MINOR ELEMENT ABUNDANCES IN THE QUATERNARY VOLCANIC ROCKS IN HOKKAIDO, JAPAN

Abstract

Thirty-six Quaternary volcanic rocks from the central and eastern Hokkaido, whose major elements were known, were newly analyzed on the minor elements, Cu, Sr, Ba, Ga, Y, Pb, V, Cr, Co and Ni. The relation between the minor and major element abundances of the above rocks were discussed. The general and characteristic features of the volcanoes and volcanic chains are summarized as follows; 1. The kutcharo, Atosanupuri and other post-caldera volcanoes of Kutcharo and Mashu have the same character as those of the Usu and Esan volcanoes of the south-western Hokkaido. 2. Also the Akan volcano has the same character as those of the above volcanoes, except Cu, Cr and Ni elements. This volcano is far richer in these elements than those of the others. 3. The Daisetsu and tokachi volcanoes have nearly the same character as that of the Niseko Volcano of the southwestern Hokkaido. The Daisetsu Volcano is characterized by the high V×1000/FeO+Fe2O3 ratio, which is one of the highest value in Hokkaido, and by the rich Cr and Ni contents. The Tokachi Volcano is far poorer in Cr and Ni than The Daisetsu Volcano. 4. The difference of minor element contents between the shiretoko-Akan and the Daisetsu-Tokachi volcanic chains is best represented in Ba and Pb contents. The latter is richer in Ba and Pb than those of the former. In the Shiretoko-Akan volcanic chain, the rocks of the pigeonitic rock series are richer in V than those of the hypersthenic rock series, as seen in the volcanoes of that in the south-western Hokkaido. The rocks of the Daisetsu-Tokachi volcanic chain, which belong mostly to the hypersthenic rock series, are rich in V and plotted in the pigeonitic rock series field of the rocks from the former chain. In this point, the rocks of the hypersthenic rock series of the latter chain are different from those of the former. The minor elements of the Tokachi welded tuff are often far from the general character of the Tokachi volcano, which suggests its different genesis.