New insights into the occurrence of 13C-depleted carbon in the mantle from two closely associated kimberlites: Letlhakane and Orapa, Botswana

P. Deines*, J. W. Harris

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

24 Citations (Scopus)

Abstract

Carbon isotope measurements on diamonds from the Letlhakane kimberlite, and the analyses of their inclusions, permit the examination of km-scale mantle-composition variations by comparing the results with those for the nearby Orapa kimberlite. Diamonds from Letlhakane have a wide range in carbon isotopic composition (-3‰ to -21‰); however, the relative abundance of diamonds depleted in 13C is significantly lower than in the Orapa kimberlite. Most of the 13C-depleted diamonds belong to the eclogictic or websteritic paragenesis. The relative abundance of inclusions in diamonds and their composition indicate that there are significant differences in petrology in the mantle below the two locations. At Letlhakane, peridotitic compositions are more prevalent than at Orapa and the protolith of P-Type inclusions in diamonds may have experienced a higher degree of partial melting at Letlhakane compared to Orapa. P/T estimates for both W- and E-Type diamonds indicate that a region of 13C-depletion may exist beneath the two kimberlites. The relationships between carbon isotopic composition of the host diamond and the Al2O3/Cr2O3 ratios of their websteritic and eclogitic garnet inclusions indicate that the low δ13C regions may represent a primary mantle feature, unrelated to a crustal component.

Original languageEnglish
Pages (from-to)125-142
Number of pages18
JournalLithos
Volume77
Issue number1-4 SPEC. ISS.
DOIs
Publication statusPublished - Sep 2004
Externally publishedYes

Keywords

  • C-depletion
  • Carbon isotopic composition
  • Diamond
  • Inclusion
  • Mantle
  • Websterite

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