the eastern termination of the zagros fold and thrust belt iran structures evolution and relationships between salt plugs folding and faulting 1 the zagros mountains result from the ongoing collision between the arabian and central iran plates the main features of the eastern zagros are 1 numerous emerged or buried salt diapirs made up of late precambrian hormuz salt and 2 the irregular along strike shape of the collision related detachment folds with frequent bending to understand this layout four geological cross sections have been constructed from the persian gulf foreland basin to the inner part of the zagros fold and thrust belt shortening in the deformed parts of the sections is less than 10 and is mainly accommodated by detachment folding we show that late cenozoic folding occurred in a region that was already punctuated by salt domes and diapirs in fact almost continuous halokinesis developed since the earlier paleozoic i e just short time after the deposition of the hormuz salt and continued up to the present these preexisting salt structures and their relevant local thickening strongly influenced both the localization and the direction of folds

control of synorogenic sedimentation on back and out of sequence thrusting insights from analog modeling of an orogenic front outer carpathians southern poland 1 scaled sandbox models based on field and seismic data were used to simulate miocene evolution of the carpathian orogenic front the experiments investigated the influence of synorogenic deposition on the geometry and kinematics of growing tectonic structures the deposition introduced at the foreland of an active fold thrust wedge resting on top of a weak ductile detachment horizon generally results in transferring the deformation to the rear part of the model depending on the rate and across strike extent of synorogenic sedimentation and on the moment it starts a single major back thrust above the rear edge of the ductile layer can form or out of sequence foreland verging thrusts can be initiated alternatively older thrust faults can be reactivated at the rear part of the model thrust wedge leading to destruction of the earlier formed structures our experiments explain the origin and evolution of three different structural geometries known from the carpathian orogenic front involving major back thrusts related to triangle zones and out of sequence breaching forethrusts that substantially reorganized deformation patterns in a growing thrust wedge the development of these geometries was controlled by massive synorogenic sedimentation in the foreland from the modeling and natural examples we infer a number of typical structural situations that can occur at an orogenic front underlain by a weak ductile horizon depending on parameters controlling synorogenic sedimentation and tectonic push exerted by an approaching thrust wedge

cyclical behavior of thrust wedges insights from high basal friction sandbox experiments scaled sandbox experiments with high basal friction simulating the growth of accretionary wedges display cycles alternating between frontal imbricate thrusting and underthrusting of long undeformed sheets by contrast low basal friction experiments with otherwise similar and constant initial conditions produce a classic frontal imbricate fan through repeated failure along frontal thrusts the cyclical behavior observed in high basal friction experiments is expressed by three quantities 1 the average spacing between frontal thrusts 2 the advance and retreat of the deformation front and 3 the frontal slope alpha of the actively deforming wedge as a long sheet is underthrust the front is steepened through slumping until the maximum critical angle is reached then frontal thrusting resumes and the accretion of imbricate slices builds the wedge forward thereby lowering the taper to the minimum critical angle at shallow tapers a long unit is underthrust and subsequently uplifts shortens and steepens the overlying wedge through backthrust deformation thus completing the cycle underthrusting of long units offers a simple mechanism for underplating overlying units it also provides a possible explanation for temporally and spatially varying wedge geometries in nature when basal frictions attain 80 90 of the internal friction

a review of brittle compressional wedge models abstract fold and thrust belts and accretionary wedges form by compression of sedimentary sequences and basement rocks into forward and backward thrusts folds nappes and duplexes for over a century models have been used to investigate the essential characteristics of such brittle wedges here i review model studies of brittle thrust wedges in orthogonal compression focussing on critical taper theory analogue and numerical techniques for modelling brittle behaviour and the most commonly investigated variations in wedge model studies those in basal dip basal strength internal strength and surface processes many model results can be placed in the context of critical taper theory which provides analytical solutions for wedge taper angle and slip line orientations for a homogeneous material on the verge of failure throughout dynamic forward models have confirmed critical taper predictions of decreasing surface dip for increasing basal dip wider wedges with steeper forward thrusts and shallower backward thrusts for decreasing basal strength narrower wedges and enhanced exhumation for surface erosion and decreasing surface dip for increasing internal strength but analogue and numerical models have been able to take these results a step further by investigating the evolution of non critical thrust wedges and the effects of non homogeneous materials with decollement layers and strain weakening shear zones these results have highlighted the strong impact of heterogeneous materials on the internal structures of thrust wedges and raise the question whether the complexity of structures that are observed in many natural fold and thrust belts requires that lithological layering inherited faults or a wide range of rheologies need to be included in forward models of brittle thrust wedges

active deformation within the zagros mountains deduced from gps measurements we present and interpret the results of global positioning system gps measurements at 35 stations in and beside the zagros mountain belt sw iran for three campaigns ending march 1998 december 1999 and june 2001 preliminary motion estimates show clearly the change in character along the strike of the belt stations to the se move at 13 22 3 mm a 1 towards n 7 5 e with respect to eurasia most of the shortening indicated by the gps velocities seems to occur in the se zagros along two major seismic zones and along the zagros front to the nw stations move oblique to the trend of the belt towards n 12 8 w at 14 19 3 mm a 1 most of the shortening in the nw zagros seems to occur along the mountain front fault with its major earthquakes as well as along the zagros front the change in direction and magnitude of the velocity vectors across the north south trending kazerun and karebas faults involves extension of up to 4 mm a 1 along the strike of the zagros belt

epicenter distribution and magnitude of earthquakes in fold thrust belts insights from sandbox models scaled analogue models are used to illustratethe eect of basal friction and erosion on fault activity andhence on epicentre distribution and magnitude of earth quakes in the sedimentary cover of active fold thrust belts model results suggest that in fold thrust belts shortenedabove low friction ductile decollements rock salt or over pressured mudstone low to moderate magnitude earth quakes mw 5 3 5 6 distributed over a wide area occuralong several long lived thrust faults conversely in areasshortened above high friction decollements large magnitudeearthquakes mw 6 6 6 8 distributed over a narrowzone are likely to occur along few short lived thrust ramps calculated magnitude of earthquakes from models and theirdistribution are in agreement with recorded earthquake pat tern from the zagros mountain belt which is partially short ened above a ductile decollement of hormuz salt formation model results also showed that erosion reactivates older in active thrusts and promotes formation of out of sequencethrusts

