craters boulders and regolith of 101955 bennu indicative of an old and dynamic surface small kilometre sized near earth asteroids are expected to have young and frequently refreshed surfaces for two reasons collisional disruptions are frequent in the main asteroid belt where they originate and thermal or tidal processes act on them once they become near earth asteroids here we present early measurements of numerous large candidate impact craters on near earth asteroid 101955 bennu by the osiris rex origins spectral interpretation resource identification and security regolith explorer mission which indicate a surface that is between 100 million and 1 billion years old predating bennu s expected duration as a near earth asteroid we also observe many fractured boulders the morphology of which suggests an influence of impact or thermal processes over a considerable amount of time since the boulders were exposed at the surface however the surface also shows signs of more recent mass movement clusters of boulders at topographic lows a deficiency of small craters and infill of large craters the oldest features likely record events from bennu s time in the main asteroid belt

implications for ice stability and particle ejection from high resolution temperature modeling of asteroid 101955 bennu the finding by the osiris rex origins spectral interpretation resource identification and security regolith explorer mission that its target 101955 bennu is an active asteroid has raised questions as to whether the observed particle ejection events are driven by temperature to investigate sublimation of water ice and rock thermal fracture as possible temperature driven causes we modeled the global temperatures of bennu and searched for correlations with the identified ejection points on the asteroid surface we computed temperatures with the advanced thermophysical model and the 75 cm resolution global shape model of bennu derived by the osiris rex mission we find that 1856 m 2 of bennu s polar regions have orbit averaged temperatures that are sufficiently cold to enable water ice if buried within the top few meters of the surface to remain stable over geological timescales millimeter thick layers of surface water ice are also stable over 10 3 year timescales within polar centimeter scale cold traps however we do not find evidence of conditions enabling ice stability in the warmer equatorial regions where ejection events have been observed implying that sublimation of water ice is not the cause of particle ejection conversely rock thermal fracture remains a possible mechanism of particle ejection we find high amplitudes of diurnal temperature variation a proxy for the efficacy of thermal fracturing at all latitudes on bennu due to its extreme ruggedness therefore if rock thermal fracture is the mechanism particles could be ejected from any latitude which is consistent with the continued observations of particle ejection by osiris rex

upwind conservative scheme for the saint venant equations an upwind conservative scheme with a weighted average water surface gradient approach is proposed to compute one dimensional open channel flows the numerical scheme is based on the control volume method the intercell flux is computed by the one sided upwind method the water surface gradient is evaluated by the weighted average of both upwind and downwind gradients the scheme is tested with various examples including dam break problems in channels with rectangular and triangular cross sections hydraulic jump partial dam break problem overtopping flow a steady flow over bump with hydraulic jump and a dam break flood case in a natural river valley comparisons between numerical and exact solutions or experimental data demonstrated that the proposed scheme is capable of accurately reproducing various open channel flows including subcritical supercritical and transcritical flows the scheme is inherently robust stable and monotone the scheme does not require any special treatment such as artificial viscosity or front tracking technique to capture steep gradients or discontinuities in the solution

simple shear deformation and quartz crystallographic fabrics a possible natural example from the torridon area of nw scotland ln this paper the microstructures and crystallographic fabrics of a 30 cm wide deformed quartz vein from the torridon area of nw scotland are described the vein which lies along a joint separating two blocks of proterozoic gneiss was deformed by crystal plastic processes when the rigid joint blocks moved in opposite directions parallel to the vein margins mylonitic foliation within this quartzose ductile shear zone locally displays the classic orientation variation expected for heterogeneous simple shear deformation in thin section the vein is a mylonite composed of dynamically recrystallized elongate quartz grains aligned oblique to the mylonitic foliation fabrics within the central part of the vein have been examined by optical and x ray texture goniometry methods together with orientation distribution function odf analysis the a axis fabric consists of a dominant single point maximum orientated within the xz plane at 9 to the lineation x this point maximum occupies a pole position to the corresponding single girdle c axis fabric for individual positions on the c axis fabric skeleton the orientations of potential crystallographic slip systems slip plane and direction relative to shear zone co ordinates have been calculated by odf analysis the calculation of relative resolved shear stresses schmidfactors for the potential slip systems assuming a simple shear kinematic framework reveals an elegantly simple relationship between individual grain c axis orientation and correspond ing orientations of potential slip systems these results are readily interpreted in terms of bulk simple shear deformation

numerical prediction of dam break flows in general geometries with complex bed topography dam break flows in general geometries with complex bed topography are simulated numerically using a high resolution godunov type cut cell method the model is based on the shallow water equations with appropriate source terms a vertical step in the bed is treated efficiently and accurately with the surface gradient method for dam break flows occurring in complicated geometries the cartesian cut cell method together with transmissive boundary conditions is incorporated verification of the method is carried out by predicting dam break flows typical of practical situations i e dam break flows over a vertical step into bent channels and a dam break flow over a bump in a bed with both transmissive and reflective boundary conditions at the channel end the results are compared with experimental data showing good agreement the method is simple efficient and conservative it shows promise for handling a wide range of dam break flows

cretaceous to neogene cooling and exhumation history of the oetztal stubai basement complex eastern alps a structural and fission track study the central austroalpine oetztal stubai basement complex osk of the eastern alps together with its overlying sedimentary brenner mesozoic bmz and tectonic units upper austroalpine nappes underwent extension and exhumation during the cretaceous before its incorporation into the hanging wall of the neogene brenner normal fault during this late cretaceous to early tertiary deformation the brenner mesozoic and the immediately underlying uppermost part of the osk developed a strong stretching lineation within a near horizontal and often mylonitic foliation related to consistent top to ese directed transport quartz and calcite behaved ductilely throughout the area whereas dolomite shows a transition from brittle fracture in the north to plastic flow in the south consistent with the known cretaceous metamorphic temperature gradient the transition to crystal plastic flow of dolomite occurs at 480 c quartz textures indicate an increase in the contribution of prism glide together with a decrease in basal glide toward the south also consistent with the temperature gradient in the osk and bmz fission track analysis of both zircon and apatite along a n s profile in combination with existing data from the literature allows a continuous cooling path to be constructed for the osk cooling of the eastern osk started at 90 ma the thermal peak of metamorphism and ended some 30 myr later at near surface temperatures at 60 ma the northern region had already cooled below the upper limit of the apatite partial annealing zone whereas in the south cooling related to this exhumation phase stopped at temperatures between 100 and 200 c the ese directed shearing is interpreted as late cretaceous to early tertiary normal faulting that exhumed the osk and brought the upper austroalpine blaser and steinacher nappes into contact with the underlying brenner mesozoic the pattern of alpine metamorphic isograds established in the osk directly reflects the geometry and kinematics of this late cretaceous early tertiary exhumation due to low angle normal faulting

simple shear experiments on calcite rocks rheology and microfabric ideal simple shearing of carrara marble and solnhofen limestone was achieved by inserting calcite rock slices into sandstone cylinders precut at 35 the experiments covered a wide range in temperatures 25 900 c at confining pressures of 200 and 250 mpa and at strain rates between 10 3 and 10 5 s 1 shear strains of up 2 7 were achieved the stress strain data for simple shear favourably compare with predictions on the basis of existing flow laws established in coaxial testing this comparison demonstrates that the simple shear experiments covered most of the previously established flow regimes for calcite rocks at the highest temperatures carrara marble exhibited substantial work softening after high shear strains a complete texture analysis was carried out with the u stage and a texture goniometer the following four distinct microfabric regimes were found 1 twinning regime an oblique c axis maximum deflected from the pole to the flattening plane towards 1 and against the imposed sense of shear results directly from e twinning extensive twinning some grains are completely twinned rapidly rotates the c axes into near parallelism with 1 this regime was observed for carrara marble deformed at temperatures below 700 c and for solnhofen limestone at room temperature 2 intracrystalline slip regime three c axis maxima were observed in both rock types at more elevated temperatures and in the absence of twinning these c axis orientations result from an alignment of slip planes and slip directions into parallelism with the shear zone boundary and the shear direction respectively this finding supports the idea of an orientation for easy slip resulting from simple shearing in addition to r and f glide basal glide is inferred to have been operative 3 grain boundary sliding regime a great circle distribution of c axes approximately perpendicular to the direction of finite shortening is observed this texture is weaker compared to the other regimes it is interpreted to result from minor contributions of f slip towards total strain this regime is restricted to fine grained solnhofen limestone deformed at the highest temperatures 4 grain boundary migration regime only in carrara marble deformed at the highest temperatures is there substantial grain boundary migration recrystallization the texture consists of a dominant c axis maximum oriented perpendicular to the shear zone boundary this single maximum corresponds to an orientation for easy slip for basal slip grain boundary migration assists rapid lattice reorientation and leads to geometrical work softening quantitative analysis of grain boundary surface orientations gave the following results within the twinning and the intracrystalline slip regimes the characteristic grain shape is elliptical for both rock types the strain ellipses derived from this analysis closely correspond to the known finite strain at the lowest temperatures at intermediate temperatures and especially in carrara marble there is a consistent trend for the aspect ratios to indicate too little flattening and for the angles between the long axis of the strain ellipse and the shear zone boundary to be too small in the absence of grain boundary migration recrystallization this finding indicates minor translations of grains with respect to one another grain boundary sliding or translations accommodated in the mantle regions of grains at the highest temperatures where extensive grain boundary migration occurs in carrara marble grain boundary migration regime two preferred orientations of grain boundaries are observed 1 parallel to the shear zone boundary and 2 parallel to an oblique direction deflected 20 away from the normal to the shear zone boundary in the sense of the imposed shear the same pattern of grain boundary alignment is observed in solnhofen limestone deformed in the grain boundary sliding regime the geological applications of this experimental work are discussed in terms of calcite tectonites in particular and sheared rocks in general

