collapse of the thickened variscan crust in the french massif central mont pilat extensional shear zone and st etienne late carboniferous basin abstract a large scale extensional shear zone is described from the mont pilat area in the northeastern part of the french massif central this shear zone is about 2 km thick and is characterized by well developed n dipping foliation and stretching lineations deformation occurred under conditions of retrograde metamorphism from high temperature conditions to greenschist facies it is superimposed on a composite foliation related to the earlier variscan 380 350 ma compressional events associated with southward emplacement of nappes and hp mt metamorphism regional n s lineations and shear criteria observed at a regional scale indicate a northward displacement of the hanging wall during extension large strains locally recorded in thick mylonitic zones suggest that displacement was substantial some tens of kilometres late superimposed extensional brittle deformation and pseudotachylites show that northward displacement on normal faults continued at a shallower depth a large granitic pluton granite du velay intruded late in the the variscan orogeny was associated with extension some small leucogranitic syntectonic melts were emplaced within the shear zone and are strongly deformed geochronological rb sr data on these leucogranite bodies give an age of 320 ma and 40 ar 39 ar dating of synkinematic biotites from gneissose rocks in the shear zone yields a plateau age of 313 ma these data show that extensional ductile deformation and magmatism were still active during the latest late carboniferous thus extension occurred immediately after the well known late palaeozoic collision type compressional tectonics which had significantly thickened the crust we propose that the extensional tectonism described here is due to the gravitational collapse of the initially thick variscan crust the stephanian intracontinental sedimentary basin of st etienne was formed along the hanging wall of the normal shear zone during the late stages of this post orogenic crustal extension

early middle paleozoic intraplate orogeny in the ogcheon belt south korea a new insight on the paleozoic buildup of east asia the polycyclic ogcheon belt of south korea represents the boundary between two precambrian blocks investigation on the timing and kinematics of the block agglomeration is of considerable bearing on the understanding of the constitution of the asian continent we report here structural evidence showing that the earlier tectonic event dates back to early middle paleozoic the ogcheon tectonism or orogeny the ductile piling up of nappes of the ogcheon belt corresponds to an intracontinental orogeny involving the opening and the subsequent closure of an aborted rift and not of a wide oceanic area the nappes contain unequivocal evidence for ductile shearing with a northwest over southeast sense of movement field evidence includes the presence of s1 and s1 2 foliations bearing an extensive stretching lineation perpendicular to the belt associated with a strongly noncoaxial deformation regime the f1 isoclinal folds are commonly a type and sheath folds whose axes are parallel to the stretching lineation whereas the southeast facing f2 recumbent folds have subhorizontal axes parallel to the belt all lines of evidence unconformity superposed deformations age of the metamorphism etc imply that the d1 2 ogcheon tectonism is pre middle carboniferous late silurian early devonian the subsequent indosinian middle triassic f3 upright synfolial folds that trend nne ssw and later structures clearly overprint the middle paleozoic ductile thrusts and isoclinal folds the early paleozoic ogcheon supergroup is formed of a thick volcanosedimentary pile deposited above an early platform sequence in a rift basin on the basis of the geochemical characteristics of the metavolcanics it appears that oceanization did not occur and ogcheon rift aborted soon after it was formed we suggest that middle paleozoic ductile nappe structures have been formed by the structural inversion of the rift extensional features during the ductile stacking episode the early formed foliation and isoclinal folds have been folded in a continuum during the same tectonic event middle carboniferous terrigenous formations have been deposited unconformably upon folded and thrust older rocks a tentative correlation with early paleozoic imjingang qinling and cathaysian belts within the asian continent reveals that ogcheon rift was emplaced within the south china plate and that imjingang belt should represent the limit between north and south china blocks in the korean peninsula

effect of wind scouring on climatic records from ice core oxygen isotope profiles removal of winter snow by wind explains why the annual mean oxygen isotope ratio at an ice divide is 2 5 less negative than it is 1 2 km downslope cores from two sites on an ice cap ellesmere island canada show past variations in the difference depending on where the ice originated relative to the scoured zone some ice core climatic records may need correction for scouring

an evaluation of criteria to deduce the sense of movement in sheared rocks some of the most useful criteria for the deduction of the sense of shear are summarized for use in areas where unequivocal field evidence is lacking apparently conflicting evidence from rotated pressure shadow regions around porphyroclasts and porphyroblasts is clarified the use of quartz crystallographic fabric asymmetry to deduce the shear sense in the bulk rock should be treated with caution and used only together with detailed microstructural observations