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

passive roof thrusting and forelandward fold propagation in scaled brittle ductile physical models of thrust wedges a set of scaled analogue models was performed to investigate the role of a decollement layer in the structural style of fold and thrust belts silicone putty sgm 36 has been employed to represent the ductile decollement while frictional material quartz sand has been used to simulate the brittle behavior of roof and floor sequences situated above and below the decollement respectively in order to explore a wide combination of strength profiles models have been deformed under five distinct rates of compression 0 15 0 3 0 45 0 6 and 1 5 cm h 1 employing four different thicknesses for the silicone layer 0 1 0 2 0 4 and 0 8 cm experimental results indicate that roof sequences exhibit two distinct styles of deformation 1 passive roof duplex prd geometry e g banks and warburton 1986 and 2 outward propagation of folding ofp along the decollement e g davis and engelder 1985 in prd geometry the roof sequence remains relatively stationary being underthrust by a wedge shaped floor duplex while in ofp displacement along the floor thrusts is transferred horizontally along the decollement layer experiments suggest the occurrence of a genetic relationship between shear stresses at the base of the roof sequence b and within the ductile layer d and the development of prd or ofp geometry for a given strain rate the deformation pattern of roof sequences depends upon the b d ratio as well as the absolute b and d values the transition field between ofp and prd styles has been approximated by curvilinear regression of transition style experimental data points with a minimum value of d varying between about 112 and 160 pa to enter the prd field syntectonic sedimentation in the molasse basin is found to inhibit development of folding into the foreland but to promote prd style experiments simulate many of the principal characteristics of fold and thrust belts developed above a basal evaporite decollement as well as the development of passive roof duplexes at mountain fronts shear stress values inferred for many fold and thrust belts correlate well the deformation fields predicted by the present experimental study allowing to propose a simple model describing the mechanical behavior of natural roof sequences underlain by a decollement layer

recent large fold nucleation in the upper crust insight from gravity magnetic magnetotelluric and seismicity data sierra de los filabres sierra de las estancias internal zones betic cordillera abstract rheological heterogeneities in the upper crust have a close relationship with the fold position where rigid bodies could constitute initial perturbations that allow the nucleation of folds consequently establish the position and geometry of anomalous rocks located in the upper crust by geophysical studies help to understand the folded structure observed on surface new geological observations in the field along with gravity magnetic magnetotelluric and seismicity data reveal the subsurface structure in the sierra de los filabres sierra de las estancias folded region part of the alpine belt in southern spain the geometry of the upper crust is determined by geological field data 2d gravity models 2d magnetic models and 2d mt resistivity model while seismicity evidences the location of the deep active structures these results allow us to propose that a basic rock body at 4 to 9 km depth has determined the nucleation and development of the sierra de los filabres kilometric antiform n vergent large late folds are subjected to a variable present day stress field earthquake focal mechanisms suggest the presence in depth of a regional nw se compressive stress field however most of the seismogenetic structures do not extend up to the surface where nw se and wnw ese outcropping active normal faults are observed thus indicating a ne sw extension in the upper crust simultaneous to orthogonal nw se compression related to reverse faults and minor folds developed in the eastern almanzora corridor and in the nearby huercal overa basin the recent and active tectonic studies of cordilleras hinterland subjected to late folding greatly benefits from the integration of surface observations together with geophysical data

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

double evaporitic decollements influence of pinch out overlapping in experimental thrust wedges abstract this article focuses on how deformation and displacements are transferred between two decollements located at different stratigraphic levels by means of analogue modeling using brittle viscous sand silicone systems we present results from ten analogue models in which we varied key parameters such as the amount of horizontal offset or overlap between the pinch outs of the upper and lower decollements the total amount of shortening and the planform geometry of the upper decollement results indicate that i structures root onto the basal and upper decollement defining an inner and an outer domain and ii the offset overlap of the decollements controls the geometry of the transition zone located between the two decollements the propagation of deformation into the foreland both in space and time and the deformation style and kinematics in the different domains of the model when the pinch out of the upper decollement is at an angle with the backstop oblique structures form and the geometry and propagation mode of the structures change progressively along strike we compare our experimental results with other silicone sand analogue models and with the natural examples of the southern pyrenees where upper triassic and eocene oligocene syn tectonic evaporites acted as basal and upper decollements respectively

folding style controlled by intermediate decollement thickness change in the lurestan region nw of the zagros fold and thrust belt using analogue models the basal and intermediate decollements play an important role in structural style of fold and thrust belts the decollement units or different mechanical stratigraphy within the rock units are not uniform throughout the zftb and show a strong spatial variation the lurestan region with varied thickness of the intermediate decollement in its northern and southern parts is one of the most important parts of the zagros fold and thrust belt regarding its hydrocarbon exploration extraction projects thickness variation of the intermediate decollement in different parts of the lurestan region allows us to address its role on folding style based on scaled analogue modeling this study outlines the impact of thickness and facies variation of sedimentary rocks in the northern and southern parts of this region on folding style two models simulated the mechanical stratigraphy and its consequent different folding styles of the northern and southern parts of the region in the models only thickness of the intermediate decollement thick and thin for the northern and southern parts of the lurestan region was varied detached minor folds above the intermediate decollement were created in response to the presence of the thicker intermediate decollement northern part of the study area which consequently deformed complexly and disharmonically folded in contrast to polyharmonic folding style in the section compared to polyharmonic folding style in the southern part where thin intermediate decollement exists the model results documented that thickness variation of intermediate decollement levels could explain complex and different folding styles in natural examples which must be taken into account for hydrocarbon exploration throughout these areas

