central zagros fold thrust belt iran new insights from seismic data field observation and sandbox modeling 1 we present five generalized cross sections across the central zagros fold and thrust belt iran these sections show that the fold geometry varies significantly both horizontally and vertically the style is closely related to the changes in the mechanical behavior of the lithostratigraphic horizons and in particular to the presence of intermediate decollements within the sedimentary pile restoration of the sections shows amounts of shortening of the same order from one section to the other however it appears to be unequally distributed suggesting variations in basal decollement shear strength analogue modeling has been performed to systematically investigate the effect of an intermediate decollement level at different depths on the style of folding the models demonstrate that the position of intermediate decollements is an important factor controlling both structural style and fold wavelength models with shallow intermediate decollement show regularly and widely spaced anticlines in these models the fold wavelength depends directly on the thickness of the dominant competent layer and short wavelength superficial structures mask broad anticlines at depth models with deep intermediate decollement are characterized by the rapid propagation of deformation with small rate of shortening along this decollement influencing localization of forthcoming anticlines in the upper levels such propagation favors the development of duplexes and multiwavelength folds on this basis fold kinematics in central zagros is discussed using the variation of structural style along different folds as an indicator of the sequence of deformation detachment folding is the main folding style at least for the initial stages of deformation and thrust faults developed only at later stages some of these faults branched on decollement levels express the progression of folding whereas others are linked to late basement faults cutting through early structures in general the decollement levels are activated sequentially from deeper horizons to shallower ones however in one case gachsaran decollement a shallow decollement is activated during the early stages of folding and then abandoned during the subsequent evolution

regional stratigraphy of the zagros fold thrust belt of iran and its proforeland evolution the latest neoproterozoic through phanerozoic stratigraphy of the zagros fold thrust belt of iran has been revised in the light of recent investigations the revised stratigraphy consists of four groups of rocks each composed of a number of unconformity bounded megasequences representing various tectonosedimentary settings in the lowest group ranging in age from latest precambrian to devonian the uppermost neoproterozoic to middle cambrian rocks constitute a megasequence of evaporites siliciclastic deposits and interlayered carbonates which were deposited in pull apart basins that developed by the najd strike slip fault system this megasequence is overlain by a second one middle to late cambrian in age which consists of shallow marine siliciclastic and carbonate rocks representing deposition in an epicontinental platform the overlying shales siltstones and partly volcanogenic sandstones of ordovician silurian and devonian age are local remnants of stratigraphic units that were extensively eroded during development of several major unconformities the second group consists of two megasequences one permian and the other triassic composed of widespread transgressive basal siliciclastic rocks and overlying evaporitic carbonates of an equatorial epi pangean very shallow platformal sea the third group is composed of four megasequences formed of shallow and deep water carbonates with some siliciclastic and evaporite deposits which accumulated on a neo tethyan continental shelf during earliest jurassic through late turonian time the fourth group comprises siliciclastic and carbonate deposits of a largely underfilled nw to se trending forward and backward migrating late cretaceous to recent proforeland basin which has evolved as an integral part of the zagros orogen this last group consists of three megasequences ix x and xi with distinctive lateral and vertical facies variations which reflect specific tectonic events megasequence ix comprises uppermost turonian to middle maastrichtian prograding and retrograding siliciclastic and carbonate deposits whose accumulations reflect emplacement obduction of ophiolite slivers and subsequent collisional events in the zagros orogen megasequence x consists of uppermost maastrichtian to upper eocene siliciclastic and carbonate rocks which deposited first progradationally in front of the zagros orogenic wedge with reduced contractional tectonic activity and then retrogradationally due to intensified thrust stacking in the interior parts of the orogen megasequence xi consists of oligocene and lower miocene carbonate strata deposited retrogradationally shortly after a period of intensified late eocene thrust faulting in the deformational wedge and an overlying succession of upward coarsening northeasterly derived siliciclastic deposits of lower miocene to recent age which are composed of erosional byproducts of the southwest vergent zagros thrust sheets

the zagros folded belt fars iran constraints from topography and critical wedge modelling summary the late miocene tectonics of the zagros folded belt fars province has for long been related solely to folding of the cover controlled by a ductile decollement between basement and the sedimentary cover however geological constraints topography analysis and seismotectonic studies reveal that basement thrusting may produce locally significant deformation in the cover to determine how the deep seated deformation in the basement may contribute to the overall topography we first examine the filtered large and short wavelengths of the topography we find that the short wavelength component of the topography 20 25 km including the zagros folds is superimposed on the differential uplift at the regional scale in other words the regional base level of folded marker horizons remains parallel to the regional topography of interest modelling reveals that the salt based wedge model alone is not able to reproduce the large wavelength component of the topography of the zagros folded belt this reveals that when a thick relatively to its overburden layer of salt forms the basal decollement it is generally too weak and cannot support the growth of significant topography we then test an alternative thick skinned crustal wedge model involving the crust of the arabian margin which is decoupled above a viscous lower crust this model satisfactorily reproduces the observed topography and is consistent with present day basement thrusting topography analyses and geological constraints we conclude that basement involved thickening and shortening is mechanically required to produce the shape of the zagros folded belt since at least 10 ma finally the involvement of the basement provides mechanical and kinematic constraints that should be accounted for cross sections balancing and further assessing the evolution of zagros at crustal or lithospheric scales

magnetostratigraphy of miocene pliocene zagros foreland deposits in the front of the push e kush arc lurestan province iran abstract the timing of the deformation in the zagros simply folded belt is poorly constrained because of the lack of an accurate absolute chronology of the syntectonic sedimentary sequences the foreland basin infill at the front of the push e kush arc is composed of fine grained fluvial plain deposits agha jari fm and coarse conglomerates at the top of the section bakhtyari fm a magnetostratigraphic study was carried out in a composite section spanning about 2800 m in order to date growth strata and to constrain the timing of the deformation in the mountain front flexure mff magnetostratigraphic correlation of the base of the agha jari fm with chron c5a yields an age of 12 8 to 12 3 ma for this base the transition to the conglomerates of the bakhtyari fm correlates with the upper gauss chron c2an at approximately 3 ma the deposition age of the top of the preserved bakhtyari fm is extrapolated around the pliocene pleistocene boundary the base of the agha jari fm growth strata and thus the beginning of the deformation in the front of the push e kush arc is dated at 8 1 7 2 ma the topmost preserved bakhtyari is folded in the ne flank of the changuleh anticline and is unconformably overlying the sw flank of the anaran anticline this indicates that the tectonic deformation in the front of the push e kush arc was active at least during 5 my the mff is a relatively long lived structure active from 8 1 to 7 2 ma to about the pliocene pleistocene boundary partly synchronous with the changuleh anticline to the foreland after mff tectonic cessation only the changuleh anticline remained active

