Petrology of a composite dike with biotite granite porphyry and hornblende quartz diorite porphyry at Shirotori, Kagawa, Japan.

Abstract

A Late Cretaceous composite dike at Kaura-goshi, Shirotori has an inner zone of biotite granite porphyry and outer zones of hornblende quartz diorite porphyry. Considerably altered fragments of the quartz diorite porphyry are distributed in the inner zone and seem to have been incorporated while plastic. The granite porphyry of the composite dike is higher in mg [=Mg/(Mg+Fe2++Fe3++Mn)] ratio and lower in normative Q/(Q+Or+Ab) ratio than similar but simple dike rocks in the area. The salic magma of the composite dike might have been slightly contaminated by the associated quartz diorite porphyry magmaat, or earlier than, the stage of magma chamber. It cannot exclude the possibility that salic magmas of different modes of intrusion have different origins.