Main Zagros Reverse Fault Research Articles

Geodynamics and tectonic stress model for the Zagros fold–thrust belt and classification of tectonic stress regimes

Stress measurement in rocks is an essential parameter in Earth and petroleum sciences. In hydrocarbon exploration and production from oilfields, a lack of sufficient knowledge on the initial stress field for the fracturing of formations limits proper simulation of the production process.To date, only a limited number of studies have investigated the state of stress in the Zagros Mountains. In this paper, well-established analytical techniques were used to determine the stress state in the Zagros Mountains. First, the Angelier method was used to invert earthquake data in different structural domains. Second, the pattern of crustal stresses was analyzed, and four classes of stress regimes were identified. The stress patterns were reconstructed for five distinct structural domains (zones 1–5). In all five zones, the compressive stress was normal to the main structures (fold axis and fault trace with NW‒SE strike). It can be inferred that the structural pattern in the sedimentary cover of the Zagros fold-and-thrust belt (ZFTB) is controlled by R1 (Regime 1) and R4 for zones 1 and 2; R3 for zone 3; R1 and R2 for zone 4; and zone 5. The reconstructed stress patterns are consistent with the observed strike-slip faulting and compressional tectonic deformation regimes. The patterns indicate that deformation in the ZFTB can be explained by a dextral transpressional tectonic model. First-order NE–SW compression stress controls the main convergence tectonics within the Zagros Mountains. Two subordinate compression directions were also identified: one oriented in a dextral main compression direction (N 241°–243°) and another in a sinistral (N135°–177°) and minor extension (N201°–229°). Classification and modeling of the stress regimes identified both thrusting and strike-slip systems; the former controls the Main Zagros Reverse Fault (hereinafter MZRF), and the latter results in a transpressional tectonic regime.

Morphotectonic and earthquake data analysis of interactional faults in Sabzevaran Area, SE Iran

We used satellite images, earthquake catalogues and field observations to study several active fault systems and their interactions in Sabzevaran Area in SE Iran. The focus of this study is to verify the link between the active faults, their kinematics and seismic activity. Field observations and geomorphological analysis highlight the interaction of the active faults. Moreover, most of the tectonic activity is observed in the area, related to the Chahmazrae- North Faryab shear zone. Most of the earthquakes in this shear zone are reverse and occur in the deeper crust while aftershocks dominantly occur in the shallower crust. The Main Zagros Reverse Fault (MZRF) is the source of reverse events and the Chahmazrae-North Faryab shear zone is source of left-lateral, oblique reverse faulting events, and strike-slip events. These types of the earthquakes in the study area confirm the idea of tectonic proximity of the root faults and shear zone. In the interaction area, minor fractures begin to develop and are progressively linked to the main faults. In the en échelon arrangement of the faults, the minor faults have grown and linked the en échelon segments of the faults. It seems that the earthquake ruptures can spontaneously propagate across both extensional and compressional fault steps. This propagation occurs along strike-slip faults such as Sabzevaran fault and its branches.

Analyzing the effects of tectonic and lithology on the occurrence of landslide along Zagros ophiolitic suture: a case study of Sarv-Abad, Kurdistan, Iran

Assessment of the landslide susceptibility can provide useful information in the management and mitigation of the negative consequences of this phenomenon. The purpose of this study was to map the landslide susceptibility and to highlight the effects of tectonic and lithology. The landslide-causing factors including distance from faults, lithology, slope gradient, slope aspect, distance from drainages, distance from roads, land use, and precipitation were used for the landslide susceptibility mapping by using analytical hierarchical process (AHP) method. Based on the landslide susceptibility zonation map, the study area was grouped into five susceptibility classes including very low, low, moderate, high, and very high. High values of landslide density in very high and high susceptible zone, and the high percentage of area under the success rate curve (72.65%) show that the AHP method has accurately predicted the landslide susceptibility zonation map of the study area. Data reveal that most landslides are close to the Zagros Main Recent Fault (MRF) and the Main Zagros Reverse Fault (MZRF) that merge with each other along the trend of Azad River. These faults have locally produced zones of extension and contraction that have caused the intense faulting and fracturing of rocks and hence the intensification of the landslides. The Oligo-Miocene marl (with high potential of plasticity, expanding, and cracking), the Oligo-Miocene limestone (with steep dip slopes and strike-slip faults) that overlies the Oligo-Miocene marls as a lubricant, and serpentinites (with high capacity of flexibility, plasticity, and sheeting) are three important lithological units that are more prone to landsliding.

