Minor element abundances in the Quaternary volcanic rocks in Hokkaid, Japan

Part 1: The rocks from southwestern Hokkaido

Abstract

Minor element abundances in the Quaternary volcanic rocks in southwestern Hokkaido were studied on 30 samples from 5 volcanoes as follows: Esan, Usu and Yôtei volcanoes of the Nasu Volcanic Zone and Niseko and Oshima-ôshima volcanoes of the Chokai Volcanic Zone. Ten minor elements, Cu, Sr, Ba, Ga, Y, Pb, V, Cr, Co, and Ni, were quantitatively determined by means of emission spectroscopy.
The purpose of this study is to show the petrochemical character of each volcano from a viewpoint of minor element chemistry and to examine the relation between the minor element contents and the lateral variation in the main compositions of the volcanic rocks across island arc.
The lateral variation in the minor elements of the volcanic rocks in southwestern Hokkaido is best shown in the distribution of Ba. This fact fits in with the K distribution. Namely, the lavas of the volcanoes in the Pacific Ocean side are poor in Ba and K, while the volcanic rocks in the Japan Sea side are richer in them, and those of Oshima-ôshima volcano are most abundant in Ba and K.
The difference in minor element contents between the lavas belonging to the pigeonitic and hypersthenic rock series is best distinguished by V content. The rocks of the pigeonitic series which involves an iron enrichment in the course of crystallization of magma, are characterized by higher V content than those of the hypersthenic rock series.