neotectonics of the nanga parbat syntaxis pakistan and crustal stacking in the northwest himalayas the northwest termination of the himalayan arc is marked by two large antiformal structures termed syntaxes and a nw se zone of intermediate depth earthquakes which have yielded both strike slip and thrust sense fault plane solutions this contribution presents new structural data from the nanga parbat area the northern syntaxis one of the fastest rising portions of the orogen 7 mm yr 1 our studies show uplift related to syntaxis growth to be accommodated by structures located along its western margin fault kinematics in the southern part of the margin indicate nw directed thrusting along a shear zone and high level cataclastic faults termed the liachar thrust zone this carries amphibolite facies basement rocks out onto quaternary sediments further north along the western margin active faults are dominantly dextral strike slip oriented north south e g the shahbatot fault overprinting relationships suggest that the strike slip fault zone has migrated southwards into the nw directed thrust zone these relationships are consistent with the northwest termination of the arcuate himalayan thrust belt at a lateral tip generating folding and radial thrust directions faulting patterns at nanga parbat suggest that this tip zone has migrated southwards active faulting is now concentrated in the northwest continuation of the hazara southern syntaxis along a seismogenic strike slip and thrust zone these deep level tips lie on the crustal stacking thrusts which cut through the higher level sse directed thrusts of pakistan

evolution of a fault surface from 3d attribute analysis and displacement measurements abstract a large fault surface evolves by growth and coalescence of numerous segments through time which results in strong undulations of the principal fault surface we interpreted a strongly segmented 13 km long fault using 3d seismic data and studied the morphology in terms of fault linkage using curvature azimuth and dip attributes displacement profiles of two horizons were measured to analyse the different displacement relations and to quantify their variation and dependence on fault morphology we identified four orders of fault segments over a scale range from a few hundred metres to several kilometres which evolved during fault growth the strong changes in orientation of the several segments might result in a heterogeneous small scale fracture distribution and different fault drag geometries displacement measurements on the undulated fault surface indicate a strong variation between real vertical and horizontal displacement values however the commonly used throw values lead to a smoothing of the real displacement curves and to an underrepresentation of their values and therefore cannot show a triangular shape that is typically identified from ruptures fault surfaces of earthquake processes therefore for any kind of fault analysis care should be taken when using throw as approximation for the real displacement

relationships between deformation and mixing processes in lava flows a case study from salina aeolian islands tyrrhenian sea the massive unit of a lava flow from porri volcano salina aeolian islands displays many unusual structures related to the physical interaction between two different magmas the magma a represents approximately 80 of the exposed lava surface it has a crystal content of 51 vol and a dacitic glass composition sio2 63 64 wt the magma b has a basaltic andesite glass composition sio2 54 55 wt and a crystal content of approximately 18 vol it occurs as pillow like enclaves banding boudin like and rolling structures which are hosted in magma a structural analysis suggests that banding and boudin like structures are the result of the deformation of enclaves at different shear strain the linear correlation between strain and stratigraphic height of the measured elements indicates a single mode of deformation we deduce that the component b deformed according to a simple shear model glass analyses of the a b boundary indicate that a and b liquids mix together at high shear strain whereas only mingling occurs at low shear strain this suggests that the amount of deformation i e forced convection plays an important role in the formation of hybrid magmas high shear strain may induce stretching shearing and rolling of fluids which promote both forced convection and dynamical diffusion processes these processes allow mixing of magmas with large differences in their physical properties

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

the development of structural geology and the historical context of the journal of structural geology a reflection by bruce hobbs abstract this paper sets the historical context for the journal of structural geology when it was first published in 1979 the major advances in structural geology over the past 40 years are then highlighted finally ten grand challenges for the next decade are nominated

nine centuries of microparticle deposition at the south pole abstract the analysis of microparticles in a 101 m core from amundsen scott south pole station antarctica has revealed a substantial increase in total particle concentration between approximately 1450 and 1850 a d a period encompassing the latest neoglacial interval or little ice age it is likely that this reflects a simultaneous increase in the concentration of particulate material in the antarctic atmosphere this is important climatologically for the antarctic atmosphere may represent the closest approximation to the natural background aerosol thus cores from east antarctica may contain long and detailed records of the natural global background aerosol such records are unavailable from any other medium additionally a cyclical variation which appears to be annual has been detected in the south pole particle record these features allow construction of a relative time scale for ice cores older than 100 yr from regions of low accumulation 1 where many traditional techniques are not applicable this is especially significant as the comparison of climatic data extracted from ice cores with other records of proxy data depends upon the ability to assign an accurate time scale to the ice core an estimated nine century record of net annual accumulation at the south pole has been compiled and the calculated error in the time scale is 90 yr

