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Introduction The purpose of physical modeling in structural geology is to reconstruct the formation, development and evolution of structures on a laboratory scale with materials similar to crustal rocks. The physical-mechanical properties of the materials used in these modeling are of particular importance; So that the characteristics of these materials should be similar to the physical and mechanical characteristics of crustal rocks, and there should be a proportionality between the model and nature in terms of rheology, viscosity, and frictional resistance. Sand, mud-clay, gypsum and silicon are among the materials used in physical modeling. Gypsum powder, plaster, or hemi-hydrate in dry and wet form (killed gypsum) has also been used in modeling. In this study, the effect of humidity on viscous behavior of wet plaster in physical modelling of strike- slip fault system has been investigated. In these modellings wet plaster with 320%, 285% and 175% of humidity as a viscous material has been used. In determination of physical and mechanical (Atterberg limits) properties of wet plaster, the liquid limit of 178% and plastic limit of 96% was obtained. This study also provides data on behavior of wet plaster with changes in its humidity. Materials and Methods Atterberg measurements were first used to measure the water content of wet (or dead) plaster. Based on this criterion, three limits are defined for the amount of wetness in the material, which includes the shrinkage limit, the plastic limit, and the liquid limit. In this study, due to the nonuse of wet plaster in the humidity range of the shrinkage limit in physical modeling, the shrinkage limit test was not performed. In the plastic limit test, the minimum moisture required to turn the soil into mud is measured. In this regard, some balls of mud prepared from wet plaster are placed on a glass and by rotating the hand on the plaster, a rod with a diameter of 3mm is prepared. If cracks on the mud is developed, its humidity is at the level of mud. To determine the liquid limit of wet plaster, the penetrator cone device was used. Then the physical modeling of strike-slip faulting has been done using wet plaster with different wetness percentages. Three tests of physical modeling of strike-slip fault system in the basement and investigation of the effect of these movements on the sedimentary cover have been carried out using wet plaster with different humidity levels of 320%, 285% and 175%. Results and Discussion The results of Physical modelling on strike- slip fault system shows that by decrease in humidity of wet plaster from 320% to 175%, the Riedel shear fractures distance is increased from 0.3cm to 1.9 cm and their lengths have increased from 2.5cm to 4.5cm. These results obtained from the distribution and frequency of shear fractures in the form of a decrease in the number of fractures, an increase in the distance and length of fractures, and the uneven development of fractures qualitatively indicate a decrease in the elastic limit of wet plaster because of the decrease on its humidity. Reduction on the humidity of the wet plaster resulted in development fault related folding in the modeling. The variations on the numbers, distance, type and lengths of shear fractures in wet plaster with different percent of humidity demonstrates that wet plaster acts as viscous behavior when its humidity is between plastic limit (96%) and liquid limit (178%). These experiments also confirm the results of previous studies on the brittle behavior of plaster at lower wettnes levels. Conclusion The results obtained from this study in the investigation of Riddle shear fractures and folds related to the fault in the physical modeling of the strike-slip fault system showed that the water content in wet plaster to the extent of the plastic limit causes its plasticity behavior. The increase of water content more than this amount due to the relative decrease of adhesion and viscosity is associated with the decrease in the plasticity behavior of wet plaster. These changes are associated with the increase in the number of Riddle shear fractures and the decrease in the development of folds related to the thrust fault has been accompanied in the experiments. This conclusion is in agreement with the former studies that documented the brittle behavior of plaster with lower humidity than the humidity of the plastic limit. [ABSTRACT FROM AUTHOR]

