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

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

the impact of cover rock rheology on the style of folding in the zagros fold thrust belt abstract the present day morphology of the zagros fold thrust belt is dominated by magnificent exposures of nw se trending folds these folds differ in their size and geometry and these differences are related mainly to the rheological profile of the cover rock the cover rock succession of the zagros consists of a sequence of competent and incompetent units which vary both along and across the belt field based study combined with the use of satellite images reveals that the thickness and facies distribution of the cover rock succession has a significant impact on the style of deformation during the shortening linked to the current convergence of the arabian and iranian plates the incompetent units act as detachment horizons which localise thrusting and which act as decollement above which detachment folds form in addition where these incompetent units are thick e g 1 km they allow the deformation above and below them to become completely decoupled enabling disharmonic folding to occur as a result the folds above and below the incompetent units in the central part of the zagros folded belt have significantly different geometries and wavelengths as the zagros folds host the majority of the hydrocarbon reserves in iran and iraq an understanding of the processes that influence their geometry and spatial organization at different levels in the cover rock is crucial for the future exploration in the region

theory of melt segregation a review abstract the processes by which melt is extracted from partially molten source regions at depth are collectively known as melt segregation during the past three years a dynamical theory has been developed which provides a unified description of the mechanical thermodynamical and chemical aspects of melt segregation in this theory a partially molten region is regarded as a deformable porous medium or matrix saturated with melt migration of melt relative to the matrix can be driven either by the buoyancy of the melt or by nonhydrostatic pressure gradients associated with the deformation of the matrix this paper reviews the basic governing equations of the theory and the solutions which have been obtained during the past three years

revised pacific antarctic plate motions and geophysics of the menard fracture zone a reconnaissance survey of multibeam bathymetry and magnetic anomaly data of the menard fracture zone allows for significant refinement of plate motion history of the south pacific over the last 44 million years the right stepping menard fracture zone developed at the northern end of the pacific antarctic ridge within a propagating rift system that generated the hudson microplate and formed the conjugate henry and hudson troughs as a response to a major plate reorganization 45 million years ago two splays originally about 30 to 35 km apart narrowed gradually to a corridor of 5 to 10 km width while lineation azimuths experienced an 8 counterclockwise reorientation owing to changes in spreading direction between chrons c13o and c6c 33 to 24 million years ago we use the improved pacific antarctic plate motions to analyze the development of the southwest end of the pacific antarctic ridge owing to a 45 counterclockwise reorientation between chrons c27 and c20 61 to 44 million years ago this section of the ridge became a long transform fault connected to the macquarie triple junction following a clockwise change starting around chron c13o 33 million years ago the transform fault opened a counterclockwise change starting around chron c10y 28 millions years ago again led to a long transform fault between chrons c6c and c5y 24 to 10 million years ago a second period of clockwise reorientation starting around chron c5y 10 million years ago put the transform fault into extension forming an array of 15 en echelon transform faults and short linking spreading centers

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

the southernmost margin of the tethys realm during the mesozoic and cenozoic initial geometry and timing of the inversion processes 1 along the northern border of africa pangea breakup has been diachronic during the jurassic the alpine tethys propagated northeastward from the atlantic to the alps during the permian the neo tethys propagated westward from oman to northwestern arabia then a secondary and late branch of neo tethys gave birth to the east mediterranean basin finally the two oceans connected at end of jurassic times achieving the development of africa northern plate boundary by the late cretaceous convergence between africa and eurasia led to the progressive closure of the tethys realm the continental collision is not completely achieved and the different segments of the confrontation zone maghreb central and east mediterranean zagros and oman expose different stages of the process however we emphasize the existence of synchronous geodynamic events from one end of the system to the other although they do not have the same meaning two of them are particularly important the campanian santonian c s event corresponds to 1 obduction and exhumation of high pressure low temperature metamorphic rocks around the arabian promontory 2 inversion along the margins of the east mediterranean basins and 3 lithosphere buckling in the atlas system maghreb and adjacent sahara platform the middle late eocene mle event corresponds to 1 the onset of collision at the northern corner of arabia 2 the onset of slab retreat in the mediterranean and 3 inversion along the margin of the east mediterranean as well as in the atlas the c s event coincides with a change in plate kinematics resulting in an abrupt increase of convergence velocity the mle event coincides with a period of strong coupling between the africa and eurasia plates and an abrupt decrease of convergence velocity in the middle of the system the central mediterranean seems to escape to the effects of convergence and is the site of quite permanent extensional movements since the triassic