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

book reviewthe techniques of modern structural geology vol 1 strain analysis j g ramsay and m i huber academic press london 1983 xiii 307 pp us 55 00 28 00 hardcover

experiments on shortening of a 4 layer model of the continental lithosphere davy ph and cobbold p r 1991 experiments on shortening of a 4layer model of the continental lithosphere in p r cobbold editor experimental and numerical modelling of continental deformation tecronophysics 188 l 25 we present an experimental method for modelhng lithospheric deformation the method is based on a simplified profile of lithosphere rheology where only four layers are considered brittle crust ductile crust brittle mantle and ductile mantle the strengths of the four layers calculated from laboratory determined flow laws depend strongly on geothenns and slightly on strain rates and deformation regimes the rheological profiles of the lithosphere have been recreated in experimental models built with analog materials sand silicone putty and golden syrup which flow under their own weight during lithospheric shortening the style of deformation depends on the relative strengths of the four layers especially those in the mantle of special importance is the existence or non existence of a brittle mantle the initial stages of compression often produce flexures or buckles without local isostatic compensation buckling exerts a strong control on the localisation of thrust faults in later stages the thrusts tend to form at the inflexion points of buckles the style of crustal thickening depends on the relative thicknesses and resistances of the lithospheric layers in 2 layer lithospheric models without resistant mantle shortening was concentrated upon a small number of thrusts widely spaced in 3 layer models shortening was concentrated into a large number of reverse faults more closely spaced and more steeply dipping than before in clayer models a single thrust formed in the brittle mantle motion on this thrust dragged the crustal layers down forming an asymmetric crustal root with steep imbricate slices

structural significance of an evaporite formation with lateral stratigraphic heterogeneities southeastern pyrenean basin ne spain we run a series of analogue models to study the effect of stratigraphic heterogeneities of an evaporite formation on thin skinned deformation of the southeastern pyrenean basin spb ne spain thi

how to build an extensional basin in a contractional setting numerical and physical modelling applied to the mejerda basin at the front of the eastern tell of tunisia abstract in tunisia africa eurasia convergence resulted in the tell fold and thrust belt ftb part of the tell rif or maghrebides associated to the south to the atlas intra continental belt the mejerda rift basin is developed over the compressional boundary between the tell and the atlas the main objective of this study is to identify the mechanism responsible for such a basin development the abundance of triassic salt structures in the northern atlas compared to the tell suggests a friction change along the basal decollement formed by the salt level this frictional contrast is expected to produce a heterogeneous deformational response and complex structures on this basis numerical and analogue modelling were used to investigate the impact of a friction change on the deformation style the kinematic approach of the limit analysis theory was applied here via the software optum g2 the onset of faulting in all numerical tests reveals extensional faults appear at the friction boundary beyond the onset of faulting sandbox experiments show extensional features such as collapsing blocks and extensional faults overall the adopted numerical and physical approaches showed evidences of extension in particular the experiment using sandpaper and silicon putty pdms for the decollement transition shows viscous deformation mimicking diapiric movement these observations of numerical and physical model behaviors highlight that compression can produce an extensional basin at the top of a thrust wedge as expression of a strong basal friction change hence the mejerda basin is interpreted as a wedge top basin it developed during the growth of the tell and atlas ftbs the same configuration likely exists in other mountain belts the case of the molasse basin between the jura and the western alps is advocated

geodetic measurement of tectonic deformation in the southern alps and provence france 1947 1994 abstract active deformation at the boundary between the eurasia and africa plates varies in style the belt between the alpine mountain range and the mediterranean sea for example differs markedly in its western and eastern parts in the western part around southeast france the mountains are higher but the seismicity lower than in the eastern part around northern italy and greece yet the inter plate convergence rate of 6 mm yr varies by less than 15 between these two areas to better understand the behaviour of this complex plate boundary we use geodesy to map the spatial distribution of the deformation in this paper we focus on southeast france a tectonic crossroads between three different domains alps ligurian sea and massif central which exhibits a moderate level of seismicity here the geodetic measurements imply low rates of horizontal deformation by combining historical triangulation measurements mostly from 1947 to 1983 with global positioning system gps surveys in 1993 and 1994 we estimate the rate of angular shear in triangular subnetworks covering the study area the estimated strain rates in thirteen of nineteen triangles are smaller than their 1 standard deviation uncertainties of about 0 1 microradian yr this value bounds the rate of deformation for a 100 km wide zone in provence between marseilles to the south and the ventoux massif to the north the geodetic estimates place an upper bound of 1 to 2 mm yr on the slip rates of two seismically active structures the durance fault and the nimes fault assuming a fault zone 20 km wide in each case we also find strain rates as high as 0 20 0 07 microradian yr in three subnetworks near the epicentre of the magnitude 5 3 haute ubaye earthquake in 1959 in a region which includes the higher summits this may be interpreted either as pure shear with compression oriented ne sw across this region or right lateral simple shear along nnw sse trending faults given that this earthquake is the only one of its magnitude recorded in the study area during the time interval spanned by the geodetic measurements we infer that most of the geodetically observed deformation occurs aseismically on the whole the geodetic results suggest that the rate of north south shortening across the 100 km wide study area is not more than 1 or 2 mm yr in agreement with kinematic models based on other types of geophysical data since this deformation represents only a small part of the convergence rate of 6 mm yr predicted by the nuvel 1 model for the entire boundary between the african and eurasian plates the remaining deformation must be accommodated elsewhere this study illustrates how a careful analysis of historical geodetic data can measure the rate of tectonic deformation even where it is low and thus meaningfully bound geophysical models

