the cenozoic evolution of the roer valley rift system integrated at a european scale the roer valley rift system rvrs is located between the west european rift and the north sea rift system during the cenozoic the rvrs was characterized by several periods of subsidence and inversion which are linked to the evolution of the adjacent rift systems combination of subsidence analysis and results from the analysis of thickness distributions and fault systems allows the determination of the cenozoic evolution and quantification of the subsidence during the early paleocene the rvrs was inverted laramide phase the backstripping method shows that the rvrs was subsequently mainly affected by two periods of subsidence during the late paleocene and the oligocene quaternary time intervals separated by an inversion phase during the late eocene during the oligocene and miocene periods the thickness of the sediments and the distribution of the active faults reveal a radical rotation of the direction of extension by about 70 80j counter clockwise integration of these results at a european scale indicates that the late paleocene subsidence was related to the evolution of the north sea basins whereas the oligocene quaternary subsidence is connected to the west european rift evolution the distribution of the inverted provinces also shows that the early paleocene inversion laramide phase has affected the whole european crust whereas the late eocene inversion was restricted to the southern north sea basins and the channel area finally comparison of these deformations in the european crust with the evolution of the alpine chain suggests that the formation of the alps has controlled the evolution of the european crust since the beginning of the cenozoic

crustal kinematics and deep structure of the northern rhine graben germany surface and subsurface geological data unpublished information gleaned from industrial seismic surveys and results from a deep reflection seismic profile across the tertiary northern rhine graben indicate that crustal extension in excess of 6 km was achieved by asymmetric detachment of the upper crust at a depth of about 15 km comparison of a simple geometric kinematic cross sectional model and its depth extrapolation with the dekorp 9 n deep crustal reflection data suggests that extension below the graben was achieved by slip along a gently westward dipping shear zone which truncated and offset lower crustal planar fabrics and which continues into the uppermost mantle the planar lower crustal reflectors probably originated mainly during late variscan permocarboniferous crustal extension and or magmatic underplating

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

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

evolution of the stress field pattern in the south of the rhine graben from the eocene to the present a stress field evolution from the eocene to the present is proposed for the southern part of the rhine graben stress tensor determinations are supported by striated microfaults and calcite twin lamellae analyses both methods lead to the determination of 1 a an e w extension contemporaneous with the opening of the graben and 2 b a n s compressive event which may be related with alpine tectonics it is shown that a n s compressive event occurred prior to the oligocene extension a permutation between the 1 and 2 axes is proposed to explain the transition between compression and extension a 1 2 inversion during the oligocene is compatible with compression in the southern part of the rhine graben infilling horizontal 1 and extension vertical 1 more to the north during the miocene the jura emplacement corresponds to a n s compression in this area there is no significant variation of the 1 direction south of the rhine graben from the eocene to the late miocene the 1 direction only turns to a n140 direction during the pliocene or the quaternary

structural evolution of intermediate crustal rocks in a strike slip and extensional setting variscan odenwald sw germany differential upward transport of metamorphic complexes and changing deformation mechanisms abstract the variscan basement exposed in the odenwald mountains southwest germany is composed of several allochthonous metamorphic complexes showing low pressure metamorphism with varying pt conditions and of syntectonic plutons i and s type during the late devonian early carboniferous times rapid uplift of these rocks caused rapid cooling before and during the thermal peak of metamorphism the metamorphic rocks experienced penetrative strain d 1 d 2 which was probably generated by crustal shortening and stacking the resulting micro structures infer distributed strain activation of c slip in quartz and postkinematic annealing during and after the thermal peak of metamorphism ne sw trending zones of normal oblique sinistral strike shearing d 3 and nne ssw trending zones of normal shearing d 4 developed these episodes of deformation are characterized by strong localization of strain strain softening was caused by reorientation of the lattice of quartz toward an orientation more favorable for easy glide along a and by a change in deformation mechanisms of feldspar from dislocation creep to grain size sensitive creep normal oblique strike shearing and normal shearing caused juxtaposition of mid crustal slivers of dissimilar pt and structural histories and provided mechanisms for their denudation detachment of rocks occurred along domains in which strain softening was operative further transtension and extension facilitated uplift and emplacement of syntectonic plutons which experienced also d 3 and d 4 strain in the plutonic rocks strain was broadly distributed in the initial hot stages and became increasingly localized as the deformation continued through cooling

