Three biotite K-Ar ages were determined for the Miocene Takatsuki-yama and Miuchi plutons, southwestern Shikoku, Japan. These plutons belong to the Outer Zone Acidic Rocks in the Southwest Japan (OZARSWJ). The obtained ages from the two granodioritic samples in the Takatsuki-yama pluton give a good coincidence; 13.9±0.2 Ma and 14.0±0.2 Ma. The granite sample of the Miuchi pluton gives slightly younger age (13.4±0.2 Ma) than those of the Takatsuki-yama pluton. Though these two plutons were considered as the different exposures of a single batholith, the different ages suggest that these two exposures might belong to the different intrusive blocks with short interval. The obtained ages for the both pultons are within the range of 13-15 Ma, which corresponds to the time interval of the other OZARSWJ granitic rocks.

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The Inaniwadake volcano, situated on the northern part of the volcanic front of Northeast (NE) Japan arc, comprises two groups of volcanic rocks which overlie the Kiritoshi Formation and the lower part of the Itsukaichi Formation. The lower group is the Joboji Andesite Member belonging to the Itsukaichi Formation, distributed in the northern and eastern flanks of the Inaniwadake volcano, and composed of lavas with pyroclastics. The Inaniwadake Formation, the upper group, is distributed in the most part of the Inaniwadake volcano, and can be divided into the Takamagezawa (lower), Hanakosodemine (middle) and Takamagehara (upper) Basalt Members, all of which are composed of lavas with minor pyroclasts.
Three samples were chosen for K-Ar dating. The sample from the Takamagehara Basalt Member, the youngest lava of the study area, shows 2.67±0.23 Ma, while the other two samples from the Joboji Andesite Member show 6.52±0.26 Ma and 6.95±0.26 Ma.
All the Inaniwadake volcanic rocks including above samples are characterized by extremely low K₂O suites like as the other late Miocene to Pliocene volcanic rocks from Mitaki and Kurohanayama, the southern part of NE Japan arc. These Tertiary volcanic rocks are mainly basalts and basaltic andesites in composition, and distinctively lower in K₂O content than those of Quaternary volcanoes on the volcanic front. These extremely low-K volcanism coincide contemporaneously with the formation of a number of late Miocene to Pliocene calderas of NE Japan arc.

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Experiments on the partitioning of Mg²⁺, Ca²⁺, Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺ and Zn²⁺ between olivine (forsterite and fayalite) and 2 N aqueous chloride solutions were performed in the temperature range of 500 to 800°C, 1 kb.
The partition coefficient, which is defined as K_PN(Fo)=(X_Me2SiO4/X_Mg2SiO4)/(m_MeCl2^°aq/m_MgCl2^°aq) or K_PN(Fa)=(X_Me2SiO4/X_Fe2SiO4)/(m_MeCl2^°aq/m_FeCl2°_aq), vs. ionic radius (PC-IR) diagrams are drawn based on the experimental results. In the case of forsterite, the PC-IR curve has a local maximum near Ni²⁺ and shows a concave curve in the region of larger ionic size. However Zn²⁺ deviates from such a trend. In the case of fayalite, the PC-IR curve shows a convex curve with a peak near Ni²⁺ except for 500°C. Also in this case, Zn²⁺ deviates from such a trend. The anomaly of Zn²⁺ may be attributable to its tetrahedral site preferency. The K_PN value for Ni²⁺ decreases with increasing temperature, whereas those for the other elements except for Ca²⁺ increase. The optimum ionic radius for forsterite and fayalite seem to increase slightly with increasing temperature.

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In the past several decades a significant number of research papers has been appeared on the international journals of earth sciences that has referred to the viscous behavior of magmatic silicate melts. It is, obviously, the reflection of importance of viscosity on the magmatic process such as magma generation and volcanic eruption and of importance for the understanding of early history of the Earth.
Contrary to the importance, the theoretical background of viscosity of a magmatic silicate melt has not been understood well.
This review paper is concerned with the introduction to some basic knowledges and two representative theories on the viscosity of magmatic silicate melts. The first part deals with the definition, methods of viscosity measurement and the effects of parameters that govern the viscous behavior. The second part deals with the free volume theory, which was the early theoretical background for the understanding of viscous behavior of a liquid. This theory emphasizes the importance of free space in a magmatic silicate melt. The third part deals with the configurational entropy theory, which is the theory in much fashion in magma science. The characters of this theory are the combination of thermodynamic data with the viscosity, and the emphasis of the number of configurational state attainable in a magmatic silicate melt. This theory succeeded in the quantitative interpretation of the change of viscosity with temperature and chemical composition.

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