contribution of the surface and down hole seismic networks to the location of earthquakes at the soultz sous forets geothermal site france seismicity induced in geo reservoirs can be a valuable observation to image fractured reservoirs to characterize hydrological properties or to mitigate seismic hazard however this requires accurate location of the seismicity which is nowadays an important seismological task in reservoir engineering the earthquake location determination of the hypocentres depends on the model used to represent the medium in which the seismic waves propagate and on the seismic monitoring network in this work location uncertainties and location inaccuracies are modeled to investigate the impact of several parameters on the determination of the hypocentres the picking uncertainty the numerical precision of picked arrival times a velocity perturbation and the seismic network configuration the method is applied to the geothermal site of soultz sous forets which is located in the upper rhine graben france and which was subject to detailed scientific investigations we focus on a massive water injection performed in the year 2000 to enhance the productivity of the well gpk2 in the granitic basement at approximately 5 km depth and which induced more than 7000 earthquakes recorded by down hole and surface seismic networks we compare the location errors obtained from the joint or the separate use of the down hole and surface networks besides the quantification of location uncertainties caused by picking uncertainties the impact of the numerical precision of the picked arrival times as provided in a reference catalogue is investigated the velocity model is also modified to mimic possible effects of a massive water injection and to evaluate its impact on earthquake hypocentres it is shown that the use of the down hole network in addition to the surface network provides smaller location uncertainties but can also lead to larger inaccuracies hence location uncertainties would not be well representative of the location errors and interpretation of the seismicity distribution possibly biased this result also emphasizes that it is still necessary to properly describe the seismic propagation medium even though the addition of down hole sensors increases the coverage of a surface network

miocene range growth along the altyn tagh fault insights from apatite fission track and u th he thermochronometry in the western danghenan shan china the left lateral strike slip altyn tagh fault that defines the northern margin of the tibetan plateau plays a crucial role in accommodating the cenozoic deformation related to the growth of plateau however the slip history along the fault remains highly debated here we report new 14 16 ma apatite fission track aft and 9 11 ma apatite u th he ahe data in the western danghenan shan north tibet age elevation relationships and aft ahe age differences suggest a period of rapid exhumation with an average rate of 0 1 0 3 km ma from 16 to 9 ma for this area thermal history modeling indicates that this was preceded by accelerated exhumation between the late oligocene and middle miocene 15 ma a northward increase in aft ages and asymmetric topography across the western danghenan shan indicate that the uplift and exhumation are mainly controlled by the thrust fault along the southern flank of the western danghenan shan as the thrust fault is a branch of the altyn tagh fault the rapid exhumation probably represents onset of the transition along the altyn tagh fault from left slip motion to crustal shortening in the dangnenan shan region our findings show that the middle miocene deformation is not only recorded in the middle and northern qilian shan but also in the southwestern portion of the qilian shan which favors a synchronous middle miocene deformation model for the entire qilian shan

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

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

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

lithospheric breakup in three dimensions necking of a work hardening plastic plate lithospheric breakup is in general oblique to the principal strain axes with shortening in one horizontal axis eh 0 local necking of the plate including the mantle part of the lithosphere is necessary for the creation of a divergent plate boundary the necking develops as a mechanical instability that decreases the resistance of the plate to extension despite the intrinsic hardening of the material we model the flow that precedes breakup stressing two aspects that have been overlooked before 1 three dimensional flow and 2 strain dependent strength of the lithosphere the model mimics spatial and temporal features of the most extensively documented rift systems the neck is oblique to the direction of principal extension and the transition from diffuse stretching to local necking is abrupt at 5 10 strain the critical strain for local necking in the model appears to be independent of the intrinsic strength therefore various rheological layers brittle upper crust ductile lower crust and stiffer but hotter mantle lithosphere may neck concomitantly to form a rift

progress in birps deep seismic reflection profiling around the british isles abstract the results of 4000 km of new birps profiles are briefly outlined as an introduction to other birps papers in this volume highlights of these profiles include the tracing for 900 km of a reflection pattern in the lower crust associated with the lapetus suture and the observation of more than 20 separate reflections from the mantle while progress in solving the problem of deep water multiples has enabled the joining of the continental and oceanic moho reflections off sw england developments in old interpretational problems are reviewed and the new problem of dating reflections is mentioned

