slab pull and indentation tectonics insights from 3d laboratory experiments abstract we investigate using 3d laboratory experiments how the dynamics of indentation process are affected by the evolution at depth of the oceanic and continental subductions lithospheric plates are modelled by sand silicone plates floating on glucose syrup and the density contrast between oceanic and continental lithospheric plates and asthenosphere is reproduced analogue experiments model the convergence between two lithospheric plates a small continent indenting a large continental plate we show that the surface deformation in front of the indenter and above the oceanic subduction zone depends on the behaviour of the slab below the collision zone slab break off following the subduction of the small continent favours the indentation process because it results in an increasing compression in front of the indenter and extension above the neighbouring oceanic subduction both of them being responsible for the appearance of the indenter like geometry of the plate boundary when the slab does not deform significantly at depth in contrast the closure of the oceanic domain in front of the indenter is followed by a longer period of continental subduction during which the tectonic regime within the wide continent remains quite homogeneous comparing the presented analogue experiments with the subductions both part of the arabian indenter within eurasia our results suggest that the different tectonic regime on both sides of the arabia indenter may partly result from the probable occurrence of a detachment at depth under eastern anatolia

seismotectonics of southern iran the oman line seismotectonic characteristics of the transition area between the zagros continental collision zone and the makran ocean continent convergence zone the oman line are carefully examined a northeast trending zone of earthquakes terminates the zagros belt of seismicity just west of the oman line this seismic zone extends northeastward beyond the main zagros thrust and coincides with a surface escarpment clearly visible on landsat imagery events with accurately determined depths along this seismic zone occurred in the upper 20 km of the crust and possibly show a shallow 10 northeastward dip east of the oman line the zendan minab fault system is relatively aseismic the oman line region may be characterized by underthrusting of a wedge of arabian shelf edge beneath iranian crust or by an indentation of arabia into the iranian crustal block as a promontory available seismological and geological data cannot uniquely distinguish between these two possible tectonic settings the area located to the northwest of the oman line region now a zone of continental collision appears to have been characterized by an episode of neogene subduction a well located intermediate depth earthquake occurred in this area to the northeast of the main zagros thrust on november 9 1970 it was accurately located at 107 km depth beneath a line of quaternary volcanoes its focal mechanism may indicate downdip tension with nodal planes that strike closely parallel to the trend of the zagros arc comparison of this event and other neotectonic features in this part of iran with those in other active convergent zones suggests that a descending oceanic lithosphere beneath the zagros volcanic arc may still be attached to the colliding arabian plate

evolution of the karebas fault system and adjacent folds central zagros fold and thrust belt iran role of pre existing halokinesis salt structures and minibasins and detachment levels abstract in the central part of the zagros fold and thrust belt of iran several diapirs of the latest precambrian early cambrian hormuz salt locally decorate the surface exposures of a series of n s to nnw sse trending right lateral tear fault systems the karebas fault system kbfs as one of these fault systems is associated with five salt diapirs there are also several nw se trending anticlines which are either cross cut by the fault system or terminated against it and the adjacent salt diapirs the neogene zagros folds are clearly affected by the surface expression of the karebas fault system suggesting that the fault system is coeval with or post dates the neogene deformation on the contrary halokinesis as old as at least late jurassic is documented by near diapir stratigraphic exposures indicating pre orogenic existence of the diapirs although the lack of older rock outcrops precludes tracking the pre jurassic records of diapirism the geometry of strata which flank these diapirs indicates long term pre folding salt rise driven by downbuilding of lateral minibasins and progressive draping of sedimentary layers over the flanks of the rising diapirs therefore presence of old salt structures along the young neogene tear fault system suggests an important role played by the presence of early formed salt structures in inducing later strike slip deformation along zones of preferential weakness which was prepared by the pre folding salt structures and thinner sedimentary pile overlying them salt diapirs and related changes in stratigraphic thicknesses i e minibasins also effectively grappled with the process of folding detachment folding is typically the main structural style across the area and was mainly developed above the hormuz salt as the basal decollement and partly by involvement of the intermediate detachment levels however preferential weakness and squeezing of the diapirs on one hand and greater strength of the minibasins on the other hand gave rise to further complexities of deformation during shortening such first order controls could led to perturbations at the scale of diapirs and minibasins in the stress pattern as the southwestward advancing front of the zagros deformation migrated across the stratigraphic section and the salt structures it occurred because strain is localized at the diapirs and squeezes them whereas tends to avoid folding the thick and hence stronger minibasins into anticlines in such a context the localization and the longitudinal propagation of the folds in the cover sequence could be remarkably influenced and irregular the consequence was variable fold geometries location and dimension and fold axes rotations with respect to the diapirs and minibasins