polyphase wrench tectonics in the southern french massif central kinematic inferences from pre and syntectonic granitoids in the variscan french massif central the south limousin area consists of low to medium grade metamorphic rocks intruded by two granitic bodies the structural and textural analyses of these plutons undertaken in parallel with the structural analysis of their host rocks allow us to characterize and to date different stages in the tectonic evolution of this area this study shows that the south limousin area experienced successivelly two strike slip events along two geographically distinct shear zones from north to south the left lateral estivaux and the right lateral south limousin strike slip faults respectively these ductile faults subdivide the south limousin into three structural units from north to south they are the upper gneiss unit thiviers payzac unit and genis unit the two granitic bodies intrude the thiviers payzac unit only the younger estivaux granite is a syntectonic pluton which emplaced during left lateral wrenching 40ar 39ar dates from biotites indicate an early carboniferous age 346 3 ma the older granite is a pretectonic body it is the ordovician saut du saumon augen orthogneiss in which detailed structural analyses show the polyphase nature of the solid state deformation our microtectonic data indicate that the right lateral motions overprint the left lateral ones and produce apparently symmetrical fabrics

kinematics and ar 40 ar 39 geochronology of the gaoligong and chongshan shear systems western yunnan china implications for early oligocene tectonic extrusion of se asia the gaoligong and chongshan shear systems glss and csss in western yunnan china have similar tectonic significance to the ailaoshan red river shear system asrrss during the cenozoic tectonic development of the southeastern tibetan syntaxis to better understand their kinematics and the cenozoic tectonic evolution of se asia this paper presents new kinematic and 40 ar 39 ar geochronological data for these shear systems all the structural and microstructural evidence indicate that the glss is a dextral strike slip shear system while the csss is a sinistral strike slip shear system and both were developed under amphibolite to greenschist grade conditions the 40 ar 39 ar dating of synkinematic minerals revealed that the strike slip shearing on the glss and csss at least began at 32ma possibly coeval with the onset of other major shear systems in se asia the latestage shearing on the glss and csss is dated at 27 29ma by the biotite 40 ar 39 ar ages consistent with that of the wang chao shear zone wcsz but 10ma earlier than that of the asrrss the dextral gaoligong shear zone within the glss may have separated the india plate from the indochina block during early oligocene combined with other data in western yunnan we propose that the baoshan southern indochina block escaped faster southeastward along the csss to the east and the glss to the west than the northern indochina block along the asrrss accompanying with the obliquely northward motion of the india plate during early oligocene 28 36ma during 28 17ma the northern indochina block was rotationally extruded along the asrrss relative to the south china block as a result of continuously impinging of the india plate

research on snow and ice this review unlike its predecessor martinelli et al 1979 is an intentionally selective survey of recent advances in selected areas of snow and ice research i have chosen to concentrate on studies relating to large scale aspects of the cryosphere and to consider their wider significance for other disciplines results obtained by new measurement techniques and the application of remote sensing methods are also stressed at the same time the broad lines of advance in glaciological research as represented in books conference themes and major field or laboratory programs are noted and a detailed bibliography is appended

diatom evidence for late holocene climatic events in granite harbor antarctica downcore diatom data from a deep basin in granite harbor antarctica provide new high resolution information concerning changes in oceanographic and depositional processes that have occurred during approximately the last 1250 years the influence of global scale climatic change during the time of the medieval warm period and possibly the little ice age is revealed by long term changes in floral assemblages as recorded by changes in the relative concentration of nitzschia cylindrus the diatom data suggest that granite harbor experienced less annual ice and pack ice cover during both these periods possibly because of higher temperatures during the medieval warm period and stronger offshore winds during the little ice age the sedimentary record reveals several distinct short lived events in which nearly monospecific blooms of corethron criophilum and chaetoceros spp occurred possibly the result of strong stabilization of the upper water column and were most likely a response to regional rather than global conditions although short lived these events may play a significant role in the delivery of organic carbon and biogenic silica to the seafloor

