modelling shoreface profile evolution current knowledge of hydro sediment and morpho dynamics in the shoreface environment is insufficient to undertake shoreface profile evolution modelling on the basis of first physical principles we propose a simple panel type model to map observed behaviour the internal dynamics are determined by slope dependent wave induced cross shoreface transports while the external driving factors are lateral sediment supply and sea level rise this model concept is tested with reasonable success against the observed behaviour of the central holland coast considering two hindcast periods one covering the evolution over the last century the other the subboreal subatlantic evolution a limitation of this model is that the cross shoreface dynamics are solely steered by the variations of shoaling short waves since a variety of other wave and current dynamics may be expected to be present in the coastal boundary layer it may well be that the effects of the mechanisms and conditions which are not represented are hidden in the coefficients of the sediment transport formula this limits the accuracy of the coefficients as used and our findings should be considered as an order of magnitude estimate only indeed behaviour oriented modelling implies that generalization of results to arbitrary situations and conditions is not straightforward yet we expect that some of the conclusions are more generally applicable this concerns the substantiation of the assumption that the upper shoreface responds on a much smaller time scale than the lower shoreface and the idea that the shoreface profile is not always and everywhere in equilibrium with its forcing a worthwhile observation from the holland coast application is that the bottom slope effect on the transport is only important at geological time scales the profile evolution at the engineering time scales say 10 to 100 years is effectively quasi static in that there is no feedback between the long term averaged transport and the state of the profile this implies that at these smaller scales the profile changes can be predicted on the basis of a static sediment balance this does not mean that the gravitational downslope transport is unimportant as a physical phenomenon in coastal profile evolution it is only unimportant if a highly aggregated model like this is applied at relatively short time scales

hydrodynamic analysis of storm movement effects on runoff hydrographs and loop rating curves of a v shaped watershed 1 the effects of storm movement on rainfall runoff processes through a v shaped watershed are investigated using a dynamic wave model based on shallow water equations the governing equations are solved by a fourth order accurate finite volume method to obtain accurate computational results once the numerical model is verified a series of rainfall runoff events on a v shaped watershed are simulated to investigate the contribution of each term in the depth averaged momentum equation a scale analysis and quantitative assessment are conducted on the basis of the computational results as a result it is found that the speed and the direction of storm movement can play an important role in determining peak discharge and peak arrival time in addition the storm movement can generate loop in the stage discharge relationship curve finally it is revealed that the rating curve depends on the watershed characteristics rather than the rainfall conditions at least in the idealized v shaped watershed

seismic discontinuities beneath the southwestern united states from s receiver functions abstract s receiver functions along the colorado plateau rio grande rift great plains transect known as la ristra in the southwestern united states have been utilized to map seismic discontinuities beneath this tectonically active region individual receiver functions were stacked according to ray piercing points with moveout corrections in order to improve the signal to noise ratio of the converted s to p phases a mantle discontinuity which is interpreted as the lithosphere asthenosphere boundary lab is observed along the profile with depth ranging from 80 km beneath the rio grande rift rgr to 100 km beneath the great plains gp and 120 180 km beneath the colorado plateau cp the shallow lab beneath the rio grande rift is indicative of lithosphere extension and asthenosphere upwarp the lab deepens sharply at the rgr cp and rgr gp boundaries providing evidence for edge driven small scale mantle convection beneath la ristra two local discontinuities beneath the southeastern colorado plateau are imaged at 250 km and 300 km and could be the top and base of the eroded lithosphere respectively the s receiver function images suggest that edge driven small scale convection is probably the mantle source for recent extension and uplift in the rio grande rift and the colorado plateau

determining shoreline response to sea level rise abstract the bruun rule is the most widely used method for determining shoreline response to sea level rise it assumes that the active portion of an offshore profile rises with rising sea level and the sand required to raise the profile is transported from the shoreline it is difficult to evaluate the efficacy of the bruun rule because sea level rise often has a lesser effect on shoreline change than that produced by sand sources sinks and longshore transport gradients in addition some shorelines have advanced seaward with rising sea level dean 1987 showed that equilibrium profile theory predicts that rising sea levels produce landward sand movement forced by nonlinear waves this paper presents an equation with terms representing all phenomena affecting shoreline change including bruun rule recession onshore sand transport sand sources and sinks and longshore transport gradients as an example of its use rates of onshore transport are determined along the 275 km florida southwest coast usa and a 19 km portion of this coast using known values for sand sources sinks and longshore transport gradients then future shoreline changes are projected for both coasts from 2015 to 2065 and for the southwest coast from 2015 to 2100 using sea level rise projections from the intergovernmental panel on climate change beach nourishment is shown to be a very effective adaptation strategy for sea level rise with shoreline change projections useful to estimate required rates of beach nourishment to counter sea level rise

sedimentology stratigraphy and geochronology of the proterozoic mazatzal group central arizona quartzite conglomerate and shale of the mazatzal group record the filling of a prot erozoic intra arc basin in central arizona u pb ages of zircons from rhyolite ash flow tuff indicate that deposition began at 1701 2 ma basal deposits of the newly defined pine creek conglomerate formed in an alluvial fan setting synchronous with the final phase of extrusive rhyolite volcanism and active faulting after volcanic activity ceased shallower slope braided stream environments developed in early deadman quartzite time subsequent marine transgression produced shallow subaqueous deposits of the upper part of the deadman quartzite these were overlain by prodelta sediments of the maverick shale indicating a phase of basin deepening finally the mazatzal peak quartzite was deposited as the basin shoaled again first to shallow marine and subsequently to fluvial conditions the quartzite is diagenetic quartz arenite originally deposited as lithic arenite and lithic arkose the provenance was initially restricted and earliest sediment was derived mainly from the subjacent red rock group when tectonic activity ceased how ever the surrounding highlands were planed down by erosion and detritus from a wider variety of source rocks was funneled into the basin this included contributions from arc related supracrustal rocks of the payson ophiolite and east verde river formation and finally a granitic basement input detrital quartz in the lower part of the mazatzal group is largely monocrystalline and volcanic in origin polycrystalline quartz associated with detrital feldspar and of probable continental affinity is concentrated in the uppermost parts of the sequence the life span of the intra arc basin was on the order of 30 m y from the formation of the payson ophiolite at 1 73 ga to the deposition of the upper mazatzal peak quartzite sometime after 1 70 ga the pre mazatzal red rock group represents the last stages of volcanic arc activity and the mazatzal group records the transition from orogenic to nonorogenic sedimentation in central arizona

towards columbia paleomagnetism of 1980 1960 ma surumu volcanic rocks northern amazonian craton abstract we present a paleomagnetic study on the well dated 1980 1960 ma u pb volcanic rocks from the surumu group northern roraima state amazonian craton after thermal and af demagnetization characteristic northwestern remanent magnetization chrm directions with downward inclinations were isolated mean d m 298 6 i m 39 4 95 10 1 n 20 k 11 4 which yielded a paleomagnetic pole sg located at 234 8 e 27 4 n a 95 9 8 magnetic mineralogy experiments show that chrm is carried by high hc and high unblocking temperature ti poor titanomagnetite and or hematite the well dated pole sg contributes to better define the apparent polar wander apw path for the guiana shield during the paleoproterozoic 2070 1960 ma comparison of the amazonian and west african craton s apw paths for the same time interval suggests that these cratonic blocks were linked together at about 1980 1960 ma ago in a paleogeography along which the guri guiana shield and sassandra west africa craton shear zones were aligned as previously proposed

shallow bias of paleomagnetic inclinations in the paleozoic and precambrian abstract an updated analysis of the global paleomagnetic database shows that the frequency distributions of paleomagnetic inclinations for the cenozoic and mesozoic eras younger than 250 ma are compatible with a random geographical sampling of a time averaged geomagnetic field that closely resembles that of a geocentric axial dipole in contrast the frequency distributions of paleomagnetic inclinations for the paleozoic and precambrian eras prior to 250 ma are over represented by shallow inclinations after discounting obvious secondary causes for the bias such as from data averaging sedimentary inclination error inhomogeneous lithological distributions and tropical remagnetization we show that the anomalous inclination distributions for the paleozoic and precambrian can be explained by a geomagnetic field source model which includes a relatively modest 25 contribution to the axial dipole from a zonal octupole field and an arbitrary zonal quadrupolar contribution the apparent change by around 250 ma to a much more axial dipolar field geometry might be due to the stabilization of the geodynamo from growth of the inner core to some critical threshold size a gross speculation which would imply that either the threshold size was rather large or the inner core nucleated rather late in earth history alternatively if a geocentric axial dipole model is assumed or can eventually be demonstrated independently the anomalous inclination distributions for the paleozoic and precambrian may reflect a tendency of continental lithosphere to be cycled into the equatorial belt perhaps because geoid highs associated with long term continental aggregates influence true polar wander

a review of the inferred geodynamic evolution of the dharwar craton over the ca 3 5 2 5 ga period and possible implications for global tectonics the geological history and evolution of the dharwar craton from ca 3 5 2 5 ga is reviewed and briefly compared with a second craton kaapvaal to allow some speculation on the nature of global tec

maximum level and time to peak of dam break waves on mobile horizontal bed this experimental study focuses the influence of bed material mobility and initial downstream water level on maximum water level and time to peak of dam break waves it covers horizontal bed conditions on fixed bed sand bed and pumice bed results include water surface level time evolution maxima wave levels and time to peak the influence of bed material mobility and downstream water level was identified and characterized stressing the importance of using mathematical models with appropriate sediment transport formulations instead of purely hydrodynamic models to simulate dam break waves on mobile bed channels

controls on precambrian sea level change and sedimentary cyclicity abstract although uniformitarianism applies in a general sense to the controls on relative and global sea level change some influences thereon were more prominent in the precambrian short term base level change due to waves and tides may have been enhanced due to possibly more uniform circulation systems on wide low gradient precambrian shelves the lack of evidence for global glacial events in the precambrian record implies that intraplate stresses and cyclic changes to earth s geoid were more likely explanations for third order sea level change than glacio eustasy higher heat flow in the earlier precambrian may have led to more rapid tectonic plate formation transport and destruction along with an increased role for hot spots aseismic ridges and mantle plumes superplumes all of which may have influenced cyclic sedimentation within the ocean basins a weak cyclicity in the occurrence of plume events has an approximate duration comparable to that of first order supercontinental cycle sea level change second order cyclicity in the precambrian largely reflects the influences of thermal epeirogeny changes to mid ocean ridge volume as well as to ridge growth and decay rates and cratonic marginal downwarping concomitant with either sediment loading or extensional tectonism third order cycles of sea level change in the precambrian also reflected cyclic loading unloading within flexural foreland basin settings and filling deflation of magma chambers associated with island arc evolution the relatively limited number of studies of precambrian sequence stratigraphy allows some preliminary conclusions to be drawn on duration of the first three orders of cyclicity archaean greenstone basins appear to have had first and second order cycle durations analogous to phanerozoic equivalents supporting steady state tectonics throughout earth history in direct contrast however preserved basin fills from neoarchaean palaeoproterozoic cratonic terranes have first and second order cycles of considerably longer duration than phanerozoic examples supporting less evolved tectonism affecting cratonic plates it is possible that oceanic tectonic realms underwent more rapid and dynamic plate movements and arc generation whereas early continental cratonic plates offered more stable platforms and may have been subject to slower migration rates the wide range of controls on precambrian sea level change allied to their apparent variability in rates and periodicity through precambrian time supports the conclusion that each order of cyclicity is relative and must be defined within the stratigraphic context of each individual case study this underlines the importance of establishing a hierarchical order of cyclicity in sequence stratigraphic interpretations of precambrian basins based on the relative importance of sequences rather than their temporal duration

