fault reactivation in brittle viscous wrench systems dynamically scaled analogue models and application to the rhine bresse transfer zone abstract analogue experiments on oblique rifting and subsequent transpressional reactivation were performed with two layer slabs of sand and silicone in this brittle viscous system transtensional and transpressional wrench faulting was induced by movements of a basal rigid plate the dynamically scaled analogue models are confronted with the structural evolution of the rhine bresse transfer zone rbtz that linked palaeogene rifting in the upper rhine and bresse grabens and that appears to have been transpressively reactivated in neogene to recent times fault patterns produced in the sand layer above the basal silicone layer are compared with structural elements in the sedimentary cover separated from the basement by an evaporitic decollement layer in order to investigate strain rate dependence of fault reactivation and graben inversion transpressional shortening was performed under different displacement rates experimental results suggest that the reactivation of pre existing structures in a brittle cover above a viscous decollement is strongly dependent on the strain rate within the viscous layer under low to intermediate displacement rates 2 6 cm h 1 deformation concentrates within the basal viscous layer and former normal faults within the cover are not reactivated the reactivation at higher displacement rates 5 cm h 1 results in a complete inversion of graben structures within the cover ongoing shortening produces lobed thrust fronts which crosscut pre existing normal faults late pliocene to recent en echelon aligned folds and isolated thrust faults in the cover of the rbtz are attributed to thick skinned reactivation of basement faults a comparison of natural and experimentally obtained structures suggests that fault reactivation occurred under low displacement rates

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

3d modeling of crustal shortening influenced by along strike lithological changes implications for continental collision in the western and central alps abstract the european alps show major along strike variations in the partitioning of crustal shortening between the upper and the lower plates either explained by lateral variation in temperature and rheology or by along strike changes in crustal scale lithology here we present the first 3d thermomechanical geodynamic model to test the potential impact of along strike lithological and associated rheological changes and lateral temperature variations on crustal shortening during continental collision in the western and central alps numerical modeling results suggest a minor impact of lateral thermal variations and lithological changes in the lower plate for the alpine orogeny in contrast lateral lithological changes in the upper plate structure defined by the presence of the buried ivrea body in the western alps should play a major role in determining the present day architecture of the alpine belt our models suggest that the ivrea body acts as a strong rigid buttress constraining crustal shortening to the lower plate promoting the formation of the jura fold and thrust belt and supporting the higher surface elevation observed in the western alps on the other hand in the central alps where the ivrea body is absent much broader distribution of crustal shortening results in lower surface elevation numerical modeling results also suggest that crustal shortening in the central alps is focused within the upper plate during the final stages of continental collision favored by the indentation of thickened upper crust of the lower plate and by detachment of the adriatic upper crust from the underlying lithosphere

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

the jura mountains an active foreland fold and thrust belt abstract recently completed in situ stress measurements using the borehole slotter at 33 new test sites within the swiss and french jura mountains combined with previously published stress data allow a detailed description of the contemporary state of stress in this fold and thrust belt and the adjacent foreland five stress provinces can be recognized with two different general orientations of maximum horizontal stress sh 1 the central and southwest provinces with a nnw sse to nne ssw orientation 2 the east northwest and southeast provinces with an e w to nw se orientation stress magnitudes are in general higher in the southern than in the northern jura mountains characteristic of the northern jura is an e w trending zone of low stress magnitudes which can be traced from the bresse depression south of besancon to the eastern end of the jura northwest of zurich boundaries of stress provinces show poor agreement with boundaries of tectonic units in the jura in addition stress provinces extend beyond the boundaries of the jura mountains into their foreland furthermore palaeo stress orientations show large discrepancies with respect to the contemporary stress orientation these findings are considered to indicate a termination of jura thin skinned foreland tectonics which probably took place some time between 9 and 4 ma according to palaeontological and tectonic evidence it is suggested that a new style of tectonics has commenced in the jura mountains deforming both the basement directly below the jura fold and thrust belt and the cover rocks in a similar mode

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

strain displacement and rotation associated with the formation of curvature in fold belts the example of the jura arc abstract a new simplified genetic classification scheme for arcuate fold thrust belts is proposed based on total strain patterns and displacement vector fields we distinguish three extreme end member models 1 oroclines pure bending of an initially straight belt 2 piedmont glacier with divergent transport directions and 3 primary arcs a simple geometric model set up for the simulation of strain patterns in primary arcs with uniform transport direction demonstrates that divergent strain trajectories and rotations of passive marker lines do not require any divergence in displacement directions these often quoted arguments are insufficient for the identification of oroclinal bending or piedmont glacier type of arc formation only three dimensional restorations of an arc provide the critical information about displacement directions in their absence arc parallel stretches and rotations in comparison with total strains provide the most useful criteria for the distinction of arc formation modes as an example the jura fold thrust belt of the external alps is discussed a large set of strain data includes total shortening estimates based on balanced cross sections local strain axes orientations from the inversion of fault populations homberg c 1996 unpublished phd thesis universite de paris vi france tectonic stylolites and micro strains from twinning in sparry calcite strain trajectories maximum shortening direction computed from these data define a strongly divergent fan with a 90 opening a complete displacement vector field for the entire jura has been determined from balanced cross sections augmented with three dimensional block mosaic restorations philippe y 1995 unpublished phd thesis universite de chambery france displacement vectors diverge by about 40 markedly less than strain trajectories the non parallelism between strain trajectories and transport directions indicates that considerable wrenching deformation did occur in both limbs of the jura arc paleomagnetically determined clockwise rotations of 0 13 from ten sites kempf o et al terra nova 10 6 10 behind the right hand half of the jura arc and two sites with a combined 23 anticlockwise rotation behind the left hand half of the arc are and additional argument in favor of such a wrenching deformation we conclude that the jura arc formed as a primary arc with a minor component of piedmont glacier type divergence in transport directions

