He, Ne and Ar in peridotitic and eclogitic paragenesis diamonds from the Jwaneng kimberlite, Botswana-Implications for mantle evolution and diamond formation ages

Masahiko Honda*, David Phillips, Jeff W. Harris, Takuya Matsumoto

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

11 Citations (Scopus)

Abstract

We have undertaken helium, neon and argon step-heating, isotopic analyses of eleven polycrystalline diamonds of known peridotite/eclogite paragenesis from the Jwaneng kimberlite pipe, Botswana. In contrast to the findings of crustal noble gases in framesites from the same kimberlite pipe (Honda et al., 2004. Unusual noble gas compositions in polycrystalline diamonds: preliminary results from the Jwaneng kimberlite, Botswana. Chem. Geol. 203, 347-358.), the Jwaneng polycrystalline diamonds appear to contain similar noble gas isotopic compositions (particularly Ne) to those representing a mantle source for MORBs. This implies that the Jwaneng polycrystalline diamonds may have formed in recent times, possibly close to the time of kimberlite emplacement at ~. 235. Ma. In contrast, Jwaneng framesites could be as old as gem diamonds (mineral inclusion ages of ~. 2.9. Ga). Furthermore, the data indicate that the sub-continental mantle lithosphere in the region has heterogeneous Ne isotopic compositions, or that these compositions changed over time from crustal Ne (as observed in the framesites) to MORB-like (as observed in the polycrystalline diamonds).

Original languageEnglish
Pages (from-to)43-51
Number of pages9
JournalEarth and Planetary Science Letters
Volume301
Issue number1-2
DOIs
Publication statusPublished - 3 Jan 2011
Externally publishedYes

Keywords

  • Diamond
  • Mantle evolution
  • Mantle lithosphere
  • Noble gas

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