lithospheric dynamics and tectonic stratigraphic evolution of the ebro basin we present analysis of two dimensional modeling of the tectonic subsidence in the ebro basin along three profiles crossing the pyrenees the ebro basin and the catalan coastal range to the east and the iberic cordillera to the west the deformation of the foreland basin during tertiary times is simulated using a lithospheric flexure model incorporating laterally varying elastic thicknesses the deflection of the plate is the combined result of pyrenean loading and the loads exerted by the iberic cordillera and catalan coastal range in the eastern part of the ebro basin no extra driving force on the iberian plate is required the flexural modeling supports the hypothesis that underplating of the iberian plate under the european plate is not associated with subduction of old oceanic lithosphere a good fit with the tertiary basin subsidence data and bouguer anomalies is obtained for an elastic plate with local weakness zones under the ebro basin the inferred lateral variation in the elastic rigidity is consistent with heat flow measurements in northern spain and with major mesozoic extension in the iberic cordillera and valencia trough

decoupled flexure in the south pyrenean foreland complex subsidence patterns during the mid late eocene of the easternmost south pyrenean foreland are well explained by a decoupled flexure model in which upper crustal buckling is accommodated by ductile flow in the mid lower crust while simultaneously and independently the lower lithosphere flexes above a ductile asthenosphere the resulting predicted subsidence values agree with observation to well within the estimated uncertainties the resulting lithospheric effective elastic thickness eet estimate 10 3 km is low but similar to values obtained in the south pyrenean foreland by other authors the separate eet obtained for the upper crust 1 5 0 8 km also agrees with tentative values given by other workers

patterns of deposition from experimental turbidity currents with reversing buoyancy turbidity currents are turbulent sediment laden gravity currents which can be generated in relatively shallow shelf settings and travel downslope before spreading out across deep water abyssal plains because of the natural stratification of the oceans and or fresh water river inputs to the source area the interstitial fluid within which the particles are suspended will often be less dense than the deep water ambient fluid consequently a turbidity current may initially be denser than the ambient sea water and propagate as a ground hugging flow but later reverse in buoyancy as its bulk density decreases through sedimentation to become lower than that of the ambient sea water when this occurs all or part of the turbidity current lofts to form a buoyant sediment laden cloud from which further deposition occurs deposition from such lofting turbidity currents containing a mixture of fine and coarse sediment suspended in light interstitial fluid is explored through analogue laboratory experiments complemented by theoretical analysis using a box and cloud model particular attention is paid to the overall deposit geometry and to the distributions of fine and coarse material within the deposit a range of beds can be deposited by bimodal lofting turbidity currents lofting may encourage the formation of tabular beds with a rapid pinch out rather than the gradually tapering beds more typical of waning turbidity currents lofting may also decouple the fates of the finer and coarser sediment depending on the initial flow composition the coarse fraction can be deposited prior to or during buoyancy reversal while the fine fraction can be swept upwards and away by the lofting cloud an important feature of the results is the non uniqueness of the deposit architecture different initial current compositions can generate deposits with very similar bed profiles and grading characteristics highlighting the difficulty of reconstructing the nature of the parent flow from field data it is proposed that deposit emplacement by lofting turbidity currents is common in the geological record and may explain a range of features observed in deep water massive sands thinly bedded turbidite sequences and linked debrites depending on the parent flow and its subsequent development for example a lofting flow may lead to a well sorted largely ungraded or weakly graded bed if the fines are transported away by the cloud however a poorly sorted largely ungraded region may form if during buoyancy reversal high local concentrations and associated hindered settling effects develop at the base of the cloud

pliocene uplift of the eastern iberian margin inferences from quantitative modelling of the valencia trough we present the results of quantitative modelling of subsidence in the valencia trough and associated uplift in the catalan coastal ranges and the balearic islands basement subsidence moho depth and gravity anomalies are calculated for different effective elastic thicknesses eet and durations of rifting along two profiles constrained by recently collected multichannel seismic and gravity data the tectonic evolution of the catalan coastal ranges cannot be explained with traditional two layer lithospheric stretching models for the valencia trough but is consistent with a thermomechanical model invoking lithospheric necking combined with a late stage uplift event the modelling of the topography of the balearic islands suggests an interaction of extension in the valencia trough with extension in the south balearic basin our study supports a rifting model with low values for the flexural rigidity an intermediate level of necking and one finite duration stretching event propagating from the northeast towards the southwestern part of the valencia trough the modelling provides constraints on the magnitude of a large scale pliocene uplift of the eastern margin of the iberian peninsula

impact of backstop thickness lateral variations on the tectonic architecture of orogens insights from sandbox analogue modeling and application to the pyrenees 1 we performed sandbox analogue models to investigate the influence of along strike tapering of the backstop on the three dimensional architecture of natural doubly vergent thrust fold belts applying the results to a natural example as the pyrenees available geological and geophysical data indicate that the european crust which provided the backstop in the pyrenean orogen has a westward tapering on both the upper westward thickening of the mesozoic cover rocks and the lower westward rising of the moho envelope surfaces accordingly we performed laboratory models characterized by backstops with an along strike tapering of either the upper or the lower surface our results indicate a significant impact of backstop lateral tapering in thrust wedge architecture in terms of the outward propagation of the deformation fronts the width and elevation of the axial zone and the timing of thrust polarity reversal along strike when compared to the pyrenees our results support the inferred westward tapering of the european basement and its commonly accepted backstop role in the pyrenean orogen moreover comparison between the map pattern of the pyrenees and of laboratory experiments suggests that the along strike tapering of the bottom envelope surface of the backstop played a most important role on the three dimensional thrust wedge architecture than the tapering of the upper envelope surface

a balanced section across the pyrenean orogenic belt evolutionary models that have been proposed for the pyrenean orogenic belt involve gravitational gliding of major thrust sheets to both the north and south of an uplifted central axial zone it has been suggested by previous workers that uplift is a result of alpine compression or long lived strike slip movement on the north pyrenean fault we critically assess these models and propose a new model based on the generation of a thin skinned linked thrust system due to alpine collision of iberia and europe pyrenean alpine tectonics is dominated by southward thrusting on a major sole fault dipping north at approximately 6 within hercynian basement northerly directed thrusts of the north pyrenean zone and northern folded foreland are backthrusts from this sole fault a total orogenic shortening of 106 km in the central pyrenees was achieved between the palaeocene and oligocene at a time averaged rate of 0 62 cm yr 1 a thin skinned model requires that the north pyrenean fault is truncated by both northward and southward moving thrusts and occurs in the footwall of the sole fault some 60km north of its present surface trace

