effects of topography on the curvature of fold and thrust belts during shortening of a 2 layer model of continental lithosphere abstract we have used analogue experiments to investigate the effects of surface topography on the curvature of fold and thrust belts under conditions of 1 initial relief but no erosion and 2 no initial relief but differential erosion sedimentation and transport in experiments where a 2 layer model lithosphere shortened and thickened in front of an advancing straight piston the geometry of the developing thrust wedge was very sensitive to variations in surface topography in models with an initially flat horizontal surface and in the absence of erosion and sedimentation thrusts were straight propagated forwards and nucleated at buckle folds far in front of an advancing piston around an initial topographic high plateau or cone thrusts tended to be arcuate forming salients towards the foreland initial plateaux and cones tended to behave rigidly while arcuate thrust slices formed around them to accommodate differential slip transfer zones developed on both sides of initial highs fault blocks rotated about vertical axes and thrusts moved in oblique slip within transfer zones in models with initially horizontal surfaces which were subject to differential erosion sedimentation and transport thrusts initially were straight but then progressively rotated around non eroded thickened and stronger areas these worked as indenters in front of which new thrusts nucleated at curved buckle folds these thrusts were also curved their apices being in front of the thickened non eroded areas in nature arcuate structural patterns are to be found around the altiplano of the central andes and around the tromen volcanic ridge in the neuquen basin of northern patagonia we infer that these areas behaved in quasi rigid fashion protected as they were by their high elevations and that differential erosion at the scale of the entire andes may have contributed to oroclinal bending

synchronous detachment folds and coeval sedimentation in the prepyrenean external sierras spain a case study for a tectonic origin of sequences and systems tracts this paper reports on the structural and sedimentary evolution of the middle to late eocene of the prepyrenean external sierras southern pyrenees spain the initiation duration and kinematics of a set of growth structures that developed in a shallow marine depositional setting is documented the detailed analysis of the syntectonic marine sediments not only confirms the already known east to west progression of deformation but also reveals the continued growth of the early formed structures as later ones propagate towards the foreland the sedimentary units coevally deposited with these growth structures are arranged in four depositional sequences their boundaries correspond to flooding surfaces which grade basinwards into correlative conformities they are also indicated by the presence of both angular unconformities and onlap geometries each depositional sequence generally consists of two systems tracts the lower one or transgressive systems tract is formed by up to 400 m of azoic marls deposited in outer ramp areas the upper one or highstand systems tract mainly consists of shallow siliciclastic and carbonate facies up to 200 m thick deposited in middle to inner ramp areas these depositional sequences are interpreted to be controlled by regional tectonic pulses an increase of tectonic activity resulted in the flooding of the basin and in the subsequent deposition of a thick succession of nearly azoic blue marls i e transgressive systems tract the overlying highstand systems tract developed following periods of diminished tectonism with the consequent growth and progradation of shallow carbonate platform facies

role of the backstop to cover thickness ratio on vergence partitioning in experimental thrust wedges the ratio between the thickness of the sedimentary sequences offscraped from the subducting plate hc and the average thickness of the backstop hb is expected to significantly influence vergence partitioning in thrust wedges a series of simple sandbox experiments was performed to study the role of the hc hb ratio in model thrust wedges the results obtained show that thrust wedges with hc hb values lower than 1 are essentially pro ward verging with minor retro ward faulting hc hb values greater than 1 imply an increase of vergence partitioning when a threshold value is exceeded fully partitioned doubly vergent thrust wedges develop comparison with natural submarine thrust wedges suggests that these experimental results may provide useful insights on the evolution of structural architecture at convergent margins

detachment folding fold amplification and diapirism in thrust wedge experiments 1 the relations between detachment folding fold amplification and salt diapirism in contractional settings have been investigated by means of scaled analogue models the viscosity of the silicone layer simulating salt in nature and the shortening rates were combined in order to reproduce weak type 1 models and strong type 2 models decollements deformation patterns in the roof sequence exhibited two contrasting styles 1 outward propagation of detachment folding along the decollement ofp mode and 2 passive roof duplex prd mode in type 2 models detachment folding propagated away from the most external thrust in the floor sequence while in type 1 models long lived detachment folds almost invariably localized amplified above a floor thrust tip as a result of strain localization a silicone wall intruded occasionally into the crestal graben of detachment folds in type 1 and ofp models best fitting of transition models data points indicates nonlinear relations with regression curves close to the equilateral hyperbola equation for both ofp prd and amplified detachment folds box folds transitions a quantitative comparison of model results with nature has been attempted by plotting salt based fold and thrust belts data points on the scaled transition curves obtained from the modeling such a comparison relates shear stress products and ratios to the conditions favoring the amplification of detachment folds and the potential emplacement of ductile diapirs in their core by reducing the roof sequence strength pore fluid pressure b is inferred to shift the equilibrium of fold and thrust belts toward the field of ofp and diapirism

fluid systems and fracture development during syn depositional fold growth an example from the pico del aguila anticline sierras exteriores southern pyrenees spain this paper reports an integrated spatio temporal analysis of the fracture controlled paleo fluid system in the pico del aguila anticline a n s trending fold located in the sierras exteriores the southern front of the spanish pyrenees eight fracture sets joints or faults are recognized throughout the fold and are separated into a fracture sequence that is defined using field relationships and the remarkable temporal constraints offered by the syn tectonic sedimentary deposits this fracture sequence records a complex paleocene to early oligocene structural evolution including map view clockwise rotation and tilting of the fold axis the geochemical analysis of calcite cements from the different mineralized fracture vein sets reveals a compartmentalized fluid system during most of fold development this initial paleofluid system was later perturbed when bending related fractures associated with foreland flexure and outer arc extension triggered small scale vertical fluid migration fractures developed in shallow strata facilitated downward migration of surficial fluids that controlled the paleo fluid system in the late priabonian stampian continental deposits the study of the pico del aguila anticline depicts for the first time the evolution of a fluid system in a shallow syn depositional compressional setting and results further strengthen the statement that fluids migrate vertically across stratigraphic boundaries take place during fold hinge related deformation

role of decollement material with different rheological properties in the structure of the aljibe thrust imbricate flysch trough gibraltar arc an analogue modelling approach abstract the miocene aljibe thrust imbricate flysch trough in the external zone of the gibraltar arc shows large changes in structural style towards the foreland rheological variation of the decollement rocks triassic evaporitic rocks and mesozoic limestones appears to be the main factor controlling the contrasts in structural style that characterise adjacent wedge domains in order to test this hypothesis we carried out analogue experiments involving three dimensional variations of decollement material a plate of viscous material was placed in the central part of the models at the base of the sand multilayers different geometries of the viscous plate were used experimental results show a strong link between the rheological properties of the decollement material and the structure of the overlying thrust wedge these results compare well with the internal geometry and vergence distribution in the aljibe thrust imbricate indeed the tectonic style of the wedge can be explained as a consequence of variations of rock type along the basal decollement

