strength and anisotropy of foliated rocks with varied mica contents abstract we have shortened 15 schists and gneisses with varying compositions 15 75 mica by volume at angles of 45 and 90 to foliation s to investigate the influence of micas on the strength and anisotropy of foliated rocks at the conditions tested t 25 c p c 200 mpa and e 10 5 s 1 compressive strengths vary by a factor 4 in the 45 and 90 orientations and individual rock types exhibit directional responses ranging from isotropic to strongly anisotropic trends of decreasing strength decreasing anisotropy and increasing ductility are observed with increasing mica content strains in all samples were localized within inclined shear zones accommodated by dislocation slip and grain scale microkinking in micas and microcracking in all other silicates stress strain response and grain scale deformation microstructures both indicate that mechanical behavior is strongly influenced by the concentration and spatial arrangement of micas shear zone formation is associated either with discrete brittle fracture transitional strain softening or steady strength ductile shear in both brittle and transitional samples extensive microcracking of strong quartzo feldspathic bridges occurs and stress drop magnitudes decrease with decreasing spacing and increasing overlap of adjacent critically oriented micas steady strength ductile shear zones develop in samples containing domains of interconnected micas and isotropic mechanical response is observed in those in which micas are contiguous in nearly all directions

measurement of the spatial distribution of fluvial bedload transport velocity in both sand and gravel maps are presented of the spatial distribution of two dimensional bedload transport velocity vectors bedload velocity data were collected using the bottom tracking feature of an acoustic doppler current pro ler adcp in both a gravel bed reach and a sand bed reach of fraser river british columbia block averaged bedload velocity vectors and bedload velocity vectors interpolated onto a uniform grid revealed coherent patterns in the bedload velocity distribution concurrent helley smith bedload sampling in the sand bed reach corroborated the trends observed in the bedload velocity map contemporaneous 2d vector maps of near bed water velocity velocity in bins centered between 25 cm and 50 cm from the bottom and depth averaged water velocity were also generated from the adcp data using a vector correlation coef cient which is independent of the choice of coordinate system the bedload velocity distribution was signi cantly correlated to the near bed and depth averaged water velocity distributions the bedload velocity distribution also compared favorably with variations in depth and estimates of the spatial distribution of shear stress published in 2004 by john wiley sons ltd

obtuse angle vs confluent sharp meander bends insights from the paraguay cuiaba confluence in the tropical pantanal wetlands brazil abstract river confluences are notable features in the drainage system with complex hydrodynamics bed morphology sediment transport and mixing processes junction planform plays a pivotal role in the confluence hydrodynamics however most investigations have concentrated on the junction of two straight channels and few studies have focused on confluent meander bends or obtuse angle confluences here we analyze a confluence with an obtuse angle planform the tributary enters the confluence at an angle higher than 180 that abruptly curves to join the main river in the pantanal wetlands the strong flood wave is responsible for significant variations of the discharge and momentum flux ratios within the confluence consequently the paraguay cuiaba confluence is able to shift from an obtuse angle working mode to a confluent meander bend working mode according to the hydrological conditions when the momentum ratio is greater than 1 mr 1 the confluence works as an obtuse angle junction whereas when the ratio is less than 1 mr

flow fields bed shear stresses and suspended bed sediment dynamics in bifurcations of a large river 1 channel bifurcations associated with bars and islands are important nodes in braided rivers and may control flow partitioning and thus affect downstream confluences as well as the formation and dynamics of bars however the morphodynamic processes associated with bar formation are poorly understood and previous studies have largely concerned laboratory experiments small natural streams or numerical analyses with large froude numbers high slopes and low shields stresses in these cases the morphologic changes at bifurcations are relatively rapid with predominant bed load transport and the suspended load playing a minor role in this paper the evolution of the flow structure and suspended bed sediment transport along four expansion diffluence units in the rio parana argentina are described the rio parana is a large multichannel river with a bed composed of medium and fine sands and possesses low froude numbers and high suspended bed material transport primary and secondary flow velocity components were measured with an acoustic doppler current profiler adcp along the expansion diffluence units and the backscatter signal of the adcp was calibrated to allow simultaneous measurements of suspended bed sediment concentrations the interactions between these variables show that the cores of primary flow velocity and suspended bed sediment concentration do not necessarily follow the thalweg at the bifurcation and that inertial effects on the suspended bed sediment may influence the morphodynamics of bar formation it is suggested that changes in flow stage as well as the presence of vegetation may further increase the deposition of suspended bed sediment at the bar head this study suggests that the ratio of suspended bed material to bed load is an important factor controlling the morphodynamics of bifurcations in large sand bed braided rivers

non linear inversion of resistivity profiling data for some regular geometrical bodies1 the inversion of resistivity profiling data involves estimation of the spatial distribution of resistivities and thicknesses of rock layers from the apparent resistivity data values measured in the field as a function of electrode separation the drawbacks of using traditional curve matching techniques to solve this inverse problem have been overcome by iterative linear techniques but these require good starting models even if the shape of the causative body is asssumed known in spite of the recent developments in inversion techniques no robust method exists for the inversion of resistivity profiling data for the simple model of dikes and spheres which are the classical models of geophysical prospecting we apply three different non linear inversion schemes to invert synthetic resistivity profiling data for the classical models embedded in a uniform matrix of contrasting resistivity the three non linear algorithms used are called the metropolis simulated annealing sa very fast simulated annealing vfsa and a genetic algorithm ga we compare the performance of the three algorithms using synthetic data for an outcropping vertical dike model although all three methods were successful in obtaining optimal solutions for arbitrary starting models vfsa proved to be computationally the most efficient

the influence of dunes on mixing in a migrating salt wedge fraser river estuary canada dune bedforms and salt wedge intrusions are common features in many estuaries with sand beds and yet little is known about the interactions between the two flow visualization with an echosounder and velocity measurements with an acoustic doppler current profiler over areas of flat bed and sand dunes in the highly stratified fraser river estuary canada were used to examine the effect of dunes on interfacial mixing as the salt wedge migrates upstream over the flat bed mixing is restricted to the lower portion of the water column however as the salt wedge migrates into the dune field from the flat bed there is a dramatic change in the flow and large internal in phase waves develop over each of the larger dunes with water from the salt wedge reaching the surface of the estuary the friction richardson number shows that bed friction is more important in interfacial mixing over the dunes than over the flat bed and a plot of internal froude number versus obstacle dune height shows that the salt wedge flow over the dunes is mainly supercritical such bedforms can be expected to cause similar effects in interfacial mixing in other estuaries and sediment laden density currents and may thus be influential in fluid mixing and sediment transport copyright 2010 john wiley sons ltd

analysis of continental midcrustal strain localization induced by microfracturing and reaction softening 1 low angle extensional shear zones which often characterize the brittle ductile transition of the continental crust are seen here to result from strain localization the potentially destabilizing deformation mechanism is assumed to be the progressive transformation of fractured coarse feldspar grains into white mica as observed in the east tenda shear zone alpine corsica the coupling between microfracturing and feldspar to mica reaction is coeval with strain localization that occurred in that field case at a depth close to 15 km this reaction is proposed as the main destabilizing factor responsible for the onset of localization with feldspar having a stationary dislocation creep flow stress larger than mica to test this hypothesis a rheological model is constructed based on the field observations for a mixture of three phases mica quartz and feldspar deforming at a common strain rate the phase concentrations change with time according to the feldspar to mica reaction which takes place only if feldspar grains are fractured a condition detected with the mohr coulomb criterion the tendency for the strain to localize is assessed by numerical means for the structure composed of an upper crust gliding rigidly over the lower crust which sustains an overall simple shear the onset of strain localization is defined by an increase of at least two orders of magnitude in strain rate over part of the lower crust the upper crust gliding velocity has to be increased by at least a factor of 5 for localization to occur the time lapse for this velocity change determines the depth of the shear zone 15 17 km the kinetics of the metamorphic reaction and the final amount of white mica control its width 1 4 km the time of the shear zone formation is less than half a million years

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

acoustic measurement of river discharge this paper presents a new moving boat method for rapidly measuring river discharge using an acoustic doppler current profiler adcp the method uses an adcp to measure current profiles and boat velocity along transects across a river measurements from the river elbe near hamburg germany are presented to illustrate the method and its associated uncertainties an adcp measures profiles of current velocity relative to the boat and the velocity of the boat relative to the bottom the discharge calculation depends only on these data and it is not necessary to know either compass heading or the actual location of the boat furthermore the transect can be an arbitrary curve as long as it starts near one side of the river and ends near the other uncertainty in discharge from random errors biases and missed data near the surface bottom and sides of the river is investigated missed data near the surface and bottom are the largest source of error unless the data are corrected by assuming model profiles

control of the geometry of precursor brittle structures on the type of ductile shear zone in the adamello tonalites southern alps italy abstract amphibolite facies ductile shear zones developed during the immediate post intrusive cooling history of the adamello tonalites southern alps italy shear zones include i thin a few mm s thick fault like shear zones that accommodate shear strain values up to several 100 s the dominant type ii mylonitic horizons dm s thick in sharp contact with the undeformed wall rock iii continuous shear zones with sigmoidal shaped s or composite s c foliations a transition between the different types occurs along strike over short distances discontinuous shear zones are also localized on pegmatite dykes and quartz veins and both i and ii are discontinuously outlined by quartz layers detailed surface mapping reveals that most fault like shear zones are arranged en echelon mainly forming contractional steps markers crosscut by shear zones allow the displacement to be measured at several positions along shear zones and this reveals very steep displacement gradients close to the shear zone tips differential displacement is mainly accommodated at contractional steps by the development of foliated domains geochemical analyses of major and trace elements show that there is no compositional change along strain gradients the overall features are consistent with nucleation of shear zones on former sets of en echelon joints in many cases intruded by pegmatite dykes or filled with quartz reactivation of joints produced strongly localized shear zones whereas broader foliated zones evolved from the contractional jogs between adjacent stepped joint terminations during progressive shearing these jogs were progressively involved in the accommodation of shear displacement and overall shear zone development

mechanisms of weak phase interconnection and the effects of phase strength contrast on fabric development abstract to determine how deformation mechanisms and fabrics evolve during the strain weakening and localization that accompany the transition from a load bearing framework to an interconnected weak phase shear experiments were conducted on a fine grained gneiss 58 quartz interconnected 28 plagioclase dispersed 13 biotite aligned but dispersed at 745 and 800 c 1500 mpa and two strain rates 2 10 5 and 2 10 6 s 1 in experiments with a high phase strength contrast hpsc 25 and 45 between dispersed biotite and framework quartz grains biotite grains become interconnected due to stress concentration at their tips that allow local semi brittle flow of intervening quartz and cataclasis of intervening plagioclase in the higher temperature hpsc samples the biotite partially dehydrated in high strain zones a single narrow shear zone formed because the psc between the quartz and biotite reaction product layers remained high in the lower temperature hpsc samples there was no reaction and a penetrative s c fabric formed the fabric is defined by the many multiply interconnected biotite strands that formed because the psc between the quartz and biotite decreased as the biotites kinked in slower strain rate experiments with a much lower psc 10 biotite interconnection occurs by shearing into quartz quartz boundaries where new weak strain free recrystallized grains form at low strain a weak s c fabric forms but it evolves to an s c fabric as the psc decreases with strain thus the magnitude of the strength contrast between a weak phase and its matrix influences the mechanism of weak phase interconnection the degree of strain localization and the fabric

