Herzberg, Claude and Ionov, Dmitri A. and Vidito, Chris A. and Jackson, Matthew G. and Geist, Dennis and Asimow, Paul D. (2013) Nickel and helium evidence for melt above the core–mantle boundary. Nature, 493 (7432). pp. 393-397. ISSN 0028-0836. http://resolver.caltech.edu/CaltechAUTHORS:20130208-132039113
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High ^(3)He/^(4)He ratios in some basalts have generally been interpreted as originating in an incompletely degassed lower-mantle source. This helium source may have been isolated at the core–mantle boundary region since Earth’s accretion. Alternatively, it may have taken part in whole-mantle convection and crust production over the age of the Earth; if so, it is now either a primitive refugium at the core–mantle boundary or is distributed throughout the lower mantle. Here we constrain the problem using lavas from Baffin Island, West Greenland, the Ontong Java Plateau, Isla Gorgona and Fernandina (Galapagos). Olivine phenocryst compositions show that these lavas originated from a peridotite source that was about 20 per cent higher in nickel content than in the modern mid-ocean-ridge basalt source. Where data are available, these lavas also have high ^(3)He/^(4)He. We propose that a less-degassed nickel-rich source formed by core–mantle interaction during the crystallization of a melt-rich layer or basal magma ocean, and that this source continues to be sampled by mantle plumes. The spatial distribution of this source may be constrained by nickel partitioning experiments at the pressures of the core–mantle boundary.
|Additional Information:||© 2013 Macmillan Publishers Limited. Received: 10 May 2012; Accepted: 05 November 2012; Published online: 09 January 2013. C.H. thanks L. Larsen, M. Portnyagin, A. Sobolev and D. Walker for discussions. We are very grateful to R. Walker for a critical review. D.A.I. acknowledges PNP grants from the French INSU-CNRS in 2010-2012 and P.D.A. acknowledges NSF grant EAR-1119522. P.D.A. thanks A. Matzen for extended discussions. D.G.’s work is funded by NSF grant EAR1145271. Author Contributions: C.H. modelled olivine compositions and developed a variety of magma ocean and core–mantle interaction interpretations. P.D.A. suggested the core– mantle interaction model in its current form and critiqued all Ni partitionmodels. D.A.I. provided high-precision olivine and whole-rock analyses for mantle peridotite. C.V. acquired high-precision olivine data for Fernandina (Galapagos). M.G.J. provided information on Pb, Nd and He isotopes. D.G. provided rock samples from Fernandina. All authors contributed to the intellectual growth of this paper.|
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|Deposited By:||Jason Perez|
|Deposited On:||09 Feb 2013 00:04|
|Last Modified:||23 Jul 2013 18:03|
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