entrainment and flushing time in the fraser river estuary and plume from a steady salt balance analysis 1 a passenger ferry equipped with oceanographic instrumentation made eight transects across the fraser river plume in the strait of georgia british columbia each day for 4 years estimates of average plume salinity and volume were made from the observations and used in a quasi steady budget to estimate the net upward flux of ambient salt water into the plume this entrainment flux increases from a minimum of 17 000 m3s 1 at low river flow to a maximum of about 27 000 m3s 1 at intermediate flow the entrainment flux then becomes essentially independent of river flow although we argue on physical grounds it must eventually decrease entrainment velocities of a few mm s 1 were estimated from the entrainment flux when assuming that mixing primarily occurs along the salt wedge estuary or in the near field plume these values are consistent with previous estimates this in turn suggests that entrainment is not important over most of the plume s full extent and that bulk plume properties are set in the near field finally the observations are used to estimate a plume freshwater flushing time of 2 2 days with essentially no dependence on river discharge even though discharge varies seasonally by almost an order of magnitude this value lies in between the expected time scales for near field and far field plumes and is long enough for rotation to play an important role there is no evidence however of a coherent bulge as observed in other systems

the j m platinum palladium reef of the stillwater complex montana ii origin by double diffusive convective magma mixing and implications for the bushveld complex sequences of cumulates form concurrently by downdip accretion from a column of liquid layers that are primarily separated by diffusive interfaces the low cumulates grow in advance of the upper cumulates in accord with their higher crystallization temperatures an important observation is that mixing of the two parent liquids lowers their crystallization temperatures and consequently should produce unsaturated hybrids that could dissolve earlier cumulates the repetition of cyclic units above the j m reef is explained by having periodic additional injections of dense magma beneath the subsiding column of crystallizing liquid layers neither the j m reef nor the bushveld ore zones should ever have been continuous across the floor of their respective magma chambers and for bushveld the circumstances resulted in zones that are actually minable modified journal abstract

hydraulic control of a highly stratified estuarine front abstract observations at the mouth of the fraser river british columbia canada indicate an abrupt frontal transition between unstratified river outflow and a highly stratified river plume with differences in salinity greater than 25 psu across a few meters in the vertical direction and several hundred meters in the horizontal direction the front roughly follows a natural break in the bathymetry crossing the channel at an angle of approximately 45 and is essentially stationary for a period of approximately 3 5 h centered on the low tide following the larger of two daily ebbs the location of the front is coincident with observations of significantly supercritical internal froude numbers at the front based on velocities in the along flow direction this observation contradicts the one dimensional theory which indicates that the froude number should be 1 however because the front is oriented obliquely to the outflow a coordinate system can be selected that is normal to the front and for which a c

postcumulus processes in layered intrusions during the postcumulus stage of solidification in layered intrusions fluid dynamic phenomena play an important role in developing the textural and chemical characteristics of the cumulate rocks one mechanism of adcumulus growth involves crystallization at the top of the cumulate pile where crystals are in direct contact with the magma reservoir convection in the chamber can enable adcumulus growth to occur to form a completely solid contact between cumulate and magma another important process may involve compositional convection in which light differentiated melt released by intercumulus crystallization is continually replaced by denser melt from the overlying magma reservoir this process favours adcumulus growth and can allow adcumulus growth within the pore space of the cumulate pile calculations indicate that this process could reduce residual porosities to a few percent in large layered intrusions but could not form pure monomineralic rocks intercumulus melt may also be replaced by more primitive melt during episodes of magma chamber replenishment dense magma emplaced over a cumulate pile containing lower density differentiated melt may sink several metres into the underlying pile in the form of fingers reactions between melt and matrix may lead to changes in mineral compositions mineral textures and whole rock isotope compositions another important mechanism for forming adcumulate rocks is compaction in which the imbalance of the hydrostatic and lithostatic pressures in the cumulate pile causes the crystalline matrix to deform and intercumulus melt to be expelled for cumulate layers from 10 to 1000 metres in thickness compaction can reduce porosities to very low values 1 and form monomineralic rocks the characteristic time scale for such compaction is theoretically short compared to the time required to solidify a large layered intrusion during compaction changes of mineral compositions and texture may occur as moving melts interact with the surrounding matrix both compaction and compositional convection can be interrupted by solidification in the pore spaces compositional convection will only occur if the rayleigh number is larger than 40 if the residual melt becomes lower in density and the convective velocity exceeds the solidification velocity measured by the rate of crystal accumulation in the chamber orthocumulates are thus more likely to form in rapidly cooled intrusions where residual melt is frozen into the pore spaces before it can be expelled by compaction or replaced by convection

advection of the salt wedge and evolution of the internal flow structure in the rotterdam waterway an analysis of field measurements recorded over a tidal cycle in the rotterdam waterway is presented these measurements are the first to elucidate the processes influencing the along channel current structure and the excursion of the salt wedge in this estuary the salt wedge structure remained stable throughout the measuring period the velocity measurements indicate decoupling effects between the layers and that bed generated turbulence is confined below the pycnocline the barotropic m4 overtide structure is imposed at the mouth of the estuary and the generation of m4 overtides within the estuary is found to be relatively small internal tidal asymmetry does not make a significant contribution to the m4 velocity frequency band instead the combination of barotropic and baroclinic forcing in conjunction with the suppression of turbulence at the interface provides the main explanation for the time dependence and mean structure of the flow in the rotterdam waterway this gives rise to the observed differences in the length of the flood and ebb in the magnitudes of the flood and ebb velocities in the length of the slack water periods and in the timing of the onset of slack water at the surface and near the bed it results in the formation of distinct exchange flow profiles at the head of the salt wedge around slack water and the creation of maximal velocities at the pycnocline during flood advection governs the displacement and structure of the salt wedge since turbulent mixing is suppressed the tidal displacement of the salt wedge controls the height of the pycnocline above the bed at a particular site hence it controls the height to which bed generated turbulence can protrude into the water column consequently the authors find asymmetries in the structure of the internal flow turbulent mixing and bed stresses that are not related to classical internal tidal asymmetry

