a geodynamic model of mantle density heterogeneity using cenozoic and mesozoic plate motion reconstructions we derive a model of present day mantle density heterogeneity under the assumption that subducted slabs sink vertically into the mantle the thermal buoyancy of these slabs is estimated from the observed thermal subsidence cooling of oceanic lithosphere slab velocities in the upper mantle are computed from the local convergence rate we assume that slabs cross the upper lower mantle interface and continue sinking into the lower mantle with a reduced velocity for a velocity reduction factor between 2 and 5 our slab heterogeneity model is as correlated with current tomographic models as these models are correlated with each other we have also computed a synthetic geoid from our density model for a viscosity increase of about a factor of 40 from the upper to lower mantle our model predicts the first 8 spherical harmonic degrees of the geoid with statistical confidence larger than 95 and explains 84 of the observed geoid assuming that the model c21 and s21 terms are absent due to a long relaxation time for earth s rotational bulge otherwise 73 of the geoid variance is explained the viscosity increase is consistent with our velocity reduction factor for slabs entering the lower mantle since downwelling velocities are expected to scale roughly as the logarithm of viscosity loge 40 3 7 these results show that the history of plate tectonics can explain the main features of the present day structure of the mantle the dynamic topography induced by this heterogeneity structure consists mainly of about 1 km amplitude lows concentrated along the active continental margins of the pacific basin our model can also be used to predict the time variation of mantle heterogeneity and the gravity field we find that the age of the geoid defined as the time in the past before which the geoid becomes uncorrelated with the present geoid is about 50 m y our model for the history of the degree 2 geoid which is equivalent to the history of the inertia tensor should give us a tool to study the variations in earth s rotation pole indicated in paleomagiietic studies

constraints on the lateral strength of slabs from three dimensional dynamic flow models if the viscosity of subducted lithosphere is described purely by temperature and pressure it should remain considerably more viscous than the surrounding material as it descends through the upper mantle many dynamic models of the long wavelength geoid associated with slabs require an increase in viscosity from the upper to the lower mantle but assume the perturbation to the lateral viscosity structure arising from the slabs themselves can be ignored previous studies indicate that strong and localized viscosity variations should have a dramatic influence on the geoid we present 3d finite element models of the regional geoid of the western pacific subduction zones slab buoyancies and viscosities are defined using the distribution of seismicity the geoid is very sensitive to the lateral strength of the slab very viscous slabs penetrating a low viscosity mantle generate significant 10 50 m long wavelength geoid lows opposite to the geoid high which is observed over slabs to obtain a geoid high comparable to that observed the lower mantle viscosity must be 60 200 times greater than the upper mantle viscosity and the slab must be in contact with the lower mantle these strict requirements suggest that slabs have been weakened and cannot act as stress guides from the deep mantle to the surface

global crustal stress pattern based on the world stress map database release 2008 the world stress map wsm project is a global compilation of information on the contemporary crustal stress field from a wide range of stress indicators the wsm database release 2008 contains 21 750 stress data records that are quality ranked using an updated and refined quality ranking scheme almost 17 000 of these data records have a c quality and are considered to record the orientation of maximum horizontal compressional stress sh to within 25 as this is almost a triplication of data records compared with the first wsm database release in 1992 we reinvestigate the spatial wave length of the stress patterns with a statistical analysis on a global 0 5 grid the resulting smoothed global stress map displays both the mean sh orientation that follows from the maximum smoothing radius for which the standard deviation is b25 and a countour map that displays the wave length of the stress pattern this smoothed global map confirms that long wave length stress patterns n2000 km exist for example in north america and ne asia these have been used in earlier analyses to conclude that the global stress pattern is primarily controlled by plate boundary forces that are transmitted into the intraplate region however our analysis reveals that rather short wave length of the stress pattern b200 km are quite frequent too particularly in western europe alaska and the aleutians the southern rocky mountains basin and range province scandinavia caucasus most of the himalayas and indonesia this implies that local stress sources such as density contrasts and active fault systems in some areas have high impact in comparison to plate boundary forces and control the regional stress pattern

effects of latent heat release at phase boundaries on flow in the earth s mantle phase boundary topography and dynamic topography at the earth s surface abstract mantle flow models that do not consider the effects of latent heat on phase boundaries typically predict dynamic surface topography too large to be compatible with observations here these effects were implemented in a mantle flow model and resulting changes in dynamic topography and topography of phase boundaries were computed inclusion of these effects was found to reduce the rms amplitude of dynamic topography by about 50 60 m still leaving a substantial misfit from observations in most cases considered generally it also leads to a slight improvement of correlation with dynamic surface and phase boundary topography constrained by observations results thus indicate that the model implemented here is applicable to the earth but that other effects need to be considered as well in order to fully explain phase boundary and dynamic surface topographies

the relationship between depth age and gravity in the oceans we reassess the applicability of the thermal plate cooling model to the subsidence of the north pacific atlantic and north indian ocean basins we use a new numerical plate model in which the thermophysical parameters of the lithosphere vary with temperature according to the results of laboratory experiments and the ridge temperature structure is consistent with the thickness of the oceanic crust we first attempt to exclude thickened crust from our data set and then to exclude swells and downwellings by masking regions of the data that remains that have significant gravity anomalies when there exists a clear regional correlation between intermediate wavelength gravity and topography we find that the average variation of depth with age is consistent with conventional half space models until about 90 myr thereafter the departure from the half space cooling curve is more rapid than predicted using simple conductive plate cooling models the depth age curves in the pacific and atlantic show 250 m of temporary shallowing between the ages of 90 130 myr a result consistent with the outcome of experiments on the initiation of small scale boundary layer convection the results do not change significantly if the estimated component of the gravity arising from plate cooling is subtracted prior to calculation of the correlation between gravity and topography a 90 km thick conductive plate is nevertheless a reasonable model for the average temperature structure of the oldest part of the pacific ocean lithosphere in the pacific the broad topographic undulations associated with the line island swell the hawaiian swell and surrounding basins have correlated gravity anomalies and an admittance of approximately 30 mgal km 1 and are likely to result from convective circulation in the upper mantle in the northeast atlantic the intermediate wavelength admittance over the cape verde swell is similar in the northwest atlantic over the bermuda swell it is slightly larger but not as well constrained

subducted slabs and the geoid 1 numerical experiments with temperature dependent viscosity one of the most powerful constraints on mantle viscosity comes from the correlation of the long wavelength degree 4 9 geoid with that predicted by a density model for subducted slabs the effect of lateral variations of viscosity should be most pronounced at subduction zones due to the strong effect of temperature on viscosity an idealized slab model with temperature dependent viscosity is considered with various lateral and vertical viscosity structures using a two dimensional finite element formulation the viscosity parameterization affects the amplitude of the long wavelength geoid anomaly but not the sign of the correlation between the geoid and density anomalies depth dependent viscosity models with a high viscosity lithospheric layer do not completely match the temperature dependent laterally varying results suggesting that the rheology of the slab does have an effect on the long wavelength surface topography and geoid however this affect is minor suggesting that the radial models of mantle viscosity inferred from surface observables are correct to first order in contrast the short wavelength features are dramatically affected by the rheology of the region surrounding the downwelling further study of the shorter wavelength geoid over subduction zones may provide better insight into subduction zone processes

isostasy dynamic topography and the elevation of the apennines of italy abstract the elevation of an orogenic belt is commonly related to crustal lithosphere thickening here we discuss the apennines as an example to show that topography at a plate margin may be controlled not only by isostatic adjustment but also by dynamic mantle driven processes using recent structural constraints for the crust and mantle we find that the expected crustal isostatic component explains only a fraction of the topography of the belt indicating positive residual topography in the central apennines and negative residual topography in the northern apennines and calabria the trend of the residual topography matches the mantle flow induced dynamic topography estimated from regional tomography models we infer that a large fraction of the apennines topography is related to mantle dynamics producing relative upwellings in the central apennines and downwellings in the northern apennines and calabria where subduction is still ongoing comparison between geodetic and geological data on vertical motions indicates that this dynamic process started in the early pleistocene and the resulting uplift appears related to the formation and enlargement of a slab window below the central apennines the case of the apennines shows that at convergent margins the elevation of a mountain belt may be significantly different from that predicted solely by crustal isostasy and that a large fraction of the elevation and its rate of change are dynamically controlled by mantle convection

