Geological and petrological study of the Miyamoto igneous complex in the south Abukuma mountains revealed a division of the following six rock types; ultrabasic rocks, gabbroic rocks (Inubotoke-, Mikabu-, Ishigami-types) and granitic rocks (Arizane- and Domeki-types).
The Arizane-type rocks, the main constituent of the complex, are mostly composed of tonalite. The Domeki-type rocks, the next abundant rock type, consist chiefly of adamellite, The Ishigami-type rocks, though subordinate in volume, range from gabbro to tonalite. The intrusive sequence among the three rock types is the Ishigami, Arizane and Domeki. Thus the composition of intruded magma became more felsic and K-rich toward the later stage.
The Miyamoto igneous complex is a crudely zoned pluton containing a gabbroic margin. Each rock type has its own petrographical characteristic and exhibits unique compositional variation trend which are easily distinguished from the other types by modal and whole-rock chemical compositions. The field occurrances and petrographical data indicate that the zonal structure of the complex was not formed by in-situ differentiation from a single primary magma, but was formed by succesive intrusions of magmas of different origins.

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K-Ar dating was carried out on the Yanagino dacite and Takaiwa rhyolite which form part of a roughly E-W chain of small felsic intrusions along the Kamiyakawa-Ikegawa tectonic line in central Shikoku.
K-Ar whole rock ages of the Yanagino dacite range from 15.2 ± 0.4 Ma to 16.9 ± 0.4 Ma and its biotite yields a little younger age of 14.2 ± 0.4 Ma. A K-Ar whole rock age of 15.0 ± 0.5 Ma was determined for the Takaiwa rhyolite.
Present study confirms the felsic intrusions are correlated in age with the Miocene Ishizuchi Group and related intrusions distributed to the north of the tectonic line.

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Geological survey has been carried out on Akita-yakeyama volcano, eastern Akita Prefecture, Japan to establish the evolutional history of the volcano. Furthermore, the volcanic products have been described in detail to contribute to the petrological investigation of the volcano, that is currently in progress.
The volcanic activities can be divided into three stages in terms of mode of volcanic activity or characteristics of the erupted products, or both. Approximately 300, 000 years ago, the volcanic activity started within a caldera formed by the eruptions of the voluminous felsic pyroclastics at 1 million years ago. This is the beginning of the early stage; the new volcano erupted number of andesitic lavas of the pigeonitic rock series while pyroclastic flows and falls were less abundant. The shape and size of the volcano built during this stage is not clear since it was covered with the following volcanic products, and severe erosion altered it much. In the middle stage the lava flow activities have been associated by explosive eruptions: pyroclastic falls and flows were repeated from central vent. The alternation of lavas and pyroclastics could have completed a large stratovolcano. All the volcanic rocks during this stage belong to hypersthenic rock series. After middle stage, the activity ceased for a while, and hydrothermal alteration expanded to nearly all over the volcano. Consequently, collapses of the altered piles of lavas and pyroclastics have led to five horseshoe-shaped calderas around the summit. After the repose period, the late stage activity started with explosive central and flank eruptions of pyroclastic fall; lava flows as well as pumice falls followed. During this stage, two andesite lava domes and two dacite domes were constructed. In the central area of the summit crater a dacite dome was built and dacitic ash was erupted; this is the latest activity. All the rocks of the last stage are of the hypersthenic rock series as well.

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High magnesian andesites from Kume-jima and Iriomote-jima, the Ryukyu islands were dated by the K-Ar method with the basalts from Kobi-sho and Sekibi-sho, the Senkaku islands. The obtained K-Ar ages of the high magnesian andesites are 6.08 ± 0.46 Ma and 13.1 ± 1.1 Ma for the sample (s) from Kume-jima and Iriomote-jima, respectively. The volcanic activity of the high magnesian andesite magma continued intermittently for at least 6 Ma. The K-Ar age of the basalt from Sekibi-sho is 2.59 ± 0.19 Ma. The age of the basalt lava from Kobi-sho is as young as 0.2 Ma or even younger, and indicates that Kobi-sho is a Quaternary volcano.

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