Diachronous initiation of post-collisional magmatism in the Arabia-Eurasia collision zone

Abstract

The continental collision between Arabia and Eurasia which gave rise to the Caucasus-Iran-Anatolia (CIA) volcanic province provides a unique opportunity for understanding collisional zone magmatism. This study reports a comprehensive dataset of ages and geochemical compositions of volcanic rocks formed during the initial phase of post-collisional magmatism in the CIA province. The age data indicate a diachronous onset of volcanism that began similar to 17 Ma in SE Anatolia, and propagated northward from similar to 11 to 9 Ma toward NE Anatolia and NW Iran. The rocks are characteristically bimodal, with dominantly basic (SiO2 = 48-52 wt%) and silicic (SiO2 = 58-71 wt%) components that feature significant isotopic variations (epsilon Nd = +6 to -5), suggesting two principal magma sources: (1) a juvenile mantle-derived component, and (2) an older continental crust component. We therefore attribute the volcanic initiation to a migrating post-collisional extension regime caused by the successive breakoff of subducted Neo-Tethyan slabs. Subsequent volcanism that began from -6.5 Ma resulted in a wide spectrum of calc-alkaline and alkaline rocks, with mafic to felsic lithologies in the entire province. From similar to 2 Ma, volcanism ceased in the western CIA province, and started propagating eastward and southeastward to SE Iran, following the Urumieh-Dokhtar magmatic belt, consistent with the notion of an oblique continental collision between Arabia and Eurasia. (C) 2020 Elsevier B.V. All rights reserved.