does flow variance affect bedload flux when the bed is dominated by grain roughness abstract previous studies have shown that spatial variance in fluid and critical shear stress caused by form roughness can increase bedload flux others have revealed that variance in flow velocity increases with relative submergence and that bed mobility is reduced at lower submergences the paper explores the link between these observations and addresses the following questions is grain roughness sufficient to cause variance in fluid shear stress and an increase in bedload flux if this variance changes with submergence does this mean that the increase is dependent on submergence and does this explain the change in mobility with submergence a simple statistical bedload model based on spatial distributions of fluid and critical shear stress has been used to explore these effects over a water worked gravel deposit estimates of spatially distributed fluid shear stress were gained from laboratory flume measurements of near bed flow velocity and a distribution of critical shear stress was simulated using a discrete particle model of the sediment distribution used in the flume the velocity data were used to describe the change in the spatial distribution of near bed velocity with relative submergence which allowed the effects of submergence on flux to also be considered the main conclusions were i spatial variance in fluid shear stress from grain roughness was not sufficient to have an appreciable effect on bedload flux over water worked gravel beds with a spatial distribution of critical shear stress ii spatial variance in critical shear stress caused by grain roughness had a much larger influence and increased bedload flux this was a similar level of increase observed in studies for conditions where form roughness was high iii spatially averaged estimates of fluid and critical shear stress should not be used to estimate bedload flux even if form roughness is low and iv a rise in relative submergence increased bedload flux this was due to changes in the spatial distribution of near bed velocity and not due to a lowering in the local flow velocity as has been suggested by previous studies

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

chemical signature of quartz from s and a type rare metal granites a summary abstract about 800 new and 1200 already published laser ablation inductively coupled plasma mass spectrometry analyses of quartz from rare metal granites and related greisens quartz tourmaline rocks and quartz veins were evaluated in order to define typical trace element signatures of quartz of different origin the studied dataset comprises typical examples of sub aluminous to slightly peraluminous plutons a type granites of the kimi stock finland eastern erzgebirge czech republic orlovka russia and ongon chairchan mongolia and strongly peraluminous plutons s type granites of beauvoir france cornwall england panasqueira and argemela portugal western erzgebirge czech republic additional 700 mostly already published analyses of quartz from barren granites of all geochemical types i s a type rhyolites and barren and rare element pegmatites were evaluated for comparison compiled data reveal high diversity in the contents of trace elements in quartz even among rocks of similar geochemical composition the most common trace elements in magmatic quartz are al li and ti with medians of 447 39 6 and 17 4 ppm in s type rare metal granites and 160 15 and 6 6 ppm in a type rare metal granites the contents of all these elements in greisens and quartz veins are significantly lower than in their parental granites al contents above 450 ppm should serve as a reliable indicator of s affinity of the analyzed granite while contents

insights from quartz cathodoluminescence zoning into crystallization of the vinalhaven granite coastal maine the vinalhaven intrusive complex provides field and petrographic evidence for multiple replenishments of mafic and silicic magmas mingling and limited mixing and rejuvenation of granite quartz in granitic rocks preserves a record of those processes in the form of cathodoluminescence cl zoning which is related to concentration of titanium and to temperature of crystallization using the new titaniq ti in quartz geothermometer injection of mafic melts into partly crystalline vinalhaven granite resulted in partial quartz resorption followed by higher temperature growth from h2o undersaturated melt this is shown by steep rimward increases in cl intensity and ti content across discordant boundaries that truncate older growth zones quartz zoning in granite affected by mafic magmas displays large rimward jumps in ti content whereas quartz in granitic feeders and in granite far from mafic rocks typically displays broad rims with decreasing ti contents consistent with slow cooling without thermal disruptions due to mafic recharge

lithofacies architecture composition and age of the carboniferous teplice rhyolite german czech border insights into the evolution of the altenberg teplice caldera abstract the teplice rhyolite tr intra caldera deposits of the altenberg teplice caldera atc central europe were investigated by lithofacies analysis stratigraphy and whole rock chemistry as well as laser ablation u pb zircon dating the aim was to demonstrate that the joint application of these methods can discern complex stratigraphy of ancient volcanic successions susceptible to erosion and alteration taking the tr as case study the tr was regarded as a formation and divided into nine members that represent three main eruptions each one separated by periods of volcanic quiescence the first two eruptions mainly portrayed opening and clearing of vents which were dominated by lithic rich ignimbrites with lateral lithofacies changes fiamme rich to crystal rich covered by lava flows domes eruption style was low pyroclastic fountaining alternated with effusive lava outpour a sustained buoyant eruption column was exclusively interpreted at the outset of the second eruption based on the presence of a basal fallout deposit the third eruption recorded three different phases further vent opening a waxing phase and final lava extrusion the vent opening phase was similar to those occurred in previous eruptions the waxing phase produced voluminous massive poorly sorted very crystal rich 50 vol ignimbrites exhibiting progressive increase in crystal contents with height and chemical composition variations that indicate deposition by progressive aggradation low pyroclastic fountaining formed these high particle concentration currents that waxed and reached quasi steady conditions eruption ended with extrusion of a lava flow the tr ignimbrites were emplaced hot and were partially to densely welded as evidenced by eutaxitic texture deformed glass shards spherulites perlitic cracks and microcrystalline to granophyric textures horizontal and vertical lithofacies variations in pyroclastic deposits together with progressive infill and association between tr feeding systems and faulting demonstrate that eruptions developed through several fissure vents or faults a volcanic explosivity index of 7 was estimated according to a minimum ejecta volume of 320 km3 dre volcanic architecture of the tr can be linked to sequential caldera subsidence that occurred synchronously with progressive deposition regional faulting ne sw trending rhyolitic dykes related to atc feeding conduits suggests that progressive subsidence and final trap door caldera collapse possibly with a piece meal component faulted caldera floor originated from post variscan tensional stress regime nnw sse direction the tr formation has a general rhyolitic composition with a type granite affinities and a normal chemical zoning u pb zircon dating yielded ages from 323 to 312 ma which compared to age data from other atc rocks indicate that the tr was generated within a time span of 325 317 ma

processes of initiation of motion leading to bedload transport in gravel bed rivers 1 transport processes that lead to the initiation of bedload motion in gravel bed rivers have not yet been clarified we report patch and grain scale processes involved in the initiation of bedload motion in a natural gravel bed stream as observed through a series of video experiments with increasing flow strength the phases of initiation of motion that have been identified are 1 within patch grain instability grain vibration pivoting and grain scale rolling 2 within patch gyratory step and rest motion and 3 general sediment motion involving downstream transport from an individual patch and the throughput of grains inherited from upstream

spatially averaged open channel flow over rough bed in this paper it is suggested that the double averaged in temporal and in spatial domains momentum equations should be used as a natural basis for the hydraulics of rough bed open channel flows especially with small relative submergence the relationships for the vertical distribution of the total stress for the simplest case of 2d steady uniform spatially averaged flow over a rough bed with flat free surface are derived these relationships explicitly include the form induced stresses and form drag as components of the total stress using this approach we define three types of rough bed flows 1 flow with high relative submergence 2 flow with small relative submergence and 3 flow over a partially inundated rough bed the relationships for the double averaged velocity distribution and hydraulic resistance for all three flow types are derived and compared with measurements where possible the double averaged turbulent and form induced intensities and stresses for the case of regular spherical segment type roughness show the dominant role of the double averaged turbulence stresses and form drag in momentum transfer in the near bed region

the variability of critical shear stress friction angle and grain protrusion in water worked sediments the erodibility of a grain on a rough bed is controlled by among other factors its relative projection above the mean bed its exposure relative to upstream grains and its friction angle here we report direct measurements of friction angles grain projection and exposure and small scale topographic structure on a variety of water worked mixed grain sediment surfaces using a simple analytical model of the force balance on individual grains we calculate the distribution of critical shear stress for idealized spherical grains on the measured bed topography the friction angle projection and exposure of single grain sizes vary widely from point to point within a given bed surface the variability within a single surface often exceeds the difference between the mean values of disparate surfaces as a result the critical shear stress for a given grain size on a sediment surface is characterized by a probability distribution rather than a single value on a given bed the crtitical shear stress distributions of different grain sizes have similar lower bounds but above their lower tails they diverge rapidly with smaller grains having substantially higher median critical shear stresses large numbers of fines trapp ed within pockets on the bed or shielded by upstream grains are effectively lost to the flow our calculations suggest that critical shear stress as conventionally measured is defined by the most erodible grains entrained during transient shear stress excursions associated with the turbulent flow this implies a physical basis for the indeterminacy of initial motion these observations suggest that transport rate shear stress relationships may be controlled in part by the increasing numbers of grains that become available for entrainment as mean shear stress increases they also suggest that bed textures and grain size distributions may be controlled within the constraints of an imposed shear stress and sediment supply regime by the influence of each size fraction on the erodibility of other grain sizes present on the bed

evolution from magmatic to hydrothermal activity beneath the cerro escorial volcano nw argentina as sampled by erupted quartz and brines abstract large quartz pebbles erupted with the escorial ignimbrite provide insight into the late magmatic evolution of the shallow cooling magmatic hydrothermal system below the cerro escorial volcano of the southern central volcanic zone in the argentine andes the ignimbrite is of relatively small volume crystal rich dacitic in composition and not particularly water rich as amphibole is absent eruption temperature was estimated to be close to 850 c the quartz pebbles provide insight into the magmatic hydrothermal transition beneath the volcano based on textures trace element composition analyzed by laser ablation inductively coupled plasma mass spectrometry and inclusion content the pebbles can be separated into pegmatite like megacrysts and lower temperature epithermal microcrystalline quartz both types are distinct from magmatic phenocrysts present in porphyritic clasts ejected by the ignimbrite the megacrysts show a wide range of trace element concentrations with elevated al concentrations and al ti and ge ti ratios compared to quartz phenocrysts although some contamination by submicroscopic inclusions and cooling to near solidus temperatures may perturb the signal in some cases the range of trace element concentrations in quartz crystals from this system may reflect a change in crystallization conditions from initial precipitation from typical evolved silicate melt to fast growth from residual melt and or fluid in pegmatitic pockets or coarse grained hydrothermal veins at locally variable precipitation conditions abundant primary and secondary silicate melt inclusions and a variety of secondary fluid inclusions are present within the megacrysts in particular brine inclusions are densely packed with salt crystals sometimes anhydrite and or a silicate crystal but no visible liquid at room temperature and co existing vapor inclusions are of very low density heating experiments of brine inclusions reveal last salt and vapor bubble dissolution temperatures around 600 700 c but an immiscible silicate melt surrounding the homogenized salt globule remains even at unreasonably high temperature the co existence of silicate melt and fluid inclusions reinforces the magmatic nature of the fluids while boiling trails of brine with cu concentrations of several percent and vapor point to relatively low pressures

present day deformation of the qaidam basin with implications for intra continental tectonics abstract the qaidam basin is a plateau of low relief about 3 km in elevation and covering a large area of 1 2 105 km2 physiographically the basin marks a transitional region between the northeastern tibetan plateau 5 0 5 km in elevation and the surrounding low lying areas the northeastern and southwestern edges of the basin are bounded by the qilian shan nan shan and qimantag eastern kunlun shan mountain belts respectively at present the entire region is under northeast southwest compression based on a synthesis of recent geological and geophysical results we propose that each flanking mountain belt consists of a sequence of crustal nappes originating from ramp thrusts at mid crustal levels 15 km deep over a distance range of 700 km these two broad fold and thrust belts operating in tandem and with some uniform shortening in the intervening qaidam basin successively raised the surface elevation from below 2 km to 5 km at depth the crust is correspondingly thickened from 40 km beneath the foreland of the qilian shan to approximately 55 km under the interior of the qaidam basin and then to nearly 70 km beneath tibet in contrast to the himalayan front where earthquake faulting occurs down to a depth of 50 km in the foreland but the zone of active thrust faulting is less than 200 km in width plateau building in the qaidam region illustrates how a wide orogen is developing along northeastern tibet in the interior of eurasia