flexural expression of european continental lithosphere under the western outer carpathians we present the results of an analysis of the flexural down bending of the european lithosphere under the western outer carpathians for a grid of five profiles with a lateral spacing of about 100 km crossing the carpathians and its foreland seismic sections including two deep seismic reflection lines and numerous wells allowed us to quantify the flexural curvature of the lithosphere in addition gravity data are used to obtain independent constraints two evolutionary scenarios involving subduction underthrusting of passive margin and a phase change in the lower crust are investigated in a context of relatively flat moho under the area furthermore recent uplift expressing itself in erosional features observed along the distal margin of the foredeep is quantified the generally modest bouguer gravity anomaly points to nonisostatic processes causing this uplift steeply dipping basement under the carpathians to about 10 km depth at the location of the pieniny klippen belt is explained by relatively weak lithosphere which is expressed in the predicted low values of effective elastic thickness of 16 km decreasing locally to 3 km the low strength of the european lithosphere in this region is probably caused by mechanical weakening controlled by partial yielding due to high flexural curvature the weakest parts of the lithosphere along the profiles corresponding to low effective elastic thicknesses are concentrated in the areas of maximum bending predicted flexural bending stresses as a function of bending moment and effective elastic thickness increase dramatically under the outer zone of the carpathian belt explaining reactivations of older basement structures in these regions

acoustic emission signatures prior to snow failure snow slab avalanches are caused by cracks forming and propagating in a weak snow layer below a cohesive slab the gradual damage process leading to the formation of the initial failure within the weak layer wl is still not entirely understood to this end we designed a novel test apparatus that allows performing loading experiments with large snow samples 0 25 m 2 including a wl at different loading rates and simultaneously monitoring the acoustic emissions ae response by analyzing the ae generated by micro cracking we studied the evolution of the damage process preceding snow failure at fast loading rates the exponent of the ae energy distribution b value gradually changed and both the energy rate and the inverse waiting time increased exponentially with increasing load these changes in ae signature indicate a transition from small to large events and an acceleration of the damage processes leading to brittle failure for the experiments at slow loading rate these changes in the ae signature were not or only partially present even if the sample failed indicating a different evolution of the damage process the observed characteristics in ae response provide new insights on how to model snow failure as a critical phenomenon

analysis of the geological evolution and vertical movements in the valencia trough area western mediterranean abstract the valencia trough located between the iberian peninsula and the balearic islands corresponds to the south west prolongation of the provencal basin the analysis of recently released seismic lines shows that the present day tectonics of the valencia trough are the result of the coeval development of 1 a system of horsts and grabens in the north west part of the basin during the late oligocene early miocene catalan valencian domain and 2 a thrust and fold system which lasted up to the middle miocene and which was followed by extensional tectonics during the late miocene betic balearic domain in an attempt to characterize the evolution of the valencia trough subsidence curves have been calculated for 18 wells and three regional cross sections distributed across the basin backstripping of these data shows two major stages of tectonic subsidence history 1 a first stage coeval with basin formation 30 15 my characterized by a rapid and strong tectonic subsidence which attains its maximum values in the central basin areas and close to the balearic islands and 2 a second stage 15 0 my in which the tectonic subsidence decreases gradually the amount of crustal thinning estimated from a comparison of the observed and modelled tectonic subsidence ranges between 1 5 iberian margin areas and 4 5 central and south western basin areas these values agree with the crustal thicknesses inferred from seismic refraction data and gravimetric modelling nevertheless such a degree of thinning cannot be explained by the neogene extensional structure the presence of thick mesozoic deposits suggests that the present crustal thinning is partly due to previous mesozoic extension

the neogene structure of the eastern iberian margin structural constraints on the crustal evolution of the valencia trough western mediterranean abstract the presence of a thinned crust beneath the valencia trough has been recognized for a long time however to date no attempt to link this thinning inferred from geophysical data with the superficial structures has been made a quantification of the neogene extensional processes in the crustal evolution of the valencia trough is presented as a consequence of the complexity of the betic balearic domain the analysis has been done for the catalan valencian domain northwestern areas of the trough crustal and superficial data in this area show that neogene extension was accommodated by a listric normal fault system detached in a deep upper crustal level 13 15 km in the marginal zone of the domain quantitative analysis of the neogene structure shows the incoherence between the upper crustal thinning inferred from the geometric analysis of the superficial structures factor 1 4 1 5 and from geophysical data 1 8 although the latter value agrees with that deduced from the analysis of neogene subsidence this incoherence suggests that the present thinned crust would be partially inherited from the mesozoic extension in this way mesozoic subsidence analysts and the recognized mesozoic structure show that the mesozoic extension was almost as important as the neogene one

tectonic model for crustal seismic reflectivity patterns in compressional orogens a pattern of crustal seismic reflectivity tentatively dated as ordovician silurian recurs along strike in the newfoundland appalachians comparable fault patterns are produced in sandbox models of asymmetric compressional systems where oppositely dipping step up shear zones are localized above a discontinuity in basal velocity the reflectivity pattern may be produced by a mechanically analogous process in which a stress discontinuity results from detachment and underthrusting of mantle and possibly lower crustal lithosphere during con tinent continent collision similar seismic reflectivity patterns exist elsewhere in the appalachian caledonide mobile belt as well as in older and younger compressional orogens suggesting that detachment and underthrusting leading to asymmetric crustal deformation may be a common feature of compressional orogens

simulation of foreland basin stratigraphy using a diffusion model of mountain belt uplift and erosion an example from the central alps switzerland foreland basin stratigraphy can be considered as the result of three interacting processes thrust deformation which builds the tectonic load sedimentary and erosional processes which redistribute that load and the flexural response of the lithosphere the resultant stratigraphy of foreland basins is commonly composed of a small number of shallowing and coarsening upward cycles bounded by regional unconformities to understand the development of these unconformities we present a simple model of these three processes coupling an evolving thrust wedge on a linear elastic plate with erosion and sedimentation defined by the diffusion equation applied to topography our model demonstrates the development of regional unconformities without recourse to either eustasy or complex viscoelastic models for the continental lithosphere the model describes the thrust wedge foreland basin system in terms of four parameters 1 the effective elastic thickness of the foreland plate te 2 the sediment transport coefficient k 3 the thrust wedge advance rate 4 the surface slope of the thrust wedge the model is applied to the oligocene miocene north alpine foreland basin nafb of eastern switzerland the stratigraphy of the nafb can be simplified into two large scale shallowing upward cycles separated by an unconformity at the base of the burdigalian 22 ma geological information is taken from the nafb to estimate suitable values for the parameters listed above assuming a linear elastic lithospheric rheology the te value is estimated at 10 5 km from decompacted sediment columns data to constrain the sequential development of the thrust wedge come from structural geology the early stages 40 24 ma of compression involved a relatively low angle thrust wedge with an advance rate of approximately 2 4 mm yr at about 24 ma the wedge advance slowed down and thickened by underplating crystalline basement of the foreland plate the value for the transport coefficient has been estimated from previous studies prior to attempting to simulate the broad scale geometry of the nafb the role of each parameter was assessed individually the values for te and k are held constant throughout the simulation of the nafb at 7 5 km and 500 m yr respectively the geometry of the base burdigalian unconformity is reproduced by variations in the parameters describing the thrust wedge the surface slope angle of the wedge is increased from 2 5 to 4 over 0 2 m y and the rate of thrust advance is decreased from 2 mm yr to 0 2 mm yr during the thickening event between 24 and 23 8 ma the rejuvenation of the internal parts of the thrust load causes backtilting of the foreland basin sediments and after a time lag erosion of the distal stratigraphy over the forebulge so simulating the base burdigalian unconformity

