double averaging concept for rough bed open channel and overland flows theoretical background the goal of this paper is to discuss the spatial averaging concept in environmental hydraulics and develop it further by considering transport equations for fluid momentum passive substances and suspended sediments the averaging theorems the double averaged in time and in space fluid momentum equation and advection diffusion equations for a passive substance and suspended sediments are introduced and their limitations and applications for modeling rough bed flows experimental design and data interpretation are discussed the suggested equations differ from those considered in terrestrial canopy aerodynamics and porous media hydrodynamics by accounting for roughness mobility change in roughness density in space and time and particle settling effects for the case of suspended sediments we show that the form of the double averaged equations may depend on the type of decomposition of flow variables and that this difference may have important implications for modeling we also show that the suggested methodology offers better definitions for hydraulic characteristics variables and parameters such as flow uniformity flow two dimensionality and bed shear stress

flow resistance in ice covered alluvial channels this paper describes the influences of floating level ice covers on flow and bed load transport in alluvial channels and proposes a semi empirical procedure for calculating flow resistance in such channels the procedure can be applied in conjunction with several existing methods for estimating flow resistance in alluvial channels under open water conditions previously cover influence was poorly understood with the consequence that flow resistance calculations for ice covered alluvial channels entailed an inordinate amount of guesswork the cover influences described herein were determined from the results of experiments conducted with a laboratory flume the main findings of the flume experiments are that ice covers increase flow depth decrease bulk flow velocity increase dune length and significantly decrease bed load transport rate additionally it was found that sediment transport relationships developed for open water flow are applicable to ice covered flow provided they are used in conjunctio

uplift structure of the southern kapuskasing zone from 2 45 ga dike swarm displacement the ca 2 ga kapuskasing zone a 500 km long belt of uplifted crust cuts across the regional structural trend of the archean superior province in canada and disrupts the continuity of 2 45 ga matachewan dikes that form a major swarm in its vicinity as expressed by positive gravity and magnetic anomalies it appears to end about 100 km east of lake superior until now the nature of this termination has remained obscure regional variations in paleomagnetic polarity and in the intensity of feldspar clouding caused by magnetite exsolution are two physical properties of the dike swarm that depend upon postemplacement erosion level they show that the kapuskasing zone as a narrow fault bounded crustal uplift continues after sinistral offset for a further 60 km to the southwest before terminating in a major cross fault dual magnetic polarity and variable levels of feldspar clouding are features found in many other proterozoic dike swarms worldwide and therefore in principle may be used to document other examples of craton response to tectonism

response of the u pb chronometer and trace elements in zircon to ultrahigh temperature metamorphism the kadavur anorthosite complex southern india abstract zircon from quartzites in the contact aureole and wider environs of the kadavur anorthosite complex se india was studied by laser ablation icp ms to assess the response of the u pb isotope system and trace element concentrations to ultrahigh temperature uht contact metamorphism 1000 c combined cathodoluminescence imaging and la icp ms analyses show that zircon grains contain detrital cores which yield ages between 3 4 ga and 1 8 ga and exhibit a large spread in ree concentrations these cores are associated with one or two rims that provide concordant age populations at 955 16 ma and 810 7 ma 2 and relatively uniform ree patterns the older ages of ca 955 ma record the imprints of regional early neoproterozoic metamorphism related to rodinia assembly the younger age is interpreted to date anorthosite emplacement and its associated contact metamorphism during a second regional metamorphic episode coeval with the intrusion of a type granites in the area zircon grains from the country rocks away from the anorthosite show additional rims yielding ages from 590 to 490 ma corresponding to regional pan african tectonometamorphism the zircon rims are either newly grown domains or represent recrystallized and re equilibrated parts of precursor zircon discordance is only observed in 25 of the detrital cores these cores have relatively high u concentrations 400 ppm which strongly suggests that pb loss occurred under u ht conditions by partial recrystallization annealing of zircon that had become metamict the preservation of old concordant ages and source ree characteristics by the low u i e weakly to non metamict detrital cores shows that pristine zircon is extremely robust to thermal disturbance and that its u pb systematics can remain unaffected despite multiple u ht metamorphic episodes these observations imply that u pb ages in zircon cannot be reset by volume diffusion under any crustal conditions disturbance of the u pb system in individual zircon crystals or parts thereof can only be achieved by recrystallization of radiation damaged zircon

three dimensional computation of flow around groyne the three dimensional 3d numerical simulation of a steady shallow turbulent flow around a groyne in a rectangular channel is presented a method used to track a moving surface boundary and to follow its evolution using a one phase 3d reynolds solver with rigid grids by means of a transient fraction of fluid or porosity field is applied some results are compared with experimental data such as the isolines of water depths and the mean velocity field a comparison of the reattachment length prediction using the free surface model and the rigid lid assumption is given other results concerning the pressure field turbulence or shear stress distribution are presented and analyzed

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

live bed scour at bridge piers in a lightweight polystyrene bed abstractexperiments on scour at bridge piers were carried out in a sediment recirculating flume with a bed of polystyrene particles the focus of the research reported in this paper was given to live bed experiments all experiments were run until equilibrium conditions with flow velocities u ranging from 0 8 8 5 times the critical velocity for the incipient motion of sediment particles uc maximum scour depth was continuously measured with an endoscopic camera from inside the pier which was constructed by a plexiglass cylinder bed load transport with dunes was identified as the main transport mode for 1 u uc 4 for ratios of u uc 4 entrainment into suspension without development of bedforms dominated results show that scour rapidly reach equilibrium in the bed of polystyrene pellets in the clear water experiments equilibrium scour depth remained constant in time in the bed load region the fluctuation of scour depth corresponded to the dune migration through the scour hole while in the suspended loa

magnetic properties of anorthosites a forgotten source for planetary magnetic anomalies 1 anorthosites igneous rocks very rich in plagioclase rarely considered to be strongly magnetic are common on earth and the moon and inferred to be on other planets magnetic properties of anorthosites could be important in investigating associated mineral deposits and in studying magnetic anomalies especially on mars here we investigate three late proterozoic anorthosites in rogaland norway for magnetic and petrographic properties two of the anorthosites have large natural remanent magnetization nrm with intensities comparable to tertiary basalts susceptibility nrm and hysteresis properties provide information about the magnetic minerals present and their response to inducing fields microscopic observations show ubiquitous hemo ilmenite in the anorthosites whereas magnetite is common in the haland helleren but rare in the ana sira and egersund ogna bodies this study illustrates that anorthosites can be important sources of magnetic anomalies and can retain a remanent field over geologic time it also supports the recently described property of lamellar magnetization

