Abstract
Many characteristic inclusions which are some-what globular and more mafic than their host rocks are in the hornblende andesites from the Myoko volcanoes. They generally contain glass and are porous. Such inclusions are also found generally in the intermediate volcanic rocks, especially in the hornblende andesites from other volcanoes in Japan. In the Myoko volcanoes, they have been called cognate inclusion, and interpreted as fragments of the rocks crystallized at a earlier stage in the same "evolutional series" as the host rocks. Many inclusions are contained in the basalt, pyroxene andesite, and hornblende andesite of the Myoko-IVth stage. The inclusions in the basalt are undoubtedly accidental xenoliths, and those in the hornblende andesite have been called cognate inclusion by previous workers, and have the same features as mentioned above. As the result of the microscopic observation, a continuous transition in texture (Table 4, Plate I〜IV), mineral assemblage (Fig. 4), and features of minerals (Table 4, Fig. 3) is traced from the accidental xenoliths in the basalt (Nishikawadani lava) through the inclusions in the pyroxene andesite (Tsubame lava) to the so-called cognate inclusions in the hornblende andesite (Otagirigawa pyroclastic flow). Therefore, such inclusions in the hornblende andesite are considered to have been formed through the reaction of accidental xenoliths with magma. Many inclusions called cognate inclusions from other volcanoes may have also originated from accidental xenoliths, because their features are very similar to those of the Myoko volcanoes.
