elastic thickness of the iranian lithosphere from gravity and seismic data abstract we estimate the effective elastic thickness of the iranian lithosphere and adjoining tectonic plates by using the approach that combines the vening meinesz moritz s vmm regional isostatic principle with the isostatic flexural model formulated based on solving a flexural differential equation for a thin elastic shell to model the response on a load more realistically we also consider the lithospheric density structure the resulting expression describes a functional relation that links gravity field and mechanical properties of the lithosphere the young modulus and the poisson ratio are computed from seismic velocity data in prior of estimating the lithospheric elastic thickness the presented results reveal that the estimated elastic thickness closely resembles a regional tectonic configuration associated with the extensional tectonism along the red sea gulf rift system the continental collision of the arabian and eurasian plates and the subduction along the makran subduction zone seismically and volcanically active convergent tectonic margins of the zagros and kopeh dagh fold and thrust belts further extending along the makran accretionary complex are characterised by a low lithospheric strength with the elastic thickness typically less than 30 km these small values of the elastic thickness are in a striking contrast to much larger values within most of the central iranian blocks according to our estimate local maxima there reach 70 km in the tabas micro block the elastic thickness of the turan and arabian platforms reaches maxima of 100 km these results generally support the hypothesis that tectonically active zones and orogens have a relatively low strength resulting in a significant response of the lithosphere on various tectonic loads compared to a significant strength of old cratonic formations interestingly however we observe a striking contrast between a low strength of the arabian shield compared to a high strength of the arabian platform a possible explanation of this finding could be given by a different thermal regime of the arabian lithosphere controlled mainly by a mantle upwelling and a consequent extensional tectonism along the red sea gulf rift system

maximum likelihood estimation of lithospheric flexural rigidity initial loading fraction and load correlation under isotropy topography and gravity are geophysical fields whose joint statistical structure derives from interface loading processes modulated by the underlying mechanics of isostatic and flexural compensation in the shallow lithosphere under this dual statistical mechanistic viewpoint an estimation problem can be formulated where the knowns are topography and gravity and the principal unknown the elastic flexural rigidity of the lithosphere in the guise of an equivalent effective elastic thickness this important geographically varying structural parameter has been the subject of many interpretative studies but precisely how well it is known or how best it can be found from the data abundant nonetheless has remained contentious and unresolved throughout the last few decades of dedicated study the popular methods whereby admittance or coherence both spectral measures of the relation between gravity and topography are inverted for the flexural rigidity have revealed themselves to have insufficient power to independently constrain both it and the additional unknown initial loading fraction and load correlation fac tors respectively solving this extremely ill posed inversion problem leads to non uniqueness and is further complicated by practical considerations such as the choice of regularizing data tapers to render the analysis sufficiently selective both in the spatial and spectral domains here we rewrite the problem in a form amenable to maximum likelihood estimation theory which we show yields unbiased minimum variance estimates of flexural rigidity initial loading frac tion and load correlation each of those separably resolved with little a posteriori correlation between their estimates we are also able to separately characterize the isotropic spectral shape of the initial loading processes

localization of the gravity field and the signature of glacial rebound the negative free air gravity anomaly centred on hudson bay canada shows a remarkable correlation with the location of the laurentide ice sheet suggesting that this gravity anomaly is the result of incomplete post glacial rebound this region however is also underlain by higher than average mantle seismic velocities suggesting that the gravity low might result instead from dynamic topography associated with convective downwellings here we analyse the global gravity field as a simultaneous function of geographic location and spectral content we find that the hudson bay gravity low is unique with anomalously high amplitude in the spectral band where the power from the laurentide ice load is greatest and the relaxation times predicted for viable models of viscous relaxation are longest we estimate that about half of the hudson bay gravity anomaly is the result of incomplete post glacial rebound and derive a mantle viscosity model that explains both this gravity signature and the characteristic uplift rates for the central laurentide and fennoscandian regions this model has a jump in viscosity at 670 km depth comparable to that in dynamic models of the geoid highs over subducted slabs but lacks a low viscosity asthenosphere consistent with a higher viscosity in the upper mantle beneath shields than in oceanic regions