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

cryogenian 830 ma mafic magmatism and metamorphism in the northern madurai block southern india a magmatic link between sri lanka and madagascar abstract the northern madurai block southern india lies directly south of and partly deformed by the palghat cauvery shear zone system pcss a potential suture of the neoproterozoic mozambique ocean the kadavur gabbro anorthosite complex lies south of the pcss in the northern madurai block and crystallized at 829 14 ma la icpms zircon data in a supra subduction zone setting the complex contains zircon e hf t values of 12 5 to 8 6 that represent palaeoproterozoic t dm model ages 2 3 2 5 ga these broadly agree with a whole rock neodymium t dm model age of 2287 ma oxygen isotope 18 o ratios range from 5 82 and 6 74 the parental magma for the gabbro anorthosites are interpreted to be derived from a juvenile neoproterozoic mantle contaminated by mesoarchaean igneous infra crustal sources the gabbro anorthosites intrude quartzites with dominantly palaeoproterozoic detrital zircons that contain neoarchaean and mesoarchaean hafnium model ages these quartzite zircons contain metamorphic rims that yield an age of 843 23 ma demonstrating the autochthonous nature of the gabbro anorthosite complex later felsic magmatism is recorded by the 766 8 ma crystallisation age of the protolith of a felsic gneiss cryogenian magmatism in the madurai block is interpreted to form part of an extensive arc magmatic province within the southern east african orogen that can be traced from central madagascar through southern india to the wanni complex of sri lanka this province is interpreted to have formed above a south west dipping subduction system as the mozambique ocean was subducted under the neoproterozoic continent azania

flow resistance and bed form geometry in a wide alluvial channel 1 this paper explores the underlying mechanism of flow resistance in a wide alluvial channel with bed forms on the basis of published data it is shown that the grain roughness can be taken as equal to 2 times the median diameter of the bed sediment an empirical equation for the bed form roughness has been proposed and it depends on the bed form height and bed form steepness the influence of the bed form length and height on the total bed shear stress and energy slope is deliberated and empirical expressions for the length of the separation zone behind the bed forms are also proposed the study proposed an equation to compute the total bed shear stress as a function of the grain and bed form roughness as well as the important role of the bed form geometry in the overall flow resistance in alluvial channels the model is tested and verified against 670 flume measurements and 1540 field observations the computed and measured energy slopes are in good agreement with close to 71 of all data sets within the 20 error band

sediment transport under ice cover a method for calculating sediment transport in ice covered flows is developed laboratory data on bed form frictional characteristics and sediment transport are obtained for equivalent free surface and covered flows comparison of the data leads to the conclusion that the lower layer in a covered flow can be treated as a free surface flow for the purpose of calculating bed load transport using the flow characteristics calculated from the k e turbulence model and a conventional bed load equation the sediment transport for covered flows can be obtained the method was verified using measured data

paleomagnetism anisotropy of magnetic susceptibility and argon argon geochronology of the clearwater anorthosite saskatchewan canada abstract the clearwater anorthosite in saskatchewan is a major gabbro anorthosite layered intrusion lying within the archean rae province along the northwestern hinterland of the paleoproterozoic trans hudson orogen tho the intrusion which could be at least 2 4 ga old carries a well defined remanent magnetization with a direction of declination 112 and inclination 38 k 316 95 3 1 n 8 the corresponding paleomagnetic pole plat 6 5 n plong 48 2 w dp 2 2 dm 3 7 is the first one obtained from the archean western granulite domain of the rae province field observations supplemented by anisotropy of magnetic susceptibility data show that the magnetization post dates ductile deformation of the anorthosite argon argon plateau dates of 1917 7 ma for hornblende and 1839 5 ma for biotite are interpreted as cooling ages with the hornblende age approximating the time of remanence the pole position and others of comparable age from the northwestern margin of the tho form a loose cluster the mean of which is about 90 of arc away from that of a broadly contemporaneous group of poles from the superior province this relation supports previous interpretations of paleomagnetic data that prior to the tho at about 1 9 ga ago a major ocean the manikewan ocean at least 5000 km across separated the superior and rae hearne provinces

paleomagnetism of the middle proterozoic laramie anorthosite complex and sherman granite southern laramie range wyoming and colorado we present the results of a combined paleomagnetic and 40ar 39ar geochronologic investigation of the middle proterozoic laramie anorthosite complex and sherman granite in the southern laramie range of wyoming and colorado anorthosites and monzosyenites of the laramie anorthosite complex yield a well defined characteristic magnetization of northeast declination d and moderate negative inclination i although antipodal normal and reverse polarity magnetizations are present at three sites a grand mean direction from 29 of 35 sites in the complex is d 44 6 i 48 7 k 77 4 95 3 1 alternating field af and thermal demagnetization behavior and rock magnetic experiments indicate that magnetization is carried by low ti titanomagnetite of single or pseudo single domain character that occurs as elongate to rod shaped inclusions in plagioclase and potassium feldspar the sherman granite contains a dual polarity magnetization that is less well defined than that of the laramie anorthosite complex but similar in declination and inclination d 53 1 i 48 1 k 46 5 95 7 6 n 8 14 sites rock magnetic data indicate the primary carrier of remanence in sherman granite is magnetite the 40ar 39ar geochronologic data from sherman granite hornblende biotite and microcline indicate that subsolidus cooling was moderate to relatively rapid through the range of temperatures over which magnetization was blocked and that the age of remanence is about 1415 ma microcline data indicate that the laramie anorthosite complex and sherman granite have probably not been thermally remagnetized paleomagnetic poles from the laramie anorthosite complex and sherman granite are indistinguishable at the 95 confidence level and individual virtual geomagnetic poles vgps from both units are combined to provide a mean pole at 215 0 e 6 7 s k 46 9 a95 3 5 n 37 vgps the location of this pole is similar to paleomagnetic poles derived from 1480 ma to 1450 ma intrusions elsewhere in north america but it plots significantly north of those from middle proterozoic sedimentary strata of the belt supergroup and sibley group in addition to the characteristic magnetization samples from some sites in sherman granite contain a remanence of southeast declination and shallow negative inclination d 154 9 i 16 0 k 90 6 95 9 7 n 4 sites this secondary magnetization was probably acquired during late paleozoic time