cenozoic subsidence and uplift of continents from time varying dynamic topography time varying global dynamic topography has been computed for the entire cenozoic the spherical viscous flow model is driven by a distribution of density heterogeneity based on mesozoic and cenozoic subduction by using the calculated topography the uplift and subsidence histories of five regions fixed to the north american indian australian indonesian and south american continents are computed predicted vertical motions are in qualitative agreement with observed values except for india and south america for australia and north america the predicted periods of uplift and subsidence are out of phase with respect to observations but display the correct overall trend the latest phase of uplift for north america is directly related to the cessation of kula plate subduction after 48 ma dynamic topography depends on the viscosity structure of the mantle a lower mantle that is 50 times more viscous than the upper mantle yields the best agreement between modeled and predicted vertical motions the presence of a low viscosity channel beneath the lithosphere has only a small influence on our results compared to dynamic topography the time varying geoid is insignificant in controlling relative sea level

ridge spreading subduction and sea level fluctuations a numerical model of mantle convection shows that sea level fluctuations are not simply associated with temporal changes in ocean c plate spreading in the dynamic model sea level rises rapidly and then falls toward a steady value but one still higher than the initial following increased ridge spreading this time dependence results from profound changes in the deep thermal structure under ocean and continent the use of past variations in oceanic spreading to infer sea level fluctuations is called into question with more realistic models and better continental stratigraphy constraints may be placed on the viscosity structure of the mantle

sorption of lead by phlogopite rich mine tailings the pb sorption capacity of apatite ore mine tailings and its potential to act as a remediation agent in a pb polluted areas were investigated the tailings originating from the siilinjarvi carbonatite complex in finland consist mainly of phlogopite and calcite accompanied by apatite residues the ability of the tailings to retain pb from an aqueous solution was investigated using an isotherm technique furthermore in a 3 month incubation experiment uncontaminated mineral soil was amended with untreated tailings and with tailings artificially weathered with acid to increase the quantity of al and fe hydr oxides tailings of two particle sizes 0 2 mm and 0 2 mm somewhat differing in their mineralogical composition were investigated as separate amendments all tailings materials were added to the soil in two dosages 5 g and 10 g of tailings per 125 g of soil following incubation tailings induced changes in the pb sorption capacity of the soil were investigated with the isotherm technique finally to investigate the distribution of sorbed pb among various chemical pools the soil samples amended with tailings were contaminated with pb and then subjected to sequential fractionation analysis the results revealed efficient removal of pb from an aqueous solution by the tailings presumably through precipitation and surface complexation mechanisms amending the soil with the tailings increased the mass based maximum pb sorption capacity from 10 8 mg kg 1 of the control soil to 14 20 5 mg kg 1 for the untreated tailings and to 32 1 72 1 mg kg 1 for the acid treated material the tailings transferred pb from the exchangeable pool to the non extracted one and thereby substantially decreased its bioavailability the material with a particle diameter of less than 0 2 mm had a higher mass based pb sorption capacity than the large sized material the results suggest that the tailings may potentially serve as an immobilizing agent in polluted areas

dynamic topography gravity and the role of lateral viscosity variations from inversion of global mantle flow lateral viscosity variations lvvs in the mantle influence geodynamic processes and their surface expressions with the observed long wavelength geoid free air anomaly gravity gradient in three directions and discrete high accuracy residual topography we invert for depth and temperature dependent and tectonically regionalized mantle viscosity with a mantle flow model the inversions suggest that long wavelength gravitational and topographic signals are mainly controlled by the radial viscosity profile the pre cambrian lithosphere viscosity is slightly one order of magnitude higher than that of oceanic and phanerozoic lithosphere plate margins are substantially weaker than plate interiors and viscosity has only a weak apparent dependence on temperature suggesting either a balancing between factors or a smoothing of actual higher amplitude but short wavelength lvvs the predicted large scale lithospheric stress regime compression or extension is consistent with the world stress map thrust or normal faulting both recent compiled high accuracy residual topography and the predicted dynamic topography yield 1 km amplitude long wavelength dynamic topography inconsistent with recent studies suggesting amplitudes of 100 to 500 m such studies use a constant positive admittance transfer function between topography and gravity in contrast to the evidence which shows that the earth has a spatially and wavelength dependent admittance with large negative admittances between 4000 and 10 4 km wavelengths

effects of lateral viscosity variations on long wavelength geoid anomalies and topography models for the earth s geoid and dynamically supported topography usually account only for radial vertical variations in mantle rheology and flow structure however expected lateral variations in viscosity due to temperature or stress dependent rheology can degrade our ability to infer mantle structure from geoid models based on seismically determined density contrasts in the mantel theoretically the main difficulty is that the harmonic components of the flow stress deformation field are no longer independent and exact analytical methods cannot account for this mode coupling for large thermal density contrasts of small lateral dimension e g subducted slabs it is difficult to form any general theory for these effects however we believe that the largest geoid anomalies which occur at the lowest harmonic degrees l 2 3 are due to a global pattern of relatively mild temperature variations for convection with mainly broadscale thermal and rheological changes some relatively straightforward ideas can be developed combining results from simple perturbation theory and numerical models for convective flow we find the following 1 if we are correct in inferring viscosity variations of less than one order of magnitude globally the longest wavelength geoid anomalies l 2 3 are not seriously contaminated by lateral viscosity variations 2 contamination of the higher degrees l 4 is expected and in particular self coupling between l 2 heterogeneity and viscosity variations may be observable at degree 4 the most severe contamination occurs at the doubled harmonic l 4 of the dominant heterogeneity harmonic l 2 3 perturbation techniques are adequate to model global scale lateral viscosity variations of an order of magnitude or less 4 the steady state surface deformation problem at the heart of our geoid models may be more robust with respect to broadscale lateral viscosity variations than are models for transient deformations e g postglacial rebound 5 for loading by broadscale density heterogeneity the effects of stress dependent rheology are probably secondary to the effects of radial viscosity stratification

effects of lateral viscosity variations on the geoid 1 we investigate the effects of lateral viscosity variations lvvs on mantle circulation model predictions of the global geoid the present study is motivated in part by earlier findings that lvvs due to stiff slabs in the lower mantle have a strong influence on the geoid and that slabs in the lower mantle are perhaps no stronger than the ambient mantle however more recently it has been argued based on global seismic tomography models that lvvs are a minor effect on the geoid in the light of these seemingly contradictory results we re visit the problem of slab strength in the lower mantle we substantiate that the geoid calculated from tomography is hardly affected by the presence of lvvs whereas the geoid computed from global slab models yields a poor fit to the observed geoid when lvvs are considered however this degradation of fit only occurs for very long wavelengths of flow indicating inherent differences between the slab and tomography models we also investigate the effects on the geoid due to weak plate boundaries strong cratonic keels and a low viscosity region in the d layer due to post perovskite in addition to the geoid we attempt to fit plate motions with a circulation model that has prescribed weak zones at plate boundaries motions are matched well and taking into account lvvs the geoid with appropriate surface velocity boundary conditions agrees with the observed geoid as well as for free slip cases

a regionalized upper mantle rum seismic model seismic velocity heterogeneity in the earth s mantle is strongly concentrated near its top the shallow heterogeneity of the mantle correlates strongly with surface tectonics we use these observations as constraints of a tomographic experiment aimed at building a regionalized upper mantle rum reference model we use a select set of teleseismic travel times to minimize the mapping of mislocation into structure the data selection emphasizes the robustness of individual picks the form of the rum model is a set of velocity profiles as functions of depth through the upper mantle for each of the different tectonic provinces of earth together the profiles constitute a three dimensional model which incorporates considerable structural detail but is described by only 90 parameters and has only about 22 degrees of freedom this is achieved by irregularly sampling a detailed regionalization of the globe by detailed mapping of subducted lithosphere in the mantle as defined by seismicity and by combining these structures in an irregular grid in which bookkeeping is efficiently handled the resulting rum model includes subducting slabs as sharp fast features in the upper mantle old continents are fast young oceans are slow models have been derived for both compressional and shear velocity the rum model is designed to represent as much of upper mantle heterogeneity as seen by body wave travel times as possible with a simple model it can be useful as a reference model for individual tectonic regions travel times are efficiently generated for the rum model mislocations of explosions of known location are significantly reduced when corrections for the rum model are applied to travel time residuals for a spherically symmetrical earth model

