particle dispersal due to interplay of motions in the surface layer of a small reservoir horizontal dispersion mechanisms must be well defined in order to determine the origin and fate of heterogeneous distributions of biogeochemical material here data from an intensive field campaign in valle de bravo reservoir mexico was used to run a three dimensional hydrodynamic model and the simulated flow field was used to characterize the horizontal motions and investigate the dispersal of waterborne particles driven by the dominant circulation patterns the surface layer horizontal motions included an oscillatory component associated with two basin scale internal wave modes and a spatially and temporally complex flow field associated mostly with topographic circulation modeling of particle advection by the horizontal motions led to areal dispersal rates of o 1 to o 10 m2 s 1 comparable with bulk dispersion rates observed in other surface layer studies the aperiodic topographic component of the horizontal flow field not the oscillatory motion or a combination of both sustained most of the particle dispersal in particular local flow features such as stagnation points were shown to be a significant driver for horizontal dispersion and should be taken into consideration when analyzing horizontal distributions of waterborne material

modeling basin scale internal waves in a stratified lake basin scale internal waves provide the driving forces for vertical and horizontal fluxes in a stratified lake below the wind mixed layer thus correct modeling of lake mixing and transport requires accurate modeling of basin scale internal waves examining this capability with a hydrostatic z coordinate three dimensional 3d numerical model at coarse grid resolutions is the focus of this paper it is demonstrated that capturing the correct thermocline forcing with a 3d mixed layer model for surface dynamics results in a good representation of low frequency internal wave dynamics the 3d estuary and lake computer model elcom is applied to modeling lake kinneret israel and is compared with field data under summer stratification conditions to identify and illustrate the spatial structure of the lowest mode basin scale kelvin and poincarewaves that provide the largest two peaks in the internal wave energy spectra the model solves the unsteady reynolds averaged navier stokes equations using a semi implicit method similar to the momentum solution in the trim code with the addition of quadratic euler lagrange dis cretization scalar e g temperature transport using a conservative flux limited approach and elimination of vertical diffusion terms in the governing equations a detailed description is provided of turbulence closure for the vertical reynolds stress terms and vertical turbulent transport using a 3d mixed layer model parameterized on wind and shear energy fluxes instead of the convential eddy viscosity diffusivity assumption this approach gives a good representation of the depth of the mixed layer at coarse vertical grid resolutions that allows the internal waves to be energized correctly at the basin scale wind stresses surface heating and density currents form the driving energy fluxes of a stratified lake the basin scale energy flux from the wind is of particular interest because of its dominant role in setting the thermocline in motion which in the absence of inflows and outflows is the primary energy store for transport and mixing below the wind mixed layer thus modeling the basin scale internal wave behavior is an a priori requirement to modeling and quantifying the flux paths of nutrients in a stratified lake imberger 1994 this paper takes a first step in this direction by analyzing our ability to model basin scale internal waves that are seen in lake kinneret israel energy flux path in a stratified lake energy flux through a stratified lake has a fundamental dependence on forced and free baroclinic motions the wind imparts both momentum and turbulent kinetic energy tke to the water in the sur face layer the tke distributes momentum vertically in the

modelled nearshore sediment transport in open water conditions central north shore of prince edward island canada the central north shore of prince edward island comprises embayments separated by subtle headlands that may constrain nearshore sediment transport the study area includes two such embayments informally known as brackley and tracadie bights both of which are sand rich onshore and sand starved between 20 and 50 m water depth storm winds and waves from the northwest and northeast are common in autumn and winter the hydrodynamic model delft3d is used to simulate waves currents water levels and sediment transport in brackley and tracadie bights during 23 autumn seasons between 1955 and 2005 when compared with wave and current measurements from a field experiment in the autumn of 1999 the model successfully simulates conditions during storms and fair weather periods results from the simulations show that in autumn the weighted mean direction of transport is to the southeast 133 bedload transport is directed onshore to the south 170 and suspended load is directed offshore to the northeast 67

three dimensional numerical modelling of wind driven circulation in a shallow homogeneous lake abstract the development validation and application of a three dimensional deterministic numerical model of the wind induced circulation in a shallow homogeneous lake are described the governing equations expressing the conservation of fluid mass and momentum are solved in the model using an implicit finite difference initial value method particular attention is paid to the representation of the bed friction the wind shear stress and turbulent diffusion the model was compared with analytical solutions for three idealised flows before being calibrated and verified with field data from esthwaite water in cumbria the model was tested for stability and parameter sensitivity and then used to generate typical circulation patterns for a variety of steady state conditions comparisons with field measurements suggest that the model is better at predicting water movements in the open water than in the sheltered bays

structural and geochronological constraints on the tectonic evolution of the dulong song chay tectonic dome in yunnan province sw china abstract the dulong song chay tectonic dome lies on the border of china se yunnan province and northern vietnam and consists of two tectonic and lithologic units a core complex and a cover sequence separated by an extensional detachment fault these two units are overlain unconformably by late triassic strata the core complex is composed of gneiss schist and amphibolite shrimp zircon u pb dating results for the orthogneiss yield an age of 799 10 ma which is considered to be the crystallization age of its igneous protolith formed in an arc related environment a granitic intrusion within the core complex occurred with an age of 436 402 ma which probably formed during partial closure of paleotethys within the core complex metamorphic grades change sharply from upper greenschist low amphibolite facies in the core to low greenschist facies in the cover sequence there are two arrays of foliation within the core complex detachment fault and the cover sequence s 1 and s 2 the pervasive s 1 is the axial plane of intrafolial s 0 folds d 1 deformation related to this foliation is characterized by extensional structures the strata were structurally thinned or selectively removed along the detachment faults indicating exhumation of the dulong song chay tectonic dome the major extension occurred at 237 ma determined by shrimp zircon u pb and 39 ar 40 ar isotopic dating techniques regionally simultaneous tectonic extension was associated with pre indosinian collision between the south china and indochina blocks the s 2 foliation appears as the axial plane of nw striking s 1 buckling folds formed during a compressional regime of d 2 d 2 is associated with collision between the south china and indochina blocks along the jinshajiang ailao shan suture zone and represents the indosinian deformation the dulong granites intruded the dulong song chay dome at 144 2 140 2 and 116 10 ma based on 39 ar 40 ar measurement on muscovite and biotite the dome was later overprinted by a conjugate strike slip fault and related thrust fault which formed a vortex structure contemporaneously with late cenozoic sinistral movement on the ailao shan red river fault

a new mechanistic model for organic carbon fluxes in the ocean based on the quantitative association of poc with ballast minerals abstract in simulation studies of the ocean s role in the global carbon cycle predicting the depth distribution for remineralization of particulate organic carbon poc is of particular importance following sarmiento et al global biogeochemical cycles 7 1993 417 most simulation models have the power law curve of martin et al deep sea research 34 1987 267 for this purpose the martin et al curve is an empirical fit to data most of which is from shallow floating sediment traps using such a fit implies that all the information necessary for prediction is contained in the carbon flux itself so that the organic carbon flux f oc z at any depth z can be predicted from the flux of organic carbon f oc z 0 at some near surface depth z 0 here we challenge this basic premise arguing that fluxes of ballast minerals silicate and carbonate biominerals and dust determine deep water poc fluxes so that a mechanism based model of poc flux must simultaneously predict fluxes of both poc and ballast minerals this assertion is based on the empirical observation that poc fluxes are tightly linked quantitatively to fluxes of ballast minerals in the deep ocean here we develop a model structure that incorporates this observation and fit this model to us jgofs eqpac data this model structure plus the preliminary parameter estimates we have obtained can be used to explore the implications of our model in studies of the ocean carbon cycle

slow science the value of long ocean biogeochemistry records sustained observations sos have provided invaluable information on the ocean s biology and biogeochemistry for over 50 years they continue to play a vital role in elucidating the functioning of the marine ecosystem particularly in the light of ongoing climate change repeated consistent observations have provided the opportunity to resolve temporal and or spatial variability in ocean biogeochemistry which has driven exploration of the factors controlling biological parameters and processes here i highlight some of the key breakthroughs in biological oceanography that have been enabled by sos which include areas such as trophic dynamics understanding variability improved biogeochemical models and the role of ocean biology in the global carbon cycle in the near future sos are poised to make progress on several fronts including detecting climate change effects on ocean biogeochemistry high resolution observations of physical biological interactions and greater observational capability in both the mesopelagic zone and harsh environments such as the arctic we are now entering a new era for biological sos one in which our motivations have evolved from the need to acquire basic understanding of the ocean s state and variability to a need to understand ocean biogeochemistry in the context of increasing pressure in the form of climate change overfishing and eutrophication

beach ridge development and sediment supply examples from west africa abstract beach ridges form the dominant mode of holocene coastal progradation in west africa they vary from minor accumulations to massively prograded plains over 100 km long variations in the patterns and morphological expression of these sandy deposits record spatial and temporal changes in various environmental parameters among these sediment supply stands out the importance of this factor is illustrated by the morphological patterns and the current sediment dynamics of minor and major beach ridge plains in this region the simplest beach ridges are related to just one or two sources of sand supply from a nearby source in these examples sand has been supplied by the nearshore zone or by eroding cliffs in many areas beach ridge formation ceased as the sediment supply dwindled because of cliff stabilization or establishment of an equilibrium nearshore profile major beach ridge plains in southern sierra leone and in the bight of benin exhibit complex patterns of development related to a bigger sediment supply from nearshore sources and rivers in southern sierra leone the beach ridge plains have been constructed essentially from sands derived from the nearshore zone locally as in the proximal part of sherbro island shallow nearshore shoals encroached upon by the beach ridge front have led to more massive progradation while engendering complex patterns of beach ridge development the sediment supply has been locally supplemented by sands drifting alongshore from the sewa and moa rivers the sediment supply involved in beach ridge development in the bight of benin highlights the role of longshore drift of sands from the volta delta early stages of progradation were characterized by the development of segmented inner beach ridge barriers separated by still infilling coastal re entrants nearshore sources were particularly important in these early stages of beach ridge progradation as coastal re entrants and their estuaries became infilled following the middle holocene eustatic highstand the longshore drift system evolved from a segmented to a unicellular one the resulting conditions of through drift east of the volta delta allowed for longshore transport of sands from this river for the construction of outer beach ridge barriers over a distance of over 250 km while rivers still actively supply sand to the coast current patterns of beach ridge development depend essentially on the coastal sand transport system which determines either the confinement of incoming sand to the vicinity of the very source area itself its regular delivery to the beach ridge front or its through drift to the local downdrift terminus

