can mesoscale models reproduce meandering motions the influence of meandering flow on dispersion of pollutants is frequently underrepresented in dispersion models in terms of measurements meandering is primarily associated with time scales between the turbulence and the applied averaging time which is usually 1 h the related spatial scales thus range roughly from 10 2 to 10 4 m referred to here as submesoscales as the state of the art mesoscale models should be capable of reproducing flow features on scales larger than the turbulence and as the meandering generating mechanisms are not fully understood yet it is useful to examine if the mesoscale models can reproduce meandering for that purpose the wrf chem model at 1 3 km horizontal resolution is used to simulate a weak wind night during the cases99 experiment the measurements are used for detailed model verification the model with its typical set up fails to reproduce the variability at submesoscales and the locus of the under representation is traced to too strong horizontal diffusion reducing or removing the model diffusion allows the appearance of the submeso variability whose spectral properties and the resulting plume behaviour agree well with the measurements the linear correlation between the simulations with reproduced variability and the measurements is low as is the case between two simulations with only slightly different set up the conclusion is that mesoscale models are able to reproduce the strength of variability and the effects of meandering but only with reduced or removed horizontal diffusion the question arises whether it is possible to obtain a linear correlation i e to correctly reproduce individual modes at these scales at all copyright c 2010 royal meteorological society

climatological features of the weakly and very stably stratified nocturnal boundary layers part iii the structure of meteorological state variables in persistent regime nights and across regime transitions abstractthe evolution of profiles of meteorological state variables during nights with and without transitions in the nocturnal stably stratified boundary layer sbl between weakly stable wsbl a

problem of folding in ductile shear zones a theoretical and experimental investigation the paper describes micro scale folds within a narrow ductile shear zone of the peninsular gneissic complex south india the characteristics of the folds indicate that they have formed by buckling on the mylonitic foliation parallel to the c fabric this raises the question of how a buckling instability could develop on the mylonitic foliation as there can be no overall shortening along the shear direction on the basis of natural observations we show that mylonitization involves sericitization locally along the c fabrics forming discrete mechanically weak zones which perturb the homogeneous shear stress field in their neighborhood and induce shortening along the bulk shear direction leading to buckling instabilities on the mylonitic foliation the weak zone model is supported with results obtained from physical experiments theoretical analysis shows that the weak bodies with large length to thickness ratios perturb the shear stress field in the shear zone significantly developing compressive stresses along the bulk shear direction required for buckle instabilities to occur on the mylonitic foliation

mechanics of kink bands during torsion deformation of muscovite aggregate abstract the growth geometry and bulk mechanical behavior of grain scale kink bands were investigated during layer parallel non coaxial deformation torsion of synthetic polycrystalline aggregates of muscovite at constant displacement rate 3 10 4 s 1 and various confining pressures cp 50 300 mpa temperatures t 300 800 c and finite shear strains 0 2 5 0 the kink instabilities were observed during elastic to plastic transition yield at finite shear strain of ca 0 2 the shear stress required to form the kinks is a function of pressure and temperature and range from ca 20 to 90 mpa within the experimental conditions the kink bands formed in non coaxial torsion tests are asymmetric involve strain partitioning show complex microstructures with increased deformation and have a limited lifetime as the structure is destroyed at ca 5 these results suggest a domain of pressure and temperature conditions where kink band structures should be common results obtained from torsion experiments are compared to those of layer parallel axial compression conducted with the same displacement rate at 600 c and 300 mpa for 5 10 and 17 bulk shortening combining microstructures viewed on surfaces parallel and perpendicular to the torsion plane a 3d geometrical model is constructed to discuss the kink mechanism the microstructural evolution and the mechanical behavior

