the mesozoic and tertiary basins of the bohemian massif and their evolution abstract the bohemian massif is a major positive element within the structural framework of the alpine carpathian foreland its basement became consolidated during the variscan orogeny crustal thicknesses range between 32 5 km and 40 km during the late carboniferous and early permian the bohemian massif became dissected by a conjugate system of wrench faults which controlled the accumulation of a continental coal bearing series late permian red beds were deposited on intramontane topographic depressions in triassic to mid jurassic times the bohemian massif formed a high from which clastics were shed into adjacent basins during the late jurassic and late cretaceous it became transected by nw se trending sedimentary basins the sub hercynian and laramide phases of foreland compression resulted in deformation and uplift of the bohemian massif the eger graben a 350 km long volcanotectonic zone cutting across the bohemian massif in an ene wsw direction came into evidence during the oligocene and is at present inactive the crust of the bohemian massif forms the autochthonous substratum of the outer carpathians which are paralleled by the neogene carpathian foredeep the neogene intramontane neo autochthonous vienna basin is superimposed on the alpine carpathian nappe systems and developed under a tensional setting

pre neogene controls on present day fault activity in the west netherlands basin and roer valley rift system southern netherlands role of variations in fault orientation in a uniform low stress regime the west netherlands basin wnb and the neighbouring roer valley rift system rvrs form the most prominent tectonic features of the onshore netherlands the two basins have a common tectonic origin and similar mesozoic evolution their neogene quaternary evolution however is markedly different while the wnb is tectonically seismically inactive and is characterised by uniform neogene quaternary subsidence in the rvrs fault controlled intra plate deformation has taken place since late oligocene times with pronounced seismic activity considering the present day ne sw regional extension as well as the similar basin orientation and mesozoic evolutions one would not expect strikingly different neotectonic activity in the two basins detailed analysis of mesozoic tertiary and quaternary fault patterns revealed that 1 the palaeozoic mesozoic tectonic fabric has great influence on the cenozoic deformation style of the basin system 2 present day faulting in the rvrs is related to the reactivation of pre existing faults and 3 the mesozoic fault pattern is slightly different in the two basins using a novel technique three dimensional 3 d slip tendency analysis we aim to determine whether these differences in fault orientation are substantial enough to produce significantly different resolved stresses along the faults this modelling not only tests a common geological phenomena but indirectly also delivers important constraints regarding the origin of faulting in the study area during the analysis 3 d geometric models of 84 mapped faults were investigated the results of this recently developed modelling technique reveal that the faults in both basins should behave similarly under the condition of a laterally homogeneous regional stress field which is in disagreement with the present day tectonic activity of the region on the other hand the modelling also reveals that the predicted tendency of slip is very sensitive to the ratio of the minimum horizontal and the vertical stress s as an explanation for the pronounced fault activity in the rvrs and the tectonic quietness of the wnb it is proposed that either the regional extension in the wnb is weaker in term of higher s ratio than that in the rvrs or the slip thresholds in the two basins are different the study emphasised that differentiation in the tectonic evolution has already started in the tertiary therefore it is reasonable to assume that the different tectonic stress field and or slip threshold between the two areas is directly related to the origin of the cenozoic rifting in the rvrs several hypotheses are discussed to account for these two possibilities taking into account the lithospheric structure and the cenozoic tectonic evolution of the two basins as well as surrounding areas 2004 elsevier ltd all rights reserved

north sea rift system abstract the mesozoic north sea rift forms an integral part of the arctic north atlantic rift system rifting activity in the north sea commenced during the earliest triassic during the mid jurassic the central north sea underwent a temporary doming stage crustal extension peaked during the late jurassic earliest cretaceous abated subsequently and terminated altogether during the paleocene the saucer shaped cenozoic post rift basin straddles the axis of the viking and central grabens this speaks for the applicability of a depth dependent pure shear model rather than a simple shear model geophysical data indicate an important discrepancy between upper and lower crustal attenuation across the north sea rift suggesting that during rifting processes the mono discontinuity was seriously destabilized this requires a basic modification of currently favoured crustal stretching models

comparative tertiary stratigraphy of the rhine graben bresse graben and molasse basin correlation of alpine foreland events abstract comparative tectonostratigraphic analysis of the tertiary middle eocene pliocene of the rhine bresse graben system and the western molasse basin demonstrates the occurrence of eleven correlative sequences crf i xi these show a close relationship between intra basinal tectonics and depositional history their punctuated sediment accumulation can be related to phases of extra alpine taphrogenesis and alpine orogenesis and to coeval eustatic changes in sea level apparent simultaneity in rift and foredeep sequence development structural deformation and global change in sea level suggests a common causal control in which the development of the alps played an important role

