure of steep slopes and resulting landslides that pose a major threat to life in areas below and lateral spreading of nearly flat sediment plains due to shaking induced liquefaction which can damage large areas of critical infrastructure unexpected catastrophic landsliding triggered by the 28 september 2018 earthquake at palu indonesia did not occur in either typical context but produced both destructive outcomes here we show that alluvial ground failure in the palu valley was a direct consequence of irrigation creating a new liquefaction hazard aqueduct supported cultivation primarily of wet rice raised the water table to near ground level saturating sandy alluvial soils that liquefied in response to strong ground shaking large displacement lateral spreads occurred on slopes of 1 slopes steeper than 1 5 sourced long runout landslides and debris flows that swept through villages occupying the gentler slopes below the resulting damage and loss of life would probably not have occurred in the absence of a raised water table earthquake triggered landsliding of gentle irrigated alluvial slopes is an under recognized but avoidable anthropogenic hazard aqueduct supported cultivation of rice resulted in liquefaction of the alluvial soils that led to the landslides triggered by the palu 2018 earthquake according to satellite analyses

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

microstructure c axis pattern microstrain and kinematics of some s c mylonites in grenville gneiss abstract in a major tectonic zone late extension related s c mylonites locally overprint the predominant coarser quartz microstructures which are related to earlier thrusting some of the s c mylonites display a microstructural evolution which began with the formation of deformation bands in the coarser pre existing microstructure and continued with the formation of asymmetric quartz microfoliations either by continued formation of deformation bands or fine new grains oblique to the deformation band boundaries the orientation of boudinaged and passively reoriented rutile needles show that i the formation of deformation bands was preceded and accompanied by the accumulation of strain ii that the deformation bands and oblique microfoliation which formed directly from them lie close to the finite stretching direction whereas iii other microfoliations form oblique to deformation bands and extended rutile needles near the probable instantaneous stretching direction the latter are therefore interpreted to be strain insensitive steady state foliations the crystallographic preferred orientation of the original deformation bands appears to determine that of the microfoliations the two types of microfoliations showing distinct but related patterns the element common to both types is the presence of two maxima near y in a yz girdle a feature inherited from the deformation bands which were formed in the initial stages of shortening of the aggregate favourably disposing it for rhomb slip and providing nucleation sites for subsequent recrystallization the data confirm that despite the fact that a variety of microstructures and crystallographic microfabrics result from recrystallization processes kinematic information is usually recoverable from the crystallographic microfabrics owing to the primacy of intracrystalline slip processes

simulation of fabric development in recrystallizing aggregates i description of the model abstract a new computer simulation of the development of grain shape and crystallographic preferred orientations in dynamically recrystallizing aggregates is presented this model is based on a uniform array of points each of which represents a small area of crystal this model combines homogeneous strains simplified versions of the lattice rotations predicted by taylor bishop hill theory mobile grain boundaries and the nucleation of subgrains it allows the progressive development of the fabrics and microstructures to be followed the limitations of the simplifying assumptions used in this model are discussed

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

seven types of subgrain boundaries in octachloropropane abstract subgrain boundaries in thin sheets of octachloropropane deformed at 0 7 0 8 t m on the stage of a microscope are seen to appear in the material in seven different ways type i boundaries show the classical evolution by polygonization of bent crystals type ii are essentially kink boundaries which migrate sideways during deformation to reach their present positions in the crystals type iii develop at the sites of former grain boundaries by reduction of misorientation of adjacent grains type iv and v originate by impingement of migrating grain boundaries or subgrain boundaries respectively type vi propagate in their own planes behind migrating grain boundaries to which they are attached type vii develop statically from optically strain free grains by a process probably otherwise similar to the type i process two thirds of the boundaries are types i or ii in view of the variety of subgrain boundary histories in ocp interpretation of similar features in minerals ought to be undertaken cautiously criteria are needed for telling the different types of subgrain boundaries apart in situations where only a final view of the structure is available as in optical and electron micrographs of rocks

application of digital image analysis in modelling recrystallization processes abstract digital image analysis has been used to interpret the recrystallization processes grain boundary migration of rhombohedral camphor which were produced by very low shear deformation in a new means type apparatus hajeck press for each stage of shearing the following parameters were computed grey value distribution of images area of selected grains and grain shape orientation the experimental investigations allow the following conclusions to be made 1 1 increasing uniformity of grey values brightness could be interpreted as indicating that a crystallographic preferred orientation developed during shear deformation 2 2 extensive increase of grain size and asymmetrical decrease of grain frequency are consequences of grain boundary migration the alterations took place in several stages 3 3 the grain shapes began changing immediately after the shear deformation started the different stages of grain boundary motion migration correspond to distinctive physical sources driving forces of migration

