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Geophysical Monograph Series

 

Keywords

  • Seamounts
  • Coral reefs and islands

Article

GEOPHYSICAL MONOGRAPH SERIES, VOL. 43, PP. 283-296, 1987

Isotopic evidence for a hotspot origin of the Louisville Seamount Chain

Q. Cheng, K.-H. Park, J. D. Macdougall, A. Zindler, G. W. Lugmair, H. Staudigel, J. Hawkins, and P. Lonsdale

The Louisville Seamount Chain (LSC) is the longest seamount chain in the South Pacific and in many ways resembles the Hawaiian-Emperor chain, suggesting a hotspot origin. Fifteen samples from ten LSC seamounts spanning the length of the LSC and covering a time span of more than 65 My were analyzed for Nd, Sr and Pb isotopic compositions. Since most of the samples are old and altered, systematic leaching experiments were conducted in order to study seawater alteration effects and to obtain age-corrected Sr and Nd isotopic compositions. These experiments show that even fresh appearing samples have elevated 87Sr/86Sr due to seawater Sr addition, and that highly altered samples may contain substantial amounts of seawater Nd, possibly hosted in secondary oxides or phosphate phases. However, after appropriate leaching, reliable, age-corrected 87Sr/86Sr and 143Nd/144Nd initial ratios can be obtained. The data for leached samples show very narrow ranges in Sr, Nd and Pb isotopic compositions (87Sr/86Sr from .7032 to .7038; 143Nd/144Nd from .51282 to .51294; 206Pb/204Pb from 19.128 to 19.452) both for different rock types within the same seamount and for the LSC chain as a whole. The LSC seamounts record a chemical plume signature that is distinct from that of MORB sources and is very homogeneous on a large scale over a long period of time. The data also imply a stationary source region for the long-lived upwelling mantle plume, thus favoring a mantle structure which is at least partly non-convective and a likely deep mantle origin for the hotspot plume as proposed by Morgan [1971, 1972a,b]. No appreciable mixing occurred between the LSC and MORB sources, which may have implications for the mechanism of plume transport.

Citation: Cheng, Q., K.-H. Park, J. D. Macdougall, A. Zindler, G. W. Lugmair, H. Staudigel, J. Hawkins, and P. Lonsdale (1987), Isotopic evidence for a hotspot origin of the Louisville Seamount Chain, in Seamounts, Islands, and Atolls, Geophys. Monogr. Ser., vol. 43, edited by B. H. Keating et al., pp. 283–296, AGU, Washington, D. C., doi:10.1029/GM043p0283.

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