cenozoic lithospheric evolution of the bohai bay basin eastern north china craton constraint from tectono thermal modeling abstract it is well established that the lithosphere beneath the eastern north china craton ncc had been thinned before the cenozoic a 2d multi phase extension model in which the initial crustal and lithospheric thicknesses are variable is presented to reconstruct the initial thicknesses of the crust and lithosphere in the early cenozoic and to further investigate the lithospheric evolution beneath the eastern ncc through the cenozoic we conduct thermal modeling along three profiles from east to west in the bohai bay basin which is the center of the lithospheric destruction and thinning of the ncc using multiple constraints such as tectonic subsidence the present day heat flow and the moho depth we determine the initial crustal and lithospheric thicknesses of the bohai bay basin before the cenozoic rift to be 33 36 km and 80 105 km respectively the model results show that the most rapid lithospheric thinning during the cenozoic occurred in the middle eocene for most depressions and the thinning activity ceased at the end of the oligocene reaching a minimum lithospheric thickness of 53 74 km followed by a thermal relaxation phase combined with previous studies we infer that the lithosphere beneath the eastern ncc experienced two stages of alternating thinning and thickening notable thinning in the early cretaceous and paleogene and thickening in the late cretaceous and late cenozoic we believe that thermo chemical erosion together with extension was probably the major mechanism of the significant lithospheric removal during the mesozoic whereas the cenozoic lithospheric thinning was mainly dominated by tectonic extension in the eastern ncc lithospheric thickening was generally a result of thermal cooling

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

late cretaceous and cenozoic tectonics of the malay peninsula constrained by thermochronology abstract new thermochronological analyses of granites from the malay peninsula record the region s thermal history during the late mesozoic and cenozoic 40 ar 39 ar and u th sm he analyses are combined with existing fission track data to provide a comprehensive set of temperature and time data fully and partially reset k feldspar and biotite mica 40 ar 39 ar analyses indicate a significant period of thermal perturbation between 100 and 90 ma and a second lesser perturbation between 51 and 43 ma zircon u th sm he analyses and existing fission track data indicate exhumation of the malay peninsula in the cretaceous and renewed localised exhumation in the early paleogene apatite u th sm he and fission track data indicate rapid exhumation of the region in the late eocene and oligocene late cretaceous tectonism is linked to the reversal of a regional dynamic topographic low following the cessation of subduction along the sundaland margin in the late cretaceous causing regional uplift and exhumation and the addition of significant heat into the crust via mantle upwelling early paleogene exhumation may reflect the continuation of cretaceous tectonism or a discrete phase of paleocene exhumation linked to localised transpressional tectonics eocene tectonism is coincident with major subsidence offshore of the malay peninsula interpreted to reflect regional block faulting in response to north south compression driven by the resumption of subduction along the southern margin of sundaland in the eocene

topographic expressions of mantle dynamics in the mediterranean abstract the surface of the earth is the ever changing expression of the dynamic processes occurring at depth and at or above its surface however our ability to read landscapes in terms of their underlying tectonic or climatic forcing remains rudimentary during the last decade particular attention has been drawn to the deep dynamic contributions to topography related to the stresses that are produced at the base of the lithosphere by mantle convection and their relevance compared to the iso static component of topography here we use examples from the mediterranean and estimate residual and dynamic topography we then compare those with surface uplift from geology for specific regions to disentangle the dynamic from the static components considering the different topographic signatures of tectonic processes e g actual residual and dynamic topography as well as uplift rates jointly provides a powerful way to distinguish between the contributions of mantle crustal and surface processes such an approach might bring us closer to reading topographic expressions in terms of their geological cause

depth age and dynamic topography of oceanic lithosphere beneath heavily sedimented atlantic margins our understanding of the thermal structure of oceanic lithosphere is based upon observations of water loaded subsidence and plate age these observations are predominantly from areas with sparse sedimentary cover which are unperturbed by crustal thickening and by regional epeirogeny few such measurements are available from old oceanic lithosphere where sediment thickness is large in order to address this omission we have analyzed a legacy dataset of seismic reflection and wide angle profiles from the margins of the atlantic ocean our aims are twofold first we determine the isostatically corrected age depth variation of old oceanic lithosphere adjacent to continental margins and compare it with existing trends secondly we isolate residual depth anomalies and compare them with dynamic topographic predictions made from long wavelength gravity anomalies within the sedimentary pile we have used a suite of coincident seismic reflection and wide angle measurements to create a method for converting two way travel time into depth and sediment density we also correct for changes in oceanic crustal thickness on the oldest portions of the atlantic ocean the corrected age depth variation is consistent with results from the pacific ocean which suggests that the oceanic plate has a thickness of 90 95 km positive and negative deviations from the global age depth trend are common and can be as large as 1 km they mostly but not always correlate with long wavelength gravity anomalies if the admittance is 30 mgal km 1 we propose that these deviations are primarily generated by convective circulation within the upper mantle

topo oz insights into the various modes of intraplate deformation in the australian continent abstract as the fastest lowest flattest and amongst the most arid of continents australia preserves a unique geomorphic record of intraplate tectonic activity evidencing at least three distinct modes of surface deformation since its rapid northward drift commenced around 43 million years ago at long wavelengths several 1000s km systematic variations in the extent of neogene marine inundation imply the continent has tilted north down southwest up at intermediate wavelengths several 100s km several undulations of 100 200 m amplitude have developed on the 1 10 myr timescale at still shorter wavelengths several 10s km fault related motion has produced local relief at rates of up to 100 m myr over several million years the long wavelength north down tilting can be related to a dynamic topographic effect associated with australia s northward drift from the geoid low dynamic topography low now south of the continent to the geoid high dynamic topography low centred above the south east asian and melanesian subduction zones the short wavelength fault related deformation is attributed in time to plate wide increases in compressional stress levels as the result of distant plate boundary interactions and in space in part to variations in the thermal structure of the australian lithosphere at the intermediate wavelengths transient low amplitude undulations can be ascribed to either lithospheric buckling or the development of instabilities in the thermal boundary layer beneath the lithosphere in the latter case topographic asymmetries suggest the australian lithosphere is moving north with respect to the mantle beneath providing a unique attribution to the progressive alignment of seismic anisotropy and absolute plate motion observed near the base of the australian lithosphere

