[1] The Ryoke metamorphic complex exposed along the western coast of the Nishiura Peninsula is composed mainly of geneissose quartzdiorite, aplitic gneiss, paragneiss and amphibolites. The regional metamorphic rocks and the gneissose quartzdiorite have a general trend of NEE-SWW. [2] The amphibolites in the gneissose quartz-diorite are grouped into three types according to their mode of occurrences: (1) metamorphosed dykes, (2) aggregate of small lenses which are elongated parallel to the gneissose structure of the gneissose quartzdiorite, and (3) agmatite. Among the metamorphosed dykes, the largest dyke is more than fortyfive metres in length and is 1.8 metres in width. This dyke elongates in NW-SE direction sharply discordant to the general trend of the surrounding gneissose quatzdiorite. However, the gneissosity of the amphibolite forming this dyke is parallel or subparallel to the general trend of the surrounding gneissose quartz-diorite. This dyke is fairly heterogeneous megascopically and the following five types of the amphibolites are distinguished: (a) fine-grained schistose biotite amphibolite (25 % in volume), (b) fine-grained biotite amphibolite (3% in volume), (c) fine- or medium-grained melanocratic amphibolite (trace in volume), (d) medium-grained biotite amphibolite (58% in volume), and (e) medium- or coarse-grained porphyritic biotite amphibolite (13% in volume). On the contrary, the other metamorphosed dykes having widths less than one metre, elongate concordantly to the general trend of the surrounding gneissose quartzdiorite and show a more granitized appearance. Judging from the petrochemistry and petrography of the above amphibolites, some amphibolites forming the largest discordant metamorphosed dyke remain intact from metasomatism during the plutono-metamorphic process : and the amphibolites forming the other small concordant metamorphosed dykes were strongly influenced by the metasomatism, while some amphibolites of the largest dyke and the agmatitic and lens-shaped amphibolites received the influence of the metasomatism in some degree. In the process of metasomatism, the amphibolites became richer in Na, K and Al contents and poorer in Mg, Fe and Ca contents. The original rock of the amphibolites is considered to be tholeiitic dolerite. [3] The geological history of plutono-metamorphism of the Ryoke metamorphic belt in this area can be summarized as the followings: (1) The Ryoke metamorphic belt is plurifacial and its metamorphism can be divided into two stages. The first stage is characterized by conditions having lower to moderate temperatures and intermediate pressure producing staurolite, pyralspite garnet and others. The rock produced by the first stage metamorphism occurs in the Hazu area, situated in the western neighbourhood of the Nishiura area. The second stage is characterized by conditions having moderate to higher temperatures and lower pressure producing sillimanite, andalusite, cordierite, pyralspite garnet and others. The rock produced by the second stage metamorphism occurs in this area. (2) Following the second stage of the Ryoke metamorphism, the gneissose quartzdiorite intruded concordantly with the surrounding Ryoke metamorphic rocks. The igneous activity of this gneissose quartzdiorite is considered to have continued for a considerable duration. In the earlier stage of the igneous activity, the gneissose quartzdiorite was intruded by some basaltic dykes, which appear as concordant metamorphosed dykes, agmatitic and lens-shaped amphibolites at present. It may also be possible that the basaltic dykes, from which agmatitic and lens-shaped amphibolites were produced, were developed before the intrusion of the gneissose quartzdiorite. In the intermediate or later stage of the igneous activity, the gneissose quartzdiorite was intruded by the tholeiitic dolerite dyke, which appears as the largest discordant metamorphosed dyke at

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