effects of a pebble cluster on the turbulent structure of a depth limited flow in a gravel bed river pebble clusters are important morphological features of gravel bed rivers and have a significant effect on the spatial and temporal response of the flow this paper presents original results from measurements of velocity taken at a high spatial and temporal resolution in a turbulent flow upstream and downstream from a pebble cluster three electromagnetic current meters 0 013 m in diameter mounted on a wading rod were deployed upstream and downstream of an isolated pebble cluster along 31 vertical profiles that contained between 7 and 13 points in a 5 m long section the high sampling resolutions in a natural environment permitted characterization of the complex dynamics of the turbulent flow in the vicinity of the cluster the description of these dynamics is based on the interpretation of contour maps of several turbulence statistics including moments of velocity distributions reynolds shear stress quadrant analysis and autocorrelation function downstream from the cluster flow is decelerated the intensity of turbulence increases and zones of strong vertical motions are present the superimposition of the maps allowed us to decompose the field of turbulent flow around a pebble cluster into distinct regions in a downstream direction from the cluster we observed zones of flow acceleration recirculation vortex shedding flow reattachment fluid upwelling and flow recovering results indicate the existence of highly dynamic boundaries between zones where strong intermittent events are generated they also highlight the difference between shedding and upwelling motions of the flow

delineation of gravel bed clusters via factorial kriging abstract gravel bed clusters are the most prevalent microforms that affect local flows and sediment transport a growing consensus is that the practice of cluster delineation should be based primarily on bed topography rather than grain sizes here we present a novel approach for cluster delineation using patch scale high resolution digital elevation models dems we use a geostatistical interpolation method i e factorial kriging to decompose the short and long range grain and microform scale dems the required parameters are determined directly from the scales of the nested variograms the short range dem exhibits a flat bed topography yet individual grains are sharply outlined making the short range dem a useful aid for grain segmentation the long range dem exhibits a smoother topography than the original full dem yet groupings of particles emerge as small scale bedforms making the contour percentile levels of the long range dem a useful tool for cluster identification individual clusters are delineated using the segmented grains and identified clusters via a range of contour percentile levels our results reveal that the density and total area of delineated clusters decrease with increasing contour percentile level while the mean grain size of clusters and average size of anchor clast i e the largest particle in a cluster increase with the contour percentile level these results support the interpretation that larger particles group as clusters and protrude higher above the bed than other smaller grains a striking feature of the delineated clusters is that anchor clasts are invariably greater than the d90 of the grain sizes even though a threshold anchor size was not adopted herein the average areal fractal dimensions hausdorff besicovich dimensions of the projected areas of individual clusters however demonstrate that clusters delineated with different contour percentile levels exhibit similar planform morphologies comparisons with a compilation of existing field data show consistency with the cluster properties documented in a wide variety of settings this study thus points toward a promising alternative dem based approach to characterizing sediment structures in gravel bed rivers

role of near bed turbulence structure in bed load transport and bed form mechanics the interactions between turbulence events and sediment motions during bed load transport were studied by means of laser doppler velocimetry and high speed cinematography sweeps u 0 w 0 w 0 which contribute negatively to the bed shear stress and are relatively rare individually move as much sediment as sweeps of comparable magnitude and duration however and much more than bursts u 0 and inward interactions u 0 w 0 when the magnitude of the outward interactions increases relative to the other events therefore the sediment flux increases even though the bed shear stress decreases thus although bed shear stress can be used to estimate bed load transport by flows with well developed boundary layers in which the flow is steady and uniform and the turbulence statistics all scale with the shear velocity it is not accurate for flows with developing boundary layers such as those over sufficiently nonuniform topography or roughness in which significant spatial variations in the magnitudes and durations of the sweeps bursts outward interactions and inward interactions occur these variations produce significant peaks in bed load transport downstream of separation points thus supporting the hypothesis that flow separation plays a significant role in the development of bed forms

extreme fractionation in a granite pegmatite system documented by quartz chemistry the case study of tres arroyos central iberian zone spain abstract the tres arroyos granite pegmatite system is located in the sw margin of the nisa alburquerque variscan batholith two granitic facies monzogranite and marginal leucogranite and three types of aplite pegmatite dykes barren intermediate and highly evolved li rich have been distinguished in the area with a zoned distribution from the granite southwards trace elements in quartz from the five facies have been analysed by la icp ms in order to obtain information about the petrogenetic links among the different lithologies of this system as well as to better understand the regional and individual fractionation processes that led to the distinct rocks aluminium ti li and ge show continuous trends from the monzogranite through the marginal granitic facies the barren and intermediate aplite pegmatites up to the most evolved li rich dykes titanium and ge contents respectively decrease and increase gradually with fractionation in contrast al and li show a more complex trend with an initial descending trend to the marginal granitic facies and then showing the highest al and li contents in the quartz from the most fractionated li rich aplite pegmatites this suggests the influence of different competing factors controlling the incorporation of these trace elements in quartz such as the chemical composition of the melt the p and t conditions and the rate of crystallization based on the good correlation between al and li the substitution si4 al3 li seems to be the dominant mechanism of li incorporation into quartz the negligible amount of other trace elements suggests that the remaining al was mainly compensated with h ions via the si4 al3 h substitution a continuous fractionation trend from the monzogranite up to the most fractionated aplite pegmatites is inferred from geochemical modelling by applying the rayleigh equation for fractional crystallization fractionation rates over 50 are needed to obtain the marginal granite and the barren aplite pegmatites compositions and over 99 for the most evolved dykes no pattern in the chemical variation of the trace elements in quartz from different layers in the layered aplite pegmatites has been found suggesting the lack of internal fractionation processes most probably due to the rapid crystallization of the pegmatitic melt intruded into a colder country rock

quartz and feldspar zoning in the eastern erzgebirge volcano plutonic complex germany czech republic evidence of multiple magma mixing abstract zoned quartz and feldspar phenocrysts of the upper carboniferous eastern erzgebirge volcano plutonic complex were studied by cathodoluminescence and minor and trace element profiling the results verify the suitability of quartz and feldspar phenocrysts as recorders of differentiation trends magma mixing and recharge events and suggest that much heterogeneity in plutonic systems may be overlooked on a whole rock scale multiple resorption surfaces and zones element concentration steps in zoned quartz ti and feldspar phenocrysts anorthite content ba sr and plagioclase mantled k feldspars etc indicate mixing of silicic magma with a more mafic magma for several magmatic phases of the eastern erzgebirge volcano plutonic complex generally feldspar appears to be sensitive to the physicochemical changes of the melt whereas quartz phenocrysts are more stable and can survive a longer period of evolution and final effusion of silicic magmas the regional distribution of mixing compatible textures suggests that magma mingling and mixing was a major process in the evolution of these late variscan granites and associated volcanic rocks quartz phenocrysts from 14 magmatic phases of the eastern erzgebirge volcano plutonic complex provide information on the relative timing of different mixing processes storage and recharge allowing a model for the distribution of magma reservoirs in space and time at least two levels of magma storage are envisioned deep reservoirs between 24 and 17 km the crystallisation level of quartz phenocrysts and subvolcanic reservoirs between 13 and 6 km deflation of the shallow reservoirs during the extrusion of the teplice rhyolites triggered the formation of the altenberg teplice caldera above the eastern erzgebirge volcano plutonic complex the deep magma reservoir of the teplice rhyolite also has a genetic relationship to the younger mineralised a type granites as indicated by quartz phenocryst populations the pre caldera biotite granites and the rhyodacitic schonfeld volcanic rocks represent temporally and spatially separate magma sources however the deep magma reservoir of both is assumed to have been at a depth of 24 17 km the drastic chemical contrast between the pre caldera schonfeld westfalian b c and the syn caldera teplice westfalian c d volcanic rocks is related to the change from late orogenic geotectonic environment to post orogenic faulting and is considered an important chronostratigraphic marker

effects of turbulence on the transport of individual particles as bedload in a gravel bed river this study investigates the association between mean and turbulent flow variables and the movement of individual particles in a gravel bed river the experimental design implemented in the eaton north river quebec canada is based on the simultaneous observations at a high temporal resolution of both particle movements as bedload using an underwater video camera and of the streamwise and vertical flow velocity components using a vertical array of three electromagnetic current meters ecms the frequency and distance of displacement of particles larger than 20 mm that were sliding or rolling on the bed were measured from a 10 minutes long film mean and turbulent flow properties obtained for periods without sediment transport are compared to those when particles were sliding and rolling when particles are sliding weak differences are present for the mean streamwise velocity and normal vertical stresses instantaneous reynolds shear stresses are significantly lower for sliding events which was not expected but could be explained by the important dominance of quadrant 3 events inward interactions when particles are rolling only the vertical normal stresses show a weak difference from those observed in the absence of transport but they tend to occur when quadrant 2 ejections dominate the flow field for both sliding and rolling particles vertical and or streamwise fluid accelerations show high magnitude values when compared to periods without transport for sliding particles streamwise acceleration is mostly negative and combines most of the time with a positive vertical acceleration for rolling particles streamwise and vertical acceleration are predominantly of opposite sign these results suggest that fluid acceleration or deceleration in the streamwise and vertical directions is affecting the pressure field around particles in this study fluid acceleration seems to play a more important role than reynolds shear stress or normal stresses for bedload movements copyright 2010 john wiley sons ltd

genetic significance of the trace element content in metamorphic and hydrothermal quartz a reconnaissance study abstract a reconnaissance study on trace elements in metamorphic and hydrothermal quartz was carried out using quartz samples from the tin district erzgebirge germany the gold mineralization at kasperske hory czech republic and the gold quartz vein deposits muruntau and myutenbai uzbekistan a new method of sample preparation has been developed to prepare pure quartz samples by combining conventional hand picking with microscopic and spectroscopic studies as well as acid wash etch procedures preparation of monomineralic samples was followed by sample dissolution and measurement by icp ms the metamorphic quartz has very low concentrations of li 0 4 ppm al 30 ppm k 35 ppm rb 50 ppb sr 0 3 ppm and y 15 ppb moreover it is characterized by light rare earth element enriched lanthanide distribution patterns lacking eu anomalies the low element concentrations in metamorphic quartz are interpreted to result from recrystallization metamorphic quartz from alteration halos enveloping tin and gold deposits has distinctly different trace element signatures these differences are related to the hydrothermal overprint of the pre existing metamorphic quartz by the mineralizing fluids hydrothermally altered metamorphic quartz from tin deposits has elevated concentrations of li 0 9 ppm al 50 ppm k 45 ppm rb 250 ppb and y 40 ppb whereas altered metamorphic quartz from gold deposits is characterized by elevated concentrations of sr 0 5 ppm the rare earth element distribution patterns of altered metamorphic quartz show variable enrichments of the heavy rare earth elements and frequently display positive eu anomalies hydrothermal vein quartz from the gold deposits usually has elevated al 50 ppm and sr 0 6 ppm contents the lanthanide distribution patterns exhibit variable enrichments of the heavy rare earth elements and commonly show positive eu anomalies the elevated sr concentrations in the quartz from gold deposits are best explained by sr release during feldspar alteration in the wall rocks this mechanism may also account for the relative enrichment of eu in the mineralizing fluids although other processes may not be unambiguously ruled out

neogene extension and volcanism in the kunlun fault zone northern tibet new constraints on the age of the kunlun fault 1 the geology of the jingyu basin north tibet provides constraints on the relationship between localized e w extension in the qiangtang block and strike slip motion along the kunlun fault eocene to oligocene sw ne compression formed topographic relief in the present western kunlun shan pull apart basins started forming in the western kunlun ranges around 15 ma possibly coincident with the initiation of subduction of the tarim qaidam lithosphere under the kunlun shan extensional tectonism is still active and the jingyu basin is extending as a normal fault connected with the kunlun fault was recently active localized extension allows tertiary and quaternary shoshonitic magmas to reach the surface from crustal depths of 50 to 60 km miocene strike slip faulting indicates that the initiation of the kunlun strike slip fault is early neogene in age and that the total amount of horizontal movement that occurred along the fault has to be reconsidered

