identifying environmental controls on the shoreline of a natural river delta river deltas form where sediment laden water debouches into a basin the spatial delineation of a delta is nontrivial and yet is fundamental to systematically evaluating fluxes across its surface here we study shoreline dynamics of the wax lake delta wld a naturally developing delta downstream of the atchafalaya river usa we demonstrate the ability to extract hydrodynamic and morphodynamic shorelines from time series of satellite imagery and topography data respectively the hydrodynamic shoreline corresponds to the traditional dry wet interface whereas we introduce the concept of a morphodynamic shoreline demarcating the topset foreset transition of a delta to quantitatively express the degree of inundation of a delta plain these shorelines enable us to assess environmental controls on inundation of the wld delta plain noting the abundance of satellite imagery whereas time series of bathymetric data from delta plains are scarce from the analysis of noaa and u s geological survey environmental data we identify the effects of river discharge tides wind and vegetation on shoreline position in particular using delft3d simulations and a simplified momentum balance we highlight the nonuniform and nonlinear effect of wind on delta plain inundation our analyses reveal that wind riverine discharge and tides significantly contribute to inundation of the wld and hence incorporating their interaction is essential to the accurate modeling of hydrodynamics and ecodynamics of the wld delta plain as well as to the dynamic shape of delta plains in general

metamorphic and post metamorphic fluid flow in the low grade rocks of the harlech dome north wales a combination of fluid inclusion stable isotope and geochemical techniques has been used to study the nature of fluids present and their behaviour during caledonian low grade metamorphism of the harlech dome north wales fluid inclusion studies show that in most of the metasedimentary sequence the peak metamorphic fluid was an aqueous na k cl brine but in the graphitic clogau formation and in parts of the overlying maentwrog formation immiscible h2o rich and ch4 rich fluids coexisted late stage inclusions are of calcium rich brine and a dilute aqueous fluid the chemical composition of chlorite in metamorphic veins and rocks varies between different formations and quartz oxygen isotopic compositions show considerable variation between different units both of these features are taken to indicate that there was little or no pervasive movement of fluid between different units at the peak of metamorphism after the metamorphic peak there was focused flow of fluid upward through the sequence along fractures in response to end caledonian uplift and unloading where the migrating fluid crossed the graphitic shales interaction between the fluid and the shales gave rise to the formation of the auriferous veins of the dolgellau gold belt subsequent to this mineralizing event there was widespread development of 18o enriched calcites and micas in the case of vein minerals it is possible that these crystallized directly from late stage fluids at lower temperature than the quartz in the same veins alternatively the original vein minerals may have re equilibrated with later 18o enriched or cooler fluid in the case of muscovites in the rock matrix it is proposed that the isotopically heavy compositions are the result of re equilibration of initially light grains with an introduced fluid requiring considerable influx of fluid this event may relate to either of two late stage fluids observed as inclusions

elevation change and stability on a prograding delta coastal wetland systems are among the most dynamic landscapes on earth s surface however interrelated processes create wetland platforms that are relatively constant in space and time theoretically stable elevations should maintain themselves through time if the balance of processes creating that elevation remains unchanged at louisiana s prograding wax lake delta we measure landscape change between 2009 and 2013 quantifying volumetric changes to the delta subaerial slope adjustment and an equilibrium elevation of 0 56 m north american vertical datum of 1988 where elevation change on average is zero around which elevations fluctuate we calculate a system average equilibrium time scale of 16 years to describe how long locations will take to approach the stable elevation this time scale increases as a function of distance from channel edge peaks in elevation probability density functions can form for multiple reasons and do not require stability e g peaks can temporarily form at elevations where elevation change rate is locally minimum

deep fluid circulation in fault zones massive fluid circulation in retrogressive ductile shear zones is a well established but poorly understood phenomenon in some cases surface derived fluids which must initially have been at hydrostatic pressures can be shown to have entered shear zones in which fluids would normally be expected to be at lithostatic pressure in these circumstances thermal convection is an unlikely driving force for fluid movement underthrusting of a surficial fluid reservoir beneath shear zones is a viable mechanism in some cases but not for metasomatic shear zones in the pyrenees where insufficient underthrusting has occurred seismic pumping provides an alternative mechanism to explain the paradox of fluid access into ductile shear zones a kinematic analysis of a hypothetical fault zone shows that stress and dilatancy cycles will be out of phase above and below the frictional quasiplastic transition if this effect is sufficiently large hydraulic gradients may force fluid downward across the transition immediately after earthquake rupture through highly permeable microcrack networks between earthquake cycles plastic creep in mylonites will overprint microcrack networks increase fluid pressure and promote slow upward movement of fluid at low permeability for smaller shear zones such as those in the pyrenees seismic pumping could occur down a shallow decollement with subsequent upward fluid flow through shear zones in the hanging wall of the decollement

fluid flow mineral reactions and metasomatism a general model that relates fluid flow along a temperature gradient to chemical reaction in rocks can be used to quantitatively interpret petrologic and geochemical data on metasomatism from ancient flow systems in terms of flow direction and time integrated fluid flux the model is applied to regional metamorphism quartz veins and a metasomatized ductile fault zone

dissolution solution transfer diffusion versus fluid flow and volume loss during deformation metamorphism dissolution and solution transfer during deformation metamorphism are controlled by the partitioning of deformation into progressive shearing and shortening components progressive shearing is readily accommodated by slip on the planar crystal structure of phyllosilicates and graphite without accumulating dislocation density gradients across grain boundaries progressive shortening is accommodated by the cores of most other minerals including sulphides these minerals develop strain and hence dislocation density gradients on their rims due to progressive shearing along grain boundaries these gradients are particularly large when the mineral abuts phyllosilicate or graphite the resulting chemical potential gradients between the core and rim drive dissolution causing removal of the highly strained grain margins removal of dissolved material by solution transfer is aided by the geometry of shearing of phyllosilicates and graphite around other grains in an active anastomosing foliation interlayers and interfaces on boundaries lying at a low angle to the direction of shearing and oriented relative to the sense of shear such that they can open gape by small amounts water present in these interlayer spaces becomes destructured considerably enhancing diffusion rates along the foliation penetrative volume loss especially in deforming metamorphosing pelitic rocks is large at all metamorphic grades increasing and becoming more penetrative with depth to at least the transition into granulite and eclogite facies transference of material by fluid flow from deep to high levels in the earth s crust is precluded because thousands to tens of thousands of rock volumes of fluid are required necessitating continual recirculation of fluid from shallow to deep crustal levels in one large or several small sets of cells unless some extremely large scale form of fluid channelling is possible reassessment of diffusion mechanisms and hence rates during deformation and pervasive foliation generation in large volumes of rock where fluid channeling cannot provide enough fluid indicates that diffusion can proceed with sufficient rapidity that massive recirculation of fluid is no longer required the amount of fluid can be reduced sufficiently to allow large volume losses by a one way flow of fluid to the earth s surface in deforming metamorphosing environments where the fluid pressure equals or exceeds the hydrostatic pressure deformation partitioning controlled dissolution progressively changes the bulk chemistry of a rock containing phyllosilicates or graphite during deformation metamorphism because matrix minerals other than phyllosilicates and graphite are preferentially removed the large size of porphyroblasts if present tends to preserve them from dissolution hence the bulk chemistry operative during subsequent porphyroblast growth can have changed considerably from that operative when the first porphyroblasts grew in rocks in which bedding is still well preserved

