reconciling subduction dynamics during tethys closure with large scale asian tectonics insights from numerical modeling we use three dimensional numerical models to investigate the relation between subduction dynamics and large scale tectonics of continent interiors the models show how the balance between forces at the plate margins such as subduction ridge push and far field forces controls the coupled plate margins and interiors evolution removal of part of the slab by lithospheric break off during subduction destabilizes the convergent margin forcing migration of the subduction zone whereas in the upper plate large scale lateral extrusion rotations and back arc stretching ensue when external forces are modeled such as ridge push and far field forces indentation increases with large collisional margin advance and thickening in the upper plate the balance between margin and external forces leads to similar convergent margin evolutions whereas major differences occur in the upper plate interiors here three strain regimes are found large scale extrusion extrusion and thickening along the collisional margin and thickening only when negligible far field forces ridge push and larger far field forces respectively add to the subduction dynamics the extrusion tectonics develops a strong asymmetry toward the oceanic margin driven by large scale subduction with no need of preexisting heterogeneities in the upper plate because the slab break off perturbation is transient the ensuing plate tectonics is time dependent the modeled deformation and its evolution are remarkably similar to the cenozoic asian tectonics explaining large scale lithospheric faulting and thickening and coupling of indentation extrusion and extension along the asian convergent margin as a result of large scale subduction process

kinematics and dynamics of the pamir central asia quantifying surface deformation and force balance in an intracontinental subduction zone kinematic and dynamic models quantify deformation and force balance in the pamir a region undergoing the rare and poorly understood process of intracontinental subduction we constrain a detailed kinematic model with 506 recent gps velocities and quaternary fault slip rates and show that the pamir is organized like the himalaya and tibet with regions of 1 localized strain rate 100e 9 yr along the pamir frontal thrust system the subduction interface similar to the himalaya and 2 distributed north south compression and east west extension similar to tibet through standard thin viscous sheet methods we demonstrate that the lithospheric force balance in the pamir is a combination of stresses caused by gravitational potential energy and india eurasia convergence accommodated at a subduction interface in this case the pamir frontal thrust system we find that strain rate and deviatoric stress patterns near the pamir frontal thrust system are characteristic of a mature subduction zone despite its initiation in continental lithosphere although the pamir and tibet are kinematically and dynamically similar the pamir is stiffer overall than tibet perhaps due to the presence of the highly arcuate geometrically stiffened continental slab at depth

contribution of gravitational potential energy differences to the global stress field summary modelling the lithospheric stress field has proved to be an efficient means of determining the role of lithospheric versus sublithospheric buoyancies and also of constraining the driving forces behind plate tectonics both these sources of buoyancies are important in generating the lithospheric stress field however these sources and the contribution that they make are dependent on a number of variables such as the role of lateral strength variation in the lithosphere the reference level for computing the gravitational potential energy per unit area gpe of the lithosphere and even the definition of deviatoric stress for the mantle contribution much depends on the mantle convection model including the role of lateral and radial viscosity variations the spatial distribution of density buoyancies and the resolution of the convection model gpe differences are influenced by both lithosphere density buoyancies and by radial basal tractions that produce dynamic topography the global lithospheric stress field can thus be divided into 1 stresses associated with gpe differences including the contribution from radial basal tractions and 2 stresses associated with the contribution of horizontal basal tractions in this paper we investigate only the contribution of gpe differences both with and without the inferred contribution of radial basal tractions we use the crust 2 0 model to compute gpe values and show that these gpe differences are not sufficient alone to match all the directions and relative magnitudes of principal strain rate axes as inferred from the comparison of our depth integrated deviatoric stress tensor field with the velocity gradient tensor field within the earth s plate boundary zones we argue that gpe differences calibrate the absolute magnitudes of depth integrated deviatoric stresses within the lithosphere shortcomings of this contribution in matching the stress indicators within the plate boundary zones can be corrected by considering the contribution from horizontal tractions associated with density buoyancy driven mantle convection deviatoric stress magnitudes arising from gpe differences are in the range of 1 4 tn m 1 a part of which is contributed by dynamic topography the egm96 geoid data set is also used as a rough proxy for gpe values in the lithosphere however gpe differences from the geoid fail to yield depth integrated deviatoric stresses that can provide a good match to the deformation indicators gpe values inferred from the geoid have significant shortcomings when used on a global scale due to the role of dynamically support of topography another important factor in estimating the depth integrated deviatoric stresses is the use of the correct level of reference in calculating gpe we also elucidate the importance of understanding the reference pressure for calculating deviatoric stress and show that overestimates of deviatoric stress may result from either simplified 2 d approximations of the thin sheet equations or the assumption that the mean stress is equal to the vertical stress

neotectonic deformation in central eurasia a geodynamic model approach funding was granted by the spanish government through the project mite cgl2014 59516 p and alpimed piecsic 201530e082

trench migration and upper plate strain over a convecting mantle trench motion and upper plate deformation ultimately respond to mantle flow herein i build upon the mantle flow model results of conrad and behn 2010 and compute the drag forces underneath all plates and show that they control the dynamics of plates and plate boundaries the small misfit angle between between the traction azimuths of mantle traction and absolute plate motion corroborates the idea that convective mantle drag is a prominent driver of plate tectonics less intuitive is the fact that the interplay between the drag forces from the upper and lower plates that amounts to 5 to 8 5 1012nm 1 per unit trench length dictates both trench migration rates and upper plate deformation at odds with the classic view that assigns the prime role to the idiosyncrasies of subduction zones slab age interplate friction water content etc i find that the intrinsic properties of subduction zones in fact only modulate this behavior more specifically the mean value of the integrated trenchward mantle drag force from the lower and upper plates from 2 to 6 5 1012nm 1 controls upper plate deformation conversely it is the difference between the lower and upper plates mantle drag forces from 3 to 10 1012nm 1 that controls trench migration rates in addition i find that a minimum trenchward force of 2 5 1012nm 1 must be supplied by mantle drag before trenches can actually advance and before upper plates undergo compression this force results from the default tendency of slabs to rollback when solely excited by their own buoyancy and is thus the effective tensional force that slab pull exerts on the plate interface

ridge torques and continental collision in the indian australian plate the excess gravitational potential energy of a collisional orogen that may be supported by focusing distributed ridge torques in a plate depends on the ratio l of the effective lengths of ridge systems and collisional fronts in the indian australian plate the net torque due to the asymmetric distribution of mid ocean ridges and young oceanic lithosphere along the southern boundary is 8 5 10 25 n m and is capable of supporting an excess potential energy of the himalayan collision zone of up to 7 5 10 12 j m 2 the concept that collision in the indian australian plate may be sustained by ridge torques suggests that collisional driving stresses may be sensitive to l in the indian australian plate l changed significantly during progressive collision from 55 to 45 ma during amalgamation of the indian and australian plates at 45 ma and during the development of the new guinea orogen through the late oligiocene and miocene such changes in l may help explain the termination of spreading between india and australia following the onset of the himalayan collision and the early miocene normal faulting in the high himalaya

dynamics of the india eurasia collision zone we present simple new dynamic calculations of a vertically averaged deviatoric stress field over a depth average of 100 km for asia from geodetic geologic topographic and seismic data a first estimate of the minimum absolute magnitudes and directions of vertically averaged deviatoric stress is obtained by solving force balance equations for deviatoric stresses associated with gravitational potential energy differences within the lithosphere plus a first order contribution of deviatoric stresses associated with stress boundary conditions this initial estimate of the vertically averaged deviatoric stress field is obtained independent of assumptions about the rheology of the lithosphere absolute magnitudes of vertically averaged deviatoric stresses vary between 5 and 40 mpa assuming bulk viscous behavior for the lithosphere the magnitudes of deviatoric stresses together with the magnitudes of strain rates inferred from quaternary fault slip rate and gps data yield vertically averaged effective viscosities for tibet of 0 5 5 1022 pa s compared with 1 2 5 1023 pa s in more rigid areas elsewhere in the region a forward modeling method that solves force balance equations using velocity boundary conditions allows us to refine our estimates of the vertically averaged effective viscosity distribution and deviatoric stress field the total vertically averaged deviatoric stress and effective viscosity field are consistent with a weak lower crust in tibet they are consistent with some eastward motion of tibet and south china lithosphere relative to eurasia and they confirm that gravitational potential energy differences have a profound effect on the spatially varying style and magnitude of strain rate around the tibetan plateau our results for the vertically averaged deviatoric stress argue for a large portion of the strength of the lithosphere to reside within the seismogenic upper crust to get deviatoric stress magnitudes there to be as high as 100 300 mpa in accord with laboratory and theoretical friction experiments indicating that stress drops in earthquakes are small fractions of the total deviatoric stress