the effect of decollement dip on geometry and kinematics of model accretionary wedges we conducted a series of sand box models shortened asymmetrically above a frictional plastic decollement to study the influence of amount and sense of the decollement dip on the geometry and kinematics of accretionary wedges model results illustrate that the amount and direction of decollement dip strongly influence the geometry and mode of deformation of the resulting wedge in general for models having similar decollement frictional parameters the resulting wedge is steeper grows higher and is shorter when shortened above a decollement that dips toward the hinterland at 42 bulk shortening the length height ratio of wedges formed above a 5 dipping decollement was equal to 2 4 whereas this ratio was equal to 3 for wedges shortened above a horizontal decollement moreover models with a hinterland dipping decollement undergo larger amounts of layer parallel compaction lpc and area loss than models shortened above a non dipping decollement the effect of decollement dip on wedge deformation is most pronounced when basal friction is relatively high b 0 55 whereas its effect is less significant in models where the basal decollement has a lower friction b 0 37 model results also show that increasing basal slope has a similar effect to that of increasing basal friction the wedge grows taller and its critical taper steepens

combined control of decollement layer thickness and cover rock cohesion on structural styles and evolution of fold belts a discrete element modelling study abstract a series of numerical experiments based on the discrete element method were performed to simulate the formation of fold belts with varied decollement layer thickness and cover rock cohesion to investigate their controls on structural styles of fold belts each model consists of a weak unbonded basal decollement layer with a relatively low to high thickness and a bonded cover with a relatively low to high cohesive strength horizontal shortening of the particle assemblage was achieved by horizontal motion of a vertical boundary wall resulting in deformations in the system the results show that shortening was mainly accommodated by detachment folds sinusoidal and box folds fault related folds and opening mode fractures in the models the combination of a lower cohesion and a thinner decollement resulted in more distributed strain and a larger number of folds whilst the combination of a higher cohesion and a thicker decollement led to more pronounced strain localisations in fewer folds surface uplift and fold amplitude diapir height are mainly positively affected by the decollement thickness i e the thicker the decollement is the greater the surface uplift and fold amplitude are the propagation rate of deformation is predominately controlled by the cover rock cohesion a lower cohesion led to a higher propagation rate of deformation the model with a relatively low cohesion and decollement thickness produced regularly spaced box folds which are comparable to those in the southern zagros fold and thrust belt the models presented demonstrate that the combined effect of decollement layer thickness and cover rock cohesion can play a critical role in the structural styles and kinematic evolution of fold belts

centrifuged models of gulf of mexico profiles abstract physical models dynamically scaled in a centrifuge are used to explore the importance of slope progradation in driving internal salt structures much further horizontally than they rise large increments of ductile plastic overburden added at normal gravity values simulated primary clastic sedimentary progradation of a clastic slope over a layer of buoyant fluid simulating salt during load increments at a nominal 800 g in a centrifuge this ductile topographic slope spread over the ductile decollement except for down to basin growth faults all the structures considered to be distinctive in the northern gulf of mexico are simulated in the models that are scaled such that 1 mm and 60 s in the model correspond to 1 1 5 km and 2 6 ma in the prototype ratios of the rate of advance to the rate of rise of the shelf break compared with the rate of advance and increase in relief of salt structures control how much of the deep autochthonous salt is squeezed ahead of the advancing shelf and the paths this salt takes to shallow structural levels the few three dimensional diapiric stocks which developed from many two dimensional mullions in the models spread stock canopies which advanced huge distances before some became tongue canopies by climbing over clastic sediments already aggraded in front of them the models emphasize the significance of ductile spreading of the clastic sediments now being discerned by backstripping

effect of basal friction on surface and volumetric strain in models of convergent settings measured by laser scanner abstract this paper uses measurements by a high accuracy laser scanner to investigate the role of basal friction on surface and volumetric strains in sandbox models simulating fold thrust belts and accretionary wedges we monitor progressive deformation wedge growth and strain distribution in three models with similar initial boundary conditions but with different basal frictions our analyses show that in addition to influencing the kinematics and geometry of model wedges basal friction also governs both the surface and volumetric strains of the wedge after 16 3 bulk shortening the volume decreased 5 0 5 9 5 0 5 and 12 5 0 5 in the models shortened above low intermediate and high friction decollements respectively applied to nature our model results suggest that more compaction and penetrative strain is expected in convergent settings with a high friction decollement than those shortened above a low friction decollement or a weak basal bed like the salt formation under parts of the zagros fold thrust belt this volume decrease probably reduces the porosity in the deformed lithologies

the ainsa fold and thrust oblique zone of the central pyrenees kinematics of a curved contractional system from paleomagnetic and structural data this work was funded by the project intectosal cgl2010 21968 c02 01 and by the grup de recerca de geodinamica i analisi de conques 2009sgr1198 secretaria d universitat i recerca del departament d economia i coneixement de la generalitat de catalunya josep poblet acknowledges financial support by research projects geociencias en iberia estudios integrados de topografia y evolucion 4d topo iberia csd2006 041 and desarrollo de fracturas y venas asociadas al plegamiento fraveple cgl2011 23628 funded by spanish ministries

formation of orogen perpendicular thrusts due to mechanical contrasts in the basal decollement in the central external sierras southern pyrenees spain two series of analogue models are used to explore the effect of ductile frictional contrasts of the basal decollement on the development of oblique and transverse structures during thin skinned shortening these models simulate the evolution of the central external sierras ces southern pyrenees spain which constitute the frontal emerging part of the southernmost pyrenean thrust the ces are characterised by the presence of n s to nw se anticlines perpendicular to the pyrenean structural trend and developed in the hanging wall of the thrust system they detach on unevenly distributed triassic materials evaporitic dolomitic interfingering the models simulated the effect of adjacent ductile versus frictional decollements during shortening model series a tests the thickness ratio between overburden and the ductile layer whereas model series b tests the width perpendicular to the shortening direction of frictional decollement model results confirms that deformation reaches further in areas detached on a ductile layer whereas above frictional decollement areas shortening is accommodated by additional uplift and penetrative strain this replicates the structural style of the ces higher structural relief of n s anticlines with regard to orogen parallel structures absence of a representative ductile decollement in the core plunging towards the hinterland and foreland side closure not thrusted by the south pyrenean thrust

the impact of analogue material properties on the geometry kinematics and dynamics of convergent sand wedges abstract simulation of geodynamic processes in sandbox experiments requires analogue materials with a deformation behaviour that reproduces the deformation mechanisms of typical crustal rocks we present data on the frictional strength of different sand types employing static and dynamic shear tests the sand types analysed are characterised by an elastic frictional plastic mechanical behaviour with a transient strain hardening and strain softening phase prior to transition to stable sliding this is in conflict with the standard assumption of an ideal cohesionless coulomb material with constant frictional properties the influence of the identified transient material properties on the kinematics growth mechanisms and internal deformation patterns of convergent sand wedges results in characteristic wedge segments which vary depending on material compaction between wedges with well defined segments i e frontal deformation zone frontal imbrication zone and internal accumulation zone with straight slopes and wedges with a continuous convex topographic profile for most materials only the frontal part of the wedge is critical during experimental runs taper and strength of the wedge segments can be shown to be controlled by the frictional properties of active faults wedge segmentation is controlled by a bulk strength increase toward the rear of the wedge due to fault rotation in mechanically less favourable orientations and plastic material hardening the limit between the frontal critical parts of a wedge and internal stable parts is largely controlled by a critical state of stress upon which either renewed failure or fault inactivation occurs on this basis we suggest that critical taper analysis of wedges must be restricted to specific kinematic segments comparison of the experimental results with the nankai accretionary wedge suggests that our interpretation also applies to natural convergent wedges moreover we provide constraints for the selection of adequate granular analogue materials to simulate typical crustal rocks in natural convergent wedges