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

the structure and evolution of the wessex basin southern england an example of inversion tectonics abstract the wessex basin of southern england consists of four main sub basins each sub basin is thought to be fundamentally controlled by the normal reactivation of hercynian basement thrust and wrench or transfer faults post hercynian polyphase reactivation of both east west thrust and northwest southeast transfer faults tended to compartmentalise the basement thereby leading to the initiation of discrete permian cretaceous depocentres while rifting was confined to the western portions of the area during the permo triassic easterly migration in the mesozoic allowed the initiation of the weald and channel basins the sub basins represent therefore simple sinistral pull apart basins opening along northwest southeast faults this same fault direction is postulated to have also played a major role in controlling and or modifying the development of european basins in general major pre aptian uplift and erosion is largely attributed to the thermal effects and hence the isostatic uplift of the basin associated with continental rifting of the bay of biscay and the north atlantic margins major inversion and hence basin destruction began in the late cretaceous early tertiary with the uplift of the channel weald and vale of pewsey basins and culminated in the oligocene miocene synchronous with the helvetic phase of alpine deformation wessex basin inversion was facilitated by the thrust reactivation of variscan faults above an intracrustal detachment surface the same surface which allowed upper crustal extension and hence basin initiation in the permo triassic the structural development of the wessex basin both during extension basin formation phase and compression inversion phase was ultimately controlled by the plate motion of africa relative to europe such plate motions successfully predict the observed nw se sinistral motion from the stephanian to the aptian e w sinistral motion during the aptian cenomanian and largely nw se dextral motion from the cenomanian to the present day

reply to comments by l michon and o merle on evolution of the european cenozoic rift system interaction of the alpine and pyrenean orogens with their foreland lithosphere by p dezes s m schmid and p a ziegler tectonophysics 389 2004 1 33

slab breakoff a model for syncollisional magmatism and tectonics in the alps slab breakoff is the buoyancy driven detachment of subducted oceanic lithosphere from the light continental lithosphere that follows it during continental collision in a recent paper davies and von blanckenburg 1994 have assessed the physical conditions leading to breakoff by quantitative thermomechanical modeling and have predicted various consequences in the evolution of mountain belts breakoff will lead to heating of the overriding lithospheric mantle by upwelling asthenosphere melting of its enriched layers and thus to bimodal magmatism breakoff will also lead to thermal weakening of the subducted crustal lithosphere thereby allowing buoyant rise of released crustal slices from mantle depths in this paper we present a test of this model in the tertiary evolution of the european alps in the alps both basaltic and granitoid magmatism occur between 42 and 25 ma following the closure of oceanic basins by subduction and continental collision the granitoids are now well established to result from mixing of basalt with assimilated continental crust to identify the tectonically crucial origin of the partial mantle melts we have compiled all published geochemical and isotopic data of numerous mafic dykes occurring throughout the whole alpine arc their trace element and isotopic composition suggests that they have been formed by low degree melting of the mechanically stable lithospheric mantle we see no evidence for melting of asthenospheric mantle it was thus not decompressed to depths shallower than 50 km once initiated rapid lateral migration of slab breakoff will result in a linear trace of magmatism in locally thermal weakened crust this explains why all alpine magmatic rocks intruded almost synchronously along a strike slip fault the periadriatic lineament a compilation of ages from penninic high pressure rocks subducted to depths of up to 100 km shows that subduction took place at circa 55 40 ma followed by uplift at 40 35 ma from the short time interval between their uplift and the onset of magmatism we infer that both processes have been induced by the breakoff the slab breakoff model fulfills its predictions in the case of the alps and therefore supports the assumptions made in the theoretical model on a geological basis we believe that the characteristic association of magmatic activity with the return of high pressure rocks to the surface allows the identification of this process in the earth s mountain belts

the pyrenean inversion phase in northern belgium an example of a relaxation inversion the analysis of 2d seismic and well data provides new insights into the late eocene to earliest oligocene dynamics along the southern border of the north sea area belgium from the start of the priabonian onwards the northwestern part of the campine basin and the london brabant massif to its west experienced subsidence and developed into a shallow trough simultaneously several other southern north sea basins including the central and eastern part of the campine basin and the roer valley graben were inverted by what is generally referred to as the pyrenean inversion phase inversion caused broad flexural uplift and minor reverse fault movements the characteristics of inversions in the southern north sea basins are very similar to each other and to those described for a phase of intraplate stress relaxation the results of this study therefore suggest that the pyrenean inversion phase was triggered by a regional stress relaxation that started around the bartonian priabonian boundary and ended before the onset of the oligocene

