dynamic topography and anomalously negative residual depth of the argentine basin a substantial portion of earth s topography is known to be caused by the viscous coupling of mantle flow to the lithosphere but the relative contributions of shallow asthenospheric flow versus deeper flow remains controversial the argentine basin located offshore of the atlantic margin of southern south america is one of the most anomalously deep ocean regions as it is significantly deeper than its age would suggest previously the anomalous depth has been attributed to asthenospheric flow and the coupling of the south american plate s westward motion to the shallow mantle using a combination of geophysical observations and geodynamic modeling we propose that subducted slab driven dynamic topography has primarily driven the long wavelength anomalous residual basin depth since the opening of the south atlantic using an inverse mantle convection model with plate motions since the early cretaceous we suggest that the median of present day dynamic topography of the basin is 400 m when the residual basement depth is low pass filtered the depth anomaly is 730 m suggesting that more than half of the residual basement depth can be attributed to deep seated mantle dynamics we conclude that coupled plate tectonic mantle convection models tied to seismic tomography bathymetry and sediment thickness data can help to elucidate the driving forces behind earth s topography one of the most fundamental characteristics of this planet

on retrodictions of global mantle flow with assimilated surface velocities modeling past states of earth s mantle and relating them to geologic observations such as continental scale uplift and subsidence is an effective method for testing mantle convection models however mantle convection is chaotic and two identical mantle models initialized with slightly different temperature fields diverge exponentially in time until they become uncorrelated thus limiting retrodictions i e reconstructions of past states of earth s mantle obtained using present information to the recent past we show with 3 d spherical mantle convection models that retrodictions of mantle flow can be extended significantly if knowledge of the surface velocity field is available assimilating surface velocities produces in some cases negative lyapunov times i e e folding times implying that even a severely perturbed initial condition may evolve toward the reference state a history of the surface velocity field for earth can be obtained from past plate motion reconstructions for time periods of a mantle overturn suggesting that mantle flow can be reconstructed over comparable times

simultaneous inversion of mantle properties and initial conditions using an adjoint of mantle convection through the assimilation of present day mantle seismic structure adjoint methods can be used to constrain the structure of the mantle at earlier times i e mantle initial conditions however the application to geophysical problems is restricted through both the high computational expense from repeated iteration between forward and adjoint models and the need to know mantle properties such as viscosity and the absolute magnitude of temperature or density a priori we propose that an optimal first guess to the initial condition can be obtained through a simple backward integration sbi of the governing equations thus lessening the computational expense given a model with known mantle properties we show that a solution based on an sbi generated first guess has smaller residuals than arbitrary guesses mantle viscosity and the effective rayleigh number are crucial for mantle convection models neither of which is exactly known we place additional constraints on these basic mantle properties when the convection induced dynamic topography on earth s surface is considered within an adjoint inverse method besides assimilating present day seismic structure as a constraint we use dynamic topography and its rate of change in an inverse method that allows simultaneous inversion of the absolute upper and lower mantle viscosities scaling between seismic velocity and thermal anomalies and initial condition the theory is derived from the governing equations of mantle convection and validated by synthetic experiments for both one layer viscosity and two layer viscosity regionally bounded spherical shells for the one layer model at any instant of time the magnitude of dynamic topography is controlled by the temperature scaling while the rate of change of topography is controlled by the absolute value of viscosity for the two layer case the rate of change of topography constrains upper mantle viscosity while the magnitude of dynamic topography determines the temperature scaling lower mantle viscosity when upper mantle lower mantle density anomaly dominates the flow field this two stage scheme minimizes the tradeoff between temperature and lower mantle viscosity for both cases we show that the theory can constrain mantle properties with errors arising through the adjoint recovery of the initial condition for the two layer model this error is manifest as a tradeoff between the temperature scaling and lower mantle viscosity

the ups and downs of north america evaluating the role of mantle dynamic topography since the mesozoic the driving force for transient vertical motions of earth s surface remains an outstanding question a main difficulty lies in the uncertain role of the underlying mantle especially during the geological past here i review previous studies on both observational constraints and physical mechanisms of north american topographic evolution since the mesozoic i first summarize the north american vertical motion history using proxies from structural geology geochronology sedimentary stratigraphy and geomorphology based on which i then discuss the published physical models overall there is a progressive consensus on the contribution of mantle dynamic topography due to buoyancy structures associated with the past subduction at the continental scale a largely west to east migrating deformation pattern suggests an eastward translation of mantle dynamic effects consistent with models involving an eastward subduction and sinking of former farallon slabs since the cretaceous among the existing models the inverse model based on an adjoint algorithm and time dependent data constraints provides the most extensive explanations for the temporal changes of north american topography since the mesozoic at regional scales debates still exist on the predicted surface subsidence and uplift within both the western and eastern united states where discrepancies are likely due to differences in model setup e g mantle dynamic properties and boundary conditions and the amount of time dependent observational constraints toward the development of the next generation predictive geodynamic models new research directions may include 1 development of enhanced data assimilation capabilities 2 exploration of multiscale and multiphysics processes and 3 cross disciplinary code coupling