experimental investigation of the effects of fluid heterogeneity upon the motion of rigid ellipsoidal inclusions during bulk inhomogeneous shortening abstract an experimental study of the motions of rigid ellipsoidal inclusions within deforming homogeneous and heterogeneous fluid systems indicated that the time behaviour of such objects measured relative to the experimental apparatus can vary significantly between the two system types during inhomogeneous time dependent flow initially aligned ellipsoidal inclusions within a deforming homogeneous fluid were rotated in the same sense as an adjacent passive strain marker introduction of heterogeneity by partially enclosing the ellipsoidal inclusions with a less viscous fluid resulted in three different rigid body behaviours during deformation the behaviours observed for initially aligned ellipsoids in the system containing fluid heterogeneities were 1 opposite sense rotation to that of the strain marker 2 negligible rotation of the objects and 3 same sense of rotation as that of the strain marker a computerized time based analysis of the deformation possible through the incorporation of marker particles into each of the two different deforming systems revealed similar deformation kinematics for the two experimental types at both the system and sub system scale results of the experiments indicate that significant differences can occur in rigid body behaviour between apparently similarly deforming homogeneous and heterogeneous systems the results suggest that fluid flow theory as derived for rigid body behaviour in homogeneous fluids may be unsuitable for the purpose of qualitatively predicting rigid object behaviour within deforming rock systems that are highly anisotropic at the porphyroblast porphyroclast scale this notion is supported by an examination of the assumptions and simplifications upon which the theory relating to rigid body behaviour in homogeneous fluids was originally based

apparent shear band geometry resulting from oblique fold sections abstract small scale shear zones inclined at intermediate angles to an earlier anisotropy are often observed in deformed rocks they are traditionally described as shear bands c bands extensional crenulation cleavage or normal kink bands formed as a result of extension along the anisotropy their asymmetries are widely used to describe the large scale kinematics of deformation and the deformational history of a given area we demonstrate that when various three dimensional fold structures are observed on two dimensional outcrop surfaces or in thin section they can appear geometrically identical we have developed a simple technique that allows the geometrical evaluation of any section across a cylindrical fold of arbitrary geometry the ranges of planar sections on which a fold exhibits shear band like geometry are presented on a stereographic projection in order to simplify the determination of critical orientations we demonstrate that for any fold geometry there are two distinct groups of sections showing shear band like geometry with opposite senses of shear criteria systematically arranged around the axial plane and which are inclined at a high angle to the major anisotropy we provide a field example from western carpathians where kinematic analysis mainly based on apparent extensional shear bands led to overemphasis of the role of post orogenic extension on the final structural pattern of the belt

kinematics of rock flow and the interpretation of geological structures with particular reference to shear zones abstract current interpretations of structures are generally based on homogeneous and steady deformation models despite the fact that both the heterogeneity of rocks materially rheologically and geometrically and the time dependence of imposed geological conditions give rise to significant heterogeneous and non steady flow in concert with field observations we emphasize that the expectation of heterogeneity and non steadiness is the key to understanding natural deformation and that in order to carry out successful structural analysis and tectonic interpretation it is necessary to recognize the first order distinction between imposed boundary conditions typically used to define the tectonic regime e g transcurrent transpression and the response recorded by rocks within the zone structures and fabrics using s c fabric as an example it is demonstrated how flow with a non zero spinning component resulting from the rheological contrasts and or geologically realistic time dependent boundary displacement can drastically change the ideal geometric and kinematic relations between the fabric and the host zone in agreement with both theoretical analysis and field observation it is shown that natural flow regimes range from pure shear to pure rotation including super simple shear in consideration of the heterogeneity and non steadiness of natural deformation kinematic analysis is justifiable only within a homogeneous domain and steady period flow kinematics and mechanisms are interrelated in that firstly mechanisms provide internal constraints on kinematics ensuring that only certain flows are possible and secondly flow kinematics will favour development of certain mechanisms

structural evolution and 40ar 39ar dating of the zanhuang metamorphic domain in the north china craton constraints on paleoproterozoic tectonothermal overprinting abstract the zanhuang domain in the hinterland of the north china craton consists of archaean paleoproterozoic mesoproterozoic and palaeozoic rocks and was previously considered a mesozoic metamorphic core complex our reappraisal of regional structural history and mineral 40 ar 39 ar geochronology shows that the domain was subjected to a number of deformation events and had a heterogeneous uplift cooling history during the paleoproterozoic four primary deformation events have been recognized in the domain the first event reflects the earliest deformation in the region however only closed and rootless folds are preserved d2 was dominated by wnw ese shortening and top to ese thrusting in a collisional environment d3 was a divergent extensional and ductile shearing event driven by the post collisional extensional collapse and exhumation of the thickened crust in the domain d4 was characterized by localized ductile shearing with the development of three nne trending ductile shear zones the 40 ar 39 ar plateau ages derived from the thermochronology analyses of the biotite concentrates from the metamorphic rocks are interpreted as cooling ages through biotite 40 ar 39 ar closure temperature 300 c and this allows us to constrain the timing of deformation events in conjunction with the evidence from structural analyses and previous geochronological data we conclude that 1870 and 1870 1826 ma define the timing of d1 and d2 events respectively while 1826 1793 ma represents the age of d3 the last event d4 occurred at 1689 1633 ma as constrained by 40 ar 39 ar plateau ages of biotite concentrates from the mylonites within the ductile shear zones these data together with k feldspar 40 ar 39 ar geochronology allows us to depict the cooling history of the region during the paleoproterozoic and mesoproterozoic it appears that the uplift cooling rate varies temporally and spatially in the region

