Petrology of Lower Cretaceous pillow lavas and diabase dykes from North of Hajiabad (SW of Bayazeh، Isfahan province، Iran)

The Lower Cretaceous pillow lavas and diabasic dykes are cropped out in several points in the North of Hajiabad belonging to Central Iran. The best exposure of these rocks is seen in Dum Kalagh Mountai. Field studies reveal that dykes intrude the pillow lavas and the space between the pillow lavas is filled by sediments، and the whole suite is covered by thr Lower Cretaceous cherts and limestones of the Biabanak Formation. Minerals of these rocks are plagioclase (labradorite to albite)، clinopyroxene (diopside)، chloritized olivine، ilmenite، termolite -actinolite، epidote، prehnite، sericite، calcite، chlorite، pyrite and magnetite. Mineral chemistry of clinopyroxenes reveal a parental magma، with low H2O، high TiO2 content and high oxygen fugacity. Based on the geochemical studies، the primary magma of the pillow lavas is alkali basalt and that of the diabasic dykes is tholeiitic basalt. Geothermometry and barometry based on clinopyroxene chemistry display 750-850 °C and 13-16 kbar. Geothermometry of chlorites shows 190-240 °C and sub -sea floor metamorphism in the prehnite-pumpellyite facies. We conclude in this region، an aborted rift system developed during Lower Cretaceous. This study shows that rifting related to the opening of Neotethys is not exclusively limited to the Zagros geosuture and the surrounding area of the Central-East Iranian microcontinental (CEIM).