deformation in the lowermost mantle from polycrystal plasticity to seismic anisotropy in the deep earth deformation occurs at many scales large scale convection produces subduction of slabs and upwelling of plumes in the mantle at the high temperature high pressure conditions strain is accommodated through crystal plasticity either by diffusion or the movement of dislocations slip causes crystal rotations and thus produces a characteristic pattern of crystal preferred orientation and corresponding anisotropy of physical properties at the macroscopic scale in this study we use polycrystal plasticity with experimentally derived deformation mechanisms for perovskite post perovskite and magnesiowuestite to predict texture development along streamlines in a 2d geodynamic convection model of the lowermost mantle strong preferred orientation develops during subduction and upwelling while during spreading along the core mantle boundary the orientation pattern is relatively stable from preferred crystal orientation and single crystal elastic properties bulk elastic properties can be calculated and compared with seismic observations post perovskite with predominant 001 slip and magnesiowuestite with 110 and 111 slip produce anisotropy patterns which are consistent with observed anisotropy i e fast s waves polarized parallel to the core mantle boundary and anti correlation between p and s wave anisotropies in contrast perovskite with dominant 001 slip and two post perovskite models with dominant slip on 010 and 100 produce anisotropy patterns which are inconsistent with seismic observations

the case for dynamic subsidence of the u s east coast since the eocene the dynamic subsidence of the united states east coast is addressed using the discrepancy between regional and global estimates of sea level elevation of paleoshorelines and adjoint models of mantle convection that assimilate plate motions and seismic tomography the positions of eocene and miocene paleoshorelines are lower than predicted by global sea levels suggesting at least 50 m and possibly as much as 200 m of subsidence since the end of the eocene dynamic models predict subsidence of the east coast since the end of eocene although the exact magnitude is uncertain this subsidence has been occurring during an overall global sea level fall with the eustatic change being larger than the dynamic subsidence this results in a regional sea level fall in the absence of land subsidence dynamic subsidence is consistent with the difference between eustasy and regional sea level at the new jersey coastal plain

multi scale depositional successions in tectonic settings observations in sedimentary basins affected by deformation show that the fault induced depositional accommodation at various spatial and temporal scales is closely linked to basin kinematics the tectonically driven sediment infill displays the history of deepening and shoaling facies that are controlled by the activation of faults and changes in their offset rates simply stated this results in shifting sedimentary facies towards the source area or towards the basin centre in response to increasing or decreasing depositional space we propose a first principle conceptual model for tectonic successions controlled by the balance between the rates of creation of depositional space and sediment supply these sediment bodies are bounded by succession boundaries and comprise sourceward or basinward shifting facies tracts that are separated at a point of reversal due to the relatively steep slopes associated with the evolution of faults changes in sediment supply rates and mass wasting are common in these systems and may complicate the normal rhythm of the shifting facies tracts once tectonic quiescence is achieved and if the basin is connected to the open ocean eurybatic or eustatic base level changes may take over and play a greater role in sedimentary rhythm and cyclicity we illustrate the efficacy of the new concept with a review of examples from extensional contractional and strike slip basins we show that the basic tectonic succession model is applicable at all temporal and spatial scales and whether the tectonics cause subsidence or uplift and in all types of tectonic settings that determine the evolution of sedimentary basins

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

evolution of the walvis ridge rio grande rise hot spot system implications for african and south american plate motions over plumes crystallization ages of volcanic rocks dredged or drilled from the walvis ridge ten sites and the rio grande rise one site have been determined by the 40ar 39ar incremental heating technique the fundamentally age progressive distribution of these basement ages suggests a common hot spot source for volcanism on the island of tristan da cunha along the walvis ridge and rio grande rise and for the formation of the continental flood basalts located in namibia africa and brazil south america the walvis ridge rio grande rise volcanic system evolved along a section of the south atlantic spreading axis as the african and south american plates migrated apart astride or in close proximity to an upwelling plume reconstructions of the spatial relationship between the spreading axis the tristan hot spot and the evolving walvis ridge rio grande rise volcanic feature show that at about 70 ma the spreading axis began to migrate westward away from the hot spot the resulting transition to intraplate hot spot volcanism along the walvis ridge and associated termination of rio grande rise formation also involved a northward migration of previously formed african seafloor over the hot spot rotation parameters for african motion over fixed hot spots i e absolute motion have been recalculated such that the predicted trail of the tristan hot spot agrees with the distribution of radiometric and fossil basement ages along the walvis ridge african absolute motion has been extended to the south and north american plates by the addition of relative motion reconstruction poles

mantle induced subsidence and compression in se asia since the early miocene rift basins developed extensively across sundaland the continental core of southeast asia since the eocene beginning in the early miocene basins in southern sundaland experienced widespread synchronous compression inversion and marine inundation despite a large drop in long term global sea level the mechanism for this large scale synchronous regional sea level rise basin inversion and subsidence is not well understood and contrary to expectations from traditional basin models and eustatic sea level trends we present geodynamic models of mantle convection with both deformable and rigid plate reconstructions to investigate this enigma models suggest that a slab stagnates within the transition zone beneath southeast asia before the miocene the stagnant slab penetrated through the 660 km mantle discontinuity during the early miocene and formed a slab avalanche event due to continuous subduction and accumulation of negatively buoyant slabs this avalanche may have induced large scale marine inundation regional compression and basin inversion across southern sundaland we argue mantle convection induced large scale basin compression in contrast to conventional plate margin induced compression this suggests mantle convection may exert a much stronger control on surface processes than previously recognized