strong remanent magnetization in pyrrhotite a structurally controlled example from the paleoproterozoic tanami orogenic gold province northern australia abstract rocks associated with an orogenic gold system in the paleoproterozoic granites tanami inlier of northern australia exhibit strong natural remanent magnetism identifiable in regional aeromagnetic data petrographical analysis indicates the two dominant magnetic minerals in the rocks of this region are multidomain magnetite and monoclinic pyrrhotite chemical analysis using an electron microprobe has determined that the magnetite and pyrrhotite are stoichiometrically pure without significant elemental substitution alternating field demagnetization curie temperature and hysteresis analysis indicates that the remanently magnetized phase is monoclinic pyrrhotite with low magnetic susceptibility in contrast multidomain magnetites lack remanence and have high magnetic susceptibilities pyrrhotite is preserved in the rock mass along with other sulfide minerals as millimeter scale veins parallel to regionally developed penetrative mylonitic shear bands c planes formed during sulfide remobilization in the waning cooling stages of hydrothermal au deposition in contrast magnetite grains exhibit porphyroblastic textures consistent with formation during prograde to peak metamorphism indicating formation prior to pyrrhotite earlier in the orogenic cycle because of the low curie temperature ca 325 c of pyrrhotite it is therefore likely that remanent magnetization effects observed in aeromagnetic images of the tanami inlier are associated with structures intimately related to the late stages of au mineralization during retrograde greenschist metamorphism after the peak thermal point of the orogenic cycle

exsolved magnetite inclusions in silicates features determining their remanence behavior submicroscopic needle shaped titanomagnetite inclusions exsolved in silicate minerals commonly occur in mafic intrusive rocks and are protected from alteration by their silicate hosts making them excellent candidates for paleomagnetic studies a suite of samples containing clinopyroxene and plagioclase hosted magnetite inclusions from five geologically diverse sites was examined using magnetic force microscopy to image the inclusions magnetic domain state alternating field demagnetization experiments indicate that some inclusions are more stable recorders than others the two factors controlling the remanence behavior of the inclusions are internal microstructures and inclusion dimensions magnetite ulvospinel unmixing within an inclusion subdivides the original titanomagnetite solid solution into a boxwork structure composed of 103 105 magnetite prisms separated by thin ulvospinel lamellae the conversion of multidomain sized needles into assemblages of interacting single domains increases the coercivity and hence relaxation time of the inclusions and results in a thermochemical magnetic remanence in samples without this exsolution microstructure the inclusions diameters determine coercivity and their magnetization is thermoremanent both styles of high coercivity inclusions successfully record paleomagnetic directions in mesozoic rocks and their ubiquity within silicate minerals clinopyroxene and plagioclase of mafic intrusive rocks indicates their value as chemically and magnetically stable tools for elucidating the ancient magnetic field marine magnetic anomalies and crustal kinematics

crustal uplift in the southern superior province canada revealed by paleomagnetism abstract a change in the polarity of magnetization with depth in the 2 45 ga matachewan dyke swarm is used to document vertical crustal movements that occurred at 1 9 2 3 ga along the kapuskasing structural zone a 500 km long fault zone that transects the archean superior province of canada at shallow crustal levels dykes have a primary magnetization dominantly of one polarity but at greater depths 20 km down a polarity change occurs associated with the growth of exsolved magnetite in feldspar due to slow crustal cooling after cessation of matachewan igneous activity regions of the dyke swarm with one dominant polarity are separated from those with opposite polarity by major faults using this polarity distribution and associated variations in the intensity of feldspar clouding and hydrous alteration maps of the southern superior province are produced that display regional crustal tilting on which are superimposed more local fault bounded blocks associated with the kapuskasing zone some of these blocks have been recognized for the first time as a result of this study the paleomagnetic work has also shown that the matachewan swarm is regionally distorted both within and north of the kapuskasing zone and originally had a more radial disposition this widespread distortion suggests that the lower crust was still relatively ductile at the time of deformation perhaps due to high heat flow associated with the waning stages of the matachewan mantle plume beneath

magnetite rods in plagioclase as the primary carrier of stable nrm in ocean floor gabbros abstract the ubiquitous occurrence of magnetite rods in plagioclase may account for the stable intense magnetization of ocean floor gabbros these single domain grains are formed by the subsolidus exsolution of fe 2 and fe 3 incorporated into the plagioclase at higher temperatures we expect that this process will be particularly important in the upper portions of the oceanic gabbro unit because of the relative paucity of femic minerals at these levels the geometry of accretion prohibits a constructive contribution to marine magnetic anomalies by the lower olivine rich gabbros as a result of the presence of these rods ocean floor gabbros may constitute an important source for marine magnetic anomalies

