| 概要 |
Basic and ultrabasic inclusions are found in the post-Miocene alkali olivine basalts of the southwestern Japan. A sharp boundary of the most inclusions with basaltic host rocks and translation lamella...e of some constituent minerals suggest that the inclusions were captured in the solid state by basaltic magmas. The main constituent minerals of the inclusions are olivine, orthopyroxene, clinopyroxene, chromite-spinel and plagioclase. All of them are separated from the host rocks and investigated through chemical and X-ray analyses. New chemical data of nine spinels, ten olivines, twenty-five clinopyroxenes, ten orthopyroxenes and five plagioclases are given. Bulk chemical composition of basaltic and limburgitic host rocks and also chemical composition of five inclusions are presented. On the grounds of the mode of occurrence, petrological and chemical characters of constituent minerals, as well as geotectonic considerations, the basic and ultrabasic inclusions from southwestern Japan can be divided into two groups on account of the assemblage of silicate and oxide minerals as follows: (1) The green type inclusions, i.e. the group of dunite, Cr-diopside peridotite, Cr-pyroxenite and anorthite-bearing Cr-pyroxenite. (2) The black type inclusions, i.e. the group of Al-pyroxenite, olivine gabbro and olivine-free gabbro. The green type inclusions are probably derived from the upper mantle materials brought up with basaltic magma, whereas the black type inclusions are formed on one hand by the reaction of the green type inclusions with the enclosing basaltic magma, and on the other hand, a part of them is formed by settling of early formed crystals in the basaltic magma. The zonal distribution of the basic and ultrabasic inclusions and acid xenolithes in the post Miocene basaltic rocks is discussed briefly on the basis of geotectonic model of the Japanese Islands.続きを見る
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Mendeley出力
20_01_p085