magnetism and transmission electron microscopy of fe ti oxides and pyroxenes in a granulite from lofoten norway granulites from southwest lofoten norway often carry intense and stable components of natural remanent magnetization nrm coercivities in excess of 100 mt and blocking temperatures up to 580 645 c are common several phases in these rocks can carry stable components of nrm clinopyroxenes augite with exsolved pigeonite and orthopyroxene usually contain abundant fe ti oxides the majority of which are too small to be studied conclusively with visible light additionally these rocks typically contain coarse grained 100 1000 m exsolution intergrowths of rhombohedral fe ti oxides and coarse grained magnetite we have studied the magnetism and mineralogy of the titanohematite and the inclusion bearing augites in one granulite sample using transmission electron microscopy tem and magnetic experiments to understand better the remanence properties of naturally occurring fe ti oxides and their relationships to silicate minerals the coarse grained titanohematite has a coercivity of 350 mt and a laboratory saturation remanence that unblocks at 570 600 c the hysteresis characteristics of this titanohematite are typical of much smaller 10 m sized single domains which apparently reflects the presence of exsolved ilmenite lamellae as small as 10 nm in thickness these lamellae presumably inhibit 1 domain wall nucleation and 2 movement of walls that manage to nucleate the inclusions in the augites serve as carriers of lower coercivity remanence with blocking temperatures less than about 560 c magnetite hematite and ilmenite are present in the augite and intergrowth of the rhombohedral phases revealed by tem persists down to the 20 nm scale the distribution of the magnetite inclusions in the augite appears to be unrelated to any silicate microstructure while that of the rhombohedral fe ti oxides is strongly controlled by silicate microstructure with intergrowths of these oxides commonly decorating lamellae of pigeonite orthopyroxene and clinoamphibole within the augite the nrm of this sample possibly dates from the amphibolite facies metamorphism that the region experienced about 1000 m y ago paleomagnetic studies of these rocks could readily recover virtual geomagnetic poles dating from this event in addition to the included oxides the augites display a number of unusual features that probably result from the protracted polymetamorphic history of these granulites pigeonite lamellae are not parallel to the b crystallographic axis pigeonite lamellae cut across those of orthopyroxene and numerous included minerals occur rare earth elements are concentrated within inclusions that reside in the augite

modification of a linear bar trough system by a standing edge wave abstract detailed fluid motions and bathymetric changes in the lacustrine nearshore zone at wymbolwood beach georgian bay canada were monitored during storms to test theoretical postulates about the importance of low frequency wave motions to nearshore circulation of water and sediments eighteen continuous resistance wave staffs and two electromagnetic current meters were deployed along one shore normal and two shore parallel instrument arrays over a period of two months during one intense storm a mode 3 standing edge wave at 0 035 hz was the predominant low frequency motion prior to the storm the bathymetry was characterized by linear bar trough systems and during the storm these features migrated onshore and became rhythmic in response to the length scales and relatively fixed locations of nodal and antinodal lines of the standing edge wave however a well defined crescentic bar as predicted by the model under the condition of zero net sediment flux divergence did not evolve because the hydrodynamic forcing ceased before an equilibrium condition could be attained nevertheless the location of scour and accretion features demonstrated the tendency towards such a crescentic form the offshore and alongshore irregularities of the post storm bathymetry are not readily explained by alternative hydrodynamic interactions

infragravity wave dynamics in a barred coastal region a numerical study this paper presents a comprehensive numerical study into the infragravity wave dynamics at a field site characterized by a gently sloping barred beach the nonhydrostatic wave flow model swash was used to simulate the local wavefield for a range of wave conditions including mild and storm conditions the extensive spatial coverage of the model allowed us to analyze the infragravity wave dynamics at spatial scales not often covered before overall the model predicted a wavefield that was representative of the natural conditions supporting the model application to analyze the wave dynamics the infragravity wave field was typically dominated by leaky waves except near the outer bar where bar trapped edge waves were observed relative contributions of bar trapped waves peaked during mild conditions when they explained up to 50 of the infragravity variance near the outer bar the infragravity wave growth was partly explained by nonlinear energy transfers from short waves this growth was strongest for mild conditions and decreased for more energetic conditions when short waves were breaking at the outer bar further shoreward infragravity waves lost most of their energy due to a combination of nonlinear transfers bottom friction and infragravity wave breaking nonlinear transfers were only effective near the inner bar whereas near the shoreline where losses were strongest the dissipation was caused by the combined effect of bottom friction and breaking this study demonstrated the model s potential to study wave dynamics at field scales not easily covered by in situ observations

mineralogy of mafic xenoliths and their reaction zones in the olivine lamproite from prairie creek arkansas and the paragenesis of haggertyite ba fe6ti5mg o19 the recently discovered mineral haggertyite which belongs to the magnetoplumbite family occurs in the prairie creek lamproite exclusively in a reaction zone at the contact between the olivine lamproite and serpentized xenoliths compositional characteristics of the lamproite are an extreme enrichment in elements such as k ba and ti associated with very low al2o3 based on textural evidence it appears that the xenoliths represent a quenched very mafic magma possibly komatiitic an absence of perovskite in the reaction zone is the consequence of si diffusion from the xenolith iron available in the xenolith may be the controlling factor for the crystallization of haggertyite and other fe and ti oxides involved in the reaction other elements k ti and ba diffused from the lamproite toward the xenolith zone but only the outermost edge of the xenoliths reacted the crystallization of haggertyite appears to have resulted from a local chemical environment created by element diffusion between the two significantly contrasting lithologies

edge waves on nonplanar bathymetry and alongshore currents a model and data comparison the numerical solutions for the dispersion of linear shallow water edge waves are compared with observed alongshore wavenumber frequency spectra of edge wave variance to examine their prediction of the effects of nonplanar bathymetry and moderate mean alongshore currents field observations were made at the two southern california nearshore sediment transport study field sites torrey pines 1978 and leadbetter 1980 beaches on torrey pines beach where the bathymetry is very planar except for a concave steepening landward beach face observed departures from the analytical plane beach dispersion solution attributed to the concave face are predicted by numerical dispersion solutions using the measured cross shore depth profile on both beaches asymmetry in observed dispersion curves of upstream and downstream progressing edge waves are well predicted by numerical dispersion solutions using the cross shore profile of measured mean alongshore current spectra of the alongshore velocity component from both beaches show changes in edge wave mode dominance with increased frequency oltman shay and guza 1987 demonstrated that mode dominance transition with frequency as observed from a fixed offshore location is associated with the seaward decay of edge waves and that the approximate frequency of mode transition is predicted by the profile solutions for edge wave variance and the assumption of equal shoreline elevation variance amongst modes a submerged concave beach face at torrey pines beach is shown to alter the predicted cross shore scaling of the edge wave profiles from that predicted when mean water is below the concave beach face and therefore to alter the mode transition frequency predictions different mode transition frequencies are observed in spectra from data runs with mean water levels both above and below the concave beach face and the differences are shown to be reasonably predicted using edge wave profile solutions for the measured beach profile for these data observed and predicted mode transition frequencies did not change appreciably in the presence of mean alongshore current implying that large changes in cross shore scaling of the edge wave profiles did not occur however as has been previously shown by howd et al 1992 there are also local edge wave profile shape changes because of the cross shore shear of the mean alongshore current verification of these predicted local shape changes can not be made with these data confidence in cross shore profile solutions is of practical importance for estimates of shoreline variances from offshore measurements on these two beaches estimates using both numerical solutions for the measured depth and current profiles and analytical solutions for plane beach approximations typically differ by only 10 to 40