instantaneous dynamics of the cratonic congo basin understanding the formation mechanisms of cratonic basins provides an examination of the rheological compositional and thermal properties of continental cratons however these mechanisms are poorly understood because there are few currently active cratonic basins one cratonic basin thought to be active is the congo basin located in equatorial africa the congo basin is coincident with a large negative free air gravity anomaly an anomalous topographic depression and a large positive upper mantle shear wave velocity anomaly localized admittance models show that the gravity anomaly cannot be explained by a flexural support of the topographic depression at the congo we analyze these data and show that they can be explained by the depression of the congo basin by the action of a downward dynamic force on the lithosphere resulting from a high density object within the lithosphere we formulate instantaneous dynamic models describing the action of this force on the lithosphere these models show that the gravity and topography of the congo basin are explained by viscous support of an anomalously dense region located at 100 km depth within the lithosphere the density anomaly has a magnitude within the range of 27 60 kg m 3 and is most likely compositional in origin our models do not provide a constraint on the lithospheric viscosity of the congo craton because the shallow location of the anomaly ensures strong coupling of the anomaly to the surface regardless of viscosity structure

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

upper mantle earthquakes beneath the arafura sea and south aru trough implications for continental rheology 1 the extent and controls of long term elastic strength and seismicity in the upper continental lithospheric mantle uclm are controversial topics in continental tectonics one key issue is the scarcity of uclm earthquakes even where the uclm is likely to be colder than 600 c the rarity of these earthquakes could be because the uclm generally relatively hydrous causing it to deform aseismically even when colder than 600 c unless it is deforming at exceptionally high strain rates alternatively the uclm could be relatively anhydrous and potentially seismogenic at temperatures below 600 c in which case the rarity of uclm earthquakes may be because areas where the uclm is colder than 600 c have such a thick seismogenic layer and such a cool mantle root that they deform exceptionally slowly the identification and study of uclm earthquakes allows us to distinguish between these possibilities here we show that two earthquakes occurred in the uclm beneath the epicontinental arafura sea both earthquakes occurred where the uclm is probably cooler than 600 c and one of these earthquakes lies 25 km below the moho in an region where there is no evidence of unusually high strain rates there at least it is probable that the uclm is relatively anhydrous and seismogenic at temperatures below 600 c we also find evidence that regions where the uclm is colder than 600 c also have a seismogenic lower crust this results in a single extremely strong layer comprising the entire crust and the uclm down to the 600 c isotherm

grace gravity data constrain ancient ice geometries and continental dynamics over laurentia the free air gravity trend over canada derived from the gravity recovery and climate experiment grace satellite mission robustly isolates the gravity signal associated with glacial isostatic adjustment gia from the longer time scale mantle convection process this trend proves that the ancient laurentian ice complex was composed of two large domes to the west and east of hudson bay in accord with one of two classes of earlier reconstructions moreover gia models that reconcile the peak rates contribute 25 to 45 to the observed static gravity field which represents an important boundary condition on the buoyancy of the continental tectosphere

comparison of modern and geological observations of dynamic support from mantle convection the topographies of africa and antarctica form patterns of interlocking swells the relationship between topography and gravity indicates that these swells are dynamically supported by mantle convection with swell diameters of 1850 450 km and full heights between 800 and 1800 m the implication is that mantle convection not only supports swells surrounding hotspots but also influences topography across the entire surface areas of africa and antarctica we investigate whether dynamically supported swells are also observed throughout the geological record focusing on intensively studied mesozoic cenozoic sedimentary rocks around britain and ireland vertical motions of britain and ireland a typical piece of continental lithosphere far from a destructive plate boundary have been demonstrably affected by dynamic support for over half of the past 200 ma period the diameters and maximum heights of the mesozoic british swells and the modern african and antarctic swells are similar the ancient british swells grew in 5 10 ma and decayed over 20 30 ma suggesting vertical motion rates comparable with those estimated from geomorphological studies of africa igneous production rate and swell height are not correlated in the modern and the geological records mantle convection should be considered as a common control on regional sea level

the influence of dynamically supported topography on estimates of te abstract the effective elastic thickness t e of continental lithosphere can be estimated from the relationship between gravity and topography in the spectral domain two methods have been used one of which depends on the coherence between bouguer gravity anomalies and topography whereas the other uses the transfer function commonly known as the admittance between the free air gravity and topography the two methods give estimates of t e which differ by as much as an order of magnitude in those continental regions where variations in elevation are small this problem has led to much controversy an important concern is the extent to which estimates of t e are affected by dynamically maintained gravity and topography arising from mantle convection and postglacial recovery unlike elastically supported anomalies these processes can generate gravity and topographic long wavelength 500 km anomalies if such anomalies are modelled as being supported by elastic forces the resulting values of t e are overestimated often by a large amount