ultrahigh pressure metamorphic rocks from the chinese continental scientific drilling project i petrology and geochemistry of the main hole 0 2 050 m the main hole mh of the chinese continental scientific drilling project ccsd in southern sulu has penetrated into an ultrahigh pressure uhp metamorphic rock slice which consists of orthogneiss paragneiss eclogite ultramafic rock and minor schist recovered eclogites have a uhp metamorphic mineral assemblage of garnet omphacite rutile phengite kyanite coesite epidote ultramafic rocks contain garnet olivine clinopyroxene orthopyroxene ti clinohumite phlogopite gneisses and schists contain an amphibolite facies paragenesis but their zircons have coesite garnet omphacite or jadeite and phengite inclusions indicating that eclogites and gneisses have been subjected to in situ uhp metamorphism using available geothermobarometers p t estimates of 3 1 4 4 gpa and 678 816 c for eclogites were obtained if surface outcrops and neighboring shallow drill holes are considered together we suggest that a huge supracrustal rock slab 50 km long 100 km wide 5 km deep was subducted to a depth 100 km and then exhumed to the surface the depth interval 0 2 050 m of the ccsd mh can be divided into six lithological units unit 1 consists of alternating layers of quartz rich and rutile rich eclogites with thin interlayers of gneiss and schist eclogites of unit 1 are characterized by nb ta sr and ti depletions low mg number and general lree enrichment unit 2 comprises rutile and ilmenite rich eclogite and minor normal eclogite and is characterized by high tio2 total fe v co and sr and very low sio2 alkali zr ba nb ta and total ree contents and lree depleted ree patterns with slightly positive eu anomalies unit 3 contains ultramafic rock and minor mgo rich eclogite protoliths of uhp rocks from units 1 2 and 3 represent a layered mafic to ultramafic intrusion at crustal depth units 4 and 6 consist of interlayered eclogite and paragneiss the eclogites are characterized by th u nb ta and ti depletion and k enrichment and lree enriched ree patterns paragneisses show nb ta sr and ti depletions and lree enriched ree patterns occasionally with slightly negative eu anomalies indicating that their protoliths represent metamorphic supracrustal series unit 5 consists mainly of orthogneisses showing distinct nb ta sr and ti depletions and lree enriched ree patterns with pronounced negative eu anomalies suggesting granitic protoliths in conclusion it is proposed that the southern sulu uhp belt consists of a series of meta supracrustal rocks a layered mafic ultramafic complex and granites

shear instability in a highly stratified estuary abstract shear instability is found to be the principal mechanism of vertical exchange within the pycnocline of a salt wedge estuary a field program involving high resolution velocity and density measurements as well as high frequency acoustic imagery allowed direct comparison of instantaneous richardson number distributions to the occurrence of shear instability the theoretical stability threshold of 0 25 is consistent with the measurements based on estimates of gradients that contain the mean as well as fluctuations due to internal waves an effective stability threshold based on mean gradients is found to be approximately one third reflecting a significant contribution of internal wave shear the integral effect of the mixing process is to homogenize the gradients of velocity and density producing linear profiles of these quantities across the pycnocline a turbulent prandtl number of unity is suggested by the vertical distributions of velocity and density during periods of active vertical mixin

mixing at camarinal sill in the strait of gibraltar during the gibraltar experiment in 1985 1986 observations of shear stratification microstructure and acoustic backscatter revealed a complex mixing regime at camarinal sill in the strait of gibraltar the mixing is forced by strong semidiurnal tidal currents and weaker but more steady baroclinic flows flows are characterized as outflow or inflow nearly equivalent to westward or eastward rising water at gibraltar coincides with outflow at all depths we observed two modes of outflow at the sill in may 1986 the transition layer separating atlantic and mediterranean water was between 0 75 mpa and 1 mpa when we sampled east of the sill near neap tide the transition turned down just before reaching the sill crest where the flow became critical increasing shear soon destabilized the transition producing billows which grew to 30 75 m on the west flank of the sill the overturning generated intense turbulence with peak dissipation rates e exceeding 10 2 w kg 1 this turbulence rapidly thickened the transition from z 30 50 m east of the sill to z 130 150 m within 1 2 km west of the sill from the rate of thickening we estimate the rate of formation of new transitional water during neap tide as 0 8 1 2 105 m3 s 1 this outflow mode did not release eastward propagating internal bores when outflow turned to inflow but the inflow did appear to arrest the deep outflow in may the largest average dissipation rate over and just west of the sill had the same magnitude as estimates of the net energy lost by adjustment of velocity and mass across the sill during outflow other averages are smaller than the energy loss presumably because the limited sampling severely underestimates the average dissipation rate during outflow strong shears were observed to rise to 100 times those in the background internal wave field however probably owing to spatial offsets between the ship s acoustic doppler current profiler and our tethered free fall profiler the only statistically significant correlations were found between overturning scales measured directly and those estimated from e in the same profile we observed the other outflow mode in october 1985 when we profiled over the sill near spring tide and the transition was east of the sill centered near 1 5 mpa after encountering the sill the transition rose sharply and remained within 10 20 m of the surface across the sill plunging steeply downward just past the west edge of the sill this was accompanied by intense turbulence and at least one rebound of the transition we did not observe release of eastward propagating bores when inflow turned to outflow but observations by armi and farmer 1988 in april 1986 found bores released at spring tide in regimes similar to the one we observed in october 1985

modulation of the semidiurnal cycle of turbulent dissipation by wind driven upwelling in a coastal embayment with two 25 hour series of turbulent microstructure and currents observations carried out in august 2013 during spring chaos 1 and neap tides chaos 2 we investigated the semidiurnal cycle of turbulent dissipation in an embayment affected by coastal upwelling ria de vigo nw iberia at the time of sampling the bay hosted a net wind driven bi directional positive exchange flow and thermal stratification turbulent kinetic energy tke dissipation e at the interface between upwelled and surface waters was enhanced by two orders of magnitude during the ebbs 10 6 w kg 1 with respect to the floods 10 8 w kg 1 this pattern was caused by the constructive interference of the shear associated with the upwelling and tidal currents the vertical structure of the tidal currents was consistent with a deformation of tidal ellipses by stratification which was tightly coupled to the intensity of upwelling this two pronged interaction resulted in a modulation of the semidiurnal cycle of turbulent dissipation by coastal upwelling thus as a result of the upwelling relaxation conditions experienced during chaos 1 depth integrated interior tke dissipation rates were higher by a factor of 2 compared to chaos 2 by using a simple model we determined that observed variations in turbulent mixing had a limited influence on the tidal variations of stratification which were dominated by straining and advection the mixing mechanism described here is potentially relevant for the ecology of upwelling bays as it can stimulate the transport of nutrients from deep upwelled waters to the sun lit surface layers where primary production takes place

a strontium isotopic investigation of the bjerkreim sokndal layered instrusion southwest norway the 230 km 2 proterozoic bjerkreim sokndal layered instrusion has a monzonoritic bulk composition and comprises a 6 km thick broadly leuconoritic layered series ls overlain by unlayered mangerite and quartz mangerite in the bjerkreim lobe the ls comprises six megacyclic units mcu 0 ia ib ii 11 and iv in a syncline this lobe is surrounded by migmatitic gneisses the roof to the instrusion is missing the mg number opx an and whole rock initial 87 sr 86 sr isotope ratios sr 0 display broadly parallel trends through mcus ii and iii and into mcu iv with decreasing mg number 75 58 and an 50 40 accompanying increasing sr 0 0 7050 0 7085 this correlation breaks down in the upper part of mcu iv and mangerite the quartz mangerite has sr 0 values of 0 7085 abrupt reversals occur across the mcu boundaries the ls crystallized on the floor of a periodically replenished magma chamber that was continually assimilating country rock gneisses strong compositional zoning of the magma developed as a result of repeated replenishments with relatively dense primitive ferrobasaltic magma sr 0 0 7049 along the floor and the development of extensive buoyant roof melts assimilation took place on a massive scale up to 50 in the upper parts of the chamber

