The enigma of inherited Zircon crystals in Qalaylan plutone, Clues from the Gondwana crust in the rocks with primitive isotopic signatures

The Qalaylan pluton of Late Jurassic age is composed of intermediate and felsic rocks that crop out in the northern Sanandaj-Sirjan Zone. A body is comprising alkaline, high K, Ferroan A1-type rocks with contrasting aspects; whiles, Nd-Sr primitive isotopic composition consistent with a mantle source. On the other hand, inherited zircon cores (with a range of 230 – 2700 Ma) and elevated Nd model ages (Avg. »670 Ma) indicate that the source of these rocks was not juvenile mantle-derived subduction related magma. Unusually large proportion of inherited zircons demonstrates that fast and non-equilibrium melting of pre-fertile crust with primitive isotopic signatures was the source of these rocks. Zoning and porphyritic texture of the body, oscillatory zoning of plagioclase grains and unusually amount of pre-magmatic zircons all are evidences of non-equilibrium condition as a result of fast cooling rate of parental magma of Qalaylan.