Although the diamond potential of cratons is linked mainly to thick and depleted Archean lithospheric keels,there are examples of craton-edge locations and circum-cratonic Proterozoic terranes underlain by diamondiferous mantle.Here,we use the results of comprehensive major and trace-element studies of detrital garnets from diamond-rich Late Triassic(Carnian)sedimentary rocks in the northeastern Siberia to constrain the thermal and chemical state of the pre-Triassic mantle and its ability to sustain the diamond storage.The studied detrital mantle-derived garnets are dominated by low-to medium-Cr lherzolitic(～45％)and low-Cr megacrystic(～39％)chemistries,with a significant proportion of eclogi-tic garnets(～11％),and only subordinate contribution from harzburgitic garnets(～5％)with variable Cr203 contents(1.2-8.4 wt.％).Low-Cr megacrysts display uniform,"normal"rare-earth element(REE)patterns with no Eu/Eu*anomalies,systematic Zr and Ti enrichment(mainly within 2.5-5),which are evidence of their crystallization from deep metasomatic melts.Lherzolitic(G9)garnets exhibit normal or humped to MREE-depleted sinusoidal REE patterns and elevated Nd/Y(up to 0.33-0.41)and Zr/Y ratios(up to 7.62).Rare low-to high-Cr harzburgitic(G10)garnets have primarily"depleted",sinusoidal REE-patterns,low Ti,Y and HREE,but vary significantly in Zr-Hf,Ti and MREE-HREE contents,Nd/Y(within 0.1-2.4)and Zr/Y(1.53-19.9)ratios.The observed trends of chemical enrichment from the most depleted,harzburgitic garnets towards lherzolitic(including high-Ti high-Cr G11-type)garnets and megacrysts result from either voluminous high-temperature metasomatism by plume-derived silicate melts or recur-rent mobilization of less voluminous kimberlitic or related carbonated mantle melts,rather than the ini-tially primitive,fertile nature of the Proterozoic SCLM.Calculated Ni-in-garnet temperatures(primarily within～1150-1250℃)indicate their derivation from at least～220 km thick Cr-undersaturated litho-sphere at the relevant Devonian to Triassic thermal flow of～45 mW/m2 or cooler.We suggest the exis-tence of rare harzburgitic domains in the primarily lherzolitic diamond-facies SCLM beneath the northeastern Siberian craton at least by Triassic,whereas the abundance of eclogitic garnets,predomi-nance of E-type inclusions in placer diamonds and specific morphologies argue for diamondiferous eclog-ites occurring within a～50-65 kbar diamond window of the Olenek province by the same time.

Sergei Skuzovatov;Vladislav S.Shatsky;Alexey L.Ragozin;Alexander P.Smelov

Vinogradov Institute of Geochemistry,Russian Academy of Sciences,Siberian Branch,1A,Favorskogo Str.,Irkutsk 664033,Russia;Sobolev Institute of Geology and Mineralogy,Russian Academy of Sciences,Siberian Branch,3,Koptyug Ave.,Novosibirsk 630090,Russia;Geology&Geophysics Department,Novosibirsk State University,2 Pirogova Str.,Novosibirsk 630090,Russia;Diamond and Precious Metal Geology Institute,Russian Academy of Sciences,Siberian Branch,39,Lenina Ave.,Yakutsk 677000,Russia

地学前缘（英文版）

[1]Sergei Skuzovatov;Vladislav S.Shatsky;Alexey L.Ragozin;Alexander P.Smelov-.The evolution of refertilized lithospheric mantle beneath the northeastern Siberian craton:Links between mantle metasomatism,thermal state and diamond potential)[J].地学前缘（英文版）,2022(06):153-169

refertilized,keels,underlain,diamondiferous,lherzolitic,megacrystic,eclogi,harzburgitic,megacrysts,Lherzolitic,humped,kimberlitic,SCLM,undersaturated,eclogitic,eclog,Olenek

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