origin of the uinta recess sevier fold thrust belt utah influence of basin architecture on fold thrust belt geometry abstract structural trends in the sevier fold thrust belt define a pronounced concave to the foreland map view curve the uinta recess in north central utah this recess separates two convex to the foreland curves the provo salient on the south and the wyoming salient on the north the two limbs of the recess comprise transverse zones fault zones at a high angle to the regional trend of the orogen that border the flanks of the east west trending uinta cottonwood arch our structural analysis indicates that the transverse zones formed during the sevier orogeny and that they differ markedly from each other in structural style the charleston transverse zone ctz on the south side of the arch initiated as a complex sinistral strike slip fault system that defines the abrupt northern boundary of the provo salient the mount raymond transverse zone mrtz on the north side of the arch represents the region in which the southeast verging southern limb of the gently curving wyoming salient was tilted northwards during the laramide phase of uplift of the uinta cottonwood arch in effect the mrtz represents an oblique cross section through a thrust belt the contrasting architecture of these transverse zones demonstrates how pre deformation basin geometry influences the geometry of a fold thrust belt analysis of isopach maps indicates that at the time the sevier fold thrust belt formed the area just north of the present site of the uinta cottonwood arch was a basement high with a gently dipping north flank and a steeply dipping south flank thus predeformational sediment thickened abruptly to the south of the high and thickened gradually to the north of the high as illustrated by sandbox models the distance that a fold thrust belt propagates into the foreland depends on the thickness of the sedimentary layer being deformed so the shape of the salient mimics the longitudinal cross sectional shape of the sedimentary basin where basins taper gradually along strike the thrust belt curves gently but where basins taper abruptly along strike the thrust belt curves so tightly that it disarticulates and becomes bounded laterally by a strike slip accommodation zone the geometry of the uinta recess provides a field example of this concept differential movement of sevier thrusts led to formation of gradually curving thrusts on the north side of the high because of the gradual slope of the high s north flank but led to the along strike disarticulation of thrusts on the south side of the high because of the steep slope of the high s south flank in effect therefore thrust belt map view geometry provides insight into predeformational basin geometry

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

structural framework of the zagros fold thrust belt iran abstract data gleaned from the literature on the zagros have been compiled and used in conjunction with new interpretations to provide a better picture of the structures sedimentation history and deformation of this hydrocarbon rich mountain belt the belt parallel mountain front the n s trending kazerun izeh and e w trending bala rud fault zones are defined as the master structural elements of the belt these fault zones divide the zagros basin into zones with different stratigraphic successions and different rheological profiles this resulted in different structural styles developing along the belt during the subsequent collision the kazerun and izeh fault zones acted as the depositional system transition zone between the lurestan and fars regions in jurassic cretaceous time and partly controlled the distribution of the kazhdumi formation one of the major source rocks by the end of the cretaceous the nw se trending mountain front fault divided the present folded belt of the zagros into a major foreland basin to the southwest and a piggyback basin to the northeast activity along other major transfer fault zones including the izeh kazerun and bala rud fault zones occurred at this time and controlled the sedimentation and subsidence of the dezful embayment the main target region for hydrocarbon exploration these fault zones controlled the thickness of the asmari formation one of the main reservoirs and also the considerable thickness and facies changes of the gachsaran formation the major seal to the asmari formation the present morphology of the mountain belt is interpreted as being mainly related to the pinning of the mountain front fault to the northwest of the dezful embayment and to the north of the strait of hormuz

