Abstract
Rb and Sr concentrations and Sr isotopic compositions were analyzed for the Ojika gabbroic complex, the S-mass in the Aji islet and the Ichinohe complex in the Kitakami mountains. The initial 87Sr/86Sr ratios of 0.7045_??_0.7050 for the former two is somewhat higher than that of 0.7041 for the latter. For the Inchinohe complex, 105±30 m. y. is obtained as the whole rock isochron age, which shows well-agreement with the biotite-whole rock isochron age of 101_??_110m. y. These ages indicate the age of emplacement of the Ichinohe complex. The low initial 87Sr/86Sr ratios for these complexes indicate that incorporation of crustal materials in the original magmas is eliminated. The K/Rb ratios of the present district is 72_??_287. These values are somewhat lower than those of some other granitic rocks in Japan.
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