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

paleostress reconstructions and geodynamics of the baikal region central asia part 2 cenozoic rifting abstract investigations on the kinematics of rift opening and the associated stress field present a renewed interest since it has recently been shown that the control of the origin and evolution of sedimentary basins depends to a large extent on the interplay between lithospheric strength and applied stresses it appears that changes of stress field with time are an important factor that either controls or results from the rifting process the object of this paper is to study the changes of fault kinematics and paleostress field with time in the baikal rift system during the cenozoic reduced paleostress tensors were determined by inversion from fault slip data measured in the central part of the rift and its southwestern termination between 1991 and 1995 results show that the stress field varies as well in time as in space two major paleostress stages are determined corresponding broadly to the classical stages of rift evolution late oligocene early pliocene and late pliocene quaternary the first paleostress stage is related to the rift initiation and the second to the major stage of rift development similarities between the recent paleostress field and the present day stress field inverted from focal mechanisms indicate that the second paleostress stage is still active therefore we propose to use proto rift for the late oligocene early pliocene stage and active rift for the late pliocene quaternary stage of rift development during the proto rift stage the stress field was characterized by a compressional to strike slip regime a progressive change from transpression to transtension is suspected for the central part of the rift baikal and barguzin basins during this period in the western termination of the rift sayan massif tunka depression a strongly compressional stress field with oblique thrusting kinematics is well constrained in the late miocene early pliocene interval the active rift stage was initiated by a marked change in fault kinematics and stress regime in the late pliocene in the central part of the rift the stress regime changed into pure extension while in the southwestern extremity it changed into pure strike slip fault kinematics suggests that rifting was initiated by an extrusion mechanism due to the interaction of far field compressional stress on a mechanically heterogeneous crust with the southwards pointing wedge of the siberian craton acting as a passive indentor the cenozoic time space evolution of the stress field is believed to reflect the increasing influence of locally generated buoyancy extensional stresses associated with density anomalies of the lithosphere on intraplate stresses generated by the india eurasia convergence and the west pacific subduction

the upper kaena sedimentary geomagnetic reversal record from southern sicily a detailed paleomagnetic and rock magnetic record of the upper kaena polarity reversal was determined from late pliocene marine marls in southern sicily two separate characteristic magnetization components were distinguished a low temperature lt component between 200 and 50 c and a high temperature ht component between 500 and 580 610 c the two components record the reversal in a slightly different way but both were acquired in an early stage following deposition most probably by authigenic biogenic formation of magnetic minerals the actual r n reversal via e and horizontal inclinations seems to take 3 3 kyr and is followed by a stable normal interval 3 3 kyr and subsequently by a significant excursion 50 60 in declination 3 6 kyr relative intensities were lower during a time span of 5 6 kyr and show a minimum of 10 of the nontransitional values but during the excursion no intensity changes are apparent the vgps of the ht component are confined to a longitude between india and australia those of the lt component oscillate between this same longitude and one passing over north and south america we conclude that most if riot all observed features are largely determined by the remanence acquisition process which is complicated by authigenic formation of magnetic minerals and cyclically fluctuating paleoredox conditions this has not only resulted in considerable smoothing but also in delayed nrm acquisition in specific sedimentary intervals we believe that the observed excursion is a sedimentary artifact and not related to geomagnetic field behavior during transitions we emphasize that many reported geomagnetic features may in fact be due to the sedimentary remanence acquisition process

evidences for pre orogenic passive margin extension in a cretaceous fold and thrust belt on the basis of combined seismic and field data western transdanubian range hungary combined sedimentological and structural analysis was carried out in the field and on 2d seismic reflection profiles to recognize pre orogenic structures in a cretaceous fold and thrust belt detailed field observations were made in the keszthely hills western hungary while 2d seismic interpretation was carried out in the neighbouring zala basin as a result a fault controlled intraplatform basin system was identified by a detailed analysis of bounding faults and related outcropscale structures the norian rhaetian 227 201 3 ma synsedimentary faulting was associated with talus breccia formation small scale faulting and dyke formation in addition to slumping and other soft sediment deformations based on the distribution of talus breccia wnw ese trending map scale normal faults were identified in the keszthely hills which is in agreement with the directly observed outcrop scale synsedimentary faults on seismic sections similar wnw or nwtrending late triassic normal faults were identified based on thickness variations of the syn rift sediments and the presence of wedge shaped bodies of talus breccia normal faulting occurred already in the norian and extensional tectonics was active through the early and middle jurassic the late triassic grabens of the western transdanubian range could be correlated with those in western part of the southern alps and the bajuvaric nappe system of the northern calcareous alps these grabens were situated on the proximal adriatic margin and they represent the first sign of the alpine tethys rifting the locus of extension was laterally migrated westward towards the distal adriatic margin during early and middle jurassic

