Lithospheric Structure Beneath the NE Iranian Plateau Revealed by S-wave Receiver Function Migration

The ongoing Arabia-Eurasia collision resulted in strong continental deformation not only along the Zagros collisional zone but also in a large part of the Iranian plateau. To better understand the geodynamic processes of continental collision and associated intra-continental deformation, in this study the lithospheric structure beneath northeast to east Iran was investigated by S-wave receiver function (S-RF) imaging. Teleseismic data used come from 53 broadband stations with an average spacing of 15 km that form a nearly N-S linear array starting from the Kopeh Dagh in the north to the Lut block in the south. This array is the major part of the second phase of seismic observations under our collaborative project named "China-Iran Geological and Geophysical Survey in the Iranian Plateau (CIGSIP)".

Considering the spatial distribution of Sp pierce points at depth, we selected east and west two profiles parallel to the seismic array and applied wave-equation based migration technique to image the lithospheric structure. Our imaging result shows a shallower Moho at the depths of 35 45 km beneath the Sistan Suture Zone and the Central Domain but a deeper one at 45 55 km depths beneath the Kopeh Dagh. The lithosphere-asthenosphere boundary (LAB) is coherently imaged along both profiles, showing obvious undulations in the study region. It rises from about 100 km beneath the Sistan Suture Zone in the south to 80 90 km beneath the Central Domain, and then deepens again northward to around 120 km beneath the Kopeh Dagh. Besides, a strong positive signal appears continuously at a depth of approximately 160 km beneath the Sistan Suture Zone and the Central Domain, possibly indicating the base of a low velocity layer in the upper mantle. Our results reveal an overall thin lithosphere but with obvious thickness variations in the northeastern and eastern part of the Iranian plateau, which may have resulted from complex lithospheric deformation in response to both the ongoing continent-continent collision and earlier multiple subduction-accretion events associated with the Tethys evolution.