constraints on the deep structure and dynamic processes beneath the alps and adjacent regions from an analysis of gravity anomalies summary gravity anomalies including terrain corrections over the western alps and the molasse basin are within 30 mgal of those calculated assuming local airy isostatic equilibrium but isostatic anomalies over regions nw and se of the alps exceed 50 mgal therefore mass excesses and deficits that must be supported by the strength of the lithosphere or by dynamically induced stress in the asthenosphere appear to be greater beneath the areas surrounding the alps than beneath the alpine chain itself attempts to account for the gravity gradient over the molasse basin and sub alpine chains and the small bouguer anomalies measured over the elevated areas of the vosges and black forest by the flexure of an elastic plate require an absurd set of parameters the high elevations of the vosges and the black forest are presumably due to high temperature in the underlying uppermost mantle but the deviations from isostatic equilibrium as well as the high temperature probably result from active upwelling in the asthenosphere beneath this area the absence of large isostatic anomalies over the alps and the failure of an elastic model to account for the gravity anomalies over the molasse basin suggest that the dynamic processes that flexed the european plate down to form the molasse basin and that built the alpine chain have waned the late cenozoic uplift of the molasse basin and the alps might be a consequence of a diminution or termination of downwelling of mantle material beneath the alps

the density contrast at the mohorovicic discontinuity summary the compilation of new global mohorovicic moho topographic data enables us to estimate the density contrast between the crust and mantle assuming that this contrast is constant the minimization of the external gravitational potential induced by the earth s topographic masses and the moho discontinuity gives the value of 0 28 gcm 3 for the density jump at the moho under the continental areas for the oceanic areas where the information about the moho depths is unavailable or poor the procedure has not been applied

3 d density model of the crust of southern and central finland obtained from joint interpretation of the svekalapko crustal p wave velocity models and gravity data 3 d density model of the crust of southern and central finland obtained from joint interpretation of the svekalapko crustal p wave velocity models and gravity data

searching for regional crustal velocity density relations with the use of 2 d gravity modelling central europe case in this paper we search for a reference relation between seismic p wave velocity v and density ref for the continental crust based on the results of modern seismic experiments we compiled 2 d seismic models into a network of four each about 1100 1400 km long continental scale seismic transects cutting all main tectonic units in central europe the moho depth about 52 km beneath the tesz in se poland to about 25 km beneath the pannonian basin and the crustal structure of this area are characterised by a large variation this structural variation provides an interesting basis for gravity studies and especially for analysing the difference of the density structure between two major tectonic provinces of distinctive age difference precambrian and phanerozoic the 2 d gravity modelling applied for crustal cross sections representing the regional structure based on a unified gravity anomaly map of the area allows for a stable determination of some general features of the regional reference velocity density relation for the continental crust in general three major seismo petrological types of rocks can be distinguished sediments crystalline crust and mantle in compacted sediments the reference velocity density relation is well described by the gardner or nafe drake model calculated gravity anomalies using unified velocity density relation for the whole crystalline crust well describe observed anomalies with an average difference of 14 mgal however calculated gravity anomalies using separated velocity density relations for the crystalline crust of precambrian and phanerozoic europe describe observed anomalies better than for the entire crust with an average difference 12 mgal the most important feature of these relations is the large differentiation of the derivative d ref dv in the crystalline crust being about 0 3 g s m4 for precambrian and about 0 1 g s m4 for the phanerozoic crystalline crust the modelling suggests a very small density value in the uppermost mantle 3 11 g cm3 below the younger area while for the older area it is 3 3 g cm3

tilting uplift volcanism and disintegration of the south german block abstract we present a large set of fault slip data together with six u pb ages on calcite vein fillings constraining the kinematics and timing of near surface uppermost 2 3 km of crust faulting of the uplifted south german block in the northern foreland of the nw ward advancing alps the structural data confirm earlier studies showing miocene subhorizontal ne directed extension with shortening mainly being subvertical but also subhorizontally nw oriented the u pb ages are between 15 3 0 2 and 2 3 1 1 ma 2 analytical uncertainty and date kinematically coordinated normal and strike slip faulting in the northern alpine foreland the faults in the south german block have limited strike lengths indicating that they do not cut deeply into the crust however the faults appear to control volcanic centers the melts of which originated at the base of the lithosphere we suggest that the miocene faults could tap the mantle because they reactivated formerly deep seated faults the ages for near surface faulting are coeval with eruption of the urach and hegau volcanics published data suggest that alpine shortening induced large wavelength lithospheric folding in the foreland since 18 16 ma volcanism in the south german block focussed along a lithospheric antiform which is in part superimposed on the foreland bulge of the alps we propose a close link between progressive southward tilting uplift and faulting of the south german block due to lithospheric scale folding and upward flow of the asthenosphere flexure of the lithosphere deep seated volcanism and the nw ward advancing alps

the rhinegraben extension subsidence and shoulder uplift abstract we apply a numerical model of the thermal evolution of a continental lithosphere undergoing extensional deformation to the rhinegraben using reasonable parameters the results of computations are in agreement with the present configuration of the rift and of its shoulders as well as with their evolution since the oligocene contrasting evolutions are reconstructed in the northern and southern rhinegraben whereas the northern history is accounted for by a simple model of homogeneous stretching of the lithosphere the history of the southern rhinegraben cannot be explained without introducing two main periods of heterogeneous stretching the results are locally supported by structural analyses of extensional patterns factors of extension average 1 2 in the axial portion of the rhinegraben and 1 15 for the whole rift section suggesting that the total amount of e w extension reaches 6 km

crustal structure and dynamics in the rhine graben and the alpine foreland summary the rhine graben rift stretches for 300 km from basel to frankfurt the axis of maximum subsidence switches from west in the southern graben to east in the northern graben subsidence in the south began in the upper eocene and was interrupted in the mid miocene by a broad uplift of 1 1 5 km in the vosges schwarzwald black forest region whereas subsidence in the north proceeded continuously from the lower oligocene to the present a combined geophysical and geological interpretation of the rhine graben is presented in the form of a 3 d gravity model and 2 d flexural plate modelling from the alps across the alpine foreland to the rhenish massif modelling is based on crustal structure revealed by geologic gravity and seismic data including ecors dekorp and egt profiles the 3 d gravity modelling supports a modest density contrast of 0 3 g cm 3 at the crust mantle boundary since there is no evidence of a large scale upper mantle anomaly a dense lower crust 2 9 3 0 g cm 3 is proposed as the cause of this modest density contrast the presence of a dense mafic lower crust in south west germany is corroborated by lower crustal xenoliths elevated p wave velocities 6 7 7 2 km s 1 and high poisson s ratios 0 26 0 29 residual gravity and magnetic data reveal strong crustal heterogeneities particularly from the dense magnetic saxothuringian terrane to the light non magnetic moldanubian terrane the polarity of the asymmetric rhine graben reverses at this variscan tectonic boundary light graben fill can account for nearly the entire 20 40 mgal short wavelength gravity minimum but the presence of intrusive bodies ranging from granitic to mafic composition can also strongly influence the local gravity field 2 d modelling of the flexure of the european lithosphere along seven 1000 km long profiles indicates a flexural bulge of 1 1 5 km in the alpine foreland of southern germany which corresponds to an ene trending moho uplift of the same magnitude and to a band of free air gravity highs longer flexural wavelengths in the east indicate increasing lithospheric rigidity and increasing elastic thickness towards the bohemian massif the vosges schwarzwald dome is interpreted as the intersection of the oligocene rhine graben rift and associated rift flank uplift with the mid miocene flexural bulge