Paleostress reconstruction through polyphase fault-slip data of a multi-deformed region suffered collisional tectonics can lead to detecting the stress phases. Based on earthquakes' focal mechanisms and morphotectonic features, multiple deformation phases model has been proposed for the Alborz Mountains located in the collision zone between the Arabian (Central Iran) and Eurasian (South Caspian block) plates during the Late Cenozoic. In this study, paleostress analysis has been carried out in an area bounded by two (Kandovan and Taleghan) regional faults in the Central Alborz Mountains using fault-slip data. This analysis resulted in the identification of three main tectonic phases. The first, compressional phase is proposed to cause the inversion of the Alborz Mountains' major initial normal faults to reverse faults during the convergence of the Arabian and Eurasian plates. The second, transpressional phase is offered as a factor for the reactivation of the hidden Alborz basement faults to form the NE-striking left-lateral strike-slip faults on the sedimentary cover. The third, transtensional phase is suggested to be responsible for the development of the NNE-SSW left-lateral transtensional faults. It is proposed that the second and third paleostress phases are affected mainly by the indentation of the South Caspian Block into the Alborz Mountains during the Late Cenozoic. [ABSTRACT FROM AUTHOR]

Structural decoupling in the Zagros fold‐and‐thrust belt, SW Iran, is controlled by the presence of intermediate detachment horizons within the Phanerozoic stratigraphic column such as intervals rich in evaporites. The effectiveness of the detachment horizons varies across the Zagros, and controls the style of folding and therefore the formation of structural traps. In this paper, field mapping, seismic interpretation and well data is used to investigate the complex structural style at six large‐scale anticlines located on either side of the surface trace of the NW‐SE trending Zagros Frontal Fault system in the South Dezful Embayment (Central Zagros). At some of these anticlines, lower – middle Miocene evaporites in the Gachsaran Formation decouple the folded overlying succession from the competent, underlying interval which includes the Asmari Formation reservoir. Anticlines to the northeast of the surface exposure of the fault have undergone four times more shortening than anticlines to the southwest. This localized shortening compared to regional values has resulted in some cases in complex asymmetric folding, and in severe structural decoupling above and below the Gachsaran Formation. However, other anticlines to the NE of the fault which underwent a similar amount of shortening, but in which the thickness of the Gachsaran Formation is reduced and the salt content is lower, show a harmonic style of folding above and below the formation. Thus, the efficiency of the Gachsaran detachment varies throughout the study area and appears to be controlled mainly by the total thickness of the formation, the net thickness of salt‐rich intervals within it, and the amount of structural shortening across the Zagros Frontal Fault system. These observations could be relevant to similar structural domains both in the Zagros and in other fold‐and‐thrust belts where intermediate detachment horizons and regional‐scale faults have together controlled the configuration of folds and structural traps. [ABSTRACT FROM AUTHOR]

Salt tectonics in the Eastern Persian Gulf (Iran) is linked to a unique salt‐bearing system involving two overlapping 'autochthonous' mobile source layers, the Ediacaran–Early Cambrian Hormuz Salt and the Late Oligocene–Early Miocene Fars Salt. Interpretations of reflection seismic profiles and sequential cross‐section restorations are presented to decipher the evolution of salt structures from the two source layers and their kinematic interaction on the style of salt flow. Seismic interpretations illustrate that the Hormuz and Fars salts started flowing in the Early Palaeozoic (likely Cambrian) and Early Miocene, respectively, shortly after their deposition. Differential sedimentary loading (downbuilding) and subsalt basement faults initiated and localized the flow of the Hormuz Salt and the related salt structures. The resultant diapirs grew by passive diapirism until Late Cretaceous, whereas the pillows became inactive during the Mesozoic after a progressive decline of growth in the Late Palaeozoic. The diapirs and pillows were then subjected to a Palaeocene–Eocene contractional deformation event, which squeezed the diapirs. The consequence was significant salt extrusion, leading to the development of allochthonous salt sheets and wings. Subsequent rise of the Hormuz Salt occurred in wider salt stocks and secondary salt walls by coeval passive diapirism and tectonic shortening since Late Oligocene. Evacuation and diapirism of the Fars Salt was driven mainly by differential sedimentary loading in annular and elongate minibasins overlying the salt and locally by downslope gliding around pre‐existing stocks of the Hormuz Salt. At earlier stages, the Fars Salt flowed not only towards the pre‐existing Hormuz stocks but also away from them to initiate ring‐like salt walls and anticlines around some of the stocks. Subsequently, once primary welds developed around these stocks, the Fars Salt flowed outwards to source the peripheral salt walls. Our results reveal that evolving pre‐existing salt structures from an older source layer have triggered the flow of a younger salt layer and controlled the resulting salt structures. This interaction complicates the flow direction of the younger salt layer, the geometry and spatial distribution of its structures, as well as minibasin depocentre migration through time. Even though dealing with a unique case of two 'autochthonous' mobile salt layers, this work may also provide constraints on our understanding of the kinematics of salt flow and diapirism in other salt basins having significant 'allochthonous' salt that is coevally affected by deformation of the deeper autochthonous salt layer and related structures. PMB‐HS and PMB‐FS: Primary minibasins and/or rim synclines above the autochthonous Hormuz Salt and Fars Salt, respectivelyPW‐HS and TW‐HS: Primary and tertiary salt welds at the autochthonous and allochthonous levels of the Hormuz Salt, respectivelyPW‐FS: Primary salt weld at the level of the autochthonous Fars Salt Salt tectonics in the Eastern Persian Gulf arises from Hormuz Salt and Fars Salt autochthonous source layers. The main driving forces of the Hormuz Salt movement were downbuilding and contractional squeezing. The diapirs of Hormuz Salt extruded significant allochthonous salt at Palaeocene–Eocene times. Pre‐existing diapirs of Hormuz Salt have influenced the flow of Fars Salt. Evacuation and diapirism of Fars Salt was driven mainly by differential sedimentary loading. [ABSTRACT FROM AUTHOR]

