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Nature 310, 198-202 (19 July 1984) | doi:10.1038/310198a0; Accepted 18 May 1984

Origin of diamonds in old enriched mantle

S. H. Richardson*, J. J. Gurney†, A. J. Erlank† & J. W. Harris‡

  1. *Center for Geoalchemy, Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
  2. †Department of Geochemistry, University of Cape Town, Rondebosch 7700, South Africa
  3. ‡Department of Applied Geology, University of Strathclyde, Glasgow G1 1XJ, UK
  4. *Present address: Institut de Physique du Globe, Université de Paris VI, 4 Place Jussieu, 75230 Paris Cedex 05, France.
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Sub-calcic garnets encapsulated by diamonds from relatively young (90 Myr) kimberlites in southern Africa, yield ancient Sm–Nd and Rb–Sr model ages (3,200–3,300 Myr). The chemistry and distribution of these and associated sub-calcic garnets from kimberlite concentrate, indicate diamonds formed following enrichment of residual sub-cratonic mantle such as that remaining after widespread extraction of 3,500-Myr komatiitic lavas.