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

block rotation by strike slip faulting structural and paleomagnetic evidence geometric analysis shows that motion of sets of strike slip faults should cause block rotation otherwise the distorted fault domain would not fit with its surrounding the sense of the block rotation depends on the sense of fault slip and the spacing and orientation of the faults all of which can be obtained from structural data the predictions of the geometric model can then be independently tested by paleomagnetic measurements the model was tested in northern israel structural data reveal several domains of contemporaneous right and left lateral strike slip faults paleomagnetic measurements show that in a domain of nnw trending left lateral faults blocks rotated 23 3 8 2 clockwise and in a domain of right lateral faults blocks rotated 22 4 9 0 anticlockwise these results are in agreement with the prediction of the geometric analysis of the structure the combined results of the heterogenous deformation of the area resembles a pure shear which allows n s extension by about 1 3 in other domains rotations of 34 6 9 1 and 53 1 11 0 were found in their original orientation the left and right lateral faults intersected at angles of 60 70 enclosing the principal axis of shortening in accordance with theories of brittle failure as a result of block rotations this angle is now larger and may reach 110 the results demonstrate large block rotations in different senses in domains of strike slip faults the independent structural and paleomagnetic data can be interpreted within the framework of a simple geometric model northern israel is considered to be a good model for this efficient mechanism of intraplate deformation which is expected to occur in similar tectonic settings elsewhere

collisional model for rapid fore arc block rotations arc curvature and episodic back arc rifting in subduction settings 1 we review geophysical and geological data from 23 active and ancient plate boundaries to document a compelling spatial and temporal relationship between collision plate boundary curvature rapid tectonic rotations and the occurrence of back arc rifting our observations support a conceptual model where the change from subduction to collision causes rapid fore arc rotation when viewed in a reference frame relative to the bounding tectonic plates leading to marked plate boundary curvature our global compilation reveals that most active back arc rifts are associated with rapidly rotating fore arcs and nearby collisions thus we propose that collision and rapid fore arc rotations play a major role in the evolution and kinematics of back arc basins we conduct numerical modeling to better understand the physical processes behind these observed rapid tectonic rotations at convergent margins our results suggest that the presence of an indentor or choke point in the subduction system e g collision can generate rapid rotation of the fore arc about a nearby pole and lead to back arc rifting the rate of fore arc rotation and back arc rifting depends on the incoming indentor velocity and can be greatly enhanced by slab rollback and the presence of a low viscosity back arc where viscosity of the back arc is low fore arc rotation dominates where back arc viscosity is high the formation of strike slip faults and tectonic escape dominates our observational and model derived results illustrate that shallow crustal forces produced by the entry of buoyant features into subduction zones are a fundamental mechanism for the generation of fore arc block rotations plate boundary curvature back arc rift evolution and tectonic escape in subduction systems rollback of the subducting slab within the mantle will certainly enhance the processes we describe but it is not the only driving force

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

tertiary block rotations in the fars arc zagros iran summary the fars arc accommodates the oblique convergence between the arabic plate and the iran block many geological observations suggest block rotations from regional to local scales we present palaeomagnetic investigations in the fars arc and its eastern termination the zagrosmakran syntaxis sixty four sites have been sampled covering the palaeocene pabdeh fm to mio pliocene agha jhari fm the latest being the most sampled formation we document pre tilting components in all formations however coarse fractions of agha jhari clastics formation retain a post tilting remagnetization as a whole block rotations rarely exceed 20 in the western fars arc clockwise and counter clockwise rotations of small amplitudes are consistent with the torsions observed near the strike slip kazerun and mangarak faults in the zagros makran syntaxis counter clockwise and clockwise rotations are observed respectively in the western and eastern part this pattern is consistent with an amplification of the shape of the syntaxis between zagros and makran palaeomagnetic data support that the presentday arcuate shape of the arc is secondary we assume that most of the block rotations took place during the plio pleistocene during a blocking stage of the zagros makran syntaxis we emphasize the role of oman peninsula which plays as an indenter for the propagation of the fars thrust belt

