Comparison of geology, petrography, geochemistry and petrogenesis of ignimbrite in Sabalan and Sahand volcanoes

In the present work, the ignimbrites of Sabalan and Sahand volcanoes have been studied. The geological, petrographic, and geochemical properties of Sabalan and Sahand ignimbrites presented here. Sabalan ignimbrites contain plagioclase, amphibole, pyroxene, biotite phenocrysts and rock fragments. The rock fragments are mostly pumice and obsidian. Sahand ignimbrites have plagioclase, sanidine, quartz, hornblende and biotite glassy groundmass. Sieve texture in plagioclase crystals and corrosion of the margin of some minerals in Sabalan and Sahand ignimbrites indicate that primary magma is affected by contamination and mixing before eruption. The Sabalan and Sahand ignimbrites have composition range of trachy- dacite to rhyolite and dacite to rhyolite, respectively. In the trace elements normalized diagrams, these rocks are enriched in LREE and LILE relative to HREE and HFSE, respectively. High content of Sr/Y-Y and La/Yb-Yb indicate that these rocks have high SiO2 adakites nature. The Sabalan and Sahand ignimbrites were sourced from the partial melting of lower crust with garnet amphibolite composition. The degree of partial melting in the primary magma of sabalan ignimbrites appear to be higher than that of Sahand ignimbrites.