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

tectonics of the central zagros iran deduced from microearthquake seismicity summary microearthquakes in central zagros recorded for 7 weeks in 1997 lie in a 6 8 km zone that is likely located beneath 11 km of sediments they are not located on an active decollement between the sediments and the crystalline crust but rather define a pattern of nnw sse trending lineaments parallel to the fold axes observed at the surface the spacing between the seismic lineaments is 15 20 km and therefore different from that between the folds 10 15 km which suggests that there is not a simple relationship between the two focal mechanisms and precise relative locations are consistent with nw se striking reverse faulting connected by nnw sse striking right lateral strike slip faults the dip of the reverse faults is not certain but is likely ne for the northernmost faults the strain pattern deduced from the p axes is remarkably similar to the shortening deduced from gps based geodesy suggesting that microearthquakes are the response of the prefractured brittle crust to strain rather than localized on single active faults

in situ observation of crystal growth in a basalt melt and the development of crystal size distribution in igneous rocks to understand the solidification processes of natural magma and the texture evolution of igneous rocks we have carried out in situ observation of the crystallization of a high k basaltic melt cooling from 1 240 c in a moissanite cell in a series of experiments with different thermal history olivine or clinopyroxene cpx appeared as the liquidus phase before the formation of plagioclase during cooling at 100 c h the morphology of olivine and cpx transited from tabular to hopper habit to first order approximation crystal grow rate 2 10 9 to 7 10 9 m s for olivine and 6 10 9 to 17 10 9 m s for cpx probably limited by chemical diffusion is proportional to crystal size in one experiment dominated by olivine crystallization the good image quality allows the analysis of texture evolution over an extended period nucleation of olivine occurred only in a narrow temperature and time interval below the liquidus two dimensional length and area based crystal size distributions csds show counterclockwise rotation around axes of 8 m and 100 m2 which is consistent with the proportionate crystal growth both csds and direct observation show the dissolution of small crystals and ostwald ripening these data suggest that conventional analyses of crystal size distributions of igneous rocks may be in error the slope of the csd cannot be interpreted in terms of a uniform growth rate and the intercept with the vertical axis does not correspond to a nucleation density

salt tectonics and tear faulting in the central part of the zagros fold thrust belt iran abstract the central part of the zagros fold thrust belt is characterized by a series of right lateral and left lateral transverse tear fault systems some of them being ornamented by salt diapirs of the late precambrian early cambrian hormuz evaporitic series many deep seated extensional faults mainly along n s and few along nw se and ne sw were formed or reactivated during the late precambrian early cambrian and generated horsts and grabens the extensional faults controlled deposition distribution and thickness of the hormuz series salt walls and diapirs initiated by the early paleozoic especially along the extensional faults long term halokinesis gave rise to thin sedimentary cover above the salt diapirs and aggregated considerable volume of salt into the salt stocks they created weak zones in the sedimentary cover located approximately above the former and inactive deep seated extensional faults the n s to nne ssw direction of tectonic shortening during the neogene zagros folding was sub parallel with the strikes of the salt walls and rows of diapirs variations in thickness of the hormuz series prepared differences in the basal friction on both sides of the precambrian cambrian extensional faults which facilitated the zagros deformation front to advance faster wherever the salt layer was thicker consequently a series of tear fault systems developed along the rows of salt diapirs approximately above the precambrian cambrian extensional faults therefore the present surface expressions of the tear fault systems developed within the sedimentary cover during the zagros orogeny although the direction of the zagros shortening could also potentially reactivate the basement faults as strike slip structures subsurface data and majority of the moderate large earthquakes do not support basement involvement this suggests that the tear fault systems are detached on top of the hormuz series from the deep seated precambrian cambrian extensional faults in the basement

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

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

the speciation of carbon dioxide in silicate melts the speciation of co2 in dacite phonolite basaltic andesite and alkali silicate melt was studied by synchrotron infrared spectroscopy in diamond anvil cells to 1 000 c and more than 200 kbar upon compression to 110 kbar at room temperature a conversion of molecular co2 into a metastable carbonate species was observed for dacite and phonolite glass upon heating under high pressure molecular co2 re appeared infrared extinction coefficients of both carbonate and molecular co2 decrease with temperature this effect can be quantitatively modeled as the result of a reduced occupancy of the vibrational ground state in alkali silicate nbo t 0 98 and basaltic andesite nbo t 0 42 melt only carbonate was detected up to the highest temperatures studied for dacite nbo t 0 09 and phonolite melts nbo t 0 14 the equilibrium co2 o2 co3 2 in the melt shifts toward co2 with increasing temperature with ln k 4 57 1 68 5 05 1 44 103 t 1 for dacite melt h 42 kj mol 1 and ln k 6 13 2 41 7 82 2 41 103 t 1 for phonolite melt h 65 kj mol 1 where k is the molar ratio of carbonate over molecular co2 and t is temperature in kelvin together with published data from annealing experiments these results suggest that s and h are linear functions of nbo t based on this relationship a general model for co2 speciation in silicate melts is developed with ln k a b t where t is temperature in kelvin and a 2 69 21 38 nbo t b 1 480 38 810 nbo t the model shows that at temperatures around 1 500 c even depolymerized melts such as basalt contain appreciable amounts of molecular co2 and therefore the diffusion coefficient of co2 is only slightly dependent on composition at such high temperatures however at temperatures close to 1 000 c the model predicts a much stronger dependence of co2 solubility and speciation on melt composition in accordance with available solubility data

lithospheric structure beneath the south eastern zagros mountains iran recent slab break off integrated lithospheric modelling based on the combined interpretation of gravity geoid and topography data sets highlights a previously undocumented lithospheric thinning beneath the zagros collisional belt iran which we propose to relate to recent slab break off at the continent ocean transitional lithosphere recent published data on the distribution of seismicity at depth support this interpretation in agreement with other published models for the zagros mountains the overlying crust exhibits by contrast a noticeable thickening reaching a maximum of 52 km the consequent thermal uplift expected from slab break off is suggested to have modified the zagros wedge taper and triggered the recently documented switch from thin skinned to thick skinned deformation in the zagros fold thrust belt

the mechanical relationship between strike slip faults and salt diapirs in the zagros fold thrust belt analogue models are used to study the mechanical relationship between basement strike slip faults and salt diapirs displacement along a strike slip fault in 1 g models resulted in extension along pre existing jogs and the formation of oblique extensional faults where reactive diapirs were triggered in some models in the centrifuge models prescribed cuts simulating pre existing structures were reactivated during simple shear deformation of the models resulting in formation of pull apart basins which were intruded by diapirs the models show that because of the low ratio of salt to overburden thickness in the zagros 0 15 0 35 it is unlikely that diapirs have formed solely if at all as a result of movement along basement strike slip faults two mechanisms are suggested first pre kinematic thin overburden and continuous movement along a releasing bend in the cover units may have triggered some of the diapirs in the zagros which were later downbuilt to their current geometry by additional sedimentation second movement along the strike slip faults e g the kazerun and mangarak faults induced oblique movement along nw se zagros structures folds or thrusts resulting in the formation of pull apart basins where diapirs were eventually intruded fault plane solution of shallow earthquakes supports the second scenario which is also in agreement with previous interpretations that some of the salt diapirs associated with basement faults are younger than zagros shortening and young southwestwards