cenozoic evolution of neotethys and implications for the causes of plate motions africa north america eurasia plate circuit rotations combined with red sea rotations and new estimates of crustal shortening in iran define the cenozoic history of the neotethyan ocean between arabia and eurasia the new constraints indicate that arabia eurasia convergence has been fairly constant at 2 to 3 cm yr since 56 ma with slowing of africa eurasia motion to 1 cm yr near 25 ma coeval with the opening of the red sea ocean closure occurred no later than 10 ma and could have occurred prior to this time only if a large amount of continental lithosphere was subducted suggesting that slowing of africa significantly predated the arabia eurasia collision these kinematics imply that africa s disconnection with the negative buoyancy of the downgoing slab of lithosphere beneath southern eurasia slowed its motion the slow steady rate of northward subduction since 56 ma contrasts with strongly variable rates of magma production in the urumieh dokhtar arc implying magma production rate in continental arcs is not linked to subduction rate

kinematics of a sigmoidal fold and vertical axis rotation in the east of the zagros makran syntaxis southern iran paleomagnetic magnetic fabric and microtectonic approaches abstract the zagros simple fold belt is characterized by elongated curved or sigmoidal folds the trend of these structures together with the structural style change suddenly across the zagros makran syntaxis which separates the continental collision domain of zagros from the oceanic subduction one in makran this work focuses on the minab anticline outcropping in the easternmost part of zagros in order to understand the kinematics of a sigmoidal fold and underscore possible vertical axis rotations in the eastern side of the syntaxis we performed a joint study of magnetic fabric microtectonics and paleomagnetism of the northern termination of this fold the two limbs have been sampled 7 sites 134 samples along three cross sections corresponding to three different orientations of the fold axis the rocks are weakly deformed fine grained mio pliocene reddish siltstones the shortening directions deduced from both magnetic fabric analysis and microtectonic observations are consistent with each other they are horizontal and roughly perpendicular to the local fold axis following the torsion of the fold hinge line and indicating a tectonic origin of the magnetic fabric rockmagnetic analyses thermomagnetic curves hysteresis loops point to the presence of magnetite in the psd and md ranges as the main magnetic carriers together with a minor contribution from hematite apart from a post tilting sub actual vrm and or crm component a paleomagnetic analyses yield mainly two pre tilting magnetization components component b is carried by magnetite spanning the intermediate to high unblocking temperature range 300 c t ubs 580 c component c has unblocking temperatures characteristic of hematite 580 c t ubs 680 c both are ante folding based on positive reversal and fold tests inside each of the cross section but also for the three sections together however because component c is biased by some inclination flattening only component b is taken into account afterwards after full tectonic correction the site mean direction of component b calculated for 6 out of the 7 sites is not statistically different from the individual site mean directions the intersection direction determined by small circle analysis in these six sites is d 18 0 i 33 7 k 482 alpha 95 2 6 compared to the mio pliocene direction expected in this area for africa it corresponds to an overall clockwise rotation of the whole structure of some 18 3 5 1 consistent with the regional geodynamic context the absence of differential paleomagnetic rotation from one cross section to the other and the fact that the magnetic lineation together with the shortening direction deduced from microtectonic analysis follows the fold curvature demonstrate that the torsion of this fold is not secondary but rather coeval with the fold amplification the torsion of the fold would stem from underlying inherited mesozoic structures and the rheological response during the deformation of two incompetent decollement layers undergoing differential velocities and a change of thickness in a constant stress field direction

dynamic constraints on the crustal scale rheology of the zagros fold belt iran thin skinned fold and thrust belts are generally considered as the result of contractional deformation of a sedimentary succession over a weak decollement layer the resulting surface expression frequently consists of anticlines and synclines spaced in a fairly regular manner it is thus tempting to use this spacing along with other geological constraints to obtain insights into the dynamics and rheology of the crust on geological time scales here we use the zagros mountains of iran as a case study as it is one of the most spectacular well studied thin skinned fold and thrust belts in the world both analytical and numerical models are employed to study what con trols fold spacing and under what conditions folding dominates over thrusting the models show that if only a single basal decollement layer is present underneath a brittle sedimentary cover deformation is dominated by thrusting which is inconsistent with the data of the zagros fold belt if we instead take into account additional decollement layers that have been documented in the fi eld a switch in deformation mode occurs and crustal scale folding is obtained with the correct spacing and time scales we show that fold spacing can be used to constrain the friction angle of the crust which is 5 the zagros fold belt this implies that on geological time scales the upper crust is signifi cantly weaker than previously thought possibly due to the effect of fl

tertiary sequence of deformation in a thin skinned thick skinned collision belt the zagros folded belt fars iran 1 we describe how thin skinned thick skinned deformation in the zagros folded belt interacted in time and space homogeneous fold wavelengths 15 8 5 3 km tectono sedimentary evidence for simultaneous fold growth in the past 5 5 2 5 ma drainage network organization and homogeneous peak differential stresses 40 15 mpa together point to buckling as the dominant process responsible for cover folding basin analysis reveals that basement inversion occurred 20 ma ago as the arabia eurasian plate convergence reduced and accumulation of neogene siliciclastics in foreland basin started by 10 ma ongoing contraction occurred by underplating of arabian crustal units beneath the iranian plate this process represents 75 of the total shortening it is not before 5 ma that the zagros foreland was incorporated into the southward propagating basement thrust wedge folds rejuvenated by 3 2 ma because of uplift driven by basement shortening and erosion since then folds grew at 0 3 0 6 mm yr and forced the rivers to flow axially a total shortening of 65 78 km 16 19 is estimated across the zagros this corresponds to shortening rates of 6 5 8 km ma consistent with current geodetic surveys we point out that although thin skinned deformation in the sedimentary cover may be important basement involved shortening should not be neglected as it requires far less shortening moreover for such foreland folded belts involving basement shortening underplating may be an efficient process accommodating a significant part of the plate convergence

a reappraisal of earthquake focal mechanisms and active shortening in the zagros mountains of iran summary the zagros mountains of sw iran are one of the most seismically active intra continental fold and thrust belts on earth and an important element in the active tectonics of the middle east surface faulting associated with earthquakes is extremely rare and so most information about the active faulting comes from earthquakes we use long period teleseismic p and sh body waves to determine the orientation and depth of faulting in 16 new earthquakes and then evaluate and synthesize all the available teleseismic data on earthquake source parameters in the zagros we use this information to investigate the style and distribution of active faulting in the zagros and how it contributes to the n s shortening of the arabia eurasia collision when the data are ranked in quality and carefully evaluated simple patterns are seen that are not apparent when routine catalogue data are taken at face value an important change in the fault configuration occurs along strike of the belt in the nw overall convergence is oblique to the trend of the belt and the surface anticlines and is achieved by a spatial separation partitioning of the orthogonal strike slip and shortening components on separate parallel fault systems by contrast in the se overall convergence is orthogonal to the regional strike and achieved purely by thrusting in the central zagros between these two structural regimes deformation involves parallel strike slip faults that rotate about vertical axes allowing extension along the strike of the belt the overall configuration is similar to that seen in other curved shortening belts such as the himalaya and the java sumatra trench all the zagros earthquakes we have been able to check have centroids shallower than 20 km and are confined to the upper crust many of the larger earthquakes are likely to occur in the basement beneath the sedimentary cover which is active even beneath areas of known shallow structural decollement such as the dezful embayment the dominant style of shortening is high angle reverse faulting with dips 30 though some lower angle thrusting occurs in places active thrust and reverse faulting is relatively confined to the lower topography on the sw edge of the belt today and only strike slip faulting affects the higher topography profound vertical changes in structural and stratigraphic level indicate that a similar style of deformation was once active across the width of the simple folded belt but has progressively migrated sw over the last 5 ma there is no evidence for a seismically active structural decollement such as a low angle thrust beneath the zagros nor is there any seismic evidence for active subduction either beneath the zagros or beneath central iran instead the arabian margin seems to have shortened by distributed thickening of the basement only in the syntaxis of the oman line at the se end of the zagros is there any evidence for a low angle thrust of regional extent here earthquakes continue 50 km north of the zagros thrust line the geological suture between the arabian margin and central iran reaching depths of 30 km and may represent thrusting of arabian basement beneath central iran to this extent