syn emplacement recrystallization and deformation microstructures in the poe mountain anorthosite wyoming plagioclase recrystallization microstructures and petrofabrics in the unmetamorphosed 1 43 ga poe mountain anorthosite wyoming are indicative of very high temperature deformation and recrystallization during the emplacement of the anorthosite body the poe mountain anorthosite consists of a core of recrystallized massive anorthosite transitional with a series of layered anorthositic cumulates at the margin of the intrusion irregular grain boundaries and dissected grain microstructures in the massive core and transitional anorthosites suggest that the anorthositic rocks recrystallized by fast grain boundary migration and possibly subgrain rotation recrystallization at very high temperatures 1050 c during emplacement of the intrusion in the mid crust 3 kbar the deformation and recrystallization of the poe mountain anorthosite was continuous from subliquidus to subsolidus temperature conditions during the emplacement of the intrusion anorthosites with the lowest modal percentages of ferromagnesian minerals and fe ti oxides are always the most recrystallized this suggests that melt interstitial to the plagioclase crystal framework was removed during deformation and recrystallization of the intrusion bulging of plagioclase grain boundaries around fe ti oxides together with deformed oikocrystic ferromagnesian minerals and plagioclase chadacrysts indicate that the deformation and recrystallization of the intrusion continued after the crystallization of the interstitial melt minerals

strain localization in homogeneous granite near the brittle ductile transition a case study of the kellyland fault zone maine usa abstract we present a detailed case study of a strike slip shear zone that cut homogeneous granite near the brittle ductile transition this zone contains three distinct strain facies 1 a 2 3 km wide belt of foliated granite 2 a 100 300 m wide belt of small localized shear zones and 3 a 200 400 m wide belt of ultramylonite that includes both homogeneous and local pinstripe ultramylonites the foliated granite formed via dislocation creep of quartz and minor dissolution precipitation creep and dislocation creep of feldspar under amphibolite facies conditions shortly after granite crystallization the localized shear zones and homogeneous ultramylonites formed directly from pseudotachylyte and cataclasite and they deformed by granular flow grain boundary sliding coupled with dissolution precipitation creep these deformation features reveal a three phase rheologic evolution in granite near the brittle ductile transition phase 1 is recorded by the foliated granite and the rheology was governed by dislocation creep of quartz phase 2 was a transient period of brittle deformation and represents a temporal strength maxima in the fault zone phase 3 was a long lived period of ductile deformation and the rheology was governed by the granular flow mechanism strain weakening in this zone was a direct result of grain size reduction and phase mixing during transient brittle deformation

flow mechanisms in sulphide minerals abstract the sulphide minerals as a group display a diverse range in strength and mechanical behaviour in crustal environments deforming by a range of different flow mechanisms which can lead to the development of characteristic microfabrics the dependence of creep rate on imposed parameters such as stress difference temperature grainsize effective confining pressure and the activities of various components varies for each type of flow mechanism for particular phases changes in the dominant operative flow mechanism may occur in response to changes in the imposed environmental variables at high applied stress differences low effective confining pressures and low temperatures brittle failure and cataclastic flow are significant deformation mechanisms in some sulphide minerals at elevated confining pressures brittle failure can be suppressed and low temperature plasticity processes involving dislocation glide and or deformation twinning may operate with decreasing applied stress difference and at elevated temperatures even though strain may be accommodated largely by dislocation glide deformation may be rate controlled by recovery processes and dynamic recrystallization may be significant in influencing microfabric development the operation of dislocation glide processes leads to the development of crystallographic preferred orientations at very low applied stress difference various grainsize dependent atomic transfer deformation mechanisms may be important in many fluid present low to medium grade metamorphic environments solution precipitation creep processes are active in the deformation of some sulphide phases in fluid absent situations grain boundary diffusion creep may be significant at higher temperatures where intragranular diffusion is relatively rapid lattice diffusion creep processes are expected to be a major deformation mechanism in fine grained sulphide assemblages at elevated temperatures grain boundary sliding may be an important deformation mechanism