contrasts of seismic velocity density and strength across the moho abstract we provide an overview of contrast of elastomechanical parameters across the moho basically contrasts in seismic wave velocities density and yield strength these can be regarded as dynamic and quasi static endmembers of elastomechanical parameters of the crust mantle transition with respect to practical applications they are closely related because seismic investigations play the role of exploring the earth structure and physical state forming the boundary conditions for determining density and rheological models we address both average global moho models and petrophysical and structural factors that cause deviations from the global averages such as variations in moho depth temperature and rock composition fabric anisotropy and macro scale heterogeneity besides principle considerations these factors are put in a regional context in order to demonstrate how they are related to past and present tectonic processes seismic velocity and density contrasts are found between 0 and 25 whereas strength or viscosity contrasts may be orders of magnitude higher but may vanish as well or show a discontinuity of higher order only especially oceanic and old cratonic crust and near moho mantle may appear as a rheological unit although they are seismically well distinguishable in terms of seismic velocities the moho may vanish mainly under the influence of serpentinization or eclogitization originally defined as a first order discontinuity in seismic velocity the moho has turned out to be an interface across which other seismic properties such as seismic velocity gradients anisotropy and heterogeneity scale parameters can change strongly too however knowledge of these parameters as well as their relation to the rheology of the crust mantle transition is still restricted to local or regional examples so no global conclusions can be drawn

a deep reflection seismic line across the northern rhine graben abstract two reflection seismic lines across the tertiary rhine graben in central europe were recorded in 1988 as a joint venture of the french ecors and the german dekorp deep seismic reflection programs in this paper the line across the northern graben is presented the main results are the asymmetry of the graben as documented by the sedimentary fill is accompanied by asymmetric features throughout the entire deep crystalline crust a thin 3 7 s twt reflective lower crust in the east a thick 5 5 s twt relatively transparent lower crust in the west total crustal thicknesses of 8 7 s twt in the east vs 10 5 s twt in the west provided a laterally homogeneous crust existed prior to rifting significant differences in upper and lower crustal thinning must be postulated extension occurred along localized shear zones that are located in the upper crust and at the crust mantle boundary the entire lower crustal layer acts as a decoupling zone

results of nfp 20 seismic reflection profiling along the alpine section of the european geotraverse egt summary recent deep crustal seismic reflection profiling across the central alps of eastern and southern switzerland has provided a detailed image of this continental collision zone as part of the swiss national science project nfp 20 a series of reflection profiles was recorded during two phases along n s transects crossing the alpine edifice the eastern and southern profiles coincide with the alpine segment of the european geotraverse egt and in part with the earlier swiss geotraverse these data together with other geophysical and extensive geologic information form a unique and comprehensive volume of crustal information for this region of the alps on a larger scale the new reflection data also add to a growing set of profiles crossing the alpine fold belt which includes an additional traverse carried out by nfp 20 across the western swiss alps and the ecors crop profile across the western alps the initial results of the reflection data across the central alps outline a crustal framework involving northward indentation of the adriatic hinterland into the subducting european foreland this occurs beneath the collapsed oceanic basins of the penninic allochthon which is defined by its highly reflective crystalline nappes the present crustal thickness within the alpine collision zone has doubled to about 60 km by both vertical and horizontal displacements along an inferred complex detachment system controlled by the adriatic wedge the south plunging european foreland implies that portions of the thickened crust have been subducted into the upper mantle this general framework of flake tectonics is laterally consistent with the ecors crop results from the western alps however the western alps show a higher degree of crustal imbrication which may be related to the presence of the rigid ivrea body and an overall greater amount of crustal shortening compared to the central alps

kinematic and geometric analysis of fault related folds in a rift setting the dannemarie basin upper rhine graben france abstract the upper rhine graben urg developed in the alpine foreland from mid eocene to pliocene as part of the west european rift system the dannemarie basin occupies the sw termination of the urg and is bordered by the vosges fault zone west and the illfurth fault zone east we constructed a 3d model of faults and principal pre and syn rift stratigraphic surfaces using all available subsurface and surface geological and geophysical data the model shows 1 syn rift strata thinning across kilometre scale fault parallel monoclinal flexures associated with basin margin faults and 2 major basin margin faults terminating laterally into major flexures sequential cross section restorations show that these flexures accommodated deposition of over 1300 m of syn rift strata salt series which is 42 63 of the basin fill these folds are interpreted as syn rift fault propagation folds that developed above normal faults their geometry is replicated in a trishear numerical model using reasonable parameter values fold development was controlled principally by 1 reactivation of favourably oriented basement faults 2 the presence of a thick viscous layer principally triassic evaporites allowing decoupling between crystalline basement and competent jurassic cover and 3 a relatively slow deformation rate

geometry of propagating continental rifts reconstruction of past plate configurations through palinspastic restoration of continental margins1 4 requires a detailed knowledge of the geometries of horizontal continental extension extension is often restricted to discrete linear zones termed rifts5 6 and rift models that invoke propagating vertical dykes and cracks7 10 are useful for assessing the relative significance and timing of uplift subsidence and extension in the tectonic evolution of rift basins however many models do not adequately account for the observed asymmetry of rifts i describe here the general three dimensional character of young and aborted continental rifts which can be used to derive a structural model for the propagation of rifts in continental lithosphere the rifts become asymmetric as a consequence of the role played by low angle normal faults in the overall rift geometry

gravity interpretation along seismic reflection profile dekorp 9 n northern rhine graben a 2 d gravity model incorporating geophysical and geological data is presented for a 110 km long transect across the northern rhine graben coinciding with the 92 km long dekorp 9 n seismic reflection profile the upper rhine graben is marked by a prominent nne striking negative anomaly of 30 40 mgal on bouguer gravity maps of sw germany surface geological contacts borehole data and the seismic reflection profile provide boundary constraints during forward modelling short wavelength 5 10 km gravity features can be correlated with geologic structures in the upper few km at deeper levels the model reflects the asymmetry visible in the seismic profile a thicker mostly transparent lower crust in the west and a thinner reflective lower crust in the east from west to east moho depth changes from 31 to 26 28 km the entire 40 mgal minimum can be accounted for by the 2 3 km of light sedimentary fdl in the graben which masks the gravitational effects of the elevated moho the thickened lower crust in the west partly compensates for the mass deficit from the depressed moho a further compensating feature is a relatively low density contrast at the crust mantle boundary of 0 25 g cm 3 the variscan must displays heterogeneity along the profile which cuts at an angle across the strike of variscan structures the asymmetry of the integrated crustal model both at the surface and at depth suggests an asymmetric mechanism of rift development

