Cumulus gabbro-diorite dikes associated with the Hioki granite stock, Kagoshima Prefecture, Japan

Abstract

The Hioki mafic dikes composed of gabbroic and dioritic rocks are associated with the Hioki granite stock of middle Miocene age in the central part of Satsuma Peninsula, Kagoshima Prefecture, Japan. The gabbroic dike consists of orthocumulus olivine-bearing pyroxene gabbro, and is chemically rich in not only compatible elements such as MgO, Ni and Cr but also incompatible elements such as K2O, Rb and Sr. The dioritic dike consists of orthocumulus biotite-bearing pyroxene diorite with intercumulus salic minerals and adcumulus plagioclase, and has chemically intermediate composition between the gabbro and the granite. Modes of occurrence, petrographical features and bulk and mineral compositions suggest that the Hioki mafic dikes were formed from cumulus phases, and the granitic intrusives could have been derived from residual liquids, through crystal fractionation of calc-alkaline andesitic magma.