Plume impingement on the Siberian SCLM: Evidence from Re–Os isotope systematics

The age and history of the lithospheric mantle of the Siberian craton: Re–Os and PGE study of peridotite xenoliths from the Obnazhennaya kimberlite

“…Eight xenoliths have very high contents of Cr 2 O 3 (0.9-1.4%) and high modal spinel or garnet. The Mg# of whole-rocks and olivine (Mg# Ol ) are close to each other except for garnet-rich (30%) Obn 21-13 with Mg# WR = 0.900 (Table 1) where the high Mg# Ol (0.923) is balanced by the low Mg# Gar (0.811); this exemplifies the uncertainties of inferring Mg# WR of garnet peridotites using Mg# Ol (Pernet-Fisher et al, 2015).…”

“…While Re-Os data on mineral separates might serve as a complement to WR analyses for well-characterized xenoliths, they suffer the same ambiguity discussed above for the application of T RD and T MA model ages defined for WR analyses. The conventional wisdom that olivine provides a good measure of whole rock Re-Os systematics in peridotites clearly is not met by the data reported by Pernet-Fisher et al (2015) as all the olivines had higher than PM Re/Os ratios with a spread in T MA ages from −6 to +27 Ga.…”

“…Very little data on peridotite xenoliths from Obnazhennaya are available in the international literature. Taylor et al (2003) and Howarth et al (2014) reported major and trace element analyses of minerals from 15 olivine-bearing xenoliths with a P-T range (including data on eclogites and pyroxenites) of 1.4-4.2 GPa and 620-1100 • C. Pernet-Fisher et al (2015) reported PGE and Re-Os data for two xenoliths as well as for olivine separated from six samples, but no modal or bulk chemical compositions for any of these xenoliths.…”

“…Recently, Pernet-Fisher et al (2015) reported PGE and Re-Os data obtained on six olivine separates and two "whole-rock" samples extracted from seven small xenoliths from Obnazhennaya; no modal or WR chemical compositions were given for these samples. While Re-Os data on mineral separates might serve as a complement to WR analyses for well-characterized xenoliths, they suffer the same ambiguity discussed above for the application of T RD and T MA model ages defined for WR analyses.…”

“…The petrographic description of the Obnazhennaya samples studied by Pernet-Fisher et al (2015) mention the presence of banding in olivine vs. garnet/cpx modal abundance. Coupled with the very high Re/Os ratios, this observation suggests that their sample suite is dominated by melt interaction products rather than the melt-residues studied in this paper.…”