sensitivity of interfacial hydraulics to the microtopographic roughness of water lain gravels flow within the interfacial layer of gravel bed rivers is poorly understood but this zone is important because the hydraulics here transport sediment generate flow structures and interact with benthic organisms we hypothesized that different gravel bed microtopographies generate measurable differences in hydraulic characteristics within the interfacial layer this was tested using a high density of spatially and vertically distributed velocity time series measured in the interfacial layers above three surfaces of contrasting microtopography these surfaces had natural water worked textures captured in the field using a casting procedure analysis was repeated for three discharges with reynolds numbers between 165000 and 287000 to evaluate whether discharge affected the impact of microtopography on interfacial flows relative submergence varied over a small range 3 5 to 8 1 characteristic of upland gravel bed rivers between surface differences in the median and variance of several time averaged and turbulent flow parameters were tested using non parametric statistics across all discharges microtopographic differences did not affect spatially averaged median values of streamwise velocity but were associated with significant differences in its spatial variance and did affect spatially averaged median turbulent kinetic energy sweep and ejection events dominated the interfacial region above all surfaces at all flows but there was a microtopographic effect with q2 and q4 events less dominant and structures less persistent above the surface with the widest relief distribution especially at the highest reynolds number flow results are broadly consistent with earlier work although this analysis is unique because of the focus on interfacial hydraulics spatially averaged patch scale metrics and a statistical approach to data analysis an important implication is that observable differences in microtopography do not necessarily produce differences in interfacial hydraulics an important observation is that appropriate roughness parameterizations for gravel bed rivers remain elusive partly because the relative contributions to flow resistance of different aspects of bed microtopography are poorly constrained 2014 the authors earth surface processes and landforms published by john wiley sons ltd

new insights into the hydrothermal evolution of skarn deposits a case study of the dongzhongla pb zn deposit in tibet sw china abstract revealing hydrothermal evolution from the early quartz sulfide to the late fluorite carbonate sulfide stages of skarn sulfide deposits is significant for understanding their ore formation processes but the detailed studies are rare in this study we choose the dongzhongla skarn pb zn deposit 0 38 mt pb zn located in central lhasa tibet as a case study and present detailed ore deposit geology and dataset of in situ chemical compositions of quartz in situ pb isotopic ratios of galena sulfur isotopic compositions of sulfides and c o isotopic compositions of hydrothermal calcite and wall rocks to address this issue there are two types of hydrothermal quartz in the early stage 1 the early phase euhedral quartz qz1 crosscut by quartz sulfide veins and 2 the late phase subhedral quartz qz2 coexisting with sulfides titaniq thermometer of qz1 and qz2 limits the two phases with a temperature range of 336 427 c mean 373 c and 357 461 c mean 386 c respectively the decreasing al concentrations of qz1 from core to rim suggest that magmatic fluids mixed with acidic meteoric water prevented the precipitation of sulfides during the early phase the increasing al and decreasing sulfur concentrations of qz2 indicate that the increasing ph values of hydrothermal fluids made principal sulfides precipitate during the late phase in addition fluid inclusions and c o isotopic studies reveal that the late stage minerals were deposited from low salinity

distribution and petrogenetic behaviour of trace elements in granitic pegmatite quartz from south norway the present study documents that the trace element distribution in granitic quartz is highly sensitive to cafc processes in granitic melts igneous quartz efficiently records both the origin and the evolution of the granitic pegmatites aluminium p li ti ge and na in that order of abundance comprises 95 of the trace elements most samples feature 1 ppm of any of these elements the remnant 5 includes k fe be b ba and sr whereas the other elements are present at concentrations lower than the detection limit potassium fe be and ti are relatively compatible hence obtain the highest concentrations in early formed quartz phosphorous ge li and al are relatively incompatible and generally obtain the highest concentrations in quartz that formed at lower temperatures from more evolved granitic melts the ge ti the ge be the p ge and the p be ratios of quartz are strongly sensitive to the origin and evolution of the granitic melts and similarly the rb sr and the rb k ratios of k feldspars may be utilised in petrogenetic interpretations however the quartz trace element ratios are better at distinguishing similarities and differences in the origin and evolution of granitic melts after evaluating the different trace element ratios the ge ti ratio appears to be most robust during subsolidus processes in the igneous systems hence probably should be the preferred ratio for analysing and understanding petrogenetic processes in granitic igneous rocks

the spatial characterization of turbulence around large roughness elements in a gravel bed river abstract this study characterizes the flow field above and around multiple instream submerged cobbles boulders and pebble clusters in order to obtain a better understanding of the hydrodynamics associated with large roughness elements lres in gravel bed rivers spatially distributed high frequency three dimensional velocity measurements were recorded in situ using acoustic doppler velocimeters at different flow stages the spatial distributions of turbulent kinetic energy ke longitudinal component integral timescales itsu and reynolds shear stresses were characterized and are presented for selected sites the longitudinal vertical reynolds shear stress increased with flow stage more strongly than the longitudinal lateral or lateral vertical reynolds shear stresses and dominate at the highest measured flows canonical redundancy analysis was used to relate lre morphometrics and mean flow conditions to the turbulence parameters estimated in the lre wakes i e ke itsu and reynolds shear stresses lre size and mean unobstructed velocity explained the highest proportion of the variance in the turbulent wake statistics multivariate regression models based on lre width mean unobstructed longitudinal velocity and flow depth are presented offering a tool to predict lre wake turbulence

transpressional salt tectonic system in western qaidam basin western china in this paper high resolution three dimensional seismic data are used to interpret a transpressional salt tectonic structure in the yingxiongling area qaidam basin china the geometries of the salt structure and the shizigou fault system that intersects it are precisely depicted the shizigou fault system is composed of suprasalt and subsalt components the suprasalt component is a y shaped reverse fault and the subsalt component is a complex flower structure in previous studies suprasalt and subsalt components were interpreted as two independent fault systems this paper proposes instead that the suprasalt and subsalt faults are kinematically related and decoupled across the salt layer

geostatistical analysis of the effects of stage and roughness on reach scale spatial patterns of velocity and turbulence intensity although previous research has documented well organized interactions between the turbulent flow field and an irregular boundary the spatial variability of turbulent flow characteristics at the reach scale remains poorly understood in this paper we present detailed field measurements of three dimensional flow velocities and turbulence intensities in a high gradient cobble bed riffle from three discharges additional data on sediment grain size and bed topography were used to characterize boundary roughness an acoustic doppler velocimeter was used to measure velocities along five cross sections within a 6 in long reach of the north fork cache la poudre river vertical profiles were also measured along the channel thalweg we adopted a spatially explicit stochastic hydraulic approach and focused not on coherent flow structures per se but rather time averaged reach scale variability and spatial pattern scaling velocities and turbulence intensities by the reach averaged friction velocity u accounted for changes in flow depth and enabled comparisons among the three discharges we quantified the effects of stage and roughness by assessing differences among probability distributions of hydraulic quantities and by examining geostatistical metrics of spatial variability we computed semivariograms for streamwise and transverse directions and fit parametric models to summarize the spatial structure of each variable at each discharge cross correlograms were also used to describe the local and lagged effects of boundary roughness on flow characteristics although the probability distributions yielded some insight incorporating spatial information revealed important elements of stage dependent flow structure the development of secondary currents and flow convergence at higher stages were clearly documented in maps and semivariograms in general the spatial structure of the flow field became smoother and more continuous as stage increased and the effects of boundary roughness diminished although roughness elements do influence velocities and turbulence intensities our data suggest that the flow primarily responds to the gross morphology of the channel and that flow depth is the primary control on flow structure the geostatistical framework proved useful and our results indicate that a complete stochastic description must also be explicitly spatial c 2006 elsevier b v all rights reserved

coherent flow structures in a depth limited flow over a gravel surface the influence of surface roughness 1 turbulent flows moving over a gravel bed develop large scale macroturbulent flow structures that are initiated at anchor clasts in the bed and grow and dissipate as they move upward through the flow depth this paper extends previous research in which we investigated the influence of the reynolds number on coherent flow structures generated over a gravel bed by assessing the importance of effective bed roughness here we report on flume experiments in which flows over beds of decreasing surface roughness have been quantified through the application of digital particle imaging velocimetry which allows study of the downstream and vertical components of velocity over the entire flow field these results indicate that as the effective roughness increases 1 the visual distinctiveness of the coherent flow structures becomes more defined throughout the flow depth 2 the upstream angle of slope of the coherent flow structure increases and 3 the reduction in streamwise flow velocity and turbulence intensity toward the upstream side of the structure becomes greater applying standard scaling laws these structures appear shear generated and form through a combination of both wake flapping and the reattachment of localized shear layers associated with flow separation around individual topographic protrusions as the effective protrusion decreases the scale of these coherent flow structures also decreases

chemistry of quartz a new insight into the origin of the orlovka ta li deposit eastern transbaikalia russia abstract the ta li deposit of orlovka in eastern transbaikalia russia is one of the best known rare metal deposits in cupola shaped plutons of li f rich rare metal granites quartz from all granite varieties from the deposit was studied using automated mineralogy tima cathodoluminescence cl and laser ablation inductively coupled mass spectrometry la icp ms in order to find new constraints on the origin of the deposit subhedral to euhedral quartz crystals strongly zoned in cl relatively enriched in ti and li up to 95 and 33 ppm respectively and free of mineral inclusions were found in all varieties of biotite granites forming the deeper part of the pluton crystals of snow ball quartz with zonally arranged inclusions of albite with low intensity of cl and slightly enriched in al and ge up to 350 and 4 8 ppm respectively are common in all types of li mica granites forming the cupola shaped upper part of the pluton the distinction between the two principal types of quartz is generally consistent with the already proposed model of two comagmatic intrusions deeper seated biotite granites underwent a complicated magmatic evolution with repeated episodes of crystallization and resorption of quartz only a limited degree of fractionation and a small if any reaction with fluid li mica granites taking position within the cupola strongly fractionated upwards the upward transfer of li and rare metals was moreover supported by fluid unmixed in the middle level of the cupola

textural and chemical evolution of a fractionated granitic system the podlesi stock czech republic the podlesigranite stock czech republic is a fractionated peraluminous f li and p rich and sn w nb ta bearing rare metal granite system its magmatic evolution involved processes typical of intrusions related to porphyry type deposits explosive breccia comb layers rare metal granites stockscheider and rare metal pegmatites extreme f p li enrichment nb ta sn minerals layering geological textural and mineralogical data suggest that the podlesigranites evolved from fractionated granitic melt progressively enriched in h2o f p li etc quartz k feldspar fe li mica and topaz bear evidence of multistage crystallization that alternated with episodes of resorption changes in chemical composition between individual crystal zones and or populations provide evidence of chemical evolution of the melt variations in rock textures mirror changes in the pressure and temperature conditions of crystallization equilibrium crystallization was interrupted several times by opening of the system and the consequent adiabatic decrease of pressure and temperature resulted in episodes of nonequilibrium crystallization the podlesigranites demonstrate that adiabatic fluctuation of pressure bswinging eutecticq and boundary layer crystallization of undercooled melt can explain magmatic layering and unidirectional solidification textures usts in highly fractionated granites d 2004 elsevier b v all rights reserved

