STRUCTURAL AND TOPOGRAPHIC SPATIO-TEMPORAL EVOLUTION OF AN ACTIVELY PROPAGATING INTRA-PLATE STRIKE-SLIP FAULT SYSTEM: THE KUH-E-FAGHAN FAULT, CENTRAL IRAN

The current understanding on how intraplate strike-slip faulting enucleates, propagates and evolves in space and time is up-to-now largely constrained by analogue and numerical modeling studies. An ideal test site to study the morphotectonic response to active strike-slip faulting in intraplate settings is provided by Central Iran. This field-based study describes the structure, tectono-sedimentary and topographic evolution of the Kuh-e-Faghan Fault (KFF), in north Central Iran. The KFF defines a narrow, ca. 100 km long, E-W trending deformation zone cutting across Mesozoic-Paleozoic rock sequences. The Neogene-Quaternary covers show evidence of fault-related sedimentation and are arranged to form a major antiformal structure, moderately plunging to the E. Optically stimulated luminescence of quartz grains from faulted alluvial deposits constrains the minimum age for Quaternary faulting at 5-50 ka. Fault zone structure shows an eastward increase in fault localization (from distributed to localized shears) and fault zone evolution (from cataclastic to breccia zones and fault gouges), cutting through the antiformal hinge zone. This is accompanied by an eastward migrating depocentre during the Neogene, attesting for an intimate linkage between the propagating fault and erosion/sedimentation. Analysis of swath profiles and filtered topography reveals an eastward decrease in landscape maturity and the narrowing of the topographic signal, respectively. The multidisciplinary dataset thus indicates that the KFF has initiated in the west during the Neogene, and has propagated and evolved eastward throughout the Neogene and Quaternary. Faulting initiated through distributed en-echelon shears with formation of a topographic high induced by fault-propagation folding. With increasing deformation, faults coalesce by sidewise propagation, resulting in a through-going principal displacement zone. We infer that syn-tectonic thickness variation of the Neogene strata induced by the eastward propagation of the KFF might have a primary control on fault zone architecture and evolution. The interplay between morphotectonics and strike-slip fault propagation has regional implication on the spatio-temporal kinematic architecture and evolution of Central Iran.