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Field evidence, seismicity, and geodetic data are combined to define the tectonic evolution along the northern domain of the Western and Central Alborz ranges, which have experienced significant earthquakes. One of our main focuses is to present the geometric-kinematic characteristics of active fault planes in the North Alborz fault zone and its subsidiary faults as a basis for seismic hazard assessment. To evaluate the seismotectonics in the region, three active segments of the seismic zone are identified. These segments primarily exhibit reverse mechanisms and left-lateral strike-slip components and act as the boundaries of neotectonic stress domains around the transition zone between Alborz and the South Caspian Basin. The spatial distribution of the strike-slip and dip-slip faulting over the Western and Central Alborz range supports our understanding of the geodynamic processes of the region. Our map of local active faults reveals five main systems with N–S, NE–SW, ENE–WSW, E–W, and NW–SE directions. Field studies indicate that strike-slip movements predominate and are consistent with a ∼WNW-ESE-oriented left-lateral wrench system. Pure left-lateral strike-slip faults trending E-W, extensional faults trending NE–SW, and compressional faults trending NW-SE are identified. Regional field investigations reveal spatial variations in the fault zone width of the northern domain of the Western and Central Alborz. The findings demonstrate that fault zone structures and their spatial distribution along the width of the area are strongly affected by the strain partitioning process in the transpressional zone. A spectacular well-exposed transpressional zone from the Western and Central Alborz region is described in detail, where outer domains are faults with a dominant reverse mechanism, and the inner domain is a wrench zone that includes faults with a dominant strike-slip mechanism. The seismic activity in the Northern Alborz region is mainly concentrated along the North Alborz fault zone and its subsidiary fault planes, of which some are identified for the first time in this research. Significant seismic events have occurred at locations where these newly identified fault planes interact. The maximum values of the geodetic strain axes in Western and Central Alborz are consistent with the area of high seismicity.

Introduction: The East Iran orogen has experienced multiple buckling phases resulting in the formation of strike-slip fault splays. The geometric and kinematic characteristics of these splays are influenced by folding mechanisms. This study focuses on investigating the structural characteristics and tectonic evolution model of the Khousf splay, located in the northern terminus of the Nehbandan right-lateral strike-slip fault system.Methods: Field visits and geometrical properties from map views were used to analyze the structural features of the Khousf splay. The splay was found to consist of a multi-plunging anticline and syncline, referred to as the Khousf anticline and Khousf syncline, respectively. Flexural slip was identified as a significant mechanism for the formation of these structures. Structural evidence, including parasitic folds, active folds, and strike-slip duplexes, suggested that flexural slip occurred on discrete movement horizons among the rock units.Results: Analysis of the parasitic folds in the cores and limbs of the Khousf anticline and syncline revealed M, W, Z, and S shapes, with complex slicken-line patterns observed on faults parallel to the beds at the limbs. The analysis results indicated strain partitioning and inclined left- and right-lateral transpressional zones. Shortening estimates obtained from profiles in the Shekarab inclined transpressional zone were approximately 33%, 65%, and 68% for NE-SW, N-S, and NW-SE profiles, respectively. In the Arc area, which is the core of the anticline, shortening estimates from NE-SW and N-S profiles ranged from 14% to 10%. Structural analysis of the folds in this area revealed broad, close, semi-elliptical, and parabolic shapes, suggesting that secondary folds with NW-SE axis directions have been superimposed on the first-generation folds with E-W axis directions in the Khousf refolded splay.Discussion: The findings of this study highlight the structural characteristics and tectonic evolution model of the Khousf splay in the northern terminus of the Nehbandan right-lateral strike-slip fault system. The results suggest that flexural slip played a crucial role in the formation of the multi-plunging anticline and syncline in the Khousf splay. The presence of parasitic folds and complex slicken-line patterns on faults indicate the complexity of deformation processes. The observed strain partitioning and inclined transpressional zones suggest a complex tectonic history in the study area. The superimposition of secondary folds with different axis directions on first-generation folds adds further complexity to the structural evolution of the Khousf refolded splay. Overall, this study provides new insights into the structural characteristics and tectonic evolution of the Khousf splay in the East Iran orogen.