the modified bruun rule extended for landward transport article i nfo the bruun rule bruun 1954 1962 provides a relationship between sea level rise and shoreline retreat and has been widely applied by the engineering and scientific communities to interpret shoreline changes and to plan for possible future increases in sea level rise rates the bruun rule assumes that all sand removed from the upper profile is deposited offshore as sea level rises although overwash during storms and landward aeolian transport clearly indicate otherwise herein we examine processes associated with sandy beach evolution in response to relative sea level rise and propose a modified form of the bruun rule that considers the full range of parsing cross shore transport from completely seaward to completely landward depending on the prevailing storm and surge conditions and whether there is a surplus or deficit of sand in the profile with respect to the equilibrium beach profile a methodology is proposed that more appropriately represents the long term processes and beach response however an improved quantitative understanding of landward transport is required for optimal application of the proposed method published by elsevier b v

allogenic controls on the evolution of storm to tidal shelf sequences in the early proterozoic uncompahgre group southwest colorado usa dominantly coarse grained shallow marine metasedimentary rocks of the early proterozoic uncompahgre group ug record periods of shoaling and drowning on different temporal scales that are attributed to episodic long term oscillations in relative sea level with superimposed shorter duration excursions in relative sea level long term events are probably tectonic whereas short term events are eustatic the 2 5 km thick uncompahgre group consists of 250 600 m thick dominantly coarse grained quartzite units q1 q4 and 200 300 m thick mudstone pelite units p1 p5 five depositional systems comprise the uncompahgre group the outer shelf system oss is composed of bouma type beds and intercalated mudstones that are transitional vertically to parallel laminated to wave rippled sandstones and hummocky cross stratified sandstones of the inner shelf system iss trough cross stratified sandstones comprise the shoreface system shs the tidal inner shelf shoreface system tis shs consists of a complex interlayering of cross bedded sandstones thin bedded conglomerates mudstones and rippled sandstones trough cross bedded pebbly sandstones and thin to thick bedded conglomerates represent the alluvial system alls depositional systems in the ug are associated in transgressive and highstand systems tracts that make up four sequences 1 to 4 sequence boundaries do not correspond with lithostratigraphic boundaries but are defined by subtle unconformities the basal q1 p1 unit lower sequence 1 consists of alls to tis shs to iss comprising a transgressive systems tract a maximum marine incursion is reflected by deposition of oss facies in stratigraphic units p1 p2 shoaling in the transition from p2 to the uppermedial portion of q2 oss iss shs to a thick tis shs alls records the highstand systems tract of upper sequence 1 a subtle disconformity paraconformity delineates a type 2 sequence boundary at the top of the highstand systems tract the drowning to shoaling pattern is replicated in sequence 2 upper q2 to p3 to upper medial q3 sequence 3 upper q3 to p4 to upper medial q4 and an incomplete sequence 4 upper q4 through p5 thinner shoaling intervals of oss iss shs in p3 and in lower q2 q3 and q4 represent parasequences sequences of 107 years duration are attributed to periods of increasing and decreasing subsidence rates due to tectonism marginal to the sedimentary basin parasequences record shorter duration temporal controls of c 104 to 105 years related to eustatic oscillations as a consequence of shoaling and aggradation progradation in the highstand systems tract tis shs and alls overlie and are temporally separated from oss to iss to shs this transition records filling of the basin to sea level leading to a shelf geometry that was conducive to tidal amplification a composite relative sea level curve integrating long term pulsatory subsidence and short term eustasy best explains the stratigraphic evolution of the uncompahgre group

phase change and thermal subsidence of the williston basin summary a mechanism of subsidence for the williston basin is proposed and tested the mechanism combines cooling and thermal contraction of the lithosphere with a phase transformation in the lower crust the cooling and the phase boundary movement following a sudden change in the thermal boundary condition at the base of the lithosphere are calculated isostatic adjustments and sea level variations are included to determine subsidence and sediment accumulation at the basin s centre which are compared with the data the subsidence record could not be explained by temperature boundary conditions the calculations show that 1 the heat flow boundary condition explains the long duration more than 350 myrs of subsidence of the williston basin and 2 the delay of the phase change subsidence about 40myrs explains an acceleration of subsidence in the early stages of the basin s evolution when isostatic adjustments and the effect of sea level variations are included the calculated sediment accumulation history fits well the sediment record of the williston basin

proterozoic farwell mountain lester mountain suture zone northern colorado subduction flip and progressive assembly of arcs this paper considers the amalgamation of arc and oceanic terranes to be the main mechanism of ca 1 8 1 6 ga continental crustal growth in southwestern laurentia on the basis of geologic and seismic reflection data and teleseismic images we propose the farwell mountain lester mountain suture zone as the northern most paleoproterozoic arc arc suture north dipping farwell mountain seismic reflections project from 18 km depths to the surface and are interpreted to represent conjugate thrusting as the 1 79 1 77 ga green mountain arc was partially underthrust beneath the archean craton we speculate that a north dipping high velocity mantle slab in the teleseismic image is a continuation of this thrust zone south dipping lester mountain reflections project from 22 km depths to the surface and are interpreted to be a thrust zone between the green mountain arc and the 1 76 1 72 ga rawah block surface features of the farwell mountain lester mountain suture zone are 1 marble chert rock with sillimanite pods ultramafic rocks sulfide deposits and pillow basalts which we interpret to be a dismembered accretionary complex 2 an axial planar fabric to north verging isoclinal folds f 2 which we interpret to be part of a north vergent fold and thrust system and 3 a metamorphic break between 500 c rocks to the north and 610 c rocks to the south which we attribute to reactivation of the zone movement on the farwell mountain backthrust is inferred to relate to cheyenne belt suturing at 1 78 1 75 ga we correlate suturing in the farwell mountain lester mountain suture zone to s 1 d 1 1 746 1 74 ga in the soda creek fish creek shear zone we attribute the complexity of this broad suture zone to initial conjugate thrusting plus overprinting and steepening of accretionary structures by subsequent tectonism

h2d morphodynamic model considering wave current and sediment interaction abstract a morphodynamic model for weakly dispersive wave and shallow flows in horizontal two dimensional h2d space is proposed the horizontal density variation and the bottom evolution are incorporated into a fully nonlinear boussinesq equation including vorticity effects by coupling the flow equation with the depth integrated sediment transport equation morphodynamic simulation is made possible a fourth order finite volume method with an approximate riemann solver is used to solve the governing equations for the hydrodynamic test under strong wave current interaction environment the accuracy of the computed velocity and water surface was verified for the three typical morphological benchmark tests such as tsunami regular wave and dam break flow good agreement was obtained when proper parameters were provided therefore the proposed morphodynamic model can be a useful tool for a wide range of shallow and wavy flows under dispersive and nonhydrostatic environments associated with wave current and sediment interaction

thermal evolution of the earth abstract models to study the thermal evolution of the earth have been developed based on a calculation of finite amplitude thermal convection in an incompressible and viscous mantle with temperature and pressure dependent physical parameters the lateral dependences of the variables are resolved through their spherical harmonic representations while the radial and time dependences are calculated using numerical procedures the major emphasis of this paper is to illustrate the effects of different factors on the thermal evolution of the earth rather than to present a definite earth model the main conclusions achieved in this study are 1 1 a significant portion of the present day temperature in the mantle and surface heat flux is due to initial heat of the earth resulting from accretion and core formation 2 2 since the effective rayleigh number of the earth s mantle is high solid state convection is found to be sufficiently efficient to maintain an almost adiabatic temperature gradient within the convecting region while large temperature gradients exist across the thermal boundary layers core mantle boundary and below the lithosphere 3 3 the convection is oscillatory with avalanche type properties this is due to the slow development of instability in the thermal boundary layer near the surface which causes the episodic behavior the periods of the oscillations are about 50 250 m y the oscillation in the mantle also induces periodic features in the surface heat flux and the thickness of the lithosphere mantle viscosity structure plays an important role in the cooling rate and nature of oscillations 4 4 the mobility of the lithosphere is an important factor controlling the thermal state of the earth s interior a mobile lithosphere will cool the interior faster

computational dam break hydraulics over erodible sediment bed this paper presents one of the first dedicated studies on mobile bed hydraulics of dam break flow and the induced sediment transport and morphological evolution a theoretical model is built upon the conservative laws of shallow water hydrodynamics and a high resolution numerical solution of the hyperbolic system is achieved using the total variation diminishing version of the second order weighted average flux method in conjunction with the hllc approximate riemann solver and superbee limiter it is found that a heavily concentrated and eroding wavefront first develops and then depresses gradually as it propagates downstream in the early stage of the dam break a hydraulic jump is formed around the dam site due to rapid bed erosion which attenuates progressively as it propagates upstream and eventually disappears while the backward wave appears to migrate at the same speed as over a fixed bed the propagation of the forward wavefront shows a complex picture compared to its fixed bed counterpart as a result of the domination of rapid bed erosion initially the density difference between the wavefront and the downstream ambient water in the intermediate period and the pattern of the deformed bed profile in the long term it is also found that the free surface profiles and hydrographs are greatly modified by bed mobility which has considerable implications for flood prediction the computed wave structure in the intermediate period exhibits great resemblance to available experiments qualitatively and yet the existence of a shear wave is found in lieu of a secondary rarefaction postulated in an existing analysis finally the use of the complete rather than simplified conservation equations is shown to be essential for correct resolution of the wave and bed structures which suggests that previous models need reformulating

shoreface sand supply to beaches the possibility of sand supply from the shoreface to beaches was evaluated based on a variety of methods involving field data and modeling results obtained from five coasts on three continents representing a wide range of coastal environments the field data include wave current measurements historical seabed soundings and geological surveys cross shore transport estimates from modeling on the annual time scale were compared against scaled down inferences from the seabed change and geological data the results are all consistent with there being net onshore transport over the long term from the lower shoreface to beaches in each of the environments these environments typify settings that occur commonly probably predominantly along the world s coasts so net shoreface sand supply to beaches may be a widespread and common but little appreciated factor in coastal stability the effect of this net supply is to offset other factors causing shoreline recession such as positive gradients in littoral transport moreover shoreline progradation occurs if sand supply from the shoreface dominates over littoral sediment losses implications are clearly significant for coastal engineering and coastal management despite the processes not being immediately apparent long term shoreface sand supply to beaches is masked by more rapid cyclical changes rates of shoreface sand supply to beaches indicated from various lines of evidence are typically on the order of 10 0 m 3 a 1 per meter of shoreline this volume corresponds to a lowering of the shoreface by only a few grain diameters per year

