Time Constraints on the Late Cenozoic Fault Evolution Along the Northern Margin of the Iranian Plateau in the Arabia-Eurasia Collision Zone

Abstract

The collisional Iranian Plateau and its recent kinematic evolution represent a natural example to study the intraplate response to the transferred deformation from an active convergent plate margin. The late Cenozoic deformation and structural evolution of the Plateau is not well understood. Here, we integrate structural, tectonostratigraphic, and morphotectonic field observations with low-temperature thermochronometric data along the NW-SE trending Kushk-e-Nosrat (KN) Fault to unravel the exhumation history and the kinematic change at the northwestern boundary of the Iranian Plateau. We found different sets of strike-slip related structures along the KN Fault zone, which are classified into four categories based on their cross-cutting relations and the superimposition of kinematic indicators. These include dextral transtension, dextral, dextral transpression, and sinistral kinematics. The unreset zircon (U-Th)/He and apatite fission track results and the reset apatite (U-Th)/He data from the restraining area along the KN Fault suggest 80–60°C of cooling during the early Miocene (∼20–18 Ma) and late Miocene–early Pliocene (∼7–5 Ma) due to dextral and dextral transpressional kinematics along the KN Fault zone, respectively. The dextral transtentional faulting was recorded as deposition of the Qom Formation within the releasing overlap areas along the KN Fault at >20–18 Ma. The kinematics of the KN Fault changed to sinistral during Pliocene–Quaternary times presumably triggered by the simultaneous clockwise rotation of central Iran, Alborz Mountains, and the South Caspian block. Our study proposes that the morphological and tectonostratigraphic evolution of the northern margin of the Iranian Plateau has mainly been controlled through local uplift and exhumation in restraining areas and local thick deposition in releasing areas of the major strike-slip faults during the late Cenozoic time.