the cenozoic lower rhine basin rifting sedimentation and cyclic stratigraphy in the cenozoic the lower rhine basin formed as a rift at the southeastern terminus of the dutch german central graben while the rhenish massif was uplifted the study focusses on the marginal marine and fluvial fill of the lower rhine basin a basin model is developed support for this study was given by extensive industry outcrop and well data by new stratigraphical and sedimentological observations the ingression and subsequent regression of the cenozoic north sea is analysed using the concept of base level cyclicity as the geohistory of the basin was complex a subsidence curve is constructed furthermore an attempt is made to trace the simultaneous uplift of the rhenish massif

small scale faulting in the upper cretaceous of the groningen block the netherlands 3d seismic interpretation fault plane analysis and regional paleostress abstract over the last years field based studies have shown that fault surfaces can exhibit a considerable self affine topography it is reasonable to assume that similar undulations are also present in fault interpretations from 3d reflection seismic data however both the interpretation uncertainty and geophysical resolution limits hinder their analysis this study analyses a set of small scale non reactivated faults in the upper cretaceous chalk group upper ommelanden formation of the nw part of the groningen block the netherlands in a high quality pre stack depth migrated 3d seismic data set the studied faults are fully contained inside the chalk group in an area located between the major tectonic bounding faults of the nw groningen block over 200 faults with offsets in the order of 30 50 m were interpreted across an area of ca 150 km 2 showing a clear preferential orientation for strike dip and dip direction detailed interpretations and 3d fault plane analyses show undulations on the fault plane we show that these undulations are not an interpretation or gridding artefact and interpret these to indicate direction of fault slip these results were used to calculate a paleostress tensor using all faults to calculate a single stress tensor for the entire study area by numerical dynamic analysis based on the orientation position and a thickness analysis it is interpreted that these faults formed due to the tectonic reactivation of salt structures in the latest cretaceous the calculated paleostress state shows a general nw se extension with a vertical maximum principle stress and a stress ratio of about 0 3 indicating that the studied faults are not the result of dewatering this interpretation agrees both with a nearby salt tectonic reconstruction as well as field based paleostress results from the uk belgium and france a first look at other surveys from the dutch sector indicates that similar faults are present in other areas with different orientations we propose that a dedicated analysis of these faults across on and offshore europe would allow extending the stress map of the late cretaceous into areas where the chalk is not outcropping

temporal variation of seismicity in a himalayan tectonic block and the 1991 uttarkashi earthquake india spatial and temporal variation of the seismicity between 1970 and august 1991 in the northwestern himalaya and adjoining areas of tibet immediately to the north were investigated using a function of the cn algorithm the aim of the exercise was to detect a pattern which if known earlier could have been used to predict the uttarkashi earthquake of 19 october 1991 in the garhwal himalaya it is observed that strong earthquakes occurring in a block defined by longitudes 75 and 83 e and latitudes 30 and 38 n approximately yield a distinctive pattern of temporal variation in the seismicity for the purpose we conclude from the analysis that the seismicity in the northwestern himalayan segment of the alpide himalayan seismic belt may not be independent of seismicity in southwestern tibet

gravity evidence for an alpine buckling of the crust beneath the paris basin abstract the processing of the gravity data of the paris basin has enlightened the existence of crustal ridges these ridges correspond to the zones of different crustal thicknesses in plan view the ridges are concentric with the alpine orogen and were probably controlled by this tertiary alpine mountain building the thinned zones related with the mesozoic and pre mesozoic basins were already existing before the alpine deformations these are of limited size and clearly associated with the basins on a large scale two different domains have been recognized the first one corresponds with a zone where the crust is 37 km thick it is also the place where the tertiary depocentres developed the second one relates with a zone where the crust is 29 30 km thick it has been uplifted during the alpine orogeny these two observations suggest the existence of a tertiary lithospheric buckling beneath the paris basin