stratigraphic record of translation down ramps in a passive margin salt detachment abstract ramp syncline basins filled with synkinematic sediments record the incremental translation history and translation rates of strata transported over basement ramps on passive margins movement of strata over a stratabound salt detachment is stratigraphically recorded as an isopach thick on the seaward side of a monoclinal ramp this growth syncline gradually moves seaward down and then off the monocline as if on a conveyor belt this shift creates accommodation space for a new isopach thick to form just landward of the older one repetition of this cycle creates a shingled series of isopach thicks within the ramp syncline basin kinematic forward models and restored cross sections from the kwanza basin angola show that the stratigraphic pattern of ramp syncline basins is most influenced by three factors 1 the relative rates of translation and aggradation control the curvature of the axial trace of the growth synclines 2 bathymetric scarps above basement ramps can create spectacular seaward dipping onlap surfaces 30 km long downdip adjoining ramps generate stacked interfering onlap surfaces 3 salt diapirs or anticlines are commonly shortened at the top of the ramp especially where this coincides with the base of the continental slope diapir shortening provides a buffer to absorb sliding from its landward side and impede sliding on its seaward side this buffering can have a major control on the entire gravity spreading system containing the diapirs

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

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

evolution and timing of salt diapirism in the iranian sector of the persian gulf abstract the iranian sector of the persian gulf is affected by more than 30 large diapiric structures triggered by the mobilization of the infracambrian hormuz complex an evaporite rich unit that overlies precambrian basement at the base of the sedimentary succession nineteen non piercing diapirs without any appreciable salt intrusion into the upper succession were studied in detail and retro deformed by the decompaction and unfolding of 13 seismic horizons that were identified by the interpretation of a dense grid of 2d seismic lines and calibrated by well data salt uplift had begun by the early palaeozoic and persists to the present day with major pulses of intensity during the middle triassic cenomanian late oligocene and post middle miocene the structural reconstructions and the analysis of the progressive deformation of the study diapirs do not show any link between diapiric uplift and local tectonic structures and no clear correlation with the regional geodynamic events acting at the boundary of the arabian plate on the contrary the salt uplift seems strongly influenced by the differential rate of sedimentation that affected the whole study basin more than 40 000 km 2 with a coefficient of correlation between the salt uplift rate and the differential rate of sedimentation expressed by the standard deviation of the sedimentation rate calculated over the entire basin of 0 95 this downbuilding mechanism of diapiric growth is apparently induced by differential sedimentation over long distances several tens of kilometers showing that the flow of salt affected the whole basin and not just the areas around the single diapiric structures

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

computerized x ray tomography analysis of sandbox models examples of thin skinned thrust systems computerized x ray tomography applied to analog sandbox experiments performed in a normal gravity field makes possible the analysis of the kinematic evolution as well as the three dimensional geometry of models that simulate tectonic deformations most of the plastic or viscous analog materials generally used in a normal gravity field for such models have x ray attenuations compatible with medical scanner images models using soft cohesionless granular materials were studied faults in granular materials corresponding to dilatant zones with lower by 30 50 x ray attenuation are thus clearly visible in the tomography images kinematic analysis was done on imbricate thrust propagation in materials with an internal friction angle of 30 thrust propagation is controlled mainly by a triangular pop up structure resulting from the nucleation of two conjugate thrusts at the basal decollement the pop up structure is created immediately in front of the previous thrust three dimensional geometry analysis was tested on lateral ramps parallel to the transport direction lateral ramps were induced by changing the frictional boundary conditions at the bottom of the model though the lateral ramps strike almost parallel to the transport direction their dip angle is comparable to the dip angle of frontal ramps

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

extinction of cloudina and namacalathus at the precambrian cambrian boundary in oman biostratigraphic carbon isotope and u pb zircon geochronological data from the ara group of oman indicate an abrupt last appearance of cloudina and namacalathus coincident with a large magnitude but short lived negative excursion in the carbon isotope composition of seawater that is globally coincident with the precambrian cambrian boundary u pb zircon age data from an intercalated ash bed directly define this negative excursion to be at 542 0 0 3 ma consistent with previous age constraints from siberia and namibia combined with the global biostratigraphic record these new data strengthen hypotheses invoking mass extinction within terminal proterozoic ecosystems at or near the precambrian cambrian boundary

the influence of diapir brine on groundwater quality of surrounding aquifers larestan iran hormuz salt breaches the surface in 122 diapirs in southern iran that source brines that generally degrade the groundwater quality in adjacent aquifers the karmustadj salt diapir larestan iran is surrounded by one karstic and two alluvial aquifers we use hydrochemical and hydrogeological measurements of brine springs and exploitation wells to investigate the impact of the karmustadj salt diapir on water quality in its surrounding aquifers our study indicates that the karmustadj salt diapir does not degrade the quality of the adjacent karstic aquifer because impermeable geological formations interrupt the potential hydraulic connectivity between them by contrast the diapir does significantly degrade water quality in part of the western alluvial aquifer and all of the eastern alluvial aquifer infiltration of surface brines draining from the diapir and discharge from perennial brine springs account for the high salinity of groundwater in the surrounding aquifers

deformation and kinematic evolution of the subsurface structures zagros foreland fold and thrust belt northern dezful embayment iran the dezful embayment is located in the foreland part of the zagros fold and thrust belt structural style of folding and thrusting vary in the dezful embayment in this study balanced cross sections and subsurface data including 2d seismic profiles and wells data decoded structural style of the subsurface structures in the northern dezful embayment presence of the multiple decollement horizons is the main controlling factor of the structural style in this area the subsurface anticlines have been formed between two main decollement horizons which include the miocene gachsaran formation as upper decollement and permian dashtak evaporites and lower cretaceous garau shales as the middle decollement horizons geometry of the subsurface anticlines differs much vertically and horizontally growth strata indicate folding is started in middle miocene time in this region anticlines formed as open wide and disharmonic structures active processes in the evolution of anticlines are limb rotation and hinge migration which was resulted in increase of inhomogeneous shortening rate more shortening rate indicates more structural relief in anticlines these anticlines are formed as a detachment folds in initiation and then during their evolution converted to fault propagation fold and fault bend fold final geometric shape of these anticlines depends on the geometry of thrusts propagation that formed in the forelimb

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

3d structural modelling of the southern zagros fold and thrust belt diapiric province 3d modelling of geological structures is a key method to improve the understanding of the geological history of an area and to serve as a drive for exploration geomodelling has been performed on a large 60000 km 2 area of the zagros fold and thrust belt of iran to reconcile a vast but heterogeneous dataset topography geological surface data and dips outcrop surveys and well and seismic data were integrated into the model the method was to construct a key surface maximizing the hard data constraints the oligo miocene top asmari layer was chosen as this formation was regionally deposited before the main zagros collision phase and because the numerous outcrops allow proper control of the bed geometry in the fold cores interpreted seismic data have been integrated to interpolate the surfaces at depth within the synclines several conceptual models of fold geometry have been applied to estimate the best way to convert seismic time signal to depth several deeper horizons down to palaeozoic strata were deduced from this key horizon by applying palaeo thickness maps during the construction the 3d interpolated surfaces could be reconverted to time using a velocity model and compared with previous seismic interpretations this exercise obliged us to revise some early interpretations of seismic lines that were badly tied to wells the 3d modelling therefore clearly improves regional interpretation in addition the 3d model is the only tool that allows drawing consistent cross sections in areas where there are no seismic lines emerging hormuz salt diapirs were added to the model dimensions and shapes of the individual diapirs were modelled using a statistical survey on the cropping out hormuz structures modelling reliably demonstrated that the diapirs when piercing show a constant mushroom shape whose diameter depends on the stratigraphic depth of observation this observation allowed us to exemplify relations between the pre existing diapirs and the anticlines of the area and to highlight the morphological changes from the inner onshore areas to the coastal and offshore areas in addition one of the surprising results of this study was the observation of the increasing diameter of the diapirs at the time of the zagros collision and folding event with growth strata and overhangs on the flanks of the diapirs

