MemGeolSocJapan_33_177.pdf 1.1 MB
Nappe structure of the Asaji metamorphic rocks, with special reference to geological structure of the basement complexes in Kyushu
The Asaji metamorphic rocks in the Notsuharu area, Oita Prefecture are composed mainly of pelitic rock, psammitic rock, chert, basic rock and serpentinite. Thelast forms serpentinite melange zone, including many blocks of metamorphic rocks, and shows an overturned fold of SE vergence with the NE plunging fold axis and NNW dipping axial plane. The metamorphic rocks are divided into two groups, separated from each other by the melange zone. One occupies the horizon below the melange zone and the other above.
Carbonaceous materials from 32 pelitic rock samples were examined by TAGIRI'S (1981) X-ray diffraction method in order to compare their metamorphic grade. The results show the distinct discontinuity of metamorphic grade between two groups of both sides of the melange zone. It is concluded that the sequence above the melange zone is a nappe (Hikata nappe), and the SE vergenced overturned fold has been formed during the formation of the nappe structure.
The Asaji metamorphic rocks are considered to be long to the Ryoke metamorphic rocks. In Kyushu, apparent continuity of the Sambagawa belt terminate at the Saga-noseki Peninsula just to the east of the Notsuharu area. It appears from the above that the nappe of the Ryoke metamophic rocks such as the Hikata nappe overlies the Sambagawa belt in Kyushu. Incidentally, the Nagasaki metamophic rocks would blong to the Sambagawa metamorphic rocks.
Copyright (c) 1989 日本地質学会