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

structural style and reservoir development in the west netherlands oil province the area of the rijswijk concession largely coincides with the onshore part of the west netherlands basin to date oil has been produced from ten fields with a total stock tank oil initially in place stoiip of ca 210 x 106 m3 1 3 x 109 bbls reservoirs comprise continental and shallow marine elastics of late jurassic to early cretaceous age deposited in syn rift and post rift settings the west netherlands basin was created during late jurassic and early cretaceous rifting characterised by divergent oblique slip faulting this created a nw se trending block faulted depression between the london brabant massif and the zandvoort ridge shallow marine elastics and marls were deposited in the subsequent post rift stage during the latest cretaceous and early tertiary regional uplift and convergent oblique slip faulting resulted in basin inversion and reverse reactivation of pre existing normal faults due to the transpressional nature of the basin inversion narrow asymmetrical anticlines were formed often bounded by upwardly divergent reverse faults in the hanging wall blocks of former normal faults these structures constitute the general trap geometry of all cretaceous oil fields in the basin the acquisition of 3d seismic data has resulted in significantly enhanced structural definition and has led to the development of new structural and depositional models which improve the prediction of reservoir development and risk assessment

workflow for analysis of compositional data in sedimentary petrology provenance changes in sedimentary basins from spatio temporal variation in heavy mineral assemblages the field of provenance analysis has seen a revival in the last decade as quantitative data acquisition techniques continue to develop in the 20th century many heavy mineral data were collected these data were mostly used as qualitative indications for stratigraphy and provenance and not incorporated in a quantitative provenance methodology even today such data are mostly only used in classic data tables or cumulative heavy mineral plots as a qualitative indication of variation the main obstacle to rigorous statistical analysis is the compositional nature of these data which makes them unfit for standard multivariate statistics to gain more information from legacy data a straightforward workflow for quantitative analysis of compositional datasets is provided first 1 a centred log ratio transformation of the data is carried out to fix the constant sum constraint and non negativity of the compositional data next 2 cluster analysis is followed by 3 principal component analysis and 4 bivariate log ratio plots several 5 proxies for the effects of sorting and weathering are included to check the provenance significance of observed variations and finally a 6 spatial interpolation of a provenance proxy extracted from the dataset can be carried out to test this methodology available heavy mineral data from the southern edge of the miocene north sea basin are analysed the results are compared with available information from literature and are used to gain improved insight into miocene sediment input variations in the study area

geochemistry of archean metavolcanic rocks from kadiri schist belt andhra pradesh india abstract the basic volcanic group exposed in the kadiri schist belt includes high mg basalt basalt basaltic andestite and dacite the basalts are tholeiitic in composition and high mg basalts basaltic andesites and dacites show calc alkaline affinity major and trace element characteristics suggest that the volcanic suite has been derived from an initial tholeiitic magma which has given rise to an early basaltic type and a later calc alkaline type of rocks an island arc and active continental margin tectonic setting was inferred for these rocks

determining the maximum overburden along thrust faults using a porosity versus effective confining pressure curve abstract this study aims to quantify the tectonically induced thrusting and erosion here we propose and evaluate a laboratory based method for determining the maximum effective stress ever sustained by a sedimentary rock formation the porosities of nineteen samples collected from two deep boreholes of the taiwan chelungpu fault drilling project were measured under different confining stresses the relation between measured porosity and confining pressure compaction curve is bilinear in log log scale the maximum effective stress of the tested rocks was determined from the intersection point of the two straight lines of the compaction curve the maximum effective stresses of the rocks below the sanyi fault reverse fault are close to the in situ vertical effective stress above the sanyi fault hanging wall where the rocks have been thrust the maximum effective stresses of the rocks are significantly greater than the in situ stress with an average value of 29 48 mpa that is the eroded thickness of the formation on the hanging wall of the sanyi fault is 2482 m a value close to that determined from the geological profile 2773 m it is inferred that the total displacements along the thrust sanyi fault is 11 5 km a value close to that determined from the geological profile 14 16 km these results indicate that the proposed laboratory based method is potentially useful for determining the thrusting and erosion in a fold thrust belt and the total displacements along a thrust fault

arcuate thrust systems in sandbox experiments a comparison to the external arcs of the western alps in the external western alps two regional structural arcs were generated during tertiary northwest directed collision between the apulian indenter and the european passive margin these arcs distinguished by their geographic position and their age are examined by using a new compilation of structural data and comparing these to the results of sandbox analogue experiments the principal western alpine arc comprises two orthogonal synchronous thrust systems in the late eocene early miocene major shortening 105 km was toward the northwest to west northwest and minor shortening 11 km was toward the southwest shortening in each branch decreased toward the core of the arc during the late miocene and pliocene the jura arc accommodated 35 km of northwest directed shortening while 10 5 km of southwest to south southwest directed shortening was accommodated on the digne thrust system sandbox experiments were used to investigate the role of the motion vector of a rigid rectangular indenter orthogonal diagonal curved or rotational paths and the mechanical stratigraphy of the foreland in the evolution of upper crustal arcuate systems e g presence of a basal easy slip silicone horizon comparison of experimental results with the external alpine arc suggests that the indenter followed a slightly diagonal path with respect to the european margin from the eocene to the early miocene and curved counterclockwise by 10 15 in the middle miocene mechanical stratigraphy experiments support the hypothesis that thick triassic evaporites played a primary role in the evolution of the jura arc the influence of mechanical stratigraphy was most prominent during weak deformation at the external boundaries of the alpine orogen jura fold and thrust belt digne thrust