scheelite powellite and paraniite y from the fe mn deposit at fianel eastern swiss alps small syngenetic exhalative fe mn deposits embedded in triassic marbles of the suretta starlera and schams nappes eastern swiss alps were subjected to a tertiary regional metamorphism under blueschist to greenschist facies conditions in one of the deposits at fianel val ferrera this polyphase metamorphism led to the formation of quartz1dolomite veinlets containing beryl scheelite powellite paraniite y monazite ce fluorapatite bergslagite fluor romeite and antimonian betafite these veinlets crosscut dolomite breccia lenses that are embedded in hematite quartz carbonate ores scheelite powellite displays a continuous range of compositions between 28 and 70 mol camoo4 its as2o5 contents range from 0 73 to 3 96 wt and are positively correlated with the y2o3 contents that vary between 0 33 and 2 47 wt the scheelite powellite grains display a two stage chemical zoning stage a generally produced a core and a rim that relative to the core is richer in w as and y during the second stage stage b w rich scheelite powellite replaces stage a grains along fractures and rims crystals of paraniite y ide ally cawo4 2 yaso4 occur as small inclusions 51 mm in stage b scheelite powellite the fianel deposit is only the second locality where paraniite y has been reported the paraniite y from fianel displays like the type material no polysomatic stacking fault in the scheelite yaso4 layering at fianel paraniite y is characterized by elevated mo contents and seems to have crystallized under influence of w and lree rich fluids during stage b i e during the metasomatic replacement of y and as rich scheelite powellite produced in stage a

experimental meteoric water basalt interactions characterization and interpretation of alteration products abstract the products from experimental alteration of crystalline and glassy basalt by meteoric water at 45 and 70 c have been analyzed with transmission electron microscopy tem selected area electron diffraction saed and x ray analytical electron microscopy aem the principal solid alteration products include quartz chrysotile talc kerolite calcite kaolinite smectite and amorphous silicate material with spongy smectite like morphology these solids act as sinks for elements that are released during the basalt alteration and they are important for controlling the chemistry of the altering fluid comparison of the reaction quotients for the various solid phases and the fluid composition shows that the approach to equilibrium between altering fluid and basalt depends on both temperature and the ratio of fluid to basalt surface area the degree of supersaturation with respect to equilibrium values for the precipitated phases can be explained by the enhanced solubility resulting from small crystal size of the alteration products the results of this study underscore the importance of metastabile phenomena in the low temperature alteration or weathering of both crystalline and glassy basalt

seismic signatures of a hydrated mantle wedge from antigorite crystal preferred orientation cpo abstract we report electron backscatter diffraction ebsd measurements of antigorite crystal preferred orientations cpos from 7 samples of antigorite schist from serpentinite melanges adjacent to the motagua fault system in central guatemala the cpos range from diffuse girdle to point distributions of 001 atg girdle distributions of 001 atg are not expected from deformation theory or experiments suggesting that they are a result of growth rather than deformation and may thus be topotactically related to the cpo of the olivine from which the antigorite grew the calculated seismic anisotropy ranges from 6 to 28 in v p and 5 to 33 in v s and is highest for samples with a point maximum of 001 atg for all samples the minimum v p corresponds to the pole to 001 atg and the maximum v p occurs within the foliation for samples with a clearly defined foliation trench parallel shear wave splitting observations for subduction zones can best be explained by a combination of olivine b type cpo and antigorite oriented with 001 parallel to the foliation only a relatively thin 20 km zone of hydrated mantle is required to explain the observed splitting times

the influence of long waves on macrotidal beach morphology the aim of the following paper is to demonstrate that standing long waves can generate intertidal morphological features in a dissipative macrotidal setting in this environment the tidal excursion can exceed the length scales associated with long waves this extends the work of simmonds et al 1995 in which it was shown that monochromatic long waves could generate sediment convergence patterns that bore a good similarity to observed topographic features namely ridges and runnels from a field site on the belgian coast the simulation is modified to include a band of long waves and it is found that a good correspondence with real topography can still be achieved on a tidally averaged basis by allowing for a degree of uncertainty in the breaking criterion it is also argued why the observed scales are more likely to correspond with the shorter end of the long wave spectrum the simulation helps to shed light on the conditions in which such features are known to form

the nature of magnetic single domains in volcanic glasses of the kbs tuff magnetic and optical variations in volcanic glasses of the east african rift have been investigated by means of experimental and analytical study the results add to the formal understanding of magnetism in volcanic glasses and give us new perspectives on the nature origin and significance of fine grained magnetic minerals and on the magnetic petrology of glassy rocks the samples that we have studied in detail glass shards from the kbs tuff of northern kenya contain a superparamagnetic precipitate of microcrystals 2 to 10 nm in size the precipitate is likely to have formed at elevated temperature during or subsequent to eruption about 1 9 m y ago we have studied these microcrystals by means of transmission electron microscopy tem ac and dc magnetic methods electron spin resonance esr mossbauer spectroscopy and optical spectroscopy our efforts have concentrated on determining the magnetic mineralogy and understanding the mechanism s responsible for the optical and magnetic behavior of these glasses the particle size determination for the larger of these microcrystals has been achieved using tem imaging and mossbauer spectroscopy the mineralogy is nonstoichiometric magnetite based on mossbauer x ray diffraction and electron diffraction results the ratio of saturation remanent magnetization to saturation magnetization for the larger microcrystals is very nearly that predicted by single domain theory for a uniaxial anisotropy the origin of which may lie with stress or surface effects we interpret magnetic and esr results to infer the possible existence of microcrystals or amorphous clusters of fe atoms 1 nm or smaller in kbs glasses that appear homogeneous in high resolution tem images results from optical absorption experiments show that the color variations in kbs shards arise due to optical absorption by the precipitate a result consistent with classical electromagnetic theory

tem and sfm of exsolution and twinning in an alkali feldspar transmission electron microscopy tem reveals exsolution lamellae in a cryptoperthite their spacing results in a greenish yellow iridescent color high resolution tem images show that the boundaries between ab rich and or rich lamellae are semi coherent along the b axis scanning force microscopy sfm of a 001 cleavage surface reveals exsolution lamellae wave like 001 surfaces of the ab rich lamellae and surface steps with heights of 6 6 and 3 a the wave like 001 surfaces of albite twin lamellae may result from surface relaxation surface height differences between ab and or rich lamellae in some areas indicate a semi coherent boundary along the c axis

