|Title:||A mantle origin for Paleoarchean peridotitic diamonds from the Panda kimberlite, Slave Craton: Evidence from 13C−, 15N− and 33,34S‐stable isotope systematics|
|Authors:||P. Cartigny, J. Farquhar, E. Thomassot, J.W. Harris, B. Wing, A. Masterson, K. McKeegan, and T. Stachel|
|Publication:||Lithos, v. 112, p. 852‐864.|
In order to address diamond formation and origin in the lithospheric mantle underlying the Central Slave Craton, we report N‐ and C‐stable isotopic compositions and N‐contents and aggregation states for 85 diamonds of known paragenesis (73 peridotitic, 8 eclogitic and 4 from lower mantle) from the Panda kimberlite (Ekati Mine, Lac de Gras Area, Canada). For 12 peridotitic and two eclogitic sulfide inclusion‐bearing diamonds from this sample set, we also report multiple‐sulfur isotope ratios. The 73 peridotitic diamonds have a mean δ13C‐value of ‐ 5.2‰ and range from ‐ 6.9 to ‐ 3.0‰, with one extreme value at − 14.1‰. The associated δ15N‐values range from ‐ 17.0 to + 8.5‰ with a mean value of − 4.0‰. N−contents range from 0 to 1280 ppm. The 8 eclogitic diamonds have δ13C‐values ranging from ‐ 11.2 to ‐ 4.4‰ with one extreme value at − 19.4‰. Their δ15N ranges from − 2.1 to + 7.9‰ and N‐contents fall between 0 and 3452 ppm. Four diamonds with an inferred lower mantle origin are all Type II (i.e. nitrogen‐free) and have a narrow range of δ13C values, between ‐ 4.5 and ‐ 3.5‰. The δ34S of the 14 analyzed peridotitic and eclogitic sulfide inclusions ranges from − 3.5 to +5.7‰. None of them provide evidence for anomalous δ33S−values; observed variations in δ33S are from +0.19 to − 0.33‰, i.e. within the 2 sigma uncertainties of mantle sulfur (δ33S = 0‰). At Panda, the N contents and the δ13C of sulfide‐bearing peridotitic diamonds show narrower ranges than silicate‐bearing peridotitic diamonds. This evidence supports the earlier suggestion established from eclogitic diamonds from the Kaapvaal that sulfide‐(±silicate) bearing diamonds sample a more restricted portion of sublithospheric mantle than silicate‐(no sulfide) bearing diamonds. Our findings at Panda suggest that sulfide‐bearing diamonds should be considered as a specific diamond population on a global‐scale. Based on our study of δ34S, Δ33S, δ15N and δ13C, we find no evidence for subduction‐related isotopic signatures in the mantle sampled by Panda diamonds.