subsidence analysis and modelling of the roer valley graben se netherlands abstract the roer valley graben southeastern netherlands forms the most northern branch of the european cenozoic rift system sedimentary backstripping of exploration wells provides control on vertical tectonic motions during the complex post paleozoic geodynamic evolution of the area the roer valley graben evolved by repeated reactivation of permo carboniferous fracture systems at least three episodes of extension related subsidence are recorded these occurred during the late permian early triassic 255 240 ma the middle jurassic 168 165 ma and the late cenozoic 36 0 ma a late jurassic early cretaceous stretching phase is weakly inferred from incomplete data crustal stretching values calculated from the tectonic subsidence curves can account for the reflection seismic controlled crustal configuration of the roer valley graben area results demonstrate a close relationship between the roer valley graben and the basins in the north sea during the mesozoic in contrast the cenozoic evolution of the roer valley graben is independent from that of the north sea and is related to the development of the rhine graben

a new multilayered model for intraplate stress induced differential subsidence of faulted lithosphere applied to rifted basins in plane horizontal stresses acting on predeformed lithosphere induce differential flexural vertical motions a high precision record of these motions can be found in the sedimentary record of rifted basins originally it was proposed that rifted basins experience flank uplift and basin center subsidence in response to a compressive change of in plane stress which agrees well with observed differential motions subsequently published models predicted that the vertical motions may be opposite because of the flexural state of the lithosphere induced by necking during extension however the total flexural and permanent geometry of the lithosphere underlying the rifted basin is the controlling parameter for the in plane stress caused vertical motions the largest part of this preexisting geometry is caused by faulting in the uppermost brittle part of the crust and ductile deformation in the underlying parts of the lithosphere we present a new multilayered model for stress induced differential subsidence taking into account the technically induced preexisting geometry of the lithosphere including faults in the upper crust as continental lithosphere may exhibit flexural decoupling due to a weak lower crustal layer the new multilayer in plane stress model discriminates the geometries of the separate competent layers at a basin wide scale the new model predicts that a compressive change of in plane force results in basin center subsidence and flank uplift confirming the original hypothesis compared to all previous models the new model requires a lower horizontal stress level change to explain observed differential vertical motions

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

geochemistry and petrogenesis of early proterozoic intracratonic volcanic rocks of the ventersdorp supergroup south africa abstract the 2 5 ga old predominantly volcanic rocks of the ventersdorp supergroup represent a cratonic cover sequence within the kaapvaal craton of southern africa they are underlain by the rocks of the witwatersrand supergroup and are overlain by sediments of the transvaal supergroup the sequence consists of six formations and is more than 3700 m thick it comprises basaltic andesitic dacitic and rhyolitic lavas with agglomeratic intercalations as well as subgreywacke conglomerate local stromatolitic limestone and shale petrographic investigations and the determination of major and trace elements were carried out on 45 samples of volcanic rocks from nine boreholes originating from the klerksdorp area the orange free state and the east rand the primary mineralogy of the mafic to intermediate volcanics consisted of clinopyroxene plagioclase and quartz but has been extensively altered during low temperature metamorphism with hornblende actinolite tremolite serpentinite epidote calcite chlorite sericite clinozoisite titanite and sphene occurring as secondary minerals the analyzed rock types consist of basalts basaltic andesites and andesites as well as felsic lavas two samples of ultramafic cumulate volcanic rock and two vitric tuffs were also investigated in spite of considerable alteration the preserved mineralogy and inter element correlations indicate that the basalts basaltic andesites and andesites are cogenetic the ultramafic and felsic rocks are probably also cogenetic but more geochemical data are required to demonstrate this relationship the systematic variations of ti y and nb vs zr throughout the volcanic succession suggest a crystal fractionation sequence involving ol pl cpx mt opx major and trace element data show that magnetite crystallized during the later stages of differentiation discrimination diagrams to infer the tectonic setting produce equivocal results and seem to have only limited validity for these early proterozoic rocks the geotectonic setting of the ventersdorp supergroup suggests a basin development whose further evolution into a proper continental rift system was aborted during the phase of basin subsidence chemical similarities with archaean greenstone belt volcanic assemblages suggest that the ventersdorp rocks reflect the evolution of an abortive greenstone belt on thick continental crust

