wave energy distribution and morphological development in and around the shadow zone of an embayed beach abstract background the curved shoreline shape of embayed beaches is one of its most notable characteristics and can be described using the parabolic bay shape equation pbse wave diffraction in and around the shadow zone is often regarded as the primary forcing mechanism leading to the prominent curvature of the shoreline however wave climate variables wave direction directional spreading and wave height are shown to be influential in redistributing wave energy throughout the bay and in the shadow zone methods in this study a process based morphological model delft3d is used for hydrodynamic and morphodynamic simulations of a schematic embayed beach wave forcing conditions are systematically varied between a mixture of time invariant and time varying cases results the role of diffraction is shown to be dominant only when the wave conditions are both narrow banded 30 otherwise as little as 6 variation in wave direction within a 90 range can account for the shoreline curvature in and around the shadow zone conclusion the degree to which wave direction and directional spreading vary through time therefore has a large effect on the equilibrium orientation and shoreline planform of the bay

magnetic susceptibility of the rock matrix related to magnetic fabric studies non ferromagnetic minerals constitute what is called the rock matrix whose susceptibility k1 is directly accessible using only high magnetic fields measurements on minerals and a wide range of rock types show that k1 is mainly due to paramagnetism and hardly exceeds 10 3 si with an anisotropy degree p less than 1 35 different methods to estimate the role of the matrix component in low field susceptibility k and its anisotropy include petrological and chemical analysis evolution of p vs k low temperature studies and comparison of k with remanent magnetizations

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

quantitative correlation of texture and magnetic anisotropy of compacted calcite muscovite aggregates abstract deformation of carbonate rocks leads to crystallographic preferred orientations cpos of calcite which in turn generates an anisotropy of magnetic susceptibility ams the use of the diamagnetic anisotropy which arises from the preferential orientation of calcite for texture characterization is usually hindered by 1 the weakness of the anisotropy and 2 overlapping contributions from paramagnetic and ferromagnetic minerals to the ams in this study the diamagnetic paramagnetic and ferromagnetic sub fabrics of synthetic calcite muscovite samples have been separated using high field torque measurements the cpo of calcite and muscovite has been determined by neutron diffraction and the magnetic sub fabrics are compared to the ams that was re calculated from the cpo the isolated diamagnetic sub fabric shows a good correlation with the calcite texture for calcite concentrations above 70 the paramagnetic sub fabric is shown to be a reliable texture parameter for muscovite even at a concentration of 5 the results demonstrate the capability of the ams method as a texture parameter in impure carbonate rocks

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

the grain fluid interaction as a self stabilizing mechanism in fluvial bed load transport a grain scale model of fluvial bed load transport is described with particular emphasis on the equilibrium between the saltating grains and the near bed flow and its role in determining transport rate the model calculates explicitly the modification of the velocity profile by the moving grains together with the consequential reduction in surface fluid shear stress as the surface fluid shear stress is reduced by the moving grains so the entrainment rate decreases and the model reaches a steady state the results provide insight into two important questions at a macroscopic level first they show that in the absence of large static roughness the dynamic roughness caused by the moving grains may be a significant contributor to flow resistance secondly the model indicates the manner in which transport may be limited by a combination of the transport capacity of the flow and the availability of sediment for entrainment only in the case of high sediment availability does the fluid shear stress acting at the surface approach the critical entrainment value reproducing the behaviour suggested by bagnold 1956 and owen 1964 this suggests that prediction formulae based on this assumption only describe the bed load transport system under particular conditions

geochemical evolution and tectonic significance of boninites and tholeiites from the koh ophiolite new caledonia the central chain ophiolites in new caledonia are fragments of a supra subduction zone ssz ophiolite now preserved from the upper layered gabbros through to volcanics and overlain by pelagic cherts and a thick middle triassic to upper jurassic volcaniclastic sequence most of the fragments were formed by a single tholeiitic magmatic episode but one of these the koh ophiolite was formed by two tholeiitic magmatic episodes separated by boninites the first event in the koh ophiolite formed cumulate gabbros dolerites plagiogranites and the first pillow lava sequence from a tholeiitic magma with strong depletion in the light rare earth elements lree and abnormally low tio2 0 5 at mg 60 shortly after their eruption these tholeiitic lavas were overlain by a high ca boninitic unit with a basal section of boninite pillows flows and breccias and an upper section of boninitic dacites and tuffs the last magmatic phase involved eruption of evolved tholeiitic basalts as pillows above the boninites and as dykes and sills intruding the older plutonic and volcanic sections of the ophiolite this second phase of tholeiitic magmatism is compositionally distinct from the first and is closest to back arc basin basalts babb erupted during the early rifting history of modern back arc basins the boninitic volcanics belong to a high ca series with slightly lower sio2 al2o3 and tio2 compared to those from modern island arc systems and they lack the positive zr spike relative to adjacent rare earth elements ree in normalised element variation patterns these boninites were formed shortly after the production of back arc basin crust represented by the depleted tholeiites and shortly before a second spreading event which caused 40 60 extension of the initial basin crust and eruption of the upper tholeiites the dominance of babb like tholeiites throughout the central chain ophiolites in new caledonia the restricted occurrence of boninites and the stratigraphy and chemistry of the koh ophiolite suggest that the boninites were erupted in response to an exceptional tectonic situation we suggest that this boninite generation event was driven by adiabatic decompression of hot depleted mantle residual from the production of the lower tholeiites during initiation of rifting of young oceanic crust intimately associated with propagation of a back arc basin spreading centre the occurrence of a thick blanket of calc alkaline volcaniclastic sediments above the ophiolite indicates proximity to a mature arc and suggests that the koh boninites were not associated with the initiation of subduction a close modern analogy for the koh ophiolite exists on the hunter ridge protoisland arc between southernmost vanuatu new hebrides island arc and the fijian islands there high ca boninites lacking positive zr spikes occur together with low ti tholeiites and more typical babb tholeiites where the southern spreading centre of the north fiji basin is propagating into the protoarc crust of the hunter ridge

restoration of the cretaceous uplift of the harz mountains north germany evidence for the geometry of a thick skinned thrust reverse movement on the harz northern boundary fault was responsible for the late cretaceous uplift of the harz mountains in northern germany using the known geometry of the surface position and dip of the fault and a published cross section of the base permian horizon we show that it is possible to predict the probable shape of the fault at depth down to a detachment level we use the inclined shear method with constant heave and argue that a shear angle of 30 was most likely in this case the detachment level is at a depth of ca 25 km kinematic restoration of the harz mountains using this fault geometry does not produce a flat horizon rather it results in a ca 4 km depression airy heiskanen isostatic equilibrium adjustment of the harz mountains restores the base permian horizon to the horizontal as well as raising the moho to a depth of 32 km a typical value for northern germany restoration also causes a rotation of tectonic fabrics within the harz mountains of about 11 clockwise we show that this model geometry is very good fit to the interpreted dekorp basin 9601 deep seismic profile

bedload a granular phenomenon bedload the transport of sediment remaining in contact with the stream bed has mainly been studied from the perspective of the correlation between fluid driving forces and the responding sediment flux yet grain grain interactions are important and bedload should also be considered as a granular phenomenon we review progress made recently in the study of granular flows especially on segregation and rheology that better illuminates the nature of bedload granular flows may exhibit gas like or fluid like flow or quasi solid deformation all three conditions might be duplicated in bedload understanding of intense bedload transport occurring continuously in a layer several grains deep typical of sand beds might greatly benefit from results in granular physics as illustrated by grain inspired bedload results however processes restricted to the surface of the bed when particles move intermittently and the bed becomes structured while characteristic in gravel bed channels are not well addressed in granular physics mutual study of these phenomena may benefit both physics and fluvial geomorphology we intend therefore to contribute to an enhanced dialogue between granular physics and bedload science communities copyright 2010 john wiley sons ltd