subduction tractions and vertical axis rotations in the zagros makran transition zone se iran the 2013 may 11 mw 6 1 minab earthquake the source parameters and slip distribution of the 2013 may 11 mw 6 1 minab earthquake are studied using seismology geodesy and field observations we observe left lateral strike slip motion on a fault striking ene wsw approximately perpendicular to previously studied faults in the minab zendan palami fault zone the fault that ruptured in 2013 is one of a series of e w striking left lateral faults visible in the geology and geomorphology these accommodate a velocity field equivalent to right lateral shear on n s striking planes by clockwise rotations about vertical axes the presence of these faults can reconcile differences in estimates of fault slip rates in the western makran from gps and quaternary dating the longitudinal range of shear in the western makran is likely to be controlled by the distance over which the underthrusting arabian lithosphere deepens in the transition from continent continent collision in the zagros to oceanic subduction in the makran

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

variations in the kinematics of deformation along the zagros inclined transpression zone iran implications for defining a curved inclined transpression zone abstract the combination of inclined collision and plate boundary shape can control the nature of deformation and the sense of shear along a transpression zone the present study investigated the effects of a boundary zone with curvilinear shape along a transpression zone on the kinematics of deformation the kinematics of the zagros transpression zone varies with the orientation of the zone boundary detailed structural and microstructural studies showed sinistral sense of shear on the southeastern part of the zagros inclined transpression zone fars arc but dextral sense of shear on the northwestern part of the zone it is inferred that the both senses of shear were developed coevally under a bulk general shear regional scale deformation along a curved inclined transpression miming the shape of the fras arc of the zagros and the reentrant of the bandar abbas syntaxis the zagros transpression zone formed by inclined continental collision between the afro arabian continent and iranian microcontinent

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

the transition between makran subduction and the zagros collision recent advances in its structure and active deformation south east iran is the site of a rare case of young transition between subduction and collision we synthesized recent results in geodesy tectonics seismology and magnetism to understand the structure and kinematics of the zagros makran transition surface observations tectonics magnetism and geodesy draw a transpressive discontinuity consisting of several faults striking obliquely to the convergent plate motion whereas deeper observations seismology support a smooth transition across the fault system no lithospheric transform fault has been created even though the transition already behaves like a major boundary in terms of tectonic style seismic structure lithology and magnetism the zendan minab palami fault system consists of several faults that accommodate a transpressive tectonic regime it is the surface expression of a southward propagation of the n trending right lateral strike slip fault system of jiroft sabzevaran within each system the numerous faults will coalesce into a single lithospheric wrench fault

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

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

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

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

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

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

thick skinned and thin skinned tectonics of the zagros orogen iran constraints from structural microstructural and kinematics analyses abstract our understanding of the geological structures and kinematics of thick skinned and thin skinned tectonics during the evolution of an orogenic system is strongly related to field evidence of decollement dominated tectonics or deformation involving the entire middle and lower continental crust in this paper we compare thin skinned and thick skinned deformation of the zagros orogen from small to large scales in the foreland thin skinned region sedimentary rocks with several decollement horizons have undergone in sequence thrusting with dominant nw striking ne dipping and sw verging displacement the gneissic basement of the foreland underwent permo triassic rifting and the normal faults were reactivated as thrust or strike slip faults during subduction to collision orogenic system there is no field exposures of deformed basement windows in this external part of orogen however in the internal parts of the orogen the newly recognized hinterland fold and thrust belt and slate belt there are outcrops of gneissic basement slices mylonitic shear zones and granite gneissic flow the tutak granite gneiss dome is associated with sole thrusts therefore it contains deformed margins of both continents thus in deformation in this part of the orogen was thick skinned measurements of quartz c axis opening angles of the exhumed mylonite nappes document high temperature 642 43 and 424 31 c relationship between kinematic vorticity number wk wm 0 76 0 06 of the mylonite nappes which are related to the hinterland fold and thrust belt indicate 55 7 8 simple shear and 45 7 4 pure shear components for instantaneous 2d flow which indicate sub simple shear deformation on the more thickened side of the zagros deformed basement involved contains continuous to discontinuous shear band boudins of eclogite and slices of blue schist this provide kinematic indicators suggesting simultaneous dip slip and strike slip and shear zones accelerating inclined lateral exhumation of the high pressure metamorphic rocks of oceanic and continental crustal origin both the thin and thick skinned portions of the zagros on three major cross sections indicate the intensity of deformation in the nw and se parts of the belt that display the opposite senses of shear on the two sides we infer that both senses of shear were developed coevally under a bulk sub simple shear regional scale deformation along a curved inclined transpression study of crustal scale cross sections of the paleozoic and mesozoic sequences shows that asymmetrical to symmetrical folding an d thrusting in the central part of the zagros foreland fold and and thrust belts in the fars area are gentle in comparison with those in the se and nw of the orogen the highest intensity of deformation occurs in the rotated asymmetrical folding and thrusting near the bandar abbas syntaxis