experimental and field study of the effects of lithological contrasts on thrust related deformation 1 the influence of mechanical contrasts related to stratigraphy on thrust related deformation are investigated by sandbox modeling using combinations of granular materials possessing different mechanical properties and by structural analysis of a natural example from the spanish pyrenees the models used in this study consist of loose sand and glass microbeads in varied stratigraphic thicknesses and sequences and the natural example consists of a weakening upward sequence of sandstones and carbonates in both cases layers of different composition had a mechanical significance and accommodated shortening differently model sand and natural sandstone exhibited most shortening by thrust imbrication irrespective of stratigraphic position whereas glass microbeads and carbonates exhibited wider deformation zones and enhanced folding accompanied by displacement reduction along thrust surfaces cutting them transitions of structural style were guided by the stratigraphy rather than by a simple unidirectional propagation from a step up layer parallel shortening was accommodated by diverse mechanisms but did not vary significantly in layers which had different properties the magnitude with which mechanical contrasts were expressed in the models was influenced by the strength at the decollement zone the effect of mechanical contrast was more profound in models shortened above a low friction decollement

deformation patterns and structural vergence in brittle ductile thrust wedges an additional analogue modelling perspective abstract scaled physical models of brittle ductile thrust wedges investigated the causes leading to the development of the various structural styles observed in fold and thrust belts and accretionary prisms this study focused on some potential controlling factors such as 1 relative strength between the brittle overburden and the viscous decollement layer brittle ductile coupling 2 the effect of very low basal friction and 3 pre shortening rheological stratigraphy including decollement strength type 1 models had a single basal decollement whereas in type 2 models the decollement was embedded in brittle material simulating an upper roof sequence and a lower floor sequence other models investigated the effects produced by an horizon of mechanical weakness at the base of the viscous decollement type 1a and the role of decollement offset type 3 the experiments suggest the occurrence of a genetic relationship between the absolute values of shear stresses and the development of dominating hinterland or foreland verging thrust faults or dually verging thrusts by controlling the orientation of the 1 axis basal friction and decollement offset is found to effectively influence the deformation pattern and structural vergence and could explain the development of dominating backthrusts in cascadian type margins the decoupling of a frontal monocline via the upper decollement type 2 models produced passive roof duplex structures termed composite roof duplex when the frontal monocline coexists with outward fold propagation

recess drawn by the internal zone outer boundary and oblique structures in the paleomargin derived units subbetic domain central betics an analogue modelling approach abstract the subbetic domain comprising the south iberian paleomargin derived units is a fold and thrust belt developed over a ductile substrate showing a complex structural pattern in the central betics a main trend can be defined with respect to which frequent oblique structures are observed these oblique structures often subperpendicular to the main trend are not located along transfer zones but rather are present everywhere in the fold and thrust belt moreover they are coetaneous with those drawing the main trend this complex pattern is situated in front of a recess marked by the outer boundary of the internal zones the alboran domain which acted as backstop analogue models were designed to study the influence of such a recess on a ductile brittle multilayer one of the models in which the backstop recess is symmetric with respect to its direction of movement shows a high variation in the orientation of the resulting structures being not only qualitatively but also quantitatively similar to the studied natural case

three dimensional geometry and kinematics of experimental piggyback thrusting the three dimensional geometry and kinematics of piggyback stacks of imbricate thrust sheets are illustrated and discussed using a single model shortened in a squeeze box strike parallel geometric elements simulated include lateral ramps eyed sheath folds splays and thrust thrust interference fine details of these structures were exposed by eroding a shortened wedge of sand using a newly developed vacuum eroding technique a kinematic analysis of the model shows a stepwise increase in imbricate thrust spacing and or a decrease in rate of nucleation of imbricate thrusts in the direction of thrust transport despite the steady forward advance of a rear wall the piggyback wedge accreted episodically recording different strain domains in longitudinal cross sections strain partitioning in single layers by bed length balancing showed an increase in layer shortening with volume loss and a corresponding decrease in imbricate thrusting and ramp folding with depth

modelling the geometry of coulomb thrust wedges internal geometry and detachment of coulomb thrust wedges is examined in a combined gravity and pressure force field under various boundary conditions and coulomb parameters frontally buttressed sand wedges accreted with narrow tapers above soles with negligible friction in these models serial imbricates stepped up in conjugate sets which operated synchronously or serially with increases in sole friction model coulomb wedges accreted in piggyback style with enhanced taper but narrower spacing of imbricates in this mode flat topped box fold anticlines nucleated at the frontal tip of a sole thrust prior to the fore limb failing as a ramp the initial ramp thrusts subsequently rotated and steepened to acquire concave upwards listric geometry when cohesion was a significant component of strength and the sand grains interlocked thoroughly ramp climb during piggyback thrusting occurred through the generation of a stack of backthrusts the taper of cohesionless sand wedges which lack any length scale was consistent with the critical cohesionless coulomb wedge taper in contrast the taper of experimental cohesive sand wedges which are scale dependent was consistent with the theoretical cohesive coulomb narrow taper only when the cohesive length scale was lr sr rar 10 6 this was constrained by comparing geometry of cohesive sand wedges shortened at different body force per unit mass

the role of salt in fold and thrust belts davis d m and engelder t 1985 the role of salt in fold and thrust belts in n l carter and s uycda editors collision tectonics deformation of continental lithosphere tectonophysics 119 67 88 the style of deformation in thin skinned fold and thrust belts is critically dependent upon the resistance to sliding along the detachment between the mass of deforming sediments and the underlying rocks evaporites can provide an extremely weak horizon within which a basal detachment can form and along which only a relatively small shear traction can be supported fold and thrust belts that form atop a salt layer such as the appalachian plateau the franklin mountains in northwestern canada and the jura of the alps among others share several readily observable characteristics as predicted by a simple mechanical model for fold and thrust belts a detachment in salt permits a thrust belt to have an extremely narrow cross sectional taper in addition predicted orientations of the principal stress axes over a salt dtcollement are consistent with the commonly observed lack of a consistently dominant vergence direction of structures within the thrust belt other common attributes of salt basal thin skinned deformation include the presence of several widely but regularly spaced folds and abrupt changes in deformational style at the edge of the salt basin

experimental modelling of orogenic wedges a review abstract experimental modelling applied to the study of orogenic wedge dynamics has been a subject of fruitful research for more than 30 years although the technique dates back as far as the early xix th century on one hand several first order parameters controlling the structural evolution of mountain belts have been intensively investigated using the classic tectonic sandbox models the main parameters are the properties of the basal decollement the deforming material the backstop and fluxes kinematics and surface processes on the other hand the morphological evolution of a mountain relief subjected to changing tectonic or climatic forcing has been addressed using another kind of approach called geomorphic models nowadays the literature is extremely rich particularly for the sandbox technique so that it becomes difficult to have an exhaustive view of the effects of the above parameters on mountain evolution in this article we propose a detailed review of the main results obtained using both tectonic and geomorphic approaches our goal is to provide an almost complete state of the art in the experimental study of relief dynamics to guide present and future researchers in their understanding of mountain belt evolution