growth stratal architectures associated to decollement folds and fault propagation folds inferences on fold kinematics abstract in many thrust and fold belts asymmetric folds with overturned or steeply dipping forelimbs and gently dipping backlimbs are commonly interpreted as thrust related folds determining the folding mechanism exclusively from the final fold geometry in the pre growth units is possible only for a limited suite of structures the nature of fold thrust interaction in shallow structures can be inferred by coupling the fold geometric analysis with the study of the syntectonic sediment stratal architectures several factors such as axial surface activity fold uplift limb rotation and limb widening rates together with sedimentation and erosion rates control growth strata patterns because the evolutionary path of most of these parameters depends on the folding kinematics different growth stratal architectures are expected for different thrust related anticlines in this paper we examine the influence of the above factors on growth stratal geometries associated to a simple kink band and then we apply the same approach to kinematic models of decollement folding and fault propagation folding four geometric approaches are used to account for the geometry and kinematics of anticlines located at the tip of a blind thrust fault propagation folding with no excess layer parallel shear fault propagation folding with progressive layer parallel shear constant limb length decollement folding and variable limb length decollement folding whereas fault propagation folding with no excess layer parallel shear is a self similar folding mechanism the other three types involve limb rotation coherent geometries between growth and pre growth sequences develop at high sedimentation rates in the crest of fault propagation folds and incoherent ones in decollement folds minor differences within growth strata patterns occur at low sedimentation rates and when erosion affects the crest of the anticlines

numerical investigation of deformation mechanics in fold and thrust belts influence of rheology of single and multiple decollements 1 thin skinned fold and thrust belts related to convergence tectonics develop by scraping off a rock sequence along a weaker basal decollement often formed by water saturated shale layers or low viscosity salt horizons a two dimensional finite element model with a viscoelastoplastic rheology is used to investigate the structural evolution of fold and thrust belts overlying different types of decollements in addition the influence of multiple weak layers in the stratigraphic column is studied model shale decollements are frictional with lower friction angles as the cover sequence model salt layers behave linear viscous due to a lower viscosity as the cover sequence or with a power law rheology single viscous decollement simulations have been compared to an analytical solution concerning faulting versus folding results show that fold and thrust belts with a single frictional basal decollement generate thrust systems ramping from the decollement to the surface spacing between thrust ramps depends on the thickness of the cover sequence the structural evolution of simulations with an additional low frictional layer depends on the strength relationship between the basal and the intersequential decollement tectonic underplating and antiformal stacking occur if the within sequence decollement is weaker in the frontal part of models deformation is restricted to the upper part and imbrication occurs with a wavelength depending on the depth of the intermediate weak layer salt decollement with a viscosity of 10 18 pa s leads to isolated box folds detachment folds multiple salt layers 10 18 pa s result in long wavelength folding our results for both frictional and viscous decollements are in bulk agreement with the mohr coulomb type critical wedge theory citation ruh j b b j p kaus and j p burg 2012 numerical investigation of deformation mechanics in fold and thrust belts influence of rheology of single and multiple decollements tectonics 31 tc3005 doi 10 1029 2011tc003047

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

variation of structural style and basin evolution in the central zagros izeh zone and dezful embayment iran abstract structural style and its relationship to sedimentary facies and the evolution of sedimentary depocenters since late cretaceous times have been studied on the basis of one regional balanced transect and several updated isopach maps in the izeh zone and the dezful embayment central zagros this study relies on fieldwork data existing geological maps seismic data and well information a new structural classification for part of the zagros sedimentary cover is presented to highlight the different mechanical behavior of the formations in the stratigraphic column it shows the existence of several local decollement levels activated during folding these decollement levels separate lithotectonic units which accommodate shortening in different ways the lower paleozoic is the basal decollement level throughout the studied area triassic evaporites albian shales eocene marls and miocene evaporites can act as intermediate decollement levels and present variable facies in the central zagros lateral facies and thickness variations the sedimentary overburden and the close relationship with inherited fault patterns influenced the wavelength amplitude and style of folding in the study area furthermore surface structures do not necessarily coincide with deeper objectives where these disharmonic levels are involved in folding the evolution of sedimentary depocenters from the late cretaceous obduction episode until early miocene collision is described based on updated isopach maps and tectonic subsidence curves this analysis shows continuous compression and movements along n s and nw se trending faults in the zagros basement which predate the neogene zagros folding and influence sedimentation history it also indicates a southwestward migration of the depocenters through time in addition to the basement involvement below some folds during the zagros orogeny

tectonics of the zagros orogenic belt of iran new data and interpretations abstract the zagros orogenic belt of iran is the result of the opening and closure of the neo tethys oceanic realm and consists from northeast to southwest of three parallel tectonic subdivisions 1 1 the urumieh dokhtar magmatic assemblage 2 2 the sanandaj sirjan zone and 3 3 the zagros simply folded belt recent detailed and reconnaissance mapping and stratigraphie structural analyses in various parts of the belt indicate that the tectonics of the sanandaj sirjan zone is dominated by either large scale composite duplex structures or low and high angle ne dipping imbricate systems these thrust systems have transported numerous horses and sheets nappes of metamorphosed and non metamorphosed phanerozoic rocks for tens or possibly hundreds of kilometers stratigraphic evidence and synorogenic conglomerates indicate that thrusting was initiated in the late cretaceous and has continued episodically since that time shear sense indicators in various parts of the zone reveal a ne sw direction of transport thrust systems generated in each episode are superimposed upon the previous structures cutting across and displacing them and producing complicated stacks of thrust sheets southwestward transport and stacking of the thrust sheets has resulted in an increase of about 10 15 km in the thickness of the continental crust in the southwestern part of this zone the so called z main zagros thrust which has been traditionally considered as the boundary between the sanandaj sirjan zone and the zagros simply folded belt is by no means a single high angle reverse fault nor is it a narrow zone of crushed rocks but a series of low angle thrusts locally cut by normal faults these thrusts are indistinguishable from those mapped in the sanandaj sirjan zone and are geometrically part of the sanandaj sirjan zone structures there is no single thrust among them that can be singled out and referred to as the main one the boundary of the sanandaj sirjan zone with the urumieh dokhtar magmatic assemblage to the northeast is characterized by a series of structural depressions formed by compression rock sequences including ophiolite complexes exposed along this boundary are strongly dismembered sheared and mylonitized shearing planes and foliations are either subvertical or dipping at high angles to the northeast this zone is suggested to be the suture between the afro arabian and the iranian plates overall the intensity of deformation increases northeastward from the persian gulf mesopotamian basin where strata are undeformed and horizontal through the zagros simply folded belt which is characterized by en echelon doubly plunging flexural slip folds gentle to open in the southwest and close to locally sw overturned in the northeast the intensity of deformation continues to increase further northeastward through the sanandaj sirjan zone where thrust faulting is dominant this pattern suggests that the deformational front has migrated through time from the northeastern part of the sanandaj sirjan zone i e the suture zone to its present position in the central portion of the persian gulf mesopotamian foreland basin