the effect of heterogeneous stress and strain on metamorphic fluid flow mary kathleen australia and a model for large scale fluid circulation in the proterozoic mary kathleen fold belt northern australia infiltration of large volumes of externally derived fluid occurred synchronously with regional amphibolite facies metamorphism and deformation this paper develops a model of structurally controlled fluid migration by comparing the distribution of fossil fluid pathways with the inferred stress and strain patterns during the deformation intense fluid flow was localized within strong relatively brittle meta intrusive bodies and in discrete veined brecciated and altered zones around their margins in metasediments folded in a ductile manner outside these areas fluid infiltration was negligible the direct correlation between structural styles and the magnitude of veining and metasomatism suggests control of permeability enhancement and hence fluid flow by deformation finite difference modelling of a strong body in a weaker matrix has been used to evaluate the variation of stresses during the deformation from which it is clear that stress and strain heterogeneities have systematically influenced the development and maintenance of metamorphic fluid pathways particular regions in which mean stress may be significantly lower than the average lithostatic pressures include the strain shadow zones adjacent to the strong bodies other dilatant zones around the bodies and the bodies themselves this geometry is favourable not only for localized brittle deformation under amphilobite facies conditions but also for focused fluid flow in the low mean stress regions as evidenced by the abundance of veins fluid access through these metamorphic aquifers occurred during tensile failure episodes with particularly large dilations and decimetre scale veining in areas of strain incompatibility it appears likely that fluid circulated many times through the fold belt with flow concentrated in the metamorphic aquifers a model is developed that explains both the structurally focused fluid flow and the postulated multi pass recirculation by dilatancy pumping the pump engines comprising the low mean stress zones

flow patterns and morphology of a prograding river delta the transition of flow between laterally confined channels and the unchannelized delta front controls the morphodynamic evolution of river deltas but has rarely been measured at the field scale we quantify flow patterns and bathymetry that define the evolution of the subaqueous delta front on the wax lake delta a rapidly prograding delta in coastal louisiana a significant portion of flow 59 departs the channel network over lateral channel margins as opposed to the downstream channel tips bathymetric surveys and remotely sensed estimates of flow direction allow spatial changes in flow velocity to be quantified and patterns of erosion and deposition to be estimated shallowing along channel margins produces spatial acceleration and erosion lateral spreading deceleration and deposition occur within three to eight channel widths outside of the channel margins in interdistributary bays the shape of each flow path is constrained by nourishment boundaries that separate the outflows from neighboring channels deposit elevation decreases with a basinward slope of 2 4 10 4 with distance from a channel margin along any flow path regardless of the channel or location that flow departed the network bathymetric depressions called interdistributary troughs form along nourishment boundaries where flow paths are the longest and deposit elevation is correspondingly low we conclude that the deposit morphology exerts a strong control on bathymetric evolution and that interaction between neighboring channels and even neighboring deltas can influence delta front morphology

delta allometry growth laws for river deltas 1 under projected scenarios of sea level rise subsidence and sediment starvation many deltas around the world are expected to drown delta growth dynamics which determine the ability of a delta to adapt to these changes are poorly understood due to the difficulty of measuring change in slowly evolving landscapes we use time series imagery of experimental numerical and field scale deltas to derive four laws that govern the growth of river dominated deltas land area grows at a constant rate in the absence of relative sea level change while wetted area keeps pace maintaining a constant wetted fraction over the delta surface scaling of edge lengths versus areas suggests delta shorelines are nonfractal even though the channel network is fractal consequently channel edge length which provides critical habitat grows more rapidly than delta area these laws provide a blueprint for delta growth that will aid in delta restoration and help predict how existing deltas will evolve

the role of thrusting in the structural development of the mount isa mine and its relevance to exploration in the surrounding region resolution and prediction of the structure underground at mount isa from the surface geology is now possible using evidence for north to south movement on large scale thrusts during the first deformation at 1610 ma this evidence for the direction of movement during thrusting is preserved 1 macroscopically within three successive thrust imbricates as the north south alignment of respective truncations of older stratigraphic units by the angular unconformity at the base of the mount isa group 2 macroscopically and mesoscopically as a zone of vertical north south striking foliation with a horizontal stretching lineation that formed on a sinistral transform fault during dalong the wonga duchess belt 3 mesoscop ically as a regionally distributed north south oriented stretching lineation li that is locally well preserved on s0 surfaces in the hinges of folds with north south axial planes that formed during the second regional deformation and 4 microscopically as a horizontal north south aligned mineral elongation lineation defined by inclusion trails preserved in porphyroblasts that grew early during the second deformation adjacent to the wonga duchess belt the swing in strike of a large scale 70o west dipping lateral ramp on the western margin of the large scale kokkalukkanurker duplex from north south parallel to the direction of movement during thrusting to north northwest south southeast caused a portion of the meerenurker roof thrust lying on this lateral ramp to be overturned for at least 50 km near mount isa this overturning resulted from tilting the 70o west dipping lateral ramp through another 70 o as it rode obliquely north south over the north northwest south southeast striking portion of the same lateral ramp on the next imbricate to the south this generated the gross structural relationships seen in three dimensions at mount isa whereby the greenstone basement that truncates mount isa group rocks below the mine overlies them to the west the second deformation involved intense east west shortening and formed macroscopic folds that conveniently expose varying levels of the thrust pile generated during the first deformation in higher grade rocks west of mount isa and to either side of the wonga belt axial plane schistosity development and or reactivation of bedding during this deformation was quite intense and tended to obliterate and or rotate foliations and lineations formed during the first deformation only in the hinges of the folds formed during the second deformation where the deformation was less intense or silicification had occurred are earlier lineations preserved relatively unaffected by this event the geology of the mount isa valley and the rocks to the west of the mine is controlled by a series of north south striking high angle reverse faults that slice through the meerenurker thrust as it crosses the above mentioned lateral ramp on the western edge of the large scale duplex two of the faults mount gordon and mount isa dip steeply west with similar dis placements of 4 to 6 km west side up the other two faults holly and tastoka dip steeply east with the latter fault having a more significant displacement of 2 5 to 3 km east side up that greatly affects the geology on the eastern side of the mount isa valley the effects of these faults on the geometry produced by thrusting during the first deformation and folding during the second allow accurate prediction of the third dimension anywhere in the mount isa valley and the region immediately to the west consequently they can be used to predict the location of structurally controlled sites of potential copper mineralization similar to those found in the mount isa mine where mineralization formed during the third deformation

defining the ecogeomorphic succession of land building for freshwater intertidal wetlands in wax lake delta louisiana abstract land building in deltaic environments occurs when sediment discharged from a river mouth is deposited subaqueously and transitions to subaerial land the transition from subaqueous deposition to subaerial land is a critical process that marks the creation of relatively stable land yet it is unclear what controls the speed and style of this transition we define how this transition herein termed the land building succession varies in time and space for the freshwater intertidal wetlands in wax lake delta la using remote sensing and field data we classify land cover into sediment water or vegetation classes at maximum and minimum biomass we see two succession patterns within wax lake delta deltaic islands near the apex are initially covered by sediment and open water through time open water and sediment coverage decreases as vegetation coverage increases on the other hand distal islands show little sediment exposure through time in both cases all deltaic islands become covered with vegetation by 2015 as vegetation colonizes the island the topography organizes into two platforms vertically separated by 0 35 m the lower intertidal platform occurs in the island interiors and is commonly inundated by water and dominated by subaqueous or floating vegetation the upper subaerial platform occurs along island edges and is dominated by a variety of vegetation species including salix nigra colocasia esculenta and polygonum punctatum it takes an average of 10 years for the intertidal platform to transition to the subaerial platform these two platforms are separated by the tidal range measured in atchafalaya bay and the different vegetation communities occupying each platform suggest they are a manifestation of multiple stable states and arise due to vegetation and sedimentation feedbacks

