岩石鉱物鉱床学会誌

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標題の接触変成帯は,泥質岩中の変成鉱物の組合せにもとづいて,黒雲母帯ときんせい石帯とに2分される。きんせい石帯はさらに2つの帯に分けられ,緑泥石と白雲母との共生関係が認められるものをきんせい石1帯,認められない場合をきんせい石II帯とよぶ。きんせい石II帯の高変成度部には,ざくろ石が頻繁にみとめられる地域が広く分布し,これを「ざくろ石帯」とした。ざくろ石の出現は,母岩の総化学組成の違いに影響されており,この「帯」は等化学的な変成分帯による帯ではない。
以上4つの帯の変成鉱物の化学的変化,共生関係の変化を調べ,各帯を分ける変成反応を提案した。
従来言われていた「ざくろ石+カリ長石帯」は,本地域では在存しない。
Arakawa 荒川
Fukazawa 深沢
Gorozawa ゴーロ沢
Kurokawa 黒川
Norogawa 野呂川
Takane 高嶺
Yakejizo 焼地蔵

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The hornfelsic, gneissic and granodioritic rocks exposed below the Miocene the Miocene deposits in the southern part of Yamagata Prefecture have been studied by the author in field and laboratory. Eleven rock specimens, purposely selected by him were placed in K-Ar dating by the courtesy of Prof. Y. Ueda. The result will be briefly given below.
There are two groups in respect to K-Ar ages. Namely, four rock specimens of them (Nos. 1, 2, 3, and 11 in Table 1) show the Middle to the Late Cretaceous in age, and one specimen shows Early Palaeogene. Other six specimens including granodioritic and hornfelsic rocks are dated as young as the Miocene, llthough they are unconformalbly covered by the lower Miocene deposits in field. The younger ages of the same samples may suggest that the originally older rock complexes may have been rejuvenated by igneous activith during Miocene time, although presence of corresponding younger igneous rocks has been not yet evidently proved.

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