著者

久保田 喜裕

出版者

日本地質学会

雑誌

地質学雜誌 = 地質学雜誌 (ISSN:00167630)

巻号頁・発行日

vol.94, no.8, pp.567-582, 1988-08

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In the Green Tuff region, holocrystalline-hypabyssal rocks which have been called “Tertiary granitoids” occur often. Many of these bodies are volcano-plutonic complex composed of plutonic, hypabyssal, and volcanic rocks with felsic to intermediate composition. The porphyritic intrusive bodies in the Yuzawa district and quartz-dioritic bodies in the Tanigawa district are one of the best examples of this kind, and thus they were studied. The Kiyotsukyo intrusive body in the Yuzawa district is concordant to the surrounding strata, thus forming a laccolith. This body is well jointed. The jointing system is interpreted as the cooling-columnar joint. Analysis of the system was useful for reconstructing the shape of the intrusive body (cf. Fig. 13). The Kiyotsukyo intrusive body and the other porphyritic and andesitic bodies in the Yuzawa district intruded concordantly to the fine-grained, marginal facies of sedimentary basin at the maximum subsidence stage of the Green-tuff disturbance. On the other hand, the large quartz-diorite body in the Tanigawa district is discordantly intrusive into the uplift area where the initial volcanism of the Green Tuff activity took place at the end of the Geen-tuff disturbance.