Ion-microprobe U-Th-Pb analyses of zircon from three high-level syenite-granite stocks in the western part of the Taimyr fold-and-thrust belt have yielded early Triassic ages of 249-241 Ma. Those syenite-granite bodies intrude unmetamorphosed late Paleozoic to early Mesozoic terrigenous and volcanic supracrustal rocks, including the early Triassic Siberian traps. Ar-40-Ar-39 isotopic ages of 245 - 233 Ma correlate well with the ion-microprobe data and define the time of closure for the K-Ar isotopic system. Limited geochemical data for the early Triassic syenite-granite plutons show that they have metaluminous compositions, high potassium, high REE and high LIL concentrations, and Sr-87/Sr-86 and epsilon(Nd) ratios intermediate between crust and mantle, suggesting A hybrid mantle-crustal origin. We tentatively suggest that they formed in an anorogenic setting as a result of the Permo-Triassic Euroasian superplume. (C) 2002 Elsevier Science B.V. All rights reserved.
