Mantle dynamics and mantle melting beneath Niuafo'ou Island and the northern Lau back-arc basin

Marcel Regelous, Simon Turner*, Trevor J. Falloon, Paul Taylor, John Gamble, Trevor Green

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    34 Citations (Scopus)

    Abstract

    A suite of young volcanic basaltic lavas erupted on the intra-plate island of Niuafo'ou and at active rifts and spreading centres (the King's Triple Junction and the Northeastern Lau Spreading Centre) in the northern Lau Basin is used to examine the pattern of mantle flow and the dynamics of melting beneath this complex back-arc system. All lavas contain variable amounts of a subduction related component inherited from the Tonga subduction zone to the east. All lavas have higher 87Sr/86Sr, lower 143Nd/144Nd and more radiogenic Pb isotope compositions than basalts erupted at the Central Lau Spreading Centre in the central Lau Basin, and are interpreted as variable mixtures of subduction-modified, depleted upper mantle, and mantle residues derived from melting beneath the Samoan Islands which has leaked through a tear in the subducting Pacific Plate beneath the Vitiaz Lineament at the northern edge of the Lau Basin. Our data can be used to map out the present-day distribution of Samoan mantle in this region, and show that it influences the compositions of lavas erupted as far as 400 km from the Samoan Islands. The distribution of Samoan-influenced lavas implies south- and southwest-wards mantle flow rates of >4 cm/year. U-series disequilibria in historic Niuafo'ou lavas have average (230Th/238U) = 1.13, (231Pa/235U) = 2.17, (226Ra/ 230Th) = 2.11, and together with major and trace element data require ∼5% partial melting of mantle at between 2 and 3 GPa, with a residual porosity of 0.002 and an upwelling rate of 1 cm year-1. We suggest that intraplate magmatism in the northern Lau Basin results from decompression melting during southward flow of mantle from beneath old (110-120 Ma), relatively thick Pacific oceanic lithosphere to beneath young (<5 Ma), thinner oceanic lithosphere beneath the northern Lau Basin.

    Original languageEnglish
    Pages (from-to)103-118
    Number of pages16
    JournalContributions to Mineralogy and Petrology
    Volume156
    Issue number1
    DOIs
    Publication statusPublished - Jul 2008

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