OICC Press Iranian Journal of Earth Sciences 2228-785X 17 3 2025 07 10 Petrology of volcanism in the Alasht-Haraz road of the Alborz mountain range, south of Amol (north of Iran) 10.57647/j.ijes.2025.16800 EN Reza Elmi Department of Geology, NT.C., Islamic Azad University, Tehran, Iran Mohammad Ali Arian Department of Geology, NT.C., Islamic Azad University, Tehran, Iran Afshin Ashja Ardalan Department of Geology, NT.C., Islamic Azad University, Tehran, Iran Abdollah Yazdi Department of Geology, Kah.C., Islamic Azad University, Kahnooj, Iran Journal Article 2025 07 10 The study area is located in the south and southeast regions of the Amol city, central Alborz mountain range, which is mainly consisted of Mesozoic sedimentary rocks, while cretaceous volcanic rocks are also found at some points of the area. Petrographical studies reveal that these rocks are consisted of basalt, andesite, trachyandesite, trachyte, dolerite, gabbro, and microgabbro, where the hypabyssal rocks are closely related to volcanic rocks through their magma origin. The above mentioned igneous rocks complex are covered with limestone’s as Tizkoh Formation. From geochemical point of view, the rocks of the region are of subalkaline and tholeiitic nature, while parts of them are alkaline. Based on petrographical studies, titanium oxides (as opaque minerals) crystallize earlier. The present findings also show that the contents of Al2O3 and MgO in comparison to that of SiO2 follow ascending and descending patterns, respectively. These findings support early partial crystallization of olivine in comparison to plagioclase crystallization in liquidus line phase. Moreover, the descending pattern observed for K2O and Na2O in comparison with MgO is also attributed to partial crystallization of the magma and their distribution to some extents is the result of their alteration or contamination with felsic crust materials. Analysis of rock samples normalized to the chondritic values shows gradual enrichment of heavy rare earth elements contents (HREES) compared to those of light rare earth elements contents (LREES). Most of basalts studied in the region are of OIB type. The magmas of basaltic rocks originate from a depth of 100-110 kilometers and a garnetic lehrzolitic source rock. According to geochemical investigations, the studied rocks originate from the melting of a mantle that undergone magmatic differentiation and is finally polluted with continental crust.