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

accommodation of the different structural styles in the foreland fold and thrust belts northern dezful embayment in the zagros belt iran structural styles in the zagros foreland fold and thrust belt vary spatially differential lateral propagation of folds causes to create tear faults in this belt in this research tear faults are studied in northern dezful embayment tear faults have been accommodated the different structural styles in sedimentary cover during the compressional regime in the zagros fold and thrust belt different structural styles indicate a difference in intensity deformation these faults originated as the pre existing inverted reactive deep seated faults or which activate in the sedimentary strata during the compressional regime investigation of the structural style of folds in the sedimentary cover is a key point to recognize tear faults in this research the structural style of the kabood qale nar bala rud and lab e safid subsurface anticlines in the northern dezful embayment has been studied the interpretation of seismic profiles balanced cross sections restoration and 3d structural modeling is investigated to study the structural style of mentioned anticlines the area of the studied region is 92 20 km2 two tear faults with nne trending have been separated qale nar and bala rud anticlines in the central part from lab e safid and kabood anticlines in eastern and western parts respectively the intensity of deformation in the lab e safid anticline is less than the qale nar and bala rud anticlines on its western side displacement and deformation of the kabood anticline are more than the qale nar anticline in its eastern side kabood anticline is multi bend fault bend fold qale nar and bala rud are fault bend folds and lab e safid is detachment fold tear faults have been accommodated by these different structural styles in this region

polyphase thermal evolution in the infra cambrian ara group south oman salt basin as deduced by maturity of solid reservoir bitumen petrographic and organic geochemical analyses on solid reservoir bitumen from the late precambrian to early cambrian ara group indicate polyphase thermal evolution in the south oman salt basin sosb the ara group constitutes a complex petroleum system in the deep subsurface 3 5 km of interior oman salt diapirs encase isolated partly highly overpressured carbonate bodies intra salt stringers which represent a predominantly self charging hydrocarbon system a large number of stringer cores show that reservoir quality is decreased by the presence of solid reservoir bitumen by using different microscopy techniques this solid reservoir bitumen has been identified within pores pore throats and microfractures of the carbonates solid bitumen reflectance measurements brr were converted to vitrinite reflectance vrr using a new improved calibration vitrinite reflectance geothermometry shows that maximum paleo temperatures have a highly heterogeneous distribution paleo temperatures of 380 c were obtained from coke like solid reservoir bitumen which most likely formed from thermal cracking of oil in our model this process is related to hydrothermal fluids deriving from deeper pre salt strata of the sosb which entered the intra salt carbonate stringers during times of basement tectonic activity via hydrofractures this caused the formation of high maturities pyrobitumens in close vicinity to the fractures and precipitation of migrabitumens with increasing distance to the ht source which is supported by the geochemical composition of the solid reservoir bitumens the influx of these fluids into the carbonate stringers is considered to represent a major contribution to their strong overpressures 2007 elsevier ltd all rights reserved

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

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

the volatile content of hypabyssal kimberlite magmas some constraints from experiments on natural rock compositions kimberlites are volatile rich magmas that ascend from deep in the mantle at high velocities then as they reach a root zone at 1 3 km in depth they either discharge explosively through to the surface or stall to form dykes and sills understanding this eruptive behaviour is difficult due to a lack of data on volatile solubility particularly at conditions where the magmas enter the root zone 30 80 mpa in this study we perform experiments on some putative primary kimberlite magma compositions to assess the amount of co2 and h2o retained if these compositions represent magma as it enters the root zone at the conditions investigated 100 200 mpa and 1 275 1 100 c the results suggest that none of these particular kimberlite compositions reproduce a magma that can retain the observed high volatile content when intruded at these pressures 4 8 km in our experiments the low volatile retention is due to a combination of factors including a high proportion of solid phases none of which are volatile bearing and inadequate volatile solubilities in the subordinate amounts of melt present modelled solubilities also suggest that the dissolved volatile contents remain too low even at super liquidus temperatures i e 100 melt for water the higher values observed in natural rocks can be explained by the addition of h2o associated with ubiquitous post emplacement serpentinization the high co2 contents in hypabyssal rocks are unlikely to be related to alteration we suggest that most kimberlites originally had lower sio2 contents and as such may have been transitional between silicate and carbonate melts this results in both higher co2 solubilities and lower liquidus temperatures for such compositions it is possible that both co2 and water solubility may first decrease and then increase as magmas decompress and crystallize such unusual behaviour can help explain why kimberlite magmas can be very explosive or form shallow hypabyssal intrusions

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

zagros phantom earthquakes reassessed the interplay of seismicity and deep salt flow in the simply folded belt unraveling the contributions of main shock slip aftershocks aseismic afterslip and postseismic relaxation to the deformation observed in earthquake sequences heightens our understanding of crustal rheology triggering phenomena and seismic hazard here we revisit two recent earthquakes in the zagros mountains iran which exhibited unusual and contentious aftereffects the mw 6 earthquakes at qeshm 2005 and fin 2006 are both associated with large interferometric synthetic aperture radar insar signals consistent with slip on steep reverse faults in carbonate rocks of the middle sedimentary cover but small aftershocks detected with local seismic networks were concentrated at significantly greater depths this discrepancy can be interpreted in one of two ways either 1 there is a genuine vertical separation between main shock and aftershocks reflecting a complex stress state near the basement cover interface or 2 the aftershocks delimit the main shock slip and the insar signals were caused by shallow updip afterslip phantom earthquakes with very similar magnitudes mechanisms and geographical positions as the original earthquakes here we show that main shock centroid depths obtained from body waveform modeling which in this instance is the only method that can reveal for certain the depth at which seismic slip was centered strongly support the first interpretation at qeshm microseismic aftershock depths are centered at the level of the hormuz formation an infracambrian sequence of intercalated evaporitic and nonevaporitic sediments these aftershocks may reflect the breaking up of harder hormuz sediments and adjacent strata as the salt flows in response to main shock strain at the base of the cover this work bolsters recent suggestions that most large earthquakes in the zagros are contained within carbonate rocks in the midlower sedimentary cover and that the crystalline basement shortens mostly aseismically

