イライト結晶度からみた長野県諏訪湖南方における三波川帯・秩父帯・四万十帯の弱変成作用

概要

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The illite crystallinity (Kubler index) was measured for the pelitic rocks from the Sanbagawa, Chichibu and Shimanto Belts in the south area of Lake Suwa, centralJapan. These belts are composed of the complexes formed through subduction- and accretion-related processes and they are characterized by the effects of high-pressure and low-temperature type metamorphism and deformation. Early Cretaceous Todai Formation is exposed in the narrow zone along the boundary faults between the Sanbagawa and Chichibu Belts. The illite crystallinity for the rocks from the Sanbagawa and Chichibu Belts corresponds to that of the higher part of the anchizone to lower part of the epizone, while that from the Todai Formation shows a range from the lower to the higher part of the anchizone. The burial metamorphism for the Sanbagawa, Chichibu Belt and the Todai Formation increases from the south to the north gradually. This fact indicates that the relatively deeper part of the complexes became exposed to the earth's surface in the northern part of the study area. It is inferred that the metamorphism recorded in the Todai Formation is correlated with the Sanbagawa metamorphism considering the depositional age of the formation.
信州大学の論文