strain pattern within and around denser blocks sinking within newtonian salt structures abstract blocks of dense material such as anhydrite entrained in salt structures have been proposed to sink through their host material here we present the results of numerical models that analyse strain patterns within and around initially horizontal anhydrite blocks viscosity 1021 pa s sinking through newtonian salt with a viscosity of 1017 pa s in addition the influence of the block aspect ratio thickness to width ratio ar is analysed the model results show that the blocks are folded and marginally sheared to approach streamlined shapes the effectiveness of this process is a function of the block ar and influences the sinking velocity of the blocks significantly final sinking velocities are in the range of ca 1 7 3 1 mm a around the block in the salt an array of folds and shear zones develops during block descent the structure of which is principally the same independent of the block ar however the size and development of the structures is a function of the block size monitoring of strain magnitudes demonstrates that the salt is subject to extremely high strains with successively changing stress regimes resulting in closely spaced zones of high adjacent to low strain in comparison to the anhydrite blocks strain magnitudes in the salt are up to one order of magnitude higher

microstructural evolution and rheological behaviour of marbles deformed at different crustal levels abstract microstructures from naturally deformed marbles were investigated from a nappe pile with inverted barrovian metamorphic zones detailed microstructural and textural work combined with existing pt data allows us to correlate microstructural types with tectonic events type 1 microstructure related to d1 continental underthrusting shows highly asymmetrical grain boundaries increasing grain size and increasing intensity of lattice preferred orientation with increasing metamorphic grade these characteristics suggest that dislocation creep with concommitant grain boundary migration operated during the simple shear dominated underthrusting regime paleopiezometric and strain rate estimates show a decrease of flow stress with increasing metamorphic temperature and a strain rate of around 10 14 s 1 thrust related microstructure type 2 is developed in upper and lower nappes and is characterised by grain size reduction increase of grain boundary symmetry and weaker textures microstructural and textural studies indicate dislocation creep with possible contribution of grain boundary sliding sub grain rotation paleopiezometry and strain rate estimates show a decrease in flow stress with respect to the type 1 microstructure and strain rate increase to around 10 12 to 10 13 s 1 type 3 microstructure is developed in thrust related shear zones in the parautochthon and syn convergent extensional zones in the top of the nappe pile this microstructure shows a high contribution of diffusion creep indicating low values of flow stress and significant weakening of marble layers the general feature of studied area is the localisation of deformation into marbles during thrusting in low metamorphic grades while in higher grades marbles are not exploited as lubricating layers

deformation experiments on anhydrite rocks of different grain sizes rheology and microfabric miiller w h schmid s m and briegel u 1981 deformation experiments on anhydrite rocks of different grain sizes rheology and microfabric in g s lister h j behr k weber and h zwart editors the effect of deformation on rocks tectonophysics 78 527 543 three anhydrite rocks of different grain size were experimentally deformed in the 20 to 45o c temperature range the strength of the finegrained varieties becomes strongly temperature and strain rate dependent above 3oo c and a flow law of the form 6 a exp h rt sinh o a with an activation energy h of 27 36 kcal mole and a very low value for the exponent n of 1 5 2 was found the course grained rock remains relatively insensitive to strain rate and temperature even at 45o c microstructural and x ray texture analyses suggest that intracrystalline glide and twinning are the major deformation mechanisms the transition from strong work hardening observed at high stresses into steady state flow at low stresses was found to correlate with the onset of dynamic recrystallization by grain boundary migration

the influence of viscosity contrast on the strain pattern and magnitude within and around dense blocks sinking through newtonian rock salt abstract dense inclusions in salt cover a wide range of materials and therefore material properties depending on their origin we have modelled the deformation associated with gravity driven sinking of horizontal initially rectangular blocks of dense material through newtonian salt our two dimensional finite differences models analyse the influence and interaction of two parameters 1 the size i e the aspect ratio ar of the block and 2 the viscosity contrast between the salt and the more viscous block over four orders of magnitude the results demonstrate that during gravity driven sinking the blocks are folded and sheared the strain magnitude within the block increases with increasing block ar and decreases with increasing viscosity contrast sinking velocities of the blocks are in the range of 6 mm a 1 and are a function of block and salt deformation that depend on the block mass and ar as well as on the viscosity contrast salt deformation is characterised by the development of an array of characteristic structures that include folds and shear zones as well as a zone characterised by extreme vertical stretching above the block termed entrainment channel strain in the salt is locally more than two orders of magnitude higher than in the block and increases with increasing block ar and viscosity contrast salt deformation is distributed in closely spaced high and low strain zones concentrated in the block vicinity and the entrainment channel

quantitative texture analysis of naturally deformed anhydrite by neutron diffraction texture goniometry abstract the crystallographic texture of coarse grained 1 mm foliated anhydrite from an evaporite diapir in the canadian arctic islands was analysed by neutron diffraction texture goniometry the orientation distribution function odf which quantatively defines the texture was calculated from eight pole figures the odf was used to calculate the pole figures for slip systems and twin planes a strong concentration of 020 was found parallel to the lineation x with 002 forming a girdle normal to the lineation with a strong maximum near the foliation normal z the maxima are slightly asymmetric with respect to the structural framework x y z which is typical of non coaxial deformation the orientation of 020 and 002 are consistent with 010 001 glide in a non coaxial flow regime the axial symmetry about the lineation x of the pole figures and the tubular structure of the odf are thought to have been caused by an important component of extension parallel to x the calculated 100 pole figure has a submaximum parallel to z presumably a direction of high compressive stress the 101 maxima at about 45 to z are then indicative of twinning on 101 approximately 30 of the odf is in a twinned orientation 100 subparallel to z and it is suggested that twinning contributed to the axial symmetry of the fabric few grains show undulary extinction their boundaries are generally straight and rarely serrated this points to extensive migration recrystallization and associated twin gliding at 300 c previous studies seem to have underestimated the contribution of twinning to texture development which is dominated by 010 001 slip

initiation and growth of gypsum piercement structures in the zechstein basin abstract the importance of tectonic processes in initiating halite diapirs has become much better understood in recent years less well understood is the development of diapiric structures involving rocks composed predominantly of gypsum below about 1000 m gypsum dehydrates to anhydrite which often obscures primary sedimentary textures if the strain associated with diapiric rise in the rock induces the transition to anhydrite obliteration of primary features in the gypsum can be expected in our study we infer that the diapiric movement in the werra anhydrite member of cycle 1 of the zechstein formation of europe occurred before the initial transition of gypsum to anhydrite based on the presence of pseudomorphs of bedded primary gypsum crystals the overburden lithologies and depositional environment and the mechanical properties of gypsum anhydrite and carbonate rocks faulting and differential loading of a shallow overburden were the key components in initiating the gypsum diapirism the transition to anhydrite occurred after burial and after cessation of diapirism in comparison the diapirism of calcium sulfate of the leine anhydrite into the leine halite members of cycle 3 of the zechstein formation probably occurred much later after burial and appears to have been triggered by halite diapirism which in turn triggered the dehydration reaction causing the calcium sulfate to become the incompetent phase relative to the halite

a storm event watershed model for surface runoff based on 2d fully dynamic wave equations the main purpose of this work concerns the development and testing of an overland flow model based on the two dimensional fully dynamic shallow water equations three key aspects fundamental to get accurate efficient and robust computation of surface runoff at basin scale are discussed by transferring the main findings obtained by the recent research on the topic of dam break wave and flood propagation in the context of rainfall runoff modelling in particular attention is focused on the numerical flux and bottom slope source terms computation on a numerical treatment of friction slope terms and on an algorithm for dealing with wetting drying fronts the performances of the numerical model have been preliminarily evaluated using experimental or ideal tests characterized by very critical conditions for the stability of a numerical model then attention was focused on a real event occurred in a sub basin of reno river in italy to analyse the suitability of the model in simulating real flood situations the numerical results highlight the good performances of the model in all the simulations discussed in the paper copyright 2012 john wiley sons ltd

