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Introduction Kimberlite magmas travel at high speed through the lithospheric mantle and crust, propelled by their high volatile contents. The origin of volatiles in kimberlite magma, however, is still debated. The loss of volatiles during eruption, the composite nature of kimberlites and their common hydrous alteration make the primary kimberlitic melt composition difficult to infer. Volatiles in the mantle source of kimberlites may come from the recycling of Archean oceanic crust into the lithospheric mantle, as suggested by the finding of Archean ages for eclogite xenoliths from the Udachnaya-East kimberlite (Siberia), thought to represent remnants of early oceanic crust (Pearson et al. 1995; Jacob & Foley 1999). However, a single Archean formation age for the Siberian lithospheric mantle has been challenged by recent publications (Doucet et al. 2015; Ionov et al. 2015 and Moyen et al. 2017) that propose a major rejuvenation of the Archean lithosphere during the paleoproterozoic (ca 1.9 Ga). Here we present new insights from multiple S-isotopes (S, S, S, S), to test whether a surface-derived Archean component is present in the mantle source of the Udachnaya-East kimberlite. Photolytic reactions in the ozone-free atmosphere of the early Earth, produced mass-independent fractionation of sulfur (corresponding to a deviation from the mass-dependent fractionation line). These anomalies were efficiently transferred to sediments such as Archean sedimentary sulfides that carry positive ∆S anomalies (and negative ∆S anomalies) and Archean sulfates that carry negative ∆S (with positive ∆S). Accordingly, the presence of these anomalies in igneous rocks may allow to identify Archean surface material recycled into the mantle. If found in kimberlites samples, mass-independent fractionation of sulfur would indicate unambiguously that recycling of Archean supracrustal material was involved in the source of the Udachnaya-East kimberlite.

Co-magmatic sulfides and sulfates in the Udachnaya-East pipe (Siberia): sulfur speciation and isotopic composition in kimberlites and their mantle sources