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Geochemistry, Geophysics, Geosystems

Recent volcanic accretion at 9°N–10°N East Pacific Rise as resolved by combined geochemical and geological observations

Authors

  • C. L. Waters,

    Corresponding author
    1. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
    2. Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming, USA
    3. Now at Geosciences Research Division, Scripps Institution of Oceanography, University of California San Diego, La Jolla, California, USA
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  • K. W. W. Sims,

    1. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
    2. Department of Geology and Geophysics, University of Wyoming, Laramie, Wyoming, USA
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  • S. A. Soule,

    1. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
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  • J. Blichert-Toft,

    1. Laboratoire de Géologie de Lyon, Ecole Normale Supérieure de Lyon and Université Claude Bernard Lyon 1, Lyon, France
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  • N.W. Dunbar,

    1. New Mexico Bureau of Geology & Mineral Resources, Earth and Environmental Science Department, New Mexico Tech, Socorro, New Mexico, USA
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  • T. Plank,

    1. Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York, USA
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  • J. Prytulak,

    1. Department of Earth Science and Engineering, Imperial College, London, UK
    2. Bristol Isotope Group, Department of Earth Sciences, University of Bristol, UK
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  • R. A. Sohn,

    1. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
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  • M. A. Tivey

    1. Department of Geology and Geophysics, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA
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Abstract

[1] The ridge crest at 9°N–10°N East Pacific Rise (EPR) is dominated by overlapping lava flows that have overflowed the axial summit trough and flowed off-axis, forming a shingle-patterned terrain up to ∼2–4 km on either side of the axial summit trough. In this study, we employ 230Th-226Ra dating methods, in conjunction with geochemistry and seafloor geological observations, in an effort to discern the stratigraphic relationships between adjacent flows. We measured major and trace elements and 87Sr/86Sr, 143Nd/144Nd, 176Hf/177Hf, and 238U-230Th-226Ra for lava glass samples collected from several flow units up to ∼2 km away from the axial summit trough on the ridge crest at 9°50′N EPR. Statistical analysis of the 238U-230Th-226Ra data indicates that all but one measured sample from these flows cannot be resolved from the zero-age population; thus, we cannot confidently assign model ages to samples for discerning stratigraphic relationships among flows. However, because groups of samples can be distinguished based on similarities in geochemical compositions, particularly incompatible element abundances with high precision-normalized variability such as U and Th, and because the range of compositions is much greater than that represented by samples from the 1991–1992 and 2005–2006 eruptions, we suggest that the dive samples represent 6–10 eruptive units despite indistinguishable model ages. Geochemical variability between individual flows with similar ages requires relatively rapid changes in parental melt composition over the past ∼2 ka, and this likely reflects variations in the relative mixing proportions of depleted and enriched melts derived from a heterogeneous mantle source.

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