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Is the African cratonic lithosphere wet or dry?

By
Ikuo Katayama
Ikuo Katayama
Department of Earth and Planetary Systems Science, Hiroshima University, Hiroshima 739-8526, Japan
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Jun Korenaga
Jun Korenaga
Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, USA
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Published:
June 01, 2011

Thick continental lithosphere (tectosphere) beneath African cratons has been stable for ~2.5 b.y. despite its mechanical interaction with sublithospheric mantle. Water is known to have significant influence on mechanical stiffness, and the depletion of water is often considered to be a key to preserving the thick lithosphere. Although water-rich environments indicated by the present water content of cratonic xenoliths appear to contradict this hypothesis, these water contents might have been modified at later stages due to the high diffusivity of hydrogen in minerals. Deformation microstructures such as lattice-preferred orientation indicate water-poor conditions (<200 ppm H/Si) during long-term plastic deformation in the continental lithosphere. Analysis of convective instability further constrains the water content to be less than 100 ppm H/Si. We suggest that the continental tectosphere beneath southern Africa must have a low water content, at least one order of magnitude less than oceanic upper mantle, and that the present-day water content of cratonic xenoliths most likely reflects localized metasomatism before eruption.

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Contents

GSA Special Papers

Volcanism and Evolution of the African Lithosphere

Luigi Beccaluva
Luigi Beccaluva
Dipartimento di Scienze della Terra, Università di Ferrara, Italy
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Gianluca Bianchini
Gianluca Bianchini
Dipartimento di Scienze della Terra, Università di Ferrara, Italy
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Marjorie Wilson
Marjorie Wilson
School of Earth & Environment, The University of Leeds, Leeds, UK
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Geological Society of America
Volume
478
ISBN print:
9780813724782
Publication date:
June 01, 2011

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