beach nourishment effects on sand porosity variability abstract a standard assumption in coastal engineering is that the porosity of natural beach sand non cohesive is 40 however is this assumption correct for all beach sand this paper proposes an accurate and simplified method to assess changes in sand porosity after beach nourishment by means of in situ density surveys through a nuclear densimeter this novel application has been applied to different beaches in the southwest of spain according to the tidal range grain size and beach morphology in several terms general results show that sand porosities range from 25 6 to 43 4 after beach nourishment works this research can be considered a support tool in coastal engineering to find shifting sand volumes as a result of sand porosity variability after beach nourishment and later marine influence

understanding mesozoic accretion in southeast asia significance of triassic thermotectonism indosinian orogeny in vietnam results from a zircon u pb study of the metamorphic basement of vietnam reveal that a large part of the continental crust was affected by a short lived episode of ductile deformation and high temperature metamorphism between 258 6 ma and 243 5 ma although coincident with final stages of north south china collision qinling orogenesis the thermotectonism in vietnam was caused by accretion of sibumasu to indochina south china this accretion event indosinian orogeny has regional significance because it contributed to the final stages of north south china collision an aspect not explicitly recognized in qinling orogenic models

a review and assessment of longshore sediment transport equations for coarse grained beaches previous assessments of analytical longshore sediment transport formulae have been heavily biased towards sand sized sediment all have noted the shortage of high quality field data from coarse grained beaches against which to test predictions of longshore transport rates in this paper 12 existing formulae were identified as being potentially applicable for coarse grained sediments and predictions from these formulae are compared using a measured annual transport rate from a shingle beach and a concurrent hindcast wave climate two new empirical equations are also derived one from a numerical model calibrated against the same data set the other derived from field experiments on coarse grained beaches energetics based equations are found to give reasonable predictions of the shingle transport despite being derived for sand beaches in contrast those dimensional analysis type equations which had been validated using laboratory data grossly over predicted the measured transport rates the most accurate predictions were from formulae previously validated at sites similar to that used for this comparison and therefore require further testing against field data from dissimilar sites

association of sinking organic matter with various types of mineral ballast in the deep sea implications for the rain ratio 1 we compiled and standardized sediment trap data below 1000 m depth from 52 locations around the globe to infer the implications of the armstrong et al 2002 ballast model to the ratio of organic carbon to calcium carbonate in the deep sea the rain ratio we distinguished three forms of mineral ballast calcium carbonate opal and lithogenic material we concur with armstrong et al 2002 that organic carbon sinking fluxes correlate tightly with mineral fluxes based on the correlations seen in the trap data we conclude that most of the organic carbon rain in the deep sea is carried by calcium carbonate because it is denser than opal and more abundant than terrigenous material this analysis explains the constancy of the organic carbon to calcium carbonate rain ratio in the deep sea today and argues against large changes in the mean value of this ratio in the past however sediment trap data show variability in the ratio in areas of high relative calcium carbonate export mass caco3 mass ratio 0 4 unexplainable by the model leaving open the possibility of regional variations in the rain ratio in the past

dynamics of large polymictic lake i field observations the internal dynamics of clear lake california a large multibasin and polymictic lake under stratified conditions is described in this work particular attention is paid to one of the subbasins of clear lake oaks arm several field experiments were conducted in the lake to obtain data of wind currents and water temperature using a wide range of devices based on field observations and previously published results on basin responses to wind stress a conceptual model of the internal circulation of the oaks arm is proposed its internal dynamics are characterized by diurnal cycles of setup and relaxation of horizontal temperature gradients driven by the wind forcing the setup and relaxation processes are modulated by the influence of the earth s rotation and create a residual cyclonic circulation this circulation mechanism is here referred to as baroclinic pumping it is in all likelihood not exclusive to clear lake but probably exists in other large and relatively shallow lakes forced by strong and almost periodic wind events where basin scale internal waves do not play a major role in the dynamics of the system

grain size components as markers of origin and depositional processes in the coastal zone of the golfe du lion mediterranean sea france abstract a study of beach and nearshore sands between the mouth of the river aude and cap d agde northwestern mediterranean sea shows the existence of four sediment types st st1 to st4 with st2 seemingly deriving from st1 revealed by grain size modal analysis and confirmed by a deconvolution program lognormal deconvolution of grain size grain size skewness is related to a much more persistent multimodality than graphic evidence can show multimodality results from mixtures of generally three sts and or variants the latter defining monotype grain size distributions monotype mixtures are unequally distributed in morphodynamic zones very abundant on the lower shoreface significantly present on the berm and inner bar but rare in the most dynamic zones i e the collision zone and outer bar on the berm and lower shoreface modal values of the three sedimentary variants retain a close grain size relationship on the berm where only bedload is present in the swash monotype grain size distribution trends towards a lognormal model this trend can also be observed on the lower shoreface where there are numerous monotype grain size distributions gsds possibly indicating a dominant process when compared with st1 dominated grain size distributions of the outer bar zone the distribution of the derived st2 on the lower shoreface has an added fine tail derived from the coarse skewed outer bar sands in addition positive skewness of the lower shoreface sands could indicate input of fine particles from deeper zones under the influence of shoaling waves and upwelling morphodynamic zones are approximately characterized by the distribution of grain size indices a change in the direction of the skewness sign can be observed between the shoaling zone and more energetic zones from the breaker zone up to the berm finally a more detailed description of the spatial properties of grain size distributions could first help explore possible mechanisms underlying sediment sorting in the coastal zone and second provide a set of indices that would be of use in paleogeographic reconstructions and organization of basin borders while improving discrimination and classification of environments

direct dating of left lateral deformation along the red river shear zone china and vietnam 1 exposures of high grade midcrustal rocks within the red river shear zone rrsz which separates the indochina and south china blocks exhibit clear evidence of left lateral ductile deformation assuming that the south china sea represents a pull apart basin formed at the southeastern termination of the rrsz it has been argued that seafloor magnetic anomalies constrain the timing of sinistral slip accommodated by the rrsz between 32 and 17 ma at a rate of 4 cm yr while 40ar 39ar thermochronometry indicates that left lateral slip occurred along the rrsz between 25 and 17 ma the timing of earlier high temperature deformation has not been directly constrained in situ th pb ion microprobe dating of monazite inclusions in garnets allows direct assessment of the timing of amphibolite grade metamorphism and synchronous left lateral shearing results from northern segments of the rrsz in yunnan china indicate that synkinematic garnet growth occurred between 34 and 21 ma and are the first to document late oligocene metamorphism and left lateral shearing data from the southern rrsz within vietnam are complicated by tertiary overprinting of rocks that experienced amphibolite facies metamorphism during the indosinian orogeny 220 ma the period during which sinistral deformation is now constrained to have occurred along the rrsz i e 34 17 ma is essentially coincident with spreading of the south china seafloor 32 17 ma this temporal and kinematic link between left lateral shearing along the rrsz and opening of the south china sea supports the view that indochina was extruded from asia as a block along lithospheric scale strike slip faults

ar ar and fission track ages in the song chay massif early triassic and cenozoic tectonics in northern vietnam the song chay massif is the northeasternmost metamorphic complex in vietnam to the east of the red river shear zone it shows a large antiformal structure involving orthogneisses and migmatites overlain on its northern flank by muscovite bearing marbles an e w striking fault bounds the dome to the south kinematic indicators along a s n section reveal top to the n shear sense along the interface between the orthogneissic core and the overlying metasediments radiometric ages were obtained by the 40ar 39ar method using purified mica separates across the dome ages range from 236 ma at the southern edge to 160 ma in the core attesting to a strong imprint in the early triassic time a clear difference is seen between these mesozoic ages and the eocene to miocene ages from 40 to 24 ma that obtained in the nearby red river shear zone using the same method these data show that the song chay massif was already high in the crust when the high temperature deformation of the red river shear zone took place the final exhumation of the song chay orthogneiss constrained by fission track analysis on samples along the same transect occurred during the early miocene and could be interpreted as the consequence of a first normal sense of motion along the fault which bounds the massif to the south timing is similar to that of exhumation in the red river shear zone

bars formed by horizontal diffusion of suspended sediment abstract the mechanism responsible for the ubiquitous presence of convex beach profiles and shoreward migration of linear bars is examined using numerical circulation and sediment transport models the models are validated against laboratory measurements and observed natural beach cross sections while not discounting the importance of infragravity and advective horizontal circulation or bed return flow mechanisms a robust diffusive process explains the convex profile shape and bar formation in the presence of concentration gradients across the surf zone a diffusive sediment flux from high to low concentration results in the transfer of sediment outwards from the breakpoint both onshore and offshore and the subsequent formation of a diffusion bar and diffusion profile the profiles are characterised by single and double convex dome like shapes developing during shoreward migration of the bars by the diffusion mechanism the mechanism explains several phenomena observed on natural beaches including i convex beach profiles ii shoreward migration of the bar with concomitant beach accretion under narrow band swell iii reduced propensity for bar formation on low gradient fine sand beaches or under wide band wave spectra even though multiple bars are common on some low gradient beaches and iv offshore migration of the bar during periods of increasing wave height the diffusion mechanism can be dependent on orbital motion alone and as such requires no frequency selection or strong correlation between multiple processes for bar formation

