中央アルプスとその西域の地質

The geological features of Japanese Central Alps, which correspond to the northeastern end of the Ryoke metamorphic zone, are outlined. 1) The Paleozoic rocks here, which belong to the later Paleozoic geosynclinal deposits of Japan, consist chiefly of sandstone, slate and chert. The most remarkable fact is that the upper part of the whole series frequently contains the conglomerate-looking facies in which elongated angular fragments are scattered in sandy matrix. For this occurrence should be invoked the frequent subaqueous sliding at the time of deposition. Moreover, the traces of the organism which are similar to Helminthoidea in the Alpine Flysch, are found frequently in the upper part of the slate lamina alternating with sandstone. From these facts, we can conclude that the depositional features are rather of the Flysch type. Judging from the existence of Yabeina limestone, the upper part of the whole series seems to be not older than the later stage of Middle Permian. 2) Essentially, there is no structural difference between the metamorphics and the nonmetamorphosed Paleozoic rocks and, also, is no remarkable zone of discontinuity or tectonic line which separates the both. 3) Metamorphic rocks are divided, progressively from NW to SE, into the zone of biotite slate, the zone of schistose hornfels and the zone of banded gneiss. The zone of biotite slate is widely developed, and makes a gradual transition to the non-metamorphosed Paleozoic rocks, lacking the chlorite zone or phyllitic zone between them. From these facts and the other petrological data, the metamorphism seems to be similar to the contact metamorphism and, possibly, to be achieved under the rather static condition v ith less stress due to tectonic deformation. The extension of metamorphism is, however, so regional that it defines the axial metamorphic zone of upper Paleozoic orogenic belt in the South-west Japan, 4) The granitic rocks occupy the wider part of the Ryoke zone than the metamorphics. They are grouped into four types, namely the Ichida granite, the Otagiri granite, the Inagawa granite and the Kisokoma granite. The Kisokoma granite, which has the discordant outline to the surrounding metamorphics, also occurs far west to the exterior of the Ryoke zone. While the others expose exclusively in the Ryoke zone and are rather conformable to the structure of the metamorphics. But the succession of the intrusion of the Kisokoma granite and the others cannot be concluded at present. Two facts of the nature of the granites are worth mentioning; the intrusion of the Otagiri granite is connected with the upheaval movement of the zone of banded gneiss, and both the Ichida and the Otaoiri granites seem to be produced through the granizatization process of meta-diabasic rocks.