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

the 2006 march 25 fin earthquakes iran insights into the vertical extents of faulting in the zagros simply folded belt summary we investigate the depth of faulting and its connection with surface folding in the zagros simply folded belt of iran our focus is a sequence of earthquakes mw 5 7 5 5 5 2 5 0 4 9 that struck the fin region in the south eastern simply folded belt on 2006 march 25 modelling ground displacements measured with radar interferometry we find that either n or s dipping model reverse faults can reproduce the observed fringe patterns despite the uncertainty in fault orientation we can constrain the vertical extents of rupture to between a top depth of 5 6 km and a bottom depth of 9 10 km consistent with the 8 km centroid depth of the largest earthquake we suggest that the faulting ruptured the thick competent group of paleozoic and mesozoic conglomerates and platform carbonates which makes up the lower part of the sedimentary cover the rupture probably terminated within the precambrian hormuz salt at its base and the cretaceous gurpi marls at its top these mechanically weak layers act as barriers to rupture separating faulting within the competent group from deformation in the layers above and below the pattern of coseismic surface uplift is centred on the common limb of the fin syncline and guniz anticline but is oblique by 20 to the trend of these open symmetric whaleback folds and also overlaps a section of the fin syncline axis these observations suggest that locally surface folding is decoupled from the underlying reverse faulting although the fin syncline and guniz anticline are symmetric structures some other nearby folds show a strong asymmetry with steep or overturned southern limbs consistent with growth above n dipping reverse faults this suggests that the simply folded belt contains a combination of forced folds and detachment folds we also investigate the distribution of locally recorded aftershocks in the weeks following the main earthquakes most of these occurred at depths of 10 30 km with a particularly high concentration of events at 20 25 km these aftershocks therefore lie within the crystalline basement rather than the sedimentary cover and are vertically separated from the main rupture this study confirms earlier suggestions that earthquakes of mw 5 6 are capable of being generated within the thick competent group of paleozoic and mesozoic sediments as well as in the basement below the hormuz salt formation

carbon dioxide speciation in silicate melts a restart abstract using infrared spectroscopy we investigated the speciation of carbon dioxide in albitic and synthetic iron free dacitic glasses after annealing the glasses below the glass transition temperature in the temperature range 673 973 k at 0 5 gpa samples were rapidly quenched under constant pressure the experiments show that the ratio of the integrated intensities of the 2350 cm 1 band due to molecular co 2 to that of the band doublet at 1700 1375 cm 1 due to co 3 2 increases with higher annealing temperatures for both glass compositions our study demonstrates that in contrast to recent suggestions the equilibrium of the co 2 species reaction co 2 o 2 co 3 2 in silicate glasses melts shifts towards molecular co 2 with increasing temperature the co 2 species concentrations and an ideal solution model were used to determine equilibrium constants for the homogeneous species reaction we derived preliminary values for the enthalpy h 0 and entropy s 0 of this reaction assuming that the species concentrations reflect those at experimental temperatures h 0 12 2 kj mol 1 and s 0 23 3 j mol 1 k 1 for albitic composition h 0 29 2 kj mol 1 and s 0 32 3 j mol 1 k 1 for dacitic composition

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

interpretation of magnetic and gravity surveys in the southern arabian gulf the strait of hormuz and the northwesternmost gulf of oman implications of pre permian basement tectonics abstract a 5 nt aeromagnetic chart and a 5 mgal bouguer gravity map of the area bounded by latitudes 25 30 27 10 n and longitudes 55 15 57 00 e in the southern arabian gulf the strait of hormuz and the entrance of the gulf of oman are collectively studied the total magnetic intensity map covering the coastal strip and the arabian side of the southern part of arabian gulf reveals three prominent anomalies of amplitudes ranging from 30 to 150 nt related to tectonically controlled igneous bodies emplaced in the deep seated pre permian basement of the arabian shield the bouguer gravity map indicates three well defined trends an effect duplicating a magnetic source in the basement a negative belt indicating an anomalous hormuz salt accumulation in the southern gulf salt basin and a continental margin gravity effect marking the transition from continental crust to the gulf of oman oceanic crust the magnetic and the gravity derived lineaments are shown to correlate with gemini interpreted strike slip basement faults in the iran s southeastern zagros fold zone

influences of surface processes on fold growth during 3 d detachment folding in order to understand the interactions between surface processes and multilayer folding systems we here present fully coupled three dimensional numerical simulations the mechanical model represents a sedimentary cover with internal weak layers detached over a much weaker basal layer representing salt or evaporites applying compression in one direction results in a series of three dimensional buckle folds of which the topographic expression consists of anticlines and synclines this topography is modified through time by mass redistribution which is achieved by a combination of fluvial and hillslope erosion as well as deposition and which can in return influence the subsequent deformation model results show that surface processes do not have a significant influence on folding patterns and aspect ratio of the folds nevertheless erosion reduces the amount of shortening required to initiate folding and increases the exhumation rates increased sedimentation in the synclines contributes to this effect by amplifying the fold growth rate by gravity the main contribution of surface processes is rather due to their ability to strongly modify the initial topography and hence the initial random noise prior to deformation if larger initial random noise is present folds amplify faster which is consistent with previous detachment folding theory variations in thickness of the sedimentary cover in one or two directions also have a significant influence on the folding pattern resulting in linear large aspect ratio folds our simulation results can be applied to folding dominated fold and thrust belt systems detached over weak basal layers such as the zagros folded belt

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

regional trends in active diapirism revealed by mountain range scale insar time series 1 we construct an orogen wide insar time series over the zagros mountains and eastern markan subduction zone in southern iran from 19 envisat tracks spanning 2003 2010 we observe active salt diapirism of the infra cambrian hormuz salt at 20 locations and identify several diapirs that are not moving all active diapirs reach the surface within the asmari limestone or older rock units while we do not observe any active diapirism occurring within younger exposures reflecting a complex vertical accumulation of the basal salt and reactivation of diapirs by erosion diapir reactivation of this sort may be a critical factor affecting the feasibility of sequestering nuclear waste and co2 in evaporite sequences over geologic time scales the distribution of active diapirism is indifferent to increases in mean elevation suggesting a relatively uniform thickness of the zagros fold belt above the basal salt with steps in topography driven by basement thickening we do not observe aseismic uplift of anticlines because rates are likely below the detection threshold of our time series this suggests that uplift is accommodated at small rates 2 3 mm yr over numerous structures instead of focused at the deformation front

origin of the hafit structure implications for timing the tertiary deformation in the northern oman mountains abstract the hafit structure belongs to a group of large scale post obduction periclines that deform the late cretaceous tertiary sediments of the oman mountains foredeep due to one sided compression from the ene the hafit structure grew as a detachment fold above a basal decollement which is probably located in the upper cretaceous lower fiqa shale its reversed vergence back thrust and the folds superposed on its limbs are explained as being caused by simple shear modification of the original structure the interpretation that the hafit structure and other foreland folds in the northern oman mountains have resulted from a zagros related late eocene miocene compressional event is at variance with the stratigraphical and sedimentological evidence from the hafit area this evidence shows that the hafit structure grew synchronously with sedimentation from just before the middle eocene until the end of the miocene whilst the related structures to the east of it were initiated at the beginning of the palaeocene with further evidence of a similar early start to the tertiary deformation emerging from other parts of the northern oman mountains it becomes necessary to push back the date of initiation of the tertiary compressional event to the palaeocene and to set it apart from the plio pleistocene zagros deformation

