TIMING OF ARABIA-EURASIA COLLISION IN IRAN CONSTRAINED BY POST-COLLISIONAL MAGMATISM

Timing of Arabia-Eurasia collision in Iran has remained controversial. The Neogene collision models are partly based on observations that until the early Miocene: 1) stable carbonate sedimentation continued in the Zagros and 2) the central Iranian plateau was largely below sea level, both indicating that collisional uplift occurred after the early Miocene. Before Arabia-Eurasia collision, the northward subduction of the Neotethys slab along the southern margin of the Asian continent gave rise to an Andean-type magmatic arc, manifested by the voluminous Sanandaj-Sirjan batholiths and Urumieh-Dokhtar and Alborz volcanics. These magmas had typical calc-alkaline compositions and were mainly emplaced from Jurassic to Paleogene but calc-alkaline magmatism persisted in the Urumieh-Dokhtar zone during the Neogene and was accompanied by significant porphyry copper mineralization in the late Miocene, demonstrating continuation of subduction of oceanic slab in post-Eocene times.

We discuss the remarkable change in magmatism by adding of small volume alkaline mafic volcanics –including melafoidite and alkaline olivine basalts- to the more common arc rocks from the late Miocene onwards throughout the above-mentioned zones. Age of ~10 Ma for the oldest known melafoidite indicates the minimum age for transition from calc-alkaline to alkaline magmatism and the associated sudden increase in uplift. Mid-lithospheric melting responsible for generation of such alkaline mafic magmas required rapid heat transfer possibly caused by slab break-off and removal of the lithospheric root.