Letter | Published:

History of the continental lithosphere recorded by ultramafic xenoliths

Nature volume 296, pages 732735 (22 April 1982) | Download Citation

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Abstract

Since the development of the plate tectonic theory, the formation, structure and properties of the continental lithosphere have been widely debated1–3. By analogy with petrological models for the oceanic lithosphere generated at ridges4–6, the continental lithosphere has been interpreted in terms of a comprehensive mechanical and petrogenetic unit by considering, for example, that the continental crust was differentiated through a process such as zone melting, the lithospheric mantle being the residue of this extraction process7,8. However, geological observations show that formation of the continental crust was quite complex, including sedimentation, metamorphism and orogenesis, and not simply direct magmatic segregation. Underneath its crust, the continental lithosphere, mainly comprises peridotites and in this respect, it resembles the oceanic lithosphere. This similarity, which is corroborated by seismic data, does not, however, mean that a chemical coupling exists between the subcontinental lithospheric mantle and continental crust in a similar way as for the oceanic lithosphere. Although magma generation and eruption through the continental lithosphere contribute to the growth of the continental crust and to the depletion of the subcontinental lithospheric mantle in incompatible elements, no simple chemical coupling should exist if the continental lithosphere were created by thermal accretion. The petrology and geochemistry of the continental lithosphere can also be studied using xenoliths brought up to the surface by kimberlitic or alkalic volcanics. This technique attracted much attention because of the determination of pyroxene geotherms9 and the claim that it permits the description of the palaeogeothermal structure of continents and oceans10,11. Although some of the original conclusions seem premature12 the basic idea is sound. We have now used radiogenic tracers, the 87Rb–87Sr system, to study the creation of the continental lithosphere. We present here results on garnet Iherzolite xenoliths from southern African kimberlites and discuss their geochemical and geodynamical implications.

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Author information

Author notes

    • Nobu Shimizu

    Present address: Center of Geoalchemy, Department of Earth and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.

Affiliations

  1. Laboratoire de Geochimie et Cosmochimie, Institut de Physique du Globe de Paris, Université de Paris 6, 75230 Paris Cedex 05, France

    • Claude J. Allègre
    • , Nobu Shimizu
    •  & Dominique Rousseau

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https://doi.org/10.1038/296732a0

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