徳島県美馬郡内の"中央構造線"

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In this paper, the writers dealt with the "Median Tectonic Line" which separates the Upper Cretaceous Izumi group in the north from the Sambagawa crystalline schist in the south along the southern foot of the central Sanuki mountain-range, and recognized that it had moved at least twice. The "Median Tectonic Line" in this district can also be divided into two phases, pre-Shobudani and Late Pleistocene Shobudani. The former is observed in the eastern part of the district, and its plane is N 80゜-N 85゜ E and N 70゜. On the other hand, the latter is represented by a thrust fault in various places of the district where the Izumi group or the crystalline schist is thrust over the Pleistocene gravel formation with a distinct fault plane having N 60゜-80゜ E strike and N 20゜-35゜ dip. Both are nearly parallel to each other in direction, but sometimes the latter cuts off the former. It is interesting to see that two kinds of the thrust faults are almost parallel to the "Median Tectonic Line" at the Shobudani phase in some places where the Izumi group also thrusts up on the gravel bed. These faults were formed in the same time or the later stage of the Shobudani phase. The Pleistocene river terrace gravel formation is divided into two members, the lower gravel bed and the upper gravel bed. The former is characterized by the presence of well sorted pebbles derived from the Sambagawa crystalline schist region, but such kinds of pebbles are entirely lacking in the latter. It seems that this phenomenon was influenced by the movement of the "Median Tectonic Line" during the Shobudani phase. It is important fact that in the eastern part of the district the both gravel formations contain well-sorted granite pebbles derived from the granite region in the north. From this point, it is deemed that the Soedani-river running south ward in the eastern part of the district may have been an antecedent river across the Sanuki range since the time when the river terrace gravel bed was deposited.
地理科学学会の論文
1969-05-20

徳島県美馬郡内の"中央構造線"

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