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

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

oligocene eustasy from two dimensional sequence stratigraphic backstripping estimates of the magnitudes of changes in third order 0 522 m y eustasy were obtained for oligocene sequences defined by a suite of largely onshore boreholes of the new jersey coastal plain benthic foraminiferal biofacies and multiple age constraints in a sequence stratigraphic framework formed the database for this study the geometry of the margin through time was determined using two dimensional backstripping the depth ranges of benthic foraminiferal biofacies were determined from a combination of standard factor analysis techniques and the backstripped geometries benthic foraminiferal biofacies were then used to determine the depths of the oligocene margin profiles obtained from backstripping the water depths of 16 of these horizons were confirmed by independent benthic biofacies determinations from at least two wells this internal consistency indicates that the data and the twodimensional backstripping approach were robust where benthic biofacies require a vertical shift of the horizons generated by two dimensional backstripping eustatic changes were required and were readily calculated results indicate a major eustatic fall from the end of the eocene to the first record of oligocene deposition subsequent long term shoaling of sea level through the oligocene was 30 m in 10 m y superimposed on this long term trend were higher frequency third order variations in eustasy with amplitudes of 40 m or less

large scale mantle convection and the history of subduction a large scale pattern of mantle convention is evident in the shape of the earth s gravity field1 lateral variations in seismic velocity2 3 the distribution of hotspots4 and long wavelength bathv metric anomalies5 paradoxically these signals of mantle convection bear little resemblance to present day plate motions1 4 although they seem to be related to past subduction zone configurations6 here we quantify this relationship by correlating a time integrated history of subduction calculated in the hotspot reference frame for the past 180 myr with regions of the deep mantle inferred from other geophysical observations to be colder than average our results support suggestions6 9 that a direct relationship exists between large scale thermal heterogeneity in the lower mantle and subduction during the cenozoic and mesozoic

cenozoic uplift and subsidence in the north atlantic region geological evidence revisited abstract the topographic evolution of the passive margins of the north atlantic during the last 65 myr is the subject of extensive debate due to inherent limitations of the geological geomorphological and geophysical methods used for studies of uplift and subsidence we have compiled a database of sign time and amplitude where possible of topographic changes in the north atlantic region during the cenozoic 65 0 ma our compilation is based on published results from reflection seismic studies aft apatite fission track studies vr vitrinite reflectance trends maximum burial sediment supply studies mass balance calculations and extrapolation of seismic profiles to onshore geomorphological features the integration of about 200 published results reveal a clear pattern of topographic changes in the north atlantic region during the cenozoic 1 the first major phase of cenozoic regional uplift occurred in the late palaeocene early eocene ca 60 50 ma probably related to the break up of the north atlantic between europe and greenland as indicated by the northward propagation of uplift it was preceded by middle palaeocene uplift and over deepening of some basins of the north sea and the surrounding areas 2 a regional increase in subsidence in the offshore marginal areas of norway the northern north sea the northern british isles and west greenland took place in the eocene ca 57 35 ma 3 the oligocene and miocene 35 5 ma were characterized by regional tectonic quiescence with only localised uplift probably related to changes in plate dynamics 4 the second major phase of regional uplift that affected all marginal areas of the north atlantic occurred in the plio pleistocene 5 0 ma its amplitude was enhanced by erosion driven glacio isostatic compensation despite inconclusive evidence this phase is likely to be ongoing at present

predicting and testing continental vertical motion histories since the paleozoic abstract dynamic topography at the earth s surface caused by mantle convection can affect a range of geophysical and geological observations including bathymetry sea level change continental flooding sedimentation and erosion these observations provide important constraints on and test of mantle dynamic models based on global mantle convection models coupled with the surface plate motion history we compute dynamic topography and its history for the last 400 ma associated with pangea assembly and breakup with particular focus on cratonic regions we propose that burial unroofing histories of cratons inferred from thermochronology data can be used as a new diagnostic to test dynamic topography and mantle dynamic models our models show that there are currently two broad dynamic topography highs in the pacific and africa for the present day earth that are associated with the broad warm structures i e superplumes in the deep mantle consistent with previous proposals of dynamical support for the pacific and african superswells our models reveal that pangea assembly and breakup by affecting subduction and mantle upwelling processes have significant effects on continental vertical motions our models predict that the slave craton in north america subsides before pangea assembly at 330 ma but uplifts significantly from 330 ma to 240 ma in response to pre pangea subduction and post assembly mantle warming the kaapvaal craton of africa is predicted to undergo uplift from 180 ma to 90 ma after pangea breakup but its dynamic topography remains stable for the last 90 ma the predicted histories of elevation change for the slave and kaapvaal cratons compare well with the burial unroofing histories inferred from thermochronology studies thus supporting our dynamic models including the development of the african superplume mantle structure the vertical motion histories for other cratons can provide further tests of and constraints on our mantle dynamic models

no global scale transgressive regressive cycles in the thanetian paleocene evidence from interregional correlation abstract a detailed examination of transgressions and regressions that occurred during the thanetian 58 7 55 8 ma may provide an important constraint on the global palaeoenvironment seven tectonically stable regions the eastern russian platform northwestern europe northwestern africa northeastern africa the arabian platform the northern gulf of mexico and southern australia represent exceptional records of transgressive regressive t r cyclicity their chronostratigraphic frameworks are sufficiently well constrained to permit accurate correlation surprisingly except for a generally regressive trend occurring in the late thanetian no common t r cycles can be delineated which indicates an absence of global scale t r cyclicity during the thanetian furthermore we find no clear correspondence between documented t r patterns and previously reported eustatic changes we suggest that a warm climate and an absence of major glaciations in the early middle thanetian coupled with only slow eustatic change expected from tectonic processes stabilized thanetian eustatic sea level regional subsidence or uplift possibly generated by mantle flow in the form of dynamic topography governed transgressions and regressions locally and resulted in an inconsistency between t r cycles in different parts of the globe the late thanetian regressive episode which preceded the paleocene eocene thermal maximum may be linked to an advance of glaciation

