development of cleavage in limestones of a fold thrust belt in eastern new york abstract tectonic cleavage has developed in lower devonian limestones of the hudson valley fold thrust belt in new york state morphology and distribution of cleavage in these limestones is controlled by the amount of clay quartz matrix present and by strain only limestones with greater than 10 clay quartz matrix developed widespread cleavage x ray diffraction analyses indicate that the clay matrix was altered during deformation the width of the 001 illite peak in cleaved lime wackestone is less than that in uncleaved lime wackestone from the same stratigraphic level a minimum of 10 clay is necessary to provide interconnectivity between sites of dissolution and the free fluid system preliminary analyses of bulk chemistry indicate that calcite is removed from the local rock system during cleavage development supporting proposals that circulation of fluid through the rock plays a major role in the development of cleavage textural evidence suggests that both pressure solution and free face dissolution contribute to the removal of ions at grain boundaries cross cutting relations indicate that cleavage was initiated early during the development of the fold thrust belt but continued to develop during the late stages of folding

quartz veins record earthquake related brittle failure and short term ductile flow in the deep crust abstract discordant quartz veins in a retrograded eclogite amphibolite western gneiss region norway formed at temperatures of about 500 to 550 c the parental fractures crosscut the foliation and show branching indicating rapid crack propagation at high differential stress the shape of the quartz veins indicates intense inhomogeneous ductile deformation of the host rock during opening and sealing controlled by the presence of the cohesionless fluid filled fractures the vein quartz microfabrics indicate crystallization in an open cavity implying a stage of very high permeability and fluid flow the event of brittle failure at 500 to 550 c followed by an episode of inhomogeneous ductile deformation is attributed to stress changes related to the earthquake cycle i e coseismic loading and postseismic creep the record suggests seismic activity at the nearby low angle normal fault at 15 to 25 km depth and provides insight into transient crustal properties and processes near active faults at great depth

3 d deformation pattern analysis and evolution of the anisclo anticline southern pyrenees understanding the genetic relationships of folding related deformation structures is of importance for both academic and industrial purposes we analysed the three dimensional deformation pattern of the anisclo anticline in the southern pyrenees the specifically designed statistical method includes sequential steps of statistical and spatial data analysis and classification our results indicate that pressure solution cleavage frequency exhibits a spatial distribution that depends on the position within the fold conversely such a dependence does not occur in joints and veins consequently our data suggest that pressure solution cleavage is the most appropriate deformation structure for unravelling fault fold kinematics in carbonate multilayer in particular we found that the spacing of solution cleavages s is related to the corresponding bed thickness h this supports the use of h s value for deformation intensity quantification instead of spacing in the anisclo anticline analysis of h s indicates the occurrence of three main deformation panels whose restoration suggests that fold evolution progressed from layer parallel shortening to decollement folding up to thrust breakthrough and fault propagation folding comparison of h s values with finite strain data indicates that line length was not preserved during fold evolution this evidence has important implications for the kinematic interpretation of layer parallel shortening and cross section balancing

correlation of strain and the anisotropy of magnetic susceptibility in the onaping formation evidence for a near circular origin of the sudbury basin abstract measurements of finite strain the anisotropy of magnetic susceptibility the magnetic carrier of the susceptibility and fieldwork have been carried out in the onaping formation of the sudbury basin ontario the magnetic fabric indicates that changes in the magnitude and type of magnetic susceptibility ellipsoids closely mirror the changing pattern of deformation from northwest to southeast across the onaping formation outcrops a quantitative correlation has been established between finite strain measurements and the magnetic susceptibility results and this allows the number of available strain measurements to be extended by more than 500 samples the finite strain results suggest a deformation path in which the onaping formation was first affected by nw se directed horizontal layer parallel shortening which produced an upright tectonic cleavage subsequently components of overthrust nw directed simple shear were superimposed upon the already deformed rocks of the onaping formation the result of removing the strain according to the sequence of superimposed deformations revealed by the deformation path suggests that the sudbury basin was nearly circular in shape prior to its deformation consequently a major objection to the meteorite impact theory for origin of the sudbury structure is eliminated