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

inception and early evolution of the ordovician macquarie arc of eastern gondwana margin zircon u pb hf evidence from the molong volcanic belt lachlan orogen abstract the ordovician macquarie arc is faulted against and surrounded by coeval gondwana derived quartz turbidites in the lachlan orogen of southeastern australia how these juvenile island arc rocks were emplaced and structurally interleaved with continental margin sequences of eastern gondwana is an ongoing debate understanding the inception of this arc is critical in building an accurate early paleozoic reconstruction for eastern gondwana however the arc s inception and early evolution are poorly constrained due to the lack of reliable geochronological data integrated field observations zircon u pb hf mineral and whole rock geochemistry are presented here for the oldest units of the molong volcanic belt which is a central strand of the dissected macquarie arc geochemistry indicates that these are calc alkaline rocks with high k locally shoshonitic to medium k affinities the stratigraphically lowest mafic volcanic and volcano sedimentary rocks of the mitchell formation have a unimodal earliest ordovician zircon u pb age of 479 8 3 8 ma with uniform depleted mantle like initial zircon ehf values of 12 to 13 the lack of pre ordovician zircons and the uniform positive initial ehf value indicate that the macquarie arc was initiated in an intra oceanic setting far from the influence of eastern gondwana the stratigraphically overlying fairbridge volcanics includes some more evolved volcano sedimentary components and has a polymodal but mostly ordovician zircon u pb age population with a youngest component at 444 3 2 4 ma overall its ordovician grains show a greater spread in initial ehf values from 14 down to 8 than the mitchell formation which suggests some continental influence at least 35 million years after the arc was initiated the lack of any significant gondwanan inheritance in early ordovician volcaniclastic rocks of the macquarie arc along with geochemical comparisons with modern island arcs suggest that the arc evolved outboard of gondwana probably as a result of steep easterly directed subduction as the macquarie arc approached eastern gondwana there would have been increasing quantities of continent derived sediment subducted beneath the arc which may account for the decreasing and more variable zircon initial ehf values and the appearance of sparse precambrian continental detritus at the arc s moribund stage the collision of the macquarie island arc with gondwana initiated the benambran orogeny and reflects an important mechanism of episodic continental growth involving the addition of juvenile oceanic crust to a continental margin which contrasts and alternates with periods of purely accretionary growth

rheology of rocksalt abstract we review progress in experimental determinations of transient and steady state flow properties and processes of natural rocksalt aggregates focusing primarily on results from avery island louisiana domal salt the steady state flow field established from constant stress and constant strain rate tests at temperatures from 50 to 200 c strain rates from 10 5 to 10 9 s 1 and differential stresses from 20 7 to 2 5 mpa has been separated into two flow regimes each fit by a power law relation at the higher stresses and strain rates this relation is e 1 6 10 4 exp 68 1 rt 10 3 5 3 for which the pre exponential constant is expressed in mpa 5 3 s 1 and the apparent activation energy is in j mol 1 creep rates predicted by equation a do not differ appreciably from those predicted previously the relatively low stress low strain rate data are very well fit by e 8 1 10 5 exp 51 6 rt 10 3 2 4 which is comparable conditions predicts creep rates higher and equivalent viscosities lower than does equation a by two orders of magnitude the change in behavior from a to b is ascribed to a change in rate limiting mechanism from cross slip of screw dislocations to the climb of edge dislocations in this dry material subgrain formation dominates microstructural development during steady state flow of salt and from determinations of average subgrain diameters in crystals from 20 different rocksalt bodies flow stress levels between 0 6 and 1 4 mpa have been estimated these values do not bear directly on arguments concerning the nature of forces initiating salt pillow growth because apparently evidence relating to the early deformational history has been overprinted at that stage fluid assisted grain boundary diffusional processes might dominate dislocation creep leading to a linear stress strain rate mechanical response considering buoyancy forces alone behavior described by equation b rather than a reduces the relief necessary to initiate pillow growth but a 1000 fold amplification is required to produce stress differences near 1 mpa that forces other than buoyancy are important is indicated by the occurrence of these same paleostress levels in bedded salts and in shallow offshore concordant intrusions differential loading generally provides the most plausible initial driving force for the growth of diapiric salt structures

ophiolite accretion in the lachlan orogen southeastern australia slivers of dismembered cambrian ophiolites are preserved in major fault zones of the turbidite dominated western and central lachlan orogen of southeastern australia geometrical chronological and metamorphic constraints indicate that these slivers did not undergo classic tethyan style obduction but were incorporated into evolving turbidite wedges as offscraped slices imbricated fault slivers or duplexes and as blocks in melange the processes involved include decoupling of the oceanic crustal stratigraphy predominantly above the moho formation and metamorphism of serpentinite talc matrix melange up to blueschist conditions and accretion via underplating or offscraping during underthrusting these processes have produced major large scale fault zones within the chevron folded turbidites that show marked along strike variation in structural complexity that relate to magnitude of displacement the fault zones may have formed preferentially where topographic highs occurred in the oceanic crust promoting fold and fault nucleation within irregularities in the layering these fault zones have predominantly brittle character due to their formation under a low geothermal gradient duplex like structures in the fault zones and the inferred development through buckling of then faulting of the oceanic lithosphere have analogues in modern oceanic environments e g indian ocean and young subduction systems e g sulu sea southeast asia they are interpreted to have formed due to convergence in a non collisional intra oceanic setting during closure of a cambrian backarc basin

late cretaceous to recent tectonic evolution of the north german basin and the transition zone to the baltic shield southwest baltic sea abstract in this study we investigate the late cretaceous to recent tectonic evolution of the southwestern baltic sea based on a dense grid of seismic reflection profiles this area covers the baltic sea sector of the salt influenced north german basin and its transition to the salt free baltic shield across the tornquist zone the upper cretaceous to recent structural evolution is discussed by means of individual seismic sections and derived high resolution time structure maps of the main horizons i e the upper cretaceous tertiary and pleistocene the upper cretaceous and tertiary layers reveal numerous significant faults throughout the study area several of these faults propagate upwards across the unconsolidated pleistocene sediments and occasionally penetrate the surface the salt influenced north german basin reveals three major fault trends nw se n s and nne ssw several of these faults are located directly above basement sub salt faults and salt pillows the majority of these faults are trending n s to nne ssw and parallel the direction of the gluckstadt graben faults in the salt free tornquist zone we identify two major shallow fault trends which are nw se and ne sw the majority of these faults are located above basement faults following the direction of the tornquist zone we conclude that generally basement tectonics controls activation and trends of shallow faults if salt is present the ductile salt layer causes a lateral shift between the sub and supra salt faults major plate reorganisation related to the africa iberia europe convergence and the subsequent alpine orogeny caused reactivation of pre existing faults and vertical salt movement in the late cretaceous the change of stress orientation from ne sw to a nw se during neogene caused another phase of fault and salt tectonic reactivation we explain that the ice sheet loading and or present day stress field may have acted in combination causing the recent tectonics and upward extension of the faults

