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

detachment folding in the southwestern tian shan tarim foreland china shortening estimates and rates abstract geologic observations of the chinese tian shan foreland reveal active contractional deformation along the entire margin to quantify the amount of shortening and understand the structural style we mapped the stratigraphy and structure of four folds expressed at the western end of the foreland north of kashi in this region upper tertiary through quaternary sediments are conformable but an abrupt transition from parallel to unconformable bedding in the uppermost strata suggests a transition from pre fold strata to strata deposited on a growing fold the folds have very steep 60 90 limbs and are box like to isoclinal suggestive of detachment folding total north south shortening across the center of the region is 9 km of which 5 7 km occurred in the kashi atushi fold system shortening estimates determined with excess area methods for individual folds decrease from a maximum of 6 8 km in the northwest to a minimum of 0 7 km in the southeast timing derived from a paleomagnetic study shows that the transition to syn folding strata occurred 1 2 ma in the middle of the study area resulting in an average shortening rate for the kashi atushi fold system of 5 mm yr if folding was coeval the shortening rate is high compared with foreland deformation east of the study area suggesting that the regional stresses or response of the foreland stratigraphy are unique to the kashi atushi fold system kinematics

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

fold patterns and multilayer rheology of the lurestan province zagros simply folded belt iran abstract anticlines of the lurestan province in the zagros fold thrust belt have been studied by integrating field based analysis with the use of high resolution satellite images and data available from the literature the distribution of folds in the southeastern lurestan province expressed in terms of axial length and wavelength distribution shows a direct link with the characteristics of the sedimentary multilayer in which the folds developed within the carbonate deposits of the late cretaceous bangestan group the transition from pelagic to neritic facies determines a threefold increase in anticline spacing and promotes the development of thrust structures in the forelimb of anticlines the oligocene miocene shahbazan asmari unit folds harmonically with the bangestan group except in the areas where the palaeogene deposits interposed between the two units exceed 1300 m of thickness in these areas the shahbazan asmari carbonates display short wavelength folds indicating a complete decoupling from the underlying folds of the bangestan group it is suggested that this decoupling occurs because the summed thickness of the incompetent units separating the two carbonate units exceeds the extension of the zone of effective contact strain of the bangestan group folds

age of synorogenic deposits and timing of folding in dezful embayment sw zagros fold belt abstract syntectonic deposits of the mesopotamian flexural basin have been dated in the lurestan and fars salients in the zagros foldbelt since the early 2000 s but not in the dezful embayment where most of the zagros foreland oil is trapped we use 237 samples collected for magnetostratigraphy to date shallow marine to fluvial alluvial pre growth and growth strata deposits along a 2700 m section in the ne flank of the jarik anticline in north dezful embayment the jarik anticline grew by a combination of compression and coeval diapirism like other structures in north dezful embayment the correlation of the local magnetostratigraphy with the geomagnetic polarity time scale indicates ages of 14 1 ma and 13 6 ma for the bases of the mishan and aghajari formations the bases of lahbari mb and bakhtyari fm are 9 0 ma and 7 0 ma the onset of growth strata in the ne flank of the jarik anticline is 12 8 ma with a duration of 5 8 myr for this anticline this study presents for the first time the age of syntectonic deposition and folding in the dezful embayment that is essential to determine burial and generation of hydrocarbons in this oil rich province

evidence for pre folding vein development in the oligo miocene asmari formation in the central zagros fold belt iran in order to understand the interplay between vein development and folding in the carbonates of the oligo miocene asmari formation one of the main hydrocarbon reservoir rocks in iran several anticlines have been investigated in the central part of the zagros folded belt combining observations of relative chronology between veins based on calcite filling phases and crosscutting abutting relationships as well as aerial satellite image interpretation on several anticlines allowed proposing a tectonic model highlighting the widespread development of veins and other extensional micro meso structures in the central zagros folded belt our data suggest that most of the veins affecting the asmari formation predated the main miocene pliocene folding episode an early regional vein set striking n50 marked the onset of collisional stress build up in the region then n150 and n20 trending vein sets were initiated in response to local extension caused by large scale flexure drape folds above n s and n140 basement faults reactivated under the regional ne compression at the onset and during miocene pliocene folding of the sedimentary cover the early formed veins were reactivated reopened and or sheared while duplexes low angle reverse faults and thrusts formed beyond regional implications this study puts emphasis on the need of carefully considering regional local vein development predating folding as well as influence of underlying basement faults in models of folded fractured reservoirs in fold thrust belts