the development of a single cleavage in an area of repeated folding abstract structural investigations in the variscan fold interference pattern of sw sardinia italy document an intriguing example of the relationship between cleavage folding and finite strain although palaeozoic sediments were affected by two major folding events both under identical low grade metamorphic conditions only a single penetrative cleavage formed which is not unambiguously correlated with either of these events cleavage orientation changes smoothly along sigmoidally curving trajectories throughout the interference pattern thus the same cleavage can be axial planar to either the first or the second phase folds or transect both when curving from one set into the other the singularity of the cleavage is supported by microscopic studies which show no evidence of a pre existing or overprinting tectonic cleavage finite strain determinations and numerous field observations demonstrate that cleavage always parallels the principal plane of finite strain even though local strain varies according to the relative position in the fold interference pattern similar strain patterns were achieved by forward modelling of superposed buckle folds based on our findings we propose i that the finite strain pattern is due to the superposition of the heterogeneous strain fields associated with the individual folding events and ii that cleavage reflects the cumulative deformations that effected the rock this has consequences for the regional interpretation of cleavage in our study area and elsewhere and for the distinction between deformation phases in general

atypical textures in quartz veins from the simplon fault zone abstract samples of monomineralic quartz veins from the simplon fault zone in southwest switzerland and north italy generally have asymmetric single girdle c axis patterns similar to textures measured from many other regions several samples have characteristically different textures however with a strong single c axis maximum near the intermediate specimen axis y the direction within the foliation perpendicular to the lineation x and a tendency for the other crystal directions to be weakly constrained in their orientation about this dominant c axis maximum this results in streaked pole figure patterns with an axis of rotation parallel to the c axis maximum these atypical samples also have a distinctive optical microstructure with advanced recrystallization and grain growth resulting in a strong shape fabric sb oblique to the dominant regional foliation sa whereas typical samples have a strong sa fabric outlined by very elongate only partially recrystallized ribbon grains the recrystallized grains of the atypical samples are themselves deformed and show strong undulose extinction and a core mantle recrystallization structure the streaked texture is likely to be a direct consequence of lattice bending and kinking during heterogeneous slip on the favoured first order prism 10 1 0 a system the heterogeneity itself being due to problems in maintaining coherence across grain boundaries when insufficient independent easy slip systems are available for homogeneous strain by dislocation glide such bending would be particularly prevalent in very elongate thin ribbon grains resulting in high internal strain energy and promoting recrystallization thus both the texture and the microstructure could be significantly modified by later strain increments affecting quartz grains with an already developed nearly single crystal texture

reconstructing historic glacial lake outburst floods through numerical modelling and geomorphological assessment extreme events in the himalaya westoby m j glasser n f hambrey m j brasington j reynolds j m hassan m a a m 2014 reconstructing historic glacial lake outburst floods through numerical modelling and geomorphological assessment extreme events in the himalaya earth surface processes and landforms 39 12 1675 1692

kinematic and temporal relationships between parallel fold hinge lines and stretching lineations a microstructural and crystallographic preferred orientation approach folds with hinge lines subparallel to stretching lineation are common features in shear zones and represent extreme cases of fold modification however their microstructures and in particular their kinematic significance remain poorly understood here we describe the meso and micro scale structures and crystallographic preferred orientation cpo of quartz and muscovite from a metric scale shear modified fold from plattjen saas fee western internal alps the studied fold is of class 2 and the samples collected around the fold have essentially the same microstructures quartz c axes plotted in the tectonic coordinate system exhibit an apparent reverse obliquity on opposing limbs muscovite fabrics are controlled essentially by the orientation of 001 planes if the cpo data are plotted in a common reference frame e g either fold or geographical all samples exhibit essentially the same patterns for both minerals in particular relative to the fold axis and axial surface the reversal of quartz cpo obliquity on opposing limbs is no longer evident the small obliquity 15 between the intersection lineation of the two planes of 001 of muscovite and the fold axis results in the apparent reversal of shear sense on opposite limbs when viewing the cpo related to the macroscopic fabric the homogeneity of the microstructures and cpos of quartz and muscovite across the fold support the interpretation that the fold developed during simultaneous activation of heterogeneous and homogeneous simple shear with the former responsible for fold development and the latter responsible for fold rotation and the overwhelming of the heterogeneous deformation these processes led to the observed parallelism between fold hinge line and local stretching lineation

calculating anisotropic physical properties from texture data using the mtex open source package this paper presents the background for the calculation of physical properties of an aggregate from constituent crystal properties and the texture of the aggregate in a coherent manner emphasis is placed on the important tensor properties of 2nd and 4th rank with applications in rock deformation structural geology geodynamics and geophysics we cover texture information that comes from pole figure diffraction and single orientation measurements electron backscattered diffraction or ebsd electron channelling pattern laue pattern optical microscope universal stage in particular we provide explicit formulae for the calculation of the averaged tensor from individual orientations or from an orientation distribution function odf for the latter we consider numerical integration and an approach based on the expansion into spherical harmonics this paper also serves as a reference paper for the mathematical tensor capabilities of the texture analysis software mtex which is a comprehensive freely available matlab toolbox that covers a wide range of problems in quantitative texture analysis for example odf modelling pole figure to odf inversion ebsd data analysis and grain detection mtex offers a programming interface which allows the processing of involved research problems as well as highly customizable visualization capabilities mtex is therefore ideal for presentations publications and teaching demonstrations

elastic properties of anisotropic synthetic calcite muscovite aggregates 1 a set of synthetic aggregates containing mixtures of calcite and muscovite were compacted with varying uniaxial loads ranging from 20 mpa up to 400 mpa their elastic properties have been measured using compressional and shear waves in confining hydrostatic pressures up to 475 mpa measured seismic velocities are shown to depend on 1 the ratio of calcite to muscovite 2 the uniaxial load used during sample manufacturing and 3 the porosity amount prior to velocity measurements the matrix framework may also affect the seismic velocities but this effect is not easily quantifiable in general measured seismic velocities decrease with increasing muscovite content and porosity elastic properties have been calculated based on texture measurements which were obtained by neutron diffraction the calculated velocities are based on the calcite and muscovite single crystal elastic tensors their orientation distribution functions and their modal fractions a large discrepancy is apparent between calculated and measured velocities where the former always overestimate the actual velocities shear waves display less of a difference between calculated and measured values than do compressional waves indicating that waves propagating by shearing are less affected by sample porosity and matrix framework a better agreement between measured and calculated seismic velocities arises when the initial porosity is taken into account using a differential effective medium model seismic anisotropy is evident from both measured and calculated velocities and is low for samples containing pure calcite but becomes prominent as the muscovite concentration increases the intensity of anisotropy further depends on the uniaxial load used during sample compaction and the initial porosity

texture of solnhofen limestone deformed to high strains in torsion solnhofen limestone was deformed in torsion to shear strains ranging from 1 to 12 at a temperature of 750 c 300 mpa confining pressure and a maximum strain rate of 10 3 s 1 these deformation conditions correspond to the intracrystalline power law dislocation creep field close to the boundary to the grain size sensitive superplastic creep field the grain shape microstructure was observed using orientation contrast by backscattered electrons in the sem the grains remain sub equant with an average grain size of around 4 m even to the highest strains lattice preferred orientation was determined using both x ray texture goniometry and automated electron back scatter diffraction the c axis preferred orientation develops from two main maxima with a weak sub maximum through two maxima to a single maximum perpendicular to the shear plane the rate of increase of the intensity of the single maximum with increasing strain diminishes and it appears that there is a tendency to a steady state texture the final single c axis maximum is displaced slightly towards the shortening direction of the applied simple shear the a axes tend to a girdle perpendicular to the c axis maximum it is proposed that the partitioning of deformation between intra and inter crystalline mechanisms results in a pulsating strain state in the grains contributing to the maintenance of sub equant grains it is argued that the lattices of constituent grains rotate continuously with no stable end orientation and that this can lead to a steady state texture the experimental preferred orientation compares well with that of natural calcite mylonites in the position of the c axis maximum and the a axis girdle

ductile extrusion of the higher himalayan crystalline in bhutan evidence from quartz microfabrics quartz textures measured from deformed quartz tectonites within the lesser himalaya and higher himalaya crystalline of bhutan show similar patterns orientation and distribution of the quartz crystallographic axes were used to confirm the regional shear sense the asymmetry of c axis and a axis patterns consistently indicates top to the south shearing the obliquity of the texture and the inferred finite strain plane strain to moderately constrictional suggest the strain regime had a combination of rotational and irrotational strain path in most of the samples from the bhutan himalaya the inferred deformation mechanisms suggest moderate to high temperature conditions of deformation that produced the observed crystallographic preferred orientation much higher temperature of deformation is indicated in the quartz veins from a leucogranite the observed ductile deformation is pervasively developed in the rocks throughout the investigated area the intensity of deformation increases only slightly in the vicinity of the main central thrust simultaneous southward shearing within a large part of the higher himalaya crystalline near and above the main central thrust and normal faulting across the south tibetan detachment is explained by the tectonically induced extrusion of a ductily deforming wedge the process of extrusive flow suggested here can be approximated quantitatively by channel flow models that have been used to describe subduction zone processes channel flow accounts for some observed phenomena in the himalayan orogen such as inverted metamorphic sequences near the main central thrust not related to an inversion of isotherms and the syntectonic emplacement of leucogranites into the extruding wedge locally leading to an inversion of isotherms due to heat advection