boromuscovite a new member of the mica group from the little three mine pegmatite ramona district san diego county california boromuscovite ideally kai2 si3b 01o oh f 2 in which 4 ai is replaced by b relative to muscovite occurs as a late stage postpocket rupture mineral within the new spaulding pocket main little three pegmatite dike ramona district san diego county california the mineral is white to cream colored and occurs as a porcelaneous veneer and coating on primary minerals the average grain size is less than 3 4 lm but the coatings may be as much as 1 cm or more thick fragments of topaz albite elbaite and other pocket minerals are included in the coating the boromuscovite precipitated from a late stage hydrothermal fluid it occurs only as a snowlike coating chemical analysis yielded wt si02 48 1 al203 28 1 b203 7 0 cao 0 1 mgo 0 15 fe203 0 1 mno 0 08 p 205 v weak for the 2m polytype the oap is normal to 010 x c 1 y a 2 z b xis in the acute angle of 3 and yis in the obtuse angle of 3 the mineral shows no absorption or pleochroism boromuscovite crystallized from the evolved fluid phase present after the growth of the primary minerals in the new spaulding pocket the coexistence of the 2m and 1m polytypes is consistent with growth in the interval 350 400 c a range consistent with fluid inclusion geothermometry on pocket minerals in related pegmatitic occurrences

exsolution of ca amphibole from glaucophane and the miscibility gap between sodic and calcic amphiboles transmission and analytical electron microscopy tem aem of glaucophane from glaucophane ca amphibole bearing blueschist and eclogite from two vermont localities ecologite brook and tillotson peak and one california locality cazadero has revealed the first evidence from exsolution for the miscibility gap between sodie and calcic amphiboles the tillotson peak samples and the cazadero samples contain coarsegrained glaucophane actinolite pairs while the eclogite brook samples contain coexisting glaucophane and actinolitic hornblende ca rich glaucophanes contain abundant fine scale lamellae of ca rich amphibole these lamellae are usually oriented near 100 and overline 2 01 high resolution tem hrtem images show them to be coherent the exsolution lamellae are so narrow beyond the resolution of aem that their true ca contents are obscured by analytical contributions from the surrounding host the aem data suggest that the lamellae are either winchite or actinolite depending on the true ca concentration in most cases the exsolution lamellae have very curved interfaces and show variable orientation this is attributed to the close similarity of unit cell parameters for the two amphiboles three dimensional optimal phase boundary calculations using eplag fleet 1982 show that the observed 100 and overline 2 01 orientations are consistent with the minimization of area strain between the two lattices along the interface some samples show evidence for incipient exsolution in the form of homogeneously distributed fine scale precipitates these results suggest that ca rich glaucophanes from other glaucophane actinolite assemblages may be exsolved at the tem scale the coexisting amphiboles from eclogite brook also have been studied using the electron microprobe emp the compositional gap defined by the eclogite brook pairs is consistent with previously reported results but shows a wider break along the glaucophane actinolite pseudobinary join suggesting very limited solid solution up to temper atures of about 500 550 c the glaucophanes are relatively poor in ca except for one anomalous grain containing ca amphibole lamellae ferric iron estimated by normalization to fixed cation numbers is strongly partitioned into the actinolitic hornblende and the glaucophanes are very poor in the riebeckite component

field observations of beach cusps and swash motions abstract we tested the hypothesis of cusp formation by the longshore structure of synchronous or subharmonic mode zero edge waves using detailed field measurements of foreshore topography incident waves and swash motions two distinct intervals of cusp formation were observed alongshore separated swash measurements were analyzed to detect structures at wavelengths and frequencies consistent with the measured cusp spacings for both events no statistical support for cusp generation by the traditional subharmonic or synchronous edge wave mechanisms was found however once cusps became well developed there was evidence of interaction between fluids and topography at a wavelength equal to the cusp spacing but at the period of the incident swash we propose that this interaction could have been responsible for the generation of the second set of cusps with a spacing of half the pre existing cusp wavelength

coastal geomorphology through the looking glass abstract coastal geomorphology will gain future prominence as environmentally sound coastal zone management strategies requiring scientific information begin to supplant engineered shoreline stabilization schemes for amelioration of coastal hazards we anticipate substantial change and progress over the next two decades but we do not predict revolutionary advances in theoretical understanding of coastal geomorphic systems paradigm shifts will not occur knowledge will advance incrementally we offer predictions for specific coastal systems delineated according to scale for the surf zone we predict advances in wave shoaling theory but not for wave breaking we also predict greater understanding of turbulent processes and substantive improvements in surf zone circulation and radiation stress models very few of these improvements are expected to be incorporated in geomorphic models of coastal processes we do not envision improvements in the theory of sediment transport although some new and exciting empirical observations are probable at the beach and nearshore scale we predict the development of theoretically based two and three dimensional morphodynamical models that account for non linear time dependent feedback processes using empirically calibrated modules most of the geomorphic research effort however will be concentrated at the scale of littoral cells this scale is appropriate for coastal zone management because processes at this scale are manageable using traditional geomorphic techniques at the largest scale little advance will occur in our understanding of how coastlines evolve any empirical knowledge that is gained will accrue indirectly finally we contend that anthropogenic influences directly and indirectly will be powerful forces in steering the future of coastal geomorphology if you should suddenly feel the need for a lesson in humility try forecasting the future kleppner 1991 p 10

interstratification and other reaction microstructures in the chlorite berthierine series transmission electron microscopy tem results show there is a series of periodically and nonperiodically interstratified structures composed of berthierine and chlorite layers in low temperature chlorite that is one of the alteration products of granulite facies archean ironstone from the eastern border of the beartooth mountains montana an antiphase domain structure suggests that the interstratified structures are intermediate transformation products formed by reaction from berthierine serpentine structure to chlorite periodically interstratified structures consisting of chlorite c and serpentine like s or berthierine layers include cs ccs cccs ccccs and ccccccs the layer sequences in interstratified chlorite berthierine are indicative of the reaction mechanisms that produce the interstratified structures e g crystallization from solution or solid state transformation the reaction from berthierine to chlorite is crystallographically much like a cell preserved phase transformation even though it is highly reconstructive berthierine can be considered a polymorph of the fe rich chlorite mineral chamosite with berthierine as the los temperature phase interstratification and integrowths in the chlorite berthierine series may be common phenomena in low temperature layer silicates resembling chlorite although such relations are difficult to recognize from chemical analyses or powder x ray diffraction patterns they can be observed readily with tem method