investigating role of the hormuz salt bodies in initiation and evolution of the strike slip faults in the fars zone of the zagros fold and thrust belt insights from seismic data and sandbox modeling the zagros belt has examples of strike slip faults affected by precursor hormuz salt bodies we attempted to examine the role of salt walls in localizing the strike slip faults using field observations seismic profiles and understandings from the sandbox modeling setting and performance of the pre hormuz features in connection to the salt tectonics are major questions the inherited topography below the salt is an important parameter which controlled the structuration of the basin the antecedent troughs provided accommodation for the thick hormuz salt differential loading above the salt helped generation of salt related structures the salt walls caused formation of elongated highs these highs were re shaped in form of strike slip faults during the zagros orogeny the intersection of the salt walls and the zagros induced deformation fronts are location of potential diapirs needless of bending points along the tear faults in contrast the underlying deep seated basement faults are hardly believed to be strike slip

phantom earthquakes and triggered aseismic creep vertical partitioning of strain during earthquake sequences in iran 1 we present evidence for significant aseismic fault slip at shallow depth above a pair of mainshock aftershock sequences in the zagros mountains of iran the two mw 5 9 earthquakes are each spanned by high quality geodetic imagery and have well recorded sequences of aftershocks that occurred beneath a salt decollement earlier studies of the geodetic data inferred that the mainshocks were located above the decollement requiring a 10 km spatial separation between aftershock cluster and earthquake centroid we find that the geodetic data simultaneously allow two slip sources of similar magnitude one within the basement collocated with aftershocks and one shallow source also equivalent to mw 6 responsible for the primary signal apparent in the geodetic imagery should this phenomenon be widespread in the zagros it would partially explain a previously noted discrepancy between observed seismic moment release in the zagros and current convergence rates between the arabian and eurasian plates

ramp flat basement structures of the zagros mountains inferred from co seismic slip and afterslip of the 2017 mw7 3 darbandikhan iran iraq earthquake abstract the november 2017 mw7 3 darbandikhan earthquake in the northern zagros mountains of iran iraq was the largest instrumentally recorded earthquake to date in this mountain belt despite extensive research in this region the nature of active faults in the arabian basement beneath the zagros mountains is largely unresolved additionally there is active debate regarding the interaction of thin and thick skin shortening of the zagros and whether these processes are accommodated seismogenically here we use interferometric synthetic aperture radar insar of co and post seismic surface displacements to document the source of the darbandikhan earthquake and the first 120 days of afterslip following the earthquake we apply a fault inversion approach that finds permissible geometries locations and slip depths as a means to image subsurface structure with remote sensing geodesy we find that the darbandikhan earthquake ruptured the shallowly dipping 14 19 mountain front fault within the arabian crystalline basement 12 22 km deep we additionally find that afterslip propagated up dip of the earthquake onto the nearly horizontal dip 1 5 basal decollement of the zagros mountains indicating that the earthquake and its initial afterslip activated a ramp flat structure we also inverted co seismic insar displacements of the january 11 2018 mandali earthquake sequence that occurred 80 km south of the darbandikhan earthquake and find that these moderate magnitude events mw5 0 5 5 ruptured the lower phanerozoic cover of the zagros together the darbandikhan and mandali sequences demonstrate that the zagros mountains actively shorten via both thin and thick skin styles and that these modes of shortening are accommodated in part by earthquakes moreover the darbandikhan earthquake and afterslip highlight the presence of seismically active low angle thrust faults beneath the zagros that were not previously recognized highlighting sources for potential future large earthquakes we compare these results to the 2015 gorkha nepal earthquake to argue that frictional characteristics of decollement govern spatial relationships between seismic and aseismic slip in ramp flat geometries

seismological evidence for crustal scale thrusting in the zagros mountain belt iran summary crustal receiver functions rfs computed from the records of 45 temporary seismological stations installed on a 620 km long profile across central zagros provide the first direct evidence for crustal thickening in this mountain belt due to a rather short 14 km average station spacing the migrated section computed from radial rfs displays the moho depth variations across the belt with good spatial resolution from the coast of the persian gulf to 25 km southwest of the main zagros thrust mzt the moho is almost horizontal with slight depth variations around 45 km crustal thickness then increases abruptly to a maximum of 70 km beneath the sanandaj sirjan metamorphic zone between 50 and 90 km northeast of the surface exposure of the mzt further northeast the moho depth decreases to 42 km beneath the urumiehdokhtar magmatic assemblage and the southern part of the central iranian microcontinent the region of thickest crust is located 75 km to the northeast of the bouguer anomaly low at 220 mgals gravity modelling shows that the measured moho depth variations can be reconciled with gravity observations by assuming that the crust of zagros underthrusts the crust of central iran along the mzt considered as a crustal scale structure this hypothesis is compatible with shortening estimates by balanced cross sections of the zagros folded belt as well as with structural and petrological studies of the metamorphic sanandaj sirjan zone

the molecular structure of melts along the carbonatite kimberlite basalt compositional joint co2and polymerisation transitional melts intermediate in composition between silicate and carbonate melts form by low degree partial melting of mantle peridotite and might be the most abundant type of melt in the asthenosphere their role in the transport of volatile elements and in metasomatic processes at the planetary scale might be significant yet they have remained largely unstudied their molecular structure has remained elusive in part because these melts are difficult to quench to glass here we use ftir raman 13c and 29si nmr spectroscopy together with first principle molecular dynamic fpmd simulations to investigate the molecular structure of transitional melts and in particular to assess the effect of co2on their structure we found that carbon in these glasses forms free ionic carbonate groups attracting cations away from their usual depolymerising role in breaking up the covalent silicate network solution of co2in these melts strongly modifies their structure resulting in a significant polymerisation of the aluminosilicate network with a decrease in nbo si of about 0 2 for every 5 mol co2dissolved this polymerisation effect is expected to influence the physical and transport properties of transitional melts an increase in viscosity is expected with increasing co2content potentially leading to melt ponding at certain levels in the mantle such as at the lithosphere asthenosphere boundary conversely an ascending and degassing transitional melt such as a kimberlite would become increasingly fluid during ascent hence potentially accelerate carbon rich transitional melts are effectively composed of two sub networks a carbonate and a silicate one leading to peculiar physical and transport properties

