Mantle compositional structure and dynamics of the Arabia-Eurasia collision zone: Insights from integrated thermochemical modelling

The tectonic evolution of the Arabia-Eurasia collision zone is enigmatic due to our poor knowledge of the compositional structure of the Zagros keel and the sub-lithospheric mantle beneath the Iranian plateau. Here, we present a thermochemical model for the upper mantle, starting from the Arabian plate toward the Zagros keel (in SW Iran) and the Iranian plateau to the Kopet Dagh Mountains in NE Iran. The crustal and (sub) lithospheric mantle structure is constrained using receiver functions and high-resolution seis-mic tomography. The crustal density is obtained by converting local Vp velocity profiles to density. The presumed mantle composition/density of different tectonic units has been inferred from the composition of mantle-derived xenoliths in Pleistocene alkaline basalts of NE Iran, mantle xenoliths from Eastern Arabia, and integrated geophysical-petrological modeling of seismic tomography as well as Bouguer and geoid anomalies. Our results indicate that the lower part of the lithosphere in the Arabian plate is -+25 kg/m3 denser than the sub-lithospheric mantle, which allows underthrusting of the Arabian litho-sphere beneath the Iranian plateau. The Zagros core-an ultra-positive seismic velocity anomaly in the tomographic models- is modeled assuming a refractory "craton-like" composition, leading to a -- 60 kg/m3 density contrast with its underlying fertile lithospheric mantle. We hypothesize that at least the upper -100 km of the hydrous Arabian lithosphere was compositionally cratonic before the collision-related shortening processes. In contrast, the anhydrous Iranian lithosphere has been refertil-ized during asthenosphere upwelling and mantle flows. The Iranian plateau is underlain by a cold sub-lithospheric body characterized by -+25 kg/m3 density contrast with respect to the ambient asthenosphere. (c) 2023 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.