Paper No. 9
Presentation Time: 10:25 AM
SPATIAL AND TEMPORAL DISTRIBUTION OF PALEO- AND NEO-TETHYS OPHIOLITES IN IRAN AND THEIR TECTONOMAGMATIC SIGNIFICANCE
Based on age, the ophiolites of Iran consist of the less abundant Paleozoic and much more abundant Mesozoic ophiolites . Geographically, the Iranian ophiolites can be divided into four groups: 1) ophiolites of northern Iran along the Alborz orogenic belt [i.e., Rasht and Mashhad ophiolites (297 Ma and 268 Ma)] which are the remnants of the Paleo-Tethys ocean crust emplaced as result of closure of the Paleo-Tethys between the Turan and the Central Iranian Microplates (CIM); 2) ophiolites of the Bitlis-Zagros suture zone including the Neyriz and the Kermanshah ophiolites which appear to be coeval with the Oman ophiolite obducted onto the Arabian continental mass (~96-94 Ma); 3) unfragmented ophiolites of the Makran accretionary prism which are located to the south of the Sanandaj-Sirjan microcontinental block, including complexes such as Band-e-Zeyarat/Dar Anar, Ganj and Remeshk/Mokhtarabad (~140-98 Ma); 4) ophiolites and colored melanges that mark the boundaries of the CIM, including some of those in the Makran region and those inside of the Sanandaj-Sirjan microcontinental block, such as Shahr-e-Babak (120 Ma), Naien (100 Ma), Baft, Sabzevar and Tchehel Kureh. The origin of formation of the Khoy ophiolite in NW Iran is not completely understood. The radiometric ages obtained as crystallization ages from amphibole gabbros from the Khoy ophiolite range from Middle to Late Jurrasic (~159-155 Ma), whereas the ages from metamorphic amphibolite at the base of the complex give Albian ages (~ 109-104 Ma) ages. Furthermore, given the location of apparently recent (Neogene) calc-akaline and alkaline volcanism in northwestern Iran, the presence of mid to late Eocene age planktonic foraminifera in the pelagic sediments within the pillow basalt of the Khoy ophiolite (NW Iran), it is possible that the northern portion of the Zagros was the last portion of the NeoTethys to be subducted beneath Eurasia, leading to closure of the Neo-Tethys and formation of Iran. The presence of these ophiolites with such wide age distribution makes Iran an excellent natural laboratory to study all aspects of tectonomagmatic processes such as magma genesis, crustal formation, subduction-related tectonism, various stages of continent-continent collision and post collision volcanism during the past nearly 300 million years.