shear zone structures in the oygarden area west norway abstract investigation of shear related sheath like folds from blastomylonitic gneisses in the oygarden complex norway shows that the folds have not initiated with fold axes systematically normal to or with another fixed angle to the lineation their short limbs do however pass from a period of thickening to final thinning as the folds close and the short limbs become inverted the formation of the folds appears to be controlled by local geometries within the shear zone and we suggest three fold generating mechanisms in one the mylonitic foliation curves ahead of a tectonic lens and starts to fold and in another mesoscopic shear bands with normal fault geometries cut subplanar mylonites and folds are generated by the accretion of material in the evolving gap between the hangingwall and the footwall the third mechanism involves perturbation of the main foliation by slip along an inclined s foliation so that shear folds may develop all the mechanisms involve a rotation of the mylonitic foliation into the compressional field of the instantaneous strain ellipse

a new model for the formation of a spaced crenulation shear band cleavage in the dalradian rocks of the tay nappe sw highlands scotland abstract the main conclusion of this study is that non coaxial strain acting parallel to a flat lying d 1 spaced cleavage was responsible for the formation of the d 2 spaced crenulation shear band cleavage in dalradian rocks of neoproterozoic lower ordovician age in the sw highlands scotland the cm dm scale d 2 microlithons are asymmetric have a geometrically distinctive nose and tail and show a thickened central portion resulting from back rotation of the constituent d 1 microlithons the current terminology used to describe crenulation cleavages is reviewed and updated aided by exceptional 3d exposures it is shown how embryonic d 2 flexural slip folds developed into a spaced cleavage comprising fold pair domains wrapped by anastomosing cleavage seams the bulk strain was partitioned into low strain domains separated by zones of high non coaxial strain this new model provides a template for determining the sense of shear in both low strain situations and in ductile higher strain zones where other indicators such as shear folds give ambiguous results analogous structures include tectonic lozenges in shear zones and flexural slip duplexes disputes over the sense and direction of shear during emplacement of the tay nappe and the apparently intractable conflict between minor fold asymmetry and shear sense appear to be resolved

horizontal meandering as a distinctive feature of the stable boundary layer abstractoscillations in the horizontal components of the wind velocity associated with oscillations in air temperature during low wind speed episodes are ubiquitous in the stable boundary layer and

progressive development of structures in a ductile shear zone in the singhbhum shear zone of eastern india successive generations of folds grew in response to a progressive ductile shearing during this deformation a mylonitic foliation was initiated and was repeatedly transposed the majority of fold hinges were formed in an arcuate manner at low angles to the y axis in an e w trending subhorizontal position and major segments of the fold hinges were then rotated towards the down dip northerly plunging x axis the striping and intersection lineations were rotated in the same manner the down dip mylonitic lineation is a composite structure represented by rotated early lineations and newly superimposed stretching lineations the consistent asymmetry of the folds the angular relations between c and s surfaces and the evidence of two dimensional boudinage indicate that the deformation was non coaxial but with a flattening type of strain with 1 2 the degree of non coaxiality varied both in space and time from the progressive development of mesoscopic structures it is concluded that the 2 3 km wide belt of ductile shear gave rise to successive anastomosing shear zones of mesoscopic scale when a new set of shear lenses was superimposed on already sheared rocks the preexisting foliation generally lay at a low angle to the lenses no new folds developed where the acute angle was sympathetic to the sense of shear displacements where the acute angle was counter to the sense of shear the pre existing foliation lying in the instantaneous shortening field was deformed into a set of asymmetric folds

structural analysis of sheath folds with horizontal x axes northeast canada abstract early proterozoic supracrustal rocks occur below a thick nappe of archaean basement gneiss in the melville peninsula where sheath folds are exposed in a wide zone of middle proterozoic dynamothermal metamorphism outcrop patterns of truncated isoclinal sheath folds resemble cylindrical folds except in relatively small areas around the paraboloidal caps bulk extension axes are parallel to strike in the belt as shown by isoclinal sheath folds with horizontal central axes x axes as well as similarly aligned mullion structure and rotated scapolite prisms extension axes converge from northeast to southwest in the apparent flow direction

book reviewthe techniques of modern structural geology vol 1 strain analysis j g ramsay and m i huber academic press london 1983 xiii 307 pp us 55 00 28 00 hardcover

