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Niu et al. 1999
Niu, Y., Collerson, K.D., Batiza, R., Wendt, J.I. and Regelous, M. (1999). Origin of enriched-type mid-ocean ridge basalt at ridges far from mantle plumes: The East Pacific Rise at 11°20'N. Journal of Geophysical Research 104: doi: 10.1029/1998JB900037. issn: 0148-0227.

The East Pacific Rise (EPR) at 11¿20'N erupts an unusually high proportion of enriched mid-ocean ridge basalts (E-MORB) and thus is ideal for studying the origin of the enriched heterogeneities in the EPR mantle far from mantle plumes. These basalts exhibit large compositional variations (e.g., N=0.68--1.47, 87Sr/86Sr=0.702508--0.702822, and 143Nd/144Nd=0.513053--0.513215). The 87Sr/86Sr and 143Nd/144Nd correlate with each other, with ratios of incompatible elements (e.g., Ba/Zr, La/Sm, and Sm/Yb) and with the abundances and ratios of major elements (TiO2, Al2O3, FeO, CaO, Na2O, and CaO/Al2O3) after correction for fractionation effect. These correlations are interpreted to result from melting of a two-component mantle with the enriched component residing as physically distinct domains in the ambient depleted matrix. The observation of PM>1 and PM>1, plus fractionated Nb/U, Ce/Pb, and Nb/La ratios, in lavas from the northern EPR region suggests that the enriched domains and depleted matrix both are constituents of recycled oceanic lithosphere. The recycled crustal/ecologitic lithologies are the major source of the enriched domains, whereas the recycled mantle/peridotitic residues are the most depleted matrix. On Pb-Sr isotope plot, the 11¿20'N data form a trend orthogonal to the main trend defined by the existing EPR data, indicating that the enriched component has high 87Sr/86Sr and low 206Pb/204Pb and 143Nd/144Nd. This isotopic relationship, together with mantle tomographic studies, suggests that the source material of 11¿20'N lavas may have come from the Hawaiian plume. This distal plume-ridge interaction between the EPR and Hawaii contrasts with the proximal plume-ridge interactions seen along the Mid-Atlantic Ridge. The so-called garnet signature in MORB is interpreted to result from partial melting of the eclogitic lithologies. The positive Na8-Si8/Fe8 and negative Ca8/Al8-Si8/Fe8 trends defined by EPR lavas result from mantle compositional (vs. temperature) variation. ¿ 1999 American Geophysical Union



Geochemistry, Composition of the mantle, Geochemistry, Trace elements
Journal of Geophysical Research
American Geophysical Union
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