Atypically depleted upper mantle component revealed by Hf isotopes at Lucky Strike segment

Type Article
Date 2013-03
Language English
Author(s) Hamelin Cedric1, Bezos Antoine2, Dosso Laure3, Escartin Javier4, Cannat Mathilde4, Mevel Catherine4
Affiliation(s) 1 : Univ Bergen, Ctr Geobiol, N-5007 Bergen, Norway.
2 : Lab Planetol & Geodynam, F-44322 Nantes 3, France.
3 : IFREMER, UMR 6538, CNRS, F-29280 Plouzane, France.
4 : Inst Phys Globe Paris, F-75252 Paris 05, France.
Source Chemical Geology (0009-2541) (Elsevier Science Bv), 2013-03 , Vol. 341 , P. 128-139
DOI 10.1016/j.chemgeo.2013.01.013
WOS© Times Cited 26
Keyword(s) Oceanic basalts, Mid-Atlantic Ridge, Lucky Strike, Mantle heterogeneity, Hf isotopes
Abstract The Earth's upper mantle is commonly depicted as a “marble cake” assemblage of a refractory component mingled with varying amounts of geochemically diverse enriched components. This depleted component controls the major element composition of Mid-Oceanic Ridge Basalts (MORBs). It has long been considered a fairly uniform reservoir, depleted by early melting and well homogenized by subsequent convective stirring. We present new Hf, Nd, Pb and Sr isotopes and trace element data for basalts from the center of the Lucky Strike segment of the Mid-Atlantic Ridge (MAR). Despite the limited size of our sampling area (1.6 km along-axis by 5 km across), these data show a large range of isotopic compositions (similar to that of the whole MAR). It has recently been shown that part of the reason for not observingmore segmentswith correlated Hf–Nd isotope systematics may be the lack of fine-scale sampling. Our data confirm this idea and showstrong correlations between all isotope ratios. The systematics of Hf–Nd isotopes in Lucky Strike basalts define an atypical correlation, distinct from the globalmantle array,with an anomalously high εHf for a given εNd.We illustrate that this atypical trend is the signature of an ancient refractory mantle rather than the product of kinetic processes during the melting event. The existence of this mantle component at Lucky Strike allows us to discuss the structure of the upper mantle around the Azores.
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