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

interaction between strike slip and thrust shear deformation of the bullbreen group central western spitsbergen field mapping and strain measurement data are used to infer a deformation history for synorogenic subgreenschist facies sedimentary rocks of the ordovician bullbreen group in central western spitsbergen evidence for true extension parallel to fold axes and comparison of incremental strains preserved by fiber filled extension veins with numerical deformation models suggest that strike slip shear was a significant component in what was generally a thrust shear deformation regime initial dextral strike slip shear parallel to the fault controlled bullbreen sedimentary basin subsequently decreased in importance relative to thrusting perpendicular to the basin margin although the presumed caledonian aged dextral strike slip motion described here may have been a local phenomenon it is difficult to reconcile with existing models of n s orientated large scale sinistral strike slip in western spitsbergen

dissolution solution transfer diffusion versus fluid flow and volume loss during deformation metamorphism dissolution and solution transfer during deformation metamorphism are controlled by the partitioning of deformation into progressive shearing and shortening components progressive shearing is readily accommodated by slip on the planar crystal structure of phyllosilicates and graphite without accumulating dislocation density gradients across grain boundaries progressive shortening is accommodated by the cores of most other minerals including sulphides these minerals develop strain and hence dislocation density gradients on their rims due to progressive shearing along grain boundaries these gradients are particularly large when the mineral abuts phyllosilicate or graphite the resulting chemical potential gradients between the core and rim drive dissolution causing removal of the highly strained grain margins removal of dissolved material by solution transfer is aided by the geometry of shearing of phyllosilicates and graphite around other grains in an active anastomosing foliation interlayers and interfaces on boundaries lying at a low angle to the direction of shearing and oriented relative to the sense of shear such that they can open gape by small amounts water present in these interlayer spaces becomes destructured considerably enhancing diffusion rates along the foliation penetrative volume loss especially in deforming metamorphosing pelitic rocks is large at all metamorphic grades increasing and becoming more penetrative with depth to at least the transition into granulite and eclogite facies transference of material by fluid flow from deep to high levels in the earth s crust is precluded because thousands to tens of thousands of rock volumes of fluid are required necessitating continual recirculation of fluid from shallow to deep crustal levels in one large or several small sets of cells unless some extremely large scale form of fluid channelling is possible reassessment of diffusion mechanisms and hence rates during deformation and pervasive foliation generation in large volumes of rock where fluid channeling cannot provide enough fluid indicates that diffusion can proceed with sufficient rapidity that massive recirculation of fluid is no longer required the amount of fluid can be reduced sufficiently to allow large volume losses by a one way flow of fluid to the earth s surface in deforming metamorphosing environments where the fluid pressure equals or exceeds the hydrostatic pressure deformation partitioning controlled dissolution progressively changes the bulk chemistry of a rock containing phyllosilicates or graphite during deformation metamorphism because matrix minerals other than phyllosilicates and graphite are preferentially removed the large size of porphyroblasts if present tends to preserve them from dissolution hence the bulk chemistry operative during subsequent porphyroblast growth can have changed considerably from that operative when the first porphyroblasts grew in rocks in which bedding is still well preserved

a new stylolite classification scheme to estimate compaction and local permeability variations we modeled the geometrical roughening of bedding parallel mainly layer dominated stylolites in order to understand their structural evolution to present an advanced classification of stylolite shapes and to relate this classification to chemical compaction and permeability variations at stylolites stylolites are rough dissolution seams that develop in sedimentary basins during chemical compaction in the zechstein 2 carbonate units an important lean gas reservoir in the southern permian zechstein basin in germany stylolites influence local fluid flow mineral replacement reactions and hence the permeability of the reservoir our simulations demonstrate that layer dominated stylolites can grow in three distinct stages an initial slow nucleation phase a fast layer pinning phase and a final freezing phase if the layer is completely dissolved during growth dissolution of the pinning layer and thus destruction of the stylolite s compaction tracking capabilities is a function of the background noise in the rock and the dissolution rate of the layer itself low background noise needs a slower dissolving layer for pinning to be successful but produces flatter teeth than higher background noise we present an advanced classification based on our simulations and separate stylolites into four classes 1 rectangular layer type 2 seismogram pinning type 3 suture sharp peak type and 4 simple wave like type rectangular layer type stylolites are the most appropriate for chemical compaction estimates because they grow linearly and record most of the actual compaction up to 40 mm in the zechstein example seismogram pinning type stylolites also provide good tracking capabilities with the largest teeth tracking most of the compaction suture sharp peak type stylolites grow in a non linear fashion and thus do not record most of the actual compaction however when a non linear growth law is used the compaction estimates are similar to those making use of the rectangular layer type stylolites simple wave like stylolites are not useful for compaction estimates since their growth is highly non linear with a very low growth exponent in the case where sealing material is collected at the tooth during dissolution stylolites can act as barriers for local fluid flow as they intensify sealing capabilities of pinning layers however the development of teeth and spikes offsets and thus destroys continuous stylolite seams so that the permeability across the stylolite becomes very heterogeneous and they are no continuous barriers this behavior is best shown in rectangular layer and seismogram pinning type stylolites that develop efficient fluid barriers at teeth tips but destroy sealing capabilities of layers by offsetting them at the flank leading to a permeability anisotropy along 2 d stylolite planes suture sharp peak stylolites can create fluid barriers if they collect enough sealing material however if the collecting material does not seal or if spikes offset the sealing material the stylolite leaks we propose that our classification can be used to realistically estimate chemical compaction in reservoirs and gives an indication on how heterogeneous the permeability of stylolites can be

rock buffered fluid rock interaction in deformed quartz rich turbidite sequences eastern australia quartz vein 18o 16o ratios across a 500 km transect through the lachlan fold belt of southeastern australia are remarkably uniform 1 1 5 permil at both local centimeter to meter and regional over 104 km2 scales they define isotopic zones that correlate with the tectonic divisions of the cambrian through devonian dominantly ordovician quartz rich turbidites determined by regional mapping from west to east these divisions are 1 stawell 18o 14 7 1 1 47 samples 2 bendigo ballarat 18o 17 5 1 3 204 samples 3 melbourne 18o 19 0 1 6 80 samples 4 tabberabbera 18o 16 3 1 9 12 samples and 5 omeo 18o 14 4 1 0 26 samples isotope profiles across zone boundaries and intrazone fault zones particularly within the bendigo ballarat zone show steps indicating abrupt changes across faults with little or no evidence of fluid mixing within the fault zones 18o values of veins are insensitive to relative age type of vein and immediate host rock lithologies the 18o values of coexisting vein and host rocks show nonequilibrium relationships which can be explained in terms of rock buffering under conditions of low fluid rock ratios water rock 1 limited d h determinations on fluid inclusions fall mainly in the range 70 and 100 with one value as low as 140 these low deuterium values when considered in the context of paleolatitude may have been inherited from deutrium depleted detrital minerals and do not necessarily require the direct penetration of meteoric fluids to midcrustal depths the work suggests that vein formation is possible in regions where the integrated water rock w r ratio is very low w r 1 as long as a pervasive fluid phase is present this fluid appears to achieve a steady state isotopic composition on scales of hundreds of meters and once a quasi steady state has been reached the isotopic compositions of the resultant quartz veins are rather insensitive to the diachronous and nonisothermal conditions under which vein growth occurs advective cycling of the fluid on this scale is by episodic dilatancy pumping in fracture networks associated with localized faulting

microfractures and their role in deformation of a quartz arenite from the central appalachian foreland abstract microfractures are pervasive in the massanutten sandstone a quartz arenite exposed in a doubly plunging synclinorium in the central appalachian foreland they are present as fluid inclusion planes fips and microveins parallel the fips fips occur in three orthogonal sets horizontal vertical and normal to the fold axis and vertical and parallel to the fold axis the geometry distribution and age of fips relative to other microstructures shows that microfractures developed during folding microfracturing followed layer parallel shortening by dislocation flow and was coeval with the peak of pressure solution that marked the final stages of folding microfracture densities are extremely high 160 mm 1 in many samples rapid closure of microfractures suppressed brecciation and prevented microfractures from propagating unstably to form joints microfracture opening accounts for significant finite strain with extensional strains of up to 11 1 and associated volume increases of over 16 0 the general lack of shortening microstructures indicates that a net volume increase is likely and that the massanutten sandstone may have served as a sink for dissolved phases from adjacent units undergoing volume loss deformation