zagros orogeny a subduction dominated process this paper presents a synthetic view of the geodynamic evolution of the zagros orogen within the frame of the arabia eurasia collision the zagros orogen and the iranian plateau preserve a record of the long standing convergence history between eurasia and arabia across the neo tethys from subduction obduction processes to present day collision from 150 to 0 ma we herein combine the results obtained on several geodynamic issues namely the location of the oceanic suture zone the age of oceanic closure and collision the magmatic and geochemical evolution of the eurasian upper plate during convergence as testified by the successive sanandaj sirjan kermanshah and urumieh dokhtar magmatic arcs the p t t history of the few zagros blueschists the convergence characteristics across the neo tethys kinematic velocities tomographic constraints subduction zones and obduction processes together with a survey of recent results gathered by others we provide lithospheric scale reconstructions of the zagros orogen from 150 to 0 ma across two sw ne transects the evolution of the zagros orogen is also compared to those of the nearby turkish and himalayan orogens in our geotectonic scenario for the zagros convergence we outline three main periods regimes 1 the mid to late cretaceous 115 85 ma corresponds to a distinctive period of perturbation of subduction processes and interplate mechanical coupling marked by blueschist exhumation and upper plate fragmentation 2 the paleocene eocene 60 40 ma witnesses slab break off major shifts in arc magmatism and distributed extension within the upper plate and 3 from the oligocene onwards 30 0 ma collision develops with a progressive sw migration of deformation and topographic build up sanandaj sirjan zone 20 15 ma high zagros 12 8 ma simply folded belt 5 0 ma and with partial slab tear at depths 10 ma to present our reconstructions underline the key role played by subduction throughout the whole convergence history we finally stress that such a long lasting subduction system with changing boundary conditions also makes the zagros orogen an ideal natural laboratory for subduction processes

pliocene growth of the dowlatabad syncline in frontal fars arc folding propagation across the zagros fold belt iran this research was funded by the darius programme as well as the group of dynamics of the lithosphere geosciences barcelona geo3bcnconsejo superior de investigaciones cientificas csic spain we thank the paleomagnetic laboratory universitat de barcelona scientific and technological centers geo3bcn csic where the paleomagnetic analyses were conducted and also the laboratorio de geocronologia y geoquimica isotopica of the universidad complutense de madrid spain where the sr samples were processed in addition the study of calcareous nannofossils was supported by the research group of the basque university system it 930 16 we are also grateful to the national iranian oil company for their support during fieldwork we thank darius programme and its sponsors and projects alpimed pie csic 201530e082 and subtetis pie csic 201830e039 for additional support

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

structures of the zagros fold thrust belt in iran the zagros fold thrust belt in iran forms the external part of the zagros active orogenic wedge it includes a sequence of heterogeneous latest neoproterozoic phanerozoic sedimentary cover strata 7 to 12 km thick and composed of alternating incompetent and competent layers overlying precambrian crystalline basement with a complex pre zagros structural fabric balancing structures of the cover statigraphic units in the zagros fold thrust belt requires in sequence and out of sequence involvement of the precambrian basement in the deformation six detailed balanced and retrodeformable cross sections which are constructed based on geological and geophysical data across various sectors of the belt show fault bend and fault propagation folds interpreted to have formed by slip on their subjacent thrusts out of sequence basement rooted thrusts as the interpretations in the constructed cross sections suggest have breached the cover basement interface and using incompetent cover strata for propagation cut across the cover structures and have created associated new folds superimposed upon the pre existing structures this style of deformation which has resulted in structural complexity of the belt characterizes a 200 to 300 km wide zone of distributed partly synchronous deformation with along strike and across strike variations it also implies that the zagros fold thrust belt as the external part of the orogenic wedge is still in its subcritical condition with internal deformation to achieve a critical taper in creating structural complexity in addition to out of sequence thrusting mechanically weak layers evaporites and mudstones of the cover strata have played a significant role by providing several detachment horizons shortening estimates across the belt are variable based on the constructed cross sections and their restorations minimum shortening estimates range from 16 percent to 30 percent in different sectors of the belt

growth strata in foreland settings abstract the accurate analysis of growth strata has revealed their significance to unravel both fold kinematics and timing of deformation in both compressive and extensive settings the increasing acquisition of 3 d multichannel seismic lines with few tens of meters of resolution in complex tectonic areas reveals complex interplay between growing structures and deposition either in marine or continental environments interestingly growth strata reveal similar relationships in both compressive folds linked to thrusts at depth and folds related to propagating normal faults in extensive regimes to completely document the complete kinematic history of an individual fault or a group of faults it is necessary to combine studies at different scales to integrate the findings revealed by field work meters of resolution and multichannel seismic lines results the margins of the ebro basin to the south of the pyrenees have been the focus of abundant studies of syntectonic deposits this is because of its special long term evolution from a foreland to an intermontane basin and a final open basin to the mediterranean sea in neogene times the complete comprehension of growth strata in these natural laboratories is essential for our present needs in both petroleum exploration and earthquake prediction

late cenozoic and modern stress fields in the western fars iran implications for the tectonic and kinematic evolution of central zagros 1 the zagros iran developed during mio pliocene times in response to arabia eurasia convergence the western fars highlights a major bend of the deformation front and displays a remarkable set of nearly n s right lateral strike slip faults the kazerun borazjan karebass sabz pushan sarvestan faults oblique at high angle to the belt the region likely plays a major kinematic role by accommodating the change in shortening modes from partitioned in the western central zagros to nonpartitioned in the eastern zagros the inversion of focal mechanisms from small and moderate earthquakes shows a consistent n020 030 compression with a low ratio between differential stresses this regime accounts for the combination of strike slip and thrust type mechanisms through likely 2 3 permutations fault slip analysis reveals two successive late cenozoic regional compressional trends ne sw then n020 the latter is in good agreement with the present day stress the significance of the ne sw compression is discussed alternatively in terms of stress deviations or block rotations in relation to the strike slip fault system fieldwork and satellite imagery suggest that these faults behave first as transfer faults during folding of the cover and later as strike slip faults in agreement with the succession of stress regimes and the evolution of the dominant deformation style from thin skinned to thick skinned the first order stability of the collision related state of stress since 5 ma supports that the arabia eurasia convergence did not give rise to partitioning in the western fars but rather was and is still accommodated by distributed deformation involving both shortening and strike slip motion throughout the cover and the basement