live bed local pier scour experiments local clear water and live bed scour tests were performed for a range of water depths and flow velocities with two different uniform cohesionless sediment diameters 0 27 and 0 84 mm and a circular pile with a diameter of 0 15 m the tests were performed in a tilting flume 1 5 m wide 1 2 m deep and 45 m long located in the hydraulics laboratory at the university of auckland in auckland new zealand these tests extend local scour data obtained in controlled experiments to velocity ratio v vc values as high as 6 this is near the velocity where the peak live bed scour occurs for the sediment and flow conditions scour depth predictions are made with four different local scour equations for the conditions of the tests and the results compared with the measured values

morphology and microstructure of magnetite and ilmenite inclusions in plagioclase from adirondack anorthositic gneiss it is well known that oriented iron and titanium oxide inclusions occur in pyroxenes and plagioclase of anorthosites and granulites and they are attributed to exsolution at subsolidus conditions the oxides occur as needles or platelets in this study we determine the morphology of oxide needles as well as their orientation in plagioclase an 30 35 in anorthosite gneiss from the adirondack mountains new york the investigation was done with electron backscatter diffraction ebsd in a scanning electron microscope as well as laue diffraction with a microfocus synchrotron x ray beam at the advanced light source in berkeley it was observed that the needle direction is 110 in magnetite and 1010 in ilmenite the needle direction is consistently parallel to 001 of plagioclase furthermore 111 of magnetite and 0001 of ilmenite are sub parallel to 120 and 120 of plagioclase we note that for directions 110 in the magnetite structure and 1010 in ilmenite o atoms are close packed and 111 and 0001 are close packed planes correspondingly in plagioclase 001 is a direction with open channels as well as approximate alignment of si tetrahedral edges thus providing nucleation sites with a coincidence lattice relationship 120 and 120 in this triclinic mineral are planes with approximate tetrahedral sides so that the relationship is structurally plausible from laue diffraction we can determine that the magnetite needle axis is subject to an extensional stress most likely attained during cooling of the inclusions within the plagioclase host

bed load at low shields stress on arbitrarily sloping beds alternative entrainment formulation 1 according to the bagnold hypothesis for equilibrium bed load transport a necessary constraint for the maintenance of equilibrium bed load transport is that the fluid shear stress at the bed must be reduced to the critical or threshold value associated with incipient motion of grains it was shown in a companion paper seminara et al 2002 however that the bagnold hypothesis breaks down when applied to equilibrium bed load transport on beds with transverse slopes above a relatively modest value that is well below the angle of repose an investigation of this failure resulted in a demonstration of its lack of validity even for nearly horizontal beds the constraint is here replaced with an entrainment formulation according to which a dynamic equilibrium is maintained by a balance between entrainment of bed grains into the bed load layer and deposition of bed load grains onto the bed the entrainment function is formulated so that the entrainment rate is an increasing function of the excess of the fluid shear stress at the bed over the threshold value the formulation is implemented with the aid of a unique set of laboratory data that characterizes equilibrium bed load transport at relatively low shear stresses for streamwise angles of bed inclination varying from nearly 0 to 22 the formulation is shown to provide a description of bed load transport on nearly horizontal beds that fits the data as well as that resulting from the bagnold constraint the entrainment formulation has the added advantage of not requiring the unrealistically high dynamic coefficient of coulomb friction resulting from the bagnold constraint finally the entrainment formulation provides reasonable and consistent results on finite streamwise and transverse bed slopes even those at which the bagnold formulation breaks down completely

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

aeromagnetic anomalies magnetic petrology and rock magnetism of hemo ilmenite and magnetite rich cumulate rocks from the sokndal region south rogaland norway aeromagnetic maps of the egersund mid proterozoic igneous province show a spectacular range of positive and negative magnetic anomalies with a contrast up to 15 600 nt the positive magnetic anomalies are over magnetite norites and overlying mangerites and quartz mangerites of the bjerkreim sokndal layered intrusion these rocks are dominated by multi domain md magnetite the negative magnetic anomalies are over ilmenite rich norites of the bjerkreim sokndal layered intrusion the tellnes ilmenite norite ore deposit and massif anorthosites these rocks are dominated by hemo ilmenite and or by silicates containing fine grained oxide exsolution lamellae electron microprobe analyzes of coexisting fe ti oxides in the layered intrusion confirm earlier observations that oxides in early magmatic rocks are dominated by hemo ilmenite with minor end member magnetite followed by more reduced oxides dominated by titanomagnetite with minor near end member ilmenite what is not fully understood is the property of ilmenite with hematite exsolution lamellae or even more striking hematite with ilmenite lamellae to produce strong remanent magnetization of high coercivity and with a neel temperature equal to or above the curie temperature of magnetite this property makes the rhombohedral oxides an important candidate to explain some high amplitude deep crustal anomalies on earth or strong remanent magnetization on other planets a remarkable feature in the egersund province is that primitive magmas produced rocks rich in hemo ilmenite causing negative magnetic anomalies related to magnetic remanence and more evolved magmas produced rocks rich in magnetite related to positive induced magnetic anomalies all in the course of crystallization differentiation

analysis of the time averaged properties of sediment motion in a local scour process 1 we examined the kinematics of sediment particles in the proximity of a vertical plate attached to the side wall of a pressurized duct the laboratory phenomenon investigated was archetypal of local scour near bridge abutments in covered rivers we conducted a clear water scour experiment where we measured the temporal evolution of the local erosion depth the latter was found to follow a logarithmic trend the concentration and velocity of the moving particles were measured on the basis of digital movies taken at various evolution stages of the process the spatial pattern of the sediment motion showed that the action of the principal vortex system becomes progressively more evident with the general lowering of the sediment transport intensity detected as the scour hole increases in time furthermore the phenomenology of local sediment transport was analyzed key findings of the research include 1 the time averaged values of the sediment transport rate are linked with those of concentration and velocity through relationships which are almost invariant regardless of the experimental time and of the location within the scour hole 2 intermittency and irregularity of the sediment fluxes increase as their mean intensity decreases 3 the relative weight of the temporal fluctuations of concentration and velocity in the time mean sediment transport activity is significant throughout the entire process potential implications of the present results for the modeling of local scour processes in pressurized flow conditions are discussed the considerations made are likely to have analogous applicability to local scour with a free surface since the large scale evolutions of the erosion depth in the two conditions may not be greatly different given the qualitative analogy of the present findings with earlier ones obtained for one dimensional bed load it is suggested that similar considerations may hold also for the small scale modeling of a wider class of sediment transport processes

