Introduction and Structural Study of the Ezedin-Rahjerd Transverse Fault Zone, One of the Seismic Potential Structures in Tafresh Area

Document Type : Articles

Author

Department of Geology, Faculty of Science, Imam Khomeini International University, Qazvin, Iran

Abstract

Accurate identification of seismic potential is the first step and one of the most important for seismic studies in each region. The study area, located in the middle part of the Urmia-Dokhtar magmatic arc belt, is one of the areas where identify and study of its seismic sources is necessary. In this study, for the first time, the Ezedin-Rahjerd fault system is introduced according to the interpretation of satellite images, field study and tectonic surveys of the area. The Cenozoic (Eocene) volcanic rocks of the Tafresh area, which are covered with Lower and Upper Red Formations have been cut by this N-150 transverse fault of 70 km. This fault system, like other transverse faults such as the Bidhend, Qom-Zefreh and Dehshir-baft faults, has cut volcanic rocks of the magmatic arc belt. Geometry pattern detection of the structures using satellite images and field observations in the area showed that the effect of this fault are observed as the change of the main structure trends such as the reverse faults and fold axes bending and the formation of minor structures with a different trend from the main structures trends of the Urmia-Dokhtar belt. The slicken lines of the fault plane and the right-lateral bending of the main fold axes along the fault zone and the formation of minor structures indicates the right lateral movement of the Ezedin-Rahjerd fault zone.
One of the prominent features of the study area is the existence of several parallel dyke sets that are not very distant and sometimes outcropping at a distance of less than 200 m. These dykes with a thickness of about 2-5 m and a length of about 15-20 m with dip of more than 80 degrees are divided into two sets with dominant trends N40-45W and N20-30E. The first set of dykes with N40-45W trending are a semi-deep dolerite and porphyro gabbro diorite that exposed around the Gyan and Lalaein villages and cutting Eocene and older units. Whereas, the second N20-30E trending shallow dikes with combining of hornblende, andesite and basaltic andesite also cuts Miocene volcanic-sedimentary rocks, Qom Formation and Lower Red Formation. Alteration of the second dyke set is significant. The trend, including rocks and tectonic setting of the dykes, show their influence in several stages. These intrusive dikes also show tension fractures, so will assist in structural analysis of the area. In such a right lateral transverse fault zone, development of the tension fractures with N20-30E trend is not unexpected. Therefore, the second shallow N20-30E dyke set are formed in these tension fractures due to the Ezedin-Rahjerd transverse fault activity. While the first set with N40-45W trending that is older than the second one, has been created due to the main structures of the Urmia-Dokhtar magmatic belt.
The most important geomorphological feature observed along the Ezedin-Rahjerd fault is the conformity of the Kamar (Tafresh) river as the main river of the area with the fault trend. The Kamar River flows north-south along the Ezedin-Rahjerd fault, passing through the Barezjan, Dadghan, and Ezedin villages, and then reaches the Ghareh-Chai River in Jalaier. Instrumental earthquakes of the area show 2

Keywords

References

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History

  • Receive Date: 27 May 2018
  • Revise Date: 10 February 2021
  • Accept Date: 26 December 2020

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