a rift drift delamination model of continental evolution palaeozoic tectonic development of eastern australia the adelaide lachlan and new england fold belts of eastern australia record the continental growth of eastern gondwanaland during the palaeozoic the new england fold belt nefb represents a tectonic collage formed by subduction accretion during the late paleozoic but contains remnants of subduction related rocks that date from the cambrian the lachlan fold belt lfb developed inboard from the nefb initially as an amalgam of proterozoic continental and cambrian oceanic fragments that formed by rift and drift at the leading edge of eastern gondwanaland convergent tectonism at 500 ma welded the fragments to the craton and formed the adelaide fold belt oceanward dispersal of detritus across the lfb produced an overlap assemblage of quartzose ordovician turbidites and a new subduction zone developed at the eastern margin the tectonic setting was similar to the modern philippines plate of the western pacific behind the arc silurian devonian convergent tectonics converted the 1700 2000 km wide continental margin of the proto lfb into a 750 km wide thin skinned fold magmatic belt within 60 ma the driving force was delamination which produced a ubiquitous basaltic underplate that generated 1 regional low p metamorphism 2 local anticlockwise p t t paths and crustal scale isobaric cooling 3 voluminous syn to late tectonic granitoids emplaced at rates approximately twice that of modern arcs and 4 normal thickness crust despite an average of 60 shortening delamination occurred in two separate areas originally 1000 km apart first in the eastern then in the western part of the lfb the lfb and its northern counterpart the thomson fold belt represent approximately one fifth of the australian continent and evolved from dispersed fragments into stable continental crust in 300 ma such rapid growth rates are typical of the 2 7 2 5 ga and 1 9 1 7 ga periods when voluminous widespread granitoids and large turbidite dominated low p metamorphic belts were produced in settings that are not obviously subduction related therefore a similar process of rift drift delamination riddel tectonics may have periodically operated throughout earth history

river width adjustment i processes and mechanisms in 1993 a task committee tc of the asce was established to study the hydraulics bank mechanics and modeling of width adjustment in alluvial channels the work of the tc in reviewing width adjustment processes and mechanisms is reported in this paper a companion paper presents the findings of the tc with regard to width adjustment modeling this paper first establishes the geomorphic context within which width adjustments occur and it demonstrates that width adjustment may take place over a wide range of scales in time and space in the past engineering analyses of channel width have tended to concentrate on prediction of the equilibrium width for stable channels most commonly the regime extremal hypothesis and rational mechanistic approaches are used and these are reviewed herein more recently attention has switched to channels that are adjusting their morphology either due to natural instability or in response to changes in watershed land use river regulation or channel engineering chara

blueschist metamorphism during accretion in the lachlan orogen south eastern australia low t intermediate to high p assemblages indicative of the prehnite pumpellyite greenschist and blueschist facies are preserved in melange zones and slivers of oceanic crust within two major fault zones of the turbidite dominated lachlan orogen in one of these fault zones governor fault zone blueschists occur as franciscan like blocks in a serpentinite talc matrix that is interleaved with phyllites and slates and structurally overlain by a fault slice or duplex of predominantly pillow basalt chert and turbidite the blueschist metavolcanics are interpreted to have formed at 450 c and at a depth of approximately 21 27 km the presence of blue amphibole in the blocks rinds and matrix indicate that the metavolcanics were emplaced in the matrix prior to blueschist metamorphism blocks and matrix were partially exhumed interleaved with tectonic slices of phyllite and slate and subsequently folded at about 10 12 km depth inferred from bo values of the dominant mica fabric in the phyllites and slates metamorphic p t is highest in the structurally lowest slice melange zone and lowest in the overlying ophiolitic fault slice suggestive of an accretionary burial metamorphic pattern formed by underplating of the melange in the other fault zone heathcote fault zone blueschists transitional to greenschist facies are interpreted to have formed at 450 c and at a depth of approximately 15 21 km they occur as blocks in serpentinite talc matrix melange and are also associated with fault slices of oceanic crust textural and mineralogical evidence suggests that the protoliths for the blueschists in both fault zones were boninitic pillow lavas the metamorphic facies and patterns and the structural and lithological associations can be interpreted in terms of disruption of oceanic crust and overlying sediments during subduction and formation of serpentinite matrix melange overprinted by blueschist metamorphism either prior to or during underplating of the melange and duplex formation the presence of blueschist metavolcanics indicate that these processes occurred at considerable depth these interpretations have implications for the evolution of large scale fault zones in noncollisional convergent oceanic settings

late cretaceous and cenozoic intra plate compressional deformations in the alpine foreland a geodynamic model abstract the mesozoic grabens and wrench induced troughs of western and central europe developed in response to triassic early cretaceous intra plate tensional stresses which affected the arctic north atlantic and the tethys borderlands during the rifting phase preceding the opening of the respective oceans this resulted in the fragmentation of the continental crust of the alpine foreland during the late cretaceous and tertiary alpine orogeny collision related compressive stresses exerted on the foreland induced the reactivation of these fracture systems causing the inversion of mesozoic grabens and the uplifting of major basement blocks at distances up to 1300 km to the north of the present alpine deformation front the structural style of these inverted basins and basement uplifts is indicative of compressional and transpressional deformations the total amount of crustal shortening associated with these deformations is unlikely to exceed a few tens of kilometres these displacements require a coupling between the foreland and the orogen at the alpine a subduction zones and within the foreland a decoupling at intra crustal levels between the crust and mantle and or at deeper lithospheric levels the example of the alpine foreland indicates that compressive stresses inducing major deformations can be transmitted from a collisional plate boundary through continental lithosphere over distances of up to 1300 km circumstantial evidence suggests that collision related compressive stresses not large enough to give rise to significant deformations can be transmitted through continental lithosphere over even greater distances

lateral bed load experiments in a flume with strong initial transversal slope in sub and supercritical conditions 1 the role of lateral slope in the generation of bed load transport and bed evolution is investigated because of the substantial lack of detailed laboratory or field data we designed new tests specifically devoted to acquiring accurate measurements in transient flows where the bed surface gradient has a dominant effect on the direction and magnitude of the bed load the bed was prepared with well sorted sand and constant nonzero slopes both longitudinally and transversally over the flume the flow in each experiment evolved to steady uniform conditions characterized by a horizontal bed profile in each section and unchanged longitudinal slope both sub and supercritical conditions were investigated the bounding edges of the bed profile were surveyed on a selected transversal section some detailed kinematic description of the grain motion in the bed load layer has been pursued a shallow water model for mobile bed able to include the most recent theories for the treatment of lateral bed load was developed and numerically applied to the experimental tests comparison between measured and calculated data and between sub and supercritical conditions offers several points of interest

intrusion of lamprophyre dyke and related deformation effects in the host rock salt a case study from the loule diapir portugal abstract a rock salt lamprophyre dyke contact zone sub vertical ne sw strike was investigated for its petrographic mechanic and physical properties by means of anisotropy of magnetic susceptibility ams and rock magnetic properties coupled with quantitative microstructural analysis and thermal mathematical modelling the quantitative microstructural analysis of halite texture and solid inclusions revealed good spatial correlation with ams and halite fabrics the fabrics of both lamprophyre and rock salt record the magmatic intrusion plastic flow and regional deformation characterized by a nw se trending steep foliation ams and microstructural analysis revealed two deformation fabrics in the rock salt 1 the deformation fabrics in rock salt on the nw side of the dyke are associated with high temperature and high fluid activity attributed to the dyke emplacement 2 on the opposite side of the dyke the emplacement related fabric is reworked by localized tectonic deformation the paleomagnetic results suggest significant rotation of the whole dyke probably during the diapir ascent and or the regional tertiary to quaternary deformation