the effect of basement step topography on the geometry of the zagros fold and thrust belt sw iran an analog modeling approach systematic analog models are run to study the variation in deformation across basement steps in the zagros fold thrust belt our model results demonstrate that basement configuration topography influences the sedimentation thickness and hence the kinematics and geometric evolution of the fold and thrust belt the greater the difference in thickness between the adjacent cover units across a basement step the sharper and clearer will be the offset of the deformation front based on model results we conclude that in a fold thrust belt where basement step topography is covered by a layer of ductile salt acting as a decollement the effect of the salt decollement on the evolution of the belt is far greater than the effect of thickness variation of the cover units

topography as a major factor in the development of arcuate thrust belts insights from sandbox experiments abstract we have used sandbox experiments to investigate and to illustrate the effects of topography upon the development of arcuate thrust belts in experiments where a sand pack shortened and thickened in front of an advancing rectilinear piston the geometry of the developing thrust wedge was highly sensitive to variations in surface topography in the absence of erosion and sedimentation the surface slope tended to become uniform as predicted by the theory of critical taper under these conditions the wedge propagated by sequential accretion of new thrust slices in contrast where erosion or sedimentation caused the topographic profile to become irregular thrusts developed out of sequence for example erosion throughout a hinterland caused underlying thrusts to remain active and inhibited the development of new thrusts in the foreland where initial topography was irregular in plan view accreting thrusts tended to be arcuate they were convex towards the foreland around an initially high area concave towards the foreland around an initially low area initial plateaux tended to behave rigidly while arcuate thrust slices accreted to them thrust motions were radial with respect to each plateau within transfer zones to each side fault blocks rotated about vertical axes and thrust motions were oblique slip at late stages of deformation the surface slope of the thrust wedge tended towards a uniform value initial mountains of conical shape representing volcanoes also escaped deformation except at depth where they detached arcuate thrust slices accreted to front and back where a developing thrust wedge was subject to local incision accreting thrust slices dipped towards surrounding areas of high topography forming vs across valleys arcuate structural patterns are to be found around the three highest plateaux on earth tibet pamirs and altiplano and around the tromen volcanic ridge in the neuquen basin of northern patagonia we infer that these areas behaved in quasi rigid fashion protected as they were by their high topography

experimental insights on the geometry and kinematics of fold and thrust belts above weak viscous evaporitic decollement abstract this paper discusses the differences in mechanical properties and kinematics between fold and thrust belts detaching on evaporitic decollements and those detaching on stronger detachments physical experiments are described that model shortening of a thick brittle cover overlying a weak viscous decollement to gain a better understanding of these differences we tested the influence of 1 the decollement layer thickness and 2 the presence of a deformable backstop on the hinterland side and of a decollement pinch out on the foreland side because of the very low shear strength of the viscous decollement folds and thrusts did not propagate according to a piggy back sequence but by centripetal back and forth propagation additional shortening was accommodated by growth of all existing structures fold symmetry and thrust vergence varied between experiments models confined between two rigid vertical endwalls always deformed by symmetric folding and thrusting in models having a deformable backstop and a foreland decollement pinch out forethrusting initially dominated folds were asymmetric and fault blocks rotated in models having a thick decollement layer folds kept growing asymmetrically diapirism also depended on the initial decollement geometry diapirs formed only in models having a deformable backstop and were restricted to the hanging wall of a fault related fold finally the implications of such kinematics on the thermal history are discussed as well as the likelihood of hydrocarbon maturation and preservation

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

tracing tectonic deformation using the sedimentary record the study of sediments and sedimentary basins in terms of their tectonic environment requires a multidisciplinary approach and has increasingly drawn both techniques and objectives from fields outside sedimentology the application of different theoretical experimental and empirical resources provided by structural geology geochemistry geophysics scale modelling and field geology complement sedimentological methods with the combined aim of achieving a deeper understanding of the origins evolution and significance of sedimentary sequences in terms of their tectonic history studies presented in this volume range across a wide spectrum from the analysis of sedimentary sequence architecture at basin scale down to the chemical properties of individual grains and include studies from a range of tectonic settings the volume will be of interest to those involved with or contemplating studies involving the linkages between tectonics and sedimentation as well as a wider audience to whom the results of such studies may provide fresh insight

early orogenic deformation in the ionian zone of the hellenides effects of slab retreat and arching on syn orogenic stress evolution abstract in this work we report on early orogenic fracture patterns affecting a cretaceous to eocene sedimentary succession exposed in western greece these rocks belong to the cenozoic external hellenides which form the western portion of the aegean orocline the analysis of fracture type orientation and crosscutting relationships provides constraints on the stress and strain patterns during the early stages of orocline formation the fracture patterns in the study area includes early orogenic extensional fractures arranged into two mutually orthogonal sets these developed during progressive burial in the forebulge foredeep system ahead of the advancing compressive front tectonic solution seams at a high angle to bedding postdate these extensional structures solution seams are arranged in different sets oblique to each other and developed in the early stages of thrusting and folding extensional structures and solution seams are oblique to each other their orientation and crosscutting relationships provide evidence for clockwise vertical axis rotation of stress directions with time this is consistent with the progressive arching of the forebulge thrust belt system during progressive slab retreat

conical folds and apparent rotations in paleomagnetism a case study in the southern pyrenees abstract the so called apparent rotation was defined as the angular deviation between a local paleomagnetic direction after the standard bedding correction and their corresponding paleomagnetic reference j geophys res 85 1980 3659 in this paper we make a theoretical exploration on this concept and we conclude that depending on the number sequence orientation and magnitude of the deformation axes that have affected to the rock volume the apparent rotation may be the addition of a vertical axis rotation plus a spurious rotation the later is an error whose origin is the inappropriate application of the bedding correction during the restoration which does not fit the reverse sequence of deformations then apparent rot s l spurious rot vertical axis rot conical folds are complex geometries that cannot be restored by using the bedding correction however appearance of apparent and spurious rotations has not been studied even though the presence of this kind of folds is very common in fold and thrust belts in this paper we show a way to restore these structures and its associated paleomagnetic data by means of forward modelling on a stereographic projection the modelling has to be based on a good characterization of the geometry fold axis orientation and understanding of the kinematics of the fold general modelling has also allowed us to predict the apparent rotation in conical synclines its magnitude depends on the semiapical angle and on the degree of development of the fold the sense of the rotation clockwise or counter clockwise will depend on the sense of rotation the fold axis the western external sierras provide an excellent case study of apparent rotations due to the presence of a conical fold in the footwall ebro foreland basin of the south pyrenean sole thrust in addition a vertical axis clockwise rotation up to 47 32 in average has been detected in the hagingwall an apparent rotation up to 28 20 in average is observed in the footwall of the structure when a simple bedding correction is used this deviation does not fit with the expected ebro basin direction reference and is caused by the effect of the riglos conical syncline developed by the flexure of the foot wall ramp of the south pyrenean sole thrust the forward modelling carried out considering the geometry and kinematics non significant rotations in the autochthonous foot wall of this structure predicts very well the paleomagnetic observations in the field geographic coordinates with angular departures of only 5 in average the only application of the bedding correction would introduce errors spurious rotations up to 21 12 in average related to the conical geometry that would not allow the differentiation of these distinct structural units

