مجله زمین ساخت
پیاپی 18 (تابستان 1400)

Seventy- four surface and subsurface sediment samples from the SaghalakSar bog were investigated to decipher their tectonic setting and provenance. The Al2O3 content showed positive correlation with MgO, Fe2O3, and K2O while it showed negative correlation with TiO2 and SiO2, suggesting that clay minerals and mica were major hosts for these elements. Average K2O values were higher than average Na2O levels, reflecting that k-feldspar was proportionally more abundant than plagioclase in the source rock. A decrease in K2O with an increase in Na2O in the northwest bog could be interpreted as alteration of rocks, suggesting possible effect of sodium feldspar on the source rock. A strong increase in MgO and Fe2O3 relative to average upper continental crust was consistent with mafic source rock. The results of comparing the major-element oxides with the S (SiO2 / 10)-CM (CaO + MgO)- NK (Na2O + K20) diagram showed that the sediments had been subjected to weathering, and were derived from magmatic rocks, Shoshonite, Dacite, Monzonite, and Gabbro (usually intermediate composition) at the Alborz magmatic zone. Based on Binary plot of SiO2 versus Al2O3+Na2O+K2O indicated semi-arid climatic condition. Binary plot of Fe2O3+MgO versus Al2O3/SiO2 and TiO2, log (K2O/Na2O) versus SiO2, and ternary diagram of trace elemental, Th, Sc, La, and Zr, it seems that the sediments originated first from a marginal Back Arc basin and then from a magmatic arc in the active continental margin. Finally, during the Quaternary, they went through a recycle of sedimentation after weathering and transport to the Saghalak-Sar Bog

The Siah-Jackouk area is located in the eastern part of the Sistan Suture Zone, southeast of Zahedan. This area has been affected by faulting, folding, bouddinage and dyke swarm. The main objective of this research is to display the deformation history of this area. For this purpose, the characteristics and spatial relationships of the structures were extracted, and the state of stress during the emplacement of the dykes was investigated using the 3D Mohr and stereographic methods. Statistical analysis and the cross-cutting relationships, as well as the geometry of the folding and boudinaged structures, suggest four main phases of deformation due to progressive deformation in this region. At first, the initial horizontal layering is inclined. Then the dykes penetrate along their weak surfaces, subsequently layering with parallel dykes, undergo shear component along that caused folding and bouddinage. At this phase, changes in the distance and thickness of dykes as resistant areas, have led to different evolutions of folding and faulting, and strain. In the last phase of deformation, the study area is affected by the north-south right-lateral faults caused by the current north-south stress regime of the Sistan Suture Zone.

Fault-related folds extend in most tectonics settings and in both extensional and compressional regimes. The widespread importance of such structures in the exploration and extraction of hydrocarbon resources and seismological aspects led to consideration beyond structural geology studies. On the other hand, understanding the geometric evolution of these folds can reveal the geometric relationship of these structures with the processes of placement and migration of hydrocarbon resources. This study uses two 2D finite element models to investigate geometric differences and stress-strain evolution differences in simple and high angle breakthrough fault-propagation folds. Results show that; A) In both types of folding, the plastic strain is concentrated on the surface of the fault, the fault tip, and the forelimb. B) In both types of folding, the pattern of stress-strain at the crest and fold limbs are similar, while it is different from the pattern of stress-strain at the fault surface, although the pattern of stress-strain at different points of faults (tip, middle, and base of the fault) are also similar to each other. C) Despite the similarity of the stress and strain evolution pattern in these two types of folds, three main differences can be identified, 1) reduction of strain-softening interval in the forelimb of breakthrough fault-propagation fold model, 2) increased differential stress in high angle breakthrough fault-propagation folds, and 3) in simple fault- propagation fold model, the strain-hardening interval increases to the fault tip, while in high angle breakthrough fault-propagation folds the reverse is true.

Alvand granitoid pluton has penetrated into the metamorphic rocks of Sanandaj-Sirjan zone in the Middle Jurassic period and it has created an aura of contact metamorphism around it. Alvand granitoid pluton is the highest elevation in Hamedan region and Its catchment area is located in the south of Hamedan. In this study, the tectonic activity of catchments of Alvand Mountain has been studied based on geomorphic indices. According to the characteristics of the catchments, Asymmetry factor (Af), Hypostometric integral index (Hi), Stream length-gradient index (Sl), Mountain-front sinuosity (Smf), Valley floor width-to-height ratio (Vf), Basin Shap index (BS) and Transverse topographic symmetry index (T) has been studied and Finally, with the overlap of the obtained indices, the relative active tectonic map (IAT) of the region was determined. The values obtained for active tectonics show that the area has three zones with high tectonic activity, medium tectonic activity and finally low tectonic activity. Northeast and east of Alvand mountain shows high tectonic activity compared to other parts and There are large reverse faults with northwest-southeast striking. Existence of many new landslides in this area indicates high tectonic activity

Adjacent to the northern border of the Sistan suture zone and the Lut block, north of the Qayen, the Paleocene-Eocene volcano-sedimentary sequence represents an interference pattern of folding. Crescent structures indicate the type 2 of superimposed folding. The axial plan of the first generation of the large-scale folds is generally east-west trended, but along their strike, they are obviously curved to the north and south. A linear dioritic-andesitic dyke swarm, is intruded on this sequence with a radial pattern, and cut the axial plane of the first generation and is affected by the second generation of folding. In order to date this tectono-magmatic event, U-Pb dating is performed on the zircon crystals of these dykes, and an age of ~40 Ma is yielded as the cooling age. The consistency between the dykes’ strikes and the curvature of the first-generation folding axial plane (in response to the second folding event) gave a redial pattern with 30o declination to this dyke swarm. This may indicate the intruding and cooling of the dykes coincide with the second folding generation. Acceptable adaptation of the declination of these dykes to that of the curved axial plane of the first folding episode on the linear regression diagram can be a new method for testing the bends that originally have been linear. Our structural analyses on the Qayen area indicate that Achani structure is a clear example of a larger oroclinal buckling in the region, during the Eocene, coinciding with the formation of the Eastern Iranian Orocline.

Iran has been affected by the convergence of the Arabian and Eurasia plates. For this reason, it has experienced destructive earthquakes throughout history. In terms of tectonic and seismic properties, Iran can be divided into 5 general seismotectonic provinces; Zagros, Central-East Iran, Alborz-Azerbaijan, Makran, and Kopeh Dagh. One of the facts that best describes the characteristics of earthquakes is their focal mechanism. In this article, the focal mechanisms of these 5 provinces were collected and classified with FMC software. For each zone, the frequency percentage of each group of faults was determined. Most faults are in the reverse class or compression type with the strike-slip component. Most of the faults of the reverse type are related to Zagros province, which includes 58% of its earthquakes and 42% of Iran's earthquakes. Thus, it seems the Zagros has been more affected by the convergence of the Eurasian and Arabian plates than other regions. Normal faults in all provinces have a small frequency so that only about 3% of the total earthquakes in Iran are in this class.