beach wizard nearshore bathymetry estimation through assimilation of model computations and remote observations article i nfo a data model assimilation method called beach wizard is presented with which the nearshore subtidal bathymetry can be accurately estimated based on video derived observations of wave roller dissipation and variation of the intertidal shoreline and or radar derived observations of wave celerity using many consecutive images these observed properties are compared with numerical model results and through a simple optimal least squares estimator approach the estimated bathymetry is adjusted gradually for each image in order to improve the fit between model output and observations the key advantages of the technique are that it is based on multiple sources of information i e different remote sensors and or data products depends on only a few free parameters to which the model results are insensitive and shows good skill herein the technique is applied to a synthetic case and two sets of field data from sites at duck nc usa and egmond the netherlands the method which may be extended with observations of other properties from other sources than the three described in this paper can deliver coastal state information i e simultaneous updates of bathymetry waves and currents with high temporal and spatial resolution and can be used in conjunction with or instead of in situ measured data

coupled and decoupled numerical modeling of flow and morphological evolution in alluvial rivers existing numerical river models are mostly built upon asynchronous solution of simplified governing equations the strong coupling between water flow sediment transport and morphological evolution is thus ignored to a certain extent an earlier study led to the development of a fully coupled model and identified the impacts of simplifications in the water sediment mixture and global bed material continuity equations as well as of the asynchronous solution procedure for aggradation processes this paper presents the results of an extended study along this line highlighting the impacts on both aggradation and degradation processes simplifications in the continuity equations for the water sediment mixture and bed material are found to have negligible effects on degradation this is however in contrast to aggradation processes in which the errors purely due to simplified continuity equations can be significant transiently the asynchronous solution procedure is found to entail appreciable inaccuracy for both aggradation and degradation processes further the asynchronous solution procedure can render the physical problem mathematically ill posed by invoking an extra upstream boundary condition in the supercritical flow regime finally the impacts of simplified continuity equations and an asynchronous solution procedure are shown to be comparable with those of largely tuned friction factors indicating their significance in calibrating numerical river models it is concluded that the coupled system of complete governing equations needs to be synchronously solved for refined modeling of alluvial rivers

crustal and upper mantle electrical conductivity structures in west africa geodynamic implications abstract measurements of the electrical and magnetic fields at the surface of the earth have been carried out in west africa in the period range 10 10 000 s in this area the method of magnetotelluric mt sounding finds its application in a variety of geological problems such as the deep shape of sedimentary basins the geometry of orogenic belts and craton deep structures the present article is an attempt to correlate the conductivity model with large scale tectonics mt surveys have revealed the presence of several areas where electrical resistivity is abnormally low at crustal and upper mantle depths and the existence of lateral electrical conductivity inhomogeneities within the lithosphere subsurface electrical conductivity distribution is in good relation with the geological features and its variation associated with lithological and structural changes a major discontinuity found at a depth of several hundred kilometers in the lithosphere separates two structural blocks the eastern one with higher resistivities being the west african craton the lithosphere derived from this work has a maximum thickness of 300 km under the senegalo mauritanian basin and more than 400 km beneath the craton the electrical asthenosphere is certainly not well developed under the craton a sketch of electric structures across west africa is presented and a geodynamic interpretation is proposed to explain the present structural pattern of the southern segment of the mauritanides belt

crust mantle interaction in continental arcs inferences from the mesozoic arc in the southwestern united states arc magmas ranging in composition from basaltic andesites to rhyolites and intrusive equivalents were emplaced into the western margin of the north american craton starting in late triassic time giving way to rift0related sedimentation in the late jurassic the region of this study cuts across proterozoic basements of contrasting nd model ages 1 7 1 8 ga average nd 11 in eastern arizona and 2 0 to 2 3 ga average nd 18 in western arizona and eastern california bennett and depaolo 1987 the mesozoic rocks have initial nd of 3 4 to 6 4 in the eastern part of the study area and 7 1 to 9 2 in the western part all of the rocks have elevated 87sr 87sr initial ratios 0 706 trends in initial nd values of mesozoic arc rocks are directly correlated with the nd model ages of the basement through which they passed simple two component mixing calculations indicate that recycled continental crust in the arc magmas represents on average about 65 a minimum of 35 mantle input into continental arc magmas as recent as the mesozoic represents a significant contribution to the growth of the continental crust in the absence of a return flow of continental material into the mantle of similar magnitude in a detailed study in the santa rita mountains arizona there is a pattern of increase of nd with time early basaltic andesites have more negative nd than later felsic rocks a correlated pattern of depletion with time is also observed with trace element and major element data we attribute this either to progressive hybridization of the lower crust by repeated injection of mantle magmas or the progressive thinning of the continental crust during prolonged arc magmatism the present data do not allow distinction between the two models progressive decrease in crustal contribution to arc magmas with time may be an important feature of continental arc evolution hybridization of the lower crust due to repeated injection of mantle melts during arc magmatism may help contribute to small scale heterogeneities in lower crust inferred from seismic and xenolith data similarly whether there is a well defined moho or sharp crust mantle boundary in any given segment of the continental crust may in part depend on the extent of crust modification as a result of continental arc magmatism

early proterozoic oceanic crust in the northern colorado front range implications for crustal growth and initiation of basement faults 1 early proterozoic oceanic crust exposed in a shear zone in the northern colorado front range provides insight into the tectonic evolution of the colorado province tectonically intermingled mylonitic amphibolite locally pillowed metagabbro clinopyroxenite metachert and melange are preserved within the buckhorn creek shear zone west of fort collins whole rock geochemical data support formation of the igneous protoliths in an oceanic environment major and trace element data overlap samples from modern oceanic ridges and are distinct from modern arc trends metagabbros and clinopyroxenites preserve a subhorizontal lineation defined by igneous pyroxenes core and mantle microstructures indicate initial deformation at temperatures 900 c secondary amphiboles define both subhorizontal and subvertical lineations kinematic analysis indicates that the rocks experienced e w strike slip deformation prior to and during amphibolite facies metamorphism followed by n s shortening 40ar 39ar data from secondary hornblende yield age steps as old as 1 9 ga based on the chemical data and kinematic evidence for strike slip deformation we propose that the buckhorn creek rocks originated at an oceanic ridge transform intersection the high t pyroxene fabrics formed during ocean floor deformation prior to 1 7 ga regional deformation of the colorado province the buckhorn creek fragment likely represents original oceanic basement for 1 8 1 7 ga arc magmatism and sedimentation that ultimately formed the colorado province continental crust reactivation of original oceanic fracture zones may be responsible for the network of regularly spaced northeast trending shear zones in colorado once formed subvertical transform faults are likely to survive the transition from oceanic to continental crust and persist as long lived crustal discontinuities

laboratory investigation of the bruun rule and beach response to sea level rise abstract rising sea levels are expected to cause widespread coastal recession over the course of the next century in this work new insight into the response of sandy beaches to sea level rise is obtained through a series of comprehensive experiments using monochromatic and random waves in medium scale laboratory wave flumes beach profile development from initially planar profiles and a 2 3 power law profile exposed to wave conditions that formed barred or bermed profiles and subsequent profile evolution following rises in water level and the same wave conditions are presented experiments assess profile response to a step change in water level as well as the influence of sediment deposition above the still water level e g overwash a continuity based profile translation model ptm is applied to both idealised and measured shoreface profiles and is used to predict overwash and deposition volumes above the shoreline quantitative agreement with the bruun rule and variants of it is found for measured shoreline recession for both barred and bermed beach profiles there is some variability between the profiles at equilibrium at the two different water levels under these idealised conditions deviations between the original bruun rule the modification by rosati et al 2013 and the ptm model predictions are of the order of 15 and all these model predictions are within 30 of the observed shoreline recession measurements of the recession of individual contour responses such as the shoreline may be subject to local profile variability therefore a measure of the mean recession of the profile is also obtained by averaging the recession of discrete contours throughout the active profile the mean recession only requires conservation of volume not conservation of profile shape to be consistent with the bruun rule concept and is found to be in better agreement with all three model predictions than the recession measured at the shoreline

brittle creep in basalt and its application to time dependent volcano deformation time dependent brittle deformation is a fundamental and pervasive process operating in the earth s upper crust its characterization is a pre requisite to understanding and unraveling the complexities of crustal evolution and dynamics the preferential chemical interaction between pore fluids and strained atomic bonds at crack tips a mechanism known as stress corrosion allows rock to fail under a constant stress that is well below its short term strength over an extended period of time a process known as brittle creep here we present the first experimental measurements of brittle creep in a basic igneous rock a basalt from mt etna volcano under triaxial stress conditions results from conventional creep experiments show that creep strain rates are highly dependent on the level of applied stress and can be equally well fit by a power law or an exponential law with a 20 increase in stress producing close to three orders of magnitude increase in creep strain rate results from stress stepping creep experiments show that creep strain rates are also influenced by the imposed effective confining pressure we show that only part of this change can be attributed to the purely mechanical influence of an increase in effective pressure with the remainder interpreted as due to a reduction in stress corrosion reactions the result of a reduction in crack aperture that restricts the rate of transport of reactive species to crack tips overall our results also suggest that a critical level of crack damage is required before the deformation starts to accelerate to failure regardless of the level of applied stress and the time taken to reach this point the experimental results are discussed in terms of microstructural observations and fits to a macroscopic creep law and compared with the observed deformation history at mt etna volcano c 2011 elsevier b v all rights reserved

models of aftershock occurrence summary the omori formula for aftershock activity can be shown to be a consequence of each of two models of a complex earthquake in the first case aftershocks are assumed to be caused by subsequent slip on asperities of a fault which are locked during the fracture in the main shock in the second aftershocks are caused by catastrophic coalescence of nearby small fractures with the fracture surface of the main shock hence the first source model describes aftershock activity in the interior of a main shock rupture zone while the second describes aftershock activity near the outer boundary of a main shock rupture zone stress corrosion cracking is assumed to be the physical cause of the quasistatic growth of the main fracture zone at the expense of the area of the locked patches in the first model and is also the cause of the growth of the small satellite fractures in the second

isotopic geochemical and temporal characterization of proterozoic basement rocks in the quitovac region northwestern sonora mexico implications for the reconstruction of the southwestern margin of laurentia a detailed geochemical characterization of 19 representative proterozoic basement rocks in the quitovac region in northwestern sonora mexico has identified two distinct paleoproterozoic basement blocks that coincide spatially with the previously proposed caborca and north america blocks new u pb zircon geochronology revises their age ranges the caborca 1 78 1 69 ga and north america 1 71 1 66 ga blocks at quitovac and precludes a simple age differentiation between them in addition grenvillian age granitoids ca 1 1 ga spatially associated with the caborca block have been identified at quitovac nd isotopes and major and trace element geochemistry support the distinction of these paleoproterozoic blocks granitoids of the north america block are characterized by depleted end values 3 4 3 9 and younger nd model ages 1800 1740 ma and have lower k 2 o y rb ba th ree and fe mg values than coeval rocks of the caborca block the caborca block granitoids are likewise characterized by slightly less depleted end 0 6 2 6 and older nd model ages 2070 1880 ma despite the subtle differences granitoids from both the caborca and north america blocks exhibit island arc like affinities we propose that the proterozoic basement rocks from the quitovac region are an extension of the proterozoic crustal provinces in the southwestern united states specifically rocks of the caborca block exhibit an affinity to rocks of either the yavapai province or the mojave yavapai transition zone whereas rocks of the north america block have signatures similar to those of the mazatzal province or possibly the yavapai province of arizona the new isotopic ages and geochemical data do not support the existence of the late jurassic mojave sonora megashear at quitovac as originally proposed however the quitovac region accounts only for a small fraction of the proterozoic basement in sonora so these findings do not eliminate the possibility of a megashear elsewhere in northern sonora our new data create the possibility of alternative hypotheses for the distribution of paleoproterozoic crustal provinces in southwestern north america that affect reconstructions of the original southwestern margin of laurentia and reduce uncertainties in the configuration timing and existence of the proterozoic supercontinent rodinia

