U-PB ZIRCON AGE OF THE PIRANSHAHR OPHIOLITE IN NW IRAN: ENIGMATIC RELICT OF AN ARC IN NEO-TETHYS BEFORE THE ARABIA AND EURASIA COLLISION

The pre-collision evolution of Neo-Tethys is fundamental in constraint the timing of the Arabia-Eurasia collision. Here we date zircons from plagiogranite in the Piranshahr ophiolite that yield a U-Pb age of 50.6 ± 1.3 Ma. This age is interpreted as dating the crystallization of plagiogranite that occur in peridotite. The plagiogranite’s trace element abundances are typical of subduction petrogenesis and can be explained by the addition of slab-derived components to a depleted mantle wedge. The Piranshahr ophiolite formation was coeval with the Paleocene-Eocene Walash volcanic formation in a similar tectonic environment. We interpret the chain of ophiolites within northwestern Iran as corollaries of the oceanic arc-related setting before they were obducted on the Arabian passive margin. These form an extensive arc system that developed as oceanic crust in Neo-Tethys. Subsequent Miocene obduction of the arc onto Arabia was the first arc-Arabia collision—a herald of the collisions to final Arabia-Eurasia collision.