Cenozoic alkali basalts (1-12 Ma) in the Chugoku district, SW Japan, are divided into two types: 1) MF-type basalts characterized by high MgO, FeO and TiO₂, and 2) SA-type basalts rich in SiO₂ and Al₂O₃. They are also distinguished in terms of the TiO₂/MnO/P₂O₅ tectonomagmatic discriminant diagram and the ε_Nd-⁸⁷Sr/⁸⁶Sr systematics. The MF-type basalts are similar in petrochemistry to oceanic island alkali basalts, while most of the SA-type basalts show the features of arc basalts. The isotopic data and trace element abundances of the rocks indicate that the SA-type basalts are not derivatives from the MF-type basalt magma. These two types of the alkali basalts should be produced from the different mantle sources.
The distribution of the SA-type basalts with arc signature is restricted to the back-arc side (Japan Sea side) of the Chugoku district. The spatial variation in Sr and Nd isotopic composition of the MF-type basalts show a reverse tendency to that shown by the Quaternary volcanics from NE Japan. These facts cannot be ascribed to subduction effect of the Pacific plate or of the Philippine Sea plate. The Cenozoic alkali basalts with oceanic island basalt signature from the Eastern Asia, including the MF-type basalts, show the highest ⁸⁷Sr/⁸⁶Sr and lowest ¹⁴³Nd/¹⁴⁴Nd ratios in the southern Japan Sea, and these ratios become lower and higher with distance from this area to both sides, respectively.

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Abundances of major elements and five trace elements, Rb, Sr, Nb, Y and Zr were determined by X-ray fluorescence analysis for the late Miocene (8-6 Ma) volcanic rocks of the central part of Northeast Japan, Systematic zonal variation of petrological features, i.e., mafic phenocryst assemblages and rock series, as well as gradual increase in K₂O, Na₂O+K₂O, Rb and Sr contents are rocognized in these volcanics from the Pacific Ocean side to the Japan Sea side across the arc. Similarity of across-arc variations with regard to both the petrological and geochemical features between the late Miocene volcanics and the Quaternary volcanics suggests that the mechanism of magma generation of the late Miocene is essentially similar to the Quaternary one.

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Granitic rocks in the central and northern Abukuma Mountains, containing abundant pegmatite, are known to produce various pegmatite minerals. Granitic rocks in the Uzumine area, one of pegmatite-producing spots in the central Abukuma Mountains, are described from the geological and petrological view points.
The granitic rocks are divided into the older foliated granodioritic rocks, the younger medium-grained two-mica granodioritic rocks, and the younger porphyritic two-mica granitic rocks. The younger porphyritic two-mica granitic rocks have been considered to be intimately related with pegmatite bearing rare element minerals, such as euxenite, monazite and xenotime etc.. The two-mica granitic rocks are the richest in potash feldspar and the highest in SiO₂ content (73-76%), and also contain biotites with low Mg/(Mg+Fe) ratio. They exhibit characteristics of S-type in mineral assemblage and normative corundum content, but are plotted in an I-type area in an ACF diagram. Moreover, their REE concentrations and strong light REE enrichment patterns, are positively comparable to those of I-type plutonic rocks.
The younger porphyritic two-mica granitic rocks may be formed either through the fractional crystallization of an I-type granodioritic magma, or from an independent granitic magma. In the latter case, the granitic magma may be originated from a parental material different from that of the I-type granodioritic magma, but the two magmas have a common residue of garnet and hornblende during partial melting of parental materials.

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