Origin of silicic magmas at spreading centres-An example from the South East Rift, Manus Basin

Christoph Beier*, Wolfgang Bach, Simon Turner, Dominik Niedermeier, Jon Woodhead, Jörg Erzinger, Stefan Krumm

*Corresponding author for this work

    Research output: Contribution to journalArticle

    19 Citations (Scopus)

    Abstract

    There has been much recent interest in the origin of silicic magmas at spreading centres away from any possible influence of continental crust. Here we present major and trace element data for 29 glasses (and 55 whole-rocks) sampled from a 40km segment of the South East Rift in the Manus Basin that span the full compositional continuum from basalt to rhyolite (50-75 wt % SiO2). The glass data are accompanied by Sr-Nd-Pb, O and U-Th-Ra isotope data for selected samples. These overlap the ranges for published data from this part of the Manus Basin. Limited increases in Cl/K ratios with increasing SiO2, La-SiO2 and Yb-SiO2 relationships, and the oxygen isotope data rule out models in which the more silicic lavas result from partial melting of altered oceanic crust or altered oceanic gabbros. Rather, the data form a coherent array that is suggestive of closed-system fractional crystallization and this is well simulated by MELTS models run at 0·2GPa and QFM (quartz-fayalite-magnetite buffer) with 1wt % H2O, using a parental magma chosen from the basaltic glasses. Although some assimilation of altered oceanic crust or gabbro cannot be completely ruled out, there is no evidence that this plays an important role in the origin of the silicic lavas. The U-series disequilibria are dominated by 238U and 226Ra excesses that limit the timescale of differentiation to less than a few millennia. Overall, the data point to rapid evolution in relatively small magma lenses located near the base of thick oceanic crust; we speculate that this was coupled with relatively low rates of basaltic recharge. A similar model may be applicable to the generation of silicic magmas elsewhere in the ocean basins.

    Original languageEnglish
    Pages (from-to)255-272
    Number of pages18
    JournalJournal of Petrology
    Volume56
    Issue number2
    DOIs
    Publication statusPublished - Feb 2015

    Keywords

    • Differentiation
    • Manus Basin
    • Oceanic spreading centre
    • Silicic lavas
    • South East Rift

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