marine mollusc exploitation in mediterranean prehistory an overview abstract marine molluscs have been recovered from sites around the mediterranean sea dating as far back as the lower palaeolithic when hominins might have started consuming them ca 300 ka during the middle palaeolithic and the early upper palaeolithic humans homo neanderthalensis and homo sapiens ate molluscs at many sites across the mediterranean at least as early as the last interglacial although the scale of this exploitation is still unclear due to biases produced in the coastal archaeological record by late glacial and post glacial sea level rise the exploitation of marine molluscs apparently increased in the late glacial and early holocene when humans collected them in relatively large quantities and from all available ecosystems the consumption of shellfish and of other small animals aquatic and continental probably contributed to the success of the flexible and opportunistic subsistence strategies adopted by mediterranean hunter gatherers for much of prehistory this is particularly evident in later foraging economic systems i e late upper palaeolithic and mesolithic in which coastal resources probably acted as buffers against the negative outcomes of environmental and anthropogenic impacts on available resources

palaeoenvironmental and cultural dynamics of the coast of malaga andalusia spain during the upper pleistocene and early holocene abstract the impact of late upper pleistocene climate change in the western mediterranean region has been mainly documented through marine records archaeological and geomorphological continental records now available for the coast of malaga complement these records for the second part of the last major glacial episode and the early stages of the holocene this paper provides an overview of the archaeological chronological and palaeoenvironmental data from the end of the middle palaeolithic period to the epipalaeolithic sequences from the two major sites nerja and bajondillo indicate a mosaic type response of ecosystems to the rapidly shifting conditions of the last glacial episode terrestrial mammals for example show no major variations from present day communities plant remains in contrast demonstrates the existence of localised refuge areas for species that would not otherwise have survived in the more widely prevailing climatic conditions of the time whereas remains of fish and secondarily birds demonstrate the existence of communities without any present day analogues combining mediterranean and boreal i e northern atlantic taxa from an archaeological standpoint the major cultural shift is the onset of marine fishing beginning in the solutrean this coincided with the end of the last glacial maximum lgm episode the faunal record also testifies to the rising importance of marine resources more generally although the data have not been used systematically to test the validity of the broad spectrum revolution bsr hypothesis the hints for it in the area seem compelling from the start of the solutrean onwards

multi scale analysis of proterozoic shear zones an integrated structural and geophysical study abstract structural mapping of poorly exposed shear zone outcrops is integrated with the analysis of aeromagnetic and bouguer gravity data to develop a multi scale kinematic and relative overprinting chronology for the palaeoproterozoic tallacootra shear zone australia d 2 mylonitic fabrics at outcrop record kimban aged ca 1730 1690 ma n s shortening and correlate with sz 1 movements overprinting d 3 sinistral shear zones record the partitioning of near ideal simple shear and initiated riedel to regional scale sz 2 strike slip on the tallacootra shear zone sz 2 previously undocumented ne sw extension led to the emplacement of aplite dykes into the shear zone and can be correlated to the ca 1595 1575 ma hiltaba magmatic event d 4 dextral transpression during the ca 1470 1450 ma coorabie orogeny reactivated the tallacootra shear zone sz 2 r4 exhuming lower crust of the northwestern fowler domain within a positive flower structure this latest shear zone movement is related to a system of west dipping shear zones that penetrate the crust and sole into a lithospheric detachment indicating wholesale crustal shortening these methods demonstrate the value of integrating multi scale structural analyses for the study of shear zones with limited exposure