the influence of flow discharge variations on the morphodynamics of a diffluence confluence unit on a large river 2017 the authors earth surface processes and landforms published by john wiley sons ltd bifurcations are key geomorphological nodes in anabranching and braided fluvial channels controlling local bed morphology the routing of sediment and water and ultimately defining the stability of their associated diffluence confluence unit recently numerical modelling of bifurcations has focused on the relationship between flow conditions and the partitioning of sediment between the bifurcate channels herein we report on field observations spanning september 2013 to july 2014 of the three dimensional flow structure bed morphological change and partitioning of both flow discharge and suspended sediment through a large diffluence confluence unit on the mekong river cambodia across a range of flow stages from 13 500 to 27 000 m 3 s 1 analysis of discharge and sediment load throughout the diffluence confluence unit reveals that during the highest flows q 27 000 m 3 s 1 the downstream island complex is a net sink of sediment losing 2600 2000 kg s 1 between the diffluence and confluence whereas during the rising limb q 19 500 m 3 s 1 and falling limb flows q 13 500 m 3 s 1 the sediment balance is in quasi equilibrium we show that the discharge asymmetry of the bifurcation varies with discharge and highlight that the influence of upstream curvature induced water surface slope and bed morphological change may be first order controls on bifurcation configuration comparison of our field data to existing bifurcation stability diagrams reveals that during lower rising and falling limb flow the bifurcation may be classified as unstable yet transitions to a stable condition at high flows however over the long term 1959 2013 aerial imagery reveals the diffluence confluence unit to be fairly stable we propose therefore that the long term stability of the bifurcation as well as the larger channel planform and morphology of the diffluence confluence unit may be controlled by the dominant sediment transport regime of the system 2017 the authors earth surface processes and landforms published by john wiley sons ltd

transverse mixing in an unregulated northern river transverse mixing in an unregulated northern river in canada was studied in different discharge conditions with and without ice cover the distribution of cumulative discharge was constructed on the basis of river cross sectional shapes and a modified streamtube method was proposed to describe transverse mixing the modified method only uses raw field data to calibrate the modeled concentration profiles and thus can produce a reliable mixing coefficient even with relatively low quality field data the effects of river discharge and ice cover on the transverse mixing coefficient were examined in a fixed study reach it was found that the transverse mixing coefficient increased approximately linearly with river discharge from 84 to 960 m3 s the dimensionless transverse mixing coefficient scaled with river shear velocity and river depth appeared unaffected within 14 by the river discharge in both open water and ice covered conditions and its value was 21 smaller in the ice covered condition than

causes of rapid mixing at a junction of two large rivers rio parana and rio paraguay argentina 1 airborne and satellite observations show that when large rivers join they can take hundreds of kilometers to mix completely but on occasion may mix very rapidly application of established semitheoretical analyses shows that long mixing lengths should be expected the first measurements of mixing processes at a large river junction rio parana and rio paraguay argentina combined width 2 8 km are presented at two occasions first when they mix in 400 km and second when mixing is complete in only 8 km downstream of the junction for the case of slower mixing at a point surveys showed that mixing driven by turbulent shear associated with a near vertical shear layer was restricted to close to the junction to 0 272 multiples of the postconfluence width downstream transect surveys showed penetration of more turbid water from the rio paraguay underneath the rio parana but this was insufficient to promote more rapid mixing there was no clear channel scale circulation present and slow mixing was compounded by reverse topographic forcing on the mainstream rio parana side of the river this kept more turbid water on the rio paraguay side of the river close to the bed in the case of rapid mixing we found clear channel scale circulation the momentum ratio between the combining flows reinforced the effects of the discordance in bed height between the tributaries at the confluence and allowed penetration of more turbid rio paraguay water further across the channel width deeper within the flow the importance of the interaction between momentum ratio and bed morphology at channel junctions makes mixing rates at the confluence dependent upon basin scale hydrological response which is more likely to differ between large confluent rivers than small rivers as a result of the different climatic topographic zones that they may capture

on the calculation of suspended load for noncohesive sediments calculation of suspended sediment transport rates requires integration of the product of sediment concentration times velocity over the depth of the flow hence accurate profiles of these quantities are required especially near the sediment bed although this would appear to be a straightforward task many effects can cause significant deviation of these quantities from those values expected from simple known relationships for example density stratification by suspended particulates can dampen turbulence fluctuations and significantly reduce the effective viscosity and diffusivity of the flow the momentum and suspended sediment equations are solved herein including the effects of stratification by suspended sediment and the effects due to size distribution and bedforms the results show that stratification and bedforms generally reduce the transport capacity of the flow whereas treating the sediment as an assemblage of different sizes rather than a single size d50 increases the expected transport

deformation partitioning and porphyroblast rotation in meta morphic rocks a radical reinterpretation abstract most porphyroblasts never rotate during ductile deformation provided they do not intern ally deform during subsequent events with the exception of relatively uncommon but spectacular examples of spiralling garnets instead the sur rounding foliation rotates and reactivates due to partitioning of the deformation around the porphyroblast consequently porphyroblasts commonly preserve the orientation of early foliations and stretching lineations within strain shadows or inclusion trails even where these structures have been rotated or obliterated in the matrix due to subsequent deformation these relationships can be readily used to help develop an understanding of the processes of foliation development and they demonstrate the prominent role of reactivation of old foliations during subse quent deformation they can also be used to determine the deformation history as porphyro blasts only rotate when the deformation cannot partition and involves progressive shearing with no combined bulk shortening component

morphology and flow fields of three dimensional dunes rio parana argentina results from simultaneous multibeam echo sounding and acoustic doppler current profiling 1 most past studies of river dune dynamics have concentrated on two dimensional 2 d bed forms with constant heights and straight crest lines transverse to the flow and their associated turbulent flow structure this morphological simplification imposes inherent limitations on the interpretation and understanding of dune form and flow dynamics in natural channels where dune form is predominantly three dimensional for example studies over 2 d forms neglect the significant influence that lateral flows and secondary circulation may have on the flow structure and thus dune morphology this paper details a field study of a swath of 3 d dunes in the rio parana argentina a large 0 35 km wide 1 2 km long area of dunes was surveyed using a multibeam echo sounder mbes that provided high resolution 3 d detail of the river bed simultaneous with the mbes survey 3 d flow information was obtained with an acoustic doppler current profiler adcp revealing a complicated pattern of dune morphology and associated flow structure within the swath dune three dimensionality appears intimately connected to the morphology of the upstream dune with changes in crest line curvature and crest line bifurcations junctions significantly influencing the downstream dune form dunes with lobe or saddle shaped crest lines were found to have larger more structured regions of vertical velocity with smaller separation zones than more 2 d straight crested dunes these results represent the first integrated study of 3 d dune form and mean flow structure from the field and show several similarities to recent laboratory models of flow over 3 d dunes

modelling hydrodynamics in the rio parana argentina an evaluation and inter comparison of reduced complexity and physics based models applied to a large sand bed river abstract depth averaged velocities and unit discharges within a 30 km reach of one of the world s largest rivers the rio parana argentina were simulated using three hydrodynamic models with different process representations a reduced complexity rc model that neglects most of the physics governing fluid flow a two dimensional model based on the shallow water equations and a three dimensional model based on the reynolds averaged navier stokes equations flow characteristics simulated using all three models were compared with data obtained by acoustic doppler current profiler surveys at four cross sections within the study reach this analysis demonstrates that surprisingly the performance of the rc model is generally equal to and in some instances better than that of the physics based models in terms of the statistical agreement between simulated and measured flow properties in addition in contrast to previous applications of rc models the present study demonstrates that the rc model can successfully predict measured flow velocities the strong performance of the rc model reflects in part the simplicity of the depth averaged mean flow patterns within the study reach and the dominant role of channel scale topographic features in controlling the flow dynamics moreover the very low water surface slopes that typify large sand bed rivers enable flow depths to be estimated reliably in the rc model using a simple fixed lid planar water surface approximation this approach overcomes a major problem encountered in the application of rc models in environments characterised by shallow flows and steep bed gradients the rc model is four orders of magnitude faster than the physics based models when performing steady state hydrodynamic calculations however the iterative nature of the rc model calculations implies a reduction in computational efficiency relative to some other rc models a further implication of this is that if used to simulate channel morphodynamics the present rc model may offer only a marginal advantage in terms of computational efficiency over approaches based on the shallow water equations these observations illustrate the trade off between model realism and efficiency that is a key consideration in rc modelling moreover this outcome highlights a need to rethink the use of rc morphodynamic models in fluvial geomorphology and to move away from existing grid based approaches such as the popular cellular automata ca models that remain essentially reductionist in nature in the case of the world s largest sand bed rivers this might be achieved by implementing the rc model outlined here as one element within a hierarchical modelling framework that would enable computationally efficient simulation of the morphodynamics of large rivers over millennial time scales

application of a roughness length representation to parameterize energy loss in 3 d numerical simulations of large rivers 1 recent technological advances in remote sensing have enabled investigation of the morphodynamics and hydrodynamics of large rivers however measuring topography and flow in these very large rivers is time consuming and thus often constrains the spatial resolution and reach length scales that can be monitored similar constraints exist for computational fluid dynamics cfd studies of large rivers requiring maximization of mesh or grid cell dimensions and implying a reduction in the representation of bedform roughness elements that are of the order of a model grid cell or less even if they are represented in available topographic data these subgrid elements must be parameterized and this paper applies and considers the impact of roughness length treatments that include the effect of bed roughness due to unmeasured topography cfd predictions were found to be sensitive to the roughness length specification model optimization was based on acoustic doppler current profiler measurements and estimates of the water surface slope for a variety of roughness lengths this proved difficult as the metrics used to assess optimal model performance diverged due to the effects of large bedforms that are not well parameterized in roughness length treatments however the general spatial flow patterns are effectively predicted by the model changes in roughness length were shown to have a major impact upon flow routing at the channel scale the results also indicate an absence of secondary flow circulation cells in the reached studied and suggest simpler two dimensional models may have great utility in the investigation of flow within large rivers

a comparison of quartz c axis preferred orientations in experimentally deformed aplites and quartzites the effect of feldspar on the development of quartz c axis preferred orientations was investigated by experimentally deforming aplite 30 quartz and pure quartzite under equivalent conditions and comparing the quartz c axis patterns axial compression experiments were performed at temperatures of 800 and 900 c strain rates of 10 6 and 10 5s 1 and a confining pressure of 1500 mpa under these conditions both quartz and feldspar deform by dislocation creep with only minor syntectonic recrystallization the quartz c axis preferred orientations produced in the two rock types at equivalent deformation conditions and quartz grain strains were found to be essentially identical in pattern and strength these results indicate that the presence of feldspar has little or no effect on the operative slip systems in adjacent quartz grains in quartzo feldspathic rocks and that quartz c axis preferred orientation analyses can be performed on a wide range of crustal rock types

factors influencing the calculation of periodic secondary circulation in a tidal river numerical modelling of the lower sacramento river usa secondary circulation is the component of three dimensional 3d flow in river channels perpendicular to the primary flow direction secondary circulation calculated from acoustic doppler current profiler adcp transects is sensitive to the calculation method and is affected by the transect angle relative to the mean flow direction and variations in the flow direction along a transect to quantify bounds on transect alignment relative to river flow for field data collection and examine tidal time scale variability in secondary circulation the 3d hydrodynamic model untrim was applied to simulate the hydrodynamics in the lower reach of the sacramento river ca usa secondary circulation was calculated using the rozovskii and the zero net discharge methods on repeated transects extracted from the model results in regions of both relatively uniform and complex flows when the depth averaged flow direction along a transect varied by more than about 5 occurring when the transect was as little as 10 to 20 out of normal to the mean flow direction the rozovskii method produced more realistic secondary circulation than the zero net discharge method analysis indicated that adcp transects should be within 20 of perpendicular to the mean flow direction when calculating secondary circulation secondary circulation strength around two tidally influenced bends generally increased with increasing flow and broke down near slack water however the strength of the secondary circulation was not only a function of the flow magnitude but also depended on the direction of the water flow and the transect location relative to the river curvature which varied with the tidal flow direction copyright 2015 john wiley sons ltd