cretaceous anomalous subsidence and its response to dynamic topography in the songliao basin northeast china to understand the formation mechanisms and evolution of the songliao basin we applied backstripping and strain rate inversion methods to 20 wells and reinterpret two seismic sections in the songliao basin the obtained data were used to reconstruct the tectonic subsidence history and further assess the potential subsidence mechanisms of this area the predicted post rift subsidence based on the uniform stretching model that followed earlier lithospheric thinning events was much lower than the subsidence provided by backstripping the anomalous subsidence during the post rift stage was between 200 m and 800 m in the songliao basin and the depocenter of anomalous subsidence moved eastward between ca 110 and 80 ma before returning to the west between ca 80 and 65 ma regional variations in the subsidence rates suggest a possible deficit in the negative buoyancy mantle loading that is induced by the sinking slab beneath the songliao basin in addition the anomalous post rift subsidence was primarily driven by downward drag pressure from the subducting western izanagi slab and asthenospheric mantle flow beneath the songliao basin the basement rifting in the songliao basin during the early cretaceous and the normal faulting that occurred during the post rift stage resulted in a secondary contribution to the anomalous post rift subsidence unlike the songliao basin several early cretaceous rift basins south of the yanshan belt were only filled during the syn rift subsidence and the anomalous post rift uplift of the yanshan belt was driven by deep mantle flow

sea level and vertical motion of continents from dynamic earth models since the late cretaceous dynamic earth models are used to better understand the impact of mantle dynamics on the vertical motion of continents and regional and global sea level change since the late cretaceous a hybrid approach combines inverse and forward models of mantle convection and accounts for the principal contributors to long term sea level change the evolving distribution of ocean floor age dynamic topography in oceanic and continental regions and the geoid we infer the relative importance of dynamic versus other factors of sea level change determine time dependent patterns of dynamic subsidence and uplift of continents and derive a sea level curve we find that both dynamic factors and the evolving distribution of sea floor age are important in controlling sea level we track the movement of continents over large scale dynamic topography by consistently mapping between mantle and plate frames of reference and we find that this movement results in dynamic subsidence and uplift of continents the amplitude of dynamic topography in continental regions is larger than global sea level in several regions and periods so that it has controlled regional sea level in north and south america and australia since the late cretaceous northern africa and arabia since the late eocene and southeast asia in the oligocene miocene eastern and southern africa have experienced dynamic uplift over the last 20 to 30 m y whereas siberia and australia have experienced cenozoic tilting the dominant factor controlling global sea level is a changing oceanic lithosphere production that has resulted in a large amplitude sea level fall since the late cretaceous with dynamic topography offsetting this fall

eroding dynamic topography 1 geological observations of mantle flow driven dynamic topography are numerous especially in the stratigraphy of sedimentary basins on the contrary when it leads to subaerial exposure of rocks dynamic topography must be substantially eroded to leave a noticeable trace in the geological record here we demonstrate that despite its low amplitude and long wavelength and thus very low slopes dynamic topography is efficiently eroded by fluvial erosion providing that drainage is strongly perturbed by the mantle flow driven surface uplift using simple scaling arguments as well as a very efficient surface processes model we show that dynamic topography erodes in direct proportion to its wavelength we demonstrate that the recent deep erosion experienced in the colorado plateau and in central patagonia is likely to be related to the passage of a wave of dynamic topography generated by mantle upwelling

the difficulty for subducted oceanic crust to accumulate at the earth s core mantle boundary 1 seismic tomography has revealed two large low shear velocity provinces llsvps in the lowermost mantle beneath the central pacific and africa the llsvps are further shown to be compositionally different from their surroundings among several hypotheses put forth in recent years to explain the cause of the llsvps one postulates that they are thermochemical piles caused by accumulation of subducted oceanic crust at the core mantle boundary cmb mineral physics experiments indicate that oceanic crust becomes denser than the surrounding mantle at lower mantle pressures in addition seismic observations provide evidence of subducted slabs arriving at the cmb however a major question pertains to whether subducted oceanic crust can survive viscous stirring associated with mantle plumes and accumulate into piles with the same spatial scale as llsvps we perform a set of high resolution convection calculations to examine this hypothesis by investigating the interaction of thin oceanic crust 6 km with mantle plumes our results show that as subducted oceanic crust is swept toward upwelling plume regions the majority of it is viscously stirred into the surrounding mantle only a small amount of oceanic crust may accumulate at the base of plumes but it is consistently entrained away into the plume at a rate equal to or greater than it is accumulated we find that it is difficult for subducted oceanic crust to accumulate into large thermochemical piles at the cmb

phanerozoic marine inundation of continents driven by dynamic topography above subducting slabs a spherical model of mantle flow constrained by the locations of trenches can be used to predict the dynamic topography of the earth s surface and hence the marine inundation of continents for past periods of high sea level the predicted geographical pattern of flooding correlates well with the geological record the high spatial correlation may result from increased plate velocities at these times leading to increased rates of subduction subsidence and inundation at convergent margins

migration of acidic pore waters at the waite amulet tailings site near rouyn noranda quebec canada pore waters found in the unsaturated zone of the waite amulet tailings have been modified by sulphide mineral oxidation resulting in acidic ph near 4 and high concentrations of dissolved iron an

topography and geoid due to lithospheric mass anomalies summary a model of lithospheric thickness and a recent compilation of moho depths are used to compute the earth s isostatic surface topography and associated gravity anomalies the results are strongly influenced by the uncertainties in lithospheric depth and crustal density profiles the preferred models explain most of the observed topography and are highly correlated with observed gravity anomalies for harmonic degrees larger than 10 comparisons of our residual topography with geodynamical calculations of dynamic topography based on mantle circulation are rather poor

