مجله زمین ساخت
پیاپی 10 (تابستان 1398)

Nezamabad fault zone with sinistral strike-slip (Dominant Mechanism) and NE-NW striking has located in the southwest of Iran, it is considered as one of the most important structures in the Zagros fold-thrust belt. This fault has caused complex structural deformations in the region. Also, there is an evidence for fault movement in the Khaftar anticline. This study aimed to fractal analysis, the impact of the Nezamabad fault on the lineaments extracted from the satellite image of Khaftar anticline. The box-counting method is an appropriate method for analyzing the fracture pattern for this study. Using this method, fractal dimensions were calculated for different parts of the Khaftar anticline. The difference between the fractal dimensions obtained from the lineaments associated with the Nezamabad fault well identifies how this fault is affected and the areas with different structural maturity in different parts of the Khaftar anticline. So that part A and C and their southern limbs, which include the SLA and SLC parts, have more fractal dimensions than other parts of the anticline, and these areas, especially the southern limbs of parts A and C are more active than other parts. Also, the difference in fractal dimensions of the Khaftar anticline as a result of differences in density, severity, and direction of stress due to Nezamabad fault performance in the area was evaluated.

The main purpose of seismic hazard analysis is to estimate the seismic loading parameters more accurately to optimize the seismic design of the structures and their costs. Kahrizak, South Rey and North Rey faults are located in the south of Tehran and some discussions have been raised about their presence. In this paper, after reviewing the discussions about the presence or absence of the mentioned structures, their effect on the peak ground acceleration is investigated in the Tehran area. The results show that considering these faults in the analysis, increases PGA values up to 100% at a great part of the study area in the south of Tehran. In addition to the variation of the PGA values, the design earthquake characteristics (in terms of the magnitude and the source to site distance) also differ substantially between the two cases of the presence and absence of the mentioned structures. Based on these results and considering the dramatic effects of uncertainties of south Tehran faults on seismic hazard parameters in the region, further studies on the presence or absence of these faults are necessary.

Fault-related folds extend across most of mountain belts, accretionary prisms, fold-and-thrust belts, and intraplate portions. The widespread importance of such structures in the exploration and extraction of hydrocarbon resources and also seismological aspects had led to consideration beyond the structural geology studies. Numerical modeling of fault-related folds using finite element method can provide valuable information on the stress and strain evolution. In this regard, present study considers the stress and strain evolution of the Aygan fault-propagation fold, which has evolved from footwall shortcut thrusts of the Mosha fault during inversion of the central Alborz basin in Oligocene-Miocene, using finite element method. In the following, the evolution of stress and strain in the Aygan fault-propagation fold considers and analyses using differential stress-strain, strain-time, and stress-time diagrams, and also effects of density change on fold geometry. The modelling results show that increasing and decreasing of density doesn’t play a significant role in stress and strain evolution, so that only slight variations appeared on backlimb. The model results, however, show that increasing and decreasing of density results in increasing and decreasing of half-wavelength, that indicate a direct relationship between density and half-wavelength in the fault-propagation fold.

Kuh-Sefid Tutak complex is a part of the southern Sanandaj-Sirjan metamorphic zone with the Northwest-Southeast trend and consists of sequences that have been undergone greenschist to lower amphibolite facies metamorphism. Augen gneisses, as one of the most important of metamorphic units in the complex, are characterized by mineralogy composition of quartz, plagioclase, alkali-feldspar, allanite, epidote, biotite, muscovite, zircon, apatite, zoisite, and clinozoisite. The different behavior of alkali feldspar (more brittle) and plagioclase (more ductile) during deformation and metamorphism in these gneisses apparently to be a principal cause for the formation of the augen texture. Evidence of the deformation such as deformation twinning, undulose extinction, deformation lamellae, folding and microstructures like mica fish, bookshelf, flanking, Window indicate dynamic recrystallization under ductile deformation. Moreover, the presence of kinking and grain migration microstructures show the condition of ductile-brittle deformation. Field and petrographic evidence such as symmetric and asymmetric porphyroclasts, foliation, lineation, strong pleochroism in biotite, sagenitic biotite, no zoning in plagioclase, grain boundary migration indicate the effect of medium metamorphism in greenschist to lower amphibolite facies and moreover, perthitic texture, accessory minerals such as apatite and zircon as trapped in biotite, as well as presence of allanite, are good indicators for the gneisses to display their igneous origin (Augen gneisses) along with the effect of dynamic deformation in the region.

Study area (Shekarab Mountains) is located in Sistan suture zone. The aim of this research is to investigate the variation of stress pattern (direction of stress tensors and stress ellipsoids shape) in Neogene units, Paleogene units and older units. In this research characteristics of brittle structures (faults) were interpreted using Win-Tensor software. Structural analysis and analysis of Steps of applied Paleo stress in Shekarab Mountains indicate that in Cretaceous time stress regime operation tectonic was pressure with the direction of the main stress axes σ1=337/26, σ2=070/06, σ3=172/64 and stress ratio was 0.1 which caused the uplifting of peridotites and ophiolites in eastern part of study area. The second step of stress has been strike slip and transpressive with the direction of the main stress axes σ1=003/31, σ2=110/26, σ3=232/47 and stress ratio was 0.29, more exhumation of igneous units is related to in the eastern part of Shekarab Mountains in these regions units' stress regime has been displaced locally from strike slip to transpressive that is due to local changes of stress direction in this regions. The third step of stress regime of in Shekarab Mountains is strike slip with the direction of the main stress axes σ1=060/10, σ2=227/72, σ3=152/08 and stress ratio 0.5. Results of stress analysis indicate that major stress axis (σ1) in Cretaceous units had N337 trend, in Eocene units had N003 trend and in Quaternary units has N060 trend.

The study area is located 34 km from Khoy city in North West Iran. This zones formation basically ophiolitic complex. In this research field surveys were carried out for structural measurements, during which major and minor faults and shear zones were made. One of the structural features of theGheris shear zone is the presence of ductile and brittle shear zones. Mesoscopic and microscopic scale analysis carried out for determining the deformation history of the area. In the Gheris shear zone (GSZ), tectonics structures and microstructures analys based on field study and statistical methods indicate that dominant fabrics have been deformed in the NE-SW direction. In the GSZ, comparison of kinematic and geometric analysis in brittle, ductile and brittle- ductile shear zone indicated that these deformations were created in a five deformational event and different physical conditions. The obtained results, four deformation phase (D1-D4) identified in GSZ. The most important deformation mechanisms including: S-C fabrics, mineral fish, S-shaped and Z-shaped shear folds and mantled porphyroclasts throughout the field area indicate dextral deformation. In this shear zone, the most reliable shear sense markers in high grade and shear sense indicators indicated that the Gheris shear zone deformed via dextral tectonics regime.