Division of the Early Proteozoic Khargituy Formation of the Sarma Group (Akitkan orogenic belt, Siberian craton) into different age sequences based on the results of U–Pb isotopic analysis of zircon

U–Pb (LA-ICP-MS) geochronological studies of detrital zircon from rocks of the Early Proterozoic Khargituy Formation of the Sarma Group, distributed in the central part of the Baikal uplift of the basement of the Siberian craton and included in the structure of the Sarma zone of the Akitkan orogenic belt, were carried out. It was established that the Khargituy Formation included rocks formed at different time intervals: 2.7, 2.15–1.95 and 1.7 Ga. It is shown that Meso- and Neoarchean age peaks (2.7–3.1 Ga) are characteristic of zircon from leucocratic gneisses, which indicates the formation of gneiss protoliths after 2.7 Ga due to the destruction of Archean granitoids of the Sarma zone of the Akitkan orogenic belt and igneous rocks of the Anabar superterrane basement of the Siberian craton. The time interval of 2.15–1.95 Ga corresponds to the accumulation of protoliths of mica-quartz schists, which is justified by the age of the youngest zircon grains – 2150 Ma and the age of metamorphism of these rocks – 1.95 Ga. The presence of an age peak at 1833 Ma and younger zircon grains with ages in the range of 1675–1785 Ma in a sample of mica-quartz schist taken from another area of rock outcrops attributed to the Khargituy Formation indicates that the accumulation of protoliths of these rocks occurred after the formation of the Akitkan orogenic belt and the South Siberian postcollisional magmatic belt. The results obtained indicate that the rocks attributed to the Khargituy Formation of the Sarma Group of the Western Baikal region cannot be considered as a single stratounit, since their formation occurred at different stages of the evolution of the Akitkan orogenic belt. Thus, as a result of the research, it was shown that, based on new data, the deposits of the Khargituy Formation should be divided into complexes of different ages (stratounits), each of which corresponds to a certain stage of the geological evolution of the territory.