subsidence and uplift by slab related mantle dynamics a driving mechanism for the late cretaceous and cenozoic evolution of continental se asia continental se asia is the site of an extensive cretaceous paleocene regional unconformity that extends from indochina to java covering an area of c 5 600 000 km the unconformity has previously been related to microcontinental collision at the java margin that halted subduction of tethyan oceanic lithosphere in the late cretaceous however given the disparity in size between the accreted continental fragments and area of the unconformity together with lack of evidence for requisite crustal shortening and thickening the unconformity is unlikely to have resulted from collisional tectonics alone instead mapping of the spatial extent of the mid late cretaceous subduction zone and the cretaceous paleocene unconformity suggests that the unconformity could be a consequence of subduction driven mantle processes cessation of subduction descent of a northward dipping slab into the mantle and consequent uplift and denudation of a sediment filled late jurassic and early cretaceous dynamic topographic low help explain the extent and timing of the unconformity sediments started to accumulate above the unconformity from the middle eocene when subduction recommenced beneath sundaland throughout continental se asia referred to here as sundaland fig 1 there are almost no upper cretaceous and paleocene strata suggesting that much of the region was elevated during this time cenozoic rocks rest on older rocks with a profound unconformity rocks beneath the unconformity are considered basement and comprise predominantly cretaceous and older granites mesozoic sedimentary rocks accreted ophiolitic and arc rocks and pre mesozoic metamorphic rocks sedimentary rocks above the unconformity are eocene and younger fig 1 and include siliciclastic volcanogenic and carbonate lithologies that were deposited across the region in extensional halfgraben basins and at the sundaland continental margins these deposits are initially commonly terrestrial and their depositional ages are often poorly constrained the unconformity has previously been interpreted as the result of a poorly defined tectonothermal event that occurred throughout indochina and the malay peninsula e g krahenbuhl 1991 ahrendt et al 1993 dunning et al 1995 upton 1999 or as a consequence of continental collision at the sundaland margin e g hall morley 2004 smyth et al 2007 hall 2009 however there has been no attempt to estimate the extent of or describe the unconformity itself or to propose a driving mechanism capable of producing uplift over such a large area in this paper we demonstrate that the area covered by the unconformity is in excess of 5 600 000 km c 2000 by c 2800 km greater than the area of the western united states fig 2 or ten times the size of mainland france and it extends from indochina to se borneo and east java fig 1 and that micro continental collisions in the late cretaceous were coincidental with the onset of regional uplift however from an assessment of the spatial extent of accreted continental crust the corresponding extent of the unconformity fig 1 and regional exhumation trends we suggest that uplift of a late jurassic to early mid cretaceous dynamic topographic low dtl also contributed to the formation of the unconformity uplift was triggered by termination of subduction slab detachment and the resulting dynamic rebound across the region furthermore we support the suggestion hall 2009 that the initiation of cenozoic basin development may have been related to resumption of subduction at c 45 ma from hall r cottam m a wilson m e j eds the se asian gateway history and tectonics of the australia asia collision geological society london special publications 355 37 51 doi 10 1144 sp355 3 0305 8719 11 15 00 the geological society of london 2011 fig 1 a our interpreted extent of the unconformity the core of sundaland as defined by hamilton 1979 and the approximate positions of accreted ophiolitic and arc type rocks and continental fragments added to the margin in the late cretaceous b sedimentary basins and their ages in the region that is affected by the unconformity highlighted basins are the malay nam con son west natuna central sumatra south sumatra kutei barito and se java basins polochan et al 1991 gwang et al 2001 doust noble 2008 smyth et al 2008 simplified lithostratigraphies are shown in figure 6 b clements et al 38

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

a simple global model of plate dynamics and mantle convection cooling and thickening of lithospheric plates with age and subduction result in large scale horizontal density contrasts tending to drive plate motions and mantle flow we quantify the driving forces associated with these density contrasts to determine if they can drive the observed plate motions first two dimensional models are computed to evaluate the effects of assumed rheologies and boundary conditions we are unable to obtain platelike behavior in viscous models with traction free boundary conditions the piecewise uniform velocities distinctive of plate motion can be imposed as boundary conditions and the dynamic consistency of the models evaluated by determining if the net force on each vanishes if the lithosphere has a newtonian viscous rheology the net force on any plate is a strong function of the effective grid spacing used leading to ambiguities in interpretation incorporating a rigid plastic lithosphere which fails at a critical yield stress into the otherwise viscous model removes these ambiguities the model is extended to the actual three dimensional spherical plate geometry the observed velocities of rigid plastic plates are matched to the solution of the viscous stokes equation at the lithosphere asthenosphere boundary body forces from the seismically observed slabs from the thickening of the lithosphere obtained from the actual lithospheric ages and from the differences in structure between continents and oceans are included interior density contrasts such as those resulting from upwellings from a hot bottom boundary layer are assumed to occur on a scale small compared to plate dimensions and are not included the driving forces from the density contrasts within the plates are calculated and compared to resisting forces resulting from viscous drag computed from the three dimensional global return flow and resistance to deformation at converging boundaries the rms residual torque is 30 of the driving torque the density contrasts within the plates themselves can reasonably account for plate motions body forces from convection in the interior may provide only a small net force on the plates at converging boundaries the lithosphere has a yield stress of 100 bars drag at the base of the plates is 5 bars and resists plate motion the net driving forces from subducting slabs and collisional resistance are localized and approximately balance driving forces from lithospheric thickening are distributed over the areas of the plates as is viscous drag the approximate balance of these two forces predicts plate velocities uncorrelated with plate area as observed the model represents a specific case of boundary layer convection the dynamical results are consistent with either upper mantle or mantle wide convection

