Petrology and geochemistry of volcanic rocks from the South of Tabriz (Sahand Volcano)

The area under study is situated in the south of Tabriz and east of Urmia Lake. The area is dominated by a sequence of volcanic rock ranging from rhyolitic to dacitic composition related to volcanic processes in the Oligo-Miocene, middle and upper Miocene, Pliocene clastic sedimentary rocks and lower Pliocene epiclastic sediments. The volcanic rocks as Dome-Ring shape,emplaced in a good order as the middle domes have rhyolitic and rhyodacitic whereas the marginal ones have dacitic and trachytic composition. The major minerals including plagioclase, hornblende and quartz, set in a fine grained and glassy matrix. Porphyritic is the dominate texture. Sieve texture and selective alteration in some plagioclases, the presence of biotite and hornblende with opacitic rims, associated with some other disequilibrium textures are characteristic features of the rocks studied. Based on the high LILE/HFSE and LREE/HREE ratios and their similar composition to that of the subduction volcanic rock suites, the rocks of the area seem to have formed in a subduction zone. Compared to rhyolitic and dacitic rocks from typical tectonic environments, the compatible and incompatible elements patterns for the rhyolitic and dacitic rocks from the study area are more consistent with a post-collision volcanic arc setting.