In southwest of the Jandaq City (northeast of Isfahan Province) and northwest of the Central-East Iranian Microcontinent (CEIM), the Eocene dykes with trachy-andesitic composition cross cut the quartz monzodioritic intrusion. The texture of these dykes is granular, intergranular and porphyritic. The studied dykes are composed of plagioclase (andesine and labradorite), clinopyroxene (diopside and augite), sanidine, mica (Biotite), and quartz as primary minerals, and amphibole (tremolite-actinolite), chlorite, magnetite and calcite as secondary ones. Mineral chemistry and distribution of elements indicate that these minerals are formed in low to medium pressure (2-5 kbar), 1150 to 1200 °C, and the high Oxygen fugacity conditions. The source rock of the magma is a mantle peridotite which previously metasomatized by fluids and melts derived from subducting oceanic slab.  Mineral chemistry of clinopyroxene and biotite reveal that these dykes have calc-alkaline nature and are formed in a subduction-related environment.

Keywords: Dyke, Trachy-andesite, Eocene, Calc-alkaline, Jandaq, Central-East Iranian Microcontinent.

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