dynamic restoration of profiles across diapiric salt structures numerical approach and its applications abstract the backstripping method that is widely used in basin analysis sometimes fails for salt bearing basins because the highly mobile and buoyant salt deforms its sedimentary overburden we present a numerical approach for 2 d dynamic restoration of cross sections through successive earlier depositional stages the approach is based on a solution of the inverse problem of the gravitational rayleigh taylor instability and combines the galerkin spline finite element method with interface tracking and a backstripping method our model interprets basin profiles as multiple layers of viscous fluids with various densities and viscosities the evolution of salt structures is modelled backward in time by removing successively younger layers and restoring older layers and any diapirs to the stage they were likely to have been we test the sensitivity of the restoration technique to small variations in density of the layers at different stages in the evolution of diapiric structures the applicability of the technique was demonstrated by reconstructions of upbuilt and downbuilt diapirs the technique is used to restore a depth converted seismic cross section through the south eastern part of the pricaspian salt basin mature salt diapirs in the section are shown to have been downbuilt from a salt layer with an initially uniform thickness as a result of differential sedimentary loading until the end of the triassic before one of the diapirs was buried and actively upbuilt the numerical approach is well suited for restoration of cross sections with ductile overburdens but despite limitations can be developed to 3 d restorations and other rheologies

forward and reverse modeling of the three dimensional viscous rayleigh taylor instability a combined nite dierence spectral method is used to model the 3d viscous rayleigh taylor instability numerically calculated growth rate spectra are presented for an initial sinusoidal perturbation of the interface sep arating two fluids with amplitude 10 3 h and 0 2h w here h is the height of the system at small initial amplitude growth rate spectra closely follow linear theory whereas the calculation with higher initial amplitude shows wavelength selection towards 3d perturbations numerical simulations and analytical theory are used to evaluate the applicability of previous 2d numerical models which is shown to depend on 1 the wavelength and amplitude of an initially 2d si nusoidal perturbation and 2 the amplitude of background noise it is also shown that reverse backward modeling is capableofrestoringtheinitialgeometryaslongasoverhangs are not developed if overhangs are present the possibility ofrestoringtheinitialconditionsislargely dependentonthe stage of overhang development

towards adjoint based inversion of time dependent mantle convection with nonlinear viscosity we develop and study an adjoint based inversion method for the simultaneous recovery of initial temperature conditions and viscosity parameters in time dependent mantle convection from the current mantle temperature and historic plate motion based on a realistic rheological model with temperature dependent and strain rate dependent viscosity we formulate the inversion as a pde constrained optimization problem the objective functional includes the misfit of surface velocity plate motion history the misfit of the current mantle temperature and a regularization for the uncertain initial condition the gradient of this functional with respect to the initial temperature and the uncertain viscosity parameters is computed by solving the adjoint of the mantle convection equations this gradient is used in a pre conditioned quasi newton minimization algorithm we study the prospects and limitations of the inversion as well as the computational performance of the method using two synthetic problems a sinking cylinder and a realistic subduction model the subduction model is characterized by the migration of a ridge toward a trench whereby both plate motions and subduction evolve the results demonstrate 1 for known viscosity parameters the initial temperature can be well recovered as in previous initial condition only inversions where the effective viscosity was given 2 for known initial temperature viscosity parameters can be recovered accurately despite the existence of trade offs due to ill conditioning 3 for the joint inversion of initial condition and viscosity parameters initial condition and effective viscosity can be reasonably recovered but the high dimension of the parameter space and the resulting ill posedness may limit recovery of viscosity parameters

late miocene pacific plate kinematic change explained with coupled global models of mantle and lithosphere dynamics the timing and magnitude of a pacific plate motion change within the past 10 ma remains enigmatic due to the noise associated with finite rotation data nonetheless it has been hypothesized that this change was driven by the arrival of the ontong java plateau ojp at the melanesian arc and the consequent subduction polarity reversal the uncertainties associated with the timing of this event however makes it difficult to quantitatively demonstrate a dynamical association here we first reconstruct the pacific plate s absolute motion since the mid miocene 15 ma at high temporal resolution building on previous efforts to mitigate the impact of finite rotation data noise we find that the largest change in pacific plate motion direction occurred between 10 and 5 ma with the plate rotating clockwise we subsequently develop and use coupled global numerical models of the mantle lithosphere system to test hypotheses on the dynamics driving this change these indicate that the arrival of the ojp at the melanesian arc between 10 and 5 ma followed by a subduction polarity reversal that marked the initiation of subduction of the australian plate underneath the pacific realm were the key drivers of this kinematic change