global dynamic topography observations reveal limited influence of large scale mantle flow mantle flow causes earth s surface to uplift and subside global analysis of dynamically generated topography suggests that temperature induced small scale mantle flow has a bigger influence on surface topography than large scale mantle flow

spatial and temporal uplift history of south america from calibrated drainage analysis a multi disciplinary approach is used to analyze the cenozoic uplift history of south america residual depth anomalies of oceanic crust abutting this continent help to determine the pattern of present day dynamic topography admittance analysis and crustal thickness measurements indicate that the elastic thickness of the borborema and altiplano regions is 10 km with evidence for sub plate support at longer wavelengths a drainage inventory of 1827 river profiles is assembled and used to investigate landscape development linear inverse modeling enables river profiles to be fitted as a function of the spatial and temporal history of regional uplift erosional parameters are calibrated using observations from the borborema plateau and tested against continent wide stratigraphic and thermochronologic constraints our results predict that two phases of regional uplift of the altiplano plateau occurred in neogene times regional uplift of the southern patagonian andes also appears to have occurred in early miocene times the consistency between observed and predicted histories for the borborema altiplano and patagonian plateaux implies that drainage networks record coherent signals that are amenable to simple modeling strategies finally the predicted pattern of incision across the amazon catchment constrains solid sedimentary flux at the foz do amazonas observed and calculated flux estimates match suggesting that erosion and deposition were triggered by regional andean uplift during miocene times

an assessment of the accuracy of admittance and coherence estimates using synthetic data previous work has shown that estimates of the admittance between topography and free air gravity anomalies are often biased by spectral leakage even after the application of multiple prolate spheroidal wavefunction data tapers despite this a number of authors who have used the free air admittance method to estimate the weighted average effective elastic thickness of the lithosphere te and to identify topography supported by mantle convection have not tested their methods using synthetic data with a known relationship between topography and gravity in this paper i perform a range of such tests using both synthetic surface data and synthetic line of sight los accelerations of satellites orbiting around an extra terrestrial planet it is found that spectral leakage can cause the estimated admittance and coherence to be significantly in error but only if the box in which they are estimated is too small the definition of small depends on the redness of the gravity spectrum there is minimal error in the whole box weighted average estimate of te if the admittance between surface gravity and topography is estimated within a box at least 3000 km wide when the synthetic uniform te is less than 20 km and the coherence is high the errors in te are mostly 5 km for all box sizes greater than 1000 km on the other hand when the true te is greater than 20 km and the box size is 1000 km the best fitting te is likely to be at least 5 10 km less than the true te however even when the coherence is high it is not possible to use elastic plate admittance models to distinguish between real and spurious small fractions of internal loading when the boxes are smaller than 2000 km in width noise in the gravity introduces error and uncertainty but no additional bias into the estimates of the admittance it does however bias estimates of te calculated using the coherence between bouguer gravity and topography the admittance at wavelengths between 1000 and 4000 km which is of interest when studying mantle convection is only well resolved when the box size is larger than 2000 km or the synthetic te is less than 15 km and the true long wavelength admittance is greater than 30 mgal km 1 when the box size is 1000 km it is not possible to distinguish between real and spurious convective support of long wavelength topography at the altitude of most orbiting satellites 200 400 km gravity is much redder than it is at ground level therefore it is necessary to use much larger boxes when using los accelerations to estimate the admittance than it is when using surface measurements however gradual changes in the altitude of the satellite or even occasional sudden changes make almost no difference to the estimate of the admittance finally three short investigations are undertaken concerning the effect on the admittance of the application of irregular windows to the data of lateral variations in te and of the infilling of flexural moats by low density sediment it is found that the bias due to the application of an irregular window is not significantly greater than the bias due to the application of a regular window of similar size that the best fitting te is strongly biased by the value associated with the highest amplitude topography and that sediment infill raises the admittance at wavelengths corresponding to the width of the moat

a comparison of the high frequency 1 hz surface and subsurface noise environment at three sites in the united states abstract surface and subsurface high frequency 1 hz noise data were recorded using nearly identical instrumentation at three widely separated sites in the united states amarillo texas datil new mexico and pinedale wyoming for extended periods of time under varying wind conditions while the sites are geologically distinct the near surface noise environments have many common features that we believe may be due in large part to the presence of a surficial layer of highly attenuative unconsolidated material at each site noise levels seen at or near the surface 5 m or less are much higher up to 30 db and much more variable power range up to 44 db than those seen at depth the smallest range was 9 db for 1951 m at amarillo the greatest gains in noise level reduction are realized within the first 100 m and probably much shallower