low latitude meteoric fluid flow along the cloncurry fault cloncurry district nw queensland australia geodynamic and metallogenic implications hydrothermal alteration within the mount isa block mib is typically largely to have ceased at the end of the isan orogeny ca 1 50 ga however late large brittle quartz rich vein systems including those of the cloncurry fault cut mesoproterozoic tectonic fabrics intrusions and products of regional na ca hydrothermal alteration associated features display affinities to iron oxide cu au ore deposits including specular hematite bearing veins and cu au u lree ba mineralization stable isotope data suggest late veins in the vicinity of the cloncurry fault eastern fold belt efb formed from fluids with 18oh2o and dh2o 250 c of 4 to 3 and 22 to 4 respectively the high dh2o moderate 18oh2o and cacl2 nacl rich character of the saline fluids indicates they were mixtures of low latitude meteoric fluids and evaporite derived basinal brines which with time became progressively dominated by meteoric water deposited barite and cooled the low latitude meteoric signature demonstrates that the fault fracture systems were active when in equatorial regions paleomagnetic data for the mib and the australian protocontinent together with structural and thermal considerations and geochronological arguments suggest the veins probably formed sometime after 1 10 ga and potentially as late as during the alice springs orogeny ca 0 34 ga the late quartz veining was unrelated to two phases of regional na ca alteration and economically significant fe oxide cu au mineralization at 1 60 1 58 and 1 53 1 50 ga

quantitative metrics that describe river deltas and their channel networks 1 densely populated river deltas are losing land at an alarming rate and to successfully restore these environments we must understand the details of their morphology toward this end we present a set of five metrics that describe delta morphology 1 the fractal dimension 2 the distribution of island sizes 3 the nearest edge distance 4 a synthetic distribution of sediment fluxes at the shoreline and 5 the nourishment area the nearest edge distance is the shortest distance to channelized or unchannelized water from a given location on the delta and is analogous to the inverse of drainage density in tributary networks the nourishment area is the downstream delta area supplied by the sediment coming through a given channel cross section and is analogous to catchment area in tributary networks as a first step we apply these metrics to four relatively simple fluvially dominated delta networks for all these deltas the average nearest edge distances are remarkably constant moving down delta suggesting that the network organizes itself to maintain a consistent distance to the nearest channel nourishment area distributions can be predicted from a river mouth bar model of delta growth and also scale with the width of the channel and with the length of the longest channel analogous to hack s law for drainage basins the four delta channel networks are fractal but power laws and scale invariance appear to be less pervasive than in tributary networks thus deltas may occupy an advantageous middle ground between complete similarity and complete dissimilarity where morphologic differences indicate different behavior

contribution of dense array analysis to the identification and quantification of basin edge induced waves part i methodology recent earthquakes have shown that edge generated surface waves can significantly contribute to increased damages most observations of edge generated surface waves are concerning long period surface waves propagating in large size valleys since travel times of such waves between valley edges can reach several tens of seconds they are quite easy to isolate in small size structures reverberating wave trains are mixed and very dense array analysis is required for the identification of basin induced surface wave trains the city of grenoble french alps is located in a small size deep alluvial valley and faces important site effects lebrun et al 2001 in order to identify and quantify multidimensional site effects in this basin a very dense array of 29 three component seismometers over a 1 km aperture was installed within the city the wave field complexity as well as the in situ noise characteristics colored correlated noise and low signal to noise ratio led us to develop a procedure based on time frequency coherence of signal waveforms and the multiple signal classification music schmidt 1981 algorithm to identify the main energetic contributions crossing the array next the nature and energy of waves were estimated using some properties of the analytical three component covariance matrix careful methodological investigations were performed in order to better understand and quantify the effects of site constraints on the estimation of wave parameters with the music technique simulations outline the ability of array antennas first to handle difficult scenarios involving multiple nonstationnary and correlated propagating phases and second to estimate the polarization and energy of waves the velocity estimation is shown to be much more unstable than backazimuth estimation and a low signal to noise ratio introduces some variation in estimates finally considering the very large number of identified waves a statistical view of final estimates is suggested for improving the reliability of analysis in an accompanying article cornou et al 2003 we use this method to investigate the entire wave field of seismic events recorded by the array in order to isolate basin induced waves manuscript received 21 june 2002

stable isotope profile across the orthoamphibole isograd in the southern marginal zone of the limpopo belt south africa abstract in the southern marginal zone of the limpopo belt the transition from granulite to amphibolite facies metamorphism is defined by a change from orthopyroxene to orthoamphibole bearing assemblages within metasedimentary rocks of the supracrustal bandelierkop formation oxygen isotope fractionations among constituent minerals within both amphibolite and granulite facies metasedimentary rocks are of similar magnitude implying a similar retrograde thermal history temperatures calculated from these fractionations can be arranged in the following order quartz garnet quartz orthoamphibole quartz pyroxene quartz plagioclase quartz biotite the observed temperature sequence is consistent with retrograde metamorphism under closed system conditions and oxygen closure of garnet orthoamphibole and orthopyroxene at or close to peak metamorphism while quartz plagioclase and biotite crystallized from and or re equilibrated via a melt fluid phase down to temperatures of 560 c small fluid rock ratios are implied by the simultaneous closure of quartz plagioclase and biotite given that quartz is the dominant oxygen bearing phase during retrogressive exchange and assuming garnet closure to oxygen diffusion at the time of formation then the quartz garnet fractionations may provide minimum peak temperature estimates of 736 52 c coarse grained concordant felsic veins within the metasediments texturally interpreted as anatectites are in isotopic equilibrium with the host rock the closed system defined here only on the basis of oxygen isotope systematics does allow for fluid melt extraction at high temperatures in contrast to the metasediments oxygen isotope systematics for mafic and ultramafic rocks of the bandelierkop formation suggest open system behaviour for at least some of the rocks such rocks are commonly cross cut by coarse grained felsic veins which are not in isotopic equilibrium with the host rock and contain quartz whose 18 o values are indistinguishable from those observed in the metasedimentary rocks the stable isotope data are consistent with a model involving anatexis of metasedimentary rocks at peak metamorphic temperatures partial extraction of the anatectic melts and their crystallization elsewhere in the sequence is suggested by the mineralogy and isotopic composition of large discordant pegmatites together with the isotopic disequilibrium and open system behaviour observed in some mafic and ultramafic rocks in the pelitic rocks the release of small amounts of fluid from residual melts and or somewhat larger amounts from partially collected melts during cooling may account for many of the retrograde mineralogic features observed for these rocks without perturbing the oxygen isotope systematics such retrograde features include the cordierite orthopyroxene symplectite after garnet and the incipient hydration of orthopyroxene and cordierite within the granulites and possibly the regional retrogression of granulites to form orthoamphibole gneisses retrograde kyanite within these rocks thus suggests an isobaric cooling path similar 13 c values of graphite separated from amphibolite and granulite facies metasediments together with significant oxygen and carbon isotope heterogeneity among charnockites metasediments banded iron formations and most mafic and ultramafic rocks are not consistent with a retrogressive influx of extraneous co 2 rich fluids as the cause of regional retrogression and orthoamphibole formation in the gneisses nor with charnockitization the data also argue against a pervasive co 2 infiltration as the cause of granulite facies metamorphism

the delta connectome a network based framework for studying connectivity in river deltas abstract many deltas including the mississippi river delta have been losing land at fast rates compromising the safety and sustainability of their ecosystems knowledge of delta vulnerability has raised global concern and stimulated active interdisciplinary research as deltas are densely populated landscapes rich in agriculture fisheries oil and gas and important means for navigation there are many ways of looking at this problem which all contribute to a deeper understanding of the functioning of coastal systems one aspect that has been overlooked thus far yet fundamental for advancing delta science is connectivity both physical how different portions of the system interact with each other as well as conceptual pathways of process coupling in this paper i propose a framework called delta connectome for studying connectivity in river deltas based on different representations of a delta as a network after analyzing the classic network representation as a set of nodes e g bifurcations and junctions or regions with distinct physical or statistical behavior and links e g channels i show that from connectivity considerations the delta emerges as a leaky network that continuously exchanges fluxes of matter energy and information with its surroundings and evolves over time i explore each network representation and show through several examples how quantifying connectivity can bring to light aspects of deltaic systems so far unexplored and yet fundamental to understanding system functioning and informing coastal management and restoration this paper serves both as an introduction to the delta connectome framework as well as a review of recent applications of the concepts of network and connectivity to deltaic systems within the connectome framework

