The alteration sequence of biotite in granitic rocks at two weathered profiles (Kisuki and Yamakata) located in Shimane Prefecture was investigated. The weathering condition in this district was also inferred from the results. The alteration products from biotite were hydrobiotite, vermiculite, kaolinite, goethite and gibbsite.
The main alteration sequence of biotite in the weathered granite of this district has been assumed as follows: biotite→hydrobiotite→vermiculite→kaolinite
Biotite grains were treated with several solutions (pH 3.0, 5.3, 8.0) at 60°C for 55 days.
It is assumed in comparison with the experiment and the alteration of biotite in some other district that biotite in this studied district was altered under the temperate condition such as recent climate in this district.

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Crystal forms of zircon in granitoids have been measured to investigate the conditions of metamorphism and igneous activity. The Precambrian Sobaegsan and the Jirisan gneiss complexes contains various zircons from the {110}>{100} to {100} prism types, probably due to the early progressive and the later retrogressive metamorphism. The Jurassic gneissose granodiorite shows the “fan-shaped” PPEF diagrams of the {110}={100} zircon, which suggest magma at moderate temperatures in the middle stages of crystallization differentiation. The Jurassic Geochang granodiorite forms the “scissor-shaped” PPEF diagrams of the middle-prismatic {110}>{100} and the short-prismatic {110}<{100}zircons, suggesting the assimilation or contamination at low temperatures in the later stages. The Jurassic to Cretaceous intermediate and basic plutonic rocks is characterized by the “bundle-shaped” diagrams of the {100} zircon, showing that new igneous activity of high temperatures started. The Cretaceous Gajo granite forms the “scissor-shaped” PPEF diagrams of the {110}>{100} and the {110}<{100} zircons, probably resulted from the assimilation or contamination at low temperatures in the later stages.

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Large amounts of basalt gravels are associated with serpentinite gravels in the Senhata Formation of the Miura Group (uppermost Miocene) in the Boso Peninsula, central Japan. The basaltic rocks possibly constitute a presumed mafic-ultramafic complex (“Fudoiwa serpentinite mass”) in the Tokyo Bay area, which belongs to the Circum-Izu Massif Serpentine Belt. They are slightly altered and have phenocrysts of olivine±clinopyroxene±plagioclase; they are sometimes picritic. Chromian spinel is common both as euhedral inclusions in olivine and as microphenocrysts, and clinopyroxene is often titanaugite. Bulk rock chemistry indicates that intraplate alkali basalts are dominant in the Senhata basalt gravels. Relic chromian spinel chemistry also suggests that the alkali basalts and the picritic basalts are of intraplate magma origin. The close association of intraplate basalts with the Fudoiwa serpentinites may be compatible with the presence of Ti-rich wehrlitic cumulates and Ti-rich metasomatites in the Fudoiwa mass reported by Arai et al. (1990). In the Circum-Izu Massif Serpentine Belt, alkali basalts tend to be associated with small-scale serpentinite masses, and tholeiitic ones, with large-scale masses.

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