numerical analysis of x ray texture data an implementation in fortran allowing triclinic or axial specimen symmetry and most crystal symmetries abstract the use of complete descriptions of preferred orientation for studies of experimentally and naturally deformed rocks is discussed diagrammatic representations of preferred orientations are defined and conventions for coordinate systems are given methods of extracting information from the orientation distribution function are described a system of fortran programs which enables the orientation distribution function to be calculated for most suitable minerals is described

preferred crystallographic orientation development during the plastic and superplastic flow of calcite rocks abstract grain size sensitive flow of fine grained rocks such as are often found in mylonitic shear zones is commonly inferred to be accomplished by grain boundary sliding so that no preferred crystallographic orientation is expected to develop pre existing fabrics are supposed to weaken and grain shapes to remain equant however many fine grained mylonites commonly exhibit marked preferred crystallographic orientation whilst displaying a stable but weak grain shape fabric we have examined preferred crystallographic orientation and shape fabric development during the flow of synthetic ultrafine grained 700 c the strong crystal plastic fabric develops more slowly but is not eliminated through the broad transition into true superplastic flow this is interpreted to reflect an important role of intracrystalline plasticity in the accommodation of grain boundary sliding from experiments designed to investigate the extent of survival or modification of an initial twinning fabric through recrystallization and subsequent hot working it was shown that although the microstructure could be totally annealed the early formed fabric survived even subsequent high temperature crystal plastic or superplastic flow this may explain the frequent occurrence of strong low temperature fabrics in calcite ultramylonites

fold controlled quartz textures in the pennine mischabel backfold near zermatt switzerland abstract quartz fabric analyses along the basal thrust of the dent blanche nappe and in the footfall pennine units indicate south directed thrusting for the last stage of austro alpine pennine nappe emplacement quartz fabrics in particular those from the pennine mischabel backfold imply complex spatial and temporal texture developments with crystallographic preferred orientations cpo that are commonly in disagreement with mesoscopic grain shape lineations in consequence kinematic directions inferred by quartz textures do not necessarily coincide with those predicted by mesoscopic structural elements such as grain shape lineations in our particular case orientation of grain shape lineations is rather complex in the study area while principal axes inferred from the quartz textures remain geographically constant and exhibit a simple geometric relationship to the mischabel backfold it is suggested that the grain shape lineations correspond to the total accommodated finite strain whereas the quartz fabrics reflect late increments of deformation quartz cpos in the hinge of the mischabel fold are similar to those along the thrust revealing asymmetric single girdles to c axes point maxima subgrain rotation is the predominant recrystallization mechanism suggesting steady state conditions in fabric development during progressive rotational deformation in contrast asymmetric cross girdles dominate the upper limb and uneven small circle c axes distributions characterize the lower limb although recrystallization in both limbs is characterized by grain boundary migration this clear separation of quartz textures and recrystallization deformation mechanism conflicts with the common view on heterogeneous deformation patterns in folds where the major component of rotational shear is expected in the fold limbs our study suggests that fabric development in the limbs of the recumbent mischabel fold was reset during progressive deformation shortly prior to the transition from an active buckling to passive fold amplification while the hinge suffered continuous bulk deformation provided by the back thrusting of the dent blanche nappe

microfabrics of calcite ultramylonites as records of coaxial and non coaxial deformation kinematics examples from the rocher de l yret shear zone western alps microfabrics were analysed in calcite mylonites from the rim of the pelvoux massif western alps france wnw directed emplacement of the internal penninic units onto the dauphinois domain produced intense deformation of an eocene age nummulitic limestone under lower anchizone metamorphic conditions slightly below 300 c two types of microfabrics developed primarily by dislocation creep accompanied by dynamic recrystallisation in the absence of twinning coaxial kinematics are inferred for samples exhibiting grain shape fabrics and textures with orthorhombic symmetry their texture crystallographic preferred orientation cpo is characterised by two c axis maxima symmetrically oriented at 15 from the normal to the macroscopic foliation non coaxial deformation is evident in samples with monoclinic shape fabrics and textures characterised by a single oblique c axis maximum tilted with the sense of shear by about 15 from the analysis of suitably oriented slip systems for the main texture components under given kinematics it is inferred that the orthorhombic textures which developed in coaxial kinematics favour activity of b10 11n and b02 21n slip along the f and r planes respectively with minor contributions of basalban slip in contrast the monoclinic textures which developed during simple shear are most suited for duplex ban slip along the basal plane the transition between the dominating slip systems for the orthorhombic and monoclinic microfabrics is interpreted to be due to the effects of dynamic recrystallisation upon texture development since oblique c axis maxima documented in the literature are most often rotated not with but against the shear sense calcite textures alone should not be used as unequivocal shear sense indicators but need to be complemented by microstructural criteria such as shape preferred orientations grain size estimates and amount of twinning

phyllosilicate preferred orientation as a control of magnetic fabric evidence from neutron texture goniometry and low and high field magnetic anisotropy se rhenohercynian zone of bohemian massif

hayabusa2 arrives at the carbonaceous asteroid 162173 ryugu a spinning top shaped rubble pile the hayabusa2 spacecraft arrived at the near earth carbonaceous asteroid 162173 ryugu in 2018 we present hayabusa2 observations of ryugu s shape mass and geomorphology ryugu has an oblate spinning top shape with a prominent circular equatorial ridge its bulk density 1 19 0 02 grams per cubic centimeter indicates a high porosity 50 interior large surface boulders suggest a rubble pile structure surface slope analysis shows ryugu s shape may have been produced from having once spun at twice the current rate coupled with the observed global material homogeneity this suggests that ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation from these remote sensing investigations we identified a suitable sample collection site on the equatorial ridge

godunov type solution of curvilinear shallow water equations this paper presents details of a second order accurate godunov type numerical model of the two dimensional conservative hyperbolic shallow water equations written in a non orthogonal curvilinear matrix form and discretized using finite volumes roe s flux function is used for the convection terms and a nonlinear limiter is applied to prevent spurious oscillations validation tests include frictionless rectangular and circular dam breaks an oblique hydraulic jump jet forced flow in a circular basin and vortex shedding from a vertical surface piercing cylinder the results indicate that the model accurately simulates sharp fronts a flow discontinuity between subcritical and supercritical conditions recirculation in a basin and unsteady wake flows

modelling outburst floods from moraine dammed glacial lakes in response to climatic change the size and number of moraine dammed supraglacial and proglacial lake systems have increased dramatically in recent decades given an appropriate trigger the natural moraine dams that impound these proglacial lakes are breached producing catastrophic glacial lake outburst floods glofs these floods are highly complex phenomena with flood characteristics controlled in the first instance by the style of breach formation downstream glofs typically exhibit transient often non newtonian fluid dynamics as a result of high rates of sediment entrainment from the dam structure and channel boundaries combined these characteristics introduce numerous modelling challenges in this review the historical contemporary and emerging approaches available to model the individual stages or components of a glof event are introduced and discussed a number of methods exist to model the stages of a glof event dam breach models can be categorised as being empirical analytical or numerical in nature with each method having significant advantages and shortcomings empirical relationships that produce estimates of peak discharge and time to peak are straightforward to implement but the applicability of these models is often limited by the nature of the case study data from which they are derived furthermore empirical models neglect the inclusion of basic hydraulic principles that describe the mechanics of breach formation analytical or parametric models simulate breach development using simplified versions of the physically based equations that describe breach enlargement whilst complex physically based codes represent the state of the art in numerical dam breach modelling to date few of the latter have been applied to investigate the moraine dam failure problem despite significant advances in the physical complexity and availability of higher order hydrodynamic solvers the majority of published accounts that have attempted to reconstruct or predict glof characteristics have been limited often by necessity to the use of relatively simplistic models this is in part attributable to the unavailability of terrain models of many high mountain catchments at the fine spatial resolutions required for the effective application of numerically sophisticated codes and their proprietary and often cost prohibitive nature however advanced models are experiencing increasing use in the glacial hazards literature in particular the suitability of emerging mesh free particle based methods for simulating dam breach and glof routing may represent a solution to many of the challenges associated with modelling this complex phenomenon sources of uncertainty in the glof modelling chain have been identified by various workers however to date their significance for the robustness of reconstructive and predictive modelling efforts have been largely unexplored and quantified in detail these sources include the geometric and material characterisation of moraine dam complexes including lake bathymetry and the presence and extent of buried ice initial conditions freeboard precise spillway dimensions spatial discretisation of the down valley domain hydrodynamic model dimensionality and the dynamic coupling of successive components in the glof model cascade