effect of bank stability on geometry of gravel rivers a bank stability analysis is incorporated into an analytical procedure for modeling the hydraulic geometry of an alluvial gravel bed channel the new analysis includes a procedure that calculates the mean bed and bank shear stress as well as assessing the bank stability the bank stability criterion accounts for the increased stability of the channel banks due to consolidation of the bank sediment cementing by fines and binding of the sediment by root masses the two key parameters in the bank stability analysis are the median grain diameter of the bank sediment d50bank and the modified friction angle of the bank sediment a sensitivity analysis of the two parameters indicate that the bank stability can exert a large influence on the channel geometry this is supported by testing the theory on published field data the bank sediment size was assumed to equal the bed sediment size and the variation of the friction angle was investigated the estimated values are seen to increase systematically

microfabrics and 3d grain shape of gorleben rock salt constraints on deformation mechanisms and paleodifferential stress abstract the permian knauel and streifensalz formations z2hs1 and z2hs2 are main constituents of the gorleben salt dome northern germany and show different amounts and distributions of anhydrite the reconstruction of 3d halite grain shape ellipsoids reveals small grain size 3 4 0 6 mm and heterogeneous grain shapes in both formations the latter attributed to the polyphase deformation of the rock salt during diapirism the halite microfabrics of both formations indicate that strain induced grain boundary migration was active during deformation crystal plastic deformation of halite is further documented by lattice bending subgrain formation and minor subgrain rotation evidence for pressure solution of halite has not been found but cannot be excluded because of the small grain size the lack of lpo and the low differential stress 1 1 1 3 mpa as deduced from subgrain size piezometry anhydrite has been deformed in the brittle ductile regime by solution precipitation creep minor dislocation creep and brittle boudinage no continuous anhydrite layers are preserved and halite has acted as a sealing matrix embedding the disrupted anhydrite fragments prohibiting any potential migration pathways for fluids thus anhydrite should not have a negative effect on the barrier properties of the gorleben rock salts investigated in this study

genetic significance of multiple enclave types in a peraluminous ignimbrite suite lachlan fold belt australia the violet town volcanics lachlan fold belt australia are an s type ignimbrite suite containing microgranitoid enclaves basaltic andesite enclaves and enclaves of high silica rhyolite the microgranitoid enclaves are similar to those in peraluminous granites they typically have lower initial sr sr and higher e i than the host and represent globules of a mafic mantle derived magma ivhich was hybridized by mixing and diffusional exchange with the host magma the basaltic andesite enclaves were incorporated into the ignimbrite as xenoliths but their parental magma may have been similar to that of the microgranitoid enclaves they are isotopically less depleted than other mantle derived rocks from the lachlan fold belt reflecting contamination by crustal material or derivation from less depleted mantle sources the high silica rhyolite enclaves previously interpreted to be related to the ignimbrite by crystal fractionation have ejw values up to 3 units higher than their host and cannot be related to their host by crystal fractionation or assimilation fractional crystallization afc processes the coexistence of s type magmas and mantle derived magmas suggests that the latter may have played a role in the palaeozoic magmatism of the lachlan fold belt acting as a heat source for melting and perhaps also contributing chemical components to the crustally derived magmas

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

direct numerical simulation of bedload transport using a local dynamic boundary condition temporally and spatially averaged models of bedload transport are inadequate to describe the highly variable nature of particle motion at low transport stages the primary sources of this variability are the resisting forces to downstream motion resulting from the geometrical relation pocket friction angle of a bed grain to the grains that it rests upon variability of the near bed turbulent velocity field and the local modification of this velocity field by upstream protruding grains a model of bedload transport is presented that captures these sources of variability by directly integrating the equations of motion of each particle of a simulated mixed grain size sediment bed experimental data from the velocity field downstream and below the tops of upstream protruding grains are presented from these data an empirical relation for the velocity modification resulting from upstream grains is provided to the bedload model the temporal variability of near bed turbulence is provided by a measured near bed time series of velocity over a gravel bed the distribution of pocket friction angles results as a consequence of directly calculating the initiation and cessation of motion of each particle as a result of the combination of fluid forcing and interaction with other particles calculations of bedload flux in a uniform boundary and simulated pocket friction angles agree favourably with previous studies

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

genesis of felsic plutonic magmas and their igneous enclaves the cobaw batholith of southeastern australia abstractthe late devonian postorogenic cobaw batholith in southeastern australia is an oval east west orientated terrane stitching lopolith that intruded low grade metaturbidites the initial intrusion at 370 ma was the small hypabyssal s type rainy creek rhyolite rcr at 369 ma the foliated s type pyalong pluton was emplaced apparently along an east west orientated fracture zone around 367 ma the main i type baynton pluton intruded as numerous shallow dipping sheets the last plutonic event was the intrusion of the broad thin flat lying and crosscutting sheet of the i type beauvallet pluton the cobaw plutons had independent origins with magmas derived from contrasting internally heterogeneous source rocks for both the rcr and the pyalong pluton the sources were old metasedimentary rocks while the magmas for the baynton and beauvallet plutons formed through partial melting of metadacitic to meta andesitic rocks probably with an admixture of immature volcaniclastic graywackes the s

microstructural evolution of deformation modified primary halite from the middle triassic rot formation at hengelo the netherlands the microstructure of halite from the subhorizontal bedded main rot evaporite member at hengelo the netherlands akzo well 382 depth interval of 420 460 m was studied by transmitted and reflected light microscopy of gamma irradiation decorated samples primary microstructures compare favourably with those found in recent ephemeral salt pans large blocky fluid inclusion poor halite grains and elongated chevrons are interpreted to have formed in the saline lake stage while void filling clear halite is interpreted to have formed during the desiccation stage of the salt pan in addition in all layers the grains are rich in deformation related substructures such as slip bands and subgrains indicating strains of a few percent the study of gamma irradiation decorated thin sections shows that the main recrystallization mechanism is grain boundary migration grain boundary migration removes primary fluid inclusions and produces clear strain free new grains differential stresses as determined by subgrain size piezometry were 0 45 0 97 mpa the deformation of the salt layers is probably related to cretaceous inversion in the area

magnetic fabrics of the morcles nappe complex abstract anisotropy of magnetic susceptibility ams measured with high fields at ambient and low temperatures 77 k has been used to separate ferromagnetic sensu lato paramagnetic and diamagnetic sub fabrics for deformed limestones located in a nappe structure from southwest switzerland the magnetic fabrics are dominantly controlled by paramagnetic and diamagnetic minerals and ferromagnetic minerals contribute significantly only at two of the eight study locations separation of the magnetic sub fabrics is possible in the root zone and overturned limb of the morcles nappe which contains a high ratio of diamagnetic matrix calcite to paramagnetic secondary phases each of the sub fabrics displays a relationship with structural cleavage and the crystallographic preferred orientation cpo of calcite in the root zone and overturned limb the maximum axis of the paramagnetic ams ellipsoid kmax lies close to the pole to cleavage with the intermediate kint and minimum kmin axes near the cleavage plane conversely the diamagnetic kmin lies close to the pole to cleavage with kmax and kint axes near the cleavage plane slight offsets in the poles to cleavage and in the principal ams directions are observed they are interpreted to be the consequence of a second phase deformation event affecting only the cpo but not the macroscopic structural elements the diamagnetic sub fabric reflects the cpo of calcite produced through recrystallization during nappe deformation iron rich calcite appears to control the paramagnetic sub fabric susceptibility ellipsoids approach oblate shapes for the diamagnetic sub fabric with the most extreme shapes reaching susceptibility differences k kmax kmin close to that of single crystal calcite whereas the paramagnetic sub fabric is represented mainly by prolate shape ellipsoids the low field ams ellipsoids show mixed oblate and prolate shapes without consistency within or between sites it is evident that when the magnetic sub fabrics of the root zone and overturned limb are separated their individual shapes and distribution of principal directions mirror the developed cpo