diagenetic and thermal history of the jurassic tertiary succession of the zagros mountains in the dezful embayment sw iran constraints from fluid inclusions to constraint the diagenetic and thermal history in the mesozoic tertiary succession of the zagros fold belt a study was performed on fluid inclusions trapped in intergranular vug and fracture filling cements in jurassic to miocene outcrop samples collected along the anneh and fahliyan valleys of khuzestan province southwest iran petrographic observations showed at least two systems of fractures that postdate intergranular cementation two different types of oil filled fluid inclusions occur in the intergranular cements and in the first fracture network but they are absent in the second fracture network microthermometry of fluid inclusions was used to determine the temperature and salinity of fluids responsible for mineral precipitation within intergranular cements and calcite fillings the oldest fractures precipitation occurred from high saline fluids in a temperature range of 60 120 c depending on the stratigraphic depth the strong correlation between fluid inclusions temperature and stratigraphic depth suggests that the intergranular cementation and the first fracture filling event occurred prior to structural deformation furthermore this correlation indicates a relatively constant paleogeothermal gradient at the time of cement precipitation of about 28 c km on the contrary fluid inclusions trapped in cements within the second fracture network lack oil and contain freshwater trapped at low temperatures that do not correlate to the stratigraphic position this suggests second fracturing event occurred after oil migration and during or after deformation of the zagros fold belt when the samples were in a near surface position

mountain ranges favour vigorous atlantic meridional overturning 1 we use a global ocean atmosphere general circulation model oagcm to show that the major mountain ranges of the world have a significant role in maintenance of the atlantic meridional overturning circulation amoc a simulation with mountains has a maximum amoc of 18 sv 1 sv 106 m3 s 1 compared with 0 sv for a simulation without mountains atlantic heat transport at 25 n is 1 1 pw with mountains compared to 0 2 pw without the difference in amoc is due to major changes in surface heat and freshwater fw fluxes over the atlantic in the pacific changed surface fluxes lead to a meridional overturning circulation of 10 sv our results suggest that the effects of mountains on the large scale atmospheric circulation is to force the ocean towards a state with a vigorous amoc and with no overturning in the pacific

cretaceous sequence of deformation in the se zagros fold thrust belt several major zones across the zagros fold thrust belt have been interpreted as indicating that orogeny took place progressively from ne to sw through discrete orogenic episodes during tertiary time this paper uses field evidence of growth onlaps and angular unconformities within the cretaceous stratigraphic column as well as existing geological maps and cross sections to indicate that deformation started as early as the late aptian and folded the whole width of the zagros belt simultaneously later events are indicated by folding at the end of the cenomanian and in the late turonian and santonian following the late cretaceous deformation phases the se zagros basin was divided into several longitudinal intra shelf basins which were separated by nw se trending cretaceous anticlines however with reference to our previous work it can be suggested that each of the sub basins was folded serially from ne to sw through a series of tectonic phases during the next episode of zagros orogeny in tertiary time the change of deformation style from concomitant to serial folding during the cretaceous and tertiary respectively is attributed to the existence of the hormuz salt and shearing at the base of the former basin and its absence at the base of the tertiary intra shelf basins

experiments on simultaneous faulting and folding above a basement wrench fault abstract wrench zones commonly show en echelon patterns of folds in the stratified cover above a basement fault examples are the darien basin in panama and the inglewood fault trend in california folds are often associated with synthetic and antithetic wrench faults but the time relationships between folds and faults may not be obvious we have done experiments where simultaneous faulting and folding occur above a basement fault four experiments were performed using a simple apparatus capable of imposing localised strike slip motions this apparatus consists of two plastic plates one can be moved laterally past the other by a piston thus modelling lateral motion on a single basement fault models were properly scaled to account for gravitational forces brittle behaviour of sandstone and ductile behaviour of clay or shales in the upper crust each model is a vertical succession of silicone layers and sand layers each layer is 2 mm thick except for the basal silicone layer which is 2 4 6 or 8 mm thick in experiments 1 2 3 or 4 respectively all models were deformed at the same slip rate on the basal fault 1 cm h 1 experiments 1 2 and 3 with 8 cm total horizontal sinistral offset were designed to investigate the influence of basal silicone layer thickness on the deformation of a multilayered model experiment 4 with 20 cm of total offset was designed to investigate the influence of an increasing left lateral offset on folding and faulting with a 2 mm thick basal silicone layer experiment 1 synthetic strike slip faults appeared en echelon above the basement fault no folds were visible at the surface of the experiment but the interfaces between sand and silicone layers showed millimetric folds en echelon above the basement fault with a 4 mm thick basal silicone layer experiment 2 en echelon synthetic strike slip faults and folds appeared above the basement fault faults and folds rotated progressively anticlockwise and synclines were activated as dextral antithetic shear zones with a 6 mm thick basal silicone layer experiment 3 synthetic faults and en echelon folds appeared as before but the fold amplitude was larger than in experiment 2 an increasing left lateral offset produced anticlockwise rotation of faults and folds as before and synclines were activated as dextral antithetic shear zones in experiment 4 after 16 cm of left lateral offset the anticlockwise rotation of the folds was such that antithetic dextral shear zones became almost parallel to the basement fault and were then reactivated as synthetic sinistral shear zones