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

seismicity wedge beneath the upper rhine graben due to backwards alpine push abstract the distribution of hypocentres in the upper rhine graben area is re examined and discussed with respect to the present day tectonic framework most earthquakes occur within a n60 striking wedge located on top of a moho dome this wedge is limited by the surface and at depth by a plane which in the south of the dome coincides with the se dipping conrad discontinuity in depth the seismicity shows a normal distribution the maximums of which are located on a surface dipping 6 towards se parallel to the south eastward dipping conrad and moho this surface outcrops along the north western edge of the uplifted crystalline vosges and black forest the main shocks in earthquake swarms in the region often occur in the vicinity of this surface and along pre existing n s to ne sw variscan or tertiary faults and show focal mechanisms of strike slip in contrast part of the aftershocks show focal mechanisms of reverse faulting associated with se nw striking compression the seismic wedge and the north westward rising seismic surface suggest initiation of crustal ramp which starts at the south eastern rim of the conrad dome and which may become a thrust plane if se nw compression continues in the south eastern edge of the graben and above the south eastern ridge of the moho dome where evidences for extension have been found we identify clustering of hypocentres along a surface that strikes n150 parallel to the main compression and dipping towards ne dominant normal faulting mechanisms along this surface suggests initiation of a normal probably listric fault at depth the onset of the future fault plane is located on top of the nw se striking ridge of the lower crust and moho which act as a an indenter in addition to thrusting of the whole wedge towards nw increasing of nw se compression would lead to the formation of a half graben at the place of the present sierentz depression

a microseismic study in the western part of the gulf of corinth greece implications for large scale normal faulting mechanisms summary we present the results of a dense seismological experiment in the western part of the gulf of corinth psathopyrgos aigion area one of the most active rifts in the aegean region for which we have precise tectonic information the network included 51 digital stations that operated during july and august 1991 covering a surface of 40 x 40 km2 among the 5000 recorded events with ml ranging between 1 0 and 3 0 we precisely located 774 events we obtained 148 well constrained focal mechanisms using p wave first motions of these 60 also have mechanisms obtained by combining the p wave first motions with the s wave polarization directions the observed seismicity is mainly located between 6 and 11 km depth most of the fault plane solutions correspond to e w striking normal faulting in agreement with the geological evidence most of the well determined mechanisms indicate a nodal plane dipping 10 25 due north and a steep south dipping plane a similar asymmetry is also seen in the seismicity distribution and in the overall geological structure of the corinth rift we discuss this evidence and the inference of a deep detachment zone a structure where the major faults seen at the surface appear to root a large part of the microseismic activity appears to cluster in regions near the junctions of the main faults with the proposed detachment zone this feature of the microseismicity is interpreted in terms of stress transfer and stress concentration in regions of probable nucleation of future large earthquakes

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

late orogenic basin evolution in the variscan internides the saar nahe basin southwest germany abstract the late variscan evolution of the saar nahe basin in southwest germany is closely controlled by the kinematics of the hunsruck boundary fault which also separates two main tectonostratigraphic units of the variscides the saar nahe basin comprises a half graben structure which formed due to extensional reactivation of a variscan thrust between the early westphalian and late rotliegend about 8 5 km of alluvial fan fluvial and lacustrine sediments accumulated during the permo carboniferous w e oriented extension was accommodated by a system of nw se trending transfer faults and orthogonal normal faults balanced cross section construction and subsidence analyses suggest a 35 extension of the previously thickened crust in the late stage of the orogeny the subsidence analyses show discontinuous depth dependent extension with laterally varying extension factors in the crust and mantle the offset between syn and post rift depocentres is explained by a mantle stretching zone shifted laterally with respect to the area of maximum crustal extension finally a geodynamic model for the evolution of the saar nahe basin with special reference to the earlier variscan development and the general evolution of permo carboniferous basins in central europe is presented