the magnetic anisotropy of mantle peridotites example from the twin sisters dunite washington abstract the twin sisters dunite massif washington state provides unweathered peridotites for magnetic analysis these rocks have been chosen to test a new magnetic fabric based on measuring the anisotropy of magnetic susceptibility ams in high field with a vibrating sample magnetometer although the dunites are fresh they host small quantities of secondary magnetite formed along cracks under low field conditions magnetite masks the magnetic fabric of olivine and thus the magnetic fabric does not reflect mantle flow deformation above the magnetic saturation at a field of 1 t the ferrimagnetic component is removed and the high field slope represents the paramagnetic ams only this high field ams originates from the magnetocrystalline anisotropy of olivine the high field ams are compared with lattice preferred orientation lpo fabric data obtained by electron backscatter diffraction lpo point distributions are formed by high temperature plastic flow and match the high field measurements in contrast girdle lpos present notable departures from the high field ams axes

microstructural analysis of anhydrite rocks from the triassic evaporites umbria marche apennines central italy an insight into deformation mechanisms and possible slip systems abstract anhydrite rich layers within foreland fold and thrust belts are frequently the weakest horizon of the sequence characterizing the microstructural textures of anhydrite is therefore important for interpreting the larger scale deformation history of these rocks the microstructure of naturally deformed anhydrite from the triassic evaporites of the umbria marche apennines italy has been analyzed using electron backscatter diffraction ebsd this technique has been used to measure the misorientation across distorted grains and the crystallographic preferred orientation cpo of the samples the reference frame of the standard space group cmcm was used to represent the structure of anhydrite during this analysis which is different to that used in previous studies some grains show significant intracrystalline distortions 4 18 misorientation lines of measurements across distortions showed a dispersion of crystallographic data around a clear misorientation axis 010 these data are combined with the trace orientations of distortions to confirm that the 100 001 slip systems previously recognized also best explains grain distortions these interpretations are based on and consistent with a tilt boundary model containing edge dislocations cpo data are also interpreted as a likely 100 001 slip system as has previously been recognized a high degree of twinning within many of the anhydrite grains apparently has little effect on the crystallographic textures observed

texture development in experimentally deformed two phase aggregates of calcite and anhydrite abstract fully quantitative textures have been measured from experimentally deformed two phase aggregates of calcite and anhydrite two sets of deformation experiments were performed firstly to investigate the development of microstructure and texture with composition samples with varying volume proportions of calcite and anhydrite were deformed to 20 strain at identical conditions secondly to study the texture development of the two materials with strain and explore the possible use of texture index as a strain gauge in polyphase materials pure calcite and pure anhydrite were deformed at the same conditions as the two phase rocks to strains of 6 12 and 20 the textures in both calcite and anhydrite were found to be similar but not identical to those reported in previous studies for pure samples our experimental investigations and measured textures show that the textures both of the pure materials and of the two phase rocks depend not only on strain but also on stress and grain size through their influence on the deformation mechanisms the dependence of texture index with change in deformation mechanism is particularly pronounced in the anhydrite component where the texture index decreases with grain size which decreases with anhydrite content the texture in the pure calcite and in the calcite component of the two phase rocks was influenced by a preexisting fabric the intensity of the texture in the deformed samples seems to correlate with the stress in the calcite rather than with strain

meteoroid impacts as a source of bennu s particle ejection events asteroid 101955 bennu a near earth object with a primitive carbonaceous chondrite like composition was observed by the origins spectral interpretation resource identification and security regolith explorer osiris rex spacecraft to undergo multiple particle ejection events near perihelion between december 2018 and february 2019 the three largest events observed during this period which all occurred 3 5 to 6 hr after local noon placed numerous particles 10 cm on temporary orbits around bennu here we examine whether these events could have been produced by sporadic meteoroid impacts using the national aeronautics and space administration s nasa meteoroid engineering model 3 0 most projectiles that impact bennu come from nearly isotropic or jupiter family comets and have evolved toward the sun by poynting robertson drag we find that 7 000 j impacts on bennu occur with a biweekly cadence near perihelion with a preference to strike in the late afternoon 6 pm local time this timing matches observations crater scaling laws also indicate that these impact energies can reproduce the sizes and masses of the largest observed particles provided the surface has the cohesive properties of weak porous materials bennu s ejection events could be caused by the same kinds of meteoroid impacts that created the moon s asymmetric debris cloud observed by the lunar atmosphere and dust environment explorer ladee our findings also suggest that fewer ejection events should take place as bennu moves further away from the sun a result that can be tested with future observations

petrofabric derived seismic properties of a mylonitic quartz simple shear zone implications for seismic reflection profiling the link between petrofabric lpo and seismic properties of an amphibolite facies quartzofeldspathic shear zone is explored using sem ebsd the shear zone lpo develops by a combination of slip systems and dauphine twinning with a maximum parallel to lineation x and c maximum normal to mylonitic foliation xy the lpo are used to predict elastic parameters from which the three dimensional seismic properties of different shear zone regions are derived results suggest that lpo evolution is reflected in the seismic properties but the precise impact is not simple in general the p wave velocity vp minimum is parallel to the a axis maximum the direction of maximum shear wave splitting avs is parallel to mylonitic foliation and the vp maximum and avs minimum are parallel to the c axis maximum the seismic anisotropy predicted is significant and increases from shear zone wall rock to mature mylonite p wave anisotropy ranges from 11 13 fast and slow shear waves anisotropy range from 6 15 and the magnitude of shear wave splitting ranges from 9 16 nevertheless such anisotropy requires a considerable thickness of rock with this lpo before it becomes seismically visible i e 100 s m for local earthquakes 10 s m for controlled source experiments however reflections and mode conversions provide much better resolution particularly across tectonic boundaries the low symmetry and strong anisotropy due to the lpo suggest that multi azimuth wide angle reflection data may be useful in the determination of the deformation characteristics of deep shear zones a number of factors may produce elastic anisotropy in rocks including variations in the spatial distribution of mineral phases layering grain size and shape fabrics grain boundary properties and the presence of oriented pores or fractures e g kern wenk 1985 mainprice et al 2003 in addition because elastic properties vary with respect to direction in single crystals the majority of rock forming minerals are elastically anisotropic e g christensen 1966 thus deformation processes such as dislocation creep which produce strong crystal lattice preferred orientations lpo in anisotropic minerals may also induce bulk elastic anisotropy it is no surprise therefore that petrophysical properties such as seismic velocities are often highly anisotropic in bulk rock aggregates e g babuska cara 1991 understanding of the impact of microstructural variables on elastic anisotropy has been obtained typically from experimental measurements of elastic properties of minerals or theoretical models that incorporate microstructural variables e g burlini kern 1994 wendt et al 2003 experimental studies have focused primarily on the influence of fractures or lpo on the elastic properties of minerals and rocks in particular the seismic properties can be measured via direct laboratory methods at ambient or elevated temperatures and pressures e g kern 1982 although it is often difficult or impossible to obtain the complete three dimensional property orientation distribution from a single experiment however see pros et al 2003 furthermore experimental investigation of seismic properties usually involves rocks in which all microstructural fabric elements contribute effectively masking any lpo component an alternative approach is to calculate the seismic properties of a rock aggregate from individual crystal orientation measurements incorporating the single crystal elastic constants and the lpo for each mineral weighted according to its modal content e g mainprice humbert 1994 the seismic phase velocities and anisotropies then can be calculated in every direction e g mainprice silver 1993 recently the advent of electron backscattered diffraction ebsd in the scanning electron microscope sem has made it possible to measure lpo in statistically viable numbers from different minerals within a rock aggregate whilst maintaining a oneto one relationship with other microstructural elements e g mainprice et al 1993 lloyd 2000 mauler et al 2000 bascou et al 2001 in this contribution the seismic properties of an amphibolite facies mylonitic quartz shear zone are predicted by averaging the single crystal elastic properties according to the sem ebsd derived lpo in order to study the relationship between microstructure petrofabric and seismic properties this approach illustrates the usefulness of integrating geological studies of rock microstructures and particularly petrofabrics with geophysical studies of seismic properties to obtain a fuller understanding of geodynamic processes

a spherical electron channelling pattern map for use in quartz petrofabric analysis correction and verification abstract the recent paper by lloyd ferguson on the use of a spherical electron channelling pattern ecp map in quartz petrofabric analysis contained an unfortunate error due to the incorrect indexing of the quartz single crystal used to construct the map this error can be corrected by a simple 60 rotation of the spherical ecp map and a re definition of the individual ecps specifically those of the positive and negative rhombs and trigonal prisms the verification of this correction and of the technique as a whole is supported by a comparison between pole figure diagrams for a quartzite obtained from the same specimen by ecp analysis and x ray texture goniometry