mantle circulation models with variational data assimilation inferring past mantle flow and structure from plate motion histories and seismic tomography summary mantle convection models require an initial condition some time in the past because this initial condition is unknown for earth we cannot infer the geological evolution of mantle flow from forward mantle convection calculations even for the most recent mesozoic and cenozoic geological history of our planet here we introduce a fluid dynamic inverse problem to constrain unknown mantle flow back in time from seismic tomographic observations of the mantle and reconstructions of past plate motions using variational data assimilation we derive the generalized inverse of mantle convection and explore the initial condition problem in high resolution 3 d spherical mantle circulation models for a time period of 100 myr roughly comparable to half a mantle overturn we present a synthetic modelling experiment to demonstrate that mid cretaceous mantle structure can be inferred accurately from fluid dynamic inverse modelling assuming present day mantle structure is well known even if an initial first guess assumption about the mid cretaceous mantle involved only a simple 1 d radial temperature profile we also demonstrate that convecting present day mantle structure back in time by reversing the time stepping of the energy equation is insufficient to model the mantle structure of the past the difficulty arises because such backward convection calculations ignore thermal diffusion effects and therefore cannot account for the generation of thermal buoyancy in boundary layers as we go back in time inverse mantle convection modelling should make it possible to infer a number of flow parameters from observational constraints of the mantle

three dimensional forward and backward numerical modeling of mantle plume evolution effects of thermal diffusion we investigate the effects of thermal diffusion on the evolution of mantle plumes by means of three dimensional numerical modeling forward and backward in time mantle plumes are fed by a hot low viscous material from the thermal boundary layer the material of the plumes is mainly advected toward the earth s surface with some effects of thermal diffusion however the feeding can become weaker with time and then thermal diffusion can take over and control the evolution of the plumes numerical experiments forward in time show that a week feeding of mantle plumes by the hot material from the boundary layer results in the diffusive disappearance of plume tails first and plume heads later this is the most likely explanation for the seismically detected low velocity mantle structures mantle plumes with prominent heads and almost invisible tails at midmantle depths we develop restoration models backward in time to recover strong features of mantle plumes in the geological past after they have dissipated due to thermal diffusion and analyze effects of thermal diffusion and temperature dependent viscosity on the reconstruction of the mantle plumes we investigate the impact of thermal diffusion on the performance of our restoration variational data assimilation algorithm for a given range of rayleigh number ra and two values of the viscosity ratio r between the upper and lower boundaries of the model domain we show that 1 the residuals between the temperature predicted by the forward model and that reconstructed by the backward modeling become larger and 2 the restoration process becomes poorer as ra decreases and r increases we assimilate temperature obtained from high resolution seismic tomography data for the southeastern carpathians and show that present diffused mantle structures can be restored to their prominent state in the miocene times we discuss the problems of smoothness of model input and output data errors associated with the modeling and some other challenges in the data assimilation for thermoconvective flow in the mantle

inverse problem of thermal convection numerical approach and application to mantle plume restoration abstract modern seismic tomographic images of the earth s interior facilitate the inference of the complex trajectories of present day convective flow in the upper mantle quantitative reconstruction of both the observed mantle structure and temperature field backwards in time requires a numerical tool for solving the inverse problem of thermal convection at infinite prandtl number in this paper we present a variational approach to three dimensional numerical restoration of thermoconvective mantle flow with temperature dependent viscosity this approach is based on a search for the mantle temperature and flow in the geological past by minimizing differences between present day mantle temperature derived from seismic velocities or their anomalies and that predicted by forward models of mantle flow for an initial temperature guess the past mantle temperatures so obtained can be employed as constraints on forward models of mantle dynamics to demonstrate the applicability of this technique we restore numerically a fluid dynamic model of the evolution of upper mantle plumes and show that the initial shape of the plumes can be accurately reconstructed we then model the evolution of the plumes forward in time plume upbuilding starting from the restored state to the state they were before the restoration and demonstrate the high accuracy of the model predictions we also show that the neglect of thermal diffusion in the backward modeling of thermal plumes in order to simplify the numerical procedure results in erroneous restorations of the plumes

palaeogeological hiatus surface mapping a tool to visualize vertical motion of the continents dynamic topography is a well established consequence of global geodynamic models of mantle convection with horizontal dimensions of 1000 km and amplitudes up to 2 km such physical models guide the interpretation of geological records on equal dimensions continent scale geological maps therefore serve as reference frames of choice to visualize erosion non deposition as a proxy for long wavelength low amplitude vertical surface motion at a resolution of systems or series such maps display conformable and unconformable time boundaries traceable over hundreds to thousands of kilometres unconformable contact surfaces define the shape and size of time gap hiatus in millions of years based on the duration of time represented by the missing systems or series hiatus for a single system or series base datum diminishes laterally to locations anchor points where it is conformable at the mapped resolution it is highly dependent upon scale a comparison of hiatus area between two successive system or series boundaries yields changes in location shape size and duration indicative of the transient nature of vertical surface motion as a single step technique it serves as a quantitative proxy for palaeotopography that can be calibrated using other geological data the tool magnifies the need for geological mapping at the temporal resolution of stages matching process rates the method has no resolving power within conformable regions basins but connects around them when applied to marine seismic sections that relate to rock record not to time biostratigraphic and radiometric data from deep wells are needed before hiatus areas that relate to time can be mapped