This research assessed stress regimes and fields in eastern Iran using fault-slip data and the tectonic events associated with these changes. Our stress analysis of the brittle structures in the Shekarab Mountains revealed significant changes in stress regimes from the late Cretaceous to the Quaternary. Reconstructing stress fields using the age and sense of fault movements showed that during the late Cretaceous, the direction of the maximum horizontal stress axes (σ1) under a compressional stress regime was ~N290°. This stress regime led to the uplifting of ophiolites and peridotites in eastern Iran. During the Eocene, the σ1 direction was NE-SW. The late Eocene and Oligocene stress states showed two distinct transpression and transtension stress regimes. This transition from transpression to transtension in the eastern Shekarab Mountains was the consequence of regional variations in stress regimes. The Quaternary stress state indicates that the tectonic regime in the Quaternary is strike-slip and the σ1 direction is ~N046°, which coincides with the current convergence direction of the Arabia–Eurasia plates. Our paleostress analysis revealed that four distinct stress regimes have been recognized in the area, including compressional, transtensional, transpressional, and strike-slip regimes. Our findings indicated that the diversity of the tectonic regimes was responsible for the formation of a variety of geological structures, including folds with different axes, faults with different mechanisms, and the current configuration of the Sistan suture zone.

Inclined transpression can be defined in terms of simultaneous contraction and strike-slip and dip-slip shearing. An example of an upper-crustal inclined transpression zone is exposed at Bazargan area, SE Iran. As with most natural transpression zones, deformation at Bazargan area is heterogeneous, and widespread kinematic strain partitioning has given rise to an irregular distribution of strain components and resulting structures. Based on structural and strati graphical evidence, deformational events are divided into two stages: (1) a Late Triassic event and (2) a Late Cretaceous to Miocene event. A wide range of known structures at the map and outcrop scales show the effect of slip partitioning on the structural evolution of this area during this period. The dynamic analysis based on folds, fault striations and calcite twin data show a NNE-SSW trend for the compressive axes in this area. The results of dynamic analysis reveal that the orientation of the compressive axes did not change during late Triassic to present. Moreover, they show that the structural evolution of the Bazargan area occurred under the effect of continues deformation phases which is related to contraction, dip slip and strike slip component. Furthermore, the results indicate that the evolution of Bazargan area in the south of Tabas block is compatible with an inclined transpression model.

Inclined transpression can be defined in terms of simultaneous contraction and strike-slip and dip-slip shearing. An example of an upper-crustal inclined transpression zone is exposed at Bazargan area, SE Iran. As with most natural transpression zones, deformation at Bazargan area is heterogeneous, and widespread kinematic strain partitioning has given rise to an irregular distribution of strain components and resulting structures. Based on structural and strati graphical evidence, deformational events are divided into two stages: (1) a Late Triassic event and (2) a Late Cretaceous to Miocene event. A wide range of known structures at the map and outcrop scales show the effect of slip partitioning on the structural evolution of this area during this period. The dynamic analysis based on folds, fault striations and calcite twin data show a NNE-SSW trend for the compressive axes in this area. The results of dynamic analysis reveal that the orientation of the compressive axes did not change during late Triassic to present. Moreover, they show that the structural evolution of the Bazargan area occurred under the effect of continues deformation phases which is related to contraction, dip slip and strike slip component. Furthermore, the results indicate that the evolution of Bazargan area in the south of Tabas block is compatible with an inclined transpression model.

The western margin of the Lut Block, in southeastern Iran, has experienced many historical and instrumental destructive earthquakes where 13 earthquakes, from 1977 to 2020, totally had surface rupture with a length of roughly 207 km. In this study, we indicated active tectonic evidence of the fundamental faults based on the DEM terrain interpretation, and satellite data analysis with field data. We investigated surface evidence related to the activity of the faults and their depth characteristics. Our results of the geometric-kinematic characteristic of the faults have general applications in describing strike-slip faults, development of releasing, and restraining bends in positive flower structures.

