مجله زمین ساخت
پیاپی 22 (تابستان 1401)

Symmetrical and closed Ezgeleh anticline is located in the fold and Thrust belt of Zagros zone and in the Lorestan subzone. The Trend of this fold is NW-SE. This fold like most of other Zagros folding is fold related fault and Detachment fold type. The oldest rock unit that outcrops in the core of the anticline is the Ilam unit, which consists of thin to thick layers of light gray to white limestone. In this research, the lateral growth of the Ezgeleh anticline due to the function of a hidden reverse fault has been investigated using morphotectonic indicators. Morphometry indicators such as BS،AF، SL، Hi, RE، C were used to examine transverse growth in this fold. Most of catchments are elongated and have parallel drainages in this fold. Investigation of tectonic morphological indices indicated transverse growth of this anticline and Its transverse growth mechanism is fixed hinges and rotating limbs. According to the evidence of fold growth the region is active and the seismic activities of the region confirm this.

For completing of studies about influences of stress changes due to impounding on foundation failure and bulk stability of large dams, the analysis of foundation failure probability due to dam impounding is necessary. Therefore, the Emarat under-construction dam (Ardabil Province) is selected as a case study for 2D numerical modelling on the basis of finite elements with applying complete non-linear analyzing with using Plaxis software. For this aim, the high resolution engineering geology was performed on Dam site and its reservoir and therefore, the needed parameters for modelling, such as compressive and uniaxial strength in dry and saturation situation, were evaluated. Then, the 2D modelling was performed by Plaxis software and the probability of foundation failure was surveyed. The results showed that after impounding and raising of pore pressure, the calculated Mohr circle of selected critical point is migrated toward the coordinate center and then, semi-tangent to failure envelope which demonstrated that failure probability of foundation is caused due to dam impounding in Emarat under constructed dam. Also, we prospect that after impounding, the existent old fault zones (as second order related to main faults) with normal and/or strike-slip components, such as Balan fault which located to dam adjacent, will activate instead of forming of new fractures.

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.

A vein-type barite deposit is occurred along the Behjatabad fault zone in Lower Cretaceous carbonates in the eastern part of Murchekhurt. In order to assess the rational relationship between structures and vein-type barite mineralization in the east of Murchekhurt area, remote sensing analysis on the satellite images with the aim to identify the structures have been done, then faults, veins and bedding have been measured in the fieldwork. The main structures are the deep basement northern and southern Behjatabad fault zone in the eastern part and the Sepahan fault zone in the western part of the study area which hosts the vein-type barite mineralization. Those fault zones show an old reverse kinematics associated with drag folds and a young right-lateral strike-slip sense of movement that is still active. Paleostress analysis documents a shift in the stress regime from NE-SW-directed to N-S-directed since the middle Miocene. Spatiality the Behjatabad fault zone is close to UDVA and acted as a dip corridor for conducting Ba-bearing hydrothermal fluids and hosting the barit mineralization.

In the Emarat Pb-Zn deposit located in the Markazi province, underground exploration and exploitation activities have been carried out at the various elevation levels through drilling tunnels and cross-cuts. In the present research, 2D and 3D modeling of surveyed faults at the variety of levels were performed studying their relationship with ore-bearing in the region qualitatively and quantitatively. To achieve the goal, a complete statistical study was done, first. Afterward, 2D strike and dip map with rose diagram, 2D grid-based map, 3D strike and dip diagram and solid model of the faults surveyed at the various elevation levels were drawn and analyzed using methods and different mathematical algorithms applied in geosciences. In addition, a stratified iso-grade map of total Pb-Zn for different elevation levels was also produced. The qualitative comparison of 2D grid-based maps and iso-grade maps for each elevation level peer to peer shows that in general, trend of mineral depositing follows the trend of faults frequency but frequency of the faults number in each zone does not much affect on the deposit grade. Also, the linear correlation coefficient between the faults number and deposit grade at the various elevation levels was obtained 0.157 on average, equaling to "very low" correlation. In fact, the results of the quantitative correlation at the different elevation levels, confirm the results of the qualitative correlation study.

The Surmaq region on the northeastern margin of the Zagros Orogenic Belt, which was chosen as the research area, includes a significant expansion of fractures and important mines, which seems to be related. Structurally, the Surmaq region is located in the central part of the Sanandaj-Sirjan zone and close to the Main Zagros Thrust. The use of remote sensing techniques, including 1-various false color combinations in order to highlight the lineaments as well as possible and identify the fault patterns and 2-false color combinations along with band ratios in addition to analysis the principle components in order to identify different alteration zones for manganese deposits identifications, provide valuable information about the relation between the alteration zones and the fault patterns. Study of the fault patterns using satellite images as well as their control in field studies showed four general directions. The map of faults density and structural nodes were prepared for identifying mineralization. Based on the Fry analysis of structural nodes, the convergence direction was obtained about NE-SW (040-220). Comparing the pattern of fault density, mineralization, and alteration zones with each other helped to identify areas with mineralization grades. In places where extensional faults intersect with other faults, especially longitudinal basement faults, more suitable places have been formed for mineralization and mineral replacement. Mineral indices with high density and richness are mostly concentrated in the fractured area of the faults and mostly in connection with the Abadeh and Surmaq faults and the junction with the N-S-trending Gashar Fault.