Document Type : Original Research Paper


Department of geology, Islamic Azad University, Mashhad Branch, Mashhad, Iran


   The study area is located in the northeast of Iran. Miankuhi Formation is 500m thick and comprises homogeneous shales, brown granular sandstone and siltstone. In this study, 45 samples were taken from Miankuhi shales and sandstones in order to determine their tectonic origin by using a polarizing microscope. Samples were analysed by X-Ray Fluorescence (XRF) method to determine their chemical compositions and tectonic origin. Twelve shale and siltstone samples were also analysed by the X-Ray Diffraction method with the aim of identifying their mineral composition. According to the investigations conducted, the type of sandstone is greywackes. Based on XRD results, quartz, albite, orthoclase, calcite, kaolinite, and illite have existed in shales and siltstones. Chemical analysis of the rocks indicated the source of these clastic rocks as oceanic arc areas and active peripheries of a landmass. The corrosive rocks of this formation are believed to originate from intermediate felsic igneous rocks and to a lesser extent from clastic quartz-containing rocks in the region. Keywords: Iran, Kopet-Dagh, Miankuhi Formation, Triassic