香川県天霧山産安山岩中のグラニュライト捕獲岩

概要

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Xenoliths of metamorphic rocks and norites have been found in the Cenozoic andesites from Amagiri-yama, which are directly underlain with the granites in the Ryoke metamorphic belt of western Kagawa Prefecture. A petrographical study was made mainly on the xenoliths of metamorphic rocks. The metamorphic rocks, sometimes with banded structure, are characterized by such mineral assemblages as two-pyroxene-plagioclase (±quartz), orthopyoxene-garnet-plagioclase (±quartz) and orthopyroxene-sillimanite-spinel-plagioclase, while the norites are grouped into two types, i.e. micro-norite and spinel-clinopyroxene norite. Petrographical and mineral ogical data and mineral-paragenetic consideration indicate that these metamorphic rocks, possibly of intermediate igneous rocks in origin, were formed under granulite facies conditions. These granulites, which distinctly differ in metamorphic grade from the Ryoke metamorphic rocks of low pressure type, were probably derived from the basement rocks which were laid beneath the granitic plutons in the Ryoke belt of the Setouchi province. The norites were also probably associated with the basement rocks. The occurrence of such granulite xenoliths as found at Amagiri-yama and in other areas of the Setouchi province may suggest an areal underground extention of the granulitic basement rocks over the Setouchi and the Chugoku provinces.
日本地質学会の論文