Geothermobarometry of volcanic rocks from N Torud, NE Iran

The study area is located in the N Turood, S Shahrood, and NE of Central Iran structural zone. Many basaltic dikes in this area intruded into the Eocene volcanic rocks and they also contain many gabbroic enclaves. Plagioclase (labradorite, bytownite-anorthite), amphibole (calcic, pargasite- magnesiohastingsite), and pyroxene (calcic, diopside-augite) are the essential minerals of these rocks. With the attention of the minerals chemistry, magma forming of these rocks has mainly subalkaline nature and during their crystallization fugacity of oxygen has been high. Geothermometry of these rocks suggest crystallization equilibrium temperatures are at 1100-1200°C for pyroxenes, and 825-888°C for amphiboles. Geobarometry calculation by using of Altot of amphiboles in host basaltic rocks, basaltic dikes and enclaves estimated between 8.51 to 9.21 kbar (depth of 30 to 33 km), 7.41 to 9.16 kbar (depth of 27 to 33 km) and 6.84 to 7.46 kbar (depth of 25 to 27 km), respectively. The chemical characteristics of studied minerals in differents diagrams show strong compositional similarities and indicate that nature and origin of these rocks are the same and most likely the magmatic reservoir or reservoirs of the studied basaltic rocks were at depths of 33 to 25 km of the lower crust.