eastern iran

Structural and petrological evidence suggests an asymmetric and two-sided subduction of the Sistan oceanic lithosphere under the Lut and Afghan blocks. The subduction under the Lut block was characterized by a steeper dip angle and a higher subduction rate, leading to the retreat of the plate boundary towards the ocean and subsequent back-arc extension. Studies on the geochemistry and possible origin of the mafic-intermediate igneous rocks of the Lut block corroborate the occurrence of crustal thinning and back-arc extension, highlighting the significant role of subduction in their formation. In this research, we employed laboratory or analog modeling with scale lengths to simulate the characteristics of the Sistan oceanic lithosphere subduction and the geodynamic processes in eastern Iran. We investigated the parameters controlling the style of subduction by examining the sinking of a thin viscoelastic silicone putty sheet with varying geometric and rheological properties in a glucose syrup-filled reservoir. Our findings revealed that an increase in length and thickness, coupled with a low viscosity ratio of the lithosphere and asthenosphere, accelerates the subduction rate. We also identified a significant correlation between the dip angle and the subduction rate. In summary, the deformation of the back-arc region was analyzed through kinematic investigation in the performed experiments. The experimental outcomes, which confirm the high rate and dip angle of subduction, and also the back-arc extension, can be identified as characteristics of the Sistan Ocean’s subduction zone under the Lut block.

The deformed Sehchangi conglomerate is exposed with an angular unconformity on the Triassic sediments on the curved northwestern border of the Sistan and Lut terrains. The Sehchangi conglomerate was undergone brittle deformation, consequently the extension and conjugate shear fractures occurred in its and no ductile deformation has been seen in matrix and pebbls of this conglomerate. According to extensional fractures, the value of strain longitudinal parameters was obtained as follows: e=0.15, S=1.15, =1.32 and =0.75. Also, the stress analysis of conjugate shear fractures in this conglomerate by the "right dihedral" and "rotational optimization" methods were calculated 1=23/190, 2=43/77, 3=38/299 and R()=0.7, R=1.23. These results indicate that the conglomerate has been experienced an elongation with some volume changes along the N70W direction. According to study of extension and conjugate shear fractures, it seems that the buckling tectonic regime in the Sechangi area which associated with the Paleogen eastern Iranian orogeny, caused the extension-shear deformations and orientation of refold structures in this area.

Calculation of geological and seismic moments is one of the methods in evaluating the level of tectonic activities in different regions. In this study the seismic potential in eastern Iran was assessed using geological and seismic moment rates. Results show that the maximum geological moment for the Sabzevaran fault is 2.61544 × 1018 and the minimum value, 9.91367 × 1015, belongs to the Jazmourian fault. Based on the obtained iso-acceleration map, the average and maximum acceleration values (0.747423) have been observed around the important Saravan, Bam posht, Asagi, Pishgiram, Zahedan and Gowk. The calculated cumulative geological moment rate for the studied region is 1.4166 × 1018. According to the cumulative geological moment rate map, the maximum value of the cumulative geological moment rate of 2.26248 × 1020 was observed in the vicinity of the Sefidabeh-Zahedan, Kahurak, Narreh Now, Gowk, and Shahdad fault systems. The minimum cumulative geological moment rate, 1.77828 × 1019, was detected in the northern region of the Narges fault.

The study area is located in the northeast of the Lut block between Nehbandan and Nayband fault zones; that in addition to sedimentary units and Cretaceous ophiolites, a wide range of Paleogene and Neogene sedimentary facies and pyroclastic sediments have been affected by deformation. Structural trends of the study area include two main groups with north-south and northwest-southeast trends. Structural data were collected in the direction of north-south trends (including Gazik, Afzalabad and east of Sahlabad) and northwest-southeast (including Birjand and Zahan); the deformed regions can be divided into three groups. Deformation in the direction of north-south zones (such as Gazik and Afzalabad stations) is mostly done as transpersonal zones. In the distance between the left-lateral en-echelon faults with north-south trend (such as Cheshmezangi, Chakhoo, and Asakoohak), according to the type of their overlap, pressure zones (such as Kasrab and Torshab) have been formed. In the mentioned compressive zones due to the operation of the thrust faults, ophiolite units have been exposed in these regions. The existence of thrust faults in the end of strike-slip faults (such as South Birjand), which are due to the interaction of the main trends in the region, has caused ophiolite outcrops in the direction of northwest-southeast trends.

The Birjand anticline is a type of the fault propagation fold that is formed above a blind thrust fault and is divided into 11 segments by 12 tear faults. In this research, the Late Cenozoic deformation associated with the Birjand blind thrust has been evaluated. To this end, the fractal dimension of drainage patterns and its statistical properties is calculated on the Birjand anticline. Accordingly, the spatial distribution of windows with the fractal dimensions close to 2 are within the regions that are low slope, low height and marl-tuff units. These windows are more relative frequency in the northern limb of the fold, also to the northwest end segments (10 and 11). This issue is related to a gentle back-limb of the fold and flat crest of the end segment 11. For Birjand anticline toward northwest, lateral growth of the fold is clearly at the Dasht-e Birjand and close to the Shekarab kuh to form as gently-dipping alluvial fans deposited. In the progressive stages of the Birjand anticline growth, segments from northwest to the southeast have grown more structurally mature and the values of the fractal dimension are lower. In the back-limb and flat crest of the fold, the drainage patterns are closer to trellis and dendritic and the fractal dimension approaches to 2 and in the fore limb are intermediate and steep slope, the drainage patterns are varies to parallel and the fractal dimension is decreasing. The surface deformation due to the Birjand blind thrust geometry controls the pattern and density of the drainage network by effects of topography and lithology and the result is a high the fractal dimension in the region with more active tectonic.