new views on the structure and rheology of the lithosphere over the last 10 years a series of developments have led to a new understanding of what controls the variations in lithosphere strength structure and evolution that produce dramatic contrasts between the geological histories of oceans ancient shields and young orogenic belts those developments involve a wide range of observations from a great diversity of geological geophysical and geochemical disciplines that none the less provide a mutually consistent and coherent overall picture this paper summarizes in one place the essential stages in the evolution of the relevant ideas and observations that have led to this situation

a reassessment of spectral te estimation in continental interiors the case of north america 1 conventional spectral te studies use the real part of the admittance between gravity anomalies and topography or alternatively the square of the magnitude of the coherency i e coherence here we show the utility of treating both the admittance and coherency as complex quantities inverting the real parts to estimate te we use the imaginary parts to tell if the inversion is biased by noise one method inverts the square of the real coherency with the internal to total load ratio f derived as a function of wave number directly from the gravity and topography the other method inverts the real part of the admittance assuming that f is wave number independent we test the methods using synthetic elastic plate models loaded at the surface and moho in such a way that the final relief is the actual north american topography in some of the models we add gravity noise generated by a model having both surface and internal loads such that the final topography is zero and find that both methods are susceptible to noise application of the two methods to north america gives te maps showing substantial agreement except in regions affected by noise but these are not a dominant part of the total area given the suggested mechanisms by which noise might arise it is not surprising that it is not a more widespread feature of the north american craton importantly both methods show that large parts of the canadian shield are characterized by te 100 km

links between climate erosion uplift and topography during intracontinental mountain building of the hangay dome mongolia 1 the hangay mountain range a dome in central mongolia provides a window into understanding how climate influences the erosion and resulting geomorphic and sedimentary signatures of continental topography specifically asymmetric erosion of the hangay associated with a distinct orographic precipitation gradient offers a natural experiment for exploring uplift erosion and the isostatic response to erosional unloading the flat topped hangay peaks preserve low relief remnant surfaces that provide markers of rock uplift this makes it possible to map the deformation of a former planar surface during doming and hence to estimate the total extent of erosion by the difference from present day topography erosion into the hangay surface has been significant but incomplete the morphology of the range indicates a nonequilibrium landscape that may have persisted for millions to tens of millions of years implying a long response time in this semiarid climate the extent of erosion across the range correlates with mean annual precipitation variability in present day peak heights across the north south climatic and erosional gradient provides empirical support for the generally accepted theory that climate driven erosion will increase the height of mountain peaks by generating greater surface uplift through isostasy correction for this isostatic response makes it possible to reconstruct primary surface uplift of the hangay results highlight the importance of considering the interplay between climate erosion and uplift in shaping intracontinental topography and thus when interpreting the geomorphic sedimentary and geodynamic signatures associated with such topography

density structure of the cratonic mantle in southern africa 1 implications for dynamic topography abstract the origin of high topography in southern africa is enigmatic by comparing topography in different cratons we demonstrate that in southern africa both the archean and proterozoic blocks have surface elevation 500 700 m higher than in any other craton worldwide except for the tanzanian craton an unusually high topography may be caused by a low density high depletion of the cratonic lithospheric mantle and or by the dynamic support of the mantle with origin below the depth of isostatic compensation assumed here to be at the lithosphere base we use free board constraints to examine the relative contributions of the both factors to surface topography in the cratons of southern africa our analysis takes advantage of the sase seismic experiment which provided high resolution regional models of the crustal thickness we calculate the model of density structure of the lithospheric mantle in southern africa and show that it has an overall agreement with xenolith based data for lithospheric terranes of different ages density of lithospheric mantle has significant short wavelength variations in all tectonic blocks of southern africa and has typical spt values of ca 3 37 3 41 g cm 3 in the cape fold and namaqua natal fold belts ca 3 34 3 35 g cm 3 in the proterozoic okwa block and the bushveld intrusion complex ca 3 34 3 37 g cm 3 in the limpopo belt and ca 3 32 3 33 g cm 3 in the kaapvaal and southern zimbabwe cratons the results indicate that 0 5 1 0 km of surface topography with the most likely value of ca 0 5 km cannot be explained by the lithosphere structure within the petrologically permitted range of mantle densities and requires the dynamic or static contribution from the sublithospheric mantle given a low amplitude of regional free air gravity anomalies ca 20 mgal on average we propose that mantle residual dynamic topography may be associated with the low density region below the depth of isostatic compensation a possible candidate is the low velocity layer between the lithospheric base and the mantle transition zone where a temperature anomaly of 100 200 c in a ca 100 150 km thick layer may explain the observed reduction in vs velocity and may produce ca 0 5 1 0 km to the regional topographic uplift

