Dike rocks in the Cretaceous Hiroshima granite in Western Chugoku

Abstract

Several types of dike rock can be found in the Hiroshima granite as follows: dolerite, pyroxene-porphyrite and hornblende-porphyrite, lamprophyre, hornblende-quartz-porphyrite, hornblende-biotite-granite-porphyry, biotite-granite-porphyry, fluidal micro-aplitic rock, coarse-grained quartz-porphyry, granophyre, felsite and felsitic quartz-porphry, plagiophyre, and pitchstone. In the broadly-distributed normal Hiroshima granite these dike rocks have sharp contacts . In the Yashiro granite which is a coarse-grained biotite-granite bearing porphyritic potash-feldspars, the dikes of spessartite and granite-porphyry are often invaded by aplite and quartz veins, and slightly granitized. The genetical history of the Yashiro granite is divided into the stage of magmatic intrusion of main body and later metasomatic replacement. The above-mentioned dikes must have intruded in the later metasomatic stage. The origin of these dikes are quitely unknown, but their original magma would be unrelated with the granite magma.