Re-Os and 40Ar/39Ar isotope measurements of inclusions in alluvial diamonds from the Ural Mountains

Constraints on diamond genesis and eruption ages

Fernando Laiginhas*, D. Graham Pearson, David Phillips, Ray Burgess, Jeff W. Harris

*Corresponding author for this work

Research output: Contribution to journalArticle

17 Citations (Scopus)

Abstract

The Re-Os isotope data for 20 syngenetic sulphide inclusions, recovered from 15 diamonds and the 40Ar/39Ar laser probe eruption ages of 7 syngenetic clinopyroxenes recovered from 5 diamonds, all from alluvial placer deposits in the Ural Mountains, have been determined. Six eclogitic sulphide inclusions, two of which coexist in the same diamond, yield an isochron age of 1280 ± 310 Ma (2σ), with an unusually high initial 187Os/188Os ratio of 2.10 ± 0.58 (2σ). The age is interpreted to date remobilisation of carbon and sulphur, and homogenisation of Os, during rift-related thermal-magmatic events that affected the East European Craton (EEC) at ca. 1.3 Ga. The high initial Os ratio suggests Re-Os evolution over a 100 to 500 Ma period within previously metasomatised lithosphere, most likely the EEC. Five eclogitic clinopyroxenes recovered from four diamonds yielded similar 40Ar/39Ar ages averaging 472 ± 28 Ma, which likely approximate the time of source kimberlite/lamproite eruption. This age suggests that the Ural diamonds are not likely to have derived either from the well known diamond-bearing kimberlites of the Siberian craton, nor from presently known Russian and Finnish kimberlite provinces on the EEC. The Urals placer deposits are mainly confined to 397-407 Ma sedimentary rocks along the western side of these mountains, with sediment transportation at that time generally from the north-west. Present evidence suggests the existence of an undiscovered kimberlite/lamproite source, probably on the Volgo-Uralia crustal segment of the EEC, which gave rise to the Urals diamond deposits.

Original languageEnglish
Pages (from-to)714-723
Number of pages10
JournalLithos
Volume112
DOIs
Publication statusPublished - Nov 2009
Externally publishedYes

Keywords

  • Ar/Ar
  • Diamond
  • East European Craton
  • Inclusions
  • Re-Os
  • Urals

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