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Mixing at mid-ocean ridges controlled by small-scale convection and plate motion

Nature Geoscience volume 7, pages 602–605 (2014)Cite this article

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Abstract

Oceanic lavas are thought to be derived from different sources within the Earth’s mantle, each with a distinct composition1,2,3,4. Large-scale plate motions provide the primary mechanism for mixing these sources, yet the geochemical signature of lavas erupted at different mid-ocean ridges can still vary significantly5,6. Geochemical variability is low where plate spreading rates are high, consistent with plate-scale mixing5,6. However, slow-spreading centres, such as the Southwest Indian Ridge in the Indian Ocean, are also geochemically homogeneous, which is inconsistent with plate-scale mixing6,7. Here we use numerical simulations of mantle flow to study mantle mixing at mid-ocean ridges, under conditions with variable plate length and spreading rate. Our simulations reveal that small-scale convection in the mantle contributes significantly to mantle mixing at slow spreading rates; faster plate velocities and smaller plates inhibit small-scale convection. We conclude that whereas fast-spreading ridge lavas are well mixed by plate-scale flow, slow-spreading ridge lavas are mixed by small-scale convection.

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Figure 1: Numerical experiment results: temperature fields and mixing efficiencies for cases with different half-spreading rates.
Figure 2: Numerical experiment results: averaged quantities and variability versus half-spreading rate.
Figure 3: Helium variability and predicted mixing times along mid-ocean ridges.

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Acknowledgements

This work benefited from comments by D. Graham. H.S. acknowledges the funds from the Deutsche Forschungsgemeinschaft (project SA 2042/2-1), from the Stifterverband für die Deutsche Wissenchaft, and from the Centre de Coopération Universitaire Franco-Bavarois. S.D.K. acknowledges the funds from the Humboldt Foundation. Figures were made with the Generic Mapping Tools (P. Wessel and W.H.F. Smith, EOS, Trans. AGU 76 (1995) 329).

Author information

Authors and Affiliations

  1. CNRS, IRAP, 14, avenue Edouard Belin, F-31400 Toulouse, France

    Henri Samuel

  2. Université de Toulouse, UPS-OMP, IRAP, F-31400 Toulouse, France

    Henri Samuel

  3. Bayerisches Geoinstitut, Universität Bayreuth, D-95447, Germany

    Henri Samuel & Scott D. King

  4. Virginia Tech, Blacksburg, Virginia 24060, USA

    Scott D. King

Authors
  1. Henri Samuel
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Contributions

H.S. and S.D.K. conceived the study and designed the experiments. H.S. performed the experiments, analysed the data and developed the semi-analytic mixing model. H.S. and S.D.K. discussed the results and wrote the text.

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Correspondence to Henri Samuel.

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Samuel, H., King, S. Mixing at mid-ocean ridges controlled by small-scale convection and plate motion. Nature Geosci 7, 602–605 (2014). https://doi.org/10.1038/ngeo2208

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