thick and thin skinned deformation rates in the central zagros simple folded zone iran indicated by displacement of geomorphic surfaces although the geology and structure of the zagros fold and thrust belt iran have been studied extensively the distribution of active deformation across the belt and its seismotectonic behaviour remain controversial we have mapped deformed fluvial terraces along the dalaki and mand rivers in the central zagros as well as marine terraces along the persian gulf in order to unravel the spatial pattern of vertical displacements and to analyse active deformation and its implications for seismicity using appropriate fold models based on structural data allows interpreting such vertical displacements in terms of horizontal shortening across the fold structures obtaining well constrained rates of deformation depends on reliably dating deformed geomorphic markers by combining different dating techniques and correlations to sea level history we propose an internally consistent set of ages which allow the first geomorphic estimates of shortening rates absorbed by individual structures in the central zagros our results show that shortening on late pleistocene timescales is concentrated in the frontal part of the belt consistent with recent gps data three or four frontal structures appear to absorb practically all of the active shortening across the zagros broadly consistent with a normal forward propagating deformation sequence but with local out of sequence activation of structures behind the forward most folds the localization rate and direction of surface shortening across individual structures appear decoupled from basement deformation as indicated by structural cross sections and the distribution of seismicity such independent behaviour suggests that the sedimentary cover of the frontal zagros is decoupled from the basement most probably at the level of the hormuz salt this weak basal detachment level together with several intermediate decollement levels appears to be responsible for the overwhelmingly aseismic deformation of the zagros sedimentary cover and also to control the development of a large panel of fold structures from detachment to fault propagation folds with varying wavelength and rooting depth

building the zagros collisional orogen timing strain distribution and the dynamics of arabia eurasia plate convergence he zagros mountains are the result of the arabia eurasia collision initiated at 35 ma as the rifted arabian lithosphere was underthrusted beneath the iranian plate due to its negative buoyancy the onset of crustal thickening started at 25 ma as recorded by the hinterland exhumation and foreland clastic deposition deformation throughout the arabia eurasia collision zone and the uplift of the iranian plateau occurred after 15 12 ma as a result of shortening thickening of the thin iranian crust we emphasize that only 42 of the post 35 ma convergence is partitioned by shortening within central iran tomographic constraints show ongoing slab steepening or breakoff in the nw zagros whereas underthrusting of the arabian plate is observed beneath central zagros the current subduction dynamics can be explained by the original lateral difference in the buoyancy of the distal margin that promoted slab sinking in nw zagros and underthrusting in central zagros critical wedge approach applied to the zagros favors the hypothesis of strong brittle crust detached above a viscous lower crust in contrast the weak sedimentary cover deforms by buckling of a thick multilayered cover thrust faulting associated with folding occurs in the competent layers and is responsible for most of the earthquakes there is evidence that the role of the slab pull force in driving the arabian plate motion was reduced after 12 ma large scale mantle flow induced by mantle upwelling at the afar plume appears to be the main driver of the arabia plate motion we stress that the main kinematic change in the zagros region occurred at 15 12 ma as the zagros uplifted before the arabian slab detached the zagros appears key to investigate coupling between continental rheology plate driving forces and mountain building in which the role of rift inheritance appears to be central

theory and application of the day plot mrs ms versus hcr hc 2 application to data for rocks sediments and soils 1 new theoretical curves relating the hysteresis parameters mrs ms and hcr hc for single domain sd superparamagnetic sp pseudo single domain psd and multidomain md grains and their mixtures are applied to published data for natural materials the day plot of mrs ms versus hcr hc has been used to crudely classify samples into box like sd psd and md or sometimes incorrectly md sp regions with arbitrary boundaries new type curves for md psd sd md and sd sp grains and mixtures permit more subtle and precise modeling the predicted md trend and its junction with the psd trend are observed in two data sets for magnetite spherules from carbonate rocks and for temperature varying hysteresis results spanning the verwey transition the latter data are the basis of a suggested new method for pinpointing the psd md threshold size selected data for pottery clays soils and paleosols generally follow sd md type curves and indicate intermediate size psd magnetite with narrow to broad size distributions a lake sediment section with known grain size progression tracks in the predicted sense along the sd md trend selected data for glaciomarine and pelagic sediments are also generally compatible with sd md trends examples of remagnetized carbonate rocks submarine basaltic glasses and glassy rims of pillow basalts all follow predicted sp sd or sp psd mixing curves with a large range in volume fraction of sp grains 0 75 but a narrow range of sp particle sizes 10 2 nm larger sp grains spanning the range to sd size 25 30 nm are absent for unknown reasons oceanic dolerites gabbros and serpentinized peridotites in some cases fall in a novel region of the day plot parallel to but below magnetite sd md mixing curves

neogene sediments and modern depositional environments of the zagros foreland basin system a sedimentological investigation of the neogene deposits of the zagros foreland basin in sw iran reveals a continuous and largely gradational passage from supratidal and sabkha sediments at the base represented by the gachsaran formation to carbonates and marine marls mishan formation with basal guri carbonate member followed by coastal plain and meandering river deposits agha jari formation and finally to braided river gravel sheets bakhtyari formation this vertical succession is interpreted to represent the southward migration of foreland basin depozones from distal foredeep and foredeep to distal wedge top and proximal wedge top respectively as the zagros fold thrust belt migrated progressively southward towards the arabian foreland this vertical succession bears a striking similarity to modern depositional environments and sedimentary deposits observed in the zagros region today where one passes from mainly braided rivers in the zagros mountains to meandering rivers close to the coast to shallow marine clastic sediments along the northern part of the persian gulf and finally to carbonate ramp and sabkha deposits along the southeastern coast of the persian gulf this link between the neogene succession and the modern day depositional environments strongly suggests that the major neogene formations of the zagros foreland basin are strongly diachronous as shown recently by others and have active modern day equivalents