restoring post impact deformation at sudbury a circular argument recent seismic reflection observations have shown a considerable shortening of the sudbury structure in a direction roughly perpendicular to its long axis using a kinematic reconstruction technique for gridded geophysical data which takes into account non uniformly distributed strain we reconstruct the pre deformation shape of the sudbury structure and show that it could have been circular at the time of its formation 1 85 ga this supports an impact origin

deformation of the sudbury structure paleomagnetic evidence from the sudbury breccia abstract paleomagnetic results from fine grained samples of sudbury breccia collected from 28 sites around the northern half of the 1 85 ga sudbury igneous complex sic reveal the existence of two major components of magnetization a and b a carried by magnetite was formed close to the time of the sic and has a direction that is related to the dip of the norite unit within the different ranges of the sic component b mainly carried by pyrrhotite is a younger secondary magnetization of more problematical origin in part related to heating during the 1 24 ga sudbury magmatic event in the northwest part of the sic a is found in breccia clasts intermediate norite sublayer levack gneiss and matachewan diabase indicating that it is due to baking by the sic tilt correcting the west range by 36 the north range by 22 and the northern east range by 36 about axes parallel to local strike of the norite minimises the dispersion of the paleomagnetic data to give a pre folding direction of 199 4 78 8 the paleomagnetic data are similar to those obtained by morris morris w a 1984 paleomagnetic constraints on the magmatic tectonic and metamorphic history of the sudbury basin region in pye e g naldrett a j giblin p e eds the geology and ore deposits of the sudbury structure special vol 1 ontario geological survey pp 411 427 on the sic suggesting for the first time that the sic and the surrounding basement were deformed probably during the 1 9 1 7 ga penokean orogen as a single unit the un folding of the paleomagnetic directions indicates that sic limbs were already inclined a result of the original intrusion configuration or a syn folding remanence it is possible that the sic was originally flatter if the distribution of paleomagnetic directions is the result of flexural flow folding this explanation could also produce a similar distribution of paleomagnetic directions across the basin but cannot be quantified due to the lack of measurable fold related strain in breccia and sic units around the northern half of the basin

solution cleavage and its relationship to major structures in the idaho utah wyoming thrust belt micrites of the jurassic twin creek formation in the idaho utah wyoming thrust belt show spaced cleavage developed during folding and thrusting cleavage in each thrust sheet forms mainly by pressure solution aided by elevated temperatures and pressures caused by increased overburden as a result of emplacement of earlier overriding thrust sheets within each thrust sheet cleavage develops early and is contemporaneous with microscopic to mesoscopic buckle folds and faults large scale ramp folds formed during major motion on the thrust postdate the cleavage and passively rotate it into major fans

riedel shear a mechanism for crenulation cleavage drag folds 1 from the microfaulting of inclined markers distinguish crenulation cleavage from other cleavage types cleavage as riedel r shears nucleates obliquely to planar anisotropy of foliated rocks and at various angles related to to the shear zone boundaries folds 2 with axes parallel to the instantaneous 1 at high angle and partway with r shears are formed in the xz plane of strain ellipsoid the angle between folds and cleavage is changed in the progressive deformation the largest antithetic counterclockwise r shears rotation and largest opening of initial angle between folds and fractures up to 170 is achieved in the progressive transtension 1 this is not geometrically possible in the simple shear and transpression but forward rotation of the r shears of excess length is prevented by the constant or diminishing thickness of the shear zone the crenulation folds 3 amplify the drag folds of the inclined faulted marker and nucleate with axial planes parallel to the cleavage at higher strains the cleavage propagates further as p shears parallel to flanks of tightened crenulation folds the r shears are in higher order folds 4 reoriented into the axial planar position by pure shear in the yz plane of the first incremental deformational ellipsoid and by the shear induced by flexural slip along the layer boundaries the stretching of the fold limbs and the non coaxial ductile deformation of microlithons in their slip perpendicular to fold axis deform former drag and crenulation folds to a characteristic pattern striation and or faint lineation preserved in the cleavage plane trace the shear directions the shear sense is indicated by the cleavage folds transection and by the asymmetrical structures in the plane cut perpendicularly to clevage and parallel to striations