paleomagnetism and tectonic evolution of the pan african damara belt southern africa paleomagnetic results are reported from the nosib otavi and mulden groups of the damara supergroup a late precambrian shelf sequence on the southern margin of the congo craton in namibia three magnetizations were isolated in the nosib group samples in order of decreasing blocking temperature they are nq1 n 6 sites 28 n 323 e 95 15 nq2 n 7 sites 51 s 213 e 95 12 and nq3 n 13 samples 09 n 295 e 95 13 overall precision of all three magnetizations upon tectonic correction suggests that they predate pan african 650 450 ma folding two magnetizations were isolated in the otavi group samples above the nosib in stratigraphic sequence the dc1 component of possible prefolding age n 4 sites 52 s 186 e 95 35 has been over printed by the dc2 magnetization n 10 sites 55 s 044 e 95 15 of probable postfolding age a single magnetization of probable pre folding age was isolated in the overlying mulden group samples n 6 sites 12 s 090 e 95 16 together with previously published paleomagnetic data from africa the new data showed that no great relative movements have occurred between the congo and kalahari cratons during the interval of pan african tectonism in the damara belt mcelhinny and mcwilliams 1977 continental collision preceded by large relative displacements and closure of a wide ocean e g a himalayan analog is effectively ruled out for the damara belt we develop an alternative model consistent with the available paleomagnetic and geologic data which invokes rifting heating and stretching of the lithosphere underneath the damara belt followed by delamination of the subcrustal lithosphere hot asthenospheric material rises to take the place of the detached and sinking lithospheric base inducing subduction and interstacking of continental crust the much thickened continental crust is partially melted at depth intruded by synorogenic and postorogenic granites and finally uplifted and eroded to its present level of exposure the model is compatible with plate tectonics in that the development of the damara belt can be broadly compared with modern marginal seas with the exception that stretching of the lithosphere was not induced by secondary convection above a downgoing slab possible causes for stretching are rising mantle plumes or intracontinental distortion within the pre damara african plate

mantle flow and lithosphere asthenosphere coupling beneath the southwestern edge of the north american craton constraints from shear wave splitting measurements abstract high quality broadband seismic data recorded by the usarray and other stations in the southwestern united states provide a unique opportunity to test different models of anisotropy forming mechanisms in the vicinity of a cratonic margin systematic spatial variations of anisotropic characteristics are revealed by 3027 pairs of splitting parameters measured at 547 broadband seismic stations the western and southern edges of the north american craton show edge parallel fast directions with larger than normal splitting times and the continental interior is characterized by smaller splitting times and spatially consistent fast directions that are mostly parallel to the absolute plate motion direction of north america at the majority of the stations no significant systematic azimuthal variations of the splitting parameters are observed suggesting that a single layer of anisotropy with a horizontal axis of symmetry can adequately explain most of the observations the spatial coherency of the splitting parameters indicates that the observed anisotropy is likely caused by shearing between the partially coupled lithosphere and asthenosphere based on previous results of seismic tomography and geodynamic modeling we propose a model involving deflecting of asthenospheric flow by the cratonic root as the cause of the observed edge parallel fast directions and large splitting times along the western and southern edges of the north american craton

a grenville age layered intrusion in the subsurface of west texas petrology petrography and possible tectonic setting the nellie intrusion is a thick more than 4420 m mafic to ultramafic layered intrusion with a radiometric age of 1163 ma rock types change abruptly with stratigraphic height and include norite pyroxenite gabbronorite hornblende gabbro gabbro anorthosite harzburgite and lherzolite norite is most abundant but gabbro and hornblende gabbro are locally abundant rare olivine rich layers are also present the general order of crystallization was olivine orthopyroxene plagioclase clinopyroxene and hornblende mg s expressed as 100 mg mg fe range from 76 3 to 85 8 for olivine 56 7 to 84 9 for orthopyroxene 62 5 to 90 3 for clinopyroxene and 52 4 to 82 8 for amphibole mg s vary with height and display abrupt reversals which indicate open system addition of new mafic magma eleven cyclic units were identified on the basis of evidence for injection of basaltic magma these can be grouped into three megacyclic units the abundance of orthopyroxene and mineral compositional evidence for

riemann wave description of erosional dam break flows this work examines the sudden erosional flow initiated by the release of a dam break wave over a loose sediment bed extended shallow water equations are formulated to describe the development of the surge accounting for bed material inertia a transport layer of finite thickness is introduced and a sharp interface view of the morphodynamic boundary is adopted approximations are sought for an intermediate range of wave evolution in which equilibration of the sediment load can be assumed instantaneous but momentum loss due to bed friction has not yet been felt the resulting homogeneous hyperbolic equations are mathematically tractable using the riemann techniques of gas dynamics dam break initial conditions give rise to self similar flow profiles the wave structure features piecewise constant states two smoothly varied simple waves and a special type of shock an erosional bore forming at the forefront of the wave profiles are constructed through a semi analytical procedure yielding a geomorphic generalization of the stoker solution for dam break waves over rigid bed for most flow properties the predictions of the theoretical treatment compare favourably with experimental tests visualized using particle imaging techniques

kinematic significance of l tectonites in the footwall of a major terrane bounding thrust fault klamath mountains california usa abstract detailed geologic mapping cross section reconstructions strain analyses and kinematic analyses enable the reconstruction of a one kilometer wide domain of l tectonites in the east west striking subhorizontal to gently south dipping pigeon point high strain zone pphsz associated with a major thrust fault separating oceanic and arc affinity terranes in the klamath mountains california l tectonites are associated with 1 a convex upward warp of the upper high strain zone boundary 2 a transition from mafic metavolcaniclastic rocks to micaceous quartzites 3 folds subparallel with mineral lineations 4 emplacement of synkinematic ultramafic mafic intrusive bodies and 5 a local temperature increase from greenschist to amphibolite facies conditions pure shear dominated deformation accommodated zone normal shortening and transport parallel elongation coupled with subordinate top to the west directed thrust style simple shear l tectonite formation was controlled by the shape of the high strain zone boundary driving lateral flow into the apex of the lens shaped zone in response to a favorable kinematic geometry and bulk strain in the constrictional field localized magmatic heating best explains the shape of the high strain zone boundary but l tectonites are not partitioned into a single rheological domain during terrane amalgamation strain path partitioning occurred with localized top to the west directed simple shear partitioned into a structurally overlying thrust zone and pure shear dominated subvertical shortening and transport parallel elongation partitioned into the pphsz

petrological evolution of the crust and mantle in its simplest form crust mantle evolution can be thought of as a study of the processes by which material is lost from the mantle and forms new crust the overall goal is achievement of mass balance between the average composition of material known to have been added to the crust and the estimated average composition of the entire crust attainment of this goal for the earth has been elusive primarily because the materials available for study have generally been involved in several stages of evolution including fractionation within both the crust and mantle and recycling of material from crust to mantle thereby complicating the interpretation of available data although the overall composition of the continental crust generally has been modelled as andesitic taylor and mclennan 1981a the present upper continental crust is granodioritic and requires a more mafic lower crust it has been proposed taylor and mclennan 1981a that originally the archean crust had an andesitic composition throughout its volume and that partial melting in the lower crust developed more felsic melts that rose to enrich the upper crust leaving a more mafic residuum of lower crust this concept has been challenged by weaver and tarney 1981a who argue that the granulites of presumed lower crustal origin do not have the correct compositions for this model if one considers more recent additions to the crust from the mantle over the past several hundred million years it appears that these latest additions are basaltic with very little if any granitic additions in fact barker 1981 in his introduction to a special issue of jgr on granites and rhyolites states to date no one has demonstrated that such magmas may form in the mantle indeed much experimental and geochemical work indicates that such siliceous liquids cannot originate there therefore such magmas must be generated in the crust in island arc environments where the average composition of added material normally is thought to be andesitic a anderson 1982 has shown that the parent melt is basaltic not andesitic in addition kay 1980 has shown that the k content of the newly added material is less than the average k content of the previously existing crust in the oceanic crust the additions from the mantle are basaltic and according to o hara 1982 probably are derived from very mafic picritic melts as parents continental flood basalts which have also added material from mantle to crust also are clearly derived from basaltic parental melts basaltic volcanism study project 1981 thus the evidence for the nature of material subtracted from the mantle and added to the crust for the past several hundred million or perhaps a billion years points to very mafic melts this contrasts significantly with the overall andesitic composition of continental crust it implies furthermore that if the overall archean crustal composition was andesitic as estimated by taylor and mclennan 1981a then additions to the crust have become more mafic with time a concept in direct conflict with most models in which secular trends are from mafic to felsic with time veizer and jansen 1979 and mclennan et al 198o a question which is beginning to appear either explicitly or implicitly is whether crustal volcanic rocks or the crust as a whole really represents the parent melt that formed in the mantle a anderson 1982 o hara 1982 and nisbet and walker 1982

high resolution finite volume method for shallow water flows a high resolution time marching method is presented for solving the two dimensional shallow water equations the method uses a cell centered formulation with collocated data rather than a space staggered approach spurious oscillations are avoided by employing monotonic upstream schemes for conservation laws muscl reconstruction with an approximate riemann solver in a two step runge kutta time stepping scheme a finite volume implementation on a boundary conforming mesh is chosen to more accurately map the complex geometries that will occur in practice these features enable the model to deal with dam break phenomena involving flow discontinuities subcritical and supercritical flows and other cases the method is applied to several bore wave propagation and dam break problems

novel numerical approach for 1d variable density shallow flows over uneven rigid and erodible beds abstractthe numerical modeling of hyperconcentrated shallow flows is a challenging task because they exhibit special features such as propagation over dry beds profound bed elevation modifications owing to erosion or deposition phenomena and flow discontinuities in this paper a novel depth positivity preserving harten lax and van leer contact hllc riemann solver is devised in order to approximate the solution of the riemann problem for the 1d one dimensional hyperconcentrated shallow flows equations over horizontal beds the solver is used as a building block for the construction of hyperconcentrated shallow flows hcsf a well balanced finite volume scheme for the solution of the hyperconcentrated shallow flows equations with variable elevation hcsf is able to handle the case of dry beds to take into account the variability of the topography also in the presence of bed discontinuities considering the flow resistance and the mass exchange between the flowing mixture and the mobile bed the

early proterozoic assembly of tectonostratigraphic terranes in southwestern north america a 500 km wide early proterozoic orogenic belt in arizona and adjacent areas is divided into lithotectonic blocks by northeast and north trending shear zones structural and u pb zircon studies suggest that these blocks may have experienced different tectonic histories prior to their juxtaposition by thrust and strike slip movements on shear zones a northwestern province here called the yavapai province is composed of at least five tectonic blocks and was assembled at about 1700 ma a southeastern province here called the mazatzal province is composed of at least three blocks and was assembled and juxtaposed with the northwestern province during the mazatzal orogeny between 1695 and 1630 ma the diversity of seemingly incompatible 1700 ma tectonic regimes now in close proximity to each other and the absence of systematic cross strike changes in age and character of deformation plutonism and metamorphism suggest a model whereby the orogenic belt developed and north america grew by assembly of d