sediment mobility and bed armoring in the st clair river insights from hydrodynamic modeling the lake levels in lake michigan huron have recently fallen to near historical lows as has the elevation difference between lake michigan huron compared to lake erie this decline in lake levels has the potential to cause detrimental impacts on the lake ecosystems together with social and economic impacts on communities in the entire great lakes region results from past work suggest that morphological changes in the st clair river which is the only natural outlet for lake michigan huron could be an appreciable factor in the recent trends of lake level decline a key research question is whether bed erosion within the river has caused an increase in water conveyance therefore contributed to the falling lake level in this paper a numerical modeling approach with field data is used to investigate the possibility of sediment movement in the st clair river and assess the likelihood of morphological change under the current flow regime a two dimensional numerical model was used to study flow structure bed shear stress and sediment mobility armoring over a range of flow discharges boundary conditions for the numerical model were provided by detailed field measurements that included high resolution bathymetry and three dimensional flow velocities the results indicate that without considering other effects under the current range of flow conditions the shear stresses produced by the river flow are too low to transport most of the coarse bed sediment within the reach and are too low to cause substantial bed erosion or bed scour however the detailed maps of the bed show mobile bedforms in the upper st clair river that are indicative of sediment transport relatively high shear stresses near a constriction at the upstream end of the river and at channel bends could cause local scour and deposition ship induced propeller wake erosion also is a likely cause of sediment movement in the entire reach other factors that may promote sediment movement such as ice cover and dredging in the lower river require further investigation copyright 2012 john wiley sons ltd

mixing layer distortion at the confluence of channels of different depth channel confluences have received considerable recent attention in the fields of geomorphology1 3 sedimentology4 9 and hydraulic engineering10 13 where channels join rapid changes in fluid velocity turbulence intensity channel hydraulic geometry and bed geometry may occur14 17 previous models of junction dynamics have tended to assume that the confluent channels are of equal depth10 18 a condition that may be found only rarely in natural junctions more often the depths of confluent channels are different19 this discordance is commonly the result of the forma tion at the mouth of each confluent channel of bars that possess steep avalanche faces which dip into a central junction scour1 2 5 20 here we suggest that when channels of different depth join the mixing layer that forms at their confluence is distorted by interacting with a separation zone which forms in the lee of the mouth of the shallower channel this mixing layer distortion imparts a complex three dimensional flow to the junction promoting vertical fluid upwelling and significantly enhancing rapid mixing within the flow of the shallow tributary while retarding the rate of mixing across the flow of the deeper channel suspended sediments or contaminants within the deeper channel may be transferred rapidly across the flow of the shallower tributary upwelling downstream of the junction

textural and mechanical evolution with progressive strain in experimentally deformed aplite determining meaningful flow laws for the polyphase aggregates that characterize the crust is difficult because the strength of such aggregates depends on the strengths volume proportions and geometrical arrangement of their constituent phases and all of those factors may change with progressive strain in order to investigate some of these factors we have performed a series of axial compression experiments on a fine grained granite aplite over a range of shortening strains 20 85 and temperatures 700 900 c at 1 5 10 6 s 1 and 1400 mpa we have also done comparison experiments on pure quartz and feldspar aggregates the aplite is composed of 1 3 quartz and 2 3 oligoclase and microcline with minor biotite and magnetite the quartz grains are dispersed in a continuous matrix of feldspar optical and tem scale microstructures indicate that the deformation mechanisms of the quartz and feldspar grains in the aplites are similar to those of pure quartz and feldspar aggregates deformed at the same conditions the feldspars deform by semi brittle flow at 700 and 800 c and by recrystallization accommodated dislocation creep at 900 c while quartz deforms by recrystallization accommodated dislocation creep at 700 c and by climb accommodated dislocation creep at 800 and 900 c pure albite aggregates are stronger than quartz aggregates over this range of conditions however in the aplite an apparent strength reversal is inferred from grain strain measurements and changes in phase distribution with increasing temperature at 700 c the dispersed quartz grains in the aplite remain less deformed than the feldspar grains because the scarcity of quartz quartz grain boundaries limits recovery by grain boundary migration recrystallization causing the quartz strength to rise above that of feldspar however the aplite is weaker than a pure feldspar aggregate because cracking is enhanced by stress concentrations at the quartz grains at 800 c the two phases undergo approximately equal strain because easy dislocation climb in quartz allows individual grains to strain homogeneously the aplite strength is close to that of a pure feldspar aggregate at 900 c the initially continuous feldspar grains deform inhomogeneously and undergo microboudinage while the quartz grains deform homogeneously and gradually become more interconnected and undergo higher strain than the feldspars the aplite strength is initially closer to that of a feldspar aggregate but with increasing strain it becomes closer to that of a quartz aggregate the aplite undergoes strain softening over the whole range of conditions at 700 and 800 c the weakening is due to grain boundary migration recrystallization of feldspar in the fine grained crush products along grain scale faults at 900 c the weakening is due to a combination of grain boundary migration recrystallization of the feldspars plus increasing interconnection of the weaker quartz grains these results demonstrate that the textural evolution of a polyphase aggregate with increasing strain is determined by both the phase distribution and the deformation mechanism of each phase and that very high strains may be required to approach microstructural and mechanical steady state therefore measuring or calculating a flow law appropriate for granite at mid crustal conditions is not simple

sediment discharge division at two tidally influenced river bifurcations 1 we characterize and quantify the sediment discharge division at two tidally influenced river bifurcations in response to mean flow and secondary circulation by employing a boat mounted acoustic doppler current profiler adcp to survey transects at bifurcating branches during a semidiurnal tidal cycle the adcp collecting flow velocity and acoustical backscatter data was used to quantify suspended sediment discharge adopting a recently introduced calibration procedure measured profiles of flow velocity and sediment concentration allowed us to compute spatiotemporal distributions of the shear velocity the roughness length and the rouse number spatiotemporal distributions of the settling velocity were obtained by combining the rouse number and shear velocity estimates with in situ measurements from a laser particle size analyzer bed load transport rates were inferred from shear stress estimates the concentration field shows a direct response to bed shear stress stressing the alluvial context of the system the flow in the bifurcation regions is characterized by counter rotating secondary flow cells which stretch over the full width and depth of the cross sections in the downstream branches and persist throughout the entire tidal cycle the pattern of secondary flow suggests the flow approaching the bifurcation is concentrated in two independent threads a two cell structure inhibits the exchange of sediment that would occur in case a single cell would stretch over the full channel width the division of suspended sediment primarily depends on the upstream transverse profile of the suspended sediment concentration which is in turn dependent on geometrical factors such as upstream curvature

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

development of crystallographic preferred orientations by nucleation and growth of new grains in experimentally deformed quartz single crystals abstract deformation experiments have been carried out to investigate the effect of dynamic recrystallisation on crystallographic preferred orientation cpo development cylindrical samples of natural single crystals of quartz were axially deformed together with 1 vol of added water and 20 mg of mn2o3 powder in a griggs solid medium deformation apparatus in different crystallographic orientations with compression direction i parallel to ii at 45 to and 45 to and iii parallel to the experiments were performed at a temperature of 800 c a confining pressure of 1 2 gpa a strain rate of 10 6 s 1 to bulk finite strains of 14 36 the deformed samples were analysed in detail using optical microscopy electron backscatter diffraction ebsd and transmission electron microscopy tem two different microstructural domains were distinguished in the deformed samples i domains with undulatory extinction and deformation lamellae and ii domains with new recrystallised grains within the domains of undulatory extinction crystal plastic deformation caused gradual rotations of the crystal lattice up to 30 away from the host orientation new recrystallised grains show a strong cpo with c axis maxima at 45 to the compression direction this is the case in all experiments irrespective of the initial crystallographic orientation the results show that c axes are not continuously rotated towards the new maxima the new grains thus developed through a mechanism different from subgrain rotation recrystallisation new grains have a subeuhedral shape and numerous microcavities voids fluid channels and fluid inclusions at their grain boundaries no host control is recorded in misorientation axes across their large angle grain boundaries new grains might have been created by nucleation from solution in the m scale voids and microfractures the cpo most likely developed due to preferred growth of the freshly precipitated grains with orientations suitable for intracrystalline deformation at the imposed experimental conditions

orientation analysis of localized shear deformation in quartz fibres at the brittle ductile transition abstract the crystallographic preferred orientation of fibrous quartz veins deformed under subgreenschist facies conditions along a temperature gradient from 270 to 370 c has been investigated to explore the active mechanism during deformation of the quartz fibres the complete crystallographic orientation of individual recrystallized grains and subgrains was determined by using a combination of cip computer integrated polarization microscopy ebsd electron back scatter diffraction and additional specially developed image analysis techniques it was found that the quartz fibres deformed along crystallographically controlled shear bands from inverse pole figures of normals to the shear band boundaries it is evident that these bands occur along the positive and negative rhomb planes of quartz it is suggested that they are initiated as fractures along these planes inside the shear bands small grains broken off from the host grain show passive rotation of the lattice consistent with the shear sense of the shear bands continued deformation and increasing temperature lead to different recrystallization microstructures inside and outside the shear bands and to a partial obliteration of the sharp orientation relationships

applicability of artificial neural networks for obtaining velocity models from synthetic seismic data seismic velocity analysis is a crucial part of seismic data processing and interpretation which has been practiced using different methods in contrast to time consuming and complicated numerical methods artificial neural networks anns are found to be of potential applicability ann ability to establish a relationship between an input and output space is considered to be appropriate for mapping seismic velocity corresponding to travel times picked from seismograms accordingly a preliminary attempt is made to evaluate the applicability of anns to determine velocity and dips of dipping layered earth models corresponding to travel time data the study is based on synthetic data generated using inverse modeling approach for three earth models the models include a three layer structure with same dips and same directions a three layer model with different dips and same directions as well as a two layer model with different dips and directions an ann structure is designed in three layers namely input output and hidden ones the training and testing process of the ann is successfully accomplished using the synthetic data the evaluation of the applicability of the trained ann to unknown data sets indicates that the ann can satisfactorily compute velocity and dips corresponding to travel times the error intervals between the desired and calculated velocity and dips are shown to be acceptably small in all cases the applicability of the trained ann in extrapolating is also evaluated using a number of data outside of the range already known to ann the results indicate that the trained ann acceptably approximates the velocity and dips furthermore the trained ann is also evaluated in terms of capability of handling deficiency in input data where acceptable results were also achieved in velocity and dip calculations generally this study shows that velocity analysis using anns can promisingly tackle the challenge of retrieving an initial velocity model from the travel time hyperbolas of seismic data

modulation of outer bank erosion by slump blocks disentangling the protective and destructive role of failed material on the three dimensional flow structure the three dimensional flow field near the banks of alluvial channels is the primary factor controlling rates of bank erosion although submerged slump blocks and associated large scale bank roughness elements have both previously been proposed to divert flow away from the bank direct observations of the interaction between eroded bank material and the 3 d flow field are lacking here we use observations from multibeam echo sounding terrestrial laser scanning and acoustic doppler current profiling to quantify for the first time the influence of submerged slump blocks on the near bank flow field in contrast to previous research emphasizing their influence on flow diversion away from the bank we show that slump blocks may also deflect flow onto the bank thereby increasing local shear stresses and rates of erosion we use our measurements to propose a conceptual model for how submerged slump blocks interact with the flow field to modulate bank erosion