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

seismotectonics of the zagros continental collision zone and a comparison with the himalayas accurate focal depths of 16 medium to large zagros earthquakes were determined from identification of surface reflected phases by comparing observed long period p waves with synthetic seismograms all events are shallow 6 12 km and show no tendency to deepen toward the main zagros thrust geological and geophysical evidence suggests that most of these earthquakes probably occurred within the uppermost precambrian basement because the focal mechanisms of these events indicate high angle reverse faulting the events do not occur on a single detachment surface but rather reflect horizontal shortening of the basement on numerous short segmented 8 probably occurred along this detachment a comparative study of the zagros with the himalayas suggests that the active tectonics of the zagros continental collision zone and the iranian blocks arc similar to those of the himalayas and the tibetan terranes in oligocene time

late cretaceous to recent deformation related to inherited structures and subsequent compression within the persian gulf a 2d seismic case study abstract the persian gulf is part of an asymmetric foreland basin related to the zagros orogen few published studies of this basin and associated onshore areas include seismic reflection data we present a seismic stratigraphic interpretation based on marine 2d seismic data which reveals the presence of two types of compressional structures within the basin 1 faulted domes related to salt movement and the offshore trace of a nne ssw trending dextral basement fault the kazerun fault 2 long wavelength 16 km low amplitude 60 ms two way travel time folds relating to the advancing deformation front associated with the orogen thinning of age constrained stratal units across structures related to the offshore trace of the kazerun fault implies a distinct pulse of uplift on this fault during the maastrichtian the geometry of growth strata across other intra basin structures suggests a second later stage of deformation which began in the middle miocene thickening and folding of post middle miocene stratal units towards the ne i e towards the zagros orogen is interpreted to reflect rapid loading subsidence and compression related to southwestwards advance of the orogen the results of this study have implications for the interaction between pre existing structures and later compressional events both within the persian gulf and elsewhere

the diffuse transition between the zagros continental collision and the makran oceanic subduction iran microearthquake seismicity and crustal structure summary the nature of the transition between the zagros intra continental collision and the makran oceanic subduction is a matter of debate either a major fault cutting the whole lithosphere or a more progressive transition associated with a shallow gently dipping fault restricted to the crust microearthquake seismicity located around the transition between the transition zone is restricted to the west of the jaz murian depression and the jiroft fault no shallow micro earthquakes seem to be related to the nnw sse trending zendan minab palami active fault system most of the shallow seismicity is related either to the zagros mountain belt located in the west or to the ns trending sabzevaran jiroft fault system located in the north the depth of microearthquakes increases northeastwards to an unusually deep value for the zagros of 40 km two dominant types of focal mechanisms are observed in this region low angle thrust faulting mostly restricted to the lower crust and strike slip at shallow depths both consistent with ns shortening the 3 d inversion of p traveltimes suggests a high velocity body dipping northeastwards to a depth of 25 km this high velocity body probably related to the lower crust is associated with the deepest earthquakes showing reverse faulting we propose that the transition between the zagros collision and the makran subduction is not a sharp lithospheric scale transform fault associated with the zendan minab palami fault system instead it is a progressive transition located in the lower crust the oblique collision results in partial partitioning between strike slip and shortening components within the shallow brittle crust because of the weakness of the pre existing zendan minab palami faults

