Contributions to Mineralogy and Petrology

, Volume 140, Issue 1, pp 1–15

Kankan diamonds (Guinea) I: from the lithosphere down to the transition zone

  • Thomas Stachel
  • Gerhard P. Brey
  • Jeff W. Harris
Article

DOI: 10.1007/s004100000173

Cite this article as:
Stachel, T., Brey, G. & Harris, J. Contrib Mineral Petrol (2000) 140: 1. doi:10.1007/s004100000173

Abstract

Peridotitic inclusions in alluvial diamonds from the Kankan region of Guinea in West Africa are mainly of lherzolitic paragenesis. Nevertheless, extreme Cr2O3 contents (max. 17 wt%) in some of the exclusively lherzolitic garnets document that the diamond source experienced a previous stage of melt extraction in the spinel stability field. This initial depletion was followed by at least two metasomatic stages: (1) enrichment of LREE and Sr and (2) introduction mainly of MREE–HREE and other HFSE (Ti, Y, Zr, Hf). The Ti- and HFSE-poor character of stage (1) points towards a CHO-rich fluid or carbonatitic melt, the high HFSE in stage (2) favour silicate melts as enriching agent. Eclogitic inclusions are derived from a large depth interval ranging from the lithosphere through the asthenosphere into the transition zone. The occurrence of negative Eu anomalies in garnet and clinopyroxene from both lithosphere and transition zone suggests a possible relationship to subducted oceanic crust. Lithospheric eclogitic inclusions are derived from heterogeneous sources, that may broadly be divided into a low-Ca group with LREE depleted trace element patterns and a high-Ca group representing a source with negative LREE–HREE slope that is moderately enriched in incompatible elements relative to primitive mantle. High-Ca inclusions of majoritic paragenesis are significantly more enriched in incompatible elements, such as in Sr and LREE. Calculated whole rock compositions require metasomatic enrichment even if a derivation from MORB is assumed.

Supplementary material

410_2000_1400001_MOESM1_ESM.pdf (39 kb)
Containing the full analytical data set (EPMA) of inclusions in diamonds from the Krankan region (Guinea, West Africa)
410_2000_1400001_MOESM2_ESM.xls (93 kb)
Containing the full analytical data set (EPMA) of inclusions in diamonds from the Krankan region (Guinea, West Africa)

Copyright information

© Springer-Verlag Berlin Heidelberg 2000

Authors and Affiliations

  • Thomas Stachel
    • 1
  • Gerhard P. Brey
    • 1
  • Jeff W. Harris
    • 2
  1. 1.Institut für Mineralogie, Universität Frankfurt, Senckenberganlage 28, 60054 Frankfurt, GermanyGermany
  2. 2.Division of Earth Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UKUK