characteristics and geological setting of synkinematic svecokarelian granitoids in southern finland abstract synkinematic granitoids are the predominant component of the svecokarelian crust their zircon u pb ages vary from 1900 to 1860 ma mainly 1890 1870 ma being roughly similar to those of mafic plutonic rocks and metavolcanic rocks synkinematic granitoids occur as distinct plutons in schist belts and also form the granitold complex of central finland with a total area in excess of 35 000 km2 the granitoids in schist belts occur as concordant plutons although locally they have cross cutting contacts and they crystallized soon after the peak of major regional deformation and metamorphism but before younger deformation phases they are composed of granodiorites tonalites and trondhjemites composite plutons are often zoned with gabbro diorite tonalite and or trondhjemite at their margins and with granodiorite and less commonly granite at their centres the granitoid complex of central finland is composed of a vast number of intrusions ranging in composition from gabbro to granite the granite intrusions comprising large parts of the complex coarse grained granitoids and polyphase deformation are common major minerals of the synkinematic granitoids are plagioclase potassium feldspar quartz biotite and hornblende typical accessories are sphene apatite magnetite and zircon whole rock analyses of 143 granitoids from throughout southern finland show calc alkaline characteristics with variable sio2 high na2o k2o and a cnk below 1 1 initial 87sr 86sr ratios are low the granitoid complex of central finland has higher feo mgo and k2o na2o than the granitoids in schist belts irrespective of silica content the synkinematic granitoids have the geological and geochemical characteristics of phanerozoic i type granitoids and are cogenetic with mafic plutonic rocks intrusion of these latter evidently caused major remelting in the lower crust giving rise to granitoid magmas so that a variable mixing of mantle derived and crustal magmas is probable according to nd isotopes studies archaean material was insignificant in the source of the granitoids except near the border zone of the archaean craton this indicates rapid recycling of material newly derived from the mantle geochemical features of the granitoid complex may also reflect a thicker crust in central finland than in surrounding areas during the generation of the granitoids many characteristics of the synkinematic granitoids strongly suggest a subduction related origin however the similarity in isotopic ages and lack of obvious linear trends in distribution of rock types combined with evidence for a minor older crustal component in their source indicates that the processes were not identical to those operating at modern continental margins

crustal growth in southern arizona u pb geochronologic and sm nd isotopic evidence for addition of the paleoproterozoic cochise block to the mazatzal province terranes composed of arc related igneous and sedimentary rocks were accreted onto the continental margin of southwestern north america from 1 9 to 1 6 ga they formed the yavapai mazatzal province in arizona of which the so called pinal schist and associated rocks in southeastern arizona form an integral part 148 u pb analyses on magmatic and detrital zircons were performed on 21 samples to constrain timing of geologic events in paleoproterozoic time in the area of southeastern arizona 25 sm nd whole rock analyses were made to infer sources of sedimentary and igneous rocks our results allow us to delineate a suture zone between the pinal tectonostratigraphic unit pinal block which consists primarily of basinal metaturbiditic rocks and a southeastern allochthonous juvenile volcano sedimentary domain the location of the suture is constrained by lithologic contrast across the boundary an increase in age of detrital zircons a marked decrease of end t and an intervening subduction complex swift and force this issue we propose the name cochise block for the southeastern part because it represents a faultbound allochthonous tectonic unit in the cochise block we document volcanic activity from about 1630 to 1647 ma quartzitic sedimentary rocks were largely derived from almost contemporaneous volcanic rocks and show detrital zircon ages from 1630 to 1729 ma with the majority 85 percent between 1630 to 1674 ma quartzites and intermediate to felsic metavolcanic rocks show a tight cluster of end t values 2 9 3 8 close to the depleted mantle model and therefore represent juvenile additions to the crust post tectonic metabasalts with end 1500 4 5 are interpreted as being derived from a depleted upper mantle source around 1 5 ga in the pinal block detrital zircons yield values from 1678 to 1731 ma end t values of metapelites and wackes range from 0 2 to 2 3 values decrease from southeast to northwest indicating progressive input of more evolved material toward the craton our data suggest that sedimentation within the pinal block was proximal to the continental margin and occurred later than 1 68 ga and ended before the intrusion of granitoids at 1 65 ga we show that the north american crust grew rapidly and progressively by addition of juvenile but evolved metavolcanic arc rocks and derived quartz rich metasedimentary rocks as documented in the cochise block timespans between depleted mantle model age and zircon crystallization on the order of 50 my attest to rapid crustal processing during this significant time of crustal growth

shear wave splitting and mantle flow beneath the colorado plateau and its boundary with the great basin shear wave splitting measurements from sks and skks phases show fast polarization azimuths that are subparallel to north american absolute plate motion within the central rio grande rift rgr and colorado plateau cp through to the western rim of the cp with anisotropy beneath the cp and central rgr showing a remarkably consistent pattern with a mean fast azimuth of 40 6 e of n approaching the rim from the southeast fast anisotropic directions become north northeast south southwest nne ssw rotate counter clockwise to north south in the cp gb transition and then to nnw sse in the western great basin gb this change is coincident with uppermost mantle s wave velocity perturbations that vary from 4 beneath the western cp and the eastern edge of the marysvale volcanic field to about 8 beneath the gb corresponding delay times average 1 5 sec beneath the central cp decrease to approximately 0 8 sec near the cp gb transition and increase to about 1 2 sec beneath the gb for the central cp we suggest anisotropy predominantly controlled by north american plate motion above the asthenosphere the observed pattern of westward rotating anisotropy from the western cp through the cp gb transition may be influenced to asthenospheric flow around a cp lithospheric keel and or by vertical flow arising from edge driven small scale convection the anisotropic transition from the cp to the gb thus marks a first order change from absolute plate motion dominated lithosphere asthenosphere shear to a new regime controlled by regional flow processes the nnw sse anisotropic fast directions of split sks waves in the eastern gb area are part of a broad circular pattern of seismic anisotropic fast direction in the central gb that has recently been hypothesized to be due to toroidal flow around the sinking juan de fuca gorda slab

back arc spreading in the proterozoic a theoretical approach abstract the early proterozoic earth probably had a hotter mantle and a lower residence time for oceanic plates at the surface than the modern one the hotter mantle may have led to thinner oceanic plates young ocean floor has low negative buoyancy and therefore exerts low slab pull forces in subduction zones this effect would have been greater if the plates were thinner since they would have warmed up more quickly as they descended into the mantle thus the negative buoyancy of slabs and the slab pull forces were probably substantially lower in the early proterozoic calculations show that this applies even if subduction rates were higher and the crust was thicker lower slab pull leads to lower rates of rollback in subduction zones and lower rates of retreat of upper plates from trenches the limited age range of oceanic crust and the more rapid heating of descending slabs in subduction zones probably leads to a smaller range of slab profiles since this range is controlled by thermal properties of the slab and therefore to more stability in subduction zones thus many of the proposed mechanisms for back arc spreading may have been less effective and backarc spreading may have been less common in early proterozoic subduction zones this may explain the apparent absence of ophiolite complexes of that age

stable numerical model for transcritical flow and sediment transport on uneven bathymetry a stable and well balanced finite volume method was proposed to solve the shallow water equations coupled with a sediment transport equation an approximate riemann solver with a monotone upstream centered schemes for conservation laws muscl reconstruction was used for the computation of the flux terms a special but relatively simple treatment of source terms made it possible to ensure numerically and physically balanced computational results on very steep sloped beds various numerical simulations conducted on rigid beds have demonstrated that the proposed numerical scheme could provide stable computational results in the cases of flat and nonflat bottoms from the comparisons of experiments on erodible beds in one and two dimensional channels good agreement was obtained when proper parameters for turbulent flow and sediment transport were provided lastly the effects of the parameters in relation to hydraulic characteristics included in the flow and the sediment transport models were investigated

a positive fold test from nipissing diabase positive fold tests are reported on two remanence components resolved from the same nipissing diabase sills these tests conclusively indicate that the region south of the sudbury basin in the southern structural province has been subjected to two distinct deformational episodes subsequent to the intrusion of the nipissing diabase one event precedes 1850 2150 ma and one event postdates 1250 1850 ma intrusion of the sudbury irruptive some evidence also exists for a third event that may be related to the development of the sudbury structure around 1850 ma evidence that the nipissing was intruded into already folded huronian sediments confirms previous suggestions of four separate orogenic pulses in the period 2300 1250 ma

palaeomagnetism of the southern zone of the lewisian precambrian foreland nw scotland summary palaeomagnetic results are reported from 11 1 localities in metamorphic rocks from the southern zone of the lewisian complex and 12 sites from similar terrain on the island of lewis and harris these rocks were magnetized during slow uplift following the ca 1800 ma laxfordian tectonic magmatic episode the southern zone experienced diachronous uplift and there is a transition from predominantly positive nw remanence directions in the north to shallow negative nw directions in the south more prolonged metamorphism in the south correlates with a transition from magnetite sulphide to magnetite hematite assemblages the relict ruadh mheallan zone relatively unaffected by laxfordian tectonism preserves a al remanence d 82 i 65 which is sporadically recovered as high blocking temperature component in areas bordering this zone elsewhere the migration of field directions is summarized as mean directions a3 d 323 i 44 a4 d 3 14 i 14 and as d 3 13 i 11 which appear to follow on sequentially from the predominant a2 direction d 286 i 55 observed in the central zone of the lewisian complex the remanence directions are linked to a first approximation to the k ar hornblende ages and imply a migration of the ambient field direction through ca 110 during an interval between 1 x lo7 and 2 x lo8 x yr at about 1600ma the weight of the evidence suggests that the interval represented is between 0 5 and 1 x 10 x yr the lewisian a2 as directions yield palaeopoles which follow on from 1800 1700 ma magnetizations from the hudsonian terrains of greenland and north america and overlap with the youngest record from these regions on the pre drift reconstruction collectively the data define part of a large apw loop

