Tectonic and magmatic settings of the Oligocene felsic outcrops in the south of Ardestan, NE of Isfahan

The Oligocene felsic outcrops are located in the south of Ardestan (NE of Isfahan). The area is a part of Uromieh –Dokhtar structural zone. These outcrops are composed of rhyolite and rhyodacite rocks. Geochemically, these rocks are sub-alkaline, calc-alkaline composition with high-K and peraluminous. Although the whole rock composition of the felsic rocks corresponds to S-type granites (i.e. high K, Al, large ion lithophile elements, and low Ca and Sr) but the studied rocks have remarkably primitive and igneous sources. The geochemical data suggest that mantle wedge is partly metasomatized with rhyolitic materials from subducted slabs; it is more likely that the rhyolite magma developed by very low degree partial melting of the metasomatized mantle wedge. The initial reason for direct eruption of the mantle-derived rhyolitic magmas would be a tensional condition of the Ardestan region during late Eocene- Oligocene time. If mantle-derived rhyolitic magmas ascended within a compression crust, the magmas should easily react with crustal materials and therefore it would be indistinguishable from felsic magmas produced by crustal fusion. The Petrological and geochemical evidences as well as the tectonic discrimination diagrams show that rhyolitic magma formed in an active volcanic arc. It seems that these rocks are formed following the subduction of Neo-Tethys oceanic crust beneath the central Iranian micro- continent.