high resolution field measurements and numerical modelling of intra wave sediment suspension on plane beds under shoaling waves abstract intra wave sediment suspension is examined using high resolution field measurements and numerical hydrodynamic and sediment models within 120 mm of a plane seabed under natural asymmetric waves the detailed measurements of suspended sediment concentration at 5 mm vertical resolution and at 4 hz showed two or three entrainment bursts around peak flow under the wave crest and another at flow reversal during the decelerating phase at flow reversal the mixing length was found to be approximately double the value attained at peak flow under the crest to examine the cause of multiple suspension peaks and increased diffusion at flow reversal a numerical side view hydrodynamic model was developed to reproduce near bed wave induced orbital currents predicted currents at the bed and above the wave boundary layer were oppositely directed around flow reversal and this effect became more pronounced with increasing wave asymmetry when the predicted orbital currents and an enhanced eddy diffusivity during periods of oppositely directed flows were applied in a lagrangian numerical sediment transport model unprecedented and extremely close predictions of the measured instantaneous concentrations were obtained the numerical models were simplified to incorporate only the essential parameters and by simulating at short time scales empirical time averaged parameterisations were not required key factors in the sediment model were fall velocities of the full grain size distribution diffusion separation of entrainment from settlement and non constant but vertically uniform eddy diffusivity over the plane bed sediment convection by wave orbital vertical currents was found to have no significant influence on the results

mesozoic magmatism and granitic dome in the wugongshan massif jiangxi province and their genetical relationship to the tectonic events in southeast china abstract in se china a mesozoic granitic dome coeval to extensional tectonics is exposed in the wugongshan massif its center is occupied by mesozoic granitoids and granitic gneisses and the e w trending late paleozoic mesozoic pingxiang and anfu basins are located along its northern and southern sides respectively in this paper the petrological geochemical major incompatible and rare earth elements and isotopic characteristics of the granitoids and granitic gneisses of this dome allow us to constrain their geodynamic evolution the wugongshan mesozoic k feldspar enriched granitoids consist of six granitic bodies and lie within a paleozoic metamorphic basement the caledonian shanzhuang granodiorite containing some dioritic enclaves occurs in the study area and is a calc alkaline type granodiorite characterised by lower sio2 and composed of andesine biotite quartz hornblende magnetite and sphene the mesozoic granitoids either indosinian plutons or yanshanian bodies show a geochemical affinity of peraluminous s type granite having higher sio2 k2o contents al k na 2ca enriched in rb th and depleted in eu they also exhibit lree enriched patterns and marked negative eu anomalies the yanshanian plutons also contain characteristic minerals such as sillimanite garnet and monazite the wugongshan mesozoic granitoids have higher isr values 0 70981 0 72885 and lower end t 10 6 to 14 7 an average of 12 6 than those of the early paleozoic shanzhuang granodiorite the mesozoic granitoids were likely derived from ancient sedimentary rocks by partial melting the wugongshan mesozoic granitoids contain three petrological zones that is an early cretaceous massive granitic zone in the core zone i a foliated granitic zone zone ii and a triassic granitic gneissic zone in the outer rim zone iii the petrological and geochemical features of massive granitoids zone i are similar to those of foliated granites zone ii and of granitic gneisses zone iii in this mesozoic dome moreover geometric and kinematic features within the ductile parts units 2 and 3 are also similar to those within the brittle part unit 1 of the dome all these features show that the geologic evolution of the wugongshan doming is a continuous process lasting from triassic to early cretaceous time published 40ar 39ar and k ar ages in the wugongshan mesozoic granitic rocks fall into two major age fields corresponding to two geodynamic events of intracontinental deformation and magmatic activity the first tectonothermal event dated at 226 259 ma on the granitic gneisses in the outer rim of dome can be linked to indosinian collision between the south china plate and the north china plate during triassic time the second event took place during the early yanshanian dated at 180 120 ma on the granites of the core of dome and are responsible for final doming of the wugongshan plutons this event may be related to a westward subduction of the paleo pacific oceanic plate under the se china continent during late jurassic early cretaceous time

influence of wind and lake morphometry on the interaction between two rivers entering a stratified lake the interaction of two rivers flowing into coeur d alene lake united states was investigated with a field experiment and three dimensional numerical simulations the focus was on the influence of basin morphology wind speed and wind direction on the fate and transport of the inflowing water data from the field campaign showed that intrusions from the two rivers propagated into the lake at different depths with the trace element polluted coeur d alene river flowing into the lake above the trace element poor and nutrient rich st joe river inflow the inflows initially intruded horizontally into the lake at their level of neutral buoyancy and later mixed vertically model results revealed that as the intrusions entered the main lake basin a forced horizontal mode two basin scale internal wave interacted with the intrusions to frequently siphon them into the lake proper and where rapid vertical mixing followed the results serve to show how detailed transport and mixing patterns in a lake can have im

the water level fluctuation zone of three gorges reservoir a unique geomorphological unit three gorges reservoir tgr has provoked a series of unprecedented environmental problems many of which are related to the transitional area between the base and capacity water levels of the reservoir commonly referred to as the water level fluctuation zone we proposed here that this zone serves as a unique geomorphological unit playing an important role of influencing the life of the tgr and named it as the tgr disturbance zone because it has been intensively interrupted by various human activities based on its geomorphological characteristics we divided this zone into three types that have hillside profiles with distinct shapes and gradients grain components and sizes and land uses although the three types of the zone have experienced the same set of geomorphological processes under the new annually cyclic hydrological regime their responses and the associated morphologies are distinguishable thus we depicted them separately accompanied with these processes are geochemical and biological processes that bring about exacerbated pollution and destroyed ecosystem in this zone we elaborated these problems and indicated the potential research directions toward fully understanding the complex geomorphological geochemical and biological processes prevalent in the zone c 2015 elsevier b v all rights reserved

40ar 39ar geochronology of the charnockites and granulites of the kan nack complex kon tum massif vietnam abstract the truong son belt forms the eastern rim of the indochina block in southeast asia the age of the metamorphism mainly along nw se mylonitic shear zones that affects this belt has been formerly determined at about 240 250 ma this age corresponds to the indosinian tectonometamorphic episode the kon tum massif situated to the south of this belt comprises high temperature rocks the kan nack complex including charnockites and granulites the main charnockitic outcrops restricted to the song ba valley establish the intrusive nature of these magmatic rocks within granulite facies material basic charnockitic rocks are mainly quartz enderbites to norites and hornblende pyroxene granulite facies rocks the 40 ar 39 ar age of intrusion cooling of charnockitic magmas is determined from primary magmatic biotites at about 245 ma in the east of the kan nack complex some granulite facies rocks exhibit relicts of primary granulite facies parageneses whereas others show evidence of overprinting by a retrogressive low grade metamorphism ar ar dating confirm this evolution giving ages of 400 ma for primary relict granulite facies phases and 260 270 ma from the most retrogressed samples establishing the youngest limit for the granulite facies metamorphism granulites intruded by charnockites in the song ba valley yield ages of about 250 ma equivalent to the ages of the charnockites and have evidently been completely reset by these high temperature intrusions therefore the kan nack complex of the kon tum massif is not an independent unit with respect to the indosinian orogen but represents the deep crustal part of this belt

sediment transport near the break point associated with cross shore gradients in vertical eddy diffusivity sediment clouds entrained and mixed vertically into the water column at the breakpoint were observed to advect offshore with the return current following wave breaking at a natural beach an advection diffusion model is applied to this phenomenon providing for cross shore gradients in vertical eddy diffusivity within and beyond the surf zone which result in differential entrainment and settlement near the break point results indicate that the horizontal gradient in turbulent vertical sediment mixing can provide a significant mechanism for bar generation even if the surface gravity and infra gravity waves remain uncoupled quantitative estimates of the rate of bar accretion are obtained after calibrating the sediment transport model using field measurements of currents and suspended sediment loads in the absence of other processes accretion rates of order 20 mm hour associated with the horizontal gradient in vertical diffusivity are predicted on the offshore bar

a comparison of observed and modeled surface waves in southern lake michigan and the implications for models of sediment resuspension 1 subsurface pressure sensors were used to make measurements of surface waves during 18 deployments in southern lake michigan between 1998 and 2000 most of the observations were made during the unstratified period november may in water depths between 10 and 55 m the observations as well as those obtained from the national data buoy center ndbc buoy 45007 which is located in the middle of the southern basin of the lake were compared to the results obtained from the great lakes environmental research laboratory glerl donelan wave model implemented on a 2 km grid the results show that the wave model does a good job of calculating the wave heights but consistently underestimates the wave periods in over 80 of the cases the bottom stresses calculated from both the observations and the wave model results agree as to whether or not resuspension occurs but over 70 of this agreement is for cases when resuspension does not occur both stresses predict resuspension about 6 of the time since the bottom stresses calculated from the model results are usually lower than those calculated from the observations resuspension estimates based on the wave model parameters are also lower than those calculated from the observed waves

the nature of the ailao shan red river asrr shear zone constraints from structural microstructural and fabric analyses of metamorphic rocks from the diancang shan ailao shan and day nui con voi massifs abstract the structural geology timing of shearing and tectonic implications of the asrr shear zone one of the most striking lineaments in southeast asia have been the topics of extensive studies over the past few decades the xuelong shan xls diancang shan dcs ailao shan als and day nui con voi dncv metamorphic massifs along the shear zone have preserved important information on its structural and tectonic evolution our field structural analysis detailed microstructural and fabric analysis as well as the quartz sillimanite and garnet fabric studies of the sheared rocks from the massifs demonstrate the dominant roles of three deformation episodes during cenozoic tectonic evolution in the shear zone among the contrasting structural and microstructural associations in the shear zone d2 structures which were formed at the brittle to ductile transition during large scale left lateral shearing in the second deformation episode predominate over the structural styles of the other two deformation episodes discrete micro shear zones with intensive grain size reduction compose the characteristic structural style of d2 deformation in addition several types of folds early shearing folds f 2 1 and late shearing folds f 2 2 were formed in the sheared rocks including discrete to distributed mylonitic foliation stretching lineation and shear fabrics e g mica fish domino structures as well as sigma and delta fabrics a sequence of microstructures from syn kinematic magmatic flow high temperature solid state deformation to brittle ductile shearing is well preserved in the syn kinematic leucocratic intrusions deformation structures from the first episode d1 are characterized by f1 folds and distributed foliations s1 in rocks due to pure shearing at high temperatures they are preserved in weakly sheared d2 rocks along the eastern margin of the als belt or in certain low strain tectonic enclaves within the shear zone furthermore semi brittle deformation structures such as hot striae and discrete retrogression zones are attributed to normal slip shearing in the third deformation episode d3 which was probably locally active along the eastern flank of the dcs range for example there are four quartz c axis fabric patterns in the mylonitic rocks including type a point maxima type b y point maxima with crossed girdles superimposition type c quadrant maxima as well as type d point and quadrant maxima combination they are consistent with microscopic observations of microstructures of high temperature pure shearing low temperature simple shearing and their superimposition integrated microstructural analysis and fabric thermometer studies provide information on both high temperature up to 750 c and dominant low temperature 300 600 c deformations of quartz grains in different rock types sillimanite and garnet fabrics especially the latter were primarily formed at the peak metamorphism during high temperature pure shearing the above structural microstructural and fabric associations were generated in the tectonic framework of the indian eurasian collision the low temperature microstructures and fabrics are attributed to left lateral shearing along the asrr shear zone from 27 to 21 ma during the southeastward extrusion of the indochina block which postdated high temperature deformation at the peak metamorphism during the collision