gravity constraints on the deep structure of the pyrenean belt along the ecors profile abstract in order to furnish further constraints to modelling the ecors pyrenees deep seismic profile gravity data were collected along a stripe 20 km wide and 220 km long containing the seismic line a total of 4020 stations have been used to derive a bouguer anomaly map of the area a large and roughly symmetrical negative anomaly 100 mgal is centered on the axial zone a local positive anomaly over the north pyrenean zone disturbs the negative regional trend somewhat detailed densities were assigned to the sedimentary cover on the basis of borehole samples refraction data and a velocity density relationship were used to constrain the densities adopted for the deeper layers the results of the two dimensional gravity modelling confirm the asymmetrical shape of the crust mantle boundary beneath the pyrenean belt the downward deflection of the iberian moho from the ebro basin leads to a maximum depth of 65 km under the paleozoic axial zone whereas a depth of 35 km is found for the european moho under the north pyrenean zone two extreme models are proposed for the northern limit of the iberian crust a vertical contact in the downward continuity of the north pyrenean fault or a 70 northward sloping interface the positive anomalies beneath the north pyrenean zone may be explained by dense intracrustal mantle slices or lower crustal sheets the outcrop of granulitic basic gneiss within the labourd massif suggests that the anomaly results from lower crustal sheets

seismic sensor array for monitoring an avalanche start zone design deployment and preliminary results in snow acoustic emissions originate from the breaking of bonds between snow crystals and the formation of cracks previous research has shown that acoustic signals emanate from a natural snowpack the relation between these signals and the stability of the snowpack has thus far remained elusive studies on other hazardous gravitational processes suggest that damage accumulation precedes major failure if increased cracking activity could be detected in snow this might be used for avalanche prediction we report on the development of a seismic sensor array to continuously monitor acoustic emissions in an avalanche start zone during three winters over 1400 sensor days of continuous acoustic data were collected with the aid of automatic cameras and a microphone the main types of background noise were identified seismic signals generated by avalanches were also identified spectrograms from seismic signals generated by avalanches exhibit a unique triangular shape unlike any source of background noise suggesting that automatic detection and classification of events is possible furthermore discriminating between loose snow and snow slab avalanches is possible thus far we have not identified precursor events for natural dry snow slab avalanche release detailed investigation of one dry snow slab avalanche showed that signals observed prior to the release originated from background noise or small loose snow avalanches

crustal parameters in the iberian peninsula abstract the structure of the crust in the iberian peninsula has been investigated for the last 15 years by spanish and portuguese groups in close collaboration with other european institutions the first experiments were carried out in portugal mueller et al 1973 with the aim of investigating the crustal structure of the hercynian belt in the southwest corner of the iberian peninsula other experiments have been subsequently realized to study different aspects of the crust in various regions of portugal in spain the main effort has been focused in alpine areas with the first experiments in the alboran sea and the betic cordilleras working group for deep seismic sounding in spain 1974 1975 1977 working group for deep seismic sounding in the alboran sea 1974 1975 1978 follow up experiments until 1981 completed the work in the betic cordillera extensive experiments were carried out in the pyrenees in 1978 further surveys covered the balearic islands in 1976 the valencia trough in 1976 and 1983 and the celtiberian chain or iberic system in 1981 the hercynian belt has only been studied in detail in the northwest corner of spain in 1982 with smaller studies in the central iberian massif in 1976 and 1986 mostaanpour 1984 has compiled some crustal parameters crustal thickness average crustal velocity and pn velocity for western europe meanwhile more complete data are available for the iberian peninsula the results presented here were derived from a large number of seismic refraction experiments which have been carried out mostly along or close to coastal areas of the iberian peninsula offshore explosions of various sizes were used as the energy source in most cases in addition to some quarry blasts unfortunately this leaves most of the inner part of the iberian peninsula unsurveyed our purpose is to summarize some of the crustal parameters obtained so far and to detail the appropriate literature for the interested reader

palaeo elevation and effective elastic thickness evolution at mountain ranges inferences from flexural modelling in the eastern pyrenees and ebro basin abstract the results are presented of a two dimensional flexural modelling study of the lithosphere underlying the southern pyrenees and the ebro basin the modelling is based on a crustal scale balanced cross section along a profile through the north eastern part of the iberian plate two time slices of the structural evolutions of the mountain chain are modelled the present day configuration and the configuration at middle lutetian time 47 ma where important structural and sedimentological changes are observed the flexure model incorporates lateral variations in the effective elastic thickness eet of the lithosphere the present day deflection in the profile is simulated using boundary forces and a northward decreasing eet that varies from 30 to 11 km models for middle lutetian times indicate eet values of 26 18 km in the northern part of the profile assuming that the eet at the distal margin of the ebro basin has not significantly changed since middle lutetian times these higher values for the eet at middle lutetian times suggest that the effect of the cretaceous extensional phase on the present day flexural rigidity is small and therfore the inferred northward decreasing rigidity is predominantly related to the pyrenean collision flexural modelling provides also constraints for the palaeo elevation of the inner part of the chain including the assumption that the eet at the distal margin of the ebro basin has not significantly changed since middle lutetian times the model predicts a maximum palaeo elevation of 2000 m which is in agreement with geological observations concerning the relation between basin fill and palaeo elevation

modelling snow failure with a fibre bundle model dry snow slab avalanches initiate from a failure in a weak snow layer below a cohesive slab snow is considered as a porous ice structure and the strength distribution of the single elements of this structure i e grains and bonds between grains shows a high degree of disorder on the bond or microstructural level the failure process is believed to start if the fracturing of bonds between snow grains is not balanced by the formation of new bonds we use a statistical fracture model a fibre bundle model to study the failure process in a weak snow layer the model consists of fibres of various strengths representing single snow grains between two rigid plates which represent the slab above and the substratum below the weak layer the fibres deform in a linear elastic manner and break instantly at their rupture strength broken fibres may sinter re bond and regain strength after a finite sintering time we show that the different characteristic times for breaking and sintering lead to the rate dependence of snow strength this is to our knowledge the first statistical model to reproduce the ductile to brittle transition which snow exhibits with increasing strain rate when the model is applied to simulate experimental stress strain curves for different strain rates the model and experimental results are in fair agreement