tectonic significance of ductile deformation in low grade sandstones in the mesozoic otago subduction wedge new zealand this study demonstrates how ductile strain measurements can determine the tectonic evolution of a large and long lived subduction wedge we provide a synthesis of the geology of the south island of new zealand with an emphasis on a wedge tectonics perspective that contrasts with a traditional view that interprets new zealand geology in the context of terrane collision and accretion we argue that the otago subduction wedge evolved in a steady fashion throughout its 290 to 105 ma history in response to accretion of trench fill and abyssal plain sediments and slow erosion of a subaerially exposed forearc high maximum temperatures for rocks in the flanks of the forearc high were no greater than 150 to 300 c with solution mass transfer active as the dominant ductile mechanism the 54 studied samples provide information about the absolute ductile strains acquired all along their flow path from the site of accretion to exhumation in the forearc high we use tensor averages to estimate strain at a regional scale these show plane strain uniaxial flattening given that the tensor averages for sy and sx are close to one on average sz is approximately 0 77 and this is balanced by a mass loss of about 23 percent the average z direction is sub horizontal in the prowedge and moderately plunging in the retrowedge a difference attributed to spatial variations in the mode of accretion we infer that rocks presently in the pro side of the otago high were sourced by frontal accretion and those in the retro side were underplated this result highlights the important role of accretion in determining the style of within wedge deformation and also demonstrates the benefit of using a tensor averaging approach to examine regional strain

evidence for syntectonic crystallization for the mudstone to slate transition at lehigh gap pennsylvania u s a data primarily for phyllosilicates have been obtained for the continuous transitional sequence from mudstone to slate with well developed slaty cleavage at lehigh gap pennsylvania and for slates from quarries in the same area samples were studied by optical microscopy powder x ray diffraction and electron microprobe analysis with emphasis on transmission and analytical electron microscopy mineral grains are virtually free of deformation induced strain concomitant with the gradual development of cleavage normal to bedding the following changes are observed or confirmed 1 the orientation of phyllosilicate grains changes discontinuously from being preferentially parallel to bedding to being parallel to cleavage 2 crystal imperfections as expressed in layer terminations low angle grain boundary like features and other defects decrease in density 3 complex mixed layering is replaced by homogeneous packets of layers of single phases and 4 illite transforms to muscovite with increase in k a1 and change from a lmd to 2m polytype slaty cleavage apparently develops due in part to pressure solution of phyllosilicates oriented parallel to bedding mass transport of components and crystallization to form new grains parallel to cleavage it reflects transitions from imperfect metastable phases toward ordered stable phases in a low temperature 225 c metamorphic environment

effects of the superposition of compaction and tectonic strain during folding of a multilayer sequence model and observations abstract sedimentary rocks deformed at shallow crustal depth can show a wide variety of planar linear and mixed planar linear fabrics depending on their structural position within folds a model has been developed which tries to explain this variation in fabric development in terms of the strain states that it represents we analyse the finite strain states that may develop during compaction and subsequent buckle folding of sedimentary multilayers composed of a regular alternation of competent and incompetent beds the geometric properties of the multilayer during buckling have been analysed from a finite element model characterized by linear viscous material properties a viscosity contrast 1 2 40 and a ratio of incompetent to competent layer thickness d 2 d 1 1 sequential matrix multiplication allows the determination of the finite strain states for all stages of fold development finite strain states predicted from the model appear to be in good agreement with observations of fabric development in naturally deformed rocks from the southern apennines during progressive deformation in the model the finite strain ellipsoid in the limb regions of folded incompetent layers is consistently oblate and the xy plane lies at a small angle to bedding as a consequence of previous compaction natural cleavage consistently lies at a low angle to bedding in folded argillites from the southern apennines and it can be interpreted to represent the xy plane of the total finite strain ellipsoid in strongly compacted sediments and not that of tectonic deformation alone in the hinge regions of open folds finite strains predicted in the incompetent layers of the model are of prolate type and they become oblate as the interlimb angle decreases the presence of a true pencil structure in open folds and of a spaced cleavage associated with a regular pencil structure in more close folds often noted in the case study of the southern apennines most probably reflects this change from prolate to oblate strain in the hinge zones as folding proceeds

slaty cleavage development and magnetic anisotropy fabrics the shale to slate transition preserved in the ordovician martinsburg formation at the lehigh water gap pennsylvania provides an opportunity to study the relationship between magnetic anisotropy fabrics and the development of slaty cleavage our previous work has indicated that anisotropy of magnetic susceptibility ams does not record changes in finite strain associated with cleavage development in these rocks but instead measures the degree of dissolution and new growth of ehlorite additional ams data presented in this paper lend further support to this conclusion conversely anhysteretie remanent magnetization anisotropy arma which is not affected by paramagnetie ehlorite accurately reflects the strain induced rock fabrics associated with cleavage formation arma results show that magnetite dimensional orientations vary from bedding parallel in shale samples to cleavage parallel in samples with well developed slaty cleavage samples with weak and pencil cleavage display scattered arma orientations which lie in between bedding and cleavage these intermediate orientations may be due to either passive rotation of magnetite from bedding parallel to cleavage parallel or re crystallization of magnetite if rotation occurred grain rotation was highly heterogeneous in the samples with incipient cleavage the intermediate arma orientations may also reflect the varying contribution of two magnetite preferred orientations a depositional orientation parallel to bedding and a new growth orientation parallel to cleavage

mass transfer and preferred orientation development during extensional microcracking in slate belt folds elura mine australia microstructures in slate belt rocks at the elura mine near cobar south eastern australia indicate that volume loss by syntectonic dissolution is coupled with mass accretion by reprecipitation of the dissolved material in dilational sites the mass accretion is sustained primarily by repetitive tensile microfracturing at high pore fluid pressures oriented growth in the inter and intragranular microcracks is locally host controlled creating lattice and shape preferred orientations the grain scale crack seal features throughout the rock reflect rhythmic fluid pressure fluctuations a balance is achieved between the fracture induced permeability and consequent flushing rates and the rate of fluid build up in a relatively sealed environment instability in the balancing factors can lead to localization and intensification of tensile failure and hence tension vein formation in the grain aggregate growth of veins by crack seal also reflects a steady state but with more localized fluctuations of fluid flow on the aggregate scale still larger imbalances between flushing and fluid accumulation i e pressure variations induce breccia veining the larger pressure gradients over greater distances associated with dilation localization from pervasive microfracturing to spaced breccia domains allow fluid channelling with an increased potential for chemical fluid rock disequilibrium therefore large breccia vein systems tend to be sites of extensive fluid rock interaction and replacement as spectacularly illustrated by the syntectonic sulphide orebodies at elura the huge amounts of silicate carbonate and sulphide accumulated during folding at elura illustrate the large scale of source and sink couples possible in solute mass transfer

finite strain heterogeneity and volume loss in slates of the taconic allochthon vermont u s a abstract slates of the taconic allochthon have ellipsoidal reduction spots which have been used to determine the finite state of strain at seven sites the strain is highly heterogeneous at all scales ranging from several centimeters to many kilometers variations in x y ratios is small but variations in y z ratios is large and this pattern is seen at all scales the heterogeneity can be used to determine a strain path which is nearly horizontal on a flinn diagram we propose that uniaxial flattening associated with late stage cleavage development was accommodated by volume loss and that the most highly strained sites have experienced an average 55 volume loss at a minimum explaining our results without volume loss requires a subhorizontal extension and creates strain compatibility problems consideration of the strain history of these rocks suggests that folding related strains have been modified by later cleavage related events the last of which was uniaxial flattening accommodated by volume loss the finite strains are reflective almost exclusively of the latest cleavage producing strains

pressure solution deformation of the purgatory conglomerate rhode island u s a quantification of volume change real strains and sedimentary shape factor abstract pressure solution has caused substantial volume redistribution within the purgatory conglomerate from rhode island material has been removed from quartzite cobble surfaces parallel to the fold axes and mostly redeposited as fibrous pressure shadows at the long axis terminations of the cobbles in the hinges of folds 23 of the mean cobble volume has been removed and in highly deformed and overturned fold limbs up to 55 volume reduction has occurred the initial cobble shape and orientation can be measured at an undeformed locality and the deformation path can be easily deduced thus these are real cobble volume reductions apparent volume losses initial shapes not removed range from 70 to 89 real strains for cobbles axial ratios ranging from 1 0 65 0 38 to 1 0 47 0 15 have values of e x e y e z which range from 0 20 11 to 0 37 42 respectively depending on structural position the conglomerate itself has been extended parallel to the fold axes e r but the extension is not recorded by the cobble shapes