strain rate and stress fields in the west and south lut block iran insights from the inversion of focal mechanism and geodetic data abstract the active tectonic deformation and hazardous earthquakes in the south and west of the lut block have been investigated for a long time in this study we compute the geodetic and seismic strain rates using focal mechanism data from the harvard cmt catalogue and various other sources including the published gps velocities moreover we also perform focal mechanism stress inversion fmsi to deduce a stress model for the region our study shows an expected correlation between the stress orientations seismic and geodetic strain rates our results show that the south and west of the lut block is generally exposed as a compressional strike slip tectonic regime the tectonic convergence in this area is taken up not only by motions along and across the faults but also by the rotation of those blocks which bounded by these faults the maximum amount of rotation rate is observed where there are the main right lateral strike slip fault systems such as sabzevaran gowk nayband bam kuhbanan and kahurak the orientation of the mean stress direction obtained from the fmsi results in the west and south of the lut block is approximated n19 e in this area faults are almost oblique relative to the tectonic motion direction moreover there are right lateral and left lateral shears in addition to the dip movements in different parts of the south and west of the lut block our analyses show three main categories of the stress regimes including strike slip faulting 43 2 thrust faulting 38 6 and unknown or oblique faulting 18 2 we also calculated seismic and geodetic moment rates for this area which indicate the seismic moment rate is relatively high between bam and shahdad where there are some segments of the gowk fault

contemporary tectonic stress pattern of the persian gulf basin iran abstract the contemporary crustal stress pattern is important to several aspects of earth sciences such as reservoir geomechanics neotectonic deformation and geodynamic modelling the persian gulf basin is a petroliferous region in southern iran that hosts hundreds of petroleum wells and hence the knowledge of the present day stress is critical for any exploration and production in this region in addition to geo resources this region has a great economic importance and the in situ stresses provide key insights on neotectonic and seismic hazard of the basin however there is limited in situ stress information in the persian gulf region in this study we analyse 8 km of borehole image logs in 20 wellbores in the persian gulf in order to provide a clear picture of the stress pattern in this region our wellbore stress analyses provide 35 quality ranked maximum horizontal stress orientations shmax data records in addition we compile 27 earthquake focal mechanisms in the study region from different seismic catalogues and published literature and present the first comprehensive quality ranked in situ stress map of the persian gulf basin with 62 data records which can be used as a valuable source of information for future exploration and seismic hazard assessment the resulting database suggests that the shmax azimuth in central and western persian gulf is ne sw parallel to the arabia eurasia tectonic plate convergence which demonstrate the key role of relative plate motion in the present day stress pattern of these areas however the shmax azimuth in the eastern part of the study area is nw se which is different from the central and western persian gulf the nw se shmax azimuth is consistent with other geological and geophysical observations that suggest an indentor model for musandam peninsula oman in the zagros makran syntaxis

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

active deformation in zagros makran transition zone inferred from gps measurements summary the bandar abbas strait of hormuz zone is considered as a transition between the zagros collision and the makran oceanic subduction we used gps network measurements collected in 2000 and 2002 to better understand the distribution of the deformation between the collision zone and the makran subduction analysing the gps velocities we show that transfer of the deformation is mainly accommodated along the nnw sse trending reverse right lateral zendan minab palami zmp fault system the rate is estimated to 10 3m m yr 1 near the faults assuming that the zmp fault system transfers the motion between the makran lut block and the arabian plate we estimate to 15 mm yr 1 and 6m m yr 1 respectively the dextral strike slip and shortening components of the long term transpressive displacement our geodetic measurements suggest also a 10 15 km locking depth for the zmp fault system the radial velocity pattern and the orientation of compressive strain axes around the straight of hormuz is probably the consequence of the subducting musandam promontory the n s jiroft sabzevaran js fault system prolongates southwards the dextral shear motion of the nayband gowk ng fault system at an apparent rate of 3 1 2 5 mm yr 1 the change from strong to weak coupling for underthrusting the arabian plate beneath the zagros strong and the makran weak may explain the dextral motion along the zmp js ng and neh zahedan fault systems which transfer the convergence from a broad zone in the western iran zagros tabriz fault system alborz caucasus and caspian sea surroundings to makran subduction