mechanical decoupling and basal duplex formation observed in sandbox experiments with application to the western mediterranean ridge accretionary complex sandbox experiments of accretionary wedges were performed incorporating a thin weak layer of micro glass beads the impact of heterogeneous sedimentary input on wedge mechanics evolution and mass transfer was investigated we report the first experimentally documented growth of basal duplexes these occurred for high basal friction conditions with restricted output of the lower section the upper and lower sections were completely decoupled due to the intervening layer of glass beads with frontal accretion occurring in the upper section simultaneously with basal duplex formation and underplating of subsequent generations of duplexes imerse multichannel seismic reflection data from the western mediterranean ridge wmr image tertiary clastics beneath a thick section of messinian evaporites the base of the evaporites is identified as the primary decollement for deformation in the frontal part of the accretionary complex constriction of the channel of subducting tertiary sediments as well as internal deformation observed as arcward dipping reflectors argue for basal underplating and or two different active decollements we propose an evolution of the wmr in accordance with the sandbox experimental results a weak mid level detachment base of evaporites combined with a strong basal detachment produce mechanical decoupling and basal accretion of toeward verging duplexes

insights from scaled analogue modelling into the seismotectonics of the iranian region abstract we show how analogue modelling provides insights into complex crustal block kinematics and the seismotectonics of active areas undergoing contraction such as the iranian region the seismotectonic model deriving from this analysis is consistent with partitioning of the n directed arabia indentation into a composite system of collision oblique and collision parallel seismogenetic belts these features include 1 two main conjugate transpressive belts the dextral nw se trending zagros belt and the ne sw trending sinistral elburz aran torud eat belt and 2 a modest lateral escape of central iran towards the lut block along the nayband belt this cinematic model fits the seismic activity and the current fault pattern of the region also the velocity field scaled from the model to nature shows a good similarity with previous numerical modelling as well as with deformation rates along the first order seismogenetic belts determined by plate tectonic models and gps data

coulomb theory applied to accretionary and nonaccretionary wedges possible causes for tectonic erosion and or frontal accretion based on observations from both modem convergent margins and sandbox modeling we examine the possible conditions favoring frontal accretion and or frontal and basal tectonic erosion mean characteristic parameters t t and are used to discuss the mechanical stability of 28 transects across the frontal part of convergent margins where the coulomb theory is applicable natural observations reveal that typical accretionary wedges are characterized by low tapers with smooth surface slope and subducting plate low convergence rates and thick trench sediment while nonaccretionary wedges display large tapers with irregular surface slopes and rough subducting plate high convergence rates and almost no trench fill sandbox experiments were performed to illustrate the effects of seamounts ridges in the subduction zone on the deformation of an accretionary wedge these experiments show that a wedge of sand is first trapped and pushed in front of the seamount which acts as a moving bulldozer this is followed by a tunnelling effect of the subducting seamount through the frontal wedge material which results in considerable sand reworking at an advanced subduction stage the d6collement jumps back from a high level in the wedge to its former basal position we conclude that a high trench sedimentation rate relative to the convergence rate leads to frontal accretion in contrast several conditions may favor tectonic erosion of the upper plate first oceanic features such as grabens seamounts or ridges may trap upper plate material during their subduction process second destabilization of the upper plate material by internal fluid overpressuring causing hydrofracturing is probably another important mechanism

intermediate decollement activation in response to the basal friction variation and its effect on folding style in the zagros fold thrust belt an analogue modeling approach although the role of various basal and intermediate decollement levels on structural style is well documented individually in many folded terrains the interaction between basal and intermediate de

thermal mechanical modeling of salt based mountain belts with pre existing basement faults application to the zagros fold and thrust belt southwest iran 1 two dimensional thermal mechanical models of thick skinned salt based fold and thrust belts such as the zagros sw iran are used to address 1 the degree of deformation and decoupling between cover and basement rocks due to the presence of a weak salt detachment 2 the reactivation potential of pre existing basement normal faults due to brittle or ductile behavior of the lower crust as related to cold or hot geothermal gradients and 3 variations in deformation style and strain distribution the geometry and kinematics of the orogenic wedge and the activity of pre existing basement faults are strongly influenced by the geothermal gradient defined by the moho temperature mt and basement rheology we infer that the mt plays a major role in how the lower and upper crust transfer deformation toward the foreland in relatively hot geotherm models mt 600 c at 36 km depth the lowermost basement deforms in a ductile fashion while the uppermost basement underlying the sedimentary cover deforms by folding thrusting and displacements along pre existing basement faults in these models cover units above the salt detachment occur within a less deformed wide plateau in the hinterland in relatively cold geotherm models mt 400 c at 36 km depth deformation is mainly restricted to basement imbricate thrusts that form within the orogenic hinterland detachment folding thrusting and gravity gliding occur within cover sediments above uplifted basement blocks gravity gliding contributes to a larger amount of shortening in the cover compared to the basement

sensitivity analysis of numerical scaled models of fold and thrust belts to granular material cohesion variation and comparison with analog experiments scaled analog and numerical brittle viscous shortening models are employed to evaluate how fold thrust structures evolve with changes in the cohesion of brittle materials a rather poorly constrained physical parameter at this scale of experiment the shortening models are characterized by various styles of shear zones and features resembling pop up structures the kinematics geometry and number of these structures are controlled by the viscous detachment layers in the models the finite deformation of the model wedges is fundamentally different in model sets with one or two viscous layers we demonstrate that the structural evolution of the numerical models is very sensitive to small changes in cohesion value this is especially pronounced in the experiments that incorporate two weak viscous layers the overall deformation of the numerical models is most similar to analog models when cohesion values are 70 80 pa