are systematic variations in thrust belt style related to plate boundary processes the western alps versus the carpathians within the mediterranean region cenozoic deformation of the western alps and the west to east carpathians has resulted in two different styles of foreland fold and thrust belt the most prominent difference between the two belts is the presence carpathians or absence western alps of contemporaneous back arc extension but other important differences in structure topography and metamorphism also exist these differences in thrust belt style developed mainly during the final stages of thrust belt evolution and appear to reflect fundamental differences in the tectonic settings of the western alps and the carpathians in middle and late cenozoic time in particular they appear to be the result of convergence that is in the first case driven primarily by major plate motions and in the second case only by local motions of small lithospheric flakes or fragments we suggest that the structural styles developed in these two mountain belts may be useful in identifying mountain belts that have evolved in similar tectonic settings elsewhere in the world in this respect the western alps and the carpathians can be regarded as typical examples of two different styles of foreland fold and thrust belt or more properly as end member examples within a broad spectrum of foreland fold and thrust belt styles we propose that continental subduction zones and orogenic belts can be loosely divided into segments that show no major back arc extensional deformation adjacent to the belt the western alps and segments that exhibit back arc extension contemporaneously with thrusting the carpathians the former are found in areas where the rate of overall plate convergence exceeds the rate of subduction and are commonly typified by extensive involvement of crystalline basement in thrusting exposure of high grade metamorphic rocks at the surface high topographic elevation and large amounts of erosion tens of kilometers the latter are found in areas where the rate of subduction exceeds the rate of overall plate convergence and are commonly typified by thrust belts with little to no involvement of crystalline basement in thrusting low grade to no metamorphism low topographic elevation little erosion and in some instances an anomalously deep foredeep basin system

variations of elastic plate thickness at continental thrust belts after examining 15 reliable estimates of the elastic thickness of the lithosphere where it underthrusts mountain belts in europe asia and the americas we conclude that the strength of continental lithosphere as a function of depth must be very different from that of oceanic lithosphere depending on the state of stress continental lithosphere may be either very much stronger or very much weaker than would be predicted for oceanic lithosphere of the same thermal age we explain this observation as the result of two competing effects a thicker thermal plate beneath the continents which allows a deeper elastic ductile transition for plates more than 100 million years old and a low activation energy for ductile creep in the continental crust which leads to massive failure of the upper elastic lithosphere at high bending stresses the 100 km values for elastic plate thickness of billion year old lithosphere require a thermal plate thickness of at least 250 km the magnitude of apparent thinning of the elastic plate at high stress is consistent with that calculated from a simple yield envelope which includes a ductile zone in the lower crust the low yield strength of continental materials leads to correlations between effective elastic plate thickness and all of the following dip of the underthrust plate radius of curvature of the thrust front in map view and total length of the mountain belt using insight derived from laboratory experiments on the buckling of spherical shells and drawing analogies with the geophysical characteristics of oceanic subduction zones we arrive at the following sequence of causes and effects the primary variable is the dip of the downgoing plate presumably prescribed by its own excess mass and pressure exerted by dynamic flow in the mantle where this dip is steep the rigidity of the plate is weakened due to inelastic yielding the weakened plate can then buckle at small wavelengths into short arcuate mountain belts thus we believe that the mantle ultimately controls the pattern of surface tectonics but that the nonelastic rheology of the lithosphere is the mechanism by which that control is imposed

the tectonic expression slab pull at continental convergent boundaries examination of five thrust belt systems developed at continental subduction boundaries suggests that they comprise two distinct groups that display pronounced and systematic differences in structural style topographic elevation denudation metamorphism postcollisional convergence and foredeep basin geometry and facies the distinctive geological features developed within each thrust belt group appear to be causally linked to the relative rates of subduction and convergence via the magnitude of horizontal compressional stress transmitted across the subduction boundary at subduction boundaries where the rate of overall plate convergence is less than the rate of subduction termed here retreating subduction boundaries the transmission of horizontal compressive stress across the plate boundary is small and regional deformation of the overriding plate is by horizontal extension the tectonic expression of these retreating subduction boundaries includes topographically low mountains little erosion or denudation low grade to no metamorphism little to no involvement of crystalline basement in shortening little to no postcollisional convergence anomalously deep foredeep basins and a protracted history of flysch deposition within the adjacent foredeep basin analysis of deflection and gravity data across three retreating subduction boundaries apennine carpathian and hellenic systems shows that subduction is driven by gravitational forces acting on dense subducted slabs at depths between about 40 and 80 km carpathians 50 and 150 km apennines and 50 and 250 km hellenides the total mass anomalies represented by the slabs are approximately 3 1012 6 1012 and 12 1012 n m respectively the slabs are partially supported by flexural stresses transmitted through the subducted lithosphere to the foreland and partially supported by dynamic viscous stresses in the asthenosphere at subduction boundaries where the rate of overall plate convergence is greater than the rate of subduction termed here advancing subduction boundaries the transmission of horizontal compressive stress across the plate boundary is large and regional deformation of the overriding plate is by horizontal shortening the tectonic expression of these advancing subduction boundaries includes topographically high mountains antithetic thrust belts large amounts of erosion and denudation exposure of high grade metamorphic rocks at the surface extensive deformation of crystalline basement to midcrustal depths protracted postcollisional convergence tens of millions of years and a protracted history of molasse deposition within the adjacent foredeep basins analysis of gravity and deflection data across two advancing subduction boundaries developed within the continental lithosphere western to eastern and southern alps and himalayas shows that the thrust sheets have been translated for great distances over the foreland lithosphere relative to the point at which the subduction forces are applied thus obscuring any flexural and gravity signals from the subducted slab however it appears that far field stresses presumably related to global plate motions drive most of the convergent motion across these subduction boundaries the concept that orogenic belts formed above retreating subduction boundaries have recognizable tectonic signatures that differ from those of orogenic belts formed above advancing subduction boundaries suggests that it may be possible to interpret the plate boundary settings in which ancient orogenic belts evolved appendix b is available with entire article on microfiche order from the american geophysical union 2000 floridaavenue n w washington d c 20009 document t92 004 2 50 payment must accompany order

modelling of piggyback basin stratigraphy record of tectonic evolution abstract the tectono stratigraphic evolution of foreland basins is influenced by processes acting on local regional and global scale in this paper the effects of these processes on the basin evolution are investigated using a forward reconstruction model based on the principles of balanced cross section the modelling incorporates the consequences of thrust deformation sedimentation erosion basement subsidence and sealevel changes on the basin stratigraphy basement subsidence due to lithospheric loading is the main cause of foreland basin formation but appears to have minor implications for the occurrence of angular unconformities in the stratigraphie record of piggyback basins thrusting is probably the dominant factor in the control of the stratigraphie evolution of piggyback basins overprinting the effect of eustasy detailed analyses of stratigraphie data enable the reconstruction of the structural evolution of the underlying thrust system modelling of the northern apenninic po basin shows that neogene stratigraphie sequences of the proximal part of the basin can be explained by tectonic activity of the apenninic fold and thrust belt strong basement subsidence accompanied with deep seated mid pliocene thrusting controls the stratigraphie record of the po piggyback basins