the origin of changes in structural style across the bandar abbas syntaxis se zagros iran abstract the bandar abbas syntaxis marks the transition between the zagros collisional belt and the makran subduction related prism and constitutes a major structural feature within the alpine himalayan mountain belt within the foreland part of the zagros the zagros fold thrust belt zftb the transition is marked by a sudden change in structural trends and style and a rapid decrease in seismicity and salt diapirism from west to east of the syntaxis the depth to decollement and lithology affect the geometry and size of the folds on each side of the syntaxis while different mechanical coupling along the basal decollement affects the degree of internal rock deformation thus the short and broad folds of the western side of the syntaxis are decoupled along the 8 km deep hormuz evaporites visible at surface in numerous salt diapirs strong seismicity in this area suggests that the basement is involved in the deformation by contrast the long and narrow folds of the eastern side of the syntaxis appear to be controlled by frictional slip along a 6 km deep detachment the absence of seismicity suggests that the basement is not involved in the deformation in this area we propose that the basal decollement for these structures corresponds to the eroded top of the nne ssw trending oman mesozoic nappes resulting from late cretaceous obduction of tethys on the arabian margin these structures are visible onshore in the northern tip of the oman peninsula and seen in offshore seismic profiles continuing northward beneath the strait of hormuz finally map view observations show that the main zagros thrust and the zendan fault separating the zftb from the internal zones of the orogen are shallow low angle thrust faults rather than steeply dipping faults

control of folding and faulting on fracturing in the zagros iran the kuh e sarbalesh anticline abstract the kuh e sarbalesh anticline fars region shows a strong and poorly studied curvature in the vicinity of the kazerun transfer zone here we investigated this structure by analyzing the orientation and distribution of fractures in the oligocene early miocene asmari formation a major reservoir rock of the zagros petroleum system and paleo burial conditions far away from the kazerun fault the orientation of fractures is similar to that observed in other folds in the zagros two tensional fracture sets f1 and f2 develop respectively parallel and perpendicular to the fold axis whereas two shear fracture sets dextral f3 and sinistral f4 develop at 30 from f2 closer to the kazerun fault f1 and f2 become less abundant whereas f3 fractures do prevail f3 dextral shear fractures are associated with dextral shear zones sz3 within sz3 sets of tensional fractures f5 occur f4 shear planes are less abundant than f3 sets and are sometimes associated with sinistral shear zones sz4 within sz4 sets of tensional fractures f6 occur the frequency of f3 and sz3 structures increases from south to north suggesting a control by dextral shear along the kazerun fault average fracture spacing is around 20 cm and fracturing saturation values is larger than 0 7 at 20 km distance from the kazerun fault whilst spacing is smaller than 1 cm and saturation is as low as 0 32 typical of well developed fracture systems close to the fault highlighting a strong strain gradient from south to north the orientation of f1 and f2 fracture sets changes from south to north according to the clockwise rotation of the northern part of the fold with respect to the southern part inorganic thermal parameters derived from x ray diffraction analysis of clay minerals indicate that the asmari formation was deformed at burial depths of 3 km assuming a geothermal gradient of 20 c km we suggest that the progressive differential advancement of the thrust front produced the curved shape of the kuh e sarbalesh anticline with associated rotation of the pre early folding f1 and f2 fracture sets observed in the field consistently with a dextral shear associated with the kazerun transfer fault

formation of dome and basin structures results from scaled experiments using non linear rock analogues abstract dome and basin folds are structures with circular or slightly elongate outcrop patterns which can form during single and polyphase deformation in various tectonic settings we used power law viscous rock analogues to simulate single phase dome and basin folding of rocks undergoing dislocation creep the viscosity ratio between a single competent layer and incompetent matrix was 5 and the stress exponent of both materials was 7 the samples underwent layer parallel shortening under bulk pure constriction increasing initial layer thickness resulted in a decrease in the number of domes and basins and an increase in amplitude a arc length l wavelength and layer thickness hf samples deformed incrementally show progressive development of domes and basins until a strain of ey z 30 is attained during the dome and basin formation the layer thickened permanently while a l and increased a dominant wavelength was not attained the normalized amplitude a increased almost linearly reaching a maximum of 0 12 at ey z 30 during the last increment of shortening ey z 30 to 40 the domes and basins did not further grow but were overprinted by a second generation of non cylindrical folds most of the geometrical parameters of the previously formed domes and basins behaved stable or decreased during this phase the normalized arc length l hf of domes and basins is significantly higher than that of 2d cylindrical folds for this reason the normalized arc length can probably be used to identify domes and basins in the field even if these structures are not fully exposed in 3d