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

geochemistry of rare earth elements in a neutral mine drainage environment anjir tangeh northern iran abstract this study investigates the geochemical characteristics of rare earth elements and yttrium ree y in the neutral mine drainage nmd and river water in the vicinity of the anjir tangeh coal washing plant mazandaran province northern iran the nmd water had a neutral ph along with high sulphate and bicarbonate concentrations the total concentrations of ree in the nmd water were lower than in the river water according to the north american shale composite nasc normalised concentrations the patterns of nmd showed heavy ree hree enrichment while the river water represented middle ree mree enhancement both negative europium eu and positive gadolinium gd anomalies were observed in the drainage and river water within the study area the sum of ree concentration increased gradually downstream of the discharging point of the plant reject water in contrast to decreasing of al fe mn and cu pb zn concentrations the river sediment with high fe concentrations was enriched with lanthanum la and cerium ce the overall ree pattern of the nmd approximates those of coal except for the depletion in light ree lree and the enrichment of eu dominant inorganic ree species in the river water included ln co3 2 and lnco3 while lnco3 ln co3 2 and ln so4 were the main complexes in the nmd the saturation index indicated that al and fe were both oversaturated in the drainage and river water which can control the fractionation of ree by the sorption process according to both hierarchical cluster analysis hca and principal component analysis pca ph al and p were the significant parameters in the ree distribution

geochemistry of the rare earth elements in hypersaline and dilute acidic natural terrestrial waters complexation behavior and middle rare earth element enrichments rare earth element ree speciation was modelled in acid 2 9 ph 3 5 hypersaline groundwaters from australia and from the palo duro basin in texas usa using a combined specific ion interaction pitzer model and ion pairing model the free metal ion species i e ln3 is the dominant form of dissolved rees in these systems accounting for 40 70 of the dissolved metal in groundwater from lake tyrrell victoria australia 50 90 of the rees in groundwater from lake gilmore western australia and always 90 of each ree in the texas groundwaters lakes tyrrell and gilmore are actually dry lakes that act as groundwater discharge zones the abundance of the free metal ion species increases in these waters with increasing ionic strength and with decreasing ph the free metal ion species is followed in abundance by ree sulfate and ree chloride complexes that account for 20 50 and 10 15 respectively of the dissolved rees in the groundwaters from lake tyrrell 15 30 and 5 20 respectively in the groundwaters from lake gilmore and 3 and 7 respectively in the palo duro basin groundwaters the groundwaters of the lake tyrrell system and the palo duro basin are enriched in the middle rees mrees compared to both the light rees lrees and the heavy rees hrees only nd sm and dy were determined in the lake gilmore groundwaters and consequently it is unclear whether these acid groundwaters are also enriched in the mrees previous investigators suggested that fe rich organic flocs ree phosphate complexation and solid liquid exchange reactions between terrestrial waters and mree enriched surface fe mn coatings suspended particulates or secondary mineral phases within aquifer materials may promote the development of mree enrichments in natural waters we propose that organic colloids and ree phosphate complexes are insignificant in acidic natural waters in regards to mree enrichments instead solid liquid exchange reactions or dissolution of surface coatings suspended particulates and or secondary phases as well as sulfate complexation more likely controls the development of mree enrichments in acidic natural terrestrial waters

current plate velocities relative to the hotspots incorporating the nuvel 1 global plate motion model nuvel 1 is a new global model of current relative plate velocities demets et al 1990 which differ significantly from those of prior models here we incorporate nuvel 1 into hs2 nuvel1 a new global model of plate velocities relative to the hotspots hs2 nuvel1 was determined from the hotspot data and errors used by minster and jordan 1978 to determine am1 2 which is their model of plate velocities relative to the hotspots am1 2 is consistent with minster and jordan s relative plate velocity model rm2 here we compare hs2 nuvel1 with am1 2 and examine how their differences relate to differences between nuvel 1 and rm2 hs2 nuvel1 plate velocities relative to the hotspots are mainly similar to those of am1 2 minor differences between the two models include the following 1 in hs2 nuvel1 the speed of the partly continental apparently non subducting indian plate is greater than that of the purely oceanic subducting nazca plate 2 in places the direction of motion of the african antarctic arabian australian caribbean cocos eurasian north american and south american plates differs between models by more than 10 3 in places the speed of the australian caribbean cocos indian and nazca plates differs between models by more than 8 mm yr although 27 of the 30 rm2 euler vectors differ with 95 confidence from those of nuvel 1 only the am1 2 arabia hotspot and india hotspot euler vectors differ with 95 confidence from those of hs2 nuvel1 thus substituting nuvel 1 for rm2 in the inversion for plate velocities relative to the hotspots changes few euler vectors significantly presumably because the uncertainty in the velocity of a plate relative to the hotspots is much greater than the uncertainty in its velocity relative to other plates

unabated acid mine drainage from cerro rico de potosi bolivia uncommon constituents of concern impact the rio pilcomayo headwaters intensive mining and processing of the polymetallic sulfide ore body of cerro rico de potosi bolivia has occurred since 1545 leading to severe degradation of surface and subsurface waters stream sediments and soils at the headwaters of the economically vital yet highly impacted rio pilcomayo previous studies have documented extremely elevated concentrations of a limited suite of metals in local waterways from acid mine drainage amd terrestrial and in stream tailings and ore processing plant discharges however contamination from a wider variety of ecotoxic metals metalloids was considered likely due to the highly mineralized polymetallic nature of the ore body to screen for this broader range of ecotoxic elements in amd and receiving streams data were gathered during two sampling events timed for the most extreme periods of the dry and wet seasons of one water year concentrations of ag b ba mo sb se sn and v in amd and receiving streams were greater than bolivian discharge limits and receiving water body guidelines as well as international agricultural use standards locally results indicate that contamination from mining cerro rico has a larger scope than previously thought and underscore the importance of remediation globally the results raise the possibility that other mining regions could have unquantified hazards from overlooked ecotoxic elements and that screening for a broader range of contaminants may be warranted

digital isochrons of the world s ocean floor we have created a digital age grid of the ocean floor with a grid node interval of 6 arc min using a self consistent set of global isochrons and associated plate reconstruction poles the age at each grid node was determined by linear interpolation between adjacent isochrons in the direction of spreading ages for ocean floor between the oldest identified magnetic anomalies and continental crust were interpolated by estimating the ages of passive continental margin segments from geological data and published plate models we have constructed an age grid with error estimates for each grid cell as a function of 1 the error of ocean floor ages identified from magnetic anomalies along ship tracks and the age of the corresponding grid cells in our age grid 2 the distance of a given grid cell to the nearest magnetic anomaly identification and 3 the gradient of the age grid i e larger errors are associated with high age gradients at fracture zones or other age discontinuities future applications of this digital grid include studies of the thermal and elastic structure of the lithosphere the heat loss of the earth ridge push forces through time asymmetry of spreading and providing constraints for seismic tomography and mantle convection models

how the continents deform the evidence from tectonic geodesy space geodesy now provides quantitative maps of the surface velocity field within tectonically active regions supplying constraints on the spatial distribution of deformation the forces that drive it and the brittle and ductile properties of continental lithosphere deformation is usefully described as relative motions among elastic blocks and is block like because major faults are weaker than adjacent intact crust despite similarities continental block kinematics differs from global plate tectonics blocks are much smaller typically 100 1000 km in size departures from block rigidity are sometimes measurable and blocks evolve over 1 10 ma timescales particularly near their often geometrically irregular boundaries quantitatively relating deformation to the forces that drive it requires simplifying assumptions about the strength distribution in the lithosphere if brittle elastic crust is strongest interactions among blocks control the deformation if ductile lithosphere is the stronger its fl

behavior of rare earth elements in acid coal mine drainage in shanxi province china rare earth element ree concentrations were determined in acid mine drainage amd bedrock pyrite and coal samples from the sitai coal mine and the malan coal mine in shanxi province china the amd displayed high ree concentrations with typical convex shale normalized patterns the ree concentrations in the bedrock samples are one order of magnitude higher than those found in pyrite and coal samples the high ree concentrations in amd most likely come from the acidic solution leached out ree in bedrock results from laboratory and field experiments show that ph is the most important factor controlling the fractionation of ree but fe al and mn colloids and secondary minerals also affects their fractionation as the ph increased from 4 to 6 the concentrations of total dissolved ree decreased from 520 to 0 875 g l 1 fe and al in amd has less influence on the fractionation of dissolved ree than low concentrations of mn hree were preferentially removed by secondary minerals and colloids followed by mree rare earth element s speciation modeling indicates that sulfate complexes lnso4 and ln so4 2 79 91 and free metal species ln3 8 8 21 are the dominant ree species in the amd but the ree sulfate complexation could not explain the mree enriched patterns

active deformation of asia from kinematics to dynamics using estimated strain rates across the actively deforming region of asia to infer variations in viscous stress it is shown that gradients of stress point uphill toward the center of tibet where gravitational potential energy per unit surface area reaches a maximum thus the dynamics of the deformation seem to obey the equation of creeping flow which expresses a balance between gradients in stress and the gravitational body force this balance in the region of the tibetan plateau yields an estimate of 10 22 pascal second for the average viscosity of the tibetan lithosphere which is only about 10 to 100 times greater than the viscosity of the convecting upper mantle

the behaviour of the rare earth elements during mixing of river and sea waters rare earth element concentrations have been measured in organic rich luce river water and coastal sea water concentrations e g 350 1850 pmol kg nd in the water of luce and 45 350 pmol kg nd in luce bay are related to the presence of particles with 30 60 of the ree associated with 0 4 0 7 m particles and to riverine fe concentrations ree fractionation occurs in the river water the submicrometre river water is heavy ree enriched whereas the coarser fraction has a more shale like ree pattern laboratory experiments show that the ree in organic rich river waters are chiefly associated with feorganic matter colloids which flocculate during estuarine mixing preferential removal of heavy ree 95 relative to light ree 60 occurs but no ce anomaly is developed in contrast no ree removal occurs during estuarine mixing with organic poor river water