deformation and recrystallization mechanisms in mylonitic shear zones in naturally deformed extrusive eocene oligocene rocksalt from eyvanekey plateau and garmsar hills central iran abstract microstructural processes in mylonitic shear zones from extrusions of eocene oligocene rocksalts from garmsar hills and eyvanekey plateau central iran are described and analyzed the halite samples were studied by transmitted light microscopy of gamma irradiated thin sections subgrain size palaeopiezometry of polished and chemically etched samples and texture measurements by electron backscatter diffraction ebsd the studied shear zones are thin using published flow laws the strain rate in the fine grained mylonites is about 10 10 l s which is in a good agreement with earlier in situ measurements on glacier salt flow rate

the 2018 mw7 5 palu supershear earthquake ruptures geological fault s multisegment separated by large bends results from integrating field measurements lidar swath bathymetry and seismic reflection data

coesite in suevites from the chesapeake bay impact structure the occurrence of coesite in suevites from the chesapeake bay impact structure is confirmed within a variety of textural domains in situ by raman spectroscopy for the first time and in mechanically separated grains by x ray diffraction microtextures of coesite identified in situ investigated under transmitted light and by scanning electron microscope reveal coesite as micrometer sized grains 1 3 m within amorphous silica of impact melt clasts and as submicrometer sized grains and polycrystalline aggregates within shocked quartz grains coesite bearing quartz grains are present both idiomorphically with original grain margins intact and as highly strained grains that underwent shock produced plastic deformation coesite commonly occurs in plastically deformed quartz grains within domains that appear brown toasted in transmitted light and rarely within quartz of spheroidal texture the coesite likely developed by a mechanism of solid state transformation from precursor quartz raman spectroscopy also showed a series of unidentified peaks associated with shocked quartz grains that likely represent unidentified silica phases possibly including a moganite like phase that has not previously been associated with coesite

modelling of mantled porphyroclasts using non newtonian rock analogue materials abstract the development of type porphyroclasts was modelled experimentally in a circular transparent shear rig using crystalline rock analogue materials rectangular camphor objects embedded in a matrix of octachloropropane were deformed in simple shear flow the camphor deformed into objects with progressive deformation up to a shear strain of 100 the development of these objects and of gradients of flow parameters in the matrix was followed from step to step during the deformation the objects in this experiment show stair stepping of wings that did not occur in earlier experiments with newtonian fluids analysis of the flow pattern indicates that this is due to an unusual flow perturbation geometry around the relatively rigid camphor objects which rotate more slowly than equivalent objects in newtonian flow the non newtonian rheology of the experimental materials may be responsible for this deviant behaviour this implies that non newtonian fluids are better analogues than newtonian fluids to study the development of structures in rocks with non newtonian rheology since the geometry of the resulting structures can be different

irrigation and the palu landslides wet rice cultivation in the palu valley indonesia prepared the ground for the devastating liquefaction induced landslides that were triggered by the mw 7 5 earthquake in 2018 suggest two studies of the spatial relationship between landslide morphology and irrigation

matrix mosaics brittle deformation and elongate porphyroclasts granulite facies microstructures in the striding athabasca mylonite zone western canada abstract the late archean striding athabasca mylonite zone western canadian shield is a 400 km long linked system of granulite facies mylonite belts developed in the continental crust the granulite facies mylonites 800 1000 c at 0 8 1 1 gpa developed in subsets of the anhydrous mineral assemblage clinopyroxene orthopyroxene garnet plagioclase quartz hornblende comparison of the microstructures of the striding athabasca mylonites with published descriptions of natural and experimental deformation of geological and analogue materials at elevated homologous temperatures provides some insight into the role played by different processes in the development of the striding athabasca mylonites in addition to dislocation creep and dynamic recrystallisation extensive mass transfer occurred contemporaneously with brittle fracture and cataclasis during granulite facies metamorphism the microstructure and extreme phase dispersal in anhydrous polymineralic matrix mosaics is indicative of efficient grain scale and aggregate scale diffusion grain boundary mobility and mass transfer at relatively slow strain rates despite their annealed appearance the granoblastic matrix mosaics developed synkinematically deformation induced dilation may enhance metamorphic reactions where products are more voluminous than reactants in the porphyroclast population highly elongate 20 1 monocrystalline orthopyroxenes appear to be fragments of dismembered kinked parent grains rather than stretched porphyroclasts granulite facies mylonites should not be treated as direct analogues of greenschist facies mylonites in particular it is essential to evaluate the potential positive feedback between structural and metamorphic processes in highly strained high temperature shear zone rocks

