Mineral Chemistry, Geochronology and Sr-Nd Isotopic Geochemistry of Ayrakan Granites

Ayrakan granitoid pluton with 12 km2 area cropped out in the northeast of Mohammad Abad Kooreh Gaz village from Khur o Biabank County and in the farthest NE end of Jandagh-Arousan Metamorphic-Igneous belt. The main part of this granitoid pluton consists of porphyroidic biotite granites. A few leucocrate aplitic granite dikes and apophyse as a late magmatic phase cut porphyroidic biotite granites. Both type of the rocks, suffered intensively plastic (mylonitisation) and brittle (catclastic or fragmentation) deformations. Porphyroidic biotite granites are supposed to show more intensive mylonitization. Based on geochemical characteristics, isotopic ratios of 87Sr/86Sri, 143Nd/144Ndi and εNd, Ayrakan mylonitized porphyroidic biotite granites and aplitic granites are belonging to peralumious S-type granites. , 87Sr/86Sri (0.712714 and 0.712490), 143Nd/144Ndi (0.5115227 and 0.511581), associated with negative εNd (-8.19 and -7.13) for porphyroidic biotite granites and aplitic granites, respectively, indicate that they are originated from melting of metapelitic lower crust. Based on, Zircon U-Pb dating, porphyroidic biotite granites and aplitic granites have 545±11 and 537±3.8 Ma age, respectively. These values confirm the earlier dating results (549±15 Ma age). Therefore, Ayrakan granitoids certainly are part of the basement and Iranian Gondwanan terrains with the Late Neoproterozoic-Early Cambrian age