geophysical geological transect and tectonic evolution of the swiss italian alps a complete alpine cross section integrates numerous seismic reflection and refraction profiles across and along strike with published and new field data the deepest parts of the profile are constrained by geophysical data only while structural features at intermediate levels are largely depicted according to the results of three dimensional models making use of seismic and field geological data the geometry of the highest structural levels is constrained by classical along strike projections of field data parallel to the pronounced easterly axial dip of all tectonic units because the transect is placed close to the western erosional margin of the austroalpine nappes of the eastern alps it contains all the major tectonic units of the alps a model for the tectonic evolution along the transect is proposed in the form of scaled and area balanced profile sketches shortening within the austroalpine nappes is testimony of a separate cretaceous age orogenic event west directed thrusting in these units is related to westward propagation of a thrust wedge resulting from continental collision along the meliata hallstatt ocean further to the east considerable amounts of oceanic and continental crustal material were subducted during tertiary orogeny which involved some 500 km of n s convergence between europe and apulia consequently only a very small percentage of this crustal material is preserved within the nappes depicted in the transect postcollisional shortening is characterized by the simultaneous activity of gently dipping north directed detachments and steeply inclined south directed detachments both detachments nucleating at the interface between lower and upper crust large scale wedging of the adriatic or apulian lower crust into a gap opening between the subduced european lower crust and the pile of thin upper crustal flakes alpine nappes indicates a relatively strong lower crust and detachment between upper and lower crust

the eastern jura relations between thin skinned and basement tectonics local and regional the thesis area of hans cloos in the eastern jura straddles the boundary between the paleogene structures of the tabular jura a part of the southeastern end of the rhine graben and the neogene folds and thrusts of the folded jura a recent reflection seismic survey in the area adjacent to the east provides new information on the subsurface structure and the relation between three superposed tectonic events the main boundary fault zones of a deep and complexly faulted late paleozoic trough trending ene were reactivated in the early tertiary faulted flexures and small folds rooted in the basement and paleozoic with an amplitude of usually 100 to 300 m were produced rather than the normal faults typical for the extensional fields of the rhine bresse graben system in the west and the bavarian molasse basin in the east this suggests their being part of a transform zone between these extensional fields during jura decollement in the neogene these inherited deeply rooted sub decollement structures remained passive their small size is kinematically incompatible with the intense subsequent thrusting and folding of the thin mesozoic tertiary skin however thrust ramps were apparently nucleated at the respective southern foot of these paleogene flexures and folds the best defined and simplest of these composite structures is the mandach structure within the tabular jura a south facing flexure of about 300 m relief developed in the paleogene by reactivation of the northern border fault zone of the paleozoic trough in the neogene a north vergent decollement thrust which is connected with the regional jura decollement in the middle triassic evaporites was initiated at its site

an unusual triangle zone in the external northern alpine foreland switzerland structural inheritance kinematics and implications for the development of the adjacent jura fold and thrust belt abstract triangle zones represent typical structural elements of thin skinned foreland fold and thrust belts here we report the results of an in depth structural analysis of a rather unusual triangle zone at the front of the easternmost jura fold and thrust belt in the otherwise only very mildly deformed alpine foreland of northern switzerland the investigation is based on the interpretation of recently reprocessed and depth migrated 2d reflection seismic sections classical bed length and area cross section balancing methods were used to validate the interpretation and unravel the tectonic evolution of the triangle zone according to our interpretation the analyzed triangle zone formed along the baden irchel herdern lineament bih lineament a regional paleozoic normal fault that shows evidence of cenozoic reactivation the triangle zone is composed of one major foreland directed thrust rooting in triassic evaporites and a back thrust splaying from it in the middle jurassic opalinus clay pointing to the importance of secondary detachments steeply dipping secondary reverse faults next to the triangle zone suggest reactivation of pre existing normal faults the formation of the thrust triangle is considered to relate to thin skinned foreland deformation in late miocene time strain estimations of the thrust triangle along strike show a laterally very uniform amount of shortening which is in contrast to the southward adjacent jura fold and thrust belt we interpret this constant shortening to represent the maximum contractional strain attainable by the specific geometry of the bih triangle zone at this point the complex structure became mechanically ineffective and further shortening led to the formation of new contractional structures in its hinterland this kinematic hypothesis suggests an early stage formation of the bih triangle zone followed by back stepping of the deformation front as such it challenges the classical view of a purely forward breaking sequence for the jura fold and thrust belt in the northwestern foreland of the alps