mantle conveyor beneath the tethyan collisional belt abstract collisional belts are generated by the arrival of continental lithosphere into a subduction zone the tethyan suture from the bitlis to the himalayas is a prime example where the arabian and indian plates collided with eurasia during the cenozoic while the kinematics of this process are well established its dynamics are more uncertain india and arabia intriguingly keep advancing in spite of large collisional resisting forces and in the absence of a substantial upper mantle slab driving force at present day we perform global mantle circulation computations to test the role of deep mantle flow as a driving force for the kinematics of the tethyan collisional belt evaluating different boundary conditions and mantle density distributions as inferred from seismic tomography or slab models our results show that mantle drag exerted on the base of the lithosphere by a large scale convective conveyor belt with an active upwelling component is likely the main cause for the ongoing indentation of the indian and arabian plates into eurasia

a dynamical model for generating eurasian lithospheric stress and strain rate fields effect of rheology and cratons for most continents stress models driven by plate boundary forces have successfully reproduced the main characteristics of the stress field however eurasia has remained a challenge due to its large areas of intraplate deformation we present a set of three dimensional models of the upper mantle lithosphere system for a simplified geometry of the eurasian plate where we try to match the first order characteristics of the stress and strain rate fields simultaneously for typical elastic viscous or plastic rheologies high stress levels are required in order to produce realistic convergence rates between india and asia our models show robustly that such stresses are transmitted throughout most of the plate dominating locally generated stresses even in distal regions such as europe in a manner that is not compatible with observations cratons with roots that extend deep into the mantle are unable to provide a significant stress shielding effect unless the viscosity contrast between the asthenosphere and the underlying mantle is around 100 or greater a damage rheology for the lithosphere with history dependent behavior and material softening by a viscosity reduction of several orders of magnitude is shown to eliminate this conundrum continental convergence at high velocity but low stress is facilitated by the formation of long lived shear zones similar to those observed north of the himalayas the low stress associated with the collision together with the decoupling effect of the shear zones causes the distal stress field in europe to be controlled by the effects of the neighboring boundaries in agreement with observations

cerium anomalies in lateritic profiles the ree geochemistry and mineralogy have been studied in four lateritic profiles one derived from a syenite akongo sw cameroon the others being developed on a gneissic basement and located along a soil toposequence goyoum e cameroon there is a fractionation between lree and hree in the lateritic samples during weathering the weathered residual products being enriched in lree from la to eu and depleted in hree from gd to lu sampled waters are enriched in hree in relation to the syenite host rock a positive ce anomaly has been found systematically at the top of the saprolite beneath a zone of iron oxide accumulation in the laterite up to 2000 ppm ce may be present in the akongo profile cerianite ceo2 is present as very fine coatings in non ferruginous clayey domains primary ree bearing accessory minerals are weathered at the bottom of the profile specifically allanite and apatite are transformed into florencite and rhabdophane but these phases have no ce anomaly all the data are interpreted as the result of the following processes 1 1 ree leaching in a reducing environment 2 2 oxidation of ce3 to ce4 in an oxidizing environment 3 3 deposition of cerium as cerianite whereas the other ree remain in solution

rare earth element resources in coal mine drainage and treatment precipitates in the appalachian basin usa abstract drainages from abandoned coal mines in the appalachian basin represent a potential source of rare earth elements and yttrium rey many of which are considered to be critical resources due to their use in electronics and batteries we report rey data from coal mine drainage cmd sites and precipitates from cmd treatment systems throughout pennsylvania most cmd discharges are enriched in total rare earth elements relative to concentrations expected in unaffected surface or ground waters generally by 1 4 orders of magnitude relative to the north american shale composite nasc which approximates the rock with which mine waters interact cmd waters generally show a pattern of enrichment in the middle ree including several identified as critical resources nd eu dy tb low ph discharges tend to have higher rey concentrations than circumneutral discharges and a precipitous drop in concentration around ph 6 6 suggests adsorption of rey in the mine water flow path at near neutral ph values treatment precipitates including fe oxy hydroxides ca mg lime slurries and si and al rich precipitates are enriched in rey relative to the average cmd discharge value by factors of 103 104 while the discharges and precipitates analyzed in this study did not overlap in space and time the overall rey pattern of the precipitates approximate those of the cmd but with a slight depletion in light rare earth elements the higher rey concentrations in precipitates from systems treating low ph discharges most likely reflects the generally higher rey concentrations in these discharges but this needs to be established through direct comparisons over multiple seasonal cycles we estimate that coal mine drainage outflows in the appalachian basin generate a total of about 538 metric tons of rey per year in a dissolved state with 83 of that from low ph

a thin viscous sheet model for continental deformation summary for the purposes of describing its large scale and long term deformation the continental lithosphere is regarded as a continuum obeying a newtonian or a power law rheology the flow of a thin sheet of power law material overlying an inviscid substrate is studied under the assumption that vertical gradients of the horizontal velocity are negligible a numerical model is used to investigate the deformation of such a sheet under conditions approximating those of continent continent collision the material flows in response to forces applied to its boundaries for example the indenting of one continent by another and to forces in its interior arising from gradients in crustal thickness the horizontal divergence of the flow produces changes in the crustal thickness and hence a time dependent form to the flow itself for a given set of boundary conditions the flow depends on the stress exponent in the power law rheology n and on the argand number which is a measure of the ratio between the stress arising from crustal thickness contrasts and the stress required to deform the material at the ambient strain rates when the effective viscosity of the medium is very high ar o crustal thickness variations do not influence the flow if the material is newtonian n l the deformation associated with an influx of material approximating an indenter is of much greater lateral dimension than the width of the indenter whereas when material has a power law rheology n 3 5 are used the deformation is confined to a region of lateral extent comparable to that of the indenter as ar increases the forces arising from crustal thickness contrasts exert more influence on the flow and the maximum crustal thickness that can be sustained by a given influx of material is related by a simple expression to the effective viscosity of the medium at the ambient strain rates in the limit of a very weak medium ar 10 the lithosphere is unable to sustain appreciable crustal elevation contrasts the results of these numerical experiments show that systems in which the effective viscosities are such that the maximum deviatoric stresses are between 1 kbar

surface motions and continental deformation in the indian plate and the india eurasia collision zone the collision of the indian plate with eurasia has played a major role in controlling the dynamics of central asia leading to the world s largest continental deformation zone in order to study the deformation within the indian plate as well as the india eurasia collision zone we model the lithospheric stress field by calculating the two primary sources of stress one arising due to topography and shallow lithospheric structure estimated by gravitational potential energy differences and the other arising from basal tractions derived from density driven mantle convection we use several tomography models to calculate horizontal tractions using the convection code hc for two radially varying viscosity structures we also take into account lateral viscosity variations in the lithosphere model arising from stiff cratons weak plate boundaries and strength variations due to old and young oceanic lithosphere we do a quantitative comparison of our predicted deviatoric stresses strain rates and plate velocities with surface observables and find that the regional tomography model of singh et al 2014 embedded in the global s wave model s40rts does a remarkable job of fitting the observations of gps velocities and strain rates as well as intraplate stress field from the world stress map

joint modeling of lithosphere and mantle dynamics evaluation of constraints from global tomography models with the advances in technology seismological theory and data acquisition a number of high resolution seismic tomography models have been published however discrepancies between tomography models often arise from different theoretical treatments of seismic wave propagation different inversion strategies and different data sets using a fixed velocity to density scaling and a fixed radial viscosity profile we compute global mantle flow models associated with the different tomography models and test the impact of these for explaining surface geophysical observations geoid dynamic topography stress and strain rates we use the joint modeling of lithosphere and mantle dynamics approach of ghosh and holt 2012 to compute the full lithosphere stresses except that we use hc for the mantle circulation model which accounts for the primary flow coupling features associated with density driven mantle flow our results show that the seismic tomography models of s40rts and saw642an provide a better match with surface observables on a global scale than other models tested both of these tomography models have important similarities including upwellings located in pacific eastern africa iceland and mid ocean ridges in the atlantic and indian ocean and downwelling flows mainly located beneath the andes the middle east and central and southeast asia