geochemical and nd isotopic systematics of granites from the arunta inlier central australia implications for proterozoic crustal evolution geochemical and sm nd isotopic results are reported for granites from the proterozoic arunta inlier of central australia these combined with new geochronological data for the granites zhao and bennett 1995 allow important constraints to be placed on proterozoic tectonic and crustal evolution in central australia granites from the arunta inlier can be divided into three major geochemical groups a calcalkaline trondhjemitic group cat a high heat production group hhp and a volumetrically significant main group the cat group which occurs only in the southern margin of the inlier is characterised by high na2o nak sr krb and sry and relatively low k2o rb rbsr th u ree nb and y analogous to calc alkaline suites occurring in modern convergent plate margins the hhp group which occurs mainly in the interior of the arunta inlier and is spatially associated with the main group is characterised by high k rb th u rbsr and rbzr and relatively low sr ba nak krb barb mgo cr and ni the main group which occurs throughout the arunta inlier is geochemically intermediate between the cat and hhp groups it is geochemically analogous to the 1880 1850 ma old barramundi igneous association recognised in other proterozoic terrains of central australia and can be further subdivided into four age subgroups 1820 1780 1750 1650 and 1615 1600 ma respectively all three groups show similar negative nb anomalies on the trace element normalized diagrams despite the geochemical diversity of the arunta granites no correlations between the nd isotopic and geochemical signatures are observed the ranges of initial nd values and nd depleted mantle model ages tnddm for the three groups of granites overlap with each other overall there are two groups of tnddm ages the most common ranging from 2 33 to 1 96 ga and the other from 1 83 to 1 72 ga although initial nd values of the granites show large variations there is a general trend for the nd values to increase i e become less negative with decreasing crystallization ages the large geochemical and isotopic variations of the arunta granites reflect considerable heterogeneity in the sources of the granites and do not support a uniform 2 3 2 1 ga old barramundi type underplate source for the origin of the granites the combined geochemical and nd isotopic data suggest the sources of the granites contain at least two main components an palaeoproterozoic mantle derived component and an older crustal component the older crustal component was incorporated into the source region of the granites either through magma assimilation of crustal materials at lower crustal levels or more probably via sediment subduction and mantle wedge metasomatism the increasing nd values with decreasing crystallization ages may be a result of progressively increasing proportions of newly accreted island arc materials being incorporated in the subducted sediments alternatively a juvenile mantle derived component may have been added to the source region of the younger granites it is apparent that the nd isotopic signatures in the granites has resulted from complex processes and neither simple mixing nor simple two stage protolith models can as yet satisfactorily explain the observations the petrogenesis of the three geochemical groups of granites can be interpreted in a plate tectonics scenario it is considered that the cat group was formed by fractionation of arc type magmas and or partial melting of arc related intrusions or underplates in a subduction related continental margin setting whilst the formation of the main group may involve partial melting of fractionated and or modified arc related underplates but not necessarily in a subduction environment the younger hhp group was probably generated by remelting of the coexisting main group during subsequent tectonothermal events

research focus crust formation in the western united states between about 1 8 1 6 ga an accretionary belt 1300 km wide was added to the southern margin of the archean wyoming craton in the prevailing arc accretion model condie 1982 karlstrom and bowring 1988 1993 most of this material is considered to be mantle derived juvenile crust and therefore represents newly formed crust at 1 8 1 6 ga the interesting and highly provocative paper by bickford and hill in this issue of geology p 167 170 challenges the view that crustal growth in southern laurentia primarily involved accretion of juvenile arc rocks to an archean core although the bickford and hill paper focuses specifi cally on paleoproterozoic crustal evolution of southern laurentia it has relevance to mechanisms and rates of crustal formation and growth throughout geologic time bickford and hill present an alternative interpretation for paleoprotero zoic crustal evolution in which they suggest that signifi cant volumes of older ca 1 85 ga trans hudson penokean crust may be present in southern laurentia and that rifting of this crust produced the widespread bimodal volcanic sequences present in the southwestern united states see also hill and bickford 2001 the principal lines of evidence cited by bickford and hill to support their interpretations are the presence of pre 1800 ma inherited zircons and nd and pb isotopic signatures suggestive of older crust and the abundant rhyolite dominated bimodal volcanic sequences present in southern laurentia in their model rifting of older crust resulted in basaltic magmatism that provided a heat source for the partial melting of trans hudson penokean crust to form the rhyolites the basaltic component of these bimodal sequences would represent juvenile additions to the crust the rifting and arc accretion models are not mutually exclusive

the correlation between the palaeoproterozoic orogens and granulite belts in the baltic shield and north america craton a suggested model of palaeoproterozoic plate tectonics abstract the earth s archaean history was completed with the formation of the first supercontinent pangaea 0 at ca 2 5 ga ago the main tectonic units of the younger palaeoproterozoic crust in the north atlantic realm include the collision and accretional orogens and in some cases the granulite thrust nappe belts three cycles of geodynamic activities are known in palaeoproterozoic at 2 5 2 33 ga 2 25 1 9 ga and 1 9 1 82 ga not only the starting and final events of the palaeoproterozoic megacycle with the corresponding extension and compression stages but also each cycle of evolution of the collision orogens including both pechenga imandra varzuga trans hudson cape smith new quebec and other suture belts and lapland snowbird queen maud granulite thrust nappe belts and of accretional orogens svecofennian penokean wopmay are strongly correlatable the palaeoproterozoic plate tectonic evolution appears unique in the absence of 1 general dispersal of the archaean supercontinent and 2 manifestation of subduction related magmatism in the accretional orogens along the craton margins of the north atlantic realm during 2 45 to 1 93 ga i e for about 600 ma an exception from the above generalization is the reported intrusion of calc alkaline granitoid complex cutting the lower part of the huron supergroup along the passive margin of the superior craton during 2 39 2 33 ga it is presumed that during palaeoproterozoic the oceanic crust in the oceanic hemisphere underwent rapid recycling that was accompanied by unusually slow wilson type evolution within the supercontinent that was probably nowhere disrupted in full rapid recycling of oceanic crust appears possible if the mid ocean ridges mors are presumed to lie above the sea level this might have prevented hydration of oceanic lithosphere which inhibited evolution of calc alkaline magmas this particular model of global tectonics during the palaeoproterozoic may be styled as microocean tectonics to distinguish it from the archaean microplate tectonics and the phanerozoic plate tectonics

secular effects of oceanic tidal dissipation on the moon s orbit and the earth s rotation the earth and moon are considered as a two body system in gravitational isolation from the sun and other planets the lunar orbit is taken as circular and the solid earth is assumed to be a rigid sphere with no tidal deformation so that there are no precessional torques other than those arising from the tidally deformed ocean numerical solutions to laplace s tidal equations with dissipation by linear bottom friction are used to obtain ocean wide distributions of tidal amplitude for two idealized continentalities a single circular continent spherical cap centered at the north pole and a single spherical cap centered on the equator calculations are made for two different values of the frictional resistance coefficient thus giving rise to four sets of solutions the computed tidal amplitudes are used to calculate the oceanic tidal torque which in turn is used to integrate the orbital equations backward in time for solution of the two body problem the coriolis parameter and the tidal frequencies change with time thus requiring that the tidal equations be solved several times during the course of each orbital integration in this manner the earth s rotational and the moon s orbital histories are determined on a geologic time scale for each of the four models the calculated position of the lunar orbit at 4 5 billion years ago is found to range from 38 to 53 earth radii in the four models and corresponds to a sidereal month of 330 to 550 hours the sidereal day would have been 12 to 18 hours with a relative inclination of 3 to 22 between the terrestrial and lunar poles these results are in sharp contrast to those from previous studies of the earth moon system most of which indicated a roche limit approach of the two bodies roughly 1 to 2 billion years ago and presented therefore a time scale difficulty in theories of lunar origin this contrast arises mainly from the fact that previous modelers avoided solution of laplace s tidal equations by prescribing a constant frictional phase lag angle between the angular position of the moon and the major axis of the second degree harmonic of the tidally deformed surface of the earth the amount of phase lag was established from the present astronomically deduced rate of tidal dissipation but this precluded dynamic variations in tidal torque over geologic time which are critical for determination of the orbital time scale the present rate of oceanic tidal dissipation is evidently anomalously high because of the near resonance of the oceanic response in both frequency and shape to the tidal forcing for the earth and moon to have evolved to their present separation from a distance of less than about 35 earth radii solely on the basis of oceanic tidal dissipation would have required the m2 response to have been near resonance for a significant portion of geologic history a rather implausible scenario the calculations reported here show that on the contrary frictional coupling between the earth and moon was much weaker than at present throughout most of the orbital history and consequently the moon s closest approach could not have been as small as 35 earth radii although idealized continentalities were used in these calculations the general conclusion of a weaker frictional coupling in the past is believed to be relatively insensitive to the continental configuration this is because at faster paleorotation the semidiurnal tidal frequencies would be resonant only with smaller scale normal modes of the ocean rather than with global scale modes as at present the time scale difficulty heretofore present in models of orbital evolution is thereby eliminated it should be noted that the orbital history developed here supports the theory of binary planetary accretion for lunar origin as opposed to fission or tidal capture

postseismic coastal development in aceh indonesia field observations and numerical modeling we model postseismic changes to the shoreline of west aceh indonesia a region largely affected by the december 2004 sumatra andaman earthquake and ensuing indian ocean tsunami using a cross shore morphodynamic model subsidence of 0 5 1 0 m and tsunami scouring during the 2004 event caused the complete destruction of the beach and the landward displacement of the western coast of aceh by an average of 110 m comparing a series of satellite images and topographic surveys we reconstruct the build up of a new beach ridge along a 6 km long stretch of coastline in the years following the event we then use the cross shore model unibest tc developed for a wave dominated sandy shoreline to determine the controlling factors of shoreline recovery input parameters include bathymetric data measured in 2015 grain size characteristics of offshore sediment samples modeled wave data tidal elevations from a nearby tide gauge station as well as measured and modeled postseismic uplift data after establishing a cross shore profile in equilibrium with the prevailing hydrodynamic conditions we simulate the post tsunami recovery the effect of the monsoon seasons as well as the influence of postseismic land level changes for up to 10 years and compare them to the observed coastal development our modeling results indicate that the recovery of the western acehnese shoreline after the 2004 tsunami was quick with littoral sediment transport normalizing to pre tsunami conditions within two to four years following the event however field data shows that the shoreline stabilized 50 90 m landward of its pre 2004 tsunami position most likely due to the build up of a prominent higher beach ridge in response to coseismic subsidence observed variability in shoreline position in the order of a few tens of meters since 2009 can be attributed to seasonal wave climate variability related to the monsoon cycle the effect of postseismic uplift on shoreline position is small and in the order of only a few meters over 10 years which is 3 to 5 times smaller than long term coastal progradation rates that are driven by abundant sediment supply to the littoral zone this overall progradational trend will promote preservation of seismically modified beach ridges which can serve as paleoseismic indicators

plates and their motions the last reviews which covered research in plate motions were those of herron and pitman 1975 on marine magnetic anomalies and dewey 1975 on plate tectonics both reporting on research for the period 1971 1974 in the last 12 years there has been considerable refinement of relative motion models as well as further development of global models also major effort has gone into defining reference frames for the study of plate motions and discriminating between them more recently the role of errors in individual plate rotations and the associated uncertainties in reconstructions have received attention in this report i concentrate on work published in the last 4 years 1983 1986 citing a minimum of publications from previous years however some papers in press for early 1987 have been included this report first reviews work on relative plate motions for the present and past and reconstructions and then models for these motions global ones for driving forces and local ones determining subduction history and back arc spreading the problem of reference frames both hotspot and paleomagnetic is discussed next i end with a review of work on the errors in plate motions

early cambrian continental reconstructions climatically related sedimentary facies and faunal distributions have been combined with palaeomagnetic data to make provisional reconstructions of the early cambrian world laurentia baltica and siberia appear to have formed a continental group which rifted apart from each other prior to 600 ma the consolidation of much of gondwana probably occurred in the pan african orogeny well before the cambrian though the assembly of several east asian terranes is still speculative the archaeocyathan reefs of siberia southern europe and morocco with their bigotinid trilobite fauna suggest that these areas were adjacent to each other and at low latitudes avalonia had close faunal links with western gondwana but lacked bigotinids and archaeocyathans and may have been situated off west africa and florida during the early cambrian there was a northward migration of laurentia towards the equator as its separation from baltica and siberia increased and a southward movement of gondwana

