EOCENE INTRA-OCEANIC SUBDUCTION SYSTEM OF NEO-TETHYS IN THE ZAGROS, IRAN

There is much debate about the formation and closure of the Tethys, because the pre-collisional tectonic evolution of Tethyan Ocean is essential in constraining the timing and process of collision between the Eurasian and Arabian continents. Here we present a combined analysis of zircon LA-ICP-MS U-Pb ages and Hf -O isotopes of two ophiolites, the Marivan and the Sardasht from the NW Zagros orogen. Our new data reveal that the Marivan ophiolite has a Late Eocene age (ca. 40.3 Ma), and was probably generated by back-arc extension. However, the Sardasht ophiolite formed in the Early Eocene (ca. 50.6 Ma), probably during initial intra-oceanic subduction. Consequently, we argue that the Tethys Ocean was undergoing incipient intra-oceanic subduction and back-arc extension in the NW Zagros during the Eocene. Accordingly, the collisional orogeny underwent intra-oceanic subduction process and arc accretion before the final continent-continent collision.