cenozoic vertical motions of the catalan coastal ranges ne spain the role of tectonics isostasy and surface transport 1 we analyze the cenozoic topographic evolution of the catalan coastal ranges ne spain and the role of fault activity erosion sedimentation and isostasy in controlling uplift and subsidence a forward numerical model constrained by an extensive geological and geophysical data set is used to examine the temporal and spatial record of cenozoic vertical motions we show that the effect of isostasy erosion and sedimentation is as important as the contribution of fault deformation to the topography of the catalan coastal ranges the model predicts that paleogene topography generation by thrusting was compensated by erosion up to 1 3 km and isostatic subsidence up to 1 2 km resulting in a 1 2 1 9 km high mountain range by the end of compression 29 ma during the neogene strong tectonic subsidence related to normal faulting and the consequent flexural uplift of 0 7 1 2 km surface erosion as much as 1 6 2 3 km and sedimentation up to 4 5 km led to the present landscape configuration extension rates along the barcelona fault controlled flexural uplift and in combination with erosion and sedimentation processes led to the migration of the topographic maximum of the prelitoral range toward the easternmost ebro basin

unusual features of sediment supply dominated transgressive regressive sequences paleogene clastic wedges se pyrenean foreland basin spain abstract the paleogene marine to nonmarine succession in the southeastern pyrenean foreland basin consists of a series of 3rd order 3 5 m y transgressive to regressive sequences that can be related directly to the stacking and southward displacement of successive basement cover thrust sheets the regressive limbs of the 3rd order clastic wedges are coeval with thrust movement with maximum subsidence developing towards peak regression this relationship between sedimentation and tectonics is sediment supply driven one of these 3rd order wedges which was produced by the montserrat and sant llorenc del munt fan delta systems demonstrates how such steep sloped coarse grained high sediment supply systems generate a hierarchy of transgressive regressive architectures striking features of this rapidly subsiding supply dominated basin margin in addition to the tectonics wedge architecture relationship include the nonperiodic character of the contained high frequency sequences the unusual thickness and landward thickening geometry of transgressive systems tracts a tendency for misfit between alluvial fan and shorezone sectors of sequences a lack of marked incision associated with the tops of coarse grained regressive phases of sequences most of the features are symptomatic of high subsidence rates and very high sediment supply the last feature suggestive of few major relative falls of sea level is also consistent with continuous rapid subsidence however it should be remembered that lack of incision may be a poor indicator for lack of base level fall in a setting where the steepness of alluvial slopes exceeds the slope of the coeval shelf

intraplate deformation in the nw iberian chain mesozoic extension and tertiary contractional inversion the iberian chain developed within the iberian plate during the palaeogene and early miocene as a result of convergence between the african and eurasian plates it is a fold and thrust belt which involves the hercynian basement and the mesozoic and cenozoic cover a generalized cross section of the nw part of the chain of 195 km length is presented mesozoic basins developed on the hercynian basement display thickness variations across normal faults that bounded them and that can be recognized in the field the tertiary contraction deformed and inverted the mesozoic basins and it is inferred to have produced a thrust sheet about 5 km thick in its frontal northeastern part which thickens to the sw the total tertiary shortening in the section is 66 6 km 26 the structure and the crustal shortening and thickening of the iberian chain are explained by a major upper crustal thrust system with simple flat and ramp geometry which may branch to the pyrenees or the betics this is combined with internal deformation of the thrust sheet the contribution of the iberian chain shortening to the convergence of the african and eurasian plates during the tertiary is about one half of that of the pyrenees and should be taken into account in any reconstruction of the kinematics of these plates

lithospheric weakening during retroforeland basin formation tectonic evolution of the central south alpine foredeep beginning with the late cretaceous convergence between europe and adria caused the southward subduction of the european plate beneath adria contractional movements at high crustal levels were partly accommodated by southward thrusting southern alps causing flexure of the loaded adriatic plate and the formation of the late cretaceous to late miocene south alpine foredeep with respect to the alpine subduction system the south alpine foredeep is a retroforeland basin in the late paleogene dip values of the base foredeep varied between 3 and 5 the shallower dips were found along profiles crossing domains which had undergone extension during previous late triassic to middle jurassic rifting with ongoing convergence the base foredeep along the entire basin steepened and dip values in the tortonian are of about 7 8 the increase in dip goes hand in hand with an increase in the curvature of the loaded plate this suggests a progressive weakening of the flexed plate modeled effective elastic thickness te values derived from the analysis of plate curvatures decrease from 15 20 km in the late paleogene to 5 km in the tortonian preconvergence values obtained from modeling studies were even higher in the 24 27 km range a practically complete decoupling of the upper middle crust from its mantle substratum enabled the increase in curvature of the hinge zone the progressive weakening of the south alpine lithosphere around the bulge zone is correlated with the its upper plate position with respect to the alpine subduction system

tectonic and climatic controls on the development of foreland fan deltas montserrat and sant llorenc del munt systems middle eocene ebro basin ne spain abstract along an early cenozoic foreland hinterland boundary in northeastern spain we synthesize the depositional environment climatic conditions structural evolution age catchment geometry and altitudinal characteristics from sedimentologic palynologic stratigraphic structural and paleomagnetic data as the transpressional catalan coastal ranges rose during the paleogene two large fan deltas prograded into the ebro foreland basin adjacent to the northeastern part of the range the apices of the fans likely were localized by lateral ramps or tear faults along which rivers from hinterland catchments debouched into the foreland beginning in the late lutetian proximal debris flow sheetflood and distal fluvial deposits maintained the fan surface at or above sea level despite rapid basin subsidence during the succeeding 4 4 my palynological data suggest that a warm humid climate prevailed throughout this interval the mapped extent of the two fans permits an estimation of their volumes whereas the spatial distribution of distinctive lithologies within the ancestral catalan coastal ranges serves to delimit the approximate catchment areas for each of the fans we estimate mean hinterland denudation rates to range from 100 to 180 m my and mean catchment elevation to range from 700 to 1250 m the steep gradients between these catchments and the low lying fan deltas is attributed to the tectonic style of the ancestral catalan coastal ranges which are characterized by an uplifted basement block along a steep frontal thrust accompanied by folding of cover rocks the considerable topographic relief of these catchments is inferred to have combined with co seismic shaking to produce landslides and rockfalls which were reworked as debris and fluid gravity deposits on the fan surfaces

