ABSTRACT

Geochemical data for 13 samples of alkalic rocks from Nemuro Peninsula, Hokkaido, are presented and discussed. Analyses for trace elements, Ni, Co, Cr, Sc, Cu, Zn, Ga, Zr, Y, Pb, Ba, Sr and Li in a differentiated sheet ranging from picritic dolerite to syenite and in an undifferentiated dolerite sheet showing pillow structure, are given. It is shown that the Nemuro alkalic rocks have distinctly higher concentrations of Ba, Zn, Cu, Pb, Y and Li, high ratios of K/Sr and Ca/Sr, and lower concentrations of Sr, Ni, Co, Cr, Sc and Zr than do alkali basaltic rocks from other districts in the world. The behavior of the major and trace elements suggests that the Nemuro alkalic rocks were modified chemically by deuteric alteration during the magmatic stage. The parental potash-rich olivine basalt magma of these alkalic rocks was formed probably by partial melting of phlogopite-peridotite in the upper mantle.