三郡帯のダナイト―ハルツバージャイト―クロミタイト複合岩体の記載岩石学的特徴

概要

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There are many ultramafic complexes in the Sangun zone in central Chugoku district, Southwest Japan: they are Shiratakiyama, Tari-Misaka, Inazumiyama, Mochimaru, Yagami, Kasamatsu, Takase, Mimuro, Ashidachi, Yufune, Yanomine, Suishoyama, Niimi, Osa, Tajibe, Fuse, Taguchi, Harashige, and Ochiai-Hokubo. Lithological variations in these complexes were determined for both primary and thermal metamorphic mineral assemblages. With one exception (the Ochiai-Hokubo complex) they consist of harzburgite, dunite and chromitite, and are intruded by some gabbroic dikes. Harzburgite is always dominant over dunite. Chromitite is closely associated with dunite: a chromitite body is enclosed by a dunite envelope and large chromitite bodies are exclusively found in relatively dunite-dominant complexes. The lithological features indicate their derivation from the transition zone or the uppermost mantle member of ophiolitic suites. The complexes are frequently suffered from the thermal metamorphism by some younger granitic masses. The contact aureole is divided into five mineral zones, Ia (chrysotile/lizardite), Ib (antigorite), II (olivine-talc), III (olivine-anthophyllite) and IV (olivine-orthopyroxene) in order of increasing metamorphic grade. The highest metamorphic grade attained is different dependent on the distance from and rock facies (temperature) of granitic magmas.
日本鉱物科学会の論文