| Реферат: | eng: Zircon from Tomtor syenites and kamaphorites was dated following the U-Pb method (SHRIMP-II), and the distribution of trace and rare-earth elements (REE)was studied at the same zircon point using an ion microprobe. The main zircon population from syenites was dated at 402 ± 7 Ma, while the age range of single zircon grains was 700–660 Mа. Different-aged zircon groups from syenites exhibited the characteristics of magmatic zircon, but their concentrations of REE and other trace elements differed markedly. The REE distribution in 700–660-Mа zircon is consistent with that of the typical zircon from syenites (Belousova et al., 2002), while the heavy rare-earth elements (HREE), P, Ti, and Y concentrations of ca. 400-Ma zircon differ from those of older zircon. This is the first isotope-geochemical study of zircon from kamaphorites, and the U-Pb age of ca. 400 Mа is within the error limits with of the main zircon population from syenites. The considerable enrichment of REE, Cа, Ti, Sr, Y, Nb, and Ba in zircon from kamaphorites may be partly due to the presence of burbankite microinclusions. The trace-element distribution pattern of zircon from kamaphorites is very similar to the geochemical characteristics of zircon from Tiksheozero carbonatites (Tichomirowa et al., 2013). The new age dates for Tomtor syenites and kamaphorites, consistent with 700–660 Mа and ca. 400 Mа events, support the zircon (Vladykin et al., 2014)and pyrochlore (Antonov et al., 2017)age dates determined following the U-Pb method and those of biotite obtained following the 40 Ar- 39 Ar method (Vladykin et al., 2014). © 2019 Elsevier GmbH
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