microstructure and micromotion in recrystallization flow of octachloropropane a first look advance of the genetic theory of metamorphic fabric depends in part on improved understanding of dynamic recrystallization processes and the effects of these processes upon various fabric elements this paper describes aspects of the microstructural evolution and associated small scale motion in a dynamically recrystallizing sheet of octachloropropane the material was deformed in progressive pure shear at 2 10 3 sec 1 with interruptions for photography and u stage measurement at 70 of its absolute melting temperature the dominant recrystallization process is migration of grain boundaries with consequent major adjustment of the shapes and sizes of grains but no marked change in the average grain size and no creation of new grains typical grains in the fully deformed material 30 bulk shortening have a composite structure with primitive high strain regions inherited directly from the undeformed state rimmed by successively younger regions of lower strain accreted behind outwardmoving boundaries an array of second phase marker particles permits distinction between grain boundary motion with and through the material and reveals an unexpected ability of grains as a whole to migrate short distances up a bulk strain gradient the markers also show that the only important deformation process is intragranular deformation and that it is proceeding at somewhat different rates in different grains the central problem posed by the observations is to explain the direction and speed of each migrating boundary two hypotheses were tested neither with outstanding success one of these hypotheses is that grain boundary migration is part of a strain accomodation process that operates between grains stretching or shortening at different rates parallel to their mutual boundary

folding and shear deformation in quartzites inferred from crystallographic preferred orientation and shape fabrics abstract folding and simple shear deformation frequently occur together on all scales the kinematic information from crystallographic preferred orientation cpo and microstructural information from shape fabrics are used to investigate the relationships of simple shear and folding in small scale folds three fold samples were analysed sample 1 with the fold axis perpendicular sample 2 oblique and sample 3 essentially parallel to the shear direction all folds have formed by buckling in a simple shear deformation regime the principal kinematic directions for each sample lie in a single plane normal to the fold axial plane and at variable angles to the fold axis the cpos allow a distinction to be identified between coaxial and simple shear deformation components in different parts of each fold the shear senses determined by cpos and shape fabrics indicate that the shear deformation and the buckling of the layers occurred approximately simultaneously in all samples cpo analysis of the flexural slip components of the folding suggests that the fold axes have not rotated substantially towards the extension direction since their initiation the variable orientations of the fold axes are explained by variable original orientations of the anisotropy with respect to the shear direction

ground motion amplification in the marina district abstract following the 18 october 1989 loma prieta earthquake triggered seismographs were deployed in and around the marina district to investigate site amplification in the 3 weeks after the mainshock 16 aftershocks were recorded by two or more of these stations two additional stations deployed in march 1990 recorded three earthquakes that occurred in contra costa county by recasting the method of spectral ratios into a generalized inverse problem we combine the shear wave spectra from these 19 aftershocks to estimate the relative site amplification as a function of frequency all five stations located in the marina district are amplified by factors of 6 to 10 at 1 hz and 2 to 4 at 3 hz relative to a station located on franciscan sandstone at fort mason irrespective of whether they are sited on artificial fill or beach sand two stations located on dune sand just outside the marina district are amplified by factors of 2 to 4 for frequencies above 1 hz four stations located on franciscan sandstone in pacific heights nob hill rincon hill and diamond heights show little relative amplification conditional estimates of the mainshock spectra can be determined at stations that only recorded aftershocks if they can be linked to stations that recorded the mainshock these estimates are predicated on the assumption that the ground behaved linearly in the mainshock an assumption that is clearly violated for those sites where there was ground failure using this method of extrapolation for a site in the marina district that showed no evidence of ground failure yields mainshock spectra that are slightly greater than the mainshock spectra from the outer harbor wharf in oakland and near the pacific park plaza in emeryville and that significantly exceed the mainshock spectra from all the free field accelerograms located in san francisco

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

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

in situ annealing experiments of octachloropropane as a rock analogue kinetics and energetics of grain growth abstract two dimensional in situ observation of the change of size of individual grains of octachloropropane ocp during post deformation annealing revealed that grain boundary migration occurred to reduce the grain boundary energy within the polycrystalline aggregate studied some grains show a cyclic change in grain size others have a stable grain size while most grains were consumed and disappeared in order that the mean grain size could increase during grain coarsening some grains were dissected then coalesced amalgamated with others and their centers migrated across the aggregate the average grain size d can be expressed by d k 0 exp q rt t n where k0 is a constant q is the activation energy r is the gas constant t is the temperature t is the annealing time and n is a constant we obtained n 0 1 0 2 and q 6 2 kcal mol the driving force p is the surface energy stored at grain boundaries the driving force can be expressed as p tm where m is the constant and hence the grain growth rate d can be expressed as d p n 1 m the value of n 1 m ranges from 4 to 10

