D/H fractionation of coexisting biotite and hornblende in some granitic rock masses - A supplement.

Biotite-hornblende pairs from granitic rocks of the northern Kitakami mountaineous dristrict and of Ryoke metamorphic belt were studied for deuterium content. Some of biotites of the pairs from the northern Kitakami type had higher deuterium content than that expected for hydrogen isotope exchange equilibrium between biotite and hornblende. This was attributed to the result of exchange of hydrogen between biotite and water after the primary equilibrium was established. Biotite-hornblende pairs of Ryoke metamorphic belt exhibited a distinct disequilibrium situation with respect to deuterium content of biotite-hornblende pairs. The disequilibrium pattern of pairs could be a common feature of granitic rocks from metamorphic belts. The water initially present in magma of Ryoke granite was inferred to be greatly depleted in deuterium.