The active changeover from the transpression to the transtensional tectonic regime in eastern Alborz, Northern Iran

Abstract

By fault kinematic approach, this article addresses the clockwise rotation of the South Caspian Basin (SCB) and northeastern Alborz because of Arabian plate collision with Eurasia. The collision is accommodated by the thrust and left-lateral strike-slip faults. One of the essential features of the eastern Alborz is that the active strike-slip faults change from transpressional in the east of Tazareh Syntax to the transtensional in the west of this tectonic node. Therefore, we introduce the Tazareh syntax as the location of this changeover where the two relatively rigid crusts of SCB and Central Iran pinch the Alborz out and make a narrow escape on the way of crustal transformation from east to the west. Indeed, the interaction between Central Iran and SCB acts as an indenter leading to the clockwise rotation of the eastern Alborz. Accordingly, the general transpressional regime in Alborz, Binalud, and Kopeh Dagh that dominated since >5Ma switched to the transtensional tectonic regime over the eastern Alborz in Quaternary while it has remained on the mode of transpression in western Alborz, Kopeh Dagh and Binalud. Therefore, the Tazareh transitional zone represents how a part of the fold and thrust belt resumes different deformational patterns concerning the other component (s) in its evolutionary history. In a brief comparison, if the Zagros fold and thrust belt could be compare to the initial stage of the Himalayan fold and thrust belt, the Iranian plateau (including eastern Alborz) looks like a prototype of the Tibetan plateau.