بررسی‏های پترولوژیکی و ژئوشیمیایی توده آذرین رزگاه،

Pertrological and geochemical investigations of the Razgah intrusion,

Sarab- Eastern Azarbaijan, NW Iran

The Razgah intrusion is located in Alborz-Azarbaijan zone and about ۲۵ Km Sarab city. Formation of these rocks is known as a result of Pernean Orogenic phase. Plutonic, sub-volcanic and volcanic rocks of the study area have emplaced as stocks and dykes, according to field evidence. Field and petrographical investigations indicate that different types of dykes and veins have cut the Razgah intrusion, such as microsyenite, porphiritic microsyenite and etc. Modal composition of the area main rocks are nepheline pseudoleucite monzosyenite and nepheline monzodiorite. The petrographical characteristics of nepheline pseudoleucite monzosyenites (main intrusion) are more complicated than nepheline monzodiorite (northwest of intrusion) which indicate to effect different processes of crystallization during their formation. According to mineralogical and geochemical characteristics the study area rocks belong to K-rich alkaline series and in class of miaskitic nepheline syenites. On the base of discrimination diagrams, tectonic setting of these rocks are «arc related» and «postcollisional arc». Enrichment of these rocks from incompatible elements such as K, Rb, Th, U are probably as a result of mantle metasomatism by fossil subduction of Neotethys oceanic crust.