Eiler, John M. and Farley, Kenneth A. and Valley, John W. and Hauri, Erik and Craig, Harmon and Hart, Stnaley R. and Stolper, Edward M. (1997) Oxygen isotope variations in ocean island basalt phenocrysts. Geochimica et Cosmochimica Acta, 61 (11). pp. 2281-2293. ISSN 0016-7037 http://resolver.caltech.edu/CaltechAUTHORS:20120823-103638494
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Oxygen isotope ratios are reported for olivine phenocrysts from sixty-seven samples of ocean island basalts (OlBs), mid-ocean ridge basalts (MORBs), and related peridotites, including representatives of the various isotopic endmembers defined by radiogenic isotope ratios. OIBs are more homogeneous in δ^(18)O by this analysis than suggested by previous studies of whole rocks and glasses. Most 0I13 samples have oxygen isotope ratios within a restricted range (δ^(18)O_(olivine) = 5.0–5.4‰), comparable to those of olivines in peridotites from ophiolites, in most peridotitic mantle xenoliths, and inferred for the sources of mid-ocean ridge basalts. The exceptions are EM2 lavas, which are enriched in ^(18)O (δ^(18)_(olivine) = 5.4–6.1‰), and a small number of samples characterized by low ^3He/^4He and distinctive lead isotope ratios, which are ^(18)O depleted (δ^(18)O = 4.7-5.1‰). The observed range in δ^(18)O and the correlations with radiogenic isotope ratios are similar to those observed in a detailed study of Hawaiian samples (Eiler et al., 1996b). These results indicate that recycled crust and/or sediments (or the imprint of extensive metasomatism by fluids derived from such materials) is present as at most a small mass fraction (⪅ l%) in the mantle sources of most OIBs. The results on most EM2 lavas are consistent with the presence of ∼2–6% recycled sediment in their source regions. Low δ^(18)O values in OIBs can be produced by assimilation of altered lavas from high-levels in the volcanic edifice, assimilation of the oceanic crust underlying the volcano, or incorporation of subducted oceanic crust in mantle sources. The only consistent correlatives with low δ^(18)O are low ^3He/^4He and anomalous ^(207)Pb/^(204)Pb-^(206)Pb/^(204)Pb relationships, and most of the low-δ^(18)O samples can be explained by contamination by the underlying oceanic crust or volcanic edifice. High-^3He/^4He lavas are indistinguishable from MORBs and most other OIBs in terms of δ^(18)O, suggesting that to the extent that the lower mantle is sampled by hotspot volcanism, there is no significant vertical stratification in oxygen isotope ratios in the mantle.
|Additional Information:||© 1997 Elsevier Science Ltd. Received 24 June 1996. Accepted 7 February 1997. Available online 8 June 1998. We thank A. Hofmann for helpful discussions of this work, Mike Spicuzza for assistance in the stable isotope laboratory at the University of Wisconsin, and Dominique Weis and Mukul Sharma for contributing samples for this study. This manuscript was improved by the thorough reviews of Emi Ito and Barry Hanan. This work was funded by NSF EAR-9628142, -9303975, and -9117588 to EMS and 93-04372 to JWV, and DOE grants DEFG03-85ER13445 to EMS and 93ER14389 to JWV. Editorial handling: F. A. Frey.|
|Official Citation:||John M. Eiler, Kenneth A. Farley, John W. Valley, Erik Hauri, Harmon Craig, Stanley R. Hart, Edward M. Stolper, Oxygen isotope variations in ocean island basalt phenocrysts, Geochimica et Cosmochimica Acta, Volume 61, Issue 11, June 1997, Pages 2281-2293, ISSN 0016-7037, 10.1016/S0016-7037(97)00075-6. (http://www.sciencedirect.com/science/article/pii/S0016703797000756)|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||23 Aug 2012 18:48|
|Last Modified:||23 Aug 2012 18:48|
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