5:15 PM - 7:15 PM
[SVC33-P03] Petrological characteristics of Tsumakoi-touge lava, Kampu volcano
Tsumakoi-touge lava, Kampu volcano is a blocky basaltic lava flow formed by a small composite volcano located in the eastern part of the Oga Peninsula, which belongs to the Northeastern Japan Arc. Although the eruptive products of Kampu volcano are predominantly andesitic, in some cases the eruption of basaltic lava marked the termination of volcanic activity. Moreover, scattered gray andesitic blocks have been observed on top of the basaltic lava; however, their petrological characteristics have not been adequately elucidated to date.
In this study, we performed a detailed investigation of the whole-rock compositions and mineralogical textures of the andesitic rock fragments scattered atop the Tsumakoi-touge lava, aiming to clarify their characteristics through a comparison with the basalt. The whole-rock chemistry of both rock types plot along the same linear trend. In the basalt, olivine and clinopyroxene exhibit either normal or reverse zoning, and plagioclase occurs in two forms—one showing sieve-textured cores associated with normal zoning, and another lacking such textures. In contrast, the basaltic andesite contains common hornblende, which was not observed in the basalt; its olivine exhibits normal zoning, clinopyroxene displays either reverse or oscillatory zoning, and orthopyroxene shows reverse zoning. Furthermore, in the andesite, common hornblende is confirmed; olivine shows both normal and reverse zoning; clinopyroxene is present in two varieties—one with a homogeneous composition lacking zoning and another exhibiting normal zoning; and plagioclase displays a variety of textures, including normal, reverse (with or without sieve-textured mantles), and oscillatory zoning.
In this study, we performed a detailed investigation of the whole-rock compositions and mineralogical textures of the andesitic rock fragments scattered atop the Tsumakoi-touge lava, aiming to clarify their characteristics through a comparison with the basalt. The whole-rock chemistry of both rock types plot along the same linear trend. In the basalt, olivine and clinopyroxene exhibit either normal or reverse zoning, and plagioclase occurs in two forms—one showing sieve-textured cores associated with normal zoning, and another lacking such textures. In contrast, the basaltic andesite contains common hornblende, which was not observed in the basalt; its olivine exhibits normal zoning, clinopyroxene displays either reverse or oscillatory zoning, and orthopyroxene shows reverse zoning. Furthermore, in the andesite, common hornblende is confirmed; olivine shows both normal and reverse zoning; clinopyroxene is present in two varieties—one with a homogeneous composition lacking zoning and another exhibiting normal zoning; and plagioclase displays a variety of textures, including normal, reverse (with or without sieve-textured mantles), and oscillatory zoning.