where is the interface of the stratocumulus topped pbl abstract various locally defined not horizontal mean interfaces between the stratocumulus topped pbl and the free atmosphere are investigated using a fine resolution large eddy simulation with a vertical grid spacing of about 4 m the local cloud top height is found to be always below the height where the maximum gradient of the local sounding occurs and the maximum gradient height is always below the interface where pbl air can reach via turbulent motions the distances between these local interfaces are of significant amount a few tens of meters on average air between the cloud top and maximum gradient interfaces is fully turbulent unsaturated but rather moist air between the maximum gradient and turbulent mixing interfaces consists of turbulent motions that are intermittent in space and time the simulated flow shows no clearly defined interface that separates cloudy turbulent air mass from clear nonturbulent air above even locally

volume loss during cleavage formation in the meguma group nova scotia canada abstract diffusive mass transfer pressure solution is a widely recognized cleavage forming mechanism under low grade conditions the amount of accompanying volume change during cleavage development however is difficult to quantify and remains controversial the distance between sites of mineral dissolution and reprecipitation and transport mechanisms also are controversial the structural history of the cambrian ordovician meguma group nova scotia canada is well known and abundant strain markers provide an opportunity to assess geometrically volume changes accompanying cleavage development during diagenesis about 70 compaction in muds and 15 in silts and sands occurred the pelitic to psammitic meguma group was cleaved prior to being folded pressure solution was the dominant cleavage forming deformation mechanism under chlorite grade metamorphic conditions during the early devonian acadian orogeny measurement of tectonic strain in principal directions x y z shows that bedding parallel coaxial shortening z is 60 and there is no evidence of fold hinge parallel extension y estimation of tectonic vertical extension x in the cleavage plane is complicated by diagenetic compaction corrections to primary strain markers but is insufficient to compensate for the observed 60 shortening in z indicating 40 60 volume loss during cleavage formation because cleavage formed at least 50 ma after deposition and under approximately 6 km of silurian to early devonian strata porosity of the sediments upon onset of cleavage was likely less than 15 pore space reduction therefore cannot account for the apparent volume loss during cleavage formation cleavage related volume loss applies regionally and to a stratigraphic thickness of several thousand meters implying that a large amount of material was removed and transported large distances when combined with 50 shortening by folding a bulk tectonic shortening of 80 is estimated for the meguma group during the acadian orogeny

differentiated layering in metamorphic rocks abstract metamorphic or differentiated layering is best developed in low prograde metamorphic rocks such as slates and metaturbidites and is most easily recognised where it cuts a demonstrably earlier layering such as bedding it commonly occurs as an axial plane foliation and typically comprises layers rich in phyllosilicates and opaque minerals alternating with layers rich in quartz or carbonate minerals the phyllosilicate layers generally have the geometry of small shear zones offsetting the earlier foliation and are mostly thinner than the adjacent quartz or carbonate rich layers both layers can vary in thickness from centimetres to microns and the structure is manifest in various forms including outcrop scale layering and thin section scale differentiated crenulation or slaty cleavage in a given sequence of rocks there is generally a strong correlation between the coarseness of the layering and the coarseness of the rock such layering may develop by local redistribution of minerals or by localised addition or removal of some components to or from the rock either way transport is believed to take place in solution and various models for the domainal localisation of the solution processes are discussed possible sources of the transporting fluid are considered and it is concluded that the most likely source in general is connate water subducted below the deforming differentiating rock body

porphyroblast nucleation growth and dissolution in regional metamorphic rocks as a function of deformation partitioning during foliation development in regional metamorphic rocks the partitioning of deformation into progressive shearing and progressive shortening components results in strain and strain rate gradients across the boundaries between the partitioned zones these generate dislocation density gradients and hence chemical potential gradients that drive dissolution and solution transfer phyllosilicates and graphite are well adapted to accommodating progressive shearing without necessarily building up large dislocation density gradients within a grain because of their uniquely layered crystal structure however most silicates and oxides cannot accommodate strain transitions within grains without associated dislocation density gradients and hence are susceptible to dissolution and solution transfer as a consequence zones of progressive shearing become zones of dissolution of most minerals and of concentration of phyllosilicates and graphite exceptions are mylonites where strain rates are commonly high enough for plastic deformation to dominate over diffusion rates and therefore over dissolution and solution transfer porphyroblastic minerals cannot nucleate and grow in zones of active progressive shearing as they would be dissolved by the effects of shearing strain on their boundaries however they can nucleate and grow in zones of progressive shortening and this is aided by the propensity for microfracturing in these zones which allows rapid access of fluids carrying the material presumed to be necessary for nucleation and growth zones of progessive shortening also have a number of characteristics that help to lower the activation energy barrier for nucleation this includes a build up of stored strain energy relative to zones of progressive shearing in which dissolution is occuring porphyroblast growth is generally syndeformational and previously accepted criteria for static growth are not valid when the role of deformation partitioning is taken into account porphyroblasts in a contact aureole do not grow statically either as microfracturing associated with emplacement allows access of fluids in a fashion that is similar to microfracturing in zones of progressive shortening the criteria used for porphyroblast timing can be readily accommodated in terms of deformation partitioning reactivation of deforming foliations and a general lack of rotation of porphyroblasts with the spectacular exception of genuinely spiralling garnet porphyroblasts

scales of equilibrium and disequilibrium during cleavage formation in chlorite and biotite grade phyllites se vermont detailed electron microprobe analyses of phyllosilicates in crenulated phyllites from south eastern vermont show that grain scale zoning is common and sympathetic zoning in adjacent minerals is nearly universal we interpret this to reflect a pressure solution mechanism for cleavage development where precipitation from a very small fluid reservoir fractionated that fluid multiple analyses along single muscovite biotite and chlorite grains 30 200 m in length show zoning patterns indicating tschermakitic substitutions in muscovite and both tschermakitic and di trioctahedral substitutions in biotite and chlorite using cross cutting relationships and mineral chemistry it is shown that these patterns persist in cleavages produced at metamorphic conditions of chlorite grade chlorite grade overprinted by biotite grade and biotite grade zoning patterns are comparable in all three settings requiring a similar cleavage forming mechanism independent of metamorphic grade moreover the use of 40ar 39ar geochronology demonstrates this is true regardless of age furthermore samples with chlorite grade cleavages overprinted by biotite porphyroblasts suggest the closure temperatures for the diffusion of al si mg and fe ions are greater than the temperature of the biotite isograd 400 c parallel and smoothly fanning tie lines produced by coexisting muscovite chlorite and muscovite biotite pairs on compositional diagrams demonstrate effectively instantaneous chemical equilibrium and probably indicate simultaneous crystallization these results do not support theories suggesting cleavages form in fluid dominated systems if crenulation cleavages formed in systems in which the chemical potentials of all major components are fixed by an external reservoir then the compositions of individual grains defining these cleavages would be uniform on the contrary the fine scale chemical zoning observed probably reflects a grain scale process consistent with a pressure solution mechanism in which the aqueous activities of major components are defined by local dissolution and precipitation thus the role of fluids was probably limited to one of catalysing pressure solution and fluids apparently did not drive cleavage development

the role of fluids in syntectonic mass transport and the localization of metamorphic vein type ore deposists abstract in low to medium grade metamorphic environments the mobilization of species is closely associated with the operation of solution precipitation creep processes during foliation development such deformation processes involve dissolution of material from source sites which are usually discrete dissolution surfaces having orientations controlled by the applied stress and displacement fields mass transfer occurs via solute diffusion in an essentially static fluid network or by transport of dissolved species in a migrating fluid precipitation of material removed from dissolution sites occurs in a variety of sink sites including pore surfaces grain scale microcracks and veins sink sites may be close to or distantly removed from source sites the transport of material during deformation involving solution precipitation creep is largely controlled by the mobility of metamorphic fluids in regions of high fluid mobility significant mass transfer may occur over large distances fluid flow mass transfer paths and the development of sink sites in such cases are constrained by the structurally controlled development of high fluid pressure domains and the consequent mechanical enhancement of permeability by hydraulic fracture processes and the development of grain scale dilatancy these processes may result in focussed fluid flow and precipitation of mobilized species in restricted regions a proportion of syntectonically mobilized material is precipitated to form vein type deposits in hydraulic fracture arrays which develop in high fluid pressure environments the microstructures developed in minerals deposited in these sites reflect the interaction of a range of nucleation and growth processes which usually involve multiple generations of fracture growth and mineral crystallization the formation of syntectonic gold quartz vein deposits in central victoria australia illustrates the importance of structural controls on both the large scale migration of metamorphic fluids and the development of sites suitable for the precipitation of metamorphically mobilized species