experiments on faulting in a two layer cover sequence overlying a reactivated basement fault with oblique slip abstract two series of experiments were undertaken to investigate the development of faults in a cover sequence overlying a reactivated basement fault with oblique slip the experiments represent physical models properly scaled to account for gravitational forces brittle behaviour of the upper cover and ductile behaviour of evaporites in the lower cover models were made with a coulomb layer sand overlying a newtonian ductile layer silicone putty in each series the thickness of the silicone layer was varied from each experiment to the next in all normal wrench experiments a domain of faults appeared in the brittle layer vertical offsets were mostly of normal sense but some reverse faults occurred in experiments with thick silicone layers the thicker the silicone the wider the fault domain the deformation zone was in all cases limited to the faulted domain in the reverse wrench experiments discrete reverse riedel faults appeared without a silicone layer as the silicone layer became thicker the importance of the reverse faults diminished with the thickest layer of silicone 3 cm no faults appeared in the overburden but a monoclinal flexure accommodated the dip slip component in the presence of silicone the deformation zone was not limited to a faulted domain and the strike slip component was accommodated by a bulk shearing of the overburden in the uplifted compartment these experiments demonstrate that in basins deformed in oblique slip mode any deformation that is localized along discrete faults at the basement level becomes distributed over a much wider zone of overburden when this overlies an interval of evaporites

structural styles in the zagros simple folded zone iran arabia eurasia convergence is achieved in the nw zagros by a combination of shortening on nw se trending folds and thrusts mainly in the simple folded zone and by right lateral strike slip on the nw se trending main recent fault a balanced and restored cross section across this part of the range indicates c 49 km of shortening this probably occurred since c 5 ma providing an estimate of the long term shortening rate across the simple folded zone of c 10 mm a 1 the geometries of exposed structures suggest both basement thrusts and thin skinned decollement levels with major folds possibly nucleated above basement faults fold geometries indicate several decollement horizons shale units are candidates as well as evaporites in the neogene mesozoic lower palaeozoic and upper proterozoic successions the se part of the simple folded zone deforms by north south shortening on broadly east west trending folds and thrusts the link between these regions occurs via a set of fault blocks c 400 km wide in total each bounded by north south right lateral faults incremental changes in the strike of some of the folds occur across these right lateral faults with more east west orientations to the east

experiments on fault reactivation in strike slip mode abstract experiments were undertaken to investigate how faults reverse or normal in a cover sequence become reactivated when an underlying basement fault is itself reactivated in strike slip mode physical models properly scaled for gravity were deformed in a large 2 1 5 m apparatus divided into two halves one half can be moved laterally or vertically past the other models were constructed with a coulomb layer sand overlying a newtonian ductile layer silicone three different configurations of the basement fault reverse normal or vertical defined three series of experiments each consisted of 1 brittle model 6 cm of sand and 2 brittle ductile models 5 cm of sand overlying 1 cm of silicone or 4 cm of sand overlying 2 cm of silicone each model was deformed in two steps 1 a pure dip slip stage and 2 a reactivation in pure strike slip mode in surface views little reactivation was observed but in all cases the deformation imposed during the strike slip episode was localized by pre existing dip slip structures in cross sections however faults were seen reactivated at depth on the basis of these experiments we suggest that 1 a previously faulted zone can control the deformation of a strike slip zone and 2 reactivation of faults in strike slip mode can occur at depth without being visible at the surface we attribute the higher probability of reactivation at depth to the mechanical properties of the sand especially cohesion

modelling approaches to understanding fold development implications for hydrocarbon reservoirs a mechanics based approach to the evolution of buckle folds is proposed existing analytic and simple numerical models are used to demonstrate that dramatic changes in layer parallel stress occur in developing folds and that the bulk effective rheology of folding rocks is strongly reduced in relation to neighbouring rocks with no folds a methodology for estimating regions of folds more or less likely to suffer fracture is set out in this methodology a simple abstraction of the natural fold is identified and the stress history during its development is calculated using linear viscosity as a proxy for competence this simple and computationally cheap approach allows all salient features of natural multilayer folds to be recreated in numerical experiments the final step in the method is to use the stress conditions for three types of fracture failure tensile failure dilatant shear failure and grain crushing to define potential functions that indicate increased or decreased probability of failure results give predictions that agree well with observation in the simple cases studied a novel method for approximating three dimensional deformations is used to model the propagation of folds in the axial direction and it is found that this occurs rapidly and allows constructive and destructive interference of propagating folds below a certain amplitude this provides a means by which perturbations may interact over a certain distance such a mechanism was an implicit requisite of classic fold theories but its identity has been obscure for three decades it is shown that many small perturbations are needed to give patches of coherent folds and that few large perturbations give single arc folds

