numerical modeling of flow processes over gravelly surfaces using structured grids and a numerical porosity treatment this article describes the development and validation of a method for representing the complex surface topography of gravel bed rivers in high resolution three dimensional computational fluid dynamic models this is based on a regular structured grid and the application of a porosity modification to the mass conservation equation in which fully blocked cells are assigned a porosity of zero fully unblocked cells are assigned a porosity of one and partly blocked cells are assigned a porosity of between 0 and 1 according to the percentage of the cell volume that is blocked the model retains an equilibrium wall function and an rng type two equation turbulence model the model is combined with a 0 002 m resolution digital elevation model of a flume based water worked gravel bed surface acquired using two media digital photogrammetry and with surface elevations that are precise to 0 001 m the model is validated by comparison with velocity data measured using a three component acoustic doppler velocimeter adv model validation demonstrates a significantly improved level of agreement than in previous studies notably in relation to shear at the bed although the resolution of model predictions was significantly higher than the adv measurements making model assessment in the presence of strong shear especially difficult a series of simulations to assess model sensitivity to bed topographic and roughness representation were undertaken these demonstrated inherent limitations in the prediction of 3 d flow fields in gravel bed rivers without high resolution topographic representation they also showed that model predictions of downstream flux were more sensitive to topographic smoothing that to changes in the roughness parameterization reflecting the importance of both mass conservation i e blockage and momentum conservation effects at the grain and bed form scale model predictions allowed visualization of the structure of form flow interactions at high resolution in particular the most protruding bed particles exerted a critical control on the turbulent kinetic energy maxima typically observed at about 20 of the flow depth above the bed

a spectrum of potentially diamondiferous lamproites and minettes from the jharia coalfield eastern india abstract abundant cretaceous 110 ma lamprophyric sills in the gondwana coalfields show a comagmatic continuum from olivine lamproites to lamproites and minettes four sills in the jharia coalfield have exotic mineralogy dominated by olivine fo 85 92 and phlogopite 5 10 tio 2 5 13 al 2 o 3 with subordinate potassium titanian richterite and or arfvedsonite and spectacularly zoned sr rich apatite up to 20 sro accessory to minor phases include clinopyroxene titanian diopside to aegirine augite k feldspar or 96 variable spinel up to 47 cr 2 o 3 perovskite niobian ilmenite niobian rutile sphene and ba poor priderite complex primary carbonate assemblages involve breunnerite ferroan dolomite witherite alstonite and strontianite the whole rocks show low al 2 o 3 5 7 combined with high k 2 o 4 5 mgo up to 30 and cr up to 1500 ppm plus extreme tio 2 up to 8 5 sr zr up to 6000 ppm each ba up to 8000 ppm and lree ce up to 3000 ppm in many rocks k al molecular 0 7 na k al 1 and k na k 0 6 radiogenic isotopes sr 7 to 21 and nd 1 5 to 3 1 imply derivation from a metasomatized lithosphere mantle source with time integrated rb sr and sm nd slightly higher than bulk earth intensive carbonation up to 14 co 2 in some rocks may reflect fluids derived from the magmas themselves from carbonatite like fluids and perhaps from coking of the invaded coal seams minor crystal fractionation within sills as little as 2 5 m thick has yielded complementary olivine lamproites and feldspathic lamproites the latter grade ultimately into minettes via increase of al 2 o 3 and decrease of mgo positive indicators of diamond potential in these rocks include their bulk compositional similarity to diamondiferous olivine lamproites elsewhere e g argyle their cr rich spinels and perhaps their tectonic position negative factors include their quiet emplacement the noted differentiation and the associated coking of the coal seams

predicting incipient motion including the effect of turbulent pressure fluctuations in the bed 1 incipient motion of particles on a river bed can in principle be understood and predicted from a balance of the forces acting on the particles on a natural river bed the exposure of particles to the flow is variable the effect of exposure on the initiation of motion including the case of deep embedding is studied in this paper so far the turbulence induced lifting force has been derived exclusively from examinations of the surface flow the understanding of destabilization processes of the riverbed is improved when turbulence induced vertical pressure gradients in the upper sediment layer are included this is particularly important for particles that lie in the lee of larger ones an analytical solution for the critical shields parameter of spherical particles is found including the effects of pressure fluctuations in the bed macroscale flow structures average bed slope and shallow flow existing laboratory data designed to test the effect of exposure and roughness conditions are in excellent agreement with the new model

sediment transport over ripples in oscillatory flow in this paper we present results of a large eddy simulation of flow and suspended sediment transport around prototypical ripples based on long wave ripples as measured at duck n c in waves of height 1 m and period of 10 s solving the volume filtered navier stokes equations for the momentum and an advection diffusion equation with a setting term for the suspended sediment we obtain time dependent three dimensional descriptions of the velocity pressure and sediment concentration fields although the main flow and sediment transport patterns are governed by a quasi two dimensional vortex formation ejection mechanism we illustrate the three dimensional structure of both and make qualitative comparisons with the results of other researchers we conclude with analysis of concentration time series measured at a point and interpret them within the larger framework of the flow the present simulations demonstrate that the flow over these larger scale ripples resembles that over vortex ripples quite s

wall roughness effects on flow and scouring in curved channels with gravel beds wall roughness effects on flow and scouring in curved channels with gravel bed in the narrow valleys in alpine regions rivers frequently flow across constructed zones passing through villages and cities due to limited space the protection from high floods often needs to be ensured by protection walls during floods these protection walls may be endangered by scour phenomena especially if they are located in bends in the past the potential danger of underscoured structures was reduced by sufficient foundation depth by providing roughness elements such as vertical ribs at the surface of walls located at the outer side of river bends the local erosion along the foot of the wall can be considerably decreased reducing the cost of wall foundations such observations were made during the review and optimization of several flood protection projects with hydraulic model tests in switzerland a literature review showed that no systematic study of the influence of these ribs on scour and flow in bends was performed up to this day 2 this research project covers this gap by investigating the development of the scour as a function of main parameters the study is based on an experimental investigation in a 90 bend with a radius of 6 m including measurements of the velocities the water level the bed topography the sediment characteristics the grain size distribution of the armoring layer the discharge and the bed load 4 and 5 the large set of tests covers a wide range of discharges bed slopes rather high froude numbers but in subcritical regimes many rib spacings and depths the formation of two scour holes was observed without macro roughness a first scour hole occurs in the prolongation of the inner sidewall of the entry reach at the outer wall and a second scour hole appears at the end of the 90 bend the analysis of the performed tests results in the following conclusions most existing scour formulae considerably underestimate the scour depth in mountain rivers with coarse gravel bed 3 significant oscillations both of the free water surface stationary waves and of the scour depth were observed especially for the second scour hole the two scour holes have different reasons the first one is essentially due to the change of the main flow direction impact on the wall and the induced secondary current whereas the second one is mainly due to increased velocity fluctuations after the point bar formed at the inner side of the channel 6 in the average flow field in a bend the highest main velocities are shifted from the centerline close to the surface toward the outer wall and then towards the bottom 6 at the first scour the highest main velocities are found next to the ground a significant grain sorting process is observed over the cross section due to the use of coarse gravel mixture resulting in the accumulation of coarse sediments at the outer wall and depositions of fine material on the inner bank by applying vertical ribs on the outer sidewall an important impact on the scour process and on the flow field can be observed 6 the macro roughness has the following effects the scour depth along the outer sidewall is significantly reduced and the prominent scours almost disappear with increasing wall roughness the first scour hole shifts in the downstream direction whereas the second one remains at about the same position significant oscillations of the water surface and the scour depth observed without macroroughness are reduced by about 50 and the scour develops in a smoother way the flow field undergoes a pronounced modification the highest velocities are kept away from the outer sidewall reducing the scour at the bottom of the outer wall foundations along the outer wall at the free surface an secondary flow cell at the outer bank can be observed the importance of this cell shows an important correlation with the bank protection effect optimum rib spacing is essential since an inappropriate spacing may lead to an important increase in scour depth the transport capacity in the bend is reduced in natural rivers this phenomenon is compensated by a steepening of the bed slope the upstream and downstream extremities of the bend are influenced by the ribs upstream of the bend the water depth increases due to the head losses in the bend and downstream some additional erosion is found in the center of the channel the grain sorting process is not significantly influenced by the presence of the ribs beside an increase of the area of the coarse sediment zone this report furthermore presents a new empirical scour formula for the estimation of the maximum scour depth for mountain rivers with wide grain size distribution 7 established with physically based parameters which are the ratio mean water depth to channel width a dimensionless ratio combining the mean velocity with the hydraulic radius and finally the friction angle of the bed material the lateral bed profile in the maximum scour cross section can also be computed with this equation an estimation of the maximum scour depth in the presence of macro roughness on the outer wall can be obtained with a formula depending on the rib spacing the hydraulic radius the froude number and the difference between the dimensionless shear stress and the critical shields parameter 7 finally recommendations for hydraulic engineers 8 3 are given to facilitate the application of vertical ribs on outer banks serving as macro roughness

flume experiments on scour downstream of wood stream restoration structures abstract river restoration aims to improve physical natural form and processes of a river techniques to control the riverbed stabilize channel alignment protect stream banks and rebuild the natural habitat are an important part of river restoration projects rivers can be stabilized and habitat restored through techniques such as rebuilding meanders and pool riffle sequences and managing large wood structures that limit channel width to accelerate the normal flows through the constricted section are referred to as stream deflectors single wing double wing and triangular deflectors are the most commonly used types of this measure log frame deflectors consist of a triangular log frame filled with rock deflector constructions singly or in series in low gradient meandering streams divert base flows toward the center of the channel and under certain conditions increase the depth and velocity of flow thereby creating scour pools and enhancing fish habitat scour characteristics and morphologies downstream of log frame deflectors have been analyzed at the hydraulic laboratory of the university of pisa all experiments have been carried out in clear water conditions the results showed that the tailwater depth plays an important role on scour characteristics in addition it was experimentally proven that using log frame deflectors instead of log deflectors result in a better river bank protection in this case for all the tested hydraulic conditions the scour hole never occurred close to the channel bank useful empirical relationships have been proposed in order to evaluate the main features of the scour geometry

measured and simulated flow near a submerged spur dike to improve knowledge of the flow and scour processes associated with spur dikes three dimensional flow velocities were measured at 2 592 points using an acoustic doppler velocimeter over a fixed flat bed with a trapezoidal shaped submerged spur dike in a laboratory flume general velocity distribution and detailed near field flow structures were revealed by the measurements and numerical simulations performed using a free surface turbulent flow model with a k e closure scheme the three dimensional flow separation characterized in this study was found to yield forces on the bed that were significantly different from nonsubmerged vertical obstructions that have been measured in other studies values of bed shear stress derived from both measured and simulated values were similar but indicated that local scour would be initiated in one rather than in the two locations of initial local scour measured in previous experiments with a similar flow