delineation of shallow resistivity structure around malvan konkan region maharashtra by neural network inversion using vertical electrical sounding measurements modeling resistivity profiles especially from hard rock areas is of specific relevance for groundwater exploration a method based on bayesian neural network bnn theory using a hybrid monte carlo hmc simulation scheme is applied to model and interpret direct current vertical electrical sounding measurements from 28 locations around the malvan region in the sindhudurg district southwest india the modeling procedure revolves around optimizing the objective function using the hmc based sampling technique which is followed by updating each trajectory by integrating the hamiltonian differential equations via a second order leapfrog discretization scheme the inversion results suggest a high resistivity structure in the north western part of the area which correlates well with the presence of laterites in the south western part a very high conductive zone is observed near the coast indicating an extensive influence of saltwater intrusion our results also show that the effect of intrusion of saline water diminishes from the south western part to the north eastern part of the region two dimensional modeling of four resistivity profiles shows that the groundwater flow is partly controlled by existing lineaments fractures and major joints groundwater occurs at a weathered semi weathered layer of laterite clayey sand and the interface of overburden and crystalline basement the presence of conduits is identified at a depth between 10 and 15 m along the dhamapur kudal and parule oros profiles which seems to be potential zone for groundwater exploration the nw se trending major lineaments and its criss cross sections are indentified from the apparent and true resistivity surface map the pseudo section at different depths in the western part of the area near parule shows extensive influence of saltwater intrusion and its impact reaching up to a depth of 50 m from the surface along the coastal area further the deduced true electrical resistivity section against depth correlates well with available borehole lithology in the area present analyses suggest that hmc based bnn method is robust for modeling resistivity data especially in hard rock terrains these results are useful for interpreting fractures major joints and lineaments and crystalline basement rock and also for constraining the higher dimensional models

brittle shear zones in experimentally deformed quartz single crystals abstract intracrystalline shear zones developed in a quartz single crystal that was experimentally deformed to 26 finite strain under conditions favourable for macroscopically ductile deformation the crystal was uniaxially compressed parallel to c in the presence of 1 vol of added water at a temperature of 800 c a confining pressure of 1200 mpa and a strain rate of 10 6 s 1 we investigated how the shear zones initiated and how their structure evolved with ongoing deformation detailed crystallographic orientation analyses were carried out with the help of the electron backscatter diffraction ebsd technique and complemented by transmission electron microscopy tem the shear zones appeared to develop along planar microcracks oriented parallel to crystallographic rhomb planes further microcracking resulted in cataclastic shear zone development new grains developed by rotation of fracture fragments the rotation of the fragments in the shear direction was probably facilitated by the high water pressure and the relatively high porosity in the shear zone shear zones finally exhibit a strong crystallographic preferred orientation cpo our results suggest that cataclastic deformation processes may lead to shear zone development the cpo developed within the shear zones through dynamic recrystallisation i e new grains with c oriented approximately perpendicular to the shear zone boundary grew at the cost of other new grains

deformation of granitic rocks across the brittle ductile transition abstract a microstructural analysis has been carried out on mylonites and mylonitic gneisses of the eastern peninsular ranges mylonite zone which were formed over a range of metamorphic conditions from lower greenschist to amphibolite facies composite planar fabrics in the form of c and s planes are found at all metamorphic grades fractured feldspars kinked biotites and ductile deformation of quartz characterize the lower greenschist facies mylonites at mid upper greenschist grade orthoclase grains show dynamic recrystallization textures whereas plagioclase exhibits low temperature plasticity with only minor recovery biotite ribbons form by progressive rotation and coalescence of kink band segments to produce chevron fold patterns at epidote amphibolite grade and above recovery processes and annealing recrystallization predominate in all minerals residual orthoclase porphyroclasts show strain related myrmekite formation along those sides of the grains that face the instantaneous shortening direction myrmekite formation due to replacement reactions cannot explain this geometry it is proposed that the myrmekites formed due to a combination of exsolution replacement and strain enhanced diffusion

nucleation and initial growth of a shear zone network within compositionally and structurally heterogeneous granitoids under amphibolite facies conditions abstract in the neves area the pre alpine intrusive protolith of the zentralgneise unit tauern window eastern alps is well preserved in a kilometric scale low strain domain without pervasive alpine deformation it is compositionally heterogeneous consisting predominantly of granodiorites with lesser leucocratic granites and different generations of lamprophyres and aplites the intrusive rocks are crosscut by fractures that were locally infiltrated by fluids and surrounded by alteration haloes incipient alpine amphibolite facies ductile deformation is strongly localized on these precursor fractures and on lithological planar heterogeneities resulting in the development of several different types of shear zones fractures without alteration haloes initially accommodate slip entirely on the fracture itself with increasing deformation a foliation is progressively developed in the adjacent host rock eventually producing a single heterogeneous ductile shear zone with the typical sigmoidal foliation pattern strong layers aplite dykes and bleached alteration haloes developed to either side of precursor fractures localize shear on their boundaries to produce characteristic paired shear zones shearing is more evenly distributed within weak layers lamprophyres and quartz veins with a marked discontinuity in shear strain against the adjacent little deformed granodiorite shear zone development was accompanied by the formation of new fractures and quartz rich veins in the host rock which in turn also localized shear magmatic contacts fractures and quartz veins are mostly steeply dipping and effectively span the complete range of strike orientations the kinematics of the overprinting strike slip shear zones was determined by the orientation of the initial discontinuities relative to the local principal compressive stress axis 1 here oriented ca 345 discontinuities of almost all orientations show shear reactivation even in the case of very low resolved shear stress indicating an overall viscous response of the system without a specific yield stress the geometry and kinematics of the shear zone network suggest that the overall deformation in low strain domains was close to coaxial during deformation along the shear zone network compatibility was maintained by fracturing with the development of new quartz veins and by distributed ductile deformation of the host rock especially within contractional domains of the shear network and at shear zone intersections deformation never propagates into the undeformed homogeneous granodiorite as discrete ductile shear zones but is limited by the original extent of the precursor discontinuities shear zone development in intact rock is always preceded by fracturing which localizes subsequent shear reactivation

deformation of granitoids at low metamorphic grade i reactions and grain size reduction abstract deformation and chemical reaction in granitoids at greenschist facies conditions were investigated in samples from three shear zones two from the alps corvatsch granodiorite and aiguilles rouges granite switzerland and one from eastern australia wyangala granite when examined by light and electron microscopy all show similar features of deformation that progressed from coarse parent rock through to fine grained mylonite quartz deformed plastically while both k feldspar and plagioclase fractured and recrystallized in conjunction with chemical change which had as its end point an assemblage albite quartz white mica caal silicates k feldspar and calcic plagioclase depending on fluid chemistry from the parent rock were unstable at low metamorphic grades in the presence of aqueous fluid since ca bearing plagioclase was not stable in these environments myrmekite did not replace k feldspar in any of the rocks examined recrystallization of feldspar which should perhaps be termed neocrystallization was initiated predominantly at clast margins or along microfractures that are marked by fluid inclusions and twin offsets in old feldspar grains particularly in plagioclases dislocations exist in wall like structures that are commonly associated with voids suggesting origins in microfractures these dislocations had severely limited mobility and subgrain rotation does not appear to have contributed to recrystallization we conclude that recrystallization mainly occurred via a classical nucleation mechanism with minor contributions from twin boundary migration we argue that the 450 550 c lower limit for recrystallization of feldspar referenced throughout the literature is not applicable to the rock systems under investigation and should be discarded as a universal limit microfracturing microboudinage and reaction are seen as the prerequisites for mylonite formation from coarse grained granitic rocks at low metamorphic grades see part ii of this paper neocrystallization fluid access and nucleation appear to have accompanied or immediately followed the first deformation increments and were primarily responsible for continued grain size reduction transgranular fracture was comparatively important only at the onset of deformation since the formation of shear zones in granitoids commonly takes place under conditions of low metamorphic grade in the presence of aqueous fluids in the earth s crust breakdown reactions and nucleation recrystallization in feldspars may be important influences upon localization of deformation in granitoids

mean flow and turbulence structure over fixed two dimensional dunes implications for sediment transport and bedform stability detailed measurements of flow velocity and its turbulent fluctuation were obtained over fixed two dimensional dunes in a laboratory channel laser doppler anemometry was used to measure the downstream and vertical components of velocity at more than 1800 points over one dune wavelength the density of the sampling grid allowed construction of a unique set of contour maps for all mean flow and turbulence parameters which are assessed using higher moment measures and quadrant analysis these flow field maps illustrate that 1 the time averaged downstream and vertical velocities agree well with previous studies of quasi equilibrium flow over fixed and mobile bedforms and show a remarkable symmetry from crest to crest 2 the maximum root mean square rms of the downstream velocity values occur at and just downstream of flow reattachment and within the flow separation cell 3 the maximum vertical rms values occur within and above the zone of flow separation along the shear layer and this zone advects and diffuses downstream extending almost to the next crest 4 positive downstream skewness values occur within the separation cell whereas positive vertical skewness values are restricted to the shear layer 5 the highest reynolds stresses are located within the zone of flow separation and along the shear layer 6 high magnitude high frequency quadrant 2 events ejections are concentrated along the shear layer kelvin helmholtz instabilities and dominate the contribution to the local reynolds stress and 7 high magnitude high frequency quadrant 4 events occur bounding the separation zone near reattachment and close to the dune crest and are significant contributors to the local reynolds stress at each location these data demonstrate that the turbulence structure associated with dunes is controlled intrinsically by the formation magnitude and downstream extent of the flow separation zone and resultant shear layer furthermore the origin of dune related macroturbulence lies in the dynamics of the shear layer rather than classical turbulent boundary layer bursting the fluid dynamic distinction between dunes and ripples is reasoned to be linked to the velocity differential across the shear layer and hence the magnitude of the kelvin helmholtz instabilities which are both greater for dunes than ripples these instabilities control the local flow and turbulence structure and dictate the modes of sediment entrainment and their transport rates

breakdown of feldspar volume gain and lateral mass transfer during mylonitization of granitoid in a low metamorphic grade shear zone abstract in a low metamorphic grade shear zone from quadrilatero ferrifero southeastern brazil granitoid rocks have been transformed into phyllonites and mylonites via activation of crystal plastic processes in quartz and fluid assisted reaction softening in feldspars quartz deformed by basal a and prism a slip with concurrent subgrain rotation recrystallization breakdown of matrix plagioclase an 22 35 via mica producing softening reactions required cationic exchanges between ca na and k forming replacement perthites in the k feldspar megacrysts which occupy around 60 of the original rock volume subsequent breakdown of the perthitic plagioclase an 12 15 led to disruption of the megacrysts enabling strain accommodation that localized the mylonite and phyllonite zones domainal volume and mass balance calculations based on major and minor elements indicate only small positive changes in mass and volume around 15 in the whole system however accentuated differences ranging from mass and volume losses of 25 and 35 at the margins to gains of 85 and 95 in the centre respectively exist between the individual longitudinal subzones occupied by the different tectonite types this scenario indicates that deformation proceeded as a nearly isochemical process although with lateral mobility of major elements principally si al and k within the shear zone these results are different from those previously reported for other granitic mylonites most of them indicating volume losses in compressional tectonic settings it is suggested that the extensional tectonic framework attributed to the moeda bonfim shear zone where mass volume losses are in principle not required enhanced the access of fluid and consequent transport of components into the shear zone principally fe si and k producing the small gains of mass and volume observed

