On the Kitaôshima Granite Gneiss Complex

In the Yanai-Yashirojima (Oshima) district, Yamaguchi Pref., in the Ryôke metamorphic belt, a composite mass consisting of granite gneiss (orthogneiss) and basic gneiss occurs surrounded by the layered syntectic granodiorite. Various features, especially such as agmatitic behaviour in granitization, the presence of metamorphic dyke and granitized "fault", strongly suggest that the granite gneiss complex had been brought up to the tectonic level of brittle fracturing in the state of gneiss before the metamorphism and granitization of the Ryôke age began. It is suggested that the Kitaôshima granite gneiss complex would represent a fragment of the basement under the Upper Palaeozoic geosyncline in the innerside of Southwest Japan. Furthermore, the possibility of pre-Permian land between the innerside and the outerside of South-west Japan is suggested.