thermal evolution and geometry of the descending lithosphere beneath the se carpathians an insight from the past abstract mantle heterogeneities imaged by seismic tomography in the se carpathians contain information on the present thermal state of the mantle based on p wave seismic velocity anomalies we develop a model of the present mantle temperature beneath the region and combine the model with a model of crustal temperature constrained by heat flow data the modeled temperatures are assimilated into the geological past using the information on the regional movement in the early and middle miocene prominent thermal states of the lithospheric slab descending in the region are restored from its diffuse present state in miocene times the slab geometry clearly shows two portions of the sinking body the northwest southeast oriented portion of the body is located in the vicinity of the boundary between the east european and scythian platforms and this portion of the sinking body may be a relic of cold lithosphere that has traveled eastward another portion has a northeast southwest orientation and is related to the present descending slab above a depth of 60 km the slab had a concave thermal shape confirming the curvature of the carpathian arc and a convex surface below that depth the slab maintained its convex shape until it split into two parts at a depth of about 220 km we propose that this change in the slab geometry which is likely to be preserved until the present can cause stress localization due to the slab bending and subsequent stress release resulting in large mantle earthquakes in the region also we hypothesize that either the processes of dehydration and partial melting of the descending lithospheric slab or dragging down of hotter rocks from the adjacent uppermost mantle by the slab are possible causes of the reduction in seismic velocities beneath the transylvanian basin

quasi reversibility method for data assimilation in models of mantle dynamics summary rapid progress in imaging deep earth structures using seismic tomography and in studies of physical and chemical properties of mantle rocks facilitates research in assimilation of data related to mantle dynamics in this paper we present a new numerical approach for data assimilation which allows for incorporating observations at present and unknown initial conditions in the past for mantle temperature and flow into a 3 d dynamic model in order to determine the initial conditions the dynamic model is described by the backward heat motion and continuity equations the use of the quasi reversibility qrv method implies the introduction into the backward heat equation of the additional term involving the product of a small regularization parameter and a higher order temperature derivative the data assimilation in this case is based on a search of the best fit between the forecast model state and the observations by minimizing the regularization parameter we apply the qrv data assimilation method to restore the evolution of i mantle plumes a synthetic case study and ii the lithospheric slab imaged by teleseismic body wave tomography in the southeastern carpathians for both models the present temperature and mantle flow are assimilated to the geological past and the prominent features of mantle structures are recovered we then model the evolution of the mantle structures forward in time starting from the restored state to the present state and estimate the accuracy of the model predictions the results of the qrv data assimilation are compared to that obtained by the variational var and backward advection data assimilation although the accuracy of the qrv data assimilation is lower than that of the var data assimilation the qrv method does not require any additional smoothing of the input data or filtering of temperature noise as the var method does based on the results and the comparison of the methods we consider the qrv method to be a highly promising approach to assimilation of data related to mantle dynamics

retrodictions of mid paleogene mantle flow and dynamic topography in the atlantic region from compressible high resolution adjoint mantle convection models sensitivity to deep mantle viscosity and tomographic input model abstract although mantle convection at earth like vigor is a chaotic process it has been shown by conceptual studies that one can constrain its flow history back in time for periods comparable to a mantle overturn 100 million years if knowledge of the tangential surface velocity field and estimates on the present day heterogeneity state are available such retrodictions enabled through computationally demanding adjoint methods are a promising tool to improve our understanding of deep earth processes and to link uncertain geodynamic modeling parameters to geologic observables here we present the first mantle flow retrodictions for geodynamically plausible compressible high resolution earth models with 670 million finite elements going back in time to the mid paleogene our retrodictions involve the dynamic effects from a low viscosity zone lvz in the upper mantle assimilate a past plate motion model for the tangential surface velocity field and probe the influence from uncertain modeling parameters by using two different estimates for the present day heterogeneity state of the mantle as imaged by two recent seismic tomographic studies and two different values for deep mantle viscosity focusing on the african hemisphere we find that our retrodictions produce a spatially and temporally highly variable asthenosphere flow with faster than plate velocities and a history of dynamic topography characterized by local doming events in agreement with considerations on plate driving forces and regional scale uplifts reported in the geologic literature our results suggest that improved constraints on non isostatic vertical motion of earth s surface provided for instance by basin analysis seismic stratigraphy landform studies or the sedimentation record will play an important role in our understanding of the recent mantle flow history

