مجله زمین ساخت
پیاپی 14 (تابستان 1399)

Parpar Mountains is located in northeastern part of Shahrkord City, in Zagros collisional orogeny, and in the transition zone from the Sanandaj Sirjan (SSZ) to High Zagros zones. The mountains consists of Jurassic and Lower Cretaceous rocks. Former structural analysis of the Zagros collisional zone resulted in two proposition in which the Zagros oblique orogeny occurred as a right lateral transpression in Early Tertiary or partitioning of displacement between the strike-slip and reverse faults in Late Tertiary. Field studies show that faults are of oblique mechanisms with generally two main trends. The NW-trending faults have oblique Dextral Reverse kinematics whereas the NE-trending strike-slip faults have reverse or normal dip-slip components. Along the NW-trending faults, which also control the region morphology, positive flower structures are developed. These faults cause the mountains to poped-up against the low land around it.  The rhomboids shape of the mountains as a result of “R” and “P” Riedel shear faults interplay as well as development of oblique inclined folds is taken into account for transpression deformation of structures in the study area as a part of Zagros oblique collisional zone. Since the faults displaced the Late Tertiary rocks, this transpression deformation is proposed to occurr at least before Late Tertiary.

In recent years have seen an increasing interest in the study of deformation characteristics like temperature in the orogenic belt. In this research, deformation temperature in the Seh-Ghalatoun metamorphic complex was estimated by using petrofabrics indicators such as quartz and feldspar recrystalization regims, quartz c-axis pattern and opening angle. The Seh-Ghalatoun metamorphic complex as a part of the Sanandaj-Sirjan metamorphic belt located in the east of Neyriz from the Fars province. Petrographic study and quartz c-axis measurements from the oriented samples of this area show that c-axis maxima concentrate in intermediate positions between the Y- and Z-axes of the finite strain ellipsoid. Also grain boundary migration and subgrain rotation recystallizations are dominant. Intermediate temperatures (400–500°C) are suggested by sub-grain rotation recrystallization microstructures (SGR) and high temperatures (>550 °C) can be inferred from grain-boundary migration (GBM) recrystallization microstructures. GBM microstructures were overprinted by partial grain-boundary migration (BLG), elongate new grains, feldspars book-shelf structures and micafish indicate two phase of deformation which earlier stage occurred on the lower temperature. Opening angles of quartz c-axis fabrics have ranging from 68° to 80° which is confirm deformation temperature between 490 and 610±50 °C. A positive correlation exists between deformation temperature yielded from quartz opening angle, active slip systems and microstructures. These results highlight greenschist-to-amphibolite-facies deformation conditions.

The study area is exposed in the western margin of the Zahedan dextral strike-slip fault in eastern part of Sistan suture zone. This study investigates the situation of paleo-stress field based on heterogeneous fault slip data and slip-lines in Eocene-Oligocene limestone blocks. The results show the position of the three axes s 1 =45/53,  s 2 =207/35, s 3 =303/09. Based on the "right Dihedron" and "rotational optimization" methods, R¢= R (F)=0.43 , which represents the simultaneous compressional - shear stress component in eastern Sistan fold and thrust belt. Accompaniment of tensional structures such as boudinage, shear fractures and Normal faulting, indicate local Tensional stress whith  N340 direction. This results, show the occurrence of a progressive deformational phases and rotational displacement of the internal elements in this right-lateral strike-slip fault.  The local maximum tensional stress direction in this area, rotated clockwise direction, about 25° from Eocene  to recent time. The location of Ghargharook area near the fault-bent, along the Zahedan dextral strike-slip fault, can be caused  to clockwise rotation of  principal stress axis.

The study area is located 80 km northwest of Birjand, the central of Southern Khorasan province, and is located in the structural province of Sistan and part of North Lut. To study the amount of tectonic activity in different parts of the study area resulting from the activity of the well fault zone, study and study of tectonic morphology indices can be a good tool to achieve this goal, in this study of tectonic morphology indices such as shape coefficient Basin (Ff), drainage density (Dd), asymmetry of the drainage basin (Af) and river channel sinusitis (S) as well as field evidence of use. After calculating the indices in each sub-basin in accordance with the faults of the region, the amount of tectonic activity was obtained. Then, for each index, a zoning map of the tectonic activity level in different parts of the study area was drawn, and finally, the relative active tectonics index (IAT) was calculated to determine the total tectonic activity level, which according to the average The study area was divided into 4 categories of very high, high, medium and low tectonic activity, which measured indices in the basin corresponding to the eastern branch of Chahak fault show higher values that indicate high activity of Chahak fault In this section.