Document Type : Original Research Paper
Authors
1 Department of Geology, Tarbiat Moallem University, Tehran, Iran
2 Department of Enviromental Geology, Geological Survey of Iran, Tehran, Iran
Abstract
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 contamination processes. In terms of geochemistry, the variations of Rb, Sr, Pb and Hf confirm this phenomenon as well. Based on low topography of volcanic rocks, suture zone, strike-slip faults, and petrologic evidence, low degrees of partial melting in source and crustal contamination in the region, the magmatism occurred in a tensional tectonomagmatic environment. Local tension and opening along the strike-slip fault zone provided a way for ascending of magma to the earth surface.
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