Crustal imbrication and mountain building in the Eastern Iranian Ranges; Insights from receiver function and Rayleigh wave dispersion analysis

The evolution of the Eastern Iranian Ranges (EIR) dates back to the Late Cretaceous, coinciding with the closure of the Neotethys and the accretion of the Lut Block to Eurasia. However, controversy remains regarding its orogenic processes due to limited knowledge of the lithospheric structure. To gain a better understanding of the tectonic processes and mountain formation in eastern Iran, we analyzed seismic data from 29 stations in the northern part of the EIR. We initially perform receiver function (RF) analyses on 2160 high-quality RFs, emphasizing single-station analysis and Common Conversion Point (CCP) stacking to examine structural variations. Subsequently, we jointly invert the RFs with Rayleigh wave group velocity dispersion curves to derive a shear-wave velocity (Vs) model for each station. Our findings reveal a complex structure with west-dipping interfaces, indicating crustal layering and imbrication. We have identified a significant west-dipping layer, approximately 100 km in length, which could potentially indicate an intra-continental decoupling or shear zone. This decoupling may be responsible for the underthrusting of the Eurasian margin beneath the Lut Block, resulting in a deepening of the Moho depth to over 50 km beneath its footwall, compared to the adjacent Moho depth of around 40 km. Additionally, this process has caused an increase in the topography of approximately 1 km. These findings reflect the potential westward underthrusting of the Eurasian margin. In the deeper parts of the model, we observe a low-velocity anomaly below the crust, shedding light on a weakened lithosphere that facilitates crustal deformation in response to the compressional forces of convergence.