Trace element variations in the volcanic rocks from the Nasu zone, northeast Japan

Abstract

Trace element concentrations were analyzed in 46 volcanic rocks from twelve recent volcanoes of the outer volcanic zone (Nasu zone) of Northeast Japan. The Ba, Hf, Th, U and REE contents in the rocks are low as expected from their low K 2 O contents. The tholeiitic rocks and calc-alkaline rocks can be distinguished by their geochemical character as well as by the character of their groundmass pyroxenes. The magmas of the tholeiitic series and calc-alkaline series appear to have been generated independently in the upper mantle so far as their trace element variations are concerned, though a few calc-alkaline rocks are derivatives of a tholeiitic magma. The two magmas have been derived from two different source materials. However, the trace element variations in the two volcanic rock series can be interpreted as the product of different degrees of partial melting of the same peridotitic upper mantle.