Geochronology and magmatic history of a calc-alkaline plutonic complex in the Urumieh-Dokhtar Magmatic Belt, Central Iran: zircon ages as evidence for two major plutonic episodes

The Kashan plutonic complex is located in the Urumieh-Dokhtar magmatic belt (Central Iran) which is part of the Alpine-Himalayan orogenic belt. This complex consists of the Mozvash micro-diorite, the Ghalhar quartz diorite, the Niyasar and the Poudalg tonalite intrusives. New U-Pb zircon ages from the plutonic rocks in the Kashan magmatic segment reveal two main episodes of plutonic activity in the Early Eocene and the Middle-Miocene. Zircon U-Pb dating by ID-TIMS shows that the Mozvash microdiorite was emplaced at 50.10 +/- 0.45 Ma. Ages of 18 Ma are obtained for the Ghalhar, Niyasar and Poudalg intrusives, which are thus representing a second plutonic event in this area. Titanite U-Pb dating also yields an emplacement age of 17.87 +/- 0.28 Ma for the Poudalg intrusive that closely confirms the zircon age. Inherited zircons yield indications for mainly Neoporoterozonic crust, which show a Gondwanan affiliation for the basement underlying the study area. The geofhronlogical data presented herein this paper provides a basis to reconstruct the temporal transition from subduction-related to post-collisional magmatism in the Kashan arc segment during the subduction of the Neotethyan Ocean.