nearly contemporaneous evolution of the a and s type fractionated granites in the krusne hory erzgebirge mts central europe abstract the krusne hory erzgebirge mountains is one of the best known provinces of granite magmatism and associated metallogenesis in europe variscan magmatic activity in the krusne hory erzgebirge area spanned the period from 330 to 295 ma for much of this time two types of magma were generated and emplaced in close proximity in this province strongly peraluminous p rich s type melts were formed alongside slightly peraluminous p poor melts a type two suites of strongly peraluminous p f li rb cs u sn rich and zr th y hree poor magmas were intruded in rapid succession over a period of about 10 ma about 330 320 ma over the entire region of the krusne hory several peraluminous rhyolitic dykes near gottesberg mark an isolated event at about 295 ma slightly peraluminous f li rb cs sn zr y hree rich and p poor magmas were intruded in several events separated in space and time 325 295 ma both magmatic episodes culminated with strongly fractionated subvolcanic granite intrusions accompanied by explosive brecciation and followed by sn w mineralization of greisen type successive volcanic eruption of rhyolites and dacites of s type and rhyolites of a type form the fill of the altenberg teplice caldera atc thus demonstrating the close temporal and spatial relationship between these two types of magma when these two geochemically distinct types of rock are in direct contact then the rocks of a type are always younger the absolute time difference between the two types can range from less than 1 ma the first eruption of the teplice rhyolite versus the schonfeld dacite in the atc to about 15 ma eruption of rhyolites at gottesberg versus emplacement of the eibenstock granite the assumed protolith of all late variscan granites in the area of krusne hory erzgebirge is a mixture of fertile quartzo feldspathic rocks with micaceous metapelites enriched in lile and sn w the differences in chemical composition of s and a type melts originated from local changes in the proportion of quartzo feldspathic and pelitic lithologies different pt conditions of melting the degree of melting and the degree of metamorphic dehydratation of the protolith prior to the melting

bridging the gap between turbulence and larger scales of flow motions in rivers although flow turbulence in rivers is of critical importance to earth scientists ecologists and engineers its relations with larger flow scales are not well understood thus leaving a fundamental gap in our knowledge from an analysis of a long time series of the streamwise and vertical flow velocity fluctuations measured in a gravel bed river we show that the signature of the fundamental turbulent flow structures e g ejections and sweeps is embedded within increasingly larger flow scales in a self similar manner the imbrication of turbulent structures into large flow pulsations of flow acceleration and deceleration covers more than two orders of magnitude from a few seconds to nearly 10 minutes this property is explained by the clustering of turbulent events creating an emergent pattern at larger scales the size of the larger flow pulsations scales with the spacing of the pools and riffles in the river this implies a mutual adjustment between turbulence generation mechanisms and long pulsations of flow acceleration and deceleration controlled by the bed morphology these results bridge a gap in our understanding of flows in rivers and offer a new perspective on the interactions between the turbulent flow with larger scales of flow motion that are critical for sediment transport habitat selection and fish behaviour copyright 2011 john wiley sons ltd

trace element evolution of quartz in the charnockitic kleivan granite sw norway the ge ti ratio of quartz as an index of igneous differentiation article i nfo trace element analyses of quartz from the layered charnockitic kleivan granite in the rogaland igneous province rogaland municipality sw norway reveal that the trace element composition of quartz can track igneous evolution during differentiation of the magma combined sem cl imaging and la icp ms analyses allow identification and analysis of primary igneous quartz al ti li and ge are the most abundant trace elements in the kleivan quartz and each element shows a characteristic evolution during differentiation of the granitic magma the ge ti ratio of quartz is a reliable index of the magmatic evolution of granitic igneous systems since ti and ge show pronounced compatible and incompatible characteristics respectively the temperature of the quartz crystallisation varies from 850 c during charnockite formation to 645 c in the most evolved aplitic granite and granitic pegmatite therefore the regular evolution of ti and ge in quartz during cooling of the melt may be used as an igneous geothermometer the li evolution pattern of quartz is mostly controlled by the li content of the melt hence by the absence or presence of li bearing phases forming during solidification of the melt al in quartz is controlled by the aluminium saturation index of the melt accordingly al in quartz is constant during crystallisation of a metaluminous magma and increases during peraluminous conditions the study of rock mineralogy and whole rock geochemistry are not the only methods that can be used to assess the petrogenesis of silica oversaturated rocks the purpose of this study is to demonstrate that the trace element chemistryof quartz and inparticular the ge ti ratio can be used as a petrogenetic tool to characterise an evolving igneous system and can provide information that otherwise may be difficult to obtain quartz is a good mineral for recording and storing the differentiation processes in granitic systems compared to other

adv measurements around a cluster microform in a shallow mountain stream a field study was conducted to examine the turbulent properties of the flow around a naturally formed cluster bedform this was carried out on a mountain river using a 3d acoustic doppler velocimeter adv concurrent with this objective the ability of the adv to make measurements in a shallow flow over a cobble bed ho d84 1 75 was examined adv measurements in natural clear water shallow flows around obstacles are inherently difficult to obtain due to 1 signal interference between the acoustic reflections from the boundary and the adv sample volume 2 regions of high turbulent intensity such as in local detached shear layers and 3 low concentrations of suspended particles passing through the adv sampling volume these processes result in velocity time series that contain a significant amount of spikes lower than average signal to noise ratios and lower than average correlation values a filtering process that optimized the removal of bad points while retaining a sufficient number of poin

titaniq a titanium in quartz geothermometer titanium is one of many trace elements to substitute for silicon in the mineral quartz here we describe the temperature dependence of that substitution in the form of a new geothermometer to calibrate the titaniq thermometer we synthesized quartz in the presence of rutile and either aqueous fluid or hydrous silicate melt at temperatures ranging from 600 to 1 000 c at 1 0 gpa the ti contents of quartz in ppm by weight from 13 experiments increase exponentially with reciprocal t as described by text log left x text qtz text ti right 5 69 pm 0 02 frac 3765 pm 24 t k application of this thermometer is straightforward typically requiring analysis of only one phase quartz this can be accomplished either by epma for crystallization temperatures above 600 c or by sims for temperatures down to at least 400 resulting temperature estimates are very precise usually better than 5 c potentially allowing detailed characterization of thermal histories within individual quartz grains although calibrated for quartz crystallized in the presence of rutile the thermometer can also be applied to rutile absent systems if tio2 activity is constrained

application of cathodoluminescence to magmatic quartz in a tin granite case study from the schellerhau granite complex eastern erzgebirge germany a model of the cooling history of tin bearing granitic magma forming the schellerhau granites eastern erzgebirge germany is shown on the basis of quartz textures similar grain size similar grain habit and correlatable growth textures of phenocrysts in different granite varieties give proof of a common crystallization history before the melts of the schellerhau granite varieties were intruded four nucleation events occurred during crystallization in different crustal levels between about 20 and 1 km depth the parental melt of the schellerhau granites is interpreted to have contained 2 5 wt h2o originally the water content of the melt during the subvolcanic intrusion stage amounted to more than 5 wt and characterizes highly evolved residual melts that enable the formation of tin deposits this study contributes to a better understanding of the development and behaviour of fractionated tin bearing granitic melts and links quartz cathodoluminescence cl with microanalytical studies

variscan silicic magmatism and related tin tungsten mineralization in the erzgebirge slavkovský les metallogenic province integration of geochemical mineralogical isotopic and geochronological data with geodynamic considerations suggests that the variscan granites in the erzgebirge slavkovsk les domain originated from repeated melting events and were emplaced over a period of about 40 ma 330 290 ma several lines of evidence exist supporting the idea that erzgebirge granites assigned to different types biotite granites two mica granites strongly peraluminous p rich li mica granites and slightly peraluminous p poor granites are in most cases not genetically related via continuous fractional crystallization from a common magmatic reservoir the genesis of the slavkovsky les granites however might be discussed in terms of an uninterrupted fractionation series geological models of sn w deposits based upon geochemical and structural results imply that the main ore depositional events followed immediately the emplacement and solidification processes of melt via fluid melt immiscibility breccia pipe formation and or pervasive rock fluid interactions

carboniferous permian volcanic evolution in central europe u pb ages of volcanic rocks in saxony germany and northern bohemia czech republic nine shrimp u pb ages on zircon and two pb pb single zircon ages have been determined from late paleozoic volcanic rocks from saxony and northern bohemia samples came from the teplice altenberg volcanic complex the meissen volcanic complex the chemnitz basin the dohlen basin the brandov olbernhau basin and the north saxon volcanic complex the teplice altenberg volcanic complex is subdivided into an early namurian phase mikulov ignimbrite 326 8 4 3 ma thus older than assumed by previous studies and a late caldera forming phase teplice ignimbrite 308 8 4 9 ma the age of the latter however is not well constrained due to a large population of inherited zircon and possible hydrothermal overprint the leutewitz ignimbrite product of an early explosive volcanic episode of the meissen volcanic complex yielded an age of 302 9 2 5 ma stephanian a volcanic rocks intercalated in the brandov olbernhau basin bob 302 2 8 ma chemnitz basin cb 296 6 3 0 ma dohlen basin db 296 3 0 ma and the north saxon volcanic complex nsvc c 300 290 ma yielded well constrained stephanian to sakmarian ages the largest late paleozoic ignimbrite forming eruption in central europe the rochlitz ignimbrite has a well defined middle asselian age of 294 4 1 8 ma ages of palingenic zircon revealed that the namurian westphalian magmatism assimilated larger amounts of crystalline basement that formed during previous paleozoic geodynamic phases the precambrian inherited ages support the chronostratigraphic structure assumed for the saxo thuringian zone of the variscan orogen the present results help to improve the chronostratigraphic allocation of the late paleozoic volcanic zones in central europe at the same time the radiometric ages have implications for the interbasinal correlation and for the geodynamic evolution of the variscan orogeny

three dimensional structural model of the rhourde el baguel field algeria the rhourde el baguel field located in the ghadames basin is one of the largest oil fields in algeria it produces oil from fractured cambrian sandstones at subsea depths of 2300 3070 m the structure is reinterpreted as a compressive fold related to two reverse faults which cut and deform a preexisting normal fault the structure formed during three main episodes of deformation 1 triassic to liassic extension resulting in normal faults having significant throw 2 middle jurassic flowage of liassic salt resulting in low amplitude structures in this unit and 3 austrian early cretaceous compression resulting in a basement involved fault propagation fold the revised structural model explains the complex fault patterns and anomalous thickness variations of units observed in a number of deep wells on the west flank of the structure the model has been used to sidetrack some existing deep wells into locations within the field and to optimize the location of new wells in the field

scales of boundary resistance in coarse grained channels turbulent velocity profiles and implications gravel bed surfaces are characterized by morphological features occurring at different roughness scales the total shear stress generated by the flow above such surfaces is balanced by the sum of friction drag grain stress and form drag components created by bed forms to facilitate a better understanding of total resistance and bed load transport processes there is a need to mathematically separate shear stress into its component parts one way to do so is to examine the properties of vertical velocity profiles above such surfaces these profiles are characterized by an inner layer that reflects grain resistance and an outer layer that reflects total resistance a flume based project was conducted to address these concerns through systematically comparing different roughness scales to ascertain how increased roughness affects the properties of vertical velocity profiles great care was taken to create natural roughness features and to obtain flow data at a high spatial and temporal resolution using an acoustic doppler velocimeter average vertical velocity profiles above each roughness scale were clearly segmented the vertical extent of the inner flow region was directly related to the scale of roughness present on the bed and independent of flow depth increasing with increased roughness on a rough but rather uniform plane bed made of heterogeneous coarse sediments with no bed forms the shape of the velocity profile was clearly dominated by the local variations in grain characteristics when pebble clusters were superimposed the average shear stress in the outer flow region increased by 100 from the plane bed conditions the ratio of inner grain shear stress to outer total shear stress for this pebble cluster experiment was 0 18 under shallow flow conditions and 0 3 under deep flow conditions the grain stress component that should be used in bed load transport equations therefore appears to vary in these experiments between 15 and 30 of the total channel stress increasing with decreased resistance roughness height ks d50 values at the grain scale for the plane bed and pebble cluster experiments were 0 73 and 0 63 respectively these are values that should be used in flow resistance equations to predict grain resistance and grain stress for bed load transport modeling