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

3d effects of strain vs velocity weakening on deformation patterns in accretionary wedges abstract shear zones are weaker than surrounding rocks whether weakening depends on accumulated strain or strain rate is debated we used a three dimensional numerical code with a visco plastic brittle rheology to investigate the influence of strain and strain rate weakening often referred to as velocity weakening on the evolution of thin skinned fold and thrust belts two model setups are used i a uniform setup to recognize the effects of each weakening mode on the structural evolution and dynamics of fold and thrust belts and ii a dual setup with two adjacent domains of decollement strength to investigate the structural response of laterally varying systems strain weakening and velocity weakening lead to remarkably different structural patterns in particular strain weakening favours out of sequence shear zones whilst some amount of finite plastic strain has to be achieved before the structural development initiates weakening in contrast velocity weakening starts with the onset of high strain rate bands and does not favour out of sequence deformation we also tested separately the influences of shortening velocity cover sequence thickness and weakening style and amount on the structural evolution of the dual systems the shortening velocity has a minor effect in strain weakened models velocity weakening and a thinner cover sequence enhance the occurrence of strike slip shear zones we conclude that the weakening mode strongly influences the fault patterns and the dynamics of thrust wedges inversely natural fault patterns are keys to discriminate weakening processes

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

coccolith sr ca as a new indicator of coccolithophorid calcification and growth rate 1 polyspecific coccolith separates from core top sediments in the eastern equatorial pacific show variations of 15 in sr ca ratios across the equatorial upwelling zone with sr ca highest at the equator and decreasing off axis these variations cannot be due to changes in the sr ca of seawater which varies by less than 2 in the surface ocean variations in sr ca of coccolith sediments are similar to variations in primary productivity and alkenone estimated coccolithophorid growth rates in overlying surface waters and to caco3 rain rates measured in sediment traps because of these relationships and because calcification rate exerts a strong control on sr ca in abiogenic calcites we suggest that the observed sr ca variations in coccoliths may be strongly controlled by coccolithophorid growth and calcification rates although temperature may also influence coccolith sr ca to a lesser degree changes in dissolution intensity and coccolith assemblages appear to exert a minor influence if any on coccolith sr ca in these sediment core tops if further work confirms relationships between coccolith sr ca and coccolithophorid productivity sr ca records of past changes in coccolithophorid productivity may be useful in reconstructing past variations in the rain ratio of organic to carbonate carbon an important control on deep ocean ph and partitioning of co2 between the atmosphere and ocean in addition coccolith sr ca might provide an independent record of past changes in coccolithophorid growth rates which in combination with data on the carbon isotopic fractionation in coccolithophorid organic matter may permit more reliable calculations of past dissolved co2 in the surface ocean

sandbox model simulation of forearc evolution and noncritical wedges convergent plate boundaries exhibit a wide range of behaviors ranging from sediment accretion and underplating to large scale erosion of the forearc we have used sandbox modeling to simulate the growth of thin skinned contractional wedges over a strong backstop at an accretionary margin the backstop in our model causes the growth of two distinct wedges with quite different growth histories analogous to the accretionary wedge and the inner deformation belt retrowedge found in at least some forearcs after starting with an initially steep slope the surface flattens as the accretionary wedge grows by frontal accretion until the wedge attains and maintains a minimum possible critical taper the retrowedge driven by uplift of the outer arc high increases its surface slope as it grows until a kinematic steady state is attained it exhibits a stable taper with slope larger than the minimum critical taper but never larger than the theoretical maximum critical taper when a basal decollement is present above the backstop in models in which the retrowedge has not developed a decollement it has a taper with a slope at the angle of repose when a basal decollement is present above the backstop the main body of the retrowedge acts as a bulldozer or a backstop pushing the sediments in front of it which then form an additional wedge with a small minimum critical taper a broad outer arc high stands above the toe of the backstop where maximum principal stresses rotate to meet the stress conditions in the two contractional belts on either side of it as these belts grow in opposite directions the accretionary wedge accretes large quantities of sediment at its front but the retrowedge does not because the retrowedge can exhibit a non critical stable taper in the absence of rapid erosion or accretion it is misleading to assume that active thin skinned wedges are necessarily at maximum or minimum critical taper

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

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

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

brittle to ductile transition due to large strains along the white rock thrust wind river mountains wyoming abstract the deformed foreland of the rocky mountain cordilleras is characterized by major reverse faults that bring precambrian basement rocks to the surface the white rock thrust in the wind river mountains of wyoming is one such fault that developed at fairly shallow levels in the crust detailed study of grain size variations and textures within the fault zone provide a framework for discussion of the mechanics of movement along the fault textural criteria are suggested for distinguishing between dominantly brittle and dominantly ductile deformation a transition from brittle fracturing to ductile deformation is seen with increasing strain and resultant decrease in grain size along the fault zone diffusional creep in the final stages of deformation leads to strain softening and may allow large strains to take place along narrow zones at low deviatoric stresses this may be one way of obtaining large displacements along major faults at shallow levels in the crust

kinematic variation within the fars arc eastern zagros and the development of fold and thrust belt curvature we analyze deformation of the fars arc in the eastern zagros iran including earthquake slip vectors gps velocities paleomagnetism data and fold orientations to understand how this fold and thrust belt works and so better understand the generic issue of fold and thrust belt curvature the fars arc is curved convex southward gps derived rotation rates are 0 5 myr 1 rotation is clockwise west of 53 e and counterclockwise to the east these rotation senses are opposite to previous predictions of passive bookshelf models for strike slip faults during north south convergence west of 53 e average gps vectors thrust earthquake slip vectors strain axes derived from gps data and orthogonal directions to fold trends are all aligned toward 218 east of this meridian the average gps vector is toward 208 but the averages of the other data sets are distinctly different all toward 190 we propose that fault blocks in eastern fars each 20 40 km long rotate predominantly counterclockwise whereas in western fars the regional clockwise rotation takes place mainly on the array of active right lateral faults in this area thus localized block faulting and rotations accumulate to produce the overall strain and regional curvature active folds of different orientations in eastern fars intersect to produce domal interference patterns without involving separate deformation phases indicating that fold interference patterns should not be interpreted in terms of changing stress orientations unless there is clear evidence fars arc curvature is best explained by deformation being restricted at tectonic boundaries at its eastern and western margins with significant gravitational spreading