Moho depth variations and Vp/Vs ratios in the seismotectonic zones of Central Iran, Eastern Iran, and Makran: using a modified Zhu and Kanamori method

Variations of the Moho depth and Vp/Vs ratio beneath the Central Iran, Eastern Iran, and Makran regions using a modified Zhu and Kanamori method are presented in this paper. Receiver functions have been calculated from 3 years of teleseismic recordings at seventeen broadband stations using a time-domain iterative deconvolution method. Our results indicate that Moho depth changes from 56 km beneath the western part of Central Iran to 40 km in Central Iran and 38 km in Eastern Iran. The relatively thick crust beneath western margin of Central Iran is due to the close proximity of this region to the Sanandaj-Sirjan Zone and the Urumieh-Dokhtar magmatic arc that are associated with underthrusting of the Arabian plate beneath Central Zagros along the main Zagros reverse fault. Also, crustal thickening of this region would be due to volcanic intrusions, magmatic. The reduction of crustal thickness beneath the eastern stations in this region could be due to the absence of a collisional zone in the tectonic evolution of the region. The results beneath the CHBR station located in Makran indicate a value of 31 km for crustal thickness and 1.70 for the Vp/Vs ratio. It is associated to subduction of the oceanic crust of the Arabian plates, beneath the southern part of the Makran crust with a very low slope. The crust beneath Central and Eastern Iran has a moderate thickness which decreases from west to east.

The relationship between fault zone structure and frictional heterogeneity, insight from faults in the High Zagros

Frictional heterogeneities within fault zones depend strongly on lithology as well as shear fabric and strain localization structures. Here we investigate the impact of fault rock composition and shear fabric on friction constitutive properties for mature High Zagros (Iran) fault rocks. We present field observations along with results from friction experiments on intact and powdered fault rock from carbonate, quartzofeldspathic and schist. We measured frictional strength and rate/state dependence over normal stresses from 25 to 100 MPa and shear slip velocities from 3 to 300 μm/s. The sliding friction coefficients of intact fault rocks are lower than their powdered equivalents. The foliated quartzofeldspathic and lensoidal carbonate rocks from the Main Zagros Reverse Fault (MZRF) exhibit velocity strengthening friction and stable sliding. In contrast, the cataclasite carbonate rocks from the younger, Main Recent Fault (MRF) exhibit potentially unstable, velocity-weakening frictional behavior, consistent with regional seismicity. Our results suggest that solution seams, cleavage processes, and development of stylolite and calcite veins in the carbonate fault rocks of the MZRF continually rejuvenate and rework shear structures, which leads to dominantly aseismic shear. In contrast, younger fault rocks of the MRF form highly localized shear zones and shear fabric that result in velocity-weakening frictional behavior and seismic slip. Our field observations and laboratory data provide insights for using friction data and fault zone structure to build predictive models of the mode of fault slip in zones of tectonic collision.

Active strike-slip faulting in the Zagros Mountains: Geological and geomorphological evidence of the pull-apart Zaribar Lake basin, Zagros, NW Iran