silicate coh melt and fluid structure their physicochemical properties and partitioning of nominally refractory oxides between melts and fluids abstract structural characterization of silicate melts and aqueous fluids equilibrated at pressures and temperatures corresponding to the earth s interior requires measurements in situ while the samples are at the pressure and temperature of interest to this end structure and structure property relations of melts and coexisting fluids in silicate coh systems have been determined at temperatures up to 1000 c and at pressures to 2 0 gpa the water component of silicate h 2 o systems shows aqueous fluids supercritical fluids and hydrous melts to comprise molecular h 2 o h 2 o 0 and oh groups bonded to si 4 and likely al 3 the abundance ratio oh h 2 o 0 is positively correlated with temperature the extent of hydrogen bonding diminishes with temperature and cannot be detected at above 450 c and 0 4 gpa its h is near 10 kj mol for water dissolved in hydrous melt as compared with 20 kj mol for pure h 2 o hydrogen bonding cannot therefore be the cause of property behavior in hydrous magmatic systems because the temperature in hydrous magmatic systems exceeds 600 c in sio 2 h 2 o fluid silicate solute comprises q 0 and q 1 species with a h of the polymerization reaction of 15 kj mol assuming no pressure effect in the q n notations the value of n indicates the number of bridging oxygen in a silicate or aluminosilicate polymeric species in chemically more complex alkali aluminosilicate systems the silicate speciation in melts in aqueous fluid and in supercritical fluids comprises the same q species but their abundance and proportions differ with the more polymerized species dominant in melt silicate water interaction in the fluids melts and supercritical fluids is described with the expression 12 q 3 13h 2 o 2 q 2 6 q 1 4 q 0 with h 400 450 kj mol the solubility of geochemically important trace elements such as for example hfse in silicate saturated aqueous fluid under deep crustal and upper mantle pressure and temperature conditions is orders of magnitude greater than in pure h 2 o at the same temperature and pressure for example the fluid melt partition coefficients for structural species such as po 4 p 2 o 7 and q n p are in the 0 15 0 7 range and increases rapidly with silica content of the fluid the fluid melt partition coefficient of tio n species in similar ti bearing systems increases from 0 1 to 0 5 in the 200 500 c and 0 4 1 0 gpa temperature and pressure range the ti abundance in aqueous fluids coexisting with rutile in the same pressure and temperature range is about 2 orders of magnitude lower these differences reflect solute dependent structural roles of ti 4 and p 5 in pure h 2 o fluid and in silicate saturated h 2 o other hfse likely behave similarly in silicate melt coh systems oxygen fugacity f o 2 is an additional variable affecting solubility and solution mechanisms from haplobasalt to haploandesite melt coh the carbon solubility at upper mantle pressures and temperatures decreases from 2 wt to 1 wt in equilibrium with co 2 gas oxidized carbon is dissolved dominantly as co 3 groups the solubility of reduced carbon in the coh system on the other hand is less than 50 of oxidized carbon reduced carbon in the coh system is dissolved in melts as a mixture of ch 3 groups and ch 4 molecules when coexisting fluid is ch 4 the isotope fractionation between coexisting coh saturated silicate melt and silicate saturated coh fluid is correlated with the ch 3 ch 4 abundance ratio in the melt by changing f o 2 from oxidized to reduced resultant changes of c solution mechanisms in melt coh systems cause nbo t changes this change can cause crystal melt element partition coefficients to vary by several tens of percent within natural abundance ranges of coh in magmatic liquids variable redox conditions will also result in variable q speciation of melts this variability in turn governs configurational properties of magmatic liquids as a result their transport properties such as viscosity and diffusion also vary with redox conditions

structure and kinematics of the central sivas basin turkey salt deposition and tectonics in an evolving fold and thrust belt this work has been made possible by funding from total s a in the framework of the structural geology chair at e2s university of pau pays adour held by jean paul callot

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

post collisional deposits in the zagros foreland basin implications for diachronous underthrusting detailed sedimentology of the neogene foreland basin deposits is investigated and classified into 11 lithofacies associations with respect to their paleo sedimentary environments the foreland deposits reveal a single coarsening upward mega sequence with continuous passage from back bulge to forebulge foredeep and wedge top sedimentary environments the gachsaran deposits form the base of the foreland strata and consist mainly of three different lithofacies associations including fluvial marine and sabkha deposits in the eastern zagros in fars and are typically dominated with evaporites toward the west in the dezful and kirkuk embayments the mishan formation has three different shallow marine lithofacies associations in a vertical succession representing foredeep deposits in the eastern zagros which tapers toward the dezful embayment and disappears in iraq the agha jari distal wedge top deposits also contain three different lithofacies associations including delta deposits mostly in the fars tidal flat deposits in dezful and mesopotamia basin and continental fluvial deposits across the entire zagros the uppermost synorogenic bakhtiari formation represents proximal wedge top deposits and consists mainly of two main lithofacies associations including shallow marine and fluvial deposits within which the fluvial succession is divided into three sub lithofacies associations with respect to distance from the mountain front and hydraulic power of the river networks synthetizing sedimentary facies association with age constraints of the old foreland deposits near the zagros suture in the high zagros area suggests that a considerable part of the arabian plate has been removed at the northern edge by underthrusting and erosion moreover preservation of the young distal foreland deposits near the suture in the western zagros implies that the magnitude and rate of removal of the proximal foreland deposits have been inconstant along strike the belt and decreases toward the east

the cenozoic kinematics of qatar evidence for high angle faulting along the dukhan anticline abstract new geological mapping and observations made across qatar favor a fault controlled model for the dukhan structure in the western part of the peninsula over previous fold related and regional erosion models regional stratigraphic relationships and sedimentology record significant fault localized accommodation development this miocene basin development may reflect far field extension in the foreland of coeval thrusting in oman the subsequent change in regional tectonics to convergence across the zagros front is interpreted to have led to basin inversion and the development of the present day topography and outcrop distribution

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

aftershocks properties of the 2013 shonbe m w 6 3 earthquake central zagros iran abstract the spatial and temporal seismicity parameters stress state as well as the partitioning of the seismic energy of the shonbe earthquake sequence have been investigated the geodetic data and the stress tensor inversions of the focal mechanisms before and after the shonbe main shock indicate the same ne sw trend of the greatest principal stress this stress orientation demonstrates a non heterogeneous stress state in that region of the central zagros which can be confirmed by the fractal dimension and the estimated p value the aftershock focal mechanisms show a diversity which may be associated with the approximately uniaxial stress field acting nearly perpendicular to the main shock fault plane in which the co seismic stress release is nearly complete the spatial distributions of the b and p values have been investigated and compared the high p value regions e g far to the southeast south and southwest of the main shock are approximately consistent with the high b value regions and the low p value regions e g the limited areas at the north northeast of the main shock are nearly consistent with the low b value regions the limited areas surrounding the main shock and also at the east southeast of the main shock the p values are not in agreement with the b values which may be attributed to the local tectonic features in those regions the seismic moment ratio and the bath s law have been used to constrain the energy partitioning between the main shock and the aftershocks it is found that a high fraction of the energy is released by the shonbe main shock and nearly one third of the energy released by the aftershocks this may be associated with the high stress imparted by the blind thrust main shock to the overlying crust in which promotes failure in the surrounding area and is often relieved by secondary faults and typically produce a high number of aftershocks

ponded melt at the boundary between the lithosphere and asthenosphere the boundary between earth s rigid lithosphere and ductile asthenosphere is marked by a seismic discontinuity laboratory experiments on basaltic magmas show that melts should pond at pressures that correspond to the lithosphere asthenosphere boundary thus magma ponding could explain the observed seismic discontinuity

