OICC Press Iranian Journal of Earth Sciences 2228-785X 2026 07 14 Thermobarometric studies of the Upper Triassic basic volcanic rocks of Pol-e Sefid (Central Alborz-Iran): Extensional regime and petrogenesis 10.57647/ijes.2026.18033 EN Saeid Samarbakhsh Department of Earth Sciences, SR.C., Islamic Azad University, Tehran, Iran Mohammad Hashem Emami Department of Earth Sciences, SR.C., Islamic Azad University, Tehran, Iran Seyed Mojtaba Mortazavi Department of Mining Engineering, Sava.C., Islamic Azad University, Savadkooh, Iran Mansour Vosoughi Abedini Department of Earth Sciences, SR.C., Islamic Azad University, Tehran, Iran Abdollah Yazdi Department of Geology, Kah.C., Islamic Azad University, Kahnooj, Iran Journal Article 2026 07 14 A new study of the volcanic rocks of the Upper Triassic of Central Albarz, northern Iran, has been conducted. This area is about 200 km from Tehran, near Pol-e-Sefid (Khatirkouh). Researchers chose this location due to the lack of detailed studies on these rocks and the area's tectonic regime. One reason for this gap is the severe alteration of the volcanic rocks. Given its central location, this research can greatly enhance our understanding of the techno-magmatic environment, especially in central Alborz. Thus, field studies, petrography, and thermobarometry were done on these rocks. The most common formations in the region, ranging in age from Lower Carboniferous to Middle Jurassic, include the Mobarak, Dorood, Ruteh, Elika, and Shemshak formation. The primary minerals in the region’s volcanic rocks (which include basalt, andesite, trachyandesite, and dolerite) are clinopyroxene, olivine, and plagioclase. These volcanic rocks exhibit textures ranging from porphyritic to mega-porphyritic, with matrices that are microlitic, glomeroporphyritic. Chemical analyses of the minerals reveal that the clinopyroxenes are predominantly diopside and augite. Additionally, the plagioclases are classified as oligoclase, labradorite, and bytownite. Based on thermobarometric diagrams and calculations, the formation temperatures are determined to be between 850 and 1100 °C, and pressures range from 6.10 to 8.5 kbar. Finally, the investigation of the tectonic setting of these rock masses based on the chemistry of clinopyroxene and plagioclase minerals indicates the formation of the region's rocks in an extensional environment.