la pacana caldera and the atana ignimbrite a major ash flow and resurgent caldera complex in the andes of northern chile the recently discovered la pacana caldera 60 35 km is the largest caldera yet described in south america this resurgent caldera of pliocene age developed in a continental platemargin environment in a major province of ignimbrite volcanism in the central andes of northern chile at about 23 s latitude collapse of la pacana caldera was initiated by the eruption of about 900 km3 of the rhyodacitic atana ignimbrite the atana ignimbrite was erupted from a composite ring fracture system and formed at least four major ash flow tuff units that are separated locally by thin air fall and surge deposits all four sheets were emplaced in rapid succession about 4 1 0 4 ma ago caldera collapse was followed closely by resurgent doming of the caldera floor accompanied by early postcaldera eruptions of dacitic to rhyolitic lava domes along the ring fractures the resurgent dome is an elongated asymmetrical uplift 48 5 12 km which is broken by a complex system of normal faults locally forming a narrow discontinuous apical graben later postcaldera eruptions produced large andesitic and dacitic stratocones along the caldera margins and dacitic domes on the resurgent dome beginning about 3 5 ma ago and persisting into the quaternary hydrothermally altered rocks occur in the eroded cores of precaldera and postcaldera stratovolcanoes and along fractures in the resurgent dome but no ore deposits are known a few warm springs located in salars within the caldera moat appear to be vestiges of the caldera geothermal system

seismic tomography surface uplift and the breakup of gondwanaland integrating mantle convection backwards in time mantle density heterogeneities imaged using seismic tomography contain information about time dependent mantle flow and mantle structures that existed in the past we model the history of mantle flow using a tomographic image of the mantle beneath southern africa as an initial condition while reversing the direction of flow and analytically incorporating cooling plates as a boundary condition if the resulting backwards integrated model for structures is used as a starting point for a forwards convection model today s mantle can be adequately reconstructed if we do not integrate backwards more than than about 50 75 ma flow can also be reliably reversed through the mesozoic but only if instability of the lower boundary layer can be suppressed our model predicts that the large seismically slow and presumably hot structure beneath southern africa produced 500 700 m of dynamic topography throughout the cenozoic since 30 ma uplift has moved from eastern to southern africa where uplift rates are 10 m myr consistent with observations during the mesozoic the modeled topographic high is situated near gondwanaland rifting raising the possibility that this buoyant structure may have been involved with this breakup

rapid south atlantic spreading changes and coeval vertical motion in surrounding continents evidence for temporal changes of pressure driven upper mantle flow the south atlantic region displays 1 a topographic gradient across the basin with africa elevated relative to south america 2 a bimodal spreading history with fast spreading rates in late cretaceous and eo oligocene and 3 episodic regional uplift events in the adjacent continents concentrated in late cretaceous and oligocene here we show that these observations can be linked by dynamic processes within earth s mantle through temporal changes in asthenosphere flow beneath the region the topographic gradient implies westward pressure driven mantle flow beneath the basin while the rapid spreading rate changes on order 10 million years require significant decoupling of regional plate motion from the large scale mantle buoyancy distribution through a mechanically weak asthenosphere andean topographic growth in late miocene can explain the most recent south atlantic spreading velocity reduction arising from increased plate boundary forcing associated with the newly elevated topography but this mechanism is unlikely to explain the late cretaceous tertiary spreading variations as changes in andean paleoelevation at the time are small we propose an unsteady pressure driven flow component in the asthenosphere beneath the south atlantic region to explain the late cretaceous tertiary spreading rate variations temporal changes in mantle flow due to temporal changes in regional mantle pressure gradients imply a correlation of horizontal and vertical motions we find that this prediction from our models agrees with geologic and geophysical observations of the south atlantic region including episodes of passive margin uplift regional basin reactivation and magmatic activity

reconstructing the cenozoic evolution of the mantle implications for mantle plume dynamics under the pacific and indian plates article history the lack of knowledge of the initial thermal state of the mantle in the geological past is an outstanding problem in mantle convection the resolution of this problem also requires the modelling of 3 d mantle evolution that yields maximum consistency with a wide suite of geophysical constraints quantifying the robustness of the reconstructed thermal evolution is another major concern to solve and estimate the robustness of the time reversed inverse problem of mantle convection we analyse two different numerical techniques the quasi reversible qrv and the backward advection bad methods our investigation extends over the 65 myr interval encompassing the cenozoic era using a pseudo spectral solution for compressible flow thermal convection in 3 d spherical geometry we find that the two dominant issues for solving the inverse problem of mantle convection are the choice of horizontally averaged temperature i e geotherm and mechanical surface boundary conditions we find in particular that the inclusion of thermal boundary layers that yield earth like heat flux at the top and bottom of the mantle has a critical impact on the reconstruction of mantle evolution we have developed a new regularisation scheme for the qrv method using a time dependent regularisation function this revised implementation of the qrv method delivers time dependent reconstructions of mantle heterogeneity that reveal 1 the stability of pacific and african large low shear velocity provinces llsvp over the last 65 myr 2 strong upward deflections of the cmb topography at 65 ma beneath the north atlantic the south central pacific the east pacific rise epr and the eastern antarctica 3 an anchored deep mantle plume ascending directly under the epr easter and pitcairn hotspots throughout the cenozoic era and 4 the appearance of the transient reunion plume head beneath the western edge of the deccan plateau at 65 ma our reconstructions of cenozoic mantle evolution thus suggest that mantle plumes play a key role in driving surface tectonic processes and large scale volcanism 2014 elsevier b v all rights reserved