kinematic analyses of the hsuehshan range taiwan a large scale pop up structure the hsuehshan range exposed in the northern and central taiwan slate belt is a fault bounded structural high cored by biotite grade slates and metasandstones syntectonic overgrowths in pyrite pressure shadows indicate that much of the eastern hsuehshan range experienced coaxial strain histories and that finite strain magnitudes generally increase toward the hinterland near the eastern boundary of the hsuehshan range however pressure shadows record noncoaxial strain histories consistent with a top to the east sense of shear along a steep nw dipping shear zone this noncoaxiality is attributed to se directed backthrusting on the lishan fault which separates the higher grade eo oligocene rocks of the hsuehshan range from the lower grade miocene rocks of the backbone range because it is bounded to the east by the se vergent lishan fault and to the west by a series of nw vergent thrusts e g the chuchih fault the hsuehshan range is envisaged as a pop up structure strain magnitudes measured from pressure shadows in the coaxial part of the range are consistently lower than those predicted by steady state wedge models that assume all deformation is accommodated by penetrative strain departure from the model predictions is attributed primarily to strain localization along discrete fault surfaces e g the lishan fault the hsuehshan range tapers in width to the south thus the pop up may be buried or die out to the south where the collision is younger

low grade metamorphism around the down dip limit of seismogenic subduction zones example from an ancient accretionary complex in the shimanto belt japan abstract reactions involving clay minerals during low grade metamorphism at the depth of an ancient accretionary complex in the shimanto belt kyushu japan were studied by integrated transmission electron microscopy energy dispersive x ray spectroscopy and x ray diffraction analyses of the bulk rock and clay fraction the analyzed metasediment the kitagawa unit contain an incipient sub horizontal slaty cleavage illite crystallinity data and mica b dimensions indicate that the conditions of metamorphic deformation were anchizone epizone grade and intermediate pressure cleavage formation was linked to two reactions involving clay minerals 1 the recrystallization of 1m dominant matrix mica inherited from the original sedimentary fabric into thick defect free 2m1 packets along cleavage planes and 2 the formation of chlorite from 7 a berthierine balanced equations among the clay phases based on compositional data and their relative abundance suggest that the decomposition of matrix mica resulted in the formation of paragenetic mica and chlorite along the cleavage planes without significant elemental outflux although a modal increase in phyllosilicates is not indicated by the data the growth of chlorite and mica along cleavage planes may have a large influence on the rheological properties of a decollement and may be related to the occurrence of the seismic aseismic transition at 350 c

deformed graptolites finite strain and volume loss during cleavage formation in rocks of the taconic slate belt new york and vermont u s a abstract an analysis of graptolites in the taconic slate belt of eastern new york and western vermont u s a shows that they are nearly ideal strain markers for the three species used in this study orthograptus whitfieldii orthograptus calcaratus and climacograptus bicornis the spacing of thecae is constant except for the first five or so thecae in the proximal part of the fossil rhabdosome further the thecal apertures are perpendicular to the long axis of the stipe observations of the thecal spacing in deformed rocks leads to a determination of extension e l f l 0 l 0 and a measure of the angle between thecal aperture and stipe axis yields a direct determination of angular shear strain in practice we find it is most straightforward to use length changes to determine the magnitude of principal strains in taconic slates e 1 ranges from 1 0 to 0 24 e 2 ranges from 0 23 to 0 43 and e 3 ranges from 0 56 to 0 74 thus we find that the absolute finite strain in these slates is constrictional at three sites plane strain at another and a true flattening at only one site an examination of volume changes based on strain results in determinations of between 81 volume loss and 7 volume gain with volume losses between 28 and 81 in 9 out of 10 calculations these conclusions are in accord with previous determinations of volume loss based on reduction spot analyses and are consistent with the observation that pressure dissolution was a common grain scale deformation process in cleavage formation but that these slates lack abundant veins fibrous overgrowths or other identifiable sites of reprecipitation

microlithon alteration associated with development of solution cleavage in argillaceous limestone textural trace elemental and stable isotopic observations abstract comparison of microlithons the rock between adjacent cleavage domains in strongly cleaved argillaceous limestone with samples of uncleaved limestone from the same stratigraphic horizon lower devonian kalkberg formation hudson valley of eastern new york indicates that the process of cleavage formation results in significant changes in microlithon fabric and in the chemistry of microlithon calcite petrographic observation indicates that at least 50 of the calcite in microlithons is recrystallized as calcite fibers whose long axes are subparallel to cleavage domains the fibrous calcite occurs as overgrowths on larger grains in thin bed parallel veins and in diffuse extension zones areas of the microlithons in which inequant crystals of microcrystalline calcite are aligned parallel to cleavage domains chemical analyses show that calcite in microlithons of strongly cleaved limestone is enriched in mn and sr relative to calcite in uncleaved limestone 18 o and possibly 13 c values for calcite in strongly cleaved rock are significantly smaller than values for calcite in uncleaved rock these results indicate that microlithon calcite is completely recrystallized i e much more calcite is recrystallized than is visible in thin section and that it underwent exchange with a fluid external to the local rock system calculation of the water rock ratio suggests that 0 1 2 6 volumes of water may have exchanged with the calcite during cleavage formation comparison of the minimum integrated and the inferred instantaneous water rock ratios suggests that bulk fluid flow occurred during microlithon recrystallization comparison of the amount of shortening across cleavage domains with the amount of extension in microlithons and of the volume of calcite dissolved in domains with the amount of fibrous presumably added calcite in microlithons suggests that microlithons are a major sink for the calcite dissolved in domains during cleavage formation and that at this locality development of disjunctive solution cleavage in the kalkberg formation resulted in volume constant plane strain

development of cleavage in lapilli bearing volcaniclastic rock abstract the development of cleavage in a suite of lithic and accretionary lapilli bearing volcaniclastic rocks of known strain ge s 0 14 2 4 has been studied analysis of these specimens reveals that various mechanisms of cleavage formation have been active during the deformation in both lithic and accretionary lapilli bearing rock the cleavage in the matrix appears to have formed directly by recrystallization of devitrified and or altered volcanic glass ash preferred alignment of the neoblasts in the matrix with increasing strain results from some combination of neocrystallization parallel to cleavage and at an angle to the cleavage followed by rotation into that plane as the deformation progresses fragments in lithic lapilli bearing rocks show two stages of rotation during cleavage development the first stage ge s 0 to 0 60 ge 1 0 to 40 ge 3 0 to 35 where ge 1 ge 2 ge 3 elongations is dominated by rigid body rotation of lapilli recrystallization and shape change of the lapilli accompanying the rotation are slight at first but increases with strain in the second stage ge s 0 60 recrystallization becomes pronounced and is accompanied by a ductile flattening of lapilli facilitated by inter and intragranular movements these movements allow the lapilli to rotate by migration of the vertex along the lapilli perimeter and is accompanied by increasing axial ratios in the accretionary lapilli bearing rocks lapilli show one continuous stage of rotation up to values of strain where ge s 1 25 ge 1 110 ge 3 65 recrystallization is active from the start rendering the lapilli ductile even in the early stages of deformation lapilli rotate and increase their axial ratios by the flattening process active in the second stage described for lithic lapilli once the values of strain exceed ge s 1 25 rotation of lapilli is essentially complete although their axial ratios continue to increase with strain primary crystals in both rock types also show two stages of rotation in the first stage ge s 0 to 0 70 ge 1 0 to 50 ge s 0 to 40 the primary crystals undergo essentially all their rotation which is accompanied by some plastic deformation fracturing and minor quartz mica beard formation in the second stage ge s 0 70 further rotation is statistically minor the mechanisms just mentioned become more common and recrystallization becomes an important response of the crystal to the deformation at strains where ge s 1 25 ge 1 110 ge 3 60 the metamorphic products of deformed and recrystallized primary crystals tend to become smeared out in the cleavage plane the effects of pressure solution can be seen in the deformation of primary crystals beard formation etc and in the response of some of the more dense lithic lapilli it is also relatively well developed in a few specimens which are crystal rich in general however it plays a minor role relative to the other mechanisms described

solution slip and separations on strike slip fault zones theory and application to the mattinata fault italy we present a set of relationships to determine the component of slip and separations generated by the cleavage controlled volume contraction in strike slip fault zones the fault walls can translate toward each other along the cleavage normal axis of maximum shortening as rock is dissolved by pressure solution along patterned cleavage surfaces within strike slip fault zones the fault zone shortening produces an apparent slip and possible separations of reference stratigraphic surfaces across the fault zone solution related slip and separations can differ in magnitude and have either the same or the opposite sense these discrepancies depend upon the amount of fault zone shortening and upon the angles between the fault and the shortening axis and between the fault and the reference stratigraphic surface separations can be considerable at any scales even for very low amounts of fault zone thinning apparent slip can be appreciable for large amounts of fault zone thinning and or high fault to cleavage incidence angles with the proper geometrical conversions the relationships here presented can apply to any fault type the application of this technique to the left lateral mattinata fault italy demonstrated that both left and right lateral strike separations can occur along the fault even for low amounts of fault zone contraction by rock dissolution q 2002 elsevier science ltd all rights reserved

