western scotia sea margins improved constraints on the opening of the drake passage 1 we present a revised tectonic interpretation from 28 ma to 3 2 ma of the western sector of the scotia sea incorporating new multichannel seismic reflection profiles and magnetic anomaly identifications for the continental margin off the tierra del fuego island and available complementary data for the conjugate margin of the northwestern flank of the south scotia ridge seismic profiles show a remarkable diversity of the pair of conjugate passive margins of the western scotia sea in both their morphology and structural framework the tierra del fuego continental margin can be related to a classic rifted passive margin while the southwestern margin of the scotia sea is characterized by steep slopes mostly generated by subvertical faults that abruptly separate the continental crust of the south scotia ridge from the oceanic crust of the western scotia sea this structural difference was caused by intense strike slip tectonism mostly concentrated along the modern south scotia ridge since the early development of the western scotia sea we find evidence for a previously unrecognized magnetic anomaly 10 28 ma at the foot of the tierra del fuego continental margin the same anomaly is present at the conjugate northern flank of the south scotia ridge the timing of events leading to the earliest development of the western scotia sea which determined the opening of the drake passage is important because this gateway opening had a profound effect on global circulation and climate the thickness and the distribution of the sedimentary cover overall in the abyssal plain off the two western scotia sea margins is different this is due to the different regimes of the bottom current flows which affected the western scotia sea both in the past and in the present time

the influence of climate on the tectonic evolution of mountain belts simple physical arguments analogue experiments and numerical experiments all suggest that the internal dynamics of actively deforming collisional mountain ranges are influenced by climate however obtaining definitive field evidence of a significant impact of climate on mountain building has proved challenging spatial correlations between intense precipitation or glaciation and zones of rapid rock uplift have indeed been documented in numerous mountain ranges and are consistent with model predictions more compelling evidence such as tectonic changes in response to rather than just coincident with climate change has however rarely been documented triggered by a climate driven increase in erosion rate friction dominated mountain ranges are expected to show a number of simultaneous responses a decrease in the width of the range a temporary increase in sediment yield a persistent increase in the rate of rock uplift and a reduction in the subsidence rate of surrounding basins the most convincing field evidence for such a coordinated response of a mountain range to climate change comes from the european alps and the st elias range of alaska field studies and experimental research during the past two decades have provided considerable evidence for a significant influence of climate on tectonics recent advances suggest that model predictions can guide future fieldwork aimed at substantiating this view

neogene stratigraphy and the sedimentary and oceanographic development of the nw european atlantic margin a regional correlation of neogene stratigraphy has been attempted along and across the nw european atlantic continental margin between mid norway and sw ireland two unconformity bounded successions are recognised these are referred to as the lower and upper neogene successions and have been dated as miocene early pliocene and early pliocene holocene respectively in age their development is interpreted to reflect plate wide tectonically driven changes in the sedimentary oceanographic and latterly climatic evolution of the ne atlantic region the lower neogene succession mainly preserves a record of deep water sedimentation that indicates an expansion of contourite sediment drifts above submarine unconformities within this succession on both sides of the eastern greenland scotland ridge from the mid miocene this is interpreted to record enhanced deep water exchange through the faroe conduit deepest part of the southern gateway and can be linked to compressive inversion of the wyville thomson ridge complex thus a pervasive interconnected arctic north atlantic deep water circulation system is a neogene phenomenon the upper neogene succession records a regional change at about 4 ma in the patterns of contourite sedimentation submarine erosion new depocentres coeval with the onset of rapid seaward progradation of the continental margin by up to 100 km this build out of the shelf and slope is inferred to record a marked increase in sediment supply in response to uplift and tilting of the continental margin associated changes in deep water circulation may be part of an atlantic wide reorganisation of ocean bottom currents glacial sediments form a major component of the prograding shelf margin shelf slope sediment wedges but stratigraphic data indicate that the onset of progradation pre dates significant high latitude glaciation by at least 1 ma and expansive northern hemisphere glaciation by at least 3 ma

glacially influenced basin plain sedimentation in the southern faeroe shetland channel northwest united kingdom continental margin abstract quaternary sediments at the southwest end of the faeroe shetland channel are preserved as a basin plain succession of variable fill geometry and lithology in high resolution seismic profiles the basin plain succession is characterised by laterally discontinuous and transparent mounded lensoid bodies interbedded with acoustically well layered sediments which display drape and onlapping reflection configurations the lensoid bodies comprise an up to 50 m thick amalgamated package of mass flow deposits consisting primarily of debris flow diamictons they represent resedimented glacigenic deposits derived from the west shetland shelf accumulation of these packages was episodic and related to specific rapid phases of downslope resedimentation most probably concomitant with ice marginal deposition on the west shetland slope the acoustically well layered sediments include glaciomarine hemipelagites and contourites these indicate phases of reduced sediment supply from the adjacent shelf and slope areas and probably represent the more pervasive background sedimentation in the basin although weak bottom current activity may have prevailed throughout the glacial episodes the onset of vigorous bottom current circulation occurred at the changeover from a glacial to an interglacial regime the debris flow packages form about 50 of the basin plain sediments in this part of the faeroe shetland channel thereby forming a significant component of the deep water succession

seismic stratigraphy and sedimentary processes at the norwegian sea margin northeast of the faeroe islands abstract sedimentary processes on the continental slope north of the faeroe islands during the cenozoic were studied in detail using high resolution multichannel reflection seismic data a wedge shaped succession of cenozoic sediments with a maximum thickness of approximately 2 km overlies the basaltic basement which forms the underlying structure of the slope the sedimentary succession represents four depositional sequences and a contourite deposition also some slump deposits are recognised the oldest sequence which is possibly of eocene late oligocene age was prone to repeated mass movements during the deposition of the sequence at the end of the oligocene the sediments on the slope stabilised and the depositional pattern was strongly influenced by sea level changes in the late pliocene a renewed instability of the slope occurred resulting in mass movements causing erosion at the middle of the slope and creating a major slide escarpment at the base of the slope subsequently the sedimentary processes change from mainly downslope progradational forms to along slope current induced contourite deposition this change most likely marks the formation of a norwegian sea deep water current pattern similar to the present variations of the current strength and sediment supply caused by glacial interglacial cycles probably results in an alternating sedimentation pattern of the contourite deposit another impact from the glaciation of the northern hemisphere is the presence of iceberg turbate at the upper parts of the northeastern faeroes slope

shear stresses on megathrusts implications for mountain building behind subduction zones 1 shear stresses on a subduction megathrust play an important role in determining the forces available for mountain building adjacent to a subduction zone in this study the temperatures and shear stresses on megathrusts in 11 subduction zones around the pacific rim hikurangi tonga izu ogasawara western nankai northeastern japan aleutians western alaska cascadia northern chile southern chile and se asia northern sumatra have been determined the main constraint is that vertical normal stresses beneath the highlands behind the subduction zone are nearly equal to horizontal normal stresses in the plane of a trench or arc normal section for a typical brittle and ductile megathrust rheology frictional shear stress gz for depth z and ductile shear stress a exp b rt at temperature t where a b are rheological parameters treated as constants rheological constants common to all the megathrusts crust mantle b are determined by simultaneously solving for the force balance in the overlying wedge and megathrust thermal structure using a simplex minimization algorithm taking account of the induced mantle corner flow at depth 65 15 km 2 and constant radiogenic heating 0 65 0 3 w m 3 2 throughout the crust the a constants are solved individually for each subduction zone assuming that the maximum depth of interplate slip earthquakes marks the brittle ductile transition the best fit solution shows two groupings of megathrusts with most subduction zones having a low mean shear stress in the range 7 15 mpa crust 0 032 0 006 mantle 0 019 0 004 and unable to support elevations 2 5 km for a typical frictional sliding coefficient 0 5 the low effective coefficients of friction suggest high pore fluid pressures at 95 lithostatic pressure tonga and northern chile require higher shear stresses with crust 0 095 0 024 mantle 0 026 0 007 suggesting slightly lower pore fluid pressures at 81 lithostatic ductile shear in the crust is poorly resolved but in the mantle appears to show a strong power law dependency with b 36 18 kj mol 1 amantle values are sensitive to the precise value of b but are in the range 1 20 kpa the power law exponent n for mantle flow is poorly constrained but is likely to be large n 4 the brittle ductile transition in the crust occurs at temperatures in the range 370 c 512 c usually close to the base of the crust and in the mantle at much lower temperatures 180 c 300 c possibly reflecting a marked change in pore fluid pressure or quasi ductile and subfrictional properties in subduction zones where the subducted slab is older than 50 ma a significant proportion of the integrated shear force on the megathrust is taken up where it cuts the mantle and temperatures are 300 c in much younger subduction zones the stress transmission is confined mainly to the crust the shear stresses particularly in the crust may be kept low by some sort of lubricant such as abundant water rich trench fill which lowers the frictional sliding coefficient or effective viscosity and or raises pore fluid pressure the unusual high stress subduction zone in northern chile lacks significant trench fill and may be poorly lubricated with a mean shear stress 37 mpa required to support elevations 4 km in the high andes however where the crust is thin in sediment starved and poorly lubricated subduction zones such as tonga the mean shear stress will still be low sediment may lubricate megathrusts accommodating underthrusting of continental crust such as in the himalayas or eastern central andes which have a low mean shear stress 15 mpa

