日本の古生代花崗岩類の岩石化学的性質とその対比(古領家帯と黒瀬川帯の構成要素と改変過程)  [in Japanese] Petrochemistry and correlation of Paleozoic granitic rocks in Japan(Geotectonic evolution of the Paleo-Ryoke and Kurosegawa Terranes)  [in Japanese]

日本列島の古生代花崗岩類の全岩化学分析を実施した.オルドビス紀-石炭紀花崗岩類のうち南部北上帯氷上花崗岩類と黒瀬川帯の花崗岩類は高K_2O/Na_2O, 高Rb/Baをもち, 日本の平均的花崗岩に近い性質を示す.それに対し, 長門構造帯の台花崗岩類は低K_2O/Na_2OをもつMタイプ花崗岩の特徴をもつ.黒瀬川帯の花崗岩類を全岩組成から台花崗岩に, また年代値から舞鶴花崗岩に対比することはできない.古領家帯のペルム紀花崗岩類および薄衣花崗岩礫は低K_2O/Na_2O, 低Rb/Ba, 低SrIをもち, Mタイプ花崗岩あるいは丹沢-新島トレンドの性質をもつ.薄衣花崗岩礫はペルム紀の年代も報告されている氷上花崗岩類とは全岩化学組成が異なり, 氷上花崗岩類がその供給源とはなり得ない.南部北上帯や黒瀬川帯のペルム紀薄衣花崗岩礫の供給源は, 古領家帯のペルム紀火成活動場と一致する未成熟な海洋性島弧もしくはそれを含む大陸であった可能性が高い.

Whole rock chemical compositions were determined for Paleozoic granitic rocks in Japan. Ordovician-Carboniferous granitic rocks (Hikami Granitic Rocks in the South Kitakami Belt, granitic rocks in the Kurosegawa Belt) are characterized by relatively high K_2O/Na_2O ratio and high Rb/Ba ratio, and their petrochemical characteristics in KCN diagram are similar to the average Japanese granites. The petrochemical similarity between Hikami Granitic Rocks and the granitic rocks in the Kurosegawa Belt is consistent with the correlation between the South Kitakami and Kurosegawa Belts.On the contrary, Dai Granitic Rocks (Ordovician-Devonian) in the Nagato Tectonic Zone show low K_2O/Na_2O ratio characteristic of M-type granitic rocks. Maizuru Granite from the Maizuru Belt is petrochemicaly similar to the Hikami Granitic Rocks or the granitic rocks from the Kurosegawa Belt, however the radiometric ages are different. Accordingly, the granitic rocks of the Kurosegawa Belt are not correlative to the Inner Zone Paleozoic granitic rocks such as Dai and Maizuru granites.Paleo-Ryoke Permian granitic rocks (Kinshozan Quartzdiorite, Hyokoshi Granite, Usukigawa Quartzdiorite) and Permian granitic clasts from the Usuginu-type conglomerate are characterized by low K_2O/Na_2O ratio, low Rb/Ba ratio and low SrI typical of the M-type granitic rocks or of the Tanzawa-Niijima trend. These results support the correlation between the Paleo-Ryoke Permian granitic rocks and the provenance of granitic clasts in the Usuginu-type conglomerate in the South Kitakami and Kurosegawa Belts. The granitic clasts from the Usuginu-type conglomerate cannot be considered to have derived from the Hikami Granitic Rocks because of the difference of petrochemical characteristics.In Permian age, the granitic rocks were generated at deeper depth of an immature volcanic arc which subsequently provided Usuginu-type granitic clasts into the already amalgamated more mature arc or continental margin, the precursor of the South Kitakami and Kurosegawa Belts where Ordovician-Carboniferous granitic rocks had already existed.