北上山地遠野接触変成帯における変成度-風化過程-組織地形の関係

抄録

The metamorphic rocks in the contact metamorphic aureole around the Cretaceous Tono Granodiorite, Central Kitakami Mountain land are originated from the Late Paleozoic formation composed chiefly of black shales and fossiliferous limestones.
The contact metamorphic aureole is divided into the four progressive mineral zones based on the mineral assemblages of the pelitic rocks. The texture of the rocks gradually changes from the slates (very-low grade metapelites) to the hornfelse (high grade metapelites).
The textures of metapelite are closely related to the types of the weathering process and physical characteristics of the rocks. For example, the area where composed of slates have thick type weathered zones, while the area where composed of hornfelse have thin weathered layer caused of different weathering prosses.
The studied area is recognized as an elevated peneplane. The flat top of the mountain seems to be a peneplane and various erosional forms are observed.
The remarkable difference of the topography is observed between low and high grade metapelites. For example, the V-shaped valley dominantly develop in the area of low grade metapelites, whereas the flat-flood valley develop in the area of high grade metapelites.
The origin of these rocks is same, and the historical development of landformes and the climate are not different from each area. Therefore the difference in topography is considered to be a structural relief developed under the affection of the contact metamorphic grade.
The structural relief in studied area is systematically explained as expression of the gradual change in texture of the rocks.