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

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

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

revised and synthetic apparent polar wander paths of the african eurasian north american and indian plates and true polar wander since 200 ma we have reviewed paleomagnetic data available for the eurasian african north american and indian plates over the last 200 ma selection criteria are those generally accepted with an emphasis on evidence for lack of remagnetization accurate dating and proper structural analysis this results in 23 35 51 and 2 poles for eurasia africa north america and india respectively we believe that this limited set of higher quality data is more likely to reveal key features of apparent polar wander apw paths than averaging of larger data sets involving less stringent selection criteria we propose and describe revised apw paths but more importantly we next use relative motion models to transfer all data in a common reference frame we find good agreement between transferred data when they are averaged separately for each plate in independent 20 ma windows this is a check on consistency of paleomagnetic data kinematic models and of the geocentric dipole hypothesis transferred data from all plates are averaged in 20 ma windows to generate synthetic apw paths for all plates studied these synthetic paths are in agreement with the original revised apw paths that use only data from a single plate moreover both geographic and time resolution are improved spatial confidence intervals are of the order of 5 the synthetic paths display interesting features such as a previously ill recognized apw loop for eurasia paleomagnetic and hotspot apw are next compared and a determination of true polar wander tpw is derived we find significant tpw amounting to over 20 in the last 200 ma tpw appears to be episodic with a standstill between 180 and 110 ma there is general agreement with a previous study of livermore et al 1984 the tpw standstill appears to correlate with a time of decreasing reversal frequency ending with the cretaceous long normal superchron other periods of fast tpw would seem to correspond to increasing reversal frequency however it is suggested that the major tpw hairpin at 50 ma might correspond to the collision of india with eurasia tentative correlations with core or mantle indicators can be understood as a result of couplings between the core mantle and lithosphere we believe primarily related to episodic evolution of the d layer

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

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

weak zone related seismic cycles in progressive failure leading to collapse in brittle crust until quite recently our understanding of the basic mechanical process responsible for earthquakes and faulting was not well known it can be argued that this was partly a consequence of the complex nature of fracture in crust and in part because evidence of brittle phenomena in the natural laboratory of the earth is often obliterated or obscured by other geological processes while it is well understood that the spatial and temporal complexity of earthquakes and the fault structures emerge from geometrical and material built in heterogeneities one important open question is how the shearing becomes localized into a band of intense fractures here we address these questions through a numerical approach of a tectonic plate by considering rockmass heterogeneity both in microscopic scale and in mesoscopic scale numerical simulations of the progressive failure leading to collapse under long range slow driving forces in the far field show earthquake like rupture behavior en echelon crack arrays are reproduced in the numerical simulation it is demonstrated that the underlying fracturing induced acoustic emissions or seismic events display self organized criticality from disorder to order the seismic cycles and the geometric structures of the fracture faces which are found greatly depending on the material heterogeneity especially on the macroscopic scale agree with that observed experimentally in real brittle materials it is concluded that in order to predict a main shock one must have extremely detailed knowledge on very minor features of the earth s crust far from the place where the earthquake originated if correct the model proposed here seemingly provides an explanation as to why earthquakes to date are not predicted so successfully the reason is not that we do not understand earthquake mechanisms very well but that we still know little about our earth s crust

comparisons of the kinematics and deep structures of the zagros and himalaya and of the iranian and tibetan plateaus and geodynamic implications 1 we compare the geologic histories the deep structures and the present day kinematics of deformation of the himalaya and the adjacent tibetan plateau with those of the zagros and iranian plateau to test geodynamic processes of continental collision shortly after india and arabia collided with eurasia horizontal shortening manifested itself by folding and thrust faulting of sedimentary rock detached from india s and arabia s underlying crystalline basement subsequently slip on thrust faults stacked slices of india s basement to build the himalaya on india s northern margin such faulting has not yet developed in the zagros where collision is more recent and arabia penetrates into eurasia more slowly than india does so that postcollision convergence with eurasia is less the greater elevation thicker crust and more marked heterogeneity of the upper mantle beneath the tibetan than beneath the iranian plateau also reflect a more advanced stage of development moreover while thrust or reverse faulting and crustal shortening continue on the margins of both plateaus normal faulting suggesting horizontal extension and crustal thinning occurs within tibet but not in iran hence the balance of forces that built the high tibetan plateau must have changed apparently some time since 15 ma removal of tibetan mantle lithosphere could have altered that balance if mantle lithosphere beneath the iranian plateau has been removed however the change in force balance has been too small to initiate normal faulting low seismic wave speeds in the uppermost mantle just beneath the moho of both plateaus suggest to us that lithosphere beneath both is thin consistent with late cenozoic removal of it but alternative explanations might account for these low speeds despite its apparently thin and hence presumably weak mantle lithosphere much of central iran undergoes little deformation it illustrates how a crustal block can behave rigidly not necessarily because it is strong but because deviatoric stresses can be small whereas differences between the two regions clearly depend on the amount that arabia and india have penetrated into eurasia which scales with both the dates of collision and rates of convergence we see no differences in the operative processes that depend on the present day rates of convergence

