Abstract
The Zao volcano is located in the central part of Abukuma Belt, and basement rocks is composed of Hbl-Bt granodiorite. Results of petrography and geochemical data indicate fractional crystallization of Pl and Hbl. Zircon U-Pb age is 97.8 +/- 1.3 Ma and initial Sr ratios are 0.7070~0.7072. Generally, initial Sr ratios of granitic rocks of Abukuma Belt are 0.705-0.706. Therefore, forming process of Zao basement rocks are different from other areas, and it can explain by the AFC model with pelitic gneiss.