palaeomagnetism of some cenozoic sediments cairo fayum area egypt abstract the palaeomagnetic and rock magnetic characteristics of some cenozoic rocks from the cairo fayum area have been investigated a total number of 259 oriented core samples were collected at 32 sites located in rocks of eocene 13 sites oligocene 11 sites and pliocene 9 sites ages most of these rocks carry a weak but stable remanent magnetisation that is principally carried by hematite goethite and magnetite are also found in some samples as subordinate constituents careful thermal demagnetisation successfully enabled the isolation of the characteristic remanent magnetisation normal and reversed polarities that passed a reversal test have been recorded in the three age groups this magnetisation is probably of primary origin and reflects the ages of the rocks the resultant palaeomagnetic poles are considered reliable and represent a good contribution to the african palaeomagnetic database and should help in further refining of the cenozoic apwp for africa

feedback between erosion and active deformation geomorphic constraints from the frontal jura fold and thrust belt eastern france a regional tectono geomorphic analysis indicates a pliocene to recent rock uplift of the outermost segment of the jura fold and thrust belt which spatially coincides with the intra continental rhine bresse transfer zone elevated remnants of the partly eroded middle pliocene sundgau foret de chaux gravels identified by heavy mineral analyses allow for a paleo topographic reconstruction that yields minimum regional latest pliocene to recent rock uplift rates of 0 05 0 02 mm year this uplift also affected the pleistocene evolution of the ognon and doubs drainage basins and is interpreted as being tectonically controlled while the ognon river was deflected from the uplifted region the doubs deeply incised into it focused incision of the doubs possibly sustained ongoing deformation along anticlines which were initiated during the neogene evolution of the thin skinned jura fold and thrust belt at present this erosion related active deformation is taking place synchronously with thick skinned tectonics controlling the inversion of the rhine bresse transfer zone this suggests local decoupling between seismogenic basement faulting and erosion related deformation of the mesozoic cover sequences

syntectonic fluid flow and deformation mechanisms within the frontal thrust of a foreland fold and thrust belt example from the internal jura eastern france abstract structural mapping and microstructural analyses are combined with stable clumped and radiogenic isotopes to unravel deformation mechanisms and syntectonic fluid flow during upward propagation along the frontal thrust fuans thrust of the internal part of the jura fold and thrust belt the fuans thrust cuts through upper jurassic lower cretaceous carbonate deposits branches into two splays and generates a system of fault propagation folds folding was accomodated by layer parallel shortening and layer parallel shear which generated flexural slip along bedding surfaces stylolites and foliated fabric in marly limestone interbeds thrusting was characterized by cycles of mutually overprinting pressure solution and brittle processes such as frictional sliding and fracturing veining this generated foliated tectonites in marls and limestones without significant cataclasis of the host rock pressure solution and micrometer slip along slickenfibers are evidence of aseismic slip in agreement with the ongoing aseismic growth of anticlines in the jura fold and thrust while crackle like vein texture may account for episodic seismic fracturing geochemical data show that fuans thrust acted as a conduit for the downward infiltration of meteoric derived fluids which channeled along foliated tectonites during syntectonic fluid flow calcite mineralizations precipitated at temperatures between 54 c and 10 c showing an increased contribution of organic carbon from soils in colder paleofluids this indicates a progressive opening of the system characterized by a more efficient and extensive meteoric fluids circulation considering the highest recorded temperature of 54 c and assuming the modern geothermal gradient of 30 c km thrusting in the study outcrop initiated at a burial depth of at least 1 4 km

high magnitude and rapid incision from river capture rhine river switzerland 1 landscape evolution is controlled by the development and organization of drainage basins as a landscape evolves drainage reorganization events can occur via river capture or piracy whereby one river basin grows at the expense of another the river downstream of a capture location will generate a transient topographic response as the added water discharge increases sediment transport and erosion efficiency this erosional response will propagate upstream through both the captured and original river basins here we focus on quantifying the impact of drainage reorganization along the rhine aare river system 45 000 km2 during the late pliocene early pleistocene where gravel remnants indicate total incision of 650 m during the last 4 2 myr in the region of the recent aare rhine confluence we develop a numerical model of drainage capture to quantify the range of possible magnitudes of erosion and the transient river response resulting from the reorganization of the rhine river the model accounts for both fluvial incision and sediment transport our model estimates 400 800 m of river elevation change lowering profiles during the last 4 myr due to river capture events providing an important component to the recent exhumation budget of the swiss alpine foreland the model indicates a rapid response to capture events re equilibration timescale of 1 myr the predicted incision magnitudes are consistent with incision measured from the elevation of pliocene and early pleistocene river gravels suggesting that across northern switzerland a significant amount of incision can be explained by drainage reorganization

