東北地方脊梁山脈周縁(岩手・秋田・宮城縣境)に発達する石英安山岩類の層位学的問題について

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In Northern Honshu, Japan, dacite and its pyroclastics are extensively developed in the backbone ranges and their foothills in the area cited below (areas in Aomori, Yamagata and Fukushima Prefectures and in the southern half Miyagi Prefecture are excluded in this paper). 1. Fukuoka and Johoji area in Ninohe-gun, Iwate Prefecture. 2. Tayama area in Ninohe-guns Iwate Prefecture. 3. Hachimantai area in Iwate-gun, Iwate Prefecture. 4. Shizukuishi area in Iwate-gun, Iwate Prefecture. 5. Kuzumaru and Toyosawa area in Iwate-gun, Iwate Prefecture. 6. Hiraga basin in Hiraga-gun, Akitn Prefecture and Waga-gun, Iwate Prefecture. 7. Eastern foothills of Kurikoma volcano including Wakayanagi-mura and Koromogawa-mura, Isawa-gun, and Genbi-mura, Nishi-Iwai-gun, Iwate Prefecture. 8. Iwagasaki area in Kuribara-gun, Miyagi Prefecture. 9. Western foothills including Minate-mura and Sukawa :r ura in Okachi-gun, Akita Prefecture. 10. Onikobe area in Tamatsukuri-gun, Miyagi Prefecture. 11. Narugo area in Tamatsukuri-gun, Miyagi Prefecture. 12. Sendai and its environs, Miyagi Prefecture. The dacites and their tuffs and agglomerates from the aforementioned localities are stratigraphically conspicuous owing to their white or light colour and remarkable thickness. Although these rocks have been given different formational names in each areas since they are discontinuous from area to area in exposure by the interventions of exposures of other kinds of rocks, the writer's stratigraphical work shows that the dacites and their pyroclastics may be summarized as to be distributed stratigraphically in the following five horizons. The horizons are as follows in ascending order: 1. Hashiba, Hanayama, Mizuyama. Toyasaki Akakura and Yumoto formations. Remarkable dacite and its tuffs including welded turffs are associated with the Upper Miocene lake deposits. It is considered that these rocks are the records of the outbursts of a considerable amount of acidic volcanic rock in the greater parts of the backbone ranges and adjacent areas immediately after the severe crustal deformation in the Upper Miocene, which took place as an embryonic stage to the formation of the backbone ranges in Northern Honshu. 2. Umeda and Onoda formations and Hirosegawa tuff. Pumiceous tuffs and breccia are usually interbedded in the non-marine Umeda 'formation and its equivalent sediments, which are extensively developed in Miyagi and Yamagata Prefectures. They are younger than the Lower Pliocene Tatsunokuchifo rmation and older than the Kitakawa dacites statad below. 3. Gohenji, Shinmachi, Gyojataki, Kabutoiwa and Kitakawa Dacites. The dacites and their pyroclastics including welded tuffs of this horizon are most widely developed. among tht same kind of the rocks now dealed with in the backbone ranges in Northern Honshu and are supposed to represent the earliest phase of the activities of the younger volcanoes in these ranges which took places in latest Pliocene or earliest Pleistocene immediately after the youngest orogenic movement of Northern Honshu. 4. Fukuoka and Aobayama formations. The dacites and its pyroclastics including welded tuffs of the Fukuoka formation . which are the continuation of the same kinds of rocks of the Towada caldera grades laterally into the andesites of Inaniwadakz and Nishidake volcanoes as well as into the Sanbongi formation, which is nuconformably covered with the Upper Pleistocene high level terrace deposits and rest upon the Paleoloxodon namadicus aomoriensis bearing Noheji formation with slight unconformity. 5. Katanuma dacite from Narugo area. This rock covers unconformably the high level river terrace deposits and is referred to Recent.
地学団体研究会の論文
1956-07-10

東北地方脊梁山脈周縁(岩手・秋田・宮城縣境)に発達する石英安山岩類の層位学的問題について

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