modeling of anisotropic grain growth in minerals the role of surface energy anisotropy during grain growth is investigated using both physical experiments on octachloropropane and numerical experiments using the elle microstructural modelling system in particular the effects of anisotropy on growth rates grain shapes and lattice preferred orientations are analysed anisotropic growth in thin polycrystalline sheets of octachloropropane is found to systematically remove certain c axis orientations from the sample without obviously modifying the grain shapes by comparison with equivalent numerical experiments we can explain these observations with a simple boundary layer model that treats each side of each grain boundary as an independent system the observed growth exponent in the physical experiment of 0 35 is significantly below the theoretical level of 1 and although the numerical experiments have growth rates as low as 0 68 apparently some other factor which suppresses the growth rate in the octachloropropane was also active the anisotropy of surface energies also leads to an increase in the grain size distribution and when it occurs in rocks with a strong pre existing crystallographic preferred orientation may even lead to the development of a shape preferred orientation which is completely unrelated to the shape of the finite strain ellipsoid corresponding author e mail address bons mail uni mainz de accepted for publication in the hans ramberg volume bulletin of the american geological society bons et al anisotropic grain growth 17 januar 2000 page 2

strain probe best fitting a homogeneous strain to the motions of scattered points abstract in laboratory experiments or e g in studies of glacier motion one sometime wants to estimate a finite strain from images or surveys of scattered marker points taken at successive times similarly crustal geodetic strain can be estimated by measuring velocities of geodetic stations the strain probe presented here is a simple formula that calculates a best fit strain from the motions of n marker points distributed over an area or a volume and monitored in a cartesian reference frame specifically it is the product of two 2 2 or 3 3 in 3 d symmetric matrices whose components are populated from the known positions and the measured displacements of the markers two examples implemented in excel workbooks illustrate how to combine the strain probe with the processing of the data and of its results speck motions in a means urai see through experiment are an example of a finite strain calculation published geodetic site velocities 120 stations in central anatolia are an example of infinitesimal strain

deformation of granitoids at low metamorphic grade ii granular flow in albite rich mylonites abstract the high strain deformation at low metamorphic grades of three investigated granitoids is dominated by the granular flow of albite rich polyphase aggregates these aggregates formed by retrograde breakdown reactions from intermediate plagioclase and k feldspar the predominant deformation mechanism changes in granitoids as the grain size is reduced coarse grained low strain examples are deformed by a combination of intracrystalline plasticity quartz and fracturing feldspar in the mylonites intracrystalline plasticity of quartz plays only a minor role and the dominant deformation mechanism is a non cataclastic granular flow of polyphase aggregates consisting largely of albite and quartz deformation appears to be stable probably because grain growth in albite quartz mixtures is inhibited these fine grained aggregates are mechanically weaker than pure quartz aggregates thus the change in deformation mechanism mainly due to feldspar breakdown reactions appears to be important for the localization of high shear strain deformation at low metamorphic grades in granitoids and other lithologies modally dominated by feldspar the rheological behaviour of albite dominated mineral aggregates may have two consequences for middle to upper crustal deformation of modally feldspar dominated lithologies 1 feldspar in the presence of aqueous fluids can be an important mineral controlling the rheology at low metamorphic grades that is below amphibolite facies p t conditions 2 the occurrence of granular flow of fine grained polyphase aggregates in low grade granitoids is probably common and calls for great care in the modelling of middle to upper crustal rheology based on flow laws for intracrystalline plasticity of single minerals such as quartz

synkinematic microscopy of transparent polycrystals abstract deformation of weak polycrystalline materials in thin section on the stage of a petrographic microscope offers insight into the origin of optical microstructures similar to microstructures in naturally deformed rocks sample materials used to date include several soft minerals ice carnallite bischofite nitratite and various organic plastic materials they can be simple sheared or pure sheared at temperatures to 300 c at a variety of strain rates using relatively simple and inexpensive apparatus the complete microstructural evolution can be recorded photographically along with the complete kinematic history research applications have focussed on dynamic recrystallization and progress has been made towards understanding how the average grain size is maintained constant in steady state recrystallization flow records have been obtained of the development of various crystal plastic microstructures and of lattice reorientation trajectories during flow teaching applications have begun to be developed and several videotapes are available future technical developments are expected to permit stress measurement or control during experiments and synkinematic recording of lattice reorientation numerous research areas invite attention these include investigation of the microstructural developments that precede faulting the behaviour of deforming crystal melt systems and the behaviour of dynamically reactive multi phase systems