The Zaribar Lake is situated along the Main Recent Fault, a dextral major strike-slip active fault system in the Zagros collision zone. The formation of the Zaribar Lake in Late Pleistocene is associated with the activities of the Main Zagros Reverse Fault, initiated in Late Oligocene, and with the Main Recent Fault, whose inception occurred about 5 Ma ago. Metamorphic, intrusive and ophiolitic rocks in the Zagros suture zone are affected by a normal fault system in the Zaribar area. Geometry and kinematics of these normal faults indicate that the Zaribar Lake is generated in a releasing zone. The strike of the Main Recent Fault varies from 300° to 330° along the Marivan fault segment. The releasing bend of the Marivan Fault around the Zaribar Lake has resulted in the extensional deformation by which the lake has been downdropped between two strike-slip faults. Besides the extensional mechanism of the main right-lateral strike-slip faults that has resulted in the formation of the Zaribar as a large-scale pull-apart basin, minor strike-slip faults have also produced specific landforms around the lake. Small-scale normal faults and large scale grabens developed around the lake are geological indicators of extensional areas. Geomorphological evidence also support the pull-apart origin for the Zaribar Lake. Beheaded rivers, numerous offsets in drainage system, half-broom shaped drainage pattern, sag ponds with different scales, linear and strike-parallel valleys and alluvial fan with high sweep angle and width/length ratio confirm the movements along right-lateral, strike slip faults around the Zaribar.

Tectonic controls on groundwater geochemistry in Hormozgan Province, Southern Iran

Hormozgan Province with arid climate is an important source of energy resources for Iran. This study investigates the results of hydrogeochemical investigation and its tectonic control in Hormozgan Province, Southern Iran. The chemical analysis of 158 groundwater samples was evaluated to determine the hydrogeochemical processes and ion concentration background in the region. Several NW-SE trending and NE-dipping basement reverse faults have intersected the area and have divided it into four tectonic terranes. Huge extension of Hormuz Formation in Zagros Foredeep tectonic terrane has increased the cations, Cl and SO4 concentration in groundwaters. HCO3 concentration in Sanandaj-Sirjan Zone and High Zagros is the result of silicate weathering or carbonates. Eighty-three percent of samples have negative CAI values in High Zagros, Sanandaj-Sirjan Zone, and eastern Zagros Fold Thrust Belt. The dominant hydrochemical facies of groundwater are Na-Mg-Ca-Cl (25.3% of samples) and Na-Mg-Cl (20.9% of samples). They are confined to the west of Main Zagros Reverse Fault and east of High Zagros Fault, respectively. The salt content of the groundwater indicates samples with very high salinity—as a result of Hormuz Formation—are mainly limited to the west of High Zagros Fault while samples with high to medium salinity are mainly limited to the east of this fault. Eastward increment of rock weathering is controlled with thrust faults activity of the area and southwestward migration of deformation front. Westward increment of evaporites is compatible with Hormuz Formation/salt dome density through the area.

40Ar/39Ar mineral ages of eclogites from North Shahrekord in the Sanandaj–Sirjan Zone, Iran: Implications for the tectonic evolution of Zagros orogen

Eclogites are high-pressure/low-temperature metamorphic rocks and are regularly considered as an indicator of ancient subduction zones. Eclogites have recently been found in the North Shahrekord metamorphic complex (NSMC) of the Sanandaj–Sirjan zone and represent the only ones within the Zagros orogen. Their occurrence and timing are important for the reconstruction of convergence history and geodynamic evolution of the Neo-Tethys Ocean and Zagros orogen. White mica from the eclogites and an associated paragneiss give 40Ar/39Ar ages ranging from 184.3±0.9 to 172.5±0.8Ma and represent the age of cooling through the closure temperature for phengitic white mica. The NSMC also comprises the ductile NW–SE trending North Shahrekord Shear Zone (NSSZ), which is located in the northeast of the Main Zagros Reverse Fault. The NSMC consists mainly of various metasedimentary rocks, orthogneiss and small-sized bodies of metabasic rocks containing also the eclogites. Furthermore, pre-metamorphic granitoids represent part of the NSMC. The North Shahrekord eclogites are composed of garnet, omphacite, zoisite, Ca–Na amphibole, phengite and rutile. The highly deformed and metamorphosed granitoids yield hornblende and biotite 40Ar/39Ar ages 170.1±0.9Ma and 110.7±0.3Ma, respectively. According to the new age dating results of eclogites, the rocks are the oldest high-pressure metamorphic rocks in the Zagros orogenic belt testifying the Neo-Tethys Ocean subduction. Our new data indicate that the eclogites formed during Early Jurassic subduction of a Panafrican microcontinental piece from the northern margin of the Neo-Tethyan Ocean under the Central Iranian microplate. We suggest that initiation of subduction in Neo-Tethyan Ocean occurred a few million years prior to 184Ma (Pliensbachian stage).