the influence of grain boundary fluids on the microstructure of quartz feldspar mylonites quartz rich domains in pre alpine water deficient amphibolite facies 510 580 c 250 450 mpa pegmatite mylonites from mont mary mm western alps preserve a fine dynamically recrystallized grain size without significant annealing despite the high synkinematic temperatures and subsequent static greenschist facies alpine overprint the microstructure is dramatically different from more typical water rich amphibolite facies mylonites such as from the simplon fault zone in the central alps where the recrystallized grain size is on the millimetre scale the difference reflects the dominant strain induced recrystallization mechanism 1 progressive subgrain rotation and grain boundary bulging for the dry mm examples and 2 fast grain boundary migration for the wet simplon examples the grain boundary microstructure imaged with sem is also very different with most grain boundaries in the dry mm samples lacking porosity whereas grain boundaries in the wet samples are decorated by a multitude of pores quartz grain boundaries from both wet and dry samples are locally coated by thin 100 s of nanometres possibly amorphous silica films despite the differences in microstructure the crystallographic preferred orientations cpos of quartz rich domains from both areas are very similar water deficient conditions hinder grain boundary mobility and thereby modify the dominant recrystallization mechanism s but apparently have little influence on the intracrystalline slip systems as reflected in the cpos strong c axis y maxima in mm mylonites both k feldspar and plagioclase an33 38 dynamically recrystallize consistent with the inferred metamorphic conditions under water deficient conditions mid to lower crustal rocks can deform heterogeneously under transitional ductile brittle conditions at high differential stress for mm ca 300 500 mpa as estimated for dry mohr coulomb failure and preserve this high stress microstructure because of the low mobility of dry grain boundaries

deformation of granitoids at low metamorphic grade ii granular flow in albite rich mylonites abstract the high strain deformation at low metamorphic grades of three investigated granitoids is dominated by the granular flow of albite rich polyphase aggregates these aggregates formed by retrograde breakdown reactions from intermediate plagioclase and k feldspar the predominant deformation mechanism changes in granitoids as the grain size is reduced coarse grained low strain examples are deformed by a combination of intracrystalline plasticity quartz and fracturing feldspar in the mylonites intracrystalline plasticity of quartz plays only a minor role and the dominant deformation mechanism is a non cataclastic granular flow of polyphase aggregates consisting largely of albite and quartz deformation appears to be stable probably because grain growth in albite quartz mixtures is inhibited these fine grained aggregates are mechanically weaker than pure quartz aggregates thus the change in deformation mechanism mainly due to feldspar breakdown reactions appears to be important for the localization of high shear strain deformation at low metamorphic grades in granitoids and other lithologies modally dominated by feldspar the rheological behaviour of albite dominated mineral aggregates may have two consequences for middle to upper crustal deformation of modally feldspar dominated lithologies 1 feldspar in the presence of aqueous fluids can be an important mineral controlling the rheology at low metamorphic grades that is below amphibolite facies p t conditions 2 the occurrence of granular flow of fine grained polyphase aggregates in low grade granitoids is probably common and calls for great care in the modelling of middle to upper crustal rheology based on flow laws for intracrystalline plasticity of single minerals such as quartz

weakening and strain localization produced by syn deformational reaction of plagioclase there are many observations in naturally deformed rocks on the effects of mineral reactions on deformation but few experimental data in order to study the effects of chemical disequilibrium on deformation we have investigated the hydration reaction plagioclase h2o more albitic plagioclase zoisite kyanite quartz we utilized fine grained 2 6 m plagioclase aggregates of two compositions an54 and an60 both dried and with 0 1 0 4 wt h2o present in shear deformation experiments at two sets of conditions 900 c 1 0 gpa in the plagioclase stability field and 750 c 1 5 gpa in the zoisite stability field dry samples and those deformed in the plagioclase stability field underwent homogeneous shearing by dislocation creep but samples with 0 1 to 0 4 wt water deformed in the zoisite stability field showed extreme strain localization into very narrow 1 3 m shear bands after low shear strain in these samples the microstructures of reaction products in the matrix differ from those in the shear bands in the matrix large up to 400 m zoisite crystals grew in the direction of finite extension and relict plagioclase grains are surrounded by rims of recrystallized grains that are more albitic in the shear bands the reaction products albitic plagioclase zoisite white mica and traces of kyanite form polyphase aggregates of very fine grained 0 1 m dislocation free grains most of the sample strain after 2 has occurred within the shear bands within which the dominant deformation mechanism is inferred to be diffusion accommodated grain boundary sliding dagbs the switch from dislocation creep in dry samples deformed without reaction to dagbs in reacted samples is associated with a decrease in flow stress from 800 to 200 mpa these experiments demonstrate that heterogeneous nucleation driven in part by chemical disequilibrium can produce an extremely fine grained polyphase assemblage leading to a switch in deformation mechanism and significant weakening thus localization of deformation in polyphase rocks may occur on any pressure p temperature t path where the equilibrium composition of the constituent minerals changes

improved flow velocity estimates from moving boat adcp measurements acoustic doppler current profilers adcps are the current standard for flow measurements in large scale open water systems existing techniques to process vessel mounted adcp data assume homogeneous or linearly changing flow between the acoustic beams this assumption is likely to fail but is nevertheless widely applied we introduce a new methodology that abandons the standard assumption of uniform flow in the area between the beams and evaluate the drawbacks of the standard approach the proposed method strongly reduces the extent over which homogeneity is assumed the method is applied to two field sites a mildly curved bend near a junction featuring a typical bend flow and a sharply curved bend that features a more complex sheared flow in both cases differences are found between the proposed method and the conventional method the proposed technique yields different results for secondary flow patterns compared with the conventional method the velocity components estimated with the conventional method can differ over 0 2 m s in regions of strong shear we investigate the number of repeat transects necessary to isolate the mean flow velocity vector from the raw adcp signal discarding the influences of noise positioning and projection errors and turbulence results show that several repeat transects are necessary the minimum number of repeat measurements needed for robust mean velocity estimates is reduced when applying the proposed method

comparison of fixed and moving vessel flow measurements with an adp in a large river a comparison of three dimensional flow velocity measurements made with an acoustic doppler profiler adp from fixed and moving vessels at cross sections of the parana river argentina was performed the purpose was to design a rapid and reliable procedure for quantifying the velocity field and related parameters such as bed shear velocity and the identification of secondary circulations in large rivers using an adp the fixed vessel measurements were performed over a period of 10 min at three vertical profiles along two of the sections these data were then compared with the results of ten moving vessel repeat transects made at each of the sections and which intersected the fixed vessel sampling locations using a number of different adp setup configurations from the velocity profiles obtained with both fixed and moving vessel measurements total bed shear velocity values were computed by applying the law of the wall the results indicate there can be significant differences between velocities obtained using the moving vessel method and fixed vessel measurements averaged over 10 min these differences in horizontal velocity can be significantly reduced by averaging five or more moving vessel transects with corresponding shear velocities calculated from five transect averages showing differences ranging between 10 and 15 dependent on the adp configuration location of the at a point vertical velocity profile in relation to large scale bed roughness may also be an influential factor and ideally the bed morphology should be quantified together with the adp derived velocities when using the adp to identify secondary flow cells it was found that although one cross section transect can provide a reasonable overall picture an average of five cross sections is necessary to resolve the finer details of flow the implications for applications that use moving vessel techniques for measurement and analysis of three dimensional flow structures including secondary flows are highlighted

flow field and morphology mapping using adcp and multibeam techniques survey in the po river an 8 km long and 250 m wide reach of the po river italy was surveyed with two vessels aiming to investigate the channel morphology and flow field characterizing this major italian river and to provide data for the calibration of a numerical model the first vessel was equipped with a multibeam ecosounder mbes whereas an acoustic doppler current profiler adcp was located on the second one fixed vessel adcp measurements were used to preliminarily investigate the turbulence variability affecting the reliability of moving vessel measurements to evaluate the friction velocity by using moving vessel measurements the vertical variance of velocity profiles as an alternative to logarithmic fitting of adcp profiles was estimated an average of 30 m cells of depth averaged velocity friction velocity and surface bottom velocity angle are presented in maps as the most relevant flow field features the flow field and channel morphology at bed form or channel scales showed noticeable correlations 0 9 in

estimating bedload transport in a large sand gravel bed river from direct sampling dune tracking and empirical formulas three methods used to estimate river bedload discharges were compared in a large sand gravel bed river the unit and total bedload transport rates estimated by sediment sampling dune tracking method and the equations of van rijn and meyer peter and muller were compared the analysis was based on a large data set obtained from field surveys that combined sediment sampling acoustic doppler profiler adp measurements and multibeam echosoundings of the middle reach of the river loire france for contrasting flow conditions ranging from low flows to 2 year floods for transport stages between 2 and 6 i e between the annual mean discharge and the discharge for a 2 year flood the tested equations predicted fairly well the unit and total bedload discharges and roughly estimated the temporal variability of the bedload during floods for these transport conditions the best agreement with the sediment sampling measurements was observed with the van rijn formula for lower flow conditions the tested formulas provide lower estimates than those sampled to improve the accuracy of the equations for low flows potential solutions include integrating near bed turbulences and non uniformity of bed particles into the models the ability of the formulas to predict the temporal variability of the bedload can be improved by using the bedform roughness to adjust the estimates the bedload transport rates calculated with dune tracking method are lower than the fluxes sampled because a substantial fraction of the bedload does not participate to the dune migration finally a first rating curve that was implemented for the river loire estimates the annual bedload discharge for 2010 to be 480 000 t

evolution of quartz microstructure and c axis crystallographic preferred orientation within ductilely deformed granitoids arolla unit western alps abstract we have studied quartz microstructures and the c axis crystallographic preferred orientations cpos in four granitoid samples representative of increasing ductile shear deformation from a weakly deformed granitoid stage 1 to a mylonitic granitoid stage 4 the quartz c axis cpo measured in the mylonitic granitoid has been compared with the one observed in a fully recrystallized quartz mylonite from the same area all the samples belong to the austroalpine arolla unit western alps and were deformed at greenschist facies conditions the quartz c axis cpo was analyzed using a u stage and the optical orientation imaging technique the magmatic plagioclase forming more than 50 of the volume of the granitoid is extensively replaced by a mica rich aggregate even in weakly deformed samples of stage 1 these aggregates flow to form an interconnected weak matrix with increasing deformation wrapping relatively less strained quartz grains that undergo dominantly coaxial strain recrystallization of quartz ranges from less than 1 in the weakly deformed granitoid to up to 85 in the mylonitic granitoid with average grain strain of 41 and 64 respectively with increasing strain and recrystallization quartz grains in the granitoids show a sequence of transient microstructures and cpos crystal plastic deformation is initially accomplished by dislocation glide with limited recovery and at 50 grain strain it results in a cpo consistent with dominantly basal a slip at 60 grain strain recrystallization is preferentially localized along shear bands which appear to develop along former intragranular cracks and the recrystallized grains develop a strong c axis cpo with maxima orthogonal to the shear band boundaries and independent of the host grain orientation within the granitoid mylonite at an average quartz grain strain of 64 recrystallization is extensive and the c axis cpo of new grains displays maxima overlapping the host c axis orientation and therefore unrelated to the bulk sense of shear the host controlled cpo is inferred to reflect pervasive recrystallization by progressive subgrain rotation the switch from shear band control to host control on c axis cpo occurred between 40 and 70 of recrystallization in the quartz mylonite the quartz c axis cpo develops an asymmetric single girdle consistent with the bulk sense of shear and the synkinematic greenschist facies conditions this study indicates that the cpo evolution of quartz may significantly differ in cases of polymineralic vs monomineralic rocks under the same deformation conditions if quartz in the polymineralic rock behaves as a strong phase

