Bindeman, I. N. and Eiler, J. M. and Yogodzinski, G. M. and Tatsumi, Y. and Stern, C. R. and Grove, T. L. and Portnyagin, M. and Hoernle, K. and Danyushevsky, L. V. (2005) Oxygen isotope evidence for slab melting in modern and ancient subduction zones. Earth and Planetary Science Letters, 235 (3-4). pp. 480-496. ISSN 0012-821X http://resolver.caltech.edu/CaltechAUTHORS:20121025-102847128
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We measured oxygen isotope compositions of 34 adakites, high-Mg andesites, and lavas suspected to contain abundant slab and sediment melts from the Western and Central Aleutians, the Andes, Panama, Fiji, Kamchatka, Setouchi (Japan), and the Cascades. This suite covers much of the diversity of arc lavas previously hypothesized to contain abundant ‘slab’ melts. Measured and calculated values of δ^(18)O for olivine phenocrysts in these samples vary between 4.88‰ and 6.78‰, corresponding to calculated melt values of 6.36‰ to 8.17‰. Values of δ^(18)O for these samples are correlated with other geochemical parameters having petrogenetic significance, including Sr/Y, La/Yb, ^(87)Sr/^(86)Sr, and ^(143)Nd/^(144)Nd. Archetypical adakites from Adak Island (Central Aleutian) and Cook Island (Andean Austral zone), previously interpreted to be nearly pure melts of basaltic and gabbroic rocks in subducting slabs, have values of δ^(18)O slightly higher than those of normal mid-ocean-ridge basalts, and in oxygen isotope equilibrium with typical mantle peridotite (i.e., their subtle ^(18)O enrichment reflects their Si-rich compositions and low liquidus temperatures, not ^(18)O-rich sources). Other primitive adakites from Panama and Fiji show only subtle sub-per mil enrichments in the source. This finding appears to rule out the hypothesis that end-member adakites are unmodified partial melts of basaltic rocks and/or sediments in the top (upper 1–2 km) of the subducted slab, which typically have δ^(18)O values of ca. 9–20‰, and also appears to rule out them being partial melts of hydrothermally altered gabbros from the slab interior, which typically have δ^(18)O values of ca. 2–5‰. One explanation of this result is that adakites are mixtures of partial melts from several different parts of the slab, so that higher- and lower-δ^(18)O components average out to have no net difference from average mantle. Alternatively, adakites might be initially generated with more extreme δ^(18)O values, but undergo isotopic exchange with the mantle wedge before eruption. Finally, adakites might not be slab melts at all, and instead come from differentation and/or partial melting processes near the base of the arc crust in the over-riding plate. High-Mg andesites and Setouchi lavas are commonly higher in δ^(18)O than equilibrium with the mantle, consistent with their containing variable amounts of partial melts of subducted sediments (as we conclude for Setouchi lavas), slab-derived aqueous fluid (as we conclude for the Cascades) and/or crustal contaminants from the over-riding plate (as we conclude for Kamchatka).
|Additional Information:||© 2005 Elsevier B.V. Received 3 November 2004; received in revised form 11 March 2005; accepted 1 April 2005. Available online 4 June 2005. Editor: K. Farley. Several collaborators of the present coauthors were involved in characterization of the present suite of samples: F. Hauff and B. Lissinna for Panamanian adakites, E. Bourdon for Ecuadorian samples, S. Tetroyeva for Fiji adakites, the sample ADK-53, the original badakiteQ, was provided by Bob Kay. Bill Leeman is thanked for discussions on the Cascades volcanism, Zhengrong Wang for his help with the UV laser fluorination, and two anonymous reviewers for their helpful comments.|
|Subject Keywords:||andesite; adakite; subduction; oxygen isotopes; setouchi; trondhjemite; zircon|
|Official Citation:||I.N. Bindeman, J.M. Eiler, G.M. Yogodzinski, Y. Tatsumi, C.R. Stern, T.L. Grove, M. Portnyagin, K. Hoernle, L.V. Danyushevsky, Oxygen isotope evidence for slab melting in modern and ancient subduction zones, Earth and Planetary Science Letters, Volume 235, Issues 3–4, 15 July 2005, Pages 480-496, ISSN 0012-821X, 10.1016/j.epsl.2005.04.014. (http://www.sciencedirect.com/science/article/pii/S0012821X05002438)|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||25 Oct 2012 18:08|
|Last Modified:||27 Dec 2012 02:55|
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