Petrology and petrogenesis of Eocene volcanic rocks of Sharafabad (NW Varzeghan, Eastern-Azarbaijan)



The study area is located in NW of Varzeghan in the Eastern Azarbaijan province. Based on tectonic units, this area is situated in the Alborz-Azarbaijan subzone of the Central Iran zone. According to field studies the studied volcanic rocks are composed of andesitic cones and lava flows with porphyritic texture. Petrographic studies indicate that they have porphyritic texture with fine-grained to glassy matrix. Glomeroporphyritic, vesicular and poikilitic textures are also present. The main phenocrysts minerals are: plagioclase, hornblende, clinopyroxene and opaque minerals. Apatite, quartz, biotite are the accessories and the secondary minerals are: sericite, iddingsite, epidote, clays minerals, chlorite and opaques. According to geochemical classification, the studied rocks are intermediate and are plotted on the field of andesite. These rocks are plotted on the fields of calc-alkaline to high-K calc-alkaline series. On the REE diagrams the studied rocks display enrichment of LREE's respect to HREE's, which is a feature of calc-alkaline rocks of active continental margin volcanoes. Based on various geochemical diagrams, tectonic setting of the studied rocks is analogous with tectonic features of active continental margin arc settings. Investigation on the source nature of the studied rocks by using various geochemical diagrams and petrological modeling indicate that they have been generated by 1-5% partial melting of garnet lherzilitic source which enriched by addition of releasing fluids from subducting slab in the subduction environment and this magma has been subjected to upper crust contamination through ascending to above levels.