the dynamics of the eastern mediterranean and eastern turkey summary in this study we investigate the dynamics of the region that includes greece the aegean sea and asia minor in a least squares inversion we solve for a continuous strain rate field and corresponding velocity field that satisfies 872 gps data the estimate of the geodetic strain rate field provides constraints for our dynamic analysis next we separately solve the depth integrated 3 d force balance equations for depth integrated deviatoric stresses within the lithosphere in which body force input comes from differences in vertically integrated vertical stress or differences in gravitational potential energy per unit area gpe these gpe estimates calibrate the absolute magnitudes of deviatoric stresses that are acting within the lithosphere further we investigate the sensitivity of our stress field solutions by using two different crustal structure models one from compiled crustal structure estimates obtained primarily from relatively recent seismic observations and the other from the crust 2 0 model in an iterative least squares inversion we then solve for stress field boundary conditions that when added to the contribution of deviatoric stresses associated with gpe differences provides a best fit to the directions of principal axes and relative magnitudes of the principal axes of the rates of strain obtained in the kinematic analysis robust features that arise from the boundary condition solution are nne forcing along the southern boundary east of about 33 e 0 5 1 2 1012 n m 1 with a rapid anticlockwise rotation of forces to the west of this along with an outward pulling force 0 4 1012 n m 1 directed ssw along the entire hellenic arc segment this force system along the hellenic arc can be interpreted as a result of slab rollback the total depth integrated 3 d deviatoric stresses in the final dynamic solution provides an excellent match to the deformation indicators throughout the region with vertically integrated stress magnitudes of order 0 5 2 5 1012 n m 1 we use constraints from derived stress magnitudes together with gps defined scalar values of strain rate magnitude to define bulk effective viscosities of the lithosphere depth averaged effective viscosities for the entire lithosphere are high within the black sea of order 0 7 3 1023 pa s relative to surrounding continental lithosphere north anatolian shear zone northern aegean sea and gulf of corinth are characterized by low depth averaged viscosities of order 1 5 1021 pa s deviatoric stresses from gpe differences and boundary condition effects combine in surprising ways in some regions resulting in near total stress cancellation in areas such as the southern aegean sea and portions of the central anatolian block gpe differences combine with boundary condition effects along the eastern segment of the north anatolian fault naf in a way that is compatible with the hypothesis that motion on the naf was facilitated by slab detachment beneath east anatolia and dynamic uplift of east anatolian plateau in general gpe differences play a nearly equal role as boundary condition influences in their contribution to the total deviatoric stress field the low depth integrated deviatoric stress magnitudes throughout the region suggest that zones of active deformation are facilitated by dramatic weakening mechanisms throughout the lithosphere

rare earth elements in chloride rich groundwater palo duro basin texas usa rare earth element ree data for groundwater samples from the deep basin brine aquifer of the palo duro basin texas usa illustrates the potential use of ree for inferring groundwater flow paths through different geologic materials the ree content of the groundwaters range over 2 5 orders of magnitude and are depleted by 102 to 105 relative to aquifer materials the shale normalized ree patterns for groundwater that have primarily interacted with arkosic sandstones granite wash are flat with similar heavy ree hree enrichments lula n 0 60 to 0 80 the samples with highest ree contents and ree patterns which are enriched in the intermediate rees irees sm tb reflect variable degrees of interaction with carbonate rocks the iree enrichment is the result of fluid interaction with fe mn coatings on carbonate minerals and or secondary minerals in fractures and vugs the chloride complex lncl2 and free ions are the predominant ree species accounting for over 95 of the rees carbonate and sulfate species account for the other 5 and have very little influence on the behavior of the rees although this study indicates a potentially important role for the rees in understanding geochemical transport and groundwater movement it also indicates the necessity for developing a better understanding of ree speciation in high ionic strength solutions

geochemistry of the rare earth elements and uranium in the acidic berkeley pit lake butte montana abstract filtered 0 45 m and nonfiltered concentrations of rare earth elements ree u zr th ba sc and y were measured as a function of depth in the berkeley pit lake a large acidic mining lake in butte mt the ree show very little variation with depth apart from a slight concentration near the surface presumably due to evaporation the ree profiles of the pit waters show a depletion in light ree when normalized against nasc and the host butte quartz monzonite bqm and a possible enrichment in middle ree vs heavy ree when normalized against bqm all of the ree partitioned weakly into secondary ferric precipitates formed by aging of deep berkeley pit water the measured distribution coefficients increased across the lanthanide series from la kd 7 7 to nd kd 10 3 and then decreased steadily to lu kd 1 4 under the conditions of the berkeley pit lake the aqueous speciation of ree and u is dominated by sulfate complexes because the stability constants of ree sulfate complexes show very little variation across the lanthanide series the observed trends in kd cannot be explained by aqueous complexation despite high concentrations of dissolved ree e g 1 1 mg l ce and u 0 85 mg l saturation indices for all solid phases were strongly negative due to the low ph of the berkeley pit lake 2 3 2 6 the mobility of ree and u is more likely constrained by adsorption or co precipitation with strengite jarosite schwertmannite or other secondary minerals forming in the lake

parallel thrust and normal faulting in peru and constraints on the state of stress abstract we present evidence for recent normal faulting in the cordillera blanca of peru along planes trending approximately n40 w parallel to the chain this type of faulting suggests that there is an important component of extension perpendicular to the chain and contrasts markedly with the underthrusting of the nazca plate on the west side of peru and with the folding and thrusting observed in the sub andes on the eastern flank of the chain these contrasting styles of deformation and associated stress fields can be explained by buoyancy forces due to the high mountains and crustal roots in so far as this explanation is correct the difference in elevation between zones of normal and thrust faulting can be used to place an upper bound of 500 bars on the average stress difference in the crust

finite strain calculations of continental deformation 2 comparison with the india asia collision zone numerical experiments on a thin viscous sheet model for deformation of continental lithosphere subjected to an indenting boundary condition yield distributions of crustal thickness of stress and strain rate and of latitudinal displacements that may be compared with observations in the india asia collision zone a simple indenting boundary condition applied to initially laterally homogeneous sheets obeying a power law rheology produces results that are in broad agreement with the observations provided that the power law exponent is three or greater and the sheet can support vertically integrated stress differences of 2 1013 5 1012 n m 1 in regions in front of the indenter under these conditions the calculated deformation shows accommodation of convergence primarily by crustal thickening to produce a plateau in front of the indenter palaeomagnetic data from india and tibet and the observed distribution of topography suggest that much of the post eocene convergence of india with asia has been taken up by deformation within asia that involved crustal thickening the principal difference between calculation and observation is the absence from the calculated strain rate fields of east west extension of the plateau in front of the indenting boundary the calculations show that once such a plateau is formed the buoyancy force associated with the crustal thickness contrast inhibits further thickening and the plateau strains at less than half the rate of its immediate surroundings seismically determined regional strain rates exhibit a similar distribution with the tibetan plateau straining at about one quarter the rate of the tien shan and ningxia gansu regions calculated principal compressive stress orientations and regional strain rates agree with the seismically determined quantities in the mongolia baikal tien shan tibet and ningxia gansu regions of asia to within the uncertainty of the latter the vertically integrated stresses that are calculated for the viscous sheet are comparable with those that can be supported by a theologically stratified continental lithosphere obeying laboratory determined flow laws we suggest that the thin viscous sheet model described in this paper and its companion gives a simple and physically plausible description of the observed deformation in central asia in this description the predominant mechanism of accommodation of continental convergence is diffuse crustal thickening with shear on vertical planes playing a subsidiary role once large crustal thickness contrasts have been established

geochemical behaviour of rare earth elements ree along a river reach receiving inputs of acid mine drainage abstract total and dissolved rare earth elements ree were studied in a river reach affected by several inputs of acid mine drainage the first four acidic discharges were of lesser importance compared to the last agrio river coming from the rio tinto mines which transported high loads of fe and al 2 1 and 4 2 ton day respectively together with ree 16 4 kg day and other trace elements in the acid mine drainage amd sources practically all the ree were dissolved and the north american shale composite nasc normalized patterns showed an enrichment in medium ree although some differences exist between the patterns of each source the ph values in the river reach upstream of the confluence with the agrio river ranged between 8 01 and 7 03 and most of the fe and al from the amd sources precipitated downstream of this acidic discharge the ph decreased to 2 98 upstream of the first amd input the dissolved and total concentrations of ree were very low 7 concentrations of ree increased up to 25 g l mainly transported by the particulate phase in the reach downstream of the agrio river with acidic conditions ree behaved conservatively the ree nasc normalized patterns of the river samples resemble that of the amd sources although an enrichment of heavy ree in the dissolved phase is observed linked to complexation by carbonates cerium and particularly la also show higher dissolved percentages similar to hree which must be due to the lower affinity of these elements to be sorbed onto fe oxyhydroxides variations in ce and eu anomalies are observed along the river reach as a consequence of the different amd inputs however the values of the ce anomaly are higher in total samples than in dissolved samples speciation results indicate that these differences are not caused by differences in oxidation states but by slight differences in the hydrogeochemical behaviour of ce with respect to la and nd

present day plate motion constraint on mantle rheology and convection large scale mantle convection to first order is a system driven by interior density anomalies modulated by variable plate thickness and extreme rheology variations at the top of the mantle the rheological difference between oceanic and continental regions significantly influences the surface velocity we apply a three dimensional newtonian viscous flow model to explain the large scale present day plate motions the density anomalies are derived from seismic tomography and a slab model with a viscosity difference of a factor of 30 60 between continents and oceans in the upper 90 km of the earth we are able to explain both the observed large scale poloidal and toroidal plate motions the viscosity difference between continental and oceanic regions has major control on both the poloidal toroidal kinematic energy partitioning and the pattern of toroidal motion nonlinear rheology can help establish toroidal motion plate motions can be explained by assuming either layered or whole mantle flow in order to match the amplitude of observed plate motions the value of the reference viscosity corresponding to that of between 400 to 670 km depth is 1 6 10 21 pa s for layered mantle flow and 3 2 10 21 pa s for whole mantle flow however the predicted net rotation of the lithosphere from both layered and whole mantle flow models is very small and cannot account for the amplitude of the net rotation obtained from the plate tectonic models assuming a fixed hotspot reference frame