magma addition and possible decoupling of major and trace element behaviour in the bushveld complex south africa abstract incompatible trace element abundances and ratios in cumulate rocks from the bushveld complex may be used to predict the levels at which new magmas may be injected sudden and sustained changes in absolute abundances suggest new magma addition while gradual increases are consistent with fractionation of a large body of magma the present data suggest input above the merensky reef at the top of the critical zone near the top of the lower and main zones there may be other additions however in the latter case the chemical effect is spread through a large vertical interval and suggests very slow diffusive mixing between new and residual liquids the different behavioral patterns may be related to whether new magma intrudes above or below the residual magma the former situation resulting in delays between timing of injection and significant influence in the chemistry of the cumulates

intratidal variations in stratification and mixing in the hudson estuary this study represents a detailed examination of intratidal variations in boundary layer structure in a relatively narrow straight section of the hudson river estuary during high river discharge the presence of active mixing is inferred from estimates of the richardson number the maximum height above bed to which mixing occurs is comparable during flood and ebb however the regions of mixing differ in density structure during the flood active mixing is confined to a well mixed near bed layer whereas during the ebb active mixing occurs throughout regions of significant stratification tidal straining maintains stratification during the ebb while it promotes the growth of a uniform bottom mixed layer during the flood in general maximum and minimum near bed stratification occur during late ebb and flood respectively reflecting the dominant role played by tidal straining in determining intratidal variation vertical stretching was also found to be an important term in the stratification balance during the ebb

density changes during the fractional crystallization of basaltic magmas fluid dynamic implications the dynamical behaviour of basaltic magma chambers is fundamentally controlled by the changes that occur in the density of magma as it crystallizes in this paper the term fractionation density is introduced and defined as the ratio of the gram formula weight to molar volume of the chemical components in the liquid phase that are being removed by fractional crystallization removal of olivine and pyroxene whose values of fractionation density are larger than the density of the magma causes the density of residual liquid to decrease removal of plagioclase with fractionation density less than the magma density can cause the density of residual liquid to increase during the progressive differentiation of basaltic magma density decreases during fractionation of olivine olivine pyroxene and pyroxene assemblages when plagioclase joins these mafic phases magma density can sometimes increase leading to a density minimum calculations of melt density changes during fractionation show that compositional effects on density are usually greater than associated thermal effects in the closed system evolution of basaltic magma several stages of distinctive fluid dynamical behaviour can be recognised that depend on the density changes which accompany crystallization as well as on the geometry of the chamber in an early stage of the evolution where olivine and or pyroxenes are the fractionating phases compositional stratification can occur due to side wall crystallization and replenishment by new magma with the most differentiated magma tending to accumulate at the roof of the chamber when plagioclase becomes a fractionating phase a zone of well mixed magma with a composition close to the density minimum of the system can form in the chamber the growth of a zone of constant composition destroys the stratification in the chamber a chamber of well mixed magma is maintained while further differentiation occurs unless the walls of the chamber slope inwards in which case dense boundary layer flows can lead to stable stratification of cool differentiated magma at the floor of the chamber in a basaltic magma chamber replenished by primitive magma the new magma ponds at the base and evolves until it reaches the same density and composition as overlying magma successive cycles of replenishment of primitive magma can also form compositional zonation if successive cycles occur before internal thermal equilibrium is reached in a chamber in a chamber containing well mixed plagioclase saturated magma the primitive magma can be either denser or lighter than the resident magma in the first case the new magma ponds at the base and fractionates until it reaches the same density as the evolved magma mixing then occurs between magmas of different temperatures and compositions in the second case a turbulent plume is generated that causes the new magma to mix immediately with the resident magma

slow dense replenishments of a basic magma chamber the layered series of the newark island layered intrusion nain labrador the newark island layered intrusion is a composite layered intrusion within the nain anorthosite complex labrador the intrusion comprises a lower layered series ls dominated by troctolites olivine gabbros and oxide rich cumulates and an upper hybrid series hs characterized by a wide range of mafic granitic and hybrid cumulates and discontinuous layers of chilled mafic rocks wiebe 1988 the hs crystallized from a series of replenishments of both silicic and basic magmas the ls crystallized from periodically replenished basic magmas the ls has a lower zone that consists mainly of olivine plagioclase cumulates and contains minor cryptic reversals in mineral compositions that resulted from replenishments of relatively primitive magma an upper zone is dominated by olivine plagioclaseaugite ilmenite cumulates cumulus titanomagnetite and pyrrhotite occur within some oxide rich cumulates and the stratigraphically highest layers contain cumulus apatite at intermediate levels in the sequence cumulus inverted pigeonite occurs in place of olivine several prominent regressions in the stratigraphy of the upper zone are marked by fine grained troctolitic layers with much higher mg no 100 mgo mgo feo and anorthite than underlying cumulates these layers coarsen upward and grade back to oxide bearing olivine gabbros within thicknesses ranging from 10 cm to 15 m dikes that cut the ls have major and trace element compositions that strongly suggest that they are feeders for the replenishments in the lower zone when olivine and plagioclase were the only cumulus phases replenishments were less dense than the resident magma and rose as plumes and mixed with it precipitation of cumulus oxides in the upper zone lowered the density of resident magma so that subsequent replenishments were more dense than resident magma replenishments that occurred after oxides began to precipitate had small injection velocities these post oxide injections flowed along the interface between resident magma and the cumulate pile and precipitated flow banded fine grained troctolites

convective exchange between pore fluid and an overlying reservoir of denser fluid a post cumulus process in layered intrusions abstract we describe experiments on buoyancy driven exchange between fluid in a porous bed of glass balls and an overlying reservoir of denser fluid fingers of the dense fluid penetrated downwards into the porous medium when the two fluids had equal viscosities the rate of convective exchange was proportional to permeability and the density difference between the fluids and was inversely proportional to viscosity when the fluids had different viscosities the rate further depended on the viscosity ratio raised to the power 0 4 if a layer of dense new melt is emplaced above a porous cumulus pile forming the floor of a magma chamber an analogous process may occur as the new melt can percolate down into the pore space and expel the less dense intercumulus liquid convective exchange may proceed at rates of metres per year to tens of metres per year in basic to ultrabasic magmatic systems this conclusion strongly depends on the porosity of the cumulus pile and is less sensitive to the magmatic viscosities chemical and textural effects will result from this process such as re equilibration and resorption of cumulus crystals when intercumulus melt exchange is incomplete lateral geochemical gradients may be preserved in cumulate rocks

