The age and history of the lithospheric mantle of the Siberian craton: Re-Os and PGE study of peridotite xenoliths from the Obnazhennaya kimberlite
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© 2015 Elsevier B.V. The formation age of the lithospheric mantle of the Siberian craton (one of the largest on Earth) is not well established; nearly all published whole-rock Re-Os data are for mantle xenoliths from a single kimberlite in the center of the craton (Udachnaya). We report Re-Os isotope and PGE concentration data for 19 spinel and garnet peridotite xenoliths from the Obnazhennaya kimberlite in the northeastern portion of the craton. Most samples in this study, and many Obnazhennaya peridotites in general, show a combination of relatively low Al < inf > 2 < /inf > O < inf > 3 < /inf > (0.1-2%) with high CaO (1.4-4%) concentrations. Only four dunites and harzburgites in our sample suite have low contents of both Al < inf > 2 < /inf > O < inf > 3 < /inf > and CaO (0.1-0.8%), but their relatively low Mg# (0.888-0.919) and highly variable Os concentrations (0.6-35 ppb) suggest they may have formed in melt migration channels rather than as residues of partial melt extraction. A group of six Ca-rich (2.0-3.2% CaO) peridotites yields the highest Re-Os model ages (mean T < inf > RD < /inf > = 2.8 Ga, mean T < inf > MA < /inf > = 3.5 Ga). Eight peridotites with low to moderate Al < inf > 2 < /inf > O < inf > 3 < /inf > ( < 2%) and Mg# =0.91, including three low-Ca harzburgites, yield lower Re-Os model ages (mean T < inf > RD < /inf > = 1.9 Ga, mean T < inf > MA < /inf > = 2.2 Ga). The remainder of the samples may not yield meaningful T < inf > RD < /inf > ages because they are not refractory (Al < inf > 2 < /inf > O < inf > 3 < /inf > > 2.6% and/or Mg# =0.90). We interpret these results as evidence for a two-stage formation of the lithospheric mantle. The peridotites formed at the two stages show very similar chemical compositions. The enrichment in Ca, which we attribute to widespread post-melting metasomatism by carbonate-rich melts, may have taken place either at the end of the Archean melting event, when at least one Ca-Al-rich peridotite was formed, or later. The combined Re-Os age data on xenoliths from Obnazhennaya and Udachnaya suggest that the lithospheric mantle beneath the Siberian craton was not formed in a single event, but grew in at least two events, one in the late Archean and the other in the Paleoproterozoic. This study further indicates that the formation of highly melt-depleted lithospheric mantle was not limited to the Archean, but continued well into the Paleoproterozoic when the Siberian craton was stabilized.
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Reworking of Archean mantle in the NE Siberian craton by carbonatite and silicate melt metasomatism: Evidence from a carbonate-bearing, dunite-to-websterite xenolith suite from the Obnazhennaya kimberliteIonov, D.; Doucet, Luc; Xu, Y.; Golovin, A.; Oleinikov, O. (2018)The Obnazhennaya kimberlite in the NE Siberian craton hosts a most unusual cratonic xenolith suite, with common rocks rich in pyroxenes and garnet, and no sheared peridotites. We report petrographic and chemical data for ...
Paleoproterozoic formation age for the Siberian cratonic mantle: Hf and Nd isotope data on refractory peridotite xenoliths from the Udachnaya kimberliteDoucet, Luc-Serge; Ionov, D.; Golovin, A. (2015)© 2014 Elsevier B.V. The formation age of the Siberian cratonic mantle is not well established as yet. Re-Os data on various mantle-derived materials have shown that it contains Archaean components, but the reported ...
High water contents in the Siberian cratonic mantle linked to metasomatism: An FTIR study of Udachnaya peridotite xenolithsDoucet, Luc-Serge; Peslier, A.; Ionov, D.; Brandon, A.; Golovin, A.; Goncharov, A.; Ashchepkov, I. (2014)The processes that control water distribution in nominally anhydrous minerals from peridotites are twofold. Melt depletion will remove water while metasomatism can potentially add water to these minerals. These processes ...