gravity modelling along the southern segment of the european geotraverse from the gulf of genoa to the swiss molasse basin abstract using gravity maps recently published in italy and switzerland we have modelled a profile running along the northern part of the southern segment of the european geotraverse the profile stretches from the ligurian coast east of genova to the swiss molasse basin the gravity modelling took into consideration geophysical cross sections and density contrasts from various sources for all models we kept the parameters for the upper crust constant and varied the options for the gravity effect of the lower crust the upper mantle was considered to be homogeneous based on the data available at the time of writing we make the following conclusions 1 1 the major contribution to the regional anomalies stems from the topography of the crust mantle boundary 2 2 in the southern part of the profile the observed bouguer anomalies can be modelled by a step in the moho beneath the ligurian coast 3 3 in the northern part of the profile a good fit between the observed and calculated bouguer anomalies can be obtained by introducing another moho jump beneath the insubric line 4 4 two models satisfy the measured profile one with a single the other with a double crust mantle transition

correlation between shear wave upper mantle structure and tectonic surface expressions application to central and southern germany we have inverted fundamental mode rayleigh waveforms in the frequency range from 20 to 100 s to obtain a three dimensional s velocity distribution beneath central and southern germany the data come from 27 teleseismic events recorded at 17 broadband stations in germany and adjacent areas this results in 56 paths between pairs of stations each pair lying on the same great circle with an epicenter the phase differences between the waveforms recorded at a pair of stations have been inverted directly for the path averaged s velocity perturbation between the two stations all path models were then combined into a single three dimensional model the most prominent features of the obtained model are 1 low velocities beneath the eger graben which are an expression of the deep reaching rift structure 2 high velocities between 40 and 120 km depth beneath northern bavaria caused by an apparent thickening of the lithosphere toward the south 3 high velocities in the uppermost mantle beneath the southern rhine graben area presently inactive with respect to rifting suggesting the absence of present upwelling hot mantle material and 4 low velocities beneath the presently experiencing rifting northern branch of the central european rift system including the northern part of the rhine graben and the rhenish massif west of the river rhine with the volcanic fields of the eifel these reduced velocities indicate a broad updoming of the lithosphere asthenosphere boundary our model suggests a strong correlation between upper mantle s wave structure at depths down to 200 km and tectonic surface expressions

spatial variations of p residuals and deep structure of the european lithosphere spatial variations of these normalized residuals as large as 2 s were derived from events in different focal regions an average residual at each station was calculated from 23 selected groups compiled from 181 events evenly distributed as to their azimuths and distances the 3 d inversion of the residuals yielded very much the same picture of the relatively high and low velocity provinces for the upper layer of the mantle as compared with the map of average residuals the map of average residuals mainly reflects variations in the thickness of the lithosphere and its thermal state regions of low velocities include the pannonian basin and central carpathians the northern apennines and the po plain as well as the rhine graben the rhenish massif and the north german polish platform high velocities are observed in the south western margin of the east european platform and in three well defined zones situated in the inner part of the western alps in the eastern part of the austrian alps and in the eastern carpathians besides the effects of inhomogeneities also anisotropic effects are anticipated from the spatial diagrams of the residuals which show a similar pattern within large tectonic provinces r

tectonic implications of transpression and transtension upper rhine graben 1 seismic reflection data from the upper rhine graben urg show a series of synclines along the linear eastern boundary faults from north of karlsruhe to the jura mountains similar structures do not characterize the northern segment of the graben the synclinal shape is portrayed by inversion related to transpression on the linear boundary faults coupled with the conserved easterly dip of the sediments farther inside the tilted hanging block the onset of transpression preceded the known early burdigalian unconformity but was also an early miocene event it suggests that the regional compression axis 1 in early miocene had a trend between 315 and 0 the continuous transtension in the northern segment suggests that at no time during the history of the urg was the regional 1 horizontal with a ne sw trend the lack of transpressional structures in the younger plio pleistocene sediments along the entire eastern boundary of the urg suggests a late change in the regional stress field the main eastern boundary faults and synclines north and south of baden baden are all continuous and have the same trend kinematically they form a single graben segment and respond to the regional stress in the same way

deflection gravity anomalies and tectonics of doubly subducted continental lithosphere adriatic and ionian seas three profiles across the southern adriatic and northern ionian seas span an intermediate foreland area that is or has recently been subducted both westward under the apennine calabrian thrust belt and eastward under the hellenide belt gravity and deflection data from the base of the pliocene along the three profiles are qualitatively similar to those predicted for a thin elastic sheet subject to end loads at both plate ends more detailed analysis of the profiles shows very good agreement between observations and predictions if the intermediate foreland lithosphere is treated as a thin elastic sheet with an effective elastic thickness between about 15 and 20 km equivalent to a flexural rigidity between 2 1022 and 6 1022 nm these results coupled with seismicity data suggest that active convergence within the hellenides extends as far north as southwestern yugoslavia analysis of the northernmost profile across the southern adriatic sea shows a well constrained elastic plate thickness of 14 km and an initial water depth prior to loading of about 1 km the distance between the two subduction systems on this profile is estimated at about 275 km analysis of the two more southerly profiles yields a minimum effective elastic plate thickness of about 15 km but no maximum value could be determined the initial water depths for these two profiles are well constrained at 1 3 and 1 6 km prior to loading and the distance between the two subduction systems is estimated at about 175 km on both profiles along the northwest trend of the two opposing subduction systems the change in distance between the two systems occurs abruptly and the hellenic subduction system appears to be segmented into a series of northwest trending roughly linear subduction segments the calculated deflection profiles also show pronounced asymmetry on the northernmost profile and an opposite sense of asymmety on the southernmost profile

crustal evolution of the rhinegraben area 1 exploring the lower crust in the rhinegraben rift by unified geophysical experiments abstract unified geophysical investigations of the lithosphere in the rhinegraben rift system have revealed new details of the lower crust and its role in the rifting process the new findings allow an assessment of the compatibility of four different geophysical notions and properties of the lower crust 1 1 the lower crust as the layer beneath the conrad discontinuity with a p wave velocity of about 6 5 km s or greater refraction seismics 2 2 the laminated band of reflections as seen in the near vertical reflection seismic experiments in many parts of the continents 3 3 the ductile part of the crust below the brittle ductile transition devoid of earthquakes in seismically active regions 4 4 the electrical conductivity of the lower crust indicative of dry or wet conditions or still unknown conduction phenomena in the rhinegraben area the lamination of the lower crust serves as an outstanding marker of deep tectonic activity during the rifting process in which the crust of the rhinegraben rift system has been subjected to three different natural dynamic processes 1 uplift by 2 to 3 km with subsequent erosion of the rhinegraben shoulders black forest and vosges mountains caused decompression possibly leading to the formation of a low velocity high electrical conductivity zone right on top of the laminated lower crust beneath the elevated shoulders of the black forest 2 the brittle crystalline wedge of the graben proper subsided nearly undeformed into the lower crust which became about 5 to 7 km thinner below the graben than below the shoulders 3 the deepest hypocentres in the black forest dinkelberg area if projected onto the neighbouring reflection profile would be located 7 to 8 km within the laminated lower crust beneath the southern black forest indicating a discrepancy between the top of the lower crust as defined by the brittle ductile transition as seen by the deepest earthquakes and by the top of the laminated reflection band the rhinegraben rift system reveals the properties and behaviour of the lower crust under a wide variety of tectonic situations