deep structure of the north tyrrhenian sea from multi channel seismic profiles and on land wide angle reflection refraction seismic recording lisa cruise geodynamical implications we present a lithospheric section of the northern tyrrhenian basin based on principal observations along a transect from corsica island to tuscany margin offshore crustal structure observations come from the lisa deep seismic cruise composed by multi channel seismic profiles and wide angle reflection refraction seismic data other parts of the section are constrained by published data from different geophysical sources a great detachment between alpine corsica and hercynian corsica constitutes the base of the corsica basin the end of this detachment is probably located below the elba island in the ductile lower crust where we observed an east dipping reflector interpreted as ductile shear zone similar detachments have been observed beneath the punta ala basin on the tuscany margin our section shows a thin crust below corsican basin 15 km thick and a thicker crust below the pianosa ridge 25 km between elba island and the tuscany coast the moho reflections shallow to 23 km depth as identified on the mcs profiles and from the modelling of the wide angle reflection refraction seismic date an asthenospheric mantle uplift produces a significant heat flow below the tuscany margin the base of the lithosphere is located at 75 km depth below the corsica margin at 50 km below the corsica basin and as shallow as 30 km below the tuscany margin the shift observed between the corsica basin and the tuscany coast suggests an asymmetric lithospheric thinning which involves a detachment fault located at the base of the corsican basin

segmentation and along strike asymmetry of the passive margin in socotra eastern gulf of aden are they controlled by detachment faults on the island of socotra the southern passive margin of the gulf of aden displays along its strike two different types of asymmetric structures western socotra is made up of a series of southward tilted blocks bounded by consistently northward dipping normal faults eastern socotra consists of a broad asymmetric anticline with a steep northern limb and a gently dipping southern limb a zone of ne sw striking strike slip and normal faults separates the two areas the overall structure is interpreted as representing two rift segments separated by a transfer zone the along strike juxtaposition of crustal scale asymmetric structures on the southern margin of the gulf of aden is complemented by the asymmetry of the conjugate margins on either side of the gulf whereas the western socotra margin is narrow and characterized by oceanward dipping normal faults the conjugate oman margin is broader and dominated by horsts and graben considering that asymmetric structures in the upper crust are often associated with synthetic shear zones at deeper ductile levels we propose that the western and eastern socotra margin segments were controlled at depth by two detachment faults with opposite dips and senses of shear the normal faults of western socotra would sole out into a top to the north ductile shear zone whereas the asymmetric anticline of eastern socotra would be associated with a top to the south detachment fault

the evolution of the layered lower crust and the moho through geological time in western europe contribution of deep seismic reflection profiles deep seismic reflection images from a set of profiles shot in western europe have been reviewed and compared and tentative conclusions have been proposed concerning the evolution of the layered lower crust and the moho the disappearance of variscan mountain roots is related to the set up of a new moho at a typical 30 km depth and the creation of seismic layering in the lower crust deep seismic profiles suggest that these processes resulted at least in part from magmatic intrusion partial crustal melting and metamorphism of deep crustal rocks into eclogite on the other hand the layered lower crust is greatly attenuated beneath cretaceous basins and tertiary rifts in relation to prominent moho upwellings the unusual amplitude of the moho reflection and the presence of anomalously high seismic velocities in the lowermost crust beneath the tertiary rifts suggest that the moho and part of the layering are comparatively young features related to interactions between crust and mantle beneath triassic jurassic basins the layered lower crust was not affected by the subsidence of the basement with the whole crustal thinning being entirely concentrated in the upper crust this indicates that the layered lower crust and the moho were formed or restored during or after the main rifting phase seismic data reveal constraints on the processes that affect the crust mantle transition and seem to restore the moho to its typical depth after any mechanical deformation of the lithosphere