progressive folding and foliation development in a sheared coticule bearing phyllite abstract an evolutionary sequence of fold and foliation development interpreted to be the result of a single progressive deformation is seen in exposures of strongly sheared phyllite and coticule 10 km south of the e w trending chedabucto fault in the meguma terrane of nova scotia canada transposition sensu sander at mesoscopic and microscopic scales is fundamental to this development as are fold hinge rotation and migration the transposition process is cyclic with folds of layering and foliation developing rotating and being refolded fold hinges and axial surfaces repeatedly tend towards stable end orientations but do not reach them due to the cyclic transposition process the foliation is a steady state feature continually reconstituted by microscale transposition and dynamic recrystallization several important consequences of these contemporaneous processes are 1 geometrical relationships between folds and foliation are variable in the same outcrop even though both developed synchronously and many folds have the geometrical relationships of cleavage transected folds 2 the foliation is transient in orientation and therefore cannot track the xy principal plane of total finite strain and 3 fold hinge migration may be a common process especially in deformations involving a large component of simple shearing the observed relationships may be applicable to study of fold and foliation development in orogenic belts in general

the structural evolution of sheath folds a case study from cap de creus abstract it has long been recognised that within zones of intense non coaxial deformation fold hinges may rotate progressively towards the transport direction ultimately resulting in highly curvilinear sheath folds however there is a surprising lack of detailed and systematic field analysis of such evolving sheath folds this case study therefore focuses on the sequential development of cm scale curvilinear folds in the greenschist facies el llimac shear zone cap de creus spain this simple shear dominated dextral shear zone displays superb three dimensional exposures of sheath folds defined by mylonitic quartz bands within phyllonite increasing amounts of fold hinge curvature are marked by hinge segments rotating into sub parallelism with the mineral lineation lm whilst the acute angle between the axial planar hinge girdle and foliation also displays a sequential reduction although lm bisects the noses of sheath folds it is also clearly folded and wrapped around the sheath hinges lm typically preserves a larger angle with the fold hinge on the lower limb l compared to the upper u limb l u suggesting that lm failed to achieve a steady orientation on the lower limb adjacent sheath fold hinges forming fold pairs may display the same sense of hinge arcing to define synthetic curvature or alternatively opposing directions of antithetic curvature such patterns reflect original buckle fold geometries coupled with the direction of shearing the ratio of long short fold limbs decreases with increasing hinge curvilinearity indicating sheath folds developed via stretching of the short limb rather than migrating or rolling hinge models this study unequivocally demonstrates that both hinges of fold pairs become curvilinear with sheaths closing in the transport direction recording greater hinge line curvilinearity compared to adjacent return hinges this may provide a useful guide to bulk shear sense

plume meander and dispersion in a stable boundary layer 1 continuous lidar measurements of elevated plume dispersion and corresponding micrometeorology data are analyzed to establish the relationship between plume behavior and nocturnal boundary layer dynamics contrasting nights of data from the jornada field campaign in the new mexico desert are analyzed the aerosol lidar measurements were used to separate the plume diffusion plume spread from plume meander displacement mutiresolution decomposition was used to separate the turbulence scale 90 s durations of turbulent kinetic energy stationarity and the wind steadiness were used to characterize the local scale and submesoscale turbulence plume meander driven by submesoscale wind motions was responsible for most of the total horizontal plume dispersion in weak and variable winds and strong stability this proportion was reduced in high winds i e 4 m s 1 weakly stable conditions but remained the dominant dispersion mechanism the remainder of the plume dispersion in all cases was accounted for by internal spread of the plume which is a small eddy diffusion process driven by turbulence turbulence stationarity and the wind steadiness are demonstrated to be closely related to plume diffusion and plume meander respectively

review on symmetric structures in ductile shear zones symmetric structures in ductile shear zones range widely in shapes and geneses matrix rheology its flow pattern its competency contrast with the clast degree of slip of the clast shear intensity and its variation across shear zone and deformation temperature and degree of confinement of clast in shear zones affects independently the degree of symmetry of objects kinematic vorticity number is one of the parameters that govern tail geometry across clasts for example symmetric and nearly straight tails develop if the clast matrix system underwent dominantly a pure shear compression prolonged deformation and concomitant recrystallization can significantly change the degree of symmetry of clasts angular relation between two shear zones or between a shear zone and anisotropy determines fundamentally the degree of symmetry of lozenges symmetry of boudinaged clasts too depends on competency contrast between the matrix and clast in some cases and on the degrees of slip of inter boudin surfaces and pure shear parasitic folds and post tectonic veins are usually symmetric