the long wavelength admittance and effective elastic thickness of the canadian shield the strength of the cratonic lithosphere has been controversial on the one hand many estimates of effective elastic thickness te greatly exceed the crustal thickness but on the other the great majority of cratonic earthquakes occur in the upper crust this implies that the seismogenic thickness of cratons is much smaller than te whereas in the ocean basins they are approximately the same leading to suspicions about the large te estimates one region where such estimates have been questioned is the canadian shield where glacial isostatic adjustment gia and mantle convection are thought to contribute to the long wavelength undulations of the topography and gravity to date these have not been included in models used to estimate te from topography and gravity which conventionally are based only on loading and flexure here we devise a theoretical expression for the free air gravity topography admittance that includes the effects of gia and convection as well as flexure and use it to estimate te over the canadian shield we use wavelet transforms for estimating the observed admittances after showing that multitaper estimates which have hitherto been popular for te studies have poor resolution at the long wavelengths where gia and convection predominate compared to wavelets our results suggest that te over most of the shield exceeds 80 km with a higher te core near the southwest shore of hudson bay this means that the lack of mantle earthquakes in this craton is simply due to its high strength compared to the applied stresses

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

new constraints on the origin of the hawaiian swell from wavelet analysis of the geoid to topography ratio abstract analyzing the formation mechanism of hotspot swells enhances our understanding of intraplate volcanism and the underlying geodynamical processes the two main hypotheses for the origin of the archetypal hawaiian swell are thermal lithospheric thinning and dynamic support by an ascending plume any successful model would have to be able to simultaneously explain the swell topography and the corresponding geoid anomaly in simple models of isostatic compensation the geoid to topography ratio gtr is linearly related to the depth of the compensating mass therefore it is often considered a fundamental parameter to assess swell support mechanisms previous estimates for the geoid to topography ratio gtr of the hawaiian swell however are biased towards low values by incomplete removal of the effects of volcanic loading and lithospheric flexure in order to resolve these issues we here apply a continuous wavelet transform which allows resolution of lateral variations of the gtr at various spatial scales in a series of synthetic tests the robustness of this approach and its power to identify the origin of hotspot swells are established with 8 m km on the youngest part of the chain the recovered gtr agrees well with the predictions for dynamic support therefore ruling out thermal rejuvenation as an important mechanism we also find that the depth of the compensating mass decays by 20 km over a distance of 500 km from hawaii to kauai and identify sublithospheric erosion by small scale convection in the ponded plume material as a viable mechanism to support this decay

the behavior of the lithosphere on seismic to geologic timescales the strength of the lithosphere and how it responds to loading and unloading are fundamental problems with wide implications flexure studies suggest that the elastic thickness a proxy for the strength of the lithosphere increases with plate age but decreases with load age the elastic thickness is significantly less than the seismic thickness of the lithosphere as indicated by the depth to the low velocity zone suggesting that the lithosphere is a strong structure at short seismic timescales and a weak one at long timescales the mechanism controlling this weakening is not known but it probably involves some form of load induced stress relaxation despite weakening the lithosphere is capable of retaining its strength and supporting loads such as volcanoes and sediments for long periods of geological time lithosphere relaxation should be included in geodynamical models especially as it has impacts on stratigraphy sea level change and dynamic topography