neogene residual subsidence and its response to a sinking slab in the deep mantle of eastern china abstract mantle convection could have a significant effect on basin evolution however research quantifying this relationship is controversial to understand the formation mechanism and evolution of the cenozoic rift basins in eastern china we applied the back stripping technique and strain rate inversion modeling to 119 wells from sangjiang basin bohai bay basin north yellow sea basin south yellow sea basin east china sea shelf basin and four basins within the northern south china sea margin the modeled results can be used to reconstruct the tectonic subsidence history and further assess the potential subsidence mechanisms of eastern china residual subsidence is defined as the difference between the theoretical and observed tectonic subsidences our results show that the residual subsidence since 20 ma in eastern china generally increases from 100 to 300 m in terrestrial areas to 1 2 1 8 km on the continental shelf our observed residual subsidence is generally consistent with the present day dynamic topography that is predicted from mantle flow models and it is associated with a stagnant slab within the mantle that has been observed by seismic tomography the migration pathway of the residual subsidence since 20 ma is consistent with the movement direction of the pacific and philippine plates therefore we suggest that the residual subsidence might be a dynamic subsidence induced by a negative buoyancy of the sinking slab in the deep mantle beneath eastern china

climate changes control offshore crustal structure at south china sea continental margin a b s t r a c t rifted continental lithosphere subsides as a consequence of combined crustal thinning and mantle lithosphere cooling yet basins on some continental margins experience anomalous subsidence events that postdate active extension deep basins on the northern margin of the south china sea notably the baiyun sag show basement subsidence accelerating after 21 ma postdating extension by several million years we combine geophysical observations and numerical forward modeling to show that loading of the offshore basins by increased sediment flux caused by faster onshore erosion following early miocene monsoon intensification is a viable trigger for ductile flow after the cessation of active extension this illustrates that offshore basin dynamics at continental margins with weak crust can be controlled by onshore surface processes in a newly recognized form of climate tectonic coupling

abrupt upper plate tilting during slab transition zone collision abstract the sinking remnant of a surface plate crosses and interacts with multiple boundaries in earth s interior here we specifically investigate the prominent dynamic interaction of the sinking plate portion with the upper mantle transition zone and its corresponding surface elevation signal we unravel for the first time that the collision of the sinking slab with the transition zone induces a sudden dramatic downward tilt of the upper plate towards the subduction trench unraveling this crucial interaction was only possible thanks to state of the art numerical modelling and post processing the new model that is introduced here to study the dynamically self consistent temporal evolution of subduction features accurate subduction zone topography robust single sided plate sinking stronger plates close to laboratory values an upper mantle phase transition and simple continents at a free surface to distinguish the impact of the new physical model features three different setups are used the simplest model setup includes a basic high viscosity lower mantle the second adds a 660 km phase transition and the third includes additionally a continental upper plate common to all models is the clear topographic signal upon slab transition zone interaction the upper plate tilts abruptly towards the subduction trench by about 0 05 and over around 10 ma this dramatic increase in upper plate tilt can be related to the slab induced excitation of the high viscosity lower mantle which introduces a wider flow pattern a large change in horizontal extent of inundation of up to 900 km is observed as a direct consequence of the upper plate tilting such an abrupt variation in surface topography and inundation extent should be clearly visible in temporal records of large scale surface elevation and might explain continental tilting as observed in australia since the eocene and north america during the phanerozoic

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

controls of mantle plumes and lithospheric folding on modes of intraplate continental tectonics differences and similarities summary mantle plume activity and lithospheric folding by far field stresses exerted from plate boundaries are two important end members as mechanisms for continental intraplate deformation the topographic expression of mantle plume impingement on continental lithosphere and lithospheric folding has some striking similarities observations from a number of areas in europe s intraplate lithosphere demonstrate that these mechanisms commonly interact in space and time we present the results of thermomechanical modelling addressing the role of factors such as the presence of a hot upper mantle the spatial dimensions of the plume and the time constants involved in the temporal succession of plume activity and lithospheric folding by stress accumulation in intraplate continental lithosphere the results demonstrate that both the processes plume lithosphere interactions and folding may interact resulting either in strong amplification attenuation or modification of their surface expression these inferences are compatible with a number of key observations on the nature and the temporal succession of topography evolution in the alpine foreland the pannonian basin the scandinavian continental margin and the iberian peninsula

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

cenozoic global plate motions cenozoic global plate motions relative to the hot spots are investigated and compared to plate motions in a mean lithosphere reference frame plate motions were analyzed over six time intervals divided by ages 10 25 43 48 and 56 ma chosen as much as possible to coincide with key plate reorganizations alternative motion circuits and rotational parameters were considered and evaluated with paleomagnetic data from the pacific and north american plates the circuit found to be in best agreement with the paleomagnetic data is one in which the hot spots in the atlantic region are assumed to be fixed relative to the hot spots in the pacific region throughout the cenozoic the hot spot and mean lithosphere reference frames have been in continual slow relative motion the rate of motion is nonuniform however most of the motion having occurred during the middle cenozoic the net cenozoic rotation of the lithosphere relative to the hot spots is described by a right handed rotation of 7 about a euler pole at 46 s 87 e which yields a 5 displacement of the north poles of the two reference frames this motion is small enough that inferences drawn about plate speeds in one reference frame should be valid in the other analysis of the global motions resulting from our preferred model showed that many characteristics of current plate motions have persisted throughout the cenozoic plate speeds correlate with latitude plates moving faster near the equator than near the poles throughout the cenozoic as at present continental plates except for the indian plate moved slower than oceanic plates throughout the cenozoic even the structure of the velocity fields as revealed in a contour of root mean square velocities in equatorial bands persists throughout the cenozoic the migration of the paleomagnetic axis over time is also compared to the hot spot and mean lithosphere reference frames the paleomagnetic axis has shifted 5 10 relative to the hot spot frame and a lesser amount relative to the mean lithosphere frame