gravel saltation 2 modeling a lagrangian model for the motion of a sediment particle in a water flow is proposed the particle motion equation is averaged over flow turbulence specialized to the case of coarse sediment particles saltating in water and coupled with a stochastic model for particle collision with the bed model predictions of statistics of gravel saltation generally agree well with experimental observations as an application of the saltation model bed load transport rates are estimated from modeled mean saltation streamwise velocity and a dynamic friction coefficient the results obtained compare favorably with typical bed load equations but they overestimate experimental measurements of gravel transport which would suggest that a bagnoldean formulation for bed load transport of coarse material by saltating particles may not be valid

dynamic routing of flow resistance and alluvial bed form changes from the lower to the upper regime on the basis of a strouhal number and the definition of the control factor m a new routing to calculate the energy slope in the lower and upper alluvial regimes is proposed the control factor m representing the interactions in alluvial rivers is reckoned as a bed form index while the flow evolves through transition the control factor m decreases from m 2 associated with two dimensional fully developed dunes to m 1 associated primarily with in phase waves the way to predict the value of the control factor m is drawn from a previously published criterion for delineating the upper regime and is calibrated with experimental data on several data from flumes and rivers the routing is tested and compared with other methods from the literature it appears that the new routing is the most robust because it allows researchers to obtain low averages of the discrepancy ratio for a wide range of ratios between the water depth and the median sediment diameter on a selection of contrasted freshet events the new routing allows for the capture of the primary dynamic of the flow resistance decrease

effect of bed sediment entrainment on debris flow resistance entrainment of sediment from hillslope and channel usually has a significant influence on resistance of debris flow this effect is studied by flume experiments of debris flow over rigid and erodible beds fifty contrast flume tests show that the flow resistance over the erodible bed is significantly larger than that over the rigid bed because of higher energy consumption resulting from sediment transport a new formula of debris flow resistance involving the entrainment effect is obtained from the erodible bed data by nondimensional multiple regression analysis

fluvial dunes initiation characterization flow structure research into fluvial dunes spans disciplines studies at grain to reach scales and methodological approaches that include theoretical experimental numerical and field investigations despite significant research efforts to date it remains difficult to provide definitive answers to some fundamental questions regarding dunes this paper reviews three notable challenges that remain regarding fluvial dunes namely scale consistent linking of bed morphologies with turbulent flow fields the intriguing question of what causes trains of highly ordered sediment waves to form in beds of river sediments and how to define the important characteristics of a dune covered bed including lengths shapes and their statistical nature in each case the particular challenge is discussed and then recent research and ways forward are presented copyright 2010 john wiley sons ltd

algorithm for resistance to flow and transport in sand bed channels an algorithm is developed that relates depth to discharge and determines bed and suspended load transport for the entire range of bed forms found in sand bed channels equilibrium state geometry of lower flow regime bedforms is also predicted grain shear stress and form resistance are differentiated using a drag coefficient closure and a two segment logarithmic velocity profile a meyer peter type formulation is used to compute sand transport in the bed load layer and for computing suspended sand transport mclean s procedure of 1991 and 1992 is adopted a bed form classification scheme is developed that uses a particle size parameter and the transport strength to predict bed form type it correctly identifies 73 of the 1 192 mostly flume scale calibration data sets for 194 sets of dune transition bed form calibration data a modified version of van rijn s 1984 bed form geometry predictor yields a geometric average predicted to observed height ratio of 1 00 after calibration the algorithm produces overall geometric averages of predicted to observed depth and predicted to observed transport of 1 00 for a verification data set of 855 observations mostly from rivers and canals the overall geometric averages of predicted to observed depth and transport are 0 87 and 1 14

experimental and numerical investigation of local scour around a submerged vertical circular cylinder in steady currents abstract local scour around a submerged vertical circular cylinder in steady currents was studied both experimentally and numerically the physical experiments were conducted for two different cylinder diameters with a range of cylinder height to diameter ratios transient scour depth at the stagnation point upstream edge of the cylinder was measured using the so called conductivity scour probes three dimensional 3d seabed topography around each model cylinder was measured using a laser profiler the effect of the height to diameter ratio on the scour depth was investigated the experimental results show that the scour depth at the stagnation point is independent on cylinder height to diameter ratio when the later is smaller than 2 the increase rate of equilibrium scour depth with cylinder height increases with an increase in shields parameter a three dimensional finite element numerical model is developed for simulating local scour around submerged vertical cylinders steady flow around the cylinder is simulated by solving the reynolds averaged navier stokes rans equations with a k turbulence closure both suspended load and bed load sediment transport rates were included in the model efforts are made to reduce the computational time associated with three dimensional morphological modelling including the use of wall function to avoid resolving the near wall boundary layers large morphological time step and parallel computing techniques scour around a submerged vertical circular cylinder founded on the seabed is simulated and the numerical results are validated against the test data the scour mechanisms around the submerged cylinder are investigated using the numerical model

quantitative estimates of emplacement level of postmetamorphic mafic dykes and subsequent erosion magnitude in the southern kapuskasing uplift the early proterozoic matachewan 2 454 ga and kapuskasing 2 04 ga dyke swarms of the central superior province have similar petrographic features including zoned igneous plagioclase and clinopyroxene and interstitial amphibole and quartz dyke crystallization conditions can be estimated using equilibria involving amphibole by assuming that igneous mineral rims reached equilibrium with the interstitial phases twq software using 33 amphibole bearing equilibria yields temperatures ranging from 552 to 811 c with an average of 680 c the average of two calibrated pressure sensitive equilibria 2 diopside 2 quartz tschermakite tremolite 2 anorthite and diopside 5 quartz pargasite tremolite anorthite albite ranges from 0 32 to 0 70 gpa for matachewan dykes and from 0 30 to 0 57 gpa for kapuskasing dykes because dyke pressures are lower than metamorphic pressures in the amphibolite and granulite facies archean country rocks the values represent feasible emplacement pressures the regi