on the predictability limit of convection models of the earth s mantle reconstructing convective flow in the earth s mantle is a crucial issue for a diversity of disciplines from seismology to sedimentology the common and fundamental limitation of these reconstructions based on geodynamic modeling is the unknown initial conditions because of the chaotic nature of convection in the earth s mantle errors in initial conditions grow exponentially with time and limit forecasting and hindcasting abilities in this work we estimate for the first time the limit of predictability of earth s mantle convection following the twin experiment method we compute the lyapunov time i e e folding time for state of the art 3 d spherical convection models varying rheology and rayleigh number our most earth like and optimistic solution gives a lyapunov time of 136 13 myr rough estimates of the uncertainties in best guessed initial conditions are around 5 leading to a limit of predictability for mantle convection of 95 myr our results suggest that error growth could produce unrealistic convective structures over time scales shorter than that of pangea dispersal

adjoint based estimation of plate coupling in a non linear mantle flow model theory and examples we develop and validate a systematic approach to infer plate boundary strength and rheological parameters in models of mantle flow from surface velocity observations based on a realistic rheological model that includes yielding and strain rate weakening from dislocation creep we formulate the inverse problem in a bayesian inference framework to study the distribution of parameters that are consistent with the observations we compute the maximum a posteriori map point gaussian approximations of the parameter distribution around that map point and employ markov chain monte carlo mcmc sampling methods the computation of the map point and the gaussian approximation require first and second derivatives of an objective function subject to non linear stokes equations these derivatives are computed efficiently using adjoint stokes equations we set up 2 d numerical experiments with many of the elements expected in a global geophysical inversion this setup incorporates three subduction zones with slab and weak zone interplate fault geometry consistent with average seismic characteristics with these experiments we demonstrate that when the temperature field is known we can recover the strength of plate boundaries the yield stress and strain rate exponent in the upper mantle when the number of uncertain parameters increases there are trade offs between the inferred parameters these trade offs depend on how well the observational data represents the surface velocities and on the weakness of plate boundaries as the plate boundary coupling drops below a threshold the uncertainty of the inferred parameters increases due to insensitivity of plate motion to plate coupling comparing the trade offs between inferred rheological parameters found from the gaussian approximation of the parameter distribution and from mcmc sampling we conclude that the gaussian approximation which is significantly cheaper to compute is often a good approximation in particular locally around the map point thus the method can be applied to the global problem of inferring non linear constitutive parameters and plate coupling factors for each subduction zone in a global geophysical inversion with known slab structure

efficient sensitivity analysis for flow and transport in the earth s crust and mantle summary this paper focuses on the role of sensitivity analysis in studies of water transport in the environmental and geophysical sciences sensitivity analysis is useful in model development to determine how changes in parameter input will affect a model s response it is also used in data assimilation to incorporate observations into a model the adjoint method allows an efficient calculation of a model s sensitivity when the number of parameters exceeds the number of observations in this paper we present studies demonstrating the use of the adjoint method for modelling water transport in both the earth s crust and mantle

assessing the role of slab rheology in coupled plate mantle convection models reconstructing the 3d structure of the earth s mantle has been a challenge for geodynamicists for about 40 yr although numerical models and computational capabilities have substantially progressed parameterizations used for modeling convection forced by plate motions are far from being earth like among the set of parameters rheology is fundamental because it defines in a non linear way the dynamics of slabs and plumes and the organization of lithosphere deformation in this study we evaluate the role of the temperature dependence of viscosity variations up to 6 orders of magnitude and the importance of pseudo plasticity on reconstructing slab evolution in 3d spherical models of convection driven by plate history models pseudo plasticity which produces plate like behavior in convection models allows a consistent coupling between imposed plate motions and global convection which is not possible with temperature dependent viscosity alone using test case models we show that increasing temperature dependence of viscosity enhances vertical and lateral coherence of slabs but leads to unrealistic slab morphologies for large viscosity contrasts introducing pseudo plasticity partially solves this issue producing thin laterally and vertically more continuous slabs and flat subduction where trench retreat is fast we evaluate the differences between convection reconstructions employing different viscosity laws to be very large and similar to the differences between two models with the same rheology but using two different plate histories or initial conditions

reconstructing earth history in three dimensions an inverse model elucidates the connection between plate tectonics at earth s surface and the dynamics of the underlying mantle

a hybrid approach to data assimilation for reconstructing the evolution of mantle dynamics quantifying past mantle dynamic processes represents a major challenge in understanding the temporal evolution of the solid earth mantle convection modeling with data assimilation is one of the most powerful tools to investigate the dynamics of plate subduction and mantle convection although various data assimilation methods both forward and inverse have been created these methods all have limitations in their capabilities to represent the real earth pure forward models tend to miss important mantle structures due to the incorrect initial condition and thus may lead to incorrect mantle evolution in contrast pure tomography based models cannot effectively resolve the fine slab structure and would fail to predict important subduction zone dynamic processes here we propose a hybrid data assimilation approach that combines the unique power of the sequential and adjoint algorithms which can properly capture the detailed evolution of the downgoing slab and the tomographically constrained mantle structures respectively we apply this new method to reconstructing mantle dynamics below the western u s while considering large lateral viscosity variations by comparing this result with those from several existing data assimilation methods we demonstrate that the hybrid modeling approach recovers the realistic 4 d mantle dynamics the best