cyclic units in the somerset dam layered gabbro intrusion southeastern queensland australia abstract the well preserved somerset dam intrusion probably represents a small relatively shallow subvolcanic magma chamber the 500 m thick exposed sequence consists of 22 macrolayers which are defined by sharp phase modal and textural contacts at least six cyclic units 30 150 m thick are exposed and the sequence from the base to the top of a cyclic unit is inferred to be leucogabbro plagioclase cumulate troctolite plagioclase olivine cumulate olivine gabbro plagioclase augite olivine cumulate and oxide gabbro plagioclase augite olivine magnetite ilmenite cumulate mineral compositions in a typical cyclic unit show a reversed fractionation trend in the sequence leucogabbro troctolite and a normal fractionation trend from troctolite the least fractionated rock type to the oxide gabbro the most fractionated rock type the most sensitive parameters for defining the cryptic trends are an in plagioclase fo and ni in olivine and cr in magnetite and augite whole rock compositions also show marked changes and fe ti v s and cu increase and al mg fe cr and ni decrease from troctolite to oxide gabbro despite the remarkable similarity of successive cyclic units significant differences exist between them in the sequences of layers thicknesses of individual layers and of the cyclic units mineral compositions and cryptic patterns average level of fractionation and the size of the reversals unit 3 is particularly unusual because it is the least fractionated and consists of two incomplete subunits unit 1 the lowest exposed is the most fractionated these differences between the units cannot be explained in terms of a closed system and are strong evidence for an open system involving periodic injections of magma the formation of a cyclic unit appears to reflect the dominant control of the order of crystallisation from a batch of replenished magma which is essentially plagioclase first followed by olivine augite magnetite and ilmenite and brown hornblende the parent magma is inferred to have been a high alumina olivine tholeiite the gradual rather than sharp reversals in the cryptic trends in the lower part of each cyclic unit may reflect some magma mixing though postcumulus processes could have been operative

temporal and spatial variability of vertical salt flux in a highly stratified estuary 1 the temporal and spatial variability of vertical salt flux in the fraser river estuary british columbia was investigated observationally using several different direct and indirect indicators of buoyancy flux data were collected from the estuary using shipboard instrumentation primarily an acoustic doppler current profiler and a towed conductivity temperature depth unit direct estimates of buoyancy flux were made from along channel control volume analyses and from measurements of overturn scales the spatial and temporal evolution of the salt wedge structure through a tidal cycle was evaluated using the results of these buoyancy flux calculations as well as gradient richardson number froude number and stratification profiles observations indicate that buoyancy flux is driven primarily by interfacial stress and not bottom stress as is common in many estuaries vertical salt flux as opposed to seaward advection of high salinity fluid was found to be the dominant mechanism responsible for removal of salt from the estuarine channel during each daily tidal cycle buoyancy flux was highly variable in time and space however with vertical salt flux during ebb tides on the order of 2 to 3 times greater than that estimated during floods this is due to an increase in the vertical shear of horizontal velocity and a sharp increase in stratification which was observed during early ebb enhanced mixing was observed spatially within a region dominated by a channel constriction in which the channel narrows by approximately 25

terminology for layered intrusions the terminology of igneous cumulates was originally formulated on the concept that the rocks were concentrations of minerals accumulated by crystal settling it is now well established for several major intrusions that plagioclase that had been typed as cumulus should in fact have floated in its parental magmatic liquid nevertheless the terminology has been valuable in the classification of the rocks of these and other intrusions and it has been useful in certain aspects of their genetic interpretation the name cumulate is therefore redefined so that crystal settling is a possible but not essential process in the origins of the rocks to which it is applied the overall nomenclature of layered intrusions is then reviewed and definitions of names are refined and systematized to clarify their applications careful distinction is made between descriptive and genetic names a cumulate is defined as an igneous rock characterized by a framework of touching mineral crystals and grains that evidently were concentrated through fractional crystallization of their parental magmatic liquids a layer is a sheetlike unit of cumulate that is a distinctive entity in its compositional and or textural features a lamina is a thin 2 5 cm sharply defined layer igneous lamination is a general name for planar structure that is pervasive through cumulates on the scale of their grain size layering is the overall structure and fabric manifest through combinations of layers laminae and lamination the difference between layers and layering is essentially the difference between individuals and a population and the terms that describe one are not necessarily appropriate to the description of the other but the fundamental variants of all of layering lamination grading in layers and layer contacts can essentially be described by one or more of the four modifiers grain size modal textural and cryptic where the last refers to cumulus miner al compositions a system for subdividing layered intrusions is proposed in which distinction is made between general divisions ranked as series zones and subzones and prominent units that are called groups members rhythmic units and cyclic units applications to the skaergaard bushveld muskox stillwater and other intrusions are briefly described

flow and sediment suspension events over low angle dunes fraser estuary canada 1 the morphodynamics of large sand bedded rivers and estuaries are ultimately controlled by the way bed material is moved and the development of large subaqueous sand dunes that control hydraulic flow resistance it is widely thought that the primary mechanism for moving sandy bed material in these channels is large scale coherent flow structures that cause suspension events whose properties vary with flow especially in tidally influenced environments here we examine mean flow and sediment suspension events over low angle dunes lee face angle 30 in the unsteady flow of the fraser estuary canada at high tide flow nearly ceased and a salt wedge entered the channel forcing salt water under the downstream moving fresh water the salt wedge persisted in the channel until late in the falling tide causing stratification in the water column and instabilities along the saline fresh water interface at low tide mean velocities peaked and forced the saline water out of the channel flow over the low angle dunes displayed topographically induced patterns previously observed over high angle dunes but permanent flow separation was not observed large scale sediment suspension events dominated sediment flux during low tide and became larger scale yet less frequent as the tide began to rise the suspension events appeared to form over the lower stoss of the dunes and grew up over the bed forms and less commonly emerged downstream of the crest suspension events move 69 of the total sediment in the flow above low angle dunes when they are present

laboratory investigation of the impact of lateral spreading on buoyancy flux in a river plume abstractthe relationship between lateral spreading and mixing in stratified gravity currents is investigated by comparing laterally confined and unconfined currents in a series of laboratory experiments the vertical turbulent buoyancy flux is determined using a control volume approach with velocity and density fields derived from combined particle image velocimetry piv and planar laser induced fluorescence plif lateral spreading is determined in the unconfined experiments based on plan view imaging using the optical thickness method otm the authors find that lateral spreading dramatically modifies the plume structure the spreading plume layer consists of approximately linear density and velocity profiles that extend to the surface whereas the channelized plume profiles are uniform near the surface lateral spreading decreases the average plume density relative to laterally confined currents with similar inflow conditions however the local turbulent buoyancy flux in the spreading experiments i