live bed scour at bridge piers the relationship between scour depth at cylindrical bridge piers founded in cohesionless sediments and mean approach flow velocity is defined for flows above the threshold of particle motion expe

a systematic analysis of eight decades of incipient motion studies with special reference to gravel bedded rivers data compiled from eight decades of incipient motion studies were used to calculate dimensionless critical shear stress values of the median grain size t c 50 calculated t c 50 values were stratified by initial motion definition median grain size type surface subsurface or laboratory mixture relative roughness and flow regime a traditional shields plot constructed from data that represent initial motion of the bed surface material reveals systematic methodological biases of incipient motion definition t c 50 values determined from reference bed load transport rates and from visual observation of grain motion define subparallel shields curves with the latter generally underlying the former values derived from competence functions define a separate but poorly developed field while theoretical values predict a wide range of generally higher stresses that likely represent instantaneous rather than time averaged critical shear stresses the available data indicate that for high critical boundary reynolds numbers and low relative roughnesses typical of gravel bedded rivers reference based and visually based studies have t c50 ranges of 0 052 0 086 and 0 030 0 073 respectively the apparent lack of a universal t 50 for gravel bedded rivers warrants great care in choosing defendable t c50 values for particular applications

nanoscale haematite ilmenite lamellae in massive ilmenite rock an example of lamellar magnetism with implications for planetary magnetic anomalies summary massive nearly pure haemo ilmenite layers from historic ore deposits in rogaland norway contain very few silicates or other oxides and typically produce remanence dominated magnetic anomalies these rocks are ideal for evaluating the magnetic properties of fine exsolution intergrowths and the larger titanohaematite lamellae in the host ilmenite grains a typical bulk composition ilm 84 exsolved at high temperature to produce host ilmenite ilm 94 and micron sized haematite lamellae ilm 23 as measured by electron microprobe emp subsequent undercooling of the ilmenite and the micron scale haematite lamellae led to metastable nucleation of nanoscale lamellae down to unit cell scale leaving depleted hosts between lamellae with compositions of ilm 98 and ilm 15 13 as measured by tem edx samples have high coercivities and average nrm values of 25 a m 1 which typically show 2 per cent saturation in the nrm state the amount of magnetization in these samples is too high to be solely accounted for by a spin canted af moment in the haematite based on monte carlo simulations of haematite ilmenite interfaces at the atomic scale and on measured rock magnetic properties we predict that the magnetization is carried by a ferrimagnetic substructure produced at the contacts of the very fine scale titanohaematite and ilmenite exsolution lamellae

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

numerical and experimental investigation of flow and scour around a circular pile the flow around a vertical circular pile exposed to a steady current is studied numerically and experimentally the numerical model is a three dimensional model the model validation was achieved against new experimental data which include two component laser doppler anemometry lda flow measurements and the hot film bed shear stress measurements and reported in the present paper and the data of others and a k w turbulence model was used for closure the model does not have a free surface facility and therefore is applicable only to cases where the froude number is small fr 0 0 2 the flow model was used to study the horseshoe vortex and lee wake vortex flow processes around the pile the influence on the horseshoe vortex of three parameters namely the boundary layer thickness the reynolds number and the bed roughness was investigated in the latter investigation the steady solution of the model was chosen a study of the influence of the unsteady solution on the previously mentioned flow processes was also carried out the ranges of the parameters covered in the numerical simulations are the boundary layer thickness to pile diameter ratio is varied from 2 x 10 2 to 10 2 the pile reynolds number from 10 2 to 2 10 6 and the pile diameter to roughness ratio from 2 to about 10 3 the amplification of the bed shear stress around the pile including the areas under the horseshoe vortex and the lee wake region was obtained for various values of the previously mentioned parameters the steady state flow model was coupled with a morphologic model to calculate scour around a vertical circular pile exposed to a steady current in the case of non cohesive sediment the morphologic model includes i a two dimensional bed load sediment transport description and ii a description of surface layer sand slides for bed slopes exceeding the angle of repose the results show that the present numerical simulation captures all the main features of the scour process the equilibrium scour depth obtained from the simulation agrees well with the experiments for the upstream scour hole some discrepancy up to 30 was observed however for the downstream scour hole the calculations show that the amplification of the bed shear stress around the pile in the equilibrium state of the scour process is reduced considerably with respect to that experienced at the initial stage where the bed is plane