the lowermost mississippi river a mixed bedrock alluvial channel in this study the distribution of channel bed sediment facies in the lowermost mississippi river is analysed using multibeam data complemented by sidescan sonar and compressed high intensity radar pulse seismic data as well as grab and core samples of bed material the channel bed is composed of a discontinuous layer of alluvial sediment and a relict substratum that is exposed on the channel bed and sidewalls the consolidated substratum is made up of latest pleistocene and early holocene fluvio deltaic deposits and is preferentially exposed in the deepest thalweg segments and on channel sidewalls in river bends the exposed substratum commonly displays a suite of erosional features including flutes that are quantitatively similar in form to those produced under known laboratory conditions a total of five bed facies are mapped three of which include modern alluvial deposits and two facies that are associated with the relict substratum a radius of curvature analysis applied to the mississippi river centreline demonstrates that the reach scale distribution of channel bed facies is related to river planform from a broader perspective the distribution of channel bed facies is related to channel sinuosity higher sinuosity promotes greater substratum exposure at the expense of alluvial sediment for example the ratio of alluvial cover to substratum is ca 1 5 1 for a 45 km segment of the river that has a sinuosity of 1 76 and this ratio increases to ca 3 1 for a 120 km segment of the river that has a sinuosity of 1 21 the exposed substratum is interpreted as bedrock and given the relative coverage of alluvial sediment in the channel the lowermost mississippi river can be classified as a mixed bedrock alluvial channel the analyses demonstrate that a mixed bedrock alluvial channel boundary can be associated with low gradient and sand bed rivers near their marine outlet

chemical and stable isotopic characteristics of syn tectonic tourmaline from the western fold belt mount isa inlier queensland australia abstract understanding hydrothermal fluid flow events related to orogenic events is important because they provide large scale redistribution of metals which may become concentrated in ore deposits in this study we determine the origin of tourmaline bearing quartz veins and pegmatites in the western fold belt of the proterozoic mount isa inlier a region which host numerous syn orogenic cu deposits this paper uses tourmaline mineral chemistry and isotopic analyses in situ b and bulk o and h isotopes to fingerprint the fluid reservoirs that contributed to the fluid budget during the isan orogeny all the tourmaline samples have schorl dravite solid solution compositions quartz tourmaline 18 o 11 0 12 6 and 7 7 9 4 v smow respectively pairs yield equilibrium formation temperatures of 305 to 575 c with the higher temperatures related to pegmatitic tourmaline tourmaline d values have a relatively narrow range from 68 to 56 v smow in most cases calculated 18 o fluid and d fluid values are compatible with primary magmatic water with a small component of metamorphic 18 o enriched formation waters however there are large variations in tourmaline 11 b values which range from 10 7 to 17 0 with the majority of values between 10 and 15 variations in 11 b tur in the pegmatites suggest that boron degassing generated relative 11 b depletion during crystallization similar 11 b tur values in quartz tourmaline veins spatially associated with the pegmatites in cordierite and sillimanite bearing metamorphic rocks west of the mount isa fault demonstrate a similar origin for b in this tourmaline in contrast quartz tourmaline veins of similar timing hosted by greenschist grade metamorphic rocks east of the mount isa fault have much higher 11 b tur values 6 2 to 10 7 which reflect the involvement of a distinct b isotopic reservoir mostly likely a near surface derived evaporitic brine thus the b isotopic data reveal important differences in fluid origin that are not reflected in the 18 o values therefore at least two isotopically distinct fluids one sourced from fractionating anatectic pegmatites and the other from external basinal brines circulated contemporaneously in separate areas during the isan orogeny there is no evidence based on the tourmaline isotopic data to suggest that these fluids mixed which demonstrates that the hydrothermal plumbing system in the western fold belt during the isan orogeny was disconnected probably due to differences in thermal structure metamorphic grade across the western fold belt during orogenesis

river flow controls on tides and tide mean water level profiles in a tidal freshwater river 1 tidal rivers feature oscillatory and steady gradients in the water surface controlled by interactions between river flow and tides the river discharge attenuates the tidal motion and tidal motion increases tidal mean friction in the river which may act as a barrier to the river discharge time series of tidal water level amplitudes at five gauge stations along the river mahakam in indonesia and tidal flow velocity amplitudes at a discharge monitoring station were obtained applying wavelet analysis temporal variations in tidal damping coefficients for quaterdiurnal semidiurnal and diurnal tidal species were quantified from the observed amplitude profiles the analysis shows that tidal damping during the rising limb of a discharge wave differs from damping during the falling limb wavelet cross correlations between surface levels yielded empirical estimates of wave numbers an empirical relation between tidal damping and river flow is derived to describe subtidal bottom friction along an idealized tidal river resembling the mahakam the subtidal friction is decomposed into contributions from the river flow only from river tide interaction and from tidal asymmetry even for high river flow and low tidal velocity river flow enhances friction attributed to river tide interaction causing subtidal water level setup a simple multilinear regression model using subtidal bottom friction is employed to predict subtidal water levels at locations upstream with a relatively good agreement between predictions and observations the explicit expression shows the nonlinear dependence of subtidal friction on river flow velocity explaining the complex behavior of tidal mean surface level profiles

metasomatic albitites and related biotite rich schists from a low pressure polymetamorphic terrane snake creek anticline mount isa inlier north eastern australia microstructures and p t d paths rocks of the snake creek anticline are mainly pelitic schists psammitic schists and quartzites that were metamorphosed during multiple high t low p events extending from d1 to d5 with the metamorphic peak occurring late to post d3 albitites are widespread but are concentrated in five areas they are typically fine to medium grained and consist of albite with or without combinations of quartz biotite staurolite cordierite garnet andalusite sillimanite kyanite gedrite and tourmaline from the presence or absence of albite inclusions in porphyroblasts the albitites are interpreted as forming early in the d3 event as a result of infiltration of external fluids psammitic schists and quartzites were preferentially altered but pelitic schists were also albitized in localities where the alteration was more extreme with the replacement of muscovite total and the replacement of quartz and biotite variable structural controls on albitization include fracturing and syn d3 shear zones in fold hinges biotite schists with abundant porphyroblasts combinations of staurolite garnet andalusite and cordierite occur adjacent to albitites and it is argued that they formed by the addition of fe and mg sourced from the albitites in several albitite rich areas cordierite grew early in d3 and was partly or entirely replaced during or after d3 by combinations of biotite andalusite tourmaline staurolite and sillimanite a postulated p t d path involved an increase in pressure with or without a decrease in temperature subsequent to early d3 albitization followed by an increase in temperature up to the metamorphic peak late d3 to early d4 the metamorphism was contemporary in part with the emplacement of the williams batholith c 1550 1500 ma which probably supplied the na rich fluids

exploring the role of organic matter accumulation on delta evolution 1 we explore the role of plant matter accumulation in the sediment column in determining the response of fluvial deltas to base level rise and simple subsidence profiles making the assumption that delta building processes operate to preserve the geometry of the delta plain we model organic sedimentation in terms of the plant matter accumulation and accommodation space made for sediment deposition rates a spatial integration of the organic sedimentation added to the known river sediment input leads to a model of delta evolution that estimates the fraction of organic sediments preserved in the delta the model predicts that the maximum organic fraction occurs when the organic matter accumulation rate matches the accommodation rate a result consistent with field observations the model also recovers the upper limit for coal accumulation previously reported in the coal literature further when the model is extended to account for differences in plant matter accumulation between fresh and saline environments i e methanogenesis versus sulfate reduction we show that an abrupt shift in the location of the fresh salt boundary can amplify the speed of shoreline retreat