discussion of kimberlites and aillikites as probes of the continental lithospheric mantle by d francis and m patterson lithos v 109 p 72 80 article the origin of kimberlites and volatile rich alkaline ultramafic magmas such as aillikites has been a matter of considerable scientific interest and the recent paper by francis and patterson francis and patterson 2009 kimberlites and aillikites as probes of the continental lithospheric mantle lithos 109 72 80 attempts to summarize advances in this research field they introduce new major element geochemical discrimination diagrams and present a petrogenetic model that allegedly has implications for diamond exploration contrary to the statements of francis and patterson we argue that kimberlite bulk chemical compositions are not determined by contamination with lithospheric mantle material alone and cannot be used to predict reliably the diamond grade of new discoveries we dispute their petrogenetic model specifically the proposal that calls for carbonate rich aillikite melts being parental to kimberlite magmas rather we promote the idea of carbonated ultramafic lamprophyre magmas such as aillikites being parental to many carbonatite intrusions in areas of rifted cratonic lithosphere from which archetypal kimberlites appear to be absent furthermore we believe that the geochemical discrimination diagrams si versus k and fe respectively introduced by francis and patterson do not effectively distinguish between kimberlites and aillikites because there is significant data overlap and bias of particular concern is the omission of relevant compositional data for the ultramafic lamprophyre group in this discussion we re iterate that bulk chemical analyses of kimberlites and alkaline ultramafic rocks need to be accompanied by petrographic descriptions and mineralogical data only by the inclusion of such data can the petrogenesis of the rocks considered be discussed

three dimensional numerical model for flow and bed deformation around river hydraulic structures this paper describes a numerical model developed to simulate flow and bed deformation around river hydraulic structures the model solved the fully three dimensional reynolds averaged navier stokes equation expressed in a moving boundary fitted coordinate system to calculate the flow field with water and bed surfaces varying in time a nonlinear k e turbulence model was employed in order to predict flow near the structure where three dimensional flow is dominant the temporal change in bed topography was calculated by coupling a stochastic model for sediment pickup and deposition using a momentum equation of sediment particles in order to account for the effect of nonequilibrium sediment transport in validating the numerical model a spur dike and a bridge pier which are considered to be typical river engineering structures were selected by comparing the numerical results with observed laboratory experimental data the model was found to reproduce flow and scour geometry around these structures with

an investigation of the flow and scour mechanisms around isolated spur dikes in a shallow open channel 1 conditions corresponding to the initiation of the erosion and deposition process 1 the present study investigates the flow physics and the role played by the main coherent structures in the scouring processes around a vertical spur dike in a straight channel at conditions corresponding to the start flat bed of the scouring process large eddy simulation les is performed at a relatively low channel reynolds number re 18 000 in the range where most flume studies with clear water scour conditions are conducted similar to these studies the incoming flow is fully turbulent and contains realistic turbulence fluctuations visualization experiments are conducted to better understand the nature of the interactions between the dominant coherent structures playing a role in the erosion process it is found that the structure of the horseshoe vortex hv system at the base of the spur dike changes considerably in time and in vertical sections perpendicular to the trajectory defined by the axis of the main necklace vortex however its intensity is the largest at vertical sections situated around the tip of the spur dike it is in this region that the core of the main necklace vortex oscillates aperiodically between two preferred modes in one of them zero flow mode the necklace vortex is closer to the spur dike and more compact and the near bed jet flow beneath it is weak in the other one back flow mode a strong near bed jet flow convects the primary necklace vortex away from the spur dike and its core is more elongated and less compact this explains the large amplification by about 1 order of magnitude compared to the surrounding turbulent flow of the turbulent kinetic energy and pressure fluctuations inside the hv system in the region situated around the tip of the spur dike and the double peak distribution of the turbulent kinetic energy past the spur dike in the legs of the necklace vortex the intensity of the bimodal oscillations decreases such that they are not observed in spanwise sections situated at more than one channel depth behind the spur dike it is found that the legs of the horseshoe vortices can interact at times with the vortex tubes shed in the detached shear layer dsl and with the tip of the spur dike these events typically result in a significant change in the coherence of the hv system the largest bed shear stress values in the mean flow are present in the strong acceleration region near the tip of the spur dike but high bed shear stress values are also observed beneath the upstream part of the dsl the bed shear stress fluctuations around the local mean values can be very high especially in the region situated beneath the upstream part of the dsl at random times some of the vortices shed in the dsl merge or interact with eddies from the recirculation region this leads to an increase in their strength and to a large increase of the bed shear stress along their path

velocity distribution and bed roughness in high gradient streams a model for the velocity field over a poorly sorted bed is derived herein and applied to flow in steep streams with coarse gravel beds in such streams large clasts often are comparable in size to stream depth and act as obstacles to the flow the effect of these obstacles on a flow is estimated by partitioning total stress proportional to the depth slope product into a purely fluid component and a form drag component associated with flow around the obstacles an eddy viscosity closure is used with a length scale dependent on both distance from the boundary and wake dimension resulting velocity profiles agree well with profiles measured by marchand et al 1984 in nine mountain streams in colorado model runs for a range of conditions reveal that the velocity distribution depends primarily on d84z and flow depth h d84z is the length of the vertically oriented axis of clasts at the 84th percentile of the grain size distribution calculated values of mean velocity normalized by shear velocity are well represented by a simple log linear relationship in terms of relative roughness d84 h

field investigation of three dimensional flow structure at stream confluences 2 turbulence stream confluences are among the most highly turbulent locations in fluvial systems this paper examines the three dimensional structure of turbulence at three stream confluences in east central illinois the analysis focuses on the characteristics of turbulence both within the shear layer and in the ambient flow results show that at the upstream end of each confluence the shear layer occupies a limited portion of the flow cross sectional area but turbulence kinetic energy within this layer is 2 3 times greater than the turbulence kinetic energy of the ambient flow which has turbulence characteristics similar to those for flow in straight channels turbulence within the shear layer can be characterized as quasi two dimensional in the sense that large scale turbulence generated by transverse shear is predominantly two dimensional whereas small scale turbulence associated with bed friction is three dimensional spectral analysis suggests that the structure of fluid motion within the shear layer differs for confluences with symmetrical versus asymmetrical planforms the shear layer dissipates rapidly as flow enters the downstream channel even though a well defined mixing interface persists at downstream locations

comment on new ar ar ages of southern indian kimberlites and a lamproite and their geochemical evolution by osborne et al precambrian res 189 2011 91 103 abstract osborne et al 2011 precambrian res 189 91 103 report new 40 ar 39 ar age results for two kimberlites muligiripalle pipe 5 and tummatapalle pipe 13 and one lamproite pochampalle from the archaean dharwar craton in southern india previous studies indicate that kimberlites and related rocks are highly susceptible to extraneous argon contamination leading to anomalously old ages although reliable 40 ar 39 ar ages can be obtained from step heating analyses of groundmass phlogopite grains osborne et al 2011 carried out single step 40 ar 39 ar fusion analyses on phlogopite phenocrysts and xenocrysts this approach is not favoured because it does not allow identification of argon loss gain effects thus complicating data interpretation and reducing confidence in the reliability of the reported ages in particular it is suggested that the pochampalle lamproite was emplaced osborne et al 2011 it is recommended that 40 ar 39 ar geochronology of kimberlite and lamproites include step heating analyses of matrix phlogopite grains with anomalous or contentious results verified using other dating methods

a study of infrasonic anisotropy and multipathing in the atmosphere using seismic networks we discuss the use of reverse time migration rtm with dense seismic networks for the detection and location of sources of atmospheric infrasound seismometers measure the response of the earth s

geological setting and chemistry of kimberlite clan rocks in the dharwar craton india abstract diamond exploration in india over the past decade has led to the discovery of over 80 kimberlite inferred and lamproite related intrusions in three of the four major archean cratons that dominate the subcontinent these intrusions are proterozoic 1 1 ga and are structurally controlled locally at the intersections of faults regionally in a 200 km wide 1000 km long diamond corridor and globally in the reconstructed supercontinent of rodinia the geochemistry of 57 samples from 13 intrusions in the southern dharwar craton of andhra pradesh has been determined by xrf spectrometry the bodies are iron rich with mg 50 70 and are neither archetypal kimberlites nor ideal lamproites this may be the underlying reason that conventional exploration techniques have thus far failed to locate the primary sources of india s historically famous diamonds the two major fields of kimberlite clan rocks kcr in the dharwar craton wajrakur and narayanpet are separated by a nw se trending transcontinental mumbai chennai gravity lineament about 80 of intrusions in wajrakur are diamondiferous but diamonds have not yet been reported in narayanpet the gravity anomaly may mark the boundary of an architectural modification in the keel of the sub continental lithosphere a suggestion that is supported by differences in kimberlite mineralogy chemistry mantle xenoliths structural setting and crustal host rocks

large eddy simulation of sediment transport currents over ripples a large eddy simulation has been performed to study the detailed sediment dynamics that occur in channel flow over ripples the code solves the navier stokes equations and an advection diffusion equation for the sediment and has been verified to produce quantitatively accurate hydrodynamic results for the flow domains used in this study the main features of interest in this flow are seen because of the high resolution of the grid especially near the ripple boundary this yields a detailed bottom shear stress distribution properly identified coherent structures and resolved sharp gradients in the sediment concentration globally the sediment is carried up into the flow from locations where the shear stress is high on the upslopes of ripple crests and is advected downstream by the current and upward by the vertical velocity component regions of positive vertical velocity are associated with gortler vortices which represent a significant sediment transport mechanism in this flow

estimation of the acoustic to seismic coupling ratio using a moving vehicle source we present a simple passive technique for estimating the acoustic to seismic signal coupling ratio sar in the ground using noise produced by moving vehicles the seismic signal received on a geophone contains some energy that has propagated as seismic waves and some energy that couples from acoustic waves to seismic waves in the vicinity of the geophone we use the frequency domain coherence between the microphone and geophone signals to determine when the seismic signal is predominantly due to acoustic to seismic wave coupling in frequency bands where the microphone and geophone coherence is above 0 8 the ratio of the seismic ground particle velocity to sound pressure sar can be determined with less than 2 db of error the method is applied to data from a summer experiment with grass ground cover and at two winter experiments with snow covered ground at 100 hz the summer analysis yields a sar value of 1 0 times 10 5 m s pa in addition at 100 hz the two winter tests yield sar between 0 1 times 10 5 and 1 0 times 10 5 m s pa in the later winter result our vehicle derived sar estimate is shown to be in excellent agreement with sar estimates obtained from blank pistol shots through the opportunistic exploitation background noise sources our approach opens the possibility for automatic adaptation of unattended acoustic area monitoring sensors to changing ground conditions

