In this paper the writer described the Cainozoic history of the Southern Kanto Region, where the younger Tertiary and Quaternary marine sediments are extensive and nearly complete. Further, he tried to deduce some generalizations concerning the structural development, the sedimentation and the igneous activities. and discussed the relations between them.

抄録全体を表示

From a viewpoint of the reciprocal relation between metamorphic aureole and its related granite, some problems on metamorphic differentiation and metasomatism were discussed in the present paper. 1. Through investigation of the AKF-relation of the metamorphic rocks to the related granites in some districts, it was found that there would have been two distinct trends of metamorphic differentiation which the author called "graniteward metamorphic differentiatian" and "anti-graniteward metamorphic differentiation" respectively. In the former the AKF-ratios of metamorphic rocks approach toward those of granites, whereas in the latter vice versa. 2. In a broader sense, the graniteward metamorphic differentiation in question belongs to the socalled "granitization". Neverthless it is of notice that fhe mineral assemblage of the finally differentiated product in any aureole may be largely controlled by the petrochemical nature of the related granite. In this respect, it is significant that most granites occurring in metamorphic terranes may be classified into the following two types according to K20/Na20 ratios: high-potassic type and low-potassic type. Consequently, in Dando- or Wantabadgery aureole related with granitic rocks of high-potassic granodioritegranite series the final products of graniteward metamorphic differentiation always fall within the muscovite-biotite-K-feldspar field. On the other hand, in those aureoles where the related granitic rocks are of quartz-diorite-trondhjemite-soda granite series of lowpotassic type such as Senmaya , Tono and Orijarvi, the assemblage, anthophyllite-cordierite, occurs at the final stage of metamorphic differentiation without exception. Thus, notwithstanding whether the external appearance takes igneous-looking or not, it seems reasonable to call the above two differentiation processes "granitization" and "trondhjemitization" respectively. 3. Besides internal migration of ions through metamorphic differentiation, it appears, the reciprocal exchange of another set of ions took place between granite and aureole. In Dando, as illustrated in the AKFdiagram of Fig.', it is reasonable to assume that a certain amount of potash was introduced into the aureole, probably from the magmatic source. According to the theory of metasomatic exchange, however, the introduction of some materials requires in return the rejection of other ions which travel toward the granite to make up for the loss. (BARTU 1952, 11362) , In this respect, the mutually compensative behavior of K and Na in the aureole is very interesting. The figure may possibly show that considerable Na-ions rejected from the outer and transitional aureoles moved toward the contact and concentrated in the zone of banded gneiss as well as. in those minor intrusives as aplitic granites and oligoclaseaplites in which K2O/Na2O ratios are usually somewhat lower than those of the major intrusives. The Kenrichment at the contact of the lowpotassic granites, to the contrary, is scarcely observed except in those aureoles of the Hikami type granites such as Hikami, Yamagami and Funazu. In Tono, though there is a remarkable decrease of potash especially in the outer aureole, it seems that the loss was compensated not with soda but with another components as SiO2 and H2O, because the introduction of soda into the aureole was exceptionally insignificant, and that only a small portion of rejected K-ions moved toward the contact.

抄録全体を表示