The chemical composition of Ti-poor and biotites from Ryoke metamorphic rocks in the Yanai district are described by the substitution, 2Ti+ ?? ^VI=2Al^VI+R²⁺. By applying this substitution to eastonite, a new endmember of Ti-biotite, K₂ ?? R²⁺₃Ti₂Si₄Al₄O₂₀(OH)₄, is defined. The compositional space defined by phlogopite-talc-eastonite-muscovite and this Ti-biotite can express the composition of Ti-bearing biotite better than other definitions of Ti-biotite endmenber.

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Abundances of major elements and seven trace elements, Rb, Sr, Nb, Y, Zr, . Ni and Cr were determined by X-ray fluorescence analysis for 111 samples from twelve Pliocene volcanic centers in the NE Japan arc, The petrographical and analytical results on these samples and other Pliocene volcanic rocks indicate that systematic zonal variation of petrological features, i.e., mafic phenocryst assemblages and rock series, as well as gradual increase in K₂O, Rb and Sr contents are recognized in the Pliocene volcanic rocks from the Pacific Ocean side to the Japan Sea side across the NE Japan arc.
Similarity of across-arc variations with regard to both the petrological and the geochemical features among the volcanic rocks from the late Miocene through Pliocene to Quaternary time suggests that a mechanism of magma generation due to plate subduction has been contineous in the NE Japan arc at least from 8 Ma to the present.

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The Oligocene Omoto pluton in the Ishigaki-jima Island, southern Ryukyus, is divided into six rock types : Miyaragawa, Chayama, Ishigaki, Naguragawa, Otake and Omoto. These rock types that make up zoned plutonic sequence are younger and more felsic inward. The most of the rocks are adamellite and alkali feldspar granite, but the outermost rock facies is quartz diorite, and innermost one is porphyrytic granite. The clearly boundaries between each rock type indicate that zoned mechanism of the Omoto pluton is multiple intrusion.
The Omoto type that is innermost and most felsic rock facies shows characteristics of S-type granitoids, while the other types exhibit those of I-type granitoids. Cr contents of the Omoto type are similar to those of more basic rock facies in this pluton. These matters suggested that the Omoto type and the other types were derived from different sorce material.
In conclusion, the Omoto pluton is composed of six rock types which are derived from two different magmas.

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