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    Submarine deep‐water lava flows at the base of the western Galápagos Platform

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    Date
    2018-10-25
    Author
    Anderson, Molly  Concept link
    Wanless, V. Dorsey  Concept link
    Schwartz, Darin M.  Concept link
    McCully, Emma  Concept link
    Fornari, Daniel J.  Concept link
    Jones, Meghan R.  Concept link
    Soule, Samuel A.  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/10771
    As published
    https://doi.org/10.1029/2018GC007632
    DOI
    10.1029/2018GC007632
    Keyword
     Submarine volcanism; Galápagos; Alkalic magmatism; Mantle plume; Mantle melting; Radiogenic isotopes 
    Abstract
    To investigate the initial phases of magmatism at the leading edge of the upwelling mantle plume, we mapped, photographed, and collected samples from two long, deep‐water lava flows located at the western base of the Galápagos Platform using the remotely operated vehicle Hercules. Lavas were recovered from four areas on the seafloor west of Fernandina volcano, including the western flow fronts of two deep‐water flows, heavily sedimented terrain between the two flows, and the eastern, shallower end of one flow. The sediment cover and morphologies are distinct between the western flow fronts and the eastern region based on seafloor imagery, suggesting that the long lava flows are not a single eruptive unit. Major and trace element concentrations reveal both tholeiitic and alkalic compositions and support the interpretation that multiple eruptive units comprise the deep‐water flows. Alkalic lavas have higher [La/Sm]N ratios (2.05–2.12) and total alkali contents (5.18–5.40) compared to tholeiitic lavas, which have [La/Sm]N ratios ranging from 1.64 to 1.68 and total alkali contents ranging from 3.07 to 4.08 wt%. Radiogenic isotope ratios are relatively homogeneous, suggesting a similar mantle source. We use petrologic models to assess three alternative mechanisms for the formation of the alkalic magmas: (1) high‐pressure crystallization of clinopyroxene, (2) mixing of high silica and mafic magmas, and (3) variable extents of melting of the same mantle source. Our modeling indicates that the alkalic samples form from lower extents of melting compared to the tholeiitic lavas and suggests that the deep‐water alkalic lavas are analogous to the initial, preshield building phase observed south of Hawaii and at the base of Loihi Seamount.
    Description
    Author Posting. © American Geophysical Union, 2018. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 19 (2018): 3945–3961, doi:10.1029/2018GC007632.
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    • Geology and Geophysics (G&G)
    Suggested Citation
    Geochemistry, Geophysics, Geosystems 19 (2018): 3945–3961
     

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