from peat bog to lignite seam a new method to calculate the consolidation coefficient of lignite seams wielkopolska region in central poland only one quantitative method is described in the literature to estimate the consolidation coefficient of lignite seams more studies concentrate on the compaction of plant tissues which explains why the obtained results are overestimated moreover most studies do commonly not determine the consolidation of the whole peat bog but usually those of some of its elements only we propose a new approach which conceptually is fairly close to the hager et al fortschr geol rheinld westf 29 319 352 1981 method our method has been tested on an example of the first middle polish lignite seam and the second lusatian lignite seam from some wielkopolska lignite deposits in central poland the consolidation coefficients cc range between 2 34 and 2 56 for the second lusatian lignite seam and between 1 80 and 2 14 for the first middle polish lignite seam

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

plate interactions at the southern end of the rhine graben abstract the southern end of the rhine graben in the basel area originated in the early tertiary as an extensional structure it is the site of a transfer zone that connected the rhine graben with the bresse rhone grabens this transfer zone is located in an area into which a late paleozic trough projects which apparently was reactivated from the beginning of miocene to recent times three distinct phases of slight compression were superimposed on the southern end of the rhine graben the first one in the aquitanian early burdigalian is coeval with the development of the helvetic nappes and the insubric fault zone in the alps the second one in the langhian tortonian interval occurred when the external massifs and an important part of the lombardic fold thrust belt in the southern alps developed and the third pliocene to recent one is contemporaneous with the inactivation of this belt and its incorporation into the foredeep of the northern apennines in the aquitanian the forebulge of the alpine orogen is recognizable as a system of flexures that developed preferably on the margin of the late paleozoic trough the middle late miocene one gave rise to uplift of the black forest vosges domain and a river system flowing from this high to the south in the pliocene to recent one alpine rivers made their appearance flowing first to the west into the rhone system and then as the rhine to the north the pliocene to recent phase seems to be decoupled from the body of the central and southern alps

integrated study on the topographic and shallow subsurface expression of the grote brogel fault at the boundary of the roer valley graben belgium abstract the grote brogel fault gbf is a major wnw ese striking normal fault in belgium that diverges westward from the nw se striking western border fault system of the roer valley graben the gbf delimits the topographically higher campine block from the subsiding roer valley graben and is expressed in the digital terrain model dtm by relief gradients or scarps by integrating dtm electrical resistivity tomography ert cone penetration test cpt and borehole data we studied the quaternary activity of the gbf and its effects on local hydrogeology in the shallow subsurface

origin and evolution of granitoids associated with the kadiri greenstone belt eastern dharwar craton a history of orogenic to anorogenic magmatism abstract different tectonic models have been proposed to explain the neoarchaean evolution of the eastern dharwar craton edc here we present whole rock elemental and nd isotopic compositions coupled with zircon u pb age and trace elemental data on granitoids associated with the neoarchaean kadiri greenstone belt edc to track the tectonic evolutionary history of the terrain earlier works on volcanic rocks of the kadiri belt tholeiitic oceanic plateau basalt high mg andesite and potassic adakite envisaged continental margin arc oceanic plateau collision in this work the oldest recognized granitoid is a 2 56 ga syntectonic sanukitoid like hornblende granodiorite enriched in large ion lithophile as well as ferromagnesian elements it was probably derived from a metasomatized mantle wedge above a subduction zone this is followed by syntectonic emplacement of 2 54 ga transitional ttgs and potassic adakitic volcanic rocks intrusion of 2 51 2 52 ga crustally derived granites mostly k rich nd 0 9 to 3 7 marks the end of orogenesis in the area a convergent orogenic setting characterized by assembly of diverse terranes repeated slab break off and crustal reworking is proposed to interpret the association of various granitoids and volcanic rocks finally intrusion of crustally derived highly silicic k rich a type granite nd 0 6 to 4 8 and mantle derived syenite occurred in a post subduction non compressive environment during palaeoproterozoic lithospheric delamination and attendant mantle melting and crustal reworking are suggested as possible mechanism for generation of these rocks the negative nd values and mesoarchaean nd depleted mantle model ages of some neoarchaean to palaeoproterozoic kadiri granitoids attest to the presence of older crust in the eastern part of the edc the final cratonization of the edc 2 52 2 50 ga occurred later than in most of the other cratons