three dimensional flow structure around small scale bedforms in a simulated gravel bed environment pebble clusters are common small scale morphological features in gravel bed rivers occupying as much as 10 per cent of the bed surface important links exist between the presence of pebble clusters and the development of flow structures these links are poorly understood at the three dimensional level particularly neglected has been the effect of clusters on the lateral flow characteristics a laboratory study was conducted using a hydraulic flume within which simulated pebble clusters were superimposed onto a plane bed of gravel material high resolution three dimensional flow data were collected above the bed at two different flow depths using an acoustic doppler velocimeter the results present evidence of the importance of lateral flow in the development of turbulent flow structure narrow regions of high lateral and downstream turbulence intensity exist to both sides of clusters and in a three dimensional separation zone in their lee this may indicate the presence of horseshoe type vortical structures analogous to those identified in less hydraulically rough environments however it is likely that these structures are more complicated given the mutual interference of the surrounding medium the lateral flow was also identified as a key component in the upwelling identified by other authors in the lee of pebble clusters the results of the vertical flow analysis confirm the hypothesis that six regions with distinct vertical flow characteristics exist above clusters flow acceleration up the stoss side of the cluster recirculation behind the cluster in the wake region vortex shedding from the pebble crest and shear layer flow reattachment downstream of the cluster upwelling of flow downstream of the point of reattachment and recovery of flow copyright 2001 john wiley sons ltd

using two dimensional hydrodynamic models at scales of ecological importance modeling of flow features that are important in assessing stream habitat conditions has been a long standing interest of stream biologists recently they have begun examining the usefulness of two dimensional 2 d hydrodynamic models in attaining this objective current modeling practices consider relatively long channel sections with their bathymetry represented in terms of large macro scale topographic features meso scale topographic features such as boulders root wads and other obstructions are typically not considered in the modeling process instead the overall effects of these flow obstructions are captured through increased values in the channel roughness parameters such an approach to 2 d modeling allows one to accurately predict average depth and velocity values however it is not capable of providing any information about the flow patterns in the vicinity of these obstructions biologists though have known that such meso scale features and the complex velocity patterns generated by their presence play an important role in the ecology of streams and thus cannot be ignored it is therefore evident that there is a need to develop better tools capable of modeling flow characteristics at scales of ecological importance the purpose of this study is to expand the utility of 2 d hydraulic models to capture these flow features that are critical for characterizing stream habitat conditions there exists a paucity of research addressing what types of topographic features should be included in 2 d model studies and to what extent a boulder or series of exposed boulders can influence predicted flow conditions and traditional useable habitat computations moreover little research has been performed to evaluate the impact mesh refinement has on model results in natural streams numerical simulations based on a natural river channel containing several large boulders indicate that explicitly modeling local obstructions boulders can significantly impact predicted flow parameters the presence of these obstructions create velocity gradients velocity shelters transverse flows and other ecologically important flow features that are not reproduced when their geometry is not incorporated into the hydraulic model sensitivity analyses show that reducing element sizes in the vicinity of obstructions and banks is crucial in modeling the spatial flow patterns created by meso scale topographic features this information combined with similar data obtained in future studies can provide guidelines for the placement of fishrocks and other structures often used in stream restoration projects as well as determining what types of mesoscale topographic features might need to be incorporated into habitat suitability studies such information may also ultimately allow new spatial habitat metrics to be developed q 2000 elsevier science b v all rights reserved

experiments on particle turbulence interactions in the near wall region of an open channel flow implications for sediment transport a high speed video system was used to study the interaction between sediment particles and turbulence in the wall region of an open channel flow with both smooth and transitionally rough beds in smooth flows particles immersed within the viscous sublayer were seen to accumulate along low speed wall streaks apparently due to the presence of quasi streamwise vortices in the wall region larger particles did not tend to group along streaks however their velocity was observed to respond to the streaky structure of the flow velocity in the wall region in transitionally rough flows particle sorting was not observed coherent flow structures in the form of shear layers typically observed in the near wall region interacted with sediment particles lying on the channel bottom resulting in the particles being entrained into suspension although there has been some speculation that this process would not be effective in entraining particles totally immersed in the viscous sublayer the results obtained demonstrate the opposite the entrainment mechanism appears to be the same independent of the roughness condition of the bottom wall smooth or transitionally rough in the latter case however hiding effects tend to preclude the entrainment of particles with sizes finer than that of the roughness elements the analysis of particle velocity during entrainment shows that the streamwise component tends to be much smaller than the local mean flow velocity while the vertical component tends to be much larger than the local standard deviation of the vertical flow velocity fluctuations which would indicate that such particles are responding to rather extreme flow ejection events

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

changes in velocity profiles at roughness transitions in coarse grained channels heterogeneous coarse grained channels are often characterized by local transitions in bed surface roughness distinct spatial zones in terms of grain size have been reported for example sand ribbons and bedload sheets the transition from areas of finer to coarser grained surface sediment is often abrupt however the effects of these transitions on the shape of the velocity profile and associated shear velocity and roughness length estimates have not been investigated in detail in coarse grained channels this paper therefore examines the combined effects of a sudden change in surface roughness and of superimposed scales of resistance on the structure of the turbulent boundary layer measurements along roughness transitions from smooth to rough beds were conducted in a flume using artificial roughness features and in a natural gravel bed river immediately at the transition from a zone of close packed roughness to a rougher section dominated by obstacles superimposed on the more or less uniform roughness surface boundary shear stress and roughness length increase considerably downstream from this transition velocity profiles become concave upwards downstream and upstream sections show significant differences in terms of near bed velocities deceleration downstream of the transition velocity gradient and turbulence intensity of the streamwise velocity component comparing the mean velocity profiles corresponding to these two different roughness surfaces gives some indication of the proportion of total shear velocity or shear stress associated with the pressure drag produced by large and isolated obstacles

reconstruction of subgrid scale topographic variability and its effect upon the spatial structure of three dimensional river flow a new approach to describing the associated topography at different scales in computational fluid dynamic applications to gravel bed rivers was developed surveyed topographic data were interpolated using geostatistical methods into different spatial discretizations and grain size data were used with fractal methods to reconstruct the microtopography at scales finer than the measurement subgrid scale the combination of both scales of topography was then used to construct the spatial discretization of a three dimensional finite volume computational fluid dynamics cfd scheme where the topography was included using a mass flux scaling approach the method was applied and tested on a 15 m stretch of solfatara creek wyoming united states using spatially distributed elevation and grain size data model runs were undertaken for each topography using a steady state solution this paper evaluates the impact of the model spatial discretization and additional reconstructed variability upon the spatial structure of predicted three dimensional flow the paper shows how microtopography modifies the spatial structure of predicted flow at scales finer than measurement scale in terms of variability whereas the characteristic scale of predicted flow is determined by the cfd scale changes in microtopography modify the predicted mean velocity value by 3 6 for a mesh resolution of 5 cm whereas a change in the computational scale modifies model results by 60 the paper also points out how the spatial variability of predicted velocities is determined by the topographic complexity at different scales of the input topographic model

unobstructed and obstructed turbulent flow in gravel bed rivers an acoustic doppler velocimeter was used to characterize turbulence in two gravel bed rivers data were collected in unobstructed flow and compared to recent investigations additional data collected in the wake of emergent boulders indicate that mean flow velocity turbulent kinetic energy gradients in the streamwise velocity and reynolds stress downstream from large rocks deviate from unobstructed flow results but similar turbulence patterns are found behind each boulder results of this study are discussed with regard to natural channel design and fish habitat

cathodoluminescence and trace element zoning in quartz phenocrysts and xenocrysts quartz phenocrysts and xenocrysts are a common component of volcanic rocks but rarely contribute to our understanding of magmatic or eruptive processes due to an apparent internal chemical and structural homogeneity scanning electron microscopy cathodoluminescence imaging sem cl and secondary ion mass spectroscopy ion microprobe analysis sims are used here to demonstrate that quartz crystals in volcanic rocks show hitherto unrecognised internal structural and chemical zoning two contrasting crystal morphologies have been studied porphyritic euhedral bipyramidal quartz crystals in dacite from bonne nuit bay jersey uk show fine scale growth zoning in sem cl zones are narrow 1 40 m wide planar parallel to crystal faces and overgrow more broadly zoned rounded cores these crystals are interpreted to have formed at small degrees of undercooling by diffusion controlled growth quiescent magma conditions are indicated by the preservation of an al rich diffusive boundary layer which has not been removed by melt shearing during convection in contrast rounded and embayed porphyritic quartz grains in a quartz dacite from the esperanza mine e1 salvador northern chile show broad internal sem cl zones with irregular boundaries some of which are truncated by grain margins indicating dissolution crystal rounding may occur by dissolution or melting due to thermal or thermal chemical disequilibrium with surrounding melt and embayments by gas bubble enhanced convective dissolution are consistent with the development of incipient ocelli textures strings of amphibole inclusions adjacent to quartz rims several episodes of rounding can be recognised in some xenocrysts ion microprobe sims analysis of quartz from both samples shows that a1 contents are higher in areas of bright cl emission previous studies of cl in quartz have suggested that several factors control luminescence although a1 substitution for si in sio4 tetrahedra may be partly responsible for sem cl zoning recorded in volcanic quartz additional mechanisms including the effect of growth rate on defect density probably also play a major role

suction removal of sediment from between armor blocks this paper presents the results of an experimental investigation on suction removal of sediment from between armor blocks stones placed on a loose bed the process of suction has been investigated it was found that the vortices that form in the holes between the armor blocks are key to the process the sediment swept into these vortices is entrained into the main body of the flow by these same vortices the suction removal of sediment from between the armor blocks the critical condition for the onset of suction was determined it was found that the onset of suction is governed by two parameters 1 the shields parameter based on the sediment size and 2 the ratio of sediment size to stone size d d the variation of the critical shields parameter for suction as a function of d d was determined for a broad range of the parameter d d namely 0 001 d d 1 the timescale of the suction process and the downward displacement of stones the general lowering of the armor layer have also been investigated

reach scale variability of turbulent flow characteristics in a gravel bed river in gravel bed rivers bed roughness is often controlled by the spatial distribution of pebble clusters and large protuberant clasts the turbulent flow structure around these roughness elements has been studied extensively as opposed to the effects of the spatial variability of the bed roughness on the structure of the flow at the reach scale in this paper we examine the effects of roughness elements on the spatial variability of the mean flow velocity profiles and of the properties of turbulent flow structures at the reach scale the experiment was carried out in two reaches of 25 m long in the eaton north river quebec we produced detailed topographic maps of the river reaches to obtain the spatial distribution of the main roughness elements the flow is characterized with velocity time series measured using electromagnetic current meters mounted on a vertical wading rod we collected 65 velocity profiles from which we derived turbulent flow characteristics results showed that in spite of the complex configuration of the bed velocity profiles are predominantly log linear mean and turbulent flow characteristics are only affected at a local scale and over short distances by the presence of roughness elements at the reach scale the distribution of individual roughness elements does not greatly control the spatial variability of turbulent flow properties

formation and evolution of snowball quartz phenocrysts in the dongping porphyritic granite hebei province china insights from fluid inclusions cathodoluminescence trace elements and crystal size distribution study abstract quartz phenocrysts are common in many granites volcanic rocks metamorphic rocks and hydrothermal deposits the dongping porphyritic granite contains large amounts of rounded to sub rounded quartz phenocrysts minerals in this porphyritic granite show weak but distinct orientation dense clusters of fluid inclusions and albite crystals exist in the quartz showing snowball texture two types of snowball quartz are recognized 1 large snowball quartz phenocrysts containing large albite grains distributed in the core and small albite grains distributed in the mantle and 2 small snowball quartz crystals containing small albite grains the granite is characterized by high sio2 7 15 73 44 wt k2o 4 70 5 10 wt and na2o 4 93 5 21 wt contents low cao 0 41 0 71 wt mgo 0 03 0 05 wt fe2o3 0 87 0 94 wt tio2 0 02 0 03 wt and ree 7 10 9 80 ppm contents the granite has similar mineral and chemical composition with the aplite in the area and they were derived from the residual melt of the shuiquangou magma that suffered assimilation fractional crystallization process fluid inclusions in the quartz phenocrysts have homogenization temperatures of 260 380 c and salinities of 1 4 12 4 wt nacl equiv for liquid vapor type inclusions and 34 1 44 3 wt nacl equiv for brine ones the quartz phenocrysts exhibit homogeneous cathodoluminescence without growth bands or zoning the trace element contents in the quartz phenocrysts are extremely low ti 3 4 5 1 ppm al 13 118 ppm li