quantifying simultaneous discrete and distributed deformation most natural deformation involves simultaneous discrete deformation e g faults and distributed deformation e g penetrative strain in order to properly understand the bulk kinematics of a given deformation the discrete and distributed components must be evaluated simultaneously the displacement diagram method has previously been utilized to quantify strain accommodated by faults or other discrete surfaces the same method is applicable to distributed deformation such as ductilely deformed conglomerates which are typically evaluated by finite strain analysis by mathematically combining the gradients in the displacement fields of both the discrete and distributed components of deformation the bulk deformation can be quantified we apply this method to several examples that contain both distributed and discrete components and characterize the bulk displacement field and finite strain for these deformed systems

basement involved reactivation in foreland fold and thrust belts the alpine carpathian junction austria the late eocene early miocene alpine carpathian fold and thrust belt ftb lies in the transition between the eastern alps and the western carpathians se of the bohemian crystalline massif our study shows the involvement of crystalline basement from the former european jurassic continental margin in two distinct events a first extensional event coeval with eggerian karpatian c 28 16 ma thin skinned thrusting reactivated the rift basement fault array and resulted from the large degree of lower plate bending promoted by high lateral gradients of lithospheric strength and slab pull forces slab break off during the final stages of collision around karpatian times c 17 16 ma promoted large wavelength uplift and an excessive topographic load this load was reduced by broadening the orogenic wedge through the reactivation of the lower plate deep detachment beneath and ahead of the thin skinned thrust front with the accompanying positive inversion of the basement fault array and ultimately by the collapse of the hinterland summits enhanced by transtensional faulting although this work specifically deals with the involvement of the basement in the alpine carpathian junction the main conclusions are of general interest to the understanding of orogenic systems

backarc extension and collision an experimental approach to the tectonics of asia summary the deformation of the eastern asian lithosphere during the first part of the india asia collision was dominated by subduction related extension interacting with far effects of the collision in order to investigate the role of large scale extension in collision tectonics we performed analogue experiments of indentation with a model of lithosphere subjected to extension we used a three layer rheological model of continental lithosphere resting upon an asthenosphere of low viscosity and strained along its southern boundary by a rigid indenter progressing northward the lithosphere model was scaled to be gravitationally unstable and to spread under its own weight so that extension occurred in the whole model the eastern boundary was free or weakly confined and always allowed eastward spreading of the model we studied the pattern of deformation for different boundary conditions the experimental pattern of deformation includes a thickened zone in front of the indenter a major northeast trending left lateral shear zone starting from the northwest corner of the indenter antithetic north south right lateral shear zones more or less developed to the east of the indenter and a purely extensional domain in the southeastern part of the model in this domain graben opening is driven by gravitational spreading whereas it is driven by gravitational spreading and indentation in the northeastern part where grabens opened along strike slip faults the results are compared with the oligomiocene deformation pattern of asia consecutive to the collision of india our experiments bring a physical basis to models which favour distributed deformation within a slowly extruded wide region extending from the baikal rift to the okhotsk sea and to southeast asia and indonesia in this large domain the opening of backarc basins japan sea okinawa trough south china sea and continental grabens north china grabens have been associated with approximately north south trending right lateral strike slip faults which accommodated the northward penetration of india into eurasia

crustal stress map of iran insight from seismic and geodetic computations we used the focal mechanisms of crustal earthquakes depth 40 km in the period 1909 2012 and the available gps velocities derived from the data collected between 1999 to 2011 to estimate the magnitude and directions of maximum principal stress and strain rates in iran the pearson product moment correlation was used to find the correlation between the stress field obtained from the focal mechanism stress inversion and that obtained using the seismic and geodetic strain rates our assumption is that stresses in a continuum are produced by tectonic forces and the consequent deformation on the crustal scale therefore the direction of the stress and strain or strain rate are ideally to be the same our results show a strong correlation between the directions of the principal components of stress and strain rate obtained using the different data methods using weighted average analysis we present a new stress map for iran

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

strain variation in thrust sheets across the sevier fold and thrust belt idaho utah wyoming implications for section restoration and wedge taper evolution abstract although strain in fold and thrust belts is typically inhomogeneous on the largest scale strain within thrust sheets shows regular patterns the strain which is a quantitative measure of the deformation of any thrust sheet is independent of the translation of the sheet the internal deformation can be represented by a deformation profile the change in shape during thrusting of a fault perpendicular line which can then be used to unstrain the sheet during restoration in cross section balancing deformation profiles in well studied thrust sheets show regular geometric patterns and compatibility constraints can be used to minimize the data needed to define the profiles in other sheets from the geometry of deformation profiles and direct field observations the most important component of internal deformation of thrust sheets in many fold and thrust belts is early layer parallel shortening lps this can be removed in a straightforward manner during restoration and significantly affects the geometry i e taper of the restored section original basin wedge taper may have important implications for the mechanical evolution of fold and thrust belts thus changes in original basin taper resulting from strain removal may affect significantly the way in which we interpret the evolution of a fold and thrust belt in an area

elasticity profile of an unconsolidated granular medium inferred from guided waves toward acoustic monitoring of analogue models abstract the monitoring of materials elastic parameters during geological analogue experiments would highly improve the interpretation of involved processes it would more particularly help the implementation of joint analytical or numerical analyses we propose laser doppler vibrometry as a probing tool for the systematic characterisation of analogue models we therefore develop an experimental set up to record small scale seismic lines at the surface of an unconsolidated granular medium in laboratory conditions pressure wave first arrival times and surface wave dispersion are then inverted for a one dimensional pressure and shear wave velocity structure inferred profiles appear to match previously thoroughly estimated properties of the probed medium thus validating our approach

