Eocene dike swarm and felsic stock in Central Iran: Roles of metasomatized mantle wedge and Neo-Tethyan slab

Abstract

The Eocene felsic stock and dike swarm with intermediate composition from Central Iran (southwest of Jandaq) are studied to understand geodynamic evolution of the Central-East Iranian Microcontinent (CEIM). Field relationships show that the dikes, composed of trachyandesite and basaltic trachyandesite, cross-cut the felsic stock. Whole rock geochemical data reveal the calc-alkaline nature of stock and high-K calc-alkaline to shoshonitic nature of dikes. The felsic stock and intermediate dikes show LREE and LILE enrichment and HFSE (Ta, Nb and Ti) depletion, suggesting that they probably formed in a subduction zone and are similar to the volcanic arc rocks. The rock samples of felsic stock have geochemical characteristics of the high silica adakites (HSA) produced by melting of a subducted oceanic crust. On the other hand, the dikes have characteristics of low silica adakites (LSA) produced by partial melting of a lithospheric mantle peridotite previously metasomatized by slab-derived melts. The Eocene felsic stock and dikes probably formed by subduction of the CEIM-confining oceanic crusts beneath the CEIM. The field and geochemical studies indicate that the magma originated from melting of basic section (amphibolite) of the subducted slab (HSA) will arrive to the Earth surface before the magma formed by melting of mantle wedge peridotites (LSA).