global slab deformation and centroid moment tensor constraints on viscosity we analyze moment tensor solutions from deep subduction zone earthquakes to determine global slab deformation patterns inferred strain rates are compared to predicted deformation patterns from fluid models to help constrain the first order radial and lateral viscosity structure of the earth while all slabs that reach the lower mantle are compressed at their tip intermediate depth patterns are more complex we compute 3 d spherical flow with various slab rheologies and compare the angular misfit between the compressive eigenvectors of the resultant stress field and global centroid moment tensor gcmt solutions we find that upper mantle slab viscosities of 10 100 and lower mantle viscosities of 30 100 times the upper mantle produce the best match to gcmts a 0 1 viscosity reduction in the asthenosphere seems preferred slab geometry and lower mantle viscosity exert significant control on deformation inclusion of the phase changes at 410 km and 660 km increases extensional deformation at intermediate depth and compressional deformation at the lower mantle improving the match to gcmts for strong slabs our conclusions are fairly insensitive to surface boundary conditions however models which include net rotations of the surface with respect to the lower mantle produce compression at intermediate depths for west directed slabs and extension for east directed slabs without allowing for regional variations these models yield the best match to gcmts while significant deviations between model and seismicity remain our results show that seismicity provides an underutilized constraint for slab dynamics

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

trace metal and as solid phase speciation in sulphide mine tailings indicators of spatial distribution of sulphide oxidation in active tailings impoundments abstract redistribution of potentially harmful metals and as was studied based on selective extractions in two active sulphide mine tailings impoundments in finland the hitura tailings area contains residue from ni ore processing while the luikonlahti site includes tailings from the processing of cu co zn ni and talc ores to characterize the element solid phase speciation with respect to sulphide oxidation intensity and the water saturation level of the tailings drill cores were collected from border zones and mid impoundment locations the mobility and solid phase fractionation of ni cu co zn cr fe ca al as and s were analysed using a 5 step non sequential parallel selective extraction procedure the results indicated that metal redistribution and sulphide oxidation intensity were largely controlled by the disposal history and strategy of the tailings sorting exposure of sulphides due to delayed burial impoundment structure and water table and reactivity of the tailings metal redistribution suggested sulphide weathering in the tailings surface but also in unsaturated proximal areas beside the earthen dams and in water saturated bottom layers where o 2 rich infiltration is possible sulphide oxidation released trace metals from sulphide minerals at both locations in the hitura tailings with sufficient buffering capacity ph remained neutral and the mobilized metals were retained by secondary fe precipitates deeper in the oxidized zone in contrast sulphide oxidation induced acidity and rise in the water table after oxidation apparently remobilized the previously retained metals in luikonlahti in general continuous disposal of tailings decreased the sulphide oxidation intensity in active tailings unless there was a delay in burial and the reactive tailings were unsaturated after deposition

thermochemical piles in the lowermost mantle and their evolution abstract two large low shear wave velocity provinces llsvps lie beneath southern africa and southern pacific ocean these llsvps may be thermochemical in origin studying the dynamic evolution of these thermochemical piles will help us understand the earth s present structure and history we investigate the entrainment and evolution of an initially isolated high viscosity thermochemical pile in detail the entrainment rate of the dense pile increases with time until it being totally entrained the pile s survival time does not monotonically varies with its viscosity the chemical pile obstructs the horizontal flow along cmb and turns it into upwelling flow this may help explain the observation of plume generation zones the morphology and location of the dense pile oscillate with time a high viscosity pile can keep its location and morphology roughly unchanged for hundreds of millions years if the convective structure in the surrounding mantle keeps steady

subducted slabs and lateral viscosity variations effects on the long wavelength geoid summary the characteristic broad local maxima exhibited by the long wavelength geoid over subduction zones are investigated with a numerical model of mantle flow in a spherical axisymmetric geometry a synthetic model of buoyancy driven subduction is used to test the effects on the geoid caused by the depth of penetration of the lithosphere into the mantle by the viscosity stratification and by lateral viscosity variations lvv in the lithosphere upper and lower mantle the presence of anomalous slab density in the lower mantle guarantees geoid amplitudes comparable with the observations favouring the picture of slabs that penetrate the transition zone and sink into the deep mantle the viscosity of the lower mantle controls the long wavelength geoid to the first order ensuring a clear positive signal when it is at least 30 times greater than the upper mantle viscosity the presence of lvv in the lithosphere in the form of weak plate margins helps to increase the contribution of the surface topography causing a pronounced reduction of the geoid localized lvv associated with the cold slab play a secondary role if they are in the upper mantle on the other hand highly viscous slabs in the lower mantle exert a large influence on the geoid they cause its amplitude to increase dramatically way beyond the values typically observed over subduction zones long wavelength flow becomes less vigorous as the slab viscosity increases deformation in the upper mantle becomes more localized and power is transferred to short wavelengths causing the long wavelength surface topography to diminish and the total geoid to increase slabs may be then weakened in the lower mantle or retain their high viscosity while other mechanisms act to lower the geoid it is shown that a phase change from perovskite to post perovskite above the core mantle boundary can cause the geoid to reduce significantly thereby helping to reconcile models and observations

gypsum a joint tomographic model of mantle density and seismic wave speeds 1 gypsum is a 3 d model of mantle shear wave s speeds compressional wave p speeds and density the model is developed through simultaneous inversion of seismic body wave travel times p and s and geodynamic observations while using realistic mineral physics parameters linking wave speeds and density geodynamic observations include the global free air gravity field divergence of the tectonic plates dynamic topography of the free surface and the flow induced excess ellipticity of the core mantle boundary gypsum is built with the philosophy that heterogeneity that most closely resembles thermal variations is the simplest possible solution models of the density field from earth s free oscillations have provided great insight into the density configuration of the mantle but are limited to very long wavelength solutions alternatively scaling higher resolution seismic images to obtain density anomalies generates density fields that do not satisfy geodynamic observations the current study provides a 3 d density model for the mantle that directly satisfies geodynamic and seismic observations through a joint seismic geodynamic inversion process notable density field observations include high density piles at the base of superplume structures supporting the general results of past normal mode studies however we find that these features are more localized and have lower amplitude than past studies would suggest when we consider both fast and slow seismic anomalies in gypsum we find that p and s wave speeds are strongly correlated throughout the mantle however we find a low correlation of fast s wave zones in the deep mantle 1500 km depth with the corresponding p wave anomalies suggesting a systematic divergence from simplified thermal effects in ancient subducted slab anomalies the cratonic lithosphere and d regions are shown to have strong compositional signatures however we argue that temperature variations are the primary cause of p wave speed s wave speed and density anomalies throughout most of the mantle

can hotter mantle have a larger viscosity in the diffusion creep regime which is believed to be appropriate for the lower mantle of the earth the viscosity of rocks depends on the grain size the grain size is normally assumed to be constant in mantle convection models however it is controlled by the kinetics of polymorphic phase transformations and post transformation grain growth and can vary substantially a simple scaling analysis demonstrates one particular feature of the interaction of rheology convection and kinetics the mantle resembles a temperature dependent viscosity fluid with an extremely unusual apparent activation enthalpy for the viscosity it can take almost any value including negative so that hotter regions can have a larger viscosity or the averaged viscosity of the mantle can increase during earth s secular cooling this affects mantle dynamics and evolution and should also be taken into account in interpretating the viscosity variations in the mantle