a comparative study of the turbulent flow field with and without a pebble cluster in a gravel bed river 1 this paper investigates the processes and spatial patterns of the turbulent flow around a naturally formed in situ pebble cluster and the interactions with large scale coherent flow structures instantaneous high frequency velocities were measured using the simultaneous deployment of four acoustic doppler velocimeters with the pebble cluster and after the cluster was removed results indicate a twofold increase in turbulent kinetic energy over the sampling area when the pebble cluster is present individual vertical component velocity spectra in the wake of the pebble cluster contain a marked peak which decreases in frequency from 1 8 hz near the cluster to 1 0 hz farther downstream this peak is associated with eddies shedding from the shear layer in the lee of the cluster and it agrees well with the values estimated using a strouhal number of 0 18 space time correlations indicate the presence of coherent depth scale macroturbulent flow structures these structures in the intermediate flow region are relatively unaffected by eddies shedding from the pebble cluster the results suggest the effects of the pebble cluster on the surrounding flow dynamics are quite localized and limited to the near bed region

influence of active subsalt normal faults on the growth and location of suprasalt structures abstract the location and deformation style of salt and overburden structures that form during subsalt normal faulting vary greatly between and within salt provinces in some areas diapirs and overburden faults appear to have formed independently of the location of the underlying basement faults elsewhere diapirs and faults formed systematically above or near the subsalt faults or the overburden was force folded above the subsalt fault into a monocline whose shape reflects the offset along the underlying basement blocks we used dynamically scaled physical experiments and conceptual models to 1 understand how much subsalt faulting controls the formation and localization of structures in the salt and overburden and 2 evaluate how this control is affected by changing selected parameters such as salt thickness strain rate or sedimentation rate both experimental and conceptual models predict that initially thick salt or slow subsalt faulting favors decoupling of the overburden from the subsalt basement instead of transmitting stresses and strains upward from basement through salt and into the overburden the salt layer diffuses localized basement slip by laterally flowing from the footwall to the hangingwall thus the salt layer thins above the basement footwall and thickens above the hangingwall once the source layer above the footwall has been thinned or depleted salt can no longer flow fast enough to entirely accommodate subsalt faulting hence the fault propagates upward as a broad forced fold whose upper hinge is affected by crestal normal faults along which further extension is accommodated experimental and conceptual models indicate that initially thick salt slow or moderately fast subsalt faulting and slow or absent syntectonic sedimentation promote decoupled deformation conversely initially thin salt very rapid subsalt faulting rapid syntectonic sedimentation or all three promote coupled deformation and formation of diapirs or overburden faulting above or near the subsalt fault

spatial structure of near bed flow properties at the grain scale abstract expanding the existing knowledge of the role of roughness on near bed flow properties is vital to provide deeper insights into the interactions between the flow sediment transport morphology and ecology this study uses four fixed beds from both the laboratory and the field to characterise the structure of near bed flow properties dense measurements over a grid of 6 mm spacing were conducted across each cast using an acoustic doppler velocimeter these measurements followed the line of the bed topography with the sampling location being 2 mm away from the maximum bed elevations near bed flow properties were calculated across the surface including velocity turbulence intensity turbulent kinetic energy reynolds stress and quadrant analysis improved visualisation of flow properties involves contour plots of the spatial distribution of flow over the dem of the gravel bed to facilitate attributions of flow patterns to roughness and topography using the standard deviation of elevations as a proxy for grain roughness of each surface we observed that a decrease in roughness led to an increase in the average near bed velocity in contrast an increase in roughness resulted in an increase in both turbulence intensity and turbulent production tke analysis of quadrant events dominating across the surface can provide indications into the potential for erosion and or deposition across the natural mobile surfaces finally second order structure function analysis is used to quantify the spatial structure of flow properties presenting novel isopleth maps of flow properties for the majority of flow properties across all surfaces the range in the spatial extent of flow structures is between 1 and 2 25 d50a except for transverse and vertical velocities which have a wider range up to 3 5 d50a

effects of macro scale bed roughness geometry on flow resistance 1 flow field over macro roughness elements as for example in flow conditions such as of steep mountain streams is investigated by means of a theoretical model and a laboratory study with the main aim of understanding the influence of concentration and planimetric disposition of grain roughness on flow resistance a theoretical model for the average velocity distribution profile over a bed with macro roughness elements is developed herein the model is based on a two layer approach which takes into account the displacement of the main flow due to the drag around the roughness the laboratory study is composed of an extensive set of flume experiments in the case of steep slopes and large relative roughness conditions for a given flow discharge and bed slope various experiments have been carried out with different pattern and spacing of the roughness elements constituted by river pebbles application of the theoretical model to the experimental results enables the determination of how flow resistance is affected by the macro roughness in particular it appears that when the concentration of the roughness is within an optimal range flow resistance is maximum

three dimensional measurement of river channel flow processes using acoustic doppler velocimetry this paper describes and assesses i the use of a new instrument for the determination of three dimensional flow velocities in natural rivers the acoustic doppler velocimeter adv and ii a method for positioning and orienting such measurements relative to a single local coordinate system to relate flow velocity vectors with the bed and water surface the adv uses the doppler shift principle to measure the velocity of small particles assuming to be moving at velocities similar to the fluid velocity is resolved into three orthogonal components and measured in a volume 5 cm below the sensor head minimizing interference of the flow field and allowing measurements to be made close to the bed a simple method for positioning and orienting the instrument using digital tacheometry is described and is used to obtain velocity measurements concurrently with measurements of both bed and water surface topography the paper includes a preliminary field assessment of the adv by comparing velocity profiles with those generated from marsh mcbirney electromagnetic current meters and a full field assessment of the position and orientation methodology these results suggest that the recommended methods in combination with an adv are able to provide reliable mean three dimensional velocity field information and accurate bed and surface topography copyright 1998 john wiley sons ltd

water worked gravel beds in laboratory flumes a natural analogue an investigation has been conducted to identify the key parameters that are likely to scale laboratory sediment deposits to the field scale two types of bed formation were examined one where sediment is manually placed and screeded and the second where sediment is fed into a running flume this later technique created deposits through sequential cycles of sediment transport and deposition detailed bed surface topography measurements have been made over a screeded bed and three fed beds in addition bulk subsurface porosity and hydraulic conductivity have been measured by comparing the four beds results revealed that certain physical properties of the screeded bed were clearly different from those of the fed beds the screeded bed had a random organization of grains on both the surface and within the subsurface the fed beds exhibited greater surface and subsurface organization and complexity and had a number of properties that closely resembled those found for water worked gravel beds the surfaces were water worked and armoured and there was preferential particle orientation and direction of imbrication in the subsurface this suggested that fed beds are able to simulate in a simplified manner both the surface and subsurface properties of established gravel bed river deposits the near bed flow properties were also compared it revealed that the use of a screeded bed will typically cause an underestimation in the degree of temporal variability in the flow furthermore time averaged streamwise velocities were found to be randomly organized over the screeded bed but were organized into long streamwise flow structures over the fed beds it clearly showed that caution should be taken when comparing velocity measurements over screeded beds with water worked beds and that the formation of fed beds offers an improved way of investigating intragravel flow and sediment water interface exchange processes in gravel bed rivers at a laboratory scale copyright 2008 john wiley sons ltd

a casting procedure for reproducing coarse grained sedimentary surfaces in the field the measurement of near bed hydraulics remains problematic greater precision is possible in the laboratory but in the case of gravels it is difficult to create a water worked channel bed that is realistic enough to replicate faithfully the conditions found in nature in this paper a technique to reproduce coarse grained sedimentary fabrics of large areal extent is described it involves moulding natural river bed surfaces from which facsimiles are cast remarkably realistic casts with dimensions of 1 m by 2 m have been produced and their quality assessed using spatial data derived using automated digital photogrammetry the casts reproduce the prototype surfaces with errors at millimetre scale 0 5 per cent of the microrelief the technique has facilitated the introduction of sedimentary surfaces that incorporate natural complex structures of grains up to cobble size into experimental channels where detailed studies of near bed hydraulics can be carried out copyright 2003 john wiley sons ltd

velocity distribution in the roughness layer of rough bed flows several models for the vertical distribution of the double averaged in time and in the plane parallel to the mean bed longitudinal velocity in the flow region between roughness troughs and roughness tops are suggested we found that the same model for velocity distribution may be applicable to a range of flow conditions and roughness types which share some common features the suggested models for velocity distribution in the near bed region are 1 constant velocity 2 exponential velocity distribution and 3 linear velocity distribution the measured velocity distributions may be approximated by a single model or by a combination of models depending on roughness geometry and flow conditions the validity of these models for velocity distribution is supported by laboratory data

the growth of northeastern tibet and its relevance to large scale continental geodynamics a review of recent studies recent studies of the northeastern part of the tibetan plateau have called attention to two emerging views of how the tibetan plateau has grown first deformation in northern tibet began essentially at the time of collision with india not 10 20 myr later as might be expected if the locus of activity migrated northward as india penetrated the rest of eurasia thus the north south dimensions of the tibetan plateau were set mainly by differences in lithospheric strength with strong lithosphere beneath india and the tarim and qaidam basins steadily encroaching on one another as the region between them the present day tibetan plateau deformed and its north south dimension became narrower second abundant evidence calls for acceleration of deformation including the formation of new faults in northeastern tibet since 15 ma and a less precisely dated change in orientation of crustal shortening since 20 ma this reorientation of crustal shortening and roughly concurrent outward growth of high terrain which swings from nne ssw in northern tibet to more ne sw and even ene wsw in the easternmost part of northeastern tibet are likely to be in part a consequence of crustal thickening within the high tibetan plateau reaching a limit and the locus of continued shortening then migrating to the northeastern and eastern flanks these changes in rates and orientation also could result from removal of some or all mantle lithosphere and increased gravitational potential energy per unit area and from a weakening of crustal material so that it could flow in response to pressure gradients set by evolving differences in elevation

flow heterogeneity over 3d cluster microform laboratory and numerical investigation the present study examines the flow around a self occurring cluster bed form and the use of general computation fluid dynamics methods for hydraulic and geophysical flow applications this is accomplished through a comprehensive experimental numerical investigation in the laboratory cluster bed forms are first formed from movable sediment and laser doppler velocimeter measurements of two dimensional fluid velocity are then taken around a formed cluster a three dimensional 3d reynolds averaged navier stokes simulation of the physical cluster and flow conditions is then conducted using near wall shear stress transport sst turbulence modeling with the inclusion of hydraulic roughness ks r 31 150 ks h 0 1 ks 274 i e in the fully rough regime sst near wall modeling is advantageous compared to the more widely used wall functions approach for flows with significant roughness and flow separation because the model equations can be integrated down to the wall therefore sst near wall model