variation in plagioclase clouding intensity in matachewan dykes evidence for the exhumation history of the northern margin of the sudbury igneous complex early proterozoic matachewan mafic dykes that cut the archean cartier granite levack gneiss complex north of the sudbury igneous complex sic canada are generally metamorphosed to lower amphibolite facies but exhibit locally unaltered plagioclase these plagioclase feldspars display a clouding similar to that found in the same swarm in the vicinity of the kapuskasing uplift about 200 km to the northwest where the clouding intensity is due to magnetite exsolution and displays a positive correlation with the depth of dyke emplacement in the sudbury area the clouding intensity obtained by image analysis of thin sections increases away from the sic opposite to the direction of increasing regional metamorphism in the archean basement this suggests that the levack gneiss complex north of the sic was exhumed prior to the intrusion of 2 47 ga matachewan dykes and therefore predates the formation of the sic and associated impact event the southward tilting of the crust inferred from the plagioclase clouding data appears to have involved uplift along the benny deformation zone but the exact age of this deformation is unknown it may be associated with the 1 8 1 9 penokean orogen 1 85 ga sudbury impact crater or 2 2 2 4 ga blezardian orogen resume les dykes mafiques de matachewan proterozoique precoce qui recoupent le complexe de granite cartier gneiss levack archeen au nord du complexe igne de sudbury sic sont generalement metamorphoses au facies inferieur des amphibolites mais ils montrent par endroits du plagioclase inaltere ces feldspaths presentent un embrouillage semblable ce que l on retrouve dans le meme essaim aux environs du bloc sureleve de kapuskasing environ 200 km au nord ouest ou l intensite de l embrouillage est causee par de l exsolution de la magnetite et demontre une correlation positive avec la profondeur de la mise en place du dyke dans la region de sudbury l intensite de l embrouillage obtenue par l analyse d images de sections minces augmente en s eloignant du sic soit dans la direction opposee du metamorphisme regional croissant dans le socle archeen cela suggere que le complexe de gneiss levack au nord du sic a ete exhume avant l intrusion des dykes mafiques de matachewan 2 47 ma et donc qu il est plus vieux que la formation du sic et associe a l evenement d impact l inclinaison vers le sud de la croute deduite a partir des donnees d embrouillage du plagioclase semble impliquer un soulevement le long de la zone de deformation de benny mais l ge exact de cette deformation est inconnu la deformation peut etre associee a l orogene penokeen 1 8 1 9 ga au cratere d impact de sudbury 1 85 ga ou a l orogene blezardien vers 2 2 2 4 ga traduit par la redaction siddorn and halls 942

crossover plots a useful method for plotting sirm data in paleomagnetism the effective grain size of magnetic minerals and therefore domain type controls the saturation isothermal remanent magnetization acquisition and subsequent demagnetization response and can be used to create crossover plots for paleomagnetic specimens where sirm is plotted as a function of the field applied using a logarithmic scale this paper presents templates of such plots for magnetite pyrrhotite hematite and goethite onto which sample data can be plotted for conventional paleomagnetic specimens to characterize their magnetic mineralogy and effective grain size

sediment transport part i bed load transport a method is presented which enables the computation of the bed load transport as the product of the saltation height the particle velocity and the bed load concentration the equations of motions for a solitary particle are solved numerically to determine the saltation height and particle velocity experiments with gravel particles transported as bed load are selected to calibrate the mathematical model using the lift coefficient as a free parameter the model is used to compute the saltation heights and lengths for a range of flow conditions the computational results are used to determine simple relationships for the saltation characteristics measured transport rates of the bed load are used to compute the sediment concentration in the bed load layer a simple expression specifying the bed load concentration as a function of the flow and sediment conditions is proposed a verification analysis using about 600 alternative data shows that about 77 of the predicted bed load transport rates are within 0 5 and 2 times the observed values

transition between two bed load transport regimes saltation and sheet flow in the saltation regime where bed shear stress is low bed load moves by sliding rolling and saltating along the bed while in the sheet flow regime where bed shear stress is high it travels by a combination of saltation and sheet flow in this paper a theoretical model is developed for predicting the onset of the sheet flow regime as shear stress increases this model is based on a new variable pb representing the proportion of grains on the bed that are entrained as bed load the model yields the equation pb 2 56g 3 in which g 1 c dimensionless bed shear stress and c critical value of at which grains begin to move the equation shows that t which is the value of at the onset of the sheet flow regime and is assumed to occur when pb 1 is around 0 5 with the exact value controlled by c for example when c 0 045 t 0 52 the theoretical model is verified by performing a nonlinear regression analysis on data from 285 flume experiments additional flume experiments with a high speed video hsv system result in consistent values of for the onset of the sheet flow regime which support the theoretical model the hsv images further reveal that 1 the sheet flow regime is characterized by granular sheets or laminations and 2 a zone of mixed saltation and rolling grains exists not only in the saltation regime but also in the sheet flow regime

live bed pier scour in a covered flow abstractresults are presented for a novel experimental investigation of live bed scour at a cylindrical pier in covered flow the experimental campaign also comprehended a reference scour test in c

flow resistance over mobile bed in an open channel flow this paper deals with the underlying mechanism of flow resistance in an alluvial channel the effects of sidewall and bed form on flow resistance einstein s divided hydraulic radius approach and engelund s energy slope division approach are reexamined these two approaches assume that the shear stress on a mobile bed is the summation of shear stresses caused by skin friction and bed form using a different approach this paper presents a theoretical relationship between the total bed shear stress with grain and bed form shear stresses the contribution of sidewall on the total bed shear stress is also discussed the writers found that the size of bed form plays a significant role for the flow resistance and developed relevant expressions for the length of the separation zone behind the bed forms in addition a systematical approach has been developed to compute the flow velocity in an alluvial channel this approach is tested and verified against 5 989 flume and field measurements the computed and mea

paleomagnetic evidence of complex tectonic rotation pattern in the nw anatolian region implications for the tectonic history since the middle eocene abstract the kinematic evolution of the almacik block and the armutlu region which are surrounded by the branches of the north anatolian fault is not completely understood because of incompatible paleomagnetic data a previous paleomagnetic study in the almacik block indicated that there have been large rotations associated with the rotation as a whole coherent block and another study postulated a more complex tectonic evolution the aim of this study was to obtain paleomagnetic directions on middle eocene volcanic volcanoclastic rocks at 25 sites in nw anatolia and to determine the tectonic deformation process along the north anatolian fault zone after rock magnetic measurements and stepwise thermal and alternating field demagnetisation most of the samples taken were characterised by one component of magnetisation after the removal of viscous magnetisation a characteristic remanent magnetisation was obtained at 500 580 c showing evidence of magnetite and titanomagnetite with a small amount of ti however in some cases a high temperature component was isolated between 600 and 650 c indicating a titanohematite composition the mean direction obtained from the istanbul zone d 191 5 i 47 1 95 7 1 indicated no tectonic rotation relative to the reference direction of the stable eurasian plate d 191 0 i 53 2 95 5 0 besse and courtillot 2002 torsvik et al 2008 in the middle eocene the paleomagnetic directions in the almacik block and the armutlu region suggest counterclockwise rotations of 22 3 7 8 and 17 7 14 6 respectively relative to the istanbul zone when integrated together with previous studies our paleomagnetic results indicate that both the armutlu region and the almacik block were emplaced in the same area during the middle eocene the deformation of the northern branch of the north anatolian fault resulted in a bend and an overstep fault offset of 25 km between lake sapanca and lake abant during this process both the almacik block and the armutlu region were separated distinctly from each other with a counter clockwise rotation with respect to the istanbul zone in addition within some parts of the almacik block an internal deformation with large declination anomalies ranging from 160 to 250 was observed in this study and in previous studies these different declinations could be the result of chemical remagnetisation of hydrothermal events stress related magnetisation or small block rotations