infragravity waves over a natural barred profile measurements of cross shore flow were made across the surf zone during a storm as a nearshore bar became better developed and migrated offshore measured infragravity band spectra were compared to synthetic spectra calculated numerically over the natural barred profile assuming a white run up spectrum of leaky mode or high mode edge waves as in earlier studies the spectra compared closely however for some frequencies the energy of the measured spectrum exceeded the energy of the synthetic spectrum suggesting that the run up spectrum was not white but had dominating frequencies utilizing cross shore flow data and synthetic spectra from a number of cross shore locations an equivalent run up spectrum was calculated for each day on the first day of the storm the equivalent run up spectrum indicated a dominant wave that had a node in velocity reasonably close to the bar crest later during the storm when the bar had migrated farther offshore there was no evidence for a dominant motion having a velocity node at the bar crest the structure of the equivalent run up spectrum compared well with spectra of direct measurements of run up obtained several hundred meters away we have no clear evidence in support of the theory that infragravity waves might form or force the offshore migration of a bar to confirm this finding longer records obtained synoptically over a developing bar are required the dominant wave observed early in the storm was consistent with symond and bowen s 1984 theoretical prediction of resonant amplification of discrete frequencies over a barred profile

observations of swash under highly dissipative conditions video measurements of swash were made at the low sloping beach of the multiple bar system at terschelling netherlands the majority of the measurements were conducted under highly dissipative conditions with iribarren numbers 0 the ratio of beach slope to the square root of offshore wave steepness less than 0 2 infragravity 0 004 0 05 hz waves dominated the swash with an average ratio of infragravity and total swash height rig r of 0 85 using linear regression we investigated the dependence of swash parameters on environmental conditions such as short wave height period and local beach slope on average rig was about 30 of the offshore wave height h0 the slope in the linear h0 dependence of rig amounted to only 0 18 considerably smaller than that observed on steeper beaches the data set shows evidence for saturation of the higher infragravity frequencies for 0 less than roughly 0 27 in our opinion this saturation caused the constant of proportionality in the linear relationship between rig h0 and 0 to be significantly larger than that observed under higher iribarren number regimes the saturated tails of the swash spectra had an approximate f 3 roll off where f is frequency whereas in general the nonsaturated parts were white this lack of significant peaks casts doubt on the causality between infragravity waves and nearshore bars

transmission electron microscopy of subsolidus oxidation and weathering of olivine olivine crystals in basaltic andesites which crop out in the abert rim south central oregon have been studied by high resolution and analytical transmission electron microscopy the observations reveal three distinct assemblages of alteration products that seem to correspond to three episodes of olivine oxidation the olivine crystals contain rare dense arrays of coherently intergrown ti free magnetite and inclusions of a phase inferred to be amorphous silica we interpret this first assemblage to be the product of an early subsolidus oxidation event in the lava the second olivine alteration assemblage contains complex ordered intergrowths on 001 of forsterite rich olivine and laihunite distorted olivine structure with fe3 charge balanced by vacancies based on experimental results for laihunite synthesis kondoh et al 1985 these intergrowths probably formed by olivine oxidation between 400 and 800 c the third episode of alteration involves the destruction of olivine by low temperature hydrothermal alteration and weathering elongate etch pits and channels in the margins of fresh olivine crystals contain semi oriented bands of smectite olivine weathers to smectite and hematite and subsequently to arrays of oriented hematite crystals the textures resemble those reported by eggleton 1984 and smith et al 1987 we find no evidence for a metastable phase intermediate between olivine and smectite m eggleton 1984 the presence of laihunite exerts a strong control on the geometry of olivine weathering single laihunite layers and laihunite forsteritic olivine intergrowths increase the resistance of crystals to weathering preferential development of channels between laihunite layers occurs where growth of laihunite produced compositional variations in olivine rather than where coherency strain is associated with laihunite olivine interfaces

edge wave trapping and amplification on barred beaches theoretical predictions show that edge waves may be trapped on bars providing a possible mechanism for bar growth simple solutions to the linear shallow water equations reveal that bar trapping is controlled by the depth of the water over the bar hbar and the geometry of the inshore trough relative to the bar for specific geometries amplification over the bar approaches an order of magnitude or more as the phase speed approaches where amplification is defined as the surface displacement over the bar relative to the surface displacement at the shoreline the amplification increases with the cross shore length scales of the profiles the amplification is somewhat frequency dependent generating stronger currents at the location of the bar in specific frequency ranges previous work showed that particular edge wave modes have the correct length scales to generate beach features such as bars and beach cusps but field observations notably shoreline run up data frequently show no evidence of edge wave energy being concentrated at the appropriate frequencies however for bar trapped modes edge wave energy is concentrated at the location of the bar therefore this edge wave energy will not necessarily be evident in shoreline measurements strong correlation exists between the energy distribution of the longshore component of the orbital velocity observed in data collected at superduck october 11 1986 and the distribution expected for a white edge wave spectrum at the shoreline this suggests that bar trapped edge waves exist in particular at incident wave frequencies

an aem tem study of weathering and diagenesis abert lake oregon i weathering reactions in the volcanics abstract abert lake in south central oregon provides a site suitable for the study of sequential weathering and diagenetic events in this first of two papers transmission electron microscopy was used to characterize the igneous mineralogy subsolidus alteration assemblage and the structural and chemical aspects of silicate weathering reactions that occur in the volcanic rocks basalts basaltic andesites and dacitic rhyolitic extrusive and pyroclastics that outcrop around the lake olivine and pyroxene replacement occurred topotactically whereas feldspar and glass alteration produced randomly oriented smectite in channels and cavities the tetrahedral octahedral and interlayer compositions of the weathering products largely dioctahedral smectites varied with primary mineral composition rock type and as the result of addition of elements released from adjacent reaction sites weathering of the highly evolved fe rich jug mountain complex at the north end of the lake produced a homogeneous smectite assemblage that contrasts with the heterogeneous smectite assemblage replacing the volcanics along the eastern margin of the lake the variability within and between the smectite assemblages highlights the microenvironmental diversity fluctuating redox conditions and variable solution chemistry associated with mineral weathering reactions in the surficial environment late stage exhalative and aqueous alteration of the volcanics redistributed many components and formed a variety of alkali and alkali earth carbonate chloride sulfate and fluoride minerals in vugs and cracks overall substantial mg si na ca and k are released by weathering reactions that include the almost complete destruction of the mg smectite that initially replaced olivine the leaching of these elements from the volcanics provides an important source of these constituents in the lake water the nature of subsequent diagenetic reactions resulting from the interaction between the materials transported to the lake and the solution will be described in part ii banfield et al 1991

sheet silicates of the lawler peak granite arizona chemistry structural variations and exsolution coarse grained muscovite biotite and chlorite from the lawler peak granite yavapai county arizona have been studied with electron microprobe analysis powder x ray diffraction transmission electron microscopy tem electron diffraction and analytical tem methods all three sheet silicates exhibit multiple polytypes and an abundance of stacking faults and dislocations chlorite formed by subsolidus replacement of biotite muscovite also may have formed by replacement of biotite and other minerals but there is no clear microstructural evidence to support either a primary or secondary origin for the coarse grained muscovite x ray and electron diffraction reveal that the muscovite consists of two separate phases which give rise to splitting of diffraction maxima tem experiments suggest that the two components resulted from exsolution which produced two symmetry related sets of irrationally oriented lamellae with a wavelength averaging about 10 nm exsolution occurred in both 1m and 2m1 muscovite although the lamellae are too small to analyze directly the muscovite bulk composition and structural data are consistent with the separation of celadonitic and muscovite components