thermal fatigue as a driving mechanism for activity on asteroid bennu many boulders on 101955 bennu a near earth rubble pile asteroid show signs of in situ disaggregation and exfoliation indicating that thermal fatigue plays an important role in its landscape evolution observations of particle ejections from its surface also show it to be an active asteroid though the driving mechanism of these events is yet to be determined exfoliation has been shown to mobilize disaggregated particles in terrestrial environments suggesting that it may be capable of ejecting material from bennu s surface we investigate the nature of thermal fatigue on the asteroid and the efficacy of fatigue driven exfoliation as a mechanism for generating asteroid activity by performing finite element modeling of stress fields induced in boulders from diurnal cycling we develop a model to predict the spacing of exfoliation fractures and the number and speed of particles that may be ejected during exfoliation events we find that crack spacing ranges from 1 mm to 10 cm and disaggregated particles have ejection speeds up to 2 m s exfoliation events are most likely to occur in the late afternoon these predictions are consistent with observed ejection events at bennu and indicate that thermal fatigue is a viable mechanism for driving asteroid activity crack propagation rates and ejection speeds are greatest at perihelion when the diurnal temperature variation is largest suggesting that events should be more energetic and more frequent when closer to the sun annual thermal stresses that arise in large boulders may influence the spacing of exfoliation cracks or frequency of ejection events

an illustration of the advantages of a complete texture analysis described by the orientation distribution function odf using quartz pole figure data abstract the preferred orientation of eight crystal directions of quartz was measured with an x ray texture goniometer for selected quartz bearing tectonites with a clear pattern of c axis preferred orientation the advantages of data analysis by means of calculations of the orientation distribution function and other forms of data presentation derived from the odf are demonstrated

textural evolution of synthetic anhydrite halite mylonites the rheology and textural evolution of mylonites for both crustal and mantle rocks are generally poorly understood stress and strain partitioning between shear zones and wall rock foliation development flow mechanisms and constitutive relations are little known to address these problems we have begun an experimental study in which anhydrite and halite aggregates are deformed in simple shear homogeneous mixes at intervals of 10 vol of anhydrite and halite powders of 90 to 180 m grain size comprise the 1 mm thick zone between the 35 precut surfaces in 2 by 4 cm right circular cylinders of anhydrite all specimens are confined under 200 mpa pc and tested at 300 c t producing an aggregate of near zero porosity all specimens are shortened at an axial displacement rate of 5 l0 6 cm s to shear strains of about 2 0 most stress strain curves have a similar form they are characterized by an initial linear response that is followed by a work hardening region that leads to a plateau of constant stress whilst strain continues to accumulate this apparent steady state behavior is followed by a drop in stress to a second apparent steady state stress the strain at this stress drop and the magnitude of the drop increase with increasing anhydrite content the second lower steady state stress for all mixes approaches that of sheared pure halite optical examination of the fabrics shows that straining under the initial apparent steady state is accommodated by both mineral phases a foliation evolves as defined by mineral segregation and grain elongation of halite at 15 to 30 to the shear zone walls anhydrite grains rotate until their 001 010 slip system parallels the foliation the anhydrite also exhibits twin lamellae kinks and microfractures following the stress drop rheologic behavior is dominated by dynamic recovery in halite the recrystallized grain size increasing consistent with the lower stress level

magnetic anisotropy rock fabrics and finite strain in deformed sediments of sw sardinia italy abstract although some empirical relationships have been established between the anisotropy of magnetic susceptibility ams and the state of finite strain in studies from specific geologic areas the mechanisms governing correlations are not well understood a comparative study has been made in order to elucidate the ams strain relationship by investigating mineral preferred orientations and the responsible microstructural deformation processes detailed analyses are presented from low grade metamorphic slates of a palaeozoic sequence exposed in the variscan of sw sardinia rock magnetic experiments suggest that paramagnetic minerals dominate the ams in these rocks excellent agreement was found between magnetic fabrics and lattice preferred orientations 001 of mica and chlorite determined from x ray texture goniometry measurements depending on the oblate or prolate ellipsoidal shape of anisotropy the minimum principal axes of ams and x ray textures can coincide with the poles to slaty cleavage or the maximum principal axes can coincide with the bedding cleavage intersection respectively the measured ams and x ray textures only partially reflect the finite strain determined from deformed micro pebbles and reduction spots axial orientations of magnetic fabrics mica and chlorite preferred orientations and finite strain ellipsoids are generally in good agreement depending on development of oblate or prolate fabric ellipsoidal shapes linear correlations can be established for magnitudes of minimum and intermediate axes of the ams and finite strain ellipsoids but shape comparisons are complex microstructural studies by scanning electron microscopy sem indicate that the preferred orientation of the phyllosilicates is caused by different grain scale deformation mechanisms such as kinking micro folding and preferential growth thus magnetic fabrics and mineral preferred orientations evidently result from different deformation mechanisms than the finite strain they reflect the heterogeneous deformation due to micro mechanical reorientation processes of mineral grains while finite strain reflects the homogeneous deformation accommodated cumulatively by the strain markers

the calculated seismic properties of quartz mylonites with typical fabrics relationship to kinematics and temperature summary quartz mylonites produced by intense ductile deformation in shear zones are often invoked as seismic reflectors in the lower continental crust the seismic properties vp vsl v av and polarization planes of v and v have been calculated for five quartz mylonites that display typical lattice preferred orientations lpos all specimens display considerable seismic anisotropy with v anisotropy coefficients of between 8 and 12 per cent there are good correlations between the lpo of the a axes and the minimum v direction and the c axes and the maximum v direction the other seismic properties are not reliable indicators of lpo as the a axis is the major flow direction in quartz a correlation between the ductile flow direction and the v minimum can be made with increasing temperature and pressure alpha quartz transforms to beta quartz in the beta field quartzites are seismically transverse isotropic furthermore there is a considerable increase in v from 6 km s l in the alpha field to nearly 7 km s in the beta field the transition is instantaneous and hence will result in a sharp seismic discontinuity with a reflection coefficient of 0 08 between pure aggregates of alpha and beta phases however under typical conditions of the continental crust the seismological importance of this phase transition will be limited by the presence of secondary minerals and partial melting

the role of crystallographic fabric in the generation of seismic anisotropy and reflectivity of high strain zones in calcite rocks abstract for a relatively pure calcite ultramylonite grain size 5 m from the ivrea verbano zone of the the n w italian alps the crystallographic preferred orientation was measured by x ray texture goniometry the fabric is characterized by a 3 times uniform axisymmetric c axis maximum normal to the mesoscopic foliation from this and available single crystal elastic properties of calcite the expected variation of acoustic p wave velocity with orientation can be calculated this is compared with high pressure up to 520 mpa at 20 c ultrasonic velocity measurements made on seven different core orientations from the same rock and good agreement obtained between the calculated and measured velocity distribution seismic velocity contrasts range up to 3 3 relative to an isotropically textured protolith sufficient to give rise to detectable seismic reflectivity for normal incidence p waves on a horizontal shear zone crystallographic texture of the type observed maximises the obtainable seismic reflectivity for a c maximum fabric oriented obliquely to the plane of the high strain zone as is observed in some other natural shear zones or for a gently dipping shear zone reflectivity may be either enhanced or weakened thus visibility may be very sensitive to the local dip of a shear zone and the fabric orientation and intensity within it

saline lake carbonates within an upper jurassic lower cretaceous continental red bed sequence in the atacama region of northern chile the codocedo limestone member is a thin but laterally persistent lacustrine sequence within the red beds of the upper jurassic lower cretaceous quebrada monardes formation in the atacama region of northern chile the thick succession of clastic terrigenous sediments of the quebrada monardes formation was deposited in an arid to semi arid environment sedimentary facies are indicative of deposition of aeolian dunes alluvial fans and braided streams playa lake mudflats and saline lakes and coastal lagoons the strata accumulated in a n s elongated extensional back arc basin on the landward side of an active volcanic arc the 3 m thick codocedo limestone member marks striking facies changes within the quebrada monardes formation it is underlain by a thick sequence of conglomerates and sandstones deposited on alluvial fans the limestone itself is characterized by evaporite minerals and laterally continuous laminations indicative of deposition by vertical accretion in a perennial saline lake the overlying siltstones and fine sandstones contain geodes and gypsum pseudomorphs and were deposited on playa lake mudflats the limestone therefore represents a relatively short period of lacustrine deposition within an essentially terrigenous succession the lake was possibly formed quite suddenly for example by damming of the basin by a lava flow sedimentation in the perennial lake was predominantly cyclical seasonal planktonic algal blooms produced millimetre scale laminations interbedded with these laminites are centimetre scale beds of evaporitic gypsum anhydrite and minor halite the evaporite minerals have been largely replaced by calcite chalcedony and quartz the centimetre scale cycles may have resulted from periodic freshwater input into the lake after a period of about 3000 yr the lake dried up to be replaced by extensive playa lake mudflats the codocedo limestone member possibly formed a plane of detachment during an early tertiary phase of e w directed regional compression the limestones and evaporites were folded and extensively brecciated this deformation probably resulted from simple shear along the bedding plane of the relatively weak evaporite minerals prior to their replacement by calcite and quartz