influence of stratification and shoreline erosion on reservoir sedimentation patterns sedimentation in the main pool of a deep maximum depth 50 m 227 km2 hydropower reservoir was modeled using a three dimensional numerical model of hydrodynamics and sedimentation for different wind inflow and outflow conditions short term velocity measurements made in the reservoir were used to validate some aspects of the hydrodynamic model the effects of thermal stratification on sedimentation patterns were investigated since the reservoir is periodically strongly stratified stratification alters velocity profiles and thus affects sedimentation in the reservoir sedimentation of reservoirs is often modeled considering only the deposition of sediments delivered by tributaries however the sediments eroding from the shorelines can contribute significantly to sedimentation if the shorelines of the reservoir erode at sufficiently high rates or if sediment delivery via tributary inflow is small thus shoreline erosion rates for a reservoir were quantified based on measured fetch parameterized be

influence of mixtures of grain size populations on the parametric and modal characteristics of coastal sands herault mediterranean sea france abstract grain size distributions in lower beach and nearshore sands of a segment of the coast of the golfe du lion france were analyzed by a parametric method and by modal analysis the results have been considered both in a spatial framework delineating geographically distinct sedimentary compartments and cells and in a morphodynamic framework separating the dynamic components of the shoreline berm collision zone inner bar outer bar lower shoreface modal statistics indicate that a mixture of three dominant components end members contributes to the grain size distribution gsd of the sediments fine sand sedimentary type i modal value 0 195 mm i 0 35 medium and coarse sand st ii modal value 0 680 mm i 0 8 and very coarse sand and gravel st iii i modal value 2 3 mm i 1 5 quasi log normal one component gsds form a minority group and mixtures produce various apparently unimodal sands and bimodal sediments a large variation of grain size indices results from mixing a simulation of mixing of log normal populations close to the end members shows the great sensitivity of parameters sorting skewness and kurtosis to small changes in the compositional formula of the mixture the procedure followed supplies a good preliminary tool enabling rapid identification and localization of the main sand sources on a regional scale these components derive from potential sources available in the region well known from previous studies st i originates from the river rhone and provides the textural base for most of the sediments st ii and iii form a local component originating either from fluvial input aude orb and herault rivers or from the nearshore reworking of ancient quaternary sediments and late holocene beachrocks each st takes on local aspects in relation to the morphological environment but the regional scale of the study was too large to precisely reflect the local morphodynamic regime a significant change in the st i sorting of bar sands is however observed probably due to the net offshore migration reported for the bar system

longshore drift trapped in an expected universe abstract on the basis of a review of current practice in coastal science and engineering with regard to quantitative determination of longshore drift we conclude that coastal scientists and engineers have been trapped in an expected universe of longshore transport sand volumes without critical assessment of assumptions made in pioneering studies as a result workers in this field have come to accept a range of sand volumes and a range of techniques to measure or predict these volumes stabilized by opinion of the leading experts the shortcomings of previous studies and subsequent practice however indicate that these transport volumes and techniques may well be wrong certainly at present we have no dependable verifiable and consistent field measure of net or gross instantaneous or annual longshore transport volumes against which predictions can be compared both field measurements and mathematical model results especially as used for applied purposes and expressed in annual terms are suspect for a number of reasons these include questionable assumptions that lag far behind our current understanding of shoreface processes fudge factor coefficients for equations the lack of storm transport measurement and a cascade of uncertainties that moderate current practice once determined annual longshore transport sand volumes tend to be long lived and in all cases are unverifiable by field measurement more fundamentally the question is raised whether an earth surface system as complex and variable as longshore transport on beaches can ever be quantitatively modeled or measured successfully qualitative mathematical modeling remains a valid and useful approach to understanding the nature of sedimentary processes

calculation of littoral sand transport rate abstract an energy related littoral sand transport rate formula is presented based on extensive laboratory tests and on a broad set of known field data an example of application of the new expression to an actual measured field situation is also given

tracer studies on the updrift margin of a complex inlet system three sediment transport studies using tracers were performed at ancao inlet southern portugal the objectives of the experiments were to understand the sediment transport pathways and to determine their magnitudes on the updrift margin of an inlet in order to apply the traditionally used space integration methodology to the tracer experiments adaptations were required the study area was divided into four morphologically defined sectors and this was found to be a key factor for the applicability of tracers in a complex area the four sectors are as follows sector a is the straight part of the updrift beach sector b is the upper area of the swash platform sector c is the lower area of the swash platform and sector d represents the inner parts of the inlet margin the integrated analysis of all collected data forcing mechanisms tracer distribution and topographic evolution led to the determination of the sediment pathways a semi quantitative conceptual model was developed in order to explain the sediment transport pathways and magnitudes that a known mass of sediment would follow after arriving at the swash platform it was found that the areas with the largest sediment accumulation were sectors b and c while almost no sediment was retained in sector d which experienced significant erosion according to the model 53 of the initial mass of sediments remain in the system after two tidal cycles it is hypothesised that sediment losses are caused by sediment transport towards the ebb delta and by sediment bypassing occurring from the ebb delta to the downdrift beach through swash bar processes the herein defined conceptual model represents a useful tool that could be applied to other tidal inlets under similar conditions facilitating sediment budget studies around tidal inlets d 2004 elsevier b v all rights reserved

intracontinental subduction a possible mechanism for the early palaeozoic orogen of se china the early palaeozoic orogen of se china consists of three lithotectonic elements from top to bottom a sedimentary upper unit a metamorphic lower unit and a gneissic basement the boundaries between these units are flat lying south directed ductile decollements the lower one is coeval with an amphibolite facies metamorphism m1 the belt is reworked by migmatite granite domes high temperature metamorphism m2 and granitic plutons related to post orogenic crustal melting we date here the syn m1 ductile shearing at 453 7 ma by u th pb method on monazite previous ages and our new 40 ar 39 ar ages of biotites and muscovites show that the metamorphic rocks experienced syn m2 exhumation from 440 to 400 ma the early palaeozoic orogen of se china is an intracontinental belt in which decollements accommodated the north directed subduction of the cathaysian continent this orogen is an example of intracontinental subduction that was not preceded by oceanic subduction

dynamic behavior of suspended sediment concentrations in a shallow lake perturbed by episodic wind events field experiments were conducted in lake balaton a large surface area 600 km2 but shallow mean depth 3 2 m lake in hungary to quantify the resuspension and deposition of bottom sediment due to episodic storm events measurements were made of windspeed and direction surface waves mean water velocity and suspended sediment concentration during significant wind events the computed bottom stress due to surface waves dominated that due to the mean current and therefore surface waves were assumed to be the major cause of sediment resuspension a simple model for the depth averaged suspended sediment concentration based on surface wave height was calibrated with about 10 h of data collected during one storm event and verified against 15 d of data collected at the same site the success of the suspended sediment model which assumes that the bottom sediment was noncohesive is surprising since the bottom material was composed predominantly of sediment in the clay and fine silt size ranges this fit may indicate the presence of a thin surface layer of loosely bound sediment that is continuously involved in resuspension the suspended sediment model could easily be integrated into a water quality model e g to predict light attenuation provided that lateral transport is negligible or it could be used to provide the bottom boundary condition for a more general suspended sediment transport model in which advective transport is included due to their small fall velocities finegrained particles i e those in the silt and clay size ranges are transported easily by flows an understanding of the dynamic behavior of these particles is particularly important in shallow lakes and estuaries since there they may repeatedly settle to the bot

post cratonization deformation processes and tectonic evolution of the north china craton abstract the timing of events during the tectonic evolution of the north china craton ncc and the east china region is debated extension compression transpression and shearing occurred throughout the ncc since 320 ma these main structural stages and the temporal evolution of the structural framework and kinematics are summarized we present here data from multiple structural and magmatic stages related to temporally varying kinematics and deformation mechanisms during the evolution of the post cratonization of the ncc the timing of each stage is constrained using isotopic dating along with the timing of magmatic intrusion dyke intrusion and basin formation associated with tectonic transformation of the ncc age data indicate distinct structural and magmatic stages at 1600 1500 1300 1100 445 315 270 200 170 155 130 110 75 65 and 25 20 ma relating to basin formation and continental uplift or collapse these stages define the tectonic evolution and structural transformation of the ncc and associated de rooting reactivation reworking and orogenic growth the tectonic setting and movement direction of adjacent plates changed multiple times during the various stages the stages are as follows separation of the ncc from the gondwana supercontinent and northwards drift formation of the central asian orogenic belt caob and northwards subduction of the yangtze plate resulting in closure of the qinling ocean the rapid initial formation of the western pacific plate and subsequent subduction and final closure of the mongol okhotsk ocean combined with closure of the bangong nujiang suture zone and southwards movement of the siberian continent as well as thinning of the north china cratonic lithosphere moreover temporal and spatial changes in deformation magmatism and basin formation as well as kinematic and mechanical transformations occurred in response to the changing tectonic setting and movement direction of surrounding plates these various factors resulted in a complex structural evolution of the ncc since 1 8 ga

