COEXISTING BIOTITES AND HORNBLENDES FROM SOME GRANITIC ROCKS IN SOUTHERN KITAKAMI MOUNTAINS, JAPAN

Abstract

Coexisting biotites and hornblendes in granitic rocks from the Kitakami mountains were chemically analyzed. Most of biotites have composition near the phlogopite-annite series. Hornblendes of the Hitokabe, Tono and Kesengawa masses are similar in composi-tion one another, but those of the Hirota mass are poorer in Al and Na+K and richer in Si than those of the former three masses. The Mg-Fe+2 distribution coefficients for coexisting biotite-hornblende pairs from the Hitokabe, Tono, Kesengawa and Hirota masses are 0.79, 0.69, 0.70 and 0.67, respectively. These differences depend largely upon Al contents in these minerals.