the tectonic evolution of the southern dutch north sea during the palaeogene basin inversion in distinct pulses abstract in this paper we discuss the response of a sedimentary basin to compressional reactivation of extensional faults in distinct pulses the inversion of the broad fourteens basin in the southern dutch north sea is used as a case study the first pulse of inversion occurred during the late mesozoic as a result of the sub hercynean phase a second pulse occurred during the mid palaeocene laramide phase a final inversion pulse occurred around the eocene oligocene boundary coinciding with the pyrenean tectonic event we reconstructed the stratigraphic and structural development of the area during the palaeogene in detail basic data are two 2d seismic surveys supported by 74 geophysical wireline logs on which newly constructed depth and thickness maps are based the reconstruction is aided by a quantitative subsidence analysis cessation of compression resulted in relaxation and tensional reactivation of faults caused differential subsidence inheritance of geological structures is a key element in the tectonic activity in the broad fourteens basin during the palaeogene tectonic movement during the palaeogene was always accommodated by reactivation of palaeozoic mesozoic faults the intensity of inversion in the southern north sea basin during the pyrenean phase appears much larger than previously noticed moreover the area affected by the inversion is much wider than during previous phases minor differences in the direction of the local stress field between the tectonic phases and by the deposition of a thick sedimentary succession during the periods of tectonic quiescence between the inversion phases can account for this

the late and post variscan tectonic evolution of the western border fault zone of the bohemian massif wbz paleostress analysis and evaluation of the stratigraphic unconformities reveal an extremely polyphase development of one of the most prominent fault zones of central europe usually known as the franconian line fl because the fl is just one fault zone although it is the most important fault zone within a complex fault system a more appropriate term is used herein western border fault zone of the bohemian massif wbz the reconstruction of the paleostress history was carried out by analysing sequences of individual strain increments that belong to the same stratigraphic units e g late variscan granites tertiary basalts a succession of at least 15 paleostress directions and tectonic regimes have been determined since late variscan time

pb sr nd isotopic behavior of deeply subducted crustal rocks from the dora maira massif western alps italy ii what is the age of the ultrahigh pressure metamorphism pb nd and sr isotope data are reported from two localities on mineral separates from mg rich metapelites and associated rocks that have been subducted to depths of at least 100 km for which metamorphic conditions are estimated at 28 33 kilobars pressure and 700 800 c and then returned to the surface initial isotope ratio data from the granitoid country rock are similar to those found in the metapelites the initial ratios indicate predominantly recycled aged granitic crustal materials for the sources of all of the samples five zircon samples 4 from pyrope megacrysts and 1 from fine grained pyrope quartzite lenses in the metapelites accurately define a chord yielding intercept ages of 304 10 and 38 0 1 4 ma in a concordia diagram zircon from the country rock also plots along the chord the zircon data together with initial nd and sr data indicate that the sedimentary sources of the rocks were derived mainly or entirely from sialic hercynian rocks ellenbergerite from pyrope megacrysts and monazite from the fine grained ground mass yield slightly younger ages of 30 34 ma apparently reflecting lower blocking temperatures than that of zircon sm nd data from a pyrope megacryst give an errorchron corresponding to an age of 38 ma in agreement with the zircon date a major question concerns the timing of the ultrahigh pressure metamorphism experimental data suggest that pyrope and quartz coesite as well as ellenbergerite formed by various metamorphic reactions if as generally assumed the ultrahigh pressure metamorphism occurred ca 100 ma ago our data require that the zircon did not experience measurable lead loss at that time but lost major amounts of lead 38 ma ago during late alpine metamorphism estimates of diffusion rates for nd in pyrope further suggest that the apparent sm nd age of 38 ma for the megacryst is not consistent with that model those problems are resolved if the ultrahigh pressure metamorphism occurred 38 40 ma ago but problems remain from ar ar dates of 100 ma on phengite an inferred 120 ma age for zircon lead loss from another study and possibly by the very rapid uplift required if the metamorphism is that young

