Presence of a layered lithosphere beneath the Zagros collision zone

Abstract

The continental collision between the Arabian and Eurasian plates following the subduction of the Neo-Tethys ocean beneath Eurasia resulted in a complex deformation across the Zagros Mountains. We used more than 700 S receiver functions obtained from 61 permanent stations to provide a detailed image of the lithospheric interaction between the Eurasian and Arabian plates. Our results suggest the existence of two different lithospheric blocks. A 200 km thick lithosphere was observed beneath the Zagros collision zone and most likely represents the Arabian lithosphere, which has been strongly deformed, thickened and depleted. Based on our results, shortening due to the collisional process is differently accommodated by the crust and mantle lithosphere of the Zagros collision zone. We localized the thick Arabian lithosphere beneath the Zagros, Sanandaj–Sirjan Zone (SSZ) and Urumieh–Dokhtar Magmatic Assemblage (UDMA), whereas the crustal thickening (~ 70 km) seems to be concentrated just beneath the SSZ. Furthermore, we found a thin lithosphere of about 80–90 km that we interpret here as the Iranian lithosphere, beneath Central Iran and Alborz. Additionally, our results suggest the presence of remnants of the fossil Neo-Tethys subduction at depths ranging between 80 and 150 km within the Arabian lithosphere. This dipping structure can be seen beneath the Zagros, SSZ and UDMA and seems to disappear towards the northeast beneath Central Iran and Alborz. These findings may support the idea of a breakoff of the oceanic Neo-Tethyan slab beneath Central Iran, which results in an asthenospheric upwelling and thinning of the Iranian lithosphere beneath Central Iran and Alborz. The boundary between the Arabian and Iranian plates seems to be located northeast of the UDMA in the northwest of Zagros and southwest of the UDMA in the Central Zagros region.