quartz trace element composition by la icp ms as proxy for granite differentiation hydrothermal episodes and related mineralization the beauvoir granite echassieres district france despite quartz being a ubiquitous mineral in the earth s crust only little is known about its trace chemical composition and whether and how this is influenced by the medium from which it precipitated using in situla icp ms analysis we investigated the trace element composition of several types of quartz from a magmatic hydrothermal system in the echassieres district of the french massif central this system consists of the colettes granite the beauvoir rare element granite a w bearing stockwork and dispersed mineralized veins all of the elements tested li be b na al ti ge rb sr nb sn sb ta w were detected in quartz from at least one sample a rigorous multivariate statistical approach permitted to assign a specific chemical signature to each of the quartz groups that were recognized by petrographic observations differences among these groups were interpreted to reflect different sources or genetic evolutionary trends within magmatic and hydrothermally derived quartz groups for example the evolution of al rb ge li and ti could be related to genetic processes such as the degree of magma differentiation and crystallization temperatures quartz from the w stockwork anterior to the beauvoir leucogranite clearly stands out from that related to the beauvoir mineralization system i e the greisen facies and proximal ta nb sn w mineralized veins it was also possible to demonstrate a similarity in composition notably the sb contents between quartz from the greisen and from distal stibnite bearing veins in addition elevated values of sb sn as well as li and rb in quartz correspond to similarly high values of these elements in the rock indicating that quartz trace chemistry can provide useful information for the mineralization potential of its host at least for these elements on the other hand nb ta and w are less reliable as they occur mostly at very low levels in quartz the highest values corresponding to samples that were not particularly enriched in these metals a comparison of our quartz data with those from a similar granitic complex at cinovec czech republic breiter et al 2017a shows a similar trend for the ge ti ratio reflecting magmatic differentiation conversely the al ti ratio values differ in the two complexes the al content of quartz from the various cinovec granites being systematically lower than in quartz from echassieres nevertheless caution must be taken when analyzing quartz for its trace element chemistry as processes occurring during i e trapping of fluid inclusions and formation of zoning and after crystal growth i e diffusion and alteration can introduce heterogeneities thus affecting the original chemistry

effect on flow structure of sand deposition on a gravel bed results from a two dimensional flume experiment 1 particle imaging velocimetry piv was used to quantify the entire two dimensional flow field over a series of fixed test beds in a laboratory flume the test beds used in the experiments provide a two dimensional representation of gravel beds with contrasting roughness the two dimensional form of the beds combined with the nonintrusive nature of piv allowed the velocity field to be quantified right down to the bed surface the three beds used were designed to simulate the progressive effect of sand deposition on a gravel bed with median grain size d50 of 25 mm such a situation is common in bimodal beds but as compared with gravel and sand cases little work has been done to investigate the interaction between the variable roughness of a bimodal bed and the flow structure above it the results demonstrate that as the effective roughness decreases the reverse flow often found in the lee of gravel particles is eliminated furthermore near bed velocities increase while shear stress and turbulent kinetic energy decrease turbulent properties are also diminished higher up in the profile although this is not the case for the mean downstream velocity which remains unaffected except at the bed quadrant analysis reveals that q2 and q4 events become less frequent around high points as effective roughness decreases all these responses to the changing bed conditions are most pronounced in areas where the effective roughness height h approaches 10 mm or less h d50 0 4 such a situation is often found immediately upstream of gravel sand transitions in natural rivers it is hypothesized that the hydraulic response outlined here provides a detailed physically based explanation for the gravel sand transition the combination of reduced bed shear stress and q2 q4 events around gravel particles will result in greater mobility of the sand fraction relative to gravel these experiments thus appear to demonstrate that there is a fundamental threshold between gravel bed and sand bed states that has not previously been quantified

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

1 min in the life of a river selecting the optimal record length for the measurement of turbulence in fluvial boundary layers in the analysis of instantaneous velocity measurements it is important to consider carefully the properties of the instruments as well as the sampling frequency and the record length although several studies have examined the influence of instrument settings on velocity measurements in rivers little information is available on the effects of the record length on these measurements and on the turbulence parameters that can be extracted from the time series decisions on the record length are often made ad hoc here we quantify the effects of the sampling period on the precision of turbulence statistics e g mean standard deviation skewness reynolds stress quadrant analysis obtained from velocity measurements in fluvial turbulent boundary layers a bootstrapping method is used to determine the standard errors s e of turbulence statistics from 19 time series the time series were sampled in three gravel bed rivers using both electromagnetic current meters ecm and acoustic doppler velocimeters adv the record lengths ranged between 20 and 60 min the sampling frequencies were 20 and 25 hz for the ecms and advs respectively we show that for most turbulence statistics the optimal record length minimum sampling effort to achieve low standard errors ranges between 60 and 90 s we discuss the implication of these record lengths for standard errors estimates and variance losses

estimation of flow resistance in gravel bedded rivers a physical explanation of the multiplier of roughness length the need to estimate velocity and discharge indirectly in gravel bedded rivers is a commonly encountered problem semilogarithmic friction equations are used to estimate mean velocity using a friction factor obtained from depth and grain size information although such equations have a semi theoretical basis in natural gravel bed channels an empirical constant 6 8 or 3 5 has to be introduced to scale up the characteristic grain size d50 or d84 to represent the effective roughness length in this paper two contrasting approaches are used to suggest that the multiplier of characteristic grain size is attributable to the effect of small scale form resistance reflecting the occurrence of microtopographic bedforms in gravel bedded environments first spatial elevation dependence in short detailed bed profiles from a single gravel bedded river is investigated using semivariogram and zero crossing analyses this leads to objective identification of two discrete scales of bed roughness associated with grain and microtopographic roughness elements second the autocorrelation structure of the three dimensional near bed velocity field is examined to identify regularities associated with eddy shedding and energy losses from larger grains and microtopographic bedforms apart from improving the capacity to determine friction factors for velocity and discharge estimation the findings have implications in general for the initial motion of gravelly bed material

spatial scale partitioning of in situ turbulent flow data over a pebble cluster in a gravel bed river 1 spatial structures within turbulent flow data were investigated through the use of a new multivariate variation partitioning analysis technique involving principal coordinates of neighbor matrices pcnm which is a form of distance based eigenvector maps dbem the analysis revealed a significant 0 01 spatial dependence 58 for the mean and turbulent flow variables the flow variables were obtained from instantaneous two dimensional velocities collected in situ along a streamwise section that crosses over a pebble cluster in a gravel bed river using the orthogonal property of the pcnm variables the explained variation was partitioned over four significant 0 01 spatial scales very large vl 17 large l 24 medium m 6 and fine f 2 nearly 75 of the variance of the main turbulent flow indicators such as the root mean square of the streamwise and vertical velocity components and the mean uv component reynolds shear stress was explained by the vl and l scale pcnm submodels which have streamwise and vertical length scales of the order of x 5 3h 2 6h and y 1 0h 0 5h where h is the flow depth respectively through a multivariate mapping procedure clear spatial patterns within the explained flow variables emerge around the cluster where the flow separation zone seems to play a significant role at a range of scales as well intervariable correlations at each spatial scale obtained through eigenvector scatterplots show intricate relationships between the flow variables the interdependence of the reynolds shear stress and the u component turbulent energy is much stronger at the vl scale than at the l and m scales the application of pcnm analysis on the turbulent flow field shows the power of the technique to resolve the relevant spatial scales and patterns and demonstrates its potential use in a variety of water resources studies

magmatic hydrothermal transition of mo w mineralized granite pegmatite greisen system recorded by trace elements in quartz krupka district eastern krusne hory erzgebirge abstract magmatic hydrothermal transition of highly evolved granitic melts enriched in volatile and incompatible elements can involve disequilibrium intermediate products between aluminosilicate melt and hydrothermal fluid hydrosilicate liquids with high ore forming potential we investigate evolution from li f rich granites through pegmatites greisens and quartz veins in a composite stock at knottel in the krupka district eastern krusne hory erzgebirge mountain range by monitoring trace element variations in quartz interelemental correlations reveal si4 li al3 and likely si4 h al3 to be the most important substitution mechanisms variations in ti vs li be and al define distinct evolutionary trends i magmatic high li ti or al ti trend granites aplites k feldspar pegmatite ii transitional medium li ti trend quartz megacrysts and pegmatite lenses in granite quartz protolithionite pegmatite iii hydrothermal low li ti or al ti trend stockwork of coarse grained hydrothermal quartzites and quartz veins quartz replacement in greisens the medium li ti trend represents hydrosilicate liquid an h2o and sio2 rich medium with low density and effective viscosity that was probably formed during disequilibrium crystallization in front of rapidly propagating solidification front thermal evolution of the magmatic hydrothermal system was monitored by ti in quartz thermometry calculated rutile activity of the granites is very low 0 3 0 05 but it increases up to 1 that is saturation towards pegmatites and hydrothermal veins magmatic crystallization granites and aplites is constrained to 700 580 c pegmatite and bulk greisenization stage occurred at 600 500 c followed by a late hydrothermal stage associated with the formation of distal quartz veins at 500 390 c the granite pegmatite systems at knottel and in erzgebirge in general reach extremely high al li rb and ge and low ti concentrations in quartz in comparison with igneous rocks worldwide the knottel stock belongs to p poor a type granites in the erzgebirge and is linked with them by similar evolutionary trends in quartz trace elements furthermore the knottel system exhibits be enrichment in quartz probably related to high contents of f and this appears to be typical feature of mo w mineralized systems in general the hydrothermal phase with mo w mineralization at knottel is closely related to the magmatic phase of parental granite body which seems to be an important condition for mo w mineralization formation

spatial heterogeneity of near bed hydraulics above a patch of river gravel 1 the spatial heterogeneity of fully turbulent near bed flows above gravel river beds is examined using a realistic replica of a natural gravel patch in a large flume three dimensional velocity time series were obtained at four heights 0 008 0 1 m above the local bed in each of 99 closely spaced verticals for three flows of increasing intensity the spatial heterogeneity of time averaged velocities and root mean square velocity fluctuations increases under stronger flows and closer to the bed however streamwise velocity becomes spatially homogeneous at a distance from the bed of between 2 4 times the median bed elevation heterogeneity in the direction of the velocity vector is independent of mean flow velocity but in all cases it decreases approximately linearly with distance above the surface skewness of the instantaneous velocity distributions suggests that slowly moving fluid emanating from the near bed region impinges upon higher levels with greater frequency and greater spatial coverage as the average flow velocity increases spatial heterogeneity in turbulent kinetic energy increases with flow velocity and maxima occurr at positions that intercept layers of intense vortex shedding in the lee of obstacle crests the spatial organization of the flow properties is nonrandom and consistent across the three flows simple regression models are developed to provide a basis for investigating the heterogeneity of near bed flow at the patch scale 2 m2 in gravel bed rivers

the impact of biological bedforms on near bed and subsurface flow a laboratory evaluated numerical study of flow in the vicinity of pits and mounds the complex surface topography of river substrates controls near bed hydraulics and drives the exchange of subsurface and surface flow in rivers the topographic structures that are studied are usually formed by the flow but it is known that many animals also create biogenic bedforms such as pits and mounds here a large eddy simulation les model of flow over a pit and a mound is evaluated with flume experiments the model includes actual bedform topography and the topographic complexity of the surrounding bed surface subsurface grains are organized in a body centered cubic packing arrangement model evaluation showed strong agreement between experimental and modelling results for velocity r2 0 8 and good agreement for reynolds stresses r2 0 7 which is comparable to other similar studies simulation of the pit shows that the length of the downwelling region is smaller than the upwelling region and that the velocity magnitude is higher in the downwelling region simulation of the mound reveals that the flow is forced into the bed upstream of the mound and re emerges near the top of the mound the recirculation zone is limited at the leeside of the mound with increasing reynolds number the depth of the upwelling region at the leeside of the mound increases the analysis of shear stress indicates that sediments on the upstream edge of the pit and on the downstream face of the mound are relatively unstable these results demonstrate the effect of biogenic structures on the near bed flow field hyporheic exchange and sediment stability

phosphorus in s type magmas the p2o5 content of feldspars from peraluminous granites pegmatites and rhyolites