kilometre scale sheath fold at mattmark and implications for transport direction in the alps folds were the first tectonic features of rocks to be studied and as such are taken as a reference for the interpretation of other structures intuitively fold axes were assumed to be subperpendicular to the direction of transport nevertheless many studies of metamorphic belts showing intense ductile deformation describe folds with axes close to the transport direction in particular sheath folds1 9 are highly curvilinear folds elongated parallel to the direction of transport we discuss here a spectacular large sheath fold situated in a crustal shear zone in the monte rosa nappe swiss alps our analysis implies that both the geometry and significance of folds in the internal alps must be re examined we further demonstrate the existence of crustal ductile shear zones in an area of the alps where previously emphasis was generally placed on fold nappes the movements on these shear zones is often tens of kilometres

when shearing is a cause of folding abstract numerous publications on shearing as a cause of folding do not refute the idea of buckling being the main process responsible for the formation of fold structures deformations of other types may either produce conditions for layer parallel shortening needed for buckling or modify fold shapes but do not generate new fold structures on any scale the origin of similar folds commonly considered to be a result of inhomogeneous shearing across layering may be explained by buckling of a multilayer where layers have uniform favourable rheological properties tightening and amplification of folds near fault surfaces is not necessarily a result of shearing caused by friction at fault surfaces on the contrary in these cases faulting is a result of strain localization during folding recumbent isoclinal folds so common in metamorphic rocks originate mainly by buckling of subvertical planar structures intrafolial folds are usually very flattened relics of former folds the idea of sheath folds being produced mostly by shearing is not confirmed by the available geological data sheath folds that were not produced by shearing are rather common more likely they are formed by constriction or flattening of folds with curved hinges the latter are a result either of fold interference or of the constriction in the layering plane

review of wave turbulence interactions in the stable atmospheric boundary layer flow in a stably stratified environment is characterized by anisotropic and intermittent turbulence and wavelike motions of varying amplitudes and periods understanding turbulence intermittency and wave turbulence interactions in a stably stratified flow remains a challenging issue in geosciences including planetary atmospheres and oceans the stable atmospheric boundary layer sabl commonly occurs when the ground surface is cooled by longwave radiation emission such as at night over land surfaces or even daytime over snow and ice surfaces and when warm air is advected over cold surfaces intermittent turbulence intensification in the sabl impacts human activities and weather variability yet it cannot be generated in state of the art numerical forecast models this failure is mainly due to a lack of understanding of the physical mechanisms for seemingly random turbulence generation in a stably stratified flow in which wave turbulence interaction is a potential mechanism for turbulence intermittency a workshop on wave turbulence interactions in the sabl addressed the current understanding and challenges of wave turbulence interactions and the role of wavelike motions in contributing to anisotropic and intermittent turbulence from the perspectives of theory observations and numerical parameterization there have been a number of reviews on waves and a few on turbulence in stably stratified flows but not much on wave turbulence interactions this review focuses on the nocturnal sabl however the discussions here on intermittent turbulence and wave turbulence interactions in stably stratified flows underscore important issues in stably stratified geophysical dynamics in general

information from folds a review abstract folds are spectacular geological structures that are seen in layered rock on many different scales to mark 30 years of the journal of structural geology we review the information that can be gained from studies of folds in theory experiment and nature we first review theoretical considerations and modeling from classical approaches to current developments the subject is dominated by single layer fold theory with the assumption of perfect layer parallel shortening but we also review multilayer fold theory and modeling and folding of layers that are oblique to principal stresses and strains this work demonstrates that viscosity ratio degree of non linearity of the flow law anisotropy and the thickness and spacing distribution of layers of different competence are all important in determining the nature and strength of the folding instability theory and modeling provide the basis for obtaining rheological information from natural folds through analysis of wavelength thickness ratios of single layer folds and fold shapes they also provide a basis for estimating the bulk strain from folded layers information about folding mechanisms can be obtained by analysis of cleavage and fabric patterns in folded rocks and the history of deformation can be revealed by understanding how asymmetry can develop in folds by how folds develop in shear zones and how folds develop in more complex three dimensional deformations