pre ore hydrothermal alteration in an unconformity type uranium deposit hydrothermal alteration associated with the formation of unconformity type uranium deposits is manifested mainly by intense chloritic replacement of metamorphic mineral assemblages at the koongarra deposit northern australia three stages of pre ore alteration were identified in chloritized metamorphic muscovite using optical microscopy the electron microprobe and transmission and analytical electron microscopy tem and aem during the first stage metamorphic muscovite was altered to a mica with very low interlayer occupancy k content as low as 0 35 compared to 1 for ideal muscovite high octahedral cation content up to 2 3 whereas ideal muscovite has 2 and high si content high resolution tem images show that these changes in composition were accompanied by frequent layer terminations in contrast to the metamorphic muscovite whereas selected area electron diffraction patterns indicate that the altered muscovite remained a two layer polytype the alteration of muscovite appears more extensive in the outer alteration halo and has been almost completely eradicated in the ore zone where chloritization is more complete during the second stage of the pre ore alteration the altered muscovite was replaced by mg rich serpentine lizardite and clinochlore high resolution tem images show two 10 a mica layers coalescing to one 14 a chlorite layer this type of coalescence appears to involve transformation of one dioctahedral layer of the mica structure to one trioctahedral brucite layer in the chlorite structure through dissolution of the tetrahedral sheets and cation influx in the octahedral site the final stage of the pre ore alteration resulted in replacement of lizardite and clinochlore by fe rich chlorite comparison of the alteration observed in metamorphic muscovite with the alteration observed in metamorphic biotite and garnet shows clearly that chloritization of these phases was also a pre ore alteration event pre ore alteration was principally characterized by the evolution of chlorite from a mg rich phase to an ferich one

reorganization of polar cap patches through shears in the background plasma convection 1 on the night of december 20 2006 630 nm airglow images obtained by an all sky camera at resolute bay canada 74 73 n 265 07 e altitude adjusted corrected geomagnetic aacgm latitude 82 9 showed the passage of successive polar cap patches shortly after convection came to a temporary halt one of the patches was reorganized into two substructures in approximately 8 min the two dimensional background ionospheric convection pattern measured using the newly deployed polardarn radar at rankin inlet 62 82 n 93 11 w aacgm latitude 72 96 showed that a velocity shear of approximately 120 m s 1 340 km suddenly appeared in the vicinity of the patch at the time of reorganization a qualitative analysis of the relationship between the magnitude of the velocity shear and the distance between the divided patches indicates that the shear in the background plasma convection velocity significantly contributed to the reorganization of the patch this shear structure appeared soon after a southward turning of the interplanetary magnetic field imf and was probably associated with the reconfiguration of the convection pattern from a pre existing northward oriented imf pattern to a southward oriented one the present observations indicate that the reconfiguration deformation of patches because of a shear in the background convection field especially reorganization of patches into smaller substructures may play an important role in the rapid structuring of patches

the behaviour of a multiple bar system in the nearshore zone of terschelling the netherlands 1965 1993 abstract the behaviour of a multiple bar system in the nearshore zone of the island of terschelling the netherlands is investigated on the time scale of years using a data set of soundings the data set covers the period from 1965 to 1993 the behaviour is analysed in terms of bar crest position and in terms of morphometric parameters such as bar crest depth height width and volume two or three breaker bars are permanently present in the study area each individual bar passes through three stages during its existence 1 generation close to the shore 2 seaward migration and 3 degeneration at the outer margin of the nearshore bar zone the key factor controlling the behaviour of the inner bars is the crest depth of the outer bar three different couplings between the behaviour of the individual bars have been observed 1 bar stage changes due to the degeneration of the outer bar 2 prevention of the transition of an inner bar from the first to the second stage caused by the appearance from alongshore of a new outer bar having a small crest depth and 3 difference in mean annual seaward migration rate caused by the possible presence of a more seaward positioned bar it is hypothesized that the crest depth of the outer bar governs the relative importance of processes inducing shoreward and seaward migration in the inner nearshore bar zone and therefore controls the behaviour of the nearshore bar zone on the time scale of years

the influence of crystallography and kinetics on phengite breakdown reactions in a low pressure metamorphic aureole a natural example of phengite that had undergone partial thermal decomposition at a pressure of about 0 5 kbar and a temperature of about 680 c in a contact aureole was exmined in the transmission electron microscope tem partially pseudomorphed phengites were found to consist of combinations of phengite biotite k feldspar mullite sillimanite spinel and cordierite different areas within individual partially pseudomorphed phengite grains show various degrees of reaction and different reaction products the cores are the least reacted and the margins have reacted most in the cores the assemblage al mg enriched phengite biotite k feldspar mullite spinel has formed whereas the assemblage k feldspar mullite sillimanite spinel biotite cordierite has formed at the edges according to our thermodynamic calculations the breakdown of phengite should have produced cordierite spinel corundum k feldspar in regions isolated from the influx of sio2 and cordierite andalusite quartz k feldspar in regions near the edge of the grains that were essentially saturated with sio2 chemical equilibrium was not achieved in any part of the partially pseudomorphed phengites on a micron scale or larger breakdown theoretically should have been complete by about 550 c the reaction temperature was overstepped by at least 130 c for 20 25 years the variations in the degree and type of reaction are probably due partly to the availability of suitable nucleation sites in different regions partly to the need to remove h2o from reaction sites and partly to the influence of sio2 which diffused into the grains during metamorphism the presence of sio2 lowers the equilibrium temperatures thus there is a higher driving force for breakdown near the grain boundaries than in the cores most of the products show an orientation relationship with the parent phengite and have consistent habit planes they have their closest packed planes and closest packed directions parallel to one another and to those of phengite such relationships minimize the strain and surface energies at nucleation and favour most rapid nucleation and growth of the reaction products the great structural similarity of biotite to phengite resulted in its having the highest rate of nucleation and growth of any product and it occurred in all areas of the phengite pseudomorphs studied mullite and sillimanite were produced metastably mullite has more rapid nucleation kinetics than other aluminosilicates because it is structurally disordered sillimanite formed rather than andalusite in regions of the partially pseudomorphed phengites where the reaction reached an advanced stage because the reaction from phengite to andalusite requires an energetically unfavourable change in aluminium co ordination state

