Ancient seafloor signals in Pitcairn Island lavas and evidence for large amplitude, small length-scale mantle heterogeneities

https://doi.org/10.1016/0012-821X(89)90145-3Get rights and content

Abstract

Isotopic data for Pitcairn island volcanic rocks reveal the presence of two markedly different sources which appear to be closely related both spatially and temporally. The isotopic variability (or amplitude ratio) of this suite relative to all other oceanic basalts (mid-ocean ridges and oceanic islands) is ∼ 30% for Pb, ∼ 40% for Sr and 50% for Nd. This confirms the findings of several recent studies indicating that, contrary to earlier conclusions, large amplitude variations can exist over limited (∼ 10 km) length scales. The unusual, unradiogenic206Pb/204Pb and143Nd/144Nd and radiogenic87Sr/86Sr isotopic compositions, lack of strong covariation between isotopic and other geochemical parameters, and variable Nb/U ratios place strong constraints on any petrogenetic model. It is suggested that the two magma types may reflect the presence of variable quantities of ancient subducted oceanic crust and ancient subducted sedimentary material in the mantle source beneath Pitcairn. The critical role of subduction zone “processing” in modifying the chemical composition of such sources is stressed; thus, for example, the trace element composition of modern pelagic sediment cannot be used as a direct analogue of the subducted sediment residuum which may be important in the source of Pitcairn and some other ocean islands. The complementary trace element abundance patterns often noted between ocean island basalts (OIB) and island arc tholeiites (IAT) are seen as a direct result of this process.

Reference (66)

  • MenziesM. et al.

    Nd and Sr isotope geochemistry of hydrous mantle nodules and their host alkali basalts: implications for local heterogeneities in metasomatically veined mantle

    Earth Planet. Sci. Lett.

    (1980)
  • NealC.R. et al.

    A negative Ce anomaly in a peridotite xenolith: evidence for crustal recycling into the mantle or mantle metasomatism

    Geochim. Cosmochim. Acta

    (1989)
  • ZartmanR.E. et al.

    The plumbotectonic model for Pb isotopic systematics among major terrestrial reservoirs — a case for bi-directional transport

    Geochim. Cosmochim. Acta

    (1988)
  • WhiteW.M. et al.

    Isotope and trace element geochemistry of sediments from the Barbados Ridge-Demerara plain region, Atlantic Ocean

    Geochim. Cosmochim. Acta

    (1985)
  • Ben OthmanD. et al.

    The geochemistry of marine sediments, island arc magmagenesis, and crust-mantle recycling

    Earth Planet. Sci. Lett.

    (1989)
  • AlbarèdeF. et al.

    Transfer of continental Mg, S, O and U to the mantle through hydrothermal alteration of the oceanic crust

    Chem. Geol.

    (1986)
  • PatchettP.J. et al.

    Hafnium/rare earth element fractionation in the sedimentary system and crustal recycling into the Earth's mantle

    Earth Planet. Sci. Lett.

    (1984)
  • TatsumiY. et al.

    Chemical characteristics of the fluid phase released from a subducted lithosphere and the origin of arc magmas: evidence from high pressure experiments and natural rocks

    J. Volcanol. Geotherm. Res.

    (1986)
  • LoubetM. et al.

    Mantle heterogeneity: a combined isotope and trace element approach and evidence for recycled continental crustal materials in some OIB sources

    Earth Planet. Sci. Lett.

    (1988)
  • MacdougallJ.D. et al.

    Sr and Nd isotopes in basalts from the East Pacific Rise: significance for mantle heterogeneity

    Earth Planet. Sci. Lett.

    (1986)
  • PalaczZ.A. et al.

    Coupled trace element and isotope enrichment in the Cook-Austral-Samoa islands, southwest Pacific

    Earth Planet. Sci. Lett.

    (1986)
  • WoodheadJ.D. et al.

    Pb, Sr and10Be isotopic studies of volcanic rocks from the Northern Mariana islands: implications for magma genesis and crustal recycling in the Western Pacific

    Geochim. Cosmochim. Acta

    (1985)
  • HartS.R.

    Large scale isotopic anomaly in the southern hemisphere mantle

    Nature

    (1984)
  • DuncanR.A. et al.

    Pitcairn island — another Pacific hot spot?

    Nature

    (1974)
  • MenardH.W.

    Marine Geology of the Pacific

    (1964)
  • HerronE.M.

    Sea-floor spreading and the Cenozoic history of the East-Central Pacific

    Bull. Geol. Soc. Am.

    (1972)
  • McDonoughW.F. et al.

    Geochemical and isotopic systematics of Cenozoic intraplate basalts from continental and oceanic regions in the south Pacific

  • RocaboyA. et al.

    Sr, Nd, Pb isotopic and trace element composition of the Gambier islands (French Polynesia)

    EOS

    (1987)
  • LacroixA.

    Les roches volcaniques de l'île Pitcairn (Océan Pacifique austral)

    C.R. Acad. Sci.

    (1936)
  • CarterR.M.

    The geology of Pitcairn Island, South Pacific ocean

    B.P. Bishop Mus. Bull.

    (1967)
  • WoodheadJ.D.

    Geochemistry of the Northern Mariana islands, W. Pacific

  • CatanzaroE.J. et al.

    Absolute isotopic abundance ratios of common, equal atom and radiogenic lead isotope standards

    J. Res. Natl. Bur. Standards Pap. 72A3-500, Appl. Phys. Chem.

    (1968)
  • RichardsJ.R.

    Lead isotopes as indicators of old stable craton in Western Australia

    Geochem. J.

    (1983)
  • Cited by (0)

    View full text