response of the tectonically erosive south peruvian forearc to subduction of the nazca ridge analysis of three dimensional analogue experiments 1 the collision zone of the obliquely subducting nazca ridge and the erosive peruvian forearc is characterized by enhanced tectonic erosion normal faulting forearc uplift and a minor indentation we apply two three dimensional sandbox experiments monitored by an optical particle imaging velocimetry system to decipher the spatial and temporal evolution of forearc deformation during oblique convergence the rigid model ridge causes a wave of uplift followed by subsidence to shift along the forearc by varying the strength of the analogue material we demonstrate that the forearc response to ridge subduction in particular the amount and rate of uplift and wedge indentation is controlled by the mechanical strength of the forearc the model using the high strength material yields results more compatible with the geological record of the peruvian forearc first the modeled amount of uplift scales to 1 2 km in nature which agrees with 1 0 km of uplift recorded by marine terraces second the calibrated model uplift rate of 0 9 km myr is similar to the natural rate of 0 7 km myr third the development of normal faults above the model ridge is in accordance with the style of faulting above the nazca ridge finally oversteepening of the uplifted wedge and local slope failure as observed in the experiment has also been identified off southern peru a comparison between the erosive peruvian and accretive margins emphasizes that the style of ridge induced deformation depends on the forearc strength and crustal structure which in turn are controlled by the long term evolution of the margin s mass transfer regime

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

quality and hydrochemistry of groundwater used for drinking in lahore pakistan analysis of source and distributed groundwater more than 7 million people of lahore city pakistan use groundwater for drinking and other household purposes the quality of drinking water from source and distribution system was investigated and the hydrochemical characteristics and formation mechanisms of groundwater were analyzed statistical summary showed higher mean values of major descriptors in distributed groundwater samples compared with source groundwater samples a total of 50 drinking water samples 16 from source and 34 from distribution system were examined for physical chemical and bacteriological parameters including ph turbidity electrical conductivity total dissolved solids total hardness total alkalinity ca2 mg2 na k so42 cl no3 f arsenic as chromium cr iron fe copper cu zinc zn cadmium cd and lead pb varying concentrations of trace amounts of cr in 8 samples fe 18 samples cu 18 samples zn 13 samples and pb 14 samples were detected however the detected trace elements were within the who permissible limits for drinking water except pb where 5 out of 14 samples showed higher than who limit value pb 0 01 mg l 19 out of 50 samples 6 from source and 13 from distributed samples showed high values of alkalinity 250 mg l all of 16 groundwater samples from source exceeded 0 01 mg l who limit value for arsenic as on the basis of bacteriological analysis 42 samples 12 from source 55 from distribution did not meet who guidelines and were unsafe for drinking especially distributed groundwater samples mg hco3 contents predominated the groundwater type followed by ca hco3 carbonate weathering was revealed to be the dominant process controlling dissolution precipitation processes phreeqc modeling showed that the aqueous phase was undersaturated with respect to significant gypsum halite and mirabilite while equilibrium to saturated with respect to aragonite calcite and dolomite was observed principal component analysis pca revealed that the concentration of as was strongly associated with that of so42 reductive dissolution and ph dependent desorption are the plausible processes responsible for the observed high as concentrations in lahore

digital photogrammetry as a tool in analogue modelling applications to volcano instability abstract three techniques of digital photogrammetry have been applied successfully to laboratory analogue models to study surface displacements caused by various volcano deformation types firstly side perspective videos are used to differentiate profile displacements between cryptodome intrusion models and models deforming by ductile inner core viscous flow both models show similar morphologic features including a bulged flank and an asymmetric upper graben however differences in displacement trajectories of the bulge crest reflect upward intrusion push contrasting with essentially downward displacement vectors of weak core models the other two techniques use vertical views correlated automatically either as time sequence monoscopic views or as coeval stereoscopic pairs this exploits to a maximum the method s potential by imaging surface displacements over the whole model successive monoscopic photograms because they suffer only moderate numerical processing for topographic effect removal can detect very small displacements occurring early in deformation processes as illustrated by analysis of intrusion models the monoscopic method allows prediction of fault locations and main displacement locations it can also anticipate the principal strain directions and separate different deformation stages on the other hand the stereo photogrammetry technique although more complicated provides topography and volume changes as well as pictures of surface displacements in three dimensions results are presented for the spreading of volcano models on a ductile substratum and viscous cored cones we have found digital photogrammetry to be a useful tool for analogue modelling because it provides quantitative data on surface displacements including movement invisible to the eye as well as topographic changes it is a good method for investigating and comparing different deformation mechanisms it is especially useful for interpretation of displacement patterns obtained from monitoring of natural active volcanoes in fact results of the methods used in the laboratory can be directly compared with field data from geodetic or photogrammetric surveys as at mount st helens in 1980

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

present day crustal deformation and plate kinematics in the middle east constrained by gps measurements in iran and northern oman summary a network of 27 gps sites was implemented in iran and northern oman to measure displacements in this part of the alpine himalayan mountain belt we present and interpret the results of two surveys performed in 1999 september and 2001 october gps sites in oman show northward motion of the arabian plate relative to eurasia slower than the nuvel 1a estimates e g 22 2m m yr 1 at n8 5 e instead of 30 5 mm yr 1 at n6 e at bahrain longitude we define a gps arabia eurasia euler vector of 27 9 0 5 n 19 5 1 4 e 0 41 0 1 myr 1 the arabia eurasia convergence is accommodated differently in eastern and western iran east of 58 e most of the shortening is accommodated by the makran subduction zone 19 5 2m m yr 1 and less by the kopet dag 6 5 2m m yr 1 west of 58 e the deformation is distributed in separate fold and thrust belts at the longitude of tehran the zagros and the alborz mountain ranges accommodate 6 5 2m m yr 1 and 8 2m m yr 1 respectively the right lateral displacement along the main recent fault in the northern zagros is about 3 2m m yr 1 smaller than what was generally expected by contrast large rightlateral displacement takes place in northwestern iran up to 8 mm yr 1 the central iranian block is characterized by coherent plate motion internal deformation 2m m yr 1 sites east of 61 e show very low displacements relative to eurasia the kinematic contrast between eastern and western iran is accommodated by strike slip motions along the lut block to the south the transition zone between zagros and makran is under transpression with right lateral displacements of 11 2m m yr 1

