Tethyan subduction and Cretaceous rift magmatism at the southern margin of Eurasia: Evidence for crustal evolution of the South Caspian Basin

The Cretaceous rift magmatic activity along the southern margin of Eurasia is ideal for testing how the far-field magmatism, with alkaline to calc-alkaline igneous rocks along the Alborz range, was influenced by the Tethyan subduction zones. Our new and compiled U-Pb ages indicate that significant Cretaceous magmatism in the Iran Armenia-Turkey Plateau occurred from-141 Ma to-75 Ma, lasting-66 Ma (Valanginian to Campanian). The resultant plutonic, sub-volcanic, and volcanic rocks are incorporated within the Lower-Upper Cretaceous sedimentary successions. The integrated geochronological, geochemical, and isotopic data suggest that the primitive mamas were derived from an enriched mantle source with subduction-related signatures. The significant variations in the composition of the magmas could be due to assimilation-fractional crystallization processes (AFC). The pre-existing Paleo-Tethys subduction beneath the Turan block is considered to have provided the initial source for the mantle wedge enrichment via penetration of slab-derived components. Subsequently, the Cretaceous Neo-Tethys subduction underneath Central Iran and slab rollback led to asthenospheric upwelling, remelting of metasomatized lithospheric mantle, and extraction of primitive magmas. These early melts underwent further fractionation and contamination within the continental crust generating less-to more-evolved melts. We propose that the Neo-Tethys subduction ignited the Cretaceous rift magmatism in the Iran Armenia-Turkey Plateau and triggered the transformation of the Eurasian South Caspian Basin crust into stretched high-velocity oceanic-like crust.