structural controls on syntectonic metasomatic tremolite and tremolite plagioclase pods in the molanite valley mt isa australia abstract in the molanite valley west of mt isa tremolite bearing metasomatic pods showing sharp contacts with enclosing rocks occur over a strike length of 7 4 km in the biotite zone bortala formation in relatively low strain rocks of the western part of the valley plagioclase tremolite pods have replaced psammite or mica schist surrounding the terminations of buck quartz veins whereas in intensively sheared rocks to the east pods of medium to coarse grained massive tremolite commonly containing greater than 95 tremolite have replaced marble quartzite and psammite talc chlorite schists formed by dissolution of carbonates during shearing of marble are associated with some of the massive tremolite pods the direct relationship between structural domains and metasomatism suggests that migration of externally derived fluids was controlled by fractures and the shear zone the fluids having migrated along fractures interacted with wall rocks to produce plagioclase tremolite pods in the shear zone buck quartz veins some tremolite bearing show no obvious geometric relationship to massive tremolite pods it is postulated that the metasomatic fluids fluxed through shear domains and penetrated progressive shortening domains to replace the host rocks and form the massive tremolite pods both styles of metasomatic rocks developed from late s 2 to early s 3 during a progressive e w shortening event which corresponds to the regional metamorphism the metasomatic rocks represent only a small part of widespread metasomatism across the mt isa inlier

inferring surface currents within submerged vegetated deltaic islands and wetlands from multi pass airborne sar abstract water flow patterns across coastal and deltaic wetlands affect biogeochemical cycling denitrification organic carbon burial and coastal landscape evolution our understanding of such patterns across these important landscapes is incomplete however because of the inherent difficulty of conducting spatially and temporally dense ground or boat based surveys in shallow vegetated terrain we conducted an airborne l band synthetic aperture radar sar acquisition campaign on wax lake delta louisiana usa in may 2015 to investigate whether water velocities and flow patterns over kilometer scales can be determined from remote sensing thirteen sar flight lines over the delta region were acquired in 3 h with six different flight directions concurrently with a small boat campaign we show that sar azimuth displacement due to doppler shift can be used to estimate the surface water flow relative to the static and submerged vegetation interspersed on delta islands using a simple bragg wave scattering model and accounting for the bragg wave s free velocity and wind drift at wax lake delta we find that 0 40 m s water velocities within the main deltaic channels slow to 0 1 0 2 m s as flow spreads laterally across and converges within the vegetated islands coinciding with shallow

proterozoic low pressure high temperature metamorphism and an anticlockwise p t t path for the hazeldene area mount isa inlier queensland australia in the hazeldene area situated in the mount isa inlier queensland the metamorphic grade changes from chlorite zone through biotite and cordierite zones to sillimanite k feldspar zone microstructural studies of rocks near the sillimanite isograd demonstrate that cordierite grew early during the development of a steep foliation s2 was replaced by biotite andalusite and sillimanite at the metamorphic peak late in s2 and in turn by kyanite chlorite adjacent to localized small post d2 shear zones although the anticlockwise p t t path is well defined the precise p t conditions are uncertain because of problems with experimental and thermodynamic data the best estimate for the metamorphic peak for rocks close to the sillimanite isograd is around 600 c at 4 kbar the metamorphism has been dated at 1544 ma and was synchronous with a major crustal shortening event because proposed extensional events occurred more than 60 ma earlier their contribution to the peak metamorphic thermal perturbation would have been insignificant the syn metamorphic mica creek pegmatites the abundance of high heat producing elements in the nearby pre d2 sybella granite and advective heat by fluids which caused considerable metasomatism in the hazeldene area may have each contributed to the thermal budget however the metamorphic thermal gradient may be 80 c km 1 or higher strongly suggesting a local magmatic control as none are known in the area such syn metamorphic plutons would have to lie beneath the exposed high grade rocks

the synchronism of crustal thickening and high t low p metamorphism in the mount isa inlier australia 1 an example the central soldiers cap belt abstract in the soldiers cap group of the central eastern part of the early to middle proterozoic mount isa inlier tracing of mesoscopic structures has led to the recognition of an early nw closing fold nappe with an e w trending coaxially shortened frontal zone d1 folded around a n s trending upright syncline d2 an andalusite sillimanite prograde metamorphic event indicating a paleo geothermal gradient of approximately 50 c km occurred during early d2 times the coexistence of such moderately high paleo geothermal gradients and crustal thickening is common in the early to middle proterozoic mobile belts of northern australia crust mantle delamination has been suggested by etheridge et al 1987 to explain this coexistence here the thermal implications of this model and the additional thermal effects of waning crustal extension magmatic events and of the radioactive selfheating of the thickened crust are qualitatively discussed

topset dominated deltas a new model for river delta stratigraphy in the late 1800s g k gilbert provided the first stratigraphic description of river delta deposits but later work revealed that the gilbert type model long thought to be universal did not apply to all deltas here we propose that in addition to gilbert type deltas herein called foreset dominated there is a class of deltas with a basic first order stratigraphy that is topset dominated we develop a geometric model that predicts the occurrence of each delta type by calculating the topset and foreset thicknesses under different fluvial and basinal conditions our model predicts that topset dominated deltas have a novel characteristic their distributary channels commonly incise into pre delta sediment this type of delta should be common on shelves where the slope is less than 0 05 and the river feeding the delta has a discharge greater than 200 m 3 s field data from gulf of mexico deltas confirm the prediction that distributary channels often incise into pre delta sediment finally we propose a new stratigraphic model for topset dominated deltas and suggest that future stratigraphic interpretation must distinguish between delta types because the cause of channel incision for each is different and may be unrelated to allogenic changes

seismic wave propagation in alluvial basins and influence of site city interaction the geometrical and mechanical features of alluvial deposits have a major influence on seismic wave propagation and amplification however for alluvial basins located in densely urbanized areas the surface structures such as buildings could influence seismic wave propagation near the free surface in this article the influence of surface structures on seismic wave propagation is analyzed numerically in the case of an actual two dimensional 2d shallow basin at a local scale the vibration of a surface structure can induce a seismic wave field in the surficial soil layers at the scale of an alluvial basin the site city models considered herein show that the city effect can lead to a significant seismic wave field modification when compared to the free field case the coincidence between the fundamental frequencies of the soil layers and eigenfrequencies of the surface structures is a key parameter to investigate site city interaction when comparing simplified sitecity models kham et al 2006 to the basin city model the influence of the lateral heterogeneities on the site city interaction is found to be significant indeed the seismic wave field radiated by the city appears to be trapped within the alluvial basin and specific directivity features are found for this wave field the influence of site city interaction on the free field seismic hazard may then be significant the effects of the site city interaction are beneficial in some parts of the city or detrimental in other parts especially city boundaries these effects strongly depend on the urban configuration city heterogeneity building density etc finally the full characterization of the seismic wave field in densely urbanized areas could often raise the need for investigating site city interaction and consider such parameters as basin and city fundamental frequencies building density and city arrangement as well as basin effects combined with the seismic wave field radiated by the city

mount isa silica dolomite and copper orebodies the result of a syntectonic hydrothermal alteration system complex hydrothermal alteration system postdates deposition of the mount isa group and the lead zinc silver orebodies silica dolomite results from differential progressive metasomatic alteration of the entire range of microfacies constituting the lead zinc sequence the main components of this alteration are phyllosilicate development dolomitization and silicification this study concentrates on the latter two components and their role in breccia host formation all stages from incipient bedding and vein controlled alteration to total pervasive brecciation can be related to a deformational history of folding cleavage development and faulting a regional folding event d 2 formed the fold limb which constitutes the ore setting dolomite replacement veins and pseudobreccia complexes developed with varying intensity in favorable zones combinations of bedding and fracture controlled replacement continued until total dolomitization of the former shales occurred all forms and stages of dolomitic pseudobreccias are preserved by pseudomorphic quartz replacement in silicification zones which form the core of the orebody systems the separation in timing and mode of formation of lead zinc and copper orebodies is significant for exploration in the mount isa inlier the lead zinc mineralization appears to accumulate either syngenetically or at a very early stage in diagenesis but the copper has a structural control and a basic igneous association and is estimated to have been introduced at least 150 m y later modified journal abstract