geometry and evolution of fold thrust structures at the boundaries between frictional and ductile detachments abstract fold thrust belts formed above a ductile detachment typically contain detachment folds whereas those formed above frictional detachments contain fault related fold complexes such as imbricate thrust systems analog models using silica sand to represent sediments and silicone gel to represent salt were conducted to study the fold geometry fold fault relations and sequential development of structures formed in each setting and at the boundaries between the two settings the results showed a relatively thinner wedge above a ductile detachment so that the deformation front propagated farther forward than that above a frictional detachment the thrust front connects across the two settings with a significant change in position and a resulting change in orientation the geometry of the deformation front is strongly controlled by that of the detachment boundary so that an oblique detachment boundary results in an oblique thrust front in the transition zone modifications in the taper geometry also result from the presence of a frictional belt behind a ductile belt the width of the ductile detachment which limits the location of the deformation front and the lateral propagation of thrust faults between the two regimes the experimental models can be used to explain observed geometries in natural examples of fold thrust belts marked by transitions between frictional and ductile detachments

effect of basement structure and salt tectonics on deformation styles along strike an example from the kuqa fold thrust belt west china abstract the kuqa fold thrust belt kftb has a complex thrust system geometry and comprises basement involved thrusts decollement thrusts triangle zones strike slip faults transpressional faults and pop up structures these structures combined with the effects of paleogene salt tectonics and paleozoic basement uplift form a complex structural zone trending e w interpretation and comprehensive analysis of recent high quality seismic data field observations boreholes and gravity data covering the kftb has been performed to understand the characteristics and mechanisms of the deformation styles along strike regional sections fold thrust system maps of the surface and the sub salt layer salt and basement structure distribution maps have been created and a comprehensive analysis of thrust systems performed the results indicate that the thrust fold system in paleogene salt range can be divided into five segments from east to west the kela 3 keshen dabei bozi and awate segments in the easternmost and westernmost parts of the paleogene salt range strike slip faulting and basement involved thrusting are the dominant deformation styles as basement uplift and the limits of the cenozoic evaporite deposit are the main controls on deformation salt core detachment fold thrust systems coincide with areas of salt tectonics and pop up imbricate and duplex structures are associated with the main thrust faults in the sub salt layer distribution maps of thrust systems basement structures and salt tectonics show that paleozoic basement uplift controlled the paleozoic foreland basin morphology and the distribution of cenozoic salt in the kftb and thus had a strong influence on the segmented structural deformation and evolution of the fold thrust belt three types of transfer zone are identified based on the characteristics of the salt layer and basement uplift and the effects of these zones on the fault systems are evaluated basement uplift and the boundary of the salt deposit generated strike slip faults in the sub salt layer and supra salt layers at the basin boundary model a when changes in the basement occurred within the salt basin strike slip faults controlled the deformation styles in the sub salt layer and shear zone dominated in the supra salt layer model b a homogeneous basement and discontinues salt layer formed different accommodation zones in the sub and supra salt layers model c in the sub salt layer the thrusts form imbricate structures on the basal decollement whereas the supra salt layer shows overlapping discontinuous faults and folds with kinds of salt tectonics and has greater structural variation than the sub salt layer

significant rotations related to cover substratum decoupling example of the dome de barrot southwestern alps france the barrot area presents an important contrast of deformation between a foliated faulted and non rotated permian substratum and a folded and strongly rotated meso cenozoic sedimentary cover the permian substratum and the sedimentary cover are separated by a decollement level of triassic gypsum while numerous studies have been done on the dome de barrot i e the permian substratum we focused our work on the deformed meso cenozoic sedimentary cover around the dome de barrot where we measured and analyzed both the magnetic susceptibility fabrics and the paleomagnetic directions our results highlight an arcuate pattern of the directions of shortening trajectories revealed by type ii iii fabrics of anisotropy of magnetic susceptibility which predates the folding and a later syn or post folding anticlockwise rotation of large amplitude 64 14 for the sedimentary cover the arcuate pattern of the directions of shortening and the different rotations between the permian substratum and the sedimentary cover can be partly explained after restoring the paleogeographic location of the sedimentary cover before the oligocene alpine compression event we tend to interpret the remaining 30 anticlockwise rotation as a result of the high efficiency of the triassic gypsum decollement surface a nearby regional left lateral shear zone rdfz and a possible near field gravitational sliding near the later exhumed dome de barrot

centrifuge modelling of deformation of a multi layered sequence over a ductile substrate 1 style and 4d geometry of active cover folds during layer parallel shortening centrifuge analogue modelling illustrates the progressive development of active folds in multilayers upon a ductile substrate during layer parallel shortening models simulate folding of a mechanically stratified sedimentary sequence upon migmatitic gneisses in a large hot orogen or upon a thick basal evaporite shale sequence in deeper levels of fold belts the absence of a weak low viscosity and low density layer at the interface promotes infolding of the cover sequence and ductile substrate whereas a planar upper surface to the basal ductile substrate is preserved when it is present whilst fold style wavelength and deformation of the interface with the ductile substrate differ depending on whether a low viscosity and low density layer is present at the base of the cover sequence there is no marked systematic curvature of fold axes as seen in previous sandbox models for fault bend or fault propagation folding during bulk shortening bulk shortening of a layered sequence with relatively thick individual layers above a ductile substrate promotes a regular and upright train of buckle folds whereas thinner layers promote a more irregular distribution of buckle folds with variable vergence style and amplitude buckle folds above a ductile substrate progressively develop during bulk shortening from open and upright to angular and tight and may further develop into cuspate structures above relatively weak horizons relatively thick weak horizons within the layered sequence during bulk shortening interrupt regular fold patterns up structural section and allow out of phase folds to develop above and below the weak horizon

deformation transfer in viscous detachments comparison of sandbox models to the south pyrenean triangle zone deformation transfer in viscous detachments comparison of sandbox models to the south pyrenean triangle zone

geometries of syntectonic sediments associated with single layer detachment folds abstract three kinematic models have been proposed to account for the geometry and kinematics of detachment folds involving a homogeneous competent layer detached over a ductile unit model 1 variable limb dip constant limb length model 2 constant limb dip variable limb length and model 3 variable limb dip variable limb length because the same fold shape can be generated by any of the above mechanisms fold kinematics are best determined by the geometries of syntectonic sediments in single layer detachment folds growth strata patterns are controlled by axial surface activity limb rotation limb lengthening fold uplift rates sedimentation rates and deformation mechanisms of the syntectonic sediments asymmetric kink folds have been modelled and compared with natural examples from the southern spanish pyrenees under conditions of high sedimentation rates model 1 folds produce characteristic fanning growth stratal wedges that initially onlap and then progressively overlap the detachment anticline whereas at low sedimentation rates anticlines with fanning growth wedges on both limbs are formed model 2 folds under conditions of high syntectonic sedimentation rates form anticlines with growth strata largely parallel to the pre growth units and thinned over the fold crest in contrast at low sedimentation rates model 2 folds show offlapping growth strata onto both limbs model 3 growth folds under conditions of high syntectonic sedimentation rates form anticlines with intermediate features from model 1 and model 2 at low sedimentation rates anticlines are formed with offlapping growth structures

