Document Type : Original Research Paper

Authors

• M Poosti ¹
• M Fadaeian ²

¹ Assistant Professor, Department of Geology, Hormozgun University, Bandarabas, Iran

² Instructor, Department of Geology, Payame Noor University, Tehran, Iran

Abstract

The study area is  located in the Ardabil province and in the north of Meshkin shahr town. A large part of the areais  formed of  Eocene igneous rocks. These rocks include basaltic andesite, basalt, tephrite and  occasionally analcimite. They are silica saturated or relatively saturated. According to tectonomagmatic diagrams, the original setting of the parental magma was a volcanic arc and subduction zone. The negative anomalies of Nb, the high ratio of LILE/HFSE, the high mounts of Al₂O₃& P₂O₅, the low  titanium contents, and the degree of partial melting of the metasomatized upper mantle, strengthens the subduction related processes for the formation of the primary magma (alkali olivine basalt). Petrographic evidences suggest that the primary magma is mixed with crustal materials. The chemical composition of rocks, according to geochemical diagrams, is shoshonitic. These rocks may have been formed by the subduction of the oceanic crust of Neoteties during the Mesozoic and early Cenozoic periods. Releasing fluids exerted from the subducting slab, metasomatism of the lithospheric mantle and subsequently the appropriate conditions for melting of the metasomatized mantle, all led to the formation of potassic magmatism and finally, generation of magma with a shoshonitic nature found its way to the surface under the influence of an extension phase and complex fault systems. 

Keywords

• Shoshonite
• Metasomatism
• Analcimite
• Magma mixing
• Partial Melting