intermittent turbulence in the stable boundary layer over land part iii a classification for observations during cases 99 abstract in this paper a classification of stable boundary layer regimes is presented based on observations of near surface turbulence during the cooperative atmosphere surface exchange study 1999 cases 99 it is found that the different nights can be divided into three subclasses a turbulent regime an intermittent regime and a radiative regime which confirms the findings of two companion papers that use a simplified theoretical model it is noted that its simpliflied structure limits the model generality to near surface flows the papers predict the occurrence of stable boundary layer regimes in terms of external forcing parameters such as the effective pressure gradient and radiative forcing the classification in the present work supports these predictions and shows that the predictions are robust in a qualitative sense as such it is for example shown that intermittent turbulence is most likely to occur in clear sky conditions with a moderately weak effective pressure gradient the quantit

multivariate analysis of remains of molluscan foods consumed by latest pleistocene and holocene humans in nerja cave malaga spain abstract nerja cave is a karstic cavity used by humans from late paleolithic to post chalcolithic times remains of molluscan foods in the uppermost pleistocene and holocene sediments were studied with cluster analysis and principal components analysis in bothqandrmodes the results from cluster analysis distinguished interval groups mainly in accordance with chronology and distinguished assemblages of species mainly according to habitat significant changes in the shellfish diet through time were revealed in the late magdalenian most molluscs consumed consisted of pulmonate gastropods and species from sandy sea bottoms the epipaleolithic diet was more varied and included species from rocky shorelines from the neolithic onward most molluscs consumed were from rocky shorelines from the principal components analysis inqmode the first factor reflected mainly changes in the predominant capture environment probably because of major paleogeographic changes the second factor may reflect selective capture along rocky coastlines during certain times the third factor correlated well with the sea surface temperature curve in the western mediterranean alboran sea during the late quaternary

turbulence in the nocturnal boundary layer with light and variable winds turbulence quantities are analyzed from nine months of data collected on the floor of a valley where nocturnal cold pools are frequent often the speed of the vectoraveraged wind over the night is less than 0 5 m s 1 near calm winds with no preference for wind direction the quantity of such near calm data is sufficiently large to allow new types of analyses as well as the opportunity to examine statistics of the previously ignored near neutral subclass of near calm winds for near calm weak winds and strong stratification the turbulence can be difficult to isolate from wave like motions and more complex small scale structures the smallest scale perturbations on time scales less than 5 s behave most like turbulence larger scale perturbations are characterized by very weak vertical velocity fluctuations and large temperature fluctuations but lead to systematic downward heat flux after extensive averaging for near calm nocturnal conditions significant turbulence is mainly generated by short term minutes accelerations of unknown origin the turbulence between such infrequent mixing events is extremely weak but not zero while the turbulence in the events approximately follows similarity theory the extremely weak turbulence scales neither with stratification nor bulk shear and its inferred vertical length scale is small compared to the distance from the ground even at the 2 m level copyright c

breaking the waves human use of marine bivalves in a microtidal range coast during the upper pleistocene and the early holocene vestibulo chamber nerja cave malaga southern spain abstract this paper presents the results obtained from the study of the bivalves recovered during the archaeological excavations in the vestibulo chamber of nerja cave malaga southern spain carried out by professor francisco jorda cerda between 1983 and 1987 these excavations recovered the archaeological record of the sequence from the gravettian to the neolithic the mollusc remains from the vestibulo chamber of nerja cave record constitute an extraordinary collection composed of more than 136000 specimens which correspond to more than 78 kg in this work only marine bivalves were studied the bivalve remains are more than 124000 specimens corresponding to more than 65 kg from 31 taxa more than 115000 of these specimens 59 kg are derived from the shell midden dated to gs 1 the archaeological record of nerja cave is distinguished by the abundant presence of human provided marine and continental molluscs with a high presence of bivalves marine bivalves increased clearly from the lgm to the mid holocene and the human inhabitants of the cave accumulated an important shell midden in the contact between mis 2 and mis 1