on the observability of epeirogenic movement in current and future gravity missions abstract next generation gravity missions are expected to improve the accuracy of temporal gravity models significantly the periodic signals and trends retrieved by these missions are induced by mass redistribution in the earth system carrying essential information on dynamic processes in the atmosphere cryosphere continental hydrosphere the oceans and the solid earth while temporal gravity signals induced by deep earth s processes are commonly thought to lie below the observational threshold of satellite gravity missions as one assumes them to be small in amplitude and restricted to the longest spatial and temporal scales there exists evidence from the geologic record for rapid uplift and subsidence events at regional scales especially along passive continental margins related to flow in the underlying mantle here we explore novel mantle flow retrodictions for geodynamically plausible compressible high resolution earth models with 670 million finite elements these time dependent earth models link to geologic observables in the late paleogene that can be tested independently while at the same time indicating mantle flow induced geoid rates on the order of 5 m year at spatial scales of 1000 km we assess the signal retrievability of the modeled rates in closed loop numerical simulations with different satellite gravity retrieval mission assumptions including grace grace fo and a next generation gravity mission we find the modeled deep earth signal to be on the edge of detectability but coming into the range of detectability in future temporal gravity field solutions suggesting the use of satellite gravity data to validate geodynamic earth models importantly the application of forward modeled dynamic mantle signals seems to be essential for improved de aliasing and signal separation in future gravity missions

nondiffuse elastic and anelastic passive imaging the property at the basis of passive acoustic imaging is that taken any two points one of them can be seen as the source of the waves and the other as the recording station this property which was shown to hold also in nondiffuse fields is here exploited 1 to allow an undistorted passive imaging through the simple use of the statistical mode to estimate wave velocity 2 to determine the azimuth of the instantaneous huygens sources of the noise wavefield and 3 to measure provided that the noise bandwidth is wide with respect to that of the local system the material dissipation constant as a function of frequency the authors applied this theory to study the seismic noise field in the ravenna north central italy shore area and found it capable to provide velocity dispersion curves matching those of independent surveys to track the sources of seismic noise to a few major firms in ravenna port with the prevailing source switching at the time scale of seconds and to measure the dissipation

use of heat as tracer to quantify vertical streambed flow in a two dimensional flow field 1 analytical solutions to the heat transport equation in porous media have been developed in the past to estimate surface water groundwater interactions these solutions however are based upon simplifying assumptions that are frequently violated in natural systems a nonvertical flow field inherent to most field settings can violate the one dimensional 1 d flow assumption and lead to erroneous velocity estimates in this study we have developed a 2 d heat and mass transport finite element based numerical model for a stream aquifer cross section experiencing flow through synthetic multilevel streambed temperature time series were generated with the model using a sinusoidal temperature boundary the temperature data was used to quantify the vertical flow velocity with a 1 d analytical solution based on the amplitude decay and phase shift of temperature with depth results demonstrate that erroneous vertical components of fluid velocity can be obtained by the 1 d analytical solution when the true vertical velocity approaches zero and the flow regime becomes almost horizontal the results also illustrate that the amplitude ratio method performs quite poorly on the gaining side of the stream where the only reliable method is phase shift on the losing side of the stream both methods can be employed but a better estimation is obtained from the amplitude ratio method in general amplitude ratio and phase shift data should be used in conjunction to maximize the information of the system

changes of the earth s rotation axis owing to advection of mantle density heterogeneities polar wander the secular motion of the earth s rotation axis relative to its surface has been studied for many years dynamical arguments1 3 show that polar wander can arise from the redistribution of mass in a plastic deformable earth the rate depending on both the rate of mass redistribution and the rate at which the earth s rotational bulge can readjust to the changing rotation axis here we use a viscosity structure obtained through geoid modelling4 a mantle flow field consistent with tomographic anomalies5 and time dependent lithospheric plate motions6 to calculate the advection of mantle density heterogeneities and corresponding changes in the degree two geoid during the cenozoic era we show that the rotation axis will follow closely any imposed changes of the axis of maximum non hydrostatic moment of inertia the resulting path of the rotation axis agrees well with palaeomagnetic results7 with the model predicting a current rate of polar motion that explains 40 of that observed geodetically8