modeling the flexural evolution of the amiran and mesopotamian foreland basins of nw zagros iran iraq the evolution of the amiran and mesopotamian flexural basins of the zagros belt is approached by coupled 2 d forward modeling of orogenic wedge formation lithospheric flexural isostasy and stream power erosion transport sedimentation thrust geometries and sequence of emplacement derived from geometric and kinematic models presented here are the inputs to our evolutionary model constrained by basin geometry sediment volume and topography modeling results confirm that the zagros flexural basins evolution is consistent with two stages of deformation 1 the obduction stage involving the kermanshah accretionary complex and a basement unit and 2 the collision stage emplacing the gaveh rud and sanandaj sirjan domains in the hinterland and forming a basement duplex in the outer part results provide quantitative insights into processes involved in mountain and basin building the lithospheric equivalent elastic thickness te changed from 20 km during the amiran stage 90 50 ma to 55 km during the mesopotamian subsidence stage last 20 myr the amiran basin results from flexure of the arabian plate below the load of the kermanshah cover and basement thrust sheets during this stage material eroded in the inner parts was enough to fill the flexural trough the mesopotamian basin formed in front of the outermost basement units flexing the arabian plate during this latter stage material eroded from the orogenic wedge was not enough to fill the mesopotamian basin an additional longitudinal sediment supply of up to 200 m myr is required to fill the flexural basin

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

the relationship between cadmium and phosphate in the atlantic ocean unravelled abstract cadmium cd is not generally considered a nutrient element but behaves like a nutrient in the oceans and might play an important role in ocean biology after all the relationship between cd and the nutrient phosphate po4 has been studied for over 40 yrs but the debate on the driving mechanism and reason behind the kink a change in the steepness of the slope is ongoing using new data of high accuracy and spatial resolution covering the west atlantic ocean from north to south in combination with a robust extended optimum multiparameter eomp water mass model we show that mixing between different water masses is the dominant factor explaining the observed correlation and its kink regeneration of cd via remineralisation explains the smaller scale variability notably in the surface ocean observations imply the availability of cd in surface waters determines the cd uptake and thus the cd po4 remineralisation ratio this ratio is variable between different ocean regions notably between the northern and southern high latitude oceans due to their role in deep water formation both the northern and southern high latitude oceans are a driving factor in the atlantic and global cd and po4 relation outside the atlantic ocean the classical kink is not expected but the relationship is by no means linear most likely this is due to the interaction between low latitude surface waters and subsurface waters from high latitude origin but more data are required to assess this in detail

new magnetic fabric data and their comparison with palaeostress markers in the western fars arc zagros iran tectonic implications the zagros simply folded belt zsfb is an active fold and thrust belt resulting from the still continuing continental collision between the arabian plate and the iranian plate which probably started in the oligocene the present day shortening n25 is well documented by focal mechanisms of earthquakes and global positioning system gps surveys we propose in this study a comparison of published palaeostress markers including magnetic fabric brittle deformation and calcite twinning data in addition we describe the magnetic fabric from palaeocene carbonates 10 sites and mio pliocene clastic deposits 15 sites the magnetic fabrics are intermediate with magnetic foliation parallel to the bedding and a magnetic lineation mostly at right angles to the shortening direction this suggests that the magnetic fabric retains the record of an early layer parallel shortening lps that occurred prior to folding the record of lps allows the identification of originally oblique folds such as the mand fold which have developed in front of the kazerun fault the shape parameter of the magnetic fabric indicates a weak strain compatible with the development of detachment folds in the zsfb the palaeostress datasets covering the palaeocene to pleistocene time interval support several folding episodes accompanied by a counter clockwise rotation of the stress field direction the palaeocene carbonates in the zsfb record a n47 lps during early to middle miocene detachment folding in the high zagros belt hzb the mio pliocene clastic deposits recorded a n38 lps prior to and during detachment folding within the zsfb at the end of the miocene pliocene similarly fault slip and calcite twin data from the zsfb also support a counter clockwise rotation from ne to n20 between the pre folding stage and the late rejuvenation of folds this counter clockwise trend of palaeostress data agrees with fault slip data from the hzb during the late stage of folding in the zsfb the plio quaternary palaeostress trends are consistently parallel to the present day shortening direction

