inverse modelling of elastic thickness by convolution method the eastern alps as a case example an unconventional scheme is used to estimate the flexural rigidity or equivalently the elastic thickness of the lithosphere given the topography and gravity data the flexural rigidity is the parameter that governs the flexural response of the lithosphere in the frame of the thin plate flexure model the scheme is an alternative to the widely used calculation of admittance of topography sea floor or continental topography and gravity bearing some advantages which are explained in the paper the scheme involves the inversion of the gravity data in order to formulate a model of the crust mantle interface cmi undulations in a second step the flexure parameter is then evaluated from the relation between topography and cmi variations instead of calculating the admittance function using a spectral analysis a set of point load response functions are used in order to retrieve the optimal flexure parameter this has two main advantages instabilities of the numerical admittance evaluation at wavenumbers with low spectral energy in the topography are overcome and the analysis can be made over an area which is not necessarily rectangular as required for the spectral analysis the proposed method allows a higher space resolution of elastic thickness than any spectral method for validation the numerical strategy is applied to the situation of a realistic synthetic model where all inputs and outputs are known a priori finally the spatial variations of the elastic thickness are studied in an area across the eastern alps 4 2002 elsevier science b v all rights reserved

late cenozoic relief evolution under evolving climate a review abstract the present review paper is an attempt to summarize quantitative evidence of late cenozoic changes in topographic relief different meanings of the word relief as it is commonly used and detail the metrics used to quantify it we then specify methodological tools used to quantify relief change primarily low temperature thermochronometry and terrestrial cosmogenic nuclides and analyze published evidence for different regions our review first shows that relief changes and rates of changes are more important at mid than high or low latitudes and appear to be insensitive to mean precipitation rates it also show that relief change is positive relief increases in most of the reported cases 80 we subsequently define two functional relationships between relief and erosion depending on the chosen definition of relief and propose a conceptual model of landscape memory we conclude following others that erosion rates depend non linearly on relief evolution itself being a function of the spatial distribution and rates of erosion the relief increases documented in this review may be to erosion rate increases during the same timescales lastly we discuss the importance of glacial and periglacial processes on late cenozoic relief and erosion rate changes and stress the importance of frost shattering and glacial erosion at mid and high latitudes

gravity anomalies flexure and the elastic thickness structure of the india eurasia collisional system wehaveusedbouguergravityanomalyandtopographydatatodeterminetheequivalentelasticthicknessofthelithosphere te in the region of the india eurasia collisional system comparison of observed and modelled gravity anomalies along 1dimensional profiles suggest there are significant variations in te along strike of the himalaya foreland estimates decrease from a high of 70 km in the central region to 30 50 km in the east and west we have verified these inferences of spatial variations using a 2 dimensional non spectral interative flexure and gravity anomaly modelling technique the himalaya foreland forms a high te 40bteb100 km rigid block with a well defined edge as shown by the localisation of faulting and deformation along its northern margin other highteblocks occur to the north beneath the qaidam and sichuan basins the tibetan plateau forms a low te 0bteb20 km weak region that extends from the central part of the plateau into south western china tectonic styles in the india eurasia collisional system therefore involve both drigidt and dnon rigidt blocks where high te rigid blocks are present the stylesdominatedbyunderthrustingofthemorerigidblock wherethecollisionalzoneisnotconstrainedbyrigidblocks however the style appears to be dominated by lower crustal flow and a more continuous style of deformation d 2005 elsevier b v all rights reserved

late cenozoic uplift of mountain ranges and global climate change chicken or egg the high altitudes of most mountain ranges have commonly been ascribed to late cenozoic uplift without reference to when crustal thickening and other tectonic processes occurred deep incision and recent denudation of these mountain ranges abundant late cenozoic coarse sediment near them and palaeobotanical evidence for warmer climates where high mountain climates today are relatively cold have traditionally been interpreted as evidence for recent uplift an alternative cause of these phenomena is late cenozoic global climate change towards lower temperatures increased alpine glaciation a stormier climate and perturbations to humidity vegetative cover and precipitation