interaction of folding and thrusting during fold and thrust belt evolution insights from numerical simulations and application to the swiss jura and the canadian foothills abstract we use two dimensional numerical simulations to investigate the interaction of folding buckling and thrusting localized shearing during the structural evolution of fold and thrust belts ftb we model layer parallel shortening of mechanically strong layers resting above a weaker layer referred to as detachment we consider a viscoplastic rheology with linear viscosity and frictional plastic drucker prager yield criterion the detachment thickness is larger in one model half and only this geometrical thickness perturbation triggers folding and thrusting in the simulations we conduct a systematic analysis to quantify the impact of model parameters such as magnitude of the thickness perturbation or detachment rheology frictional or viscous on the ftb evolution the magnitude of the perturbation determines whether or not folding is favoured over thrusting and hence controls the progressive interaction of folding and thrusting during ftb evolution the asymmetry of modelled anticlines is proportional to the relative height of the initial perturbation we also adapt the model configuration to specific mechanical stratigraphies of two regions in natural ftb namely the haute chaine of the jura mountains switzerland and the foothills of alberta canada the modelled fold and thrust geometries agree with different types of observed anticlinal structures such as symmetric detachments folds and asymmetric thrust folds our results suggest that an initial stage of low amplitude buckling likely occurred prior to the main folding and thrusting phase we argue that folding and thrusting are equally important and interacting processes during the structural evolution of many natural ftb

crescent like large scale structures in the external zones of the western gibraltar arc betic rif orogenic wedge the external wedge of the gibraltar arc orogenic system western mediterranean is a natural case of a fold and thrust salient although at the scale of the arc a swing of the structural trend can be observed the presence of closed crescent like structures some of them more than 25 km long and scattered over an area of 3500 km 2 characterize the gibraltar arc external wedge this feature makes it very different from a classical arc shaped fold and thrust belt detailed structural maps of representative crescent like structures are presented synorogenic sediments reveal that they probably formed during a short time interval most probably during a single shortening event the crescent like structures are localized in front of a recess formed by the internal zones that acted as backstop this backstop shape and a viscous substrate essentially triassic evaporites below the fold and thrust external wedge constrain the experimental setting of an analogue model in which we were able to reproduce structures that developed originally with a highly non cylindrical shape during a single straight convergence moreover the tectonic transport directions along the thrusts are broadly comparable in the natural case and the model

gyroremanent magnetization and the magnetic properties of greigite bearing clays in southern sweden summary the acquisition of a gyroremanent magnetization grm by single domain sd greigite particles during alternating field af demagnetization is demonstrated previous palaeomagnetic studies failed to identify the presence of authigenic greigite in the glacio marine clays studied these clays formed the subject of an earlier debate about the validity of a late weichselian geomagnetic excursion the gothenburg flip in southern sweden the greigite carries a stable chemical remanent magnetization crm which coexists with a detrital remanent magnetization drm carried by magnetite af demagnetization could not isolate the primary remanence in the sediments where magnetite and greigite coexist due to the overlapping coercivity spectra of the two minerals and the inability to determine the time lag between sediment deposition and crm formation thermal demagnetization removed the crm at temperatures below 400 dc but this method was hindered by the unconsolidated nature of the sediments and the formation of secondary magnetic minerals at higher temperatures the results suggest that the low coercivity drm carried by magnetite was mistaken for a viscous component in the earlier studies hence the former debate about the record of the gothenburg flip may have been based on erroneous palaeomagnetic interpretations or non reproducible results af demagnetization procedures applied to samples suspected of bearing sd magnetic particles such as greigite should be carefully selected to recognize and account for grm acquisition

thrust development in the eastern jura mountains related to pre existing extensional structures abstract from tunnel and map data three detailed balanced cross sections of the mesozoic cover of the jura fold and thrust belt in the hauenstein area eastern jura mountains switzerland were constructed viable models of the kinematic evolution of the structures document different stages of thrust development most thrust propagate first from the basal decollement in the middle triassic evaporites to the opalinus shales in some cases they continue for a short distance layer parallel and then break through to the surface in other cases they get stuck in the opalinus shales with further shortening either a delamination occurs where the incompetent layers were wedged under the overlying competent limestones the thrust breaks through the limb of the anticline at a higher level otherwise the thrust steepens and breaks through the hinge of the fold the resulting kinematically viable sections confirm that the miocene thrusts nucleate at inhomogeneities of the sub decollement relief these are possibly related to the borders of an underlying palaeozoic trough system reactivated as faulted flexures during the eocene to early miocene

relationship between eustatic sea level changes and basement subsidence geohistory reconstructions based on well data provide a direct and quantitative method of estimating basement subsidence geohistories in addition to responding to rates of sediment accumulation and to local and regional subsidence mechanisms also reflect eustatic sea level changes we have determined quantitatively that component of subsidence that is common to a worldwide set of wells after compensating for the response of the crust to sedimentation we find some correlations between the global rate of subsidence and low frequency changes in the height of eustatic sea level as determined from the stratigraphic interpretation of seismic data these results suggest that basement subsidence data which are independent of the techniques used previously may be used to re ognize variations in eustatic sea level however we are unable to determine the size of the eustatic sea level excursions because of difficulties in determining and separating variations in lithospheric rigidity thermal subsidence and sediment supply independent of tectonic subsidence and sea level variation we compare subsidence curves in an empirical fashion with published eustatic sea level curves thus avoiding the application of geologic models involving crustal properties we cannot quantify geohistory analysis is also a powerful means of studying subsidence on a regional scale and so of deducing the regional tectonic history we illustrate this point by subsidence maps through time for the north sea