anatomy and kinematics of oblique continental rifting revealed a three dimensional case study of the southeast upper rhine graben germany the upper rhine graben is a north northeast trending small displacement crustal scale rift of tertiary age retrodeformation of its southeastern part demonstrates that it is a product of sinistral oblique rifting early extension was toward 80 later the major stretching axis changed to a 60 direction the modeling results suggest that the eastern main border fault developed first and that faulting later propagated into the evolving graben interior considerable along strike variations in heave throw and displacement are evident displacement partitioning causes warping of the rift floor with a 30 35 km wavelength we consider this to be a characteristic of oblique rifting contact deformation of the wall rocks to the major faults may have caused widespread smaller scale faulting and brecciation and may be the location of later movements close spatial coincidence of the depth projections of some of the faults studied and the hypocenters of recent small earthquakes indicates continuing activity of the fault system apparently three fault segments in the freiburg area are currently active and may be an increased earthquake risk

lower crustal thinning in the rhinegraben implications for recent rifting seismic near vertical and undershooting experiments carried out in the southern upper rhinegraben area between 1984 and 1991 show pronounced lateral variations of deep crustal properties significant differences in the apparent thickness of the reflective lower crust and the transparent upper crust appear to be related to different structural settings a 12 to 14 km thick reflective lower crust beneath a 15 km thick transparent upper crust of the eastern graben shoulder black forest probably originated during permo carboniferous reequilibration of thickened variscan orogenic crust thinning of this lower crust by about 5 km beneath the graben and rifted domains transitional between graben and shoulder the dinkelberg block is interpreted to be related to cenozoic extensional faulting a discrepancy between moderate extension of upper crust and lower crustal geometry indicates mechanical decoupling at depth during extension congruent modification of other physical properties is suggested by strong single reflective elements in the topmost parts of the thinned lower crust in the transitional dinkelberg block such an anomalously strong reflector occurs at a depth of 20 km below a pronounced local maximum of earthquake activity it is interpreted to be the presently active zone of decoupling which in time shifted from the rift axis to the eastern transition area

neotectonics and intraplate continental topography of the northern alpine foreland research on neotectonics and related seismicity has hitherto been mostly focused on active plate boundaries that are characterized by generally high levels of earthquake activity current seismic hazard estimates for intraplate domains are mainly based on probabilistic analyses of historical and instrumental earthquake catalogues the accuracy of such hazard estimates is limited by the fact that available catalogues are restricted to a few hundred years which on geological time scales is insignificant and not suitable for the assessment of tectonic processes controlling the observed earthquake activity more reliable hazard prediction requires access to high quality data sets covering a geologically significant time span in order to obtain a better understanding of processes controlling on going intraplate deformation the alpine orogen and the intraplate sedimentary basins and rifts in its northern foreland are associated with a much higher level of neotectonic activity than hitherto assumed seismicity and stress indicator data combined with geodetic and geomorphologic observations demonstrate that deformation of the northern alpine foreland is still on going and will continue in the future this has major implications for the assessment of natural hazards and the environmental degradation potential of this densely populated area we examine relationships between deeper lithospheric processes neotectonics and surface processes in the northern alpine foreland and their implications for tectonically induced topography for the environmental tectonics project entec the upper and lower rhine graben urg and lrg and the vienna basin vb were selected as natural laboratories the vienna basin developed during the middle miocene as a sinistral pull apart structure on top of the east alpine nappe stack whereas the upper and lower rhine grabens are typical intracontinental rifts the upper rhine graben opened during its late eocene and oligocene initial rifting phase by nearly orthogonal crustal extension whereas its neogene evolution was controlled by oblique extension seismic tomography suggests that during extension the mantle lithosphere was partially decoupled from the upper crust at the level of the lower crust however whole lithospheric folding controlled the mid miocene to pliocene uplift of the vosges black forest arch whereas thermal thinning of the mantle lithosphere above a mantle plume contributed substantially to the past and present uplift of the rhenish massif by contrast oblique crustal extension controlling the late oligocene initial subsidence stage of the lower rhine graben gave way to orthogonal extension at the transition to the neogene the entec project integrated geological geophysical geomorphologic geodetic and seismological data and developed dynamic models to quantify the societal impact of neotectonics in areas hosting major urban and industrial activity concentrations the response of europe s intraplate lithosphere to late neogene compressional stresses depends largely on its thermo mechanical structure which in turn controls vertical motions topography evolution and related surface processes