styles of positive inversion tectonics in the central apennines and in the adriatic foreland implications for the evolution of the apennine chain italy abstract integration of new field structural and geophysical data with existing information from the apennines chain in italy and its adjacent adriatic foreland indicates that the styles of positive inversion tectonics and the modes of interaction between the extensional and the subsequent compressive structures vary starting from the cretaceous the contractional deformation induced by the mainly north directed convergence of africa adria with respect to the european plate promoted the closure of various arms of the atlantic and the neo tethys oceans which opened in different times and with distinct orientations the mosaic of continental blocks carbonate platforms rift basins and oceanic domains with several geometries and orientations with respect to the axis of the subsequent compression and the resulting heterogeneities within the shallow sedimentary cover and the overall lithosphere strongly influenced both the structural evolution of the apennine orogenic belt and the intra continental deformation within the adriatic foreland field observations reveal that the steeply e and w dipping mesozoic cenozoic normal faults are systematically decapitated by sub horizontal or gently west dipping thrusts propagating with short cut trajectories pre thrusting normal faults were commonly deformed by later thrusts but little evidence seems to support their entire reactivation as high angle reverse faults this suggests that these shallow and steeply dipping discontinuities were not suitable to be reutilized by the superficial thin skinned thrust faults propagating within the sedimentary cover in contrast presumably late paleozoic and mesozoic w dipping normal faults appear moderately reactivated in the adriatic foreland and strong positive inversion tectonics affect the deeper and buried structural levels of the apennine chain within the latter the syn rift sediments in the hangingwall blocks of the fault bounded basins were totally extruded and generated the strong uplift of the thinned adria continental crust finally the contrasting styles of interactions of the pre existing normal faults with later thrusts i e passive truncation or positive reactivation strictly result from the different evolution of the apennine chain and the combined thin and thick skinned modes of deformation of the stretched lithosphere of the adria plate

reactivated basement structures affecting the sedimentary facies in a tectonically quiescent epicontinental basin an example from nw switzerland abstract the jurassic deposits in the southern part of central europe accumulated in a shallow epicontinental sea and their deposition has usually been believed to have corresponded to a phase of tectonic quiescence neither on conventional seismic records nor in outcrops obvious indications of synsedimentary tectonics were found nonetheless subtle variations in lithofacies and thickness occur above faults in the crystalline basement in fact preexisting structures became reactivated in the jurassic during major extensional phases when the tethys and the north atlantic opened this reactivation led to differential subsidence and or to rotation of fault bounded blocks but the sediments were deformed mainly flexurally as vertical movements in the basement were dissipated by triassic salt thus the depositional area was morphologically differentiated into swells and depressions in siliciclastic muddy environments swells were characterized by hardbottoms and hiatus beds depressions were filled by distal tempestites and gravity deposits in carbonate settings reefs nucleated on swells marls and muds were deposited in depressions many of them gravity deposits reactivation of faults occurred only during short episodes and was not synchronous throughout the study area and reactivation of individual faults was episodic and probably controlled by the palaeostress field and the faults orientation reactivation of deep rooted faults is also documented by hydrothermal activity which led to vein mineralization and alteration of minerals today exposed in nearby basement units the chronostratigraphic ages of the hydrothermal processes coincide with phases of enhanced subsidence during the sinemurian aalenian bajocian bathonian and oxfordian in turn facies changes of the sedimentary cover should be useful to predict basement structures when no seismic records are available

decollement tectonics in the jura forelandfold and thrust belt abstract interpretation of more than 1500 km of industry seismic reflection lines from theswiss and french jura mountains and the western swiss molasse basin demonstrates that themesozoic and cenozoic cover of the jura fold and thrust belt has been deformed over a veryweak basal decollement and displaced for many kilometers toward the nw and that thebasement is not involved a depth to the basement map derived from depth conversion of theseismic lines shows a rather smooth flat basement dipping 1 3 to the s se the low amplitudebroad folds of the molasse basin and the external plateau jura are controlled by evaporitepillows or anticlines of middle triassic age the high amplitude folds of the haute chaine jura however are related to nw or se vergent thrusts with at least kilometric dipslip displacementthat has doubled the entire jurassic sequence the plateau jura evaporite related folds located in the foreland are interpreted as early stage buckle folds with further deformation afault ramp nucleates and develops into thrust related folds as observed in the haute chaine thus within the fold and thrust belt deformation increases toward the hinterland in the molassebasin however low amplitude folds represent an early deformation stage which could notdevelop further owing to the load of the overlying thick tertiary clastic wedge

a unified kinematic model for the evolution of detachment folds abstract detachment folds represent a major structural element in a number of fold belts they are common in the jura mountains the zagros fold belt the central appalachian fold belt the wyoming fold belt the brooks range the parry islands fold belt and parts of the subandean belt these structures form in stratigraphic packages with high competency contrasts among units the competent upper units exhibit parallel fold geometries whereas the weak lower unit displays disharmonic folding and significant penetrative deformation two distinct geometric types disharmonic detachment folds and lift off folds have been recognized however these structures commonly represent different stages in the progressive evolution of detachment folds the structures first form by symmetric or asymmetric folding with the fold wavelength controlled by the thickness of the dominant units volumetric constraints require sinking of units in the synclines and movement of the ductile unit from the synclines to the anticlines continuing deformation results in increasing fold amplitudes and tighter geometries resulting from both limb segment rotation and hinge migration initially limb rotation occurs primarily by flexural slip folding but in the late stages of deformation the rotation may involve significant internal deformation of units between locked hinges the folds eventually assume tight isoclinal geometries resembling lift off folds variations in the geometry of detachment fold geometry such as fold asymmetry significant faulting and fold associated with multiple detachments are related to variations in the mechanical stratigraphy and pre existing structure