Abstract: We reveal transient surface deformation following the 2017 Mw7.3 Sarpol Zahab (Iran) earthquake using Interferometric Synthetic Aperture Radar (InSAR) measurements. Based on the coseismic interferograms derived from the Advanced Land Observing Satellite‐2 (ALOS‐2) data, the preferred slip model of the earthquake has a centroid depth of 14.5 ± 4 km and suggests that a basement fault is most likely responsible for the 2017 earthquake in the northwest Zagros fold‐thrust belt zone. Two slip asperities with a maximum slip of 6 m separated by 16 km are observed in the best fitting slip model. The accumulated afterslip in the first month after the mainshock determined from the Sentinel‐1 postseismic interferograms reveals a slip distribution that lies immediately updip of the coseismic slip, implying that frictional properties of the fault vary along the rupture patch. The Bamo Mount in the earthquake area was uplifted by approximately 1 m during the earthquake. We suggest that local topographic growth from both seismic and aseismic faulting behaviors is common within the Zagros fold‐thrust belt zone based on our findings regarding the 2017 earthquake and other significant events in the region. [ABSTRACT FROM AUTHOR]

The Talesh Mountains at the NW margin of the Iranian Plateau curve around the southwestern corner of the South Caspian Block and developed in response to the collision of the Arabian-Eurasian Plates. The timing, rates, and regional changes in late Cenozoic deformation of the Talesh Mountains are not fully understood. In this study, we integrate 23 new apatite and zircon bedrock U-Th/He ages and structurally restored geologic cross sections with previously published detrital apatite fission track data to reconstruct the deformation history of the Talesh Mountains. Our results reveal that slow rock exhumation initiated during the late Oligocene (~27-23 Ma) and then accelerated in the middle Miocene (~12 Ma). These events resulted in the present-day high-elevation and curved geometry of the mountains. The spatial and temporal distribution of cooling ages suggest that the Oligocene bending of the Talesh Mountains was earlier than in the eastern Alborz, Kopeh Dagh, and central Alborz Mountains that initiated during the late Cenozoic. Late Oligocene and middle Miocene deformation episodes recorded in the Talesh Mountains can be related to the collisional phases of the Arabian and Eurasian Plates. The lower rate of exhumation recorded in the Talesh Mountains occurred during the initial soft collision of the Arabian-Eurasian Plates in the late Oligocene. The accelerated exhumation that occurred during final collision since the middle Miocene resulted from collision of the harder continental margin. [ABSTRACT FROM AUTHOR]

