DETRITAL U-PB ZIRCON DATING OF GRANITOIDS IN THE SOURSAT COMPLEX(NW IRAN)

The Soursat Complex in northwestern Iran is part of the Sanandaj-Sirjan metamorphic belt that parallels the Zagros orogen and contains granitoids related to the subduction zone. Three granitoid suites are present: type I - monzosyenite and deformed monzosyenite; type II - Turkeh Dare and Pichagchi plutons; and type III - quartz porphyry. The granites can be assigned to a medium-K calc-alkalic to high-K calc-alkalic series. The type I granitoids are weakly to strongly peraluminous and belong to a S-type suite whereas. Type II plutons are metaluminous to weakly peraluminous with I-type character. Type III granitoids are weakly peraluminous and can be labeled as a highly fractionated I-type suite.

U/Pb zircon dating of the monzosyenite and deformed monzosyenite from type I granitoids and Turkeh Dare pluton from type II granitoids by laser inductively coupled plasma mass spectrometry (LA-ICP-MS) yielded 238U/206Pb crystallisation ages of ~ 540 Ma and ~ 60 Ma, respectively. Based on these ages, Soursat Complex is dominated by plutons which belong to the Pan-African syn- to post-collisional and the Laramide syn- to post-collisional group. Small outcrops of quartz porphyric type III granitoids made a distinctive aureole in their regionally metamorphosed parent schists. It could be concluded the younger age for type III than type II granitoids. However, based on similar geochemical behavior, type III granites could be the late magmatic product of type II granitoids.

The source of the I-type granitoids is characterized by juvenile mantle and lower crust components during the collision of Arabian plate with Iranian block and closure of Neotethys.