structure of the southern rhine graben from gravity and reflection seismic data ecors dekorp program the southern rhine graben was investigated by the seismic reflection ecors dekorp program gravity data available in this region have been reprocessed in order to develop a coherent map along the seismic line the new map has been corrected for the gravity effects of tertiary sediment and crust mantle discontinuity the strong negative gradient towards the alps may be explained by a density contrast of 300 500 kg m3 at the crust mantle interface the residual map shows a negative long wavelength anomaly superimposed on the moldanubian domain of the variscan belt along a vosges black forest swabian jura axis this anomaly cannot be explained by the properties of the variscan crust but may result from a low density body within the upper mantle however its ene wsw direction rules out any connection with the formation of the tertiary grabens which trend north south the recent uplift of topography and the volcanic activity 20 ma of the southern rhine graben may partly be a consequence of an asthenospheric upwelling beneath this area the analysis of the residual short wavelength anomalies shows a fundamental difference between the light variscan terranes of the moldanubian zone and the dense barrandian saverne kraighau structures of the saxothuringian domain a density cross section along the ecors dekorp line confirms that the moho uplift extends beyond the graben whereas thinning of the lower crust affects the graben area only we interpret this crustal structure as an initially thin hercynian crust later deformed by asymmetric extension during oligocene rifting

the deep lithosphere in the alps a model inferred from p residuals abstract the tomographic studies of the alps and their surroundings based on the relative p residuals indicated two lithosphere roots attaining depths over 200 km separated by an upwelling of the lithosphere asthenosphere transition beneath the central part of this mountain range the directional dependence of relative p velocities indicates an anisotropic wave propagation in the subcrustal lithosphere beneath the alps and their surroundings the presented model of the deep lithosphere structure suggests several phases of the tectonic development of this region collision of a tip of the adriatic plate with europe in the eastern alps and dextral strike slip movement of the adriatic ending with underthrusting of europe beneath the western alps and counterclockwise rotation the latter contributes to a steep plunge of both plates beneath the eastern alps and to stress accumulation in the friuli region a model with delamination of the rigid upper crust and its rotation resolves some of the inconsistencies between the near surface and deep tectonics and also explains the distribution of seismicity

winter to winter recurrence of sea surface temperature salinity and mixed layer depth anomalies abstract the mean seasonal cycle of mixed layer depth mld in the extratropical oceans has the potential to influence temperature salinity and mixed layer depth anomalies from one winter to the next temperature and salinity anomalies that form at the surface and spread throughout the deep winter mixed layer are sequestered beneath the mixed layer when it shoals in spring and are then re entrained into the surface layer in the subsequent fall and winter here we document this re emergence mechanism in the north pacific ocean using observed ssts subsurface temperature fields from a data assimilation system and coupled atmosphere ocean model simulations observations indicate that the dominant large scale sst anomaly pattern that forms in the north pacific during winter recurs in the following winter the model simulation with mixed layer ocean physics reproduced the winter to winter recurrence while model simulations with observed ssts specified in the tropical pacific and a 50 m slab in the north pacific did not this difference between the model results indicates that the winter to winter sst correlations are the result of the re emergence mechanism and not of similar atmospheric forcing of the ocean in consecutive winters the model experiments also indicate that sst anomalies in the tropical pacific associated with el nino are not essential for re emergence to occur the recurrence of observed sst and simulated sst and sss anomalies are found in several regions in the central north pacific and are quite strong in the northern 50 n part of the basin the winter to winter autocorrelation of sss anomalies exceed those of sst since only the latter are strongly damped by surface fluxes the re emergence mechanism also has a modest influence on mld through changes in the vertical stratification in the seasonal thermocline

lithospheric cross sections of the european cenozoic rift system abstract the lithospheric structure of the european cenozoic rift system ecris is presented in transects through the southern rhine graben and the rhenish massif hessen depression emphasizing the geophysical structure of the lithosphere based on seismic refraction reflection investigations teleseismic tomography electromagnetic depth sounding models and gravity aeromagnetic earthquake uplift subsidence and heat flow data the rift is clearly expressed in the rhine graben but is not evident at the surface in the area of the rhenish massif where its existence is indicated by seismicity it is characterized by abnormal crustal and upper mantle structures which vary considerably in horizontal direction for example under the rhine graben the crust is thinned to 25 km but at 40 km depth anomalously high velocities are observed in contrast beneath the rhenish massif the crust is thickened to 35 37 km and under its eastern part a high velocity thin upper mantle slice is seen at 30 km depth within the lower crust which towards the hessen depression is gradually replaced by normal variscan mantle with the moho near 30 km depth under the western part of the rhenish massif p and s wave velocities are reduced below 50 km depth which is not seen east of the rhine river under the rhine graben the existence of a low velocity upper mantle above 100 km cannot be generalized but is restricted to confined regions

gravity anomalies and flexure of the lithosphere at mountain ranges the bouguer gravity anomaly over the himalayan alpine and appalachian mountains is characterized by a generally asymmetric gravity low which spans the mountains and associated foreland basins the minimum of the gravity low is generally systematically displaced from the region of greatest topographic relief and shows no obvious relationship to surface geology in addition the alps and appalachians are associated with a generally symmetric gravity high that is unrelated to the topographic relief together the gravity low and high form a characteristic positive negative anomaly couple the steep gravity gradient between the positive and negative couple correlates with the insubric line and its equivalents in the alps and the brevard zone in the southern appalachians this gravity anomaly couple is interpreted as evidence for flexure of the continental lithosphere by subsurface buried and surface topographic loading the magnitude of the subsurface load is estimated from the integrated excess mass represented by the positive anomaly and the magnitude of the surface load from the topography by combining these loads the flexure of the lithosphere and the associated bouguer gravity anomaly are calculated for different assumed values of the elastic thickness te of continental lithosphere the best fitting value of te for the himalayas is 80 100 km for the alps 25 50 km and for the appalachians 80 130 km the model calculations suggest that the main contribution to the gravity couple in the alps and appalachians arises not from surface loads such as thrust sheets and nappes but from subsurface loads however in the case of the himalayas the topography appears to be a sufficient load to explain the observed asymmetric gravity low when subsurface loads do exist therefore we would not expect a close correlation between mountain topographic relief and depth to the m discontinuity as required by classical models of isostasy rather the m discontinuity is expected to relate to the center of mass of all the loads acting on the lithosphere the surface and subsurface loads inferred from the gravity anomaly play a major role in the development of mountains and foreland basins the emplacement of large subsurface loads represents the primary event in the alps and appalachians while in the himalayas the emplacement of the surface load is the primary event the emplacement of the subsurface load probably marks the initiation of foreland basin development the regional characteristics of the basin are controlled by the primary load while local variations are controlled by the secondary thrust sheet loads subsequent movement of either load will produce migration of the basin depocenter the origin of the subsurface load is not clear but its association with the insubric line in the alps and the brevard zone in the appalachians suggests that it may be related to the obduction of crustal blocks flakes onto the underlying plate during continental collision or possibly to the preloaded crustal structure of the underlying plate

flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension we suggest that the uplift of rift flanks results from mechanical unloading of the lithosphere during extension and consequent isostatic rebound this mechanism is presented as an alternative to explanations for rift flank uplift involving thermal or dynamic processes and magmatic thickening of the crust our hypothesis is based on two critical concepts first the lithosphere retains finite mechanical strength or flexural rigidity during extension second isostatic rebound uplift of the lithosphere follows when the kinematics of extension produces a surface topographic depression that is deeper than the level to which the surface of the extended lithosphere would subside assuming local isostatic compensation we develop and analyze two kinematic models for instantaneous extension of the lithosphere to show that flexural rebound is a viable explanation for the uplift of rift flanks we first investigate the isostatic consequences of finite simple slip on an initially planar dipping normal fault cutting the entire lithosphere when the lithosphere retains flexural rigidity during extension the topography resulting from this model resembles a half graben and the footwall rift flank is flexurally uplifted this simple normal faulting model explains free air gravity anomalies and topography observed at rift flanks in oceanic lithosphere such as broken ridge in the eastern indian ocean the caroline ridges sorol trough in the western equatorial pacific and the coriolis trough behind the new hebrides island arc we then investigate a general kinematic model for lithospheric extension where simple slip on a surface of arbitrary shape is accompanied by pure shear extension in the upper and lower plates when the simple slip component is not zero or the distribution of pure shear in the upper and lower plates is not identical the surface of slip can be regarded as a detachment by simplification our general model accounts for pure shear extension of the lithosphere that is uniform with depth in this case detachments have no meaning in the geologic sense however the kinematics of depth independent pure shear may nevertheless be described in terms of a surface which we term a kinematic reference surface at some depth in the lithosphere we speculate that the depth of this surface may be rheologically controlled the magnitude of rift flank uplift by flexure depends critically on the depth of this reference surface in contrast if local isostasy is assumed when the lithosphere undergoes a given amount of depth independent pure shear the resulting topography will be the same regardless of how the kinematics of that extension are formulated the basin and rift flank topography and free air gravity anomaly over young continental rifts such as the rhine graben can be satisfied using our general extensional model with a small amount 5 km of extension along a listric shaped detachment soling into the crust mantle boundary because the flexural rebound mechanism explains the observed topography and gravity anomaly over both oceanic and continental extensional domains we suggest that rheological differences between the two lithospheric types may not be important in their overall response to extension

simultaneous inversion for 3 d crustal structure and hypocentres including direct refracted and reflected phases iii application to the southern rhine graben seismic region germany summary the new technique of simultaneous inversion for hypocentres and crustal structure ssh is applied to the southern rhine graben p and s wave first and later arrival times of direct refracted and reflected phases of 350 seismic events are used in the study substantial improvements of over 100 per cent in the non linear residual fit are obtained for the 3 d and less for the 1 d models many of the structural results of the 3 d ssh models are consistent with major findings from other seismic refraction experiments and fit into the general geological petrological and geodynamica1 frame of this area thus the thick sedimentary layer in the rhine graben proper manifests itself by large negative seismic velocity anomalies for the middle crust the ssh models show a strong seismic differentiation between sections of the graben proper and the areas under its western and eastern shoulders of the vosges and the black forest respectively using a new a priori bayesian inversion technique it has been attempted to substantiate the refraction seismic low velocity zone of gajewski prodehl 1987 in the middle crust under the black forest the results demonstrate that such a velocity low is compatible with the observed traveltimes only if one assumes it as a more local crustal phenomenon in this area in the lower crust the ssh models are able to clarify some controversies from earlier refraction experiments in the region the models reveal many seismic features which are typical for continental rift zones such as high transitional velocity anomalies 7 4 km s l under parts of the graben proper rift cushion in the upper mantle the models show a ring like high velocity structure of 8 30 8 40 km s l centred around a low velocity area 7 9 km s l beneath the kaiserstuhl i conjecture this to be a thermal fingerprint of a partially molten upwelling asthenospheric diapir bulging under the moho the simultaneously relocated hypocentres for the 1 d models show some systematic downward movements for the events in the lower crust of the southern black forest area but otherwise do not differ too much from the initial ones to alter the present seismotectonic picture of the southern rhine graben thus the hypothesized phenomenon of the seismic gap along the southern section of the graben black forest wedge can both structurally and seismically be substantiated the relocated hypocentres suggest optically even a widening of this seismic gap the later has thus to be accepted as a possibly more general characteristic of a graben formation

extreme events and the general circulation observations and stochastic model dynamics abstract this study explores the dynamical role of non gaussian potential vorticity variability extreme events in the zonally averaged circulation of the atmosphere within a stochastic framework first the zonally averaged skewness and kurtosis patterns of relative and potential vorticity anomalies from ncep ncar reanalysis data are presented in the troposphere midlatitude regions of near zero skewness coincide with regions of maximum variability equatorward of the northern hemisphere storm track positive relative potential vorticity skewness is observed poleward of the same storm track the vorticity skewness is negative in the southern hemisphere the relation is reversed resulting in negative relative potential vorticity skewness equatorward and positive skewness poleward of the storm track the dynamical role of extreme events in the zonally averaged general circulation is then explored in terms of the potential enstrophy budget by linking eddy enstrophy fluxes to a stochastic representation of

deep reflection seismic data along the central part of the european geotraverse in germany a review abstract deep reflection seismic data collected in germany during the last three decades allow an insight into the structure of the variscan crust in germany although the crustal thickness is relatively constant reflection data revealed important internal structures most profiles show a poorly reflective upper crust disregarding fault zones while its lower part is characterized by many flat lying reflections but also dipping reflections in the upper and lower crust have been observed on dekorp reflection lines beneath the geothermal anomaly of urach an updoming of the reflective lower crust coinciding with a pronounced low velocity body can be observed near the suture zones between moldanubian saxothuringian and rhenohercynian abundant diffractions appear in the middle and lower crust one exception is found in the west where post variscan developments created the deep saar nahe trough the north variscan deformation front exhibits thin skinned tectonics west of the rhine while farther east more steeply dipping fault zones are observed in the north german basin just north of the variscides an industrial north south profile shows strong bands of reflections from both midcrustal and moho levels the distance between these bands becomes smaller to the north an industrial west east line of 90 km length in schleswig holstein south of kiel shows a thinning of the crust of about 6 km towards the north sea although the moho is not faulted the sediments reach down to at least 15 km

an interpretation of wide angle compressional and shear wave data in southwest germany poisson s ratio and petrological implications shear wave velocity especially when used with compressional wave velocity is an important constraint on estimates of the composition and physical state of the continental lithosphere we present shear velocity s models derived from high quality s wave data along three profiles in southwest germany which combine with existing p wave velocity p models to give poisson s ratio in the crust and uppermost mantle we then construct a laterally varying petrological model of the crust by comparing our p and s models with published laboratory measured rock velocities in general poisson s ratio is 0 25 in the uppermost crust 0 22 0 23 in the mid crust but reaching a low of 0 15 in the black forest low p zone and varies laterally from 0 24 to 0 30 in the lower crust the average poisson s ratio of the whole crust is everywhere about 0 25 the laminated signature of the lower crust prominent on reflection and p wave refraction data is absent on the s wave refraction data implying a strong high low alternation of poisson s ratio in the lower crust this suggests that the lower crustal laminae represent mafic silicic compositional layering for example basic sills in an originally more quartz rich lower crust rather than alternating zones of high and low pore pressure there is no evidence for a shear wave low velocity zone lvz in the black forest mid crust despite the presence of a strong p wave lvz this suggests high quartz content and the presence of pore fluids at low not high pore pressure a clear p to s converted moho reflection pm s is visible on several shots indicating that the moho is at least locally a first order discontinuity no shear wave refractions from the upper mantle are present even where strong p wave refractions are observed possibly indicating an increase of poisson s ratio with depth in the upper mantle the petrological modeling indicates that the upper and middle crust are probably of granitic composition that the mid crustal low p zones have high quartz content and that the lower crust probably consists of granulites of laterally varying bulk composition from granodioritic to gabbroic the lower crust is more mafic in areas of high reflection density on seismic reflection profiles suggesting that the laminations are caused by mafic intrusions into the lower crust either prior to the variscan orogeny or during tertiary volcanic activity

