Oxidation of the Kaapvaal lithospheric mantle driven by metasomatism

Steven Creighton*, Thomas Stachel, Sergei Matveev, Heidi Höfer, Catherine McCammon, Robert W. Luth

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

112 Citations (Scopus)


The oxidation state, reflected in the oxygen fugacity (fO2), of the subcratonic lithospheric mantle is laterally and vertically heterogeneous. In the garnet stability field, the Kaapvaal lithospheric mantle becomes progressively more reducing with increasing depth from Δlog fO2 FMQ-2 at 110 km to FMQ-4 at 210 km. Oxidation accompanying metasomatism has obscured this crystal-chemical controlled depth-fO2 trend in the mantle beneath Kimberley, South Africa. Chondrite normalized REE patterns for garnets, preserve evidence of a range in metasomatic enrichment from mild metasomatism in harzburgites to extensive metasomatism by LREE-enriched fluids and melts with fairly unfractionated LREE/HREE ratios in phlogopite-bearing lherzolites. The metasomatized xenoliths record redox conditions extending up to Δlog fO2 = FMQ, sufficiently oxidized that magnesite would be the stable host of carbon in the most metasomatized samples. The most oxidized lherzolites, those in or near the carbonate stability field, have the greatest modal abundance of phlogopite and clinopyroxene. Clinopyroxene is modally less abundant or absent in the most reduced peridotite samples. The infiltration of metasomatic fluids/melts into diamondiferous lithospheric mantle beneath the Kaapvaal craton converted reduced, anhydrous harzburgite into variably oxidized phlogopite-bearing lherzolite. Locally, portions of the lithospheric mantle were metasomatized and oxidized to an extent that conversion of diamond into carbonate should have occurred.

Original languageEnglish
Pages (from-to)491-504
Number of pages14
JournalContributions to Mineralogy and Petrology
Issue number4
Publication statusPublished - 2009
Externally publishedYes


  • Kaapvaal craton
  • Kimberley kimberlite
  • Mantle metasomatism
  • Mantle oxidation state


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