magnetism and magnetic mineralogy of ash flow tuffs from yucca mountain nevada the magnetic susceptibility and remanent magnetization of an ash flow sheet are profoundly influenced by cooling history after emplacement spatial variations in these properties therefore provide a potentially useful tool for geological studies maxima and minima in measured along profiles at yucca mountain nevada identify persistent magnetic marker horizons within vitric portions of the tiva canyon and underlying topopah spring members of the paintbrush tuff the correlatable variations of with vertical position in these units exist over the 8 km of strike examined the observed stratigraphic changes in magnetic properties reflect variations in amounts and mineralogy of fe ti oxide phenocrysts and the presence shape size and mineralogy of magnetic fe oxide microcrystals that precipitated at high temperature after emplacement of each sheet vitrophyre near the top of the topopah spring member has a distinctive maximum in due to titanomagnetite phenocrysts susceptibility in the lower portion of the overlying tiva canyon member reaches maximum values of about 1 3 10 2 si near the base of the member beneath the columnarly jointed vitrophyre due to the presence of abundant superparamagnetic cubic fe oxide these elongate microcrystals are several tens of nm long and are typically deformed and tapered up section in the tiva canyon member the susceptibility decreases going to a minimum within the columnar vitrophyre at this stratigraphic level the precipitated fe oxides are larger and carry intense nrm of up to 30 a m is only 3 10 3 the whisker like microcrystals of fe oxide which typically nucleated on what appears to be chain silicate grew as needles up to 25 m in length the size variations of the precipitated fe oxides which were established using transmission electron microscopy tem and petrographic observation are consistent both with variations in magnetic susceptibility measured at the outcrop and with variations in the intensity of remanent magnetization several interpretations of the shape anisotropy of the precipitated feoxide are possible including growth by a dislocation mechanism additionally the observed elongation of precipitated microcrystals is consistent with theoretical predictions for growth in a uniaxial stress field susceptibility variations as established at the outcrop as well as in the borehole offer a potentially useful tool for stratigraphic correlation of ash flow sheets

tem aem observations of cl rich amphibole and biotite and possible petrologic implications cl rich amphibole and biotite 2 9 and 2 8 wt cl respectively were analyzed with high resolution transmission electron microscopy hrtem selected area electron diffraction saed and x ray emission analytical electron microscopy aem the samples are from archean granulite facies metamorphosed iron formations located in the beartooth mountains montana u s a two types of amphibole and biotite were found 1 high cl prograde hastingsite and biotite and 2 retrograde amphibole of grunerite composition containing no detectable amount of cl but intergrown with submicrometer sized slabs ofci rich annite 2 8 wt fe rich talc fe rich clinojimthompsonite and very wide chain silicate tem aem study of prograde hastingsite and biotite suggests that cl is dissolved in the crystal structures and that cl distribution is homogeneous aem analyses show that cl occupies up to about 30 and 15 of the oh positions in hastingsite and biotite respectively calculations of the cl oh exchange reaction for apatite indicate a high 10g ahoo ah o ratio of about 1 8 2 2 suggesting equilibrium with a cl rich fluid speciation and solubility modeling of the equilibrium between an aqueous fluid and the cl rich apatite biotite and hastingsite suggest that reactions with a saline brine of about 25 wt naci could explain the cl enrichment in these hydrous phases whereas the brine may coexist with an immiscible c02 dominated vapor during the granulite facies metamorphism in light of low calculated h20 activities and c02 rich fluid inclusions this explanation is consistent with the results from studies of natural and synthetic fluid inclusions and phase equilibrium experiments reported in the literature the widespread occurrence of cl rich amphibole and biotite in granulite facies rocks thus has significant implications for the nature of high grade metamorphism tem aem observations of submicrometer sized inclusions of cl rich phases within retrograde amphibole may help to explain the commonly observed heterogeneities of electron microprobe cl analyses found in samples from a variety of geologic settings microprobe analyses using typical beam diameters may sample areas with different proportions of submicroscopic intergrowths this will give apparent cl heterogeneities and fortuitous correlations between cl and concentrations of k ai and si although compositional correlations sometimes indicate reciprocal effects that are likely important for amphibole we emphasize the potential danger of artifacts resulting from submicroscopic solid inclusions additional tem aem studies on complex samples are needed to explain the compositional heterogeneities with confidence

the solubility of tio2 in olivine implications for the mantle wedge environment abstract one characteristic of many subduction zone garnet peridotites is that they contain titanium bearing phases not otherwise found in mantle rocks in particular titanoclinohumite tich and or its breakdown assemblage consisting of symplectic intergrowths of olivine and ilmenite is common in many of these bodies the alpe arami garnet lherzolite of the lepontine alps while lacking tich displays instead large numbers of fetio 3 rod shaped precipitates in the oldest generation of olivine amounting to approximately 1 by volume indicating that at some time in its past the peridotite experienced conditions under which the solubility of tio 2 in olivine was greater than 0 6 wt in order to test the hypothesis that the environment of very high solubility of tio 2 in olivine is to be found at very high pressures we have conducted experiments on lherzolite compositions with added ilmenite at pressures between 5 and 12 gpa and temperatures of 1350 1700 k our results on anhydrous compositions show that whereas solubility of tio 2 was not detected in olivine at 5 gpa 1400 k where it coexists with rutile when rutile disappeared from the paragenesis the solubility climbed to 0 5 wt at 8 and 10 gpa and to 1 wt at 12 gpa all at 1600 k these results support our previous interpretations from titanate morphology and abundance that the alpe arami massif has surfaced from depths 300 km corresponding to pressures 10 gpa but remove the need to suggest a deeper origin and possible precursor phase such as wadsleyite they also support the hypothesis that garnet peridotites with unusual ti bearing phases reflect a unique mantle environment occurring in the mantle wedge overlying subduction zones 2000 elsevier science b v all rights reserved

spectral signatures for swash on reflective intermediate and dissipative beaches in this paper we synthesise a large data set gathered from a wide variety of field deployments and integrate it with previously published results to identify the spectral signatures of swash from contrasting beach types the field data set includes the full range of micro tidal beach types reflective intermediate and dissipative with beach gradients ranging from approximately 1 6 to 1 60 exposed to offshore significant wave heights of 0 5 3 0 m the ratio of swash energy in the short wave f 0 05 hz to long wave f 0 05 hz frequency bands is found to be significantly different between the three beach types swash energy at short wave frequencies is dominant on reflective and intermediate beaches and swash at long wave frequencies is dominant on dissipative beaches consistent with previously reported spectral signatures for the surf zone on these beach types the available swash spectra were classified using an automated algorithm clara into five different classes the ordered classes represent an evolution in the spectrum shape described by a frequency downshifting of the energy peak from the short wave into the long wave frequency band and an increase in the long wave swash energy level compared to a relatively minor variation in the short wave swash energy level a universally common feature of spectra from all beach states was an f 4energy roll off in the short wave frequency band in contrast to the broadly uniform appearance of the short wave frequency band the appearance of the long wave frequency band was highly variable across the beach states we incorporate the results presented here and previously published observations into the morphodynamic beach state model and propose an ordered sequence of swash spectra under increasing and decreasing incident wave energy level this extension of the beach state model to include the swash zone leads to the following propositions for morphodynamic controls on the nature of the swash spectrum 1 the short wave part of the swash spectrum is relatively constant in form across all beach states f 4 energy roll off and the energy density per unit frequency is controlled by the beach face gradient alone 2 the spectral bandwidth of the energy roll off varies directly with offshore wave energy level and inversely with beach face gradient or beach state in a manner consistent with the non linear wave breaking criterion 3 the infragravity part of the swash spectrum is highly variable in form across all beach states and the energy level is related to the offshore wave energy level and surf zone morphology