variscan crustal thickening extension and late overstacking during the namurian westphalian in the western montagne noire france abstract study of the structural relationships between major lithotectonic units that is the axial zone x schists and southern thrust sheets on the southwestern slopes of the montagne noire in southern france has cast new light on the main processes and timing for this segment of the variscan mountain belt the contact between x schists and the gneissic axial zone is a major shear zone early movements to the southwest along this contact appear to have been contemporary with the emplacement of nappes on the south slope subsequent anatexis of the axial zone was synchronous with regional dextral strike slip shearing and granitization at the end of anatexis sealed the transcurrent structures extension commenced during the final stage of granite crystallization finally crustal shortening with north northeast vergence completed the deformation and controlled the emplacement of gold mineralization we propose a new model for the geodynamic evolution of the montagne noire during namurian westphalian times crustal thickening took place around 330 325 ma and was followed by uplift anatexis and dextral transcurrent shearing between 325 and 319 ma the subsequent unroofing of the thickened domain continued between 319 and 315 ma during a stage of doming and extensional detachment this crustal thinning was succeeded in the westphalian early stephanian 315 300 ma by compressive tectonism during which the lithological stacking of the southern thrust sheets was achieved

the tunguska explosion of 1908 discovery of meteoritic debris near the explosion site and at the south pole submillimeter sized metallic spheres extracted from soil in the tunguska region of central siberia contain noble metals in cosmic proportions the trace element composition and geographical distribution of these spheres suggest that they are from the 30 june 1908 tunguska explosion and not meteoritic ablation products falling continuously on the earth debris from this explosion was also discovered in a south pole ice core this discovery indicates that the tunguska object exploded in the atmosphere with subsequent stratospheric injection and transport of the debris the celestial body that exploded over tunguska weighed more than 7 million tons was more than 0 16 kilometer in diameter and may well have been a stony meteorite this discovery offers a new precision time marker in polar ice strata for the year 1909 the steady state influx of cosmic matter at the south pole is estimated to be 1 8 x 10 8grams per square centimeter per year which corresponds to a global influx of 4 x l05tons per year

behaviour of spherical rigid objects and passive markers during bulk inhomogeneous shortening of a fluid abstract quantitative analysis of the kinematics of an experimental gravity driven inhomogeneous time dependent flow showed that the kinematics of the flow varied both temporally and spatially the variation in kinematics of the flow included vorticity rotation sense reversals and the results provide possible insight into the kinematics of gravity spreading flows the variation of the kinematics reflected the influence of the boundary conditions upon the flow spherical inclusions and thin columnar passive markers placed within the fluid prior to deformation also allowed the fluid flow to be used to examine some of the possible relationships that may form between porphyroblasts and passive foliations in inhomogeneous time dependent flows comparison of initial and final orientations of several spherical inclusions suggested an apparent lack of rotation during deformation conversely comparison of the initial and final orientation of passive strain markers placed in close proximity to these inclusions suggested a non coaxial deformation environment rather than a coaxial environment the apparent lack of rotation of these inclusions resulted from a reversal in their rotation sense during deformation of the system the reversal in rotation sense of these inclusions was the result of time varying levels of spin and shear induced vorticity during deformation fold like structures were produced in the passive markers this allowed the flow to be used to examine possible relationships that may form between porphyroblasts and layers passively folded during inhomogeneous time dependent flow the inclusion passive marker relationships across the folds suggest that relationships between porphyroblasts with inclusion trails and foliations in rock layers passively folded by an inhomogeneous time dependent flow may contain similar relationships to folds that formed by layer buckling knowledge of the level of passive behaviour of the layers and boundary conditions during this type of deformation is essential for utilizing porphyroblast foliation geometry to evaluate deformation history