Tectonic geomorphology of High Zagros Ranges, SW Iran: an initiative towards seismic hazard assessment

The High Zagros Ranges, SW Iran is considered to be tectonically active where damaging earthquakes have occurred. These ranges were uplifted by approximately 4550 m with respect to sea level following the collision between the Afro-Arabian and Central-Iranian plates. The Plio-Quaternary active tectonics was assessed through a detailed quantitative geomorphological study of fault-generated mountain fronts and alluvial/fluvial systems of the High Zagros Ranges. Quantitative measurement of geomorphological indices such as the stream-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), valley floor width–valley height ratio (Vf), drainage basin shape (Bs), and mountain-front sinuosity (Smf) and field data suggests a relatively medium to high degree of tectonic activity along the High Zagros Ranges. The obtained results from these indices were combined to yield an index of active tectonics (Iat). The indicative values of this index are consistent with the landforms and geology of the study area. The Iat is low to moderate in northern part of the study area which corresponds to the inactive Main Zagros Reverse Fault. The high values of Iat mainly occur in southern parts of the study area where straight mountain fronts and triangular facets along the Dena Fault suggest high tectonic activity. Moreover, the data plotted for earthquakes occurrences are consistent with morphotectonic map of relative tectonic activity and can be used as an initiative towards seismic hazard assessment. Most of the major faults are considered to be active and have potential to generate large earthquake in future and need to be evaluated more carefully for the regional seismic hazard.

Active faulting of the southeastern-most Zagros (Iran): Microearthquake seismicity and crustal structure

The microseismicity of the southeastern-most Zagros is examined by high-resolution data recorded by a temporary dense local seismic network. The seismicity defines a diffuse pattern, mostly located beneath folds in the southern part of the High Zagros Fault (HZF). Seismicity dips gently northward in the depth range 6–25km, implying slip on a major intracrustal thrust fault extending to the north of the Main Zagros Reverse Fault (MZRF) which seems to connect to the Mountain Frontal Fault (MFF). Furthermore, observed focal mechanisms suggest transpressive motion on the HZF located west of the Zendan-Minab-Palami (ZMP) fault system and striking obliquely to the convergent motion. These observations suggest that the transition zone between the Zagros continental collision zone and the Makran oceanic subduction zone is not confined to the east of the ZMP and some part of the this diffuse transition is accommodated north of the Hormuz Strait in the west by partitioning between strike-slip and shortening components. The Zagros reverse domain is terminated by a transpressive tectonic regime. Moho depth beneath the MZRF, deduced from receiver functions, is almost 45km thinner than is observed in the central and northern parts of the Zagros. These observations support a model of active underthrusting of the Arabian plate beneath central Iran in the southeastern-most Zagros.

Active tectonic assessment around Rudbar Lorestan dam site, High Zagros Belt (SW of Iran)

The aim of this study is to improve a method to develop an integrated quantitative geomorphic analysis of tectonic activity around the Rudbar Lorestan dam site and powerhouse in the High Zagros Belt (HZB), southwest Iran, using several tectonic geomorphic indexes including stream length–gradient index ( SL), drainage basin asymmetry ( Af), hypsometric integral ( Hi), ratio of valley floor width to valley height ( Vf), and transverse topographic symmetry factor ( T). Considering the results obtained from each of the above indexes, as combined and weighted by the “analytic hierarchy process” (AHP) and plotted on the “index map of relative active tectonics” ( Iat) by El Hamdouni et al. (2008), four classes are recognized in the study area; i.e. low, moderate, high, and very high, according to the rate of tectonic activity in the subbasins. Low to moderate intensities correspond to the northeast (along the Main Zagros Reverse Fault: MZRF) and southwest parts of the study area; whereas subbasins in the middle parts, along the Saravand–Baznavid strike-slip fault, are classified into high or very high intensities because of recent activity and the oblique-slip movement of the Saravand–Baznavid fault. The results show that the Rudbar Lorestan dam site and powerhouse are located in an active strike-slip fault zone and that a seismic hazard may occur along this zone in the future.

