抄録
A thick quartz dolerite dyke (belong to calc-alkali rock series or hypersthenic rock series) of late Miocene age has been found in Kabeshima island, Saga Prefecture. The dyke is intruded into the sandstone of the Miocene and is covered by trachybasalts of Pleistocene. After the intrusion, quartz dolerite magma fractionated small segregation veins of granophyric composition by crystallization differentiation in situ. The chemical composition of the granophyre is similar to those of granitic rocks.
It is considered that the quartz dolerite magma is produced by crystallization differentiation associating with contamination of granitic rocks of a tholeiite magma. A trend of the differentiation of tholeiite-quartz dolerite-granophyre is proceeded toward alkalies, without iron enrichment in the middle stage. This trend accorded with that of basalt-andesite-dacite-rhyolite of the hypersthenic rock series of the Izu-Hakone district.