evolution of north himalayan gneiss domes structural and metamorphic studies in mabja dome southern tibet field structural and metamorphic petrology investigations of mabja gneiss dome southern tibet suggest that contractional extensional and diapiric processes contributed to the structural evolution and formation of the domal geometry the dome is cored by migmatites overlain by sillimanite zone metasedimentary rocks and orthogneiss metamorphic grade diminishes upsection and is defined by a series of concentric isograds evidence for three major deformational events two older penetrative contractional and extensional events and a younger doming event is preserved metamorphism migmitization and emplacement of a leucocratic dike swarm were syntectonic with the extensional event at mid crustal levels metamorphic temperatures and pressures range from 500 8c and 150 450 mpa in chloritoid zone rocks to 705 65 8c and 820 100 mpa in sillimanite zone rocks we suggest that adiabatic decompression during extensional collapse contributed to development of migmatites diapiric rise of low density migmatites was the driving force at least in part for the development of the domal geometry the structural and metamorphic histories documented in mabja dome are similar to kangmar dome suggesting widespread occurrence of these events throughout southern tibet q 2004 elsevier ltd all rights reserved

tertiary deformation history of southeastern and southwestern tibet during the indo asian collision geologic mapping and geochronological analysis in southwest kailas area and southeast zedong area tibet reveal two major episodes of tertiary crustal shortening along the classic indus tsangpo suture in the yalu river valley the older event occurred between ca 30 and 24 ma during movement along the north dipping gangdese thrust the development of this thrust caused extensive denudation of the gangdese batholith in its hanging wall and underthrusting of the xigaze forearc strata in its footwall examination of timing of major tectonic events in central asia suggests that the initiation of the gangdese thrust was approximately coeval with the late oligocene initiation and development of north south shortening in the eastern kunlun shan of northern tibet the nan shan at the northeastern end of the altyn tagh fault the western kunlun shan at the southwestern end of the altyn tagh fault and finally the tian shan north of the tarim basin such regionally synchronous initiation of crustal shortening in and around the plateau may have been related to changes in convergence rate and direction between the eurasian plate and the indian and pacific plates the younger thrusting event along the yalu river valley occurred between 19 and 10 ma along the south dipping great counter thrust system equivalent to the locally named renbu zedong thrust in southeastern tibet the backthrust system in south central tibet and the south kailas thrust in southwest tibet the coeval development of the great counter thrust and the north himalayan granite gneiss dome belt is consistent with their development being related to thermal weakening of the north himalayan and south tibetan crust due perhaps to thermal relaxation of an already thickened crust created by the early phase of collision between india and asia or frictional heating along major thrusts such as the main central thrust beneath the himalaya

empirical model of morphodynamic beachface behaviour for low energy mesotidal environments abstract four years of monthly monitoring were carried out on a south atlantic beach in spain in a low energy mesotidal environment where beaches change slowly from reflective to dissipative states following a typical seasonal behaviour in this work a two dimensional study of beach morphological variations has been made related to the incident wave variations after applying several morphodynamic parameters to the field data poor or null representative results were obtained it was then necessary to design other type of characterisation of the incident wave energy in this sense the intertidal normalised beach slope was compared with the erosive potential of the incident waves expressed as a combination of the dimensionless grain fall velocity parameter and the energy density of waves median grain size did not vary significantly during the surveys for this reason a new parameter named wave erosivity factor was introduced by considering the fall velocity of grains as a constant in the parameter the resulting ratio between normalised beach slope and wave erosivity expresses the equilibrium state of the beach for any given energy level the departure from the equilibrium curve is largest in the intermediate situations while at the extremes the points are better adjusted to asymptotic tendencies towards equilibrium on reflective states small increases in the wave erosivity will produce important beach changes on dissipative beaches important increases in the wave erosivity will not produce significant morphological modifications the resulting equilibrium curve is presented as a function of the natural range of morphological variation of this beach

radius rapid particle analysis of digital images by ultra high resolution scanning of thin sections radius is a newly developed particle size measurement technique based on evaluation of digital images of thin sections analyses are performed with sub millimetre sample resolution and are thus designed to work on a single lamina of laminated sediments the method covers grain sizes from medium silt to coarse sand the application contains pattern recognition modules that allow the detection of typical particle distributions of loess organic detritus turbidites and tephra layers cutting and hiding effects of particles on thin sections are corrected by empirical correction matrices the calculated analysis results are compared with manually counted and measured samples to calibrate the application settings the method can be applied to all fine grained clastic sediments particularly to laminated lake sediments

indosinian nw trending shear zones within the truong son belt vietnam 40ar39ar triassic ages and cretaceous to cenozoic overprints abstract several nw trending ductile and partly mylonitic shear zones cross the truong son belt of central vietnam along the song ma and song ca valleys and north of the kontum block from da nang to aluoi and khe sanh high grade metamorphic rocks of amphibolite facies showing a retrograde evolution and consisting of ortho and paragneisses metavolcanics amphibolites marbles and quartzites are exposed along these structures they display a homogeneous deformation pattern characterized by a generally steeply dipping foliation and a near horizontal to gently plunging mineral stretching lineation indicating a strike slip tectonic regime of deformation along the southernmost fault zone at least various and consistent kinematic indicators including s c structures asymmetric tails of porphyroclasts prove that the strain and metamorphism have been generated by a phase of dominantly non coaxial deformation with a dextral sense of shear 40ar 39ar dating applied on the high grade metamorphic rocks minerals occurring along these zones provide plateau cooling ages closely around 245 ma establishing that this event took place in the lowermost triassic as an early phase of the indosinian orogeny the existence of indosinian movements in vietnam as they have been defined by previous authors during the early century is now accurately confirmed and this is the first insight in the occurrence of ductile strike slip tectonics of indosinian age along nw se fault zones well expressed in central vietnam is a cretaceous thermal and deformational overprint marked by epimetamorphism which took place between 90 and 120 ma as attested by low temperature degassing ages this cretaceous event is not found further north in the song ma zone where younger ages appear as a result of the influence of cenozoic shear movements along the red river fault which displays 20 30 ma ages on the northern flank of song ca in the bu khang phu hoat core complex comparable oligocene lower miocene ages 20 35 ma yielded by biotite and phlogopite reflect a strong overprinting and attest to a rapid uplift of the basement

wind and buoyancy driven horizontal exchange in shallow embayments of a tropical reservoir lake argyle western australia many factors including depth vegetation density wind and gyres may act to influence the littoral exchange in a water body but very few studies have investigated the interaction between more than two of these factors at any time to investigate these controls on horizontal exchange in a large tropical reservoir we conducted a 9 d intensive field experiment in lake argyle western australia the experiment began with a 7 d cooling period that generated water in the shallows of the reservoir embayments that was persistently cooler than the interior this led to an underflow of dense water that moved from the lake boundary toward the center of the reservoir a three dimensional hydrodynamic model elcom was able to adequately reproduce this thermal structure and was used to demonstrate its sensitivity to wind sheltering effects and submerged macrophyte presence further analysis of the predictions indicated that when the ratio of the shear and buoyancy force averaged over 6 h b6h and 6 h averaged wind speed in the direction of the embayment u6h was 1 greater than 0 5 ms 1 and 4 5 ms 1 respectively the exchange was dominated by a topographic gyre formation 2 when 0 1 b6h 0 5 and 2 4 ms 1 u6h 4 5 ms 1 the resulting circulation was a combination of differential cooling flows and a topographic gyre circulation and 3 when u6h fell below 2 4 ms 1 purely buoyancy driven flow occurred but only if the buoyancy forces across the embayments were an order of magnitude greater than wind induced velocity shear

structural doming tectonics intracontinental deformation of the sw margin of the yangtze block china the southwest margin of the yangtze block underwent multiple tectonic events including the collision between the yangtze and the south china plate caledonian folding and uplift of south china subduction of the western pacific plate and cenozoic continental escape during the indo asia collision the structural framework and tectonic evolution of the area are currently unclear through field petrologic and structural studies microstructures within the deformed units and estimates of the temperature of deformation we constrain the conditions of deformation and further classify at least four stage deformation the first stage involved northeastward thrusting that produced folds mylonites and dynamically recrystallized quartz and calcite electron backscatter diffraction data indicate that deformation during this event occurred at 400 c corresponding to a depth of 10 km the second stage of deformation involved uplift extension and the generation of a domal structure during the third event high angle normal faults formed within the cover sequence that surrounds the dome the fourth stage of deformation occurred in the cenozoic and involved motion along sinistral and dextral strike slip faults which cut structures that formed during the previous stages of deformation the first deformation event was related to triassic n s collision with the indochina block the second and third stages resulted from far field compression related to westward subduction of the paleo pacific plate and the fourth event was related to displacement along the ailaoshan red river strike slip fault the dome in the study area represents a transitional structure between a metamorphic core complex and a gneissic dome which we refer to as structural doming

role of lithosphere in intra continental deformation central australia abstract since the proterozoic there has been a set of deformation cycles in central australia culminating in the alice springs orogeny around 400 ma these events occurred away from plate boundaries and involved extension as well as compression although their precise history remains difficult to unravel from the geologic record much evidence of deformation is left in the central australian crust which features significant moho topography and an associated gravity signal in the past several mechanical models invoked crustal thickening and considerable compression to explain these geophysical characteristics however it is hard to envisage extensive deformation affecting the crust alone but leaving no deformation record in the sub crustal lithosphere in recent seismic tomography studies there is continuous seismically fast lithosphere in central australia below depths of about 100 km in this region the uppermost lithospheric mantle is seismically slow but exhibits no significant attenuation of seismic waves these new constraints make simple crustal thickening unlikely to be the main mechanism to generate variations of the moho depth in central australia here we propose a mechanical model of deformation that involves the entire lithosphere we make no strong assumptions about the history of deformation cycles our model does not require lithospheric thickening at any stage of the deformation cycle and results in a present day scenario compatible with shallow as well as deep constraints on the lithosphere structure