response of glacial landscapes to spatial variations in rock uplift rate 1 the response of glaciated landscapes to rapid rock uplift driven by tectonic convergence is an important often neglected aspect of proposed interactions between plate tectonic processes and climate change rivers typically respond to more rapid rock uplift in part through increasing channel gradients in contrast the glacial buzzsaw hypothesis suggests that glaciers can erode as quickly as the fastest rock uplift rates 6 10 mm yr without any increase in mean elevations however it has not been established how this is achieved we examined moving window maps swath and longitudinal profiles hillslope relief and hypsometry for glacierized and formerly glacierized basins in areas of spatially variable rock uplift rate in the southern alps new zealand and around nanga parbat pakistan to determine whether glaciers have a specific response to rapid rock uplift the response of these glaciated landscapes to rapid rock uplift 6 10 mm yr comprises 1 modest steepening of the longitudinal profiles in smaller glaciated basins 2 maintenance of shallow downvalley slopes in larger glaciated basins 30 km2 southern alps 100 km2 nanga parbat 3 development of tall headwalls and 4 steepening of the basin as a whole dominated by hillslope lengthening around nanga parbat headwalls several kilometers high constitute 50 of the basin relief at rapid rock uplift rates although glaciers can incise the valley floor swiftly they cannot prevent headwalls from reaching exceptional heights the associated increase in mean distance between cirque heads i e a decrease in drainage density causes regional mean elevation to rise with increasing rock uplift rate however this is much less than the changes in elevation expected in unglaciated ranges

elastic thickness of the himalayan tibetan orogen estimated from the fan wavelet coherence method and its implications for lithospheric structure abstract this paper is concerned with the spatial variation of the elastic thickness t e in the himalayan tibetan orogen and its implications for the understanding of lithospheric structure and deformation new t e maps of the himalayan tibetan orogen are generated from the new combined satellite terrestrial gravity eigen6c3stat and topography etopo1 models using the fan wavelet coherence technique the high t e values 60 km are observed in the indian shield and the tarim basin while the low t e values 40 km are prevailing over most of the tibetan plateau we also find that the t e distributions estimated using the high and low central wavenumber i e k 0 wavelets are different in southern tibet by combining constraints from the current seismic and thermo rheological modeling this difference may reflect that the strength of the lithosphere in southern tibet mainly resides in the lithospheric mantle within most parts of central and northern tibet the t e values are relatively low 30 km indicating that the entire lithosphere is weak our analysis finds that the t e variations are probably associated with changes in lithosphere structure we interpret the abrupt changes in t e between southern and northern tibet to indicate the location of the underthrusting strong indian lithosphere beneath tibet our results suggest that the northern limit of the underthrusting indian plate reaches as far north as the hindu kush and the southwestern margin of the tarim basin near 70 80 e and extends along the bangong nujiang suture in the central 80 87 e eastward between 87 e 93 e it may move to the indus tsangpo suture indicating a delamination of indian mantle lithosphere there further to the east it may underthrust northward beneath the eastern qiangtang block

climatic limits to headwall retreat in the khumbu himalaya eastern nepal ice free bedrock headwalls are widespread landforms of many glacial landscapes but their formation and evolution are not well understood here i present observations from the khumbu himalaya eastern nepal of a distinct elevation zone that aligns the base of many steep headwalls with the highest predicted frost cracking intensity fci below this zone median ice free hillslope angles are 40 and similar to those of other areas in the himalaya where threshold hillslopes that are close to the critical angle of stability have been inferred at higher elevations ice free hillslopes of different rock types have median slope angles of 50 55 suggesting threshold hillslopes with higher rock mass strength possibly related to the presence of deep reaching permafrost high altitude meteorological data combined with fci models support frost cracking as a mechanism for headwall retreat by undercutting of threshold headwalls while glacial transport inhibits the accumulation of scree deposits at their base this mechanism could account for continued headwall retreat as long as climatic conditions enable frost cracking near the base of headwalls that are high enough to sustain glaciers at their base even if subglacial erosion is minor

