ويژگي هاي سنگ هاي آتشفشاني جوان در جنوب خاوري بيجار

Properties of Young Volcanic Rocks in southeast of Bijar

In the south of Bijar, north east of Sanandaj in the Kordestan Province, and in the Sanandaj-Sirjan structural zone, young volcanic rocks are present. In this area, rocks with Cretaceous, Oligocene, Miocene and Pliocene ages are also observed. Based on field observations, volcanic activities occurred during two main stages. In the first stage, eruption of pyroclastic material made a volcanic cone and a crater. In the next stage, lava erupted. Volcanic rocks are a combination of trachy¬andesite, andesite, andesite-basalt and basalt. In the magma poor in silica, presence of olivine and analcime and lack of orthopyroxene and pygeonite are the evidence of alkaline type magma series. Petrographical evidences such as the existence of gneiss xenoliths and quartz xenocrysts with reaction rims are the results of v^ojQQk: Scientific Quarterly Journal, GEOSCIENCES, Vol 19, No 75,Spring 2010