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

on the role of incompetent strata in the structural evolution of the zagros fold thrust belt dezful embayment iran abstract the dezful embayment is the most important fertile oil province of the zagros fold thrust belt it includes several incompetent strata as basal and intermediate decollement levels that play a significant role on the structural styles and hydrocarbon preservation based on the interpretation of seismic profiles the influence of the gachsaran formation and the evaporitic kalhur member of the asmari formation on the geometry of deformation was investigated in different parts of the dezful embayment obtained results revealed that the thickness of the incompetent strata plays a crucial role in the formation and geometry of different types of fold structures e g rounded box chevron detachment fold in the dezful embayment there is a sharp difference between the geometry of surface and deep seated structures due to the existence of thick intermediate decollements e g gachsaran and kalhur in the dezful embayment therefore fault geometry and fold styles in upper and lower parts of these decollements are totally different in addition these incompetent strata act as a barrier level against the propagation of deep seated faults into the overlying layers therefore it seems that most of the faults exposed on the surface have originated from the upper decollement levels in the study area

transpressional deformations within the sanandaj sirjan metamorphic belt zagros mountains iran abstract polyphase deformation structures of the sanandaj sirjan metamorphic belt in the neyriz area zagros mountains iran are consistent with dextral transpressional deformation which is related to the oblique collision between the african arabian continent and the iranian microcontinent the collision started in the late cretaceous and is continuing to the present day quantitative kinematic analyses quartz textures suggest localized shear zones deformed with a significant pure shear component spatial orientation of lineation and semi quantitative kinematic indicators indicate shear zone parallel stretching and shear zone perpendicular shortening the occurrence of a horizontal stretching component parallel to the deformation zone boundary allows a kinematic model of combined transpression and lateral extrusion for this part of the zagros orogeny

presence of a layered lithosphere beneath the zagros collision zone abstract the continental collision between the arabian and eurasian plates following the subduction of the neo tethys ocean beneath eurasia resulted in a complex deformation across the zagros mountains we used more than 700 s receiver functions obtained from 61 permanent stations to provide a detailed image of the lithospheric interaction between the eurasian and arabian plates our results suggest the existence of two different lithospheric blocks a 200 km thick lithosphere was observed beneath the zagros collision zone and most likely represents the arabian lithosphere which has been strongly deformed thickened and depleted based on our results shortening due to the collisional process is differently accommodated by the crust and mantle lithosphere of the zagros collision zone we localized the thick arabian lithosphere beneath the zagros sanandaj sirjan zone ssz and urumieh dokhtar magmatic assemblage udma whereas the crustal thickening 70 km seems to be concentrated just beneath the ssz furthermore we found a thin lithosphere of about 80 90 km that we interpret here as the iranian lithosphere beneath central iran and alborz additionally our results suggest the presence of remnants of the fossil neo tethys subduction at depths ranging between 80 and 150 km within the arabian lithosphere this dipping structure can be seen beneath the zagros ssz and udma and seems to disappear towards the northeast beneath central iran and alborz these findings may support the idea of a breakoff of the oceanic neo tethyan slab beneath central iran which results in an asthenospheric upwelling and thinning of the iranian lithosphere beneath central iran and alborz the boundary between the arabian and iranian plates seems to be located northeast of the udma in the northwest of zagros and southwest of the udma in the central zagros region

a laboratory study on capillary sealing efficiency of iranian shale and anhydrite caprocks abstract caprock has the most important role in the long term safety of formation gas storage the caprocks trap fluid accumulated beneath contribute to lateral migration of this fluid and impede its upward migration the rapid upward passage of invasive plumes due to buoyancy pressure is prevented by capillary pressure within these seal rocks in the present study two main seal rocks from the zagros basin in the southwest of iran a shale core sample of asmari formation and an anhydrite core sample of gachsaran formation were provided absolute permeabilities of shale and anhydrite cores considering the klinkenberg effect were measured as 6 09 10 18 and 0 89 10 18 m 2 respectively capillary sealing efficiency of the cores was investigated using gas breakthrough experiments to do so two distinct techniques including step by step and residual capillary pressure approaches were performed using carbon dioxide nitrogen and methane gases at temperatures of 70 and 90 c under confining pressures in the range 24 13 37 92 mpa in the first technique it was found that capillary breakthrough pressure of the cores varies in the range from 2 76 to 34 34 mpa moreover the measurements indicated that after capillary breakthrough gas effective permeabilities lie in range 1 85 10 21 1 66 10 19 m 2 in the second technique the minimum capillary displacement pressure of shale varied from 0 66 to 1 45 mpa with the maximum effective permeability around 7 76 10 21 6 69 10 20 m 2 the results indicate that anhydrite caprock of the gachsaran formation provides proper capillary sealing efficacy suitable for long term storage of the injected co 2 plumes due to its higher capillary breakthrough pressure and lower gas effective permeability