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

structural evolution metamorphism and restoration of the arabian continental margin saih hatat region oman mountains abstract 170 m y of relatively stable passive margin sedimentation along the northern continental margin of arabia was abruptly terminated during the cenomanian turonian 95 ma when the oman continental margin collapsed and subsided rapidly aruma basin to accommodate obduction of the semail ophiolite complex and underlying thrust sheets haybi and hawasina complexes in the oman mountains the ophiolite was emplaced at least 200 km over the passive margin probably over 450 km in total from ne to sw during the later stages of obduction the leading edge of the continental margin was subducted to depths where carpholite bearing rocks 6 8 kbar blueschist 12 15 kbar and eclogite ca 20 kbar facies metamorphism formed in a ductile deforming ne dipping subduction zone along the northeastern margin of the saih hatat culmination in ne oman the mesozoic shelf carbonates are deformed by recumbent folding on all scales the present day structure is dominated by four sw vergent thrust slices in carpholite grade rocks at higher structural levels overlying lower units of crossite bearing blueschist hulw unit garnet glaucophane chloritoid blueschists and garnet clinopyroxene phengite glaucophane eclogites 15 20 kbar the largest shear zone separates 7 8 kbar hulw unit blueschists above from 12 15 kbar retrogressed eclogites and ca 20 kbar eclogites of the as sifah unit below further inboard sw a major shear zone separates the lower plate hulw blueschist facies rocks from the upper plate sedimentary rocks upper plate lower plate discontinuity which also show carpholite grade hp metamorphism towards the ne restoration of the entire saih hatat continental margin shows that the upper plate lower plate discontinuity cuts down section to the sw as far as the proterozoic hatat schists ne directed extensional crenulation schistosity and nne oriented stretching lineations in the eclogite and blueschist facies rocks are consistent with sw directed exhumation of footwall hp rocks ne facing folds and spectacular sheath folds with greatly attenuated limbs in the upper plate sediments are interpreted as antithetic backfolds with shortening in the upper plate balanced by the subduction of the lower plate consistent with a ne directed subduction of the continental margin rocks beneath the sw obducting ophiolite haybi and hawasina thrust sheets recent suggestions of a nascent sw directed subduction beneath the oman margin are not consistent with the sedimentary evolution of the shelf and slope carbonates or the geological structure of saih hatat two main phases of tectonic uplift of saih hatat and jebel akhdar are firstly the latest cretaceous ramp culmination associated with foreland propagating thrusts in the sw and backfolds in the ne and secondly post late eocene oligocene uplift by ca 2000 m

the southern zagros collisional orogen new insights from transdimensional trees inversion of seismic noise the natural environmental research council nerc grant ne r013500 1 and from the european union s horizon 2020 research and innovation program under marie sklodowska curie grant agreement 790203

early jurassic rifting of the arabian passive continental margin of the neo tethys field evidence from the lurestan region of the zagros fold and thrust belt iran

effect of spatial distribution of hormuz salt on deformation style in the zagros fold and thrust belt an analogue modelling approach scaled analogue models of thin skinned simultaneous shortening above adjacent viscous and frictional decollements simulate the effect of hormuz salt on the shortening in the zagros fold and thrust belt the models consisted of sand layers that partly overlay a viscous layer of silicone and were shortened from one end spatial distribution of the viscous decollement varied along strike and dip as occurs in part of the zagros fold and thrust belt in this belt phanerozoic sedimentary cover was shortened partly above the hormuz salt lying on the precambrian crystalline basement behaving as a basal viscous decollement model results display how the nature of the decollement affects the evolution of an orogenic belt using model results we explain the development of deflection zones and discuss strain partitioning formation of different topographic wedges and differential sedimentation along the zagros fold and thrust belt model results suggest the formation of a gentle taper consisting of both foreward and backward thrusts above a viscous decollement and a relatively steeper taper consisting only of forward vergent imbricates above a frictional decollement however in our models the steepest wedge with the highest topography formed where the viscous substrate had a limited extent with a transitional boundary pinch out perpendicular to the shortening direction shortening of this boundary led to development of frontal ramps associated with significant uplift of the area behind the deformation front

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

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

control of cambrian evaporites on fracturing in fault related anticlines in the zagros fold and thrust belt orientation and distribution of fractures in the oligocene early miocene asmari formation a major reservoir rock of the zagros petroleum system were investigated in two anticlines of the zagros fold and thrust belt the sim and kuh e asmari anticlines developed in the areas of the zagros characterized by the occurrence and absence of cambrian evaporites at the bottom of the stratigraphic pile respectively the aim was to outline major differences in terms of fracture spacing and saturation organic matter maturity and clay minerals based geothermometers suggest that the depth of deformation for the top of the asmari formation in the kuh e asmari anticline was in the range of 1 5 2 7 km assuming a geothermal gradient of 22 5 c km the asmari formation in the sim anticline probably experienced a slightly deeper sedimentary burial maximum 3 km with a geothermal gradient of 20 c km the spacing of fractures is generally 2 3 times larger i e strain accommodated by fracturing is smaller in the sim anticline than in the kuh e asmari anticline this is consistent with regional geological studies analogue and numerical models that suggest that thrust faults geometry and related folds are markedly different in the absence or presence of a weak decollement evaporites the larger spacing in the sim anticline is also consistent with higher temperature predicted for the asmari formation in this area by contrast the orientation of fractures with respect to the fold axes is the same in both anticlines the fracture systems are rather immature in both anticlines the amount and density of fractures in the twofolds are controlled by regional occurrence absence of salt and probably different burial rather than local features fold geometry

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

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

facies partitioning and stratal pattern in salt controlled marine to continental mini basins examples from the late oligocene to early miocene of the sivas basin turkey the sivas basin turkey records a complex interaction between sedimentation salt tectonics and regional shortening leading to the formation of numerous mini basins the segmentation into mini basins was initiated during the oligocene by the deposition of the fluvio lacustrine karayun fm this continental succession is overlain abruptly by an oligo miocene shallow marine succession karacaoren fm which comprises two main sub environments i mixed deltaic and carbonate ramp ii coastal plain and lagoon the karacaoren fm forms a marine succession more than 1500 m thick that passes vertically upwards into a continental succession the fluvial dominated benlikaya fm these two formations are the focus of the present study during the period of marine sedimentation the competing accumulation of carbonates and clastics is related not only to the topography inherited from salt tectonics but also to relative sea level variations expressed by two large scale transgressive regressive cycles we analyse these complex facies and stratal relationships to illustrate the modifications induced by salt tectonics this study is based on extensive fieldwork and mapping making use of numerous measured stratigraphic sections and aerial photos over a large area comprising more than fifteen adjacent outcropping mini basins the aim of this study is to provide a detailed description of the stratigraphic relationships correlations and sedimentary systems distribution in mini basins during deposition of the oligo miocene shallow marine and continental successions we first clarify the vertical stratigraphic succession of the oligo miocene marine and continental deposits and establish correlations between the studied mini basins these correlations then allow us to characterize and assess the local effects of salt withdrawal in relation to the regional forcings associated with flexural subsidence tectonic shortening and relative sea level changes an improved understanding of the complex interactions of these variables provides a framework to distinguish the mechanisms that control facies distribution and stratal geometry in salt basins

the gutenberg discontinuity melt at the lithosphere asthenosphere boundary the lithosphere asthenosphere boundary lab beneath ocean basins separates the upper thermal boundary layer of rigid conductively cooling plates from the underlying ductile convecting mantle the origin of a seismic discontinuity associated with this interface known as the gutenberg discontinuity g remains enigmatic high frequency ss precursors sampling below the pacific plate intermittently detect the g as a sharp negative velocity contrast at 40 to 75 kilometer depth these observations lie near the depth of the lab in regions associated with recent surface volcanism and mantle melt production and are consistent with an intermittent layer of asthenospheric partial melt residing at the lithospheric base i propose that the g reflectivity is regionally enhanced by dynamical processes that produce melt including hot mantle upwellings small scale convection and fluid release during subduction