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

graben width controlling syn rift sedimentation the palaeogene southern upper rhine graben as an example eocene to early oligocene syn rift deposits of the southern upper rhine graben urg accumulated in restricted environments sedimentation was controlled by local clastic supply from the graben flanks as well as by strong intra basinal variations in accommodation space due to differential tectonic subsidence that in turn led to pronounced lateral variations in depositional environment three large scale cycles of intensified evaporite sedimentation were interrupted by temporary changes towards brackish or freshwater conditions they form three major base level cycles that can be traced throughout the basin each of them representing a stratigraphic sub unit a relatively constant amount of horizontal extension l in the range of 4 5 km has been estimated for the urg from numerous cross sections the width of the rift lf however varies between 35 and more than 60 km resulting in a variable crustal stretching factor between the bounding masterfaults apart from block tilting tectonic subsidence was therefore largely controlled by changes in the initial rift width l0 the along strike variations of the graben width are responsible for the development of a deep trough like evaporite basin potash basin in the narrowest part of the southern urg adjacent to shallow areas in the wider parts of the rift such as the colmar swell in the north and the rhine bresse transfer zone that delimits the urg to the south under a constant amount of extension the along strike variation in rift width is the principal factor controlling depo centre development in extensional basins

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

on the number and spacing of faults orogens and rift zones have a finite number of regional faults the accretionary prisms analysed here have a number of thrusts 50 whereas extensional areas have a number of normal faults ranging between six and 44 the average spacing of thrusts is between 5 and 25 km spacing of normal faults is more restricted into two peaks at 25 29 km and 4 6 km in which the latter is the most common the number and spacing of faults appear to be mainly controlled by the depth of the decollement plane which seems to be more variable in compressive settings with respect to rift zones basementinvolved orogens present fewer and more spaced thrusts by contrast a greater number of thrusts with shorter spacing characterize thin skinned thrust belts the shallower the decollement is the stronger it appears to control the palaeogeography in the sense of rheological lateral variations in the sedimentary cover

the permo carboniferous saar nahe basin south west germany and north east france basin formation and deformation in a strike slip regime the permo carboniferous saar nahe basin in south west germany and north east france formed at the boundary between the rhenohercynian and saxothuringian zones within the variscan orogen where non marine sediments were deposited in a narrow structurally controlled basin the basin has an asymmetrical geometry perpendicular to the south hunsruck fault however there is a lack of growth of the sediment pile into the fault and isopach maps show the depocentre always located adjacent to the south hunsruck fault but migrating towards the north east with time this pattern is typical of a strike slip basin indicating that the south hunsruck fault was a dextral strike slip fault during sedimentation tectonic subsidence curves indicate that during the middle devonian to early carboniferous the basin subsided due to thermal relaxation of the lithosphere a change to very rapid subsidence at the start of the westphalian continued until late in the autunian this was due to mechanical subsidence associated with strike slip movement on the south hunsruck fault towards the end of subsidence in the saar nahe basin the grenzlager volcanics introduced a thermal pulse into the crust leading to thermal cooling and relaxation of the lithosphere

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

gravity and magnetic constraints on deep and intermediate crustal structure and evolution models for the rhine graben abstract the dekorp ecors project comprises two deep seismic reflection lines shot across the rhine graben in its southern part s of strasbourg and in its northern portion 30 km to the n of mannheim respectively in order to assist the geologic interpretation of the northern deep seismic line dekorp 9n an analysis of the gravity and magnetic data of the study area was undertaken in particular the removal stripping of the gravity effect of the tertiary and quaternary sedimentary infill enabled us to establish the existence of a gravity high over the graben proper this gravity high is asymmetrical with a steep gradient to the east and a gentler one to the west interpretation of a regional anomaly obtained by low pass filtering from a 400 km gravity profile incorporating the results from the stripping in terms of the moho topography indicates that the moho is shallower under the graben proper estimates of depths to the magnetic sources by spectral statistical analysis were conducted the mean depth to the magnetic sources ranges between 2 and 3 km the depth to the curie isotherm is estimated to be located between 15 and 18 km magnetic modelling indicates the existence of discontinuities in the crystalline basement that can be correlated with faults affecting the sedimentary infill a density model was produced that incorporated the image obtained by the deep seismic geotraverse constrained by the geology the known petrophysical parameters density magnetic properties results from seismic refraction studies and the information derived here this indicated the feasibility of an asymmetric heterogeneous extension related mechanism for the northern part of the rhine graben the lithosphere is characterized by a thicker lower crust to the west a mantle upwelling beneath the graben proper and a shear zone crossing the lithosphere