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

structural style variation and its impact on hydrocarbon traps in central fars southern zagros folded belt iran abstract the fars area is the main target for permian gas exploration in the zagros fold belt it contains approximately 15 percent of the world s proven gas reserves the geometrical characteristics of the folded structures change dramatically across the n s trending gavbandi high we used seismic profiles well data magnetic survey information and field observations to show that thickness variation of the sedimentary pile inherited from basement geometry is the main reason behind structural style variation in this area which occurred during the zagros folding differences in thickness were more significant in early middle paleozoic time and decreased considerably upward in time the total thickness of the lower paleozoic succession in the eastern side of the gavbandi high is approximately 40 50 thicker than on the summit of this basement high sedimentary pinch outs through cretaceous and tertiary times indicate that the activity of the basement faults decreased but did not stop the impact on hydrocarbon traps of the pre folding basin architecture and the differences in the behavior of the sedimentary cover after miocene folding is discussed and documented

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

evolution of the nourooz anticline nw persian gulf deciphered using growth strata structural inferences to constrain hydrocarbon exploration in persian offshore anticlines abstract the structural features and kinematic evolution of the nourooz anticline an oil producing structure located in the nw persian gulf are unravelled based on the interpretation of a seismic profile grid and well data construction of a 3d depth model and sequential restoration of a 2d geological section the nourooz anticline is a kilometre scale slightly asymmetrical fold that comprises pre growth and growth strata the main stratigraphic feature is an upper cretaceous unconformity the amplification of the nourooz anticline from upper cretaceous to present day probably took place by hinge migration with minor contribution of limb rotation assuming that the structure resulted from horizontal compression and maintained constant bed length the estimated average fold shortening rate is 0 002 mm a assuming that the structure resulted from horizontal shortening and the average fold uplift rate calculated is 0 019 mm a although the fold amplification rates decreased with time the anticline does not seem to be related to a detachment at depth and its growth may have been caused by motion along a basement fault that favoured movement of deep evaporite bodies underneath the anticline and buckling caused by propagation of the zagros belt deformation into the foreland basin the processes involved in the formation of this anticline coincide with those documented for an adjacent structure and seem to be the main processes that controlled the structural style in the persian gulf basin

impact of the late triassic dashtak intermediate detachment horizon on anticline geometry in the central frontal fars se zagros fold belt iran abstract integration of 2 d seismic lines well data and field studies allow us to determine the geometry variations of anticlines in the highly prolific central frontal fars region in the se zagros fold belt these variations are directly related to changes in thickness of the principal evaporitic intermediate detachment level located along the late triassic dashtak formation anticlines of short wavelength contain a significant over thickening of the evaporitic detachment level in their crestal domain that may reach 1900 m from an original thickness of 550 800 m folds containing thick dashtak evaporites show decoupling across the detachment level and thus a shift of the anticline crest in the underlying permo triassic carbonates of the dehram group which form the major gas reservoir in the central frontal fars four main parameters control the extent and distribution of the decoupled anticlines in the study area a original large thickness of the late triassic evaporitic basin b coinciding larger amounts of anhydrites with increasing total thickness of formation c parallel occurrences of abnormally high fluid pressures and d shortening variations across and along the strike of specific folds the present work relating the different parameters of the dashtak evaporites with the anticline geometry allows a better understanding of the fold geometry variations with depth which is applicable to oil and gas exploration in the se zagros and other similar hydrocarbon provinces characterised by intermediate detachment horizons