stress in the indo australian plate cloetingh s and wortel r 1986 stress in the ind austr ian plate in b johnson and a w bally editors intraplate deformation characteristics processes and causes tectonophysics 132 49 67 we modelled the state of stress in the indo australian plate in order to investigate quantitatively variations observed in tectonic style the numerical procedure incorporates the dependence of slab pull and ridge push on the age of the oceanic lithosphere estimates are presented for the average net resistive forces at the himalayan collision zone the suction force acting on the overriding indo australian plate segment at the tonga kermadec trench and the drag at the base of the lithosphere our modelhng shows a concen ation of compressive stresses of the order of 3 5 lcbar in the ninetyeast ridge area the effects of the compressive resistance associated with himalayan collision and subduction of young lithosphere off the northern part of the sunda arc are focused in this region the stress field as calculated gives a consistent explanation for the observed concentration of seismic activity stein and okal 1978 and significant deformation in the oceanic crust weissel et al 1980 mcadoo and sandwell 1985 in the area the calculated stress field in the area adjacent to the southeast and central india ridges is characterized by tension parallel to the spreading axis this explains the concentration of near ridge normal faulting seismicity with t axes subparaile1 to the spreading ridge in the indian ocean as recently observed by bergman et al 1984 and wiens and stein 1984 the regional stress field along the strike of the sunda arc varies from compression seaward of and parallel to the sumatra trench segment to tension perpendicular to the java flores segment this explains the selective occurrence of well developed grabens seaward off the java flores segment of the trench observed by hilde 1983 our modelling shows that the observed rotation of the stress field denham et al 1979 in the australian continent is mainly the consequence of its geographic position relative to the surrounding trench segments and the variations of the forces acting on the down going slab in each of these the state of compression in west and central australia is induced by the action of resistive forces at the himalayan and banda arc collision zones the joint occurrence of high levels of compression in the plate s interior and normal faulting seismicity in the near ridge areas is a transient feature unique to the present dynamic situation of the indo australian plate

ridge forces absolute plate motions and the intraplate stress field torque poles are calculated for a variety of possible forces acting on the plates including ridge push slab pull and collisional resistance these torque poles are then compared to the directions of absolute plate motions there is a strong correlation between ridge torque poles and the azimuth of absolute plate motions for the north american south american pacific cocos and eurasian plates simple slab pull torques correlate well with absolute motion azimuths for the pacific nazca and cocos plates and moderately well with the absolute motion azimuth of the indoaustralian plate collisional resistance torque poles correlate with the absolute motion azimuth of the eurasian plate only the correlations are presented as further evidence that the absolute reference frame for plate motion is determined by the surface plates themselves torque poles for various forces are also compared with several long wavelength features of the global intraplate stress field that also tend to be aligned with absolute motion directions in general ridge torque directions agree well with the orientations of maximum horizontal stresses for stable north america western europe and south america and provide an alternative explanation for the alignment in terms of ridge push forces rather than basal drag collisional resistance forces can also explain the alignment of stresses in western europe for the indoaustralian plate the torque pole for collisional resistance forces is consistent with the general pattern of stresses in at least the western half of the plate but is not a good predictor of the entire data set for the plate other processes in addition to collisional resistance must be important for the indo australian plate ridge push forces may account for a significant portion of the long wavelength features of the intraplate stress field especially away from continental collisions such a conclusion is consistent with negative buoyancy of the slab being an important component of the driving mechanism as previously suggested slab forces may be largely balanced within the subducted slab itself and thus have limited effect on deformation of the surface plates

a stress interpretation scheme applied to lunar gravity and topography data 1 we present an approach of the inverse gravimetric problem that allows the gravity to be directly related to the deviatoric stresses without any rheological assumptions in this approach a new set of parameters is considered 1 the density variations over equipotential surfaces and the height of interfaces above the corresponding equipotential surfaces and 2 the stress difference the method is applied to lunar topographic and gravimetric data that are interpreted in term of transversally isotropic deviatoric stress within the moon it also provides inference on density and crustal thickness variations the estimated lateral variation in deviatoric stress is about 500 bars within the crust and upper mantle in the crust because of topography the strongest stress differences take place on the far side with large lateral compressions beneath the south pole aitken basin vertical compression under the mascons of the nearside is the main feature within the upper mantle

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

joint modeling of lithosphere and mantle dynamics elucidating lithosphere mantle coupling 1 we provide new insights into the lithosphere mantle coupling problem through a joint modeling of lithosphere dynamics and mantle convection and through comparison of model results with the high resolution velocity gradient tensor model along the earth s plate boundary zones using a laterally variable effective viscosity lithosphere model we compute depth integrated deviatoric stresses associated with both gravitational potential energy gpe differences and deeper mantle density buoyancy driven convection when deviatoric stresses from horizontal basal tractions associated with deeper density buoyancy driven convective circulation of the mantle are added to those from gpe differences the fit between the model deviatoric stress field and the deformation indicators improves dramatically in most areas of continental deformation we find that the stresses induced by the horizontal tractions arising from deep mantle convection contribute approximately 50 of the magnitude of the earth s deviatoric lithospheric stress field we also demonstrate that lithosphere asthenosphere viscosity contrasts and lateral variations within the lithospheric plate boundary zones play an important role in generating the right direction and magnitude of tractions that yield an optimal match between deviatoric stress tensor patterns and the deformation indicators

subduction initiation during collision induced subduction transference numerical modeling and implications for the tethyan evolution the collision induced subduction transference is a composite dynamic process including both the terrane collision accretion and the subduction initiation si at the neighboring passive margin thi

predicting the lithospheric stress field and plate motions by joint modeling of lithosphere and mantle dynamics the way in which basal tractions associated with mantle convection couples with the lithosphere is a fundamental problem in geodynamics a successful lithosphere mantle coupling model for the earth will satisfy observations of plate motions intraplate stresses and the plate boundary zone deformation we solve the depth integrated three dimensional force balance equations in a global finite element model that takes into account effects of both topography and shallow lithosphere structure as well as tractions originating from deeper mantle convection the contribution from topography and lithosphere structure is estimated by calculating gravitational potential energy differences the basal tractions are derived from a fully dynamic flow model with both radial and lateral viscosity variations we simultaneously fit stresses and plate motions in order to delineate a best fit lithosphere mantle coupling model we use both the world stress map and the global strain rate model to constrain the models we find that a strongly coupled model with a stiff lithosphere and 3 4 orders of lateral viscosity variations in the lithosphere are best able to match the observational constraints our predicted deviatoric stresses which are dominated by contribution from mantle tractions range between 20 70 mpa the best fitting coupled models predict strain rates that are consistent with observations that is the intraplate areas are nearly rigid whereas plate boundaries and some other continental deformation zones display high strain rates comparison of mantle tractions and surface velocities indicate that in most areas tractions are driving although in a few regions including western north america tractions are resistive citation ghosh a w e holt and l m wen 2013 predicting the lithospheric stress field and plate motions by joint modeling of lithosphere and mantle dynamics

development of topography in 3 d continental collision models understanding the formation and evolution of high mountain belts such as the himalayas and the adjacent tibetan plateau has been the focus of many tectonic and numerical models here we employ 3 d numerical simulations to investigate the role that subduction collision and indentation play on lithosphere dynamics at convergent margins and to analyze the conditions under which large topographic plateaus can form in an integrated lithospheric and upper mantle scale model distinct dynamics are obtained for the oceanic subduction side trench retreat slab rollback and the continental collision side trench advance slab detachment topographic uplift lateral extrusion we show that slab pull alone is insufficient to generate high topography in the upper plate and that external forcing and the presence of strong blocks such as the tarim basin are necessary to create and shape anomalously high topographic fronts and plateaus moreover scaling is used to predict four different modes of surface expression in continental collision models i low amplitude homogeneous shortening ii high amplitude homogeneous shortening iii alpine type topography with topographic front and low plateau and iv tibet himalaya type topography with topographic front and high plateau results of semianalytical models suggest that the argand number governs the formation of high topographic fronts while the amplitude of plateaus is controlled by the initial buoyancy ratio of the upper plate applying these results to natural examples we show that the alps belong to regime iii the himalaya tibet to regime iv whereas the andes altiplano fall at the boundary between regimes iii and iv