solution mass transfer deformation adjacent to the glarus thrust with implications for the tectonic evolution of the alpine wedge in eastern switzerland abstract we have studied aspects of absolute finite strain of sandstones and the deformation history above and below the glarus thrust in eastern switzerland the dominant deformation mechanism is solution mass transfer smt which resulted in the formation of a semi penetrative cleavage our analysis indicates that the verrucano and melser sandstones which lie above the thrust were deformed coaxially with pronounced contraction in a subvertical z direction and minor extension in a subhorizontal x direction trending at 200 most of the contraction in z was balanced by mass loss volume strains averaging 36 below the glarus thrust sandstones of the north helvetic flysch have smaller principal strains but similar volume strains deformation there was also approximately coaxial the x direction is horizontal and trends 160 which is different by 40 from the x direction in the hanging wall the hanging wall of the glarus thrust verrucano and melser sandstones was deformed first after it was accreted deep beneath the alpine wedge continued northward advance of the wedge accomplished in part by motion on the glarus thrust allowed the wedge to override and accrete the north helvetic flysch which then started to form an smt cleavage the difference in x directions may reflect a change in transport direction but this conclusion is difficult to accept since extension was minor and was accommodated by coaxial flattening and not simple shear our work indicates that mass loss volume strains were important in sandstones of the helvetic nappes the missing mass cannot be accounted for at the local scale and appears to have been transported beyond the helvetic zone

including strain data in balanced cross sections abstract almost all published balanced cross sections include cleaved and or strained rocks and may therefore violate the requirement that bed lengths and formation areas are preserved between undeformed and deformed states knowledge of distortions presence and type of cleavage and overprinting relations in poly deformed segments are necessary to define area changes related to volume loss strike elongation and poly deformation work in the southern and central appalachians has shown variation in structural complexity and changing deformation styles both along and across the thrust belt this necessitates separate treatment of individual sheets during balancing regions of little or no interstratal slip pinning points should be chosen for each thrust sheet and each fold strain in the sheet in external sheets where deformation intensity increases towards thrusts pin points should be back limb inflection points in intermediate and internal sheets where cleavage is approximately coeval with folding pin points should be at fold hinges where cleavage and strain are heterogeneously developed throughout a stratigraphic sequence a line length balance using massive relatively uncleaved beds e g knox group southern appalachians can be used as a basis for restoring the section unstraining of deformed layers given strain data and cleavage trajectories for individual thrust sheets provides line lengths and formation areas which can be fitted to the key bed of the undeformed section cleavages which partially or fully postdate folding indicate continued shortening in the thrust wedge and modify earlier pinning points in upper sheets these cleavages and poly deformed segments are difficult to restore as strain data are generally scarce in the metamorphosed internal thrust sheets

strain partitioning across a fold and thrust belt the rhenish massif mid european variscides abstract strain data across the entire western rhenish massif illustrate the pattern of deformation partitioning within a fold and thrust belt from the foreland on the northern front of the european variscides to the suture with the internal zones of higher metamorphic grade shortening perpendicular to cleavage increases from 16 to 27 constant volume assumed in the northern rhenish massif to 51 at the southern border these values correspond to a weak general layer parallel shortening of the basin filling in cross section on the order of about 5 15 and more in the case of volume loss the geometry of apparent finite strain is nearly plane strain except in the venn anticlinorium where strain is apparent prolate and near the southern margin of the massif where it is apparent oblate net orogenic shortening in the upper crust of the fold and thrust belt is approximately 42 it is mainly achieved by folding and tectonic stacking of the deformed basin filling which was apparently detached from the lower crust distribution of strain in the orogenic wedge is controlled by different factors at different scales heterogeneity is caused by changes in lithology and average grain size by the structural position of samples in folds and their distance from thrusts in the hangingwall at deeper crustal levels and by the regional distribution of the metamorphic grade i e by the dominant deformation mechanism this last factor causes an exponential increase of strain with approach to the ductile lower crust the superposition of strain partitioning mechanisms on different scales creates a complex regional strain pattern the southern part of the thrust belt apparently suffered late westward motion in gently dipping imbricates or strike parallel motion in steeply dipping imbricates which is probably due to oblique convergence between the rhenohercynian and saxothuringian microplates

isotopic and structural responses of granite to successive deformation and metamorphism within the sybella granite west of mount isa in northern australia differential response of u pb and rb sr isotopic systems to deformation metamorphism enables ages of emplacement and three discrete deformation metamorphic events to be determined based on zircon u pb systems two of the plutons were emplaced at 1671 pm 8 ma and 1668 pm 26 21 ma and the third at 1610 pm 10 ma a separate microgranite body gives aberrantly old u pb ages of up to 1780 ma due to partial inheritance of older zircon the three discrete deformation metamorphic events d 1 d 2 and d 3 occurred at 1610 pm 13 ma 1544 pm 12 ma and 1510 pm 13 ma respectively based on whole rock rb sr isotopic systems the youngest body was emplaced syntectonically and has possible significance to the origin of the mount isa ag pb zn orebodies homogenization of rb and sr isotopes via extensive syntectonic fluid migration associated with deformation partitioning and resultant solution transfer appears to have been

the relationship of strain and preferred orientation of phyllosilicate grains in rocks a review abstract the calculation of strain from the preferred orientation of platy phyllosilicate grains taking strain to be homogeneous is surprisingly often successful from a pragmatic point of view although numerous theoretical objections to this procedure can be and have been raised for the calculation to succeed the original distribution of mica or clay mineral grains must be known or assumed the usual assumption that the starting distribution was random and therefore nearly uniform implies that the strain history of pelitic sediments is taken to start when the watery sediment was last stirred by waves or bioturbation or if it was laid down in still anoxic waters from the moment of first deposition it therefore includes compaction as part of the strain history which is usually neglected by structural geologists originally random distribution of clay flake orientations has been observed in recently deposited sediments in many instances and has been theoretically explained in various ways exceptions probably exist but their frequency has not been estimated biologically disturbed sediments may be brought nearer to a state of random orientation of clay flakes than they were at deposition with the exception of whole beds or concretions in which pores are early filled with cement mudrocks are almost always compacted by the weight of later deposits the strain so induced is axially symmetric about the vertical and thus about the pole of the bedding planes compaction acts on soft unconsolidated rocks but may continue with increasing overburden on rocks strengthened by cementation and by increasing interlocking of grains tectonic deformation may start early before the rock is fully compacted or it may begin only much later and the mechanisms of deformation increase in complexity with the increasing temperature and hydrostatic stress of deeper burial up to a certain level of mild metamorphism however phyllosilicate grains seem to be rather permanent if not as mineral species then at least by preservation of their constituent sheets of silica tetrahedra given this permanence the mechanisms of rock deformation whether intergranular slip cataclasis or dissolution and reprecipitation and various intragranular processes in the non phyllosilicate matrix hardly matter as far as the recording of strain is concerned even a certain amount of stress solution at especially heavily loaded points of the phyllosilicate grains themselves does not destroy their value as strain markers as long as the dissolved material is disposed of mainly by crystallographically continuous overgrowth on existing grains the same holds for local dissolution of phyllosilicates in portions of old grains that have become thermodynamically unstable by bending widespread irregular or random nucleation and growth of newly nucleated phyllosilicate grains at intermediate or high grades of metamorphism can reduce the reliability of the strain record and so can domainal structure of the deformed rock if both the volume fraction of phyllosilicate grains and the intensity of total strain differ sharply from one domain to another if distinct domains are not equant and have themselves a strong preferred orientation of shape nevertheless rocks containing an anastomosing network of zones rich in phyllosilicate grains as slates and other deformed mudrocks commonly do have in many cases been found to have average preferred orientations of mica or chlorite which if used to estimate the strain give results similar to those obtained from independent strain markers in the same rocks thus the most significant verification of the usefulness of strain estimates by measurement of preferred orientation is the mutual confirmation with independently determined strain the limit to such verification is the rarity of strain markers so that the coexistence of two independent ones is exceptionally rare for this reason however it is important to make full use of the orientation of phyllosilicate grains where they are available the alternative to have no strain measurements at all causes structural geologists to miss potential information

