Geochemistry, petrogenesis, and tectonic setting of Nepheline syenite intrusive rocks in Razgah Sarab, East of Azerbaijan Province

Razgah, Kalibar, and Bozghosh intrusive rocks, located in East Azarbaijan province, are among the most important alkaline nepheline syenite rocks known in Iran. Several theories reported regarding the geochemical characteristics as well as the geotectonic environment of the Tertiary igneous rocks exposed in the Ahar-Arasbaran belt (Jamali et al., 2012). Some workers have considered the magmatism of this belt as an important extensional phase of the late Cretaceous, while, some others believe it is related to subduction zones. Although the mineralogy, petrology, geochemistry, and petrogenesis of these rocks have been studied by several people (i.e., Esmaeili, 1997; Ameri, 2004; Ashrafi, 2009), in none of them the origin and geotectonic setting of the area has been discussed in detail. Thus, for the present study, mineralogical, petrological, and geochemical studies are applied to understand the origin, the petrogenesis, and the geotectonic setting of the intrusive rocks from the nepheline syenite exploration areas, particularly the Razgah intrusive rocks. Regional GeologyThe Razgah intrusive. a part of the Western Alborz-Azarbaijan zone lies on the southern edge of the Ahar-Arasbaran volcanic belt. Geologically, the Eocene volcanic rocks cover the Jurassic-Cretaceous flysch is intruded by the Oligo-Miocene plutonic rocks (Mahdavi and Fazli, 2008). The Razgah nepheline syenite intrusive intruded the sediments of evaporate basins including gypsum marl, limestone marl, sandstone, and the Miocene conglomerates. Their contact with previous rocks has vanished due to weathering and erosion of itself and the Quaternary sediments surrounding it. Copper mineralization (malachite and azurite) can be identified in the western part of Razgah intrusive. In addition, a number of dykes are distributed especially in the western and northwestern parts. Also, numerous silica veins were observed in different parts, mainly along, in parallel, and in contact with dykes, more widespread in the western part.Materials and methodsFollowing the sampling (150 rock pieces) and preparation of 70 thin sections for petrographic and mineralogical investigations, trace and REE were determined on 93 samples using the ICP-MS method.PetrographyThe Razgah intrusive rocks are dominated by olivine-bearing nepheline gabbro, nepheline monzosyenite, pseudolucite syenite, and K-feldspar nepheline syenite. Also, basic dykes (lamprophyre), similar to their host (altered syenite nepheline), syenite and