Grand Comore Island: A well-constrained "low 3He/4He" mantle plume

Cornelia Class, Steven L. Goldstein, Martin Stute, Mark D. Kurz, Peter Schlosser

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Abstract

We report He isotope (3He/4He) variations in samples from alkali basaltic and basanitic lava flows from Grande Comore Island complemented by existing [1,2] [C. Class, S.L. Goldstein, Plume-lithosphere interactions in the ocean basins: constraints from the source mineralogy. Earth Planet. Sci. Lett., 150 (1997) 245-260, C. Class, S.L. Goldstein, R. Altherr, P. Bachèchlery, The process of plume-lithosphere interaction in the ocean basins - the case of Grande Comore. J. Petrol., 39 (5) (1998) 881-903] and new Sr-Nd-Pb isotope ratios and major and trace element abundances. He isotope data in samples from Tristan da Cunha and Gough islands and the Huri Hills in Kenya are reported also. Grande Comore 3He/4He ratios vary between 5.05 and 7.08 RA (4He/ 3He ≈ 141,000-101,000). Chemical and Sr-Nd-Pb isotopic variations of Grande Comore lavas were previously shown to reflect melts derived from the deep mantle plume and the shallow lithospheric mantle [1-3] [C. Class, S.L. Goldstein, Plume-lithosphere interactions in the ocean basins: constraints from the source mineralogy. Earth Planet. Sci. Lett., 150 (1997) 245-260, C. Class, S.L. Goldstein, R. Altherr, P. Bachèchlery, The process of plume-lithosphere interaction in the ocean basins - the case of Grande Comore. J. Petrol., 39 (5) (1998) 881-903, C. Claude-Ivanaj, B. Bourdon, C.J. Allègre, Ra-Th-Sr isotope systematics in Grande Comore Island: a case study of plume-lithosphere interaction. Earth Planet. Sci. Lett. 164 (1998) 99-117]. The lithosphere-dominated end-member (La Grille volcano) shows uniform 3He/ 4He ratios within error of 6.75 - 7.08 RA (4He/3He ≈ 106,000 - 101,000) over a range of [He] = 36-428 × 10-9 ccSTP/g. The plume end-member (of the Karthala volcano suite), as constrained by Sr, Nd, Pb isotope ratios, shows uniformly lower 3He/4He ratios with 5.05 - 5.41 RA (4He/3He -132,000) over a range of [He] = 11-136 × 10-9 ccSTP/g. All samples show good correlations between Sr-Nd-He isotope ratios, indicating that the Grande Comore 3He/4He ratios are not significantly influenced by crustal contamination and reflect recent mixing between plume- and lithosphere-derived melts. The lithosphere beneath Grande Comore has retained its MORB-like helium isotopic composition, which suggests that the previously identified amphibole-forming metasomatism of the lithospheric mantle [1] [C. Class, S.L. Goldstein, Plume-lithosphere interactions in the ocean basins: constraints from the source mineralogy. Earth Planet. Sci. Lett., 150 (1997) 245-260] occurred prior to the arrival of the Comoro plume. The well-constrained 3He/4He = 5.2 ± 0.2 RA (4He/3He ≈ 137,000 ± 5000) of the Comoro plume confirms the existence of "low 3He/4He" mantle plumes. A global compilation of OIB shows that OIB from "low 3He/4He" plumes form one "side" of the roughly triangular distribution of the global OIB data set in 143Nd/144Nd versus 206Pb/204Pb and 208Pb/204Pb, encompassing the lowest Nd to the highest Pb isotope ratios. It is also shown that "low 3He/4He" plumes are more enriched in Th and U relative to other plumes.

Original languageEnglish (US)
Pages (from-to)391-409
Number of pages19
JournalEarth and Planetary Science Letters
Volume233
Issue number3-4
DOIs
StatePublished - May 15 2005
Externally publishedYes

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Keywords

  • Grande Comore Island
  • Helium isotopes
  • Mantle geochemistry
  • Mantle plumes
  • Noble gas

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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