a model for tectonic rotations about a vertical axis abstract the rotation of a rigid ellipsoidal inclusion within a highly viscous fluid orientated so that two of the principal axes remain horizontal is used as a model for the rotation of crustal inclusions in wide zones of continental deformation this model is also applicable to other geological problems involving the rotation of inclusions in a matrix the pattern of behaviour in such a model is shown to be complex in general the rotation rate of the inclusion is a function of all components of the velocity field of the deforming medium and the horizontal aspect ratio of the inclusion however for a given velocity field this aspect ratio must exceed a critical value before the inclusion can rotate continuously inclusions with lower aspect ratios will rotate for a certain range of orientations in an opposite direction to the sense of shear in the deforming zone the possibility of the inclusion changing shape during rotation adds to the complexity of behaviour

the evolution of deformation and topography of high elevated plateaus 1 model numerical analysis and general results a temperature dependent viscoplastic flow model of continental lithosphere is used to investigate the evolution of deformation and topography of high elevated plateaus such plateaus are products of both continent continent collision tibetan plateau and ocean continent collision the altiplano and develop in the overriding continental plate in this study we emphasize the mechanically simpler case of oceanic collision because it does not involve mass transfer between the two plates the lithosphere is deformed in response to tectonic and buoyancy forces the tectonic forces arise from subduction of an oceanic plate or underthrusting of continental lithosphere that horizontally indents and vertically shears the overriding lithosphere the buoyancy forces arise in response to horizontal density variations and tend to relax existing topography or thick crust the time evolution of the deformation and topography is investigated using a finite element technique that solves for the flow field in the overriding lithosphere the model produces dynamically supported near trench topography and inland mountain topography that is isostatically supported by a thick crust a finite region of localized deformation thick crust and high topography develops only if the model includes a horizontal thermal perturbation or an initially thick crust however only thermally perturbed lithosphere generates a plateau topography the shape and size of the calculated plateau depend on the wavelength of the thermal perturbation grashof number and density contrast between the crust and mantle the time evolution of the deformation shows a significant change in the deformation pattern as the high elevated plateau evolves during early stages compressional deformation of the crust and mantle are localized in the thermally perturbed weak zone at later stages as the crust thickens buoyancy forces of larger magnitude resist further thickening of the crust and the locus of compressional crustal deformation migrates inland this migration does not affect the location of the mantle deformation which remains in the thermally weak region but it is accompanied by a significant shear deformation in the weak lower crust the separation of the crustal locus from the mantle locus of deformation emphasizes the importance of vertically dependent deformation in the formation of high elevated plateaus this demonstrates the limitations of models that ignore changes of deformation with depth such as plane stress or thin sheet models

active deformation in the bolivian andes south america a method is described for determining the horizontal field of velocity and velocity gradients in the bolivian andes in the vicinity of the bolivian orocline using the following data 1 space geodetic measurements of crustal motions 2 the style distribution and rate of late miocene quaternary folding and faulting and 3 paleomagnetic measurements of rigid body rotations about a vertical axis these data were analyzed in a network of 26 triangles which spanned the bolivian andes by solving the velocity gradient compatibility equations between adjacent triangles subject to the input data constraints this yielded 120 140 linear equations to constrain 108 unknowns making the problem moderately overdetermined a series of experiments were carried out with different combinations of the input data to determine the best fit in the least squares sense field of quaternary horizontal velocities and velocity gradients the azimuths of velocity vectors in the high andes are subparallel to both the relative plate convergence vector and the symmetry axis of the bolivian orocline with magnitudes relative to stable south america in the range 7 17 mm yr 1 accommodating up to 30 of the relative plate convergence however the azimuths of velocities along the range front are nearly orthogonal to the range with a component of distributed range parallel dextral or sinistral shear within the eastern cordillera and altiplano the horizontal velocity field requires bending about a vertical axis of both limbs of the bolivian orocline the field of horizontal dilatation assuming homogeneous deformation of the entire crustal thickness requires vertical velocities of material points up to 2 5 mm yr in the sub andean zone decreasing to 0 1 mm yr farther east in the eastern cordillera and altiplano the direction of maximum gradients of buoyancy stress determined from the field of gradients of appropriate combinations of velocity gradients using a thin sheet model of viscous flow are broadly parallel to the direction of maximum topographic gradients in the eastern cordillera providing support for the idea that the bulk behaviour of the bolivian lithosphere is fluid like a comparison of these gradients with buoyancy stress gradients calculated from crustal thickness contrasts suggest that the bulk lithospheric viscosity is in the range 0 5 1 0 1022 pa s gradients of velocity gradients along the eastern margin of the bolivian andes can be interpreted in terms of marked gradients of viscosity with viscosity increasing toward the brazilan shield in the cratonic core of south america buoyancy stresses calculated from crustal thickness contrasts calibrated with the crustal thicknesses at the changeovers from thrust to strike slip or normal faulting suggest that the average lithosphericscale deviatoric stresses are in the range 7 15 mpa

the production of north atlantic deep water sources rates and pathways updating an earlier account by dickson et al 1990 this paper reviews the initial development phase of north atlantic deep water nadw production from the points where the dense inflows from nordic seas cross the greenland scotland ridge to the point off south greenland where the buildup of new production appears almost complete in particular three long term current meter arrays totaling 91 instruments and set at 160 km intervals south from the denmark strait sill are used to validate earlier short term arrays by others and in combination with these earlier arrays to describe the downstream evolution of mean speed depth and entrainment the variability of the overflow current in space and time and the likely contribution of the other three main constituents of nadw production at densities greater than 27 8 from the points of overflow 5 6 sv the transport within this range increases by entrainment and confluence with other contributory streams to around 13 3 sv at cape farewell while recirculating elements prevent us from determining the net southgoing transport a nadw transport of this order appears consistent with recent estimates of net abyssal flow passing south through the north and south atlantic

mountain height might be controlled by tectonic force rather than erosion what controls the height of mountain ranges an analysis of the forces acting on mountains near tectonic plate boundaries suggests that tectonic forces are the main controller rather than climate driven erosion tectonic force controls mountain height near subduction zones

stress modeling in the andes constraints on the south american intraplate stress magnitudes regions of high topography which exhibit both compressional and extensional deformation provide a natural laboratory to place constraints on horizontal intraplate stress magnitudes an elastic finite element analysis of the lithospheric stress field in the cordillera bianca region of peru has been used to evaluate the lithospheric stress state and constrain the south american intraplate stress magnitudes the orthogonal orientation of the andean high topography to the east west regional stress field in conjunction with the well documented change in deformation style from compression to extension across the cordillera provides a unique setting for the stress modeling a two dimensional finite element grid consisting of an assembly of isotropic elastic quadrilateral elements in a state of plane strain was used to represent the lithosphere an isostatically balanced crustal density model was used to calculate the stresses associated with the lateral density variations between the andean topography and the brazilian shield in some models horizontal stress was concentrated at midcrustal depths by including vertical variation in young s modulus the modeling results indicate bounds of 10 and 75 mpa for the magnitude of the average horizontal stress averaged over a 100 km thick lithosphere a preferred value of 25 mpa is obtained on the basis of fitting all of the data for the rheological models considered and predicting a transition from extension to compression near the 3000 m elevation contour such a far field average stress is consistent with a ridge push origin because the modeling performed in this study assumes that the topographic load is entirely compensated by the buoyancy of the deflected moho these estimates represent upper bounds the effect of incorporating thermal support for the topographic load of the cordillera bianca would be to further reduce our estimate of the intraplate stress magnitudes analysis of the distribution of calculated stress with depth indicates that previous assumptions about the vertical plane shear stress within the lithosphere being negligible are acceptable for the geometry of the andes

glacially influenced morphodynamic features examples from the north faroe margin abstract high resolution reflection seismic data subbottom profiler and side scan sonar information together with results from sediment core studies have been used to study various glacially influenced morphodynamic features on the northern faroese continental margin on the shelf and upper slope a thick buried turbate complex has been found which we estimate to have been formed between ca 470 000 and 120 000 years bp we interpret this turbate to be the result of episodic extensive iceberg grounding during extreme glaciation within the period mis 12 mis 6 elster saale complex late mis 6 is found to be the most likely age of the last episode of turbate formation as suggested by age depth correlation with dated sediment cores from the nearby area the origin of the iceberg turbate may be attributed to deglacial drift of deep draft icebergs from icestream sources in the arctic east greenland and or northern iceland at the base of slope and adjacent deep water area a complex of mud diapir features has been observed our data show that activation of these features are the result of density inversion processes caused by fine grained unconsolidated hemipelagic deposits being overlain by dense glacigenic north sea fan nsf deposits due to sudden and fast accumulation of the fan sediments a normal and regular compaction and dewatering of the underlying hemipelagic sediments could not occur instead sub seabed sediment mobilisation took place resulting in enhanced diapir formation a general intensification of the diapiric processes is likely related to the mis 6 saalian glacial period as nsf derived glacigenic debris flows reached the northern outlet of the faroe shetland channel the most recent diapir activity is concluded to have occurred during the last weichselian glaciation