subsurface seismic record of salt glaciers in an extensional intracontinental setting late triassic of northwestern germany in the northwest german basin of central europe late triassic interaction of normal faulting and salt diapirism during regional extension in subsalt basement locally initiated lateral fl ow of surface piercing salt in namakiers salt glaciers using seismic sections and variance attribute maps derived from high resolution three dimensional seismic data we show that when a syndepositional fault cuts a near emergent diapir crest the caprock carapace was breached opening a pathway for salt extrusion the fault escarpment and the adjacent fault induced depression allowed focused gravity driven downward fl ow of salt across the land surface a namakier and its subsequent preservation and encasement in continental arid redbed sediments geodynamically there is an apparent distinction between the compressional setting of modern namakiers in the arid deserts of iran and the fault intersected extensional setting of stacked keuper namakiers stacked namakiers preserved in thicknesses that are seismically resolvable are interpreted to indicate hyperarid conditions in keuper time the climate was typical of the highly continental late triassic pangaean supercontinent as it rifted and sagged to form the incipient atlantic ocean

high resolution upper crustal velocity structure beneath qeshm island se zagros from surface wave first arrival and interevent interferometry tomography methods abstract the qeshm earthquake with magnitude mw 6 0 occurred on november 27 2005 on a southern island in iran and was followed by many aftershocks we analyzed the aftershock waveforms and the first arrival traveltimes to calculate the 3d velocity model the tomographic procedure was conducted in three different depth ranges from the subsurface to a depth of 17 km beneath qeshm island the subsurface was probed by the rayleigh wave tomographic method the waveforms were filtered in the period range of 0 6 to 6 s the dispersion curves were calculated for the selected signals and a 2d tomography procedure was then performed the resulting group dispersion measurement maps were inverted to obtain the shear wave velocity model to a depth of 5 km however the first arrival traveltimes were applied to obtain the vp and vp vs models using the simulps program in the depth range of 5 to 14 km while depths ranging from 14 to 17 km were considered by the event interferometric approach all appropriate interevent empirical green s functions egfs were extracted in the 4 different slices depths and the rayleigh wave tomography processing was then repeated for these layers at the period of 1 2 s our results demonstrate that analysis of the interevent egfs can yield useful information from depths for which a velocity model cannot be obtained via classic techniques in addition to the qeshm fault which appears as a stretched low velocity anomaly the hormuz salt and evaporites may be other sources with low velocity although finding a direct relation between faulting and folding and or any other mechanism of folding is difficult on qeshm island the role of the hormuz salt in generating them is undeniable the rise of the hormuz salt and evaporites which appear as a low velocity weak zone can directly affect crustal layering lower sedimentary cover and basement fault dip and anticline formation and deformation at depths to 14 km according to the effect of these tectonic features folding and secondary faults the soft sedimentary thickness varies between 2 and 3 km

structural evolution of salt influenced fold and thrust belts a synthesis and new insights from basins containing isolated salt diapirs abstract lateral shortening is expressed in unique ways in salt basins especially if pre shortening diapirs are present we present an overview of previously published and new physical models and present new 3 d conceptual models that capture the evolution of shortening structures in salt provinces dominated by precursor isolated diapirs termed isolated diapir provinces in such provinces isolated diapirs form only a minor volumetric component of a sedimentary basin however due to the relative weakness of rock salt and their ability to localize strain during shortening they have a disproportionately large influence on structural development we find three key mechanical principles govern the processes and structural styles developed during shortening of isolated diapir provinces first salt diapirs shorten before surrounding sedimentary rocks due to their relative weakness and so form salients in the thrust front during early shortening second diapirs tend to nucleate folds and faults which radiate out from the diapirs third as diapir walls converge the roof must shorten extrusive salt sheets are expelled through thin roofs but thicker roofs resist piercement and so tend to undergo complex folding and faulting as a result of these principles the first order controls on the structural styles expressed across a shortened isolated diapir province are the configuration the diapir array prior to shortening the connectivity of these diapirs prior to shortening total strain magnitude and diapir roof thickness second order controls include the initial cross sectional and map view geometry of diapirs diapir size and diapir orientation with respect to the shortening direction

analogue modeling of the role of multi level decollement layers on the geometry of orogenic wedge an application to the zagros fold thrust belt sw iran the presence of evaporate and incompetent formations i e decollement horizons within the sedimentary sequence of fold thrust belts can control their structural style and deformation evolution in the present study the influence of the decollement layers e g basal and internal decollement layers on the deformation style of several segments of the zagros fold thrust belt zftb sw iran e g fars arc dezful embayment and izeh zone was investigated using a series of analogue models of accretionary wedges the study of seismic profiles to understand the structural evolution of these segments of the belt where several decollement intervals acted as basal and internal decollements is complemented by the analogue model results the experimental results reveal that the thickness of the internal decollement layers influences the creation of fold dominated or thrust dominated deformations respectively experimental models and seismic data highlight that incompetent layers act as barrier units against fault propagation in sequence and or out of sequence faults into overlying strata towards southwest by fore deformation and control the rate of deformation propagation in the zftb the presence of both the basal and internal decollement layers located at different stratigraphic levels is required to form disharmonic decollement folds in the foreland of the zftb in addition the geometry spacing activity and propagation of faults as well as the topographic height of the critical wedges are directly controlled by low frictional decollements geophys j int 165 1 336 356 2006 geochem geophys geosyst 14 1131 1155 2013 the seismic profiles of the zftb showed that in addition to lithological contrasts the existence and activity of deep seated and basement faults had a big impact on the structural styles of the region

prediction of silicate melt viscosity from electrical conductivity a model and its geophysical implications 1 our knowledge of magma dynamics would be improved if geophysical data could be used to infer rheological constraints in melt bearing zones geophysical images of the earth s interior provide frozen snapshots of a dynamical system however knowledge of a rheological parameter such as viscosity would constrain the time dependent dynamics of melt bearing zones we propose a model that relates melt viscosity to electrical conductivity for naturally occurring melt compositions including h2o and temperature based on laboratory measurements of melt conductivity and viscosity our model provides a rheological dimension to the interpretation of electromagnetic anomalies caused by melt and partially molten rocks melt fraction 0 7

how subaerial salt extrusions influence water quality in adjacent aquifers summary brines supplied from salt extrusions cause significant groundwater salinization in arid and semi arid regions where salt rock is exposed to dissolution by episodic rainfalls here we focus on 62 of the 122 diapirs of hormuz salt emergent in the southern iran to consider managing the degradation effect that salt extrusions have on the quality of adjoining aquifers it is first necessary to understand how they influence adjacent water resources we evaluate here the impacts that these diapirs have on adjacent aquifers based on investigating their geomorphologies geologies hydrologies and hydrogeologies the results indicate that 28 62 45 of our sample of salt diapirs have no significant impact on the quality of groundwater in adjoining aquifers namely type n while the remaining 34 62 55 degrade nearby groundwater quality we offer simple conceptual models that account for how brines flowing from each of these types of salt extrusions contaminate adjacent aquifers we identify three main mechanisms that lead to contamination surface impact type a subsurface intrusion type b and indirect infiltration type c a combination of all these mechanisms degrades the water quality in nearby aquifers in 19 62 31 of the salt diapirs studied having characterized the mechanism s by which each diapir affects the adjacent aquifer we suggest a few possible remediation strategies to be considered for instance engineering the surface runoff of diapirs types a and c into nearby evaporation basins would improve groundwater quality