tectonics of the central swiss molasse basin post miocene transition to incipient thick skinned tectonics in this paper we investigate the tectonics of the central swiss molasse basin smb situated between the central european alps and the jura fold and thrust belt based on re interpreted 2d reflection seismic data and geological 3d modeling we present new insights into the structural configuration and evolution of the central smb during the thin skinned main deformation phase of the jura fold and thrust belt 12 4 ma the central smb was riding passively above a major detachment horizon within triassic evaporites which roots beneath the external crystalline massifs of the central alps in the smb low amplitude detachment folds and detachment rooted wsw ene striking thrust and reverse faults are related to this event younger major nne ssw and nnw sse trending strike slip fault zones cross the basin over a length of several kilometers affecting the cenozoic and mesozoic cover units and extending into the pre mesozoic crystalline basement in cases the fault zones apparently reactivate inherited permo carboniferous trough pct bounding paleozoic normal faults seismic data further reveals mild inversion of wsw ene striking pcts these structures clearly cut the basement cover contact thus postdating the main deformation phase of the jura fold and thrust belt present day earthquake focal mechanisms and epicenter distribution show strike slip faulting and basement seated seismicity respectively thus corroborating our observations from seismic interpretation our data suggests a change from late miocene thin skinned to pliocene to present day incipient thick skinned tectonics this major change reflects the establishment of a mid crustal detachment and may be related to changes in slab dynamics of the subducting european lithosphere

propagation of a fold and thrust belt over a basement graben abstract we demonstrate the mechanical feasibility of the propagation of a thin skin deformation front on a decollement previously cut and lowered by a normal fault using a numerical implementation of the limit analysis theory we confirm the common understanding that any discontinuity of the decollement layer will trigger the formation of a ramp conducting the slip to the surface upon further remotely applied shortening we show with both numerical and analogue models that the growing relief created by the ramp will reach a height and a horizontal extent such that the lower portion of the decollement will eventually be activated and the belt will resume its growth further along its initial decollement layer even though it is deeper the required extra relief depends mainly on the friction angles of the bulk material and of the existing faults the analogue experiments show that the step in the decollement acts as a temporary catching point in the propagation of the deformation front resulting in a characteristic tectonic style composed of a stack of faults above the step separated from the following structures by a long and flat partially buried syncline the thin skin jura fold and thrust belt developed during mio pliocene times on a triassic decollement locally lowered by reactivation of earlier grabens with a dedicated mechanical prototype we show that realistic friction values are compatible with the propagation of deformation across these grabens along the depressed zones of the triassic decollement without having recourse to thick skinned tectonics

different modes of the late cretaceous early tertiary inversion in the north german and polish basins several selected seismic lines are used to show and compare the modes of late cretaceous early tertiary inversion within the north german and polish basins these seismic data illustrate an important difference in the allocation of major zones of basement thick skinned deformation and maximum uplift within both basins the most important inversion related uplift of the polish basin was localised in its axial part the mid polish trough whereas the basement in the axial part of the north german basin remained virtually flat the latter was uplifted along the sw and to a smaller degree the ne margins of the north german basin presently defined by the elbe fault system and the grimmen high respectively the different location of the basement inversion and uplift within the north german and polish basins is interpreted to reflect the position of major zones of crustal weakness represented by the wnw ese trending elbe fault system and by the nw se striking teisseyre tornquist zone the latter underlying the mid polish trough therefore the inversion of the polish and north german basins demonstrates the significance of an inherited basement structure regardless of its relationship to the position of the basin axis the inversion of the mid polish trough was connected with the reactivation of normal basement fault zones responsible for its permo mesozoic subsidence these faults zones inverted as reverse faults facilitated the uplift of the mid polish trough in the order of 1 3 km in contrast inversion of the north german basin rarely re used structures active during its subsidence basement inversion and uplift in the range of 3 4 km was focused at the elbe fault system which has remained quiescent in the triassic and jurassic but reproduced the direction of an earlier variscan structural grain in contrast n s oriented mesozoic grabens and troughs in the central part of the north german basin avoided significant inversion as they were oriented parallel to the direction of the inferred late cretaceous early tertiary compression the comparison of the north german and polish basins shows that inversion structures can follow an earlier subsidence pattern only under a favourable orientation of the stress field a thick zechstein salt layer in the central parts of the north german basin and the mid polish trough caused mechanical decoupling between the sub salt basement and the supra salt sedimentary cover resultant thin skinned inversion was manifested by the formation of various structures developed entirely in the supra salt mesozoic cenozoic succession the zechstein salt provided a mechanical buffer accommodating compressional stress and responding to the inversion through salt mobilisation and redistribution only in parts of the ngb and mpt characterised by either thin or missing zechstein evaporites thick skinned inversion directly controlled inversion related deformations of the sedimentary cover inversion of the permo mesozoic fill within the mid polish trough was achieved by a regional elevation above uplifted basement blocks conversely in the north german basin horizontal stress must have been transferred into the salt cover across the basin from its sw margin towards the basins centre this must be the case since compressional deformations are concentrated mostly above the salt and no significant inversion related basement faults are seismically detected apart from the basin margins this strain decoupling in the interior of the north german basin was enhanced by the presence of the elbe fault system which allowed strain localization in the basin floor due to its orientation perpendicular to the inferred late cretaceous early tertiary far field compression

sequence of deformation at the front of an orogen lublin basin case study poland abstract we provide a detailed description of a late carboniferous fold and thrust belt in the lublin basin based on seismic lines including new high resolution acquisitions and legacy borehole and gravimetric data a series of regional cross sections integrate results of the joint seismic borehole gravimetric interpretation cross section restoration provides estimates of the minimum incremental and total shortening and reveals its along strike variations the lublin basin straddles a leading edge of the variscan orogen and its undeformed foreland therefore it experienced only a minor deformation it preserves a fossilized record of early phases of shortening seismic scale divergent intra formational thrusts and folds in horizontal strata that were later passively rotated by subsequent folds developed above a regional decollement lateral variations of deformation styles from displacement of the entire basin with little internal deformation to dispersion of shortening by numerous contractional structures is attributed to along strike changes in lithology and thickness of the silurian detachment horizon lateral change of detachment strength is quantified using the critical wedge theory our observations deliver a new perspective on factors controlling the localization of incipient structures their differentiation as a function of detachment strength and interplay between folding and thrusting along a leading edge of an organic system