the zagros core deformation of the continental lithospheric mantle 1 the zagros of iran form one of the youngest collisional orogenic belts on earth at shallow depths shortening across the zagros is accommodated by folding in the sediments high angle thrust faulting in the basement and thickening of the lower crust but how shortening is accommodated by the lithospheric mantle has been uncertain largely because the upper mantle seismic structure has been poorly known we map the lateral variations in upper mantle shear wave speed beneath this region using a large multimode surface wave data set the upper mantle is slow for most of the middle east but a high shear wave speed lid extending to 225 km depth exists beneath the zagros we use at vs z relation to convert the shear wave speed profiles to temperature profiles and fit these with geotherms to identify the base of the lithosphere the upper mantle temperatures from the seismic model are consistent with temperatures derived from geochemical modeling the lithosphere is less than 120 km thick over the region except for a thick lithospheric root beneath the zagros implying that shortening in the mantle is accommodated by lithospheric thickening the composition of the volcanic rocks from above the area of the thickened lithosphere has depleted magma source regions with densities 60 kg m 3 less than the morb source elsewhere in the middle east the volcanic source regions have compositions and densities similar to that of morb the shortening across the zagros is accommodated by lithospheric thickening but the cool thickened lithosphere has been stabilized from delamination by depletion

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

morphometry of drainage basins and stream networks as an indicator of active fold growth gorm anticline fars province iran abstract the zagros folded belt as one of the most tectonically active areas in the world contains nw se trending whaleback anticlines that are growing vertically and laterally morphometric indices are widely used in tectonic geomorphological research because of their low cost and relative ease of application drainage basins and their networks adapt to tectonically induced changes in surface slope and hence their qualitative and quantitative analysis can reveal aspects of active anticlinal growth this study evaluates the morphometric properties of drainage basins and their networks developed on the fold limbs using this quantitative data to detect lateral propagation of the gorm anticline in the zagros simply folded belt zsfb the gorm anticline was considered to be suitable for this approach because of the variability of drainage basins and their networks along the axis of the anticline and also transversely across its forelimb and backlimb the morphometric properties of stream networks including drainage density dd drainage frequency df ratio of 1st order streams to the total number of streams of all orders n1 n length of 1st order streams l1 spacing ratio r of main streams on flanks and drainage patterns were analyzed in three zones of the anticline southeastern se central and northwestern nw also the morphometric indices of drainage basins such as basin area ba shape bs asymmetry factor af hypsometric integral hi a new proposed crescentness index ci and sinuosity of anticline divide sad were evaluated results show that an increase in n1 n ratio and l1 from the center towards both the southeastern and northwestern fold noses suggests lateral growth of the anticline towards the southeast and northwest the se and nw zones are characterized by the smaller elongated and crescent shaped basins lower elevations lower dip slopes higher hypsometric integral and lower sinuosity of anticline ridge these results collectively suggest that the southeastern and northwestern fold noses are younger less eroded and laterally growing the formation of crescent shaped basins with asymmetric forked drainages developed in the se and nw zones are considered to be useful indicators of lateral growth of the gorm anticline although higher values of ba sad df and s indexes in the central part of the fold can be attributed to the older relative age of this area the activity of the nezamabad fault and the exposure of some weak rocks also play some roles in explaining the increase the values of parameters overall the n1 n l1 ci sad indexes as well as the fan shaped and asymmetric forked drainage pattern are the most useful tectonic geomorphological criteria to detect lateral propagation of anticlines

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

a study of fold characteristics and deformation style using the evolution of the land surface zagros simply folded belt iran abstract deformation styles within a fold thrust belt can be understood in terms of the spatial organization and geometry of the fold structures in young fold thrust belts such as the zagros this geometry is reflected topographically by concordant landform morphology thus the distribution of deformation structures can be characterized using satellite image analysis digital ele vation models the drainage network and geomorphological indicators the two distinct fold types considered in this study fault bend folds and detachment folds both trending nw se interact with streams flowing ne sw from the high zagros mountains into the persian gulf multiple abandoned stream channels cross fault bend folds related to deep seated thrust faults in contrast detachment folds which propagate laterally relatively rapidly are characterized by diverted major stream channels and dendritic minor channels at the fold tips thus these two fold types can be differentiated on the basis of their ge ometry fault bend folds being long linear and asymmetrical can be distinguished from detachment folds which tend to be shorter and symmetrical and on their associated geomorphological structures the spatial organization of these structures in the zagros simply folded belt indicates that deformation is the result of the interaction of footwall collapse and the associ ated formation of long linear fault bend folds and serial folding characterized by relatively short periclinal folds footwall collapse occurs first followed by serial folding to the ne i e in the hanging wall of the fault bend folds often on higher de tachments within the sediment pile 139