orogeny and orography the effects of erosion on the structure of mountain belts a numerical model of the coupled processes of tectonic deformation and surface erosion in convergent orogens is developed to investigate the nature of the interaction between these processes crustal deformation is calculated by a two dimensional finite element model of deformation in response to subduction and accretion of continental crust erosion operates on the uplifted surface of this model through fluvial incision which is taken to be proportional to stream power the relative importance of the tectonic and erosion processes is given by a dimensionless erosion number relating convergence velocity rock erodibility and precipitation rate this number determines the time required for a system to reach steady state and the final topographic shape and size of a mountain belt fundamental characteristics of the model orogens include asymmetric topography with shallower slopes facing the subducting plate and an asymmetric pattern of exhumation with the deepest levels of exhumation opposite to subduction these characteristics are modified when the regional climate exhibits a dominant wind direction and orographically enhanced precipitation on one side of the mountain belt the two possible cases are dominant wind in the direction of motion of the subducting plate and dominant wind direction in the opposite direction of the subducting plate velocity models of the former case predict a broad zone of exhumation with maximum exhumation in the orogen interior models of the latter case predict a focused zone of exhumation at the margin of the orogen and at high erosion number a reversal in the topographic asymmetry natural examples of these two cases are presented the southern alps of new zealand exhibits the climate and exhumation asymmetry characteristic of wind in the direction opposite to motion of the subducting plate the asymmetry of topography suggests that erosion is not efficient enough to have reversed the topographic asymmetry the contrasting example of dominant wind in the direction of subduction motion is provided by the olympic mountains of washington state in this case exhumation of deep levels of the cascadia accretionary wedge shows a broad domal pattern consistent with the observed orographic precipitation

glaciation as a destructive and constructive control on mountain building glacial erosion is thought to have an important role in controlling mountain height a common perception is that glaciers are powerful erosive agents inhibiting the ability of active mountains to rise significantly above the elevation of permanent glaciation through a process known as the glacial buzzsaw but now a study of erosion patterns and climate data from the late cenozoic in the glaciated patagonian andes suggests that glaciation can also have the reverse effect in effect making mountains higher at these polar latitudes glaciation acts as a protective layer preserving the uplifting mountains from erosion and allowing them to reach heights well above those predicted had a glacial buzzsaw been active it has been suggested that glacial erosion has an important role in controlling mountain height here spatial and temporal patterns of erosion in the glaciated patagonian andes have been assessed with the help of a low temperature thermochronologic data set the results show that between 38 s and 49 s accelerated erosion at the onset of widespread glaciation limits mountain height but at higher latitudes glaciation protects the landscape from erosion and leads to growth in mountain height and width theoretical analysis predicts that enhanced erosion related to late cenozoic global cooling can act as a first order influence on the internal dynamics of mountain building leading to a reduction in orogen width and height1 2 3 the strongest response is predicted in orogens dominated by highly efficient alpine glacial erosion producing a characteristic pattern of enhanced erosion on the windward flank of the orogen and maximum elevation controlled by glacier equilibrium line altitude3 4 where long term glacier mass gain equals mass loss however acquiring definitive field evidence of an active tectonic response to global climate cooling has been elusive5 here we present an extensive new low temperature thermochronologic data set from the patagonian andes a high latitude active orogen with a well documented late cenozoic tectonic climatic and glacial history data from 38 s to 49 s record a marked acceleration in erosion 7 to 5 myr ago coeval with the onset of major patagonian glaciation6 and retreat of deformation from the easternmost thrust front7 the highest rates and magnitudes of erosion are restricted to the glacial equilibrium line altitude on the windward western flank of the orogen as predicted in models of glaciated critical taper orogens where erosion rate is a function of ice sliding velocity3 8 in contrast towards higher latitudes 49 s to 56 s a transition to older bedrock cooling ages signifies much reduced late cenozoic erosion despite dominantly glacial conditions here since the latest miocene6 the increased height of the orogenic divide at these latitudes well above the equilibrium line altitude leads us to conclude that the southernmost patagonian andes represent the first recognized example of regional glacial protection of an active orogen from erosion leading to constructive growth in orogen height and width