geochemistry and tectonic setting of the central loei volcanic rocks pak chom area loei northeastern thailand abstract the central loei volcanic rocks as evidenced by those in the pak chom area were formed in the late devonian early carboniferous and can be separated into three magmatic groups transitional tholeiitic basalt tholeiitic microgabbro and calc alkalic basalt andesite on the basis of immobile element contents and ratios of least altered samples all the tholeiitic microgabbro possibly occurred as dikes chemically the transitional tholeittic basalt and tholeiitic microgabbro have higher abundances of tio 2 ni and cr relative to the calc alkalic basalt andesite at similar values for feo mgo they also contain higher ti zr but lower zr nb the transitional tholeiitic basalt has higher concentrations of p 2 o 5 and nb relative to the tholeiitic microgabbro at similar levels of feo mgo and also has higher ratios of nb y and ti v but lower values for ti zr and zr nb in terms of chondrite normalized ree and n morb normalized patterns the transitional tholeiitic basalt tholeiitic basalt and calc alkalic basalt andesite are analogous to those from north atlantic southwest indian ridge and new britain arc on this basis the central loei volcanic rocks are comprised of morbs and oceanic island arc lavas these arc lavas may have erupted on an oceanic basement in the same ocean basin as those in the chiang rai chiang mai volcanic belt

sediment transport on arbitrary slopes simplified model the paper presents a study on the influence of gravity on the incipient motion and the bed load transport of sediment the computation of critical bed shear stress is revisited considering the balance of forces hydrodynamic forces and submerged self weight acting on a solitary sediment particle lying on an arbitrary sloping bed modified effective bed shear stress and the corresponding critical bed shear stress which are defined to assess the incipient motion of sediment in the direction of resultant force are applied for the estimation of bed load transport rate in the direction of resultant force the sediment transport induced by the gravitational force which is oblique to the direction of the drag force induced by flow is incorporated into the bed load transport equation this modified model provides a reasonable prediction of the critical bed shear stress and the bed load transport rate the model is validated by experimental data it can be applied to steep slopes and can also avoid the problem of singularity that arises in numerically calculation of sediment transport rate additionally the vectorial transport rate obtained in the model calculation can be implemented in a numerical simulation of channel bed evolution

applicability of magnetic fabrics in rocks associated with the emplacement of salt structures the bicorb quesa and navarres salt walls prebetics se spain abstract this work assesses the applicability of the analysis of the anisotropy of magnetic susceptibility ams to rocks associated with salt structures magnetic fabrics from 16 sites sampled on upper triassic clays keuper facies interbedded within the salt layers of the bicorb quesa and navarres salt walls prebetic zone se spain are mostly characterized by oblate magnetic ellipsoids with their magnetic foliation parallel to the bedding and magnetic lineation contained in the bedding plane but without a constant relationship with dip direction to evaluate the quality and significance of the low field ams several experiments were carried out to characterize the magnetic mineralogy of representative samples and enable separation of the contributions from paramagnetic and ferromagnetic s l minerals the comparison between the orientation of the observed magnetic lineation and that of the structural elements characterizing the internal geometry of the studied salt structures antiforms minor folds faults and shear zones and flanks indicates that the magnetic fabric is controlled by deformation processes affecting the salt walls during their growth and or evolution samples were also analyzed from sixteen sites from miocene rocks outcropping in several syn diapiric miocene half grabens related to the salt walls studied their magnetic fabric is interpreted to reflect the dominant stretching direction at the syn diapiric half grabens during and or shortly after deposition our results indicate that caution is required in interpreting magnetic lineations related to salt flow mechanics from rocks associated with salt structures

comparison of methods for predicting incipient motion for sand beds a comparison of four methods for predicting the incipient motion conditions of a uniform sand bed is presented the four methods are 1 the shields diagram 2 an empirical approach 3 a method derived from resolution of rotational forces and 4 a simplified resolution of rotational forces with a variable lift force coefficient the four methods are used to predict the incipient motion conditions for 97 experimental runs taken from seven independent experimental flume studies the effectiveness of predicting depth averaged incipient motion velocity for each of the four methods are compared the simplified resolution of rotational forces model 4 and shields method 1 were most successful in predicting the incipient motion velocity r2 0 77 0 74 and root mean square error rmse 0 18 0 15 respectively the slope of line of best fit for plots illustrating predicted versus measured incipient motion velocity were similar slope 0 63 0 65 respectively illustrating that both methods provide a s

deformation and recrystallization mechanisms in actively extruding salt fountain microstructural evidence for a switch in deformation mechanisms with increased availability of meteoric water and decreased grain size qum kuh central iran microstructural study of rocksalt samples from an active salt fountain qum kuh central iran enabled to identify the relative contribution of different deformation mechanisms on extrusive salt flow the microstructural study combined reflected and transmitted light microscopy of gamma irradiated thin sections textural analysis of digitized microstructures and electron back scattered diffraction ebsd deformation microstructures record the strongly variable deformation conditions of salt flow in the diapiric system from the diapiric stem towards the distal part of the mature viscous fountain high stress deformation conditions typical for diapiric stems are recorded in the small subgrains within the porphyroclasts of all documented samples recovery and recrystallization due to divergent and decelerating flow associated with differential stress drop in the salt extrusion above the diapiric orifice is reflected by abundant growth band microstructures this study reveals also evidence for penetration of rainwater into the salt mass and documents the switch from the dominant dislocation creep into dominant solution precipitation creep from the upper part to the distal part of the fountain this deformation mechanism switch is provided by influx of meteoric water and grain size decrease likely controlled by subgrain rotation and grain boundary migration recrystallization

anisotropy of diamagnetic susceptibility in thassos marble a comparison between measured and modeled data abstract a study of shear zones within the calcite marble complex of the island of thassos greece shows that the low field anisotropy of magnetic susceptibility ams technique can be successfully applied to diamagnetic rocks for characterizing rock fabrics the strain path involves both an early pure shear stage and a simple shear overprint that is documented by a transition from triaxial neutral to uniaxial prolate shapes of ams ellipsoids the maximum susceptibility is oriented perpendicular to the rock foliation reflecting the preferred orientation of calcite c axes in the protolith as well as in the mylonites for three samples that represent different types of calcite fabrics the ams was recalculated from neutron and electron backscatter diffraction textural data a comparison of the measured and modeled data shows a good coincidence for the orientation of the principal ams axes and for the recalculated anisotropy data both measured and modeled data sets reflect the change from neutral to distinct prolate ellipsoids during progressive deformation

rheological behaviour of synthetic rocksalt the interplay between water dynamic recrystallization and deformation mechanisms abstract the ductile deformation of rocks in nature can be greatly enhanced by the presence of water part of the water induced weakening of rocks at depth may come from fluid assisted deformation or recrystallization mechanisms that are absent in dry rocks in this study we investigate the effect of water on the rheological behaviour of rocksalt we focus on quantification of the contribution of individual deformation and recrystallization mechanisms to deformation we also aim to calibrate a flow law that incorporates the effect of all the relevant microphysical processes and hence more accurately describes the flow of rocksalt in nature for this purpose the mechanical behaviour and microstructural evolution of synthetic rocksalt samples that are similar except for differences in water content determined using ftir analysis are investigated the samples are deformed to natural strains of 0 07 0 46 at 50 mpa confining pressure strain rates of 5 10 7 1 10 4 s 1 and temperatures of 75 240 c resulting in flow stresses of 7 22 mpa the flow stress of samples with a water content below 5 ppm dry is higher than that of samples with a water content of 9 46 ppm wet at all strains under the investigated conditions the difference in flow stress can be explained as due to the operation of only work hardening dislocation creep without dynamic recrystallization in the dry material versus combined dislocation and solution precipitation creep plus fluid assisted grain boundary migration in the wet material the results allow us to calibrate a flow law for wet rocksalt that incorporates the effects of solution precipitation creep and fluid assisted grain boundary migration the results also suggest that strain localization in natural rocksalt is more likely to be localized due to fluid infiltration and associated rheological weakening than due to progressive removal of strain hardening substructure by grain boundary migration

