Hydrogen isotopic ratio of hornblende from Quaternary volcanic rocks in Japan


Osamu Matsubaya and Isoji Miyagi
Water-Rock Interaction, Kharaka & Maest (eds)
Balkema, Rotterdam. ISBN 90 5410 0753
(1992)

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Abstract:

Hornblendes from 16 volcanoes in Japan were analyzed for hydrogen
isotopic ratios. Amphiboles from pumice flow and pumice fall, which
must have been quickly cooled, have rather uniform D/H ratio, while
those from lava and pyroclastic flow show a large variation. Because
such large variations are considered caused by isotopic fractionation
through dehydration from magma during its cooling and also through
oxidation to basaltic hornblende, pumice seems to keep an original
isotopic values. Most D/H ratios of amphiboles from pumice have del-D
values that range from -40 to -60 permil SMOW. This range is similar
to the range of volcanic steam in Japan rather than the range of
mantle water, and suggests that some water derived from other than
mantle may involve the magma genesis of island arc volcanoes.