山口県三郡帯東部における結晶片岩系と非変成古生代層群との関係

The Relation between the Crystalline Schist Formations and the Non-Metamorphic Paleozoic Formations in the Eastern Part of the Sangun Zone in Yamaguchi Prefecture.

岡村 義彦

廣島大學地學研究報告

Geological report of the Hiroshima University

The district is zonally occupied by the Paleozoic formations (The Ôda formation), the Sangun metamorphic rocks and the Paleozoic formations (The Kuga formation) from the north to the south. While general geological and structural relations of the district are described, the sheared rocks of the Paleozoic formations are especially discussed.
The Paleozoic formations (The Ôda formation) and the Sangun metamorphic zone are bounded by the Kitayama over-thrust named by G. Kojima. Between the Sangun metamorphic zone and the Kuga formation, which is the original rock of the Ryôke metamorphics, a sheared zone is developed. The sheared zone is mainly composed of shear-slate and pelitic semi-schist, in which torn blocks of sandstone, chert and limestone are included, and arranged parallel to the shear plane. In limestone lenses in the shear zone belonging to the Kuga formation Parafusulina and Neoschwagerina were obtained, that showing the age of the Middle to Upper Permian of the formation.
Structural geometry of the Sangun metamorphic rocks and the Kuga formation in the district is investigated according to the statistical analysis of orientation of structural elements such as foliation and lineation. The Kuga formation is structurally continuous and parallel to the sheared zone, viewed from the orientation of structural elements, and the sheared zone is subparallel to the Sangun metamorphic zone.
It is difficult to establish the stratigraphical succession of the schist formations and the Paleozoic formations owing to many faults. The western end of the Kuga formation and the sheared zone are cut off by the Suetakegawa tectonic line which is a normal fault trending N-S. And the Suetakegawa tectonic line is cut by the strike fault trending E-W. In the district the normal faults are developed in the. NE-SW direction. The geological structure of the eastern area is characterized by monoclinic and locally isoclinal folding. The Ôda formation, which corresponds to the upper formation of the Sangun group, may be correlated to the Kuga formation.

日本語

廣島大學理學部地學教室

[ISSN] 0073-2303

[NCID] AN00213676