the jan mayen microcontinent s cenozoic stratigraphic succession and structural evolution within the ne atlantic abstract cenozoic seismic stratigraphic units of the jan mayen microcontinent jmmc are presented in context with kinematic modelling of plate reorganisation correlation with conjugate margins and their chrono stratigraphic correlations our model of development of the microcontinent from continental breakup to present day is based on the interpretation of new and legacy geological and geophysical data from these data we have established eleven cenozoic seismic stratigraphic units jm 70 to jm 01 separated by ten locally varying unconformities and disconformities six of which are regional and reflect discrete tectonostratigraphic phases in the evolution of the jan mayen region these six main phases are 1 pre breakup paleocene 55 ma extension represented by seismic unit jm 70 which comprises terrigenous and marine sedimentary rocks and a thick plateau basalt volcanic succession 2 early eocene 55 52 ma syn breakup rift to drift represented by seismic unit jm 60 and comprises a mix of intrusive igneous rocks subaerial lavas and hyaloclastites and non marine to shallow marine sedimentary rocks 3 early to mid eocene 52 43 ma syn breakup rift to drift and rift transfer across the iceland plateau rift represented by seismic unit jm 50 that comprises volcanic rocks and shelf margin deltaic sediment succession 4 late eocene early oligocene 43 30 ma ridge transfer and tectonic re arrangement in proximity of the iceland hotspot represented in the rock record by shallow to deep marine deposits preserved as units jm 40 jm 35 and jm 30 5 in the late oligocene 30 22 ma a second breakup occurred along the western jmmc igneous margin together with the formation of the south western jan mayen igneous province the proto kolbeinsey ridge and the initiation of proto iceland all of which is represented in the rock record by seismic units jm 20 and jm 15 and 6 miocene to present day separation of the jmmc from east greenland since 22 ma which is represented by seismic units jm 10 jm 05 and jm 01 that reflect a general deepening of the microcontinent

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

tectonics climate and mountain topography 1 by regressing simple independent variables that describe climate and tectonic processes against measures of topography and relief of 69 mountain ranges worldwide we quantify the relative importance of these processes in shaping observed landscapes climate variables include latitude as a surrogate for mean annual temperature and insolation but most importantly for the likelihood of glaciation and mean annual precipitation to quantify tectonics we use shortening rates across each range as a measure of topography we use mean and maximum elevations and relief calculated over different length scales we show that the combination of climate negative correlation and tectonics positive correlation explain substantial fractions 25 but 50 of mean and maximum elevations of mountain ranges but that shortening rates account for smaller portions 25 of the variance in most measures of topography and relief i e with low correlations and large scatter relief is insensitive to mean annual precipitation but does depend on latitude especially for relief calculated over small 1 km length scales which we infer to reflect the importance of glacial erosion larger scale averaged over length scales of 10 km relief however correlates positively with tectonic shortening rate moreover the ratio between small scale and large scale relief as well as the relative relief the relief normalized by the mean elevation of the region varies most strongly with latitude strong positive correlation therefore the location of a mountain range on earth with its corresponding climatic conditions not just tectonic forcing appears to be a key factor in determining its shape and size in any case the combination of tectonics and climate as quantified here can account for approximately half of the variance in these measures of topography the failure of present day shortening rates to account for more than 25 of most measures of relief raises the question is active tectonics overrated in attempts to account for present day relief and exhumation rates of high terrain

cenozoic alongslope processes and sedimentation on the nw european atlantic margin based on studies of sediment accumulations deposited from and erode by alongslope flowing ocean currents on the european continental margin from porcupine ireland to lofoten norway the evolution of the cenozoic paleocirculation was reconstructed as part of the stratagem project there is evidence of ocean current controlled erosion and deposition in the rockall trough in the faeroe shetland channel and on the voring plateau since the late eocene although the circulation pattern remains ambiguous the late palaeogene flow in the rockall trough was almost probably driven by southerly derived tethyan outflow water the extent and strength of any northerly derived flow is uncertain from the early neogene early mid miocene there was a massive regional expansion of contourite drift development both in the north atlantic and in the norwegian greenland sea this was most probably related to the development of the faroe conduit the opening of the fram strait and the general subsidence of the greenland scotland ridge these may have combined to cause a considerable acceleration in the exchange and overflow of deep waters between the arctic and atlantic oceans an early late neogene late early pliocene regional erosional event has been ascribed to a vigorous pulse of bottom current activity most probably the result of a global reorganisation of ocean currents associated with the closure of the central american seaway during the late neogene contourites and sediment drifts developed in deep water basins between units of glacigenic sediments as well as infill of several paleo slide scars these sediments were derived from areas of bottom current erosion as well as from the development of plio pleistocene prograding sediment wedges incorporating the extensive sediment supply derived from shelf wide ice sheets presently a profound winnowing prevails along the shelf and upper slope due to the inflowing currents of atlantic water depocentres of sediments derived from the winnowing are located locally in lower slope embayments and in slide scars

quaternary sedimentation margin architecture and ocean circulation variability around the faroe islands north atlantic abstract the quaternary development offshore the faroe islands has been studied using high resolution seismic and core data from the r v dana 2000 cruise and previous cruises several glacial related features and deposits are observed all bearing witness to former extensive glaciations of the faroe area on the shelves overlaying a mid pleistocene glacial erosional surface glacial and glacimarine deposits form a sheet geometry interrupted by ridges of sediment that are likely to represent ice front deposits an iceberg turbate north of the faroe islands provides evidence of large scale drift of ultra deep draft 600 m icebergs in the nordic seas at pre weichselian glacial stage s marginal and transverse troughs found on the eastern and western shelf are suggested to have formed during the same glacial period s as the iceberg turbate iceberg plough marks and abundant ice rafted material of non faroese origin together with the relict moraine ridges encircling the faroe islands at around the 100 and 200 m water depth contours indicate that the outer shelf was probably ice free during the weichselian ice age on the slopes and basinal parts the formation of fine grained contourites was favoured during weichselian glacial stages when bottom currents were reduced sediment overloading during these glacial stages resulted in repeated slope instability causing mass failures of the contourite deposits

3d seismic analysis of the west shetland drift system implications for late neogene palaeoceanography of the ne atlantic abstract detailed seismic stratigraphic analysis of the west shetland drift located on the shetland margin of the faeroe shetland channel has been undertaken using commercial 3d seismic data emphasis was placed on the interpretation of a significant plastered contourite drift body the west shetland drift slope section with the aim of reconstructing the palaeoceanographic regime of the west shetland slope during the past 5 ma although limited in areal extent the west shetland drift slope section provides a key record of the depositional environment and bottom current activity on the west shetland slope during the late neogene the drift body was divided into three seismic stratigraphic units and depositional processes responsible for each unit were interpreted resulting in proposal of an evolutionary model in which a mixed downslope alongslope depositional system was succeeded by alongslope current derived contourite drift deposition during the early pliocene to mid pleistocene during this time sw flowing alongslope currents impinged upon the west shetland slope between the basin floor and a mid to upper slope position the final stage of deposition consisted of slope wedge progradation associated with mid to late pleistocene glaciation contourite deposition on the west shetland slope was punctuated by periods of glaciation activity during which alongslope current activity appears to have been disrupted suggesting a link between alongslope current activity and glaciation detailed mapping of key smaller scale features including a spectacular bottom current sediment wave field and iceberg ploughmarks both of which were identified for the first time during this study was instrumental in constraining the palaeocurrent regime and would not have been possible without the high spatial resolution of the 3d seismic data this study therefore highlights the efficacy of 3d seismic data as a tool for large scale spatial and temporal analysis of contourite drifts palaeoceanographic research

