TY - JOUR
T1 - Re-Os and 40Ar/39Ar isotope measurements of inclusions in alluvial diamonds from the Ural Mountains
T2 - Constraints on diamond genesis and eruption ages
AU - Laiginhas, Fernando
AU - Pearson, D. Graham
AU - Phillips, David
AU - Burgess, Ray
AU - Harris, Jeff W.
PY - 2009/11
Y1 - 2009/11
N2 - 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.
AB - 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.
KW - Ar/Ar
KW - Diamond
KW - East European Craton
KW - Inclusions
KW - Re-Os
KW - Urals
UR - http://www.scopus.com/inward/record.url?scp=71749100638&partnerID=8YFLogxK
U2 - 10.1016/j.lithos.2009.03.003
DO - 10.1016/j.lithos.2009.03.003
M3 - Article
AN - SCOPUS:71749100638
SN - 0024-4937
VL - 112
SP - 714
EP - 723
JO - Lithos
JF - Lithos
ER -