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

a multi scale approach to study the lithospheric structure of the southern upper rhine graben from seismic tomography through reflection seismics to surface geology this paper integrates the results of different techniques local and regional travel time tomography reflection seismics and surface geology with this integration of different techniques working on different scales it is possible to derive a comprehensive picture of the present day structures in the lithosphere of the upper rhine graben it is shown that the stucture of the lithosphere is dominated by structures related to the variscan orogeny late stage strike slip reactivation of the internal faults of the rhine graben is observed in the field this reactivation is of dominant influence on the geomorphology in the southern end of the upper rhine graben

crustal scale thrusting and extension in the hercynian schwarzwald and vosges central europe the hercynian outcrop areas in the schwarzwald of sw germany and vosges of easternmost france consist from north to south of three major lithotectonic complexes very low to medium grade metamorphics of the saxothuringian belt the polymetamorphic central gneiss complex and the tectonic melange of the southern complex juxtaposition of these three complexes occurred by oblique convergent motions in early carboniferous time the saxothuringian belt is part of a major se dipping accretionary wedge that consists of lower paleozoic meta sedimentary and metaigneous rocks and superimposed upper devonian to lower carboniferous synorogenic volcanics and elastics the central gneiss complex consists of polymetamorphic paragneisses orthogneisses metabasites and meta ultramafics dipping to the nw the southern complex consists of an imbricated melange of north to nw dipping synorogenic elastics volcanics and blocks of ultramafics and gneissic basement the central gneiss complex cgc experienced pervasive hercynian low pressure high temperature metamorphisrn before it was emplaced against and thrust over the sedimentary and volcanic fill of the adjacent synorogenic basins this convergence 340 330 ma produced mylonitic cataclastic shear zones in the cgc the most significant shear zones are the se verging todtnau fault zone between the cgc and the southern complex and the nw verging lubine fault zone between the central gneiss complex and the rocks of the saxothuringian belt these two fault zones enclose a bivergent pop up of the polymetamorphic basement the todtnau fault zone probably extends for more than 100 km along strike and can be traced to a depth of 10 km by deep seismic reflection studies detachment probably occurred along a mid crustal zone of anatexis expressed by a domain of low seismic reflectivity between about 10 and 15 km crustal thickening during early carboniferous convergence led to an extensional phase of crustal reordering between about 330 and 280 ma that was accompanied by the massive rise of posttectonic granitic plutons from middle to high crustal levels simultaneous creation of a structural lamination in the refractory lower crust neglected the main convergent tectonic boundaries it produced a basin and range type lower crust and mantle crust transition in early permian time and involved a major advective input of heat