dating the northern deposits of the ebro foreland basin implications for the kinematics of the sw pyrenean front abstract dating the sedimentary infill of the northern margin of the ebro foreland basin informs about the orogen basin evolution a magnetostratigraphic section of 5 km thick combines new magnetostratigraphic results from the syntectonic alluvial uncastillo fm upper oligocene lower miocene 1 km thick the fuencalderas section with previous 3 3 km thick and new 0 7 km thick magnetostratigraphic data from the underlying fluvial campodarbe fm luesia and san marzal sections eocene oligocene this composite section allows dating the entire basin infill in this sector therefore bracketing the timing of the deformation in the southern margin of the pyrenees after considering previous kinematic studies deformation recorded by the continental deposits spans from syn gavarnie nappe activity broto and fiscal basement thrust sheets from 31 3 to 24 55 ma rupelian chattian oligocene to the syn guarga thrust activity from 24 55 to 21 2 ma chattian aquitanian oligocene miocene the accumulation rates vary from ca 22 to ca 39 cm kyr between the genetic stratigraphic units in the uncastillo fm through the section these rates are close to those of the underlying deposits of the campodarbe fm average of ca 36 cm kyr deformation for the latest pyrenean front syn guarga thrust is younger than previously assigned in 5 4 1 5 and 1 1 myr of the beginning of the punta comun thrust sheet from 29 4 ma to 24 ma lower riglos thrust sheet system from 24 to 22 5 ma and the upper riglos thrust system 22 5 to 21 4 ma respectively other significant changes in accumulation rate and its derivative also indicate variations in the tectonic activity ca 33 and 28 ma

complex tectonic and tectonostratigraphic evolution of an alpine foreland basin the western duero basin and the related tertiary depressions of the nw iberian peninsula abstract the tectonic and tectonostratigaphic evolution of foreland basins and related tertiary depressions are the key to investigate deformation history and the uplifting of the continental lithosphere of the alpine pyrenean orogeny the northern part of the duero basin is the foreland basin of the cantabrian mountains which are in turn the western part of the pyrenean orogen we have studied the western sharp end of the duero foreland basin and its relation to the tertiary deposits of the nw iberian peninsula and the topography evolution in order to propose a coherent tectonic and tectonosedimentary model that could explain all tertiary deposits we have analysed the depositional environment stratigraphic sequences paleocurrents and established a correlation of the main outcrops besides a detailed structural mapping of the alpine structures that limit and affect the main tertiary outcrops has been carried out the tertiary deposits of the nw iberian peninsula depressions are affected and fragmented by alpine structures that limit their extensions and locations the stratigraphic succession is similar in the nw tertiary outcrops they are mainly terrigenous and carbonated continental deposits formed by assemblage of alluvial fans developed at the mountains front in arid or semiarid conditions three formations can be identified in the main depressions toral fm santalla fm and medulas fm the nw tertiary outcrops were the western deposits of the duero foreland basin that surrounded the lateral termination of the pyrenean orogen these deposits were fragmented and eroded by the subsequent uplift of the galaico leoneses mountains and the ne sw strike slip faults activity broken foreland basin only the latest stages of some of these outcrops can be considered as intramontane basins as traditionally have been interpreted the sedimentation started in the northeast oviedo infiesto during the eocene and migrated to the west as pontes during the late oligocene early miocene times meanwhile southern areas were far away from the tectonic activity el bierzo o barco monforte sarria depressions

decoupling of foreland basin subsidence from topography linked to faulting and erosion many mountain ranges in regions of plate convergence are flanked by foreland sedimentary basins that are usually thought to result from flexing of the elastic lithosphere under the passive weight of sediments and thrust sheets emplaced in the mountain belt however in some places the depth of the foreland basin bears little relation to the weight of basin sediments and neighboring mountains implying that this model is too simple and or that additional forces must affect subsidence here i investigate this problem using a numerical model that incorporates coupling between an upthrusting mountain range and a subsiding basin i show that only part of the subsidence reflected in the shape of a foreland basin is a flexural isostatic response to crustal thickening and sediment loading the remaining subsidence results from dragging of the basin margin downward by slip on a range front fault and related flexural deformation of the surrounding lithosphere the maximum basin depth is shown to increase with increasing fault displacement and can become decoupled from the elevation of the mountain range especially as erosion becomes increasingly important deeply eroded model mountain belts may have foreland basins several times deeper than flexural models predict on the basis of surface loads these results challenge the prevailing view that fault bounded foreland basins result solely from the passive weight of mountains and sediments acting on the lithosphere and they highlight that slip on major range front reverse faults when repeated over many earthquake cycles may be recorded in their geometry and stratigraphic records

cyclicity and basin axis shift in a piggyback basin towards modelling of the eocene tremp ager basin south pyrenees spain

first u pb detrital zircon ages from numidian sandstones in southern apennines italy evidences of african provenance abstract two samples of quartz rich sandstones collected in the numidian flysch of southern apennines italy have been studied to highlight the provenance of detritus using radiometric dating by la icp ms of detrital zircons and to compare the obtained ages with those of the betic and maghrebian chains the provenance of quartzose detritus from european or african plates is still debated in these chains accordingly the ages of the detrital zircons can contribute significantly to discriminate the origin of the quartzose supply the u pb zircon ages n 47 vary from 3047 13 ma mesoarchean to 516 19 ma cambrian the predominance of paleo proteozoic ages 2500 1600 ma and the lack of hercynian and alpine ones suggest a provenance of the numidian supply from north african cratonic areas during the early middle langhian when the numidian successions of southern apennines were deposited in addition a cluster of ages at 773 24 ma and 668 12 ma in one sample and at 664 17 ma in the other sample calculated on zircon domains with magmatic zoning testify to an important contribution from neo proterozoic granitic rocks widely outcropping in the north african craton the age data on detrital zircons from numidian sandstones in southern apennines overlap those found in the numidian sandstones widespread in the betic cordillera and in the maghrebian chain from south spain to sicily this suggests that the entire depositional zone in which numidian flysch deposited was fed from a southerly source represented by the african craton where archean proterozoic and cambrian rocks widely crop out from the atlantic coast to the hoggar and tibesti massifs finally it must be outlined that a meso archean zircon age 3047 ma has been found in the numidian flysch of the southern apennines whereas in the numidian flysch of the maghrebian chain zircons older than paleo proterozoic 1840 ma have not yet been found

implications of the seismic structure for the orogenic evolution of the pyrenean range abstract the dynamic evolution of the pyrenees is discussed in the light of geophysical data recent deep seismic sounding have revealed the crustal structure of the pyrenees which is used to test the different evolutionary models proposed until now the crustal thickness of the paleozoic axial zone paz and the north pyrenean zone npz differ by more than 10 km ranging from about 30 km in the npz to 40 50 km in the paz the transition from paz to the npz identified at the surface as the north pyrenean fault npf is sharp at depth and marked by a vertical step at least in the eastern half of the range the npz is characterized by additional throws and dips of the moho in the east whereas in the west a heterogeneous middle to lower crust is encountered with high velocity anomalies the seismic results suggest that the paz and the npz belong to different plates the npf being the plate boundary these results are inconsistent with evolutionary models involving lithospheric subduction or crustal doubling and intracratonic rifting with the main tectonic lineations following nne ssw directions they rather suggest that after a period of extension two main orogenic events took place a phase involving shearing and thinning which affected mainly the present day npz and a later compressive phase which explains the building up of the chain the thickening of the crust and the enhancement of a pre existing difference in crustal thickness between the european and iberian plates