glacial effects limiting mountain height the height of mountain ranges reflects the balance between tectonic rock uplift crustal strength and surface denudation tectonic deformation and surface denudation are interdependent however and feedback mechanisms in particular the potential link to climate are subjects of intense debate spatial variations in fluvial denudation rate caused by precipitation gradients are known to provide first order controls on mountain range width crustal deformation rates and rock uplift moreover limits to crustal strength are thought to constrain the maximum elevation of large continental plateaus such as those in tibet and the central andes there are indications that the general height of mountain ranges is also directly influenced by the extent of glaciation through an efficient denudation mechanism known as the glacial buzzsaw here we use a global analysis of topography and show that variations in maximum mountain height correlate closely with climate controlled gradients in snowline altitude for many high mountain ranges across orogenic ages and tectonic styles with the aid of a numerical model we further demonstrate how a combination of erosional destruction of topography above the snowline by glacier sliding and commensurate isostatic landscape uplift caused by erosional unloading can explain observations of maximum mountain height by driving elevations towards an altitude window just below the snowline the model thereby self consistently produces the hypsometric signature of the glacial buzzsaw and suggests that differences in the height of mountain ranges mainly reflect variations in local climate rather than tectonic forces

significant increase in relief of the european alps during mid pleistocene glaciations the effect of expanded glaciation on the relief of mountain ranges is debated chronometric and model data from the european alps suggest that relief in the rhone valley was enhanced as a result of the increased incision of the valley following the mid pleistocene climate transition

glacial erosion promotes high mountains on thin crust abstract every mountain range on earth is unique in its tectonic evolution but quaternary climate cooling resulted in alpine landscapes with globally similar landforms such as horn shaped peaks cirques and overdeepened valleys on a global scale the impact of glacial and periglacial processes on the geometry of mountain ranges and the relative efficiency of glacial and fluvial erosion are still discussed to address these issues we analyse a novel worldwide dataset of more than 16 000 mountain peaks we relate peak height and steepness to mean elevation and crustal thickness we show that the geometry of mountain ranges systematically varies with latitude and thus with climate for peaks of similar height the steepness increases towards high latitudes while mean elevation and thickness of the supporting crust decrease modelling flexural isostasy based on the topographic load of mountain ranges demonstrates that the crustal thickness required to support peaks of similar height dramatically declines with intensity of glacial erosion in concert with latitudinal trends in peak steepness mean elevation and crustal thickness this shows that quaternary climate cooling reduces the topographic load by transforming the geometry of mountain landscapes from fluvial to glacial conditions we conclude that the prevalence of glacial erosion in cold climate reduces the topographic load of mountain ranges and enables the growth of high mountain peaks even on moderately over thickened crust

geomorphic limits to climate induced increases in topographic relief recognition of the potential for strong dynamic coupling between atmospheric and tectonic processes has sparked intense cross disciplinary investigation and debate on the question of whether tectonics have driven long term climate change or vice versa it has been proposed that climate change might have driven the uplift of mountain summits through an isostatic response to valley incision because isostasy acts to compensate mean elevations the debate hinges on the question of whether climate change can significantly increase topographic relief or more precisely increase the volume of missing mass between summits and ridges here we show that in tectonically active mountain ranges geomorphic constraints allow only a relatively small increase in topographic relief in response to climate change thus although climate change may cause significant increases in denudation rates potentially establishing an important feedback between surficial and crustal processes neither fluvial nor glacial erosion is likely to induce significant isostatic peak uplift

the role of ocean atmosphere reorganizations in glacial cycles abstract a case is made that glacial to interglacial transitions involve major reorganizations of the ocean atmosphere system such reorganizations constitute jumps between stable modes of operation which cause changes in the greenhouse gas content and albedo of the atmosphere only in this way can the rapidity of glacial terminations the hemispheric synchroneity and symmetry of mountain glaciation and the large polar air temperature and dustiness variations be accounted for if these reorganizations are driven in some fashion by orbitally induced seasonal insolation changes then the connection between insolation and climate is most likely through impacts of fresh water transport on the ocean s salinity distribution

