New insights into the origin of O-Hf-Os isotope signatures in arc lavas from Tonga-Kermadec

Simon Turner*, Monica Handler, Ilya Bindeman, Katsuhiko Suzuki

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    43 Citations (Scopus)

    Abstract

    O, Hf and Os isotope data are presented for lavas from the highly depleted Tonga-Kermadec arc. O isotope values overlap with those of MORB limiting the amount of interaction with the arc crust. δ18O does not increase northwards as would be expected from the ~ 4 fold increase in subduction rate if slab-derived fluids had high 18O/16O ratios. Thus, the overall northward decrease in HFSE concentrations likely reflects depletion due to prior melt extraction, not increasing extents of melting. Hf isotopes are strongly negatively correlated with Be isotopes consistent with mixing of subducted pelagic sediment into the mantle wedge and do not require Hf to be fluid mobile. With the exception of a boninite from the north Tongan trench, the northern Tonga lavas do not overlap the Hf isotope composition of either the Samoan plume or the subducting Louisville volcaniclastic sediments. Thus, the Pb isotope signatures in these lavas must have been added by fluids and sediment melts derived from the Louisville volcaniclastics with minimal mobilisation of Hf. This suggests conservative behaviour for this element due to the formation of residual zircon during partial melting of the subducted sediments. 187Os/188Os ranges from 0.1275 to 0.4731 and the higher Os isotope ratios reflect the sensitivity of this system to even minor interaction with altered arc crust. Conversely, the lowest Os ratios are subchondritic and indicate that transfer of radiogenic Os from the slab is not all pervasive and provide an important constraint on the composition of the mantle wedge. Remarkably, the least radiogenic sample is a dacite demonstrating that evolved magmas can develop by fractionation from mantle-derived magmas with minimal interaction with the arc crust.

    Original languageEnglish
    Pages (from-to)196-202
    Number of pages7
    JournalChemical Geology
    Volume266
    Issue number3-4
    DOIs
    Publication statusPublished - 30 Aug 2009

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