graben inversion in nature and experiments the inversion of crustal scale basement grabens is studied here through laboratory experiments on small scale models and available oil industry seismic lines from the southern north sea two basic configurations are considered first both the basement and the sedimentary cover are brittle and inversion does not involve any potential decollement between them second the basement and sedimentary cover are separated by a weak ductile layer e g salt which can allow decollement of the cover during both extension and later compression and inversion the second configuration is more complicated and can lead to a large variety of geological structures laboratory experiments were carried out on brittle ductile models built with sand to represent brittle layers basement and sedimentary cover and silicone putty to simulate the decollement layer between basement and cover a mechanically based classification of inversion structures is proposed the effects of some crucial parameters are investigated including obliquity between the direction of shortening and normal faults as well as strength profiles and the presence or absence of salt diapirs the experimental investigation leads to the following conclusions 1 the inversion of the graben by reactivation of normal faults implies that the angle between the direction of compression and the graben is less than 45 2 if there is a superficial decollement e g basement cover interface inversion initiates low dipping thrust faults in the cover localized at graben borders 3 salt diapirs or salt walls localized along the graben borders in the cover are preferential sites for the development of thrust faults and 4 when the cover is decoupled from the basement by a decollement layer inversion induced deformation in the cover which is partitioned between thrust faults along the graben borders and strike slip faults within the graben trending oblique to the graben borders experimental results are compared with field examples in particular from the southern north sea

regional patterns of tectonic stress in europe nearly 1500 stress orientation determinations are now available for europe the data come from earthquake focal mechanisms overcoring measurements well bore breakouts hydraulic fracturing measurements and young fault slip studies and sample the stress field from the surface to seismogenic depths three distinct regional patterns of maximum compressive horizontal stress shmax orientation can be defined from these data a consistent nw to nnw shmax stress orientation in western europe a wnw ese shmax orientation in scandinavia similar to western europe but with a larger variability of shmax orientations and a consistent e w shmax orientation and n s extension in the aegean sea and western anatolia the different stress fields can be attributed to plate driving forces acting on the boundaries of the eurasian plate locally modified by lithospheric properties in different regions on average the orientation of maximum stress in western europe is subparallel to the direction of relative plate motion between africa and europe and is rotated 17 clockwise from the direction of absolute plate motion the uniformly oriented stress field in western europe coincides with thin to medium lithospheric thickness approximately 50 90 km and high heat flow values 80 m w m2 in western europe a predominance of strike slip focal mechanisms implies that the intermediate principal stress is vertical the more irregular horizontal stress orientations in scandinavia coincide with thick continental lithosphere 110 170 km and low heat flow 50 m w m2 the cold thick lithosphere in this region may result in lower mean stresses associated with far field tectonic forces and allow the stress field to be more easily perturbed by local effects such as deglaciation flexure and topography the stress field of the aegean sea and western anatolia is consistent with n s extension in a back arc setting behind the hellenic trench subduction zone the stress field is influenced in places by regional geologic structures e g in the western alps where shmax directions show a slight tendency toward a radial stress pattern not all major geologic structures however appear to affect the shmax orientation e g in the vicinity of the rhine rift system horizontal stress orientations are continuous

characterization and quantification of active faulting in the roer valley rift system based on high precision digital elevation models the roer valley rift system rvrs is located in the northern prolongation of the upper rhine graben during the cenozoic the evolution of the rvrs was influenced by two different rift systems situated in the north and in the south the north sea rift system and the west european rift system respectively during the last decades moderate seismicity revealed the continuous activity of the graben border faults the peel boundary fault zone pbfz and the feldbiss fault zone ffz we use a high precision digital elevation model dem to characterize and quantify the present day deformation along these faults the fault pattern shows similarity to a strike slip structure however analysis of the dem reveals that the recent to quaternary formations and landforms affected by the fault activity are only vertically offset this suggests a pure normal faulting mode for the main border faults and a direction of extension perpendicular to the graben i e ne sw quantification of the offset dated markers allows the determination of the displacement rates along the fault segments in the southeastern part of the rvrs the vertical displacement rates inferred for the ffz and the southeastern pbfz range between 55 and 65 mm ky and around 65 mm ky respectively in contrast the displacement rates determined for the northwestern segment of the pbfz are around 200 mm ky we explain these differences between the northwestern and southeastern parts of the rvrs by the large scale geometry of the graben the rvrs being symmetric in the south east and asymmetric half graben in the north west the deformation is accommodated by two border faults ffz and the south eastern part of the pbfz in the south east and by only one fault in the north west the north western segment of the pbfz in addition the thickness of the neogene main depocentre in the northwestern half of the rvrs indicates a larger amount of extension in this part of the graben than in the south east the combination of the graben geometry and the amount of extension can explain the differences in the displacement rate