isotope stratigraphy of the lapa formation sao francisco basin brazil implications for late neoproterozoic glacial events in south america the lapa formation is a thick carbonate sequence 900 m that constitutes the upper part of the vazante group on the s francisco craton brazil it conformably overlies a previously unrecognized glacial diamictite unit of poorly constrained age the sequence above the glacial unconformity consists predominantly of organic rich shale subtidal rhythmic dolomicrites and microbialaminites and intertidal stromatolites four boreholes spanning different depositional settings were sampled at highresolution and investigated for their petrographic and chemical criteria to evaluate their degree of preservation the 13 c and 18 o values of well preserved lapa carbonate microsamples range from 8 2 to 3 3 vpdb and from 13 6 to 0 9 vpdb respectively each of the 13 c profiles of the investigated cores reveals two strong negative excursions of up to 8 an event in post glacial dolomicrites immediately above the glaciogenic unit and a 10 m interval of organic rich shale and a second near the top of the sequence associated with a shale interval based on the observation of dropstones and sedimentary iron formation in the underlying diamictite as well as the distinguishable carbon isotope trends the lapa formation is considered as a cap carbonate lithofacies the age of the lapa formation is presently unknown but the least radiogenic 87 sr 86 sr value 0 7068 associated with a negative carbon isotope excursion matches that from the rasthof formation in namiba on the congo craton which is radiometrically constrained to be younger than ca 750 ma

rapid development of negative ce anomalies in surface waters and contrasting ree patterns in groundwaters associated with zn pb massive sulphide deposits ground and surface waters collected from two undisturbed zn pb massive sulphide deposits the halfmile lake and restigouche deposits and active mines in the bathurst mining camp bmc nb canada were analysed for the rare earth elements ree ree contents are highly variable in waters of the bmc with higher contents typical of waters with higher fe and lower ph there are significant differences between ground and surface waters and between groundwaters from different deposits the ree contents of surface waters are broadly similar within and between deposit areas although there are spatial variations reflecting differences in ph and redox conditions surface waters are characterised by strong negative ce anomalies ce ce nasc as low as 0 08 produced by oxidation of ce3 to ce4 and preferential removal of ce4 from solution upon leaving the shallow groundwater environment groundwaters and seeps typically lack significant ce anomalies reflecting generally more reducing conditions in the subsurface environment and indicating that ce oxidation is a rapid process in the surface waters deeper groundwaters at the halfmile lake deposit are characterised by ree patterns that are similar to the host lithologies whereas most groundwaters at the restigouche deposit have lree depleted patterns compared to nasc halfmile lake deposit groundwaters have generally lower ph values whereas restigouche deposit groundwaters show greater heavy ree complexation by carbonate ions shallow waters at the halfmile lake and stratmat main zone deposits have unusual patterns which reflect either the adsorption of light ree onto colloids and fracture zone minerals and or precipitation of ree phosphate minerals middle ree enrichment is typical for ground and surface waters and is highest for neutral ph waters the labile portion of stream sediments are generally more middle ree enriched than total sediment and surface waters indicating that the ree are removed from solution by adsorption to fe and mn oxyhydroxides in the order middle ree light ree heavy ree

water rock interaction in an acidic mine discharge as indicated by rare earth element patterns abstract the rare earth element ree composition of an acidic spring discharging at ph 2 7 was studied in relation to the ree composition of selected extracts of the coal bearing strata hydrologically above the discharge the low ph of the discharge and the access to the strata through which it flows provides an excellent opportunity to study the use of rees as tracers of water rock interaction extraction techniques were used to mimic the process of acidic groundwater generation in coal bearing strata samples were treated to remove exchangeable ions and then treated sequentially with solutions buffered at ph 5 5 3 6 and 1 6 in order to mimic the natural buffering systems of groundwaters finally samples were oxidised with hydrogen peroxide in an attempt to remove the pyrite the results show that the composition of the spring is controlled by pyrite oxidation and buffering by fe oxy hydroxides the latter with compositions inherited from carbonates from within the sequence the similarity of ree patterns of the carbonate and the silicate extracts tends to obscure information concerning the relative roles of carbonate or silicate phases the source strata of the spring has evolved over time and shows that different coal seams have a unique contribution this distinct contribution appears more related to the mixture of sedimentary components i e carbonates silicates etc in the coal seam and the combination of shale and sandstone layers surrounding coal seams than the composition of the components themselves the similarity between ree compositions of the sequential extracts suggests that relationships discovered for this spring will be applicable elsewhere in the basin however this very property will hamper the use of such lithophilic elements in cases where characterisation of the source area is not possible

tracing the indian lithospheric mantle beneath central tibetan plateau using teleseismic tomography abstract we determined a detailed three dimensional p wave velocity structure of the crust and upper mantle down to 400 km depth beneath central tibet by applying teleseismic tomography to 28 146 high quality p wave arrival times the data were collected very carefully from the original seismograms of 1625 teleseismic events recorded by 131 broadband stations of five portable seismic networks deployed in central tibet our results show that the indian lithospheric mantle has subducted beneath central tibet and its frontier has passed through the bangong nujiang suture and extended northward beneath the qiangtang terrane at 34 north latitude a prominent low velocity anomaly is revealed within the tethyan himalayan sequences close to the yarlung zangbo suture which is the boundary between the tethyan himalayan sequences and the lhasa terrane the subduction of the indian lithospheric mantle has caused the east west extension in central tibet the indian slab beneath the region has not sutured with the asian lithospheric mantle in the north the obtained tomographic images can explain many geological and geophysical features such as strong seismic anisotropy in the upper mantle and k rich and ultra potassic lavas in northern tibet

monsoon speeds up indian plate motion article i nfo short term plate motion variations on the order of a few myr are a powerful probe into the nature of plate boundary forces as mantle related buoyancies evolve on longer time scales new reconstructions of the ocean floor spreading record reveal an increasing number of such variations but the dynamic mechanisms producing them are still unclear here we show quantitatively that climate changes may impact the short term evolution of plate motion by linking explicitly the observed counter clockwise rotation of the indian plate since 10 ma to increased erosion and reduced elevation along the eastern himalayas due to temporal variations in monsoon intensity by assimilating observations into empirical relations for the competing contributions of erosion and mountain building we estimate the first order decrease in elevation along the eastern himalayas since initial strengthening of the monsoon furthermore we show with global geodynamic models of the coupled mantle lithosphere system that the inferred reduction in elevation is consistent with the indian plate motion record over the same period of time and that lowered gravitational potential energy in the eastern himalayas following stronger erosion is a key factor to foster plate convergence in this region our study implicates lateral variations in plate coupling and their temporal changes as an efficient source to induce an uncommon form of plate motion where the euler pole falls within its associated plate

the role of gravitational potential energy in active deformation in the southwestern united states in orogenic belts intrinsic buoyancy and extrinsic boundary forces act on the continental lithosphere determining the relative importance of these forces is fundamental to understanding the dynamics of continental deformation in the western united states estimates of gravitational potential energy show that given available constraints on rheology buoyancy forces are sufficient to produce the wide variety of rates and styles of observed deformation including absence of deformation this underscores the importance of gravitational potential energy for deformation in orogenic belts

great earthquakes and slab pull interaction between seismic coupling and plate slab coupling great earthquakes the few largest earthquakes that account for most of the earth s seismic energy release have occurred at only a few subduction zones around the world strong locking or seismic coupling of the interface between plates at certain subduction zones is often invoked to explain these great earthquakes although past studies have correlated strong seismic coupling with a compressional stress environment that is characterized by back arc compression and caused by trenchward motion of the overriding plate the consequences of this compressional environment for the tectonic forces that drive global plate motions are not yet clear to examine these consequences we compared subduction zone earthquake magnitudes to tectonically constrained estimates of the degree to which each slab transmits its excess weight as a direct pull force on a subducting plate at seismically uncoupled subduction zones that generate only moderate sized earthquakes we find that slabs must transmit nearly their entire upper mantle weight as a pull force on the subducting plate at seismically coupled subduction zones that produce great earthquakes however we find that slabs must be nearly completely detached from their subducting plates this suggests that slabs subducting in a compressional environment experience stress induced weakening that prevents the effective transmission of the slab pull force convergent mantle flow above a descending slab that becomes decoupled from its surface plate may induce additional surface compression that further locks the subduction zone and leads to additional slab decoupling and detachment the resulting redistribution of plate driving forces may be responsible for rapid changes in plate motion c 2003 elsevier b v all rights reserved

metal enrichment in the groundwater of the arid environment in south africa this paper presents the enrichment tendency and spatial distribution of metals in the groundwater which is pumped out from the granitic aquifers in south africa groundwater is the sole source of water supply for the local community in the study area namaqualand and hence it was necessary to understand the controlling geochemical processes and interrelationship of metals in the groundwater the geochemical association of metals has been assessed based on the geostatistical methods the results show that geochemical processes such as oxidation leaching and evaporation besides water rock interaction are very important in controlling metal enrichment in the groundwater from highly mineralized rocks the metal enrichment index for selected toxic metals in groundwater increases in the order of cd u cr pb the observed enrichment trend could be considered as a result of mineralization of basement rocks which is facilitated by active geochemical process in the arid environment the lack of aquifer flushing due to negligible recharge helps the metals to concentrate at shallow groundwater zones supported by severe evaporation process