discrete particle modeling of entrainment from flat uniformly sized sediment beds the stability of randomly deposited sediment beds is examined using a discrete particle model in which individual grains are represented by spheres the results indicate that the threshold shear stress for flat beds consisting of cohesionless uniformly sized grains cannot be adequately described by a single valued parameter rather it is best represented by a distribution of values physically this result stems from the localized heterogeneity in the arrangement of surface grains for uniformly sized beds geometric similarity exists such that the critical entrainment shear stress distributions scale directly with grain size a shields parameter of 0 06 is commonly used to define threshold conditions and it was found that this corresponds to a point on the distributions where approximately 1 4 by weight of the surface is mobile furthermore the analysis includes a comparison of the contributions of sheltering to variation in critical entrainment shear stress it was found that remote sheltering ind

strain partitioning of deformation mechanisms in limestones examining the relationship of strain and anisotropy of magnetic susceptibility ams abstract in order to investigate the relationship between rock strain and anisotropy of magnetic susceptibility ams strain partitioning and ams analysis was conducted at 35 sites from two stratigraphically adjacent paleozoic limestone units in the patterson creek and wills mountain anticlines in the central appalachian orogen of west virginia in addition anisotropy of anhysteretic remanent magnetization aarm was conducted on selected samples to examine the role of preferentially oriented magnetite on the ams fabric strain is partitioned into bed normal shortening due to compaction solution strain 35 0 shortening bed parallel shortening due to tectonic solution strain 13 3 shortening calcite twinning strain 5 8 shortening and grain boundary sliding 26 7 shortening the ams fabrics in the rocks were found to be a result of a complex interaction between rock lithology deformation mechanisms and strain magnitude although all the rocks have experienced the same deformation conditions six different ams fabrics are exhibited each of the different ams fabrics is a composite fabric resulting from the overprinting of three components 1 an inherent primary depositional ams fabric that is attributed to preferentially oriented phyllosilicates in the rock matrix 2 a diagenetic and or compaction ams fabric formed during burial that is due to preferentially oriented phyllosilicates in solution structures and in the rock matrix and 3 a tectonic ams fabric that was imparted on the rocks by layer parallel shortening deformation prior to folding and is also attributed to preferentially oriented phyllosilicates in solution structures and in the rock matrix as well as twinning of ferroan calcite

paleozoic ophiolitic assemblages within the southern new england orogen of eastern australia implications for growth of the gondwana margin several ophiolitic assemblages occur in the southern new england orogen the development of these rocks and their relations to the rest of the orogen have major implications for the tectonic evolution of eastern gondwana a major narrow but elongate belt of early cambrian supra subduction zone ophiolite crops out along and near the peel manning fault system and is juxtaposed against younger arc and subduction complex terranes no pre permian links with the rest of the new england orogen have been established for this terrane it may represent portions of lachlan fold belt basement which underlies younger westward overthrust new england terranes and has been diapirically emplaced at higher crustal levels as serpentinite matrix melange middle to late devonian ophiolitic rocks in the yarras complex comprise basement to the birpai subterrane and represent a crustal cross section through a rifted island arc correlatives of this terrane also occur within the more extensive gamilaroi terrane to the west of which deeper crustal levels are not exposed the various components of serpentinite matrix melange in the ngamba terrane at port macquarie superficially appear to represent a dismembered ophiolite association however the various components of the melange exhibit a wide range of ages metamorphism and tectonic affinities rendering a genetically related origin unlikely this terrane includes fragments of ocean floor accreted into a late devonian subduction complex which was later affected by early carboniferous forearc serpentinite diapirism and high mg series magmatism zircon inheritance in triassic dikes which intrude the melange attest to the development or later emplacement of this forearc region over an older lachlan fold belt basement ultramafic rocks of the bundjalung terrane in the east of the new england region probably formed at deep levels in an intraoceanic island arc and are intruded by boninitic dikes the tectonic development of the neo was significantly more complicated than has been suggested in earlier published models periodic accretion of island arc systems some of which are now represented by supra subduction zone ophiolites to the eastern margin of gondwana suggests multiple phases of subduction with the possibility of polarity reversals throughout the history of accretion lateral accretion was not the only means by which gondwana continental crust grew and there was considerable postaccretion continentward overthrusting of younger terranes copyright 1994 by the american geophysical union

deformation and recrystallization mechanisms in mylonitic shear zones in naturally deformed extrusive eocene oligocene rocksalt from eyvanekey plateau and garmsar hills central iran abstract microstructural processes in mylonitic shear zones from extrusions of eocene oligocene rocksalts from garmsar hills and eyvanekey plateau central iran are described and analyzed the halite samples were studied by transmitted light microscopy of gamma irradiated thin sections subgrain size palaeopiezometry of polished and chemically etched samples and texture measurements by electron backscatter diffraction ebsd the studied shear zones are thin using published flow laws the strain rate in the fine grained mylonites is about 10 10 l s which is in a good agreement with earlier in situ measurements on glacier salt flow rate

model for calculating bed load transport of sediment a bed load transport model based on the mechanics of sediment moving by saltation yields predicted values of bed load flux as a function of boundary shear stress grain diameter and density the parameters required to calculate bed load transport particle velocity bed load sediment concentration and the height of the bed load layer can all be determined from our model which computes sequences of trajectories of individual saltating grains as well as the concentration of moving grains that the flow can support the latter is related to the momentum the accelerating grains extract from the flow predicted curves of bed load transport vs boundary shear stress agree well with transport data collected by gilbert meyer peter iet al n and the waterways experimental station measured shear stress was corrected for pressure drag when bed forms were present comparison of predicted bed load transport with common bed load equations reveals considerable similarity among the relationships the best agreement with the data is produced by relationships in which the transport rate vanishes as the shear stress approaches the critical shields number as in our model and yalin s equation

the tectonic significance of ordovician magmatism in the eastern lachlan fold belt abstract the shoshonitic rock series is a suite of igneous rocks derived from the mantle and containing high potassium plus low abundances of high field strength elements it is commonly associated with calcalkaline igneous rocks but in most modern examples a contemporary active subduction zone is not present mantle derived shoshonitic magmatism in the lachlan fold belt commenced in the early ordovician and terminated at the end of the ordovician when it was replaced by tholeiitic magmatism and the onset of wholesale melting of the lower to middle crust associated calcalkaline igneous rocks are insignificant the shoshonites are widely distributed across the eastern part of the fold belt in a series of discontinuous belts and volcanic centres the largest of which is the orange wellington belt extending from east of cowra to dubbo the broad geographical distribution is not typical of the curvilinear belts of volcanics associated with subduction zones and would be even greater if the intervening basins or troughs were unfolded all rocks analyzed to date are either clearly shoshonitic or show chemical features that indicate shoshonitic affinities prior to alteration and metamorphism in some areas lavas rich in olivine and clinopyroxene potassic trachybasalts dominate in others the more evolved plagioclase rich shoshonites are most abundant it is suggested that the ordovician magmatism was not accompanied by coeval subduction as has been generally assumed more likely the lithospheric mantle beneath the lachlan fold belt was modified during an earlier subduction event associated with the assembling of the basement blocks recognized from granite studies the cause of melting in the ordovician may be related to lithospheric heating or overturning prior to the upwelling of unmodified asthenosphere the hot 1200 c asthenosphere was the source for the silurian tholeiites and provided conductive heat for the melting of the lower to middle crust