the geoid constraint in global geodynamics viscosity structure mantle heterogeneity models and boundary conditions summary the earth s non hydrostatic gravity field or geoid provides a first order constraint on mantle density structure and dynamics geodynamic models for the geoid have proliferated since the advent of seismic mapping of mantle heterogeneity structure tomography because the geoid offers perhaps the best measured independent constraint on mantle density heterogeneity however dynamic geoid models involve a number of questionable physical assumptions and uncertainties whose effects need to be evaluated before geodynamic inferences based upon the geoid can be considered sound troubling issues include the appropriate surface boundary conditions free slip no slip plates and parametrization of radial viscosity variations how many layers can be resolved in addition to lateral viscosity variations possible chemical layering of the mantle phase transitions etc there are also uncertainties in the density heterogeneity models used as input to dynamic geoid models most of which are derived from seismic tomography and require weakly constrained empirical conversion factors to go from seismic velocity variations to density variations here we address several of the most straightforward problems inherent in geoid modelling namely the issues of viscosity structure resolution uncertainties in appropriate boundary conditions and differences among mantle heterogeneity models a robust feature of all models is a lower mantle viscosity at least a factor of 30 greater than that of the upper mantle but there is little resolution with regard to finer details such as lithospheric or uppermost mantle low viscosity zone viscosity ironically free slip boundary conditions result in the best fits to the geoid in all cases but all boundary conditions exhibit predictable trade offs with the uppermost mantle viscosity models with a single viscosity layer representing the lower mantle yield similar dynamic topography estimates of the order of 700 1000 m in amplitude regardless of the finer details of upper mantle viscosity structure boundary conditions or input heterogeneity models comparing mantle heterogeneity models based on two independent seismological determinations harvard and berkeley models and on the history of subduction we find that these models are virtually indistinguishable regarding inferences of mantle viscosity structure and amplitude of dynamic topography and in terms of the effects of different boundary conditions uncertainties concerning which type of boundary condition is appropriate are much more important than which mantle heterogeneity model is chosen given other uncertainties in modelling the geoid particularly the strong effects due to lateral viscosity variations for intermediate 10 000 km wavelengths we conclude that the class of dynamic geoid models explored so far cannot reliably elucidate the details of upper mantle viscosity structure

the long wavelength geoid from three dimensional spherical models of thermal and thermochemical mantle convection the earth s long wavelength geoid anomalies have long been used to constrain the dynamics and viscosity structure of the mantle in an isochemical whole mantle convection model however there is strong evidence that the seismically observed large low shear velocity provinces llsvps in the lower mantle underneath the pacific and africa are chemically distinct and likely denser than the ambient mantle in this study we have formulated dynamically self consistent 3 d spherical mantle convection models to investigate how chemically distinct and dense piles above the core mantle boundary may influence the geoid our dynamic models with realistic mantle viscosity structure produce dominantly spherical harmonic degree 2 convection similar to that of the present day earth the models produce two broad geoid and topography highs over two major thermochemical piles in the lower mantle consistent with the positive geoid anomalies over the pacific and african llsvps our geoid analysis showed that the bottom layer with dense chemical piles contributes negatively to the total geoid while the layer immediately above the chemical piles contributes positively to the geoid canceling out the effect of the piles thus the bottom part of the mantle as a compensation layer has zero net contribution to the total geoid and the thickness of the compensation layer is 1000 km or 2 to 3 times as thick as the chemical piles our results help constrain and interpret the large scale thermochemical structure of the mantle using surface observations of the geoid and topography as well as seismic models of the mantle

inversion for mantle viscosity profiles constrained by dynamic topography and the geoid and their estimated errors summary we perform a joint inversion of earth s geoid and dynamic topography for radial mantle viscosity structure using a number of models of interior density heterogeneities including an assessment of the error budget we identify three classes of errors those related to the density perturbations used as input those due to insufficiently constrained observables and those due to the limitations of our analytical model we estimate the amplitudes of these errors in the spectral domain our minimization function weights the squared deviations of the compared quantities with the corresponding errors so that the components with more reliability contribute to the solution more strongly than less certain ones we develop a quasi analytical solution for mantle flow in a compressible spherical shell with newtonian rheology allowing for continuous radial variations of viscosity together with a possible reduction of viscosity within the phase change regions due to the effects of transformational superplasticity the inversion reveals three distinct families of viscosity profiles all of which have an order of magnitude stiffening within the lower mantle with a soft d layer below the main distinction among the families is the location of the lowest viscosity region directly beneath the lithosphere just above 400 km depth or just above 670 km depth all profiles have a reduction of viscosity within one or more of the major phase transformations leading to reduced dynamic topography so that whole mantle convection is consistent with small surface topography

localization of gravity and topography constraints on the tectonics and mantle dynamics of venus summary we develop a method for spatio spectral localization of harmonic data on a sphere and use it to interpret recent high resolution global estimates of the gravity and topography of venus in the context of geodynamical models our approach applies equally to the simple spatial windowing of harmonic data and to variable length scale analyses which are analogous to a wavelet transform in the cartesian domain using the variable length scale approach we calculate the localized rms amplitudes of gravity and topography as well as the spectral admittance between the two fields as functions of position and wavelength the observed admittances over 10 per cent of the surface of venus highland plateaus and tessera regions are consistent with isostatic compensation of topography by variations in crustal thickness while admittances over the remaining 90 per cent of the surface rises plains and lowlands indicate that longwavelength topography is dominantly the result of vertical convective tractions at the base of the lithosphere the global average crustal thickness is less than 30 km but can reach values as large as 40 km beneath tesserae and highland plateaus we also note that an earth like radial viscosity structure cannot be rejected by the gravity and topography data and that without a mechanical model of the lithosphere admittance values cannot constrain the thickness of the thermal boundary layer of venus modelling the lithosphere as a thin elastic plate indicates that at the time of formation of relief in highland plateaus and tesserae the effective elastic plate thickness k was less than 20 km estimates of t at highland rises are consistently less than 30 km our inability to find regions with t 30 km is inconsistent with predictions made by a class of catastrophic resurfacing models

models of isostatic and dynamic topography geoid anomalies and their uncertainties knowledge of the dynamic topography at earth s surface caused by sublithospheric density contrasts would provide crucial constraints on models of mantle dynamics we calculate global models of this dynamic topography by subtracting from the observed topography estimates of the topography caused by assumed isostatically compensated density variations in the crust the oceanic lithosphere and the continental tectosphere we also calculate the isostatic geoid anomaly that would result from these compensated near surface density anomalies because there is controversy about the thermal structure of old oceanic lithosphere we investigate two models of the cooling of the oceanic lithosphere half space and plate and calculate the effect of each on the inferred dynamic topography peak amplitudes of dynamic topography from sublithospheric sources expanded to spherical harmonic degree 6 are approximately 1 km we estimate the uncertainties in the calculated dynamic topography and geoid by combining the errors in the data and systematic errors to obtain the spectral coefficients of the fields we use weighted least squares inversions the calculated dynamic topography arising from sublithospheric sources residual geoid and errors associated with these fields can be used in studies of mantle dynamics

enormous lithium isotopic variations of abyssal peridotites reveal fast cooling and melt fluid rock interactions author posting american geophysical union 2020 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research solid earth 125 9 2020 e2020jb020393 doi 10 1029 2020jb020393

computations of the viscoelastic response of a 3 d compressible earth to surface loading an application to glacial isostatic adjustment in antarctica and canada s u m m a r y we develop a 3 d finite element model to study the viscoelastic response of a compressible earth to surface loads the effects of centre of mass motion polar wander feedback and selfconsistent ocean loading are implemented to assess the model s accuracy we benchmark the numerical results against a semi analytic solution for spherically symmetric structure we force our model with the ice 5g global ice loading history to study the effects of laterally varying viscosity structure on several glacial isostatic adjustment gia observables including relative sea level rsl measurements incanada and present day time variable gravity and uplift rates in antarctica canadian rsl observations have been used to determine the earth s globally averaged viscosity profile antarcticgps uplift rates have been used to constrainantarcticgia models and gia time variable gravity and uplift signals are error sources for grace and altimeter estimates of present day antarctic ice mass loss and must be modelled and removed from those estimates computinggia results for a 3 d viscosity profile derived from a realistic seismic tomography model and comparing with results computed for 1 d averages of that 3 d profile we conclude that 1 a gia viscosity model based on canadian relative sea level data is more likely to represent a canadian average than a true global average 2 the effects of 3 d viscosity structure on grace estimates of present day antarctic mass loss are probably smaller than the difference between gia models based on different antarctic deglaciation histories and 3 the effects of 3 d viscosity structure on antarctic gps observations of present day uplift rate can be significant and can complicate efforts to use gps observations to constrain 1 d gia models