calculation of shortening due to outcrop scale deformation and its relation to regional deformation patterns abstract the objectives of this study are to assess the regional contribution of outcrop scale structures in well exposed rocks of a tectonic province and evaluate how failure to measure this scale of structure affects the assessment of regional deformation the contribution of outcrop scale structures to regional deformation has not been quantified previously because of the need for long continuous exposures to regionally characterize the structures this study used 18 6 km of semi continuous roadcut and streambed exposures in well exposed devonian clastic rocks to construct 1 200 scale profiles to address the objectives key results are 1 outcrop scale structures contribute about 1 6 to 1 4 of total regional shortening 2 submapscale shortening components from microscale and outcrop scale structures equal mapscale shortening that would be interpreted from a regional cross section 3 analysis of submapscale structures in the target blind thrust belt is needed to identify that the roof sequence deformation preceded and continued through duplex formation 4 the kinematic response of the roof sequence would be incorrectly identified as backthrusting if the shortening contribution of outcrop scale structures is ignored 5 although measured outcrop scale shortening does not match that predicted by the fractal analysis of other workers the fractal approach to predicting deformation as a function of scale may still be valid

stresses beneath a ramping thrust sheet abstract there is a systematic progression of both the timing of motion of thrust sheets and the spacing of thrust ramps during the development of some thrust dominated foreland fold and thrust belts on the basis of these observations we suggest that a regional mechanical process that controls frontal ramp formation may dominate local effects such as stratigraphic pinchouts and interaction with basement to investigate this process we have developed elastic plane strain models of the state of stress in the footwall of the last formed or most forward thrust ramp these models include the load of an overriding thrust sheet and a synorogenic sedimentary cover the effect of emplacing a thrust sheet or developing a synorogenic sedimentary cover above an incipient thrust sheet is to stabilize the footwall toward the hinterland with respect to failure and thereby move failure more to the foreland failure is localized where there is a favorable trade off between the spatial rates at which mean stress and differential stress decrease toward the foreland the models also predict that frontal ramps nucleate well above the basal decollement and propagate upward and downward eventually linking with the regional decollement fault trajectories predicted by using a coulomb criterion are subhorizontal in the hinterland portion of the model and curve upward to the foreland resulting in a curved flat and ramp geometry these analyses show that each successive thrust sheet would be thinner as well as shorter than the previous thrust sheet based on these results we propose a model for the formation of the first thin skinned thrust sheet in the external portions of orogenic belts the synorogenic sediments that form during uplift of the internal zones of mountain belts will cover the preorogenic strata to the foreland as deformation progresses to the foreland and deformation becomes more shallow and more brittle in nature the preorogenic strata will interact with the synorogenic strata and failure will occur creating the first brittle thrust sheet the location of this first thrust will be controlled by the mechanisms outlined in our models to the foreland of this point each sucessive thrust fault will localize as a result of the combined effects of an overriding thrust sheet and synorogenic deposits

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

seismic reflection evidence for thick skinned tectonics in the northern jura newly released seismic reflection data from the northern jura mountains and southern rhine graben provide the first high quality subsurface images from this area these throw light on the details of the fault patterns in the area and show that the ferrette and le glaserberg jura structures are largely the result of thrust faulting however the faults differ in their nature from those usually assumed in jura tectonics they are not low angle thrusts converging on a decollement zone in triassic evaporites they appear instead to be high angle faults that cross the entire sedimentary section indicating that thick skinned tectonics prevailed in this part of the jura embryonic jura folds can be seen on the images from the nearby mulhouse horst folds that are not supported by thickened triassic evaporites the existence of recent earthquake activity taken together with the prevalence of thick skinned tectonics suggests that occasional large earthquakes cannot be ruled out in this area

mineralogical and geochemical characterization of supergene cu pb zn v ores in the oriental high atlas morocco in the moroccan high atlas two sulfide deposits hosted by jurassic dolostones underwent significant weathering in the cu deposit of jbel klakh several stages of supergene mineralization are distinguished 1 the replacement of hypogene sulfides in the protolith chalcopyrite by secondary sulfides in the cementation zone bornite digenite chalcocite covellite 2 the formation of oxidized minerals in the saprolite malachite azurite brochantite where the environment becomes more oxidizing and neutral and 3 the precipitation of late carbonates calcite and iron hydr oxides in the laterite the precipitation of carbonates is related to the dissolution of dolomitic host rocks which buffers the fluid acidity due to the oxidation of sulfides in the jbel haouanit pb zn deposit the mineral assemblage is dominated by typical calamine minerals cu minerals chalcocite covellite malachite and a cu pb zn vanadate mottramite galena is successively weathered in anglesite and cerussite sphalerite is weathered in smithsonite which is rapidly replaced by hydrozincite late iron hydr oxides are mainly found at the top of both deposits laterite both deposits are thus characterized by specific mineral zoning from laterite to protolith related to variations in the mineralogy and ore grades and probably caused by varying eh ph conditions