flexure of the lithosphere and the geodynamical evolution of non cylindrical rifted passive margins results from a numerical model incorporating variable elastic thickness surface processes and 3d thermal subsidence we present a new numerical model to calculate the surface deflection of a two dimensional yet variable thickness thin elastic plate the model is based on a multi grid finite difference solution of the fourth order differential equation that incorporates the terms arising from the non uniform thickness assumption the model has been developed to calculate the flexural response of the continental lithosphere subjected to an arbitrary instantaneous stretching the flexural model is coupled to a a finite element three dimensional thermal model incorporating the conduction advection and production terms that allows the computation of the thermal subsidence resulting from the stretching induced perturbation of the isotherms assuming that the effective elastic thickness is controlled by the depth to a given isotherm and b a finite difference surface process model that assumes that transport is linearly proportional to slope leading to a second order diffusion type partial differential equation the model also incorporates the effect of sediment compaction we present a series of simple benchmarks that demonstrate the accuracy of the model we also present results of simple 2d and 3d stretching experiments highlighting the importance of 3d flexural effects and the assumed variable elastic thickness on the development of a passive margin and its thermal evolution finally we perform a numerical experiment based on a stretching geometry derived from the present day geometry of the western africatransform margin to predict sediment accumulation patterns and a stratigraphic architecture which we can compare to observations

quaternary erosion induced isostatic rebound in the western alps the high elevation and deep incision of the alps have traditionally been used as an argument for recent tectonic activity that has elevated the belt and increased erosion rates normal faulting and horizontal extension however dominate current tectonic activity and isostatic compensation of thinning crust should lead not to increased but to decreased mean elevations here we test the idea that enhanced quaternary erosion of the alps and isostatic compensation of the mass removed can account for the distribution of present day geodetically measured rates of vertical movement in the western alps using geophysical relief and kuhlemann s estimated average erosion rate for the alps we quantify the spatial distribution of erosion and the volume of eroded rock respectively from these we obtain a map of rock eroded within a given time span the calculated isostatic response of the alpine lithosphere to erosional unloading for a variety of values of the flexural rigidity of the alpine lithosphere reaches a maximum of 500 m since 1 ma in the inner swiss alps and vertical movement extends across the entire belt including peri alpine basins assuming a steady erosion rate since 1 ma this rebound accounts for half of the measured vertical motion of 1 1 mm yr in the southern valais thus a significant fraction 50 of the present day vertical movement results from the isostatic response to enhanced erosion during plio quaternary time

the salinity signature of the cross shelf exchanges in the southwestern atlantic ocean numerical simulations a high resolution model is used to characterize the dominant patterns of sea surface salinity sss variability generated by the freshwater discharges of the rio de la plata rdlp and the patos mirim lagoon in the southwestern atlantic region we identify three dominant modes of sss variability the first two which have been discussed in previous studies represent the seasonal and the interannual variations of the freshwater plumes over the continental shelf the third mode of sss variability which has not been discussed hitherto represents the salinity exchanges between the shelf and the deep ocean a diagnostic study using floats and passive tracers identifies the pathways taken by the freshwater plumes during the austral winter jja the plumes leave the shelf region north of the bmc during the austral summer djf the plumes are entrained more directly into the bmc a sensitivity study indicates that the high frequency component of the wind stress forcing controls the vertical structure of the plumes while the low frequency component of the wind stress forcing and the interannual variations of the rdlp discharge controls the horizontal structure of the plumes dynamical analysis reveals that the cross shelf flow has a dominant barotropic structure and therefore the sss anomalies detected by aquarius represent net mass exchanges between the shelf and the deep ocean the net cross shelf volume flux is 1 21 sv this outflow is largely compensated by an inflow from the patagonian shelf

