The morphological analysis of the Kiyotsukyo porphyritic intrusive body and its geological setting in the Yuzawa district,Niigata Prefecture : The geological setting of Tertiary granitic rocks in the Green Tuff region

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.本論では，越後湯沢地域に分布する「清津峡石英閃緑ひん岩体」の迸入形態の復元を行い，さらに谷川岳地域の石英閃緑岩体も含め，グリーンタフ変動における第三紀花崗岩類の活動様式について検討した．その大要は，以下のようにまとめられる．（1）清津峡岩体は，餅盤状の調和的（concordant）な岩体である．迸入形態の復元には，この岩体全域に発達している冷却柱状節理の性質を応用した．（2）清津峡岩体をはじめとする越後湯沢地域の層状火成岩は，中新世中期の最大沈降期に堆積盆地の縁辺部の細粒岩層（頁岩・細互層）中に，調和的（concordant）に迸入したものである．一方，谷川岳地域の大規模な石英閃緑岩類は，中新世末期にこの地域の初期火成活動の場が著しい隆起に転じた部位に，非調和的（discordant）に貫入したものである