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 strength of intraplate lithosphere abstract the deformation of intraplate lithosphere in response to laterally applied stress has been investigated using a mathematical model of the elastic brittle and viscous response of the lithosphere fundamental to the model is the conservation of the horizontal force associated with the applied stress and the redistribution of stress within the lithosphere after stress release by ductile or brittle failure ductile deformation is assumed to be controlled by dislocation creep in quartz in the crust and by dislocation and dorn law creep in olivine in the mantle brittle failure is predicted using griffith theory the redistribution of stress after brittle and ductile deformation results in large levels of stress in the middle and lower crust immediately above the elastic ductile or brittle ductile transition lithosphere deformation is controlled critically by the lithosphere thermal structure of which surface heat flow q is taken as a convenient indicator for hotter lithosphere stress release by ductile deformation in the middle and lower lithosphere is more extensive and rapidly leads to larger levels of stress in the upper lithosphere for sufficiently large levels of applied stress or sufficiently hot lithosphere complete failure whole lithosphere failure of the lithosphere occurs by ductile and brittle deformation resulting in geologically significant strains critical levels of applied stress required to produce whole lithosphere failure have been computed as a function of the lithosphere surface heat flow the predicted strength of the lithosphere has been compared with expected levels of intraplate stress arising from plate boundary forces and isostatically compensated loads the model predicts significant extensional intraplate deformation in regions of moderate heat flow with q 60 m w m 2 for compressional deformation however a hotter lithosphere is required with q c 75 m w m 2 the model predictions are in general agreement with the comparatively widespread occurrence of extensional intraplate deformation and the restricted occurrence of compressional deformation the model has also been used to investigate the relationship between the depth of the brittle ductile transition and lithosphere temperature structure the brittle ductile transition depth is shown to become shallower with increasing heat flow in good agreement with seismic evidence

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

s p wave travel time residuals and lateral inhomogeneity in the mantle beneath tibet and the himalaya the average s wave travel time residuals from 11 earthquakes each in tibet and the himalaya imply that there are marked lateral variations in structure beneath tibet and the himalaya average s p wave residuals measured with respect to the jeffreys bullen j b tables for each of 11 earthquakes in the himalaya are less than 1 s average j b s p residuals from 10 of 11 earthquakes in tibet however are greater than 1 s even when corrected for the large crustal thickness of tibet the largest values 2 5 3 2 3 8 4 5 and 4 9 s are for five events in central and northern tibet and they imply that the average velocities in the crust and upper mantle of these portions of tibet are 4 10 lower than those beneath the himalaya therefore it is unlikely that a shield structure underlies these parts of tibet unless these s p residuals are due to variations in structure deeper than 250 km s p residuals from two other events each in western and eastern tibet are 1 2 s late and hence suggest that velocities beneath these areas are also somewhat lower than beneath shields the mean s wave velocity seems not only to be different beneath tibet and the himalaya but also seems to increase from a minimum beneath northern tibet to values close to those of the average earth toward the east south and west appendix a is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b84 010 2 50 payment must accompany order

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

implications of incremental emplacement of magma bodies for magma differentiation thermal aureole dimensions and plutonism volcanism relationships abstract field observations and geophysical data indicate that many igneous bodies grow by amalgamation of successive magma pulses that commonly take the shape of horizontal sheets sills emplacement styles and emplacement rates of magma bodies have fundamental implications on magma differentiation country rock metamorphism and assimilation and for the formation of large magma chambers in the upper crust when a magma body begins to grow by slow accretion of sills each successive intrusion solidifies before the injection of the next one when the system is thermally mature sill temperatures equilibrate above the solidus melts accumulate and older sills can re melt the time needed for each magma injection to cool down and equilibrate with its surrounding is short relatively to the total emplacement time of the body the transition from a mafic crystal poor magma to a partially molten rock that retains a highly differentiated melt is fast whereas the resulting evolved residual melt can reside in the crust for protracted periods as long as temperatures in the system are relatively low highly differentiated melts are generated which may explain the bi modal character and the absence of intermediate compositions in some magmatic provinces the level of emplacement of successive magma pulses controls the shape of the thermal anomaly associated with the magma body growth metamorphism partial melting and assimilation of the country rock are favoured if successive magma sheets are emplaced at or close to the country rock magma body boundary if the magma emplacement rate is low the size of the thermal aureole is controlled by the size of one pulse and not by the size of the entire igneous body understanding emplacement of magma bodies is fundamental for our understanding of the plutonism volcanism relationship magma emplacement rates of several centimetres per year are needed for a magma body to evolve into a large magma chamber able to feed large silicic explosive eruptions the time averaged emplacement rates of plutons are lower than this critical emplacement rate eruptions of 100s to 1000s cubic kilometres of silicic products show that such high volumes of magmas can accumulate in the upper crust this suggests that the emplacement of magma bodies is a multi timescale process with the development of large magma chambers corresponding to the highest magma fluxes because they control magmatic processes and the impact of magma intrusion on the country rock future studies should focus on magma emplacement rates and on magma emplacement geometries these studies should integrate field observation on plutons and geophysical data on active magmatic systems coupled with laboratory experiments and numerical simulations