PETROLOGY OF MANTLE PERIDOTITES AND INTRUSIVE MAFIC ROCKS FROM THE KERMANSHAH OPHIOLITIC COMPLEX (ZAGROS BELT, IRAN): IMPLICATIONS FOR THE GEODYNAMIC EVOLUTION OF THE NEO-TETHYAN OCEANIC BRANCH BETWEEN ARABIA AND IRAN

The Kermanshah ophiolitic complex consists of a melange formation, which includes dismembered ophiolitic sequences. These ophiolites are located along the Main Zagros Reverse Fault, which marks the ophiolitic suture zone between the Zagros belt and the Sanandaj-Sirjan zone. They represent the Neo- Tethyan oceanic lithosphere, which originally existed between the Arabian (to the south) and Eurasian (to the north) continental margins. The Kermanshah ophiolites were emplaced onto platform carbonate rocks, which represented the northeastern Arabian margin. The Kermanshah ophiolitic complex is composed of various partial sequences, which are represented by: (1) mantle tectonites consisting of depleted lherzolites and both clinopyroxene- (cpx-) rich and cpx-free harzburgites; (2) a troctolite-cumulate gabbro-isotropic gabbro sequence mainly showing pegmatoid texture; (3) a wehrlite-cumulate gabbro-isotropic gabbro sequence showing foliated texture; (4) a dyke complex; (5) very scarce pillow basalts. Mantle tectonites are volumetrically predominant and tectonically overlay the gabbroic sequences. A number of conclusions may be drawn based on petrographic observations, mineral chemistry, whole-rock chemistry, and rare earth elements (REE) modelling carried out on both mantle tectonites and intrusive rock associations. (1) The Foliated Gabbro Unit has an N-MORB chemical signature and represents a portion of oceanic crust generated in a mid-ocean ridge setting from an N-MORB-type sub-oceanic mantle. (2) The Pegmatoid Gabbro Unit displays an E-MORB signature and represents a portion of oceanic crust most likely generated from a sub-oceanic mantle source enriched in light REE (LREE). A comparison with the well-studied Oman ophiolites suggests that this sequence may have formed during the early stage of oceanic spreading. (3) The depleted lherzolites present mild depletions in heavy REE (HREE) and variable depletion in LREE. REE modelling shows that they may represent a residual mantle after 15-20% removal of N-MORB melts. Some lherzolites show a moderate enrichment in La and Ce with respect to Sm, suggesting that this residual MORB mantle was subsequently trapped in a supra-subduction zone (SSZ) mantle wedge and enriched in LREE by subduction-derived fluids. (4) The depleted harzburgites present a significant depletion in incompatible elements and REE, coupled with a marked LREE enrichment with respect to medium REE. REE modelling shows that they may represent a residual mantle after 25-30% removal of boninitic-type melts in an intra-oceanic arc setting.

Seismic imaging of the lithospheric structure of the Zagros mountain belt (Iran)