a new inference of mantle viscosity based upon joint inversion of convection and glacial isostatic adjustment data we present new profiles of mantle viscosity derived on the basis of non linear occam style joint inversions of an extensive set of data associated with mantle convection and glacial isostatic adjustment gia the convection related observables include satellite derived free air gravity harmonics the geodetically inferred excess ellipticity of the cmb and tectonic plate motions the gia constraints involve two classes of observables previously shown to be relatively insensitive to errors in the late pleistocene ice history the so called fennoscandian relaxation spectrum frs and a set of site specific decay times determined from the postglacial sea level history in hudson bay and sweden the inverted viscosity profiles show a significant three orders of magnitude increase from the upper mantle mean value of f4 10 20 pa s to a high viscosity 10 23 pa s peak at

global sediment thickness data set updated for the australian antarctic southern ocean we present a new 5 min sediment thickness grid for the australian antarctic region 60 e 155 e 30 s 70 s new seismic reflection and refraction data have been used to add detail to the conjugate australian and antarctic margins and intervening ocean floor where regional sediment thickness patterns were poorly known previously on the margins sediment thickness estimates were computed from velocity depth functions from sonobuoy refraction velocity solutions ground truthed against seismic reflection data for the southeast indian ridge abyssal plains sediment thickness contours from geli et al 2007 were used the new regional minimum sediment thickness grid was combined with the global national geophysical data center ngdc sediment grid to create an updated global grid even using the minimum estimates sediment accumulations on the extended australian and antarctic continental margins are 2 km thicker across large regions and up to 9 km thicker in the ceduna basin compared to the global ngdc compilation of sediment thickness data

effects on the long wavelength geoid anomaly of lateral viscosity variations caused by stiff subducting slabs weak plate margins and lower mantle rheology abstract instantaneous flow numerical calculations in a three dimensional spherical shell are employed to investigate the effects of lateral viscosity variations lvvs in the lithosphere and mantle on the long wavelength geoid anomaly the density anomaly model employed is a combination of seismic tomography and subducting slab models based on seismicity the global strain rate model is used to represent weak low viscosity plate margins in the lithosphere lvvs in the mantle are represented on the basis of the relation between seismic velocity and temperature i e temperature dependent rheology when highly viscous slabs in the upper mantle are considered the observed positive geoid anomaly over subduction zones can be accounted for only when the viscosity contrast between the reference upper mantle and the lower mantle is approximately 1 0 3 or lower and weak plate margins are imposed on the lithosphere lvvs in the lower mantle exert a large influence on the geoid pattern the calculated geoid anomalies over subduction zones exhibit generally positive patterns with quite high amplitudes compared with observations even when the low activation enthalpy of perovskite in the lower mantle is employed inferred weak slabs in the lower mantle may be explained in terms of recent mineral physics results highlighting the possibility of grain size reduction due to the postspinel phase transition

the relative density to shear velocity scaling in the uppermost mantle we perform inversions of gravity data geopotential model egm96 and seismic tomography model s16rlbm for the scaling factor which relates relative density anomalies to relative s wave velocity anomalies the gravity data and tomographic model are anti correlated below continents down to a depth of z 200 km this anti correlation is not present below oceans except for smoothness which is controlled by a damping factor no a priori information is added to the inversion data are filtered between degrees 11 and 16 of the spherical harmonic expansion this spectral window is well suited for the study of intermediate size 2000 4000 km anomalies in the uppermost mantle calculations are made separately for sub continental and sub oceanic mantle the sub continental and sub oceanic scaling factors are significantly different at depths shallower than 260 km in both cases the magnitude of is around 0 05 the sub continental scaling factor has a positive root down to z 220 km whereas the sub oceanic scaling factor yields positive values down to z 140 km only at depth shallower than 350 km models of do not depend on the damping factor or the viscosity model at depths greater than 350 km the resolution of z decreases significantly and low degrees 2 4 add information from large scale anomalies and from the lower mantle as a result the shape and values of for 2 16 and 11 16 are significantly different at depths greater than 350 km a possible explanation of the discrepancies between the sub continental and sub oceanic scaling factor is that intermediate scale anomalies are more important in the continental uppermost mantle than in the oceanic uppermost mantle 2001 elsevier science b v all rights reserved

modification of the lithospheric stress field by lateral variations in plate mantle coupling 1 the presence of deeply penetrating continental roots may locally increase the magnitude of basal shear tractions by up to a factor of 4 compared to a layered viscosity structure here we examine how these increases in mantle lithosphere coupling influence stress patterns in the overlying elastic lithosphere by coupling a mantle flow model to a model for the elastic lithosphere we show that the amplification of mantle tractions beneath cratons increases elastic stress magnitudes by at most a factor of only 1 5 in a pattern not correlated to local basal traction changes this disconnect is explained by the transmission of elastic stresses across large distances which makes them sensitive to regionally averaged changes in basal tractions but not local variations our results highlight the importance of regional variations in lithospheric strength which could allow stress patterns to more closely match regional changes in basal shear

accurate measurements of residual topography from the oceanic realm in the oceans our understanding of plate subsidence as a function of age permits residual depth anomalies to be identified and mapped these anomalies may reflect dynamic topography and could be an important means for constraining convective circulation of the sublithospheric mantle here we analyze a global database of seismic reflection and wide angle profiles from heavily sedimented oceanic crust which abuts continental lithosphere at 449 locations we calculated water loaded subsidence compared it with a reference age depth relationship and determined residual depth we then combined these spot measurements of residual depth with observations from mid oceanic ridges and from selected ship track bathymetry to construct a global map of residual depth our results suggest that the amplitude of residual depth varies by up to 1 km with wavelengths of order 103 km we compare our residual depths with free air gravity and seismic tomographic anomalies our results show that residual depths correlate with long wavelength gravity anomalies in contrast correlations between residual depths and vertically averaged shear velocity anomalies within the upper and or the lower mantle are weaker the largest discrepancies occur at short 1000 km wavelengths these combined observations suggest that residual depth anomalies could be generate by density variations within a thin 102 km low viscosity layer beneath the lithosphere our global compilation should play a significant role in helping to refine predictive geodynamical models

an integrated global model of present day plate motions and plate boundary deformation summary in this paper we present a global model gsrm 1 of both horizontal velocities on the earth s surface and horizontal strain rates for almost all deforming plate boundary zones a model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field in our model we perform a least squares fit between model velocities and observed geodetic velocities as well as between model strain rates and observed geological strain rates model velocities and strain rates are interpolated over a spherical earth using bi cubic bessel splines we include 3000 geodetic velocities from 50 different mostly published studies geological strain rates are obtained for central asia only and they are inferred from quaternary fault slip rates for all areas where no geological information is included a priori constraints are placed on the style and direction but not magnitude of the model strain rate field these constraints are taken from a seismic strain rate field inferred from normalized focal mechanisms of shallow earthquakes we present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones generally the strain rate tensor field is consistent with geological and seismological data with the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs we find that in general there is a good agreement between the present day plate motions we obtain and longterm plate motions but a few significant differences exist the rotation rates for the indian arabian and nubian plates relative to eurasia are 30 13 and 50 per cent slower than the nuvel1a estimate respectively and the rotation rate for the nazca plate relative to south america is 17 per cent slower on the other hand caribbean north america motion is 76 per cent faster than the nuvel 1a estimate while crustal blocks in the india eurasia collision zone move significantly and self consistently with respect to bounding plates only a very small motion is predicted between the nubian and somalian plates by integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in for instance redefining a no net rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation

mantle dynamics isostasy and the support of high terrain dynamic topography is commonly understood to be deflection of the earth s surface that results from convection of the mantle because different authors use the words dynamic topography differently topography designated as dynamic may amount to only a few hundred meters or may exceed 2000 m for most regions however surface heights computed on the assumption that the lithospheric column is in isostatic equilibrium provide good approximations to observed topography the small free air gravity anomalies and still smaller isostatic anomalies 2000 m of dynamic topography moreover simple examples show that if flow induced stresses maintain a given density distribution then the resultant surface deflections can be smaller than those that would exist in isostatic equilibrium in light of confusion over the term dynamic topography we offer readers simple tools that we hope will enable them to diagnose the component of topography that results from flow induced stresses and to distinguish it from topography that is compensated isostatically