magnetostratigraphic constraints on relationships between evolution of the central swiss molasse basin and alpine orogenic events magnetostratigraphic chronologies together with lithostratigraphic sedimentological and petrological data enable detailed reconstruction of the oligocene to miocene history of the north alpine foreland basin in relation to specific orogenic events and exhumation of the alps the molasse of the study area was deposited by three major dispersal systems rigi hohronen napf distinguished by characteristic heavy mineral suites conglomerate clast populations and the presence of key clasts these systems record three major phases of denudation of the alpine edifice the rigi system eroded the austroalpine and penninic nappes of eastern switzerland from 30 to 25 5 ma as a result of backthrusting and uplift of these units along the insubric line subsequent uplift of the aar massif some 40 km to the north appears to have controlled the duration of the hohronen and napf dispersal systems spanning 24 22 ma and 21 5 15 ma respectively they record downcutting into the crystalline cores of the penninic and austroalpine nappes of eastern hohronen and western napf switzerland high resolution reconstruction of the structural and geometrical evolution of the proximal molasse reveals in sequence and out of sequence thrusting events at the alpine front and incorporation of the molasse into the orogenic wedge by in sequence thrusting and underplating furthermore it reveals close relationships between periods of rapid denudation in the central alps and phases of increased sediment accumulation rates at the proximal basin border an initial increase in molasse accumulation rates to 1 km m y occurred between 30 and 25 5 ma and coincides with the insubric phase of backthrusting along the eastern insubric line where 10 km of vertical displacement is interpreted during the same time span the alpine wedge propagated forward along the basal alpine thrust as indicated by the coarsening and thickening upward megasequence and by occurrence of bajada fans derived from the alpine border the end of this tectonic event is marked by a basinwide unconformity interpreted to have resulted from crustal rebound after initial loading a subsequent increase in accumulation rates to 1 km m y between 23 and 21 5 ma coincides with initial uplift of the eastern aar massif by at least 4 km this phase of high accumulation rates is associated with incorporation of early chattian conglomerates into the orogenic wedge the third advance of the alpine wedge between 21 and 15 5 ma caused underplating of molasse deposits resulting in synsedimentary backthrusting of previously deposited molasse sequences and in the development of a progressive unconformity a rapid increase in accumulation rates from 0 35 to 1 km m y between 15 5 and 15 ma marks the final loading event in the wedge which may be caused by further major displacement and loading of the aar massif this deformation is coeval with out of sequence thrusting of the helvetic border chain and of the piggyback stack of north penninic and ultrahelvetic flysch nappes along the basal alpine thrust

convergence history across zagros iran constraints from collisional and earlier deformation the zagros orogen provides a unique opportunity within the alpine system to evaluate the interplay between a young tertiary collision and earlier subduction obduction processes within the crush zone and the sanandaj sirjan internal zone separating the zagros fold belt from central iran we document several major tectonic events taking place at the end of the cretaceous of the eocene and from the mio pliocene onwards ca 20 15 ma contrary to recent interpretations our data cross sections and description of the overall deformation style strongly suggest that the main zagros thrust mzt is deeply rooted possibly to moho depths and that the suture zone effectively runs along the mzt field observations show that the final resorption of the oceanic domain took place slightly after 35 ma and that collision must have started before ca 23 25 ma in northern zagros the shortening rate across the crush zone since the mid miocene 20 15 ma is estimated at a minimum 3 4 mm year shear movements in the crush zone during the eocene oligocene period and extensional strike slip movements in the internal zones during the late cretaceous point to an oblique setting early in the convergence history a geotectonic scenario for convergence from the time of obduction to the present is finally proposed

contractional salt tectonic system in the south dezful embayment zagros abstract the dezful embayment in zagros has traditionally been interpreted as a typical fold belt with multiple detachment levels including a lower detachment at the basement cover interface and an upper detachment along the miocene gachsaran halite bearing evaporites this paper constrains diapiric processes in the gachsaran detachment coeval with regional shortening that resulted in complex and hitherto unstudied salt structures and flanking synclinal minibasins in this paper well tied seismic interpretation is integrated with field and remote sensing mapping cross section construction and stepwise tectono sedimentary restoration the results indicate that after the deposition of mishan lower aghajari pre kinematic overburden sediments detachment folding initiated above the gachsaran evaporites during late tortonian times as a result of regional shortening the salt cored anticlines later actively pierced their roof to subsequently rise as passive diapirs and evolve into salt walls synclinal minibasins developed due to salt evacuation into flanking walls during the deposition of the lahbari mb in messinian pliocene remarkable sedimentary thickening and lateral shifts in minibasin depocenter towards the salt walls accompanied by overturned collars and hook halokinetic sequences are diagnostics of near surface syndepositional passive growth of diapirs during this stage from pliocene to recent the major episode of regional shortening has squeezed these precursor salt walls to form thrust welds in conclusion the well exposed structures of south dezful show an early shortening stage then a transition to a combination of shortening and passive diapirism and final thrusting along diapirs this evolution model may be more common in other salt influenced fold thrust belts than is currently recognized

early neogene foreland of the zagros implications for the initial closure of the neo tethys and kinematics of crustal shortening we study the transition from passive margin to foreland basin sedimentation now exposed in the high zagros belt to provide chronological constraints on the initial stage of arabia eurasia collision and closure of the neo tethys we performed magnetostratigraphy and strontium isotope stratigraphy along two sections near the zagros suture which expose the oldest preserved foreland deposits the shalamzar section in the west and the dehmoord section in the east the top of the passive margin asmari formation has an age of 28 29 ma in the high zagros and is overlain by foreland deposits with a major basal unconformity representing 7 myr of hiatus the base of the foreland deposits has an age of 21 5 ma at dehmoord and ca 26 ma at shalamzar the sedimentation rate increased from 30 m myr in the passive margin to 247 m myr in the foreland combined with available age constraints across the zagros our results show that the unconformity is diachronous and records the southwestward migration of the flexural bulge within the arabian plate at an average rate of 24 2 mm yr over the last 27 ma the time evolution of sediment accumulation in the zagros foreland follows the prediction from a flexural model as the foreland is thrust beneath the orogenic wedge and loaded by the wedge and basin fill we detect the onset of forebulge formation within the asmari formation around 25 ma we conclude that closure of the neo tethys formed the zagros collisional wedge at 27 2 ma hence the arabia eurasia collision was probably not the main driver of global cooling which started near the eocene oligocene boundary ca 33 7 ma we estimate 650 km of forebulge migration since the onset of the collision which consists of 350 km of shortening across the orogen and 300 km of widening of the wedge and increasing flexural rigidity of arabia we conclude the average rate of shortening across the zagros to be ca 13 mm yr over the last 27 myr a value comparable to the modern rate palinspastic restoration of structural cross sections and crustal volume conservation comprise only ca 200 km of shortening across the zagros and metamorphic sanandaj sirjan belt implying that at least 150 km of the arabian crust was underthrust beneath eurasia without contributing to crustal thickening possibly due to eclogitization

