Age and sources of the kodar group rocks of the udokan complex (Aldan shield): results of geochemical, U–Th–Pb (LA-ICP-MS) geochronological and Nd–Hf isotopic studies

The paper presents the results of geochemical and Nd whole rock isotopic studies, as well as U–Th–Pb (LA-ICP-MS) geochronological and Hf isotope studies of detrital zircon from metaterrigenous rocks of the Kodar Group of the Udokan Complex, Aldan Shield. It has been established that the rocks of the Kodar Group have an age of 1.99–1.91 Ga, and the rocks of the Chinei and Kemen groups of the Udokan Complex are in the range of 1.90–1.87 Ga. This allows us to raise the question of identifying the Kodar Group as an independent stratigraphic unit. Archean igneous and metamorphic rocks of the Chara-Olekma Geoblock and, probably, the Kalar and Kurulta blocks of the Stanovoy suture zone, as well as Paleoproterozoic (2.04–1.99, 2.08, 2.20 and 2.30 Ga) complexes of active continental margins or ensialic island arcs in the western–northwestern and southern (in modern coordinates) framing of the Chara-Olekma Geoblock, not identified in the region on the modern erosion level, were the sources of terrigenous rocks of the Kodar Group. Erosion of rocks of the igneous arcs and the continental slope led to the accumulation of sediments of the Kodar Group in the retro-arc foreland basin setting, and the subsequent collapse of the orogen and the formation of an intracontinental extension basin led to the accumulation of terrigenous rocks of the Chinei and Kemen groups. Obtained data indicate widespread previously unidentified Paleoproterozoic continental crust formation at about 2.04–1.97 Ga in the western part of the Aldan Shield.