change in dominant mechanisms for phyllosilicate preferred orientation during cleavage development in the kitakami slates of ne japan abstract selected slates from the kitakami mountains of ne japan were studied by means of finite strain measurement x ray texture goniometry optical microscopy back scattered sem and x ray fluorescence and diffraction analyses finite strain recorded by radiolarians in slates although not equivalent to bulk strain shows a positive correlation with strength of phyllosilicate basal plane fabrics however there is a possible difference between the fabric pattern and radiolarian strain ellipsoid shape as well as a difference in fabric pattern between chlorite and illite mica these relationships between phyllosilicate fabrics and finite strains suggest that strain estimation from phyllosilicate fabrics based on the march model may be unreliable unless their relationship is established in each case optical and back scattered sem studies revealed a change in microstructures in accordance with increasing fabric strength in slates with weak fabric strength cleavage domains are dark to opaque in appearance and characterized by a concentration of insoluble residues such as carbonaceous matter sphene ilmenite rutile epidote and apatite as well as phyllosilicates phyllosilicates in cleavage domains are oriented subparallel to cleavage whereas those in intercleavage domains are variously oriented as fabric strength increases cleavage domains become transparent and composed mainly of phyllosilicates phyllosilicates become finer grained and more uniform in grain size they are well oriented in both cleavage and intercleavage domains as fabric strength further increases phyllosilicates tend to coarsen these lines of microstructural evidence suggest that the dominant mechanism for phyllosilicate preferred orientation changes as cleavage develops from pressure solution transfer through syntectonic crystallization recrystallization and possibly to oriented grain growth because fabric strength increases with increasing illite crystallinity metamorphic grade mainly temperature must be one of the major factors which control the dominance of phyllosilicate preferred orientation mechanisms

review of major shale dominated detachment and thrust characteristics in the diagenetic zone part i meso and macro scopic scale there is considerable variability in the thickness structure and macroscopic deformation style within shale prone major thrust zones which also impacts the structural style in the overlying and sometimes the underlying section the properties and percentages of clay minerals and percentages of organic material quartz and calcite affect fault zone weakness and behaviour the distribution of competent units within a shale prone zone can also significantly affect fault zone architecture even over short strike distance of 10s to 100s of metres other influences include high pore fluid pressures and associated veins deformation of the fault zone may disrupt the original principal displacement zones and force them to relocate including switching lithologies calcite veins can become concentrated locally in the fault zone and become a focus of fault zone weakness we still need many more descriptions of shale prone fault zones to understand the potential variations in thrust sheet structural style caused by differences in shale detachment characteristics the variations in structural style in the hanging walls of shale detachments are broad and range between the sledge runner style in many appalachian examples and the extensive closely spaced imbricate style of the osen roa detachment southern norway such contrasts are related to several factors including thrust sheet mechanical stratigraphy thickness of the overburden lateral continuity of the detachment detachment mechanical properties composition pore fluid pressures presence absence of higher level detachments and strain rate in many structural locations and at many scales shale prone sequences will pile up to produce over thickened masses cleavage duplexes s c fabrics duplexes imbricates pseudo duplexes and vein formation can all contribute to the thickening at nested scales a mixture of brittle and solution diffusion processes overall cause the affected unit to exhibit flow like characteristics while the broad principles are now well established considerable work remains to be done understanding the full range of structural geometries associated with shale detachments what factors regarding the nature of the detachments affect overlying structural styles rates of deformation and the controls on deformation mechanisms within the thrust zones

magnetite dissolution and neocrystallization during cleavage formation paleomagnetic study of the martinsburg formation lehigh gap pennsylvania paleomagnetic study of the shale to slate transition in the ordovician martinsburg formation at lehigh gap pennsylvania reveals that the remanence of the relatively undeformed shales predates cleavage formation and that the slates were remagnetized during cleavage development the shales display two components of remanence component 1 c1 was the only magnetization direction in the majority of the shales and the first removed component in 10 shale specimens component 2 c2 is observed as a single component remanence with a low 300 400 c unblocking temperature range in samples from one shale station and as a second removed component in 10 shale specimens the mean directions are declination inclination 347 04 346 47 in situ tilt corrected for c1 and 80 63 135 40 for c2 the pencil slates and well cleaved slates both display single component remanences the mean directions are 198 12 201 26 for the pencil slates and 199 24 225 54 for the well cleaved slates using the relationship between cleavage development and remagnetization in the slates the timing of cleavage development and folding and the regional geology we can constrain the relative ages of the remanences as follows 1 the shale c1 direction is most likely prefolding and represents a primary upper ordovician direction 2 the slate directions are younger in age than the shale directions and are probably of permo carboniferous alleghenian age these results show that remagnetization occurred during development of slaty cleavage in these rocks we interpret the mechanism for this remagnetization to have been strain induced dissolution and neocrystallization of magnetite the additional difference in the characteristic directions of the pencil slates and well cleaved slates may be attributed to strain reorientation of the pencil slate remanence after new growth of magnetite the unknown temporal relationship between dissolution and neocrystallization and strain precludes any quantitative attempt to correct remanence for strain in these samples our study shows that paleomagnetic studies of deformed sediments must consider the possibility of dissolution and neocrystallization of remanence carriers in addition to strain induced rotation

regional structural and strain analyses of terranes in the western metamorphic belt central sierra nevada california abstract a comparison of total strains in 225 samples from the western metamorphic belt sierra nevada shows that strain types and intensities strongly depend on rock type greywackes and clast supported conglomerates are least strained whereas more intense strains occur in lapilli tuffs pebbly mudstones and slates large belts of volcanic rock record plane strain whereas nearby slate and greywacke sequences record flattening type strain suggesting that volume losses of 45 65 occurred in slates and 0 26 in greywackes lapilli tuffs record less than 11 volume loss the differences in volume loss and strain from one rock type to another require that discontinuities in total strain occur at most lithologic contacts independently of the lithologic control regional structural patterns and strain fields support the delineation of three terranes foothills merced river and northern sierra and two distinct domains western and eastern foothills terranes at these latitudes within the western metamorphic belt these terranes each bordered by large ductile shear zones differ in average strain intensity and orientation but not in strain type in the foothills terrane strain intensities decrease from moderate values in the western foothills terrane to low values in the eastern foothills terrane strain intensities in the study area are highest in the melones and bear mountains fault zones and in terranes east of the melones fault structures associated with regional deformation in each terrane do not extend far across terrane boundaries multiple generations of regionally developed structures are therefore rare in this part of the western metamorphic belt outside of fault zones we see one regionally developed cleavage in the foothills terrane a single but older cleavage in the merced river terrane and two still older cleavages in the northern sierra terrane however younger deformations may have reactivated and rotated older structures in adjacent terranes the timing and kinematics of the deformation in the foothills terrane suggest that faulting and rigid body rotations preceded pervasive shortening continued fault movement and rotation of faults to steep dips if orientations of ductile structures reflect plate motions structures in the merced river terrane suggest jurassic triassic orthogonal nne convergence whereas structures in the foothills terrane support late jurassic orthogonal ne convergence changing to oblique ene convergence about 150 ma ago

stylolites a review abstract stylolites are ubiquitous geo patterns observed in rocks in the upper crust from geological reservoirs in sedimentary rocks to deformation zones in folds faults and shear zones these rough surfaces play a major role in the dissolution of rocks around stressed contacts the transport of dissolved material and the precipitation in surrounding pores consequently they play an active role in the evolution of rock microstructures and rheological properties in the earth s crust they are observed individually or in networks in proximity to fractures and joints and in numerous geological settings this review article deals with their geometrical and compositional characteristics and the factors leading to their genesis the main questions this review focuses on are the following how do they form how can they be used to measure strain and formation stress how do they control fluid flow in the upper crust geometrically stylolites have fractal roughness with fractal geometrical properties exhibiting typically three scaling regimes a self affine scaling with hurst exponent 1 1 0 1 at small scale up to tens or hundreds of microns another one with hurst exponent around 0 5 to 0 6 at intermediate scale up to millimeters or centimeters and in the case of sedimentary stylolites a flat scaling at large scale more complicated anisotropic scaling scaling laws depending of the direction of the profile considered is found in the case of tectonic stylolites we report models based on first principles from physical chemistry and statistical physics including a mechanical component for the free energy associated with stress concentrations and a precise tracking of the influence of grain scale heterogeneities and disorder on the resulting micro structures experimental efforts to reproduce stylolites in the laboratory are also reviewed we show that although micrometer size stylolite teeth are obtained in laboratory experiments teeth deforming numerous grains have not yet been obtained experimentally which is understandable given the very long formation time of such geometries finally the applications of stylolites as strain and stress markers to determine paleostress magnitude are reviewed we show that the scalings in stylolite heights and the crossover scale between these scalings can be used to determine the stress magnitude its scalar value perpendicular to the stylolite surface during the stylolite formation and that the stress anisotropy in the stylolite plane can be determined for the case of tectonic stylolites we also show that the crossover between medium millimetric scales and large pluricentimetric scales in the case of sedimentary stylolites provides a good marker for the total amount of dissolution which is still valid even when the largest teeth start to dissolve which leads to the loss of information since the total deformation is not anymore recorded in a single marker structure we discuss the impact of the stylolites on the evolution of the transport properties of the hosting rock and show that they promote a permeability increase parallel to the stylolites whereas their effect on the permeability transverse to the stylolite can be negligible or may reduce the permeability depending on the development of the stylolite

