Quaternary slip-rates of the Kazerun and the Main Recent Faults: active strike-slip partitioning in the Zagros fold-and-thrust belt

Abstract : The aim of this work is to constrain the Late Quaternary activity of two major dextral strike-slip faults of the Zagros fold-and-thrust belt of Southern Iran, within the framework of right-oblique convergence between Arabia and Eurasia. The NW-trending Main Recent fault marks the rear of the belt along two thirds of its length. Its southeastern tip connects to the northern termination of the N-trending Kazerun Fault, which affects the entire width of the belt. Horizontal slip rates have been estimated on these two faults over the last 140 ka from lateral offsets of streams and fans and in situ cosmogenic ³⁶Cl exposure dating of cobbles sampled on the surface of these geomorphic features. Compared to GPS data, the obtained minimum slip rate of 3.5–12.5 mm yr⁻¹ on the Main Recent Fault implies strike-slip partitioning of the convergence along this fault. Minimum slip rate of the Kazerun Fault is 2.5–4 mm yr⁻¹ for its northern strand, 1.5–3.5 mm yr⁻¹ for its central segment and is negligible for its southern segment. These results are consistent with southward distribution of the slip from along the Main Recent Fault to the longitudinal thrusts and folds of the fold-and-thrust belt through the Kazerun Fault, with a decrease of slip from the southeastern tip of the Main Recent Fault towards the southern termination of the Kazerun Fault. The Kazerun and associated faults form the horsetail termination of the Main Recent fault and may be seen as the propagating southeastern front of the fault system that accommodates indentation of Eurasia by Arabia.