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

pleistocene glacial history of the nw european continental margin abstract in this paper new and previously published data on the pleistocene glacial impact on the nw european margin from ireland to svalbard between c 48 n 80 n are compiled the morphology of the glaciated part of the european margin strongly reflects repeated occurrence of fast moving ice streams creating numerous glacial troughs channels that are separated by shallow bank areas end moraines have been identified at several locations on the shelf suggesting shelf edge glaciation along the major part of the margin during the last glacial maximum deposition of stacked units of glacigenic debris flows on the continental slope form fans at a number of locations from 55 n and northwards whereas the margin to the south of this is characterised by the presence of submarine canyons glaciation curves based primarily on information from the glacial fed fan systems that depict the pleistocene trends in extent of glaciations along the margin have been compiled these curves suggest that extensive shelf glaciations started around svalbard at 1 6 1 3 ma while repeated periods of shelf edge glaciations on the uk margin started with mis 12 c 0 45 ma the available evidence for mis 2 suggest that shelf edge glaciation for the whole margin was reached between c 28 and 22 14 c ka bp and maximum positions after this were more limited in some regions north sea and lofoten the last glacial advance on the margin has been dated to 15 13 5 14 c ka bp and by c 13 14 c ka bp the shelf areas were completely deglaciated the younger dryas loch lomond advance reached the coastal areas in only a few regions

continental crust crustal underplating and low q upper mantle beneath an oceanic island arc a detailed structural model of the crust subducting slab and underlying upper mantle across the northern izu ogasawara bonin island arc system is derived from a marine seismic reflection and ocean bottom seismographic refraction survey and subsequent forward modeling combined with tomographic inversion the model indicates that the crust is thickest beneath the presently active rift zone and a granitic crust may have formed in the mid crust a highly attenuative mantle that is one with low quality q seems to be confined mainly beneath the presently active rift zone in contrast high p wave velocity persists in the lower crust between the forearc and eastern margin of the back arc basin suggesting a large scale magma input responsible for the arc formation

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

holocene marine diatoms from the faeroe islands and their paleoceanographic implications abstract temporal oceanographic changes based on mid and late holocene marine diatom floras from the faeroe islands region have been studied the four studied coring sites are located in the skalafjord and a more open ocean environment the mouth of the kaldbaksfjord at water depths ranging between 50 and 70 m comparison of the diatom records in the fjord sediments with those from the outer part of the fjord shows that the fjord provides a more optimum potential for paleoceanographic reconstructions the concentrations of marine taxa and relative abundance of freshwater diatom species in the marine environment were analyzed with the aim of relating them to environmental conditions estimated diatom concentrations were very low and ranged from a maximum of 14 4 10 6 valves per gram dry sediment in the inner part of the fjord to a minimum of 0 1 10 6 outside the fjord the freshwater diatom flora that occurred between 1200 and 700 cal yr bp in the inner part of the fjord suggests much higher precipitation during this time and increased freshwater discharge into the fjord presence of actinocyclus normanii which is an indicator of increasing trophy is related to the first human settlement on the faeroe islands maximum likelihood factor analysis mlfa was used to describe the most essential relationship among the diatom species and to employ these relationships for inferring holocene environmental changes in the faeroe islands the first two mlfa factors are related to oceanic influences in the region factor 1 is represented by a warmer water diatom assemblage and is suggested to correspond to inflow of the norwegian atlantic current to the skalafjord whereas factor 2 is an indicator of a colder water diatom assemblage that corresponds to inflow of arctic norwegian water mixing anwm during the 4900 3200 cal yr bp time interval

morphology and late quaternary sedimentation on the north faeroes slope and abyssal plain north atlantic whilst the interplay between tectonics glaciation and oceanography is reasonably well understood on some high latitude margins relatively little is known about the nature of quaternary processes affecting the continental margin north of the faeroe islands we therefore present side scan sonar gloria and tobi and 3 5 khz data in combination with a new regional bathymetry in order to characterise and analyse the margin s physiography and the sedimentary processes that have occurred in the area during the late quaternary seven acoustic facies are identified and interpreted in combination with published core records the margin is subject to differing sedimentation regimes over glacial interglacial cycles relating to the changing importance of contouritic hemipelagic glacimarine and mass movement processes mass movement is much more extensive than previously thought with a total sediment volume of 2000 km3 similar to that of the storegga slide 5500 km3 and may occur primarily at glacial terminations the downslope limit of instabilities is associated with a series of channels focusing the deposition of distal turbiditic sediments into the regional deep beyond together with glacigenic debris flows from the western margin of the north sea fan mass movement processes are identified to have affected 52 70 of the north faeroes margin area in contrast distal glacimarine sedimentation alternating with hemipelagic and contouritic development is found on the remaining 30 48 of the margin during glacials and hemipelagic and contouritic sedimentation are active across 90 of the margin in interglacial conditions despite a lack of any local direct glacial influence these observations on the relative importance of sedimentation processes are comparable with other glacially influenced passive margins

analysis of the south american intraplate stress field the first order south american intraplate stress field was modeled through a finite element analysis to evaluate the relative contribution of plate boundary forces and intraplate stress sources the finite element mesh consisted of 3100 nodes in a network of 5993 equal area triangular elements which provided a spatial resolution of about 1 at the equator an important aspect of our modeling is the inclusion of topographic forces due to the cooling oceanic lithosphere along the mid atlantic ridge e g ridge push the continental margins along the east coast of brazil and argentina and the elevated continental crust e g the andean cordillera predicted intraplate stresses for two representations of the western collisional boundary forces are evaluated pinned collisional boundaries and applied collisional boundary forces constraint for the modeling was provided by information about the orientation of the maximum horizontal compressive stress shmax provided by 217 stress indicators from the world stress map project as well as by shmax magnitude estimates and torque information from previous investigations our modeling results demonstrate that the first order features of the observed stress field can be explained with simple tectonic models which balance the torque acting on the plate either with a fixed western margin or drag forces applied along the base of the plate the predicted intraplate stress field is characterized by a nearly uniform e w shmax orientation throughout most regions of the plate with stress magnitudes generally less than 20 mpa averaged over a 100 km thick lithosphere significant perturbation of this regional stress field occurs in the western part of the plate in response to forces associated with the high topography of the andes although the magnitude of the collisional boundary forces acting along the western margin remains poorly constrained we estimate a plausible upper bound on the force per unit length acting along the peru chile trench to be about 2 5 1012 n m 1 while some of our models are consistent with a driving basal drag to balance the torques acting on the plate the magnitude of the drag torque is small compared to the contribution from other sources of stress such as the ridge push force

space geodetic estimation of the nazca south america euler vector abstract gps data from four sites in the nazca plate easter island galapagos robinson crusoe and san felix islands and from five sites in the stable core of the south american plate enabled us to estimate the euler vector of the nazca plate with respect to south america the observed velocities of easter island 6 6 cm yr at 102 3 galapagos 5 1 cm yr at 90 0 robinson crusoe 6 6 cm yr at 80 1 and san felix 6 0 cm yr at 82 1 are significantly slower than the global plate model nuvel 1a velocites for those four sites our estimated euler pole is located at 48 8 n 91 7 w with a rate of 0 59 m y the nuvel 1a and earlier space geodetic studies give rotation rates that are 20 faster

edge deep seismic reflection transect of the eastern aleutian arc trench layered lower crust reveals underplating and continental growth an edge deep crustal seismic reflection transect of the eastern aleutian arc trench traces oceanic crust and moho more than 200 km beneath the accretionary prism to depths of more than 30 km these horizons project beneath a prominent sequence of layered reflectors that extends from about 9 to 35 km beneath the mesozoic core of the prism earthquake hypocenters imply continuity of the downgoing lithosphere from the base of the layered reflectors to beneath and beyond the active augustine volcano rapid lateral growth of the prism in eocene oligocene time coincided with uplift of the mesozoic core of the prism during lateral growth maintenance of critical taper requires thickening either by internal deformation or underplating because exposed rocks show only modest postemplacement shortening thickening most likely occurred by underplating probably of the layered reflectors the overall geometry of the layered reflectors is reminiscent of nappe structures and their emplacement may represent crustal scale duplexing associated with underplating the edge reflection data and borehole results indicate that the self edge is marked by an active out of sequence thrust that separates the paleogene and neogene prisms this thrust apparently developed in response to the prism s need to maintain critical taper and demonstrates that contrasts inmore lithology can result from mechanisms other than terrane emplacement less