discrimination and origin of the sanukitoid series geochemical constraints from the neoarchean western karelian province finland abstract neoarchean late to post tectonic sanukitoid intrusions are found in the western part of the karelian province in finland variable sized even grained to k feldspar porphyritic intrusions form a series of diorites tonalites and granodiorites that are calc alkaline to alkali calcic magnesian and mostly peraluminous the major and trace element geochemistry of the intrusions show typical sanukitoid affinities a mantle signature high content of mg ni cr and high mg and enrichment in lile especially k ba and sr the intrusions form a distinctive series that can be distinguished from the ttg series of the karelian province by their high ba sr signature low na 2 o k 2 o ratio and uniform hree pattern the sanukitoid series can be compositionally constrained as follows sio 2 55 70 wt na 2 o k 2 o 0 5 3 mgo 1 5 9 wt mg 45 65 k 2 o 1 5 5 0 wt ba sr 1400 ppm and gd er n 2 6 the probable source was enriched subcontinental lithosphere mantle with high lile concentrations in phlogopite and or sanidine the accumulation of k ba and sr in the mantle source may have occurred as a consequence of two separate metasomatic events 1 by subduction related fluids melts and 2 by metasomatism related to asthenospheric mantle upwelling caused by slab breakoff the slab breakoff at the end stage of subduction is also a viable trigger for the sanukitoid magmatism

deep origin of the dome shaped hyblean plateau southeastern sicily a new tectono magmatic model southeastern sicily is characterized by a prominent topography known as the hyblean plateau it is commonly considered as a flexural bulge formed by the northwest plunging of the hyblean malta platform beneath the sicilian fold and thrust belt however its noncylindrical shape and multiphase uplift history correlated to the late miocene and plio pleistocene volcanism outline a possible magmatic control on the hyblean plateau topographic expression we argue using 2 d flexural models that the flexural bending alone is unlikely to explain the high anomalous elevation of the hyblean plateau moreover topographic analysis show that the hyblean plateau has a dome shape composed of radially tilted preserved surfaces defining individual blocks the block edges seem to be related to deep seated inherited faults using an analogue modeling approach we show that magmatic intrusions beneath the thick meso cenozoic sedimentary cover can reproduce the first order morphology of the hyblean plateau when a structural inheritance is imposed accordingly we propose a tectono magmatic model that favors mafic sill intrusions as the major uplift source for the topographic anomaly however to explain the strong positive bouguer anomaly a deeper high density intracrustal body is needed moho uprising related to mesozoic rifting or mafic lower crust underplating intraplating since the late cretaceous can be evoked the small wavelength of the topography and the deep intracrustal mass anomaly makes the lithospheric elastic stresses sufficiently high to maintain a nonisostatic state over the geological time scales

flexural isostasy constraints from gravity and topography power spectra we have used spherical harmonic coefficients that describe earth s gravity anomaly and topography fields to quantify the role of isostasy in contributing to crustal and upper mantle structure power spectra reveal that the gravity effect of topography and its flexural compensation contributes significantly to the observed free air gravity anomaly spectra for spherical harmonic degree 33 400 and lower n 33 degrees but topography appears either uncompensated or fully compensated at these degrees irrespective of the actual te all isostatic models underpredict the spectra at 2 n 12 and so we interpret the low order earth s gravity field as caused at least in part by non isostatic processes due to dynamic motions such as those associated with convective upwellings and downwellings in earth s mantle

a neogene history of mantle convective support beneath borneo abstract most but not all geodynamic models predict 1 2 km of mantle convective draw down of the earth s surface in a region centered on borneo within southeast asia nevertheless there is geomorphic geologic and geophysical evidence which suggests that convective uplift might have played some role in sculpting bornean physiography for example a long wavelength free air gravity anomaly of 60 mgal centered on borneo coincides with the distribution of neogene basaltic magmatism and with the locus of sub plate slow shear wave velocity anomalies global positioning system measurements an estimate of elastic thickness and crustal isostatic considerations suggest that regional shortening does not entirely account for kilometer scale regional elevation here we explore the possible evolution of the bornean landscape by extracting and modeling an inventory of 90 longitudinal river profiles misfit between observed and calculated river profiles is minimized by smoothly varying uplift rate as a function of space and time erosional parameters are chosen by assuming that regional uplift post dates eocene deposition of marine carbonate rocks the robustness of this calibration is tested against independent geologic observations such as thermochronometric measurements offshore sedimentary flux calculations and the history of volcanism a calculated cumulative uplift history suggests that kilometer scale bornean topography grew rapidly during neogene times this suggestion is corroborated by an offshore miocene transition from carbonate to clastic deposition co location of regional uplift and slow shear wave velocity anomalies immediately beneath the lithospheric plate implies that regional uplift could have been at least partly generated and maintained by temperature anomalies within an asthenospheric channel