barrier island migration and onshore sediment transport southwestern delaware bay delaware u s a abstract a detailed sediment budget for part of a rapidly migrating 3 m yr 1 barrier system of southwestern delaware bay demonstrates that longshore drift and other principal sources of sediment are insufficient to balance the sediment budget during 1926 1981 changes in bathymetry from 1964 to 1984 indicate that erosion is occurring in shallow areas outside the surf zone if approximately half of the sediment eroded offshore is transported onto the beach the sediment budget balances these results suggest that sand and gravel is supplied to the barriers of the study area from offshore several processes probably combine to carry sediment landwards tidal currents are weak and probably rarely entrain sediment without the assistance of waves once entrained sediment may be carried onshore by the combined influence of dominant ebb tidal currents and frequent northwest winds this process is probably also aided by a residual onshore shear stress associated with 2nd order stokes waves

plate tectonics model for proterozoic continental accretion in the southwestern united states proterozoic crustal provinces in the southwestern united states decrease in age south from the archean wyoming province supracrustal rocks define three major age provinces from north to south 1 72 to 1 80 1 65 to 1 72 and 1 1 to 1 2 b y successions within each province are similar and define two assemblages a bimodal volcanic assemblage commonly overlain by a quartzite shale assemblage precambrian granitic plutons intrude all three provinces geochemical and sr isotope data indicate a variably depleted upper mantle source for basalts and a short lived these observations can be explained by a plate tectonics model involving successive marginal basin closures and andean type orogenies associated with southward migrating arcs the net result is to accrete 1 300 km of continental crust to the southwestern margin of north america between 1 8 and 1 1 b y ago

one dimensional modeling of dam break flow over movable beds a one dimensional model has been established to simulate the fluvial processes under dam break flow over movable beds the hydrodynamic model adopts the generalized shallow water equations which consider the effects of sediment transport and bed change on the flow the sediment model computes the nonequilibrium transport of bed load and suspended load the effects of sediment concentration on sediment settling and entrainment are considered in determining the sediment settling velocity and transport capacity in particular a correction factor is proposed to modify the van rijn formulas of equilibrium bed load transport rate and near bed suspended load concentration for the simulation of sediment transport under high shear flow conditions the governing equations are solved by an explicit finite volume method with the first order upwind scheme for intercell fluxes the model has been tested in two experimental cases with fairly good agreement between simulations and measurements the sensitivities of the model results to parameters such as the sediment nonequilibrium adaptation length manning s roughness coefficient and the proposed correction factor have been verified the proposed model has also been compared to an existing model and the results indicate the new model is more reliable

dam break in channels with 90 bend in practice dam break modeling is generally performed using a one dimensional 1d approach for its limited requirements in data and computation however for valleys with multiple sharp bends such a 1d model may fail for predicting as well the maximum water level as the wave arrival time this paper presents an experimental study of a dam break flow in an initially dry channel with a 90 bend with refined measurements of water level and velocity field the measured data are compared to some numerical results computed with finite volume schemes associated with roe type flux calculation the 1d approach reveals the expected limits while a full two dimensional 2d approach provides fine level prediction and rather satisfactory information about the arrival time a hybrid approach is now proposed mixing the 1d model for the straight reaches and local 2d models for the bends the compatibility of the roe fluxes at the interfaces requires a careful formulation but the resulting scheme seems able to capture reflection and diffraction processes in such a way that the results are really good in what concerns the water level

design requirement for mixed sand and gravel beach defences under scenarios of sea level rise abstract along many coastlines of the world beaches provide the primary defence against flooding or erosion with their fate under rising sea levels still only poorly researched this is particularly the case for the coastline of southeast england where 190 km of shingle barriers protect low lying hinterland or a coastal plain that is at or barely above the present reach of waves during the holocene transgression these beaches moved into their present position through longshore extension and cross shore roll back this process stopped more than a century ago with port developments affecting longshore transport and the construction of groynes to hold the beach in place this was followed by beach recharge and recycling towards the end of the 20th century to build up and maintain beaches as coastal defences in their mid 19th century position this paper explores the design requirements for these beaches under future sea level rise scenarios of 1 to 5 m using recently developed tools it shows that the presently still semi natural beaches have to increase in size with crest height elevations having to rise by at least up to 1 26 times the rate of sea level rise and that due to higher longshore wave power especially during storm conditions in the future higher and stronger groynes are needed to hold these larger beaches in place future design requirements for beaches are sensitive to foreshore levels and orientation of the beach to the dominant waves with those presently characterised by shallow foreshores and oblique wave approach requiring the biggest adjustments required size increases will be difficult to implement due to the built up nature of the hinterland the engineering alternative would be to replace beaches with hard structures a process that has already started where maintaining a beach is no longer economically viable or the residual risk associated with overwashing and an eventual tidal breach has become unacceptable

loading configurations and driving mechanisms for joints based on the griffith energy balance concept abstract using the griffith energy balance concept to model joint propagation in the brittle crust two laboratory loading configurations serve as appropriate analogs for in situ conditions the dead weight load and the fixed grips load the distinction between these loading configurations is based largely on whether or not a loaded boundary moves as a joint grows during displacement of a loaded boundary the energy necessary for joint propagation comes from work by the dead weight i e a remote stress when the loaded boundary remains stationary as if held by rigid grips the energy for joint propagation develops upon release of elastic strain energy within the rock mass these two generic loading configurations serve as models for four common natural loading configurations a joint normal load a thermoelastic load a fluid load and an axial load each loading configuration triggers a different joint driving mechanism each of which is the release of energy through elastic strain and or work the four mechanisms for energy release are joint normal stretching elastic contraction poroelastic contraction under either a constant fluid drive or fluid decompression and axial shortening respectively geological circumstances favoring each of the joint driving mechanisms are as follows the release of work under joint normal stretching occurs whenever layer parallel extension keeps pace with slow or subcritical joint propagation under fixed grips a substantial crack normal tensile stress can accumulate by thermoelastic contraction until joint propagation is driven by the release of elastic strain energy within the earth the rate of joint propagation dictates which of these two driving mechanisms operates with faster propagation driven by release of strain energy like a dead weight load acting to separate the joint walls pore fluid exerts a traction on the interior of some joints joint propagation under fluid loading may be driven by a release of elastic strain energy and or work by the pore fluid during poroelastic contraction again propagation velocity dictates the driving mechanism with critical to supercritical joint propagation accompanying fluid decompression and subcritical crack propagation taking place under a constant fluid drive during axial shortening a jointing process called axial splitting may occur following wing crack growth from an initial crack tilted relative to the maximum compressive stress here the joint driving mechanism may be either the work of a remote stress i e a dead weight or the release of elastic strain energy i e fixed grips

speculations on the thermal and tectonic history of the earth summary the connection between the earth s thermal history and convection in the mantle is exploited to elucidate the early evolution of the earth it appears probable that convection extending over almost all of the mantle has dominated vertical heat transport throughout the whole of the earth s history only in boundary layers at the surface and at a depth of 650 700 km is conduction likely to be important the resulting evolution appears to be consistent with geological observations on early precambrian rocks various arguments are put forward in favour of two horizontal scales of convective flow in the mantle at depths less than 650 km the large scale flow is related to the motion of major plates and must be ordered over distances of more than 5000 km its evolution and energetics are discussed and there are no obvious problems in maintaining the proposed convective motions small scale flow with an extent of the order of 500 km appears necessary both to explain the heat flow through older parts of the earth s surface and to reconcile the geophysical observations with the results of numerical experiments though the existence of the small scale flow is at present speculative various tests of its presence are proposed

tides and the evolution of the earth moon system summary a model of the tides in a hemispherical ocean is used to investigate the effect of changes in the earth s rotation rate on the power dissipated by the ocean tides the results obtained are then used in an idealized astronomical model to investigate how they affect the history of the earth moon system using the tidal model it is found that at rotation rates higher than that of the present earth the power dissipated by the semi diurnal tides in the ocean drops off rapidly as a result of the increased tidal frequency thus if the earth s rotation rate is doubled from its present value then the rate of energy dissipation in the ocean is reduced to approximately one third of its present value and the tidal torque is reduced by a factor of about 6 the present value for secular acceleration of the moon calculated from the results of the tidal model is 30 5 arcsec century 2 using this value in the astronomical model which has the moon and sun in circular orbits above the equator and assuming that the tidal torque is independent of the tidal frequency the gerstenkorn event is predicted to have occurred 1 3 109 yr ago when the astronomical model is run with a torque determined at all times from the tidal model the reduction in the energy dissipated early in the history of the system leads to a gerstenkorn date of 5 3 109 yr ago however dissipation within the solid earth is found to be important early in the history of the system and when this effect is included it gives a date for the gerstenkorn event of 3 9 109 yr ago

sediment transport and budget of the central coastal zone of holland abstract based on the available short term morphological data 1964 1992 the net yearly averaged sand volume change in the surfzone 3 8 m nap to local datum approximately mean sea level along the coast of holland was found to be 125 000 m 3 year sedimentation including beach nourishments a sand budget model has been developed which describes the sand volume change in m 3 year in each compartment of the coastal area given known gradients of the computed longshore and cross shore transport rates and known source sink terms nourishment dumping and dredging the model area extends in cross shore direction from the 3 m nap contour to the 20 m nap contour the sand budget model has been calibrated hindcast study using the yearly averaged sand volume changes derived from bathymetry data jarkus data base collected during the period 1964 1992 input data are the gradients of the yearly averaged longshore and cross shore transport rates at the boundaries of the compartments and the available data of beach nourishment dumping and dredging in the same period a 2dv mathematical model representing the hydrodynamic waves and currents and sand transport processes in a cross shore profile was applied to compute the yearly averaged transport rates in various profiles along the coast at depths of 20 and 8 m and in the surf zone a detailed sensitivity study was performed to determine the variation ranges of the transport rates

physical model study of beach profile evolution by sea level rise in the presence of seawalls abstract persistent and accelerating sea level rise slr may have a significant impact on the evolution of sandy coastlines this century the response of natural sandy beaches to slr has been much discussed in the literature however there is a lack of knowledge about the impact of slr on engineered coasts laboratory experiments comprising over 320 h of testing were conducted in a 44 m l x 1 2 m w x 1 6 m d wave flume to investigate the influence of coastal armouring in the form of seawalls on coastal response to slr the study was designed to investigate the effects of contrasting types of seawalls reflective impermeable versus dissipative permeable on beach profile response to increased water levels in the presence of both erosive and accretionary wave conditions the results obtained showed that seawalls alter the evolution of the equilibrium profile with rising water level causing increased lowering of the profile adjacent to the structure under erosive wave conditions modelled profiles both with and without seawall structures in place were observed to translate landward in response to slr and erode the upper profile it was found that the erosion demand at the upper beach due to a rise in water level remains similar whether a structure is present or not but that a seawall concentrates the erosion in the area adjacent to the seawall resulting in enhanced and localised profile lowering the type of structure present dissipative permeable versus reflective impermeable was not observed to have a significant influence on this response under accretive conditions the preservation of a large shoreface and berm resulted in no wave structure interaction occurring with the result that the presence of a seawall had no impact on profile evolution a potential two step method for estimating the observed profile response to water level rise in the presence of seawalls is proposed whereby a simple profile translation model is used to provide a first estimate of the erosion demand and then this eroded volume is redistributed in front of the seawall out to the position of the offshore bar