temporal variability of microparticle properties in polar ice sheets abstract four recent ice core studies reveal a consistently recurring temporal correlation between increased microparticle concentrations and lower global temperatures more negative 13 o 16 o ratios a continuous 900 year record of particle deposition from the 101 m south pole core was obtained by analyzing 6218 samples the concentration of insoluble particles with diameters 0 63 m increases substantially between a d 1450 and 1850 a period of slightly reduced global temperatures encompassing the latest neoglacial or little ice age there is evidence suggesting that some of the additional material may be volcanic although further substantiation is required the microparticle analyses of selected sections from three deep cores coupled with the respective 18 o measurements reveal that in all three cores the last glacial or late wisconsin ice contained great quantities of microparticles the ratio of the average microparticle concentration in wisconsin sections to that in holocene sections is 6 for the 905 m dome c antarctica core 3 for the 2164 m byrd station antarctica core and 12 for the 1387 m camp century greenland core microparticle increases of this magnitude can not be accounted for merely by a reduction in net accumulation these data suggest that the global atmosphere was heavily laden with suspended particulates near the end of the last major glaciation

slip system domains i plane strain kinematics of arrays of coherent bands with twinned fibre orientations abstract slip system in rocks often occupy domains each of uniform slip system orientation examples are conjugate faults shear zones folded bedding and crystal lattices domainal behaviour in plane strain is modelled as simple shearing along inextensible fibres an array of alternating band domains with coherent boundaries can undergo a uniform bulk strain with local perturbations in the domains if 1 domain boundaries are planes of mirror symmetry with respect to fibre attitude and 2 domains have alternating fractional widths a and 1 a motion in the models is shown to be a combination of three independent modes plus a bulk rigid motion during mode 1 motion domain boundaries stretch but do not migrate during mode 2 they do not stretch but migrate by lateral translation during mode 3 they migrate by translation and rotation orientation distribution functions odfs are defined by assigning frequencies a and 1 a to orientations and changes in are shown to be due to mode 1 alone changes in a to mode 2 alone mode 3 has no effect on an odf combinations of modes 1 2 and 3 can be used to accommodate an imposed bulk motion two examples are discussed a bulk simple shear and a rigid motion large amounts of simple shear are possible if fibres are on average parallel to the imposed shear direction if modes 1 and 2 are operative the resulting odf has a maximum peak close to the shear direction this may explain the asymmetry of preferred lattice orientations and the occurrence of unique fault sets in rocks that have undergone a progressive simple shear

a new simple shear deformation apparatus for rocks and soils abstract we present a new design for a simple shear type deformation apparatus which has the capacity to deform medium strength anisotropic rocks as well as soils and similar strength materials the special feature of the design is that the deformation is achieved by the application of a particular set of boundary displacements so that a specimen is constrained to deform by a progressive simple shearing history these boundary displacements are applied through three pairs of steel platens each of which are in contact with opposite sides of the specimen which is initially a right rectangular prism one pair of platens is fixed so that deformations are plane strain a second pair of platens remains horizontal but they are free to slide against the reaction frame in the shear direction while at the same time they can apply a vertical normal force through hydraulic actuators the third pair of platens are vertical faces cut longitudinally through two steel shafts so that the shaft axes lie horizontally through the centre of the faces shear is applied by rotation of the two shafts so that the two vertical end faces of the specimen are rotated about the shaft axes this rotation means that horizontal planes in the specimen remain horizontal and suffer no shape change while vertical planes normal to the shaft axes remain vertical but suffer a shearing type change in shape the combination of these boundary displacements is a progressive simple shearing of the specimen we show typical stress strain responses for a number of different material types and discuss the degree of strain homogeneity throughout the specimen examples are presented of the microstructural changes which occur in specimens deformed in the apparatus

geometry and kinematics of recumbent folding and low angle detachment in the pardailhan nappe montagne noire southern french massif central abstract the pardailhan nappe is the uppermost unit of the superimposed variscan recumbent fold nappes in the southern montagne noire thrust belt detailed mapping and structural investigation demonstrates the presence of a welldevel oped upper normal limb a frontal ene wsw oriented major hinge and a predominant overturned limb many kilometres in size in lower palaeozoic non metamorphic sediments finite strain and microstructures related to recumbent folding show maximum elongation and stretching perpendicular to the fold axes consistent with tangential shortening and general south southwestward overthrust tectonics minor internal deformation throughout the fold structure suggests a rigid overturning mechanism and only small amounts of progressive shear during the variscan recumbent folding late early carboniferous post shortening deformation in the nappe is accounted for by subsequent heterogeneous deformation in extensional shear and fault zones the earlier folded and schistose structures were displaced along e w trending low angle normal faults microstructures of the superimposed brittle and ductile deformation in gently s dipping detachment zones indicate southwest to southward hanging wall movements in the uppermost units throughout the lower limb the extensional features show a progressive rotation into a w sw direction and a dextral wrench component along the tectonic and metamorphic discontinuity with underlying metamorphic polyphase fold structures mechanisms and timing of recumbent fold development and subsequent detachment tectonics are discussed in relation to variscan orogenic convergence and late orogenic late carboniferous extension induced by the uplift of metamorphic basement the compressional and subsequent extensional tectonics in the southern montagne noire nappe belt are associated with the evolution of a late variscan metamorphic core complex