large fluctuations of shallow seas in low lying southeast asia driven by mantle flow the sundaland continental promontory as the core of southeast asia is one of the lowest lying continental regions with half of the continental area presently inundated by a shallow sea the role of mantle convection in driving long wavelength topography and vertical motion of the lithosphere in this region has often been ignored when interpreting regional stratigraphy including a widespread late cretaceous eocene unconformity despite a consensus that southeast asia is presently situated over a large amplitude dynamic topography low resulting from long term post pangea subduction we use forward numerical models to link mantle flow with surface tectonics and compare predicted trends of dynamic topography with eustasy and regional paleogeography to determine the influence of mantle convection on regional basin histories a late cretaceous collision of gondwana derived terranes with sundaland choked the active margin leading to slab breakoff and a 10 15 myr long subduction hiatus slab breakoff likely resulted in several hundred meters of dynamic uplift and emergence of sundaland between 80 and 60 ma and may explain the absence of a late cretaceous eocene sedimentary record renewed subduction from 60 ma reinitiated dynamic subsidence of sundaland leading to submergence from 40 ma despite falling long term global sea levels our results highlight a complete down up down dynamic topography cycle experienced by sundaland with transient dynamic topography manifesting as a major regional unconformity in sedimentary basins

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

glacial rebound of the british isles iii constraints on mantle viscosity summary observations of sea level change since the time of the last glacial maximum provide important constraints on the response of the earth to changes in surface loading on time scales of 103 104 years this response is conveniently described by an effective elastic lithospheric thickness and effective viscosities for one or more mantle layers considerable trade off between the parameters describing these layers can occur and different combinations can give rise to comparable predictions of sea level change in particular the trade off between lithospheric thickness and upper mantle viscosity can be important and for any reasonable value for the lithospheric thickness a corresponding mantle viscosity structure can be found that gives a plausible comparison of sealevel predictions with observations in particular thin lithosphere models will lead to low estimates for the upper mantle viscosity while thick lithosphere models lead to high viscosity values however either solution may represent only a local minimum in the model parameter space and may not correspond to the optimum solution it becomes important therefore that in the inversion of observational data a comprehensive search is conducted throughout the entire model parameter space to ensure that the solution identified does indeed correspond to the optimum solution the sea level data for the british isles lend themselves well to such an inversion because of the relatively high quality of the data the good geographic distribution of the data relative to the former ice sheet and reasonable observational constraints on the dimensions of the former ice sheet and on its retreat furthermore because of the contribution to the sea level signal from the distant ice sheets as well as from the melt water load the observational data base for the region also has some resolving power for the viscosity of the deeper mantle the parameter space explored is defined by up to five mantle layers the lithosphere of effective elastic thickness d and a series of upper mantle layers i 2 4 extending down to depths of 200 400 and 670 km respectively each of viscosity qi and a lower mantle layer of viscosity qlm extending down to the coremantle boundary the range of parameters explored is 30 d i 120 km 3 x loi9 iqi

glacial isostatic adjustment in the static gravity field of fennoscandia in the central part of fennoscandia the crust is currently rising because of the delayed response of the viscous mantle to melting of the late pleistocene ice sheet this process called glacial isostatic adjustment gia causes a negative anomaly in the present day static gravity field as isostatic equilibrium has not been reached yet several studies have tried to use this anomaly as a constraint on models of gia but the uncertainty in crustal and upper mantle structures has not been fully taken into account therefore our aim is to revisit this using improved crustal models and compensation techniques we find that in contrast with other studies the effect of crustal anomalies on the gravity field cannot be effectively removed because of uncertainties in the crustal and upper mantle density models our second aim is to estimate the effects on geophysical models which assume isostatic equilibrium after correcting the observed gravity field with numerical models for gia we show that correcting for gia in geophysical modelling can give changes of several kilometer in the thickness of structural layers of modeled lithosphere which is a small but significant correction correcting the gravity field for gia prior to assuming isostatic equilibrium and inferring density anomalies might be relevant in other areas with ongoing postglacial rebound such as north america and the polar regions

