Segmented Up-Bending of the Arabian Continental Plate Revealed by Pn Attenuation Tomography

The Zagros orogen in the Iranian Plateau serves as a natural laboratory for studying the tectonic evolution of the transition from oceanic subduction to continental collision. Various observations from both geology and geophysics show that deep oceanic slabs may have detached one after another from the Arabian continental margin, forming a complex plate front beneath the Zagros orogen. However, where slab detachment occurred and how slab detachment affects shallower continental underthrusting remain poorly understood. The mechanism behind the complex post-collision magmatism remains elusive. While the uppermost mantle is often considered the heart of the mantle lid, its rheological variations can provide insights into the underlying thermal structure. Here, we construct a high-resolution Pn-wave attenuation model for the uppermost mantle beneath the Iranian Plateau and surrounding areas using a newly compiled data set and constrain the lithospheric structure by combining the Lg-wave attenuation within the crust. Weak Pn-wave attenuation outlines the boundary of the Arabian Plate near the Moho discontinuity, extending further in the direction of underthrusting in the northwestern and southeastern regions. This is likely due to the up-bending and underplating of the Arabian lithosphere following the cessation of slab pull. The overlying crusts in northwestern and southeastern Zagros thickened under the compressive force from plate underplating. The correlations among the surface Miocene-Quaternary volcanism, strong Lg attenuation in the crust and strong Pn attenuation in the uppermost mantle suggest that asthenospheric materials escaped from slab windows and further intruded into the upper mantle and crust to feed the post-collision volcanoes.