Evolution of the stress field at the junction of Talesh – Alborz – Central Iran during the past 5 Ma: Implications for the tectonics of NW Iran

Abstract

Tectonic stresses governed by the Arabia – Central Iran collision are transferred throughout the Iranian Plateau. The orientation of the maximum horizontal stress (σ1) significantly changes (~90°) in the Persian block of NW Iran. However, the exact spatial extent and boundary conditions for these changes are poorly defined. This study investigates the late Cenozoic stress regime in a key region in NW Iran including the Mahneshan – Mianeh Cenozoic Basin (MMCB), the Garmachay Fault Zone (GFZ), and the southern flank of the Bozqush Mountains (SBM). We mapped folds and fault zones in detail using high-resolution satellite imageries and field surveys. We have measured fault-slip data at 49 localities distributed over the study area. The results of fault-slip inversion analysis indicate significant temporal and spatial changes in both the modern and paleostress fields. In the MMCB and GFZ, the orientation of the horizontal σ1 axis changed from N148°E to N041°E, during the Pliocene and Quaternary times. During the same period of time, it changes from NE-SW to N138°E in the SBM. Our study reveals that the southern boundary of the Persian block corresponds to the deep-seated North Tabriz fault (NTF), which is spread out over several splays at the southern flank of the Bozqush Mountains. The NTF acts as a boundary condition in both the stress and strain fields of the region. The GFZ defines the southeastern border of the Persian block, where the NW-trending maximum compression encounters the remote stress field in the hinterland of the Zagros collision. Our results indicate that independent movements of crustal blocks transfer crustal stresses beyond the collision zone and produce large-scale stress perturbations by discarding compatibility in regional strain/stress fields.