砂質岩・泥質岩の化学組成からみた四国中央-東部における三波川帯(緑泥石帯)とジュラ-白亜紀付加体(秩父累帯南帯-四万十帯北帯)との関連  [in Japanese] Geochemical relationships between psammitic-pelitic rocks from the Sanbagawa Belt (chlorite zone) and Jurassic-Cretaceous accretionary complexes (Southern Chichibu-Northern Shimanto Belts), central-eastern Shikoku, Japan  [in Japanese]

四国中央部の三波川帯(別子・大歩危ユニット)中の砂質・泥質片岩の化学組成を検討し, 秩父累帯南部〜四万十帯北帯の岩石相ユニットと比較した.大歩危ユニットと祖谷-井内谷地域・汗見-立川地域北部の別子ユニットの片岩は四万十帯北帯のKS IIユニットに, 汗見-立川地域南部の別子ユニットの片岩は四万十帯北帯のKS I(KS I c)ユニットに化学組成が類似する.すなわち, 前者の原岩が堆積した年代はコニアシアン〜カンパニアン, 後者のそれはアルビアン〜コニアシアン前期と推定される.さらに, 大歩危ユニットは, 岩相的特徴からKS IIユニット中の日和佐累層に対比される可能性が高い.別子ユニットの原岩の岩相は, 化学組成が類似するKS I c・KS IIユニットよりも泥質岩に富む.この岩相的相違は, 別子ユニットの原岩堆積場がKS I c・KS IIユニットの堆積場(海溝扇状地)よりもさらに沖合であったことを示唆している.

A geochemical study of psammitic and pelitic schists from the Besshi and Oboke units belonging to the chlorite zone in the Sanbagawa Metamorphic Belt, central Shikoku, has been performed for the purpose of correlation of the metamorphic belt with the non-metamorphic accretionary complexes (Southern Chichibu and Northern Shimanto Belts) in eastern Shikoku. Geochemical signatures of psammitic schists in the Besshi and Oboke units are different from those of sandstones in the Southern Chichibu Belt. Psammitic schists in the Besshi unit of Iya-Inouchidani area and the Oboke unit have a chemical affinity to the sandstones in KS II unit of the Northern Shimanto Belt. The Besshi unit of Asemi-Tachikawa area can be divided on the basis of chemical features into northern and southern parts of which psammitic and pelitic schists are chemically similar to KS II and KS I (KS I c) units in the Northern Shimanto Belt, respectively.On the basis of these geochemical data, the depositional ages of protoliths of the Sanbagawa psammitic and pelitic schists are inferred to be the Albian-Early Coniacian as to the Besshi unit of the southern part of Asemi-Tachikawa area, and the Coniacian-Campanian as to the Besshi unit of the Iya-Inouchidani area and northern part of the Asemi-Tachikawa area and the Oboke unit. These conclusions are consistent with radiometric ages of the schists.Sedimentary facies of protoliths of the Oboke unit indicate that the unit is correlative with the Hiwasa Formation (Campanian) in KS II unit. Protoliths of the Besshi unit are composed mainly of muddy facies, although KS I c and KS II units which are equivalent to Besshi unit, are mainly made up of sandy facies. The lithologic contrast between KS I c/KS II and Besshi units may be explained as the difference in sedimentary environments between deep-sea (trench) fan and more distal setting.