Petrogenesis and U-Pb dating of the Late Neoprotrozoic Metarhyolites of the Majerad Igneous-Metamorphic Complex (SE Shahrood): An implication to the Formation and Development of the Intracontinental Extensional basins in the Iranian Gondowanan Terrenes

Majerad igneous - metamorphic complex is located in the southeast of Shahrood and in the northern edge of the central structural zone of Iran. Metarhyolites are important compositional constituent of this complex and cropped out in the form of domes and/or intercalations with calcitic and dolomitic marbles, metapelites and metapsammites. Foliation and lineation were developed in metarhyolites due to metamorphism and mylonitisation. Based on the geochemical evidence, metarhyolites have medium to high K calc-alkaline nature. These rocks are enriched in light rare earth elements (exception of Eu) with respect to heavy rare earth elements in primitive mantle normalized REE diagram, and enriched in U, Th, Pb and K, and depleted in Zr Ti, P, Sr, and Nb in primitive mantle normalized spider diagram. Metarhyolites belong to category of dry or high temperature rhyolites and formed in intracontinental extensional setting. U-Pb dating obtained on the extracted zircons of metarhyolites, is an indicative of age range from 587.6 to 508 Ma (Ediacaran (Late Neoproterozoic) - Early Cambrian), but according to the age of granitoid cutting this complex (553 ± 3.8 Ma), Late Neoprotrozoic (Ediacaran) is more reasonable age for metarhyolites and meanwhile confirms their belonging to crystalline basement and Gondoanwan terrains of Iran.