deformation of brittle ductile thrust wedges in experiments and nature 1 even though the rheology of thrust wedges is mostly frictional a basal ductile decollement is often involved by comparison with purely frictional wedges such brittle ductile wedges generally display anomalous structures such as backward vergence widely spaced thrust units and nonfrontward sequences of thrust development laboratory experiments are used here to study the deformation of brittle ductile thrust wedges results are compared with natural systems in the jura mountains and the northern pakistan salt range and potwar plateau two series of three models are used to illustrate the effects of varying the basal wedge angle and shortening rate v these two parameters directly control variations in relative strength between brittle and ductile layers bd coupling wedges with strong bd coupling low and high v give almost regular frontward sequences with closely spaced thrust units and as such are not significantly different from purely frictional wedges weak bd coupling high and low v gives dominantly backward thrusting sequences intermediate bd coupling produces frontward backward oscillating sequences the spacing of thrust units increases as coupling decreases back thrusts develop in parts of a wedge where bd coupling is weak regardless of the thrust sequence wedges with weak bd coupling need large amounts of bulk shortening more than 30 to attain a state of equilibrium at which stable sliding along the base occurs on this basis we argue that a state of equilibrium has not yet been attained in at least some parts of the jura mountains and eastern salt range and potwar plateau thrust systems

why rifts invert in compression abstract the common observation of sedimentary basin inversion in orogenic forelands implies that rifts constitute weak areas of the continental lithosphere when compressed the rifts respond with uplift of the deepest parts and erosion of sediments therein simultaneously syn compressional marginal troughs are formed flanking the inversion zone since rifting and subsequent post rift thermal re equilibration are processes expected to alter the long term mechanical state of the lithosphere the phenomenon of basin inversion is non trivial from a rheological point of view stochastic modelling of the long term thermal structure beneath sedimentary basins indicates that the crustal part of a rift is warmer and hence weaker than the surrounding crustal blocks in contrast the mantle part is cold and strong beneath the basin centre in this paper it is investigated whether the rifting induced strength alterations constitute a sufficient condition for a thermally equilibrated rift to invert by compression numerical experiments with two dimensional dynamic thermo mechanical models are performed in particular the focus is on rifting related mechanical instabilities that reduce the load bearing capacity of the lithosphere in the experiments strain softening behaviour is introduced in the non associated plasticity model representing brittle yielding the result is self consistent large scale fault formation the models predict that the rifting related necking instability induces differential crustal thinning increasing the post rift crustal weakness strain softening and the associated fault formation amplifies the necking instability and introduces zones of structural weakness exposed for compressional re activation under these circumstances basin inversion follows as a natural consequence of rift compression

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

structure and kinematics of an outcrop scale fold cored triangle zone triangle zones are widespread structural elements that link fold and thrust belts with their foreland basins we present a structural analysis of an outcrop scale 6 m 20 ft wide triangle zone that is exposed in the siliciclastic carboniferous strata of the harz mountains in northern germany the geometry of the triangle zone is critically compared with larger outcrop and seismic scale structures the external form of the triangle zone is the same as that proposed for larger examples with two bounding detachments that dip in opposing directions however the interior of the triangle zone is characterized by tight to isoclinal folds we demonstrate how the triangle zone probably evolved from a fault bend fold which accreted further folds behind it this is an alternative fold based interpretation for a structure that is commonly modeled as a duplex stack we present the resulting consequences for seismic interpretation and hydrocarbon reservoir evaluation

kinematic model of detachment folding including limb rotation fixed hinges and layer parallel strain abstract detachment anticlines formed above a stratigraphically fixed detachment horizon and without thinning in the syncline will in general require layer parallel shortening a kinematic model for detachment folds is presented that has planar limbs and is area balanced but requires bed length changes that can be expressed as layer parallel strain the fold grows primarily by limb rotation not by limb lengthening at constant dip the kinematic evolution of the geometry and strain is examined fold geometry is well predicted and the strain estimated in applications of the model to two map scale detachment folds a triangle zone from the front of the wyoming thrust belt and a duplex cored anticline from the appalachian plateau

architecture and kinematics of the constance frick trough northern switzerland implications for the formation of post variscan basins in the foreland of the alps and scenarios of their neogene reactivation post variscan basins are commonly inferred to represent important precursor structures of later extensional and contractional tectonic events in the foreland of the european alps nevertheless their structural characteristics are typically poorly constrained our investigation sheds new light on the architecture and kinematics of the constance frick trough cft in northern switzerland according to our analysis of an extensive and revised 2 d reflection seismic data set the ene wsw striking cft is divided into an eastern segment and a western segment characterized by opposing half graben geometries the transition between the two segments coincides with the prolongation of a preexisting wnw ese trending strike slip fault zone exposed in the adjacent black forest massif to the north field based analysis of outcrop scale faults in the latter area implies that the minimum horizontal stress during the formation of the cft was roughly oriented ne sw which is oblique to the trough axis while previously published analogue models imply that some characteristics of the cft could be explained by lateral linkage of graben segments under oblique extension the pronounced half graben geometry of the cft suggests that low angle normal faulting may also have contributed to trough formation the observed structural complexities of the cft and uncertainties regarding its deep structure must be taken into account for interpretations of similar late paleozoic basins inferred in the subsurface of the northern alpine foreland basin in particular concerning scenarios of their neogene reactivation during alpine orogeny

