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Abstract: Lithospheric domains in the Slave Province, inferred from regional variations in chemistry of mantle-derived garnets, are parallel with northeasterly structural trends in Neoarchean surface rocks and were used previously to infer Late Neoarchean crust–mantle coupling and argue against the presence of diamondiferous Mesoarchean lithosphere under the western Slave craton prior to its late Neoarchean orogenic climax. A review of more recent evidence does not support this view but concludes that a Mesoarchean lithospheric root was coupled to Mesoarchean crust of the Central Slave superterrane (CSST) prior to accretion of adjacent juvenile Neoarchean terranes. A significant part of this root survived the Neoarchean break-up of the CSST, Neoarchean terrane accretion and a complex sequence of post-accretion deformation, granitoid plutonism and metamorphism. It was least modified in the ultra-depleted harzburgitic layer (UDL) under the central part of the Contwoyto terrane, where it is trapped above the deepest part of an underplated Paleoproterozoic slab which stabilized the remnants of the Archean root and caused downward younging of the lithosphere. Upper mantle domains recognized on the basis of the distribution of peridotitic garnets are not primary Neoarchean features but were either inherited from the original Mesoarchean root or resulted from Neoarchean and Paleoproterozoic tectonic erosion and/or metasomatism of this root. The Slave Province resembles other diamondiferous cratons in that its diamond endowment consists of both Mesoarchean and Paleoproterozoic stones. [Copyright &y& Elsevier]

Abstract: The longevity of the continental lithosphere mantle is explained by its unusual composition. This part of the mantle is made up mainly of forsterite-rich olivine (Fo92–94), with or without orthopyroxene, and it is essentially anhydrous. The former characteristic makes it buoyant, the latter makes it viscous, and the combination of these features that allow it to remain isolated from the convecting mantle. Highly forsteritic olivine is not normally produced during mantle melting. Possible explanations for its abundance in old Archean subcontinental lithospheric mantle include: (a) high-degree mantle melting in a plume or at an Archean ocean ridge; (b) accretion of this material to older lithosphere and its reworking in a subduction zone; (c) redistribution of material to eliminate high-density, low-viscosity lithologies. Following an evaluation of these models based on petrological and numerical modeling, we conclude that the most likely explanation is the accumulation of the residues of melting of one or more mantle plumes following by gravity-driven ejection of denser, Fe-rich components. [Copyright &y& Elsevier]