carnivore diversity in the late quaternary of israel abstract during the past 70 000 years israeli carnivore faunas have varied only slightly in richness number of species but widely in diversity including the relative abundances of the different species human population growth sedentism and the beginning of agriculture are often considered to have caused habitat destruction toward the end of the pleistocene that may have affected animal populations however patterns of changing carnivore diversities from three sites in the mediterranean region of israel correlate well with changes in precipitation species diversity is higher during more humid phases and lower during drier phases the environmental effect of sedentism may have accelerated the later drop in carnivore diversity but cannot account for fluctuations in diversity preceding it

a reinterpretation of the ages and depositional environments of the lower and middle miocene stratigraphic records in a key area along the southern margin of the north sea basin the stratigraphic reinterpretation of the palynologically analysed miocene succession of the wijshagen borehole along the southern margin of the north sea basin allowed an age assessment late burdigalian to early serravalian for the genk sand member of the bolderberg formation the depositional environment varied during burdigalian to serravalian times from continental peat formation to open marine glauconitic sands respectively from south to north in the roer valley rift system the study area of the wijshagen borehole is located in the central part of the roer valley rift system between these extreme environments during the burdigalian the glauconitic fine clayey sands of the houthalen sand member were deposited in the study area from the late burdigalian onwards the glauconite content decreased and lignite content increased as a result of high influx of clastic material in the roer valley rift system and marked the start of the deposition of the genk sand member the genk sand member shows an overall coarsening upwards trend which is consistent with the gradual infill of the available accommodation space in the roer valley rift system by northwest prograding clastic delta sequences dinoflagellate cyst analyses indicate that the genk sand member was largely deposited in a marginal marine environment with only short pulses of continental input these pulses of continental input increase in a southerly or landward direction where they led to the development of thick lignite seams

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

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

analogue experiments of propagation of oblique rifts abstract we present the results of analogue models of oblique rifting which were carried out using a isostatically compensated two layered small scale models the experiments show that structures formed in the brittle layer under oblique extension comprise a series of lenticular rifted basins set en echelon along the axial zone of the experiment box in time the basins propagate lengthways to merge and form a unified composite rift however traces of the initial en echelon rifts expressed in deeper axial basins separated by shallower threshold zones are clearly discernible in the mature rifts both the basins and the threshold zones are located within the composite rift so that the rift margins are abrupt and steep along the basins and more diffuse along the threshold zones the thinning in the brittle layer along the rift is enhanced by diapirs that ascend from the ductile layer and penetrate the rift floor model experiments of nearly orthogonal extension showed a single unified rift which differed conspicuously from the composite oblique rifts the results of the experiments suggest that oblique extension forms en echelon rift segments the axes of which are perpendicular to the extension direction separated by threshold zones therefore there is ground to presume that occurrence of a series of alternating basins and threshold zones inside the axial section of a major rift could suggest a regime of oblique tectonic extension

the experimental deformation of dunite deformation experiments have been carried out on two dunites anita bay of 100 m grain size and aheim of 900 m grain size at strain rates from 10 3 to 10 6 s 1 and temperatures from 1000 c to 1300 c in a gas medium deformation apparatus at 300 mpa confining pressure most of the tests were under wet conditions defined by the presence of small amounts of water from hydrous minerals initially present constant strain rate and relaxation experiments covering ranges of flow stress down to about 70 mpa and 7 mpa respectively show that there is a change in flow law in going below about 100 mpa differential stress and that the coarser grained rock is stronger than the finer grained one power law parameters above the transition are n 4 48 0 31 and q 498 38 kj mol 1 for aheim dunite and n 3 35 0 17 and q 444 24 kj mol 1 for anita bay dunite while below the transition relaxation tests on anita bay dunite give n 2 44 0 18 and q 386 27 kj mol 1 it is concluded that there is a weakening effect of water that this effect is mainly in the grain boundaries and that grain boundary sliding is probably a significant deformation mechanism at the lower stresses under wet conditions