characteristics of a kilometer scale high strain zone in the lower continental crust mt hay block central australia abstract a granulite facies high strain zone was studied on capricorn ridge part of the mt hay block granulites in the arunta inlier central australia deformation occurred in these primarily mafic composition granulites at lower crustal conditions 8 kb 800 c at 1740 1690 ma pervasive and consistently oriented foliation striking ssw and dipping steeply and lineations pitching steeply eastward occur within the shear zone the high strain zone is recognized by the presence of sl tectonites parallelism of grain shape fabrics and lithologic boundaries transposition of lithologic boundaries into parallelism with the foliation and the local occurrence of sheath like folds field based fabric mapping uses compositional foliation intensity as a proxy for finite strain to document strain variations within the capricorn ridge high strain zone there is no observed microstructural grain size reduction that corresponds to these strain variations fabric intensity increases from the centers of the major lithologic units towards the contacts 100 m scale strain localization within capricorn ridge occurs adjacent to major lithologic contacts indicating competency contrast during lower crustal deformation

structural signatures and 40ar 39ar geochronology of the indosinian xuefengshan tectonic belt south china block abstract to advance our understanding of the kinematics of the xuefengshan tectonic belt xfstb and the mesozoic tectonics of the south china block scb this paper presents new data and interpretations from our structural studies and thermochronological dating the xfstb is characterized by greenschist facies metamorphism and development of s and s l tectonic fabrics an asymmetric positive flower structural pattern is composed of nw wnw and se ese dipping cleavages faults and shear zones kinematic indicators indicate a dominant top to wnw thrusting with a sinistral strike slip component on the ese dipping shear zones and top to ese back thrusting on the wnw dipping shear zones the quartz c axis orientations of mylonitic rocks exhibit monoclinic point maximum asymmetry indicative of a sinistral shear sense under the a basal gliding condition the timing of the major deformation event has been constrained to the middle triassic to early jurassic 244 195 ma on the basis of 40ar 39ar geochronology and other geological observations the structural characteristics of the xfstb are probably related to an indosinian oblique convergent zone in combination with tectonic wedging and associated back thrusting all above a low angle se dipping basal detachment oblique northwestward and upward movement along the basal detachment was partitioned into the nw wnw directed thrusting se ese directed back thrusting and subsidiary strike slip movement along the ne and nne trending faults and shear zones the xfstb may represent part of a huge structural fan between the yangtze and cathaysian blocks and can be interpreted as a product of the indosinian intracontinental collision involving a weak zone

archimedes revisited a structural test of eclogite emplacement models in the austrian alps high pressure rocks of the eclogite zone tauern window eastern alps formed at 20 kb 600 c uplift was fast without post burial heating extensive near field and far field deformation of the eclogite zone and its surroundings provide evidence for a tectonic uplift mechanism published emplacement models buoyant rise underplating and extension wrench faulting create distinct patterns of crustal deformation and are therefore testable by structural analysis we show that emplacement related deformation and its kinematics are consistent with underplating and extension extension is two phased the first phase may be driven by changes in rate or direction of plate convergence the second phase is due to large scale underplating of continental crust

deformation history of the roanoke recess appalachians usa the evolution of the roanoke recess is controversial because agreement is lacking about the timing and continuity of deformation increments because it may or may not have behaved like an adjacent salient and recess because while many salients have been investigated few recesses have and because the role of blind thrusts is unclear to gain insight into these controversies we estimated shortening directions shortening magnitudes and relative timing in the recess from map scale folds outcrop scale stylolites and grain scale solution structures and twins the key results from combining these new data with previous work are as follows 1 the deformation history around the roanoke recess is most simply described as temporally continuous with deformation migrating northeastward while the primary shortening direction rotated counterclockwise from n directed to almost w directed 2 consequently the roanoke recess did not deform in the symmetrical manner of the adjacent pennsylvania salient nor with the two step history of the kingston recess further to the north in the appalachians 3 the timing and magnitude of shortening increments are sufficient to necessitate a blind thrust under the present surface rocks of the inner recess throughout the deformation history