bar formation due to wave groups and associated long waves abstract field observations reveal that waves propagating onto a beach from deeper water have a grouped structure associated with this pattern of alternating high and low waves is a long wave forced by radiation stress variations due to the changing short wave height as the wave groups propagate onshore the relationship between the variation in the short wave height and the long wave motion is complicated by breaking of the short waves reflection of the long wave and the generation of a free long wave by time variation of the breakpoint position nevertheless there may still be a fixed phase relation between the short wave envelope and the long wave motion at any particular location resulting in a net transport of sediment over the timescale of the short wave groups this transport arises from sediment grains mobilised by short waves and moved by the long wave motion model predictions of wave group propagation onto a beach and the associated long wave motions are presented which suggest that sediment transport due to short wave long wave coupling may result in the formation of a bar within the inner surf zone and the possibility of additional bars further offshore outside the surf zone this mechanism for bar formation may provide a new framework for understanding bar morphodynamics

long wave forcing on a barred beach we present new laboratory data on long wave forcing over a barred beach profile under random wave breaking conditions the data include incident and radiated wave amplitudes wave set up and detailed measurements of the cross shore variation in long wave amplitude including shoreline swash amplitudes the total surf zone width was varied via changes in both wave height and the water level over the bar crest the data obtained from the barred beach are also compared with previous data obtained from a plane beach under essentially identical short wave forcing conditions the presence of the bar induces a frequency downshift in the spectral peak of the radiated long waves a consequence of the increased surf zone width on the barred beach and a clear signature of long wave forcing by a time varying breakpoint further comparisons of the two data sets suggest that the bar leads to resonant trapping and amplification or suppression of the shoreline motion at discrete long wave frequencies well defined standing long wave motion occurs at discrete frequencies inside the bar and the resonant response is consistent with a simple seiche between the bar crest and shoreline in agreement with previous numerical model studies the long wave structure offshore of the breakpoint depends on the relative positions of the bar shoreline and breakpoint and is inconsistent with a numerical solution for a free standing long wave over the barred beach profile

waves long waves and nearshore morphology abstract recent field measurements on beaches of different slopes have established that wave motion at periods substantially longer than the incident waves dominates the velocity field close to the shore analysis of a number of extensive data sets shows that much of this long wave motion is in the form of progessive edge waves though forced wave motion standing edge waves and free waves propagating away from the shore may also contribute to the energy theoretically the drift velocities in bottom boundary layers due to edge waves show spatial patterns of convergence and divergence which may move sediment to form either regular crescentic or cuspate features when only one edge wave mode dominates or a bewildering array of bars bumps and holes when several phase locked modes exist together convincing field demonstration of the link between nearshore topography and edge waves only exists for the special case of small scale beach cusps on steep beaches formed by edge waves at the subharmonic twice the period of the incident waves at longer periods the link is proving more difficult to establish due to the longer time scales of topographic changes the interaction between pre existing topography and the water motion and the observation of broad banded edge wave motion which is not readily linked to topography with a well defined scale these ideas are however central to the study of nearshore processes as most of the plausible alternate hypotheses do not seem to lead to quantitative predictions clearly further theoretical and observational work is essential

pyribole evolution during tremolite synthesis from oxides the formation mechanisms of tremolite in a time series of hydrothermal experiments at 850 c and 6 1 kbar were studied using transmission electron microscopy tem analytical tem and x ray diffraction the starting materials were unseeded mixtures of reagent grade oxides after the first 8 min of reaction the synthesis products were diopside enstatite clinoenstatite quartz and minor c centered and primitive monoclinic amphibole 13 wt total the compositions of the first formed amphiboles vary considerably from essentially pure cummingtonite ca mg 0 to nearly ideal tremolite ca mg 0 4 three groupings of amphiboles with successively higher ca mg ratios were identified respectively 0 1 0 22 and 0 35 over a period of 97 h the proportions of mg rich amphibole gradually decrease and the average ca mg ratios of all amphiboles steadily increase from about 0 22 to 0 35 other changes include 1 a decrease in the aspect ratio of amphibole crystals with increasing time 2 a decrease in the number of non amphibole chain multiplicity faults cmfs from early a 2 values as low as 0 81 to a final value of 0 94 and 3 a distinct change in the rate of amphibole growth after 1 h of synthesis these observations suggest that two mechanisms of amphibole formation are dominant 1 formation of pyroxene modules with subsequent hydration and arrangement into the double chain amphibole structure and 2 direct nucleation and growth of amphibole from hydrothermal solution a third mechanism involving formation of talc like modules followed by their breakdown into double chain modules incorporation of ca and ordering into the amphibole structure may also occur but probably only at the lamellar or unit cell scale because these syntheses were performed outside the stability field of talc

serpentinization of phlogopite phenocrysts from a micaceous kimberlite phenocrysts of phlogopite from a micaceous kimberlite contain finely interlayered serpentine these phenocrysts occur in the kimberlite groundmass and are altered along the mica layers and are slightly deformed lizardite is the predominant serpentine mineral but chrysotile and mixed structures also occur the lizardite occurs as lamellae within phlogopite oriented such that 001 layers of the two minerals are parallel and the 100 direction of lizardite is parallel to the 100 or 110 directions of phlogopite the serpentinized regions of phlogopite are localized and extensive along the 001 layers chrysotile fibers and chrysotile like curled serpentine occur within regions of disrupted material and polygonal structures occur in folded lizardite lamellae textural relations suggest three events 1 replacement of phlogopite by lizardite 2 deformation of the phenocrysts and 3 partial transformation of the lizardite to chrysotile like structures deformation features include openings along 001 folds and regions of disrupted or broken material the folded and broken material consists of lamellar lizardite and phlogopite indicating that lamellar replacement preceded deformation intergrowths of lizardite and curled serpentine are associated with cleavage openings and voids in disrupted material suggesting that a partial transformation of lizardite to chrysotile occurred within openings created by deformation clay minerals also occur within phlogopite as either a minor product of serpentinization or of late stage alteration

motion of polar cap patches a statistical study with all sky airglow imager at resolute bay canada 1 a highly sensitive all sky airglow imager part of the optical mesosphere thermosphere imagers omtis has been operating for 3 years at resolute bay canada geographic latitude 74 7 n geomagnetic latitude 82 9 n since january 2005 one of its major applications is the observation of polar cap patches polar cap patches are generated in the vicinity of the cusp during southward interplanetary magnetic field imf conditions and they exhibit dynamic movement possibly in association with the changes in the imf orientation in order to determine how their motions are controlled by the upstream imf conditions we applied a motion tracking algorithm that was based on two dimensional cross correlation analysis to consecutive images obtained from january 2005 to december 2007 by the all sky airglow imager at resolute bay we identified and extracted 561 individual patches and then carried out a statistical study of their motion it is demonstrated that the speed of patches is primarily controlled by the imf bz furthermore the dawn dusk component of the patch drift velocities is well correlated with the imf by which is in good agreement with the published by dependence of the nightside polar cap convection this enables us to monitor the plasma convection within the polar cap by using polar cap patches as tracers

