Open Journal of Geology, 2016, 6, 131-145 Published Online March 2016 in SciRes. http://www.scirp.org/journal/ojg http://dx.doi.org/10.4236/ojg.2016.63013 How to cite this paper: Arian, M.A., Bazoobandi, M.H. and Elmi, R. (2016) Petrogenesis of Volcanic Rocks in Alasht, Mazan- daran, Iran. Open Journal of Geology, 6, 131-145. http://dx.doi.org/10.4236/ojg.2016.63013 Petrogenesis of Volcanic Rocks in Alasht, Mazandaran, Iran Mohammad Ali Arian 1 , Mohammad Hasan Bazoobandi 2 , Reza Elmi 1 1 Department of Geology, Faculty of Sciences, North Tehran Branch, Islamic Azad University, Tehran, Iran 2 Faculty of Science, Shahid Sherafat, University of Farhangian, Tehran, Iran Received 30 January 2016; accepted 6 March 2016; published 9 March 2016 Copyright © 2016 by authors and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/ Abstract Area studied in this paper is located in the northwest of city of Alasht. The most important varie- ties of studied rocks are volcanic and semi-volcanic rocks of basic nature. These rocks, which form a distinguishable solid mass on 1:100,000 geological map, belong to Cretaceous period. According to results of petrographic study, rocks of this area include olivine basalt, dolerite, gabbro and mi- crogabbro, and all have almost similar chemical compositions. According to chemistry-based nam- ing process carried out through TAS method, these rocks are entirely basalt and basic and are all products of Sub-alkaline-Tholeiitic magma. According to Harker diagrams, a magmatic differen- tiation can be observed in all volcanic rocks; furthermore, basaltic magma erupted in this area has undergone an alteration and possibly a crustal contamination. The spider diagrams plotted in this paper show that basic rocks of Alasht area (basalts, andesite basalts, dolerites, gabbros and mi- crogabbros) are all mostly similar to ocean island basalts (OIB). Once field study, sampling and microscopic study stages were complete, ten samples were selected for chemical analysis and were analyzed by XRF method. Keywords Alasht Area, Crustal Contamination, Olivine Basalt, Sub-Alkaline 1. Introduction The study area is located around the city of Savad kuh in Mazandaran province roughly 200 kilometers away from Tehran. This area is positioned between 52˚46' and 52˚52' eastern longitudes and 36 ˚01' and 36˚03' northern latitudes. It has a total area of about 105 square kilometers, a mountainous terrain, and an average altitude of 1800 meters above sea level. The maximum altitude of the study area is 2882 meters in its minimum altitude is