Petrology and Geochemistry of Low- SiO2 adakites Quaternary Volcanic Rocks in the West of Kohin, East of Qorveh (Northwest of Iran)

Abstract: This study presents in combination with petrography, Microprobe analysis of minerals, major and trace element geochemistry and Sr, Nd, Pb radiogenic isotope data in order to characterize and discuss the origin of volcanic rocks in Case Study. In the northern part of the Sanandaj- Sirjan Zone (SSZ), northwestern Iran, in the west of Kohin, east of Qorveh there are a number of young (0.339- 0.112 Ma) dismembered volcanic complexes that extend parallel to the Zagros Suture Zone in a northwest– southeast direction. The major lithologies associated with these complexes Trachy andesite, andesite, dacite. These rocks display microlitic to porphyritic textures with plagioclase, pyroxene, amphibole as phenocrysts. These rocks are characterized by Na2O (3.5-7.5wt %) and low Y (<18), high Sr (>400), high Sr/Y (>40) and La/Yb (>25) ratios. Initial 87Sr/86Sr ratios are relatively of high (0.7064–0.7066). Major and trace element bulk rock geochemistry and initial Sr, Nd, Pb radiogenic isotope data on the rocks provide new constraints on the Quaternary volcanism in this region. Analyses of chemical compositions confirm that these rocks belong to the low silica adakite group. The Sr–Nd ratios, Isotope ratios of Pb and also geochemistry studies indicate that the samples of the study area are located near the crust and these rocks are from continental crust derived from partial melting and suggest that the parent magma originated from melting of the crust after continental collision. Keywords: volcanic rocks, adakite, geochemistry, Quaternary, west of Kohin, Sanandaj-Sirjan