Investigation of petrology and geochemistry of volcanic rocks in the Kasian area, Northeast of Khorramabad

The volcanic masses in Kasian area with northwest-southeast trending، lie in Zagros crushed zone، between Sanandaj-Sirjan and Zagros thrust zones. Based on the microscopic studies، the studied volcanic rocks are: andesite- basalt and andesite. The main textures exhibited in these rocks consist of porphyritic hypocrystaline، porphyritic and hialoporphyritic. The important feature in this region is the severe and intense alteration caused the great changes in the studied rocks، especially in those susceptible to alteration. Three alteration zones including: sericitic، argillitic and propylitic zones developed in this region. The geochemical data indicate that these rocks are low to medium K oceanic island arc tholeiites. Nb depletion and Ba and Sr enrichment in the primitive mantle normalized diagram point to subduction setting. These results، in accompany with LREE enrichment in the chondrite normalized trace element، represent the island arc setting for these rocks. The lack of significant Eu anomaly in REE pattern is representing oxidation condition during magma crystallization proposing volcanic arc environment for the studied rocks. The Kasian volcanic rocks lie in young and immature volcanic arcs or in the initial stages of volcanic arc formation. This situation is consistent with geological history of Sanandaj-Sirjan zone in the Jurrasic to Cretaceous age.