short lived reheating events in the sommartuva shear zone hosted in cold crust ar diffusion modelling constraints for the exhumation of eclogites in flakstadoy lofoten islands norway abstract the exhumation of the norwegian lofoten eclogites formed during the continental collision of laurentia and baltica is mainly due to the reactivation of shear zones during the collapse of the caledonian orogen the current cooling history temperature time t t paths for the exhumation of these rocks as determined by 40 ar 39 ar dating and geothermometry involves a protracted period of slow cooling c 1 7 c ma 1 from high t the sommartuva shear zone hosted in a palaeoproterozoic anorthosite contains retrogressed eclogite and amphibolite facies lenses and served as an open system for ar with 40 ar rich and 40 ar poor hot fluid infiltration ca rich amphiboles from amphibolites contain excess ar and are mantled by phlogopites that yield ar diffusion loss profiles with plateau ages of 413 400 ma associated with an extensional event in lofoten locally the zone was intruded in its late stage history c 333 ma by a granitoid rock crystallizing annite and muscovite previously inferred to be injected synchronously with amphibolite facies metamorphism an alternative cooling path related to the exhumation of the eclogites was determined by a combination of i 40 ar 39 ar ages in minerals that grew during different thermal events ii thermal modelling of the ar systematics in these minerals and iii exploration of the thermal effects caused by the superposition of each event on pre existing mineral phases the best fit t t path as constrained by the ar data reveals that in order to preserve ar radiogenic and excess within the minerals the ambient t must have been relatively low 300 c over 80 ma 413 333 ma likewise the associated intrusion of the granitoid and the hot fluid that percolated the shear zone and crystallized the phlogopites were likely to have been short lived c 100 25 ka and at relatively moderate t 500 c in contrast to previous thermal models where the thermal events are represented as simple inflexions in a t t curve our cold crust model incorporates short lived thermal disturbances including estimates of the magnitude of their maximum temperature and duration superimposed on protracted periods of slow cooling from high t a new proposed t t path obtained for the exhumation of this terrane indicates that the eclogites resided for 80 ma 413 333 ma at relatively cool ambient temperatures c 300 c highlighting the enormous potential of coupling geochronological data from multiple isotopic systems with thermal modelling to identify and constrain the duration of short lived events

late cenozoic partitioning of oblique plate convergence in the zagros fold and thrust belt iran the nw trending zagros fold and thrust belt is affected by two major dextral faults 1 the nw trending main recent fault that accommodates partitioning of oblique convergence at the rear of the western zagros and 2 the north trending kazerun fault located in the central zagros combined structural and fault kinematics studies and spot images analysis have shown a pliocene kinematic change accompanied by a fault pattern reorganization which has led to a modification in the accommodation of oblique convergence since the late pliocene the distributed transpressional deformation operating at the rear of the belt has become partitioned along the newly formed main recent fault this fault cuts through early pliocene nappes and transpressional structures by right laterally reactivating high angle thrusts the southeastern termination of the main recent fault connects to the northern termination of kazerun fault that consists of three fault zones that end in bent orogen parallel splay thrust faults the kazerun fault together with a series of north to nnw trending inherited basement strike slip faults define an orogen scale fan shaped fault pattern pointing toward the main recent fault kazerun fault junction this structural pattern allows slip from along the main recent fault to become distributed by transfer to the longitudinal thrust faults and folds of the zagros belt with the fan shaped fault pattern acting as a horse tail termination of the main recent fault