plio pleistocene transpressional reactivation of paleozoic and paleogene structures in the rhine bresse transform zone northern switzerland and eastern france pliocene to recent uplift and shortening in the southern rhinegraben is documented by deformation of pliocene fluvial gravels deposited on a nearly planar surface as well as by progressive deflection and capture of rivers this deformation is suggested to result from thick skinned tectonic movements as evidenced by ob servations on seismic records which demonstrate a spatial coincidence between en chelon anticlines at the surface and faults located in the crystalline basement these findings contradict the often invoked thin skinned tectonism in the recent tectonic history of the rhine graben in particular the transfer zone between the rhinegraben and the bressegraben is very suitable for reactivation under the present day stress field thick skinned reactivation of faults in the basement is also expressed by focal plane mechanisms of recent earth quakes showing strike slip rather than reverse faulting characteristics this is of importance for the densely populated and industrialised southern rhinegraben pre viously affected by large earthquakes in historical times e g basel 1356

new insight in the tectonics of the southern rhine graben jura region using local earthquake seismology 1 a new seismic data set was acquired using a dense temporary network of mobile seismic stations it is combined with existing seismological data for the southern rhine graben the data yielded some new focal mechanisms and allowed for a detailed local earthquake tomography these methods give new insight in the structure of the crust and stress conditions in the area by combining the tomography with the earthquake hypocenter locations and focal mechanisms some of the structures in the p wave velocity model are interpreted as active faults the eastern boundary fault zone of the graben is found to be activated in a left lateral strike slip sense the southern continuation of these faults is formed by variscan structures in the basement a change in orientation of the graben axis between the main graben and its southern end have played a role during the development of the system this difference in orientation caused the development of the dannemarie and allschwil subbasins during a late stage of the opening of the rhine graben this study shows evidence for active faulting in the basement underneath the detachment of the jura mountains these faults which are interpreted as reactivated permo carboniferous troughs coincide with the frontal thrusts of the jura mountains it might be that these structures in the basement have influence on the detachment tectonics in the region

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

magnetic overprints and their removal abstract procedures for removing magnetic overprints are analyzed it is concluded that an overprint carried by single domain grains cannot be removed by alternating field demagnetization without first removing the original remanance the natural remanent magnetization nrm however if the coercive force spectra are sufficiently separate it may still be possible to isolate the nrm as the first moment removed the safest way to remove overprints is thermally but this will require elevated temperatures

post variscan evolution of the lithosphere in the rhine graben area constraints from subsidence modelling in the area of the cenozoic rhine rift system crustal and lithospheric thicknesses range between 24 and 35 km and 60 and 120 km respectively this rift system transects the deeply truncated variscan orogen and superimposed permo carboniferous wrench induced troughs and late permian and mesozoic thermal sag basins at the time of its westphlian consolidation the variscan orogen was probably characterized by 45 60 km deep crustal roots that were associated with its rheno hercynian saxo thuringian saxo thuringian bohemian and bohemian moldanubian sutures all of which are transected by the cenozoic rhine rift system during the stephanian early permian wrench induced disruption of the variscan orogen subducted lithospheric slabs were detached causing upwelling of hot mantle material during the resulting thermal surge partial delamination and or thermal thinning of the continental mantle lithosphere induced regional uplift at the same time the variscan orogenic roots were destroyed and crustal thicknesses reduced to 28 35 km in response to the combined effects of mantle derived melts interacting with the lower crust regional erosional unroofing of the crust and on a more local scale by its mechanical stretching towards the end of the early permian the potential temperature of the asthenosphere returned to ambient levels with this regional long term thermal subsidence of the lithosphere commenced controlling the development of a new system of late permian and mesozoic thermal sag basins however the evolution of these basins was repeatedly overprinted by minor short term subsidence accelerations that reflect the build up of far field stresses related to rifting in the tethyan and atlantic domains comparison of observed and modelled subsidence curves suggests that in the area of the rhine rift system the lithosphere had equilibrated with the asthenosphere at the end of the cretaceous at depths of 100 120 km before it became thermally destabilized again by cenozoic rifting and plume related magmatism modelled subsidence curves indicate that by the end of early permian times the thermal thickness of the remnant mantle lithosphere ranged between 10 and 50 km in areas that were later incorporated into mesozoic thermal sag basins this corresponds to mid permian thermal lithosphere thicknesses of 40 80 km the geological society of london 2004

