Petrogenesis of Plio-Quaternary Post-Collisional Potassic and Ultra-Potassic Rocks in Northwest Marand

In this paper the study of Plio-Quaternary post-collisional magmatism in northwest of Iran and northwest of Marand is considered. The studied Potassic and ultrapotassic (UP) alkaline rocks were erupted at northern part of Urumieh-Dokhtar magmatic arc (UDMA). The studied rocks dispaly microlithic porphyritic texture with phenocrysts of clinopyroxene, leucite, and plagioclase ± biotite ± olivine. The UP volcanic rocks are mostly silica undersatuated with normative nephline, high Mg# and high K2O/Na2O ratios. They characterized with significant enrichment in LILEs and LREEs and depletion in high field strength elements such as Nb, Ta and Ti. Exhibit high Ba/Nb (41-60) and Ba/Ta (682-1139) ratios, which are a typical feature of subduction. With considering end of subduction (upper cretaceouse) and stratigraphic age of studed rocks (plio-quaternary), we can say that these rocks has formed in post collisional environment and metasomatic mantle due to addition of volatiles and incompatible elements lead to enrichment of these magmas. And in fact we can say that the subduction properties of these rocks inherited from an ancient subduction. On the otherhand, high contents of LILE such as Th and Ba and Ba/Nb, Ba/Ta ratios indicate the involvement of crustal components in genesis of these rocks by addition of crustal components to source and contamination through ascent of magma. Rare earth elements modeling indicate that they can be generated from low degree partial melting of lithospheric mantle with garnet-spinel peridotite source.