triaxial tests on snow at low strain rate part ii constitutive behaviour fine grained dry snow with a density range of 190 435 kg m 3 was tested in triaxial compression at 12 c with confining pressures varying between 0 and 40 kpa the tests were strain rate controlled with strain rates ranging between 7 4 x 10 7 s 1 and 6 6 10 5 s 1 the analysis of the test results revealed that the relationship between yield stress and viscous strain rate is best given by a power law similar to polycrystalline ice however the power law exponent n is a function of density and varies between 1 8 low density snow p 320 kg in 3 the tests also showed that lower density snow displays a significant non linear stress strain response before yielding two further aspects of the constitutive behaviour of snow were identified 1 the strain rate independence of the post yield work hardening behaviour in compression and 2 the independence of the axial yield stress in relation to the confining pressure the experimental observations are discussed with respect to the mechanical properties of polycrystalline ice which is the constituent material of the load bearing ice skeleton

a synthetic stratigraphic model of foreland basin development the processes of erosion and deposition must be included in foreland basin models to predict correctly basin geometry and stratigraphy we present a synthetic stratigraphic model of the development of nonmarine foreland basins that predicts progressive geometry topography and facies patterns in the model steady crustal shortening occurs according to a wedgethickening model erosion and deposition follow a diffusive process and the lithosphere is compensated elastically erosion and deposition are controlled by the transport coefficients r of the diffusion equation for a range of thrust velocities and lithospheric rigidities transport coefficients are of order 102 103 m yr in the mountain belt these values are much higher than those derived from the study of scarp degradation in the sedimentary basin transport coefficients of order 104 m2 yr are appropriate and are compatible with previous studies of fluvial and deltaic deposition rapid thrusting results in a narrow underfilled basin while slow thrusting results in a wide overfilled basin in addition by varying the erosional and depositional transport coefficients while holding other parameters constant we generate both overfilled and underfilled basins these results suggest that changes in the rate of thrust loading the climate or the source rock lithology can create stratigraphic signatures that have been interpreted to record viscoelastic relaxation of the lithosphere clearly to understand either the long term behavior of the lithosphere or to interpret orogenic history from preserved foreland strata the manner in which a basin was filled must be considered we apply the model to the evolution of the modern sub andean foreland and find that an erosional transport coefficient of 3000 m2 yr and a depositional transport coefficient of 20 000 m2 yr successfully predict the observed basin geometry

three dimensional flexural modelling of the ebro basin ne iberia summary the ebro basin the southern foreland basin of the pyrenees has undergone a complex evolution in which apart from the pyrenees the iberian range and the catalan coastal ranges have played an important role both as sediment sources and as basin confining structures the deflected basement underlying the ebro basin dips north suggesting a lithospheric scale control on the structure of this basin this is compatible with the results of subsidence analyses which show that the study area is not in a local mode of isostatic compensation in order better to understand the mechanisms that led to the present configuration of the ebro basin and particularly the relevance of the various kinds of un loading e g surrounding fold and thrust belts basin topography subsurface loads we carried out a 3 d kinematic modelling study that accounts for the flexural state of the lithosphere subjected to various loads applied at its lateral boundaries and the sedimentary fill of the basin we also included the effect of neogene extensional tectonics along the eastern basin margin which is related to the opening of the valencia trough we show the suitability of the 3 d lithospheric scale flexural modelling approach to the study of ne iberia modelling results point to a relatively strong lithosphere in this area with values of effective elastic thickness ranging from 10 to 35 km in the ebro basin increasing towards the pyrenees we also find that the topographic tectonic load itself is insufficient to explain the observed basement deflection thus an extra subsurface load beneath the pyrenees corresponding to the underthrusted iberian lithosphere is required the effect of lithospheric stretching in the valencia trough on the ebro basin is appreciable only in its eastern part where the lithosphere was uplifted this had considerable repercussions on the sedimentary and erosional regime of the ebro basin we have analysed the link between the stretching related tectonically uplifted areas and the erosional patterns observed onshore northeast iberia

late cretaceous to late eocene palaeogeographic evolution of southwest europe abstract a synthesis of personal research concerning the peri pyrenean region and previously published data is presented as a series of palaeogeographic reconstructions subsequent to the progressive regression at the end of the cretaceous the sea invaded three times parts of the earlier senonian marine domain on both sides of the eastern palaeo pyrenees pre cuisian climatic rewarming combined with cuisian continental epeirogenic deformations resulted in major biogeographic modifications during the cuisian local tectonics forced the sea from the northern pyrenean basin whereas in the southern pyrenean basin the sea retreated much later as a consequence of the pyrenean tectonic phase however the pyrenean tectogenesis seems to have affected a much larger region including the alps shoreline migrations are compared and related to the geodynamic behaviour of the meridional and septentrional european provinces in order to distinguish between tectonic and eustatic causes

geological evidence for a global tectonic polarity inferences about plate motions over the past 40 ma based on structural and geodetic data suggest that there is a coherent movement direction on a global scale moreover a westward drift of the lithosphere relative to the asthenosphere is indicated by plate motions in the hot spot reference frame independent geological observations such as the different styles of deformation in thrust belts associated with subduction following or opposing the relative eastward or northeastward mantle flow also support this global tectonic polarity unfortunately most hot spot reference frames are based on assumptions which strongly limit their validity for example many combine magmatic sources originating from different depths in the mantle including hot spots located along oceanic ridges which are not fixed relative to one another using a hot spot reference frame filtered to exclude shallow hot spots and anomalous wet spots we would predict a much higher relative westward drift of the lithosphere plate motions are not random rather that they are controlled by the relative motion between lithosphere and asthenosphere and by gradients in lithospheric thickness and composition triangular shaped plates may experience rotations resulting from differential drag at the base of the lithosphere with respect to the asthenosphere e g the clockwise rotation of south america plates appear to follow an undulatory pattern of motion on a global scale and their poles of rotation fall into a main cone located near the earth s rotation poles plate rotations induced by triangular shape differential basal drag or lithospheric anisotropies along subduction zones may generate the scattered distribution of euler poles this might have inhibited the recognition of a coherent global tectonic pattern

structural controls on sedimentary basin evolution introduction this volume contains a collection of papers on structural controls on sedimentary basin evolution presented at the sixth annual workshop of the international lithosphere program task force origin of sedimentary basins in sitges at the rim of the ebro basin september 1995 previous workshops of the ilp task force had been in rueil malmaison france 1990 in matrahaza hungary 1991 on the rim of the pannonian basin in sundvollen norway 1992 in the oslo graben in benevento italy 1993 in the southern apennines fold andthrust belt and in the dead sea rift of israel 1994 the task force also organized a number of sessions during the 1992 and 1996 european geophysical society and the 1993 and 1995 european union of geosciences conferences reports of these meetings have been published in a number of special volumes and papers cloetingh et al 1993a b 1994 1995a b 1996 stephenson 1993 stephenson et al 1996 a position paper cloetingh sassi and task force team 1994 published in m a r i n e a n d p e t r o l e u m geo logy has outlined the task force strategy to pursue the development of a new generation of basin models using natural laboratories with high quality data sets obtained through close partnership with industry the 7th task force workshop was held on the faroe islands northern atlantic in 1996 with the aim of examining the dynamics of rifting

