関東山地北西部の第三系(その1) : 長野県東部香坂川〜内山川流域,特に駒込帯の地質とその地質学的意義について

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The area studied is at the northwestern corner of the Kanto Mountainland. It is underlain mainly by various kinds of both clastic and volcanic sediments, ranging in age from the early Miocene to the early Pleistocene. The area is divided into three parts by two parallel faults running from west to east. The one the south is the Uchiyama Fault (Watanabe, 1954), and that to the north is the Yaekubo Fault (Takano, 1986). The area between the two faults, about 2km wide is named the Komagome Belt (Kosaka et al., 1988). The formation in this area are as follows. Otsuki Formation. This is the basements of the Tertiary in this area. Uchiyama Formation. It is composed mainly of tuffaceous sandstones. Ill sorted conglomerates occur at the base of this formation. Planctonic foraminifers from this formation shows the lower Miocene age. Komagome Formation. It is confined to the Komagome Belt, and is composed of pale greenish tuffaceous sandstones. Yaekubo Formation. This formation is composed of pumiceous coarse sandstones and dark glassy andesitic lava flows. K-Ar ages indicate them to be middle Miocene in age. Kousaka Formation. It consists mainly of greenish altered andestic lava flows and some pyloclastics. Plant fossils suggest the late Miocene age. Kousaka Conglomerate Member. This member is made up mainly of ill-sorted conglomerates. Plant fossils indicate this member the Pliocene in age. Hirao Volcanics Member. This member is characterised by the andesitic volcanic rocks. K-Ar age of 3.4Ma is reported. Shiga Welded Tuff Member. This member is developed extensively not only in this area but also in the surrounding area. A K-Ar age of 3.2±0.2Ma is reported. Mizuochikannon Lava Member. This member is found as several patches on tops of the mountains and ridges. The rocks are basaltic or variable from place to place. Significance in this area is the Komagome Belt. It is a nallow belt, running from west to east and about 2km wide, composed exclusively of the Komagome Formation. While the formations on both the northern and southern sides of this belt are rather flat in their attitude, the formation in this belt i.e. the Komagome Formation shows quite different attitude. The beds of this are steeply inclined,and run from NW to SE, namely obliquely to the general strike of the belt. To the east of this area, there are Shimonita Tectonic Belt (Arai et al., 1966) of the Shimonita area and the Namekawa Belt (Takei and Koike, 1981) of the Yorii area, which represent the northern and northeastern margin of the Kanto Mountainland. The Komagome Belt of the present-area is just on the western extension of the Shimonita Tectonic Belt and the Namekawa Belt. So the author proposed the new name for these three belts in this article 「The Northern Marginal Tectonic Belt of the Kanto Mountainland」.
地学団体研究会の論文
1991-05-25

関東山地北西部の第三系(その1) : 長野県東部香坂川〜内山川流域,特に駒込帯の地質とその地質学的意義について

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