palaeostress estimation using calcite twinning experimental calibration and application to nature abstract by means of high temperature deformation experiments on calcite rocks of different grain sizes we have established the relationships between differential stress and twinning incidence twin density and volume fraction and the way that these relationships depend on grain size both twinning incidence and volume fraction increase with grain size at a constant level of differential stress log twin density is proportional to stress but is independent of grain size at a given grain size volume fraction of twinning increases non linearly with differential stress twinning activity measured by twinning incidence increases linearly with stress the behaviour of each of these parameters is independent of temperature strain and strain rate these relationships can be used as a basis for the estimation of palaeostress values in naturally deformed calcite rocks this is illustrated by a study of twinning activity in limestones close to thrust faults in the cantabrian zone of the variscan orogenic belt in northwestern spain high peak differential stresses were measured ranging from 150 to 250 mpa using the turner dynamic analysis technique however it is clear that shear stresses resolved parallel to the fault planes were very low the attainment of high stress differences when the resistance to faulting was low is attributed either to bending forces induced during the motion of the non planar surfaces relative to each other or to the stress peak being attained prior to the localization of deformation onto the fault surfaces

the origin of contractional structures in extensional gneiss domes the juxtaposition of domains of shortening and extension at different scales in orogens has fueled many debates about driving forces and tectonic interpretations including timing of deformation at the orogen scale gravitational collapse and mass transfer from orogenic plateaux to forelands explain some of these juxtapositions at a regional scale structures in gneiss domes are commonly contractional yet are coeval with regional extension and denudation here we use three dimensional numerical experiments to show that crustal flow in orogenic domains does not necessarily conform to plate motion we document contractional crustal flow associated with the formation of a gneiss dome in an orogenic pull apart setting where localized extension and crustal thinning focus the exhumation of deep crust we show that the flow field results in a complex strain pattern in which an extensional strain regime that is collinear with the direction of plate motion is partitioned into the shallow crust whereas contractional structures and fabrics at a high angle to the direction of imposed transport develop in the deep crust advective mass transfer across regions of contrasting yet coeval strain regimes leads to a polyphase tectonic history we observe structural features remarkably similar to those documented in some natural gneiss domes such as the montagne noire which developed in a dextral pull apart domain at the southern margin of the french massif central

precision and accuracy of the calcite strain gage technique the twinned calcite strain gage technique allows the determination of strain magnitude and direction in mildly deformed sedimentary rocks in that the measurements required for the calculation are rather time consuming it is important to know the minimum number required to obtain a precision that is comparable with the accuracy of the result this paper documents a series of tests on three different limestones having different textures and porosities in order to determine the precision and accuracy of the technique as a function of the number of measurements and the number of perpendicular thin sections the tests show that for most purposes the best measurement strategy will be to make 25 measurements on each of two perpendicular thin sections the best determined principal strain axis is the one having a magnitude that is opposite in sign from the other two over the range of zero to 11 shortening the magnitude of the odd signed strain axis will than have a precision and accuracy of about 11 in magnitude and a precision and accuracy of about 6 to 8 in orientation differences in texture and porosity do not appear to have significant effects upon precision and accuracy

a virtual power function for estimating the alongshore transport of sediment by waves abstract a transport formula is presented which is based upon the rate of energy dissipation in breaking waves it incorporates a dimensionless grain size parameter and has been calibrated against field and laboratory data

three dimensional layer integrated modelling of estuarine flows with flooding and drying abstract details are given of the refinement and application of a thee dimensional 3 d layer integrated numerical model of tidal circulation with the aim of simulating severe tidal conditions for practical engineering applications the mode splitting strategy has been used in the model a set of depth integrated 2 d equations are first solved to give the pressure gradient and the layer integrated 3 d equations are then solved to obtain the vertical distributions of the flow velocities attention has been given to maintaining consistency of the physical quantities derived from the 2 d and 3 d equations a two layer mixing length turbulence model for the vertical shear stress distribution has been included in the model emphasis has been focused on applying the model to a real estuary which is geometrically complicated and has large tidal ranges giving rise to extensive flooding and drying the model has been applied to three examples including wind driven flow in a rectangular lake tidal circulation in a model rectangular harbour and tidal circulation in a large estuary favourable results have been obtained for both the simple and complex flow beds

factors controlling the flux of organic carbon to the bathypelagic zone of the ocean 1 particle fluxes measured with time series sediment traps deployed below 2000 m at 68 sites in the world ocean are combined with satellite derived estimates of export production from the overlying water to assess the factors affecting the transfer of particulate organic matter from surface to deep water multiple linear regression is used to derive an algorithm suggesting that the transfer efficiency of organic carbon defined as the settling flux of organic carbon normalized to export production increases with the flux of carbonate and decreases with water depth and seasonality the algorithm predicts 80 of the organic carbon transfer efficiency variability in diverse oceanic regions the influence of the carbonate flux suggests that the ballasting effect of this biogenic mineral may be an important factor promoting export of organic carbon to the deep sea by increasing the density of settling particles however the lack of a similar effect for biogenic opal suggests that factors other than particle density also play a role the adverse effect of increasing seasonality on the transfer efficiency of carbon to the deep sea is tentatively attributed to greater biodegradability of organic matter exported during bloom events in high latitude opal dominated regions with high f ratios and seasonality while a higher fraction of net production is exported a higher fraction of the exported organic matter is remineralized before reaching bathypelagic depths on the other hand in warm low latitude carbonate dominated regions with low f ratios and seasonality a higher fraction of the exported organic matter sinks to the deep sea

review of the field data base for longshore sediment transport abstract a literature search was undertaken to collect field data on longshore sediment transport this yielded a large number of data sets 273 points for bulk transport rates from a variety of sites around the world data are especially lacking for transport rates exceeding 0 2 106 m3 year significant wave heights higher than 1 8 m sediment grain sizes coarser than 0 6 mm and beach slopes steeper than 0 06 1 14 a point rating system was devised whereby the quality of the data could be assessed the recording method and the accuracy thereof as well as the representativeness of the data were taken into account it was found that the evaluation was done reasonably objectively and consistently the data were divided into three categories the highest score achieved in the evaluation was only 71 thus reflecting the difficulty of measuring longshore transport accurately it is recommended that longshore transport formulae be calibrated against the data in the higher category 60 and better and then be tested against all the other data this will ensure that the formulae will be tested in as many different conditions and sites as possible without the lower quality data contributing to the calibration constants

spatial variation of cold front wind driven circulation and quasi steady state balance in lake pontchartrain estuary abstract circulation in a low salinity estuary with restricted openings to the ocean is mainly driven by wind and to a lesser extent by water level fluctuations at the open boundaries numerical model experiments are conducted using a baroclinic finite volume community ocean model fvcom for wind driven circulations during a period encompassing a total of 16 cold fronts in the lake pontchartrain estuary the work is focused on the examination of the spatial structure of circulation in response to local and remote winds a quasi steady state balance between the surface slope and wind stress is further analyzed the accuracy of the balance is evaluated by comparing the fvcom calculated surface slope with that from the steady state balance equation results show that this balance is more accurate in the cross estuary direction than that in the along estuary direction r2 0 94 vs 0 60 this difference in the accuracy of the quasi steady state balance between the cross and along estuary directions is caused by the open boundary a tidally induced mean slope exists in addition even if the tidal effect is removed the accuracy still decreases toward the open end for slopes in both directions remote wind effect and residual flow through the eastern open boundary tend to introduce a departure from the quasi steady state balance in both along and cross estuary directions remote wind effect decreases into the interior due to bottom friction local wind effect tends to produce downwind flows in coastal shallow water regions and on the surface but upwind flows near the bottom a result consistent with barotropic wind driven circulations while the remote wind effect is important mostly near the open boundary furthermore quasi steady state balance is more accurate in the along estuary direction before cold front passages then after because of the relatively higher occurrence of the wind in that direction before the cold fronts than after in contrast this quasi steady state balance is less accurate in the cross estuary direction before cold front passages than after because of the relatively lower occurrence of the wind in that direction before the cold fronts than after

structural style and tectonic significance of the jianglang dome in the eastern margin of the tibetan plateau china abstract the jianglang tectonic dome jtd lies on the eastern margin of the tibetan plateau and consists of three tectono stratigraphic units separated by two extensional detachment faults a schist complex a middle ductile slab and an overlying sedimentary unit the schist complex is composed of quartz mica schists and amphibolites of possible mesoproterozoic age and exhibits two early foliations s 1 and s 2 overprinted by two later foliations s 3 and s 4 the ductilely deformed middle slab consists of paleozoic quartzite phyllite marble amphibolite and meta basalt it is characterized by pervasive intrafolial and intraformational recumbent folds with a penetrative axial foliation s 1 an equivalent of s 3 in the basement rocks the cover unit the triassic xikang group of flysch sedimentary rocks experienced shallow level buckling and flattening deformation with an axial cleavage defining s 1 an equivalent of s 4 in the middle slab and basement rocks the jtd appears to have experienced three stages of extension immediately after orogeny the earliest d 1 recorded by an axial surface s 1 of s 0 intrafolial folds and sub parallel to s 0 in the schist complex probably occurred prior to the collision between the south china and north china blocks this extensional event was followed by subduction of the yangtze block to the west towards the eastern margin of the tibetan plateau the two detachment faults are characterized by structures formed by ductile brittle to brittle shear deformation which are sub parallel to the layer of s 2 in the lower detachment and to s 0 in the upper detachment these faults mark the second stage of extension and may have caused thinning and selective removal of the sinian and paleozoic strata as well as exhumation of the schist complex and the middle slab in the middle jurassic 177 ma the final stage of extension d 5 shown by brittle deformation and thermo metamorphism from the lower detachment to the xikang group was associated with the indian eurasia collision

extensional tectonics within a subduction type orogen the case study of the wugongshan dome jiangxi province southeastern china abstract in southeastern china the wugongshan massif consists of metamorphic rocks and granites generally considered as basement rocks formed during an early paleozoic orogeny our structural and radiometric reappraisal of this massif shows that it results from a mesozoic doming in the metamorphic rocks the foliation defines an e w elliptical shape and bears a n s stretching lineation the axial zone of the dome is occupied by oriented plutons the outer part of the dome consists of devonian quartzite carboniferous permian limestone and triassic jurassic sandstone ductile deformation observed in the permian carbonates and older units develops contrasting kinematics the northern and southern flanks present top to the north and top to the south motions respectively the same divergent pattern of motion is recorded from brittle structures up to the jurassic sandstone the late cretaceous red beds are undeformed in the axial zone coaxial flow indicated by symmetric pressure shadows and quartz fabrics predominates along the n and s flanks of the dome post folial recumbent folds are symmetrically overturned to the n and s respectively but at the two extremities of the dome the fold axes are parallel to the stretching lineation 40 ar 39 ar ages of biotite and muscovite from mylonite and granite suggest a late triassic age for the ductile deformation and an early cretaceous age for the final doming the wugongshan dome is similar to a metamorphic core complex formed in an extensional tectonic regime a model which emphasizes plutonism is discussed from permian to early cretaceous southeastern china was a subduction type orogen the crust of which was thickened by accretion of mantle derived magmas the emplacement of a large amount of mesozoic granitoids in southeastern china promoted thermal softening and gravitational instability that allowed the crust to extend the formation of the wugongshan dome and other metamorphic core complexes appears to be a the direct consequence of plutonic activity and crust rheology