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

western nankai trough seismogenic zone results from a wide angle ocean bottom seismic survey the nankai trough southwestern japan is recognized as a vigorous seismogenic zone with well studied historic earthquakes this paper presents results of a wide angle ocean bottom seismographs obs study at the western nankai trough seismogenic zone the obs data used were acquired on a profile 250 km long across the presumed coseismic slip zone of the 1946 nankaido earthquake ms 8 2 the main purpose of the seismic study is to obtain an entire crustal cross section of the seismogenic zone for the 1946 earthquake the crustal model is characterized by a gentle sloping of subducting oceanic crust and thick overlying sedimentary wedge p wave seismic velocities of the subducting oceanic crust show normal oceanic crustal velocities vp 5 0 5 6 km s and 6 6 6 8 km s in oceanic layers 2 and 3 respectively the maximum thickness of the sedimentary wedge is 9 km at 70 km from the trough axis with vp 3 4 4 6 km s in the deeper part the subducting oceanic crust traced down to 25 km depth shows that the subduction angle becomes steeper landward 3 2 and 7 2 at 0 50 km and 50 100 km from the trough axis respectively the oceanic crust is smooth to the hypocenter zone down to 40 km depth beneath shikoku island our crustal model shows that the downdip limit of the coseismic slip area does not extend to the deep end of the oceanic crust island arc crust contact zone even though there is large uncertainty about the seaward limit of the coseismic slip zone the crustal model clearly indicates that the updip limit of the coseismic slip zone extends beneath the young accretionary prism

giant iceberg plow marks at more than 1 km water depth offshore west greenland abstract during a recent 2006 cruise of rv dana high resolution side scan sonar and sub bottom profiling was carried out on selected shelf and slope transects offshore disko bugt central west greenland available commercial seismic data from the margin indicate here irregular seabed morphology with erosional features locally extending down to c 1100 m water depth the newly acquired side scan sonar data reveal the presence of giant iceberg plow marks extending sub parallel to the slope between about 800 and 1085 m water depth the height difference between bottom of the scours and rim crest is up to 40 m the largest plow marks are about 750 m wide to date no observed modern icebergs including those from antarctica have drafts in excess of c 500 m taking into account maximum glacial sea level lowering of c 120 m the paleo iceberg keel depth was at least 950 m due to the presence of the relatively shallow 1000 m and dimensions of the plow marks are concluded to be exceptional and comparable to glacial scouring features reported from the arctic ocean

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

the stratigraphy and structure of the faroese continental margin this paper presents a summary of the stratigraphy and structure of the faroese region as the faroese area is mostly covered by volcanic material the nature of the pre volcanic geology remains largely unproven seismic refraction data provide some indications of the distribution of crystalline basement which probably comprises archaean rocks with the overlying cover composed predominantly of upper mesozoic cretaceous and cenozoic strata the cenozoic succession is dominated by the syn break up faroe islands basalt group which crops out on the faroe islands where it is up to 6 6 km thick and shelf areas post break up sediments are preserved in the adjacent deep water basins including the faroe shetland basin seismic interpretation of the post volcanic strata shows that almost every sub basin in the faroe shetland basin has been affected by structural inversion particularly during the miocene these effects are also observed on the faroe platform the munkagrunnur ridge and the fugloy ridge where interpretation of low gravity anomalies suggests a large scale fold pattern the structure of the iceland faroe ridge which borders the nw part of the faroe area remains ambiguous the generally thick crust together with the absence of well defined seawards dipping reflectors may indicate that much of it is underlain by continental material

cenozoic sediment accumulation on drifts in the northern north atlantic the northern north atlantic sediment drifts have a much greater areal extent than has previously been indicated the northern north atlantic extends from the east greenland to european continental shelves and from the charlie gibbs fracture zone to the greenland scotland ridge within this region are seven major sediment drifts containing some of the best clues for pre quaternary bottom water circulation in the north atlantic feni drift is the oldest in the region originating near the eocene oligocene boundary it was followed by accumulation of bjorn gardar hatton and snorri drifts from the late early to middle miocene eirik drift may have started to accumulate in the late miocene and gloria drift in the early pliocene through analysis of the cenozoic sediment mass age distribution and the change in area of seafloor for the study area through time it can be concluded that there is a deficit of oligocene to miocene sediment in the region this could be explained by sediment cycling the erosion of older sediment to produce young sediment the mass of pliocene to quaternary sediment is much larger than that of the older sediment and may have been derived primarily through the erosion of eocene and oligocene sediment by deepwater currents the sediment drift portion of the total regional sediment mass increased significantly three times during the cenozoic each of these drift growth phases lasted between 3 and 4 m y the first two growth phases from the late eocene to early oligocene and from the early to middle miocene were accompanied by northward shifts of depocenters to the newly forming sediment drifts the third and largest growth phase occurred between 7 and 3 ma and may have been preceded by the initiation of accumulation on eirik drift 8 7 ma this most recent growth phase was accompanied by high apparent accumulation rates over southern gardar drift as it expanded to the east erosion rates over reykjanes ridge may have been higher during the mid pliocene than in the quaternary there are two main sites where dense water could have formed and flowed south through the rockall trough to start the accumulation of feni drift if the atmosphere were cool enough dense water could have formed in the norwegian sea or on the faeroe shelf dense water may also have formed on the rockall plateau due to salinity increase through evaporation in an arid climate as an alternative to the hypothesis of arctic ocean water overflowing the iceland faeroe ridge in the early middle miocene it is suggested that dense water formed along shallow segments of the iceland faeroe ridge and then flowed into the south iceland basin to begin accumulation of bjorn gardar and snorri drifts the initiation of sediment drift formation in the south iceland basin may have been caused by a decreased rate of deep water production combined with a higher rate of detrital input due to a middle miocene uplift event along the iceland faeroe ridge a second uplift event along the greenland scotland ridge and a decreased production of northern component water in the early pliocene may be responsible for increased sediment accumulation in bjorn gardar and eirik drifts

depth of seismic coupling along subduction zones underthrusting at subduction zones can cause large earthquakes at shallow depths but it is always accommodated by aseismic deformation below a certain depth the maximum depth of the seismically coupled zone or seismogenic zone is a transition from unstable to stable sliding along the plate interface we have determined the depth of this stability transition for the circurn pacific subduction zones of honshu kuriles kamchatka aleutians alaska mexico and chile these subduction zones have experienced great interplate earthquakes and the aftershock regions are well located depth estimates of interplate events that are located at the downdip edge of the aftershock regions are used to determine the maximum depth of seismic coupling for an average p wave velocity of 6 7 km s 1 above the plate interface we find that for most subduction zones the stability transition occurs at 40 5 km depth there are however several exceptions at the hokkaido trench junction where the japan trench and the kurile trench intersect seismic coupling is deep and extends down to 52 55 km deep coupling was also found in the coquimbo region in central chile the mexico subduction zone has shallow coupling the transition occurs at 20 30 km depth previous studies of micro earthquakes in honshu hokkaido the aleutians and alaska show that earthquakes within the upper plate extend no deeper than the downdip edge of the coupled zone that we find given our measurements of seismic coupling depth we then explore the mechanism that may determine coupling depth the concept of critical temperature has been used to explain the depth of seismic coupling in other tectonic environments thus we first test whether a critical temperature can explain our results temperatures at the plate interface are dependent on many variables but two that are poorly determined are shear stress and radiogenic heat generation shear stress has been constrained by inversion of heat flow data assuming a crustal radiogenic heat production rate of 3 1 exp z 8 5 wm 3 and a constant coefficient of friction we find two critical temperatures of about 400 c and 550 c the lower critical temperature may be characteristic of regions with a relatively thick continental crust and the higher temperature of regions with a relatively thin continental crust on the other hand one single critical temperature of about 250 c can explain the coupling depths if shear stresses are constant with depth

the relationship between strain rates crustal thickening palaeomagnetism finite strain and fault movements within a deforming zone the deformation of continental lithosphere generally does not occur on a single fault but is distributed over a zone up to a few hundred kilometers wide if the deformation rate is constant throughout the zone and if the velocity is continuous everywhere and does not change with time the deformation gradient tensor can be obtained analytically this tensor directly determines the amount of crustal thickening and is related in a complicated manner to the finite strain tensor the declination of remnant magnetization measured within the zone can also be rotated by the deformation because palaeomagnetic measurements are generally made on rigid blocks which have not been deformed there is no simple relationship between such rotations and the finite strain expressions for all these quantities are obtained in terms of the velocity gradients which are taken to be constant the history of western north america is used to illustrate the relationship between the present deformation by strike slip and thrust motions the rotations of the remnant magnetization vectors and the shape of accreted terranes at the surface distributed deformation is taken up by motion on faults which separate the zone into blocks the displacement rate on the faults their strike and the finite rotations of the blocks are all controlled by the velocity gradients analytic expressions relating these quantities are obtained a deforming zone containing normal faults which crosses central greece takes up both strike slip and extension and illustrates the relationship between the structures within and the motion across the zone a similar but more complicated zone in northeastern iran involves both strike slip and shortening

the origin of massive diamicton facies by iceberg rafting and scouring scoresby sund east greenland almost 90 of 39 m of core material recovered from scoresby sund and the adjacent east greenland shelf is massive diamicton interpreted to be formed predominantly by the release of iceberg rafted debris and reworking by iceberg scouring there is also likely to be a contribution from suspension settling of fines derived from glaciofluvial sources model calculations suggest that the 14c derived holocene sedimentation rate of 0 1 0 3 m 1000 yr 1 in scoresby sund can be accounted for mainly by iceberg rafting of debris a further 4 of core material is of gravel or coarse sand lenses interpreted to reflect iceberg dumping of debris intensive iceberg scouring which reworks sea floor sediments is observed on acoustic records from over 30 000 km2 of the scoresby sund fiord system and the adjacent east greenland shelf 69 72 n and 75 n the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg rafting and scouring may be important over a significant proportion of the 500 000 km2 area above the shelf break the relatively extensive modern occurrence of massive diamicton formed by iceberg rafting and scouring together with suspension settling of fines suggests that it may also be a significant facies in the glacier influenced geological record the recognition in the geological record of the massive diamicton facies described above may also indicate the former presence of fast flowing ice sheet outlet glaciers