strain magnetic fabric and paleomagnetism of the deformed red beds of the pont rean formation brittany france a joint study of strain anisotropy of magnetic susceptibility ams and paleomagnetism has been conducted in the deformed red beds of the ordovician pont rean formation brittany france analysis of results from 13 sampling sites shows that homogeneous strain estimated from the shape of elliptical reduction spots in each site controls the development of a magnetic fabric during the hercynian folding of this formation the good correlation between strain and ams tensors is interpreted as mainly arising from a strain induced progressive rotation of planar hematite that tends to align within cleavage plane this rotation of magnetic carriers in turn induces a rotation of net measurable pretectonic remanent magnetization toward cleavage because of the high angle between the initially subvertical ordovician remanent magnetization and the regionally subhorizontal shortening direction this deviation of the pretectonic magnetization is achieved without any scattering but with a probable clustering effect upon within site initial dispersions for the same reason the overall distribution of mean site pretectonic magnetization vectors is clustered at the in situ deformed state this results in an anomalous behavior of the classical fold test that could erroneously lead to assignment of a syntectonic to post tectonic age to the magnetizations finally the strain removal technique based upon the passive behavior hypothesis is applied to the deviated vectors it allows recovery of the initial direction of these pretectonic ordovician magnetizations d 235 i 75 95 6 5

finite strain patterns and their significance in permian rocks of the alpes maritimes france abstract more finite strain data has been obtained from autochthonous permian mudstones of the alpes maritimes s e france these new data were computed from field measurements of green spots on all available sections deformed mudcracks and from the quantitative correlation between magnetic susceptibility anisotropy and finite strain in these rocks previously published finite strain data and the new results are presented on a series of structural maps and cross sections for the dome de barrot the tinee and vionene region and the roya region as in previous studies difficulties arise in explaining the apparently variable extension parallel with the 100 subhorizontal bedding cleavage intersection either this is real or there were large volume changes during the tectonic deformation study of quartz fibres developed in deformed mudcracks in the tinee valley suggest that early in the tectonic history incremental stretching directions were parallel with the bedding cleavage intersection while later they were down dip in the 100 trending cleavage since these permian rocks have remained stuck to the argentera basement they also record displacements and deformations in the basement the early 100 subhorizontal stretching is consistent with nw se dextral strike slip basement faulting while later down dip stretching in the cleavage is consistent with contraction faults in the basement this information and new palaeomagnetic data on the same samples are combined with recent geophysical evidence and regional tectonic studies to provide a new precision to the tectonic history of this part of the western alpine external zone

some guidelines for the practical application of fry s method of strain analysis abstract a systematic analysis of patterns in artificial and natural point distributions is presented in order to demonstrate how the nature and degree of anticlustering of point distributions affect the character of fry diagrams derived from them ideally anticlustered artificial point distributions illustrate the nature of the dependence between the degree of anticlustering and the minimum number of points required in such a distribution if it is to reveal strain accurately by fry s method in addition these distributions provide straightforward results which aid in the interpretation of less ideally anticlustered natural point distributions the results from the artificial distributions may be used to estimate the minimum number of points required for strain determination in natural distributions of varying degrees of anticlustering as long as the anticlustering is sufficiently strong however application of the results from the artificial distributions to less strongly anticlustered natural point distributions shows not only that the existence of a vacancy field is an insufficient criterion for determining whether or not fry s method is appropriate for strain determination but also that the nature of the anticlustering in these natural distributions limits the effectiveness of enhancing strain definition by increasing the number of points composing the distribution

geoscience impact a synthesis of studies of the sudbury structure geophysical probing results are synthesized into a three dimensional framework necessary for understanding the genesis of the sudbury structure based primarily on seismic reflection results centred on the sudbury igneous complex remnants of crustal melting from a catastrophic meteorite impact are superimposed on the juxtaposition of mid crustal rocks exhumed during the archean against deformed paleoproterozoic sedimentary rocks sedimentation metamorphism deformation and metasomatic overprints are all part of the post impact history of sudbury and tend to dominate the geophysical response of the structure pre impact deformation although certainly preserved in some aspects of sudbury geology is not clearly expressed in the geophysical data nor are any elements of impact induced deformation geophysical views of the sudbury igneous complex are thus somewhat biased in representing mostly the post impact but pre grenvillian history of the region with the exception of igneous events establishing th

