Crustal and uppermost mantle shear-wave velocity structure beneath the Northeastern Iranian Plateau using an analysis of receiver function and surface‑wave tomography

Abstract

In this study, we investigate the crustal velocity structure and Moho discontinuity depth beneath the NE Iran continental collision zone through joint inversion of P receiver function and Rayleigh wave group velocity dispersion curves. Local Rayleigh wave group velocity dispersion curves were estimated using time-frequency analysis method and two-dimensional surface wave tomography method. Our results distinctly highlight prominent changes in velocity structure along both the northern and southern flanks of Daruneh fault, occurring at both the crustal and lithospheric scales. This fault boundary can consequently be characterized as a microplate demarcation. In addition, our analysis indicates that variations in the average thickness of low-velocity layers within the upper crust and sedimentary cover are distinguishable between central Iran and the Kopeh Dagh and Binalud mountain ranges. We think that the greater thickness of low-velocity layers beneath Kopeh Dagh and Binalud is caused by the convergence of the Iran and Turan plates, the presence of thickened sedimentary layers, mountainous terrain, and folded sedimentary structures in these areas. Our study reveals that the South Caspian Basin has a distinct crust and lithosphere compared to its surrounding area in the northeast of Iran. Our results reveal some evidence indicating that the Kashafrud reverse fault between Binaloud and Kopeh Dagh mountains is the suture line of the closed Palaeotethys Ocean. We also found the maximum and minimum values for Moho depth beneath Kopeh Dagh mountain range (~56 km) and Central Iran microplate (~32 km), respectively.