high resolution surveys along the hot spot affected galapagos spreading center 1 distribution of hydrothermal activity the spatial density of hydrothermal activity along most mid ocean ridges is a robust linear function of spreading rate or magmatic budget but extreme crustal properties may alter this relationship in 2005 2006 we tested the effect of thickened crust on hydrothermal activity using high resolution mapping of plumes overlying the hot spot affected galapagos spreading center from 95 to 89 42 w 560 km of ridge crest plume mapping discovered only two active high temperature vent fields subsequently confirmed by camera tows though strong plume evidence indicated minor venting from at least six other locations total plume incidence ph the fraction of ridge crest overlain by significant plumes was 0 11 0 014 about half that expected for a non hot spot mid ocean ridge with a similar magmatic budget plume distributions on the galapagos spreading center were uncorrelated with abrupt variations in the depth of the along axis melt lens so these variations are apparently not controlled by hydrothermal cooling differences we also found no statistical difference for a significance level of 0 05 in plume incidence between where the seismically imaged melt lens is shallow 2 0 56 km ph 0 108 0 045 and where it is deep 3 4 0 7 km ph 0 121 0 015 the galapagos spreading center thus joins mid ocean ridges near the iceland reykjanes ridge st paul amsterdam south east indian ridge and ascension mid atlantic ridge hot spots as locations of anomalously scarce high temperature venting this scarcity implies that convective cooling along hot spot affected ridge sections occurs primarily by undetected diffuse flow or is permanently or episodically reduced compared to normal mid ocean ridges

cool water carbonates in a paleoequatorial shallow water environment the paradox of the auernig cyclic sediments upper pennsylvanian carnic alps austria italy and its implications distinct parts of limestones within the upper paleozoic auernig group of the carnic alps austria and italy are characteristic of cool water carbonates the carnic alps were between 5 n and 10 s paleolatitude during the late carboniferous a position confirmed by dasyclad algae and fossil plants the floral association occurrence of coal seams and absence of evaporites indicate a humid tropical environment the entire section lacks abiotic components of typical warm water limestones no ooids and no aggregates occur within the auernig group parts of the limestones show surprisingly a cool water association of high diversity bryozoans brachiopods crinoids red algae sponge spicules and entomozoan ostracodes the genesis of these limestones atypical for a paleoequatorial setting cannot be explained by changes in salinity bathymetry or terrigenous input the water temperature possibly linked with upwelling nutrient supply and paleoceanographic currents is the most convincing cause of this unusual association paleoceanographic changes are interpreted as linked to contemporaneous glaciation deglaciation cycles in gondwana this paper shows that cool water carbonates in shallow water environments are not necessarily nontropical as generally interpreted future studies should consider water temperature oceanic circulation and availability of nutrients supplementary to bathymetry salinity and latitude related climate in interpretation of carbonate components

pleistocene relief production in laramide mountain ranges western united states gently sloped summits and ridges collectively referred to as summit flats are abundant in many laramide ranges in the western united states the erosion rate of summit flats is 10 m m y on the basis of the concentrations of cosmogenic radionuclides because erosion rates in valleys between summit flats are an order of magnitude faster relief within these ranges is currently increasing by about 100 m m y if summit flat erosion is slower than rock uplift driven by the isostatic response to valley erosion then this relief production could result in increased summit elevations the mean depth of material eroded from a smooth surface fit to existing summit flats varies from 280 to 340 m in four laramide ranges based on geographic information system gis analyses of digital elevation models this erosion would result in a maximum of 250 300 m of rock uplift assuming airy isostasy however because the laramide ranges examined here are narrow relative to the flexural wavelength of the lithosphere erosionally driven rock uplift is limited to 50 100 m over the past several million years summit erosion would approximately offset this rock uplift therefore we conclude that summit elevations have remained essentially constant even though several hundred meters of relief has been produced on the basis of valley and summit erosion rates and the average depth of erosion we estimate that relief production in laramide ranges began at ca 3 ma we hypothesize that this relief production was climatically driven and was associated with the onset or enhancement of alpine glaciation in these ranges