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

lignin phenols and bit index distributions in the amur river and the sea of okhotsk implications for the source and transport of particulate terrestrial organic matter to the ocean delta and coastal regions play a key role in the global carbon cycle as the main repository of inputs of terrestrial organic matter delivered by rivers to marine sediments the amur river system is one of the largest in asia and supplies organic matter to the sea of okhotsk and the north pacific ocean we measured lignin phenols a proxy for terrestrial plant derived organic matter and the branched and isoprenoidal tetraether bit index a proxy for riverborne soil organic matter in soils and river bed sediments from the amur river basin and surface sediments from the sea of okhotsk to study the source transport and deposition of fluvial particulate organic matter to the ocean concentrations of lignin phenols are relatively high in sediments from the shallow continental shelf compared to that of the deep offshore basin for the first time we report a spatial distribution of the bit index which shows a similar pattern to that of lignin phenol concentrations with relatively high values in the coastal sites the highest values of both lignin concentrations and bit values are observed in a site proximal to mouth of amur river these results indicate that terrestrial organic matter deposited in the sea of okhotsk mostly originates from soil organic matter supplied from amur river spatial distributions of lignin phenols toc lp toc and the bit index in the sea of okhotsk and comparison with s v a contribution index of angiosperm vs gymnosperms and c v ratios indicative of the relative contribution of non woody tissue vs woody tissue between the amur river basin and okhotsk sea samples suggest that amur river fluvial organic matter is supplied and deposited to the northwestern continental shelf furthermore s v values from our amur river and okhotsk sea continental shelf sediment samples are consistent with the reported s v ratio 0 32 of particulate organic matter in the north pacific intermediate water npiw layer 750 m depth hence our study supports previous studies from the nw pacific ocean which suggest inputs of terrestrial organic matter from the amur river via the sea of okhotsk as a major source of particulate organic matter to the north pacific ocean

the correlation of magnetic anisotropy with strain in the chelmsford formation of the sudbury basin ontario abstract a quantitative correlation has been established between finite strain and the anisotropy of magnetic susceptibility ams in sandstones of the precambrian chelmsford formation of the sudbury basin ontario investigations of the progressive acquisition of isothermal remanent magnetization and its destruction with reverse field and thermal demagnetization as well as microscopic examination of polished thin sections show that both pyrrhotite and magnetite are present in the sandstone measurements of the ams have been carried out at 16 sites distributed throughout the chelmsford formation outcrop considerable variation in the shapes of the magnetic susceptibility ellipsoids axes k max k int k min exists within each site with the k max and k int axes contained in the cleavage planes where developed the magnitudes of the magnetic susceptibility axes have been quantitatively correlated with strain measurements carried out by clendenen et al this issue two different strain to magnetics correlations have been carried out between the site mean strain determined using deformed concretions and the mean values of the ams at each site and between individual specimen strain values determined at the microscopic scale and the individual specimen ams in both cases separate correlations were made between strain long intermediate and short axes and their corresponding magnetic k max k int and k min axes at 10 sites the site mean strain values were derived from strain analysis of the concretions and at an additional 6 sites the site mean strain values were derived from the ams to strain correlation 527 individual cores were converted to equivalent strain values using the ams structural correlation of individual specimens this study extends the use of ams methods to include strain determination in sandstones and provides an order of magnitude increase in the available number of such data for further structural analysis