neotectonics at the arabian plate margins abstract opening of the red sea is accompanied by convergence between the arabian plate and eurasia regional topography and structure favour gravity glide as the main driving force of plate translation at the leading edge of the plate the zagros mountains undergo coseismic serial folding which is equivalent to holocene shortening by 20 mm year and which has led to major episodes of coastal uplift of which the last was 1700 years bp at the jordan rift transform which bounds the arabian plate on the west a recurrence interval of 1600 years is reported for events of m l 5 5 the palaeomagnetic record for the last 3 2 ma indicates an average spreading rate for the red sea of 20 mm year there is some evidence that hydrothermal activity in the red sea is pulsatory with a period of 2000 year and that it reflects discontinuous spreading the holocene neotectonic records of the zagros the jordan rift and the red sea are the product of complex plate interactions and of the accumulation and release of strain in the crust along the plate margins but they also reflect elastic strain energy storage and release within the arabian plate whence parallels in the period of major deformation episodes in the three deforming zones and the apparent discrepancy between the seismic moment predicted by plate kinematics and that recorded in the zagros any associated intraplate deformation if detected geodetically would thus help the assessment of seismic hazard

geochemical investigation of oils from cretaceous to eocene sedimentary sequences of the abadan plain southwest iran abstract oil samples from lower cretaceous to eocene reservoirs in southwest iran were analyzed using gas chromatography mass spectrometry and gas chromatography isotope ratio mass spectrometry for genetic classification of oil families and determining their maturity the studied oil samples are non biodegraded and their gravity range from 18 3 to 37 api the slight even odd n alkane predominance coupled with low pr ph values suggests their likely source rocks with a predominance of algal organic matter type iis kerogen deposited under strongly reducing marine environments the biomarker distribution of investigated oils is characterized by high concentration of both c29 and c30 hopanes and ratios of c29 c30h are generally greater than unity there is a marked predominance of c29 regular sterane over c27 and c28 homologs in our studied oils high sterane hopane values and cross plot of the 13c sat versus 13c aro show contribution of marine organic matter medium value of gammacerane index and other salinity indices show water density stratification and high salinity conditions of the environment of deposition it can be concluded that the studied reservoirs due to their variable maturity have different api gravity and contain two oil families types a and b with latter being deeper and comprising more mature oils

characterization and impact on reservoir quality of fractures in the cretaceous qamchuqa formation zagros folded belt abstract reservoir quality in tight fractured carbonate rocks is controlled by the fracture properties the tectonic origin of fractures the relationship of fractures to other sedimentary features within the rockmass and diagenesis in this study fracture analysis porosity and permeability of the qamchuqa formation in the miran west block of the zagros folded belt in kurdistan has been studied this was undertaken using core analysis micro resistivity image logs drill stem tests dst mud logging data repeat formation test rft drilled cutting samples and wireline log data the integrated analysis shows that the qamchuqa formation is characterized by heterogeneous sedimentary and tectonic features the sedimentary features include burial stylolites dissolution seams and some fractures which formed at early stages of burial and diagenesis phase 1 open fractures partially open mineralized fractures veins and tectonic stylolites were formed by later tectonic activity phase 2 the finding of this study highlight that the fracture properties including aperture length frequency and origin play an important role in controlling the reservoir s quality the open fractures and partially open mineralized fractures enhance permeability providing an inter connected fracture network leading to a high fracture permeability that controls fluid flow in this tight carbonate reservoir rock the fracture network had little impact on the volume of hydrocarbon storage which is controlled by the pore matrix in contrast structures including stylolites dissolution seams and veins generally have a negative impact on the reservoir quality by blocking the fluid flow this work emphasizes the importance of understanding the regional geological history and the role of sedimentary and tectonic features when investigating in tight carbonate reservoirs