Petrography investigation of volcanic units in Mahneshan area based on mineralogy studies

Mahneshan region, especially its northwest, lies on the Alborz sedimentary_ structural zone and Urumie-Dokhtar. This range was investigated in 1.100,000 scale geological map of Mahneshan. The rock units which are exposed in this area include Precambrian metamorphic rocks and their fellow intrusive indicate a continental granitic metamorphic crust. These rock units are overlain by Tertiary (especially Oligocene-Miocene) units which mostly contain volcanic rocks, especially pyroclastic. In Mahneshan area, between basic-ultrabasic lavas and their pyroclastic fellow, siliceous veins can be seen with considerable amount. It should be noted that, investigation of Oligocene- Miocene volcanic rocks in northeast of Mehneshan during some processes such as providing preparations (collection of data and research essentials), field observations, systematic sampling from area’s rocks, recording sampling points by using GPS, library research and laboratory studies, including providing 22 thin sections from the samples and microscopic petrography study and preparing microscopic pictures (with appropriate magnification), has been done. Finally, since the studied area is unique in terms of the amount of pyroclastic rocks and size of their components, the aim of the present research is to perform a petrographic investigation of volcanic and pyroclastic rocks of the area and petrographic comparison of the existing unit. According to the investigations, volcanic rocks in west and northwest of Mahestan, including lava rocks containing Andesite, Andesite-Basalt, Basalt and Pyroclastic rocks containing Agglomerate and Breccia with a thin to moderate combination and acid tuffs, and among these, the amount of moderate to thin pyroclastic rocks is more than other volcanic rocks.