forward propagation of the zagros simply folded belt constrained from magnetostratigraphy of growth strata the temporal evolution of the zagros simply folded belt is constrained by a magnetostratigraphic sequence containing a progressive unconformity on the southern limb of the kuh e ghol ghol anticline in the central fars the investigated similar to 1400m thick sequence exposes a regressive megacycle containing from bottom to top open and shallow marine marls and sandy limestones fine to coarse grained fluvial deposits and alluvial conglomerates correlating the magnetostratigraphic section with the geomagnetic polarity time scale constrains the transition from marine to fluvial sediment deposition at similar to 6ma this transition was accompanied by a change in the accumulation rate from similar to 15cm ka to similar to 40cm ka as measured on lithified sediments alluvial river deposits first occurred at similar to 3 2ma the kuh e ghol ghol anticline began to grow at similar to 3 8ma witnessing fastest limb rotation rates of 40 degrees ma at similar to 3 3ma reporting magnetostratigraphic sections and ages of growth strata on a map of ne fars reveal an similar to 1cm a southwestward migration rate of the deformation front during the middle and late miocene

assessing the role of bitumen in the formation of stratabound cu ag deposits insights from the lorena deposit las luces district northern chile abstract stratabound cu ag deposits located in north central chile have been grouped into two ns parallel belts according to the age of their volcanic and volcanoclastic host rocks deposits from the cretaceous belt are characterized by an unusual assemblage of cu sulfides with migrated hydrocarbons whereas the presence of organic matter has not yet been recognized in deposits from the jurassic belt here we report the first evidence of pyrobitumen in a jurassic stratabound cu ag deposit and evaluate its role in ore formation we present a micro analytical study of pyrobitumen associated with cu fe sulfides in the lorena deposit located in northern chile our approach involved a combination of surface and drill core sample characterization fe sem observations empa and xrf mapping of pyrobitumen in addition we determined the speciation of sulfur in pyrobitumen by using synchrotron xanes two main events of hypogene mineralization were identified at lorena deposit i e a pre ore and a main cu ore stage the pre ore stage is characterized by globularly shaped pyrobitumen and minor pyrite and a widespread albite alteration of the andesite host rock pre ore pyrite was replaced by chalcopyrite bornite and chalcocite providing evidence for a late cu inception in the main cu ore stage chalcocite is often associated with sharp edged angular pyrobitumen most likely indicating remobilization or a later pulse of hydrocarbons empa data show that pyrobitumen at lorena is enriched in fe 0 02 1 74 wt cu 0 02 0 87 wt s 0 01 0 43 wt and cl 0 01 0 4 wt other elements detected include v co ni cr sb as ag and au both ag and au were only detected in a few spots with au reaching up to 600 ppm desktop and synchrotron xrf mapping shows that s is homogeneously distributed within pyrobitumen with lower s concentrations observed at grain rims on the other hand empa wds x ray maps show that cu precipitated on pyrobitumen grain surfaces filling fractures and forming veinlets in addition textures showing the presence of micro to nano sized pyrobitumen inclusions within both pre ore pyrite and main ore chalcocite grains point unequivocally to the interaction of hydrothermal fluids with hydrocarbons during the formation of this deposit the high s concentrations measured in pyrobitumen and the presence of organosulfur compounds detected by xanes can be attributed to an organic source the pre ore assemblage is interpreted as formed from a petroleum aqueous fluid connate waters mixture that migrated from the sedimentary source rock into the jurassic host rocks where pyrite and pyrobitumen precipitated in the andesite late cu bearing hydrothermal fluids interacted with this pyrobitumen pyrite assemblage to form cu sulfides either by replacement of pyrite or precipitation we conclude that some of the s contained in pyrobitumen could have been released during interaction with the cu bearing hydrothermal fluid contributing at least partially to the s budget required for sulfide mineralization in the main ore stage our results provide evidence supporting pyrobitumen fluid interaction as a key process in the formation of the lorena deposit and possibly other stratabound cu ag deposits in chile

basin architecture and growth folding of the nw zagros early foreland basin during the late cretaceous and early tertiary abstract we present and use the chronostratigraphy of 13 field logs and detailed mapping to constrain the evolution of the early zagros foreland basin in nw iran large foraminifera calcareous nannofossil palynological and 87 sr 86 sr analysis supplied ages indicating a campanian early eocene age of the basin infill which is characterizd by a diachronous southwestward migrating shallowing upwards mixed clastic carbonate succession growth synclines and local palaeoslope variations indicate syndepositional folding from maastrichtian to eocene time and suggest forelandward migration of the deformation front we also illustrate the basin architecture with a synthetic stratigraphic transect from internal to external areas time lines cross the formation boundaries from continental kashkan red beds to taleh zang mixed clastic carbonate platforms amiran slope deposits and basinal gurpi pabdeh shales and marls the foreland basin depocentres show a progressive migration from the campanian to eocene c 83 52 7 ma with rates of c 2 4 mm a 1 during the early middle palaeocene c 65 5 58 7 ma increasing to c 6 mm a 1 during the late palaeocene earliest eocene c 58 7 52 8 ma coeval subsidence remained at c 0 27 mm a 1 during the first 12 7 ma and decreased to c 0 16 mm a 1 during the last 4 2 ma of basin filling finally we integrate our results with published large scale maps and discuss their implications in the context of the zagros orogeny supplementary material tables with dating results are available at http www geolsoc org uk sup18439

revised age of proximal deposits in the zagros foreland basin and implications for cenozoic evolution of the high zagros the regionally extensive coarse grained bakhtiyari formation represents the youngest synorogenic fill in the zagros foreland basin of iran the bakhtiyari is present throughout the zagros fold thrust belt and consists of conglomerate with subordinate sandstone and marl the formation is up to 3000 m thick and was deposited in foredeep and wedge top depocenters flanked by fold thrust structures although the bakhtiyari concordantly overlies miocene deposits in foreland regions an angular unconformity above tilted paleozoic to miocene rocks is expressed in the hinterland high zagros the bakhtiyari formation has been widely considered to be a regional sheet of pliocene pleistocene conglomerate deposited during and after major late miocene pliocene shortening it is further believed that rapid fold growth and bakhtiyari deposition commenced simultaneously across the fold thrust belt with limited migration from hinterland ne to foreland sw thus the bakhtiyari is generally interpreted as an unmistakable time indicator for shortening and surface uplift across the zagros however new structural and stratigraphic data show that the most proximal bakhtiyari exposures in the high zagros south of shahr kord were deposited during the early miocene and probably oligocene in this locality a coarse grained bakhtiyari succession several hundred meters thick contains gray marl limestone and sandstone with diagnostic marine pelecypod gastropod coral and coralline algae fossils foraminiferal and palynological species indicate deposition during early miocene time however the lower miocene marine interval lies in angular unconformity above 150 m of bakhtiyari conglomerate that in turn unconformably caps an oligocene marine sequence these relationships attest to syndepositional deformation and suggest that the oldest bakhtiyari conglomerate could be oligocene in age the new age information constrains the timing of initial foreland basin development and proximal bakhtiyari deposition in the zagros hinterland these findings reveal that structural evolution of the high zagros was underway by early miocene and probably oligocene time earlier than commonly envisioned the age of the bakhtiyari formation in the high zagros contrasts significantly with the pliocene quaternary bakhtiyari deposits near the modern deformation front suggesting a long term 20 myr advance of deformation toward the foreland