an autocorrelation method for three dimensional strain analysis abstract we present a method of finite strain estimation using the autocorrelation properties of deformed rock autocorrelation is the correlation of an image with itself as a function of an offset or lag in two and three dimensions the lag has both distance and direction many geologic materials are initially isotropic which means that the autocorrelation function acf will be initially isotropic as well deformation imposes an anisotropic distortion which can be measured using the ramsay and fry strain methods for example but can also be estimated from the acf x ray tomography now provides a rapid way to measure the three dimensional acf of a geologic sample strain parameters are estimated by using a non linear best fit method to minimize the anisotropy in the acf the acf method works best for materials where the objects are internally uniform and contrast strongly with the matrix and other grains

remanence rotation due to rock strain during folding and the stepwise application of the fold test numerical modeling was conducted to determine the effects of simple models of folding strain on prefolding fisherian distributions of magnetization i found that the constant volume simple shear associated with flexural slip flexural flow folding can rotate a prefolding magnetization to have a maximum precision parameter k value at partial unfolding and thus appear to be synfolding in age if the magnetization is treated as a passive line marker this behavior only occurs for steep initial magnetizations the initial homogeneity of the fisherian precision parameters from each limb is degraded by this type of deformation and may be used to detect a strain modified remanence if the magnetization is carried by rigid mechanically active ellipsoidal or spherical particles a maximum k value at partial unfolding will occur for any initial inclination with the special case that rigid spheres will be rotated to cause a maximum k value at 50 unfolding for any initial inclination homogeneity of limb precisions is not affected in this case a discontinuous model of strain during folding in which pressure solution removes material at an axial planar spaced cleavage and causes limb dips steeper than bedding dips could also produce a maximum k value at partial unfolding strain and remanence studies of flexural slip folding in the allentown formation dolomite and the bloomsburg formation red sandstones and mudstones suggest that 1 the rigid grain model may be a more realistic model of magnetic particle behavior during shear strain and 2 about one quarter to one third of the theoretically predicted simple shear strain occurs in these rocks this amount of strain cannot explain the synfolding behavior observed in the allentown formation but could explain the maximum k values at 80 90 unfolding seen in the bloomsburg formation and perhaps other appalachian clastic rocks

strain studies of cleavage development in the chelmsford formation sudbury basin ontario abstract cleavage formation in the precambrian chelmsford formation of the sudbury basin ontario is directly related to the finite strain and deformation path finite strain was measured at the outcrop scale from the shapes and orientations of deformed concretions within sandstones at the microscopic scale from the relative positions of quartz grain centers and via quantitative correlations between the anisotropy of magnetic susceptibility and strain two dimensional strains measured in different sections at each site were combined into three dimensional strain ellipsoids at 16 sites distributed throughout the chelmsford formation outcrop using the magnetic susceptibility correlation a further 527 individual strain ellipsoids were obtained throughout the sites a prominent strain gradient is mirrored by the progressive development of cleavage in the chelmsford formation with strain and fabric development increasing in intensity from nw to se at the least deformed sites cleavage is weak or absent the finite strain reflects a combination of vertical compaction followed by coaxial tectonic layer parallel shortening acting in a subhorizontal nw se direction pressure solution is the dominant deformation mechanism responsible for the formation of cleavage material removed by pressure solution is redeposited as pressure fringes on quartz grains an observation which is compatible with the form of the deformation path which indicates little effect due to volume loss in cleavage formation in these sandstones folds within the chelmsford formation indicate formation by buckling but have very low limb dips decomposition of the finite strain tensor into a compactional part and a layer parallel shortening part suggests that fold initiation and amplification was preceded by about 38 layer parallel shortening the large number of strain ellipsoids obtained from the chelmsford formation provide a significant data base from which a number of important tectonic problems can be examined including the predeformational shape of the sudbury structure

competence contrasts in ductile deformation as illustrated from naturally deformed chert mudstone layers abstract a sample of chert mudstone layers provides a rare opportunity for quantitative analyses of competence contrasts in naturally deformed rocks this sample contains deformed quartz veins possibly formed subperpendicular to bedding during initial bedding normal compaction and abundant radiolarians as strain markers whose viscosity during deformation is approximated by that of chert under several assumptions these allow quantitative analyses of two types of competence contrast in ductile deformation layer competence contrast and inclusion matrix competence contrast layer competence contrast results in strain and cleavage refraction through the layers while inclusion matrix competence contrast is illustrated by the difference in strain state between radiolarians and their matrix a quartz vein presumed to be initially perpendicular to bedding provides estimates of layer parallel shear strains and chert mudstone layer viscosity ratios which were also used as radiolaria matrix viscosity ratios in different layers radiolarian shapes are factorized into cleavage strains and pre cleavage shapes cleavage strains in matrix are then determined from radiolarian strains applying eshelby s equations and their variations as well as the refraction of cleavage through the layers are compared with treagus s theoretical modeling of strain refraction with decreasing layer competence cleavage refracts toward bedding and increases in intensity so that cleavage bedding intersections vary slightly but systematically through the layers suggesting a threedimensional strain refraction all three principal axes of radiolarian and matrix cleavage strain ellipsoids estimated indeed refract from layer to layer strain magnitude systematically increases with decreasing layer competence these results are consistent with the strain refraction theory however no systematic change in strain ellipsoid shape associated with strain refraction is recognized

ability of the fry method to characterize pressure solution deformation abstract the applicability of the fry method to marker distributions deformed by pressure solution is examined four types of pressure solution deformation were modeled they differ by the spacing of the dissolution surfaces relative to the distance between marker centers the amount of volume loss and whether or not markers in contact with dissolution surfaces are dissolved completely the results show that the fry method correctly characterizes each type of deformation but without additional information such as the amount of volume loss it can be used only where the deformation is constant volume and where dissolution surfaces are more closely spaced than marker centers

palinspastic restoration of a post taconian successor basin deformed within a transpressive regime northern appalachians restoration of transpressional orogens requires a three dimensional analysis of the strain state in order to take into account both the pure shear and simple shear components of the deformation and assess their relative contribution throughout the deformation history restoration of the post taconian successor basin the gaspe belt located within the external part of the acadian orogen in the canadian appalachians was performed by using a step by step method based on the successive removal of strain increments the pure shear component contributed 70 of the total strain during the first stages of the deformation whereas the simple shear component contributed 30 of the total strain during the last stages three retrodeformation steps are defined starting with restoration of the last deformation stage and working back to the first deformation stage the first step is to restore slip along acadian strike slip faults the second step is to restore shortening related to the horizontal extension during the acadian regional simple shear event finally the third step is to restore vertical extension related to the pure shear event by removing slip along the reverse faults unfolding and removing internal strain associated with cleavage development retrodeformation of the simple shear component of the transpressive deformation during the first two steps is performed on a horizontal view of the gaspe belt basin which contains the horizontal extension direction and which is perpendicular to the acadian nw se directed compression likewise restoration of the pure shear component is performed in vertical sections which contain the vertical extension and which are perpendicular to the acadian nw se directed compression the palinspastic map presented here is a much more appropriate base map for the basin and allows for a more realistic paleogeographic interpretation of the gaspe belt

