Blichert-Toft, J.

Geldmacher, Jörg

Hanan, B. B.

Hoernle, Kaj

English

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Geophysical Research Abstracts,Vol. 11, EGU2009-2528, 2009EGU General Assembly 2009© Author(s) 2009Hafnium Isotopic Variations in East Atlantic Intraplate VolcanismJ. Geldmacher (1), B.B. Hanan (2), K. Hoernle (3), and J. Blichert-Toft (4)(1) IODP, Texas A&M University, 1000 Discovery Drive, College Station 77845, USA (geldmacher@iodp.tamu.edu), (2)Dept. Geological Sciences, 5500 Campanile Dr., San Diego State University, San Diego, CA 92182, USA(bhanan@mail.sdsu.edu), (3) IFM-GEOMAR Leibniz Institute for Marine Sciences, Wischhofstr. 1-3, D-24148 Kiel,Germany (khoernle@ifm-geomar.de), (4) Laboratoire des Sciences de la Terre, Ecole Normale Supérieure de Lyon, 69364Lyon, France (jblicher@ens-lyon.fr)Based on age determinations, plate tectonic reconstructions and systematically different Pb and Nd isotope ratios,two individual hotspot tracks (Madeira and Canary track) are proposed to explain the broad belt of intraplatevolcanism in the East Atlantic between 25ºN and 36ºN (e.g., Geldmacher et al., 2005, EPSL 237). This studypresents, for the first time, 176Hf/177Hf ratios from seamounts and islands of both provinces, encompassing thefull range of different evolutionary stages and isotopic endmembers. The majority of samples have mafic, mainlybasaltic compositions with Mg-numbers within or near the range of magmas in equilibrium with mantle olivine(68-75).In comparison to published Nd isotope variations (6 epsilon Nd units), 176Hf/177Hf ratios span a muchlarger range (14 epsilon Hf units). Samples from the Madeira archipelago have the most radiogenic compositions(176Hf/177Hfm= 0.283132-0.283335), widely overlapping the field for central Atlantic N-MORB. They form arelatively narrow, elongated trend (stretching over >6 epsilon Hf units) between a radiogenic MORB-like end-member and a composition located on the Nd-Hf mantle array. Although samples of Seine and Unicorn seamounts,attributed to the Madeira hotspot track, show less radiogenic Hf and Nd isotope ratios than Madeira, their isotopiccompositions lie along an extension of the Madeira trend in plots of Hf versus Sr, Nd, Pb isotopes. In contrast,all samples from the Canary hotspot track plot below the mantle array (176Hf/177Hfm = 0.282943-0.283067)and, despite being from a larger geographic area, form a much denser cluster with less compositional variation( 4 epsilon Hf units). The cluster largely overlaps the composition of the proposed common mantle endmember“C” (Hanan and Graham, 1996, Science 272) but spans a space between “C”, a more depleted composition and aHIMU-type endmember. The new Hf isotope ratios confirm the existence of at least two geochemically distinctvolcanic provinces (Canary and Madeira) in the East Atlantic as previously proposed. Their different isotopiccomposition is best explained by different recycling ages of their respective enriched mantle source endmembers,which are believed to represent subducted oceanic lithosphere that is preserved in the mantle.

Hafnium isotopic variations in East Atlantic intraplate volcanism

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