displacement fields and finite strains in a sandbox model simulating a fold thrust belt this thesis uses geodetic satellite data to measure present day crustal deformation in the zagros fold thrust belt sw iran geodetic type measurements are also used in down scaled models that simulate the surface deformations seen in convergent settings like the zagros fold thrust belt global positioning system gps measurements of three surveys between 1998 and 2001 indicate 9 3 mm yr and 5 3 mm yr shortening across the se and nw zagros respectively gps results show that in addition to the different rates and directions of shortening on either side of the ns trending kazerun fault local along belt extension occurs to the east differential sar interferograms of ers1 2 images between 1992 and 1999 detect 8 4 mm yr uplift rate across a newly recognized fault in sw qeshm island this can be attributed to a steep imbricate thrust that may still represent the local zagros deformation front the salt diapirs in the zagros rise from a source layer that acts as a low frictional decollement that decouples the deformation of the cover sediments from their basement in the eastern zagros whereas the cover to the west deforms above a high friction decollement physical models were prepared to simulate cover deformation in the zagros by shortening a sand pack above adjacent high and low frictional decollements represented by a ductile layer the strain distributions differed above the two types of decollements it was more heterogeneous above the salt where local extension in the shortening direction was dominant a separate work also investigated systematically the role of basal friction on cover deformation in convergent settings accurate height measurements of the model surface by laser scanner indicated a deformation front more distal than usual particularly in the low basal frictional models the volume reduction in our shortened sand models correlated directly with their basal friction

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

influence of basement faults on the development of salt structures in the danish basin scaled centrifuged models based on interpreted seismic profiles were used to simulate the salt structures in the danish basin the models consisted of a viscous layer simulating rock salt overlain by layers of cohesive sand that mimic brittle failure in natural overburdens model results support the hypothesis that basement faults trigger the growth of many salt diapirs in the danish basin in plan view model diapirs are localized as buoyant walls along faults in the overburden which collapsed due to basement fault movement with further burial single diapirs rose from these buoyant walls some of the diapirs surfaced through the faulted overburden a few were trapped beneath the competent cretaceous units and others were starved due to lack of supply from below in section model diapirs were asymmetric and were rooted on the tip of the faults or located on the rotated footwall blocks model diapirs not located over faults were triggered by differential loading and collapsing of overburden layers due to basement block rotation models show that the presence of fewer salt structures in the northern than the southern part of the basin is due to differential subsidence and flow of buoyant material from north to south where they rise diapirically in the model the pressure due to loading by overburden layers changed from 1 3 102 pa in the south to 2 3 102 pa in the northern part of the basin in general the model results illustrate that basement faults influence diapirs by accumulating buoyant material in half grabens and introducing a slope and steps at the base of the buoyant layer weakening its overburden and causing differential loading and compaction the spreading overhangs of salt diapirs beneath the cretaceous chalk in the danish basin would seal any potential pre cretaceous reservoir rocks

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

role of the kazerun fault zone in the formation and deformation of the zagros fold thrust belt iran 1 the kazerun fault is a n s trending fault zone which obliquely truncates the nw se trending zagros fold thrust belt this active fault zone is an ancient structural lineament which has controlled the structure sedimentation and subsidence of the central part of the zagros since the early cambrian and has had an influence on the formation of the hydrocarbon system of the belt the kazerun fault limited the distribution of the cambrian hormuz salt the major decollement horizon that separates the precambrian basement from the thick sedimentary cover to the west its later reactivation with other n s trending fault zones e g the izeh fault zone during the cretaceous resulted in major sedimentary thickness and facies variations along the belt this study presents a new interpretation for the evolution of the kazerun fault zone based on field evidence and a review of various published and unpublished data it is argued that at the surface the fault zone is delineated by four north south trending segments and that marked differences occur in the distribution of deformation on either side of the fault segments in the late tertiary during this time these segments acted as transfer faults lateral ramps linking different segments of the zagros deformation fronts

geodetic measurement of tectonic deformation in the santa maria fold and thrust belt california we have analyzed geodetic observations to resolve tectonic deformation across the santa maria fold and thrust belt northwest of santa barbara california the geodetic network forms a braced quadrilateral with 40 km sides whose southwest corner is the vandenberg very long baseline interferometry station the data include 1 historical triangulation from the 1880s 1920s and 1950s 2 electronic distance measurement trilateration from 1971 and 1985 and 3 global positioning system observations from 1986 and 1987 we combine the three different types of data to estimate two dimensional station positions and strain rate parameters simultaneously using a model which constrains the relative velocity field to be linear in space and constant in time we find significant strain rates the maximum compressive strain is oriented n17 e 5 e and the compressive strain rate in this direction is 0 13 0 03 strain yr under the assumption that the unresolved rotational component of the velocity field is zero we estimate that the integrated rate of deformation across the basin is 7 1 mm yr oriented at n03 e 13 this vector can be decomposed into 6 2 mm yr of crustal shortening on the general structural trend of n30 e and 3 1 mm yr of right lateral shear across this axis on the basis of these values and earthquake focal mechanisms in the area we infer that the deformation occurs on northwest trending folds and thrusts within the belt these results are consistent with the rate and direction of deformation across the central california coast ranges inferred by balancing pacific north america plate motion against san andreas slip and basin and range extension they imply that the santa maria fold and thrust belt is the primary active element in transforming motion from the coast ranges to the western transverse ranges and the santa barbara channel