systematic variation in the depths of slabs beneath arc volcanoes summary the depths to the tops of the zones of intermediate depth seismicity beneath arc volcanoes are determined using the hypocentral locations of engdahl et al these depths are constant to within a few kilometres within individual arc segments but differ by tens of kilometres from one arc segment to another the range in depths is from 65 km to 130 km inconsistent with the common belief that the volcanoes directly overlie the places where the slabs reach a critical depth that is roughly constant for all arcs the depth to the top of the intermediate depth seismicity beneath volcanoes correlates neither with age of the descending ocean floor nor with the thermal parameter of the slab this depth does however exhibit an inverse correlation with the descent speed of the subducting plate which is the controlling factor both for the thermal structure of the wedge of mantle above the slab and for the temperature at the top of the slab we interpret this result as indicating that the location of arc volcanoes is controlled by a process that depends critically upon the temperature at the top of the slab or in the wedge of mantle immediately below the volcanic arc

crystallization processes in migmatites an important prerequisite for interpreting microstructures in plutonic and metamorphic rocks is understanding crystallization processes this study uses crystal size distribution csd and grain shape parameters to investigate mineral reaction controlled crystal growth and melt solidification in migmatites of the bayerische wald variscan orogeny germany partially molten rocks were studied because they allow the simultaneous investigation of crystallization of a melt and the growth of solid products of a metamorphic reaction csd and shape factors were obtained for three different minerals 1 cordierite in a diatexite where the melt remained in the system 2 k feldspar in a segregated k feldspar quartz leucosome and 3 plagioclase from a segregated plagioclase quartz leucosome cordierite crystals exhibit a nearly linear csd pattern and subeuhedral crystal shapes k feldspar grains display an approximately linear csd except for a marked increase at large crystal size classes k feldspar grains are characterized by strongly lobate grain boundaries the csd of plagioclase crystals is nearly linear with a slight decrease at small crystal size classes plagioclase shape factors also indicate lobate grain boundaries however with lower values than k feldspar cordierite csd and shape data are consistent with interface controlled crystallization the csd indicates that nucleation and growth is the rate limiting step during the cordierite producing reaction in contrast to porphyroblast growth in solid rocks where mass transfer is typically rate limiting csd combined with information on the duration of crystallization yields growth rates of 10 17 to 10 18 m s the plagioclase data are consistent with magmatic crystallization and are well described by the communicating neighbor theory the k feldspar data also indicate magmatic crystallization the overproduction of large grains of k feldspar reflects the interplay between nucleation and growth rates at the initial stage of crystallization because of different environments between solid and anatectic rocks the csd may help to decipher metamorphic from anatectic migmatites

changes in planview geometry and erosion deposition patterns along a channel levee complex in the southern corner of the kurile basin okhotsk sea abstract high resolution seismic profiles reveal the changes in planform and erosion deposition pattern in the abashiri oki trough aot the southwestern corner of the kurile basin the aot originated from a syncline in the late miocene early pliocene and is characterised by plio pleistocene channel levee complexes and debris flows mainly composed of hummocky chaotic and convergent reflectors the channel planform was changed by eustacy tectonics climate and hinterland volcanism regressive surfaces probably occur as the two reflectors of erosional surface and debris flow deposits the erosional depositional pattern suggests that the channel profile tends to evolve towards an exponential like form in the upper trough channels are incised probably inland volcanism induced to increase sedimentary supply consequently the slope progradation and steepened gradient volcanism also caused an additional channel in the middle trough channels show braided pattern related to subsidence and mildened gradient of the trough floor which lead to accommodation in the lower trough channels anastomose and in the lowermost trough finally the merged channel incises and cut offs the anticline dividing the aot from the kurile basin

finite strain calculations of continental deformation 1 method and general results for convergent zones a finite element method is used to calculate stresses and strain rates in a thin viscous sheet representing the continental lithosphere that is bordered in one part by an indenting boundary we calculate solutions for velocity fields crustal thickness distributions strain rates rotation time integrated vorticity and finite strain ellipsoids to show the dependence of these quantities on the controlling parameters the stress strain exponent n and the strength of the sheet relative to the gravitational forces which may be expressed as a dimensionless number the argand number ar for n 3 and ar between 1 and 10 a plateau of thickened crust is formed in front of the indenter the strain histories of individual elements within the viscous sheet may be quite complex and the finite strain at the end of deformation may bear no obvious relation to the principal stress orientations during the deformation the strain rate fields are interpreted in terms of the style of faulting that would be expected in the brittle upper crust if it were coupled to the ductile but stronger upper mantle in general the length scale of deformation increases with ar and time since the start of the collision and decreases with n for ar 3 the increase in length scale is accompanied by a change in the style of deformation from predominantly crustal thickening with thrust faulting in the brittle layer to predominantly transcurrent deformation strike slip faulting in the brittle layer

seismic imaging of a convergent continental margin and plateau in the central andes andean continental research project 1996 ancorp 96 1 a 400 km long seismic reflection profile andean continental research project 1996 ancorp 96 and integrated geophysical experiments wide angle seismology passive seismology gravity and magnetotelluric depth sounding across the central andes 21 s observed subduction of the nazca plate under the south american continent an east dipping reflector nazca reflector is linked to the down going oceanic crust and shows increasing downdip intensity before gradual breakdown below 80 km we interpret parts of the nazca reflector as a fluid trap located at the front of recent hydration and shearing of the mantle the fluids being supplied by dehydration of the oceanic plate patches of bright quebrada blanca bright spot to more diffuse reflectivity underlie the plateau domain at 15 30 km depth this reflectivity is associated with a low velocity zone p to s wave conversions the upper limits of high conductivity and high vp vs ratios and to the occurrence of neogene volcanic rocks at surface we interpret this feature as evidence of widespread partial melting of the plateau crust causing decoupling of the upper and lower crust during neogene shortening and plateau growth the imaging properties of the continental moho beneath the andes indicate a broad transitional character of the crust mantle boundary owing to active processes like hydration of mantle rocks in the cooler parts of the plate margin system magmatic underplating and intraplating under and into the lowermost crust mechanical instability at moho etc hence all first order features appear to be related to fluid assisted processes in a subduction setting

icebergs rework shelf sediments to 500 m off antarctica icebergs and sea ice rework the sediments of high latitude shelves producing modern diamicts ice keel turbates unrelated to glacial proximity off antarctica sidescan sonar data indicate the presence of ice gouge features formed by the physical interaction between ice keels and the sea bed these are recognized as incisions a few metres deep and tens of metres wide in water depths up to 500 m on the submarine bank tops and slopes off wilkes land and in the weddell sea subcircular depressions 30 to 150 m in diameter a washboard pattern and hummocky bed features also represent iceberg resting sites the freshness of sea bed morphology nearby holocene sediment ponding and active hydraulic sedimentary processes indicate that the sea floor is being reworked by iceberg keels tabular iceberg drafts in excess of 330 m have been measured and modeling studies suggest that nontabular iceberg drafts of 500 m are possible we conclude that a modern ice keel turbate deposit in the form of a poorly stratified diamicton is probably widespread on that part 54 of the antarctic shelf less than 500 m deep

the faroe shetland gateway late quaternary water mass exchange between the nordic seas and the northeastern atlantic abstract thirteen piston and gravity cores from the faroe shetland area were investigated for their planktic and benthic foraminiferal and oxygen isotopic distributions eight time slices between 18 ka bp and the present were reconstructed to study variations in surface and deep water exchange between the se norwegian sea and the northeast atlantic ocean today a relatively strong northward flow of warm north atlantic surface water is counterbalanced by a southward outflow of newly convected cold bottom water the norwegian sea overflow water during the last glacial maximum at 18 ka bp both the surface and bottom flows were slow and the climate conditions were arctic the convection north of the faroe area was weak and unstable the first indication of the deglaciation is a decrease in the planktic oxygen isotope values discernible southwest of the faroe islands at 15 5 ka bp the deglaciation proceeded northeast and eastward synchronous with a gradual intensification of northward flowing warmer atlantic intermediate water along the sea bottom meltwater fluxes increased between 14 and 13 ka bp producing cold surface waters and the climatic cooling was extreme there was no southward overflow of cold bottom water during this time period and the exchange of water masses between the nordic seas and the north atlantic ocean was essentially reversed i e estuarine during the bolling interstadial at 12 5 ka bp northward flowing warm surface water was present to the east of the faroe shetland channel wedged below a tongue of polar water spreading from the northwest and reaching into the faroe shetland channel convection in the nordic seas and overflow of cold deep water started during the bolling interstadial the polar water spread more eastward and southward during the following cold spell the younger dryas around 10 3 ka bp the polar water was overlying the warmer but more saline atlantic water which flowed northward below the cold surface water the overflow of cold bottom water was supposedly only slightly weaker than during the bolling interstadial strong inflow of warm surface water took place during the early holocene at 9 5 ka bp and relatively dense cold water flowed southward along the bottom the rate of water mass exchange reached a maximum at 6 5 ka bp when both the inflow of warm atlantic surface water and the outflow of cold dense bottom water appear to have been stronger than today