characterization of river delta shorelines 1 coastline shape is among the basic geometric properties of the earth s surface yet defining and quantifying coastline shape precisely remains challenging here we propose new methods based on the dilation and erosion operators of mathematical morphology mm for the characterization of delta shorelines a class of open coasts we demonstrate the suitability of mm based methods for noise removal and shoreline identification from digital images of river deltas of varying geometric complexity we also show that a global a regional and a local shoreline parameter provide a first step in distinguishing among river wave and tidal dominated delta shapes

age constraints on the tectonothermal evolution of the selwyn zone eastern fold belt mount isa inlier the selwyn zone is characterized by multiple ductile deformation and metamorphic events there is general consensus that early in the isan orogeny there were both extensional and thrust events that produced bedding parallel foliation sbp we propose that these were followed by the d1 event that resulted in a regional steep east west foliation and that the snake creek anticline and the dominant s2a regional foliation formed as upright north south structures local overturning of d2 structures was due to subsequent localized deformation d2b that resulted in structures with flat lying axial planes d3 and d4 produced steep upright folds and crenulations with north northwest and northeast trending axial surfaces metamorphism largely controlled by the emplacement of mafic rocks is dominantly low pressure but the p t t path is complex early growth of cordierite m1 followed by andalusite was succeeded by a clockwise medium pressure loop of ca 500 600 mpa in the northern snake creek anticline as indicated by early d2a kyanite growth the metamorphic peak during d2 was around 580 c and 400 mpa at the sillimanite isograd and reached a maximum of around 670 c and 400 500 mpa in the migmatitic sillimanite k feldspar zone at the cannington and osborne mines previous age determinations for the metamorphic peak of 1580 1600 ma are confirmed with new electron microprobe dating of monazite whereas an age grouping of 1600 1630 ma may represent the d1 m2 event additional ages in the range 1640 1680 ma are recorded in albitites from the soldiers cap group and it is suggested that they formed by infiltration of hydrothermal fluids during extension and the emplacement of mafic sills this is supported by shrimp dating of zircon from a trondhjemite lens in a largely mafic sill complex in the snake creek anticline that provided an age of 1686 8 ma also indicating that at least part of the soldiers cap group is older than previously indicated a zircon shrimp age of 1527 4 ma was obtained for a sample of albitized saxby granite this age also represents the d4 m6 event and is the timing of the extensive brecciation and albitization of calc silicate rocks of the corella formation in the selwyn zone

isotopic and structural responses of granite to successive deformation and metamorphism within the sybella granite west of mount isa in northern australia differential response of u pb and rb sr isotopic systems to deformation metamorphism enables ages of emplacement and three discrete deformation metamorphic events to be determined based on zircon u pb systems two of the plutons were emplaced at 1671 pm 8 ma and 1668 pm 26 21 ma and the third at 1610 pm 10 ma a separate microgranite body gives aberrantly old u pb ages of up to 1780 ma due to partial inheritance of older zircon the three discrete deformation metamorphic events d 1 d 2 and d 3 occurred at 1610 pm 13 ma 1544 pm 12 ma and 1510 pm 13 ma respectively based on whole rock rb sr isotopic systems the youngest body was emplaced syntectonically and has possible significance to the origin of the mount isa ag pb zn orebodies homogenization of rb and sr isotopes via extensive syntectonic fluid migration associated with deformation partitioning and resultant solution transfer appears to have been

fluid channelling during ductile shearing transformation of granodiorite into aluminous schist in the tauern window eastern alps ductile shearing in the core of the tauern window austria transformed metagranodiorite into si undersaturated garnet chlorite staurolite schist at a depth of c 35 40 km during the alpine orogeny four distinct zones have been recognized extending from the wallrock into the centre of the shear zone zone i unaltered metagranodiorite with subordinate amphibolite zone ii biotite white mica garnet schist zone iii biotite phengite schist zone iv quartz absent garnet chlorite staurolite schist with garnets up to 10 cm across whole rock analyses show a dramatic decrease in sio2 from 65 wt in zone i to 35 wt in zone iv ca na and sr also decrease across the shear zone whereas al ti fe mg p cr ni zn and rb all increase towards zone iv mass balance calculations indicate that shearing was accompanied by up to 60 volume loss near the centre of the shear zone comparison of the tauern window samples with other shear zones in granitic hosts indicates that silica loss accompanied by gains in mg fe and ti is typical for volume loss shear zones but is distinctly different from the element behaviour exhibited in shear zones that are thought to represent approximately isovolumetric behaviour in the samples studied here volume loss appears to have resulted from channellized fluid flow during shearing producing time integrated fluid fluxes of 108 cm3 cm 2 in zone iv this large volume of fluid may have originated in part from dehydration of flysch carried beneath the metagranodiorites during eocene movement on the north penninic subduction zone development of an inverted thermal gradient during subduction would have allowed the fluid to scavenge large amounts of silica from the shear zone during ascent and heating

magmatic hydrothermal albite actinolite apatite rich rocks from the cloncurry district nw queensland australia abstract albite quartz actinolite apatite rich rocks with accessory titanite form a carapace that caps a small dome like intrusion of roxmere pluton and provide evidence of the accumulation and release of magmatic fluids that may have contributed to regionally extensive na ca alteration in the proterozoic cloncurry district australia the roxmere pluton was emplaced after the peak amphibolite facies metamorphism and into psammitic metasedimentary rocks that are stratigraphically younger and overlie the calc silicate rich mary kathleen group na ca hydrothermal assemblages closely spatially related to the roxmere pluton suggest that na ca alteration in this case is inconsistent with excepted up temperature metamorphic fluid circulation models the carapace rocks comprise two variants aplite and pegmatite both of which were affected by alteration and brecciation aplitic material predominates and the carapace has a brecciated top and a distinct textural zonation from an aplite rich pegmatite poor base to a relatively aplite poor pegmatite rich top this zonation is interpreted to represent the progressive accumulation of volatile phases toward the top of the carapace which culminated in fluid overpressuring and brecciation of the granitoid stock the convoluted and ptygmatic habit of the aplitic and pegmatitic material within the carapace is similar in nature to the comb quartz unidirectional solidification textures that are developed in the roof zones of some porphyry stocks these complex textures are interpreted to have formed from a single phase of fluid saturation the roxmere pluton or a deeper equivalent has a na mg and ca rich composition and a clinopyroxene amphibole rich mineralogy that is consistent with the formation of the contained albite actinolite apatite rich phases however the source of the rocks within the carapace is equivocal given that their contact relationships are obscured the 18 o composition of minerals within the carapace has the following ranges albite 7 1 8 7 actinolite 8 0 8 5 and quartz 8 9 11 4 albite and quartz 18 o equilibria suggest that these minerals in the pegmatitic and aplitic components formed at temperatures of 510 c to 540 c the calculated 18 o composition of a fluid in equilibrium with these minerals 6 0 to 8 0 at temperatures between 450 c and 550 c is consistent with a magmatic origin these estimated temperatures and 18 o fluid composition are comparable to estimates for regional na ca alteration in contrast d analysis of actinolite 136 to 150 within the carapace demonstrates that these fluids have a significantly lower d signature compared to na ca alteration assemblages associated with regional alteration 70 to 90 the low values in the carapace could either be interpreted as being produced from meteoric fluids or from degassed magmatic fluids although a meteoric fluid model is deemed improbable as meteoric fluids in the district have a documented d composition of ca 0 0 as a consequence an open system degassed magmatic hydrothermal fluid origin is considered to be the most plausible explanation for the low isotopic signatures and is also consistent with the complex textural relationships described within the carapace

