Mantle and crustal controls on the geochemical and isotopic evolution of collisional magmatism: NE Iran
Magmatic activity that accompanied the collision between Arabia and Eurasia at ~27 Ma, provides unique opportunities for understanding the triggers and magma reservoirs for collisional magmatism and its different styles in magmatic front and back-arcs. We present new ages and geochemical-isotopic results for magmatic rocks that formed during the collision between Arabia and Eurasia in NE Iran, which was a back-arc region to the main magmatic arcs of Iran. We also compile an inclusive dataset for igneous rocks that formed before, during and after the collision between Arabia and Eurasia, from both the back-arc and the magmatic front (Urumieh-Dokhtar Magmatic Belt) of Iran. Our new zircon U-Pb ages indicate that collisional magmatism began at ~24 Ma in the NE Iran back-arc, although magmatism in this area started in Late Cretaceous time and continued until the Pleistocene. The collisional igneous rocks are characteristically bimodal, and basaltic-andesitic and dacitic-rhyolitic components show significant isotopic differences; εNd(t)= +4.4 to +7.4 and εHf(t)= +5.4 to +9.5 for mafic rocks and εNd(t)= +0.2 to +8.4 and εHf(t)= +3.4 to +12.3 for silicic rocks. The isotopic values and modelling suggest that fractional crystallization and assimilation-fractional crystallization play important roles in the genesis of the NE Iran collisional volcanic rocks. Isotopic modelling further emphasises that three components, comprising a depleted mantle, an enriched lithospheric mantle similar to the source of the Main Ethiopian Rift lavas, and the Cadomian continental crust of Iran were the main magmatic triggers. Our results also emphasise the temporal and spatial magmatic variations both in the NE Iran back-arc and between the magmatic front and the NE Iran back-arc.