Petrography, whole-rock geochemistry and mineral chemistry of clinopyroxene and amphibole in basic alkaline igneous rocks of Shemshak Formation, S Azadshahr, Eastern Alborz

At the base of Shemshak Formation in the south Azadshahr area, some igneous mafic rocks are discovered recently  as olivine gabbro bodies and pegmatoid alkali-diorite dikes. Rock-forming minerals of olivine gabbro includes olivine, clinopyroxene and plagioclase, alkali-diorites are composed of large amphiboles and plagioclase. Major and trace elements characteristics of these rocks indicate they have alkaline nature and derived from OIB-like mantle source. Mineral chemistry of olivines and plagioclases in olivine gabbros determined as chrysolite and labradorite, respectively. Clinopyroxenes in olivine gabbros have diopsidic to augitic composition  and alkaline (Non-orogenic) affinity, and they formed in 2-11 Kbar, 1200-1250˚C and high oxygene fugasity conditions. Amphiboles in alkai-diorites are calcic and characterized with kaersutite to magnesiohastingsite in composition, igneous nature and derived from mantle sources. Their crystallization temperature and pressure are 950˚C and 600-750 MPa (equivalent 6-7/5 Kbar). Plagioclases in alkali-diorites are albite.