age spreading rates and spreading asymmetry of the world s ocean crust we present four companion digital models of the age age uncertainty spreading rates and spreading asymmetries of the world s ocean basins as geographic and mercator grids with 2 arc min resolution the grids include data from all the major ocean basins as well as detailed reconstructions of back arc basins the age spreading rate and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments the age uncertainties for grid cells coinciding with marine magnetic anomaly identifications observed or rotated to their conjugate ridge flanks are based on the difference between gridded age and observed age the uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges resulting in ridge jumps toward hot spots we also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age depth relationships the new set of grids helps to investigate prominent negative depth anomalies which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow a combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems

variations in grain size and viscosity based on vacancy diffusion in minerals seismic tomography and geodynamically inferred mantle rheology the effect of grain size on mantle viscosity is comparable to that of temperature and pressure the current 3 d distribution of grain size in the mantle is however unknown to explore the possible variability of grain size we use the following geodynamic inferences of effective viscosity vacancy diffusion rates in upper mantle minerals and perovskite in the lower mantle lateral variations in temperature derived from seismic images and different geotherms an important outcome of this modeling is a new mapping of lateral viscosity variations throughout the mantle the corresponding 3 d variations in grain size are characterized by 2 orders of magnitude changes we find a correlation between grain size variability in the mantle and absolute viscosity changes with depth our findings suggest that the traditional assumption of arrhenius temperature dependence for vacancy diffusion in the lower mantle is not sufficient to constrain the deformation mechanisms that determine its effective bulk viscosity

the dynamics of plate tectonics and mantle flow from local to global scales plate tectonics is regulated by driving and resisting forces concentrated at plate boundaries but observationally constrained high resolution models of global mantle flow remain a computational challenge we capitalized on advances in adaptive mesh refinement algorithms on parallel computers to simulate global mantle flow by incorporating plate motions with individual plate margins resolved down to a scale of 1 kilometer back arc extension and slab rollback are emergent consequences of slab descent in the upper mantle cold thermal anomalies within the lower mantle couple into oceanic plates through narrow high viscosity slabs altering the velocity of oceanic plates viscous dissipation within the bending lithosphere at trenches amounts to 5 to 20 of the total dissipation through the entire lithosphere and mantle

phosphorus retention by phlogopite rich mine tailings abstract sewage water rich in p poses a threat to natural water systems in households that are not connected to a sewer network an easily maintained purification technique is needed to remove p from domestic waste waters in the present study the p retention properties of phlogopite rich mine tailings were studied to determine whether the untapped tailings can be utilised in wastewater treatment for this purpose on the basis of its chemical and mineralogical properties this material produced in the enrichment process of apatite ore in siilinjarvi finland can be assumed to act as a p sorbent the p retention capacity and the p sorption mechanisms of phlogopite rich tailings were studied with desorption sorption isotherms and various chemical extractions the impact of the artificial weathering of the material as well as the reaction time and particle size on p retention were also investigated the fluctuating shape of the isotherm determined for the untreated material suggests the operation of several sorption mechanisms the results imply that phlogopite rich tailings retain p efficiently through specific sorption by amorphous al and fe oxides and possibly also by calcite present as an accessory mineral acidification of the material extended reaction time and decrease in particle size markedly increased the p retention

the relationship between topography and gravity on earth and venus abstract the measurement of the admittance between the topography and the gravity of a planet as a function of wavelength provides important constraints on its interior processes a detailed discussion of the influence of noise on such measurements shows that at long wavelengths the admittance is best determined in the frequency domain using gravity as input and topography as output this procedure is used to estimate the admittance in the pacific and indian oceans the observed values are reduced by volcanism above plumes which produces a contribution to the long wavelength compensated topography when this effect is taken into account there is little evidence that the admittance is reduced by the presence of a low viscosity zone in the upper mantle a similar study of venus shows an excellent correlation between gravity g and topography h for wavelengths greater than 700 km with an admittance of about 50 mgal km 1 this value agrees well with that expected from numerical axisymmetric models of plumes and can be used to construct maps of residual topography by calculating h g 50 where h is in kilometers and g in milligals the power spectrum of the gravity field and its skewness with positive anomalies covering a smaller area but being larger than the negative ones are also in agreement with those of the numerical models of the major topographic features only aphrodite and ishtar terrae behave differently with a value of admittance of about one third of other large structures this difference requires their topography to be partly supported by variations in crustal thickness by analogy with similar structures on earth both are likely to be supported by volcanically thickened crust on top of rising plumes though the observed relationships do not rule out other models the behavior of the admittance at long wavelengths is important because it can constrain the thickness of the convecting layer at wavelengths of more than 3000 km the gravity data provides some evidence that the layer depth is about 1000 km over the center of beta and phoebe regiones there are short wavelength anomalies of residual topography produced by crust that is thinner than that elsewhere flanked by positive anomalies of thicker crust the regions of thin crust occur beneath rift zones this behavior can be explained if crust flows down the flanks of elevated regions above plumes and can generate coronae when the plume support disappears

measuring dynamic topography an analysis of southeast asia 1 theoretical models of dynamic topography generated by subducting slabs and consistent with the observed geoid predict 1 2 km of subsidence on wavelengths of 102 103 km the demonstrable existence of such subsidence has important implications for understanding sedimentary basin formation relative sea level changes as well as the earth s viscosity and density structure here we present the results of a combined analysis of subsidence data from oceanic marginal basins and their fringing continental shelves we have chosen to analyze a large area of southeast asia where dynamical predictions are believed to be well constrained by the history of subduction our joint analysis constrains the maximum amplitude of dynamic subsidence to be 300 m with a range of 0 500 m significantly less than predicted actively spreading marginal basins have no resolvable dynamic subsidence but after removing the effects of crustal thickness variation a few inactive marginal basins are consistently 200 500 m deeper than normal adjacent continental sedimentary basins record a possible dynamic subsidence of 0 500 m although wavelengths are shorter than expected 102 km there is also disagreement between the predicted and observed distribution of anomalous subsidence as well as inconsistencies in initiation and duration these results suggest that mass excess within the mantle represented by subducted slabs has little discernible effect on surface topography instead subsidence and marine inundations throughout southeast asia are predominantly controlled by lithospheric extension and or by foreland loading the spatial and temporal distribution of anomalous subsidence suggests that it might not be caused by dynamic topography associated with subducting slabs a large discrepancy between predicted and observed dynamic topography could be reconciled by changing the density structure of subducted slabs by supporting mass excess with a marked increase in viscosity at depth or by decoupling slabs from the surface with a very low viscosity layer

slab stress and strain rate as constraints on global mantle flow dynamically consistent global models of mantle convection with plates are developed that are consistent with detailed constraints on the state of stress and strain rate from deep focus earthquakes models that best fit plateness criteria and plate motion data have strong slabs that have high stresses the regions containing the m w 8 3 bolivia and m w 7 6 tonga 1994 events are considered in detail modeled stress orientations match stress patterns from earthquake focal mechanisms a yield stress of at least 100 mpa is required to fit plate motions and matches the minimum stress requirement obtained from the stress drop for the bolivia 1994 deep focus event the minimum strain rate determined from seismic moment release in the tonga slab provides an upper limit of 200 mpa on the strength in the slab

subducted slabs and the geoid constraints on mantle rheology and flow geoid anomalies are primarily the result of the density contrasts driving mantle convection and plate motion the total geoid anomaly resulting from a given density contrast in a convecting earth is affected by the mass anomalies associated with the flow induced deformation of the upper surface and internal compositional boundaries as well as by the density contrast itself these boundary deformations and hence the total gravity field depend on the radial distribution of effective viscosity if the internal density contrasts can be estimated as is the case for subducted slabs useful constraints can be placed on the depth and on the variation of viscosity with depth of the convecting system the degree 4 9 components of the observed long wavelength geoid are highly correlated with those predicted by a density model for seismically active subducted slabs the positive sign of the correlation requires that the effective viscosity increases with depth by a factor of 30 or more the amplitude of the correlation cannot be explained by the density contrasts associated with just the seismically active parts of subducted slabs however the amplitude can be explained if the density contrasts associated with subduction extend into the lower mantle or if old lithosphere is piled up at the base of the upper mantle beneath subduction zones to a thickness in excess of 350 km over horizontal distances of thousands of kilometers mantlewide convection in a mantle that has a viscosity increasing with depth provides a simple explanation of the long wavelength geoid anomalies over subduction zones