global paleo lithospheric models for geodynamical analysis of plate reconstructions we present a general framework to generate time dependent global subduction history models from kinematic plate reconstructions and explore their associated coupled plate mantle dynamic behaviour slabs are constructed by advecting material into the mantle by prescribing its radial velocity and following the absolute tangential motion of the subducting plate a simple geodynamic scenario where plates and slabs define isopycnic and isoviscous regions in an homogeneous or layered mantle was explored using the boundary element method based software bemearth the resulting dynamic behaviour was used to predict the absolute plate motion directions for the present day and a particular mid cretaceous 125 ma kinematic model we show how the methodology can be used to compare and revise kinematic reconstructions based on their effect on the balance of plate driving forces and the resulting euler poles of subducting plates as an example we compare the farallon plate dynamics at 125 ma in a global model with two reconstructions in the context of the evolution of the western north american cordillera our results suggest a method to identify episodes of absolute plate motions that are inconsistent with the expected plate dynamics

locally layered convection inferred from dynamic models of the earth s mantle the structure of convection in the mantle is still the subject of considerable debate the now standard modelling of the convective flow as driven in a viscous mantle by density anomalies derived from seismic tomography has successfully explained the longest wavelength degree 2 to 8 geoid anomalies and provided important information concerning the viscosity structure of the mantle1 8 with this approach however the predicted response of surface topography to convective stresses the dynamic topography has a typical magnitude of several kilometres which does not conform with observations9 11 a possible source of this discrepancy lies in the severe underestimation by tomography of density anomalies due to deflections of the boundary between the upper and lower mantle at 660 km depth here we model the mantle flow implied by seismically derived density heterogeneities using an empirical method to account for the 660 km boundary topography the predicted dynamic surface topography thus obtained is significantly reduced to values that conform with the observations in addition the 660 km boundary topography appears to have a strong influence on the computed mantle circulation inducing local layering of the convective flow

flat slab subduction topography and mantle dynamics in southwestern mexico topography above subduction zones arises from the isostatic contribution of crustal and lithospheric buoyancy as well as the dynamic contribution from slab driven mantle flow we evaluate those effects in southwestern mexico where a segment of the cocos slab subducts horizontally the eastern part of the volcanic arc the trans mexican volcanic belt stands at an average elevation of 2 3 km nearly 1 3 km above the fore arc lateral changes in bulk crustal density are relatively small and seismic imaging shows that there is little variation in crustal thickness between these two regions thus the elevation difference between the arc and the fore arc should arise from differences in mantle properties we present finite element models of flat slab subduction that provide a simultaneous match to topography plate velocities and stress state in the overriding plate we find that the dynamic effects are primarily controlled by the amount of coupling at the subduction interface and in the mantle wedge the lack of slab anchoring into the lower mantle and the absence of continental mantle lithosphere with a mantle wedge and a subduction interface that are respectively 2 and 4 orders of magnitude weaker than the asthenosphere the flat slab exerts a downward pull that can explain most of the elevation difference between the fore arc and the arc we infer that lateral viscosity variations play a significant role in shaping dynamic topography in complex tectonic settings and that sublithospheric dynamics can influence the topography at wavelengths that are significantly shorter than previously recognized

the formation and potential importance of cemented layers in inactive sulfide mine tailings abstract investigations of inactive sulfide rich tailings impoundments at the heath steele new brunswick and waite amulet quebec minesites have revealed two distinct types of cemented layers or hardpans that at heath steele is 10 15 cm thick occurs 20 30 cm below the depth of active oxidation is continuous throughout the tailings impoundment and is characterized by cementation of tailings by gypsum and fe ii solid phases principally melanterite hardpan at the waite amulet site is only 1 5 cm thick is laterally discontinuous 10 100 cm occurs at the depth of active oxidation and is characterized by cementation of tailings by fe iii minerals principally goethite lepidocrocite ferrihydrite and jarosite at heath steele an accumulation of gas phase co2 of up to 60 of the pore gas occurs below the hardpan the calculated diffusivity of the hardpan layer is only about 1 100 that of the overlying uncemented tailings the pore water chemistry at heath steele has changed little over a 10 year period suggesting that the cemented layer restricts the movement of dissolved metals through the tailings and also acts as a zone of metal accumulation generation of a cemented layer therefore has significant environmental and economic implications it is likely that in sulfide rich tailings impoundments the addition of carbonate rich buffering material during the late stages of tailings deposition would enhance the formation of hardpan layers

climatic control of continental physiography abstract the spatial distribution of elevations and slopes on continents is a primary expression of complex interactions between tectonic and climatic systems because rates of tectonism and climatically mediated erosion vary in both space and time it is possible that heights of land and steepness of associated slopes change both across climatic regimes and during the tectonic evolution of any particular landmass as a geomorphic record spatial variations of continental physiography with latitude afford some insight into the relative importance of tectonic and climatic processes in controlling earth surface elevations because modern digital elevation models afford abundant data on continent surfaces across the complete set of equator to pole climate ranges we have undertaken an evaluation of the dependence of continental physiography on climate using the latitudinal gradient as a proxy for first order change in temperature and precipitation continental hypsometries can be largely explained by elevati

cenozoic plate driving forces past studies of plate driving forces have concluded that the forces due to subducted slabs in the upper mantle and those due to the thickening of the oceanic lithosphere are the principal driving forces we reexamine the balance of driving forces for the present day and extend our analysis through the cenozoic using an analytical torque balance method which accounts for interactions between plates via viscous coupling to the induced mantle flow we use an evolving mantle density heterogeneity field based on the last 200 myr of subduction to drive plate motions an approach which has proven successful in predicting the present day mantle heterogeneity field we find that for plausible upper mantle viscosities the forces due to subducted slabs in the cenozoic and mesozoic account for in excess of 90 of plate driving forces and those due to lithospheric thickening for less than 10