variability of the western mediterranean sea surface temperature during the last 25 000 years and its connection with the northern hemisphere climatic changes sea surface temperature sst profiles over the last 25 kyr derived from alkenone measurements are studied in four cores from a w e latitudinal transect encompassing the gulf of cadiz atlantic ocean the alboran sea and the southern tyrrhenian sea western mediterranean the results document the sensitivity of the mediterranean region to the short climatic changes of the north atlantic ocean particularly those involving the latitudinal position of the polar front the amplitude of the sst oscillations increases toward the tyrrhenian sea indicating an amplification effect of the atlantic signal by the climatic regime of the mediterranean region all studied cores show a shorter cooling phase 700 years for the younger dryas yd than that observed in the north atlantic region 1200 years this time diachroneity is related to an intra yd climatic change documented in the european continent minor oscillations in the southward displacement of the north atlantic polar front may also have driven this early warming in the studied area during the holocene a regional diachroneity propagating west to east is observed for the sst maxima 11 5 10 2 kyr b p in the gulf of cadiz 10 9 kyr b p in the alboran sea and 8 9 8 4 kyr b p in the thyrrenian sea a general cooling trend from these sst maxima to present day is observed during this stage which is marked by short cooling oscillations with a periodicity of 730 40 years and its harmonics

folding in high grade rocks due to back rotation between shear zones abstract folds with a sense of asymmetry opposite to the bulk shear sense may form in high grade rocks due to back rotation between ductile shear zones layers back rotated into the shortening field can undergo additional buckle folding with progressive deformation shear zones and domains of back rotated foliation between shears rotate towards the x y flattening plane of the finite strain ellipsoid in high grade gneiss the migration of melt into shear zones may facilitate displacement along them and accentuate back rotation of material between shear zones folding during back rotation occurs when the spacing between shear zones does not increase sufficiently to accommodate the length of back rotated layers or between non parallel shear zones folds formed by back rotation between shear zones commonly have pegmatites sub parallel to their axial planes thickened overturned limbs and occur in localised packages associated shear zones have the same sense of shear on both attenuated limbs of folds formed by back rotation examples are given for folds between transcurrent and normal ductile shear zones in the albany mobile belt and leeuwin complex western australia and the dharwar craton india

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

structural analysis of progressive deformation within complex transcurrent shear zone systems southern narragansett basin rhode island abstract complex progressive ductile deformation on dutch island narragansett basin rhode island is localized along a system of non parallel intersecting shear zones with opposite senses of strike and oblique slip motion the structural intensity and complexity of this area can be attributed in part to the proximity of nne ne and ene trending pre existing basement faults bounding early horsts and grabens reactivation of these faults caused the formation of shear zones within the overlying metasediments structural superposition of non coaxial mesoscopic folds and crenulation cleavages formed as a result of progressive movement along these shear zones provide unusual and accurate kinematic indicators that track movement along individual zones through time sinistral motion on nne trending zones preceded dextral motion on ne trending zones dextral oblique slip motion on ene trending zones followed deformation became increasingly brittle with time the deformation is the result of two transcurrent shear systems with opposite senses of motion that formed adjacent to the north american and african plate boundary after plate collision