structural evolution of the pyrenees tectonic inheritance and flexural behaviour in the continental crust abstract the ecors deep seismic reflection profile and additional geological data are used to understand deformation processes in the pyrenees the middle crust shows two major sets of seismic reflectors interpreted as hercynian structures during permian and the late jurassic early cretaceous rifting events these structures were extensionally reactivated mainly within the european plate during the pyrenean orogeny tectonic inversion of the early cretaceous basins took place located mainly on the european plate and hercynian southward directed verging thrusts were also reactivated in the iberian foreland a regional model is proposed which takes into account the lithospheric flexure and the evolution of the sedimentary load this study shows the different rigidities of the european and iberian plates difference related to differential thinning events as well as an east west diachronism of the flexure for the european plate and unflexing behaviour after the orogeny

a three dimensional model of the crust and upper mantle along the alpine part of the european geotraverse egt abstract we investigated the structure of the crust and the upper mantle in the alpine part of the european geotraverse by integrating gravity and seismic refraction data into a three dimensional 3 d model of the crust the gravity data came from swiss italian and german sources the study area included the swiss molasse basin north of the alps and the po plain in the south to enhance the resolving power of this data for short wavelength anomalies in the alps 550 additional stations were surveyed on a 10 km wide swath from lake constance bordering switzerland and the federal republic of germany to bergamo italy the bouguer anomalies were reduced with 3 d models for the effect of the sediments of the swiss molasse basin the po plain and other bodies of known geometry such as the quaternary sediments of the alpine valleys and the mafic and ultramafic rocks of the ivrea body this resulted in a map of stripped bouguer anomalies a 3 d model of the crust was built using seismic data the densities were determined by a least squares inversion technique after subtraction of the model effect from the stripped bouguer anomalies we found a residual gravity anomaly of more than 400 km length that can be explained with a positive density anomaly in the upper mantle which is in agreement with seismological results these findings fit well into a tectonic model with subducted material of higher density and seismic velocity in the upper mantle beneath the boundary between the european plate and the adriatic promontory african plate

the upper rhenish shield basement vosges upper rhinegraben and schwarzwald main structural features deduced from magnetic gravimetric and geological data abstract interpretation of magnetic and gravimetric data and correlations with geological observations on outcrops and in boreholes have enabled the construction of a geological sketch map of the pre westphalian basement in the area of the upper rhenish shield the map demonstrates the contrast between the heavy and magnetic saxothuringian characterized by palaeozoic units metamorphosed to varying degrees and intruded by early carboniferous basites and the lighter moldanubian consisting mainly of gneisses and granites geological structures and tectonic features are recorded beneath the mesozoic and cenozoic cover the present picture of the basement is mainly the result of late visean early namurian structural features represented by a linear arrangement of magmatic bodies and the distribution of strike slip and thrust faults the major structural features are the e w vittel lalaye lubine baden baden fault that marks the border between saxothuringian and moldanubian the n35 left lateral wrench fault system running along the present rhinegraben the n60 grain of the northern vosges and the saar basin and the s verging crustal thrusts of moldanubian

crustal structure along the central segment of the egt from seismic refraction studies abstract the seismic refraction line between the gulf of genova and the baltic sea was carried out in 1986 as part of the european geotraverse egt 86 the central segment of the egt also known as eugemi european geotraverse middle part has a total length of 825 km and runs from the northern margin of the alps to the baltic sea traversing mainly the variscan mountain area of western germany the p wave data of nine shotpoints were interpreted in detail and a two dimensional p velocity model of the crust was developed between the molasse basin and the southern end of the north german basin for the north german basin the data quality justifies only the construction of a simplified model the internal crustal structure is quite complex in the upper crust of the moldanubian and saxothuringian zones of the variscan orogen the velocities are lower than in the rhenohercynian area the velocity of 6 0 km s representing consolidated seismic basement is reached at depths of as much as 10 12 km northern margin of alps and north german basin and of only 3 km under the mid german crystalline rise mid crustal velocities range from 5 8 to 6 1 km s forming weak velocity reversals in some parts in the lower crust velocities as low as 6 2 km s are seen near the alps in contrast to velocities between 6 8 and 7 2 km s in the exposed variscan orogen north of shotpoint e between hannover and the river elbe the velocity of the lower crust is about 6 4 km s north of the elbe line it increases abruptly to 6 9 km s the crust mantle boundary rises from 34 km depth under the northern margin of the alps to 29 km under the swabian jura under the variscan orogen to the north the crustal thickness varies only slightly around an average depth of about 29 1 k but drops to about 30 km under the north german basin between the elbe line and the ringkobing fyn high the moho rises to a depth of about 26 km and the data indicate at least one fault like step of 1 km before the crust thickens toward the basement high the velocities in the uppermost mantle show considerable variation the highest velocity of 8 4 km s is observed beneath the saxothuringian zone and the lowest values of 7 8 7 9 km s are recorded under the hessen depression

probing into extensional sedimentary basins comparison of recent data and derivation of tentative models abstract more and more deep seismic profiling is revealing the complex evolution of the continental crust which bears the imprints of former plate movements previous subduction zones and mountain belts affected the crust before the formation of intra cratonic sedimentary basins or passive margins therefore the former geological setting must always be taken into account in deep reflection studies of such areas recent deep seismic profiles in europe and other parts of the world have demonstrated the largely heterogeneous nature of the continental crust with dipping reflectors within the crust while bedding heterogeneities or intrusive sill complexes may be invoked these reflectors are most often associated with inherited thrust planes related to crustal shortening during previous orogenies some of these inherited faults have been imaged beneath sedimentary basins with contrasting styles and their reactivation depends on their strike in relation to the regional stress field these pre existing zones of weakness induce a heterogeneity in the upper crust which may control the geometry of future extensional tectonics when the strike of the inherited faults is perpendicular to the extensional stress field they may be reactivated as a detachment surface controlling the sedimentary infill more often the obliquity of these structures induces local changes and segmentation of the rif when they are crossed in such a case they correspond to transfer faults acting as relays between major normal faults or to twist zones where changes occur in the throw of the normal faults sometimes evolving to an inversion of the polarity in the tilting of the major blocks during extension the top of the lower crust may act as a mechanical decoupling boundary separating asymmetrical brittle failure within the upper crust and symmetrical ductile creep within the lower crust extensional modes may explain the great values of crustal thinning observed in both upper and lower crusts beneath rifts and passive margins related to the opening of an oceanic domain it is more difficult to explain the comparatively small amount of horizontal extension generally observed