evolution of product phase assemblages during thermal decomposition of muscovite under strong disequilibrium conditions we investigated the thermal decomposition of muscovite in natural granite powders heated to 1175 c for durations from 5 min to 68 h at 1 bar paying special attention to the early stages of decomposition this study shows that muscovite is completely transformed after 5 min muscovite pseudomorphs consist of glass mullite and al rich oxides for short durations 5 and 40 min the al rich phase was identified by xrd electron diffraction and tem microanalysis as al 2 o 3 containing 4 8 wt feo total fe probably a few weight percents of mgo and possibly up to 10 wt sio 2 faint superstructure spots and diffuse streaks observed in electron diffraction patterns suggest vacancy or trace elements ordering in the al 2 o 3 defect spinel structure al 2 o 3 displays an unexpected acicular morphology elongated along three directions at 120 in the basal 001 musc planes and parallel to lateral faces of the former muscovite mullite forms rods elongated in the basal 001 musc planes along a direction at 90 from one set of al 2 o 3 needles the al 2 o 3 structure appears to be a metastable phase that is replaced by corundum for longer durations

norwegian sea warm pulses during dansgaard oeschger stadials zooming in on these anomalies over the 35 41 ka cal bp interval and their impacts on proximal european ice sheet dynamics abstract the last glacial millennial climatic events i e dansgaard oeschger and heinrich events constitute outstanding case studies of coupled atmosphere ocean cryosphere interactions here we investigate the evolution of sea surface and subsurface conditions in terms of temperature salinity and sea ice cover at very high resolution mean resolution between 55 and 155 years depending on proxies during the 35 41 ka cal bp interval covering three dansgaard oeschger cycles and including heinrich event 4 in a new unpublished marine record i e the md99 2285 core 62 69 n 3 57s e we use a large panel of complementary tools which notably includes dinocyst derived sea ice cover duration quantifications the high temporal resolution and multiproxy approach of this work allows us to identify the sequence of processes and to assess ocean cryosphere interactions occurring during these periodic ice sheet collapse events our results evidence a paradoxical hydrological scheme where i greenland interstadials are marked by a homogeneous and cold upper water column with intensive winter sea ice formation and summer sea ice melting and ii greenland and heinrich stadials are characterized by a very warm and low saline surface layer with iceberg calving and reduced sea ice formation separated by a strong halocline from a less warm and saltier subsurface layer our work also suggests that this stadial surface subsurface warming started before massive iceberg release in relation with warm atlantic water advection these findings thus support the theory that upper ocean warming might have triggered european ice sheet destabilization besides previous paleoceanographic studies conducted along the atlantic inflow pathways close to the edge of european ice sheets suggest that such a feature might have occurred in this whole area nonetheless additional high resolution paleoreconstructions are required to confirm such a regional scheme

a new view into the cascadia subduction zone and volcanic arc implications for earthquake hazards along the washington margin in light of suggestions that the cascadia subduction margin may pose a significant seismic hazard for the highly populated pacific northwest region of the united states the u s geological survey usgs the research center for marine geosciences geomar and university collaborators collected and interpreted a 530 km long wide angle onshore offshore seismic transect across the subduction zone and volcanic arc to study the major structures that contribute to seismogenic deformation we observed 1 an increase in the dip of the juan de fuca slab from 2 7 to 12 where it encounters a 20 km thick block of the siletz terrane or other accreted oceanic crust 2 a distinct transition from siletz crust into cascade arc crust that coincides with the mount st helens seismic zone supporting the idea that the mafic siletz block focuses seismic deformation at its edges and 3 a crustal root 35 45 km deep beneath the cascade range with thinner crust 30 35 km east of the volcanic arc beneath the columbia plateau flood basalt province from the measured crustal structure and subduction geometry we identify two zones that may concentrate future seismic activity 1 a broad because of the shallow dip possibly locked part of the interplate contact that extends from 25 km depth beneath the coastline to perhaps as far west as the deformation front 120 km offshore and 2 a crustal zone at the eastern boundary between the siletz terrane and the cascade range

deep pleistocene iceberg plowmarks on the yermak plateau sidescan and 3 5 khz evidence for thick calving ice fronts and a possible marine ice sheet in the arctic ocean the southern yermak plateau northwest of spitsbergen was investigated with 11 12 khz sidescan sonar and 3 5 khz profiler to test whether thick pleistocene ice streams ever calved into the arctic ocean and or whether a continuous arctic ice sheet existed in either case the ice would have grounded on the plateau crest on its way out of the arctic several distinct sets of relict iceberg plowmarks were discovered at present water depths from less than 450 m to at least 850 m perhaps recording the deepest iceberg keels known the plateau crest 510 530 m is nearly bare of plowmarks perhaps because of beveling by an ice rise formed of grounding shelf ice this implies continuous 400 600 m thick grounded ice consistent with but not proving the postulated existence of an arctic ice sheet most plowmarks are probably late pleistocene products of the calving of barents kara ice sheets into the arctic ocean plowmarks in 450 850 m deep water require unusually deep ice sheet grounding lines e g svyataya anna trough and or drat increasing capsizing events even if sea levels were 100 50 m lower than today at water depths of 800 to 1800 m the sidescan texture and topography suggest bottom currents descending the northeast slope of the plateau

cenozoic climate change as a possible cause for the rise of the andes causal links between the rise of a large mountain range and climate have often been considered to work in one direction with significant uplift provoking climate change here we propose a mechanism by which cenozoic climate change could have caused the rise of the andes based on considerations of the force balance in the south american lithosphere we suggest that the height of and tectonics in the andes are strongly controlled both by shear stresses along the plate interface in the subduction zone and by buoyancy stress contrasts between the trench and highlands and shear stresses in the subduction zone depend on the amount of subducted sediments we propose that the dynamics of subduction and mountain building in this region are controlled by the processes of erosion and sediment deposition and ultimately climate in central south america climate controlled sediment starvation would then cause high shear stress focusing the plate boundary stresses that support the high andes

temperatures heat flux and frictional stress near major thrust faults we examine the two dimensional advective and conductive transport of heat in a region of thrust faulting both simple theoretical considerations and numerical experiments show that the steady state temperatures near the fault are reduced by a divisor s 1 b z vsin below what they would be with the same heat sources but in the absence of advection in this expression z is the depth to the fault v is the slip rate is the component of the dip of the fault in the direction of underthrusting is thermal diffusivity and b is a dimensionless factor that is essentially equal to one for most forms of heating initial changes in temperatures near the fault are given by t z t t z 0 12vsin t z 0 z these simple formulae are successful because of the neglible influence of lateral conduction of heat at least for slip rates of a few mm yr or more two time constants govern the transition from the initial change in temperature to steady state t1 u v where u is the distance along the fault in the direction of underthrusting from the surface to the depth in question and t2 z 2 2 where z is the depth to the fault when elapsed times exceed the sum of these two time constants temperatures differ from their steady state values by only about 10 percent the numerical experiments indicate that the simple formulae are sufficiently accurate that sophisticiated numerical modeling of temperatures in specific regions is unwarranted putain an application of these simple formulae to measurements of conductive heat flow at island arcs implies that shear stresses at island arcs approach 100 mpa and are greater than 30 mpa calculations of temperatures appropriate for the himalaya suggest that shear stresses of 100 mpa on the main central thrust probably are required to account for the tertiary granites of the region if melting took place after slip began on the thrust similarly the cut off in seismicity at a depth of about 15 km in the himalaya if due to temperatures exceeding 350 to 450 c implies a deviatoric stress close to 100 mpa

strength of stick slip and creeping subduction megathrusts from heat flow observations subduction faults called megathrusts can generate large and hazardous earthquakes the mode of slip and seismicity of a megathrust is controlled by the structural complexity of the fault zone however the relative strength of a megathrust based on the mode of slip is far from clear the fault strength affects surface heat flow by frictional heating during slip we model heat flow data for a number of subduction zones to determine the fault strength we find that smooth megathrusts that produce great earthquakes tend to be weaker and therefore dissipate less heat than geometrically rough megathrusts that slip mainly by creeping