influence of synkinematic sedimentation in a thrust system with two decollement levels analogue modelling abstract compressive systems in foreland domains are characterised by fold and thrust belts linked to the presence of one or several ductile layers in depth acting as a decollement level the main parameters controlling the structural evolution are the presence of a decollement level the amount and rate of shortening and the amount of synkinematic sedimentation the effect of these parameters has only been studied on a thrust belt scale furthermore only the effect of synkinematic sedimentation on a simple system with one decollement level has been studied at the scale of a single structure the aim of this study was to use analogue modelling to test the effect of shortening rate velocity and the localization of sedimentation on a single system characterised by the presence of two prekinematic decollement levels the main results showed variations in the structural vergence folding geometry symmetric or asymmetric the evolution of the deformation horizontal propagation versus vertical uplift and the decoupling of the lower and upper brittle structures in relation with the main parameters shortening rate and mass transfer the results of the experiments were then compared to natural examples from the sub andean thrust belt

geochemical investigation oil oil and oil source rock correlation in the dezful embayment marun oilfield zagros iran the authors wish to thank m l bordenave for many fruitful discussions critical and helpful comments and reviewing an earlier draft of manuscript we also wish to thank hormoz ghalavand national iranian oil company for providing the oil samples and support provided by shahid beheshti university tehran chamran university ahwaz the work depended on support provided by technical staff at the university of aberdeen u k and kharazmi university the work was much improved by reviews and comments provided by anonymous reviewers

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

thrust wedges with decollement levels and syntectonic erosion a view from analog models abstract analog sandbox models have been set up to study the impact of syntectonic erosion on thrust wedges with one and two decollement levels different accretion mechanisms are activated depending on interactions between surface processes and wedge mechanics frontal accretion backthrusting underthrusting and underplating due to decollement induced duplex formation at depth these mechanisms may function simultaneously being located at different parts across the wedge for all the experiments a high friction is imposed at the base of models and the volume of eroded material remains equal to the volume of newly accreted material maintaining a constant surface slope during the shortening erosion limits the forward propagation of thrust wedges and favors the underthrusting of basal layers allowing duplex formation erosion promotes development of major backthrusts in the thrust wedges without or with one decollement but no backthrusts was formed in the wedges with two decollements slow erosion allows lower extent of basal underthrusting in comparison with regular rate erosion variations in the erosion taper lead to changes in duplex geometry and exhumation rate in thrust wedges with one or two decollements the 6 erosion taper promotes formation of antiformal stack at the rear part of thrust wedge high rate of basal underthrusting and high extent of erosional removal the cover layers are nearly completely eroded above the antiformal stack and form the synformal klippe in frontal part of thrust wedges the 8 erosion taper allows development of individual ramp anticlines and active forward thrusting of cover layers above the decollement and low rate of basal underplating below it with consequent low extent of erosional removal the results of our experiments support the observations on structural evolution and erosion in the alberta foothills of the canadian rockies

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

tectono sedimentary framework of the gachsaran formation in the zagros foreland basin abstract continental collision between iranian and arabian plates resulted in the formation of the zagros fold thrust belt and its associated foreland basin during convergence pre existing faults in the basement were reactivated and the sedimentary cover was shortened above two different types of basal decollement viscous frictional this led to heterogeneous deformation which segmented not only the zagros fold thrust belt but also its foreland basin into different compartments resulting in variation in facies thickness and age of the sediment infill based on this concept a new tectono sedimentary model is proposed for one of the most important syn tectonic sedimentary unit the gachsaran salt in the zagros foreland basin in this proposed model it is argued that differential propagation of the deformation front above decollements with different mechanical properties viscous versus frictional results in along strike irregularity of the zagros deformation front whereas movement along pre existing basement faults leads to development of barriers across the zagros basin the irregularity of the deformation front and the cross basin barriers divided the zagros foreland basin into six almost alternating sub basins where gachsaran salt and its non salt equivalents are deposited in the salt sub basins two different processes were responsible for the deposition of gachsaran salt 1 evaporation and 2 dissolution of extruding hormuz salt and its re precipitation as gachsaran salt re precipitation was probably the most significant process responsible for the huge deposit of gachsaran salt in the extreme south east part of the zagros foreland basin

