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]. Geoscience Frontiers, 2022, 13(6): 101455. DOI: 10.1016/j.gsf.2022.101455
Citation: 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]. Geoscience Frontiers, 2022, 13(6): 101455. DOI: 10.1016/j.gsf.2022.101455

The evolution of refertilized lithospheric mantle beneath the northeastern Siberian craton: Links between mantle metasomatism, thermal state and diamond potential

  • 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 eclogitic garnets (~11%), and only subordinate contribution from harzburgitic garnets (~5%) with variable Cr2O3 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 recurrent mobilization of less voluminous kimberlitic or related carbonated mantle melts, rather than the initially 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 lithosphere at the relevant Devonian to Triassic thermal flow of ~45 mW/m2 or cooler. We suggest the existence 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, predominance of E-type inclusions in placer diamonds and specific morphologies argue for diamondiferous eclogites occurring within a ~50–65 kbar diamond window of the Olenek province by the same time.
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