accommodation of arabia eurasia convergence in the zagros makran transfer zone se iran a transition between collision and subduction through a young deforming system 1 at iranian longitude the arabian plate is moving northward relative to eurasia 20 mm yr 1 according to gps to the east this relative motion is accommodated by northward subduction under the e w makran emerged accretionary prism to the west it is accommodated partly by the zagros fold and thrust belt and partly by the alborz kopet dagh deforming zones further north this work investigates the nnw striking transition zone that connects zagros and makran the minab zendan fault system satellite images and structural and geomorphic field observations show a distributed deformation pattern covering a wide domain five north to nw trending major faults were identified they exhibit evidence for late quaternary reverse right lateral slip and correspond to two distinct fault systems the western one transferring the zagros deformation to the makran prism and the eastern one northward transferring the deformation to the alborz kopet dagh tectonic study and fault slip vector analyses indicate that two distinct tectonic regimes have occurred successively since the miocene within a consistent regional ne trending compression 1 an upper miocene to pliocene tectonic regime characterized by partitioned deformation between reverse faulting and en echelon folding 2 a ne trending 1 axis transpressional regime homogeneously affecting the region since upper pliocene the change is contemporaneous with major tectonic reorganization regionally recorded therefore this study provides evidence for active deformation that is not localized but distributed across a wide zone it accommodates the convergence and transfers it from collision to subduction by transpressional tectonics without any partitioning process in the present day period

anomalous low palaeomagnetic inclinations from oligocene lower miocene red beds of the south west tien shan central asia summary we studied oligocene to lower miocene red beds from the western margins of the south west ghissar range the westernmost part of the tien shan fold belt central asia a total of 19 sites were sampled on both limbs of a gentle syncline after removal of an unstable component at 200 to 300 c the natural remanent magnetization in these red beds from 18 sites is accounted for by one characteristic component chrm which persists up to 680 c intermediate directions of the geomagnetic field were recorded at five sites after tilt correction the overall mean direction for the remaining 13 sites is d 3 i 30 k 19 95 8 9 both the reversal and the fold tests are positive haematite is found to be the main remanence carrier in these red beds the calculated mean declination fits well with the reference data besse courtillot 1991 and no rotation with respect to eurasia is detected in accord with geological data in contrast the mean inclination is about 30 shallower than expected we argue that this result is not due to large scale northward transport of the area mean inclinations showing a similar amount of shallowing were also reported from the tadzhik and fergana basins and kirghiz tien shan from various rock types thomas et al 1993 1994 and we are of the opinion that neither inclination error nor compaction could have led to such a consistent pattern the analysis of all reliable early tertiary palaeomagnetic results extracted from the global paleomagnetic data base for the northern part of the eurasian plate reveals that inclination anomalies are very common in this data set whatever the rock type the general tendency is a progressive increase in the anomaly amplitude from the atlantic ocean to central asia the size and localization of this tertiary field anomaly is comparable with the present day non dipole field anomaly this suggests that there may have been a long term standing non dipole anomaly in the tertiary earth magnetic field perhaps correlated to major features of the contemporaneous plate tectonics for example the india asia collision

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

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

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

kinematics and surface fracture pattern of the anaran basement fault zone in nw of the zagros fold thrust belt the preexisting north south trending basement faults and their reactivation played an important role during the evolution of the zagros fold thrust belt the anaran basement fault in the lurestan r

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

fracture patterns in the zagros simply folded belt fars iran constraints on early collisional tectonic history and role of basement faults pre early folding fracture patterns were recognized in several anticlines from three structural domains in the simply folded belt of the fars arc these fracture sets were characterized in terms of opening mode and relative chronology and used to reconstruct the main compressional trends related to the early zagros collisional history the palaeostress reconstructions based on these fracture sets were further refined by combination with newly collected or already available fault slip and calcite twin data as an alternative to previous models of rigid block rotations or regional stress rotation we propose that the complex pattern of pre folding fractures and the contrasting palaeostress orientations through time in the different domains investigated are related to the presence of basement faults with n s and wnw trends above which basement and cover were variably coupled during stress build up and early deformation of the arabian margin beyond regional implications this study draws attention to the need to carefully consider pre existing fractures possibly unrelated to folding to build more realistic conceptual fold fracture models