influence of continental roots and asthenosphere on plate mantle coupling the shear tractions that mantle flow exerts on the base of earth s lithosphere contribute to plate driving forces and lithospheric stresses we investigate the sensitivity of these tractions to sub lithospheric viscosity variations by comparing shear tractions computed from a mantle flow model featuring laterally varying lithosphere and asthenosphere viscosity with those from a model with layered viscosity lateral viscosity variations generally do not change the direction of shear tractions but deeply penetrating continental roots increase traction magnitudes by a factor of 2 5 compared to 100 km thick lithosphere a low viscosity asthenosphere decreases traction magnitudes by a smaller amount and is important only if 100 km thick increased plate mantle coupling beneath thick continental lithosphere may increase plate driving forces surface deformation and mantle derived lithospheric stresses in these regions by contrast a low viscosity asthenosphere does not decouple the lithosphere from mantle flow highlighting the geological importance of mantle tractions on the lithosphere

phosphate sorption by calcium carbonate in some soils of the mediterranean part of spain abstract we studied the properties of caco3 and phosphate sorption of 36 calcareous soil samples collected across the mediterranean part of spain owing to its low surface area and to its relatively low phosphate sorption capacity caco3 did not influence sorption markedly other soil components of calcareous soils such as fe oxides or silicate clays appear to be quantitatively more important at least for sorption at low phosphate equilibrium concentrations

influence of variable uncertainties in seismic tomography models on constraining mantle viscosity from geoid observations the radial viscosity structure of the earth is explored on the basis of the geoid observations the variations of uncertainty in seismic tomography models are accounted for when finding the radial viscosity structure the new methodology we propose attempts to fit more closely those features of the geoid that are better constrained by tomography models and avoids to fit those features that are poorly constrained this approach is particularly important because the error of geoid predictions caused by uncertainties in seismic tomography models is overwhelmingly larger than the noise in the geoid measurements the synthetic tests indicate that the viscosity structures obtained by disregarding the uncertainty variations in seismic tomography models can be biased depending on the geoid spectral band and on the input seismic tomography model when the uncertainty variations in seismic models are considered in the inversion process results do not indicate a viscosity in the transition zone lower than in the upper mantle a robust feature found with the new method is a viscosity in the upper mantle two orders of magnitude smaller than in the lower mantle the error covariance of seismic tomography models is critical for the method we suggest a covariance matrix rigorously derived by seismologists should help to even more reliably infer the viscosity structure and relation between anomalies in density and seismic velocities from surface observations such as the geoid and thus lead to a better knowledge of the earth interior

subduction zone evolution and low viscosity wedges and channels dehydration of subducting lithosphere likely transports fluid into the mantle wedge where the viscosity is decreased such a decrease in viscosity could form a low viscosity wedge lvw or a low viscosity channel lvc on top of the subducting slab using numerical models we investigate the influence of low viscosity wedges and channels on subduction zone structure slab dip changes substantially with the viscosity reduction within the lvws and lvcs for models with or without trench rollback overthickening of slabs is greatly reduced bylvws or lvcs two divergent evolutionary pathways have been found depending on the maximum depth extentofthelvwandwedgeviscosity assumingaviscositycontrastof0 1withbackgroundasthenosphere modelswithalvwthat extendsdown to 400km depthshow asteeply dipping slab while models with anlvw that extends to muchshallower depth such as 200 km can produce slabs that are flat lying beneath the overriding plate there is a narrow range of mantle viscosities that produces flatslabs 5to10 10 19 pas andthe slab flatteningprocessisenhanced bytrenchrollback slabcanbedecoupled fromthe overriding platewithalvcifthe thicknessisatleastafew10s ofkm the viscosityreduction isatleastafactor oftwoandthedepthextentofthe lvc is several hundred km these models have important implications for the geochemical and spatial evolution of volcanic arcs and the state of stress within the overriding plate the models explain the poor correlation between traditional geodynamic controls subductingplateageandconvergencerates onslabdip wepredictthatwhenvolcanicarcschangetheirdistancefromthetrench they could be preceded by changes in arc chemistry we predict that there could be a larger volatile input into the wedge when arcs migrate toward the trench and visa versa the transition of a subduction zone into the flat lying regime could be preceded by changes in the volatile budget such that the dehydration front moves to shallower depths our flat slab models shed some light on puzzling flat subductionsystems likeincentralmexico wherethereisnodeformationwithintheoverridingplateabovetheflatsegment thelack

mapping the mass distribution of earth s mantle using satellite derived gravity gradients the dynamics of earth s mantle are difficult to constrain analysis of goce satellite gravity data can be used to identify gravity anomalies to mid mantle depths and hence to identify regions of tectonic plate subduction and plume upwelling in the mantle

multiscale dynamics of the tonga kermadec subduction zone our understanding of mantle convection and the motion of plates depends intimately on our understanding of the viscosity structure of the mantle while geoid and gravity observations have provided fundamental constraints on the radial viscosity structure of the mantle the influence of short wavelength variations in viscosity is still poorly understood we present 2 d and 3 d finite element models of mantle flow including strong lateral viscosity variations and local sources of buoyancy owing to both thermal and compositional effects we first use generic 2 d models of a subduction zone to investigate how different observations depend on various aspects of the viscosity structure in particular the slab and lower mantle viscosity and the presence of a low viscosity region in the mantle wedge above the slab we find that 1 the strain rate provides a strong constraint on the absolute viscosity of the slab 10 23 pa s 2 stress orientation within the slab is sensitive to the relative viscosity of the slab lower mantle and the wedge and 3 the stress state and topography of the overriding plate depend on the wedge viscosity and local sources of buoyancy in particular the state of stress in the overriding plate changes from compression to extension with the addition of a low viscosity wedge we then use observations of strain rate stress orientation dynamic topography and the geoid for the tonga kermadec subduction zone as simultaneous constraints on the viscosity and buoyancy in a 3 d regional dynamic model together these observations are used to develop a self consistent model of the viscosity and buoyancy by taking advantage of the sensitivity of each observation to different aspects of the dynamics over a broad range of length scales the presence of a low viscosity wedge makes it possible to match observations of shallow dynamic topography and horizontal extension within the backarc and down dip compression in the shallow portion of the slab these results suggest that a low viscosity wedge plays an important role in controlling the presence of backarc spreading however for a model with a low viscosity and low density region that provides a good fit to the observed topography we find that a reduction of the slab density by a factor of 1 3 relative to the reference density model is required to match the observed geoid these results suggest that compensation of the slab by dynamic topography may be a much smaller effect at short to intermediate wavelengths than predicted by long wavelength modelling of the geoid

unraveling topography around subduction zones from laboratory models the relief around subduction zones results from the interplay of dynamic processes that may locally exceed the iso static contributions the viscous dissipation of the energy in and around subduction zones is capable of generating kilometer scale vertical ground movements in order to evaluate dynamic topography in a selfconsistent subduction system we carried out a set of laboratory experiments wherein the lithosphere and mantle are simulated by means of newtonian viscous materials namely silicone putty and glucose syrup models are kept in their most simple form and are made of negative buoyancy plates of variable width and thickness freely plunging into the syrup the surface of the model and the top of the slab are scanned in three dimensions a forebulge systematically emerges from the bending of the viscous plate adjacent to the trench with a large wavelength dynamic pressure offsets the foreside and backside of the slab by 500 m on average the suction that accompanies the vertical descent of the slab depresses the surface on both sides at a distance equal to the half width of the slab the topographic depression amounts to 500 m on average and becomes negligible at a distance that equals the width of the slab in order to explore the impact of slab rollback on the topography the trailing edge of the plates is alternatively fixed to fixed mode and freed from free mode the end wall of the tank both the pressure and suction components of the topography are 30 lower in the free mode indicating that slab rollback fosters the dynamic subsidence of upper plates our models are compatible with first order observations of the topography around the east scotia tonga kermadec and banda subduction zones which exhibit anomalous depths of nearly 1 km as compared to adjacent sea floor of comparable age

