Mantle flow, volatiles, slab-surface temperatures and melting dynamics in the north Tonga arc-Lau back-arc basin

John Caulfield, Simon Turner*, Richard Arculus, Chris Dale, Frances Jenner, Julian Pearce, Colin Macpherson, Heather Handley

*Corresponding author for this work

    Research output: Contribution to journalArticle

    13 Citations (Scopus)

    Abstract

    The Fonualei Spreading Center affords an excellent opportunity to evaluate geochemical changes with increasing depth to the slab in the Lau back-arc basin. We present H2O and CO2 concentrations and Sr, Nd, Pb, Hf and U-Th-Ra isotope data for selected glasses as well as new Hf isotope data from boninites and seamounts to the north of the Tonga arc. The Pb and Hf isotope data are used to show that mantle flow is oriented to the southwest and that the tear in the northern end of the slab may not extend east as far as the boninite locality. Along the Fonualei Spreading Center, key geochemical parameters change smoothly with increasing distance from the arc front and increasing slab surface temperatures. The latter may range from 720 to 866 degrees C, based on decreasing H2O/Ce ratios. Consistent with experimental data, the geochemical trends are interpreted to reflect changes in the amount and composition of wet pelite melts or super-critical fluids and aqueous fluids derived from the slab. With one exception, all of the lavas preserve both U-238 excesses and Ra-226 excesses. We suggest that lavas from the Fonualei Spreading Center and Valu Fa Ridge are dominated by fluid-fluxed melting whereas those from the East and Central Lau Spreading Centers, where slab surface temperatures exceed similar to 850-900 degrees C, are largely derived through decompression. A similar observation is found for the Manus and East Scotia back-arc basins and may reflect the expiry of a key phase such as lawsonite in the subducted basaltic crust.

    Original languageEnglish
    Article number11209
    Number of pages17
    JournalJournal of Geophysical Research
    Volume117
    Issue number11
    DOIs
    Publication statusPublished - 21 Nov 2012

    Keywords

    • TRACE-ELEMENT SIGNATURE
    • SUBDUCTION-ZONE FLUIDS
    • KERMADEC ISLAND-ARC
    • COLLECTOR-ICP-MS
    • TH-230-U-238 DISEQUILIBRIUM
    • MAGMA EVOLUTION
    • ISOTOPE RATIOS
    • SEDIMENT MELTS
    • MARIANA ARC
    • FLUX RATES

    ASJC Scopus subject areas

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

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