local scour associated with angled spur dikes a series of experiments were conducted in which the volume of the scour hole associated with model spur dikes was measured in a laboratory flume under clear water overtopping flows spur dike models were angled at 45 90 and 135 to the downstream channel sidewall with contraction ratios of 0 125 and 0 250 the main goals of the experiments were to evaluate the effect of the three angles on the volume of scour and potential aquatic habitat and on minimizing erosion adjacent to the streambanks the experiments showed that of the three angles tested the least erosion of the bed in the near bank region was associated with the spur dikes with 90 angles while the greatest volume of the scour hole was associated with the 135 spur dikes it was concluded that spur dikes with 135 angles showed the best potential for providing improved aquatic habitats while minimizing the potential for erosion of the channel bank

a numerical investigation of coherent structures and mass exchange processes in channel flow with two lateral submerged groynes 1 large eddy simulation is used to investigate the dynamics of the main coherent structures present in the flow around two vertical submerged groynes situated in a long flatbed open channel the mass exchange processes between the embayment region and the main channel are investigated by studying the ejection of a contaminant introduced instantaneously inside the embayment the instantaneous and mean structure of the horseshoe vortex system forming at the base of the upstream groyne and the bed shear distributions that determine the evolution of the scour in the groyne region are investigated it is found that the amplification of the bed shear stress in the accelerating region around the tip of the upstream groyne is around one order of magnitude larger relative to the mean bed shear stress in the incoming flow analysis of the instantaneous flow fields shows that the eddies that are shed inside the horizontal and vertical detached shear layers play an important role in controlling the mass exchange at the lateral and roof interfaces it is found that most of the pollutant leaves the embayment through the roof and bottom lateral sections the overall mass exchange process is qualitatively different and substantially accelerated compared to the case when the groynes are emerged however it is shown that similar to the emerged case the decay of the mass of contaminant within the embayment cannot be characterized by a unique value of the exchange coefficient used in simple dead zone theory models

smnd pbpb and rbsr geochronology and petrogenesis of the mafic dyke swarm of mahbubnagar south india implications for paleoproterozoic crustal evolution of the eastern dharwar craton abstract the sm nd rb sr and pb pb isotopic systematics of whole rock and separated mineral fractions from four tholeiitic mafic dykes of the mahbubnagar swarm have been investigated this dyke swarm intrudes the granitic basement of the cuddapah basin in the eastern dharwar craton edc the sm nd data on whole rock samples of four gabbros and one dolerite and 15 mineral fractions yielded a linear array with an isochron age of 2173 64 ma and an initial nd value of 0 4 0 3 the sm nd data of a metapyroxenite and its three mineral fractions plot parallel to this array yielding an isochron age of 2189 123 ma with a negative initial nd value of 1 8 1 4 rb sr and pb pb internal isochron ages of three gabbros and a pb pb internal isochron age of a metapyroxenite dyke range between 2031 and 2284 ma and within the limits of experimental error broadly conform to the sm nd isochron age by contrast rb sr internal isochron ages of three other samples range between 1474 and 1952 ma and one sample yields a pb pb internal isochron age of 3446 ma showing the effects of partial isotopic resetting possibly due to hydrothermal alteration these data suggest that mafic dykes of the mahbubnagar swarm were emplaced at c 2170 ma marking an episode of the crustal extension and fracturing which ultimately resulted in the formation of the cuddapah basin different petrological and geochemical variants of mafic dykes seen in the area most probably represent generation and or crystallization of the progressively evolved batches of magma during a relatively short time interval the initial nd values calculated at 2170 ma range from 0 6 to 2 0 and can be explained as reflecting contamination of depleted mantle derived magma by crustal rocks of edc the initial 87 sr 86 sr ratios 0 7027 0 7064 and model 1 values 8 3 8 5 of apparently undisturbed samples are also consistent with this suggestion

on large scale flow structures in a gravel bed river abstract previous studies have suggested the presence of large scale flow structures in gravel bed rivers these structures are pictured as intermittent high speed wedges separated by regions of lower velocity however the characteristics of these structures have not been examined in detail through either visualisation techniques or detailed field measurements this paper confirms the presence of large scale flow structures in gravel bed rivers pictures their sequence and patterns and characterises their mean and individual properties the analysis relies on a new technique for displaying velocity fluctuations in a space time matrix that allows one to see the structures as they pass an array of current meters streamwise and vertical velocities were measured simultaneously with an array of three electromagnetic current meters the sampling frequency was 20 hz five velocity profiles of up to 13 1 min series of measurements and one profile of three 20 min measurements were sampled these data suggest the presence of large wedges of faster fluid joined by regions of slower fluid space time correlation analysis confirmed the presence of vertical coherence of the flow the average angle of the front of the wedges is 36 although individual structures are variable in size and shape a new detection technique using all three velocity signals simultaneously showed that their average frequency is nine events per minute and their duration is more than 2 s the high speed wedges display a complex organisation and do not show a preferred sequence of events as was postulated by previous studies because of their duration and size these high speed wedges are likely to play a major role in bedload sediment transport

flow in alluvial river curves uniform flow in curved wide erodible bed channels is formulated on the basis of the conservation of flux of moment of momentum to obtain relations for the vertical distributions of radial plane velocity and radial shear stress the expression for the radial stress exerted on the bed is utilized in a force equilibrium analysis of the moving bed layer to obtain relations for the average transverse slope of the bed and for the radial bed profile the reduction of primary bed shear stress due to the net radial transport of streamwise momentum toward the outer concave bank is then calculated by introducing the derived expressions for the velocity components into the momentum equation for the primary flow direction it is found that the stress reductions in deep narrow channels can exceed 50 bed profiles and velocity distributions measured in natural and laboratory streams are found to be in good conformity with those calculated from this moment based theory

numerical investigation of flow hydrodynamics in a channel with a series of groynes the flow hydrodynamics in a straight open channel containing a multiple embayment groyne field on one of its sides is investigated numerically using large eddy simulation the vertical groynes are fully emerged the mean flow depth in the groyne region is about half that of the main channel and the length and width of the embayments are much larger than the mean depth in the embayment region the model is validated using mean velocity and turbulent fluctuations data collected at the free surface in a previous experimental study it is found that despite the fact that the flow inside the main recirculation eddy in the embayments can be characterized as being quasi two dimensional the flow inside the mixing layer region between the embayments and the channel is strongly nonuniform over the depth as this region controls the mass exchange processes between the groyne field and the main channel a three dimensional description of the flow in this area is essential the large scale eddies that populate the mixing layer can penetrate the embayment region over lateral distances of the order of the channel depth these eddies advect with them channel fluid inside the embayment eventually the channel fluid is mixed with the embayment fluid by the small scales the other main mixing mechanism is due to the injection of patches of high vorticity mixing layer fluid near the tip of the downstream groyne and their subsequent convection in the form of a wall attached jet like flow into the embayment first parallel to the downstream groyne face and then to the sidewall it is shown that on average most of the fluid leaves the embayment region via the top layer of the embayment channel interface upstream half and enters the embayment region at levels situated around the middepth practically over the whole length of the embayment of the interface surface this explains why the mass exchange coefficients are overestimated when predicted using methods that employ floating particles as a tracer the instantaneous bed shear stress inside the cavity is found to peak close to the downstream groyne face of each embayment and to show a high variability around the mean values due to the interaction of the mixing layer eddies with the tip of the groynes and the formation of the jet like flow parallel to the droyne face

the rapid drift of the indian tectonic plate the breakup of the supercontinent gondwanaland into africa antarctica australia and india about 140 million years ago and consequently the opening of the indian ocean is thought to have been caused by heating of the lithosphere from below by a large plume whose relicts are now the marion kerguelen and reunion plumes plate reconstructions based on palaeomagnetic data suggest that the indian plate attained a very high speed 18 20 cm yr 1 during the late cretaceous period subsequent to its breakup from gondwanaland and then slowed to approximately 5 cm yr 1 after the continental collision with asia approximately 50 myr ago the australian and african plates moved comparatively less distance and at much lower speeds of 2 4 cm yr 1 refs 3 5 antarctica remained almost stationary this mobility makes india unique among the fragments of gondwanaland here we propose that when the fragments of gondwanaland were separated by the plume the penetration of their lithospheric roots into the asthenosphere were important in determining their speed we estimated the thickness of the lithospheric plates of the different fragments of gondwanaland around the indian ocean by using the shear wave receiver function technique we found that the fragment of gondwanaland with clearly the thinnest lithosphere is india the lithospheric roots in south africa australia and antarctica are between 180 and 300 km deep whereas the indian lithosphere extends only about 100 km deep we infer that the plume that partitioned gondwanaland may have also melted the lower half of the indian lithosphere thus permitting faster motion due to ridge push or slab pull

petrology and petrogenesis of mesoproterozoic lamproites from the ramadugu field nw margin of the cuddapah basin eastern dharwar craton southern india abstract petrography mineral chemistry and major and trace element data are presented for the newly discovered mesoproterozoic 1 33 1 43 ga lamproites from the ramadugu field rlf at the nw margin of the paleo mesoproterozoic cuddapah basin in the eastern dharwar craton edc southern india rlf lamproites are emplaced as dykes have a nw se trend and their petrography reveal the effects of low temperature alteration however their textural features mineralogy and geochemistry are closely similar to other well characterised lamproites worldwide including examples from the eastern dharwar craton leucite hills west kimberley smoky butte and labrador the rlf magmas have undergone varying degrees of olivine clinopyroxene fractionation yet their compatible and incompatible trace element concentrations are sufficiently high to signal a primitive character incompatible element ratios suggest limited contamination by continental crust geochemical evidence indicates the derivation of rlf magmas from metasomatised harzburgite within the garnet stability field rare earth element inversion modelling further highlights substantial involvement of the sub continental lithospheric mantle in their genesis the rlf lamproites are geochemically similar to the well known extension related ultrapotassic lavas from eastern virunga and western anatolia and exclude an affinity with orogenic lamproites such as those from the mediterranean region bulk rock geochemical models recently developed to infer diamond potential reveals that rlf lamproites are non prospective lamproites of the rlf together with those from the krishna lamproite field and cuddapah basin are interpreted as an expression of extensional events in the eastern dharwar craton possibly related to the break up of the supercontinent of columbia between 1 5 and 1 3 ga