structural inheritance in mountain belts an alpine apennine perspective abstract the geological structure of continental lithosphere shows complex variety that is inherited into orogenic belts and influences the localization and amplification of contractional structures during mountain building in the alpine apennine sector together with other sectors of the tethyan orogenic system the pre orogenic crustal template can include arrays of extensional faults other faults can form adjacent to the evolving mountain belt and subsequently become incorporated as the thrust belts migrate into their forelands while in some areas these inherited features may simply reactivate under inversion more commonly faults show complex partial reactivation structures in volumes of distributed strain faults may serve to nucleate large scale buckle folds for example along basement cover interfaces these different patterns of basement reactivation may reflect spatially varying strength depth profiles in continental lithosphere that are themselves inherited from spatially distinct geological histories even when not themselves reactivating basement faults can control deformation in the overlying sedimentary cover by offsetting otherwise regionally extensive detachment horizons the 3d form of thrust systems can be strongly compartmentalized by pre existing cross faults such as the oblique lineaments of the apennines on a large scale the distribution of pre existing faults and other weaknesses may affect the propensity for orogenic contraction in basement and therefore directly control larger scale tectonic processes in the central mediterranean the evolution of slab roll back and the related growth of overlying extensional basins e g tyrrhenian sea may be strongly modulated by the distribution of rift related weak zones in the adjacent continental crust the subduction of continental crust will strongly depend on the inherited structure of this crust specifically the distribution of deep crust of basic composition this develops relatively higher densities associated with eclogite metamorphism which act in turn to reduce the buoyancy of thickened continental crust that otherwise serves to inhibit further shortening investigating all these aspects from the scale of bulk crustal compositions to the geometry timing and strength of earlier fault zones preserved in orogenic belts requires the integration of substantial multidisciplinary geological data sets the extent to which continental orogenic belts represent the amplification of inherited geological heterogeneities as opposed to self ordered phenomena modulated by the syntectonic environment remains unclear

miocene to pleistocene glacial history of west antarctica inferred from nunatak geomorphology and cosmogenic nuclide measurements on bedrock surfaces we report geomorphic observations and cosmogenic nuclide measurements on bedrock surfaces from three isolated nunatak groups in west antarctica the pirrit hills and nash hills located in the weddell sea sector and the whitmore mountains located on the ross weddell divide the objectives of this paper are to i establish a chronology for landscape development at these sites and ii quantify the long term history of ice thickness variations in west antarctica these nunataks display relic alpine landscapes on which weathered bedrock surfaces are superimposed in the pirrit hills an erosional trimline is etched into alpine ridges and separates smooth crested ridges below from serrated ridges above below the trimline geomorphic evidence indicates repeated frozen based ice cover while above the trimline evidence for ice cover is entirely absent there is also no geomorphic evidence for thicker than present ice at the whitmore mountains cosmogenic nuclide concentrations in the oldest bedrock surfaces from the whitmore mountains and from above the pirrit hills trimline indicate uninterrupted exposure for 12 myr at extraordinarily low erosion rates this places a lower limit on the timing of the formation of alpine landscapes in west antarctica and we hypothesize that this occurred during the relatively warm climates prior to the mid miocene cooling the absence of evidence for thicker ice at the whitmore mountains is consistent with the hypothesis that the divide was typically thinner than present during pleistocene glacial periods due to reduced accumulation bedrock surfaces below the trimline have much lower nuclide concentrations and are most easily explained by a scenario of repeated frozen based ice cover and occasional subglacial plucking which is consistent with geomorphic observations bedrock surfaces near the modern ice level appear to have been covered more than half of the time while higher elevation surfaces indicate progressively less cover the trimline and associated geomorphic features are very similar to a prominent trimline in the ellsworth mountains and we conclude that these are in fact part of the same feature the ellsworth trimline is hypothesized to have formed during the mid miocene cooling and the transition from alpine to continental glaciation and our results are consistent with this hypothesis

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

stress pattern and strain release in the alpine foreland abstract illies j h baumann h and hoffers b 1981 stress pattern and strain release in the alpine foreland in p vyskocil r green and h malzer editors recent crustal movements 1979 tectonophysics 71 157 172 the tectonism of central europe is governed by a generally se nw 140 directed compressive stress flux from the alps towards their northern foreland since alpine folding had relaxed in the late miocene to early pliocene times only to be replaced by high rates of post orogenic uplift these stresses are understood to be of mainly topographic origin the strain release in the foreland is predominantly restricted to pre existing block boundaries shear or extensional movements could come about along those boundaries under the active regional stress regime the rhinegraben which was an extensional rift valley during the eocene to lower miocene has been subjected to a sinistral strike slip motion with shear controlled en echelon faulting on the present surface hydrothermal convection is observed along deep seated fissure systems held open by continuous shear strain since the central segment of the rift caused by its deviatory trend is under compressive shear strike slip motion will be slowed down in the near geological future a parallel shear belt about 100 km e of the rhinegraben became active by changing its function of primary normal faulting this belt characterized locally by high rates of pleistocene movements and some dense clusters of seismic epicenters swings around the impediment to shear which is situated in the central segment of the rhinegraben the shear motion of both belts converging towards the northernmost segment of the rhinegraben is blocked by the rhenish shield which interrupts the extension of the rift system transversally from here on a belt of seismic activity and slight pleistocene normal faulting traverses the shield in the northwesterly direction of maximum horizontal compression crustal rifting is lacking at this segment due to the tectonic incompetency of the prevailing slaty rocks of the hercynian basement to the north of this lithological unit the seismic belt extends to the rift segment of the lower rhine embayment which shows active crustal spreading along discrete dip slip faults