structural evolution of a fold and thrust belt generated by multiple decollements analogue models and natural examples from the northern apennines italy this study analyses the role played by the mechanical proprieties of the rocks involved in a thrust system focusing on the problem of multiple decollements and of related compressional structures integration of geophysical seismic reflection profiles and geological data and scaled sandbox models are used to study the deformation style of two areas of the northern apennines italy the po plain and the umbria marche apennines both areas are characterised by a complex stratigraphy consisting of decollements located at different depths that influence the geometry and kinematics of the thrust system the main characteristic of the models presented here is the presence of two decollement horizons situated at the base and in an intermediate level of the models during deformation of the models these two decollement horizons generate two sets of structures with different geometrical characteristics and significance through the joint analysis of geophysical and geological data and model results wavelengths of the compressional structures analysed show that the structural style of the two analysed areas is almost similar moreover model results prove that the final configuration of the thrust system follows the general rules of evolution of a wedge deformed above a weak decollement and is largely governed by the larger deep seated structures

effects of cohesion on the structural and mechanical evolution of fold and thrust belts and contractional wedges discrete element simulations particle based numerical simulations of cohesive contractional wedges can yield important perspectives on the formation and evolution of fold and thrust belts offering particular insights into the mechanical evolution of the systems results of several discrete element method simulations are presented here demonstrating the stress and strain evolution of systems with different initial cohesive strengths particle assemblages consolidated under gravity and bonded to impart cohesion are pushed from the left at a constant velocity above a weak unbonded decollement surface internal thrusting causes horizontal shortening and vertical thickening forming wedge geometries the mean wedge taper is similar for all simulations consistent with their similar residual and basal sliding friction values in all examples presented here both forethrusts and back thrusts occur but forethrusts accommodate most of the shortening fault spacing and offset increase with increasing cohesion significant tectonic volume strain also occurs with the greatest incremental volume strain occurring just outboard of the deformation front this diffuse shortening serves to strengthen the unfaulted domain in front of the deformed wedge preconditioning these materials for brittle dilative failure the reach of this volumetric strain and extent of decollement slip increase with cohesive strength defining the extent of stress transmission stress paths for elements tracked through the simulations demonstrate systematic variations in shear stress in response to episodes of both decollement slip and thrust fault activity providing a direct explanation for stress fluctuations during convergence

paleomagnetically derived folding rates southern pyrenees spain well dated syntectonic unconformities with the spanish pyrenees allow characterization of sedimentation and deformation within an orogenic foreland the spanish pyrenees are composed of a south vergent thrust belt and foreland basin in which folds developed both parallel and perpendicular to tectonic transport unconformity geometries and magnetostratigraphic data from synorogenic strata provide a precise temporal framework for the quantitative analysis of the mediano anticline the largest of the transverse folds folding began in the early eocene and ended by 42 ma at which time an anticline 20 km long and 5 km in wavelength had been produced angular and progressive unconformities within syntectonic sedimentary units preserve the history of fold development fold growth resulted from west ward salt movement driven by prograding sediments and was characterized by 2 3 m y intervals of slow continuous limb tilting 2 2 4 2 m y preserved as progressive unconformities within syntectonic strata because the emplacement of the cotiella montsec thrust sheet was episodic intervals of slow fold growth were punctuated by intervals lasting

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

impact of an interbedded viscous decollement on the structural and kinematic coupling in fold and thrust belts insights from analogue modeling abstract fold and thrust belts ftbs can be segmented both across and along strike because of various factors including tectonic and stratigraphic inheritance in this study we investigated along across strike structural interactions in a ftb propagating toward a foreland which displays contrasted lithological sequences a set of analogue models was performed in a compressional box where a single viscous level of varying width was interbedded within a frictional series the tectonic interaction between the viscous and the frictional provinces was tested both along and across strike results indicate that a frictional province influences the along strike tectonic evolution of an adjacent viscous province this influence decreases when the width of the viscous province increases the frictional provinces control the taper structural style obliquity of the structures trend and kinematics of the shallow deformation front of the viscous province results evidence how far a frictional province can impact the deformation of an adjacent viscous province for frictional viscous wedges it appears that the critical taper theory which is generally applied in 2 d should be likely considered in terms of 3 d moreover the kinematics of the deep deformation front shows mutual influences between the adjacent viscous and frictional provinces experimental results are compared to natural examples in the kuqa basin southern tian shan china and the salt range pakistan and give an insight to a better understanding of the dynamics of fold and thrust belts bearing a viscous decollement such as salt

integration of palaeomagnetic data basement cover relationships and theoretical calculations to characterize the obliquity of the altomira loranca structures central spain this work was funded by the project kinesal cgl2010 21968 c02 02 of the spanish ministry of economy and competitiveness and a phd igme grant for the first author it is a contribution of the geomodels research institute and the grup de recerca de geodinamica i analisi de conques 2014sgr467 supported by the agencia de gestio d ajuts universitaris i de recerca and the secretaria d universitats i recerca del departament d economia i coneixement de la generalitat de catalunya

rotation velocity of a thrust a paleomagnetic study in the external sierras southern pyrenees abstract an accurate calibration of chronologic and geologic data biostratigraphic and magnetostratigraphic with gpts has been performed for the middle and upper eocene syntectonic deposits in the surrounding areas of the pico del aguila anticline south pyrenean external sierras this calibration shows a variable sedimentation rate that changes from 4 8 cm ka at the bottom to 34 cm ka at the top with a maximum of 58 6 cm ka in the upper part of the studied stratigraphic section and gives a fine and continuous chronologic frame to understand the rotational kinematics of the infrajacent thrust system at the same time a detailed paleomagnetic study has been carried out 14 sites and a total of 157 thermally demagnetised samples to know the amount of rotation in the area taking advantage the tape recording effect of the syntectonic materials these samples display a chrm between 250 and 400 c both polarities that agree very well with the sequence of magnetostratigraphic zones and consistency with the magnetic reference due to the decreasing value of the magnetic declination from 46 to 3 of the primary components checked by fold and reversal test the calibration has been useful to assign an absolute age to every rotation value from 40 32 to 37 05 ma a time versus rotation curve does not show significant differences of rotation between the flanks of the pico del aguila anticline less than 8 thus the clockwise rotations detected in the study area result from the kinematics of the imbricate basal thrust system which is also responsible for the development of detachment folds e g pico del aguila anticline in a time against rotation graph the simplest fit for the overall rotation values is given by a linear segment rotation velocity of 10 ma however the best fit is given by a segment of a parabolic curve this pattern implies that there were changes of the rotation velocities between 21 ma and 5 3 ma that in this segment of the external sierras were caused by an acceleration of the rotational movement between 9 ma2 and 5 5 ma2 the thrust sheet shows maximum values of at least 40 of clockwise rotation

modeling of thrust fronts above ductile and frictional detachments application to structures in the salt range and potwar plateau pakistan series of scaled sandbox models are used to simulate the development of thin skinned simultaneous shortening above adjacent ductile and frictional substrates these models simulate the evolution of the potwar plateau and salt range in pakistan where pale