ground penetrating radar reflection profiling of groundwater and bedrock in an area of discontinuous permafrost we have used ground penetrating radar to profile the depth of permafrost to groundwater beneath permafrost and to bedrock within permafrost in alluvial sediments of interior alaska we used well log data to aid the interpretations and to calculate dielectric permittivities for frozen and unfrozen materials interfaces between unfrozen and frozen sediments above permafrost were best resolved with wavelet bandwidths centered at and above 100 mhz the resolution also required consideration of antenna configuration season and surface conditions depths to subpermafrost groundwater were profiled where it was in continuous contact with the bottom of the permafrost except near transitions to unfrozen zones where the contact appeared to dip steeply the complexity of the responses to intrapermafrost bedrock detected at a maximum depth of 47 m appears to distinguish these events from those of subpermafrost saturated sediments the relative dielectric permittivity ranged between 4 4 and 8 3 for the permafro

flow around bridge piers this paper presents the results of a laboratory study on flow past cylindrical piers placed on smooth rough and mobile beds experimental results are presented on the flow in the plane of symmetry including the frontal downflow and the effects of bed roughness and the scour hole on it the clauser type defect scheme describes the velocity profiles better than the log law and defect law frontal downflows as large as 95 of the approach flow were observed experimental results are also presented on the deflected flow and bed shear stress field bed roughness increased the magnitude of bed shear stress and the area over which the shear amplification was felt and also resisted the skewing of the flow near the bed thus leading to smaller yaw angles of the bed shear vectors

windshield and sound barrier for seismic sensors a system and method for reducing acoustic wind or other background noise that may interfere with sensing of a seismic signal is provided more specifically a shield is provided to enclose a geophone and thereby protect it from harmful noise the shield may comprise a rigid shell a structural damping material an acoustically absorptive material and a compliant seal for coupling the shield to the ground or reference surface

complex polarization analysis of particle motion knowledge of particle motion polarization aids in identifying phases on three component seismograms the scheme of montalbetti and kanasewich 1970 is extended to analytic three component seismograms where the imaginary part of the signal is the hilbert transform of the real part this scheme has only one free parameter the length of the time window over which the polarization parameters are estimated so it can be applied in a routine way to three component data the azimuth and dip of the direction of maximum polarization and the degree of elliptical polarization as a function of time for the seismograms are obtained polarization analysis of strong motion data from the 1971 san fernando earthquake aids in the discrimination between wave types which is important for the understanding of the complicated earthquake induced shaking observed in basins most arrivals are incident on the receivers in the direction of the back azimuth to the epicenter which suggests that despite the complicated motions two dimensional finite difference methods are sufficient to understand the effect on seismic waves of the los angeles and san fernando basins vidale and helmberger 1986b

quantitative measurements of shear wave polarizations at the anza seismic network southern california implications for shear wave splitting and earthquake prediction we analyze shear wave polarizations from local earthquakes recorded by the anza network in southern california using an automated method which provides unbiased and quantitative measurements of the polarization and the duration of linear motion following the shear wave arrival the linearity interval initial shear wave particle motions are strongly aligned at four stations a feature that is not predicted by focal mechanisms the particle motion alignment is most likely caused by shear wave splitting due to anisotropy beneath these stations a result supported by the clear shear wave splitting seen in a borehole recording near one of the anza stations these results are consistent with an earlier analysis of these data by peacock et al 1988 however our analysis does not support claims by crampin et al 1990 that shear wave splitting delay times at station knw exhibit temporal variations which can be correlated with the occurrence of the north palm springs earthquake ml 5 6 of july 8 1986 automatically determined linearity intervals scatter widely from 0 02 to 0 15 s and exhibit no clear temporal trends we find a correlation between earthquake moment and the linearity interval possibly a result of longer effective source time functions for the larger events the inability to identify a distinct slow quasi shear wave pulse for the vast majority of these events indicates that scattering strongly affects the particle motion even in the very early shear wave coda analysis of earthquake clusters with similar waveforms recorded at knw shows that seismic green functions are stable throughout the observational period and that most linearity interval variation is due to source and ray path differences between events if shear wave splitting is causing the observed delay times between horizontal components the waveform stability for events in these clusters restricts any temporal changes in shear wave splitting delay times to less than 5 10

studies of high frequency seismic noise in eastern kazakhstan abstract three seismographic stations have been established in the region of the principal underground nuclear weapons test site in the republic of kazakhstan in the soviet union instrumentation includes both surface and borehole seismometers with a bandwidth of 100 hz and a system dynamic range of 180 db power spectra of the regional ambient ground acceleration peak between 4 and 6 hz and are on average frequency independent above 10 hz where levels are approximately equal to 10 15 to 10 16 m sec 2 2 hz 1 kazakh noise levels are roughly equivalent to those observed by the regional seismic test network between 1 and 20 hz and about 10 to 20 db higher than the very low noise model for lajitas texas in the same band noise observed by the borehole sensors is about 10 db less than that observed by the surface instruments above about 20 hz under low wind conditions at two of the three kazakh sites borehole improvement is greater under high winds the third kazakh site karasu is characterized by much higher surface noise levels 15 to 20 db higher than the borehole levels from 4 to 40 hz under both low or high wind conditions which is attributed to amplification by local site conditions and the exposed terrain power spectra of individual runs of ambient vertical ground acceleration measured down the borehole show that high frequency slopes between 10 and 80 hz vary between f 0 60 and f 0 22 depending on wind and site conditions

dynamics of a river channel confluence with discordant beds flow turbulence bed load sediment transport and bed morphology 1 river channel confluences play a major role in the dynamics of all fluvial systems and yet our understanding of bed load routing at these sites is very sparse the dynamics of confluences are a function of the momentum ratio between the combining flows and the three dimensional geometry of the junction recent experiments have shown that discordance in bed height between the confluent rivers increases turbulence intensity and enhances upwelling of flow within the confluence however the significance of these flow characteristics on sediment transport is still unknown to examine the relations between flow and sediment transport we have measured near bed flow turbulence bed load transport rates and changes in bed morphology for eight different flow conditions at a sand bed discordant confluence detailed analysis of the near bed flow patterns reveals that within the shear layer low mean flow velocities are combined with the highest values of reynolds shear stresses and that turbulence generation is associated with intense upward movements of flow high sediment transport rates are found at the edges of the shear layer region where horizontal vertical cross stresses uw are high these patterns match changes in bed morphology where erosion occurs along the shear layer the relation between the shear layer and sediment transport confirms the role of bed discordance on the dynamics of the confluence migration of the shear layer into the confluence as a result of a change in momentum ratio modifies local near bed flow characteristics sediment transport rates and the spatial distribution of deposition and erosion zones

a comparison of the high frequency 1 hz surface and subsurface noise environment at three sites in the united states abstract surface and subsurface high frequency 1 hz noise data were recorded using nearly identical instrumentation at three widely separated sites in the united states amarillo texas datil new mexico and pinedale wyoming for extended periods of time under varying wind conditions while the sites are geologically distinct the near surface noise environments have many common features that we believe may be due in large part to the presence of a surficial layer of highly attenuative unconsolidated material at each site noise levels seen at or near the surface 5 m or less are much higher up to 30 db and much more variable power range up to 44 db than those seen at depth the smallest range was 9 db for 1951 m at amarillo the greatest gains in noise level reduction are realized within the first 100 m and probably much shallower

geometry of scour holes associated with 90 spur dikes the stable pools formed by spur dikes can be a significant factor for improving aquatic habitat in unstable degraded streams prediction of the volume and geometry of the scour hole associated with a spur dike yields information that is valuable for assessing the potential benefit to the aquatic habitat volumes of the scour hole in the vicinity of model spur dikes were measured in a laboratory flume under clear water overtopping flows spur dike length flow depth and shear velocity ratio were varied in the experiments and found to significantly influence the volume of the scour hole for overtopping flows the ratio of the flow depth to the spur dike height was found to be an important control on the geometry of the resulting scour hole at higher flow depth to spur dike height ratios the location of the maximum depth of scour changed from the upstream point of the dike toward the channel bank and caused a secondary scour zone to form downstream of the spur dike a preliminary technique is proposed to predict the volume of scour for spur dikes perpendicular to the bank

macroturbulent structure of open channel flow over gravel beds the turbulent structure of open channel flow over a mobile gravel bed was investigated in an 8 m long 0 3 m wide and 0 3 m deep tilting flume a flow visualization technique was used and complemented by measurements of flow velocity fluctuations near the bed the experiments reveal that turbulent flow consists of a sequence of large scale eddies with a vertical size close to the flow depth an average length equal to four to five depths and a width of about two depths the downstream motion of these eddies causes quasiperiodic fluctuations of the local flow velocity components the development of longitudinal troughs and ridges on the mobile bed and preferential transport of bed particles along troughs are related to the effect of the eddies the experimental results indicate that the depth scale eddies are an important turbulence mechanism contributing to sediment transport

early proterozoic melt generation processes beneath the intra cratonic cuddapah basin southern india early proterozoic tholeiitic lavas and sills were emplaced during the initial phase of extension of the intra cratonic cuddapah basin southern india ar 40 ar 39 laser fusion determinations on phlogopite mica from the tadpatri fm mafic ultramafic sill complex constrain the age of the initial phase of extension and volcanism in the basin at 1 9 ga despite their early proterozoic age the igneous rocks are unmetamorphosed undeformed and remarkably fresh they exhibit a wide range in mgo contents 4 28 wt and have undergone varying degrees of accumulation or crystal fractionation variable la nb ratios 1 2 3 7 and epsilon nd values 1 to 10 suggest that some but not all of the mafic rocks have been affected by crustal contamination this appears to have taken place in magma chambers at similar to9 kbar i e the base of the continental crust forward modelling of major and trace elements fe and nd and inverse modelling of rare earth elements suggest that the primary cuddapah melts were generated by similar to10 15 partial melting of a lherzolite mantle source this corresponds to a mantle potential temperature of similar to1500degreesc the thickness of the mechanical boundary layer predicted by the geochemical modelling is 70 km with a minimum initial lithospheric thickness of 120 kin this corresponds to a stretching factor of 1 6 1 8 richter s 1988 secular cooling model for the earth predicts that at 1 9 ga the ambient mantle had a potential temperature of similar to1500degreesc i e similar to200degreesc hotter than phanerozoic mantle if the cooling model is correct then proterozoic lithospheric stretching and mantle melting beneath the intra cratonic cuddapah basin could have been caused by passive rather than active rifting

