Geochemistry of the Eocene volcanic rocks in the SW of Jandaq (NE of Isfahan province)

The Eocene volcanic rocks in the SW Jandaq that outcrop in the south of Doruneh fault constitute a part of the Central Iran zone. The predominant rocks consist of basalt andesite، trachyandesite and dacite that porphyritic، microlitic porphyritic and hyaloporphyritic textures are common. The essential minerals are represented by intermediate plagioclase، diopside، augite، phlogopite and magnesiohastingsite and the secondary minerals are Fe -oxide and chlorite. Based on geochemical data، these rocks belong to high-K calc-alkaline and shoshonitic series which with K2O، Ta/Yb، Th/Yb and Ce/Yb. Lava eruption in subduction setting can be demonstrated by highly negative Nb and Ti anomalies، and also by comparison with mantle normalized trace element trend with that of the volcanic arc. In addition، the discrimination diagrams (TiO2/Al2O3 and Zr/Y) display a continental volcanic arc setting for these rocks. The REE patterns (chondorite normalized) and their ratios plus positive Pb anomaly، point to the effective role of low grade partial melting of a metasomatized mantle and garnet amphibolites source accompanied by crustal contamination in the course of formation these rocks.