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Ephemeral isopycnicity of cratonic mantle keels

Nature Geoscience volume 6, pages 967–970 (2013)Cite this article

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Abstract

Cratons, the ancient nuclei of continents that have been stable for billions of years, are underlain by keels of lithosphere with strongly melt-depleted compositions1,2. These cratonic keels may have formed either from partial melting in a mantle-plume environment3,4, or alternatively by melting at shallow depths in a subduction zone, during the successive accretion of slabs of oceanic lithosphere5. The stability of cratonic keels has been attributed to a pervasive state of near-neutral buoyancy—isopycnicity—created by offsetting thermal and compositional effects on density6. However, it is unclear how an isopycnic state can be sustained over geological time2. Here we simulate the evolution of a simplified southern African cratonic keel, initiated in either a hot-plume or a cold-slab environment, over 3 billion years, using a numerical model that incorporates secular cooling of the mantle, coupled with gradual loss of radiogenic heating in the lithosphere. We find that the simulation that starts from a cold-slab environment best explains the subsidence history of the southern African craton7. However, irrespective of how the cratonic keel formed, we find that the isopycnic state is inherently ephemeral: a cratonic keel that is approximately isopycnic under present conditions was more, or less, buoyant in the geologic past.

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Figure 1: Model set-up for thermal calculations.
Figure 2: Snapshots of secular evolution of a dry lithospheric keel starting from a hot initial state.
Figure 3: Snapshots of secular evolution of a dry lithospheric keel, starting from a cold initial state.
Figure 4: Secular evolution of isostatic elevation profiles.

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Acknowledgements

This work was supported by the Natural Sciences and Engineering Research Council of Canada.

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Authors and Affiliations

  1. Department of Geoscience, University of Calgary, 2500 University Drive NW, Calgary, Alberta, T2N 1N4, Canada

    David W. Eaton

  2. Centre de recherche GEOTOP, Université du Québec à Montréal, CP 8888 succursale Centre-Ville, Montréal, Quebec, H3C 3P8, Canada

    H. K. Claire Perry

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  1. David W. Eaton
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  2. H. K. Claire Perry
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Contributions

Both authors contributed extensively to the work presented in this paper. D.W.E. wrote the simulation code, ran the model and wrote the manuscript. H.K.C.P. edited the manuscript and provided conceptual advice.

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Correspondence to David W. Eaton.

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The authors declare no competing financial interests.

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Eaton, D., Claire Perry, H. Ephemeral isopycnicity of cratonic mantle keels. Nature Geosci 6, 967–970 (2013). https://doi.org/10.1038/ngeo1950

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