alluvial resistance in transition regime the resistance of alluvial channels depends upon flow and sediment characteristics this paper considers the bed features and alluvial resistance that occur at and close to the transition zone between the upper and lower flow regimes new flume and river data are published and the results are analyzed to provide satisfactory predictive techniques covering the lower transition and upper regimes for use by river engineers the bed features that occur in the transition regime are shown to be washed out dunes that diminish rapidly in height and steepness with increasing shear stress the increase in depth with increasing unit discharge is much reduced in the transition regime due to lower hydraulic resistance in certain circumstances depths in the transition region can decrease with increasing unit discharge a criterion for the upper limit of the transition regime corresponding to a moving flat bed is proposed by the writers

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

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

controls of channel morphology and sediment concentration on flow resistance in a large sand bed river a case study of the lower yellow river abstract accurate estimation of flow resistance is crucial for flood routing flow discharge and velocity estimation and engineering design various empirical and semiempirical flow resistance models have been developed during the past century however a universal flow resistance model for varying types of rivers has remained difficult to be achieved to date in this study hydrometric data sets from six stations in the lower yellow river during 1958 1959 are used to calibrate three empirical flow resistance models eqs 5 7 and evaluate their predictability a group of statistical measures have been used to evaluate the goodness of fit of these models including root mean square error rmse coefficient of determination cd the nash coefficient na mean relative error mre mean symmetry error mse percentage of data with a relative error 50 and 25 p 50 p 25 and percentage of data with overestimated error poe three model selection criterions are also employed to assess the model predictability akaike information criterion aic bayesian information criterion bic and a modified model selection criterion msc the results show that mean flow depth d and water surface slope s can only explain a small proportion of variance in flow resistance when channel width w and suspended sediment concentration ssc are involved the new model 7 achieves a better performance than the previous ones the mre of model 7 is generally

nature and origin of lamellar magnetism in the hematite ilmenite series grains consisting of finely exsolved members of the hematite ilmenite solid solution series such as are present in some slowly cooled middle proterozoic igneous and metamorphic rocks impart unusually strong and stable remanent magnetization tem analysis shows multiple generations of ilmenite and hematite exsolution lamellae with lamellar widths ranging from millimeters to nanometers rock magnetic experiments suggest remanence is thermally locked to the antiferromagnetism of the hematite component of the intergrowths yet is stronger than can be explained by canted antiferromagnetic caf hematite or coexisting paramagnetic pm fe ti ordered r 3 ilmenite alone in alternating field demagnetization to 100 mt many samples lose little remanence indicating that the nrm is stable over billions of years this feature has implications for understanding magnetism of deep rocks on earth or on planets like mars that no longer have a magnetic field atomic scale simulations of an r 3 ilmenite lamella in a caf hematite host based on empirical cation cation and spin spin pair interaction parameters show that contacts of the lamella are occupied by contact layers with a hybrid composition of fe ions intermediate between fe2 rich layers in ilmenite and fe3 rich layers in hematite structural configurations dictate that each lamella has two contact layers magnetically in phase with each other and out of phase with the magnetic moment of an odd non self canceling fe3 rich layer in the hematite host the two contact layers and the odd hematite layer form a magnetic substructure with opposite but unequal magnetic moments a lamellar ferrimagnetism made possible by the exsolution because it is confined to magnetic interaction involving the moments of just three ionic layers associated with each individual exsolution lamella lamellar magnetism is unique and quite distinct from conventional ferrimagnetism simulation cells indicate that the magnetic moments of contact layers are locked to the magnetic moments of adjacent af hematite layers and are parallel to the basal plane 001 thus lamellar magnetism is created at the temperature of chemical exsolution and is a chemical remanent rather than thermal remanent magnetization however in thermal demagnetization experiments too short for lamellar resorption demagnetization temperatures are those of the caf hematite considerably higher than temperatures of original lamellae formation internal crystal structure cannot dictate that the contact layers of different lamellae will form magnetically in phase with each other to give the highest net magnetic moment but magnetic moments of lamellae can be made to form in phase by the external force of the magnetizing field at the time of exsolution a thesis of this paper is that an external magnetic field can dictate the magnetic moments and hence the chemical location of ilmenite lamellae in a hematite host and that once in place neither the location nor the magnetic moment will be easily disturbed in an ilmenite host the external magnetic field cannot control the chemical location of a hematite lamella which is dictated by the enclosing ilmenite but once lamellae have formed the field can dictate their magnetic moments these moments however are not locked chemically to the host resulting in lower coercivity the effectiveness of the external force in single crystals is dictated by their orientation with respect to the magnetizing field in grains with 001 oriented parallel to the field it would be effective in producing in phase magnetic moments and very strong remanence in grains with 001 normal to the field the field would be less effective in producing in phase magnetic moments hence producing weak remanence the most intense lamellar magnetism per formula unit occurs with in phase magnetization high lamellar yields and the largest number of lamellae per unit volume i e smallest lamellar size compared to the magnetic moment per formula unit m pfu and magnetic moment per unit volume m v of end member magnetite m pfu 4 b m v 480 ka m and hematite m pfu 0 0115 b m v 2 1 ka m results for some atomic models reasonably tied to natural conditions are m pfu 0 46 1 36 b and m v 84 250 ka m

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