controlling mechanism of local scouring experimental study of clear water scouring around a circular cylinder shows that the scour mechanism is coupled to the three dimensional separation of the upstream boundary layer and the periodic vortex shedding in the wake of the cylinder the first scour appears in the wake of the cylinder the main scouring agent in the upstream region is a system of horseshoe vortices the vortices have a periodical character that causes a triple scour profile to develop in the upstream region during scouring the number and periods of horseshoe vortex shedding undergo no appreciable change despite the clear water stage the transport phenomenon is periodical transport of sediment takes place through turbulent scales of comparable size to macro length scales the size of horseshoe vortices are representative for the macroscale wake scouring is caused by the primary wake vortices and the accelerated side flow the process is characterized by a strong periodical transport and the formation of ripples the periodicity is controlled by the shedding frequency of the wake vortices collars attached to the cylinder cannot prevent the formation of the vortices

high frequency analysis of seismic background noise as a function of wind speed and shallow depth we used a deep 1500 m cased borehole near the town of datil in west central new mexico to study high frequency 1 hz seismic noise characteristics the remote site had very low levels of cultural noise but strong winds winter and spring made the site an excellent candidate to study the effects of wind noise on seismograms along with a three component set of surface sensors teledyne geotech gs 13 a vertical borehole seismometer gs 28 was deployed at a variety of depths 5 43 and 85 m to investigate signal and noise variations wind speed was measured with an anemometer event triggered and time triggered data streams were recorded on a reftek 72 02 data acquisition system located at the site our data show little cultural noise and a strong correlation between wind speed and seismic background noise the minimum wind speed at which the seismic background noise appears to be influenced varies with depth 3 m sec at the surface 3 5 m sec at 43 m in depth and 4 m sec at 85 m in depth for wind speed below 3 to 4 m sec we observe omni directional background noise that is coherent at frequencies below 15 hz this coherence is destroyed when wind speeds exceed 3 to 4 m sec we use a test event md 1 6 and superimposed noise to investigate signal to noise ratio snr improvement with sensor depth for the low q valley fill of the datil borehole dbh site we have found that snr can be improved by as much as 20 to 40 db between 23 and 55 hz and 10 to 20 db between 10 and 20 hz by deploying at a 43 m depth rather than at the surface at the surface there is little signal above noise in the 23 to 55 hz frequency band for wind speeds greater than 8 m sec thus high frequency signal information that is lost at the surface can be recorded by deploying at the relatively shallow depth of 40 m because we observe only minor further reductions in seismic background noise sbn at deeper depths 40 m is likely to be a reasonable deployment depth for other high frequency monitoring sites in similar environmental and geologic conditions

age distribution of lamproites along the socovos fault southern spain and lithospheric scale tearing lithospheric scale tearing is commonly linked to the lateral termination of subduction rollback and slab segmentation the upper crustal expression of this process can be associated with the development of arcuate orogenic belts oroclines generated by a combination of vertical axis block rotations and strike slip faulting however the link between such strike slip faults and slab tearing is relatively poorly constrained we show here an example from the gibraltar arc in the westernmost mediterranean where lithospheric scale tear faulting during the late miocene accommodated westward subduction rollback the dextral strike slip socovos fault in the eastern betics may represent one of the surface expressions of this process we document a high concentration of mantle derived volcanic rocks lamproites along the socovos fault which were intruded as dikes during the late miocene phlogopite and whole rock 40ar 39ar ages of lamproites along the socovos fault show a spatial age zonation with older ages 9 3 8 2ma in the east and younger ages 7 3 7 1ma in the west this age distribution of the lamproites along the socovos fault is compatible with the westward retreat of the lithospheric slab that was active beneath the eastern betics in the late miocene we therefore hypothesize that tearing allowed pathways for lamproite melts in the subcontinental lithospheric mantle and lower crust with the socovos fault channelizing these magmas in the upper crust

trace element incorporation in titanite constraints from experimentally determined solid liquid partition coefficients titanite liquid partition coefficients for most of the trace elements relevant in petrogenetic studies are provided for titanite saturated liquids equilibrated at 1 5 gpa and 850 c starting from lamproitic compositions the high compatibility observed for ree hfse sr v and sc and the strong incompatibility observed for actinides large ion lithophile and light elements are discussed in terms of available crystal chemical mechanisms for incorporation and crystal structure control the exchange vectors na1ca 1 and al1ti 1 allow local charge balance to be achieved after incorporation of ree3 and r5 at the ca and ti site respectively the significant amounts of h measured are also relevant in this regard the exchange mechanism being oh 1o 1 at the o1 site the incorporation of u4 and th4 at the ca site is scarce and is likely balanced by that of mg2 at the ti site both these substitutions are responsible for strong structural strain titanite can thus be considered an important repository for ree and hfse in metamorphic and igneous rocks and its role must be accounted for when modelling trace element residence during metamorphic reactions and late magmatic crystallisation history due to the measured differences in compatibility titanite crystallisation increases the values of nb ta and lree hree ratios in residual liquids the similar compatibility of u and pb makes titanite suitable for u pb geochronology of igneous rocks only after common pb correction finally this study confirms that the titanite end member is not suitable for radioactive waste disposal due to the discussed crystal chemical constraints and that titanite based waste forms should contain high amounts of na and mg2

emergence of coherent flow structures over a gravel surface a numerical experiment 1 gravel bed rivers have complex porous and irregular surfaces characterized by a range of morphological forms these topographical structures determine the flow structures that develop over the river bed primarily by the shedding of vortices in the downstream wake of protruding clasts previous research into these flow structures has come from experimental studies which have used either flow visualization or single point measurements techniques here we present a numerical experiment where large eddy simulation les is used to study the generation evolution and destruction of these flow structures over a naturally water worked gravel surface the numerical simulations reported in this paper show that there are two distinct scales of boundary influence upon the shallow flow and emphasize that the measured flow variability at any one point in a natural river will contain both locally derived and upstream inherited flow structures according to the range of scales of bed topography present

acoustic signature of thunder from seismic records thunder the sound wave through the air associated with lightning transfers sufficient energy to the ground to trigger seismometers set to record regional earthquakes the acoustic signature recorded on seismometers in the form of ground velocity as a function of time contains the same type features as pressure variations recorded with microphones in air at a seismic station in kislovodsk ussr a nearly direct lightning strike caused electronic failure of borehole instruments while leaving a brief impulsive acoustic signature on the surface instruments the peak frequency of 25 55 hz is consistent with previously published values for cloud to ground lightning strikes but spectra from this station are contaminated by very strong wind noise in this band a thunderstorm near a similar station in karasu triggered more than a dozen records of individual lightning strikes during a 2 hour period the spectra for these events are fairly broadband with peaks at low frequencies varying from 6 to 13 hz the spectra were all computed by multitaper analysis which deals appropriately with the nonstationary thunder signal these independent measurements of low frequency peaks corroborate the occasional occurrences in traditional microphone records but a theory concerning the physical mechanism to account for them is still in question examined separately the individual claps in each record have similar frequency distributions discounting a need for multiple mechanisms to explain different phases of the thunder sequence particle motion determined from polarization analysis of the three component records is predominantly vertical downward with smaller horizontal components indicative of the direction to the lightning bolt in three of the records the azimuth to the lightning bolt changes with time confirming a significant horizontal component to the lightning channel itself

petrological characterization of the mantle source of mediterranean lamproites indications from major and trace elements of phlogopite lamproites are among the most enigmatic mantle generated melts and are typically abundant in phlogopite we investigated the major and trace element chemistry of phlogopite crystals from mediterranean lamproite occurrences in spain serbia and turkey the most primitive lamproite samples were selected in order to evaluate the generation of the different phlogopite populations in their distinct mantle setting s phlogopite hosted in mediterranean lamproites can be grouped into different compositional arrays on the basis of their major element chemistry using al2o3 feot and tio2 concentrations contents of cr f and presumably ti allow discrimination of the macrocrysts into phlogopite phenocrysts which are liquidus and near liquidus phases and mantle xenocrysts further distinction among different populations of mantle derived phlogopite can be achieved considering trace element and isotopic ratios the latter also distinguish between crustal and asthenospheric imprints on the source of the lamproitic parental melt

turbulence structure in an ice covered sand bed river although many high latitude rivers are characterized by seasonal ice cover few empirical studies have examined the effect of surface ice on the turbulent properties of the underlying flowing water this study presents three dimensional turbulence measurements obtained with an acoustic doppler velocimeter adv in a straight reach of an ice covered sand bed river the statistical properties of three dimensional turbulence were analyzed it is shown that the spatial structure of the flow was nonuniform due to nonuniformity of the ice cover in the cross stream direction and due to the riverbed geometry these factors are responsible for the complex spatial structure of the flow field which limits the predictability of available physical models observed distributions over depth of reynolds stresses and mean streamwise velocities generally conform with distributions derived from piecewise solutions of a two dimensional flow model at least in the central part of the flow but observed and expected values of some parameters differ substantially we have hypothetically addressed these differences to the effect of flow stratification and the values of a stratification parameter have been estimated the velocity measurements allowed to analyze the coherent structures near the bed and beneath the ice cover their spatial scales were evaluated to be as large as the river depth for ejections and 0 7 0 8 times the river depth for sweeps whereas low frequency variations of the streamwise velocity were observed to have scales of two to four river depths