the contourite depositional system of the gulf of cadiz a sedimentary model related to the bottom current activity of the mediterranean outflow water and its interaction with the continental margin the present paper is mostly a synthesis of work conducted on the continental margin of the gulf of cadiz using a broad database collected by several cruises and projects supported by the spanish research council and the nrl and naval oceanographic office usa including bathymetry sidescan sonar imagery seismic profiles sediment cores submarine photographs and physical oceanographic data these data have enabled us to establish a detailed understanding of the morphologic development of the margin its pliocene and quaternary stratigraphy and a full characterization of the contourite depositional system cds generated by the mediterranean outflow water mow the northern margin of the gulf of cadiz shows the following distinct features a an active compressive framework where the cadiz allocthonous unit provides an unstable substratum for late miocene pliocene and quaternary sedimentation b a relative lack of submarine canyons except in the western area of the algarve margin c a very broad continental slope that lacks a marked continental rise d a middle slope dominated by along slope processes driven by the mow which has generated a complex cds during the pliocene and quaternary and e an irregular lower slope and abyssal plain region dominated by down slope processes that is partly detached from an upper slope source region the cds is composed of both depositional and erosive features the main depositional features are characterised by sedimentary wave fields sedimentary lobes mixed drifts plastered drifts elongated mounded and separated drifts and sheeted drifts the main erosive features are contourite channels furrows marginal valleys and moats these various depositional and erosive features have a specific location along the margin and their detailed distribution is essential to understand the present and past interaction of the mow with the middle slope based on this distribution five morphosedimentary sectors have been identified within the cds which from east to west are 1 proximal scour and sand ribbons 2 overflow sedimentary lobe 3 channels and ridges 4 active contourite drifts and 5 submarine canyons the development of the cds has been controlled in general by the pliocene and quaternary environmental and paleoceanographic changes and by the morphology of the margin but in detail the development of each of these sectors is related to systematic deceleration of the mow as it flows westwards to the interaction with the margin bathymetry and to the effects of coriolis force our comprehensive sedimentary model for the cds defines the gulf of cadiz margin as a mixed contourite turbidite system with a detached combined drift fan morphology this is different from many other contourite influenced margins where the contourite processes are dominant on the middle slope and separated from the down slope processes which are characteristic on the lower slope and abyssal plains

structure and composition of the aleutian island arc and implications for continental crustal growth we present results of a seismic reflection and refraction investigation of the aleutian island arc designed to test the hypothesis that volcanic arcs constitute the building blocks of continental crust the aleutian arc has the requisite thickness 30 km to build continental crust but it differs strongly from continental crust in its composition and reflectivity structure seismic velocities and the compositions of erupted lavas suggest that the aleutian crust has a mafic bulk composition in contrast to the andesitic bulk composition of continents the silicic upper crust and reflective lower crust that are characteristic of continental crust are conspicuously lacking in the aleutian intraoceanic arc therefore if island arcs form a significant source of continental crust the bulk properties of arc crust must be substantially modified during or after accretion to a continental margin the pervasive deformation intracrustal melting and delamination of mafic to ultramafic residuum necessary to transform arc crust into mature continental crust probably occur during arc continent collision or through subsequent establishment of a continental arc the volume of crust created along the arc exceeds that estimated by previous workers by about a factor of two

sequential kinetics of a muscovite out reaction a natural example a natural example of sequential kinetics for the muscovite dehydration reaction in highly deformed mylonitic gneisses is analyzed studied textures consist of deformed pegmatitic muscovite crystals surrounded by fibrolitic sillimanite tightly intergrown with biotite and with potassium feldspar in the pressure shadows potassium feldspar andalusite biotite and quartz appearing in the crystal core constitute the products of muscovite breakdown produced by topotactic replacement of muscovite within a single crystal non isochemical decomposition of muscovite is proposed in which diffusion of k outward from the crystal took place along the muscovite interlayer and shear planes parallel to 001 the chemical potential gradient calculated for k capable of producing the texture observed within the pegmatitic crystals results not only from the overstepping of the muscovite out reaction but also from the difference in free energy between andalusite and sillimanite under p t conditions where andalusite is stable the overall reaction within the andalusite stability field consists of the transformation 1 ms 1 qtz 1 and 1 kfs 1 h 2 o and of the indirect replacement 0 25 sil 0 25 and andalusite nucleation and growth took place completely inside muscovite whereas most of the potassium feldspar was produced outside preferentially at pressure shadows after out ward intracrystalline diffusion of k super and fibrolitic sillimanite dissolution in the matrix the rate limiting step of this reaction process was initially the migration rate of the muscovite andalusite and muscovite potassium feldspar interfaces however it was followed by a diffusion controlled step the change in the relative rates of the reaction mechanisms was due to the coarsening of the reaction products the low amount of energy and time required for non reconstructive transformations periodic bond chains of the tetrahedral sheet of muscovite are inherited by potassium feldspar and those of the octahedral sheet by andalusite the magnitude of the heat flow associated with a possible contact metamorphic episode and the slow diffusion of k within the crystal intracrystalline diffusion took place through a double monolayer of absorbed molecules of water approximately 10 aa localized at microcleavages produced by basal slip in the interlayer level instead of a proper lattice diffusion process the derived rate law at constant p and t considering the cases of 2 kbar and 605 degrees c and 3 kbar and 639 degrees c for the diffusion controlled process gives a time span of about 10 000 years for the growth of these metamorphic textures which seems to be a reasonable estimate for a contact metamorphic event

evolution of the norwegian current and the scandinavian ice sheets during the past 2 6 m y evidence from odp leg 104 biogenic carbonate and terrigenous records abstract records of biogenic and terrigenous components have been obtained from the interval corresponding to the last 2 6 m y of odp sites 643 and 644 in order to reconstruct surface and deep water regimes in the norwegian sea surface water regimes record long lasting moderate glacial conditions during the interval 2 6 1 0 ma small intrusions of atlantic water episodically penetrated into the norwegian sea forming a narrow tongue along the eastern margin which is documented at site 644 the polar front was most probably situated between the site 644 and 643 locations on the outer voring plateau during these time intervals deep water regimes reflect long term persistent corrosive bottom waters most probably due to a weakly undersaturated water column and a low rate of carbonate shell production in surface waters deep water production in the norwegian greenland sea may have operated in a different way e g brine formation during winter sea ice growth bottom waters were oxygenated throughout the entire period and deep water was exchanged persistently with the north atlantic increased glacial interglacial environmental contrasts are documented reflecting a strengthening of the norwegian current and intensified glaciations on the surrounding land masses during the interval 1 0 0 6 ma during this time a major shift in the mode of deep water production occurred the onset of large amplitudes in glacial interglacial environmental conditions with maximum contrasts in surface water regimes different modes of deep water production and intensified exchange with the north atlantic marks the last 0 6 ma a broad development of the norwegian current is observed during peak interglacials while during glacials seasonally variable sea ice cover and iceberg drift dominate surface water conditions

climatic limits on landscape development in the northwestern himalaya the interaction between tectonism and erosion produces rugged landscapes in actively deforming regions in the northwestern himalaya the form of the landscape was found to be largely independent of exhumation rates but regional trends in mean and modal elevations hypsometry frequency distribution of altitude and slope distributions were correlated with the extent of glaciation these observations imply that in mountain belts that intersect the snowline glacial and periglacial processes place an upper limit on altitude relief and the development of topography irrespective of the rate of tectonic processes operating

is it all in the crust new observations suggest that earthquakes on land are only skin deep confined to the earth s outermost layer of crust this has prompted a rethink of what gives the tectonic plates their strength

megathrust shear force controls mountain height at convergent plate margins the shear force along convergent plate boundary faults megathrusts determines the height of mountain ranges that can be mechanically sustained1 4 however whether the true height of mountain ranges corresponds to this tectonically supported elevation is debated4 7 in particular climate dependent erosional processes are often assumed to exert a first order control on mountain height5 12 although this assumption has remained difficult to validate12 here we constrain the shear force along active megathrusts using their rheological properties and then determine the tectonically supported elevation using a force balance model we show that the height of mountain ranges around the globe matches this elevation irrespective of climatic conditions and the rate of erosion this finding indicates that mountain ranges are close to force equilibrium and that their height is primarily controlled by the megathrust shear force we conclude that temporal variations in mountain height reflect long term changes in the force balance but are not indicative of a direct climate control on mountain elevation

the stratagem project stratigraphic development of the glaciated european margin the ec funded stratagem project ran from 2000 to 2003 and was a study of the neogene evolution of the glaciated northeast atlantic margin from lofoten to porcupine an area extending over nearly 20 degrees of latitude an extensive seismic borehole and sample database has been used much of it supplied by the oil industry the main products of stratagem have been an integrated unified stratigraphic framework in the form of an atlas documenting and illustrating the detailed stratigraphy of the entire margin and a detailed evolution model for this margin a brief summary of the background to and organisation of the project is presented together with an outline of the main objectives the physiographic setting of the area and the database