gneiss domes and orogeny many gneiss domes record positive feedback between decompression and partial melting of orogenic middle crust exhumed orogens are riddled with gneiss domes cored by migmatites that underwent dehydration melting during decompression the decreasing buoyancy associated with increasing melt fraction drives further decompression at near isothermal conditions as the partially molten crust rises diapirically this combination of processes may explain the generation and retention of large volumes of crustally derived melt recorded in many deep seated migmatite terranes and inferred for active orogens in exhumed orogens the signature of the rapid ascent of partially molten crust is a gneiss dome cored by migmatite granite the large volume of material involved in the vertical transfer of partially molten crust indicates that the formation of gneiss domes is an efficient mechanism for heat advection during orogenesis

sediment transport by waves and currents a bed load model based on a generalization of bagnold s 1954 constitutive equations together with the assumption of similarity profiles for velocity and concentration was proposed for sediment transport by waves by sleath 1994 this model is now extended to wave current flows and applied to three different situations a oscillatory flows with superimposed currents b net transport produced by progressive waves over a flat horizontal bed and c longshore transport induced by waves approaching a beach in all three cases the model gives reasonable agreement with experiment in the case of longshore transport the model produces almost the same formula as that of the coastal engineering research center 1977 apart from additional terms for density and grain size

kinematics and vorticity in kangmar dome southern tibet testing midcrustal channel flow models for the himalaya 1 kinematic kinematic vorticity wm and deformation temperature analyses were completed to test the hypothesis that midcrustal rocks exposed in the core of the kangmar gneiss dome southern tibet record ductile deformation patterns of a frozen segment of a southward flowing midcrustal channel microscopic and mesoscopic kinematic indicators exhibit a downward transition from a subequal mix of top north and top south shear in garnet zone rocks to dominantly top north shear in staurolite kyanite zone and deeper rocks kinematic vorticity values indicate an increase in pure shear component with depth from 48 pure shear in chloritoid zone rocks through 62 in garnet zone to staurolite kyanite zone rocks to 68 pure shear in an orthogneiss the deepest exposed rocks deformation temperatures inferred from grain scale microstructures and quartz lattice preferred orientations increase from 300 c 400 c in chloritoid zone rocks to 600 c in the deepest exposed rocks these temperatures are equivalent to temperatures derived from garnet biotite thermobarometry indicating that wm was recorded during peak metamorphism this ductile deformation zone was cut by the brittle southern tibetan detachment system stds that juxtaposed metasedimentary rocks upon the orthogneiss on the basis of these relations midcrustal rocks in the core of kangmar dome record 1 general shear vertical thinning and n s horizontal extension with a component of top north shear during peak metamorphism within a ductile shear zone corresponding to the northern and deeper portion of the stds 2 an increase in pure shear with structural depth a consequence of an increase in lithostatic load and 3 displacement of the high temperature shear zone by the brittle stds our data are compatible with the deformation patterns predicted for the top part of a southward flowing midcrustal channel

observation and simulation of surface waves in two water supply reservoirs observations and model predictions of progressive surface waves were made for cannonsville and schoharie reservoirs located in southeastern new york state these reservoirs are deep with steep bottom slopes and relatively small fetch the donelan great lakes environmental research lab model a parametric second generation wave model was applied to these reservoirs assuming deep water throughout the domain this assumption was based on the relatively small waves and steep bottom slopes resulting in a very narrow region of wave interaction with the bottom along a lee shore previous applications of this model have been for water bodies with larger fetch observations of wave characteristics were made near the shoreline at two sites in cannonsville and one site in schoharie using submerged pressure sensors from which the height of larger waves was determined model hindcasts were made for the observation periods with model inputs being wind speed and direction and water surface elevation the model performed well in simulating significant wave height determined from observations some implications of the use of wave model simulations to predict sediment resuspension in these and other deep lakes and reservoirs are discussed

downscaling model resolution to illuminate the internal wave field in a small stratified lake this paper presents the application of hydrostatic and nonhydrostatic three dimensional hydrodynamic models to a stratified lake focus was given to the multiscale response of the internal wave field to strong wind gusts exceeding 20 m s 1 simulations were performed using different horizontal grid resolutions with uniform grid sizes varying from 100 100 to 10 10 m results of the hydrostatic models were used to investigate the large scale features of the internal wave motion with the intent of investigating the high frequency waves observed results of these simulations were used as initial conditions for nonhydrostatic simulations using smaller grids wavelength of the high frequency waves decreased with grid resolution however none of the uniform grids were sufficiently fine to capture the waves of the highest frequency simulations performed using a nonuniform grid produced internal waves of similar frequency of the waves observed in the field the simulations showed that these waves were shear u

saltation on gravel beaches tierra del fuego argentina abstract saltation is a common phenomenon on gravel beaches sediment traps across two beaches of the el paramo spit tierra del fuego argentina yielded different results on mean grain size sorting saltating load shape and height above the bed mean clast size increases with height above the bed to an altitude where the saltating size diminishes the sorting of the saltating populations also increases until an altitude where it begins to diminish spheres are preferentially set into saltation although the bed is dominated by platy bladed and elongated gravels much of the behavior of the saltation population is related to local wave dynamics beach steepness and stage of the tide the processes of gravel segregation size and shape on beaches obey to particular phenomena not considered in present day sediment transport equations but of much importance in relation to coastal defense improvements as dynamic revetments

vertical and horizontal structure in cross shore flows an example of undertow and wave set up on a barred beach greenwood b and osborne p d 1990 vertical and horizontal structure in cross shore flows an example of undertow and wave set up on a barred beach coastal eng 14 543 580 eulerian measurements of the horizontal cross shore velocity field in the lowermost meter of the water column in association with measurements of waves and the mean elevation of the water surface across a nontidal low relief barred surf zone reveal a spatially coherent patterns of the timeaveraged first second and third moments of the velocity field which vary temporally in direct response to the incident waves b large asymmetries in the flow field with offshore directed mean flows upto 0 20 m s a and onshore directed velocity skewness the third moment normalized by the standard deviation upto 0 60 c mean flows decrease and oscillatory flows measured by the standard deviation of the velocity field increase towards the water surface d a fourth order polynomial provides the best fit to the cross shore set up reflecting the influence of variable energy dissipation due to topographic controls on wave breaking e significant linear correlations exist between the cross shore mean velocities and the maximum set up of the still water surface near to the shoreline upto 82 of the observed variability in the former can be accounted for by linear regressions f set up is highly correlated with the incident wave height 86 of the observed variability in the former can be accounted for by a linear regression g gradients in the mean water surface are significantly less than those predicted by a linear function of beach slope as originally proposed by bowen et al even using an appropriate breaking criterion 0 4 0 6 for the spilling breakers recorded cross shore circulation over the low relief barred nearshore slope is predominantly two dimensional over the outer bar in this case study the near bed mean flow is an undertow responding to the balance between the wave generated depth dependent momentum flux directed onshore the stress induced by the onshore mass transport under waves and wind and the hydraulic pressure gradient induced by set up of the mean water level

basin scale internal wave dynamics during a winter cooling period in a large lake 1 basin scale internal waves are examined using a combined field observation and 3 d numerical approach the field site lake tahoe ca nv during winter is characterized by the presence of a weak density stratification and the passage of several storm fronts of varying character under these conditions internal waves with periods greater than 5 days and displacements of 30 m are possible the model used is shown to have negligible numerical dissipation and sufficiently small phase lag over the time periods needed to represent basin scale waves both the numerical results and the observations identify the presence of three kelvin modes and one poincare mode while the wave periods are consistent with theoretical predictions the spatial characteristics are far more complex than theory can predict the spatial features are revealed through analysis of the integrated potential and kinetic energy fields yielded by the model this shows that the basin topography exerts an influence on both kelvin and poincare waves the effect of the variable storms and in particular the phasing of the storms with respect to the internal waves is shown to be responsible for the amplification and annihilation of the basin scale waves

a new windstorm proxy from lake sediments a comparison of geological and meteorological data from western germany for the period 1965 2001 1 the feasibility of detecting windstorm layers in lake sediments is explored by comparing quartz grain size data from a freeze core obtained from the schalkenmehrener maar eifel region western germany to recent meteorological wind data the schalkenmehrener maar is appropriate for such a calibration study because the morphological settings of the lake allow the conservation of windstorm layers in particular there is no fluvial sediment inflow and long term wind measurements are available from nearby stations the age model for the uppermost 30 cm of the sediment core is based on measurements of 137cs and 210pb concentrations an ultra high resolution grain size analysis is performed digitally on thin sections and reveals distinct 1 mm thick layers with increased quartz grain content and sharp gaussian grain size distributions which are shifted to larger grain sizes compared to the normal lake sediment in order to compare the occurrence of these layers with meteorological wind data a windstorm index is developed combining data from meteorological stations in the eifel region and reanalyses from the european centre for medium range weather forecast a statistical evaluation of matches between the windstorm index and the core s silt fraction data indicates that the sediment layers very likely coincide with the major windstorm events in the eifel region during the last decades six historical storm are identified this pilot study identifies the main requirements and proposes a novel methodological approach for using sediment data from lakes with similar settings as the schalkenmehrener maar as a new proxy to reconstruct the windstorm record of the geological past

