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Stable isotope compositions and water contents of boninite series volcanic rocks from Chichi-jima, Bonin Islands, Japan

P.F. Dobson·J. R. O’Neil
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Abstract

Measurements of stable isotope compositions and water contents of boninite series volcanic rocks from the island of Chichi-jima, Bonin Islands, Japan, confirm that a large amount (1.6–2.4 wt.%) of primary water was present in these unusual magmas. An enrichment of 0.6‰ in 18 O during differentiation is explained by crystallization of 18 O-depleted mafic phases. Silicic glasses have elevated δ 18 O values and relatively low δD values indicating that they were modified by low-temperature alteration and hydration processes. Mafic glasses, on the other hand, have for the most part retained their primary isotopic signatures since Eocene time. Primary δD values of −53 for boninite glasses are higher than those of MORB and suggest that the water was derived from subducted oceanic lithosphere.

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P.F. Dobson, J. R. O’Neil. 1987. Stable isotope compositions and water contents of boninite series volcanic rocks from Chichi-jima, Bonin Islands, Japan. https://doi.org/10.1016/0012-821x(87)90108-7

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