influence of bottom stress on the two layer flow induced by gravity currents in estuaries abstract baroclinic circulation in highly stratified and partially stratified estuaries is characterised by a two layer flow a bottom salt water inflow and a surface brackish water outflow tidal period variation of the thicknesses of a two layer flow is observed to be associated with mixing bottom stress and hydraulic characteristics of superposed tidal and gravity currents here both analytical two layer hydraulic equations with weak friction and a numerical model including a turbulence closure were utilised to understand the mechanism of the layer tendency within a two layer flow under different barotropic flow conditions it has been found that in the weak bottom friction case a gravity current has two critical solutions at the layer thickness equal to 0 5 h and 0 292 h the layer thickness towards a particular critical solution is dependent on the sign of the bottom stress i e when the bottom stress is opposite favor to the bottom gravity current its layer thickness converges to 0 5 h 0 292 h in the case of strong bottom stress and mixing opposing the gravity current the solutions of the gravity current layer thickness at 0 5 h and 0 292 h will not be valid both mixing and vorticity produced by bottom stress erode the halocline and produce a high velocity core in the mid depth which leads to the thickness of a bottom gravity current greater than 0 5 h these internal hydraulic tendency and mixing processes varying with time dependent barotropic tidal current forcing determine the tidal period variation of the gravity current structure

vertical boil propagation from a submerged estuarine sill 1 surface disruptions by boils during strong tidal flows over a rocky sill were observed in thermal infrared imagery collected at the snohomish river estuary in washington state locations of boil disruptions and boil diameters at the surface were quantified and are used to test an idealized model of vertical boil propagation the model is developed as a two dimensional approximation of a three dimensional vortex loop and boil vorticity is derived from the flow shear over the sill predictions of boil disruption locations were determined from the modeled vertical velocity the sill depth and the over sill velocity predictions by the vertical velocity model agree well with measured locations rms difference 3 0 m and improve by using measured velocity and shear rms difference 1 8 m in comparison a boil surfacing model derived from laboratory turbulent mixed layer wakes agrees with the measurements only when stratification is insignificant

the role of fluids in syntectonic mass transport and the localization of metamorphic vein type ore deposists abstract in low to medium grade metamorphic environments the mobilization of species is closely associated with the operation of solution precipitation creep processes during foliation development such deformation processes involve dissolution of material from source sites which are usually discrete dissolution surfaces having orientations controlled by the applied stress and displacement fields mass transfer occurs via solute diffusion in an essentially static fluid network or by transport of dissolved species in a migrating fluid precipitation of material removed from dissolution sites occurs in a variety of sink sites including pore surfaces grain scale microcracks and veins sink sites may be close to or distantly removed from source sites the transport of material during deformation involving solution precipitation creep is largely controlled by the mobility of metamorphic fluids in regions of high fluid mobility significant mass transfer may occur over large distances fluid flow mass transfer paths and the development of sink sites in such cases are constrained by the structurally controlled development of high fluid pressure domains and the consequent mechanical enhancement of permeability by hydraulic fracture processes and the development of grain scale dilatancy these processes may result in focussed fluid flow and precipitation of mobilized species in restricted regions a proportion of syntectonically mobilized material is precipitated to form vein type deposits in hydraulic fracture arrays which develop in high fluid pressure environments the microstructures developed in minerals deposited in these sites reflect the interaction of a range of nucleation and growth processes which usually involve multiple generations of fracture growth and mineral crystallization the formation of syntectonic gold quartz vein deposits in central victoria australia illustrates the importance of structural controls on both the large scale migration of metamorphic fluids and the development of sites suitable for the precipitation of metamorphically mobilized species

experimental study of liquid evolution in an fe rich layered mafic intrusion constraints of fe ti oxide precipitation on the t f o 2 and t ϱ paths of tholeiitic magmas the newark island layered intrusion a composite intrusion displaying a similar fractionation sequence to the skaergaard has both dikes which preserved liquids fed into the intrusion and chilled pillows of liquids resident in the chamber this study reports experimentally determined one atmosphere liquid lines of descent of these compositions as a function of oxygen fugacity which varies from qfm quartz fayalite magnetite to 0 5 log10 units above iw iron wustite these experiments reveal a strong oxygen fugacity dependence on the order of appearance and relative abundances of the fe ti oxide minerals titanomagnetite saturates prior to ilmenite at qfm but the order is reversed at lower oxygen fugacities in the layered series of the newark island intrusion ilmenite arrives shortly before titanomagnetite and the titanomagnetite ilmenite ratio decreases monotonically after the cumulus appearance of titanomagnetite comparison of the crystallization sequence in the intrusion with that of the experiments requires that the oxygen fugacity in the intrusion increased relative to qfm before titanomagnetite saturation and decreased afterward but always remained between the qfm and iw buffers similar trends in the modes of the fe ti oxides ilmenite and titanomagnetite in the skaergaard kiglapait and somerset dam intrusions along with fe2o3 feo ratios in morbs suggest that such a temperature oxygen fugacity path may be typical of tholeiitic magma differentiation calculations of the temperature density paths of the experimental liquids indicate that at all possible oxygen fugacities the density must have decreased abruptly after fe ti oxide saturation accordingly liquids replenishing the intrusion after fe ti oxide saturation should pond at the bottom of the chamber quenching against older cumulates field observation at the newark island intrusion confirm this prediction the similarities in the fractionation paths of several other layered intrusions to that of the newark island intrusion suggest that the density of the liquids in these intrusions also decreased after fe ti oxide saturation experiments on a suggested initial skaergaard liquid are consistent with this model

volcanic rock hosted gold and base metal mineralization associated with neoproterozoic early paleozoic back arc extension in the carolina terrane southern appalachian piedmont volcanogenic mineral deposits in the carolina terrane southern appalachian piedmont include kuroko type polymetallic massive sulfide deposits and disseminated gold pyrite deposits associated with propylitic silicic argillic and advanced argillic alteration host rocks are metavolcaniclastic and metaepiclastic rocks of a neoproterozoic early cambrian magmatic arc the favorable gold horizon is the transition from a lower succession of andesitic and rhyolitic pyroclastic rocks with basal mafic lavas to an upper sequence of epiclastic sedimentary units and minor lava and ash flows kuroko type deposits are associated with mafic to bimodal volcanic rocks in the upper sequence whole rock oxygen isotope analyses indicate that gold mineralization is associated with a transition from hydrothermal systems dominated by isotopically relatively light 18o 6 to 10 waters typical of high latitude subaerial systems to seawater 18o 0 plots of 18o vs sio2 of the host rocks show a compositional gap associated with mineralization at the subaerial to submarine transition values of 18o for the hydrothermal waters lithostratigraphic analyses and tectonic models of the carolina terrane demonstrate that mineralization coincided with extension in a rifted arc

near bottom turbulence measurements in a partially mixed estuary turbulent energy balance velocity structure and along channel momentum balance abstract a set of moored bottom mounted and shipboard measurements obtained in a straight section of the lower hudson estuary during late summer and early fall of 1995 determine velocity density and along channel pressure gradient throughout the 15 m water column as well as providing direct eddy correlation estimates of reynolds stress and indirect inertial range estimates of dissipation within 3 m of the bottom the analysis focuses on testing 1 a simplified turbulent kinetic energy equation in which production balances dissipation 2 the prandtl karman law of the wall which is a relationship between bottom stress and near bottom velocity gradient and 3 a simplified depth integrated along channel momentum balance involving local acceleration pressure gradient and bottom stress estimates of production and dissipation agree well throughout the entire record the relationship between bottom stress and velocity gradient is consistent with the law of the wall within approximately 1 m of the sea