rheology of some continental lower crustal rocks abstract to gain insight into the rheology of selected feldspar bearing rocks from the continental lower crust clc three granulites from exposed lower crustal terrains and a microgabbro have been deformed to ca 10 strain at confining pressures of 0 8 1 0 gpa temperatures of 600 900 c and constant strain rates of 10 4 10 7 s 1 the most extensive work was done on the mafic pikwitonei and felsic adirondack granulites the pikwitonei mg hornblende plag an70 2 px has only a limited t range of apparent steady state behavior and strain softens at t 800 c at 10 5 10 6s 1 apparently associated with developing shear zones this strain softening is pressure insensitive from pc 0 8 1 0 gpa at t 850 c 10 6s 1 even though the dominant strain accommodation mechanisms change from semibrittle cataclastic to crystal plastic including dynamic recrystallization with increasing pressure plagioclase appears to bear more of the creep strain than amphibole at most experimental conditions except in those runs where both plagioclase and amphibole recrystallization occurs kapuskasing plag cpx gt granulite deformed at 800 c and at 850 c 10 6 s 1 has deformed in the steady state at stress levels only slightly greater than the pikwitonei the stillwater microgabbro and adirondack granulite are appreciably weaker and the latter exhibits homogeneous semibrittle steady state behavior over the entire range of conditions investigated for the adirondack 2 felds 2 px gt qtz granulite quartz 21 appears to control the creep rate at these low strains and steady state mechanical data fit well a creep power law with a 8 10 3 mpa ns 1 qc 243 kj mol and n 3 1 extrapolation of this flow law and of preliminary power law creep relations for the pikwitonei and microgabbro to a range of physical conditions assumed to encompass those at the continental moho supports geological and geophysical inferences that a mechanical discontinuity occurs at this transition zone with the lower crust generally being the weaker material in addition the stain softening exhibited by the pikwitonei may bear directly on the development of detachment zones at mid to lower crustal depths during prograde metamorphism

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

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

heat flow variations in continental rifts abstract in the terrestrial thermal field continental rifts stand out as rather narrow regional thermal anomalies in which augmented heat flow is unevenly distributed heat flow variations are discussed on the example of the baikal east african cordilleran and rhine lybian rift systems rift related disturbance of the asthenosphere lithosphere system is accompanied by a general increase in the surficial heat flow regional thermal anomalies are mainly caused by conductive heat transfer from the asthenosphere local thermal anomalies are caused by magmatic mass transfer into the crust and by fluid convection along porous fracture systems

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

recent crustal movements in the southern black forest western germany precise levelling data are examined in the southern black forest massif by comparing them analytically along levelling profiles instead of generalizing regional vertical motion trends the method emphasizes the current activity of accurately located individual structural elements measured recent crustal movement rates range from 0 2 to 1 1 mm year for the 1930 1961 1972 period the inferred motions corresponding to aseismic fault creep based on the near infrared band image of a landsat mss scene a lineament map of the study area is compared with the recent crustal movement rcm map the upper rhine graben eastern border fault between badenweiler and freiburg displays the highest rcm these displacements are consistent with the geological motion and the topographic expression of that structure within the massif both the lineament map and the rcm map demonstrate the predominant role played by wnw ese to nw se striking structures in accommodating the deformation moreover with the seismic dislocations in the southern black forest taking place also mainly on n120 and n20 faults it is most probable that these active structures are deep reaching zones of crustal weakness to some extent seismicity and rcm appear however to be mutually exclusive in their spatial distribution the seismic black forest flexure and dinkelberg block being opposed to the aseismically moving eastern and northern parts of the study area