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

microwave palaeointensity study of the jorullo volcano central mexico summary a single lava flow from the earliest eruption period ca ad 1759 1774 of the jorullo vol cano michoacan guanajuato volcanic field mgvf mexico has been sampled to determine the palaeointensity of the magnetic field at the time of extrusion both conventional thellier thellier experiments and two variants of the microwave palaeointensity technique coe variant of the thellier thellier method and the perpendicular applied field method have been con ducted high quality palaeointensity results mean of 46 6 6 3 t from 15 samples using all three methods have been obtained with both techniques in good agreement this study presents further evidence of the equivalence of both microwave and thermal methods and adds to the database of palaeomagnetic data from the monogenetic volcanoes of central america

linking the northern alps with their foreland the latest exhumation history resolved by low temperature thermochronology the evolution of the central alpine deformation front subalpine molasse and its undeformed foreland is recently debated because of their role for deciphering the late orogenic evolution of the alps its latest exhumation history is poorly understood due to the lack of late miocene to pliocene sediments we constrain the late miocene to pliocene history of this transitional zone with apatite fission track and u th he data we used laser ablation inductively coupled mass spectrometry for apatite fission track dating and compare this method with previously published and unpublished external detector method fission track data two investigated sections across tectonic slices show that the subalpine molasse was tectonically active after the onset of folding of the jura mountains this is much younger than hitherto assumed thrusting occurred at 10 8 6 5 ma and potentially thereafter this is contemporaneous with reported exhumation of the external crystalline massifs in the central alps the jura mountains and the subalpine molasse used the same detachments as the external crystalline massifs and are therefore kinematically coupled estimates on the amount of shortening and thrust displacement corroborate this idea we argue that the tectonic signal is related to active shortening during the late stage of orogenesis

map view retrodeformation of an arcuate fold and thrust belt the jura case 1 the mechanism of arcuate mountain range formation is a matter of debate here we perform a map view restoration of a detailed three dimensional model of the jura arc a typical arcuate mountain range in the foothills of the swiss and french alps this retrodeformation is performed using the unfold surface balanced program based on a block mosaic method it results in a displacement field divergent toward the deformation front this displacement field suggests counterclockwise rigid rotations in the horizontal plane up to 30 in the southern internal jura and a corresponding vertical axis rotation or shear strain of the savoie molasse basin hinterlandward we also predict a 10 clockwise vertical axis rotation of the molasse basin in switzerland all these rotations agree with those documented by paleomagnetic data the former are taken to result from a substantial decrease in shortening at the southern jura end while the divergence of displacements is interpreted to result from variations in the detachment level distribution

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

stress field variations in the swiss alps and the northern alpine foreland derived from inversion of fault plane solutions 1 this study is devoted to a systematic analysis of the state of stress of the central european alps and northern alpine foreland in switzerland based on focal mechanisms of 138 earthquakes with magnitudes between 1 and 5 the most robust feature of the results is that the azimuth of the minimum compressive stress s3 is generally well constrained for all data subsets and always lies in the ne quadrant however within this quadrant the orientation of s3 changes systematically both along the structural strike of the alpine chain and across it the variation in stress along the mountain belt from ne to sw involves a progressive counterclockwise rotation of s3 and is most clear in the foreland where it amounts to 45 50 this pattern of rotation is compatible with the disturbance to the stress field expected from the indentation of the adriatic block into the central european plate possibly together with buoyancy forces arising from the strongly arcuate structure of the moho to the immediate west of our study area across the alps the variation in azimuth of s3 is defined by a progressive counterclockwise rotation of about 45 from the foreland in the north across the helvetic domain to the penninic nappes in the south and is accompanied by a change from a slight predominance of strike slip mechanisms in the foreland to a strong predominance of normal faulting in the high parts of the alps the observed rotation can be explained by the perturbation of the large scale regional stress by a local uniaxial deviatoric tension with a magnitude similar to that of the regional differential stress and with an orientation perpendicular to the strike of the alpine belt the tensile nature and orientation of this stress is consistent with the spreading stress expected from lateral density changes due to a crustal root beneath the alps

simultaneous normal faulting and extensional flexuring during rifting an example from the southernmost upper rhine graben the southern end of the upper rhine graben urg is formed by a major continental transfer zone which was localised by the reactivation of ene oriented basement faults of late palaeozoic origin a combination of subcrop data derived from exploration wells and reflection seismic lines and palaeostress analysis provided new constraints on the timing and kinematics of interacting basement faults rifting in the southern urg began in the upper priabonian under regional wnw ese directed extension oriented roughly perpendicular to the graben axis in the study area this led to the formation of nne trending half grabens simultaneously ene trending basement faults situated in the area of the future rhine bresse transfer zone rbtz were reactivated in a sinistrally transtensive mode in the sedimentary cover the strike slip component was accommodated by the development of en echelon aligned extensional flexures flexuring and interference between the differently oriented basement faults imposed additional but locally confined extension in the sedimentary cover which deviated by as much as 90 from the regional wnw ese extension the interference of regional and local stresses led to a regime approaching radial extension at the intersection between the urg and rbtz