tephra layers in the byrd station ice core and the dome c ice core antarctica and their climatic importance abstract volcanic glass shards from tephra layers in the byrd station ice core were chemically analyzed by electron microprobe tephra in seven layers have similar peralkaline trachyte compositions the tephra are believed to originate from mt takahe on the basis of their chemical similarity to analyzed rocks from mt takahe and because dated rock samples from the volcano are younger than 250 000 years old glass shards from 726 m deep in the dome c ice core which is 2400 km from byrd station are composed of peralkaline trachyte and may have also been derived from mt takahe the tephra could have resulted from eruptions which were triggered by increased ice loading during the late wisconsin glaciation preliminary grain size data suggest the eruptions were only minor and they were unlikely to have instantaneously altered global climate as have explosive eruptions in the tropics nevertheless the effect of this localized volcanic activity upon the antarctic energy budget warrants further investigation

the miocene bending of southwest japan new 39ar 40ar and microtectonic constraints from the nagasaki schists western kyushu an extension of the sanbagawa high pressure belt abstract in the westernmost part of kyushu the nagasaki metamorphics also observed in amakusa consist of oceanic sediments and fragments of ophiolite these rocks underwent a high pressure metamorphism followed by an increase in temperature up to the upper greenschist facies prior to the late cretaceous microtectonic and kinematic analyses indicate a synmetamorphic ductile shear from south to north dating of glaucophane phengite and biotite by 39ar 40ar method suggests that the peak of metamorphism and the related deformation occurred approximately 90 95 ma ago i e cenomanian but a resetting by an oligo miocene tectonic event is also evidenced due to discontinuous exposures the metamorphic rocks of kyushu cannot be continuously traced to the metamorphic belts of honshu and shikoku nonetheless the lithostratigraphy metamorphic environment radiometric data and deformation style strongly support a correlation of the nagasaki metamorphics with the green schist nappe of southwest japan which underwent the late jurassic early cretaceous high pressure sanbagawa metamorphism such a correlation implies that 1 in the amakusa area the nagasaki metamorphics form a window north of a meta olistostrome that belongs to the tanba ryoke zone 2 the trend discrepancy of the stretching lineations between west kyushu and southwest japan is in agreement with a clockwise rotation of the latter with respect to the former assumed to be fixed to eurasia such a bending occurred after paleogene times probably during the opening of the sea of japan

pre eocene synmetamorphic structure in the mindoro romblon palawan area west philippines and implications for the history of southeast asia the structure of the pre eocene rocks considered as the basement of the philippines has been investigated in the mindoro lubang romblon tablas sibuyan and north palawan areas in the former two areas the same pre eocene succession of units is recognized from top to bottom 1 a pre eocene olistostrome 2 an ophiolitic nappe 3 a schistose sequence pelites sandstones basic schists and marbles and 4 a gneissic unit the nature of the contact between the olistostrome and the underlying units is unclear but the ophiolite and the schistose sequence form two thrust sheets of oceanic origin thrust upon the gneissic unit that is considered a part of a continental basement called the west philippines block small scale structures show that the early deformation stage is characterized by a submeridian 0 n40 e lineation formed in greenschist to amphibolite facies conditions during the thrusting kinematic analysis show that the thrusting was from north to south in north palawan metamorphic rocks with similar microtectonic and kinematic characteristics are found they are overlain by a late jurassic olistostrome which is correlated with the olistostromes found in calamian north mindoro carabao and buruanga peninsula north panay the microstructural features and the presence of the olistostrome suggest that the north palawan mindoro tablas romblon sibuyan and carabao islands belong to the same north palawan block of hamilton 1979 which is a continental fragment rifted from asia in cenozoic times it is assumed that the western panay and zamboanga areas which are characterized by mesozoic ophiolites and metamorphic rocks also belong to the north palawan block all these islands experienced to some extent the same mesozoic geohistory the south verging thrusting is interpreted as the result of an oblique collision of the west philippines block with asia the contemporaneous left lateral strike slip faulting and the calc alkaline magmatism widespread along the chinese margin are also included in the geodynamic model

megathrust earthquakes can nucleate in the forearc mantle evidence from the 2004 sumatra event current models predict that the seismogenic zone along subduction thrusts where the largest earthquakes nucleate and propagate does not extend to the forearc mantle below the crust of the upper plate stable sliding conditions have been shown to prevail there particularly along several circum pacific margins that underwent great megathrust earthquakes mw 8 5 during the twentieth century based on geophysical investigation we show that the great 2004 sumatra andaman earthquake mw 9 9 3 contradicts these models not only did it propagate downdip along the interface between the forearc mantle and the subducting plate but it actually nucleated along this reportedly aseismic part of the interplate contact petrological models can therefore underestimate the downdip extent of rupture zones to be expected in megathrust earthquakes and need to be revised to account for this observation albeit unusual