pencil structure and strain in weakly deformed mudstone and siltstone abstract weakly deformed mudstone and siltstone middle ordovician knobs formation of the appalachian valley and ridge province south western virginia u s a show strain dependent transitions between bedding fissility pencil structure and cleavage pencil structures are associated with a bulk inhomogeneous shortening deformation where minimum principal strain z ranges between 9 and 26 shortening assuming a plane strain and constant volume where strains are less bedding fissility dominates pencil fragments are defined by intersecting fracture sets subparallel to the pre existing bedding fissility and cleavage their long axes are both parallel to the bedding cleavage intersection and to the inferred y axis of the tectonic strain ellipsoid pencil development is considered to result from fracturing along both fabric anisotropies during weathering and post tectonic stress relaxation pencils show variations in size and shape depending on lithology grain size and composition degree of initial clay preferred orientation degree of cleavage development type of cleavage total bulk strain and degree of strain homogeneity their shape l w however is a direct measure of total y z strain since strain determinations from chlorite pressure fringes on framboidal pyrite within the pencil fragments give y z 0 913 0 019 l w pencil structure is therefore a potential strain marker in weakly deformed rocks

a trishear model for the deformation of the sudbury igneous complex canada abstract the sudbury igneous complex sic canada is an impact induced layered sheet of crystalline rocks deformed into an asymmetrical fold basin the sudbury basin the basin geometry at depth is largely unknown as few attempts were made to quantify displacement and rotation of layer contacts we propose that the dip of layer contacts and foliation surfaces in the southern sic can be approximated by trishear fault propagation folding trishear deformation accounts for 1 angular discordances between upper and basal sic contacts 2 local overturning of the sic 3 progressive steepening of foliation surfaces from nw to se 4 strain gradient in the sudbury basin sedimentary rocks and 5 thickness variations in sic layers moreover the south range shear zone a zone of moderately strong metamorphic fabrics coincides with the surface manifestation of the proposed trishear zone we demonstrate the use of structural data together with forward kinematic modelling to identify the strain distribution within the sic rotation of sic contacts and thickness changes of sic layers backward kinematic modelling provides information on the initial geometry of the sic and is used to restore the shape of the igneous sheet showing that the sic was shortened by approximately 10 km in nw se diameter most of the shortening was accommodated by 40 reduction in the thickness of the upper sic layer

strain paths during slaty cleavage formation the role of volume loss abstract strain analyses of slates commonly investigate the sequence of shapes that must have been superimposed to produce the observed strained state methods such as rf try to quantify the cleavage forming deformation and see through that component to examine any initial shape an alternative approach is to reverse this process by considering the variation in final shapes derived when plausible cleavage forming strain ellipsoids are superimposed on realistic initial shapes specifically a deformation involving both plane strain and volume loss may be superimposed on an initial shape formed by diagenetic flattening in this case the angle between bedding and the incipient cleavage plane is an important variable in controlling final ellipsoid shapes this approach has been adopted for a data set measured from the ordovician borrowdale volcanics in the english lake district results show that neither successive increments of plane strain without volume loss nor incremental plane strain plus volume loss adequately explain the observed pattern of final shapes one permissible solution is generated if increments of pure volume loss perpendicular to the incipient cleavage plane precedes plane strain distortion initial layer parallel shortening may therefore play an important part during cleavage development in these slates

strain partitioning in the helvetic thrust belt of eastern switzerland from the leading edge to the internal zone abstract the strain and strain partitioning in the helvetic thrust belt are analysed in order to determine their variation across the belt from the external thin skinned portion to the internal thick skinned portion and in order to begin the detailed mechanical analysis of the entire fold and thrust belt coarse grained limestones of jurassic and cretaceous age were chosen for analysis because they can be traced from the external to the internal zones the strain within a bed is partitioned into three components transgranular pressure solution microfaults veins twinning granular and intragranular exclusive of twinning crystal plasticity associated with recrystallization transgranular strain was very important in the early history of the helvetic nappes giving way to twinning at a later stage under tectonic burial twinning strain was early in the infrahelvetic complex giving way to intracrystalline deformation at the later stage of burial the transition from transgranular to intragranular dominated strain occurred at a vitrinite reflectance value of 3 5 significantly below the greenschist grade of metamorphism in a large scale fold at the leading edge of the helvetic nappes transgranular strains were associated with the buckling stage of the fold and twinning occurred during fold tightening in more internal parts of the helvetic nappes twinning strains are also late with regard to transgranular strains but here their pattern corresponds to the regional finite strain pattern in the internal zone the infrahelvetic complex twinning seems to have been an early event and records an initial layer parallel shortening followed by regional internal deformation with intragranular strains