Petrology of Eocene Volcanic Rocks in the East of Sanandaj

Volcanic rocks with mainly andesite composition and lenzoid form outcropped in the Eocene sedimentary host rocks in the east of Sanandaj. Field studies confirm that they are intercalation with the sedimentary host rocks. In thin section, those have porphyritic, glomoroporphyric microlithic and microlithic porphyric textures. Some texture evidences such as glassy inclusion in the center of plagioclase phenocrysts, displacement of plagioclase and mafic phenocrysts with mafic hydrate minerals imply amalgamation of volcanic activity with soft sediments in shallow water; also cracking of plagioclase phenocrysts confirms this subject. Geochemical study shows that these rocks are enriched in incompatible elements such as U, Th, Pb and depleted in Nb, and Ti elements compared with chondrites, primitive mantle and NMORB. If crustal contamination can be responsible for these changes, but as usual these anomalies imply the primary magma generated above the subduction zone. This volcanic rock may have a unique origin the same as Urumieh-Dokhtar volcanic belt.