Mantle sources of kimberlites through time: A U-Pb and Lu-Hf isotope study of zircon megacrysts from the Siberian diamond fields

Abstract

A comprehensive, internally consistent U-Pb and Lu-Hf isotope data set for 93 mantle-derived zircons from the Yakutian kimberlite province confirms and further refines the four major episodes of kimberlite magmatism on the Siberian craton: 421–409 Ma (Late Silurian-Early Devonian), 358–353 Ma (Late Devonian-Early Carboniferous), 226–218 Ma (Late Triassic), and 161–144 Ma (Middle-Late Jurassic). The relatively narrow, constant range of εHf values between +2 and +10 for both the Paleozoic and Mesozoic mantle-derived zircons (and by inference kimberlites) suggests that the volatile-rich magmas were repeatedly sourced from the convecting upper mantle beneath the Siberian craton. This finding is in keeping with the narrow and constant range of εNd values for groundmass perovskites from the Yakutian kimberlite province between +1.8 and +5.5 between 420 and 150 Ma. Our preferred model implies that the convecting upper mantle beneath the Yakutian kimberlite province ‘recovered’ rapidly back to ambient conditions shortly after the giant plume-related flood volcanic event that produced the Siberian Traps at 250 Ma. Although close spatial relationships exist between kimberlites and flood basalts on the Siberian craton during both the Paleozoic and Mesozoic, exact timing of the igneous events and the isotopic compositions of the diverse deep-sourced melting products rule out any direct genetic links.Besides the highly economic kimberlite-hosted diamond deposits of Late Devonian age (e.g., Mir and Udachnaya), the Siberian craton also contains significant Mesozoic placer diamond deposits (e.g., along the Anabar river), for which lamproite sources have been suggested recently. Our study shows that mantle-derived zircon megacryst fragments from the Ebelyakh placer deposit have Late Triassic ages of ca. 224 Ma. Their long-term depleted Hf isotopic compositions (+8.5 εHf) suggest that the alluvial diamonds were sourced from asthenosphere-derived Triassic kimberlites rather than from lithospheric mantle derived isotopically enriched lamproites.