from carbonate sulphate interbeds to carbonate breccias the role of tectonic deformation and diagenetic processes cameros basin lower cretaceous n spain interpreting the origin of carbonate breccias requires a detailed analysis because they may be the result of a wide variety of processes that produce similar features this is the case of the lower cretaceous carbonate breccias of the cameros basin previously interpreted as slump or collapse breccias whose origin is interpreted after performing a detailed sedimentary petrographic and tectonic study the studied carbonate breccias consist of angular carbonate mudstone fragments floating in a matrix of calcite and quartz crystals the breccias are interbedded with and laterally associated to alternating layers of carbonate mudstone and calcite and quartz pseudomorphs after gypsum which show strong similirities to the breccia fragments and matrix respectively suggesting that the brecciated beds were originally composed of identical alternating carbonate mudstone and gypsum layers as the unbrecciated layers the breccias are associated with frequently polyharmonic deformation structures which are similarly oriented as the regional tectonic structures indicating that they are related with the alpine contractional deformation of this area of the cameros basin all these features suggest that the carbonate breccias were formed by tectonic deformation of alternating layers of carbonate mudstone and calcium sulphate which have very different rheological behaviours as a result during tectonic deformation sulphate flowed and carbonate layers were broken and displaced producing a breccia of carbonate fragments within a sulphate groundmass afterwards the sulphate groundmass was replaced by quartz and calcite and the breccia acquired its final composition

quartz textures from the simplon fault zone southwest switzerland and north italy quartz textures measured from monomineralic veins within the simplon fault zone show very similar patterns over a strike length of some 30 km the c axes form asymmetric kinked single girdles with variably developed vestiges of crossed girdle limbs the kinking of the girdle may be controlled by the two c axis orientations where double rhomb a slip is possible a strong a maximum lies between 20 and 30 to the lineation in the xz plane which seems too large to be the angle to the bulk shear plane straight single girdle patterns may be possible for strict simple shear in natural fault zones where deformation is in general heterogeneous on all scales kinked single girdles and type i crossed girdle textures are much more common perhaps because such textures provide more freedom to accommodate a general two dimensional strain

numerical study of tectonic structure evolution in a multi layer evaporite sequence abstract field studies carried out in the klodawa salt structure kss poland reveal that within a carnallite halite kieserite sequence finger like structures developed during an early pre diapiric stage of the kss evolution we used 99 numerical simulations to model finger development and investigate mechanical properties of carnallite halite and kieserite during deformation models used inverse density stratification of a three layer set with varying 1 layer viscosities 2 thicknesses and 3 density difference ratios finger shapes in the models were categorized into single and multiwavelength structures among the single wavelength shapes bulb mushroom thumb and bloated i e without a regular shape structures were distinguished we show two transitions between the single and multiwavelength structures which correspond to the cases of either the lower or upper layer having viscosity more than an order of magnitude larger than the two other layers through comparison of finger shapes developed in the models and in the natural structures we estimate viscosities of 1017 pa s for halite

mathematical simulations of anisotropy of magnetic susceptibility on composite fabrics 1 the anisotropy of magnetic susceptibility ams is an integral measure of the preferred orientation of all minerals present in a rock when the ams is carried by paramagnetic minerals alone the principal directions of the susceptibility ellipsoid should reflect the crystallographic orientation of the minerals the relationship between the ams and deformation depends on several factors which control the development of lattice preferred orientation lpo in a rock a mathematical model is presented that simulates the magnetic susceptibility ellipsoid for samples composed of more than one mineral phase measurements of the ams are compared with fabric based anisotropy models for black slates from the navia alto sil slate belt in northern spain the ams is carried by paramagnetic minerals as has been confirmed by high field torque magnetometry low temperature ams and magnetization curves the lpo of mica and chlorite has been determined by x ray texture goniometry pole figures and orientation ellipsoids show the changes in the degree of alignment of the phyllosilicates the models have been tested in samples displaying three types of pole figures a high intensity point maximum a medium intensity elliptical maximum and a girdle shaped distribution at one site displaying kink bands the lpo shows variations between these types at the outcrop scale the case studies illustrate the success in modeling different lpo types

one dimensional kinematic model of preferred orientation development abstract the one dimensional model to analyse the kinematics of crystallographic preferred orientation of ribe 1989 is presented and developed further it is argued that this approach can be applied to rotational deformations where the predominant deformation mechanism is grain boundary sliding two contrasting situations are distinguished the first is where lattice rotations of opposing sense occur and there are orientations for which the rotation rate is zero in this case a continually intensifying preferred orientation at an orientation with zero rotation rate will result the second situation is where the rotation of the lattice is in the same sense for all orientations initially maxima develop in the orientation of greatest negative divergence in the lattice rotation rate function a steady state preferred orientation profile is possible which is the normalised inverse of the function describing lattice rotation rate vs orientation and the maxima are at the orientations for which the lattice rotation rate is a minimum the intensity of the preferred orientation is a function of the ratio of the greatest to least lattice rotation rates the results are applied to a natural mylonite preferred orientation which consists of a c axis maximum in the mylonitic foliation perpendicular to the stretching lineation it is argued that the crystal lattices rotate about a stably oriented c axis and the profile through the orientation distribution describing the probability of finding particular orientations differing by a rotation about c is inverted to give an estimate of the lattice rotation rate profile it is found that the lattice rotates slowest when the second order prism direction a is aligned parallel to the foliation normal and fastest when a is aligned sub parallel to the stretching lineation

introduction to the special issue exploration of the activity of asteroid 101955 bennu near earth asteroid 101955 bennu is an active asteroid experiencing mass loss the activity manifests itself in the form of ejection events emitting up to hundreds of millimeter to centimeter scale particles the origins spectral interpretation resource identification and security regolith explorer spacecraft monitored particle activity for a 10 month period that included bennu s perihelion and aphelion novel and classical methods were utilized to detect the particles and characterize their orbital and physical properties roughly 30 of the observed particle mass escaped to heliocentric orbit a majority of particles fell back onto the surface of bennu after ejection with the longest lived particle surviving for 6 days on a temporary orbit particle ejection events appear to preferentially take place in the afternoon and evening and from low latitudes although they can occur at any time or latitude the reaccumulation of material is biased toward low latitudes resulting in the possible in fill of craters and growth of bennu s equatorial bulge of the potential mechanisms behind this activity that were investigated in focused studies meteoroid impacts thermal fracturing and ricochet but not water ice sublimation were found to be consistent with observations while phyllosilicate dehydration was not investigated with a focused study it remains a possible mechanism these mechanisms are not unique to bennu suggesting that many near earth asteroids may exhibit activity that has gone undetected thus far spacecraft missions with wide field imagers are encouraged to further characterize this phenomenon

lattice preferred orientation and seismic anisotropy in sedimentary rocks summary although it is well known that sedimentary rocks can be seismically anisotropic there have been few detailed investigations of the underlying cause of such anisotropy here we investigate anisotropy due to the preferred orientation of minerals or lattice preferred orientation lpo in a suite of sedimentary rocks seismic properties are predicted by averaging single crystal elastic constants of minerals according to their crystal orientation and modal volume fraction in the rock aggregate both electron backscattered diffraction ebsd and x ray texture goniometry xtg are tested as quantitative techniques for measuring the lpo of sedimentary rocks although ebsd has promise for future lpo measurements in polymineralic sedimentary rocks problems currently remain in measuring low symmetry phases e g feldspars and very small clay or mica particles however the lpo of very fine grained phyllosilicates can be measured using xtg and the lpo of low symmetry minerals can be measured using manual ebsd pattern analysis here we use such a hybrid approach to estimate lpo in a suite of sedimentary samples the seismic properties calculated from lpo data show anisotropy values for p waves ranging from 1 5 per cent in sandstones to over 3 5 per cent in a siltstone to 12 per cent in a shale the effect of thin multilayering on long wavelength propagation in a siltstone is predicted by applying backus type averaging the layering does not enhance the anisotropy because of the small differences in density and in elasticity between the two layer types the lpo of phyllosilicates and to a lesser extent dolomite and siderite seem to contribute significantly to the seismic anisotropy of phyllosilicate rich rocks siltstones and shales the weak lpo of quartz in sandstones causes a few per cent anisotropy cumulatively our results suggest that field observations of seismic anisotropy have the potential to be used as an indicator of rock lithology