dynamics of large polymictic lake ii numerical simulations the internal dynamics of clear lake california a large multibasin and polymictic lake are examined using simulations conducted with a three dimensional 3d hydrodynamic model the model is based on an accurate and efficient semi implicit finite difference algorithm for the hydrodynamic equations that has been previously subject to extensive verification with analytical test cases the high level of agreement without extensive calibration between the model results and the observations at several locations in the lake is comparable with previously published 3d modeling results the model results confirm the baroclinic pumping model of circulation proposed for the oaks arm of clear lake in part i the simulations show that the interaction of stratification periodic wind forcing and coriolis effects drive this circulation the diurnal readjustment of the circulation from being wind driven to baroclinically driven is examined and shown to vary spatially this transition in circulation type has a wavelike nature with a distinct frontal structure and converging currents at the surface asymmetries in the forcing and response combined with rotational effects impart a cyclonic residual circulation on the flow

kinematics and timing of continental block deformation from margins to interiors during the deformation of continental blocks the magnitude of tectonic stress generally decreases with increasing distance from the margin of the block however the timing and kinematics of stress transmission from the margins to the interiors of continents are poorly resolved even though this information is critical to our understanding of the dynamics of continental deformation here we present a case study of mesozoic deformation of the north china craton ncc field investigations of mesozoic thrust faults and folds granitic intrusions and dykes combined with zircon shrimp and la icp ms dating and muscovite 40ar 39ar plateau ages reveal the age of the ne sw trending tectonic belts as 180 155 ma where the deformation of the craton margin occurred 10 20 ma earlier than that of the craton s interior although the kinematics of deformation are similar for the interior and the margin of the ncc strain decreases with increasing distance from the margin notably the bulk of the strain in the cratonic interior was focused in zones of pre existing weakness overall we determined that the ncc deformed under conditions of uniaxial compression a conclusion that is compatible with simple rheological models and that the stress magnitude attained in the cratonic interior was much less than that along its margin

longshore sediment transport rate measurement and estimation central west coast of india abstract measurements of the longshore sediment transport rate lstr along the surf zone at a 4 km long beach on the central west coast of india were made over a 4 month period during the study both the lateral and vertical distributions of the sediment transport rate were measured with traps deployed on a line spanning the surf zone sediment transport in the swash zone was not considered in the present study the longshore current was measured at each trap location the breaking wave parameters were calculated from a directional wave buoy at 16 m water depth the measured values were compared with those calculated from three selected empirical formulas the standard coefficient values in the empirical formulas were used without calibration to the data sets the measured average gross transport was 726 m3 day and that calculated were 1108 1017 and 781 m3 day based on cerc walton and bruno and van rijn formula during the data collection 69 of the time the transport was direct towards north and in the remaining period it was direct towards south the correlation coefficient between the longshore sediment transport rates measured and those calculated by cerc walton and bruno and van rijn formula were 0 38 0 71 and 0 74 respectively the average rms error between the measured and the calculated longshore sediment transport rate based on cerc walton and bruno and van rijn formula were 0 91 0 57 and 0 47

zircon and monazite upb dating of the doi inthanon core complex northern thailand implications for extension within the indosinian orogen abstract the doi inthanon metamorphic core complex occupies a prominent central position within the northwestern thai gneiss belt which has been inferred to be as old as precambrian and as young as permo triassic u pb dating of zircon from core orthogneisses of the complex suggests that the orthogneisses were derived from granitic protoliths with essentially the same late triassic early jurassic age as the mae cham pluton 205 3 4 ma to the west of the doi inthanon complex monazite ages from the orthogneisses indicate that low pressure and high temperature metamorphism and migmatitization occurred in the late cretaceous 84 72 ma limited published radiometric age data from elsewhere in the migmatitic gneiss belt suggest that widespread minor plutonism accompanied this thermal event a younger u pb data of 26 8 0 5 ma for zircon and monazite from the mae klang granite which intruded mylonitic gneisses on the eastern side of the doi inthanon complex indicates that there was also significant plutonism in the late oligocene these u pb ages constrain the development of the complex and hence of the migmatitic gneiss belt as a whole to an interval between late cretaceous and early miocene ductile shearing uplift and tectonic denudation via detachment faulting chronologically overlap the initiation of extensional basin development to the east and southeast of the gneiss belt and imply a genetic connection thus oligocene early miocene thermal rifting from the gulf of thailand northward into mainland thailand may have been the direct product of crustal extension rather than the transtensional product of regional strike slip faulting

conditions for early cretaceous emerald formation at dyakou china fluid inclusion ar ar and stable isotope studies the dyakou emerald occurrence is located in malipo county in the province of yunnan southern china the occurrence lies in the northern part of the laojunshan song chay metamorphic core complex which is exposed in an area of approximately 2 000 km2 and extends across the border between china and vietnam emerald mineralization is hosted by pegmatite and associated quartz veins that intrude deformed proterozoic biotite muscovite granofels and schist hydrogen and oxygen isotope results from the emerald channel waters and emerald respectively are consistent with an igneous fluid source the 18o fractionation between emerald and quartz yields vein temperatures of 365 to 420 c fluid inclusions indicate that the emerald precipitated from saline brines ranging from almost pure water to 10 5 mass percent nacl equiv fluid inclusion isochores intersected with 18o data yield pressures changing along the geothermal gradient from 1 500 to 3 300 bars ar ar geochronology of biotite and muscovite from the emerald veins yields consistent ages of 124 1 ma these constraints combined with field observations indicate that the dyakou emerald deposit is consistent with the igneous related model for emerald formation

triassic tectonics of the ailaoshan belt sw china early triassic collision between the south china and indochina blocks and middle triassic intracontinental shearing in se yunnan the ailaoshan belt has been extensively studied for the ductile shearing coeval with the left lateral cenozoic activity of the red river fault however the late triassic unconformity of the continental red beds upon metamorphic and ductilely deformed rocks demonstrates that the ailaoshan belt was already built up by early mesozoic tectonics from west to east the belt is subdivided into western central eastern ailaoshan and jinping zones the western ailaoshan and central ailaoshan zones correspond to a carboniferous permian magmatic arc and an ophiolitic melange respectively the eastern ailaoshan and the jinping zones consist of deformed proterozoic basement and paleozoic to early triassic sedimentary cover series both belonging to the south china block this litho tectonic zonation indicates that the ailaoshan belt developed through a sw directed subduction followed by the collision between indochina and south china blocks crustal thickening triggered per aluminous magmatism dated at ca 247 240 ma field and microscope scale top to the ne ductile shearing observed only in the pre late triassic formations but never in late triassic or younger formations complies with this geodynamic polarity furthermore the late collisional two mica granitoids and felsic per aluminous volcanites record a ductile deformation that argues for a continuing crustal shearing deformation after the early triassic collision up to the middle triassic therefore a two stage tectonic evolution accounts well for the documented structural and magmatic features the triassic architecture of the ailaoshan belt and its geodynamic evolution correlate well to the south and north with the north vietnam orogens and the jinshajiang belt respectively

long and complex thermal history of the song chay metamorphic dome northern vietnam by multi system geochronology multi system geochronology was used to unravel the long and complex thermal history of the song chay range northern vietnam a high grade granitic and metamorphic dome in the vicinity of the cenozoic ailao shan red river fault zone it was considered to be proterozoic south china basement but its geological history was basically unknown scattered field observations suggest three episodes of high temperature deformation firstly at the time of granite emplacement secondly a decollement with top to the north shear and thirdly anticlinal doming of the foliations formed during the two first stages p t estimates suggest that metamorphism coeval with the second deformation phase culminated at 580 ca nd 4 5 kbar 16 km depth multi system geochronology is applied to a two micas granite sample slightly deformed within the decollement u pb dating of zircon yields an age of 428 5m a 2s interpreted as the time of granite crystallization within the south china caledonian belt rb sr on white micas and biotite yields ages of 206 10 ma and 176 5 3 ma respectively 2s whereas 39ar 40 ar ages of the same minerals are 210 9a nd 190 8m a 2s these ages suggest an upper triassic episode of rapid cooling interpreted as due to doming a few million years after the end of movement on the decollement the k feldspar irregular 39ar 40ar age spectrum can to the first order be explained by a cooling history with two episodes of rapid cooling one at 140 ma and a second around 41 to 25 ma apatite fission tracks central age 33 6 3 6 ma 1s confirms a tertiary rapid cooling event interpreted as the final exhumation of the song chay dome 2000 elsevier science b v all rights reserved

calcite twin morphology a low temperature deformation geothermometer abstract twinning of the e plane is the dominant crystal plastic deformation mechanism in calcite deformed below about 400 c calcite in a twin domain has a different crystallographic orientation from the host calcite grain so called thin twins appear as thin black lines when viewed parallel to the twin plane at 200 320 magnification under a petrographic microscope thick twins viewed in the same way have a microscopically visible width of twinned material between black lines calcite e twin width and morphology has been correlated with temperature of deformation in naturally deformed coarse grained calcite in this paper we present a compilation and analysis of data from limestones of the frontal alps france and switzerland and the appalachian valley and ridge and plateau provinces eastern united states to document this temperature dependence mean calcite twin width correlates directly with temperature of deformation such that thin twins dominate below 170 c and thick twins dominate above 200 c above 250 c dynamic recrystallization is an important deformation mechanism in calcite mean twin intensity twin planes mm correlates negatively with temperature and a cross plot of twin intensity with twin width can yield information about both strain and temperature of deformation these relationships provide a deformation geothermometer for rocks that might otherwise yield little or no paleotemperature data

surface seiche formation on a shallow reservoir in complex terrain this study presents field observations and numerical modeling of surface seiche formations on a shallow reservoir in a complex terrain rules reservoir spain the influence of the surrounding topography on the atmospheric loading barometric pressure and wind speed is investigated with the associated atmospheric hydrodynamic coupling during a 13 day field study maximum free surface oscillations of 4 cm were recorded after the passing of a short duration storm 5 min which included a peak wind gust of 22 m s observations also present evidence of resonant excitation of the free surface caused by high frequency microscale harmonics 10 min in the atmospheric forcing resonant excitation caused by harmonics in the atmospheric forcing is significant for small reservoirs situated in regions of complex terrain where topographical obstacles modify the flow patterns in the near surface boundary layer generating eddies with harmonics in the microscale range of the atmospheric forcing spectrum harmo