observation and analysis of shear instability in the fraser river estuary 1 we investigate the occurrence of shear instability in the fraser river estuary instabilities observed with an echo sounder are compared with a linear stability analysis based on observed velocity and density profiles we find that each set of observed instabilities coincides with an unstable mode predicted by the taylor goldstein equation each of these instabilities occurs in a region where the gradient richardson number is less than the critical value of 1 4 both the taylor goldstein predictions and the echo soundings indicate the instabilities are concentrated either above or below the density interface this one sidedness is in contrast to the archetypal kelvin helmholtz instability although the dominant source of mixing in the estuary appears to be caused by shear instability when the tide produces strong near bed velocities small scale overturning due to boundary layer turbulence is apparent throughout the depth

using depth normalized coordinates to examine mass transport residual circulation in estuaries with large tidal amplitude relative to the mean depth abstractresidual subtidal circulation profiles in estuaries with a large tidal amplitude to depth ratio often are quite complex and do not resemble the traditional estuarine gravitational circulation profile this paper describes how a depth normalized coordinate system allows for a more physical interpretation of residual circulation profiles than does a fixed vertical coordinate system in an estuary with a tidal amplitude comparable to the mean depth depth normalized coordinates permit the approximation of lagrangian residuals performance of empirical orthogonal function eof analysis estimation of terms in the along stream momentum equations throughout depth and computation of a tidally averaged momentum balance the residual mass transport velocity has an enhanced two layer exchange flow relative to an eulerian mean because of the stokes wave transport velocity directed upstream at all depths while the observed coordinate profiles resemble gravitational circulation and pressure and fricti

the soapstone ridge complex southern appalachians petrographic mineral compositional and oxygen isotope investigation samples of the soapstone ridge complex ssr in the southern appalachians examined for this study are composed of megacrystic orthopyroxenites amphibole schists and talc chlorite amphibole schists the mineralogy of the ssr samples studied consists of varying proportions of amphibole chlorite talc orthopyroxene and fe ti oxides amphibole is the domi nant mineral in almost all ssr samples studied the amphiboles display zoning whereby cores that are composed of magne siohornblende and edenite consistent with amphibolite facies conditions are rimmed by tremolite actinolite consistent with greenschist facies conditions oxygen isotope compositions of ssr amphiboles investigated show a wide range in 18o values from a low value of 1 8 to a high value of 6 1 such wide ranges in 18oamphibole values occur in ophiolite complexes and oceanic crustal rocks relict orthopyroxene from the ssr has a 18o value of 3 4 a value lower than those from layered intrusions but comparable to some pyroxene 18o values from ophiolites equilibration temperatures calculated for actinolite chlorite yield a temperature of 227 c consistent with greenschist facies conditions it is proposed that the ssr amphibole cores were metamorphosed probably during terrane terrane collision under amphibolite facies conditions with the actinolite rims possibly being formed during thrusting of the ssr rocks onto the continental margin

the importance of aspiration and channel curvature in producing strong vertical mixing over a sill on the basis of observations of the time dependent tidally forced flow over a long sill we find that aspiration and channel curvature set the flow structure and condition the flow to allow intense vertical mixing aspiration reduces the potential energy of the water column by thinning it while maintaining its density contrast channel curvature induces a cross channel circulation that can rapidly overturn a stratified flow eighteen along channel sections of density velocity and dissipation rate of turbulent kinetic energy were collected in and around the tacoma narrows of puget sound a site suspected of driving a strong vertical circulation in adjoining main basin rapid inflow to the narrows on flood from one channel of a triple junction reduces dynamic pressure allowing dense water from below sill depth to be uplifted or aspirated into the narrows we estimate water from below 150 m 3 times the sill depth is drawn into the narrows on a 3 m flood tide once in the narrows the flow remains stratified until it passes a 50 bend where a strong secondary circulation overturns the 50 m deep water column and generates intense turbulent mixing cross channel velocities of up to 0 4 m s 1 are observed and maximum values of exceed 10 3 w kg 1 upon leaving the sill stratification is reestablished and turbulence decays a similar set of sequences occurs on ebb except that the outflow bypasses the flood inflow channel and instead discharges into colvos passage the third branch of the triple junction colvos passage ultimately discharges the ebb effluent back into main basin enhancing the impact of mixing at the narrows by discharging the mixed product far from the source scaling of the cross channel momentum equation suggests that below a threshold value of along channel velocity stratification should suppress secondary circulation for a given vertical shear radius of curvature and channel width above the threshold velocity the magnitude of the cross channel velocity is roughly consistent with predictions for unstratified flow we estimate the maximum effective eddy diffusivity that aspiration and mixing in the narrows can produce in main basin to be 10 3 m2 s 1

mixing in the romanche fracture zone the romanche fracture zone is a major gap in the mid atlantic ridge at the equator which is deep enough to allow significant eastward flows of antarctic bottom water from the brazil basin to the sierra leone and guinea abyssal plains while flowing through the romanche fracture zone bottom water properties are strongly modified due to intense vertical mixing the diapycnal mixing coefficient in the bottom water of the romanche fracture zone is estimated by using the finestructure of ctd profiles the microstructure of high resolution profiler data and by constructing a heat budget from current meter data the finestructure of density profiles is described using the thorpe scaleslt it is shown from microstructure data taken in the bottom water that the ozmidov scale lo is related to lt by the linear relationship lo 5 0 95lt similar to other studies which allows an estimate of the diapycnal mixing coefficient using the osborn relation the thorpe scale and the diapycnal mixing coefficient estimates show enhanced mixing downstream eastward of the main sill of the romanche fracture zone in this region a mean diapycnal mixing coefficient of about 1000 3 1024 m2 s21 is found for the bottom water estimates of cross isothermal mixing coefficient derived from the heat budgets constructed downstream of the current meter arrays deployed in the romanche fracture zone and the nearby chain fracture zone are in agreement with the finestructure estimates of the diapycnal mixing coefficient within the romanche fracture zone although the two fracture zones occupy only 0 4 of the area covered by the sierra leone and guinea abyssal plains the diffusive heat fluxes across the 1 4 8c isotherm in the romanche and chain fracture zones are half that found over the abyssal plains across the 1 88c isotherm emphasizing the role of these passages for bottom water property modifications

observations and numerical modeling of the pearl river plume in summer season a cruise survey of the pearl river plume during southeasterly and southwesterly winds two typical wind patterns in summer in guangdong coastal waters is reported and the cruise data are analyzed to unveil the plume dynamics the kelvin number is derived from the in situ data revealing that the pearl river plume exhibits two different scales in response to the two kinds of the wind forcing numerical model simulations based on the regional oceanic modeling system roms with nesting domains are implemented to explore details of the plume dynamics validated by cruise observations and tidal gauge sea level data modeling results suggest that there is a subtidal anticyclonic recirculation bulge on the west side out of the estuary mouth under southeasterly winds showing a recirculating plume in the near field when the wind changes to the southwesterly however the recirculating plume vanishes the distinct supercritical tidal plume front occurs with southeasterly winds prevailing in spring tide due to the strong advection in the tidal plume the tidal salt deficit flux can reach as high as 12 5 of the mean current flux and illustrates the combined forcing of tide and wind key points the paper clarifies the pearl river plume anatomy under two typical winds spring tide facilitates the supercritical pearl river tidal plume front tide determines tidal salt deficit flux strength wind determines the direction

