A volcanic rocks sequence which is composed of stratoid trachyandesite, basaltic trachyandesite lava flows and interbeds of paleosols is cropping out in the northeast of Zarjebostan area, as a part of Alborz paleogene volcanic belt. Petrographical evidences such as sieve textures, crystal zoning in the plagioclase phenocrysts and present of rounded phenocrysts all are indications of disequilibrium between the preexisting crystals and refreshed magma. Geochemical data from the studied volcanic sequence such as increase in the abundance of incompatible elements and concordant decrease in compatible ones are an indication of a magmatic evolution from bottom to top.