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

mechanical stratigraphy and folding style of the lurestan region in the zagros fold thrust belt iran abstract the structural style of the folds from the central part of the lurestan salient located in the nw portion of the zagros fold thrust belt has been studied by constructing a regional balanced cross section from field data existing geological maps seismic profiles stratigraphic surface sections and well data the regional balanced structural cross section that is constructed from the high zagros fault to the mountain front fault highlights the difference in the folding style across the area the vertical and lateral changes in the style of the folding indicate the influence of mechano stratigraphic contrast between the sedimentary units three main decollement levels the basal lower palaeozoic the intermediate triassic and the upper upper cretaceous lower palaeocene have been interpreted folds developed during the zagros fold thrust belt evolution above and below these decollement horizons are decoupled from each other and are different in both geometry and size similarly thickness and facies changes of some formations across the region cause lateral variation in folding pattern from the north to the south polyharmonic folds exist in the south where the different structural levels are relatively strongly coupled to the north however strongly disharmonic folding occurs where a combination of increased decollement thickness and decreased mechanical competence has led to decoupling at different structural levels this change in folding style has a direct impact on hydrocarbon exploration in the area to reduce structural risk in exploration the incorporation of high resolution deep seismic data with the surface geology is recommended for future hydrocarbon exploration activities within the lurestan region

fold interaction and wavelength selection in 3d models of multilayer detachment folding abstract many fold and thrust belts are dominated by folding and exhibit a fairly regular fold spacing yet in map view the aspect ratio of doubly plunging anticlines varies considerably from very elongated and sometimes slightly curved cylindrical folds to nearly circular dome like structures in addition the fold spacing often varies significantly around an average value so far it remains unclear whether these features are consistent with a folding instability therefore we here study the dynamics of multilayer detachment folding process by which shortening can be accommodated in thin skinned fold and thrust belts we start by analysing the physics of this process by using both a semi analytical thick plate theory and numerical simulations results show that several different folding modes occur about half of which are affected by gravity and have a wavelength that depends on the background deformation rate non dimensional expressions are derived that predict the dominant wavelength and growth rate of each of these folding modes and mechanical phase diagrams are presented that illustrate the applicability of each of the modes next we perform 3d simulations and compare the results with those of 2d models and analytical theory both 2d and 3d numerical simulations have wavelengths that are in good agreement with the analytical predictions in the high resolution 3d simulations the lateral growth of folds is studied in particular with respect to fold segment interactions and evolution of fold width length aspect ratio the numerical simulations show a number of similarities with the fars region of the zagros fold and thrust belt including a large range of fold aspect ratio and a normally distributed fold wavelength around a dominant one

orogenic plateau growth expansion of the turkish iranian plateau across the zagros fold and thrust belt 1 this paper shows how the turkish iranian plateau grows laterally by incrementally incorporating adjacent parts of the zagros fold and thrust belt the limit of significant seismogenic thrusting in the zagros mw 5 occurs close to the regional 1250 m elevation contour the seismicity cutoff is not a significant bedrock geology boundary elevations increase northward toward regional plateau elevations of 2 km implying that another process produced the extra elevation between the seismogenic limit of thrusting and the suture this process is a plausibly ductile thickening of the basement suggesting depth dependent strain during compression similar depth dependant crustal strain may explain why the tibetan plateau has regional elevations 1500 m greater than the elevation limit of seismogenic thrusting at its margins we estimate 68 km shortening across the zagros simply folded belt in the fars region and 120 km total shortening of the arabian plate the dezful embayment is a low strain zone in the western zagros deformation is more intense to its northeast in the bakhtyari culmination the orogenic taper across strike topographic gradient across the dezful embayment is 0 0004 and across the bakhtyari culmination 0 022 lateral plateau growth is more pronounced farther east fars where a more uniform structure has a taper of 0 010 up to elevations of 1750 m a 100 km wide region of the zagros further northeast has a taper of 0 002 and is effectively part of the turkish iranian plateau internal drainage enhances plateau development but is not a pre requisite aspects of the seismicity structure and geomorphology of the zagros do not support critical taper models for fold and thrust belts

identifying multiple detachment horizons and an evolving thrust history through cross section restoration and appraisal in the moine thrust belt nw scotland abstract many thrust systems including parts of the moine thrust belt are commonly interpreted as rather simple imbricate fans splaying from a master detachment floor thrust at depth we use field observations and geological map data to construct cross sections through the achnashellach culmination southern moine thrust belt northwest scotland to test this interpretation initially cross sections are constructed by assuming a single lower detachment line length imbalances and thrust trajectory mismatches between deformed and restored state sections indicate an invalid model significant differences in horizon lengths between two rock units are seen indicating the position of a second detachment which when incorporated into the deformed state cross section creates a valid structural model the presence of this second detachment accounts for complex geometries seen at outcrop and indicates that the achnashellach culmination is likely to have formed by the sequential activation of two detachment horizons this new structural model has been derived using an iterative workflow involving cross section construction section balancing and integration of field observations from across the study area ensuring model validity in three dimensions this workflow is applicable to other systems in general