the long term strength of europe and its implications for plate forming processes field based geological studies show that continental deformation preferentially occurs in young tectonic provinces rather than in old cratons this partitioning of deformation suggests that the cratons are stronger than surrounding younger phanerozoic provinces however although archaean and phanerozoic lithosphere differ in their thickness and composition their relative strength is a matter of much debate one proxy of strength is the effective elastic thickness of the lithosphere te unfortunately spatial variations in te are not well understood as different methods yield different results the differences are most apparent in cratons where the bouguer coherence method yields large te values 60 km whereas the free air admittance method yields low values or 1 5 gyr old is much larger mean te 60 km than that of younger lithosphere mean te 30 km we propose that this strength difference reflects changes in lithospheric plate structure thickness geothermal gradient and composition that result from mantle temperature and volatile content decrease through earth s history

extricating dynamic topography from subsidence patterns examples from eastern north america s passive margin abstract global sea level eustatic histories generated by backstripping stratigraphy are predicated upon the lithosphere having a well understood tectonic history however sub plate processes play a role in governing lithospheric vertical motions with timescales and amplitudes akin to eustasy which are difficult to predict we examine how stratigraphic and geophysical observations combined with simple isostatic models can be used to disentangle histories of sub plate support and eustasy we focus on the passive margin of eastern north america where a generally accepted history of eustasy has been estimated negative long wavelength free air gravity anomalies residual ocean age depth estimates fast upper mantle shear wave velocities and geodynamic models suggest that cenozoic evolution of this passive margin has been influenced by upper mantle drawdown we build on existing analyses to backstrip sixteen wells which combined with seismic data constrain timing and extent of cenozoic subsidence results indicate up to 1000 m of water loaded subsidence between 20 0 ma centered on the baltimore canyon trough seismic data from the trough shows neogene aggrading clinoforms there is little evidence for faulting or stratigraphic growth which indicates that neogene lithospheric strain rates were low amplitude and spatial extent of neogene subsidence are difficult to explain by glacio eustasy or glacio isostatic adjustment instead sub plate support calculated from conversion of shear wave velocities to temperature and isostatic calculations indicate that upper mantle drawdown was responsible for subsidence of the margin because mantle convection is vigorous such observations are expected throughout the stratigraphic archive

structure of the scandes lithosphere from surface to depth abstract in this review we give an overview of geophysical data and models available for the scandinavian mountains and adjacent areas as they are of relevance to the debate about the existence and cause of neogene uplift emphasis is given to potential field and petrophysical data of which the earth science communities of norway and sweden have a long tradition of acquisition and interpretation this is reflected in the wealth and dense coverage of data available the topography of the scandes mountain chain correlates to a large degree with a bouguer gravity low which suggests isostatic compensation but comparison with magnetic and petrophysical data shows that the gravity low is partly influenced by the trans scandinavian igneous belt signals due to the effects of surface geology can be further eliminated by considering the near surface density distribution as provided by petrophysical sampling to illuminate the entire lithospheric structure active and passive seismic and magnetotelluric data can be used recent and ongoing experiments are aimed at improving the existing models of the lithosphere integration of these different geophysical data sets allows the structure of the lithosphere of the scandes and its surroundings to be addressed seismic models show no pronounced crustal root below the scandes which could provide isostatic compensation but instead an increase of crustal thickness towards the central fennoscandian shield from the integrated model isostatic compensation is inferred to be largely controlled by the density distribution of the crust and that a high density lower crust to the east of the scandes is necessary to achieve isostatic equilibrium on a regional scale we demonstrate the typical crustal structure with profiles crossing from the scandes into the shield and a combined onshore offshore basement map

glacial rebound and sea level change an example of a relationship between mantle and surface processes lambeck k 1993 glacial rebound and sea level change an example of a relationship between mantle and surface processes in r wortel u hansen and r sabadini editors relationships between mantle processes and geological processes at or near the earth s surface tectonophysics 223 15 37 the problem of glacial rebound provides an outstanding example of the relationship between surface and mantle processes on time scales of 103 to 105 years changes in surface loading of ice and melt water associated with the growth and decay of the great ice sheets deform the surface of the planet and induces flow in the mantle a measure of the earth s response to the changing surface loads and internal deformation is provided by observations of past sea levels relative to the present level and inversion of these observations provides constraints on both the models of the rheological response of the earth to loading and on models of the ice sheets constraints on ice sheet models include the total volume of the grounded ice at the time of maximum glaciation the global rates of melting of the ice sheets the thickness of the ice at maximum glaciation the extent of ice cover over shallow seas such as the north sea and the barents sea and the role of antarctica in the global ice balance constraints on mantle parameters include the effective lithospheric thickness and the effective viscosity of the mantle some recent results for both sets of parameters are discussed