Geochemistry and Petrogenesis of doleritic dykes containing megacrystic plagioclases in the middle part of Dehaj-Sarduieh volcano-plutonic belt (Kerman province)

In the central part of Dehaj-Sarduieh volcano-plutonic belt in Kerman province، there are some special doleritic dykes containing plagioclase megacrysts. This area is located 70 km south of Kerman city، and represents a part of Urumieh-Dokhtar volcanic belt. The most abundant rocks in the area include pyroclastic rocks and basaltic to andesitic lava flows with Eocene in age and are considered as the host rocks for the studied dykes. The thickness of the dykes reach up to 7 meters in the field، in which plagioclases are the only minerals can be recognized. Plagioclase crystals show a clear flow differentiation and generally، tend to concentrate in the central parts of the dykes. Under the microscope، the studied dykes contain plagioclase megacrysts and olivine phenocrysts set in a fine-grained and microlithic matrix. Different types of non-equilibrium textures such as mesh، dusty and zoning are found in the plagioclases. These evidences suggest some processes such as replenishment of magma chamber and decompression due to rapid ascent of magma. Geochemically، these rocks belong to the calc-alkaline magmatic series with some tendency toward the tholeiitic ones. Depletion of Nb، P، Ta and Ti elements suggest that the parent magmas relate to the subduction zone setting and affected by crustal contamination. According to the petrogenetic studies، the dykes formed in an active continental margin environment. Trace element concentrations revealed that the parent magmas probably، produced by partial melting of mantle sources. The source may have been metasomatized by slab-derived fluids and variations in Th/Yb and Ta/Yb ratios indicate that the resulted magmas have been affected by crustal contamination en route to the surface.