Abstract We present a synthesis and a comparison of the results of two temporary passive seismic experiments installed for a few months across the Central and Northern Zagros. The receiver function analysis of teleseismic earthquake records gives a high-resolution image of the Moho beneath the seismic transects. On both cross-sections, the crust has an average thickness of 42±2 km beneath the Zagros fold-and-thrust belt and the Central domain. The crust is thicker beneath the hanging wall of the Main Zagros Reverse Fault (MZRF), with a greater maximum Moho depth in the Central (69±2 km) than in the Northern Zagros (56±2 km). The thickening affects a narrower region (170 km) beneath the Sanandaj–Sirjan zone of the Central Zagros and a wider region (320 km) in the Northern Zagros. We propose that this thickening is related to overthrusting of the crust of the Arabian margin by the crust of Central Iran along the MZRF, which is considered as a major thrust fault cross-cutting the whole crust. The fault is imaged as a low-velocity layer in the receiver function data of the Northern Zagros profile. Moreover, the crustal-scale thrust model reconciles the imaged seismic Moho with the Bouguer anomaly data measured on the Central Zagros transect. At upper mantle depth, P-wave tomography confirms the previously observed strong contrast between the faster velocities of the Arabian margin and the lower velocities of the Iranian micro-blocks. Our higher-resolution tomography combined with surface-wave analysis locates the suture in the shallow mantle of the Sanandaj–Sirjan zone beneath the Central Zagros. The Arabian upper mantle has shield-like shear-wave velocities, whereas the lower velocities of the Iranian upper mantle are probably due to higher temperature. However, these velocities are not low enough and the low-velocity layer not thick enough to conclude that delamination of the lithospheric mantle lid has occurred beneath Iran. The lack of a high-velocity anomaly in the mantle beneath Central Iran suggests that the Neotethyan oceanic lithosphere is probably detached from the Arabian margin.

The kinematics of the Zagros Mountains (Iran)

Abstract We present a synthesis of recently conducted tectonic, global positioning system (GPS), geomorphological and seismic studies to describe the kinematics of the Zagros mountain belt, with a special focus on the transverse right-lateral strike-slip Kazerun Fault System (KFS). Both the seismicity and present-day deformation (as observed from tectonics, geomorphology and GPS) appear to concentrate near the 1000 m elevation contour, suggesting that basement and shallow deformation are related. This observation supports a thick-skinned model of southwestward propagation of deformation, starting from the Main Zagros Reverse Fault. The KFS distributes right-lateral strike-slip motion of the Main Recent Fault onto several segments located in an en echelon system to the east. We observe a marked difference in the kinematics of the Zagros across the Kazerun Fault System. To the NW, in the North Zagros, present-day deformation is partitioned between localized strike-slip motion on the Main Recent Fault and shortening located on the deformation front. To the SE, in the Central Zagros, strike-slip motion is distributed on several branches of the KFS. The decoupling of the Hormuz Salt layer, restricted to the east of the KFS and favouring the spreading of the sedimentary cover, cannot be the only cause of this distributed mechanism because seismicity (and therefore basement deformation) is associated with all active strike-slip faults, including those to the east of the Kazerun Fault System.

Petrology of eclogites from north of Shahrekord, Sanandaj-Sirjan Zone, Iran

Metabasic rocks were recently found within a ductile shear zone in the north of Shahrekord, being a part of the structural zone of Sanandaj-Sirjan, SW Iran. The rocks give evidence of a so far unrecognized eclogite facies metamorphic event and testify to high pressure metamorphism in the Sanandaj-Sirjan Zone, near the Main Zagros Reverse Fault, which is the assumed suture zone between the Arabian plate and the Iranian block. The eclogites occur as lenses or blocks within ortho- and paragneisses. The petrographic features and reaction textures display at least two main metamorphic stages: (1) a peak eclogite facies stage, and (2) a subsequent amphibolite facies stage. The eclogite facies metamorphism is indicated by omphacite + garnet + sodic-calcic amphiboles (barroisite, magnesiokatophorite and magnesiotaramite) + phengite + rutile + (clino-)zoisite + quartz ± dolomite. The garnets are mainly almandine-rich, which fits with the C-type eclogite classification. Calcic amphiboles (hornblende, tschermakite and pargasite) + plagioclase are secondary phases formed during the retrograde amphibolite-facies metamorphism. P-T estimates for the eclogite facies give pressures of 21–24 kbar and temperatures of 590–630 °C (geothermometry) and 470–520 °C (THERMOCALC), respectively. Geothermobarometry for the amphibolite-facies metamorphism yields 10–11 kbar and 650–700 °C.