evolution and structure of the upper rhine graben insights from three dimensional thermomechanical modelling the evolution and geometry of the tertiary upper rhine graben were controlled by a continually changing stress field and the reactivation of pre existing crustal discontinuities a period of wnw ese extension in the late eocene and oligocene was followed by lateral translation from the early miocene onwards this study utilizes 3d finite element techniques to simulate extension and lateral translation on a lithospheric scale brittle and creep behaviour of lithospheric rocks are represented by elastoplasticity and thermally activated power law viscoplasticity respectively contact elements allocated with cohesion and frictional coefficients are used to describe pre existing zones of weakness in the elastic brittle field our results suggest that 1 extension is accommodated along listric border faults to midcrustal depth of 15 16 km beneath pure shear stretching occurs without a need for localized shear zones in lower crust and upper mantle 2 ductile flow at midcrustal depth across the graben accounts for the pronounced halfgraben morphology thereby the shape of the border faults their frictional coefficients and sedimentary loads have profound effects on the rate of ductile flow across the graben 3 horizontal extension of 8 8 5 km and sinistral displacement across the rift of 3 4 km are needed to accommodate the observed sediment thickness

insight into the structure of the upper rhine graben and its basement from a new compilation of bouguer gravity abstract a compilation of gravity data from the upper rhine graben urg is presented that includes all the main data sources from its german and french parts this data is used to show that the urg consists of at least two arc shaped and asymmetric rift units that tectonically are the basic building blocks of the graben in this sense the urg does not differ from other continental rifts such as the african rifts this division should replace the now classical geomorphologic division of the urg into three segments based on their different trends moreover the gravity suggests that the faults in the central and southern segments are continuous and have the same trend appearing to respond as a single kinematic unit changes in the gravity field in the graben are shown to reflect not only the structure of the graben but also the highly variable composition of the basement in this respect the urg is quite different from some other tertiary continental rifts where possible changes in the composition of the basement are mostly masked in the gravity field by the effect of the overlying low density sediments this characteristic is used to study the extent of some of the main basement units that underlie the graben

crustal xenoliths from cenozoic volcanic fields of west germany implications for structure and composition of the continental crust crustal xenoliths in three cenozoic volcanic fields of west germany the northern hessian depression nhd the eifel and the urach hegau include medium to high grade meta sedimentary and felsic to mafic meta igneous rocks also present in all three suites are pyroxenites and hornblendites for each volcanic field a model crustal profile is proposed based on calculated or measured p wave velocities of xenoliths and depth vp relationships egt central segment and rhenish massif traverses the xenolith lithologies from the nhd and the eifel show some similarities the middle crust between the depths of about 10 and 25 km consists mainly of meta sediments felsic gneisses and granulites meta sedimentary rock types are particularly abundant in the eifel at depths of between about 5 and 15 km but are less common within the nhd xenolith collection the felsic gneisses range from meta granites to meta tonalites i and s type eifel meta sediments range from meta pelites to meta greywackes and meta quartzites the nhd xenolith suite contains a few highly depleted granulite facies meta sedimentary fragments at depths between 24 and 26 km the increase in vp from about 6 8 to 8 km s 1 28 34 km is correlated with the presence of mafic granulites intercalated with eclogites pyroxenites and hornblendites beneath north hessia the granulite layer problably grades into a composite eclogite peridotite layer at the lower part of this transition zone the crust beneath the urach hegau consists largely of meta sediments with subordinate felsic meta igneous rocks most of the meta sedimentary samples seem to be depleted in felsic components suggesting intra crustal differentiation by partial melting the urach crust contains lithologies which are similar to the outcropping moldanubian type para gneisses of the black forest mafic and ultramafic xenoliths from the urach hegau differ in their mineralogy and chemical composition from the eifel and nhd mafic granulites they represent meta cumulates derived from alkaline magmas which intruded the base of the crust and underwent deformation and recrystallization petrographic and chemical differences between urach hegau and eifel nhd are believed to reflect the contrasting styles of crustal evolution in the rhenohercynian and the moldanubian belts of the variscan orogen

uniform sense normal simple shear of the continental lithosphere geophysical studies suggest that the thin crust characteristic of the basin and range province extends eastward beneath the west margin of the colorado plateau and rocky mountain regions in arizona and utah zones perhaps over 100 km wide may be defined bounded on the west by the east limit of upper crustal normal faults that account for more that 10 extension and on the east by the east limit of thinning beneath the colorado plateau a discrepancy exists within these zones between the negligible extension measurable in the upper crust and the substantial extension apparent from crustal thinning assuming the discrepant zone crust was as thick as or thicker than the colorado plateau rocky mountain crust prior to extensional tectonism if various theories appealing to crustal erosion are dismissed mass balance problems evident in the discrepant zones are most easily resolved by down to the east normal simple shear of the crust moving lower and middle crustal rocks that initially were within the zones up and to the west to where they now are locally exposed in the basin and range province west of the discrepant zones in both arizona and utah east directed extensional allochthons with large displacement are exposed these geophysical and geological observations complement one another if it is accepted that the entire crust in both arizona and utah failed during extension on gently east dipping east directed low angle normal faults and shear zones over a region several hundred kilometres wide large scale uniform sense normal simple shear of the crust suggests the entire lithosphere may do the same such a hypothesis predicts major lithospheric thinning without crustal thinning will occur in plateau areas in the direction of crustal shear in the case of the arizona utah and red sea extensional systems and possibly the death valley extensional terrain a broad topographic arch typically 1500 2000 m higher than the extended terrain is present suggesting lithospheric thinning in areas predicted by the hypothesis

the variscan tectonic inheritance of the upper rhine graben evidence of reactivations in the lias late eocene oligocene up to the recent processing of gravity and magnetic maps shows that the basement of the upper rhine graben area is characterized by a series of ne sw trending discontinuities and elongated structures identified in outcrops in the vosges black forest and the odenwald mountains they form a 40 km wide n30 40 striking sinistral wrench zone that in the visean shifted the variscan and pre variscan structures by at least 43 km to the ne wrenching was associated with emplacement of several generations of plutonic bodies emplaced in the time range 340 325 ma the sub vertical ne sw trending discontinuities in the basement acted as zones of weakness susceptible to reactivation by subsequent tectonism the first reactivation marked by mineralizations and palaeomagnetic overprinting along ne sw faults of the vosges mountains results from the liassic nw se extension contemporaneous with the break up of pangea the major reactivation occurred during the late eocene n s compression and the early middle oligocene e w extension the ne sw striking basement discontinuities were successively reactivated as sinistral strike slip faults and as oblique normal faults elongated depocenters appear to form in association with reactivated variscan wrench faults some of the recent earthquakes are located on ne sw striking variscan fault zones and show sinistral strike slip focal mechanisms with the same direction suggesting also present reactivation

the variscan belt in central europe main structures geodynamic implications open questions abstract the variscan belt of europe originated from the confrontation of northern europe and gondwana with intervening pre variscan blocks cadomian and older armorica tepla barrandean moravo silesian though a strike slip component cannot be excluded geological evidence suggests a subduction collision process newly discovered features include basaltic rocks with morb affinities high pressure metamorphic rocks trench deposits and large scale allochthonism which also affects the pre variscan basement and has often led to an inversion of the metamorphic isogrades large scale thrusting is evident at all crustal levels and is also observable by geophysical methods the structure of the variscan crust is best described as horizontal tectonic layering late ordovician through carboniferous convergence closed one rhenohercynian and one saxo thuringian basin to the north and at least one mediterranean basin to the south of the pre variscan blocks subduction occurred from the north as well as from the south down under the dorsal core region the exact timing and the driving mechanism of this bilateral activity remains a problem likewise uncertain are the exact limination of the pre variscan blocks and the existence and width of oceanic areas in the saxothuringian zone and in the south facing part of the moldanubian zone there is good evidence of early palaeozoic rifting and of late ordovician through carboniferous plate convergence palaeomagnetic and palaeoclimatic constraints however suggest only a limited extent of oceanic basins in these areas while they appear to allow a wider ocean at the rhenohercynian saxothuringian boundary which is relatively unobtrusive from the geological point of view research during the past decade has produced a wealth of information on the variscan fold belt in europe the resulting geodynamic models however are extremely diverging evidently it is not the time yet for definitive statements the present paper intends to review the state of knowledge to deduce such basic items of a geodynamic model as appear reasonably well documented and to point out the most urgent open questions stress will be laid on central europe which offers a complete cross section through the northern flank of the variscan belt and where we have carried out most of our studies during the last years