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

tectonics and surface effects of the supercontinent columbia abstract assembly of the supercontinent columbia at about 1 85 1 90 ga coincided with several events that affected the entire earth the oldest worldwide network of orogenic belts formed at the same time although some granite granodiorite gg suites had formed earlier the gg suites became common in the 1 8 1 9 ga orogenic belts these suites succeeded the older tonalite trondhjemite granodiorite ttg suites which were not produced after 1 8 ga changes on the earth s surface at 1 8 1 9 ga include rapid increase in the concentration of oxygen in the atmosphere and oceans and probably the evolution of eukaryotes all of these surface changes occurred as columbia accreted and the assembly of columbia may have contributed to the drastic changes in the earth s surface environment as well as to the evolution of primitive life forms

spatial and temporal structure of shear layer turbulence at a stream confluence 1 the shear layer that develops at the interface between converging flows is a prominent but poorly understood hydrodynamic feature at stream confluences to examine the spatial and temporal characteristics of turbulence and coherent turbulent structures within a shear layer three dimensional velocity measurements were obtained at a small stream confluence in illinois using two acoustic doppler velocimeters spaced at various separation distances results indicate that coherent structures can be readily identified through cross correlation analysis of the velocity time series for different measurement locations maximum correlations decrease relatively slowly over short separation distances but decrease rapidly for separation distances greater than about 2 times the flow depth convective velocities of coherent structures derived from the correlation analysis differ from local mean velocities and from spatially averaged mean velocities indicating that coherent structures evolve as they are transported along the shear layer a finding consistent with dye tracing experiments despite this evolution correlation and spectral analyses indicate that the frozen turbulence hypothesis holds for frequencies corresponding to length scales of at least some shear generated coherent vortices a domain of quasi two dimensional turbulence energy at low frequencies appears to be associated with large scale intrusions of fluid from one stream into the other along the mixing interface

continuous catchment scale monitoring of geomorphic processes with a 2 d seismological array 1 distributed activity of geomorphic processes with different spatiotemporal scales is hard to monitor in detail with conventional methods but might be detected with seismometers from july to september 2010 we deployed 14 seismometers to evaluate the ability of a two dimensional array with small interstation distances 11 km to continuously monitor geomorphic processes in a mountain catchment 370 km2 in taiwan spectral analysis of seismic records highlights different sources with high frequency content 1 hz consistent with hillslope and river processes using a common detection algorithm and a location technique based on the timing of seismic amplitude we have located 314 near surface events most of which 69 occurred during daily convective storms event activity was positively correlated with the precipitation intensity but this relation was not uniform in the catchment high resolution satellite images and air photos did not show geomorphic change during the study which did not have any episodes of extreme precipitation a majority of events 61 were collocated with preexisting geomorphic features landslide scars gullies within the uncertainty on location 9 of interstation distance the combination of event location and timing suggests a geomorphic source of recorded signals and most events had the seismic characteristics of rockfall debris avalanches or slides reactivation of prior erosion sites by such processes is difficult to detect with imagery but can possibly be resolved by seismic monitoring when proven this approach will allow a spatially comprehensive survey of geomorphic activity at the catchment scale with temporal detail sufficient to evaluate the exact meteorological conditions under which process events occur

the theoretical foundations and potential for large eddy simulation les in fluvial geomorphic and sedimentological research abstract large eddy simulation les is a method for resolving the time dependent structure of high reynolds number turbulent flows with les it is possible to model and track the behaviour of coherent turbulent structures and study their effect on the flow field hence les is potentially an important research tool in the fluvial sciences where flow mixing sediment entrainment and sediment transport are all affected by the presence of coherent vortices and their interactions with channel boundaries and other flow structures this paper introduces the les methodology discusses a variety of ways for representing small scale processes within les the subgrid scale modelling problem and provides some examples of early work into the use of les in a fluvial context a number of advances in computational power and numerical methods are required before les can be effectively applied at the river reach scale this paper considers some recent developments and their potential for providing validated large eddy simulations of river flow at the channel scale

observations of low frequency acoustic to seismic coupling in the summer and winter experiments were conducted at a site in northern vermont to investigate low energy acoustic to seismic coupling in the 5 to 500 hz frequency band for propagation distances between 1 and 274 m pistol shots were used as the source of the acoustic waves with geophones and microphones serving as the receivers the strongest coupling into the ground occurred as the air wave passed with measured ratios of about 7 and 6 10 6 m s 1 pa 1 in the summer and winter respectively compressional waves induced in the ground immediately under the source were observed as first arrivals since they travel at the higher subsurface seismic wave velocity but their amplitudes were one to two orders of magnitude lower than those of the later arriving air wave a comparison of the summer and winter recordings revealed a number of effects caused by the introduction of a 0 25 m thick snow cover the peak amplitude of the seismic arrival induced by the passage of the acoustic wave was more strongly attenuated in the winter wi

flow field at a vertical wall abutment experiments were conducted to measure the three dimensional turbulent flow field using the acoustic doppler velocimeter at a short vertical wall abutment ratio of abutment length to approach flow depth less than unity before and after the development of a scour hole under a clear water scour condition in the upstream the presentation of flow field through vectors at vertical sections shows a primary vortex associated with the downflow in the downstream the upward flow is comprised of with irregularities owing to the vortex shedding the flow separation near the bed and within the scour hole is evident from the turbulent kinetic energy distribution using reynolds stresses the bed shear stresses are calculated

torngat ultramafic lamprophyres and their relation to the north atlantic alkaline province geological mapping and diamond exploration in northern quebec and labrador has revealed an undeformed ultramafic dyke swarm in the northern torngat mountains the dyke rocks are dominated by an olivine phlogopite mineralogy and contain varying amounts of primary carbonate their mineralogy mineral compositional trends and the presence of typomorphic minerals e g kimzeyitic garnet indicate that these dykes comprise an ultramafic lamprophyre suite grading into carbonatite recognized rock varieties are aillikite mela aillikite and subordinate carbonatite carbonatite and aillikite have in common high carbonate content and a lack of clinopyroxene in contrast mela aillikites are richer in mafic silicate minerals in particular clinopyroxene and amphibole and contain only small amounts of primary carbonate the modal mineralogy and textures of the dyke varieties are gradational indicating that they represent end members in a compositional continuum the torngat ultramafic lamprophyres are characterized by high but variable mgo 10 25 wt cao 5 20 wt tio2 3 10 wt and k2o 1 4 wt but low sio2 22 37 wt and al2o3 2 6 wt higher sio2 al2o3 na2o and lower co2 content distinguish the mela aillikites from the aillikites whereas the bulk rock major and trace element concentrations of the aillikites and mela aillikites overlap there is no fractional crystallization relation between them the major and trace element characteristics imply related parental magmas with minor olivine and cr spinel fractionation accounting for intra group variation the torngat ultramafic lamprophyres have a neoproterozoic age and are spatially and compositionally closely related with the neoproterozoic ultramafic lamprophyres from central west greenland ultramafic potassic to carbonatitic magmatism occurred in both eastern laurentia and western baltica during the late neoproterozoic it can be inferred from the emplacement ages of the alkaline complexes and timing of late proterozoic processes in the north atlantic region that this volatile rich deep seated igneous activity was a distal effect of the breakup of rodinia this occurred during and or after the rift to drift transition that led to the opening of the iapetus ocean

analysis of high frequency seismic noise in the western united states and eastern kazakhstan seismographic stations were operated for several months during 1987 at three sites within 250 km of the kazakh test site in the u s s r and through most of 1988 and early 1989 at three sites within 250 km of the nevada test site in the united states we have analyzed surface and borehole noise levels at these sites as a function of wind speed using nearly 2000 recordings of ambient ground noise collected at the u s stations and several hundred noise measurements from the u s s r sites at the surface wind did not become a noticeable source of noise until a minimum speed of 4 to 5 m sec in the boreholes noise levels were affected by wind conditions to a much smaller degree than at the surface between 3 and 10 hz surface and borehole noise levels were typically comparable and western u s sites were generally quieter than kazakh sites in the 10 to 80 hz band surface noise in the western united states was much higher than in kazakhstan but downhole noise levels in both regions were similar and greatly reduced compared to surface noise we suspect that this is due to differences in surface vault quality between the two sets of stations

coherent structures in the flow field around a circular cylinder with scour hole large eddy simulation les and laboratory flume visualizations were used to investigate coherent structures present in the flow field around a circular cylinder located in a scour hole the bathymetry corresponds to equilibrium scour conditions and is fixed in les the flow parameters in the simulation correspond to the experimental conditions in which the approach flow is fully turbulent detailed consideration is given to the interaction of the horseshoe vortex hv system within the scour hole with the detached shear layers formed from the cylinder and the near bed turbulence it is found that the overall structure of the hv system varies considerably in space and time though a large relatively stable primary necklace vortex is present at practically all times inside the scour hole the simulation captures the presence of bimodal chaotic oscillations inside the hv system as well as the sharp increase in the resolved turbulent kinetic energy levels and pressure fluctuations reported in prior experimental investigations high levels of the mean bed shear stress are observed beneath the primary necklace vortex especially over the region where the bimodal oscillations are strong as well as beneath the small junction vortex at the base of the cylinder it is also found that the detachment and advection of patches of vorticity from the downstream part of the legs of the necklace vortices can induce large instantaneous bed shear stress values when the critical bed shear stress value for sediment entrainment on a flat surface is adjusted for bed slope effects the les simulation correctly predicts that the distribution of the mean bed shear stress is consistent with equilibrium scour conditions

western u s infrasonic catalog illuminating infrasonic hot spots with the usarray 1 in this study reverse time migration is applied to signals recorded by the 2007 08 usarray presumably due to acoustic to seismic coupling to detect and locate in two dimensional space and time 901 sources of atmospheric infrasound defining the western united states infrasonic catalog wusic the detections are visually inspected and ranked uncertainties are estimated using a bootstrap technique the method correctly locates most rocket motor detonations in utah and a bolide explosion in oregon with an average spatial accuracy of 50 km and 25 km respectively the origin time statistics for 2007 and 2008 events are nearly identical and suggest a predominant human origin the event locations illuminate repeating sources of infrasound or infrasonic hot spots in nevada utah and idaho that are spatially associated with active military areas the infrasonic arrivals comprise several branches that are observed to a range between 200 and 1500 km to the east and west of the epicenter in the winter and summer respectively the optimum group velocities are gaussian distributed and centered at 295 m s a seasonal variation in optimum group velocities exhibits good correlation with atmospheric temperature the results show that relatively dense seismic networks fill in the gaps between sparsely located infrasound arrays and provide valuable information for regional infrasonic source location and propagation studies specifically the catalogs presented here can be used to statistically validate and improve propagation models especially above the middle stratosphere where winds are not directly measured by ground based weather stations or meteorological satellites

