Alkaline basic dykes in the central part of Sanandaj-Sirjan zone (Iran)

There are three different basic dykes in the northeast of Golpayegan area, central part of Sanandaj-Sirjan Zone (SSZ) including: mylonitic gabbros (group 1), alkali dioritic-basanitic dykes (group 2) and alkali monzogabbroic to monzodioritic dykes (group 3). Group 2 and 3 cut post-collisional rocks and are related to after subduction processes of Neo-Tethys. Geochemistry characteristic of studied rocks indicate that group 2 is alkali basalt and two other groups are subalkali basalt-basaltic andesi. Group 2 and 3 are derived from an enriched mantle source. Group 2 is more enriched in HFSE, LILE and REE rather than other groups indicating that its source should be more enriched than group 1 and 3’s. It can be inferred that magma forming rocks of group 2 was derived from an asthenospheric mantle, while magma forming two other groups was resulted from a lithospheric mantle. Magmas forming dykes were generated by intermediate degrees of partial melting (about 7-20% and 12-20% for group 2 and 3 respectively). Source of magma was maybe a peridotite which was previously metasomatised. It is probable that the cause of metasomatism in the source was the subducted slab related to subduction of Neo-Tethys beneath the studied area.