finite element modelling of shear zone development in viscoelastic materials and its implications for localisation of partial melting the development of shear zones initiating on random weaker initial perturbations is modelled numerically for low deborah number viscoelastic materials considering the influence of effective viscosity contrast power law rheology strain softening and different imposed bulk deformation geometries ranging from pure to simple shear conjugate shear zones initiate at 90 to one another and rotate with increasing bulk deformation the basic pattern not being markedly influenced by the vorticity of imposed deformation the rate of propagation of individual conjugate shear zones is little affected by increased effective viscosity contrast between matrix and inclusion but is promoted by power law rheology however the most marked effect is observed for strain softening behaviour where rapid propagation produces straighter and narrower shear zones the localisation of strain is reflected in a correspondingly heterogeneous stress distribution in particular mean stress or pressure is higher in the extending near planar weaker zones of localised shear melting of gneissic or pelitic compositions is pressure dependent with free water present increased pressure promotes melting whereas the opposite is true for water absent melting for water present conditions a positive feedback could develop between localised shearing increased pressure and partial melting this is potentially more effective in concentrating melt in shear zones than shear heating where melt related softening has a negative feedback effect

the petrological significance of misorientations between grains misorientation analysis quantifies microstructural features in tectonites metamorphic and igneous rocks and allows hypotheses on their formation to be tested the misorientation between two lattices can be expressed by a rotation axis and rotation angle for lattices with symmetry it is conventional to take the minimum angle that enables one lattice to be rotated into the other for a group of lattice measurements two types of misorientation distribution can be calculated selecting random pairs of grains gives the random pair misorientation distribution selecting neighbouring pairs gives the neighbour pair misorientation distribution the forms of both distributions are visualised using histograms or cumulative frequency diagrams they are strongly influenced by any overall crystallographic preferred orientation and by intrinsic crystal symmetry in many rocks the random pair misorientation distribution and neighbour pair misorientation distribution are statistically significantly different quantified using the kolmogorov smirnov test differences between the random pair misorientation distribution and neighbour pair misorientation distribution imply that adjacent grains have physically interacted or are inherited from a precursor microstructure interactions include 1 reduction in surface energy by lattice alignment we show this may have occurred in garnet clusters in schist and olivine in a cumulate it is well known in metals and may be a common geological process 2 nucleation where those nuclei have influenced the orientation of adjacent nuclei 3 mechanical rotations of facetted grains in compacting crystal mushes so that faces become parallel 4 growth twinning inheritance includes 1 subgrain rotation recrystallisation in tectonites deforming by crystal plastic processes 2 mechanical and transformation related twinning 3 domainal microstructures e g where grains have formed from a few large original grains may give rise to spurious correlations when the orientation data cover more than one domain with this proviso misorientation analysis can be used to investigate many important microstructural processes

ann based inversion of dc resistivity data for groundwater exploration in hard rock terrain of western maharashtra india summary inversion of vertical electrical sounding ves data especially from the crystalline hard rock area assumes a special significance for groundwater exploration here we used a newly developed algorithm based on the bayesian neural network bnn theory combined with hybrid monte carlo hmc markov chain monte carlo mcmc simulation scheme to invert the direct current dc ves measurements obtained from 30 locations around tenduli vengurla sindhudurg district maharashtra india the inversion results suggest that the top layer is mostly comprised of laterites followed by mixture of clay clayey sand and garnulites granite as basement rocks the source of groundwater appears to be accessible in weathered semi weathered layer of laterite clayey sand that exists within the depth of 10 15 m from the surface the nw se trending major lineaments and its criss crosses are also identified from the apparent and true resistivity surface map the pseudo section at different depths in the western part of the area near nivti shows extensive influence of saltwater intrusion and its impact reaching up to the depth of 30 m from the surface along the coastal area our results also show that intrusion of saline water decreases from the western part to the eastern part of the region two dimensional modeling of four resistivity profiles from the study region identified two potential groundwater reservoirs one lying between path tenduli and another in between mat and zaraph the deduced true electrical resistivity section against depth correlates well with available borehole lithology in the area the results presented here would be useful for interpreting the geological signatures like fractures major joints and lineaments which in turn will be helpful for identifying groundwater reservoirs and drainage pattern in the crystalline hard rock area the newly developed hmc based bnn method is robust and would provide insights for constraining the geophysical models and criteria for modeling resistivity data

the role of dynamic recrystallization in the development of lattice preferred orientations in experimentally deformed quartz aggregates abstract experiments on coaxially deformed quartz aggregates show that when dynamic recrystallization involves grain size reduction the lattice preferred orientation lpo of the recrystallized grains depends on the recrystallization mechanism at low temperatures and fast strain rates strain induced grain boundary migration recrystallization favors growth of grains oriented poorly for slip on the basal and prism planes resulting in an lpo of c axes parallel to the 1 direction at higher temperatures or slower strain rates progressive subgrain rotation produces recrystallized grains which inherit the small circle girdle lpo of their deformed host grains and which continue to re orient by slip at even higher temperatures and slower strain rates progressive subgrain rotation is accompanied by rapid grain boundary migration which does not favor grains of any particular orientation thus the lpo is again similar to that of non recrystallized grains in contrast when dynamic recrystallization involves grain growth driven by surface energy reduction a strong lpo of c axes parallel to 1 develops during grain growth but then evolves with increasing strain toward a small circle girdle the correlation of lpos with recrystallization mechanisms has important implications for the assumption of homogeneous strain in theoretical models of lpos and for interpreting natural lpos in recrystallized rocks

dynamics of nonmigrating mid channel bar and superimposed dunes in a sandy gravelly river loire river france abstract a field study was carried out to investigate the dynamics during floods of a nonmigrating mid channel bar of the loire river france forced by a riffle and renewed by fluvial management works interactions between the bar and superimposed dunes developed from an initial flat bed were analyzed during floods using frequent mono and multibeam echosoundings acoustic doppler profiler measurements and sediment grain size analysis when water left the bar terrestrial laser scanning and sediment sampling documented the effect of post flood sediment reworking during floods a significant bar front elongation spreading on margins and swelling was shown whereas a stable area no significant changes was present close to the riffle during low flows and falling limbs of floods intense sediment reworking on the top of the bar and lateral scouring occurred hydrological variations controlled the sediment supply in terms of phasing quantity and grain size delivered by surrounding channels during floods and thus superimposed dune development their development was also linked to the sediment availability armor layers riffle proximity their relatively constant height highlights a preferential adaptation on dune length during floods the role of each morphological forcing parameters riffle vs channel widening and curvature on the bar dynamics and evolution is stage dependent the shape dynamics and long term morphological evolution of the bar and of the river reach surrounding islands channel translation mainly depends on the presence of the natural riffle

evaluation of adcp apparent bed load velocity in a large sand bed river moving versus stationary boat conditions detailed mapping of bathymetry and apparent bed load velocity using a boat mounted acoustic doppler current profiler adcp was carried out along a 388 m section of the lower missouri river near columbia missouri sampling transects moving boat were completed at 5 and 20 m spacing along the study section stationary fixed boat measurements were made by maintaining constant boat position over a target point where the position of the boat did not deviate more than 3 m in any direction for each transect and stationary measurement apparent bed load velocity vb was estimated using adcp bottom tracking data and high precision real time kinematic rtk global positioning system gps the principal objectives of this research are to 1 determine whether boat motion introduces a bias in apparent bed load velocity measurements and 2 evaluate the reliability of adcp bed velocity measurements for a range of sediment transport environments results indicate that both high transport v b 0 6 m s and mo

time averaged flow structure in the central region of a stream confluence previous process oriented field studies of stream confluences have focused mainly on fluvial dynamics at or immediately downstream of the location where the confluent flows enter the downstream channel this study examines in detail the spatial evolution of the time averaged downstream velocity cross stream velocity and temperature fields between the junction apex where the flows initially meet and the entrance to the downstream channel a well defined vertically oriented mixing interface exists within this portion of the confluence suggesting that lateral mixing of the incoming flows is limited the downstream velocity field near the junction apex is characterized by two high velocity cores separated by an intervening region of low velocity or recirculating fluid in the downstream direction the high velocity cores move inwards towards the mixing interface and high velocity fluid progressively extends downwards into a zone of scour resulting in an increase in flow velocity in the centre of the confluence the cross stream velocity field is dominated by flow convergence but also includes a component associated with a consistent pattern of secondary circulation this pattern is characterized by two surface convergent helical cells one on each side of the mixing interface the helical cells appear to be the mechanism by which high momentum fluid near the surface is advected downwards into the zone of scour for transport ineffective flows the dimensions and intensities of the cells are controlled by the momentum ratio of the confluent streams and by the extant bed morphology within the confluence although the flow structure of formative events was not measured directly in this study documented patterns of erosion and deposition within the central region of the confluence suggest that these events are dynamically similar to the measured flows except for the fact that formative flows are not constrained by but can reshape the bed morphology the results of this investigation are consistent with and augment previous findings on time averaged flow structure in the downstream portion of the confluence 1998 john wiley sons ltd

simulating coseismic deformation of quartz in the middle crust and fabric evolution during postseismic stress relaxation an experimental study abstract non steady state deformation and annealing experiments on vein quartz are designed to simulate earthquake driven episodic deformation in the middle crust three types of experiments were carried out using a modified griggs type solid medium deformation apparatus all three start with high stress deformation at a temperature of 400 c and a constant strain rate of 10 4 s 1 type a some are followed by annealing in the stability field of quartz for 14 15 h at zero nominal differential stress and temperatures of 800 1000 c type a b or by annealing for 15 h at 900 c and at a residual stress type a c the quartz samples reveal a very high strength 2 gpa at a few percent of permanent strain the microstructures after short term high stress deformation type a record localized brittle and plastic deformation statisc annealing type a b results in recrystallisation restricted to the highly damaged zones the new grains aligned in strings and without crystallographic preferred orientation indicate nucleation and growth annealing at non hydrostatic conditions type a c results in shear zones that also develop from deformation bands or cracks that formed during the preceding high stress deformation in this case however the recrystallised zone is several grain diameters wide the grains are elongate and a marked crystallographic preferred orientation indicates flow by dislocation creep with dynamic recrystallisation quartz microstructures identical to those produced in type a b experiments are observed in cores recovered from long valley exploratory well in the quaternary long valley caldera california with considerable seismic activity the experiments demonstrate the behaviour of quartz at coseismic loading type a and subsequent static annealing type a b or creep at decaying stress type a c in the middle crust the experimentally produced microfabrics allow to identify similar processes and conditions in exhumed rocks

crystallographic orientation of microcracks in quartz and inferred deformation processes a study on gneisses from the german continental deep drilling project ktb abstract this study was carried out on four gneiss samples from the german continental deep drilling project ktb taken at depths between 556 and 8633 m the crystallographic orientation of microcracks in quartz was determined by a combination of the electron channelling pattern method ecp and u stage microscopy the distinct preferred crystallographic orientations of various crack generations point to different processes of crack initiation and propagation which partly seem to be depth dependent for older healed cracks a crystalplastic initiation due to dislocation pile up and related lattice distortion is indicated by cracking normal to prominent slip directions which are a at lower or c at comparatively higher temperatures in contrast younger open cracks preferentially formed on crystallographic planes with low surface energy rhombs and prisms which is interpreted in terms of pure elastic crack mechanisms because of the thermoelastic anisotropy of quartz internal stresses resulting from thermal contraction during cooling may be the main driving force for the initiation or further propagation of cracks parallel to the c axis crack propagation preferentially affects grains with crystal lattices and operating crack mechanisms being in a direction appropriate to the applied external tectonic stresses this selective cracking explains why cracks also show constant orientations with respect to geographic directions up to regional dimensions

