四国西部の中央構造線についての新事実
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概要
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A new fault, herein named the Kaminada fault, has recently been discovered near Kaminada, Futaumi-cho, Iyo-gun, Ehime Prefecture in Western Shikoku, Japan. The fault lies within the zone of the Median dislocation line, and where seen in outcrop, shows rocks of the Sanbagawa metamorphic complex thrust northward over rocks of the Upper Cretaceous Izumi group. From this relationship the presumption is made that the primary tectonic movement of the Median dislocation line of Southwest Japan in Shikoku took place after the deposition of the Upper Cretaceous Izumi group and before the deposition of the Eocene Kuma group.<BR>Those metamorphic rocks which make up the resulting klippen have been named the Futaumi Formation of the Sanbagawa metamorphic complex and are considered to be of Paleozoic age.<BR>A second new fault, herein designated as the Konokawa fault, extends along the northern foot of Mt. Myojin from Koami to Karakawa where it joins the fault of the Tobe phase of the Median dislocation line of Southwest Japan. This fault shows rocks of the Izumi group to be thrust southward to overlie those of the Futaumi formation.<BR>The westernmost portion of the fault of the Tobe phase which extends from Karakawa via Inuyose to Kaminada is herein designated as the Inuyose fault.<BR>Since the area under discussion here is located at the easternmost apex of the so-called Nagasaki triangle of Kyushu, and since there has been much discussion as to whether or not the rocks of the Nagasaki triangle should belong to the Inner zone or the Outer zone of Southwest Japan, it is very interesting to note that within the area lying between the Konokawa and Inuyose faults, one can see outcrops of both the Izumi group, which belongs to the Inner zone, and the Sanbagawa metamorphics, which belong to the Outer zone.