on the turbulence structure of deep katabatic flows on a gentle mesoscale slope a comprehensive analysis of the turbulence structure of relatively deep midlatitude katabatic flows with jet maxima between 20 and 50 m developing over a gentle 1 mesoscale slope with a long fetch upstream of the meteor crater in arizona is presented the turbulence structure of flow below the katabatic jet maximum shows many similarities with the turbulence structure of shallower katabatic flows with decreasing turbulence fluxes with height and almost constant turbulent prandtl number still stark differences occur above the jet maximum where turbulence is suppressed by strong stability is anisotropic and there is a large sub mesoscale contribution to the flux detecting the stable boundary layer top depends on the method used flux vs anisotropy profiles but both methods are highly correlated the top of the stable boundary layer however mostly deviates from the jet maximum height or the top of the near surface inversion the flat terrain formulations for the boundary layer height correlate well with the detected top of the stable boundary layer if the near surface and not the background stratification is used in their formulations however they mostly largely overestimate this boundary layer height the difference from flat terrain boundary layers is also shown through the dependence of size of the dominant eddy with height in katabatic flows the eddy size is semi constant with height throughout the stable boundary layer depth whereas in flat terrain eddy size varies significantly with height flux gradient and flux variance relationships show that turbulence data from different stable boundary layer scaling regimes collapse on top of each other showing that the dominant dependence is not on the scaling regime but on the local stability

an apparatus to experimentally model the dynamics of ductile shear zones abstract we present a ring shear apparatus designed to deform soft ductile rock analogues to arbitraily high shear strains in simple shear in experiments attempting to model processes that occur in natural ductile shear zones the sintered specimen is deformed between two unsupported cylinders by two rotating grips under a normal and shear stress up to 5 mpa and at temperatures up to 600 k first results of experiments with octachloropropane ocp c 3 cl 8 and camphor c 10 h 16 o are presented experiments with pure ocp samples show that a steady state strain rate is achieved at a shear strain of around 4 when a steady state grain shape and crystallographic preferred orientation is established mechanical properties compare well with those of cylindrical samples deformed in triaxial compression shear localisation is relatively minor samples of pure camphor on the other hand show very strong shear localisation behaviour and mechanical properties which do not compare well with those of cylindrical samples deformed in triaxial compression experiments with two phase samples ocp containing stronger camphor inclusions show an initial softening of the composite followed by hardening this is associated with the development of a foliation defined by camphor inclusions that stretched to lenses and layers and the subsequent folding of this foliation at shear strains above 50 a steady state strain rate is not reached even at strains of 100 the experiments produce results closely resembling the kinematics observed in natural shear zones and give a first look into the complex changes in mechanical properties which occur at very high shear strains they show how this technique in conjunction with transparent deformation cells can be used to study both microstructural and rheological development during long simple shear deformation histories

mathematical model for folding of layering near rigid objects in shear deformation abstract the asymmetric arrangement of deformed layering around rigid objects in shear zones is among the most reliable criteria for inferring shear sense in rock a mathematical model which simulates shear deformation of a ductile medium containing a rigid inclusion gives insight into the genesis of this type of shear sense indicator the model which is based on the velocity field solution for viscous flow around a sphere demonstrates that many common strtuctures can arise in a mechanically passive matrix as the model simulates increasing shear strain structures in the matrix pass through distinct evolutionary stages similar results have been obtained in experimental models suggesting that it may be possible to read shear strain magnitude from the geometry of deformed layering near clasts and porphyroclasts in sheared rocks

shear zone related folds folds in ductile shear zones are common structures that have a variety of origins these can be pre existing folds that become modified or folds developed during the shearing event among the syn shearing folds a second subdivision is based on the relative age of the folded surface which can be pre existing or newly formed during the shearing event in each of the three categories final fold geometry and orientation show complex relationships with the kinematic frame the final fold geometry depends on the vorticity within the shear zone the rheology and the initial orientation of the folded surface relative to the kinematic framework it follows that folds are complex structures difficult to use as kinematic indicators however in shear zones where undeformed wall rocks with pre shear structures are accessible and where kinematics can be well established folds can provide a valuable natural means to understand the initiation and evolution of structures under non coaxial regimes we point to the need of discriminating among different plausible categories based on the nature of the folded surface and on the inherent structural features of each category q 2004 elsevier ltd all rights reserved