differentiation in impact melt sheets as a mechanism to produce evolved magmas on mars abstract asteroid bombardment contributed to extensive melting and resurfacing of ancient 3 5 ga mars evidence from the largest impact structures on earth and the moon suggests that vertically thick impact melt sheets experience chemical differentiation recently observed materials in gale crater are enriched in alkalis up to 14 wt na2o k2o and silica up to 67 wt sio2 with low mgo

transverse fold evolution in the external sierra southern pyrenees spain fault slip data are used to reconstruct varying tectonic regimes associated with transverse fold development along the eastern and southern margins of the jaca basin southern pyrenees spain the spanish pyrenean foreland consists of thrust sheets and leading edge decollement folds which developed within piggyback basins guara formation limestones on the margins of the jaca basin were deposited synchronously with deformation and are exposed in the external sierra within the transverse folds principal shortening axes determined from p and t dihedra plots of fault slip data show a shift from steep shortening in stratigraphically older beds to nne ssw horizontal shortening in younger beds older strata are characterized by extensional faults interpreted to result from halotectonic salt tectonics deformation whereas younger strata are characterized by contraction and strike slip faults interpreted to result from thrust sheet emplacement the interpretation of the timing for the shortening axes in the younger strata is supported by the observation that these axes are parallel to shortening axes determined from finite strain analysis calcite twins and regional thrusting directions determined from fault related folds and slickenlines this study shows that fault population analysis in syntectonic strata provides an opportunity to constrain kinematic evolution during orogeny

episodic accretion and strain partitioning in a model sand wedge we model led thrust wedge accretion and deformation partitioning in a passively layered sand detached and shortened above a smooth rigid decollement the thrust wedge accretes in piggyback style during forward advance of a rear wall the passively layered sand accommodates the shortening penetratively by kinking ramp folding and by imbrication in single layers the style of compression changes with time and or stratigraphic position within the sand prism initial penetrative layer shortening above a slipped zone of decollement is succeeded by formation of monoclinal or conjugate shear bands at temporary terminations of decollement the shear bands subsequently narrow down and lock as thrust ramps the model sand wedge accrets episodically rather than steadily episodicity is controlled by the stick slip mode of decollement propagation and by volume loss and compaction of the wedge material in response to convergence this results in formation of a wedge with a convex upwards cross sectional topography

quantitative study on experimentally observed poroelastic behavior of berea sandstone in two phase fluid system coupled two phase fluid flow and poroelastic deformation of berea sandstone is studied through laboratory experiment and numerical simulation in the experiment compressed air was infiltrated from the bottom of a water saturated cylindrical berea sandstone sample under hydrostatic external stress condition both axial and circumferential strains at half the height of the sample showed sudden extension and monotonic and gradual extension afterward numerical simulation based on thermodynamically consistent constitutive equations was conducted in order to quantitatively analyze the experimental results in a simulation assuming isotropy of material properties the volumetric discharge rate of water at the outlet and one of the axial circumferential and volumetric strains at half the height of the sample were reproduced well by each parameter set while the other two strains were not when introducing transverse isotropy all the experimental data were reproduced well in addition the effect of saturation dependency of bishop s effective stress coefficient on the deformation behavior of porous media was discussed and it was found that strains both axial and circumferential are sensitive to the coefficient

seismic models of detachment and faulted detachment folds abstract detachment folds constitute a common structural style in fold thrust belts and typically form in stratigraphic packages defined by relatively competent cover units underlain by ductile units pstm images through these structures contain artifacts resulting from lateral velocity variations between the cover sediments and the core units steep dips and complex fold fault relationships making them difficult to interpret understanding these artifacts and pitfalls in pstm seismic models enables improved interpretations of pstm data in natural structures we conducted 2d seismic modeling for detachment folds models to study the effect of these complexities on pstm data seismic pull ups and push downs of the strata underneath the salt or shale substrate are related to the relative velocities of the cover sediments and the core units a specific example of an appalachian plateau structure demonstrates how the relative velocities can influence the seismic image progressive evolution of the structures to disharmonic and lift off folds results in enhanced pull ups and poorer imaging of steep limb segments for faulted detachment folds faulted limbs and footwall zones are poorly imaged and marked by wide low reflectivity bands making fault interpretation difficult

transfer of deformation in back arc basins with a laterally variable rheology constraints from analogue modelling of the balkanides western black sea inversion the balance between extension and contraction in back arc basins is very sensitive to a number of parameters related to on going subduction and collision processes this leads to complex back arc geometries where a lateral transition between crustal blocks with contrasting rheologies is often recorded one good example is the back arc region of the balkanides pontides orogens where lateral variations in rheologies are observed between the balkanides moesian block and the pontides western black sea basin the latter opened during cretaceous eocene and has been inverted together with the former starting during late middle eocene the inversion generated contrasting geometries along the orogenic strike with a narrow zone of high deformation in the balkanides moesia region wide areas of thrusting with low offsets in the pontides western black sea basin and a transitional zone characterized by highly curved geometries this overall type of inversion is investigated here by the means of analogue modelling testing the role of inherited crustal geometries during inversion our modelling suggests that the contrasting architecture of inverted structures observed in the balkanides pontides domain are the result of pre existing crustal stretching geometries of various blocks inherited from the cretaceous eocene extension the stretched and weak back arc basins can transfer contraction deformation at large distances explaining structures derived by observational studies the collisional deformation recorded in the pontides was transmitted at large distances that are in the range of the contraction structures observed in the centre and northern part of the western black sea in the light of analogue modelling results we argue that the western black sea was a rheologically weaker domain when compared with the adjacent western onshore at the beginning of the inversion in contrast with previous results derived from numerical modelling studies that argued for a strong west black sea domain at the beginning of inversion

role of lateral thickness variations on the development of oblique structures at the western end of the south pyrenean central unit abstract the montsec unit is one of the most important detached south verging nappes within the south pyrenean central unit spcu southern pyrenees a n s cross section of its western sector based on seismic reflection profiles shows a hangingwall ramp geometry in mesozoic strata overlain by a syntectonic series of lower eocene sediments with growth geometry the geometry of growth strata constrains the age of its movement between the paleocene and the middle eocene the geometry of the western oblique ramp of the south pyrenean central unit is defined by a series of n s folds in some cases associated with underlying west verging thrusts as indicated by seismic reflection profiles and field data in this paper we propose that the geometry of the thrust wedge of mesozoic units progressively thinning from east to west strongly contributed to constrain the location and geometry of the western termination of the montsec thrust the hypothesis proposed is checked by a series of experimental wedges developed in a sandpack with lateral and three dimensional thickness variations oblique structures form as thrusting progresses at the tip of the sand wedge

experimental modeling of role of gravity and lateral shortening in zagros mountain belt dynamically scaled analogs of the geologic structures of the zagros mountain belt are used to argue that different parts of the zagros mountains of iran record different combinations of the effects of a gravity driven overturn and a southwest northeast lateral shortening superimposed on the zagros overturn partially scaled material models have been used to simulate the zagros geodynamics which involve layer parallel compression of a 6 to 7 km thick phanerozoic carbonate cover containing a pattern of preshortening diapirs the folds in the zagros form rapidly 1 5 mm yr in a 20 to 30 km wide zone reactive some of the preshortening diapirs and generate new synshortening listric diapirs a third set of postshortening diapirs rises from the hormuz decollement behind the fold thrust front model buckle folds superimposed on diapirs or pillows tend to avoid and curve around preshortening diapirs which flatten in the synclines model profiles show that lateral shortening induces residual salt at depth to flow toward and rise through the anticlinal cores as synshortening or postshortening diapirs i suggest that any salt pillows in currently diapir free zones of the zagros fold thrust belt may surface as diapirs through the anticlines in the future in the absence of well data seismic and field observations i have used only three map pattern criteria to recognize the timing of diapirs these are locally obscured by extrusive salt sheets preshortening diapirs are generally small and elongate parallel to fold axes and are restricted to synclines synshortening diapirs are elongate perpendicular to the fold axes and are restricted to anticlines postshortening diapirs can be the same size as synshortening diapirs or larger and can be circular they are more common in the anticlines