geometric and numerical model of progressive limb rotation in detachment folds a simple area balanced geometric model of progressive limb rotation in detachment folds allows the quantification of displacement uplift and rotation and the assessment of their effect upon growth strata geometries translation of this geometric model into a velocity model of deformation allows the modeling of associated growth strata resulting from background sedimentation and local erosion transport and deposition we show that with constant displacement and sedimentation rate this model predicts a progressive unconformity indicating the onlap and eventual overlap of the fold limb caused by a decreasing uplift rate this decrease is a consequence of the kinematics of progressive limb rotation increases in displacement rate with sedimentation rate kept constant can lead to offlap and angular unconformities although subsequent onlap does not necessarily reflect a return to a lower displacement rate modeled growth strata geometries exhibit many of the features reported from the literature

texture mineralogy and rock strength in horizontal stress related coal mine roof falls abstract geologic structures can represent planes of preferential weakness that by dismembering the roof beam may contribute to the failure of roof spans however beam deflection and roof failure also occur in rocks where no visible geologic discontinuities are present this suggests that roof failure may depend on rock strength which in turn depends on intrinsic textural properties inherent to the rock in this study rock samples were collected from horizontal stress related roof fall material in coal mines for petrographic characterization and compressive strength testing brittle stress failure prone rock types include thinly interlaminated siltstone and shale and black shale that had been lightly recrystallized samples exhibit a narrow range of density values between approximately 2 5 3 0 g cm3 but exhibit a wide range of unconfined compressive strength values between approximately 20 70 mpa results of laboratory observations suggest that for samples of coal mine immediate roof shale compressive strength is not well correlated with density grain size sutured grain boundaries or quartz content these results for shale are generally at odds with the results of similar studies for sandstone the great variability of strength texture and mineralogy documented in these samples may be an indication of their complexity and the need for specialized methodology in the study of shale strength

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

progressive unconformities within an evolving foreland fold thrust belt zagros mountains a major angular unconformity between the bakhtyari conglomerates and the underlying agha jari formation has long been interpreted as indicating that orogeny in the zagros simply folded zone took place in plio pleistocene times this study uses field evidence of unconformities between older units in conjunction with geological maps and cross sections to argue that the front of the zagros simply folded zone has propagated in time and space these unconformities indicate that deformation started as early as end eocene in the northeast of the simply folded zone and propagated progressively to the southwest where unconformable contacts are only seen between younger units as shortening continued the southwest migration of the deformation front drove the foreland basin in front of it to its present position along the persian gulf and mesopotamia the climax of orogeny took place at end pliocene time when the most extensive unconformity in the zagros simply folded zone developed between the upper bakhtyari formation and older units active seismicity and documented present uplift imply that the simply folded zone is still propagating southwestward

detachment folding in the central and eastern zagros fold belt iran salt mobility multiple detachments and late basement control abstract detachment folding has been studied on the basis of field and subsurface examples from the central and eastern zagros iran we discuss different aspects of detachment folding well illustrated in the studied area in particular we focus on salt mobility multiple decollements and late basement control salt mobility concerns the hormuz basal detachment and the gachsaran upper detachment for the latter it is shown that mobility results not only from folding related diapirism but also from early gravity driven migration from growing anticlines towards intervening synclines concentric folding between two detachment levels is directly observed in the izeh zone central zagros where it is shown that the wave length depends on the distance between the two active decollements and that the fold shape is a function of the level of erosion throughout the zagros detachment folds mainly developed during an initial thin skinned phase of deformation which was followed by the current thick skinned stage this succession is particularly well expressed in the eastern zagros where basement faults cut early detachment folds obliquely

the structure and kinematics of the southeastern zagros fold thrust belt iran from thin skinned to thick skinned tectonics 1 we present the first complete balanced cross section across the southeastern zagros fold thrust belt zftb the following main structural features emerge from this section 1 in the south of the zftb the proterozoic to recent sedimentary sequence has been decoupled from its panafrican basement along the ductile basal evaporites and folded into a series of large detachment anticlines ongoing shortening of these structures has resulted in migration of the basal salt layers into the cores of the anticlines and propagation of forelimb thrusts 2 in the north of the zftb deep seated ramps have folded the hanging wall rocks and produced imbrications and duplex structures within the higher levels of the sedimentary sequence 3 out of sequence thrusts linked to major seismogenic basement faults have cut through the structures in the cover of the zftb a three step incremental restoration of the section shows that two main phases of deformation can be separated in the tectonic evolution of the zftb a mio pliocene thin skinned phase in the course of which most of the structures in the cover were generated followed by a pliocene to recent thick skinned phase expressed as out of sequence faulting in the cover which is currently underlined by the seismicity within the basement in plan view the initial structures of the southeastern zftb developed with a curved shape essentially controlled by the shape and thickness of the underlying proterozoic salt basin i e the jura style in the following basement involved phase out of sequence thrusts cut at oblique angles through the preexisting structures of the cover the total shortening absorbed in the cover amounts to at least 45 km corresponding to a ratio of 22

structural variation along the zagros and the nature of the dezful embayment structure varies along strike in the zagros fold and thrust belt of iran which is a principal element in the arabia eurasia continental collision pre collision late cretaceous ophiolite nappes kermanshah neyriz and related nappes of deep marine sediments radiolarite series were emplaced next to two regions pusht e kuh arc fars which later developed a consistent structural style across the range from the high zagros fault to the foreland limit of deformation the intervening area has a zone of highly imbricated arabian plate strata the bakhtyari culmination thrust southwest towards and over a low relief low elevation region the dezful embayment there are no ophiolite nappes northeast of the bakhtyari culmination isopachs reflect these different structural patterns from late cretaceous time but not earlier in late cretaceous time the dezful embayment recorded less deposition than adjacent areas to the northwest and southeast in the palaeogene there was little net difference between the dezful embayment and its margins the dezful embayment has been a depocentre since roughly 35 ma which is the likely time of initial collision between arabia and eurasia we propose that the syn collision structure and stratigraphy of the zagros is therefore strongly influenced by the variation in late cretaceous ophiolite emplacement but the original cause of this variation is not clear

neogene salt in sw iran and its interaction with zagros folding we present and use seismic images to constrain possible scenarios for the evolution of the middle miocene gachsaran formation in the central iranian zagros during the neogene folding this evaporitic sequence plays an important role in sealing the oligocene miocene asmari reservoirs in the dezful embayment and offshore regions it was deposited in the flexural basin south of the mountain front fault during the progressive southwestward propagation of the zagros folding its thickness changes very rapidly from several hundred to more than 4000 m this thickness variation is related to faulting folding and flow seismic and subsurface data show that the gachsaran evaporite sequence is a major disharmonic level in the dezful embayment and shallow molassic synclines often overlie anticlinal axes at depth the lithological composition of the gachsaran formation is mainly a combination of salt shale and anhydrite which have a high interval velocity contrast anomalous velocity behaviours of these sedimentary units after deformation affect the seismic quality of the surrounding area especially the southern flank of the main anticline structures