1. Department of Earth Sciences, ETH Zurich, Sonneggstrasse 5, 8092 Zurich, Switzerland
2. GEMOC, Department of Earth and Planetary Sciences, Macquarie University, 2109 New South Wales, Australia
3. Department of Earth Science and Engineering, Imperial College, London SW7 2AZ, UK
4. Research School of Earth Sciences, Australian National University, Canberra, Australian Capital Territory 0200, Australia
5. Department of Earth Sciences, University of Oxford, Parks Road, Oxford OX1 3PR, UK

Correspondence to: Sune G. Nielsen^1,2 Correspondence and requests for materials should be addressed to S.G.N. (Email: snielsen@els.mq.edu.au).

Abstract

Ocean island basalts are generally thought to be the surface expression of mantle plumes, but the nature of the components in the source regions of such mantle plumes is a subject of long-standing debate. The lavas erupted at Hawaii have attracted particular attention, as it has been proposed that coupled ¹⁸⁶Os and ¹⁸⁷Os anomalies reflect interaction with the Earth's metallic core^{1, 2}. It has recently been suggested, however, that such variations could also result from addition of oceanic ferromanganese sediments to the mantle source of these lavas^{3, 4, 5}. Here we show that Hawaiian picrites with osmium isotope anomalies also exhibit pronounced thallium isotope variations, which are coupled with caesium/thallium ratios that extend to values much lower than commonly observed for mantle-derived rocks. This correlation cannot be created by admixing of core material, and is best explained by the addition of ferromanganese sediments into the Hawaii mantle source region. However, the lack of correlation between thallium and osmium isotopes and the high thallium/osmium ratios of ferromanganese sediments preclude a sedimentary origin for the osmium isotope anomalies, and leaves core–mantle interaction as a viable explanation for the osmium isotope variations of the Hawaiian picrites.

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