lithospheric folding in iberia integration of stress indicator data gravity data crustal kinematics data and analysis of topography and recent vertical motions demonstrates the occurrence of consistently oriented spatial patterns of large scale alpine to recent intraplate deformation in iberia the inferred upper crustal and lithospheric deformation patterns and the timing of the associated expressions at or near the surface support the existence of a close coupling with plate boundary processes operating at the margins of iberia patterns of lithosphere and upper crustal folds are oriented perpendicular to the main axis of present day intraplate compression in iberia inferred from structural analysis of stress indicator data and focal mechanism solutions these findings suggest the presence of lithospheric folds with wavelengths compatible with theoretical predictions of folding wavelengths of variscan lithosphere stress induced intraplate deformation set up by plate interactions is compatible with indications for the absence of present day deep mantle lithosphere interactions inferred from seismic tomography

palaeogene evolution of deformation in the northeastern iberian peninsula during the palaeogene alpine compression three units were differentiated in the studied area south of the ebro basin the catalan coastal range dominated by ne sw major basement faults with a sinistral movement the iberian range where the important basement faults have a nw se direction and a reverse movement often with a dextral component the linking zone between these two ranges where an e w dominant structural direction is marked by an array of folds and thrusts with a northward vergence in the mesozoic cover from the analysis of both these major structures and the small scale structures it can be deduced that the compression in the studied area has evolved from a nw se direction lower middle eocene to a n s direction and to a ne sw one uppermost oligocene the major structures are due to the n s compression later the stress field progressively changed to a distensive regime we suggest a relation between the compressive phases and the displacement direction of the iberian plate with reference to the european plate

two sided orogen collision and erosion from the sandbox to the southern alps new zealand in continental collision zones the indentor is of approximately the same vertical dimension as the material being deformed thereby allowing material to move over the indentor and out of the deforming orogen this simple constraint on the height of the indentor differs from that imposed by the bulldozer model of wedge deformation and results in the formation of an orogen with two opposite dipping topographic slopes these two wedges are mechanically coupled and the mechanics are strongly influenced by the erosion conditions imposed on the wedge where the growing mountains perturb prevailing moisture laden winds the erosion pattern is highly asymmetric erosional work being concentrated at the toe of the steep wedge facing the indentor the inboard wedge concentration of erosional energy results in concentration of mechanical energy in the same region and produces the distinctive geological and geophysical patterns associated with continental collision these include rapid uplift and exposure of deep crustal assemblages adjacent to the indentor accompanied by high crustal heat flow and anomalously low seismicity the outcrop pattern along the inboard wedge evolves from that of a crustal cross section currently exposed in the southern alps to one dominated by repetitive nappe structures consisting predominantly of lower crustal units as in the western alps of europe the other wedge the outboard wedge undergoes relatively little erosion is broad with a more gentle surface slope and maintains an outcrop pattern consisting of upper crustal material

the influence of the evolution of the pyrenees on adjacent basins abstract important thicknesses of syn and post orogenic sediments are observed in the southern part of the aquitaine basin and in the north of the ebro basin their deposition cannot be explained only as a result of the extensional history of the early cretaceous thus the influence of the compression associated with the pyrenees formation upon the subsidence of these basins is studied europe and iberia are considered to behave as two semi infinite elastic plates the evolution through time of the sedimentary thicknesses is explained by the deflections of these two plates induced not only by the topographic load of the pyrenees but also by additional forces 10 12 n m that may have their origin in the formation of a cold lithospheric root during the shortening a series of calculations is presented for an approximately north south profile across the aquitaine basin the pyrenees and the ebro basin a good fit for the shape of the basins and the gravity anomalies was obtained with flexural rigidities of 1 5 10 23 nm for the northern plate and the outer part of the southern plate and 1 4 10 21 nm for the inner part of the southern plate

thrust tectonics in the north pyrenees abstract balanced and restored cross sections through the central and eastern pyrenees constructed using both surface and borehole data demonstrate the presence of c 18km of shortening above a flat lying n directed alpine decollement surface hangingwall diagrams show how the north pyrenean satellite massifs are culminations within this thrust system pre thrusting structures such as subhorizontal stretching lineations in the north pyrenean fault zone became rotated above these culminations as the north pyrenean fault was cut by alpine thrusts stratigraphic evidence demonstrates that n directed thrust movements occurred between mid eocene and oligocene time and this is similar to the age of major s directed thrust movements on the south side of the axial zone the n directed thrust system probably originated as a series of backthrusts to the dominant s directed structures

large scale facies change in the middle eocene south pyrenean foreland basin the role of tectonics and prelude to cenozoic ice ages abstract the present study reports a sedimentological analysis of the guara limestone formation deposited during the lutetian in the sierras exteriores in the south pyrenean foreland basin we provide a detailed facies analysis of the carbonates to precise the paleoenvironmental context during their deposition we show that those limestones are mainly composed of shallow water foraminifers and were deposited in relative shallow water environments

the ecors deep reflection seismic survey across the pyrenees the pyrenees are an alpine age mountain belt located on the boundary between the iberian and european plates using the same geological and geophysical data earth scientists studying the structure of the pyrenees during the past ten years have not reached a consensus here we report the first results from a nearly continuous 255 km long reflection seismic survey across the pyrenean chain this first deep reflection profile of an entire erogenic belt will help to constrain possible models for the structure and formation of the pyrenean chain

triaxial tests on snow at low strain rate part i experimental device a deformation controlled triaxial apparatus has been developed in order too investigate the mechanical behaviour of alpine snow cylindrical specimens 58 mm in diameter 126 mm in height can be axially deformed by applying tensile or compressive strain rates between 2 4 10 7 s 1 and 2 4 10 2 s 1 compressed air is used to laterally load the snow specimens with pressures of up to 40 kpa the volumetric deformation is found by carefully encapsulating the snow samples in an airtight mylar foil and measuring the expelled pore air during sample deformation the multidimensional stress strain behaviour can therefore be determined and constitutive theories of snow advanced the device is located run the cold rooms of the weissfluhjoch research station of the swiss federal institute for snow anti avalanche research seine 180 tests have been performed over the last four winters the density of the snow specimens varied between 190 and 435 kg m 3 part i of this two part paper discusses the development of the apparatus and the applied testing methodology qualitative results are provided in part ii a detailed analysis of the results is presented and the viscoclastic properties of snow quantified