estimating drift velocity of polar cap patches with all sky airglow imager at resolute bay canada 1 highly sensitive all sky airglow imager has been operative at resolute bay canada 74 73 n 265 07 e aacgm latitude 82 9 since january 2005 we present as a first result from the imager an event of polar cap patches drifting anti sunward during the southward imf conditions magnitude and direction of patch drift velocities are computed with a temporal resolution of 2 min by using the newly developed patch tracking algorithm based on 2d cross correlation analysis it is well visualized that the patches change their moving speed and direction drastically in a short time scale a few minutes speed of the patch is primally controlled by the imf bz dawn dusk component of the patch drift velocities is well correlated with the imf by in agreement with published by dependence of the nightside polar cap convection however response of the patch drift direction to the imf by is found to be much slower 20 min than that of the drift speed to the imf bz almost instantaneous

bar trapped edge waves and longshore currents edge waves react to the presence of a mean longshore current as though the current was a change in bottom topography in this way the cross shore shape of the edge wave can be amplified over the current relative to the shoreline in the same way as the edge wave shape can be amplified over bars on a beach with both longshore currents and bars the degree of edge wave amplification or trapping depends on the strength and location of the longshore current shear relative to the steepness of the bottom slope and also on the direction of edge wave propagation relative to the longshore current weak longshore current shear over well developed bars does not significantly alter edge wave trapping over bars simply enhancing or reducing the existing bar trapping effect conversely strong current shears over gentle topography can govern the existence and location of edge wave trapping the extreme example being edge wave trapping on plane beaches where the amplification is entirely due to the existence of mean longshore currents in reality the possibilities are restricted since the shape of the longshore current profile is primarily determined by the pattern of incident wave breaking which itself depends on the beach profile the importance of realistic current shear relative to realistic bottom slope in determining edge wave shape is demonstrated using frequency wavenumber spectra taken during the duck experiment on low frequency and incident band longshore and across shore hydrodynamics delilah at duck north carolina these frequency wavenumber spectra show a general dominance of edge waves traveling with the longshore current in cases where the current shear is strong relative to the bottom slope the location of edge wave trapping changes as the longshore current profile changes with the tide when the bar was well defined the longshore current shear was rarely strong enough to influence the existence or location of edge wave trapping but could have a enhancing effect while past work i e schonfeldt 1995 has suggested that edge waves trapped and amplified on longshore currents may cause bars to form on plane beaches and bars to move on barred beaches these observations suggest that under most conditions edge wave trapping on longshore currents is a subtle effect modulated by sea level changes and is unlikely to produce significant morphological change unless the current is very strong

modification of edge waves by barred beach topography a numerical model to calculate edge wave profiles and wavelengths for arbitrary bottom profiles and given frequency was developed utilizing the model wave equation of berkhoff 1972 following smith and sprinks 1975 surface profiles and longshore wave numbers were found for fixed wave periods using an eigenvalue approach the model was verified by calculating profiles and dispersion for a plane beach of mild slope and comparing results with the analytic solution of eckart 1951 and ursell 1952 the model was then applied to the case of a beach with multiple offshore bars with bar positions determined by the antinodal positions of a standing incident wave of a set frequency calculation of surface profiles for a range of frequencies using a fixed beach indicated that antinodes of the edgewave profiles tend to be trapped by the bars suggesting the possibility that bars affect the long wave climate in such a way as to lead to self maintenance over extended periods no effect of the bars on the dispersion relationship was found and it was concluded that for the particular beach profile used the edge waves respond to the mean beach slope over the offshore length of the profile

infragravity waves and nearshore bars in protected storm dominated coastal environments abstract field measurements of run up oscillations were conducted on fetch restricted storm wave dominated beaches in denmark experiments took place under conditions with breaker heights of 1 5 3 m and wave periods of 5 7 s statistically significant spectral peaks were identified in the infragravity regime the frequencies of these peaks were compared to frequencies predicted by the edge wave cut off model originally proposed by huntley j geophys res 81 1976 and it was found that the waves were probably cut off mode edge waves with the mode number corresponding to the number of nearshore bars at the locality in question the waves were usually standing alongshore but during an experiment in which a very high energy level prevailed the edge waves were probably progressive the selection of only one or two cut off modes may be the result of an interrelationship between the topographic cut off and offshore wave groups the nearshore region was surveyed following storms it was found that there was generally a good correlation between bar positions and rhythmic dimensions and the theoretical cross shore and longshore structure of the recorded edge waves it is concluded that infragravity waves may be important in the formation migration and morphology of nearshore bars with the number of bars depending on the edge wave mode number

an aem tem study of weathering and diagenesis abert lake oregon ii diagenetic modification of the sedimentary assemblage abstract this paper compares the mineralogy and chemistry of clay minerals in sediments from various depths and positions in abert lake and surrounding playa with those of the weathered materials entering the lake in order to reveal the nature and extent of post depositional mineralogical modification analytical electron microscope aem data from individual clay particles reveal that each sample is comprised of a highly inhomogeneous smectite assemblage the thin clay flakes commonly less than 10 nm wide display a complete range in octahedral sheet compositions from nearly dioctahedral to nearly trioctahedral the very abundant mg rich lake smectites with an estimated composition k 0 29 al 0 23 mg 2 16 fe 0 30 si 3 80 al 0 20 o 10 oh 2 are not formed by weathering this confirms the importance of diagenetic mg uptake lattice fringe imaging failed to reveal distinct brucite like or vermiculite like layers suggesting that interstratifications of this type are rare or absent siliceous coatings on clay particles identified by silica excess in smectite analyses seem to favor topotactic overgrowth of stevensite rather than addition of brucite like layers to the dioctahedral nuclei the growth of k stevensite dilutes the al content of the crystal and thus the increasing diagenetic modification reduces rather than supplements its illite component smectite compositions within individual samples were highly variable yet source related characteristics such as the abundance of fe rich smectite were apparent little evidence for systematic k or mg enrichment with depth was identified in samples from depths of down to 16 feet below the sediment water interface the most magnesian assemblages are associated both with weathering sources of mg rich smectite and playa environments subjected to repeated wetting and drying cycles thus the observations suggest that clay compositions primarily reflect changes in lake levels brine composition and source characteristics rather than time and depth compaction effects other diagenetic reactions in the sediment include recrystallization of na rich silica gel and diatom fragments abundant submicron sized untwinned euhedral crystals of k feldspar are interpreted to be authigenic in origin