influence of basement faults on the development of salt structures in the danish basin scaled centrifuged models based on interpreted seismic profiles were used to simulate the salt structures in the danish basin the models consisted of a viscous layer simulating rock salt overlain by layers of cohesive sand that mimic brittle failure in natural overburdens model results support the hypothesis that basement faults trigger the growth of many salt diapirs in the danish basin in plan view model diapirs are localized as buoyant walls along faults in the overburden which collapsed due to basement fault movement with further burial single diapirs rose from these buoyant walls some of the diapirs surfaced through the faulted overburden a few were trapped beneath the competent cretaceous units and others were starved due to lack of supply from below in section model diapirs were asymmetric and were rooted on the tip of the faults or located on the rotated footwall blocks model diapirs not located over faults were triggered by differential loading and collapsing of overburden layers due to basement block rotation models show that the presence of fewer salt structures in the northern than the southern part of the basin is due to differential subsidence and flow of buoyant material from north to south where they rise diapirically in the model the pressure due to loading by overburden layers changed from 1 3 102 pa in the south to 2 3 102 pa in the northern part of the basin in general the model results illustrate that basement faults influence diapirs by accumulating buoyant material in half grabens and introducing a slope and steps at the base of the buoyant layer weakening its overburden and causing differential loading and compaction the spreading overhangs of salt diapirs beneath the cretaceous chalk in the danish basin would seal any potential pre cretaceous reservoir rocks

bedload transport of fine gravel observed by motion picture photography motion pictures taken at duck creek a clear stream 6 5 m wide and 35 cm deep near pinedale wyoming provide detailed quantitative information on both the modes of motion of individual bedload particles and the collective motions of large numbers of them bed shear stress was approximately 6 pa 60 dynes cm 2 which was about twice the threshold for movement of the 4 mm median diameter fine gravel bed material and transport was almost entirely as bedload the displacements of individual particles occurred mainly by rolling of the majority of the particles and saltation of the smallest ones and rarely by brief sliding of large angular ones entrainment was principally by rollover of the larger particles and liftoff of the smaller ones and infrequently by ejection caused by impacts whereas distrainment was primarily by diminution of fluid forces in the case of rolling particles and by collisions with larger bed particles in the case of saltating ones the displacement times averaged about 0 2 0 4 s and generally were much shorter than the intervening repose times the collective motions of the particles were characterized by frequent brief localized random sweep transport events of very high rates of entrainment and transport which in the aggregate transported approximately 70 of the total load moved these events occurred 9 of the time at any particular point of the bed lasted 1 2 s affected areas typically 20 50 cm long by 10 20 cm wide and involved bedload concentrations approximately 10 times greater than background the distances travelled during displacements averaged about 15 times the particle diameter despite the differences in their dominant modes of movement the 8 16 mm particles typically travelled only about 30 slower during displacement than the 2 4 mm ones whose speeds averaged 21 cm s 1 particles starting from the same point not only moved intermittently downstream but also dispersed both longitudinally and transversely with diffusivities of 4 6 and 0 26 cm 2 s 1 respectively the bedload transport rates measured from the films were consistent with those determined conventionally with a bedload sampler the 2 4 mm particles were entrained 6 times faster on finer areas of the bed where 8 16 mm particles covered 6 of the surface area than on coarser ones where they covered 12 even though 2 4 and 4 8 mm particles covered practically the same percentage areas in both cases the 4 8 and 8 16 mm particles in contrast were entrained at the same rates in both cases to within the statistical uncertainty the rates of distrainment balanced the rates of entrainment for all three sizes and were approximately proportional to the corresponding concentrations of bedload

trace element composition of quartz from the variscan altenberg teplice caldera krusne hory erzgebirge mts czech republic germany insights into the volcano plutonic complex evolution abstract in this study the internal structures and appropriate trace element distributions within quartz grains were investigated using a laser ablation icp ms technique combined with a hot cathode and scanning cathodoluminescence analysis the studied variscan magmatic suite is located in the altenberg teplice caldera eastern krusne hory erzebirge along the czech republic germany border and composed of co magmatic volcanics peraluminous basal rhyolite and associated dacite overlying three units of subaluminous teplice rhyolite and granite porphyry and plutonic granites two intrusions of a type biotite and zinnwaldite granites the trace element distribution in the granite porphyry and rhyolite quartz demonstrates a distinct zoning in the cathodoluminescence images and chemical compositions the core is poor in ti the outer rim zones are enriched in ti and the trends recorded for al are opposite to those of ti the quartz from granites is either very weakly zoned or homogeneous based on the chemical composition of quartz and its zoning we assume that the quartz crystals began to crystallize gradually in the primary deep seated magma chamber with a p t condition of 10 kbar and 750 c and in an environment with an increasing concentration of al and decreasing concentration of ti the early stage was followed by the subsequent adiabatic ascent into a shallow magma chamber estimated by the ti in quartz thermobarometry at approximately 700 c 2 kbar during which crystal rims rich in ti formed and then extruded after the caldera collapse part of the magma intruded as granite and in the environment of the residual melt rich in water and flux agents late quartz grew in the form of snowball quartz with an increased al content and decreased ti content

textural and chemical constraints on the formation of disseminated granite hosted w ta nb mineralization at the dajishan deposit nanling range southeastern china the dajishan deposit located in the nanling range of southeastern china is the largest wolframite deposit in the world approximately two thirds of the tungsten resource is contained in large quartz wolframite k feldspar muscovite scheelite sulfide beryl veins but the remainder occurs as wolframite and lesser scheelite disseminated through the nb ta mineralized no 69 granite which is characterized by abundant snowball quartz crystals disseminated granite hosted wolframite mostly occurs as a replacement after lath shaped muscovite although an interstitial variety is present in some samples the major element chemistry of the disseminated and vein hosted wolframite is similar however the former has one to two orders of magnitude higher concentrations of high field strength elements hfse including nb and ta disseminated muscovite in the no 69 granite is fe and mg rich replacement rims on these muscovite crystals are enriched in ta sn and cs but more depleted in nb related to the original phase vein hosted muscovite is characterized by lower nb ta rb and cs contents than the granite hosted muscovite although sn and w concentrations are comparable columbite mn is the principal nb ta ore mineral and occurs disseminated through the no 69 granite where it is hosted by snowball quartz crystals some of the columbite has been altered and overgrown by wodginite the restriction of these altered columbite crystals to within snowball quartz along with the ta and sn enrichment of the alteration rims on muscovite tie the formation of snowball quartz to a ta sn metasomatic event high ge ti and al ti ratios in the snowball quartz relative to interstitial quartz are also consistent with a late stage of formation for the former variety the disseminated granite hosted w mineralization formed through fluid rock interaction the fluids that precipitated the disseminated wolframite were most likely those that formed the veins but were modified through reaction with the hfse enriched no 69 granite nb ta mineralization however is represented by magmatic columbite and by a later metasomatic stage of wodginite the low solubility of ta in aqueous fluids combined with the evidence for ta sn metasomatism suggests that the ta sn metasomatic event was caused by hydrosilicate liquids a transitional fluid that lies compositionally between silicate magmas and hydrothermal fluids whole rock and mineral chemistry both suggest that deep level fractional crystallization of the no 69 granite was required to elevate ta and nb concentrations to allow saturation of columbite

coherent flow structures in a depth limited flow over a gravel surface the role of near bed turbulence and influence of reynolds number 1 in gravel bed rivers the microtopography of the bed exerts a significant effect on the generation of turbulent flow structures although field and laboratory measurements have indicated that flows over gravel beds contain coherent macroturbulent flow structures the origin of these phenomena and their relationship to the ensemble of individual roughness elements forming the bed is not quantitatively well understood here we report upon a flume experiment in which flow over a gravel surface is quantified through the application of digital particle imaging velocimetry which allows study of the downstream and vertical components of velocity over the entire flow field the results indicate that as the reynolds number increases 1 the visual distinctiveness of the coherent flow structures becomes more defined 2 the upstream slope of the structures increases and 3 the turbulence intensity of the structures increases analysis of the mean velocity components the turbulence intensity and the flow structure using quadrant analysis demonstrates that these large scale turbulent structures originate from flow interactions with the bed topography detection of the dominant temporal length scales through wavelet analysis enables calculation of mean separation zone lengths associated with the gravel roughness through standard scaling laws the calculated separation zone lengths demonstrate that wake flapping is a dominant mechanism in the production of large scale coherent flow structures in gravel bed rivers thus we show that coherent flow structures over gravels owe their origin to bed generated turbulence and that large scale outer layer structures are the result of flow topography interactions in the near bed region associated with wake flapping

behavior of trace elements in quartz from plutons of different geochemical signature a case study from the bohemian massif czech republic article i nfo in this study the trace element content in igneous quartz from granitoids of different geochemical types was investigated using the laser ablation icp ms technique the variscan granitoids in the bohemian massif pro vide an excellent opportunity to study the chemical composition of magmatic quartz from the following granite types 1 geochemically primitive i type tonalites and granodiorites 2 peraluminous s type two mica granites 3 moderately fractionated a type volcano plutonic complexes of the teplice caldera and 4 highly fractionated s and a type rare metal granites this diversity of granitoids permitted the study of the chemical composition of magmatic quartz as the result of i different magma protoliths and ii variable degrees of differentiation there were only small differences in the quartz trace element con tents ranging from weakly to moderately differentiated plutons of all geochemical types al mostly in the range between 20 and 250 ppm ti mostly 20 110 ppm b b13 ppm be b0 7 ppm ge b1 ppm li b30 ppm and rb b2 ppm only the s type granites from western erzgebirge contain al enriched quartz mostly 200 400 ppm al since the beginning of its evolution however quartz from the highly fractionated granites group 4 differs significantly this quartz is generally poor in ti b20 ppm ti and enriched in al up to 600 ppm in a type and up to 1000 ppm in s type granites be up to 3 2 ppm ge up to 5 7 ppm li up to 132 ppm particularly in the s type granites and rb up to 15 ppm the contents of the analyzed lithophile elements in the quartz from the highly fractionated granites are similar to the contents reported to be present in evolved complex pegmatites although the input of ti into quartz is controlled mainly by the temperature and pressure of quartz crystallization the entry of al into quartz increases as a function of the water and fluorine content of the residual melt the contents of ge and li increase significantly with the fractionation of parental melt the concentrations of these elements in quartz from highly fractionated granites are controlled by the order of crystallization of the major minerals comb quartz crystallizing before li mica is strongly li enriched whereas groundmass and snowball quartz crystallizing after mica is relatively enriched in ge

near bed turbulence characteristics at the entrainment threshold of sediment beds this experimental study is devoted to quantification of the near bed turbulence characteristics at an entrainment threshold of noncohesive sediments near the bed the departure in the distributions of the observed time averaged streamwise velocity from the logarithmic law is more for immobile beds than for entrainment threshold beds in the reynolds shear stress distributions a damping that occurs near the bed for sediment entrainment is higher than that for immobile beds quadrant analysis reveals that in the near bed flow zone ejections and sweeps on immobile beds cancel each other giving rise to the outward interactions whereas sweeps are the dominant mechanism toward sediment entrainment the bursting duration for entrainment threshold beds is smaller than that for immobile beds on the other hand the bursting frequency for entrainment threshold beds is larger than that for immobile beds the third order correlations indicate that during sediment entrainment a streamwise acceleration associated

evaluation of dem size and grid spacing for fluvial patch scale roughness parameterisation abstract surface roughness is a term used in fluvial research without a unanimous definition clarification of the term and improved parameterisation is needed in future research improvements to the collection of topographic data using photogrammetry have provided accurate digital elevation models dems of field and laboratory gravel bed patches of varied sediment size and surface structure in this study a moving window process is used for analysing spatial variability within dems using this information and in unison the effect of dem size and grid spacing are considered on an extensive range of roughness parameters in order to provide insights for obtaining grain roughness statistics it is shown that dem size influences the calculated roughness statistics and the observation of plateaus in statistics for dem window sizes above 16 d50a in both directions where d50a is the median grain size of the bed surface material suggests this as a minimum dem size for grain scale roughness analysis further the dem grid spacing should be 1 mm or below in order to adequately capture grain roughness as coarser resolutions failed to detect particle imbrication finally variability in roughness parameters was evident due to natural spatial variation in gravel bed microtopography suggesting using a single roughness parameter is not appropriate to holistically describe the roughness of a gravel patch as the importance of topographic information continues to grow in geomorphology the results of this study will assist researchers in the collection and subsequent analysis of dems