chemical weathering in the drainage basin of a tropical watershed nsimi zoetele site cameroon comparison between organic poor and organic rich waters abstract this study deals with the weathering processes operating at the scale of a small catchment nsimi zoetele cameroon and is focused on the role of organic colloids on mineral weathering and transport of elements in natural waters samples of river spring and groundwaters from nsimi zoetele were filtered through membranes of decreasing pore size 0 22 m 0 025 m or 300 000 da 5000 da to separate colloidal fractions from the truly dissolved one major and trace elements and dissolved organic carbon doc were analysed in each fraction two kinds of waters can be distinguished in the catchment clear and coloured waters clear waters exhibit low concentrations of major and trace elements and doc elements are carried in these solutions in a true dissolved form except al and rare earth elements rees by contrast the higher abundances of al fe and trace elements in coloured waters are controlled by the colloidal fraction thermodynamic equilibrium calculations show that clear waters are in equilibrium with kaolinite and iron oxi hydroxide which are major minerals in the weathered soil for coloured waters the aqueous speciation of ca mg cu fe al la and th was calculated taking into account the complexes with humic acids speciation calculations for cu fe al la th show a strong complexation with humic acids in good agreement with the results of the filtration experiments by contrast although filtration experiments show a strong control of major cations by organic matter for example 75 for ca speciation calculations reveal that their complexes with humic ligands do not exceed a few percent of total dissolved elements this discrepancy is explained as an artefact induced by the organic colloids and occurring during the filtration procedure finally both filtration experiments and speciation calculations show that organic matter plays an important role in natural doc rich waters organic acids increase significantly the dissolution rates of silicates and oxi hydroxides and thus the amounts of solutes and of complexed elements leaving the catchment

topography boundary forces and the indo australian intraplate stress field the relative contribution of topographic e g ridge push continental margins and elevated continental crust and plate boundary e g subduction and collisional forces to the intraplate stress field in the indo australian plate iap is evaluated through a finite element analysis two important aspects of the iap intraplate stress field are highlighted in the present study 1 if substantial focusing of the ridge push torque occurs along the collisional boundaries i e himalaya new guinea and new zealand many of the first order features of the observed stress field can be explained without appealing to either subduction or basal drag forces and 2 it is possible to fit the observed shmax maximum horizontal stress orientation and stress regime information with a set of boundary conditions that results in low tectonic stress magnitudes e g tens of megapascals averaged over the thickness of the lithosphere throughout the plate this study therefore presents a plausible alternative to previous studies of the iap intraplate stress field which predicted very large tectonic stress magnitudes hundreds of megapascals in some parts of the plate in addition topographic forces due to continental margins and elevated continental material were found to play an important role in the predicted stress fields of continental india and australia and the inclusion of these forces in the modeling produced a significant improvement in the fit of the predicted intraplate stresses to the available observed stress information in these continental regions a central focus of this study is the relative importance of the boundary conditions used to represent forces acting along the northern plate margin we note that a wide range of boundary conditions can be configured to match the large portion of the observed intraplate stress field and this nonuniqueness continues to make modeling the iap stress field problematic while our study is an important step forward in understanding the sources of the iap intraplate stress field a more complete understanding awaits a better understanding of the relative magnitude of the boundary forces acting along the northern plate margin

gravitational potential energy of the tibetan plateau and the forces driving the indian plate we present a study of the vertically integrated deviatoric stress field for the indian plate and the tibetan plateau associated with gravitational potential energy gpe differences although the driving forces for the indian plate have been attributed solely to the mid oceanic ridges that surround the entire southern boundary of the plate previous estimates of vertically integrated stress magnitudes of 6 7 x 1012 n m in tibet far exceed those of 3 x 1012 n m associated with gpe at mid oceanic ridges calling for an additional force to satisfy the stress magnitudes in tibet we use the crust 2 0 data set to infer gravitational potential energy differences in the lithosphere we then apply the thin sheet approach in order to obtain a global solution of vertically integrated deviatoric stresses associated only with gpe differences our results show large n s extensional deviatoric stresses in tibet that the ridge push force fails to cancel our results calibrate the magnitude of the basal tractions associated with density buoyancy driven mantle flow that are applied at the base of the lithosphere in order to drive india into tibet and cancel the n s extensional stresses within tibet moreover our deviatoric stress field solution indicates that both the ridge push influence 1 x 1012 n m and the vertically integrated deviatoric stresses associated with gpe differences around the tibetan plateau 3 x 1012 n m have previously been overestimated by a factor of two or more these overestimates have resulted from either simplified two dimensional approximations of the thin sheet equations or from an assumption about the mean stress that is unlikely to be correct

estimations of clarkes for carbonaceous biolithes world averages for trace element contents in black shales and coals abstract black shale and coal clarke values are the average trace element contents in the world black shales and coals these calculations are made in russian geochemistry but up to now are poorly known in the west modern tables of black shale and coal clarkes are presented based on comprehensive calculations using very large amount of information thousands analyses of black shales coals and coal ashes for trace elements in black shale geochemistry three figures were calculated for each main lithologies terrigenous tuff chert and carbonate two clarke estimations are presented named lithological k1 and lithostratigraphical k2 in coal geochemistry seven figures were calculated for each trace element average content in hard coals and their ashes average content in brown coals and their ashes average content in all coals and their ashes and coal affinity index or coalphile index average content in all ashes clarke values of sedimentary rocks the black shale and coal clarkes presented here provide an important scientific base for many geochemical comparisons and issues

plate motions and stresses from global dynamic models delineating the driving forces behind plate motions is important for understanding the processes that have shaped earth throughout its history however the accurate prediction of plate motions boundary zone deformation rigidity and stresses remains a difficult frontier in numerical modeling we present a global dynamic model that produces a good fit to such parameters by accounting for lateral viscosity variations in the top 200 kilometers of earth together with forces associated with topography and lithosphere structure as well as coupling with mantle flow the relative importance of shallow structure versus deeper mantle flow varies over earth s surface our model reveals where mantle flow contributes toward driving or resisting plate motions furthermore subducted slabs need not act as strong stress guides to satisfy global observations of plate motions and stress

the distribution of rare earth elements in groundwaters assessing the role of source rock composition redox changes and colloidal particles rare earth element ree dissolved organic carbon doc and trace element al mn fe sr ba u and th concentrations were measured in fourteen well water samples 0 22 m and one spring located along two transects set up in a catchment from western europe kervidy coet dan catchment france previous hydrological and hydrochemical no3 so42 investigations demonstrated that three chemically and spatially distinct groundwater types are present in this catchment which is fully confirmed by the ree and doc results these include i a shallow organic rich groundwater 4 4 doc 34 6 mg l from the wetland areas close to the river network this first groundwater type characterized by the development of temporary reducing conditions records high and variable ree contents 2 ree 16 ppb and displays slight or no negative ce anomaly ce ce 0 8 1 05 ii a shallow organic poor doc 3 mg l no3 rich groundwater type 86 8 no3 155 mg l located in the weathered schists below the hillslope domains this second type corresponds to recently recharged oxidized water and displays also high and variable ree concentrations 2 ppb ree 15 ppb but distinguish from the former by the occurrence of very strong negative ce anomalies ce ce 0 05 0 10 finally iii a deep organic poor doc 1 mg l nitrate poor no3 close to 0 2 mg l detection limit groundwater this third type corresponds to reduced water flowing into the deep fresh schists and yields low to very low ree contents ree 0 15 ppb as well as slight negative ce anomaly ce ce 0 8 to 0 9 temporal ree concentration variations were assessed using samples regularly collected over a six month period results show that the spatially distributed ce anomaly and ree pattern signatures are preserved throughout the studied period by contrast ree concentrations are quite variable through time especially in the wetland waters where the ree concentrations are seen to vary in phase with both redox changes and doc fe u and th content variations three ree rich water samples one doc rich and two doc poor were also filtered through membranes of decreasing pore size 100 000 d 30 000 d 5 000 d the results show that between about 40 to 65 of the ree present in the shallow doc poor groundwater samples are controlled by the colloidal fraction which is likely to consist in these inorganic waters of a mixture of mineral phases in the wetland groundwaters the fraction of ree controlled by microparticles is higher than 65 which confirms the predominant role of organic colloids as major ree carriers in wetland waters using the above data set in conjunction with analyses of soil samples we show that the deep ce anomalies found in the upper non organic part of the aquifer are probably not source rock inherited features most likely these anomalies arise from the oxidative precipitation of ce the very low ree content displayed by waters flooding the deep fresh schists is interpreted as due to the combined effects of i ph variation ii secondary sulfate mineral precipitation and iii the trapping of colloids borne ree by the aquifer rock pores data from wetland groundwaters show that the ree fe u and th budgets of these waters are mainly controlled by seasonal changes in redox conditions and organic matter content however unlike organic poor waters it appears difficult to relate the ce behaviour in these organic rich waters solely to redox conditions it is likely that the complexation of ce by organic colloids in the organic rich waters may mask redox changes by inhibiting the development of negative ce anomalies

regional stress field of the indian plate we have calculated the regional stress field in the indian plate implementing dependence of slab pull and ridge push on the age of the oceanic lithosphere in the finite element procedure the high level of the calculated stress field order of a few kbar and the dominance of compression in the plate are consequences of the unique dynamic situation of the present day indian plate the calculated stress field explains the concentration of intraplate deformation in the region of the ninetyeast ridge and yields insight into the variations in stress directions in the australian continent