resolution of ferrimagnetic and paramagnetic anisotropies in rocks using combined low field and high field measurements summary a method of separation of ferrimagnetic and paramagnetic components of magnetic anisotropy from the total anisotropy is developed from the anisotropy measurement of a specimen in a low field susceptibility anisotropy and from measurement in two high fields stronger than the saturation field of the ferrimagnetic fraction present the following anisotropy components can be calculated susceptibility anisotropy field independent of the paramagnetic fraction low field susceptibility anisotropy of the ferrimagnetic fraction and high field anisotropy of the ferrimagnetic fraction errors possibly arising from imperfect saturation of the ferrimagnetic fraction in the field practically available are analysed

the finne fault zone central germany structural analysis of a partially inverted extensional fault zone by balanced cross sections the finne fault zone located in central germany to the southwest of the harz mountains was studied by means of detailed map analysis investigations of fault displacement and balanced cross sections for the most strongly deformed area in the center of the fault zone ca 50 of total fault zone length the system of the finne fault zone shows a nearly 100 km long straight flexure that symbolizes the morphological and geological northeastern border of the thuringian basin in the central part which should be surveyed here the fault zone corresponds to a distinctive narrow band of highly deformed triassic sedimentary rocks the northwestern and especially the southeastern parts of the research area are developed as several parallel branch faults in the southeastern elongation of the fault zone which is not part of our survey the sedimentary cover is missing here it is possible to gain insight to the fact that the basement is also involved to the kinematics of the fault zone based on our results we propose a subdivision of the fault zone into four sectors from the northwest to the southeast we interpret the structure of these sectors to reflect 1 a compressional flexure 2 an overthrust graben and 3 a partially inverted and folded half graben in the extreme southeast 4 the fault zone is characterized by an anticline with some strike slip movement parallel to the fold axis this segmentation is caused by a thrust fault system whose strike direction deviates slightly from that of the earlier formed graben system the structural configuration can be explained by a two phase deformation in which the contractional strain exceeded the preceding extensional deformation in the investigated area the horizontal shortening attains a maximum of ca 1 km the present study confirms many earlier hypotheses presents new results on the deformation history of the fault zone and attempts to evaluate the deformation in a regional geological context the results of earlier studies were refined and revised using modern methods and a unified structural and kinematic model of the finne fault zone was created

paleoproterozoic turbidite hosted gold deposits of the ashanti gold belt ghana west africa comparative analysis of turbidite hosted gold deposits and an updated genetic model abstract the paleoproterozoic gold deposits of the ashanti gold belt ghana occur mainly as auriferous quartz veins in graphitic shears proximal to contacts between deformed and metamorphosed turbidites and tholeiitic volcanics alternately block faulted tarkwaian sediments they are suggested in this article to belong to that class of gold deposits recognized as turbidite hosted hence evidence from previous investigations of turbidite hosted and turbidite associated gold deposits occurring in circumstances roughly similar to the ashanti deposits are used where relevant to produce an updated genetic model for the latter given the relatively significant amounts of graphite associated with the major ashanti deposits the role of non carbonate carbon is assessed in the light of conclusions reached by work on other turbidite hosted and turbidite associated gold belts conclusions as to the origins of mineralizing fluids and temporary repositories of gold auriferous interflow sediments reached by work on these other belts are also analysed a concept of the tectonic development of the ashanti belt kumasi basin area introduced in this article is deemed to be critical to the origin of the ashanti gold deposits it encompasses the role of non carbonate carbon turbidites and the primary sources and secondary repositories of au and as in the genesis of the major ashanti gold deposits it examines the significance of the intimate relationship between calc alkaline volcanism and the basin sediments the occurrences of felsic metasandstones in transition zone sediments and ttg granitic material and fragments of chemical sediments in turbidites all of which are incompatible with one or the other of existing concepts of tectonic development in the area

evaluating magnetic lineations ams in deformed rocks magnetic lineation in rocks is given by a cluster of the principal axes of maximum susceptibility kmax of the anisotropy of magnetic susceptibility ams tensor in deformed rocks magnetic lineations are generally considered to be the result of either bedding and cleavage intersection or they parallel the tectonic extension direction in high strain zones our ams determinations based on a variety of samples that were taken from mudstones slates and schists from the pyrenees and appalachians show that strain is not the only factor controlling the development of magnetic lineation we find that the development and extent to which the magnetic lineation parallels the tectonic extension direction depends on both the original ams tensor which in turn depends on the lithology and the deformation intensity rocks having a weak pre deformational fabric will develop magnetic lineations that more readily will track the tectonic extension

pyrite and pyrrhotite textures and composition in sediments laminated quartz veins and reefs at bendigo gold mine australia insights for ore genesis the various types textures and compositional zoning of pyrite in the gold bearing saddle reefs quartz veins and surrounding sedimentary rocks provide new information on the potential source and timing of gold and arsenic and related fluid processes responsible for mineralization at bendigo nodular diagenetic pyrite in the black shale tops to sandstone turbidites is enriched in invisible gold and arsenic with mean values of 0 61 ppm au 1 300 ppm as and au ag 1 based on la icpms analyses other elements enriched in the diagenetic pyrite within the organic rich shales are mn zn mo cu v ba ag cd tl co ni bi pb and te in contrast euhedral and growth zoned hydrothermal pyrite in the turbidites and bedding parallel laminated quartz veins contains lower contents of most trace elements but has higher contents of invisible au and as especially on the outermost rim of the pyrite the gold rich pyrite rims generally become thicker a few to hundreds of microns in proximity to the gold bearing saddle reefs pyrite in the reef commonly has the highest levels of invisible au and as and the lowest levels of other trace elements it is characterized by au ag 1 and au pb 0 01 in the deepest stratigraphic levels below known productive gold reefs diagenetic pyrite in the most carbonaceous shales has been replaced by pyrrhotite during metamorphism la icpms analyses reveal that the disseminated pyrrhotite contains similar levels of ni and co to the diagenetic pyrite but is strongly depleted in as and au the spatial relationships between organic rich shales folded bedding parallel laminated quartz veins and gold arsenic bearing saddle reefs combined with the consistent trends in the trace element composition of pyrite hosted by these three geological elements is interpreted to indicate that the black shales were an initial source of au and as and the laminated quartz veins acted as the initial pathways for hydrothermal fluid flow carrying au and as from the source shales to the saddle reefs maximum gold and arsenic input into the reefs principally as free gold plus arsenopyrite occurred late during deformation toward the end of the hydrothermal cycle and is expressed by the au as rich rims to hydrothermal pyrite in the sedimentary host rocks laminated quartz veins and reefs this corresponds with final fold lockup and the development of through going fault arrays linking adjacent anticlines the source of au and as for this final and most economically important fluid flow event is considered to be from carbonaceous shales deeper in the basin where original gold bearing diagenetic arsenian pyrite reacts with organic matter and is converted to pyrrhotite with release of au as and s to the metamorphic fluid