exploration history and geology of the diamondiferous ultramafic saptarshi intrusions madhya pradesh india abstract the saptarshi field comprises a suite of at least eight known diamondiferous pipes and dykes within rio tinto s bunder project on the bundelkhand craton of madhya pradesh india the discovery made in 2004 followed regional scale area selection gravel sampling and subsequent ground geophysics soil geochemistry and prospecting the geology and petrography of the largest and most economically prospective pipe atri suggests that near the surface it forms a large vent comprised of two distinct lobes filled predominantly with primary pyroclastic rocks atri is composed of relict olivine phlogopite apatite minor spinel and ti oxides the rock is altered no primary olivine and little phlogopite remains instead much of the rock is now composed of serpentine chlorite carbonate other occurrences within the saptarshi field include small pipes and altered dykes atri is one example of the diverse assemblage of potassic rocks found on the indian subcontinent many parallels may be drawn with the nearby diamondiferous majhgawan pipe including mineral chemistry and petrography atri has many characteristics in common with olivine lamproite but many subtle deviations from type lamproite are observed we suggest that atri represents a local expression of potassic magmatism unique to the bundelkhand craton of india and is the product of partial melting of modally diverse veins in ancient metasomatized lithospheric mantle these rocks are not readily classified according to existing schemes devised for potassic rocks known from other petrological provinces a practical and workable scheme has not been devised that recognizes the unique characteristics of the diversity of lamproite like rocks the authors tentatively classify atri as a diamondiferous ultramafic intrusion with lamproitic affinities recognizing its obscured primary mineralogy its petrographic and textural characteristics and the important implications this classification has with respect to exploration the 1100 ma age of the saptarshi intrusions imply that they are part of a larger igneous province which includes the nearby majhgawan and hinota diamondiferous pipes this age temporally relates to the lamproites of western australia rio tinto completed an order of magnitude oom scoping study comprising large diameter and slim line delineation drilling and surface bulk sampling on the project in 2008

ferric iron in catio3 perovskite as an oxygen barometer for kimberlite magmas ii applications we apply an oxygen barometer based on the fe content of catio3 perovskite to estimate the oxygen fugacity fo2 during the crystallization and emplacement of kimberlites in different eruptive phases of a single pipe or between different pipes clusters or provinces mineral chemical data for perovskite were compiled from the literature and obtained in our detailed study of perovskites from 11 kimberlites at somerset island and lac de gras canada perovskite compositions in kimberlites record a range in fo2 of many orders of magnitude from nno 5 to nno 6 where log fo2 is given relative to the nickel nickel oxide nno buffer the range of fo2 recorded by different parageneses of perovskite within a single pipe can vary up to three orders of magnitude with trends toward both oxidation and reduction during crystallization kimberlites record some of the greatest ranges and the highest known fo2 conditions for any terrestrial magma this is attributed to the presence of deep and oxidized source regions and the variable interplay of ferric ferrous vs carbon fluid equilibria during ascent of kimberlite magmas three kimberlite pipes from the lac de gras field show that higher fo2 values correlate with higher proportions of more resorbed diamonds suggesting that this variable has a measurable effect on the physical properties of diamonds in a pipe

on the location of frequencies of maximum acoustic to seismic coupling measurements of the acoustic to seismic transfer function ratio of the normal soil particle velocity at a depth d to the acoustic pressure at the surface for outdoor ground surfaces quite typically reveal a series of maxima and minima in a publication sabatier et al j acoust soc am 80 646 649 1986 the location and magnitude of these maxima are measured and predicted for several outdoor ground surfaces using a layered poroelastic model of the ground surface in this paper the seismic transfer function for a desert site is compared to the seismic transfer function for holes dug in the desert floor which were filled with pumice volcanic rock the hole geometry was rectangular and the hole depths varied from 0 25 2 0 m the p and s wave speeds densities porosities and flow resistivities for the desert floor and pumice were all measured by varying the hole depth and the fill material the maxima in the seismic transfer function can be shifted in frequency and the locations of the maxima

size shape and dynamics of large scale turbulent flow structures in a gravel bed river in this paper we present a detailed investigation of the size scale and dynamics of macro turbulent flow structures in gravel bed rivers we used an array of seven electromagnetic current meters with high resolution in both space and time to measure the streamwise velocity fluctuations in a gravel bed river the array was deployed successively in various configurations in order to quantify the vertical lateral and longitudinal extent of the flow structures and to estimate their advecting velocities to depict the spatial and temporal properties of the flow structures we used space time velocity matrices space time correlation analysis and coherent structure detection schemes the results show that the large scale turbulent flow structures in a gravel bed river occupy the entire depth of the flow and that they are elongated and narrow the length of the structures is 3 to 5 times the flow depth while the width is between 0 5 and 1 times flow depth in spite of the high roughness of the bed these values are similar to those reported in the literature for laboratory experiments on large scale turbulent flow structures the dynamics of the large scale turbulent flow structures investigated using flow visualization highlight the interactions between the outer flow region and the near bed region our evidence suggests that large scale flow incursions trigger ejections in the near bed region that can develop into megabursts that can reach the water surface

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

neoarchean greenstone volcanism and continental growth dharwar craton southern india constraints from sims u pb zircon geochronology and nd isotopes abstract we present sims u pb zircon ages and nd isotope data for the felsic volcanic rocks from seven neoarchean greenstone belts of the eastern dharwar craton edc and from the chitradurga greenstone belt in the western dharwar craton wdc zircon ages show bimodal age distribution of felsic volcanism the ca 2 70 2 65 ga felsic volcanic event is contemporaneous with 2 7 ga mafic greenstone volcanism and emplacement of juvenile tonalitic to granodioritic crust while 2 58 2 54 ga felsic volcanics are coeval and spatially and probably genetically in some cases linked to the major episode calc alkaline magmatic accretion in the edc the chitradurga and veligallu greenstone belts host felsic volcanics of the first generation the latter showing inheritance at ca 2 95 ga four of the five greenstone belts hosting the second generation of felsic volcanics chitradurga kolar kadiri hutti show crustal inheritance at ca 2 6 2 7 2 9 3 0 3 1 and 3 3 ga ndt indicate derivation of the felsic volcanics from juvenile sources or short lived crustal sources with minor influence of older crust the new and existing data are consistent with two stage growth of the dharwar craton in the neoarchean first stage accretion led to the growth of a 2 7 2 6 ga juvenile crustal province of mafic volcanics and felsic plutons along the eastern margin of the wdc second stage accretion 2 58 2 52 ga led to the emplacement of ttg and calc alkaline plutons and felsic volcanics throughout the eastern dharwar craton an active margin context could apply for the two stage accretion scenario considering a west dipping subducting slab beneath the craton in the framework of long lived ultra hot accretionary orogen but the great width of influence of magmatic accretion and or reworking particularly during the second stage would suggest large scale mantle flow reorganization that would have generated large plume s

mineralogy of the tk1 and tk4 kimberlites in the timmasamudram cluster wajrakarur kimberlite field india implications for lamproite magmatism in a field of kimberlites and ultramafic lamprophyres abstract a mineralogical study of the hypabyssal facies late cretaceous macrocrystic pulse of tk1 intrusion and the mesoproterozoic aphanitic pulse of tk4 intrusion in the wajrakarur kimberlite field of southern india shows that the rocks contain macrocrysts of forsteritic olivine phenocrysts and microphenocrysts of al na poor diopside and phlogopite set in a groundmass mainly of al na poor diopside and phlogopite other groundmass minerals are spinel perovskite and fluorapatite in tk1 and spinel titanite chlorite calcite and gittinsite in tk4 k richterite and perovskite occur only as inclusions in phlogopite and titanite respectively in tk4 late stage deuteric phases include pyrite and barite in tk1 and strontianite chalcopyrite galena and pentlandite in tk4 diopside microphenocrysts in tk4 exhibit oscillatory zoning with characteristics of diffusion controlled magmatic growth tk1 spinels show magmatic trend 2 that evolves from magnesiochromite and culminates in titaniferous magnetite whereas tk4 spinels are less evolved with magnesiochromite composition only tk1 phlogopites show a simple compositional trend that is typical of lamproite micas while four distinct growth zones are observed in tk4 phlogopites with the following compositional characteristics zone i high cr 2 o 3 and tio 2 and low bao zone ii low cr 2 o 3 zone iii low tio 2 and high bao zone iv low bao forsterite contents and trace element concentrations reveal two xenocrystic core populations and one magmatic rim population for tk1 olivines mineralogically both tk1 and tk4 are classified as diopside phlogopite lamproites rather than archetypal kimberlites the two lamproites are considered to have formed from the same parent magma but crystallised under distinct oxygen fugacity conditions with elevated content of fe 3 in phlogopite spinel and perovskite tk1 appears to have crystallised in a relatively high oxygen fugacity environment multiple growth generations of phlogopite spinel and fluorapatite in tk4 indicate a complex evolutionary history of the magma close spatial and temporal associations of mesoproterozoic kimberlites and lamproites in southern india can possibly be explained by a unifying model which accounts for the generation of diverse magmas from a range of geochemical resevoirs in a continental rift setting

3d flow and sediment dynamics in a laboratory channel bend with and without stream barbs abstracta series of laboratory flume experiments were performed to study the effect of stream barbs on flow field dynamics and sediment erosion in a 135 mobile bed channel bend stream barbs also known as spur dikes or submerged groynes are low profile linear rock features that redirect high velocity flow away from the outer bank of channel bends unlike emergent groynes the submerged nature of these structures creates a unique combination of horizontal shear plunging type flow and vertical shear at the groyne tip spatially dense high frequency velocity data were collected and analyzed to describe the pattern and magnitude of three dimensional 3d velocity throughout the bend and in the vicinity of the stream barbs this paper demonstrates that the outer bank region particularly between barbs may still be at risk of erosion or even increased erosion greater than the same case without barbs if stream barbs generate excessive secondary velocities because of their size and layout that are op

the nature of the crust in southern india implications for precambrian crustal evolution 1 we present crustal thickness and poisson s ratio determinations from receiver function analyzes at 32 sites on the archaean and proterozoic terrains of south india the crustal thickness in the late archaean 2 5 ga eastern dharwar craton varies from 34 39 km similar crustal thickness is observed beneath the deccan volcanic province and the cuddapah basin the most unexpected result is the anomalous present day crustal thickness of 42 51 km beneath the mid archaean 3 4 3 0 ga segment of the western dharwar craton since the amphibolite grade metamorphic mineral assemblages 5 7 kbar paleopressures in this part of western dharwar craton equilibrated at the depths of 15 20 km our observations suggest the existence of an exceptionally thick 57 70 km crust 3 0 ga ago beneath the exhumed granulite terrain in southernmost india the crustal thickness varies between 42 60 km the poisson s ratio ranges between 0 24 0 28 beneath the precambrian terrains indicating the presence of intermediate rock type in the lower crust these observations of thickened crust suggest significant crustal shortening in south india during the archaean