application of stratigraphic frameworks and thermochronological data on the mesozoic sw gondwana intraplate environment to retrieve the parana etendeka plume movement abstract since plate tectonics has been linked to material flow in the earth s mantle it is commonly accepted that convective motion in the sublithospheric mantle results in vertical deflections and horizontal plate motion on the earths surface those mantle flow driven vertical deflections are recognized through significant signals and traces in the sedimentary records unconformities and missing sections recently friedrich et al 2018 introduced an event based plume stratigraphic framework that uses such signals in the stratigraphic record to detect the geological evolution near and on the earth s surface in areas of interregional scale caused by mantle plume movement information about these dynamic processes is stored in geological archives such as 1 stratigraphic records of sedimentary basins and 2 thermochronological data sets of igneous metamorphic and sedimentary rocks for the first time this research combines these two geological archives and applies them to the mesozoic sw gondwana intraplate environment to retrieve the parana etendeka plume movement prior to the parana etendeka lip we compiled 18 stratigraphic records of the major continental and marine sedimentary basins and over 35 thermochronological data sets including 1300 apatite fission track ages surrounding the parana etendeka large igneous province to test the event based plume stratigraphic framework and its plume stratigraphic mapping to retrieve the timing and spatial distribution of the parana etendeka plume the plume stratigraphic mapping using the stratigraphic records is suitable to demark a possible plume center plume margins and distal regions friedrich et al 2018 thermochronological data reveal centers of a significant thermal parana etendeka plume influence both archives show significant signals and traces of mantle plume movement well in advance of the flood basalt eruptions our ltt data combined with stratigraphic records are modeled successfully with respect to a viable mantle plume driven thermal evolution and therefore we suggest that thermochronological data in combination with stratigraphy records have the potential to retrieve the parana etendeka plume movement

relative sea level fall since the last interglacial stage are coasts uplifting worldwide the growing interest in quantification of vertical ground motion stems from the need to understand in detail how the earth s crust behaves for both scientific and social reasons however only recently has the refinement of dating techniques made possible the use of paleoshorelines as reliable tools for tectonic studies although there are many local studies of quaternary vertical motions of coastlines we know of no comprehensive worldwide synthesis here we provide a compilation of 890 records of paleoshoreline sequences with particular emphasis on the last interglacial stage marine isotopic stage mis 5e 122 ka the quality of dating mis 5e makes it a reliable marker to evaluate vertical ground motion rates during the late quaternary on a global scale the results show that most coastal segments have risen relative to sea level with a mean uplift rate higher than 0 2 mm yr i e more than four times faster than the estimated eustatic drop in sea level the results also reveal that the uplift rate is faster on average for active margins than for passive margins neither dynamic topography nor glacio hydro isostasy may explain sustained uplift of all continental margins as revealed by the wide distribution of uplifted sequences of paleoshorelines instead we suggest that only plate tectonic processes reconcile all observations of quaternary coastal uplift we propose that long term continental accretion has led to compression of continental plates and uplift of their margins therefore this study concludes that plate tectonics processes impact all margins and emphasizes the fact that the notion of a stable platform is unrealistic these results therefore seriously challenge the evaluation of past sea levels from the fossil shoreline record

the pore water geochemistry and the mineralogy of the vadose zone of sulfide tailings waite amulet quebec canada low ph waters requiring treatment because of high concentrations of dissolved metals are being discharged from a decommissioned tailings impoundment at the former waite amulet zncu mine in northeastern quebec canada a detailed study of the vadose zone of the tailings comparing mineralogical and geochemical analyses of the tailings solids with geochemical analysis of the tailings pore water and pore gas indicates the presence of three zones within the tailings these zones include an upper sulfide depleted zone in which the sulfides have been extensively removed and oxidation is largely complete an intermediate zone where sulfide oxidation and acid neutralization reactions are occurring and an unoxidized zone below the depth of oxygen penetration where sulfides are unoxidized high aqueous concentrations of dissolved solids are being displaced downward from the sulfide depleted zone through the unoxidized zone toward the water table sulfide oxidation and acid neutralization reactions have generated concentrations of dissolved solids high enough to lead to the precipitation of a series of secondary solid phases precipitation dissolution reactions involving these solid phases control the concentrations of the major ions in the tailings pore water concentrations of dissolved metals are controlled by precipitation dissolution crystal structural replacement and adsorption coprecipitation reactions predictions based on the observed data and numerical simulations suggest that in the absence of an effective remedial program sulfide oxidation and h production will continue for several centuries

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle

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

isostasy flexure and dynamic topography abstract a fundamental scientific question is what controls the earth s topography although the theoretical principles of isostasy flexure and dynamic topography are widely discussed the parameters needed to apply these principles are frequently not available isostatic factors controlling lithospheric buoyancy are frequently uncertain and non isostatic factors such as lithospheric bending towards subduction zones and dynamic topography are hard to distinguish the question discussed here is whether a set of simple rules that relate topography to lithospheric structure in various tectonic environments can be deduced in a way that missing parameters can be approximated or does each area behave differently making generalizations problematic we contribute to this issue analyzing the asia africa arabia europe domain following a top down strategy we compile a new crustal thickness map and remove the contribution of the crust from the observed elevation then the challenge is to interpret the residual topography in terms of mantle lithosphere buoyancy and dynamics based on systematic relationships between tectonic environments and factors controlling topography we argue that crustal buoyancy and mantle lithospheric density can be approximated from available geological data and that regions near mantle upwelling or downwelling are easily identified by their extreme residual topography yet even for other areas calculating lithospheric thickness from residual topography is problematic because distinguishing variations in mantle lithosphere thickness from sub lithospheric dynamics is difficult fortunately the area studied here provides an opportunity to examine this issue based on the conjunction between the afar plume and the mid ocean ridge in the nearby gulf of aden and southern red sea we constrain the maximal amplitude of dynamic topography to 1 km this estimate is based on a narrow definition of dynamic topography that only includes sub lithospheric processes and using mid ocean ridges as reference where mantle lithosphere buoyancy is zero