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

orogenic disseminated gold in phanerozoic fold belts examples from victoria australia and elsewhere abstract orogenic gold mineralisation in the lachlan orogen of southeastern australia and in other phanerozoic fold belts has generally been assumed to be confined entirely to quartz veins however an improved understanding of the tectonic structural and geochronological framework in which these occurrences form and recent advances towards the extent of wallrock alteration around these veins cast doubt on the validity of this deeply entrenched lode gold paradigm ore grade orogenic disseminated gold mineralisation has been recognised in a number of fold belts that are known to host significant orogenic lode gold deposits lachlan orogen australia buller terrane and otago schist new zealand meguma terrane canada tien shan mountains in uzbekistan and kyrgyzstan yana kolyma province baikal verhoyansk and allakh yun fold belts in north central mongolia and far east russia disseminated mineralisation in these collisional belts is invariably hosted by pervasively altered greenschist to subgreenschist facies rocks these occurrences also share a number of characteristics with some carlin type gold deposits in the great basin of western north america e g getchell regarding structural relationships fluid composition mineral paragenesis and a common association of carbonaceous matter with mineralisation features of alteration physico chemical characteristics of the ore bearing fluids and strong structural control in all of the studied occurrences point to a close genetic association with lode gold mineralisation the two styles are considered to represent end members of a crustal continuum of orogenic gold emplacement in phanerozoic fold belts with disseminated mineralisation more likely to develop at shallower levels and within more permeable units during the waning stages of uplift and exhumation these conditions facilitate ground preparation via brittle fracturing and the development of intricate stockwork systems efficient gold segregation from bisulphide complexes is largely controlled by fluid mixing of an evolved metamorphic fluid with either more oxidised ascending fluids or meteoric fluids and accelerated by the presence of carbonaceous matter at the site of deposition

a method for the separation of paramagnetic ferrimagnetic and haematite magnetic subfabrics using high field torque magnetometry summary in this study the contribution of the paramagnetic ferrimagnetic and haematite components to the magnetic anisotropy is separated by means of high field torque magnetometry torque measurements at different fields which are high enough to saturate the ferrimagnetic minerals however still low enough that the torque resulting from the haematite is linear with field allow for the separation of the three magnetic anisotropy components the method has been applied to haematite single crystals in which no paramagnetic or ferrimagnetic components have been found contribute to the torque signal the mean direction of the poles to the crystallographic basal plane in the haematite single crystals is subparallel to the minimum susceptibility direction measured in low field the separation analysis has also been applied to highly deformed red beds from the lower glarus nappe complex switzerland no ferrimagnetic phases are present in the rocks and therefore they cannot contribute to the anisotropy of magnetic susceptibility the magnetic fabric arises from a paramagnetic subfabric carried by the phyllosilicate minerals and haematite in which the basal planes of both phases are in the cleavage plane the measured magnetic lineation seen in low field anisotropy of magnetic susceptibility appears to be an apparent lineation that arises from a weak girdling of haematite and the paramagnetic minerals conforming the rock

isotopic evidence for rapid continental growth in an extensional accretionary orogen the tasmanides eastern australia the trace element signature of earth s continental crust resembles that of arc lavas but the continents may have formed during ancient igneous pulses that are hard to reconcile with supra subduction zone magmatism we explore the role of coupled arc back arc accretionary processes in crust generation by considering the tectonic context of whole rock nd isotope and zircon hf o isotope data from igneous rocks of the australian tasmanides 515 230 ma which is thought to have evolved by the repeated opening and closure of sediment filled back arc basins behind a long lived subduction zone the significance of this process for continental crust formation has yet to be evaluated from an isotopic perspective granitic rocks in this area define striking secular end ehf 18o trends that correlate with the pattern of deformational events and register changes in magma source during tectonic activity these trends reveal that juvenile magmatic input was enhanced during extensional back arc rifting episodes that immediately followed crustal thickening suggesting a relationship between slab rollback and continental growth interaction between juvenile magma and sedimentary units deposited during a preceding back arc rifting cycle was integral to the formation of stable continental material this highlights the importance of back arc environments for both the generation and differentiation of continental crust the juvenile component within the tasmanide igneous rocks increased from the cambrian to the triassic consistent with a diminished input from cratonderived metasedimentary material as the subduction zone migrated outboard of the gondwana margin subduction zone retreat formed large tracts of new crust in eastern australia at comparable rates to crust generation at modern island arcs providing a mechanism for rapid continental growth at convergent margins using isotopic tracers to link tectonic evolution and crust generation in modern and ancient orogens can lead to a better understanding of the geodynamic controls on planetary differentiation

the origin of tectonic fabrics in undeformed clays the early stages of deformation in extensional sedimentary basins 1 an integrated approach was used to detect tectonic effects in apparently undeformed fine grained clay sediments filling extensional basins in southern italy results from low and high field anisotropy of magnetic susceptibility and mineral fabric deduced by neutron texture analysis show penetrative deformation on a grain scale the well defined tectonic magnetic lineation is parallel to the stretching direction and located at the intersection of the basal planes of phyllosilicates forming grain scale folds and crenulations this spatial configuration reflects basin scale deformation processes and suggests the existence of a nearly uniaxial stress field during the incipient extensional phases the integrated approach of magnetic and mineral fabric investigations is a valid tool to detect grain scale and regional deformation pattern in weakly deformed extensional basins where macroscopic evidence of deformation is not visible

bed load at low shields stress on arbitrarily sloping beds failure of the bagnold hypothesis 1 the bagnold hypothesis has been a major tool in the development of mechanistic models of bed load transport according to the hypothesis 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 the constraint determines a functional form for the areal concentration of bed load grains as a function of flow parameters it is shown here 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 in particular under such conditions it is shown that no areal concentration no matter how large is sufficient to reduce the fluid shear stress at the bed to the critical value this failure motivates the abandonment of the bagnold constraint even for nearly horizontal beds the framework presented here however provides a natural basis for an entrainment based model of sediment transport that neither satisfies nor suffers from the drawbacks of the bagnold constraint

petrogenesis of ultramafics in the neoarchean veligallu greenstone terrane eastern dharwar craton india constraints from bulk rock geochemistry and lu hf isotopes abstract we report on the bulk rock geochemistry and lu hf isotope systematics and infer the petrogenesis of the ultramafic rocks in the neoarchean veligallu greenstone terrane eastern dharwar craton india the ultramafics along with the basalts and adakites yield a bulk rock lu hf isochron age of 2 696 0 054 ga consistent with the available sims zircon u pb age of 2 697 5 ma reported for the felsic volcanics in the literature the rocks have positive initial ehf 2 696 ga 3 0 to 6 5 consistent with an origin from a long term depleted mantle source relative to a chondritic reservoir at 2 7 ga geochemically the ultramafic rocks are characterized by high mgo 24 34 wt mg 89 cr 2290 3855 ppm and ni 604 966 ppm contents moderate to low sio2 52 49 wt al2o3 9 2 4 7 wt and tio2 0 30 0 14 wt to first order these chemical compositions broadly resemble komatiites the rocks exhibit higher than chondrite al2o3 tio2 21 37 ratio depletions in their middle ree relative to the heavy ree i e gdn ybn

incipient motion of sand particles on side slopes several criteria have been theoretically proposed for the critical shear stress of noncohesive sediment on side slopes however no laboratory work has ever been done on this problem a theoretical study of the incipient motion of sediment particles on side slopes is presented including the effects of viscous sublayer turbulence and lift force as a special case of level beds the theory describes the experimental values reported by several workers a specially designed rotary wind tunnel permits the evaluation of the critical shear stress on side slopes and the experiment supports the theory these works reveal that the lift force can be neglected in estimating the critical shear stress using the proposed theory if the averaged experimental values are concerned but inclusion of the lift force in the theory is recommended for safety and for describing the lower limit of the possibility of incipient motion