the relative roles of diapycnal and isopycnal mixing on subsurface water mass conversion abstract fluid motion in the sea is known to occur predominantly along quasi horizontal neutral surfaces but the very small diapycnal i e across isopycnal velocities often make a significant contribution to the conversation equations of heat salt and tracer by eliminating the diapycnal advection term between the conservation equations for i heat and ii salt an equation is derived for the rate of change lagrangian derivative of potential temperature on a neutral surface which has terms caused by a turbulent mixing along isopycnal surfaces i e isopycnal mixing b diapycnal turbulent mixing and c double diffusive convection bemuse of the nature of the isopycnal reference frame the diapycnal mixing terms do not take their expected forms for example the diapycnal turbulent mixing term is proportional to the diapycnal eddy diffusivity d multiplied by the curvature of the s curve d2s d 2 rather than the usual form d x x if the s curve is locally straight small scale turbulen

sill processes related to deep water renewal in a fjord observations of the gravitational circulation over the sill at the entrance to puget sound indicate a fortnightly modulation of the two layer flow with a corresponding variation in stratification gravitational circulation and stratification reach a maximum during neap tides and a minimum during spring tides the modulation appears to be a function of the turbulence generation by tidal flow over the sill which varies as a function of tidal amplitude the enhanced gravitational circulation during neap tides augments the flux of dense water across the sill region and episodes of bottom water renewal in puget sound result intrusions of dense water in the main basin of the sound show a fortnightly periodicity with a phase lag appropriate for the propagation of an internal bore from the sill region commencing at the neap tide observations indicate that the intrusions take the form of gravity currents propagating at approximately 20 cm s 1 down the main basin the detailed dynamics of the turbulent mixing processes that modulate the onset of inflow were not resolved in this study but the integrated effect of tidal mixing on the low frequency circulation is clearly demonstrated

architecture and emplacement of the nebo babel gabbronorite hosted magmatic ni cu pge sulphide deposit west musgrave western australia the nebo babel ni cu platinum group element pge sulphide deposit in the west musgrave block western australia is the largest nickel sulphide discovery in the last 10 years the deposit is hosted within a concentrically zoned olivine free tube like chonolithic gabbronorite intrusion associated with the approximately 1 078 ma giles complex layered intrusions in the warakurna large igneous province emplaced into sulphide free amphibolite facies orthogneiss the fault offset nebo babel chonolith extends for 5 km and has a cross section of 1 0 5 km igneous mineralogy fabrics and textures are well preserved the lithostratigraphy includes variably textured leucogabbronorites vlgn that form an outer shell around mineralised gabbronorite mgn with barren gabbronorite bgn and oxide apatite gabbronorite oagn in the middle and lower parts of the chonolith mineral and whole rock geochemistry indicate that the units become progressively evolved in the order vlgn mgn bgn and oagn and that incompatible trace element concentrations increase downwards within the mgn and bgn the mineralisation which is confined to the early more primitive units vlgn and mgn occurs as massive sulphide breccias and stringers and as disseminated gabbronorite hosted sulphides the massive sulphides were emplaced late in the intrusive sequence have different pge chemistry and cu tenor to the disseminated sulphides and have undergone sulphide fractionation the distribution of disseminated sulphides which are primary magmatic in origin is related to chonolith geometry and magma flow regimes rather than to gravitational settling sulfur bearing country rocks are absent in the nebo babel deposit area and thus local crustal s addition was unlikely to have been the major mechanism in achieving sulphide immiscibility the nebo babel intrusion is part of an originally continuous magma chonolith with multiple and related magma pulses the parental magma was medium to low k tholeiite with 8 9 wt mgo the initial magma pulse vlgn the most primitive and sulphide saturated was probably emplaced along a linear weakness in the country rock after crystallisation of vlgn marginally more fractionated sulphide saturated magma was injected through the thermally insulated core of the conduit forming the mgn successive pulse s of more fractionated magma bgn were emplaced in the core of the intrusion after magma flow ceased closed system crystal fractionation produced consistent mineral and chemical fractionation trends within bgn and oagn after crystallisation the intrusion was overturned and then offset by the jameson fault resulting in the apparent reverse chemical and mineral trends in nebo babel

turbulent mixing in a strongly forced salt wedge estuary up to about 400 m 3 s 1 above which a majority of the mixing occurs offshore observed buoyancy fluxes were more consistent with the k turbulence closure than the mellor yamada closure and more total mixing occurred in the estuary with k calculated buoyancy fluxes were sensitive to horizontal grid resolution as a lower resolution grid yielded less integrated buoyancy flux in the estuary and exported lower salinity water but likely had greater numerical mixing

observations at the tidal plume front of a high volume river outflow 1 we present shipboard observations of very strong convergence vertical velocities and mixing and near bed impacts associated with the leading edge front of the tidally pulsed columbia river plume with upwelling favorable winds and riverflow of 4900 m3s 1 the plume propagates as a buoyant gravity current with a rotary bore like vertical frontal circulation and downwelling as strong as 0 35 m s 1 in waters as deep as 65 m near bed currents intensify to as much as 1 0 m s 1 after frontal passage and are often associated with elevated acoustic backscatter mixing is locally strong with an eddy diffusivity of o 0 2 m2s 1 50 m behind the front and t s diagrams imply plume mixing with 10 m deep ocean water these observations indicate that the leading edge front of a surface advected plume can cause exchanges of a nutrients between cold subsurface shelf waters and the river plume and b nutrients and sediments across the sediment water interface

