Lateral variation of major and trace elements in the Pliocene volcanic rocks of the Northeast Japan arc
Abundances of major elements and seven trace elements, Rb, Sr, Nb, Y, Zr, . Ni and Cr were determined by X-ray fluorescence analysis for 111 samples from twelve Pliocene volcanic centers in the NE Japan arc, The petrographical and analytical results on these samples and other Pliocene volcanic rocks indicate that systematic zonal variation of petrological features, i.e., mafic phenocryst assemblages and rock series, as well as gradual increase in K2O, Rb and Sr contents are recognized in the Pliocene volcanic rocks from the Pacific Ocean side to the Japan Sea side across the NE Japan arc. Similarity of across-arc variations with regard to both the petrological and the geochemical features among the volcanic rocks from the late Miocene through Pliocene to Quaternary time suggests that a mechanism of magma generation due to plate subduction has been contineous in the NE Japan arc at least from 8 Ma to the present.