intraplate brittle deformation and states of paleostress constrained by fault kinematics in the central german platform abstract the structural evolution of central europe reflects contrasting tectonic regimes after the variscan orogeny during mesozoic cenozoic time the brittle deformation related to each tectonic regime is localized mainly along major fault zones creating complex fracture patterns and kinematics through time with diverging interpretations on the number and succession of the causing events by contrast fracture patterns in less deformed domains often provide a pristine structural inventory we investigate the brittle deformation of a relatively stable wide area of the central german platform using fault slip data to identify the regional stress fields required to satisfy the data in a non classical approach and in order to avoid local stress variations and misinterpretations the fault slip data are scaled up throughout the study area into subsets of consistent kinematics and chronology for sedimentary cover and crystalline basement rocks direct stress tensor inversion was performed through an iterative refining process and the computed stress tensors were verified using field based observations criteria on relative tilt geometry and indicators of kinematic change suggest a succession of events which begins with a post triassic normal faulting regime with 3 axis trending ne sw the deformation then follows by strike slip and thrust faulting regimes with a change of 1 axis from n s to ne sw supposedly in the late cretaceous two younger events are characterized by cenozoic normal and oblique thrust faulting regimes with nw se trending 3 and 1 axes respectively the fracture patterns of both the cover and basement rocks appear to record the same states of stress

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

control of preexisting faults on geometry and kinematics in the northernmost part of the jura fold and thrust belt 1 this study investigates the formation of the northernmost anticlines of the late miocene to early pliocene thin skinned jura fold and thrust belt and provides evidence that a transition to thick skinned tectonics did occur in this particular area during the late pliocene the northernmost anticlines of the jura fold and thrust belt are characterized by pronounced along strike asymmetries that were predetermined by a fault pattern inherited from paleogene upper rhine graben rifting this fault pattern had disrupted the triassic basal decollement of the jura mountains and controlled the nucleation of thrusts and folds as well as transfer zones during the generally n nw directed transport of the detached sedimentary cover sinistral transpressive oblique ramps nucleated along paleogene nne trending basement normal faults and led to a northward protrusion of the jura front encroaching onto the southernmost upper rhine graben shortening across the frontal anticlines is greatest along the oblique ramps and decreases along strike toward the east necessitating a gentle clockwise rotation of the detached sediments despite the fact that the stress field in the sedimentary cover remained unchanged thin skinned folding and thrusting came to a halt in the early pliocene giving way to thick skinned tectonics very probably governing neotectonic activity in the area this transition might represent a geodynamic reorganization of the northwestern alpine foreland

paleomagnetism and tectonics of the jura arcuate mountain belt in france and switzerland abstract goethite and hematite in ferriferous oolitic beds of callovian age from the jura mountains switzerland france carry either pre and or post tectonic magnetization the frequent pre tectonic origin of goethite magnetization indicates a temperature range during formation of the arcuate jura mountain belt below the goethite neel temperature of about 100 c the scatter of the pre tectonic paleomagnetic directions d 11 5 e i 55 5 95 4 7 which reside both in goethite and hematite provides strong evidence that the arcuate mountain belt was shaped without significant rotation the paleomagnetic results support tectonic thin skinned models for the formation of the jura mountain belt

climate induced rebound and exhumation of the european alps foreland basins record the regional isostatic compensation of mountain belts during periods of crustal thickening they subside and when erosion unloads the mass of the mountains the basins rebound and are eroded in order to evaluate this mechanism for rebound it is critical that the timing and magnitude of erosion are documented we present data estimating the timing and magnitude of late orogenic or postorogenic erosion in the north alpine foreland basin of switzerland mineral cooling ages demonstrate that the basin underwent 1 3 km of erosion soon after 5 ma this erosion coincided with a decline in structural deformation in the swiss alps and a doubling of sediment accu mulation rates in surrounding depocenters we propose that accelerated erosional un roofing of the swiss alps triggered isostatic rebound and erosion of the foreland basin after 5 ma a projection of the isostatic rebound of the basin into the mountains suggests that at least 6 5 km of erosion should have occurred in the high topography of the aar massif accelerated erosion in the swiss alps at that time is explained by an increase in atmospheric moisture driven by an intensification of the atlantic gulf stream at 4 6 ma consequently we propose that the changing erosional capacity of the climate triggered late orogenic to postorogenic mass reduction and isostatic rebound of the swiss alps and their neighboring foreland basin

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

present day deformations of the jura arc inferred by gps surveying and earthquake focal mechanisms this study presents a compilation of more than 40 years of seismotectonic data including 54 computed focal mechanisms combined with 15 years of gps data coming from a dense network of 35 permanent gps stations within the jura arc and its vicinity these data are compared to previous available geomorphological geophysical and structural studies in order to discuss the 3d distribution of the deformation within the jura arc gps data show coherent schemes in terms of velocities and allowed to discriminate between two provinces ne of the belt and in its front foreland they also constrain a low but significant overall strain tensor with a nnw sse shortening of 2 16 nanostrain year associated with an ene wsw extension of 0 44 nanostrain year the seismotectonic approach is based on a data set of 2 400 events and 54 focal mechanisms inversions of the focal mechanisms both globally and in homogeneous sectors highlight a general strike slip deformation regime with sigma1 oriented nw se and sigma3 oriented ne sw we discriminate two different sectors in terms of basement cover un coupling 1 potentially decoupled deformation between the basement and the sedimentary cover in the ne part and 2 coupled deformation in the sedimentary cover and its basement in the jura foreland

