イライトの結晶度からみた美濃帯泥質岩の弱変成作用  [in Japanese] Illite crystallinity and low-grade metamorphism of pelitic rocks in the Mino Terrane, central Japan  [in Japanese]

美濃帯および領家帯弱変成部の泥質岩のイライトの緑泥岩の結晶度を測定した。イライトの結晶度からみた変成度には, diagenetic zoneからanchizoneを経てepizoneまで, さまざまな程度のものが識別された。結晶度の分布からみると, 白亜紀の領家変成作用の熱の影響は, 従来考えられていたよりも広く内側にまで及んでいる。白亜紀末に貫入した花崗岩類による熱の影響によって, それまでに形成された温度構造は不鮮明になっている。さらに第四紀の断層による垂直運動によって, それ以前につくられた温度構造は大きく変形させられている。

The Mino Terrane, central Japan is characterized by a widely outcropping Jurassic subduction-accretion complex. Diagenetic and metamorphic grades of the Mino Terrane were estimated from measuring the crystallinity of illite and chloritese parated from pelitic rocks. The processes responsible for the thermal structure of the Mino Terrane are discussed in this paper. Although melanges in some cases display a slightly higher crystallinity compared with coherent units, distinct differences in depth of Jurassic subduction and deformation can not be found between both geologic units. Illite crystallinity clearly shows that low-grade metamorphism gradually increases southward with terrupted twice at Quaternary faults. It is demonstrated that a larger area of the Mino Terrane has undergone Cretaceous Ryoke metamorphism than had previously been proposed. The subduction complex of the Mino Terrane has been intruded by Late Cretaceous granitic rocks and as are sult has been extensively overprinted by a secondary thermal structure. Finally, the thermal structure has been highly modified by large vertical movements along Quaternary faults.