the ups and downs of tectonic quiescence recognizing differential subsidence in the epicontinental sea of the oxfordian in the swiss jura mountains abstract recent studies in northern switzerland have shown that epicontinental areas thought to have been tectonically stable during the mesozoic were not necessarily as rigid as presumed by comparing oxfordian facies boundaries and depocenters in their palinspastic position with known faults in the basement a direct relationship between the two can be demonstrated previously the lack of obvious synsedimentary tectonic features has lulled scientists into believing that the realm of the swiss jura was tectonically stable during the mesozoic however it can be shown that facies and sedimentary structures are largely influenced by tectonics subsurface data provide evidence for the presence of paleozoic troughs in the basement which apparently were prone to reactivation during the pan european stress field reorganization taking place in the late jurassic this led to differential subsidence along pre existing lineaments within the study area which can be recognized in the distribution of oxfordian epicontinental basins and their coeval shallow water counterparts eustatic sea level fluctuations played an important role in the development of shallow water facies patterns but a subordinate role in the control of accommodation space in basins while tectonic activity is often recorded in the sedimentary record in the form of platform break ups and associated sedimentary debris more subtle indicators may be overlooked or even misinterpreted sedimentary structures and isopach maps as well as subsurface data in the study area suggest that subtle synsedimentary tectonic movements led to the formation of two shallow diachronous epicontinental basins during the late jurassic it becomes possible to recognize and differentiate the combined effects of local and regional tectonism eustasy and sedimentation

thick skinned tectonics and basement involved fold thrust belts insights from selected cenozoic orogens defining the structural style of fold thrust belts and understanding the controlling factors are necessary steps towards prediction of their long term and short term dynamics including seismic hazard and to assess their potential in terms of hydrocarbon exploration while the thin skinned structural style has long been a fashionable view for outer parts of orogens worldwide a wealth of new geological and geophysical studies has pointed out that a description in terms of thick skinned deformation is in many cases more appropriate this paper aims at providing a review of what we know about basement involved shortening in foreland fold thrust belts on the basis of the examination of selected cenozoic orogens after describing how structural interpretations of fold thrust belts have evolved through time this paper addresses how and the extent to which basement tectonics influence their geometry and their kinematics and emphasizes the key control exerted by lithosphere rheology including structural and thermal inheritance and local regional boundary conditions on the occurrence of thick skinned tectonics in the outer parts of orogens

basin inversion and contractional reactivation of inherited normal faults a review based on previous and new experimental models abstract compressional inversion of former extensional sedimentary basins is a particularly common phenomenon given that passive margins share the same destiny of being subsequently incorporated into fold and thrust belts during basin inversion pre existing faults may concentrate stress and localise future thrust ramps or may be reactivated recording reversal of movement from extension to reverse this process has attracted attention largely because of its economic implications related to petroleum and ore deposit prospects and seismic hazard assessment since more than two decades analogue modelling has been used to indentify and or test a number of parameters relevant for the inversion process this paper aims therefore to offer a reasoned review of the analogue modelling work done on the subject coupling such previous results with those of a new experimental series inspired to the northern apennines stratigraphy and evolution past models have explored the role of main factors governing fault reactivation susceptibility such as fluid pressure fault weakness fault steepness angle of shortening and sediment loading the new models have addressed the role played by geometry and strength of a basal ductile layer during inversion two sets of sand silicone models were first extended orthogonally at different velocities to produce dissimilar pre inversion internal geometries and then shortened coaxially at different velocities to vary the brittle ductile coupling the experimental results confirm the selectiveness of fault inversion and reveal strong similarities with structural styles of tectonic inversion reported from the northern apennines and various areas worldwide the preferred geological model inferred from this modelling involves contribution of 1 syn inversion rotation of pre existing faults to shallower dip and 2 rotation of principal stress axes which could explain the invariable reactivation of only one of the two oppositely dipping graben bounding faults these factors would thus interact with the other well established parameters controlling the fault reactivation process

interactions between thin and thick skinned tectonics at the northwestern front of the jura fold and thrust belt eastern france 1 this study investigates spatial and temporal interactions of thin and thick skinned tectonics in a classical foreland setting located at the front of the jura fold and thrust belt in eastern france the working area coincides with the intracontinental rhine bresse transfer zone and represents the most external front of the deformed alpine foreland the investigation combines analyses of largely unpublished and newly available subsurface information with our own structural data including an exhaustive paleostress analysis and geomorphologic observations results are provided in the form of a new tectonic map and a series of regional cross sections through the study area the besancon zone forming the most external part of the thin skinned fold and thrust belt encroached onto the eo oligocene rhine bresse transfer fault system until early pliocene times thrust propagation was largely controlled by the late paleozoic to paleogene preexisting fault pattern that characterizes the rhine bresse transfer zone thick skinned deformation dominant throughout the avant monts zone located farther to the west was associated with compressional to transpressional reactivation of such faults overprinting and crosscutting criteria of fault slip data allow distinguishing between systematically fanning maximum horizontal stress axes that define the front of the thin skinned jura fold and thrust belt and consistently nw se directed maximum horizontal stress axes that characterize deformation of the autochthonous cover of the foreland which is affected by thick skinned tectonics tectonic and geomorphic analyses indicate that thick skinned tectonics started at a very late stage of foreland deformation post early pliocene geomorphic observations imply that deformation between mesozoic cover and basement is locally still decoupled however overprinting relationships and recent seismicity suggest that present day tectonic activity is thick skinned which probably reflects ongoing tectonic underplating in the alpine foreland