present day and future tectonic underplating in the western swiss alps reconciliation of basement wrench faulting and decollement folding of the jura and molasse basin in the alpine foreland abstract the western alps form a geodynamically active mountain belt showing the typical features of an evolving orogenic wedge with its pro wedge geometry to the nnw and its retro wedge structures to the sse renewed tectonic underplating of european continental crust occurred after the orogenic wedge underwent major dynamic disequilibrium following the break off of the southward subducting slab of the european passive margin the most important of these basement imbricates are the mont blanc aiguilles rouges and gastern aar crystalline massifs also forming the alps highest mountains the upper plate present day orogenic wedge of the western alps includes the molasse basin and the jura fold and thrust belt both decoupled from the basement over a basal decollement surface the overall geometry of this wedge appears to be strongly unstable according to simple wedge models in its attempt to regain stability out of sequence thrusts form in the existing basement nappes but also new basement nappes should develop beneath the southern portion of the molasse basin new out of sequence thrusts in the cover trigger higher than average uplift rates concentrated around the newly forming structures and are accompanied by a concentration of earthquakes tectonic underplating is further corroborated by neotectonics and the tectonic structures observed in the prealpes molasse basin and jura similarly uplift rates and earthquakes along the southern edge of the jura mountains seem to witness the development of a new incipient basement nappe at depth partial inversion of former permo carboniferous grabens in the basement a possible spatial coincidence of areas with strong earthquake activity and zones with uplift rates above surrounding values suggest a common mechanism for their origin in the western swiss alpine foreland combined with information from basement geometry and wedge dynamics it is proposed that the common mechanism is the development of basement imbricates by tectonic underplating the proposed model for ongoing and possible future tectonic underplating beneath an active alpine orogenic wedge also allows to reconcile the models of basement wrench faulting in the molasse basin and jura with the distant push theory where the molasse basin and jura develop over a basal decollement horizon

the basel 1356 earthquake which fault produced it the 1356 basel earthquake was the strongest event to have shaken nw europe in the last thousand years the peculiar location of this historical event makes it possible to relate it to normal faulting along the edges of the rhine graben as well as to reverse faulting along the jura frontal thrust or to fault reactivation within the hercynian basement alternate hypotheses are discussed and their implications compared taking into account available structural data and results of the morphotectonic study performed in the epicentral area this study combines field observations with the analysis of spot satellite imagery aerial photographs and detailed topography it is concluded that the basel earthquake most probably reactivated a basement fault reverse or wrench fault beneath the shallow depth aseismic detachment that underlies the jura mountains

clues for a tortonian reconstruction of the gibraltar arc structural pattern deformation diachronism and block rotations abstract we proposed a reconstruction of one of the tightest orogenic arcs on earth the gibraltar arc system this reconstruction which includes onshore and offshore data is completed for approximately 9 ma the clues that lead us to draw it are based on a review in terms of structures and age of the superposed deformational events that took place during miocene with special attention to the external zones this review and new structural data presented in this paper permit us to constrain the timing of vertical axis rotations evidenced by previously published paleomagnetic data and to identify homogeneous domains in terms of relationships between timing of deformation events re magnetization and rotations in particular remagnetization in the betics took place after the main shortening which produced the external fold and thrust belts pre upper miocene but was mostly previous to a contractive reorganization that affected the whole area it should have occurred during lower tortonian between 9 9 and 11 ma from tortonian to present block rotations as high as 53 took place together with plate convergence they accommodated a tightening and lengthening of the gibraltar arc system and drastically altered its geometry as the orientation and position of any pre 9 ma kinematic indicator or structural element is also modified our reconstruction should be used as starting point for any pre tortonian model of the westernmost orogenic segment of the alpine mediterranean system

curved fold and thrust accretion during the extrusion of a synorogenic viscous allochthonous sheet the estepa range external zones western betic cordillera spain 1 new structural borehole and time domain electromagnetic data allow us to reconstruct the 3 d geometry of the estepa range external zones of the western betic cordillera which constitutes an isolated curved fold and thrust range made up of jurassic shallow marine carbonates and cretaceous to paleocene marls and marly limestones contraction and rising load linked to the accretion of the subbetic nappe enhanced the expulsion of triassic evaporites and overpressured clays during the early and middle miocene finally forming part of a highly deformed melange unit this plastic extrusion favored the disconnection of external and middle subbetic blocks including the sierra de estepa range there deformation is characterized by northwest vergent curved folds and thrusts associated with ne sw frontal ramps and nw se lateral transfer faults that segmented the folds active between 18 and 12 ma at a local scale curvature was achieved under a nearly uniform nw wnw transport direction suggesting a primary arc type friction variation across the heterogeneous detached plastic basal triassic unit mainly controlled the curvature and segmentation of the fold systems transport direction is consistent with previously published slip data from the internal subbetic and the campo de gibraltar units after the late serravallian accretion slowed down and a shallow marine unit deposited unconformably placed over the main thrust and folds the sequence of deformation and emplacement of these ranges is interpreted as a continuous process linked to the early miocene e continental collision of the iberian margin thin continental crust and subduction of the flysch trough oceanic crust beneath the alboran continental domain