The Sarduiyeh area in the central part of the Kerman Porphyry Copper Belt (KPCB), SE Iran, contains numerous Cu deposits and prospects. This area is bound by E-W trending major faults, which show the northern and southern borders of fault duplex. Minor faults (first, second or third orders) were identified in three trends of NW, N-S and NE. Analysis of the fault kinematics data revealed an extensional fault duplex pattern for this area. In this fault zone, Cu deposits are associated with faults that have a special trend. This proposed kinematic model for evolution of Sarduiyeh extensional fault duplex emphasizes that the main Cu deposits in the Sarduiyeh area are located within the dilatational zones related to NW-SE trending normal faults. In this study, the spatial pattern analysis conducted by Fry, Fractal, Fracture density and buffer zones methods support the conceptual model of district-scale mechanism of structural controls on final emplacement of Cu deposits. This investigation of Sarduiyeh Cu mineralization revealed that the NW-SE trending faults are effective in localization of Cu mineralization in the central part of KPCB.

This data article provides a precise level data on alluvial fans of the western border of Lut desert, a unique location on the Earth, known as one of the hottest spot on the Earth. This data is essential for morphotectonic investigations and is valuable in the field of tectonic and geomorphology studies. It helps to evaluate the region from the viewpoint of tectonic activity by considering the dynamics of alluvial fans, climate and tectonic setting. The data which are presented for 68 quaternary alluvial fans, is taken by processing of remotely sensed Landsat satellite data, photogeology of aerial photographs, measuring on topographic maps and controlled by field checking. This data is useful for defining of a morphotectonic model of this limited access region considering the uplift of the source area along Nayband fault, as the basin–margin fault, respect to the base level. Keywords: Tectonics, Geomorphology, Morphometrics, Geology, Kerman

Department of Geology, Shahid Bahonar University of Kerman, Iran (1); Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands (2) Morphotectonic indices are useful for investigating the effect of tectonic activity in a region. Analysing of these indicators could be applied for zoning an area by using advantages of Geographical Information System, GIS, especially for areas where few morphotectonic studies have been conducted. An example of such areas is the southern end of Nayband Fault located in Central Iranian zone. Nayband fault with a length of about 400 km is a right lateral strike slip fault, that by N-S trending eliminated Lut desert at the west. In this study, the drainage basins of this region are surveyed to analyses the morphotectonic situation. Form Factor, Compaction Coefficient, Ratio of Circularity, Ratio of Elongation, relative Basin Height, and Ruggedness Number are some of the morphometric indices that are calculated for this purpose. After measuring the indices and preparing different zoning maps, it was found that the drainage basins of the region have different rates of morphometric values that could be related to the activity of the Nayband fault and the tectonic regime of the area.

Department of Geology, Shahid Bahonar University of Kerman, Kerman, Iran (1); Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands (2); Department of Geology, Zahedan Branch, Islamic Azad University, Zahedan, Iran (3); Department of Geography, Shahid Bahonar University of Kerman, Kerman, Iran (4) Kouhbanan fault is known as one of the faults that caused many seismic events in Iran. The aim of this study was to investigate the role of tectonics in the development and geometry of the alluvial fans adjacent to this fault. To achieve more accurate results some morphometric indices measured and analysed after considering various factors such as weather, catchment area, regional lithology, tectonic setting, roughness index and field survey. Accordingly, the alluvial fans that were most affected by tectonic were identified.

The Sarduiyeh area in the central part of the Kerman Porphyry Copper Belt (KPCB), SE Iran, contains numerous Cu deposits and prospects. This area is bound by E-W trending major faults, which show the northern and southern borders of fault duplex. Minor faults (first, second or third orders) were identified in three trends of NW, N-S and NE. Analysis of the fault kinematics data revealed an extensional fault duplex pattern for this area. In this fault zone, Cu deposits are associated with faults that have a special trend. This proposed kinematic model for evolution of Sarduiyeh extensional fault duplex emphasizes that the main Cu deposits in the Sarduiyeh area are located within the dilatational zones related to NW-SE trending normal faults. In this study, the spatial pattern analysis conducted by Fry, Fractal, Fracture density and buffer zones methods support the conceptual model of district-scale mechanism of structural controls on final emplacement of Cu deposits. This investigation of Sarduiyeh Cu mineralization revealed that the NW-SE trending faults are effective in localization of Cu mineralization in the central part of KPCB.