Microearthquake seismicity at the intersection between the Kazerun fault and the Main Recent Fault (Zagros, Iran)

Seismicity and fault plane solutions of earthquakes at the intersection between the Main Recent Fault (a right-lateral strike-slip fault that bounds the Zagros to the NE) and the Kazerun Fault system (another right-lateral zone that crosses the Zagros) show slip to be partitioned into nearly pure strike-slip at shallow depths and nearly pure thrust slip below 12 km. Such slip partitioning is commonly observed where oblique convergence occurs, but in general faults of different styles lie adjacent to one another, not at different depths with one below the other. We provide evidence for this partitioning in a microearthquake study in which we deployed a temporary network of 29 seismographs for 7 weeks. We located no activity north of the Main Zagros Reverse Fault (MZRF), which separates the Zagros fold belt from Central Iran. Most earthquakes occurred between the northern termination of the Kazerun Fault and the MZRF, but not near to known major faults. Activity is limited to the upper crust, between 2 and 16 km. Most of the focal mechanisms show strike-slip faulting, dextral if the NS striking plane is the active plane, but a few for the deepest events show reverse faulting, distributed between the Kazerun Fault and the MZRF, with P-axis trending consistently ∼NS. This partitioning of the deformation with depth suggests that the brittle upper crust deforms by slip on pre-existing faults that strike obliquely but that the lower crust accommodates the shortening by reverse faulting. We infer that the deformation in the upper part of the crust reflects a stiffer medium in which pre-existing faults localize the deformation. The largest event recorded during this experiment, located at the same place as the destructive 1977 Naghan earthquake (Mw ∼5.9, 348 victims), shows reverse faulting, likely related to the Dopolan High Zagros Fault. The crustal thickness deduced from receiver function analysis does not show a marked difference across the Kazerun fault, which suggests a pure strike-slip motion on the fault.

The present‐day deformation of the central Zagros from GPS measurements

In 1997 and in 2000, we measured the distances between 14 geodetic benchmarks across the central Zagros mountain belt. The results show that about 10 mm/yr of shortening in the central Zagros is distributed across the mountain belt. This shortening corresponds to roughly 50% of the total convergence between Arabia and Eurasia and is consistent in direction. The Persian Gulf does not deform significantly. The Main Zagros Reverse Fault is not an active kinematic boundary. The internal deformation of the folded belt is rather homogeneous, at the scale of our survey, which does not allow us to detect any individual active blind fault. However, the strain pattern suggests that N‐S dextral strike slip faults may accommodate part of the deformation.

Salt tectonism in the Persian Gulf Basin

Abstract The Persian Gulf Basin is an elongate, margin sag-interior sag, sedimentary basin spanning the last 650 Ma along the northeastern subducting margin of the Arabian Plate and is the largest basin with active salt tectonism in the world. This basin is asymmetrical in NE-SW cross section with sediments thickening from 4,500 m near the Arabian Shield to 18,000 m beside the Main Zagros Reverse Fault. Halokinesis in the Persian Gulf Basin originates where major intersecting basement faults cut the buoyant salt beds of the Neoproterozoic Hormuz Series (1.5 to 2.5 km thick) and the equivalent Ara Formation of Oman where salt thickness reaches 4 km. Another source of salt is the Oligo-Miocene Gachsaran Formation, forming Lali salt plug. Major basement fault trends control salt tectonism in the basin, namely the extensional N-S Arabian Trend, the sinistral NE-SW Aulitic Trend, the dextral Erythaean Trend and the extensional E-W Tethyan Trend. The main types of salt structures in the Persian Gulf Basin are salt domes, salt pillows, salt walls, salt piercements, rim anticlines, turtleback structures, disharmonic folds, orogenic fold fillings and dissolution drapes. Diapiric oil fields, account for 60% of the 600 billion barrels of recoverable oil reserves of the Persian Gulf Basin and have grown continuously since Late Jurassic, or since Permian in some large structures, such as Bahrain.