inversion of nuclear well logging data using neural networks this work looks at the application of neural networks in geophysical well logging problems and specifically their utilization for inversion of nuclear downhole data simulated neutron and ray fluxes at a given detector location within a neutron logging tool were inverted to obtain formation properties such as porosity salinity and oil water saturation to achieve this the forward particle radiation transport problem was first solved for different energy groups 47 neutron groups and 20 ray groups using the multigroup code event a neural network for each of the neutron and ray energy groups was trained to re produce the detector fluxes using the forward modelling results from 504 scenarios the networks were subsequently tested on unseen data sets and the unseen input parameters formation properties were then predicted using a global search procedure the results obtained are very encouraging with formation properties being predicted to within 10 average relative error the examples presented show that neural networks can be applied successfully to nuclear well logging problems this enables the implementation of a fast inversion procedure yielding quick and reliable values for unknown subsurface properties such as porosity salinity and oil saturation

pattern recognition of geophysical data abstract a new rock classification method for ground penetrating radar gpr data is presented for cases where no additional geological information is available from boreholes there are non linear relationships between petrophysical properties of rocks and electromagnetic waves which can be handled using two methods derived from statistical learning theory on pattern recognition an investigation was carried out looking at proving the feasibility of the method in principle for use on synthetic models as well as measurement data the different learning methods were also compared the method is based on multivariate statistical learning algorithms for the discrimination of layer boundaries between different rocks the discrimination developed works with artificial neural networks ann and support vector machines svm the processing procedure starts with geological models with varying petrophysical rock parameters which are to be sought in the measurement data the models are used to generate synthetic radargrams from which rock properties can be derived using wave attributes the calculated values of the wave attributes are stored in a multivariate data pool this data pool is used to train the ann and the svm the same wave attributes are derived from the gpr data and also saved in a data pool this generates two data sets for pattern recognition with which to directly classify rock layers wave attributes can therefore be used to derive the non linear correlative relationships between rock properties and gpr data by the weighted matrices of ann and svm the presented method can be used to match reflections in the grr data directly with the layer boundaries of rock formations the classification of a boundary horizon between rock salt and anhydrite is demonstrated on synthetic gpr traces and measurement data from a rock salt mine the advantage of this method is that rock classification is not a priori dependent on borehole data

thermomechanical evolution of a ductile duplex the thermomechanical evolution of a midcrustal ductile duplex in central australia has been reconstructed through space and time using 40ar 39ar thermochronology flow stress estimates cross sectional restoration of dislocation creep microstructures and microstructural and structural analysis a critical aspect of this analysis is the identification of populations of white micas in quartzite mylonites that have neocrystallized below their closure temperature and which record the time when ductile deformation ceased in dating these micas the mylonitic microstructures have effectively been dated the time temperature history of the duplex has been constrained through multidomain thermal modeling of k feldspar 40ar 39ar data the modeling demonstrates that a temperature gradient existed across the duplex during its formation the concept of microstructural continuity during ductile deformation has great potential for elucidating the kinematic evolution of ductile duplexes mapping of the deformation mechanisms and recrystallized grain sizes of quartzites deformed under greenschist facies conditions has been used to evaluate tectonic offsets that occurred after microstructural freezing this analysis shows that the duplex formed as a forward propagating thrust system accommodating 60 km of convergence between the upper and lower plates of the megathrust with a significant fraction of the displacement occurring after microstructural freezing finally using the data as input to published flow laws for quartz aggregates provides a strain rate history for the duplex although uncertainties are clearly large the timing of highest estimated strain rates during duplex evolution does indeed correlate with the highest rates of convergence between the upper and lower plates of the megathrust system according to regional cooling history studies and with coeval sedimentation in adjoining molasse basins

evolution of c axis pole figures and grain size during dynamic recrystallization results from experimentally sheared quartzite 1 quartzite samples experimentally sheared at conditions where subgrain rotation and grain boundary migration recrystallization are active show a striking change in the c axis crystallographic preferred orientation cpo with increasing shear strain up to 8 and degree of recrystallization up to 100 we used optical methods to determine the c axis cpo for the bulk samples and for porphyroclasts and recrystallized grains separately and to track the strengths of the cpos in five different orientation domains with increasing the c axis pole figure evolves from a broad peripheral maximum indicative of basal a slip to an inclined single girdle with two maxima indicative of rhomb a slip and finally an elongate single maximum at the girdle center indicative of prism a slip throughout this sequence the fabric skeleton rotates with the sense of shear the bulk preferred c axis orientation results from growth and shrinkage of differently oriented crystallographic domains grain boundary density analysis indicates that the size of prism a recrystallized grains is 1 5 times that of average and 2 times that of rhomb grains indicating that prism a slip is significantly easier at our experimental conditions this inference is supported by autocorrelation function analysis of the various orientation domains and how they evolve with strain similar progressive changes in c axis cpo are observed in quartzites naturally sheared at conditions where grain boundary migration recrystallization operates these results indicate that achievement of microstructural and mechanical steady state requires high strain and complete recrystallization

weakening of deforming granitic rocks with layer development at middle crust abstract in the middle crust deformation of granitic rocks is characterized by crystal plastic deformation of quartz and cataclasis of feldspar for common granitic rocks with textures of framework feldspar and interstice filling quartz brittle strength of feldspar is a close approximation of the bulk rock strength because feldspar forms the load bearing framework with deformation these rocks tend to develop localized high strain zones the high strain zones commonly consist of quartz rich layers and feldspar rich layers we have examined how the strength of granitic rocks changes with the volume fraction of these layers by combining the flow laws developed by handy et al handy m r wissing s b streit l e 1999 frictional viscous flow in mylonite with varied bimineralic composition and its effect on lithospheric strength tectonophysics 303 175 191 our results suggest a dramatic weakening of the bulk rock strength at an early stage of the layer development we also found that formation of muscovite in the layer structures by breakdown of feldspar can result in further weakening in the layer structure the bulk rock strength with mica bearing layers is reduced by a significant amount compared with the mica absent layers our analysis suggests that layer development with syntectonic formation of mica can be a major source of weakening for granitic rocks

the partitioning of deformation in flowing rock masses abstract most geological structures owe their development to heterogeneous and or non steady flow flow partitioning refers to the division of the instantaneous velocity field into components related to translation strain and rotation flow partitioning during the development of a geological structure usually changes with time and different histories of flow are involved at different points in the developing structure heterogeneity leads to the development of flow domains with different characteristics notably the degree of non coaxiality of deformation and different partitionings of the rotational component of flow into shear induced vorticity and spin during non steady flow there is often continual repartitioning of vorticity between the spin and shear induced components spin is an important aspect of flow leading to the development of structure this paper discusses the partitioning of deformation in a flowing rock mass coaxial flow tends to occur in isotropic materials in regions near weakly constrained boundaries non coaxial flow is favoured by suitably oriented material anisotropy and or the presence of well defined boundary constraints involving parallel relative displacements a developing anisotropy e g a crystallographic fabric in a shear zone can induce a change from coaxial to non coaxial flow other effects are related to the scale of approximation for example bulk shear induced vorticity can be locally converted to spin flow in the crust and mantle of the earth produces geological structures on all scales and involves many different types of rheological response the factors that affect flow partitioning e g spin versus non coaxial deformation are therefore of interest

3 d flow and scour near a submerged wing dike adcp measurements on the missouri river 1 detailed mapping of bathymetry and three dimensional water velocities using a boat mounted single beam sonar and acoustic doppler current profiler adcp was carried out in the vicinity of two submerged wing dikes located in the lower missouri river near columbia missouri during high spring flows the wing dikes become submerged creating a unique combination of vertical flow separation and overtopping plunging flow conditions causing large scale three dimensional turbulent flow structures to form on three different days and for a range of discharges sampling transects at 5 and 20 m spacing were completed covering the area adjacent to and upstream and downstream from two different wing dikes the objectives of this research are to evaluate whether an adcp can identify and measure large scale flow features such as recirculating flow and vortex shedding that develop in the vicinity of a submerged wing dike and whether or not moving boat single transect data are sufficient for resolving complex three dimensional flow fields results indicate that spatial averaging from multiple nearby single transects may be more representative of an inherently complex temporally and spatially variable three dimensional flow field than repeated single transects results also indicate a correspondence between the location of calculated vortex cores resolved from the interpolated three dimensional flow field and the nearby scour holes providing new insight into the connections between vertically oriented coherent structures and local scour with the unique perspective of flow and morphology in a large river

comparing fixed vessel and moving vessel adcp measurements in a large laboratory flume abstractthe error of the spatiotemporally averaged sta velocities of moving vessel mv acoustic doppler current profiler adcp measurements was estimated by comparison with time averaged fixed

measuring velocity and shear stress over dunes with acoustic doppler profiler this study evaluates the use of an acoustic doppler profiler adp for measurement of velocity profiles over dunes in an estuary the adp can be deployed from a moving launch and provides three dimensional velocity profiles that can be used to describe flow structure and to provide rough estimates of shear stress quadratic stress models are recommended for shear stress because they estimate skin friction and form stress whereas the law of the wall only reliably estimates total stress over dunes the most serious limitation of the adp is a beam geometry that results in a large sampling diameter close to the bed that does not adequately measure velocity in dune troughs

flow structure and channel morphodynamics of meander bend chute cutoffs a case study of the wabash river usa received 25 october 2012 revised 23 september 2013 accepted 25 september 2013 published 12 december 2013 1 this paper documents the three dimensional structure of flow and bed morphology of two developing chute cutoffs on a single meander bend on the lower wabash river usa and relates the flow structure to patterns of morphologic change in the evolving cutoff channels the upstream end of the cutoff channels is characterized by 1 a zone of flow velocity reduction stagnation and bar development in the main channel across from the cutoff entrance 2 flow separation and bar development along the inner left bank of the cutoff channel immediately downstream from the cutoff entrance and 3 helical motion and outward advection of flow momentum entering the cutoff channel leading to erosion of the outer right bank of the cutoff channel at the downstream end of the cutoff channels the majorhydrodynamic and morphologic features are 1 flow stagnation along the bank of the main channel immediately upstream of the cutoff channel mouth 2 convergence of flows from the cutoff and main channels 3 helical motion of flow from the cutoff 4 a zone of reduced velocity along the bank of the main channel immediately downstream from the cutoff channel mouth and 5 development of a prominent bar complex that penetrates into the main channel and extends from the stagnation zone upstream to downstream of the cutoff mouth these results provide the basis for a conceptual model of chute cutoff dynamics in which the upstream and downstream ends of a cutoff channel are treated as a bifurcation and confluence respectively

ultrafine grained quartz mylonites from high grade shear zones evidence for strong dry middle to lower crust creep strength of the crust depends upon the rheology of the most common mineral usually quartz recrystallized quartz grains in many high grade shear zones from the middle to lower crust are typically large millimeter sized implying active grain boundary migration but equivalents from old polymetamorphic and water deficient basement sheared at similar crustal depths can be very small for the latter strong crystallographic preferred orientation cpo of quartz with c axes aligned close to y progressive misorientation of crystals subgrain and dislocation development and core mantle structures with recrystallized grains of 2 8 m size all point to dislocation glide dominantly on the prism a system with recrystallization by subgrain rotation recrystallized grain size piezometry of such quartz indicates high flow stress in fine grained shear zones while the synkinematic metamorphic mineral assemblage and the cpo are typical of amphibolite facies conditions this is evidence that middle to lower crust is not inevitably weak due to its high temperature water content also has an important influence