fluvial and marine controls on combined subaerial and subaqueous delta progradation morphodynamic modeling of compound clinoform development 1 fluviodeltaic systems commonly display a compound clinoform geometry that consists of a subaerial subaqueous delta couplet the extent of subaqueous delta development varies significantly and in modern systems is a function of fluvial input and basin hydrodynamics we present a model of fluviodeltaic progradation in which the repeated occurrence of characteristic terrestrial floods and large coastal storms drives fluvial and shallow marine morphodynamics respectively we couple fluvial and shallow marine sediment dynamics via the surf zone which we collapse to a shock condition and treat as a moving boundary with steady sediment supply and sea level and simple basin geometry our model naturally develops prograding deltas with compound clinoform geometries the subaerial delta grows via fluvial aggradation and shoreface progradation whereas the subaqueous delta expands through foreset progradation with only minor topset aggradation the interplay of fluvial input with the wave current field controls the basic partitioning of sediment between subaerial and subaqueous deltas and by extension the compound clinoform geometry increasing the frequency or magnitude of coastal storms decreasing flood frequency or discharge and reducing grain size all increase the fraction of sediment delivered to the shallow marine environment and the extent of subaqueous delta progradation relative to subaerial delta development our model which emphasizes the intrinsic coupling of fluvial and shallow marine sediment dynamics and downplays the importance of allogenic fluctuations can explain many of the first order morphologic features of natural delta systems including significant lateral separation of the shoreline and clinoform rollover and differing rates of subaerial and subaqueous delta progradation

seismic site city interaction main governing phenomena through simplified numerical models this work focuses on the analysis of the multiple interactions between soil layers and civil engineering structures in dense urban areas submitted to a seismic wave to investigate such phenomena called site city interaction sci herein two simplified site city configurations are considered a homogeneous periodically spaced city and a heterogeneous nonperiodically spaced city both on a constant depth basin model these 2d boundary element method models are subjected to a vertically incident plane sh ricker wavelet a parametric study of the city parameters density of buildings and their natural frequencies and the thickness of the basin is carried out to characterize the sci and to investigate its sensitivity to some governing parameters the following parameters are analyzed building vibrations induced ground motion ground motion perturbations inside and outside the city spatial coherency and kinetic energy of the urban wave field a so called site city resonance is reached when the soil fundamental frequency and structure eigenfrequencies coincide building vibrations and ground motion are then significantly decreased and the spatial coherency of the urban field is also strongly modified building density and city configuration play a crucial role in the energy distribution inside the city

what controls the transition from confined to unconfined flow analysis of hydraulics in a river delta abstractrecent field work at the wax lake delta wld in coastal louisiana indicates lateral outflow from channels to islands upstream of the receiving basin in this region of the delta the flow t

a three dimensional simulation of seismic waves in the santa clara valley california from a loma prieta aftershock abstract the finite difference method is used to propagate elastic waves through a 3 d model of the santa clara valley an alluvium filled basin that underlies the city of san jose california the model was based on depth to bedrock information from water wells in the area the simulation corresponded to a region 30 east west by 22 north south by 6 depth km and contained about 4 million grid points synthetic seismograms from the simulation are accurate at frequencies up to 1 hz motions from a magnitude 4 4 aftershock of the loma prieta earthquake were modeled snapshots of ground motion and synthetic seismograms from the simulation are presented the simulation illustrates s to surface wave conversion at the edges of the basin and the large amplitude and long duration of ground motion in the basin compared to the surrounding rock love waves produced at the edge of the basin are the largest arrivals in the transverse synthetics because of the slow group velocity of the love waves sites near the center of the basin have longer durations of significant motions than basin sites near the valley edges sites near the center of the basin also show larger peak amplitudes on the transverse component array analysis of the synthetic seismograms indicates that love waves tend to propagate parallel to the eastern and western edges of the valley rayleigh waves are produced along the southern margin of the basin from incident s waves large radial motions occur where a rayleigh wave impinges on the northeast margin of the valley some rayleigh waves travel westward across the basin after being scattered from the eastern edge of the valley synthetic seismograms from the simulation have similar peak amplitudes as seismograms recorded by the sunnyvale dense array for this aftershock although the duration of the tranverse component is not matched by the synthetic seismogram using this basin model the simulation indicates that the love waves observed on the actual seismograms were produced by conversion of incident s waves at the southern margin of the santa clara valley 2 d simulations show how the s to love wave conversion is affected by the angle of incidence of the s wave and the sharpness of the velocity transition between the alluvium and bedrock as more accurate basin models are developed 3 d simulations should become valuable for predicting ground motions in sedimentary basins for future large earthquakes

controls on river delta formation insights from numerical modelling abstract primary hydraulic and sedimentary controls on river deltas were previously postulated in classification schemes in the field of sedimentary geology based on many field observations however detailed mechanistic models were restricted to the river dominated delta class analogous to the concept of morphological conditioning here we show that antecedent stratigraphy controls morphometrics of prograding river dominated delta distributary networks under steady sea level further we use coupled hydrodynamic morphodynamic stratigraphic detailed numerical modelling to assess the influence of wind generated waves and tides on clastic river delta formation our synthetic simulations show that deltas forming under mere riverine forcing prograde via sequences of mouth bar induced flow bifurcation and upstream channel shifting windwave action suppresses sequestration of fine sediments on the developing delta plain entailing relatively smooth shorelines perturbed by a limited number of distributary channels in contrast tide influenced river deltas are found to prograde mainly via lengthening of initially formed relatively stable distributaries as well as being characterized by cyclicity in deposits interbedding of sands and silts these results provide a framework for physics based river delta modelling under various environmental conditions particularly our findings suggest that relatively low energetic basin conditions can already significantly impact morphological and stratal patterns of prograding river deltas

backwater controls of avulsion location on deltas river delta complexes are built in part through repeated river channel avulsions which often occur about a persistent spatial node creating delta lobes that form a fan like morphology predicting the location of avulsions is poorly understood but it is essential for wetland restoration hazard mitigation reservoir characterization and delta morphodynamics following previous work we show that the upstream distance from the river mouth where avulsions occur is coincident with the backwater length i e the upstream extent of river flow that is affected by hydrodynamic processes in the receiving basin to explain this observation we formulate a fluvial morphodynamic model that is coupled to an offshore spreading river plume and subject it to a range of river discharges results show that avulsion is less likely in the downstream portion of the backwater zone because during high flow events the water surface is drawn down near the river mouth to match that of the offshore plume resulting in river bed scour and a reduced likelihood of overbank flow furthermore during low discharge events flow deceleration near the upstream extent of backwater causes enhanced deposition locally and a reduced channel fill timescale there both mechanisms favor preferential avulsion in the upstream part of the backwater zone these dynamics are fundamentally due to variable river discharges and a coupled offshore river plume with implications for predicting delta response to climate and sea level change and fluvio deltaic stratigraphy

