The Mountain Front Fault in the Lorestan region of the Zagros belt (Iran): coupling tectonic uplift and structural inheritance in a Mass Rock Creep deforming slope

A Deep-seated Gravitational Slope Deformation (DGSD) affects the SE slope of the Siah-Kuh anticline in the Lorestan arc (Zagros Mts., Iran), upstream to the intersection between the Mountain Front Fault (MFF) and the Balarud fault zone. The DGSD is driven by a Mass Rock Creep (MRC) process and involves an area of about 8 km². The DSGD is strictly related to the evolution of the Dowairij River drainage system as well as to the tectonic and structural setting of the MFF.  

Nevertheless, such instability has not been documented in any study, and the amplitude of the coupling among time-dependent rock mass deformations, tectonics and landscape evolution rates remain unresolved. 

In this regard, we present an integrated study, based on quantitative geomorphic analysis, optically stimulated luminescence (OSL) dating, and InSAR techniques to assess the long-term to present-day landscaping processes. 

In detail, we semi-automatically extracted the fluvial treads to which we associated an elevation above the thalweg based on the Relative Elevation Model (REM) allowing the order definition. Then, OSL technique was used to date two strath terraces located across the MFF, whose plano-altimetric distribution has been correlated along the river longitudinal profile, allowing the estimate of an uplift rate of 2.8±0.2 mm yr^-1. InSAR techniques were performed by processing 279 satellite Sentinel-1 (A and B) radar images of the ascending and descending orbit spanning from 06 October 2014 to 31 March 2019. A maximum ground displacement rate of 6 mm yr^-1 associated with tension cracks and scars involving the limestone caprock in the upper slope has been observed. Consequently, the role of the inherited Jurassic extensional fault pattern in the rock damaging has been documented.