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

modeling two sequential coaxial phases of shortening in a foreland thrust belt abstract analog sandbox models are used to simulate two sequential coaxial phases of shortening in a foreland thrust belt a sufficient hiatus is considered so that erosion and sedimentation after the first phase create an angular unconformity that is subsequently deformed the effect of variation in thickness of post erosional sediment package and presence of a weak layer at the unconformity level are analyzed during the second phase some first phase thrusts are reactivated and new thrusts are also initiated thrust reactivation results in a structure spacing that is smaller than the expected spacing for a thicker sediment package reactivation of pre existing structures prevents the weak layer from acting as an intermediate decollement an increase in thickness ratio tends to weaken reactivation of pre existing thrusts model results also show that total displacement along individual reactivated thrusts generally increases downwards across the unconformity which could be used to distinguish thrust reactivation in the field two regional examples from the northern eastern cordillera in colombia and from the variscan frontal zone in western europe respectively where multiphase coaxial shortening occurred are compared with model results both natural cases show features such as partially eroded first generation folds and truncated first generation thrusts that are indicators for two sequential phases of deformation as observed in the models

controls on the geometry of fold thrust belt salients salients convex to the foreland curves in the map traces of orogens typically involve fold thrust belts formed along the foreland margin of orogens an examination of the map view shape degree of asymmetry dimensions and structural trend line patterns i e the variation in fold trend and fault strike along the length of the belt of 20 fold thrust belt salients worldwide illustrates relationships between salient geometry and the geologic setting in which the salient formed in order to understand these relationships we used simple sandbox models to simulate the formation of three of the several types of salients specifically we examined indenter controlled salients the geometry of which reflects interaction of a fold thrust belt with a hinterland indenter basin controlled salients the geometry of which reflects lateral variations in the thickness of predeformational basin fill and detachment controlled salients the geometry of which reflects lateral variations in the strength of a detachment surface our models demonstrate that thrusts in these three types of salients initiate with a curved shape and that rocks within thrust sheets on the limbs of salients can undergo a vertical axis rotation in response to simple shear without requiring major rotation of the fault trace furthermore trend line patterns distinguish basin controlled from indenter controlled salients specifically structural trend lines in basin controlled salients converge at the end points of the curve while in indenter controlled salients they diverge at the end points of the curve the asymmetry of a salient correlates with the asymmetry of the predeformational basin and or of the indenter and with the convergence direction thus our results explain geometric characteristics of individual salients and address controversies concerning paleomagnetic data in salients they also may help prioritize petroleum exploration targets in salients foreland basin oil fields concentrate at the apex of basin controlled salients because the geologic factors that generate the salient also contribute to localizing oil fields

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

pre existing salt structures and the folding of the zagros mountains four dimensional analogue x ray tomography imagery is used to investigate the role played by pre existing salt structures during compressive deformation initially linear salt structures evolve towards more axisymmetric diapirs depending on the diapir geometry and on its thickness relative to the sedimentary column thickness the diapirs are either 1 shortened and localize sharp overturned folds for vertical pipe like diapirs or else 2 act as preferentially oriented ramps the diapir being incorporated in the fold for pillow like diapirs the ridges have a strong effect on the lateral extent and orientation of folds they disconnect the folds formed on either side of the salt wall compressional relays between ridges allow for a folded connection between both sides the zagros mountains in southern iran offer a large variety of comparable structures associated with the hormuz salt level which acts as the regional decollement most of the salt structures have been active from the early palaeozoic until the present day the firstorder critical taper is controlled by the distribution of hormuz decollement level and by its thickness at a smaller scale the fold geometry and size are locally controlled by the pre existing salt structures which are the main source of heterogeneity in the deformation