Geochemistry and tectonic setting of basic dykes in the Boroujerd area (Sanandaj- Sirjan Zone)

Basic dykes, trending NE-SW and cross cutting the middle Jurassic granodioritic rocks exposed in the Boroujerd area. They are dark green and fine to medium–grained rocks and are characterized by ophitic to subophitic texture. These rocks are dominated by major minerals including amphibole and plagioclase as well as minor biotite, apatite, sphene and prehnite. Amphibole is calcic, with magnesia-hornblende to actinolitehornblende composition. T = 600-700ºC and P = 3.5-5.2 kbar were calculated for crystallization of these minerals. The composition of plagioclases ranges from albite to oligoclase. The basic dykes studied are undeformed and the youngest magmatic activity in the area.. The collision of Arabian and Central Iranian plates, gave rise to the pressure in the Central Iranian plate, which expanded the extension fractures in the direction of the plate movement. As a result, the dykes in discussion formed in direction of plate movement. Thus, development of basic dykes in the Northeast-Southwest direction with respect to the convergence zone is justified. The basic dykes, on the discrimination tectonic diagrams, are classified as alkaline series and plotted on within plate environment field, which originated from partial melting of an enriched mantle source.