tonalites in crustal evolution tonalites including trondhjemite as a variety played three roles through geological time in the generation of earth s crust before about 2 9 ga ago they were produced largely by simple partial melting of metabasalt to give the dominant part of archaean grey gneiss terranes these terranes are notably bimodal andesitic rocks are rare tonalites played a crucial role in the generation of this protocontinental and oldest crust 3 7 2 9 ga ago in that they were the only low density high sio 2 rocks produced directly from basaltic crust in the enormous event giving the greenstone granite terranes mostly 2 8 2 6 ga ago tonalites formed in lesser but still important proportions by partial melting of metabasalt in the lower regions of down buckled greenstone belts and by remobilization of older grey gneisses tectonism in the archaean 3 9 2 5 ga ago perhaps was controlled by small cell convection mckenzie weiss 1975 little or no ophiolite or eclogite formed and only minor andesite plate tectonics of modern type involving large rigid plates commenced in the early proterozoic uniformitarianism thus goes back one half of the age of the earth tonalites compose about 5 10 of crust generated in proterozoic and phanerozoic time at convergent oceanic continental margins they occur here as minor to prominent members of the compositionally continuous continental margin batholiths a simple model of generation of these batholiths is offered mantle derived mafic magma pools in the lower crust above a subduction zone reacts with and incorporates wall rock components bowen 1922 and breaches its roof rocks as an initial diapir this mantle magma also develops a gradient of partial melting in its wall rocks this wall rock melt accretes in the collapsed chamber and moves up the conduit broached by the initial diapir the higher less siliceous fractions of melting first the lower more siliceous and further removed fractions of melting last the process gives in the optimum case a mafic to siliceous sequence of diorite or quartz diorite through tonalite or quartz monzodiorite to granodiorite and granite the model implies that great masses of cumulate phases and refractory wall rock form the roots of continentalmargin batholiths and that migmatites overlie that residuum and underlie the batholiths

monitoring shallow coastal environment using landsat altimetry data under rapid sea level change abstract the caspian sea cs is the largest enclosed inland body of water and eminent for its rapid sea level change from 1929 to 1955 rapid cyclic changes with amplitudes of 3 m led to the formation of large submerged and emerged areas the present study seeks to incorporate multi source sensor data such as the landsat time series data i e mss tm etm and oli alongside radar altimetry products i e topex jason 1 ostm jason 3 as a means for extracting morphological features gorgan bay and gomishan lagoon of the southeastern shorelines of the caspian sea as well as to investigate changes in the shoreline for a given period of 42 years 1975 2016 we also employ particle swarm optimization pso algorithm as an automated method to extract shoreline change in shallow marine environments over the past century the cs has experienced a lowstand in 1977 and a highstand in 1995 despite an approximate 1 5 m drop in sea level from 1995 to 2015 gorgan bay and gomishan lagoon with depths of 4 5 and 2 5 m appear to have outlasted and emerged respectively pso is a highly efficient method capable of defining shorelines and extracting water bodies the surface area estimations using the pso method are consistent with corresponding reference values with an average error of 1 73 and a high coefficient of determination r2 0 99 differences between calculated and reference areas were mainly observed in muddy and swamp sectors of the study area this study highlights the key role of satellite time series in shoreline monitoring and management under rapid sea level change conditions moreover the study demonstrates the capabilities of the pso algorithm as an automated and accurate method for shoreline detection

laboratory investigation of nourishment options to mitigate sea level rise induced erosion abstract the response of nourished beaches to sea level rise is investigated experimentally with random waves in a laboratory wave flume 20 m 1 m 1 m following on from a previous investigation of the response of non nourished beaches atkinson et al 2018 the nourishments are placed on beach profiles previously exposed to sufficient durations of waves to have approached a near equilibrium state i e with stable shoreline bars and berms nourishment was placed in three different locations on the berm within the bar trough and as a shoreline placement in the latter case and following bruun rule concepts bruun 1962 the volume of sediment placed was estimated a priori to lead to zero recession under the chosen water level rise the nourished beaches were then exposed again to sufficient durations of waves to reach a near equilibrium state at the raised water level the shoreline recession and the mean recession of the profile following a rise in water level are compared for both the nourished and non nourished beaches and to theoretical estimates based on bruun rule concepts and a previously developed profile translation model ptm quantitative agreement is found with the variants of the bruun rule that account for nourishment and with the ptm and the predicted recession is within an order of 30 of the observed recession overall the ptm provides the best estimate of the recession the mean recession of the profile is found to be in better agreement with the model predictions than the recession measured at the shoreline because the latter is affected by changes in profile shape around the still water line the efficacy of the nourishment was investigated from the reduction in the observed recession the efficacy depends on how the recession is measured for the mean recession highest efficacy was observed when all the nourishment is added into the active profile conversely for the shoreline recession highest efficacy was observed with the nourishment placed on the upper beach because it prevents additional recession through wave overtopping

dam break wave front celerity this work is concerned with the role that friction and inertia effects can play on the magnitude of dam break wave front celerity classic analytical solutions are presented a large collection of experimental data is used covering a wide range of different initial conditions fixed bed or mobile bed five types of bed material dry or wet bed downstream and with or without bed step to overcome the limitations of analytical solutions a numerical model is used the model is based on the shallow water approach with contact load dominated sediment transport and it makes use of developments recently made in the study of sheet flows the analytical and numerical results are compared with experimental data it was found that the celerity is mainly dictated by the friction coefficient by the sediment inertia by the initial downstream water depth and by the initial bed step height for good data fitting the friction coefficient must be influenced by the type of bed fixed or mobile in the latter the coefficient must vary with the bed material characteristics the dissimilarities between the experimental analytical and numerical results are interpreted

finite volume model for shallow water flooding of arbitrary topography a model based on the finite volume method is developed for unsteady two dimensional shallow water flow over arbitrary topography with moving lateral boundaries caused by flooding or recession the model uses roe s approximate riemann solver to compute fluxes while the monotone upstream scheme for conservation laws and predictor corrector time stepping are used to provide a second order accurate solution that is free from spurious oscillations a robust novel procedure is presented to efficiently and accurately simulate the movement of a wet dry boundary without diffusing it in addition a new technique is introduced to prevent numerical truncation errors due to the pressure and bed slope terms from artificially accelerating quiescent water over an arbitrary bed model predictions compare favorably with analytical solutions experimental data and other numerical solutions for one and two dimensional problems

deep seismic structure and thermo mechanical modelling of continental collision zones abstract a series of 2d thermo mechanical models are presented which quantify crustal thickening and the resulting temperature perturbations associated with thrusting in an attempt to constrain the existence of temperatures responsible for the generation of anatectic granites in a compressional environment deformation is assumed to occur in the crust by a simple thrusting mechanism the moho acting as a detachment surface as has been observed on deep seismic reflection data while the more ductile sub crustal lithosphere is assumed to behave elastically and deform in a pure shear manner investigated are the relative effects of the rate of crustal shortening the distribution of radioactive elements within the crust the reduced heat flow from the mantle isostasy and erosion our results show that previous oversimplified 1d models significantly overestimate the elevated temperatures in lower crustal regions caused by radiogenic heating and that this mechanism will only have a significant effect in regions of relatively thin lithosphere or where there are unusually high rates of radiogenic heating in the crust generation of synthetic p t t data for locations deep down in the lower crust enables us to quantify the temperatures produced following a period of compressional deformation providing insight into the time scales involved for the generation of crustal melt granites within an orogenic belt

proterozoic palaeomagne tism and single continent plate tectonics summary proterozoic 2700 570 ma palaeomagnetic poles from the major shields conform to a single apparent polar wander path on a contiguous reconstruction which brings into alignment both with each other and with the long axis of the primary continental crust tectonic and magmatic features ranging from late archaean 2900 ma to late proterozoic 1100 ma age this discovery implies that the continental lithosphere behaved on a megatectonic scale as a single coherent plate during this era subject to internal deformation but not breaking up in a brittle fashion until late precambrian times peripheral parts of the supercontinent were redistributed over a short interval at ca 1100 ma but the continental crust was not dismembered and widely dispersed until 570 530 ma this latter episode correlates with the proterozoic phanerozoic transition and defines the onset of multi continent plate tectonics the proterozoic apw record comprises nine large loops with periods ranging from 270 to 110ma and averaging 200ma between 2150 and 1000 ma the loops had a similar signature and their resultant effect was to return the continental lithosphere repeatedly to a stable position with its centre at the geographic pole probably by the goldreich toomre mechanism this periodicity correlates with theoretical and experimental studies of mantle convection predicting avalanche type behaviour due to build up of instability in the surface boundary layer with cycles of 50 200 ma the consolidation of the continental lithosphere defines several phases in the history of mantle convection 1 between 3500 and 2800 ma the sialic scum resulting from differentiation of a thickened and subducting lithosphere was accumulated into the primary body by a large scale mantle convection system 2 this operated simultaneously with a subcontinental lithosphere small scale 50 100 km convection system showing a transition from bimodal to cylindrical roll mode represented by the later greenstone belts 2900 2200 ma and straight belts ca 2800 2400 ma 3 a transition to larger scale episodic subcontinental convection is represented by the proterozoic mobile belts 2200 1100 ma 4 a modification of the major suboceanic lithosphere convection is suggested by reorganization of the peripheral shields at 1100 ma and 5 a subdivision of this major system resulted in continental dispersal during lower cambrian times

geochemistry and petrogenesis of early proterozoic amphibolites west central colorado u s a abstract early proterozoic supracrustal rocks exposed in west central colorado include amphibolites intimately associated with felsic volcanics and associated volcaniclastic sediments three successions are recognized the dubois succession 1770 1760 ma is comprised chiefly of amphibolites and felsic volcanics the amphibolites exhibit low concentrations of light ree and hfse and are broadly similar in composition to tholeiites from immature island arcs and in some respects to nmorb the cochetopa succession 1745 1730 ma includes large amounts of felsic volcanics and volcaniclastic sediments together with amphibolites that exhibit variable but slight incompatible element enrichment similar to basalts from evolved island arc systems and associated back arc basins the black canyon succession is coeval with the cochetopa succession and is comprised chiefly of volcaniclastic sediments with minor amphibolite these amphibolites exhibit significant incompatible element enrichment similar to basalts from continental margin arc systems geochemical modeling indicates that the amphibolites evolved by closed system fractional crystallization of depleted for the dubois succession to variably enriched parental basalts for the cochetopa and black canyon successions chiefly at shallow depths incompatible element distributions in the amphibolites indicate that mantle sources changed with time from relatively depleted 1770 1760 ma to variable but slightly enriched 1745 1730 ma a provisional model calls upon the dubois succession forming in an island arc system followed by collision with the archean wyoming province at 1750 ma the cochetopa succession was deposited in an intra arc basin developed within a new continental margin arc and the black canyon succession formed in a back arc basin associated with this arc