neural network modelling and classification of lithofacies using well log data a case study from ktb borehole site summary a novel approach based on the concept of super self adapting back propagation ssabp neural network has been developed for classifying lithofacies boundaries from well log data the ssabp learning paradigm has been applied to constrain the lithofacies boundaries by parameterzing three sets of well log data that is density neutron porosity and gamma ray obtained from the german continental deep drilling project ktb a multilayer perceptron mlp neural networks model was generated in a supervised feed forward mode for training the published core sample data a total of 351 pairs of input and output examples were used for self adaptive network learning and weight and bias values were appropriately updated during each epoch according to the gradient descent momentum scheme the actual data analysis suggests that the ssabp network is able to emulate the pattern of all three sets of ktb data and identify lithofacies boundaries correctly the comparisons of the maximum likelihood geological sections with the available geological information and the existing geophysical findings over the ktb area suggest that in addition to the known main lithofacies boundaries units namely paragneisses metabasites and heterogeneous series containing partly calc silicate bearing paragneisses metabasites and alternations of former volcano sedimentary sequences the ssabp neural network technique resolves more detailed finer structures embedded in bigger units at certain depths over the ktb region which seems to be of some geological significance the efficacy of the method and stability of results was also tested in presence of different levels of coloured noise the test results suggest that the designed network topology is considerably unwavering for up to 20 per cent correlated noise however adding more noise 50 per cent or more degrades the results our analyses demonstrate that the ssabp based approach renders a robust means for the classification of complex lithofacies successions from the ktb borehole log data and thus may provide useful guide information for understanding the crustal inhomogeneity and structural discontinuity in many other regions

comparison of five least squares inversion techniques in resistivity sounding a brief history of the development of the inverse problem in resistivity sounding is presented with the development of the equations governing the least squares inverse five algorithms for finding the minimum of the least square problem are described and their speed of convergence is compared on data from two planar earth models of the five algorithms studied the ridge regression algorithm required the fewest numbers of forward problem evaluations to reach a desired minimum solution space statistics including 1 parameter standard errors 2 parameter correlation coefficients 3 model parameter eigenvectors and 4 data eigenvectors are discussed the type of weighting applied to the data affects these statistical parameters weighting the data by taking log 10 of the observed and calculated values is comparable to weighting by the inverse of a constant data error the most reliable parameter standard errors are obtained by weighting by the inverse of observed data errors all other solution statistics such as dataparameter eigenvector pairs have more physical significance when inverse data error weighting is used

sediment transport and bed morphology at river channel confluences river channel confluences form important morphological elements of every river system being points at which rapid changes in flow sediment discharge and hydraulic geometry must be accommodated this article presents results of a quantitative investigation of sediment transport at channel confluences accomplished through both scaled laboratory flume simulation and complementary monitoring of a natural channel confluence bed morphology at channel confluences is characterized by three distinct elements avalanche faces at the mouth of each confluent channel a deep central scour and a bar within the separation zone formed at the downstream junction corner these elements are controlled predominantly by the confluence angle and the ratio of discharges between the tributary and mainstream channels as confluence angle and discharge ratio increase the sediment contributions from the confluent channels are progressively segregated in their paths through the junction with sediment being transported around rather than through the centre of the confluence this segregation of sediment loads is accompanied by the retreat of the main channel avalanche face from the confluence an increase in the scour depth a change in the orientation of the scour and an increase in the size of the separation zone bar field measurements closely replicate the flume simulation a model of sediment transport and bed morphology links these features to the fluid dynamics of these sites an understanding of confluence dynamics is important not only in considerations of channel morphology and design criteria but must form the basis for the interpretation of confluence sediments in the ancient record

artificial neural networks for parameter estimation in geophysics artificial neural systems have been used in a variety of problems in the fields of science and engineering here we describe a study of the applicability of neural networks to solving some geophysical inverse problems in particular we study the problem of obtaining formation resistivities and layer thicknesses from vertical electrical sounding ves data and that of obtaining 1d velocity models from seismic waveform data we use a two layer feedforward neural network fnn that is trained to predict earth models from measured data part of the interest in using fnns for geophysical inversion is that they are adaptive systems that perform a non linear mapping between two sets of data from a given domain in both of our applications we train fnns using synthetic data as input to the networks and a layer parametrization of the models as the network output the earth models used for network training are drawn from an ensemble of random models within some prespecified parameter limits for network training we use the back propagation algorithm and a hybrid back propagation simulated annealing method for the ves and seismic inverse problems respectively other fundamental issues for obtaining accurate model parameter estimates using trained fnns are the size of the training data the network configuration the description of the data and the model parametrization our simulations indicate that fnns if adequately trained produce reasonably accurate earth models when observed data are input to the fnns

fabric domains in quartz mylonites localized three dimensional analysis of microstructure and texture fabric domains of a quartz vein deformed under greenschist facies conditions arc analysed with domainal x ray texture goniometry optical microscopy computer integrated polarization microscopy cip and shape analysis in two mutually perpendicular sections the analysed domains consist of large non recrystallized deformed clast fragments prolate non recrystallized ribbon grains and prolate recrystallized domains in terms of texture monomaximal and polymaximal domains have been distinguished pronounced partitioning of deformation is observed between these domains this strain partitioning asks for caution when making kinematic inferences for fault zones based on a study of domainal fabrics domains persist as fabric elements up to high strains this emphasizes the often neglected role of a non random initial fabric neighbouring domains with alternating c axis orientations and grain boundary preferred orientations indicating opposing senses of shear occur in both sections the bulk texture is controlled by clast and ribbon domains rather than being strictly deformation induced we infer that prolate elongation of clasts and ribbons is achieved mainly by combined prism and basal slip recrystallized domains are characterized by different textures they are deformed by intracrystalline slip combined with grain boundary migration and sliding inclined preferred grain boundary orientations are continuously maintained by grain boundary migration copyright 0 1996 elsevier science ltd

dislocation creep regimes in quartz aggregates abstract using optical and tem microscopy we have determined that three regimes of dislocation creep occur in experimentally deformed quartz aggregates depending on the relative rates of grain boundary migration dislocation climb and dislocation production within each regime a distinctive microstructure is produced due primarily to the operation of different mechanisms of dynamic recrystallization at lower temperatures and faster strain rates the rate of dislocation production is too great for diffusion controlled dislocation climb to be an effective recovery mechanism in this regime recovery is accommodated by strain induced grain boundary migration recrystallization with an increase in temperature or decrease in strain rate the rate of dislocation climb becomes sufficiently rapid to accommodate recovery in this regime dynamic recrystallization occurs by progressive subgrain rotation with a further increase in temperature or decrease in strain rate dislocation climb remains sufficiently rapid to accommodate recovery however in this regime grain boundary migration is rapid thus recrystallization occurs by both grain boundary migration and progressive subgrain rotation the identification of the three regimes of dislocation creep may have important implications for the determination of flow law parameters and the calibration of recrystallized grain size piezometers in addition the identification of a particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural deformation has occurred

the influence of tributary flow density differences on the hydrodynamic behavior of a confluent meander bend and implications for flow mixing abstract the goal of this study is to evaluate the influence of tributary flow density differences on hydrodynamics and mixing at a confluent meander bend a detailed field characterization is performed using an acoustic doppler current profiler adcp for quantification of the 3d flow field flow discharge and bathymetry as well as ctd measurements conductivity temperature depth to characterize the patterns of mixing satellite images of the confluence taken at complementary times to the field surveys were analyzed to evaluate the confluence hydrodynamics at different flow conditions the results illustrate the differences in hydrodynamics and mixing length in relation to confluences with equal density tributaries at low density differences and higher discharge ratio qr between the two rivers the flow is similar to equi density confluent meander bends in contrast at high density differences low qr the tributary flow is confined to near the confluence but the density difference causes the flow to move across channel in this case the density difference causes the lateral spread of the tributary flow to be greater than at a greater qr when the density difference is less these results illustrate the potential importance of density differences between tributaries in determining the rate and spatial extent of mixing and sediment dispersal at confluent meander bends

inversion of dc resistivity data using neural networks the inversion of geoelectrical resistivity data is a difficult task due to its non linear nature in this work the neural network nn approach is studied to solve both 1d and 2d resistivity inverse problems the efficiency of a widespread supervised training network the back propagation technique and its applicability to the resistivity problem is investigated several nn paradigms have been tried on a basis of trial and error for two types of data set in the 1d problem the batch back propagation paradigm was efficient while another paradigm called resilient propagation was used in the 2d problem the network was trained with synthetic examples and tested on another set of synthetic data as well as on the field data the neural network gave a result highly correlated with that of conventional serial algorithms it proved to be a fast accurate and objective method for depth and resistivity estimation of both 1d and 2d dc resistivity data the main advantage of using nn for resistivity inversion is that once the network has been trained it can perform the inversion of any vertical electrical sounding data set very rapidly

new polygonal grains formed by dissolution redeposition in quartz mylonite abstract arrays of polygonal grains are common along original grain margins subgrain boundaries and intragranular fractures of deformed quartz porphyroclasts we investigated these internal polygonal grains within quartz porphyroclasts of a partially recrystallized quartz mylonite deformed in the presence of fluid in a greenschist facies shear zone from quadrilatero ferrifero southeastern brazil optical observation showed profuse fluid inclusions and muscovite flakes inside the deformed porphyroclasts observation by sem revealed the presence of crystal faces on the internal polygonal grains domainal c axis analysis showed that the internal polygonal grains have a preferred orientation similar to the host porphyroclasts c axes at low angles to the stretching lineation but different from the fabric of recrystallized matrix grains type 1 cross girdle based on these observations we suggest a mechanism of in situ solution reprecipitation where the new grains are nucleated in the intergranular fluid filled pores present along the internal discontinuities of the porphyroclasts the grains grow with their boundaries largely in contact with fluid allowing the development of crystal faces at least during the early growth stages after the new grain reaches the opposite pore wall further grain growth should occur through ordinary grain boundary migration mechanisms driven by the strain energy difference between the new grain and the host porphyroclast we conclude that in these rocks in situ solution reprecipitation operated in conjunction with crystal plastic processes accounting for the nucleation of new grains during deformation recrystallization in the presence of fluid under low grade metamorphic conditions

origin and incremental evolution of brittle ductile shear zones in granitic rocks natural examples from the southern abitibi belt canada abstract metre scale shear zones developed in the mooshla granitic pluton exhibit a plethora of internal mesoand microstructures revealing their mode of nucleation growth and termination the subvertical e w brittle ductile shear zones are developed in the most isotropic part of the intrusion and consist of phyllonites characterized by mylonitic fabrics and well developed down dip mineral lineations they are exposed on a single large and flat outcrop perpendicular to the mineral lineation these brittle ductile shear zones are in close spatial association with a fracture system along which they have nucleated and propagated joints fractures and brittle faults contain abundant evidence of ductilely deformed and recrystallized minerals suggesting that they underwent ductile shearing after their formation the deformation was accompanied by the influx of a metasomatic fluid which altered original fe mg bearing minerals and plagioclase into quartz epidote chlorite sericite and carbonate that precipitated in dilatant fractures and narrow breccia zones we recognize two different types of lateral terminations i shear zones that terminate into joints and fractures that are parallel or oblique to the shear direction and ii curved segments of shear zones that connected with neoformed splay fractures at high angle to the shear direction in the latter case sharp bending and severe perturbation of the shear zone orientation occur at the shear zone termination where ductile shearing is transfered into an adjacent shear zone via dilatational fractures this demonstrates that shear zones tended to grow towards each other and coalesce to form a well developed anastomosing network we propose that narrow dilatational fractures and joints acted as paleo weakness planes along which fluid rock interaction and resulting reaction softening occurred the deformation scenario involves episodic fluid drawn into dilatant sites responsible for cyclic fluid pressure fluctuation in the system dilatancy related fracturing and reaction softening lead to deformation under brittle to plastic conditions and to shear strain localization