upper rhine graben role of preexisting structures during rift evolution 1 the evolution of the cenozoic upper rhine graben was controlled by a repeatedly changing stress field and the reactivation of a complex set of crustal discontinuities that had come into evidence during permo carboniferous times a comparison of the spatial and temporal thickness distribution of synrift deposits with preexisting fault patterns permits to infer a sequence of distinct basin subsidence phases that can be related to changes in the ambient stress field reactivation of a system of late palaeozoic fault systems outlining troughs and highs controlled the nucleation of initially separated middle and late eocene basins the depocenters of which coincided with a preexisting wsw ene trend during oligocene crustal extension the individual basins coalesced resulting in the development of the ssw nne striking upper rhine graben during the late oligocene chattian change in stress field the upper rhine graben was probably reactivated as a dextral strike slip system with the central graben segment forming a releasing bend during the early miocene aquitanian a major reorientation of the regional stress field is held responsible for the main subsidence phase of the northern parts of the upper rhine graben this is reflected by a counterclockwise rotation and northeastward shift of the depocenter axis and later by the middle miocene uplift and erosion of the southern parts of the upper rhine graben during the plio quaternary the upper rhine graben was reactivated as a sinistral strike slip system with the central graben segment forming a restraining bend

european cenozoic rift system abstract the european cenozoic rift system extends from the coast of the north sea to the mediterranean over a distance of some 1100 km it finds its southern prolongation in the valencia trough and a plio pleistocene volcanic chain crossing the atlas ranges development of this mega rift was paralleled by orogenic activity in the alps and pyrenees major rift domes accompanied by subsidence reversal of their axial grabens developed 20 40 ma after beginning of rifting uplift of the rhenish shield is related to progressive thermal lithospheric thinning the vosges black forest and the massif central domes are probably underlain by asthenoliths emplaced at the crust mantle boundary evolution of this rift system is thought to be governed by the interaction of the eurasian and african plates and by early phases of a plate boundary reorganization that may lead to the break up of the present continent assembly

the gravity field along the central segment of the egt abstract we give an overview of the gravity field of central europe based on a compilation of bouguer maps available by mid 1989 a generalized gravity map corrected for moho effects is presented as well as several filtered maps of the second derivative additionally sediment stripped bouguer maps are used in the case of the northwest german basin and for northeastern franconia the north german line the erzgebirge minimum the kraichgau high and the regensburg gottingen low are treated in detail and a number of geologic interpretations are discussed

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

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

contraints on the evolution of the mid german crystalline rise a study of outcrops west of the river rhine several small outcrops along the western rhinegraben escarpment expose rocks which represent the western prolongation of the so called mid german crystalline rise this basement ridge separates the rhenohercynian and saxothuringian zones of the variscan belt of europe and thus marks the boundary between the external and the internal zones the variable rock association includes an orthogneissamphibolite complex weakly deformed low grade sediments devonian and visean and a number of different syn to post orogenic granodioritic to granitic intrusives all crosscut by late lower carboniferous undeformed lamprophyric dikes and unconformable overlain by permian sediments and volcanics

transfer faults and pull apart model in the rhinegraben from analysis of multisource data from analysis of gravimetric data comparisons of levelings seismic profiling paleostress analysis and seismicity together with remotely sensed and morphological data the rhinegraben may be divided into several rhomb shaped basins separated by ene trending basement highs these data express neotectonic movements and slight spatial differences in the subsidence rate these basins are asymmetrical on one side they are bounded by a large several kilometers of vertical throw normal fault zone on the opposite side there is a megaflexure cut by smaller normal faults shaping tilted blocks since the middle miocene extensional directions are subparallel to the ene trending basement highs that consequently may be interpreted as strike slip fault zones of transfer type across the erstein basement high there is a reversal in the rift asymmetry major bordering fault on the western side to the south on the eastern side to the north when considered in the context of the west european rift the rhinegraben is interpreted in terms of a pull apart depression formed during the horizontal movement of blocks guided by large ene trending transcurrent faults the normal faults that are curved shaped in map view may mark the boundaries between areas where the maximum component 1 of the paleostress field developed in pull apart patterns was changing from horizontal to vertical