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    Evidence for melting mud in Earth's mantle from extreme oxygen isotope signatures in zircon

    Access Status
    Fulltext not available
    Authors
    Spencer, C.
    Cavosie, A.
    Raub, T.
    Rollinson, H.
    Jeon, H.
    Searle, M.
    Miller, J.
    McDonald, B.
    Evans, Noreen
    Date
    2017
    Type
    Journal Article
    
    Metadata
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    Citation
    Spencer, C. and Cavosie, A. and Raub, T. and Rollinson, H. and Jeon, H. and Searle, M. and Miller, J. et al. 2017. Evidence for melting mud in Earth's mantle from extreme oxygen isotope signatures in zircon. Geology. 45 (11): pp. 975-978.
    Source Title
    Geology
    DOI
    10.1130/G39402.1
    ISSN
    0091-7613
    School
    Department of Applied Geology
    URI
    http://hdl.handle.net/20.500.11937/58076
    Collection
    • Curtin Research Publications
    Abstract

    © 2017 Geological Society of America. Melting of subducted sediment remains controversial, as direct observation of sediment melt generation at mantle depths is not possible. Geochemical fingerprints provide indirect evidence for subduction delivery of sediment to the mantle; however, sediment abundance in mantle-derived melt is generally low (0%-2%), and difficult to detect. Here we provide evidence for melting of subducted sediment in granite sampled from an exhumed mantle section. Peraluminous granite dikes that intrude peridotite in the Oman-United Arab Emirates ophiolite have U-Pb ages of 99.8 ± 3.3 Ma that predate obduction. The dikes have unusually high oxygen isotope (d 18 O) values for whole rock (14-23‰) and quartz (20-22‰), and yield the highest d 18 O zircon values known (14-28‰ values relative to Vienna standard mean ocean water [VSMOW]). The extremely high oxygen isotope ratios uniquely identify the melt source as high-d 18 O marine sediment (pelitic and/or siliciceous mud), as no other source could produce granite with such anomalously high d 18 O. Formation of high-d 18 O sediment-derived (S-type) granite within peridotite requires subduction of sediment to the mantle, where it melted and intruded overlying mantle wedge. The granite suite described here contains the highest oxygen isotope ratios reported for igneous rocks, yet intruded mantle peridotite below the Mohorovicic seismic discontinuity, the most primitive oxygen isotope reservoir in the silicate Earth. Identifying the presence and quantifying the extent of sediment melting within the mantle has important implications for understanding subduction recycling of supracrustal material and effects on mantle heterogeneity over time.

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