In this paper, the effect of transverse faults on the orientation, density and fractures apertures and amount of mud loss is investigated in Asmari Formation as a major oil reservoir in Zagros folded belt zone, Iran. This carried out on three selected anticlines as the surface Kuh-e-Kamarab, and subsurface Marun and Aghajari oil fields. Subsurface data on fracture characteristics were obtained from Image logs, mud losses, and reported drilling data. These are compared with outcrop fracture characteristics gathered from fieldwork and satellite image interpretation. The results show that fracture orientations are almost identical in both outcrops and subsurface data, whereas the fractures density and aperture are different along and across the folded layers and are generally governed by their location with respect to the transverse faults. The closest sector to the faults displays the highest fracture density and greater aperture. Quantitative analysis of fractures from the Kuh-e-Kamarab Anticline indicates average fracture density almost two times greater close to the Izeh-Hendijan transverse (IZH) fault than the other parts of the fold. In the Marun and Aghajari oil fields, fracture density shows three to five times greater close to the transverse faults. Analysis of the Breakout (BO) and Drilling Induce Tensile Fractures (DITF) indicate that the directions of maximum horizontal stress (SH max) in the wells located in the bent part of the Marun field consistent with the stress state of the Mn transverse fault. Moreover, the SH max orientation of wells in the southern periclinal closure of the Aghajari Field is also affected by the IZH transverse fault. The result of Iso-mud loss maps in the oil fields reveals that the severe mud loss occurred in areas close to the transverse faults. • The effect of transverse faults on fractures density and aperture in Dezful Embayment anticlines of Zagros is presented. • Comparison of fracture characteristics of reservoir rocks show that transverse faults control borehole instability. • The transverse faults have more impact on fracture characteristics and severe mud loss than the folding and thrust faulting. • Analysis of SH max orientation in oil fields shows fractures affected by the transverse faults are stress-sensitive. [ABSTRACT FROM AUTHOR]

The integration of biostratigraphy, strontium isotope stratigraphy, and magnetostratigraphy allowed for the precise dating of the >3.0kmthick marine to nonmarine foreland sedimentary succession within the Dowlatabad growth syncline along the Frontal Fars arc in the Zagros Fold Belt that extends from eastern Turkey to southern Iran. This area was the missing link to complete the dating of syntectonic deposits in the Fars arc and quantify the migration of sedimentary belts as well as the propagation of folding across the entire Mesopotamian foreland basin. Both are essential for defining the interplay of basin evolution and sequence of folding. Deposition of the foreland marine marls in the Mishan Formation started at ca. 11.5 Ma. The transition to a nonmarine basin infill occurred at 4.9 Ma by the progradation of thick fluvial deposits of the Aghajari Formation with a fast accumulation rate of 63 cm/k.y. The beginning of growth strata deposition and thus the onset of folding in the Dowlatabad syncline is dated at 4.65 Ma. The first appearance of carbonate conglomerates sourced from the Guri limestone at 2.8 Ma marked the progressive dismantling of the nearby growing anticlines. The tectonic deformation in the front of the Fars arc was active for at least 2.85 m.y. and ceased at 1.8 Ma before the deposition of the discordant and slightly folded Bakhtyari conglomerates characterized by a clast composition derived from the Zagros hinterland. The compilation of magnetostratigraphic ages reveals that both the migration of the AghajariBakhtyari sedimentary belts and the propagation of the folding front was insequence toward the foreland at a rate close to 20 mm/yr in the Fars arc and 15 mm/ yr in the Lurestan arc, in the last 20 m.y. These high rates of folding propagation are about one order of magnitude larger than age equivalent shortening rates (~4 mm/yr in Fars arc and ~2 mm/yr in Lurestan arc) and thus imply an efficient detachment level at the base of the deformed Arabian sedimentary cover. Numerical experiments on both the cover and basement sequences are designed to test the influence of inherited basement structures on the deformation propagation within the cover sequence, providing clues on the partly coeval insequence deformation of the Zagros Simply Folded Belt and the local outofsequence Mountain Frontal Fault system as illustrated by regional and local geology. [ABSTRACT FROM AUTHOR]