oldest lamproites from peninsular india track the onset of paleoproterozoic plume induced rifting and the birth of large igneous province abstract potassic and ultrapotassic magmatism from deep lithospheric sources in intra cratonic settings can be the signal of subsequent voluminous mafic magmatism and the formation of large igneous provinces lips triggered by mantle plumes here we report for the first time precise zircon u pb age data from a suite of lamproites in the bastar craton of central india that mark the onset of paleoproterozoic rifting and culminating in the formation of extensive mafic dyke swarms as the bar codes of one of the major lip events during the precambrian evolution of the indian shield the lamproites from the nuapada field occur as dismembered dykes and are composed of phenocrysts and microphenocrysts of altered olivine together with microphenocrysts of phlogopite and magnetite within a groundmass of chlorite and calcite with accessory rutile apatite and zircon the rocks compositionally correspond to olivine phlogopite lamproite and phlogopite lamproite geochemical features of the lamproites correlate with their counterparts in peninsular india and other similar suites elsewhere in the world related to rift settings and also indicate oib like magma source the associated syenite shows subduction related features possibly generated in a post collisional setting magmatic zircon grains with high th u ratios in the syenite from the nuapada lamproite form a coherent group with an upper intercept age of 2473 8 ma representing the timing of emplacement of the magma zircon grains in three lamproite samples yield four distinct age groups at ca 2 4 ga 2 2 ga 2 0 ga and 0 8 ga the 2 4 ga group corresponds to xenocrysts entrained from the syenite whereas the 2 2 ga group is considered to represent the timing of emplacement of the lamproites the ca 2 0 ga zircon grains correlate with the major thermal imprint associated with mafic magmatism and dyke emplacement in southern bastar and the adjacent dharwar cratons a few young zircon grains in the syenite and lamproites show a range of early to middle neoproterozoic ages from 879 to 651 ma corresponding to younger thermal event s as also represented by granitic veins cutting across these rocks and extensive silicification zircon lu hf isotope data suggest magma derivation from a refertilized paleo mesoarchean sub continental lithospheric mantle or oib type sources the differences in hf isotope composition among the zircon grains from different age groups indicate that the mantle sources of the lamproite are heterogeneous at the regional scale a combination of the features from geochemical and zircon hf isotope data is consistent with asthenosphere lithosphere interaction during the lamproite magma evolution the timing of lamproite emplacement in central india correlates with the global 2 2 ga record of lips we link the origin of the related mantle plume to the recycling of subducted slabs associated with the prolonged subduction accretion history prior to the neoarchean cratonization as well as the thermal blanket effect of the earth s oldest supercontinent pulsating plumes and continued rifting generated voluminous dyke swarms across the bastar and dharwar cratons forming part of a major global rifting and lip event

k richterite olivine phlogopite diopside sanidine lamproites from the afyon volcanic province turkey middle miocene volcanic activity in the afyon volcanic province eastern part of western anatolia is characterized by multistage potassic and ultrapotassic alkaline volcanic successions the volcanism is generally related to the northward subduction of the african plate beneath the eurasian plate in afyon the middle miocene volcanic products consist of melilite leucitite tephriphonolite trachyte basaltic trachyandesite phonolite phonotephrite tephriphonolite and lamproite rocks near surface emplacement and relatively quiescent subaerial eruptions of lamproitic magma produced different emplacement forms such as dome plug shaped bodies and lava flows showing variation in volume and texture the mineralogical constituents of the lamproites are sanidine olivine 77 mg no 81 phlogopite 74 mg no 78 k richterite clinopyroxene 74 mg no 78 with accessory apatite calcite and opaque minerals afyon lamproites resemble mediterranean type si rich lamproites their compositional range is 50 52 wt sio2 4 8 wt mgo and they display a typical lamproitic affinity chondrite normalized ree patterns exhibit enrichment in lree relative to hree la yb cn 15 3 17 0 they show extreme enrichment in lile relative to primitive mantle values and troughs of nb and ti the lamproites give a range of high initial 87sr 86sr ratios and low 143nd 144nd ratios the geochemical and isotopic characteristics suggest that lamproitic magma is derived from highly metasomatized mantle the enrichment history may include metasomatic events related to subduction as in other active orogenic areas of the mediterranean

paleomagnetism and u pb geochronology of easterly trending dykes in the dharwar craton india feldspar clouding radiating dyke swarms and the position of india at 2 37 ga abstract a u pb baddeleyite age of 2367 1 ma from a diabase dyke together with previously published age data suggests that a major early proterozoic dyke swarm cuts across the structural grain of the archean dharwar craton in india paleomagnetic data suggest the swarm is at least 300 km wide and 300 km long and has a fan angle of at least 30 with convergence to the west it was originally emplaced at high latitudes and together with the widgiemooltha dykes of the yilgarn block of australia may have been a segment of a larger radiating swarm related to a long lived plume event that was active for about 50 my from 2418 to 2367 ma a regional change in the intensity of brown feldspar clouding in the dykes suggests that the dharwar craton was tilted northwards in harmony with previous observations on the structure and metamorphism of the archean rocks towards the south the brown feldspar clouding becomes more intense and locally assumes a blacker more sooty appearance the black clouding whose precise origins remain unknown is accompanied by a remagnetization and appears to coincide closely with a region of carbonatite magmatism at 800 ma and with a shear zone and change in structural trend related to pan african deformation at 550 ma paleomagnetic studies suggest that i the high coercivity part of the remanent magnetization is carried by magnetite exsolved within either brown or black clouded feldspars and ii as a more general observation diabase with brown clouded feldspar can carry a primary magnetization but not if the clouding is black

acoustically induced seismic waves when an airborne acoustic wave is incident at the ground surface energy is coupled into the ground as seismic motion in a previous publication sabatier et al j acoust soc am 78 1345 1352 1986 the ground surface was modeled as an air filled poroelastic layer overlying a semi infinite nonporous elastic substrate in this work the model is extended to include calculations of the normal seismic transfer function ratio of the normal soil particle velocity at a depth d to the acoustic pressure at the surface measurements of the seismic transfer function for three sites are considered and compared to the predicted values generally good agreement between theory and experiment is achieved by best fits assuming the soil or seismic attenuation this is accomplished by specifying the ratio of the imaginary to real part of the measured seismic p and s wave speeds the seismic transfer functions quite typically exhibit minima and maxima which are associated with the seismic layering of the ground su

the time frequency characteristics of quarry blasts and calibration explosions recorded in kazakhstan ussr summary in this paper we consider two fundamentally different processes that can be responsible for the organization of energy in seismic coda into discrete time independent frequency bands one process involves the resonance of energy in low velocity horizons and the other requires the interaction of time offset wavefields produced by subevents within multiple event mine explosions ripple fired quarry blasts we examined data collected by high frequency seismometers in kazakhstan ussr and observed regular time independent spectral modulations in coda resulting from events strongly suspected to be soviet quarry blasts but not in the coda from single event calibration explosions detonated at similar ranges we conclude these modulations are a source effect and due to ripple firing this modulation is independent of the source receiver azimuth and we infer that the spatial array of subshots in each event must be small we demonstrate that simple linear superposition theory can be used to reproduce effectively the spectral modulation observed in real quarry blasts on the basis of these observations we attempt to discriminate between the two types of events using a spectral pattern based algorithm that seeks time independent features we consider the detrimental effect that resonant energy in low velocity horizons can have on the successful application of our algorithm

turbulence and vorticity in a laboratory channel bend at equilibrium clear water scour with and without stream barbs abstractlaboratory flume experiments were conducted to study the flow field and sediment dynamics in a mobile bed channel bend with and without the presence of stream barbs upstream angled submerged groynes this paper presents spatial distributions of the vorticity field and the turbulent reynolds shear stresses kinetic energy and integral scales the objectives of the present paper were to 1 advance understanding of the role that vorticity and turbulence play in the erosion process in channel bends with and without barbs and 2 optimize barb design for reducing erosion along the outer bank regions of channel bends through consideration of flow field turbulence and vorticity results indicate that 1 increased z vorticity occurred in the outer bank scour zone for all runs with and without barbs 2 for the runs without barbs and with moderately sized barbs increased streamwise cross stream reynolds stress uv was found to coincide with locations of scour and 3 for the run with large barbs

local scour at vertical wall abutments under clear water flow conditions 1 new clear water tests on abutment scour are presented thirty one tests with sand bed and nine tests with lightweight pumice bed were carried out in a 28 m long 4 m wide flume tests typically lasted for 1 week or more vertical wall abutments with length to depth l d ratios from 9 up to 36 were used other test campaigns in the literature are added to the data focusing on abutments with 2 l d 100 the critical flow for scour inception at the abutment nose is found to decrease as l d increases the whole data are analyzed for searching the equilibrium scour depths with different methods the slope change in the plot of scour depth against the logarithm of time is the method selected for the group of tests run close to the threshold condition some trends regarding the dimensionless equilibrium scour depth are 1 dependence on the bed material specific gravity in the sense that pumice tests produce less scour and 2 increase of the scour depth as l d increases finally the morphology of the scour area in terms of volume and plan dimensions is given by new regression equations

crystallization of groundmass spinel in kimberlite groundmass spinel grains in 46 kimberlite and related rocks have been analyzed and compared the majority of the spinel analyses are classified as high chromium chromite chr and magnesioulvo spinel magnetite mum and represent two significant stages of spinel growth there are also a significant number of spinel grains that are classified as xenocryst spinel xen pleonaste spinel ple and magnetite mag eight different spinel zoning trends are identified the majority of the chr spinel grains are interpreted as a primary phase that crystallized as small octahedra from kimberlite magma on the journey from the upper mantle to the final resting place in the upper crust three zoning trends lead directly away from primary chromite the major zoning trend trend 1 is from chromite to magnesio ulvo spinel magnetite this zoning trend is unique to spinel in kimberlite carbonatites and lamprophyres we suggest that this somewhat oxidizing and more magnesian trend was influenced by the high carbonate content of group i kimberlites and the rapid crystallization of the minerals during the evolution of volatiles the zoningtrend 2 involves increasing titanium and ferric iron as a function of increasing fe 2 fe 2 mg this trend is similar to the zoning of spinel in basalt and is thought to be due to co crystallization of magnesium and aluminum rich silicate minerals such as olivine and phlogopite in kimberlites or pyroxene and plagioclase in basalt zoning trend 3 in kimberlite leads away from primary chromite and towards an aluminous pleonaste ple spinel this trend is characterized by a large decease of cr cr al parallel to so called olivine spinel iso potential lines similar trends of lesser magnitude and cyclic al cr zoning have been identified in basaltic spinel this trend is thought to be due to very rapid crystallization under conditions of supersaturation where the crystallization of spinel affects the local environment ahead of the growing spinel crystal i e diffusion controlled crystallization the tendency for immiscibility between ferrite or titanate rich spinel and aluminate rich spinel pleonaste has a great influence on trends 1 and 3 zoning and also on atoll spinel formation very local conditions such as nucleation or lack of nucleation of other minerals can influence both the textural environment and composition of kimberlitic spinel