identification of the scales of differential element mobility in a ductile fault zone two fundamentally different scales of element mobility have been identified in the upper amphibolite facies hunts brook fault zone of south central connecticut usa field relations mineral chemistry and 80 bulk rock analyses provide overwhelming evidence that the blastomylonitic schists and gneisses of the fault zone were derived from the enclosing granodioritic rope ferry orthogneiss two sample mass balance calculations between the rope ferry gneiss and fault rocks strongly suggest that the rope ferry gneiss was segregated into biotite rich schists and quartz plagioclase rich gneisses through the centimetre scale transfer of si al ca na ba and zr from schists to gneisses three and four sample mass balance calculations provide convincing evidence that al ca na and ba were lost and si and k gained by the entire fault zone both scales of metasomatism have been identified at two localities separated by 20 km implying that the metasomatic processes were pervasive throughout the fault zone from the mass balance calculations an apparent disparity in k mobility arises k appears to be gained by the entire fault zone but is immobile during the centimetre scale segregation this is because mass balance calculations can only detect differential element mobility differential element mobility requires that the mechanism of metasomatism produces chemical potential gradients therefore the identification of differentially mobile elements provides insight into the mechanisms of metasomatism the immobility of k during segregation of schists and gneisses implies that the segregation was not achieved through the extraction of partial melt however the element mobility is reconcilable with deformation driven metamorphic differentiation the gains of si and k and losses of ca na al and ba for the entire fault zone are also inconsistent with the intrusion or extraction of partial melt but may reflect the infiltration of a metasomatizing aqueous fluid

an image based method for shoreline mapping on complex coasts 1 the ready availability of satellite and other images of the earth together with increasing societal interest in coastal processes and morphology make it desirable to have a consistent way of defining and mapping shorelines from images the obvious choice the land water interface is inadequate because it includes the back sides of islands and the edges of river and tidal channels that are not directly exposed to open water on complex coasts inclusion of these portions of the land water interface would significantly affect quantitative measures of shoreline geometry here we propose a method to map shorelines consistently while accounting for ambiguity the opening anglemethod oam uses a visibility criterion to define the shoreline first a region of unambiguous open water is defined next the shoreline is defined as the locus of points for which the sum of viewing angles extending to open water unobstructed by land exceeds a specified critical value shorelines defined by the oam follow the land water interface where the shoreline is unambiguous and in more complex cases oam shorelines are consistent with the idea that the shoreline is that part of the land water interface that is directly exposed to open water

earthquake ground motion and structural response in alluvial valleys this paper is concerned with the problem of soil amplification and structural damage due to local site conditions in sedimentary valleys during earthquakes it focuses on a small valley in kirovakan for which 1d wave propagation analyses have failed to provide adequate answers for the large extent and spatial distribution of damage during the 1988 armenia earthquake a more realistic 2d finite element analysis is performed herein in search of an explanation of the observed behavior using as input an inferred rock accelerogram the response of the valley is calculated for a vertically incident sh wave synthetic accelerograms of the surface ground motion are presented for different sites these accelerograms are then used to determine the amplification ratios of the surface response with respect to that of the free field motion of the rock outcrop for different frequencies and for a continuous set of sites in addition response spectra are evaluated for simple oscillators representing structures located at various sites results of the 2d simulations show striking differences with respect to those from 1d analyses in particular 1 while the resonant frequencies exhibited by a 1d model for a given site also appear in the 2d model the peak ground response and structural response are almost twice as large for the 2d as for the 1d model 2 the 2d model exhibits in addition a new set of resonant frequencies and concomitant mode shapes across the valley which are directly related to its finite width and 3 due to these additional resonances the ground amplification ratio tends to oscillate very rapidly both spatially and with frequency leading to the observation that two identical structures located in the same vicinity or two slightly different structures located essentially on the same site can be subjected to significantly different seismic forces even if the underlying soils have very similar characteristics these results provide a meaningful explanation for the observed damage and thus serve to exemplify a situation in which site effects caused by the finite lateral extent of a valley must be taken into consideration in order to model satisfactorily seismic behavior

evidence for a regional scale fluid loss event during mid crustal metamorphism how fluid is released from the deep crust during metamorphism remains controversial whereas some authors advocate large scale fluid fluxes due to convective circulation of metamorphic fluid1 others consider that only one way flow is possible2 3 furthermore some flow models imply that fluid moves across and largely independently of sedimentary layering1 2 whereas many fluid based studies find evidence for focusing of flow by particular lithologies2 4 7 here we report a study of metamorphic fluid flow on a regional rather than an outcrop scale using a combination of field geology petrology and theoretical and isotope geochemistry we identify metasomatic lithologies at the top of a dolomitic marble unit which must have drawn in water over a kilometre scale from adjacent pelitic formations we suggest that this flow was part of a single major fluid loss event near the metamorphic peak fluid followed the metasomatic layers to structural highs where it broke out into adjacent schists to form skarns this fluid loss may have changed the rheology of the rock involved and terminated regional folding

thrusting and duplex formation at mount isa queensland australia large scale repetition of mount isa and haslingden group rocks in the anticline north of mount isa is interpreted as the core of a thrust duplex which has been subsequently folded parallel to the direction of thrusting displacement of mount isa group rocks above the duplex is extremely significant to the regional geology and exploration for more mount isa style pb zn and cu orebodies interpretation of the geometry of the thrust belt indicates thrusting on different stratigraphical levels below and above the duplex during its formation horses formed from a heelwards protruding footwall ridge instead of a trough and the complex effects on stratigraphical cross sections through duplexes of sloping lateral footwall ramps on horses

distributary channels and their impact on sediment dispersal a global analysis of world deltas with details from a natural and an anthropogenic influenced delta demonstrates how distributary channels control the flux of sediment into the coastal ocean the study addresses the range in the number of distributary channels across world deltas using remote sensing techniques a power law relationship is found between the number of distributary channels and the length of river and separately the delta gradient these relationships hold for all types of deltas whether controlled or strongly influenced by waves river discharge tides or ice permafrost or sea ice nature controlled deltas such as the klinaklini delta have distributary channels that act as overflow conduits that become active during flooding events anthropogenic controlled deltas like the po delta have distributary channels that are controlled for flood mitigation or low flow maintenance anthropogenic influences greatly impact the natural rate of delta progradation through changes in sediment supply controlling the position of distributary channels and impacting subsidence from gas and groundwater extraction even with flood controls the po delta traps 16 of the sediment load in its channels that are becoming super elevated at rates of 4 to 10 cm yr with respect to the delta plain a new model is formulated and shown to predict accurately the sediment flux through each channel along with their hydraulic properties deltas with high numbers of distributary channels produce hypopycnal plumes with reduced transport capacity as a result sediment diffuses out of the multi channel deltas as a buoyantly driven plume rather than as a momentum driven jet

stable isotopic evidence for large scale seawater infiltration in a regional metamorphic terrane the trois seigneurs massif pyrenees france oxygen isotopic analyses of 95 metamorphic and igneous rocks and minerals from a hercynian metamorphic sequence in the trois seigneurs massif pyrenees france indicate that all lithologies at higher metamorphic grades than the andalusite in isograd have relatively homogeneous 18o values the extent of homogenization is shown by the similarity of 18o values in metacarbonates metapelites and granitic rocks 11 to 13 and by the narrow range of oxygen isotopic composition shown by quartz from these lithologies these values contrast with the 18o values of metapelites of lower metamorphic grade 18o about 15 homogenization was caused by a pervasive influx of hydrous fluid mass balance calculations imply that the fluid influx was so large that its source was probably high level groundwaters or connate formation water hydrogen isotopic analyses of muscovite from various lithologies are uniform and exceptionally heavy at d 25 to 30 suggesting a seawater origin many lines of petrological evidence from the area independently suggest that metamorphism and anatexis of pelitic metasediment occurred at depths of 6 12 km in the presence of this water rich fluid the composition of which was externally buffered deep penetration of surface waters in such environments has been hitherto unrecognized and may be a key factor in promoting major anatexis of the continental crust at shallow depth three types of granitoid are exposed in the area the leucogranites and the biotite granite quartz diorite are both mainly derived from fusion of local paleozoic pelitic metasediment because all these rocks have similar whole rock 18o values 11 to 13 the post metamorphic biotite granodiorite has a distinctly different 18o 9 5 to 10 0 and was probably derived from a deeper level in the crust rare mafic xenoliths within the deeper parts of the biotite granite quartz diorite also have different 18o 8 0 to 8 5 and possibly represent input of mantle derived magma which may have provided a heat source for the metamorphism