grain size variations in the earth s mantle and the evolution of primordial chemical heterogeneities 1 chemical heterogeneities with relatively high viscosity are known to be poorly mixed by mantle convection one of the factors which can cause viscosity variations is the grain size analysis of various physical processes in the earth s mantle suggests that variation in the grain size can be extremely large even outside of subducting slabs the largest grains are formed in the early molten earth where ostwald ripening is controlled by liquid state diffusion the smallest grains are formed due to recrystallization by the spinel perovskite phase transformation in downwelling flow and subsequent ostwald ripening the viscosity contrast between primordial large grain size material and recrystallized material is likely to be many orders of magnitude preliminary numerical simulations show that strongly time dependent mantle convection can process primordial large grain size heterogeneities through the spinel perovskite phase boundary only after a few overturns this reduces the viscosity contrasts and leads to rapid mixing by mantle convection a more steady flow in the lower mantle may lead to the formation of stagnant poorly mixed regions which may never have had a chance to cross the 660 km discontinuity and be recrystallized by the spinel perovskite phase transformation heterogeneities can also avoid grain size reduction and mixing if their density is slightly larger than the surrounding mantle in this case they accumulate at the core mantle boundary

inferring radial models of mantle viscosity from gravity grace data and an evolutionary algorithm convective flow in the mantle can be thought of and modeled as exclusively driven by density heterogeneities in the mantle itself and the resulting lateral variations in the earth s gravity field with this assumption and a model of mantle rheology a theoretical relationship can be found between 3d mantle structure and flow related quantities that can be measured on the earth s surface like free air gravity anomalies this relationship can be used to set up an inverse problem with 1d mantle viscosity as a solution in the assumption that seismic velocity anomalies be of purely thermal origin and related to density anomalies by a simple scaling factor we invert the large scale length component of the above mentioned measurements jointly with seismic observations waveforms and or travel times to derive an accurate 5 layer spherically symmetric model of upper and lower mantle viscosity we attempt to account for non uniqueness in the inverse problem by exploring the solution space formed of all possible radial profiles of earth viscosity by means of a non deterministic global optimization method the evolutionary algorithm ea for each sampled point of the solution space a forward calculation is conducted to determine a map of gravity anomalies whose similarity to grace gravity recovery and climate experiment is then measured the procedure is iterated to convergence according to ea criteria the robustness of the inversion is tested by means of synthetic tests indicating that our gravity data set is able to constrain less than 6 radial layers each with uniform viscosity independently of the tomographic model or the scaling factor adopted to convert seismic velocity into density structure the ea optimization method finds viscosity profiles characterized by low viscosity in a depth range corresponding to the transition zone and relatively uniform elsewhere

spatial and temporal patterns of cenozoic dynamic topography around australia 1 despite its importance the spatial and temporal pattern of dynamic topography generated by mantle convective circulation is poorly known we present accurate estimates of dynamic topography from oceanic basins and continental margins surrounding australia our starting point is measurement of residual depth anomalies on the oldest oceanic floor adjacent to the continental shelf these anomalies were determined from a combined dataset of 200 seismic reflection and wide angle images of well sedimented oceanic crust they have amplitudes of between 1 km and 0 5 km and their spatial variation is broadly consistent with long wavelength free air gravity and shallow seismic tomographic anomalies along the northwest shelf a regional depth anomaly of 300 to 700 m intersects the adjacent continental shelf the temporal evolution of this anomaly was determined by analyzing the stratigraphic architecture of an extensive carbonate platform which fringes the shelf and records a dramatic switch from progradation to aggradation during neogene times three dimensional seismic mapping calibrated by boreholes was used to calculate water loaded subsidence histories at rollover points of clinoforms along the shelf at 9 3 ma the rate of subsidence increases from 5 to up 75 m myr 1 generating a subsidence anomaly of 300 to 700 m the amplitude of this anomaly varies along the shelf and cannot be generated by glacio eustatic sea level variation instead we propose that a regional subsidence episode which affects both the proximal shelf and the distal oceanic basin was generated by convective drawdown by combining our results with other published estimates of uplift and subsidence a map of australia which shows the spatial and temporal pattern of dynamic topography is presented most but not all of australia s epeirogeny can be attributed to rapid northward motion of the australian plate over a pre existing pattern of convective circulation

interpreting gravity geoid and topography for convection with temperature dependent viscosity application to surface features on venus while venus and earth are similar in size venus does not appear to have developed the same system of mobile surface plates which dominates convective heat transfer from the interior of earth numerical models with temperature dependent viscosity do not produce plate boundaries and are more closely reminiscent of venus than earth we demonstrate that many puzzling aspects of surface features on venus are also found in the analysis of the surface observables in these models despite having no strong lithosphere our calculations exhibit very high geoid topography ratios and uncompensated short wavelength topography surface heat flux values are not required to be very different from earth scaled values and the mantle remains below the likely solidus

sensitivity of the short to intermediate wavelength geoid to rheologic structure in subduction zones 1 the rheologic structure of subduction zones determines how the negative buoyancy of sinking lithosphere slabs couples to the surface to cause surface deformation and plate motion however the rheologic structures determined using different methods are inconsistent analysis of the geoid and some dynamical models conclude that slabs must be weak whereas other dynamical models and experimentally determined rheology predict that slabs are strong using idealized three dimensional models of a subduction zone we show that lateral variations in viscosity lvvs within a slab caused by yielding render the geoid insensitive to the viscosity structure outside of the bending region of the slab spectral analysis of the geoid up to harmonic degree 360 features at wavelengths down to 110 km shows that lvvs cause significant mode coupling with changes to the long wavelength geoid 1000 km caused by short wavelength 500 km changes to dynamic topography models with either a uniformly weak slab or a strong slab with yielding provide a good match to the observed geoid spectrum and characteristic features of the geoid over subduction zones therefore observations other than the geoid are needed to constrain the strength profile of subducting slabs

static and dynamic support of western united states topography article history accepted 7 october 2013 available online 31 october 2013 editor p shearer isostatic and dynamic models of earth s surface topography can provide important insights into the driving processes of tectonic deformation we analyze these two estimates for the tectonically active western united states using refined structural models derived from earthscope usarray for the crust use of recent moho depth measurements and crustal density anomalies inferred from passive source seismology improve isostatic models however seismically determined lithospheric thickness variations from lithosphere asthenosphere boundary lab maps and lithospheric and mantle density anomalies derived from heat flow or uppermost mantle tomography do not improve isostatic models substantially perhaps this is a consequence of compositional heterogeneity a mismatch between thermal and seismological lab and structural complexity caused by smaller scale dynamics the remaining non isostatic dynamic component of topography is large topography anomalies include negative residuals likely due to active subduction of the juan de fuca plate and perhaps remnants of formerly active convergence further south along the margin our finding of broad scale positive residual topography in the basin and range substantiates previous results implying the presence of anomalous buoyancy there which we cannot fully explain the colorado plateau does not appear dynamically anomalous at present except at its edges many of the residual topography features are consistent with predictions from mantle flow computations this suggests a convective origin and important interactions between vigorous upper mantle convection and intraplate deformation

quest for dynamic topography observations from southeast asia transient dynamic topography is maintained by time varying density anomalies deep within earth9s mantle there is considerable interest in predicting and measuring dynamic topography because its spatial and temporal variation will help to track changes in the pattern of mantle convection despite the availability of increasingly elaborate predictive models there is little agreement about the amplitude wavelength and rate of change of dynamic topography here we analyze a hybrid data set of subsidence observations from continental and oceanic basins in southeast asia where published dynamic models predict 1 2 km of regional subsidence residual subsidence was isolated by removing the well defined effects of lithospheric extension and or cooling at long wavelengths 10 3 km the amplitude of residual subsidence i e maximum permissible dynamic subsidence has an upper bound of only 300 m the spatial distribution of permissible dynamic topography has no simple spatial or temporal relationship to the pattern of subduction over the past 65 m y anomalous subsidence commenced 5 10 m y ago accelerating to a present day rate of 100 m m y our results show that density anomalies within the lower mantle have little apparent influence at earth9s surface instead the distribution of residual subsidence reported here can be accounted for by minor variations in lithospheric thickness or by transient density variations beneath the lithospheric plate the absence of measurable dynamic topography is surprising and indicates that mantle mass anomalies are supported elsewhere presumably at internal boundaries within earth our hybrid data set can thus be used as an independent constraint on the viscosity structure of the mantle