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

spatial variations of earthquake occurrence and coseismic deformation in the upper rhine graben central europe abstract seismic activity in the densely populated upper rhine graben urg is an aspect in the public political and industrial decision making process the spatial analysis of magnitude frequency distributions provides valuable information about local seismicity patterns and regional seismic hazard assessment and can be used also as a proxy for coseismic deformation to explore the seismo tectonic setting of the urg we combine five instrumental and one historic earthquake bulletins to obtain for the first time a consistent database for events with local magnitudes m l 2 0 in the whole urg and use it for the determination of magnitude frequencies the data processing results in a dataset with 274 poisson distributed instrumentally recorded earthquakes within the urg between 01 1971 and 02 2012 and 34 historic events since the year 1250 our analysis reveals significant b value variations along the urg that allow us to differentiate four distinct sections i iv with significant differences in earthquake magnitude distributions i basel region in the swiss france german border region b 0 83 ii region between mulhouse and freiburg in the southern urg b 1 42 iii central urg b 0 93 and iv northern urg b 1 06 high b values and thus a relatively low amount of high magnitude events in the freiburg section are possibly a consequence of strongly segmented small scale structures that are not able to accumulate high stresses we use the obtained magnitude frequency distributions and representative source mechanisms for each section to determine coseismic displacement rates a maximum horizontal displacement rate of 41 m a around basel is found whereas only 8 m a are derived for the central and northern urg a comparison with geodetic and geological constraints implies that the coseismic displacement rates cover less than 10 of the overall displacement rates suggesting a high amount of aseismic deformation in the urg

reflectivity patterns in the variscan mountain belts and adjacent areas an attempt for a pattern recognition and correlation to tectonic units abstract the seismic reflection profiles of dekorp deutsches kontinentales reflexionsseismisches programm in the federal republic of germany to date have been limited to areas of the variscan orogeny nevertheless the character of their reflections differs considerably and may be correlated to certain variscan and post variscan developments lower crust lamellae develop in areas of high heat flow mostly associated with post variscan extensional processes crocodile and nappe tectonics are best preserved in the cores and at the flanks of older massifs which were incorporated into the variscan orogeny so far poor reflectivity has been observed only in the area of the london brabant massif which was not involved in any of the phanerozoic orogenies

orogenic mass transfer and reflection seismic patterns evidence from dekorp sections across the european variscides central germany abstract orogenic wedges evolve by different mass transfer modes which control different styles of deformation metamorphic pattern and bulk reflectivity structural patterns and reflectivity strongly vary depending mainly on the length thickness ratio of thrust sheets and on their displacement length ratio reevaluation of dekorp seismic sections across the central european variscides lines dekorp 1a c 9n 2n 2s 3b underlines the usefulness of the integrated interpretation strategy in establishing orogenic growth mode and evolution the results are in contrast with reflectivity patterns predicted from critical taper theory the northern flank of the mid european variscides is formed by a doubly vergent orogenic wedge system which evolved from collision of a passive margin rhenohercynian zone with a continental arc mid german crystalline rise mgcr of the saxothuringian zone the two fold and thrust wedges show inward dipping shear zone related reflections above subhorizontal mid crustal reflection bands evidence of dominantly frontal accretion of upper crustal material in both wedges in contrast the sections crossing the axial zone mgcr either show arched reflection stacks related to underplated amphibolite facies rocks in exposed antiformal nappe stacks or a transparent wedge shaped unit related to low grade calcalkaline magmatics and steeply dipping devono carboniferous sediments of the former upper plate magmatic arc analysis suggests that part of this arc was tectonically eroded prior to collision in combination with isograd and structural patterns the observed features indicate that heterogeneous basal accretion was the dominant accretion mode in the axial zone during collision the discussed patterns are suggested to reflect the material transfer site into the orogenic wedge and therefore also growth mode and material provenance in collisional belts