3d evolution of fold and thrust belts formed by oblique convergence abstract this paper presents the results of a series of scaled analogue models designed to simulate thrust belt development formed by orthogonal and oblique convergence the models were constructed to produce doubly vergent orogenic wedges with a pro wedge and a retro wedge separated by an uplifted orogenic core models were constructed from homogeneous layered sandpacks in a 3 m 1 3 m deformation rig the progressive evolution of the models was recorded using digital photography and the photographs were animated for analysis the experiments investigated convergence obliquities from orthogonal 90 to as low as 15 obliquity orthogonal models produced long linear critically tapered pro wedge fold and thrust belts parallel to the convergence margin together with a narrow uplifted core and a steep retro wedge thrust system the taper angle of the pro wedge was typically 11 12 whereas the retro wedge maintained a steeper taper of 38 42 models where the convergence vector was oblique at angles of 60 and 45 to the margin produced doubly vergent thrust wedges with thrust faults trending parallel to the margin there was little evidence of linked penetrative strike slip faulting but en echelon riedel like shear systems developed in the 45 oblique model subordinate oblique slip motion was observed on some thrust faults in contrast for 30 and 15 oblique convergence models strong deformation partitioning developed with steeply sloping pro wedges that did not have critical tapers through going linked strike slip faulting was developed that cut the uplifted axial zones of these models analysis of the models by animation of the digital photographs shows how the thrust systems initiated and propagated in particular it is clear that at any one time several thrusts were moving simultaneously serial cross sections through the moderately oblique convergence models 60 45 are almost indistinguishable from the orthogonal model cross sections the results of orthogonal convergence experiments compare well to the map patterns of faults and folds in the salt range pakistan 60 and 45 oblique convergence models compare well to the zagros where some strain partitioning on strike slip faults occurs the highly oblique models show very strong strain partitioning with penetrative margin parallel strike slip faulting similar to that found in ne venezuela

effect of spatial distribution of hormuz salt on deformation style in the zagros fold and thrust belt an analogue modelling approach scaled analogue models of thin skinned simultaneous shortening above adjacent viscous and frictional decollements simulate the effect of hormuz salt on the shortening in the zagros fold and thrust belt the models consisted of sand layers that partly overlay a viscous layer of silicone and were shortened from one end spatial distribution of the viscous decollement varied along strike and dip as occurs in part of the zagros fold and thrust belt in this belt phanerozoic sedimentary cover was shortened partly above the hormuz salt lying on the precambrian crystalline basement behaving as a basal viscous decollement model results display how the nature of the decollement affects the evolution of an orogenic belt using model results we explain the development of deflection zones and discuss strain partitioning formation of different topographic wedges and differential sedimentation along the zagros fold and thrust belt model results suggest the formation of a gentle taper consisting of both foreward and backward thrusts above a viscous decollement and a relatively steeper taper consisting only of forward vergent imbricates above a frictional decollement however in our models the steepest wedge with the highest topography formed where the viscous substrate had a limited extent with a transitional boundary pinch out perpendicular to the shortening direction shortening of this boundary led to development of frontal ramps associated with significant uplift of the area behind the deformation front

the transition from thick skinned to thin skinned tectonics in the basque cantabrian pyrenees the burgalesa platform and surroundings interpretation of seismic data in the margins of the burgalesa platform in the basque cantabrian pyrenees has allowed proposition of a new structural model that combines different modes of deformation during oblique tectonic inversion conditioned by the distribution of triassic salts deformation was decoupled by the presence of the salt horizon between basement involved thrusts inverting formerly triassic and late jurassic early cretaceous extensional faults and a detached thrust system involving the upper triassic to neogene sedimentary package structural units experiencing different styles of deformation are not only stacked vertically above and below the salt but most importantly they change from one to the other along strike across the transversal edges of the triassic salts the burgalesa platform detached thrust system was confined between the basement involved structures of the cantabrian mountains westward and the nw tip of the iberian basement involved structures san pedro southward this together with the obliquity between the pyrenean shortening direction and the strike of the previous extensional faults mostly during the late stages of deformation determined the strike slip reactivation of the basement involved inverted faults and the lateral extrusion of the burgalesa platform detached mesozoic successions above the salt towards the se to form a prominent thrust salient oblique to the main pyrenean trend the proposed model combines thick skinned with thin skinned structural styles during oblique tectonic inversion and is consistent with the surface data including the fracture system the available subsurface data and the mechanical stratigraphy

reverse modelling of detachment folds application to the pico del aguila anticline in the south central pyrenees spain abstract a simple method to estimate fold amplification and thrust movement rates for detachment folds is documented and illustrated by its application to a symmetrical detachment fold in the southern pyrenees spain the technique provides a complete record of the kinematic evolution of detachment folds and is based on the application of equations for detachment folds involving limb rotation the method uses the stratal pattern of the syntectonic sediments and assumes that these growth strata were deposited horizontally that the folds involve a homogeneous competent unit detached over a ductile horizon and that the folds can be represented by chevronkink bands the procedure is applicable to any detachment fold with associated growth strata that display wedge geometries progressive unconformities indicating limb rotation through time this method can be used for both detachment folds formed with constant limb length or variable limb length and it can also accommodate undecompacted or decompacted growth strata

evolution of experimental thrust wedges accreted from along strike tapered silicone floored multilayers the possible effect of pre deformational along strike sedimentary tapers on the structural architecture of thrust wedges accreted above viscous materials has been commonly underestimated or neglected we illustrate results of an experimental programme specifically designed to study the impact of this parameter on thrust wedge evolution using sandbox analogue modelling two series of experiments were performed the first series was designed to investigate the sensitivity of wedge growth to the along strike sedimentary taper variability the second was designed to investigate the sensitivity of a growing along strike tapered wedge to the convergence rate our experimental results indicate that even gentle pre deformational along strike thickness variations in foredeep clastic sequences overlying viscous materials such as evaporites or overpressured shales can produce dramatic changes in the first order structural architecture and kinematic evolution of accreting thrust wedges

experimental insights on the geometry and kinematics of fold and thrust belts above weak viscous evaporitic decollement a discussion experimental insights on the geometry and kinematics of fold and thrust belts above weak viscous evaporitic decollement a discussion