a teleseismic and petrological study of the crust and upper mantle beneath the geothermal anomaly urach sw germany abstract teleseismic p wave travel time residuals recorded by a mobile shortperiod network are interpreted using the composition of crustal and upper mantle xenoliths a three dimensional inversion of the p residuals revealed a small scale anomalous domain with a velocity reduction of 3 in the crust and a broad low velocity anomaly of 4 beneath the moho down to a depth of 50 km xenoliths of the miocene urach volcanic field uvf 1300 km2 355 eruptive centres mostly diatremes comprise phlogopite bearing clinopyroxene rich mantle xenoliths evidence for large ion lithophile element lil metasomatism in an originally depleted harzburgitic mantle reflecting chemical modification of the upper mantle beneath the uvf the metasomatism caused partial melting in the spinel peridotite stability field indicated by glasses in xenoliths and a diapiric uprise of the partially molten metasomatized mantle the observed reduction of the p wave velocity of 4 in the lithospheric mantle can be explained by a local enrichment of phlogopite accompanied by increased temperatures the crustal low velocity body coincides very well with the postulated volume of an ancient intracrustal magma chamber or system of chambers required by the composition of xenoliths the magnetization of the diatremes and the spatial distribution of the volcanic eruption centres

southern rhine graben small wavelength tomographic study and implications for the dynamic evolution of the graben summary inversion of p wave traveltime residuals of teleseismic events recorded by a dense network of short period stations yielded a detailed image of the 3 d velocity structure of the lithosphere asthenosphere system beneath the southern rhine graben area the upper part of the lithosphere marked by velocity anomalies orientated along the graben strike can be related to the development of the graben these upper 50 km display stronger lateral heterogeneities than the weak anomalies observed at deeper levels which show roughtly an e w orientation the teleseismic inversion models yield no indications for significantly reduced seismic velocities in the upper mantle as could be expected from an actively upwelling mantle diapir located beneath the southern rhine graben area the observation of generally weak velocity variations at greater depth indicates a rather smooth transition from the lower lithosphere to the upper asthenosphere deeper parts of the lithosphere were probably altered by metasomatic processes as a consequence of the intrusion of melts during middle and late miocene times these melts cooled and solidified from the end of the miocene when rifting and thermal doming ceased in the southern rhine graben area

deep crustal structure of the rhine graben from dekorp ecors seismic reflection data a summary abstract results of two deep reflection seismic lines crossing the northern and southern part of the rhine graben which were recorded in 1988 by the french ecors and the german dekorp teams indicate that the asymmetry of this rift persists to the base of the crust the brittle ductile transition zone approximately coincides with the top of the lower crust ductile shear zones appear to affect the crust mantle boundary upper crustal extension by faulting accounts for a divergence of the graben flanks by 5 7 km whereas the crustal configuration of the rhine graben suggest an extension value of some 17 km

the deep crust of the southern rhine graben reflectivity and seismicity as images of dynamic processes abstract the rhine graben part of the european cenozoic rift system deserves special attention because of its location in the foreland of the alpine orogen the phanerozoic evolution of the lithosphere in this region is defined by a set of major geodynamic events ranging from the variscan orogeny late orogenic crustal re equilibration to the interference of rifting and alpine orogeny in tertiary times the rhine graben is one of the most detailedly studied continental grabens prospecting for hydrocarbons in its sedimentary fill and intensive pre site studies for the continental deep drilling program ktb on its eastern crystalline flank black forest provided a comprehensive set of geoscience data seismic investigations ranging from a deep seismic network of near vertical reflection to concurrent wide angle refraction experiments were accompanied by seismological and geological surveys therefore a direct observational comparison between the two depth definitions of crustal subdivisions elastic vs strength rheological was possible in large parts of western europe deep seismic sounding dss investigation distinguishes between a crystalline upper crust of comparatively low p wave velocities 5 9 6 0 km s with little and discrete reflectivity and a strongly reflective lower crust with higher p wave velocities about 6 4 6 8 km s both are separated by the conrad discontinuity in contrast strength and rheological considerations define a brittle upper crust and a ductile lower crust the boundary between these two realms is usually referred to as the brittle ductile transition zone which in seismically active regions is imaged by the deepest crustal hypocentres the present brittle ductile transition in the rhine graben region as defined by the deepest hypocentres does not necessarily coincide with the structural separation in an upper and lower crust as seen in deep seismic studies this suggests that the laminated lower crust developed during the crustal re equilibration phase at the end of the variscan orogeny the second part of this paper concentrates on evidence of recent tectonic activities related to rifting processes impacting on the variscan lower crust a remarkable concentration of deep crustal earthquakes reaching to the top of an asymmetrical thinned lower crust is observed at or near the eastern border fault of the southern rhine graben and is possibly induced by the young rifting process we suggest that this asymmetry could be a consequence of the uppermost mantle detaching from the upper crust in collision with the alpine orogen this allows us to propose the distinction between the influence of compression extension continental subduction and intra crustal detachment during graben formation the dynamic interference of rifting and foreland compression shown by structural and seismological observations leads to the notion of small scale collisional escape tectonics associated with an intra continental transform fault at the southern end of the rhine graben the rhine sao ne transform zone

normal faulting from simple shear rifting in south tibet using evidence from passive seismic profiling across the yadong gulu rift abstract the tibetan plateau is undergoing north south shortening accompanied by west east extension as evidenced by the widespread development of north south trending normal faults grabens and rifts while the mode of the north south shortening has been the main focus of most international studies knowledge of the deep structure beneath south tibet is required for understanding the mechanism of the west east extension the onset of the north south trending normal faulting is commonly taken as an indicator that the tibetan plateau was uplifted to a near maximum elevation before entering a collapsing stage here we report on the receiver functions of a seismological experiment across the northern segment of the yadong gulu rift ygr one of the youngest rifts in south tibet the migrated receiver function images reveal that the ygr is a high angle normal fault characterized by a 5 km moho rise from its western to eastern flank together with distinct differences in the crustal structure and intracrustal seismic conversion patterns between the two flanks this highly asymmetric lithospheric structure suggests whole crustal extension controlled by a simple general shear rifting mechanism this simple general shear rifting in the ygr is attributed to an eastward horizontal shear at the base of the upper crust as evidenced by the observed tibetan gps velocity field and our observation of shear wave splitting discrepancy among the upper crust lower crust and lithospheric mantle we propose that in the ygr simple shear rifting accommodates the northward injection of the indian lithosphere which may suggest that the onset of the north south normal faulting does not indicate gravitational collapse of the tibetan lithosphere