fault related folding a review of kinematic models and their application abstract folding that is directly related to fault activity is an important deformation feature that occurs all over the world in mountain belts accretionary wedges fold and thrust belts and intra plate settings in either strike slip compressional or extensional regimes due to their widespread occurrence knowledge about the development of these structures is important to a broad spectrum of geoscience sub disciplines such as structural geology seismology geomorphology petroleum geology and quaternary geology fault related folding has been analyzed intensively over the last 140 years for the sake of this review we divide the folds according to the way the faults and the folds form that is into detachment fault bend and fault propagation folds all fault related folds are caused by changes in fault parameters the simplest method to produce folds is to transport material along faults that have stepped flat ramp flat geometries fault bend fold alternatively the slip can decrease along the length of the fault and depending on whether the fault remains within a detachment layer or steps up through mechanical stratigraphy either a detachment fold or a fault propagation fold is formed respectively detachment folding was first investigated in the early 20th century whereas the full significance of fault propagation folds was recognized quite late in the 1980s seminal work on fault related folding was carried out in the 1930s but quantitative kinematic models have only been available in the last 30 years these models are extremely valuable because they allow a comprehensive understanding of the evolution of fault related folds and lead to more accurate predictions of the sub surface structure from the mid 1990s onwards numerical simulations have been used to identify how fault parameters such as dip and fault bend angle propagation to slip ratio and shape of the trishear zone influence the geometry of the related folding this is directly applicable to the analysis of the shape of anticlines produced however this does not mean that fold geometry is uniquely related to fault geometry on the contrary different kinematic approaches can lead to a similar fold shape

basement involved thin skinned and thick skinned tectonics in the alps the deformation of continental crust during continental collision by folding and thrusting follows three types of structural styles 1 in a true thin skinned style only cover rocks are involved 2 in the case of a thin skinned basement involved style thin slabs of crystalline basement rocks are piled up into a nappe stack 3 in a true thick skinned style the entire upper crust is involved in the deformation in the alps all three styles can be recognized the helvetic nappes and parts of the penninic nappes exhibit true thin skinned style tectonics triassic evaporites jurassic shales and cretaceous marls acted as detachment horizons basement involved thin skinned tectonics is typical for the penninic nappes in the core of the orogen the thickness of the basement thrust sheets is controlled by the effects of mesozoic rifting by deep burial and heating of the subducting crust and by the presence of late palaeozoic structures thick skinned style is observed in the more external parts of the orogen the external massifs and the southalpine nappe system it occurred in the late phase of collision and involved the entire upper crust the basal detachment occurred possibly along phyllonites generated by the breakdown of load bearing feldspar considering the alpine orogen as a whole the lower crust deformed seemingly independently from the upper crust the detachment of the cover units by thin skinned tectonics occurred prior to thrusting related to basement involved thin skinned tectonics thrust faults of both types were overprinted by post nappe folding

a note on fault reactivation reactivation of existing faults whose normal lies in the 1 3 plane of a stress field with effective principal compressive stresses 1 2 3 is considered for the simplest frictional failure criterion n n p where and n are respectively the shear and normal stresses to the existing fault p is the fluid pressure and is the static friction for a plane oriented at to 1 the stress ratio for reactivation is 1 3 1 cot 1 tan this ratio has a minimum positive value at the optimum angle for reactivation given by 12tan 1 1 but reaches infinity when 2 beyond which 3 0 is a necessary condition for reactivation an important consequence is that for typical rock friction coefficients it is unlikely that normal faults will be reactivated as high angle reverse faults or thrusts as low angle normal faults unless the effective least principal stress is tensile

influence of preexisting fault fabric on inversion related deformation a case study of the inverted fundy rift basin southeastern canada 1 preexisting zones of weakness significantly influenced the structural development of the fundy basin during rifting and subsequent basin inversion the preexisting fabric consisting of ne striking faults with gentle dips and east striking faults with steeply dipping upper segments and gently dipping lower segments formed during paleozoic and older orogenic activity during mesozoic rifting the preexisting fabric was reactivated creating a border fault system composed of linked ne and east striking extensional fault zones with anomalous dips gentle and steep compared to those of newly formed normal faults during inversion the preexisting fabric was again reactivated as the hanging wall of the composite border fault system moved nne relative to the footwall inversion was highly oblique on the ne striking fault zones producing gentle fault parallel buttress folds and fault perpendicular detachment folds above the low angle fault zones inversion was moderately oblique on the east striking fault zone producing relatively tight fault parallel buttress and detachment folds above the gently dipping lower fault segments and reactivating the steeply dipping upper fault segments as left lateral strike slip faults thus inversion related deformation on the east striking fault zone was partitioned at shallow levels i e partitioned updip our work shows that the geometry of preexisting extensional faults and their obliquity relative to the shortening direction profoundly affect deformation style during basin inversion namely the type of inversion related faults the type and shape of inversion related folds and the distribution of deformation e g updip partitioning depend in part on the geometry of the preexisting extensional faults and the variations in these geometries with depth and along strike