مجله زمین ساخت
پیاپی 17 (بهار 1400)

In this research, the seismicity and neomorphotectonics of the eastern part of the Alborz range, which is delimited by the North Alborz fault zone and Firoozkuh Fault zone to the north and south respectively, has been studied. Eleven sub drainage basins in the study area along with the general northeast-southwest north-south trend and a sub-basin along the eastern-west trend were identified. The stream gradient (Ksn) and stream concavity (θ) morphotectonic indexes for all sub-basins were calculated where the range between 0.36-1 for θ and 72-288 for Ksn. The northern and southern rivers of sub-basins were tilted and several knickpoints were made by fault movements. A NE-SW striking fault zone with a width of 15 kilometers, is confined between Zarkin-Firoozkooh, Chashm, and Orim fault zones in the south, and Badroud and Lord faults in the north host the more magnificent earthquakes that have been occurred. a and b values were calculated to 3.84 and 0.85, respectively. The magnitude of earthquakes is between 2.4 to 4.2 values and the concentration depth of 60.7 percent of earthquakes is between 4.5 to 10 kilometers. Comparison of field evidence with calculations based on Ksn and θ indicators along North Alborz, Firuzkuh, Nord, LaleBand, and other fault branches, creating consecutive knickpoints from their activity is confirmed. Our results reveal low signals of neomorphotectonic and seismic activity in the middle part of the study area, which we would recommend for the development of the urban compared to the rest of the region.

Kharanagh Mountain which has NW-SE trend is located in Central Iran Zone, northeast Yazd block. Stratigraphically, the area is composed of Paleozoic (Devonian) to Quaternary strata. The rotation of the blocks of Central Iran, the collision of the Arabic plate with Iran, and also the structural interaction between the blocks of Central Iran during its tectonic evolution, has caused a change in the direction of the kinematic stress tensors (P-T-B). As a result, the formation of new structures and changes in paleo-structures had chronologically occurred throughout the study area. In this research, stress field variations of Mesozoic era of Fahraj-Kharanagh areas is evaluated. Hence, geological fault and fault-slip data and other tectonic and stratigraphic evidence were collected at 13 stations. The general trend of faults in the study area is NW-SE which are right-lateral strike-slip in type similar to features of Anar Fault. The change in direction of the pressure axis (P Axis) occurred counterclockwise from the vertical position of the Anar Fault to parallel to it in the period of Lower Paleozoic to Upper Cenozoic, which has changed the kinematic mechanism in the area. The presence of fault-slip in the Quaternary sediments, as well as the great thickness of the deposits in the area, indicate that the Anar fault is active presently.

In this research the impact of structural controlling factors in the fluorite mineralization was evaluated, north west of the Sanandaj-Sirjan metamorphic zone. The structural and microstructural analysis indicated the major structure in the Bagher Abad region is fold related structures and shear fractures that cut the fold axes are the host for fluorite mineralization. In the Qahr-Abad area, fluorite deposits are reverse fault-related. Satellite image analysis with band ratio, PCA, and SAM techniques revealed the hydrothermal fluid circulation in the host rock caused the propagation of propylitic and phyllic alterations in the BA region whereas phyllic and argillic alteration in the QA region is dominated. The fluid inclusions micro-thermometry indicated in the BA region, mineralization occurred in the shallow depth approximately at 30 meters and low temperature 50-100 Cº. In the QA region, mineralization takes place in the 150-200 meters and higher tempreture. Analysis of salinity of the fluid inclusion shows in the BA region, mixing of meteoric water with hydrothermal fluid and Dissolution of host rock increase the salinity percent of fluid inclusion.

The geometry of mineral deposits in brittle shear zones depends on the open spaces in these zones and especially in the Riedel structures. The systematic intersection of Riedel fractures in the path of these zones causes the formation of Riedel blocks, the dimensions of which are proportional to the spacing between these fractures. By increasing the shear strain (γ) in a shear zone and consequently the rotation of these blocks, it is expected to create proportionate open spaces that with the penetration and deposition of ores in these spaces, causes the formation of mineral veins in all these spaces. Since the amount of open spaces in shear zones is different, in this study, through analogue and numerical modeling using 3DEC software, it was shown that the change in the dimensions of the blocks in equal kinetic conditions is one of the parameters affecting the amount of open spaces of these zones. Therefore, this volume of open spaces in a single range of different shear zones, which are different from each other in terms of spacing of Riedel fractures, is inversely related to increasing the dimensions of Riedel blocks; the more Riedel blocks, the more block rotation and consequently more space is expected. As the shear strain increases during a progressive deformation, in bigger dimensions of the Riedel blocks tested, more force is expended on inter-block slips than on block rotation and open space. The amount of open spaces created in numerical modeling shows good agreement with this type of modeling.

Regarding to that fault geomorphology could be an information layer in earthquake hazard assessment, is so important. In this research, only landforms of active tectonic within all geomorphs are investigated. These geomorphological features in east of Iran have been investigated using displacement of seasonal streams in field work and on sattlite images. Greatest vertical cumulative movements, more than 2000 m (Golbaf fault) and 1800 m (Kuhbanan) are manifest specifications of the faults in Kerman province. Lakarkuh fault, also, has 1700 m and 1500 m maximum vertical and horizontal displacements, respectively. On the two investigable points on Jiroft and Sabzevaran faults, 110 m and 150 m horizontal displacements were seen, respectively. In sections of streams, from a few centimeters (Jiroft fault), near one meter (Shasdad fault) to few meters (Sarvestan fault) vertical displacements were seen. Among the reverse faults in Kerman province, Nayband, Sarvestsn, Kuhbanan, Shahdad faults, at least in part of their lenghts, created an obvious boundary between mountain and plain. Lakarkuh and Nayband faults have bending on their one or two terminations. The 1978 Tabas earthquke on north termination and Godar earthquake fault (the 2017 Hojedk earthquakes) on south termination of the Lakarkuh fault, are from these active and important fault terminations in eastern Iran and Kerman province. Following field work, on of the eastern Iran specifications was confirmed: coseismic displacements of earthquakes of the Golbaf fault are measurable after at least 26 years.

Kermanshah province, geologically is located in high Zagros zone.The Neo-Tethys closure and Iranian – Arabian plate collision, which causes the obduction of oceanic crust sequence and various tectonic structures such as the folds, faults, joints, shear zones, unconformity and klippe have formed the remarkable geological units of the Kermanshah region. First of all, this study aims to introduce and designate the geodiversity of theSahne-Harsin region (mostly tectonically) including the unique folding in radiolarites, faults, unconformities, joints, etc. Secondly, using the genetic characteristics (structural, stratigraphic), the diversity of tectonic modes of the region and their values was studied. Subsequently, after the designation of the tectonic heritages, they were classified and introduced. The importance of this Italian assessment model is based on geological evolution, chronostratigraphy, palaeo-environmental and educational values. The designation of tectonic geoheritage as natural heritage in the Sahne-Harsin region of Kermanshah province in Iran is an initiative and promising result for further studies towards the establishment of a geopark at the national level and a member of the GGN.