modeling deformation and salt tectonics in the eastern mediterranean ridge accretionary wedge this study addresses some aspects of the kinematics and structural setting of the mediterranean ridge accretionary complex particularly those aspects related to the occurrence and distribution of messinian evaporites the approach is by 1 identification of the geometry of deformation through reprocessing of existing multichannel seismic reflection data from the levantine basin aimed at the definition of the velocity field and depth imaging 2 physical modeling in the laboratory aimed at the study of the kinematics of shortening of sedimentary sequences detaching on viscous decollements and 3 comparison between the results of the two approaches we conclude that the thick messinian sequence of the levantine basin is composed primarily of salt so that the entire evaporitic sequence can be expected to behave as a viscous material it follows that the main detachment of the post messinian wedge is located at the base of the messinian salt layer a viscous salt decollement would produce thrusting trending normal to the shortening direction but boundary conditions affect structural trends even more than stress and or movement direction both strain partitioning and the formation of major strike slip faults within the post messinian wedge are prevented by the high angle of convergence between the african and aegean plates as well as by the low intraplate friction in addition we show that curved and anastomosing thrust fronts are reflected in the cobblestone topography of the mediterranean ridge we finally postulate that extension may occur in the central mediterranean ridge as a result of the geometry of the plate boundaries this extension is considered as a possible cause of mud volcanism and mud diapirism

numerical simulation of a dam break for an actual river terrain environment a two dimensional 2d finite difference shallow water model based on a second order hybrid type of total variation diminishing tvd approximate solver with a muscl limiter function was developed to model flooding and inundation problems where the evolution of the drying and wetting interface is numerically challenging both a minimum positive depth mpd scheme and a non mpd scheme were employed to handle the advancement of drying and wetting fronts we used several model problems to verify the model including a dam break in a slope channel a dam break flooding over a triangular obstacle an idealized circular dam break and a tide flow over a mound computed results agreed well with the experiment data and other numerical results available the model was then applied to simulate the dam breaking and flooding of hsindien creek taiwan with the detailed river basin topography computed flooding scenarios show reasonable flow characteristics though the average speed of flooding is 6 7 m s 1 which corresponds to the subcritical flow condition fr 1 the local maximum speed of flooding is 14 12 m s 1 which corresponds to the supercritical flow condition fr 1 31 it is necessary to conduct some kind of comparison of the numerical results with measurements experiments in further studies nevertheless the model exhibits its capability to capture the essential features of dam break flows with drying and wetting fronts it also exhibits the potential to provide the basis for computationally efficient flood routing and warning information copyright 2006 john wiley sons ltd

nature origin and evolution of the granitoid hosted early proterozoic copper molybdenum mineralization at malanjkhand central india at malanjkhand central india lode type copper molybdenum mineralization occurs within calcalkaline tonalite granodiorite plutonic rocks of early proterozoic age the bulk of the mineralization occurs in sheeted quartz sulfide veins and k silicate alteration assemblages defined by alkali feldspar k feldspar albite dusty hematite in feldspar biotite muscovite are prominent within the ore zone and the adjacent host rock weak propylitic alteration defined by albite biotite epidote zoisite surrounds the k silicate alteration zone the mineralized zone is approximately 2 km in strike length has a maximum thickness of 200 m and dips 65 75 along which low grade mineralization has been traced up to a depth of about 1 km the ore reserve has been conservatively estimated to be 92 million tonnes with an average cu content of 1 30 supergene oxidation accompanied by limited copper enrichment is observed down to a depth of 100m or more from the surface primary ores consist essentially of chalcopyrite and pyrite with minor magnetite and molybdenite 34s values in pyrite and chalcopyrite 0 38 to 2 90 fall within the range characteristic of granitoid hosted copper deposits 18o values for vein quartz 6 99 to 8 80 suggest exclusive involvement of juvenile water annealed fabrics are common in the ore the sequence of events that led to the present state of hypogene mineralization is suggested to be as follows fracturing of the host rock emplacement of barren vein quartz pronounced wall rock alteration accompanied by disseminated mineralization and the ultimate stage of intense silicification accompanied by copper mineralization fragments of vein quartz and altered wall rocks and striae in the ore suggest post mineralization deformation the recrystallization fabric particularly in chalcopyrite and sphalerite is a product of dynamic recrystallization associated with the post mineralization shearing the petrology of the host rocks hydrothermal alteration assemblages ore mineral associations fluid inclusions and the sulfur and oxygen isotopes of ores are comparable to those in phanerozoic and reported precambrian porphyry copper systems and the malanjkhand deposit has important implications for both metallogenic models for and mineral exploration in precambrian terrains

wavelet transform a future of rock fabric analysis abstract although twenty years ago fabric was defined as the complete spatial and geometrical configuration of all those components that make up a deformed rock fabric was mainly synonymous with lattice preferred orientation very little attention has been paid to the multi scale geometrical and spatial relationships of the rock components fabric quantification in terms of size shape orientation and location at all scales is now performed in two dimensions using anisotropic wavelets as a first example the wavelets are applied to the famous colour plate of sander and the results compared to his axial distribution analysis applied to the k feldspars of a rock section from the sidobre granite pluton montagne noire france the wavelet analysis shows i alignment of grains resulting from mechanical interactions between grains and shows that shearing occurred within the crystalline frame ii preferred grain orientation the classical grain shape fabric parallel to the overall mineral lineation and iii small tensional domains elongate perpendicular to the lineation infilled by the residual melt just before total crystallisation attesting to the stretching nature of the mineral lineation the future of rock fabric analysis will come from new steps in understanding the processes acting during fabric development along with a further development of wavelet analysis using high resolution three dimensional fabric data

episodes of particle ejection from the surface of the active asteroid 101955 bennu introduction active asteroids are small bodies in the solar system that show ongoing mass loss such as the ejection of dust which may be caused by large impacts volatile release or rotational acceleration studying them informs our understanding of the evolution and destruction of asteroids and the origin of volatile materials such as water on earth the osiris rex origins spectral interpretation resource identification and security regolith explorer spacecraft has rendezvoused with the near earth asteroid 101955 bennu the selection of bennu as the osiris rex target was partially based on its spectral similarity to some active asteroids observations designed to detect mass loss at bennu were conducted from earth and during the spacecraft s approach but no signs of asteroid activity were found however when the spacecraft entered orbit in january 2019 we serendipitously observed particles in the vicinity of bennu that had apparently been ejected from its surface rationale we analyzed the properties and behavior of particles ejected from bennu to determine the possible mechanisms of ejection and provide understanding of the broader population of active asteroids images obtained by the spacecraft indicate multiple discrete ejection events with a range of energies and resultant particle trajectories we characterized three large ejection events that respectively occurred on 6 january 19 january and 11 february 2019 tracking of individual particles across multiple images by means of optical navigation techniques provided the initial conditions for orbit determination modeling by combining these approaches we estimated the locations and times of ejection events and determined initial velocity vectors of particles we estimated the particle sizes and the minimum energies of the ejection events using a particle albedo and density consistent with observations of bennu results particles with diameters from 3 m s 1 estimated energies ranged from 270 mj for the 6 january event to 8 mj for the 11 february event the three events arose from widely separated sites which do not show any obvious geological distinction from the rest of bennu s surface however these events all occurred in the late afternoon between about 15 00 and 18 00 local solar time in addition to discrete ejection events we detected a persistent background of particles in the bennu environment some of these background particles have been observed to persist on temporary orbits that last several days in one case with a semimajor axis 1 km the orbital characteristics of these gravitationally bound objects make it possible to determine the ratio of their cross sectional area to their mass combined with their photometric phase functions this information constrains the parameter space of the particles diameters densities and albedos conclusion plausible mechanisms for the large ejection events include thermal fracturing volatile release through dehydration of phyllosilicates and meteoroid impacts the late afternoon timing of the events is consistent with any of these mechanisms bennu s boulder geology indicates that thermal fracturing perhaps enhanced by volatile release could occur on the asteroid surface smaller events especially those that occur on the night side of bennu could be attributable to reimpacting particles our observations classify bennu as an active asteroid active asteroids are commonly identified by major mass loss events observable with telescopes on scales much greater than we observed at bennu our findings indicate that there is a continuum of mass loss event magnitudes among active asteroids

shape of 101955 bennu indicative of a rubble pile with internal stiffness the shapes of asteroids reflect interplay between their interior properties and the processes responsible for their formation and evolution as they journey through the solar system prior to the osiris rex origins spectral interpretation resource identification and security regolith explorer mission earth based radar imaging gave an overview of 101955 bennu s shape here we construct a high resolution shape model from osiris rex images we find that bennu s top like shape considerable macroporosity and prominent surface boulders suggest that it is a rubble pile high standing north south ridges that extend from pole to pole many long grooves and surface mass wasting indicate some low levels of internal friction and or cohesion our shape model indicates that similar to other top shaped asteroids bennu formed by reaccumulation and underwent past periods of fast spin which led to its current shape today bennu might follow a different evolutionary pathway with an interior stiffness that permits surface cracking and mass wasting near earth asteroid bennu has a top like shape with longitudinal ridges macroporosity prominent boulders and surface mass wasting suggesting that it is a stiff rubble pile according to early observations by the osiris rex mission