synchronous deformation and hydrothermal activity in the shear zone hosted high sulphidation au cu deposit at peak hill nsw australia altered and mineralised rocks at peak hill are confined to a 300 500 m wide north south striking steeply dipping shear zone that is flanked by the mingelo volcanics along its western side and cotton formation siltstones along its eastern side this shear zone is defined by extensive zones of cataclasite and strongly foliated micaceous schists in marked contrast to the largely undeformed nature of the adjacent rocks advanced argillic assemblages quartz kaolinite pyrite alunite illite occur throughout the core of the peak hill deposit propylitic assemblages including albite quartz interlayered chlorite smectite illite and ankerite and a narrow discontinuous zone of argillic quartz illite pyrite alteration are developed in the mingelo volcanics along the western side of the deposit propylitic argillic and advanced argillic assemblages are overprinted by an internally zoned phase of phyllosilicate alteration that grades inwards from a peripheral sericite clay chlorite assemblage through phyllic assemblages muscovite illite pyrite paragonite to a pyrophyllite pyrite diaspore andalusite altered core au cu mineralisation is hosted by barite pyrite veins that cut the advanced argillic assemblage but pre date the phyllosilicate dominated alteration native au lacking ag calaverite te rich tennantite tetrahedrite goldfieldite chalcopyrite covellite and chalcocite occur in the barite pyrite veins no ore bearing minerals were detected in any of the alteration assemblages the total gold content of the peak hill deposit is currently 720 k ounces and this includes 100 k ounces of unmined reserves within the shear zone phyllosilicate minerals are developed in strain shadows and partly define the stretching lineation associated with dip slip movement the zonation within the phyllosilicate assemblages mimics the geometry of bends in the shear zone and minor internal structures these textures indicate that the phyllosilicate alteration developed synchronous with movement on the shear zone earlier advanced argillic alteration and mineralisation are developed in rocks derived from both sides of the shear zone hydrothermal activity associated with the earlier advanced argillic alteration was therefore either synchronous with juxtaposition of these distinct rock units or occurred during a later phase of movement on the shear zone cross cutting fibrous textures in the auriferous barite pyrite veins indicate that repeated fracturing of the advanced argillic altered rocks accompanied development of successive generations of auriferous veins concentrations of auriferous veins are localised in steeply plunging shoots that are oriented parallel to the stretching lineation in the shear zone these features all indicate movement on the host shear zone accompanied each phase of hydrothermal activity in the peak hill deposit the location alteration zonation and distribution of mineralised veins within the deposit are intimately controlled by deformation on the host shear zone synchronous with hydrothermal activity the development of high sulphidation hydrothermal systems synchronous with deformation along brittle ductile shear zones is a predictable consequence of intrusive activity during deformation in areas characterised by a high geothermal gradient the close relationship between tectonism and hydrothermal activity indicates that these deposits are likely to be located in the vicinity of regional scale shear zones deposits are likely to be aligned parallel to the regional scale structural grain and restricted to areas of conspicuous deformation as is the case at peak hill and temora nsw aluminous alteration zones concentrated in the vicinity of regional scale structures in the carolina slate belt may be a further example of this style of hydrothermal activity

mineral chemistry petrogenesis and tectonic setting of the wateranga layered intrusion southeast queensland australia the wateranga layered mafic intrusion 28 km2 in area 500 m thick is a tholeiitic undeformed unmetamorphosed permo triassic layered gabbroic pluton intruded into the late carboniferous goodnight beds of the goodnight block in southeast queensland the intrusion mainly consists of gabbro and norite associated with subordinate amounts of troctolite anorthosite and orthopyroxenite and rare picrite olivine gabbro is the dominant rock type of the intrusion fractionation followed a tholeiitic trend with iron enrichment in the liquid petrographic mineral chemical and whole rock geochemical data have been used to divide the intrusion into lower middle and upper zones which are interpreted as reflecting magma chamber replenishment the observed changes in the crystallization order between the zones reveal that a single parental magma is inadequate to explain the data the common differentiation indices such as an content of plagioclase mg s of olivine clinopyroxene orthopyroxene and whole ro

pyroxene oikocrysts in troctolitic cumulates evidence for supercooled crystallisation and postcumulus modification studies of pyroxene oikocrysts in plagioclase olivine cumulates crystallised from high alumina olivine tholeiite magmas in layered intrusions inferred to represent periodically replenished magma chambers show that small plagioclases enclosed within the oikocrysts differ significantly from plagioclases in the host rock plagioclases within oikocrysts are very elongate with a high surface area show extensive mutual attachment at high angles resembling skeletal growth and tend to be randomly orientated some are rounded and embayed are reversely zoned and more sodic by an 5 10 than some of the plagioclase in the host rock plagioclase crystal centres tend to be closer spaced in the oikocrysts than in the host rock in contrast plagioclases in the host rock are discrete coarser grained less elongate strongly aligned and locally polygonised

tide induced variation of the dynamics of a salt wedge estuary abstract the time variations of the salt wedge intrusion in the fraser estuary british columbia were monitored during a variety of tidal and run off conditions using instruments and sampling methods that provided high resolution of the velocity and water properties in space and time the salt wedge was found to vary considerably in position and vertical structure through the tidal cycle due to the interaction of the tidal flow with the density driven motion of the salt wedge during the flood the salt wedge progressed up the estuary as a gravity current while during the ebb the salinity structure was eroded by shear instability the difference in character of the flow between flood and ebb is attributed to the transition between a subcritical and supercritical internal froude number during flood tide the internal state is subcritical and the estuarine shear flow is maintained with a small amount of vertical mixing while in the supercritical ebb flow vertical shears become so large that the pycnoc

hydraulics and mixing in a laterally divergent channel of a highly stratified estuary author posting american geophysical union 2017 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 122 2017 4743 4760 doi 10 1002 2016jc012455

mixing layer dynamics in separated flow over an estuarine sill with variable stratification 1 we investigate the generation of a mixing layer in the separated flow behind an estuarine sill height h 4 m in the snohomish river washington as part of a larger investigation of coherent structures using remote and in situ sensing during increasing ebb flows the depth d and stratification decrease and a region of sheared flow characterized by elevated production of turbulent kinetic energy develops profiles of velocity and acoustic backscatter exhibit coherent fluctuations of order 0 1 hz and are used to define the boundaries of the mixing layer variations in the mixing layer width and its embedded coherent structures are caused by changes to both the normalized sill height h d and to a bulk richardson number rih defined using the depth of flow over the sill entrainment et and the mixing layer expansion angle increase as stratification and the bulk richardson number decrease this relationship is parameterized as et 0 07rih 0 5 and is valid for approximately 0 1 0 8 due to blocking of flow by the sill

role of straining and advection in the intratidal evolution of stratification vertical mixing and longitudinal dispersion of a shallow macrotidal salt wedge estuary 1 a month of flow observations in the snohomish river estuary reveals the complex intratidal and fortnightly stratification mixing and dispersion dynamics in this macrotidal shallow salt wedge estuary system both salt wedge propagation and concomitant straining of the density field dominate temporal and spatial variations in stratification leading to intratidal variability of shear and mixing that differs in important ways from observations in partially mixed estuaries bottom generated turbulent kinetic energy production is enhanced during spring tides and acts in concert with straining to counteract advection and minimize vertical stratification during the spring flood tides this bottom generated mixing contributes to a buoyancy flux near the top of a well mixed layer during strong flood tides during strong ebb tides interfacial shear production and buoyancy flux occur along the sharp straining enhanced interface just before the system becomes well mixed longitudinal dispersion is less sensitive to the spring neap cycle yet exhibits strong intratidal variability reduced longitudinal dispersion is observed during the large floods relative to the rest of the tidal cycle behavior we attribute to a lack of vertical shear overall ebb tide advection and straining enhance stratification and longitudinal dispersion and allow for interfacial mixing intratidal variability which varies on the spring neap scale is a dominant feature of this estuary suggesting the importance of intratidal processes and tidally varying mixing coefficients in similar strongly stratified strongly forced estuaries