effective elastic thickness variations along the andean margin and their relationship to subduction geometry 1 we present a new map of the spatial variations in effective elastic thickness te along the andes estimated using bouguer coherence the te variations reflect interactions between subducting slab and preexisting terrane structure in the forearc conductive cooling of the continent by the subducting slab exerts primary control on rigidity resulting in te that is highest 40 km where the oceanic lithosphere is oldest and coldest 20 s in the central andes te is relatively low 20 km along the volcanic chain and the altiplano and puna plateaus we interpret this weakening to reflect a high geothermal gradient maintained by advective magmatic processes a shallow and hot asthenosphere and a very weak lower crust throughout this region east of the plateaus high te delineates underthrusting of the brazilian shield finally north and south of the plateaus flat subduction areas are characterized by high te high shear wave velocity thick thermal lithosphere and low heat flow indicating that continental lithosphere there is thicker colder and stronger on the basis of these relationships we suggest that variations in slab dip along the margin relate to variations in structure of the continental lithosphere in particular we propose that upper plate structure influences the width and viscosity of the asthenospheric wedge which control the suction moment responsible for the subduction angle at depths 70 100 km for example when oceanic lithosphere subducts beneath thin continental lithosphere the low viscosity asthenosphere allows the slab to detach from the continent and sink into the mantle at normal angles however when oceanic lithosphere subducts close or beneath thick and strong continental lithosphere the asthenospheric wedge narrows and corner flow drags high viscosity mantle from the base of the thick 150 km cold continent into the wedge suction forces increase with both narrowing of the wedge and its increasing viscosity we estimate the asthenospheric viscosity underneath thick cold continents to be 1020 pa s sufficient to induce flat subduction later after prolonged hydration and weakening of the continent s base asthenospheric flow into the wedge may resume allowing the slab to sink again into the mantle at normal angles

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

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

messinian climate change and erosional destruction of the central european alps at the end of the miocene the european alps ceased outward expansion and tectonic uplift and exhumation shifted into the orogen interior this shift is consistent with a change from orogenic construction to orogenic destruction reflecting an increase in the ratio of erosional flux to accretionary flux the coincidence of this change with an increase in sediment yield from the alps suggests a climate driven increase in erosional flux the timing of deformation and sediment release from the southern alps indicates that the tectonic change occurred synchronous with the last phase of the messinian salinity crisis we attribute the increase in erosional flux to a climatic shift to wetter conditions throughout europe likely augmented by the base level fall that occurred during the mediterranean dessication this climate change is represented in the stratigraphic record by the lago mare deposits of the mediterranean salinity crisis

the null hypothesis globally steady rates of erosion weathering fluxes and shelf sediment accumulation during late cenozoic mountain uplift and glaciation at the largest time and space scales the pace of erosion and chemical weathering is determined by tectonic uplift rates deviations from equilibrium arise from the transient response of landscape denudation to climatic and tectonic perturbations we posit that the constraint of mass balance however makes it unlikely that such disequilibrium persists at the global scale over millions of years as has been proposed for late cenozoic erosion we synthesize weathering fluxes global sedimentation rates sediment yields and tectonic motions to show a remarkable constancy in the pace of earth surface evolution over the last 10 ma and support the null hypothesis that global rates of landscape change have remained constant over this time period despite global climate change and mountain building events this work undermines the hypothesis that increased weathering due to mountain building or climate change was the primary agent for a decrease in global temperatures

glaciations in response to climate variations preconditioned by evolving topography landscapes modified by glacial erosion show a distinct distribution of surface area with elevation hypsometry in particular the height of these regions is influenced by climatic gradients controlling the altitude where glacial and periglacial processes are the most active and as a result surface area is focused just below the snowline altitude yet the effect of this distinct glacial hypsometric signature on glacial extent and therefore on continued glacial erosion has not previously been examined here we show how this topographic configuration influences the climatic sensitivity of alpine glaciers and how the development of a glacial hypsometric distribution influences the intensity of glaciations on timescales of more than a few glacial cycles we find that the relationship between variations in climate and the resulting variation in areal extent of glaciation changes drastically with the degree of glacial modification in the landscape first in landscapes with novel glaciations a nearly linear relationship between climate and glacial area exists second in previously glaciated landscapes with extensive area at a similar elevation highly nonlinear and rapid glacial expansions occur with minimal climate forcing once the snowline reaches the hypsometric maximum our results also show that erosion associated with glaciations before the mid pleistocene transition at around 950 000 years ago probably preconditioned the landscape producing glacial landforms and hypsometric maxima such that ongoing cooling led to a significant change in glacial extent and erosion resulting in more extensive glaciations and valley deepening in the late pleistocene epoch we thus provide a mechanism that explains previous observations from exposure dating and low temperature thermochronology in the european alps and suggest that there is a strong topographic control on the most recent quaternary period glaciations