Ar-Ar age determinations of eclogitic clinopyroxene and garnet inclusions in diamonds from the Venetia and Orapa kimberlites

R. Burgess*, G. B. Kiviets, J. W. Harris

*Corresponding author for this work

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

Ar-Ar age measurements are reported for selected eclogitic clinopyroxene and garnet inclusions in Orapa diamonds and clinopyroxene inclusions in Venetia diamonds. Laser drilling of encapsulated clinopyroxene inclusions within Venetia diamonds released a maximum of 3% of the total 40Ar, indicating little diffusive transfer and storage of radiogenic 40Ar at the diamond-inclusion boundary. Apparent ages obtained during stepped heating of three diamonds are consistent with diamond crystallisation occurring just prior to the kimberlite eruption ∼520 Ma ago. Stepped heating of three clinopyroxene-bearing Orapa diamonds gave ages of 906-1032 Ma, significantly above the eruption age, but consistent with previously determined isotopic ages. A few higher apparent ages hint at the presence an older generation of Orapa diamonds that formed >2500 Ma ago. Orapa garnets also contain measurable K contents, and record a range of ages between 1000 and 2500 Ma. The old apparent ages and lack of significant interface 40Ar released by the laser probe, suggests that pre-eruption radiogenic 40Ar and mantle-derived 40Ar components are trapped in microinclusions within the pyroxene and garnet inclusions.

Original languageEnglish
Pages (from-to)113-124
Number of pages12
JournalLithos
Volume77
Issue number1-4 SPEC. ISS.
DOIs
Publication statusPublished - Sep 2004
Externally publishedYes

Keywords

  • Ar-Ar
  • Clinopyroxene
  • Dating
  • Diamond
  • Garnet

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