Abstract
Volcanic rocks from Daito-dake area, Miyagi prefecture, represent early Pleistocene volcanism predating Zao and Funagata volcanoes. Stratigraphical and petrological study of these volcanic rocks revealed that they were derived from three sources. After the formation of late Tertiary Anadozawa lake deposits, but partly overlapping then, volcanism belonging to subaqueous lava domes became active. These lava domes accompany hyalloclastites. Banjiiwa Volcanics, consist of lavas, pyroclastic rocks, and dikes. The lower part shows evidence of subaqueous erupting and deposition, such as concentric pillows, pillow lobes, lava lobes. Toward the end of Banjiiwa activity, volcanism of Daito-dake, Kamuro-dake and Senohara-yama started, which consists of lavas and pyroclastic rocks. After the Banjiiwa volcanism, but during the same period as Kamuro-dake, Daito-dake volcanism started.
Volcanic rocks from subaqueous lava domes are made of dacite, whereas those from Banji-iwa, Daito-dake, Kamuro-dake and Senohara-yama change composition from basaltic andesite to dacite with time, and include both pigeonitic rock series and hypersthene rock series. Most volcanic rocks from Kamuro-dake are similar to Banjiiwa. These rocks of pigeonitic rock series and hypersthene rock series also show different chemical compositions in variation diagrams and FeO*/MgO-SiO2 plot.
