Geology, Petrology and Tectonomagmatic Evolution of the Eocene Volcanic Rocks in Aq Dag Area, NE Abhar

The study area is comprised of lavas and volcanoclastic rocks with basaltic andesite, andesite, trachy-andesite, trachyte-trachydacite, dacite and rhyolite-ignimbrite compositions which erupted in five episodes in an aqueous to sub-aerial environments. All the volcanic-sedimentary series intruded by younger acidic sub-volcanic massifs. The intermediate-acidic volcanic rocks recorded evidences of magma mixing and mingling. In discrimination magmatic diagrams, the lavas represent calc-alkaline, high-K calc-alkaline and shoshonitic characteristics. In spider diagrams, the basic-intermediate samples follow continental arc pattern. The spider diagrams of acidic samples follow the patterns of peraluminous rhyolite and upper crust. REE and spider patterns of the volcanic rocks, display enrichment of LREE, LILE relative to HREE, and clear depletion of HFSE (such as Nb, Ta and Ti), which signifies subduction zones. After collision of the Arabian and Iranian plates and shortening of the Alborz in Eocene, by subsequence lithospheric delamination, partial melting occurred in sub continental lithospheric mantle (SCLM). The resulted melt accumulated in the upper crust, and formed shallow magma chamber(s). Partial melting of the upper crust produced acidic magma. It seems that magma mixing and mingling had important role in generation of the basic-intermediate rocks.