duplexes as slip transfer zones application to the himalayan fold thrust belt abstract duplex fault zones and imbricate fans originally termed schuppen schuppenstruktur or imbricate structure were first described in the late 1800s from the alps nw highlands scotland and montana rockies lewis thrust sheet as originally defined duplexes contained shingled imbricate slices bounded above and below by through going thrusts these duplex fault zones commonly occur along the base of major regional thrust sheets or within the body of such sheets accommodating regional bed parallel shortening and transferring slip from a lower stratigraphic horizon to a higher one thereby providing a mechanical advantage to the emplacement of large thrust sheets however faulting is not the only means of layer parallel shortening lps and displacement transfer within duplexes lps cleavage and detachment folds are also common and can play the same role as imbricate faults based on some selected examples we recognize three types of duplexes 1 fault duplex 2 cleavage duplex and 3 fold duplex the style of duplex that forms is likely a function of mechanical stratigraphy and deformation conditions the relationships among the three basic duplex styles can be plotted on a ternary diagram each duplex type constituting an apex given the complexities of most sedimentary sequences hybrid duplexes with a mix of fault fold and cleavage shortening can also form hybrid duplexes plot along the side of the triangle as fault fold fold cleavage and fault cleavage duplexes while those combining all three mechanisms plot in the middle if the partitioning of shortening by the different mechanisms can be quantified the ternary diagram provides a means of representing the contributions of the three mechanisms in shortening and slip transfer along much of the himalayan fold thrust belt a significant portion of the lesser himalayan shortening is taken up by the lesser himalayan duplex a first order fault duplex with subsidiary cleavage and fold development the geometry of and shortening within the duplex varies significantly along the length of the himalaya

contemporary kinematics of the western united states determined from earthquake moment tensors very long baseline interferometry and gps observations using moment tensors from earthquakes between 1850 and 1995 we determine the horizontal velocity gradient tensor field associated with the seismic deformation in the western u s plate boundary zone the velocity vectors obtained from the integration of the seismic strain rates across the entire plate boundary lie within 5 of the nuvel ia pacific north american plate motion direction the magnitude of the earthquake related velocity is 62 of the nuvel 1a total pacific north american plate motion if earthquake occurrence is a random poisson like process then the large formal errors associated with the model velocity estimates are an indication that the 144 year interval is too short to define the long term seismic moment release rate to within an uncertainty less than the deficit between the observed seismic moment release rate and the total long term moment release rate associated with both the seismic and aseismic deformation to spatially resolve the deficit of the earthquake moment release in the last 144 years we have also estimated the total long term horizontal velocity gradient tensor field using seismic strain rate tensors and recent geodetic velocities both with and without the nuvel 1a pacific north american rigid plate motion constraint we find a systematic difference between the southern california earthquake center scec geodetic velocity map and nuvel 1a north american reference frames with a pole at 38 8 n 124 2 w 0 33 m y 1 this difference is significant at the 99 confidence level and indicates that 4 7 mm yr of ne sw convergence is absorbed in offshore areas of southern california if both the scec velocity map and nuvel 1a correctly describe the relative motion between the pacific and north america plates deficit strain rates calculated from comparison of observed seismic strain rates over the last 144 years with long term model strain rate tensors are largest in areas east of san francisco bay in the transverse ranges and along the southern san andreas fault and san jacinto fault the deficit in each 100 by 50 km grid area within these regions is equivalent to an accumulation of strain in the last 144 years that would be released by an mw 7 earthquake elsewhere the accumulated strain in the last 144 years is small except in northern mojave desert along the garlock fault and in the region southwest of the southern san andreas san jacinto fault zone within each 100 by 50 km grid area in these regions the accumulated strain is equivalent to that released by an mw 6 5 7 0 earthquake

the determination of progressive deformation histories from antitaxial syntectonic crystal fibres abstract antitaxial syntectonic crystal fibres are modelled here as mechanically passive features the fibres representing displacement paths forming within a homogeneously deforming material evidence that many fibres develop in this way is widespread asymptotic curvature thinning of fibres and strained old fibres a measuring technique is proposed by which the complete deformation history excluding translation may be determined the method involves the iterative unstraining of two complete fibres whose development began and ended simultaneously a source of error is introduced by assuming that each of the two fibres developed at constant proportional rates although synthetic examples suggest this error to be minimal it is suggested that the kinematics of non passive fibres are unobtainable since the rheologies and boundary conditions of the material involved are relatively unknown and cannot be determined from geometry alone analysis of natural fibres found within the ordovician slates in new jersey u s a indicates that volume losses of up to 50 may occur during the formation of some slates general constraints concerning the geometrical analysis of syntectonic crystal fibres are briefly discussed and it is concluded that deformation histories must be interpreted with some modicum of caution

kinematics stress deformation and material behavior abstract a compact review is given of some fundamentals of the theory of flow in materials and of the bulk behavior of experimentally deformed rocks kinematics is discussed first because it provides an easy introduction to second order tensor quantities these are explained as quantities linking the components of pairs of vectors to one another for example velocity vectors to position vectors the velocity gradient tensor or stress vectors to plane normal vectors the stress tensor the fundamental theorem of stress theory is derived from the requirement of force balance at a point here and elsewhere the treatment is mostly two dimensional this saves space yet provides an introduction to principles that are important again in three dimensions mohr circles are used extensively to represent two dimensional tensor quantities geometrically including asymmetric velocity gradient and deformation tensors the decomposition of a general deformation into components of translation rotation and strain is explained and this may lead to greater appreciation of such unfamiliar possibilities as coaxial accumulation of a simple shear deformation the section on experimental deformation is concerned mainly with the measured strengths of rocks and how these can be extrapolated to strengths at geological strain rates the text is followed by a glossary

orientation history and rheology in slates kodiak and afognak islands alaska abstract theoretical and experimental studies have shown that slates have a roughly parabolic yield curve in and space where is the orientation of cleavage relative to the maximum compressive stress is the orientation of cleavage relative to the incremental shortening direction and is the deviatoric stress deformation mechanisms that operate in low grade rocks such as diffusive mass transfer in a grain boundary fluid dislocation creep and frictional grain boundary sliding may have stress strain rate relationships that depend on during a progressive strain history and may vary as a function of the strain path thus the sequence of dominant deformation mechanisms as well as the stress strain history may depend on the orientation history or variations in as strain accumulates in the kodiak formation a slate belt in southwest alaska the orientation history and deformation mechanisms were evaluated using incremental strain indicators and microstructures there are four successive textural events 1 development of a slaty cleavage s2 with antitaxial growth of fibrous quartz and mica in pressure shadows fi2 2 static growth of siderite and chlorite porphyroblasts 3 10 70 rotation of porphyroblasts relative to s2 with growth of curved syntaxial siderite fibers and 4 antitaxial growth of fibrous quartz and micas with local development of a crenulation cleavage s3 cumulative incremental strain and progressive finite strain histories were determined in 23 samples from syntectonic fibers and orientation histories were reconstructed from information provided by cumulative incremental strain histories textural and strain analyses indicate that 1 the strain history of nearly all samples can be approximated by two coaxial strain accumulations separated by a rigid rotation 2 development of crenulation cleavages was dependent on the orientation history and the magnitude of the early strain accumulation i e the degree of mica alignment at the completion of d2 3 unstable behavior or buckling occurred when suggesting that the angle of internal friction was close to 0 i e basal slip in micas may have been more important than frictional grain boundary sliding and 4 diffusive mass transfer was accompanied by anisotropic plastic deformation so the orientation history could be used to reconstruct the history

mica beards in three slates morphology formation and bearing on the strain history beards are intergrowths of mica chlorite and quartz or feldspar on detrital grains in weakly metamorphosed sedimentary rocks the three samples studied contain beards of mica and quartz or feldspar their internal morphology shows a variation in mica orientation related to the external foliation matrix formation occurred during foliation development with a syntaxial growth history in three dimensions the beards have oblate shapes so that they are present in all planes cut parallel to the shortening direction this indicates flattening strain conditions around the detrital grains during the beard formation

the influence of deformation partitioning on dissolution and solution transfer in low grade tectonic melange dissolution of quartz and the recryst allization and re equilibration of phyllosilicates produce the dark anastomosing seams that dominate microstructures of tectonic melange which occur in a low grade imbricated and multiply deformed mid palaeozoic intracra tonic fiysch sequence in northeastern australia seams are composed of very closely spaced or coalesced cleavage lamellae which are very thin layers of extremely fine grained phyllosilicates cleavage seams enclose lenses of silt stone or greywacke which formerly occurred in continuous sedimentary layers indicating extremely heterogeneous and disruptive deformation microphacoids enclosed by cleavage seams have subtle shape asymmetries analogous to those of porphyroclasts phyllosilicate preferred orientations within microphacoids commonly lie at a low angle to enclosing seams and asymmetric relationships occur within seams the shape and fabric asymmetries appear to be constant and are regarded as analgous to s and c planes the number and extent of seams the amount of dissolution they indicate and the efficiency of deformation partitioning imply some enhancement of chemical activity and substantial silica loss from the system this in turn suggests the passage of large amount of silica undersaturated fluid and melanges may be zones of high fluid flow however the microstructures and the disruptive nature of the fabrics may also reflect the influence of high bulk shear strains and suggest some relationship between the shearing component of deformation and the development of cleavages and foliations