The gabbroic rocks in the southeast of Arak of the zone Sanandaj-Sirjan in are intruded into the Middle and Upper Cretaceous sedimentary units. The main gabbroic rocks varieties include olivine gabbro, monzogabbro, diorite, and monzodiorite. The main minerals phases in the rocks are plagioclase and pyroxene and the chief textures are sub-hedral granular, porphyritic, intergranular and poikilitic. Electron microprobe analyses on minerals in the rock samples shows that plagioclase composition ranges from labradorite to bytonite, with oscillatory and normal chemical zonings. Clinopyroxene is diopside, augite and salite in composition and characterized with alkaline nature. Thermometry calculations indicate temperatures of 750˚C to 950˚C for plagioclase crystallization and 950˚C to 1120˚C for pyroxene crystallization. According to tectonic diagrams and mineral chemistry studies, the rocks of the region were formed in an intercontinental environment(rift).