(Geology and petrology of Adatara volcano.)

Abstract

Geological and petrological studies were carried out on this volcano of the Nasu volcanic zone of NE Japan. The volcano consists of three cones (in order of formation): Maegatake, old Osyozan and Adatara main cones. Maegatake consists of calc-alkaline andesite; the old Osyozan cone is composed of tholeiitic basalt and andesite. The Adatara main cone consists of calc-alkaline andesite and tholeiitic andesite. The calc-alkaline rock is more enriched in K2O than the tholeiitic rock; this chemical difference is not explained by simple fractional crystallization from their common parental magma.-M.Ak.