Whore-rock geochemistry of diorite and dikes from Mt. Shaku-dake area, Fukuoka, Kyushu

Abstract

A diorite stock and mafic-felsic dikes, which intrude Cretaceous sedimentary rocks of the Wakino sub-group, are exposed on the western side of Mt. Shaku-dake. In terms of modal mineralogy and chemical composition, the diorite stock is classified as a two-pyroxene diorite and contains euhedral clinopyroxene and orthopyroxene. The dikes are dolerite, porphyritic fine-grained tonalite, fine-grained clinopyroxene granodiorite, and fine-grained biotite granite. Whole-rock chemical analyses reveal that some of the diorites and dolerites possess high Mg-numbers (100×MgO/(MgO+FeO*) in moles) of >64 and that these rocks are geochemically similar to Sanukitic high-Mg andesites (HMA).