the development of middle rare earth element enrichments in freshwaters weathering of phosphate minerals abstract many phosphatic minerals of biogenic authigenic and diagenetic origin are distinguished by rare earth element ree compositions which have a well developed middle rare earth element mree enrichment defined by a gradual increase in the shale normalized ratios of ree toward the middle of the ree series la to lu also the ree composition of dissolved matter in the waters of the amazon fly and sepik rivers as well as other river lake and ground waters have well developed mree enrichments the development of mree enrichments was studied through a series of leaching experiments using river bank sediments from the amazon fly sepik and mississippi rivers a well characterized phosphate mineral rich shale with a pronounced mree enrichment in its bulk composition was also leached in order to better assess the relationship between the weathering of phosphate minerals and the formation of mree enriched solutions the two leaching solutions per sediment consisted of filtered lake water at ph 5 and the same water adjusted to ph 2 leaching experiments with the four river sediments result in extensive fractionation whereby the ree compositions of the solutions develop mree enrichments from starting sediments that show no mree enrichments the ph 2 leachates have much higher concentrations of the ree and more fully developed mree enrichments than do the ph 5 leachates the mree enrichments at ph 2 usually form within an hour of starting the experiments the phosphatic shale results show that there is preferential release of large amounts of mree at ph 5 as well as at ph 2 demonstrating the weather ability of the phosphatic minerals at phs of natural freshwaters the sepik river ph 5 experiment also shows significant mree enrichment under near neutral conditions the development and retention of the mree enrichments in the leaching solutions is accompanied by an increase in dissolved phosphate concentrations although the magnitudes of the mree enrichment do not directly correlate with the percent of phosphate released the experimental data suggest that the preferential dissolution of phosphatic minerals during weathering can result in extensive ree fractionation between bulk river sediment and water leading to freshwaters with mree enrichments

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

deepwater fold and thrust belt classification tectonics structure and hydrocarbon prospectivity a review abstract deepwater fold and thrust belts dwftbs are classified into near field stress driven type 1 systems confined to the sedimentary section and type 2 systems deformed by either far field stresses alone or mixed near and far field stresses dwftbs can occur at all stages of the wilson cycle up to early stage continent continent collision type 1 systems have either weak shale or salt detachments they occur predominantly on passive margins but can also be found in convergent related areas such as the mediterranean and n borneo examples include the niger and nile deltas the west coast of africa and the gulf of mexico type 2 systems are subdivided on a tectonic setting basis into continent convergence zones and active margin dwftbs continent convergence zones cover dwftbs developed during continent arc or continent continent collision and those in a deepwater intracontinental setting e g w sulawesi makassar straits active margins include accretionary prisms and transform margins the greatest variability in dwftb structural style occurs between salt and shale detachments and not between tectonic settings changes in fold amplitude and wavelength appear to be more related to thickness of the sedimentary section than to dwftb type in comparison with shale salt detachment dwftbs display a lower critical wedge taper more detachment folds long and episodic duration of deformation and more variation in vergence structures unique to salt include canopies and nappes accretionary prisms also standout from other dwftbs due to their relatively long continuous duration rapid offshore propagation of the thrust front and large amount of shortening in terms of petroleum systems many similar issues affect all dwftbs these include the oceanward decrease in heat flow offshore increase in age of mature source rock and causes of trap failure e g leaky oblique and frontal thrust faults breach of top seal by fluid pipes one major difference between type 1 and type 2 systems is reservoir rock high quality continent derived quartz rich sandstones are generally prevalent in type 1 systems more diagenetically reactive minerals derived from igneous and ophiolitic sources are commonly present in type 2 systems or many are simply poor in well developed turbidite sandstone units however some type 2 systems particularly those adjacent to active orogenic belts are partially sourced by high quality continent derived sandstones e g nw borneo s caspian sea columbus basin in some cases very high rates of deposition in accretionary prisms adjacent to orogenic belts coupled with uplift due to collision results in accretionary prism related fold belts that pass laterally from sub aerial to deepwater conditions e g s caspian sea indo burma ranges the six major hydrocarbon producing regions of dwftbs worldwide gulf of mexico niger delta nw borneo brazil west africa s caspian sea stand out as differing from most other dwftbs in certain fundamental ways particularly the very large volume of sediment deposited in the basins and or the great thickness and extent of salt or overpressured shale sdetachments

mountain building and mantle dynamics 1 mountain building at convergent margins requires tectonic forces that can overcome frictional resistance along large scale thrust faults and support the gravitational potential energy stored within the thickened crust of the orogen a general dynamic model for this process is still lacking here we propose that mountain belts can be classified between two end members first those of slab pull type where subduction is mainly confined to the upper mantle and rollback trench motion lead to moderately thick crustal stacks such as in the mediterranean second those of slab suction type where whole mantle convection cells conveyor belts lead to the more extreme expressions of orogeny such as the largely thickened crust and high plateaus of present day tibet and the altiplano for the slab suction type deep mantle convection produces the unique conditions to drag plates toward each other irrespective of their nature and other boundary conditions we support this hypothesis by analyzing the orogenic volcanic and convective history associated with the tertiary formation of the andes after 40 ma and himalayas after collision at 55 ma based on mantle circulation modeling and tectonic reconstructions we surmise that the forces necessary to sustain slab suction mountain building in those orogens derive after transient slab ponding from the mantle drag induced upon slab penetration into the lower mantle and from an associated surge of mantle upwelling beneath africa this process started at 65 55 ma for tibet himalaya when the tethyan slab penetrated into the lower mantle and 10 myr later in the andes when the nazca slab did this surge of mantle convection drags plates against each other generating the necessary compressional forces to create and sustain these two orogenic belts if our model is correct the available geological records of orogeny can be used to decipher time dependent mantle convection with implications for the supercontinental cycle

topographic constraints on deviatoric stress field in the indo eurasian collision region seismo tectonic implications the deviatoric stress field are computed from the inversion of gravitational potential energy gpe for the indo eurasian plate collision region including the himalaya and the tibet plateau the resulting stress pattern in combination with stress and strain rates obtained by inverting respectively the focal mechanism solution of large earthquakes and gps derived plate motions are used to study the nature of the present day deformations a narrow belt bordering the himalayan collision zone from the south is characterized by strong compressive stresses the variations in stress pattern along this belt coincide with arc normal ridges extending into the himalaya and are able to explain arc parallel segmentation of seismicity gravitational collapse seems to play an important role in the southeastern tibet plateau depth sensitivity of the seismic derived stresses and gps derived surface strain rates coupled with evidence of arcuate shaped high electrical conductivity favour strong ductile flow around the eastern himalaya syntaxis ehs at mid crustal depth the deflection of crustal flow indicted by the viscous resistance offered by the rigid sichuan basin adds to the traction stresses to cause clockwise rotation of the block around ehs

dynamic topography and lithospheric stresses since 400 ma we present a global model of dynamic topography and lithospheric stresses for the last 400 ma our starting point is a simple geodynamic model combining both contributions of subducted lithosphere and long wavelength upwellings in a reference frame linked to the fixed african plate a dominant feature of plate tectonics is the quasi permanence of a girdle of subductions around the pacific ocean or its ancestor which creates large wavelength positive topography anomaly within the ring they form the superimposition of the resultant extension with the one induced by the dome leads to a permanent extensional regime over africa and the future indian ocean which creates faults with azimuth directions depending on the direction of the most active part of the ring of subductions we thus obtain fractures with nw se azimuth during the period 275 165 ma parallel to the strike of the subduction zone of the west south american active margin which appears to be very active during this period between 155 95 ma subduction became more active along the eastern australian coast involving a change in the direction of the faults toward an e w direction in agreement with the observed fault systems between africa and india antartica and australia during the mesozoic and the cenozoic we correlate the permanent extensional regime over africa and indian ocean with the observed rift systems finally we emphasize the role of three primary hotspots as local additional contributors to the stress field imposed by our proposed subduction doming system which help in the opening of indian and south atlantic oceans

role of large scale tectonic forces in intraplate earthquakes of central and eastern north america central and eastern united states ceus have experienced large intraplate earthquakes yet at present there is no comprehensive model to explain stresses strain and seismicity in this intraplate setting models to explain the intraplate stresses in ceus include glacio isostatic adjustment ridge push effects local stresses along preexisting fracture zones and large scale convection in this paper we present a self consistent model of the dynamics of ceus that explains the stress field responsible for these intraplate earthquakes the earthquakes represent slow ongoing deformation associated with forces arising from a combination of lithosphere topography and structure together with the effects of density driven mantle flow using gps data we calculate strain rates that are likely to arise from tectonic effects and conclude that intraplate strain rates associated with tectonic effects are unlikely to exceed 1 x 10 9 year 1 we test several models of lateral viscosity variations by comparing model stress orientation output with earthquake moment tensors shmax directions from stress inversion and p axes of earthquakes a model that satisfies stress and earthquake constraints and also strain rate magnitude constraints requires high viscosity 1025 pa s craton and old oceanic lithosphere of the western atlantic block and weaker 5 x 1024 pa s accreted appalachian terrane other strength contrasts within the lithosphere are likely present incorporation of these into future models using constraints from seismology along with refined geodetic measurements and improved estimates of crust and upper mantle densities is needed to further refine long term dynamic models and better evaluate the hazards associated with this very slow ongoing permanent deformation within the eastern and central united states