Results of research on the geological, petrochemical, and isotopic-geochronological characteristics of plagiogranites from the Chelyuskin ophiolitic belt, on the northern part of East Siberias Taymyr Peninsula, are presented. Petro-geochemical features and REE distributions for this tonalite-trondhjemite series resemble those of plagiogranites from different ophiolitic complexes. The plagiogranites considered here belong to the low-potassium series of ophiolitic maficsgabbro, gabbro-dolerite dikes, and basalts. Their spatial relationships; low K2O, Rb, Nb, Ta, U, and Th contents; similar REE patterns; and tonalite and trondhjemite Nd- and Sm-Nd-isotopic ratios typical of mafic rocks confirm the oogenetic nature of these rocks. Zircon U-Pb dating and an Sm-Nd isotopic study suggest a Late Riphean age for the plagiogranites. We regard the 740 38 Ma age as the upper age boundary for the formation of the Chelyuskin ophiolitic belt, and Sm-Nd model ages (850785 Ma) as its lower boundary. Tonalite-trondhjemite series could be formed as a result of partial melting of previously formed oceanic crust in a back-arc environment, in association with minor portions of the sediments of the ancient arc.