the accommodation of arabia eurasia plate convergence in iran continental convergence between arabia and eurasia is taken up by distributed deformation in iran at wavelengths large compared with the thickness of the lithosphere this deformation is best described by a continuous velocity field the only quantitative source of information on the spatial distribution of strain rates within iran is the record of earthquakes we find that we can reproduce the style of deformation observed in the seismicity by simply minimizing the rate of work in a continuous viscous medium that has to accommodate the arabia eurasia plate motion between the defined shapes of iran s rigid borders when in addition we specify central iran azerbaijan and the southern caspian basin to be relatively rigid blocks within the deforming zone then the fit to the style of the observed strain rate distribution is even better we conclude that much of the pattern of deformation in iran is predetermined by the shape of its rigid borders and by the disposition of relatively rigid blocks within it this is likely also to have been a common occurrence in older orogenic belts we confirm earlier suggestions that earthquakes between 1909 and 1992 can account for only a small part 10 20 of the total deformation required by the convergence between the arabia and eurasia plates we then show that the whole plate motion can be accommodated by a velocity field with the same orientations and relative magnitudes of principal strain rates seen in the earthquakes but with larger absolute magnitudes there is therefore no requirement that the large proportion of aseismic deformation in iran is substantially different in style orientation or distribution from that released seismically in the earthquakes

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

composite ferromagnetic fabrics magnetite greigite measured by ams and partial aarm in weakly strained sandstones from western makran iran summary we present examples of composite magnetic fabrics ams and partial aarm in five sites from the western makran accretionnary prism these rocks are weakly strained sandstones of mio pliocene age rock magnetic investigations show a large occurrence of magnetite and also some greigite at two sites partial anhysteretic remanent magnetization coercivity spectra reveal that grain size is not homogeneous suggesting several grain fractions ams foliations are close to bedding except at one greigite bearing site where ams foliation is almost perpendicular to bedding soft aarm 0 50 mt foliations are slightly oblique both to bedding and ams foliation surprisingly hard aarm 50 100 mt foliations are perpendicular to bedding comparison of two limbs of one fold suggests that ams foliations are pre tilting while hardaarm foliations are post tilting corrected degree of anisotropy parameters display similar trends for all sites p 1 04 p 1 11 p hardaarm 1 19 we suggest that ams soft aarm and hard aarm reflect distinct magnetic grain populations however a possible relationship between hard aarm and a component of natural remanent magnetization is possible our study shows that two orthogonal fabrics exist in these weakly strained rocks coarse grains are parallel to bedding while fine grains are aligned perpendicular to bedding

new views on earthquake faulting in the zagros fold and thrust belt of iran the zagros fold and thrust belt is amongst the world s most seismically active mountain ranges and is influential in our understanding of continental collisions the presence of hormuz salt at the base of the 10 km thick folded sedimentary cover together with the general absence of coseismic surface rupturing have led to an assumption that earthquakes are concentrated within the basement here we reinterpret the seismicity of the zagros in light of insar studies that show some recent earthquakes ruptured the competent group of mechanically strong strata in the lower sedimentary cover local network data demonstrate that microseismicity occurs within the basement reaching depths of 20 km and in places 30 km centroid depths of larger mw 5 earthquakes are mostly 4 14 km with rare events up to 20 km and 28 km along the oman line within the simply folded belt most of these events are contained within the competent group and are limited to mw 6 5 earthquakes occur earthquakes within the competent group can account for much of the overall shortening at this level but the seismic strain rate in the basement is much lower it is unclear whether the basement deforms by aseismic creep or folding beneath the sfb or by ductile shortening beneath the high zagros or iranian plateau

surface expression of thrust faulting in eastern iran source parameters and surface deformation of the 1978 tabas and 1968 ferdows earthquake sequences summary previously unrecognised thrust faults in eastern iran were responsible for a destructive earthquake at tabas 1978 september 16 which produced over 80 km of distributed and discontinuous surface ruptures above a series of low anticlinal hills to the west of a major range front analysis of long period body wave seismograms shows a simple rupture on a gently dipping 16 thrust with a slight right lateral component this is compatible with the locally recorded aftershock distribution body wave analysis of two later smaller events show similar source orientations several indicators of long term active folding at tabas can be recognised in the geomorphology and surface ruptures from 1978 are consistent with co seismic fold growth drainage incision also indicates uplift at depth on thrust faults dipping eastwards beneath the folds body wave seismograms for two earthquakes near ferdows 150 km east of tabas in september 1968 also show thrust faulting at depths of 10 km again the surface geomorphology indicates a region of folding above an eastward dipping thrust fault which is 10 km west of a fault bounded range front in both tabas and ferdows the active faulting appears to show quaternary migration away from the range front possibly in response to stresses produced by the elevated topography the identification of zones of active fault related folding is important for earthquake hazard assessment and also for an understanding of the local tectonics we conclude that the structures which gave rise to the 1968 and 1978 earthquakes could have been recognised beforehand from the clear signals in the geomorphology had we known what to look for at that time