geodynamics and intermediate depth seismicity in vrancea the south eastern carpathians current state of the art abstract the vrancea region of the south eastern carpathians is a remarkable site of intra continental intermediate depth seismicity a large set of geological geophysical and geodetic observations has been accumulated for the last few decades and utilised to improve our knowledge of the shallow and deep structures beneath vrancea the crustal and mantle dynamics and the linkage between deep and surface processes in the region in this article we review geology and tectonics of the vrancea region including post collisional to recent deformations syn to post collisional magmatism and orogenic exhumation along the east and south carpathians the regional seismicity is analysed and the recent seismic studies including reflection refraction body and surface wave tomography are reviewed we discuss new geodetic measurements of horizontal and vertical movements in the region geoelectric studies density gravity and thermal modelling qualitative and quantitative including retrospective geodynamic models developed for vrancea are analysed the knowledge of regional tectonics geodynamics seismicity lithospheric deformation and stress regime in the vrancea earthquake prone region assists in an assessment of strong ground motion seismic hazard and risk the earthquake simulation seismic hazard and earthquake forecasting models have also been reviewed providing a link between deep geodynamic processes and their manifestation on the surface finally we discuss unresolved problems in vrancea in order to improve our understanding of the regional evolution present tectonics mantle dynamics intermediate depth seismicity and surface manifestations of the lithosphere dynamics and to enhance our ability to forecast strong earthquakes in the vrancea region the problems to be solved include i the origin of the high velocity body revealed by seismic tomography studies oceanic versus continental ii the lithospheric scale mechanism driving the miocene subsidence of the transylvania basin iii sub crustal structure between 40 and 70 km iv contemporary regional horizontal and vertical movements and v a comprehensive seismic hazard assessment in the region

the neapolitan yellow tuff a large magnitude trachytic phreatoplinian eruption eruptive dynamics magma withdrawal and caldera collapse the results of a detailed stratigraphical and volcanological study has allowed the definition of the neapolitan yellow tuff nyt as the largest known trachytic phreatoplinian eruption with an estimated volume of not less than 30 km3 dre the nyt sequence can be subdivided in a lower and an upper member sedimentological and textural variations in time and space indicate that different eruptive and depositional mechanisms operated during the eruption the lower member eruptive phase was characterized by alternating phreatoplinian and magmatic explosions while the upper member eruptive phase was characterized by a random sequence of phreatomagmatic and magmatic explosions particles produced by the same explosion were deposited contemporaneously by fallout and surge mechanisms either at different or at the same distance from the vent compositional variations show that the nyt sequence cannot be modeled as an inverted compositionally zoned magma body with magma becoming more basic in the course of the eruption the chamber composed of three geochemically distinct magma layers was tapped at different depths according to the eruption dynamics each phreatoplinian explosion tapped concurrently all the magma layers while magmatic explosions tapped only one of them the onset of the nyt caldera collapse is well constrained between lower and upper member eruptive phases the collapse which is only gravimetrically detectable occurred inside the larger phlegrean fields caldera which therefore can be defined as a nested caldera

analysis of geological hiatus surfaces across africa in the cenozoic and implications for the timescales of convectively maintained topography geological maps are a powerful but underutilized tool for constraining geodynamic processes and models unraveling the cenozoic elevation history of africa and distinguishing between competing upli

formation of the mid fifteenth century kuwae caldera vanuatu by an initial hydroclastic and subsequent ignimbritic eruption in the mid fifteenth century one of the largest eruptions of the last 10 000 years occurred in the central new hebrides arc forming the kuwae caldera 12x6 km this eruption followed a late maar phase in the pre caldera edifice responsible for a series of alternating hydromagmatic deposits and airfall lapilli layers tuffs related to caldera formation 120 m of deposits on a composite section from the caldera wall were emitted during two main ignimbritic phases associated with two additional hydromagmatic episodes the lower hydromagmatic tuffs from the precaldera maar phase are mainly basaltic andesite in composition but clasts show compositions ranging from 48 to 60 sio2 the unwelded and welded ashflow deposits from the ignimbritic phases and the associated intermediate and upper hydromagmatic deposits also show a wide compositional range 60 73 sio2 but are dominantly dacitic this broad compositional range is thought to be due to crystal fractionation the striking evolution from one eruptive style hydromagmatic to the other magmatic with emission of a large volume of ignimbrites which occurred either over the tuff series as a whole or at the beginning of each ignimbritic phase is the most impressive characteristic of the caldera forming event this strongly suggests triggering of the main eruptive phases by magma water interaction a three step model of caldera formation is presented 1 moderate hydromagmatic sequences hd 1 4 and magmatic fallout deposits activity from a central vent probably over a period of months or years affected an area slightly wider than the present caldera at the end of this stage intense seismic activity and extrusion of differentiated magma outside the caldera area occurred 2 unhomogenized dacite was released during a hydromagmatic episode hd 5 this was immediately followed by two major pyroclastic flows pfd 1 and 2 the vents spread and intense magma water interaction at the beginning of this stage decreased rapidly as magma discharge increased subsequent collapse of the caldera probably commenced in the southeastern sector of the caldera 3 dacitic welded tuffs were emplaced during a second main phase wfd 1 5 at the beginning of this phase magma water interaction continued producing typical hydromagmatic deposits hd 6 caldera collapse extended to the northern part of the caldera previous c14 dates and records of explosive volcanism in ice from the south pole show that the climactic phase of this event occurred in 1452 a d