A TRIP TO THE ZOO: ZAGROS OPHIOLITE OVERVIEW

The Zagros Fold-and-Thrust belt of SW Iran is among the youngest continental convergence zones on Earth, continuing to accommodate ~20mm/yr of convergence between Arabia and Eurasia. This belt extends NW-SE from eastern Turkey, through northern Iraq and the length of Iran to the Strait of Hormuz and into northern Oman. The Zagros Fold-and-Thrust belt reflects the shortening and off-scraping of thick sediments from the northern margin of the Arabia platform, essentially behaving as the accretionary prism for the Iranian convergent margin. Distribution of ophiolites in the Zagros orogenic belt defines the northern limit of the evolving suture between Arabia and Eurasia and comprises two parallel belts: 1- Outer Zagros Ophiolitic Belt (OB) and 2- Inner Zagros Ophiolitic Belt (IB). These ophiolite belts contain abundant, complete (if disrupted) ophiolites. Mantle sequences include tectonized mantle harzburgites and rare ultramafic-mafic cumulates as well as isotropic gabbros as lenses and isolated dikes within mantle peridotite. Crustal sequences include gabbros, sheeted dike complexes, pillowed lavas, and felsic extrusives. All the inner and outer Zagros ophiolites are overlain by late Cretaceous pelagic limestone. Limited radiometric dating indicates that OB and IB formed at the same time during the late Cretaceous. All components of outer and inner Zagros ophiolites show strong supra-subduction zone affinity from mantle harzburgites to overlying crustal lavas. This supra-subduction zone affinity is distinguished by spinel and orthopyroxene compositions of mantle harzburgites as well as by REE and trace elements characteristics of overlying lavas. These similarities compel the conclusion that IB and OB once defined a single tract of forearc lithosphere that has since been disrupted by exhumation of metamorphic ricks of the Sanandaj-Sirjan zone. Our data for the OB and IB along with better-studied ophiolites in Cyprus and Oman compel the conclusion that a broad and continuous tract of fore-arc lithosphere was created during the late Cretaceous as the magmatic expression of a newly-formed subduction zone developed along the SW margin of Eurasia. This subduction zone has persisted for 85 Ma, forming the Urumieh-Dokhtar arc of Iran. The development of this subduction zone has played a key role in the evolution of the region.