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Origin of enriched-type mid-ocean ridge basalt at ridges far from mantle plumes : the East Pacific Rise at 11°20′N.

Niu, Y.L. and Collerson, K.D. and Batiza, R. and Wendt, 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 : solid earth., 104 (B4). pp. 7067-7087.

Abstract

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., [La/Sm]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 [Nb/Th]PM > 1 and [Ta/U]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/eclogitic 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.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:http://dx.doi.org/10.1029/1998jb900037
Publisher statement:Niu, Y., K. D. Collerson, R. Batiza, J. I. Wendt, and M. Regelous (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: Solid Earth (1978–2012), 104(B4), 7067-7087, 10.1029/1998JB900037 (DOI). To view the published open abstract, go to http://dx.doi.org and enter the DOI.
Date accepted:No date available
Date deposited:19 April 2016
Date of first online publication:April 1999
Date first made open access:No date available

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